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The 2017 CAP Congress is being hosted by the Queen's University (Kingston, ON), May 29 to June 2, 2017. This Congress is an opportunity to showcase and celebrate the achievements of physicists in Canada and abroad. Mark your calendars and bookmark the main Congress website for easy access to updates and program information.
Le Congrès 2017 de l'ACP se tiendra à l'université Queen's (Kingston, ON) du 29 mai au 2 juin 2017. Au cours de cet événement nous pourrons profiter des présentations et des réalisations de physiciens et physiciennes du Canada et d'ailleurs, et les célébrer. Inscrivez la date du congrès à votre agenda et créez un signet de l'adresse du site web du congrès pour accéder facilement aux mises à jour et au contenu de la programmation.
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A satellite meeting to the CAP Congress that will consist of a full day of events including talks and networking time, with a focus on supporting the network of Canadian physicists working in soft matter, which includes people working with polymers, colloids, and bio-inspired systems.
Many polymers exhibit structural heterogeneity on the nanoscale, either by partially crystallizing or, in the case of copolymers, by phase separation. Their mechanical properties are controlled by molecular level mechanisms at interfaces between crystalline-amorphous or rubbery-glassy regions, respectively. In this talk, we employ multiscale molecular dynamics simulations to investigate deformation and plastic flow of such polymers. For the semicrystalline case, we consider an ensemble of randomly nucleated crystallites embedded in an amorphous matrix. When stretched at constant rate, crystallites first reorient and partially fragment in the strain-softening regime, while chain alignment and recrystallization is observed in the strain-hardening regime [1]. We show that a significant contribution to the fracture toughness originates in cross-ties between crystallites. We also present results for sphere-forming triblock elastomers, where chain ends embedded in glassy spheres effectively cross-link a rubbery matrix. The evolution of the spherical morphology and chain on formations are compared for different deformation protocols and polymer molecular weight, and the consequences for the macroscopic stress-strain response will be discussed [2]. By tracking polymer entanglements throughout the deformation process, we test and improve upon current network models for crosslinked entangled polymer networks.
[1] Sara Jabbari-Farouji, Joerg Rottler, Olivier Lame, Ali Makke, Michel Perez,
and Jean-Louis Barrat, ACS Macro Lett. 4, 147 (2015)
[2] Amanda J. Parker and Joerg Rottler, Macromolecules 48, 8253 (2015)
Polymers subject to confinement in a narrow channel tend to be linearly ordered along the axis of the channel. When such a confined polymer is in a folded state, the internal overlap leads to a reduction in conformational entropy that increases the free energy. A similar effect arises when two different polymers overlap along the channel. In each case, the free energy tends to increase with increasing overlap, giving rise to entropic forces that drive unfolding or chain segregation. In this study, Monte Carlo simulations are used to measure the free energy of polymers subject to cylindrical confinement. The calculated free energy functions are used to test the predictions of scaling theories and quantify the finite-size effects. We focus on the effects of bending rigidity and macromolecular crowding. For a single-polymer system, we calculate the free energy as a function of extension length for a wormlike chain in the Odijk regime in cases where there is either one or two folds in the chain. The results are generally in agreement with the predictions of simple scaling arguments, though quantitative discrepancies persist for chains up to 400 monomers in length due to finite-size effects. We also measure the free energy functions for a system of two flexible polymers in the presence of mobile crowding agents. We find that increasing crowder packing fraction tends to decrease the overlap free energy cost. However, for fixed packing fraction, the free energy barrier increases as the crowder/monomer size ratio decreases. The relevance of these results to the process of chromosome segregation in replicating bacteria is discussed.
The equivalent behavior among analogous block copolymer systems involving chemically distinct molecules or mathematically different models has long hinted at an underlying universality, but only recently has it been rigorously demonstrated by matching results from different simulations. The profound implication of universality is that simple coarse-grained models can be calibrated so as to provide quantitatively accurate predictions to experiment. Here, we provide the first compelling demonstration of this by simulating a polyisoprene-polylactide diblock copolymer melt using a previously calibrated lattice model. The simulation successfully predicts the peak in the disordered-state structure function, the position of the order-disorder transition and the latent heat of the transition in excellent quantitative agreement with experiment. This could mark a new era of precision in the field of block copolymer research.
Block copolymers, which are composed of two or more chemically distinct sub-chains or blocks, could self-assembled to form various ordered phases. Among the block copolymer phases, the spherical packing phases are of particular interest because it resembles the familiar atomic crystals. For a very long time, it had been believed that the stable spherical phases of diblock copolymers are mainly of body-centered-cubic (BCC) symmetry. Recent experiments have shown that more complex spherical packing phases, such as the A15 and Frank-Kasper σ-phase, could become equilibrium phases of diblock and tetrablock copolymers. We have carried out a systematic study to understand the mechanisms stabilizing these complex spherical packing phases. We demonstrated that the A15 and Frank-Kaspe σ-phases could be stabilized in various polymeric systems. Furthermore, we revealed that a generic mechanism to stabilize the complex spherical packing phases is the formation of nonspherical domains with different sizes, which could be achieved in various molecular formulations such as conformational asymmetry, topological architectures, and polydispersity distribution of macromolecules.
The polymerisation index, N, is the most important parameter describing a particular polymer. Properties such as the glass transition temperature, solubility, and phase behaviour depend strongly on N. In most cases, the small N region describes the transition between oligomer and polymer, where the change in physical parameters is most pronounced. The most monodisperse polymers widely available are those produced by living polymerisation. This sophisticated chemical technique leads to a final sample containing many different N. We describe a simple technique, applicable to a wide range of polymers, which can produce almost pure N-mer systems. Examples of polystyrene and polyethylene oxide are considered and characterised by melting and glass transition temperatures.
Students and Postdocs will have an opportunity to introduce themselves to the community and summarize their project.
In this talk we first introduce a new extension to the structural phase field crystal (XPFC) approach that employs rotationally invariant multi-point correlation functions which allow for a progression of complex materials phenomena to be simulated, ranging from pressure-induced phase transitions between vapor-liquid-solid phases to polycrystalline solidification and grain growth in both metallic and complex non-metallic solids. New results from two recent studies made using the XPFC modelling will be presented. The first examines defect-assisted nucleation of precipitate solute clusters in ternary alloys (Al-Mg-Si). The second study uses a new XPFC model to examine the role of pressure and on growth rates and defect structures in graphene.
Block copolymers that form thermoplastic elastomers have some blocks that form glassy domains and other elastic blocks that bind the glassy domains together, leading to strong, and yet elastic materials. Binding glassy domains requires molecular bridges between domains, with the greatest number of molecules bridging between domains being the most desirable. Starblock copolymers have several glassy end blocks and therefore a high potential to enter multiple domains. We investigate bridging fractions and other statistical properties of starblock arms using self-consistent field theory. For 9-arm stars, the fraction of stars that bridge domains can exceed $99.9\%$ - far above bridging fractions found for triblocks or linear multiblocks. High bridging fractions, combined with the ability for a single molecule to bridge more than two domains makes starblock copolymers an excellent candidate for strong thermoplastic elastomers.
The Sanchez-Lacombe equation of state, despite an inherent thermodynamic inconsistency, can be shown to be consistent, predictive and quantitative for numerical solubility calculations. The theory can thus be shown to be one of the simplest and most versatile equations of state with a predictive capacity which, in a sense, has no free parameters. Diverse solubility phenomena such as blowing agents dissolved in polymer melts for the creation of lightweight nanocellular polymeric foams, and hydrogen storage in metal organic frameworks will be mentioned.
Collagen is the fundamental structural protein in vertebrates and is widely used as biomaterial, for example as a substrate for tissue engineering. Assembled from individual triple-helical proteins to make strong fibres, collagen is a beautiful example of a hierarchical self-assembling system. Using a combination of biophysical and biochemical techniques, we are investigating how its composition relates to its mechanics at the single-molecule level, and to the interactions driving self-assembly into fibrillar structures. In this talk, I will focus on our optical-tweezers-based microrheology studies, which investigated dynamics of interactions between collagen proteins and the development of heterogeneous microscale mechanics during self-assembly into fibrillar gels.
Telopeptides, short non-helical regions that flank collagen’s triple helix, have long been known to facilitate fibril self-assembly. Our studies show that their removal not only slows down fibril nucleation but also results in a significant frequency-dependent reduction in the elastic modulus of collagens in solution. We interpret these results in terms of a polymer association model, in which telopeptides facilitate transient intermolecular interactions that enhance network connectivity in solution and lead to more rapid assembly in fibril-forming conditions. Furthermore, by measuring the evolving viscoelastic properties of collagen solutions as telopeptides are cleaved, we demonstrate the ability to read out the progress of enzymatic reactions with microrheology. These findings enhance our ability to rationally engineer the self-assembly process.
We study the effects of binding kinetics on the diffusive transport of particles within narrow channels, which exhibit single-file diffusion (SFD). We computationally study the binding of particles to the channel wall, leading to transient immobility. We find rapid binding kinetics leads to the canonical result that diffusive transport is unchanged by SFD, while slow binding kinetics leads to an anomalously slow diffusive transport. Nevertheless, the relationship between diffusive transport and the subdiffusive motion of tracked particles is maintained in all cases. We exploit this relationship to study transport in the fully-occupied limit, through the diffusion of individual holes. Remarkably, the scaled diffusivity $\hat{D}$ characterizing transport exhibits scaling collapse with respect to the occupation fraction $p$ of sites along the channel. We present a simple physical picture that captures the characteristic occupation fraction $p_{scale}$ and the asymptotic dependence on $p$.
Our goal is to uncover mechanisms for macromolecular transport in the crowded environment of living cells. We use a nanoscale (experimental) model polymer-colloid system to examine the interplay between excluded volume and charge in macromolecular crowding. In this system, we measure polymer structure by small-angle neutron scattering (SANS) and polymer and crowder dynamics by pulsed-field-gradient NMR (PFG-NMR) and rheology [1]. We focus on the case where polymer and crowder size are comparable. The polymer is non-ionic, and crowder charge can be controlled.
For uncharged crowder, polymer size in the polymer-dilute limit is unaffected by crowder (colloid) volume fraction $\Phi_F$ when the crowder is uncharged, but the polymer expands at high $\Phi_F$ when the crowder is charged. In addition, we find at all $\Phi_F$ that the micro-viscosity of the crowder is somewhat larger/smaller than the bulk viscosity (for charged/uncharged colloid), but that of the flexible polymer is much smaller than the bulk viscosity, and also dependent on crowder charge. We thus observe shape-dependent transport in a simple model system for macromolecular crowding.
[1] Swomitra Palit, Lilin He, William A. Hamilton, Arun Yethiraj, Anand Yethiraj, Phys. Rev. Lett. (2017).
Sensitive visualization and conformational control of biopolymer interactions at super-molecular (tens to hundreds of nanometers) dimensions is important because it is at these scales that biopolymers undergo liquid-liquid phase separation. In particular, it remains unclear how protein-protein interactions regulate the formation of non-membranous organelles, with specific functions inside the cell and how nanoscale confinement may regulate the physical properties of these structures. We address these challenges by using Convex Lens-induced Confinement (CLiC) technology to gently load polymers and biopolymers into a nanofabricated array of pits. We have tested this approach using solutions of two water-soluble polymers, polyethylene glycol and dextran, as a model system. Our tools enable us to confine polymeric solutions in 10-100 nanometer scales and visualize the phase separation directly. Additionally, we are performing particle tracking microrheology to study the mesoscale properties of dextran liquid droplets in order to explore the relationship between droplet sizes and their viscoelastic properties.
We have investigated the start-up flow and yielding transition of Carbopol 940 in a vertical pipe. Carbopol is a soft solid when the applied shear stress is lower than its yield stress, but flows for higher stresses. Carbopol in a vertical pipe was displaced by an immiscible Newtonian fluid injected at a constant rate at the bottom of the pipe. Measurements of the wall shear stress and the velocity field in the Carbopol indicate that the flow undergoes a complex transient as the material yields, with the flow profile being parabolic at early times before approaching the expected plug-like flow at sufficiently long times. For rough boundary conditions, yielding took place when the wall stress was equal to the yield stress. For smooth boundaries, flow occurred at lower stresses due to slip at the walls. I will discuss our results in the context of our understanding of the yielding transition and the viscoelastic properties of the material.
Nature offers amazing examples of nanostructured molecules and materials. I will focus on phytoglycogen, a highly branched polymer of glucose produced in the form of dense, monodisperse nanoparticles by some varieties of plants such as sweet corn. The particles are chemically simple, but have a special dendrimeric or tree-like structure that produces interesting and unusual properties such as extraordinary water retention, and low viscosity and exceptional stability in water. These properties point to a wide variety of potential applications from cosmetics to drug delivery, yet these applications need to be enabled by a deeper understanding of the unique structure of the particles and their interaction with water. To achieve this, we have used a wide range of techniques. Neutron scattering has revealed that the nanoparticles have uniform size and density and are highly hydrated, with each nanoparticle containing about 250% of its mass in water. Surface-sensitive infrared absorption measurements on phytoglycogen films show that the high degree of branching in phytoglycogen leads to a well ordered “network” structure of the hydration water within the particles. Rheology measurements have revealed weak interactions between the particles, allowing loading of the particles into water up to 20% w/w before significant increases in viscosity are observed, showing that this is an interesting model system for studying soft colloid physics. This work has also benefitted from molecular dynamics simulations by the group of Hendrick de Haan. Taken together, these studies provide new insights that are key to fully understanding and exploiting these materials in new technologies and therapies.
This talk discusses x-ray photon correlation spectroscopy under shear (Rheo-XPCS) as a method for studying the behaviour of soft nanostructured materials in response to applied deformation. In XPCS, the characteristic “speckle” patterns resulting from the scattering of coherent x-rays are auto-correlated to uncover collective dynamics in a sample. XPCS can currently be used to study the dynamical behavior of non-ergodic materials on the nanoscale over a wide range of time scales (from $10^{-3}$-$10^3$s). Here we present studies of a set of soft disordered solids (concentrated nano-colloidal gels, nano-emulsions and clay suspensions) subjected to in-situ shear strain that provide insight into particle rearrangements at the nanometer scale and their connection to dynamical and mechanical behaviour of the materials. These studies illustrate a range of fascinating phenomena, including shear-induced rejuvenation and over-aging, mechanical training by large amplitude oscillatory strain, and nanoplasticity, that will be discussed.
Soft colloidal particles have inspired fundamental and practical interest recently for their rich and tunable properties, both on the single-particle level and collectively in bulk suspensions. Interdisciplinary research has led to applications in the chemical, biomedical, food, consumer care, and pharmaceutical industries. The simplest example of a soft colloid may be a linear polymer coil, which can be modeled as a deformable particle, whose size and shape respond to confinement. In biological cells, macromolecular crowding in the cytoplasm and nucleoplasm tightly constrains the conformations of biopolymers, such as proteins, DNA, and RNA. By combining Monte Carlo simulations with free-volume theory, we demonstrate that crowding by nanoparticles affects both the sizes and shapes of random-walk polymer coils, with implications for the structure and function of biopolymers.
Another class of soft colloids is comprised of microgels -- microscopic porous networks of cross-linked polymers. When dispersed in water, microgels swell in size and can acquire charge through dissociation of counterions. The equilibrium size of a microgel particle is governed by a delicate balance of osmotic pressures, which can be tuned by varying single-particle properties and externally controlled conditions, such as temperature, pH, ionic strength, and concentration. Because of their tunable size and capacity to encapsulate dye or drug molecules, these soft colloidal particles have practical relevance for biosensing, drug delivery, carbon capture, and filtration. Combining molecular dynamics simulations with Poisson-Boltzmann and Flory theories for a model of elastic, compressible particles, we demonstrate that, with increasing concentration, ionic microgels can deswell due to a redistribution of counterions. In contrast, nonionic microgels respond mainly to steric interparticle forces. We further explore consequences of size polydispersity for the structure, thermodynamic phase behavior, and rheology of microgel suspensions.
We will make a reservation at a local restaurant - please let us know if you are interested.
Barbara Frisken frisken@sfu.ca
Anand Yethiraj ayethiraj@mun.ca
CINP Board meeting
An intriguing connection was noticed recently by Kitaev between a simple model of Majorana fermions with random infinite range interactions – the Sachdev-Ye-Kitaev (SYK) model – and the horizons of extremal black holes in two-dimensional anti-de Sitter (AdS2) space. This connection furnishes a rare example of holographic duality between a solvable quantum-mechanical model and Einstein gravity. In this talk I will review some of these developments and describe a proposed physical realization of the SYK model in a solid state system. The system employs the Fu-Kane superconductor realized at the interface between a three dimensional topological insulator (TI) and an ordinary superconductor.
The requisite Majorana fermions are bound to a nanoscale hole fabricated in the superconductor that is threaded by N quanta of magnetic flux.
Under the right conditions the Majorana zero modes are described by the SYK Hamiltonian. Extensive numerical simulations demonstrate that the system indeed exhibits physical properties expected of the SYK model, including thermodynamic quantities and two-point as well as four-point correlators, and suggest ways in which these can be observed experimentally.
Characterization of transport properties of liquid Ni and Fe at high pressures has important geophysical implications for heat flow and dynamo action in terrestrial planetary interiors. Ni is a close electronic analogue of Fe and it is also integral to the Earth’s core. We report the measurements of electrical resistivity of solid and liquid Ni, and the preliminary results for Fe at pressures 3 – 9 GPa using a 3000 ton multi-anvil press.
A 4-wire method, along with a rapid acquisition meter and polarity switch, were used to overcome experimental challenges such as melt containment and maintaining sample geometry, and to mitigate the extreme reactivity/solubility of liquid Ni and Fe with most thermocouple materials. Thermal conductivity was calculated using the Wiedemann-Franz law.
Electrical resistivity of solid Ni and Fe exhibits the expected pressure dependence and is consistent with earlier experimental values which are mainly at 1 atm. Our results demonstrate that electrical resistivity of liquid Ni remains invariant along the pressure and temperature-dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. However, preliminary results on Fe indicate that electrical resistivity of decreases along its melting boundary.
Potential reasons are examined qualitatively for such behaviour in Ni through the impact of pressure-independent local short range ordering on electron mean free path and the possibility of a constant Fermi surface at the onset of melting.
While the correlation among metals obeying the Kadowaki-Woods ratio and the group of late transition metals with unfilled d-electron band displaying anomalously shallow melting curves suggest similar thermoelectric transport behaviour, Fe appears to behave differently than Ni, Pt and Mo. This is consistent with earlier theoretical predictions, however comprehensive physical understanding of such behaviour is insufficient at the moment.
Amir Hassanpour, Lionel Vayssieres, and Pablo Bianucci
Email: amir.hassanpour@concordia.ca
Metal doping of ZnO nanocrystals has great potential to increase the performance of advanced semiconductor devices such as gas sensors. The oxygen gas sensitivity of pure ZnO can be improved by Manganese (Mn) addition. In our report arrays of Mn-doped ZnO nanorods were synthesized by a hydrothermal method at a temperature as low as 60 ̊C. The low temperature makes our method applicable on a variety of substrates including polymer materials. In addition, our process does not require pH surveillance as previous works do. Forests of Mn-doped ZnO nanorods were synthesized on silicon substrates and their morphology was visualized by taking their cross section and top SEM images. The results show that substrate surface coverage and the nanorods uniformity were improved by Mn addition. Moreover, the nanorods aspect ratio increased from 6.5 to 10.2 for pure and Mn-doped ZnO nanorods, respectively. The crystallinity of the ZnO nanorods due to Mn doping was thoroughly investigated according to their X-ray Diffraction (XRD) patterns. The crystal structure of the Mn-doped ZnO nanorods remains unchanged as compared to pure ZnO, while their lattice constants have slightly increased. More detailed analysis on the effect of incorporation of Mn into ZnO crystal was done by micro-Raman spectroscopy. Raman spectra also confirmed the single wurtzite crystal structure for both pure and Mn-doped ZnO, while some of the common peaks were slightly shifted towards higher frequency due to lattice distortion. The average atomic percentage of Mn across the ZnO nanorods was measured to be 5% by using X-ray photoelectron spectroscopy (XPS). Finally, the band gap shift and defect related emission were measured by a photoluminescence set up (PL) at room temperature. The near band edge emission of Mn-doped ZnO nanorods red-shifted for 5 nm in comparison to pure ZnO nanorods, implying a band gap shrinkage by Mn addition. Our results show that low-temperature hydrothermal growth of Mn-doped ZnO nanorods is a feasible technique for obtaining high-quality material.
There is currently a great deal of interest in single photon sources specially for use in quantum information processing. Single photons, once produced, can be reliably manipulated and can travel long distances unaffected. Single quantum emitters such as quantum dots are one of the most promising methods for generating single photons on demand. In this work, we study InAsP quantum dots embedded in InP nanowires as a source of single photons which is potentially capable of producing photons in the optical C-band wavelength. To modulate the properties of our device, we generate a surface acoustic wave (SAW) on the device substrate by fabricating interdigitated transducers that causes two effects. First, a strain field is generated by the SAW that dynamically modulates the quantum dot properties. In addition, a piezoelectric field can be produced to manipulate the electrons and holes. As a result, transition energies within the quantum dot can oscillate at the same frequency of the SAW. This periodic tuning of the transition energy can then be used as a method to regulate the output of a device containing a single quantum dot.
We study the process of drop break up as well as the non-equilibrium analog of collective behaviours such as crystal melting using tunable electrohydrodynamic interactions in an oil-in-oil emulsion of silicone oil drops in the “leaky dielectric, castor oil. The experiments were carried out in capacitors made of ITO where the lateral extent is much smaller than the vertical dimension.
First, we examine the dependence of the drop breakup on cell thickness in the presence of an external DC electric field. Above a thickness of 100 $\mu$ m , the threshold of drop breakup is characterized by an electric Capillary number Ca_E which is of order unity, while it is much larger in thinner cells. Moreover, for thick cells, there is a convective instability that enhances the flows and the drop breakup [1].
In the second set of experiments, the ITO bottom plate of the capacitor was selectively etched such that a hexagonal array of roughly circular ITO-free regions was obtained. In this study, we used an external AC electric field to trap drops in the hexagonal array [2]. Varying frequency and field amplitude, we tune the strength of EHD interactions [3] and observe shape deformations, translational and orientational dynamics across the resulting order-to-disorder transition [4].
1- S. Khajehpour Tadavani, J. R. Munroe, and A. Yethiraj. Electrohydrodynamic behavior of droplets in a micro fluidic oil-in-oil emulsion. Physics of Fluids. Submitted 2016.
2- A. Varshney, S. Gohil, S. Khajehpour Tadavani, A. Yethiraj, S. Bhattacharya, and S. Ghosh. Large scale arrays of tunable microlenses. Lab on a Chip, 14:13301335, 2014.
3- A. Varshney, S. Ghosh, S. Bhattacharya, and A. Yethiraj. Self organization of exotic oil-in-oil phases driven by tunable electrohydrodynamics. Scientifiec Reports, 2:1–6, 2012.
4- S. Khajehpour Tadavani and A. Yethiraj, Melting of a granular oil-droplet crystal under the influence of tunable hydrodynamic interactions, Submitted, 2017.
Though lasers are ubiquitous in manufacturing, the vast majority of applications involve no depth control due to the inherent beam nature of light. Even the most deterministic of processes (like ultrafast micromachining) suffer from variability when scaled up to sufficient repetition rates and powers to provide material removal rates to meet industrial needs. Instead of trying to control the light-matter process, we exploit coherent imaging to monitor laser depth in situ at high speeds (>200 kHz). Full sample morphology during processing can be recorded with micron precision even in the presence of intense laser light, plasma and black-body radiation. Monitoring is so robust that we have achieved fully closed-loop control of laser cutting and welding. Laser Depth Dynamics was formed in 2012 to commercialize this approach and has sold systems in Europe, North America and Asia primarily in the fields of automotive and aerospace manufacturing.
In partnership with the Royal Canadian Mint (RCM), a new laser colouring technique was developed using ultrafast lasers. The colouring of noble metals is initiated by laser ablation. We discuss the creation of nanoparticle arrays on the metal’s surface by the cooling of the plasma plume. The ablation is done in air, where the content of the plasma is re-deposited onto the metal’s surface. We show that these structures can be controlled to produce any desired colour on the surface of silver, gold, copper and aluminum while preserving purity. Large-scale simulations of metallic nanospheres distributed on a surface by using a bulk plasma model, i.e., Drude with two critical points, which takes into account the interband transition region, well reproduce the colour trends observed in experiments. We present a plasmonic coloured coin of diameter of 21 cm, thickness of 2.5 cm and overall topography of 1.5 cm. The process of generating the colours is fast and reproducible making it viable for large scale industrial applications. We also demonstrate the passivation and colour tuning of the coloured surfaces via the deposition of thin layers of aluminum oxide by atomic layer deposition (ALD).
Belle II is a high-luminosity B quark factory facility located at the SuperKEKB electron-positron collider at the KEK laboratory in Japan. The main goal of Belle II is the search for evidence of new physics beyond the standard model of particle physics, through measurements of CP violation, rare decays, and searches for forbidden decays. It will improve the sensitivity to new physics by 1 to 2 orders of magnitude compared to previous B factory experiments. Belle II is currently in its commissioning phase, with first physics collisions planned for 2018. Due to higher beam currents and smaller beam sizes, beam-related backgrounds will be larger in Belle II than the ones experienced in Belle, the predecessor experiment of Belle II. Because these backgrounds can result in radiation damage and degraded detector performance due to high occupancy, real-time monitoring of backgrounds rates is essential. This talk will present the design of a system of fast scintillation detectors arrayed around the Belle II interaction region with the goal of monitoring all major sources of background including injection background during the operation of Belle II.
The Beast-II experiment aims to measure machine-induced backgrounds during commissioning of the SuperKEKB accelerator. The physical processes behind such backgrounds are notoriously difficult to simulate, hence the importance of conducting experimental validation as early as possible during the commissioning process. These results are critical to be able to predict the physics performance and lifetime of sensitive components of the Belle-II detector.
This presentation gives a brief overview of the BEAST-II detector, with focus on the crystal calorimeter system. The data-taking campaign can be split in two broad classes of measurements. The first consists of continuously recording data to study the long-term time structure of the backgrounds following dynamic pressure and vacuum scrubbing effects. The second class of measurements consists of dedicated "beam study" runs that artificially enhances specific contributions in order to disentangle the main background mechanisms and study their scaling with beam parameters.
The recorded data span from early February 2016 to the end of June 2016. The crystal calorimeter system was able to observe a broad range of background-related phenomena despite suffering notable radiation damage. The first comparisons of measured and simulation backgrounds are presented, together with first measurements of the injection background and an empirical description of the vacuum scrubbing process and the time structure of so-called "beam-dust" events.
The Belle II experiment at the KEK laboratory is currently undergoing
commissioning, with first physics data anticipated in 2018.
Understanding the material distribution of detector components is of
critical importance for precision e+e- collider experiments like
Belle-II, as the density and distribution of this material impacts
tracking and vertex reconstruction, as well as other aspects of detector
performance. In the talk I will present a comparison of test beam
experiments using high resolution tracking telescopes to obtain precise
2D images silicon vertex detector modules with the detector model
implemented in the Belle-II simulation. I will also present detailed
studies of material profiles of other components of the Belle II
detector and compare these with the as-built detector
In early 2016, BEAST, a detector designed to monitor beam conditions for SuperKEKB, was deployed for 4 months during phase-1 of beam commissioning. The BEAST detector consisted of multiple sub-detectors including the $^3$He proportional counters. During the beam commissioning the $^3$He tubes were successful in monitoring thermal neutron backgrounds caused by collisions with beam gas and Touschek interactions. These background measurements were then compared with GEANT4 simulations. As these measurements were taken without the Belle-II detector in place, BEAST will be redeployed after the Belle-II roll-in scheduled for 2017. It is expected that electron-positron collisions will begin by early 2018 for phase-2 beam commissioning.
During the second phase of BEAST the $^3$He tubes will continue to monitor thermal neutron rates. During phase-2 commissioning positron-electron collisions will begin which produces a large number of high energy by-products. These by-products could be damaging to sensitive components of the Belle-II detector, so the $^3$He detectors will measure the thermal neutron rate and the rates will be extrapolated to higher collision rates and beam currents.
Installation of the majority of BEAST, including the $^3$He tubes, is expected to occur in September 2017. Before the $^3$He tubes are reinstalled they will be recalibrated at the University of Victoria, and the data acquisition system will be upgraded. In particular, the cabling will be replaced with zero-halogen components to meet requirements for high radiation environments. When phase-2 begins $^3$He will be ready to provide useful insights into the SuperKEKB beam and the operating environment of Belle-II.
CMB and LSS allow us to probe the relics of inflation: phonons aka spatial volume fluctuations, which combine into an entropy-like measure, the orthogonal though entangled isocons, the holy grail gravitons, and the 4-volume dilaton fluctuations. The Standard Model of Cosmology is an amazing few parameter characterization of Planck and other data, but our theorizing and CMB + LSS experiments are in quest of what lies Beyond the SMc.
We consider a massless conformally (Weyl) invariant classical action consisting
of a magnetic monopole coupled to gravity in an anti-de Sitter background spacetime. We implement quantum corrections and this breaks the conformal (Weyl) symmetry, introduces a length scale via the process of renormalization and leads to the trace anomaly. We calculate the one-loop effective potential and determine from it the vacuum expectation value (VEV). Spontaneous symmetry breaking is radiatively induced à la Coleman-Weinberg and the scalar
coupling constant is exchanged for the dimensionful VEV via dimensional transmutation. An important result is that the Ricci scalar of the AdS background spacetime is determined entirely by the value of the VEV.
Analytic solutions of the field equations of scalar-tensor gravity can look very different in different conformal frame representations. For example, certain Brans class IV solutions describing wormholes in the Jordan frame correspond to horizonless geometries in the Einstein frame. The reasons for such a change of behaviour under conformal mappings are elucidated in general.
[Based on Phys. Rev. D 93, 024005 (2016)]
Classical nova explosions take place in binary star systems, in which a white dwarf is accreting matter from its companion star. Once enough material has been accreted, a thermonuclear runaway occurs on the white dwarf's surface, and the subsequent explosion ejects material into the interstellar medium. The thermonuclear 30P(p,γ)31S reaction rate influences the elemental and isotopic abundances of O-Ne nova nucleosynthesis, which affect the calibration of proposed nova thermometers and the identification of presolar grains of nova origin. The 38K(p,γ)39Ca reaction in turn influences the dynamics of the nucleosynthesis endpoint near A = 40, producing Ar and Ca in potentially observable amounts. Both reactions have lacked sufficient constraints from experiments. We will present experiments on these two reactions, using the β decay of 31Cl to populate levels of 31S of importance to the 30P(p,γ)31S reaction; and the first direct measurement of the 38K(p,γ)39Ca reaction using a beam of radioactive 38K.
Galactic chemical evolution is a multidisciplinary topic that involves nuclear physics, stellar evolution, galaxy evolution, and cosmology. Observations, experiments, and theories need to work together in order to build a comprehensive understanding of how the chemical elements synthesized in astronomical events are ejected and spread inside galaxies and recycled into new generations of stars. Nuclear physics provides nuclear reaction rates, stellar models provide the composition of stellar ejecta, galaxy models follow the evolution of chemical species driven by multiple stellar populations, cosmological simulations dictate how galaxies form and evolve in general, and observations provide constraints to test and improve numerical recipes driven by theories. During this talk, I will introduce the topic of galactic chemical evolution and present our efforts to create permanent connections between different fields of research (including nucleosynthesis and gravitational wave physics). Our ultimate goal is to better understand the origin of the elements in the universe and to explain the diverse chemical evolution patterns observed in nearby galaxies.
It is well understood that chains ends have an entropic preference for the surface of a polymer melt, and consequently the shorter chains of a polydisperse melt are favored at the surface. We study this effect for a bidisperse melt using numerical self-consistent field theory (SCFT). Semi-analytical approximations to the SCFT are derived for the concentration profiles resulting in simple expressions for the integrated excess or depletion of each component.
We examine the elastocapillary deformation of flexible microfibers in contact with liquid droplets. As the size of the contacting droplet increases, the fiber is observed to bend more in response. Finally, at a critical droplet size, proportional to the bending elastocapillary length, the fiber spontaneously winds itself around the droplet. Simple theoretical models yield predictions which are in agreement with the experimental findings.
Intricate patterns are abundant in nature, from the stripes of a zebra, to the formation of snowflakes, to the wavy peaks and valleys on a beach shore. Instabilities often drive this pattern formation where two competing interactions result in a frustration that is alleviated through the development of these beautiful patterns. One such instability occurs when a soft elastomeric film bonded to a rigid substrate deforms to adhere to an upper rigid surface brought into contact with the film. In this system, the balance of interfacial surface energy and elastic strain energy leads to distinct labyrinth patterns. We study the formation of this adhesion-induced instability by indenting elastomeric films with indenters of various geometries. This indentation method allows us to observe the fingering labyrinth instability both statically to measure wavelength as a function of film thickness, as well as dynamically where we see patterns similar to nanoscale snakes meandering along the ground. We also investigate the effect of film tension on instability growth by observing the pattern go from isotropic to anisotropic as a function of increasing biaxial strain.
We report on the elastocapillary deformation of flexible microfibers in contact with bubbles trapped at the surface of a liquid bath resulting in stunning 2-dimensional microfiber coils. Microfibers are placed on top of bubbles and are found to migrate to and wrap around the perimeter of the deformed liquid surface for certain bubble-fiber size combinations. A simple model incorporating surface and bending energies is used to describe the winding process.
Studying nano-scale flow in thin viscous films is of both practical and theoretical interest, particularly when considering the role of the hydrodynamic boundary conditions. Here, thin bilayer polystyrene films were prepared freestanding in air, with one of the two films having micrometer scale cylindrical holes. Because of the free interfaces, such films flow without interfacial friction at either surface. The viscoelastic relaxation of the holes was studied using atomic force microscopy. The temporal evolution of the holes shows three distinct regimes: an early time regime where the film has an elastic response; an intermediate regime where the hole undergoes viscoelastic symmetrization to equilibrate internal Laplace pressure; and a late time regime where the film undergoes capillary driven flow.
A crystal and a glass are different at a molecular level which leads to strong consequences at the macroscopic scale. We have developed an ideal experimental system to model such structures. The 2D clusters are made of an emulsion of lightly attractive, stabilized oil droplets ($R \sim 10$ $\mu m$) in water which are assembled droplet by droplet (tens of droplets). We study the response of the cluster when it is compressed between two thin glass rods ($R_c \sim 10$ $\mu m$). One glass rod is used as a force transducer in order to measure the forces as the droplets spatially rearrange under compression. Coupling the optical microscopy images of structural rearrangements within the 2D cluster with the direct force measurements provides insight into the failure mechanisms. Perfectly ordered crystals (highly monodisperse droplets) show well defined transitions. As the number of defects (substitution of a droplet by a smaller one) is increased in the crystal, we can study the transition toward a glassy system (bidisperse cluster). Additionally, the impact of the size of the cluster, the geometry of the initial aggregate, the relative size of a defect or even its position can be studied.
Optimum capture of the incident light through efficient photon management is considered a crucial requirement for realization of ultra-efficient photovoltaic devices. For this purpose, diffraction gratings have been applied for photon management in solar energy conversion. Specifically, due to the hexagonal arrangement of the grating structure, hexagonal gratings can be favorable in integrated optics since they occupy the least space compared to any other periodic arrangement. Here, our recent progress in development of nanostructured hexagonal diffraction gratings for application in light absorption enhancement in thin-film solar cells is presented. Leveraging the photon management ability of polystyrene nano-sphere arrays, the simplicity of the self-assembly fabrication process, and highly elastomeric properties of polydimethylsiloxane (PDMS), a novel stretchable transmissive hexagonal diffraction grating is introduced. Thanks to its unique flexible yet hexagonal structure, the proposed grating is capable of reproducible in-situ tuning of both diffraction efficiency and spectral range. The developed grating exhibits highly efficient and broadband light diffraction fairly independent of incident light polarization and angle of incidence while concurrently being able to achieve high diffraction efficiencies of about 80%. As a proof of concept, the proposed hexagonal diffraction grating is utilized for light absorption enhancement in colloidal quantum dot semiconductor thin-films. In addition, taking advantage of the same qualities of hexagonal arrangement induced by nano-sphere lithography, metallic reflective hexagonal diffraction gratings are also demonstrated to have a great potential for photon management through plasmonics. By careful engineering of the geometry of the gratings through controlling the size and the distance between grating components, both forward and backward propagating surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) were observed in a hexagonal diffraction grating for the first time. Simultaneous excitation of SPPs and LSPs demonstrated here can have a considerable impact on light absorption enhancement in nanostructured thin-film solar cells through both local and interfacial light confinement.
Fiber lasers have many applications in industry and medicine because of their unique characteristics—an all-fiber design, compact size, cost-effective production and operation, and no need for re-alignment and external cooling. A fiber laser emitting in the infrared region has applications in optical communication, sensing, spectroscopy and nonlinear optics.
The Photonics Research Group is currently developing (i) A sensor to detect trace gases— a stand-alone gas analyzer, for real-time use at ambient temperature, to monitor N2O emissions was developed; research in trace-gas sensing, especially detecting and quantifying greenhouse gases, is growing rapidly; and (ii) A plasmonic nanostructure to detect chemicals at a molecular level using fiber laser technology—using optical tweezing to trap dielectric particles revolutionized research in nanotechnology and spectroscopy. An optical tweezer based on a single-mode or a multimode tapered fiber is attractive because it is simple to fabricate. A plasmonic substrate was fabricated using gold nanorods (GNR). The GNRs were tweezed by the gradient force on the surface of the tapered fiber. The gradient force was produced by the laser light coupled to the fiber from the untapered end. The GNRs formed a periodic structure like a fiber Bragg grating.
In this talk, the author will present details of the gas detection system and its unique features, and discuss the fabrication of plasmonic structures on a tapered optical fiber using optical tweezing.
This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI) and Agrium Inc.
In recent decades, thin-film technologies have emerged as front-runners in solar light harvesting for their highly-reduced material volume and cost. Absorption lengths exceeding film thickness restricts absorption, but this scale allows us to take advantage of state-of-the-art light-trapping and field enhancing techniques that increase photon lifetimes. One type of structure is the scattering entrance layer, generally using a rough film or engineered patterning. In this work, we study the scattering enhanced absorption due to photonic crystal (PC) nanowire and nanohole geometries (1 micron in height), and optimize each geometry using finite-difference time-domain (FDTD) techniques. These structures can trap light via coupling into leaky PC modes, strongly enhancing the photonic local density of states (LDOS) and light-matter interactions. We show that these structures are not only robust to different classes (positional and radial) and magnitudes of disorder, but that broadband absorption is improved by the disorder-induced induced broadening of PC modes. We also compare these effects between (crystalline) Si and GaAs. We find that GaAs, unexpectedly, does not show the same qualitative behavior in the presence of structural disorder, remaining relatively unaffected while Si experiences improvements upwards of 30%. Careful calculations and analysis of the LDOS (local density of photon states) shows that the higher natural absorption of GaAs broadens the PC modes; thus, GaAs remains robust to disorder, but does not have as much room for improvement, relative to Si for enhanced scattering.
Optical tweezing is a well-known phenomenon for trapping or manipulating dielectric and metallic nanoparticles. The application of metallic nanoparticles in sensing has attracted a lot of attention due to their unique optical and chemical properties. We have developed a unique plasmonic structure on the surface of a multimode tapered optical fiber by optical tweezing of gold nanorods. In order to explain the formation of the nanostructure on the surface of the tapered fiber we will present both the results of our theoretical and experimental investigation. The theoretical results will include the variation of the scattering and gradient forces for trapping gold nanorods as the diameter of the tapered fiber section changes. It was found that as the tip diameter of the fiber decreases, the gradient force increases more rapidly than the scattering force. The theoretical results will lead to an estimate of the tip diameter of the tapered fiber to trap a single gold nanorod.
The research was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Foundations for Innovations.
Dark matter direct detection experiments have been traditionally reporting their results in terms of limits on the spin-independent and spin-dependent cross sections. However, these two types of interactions are only a subset of possible interactions between WIMPs and nucleons. The full set of couplings can be derived in the effective field theory (EFT) framework. In this approach “new" interactions depend on nuclear properties such as the orbital angular momentum and spin-orbit interactions. The focal point of the talk will be the interpretation of limits set by the PICO experiment in this theoretical context and the complementarity of different dark matter experiments.
NEWS-G is a dark matter direct-detection experiment using spherical proportional counters with light noble gases in the search for low-mass WIMPs. We report on the final results of the analysis of 42 days of WIMP-search data taken at the Laboratoire Souterrain de Modane using a 60 cm diameter sphere filled with a mixture of Ne + CH4 (0.7%) at 3.1 bars. Competitive constraints are set on the spin-independent WIMP-nucleon scattering cross-section for WIMP masses in the 1 GeV region. The next phase of the NEWS-G experiment is also presented : a 140 cm diameter sphere capable of handling 10 bars to be operated at SNOLAB. The use of lighter nuclei such as H and He will improve the sensitivity to sub-GeV WIMP masses.
During its first physics run the PICO-60 C$_3$F$_8$ bubble chamber was operated at a thermodynamic energy threshold of 3.3 keV, acquiring a background-free WIMP-search exposure of 1167 kg-days.
Following the acquisition of this dataset, the temperature and pressure of the superheated C$_3$F$_8$ target were altered to lower the energy threshold across a range of values from 2.5 keV to 1.8 keV. Stable operation at very low pressure is made possible by a 100 Hz recompression trigger on changes in the information content of live images of the chamber as seen by four high-speed cameras.
The background gamma rates measured at these thresholds were several times lower than predicted by conservative Monte Carlo estimates of the environmental gamma flux, suggesting the possibility of background-free operation at some subset of these lowered thresholds. Such a dataset would have significantly increased sensitivity to WIMP masses below 10 GeV/$c^2$.
Thermal relic dark matter models predict dark matter particles with masses of ~10 keV/c$^2$ to 10 TeV/c$^2$. As existing experiments are insensitive to the lowest masses in this range, new technologies for light dark matter searches are being pursued. The SuperCDMS, NEWS, DAMIC, and CRESST experiments are beginning to exploring the light dark matter regime while pushing towards the physical limits of ionization calorimetry with single photon or electron sensitivity. Future technologies measuring low-gap excitations will be required to search for the lightest possible thermal relic dark matter masses. Ideas for these future searches have recently been presented at the SLAC Dark Sectors and Lawrence Berkeley National Laboratory Sub-eV workshops.
These experiments face new challenges in understanding detector responses and backgrounds. Traditional nuclear recoil calibration techniques lack resolution at eV-scale energies and structure effects complicate the simple elastic recoil physics assumed by weak-scale dark matter searches. New mechanisms for backgrounds from radiation, leakage currents, and vibration in a cryogenic environment challenge the design of these low-threshold searches. A conceptual review of the prospects and challenges facing this frontier will be presented.
Recent results have highlighted that local measurement of a quantum field can reveal information about the global structure of spacetime. We therefore investigate the RP3 geon, which is identical to the Schwarzschild black hole except for a topological identification behind the event horizon. In order to model local measurements, we use the Unruh-DeWitt particle detector model. We find that a suitable detector can detect differences in the Hawking radiation that the detector measures in the two different spacetimes. We will analyze and discuss the implications of this result.
Single photon absorption is the process when an atom absorbs a photon whose energy is equal to the atoms next closest energy level. Two photon absorption however is when an atom absorbs any two photons whose energy sums up to the transition energy. The study of two photon absorption has multiple applications in several fields of physics. One area which has not been completely explored is its applications to astrophysics, particularly its application as a correction to the spectroscopy at cosmological distances. Hydrogen is the most abundant element in the universe and is therefore likely the biggest contributor to see how many photons in an emitted radiation field are lost to two photon absorption, in the immense distance traveled from a distant stars to ours. Although the absorption coefficient for such low intensity radiation is mostly insignificant, over such a huge distance it could contribute a significant correction to the radiation field. We will present calculations of the two photon absorption coefficient of hydrogen for low intensity radiation fields and show its application as a correction to said radiation field.
Blood Oxygen Level Dependent functional Magnetic Resonance Imaging (BOLD-fMRI) is a powerful tool to measure brain activity non-invasively. Over the past 25 years, it has become widely used in neuroscience research. However, BOLD does not measure neurons directly, but instead results from a complex interplay of vascular and metabolic processes, termed the ‘hemodynamic response’. Therefore, BOLD is influenced by various cell types as well as individual physiology and must be interpreted with caution. In particular, the use of BOLD to compare brain activity between groups with known physiological systematic differences, such as sex or age groups, is subject to bias.
My work makes use of a combination of imaging techniques (multimodal imaging), animal models, and biophysical modeling to measure and compute a maximum of physiological parameters influencing BOLD. The goal is to improve interpretation of past and future neuroscience studies based on BOLD and to improve its applications in atypical populations (e.g. persons with diseases that affect brain blood flow).
In this talk, I will present different brain imaging techniques and briefly discuss their biophysical basis. I will discuss our results from a study on the effects of aging on vascular physiology and how it affects the BOLD. This two-part study was conducted both in humans using non-invasive imaging and in a rat model of aging using microscopy.
Understanding the relation of BOLD to neural activity requires elucidating the mechanisms of what we call ‘neuro-vascular coupling’, i.e. the relation between neural activity and changes in local cerebral blood flow. One of the most exciting recent tools available to study this in animal models is the use of optogenetics, which allows control of specific cell types by means of laser illumination. I will illustrate how, combined with two-photon imaging of blood vessels, optogenetics allowed us to measure the contribution of specific neuronal types (e.g. excitatory vs inhibitory neurons) to the BOLD signal.
I will finally present my most recent work from imaging in awake, normally behaving mice, to elucidate the origins of the BOLD signal. I will discuss potential applications of these techniques in models of disease affecting blood flow and oxygenation, such as tumors.
There are important evidences that spontaneous fluctuations of the brain are sustained by a structural architecture of axonal fiber bundles. As recently suggested, this well-defined fiber distribution could be highly informative to understand the underlying principles of spontaneous fluctuations as well as to infer the functional connectivity patterns of the brain. Various models have been employed to investigate the structure function relationship of the brain. In this work we implemented the generalized Ising model using the fiber distribution as the input and compared its outcome with the empirical functional connectivity and investigated its properties. A simpler 2-dimensional classical Ising model was used as the baseline model. Thermodynamic properties, such as the magnetic susceptibility and the specific heat, illustrated a phase transition from ordered phase to the disordered phase at the critical temperature. Furthermore, graph properties were extracted from the simulated functional patterns and compared with the empirically created graph. The two graph properties, global degree and global efficiency, clearly depicted a maximum at criticality. Additionally, the generalized Ising model exhibited the emergence of the resting state networks at the critical temperature, thus suggesting its capability to predict the spontaneous fluctuations of the brain at criticality from the anatomical fiber distribution. Despite the contrast between the input structural connectivities, both models exhibited similar behaviour of the global properties such as the global degree and efficiency. This could be explained by the notion of both models being in the same universality class obeying the same scaling relations. This leads to the calculation of the dimensionality of the Brain which could be used to explain the behaviour of the model around criticality. By following this procedure it is possible to investigate properties of other systems in the same universality class to better understand the behaviour of the systems.
Interaction vertex imaging in an imaging method relying on detection of secondary particles created by beam interactions in the target. This method is believed to be viable for tracking dose deposition in patients undergoing heavy-ion radiotherapy. We investigated the impact of two key reconstruction algorithms on image accuracy: a single-particle-and-beam method, as proposed by previous work, and a triangulation approach believed to achieve greater accuracy than previously-examined techniques. Using Geant4, we simulated fragmentation and secondary particle production by a 145 MeV/u 12C beam with Gaussian distribution (FWHM = 5mm) in a water target, collecting data on particles exiting in a forward direction using thin silicon detectors. The best vertex accuracy was observed using triangulation reconstruction with the incoming beam and two coincident secondary particles. Accuracy was further improved by considering only particles detected more than 45 degrees from the beam axis, and with incident energy above 40 MeV for use in the reconstruction algorithm. Under these criteria, reconstructed vertices displayed an error of just over 2mm, with close to 90% directly corresponding to beam interactions in the target. Recent developments include further improvements in accuracy using narrower beams (FWHM = 1mm), and implementation of a human phantom in Geant4 based on CT scan data, in preparation for testing in more medically-relevant scenarios.
The measurement of brain axon diameter distributions is important in neuroscience, because axon diameter is directly proportional to nerve conduction velocity. Recent studies indicate possible changes in axon diameter distributions associated with diseases such as Alzheimer’s disease, autism, diabetes, dyslexia, fetal alcohol spectrum disorders and schizophrenia. The methods currently available for measuring axon diameters are highly invasive, requiring sectioning of brain tissue for electron microscopy, and are limited due to fixation and cutting artifacts, the need to use post mortem tissue, and the use of only small tissue sample sizes.
Combining oscillating gradient spin-echo sequences (OGSE) with models for axon distributions allowed us to infer sizes of structures, similar to axons, in phantoms, more accurately than previously done. For instance, capillary tubes were inferred to have diameters of 184 ± 25 µm. Methods to reduce imaging time while maintaining measurement precision will be discussed. For instance, reducing the number of diffusion gradient measurements made can shorten imaging time by a factor of 2.5 which results in a decrease in precision of 18%.
This work provides experimental evidence for using OGSE to infer the size of small structures. and lays the foundation for inferring the size of tissue structures, such as axon diameters in samples using MRI.
Optoacoustic (OA) imaging is being investigated as a non-invasive technique to characterize tissue microvasculature. The technique involves exposing tissues to nanosecond pulsed near infrared laser light. The optical energy is absorbed by tissue chromophores (eg hemoglobin) and converted into heat, leading to thermoelastic expansion, and the production of acoustic waves. The generated acoustic waves are in the ultrasonic frequency range and are detected by transducers positioned outside the body. The intensity and frequency of the OA signals is dependent on the concentration and size of the absorbers, respectively. As such, interpretation of OA signals/images relies on knowledge of the vasculature architecture such as vessel diameter, density and branching ratios, which differ in tumour compared to healthy normal tissues.
In this study, murine hepatic and renal normal vascular architectures were generated using a vascular casting method. All procedures performed were conducted in accordance with the guidelines of the Canadian Council for Animal Care. A casting solution of methyl methacrylate (Mercox®) with benzoyl peroxide (catalyst) was prepared and injected into the left ventricle. The soft tissue was then removed using sodium hydroxide (40%). The casts were cleaned and embedded into a gelatin matrix prior to OA imaging. Casts were imaged using a reverse-mode optoacoustic imaging system (Seno Medical, San Antonio, TX) consisting of a 775 nm laser and an 8-element annular transducer array with a central frequency of 5 MHz. Three mice were used in the study for a total of 3 hepatic casts and 6 renal casts. Optoacoustic signals were acquired in a 2 by 2 mm ROI centered on each cast.
Integrated OA signal amplitude values for the hepatic and renal vascular casts yielded no significant differences. However optoacoustic frequency spectral analysis, carried out by applying a linear fit to the calibrated power spectra, demonstrated a significant difference (p<0.001) in the midband fit (dB), slope (dB/MHz) and intercept (dB) values between the renal and hepatic casts. All three linear fit metrics were higher for the hepatic casts compared to the renal casts. The higher midband fit and slope observed for hepatic casts is associated with increased vessel density and decreased vessel size, compared to the renal casts, which agrees with the literature on these vascular architectures. The results demonstrate the ability of OA imaging to discriminate between different vascular architectures. Furthermore, frequency spectral analysis of OA signals can provide sub-resolution details about relative vessel size in the imaging field of view.
This research is supported by a NSERC Discovery Grant to W. Whelan
The methods of finite group theory are a powerful means of reducing the complexity of highly symmetric crystals such as the rare-earth pyrochlores. In these materials, the rare-earth ions are located at the vertices of a network of corner-sharing tetrahedra, an arrangement known as "geometric frustration". The family of rare-earth pyrochlores has a diverse membership which exhibit a variety of interesting magnetic phenomena, including spin ice, spin liquid and magnetically ordered states. Recently, there has been a great deal of effort to analyse many of these systems in terms of a single, general model containing four anisotropic exchange parameters. The application of this model to different materials will be discussed in this talk.
Since crystals are made of periodic structures in space, how to determine their three independent period vectors (starting from any values) is a basic physics problem. One choice is to minimize (Gibbs) energy or enthalpy for the situation where crystals are under constant external pressure. For crystals under constant external stress, we derived dynamical equations of the period vectors, for pair potentials recently (Can. J. Phys. 93: 974-978, dx.doi.org/10.1139/cjp-2014-0518). The derived dynamical equations show that the period vectors are driven by the imbalance between the internal and external stresses. The internal stress has both the kinetic energy term and a full virial term. Here we will extend it to many-body potentials.
Granular chains have numerous applications, ranging from shock absorption and vibration reduction, to detecting buried objects, to energy localization. As energy is transferred between grains they deform slightly, and the contact potential arising from the elastic deformation of grains is given by the Hertz law. The discrete nature of these systems in combination with the nonlinear contact force between neighboring grains leads to complex collective behavior. I will discuss the dynamics of granular chains and, in particular, will show how solitary wave propagation in these systems is affected by grain softness, and how introducing inertial mismatches affects the reflection of solitary waves at boundaries. I will further show how initial solitary wave energy can be trapped into localized modes with predictable frequencies in chains with soft central grains.
Graphene as a zero-bandgap two-dimensional semiconductor with a linear electron band dispersion
near the Dirac points has potential to exhibit very interesting nonlinear optical properties [1]. In particular, third harmonic generation of terahertz (THz) radiation should occur both due to the nonlinear relationship between the crystal momentum and the current density, and due to the interaction between interband and intraband parts of the current densities due to the vanishing bandgap [2]. In this work, we investigate THz nonlinear response of graphene situated inside a parallel plate waveguide (PPW). The graphene is contained in a PPW to increase the interaction time between THz radiation and graphene which, offers the potential to generate a larger third harmonic field.
In this work, we employ a Green function approach to solve for the generated third harmonic field in the PPW, inducing self-consistently the loss to the graphene at the fundamental and third harmonic. We optimize the plate separation and Fermi energy of the graphene to obtain phase matching and low loss, and thereby maximize third harmonic generation. We find that the best phase matching is obtained between the $TE1$ mode at the fundamental and the $TH3$ mode at the third harmonic.
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[2] I. Al-Naib, J. E. Sipe, M. M. Dignam, Phys. Rev. B 90
, 245423 (2015).
I will give a general update of our photoemission endstations at Canadian Light Source Inc. first, present some recent work in VUV photoemission (UPS) and hard x-ray photoemission (HXPS). I will also introduce the new angular resolved photoemission spectroscopy capability at CLS in the coming year.
The idea of using photonic crystals (PCs) to alter the dispersion relation of photons has received widespread interest. However, most of the existing research focused on the stationary PCs, while moving PCs were somewhat overlooked. In this abstract, we explore the guidance properties of moving hollow-core (HC) PCs. We find that the interaction between light and a moving HC-PC can lead to generation of frequency combs. Besides, amplitude of the sidebands in the frequency combs is dependent on the modal distribution of the PC guided modes, and could be considerably enhanced by introducing periodical point defects to the innermost rows of the HC-PC.
Consider two reference frames - a stationary frame S with coordinates (x, y, z, t) and a moving frame S’ with coordinates (x’, y’, z’, t’). The corresponding axes of the two frames are mutually parallel, and the frame S’ moves at a constant velocity v with respect to the frame S along its x-axis. The spacetime in the frame S’ could be related to the spacetime in the frame S via Lorentz transformation (LT). A HC-PC is moving along the x-axis in the frame S, so it is stationary in the frame S’. The hollow core of the PC is a defect introduced into the infinite PC by removing one row of lattice rods. For such a PC waveguide, one could readily find the modal solution of the core-guide modes at a certain frequency in the moving frame S’. Then, by applying LT to this modal solution, the corresponding solution of the guided mode in the frame S could be obtained. Therefore, the dispersion relation of the guided mode could be also obtained by performing modal analysis at a continuous range of frequencies. From the dispersion relation, we could find that two frequency combs are generated inside of the hollow core of a moving PC in the frame S. By analyzing the modal solution of the guided mode in the frame S, we also find that amplitude of the sidebands in the generated frequency combs is dependent on the modal distribution of the PC guide mode, which could be varied by introducing periodic point defects to the innermost rows of the hollow-core PC. Based on the results of our Comsol simulation, we conclude that the amplitude of the sidebands generated by regular moving PC is generally one to three order smaller than those of the sidebands generated by the moving PCs with periodic point defects.
In this study we present our latest measurement and theoretical results for self- and air-broadened transitions in the methane octad range. For this project we have used a set of 14 spectra of pure methane and lean mixtures of methane and air, recorded at the Jet Propulsion Laboratory. The spectra were analysed using a multispectrum fit program. We have measured the line positions, intensities, self- and air-broadened line width and pressure-induced shifts and their temperature dependencies and line mixing coefficients. The line positions and intensities have been compared with theoretical results. We will present comparisons of our results with database entries and previous studies.
The beta-decay of the halo nucleus helium-6 is investigated, with analysis of the relative abundances of the daughter states and the angular correlations between the products of the beta-decay. The corrected, higher precision, ion recoil spectrum is calculated, taking into account the momentum of ejected electrons. This spectrum contains the antineutrino signature, which is one of the products of the beta-decay. The standard model predicts that this should be a pure Gamow-Teller process of the axial vector type. A recent paper computed and investigated the probabilities for the various daughter states of the aforementioned beta-decay. Study of the recoil corrections to shake-up (( ^6)Li^+ bound states) and shake-off 6Li++ continuum states) was achieved by plotting the fractional abundance of ( ^6)Li^(++) versus the recoil energy. This work has revealed a 7σ disagreement with previously well-accepted experiment results. Our theoretical work is in collaboration with experimental groups performing spectroscopic analysis at Argonne National Laboratory and the University of Washington. The conceptual formulation of plausible mechanisms, and their subsequent testing, will aim to explain why such discrepancies exist. One such idea is that the continuum threshold could have been suppressed in an unaccounted fashion, due to the relatively high pressure of the background gas, compared to what can be achieved today. Another potential mechanism is the possible production of higher than expected quantities of neutral Lithium (( ^6)Li), which is analyzed theoretically by solving the Dirac equation for an electron moving in a Coulomb field, overlapped with the orbitals of ( ^6)Li. These, and other possibilities identified, are thoroughly scrutinized as potential sources of error.
We present the results of a spectroscopic study of 27 spectra of the fundamental band of pure carbon monoxide and carbon monoxide mixed with air, recorded over a range of temperatures. The Voigt, speed-dependent Voigt and Rautian line shape models have been employed in the analysis. Line intensities, air- and self-broadening coefficients, pressure induced air- and self-shift coefficients, Einstein A-coefficients and line-mixing parameters have been retrieved. The Exponential Power Gap and Energy Corrected Sudden scaling laws have been used to calculate line-mixing parameters. The pure carbon monoxide half widths have been calculated at different temperatures using a potential energy surface based on a Tipping-Herman intermolecular interaction potential and taking the electrostatic interactions into account. We have compared our measurement results with theoretical results (for the CO-CO system) and with previous published studies.
The tune-out wavelength is the wavelength at which the frequency dependent polarizability of an atom vanishes. It can be measured to very high precision by means of an interferometric comparison between two beams. This paper is part of a joint theoretical/ experimental project with K. Baldwin et al.\ (Australian National University) [1] and L.-Y. Tang et al.\ (Wuhan Institute of Physics and Mathematics) [2] to perform a high precision comparison between theory and experiment as a probe of atomic structure, including relativistic and quantum electrodynamic effects. We will report the results of calculations for the
tune-out wavelength that is closest to the $1s2s\;^3S - 1s3p\; ^3P$ transition of $^4$He. Our result for the $M = 0$ magnetic substate, obtained with a fully correlated Hylleraas basis set, is $413.079\,958\,51(12)$ nm. This includes a leading relativistic contribution of $-0.059\,218\,5(16)$ nm from the Breit interaction as a perturbation, and a relativistic recoil contribution of $-0.000\,044\,47(17)$ nm. The results will be compared with recent relativistic CI calculations [2].
\newline
[1] B. M. Henson et al., Phys.\ Rev.\ Lett.\ {\bf 115}, 043004 (2015).\newline
[2] Y.-H. Zhang et al., Phys.\ Rev.\ A {\bf 93}, 052516 (2016).
One of the rarest elements in the universe is astatine. All isotopes of astatine are radioactive and decay into other elements. The most stable astatine isotope $^{210}$At has a half-life of only 8.2 h. For this reason its elemental properties are difficult to study. Laser resonance ionization spectroscopy of astatine allows finding atomic energy levels and consequently, via the hyperfine interactions, information about nuclear structure. Finding auto-ionizing states of At, boost the overall ionization efficiency of Resonance Ionization Laser Ion Source (RILIS) such that even more exotic, shorter lived isotopes of At become accessible. A number of planned experiments rely on the predicted large octupole deformation of the heaviest At isotopes (A>220). Laser spectroscopic identification of auto-ionizing atomic states is a means to provide ionization efficiencies beyond those presently achieved by non-resonant ionization. Recent results from our experiments at TRIUMF will be presented.
The SuperCDMS experiment is a leading experiment in the direct search for Weakly Interacting Massive dark matter Particles (WIMPs) focusing on masses below about 10 GeV/c^2. The search method is based on deploying ultra-pure germanium and silicon detectors at cryogenic temperatures in a well-shielded environment. The WIMPs are detected via lattice vibrations induced by their elastic scattering off of atomic nuclei. For the new phase at SNOLAB, SuperCDMS is aiming to push the energy threshold for particle detection from the keV to the eV scale. I will discuss first studies towards a new proposed calibration method utilizing infrared photons rather the radioactive sources with the long-term goal to excited individual electron-hole pairs, mapping the energy scale down to about 1 eV.
The 40K isotope is the only known example of a unique-third forbidden transition. Its branching ratio directly to the ground state of 40Ar through electron capture has never been experimentally measured. This branching ratio will help with understanding the background in the DAMA/LIBRA experiment and other dark matter searches. “KDK” is the name of an international collaboration that is dedicated to this measurement.
The experiment will be performed by having a small, inner detector that will trigger on the x-rays and Auger electrons from 40K. This detector is currently a cooled Large Area Avalanche Photodiode (LAAPD) with an attached signal amplifier module. LAAPD’s are silicon based solid state detectors that convert photons into a charge current and have been shown to be capable of measuring low energy x-rays and electrons. The LAAPD will be surrounded (4π solid angle coverage) by an outer detector to tag the 1460 keV gammas released from the excited state of 40Ar. The outer detector is the Modular Total Absorption Spectrometer (MTAS) at Oak Ridge National Lab (ORNL), Tennessee. MTAS can provide a ~98-99% efficiency on tagging the 1460 keV gammas. By running the two detectors in coincidence we can separate the events caused by the decay of the excited state of 40Ar* through electron capture from the direct decay to ground state. Through this separation, we can perform a dedicated measurement of the EC channel.
We report on the performance of a Large Area Avalanche Photo Diode (LAAPD) for the direct measurement of the low energy x-rays and electrons. By observing multiple sources (65Zn, 54Mn, 55Fe and 40K) the LAAPD can be studied and characterised for the 40K energy range. Their viability for the use in a dedicated measurement of the EC branching ratio will then be determined.
The search for particle dark matter is one of the most active fields in physics, with many experiments using different methods to search for possible dark matter candidates. Direct-detection experiments look for rare interactions between some detector mass and these dark matter particles. The DAMA/LIBRA experiment utilizes Thallium-doped Sodium Iodide (NaI(Tl)) crystals at room temperature to search for dark matter direct-detection, and have claimed an annual modulation signal for dark matter.
There has been recent interest in the use of Cesium Iodide (CsI) as a doped or undoped scintillator as a target material in cryogenic scintillator detectors. Cryogenic scintillator detectors compare light and phonon signals from particle interactions to discriminate between nuclear and electron recoils. Pure CsI is an interesting target because of its chemical similarity to NaI(Tl) for direct comparison with the DAMA/LIBRA experiment.
We have measured the scintillation of CsI under alpha and gamma radiation using an optical cryostat installed at Queen’s University. Using PMTs and a fast digitizer, we can measure the light output of the CsI crystal to nanosecond precision over a large, millisecond timescale to completely capture individual scintillation events. We present the evolution of the light yield, scintillation time constants and alpha/gamma quenching factor of CsI from 300K to 3.4K. We observe a promising high light yield at low temperature, and an alpha/gamma quenching factor surprisingly greater than one for temperatures lower than 100K.
The NEWS-G collaboration is developing new detectors sensitive to low mass WIMPs. The detector is made of a spherical copper vessel filled with gas and radial electric field. The electric field is induced by a sensor bring to the middle of the sphere. Detector behaviour like stability on time or homogeneity are strongly correlated to sensor characteristics and gas quality. This talk will focus on both aspects.
Spherical gaseous particle detectors being developed with the NEWS-G collaboration are a new type of dark matter detector being used to detect low-mass WIMPs (Weakly Interacting Massive Particles). They consist of a metal sphere filled with gas, with a central electrode producing a radial electric field throughout. Incident particles ionize some of the gas, the charge from which creates a current pulse in the electrode. Understanding the behaviour of these detectors involves different calibration strategies. Properties investigated include among others, the homogeneity of the response of the detector, event energy reconstruction, discrimination between track-like and point-like events. This talk will concentrate on activities related to calibrations schemes using gaseous radioactive sources and ultraviolet lasers.
Astronomers have observed, through galaxy rotation curves, that our understanding of the dynamics at the scale of galaxies is rather incomplete; these observations amongst others led to the conclusion that there is something missing in our model or lacking in our understanding of the universe. A possible solution is the addition of dark matter, which can only interact very weakly and through gravity. As dark matter barely interacts with anything as it is extremely difficult to detect; it requires experiments with extremely low backgrounds and either extremely large detectors or extremely long exposure times or a combination of both. PICO is one of many dark matter search experiments, it utilises acoustic amplification of minute energy deposition within a superheated liquid to detect nuclear recoils from dark matter particles. Phenomenologically, we know different background particle interactions generate different acoustics, which we score with a parameter. All background particles will have known characteristics and a known distribution of scores, therefore we can infer that something is not one of the backgrounds. The bubble growth is responsible for the acoustic signal, therefore investigating its mechanics may enhance our discriminative tools.
An analysis algorithm is being developed for the DEAP-3600 dark matter search in order to correct the effects of signal saturation on key observables in the experiment. High energy events, such as alpha decays and some gamma decays, can produce enough scintillation photons to saturate the electronics in the signal-digitization stage. For this reason, a second channel of digitizers operated at lower gain is used for preserving the quality of data. The key feature of this analysis algorithm is a deconvolution on the low-gain readout channels for high energy events. By comparing low-gain channel signals, after deconvolution, with high-gain channel signals, the effect of saturation can be corrected. Once fully implemented into the data acquisition stream, this analysis tool will enable us to fully characterize the linearity of the detector energy response across the full energy spectrum.
According to the Independent Particle Model (IPM) single-particle states are fully occupied up to the Fermi energy with spectroscopic factors of one. However, it is well known from electron-induced proton knockout that the single-particle strength is reduced to about 60-70% for stable nuclei, which has been attributed to the presence of short-range and long-range correlations[1]. This finding has been confirmed by nuclear knockout reactions using stable and exotic beams, however, with a strong dependency on the proton-neutron asymmetry [2]. The observed strong reduction of single-particle cross sections for the deeply bound valence nucleons in asymmetric nuclei is theoretically not understood. To understand this dependency quantitatively a complementary approach, quasi-free knockout reactions, is introduced. Quasi-free knockout reactions in inverse kinematics at relativistic energies provide a direct way to investigate the single-particle structure of stable and exotic nuclei [3].
We have performed a systematic study of spectroscopic strength of oxygen isotopes using quasi-free (p,2p) knockout reactions in complete kinematics at the R3B/LAND setup at GSI with secondary beams containing $^{13−24}$O. The oxygen isotopic chain covers a large variation of separation energies, which allow a systematic study of spectroscopic factors with respect to neutron-proton asymmetry.
We will present results on the (p,2p) cross sections for the entire oxygen isotopic chain obtained from a single experiment. By comparison with the Eikonal reaction theory [4] the spectroscopic factors and reduction factors as a function of separation energy have been extracted and will be compared to existing data in literature. The results include total and partial cross sections extracted by means of gamma-coincidence measurements as well as momentum distributions. The latter are sensitive to the angular momentum of the knocked-out nucleon in the projectile.
Finally, a brief report will be given on a pioneer experiment performed at RIKEN where the quasi-free (p,2p)-fission reaction was employed for the first time on $^{238}$U as a benchmark test for future applications to determine fission barriers of neutron-rich exotic nuclei near $^{208}$Pb and $^{214}$Bi.
This work is supported by the GSI-TU Darmstadt cooperation agreement and the BMBF Verbundforschung under contract 05P15RDFN1 and the University of Guelph.
[1] L. Lapikas Nucl. Phys. A553, 297c (1993).
[2] J. A. Tostevin, A. Gade Phys. Rev. C 90, 057602 (2014).
[3] V. Panin et al. Phys. Letters B 753, 204-210 (2016).
[4] T. Aumann, C. Bertulani, J. Ryckebusch Phsy. Rev. C 88, 064610 (2013).
Electromagnetic transition rate measurements provide fundamental probes of the structure of nuclei and stringent tests for theoretical models important to our understanding of these many-bodied ensembles. Re-accelerated beams delivered by the ISAC-II facility at TRIUMF, Canada’s National Laboratory for Particle and Nuclear Physics, permit access to nuclear structure information for a wide range of radionuclides via in-beam gamma-ray spectroscopy with TIGRESS, a high-efficiency and Compton-suppressed segmented germanium clover array. Precise Doppler-shift lifetime measurements play an important role in this pursuit. Accordingly, the development of the TIGRESS Integrated Plunger (TIP) at Simon Fraser University presents the opportunity for Doppler-shift lifetime measurements of short-lived excited states using TIGRESS in combination with a plunger and an extensive suite of auxiliary charged-particle detector systems for exit channel selection following a variety of reaction mechanisms. Construction, characteristics, and implementation of the TIP plunger and its ancillary detectors will be discussed as they enable a rich set of electromagnetic transition rate measurements via Doppler-shift lifetime techniques following fusion-evaporation as well as unsafe Coulomb excitation. Recent results obtained with radioactive and stable beams will be presented.
Electromagnetic transition rate measurements serve as a fundamental probe of nuclear structure and provide a stringent test for theoretical models. Doppler shift lifetime measurements offer an opportunity to directly access information about electromagnetic transition rates and discriminate between model calculations. The TIGRESS Integrated Plunger device (TIP), constructed at SFU, supports Doppler shift lifetime measurements via gamma-ray spectroscopy with the TIGRESS segmented HPGe clover array as part of the experimental program at the ISAC-II facility of TRIUMF.
A method for determining lifetimes of excited states in nuclei populated using fusion-evaporation and measured using the Doppler-shift attenuation method (DSAM) will be presented. This method is applied to data collected for the benchmark nucleus $^{22}$Ne during a commissioning experiment for TIP and TIGRESS which employed the $^{12}$C($^{18}$O,2$\alpha$) $^{22}$Ne fusion-evaporation reaction. Mean lifetimes of populated states in $^{22}$Ne were measured via a comparison of the experimental data to Monte-Carlo lineshape simulations developed using the GEANT4 framework. Best fit lifetimes obtained using $\chi^2$ analysis were in agreement with the existing evaluated data, validating the analysis method used. Recent improvements in the TIP setup and planned future experiments will also be discussed.
Excited states of the proton-unbound nucleus $^{177}$Au have been populated following the $^{92}$Mo($^{88}$Sr,$ 2pn$) reaction in an experiment performed at the University of Jyv\"askyl\"a Accelerator Laboratory. Gamma rays detected in the JUROGAM spectrometer were correlated with the characteristic $\alpha$ decays of $^{177}$Au detected following a recoil implantation in the GREAT spectrometer. A large number of transitions ($\sim 60$ $\gamma$ rays) have been assigned unambiguously to $^{177}$Au and ordered into four collective band structures and other single-particle excitations.
Several intruder configurations formed by single-proton excitations across the $Z = 82$ shell gap have been established. These have been interpreted as $\pi i_{13/2}$, $\pi f_{7/2} \oplus h_{9/2}$ and $\pi h_{9/2}$ prolate configurations. It has been established that the $\pi i_{13/2}$ and $\pi f_{7/2} \oplus h_{9/2}$ bands have decay paths to both the positive-parity mixed (1/2$^{+} \oplus$ 3/2$^{+}$) ground state and the negative-parity 11/2$^-$ isomer, which is unusual in this mass region. Structures based on the coupling of the odd $\pi$ $h_{11/2}^{-1}$ proton hole to excitations of the $^{178}$Hg core have been established in the excitation level scheme. An oblate $\pi h_{11/2}^{-1}$ $\otimes$ $^{178}$Hg($2_{1}^{+}$) state and a prolate strongly coupled band based on the $\pi h_{11/2}^{-1}$ $\otimes$ $^{178}$Hg($0_{2}^{+}$) configuration have been identified. The decay paths from the strongly coupled band and the search for evidence of electric monopole decays are discussed.
Subcellular dynamics emerge from the interactions of molecules of many different types, and it seems a priori hopeless to build predictive theories, similar to what is done in physics. In this talk, I will use the example of early immune detection to (briefly) illustrate how approaches inspired by physics -from phenomenology to coarse graining- allow us to untangle the biological interaction “hairball”. This led us to the discovery of the so-called “adaptive sorting” principle, and to the experimental validation of some of its most counterintuitive aspects (in collaboration with Grégoire Altan-Bonnet, NIH).
Polymer light-emitting electrochemical cells (PLEC) are photonic devices that function by in situ electrochemical doping for luminescent polymers. Doping in PLECs is achieved via electrically activated redox reactions in the presence of mobile counter-ions. In operation, p- and n- doping fronts form at the anode and the cathode. The fronts then propagate through the polymer film and form a p-n junction where electrons and holes recombine radiatively and emit light. The formed p-n junction is the active area of the cell and it sets the operational electrical and optical characteristics of the device. Therefore is important to understand the electronic structure and the extension of this region. The dynamic nature of electrochemical doping introduces a challenge in studying the stabilized PLECs. To overcome this problem, the doping should be fixed by reducing the mobility of the counter-ions. One way to achieve this is by cooling the device after forming the junction. Frozen PLECs p-n junctions exhibit pronounced photovoltaic response that is independent of the electrodes work functions. Moreover, the photoluminescence of the polymer is modified upon doping due to luminescence quenching. Therefore, the doping in a frozen PLEC could be mapped by optical beam induced current (OBIC) and photoluminescence (PL) scanning. We present high-resolution OBIC and PL imaging of the doping structure in a doped and frozen planar PLEC. A custom-built cryogenic and optical apparatus was employed to activate, freeze and scan the cell with a laser beam with ~2 µm width. An extremely narrow OBIC profile of 4.5 µm in average width was resolved that accounts for less than 1% of the interelectrode spacing of the device. The OBIC and the PL measurements were used to propose the doping profile of the scanned junction. The proposed profile was tested against the experimental OBIC data via drift-diffusion numerical calculations.
We study the electrical and mechanical properties of poly(ethylene oxide)/multiwalled carbon
nanotube (PEO/MWCNT) composites made by melt mixing and compression molding. The dielec-
tric properties of the PEO/MWCNT composites have been studied in the frequency range from
100 mHz to 1 MHz as a function of temperature and ?ller concentration. Dielectric relaxation
times and DC conductivity were extracted from the data by ?tting to existing models. The perco-
lation transition of the MWCNT in the composites occurs for a MWCNT concentration between
2 and 3 wt%. Storage and loss moduli and the mechanical relaxation time were examined as a
function of MWCNT concentration and temperature using a shear rheometer. We examined the
dispersion of the MWCNT in the PEO matrix using atomic force microscopy and scanning electron
microscopy. The results of these experiments provide information about the microstructure of the
nanocomposite and the interactions between the polymer molecules and the CNTs.
Diblock copolymers are composed of two chemically distinct homopolymers, covalently bound end-to-end. One of the most notable features of block copolymers is their ability to self-assembly into a wide range of ordered periodic structures. There are many factors affecting the equilibrium morphology of diblock copolymers, one of which is polydispersity. The rich phase behaviour of polydispersed diblocks offers an opportunity to realize exotic phases that are not found in monodispersed systems. In this work, we explore the possibility of using polydispersity, in the form of binary mixtures of AB diblock copolymers, to stabilize the various bicontinuous structures, such as the double-diamond morphology. We focus on binary blends of B-majority diblock copolymers forming the double-gyroid phase, and A-majority chains that forms the homogeneous phase. The principal methodology of our study is the self-consistent field theory (SCFT). Solutions of the SCFT equations corresponding to the bicontinuous phases are obtained numerically, and the relative stability of the different ordered phases is then determined through a comparison of their free energy. The formation of the double-diamond phase is predicted for mixtures of specific compositions. Furthermore, we show that the stability of the double-gyroid phase can be greatly enhanced, such that the volume fraction of component A constituting the bicontinuous network exceeds $50\%$.
The ability of a feed-forward neural network to learn and classify different states of polymer configurations is systematically explored. Performing numerical experiments, we find that a simple network model can, after adequate training, recognize multiple structures, including gas-like coil, liquid-like globular, and crystalline anti-Mackay and Mackay structures produced from Monte Carlo simulations. The network can be trained to identify the transition points between various states, which compare well with those identified by independent specific-heat calculations. Our study demonstrates that neural network provides an unconventional tool to study the phase transitions in polymeric systems. The direct use of molecular coordinates as input into the network underlies the robustness and simplicity of our approach, and suggests that other simulation tools, such as molecular dynamics, could be incorporated as well. The outcome of this work provides a compelling reason to incorporate machine learning techniques into molecular simulations more generally, as a powerful hybridized computational tool for the future study of soft-matter systems.
Ultrafast optical demagnetization is a phenomena whose origins have yet to be completely understood. One challenge in studying this phenomena is the low availability of femtosecond light sources in the XUV and X-ray regimes. By exploiting the process of High Harmonic Generation (HHG) in argon, we have developed a high-flux, table-top femtosecond XUV source. We use it for probing ultrafast optical demagnetization at the M-edge of cobalt through a pump-probe system. First, a femtosecond, infrared pump pulse demagnetizes the sample. Then, a XUV probe pulse illuminates the sample, where small-angle X-ray scattering on magnetic domains allows for the observation of contrast due to the X-ray magnetic circular dichroism effect. This scheme allows us to recover demagnetization curves for different pump wavelengths ranging from 1800nm to 400nm. At 800nm, we also produce demagnetization curves for various pump durations.
Driven-dissipative quantum optical systems may display dynamics that is difficult to accurately capture using a master equation approach, particularly in the limit of large excitation numbers. To keep pace with rapid experimental progress and increasing complexity in quantum optical systems, an effective computational approach is needed that is not limited by Hilbert space truncation. We first present a stochastic differential equation method to calculate dynamical quantum observables which is based on a phase-space representation of the quantum density matrix. This formalism is ideally suited to large systems where quantum effects are still important and whose semiclassical dynamics do not settle into a steady state, and we apply it to study the role of quantum noise in mesoscopic excitable laser systems. We find that for a wide parameter range, quantum noise significantly reshapes the output laser pulse and yields non-classical photon number distributions. Quantum fluctuations are also shown to drive self-sustaining laser output pulses without any input near the semiclassical self-pulsing threshold and thus soften the transition to this regime. Our stochastic approach elucidates the significant role of quantum noise in the excitable laser systems and allows for an intuitive understanding of how it modifies the dynamics of observables.
Materials containing azobenzene chromophores have been utilised for all-optical surface patterning because of their photoresponsive properties. When azobenzene derivatives are irradiated with a polarized light beam with wavelengths within their absorption band, they undergo a reversible cis-trans isomerization process leading to a molecular reorientation, and further illumination results in mass movement. Irradiation of thin films of azobenzene moieties with a light interference pattern leads to the formation of surface relief gratings (SRG). Surface relief structures can also be formed under single-beam exposure, where no external interference pattern is applied, and thus the structures form spontaneously. The profile of these spontaneous surface relief gratings (SSRG) depends enormously on the polarization and the incidence angle of the pump beam. In this work, dependence of SSRGs on the polarization and the incident angle of the pump beam has been studied on thin films of a Disperse Red 1- functionalized glass-forming compound. Under normal irradiation of linearly polarized beam, the SSRG consists of a patchwork of domains with gratings along two different directions with a grating vector of 40 degrees relative to the pump beam polarization direction. However, for oblique irradiation, SSRGs with distinct pitches and directions form. Samples were rotated about y axis (vertical axis) to obtain different incident angles. Polarisation on the surface of the sample remain unchanged for s (vertical) polarization regardless of incidence angle. In this case, rotating of the sample only modifies the k-vector of the pump beam on the surface of the sample. As the angle of incidence increases the pitch of the SSRG also increase. However, for other polarization states, changing incidence angle also affects the polarisation state on the surface of the samples. As polarization component in z direction (in direction of the sample thickness) increases, the amplitude of the SSRGs increases.
Hyperfine splittings in methanol (CH$_{3}$OH) have been revisited in three recent publications.
[i] Coudert et al. [JCP 143 (2015) 044304] published an analysis of splittings observed in the low-J range. They calculated 32 spin-rotation, 32 spin-spin, and 16 spin-torsion hyperfine constants using the ACES2 package. Three of these constants (c$_{zz}^{0}$, c$_{zz}^{0,h}$ and s$_{z}^{0,h}$) were adjusted to fit hyperfine patterns for 12 transitions.
[ii] Three present authors and collaborators [JCP 145 (2016) 024307] analyzed medium to high-J experimental Lamb-dip measurements in methanol and presented a theoretical spin-rotation explanation that was based on torsionally mediated spin-rotation hyperfine operators. These contain, in addition to the usual nuclear spin and overall rotational operators, factors in the torsional angle $\alpha$. Such operators have non-zero matrix elements between the two components of a torsion-rotation $^{tr}$E state, but have zero matrix elements within a $^{tr}$A state. More than 55 hyperfine splittings were successfully fitted using three parameters (c$_{xx}^{2}$, c$_{yy}^{2}$, and c$_{xy}^{2}$) and the fitted values agree well with ab initio values obtained in [i].
[iii] Lankhaar et al. [JCP 145 (2016) 244301] published a reanalysis of the data set from [i], using CFOUR recalculated hyperfine constants based on their rederivation of the relevant expressions. They explain why their choice of fixed and floated parameters leads to numerical values for all parameters that seem to be more physical than those in [i]. The results in (ii) raise the question of whether large torsionally-mediated spin-rotation splittings will occur in other methyl-rotor-containing molecules. This abstract presents ab initio calculations of torsionally mediated hyperfine splittings in the E states of acetaldehyde using the same three operators as in [ii], and spin-rotation constants computed by Gaussian09. We explore the first 13 K states for J from 10 to 40 and ${v}_{t}$ = 0, 1, and 2. Our calculations indicate that hyperfine splittings in CH$_{3}$CHO are just below current measurement capability. This conclusion is confirmed by available experimental measurements.
An overview of recent results in Higgs boson physics obtained with the ATLAS experiment at the Large Hadron Collider located at CERN, Geneva will be presented. It will consist of the description of key measurements about the properties of the recently discovered Higgs boson and of its consistency within the Standard Model of particle physics. The emphasis will be on the analyses performed with the collision data sample recorded by the ATLAS experiment at the centre-of-mass energy of 13 TeV. The Higgs physics prospects at the high-luminosity LHC will also be discussed.
The hierarchy problem suggests that there must be physics beyond the Standard Model (SM) in the electroweak sector. A deviation from SM-predicted values in the Higgs coupling to vector bosons would allow these new physics in the form of an extension to the Higgs sector. The Georgi-Machacek model introduces scalars in higher isospin multiplets to the SM, including a doubly-charged Higgs, while preserving custodial symmetry. This new scalar is potentially accessible as a resonance through charged vector boson scattering ($W^+ + W^+ \rightarrow W^+ + W^+$) in the 30 fb$^{-1}$ of $\sqrt{s} = 13$ TeV data collected by the ATLAS detector at the Large Hadron Collider (LHC).
This search focuses on the final state of this resonance which includes a pair of same-sign leptons accompanied by a pair of forward jets and missing transverse momentum (MET). Same-sign leptons in the final state are a rare feature of the standard model, and so the background is dominated by charge misidentification. Techniques to reduce these types of background are presented, and the potential for discovery or exclusion is discussed.
Since the Higgs boson was discovered in 2012, various production and decay modes of the Higgs have been measured. One production mode that has not yet been observed is Higgs production in association with a top quark pair. Discovery of this mode would yield a direct measurement of the Higgs coupling strength to the top quark, a measurement not easily accessible. This talk presents an ongoing analysis searching for Higgs boson production in association with a top quark pair in the $H \rightarrow b\bar{b}$ decay mode, in the lepton + jets final state. Multivariate techniques are used to separate signal-like events from background-like events. The reported studies use data recorded by the ATLAS experiment at $\sqrt{s}$ = 13 TeV during 2015 and 2016.
Black hole thermodynamics has motivated a search for deeper connection of entropy and gravity. We investigate this using a formulation of quantum field theory using non-unitary operators which give rise to entropy production. We try to obtain the physical consequences of this for quantum cosmology.
The canonical quantization of gravity leads to the Hamiltonian constraint: physical states of the theory are annihilated by the Hamiltonian. Combined with the Schrodinger equation, the Hamiltonian constraint dictates that the physical states of the theory do not evolve in time. Given that the physical states do not evolve, how do we explain the time evolution we see around us? The conditional probability interpretation of time offers an answer. In this talk, I will review this interpretation of time and extend the formalism to include the possibility of clocks interacting with the system whose evolution they are tracking and to include finite size clocks. These generalizations are necessary if the conditional probability interpretation of time is to be applied in a quantum gravitational setting.
As a black hole grows, its Hawking radiation is not thermal and, depending on the extent to which the Hawking spectrum is modulated, it can carry information about the infalling matter. Analogously, via the equivalence principle, the Unruh spectrum of non-uniformly accelerated trajectories is not thermal and, depending on the extent to which the Unruh radiation is modulated, it can carry information about the trajectory. Here, we calculate the exact extent to which Unruh spectra can be modulated through non-uniform acceleration. We find evidence that the conditions for a strong modulation, and therefore for a strong information-carrying capacity of the spectrum, can realistically be met in the cases of both the Unruh and Hawking effects.
Medal for Excellence in Teaching Undergraduate Physics | Médaille pour l'excellence en enseignement de la physique au premier cycle
Instructional labs are a major part of the undergraduate physics curriculum. Typically, they involve substantial financial, instructional and infrastructural resources. Do conventional labs contribute significantly to curriculum learning goals, and are they the most effective use of limited departmental resources?
In this presentation, I will review the changing role of the undergraduate physics lab as a major teaching instrument in the undergraduate curriculum with emphasis on introductory physics labs. Current trends will be examined and various initiatives that have been undertaken at local and national levels will be discussed.
NSERC EG Chair Report | Rapport de la présidente du GE
CAP-NSERC Liaison Committee Report | Rapport du Comité de liaison ACP-CRSNG
In two-dimensional (2D) crystals with broken inversion symmetry, the spin degeneracy of the electronic band structure may be lifted by Rashba spin-orbit coupling. The resulting spin-split dispersion is responsible for the spin Hall effect and can also be observed in ultra-cold atoms. This spin-split dispersion is described in terms of two distinct helicity bands, but below a threshold energy, electrons are confined to one of these. At the bottom of this lower band, the density of states is enhanced to form a van Hove singularity. This is the relevant regime for a dilute spin-orbit coupled 2D electron gas, which has been shown to host a variety of exotic phases in the presence of electron-electron interactions. In this limit, electron scattering from a hard disk potential has been shown to exhibit an unusual one-dimensional characteristic in its S matrix and scattering cross-section. In this talk we show that this behaviour is universal for Rashba scattering off of any circular, finite range potential. This is relevant both for impurity scattering in the noninteracting limit as well as for short-range two-particle scattering in the interacting problem. A generic solution of the T matrix is computed, which produces the one-dimensional character of the scattering physics.
We explore numerically the morphological patterns of thermo-diffusive instabilities in combustion fronts with a continuum fuel source, within a range of Lewis numbers and ignition temperatures, focusing on the cellular regime. For this purpose, we generalize the recent model of Brailovsky et al. [1] to include distinct process kinetics and reactant heterogeneity. The generalized model is derived analytically and validated with other established models in the limit of infinite Lewis number for zero-order and first-order kinetics. Cellular and dendritic instabilities are found at low Lewis numbers. These are studied using a dynamic adaptive mesh refinement technique that allows very large computational domains, thus allowing us to reduce finite-size effects that can affect or even preclude the emergence of these patterns. Our numerical linear stability analysis is consistent with the analytical results of Brailovsky et al. [1]. The distinct types of dynamics found in the vicinity of the critical Lewis number, ranging from steady-state cells to continued tip-splitting and cell-merging, are well described within the framework of thermo-diffusive instabilities and are consistent with previous numerical studies. These types of dynamics are classified as “quasi-linear” and characterized by low amplitude cells that may be strongly affected by the mode selection mechanism and growth prescribed by the linear theory. Below this range of Lewis number, highly non-linear effects become prominent and large amplitude, complex cellular and seaweed dendritic morphologies emerge.
The cellular patterns simulated in this work are similar to those observed in experiments of flame propagation over a bed of nano-aluminum powder burning with a counter flowing oxidizer [2]. These resemble the dendritic fingers observed in this study, in the limit of low-Lewis number (Fig. 1). It is noteworthy that the physical dimension of our computational domain is roughly close to their experimental setup.
[1] I. Brailovsky, I., P.V. Gordon, L. Kagan, and G. Sivashinsky , Combustion and Flame , 162, 2077 (2015).
[2] J.Y. Malchi, R.A. Yetter, S.F. Son, and G.A. Risha, Proceedings of the Combustion Institute, 31, 2617 (2007).
The combination of disorder and interactions generally leads to a suppression in the single-particle density of states in bulk electronic systems. Numerical studies of the Anderson-Hubbard model point to a unique zero-bias anomaly in strongly correlated materials with a width proportional to the inter-site hopping amplitude $t$. A zero-bias anomaly with the same parameter dependence also appears in ensembles of two-site systems. We describe how this zero-bias anomaly in two-site systems is reflected in existing data from double quantum dots, and we propose a method to see the zero bias anomaly explicitly, emphasizing that it is a unique signature of the presence of strong correlations.
The self-assembly of block copolymers into ordered microphases typically proceeds through nucleation. The free-energy barrier and the nucleation pathway are altered in the presence of a nucleating agent. By exploiting this fact, recent theoretical work has shown that an appropriately designed substrate may be used to fabricate defect-free films of block copolymers in an ordered phase. In this work, we look at a method for quantifying the effect of heterogeneities on the nucleation pathway in a model system. We find the minimum free energy path between the initial, metastable state and the stable state using the string method. We investigate the change in height of the free-energy barrier when the interface is included. The results obtained are compared with those from classical nucleation theory.
Gravitational wave (GW) astronomy has entered a new era with the direct detection of acoustic-band GW signals by laser interferometers. As with the electromagnetic spectrum, observing gravitational waves in a range of different frequency bands will yield complementary insights into the astrophysics of gravitating objects. Gravitational waves at micro-hertz to milli-hertz frequencies can be detected using an array of optical atomic clocks on satellites, by leveraging the extreme precision available with such clocks. This method affords a technologically feasible approach to imaging the universe in a novel GW band. To unlock this possibility, we are developing compact optical atomic clocks for eventual use on board satellites. In this talk, I will describe the method of GW detection using optical atomic clocks, and present our efforts towards realizing a portable optical clock.
We report on progress towards the construction of an optical atomic clock based on the $4s^{2}\,^{1}S_{0}\rightarrow4s3d\,^{1}D_{2}$ two-photon transition in $^{40}\mathrm{Ca}$ atoms. Two-photon transitions are inherently Doppler and recoil free, which eliminates the need for tight confinement of the atoms during interrogation. This allows for a simplified design that can be made robust, compact and portable. A compact magneto-optical trap for calcium atoms is constructed with 423 nm external cavity diode lasers. Two portable ultra-stable lasers at 915 nm, with linewidths below 50 Hz, have been developed for interrogation of the two-photon clock transition.
We present two complete maximally hyperentangled state analysis protocols for photons entangled in the polarization and spatial-mode degrees of freedom. The first protocol is a hyperentangled Bell state analysis scheme for two photons, and the second is a hyperentangled Greenberger-Horne-Zeilinger (GHZ) state analysis scheme for three photons. In each scheme, a set of mutually orthogonal hyperentangled basis states are completely and deterministically discriminated with the aid of cross-Kerr nonlinearities and linear optics. We also generalize the schemes to unambiguously analyze the N-photon hyperentangled GHZ state. Compared with previous protocols, our schemes greatly simplify the discrimination process and reduce the requirements on nonlinearities by using the measured spatial-mode state to assist in the analysis of the polarization state. These advantages make our schemes useful for practical applications in long-distance high-capacity quantum communication.
Precision measurements are testing the Standard Model of Particle Physics with increasing accuracy.This allows to constrain new physics beyond the Standard Model and access very high energy scales, often beyond those studied at the highest energy colliders such as the LHC. It will be described how the masses of the top quark and the Higgs boson were predicted before their discoveries, and how experiments at lower energies play an increasingly important role.
We explore the low scale implications of the Pati-Salam Model including the TeV scale right-handed neutrinos interacting and mixing with the MSSM fields through the inverse seesaw (IS) mechanism, in light of the muon $g-2$ resolution and highlight the solutions which are compatible with the Quasi-Yukawa Unification condition (QYU). We found that the presence of the right-handed neutrinos cause the smuons are rather heavy as $m_{\tilde{\mu}} > 800$ GeV in order to avoid tachyonic staus at the low scale. On the other hand, the sneutrinos can be as light as about 100 GeV along with the light charginos of mass $< 400$ GeV can yield so large contributions to muon anomalous magnetic moment (muon $g-2$) that the discrepancy between the experiment and the theory can be resolved. In addition, the model predicts relatively light Higgsinos ($\mu < 700$ GeV); and hence the second chargino mass is also light enough ($< 700$ GeV) to contribute to muon $g-2$. Light Higgsinos also yield less fine-tuning at the electroweak scale, and the regions compatible with the muon $g-2$ restricts $\Delta_{EW}< 100$ strictly, and this region is also compatible with QYU. In addition, the ratios among the Yukawa couplings should be as $1.8 < y_{t}/y_{b} < 2.6$, $y_{\tau}/y_{b}\sim 1.3 $ to yield correct fermion masses. In addition, even though the right-handed neutrino Yukawa coupling can be varied freely, the solutions restrict its range as $0.8< y_{\nu}/y_{b} < 1.7$.
%\section*{Abstract}
We performed a detailed analysis of the mass spectrum of $ U(1)^\prime $ extended MSSM models for both right-handed scalar neutrino and neutralino dark matter candidates. The analysis aims to differentiate among the anomaly free solutions of $ U(1)^\prime $ models obtained from supersymmetric $ SO(10) $ breaking. We impose standard unification conditions at GUT scale and include all recent experimental constraints, such as Higgs signal strengths, B-physics restrictions, and supersymmetric particle mass limits. Within these constraints, we analysed the validity of parameter space by using the muon anomalous magnetic moment and relic abundance constraints. The analysis of the spectrum leads to neutralino and sneutrino dark matter candidates, with the former naturally satisfying the relic conditions in a large portion of the parameter space, while the latter can be consistent with these conditions, but with much more strictly restricted parameter space. Differences among the models, and between the two candidates using cosmological constraints, occur in relic abundance and spin-independent cross section predictions. We also discuss the possibility of detecting these scenarios in future collider experiments.
In this talk I will discuss estimation of the migration flightpath of the songbirds where the daily location of the birds is recovered from small geolocator "backpacks" attached to the birds' backs. The data collection process produces very particular challenges, with potentially large errors as to the day-by-day locations. We propose to overcome these using Bayesian methodology, where the prior is used to smooth the recovered paths, thereby (hopefully) overcoming the errors within the observed data. The data was provided by the Bridget Stutchbury lab.
Based on the theory of large elastic deformation, a mathematical expression describing a non-linear model of the end-systolic pressure-volume relation (ESPVR) in the heart ventricles has been derived. Relations between ejection fraction (EF) and the parameters describing the ESPVR were used to obtain new indexes that can be used to assess the performance of the heart ventricles, those indexes offer a new approach for the understanding of the problem of heart failure with normal or preserved ejection fraction (HFpEF). The new indexes are based not only on the calculation of the change of the geometry of the ventricles, but also on the pressures acting on the myocardium and the areas below the ESPVR that have units of energy. Calculation can be performed in a non-invasive way when ratio of pressures is used. Applications published in the literature to a wide range of clinical data show consistent results that can be used for prognostic, diagnostic and monitoring of patients. Results show that the EF is just one of several indexes that can be used to assess the ventricular contraction, and that bivariate (or multivariate) analysis of indexes is superior to univariate analysis for the purpose of segregation between different clinical groups. The work is an example that shows the impact that mathematical physiology has on medicine, similar to the impact that mathematical physics had on the advancement of experimental physics.
Experiments have shown that hepatitis C virus (HCV) infections in vitro disseminate both distally via the release and diffusion of cell-free virus through the medium, and locally via direct, cell-to-cell transmission. To determine the relative contribution of each mode of infection to HCV dissemination, we developed an agent-based model that explicitly incorporates both distal and local modes of infection. The model tracks the concentration of extracellular infectious virus in the infection medium and the number of intracellular HCV RNA segments within each infected cell over the course of simulated in vitro HCV infections. The model was challenged with data from in vitro HCV infections conducted in the presence and absence of free-virus neutralizing antibodies. We found that direct, cell-to-cell infection accounts for 95% of infection events. In contrast, blocking the 5% of infections occurring via free virus results in a 60% reduction in the number of infection events at 72h post-infection. Taken together, these findings show that while HCV spread via cell-free virus contributes little to the number of infection events, it plays a critical role in speeding up cell-to-cell HCV dissemination in vitro by providing access to distant, uninfected areas, away from the already established large infection foci.
General Fusion (GF) is a private company developing fusion energy with the ultimate goal of building a fusion power plant. We are using a novel technique called Magnetized Target Fusion (MTF), first proposed by the US Naval Research Lab in the 1970’s. In MTF, one first creates a magnetically confined moderately warm plasma of around 100 eV in a flux conserver. The flux conserver is then rapidly compressed. The magnetic field cannot penetrate the flux conserver on the time scale of the implosion. Magnetic field and plasma are compressed to the high temperature, magnetic field and pressure required for a fast fusion burn (microseconds).
General Fusion’s Magnetized Target Fusion system uses a ~3m sphere filled with molten lead-lithium that is pumped to form a cavity. A pulse of magnetically-confined plasma fuel is then injected into the cavity. Around the sphere, an array of pistons drive a pressure wave into the centre of the sphere, compressing the plasma to fusion conditions. This process is then repeated, while the fusion neutrons from the reaction are captured in the liquid metal and used to generate electricity via a steam turbine. A standard heat exchanger-steam turbine produces electric power, and some of the steam is recycled to run the pistons.
Initial plasmas with performance sufficient to do compression experiments have been developed. Because of the size and capital cost of building a large-scale piston driven compression system, plasma compression experiments presently form these plasmas in an aluminum flux conserver that is rapidly compressed using a chemical driver. The results of these experiments will be presented.
Titanium is used pervasively over a range of fields [1], e.g. Ti is ubiquitous in biomedical implants, due to its low reactivity with the surrounding tissues. When Ti is exposed to air or water the resultant oxide is strongly adherent and thermodynamically stable, which protects the underlying metal from further oxidation The ability of Ti to withstand corrosion depends on the quality and characteristics of its unique passive oxide [2] which in turn depend on oxidation parameters. For example, electrochemically formed oxide films on Ti can be amorphous or crystalline, depending on the final anodization potential and electrolyte involved [3]. This can directly affect the biocompatibility of Ti, as thickness and crystallinity (rutile vs. anatase) can affect the degree of adsorption from human blood plasma [4]. Thus understanding the oxidation at an atomistic level is necessary if one wishes to develop better protective films. Isotopic labeling is used in conjunction with high-resolution ion depth profiling methods, including medium energy backscattering (MEIS) and nuclear reaction profiling (NRP) to determine O depth profiles and elucidate the transport and reaction mechanisms of the oxidation [5]. Magnetron sputtering was used to deposit Ti on Si(001), then exposed to isotopic 18O water vapour in Ar atmosphere to form an ultra-thin TiO2 film. The TiO2/Ti/Si(001) film was then electrochemically oxidized in D216O water over a range of voltages from 0-10 V, resulting in ∼40–295 Å thick oxide regions. As oxide thickness increases as a function of anodization voltage while the total concentration of 18O remains constant, the 18O is found at increasingly greater depths, while the 16O concentration rises monotonically at the oxide-electrolytle interface indicating O exchange reactions. New titanium oxide is created by 18O being diffusing towards the oxide-metal interface, all of which is consistent with O ions as a mobile species but additionally with the Ti ions will transported towards the oxide-oxidant interface resulting in growth at that interface as well.
[1] J.R.B. Gilbert. “The uses of titanium”, Mat. Sci. and Tech. 1 (1985) pp 257-262
[2] U. Diebold. “The surface science of titanium dioxide”, Surface science reports 48 (2003) pp 53-229
[3] O.R. Camara, C.P. Pauli, M.C. Giordano. “Potentiodynamic behavior of mechanically polished titanium electrodes” Electrochimica Acta 29 (1984) pp 1111-1117
[4] J. Weng, Q. Liu, J.G. Wolke, X. Zhang, K. de Groot. “Formation and characteristics of the apatite layer on plasma-sprayed hydroxyapatite coatings in simulated body Fluid”, Biomaterials 18 (2997) pp 1027-1035
[5] A. Akerman. “The Use of Oxygen Isotopic Labeling to Understand Oxidation Mechanisms”, Oxidation of Metals 590 (1997) pp.314
Herbertsmithite ZnCu_(3)OH_(6)Cl_(2) is a mineral material that hosts a kagome plane consisting of Cu2+ ions with spin S = 1/2. We will discuss our single crystal NMR measurements to probe the local spin susceptibility (based on the NMR frequency shift), low frequency spin fluctuations (based on the spin-lattice relaxation rate 1/T_1), and the effects of defect Cu2+ spins occupying the Zn2+ sites. We will show that both the local spin susceptibility and spin fluctuations in low magnetic fields show a signature of a small energy gap in the excitation spectrum [1,2].
Ref.
[1] M. Fu et al., Science 350 (2015) 655 and references therein.
[2] N. E. Sherman et al., Phys. Rev. B 94 (2016) 140415R.
Title: Thermodynamic and transport properties of single crystal YbNi$_4$Cd
Author: J. Lee, H. Park, E. Mun
Affiliation: Department of Physics, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6
Single crystals of YbNi$_4$Cd and LuNi$_4$Cd were grown via solution growth techniques. We have studied the thermal, magnetic, and electrical properties of the intermetallic system YbNi$_4$Cd and LuNi$_4$Cd by means of specific heat, magnetization, and resistivity measurements. In zero field YbNi$_4$Cd exhibits a long range magnetic order below ~1 K. The electrical resistivity and specific heat measurements show the magnetic as well as Kondo contributions. We will discuss the results in relation to the cubic compounds YbCu$_4$X (X = Ag, Cd, In) which show a wide variety of physical properties. The compounds crystallize in a cubic MgCu$_4$Sn-type crystal structure. YbCu$_4$Ag and YbCu$_4$Cd are a heavy-fermion compound with no magnetic ordering. YbCu$_4$In has attracted the greatest interest due to the first-order valence transition below 42 K.
Results are presented on analytic and computational analyses of the spin states associated with ABC stacked kagome planes of magnetic ions with only long-range dipole-dipole interactions. Extending previous work on the 2D kagome system, where six-fold discrete degeneracy of the ground state was revealed [1], we show that the 3D FCC kagome lattice exhibits a continuous degeneracy characterized by just six sub-lattice spin vectors and two spherical angles. Thermal fluctuations are shown to lift this degeneracy in an order-by-disorder process. Degaussing the lattice with a magnetic field applied along directions of high symmetry also results in lifting the continuous degeneracy to a subset of states from the original set of ground states, characterized by a single parameter. This lattice type is a model for the magnetic Mn ions in IrMn3, the most popular compound used as the antiferromagnetic pinning layer in hard-drive spin valve structures [2]. Analysis of these spin states is relevant for a deeper understanding of magnetic and thermal stability at surfaces and in thin films of IrMn3.
[1] M. S. Holden, M. L. Plumer, I. Saika-Voivod, and B. W. Southern , Phys. Rev. B 91, 224425 (2015); M. Maksymenko, V. R. Chandra, R. Moessner, Phys. Rev. B 91, 184407 (2015).
[2] M.D. LeBlanc, M.L. Plumer, J.P. Whitehead, and B.W. Southern, Phys. Rev. B 88, 094406 (2013).
In a variety of frustrated triangular lattice antiferromagnets with easy-plane anisotropy, it has been shown that a magnetization plateau is produced at $1/3$ of the saturation value for a magnetic field parallel to the basal plane.
This magnetization plateau is associated with a collinear up-up-down state where two spins are parallel to the field while the third one is antiparallel.
So far, this plateau has been shown to be accounted for by quantum and thermal fluctuations.
With perfect triangular lattices, weak interlayer interaction, and an effective $1/2$ spin, $Ba_3CoSb_2O_9$ is probably the best prototype of a frustrated quantum system.
We determined the $H$-$T$ phase diagrams of $Ba_3CoSb_2O_9$ for magnetic fields applied parallel and perpendicular to the basal plane using sound velocity measurements.
As the Landau model approach fails to explain all experimental observations, we studied the field dependence of magnetization at T = 0 using a classical model which considers the effect of the bi-quadratic ($\sim$$S^4$) coupling term.
Such interaction has been shown to arise from fluctuations or the coupling between spins and elastic degrees of freedom.
Taking into account the intralayer and interlayer interaction, the easy plane anisotropy and the bi-quadratic coupling, the model numerical results agree very well with the phase sequences observed for $\mathbf{H}\parallel a$ and $\mathbf{H}\parallel c$.
Moreover, in order to determine the magnitude of bi-quadratic coupling, we also estimated the magnetoelastic coupling strength by measuring the relative ultrasound velocity variation as a function of the field orientation at constant temperatures and field values.
The Verwey transition is a phase transition in which the development of charge order results in a rapid increase in electrical resistivity. This transition was first observed in magnetite (Fe3O4), which undergoes a metal-insulator transition at T ~ 125 K, driven by the formation of complex Fe2+/Fe3+ order. Recently, it was proposed that a similar type of transition may occur in Pb3Rh7O15, a mixed valence (Rh3+/Rh4+) rhodate which displays an abrupt increase in resistivity at T ~ 185 K, accompanied by corresponding anomalies in specific heat, magnetic susceptibility, and diffraction data. If true, this material would mark the first example of Verwey-type physics in a heavy 4d or 5d transition metal oxide system. We have carried out a series of synchrotron x-ray scattering measurements on single crystal samples of Pb3Rh7O15 with the goal of (a) clarifying the high and low temperature crystal structure of this compound, and (b) identifying any evidence of Rh3+/Rh4+ charge ordering below T ~ 185 K.
Miniaturization of quantum technologies have led to physics that require the marriage of atomic physics and nanomaterials science. Some of the resulting areas of research are hybrid quantum devices, single-molecule spectroscopies, table-top intense field generators, etc. I will present an exciting way of controlling light and nanomatter - the control of hybrid atom-plasmonic systems. By combining the electromagnetic enhancement properties of plasmonic nanomaterials with the modification of the atomic properties, we can achieve an unprecedented level of control over quantum dynamics.
The practical implementation of quantum computers places two specific requirements on the lifetime of a qubit, namely, long relevant decoherence times, and rapid state initialization times. There is a need for protocols wherein the spontaneous emission rate of a quantum system can be selectively increased so that long state lifetimes can be maintained during operation, and upon demand, selectively decreased so that the cooling time can be drastically shortened in duration when qubit purity needs to be restored.
Chris DiLoreto and I propose an efficient method to selectively enhance the spontaneous emission rate of a quantum system by changing the polarization of an incident control field, and exploiting the polarization dependence of the system's spontaneous emission rate. This differs from the usual Purcell enhancement of spontaneous emission rates as it can be selectively turned on and off. Using a three-level "Lambda" system in a quantum dot placed in between two silver nanoparticles and a linearly-polarized, monochromatic driving field, we present a protocol for rapid quantum state initialization; while maintaining long coherence times for control operations. This process increases the overall amount of time that a quantum system can be effectively utilized for quantum operations.
We characterize the propagation of surface plasmon polaritons (SPPs) at planar lossy interfaces by investigating the behavior of the energy flux and field intensity at the interface. For interfaces between dispersive and nondispersive linear, homogeneous and isotropic materials with positive, zero, and negative permittivity and permeability, a narrow transition frequency window separates propagating SPPs from leaky SPPs. We derive conditions on the permittivity and permeability corresponding to whether the SPPs are propagating or leaky. Ascertaining propagation characteristics of surface plasmon polaritons is important to check the viability of a given study or application. As an application we show that in frequency regions where one material has a double-negative refractive index, the SPPs are leaky, rather than propagating.
We acknowledge financial support from NSERC, Alberta Innovates Technology Futures, China's 1000 Talent Plan and the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center (NSF Grant PHY-1125565) with support of the Gordon and Betty Moore Foundation (GBMF-2644).
We propose to use squeezed hollow-core photonic bandgap Bragg fibers for surface sensing applications. We demonstrate theoretically and confirm experimentally that squeezing of the Bragg fiber core increases overlap between the optical fields of the core guided modes and the modes bound to the sensing layer, thus, significantly enhancing their interaction via anticrossing phenomenon, which, in turn, enhances surface sensitivity of the fiber sensor. As a practical demonstration, we apply our fiber sensor to in-situ monitoring of the dissolution dynamics of a sub-micron-thick polyvinyl butyral (PVB) film coated on the surface of the liquid-filled Bragg fiber core. Strong spectral shift is observed during the dissolution of the PVB film, and a surface spectral sensitivity of ~0.07nm/nm is achieved experimentally with aqueous analytes. The proposed fiber sensor offers a new sensing modality and opens new sensing applications for photonic bandgap fibers, such as real-time detection of binding and affinity, study of kinetics, etc. for a range of chemical and biological samples.
An analysis of several machine learning algorithms performing position classification on data in the DEAP-3600 detector will be presented. Due to possible surface contamination, the sensitivity of the experiment can be improved by selecting an inner sub-volume (fiducial volume) from the data. One method used to do this is called the ``MBLikelihood'' algorithm, which maximizes a likelihood function to determine the location of an event in the detector. A machine learning approach simply tries to classify each event as surface or fiducial in a binary fashion. This technique for fiducialization is more direct, and can thus be more aggressively optimized. Results will be presented on a comparison of the performance of several widely used machine learning algorithms, as well as their robustness against changes in the Monte Carlo detector optical parameters. Finally, the performance of each algorithm on a small data set of real events will be discussed. A limited sample of data expected to have come from the surface, based on other considerations than position reconstruction, is used as a validation of each algorithm outside of the Monte Carlo environment.
PICO is a direct Dark Matter detection experiment which focuses on elastic scattering of WIMPs (Weakly Interacting Massive Particle) with baryonic matter. The physics of the detector is based on the super heated liquid technique. The active liquid, presently C3F8, is kept at a temperature and pressure just above the boiling point. A slight perturbation in the liquid, e.g. energy deposited by a recoiling nucleus due to its elastic collision with an incoming neutron, can create a bubble. The neutron-induced bubbles develop indistinguishably from those induced by WIMPs. Therefore, understanding and predicting the expected neutron background is fundamental for the success of the experiment. One of the components of the neutron background are neutrons generated by muon interaction around the detector's active volume. In order to identify those background events the PICO experiment utilizes a muon veto. This presentation discusses the latest results of the muon veto GEANT4 simulations and MCNP neutron simulations used for the design of future muon veto for PICO500.
The fractoluminescent properties of BGO (Bi4Ge3O12) scintillators used as particle detectors have been studied in order to quantify the background light generation from fracture. BGO samples in a double-cleavage drilled compression (DCDC) geometry have been stressed to fracture with the crack length and acoustic and light emissions measured in both ambient and vacuum conditions. Using this system, we have been able to identify the light and acoustic output as a fracture propagates. Further experiments should allow for the characterization of these emissions which will aid in the design of particle detectors.
DEAP-3600 is a single phase liquid argon dark matter search experiment. The liquid argon target mass is contained in a spherical acrylic vessel and viewed by a surrounding array of photomultiplier tubes. Particle interaction in liquid argon produce scintillation light in the vacuum ultraviolet (VUV) spectrum, which is efficiently absorbed by the surrounding acrylic. To make visible interactions in the target volume, the inner surface of the acrylic sphere was coated in the organic wavelength shifter, 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), which has a re-emission spectrum for VUV light in the blue-visible regime. During the final stage of construction, a 3 micrometer thick coating of TPB was applied to the vessel's inner surface using vacuum deposition. Details on the final deposition, thickness considerations, and ex-situ measurements of the coating structure from removable witness samples in place during the evaporation will be presented.
Uncovered mysteries about neutrinos bring us deep underground to answer questions about the Universe. SNO+ is a multipurpose experiment situated at the SNOLAB facility located at Creighton mine 2km deep. The SNO+ experiment has three phases: water, pure scintillator and Te loaded scintillator. With this scintillator filled detector, solar neutrinos, geo and reactor anti-neutrinos, even supernova neutrinos can be studied. To analyze the data collected by the detector, it is important to have detailed knowledge of the detector response.This is why calibration is a crucial part of the experiment. The detector response to neutrons will allow us to study the anti-neutrino flux coming form reactors in Canada. Anti-neutrinos can be detected via inverse beta decay reaction which can be tagged using neutrons it produces.This presentation will discuss the radioactive calibration source Americium Beryllium (AmBe) which produces neutrons and gammas. The existing AmBe source - inherited from the SNO experiment - will be used in water phase has to be modified for the scintillator and loaded scintillator phases. Simulations were carried out to determine the optimal additional shielding required for the scintillator phase. The results of the simulation and general overview over the AmBe source and it's use for SNO+ will be discussed.
The SNO+ experiment is a kilo-tonne scale liquid scintillator detector located at SNOLAB which is currently operating in its water phase. The water phase is used for testing the detector performance, photomultiplier tube (PMT) response and test the data acquisition system (DAQ). One of the main physics includes the search for invisible nucleon decay in 16O, where a decaying neutron will result in a 6.18 MeV gamma 44% of the time from the de-excitation of 15O and for proton decay a 6.32 MeV gamma 41% of the time from the de-excitation of 15N. SNO+ will be using a 16N source to calibrate the energy response detector during the water phase because it primarily produces 6.13 MeV gamma (67% of the time) following the beta decay which will be used to tag the events. This talk will discuss the efforts involved in recommission the 16N source and the status of the energy reconstruction in Monte Carlo.
It is a well-known fact that quantum field theory usually requires renormalization to deal with divergent terms in perturbation theory. For relativistic quantum systems, Epstein and Glaser have proposed causal perturbation theory (CPT) as a method to avoid divergences before they occur. The key part of this method is to employ distribution splitting to define retarded and advanced propagators. In this talk I will describe how CPT can be used to provide a finite perturbation theory for quantum optical systems consisting of atoms or molecules and light.
The quantum harmonic oscillator (QHO) is one of the most important quantum systems. It appears in nonrelativistic physical scenarios, such as the vibrational modes of diatomic molecules but also in relativistic quantum field theory when one quantizes the electromagnetic field. Due to its importance, it is natural to seek relativistic corrections to the QHO. One of the most straightforward relativistic generalizations is a model of the Klein-Gordon HO derived by Znojil from the spinless Salpeter equation (we will refer to this as the ZHO). This model cannot be solved exactly and authors have obtained results using perturbation theory in one and three dimensions. In this work we obtain compact formulas for the first and second order relativistic corrections to the ZHO valid in any dimension. This includes novel results for the physically relevant two-dimensional QHO.
Ideas like anti-de Sitter/conformal field theory correspondence and the membrane paradigm have illuminated many aspects of string and field theory, giving insights into field ranging from quantum gravity to condensed matter. In essence, these ideas are a statement of the holographic principle: the observation that all of the information contained in a bulk region of space-time can be encoded on the boundary of that region. However, these approaches are restricted to situations where knowledge of the boundary of space or the end of time are required. From a practical point of view this is unsatisfactory. As local observers, we are generally not able to access these boundaries.
To overcome these limitations, we use 'gravitational screens', two-dimensional hypersurfaces that can surround arbitrary regions of space. Projecting Einstein's equations onto the screen results in the equations of non-equilibrium thermodynamics for a viscous fluid, which encode all of the information about gravitational dynamics inside the screen in terms of a holographic fluid on the surface, without being restricted to a particular choice of boundary. We study the dynamics and equations of state for screens in various space-times, and determine the properties of the fluids that arise from different evolution/geometries, as well as clarifying the deep relationship between the gravitational degrees of freedom in the bulk, and the thermodynamic degrees of freedom on the screen.
The modular S matrix is fundamental in any rational conformal field theory, including the Wess-Zumino-Witten (WZW) models. A strong similarity was noticed by the authors between the WZW modular S matrix, or affine S matrix, and certain discretized orbit functions. New properties of the orbit functions were found, mimicking the known characteristics of the affine S matrix. After reviewing this work, we will describe further new relations obeyed by the orbit functions. Finally, we will show how a discretization of the orbit functions, different from the original one, produces exactly the affine S matrix.
Abstract:
We analyze the spectrum of the Hamiltonian of a photon propagating in a strong magnetic field $B\sim B_{\rm{cr}}$, where $B_{\rm cr}= \frac{m^2}{e} \simeq 4.4 \times 10^{13}$ Gauss is the Schwinger critical field .
We show that the expected value of the Hamiltonian of a quantized photon for a perpendicular mode is a concave function of the magnetic field $B$. We show by a partially analytic and numerical method that the anomalous magnetic moment of a photon in the one loop approximation is a non - decreasing function of the magnetic field $B$ in the range $0\leq B \leq 30 \, B_{\rm cr}$ We provide a numerical representation of the expression for the anomalous magnetic moment in terms of special functions. We find that the anomalous magnetic moment $\mu_\gamma$ of a photon for $B=30\, B_{\rm cr }$ is $8/3$ of the anomalous magnetic moment of a photon for $B = 1/2 ~ B_{\rm cr}$.
Several exotic hadrons have been discovered experimentally in recent years, some of which appear to be four-quark objects called tetraquarks. Our theoretical study uses lattice QCD to investigate the possibility of a tetraquark containing two light quarks (up, down or strange) and two bottom anti-quarks. Our results indicate a significant binding in two cases, with each tetraquark state well below the corresponding two-meson threshold.
We are about to enter a revolutionary new period in our understanding of the
charged pion form factor, $F_{\pi}$. As the lightest meson, it is the particle
responsible for the long-range character of the $N-N$ interaction that binds
the atomic nucleus. Furthermore, if QCD were chirally symmetric, the pion
would be massless. But chiral symmetry is dynamically broken by quark-gluon
interactions and the inclusion of light quark masses, giving the pion (and
ultimately all other hadrons) significant mass. Thus, the pion is central to
many of the key questions of strong-interaction physics. There have been
enormous advances in the last several years. Recent $F_{\pi}$ calculations
have shed much light on the links between dynamical chiral symmetry
breaking, quark confinement and the generation of hadron mass. There have also
been great advances in lattice QCD calculations, providing for the first time
reliable predictions of $F_{\pi}$ in the $1\lt Q^2\lt 6$ GeV$^2$ region.
Experimentally, there is also much promise. The measurement of $F_{\pi}$ is
challenging, as it must make use of the dominance of the nucleon's virtual pion
cloud in pion electroproduction at low $-t$. With the recent completion of the
Jefferson Lab Hall C apparatus, we will (for the first time since the
pioneering Cornel data of the 1970's) be able to acquire the high quality data
needed to provide rigorous tests of the recent theoretical developments. The
new instrumentation will nearly triple the momentum transfer over which
$F_{\pi}$ is accurately known, probing the regime in which QCD begins to
transition from large- to short-distance behavior. It will be an exciting time,
and my talk will provide a glimpse into the path ahead.
(*) Supported by NSERC SAPIN-2016-00031
The goal of the GlueX experiment is to carry out a definitive mapping of states in the light meson sector. The primary search is focused on exotic hybrid mesons as evidence of gluonic excitations, in an effort to understand the phenomenon of confinement in Quantum Chromo Dynamics. The experiment, housed in the Hall-D facility at Jefferson Lab, employs linearly polarized photons in the 8-9 GeV range and is now in its initial physics data taking phase. The key features of this compelling physics program will be presented with emphasis on the first results from the beam asymmetry for light pseudoscalar mesons.
Measurements of exclusive meson production are a useful tool in the study of
hadronic structure. In particular, one can discern the relevant degrees of
freedom at different scales through these studies. In the transition region
between low momentum transfer (where description of hadronic degrees of freedom
in terms of effective hadronic Lagrangians is valid) and high momentum transfer
(where degrees of freedom are quarks and gluons), $t$-channel exchange of a few
Regge trajectories permits an efficient description of the energy dependence
and the forward angular distribution of many real- and virtual-photon-induced
reactions. In this work, we study the $p(e,e'\pi^+)n$ reaction at fixed $Q^2$
and $W$ of 2.5 GeV$^2$ and 2.0 GeV, respectively, while varying the four
momentum transfer to the nucleon $-t$ from 0.2 to 2.1 GeV$2$. As $-t$ is
increased, the hadronic interaction scale is reduced independently of the
observation scale of the virtual photon, providing valuable information about
the hard-scattering process in general. The data was taken at Jefferson Lab
Hall C in 2004 using the HMS and SOS magnetic spectrometers, and I will present
the preliminary result of the differential cross section analysis in this talk.
(*) Supported by NSERC SAPIN-2016-00031
When modelling excited states of deformed nuclei, nucleons can be taken collectively as a rotor, significantly simplifying the system. However, in order to take into account single-particle effects it is important to properly model the valence nucleons, especially those occupying large angular momenta orbitals near the Fermi level. For that purpose a model has been developed in which two valence nucleons of the same kind are coupled to an axially symmetric quadrupole deformed rotor of the D$_2$ symmetry. These identical valence nucleons form a pair, with the pair-coupling strength controlled by the the nuclear delta force, a pairing contact force. In this two-particle-rotor model a Coriolis force emerges resulting in the breaking of the pair formed by the valence nucleons. With this, both single particle and collective degrees of freedom are encapsulated in the model and compared to the yrast line of $^{178}$Hf and $^{162}$Er. This model may be extended to triaxial symmetries encompassing a broader range of quadrupole deformed nuclei.
This talk will report on my experience in teaching and learning physics at undergraduate level using videos, animations, physlets and physclips.Based on the perceived effectiveness of this teaching method, and published works that outline the success of using effectively multimedia resources in classrooms or online based teaching, I have tested it on two introductory physics courses: i) one taken by physics or other science majors and by science education students; ii) a course taken mainly be pre-engineering students and physics majors. I will discuss the observed improvements in the way the students learned physics and the feed-back received from students.
Undergraduate students in many disciplines must take heavily restrictive course-loads, leaving little room for electives outside their chosen field. This contributes to students graduating without having been exposed to varied modes of academic thinking. We will discuss the development and delivery of a new, highly interdisciplinary course (lectures and labs) designed to provide students with the skills to approach problems with a wider context than they would otherwise have been exposed to within their narrow academic ‘silos’.
This interdisciplinary course is the first of its kind at our university. The course is designed to teach undergraduate students about the limitations of approaching topics with narrow, field-specific viewpoints and demonstrate the benefits of approaching material with a broader context than they would otherwise likely encounter within their individual academic ‘silos’. The course involves people in a large range of disciplines, nearly every department on campus. Students are placed into teams of mixed academic background for the duration of the course. Conceptual scaffolding takes the students through the relevant fundamental concepts in the various disciplines to finding connections between related disciplines and, finally, to finding connections between seemingly unrelated fields.
We measured the personality type of the students in a large introductory physics course of mostly life science students using the True Colors instrument. We found large correlations of personality type with performance on the Pre-Course Force Concept Inventory (FCI), both term tests, the Post-Course FCI, and the final examination. We also saw correlations with the normalised gain on the FCI. The personality profile of the students in this course is very different from the profile of the physics faculty, and also very different from the profile of students taking the introductory physics course intended for physics majors. The dominant personality type of both physics faculty and majors matched the personality type that performed best on both the summative and formative assessments in the course for life science students. These results support the hypothesis that the assessment and teaching techniques we employ have an inherent bias that benefit students that are similar to the teacher. The personality types give hints about how we might reduce this bias or mitigate its effects on student success.
We live in an exciting time for teaching physics. Over 30 years of education research by physics professionals is transforming physics teaching from a mystical art into a practical science. In the process, many educational myths have been successfully challenged. Research is providing great insight into the cognitive development of our students’ physics understanding and the accompanying physical changes that take place in the brain. As a result, pedagogical techniques have broken free from the traditions and fads of the past, and are now grounded in an empirical understanding of how humans learn. By creating a research-based learning environment, we can literally build better students and build better teachers. In this talk, Chris Meyer will share the key results from education research that inspired him to create a lecture-free high school physics program that is now spreading across Ontario.
Polymer translocation is relevant both in vivo and for nanotechnology applications. Not surprisingly, this apparently simple process has been the subject of intense study over the last 20 years or so. For instance, there have been numerous simulation studies examining aspects of both biased and unbiased translocation. In the first part of this talk, I will review our Molecular Dynamics simulation results for unbiased translocation, and I will focus on the fact that there appears to be no experimentally relevant scaling exponent. I will then present results for translocation driven by unusual system asymmetries. First, I will consider the case of a gradient of solvent viscosity across the membrane: can this drive the translocation, and if so, towards which side? For the second example, I will consider translocation when different obstacle arrangements are present on both sides of the pore. Interestingly, we find that even with uniform concentrations of obstacles, varying arrangement of the obstacles can yield a preferential direction. Finally, I will look at the sources of diffusion in the problem, with on a focus on “conformational noise” and ways to control it.
Curcumin is the main ingredient in turmeric, a common Indian spice. Curcumin has been used for centuries in traditional medicine, and has been speculated to have anti-inflammatory and anti-oxidant abilities. Modern medicine has also identified a potential anti-Alzheimer’s benefit. However there is no good theory of a common molecular mechanism to describe all these benefits. This has led to speculation that curcumin interacts with and protects lipid membranes. However, even the details of this interaction are debated, as researchers observe two kinds of interactions. Curcumin has been observed lying flat on lipid head groups (a carpet model), where it provides a physical barrier to entry into the membrane. Curcumin may also embed deeper in the membrane and stiffen the tails, thereby providing protection.
Using X-ray diffraction and molecular dynamics (MD) simulations, we observe curcumin interacting and binding with lipid bilayers [1]. Most importantly, we observed both the carpet and insertion models. In both simulation and experiment, the hydration water thickness was varied and we found that the insertion model is preferred in fully hydrated environments, whereas the carpet model is preferred in low hydration. In a physiological environment, lipid hydration is controlled by osmotic pressure, i.e. by the concentration of solutes such as proteins and salts. Our results demonstrate that curcumin can be found in both locations, inserted or in carpet, tissue dependent.
[1] R.J. Alsop, A. Dhaliwal, M.C. Rheinstadter. Curcumin protects membranes through carpet or insertion model depending on hydration. Submitted.
All commercially available pharmaceutical products must undergo rigorous testing to determine their safety and efficacy, however these drugs interact with our bodies on a cellular level is often unknown. Hormonal oral contraceptives are commonly used by women to prevent pregnancy and treat symptoms, such as acne. While the drug mechanism that causes the desired effect – prevention of ovulation – is well understood, little is known about how the synthetic steroidal hormones interact with human cells. Understanding the non-specific interactions of these molecules with human cells could provide insight into the underlying causes of previously documented side effects and provide a more comprehensive understanding of how oral contraceptives interact with the human body.
In this study, Molecular Dynamics (MD) simulations were used to examine the behaviour of lipid membrane systems when introduced to norethindrone and ethinyl estradiol, two hormones used in oral contraceptives. Simulations containing 10mol% norethindrone, 10mol% ethynyl estradiol, and a 10mol% mix, with a 90mol% 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membrane were run for 200ns. From this we visualized the location of the hormone molecules in the system, their effect on the membrane, as well as obtained electron density profiles of the system. This was compared to analysis of X-ray diffraction data of analogous experimental systems to see if MD corroborates the experimental results. This will improve our understanding of how oral contraceptives interact with human tissue, and potentially inform a mechanism as to the underlying causes of their side effects.
Dynamin-related protein 1 (Drp1), a member of the Dynamin superfamily of large GTPases, is the primary mechanoenzyme responsible for mitochondrial fission. It is composed of three main domains: a G domain that weakly binds GTP and hydrolyzes it to GDP, a coiled-coil stalk domain which is involved in self-assembly of Drp1 into into spiral-like aggregates around the circumference of a mitochondrion, and a variable domain (B domain) that is thought to modulate the self-assembly process. The B domain possesses several unique properties that suggest it is physiologically important, but its function is not well understood. In this talk, we present computer simulation studies that suggest the B domain is intrinsically disordered, in agreement with recent experimental studies. In spite of being intrinsically disordered, we also find that B domains interact specifically with each other to form dimers (and potentially higher order oligomers), thereby facilitating the Drp1 self-assembly process in an unexpected way. Moreover, we find that in the presence of a model osmolyte, trimethylamine N-oxide (TMAO), the specific intermolecular assembly of B domains is significantly enhanced. The implications of these findings for recent studies of Drp1 assembly and mitochondrial fission will be discussed.
At the dawn of the post-antibiotic era, the use of “last-line” antibiotics continues to rise due to emergence of antimicrobial resistant bacteria. Until 2015, polymyxin B (PmB), a membrane rupturing antibiotic, was the last without known resistance. Unfortunately, the drug has been clinically hindered from conception due to the occurrence of kidney-related side effects. However, the mechanisms by which PmB damages kidney tissue has remained unknown. We have prepared analogues for renal membranes to uncover the mechanisms of PmB nephrotoxicity and the carpet model of insertion through X-ray diffraction, Molecular Dynamics (MD) simulations, and electrochemistry.
By probing the membrane at angstrom level resolution, we observe cubic phases with the incorporation of PmB indicating the formation of a “spongy” porous membranes. We find that PmB exists in two states, either membrane-bound or inserted. PmB in the membrane-bound state is able to form aggregates, induce membrane thinning and increase membrane curvature, whereas PmB in an inserted state can increase water permeation. The presence of cholesterol in the membrane greatly diminishes the membrane-damaging interaction of PmB. With MD simulations, we show that inserted PmB have 4-fold decreased lateral diffusivity when cholesterol is present. From this, we show that antimicrobial peptides induce membrane damage by puncturing the membrane and subsequent membrane effects. Membrane cholesterol inhibits the following resulting membrane effects. In summary, we provide mechanistic understanding of PmB’s mechanism of action and the carpet model of antimicrobial insertion.
In December 2015, during oral arguments in a US Supreme Court case on affirmative action policies in university admissions, Chief Justice John Roberts asked the controversial question "What unique perspective does a minority student bring to a physics class?" This panel discussion will focus on what it means to be a member of a minority or under-represented group in physics, how diversity impacts physics in Canada, and what we can do to build an inclusive and equitable physics community that can enhance physics research and development in Canada.
Using the Büttiker-Landauer formulation of transport theory in the linear response regime, the valley currents and non-local resistances of bilayer graphene nanostructures with broken inversion symmetry are calculated. It is shown that broken inversion symmetry in bilayer graphene nanostructures leads to striking enhancement of the non-local 4-terminal resistance and to valley currents several times stronger than the conventional electric current when the Fermi energy is in the spectral gap close to the energy of Dirac point. The scaling relation between local and non-local resistances is investigated as the gate voltage varies at zero Fermi energy and a power-law is found to be satisfied. The valley velocity field and valley accumulation in four-terminal bilayer graphene nanostructures are evaluated in the presence of inversion symmetry breaking. The valley velocity and non-local resistance are found to scale differently with the applied gate voltage. The unit cell-averaged valley accumulation is found to exhibit a dipolar spatial distribution consistent with the accumulation arising from the valley currents. We define and calculate a valley capacitance that characterizes the valley accumulation response to voltages applied to the nanostructure's contacts.
Nanomechanical devices have allowed for the study of the motion of macroscopic objects near their quantum ground state for mechanical motion. Coupling these devices to resonant electrical circuits provides a method of measuring with standard laboratory electronics, and a means to interact and cool towards the ground state. We report on current work, in microwave $L C$ resonators, using graphene and niobium diselenide (NbSe$_2$) membranes as one electrode in a parallel plate capacitor with a mechanical degree of freedom. The membrane's light mass, non-linear response to an applied force and tunability potentially enable stronger electromechanical amplification and coupling than bulk materials. Previous work using graphene in similar devices shows that its electrical resistance is a limiting factor when attempting to cool via electromechanical sideband interactions. NbSe$_2$ is a superconductor even in single layer form, and this property provides a system with lower loss while driving with increasing photon number, as compared to the graphene-based systems. Such resonant systems also allow study of the material behaviours of graphene and NbSe$_2$, including nonlinear effects from a strong drive signal. In this talk we show fabrication, modelling and progress towards quantum-limited measurements.
Graphene is an ideal material for high quality nano-electro-mechanical resonators due to its high Young's modulus, low mass to surface ratio, ability to sustain high in-plane strain, and unique electrical properties like high carrier mobility, ballistic transport and nonlinear modulation of conductance under the electric field effect. In this work, atmospheric pressure chemical vapour deposition is employed to obtain monolayer graphene on copper. Scanning electron microscopy, Raman analysis and two-terminal electrical measurements reveal the presence of high quality, predominantly monolayer graphene. The graphene is transferred to Si/SiO2 wafers and multiple step electron beam lithography, metal deposition, substrate etching and critical point drying are used to fabricate suspended graphene doubly-clamped resonators. The devices are electrostatically actuated and their motion is read out using nonlinear mixing of graphene's electrical conductivity (1). Modeling the devices as Duffing resonators (2) shows the presence of mechanical nonlinearity in response to an applied force even at moderate bias voltages. We discuss the implications of this nonlinearity for parametric amplification, mode-mixing and the generation and measurement of squeezed thermomechanical states (3). The models are compared with experimental data and prospects for developing measurement techniques for high precision sensors and quantum-limited mechanical measurements of graphene are explored.
Silicon quantum dots (QD) stimulated to form excitons can decay by emitting a photon at a wavelength determined by it’s size, or tunnel to another QD. Films of a-SiO2 on Si wafer were subject to (<1MeV) Si+ implantation and annealed to form QD in a dielectric matrix. The density of implanted Si+ is non-uniform with respect to depth into the film, as are the densities of ionizations and atomic dislocations caused by the stopping of the implanted Si+. This results in post-anneal distributions of QD size and QD-QD separation distances that vary with depth in an unpredictable way. The ionization and dislocation processes (radiation “damage” due to Si+ implantation) cause a variety of bonding defects in the local structure of a-SiO2. Annealing out the defects helps rearrange atoms to form QD but this is not fully understood, quantitatively. This study uses depth-resolved positron annihilation spectroscopy to observe the evolution of the defect distribution and QDs at each stage of production. Electron spin resonance (ESR) and x-ray absorption near edge spectroscopy (XANES) are used for identifying paramagnetic defects and phase quantification, respectively. Finally, these observations are correlated to the photoluminescent output of finished samples.
Experimental measurements of the speed distribution of atoms in an equilibrium gas agree with the predicted Maxwell-Boltzmann (MB) distribution from kinetic theory. It has been almost universally presumed that the MB distribution also applies to vapour atoms that are ballistically ejected into vacuum from liquid or solid surfaces, calculated assuming that the vapour is an equilibrium gas with a temperature equal to the temperature of the condensed phase. We identify, however, that ballistic evaporation of a vapour is entirely different from the effusion of a gas from an oven due to the lack of gas-phase collisions and surface adsorption-desorption events on the isothermal walls of the oven that establish thermal equilibrium. Remarkably, and to the best of our knowledge, there currently exist no experimental studies that have rigorously measured the speed distribution of ballistically-evaporated atomic vapour. These measurements are necessary experimental validation for theoretical models of thin film coatings and their technological use. Our main research objective is to develop an experimental apparatus and procedure to accurately and precisely measure this distribution using modern experimentation techniques.
Our current experimental setup evaporates silver into vacuum using a commercially available rod-fed electron-beam evaporator. The speeds of evaporated atoms are then mechanically filtered using a high-transmission slotted cylinder velocity selector (or, spindle) that is capable of rotation up to 170 hertz (10,000 rotations per minute). It was constructed from stainless steel using direct metal laser sintering and has 83 helical channels; each channel has an angular aperture of 3.33 degrees tilted at a 4.00-degree pitch angle. Evaporated atoms that travel parallel to the cylinder axis are aligned with only one of its channels, and, when rotating, it selectively transmits atoms within a restricted range of speeds. Two detectors that operate on different physical principles, namely a hot-filament ionization gauge and a quartz crystal microbalance, are positioned directly above the spindle and detect transmitted atoms. The speed distribution is determined from transmission measurements as a function of the spindle's rotation speed. Currently, the apparatus and control system is substantially complete: this talk will focus on its development and testing.
Ultrathin film materials have attracted significant attention in light of their potential applications in integrated electronics and data storage. The amount of data that can be addressed and stored in resistive memory devices scales inversely with their thickness, and ultrathin thermal sinks are required to evacuate heat from such electronic components. So far, virtually any techniques used to image the thermal properties of thin films at the nanoscale required to position the sample in contact with voluminous probes that dramatically limit the measurement reliability. In our thesis, we have developed [1] a new contactless instrument in which a scanning near-field optical microscope has been modified to image the thermal conductivity from measurements, in liftoff mode, of thermally induced oscillations of the reflectivity at the interface between air and nanostructured thin films. With this technique, that can be named near-field scanning thermoreflectance imaging (NeSTRI), we demonstrated quantitative and qualitative predictions of the thermal properties of different thin-film systems: metallic layers, multilayer graphene films, graphene films decorated with copper nanoparticles, [2] and ultrathin films of poly-[1,5-diisopropyl-3-(cis-5-norbornene-exo-2,3-dicarboxiimide)-6-oxo-verdazyl] (P6OV), an organic radical polymer specially designed for memory device applications. [3] As P6OV thin films revealed interesting electronic and thermal properties depending on the charge state (positive neutral or negative) of each radical monomer, we performed additional scanning probe investigations based on Kelvin-probe force microscopy (KPFM) that enabled the identification of the quantum energy levels associated to gap states in this polyradical, and, eventually, enabled the fabrication of resistive flash memory devices from this material. [3] So far, our P6OV flash memories are the thinnest organic devices of this type obtained to date.
[1] S. Ezugwu, S. Kazemian, D.Y.W. Choi, G.Fanchini, Nanoscale (2017) DOI: 10.1039/c6nr09199g
[2] A. Akbari-Sharbaf, S. Ezugwu, M.S. Ahmed, M. Cottam, G. Fanchini, Carbon 95 (2015) 199
[3] S. Ezugwu, J.A. Paquette, J.B. Gilroy, G. Fanchini, Adv. Electronic Mater. 2(11) (2016) 1600253
The use of silicon (Si) in optical and optoelectronic devices depends heavily on the development of a Si-based light source. The ability to use Si in such applications will have many advantages, including low fabrication cost and high compatibility with existing technology. Therefore, researchers have explored the use of various techniques to improve the inherently poor luminescence of bulk Si. In recent years, self-assembled Si nanoclusters (Si-NCs) have been shown to be a promising candidate, due to their improved tunable light emission.[1] In spite of such achievements, the luminescence of self-assembled Si-NC devices is still too low in intensity to be used in commercial devices.[2,3] There are also many unanswered questions about the mechanisms responsible for the luminescence displayed by such systems. In our group, we manipulate the growth of self-assembled Si-NCs and study their optical and electrical properties.[4,5] We have examined aspects of this type of system such as the effect of the host material’s crystallinity on Si-NC growth, and the impact that doped matrices have on luminescence.
1) Park, N.-M., et al. Appl. Phys. Lett., 2001, 78, (17), 2575.
2) Wang, Y. Q., et al. Appl. Phys. Lett., 83, 3474 (2003).
3) Cen, Z. H., et al. J. Appl. Phys., 105, 123101 (2009).
4) Cadogan, C.,et al. J. Vac. Sci. Technol. B, 2016, 34 (6), 061202.
5) Goncharova, L. V., et al. J. Appl. Phys., 118, 224302 (2015).
Hollow-core photonic-crystal fibers (HCPCFs) loaded with atomic ensembles have been used in the past for demonstrations of strong optical nonlinearities arising from the tight transverse confinement of both photons and atoms. Integrating high-finesse optical resonators into HCPCFs would further enhance these nonlinearities and enable implementation of a variety of novel photonic devices, such as unconventional light sources and all-optical transistors controlled by single photons.
Here, we describe our recent experimental progress in development of such resonators, in particular using photonic-crystal membranes acting as dielectric metasurface mirrors, and the perspectives of loading laser-cooled atoms into these resonators.
We have demonstrated that a supersonic beam of methyl radicals (CH$_3$) in the ground rotational state has been slowed down to standstill with a magnetic molecular decelerator, and successfully captured spatially in an anti-Helmholtz magnetic trap for longer than 1 sec. The trapped CH$_3$ radicals have a mean translational temperature of about 200 mK with an estimated density of $>$ 5.0 $\times$ $10^7$ cm$^{−3}$.
The methyl radical is an ideal system for the study of cold molecules not only because of its high reactivities at low temperatures, but also because further cooling below 1 mK is plausible via sympathetic cooling with ultracold atoms. We will discuss properties of cold collisions between the trapped radicals and foreign gases.
Laser-cooled trapped ions are among the most versatile experimental platforms for the simulation of non-trivial quantum Hamiltonians. What distinguishes this platform from others is the extent to which it is experimentally possible to control this system at the level of individual particles and interactions between them. Internal states of these ions, such as hyperfine states, constitute well isolated qubits (or spin-1/2 states) with long quantum coherence, and can be initialized as well as detected using laser beams with near perfection. Quantum logic gates and interacting spin Hamiltonians are engineered by coupling the spin states of multiple ions to their collective vibrational (phonon) modes using optical forces. By suitably tailoring these spin-phonon couplings, interactions between ion-spins can be tuned in magnitude, range, and sign, and in principle can be made arbitrary. In this talk, I will describe the quantum simulator that we are building at IQC, University of Waterloo to explore problems in quantum information and many-body physics in a regime that is intractable with classical computers.
Nonresonant rotational Raman excitation of linear molecules by periodic sequences of ultra-short laser pulses allows for the realization of a paradigm system - the quantum kicked rotor. This apparently simple physical system has drawn much interest within the last decades, especially due to its role in the field of quantum chaos. In the case of periodic kicking, the wave function of a quantum rotor dynamically localizes in the angular momentum space, similarly to Anderson localization of the electronic wave function in disordered solids. I will present the first direct observation of dynamical localization in a system of true rotors. The suppressed growth of rotational energy is demonstrated, as well as the noise-induced recovery of diffusion, indicative of classical dynamics. In a second study I demonstrate the coherent control of quantum chaos and a loss of control in the classical limit of laser-molecule interaction.
This work advances the general understanding of the dynamics of laser kicked molecules and complements previous studies of the quantum kicked rotor in a system of cold atoms. The possibility of control in classically chaotic systems has far reaching implications for the ultimate prospect of using coherence to control chemical reactions.
Canada has been part of the ATLAS collaboration from inception:
Canadian groups built significant parts of the original ATLAS
detector, and have operated it and analyzed the data taken
since the Large Hadron Collider (LHC) turned on. To keep up with the further
increases in luminosity that will come from upgrades to the
accelerator, portions of ATLAS must be replaced during two
long shutdowns of the LHC. ATLAS Phase-I upgrades, to be installed during the 2019-20 shutdown, include replacement of the 10-metre ``small wheels'' of the
Muon Spectrometer. Canadian groups are collaborating to build
fifty of the 192 precision thin-gap chambers that will provide the
triggers for the New Small Wheels. Continuing a long involvement in ATLAS
liquid argon calorimetry, Canada is also building new
electronics to allow the trigger-level granularity of the calorimeters
to approach the full offline capability of the detector for Phase-I,
and add new digital readout electronics for Phase-II.
Phase-II upgrades will be installed during the final long shutdown (around 2024-26) before full High-Luminosity LHC (HL-LHC) operation at five to seven times the nominal design luminosity. Canadians are also participating in the
Phase-II replacement of the entire inner tracking detector of ATLAS with an all-silicon tracker (ITk) consisting of both pixels and strips. Canada proposes to
build a significant fraction of the endcap strips detector.
The talk will describe these efforts in the context of the
overall upgrade goals for Phases I and II.
We present a summary of the recent results of searches for supersymmetry and other new phenomena conducted by the ATLAS experiment using 36 fb$^{-1}$ of pp collisions data at $\sqrt{s}$ = 13 TeV collected in 2015 and 2016. Several searches are reported that use various experimental signatures and methods. The results presented include searches for new heavy bosons, vector-like quarks, supersymmetric partners of quarks, leptons and gauge bosons, and R-parity violating supersymmetry.
The ATLAS detector recorded approximately 34 fb$^{-1}$ of good quality pp collision data at ⎷s = 13 TeV during 2016. This was made possible due to the excellent LHC performance and the high data-taking efficiency of 92.4% achieved at ATLAS.
There is significant involvement from Canadian institutes in the areas of trigger operations, inner detector performance, muon spectrometer performance and the operation of and data quality assessment for the liquid argon calorimeter. At the end of the 2016 data-taking campaign a period of machine maintenance commenced to prepare the LHC and detectors for further operation in 2017 and 2018. This talk presents an overview of the data quality and performance of the ATLAS detector in 2016 and the status looking forward to 2017+2018 following the upgrade and maintenance activities carried out during the extended year end technical stop.
During the ATLAS phase 1 upgrade, which will take place beginning in
2019, the muon system will be upgraded to install a New Small Wheel
(NSW) in the forward region in order to improve tracking and trigger
performance at very high luminosities. Canadian groups are
responsible for construction and testing of small thin gap chambers
(sTGC) that will be used in the NSW. The McGill group is responsible
for testing these chambers using cosmic ray muons. This talk will
describe the selection and analysis of cosmic ray events, based on
simulation and cosmic ray data collected using a prototype 40x60cm
sTGC quadruplet module, and focusing in particular on events with
multiple reconstructed tracks in the detector.
Numerical studies of gravitational collapse to black holes used to predict gravitational waves make use of apparent horizons, which are intrinsically foliation-dependent. We discuss possible solutions to this problem using the Hawking-Hayward quasilocal mass. In spherical symmetry, a sensible approach consists of restricting to spherical spacetime slicings. Then the apparent horizons enjoy a restricted gauge independence but thermodynamical quantities associated with them are fully gauge-dependent. The widely used comoving and Kodama foliations are of particular interest and are discussed explicitly.
[Based on Phys. Rev. D 95, 024008 (2017)]
The Tolman~VII solution for a static perfect fluid sphere
to the Einstein equations is reexamined, and a closed form
class of equations of state (EOSs) is deduced for the first time.
These EOSs allow further analysis to be carried out, leading to a
viable model for compact stars with arbitrary boundary mass density
to be obtained. Explicit application
of causality conditions places further constraints on the model, and
recent observations of masses and radii of neutron stars prove to be
within the predictions of the model. The adiabatic index predicted
is $\gamma \geq 2,$ but self-bound crust solutions are not excluded
if we allow for higher polytropic indices in the crustal regions of
the star. The solution is also shown to obey known stability
criteria often used in modeling such stars. It is argued that
this solution provides realistic limits on models of compact stars,
maybe even independently of the type of EOS, since most of the EOSs
usually considered do show a quadratic density falloff to first
order, and this solution is the unique exact solution that has this
property.
In my talk I will discuss a recently discovered class of black holes which are the first such examples to exhibit a lambda-transition, that is a line of second order (continuous) phase transitions. The lambda-transition resembles those which occur in the context of condensed matter systems which, in the case of $^4$He marks the normal fluid/superfluid transition. The transition occurs within the context of black hole chemistry for a class of asymptotically anti de Sitter black holes in cubic (and higher) order Lovelock gravity conformally coupled to a real scalar field. In my talk, I will introduce the model and the phase transition and also present the necessary conditions which allow for such a transition to occur more generally.
We construct several classes of exact wormhole solutions in 5-dimensional Einstein-Maxwell theory. We demonstrate that without requiring exotic matter, these spacetimes become singularity-free with an appropriate choice of parameters and maybe interpreted as models of charged or uncharged particles and particle-antiparticle pairs. We show that the electric field approaches Coulombic limit for large distances r away from the wormhole throat but has a more complicated structure for very small r and a very small mass parameter. We generalize the solutions to arbitrarily high dimensions and also provide cosmological solutions. Finally, we explore if the intricate combination of electric and gravitational fields near the throat can provide physically realistic models of atomic and subatomic phenomena in general relativity.
Studies of massive rotating bodies in the context of General Relativity are mostly based, directly or indirectly, on the Kerr metric. The rotation is assumed from the start and investigators try to fit various parameters to mimic the observed phenomena. None of the current approaches starts from scratch and proposes a metric from which the rotation terms intrinsically emerge. Over the last CAP conferences, we have studied in detail the static symmetric geometry described by a metric based on an erfc gravitational potential. This emergent potential had been derived from a general representation paradigm based on two fundamental assumptions (the principle of interdependence and the principle of asymptotic congruence) and on the exploitation of the Central Limit Theorem. Although this new metric provides a consistent set of predictions and interpretations regarding some open problems in the solar system, the residual offset incorporated in the erfc potential remains partly justified while its presence is a key element to support the new rationale. In this paper, we propose an axisymmetric interpretation of this general metric. The resulting axisymmetric geometry describes any massive body and its curved space-time, subject to a rotation and an expansion. The resulting solutions to the Einstein equations are simulated. The geodesics are derived in their second and first order mathematical description. Finally, the equatorial radial and orbital trajectories of particles and photons are studied suggesting that the axisymmetric geometry is a fundamental representation that could be used to study a large class of rotating massive objects.
We study the possibility that a graviton in the presence of a black hole can be coherently amplified through stimulated emission. Because of the extremely weak coupling of gravitons to matter, the gain that can be obtained as the graviton passes through a lasing medium is untenably small, to achieve significant gains, with a typical absorption cross section, it will take a trajectory that is longer than the observable universe. However, in a black hole background, if emitted in the right direction at the right radius, a graviton can make arbitrarily many trips around the black hole before eventually escaping to infinity. If the black hole is surrounded by a lasing medium, the graviton can be amplified to arbitrarily high intensity if it makes enough circuits. The existence of very light axions or other bosonic dark matter, can give rise to exactly the required lasing medium. In principle, amplified gravitons are being emitted at all times from all black holes but since the big bang, there has not been enough time to have significant amplification. Eventually, after a sufficient amount of time, black holes will start emitting coherent rays of extremely amplified, intense, gravitons, that will in principle destroy everything in their path.
The astrophysical rapid neutron capture process (r-process) is thought to be responsible for the production of roughly half of the heavy elements found in nature. At present the site and many other details of this process remain uncertain, making the detailed understanding of the r-process one of the most active areas of research in nuclear astrophysics. Testing the models describing the r-process requires experimental nuclear data such as masses, beta-decay properties, and neutron-capture rates among neutron-rich nuclides, far from the region of stability. Such data are sparse and because it is difficult for experiments to access the nuclides of interest. Radioactive ion beam (RIB) facilities have been a valuable resource in addressing this problem. As existing RIB facilities improve and next-generation facilities come online, the opportunities to obtain such data are quickly growing. They should provide a wealth of new nuclear data, and make it possible to evaluate and improve the results of existing r-process calculations, and possibly inspire new approaches.
One such facility is CARIBU, located at Argonne National Laboratory, where intense beams of neutron-rich isotopes are produced from the spontaneous fission of 252Cf. The Canadian Penning Trap (CPT) mass spectrometer uses the ion-beams produced by CARIBU to determine the masses of nuclides, near the r-process path. Recent improvements to our apparatus include the addition of a high-resolution multiple reflection Time-of-Flight (MR-TOF) mass spectrometer, and the implementation of a contemporary Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) mass measurement technique. These enhancements allow use to press further from the region of stability and ever closer to nuclides that lie on the proposed path of the r-process.
An overview of the current configuration of our apparatus and some highlights from our recent results will be presented.
The Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) is a new state-of-the-art gamma-ray spectrometer. GRIFFIN is composed of 64 large-volume high-purity germanium detectors arranged in 16 clovers and is designed to measure the decay of radioactive-isotopes beams produced by the TRIUMF Isotope Separator and Accelerator (ISAC). The array can be coupled to a variety of auxiliary detectors which detect electrons as well as neutrons, allowing for increased sensitivity by using particle-$\gamma$ and particle-$\gamma$-$\gamma$ coincidences. In addition, fast-timing scintillators can be used to measure lifetimes of nuclear states. The high efficiency of the array also makes it possible to perform detailed $\gamma$-ray angular correlation measurements, making GRIFFIN a powerful tool for nuclear spectroscopy.
Since being installed and commissioned in 2014, the GRIFFIN array has been used in several experimental programs with applications ranging from the astrophysical $r$-process to tests of $ab$-$initio$ theory near shell closures. In this talk, I will present the results of several of the first experiments using GRIFFIN and give an outlook for future capabilities.
The Electromagnetic Mass Analyzer, EMMA, is a recoil mass spectrometer installed at the ISAC-II facility of TRIUMF. It is designed to spatially separate the recoils of nuclear reactions from the beams that induce them and to disperse the products in a focal plane according to their mass-to-charge ratios. A first test of the spectrometer was carried out in December 2016 in which an 80 MeV $^{36}$Ar beam struck an Au foil. The results of this test will be presented.
Nuclei around doubly magic $^{132}$Sn are of particular interest in terms nuclear structure as well as nuclear astrophysics. The properties of these nuclei provide important input parameters for the astrophysical $r$-process (rapid neutron-capture process) since they play an role as waiting-point nuclei and their shell structure and half-lives affect the shape of the second $r$-abundance peak. From the perspective of nuclear structure, the evolution of single-particle levels near shell closures is ideal for testing the current nuclear models far from stability.
In addition to the limited number of the known excited states of $^{129}$Cd, the spin assignment of the ground state and the first excited state has been the subject of investigation. Recently, the half lives of those two state were remeasured and it was reported that both states have similar half lives of $\sim$150 ms [1, 2]. Also, the excited states of the daughter nucleus $^{129}$In were investigated, however, most of the spin assignments of the levels remain unclear [1].
This experiment was performed at TRIUMF, Canada. New data for the decay of $^{129}$Cd was collected with the high-purity germanium detector array GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei), along with the auxiliary $\beta$-particle detector SCEPTAR, for about 13 hours with the beam intensity of $\sim$250 pps. This high statistics of the data and the high sensitivity of the detectors enabled us to perform detailed spectroscopy, including $\beta$-$\gamma$-$\gamma$ coincidence analysis and angular correlation analysis, which is essential for building the level scheme and assignment of the spins of each level. The results from the ongoing analysis will be reported.
The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction largely impacts the abundance of the only stable sodium isotope, $^{23}$Na, in various stellar environments, such as AGB stars, massive enough to undergo hot-bottom burning, type Ia supernovae and novae. However, the $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction rate still carries one of the highest uncertainties among the astrophysical reactions involved in the NeNa cycle, thereby also affecting the abundance predictions of elements between $^{20}$Ne and $^{27}$Al.
With the discovery of the anticorrelation between sodium and oxygen abundances in globular cluster stars, constraining the relevant reaction rates in order to reduce uncertainties in the abundance predictions for NeNa cycle elements has becomes of increased importance.
The thermonuclear reaction rate for the $^{22}$Ne(p,$\gamma$)$^{23}$Na proton capture reaction is dominated by a number of narrow resonances within the Gamow window.
Recently, a study with the objective to directly measure the strengths of the most relevant resonances in the $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction in inverse kinematics was carried out using the DRAGON (Detector of Recoils and Gammas Of Nuclear Reactions) recoil separator at TRIUMF. Resonances within an energy range from E$_{c.m.}$=178~keV to E$_{c.m.}$=1.222~keV were investigated.
In this contribution the astrophysical motivation behind this measurement, as well as first results of this inverse kinematics study of the $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction will be presented.
Nearly 300 years have passed since the watchmaker
G. Graham constructed a more sensitive compass and showed
that the variations in geomagnetic direction varied with an
irregular daily pattern.
More recently, but still 75 years ago, Loeve showed
that a proper description of such nonstationary
processes required at least two time or frequency variables.
Forty years of experience studying geomagnetic and
related problems, however, have shown few, if any,
proper computations of such spectra in the literature
including my own. The purpose of this talk
is to suggest a way to remedy this.
The solution to these problems, the multitaper method of
spectrum analysis, was introduced in 1982 but its implications
for geomagnetism not recognized until recently.
Taking long (> 4 months) blocks of geomagnetic
data, and concentrating on frequencies below
1000 uHz to avoid ultraviolet effects, one
finds that:
Two recent discoveries from the Canadian ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transfer Spectrometer) satellite instrument will be discussed. The first is the production of N2O in the lower thermosphere, and the second is a global enhancement of HCN in the upper troposphere – lower stratosphere throughout 2016. ACE-FTS has the only available satellite measurements of vertically resolved HCN in the upper troposphere - lower stratosphere and N2O in the lower thermosphere.
The N2O measurements show that there is a consistent lower thermospheric source of N2O via energetic particle precipitation (EPP). This leads to average polar winter concentrations on the order of ~20-40 ppbv near 90 km. In the polar winter, N2O-rich air descends into the lower mesosphere, and especially during sudden stratospheric warmings ACE-FTS observes N2O being transported as far down as ~45 km.
In late 2015, a large amount of HCN was emitted from Southeast Asia into the upper troposphere and lower stratosphere. The emitted HCN was then transported by the general circulation from the tropics to polar latitudes. By early 2016, the daily mean concentrations of HCN in the lower stratosphere at all latitudes, as measured by the ACE-FTS instrument, were consistently the largest on record for the region, on the order of 50-90% greater than the climatological mean, and ~30% greater than the 2007 El Niño-driven values.
Radio waves propagating through plasma in the Earth's ambient magnetic field experience Faraday rotation; the plane of a linearly polarized wave changes as a function of the distance travelled through a plasma. Linearly polarized radio waves at 1090 MHz frequency are emitted by ADS-B devices which are installed on most commercial aircraft. These radio waves can be detected by satellites in low earth orbits, and the change of the polarization angle caused by propagation through the terrestrial ionosphere can be measured. This work will discuss how these measurements can be used to characterize the ionospheric conditions.
All optically detectable meteors, as well as many of the strong radio-detectable meteors, produce shockwaves prior to their terminal stage in the MLT (Mesosphere-Lower Thermosphere) region of the atmosphere, at altitudes between 75 km and 100 km. The strengths of the meteor-generated shock waves depend on meteor atmospheric velocities and the values of the relevant Knudsen number. However, practical detection and determination of the altitude at which these shock waves form have not been possible up to this point because of their rapid spatial and temporal attenuation, as well as the presence of radiative phenomena that extend to the meteor wake.
Moreover, while shock waves generated by bright meteors in MLT appear during the transitional flow regimes, good estimates of the relevant meteoroid parameters (such as velocity, shape, bulk density and size), and the altitudes at which shock waves are generated, remain elusive. This is largely because of the uncertainty introduced by the presence of the ablation-amplified hydrodynamic shielding, which subsequently alters the considerations of the flow regime.
To address this, we consider a measurement of the radar detectable meteor head echo (MHE) termination altitudes. The size of MHE plasma radius depends upon altitude, and it scales with the atmospheric mean free path and meteoroid velocity. Thus, the MHE termination altitudes are also strongly correlated with meteoroid parameters and the flow regime, and could be used to indicate the formation of the denser hydrodynamic shielding and flow fields around a meteoroid. Since these are the precursors to the appearance of the shock wave, knowledge about these phenomena can be used to better predict the onset of shock fronts.
Consequently, we suggest that the radar-detectable MHE termination points can be used as a reasonable indicator of the meteor shock wave formation. Moreover, this can be used to better characterize and constrain the meteoroid properties, altitudes and flow regime parameters associated with the shock wave formation.
E region irregularities have been probed for decades through various frequency radars as well as rockets. Even though the maximum growth rate of the instability responsible for the development of the underlying structures should have produced magnetic field aligned irregularities moving at the electron ExB drift, they have been found instead to often move at the ion-acoustic speed times the cosine of the angle between the line-of-sight and the ExB drift, with a spectral width from 1/3 of the ion-acoustic speed along the ExB direction to something of the order of the ion-acoustic speed at right angles to that direction. There have also been many puzzling exceptions to the rule, with the detection at times of very narrow spectra moving at either the ExB drift or at something like 200 m/s, well below the ion-acoustic speed. Additional puzzles have included the detection of irregularities at aspect angles well beyond the values expected from linear growth rate expectations and the clear realization that the large scale structures were heating the electron gas at temperatures sometimes thousands of degrees above the expected 400K value. We now have acquired basic explanations to all the observed features, in large part because of additional insights provided by modern interferometry techniques. This talk will focus on the physical insights gained from the explanations, as there will be little time to go over much mathematics.
Droplet-based two-phase microfluidics enables high throughput screening analysis by utilizing monodispersed nanoliter-sized droplets as mobilized test tubes. Other advantages of droplet microfluidics over traditional high throughput technology include continuous flow offering continuous processing, minimized cross contamination benefiting from well encapsulated droplets, and rapid mixing due to three-dimensional flow occurring in droplets. Both gas-liquid and two immiscible liquids (water and oil) systems have been employed to make liquid droplets in microfluidic platforms. This talk only focuses on the system employing two immiscible liquids to generate droplets.
The first half of the talk will discuss fundamentals and physical modelling of droplet generation in T-junctions1-3 and flow focusing geometries4-5 and droplet trafficking and sorting through a channel network6. The second half will focus on electrical sensing and manipulation and imaging assisted manipulation of droplets. In particular, capacitance sensing7, microwave sensing/heating8-9, and imaging assisted manipulation10 of droplets will be discussed and then followed with microwave heating and mixing of droplets11.
References
1. Glawdel, T.; Elbuken, C.; Ren, C.L. Phys Rev E, 2012, 85, 016322 (9 pp).
2. Glawdel, T.; Elbuken, C.; Ren, C.L. Phys Rev E, 2012, 85, 016323 (12 pp).
3. Glawdel, T.; Ren, C.L. Phys Rev E, 2012, 86, 026308 (12 pages).
4. Chen, X.; Glawdel, T.; Cui, N.; Ren, C.L. Microfluidics Nanofluidics, 2015, 18, 1341-1353.
5. Chen, X.; Ren, C.L., Chem Eng Sci, 2017, accepted.
6. Glawdel, T.; Elbuken, C.; Ren, C.L. Lab Chip, 2011,11, 3774-3784
7. Elbuken, C.; Glawdel, T.; Chan, D.; Ren, C.L. Sens Actuator A: Phys, 2011, 171, 55-62.
8. Boybay, M.S.; Jiao, A.; Glawdel, T.; Ren, C. L. Lab Chip, 2013, 13, 3840-3846.
9. Yesiloz, G.; Boybay, M.S.; Ren, C.L. Lab Chip, 2015, 21, 4008-4019.
10. Wong, D.; Ren, C.L., Lab Chip, 2016, 16, 3317-3329.
11. Yesiloz, G.; Boybay, M.S.; Ren, C.L. Anal Chem, accepted, 2017.
The interaction of phospholipid bilayers and monosaccharides constitutes one of the most important and fundamental physical relationships in cellular biology, as both elements are ubiquitous to living cells. The physical effects of sugars in bilayer systems have been studied for decades due their membrane stabilization properties. Sugars have been observed to decrease phase transition temperature, thicken bilayers, and promote more fluid structures, all results in support of the hypothesis that sugars allow bilayers to mimic a hydrated state; however, an exact molecular mechanism regarding this interaction is unknown. Notably, the influence of sugar concentration on bilayer properties in dehydrated settings has been hotly debated.
We provide holistic data regarding the position and physical effects of glucose within oriented 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) samples using both X-ray diffraction and Molecular Dynamics (MD) simulations [1]. Glucose preferentially localizes to the outer head region of phospholipid bilayers. At reduced concentrations, it results in an increase in water penetration into the bilayer, increasing lateral diffusion. At high concentrations, it functions to vitrify the bilayer structure, allowing it to adopt a disorganized, fluid-like structure while maintaining a reduced range of lipid motions. These findings corroborate previous results regarding sugar-lipid interactions through a unified molecular mechanism. This supports the evidence regarding the function of sugars as cryoprotective agents, as they promote the retention of fluid-like bilayer properties in environments of reduced hydration in a concentration-dependent manner.
[1] A. Dhaliwal, M.C. Rheinstädter. Exploring the Molecular Mechanism for the Vitrifying Properties of Glucose in Dehydrated Lipid Bilayers Using X-Ray Diffraction and Molecular Dynamics Simulations. In Preparation.
A key biophysical consideration in cellular biology is the role of motility. That is, can (and how does) a cell move in a preferred direction on its own accord (i.e., swim) for some physiological purpose (e.g., a bias due chemotactic gradient). One means to empirically characterize the result is by quantifying the so-called ‘anomalous diffusion,’ which directly arises from biases, of an ensemble of cells. Commonly, the observed response is that of superdiffusion, where the ensemble mean-squared displacement (MSD) is supra-linear (i.e., MSD exhibits a nonlinear time dependence with an exponent greater than unity). However, if the bias led to cell attraction (i.e. movement towards a localized high-oxygen concentration) the response is reversed. This suggests that quantification of the deviation from linearity can lead not only to distinguish cells which are capable of motility but also the degree, or strength, of their motion bias. Here we develop a heuristic computational model for E. coli motility to distinguish between swimming biases using the macroscopic effect on the MSD. Initial results indicate that objects which are motile, yet lack bias, exhibit characteristics consistent with normal diffusion. This observation motivates a deeper biophysical question as to how/if swimming and bias can be meaningfully disentangled and suggests that direct comparison to the diffusive motion, of similarly-sized not motile objects, under the same conditions is necessary.
Caffeine is the most common adjuvant in drug “cocktails”; however, the mechanisms by which the molecule elicits its adjuvant effects remain unknown. The prevalence of membrane mediated drug-lipid interactions for amphiphilic molecules, such as caffeine, is indisputable through membrane partitioning, bioenergetics, and structure. Here, we characterized caffeine’s interactions with cell membranes with respect to hydration with time-resolved X-ray diffraction and Molecular Dynamics simulations [1].
Evidence from both simulation and experiment suggest that caffeine localizes within the head-tail interface of lipid bilayers and increases the thickness of the membrane. By attracting water molecules from neighboring lipid molecules, the partitioning of caffeine leads to the formation of “water pockets”, i.e., a local increase of water density in the head-tail interface. Through this mechanism, caffeine leads to an overall decrease of the gauche defect density in the membranes and an increase of membrane thickness, indicating a loss of membrane fluidity. This provides a mechanism by which caffeine can inhibit drug metabolizing enzymes, such as cytochrome P450, which in turn would increase the bioavailability of primary drugs in active-form.
[1] A Khondker, A Dhaliwal, RJ Alsop, J Tang, M. Backholm, AC Shi, MC Rheinstädter. Phys. Chem. Chem. Phys., 2017, Advance Article, DOI: 10.1039/C6CP08104E
Chemotaxis is a classic mechanism for guiding cell migration and an important topic in both fundamental cell biology and health science. Neutrophil is a widely used model to study eukaryotic cell migration and neutrophil chemotaxis itself can lead to protective or harmful immune actions to the body. While much has been learnt from past research about how neutrophils effectively navigate through a chemoattractant gradient, many interesting questions remain unclear. For example, while it is tempting to model neutrophil chemotaxis using the well-established biased random walk theory, the experimental proof was challenged by the cell’s highly persistent migration nature. Special experimental design is required to test the key predictions from the random walk model. Another question that interests the cell migration community for decades concerns the existence of chemotactic memory and its underlying mechanism. Although chemotactic memory has been suggested in various studies, a clear quantitative experimental demonstration will improve our understanding of the migratory memory effect. Motivated by these questions, we developed a microfluidic cell migration assay (so-called dual-docking chip or D2-Chip) that can test both the biased random walk model and the memory effect for neutrophil chemotaxis on a single chip enabled by multi-region gradient generation and dual-region cell alignment. Our results provided evidence to support the biased random walk as a possible mechanism for neutrophil chemotaxis and clearly demonstrated chemotactic memory. In summary, this work highlights the possible biophysical mechanism employed by neutrophils for directional migratory response to their guiding chemical microenvironment and integrates the microfluidics approach to address cell migration questions.
For over 40 years spin polarized muons at TRIUMF have been used as a magnetic probe of solids via the technique of muon spin rotation/relaxation/resonance (µSR). With the increasing need to understand more complex materials, sophisticated scientific tools like µSR are necessary. Through the years innovative advances in instrumentation and refurbishment of muon beam lines have expanded µSR applications. Today µSR at TRIUMF is well suited to research of many important topics in condensed matter physics. In this talk, some recent µSR studies of quantum materials and the immediate future of µSR as a tool in condensed matter physics will be discussed.
Recent measurements using resonant soft x-ray scattering in the cuprate superconductors have shown that charge density wave order and electronic nematicity are key ingredients in the long-standing problem of high-temperature superconductivity. I will discuss the development of this technique at the Canadian Light Source and show how it has led to new insights in the physics of the cuprates and other quantum materials.
The advent of new time-of-flight neutron spectrometers at both spallation-based and reactor-based neutron sources has fundamentally changed the nature of the information that can be obtained using inelastic neutron scattering. Measurements on single crystals can now map out comprehensive four-dimensional (three momenta and one energy dimensions) data sets of inelastic scattering from both spin and lattice degrees of freedom. I will discuss the evolution of neutron sources since the discovery of the neutron by Chadwick in 1932, and show how revolutionary recent progress has been. The power of new time-of-flight techniques will be illustrated , taking examples from my groups studies of frustrated quantum magnets and materials related to high temperature superconductors.
High magnetic field laboratories provide users with a wide range of sample environments that are difficult to set up in a conventional research laboratory: steady magnetic fields up to 45 tesla, pulsed fields up to 100 tesla, temperatures down to the low mK range, and high pressures up to 10’s of GPa. Moreover, they offer a wide variety of measurement capabilities, including transport, magnetization, torque, specific heat, optics, etc.. Most importantly, they offer expertise, so that a user with comparatively little experience can travel to a magnet lab, participate in a technically difficult measurement, and produce first-rate results.
In this talk, I will give an overview of high magnetic field laboratories around the world, focusing on the specialized capabilities they offer, illustrated by examples of key results. I will follow this by discussing results that my research group has obtained at high field labs, including quantum oscillation measurements in strongly correlated electron systems, measurements of diamagnetic susceptibility in high temperature superconductors, and transport measurements at ultra-low temperatures.
Data recorded simultaneously by different instruments on the payload of the Enhanced Polar Outflow Probe (e-POP) provide evidence about the relationships of ionospheric processes. Launched in September 2013 on the Canadian small satellite CASSIOPE into low-earth orbit, the e-POP ensemble has been able to exploit novel ionospheric perspectives. The understanding of auroral-latitude physics is advancing thanks to movies of auroral luminosity below the spacecraft recorded by the e-POP Fast Auroral Imager (FAI) that provide a setting for processes detected by other e-POP instruments. By producing one image per second of near-infrared (NIR) emissions at a heights near 110 km, the FAI contributes to a knowledge of what is happening in the three-dimensional space surrounding the magnetic field line through the spacecraft.
FAI measurements have been compared with radio observations by the e-POP Radio Receiver Instrument (RRI). Both kinds of emissions are excited by free energy available from nonequilibrium electron distributions. Understanding these processes monitored simultaneously at both wavelengths may help to improve models of energy input to the ionosphere. Very-low-frequency (VLF) hiss recorded in the neighbourhood of pulsating aurora lends credibility to the agency of electron precipitation that is sufficiently energetic (10-100 keV) to create whistler-mode propagation with wave-vectors aligned predominantly close to the axis of the terrestrial magnetic field. With such particle energies, parallel-propagating electromagnetic whistler-mode waves can be created throughout their observed band-width on the RRI. Such RRI spectrograms contrast with those supplying evidence of oblique quasi-electrostatic whistler-mode propagation of auroral hiss.
In e-POP crossings of auroral arcs, contemporaneous measurements from FAI and RRI confirm that stable NIR auroral arcs locate the spectrographic vertex of V-shaped VLF hiss emission. We intend to evaluate concepts proposed for the structure and dynamics of auroral-latitude phenomena by recourse to data from various other e-POP and ground instruments
The Swarm satellite mission is well into its four-year mission to provide precise, multi-point in situ observations of magnetic and electric fields, along with plasma properties of the ionosphere. When combined with ground-based cameras, Swarm provides an excellent opportunity to study the electrodynamic properties of auroral forms such as arcs and pulsating patches. This talk will provide an overview of recent observations of electric and magnetic fields associated with field-line resonance arcs, pulsating patches, and multiple arc systems. Availability and quality of data for those interested in carrying out related studies will also be discussed.
We investigate whether the boundaries of a region of plasma in the ionosphere of different density than its surroundings will drift relative to the background ambipolar drift and, if so, how the drift depends on the degree of density enhancement, or on the altitude. There are analytical solutions for discrete circular features both with and without neutral collisions. We find that the drift is proportional to the density difference, which suggests that where density gradients occur they should tend to steepen on one side of a patch while they are weakened on the other. This may have relevance to the morphology of polar ionospheric patches and auroral arcs. The drift of the boundaries of a patch is seen to be distinct from the ion particle drift; nevertheless it appears that density structures can retain a cohesive shape even while the plasma that constitutes the enhancement or depletion moves into, through, and out of the structure again. There is also an altitude dependence (through the ion-neutral collision frequency) which may generate E-region shears and concomitant field-aligned currents above the edges of sharp density gradients.
The study of geomagnetism has been documented as far back as 1722 (Graham) with increased interest at the end of the 19th century (Lamb, Schuster, Chapman, and Price). The Magnetotelluric Method was first introduced in the 1950's (Cagniard and Tikhonov), and, at its core, is simply a regression problem. The result of this method is a transfer function estimate which describes the earth's response to magnetic field variations. This estimate can then be used to infer the earth's subsurface structure; useful for applications such as natural resource exploration.
The statistical problem of estimating a transfer function between geomagnetic and induced current measurements has evolved since the 1950's due to a variety of problems: non-stationarity, outliers, and violation of Gaussian assumptions. To address some of these issues, robust regression methods (Chave and Thomson, 2004) and the remote reference method (Gambel, 1979) have been proposed. The current method provides reasonable estimates, but requires a large amount of data.
An examination of the correlation between geomagnetic and induced current measurements shows strong correlation between these series at offset frequencies such as one cycle per day. The current method does not incorporate this correlation information. This talk will discuss the results of incorporating this high correlation offset frequency information into the statistical model.
Solar modes are normal modes whose origin lies in the solar interior or the solar surface. Recent findings in the fields of geophysics and space weather have demonstrated that the power spectra of time-series outputs in ground-based detection systems exhibit structure which is characteristic of solar modes. In a physical model which describes the induction of solar-mode disturbances at ground level, it is necessary to identify mode generation and mode transport mechanisms in the ionosphere.
Relative ionospheric opacity meters (riometers) use the intensity of cosmic radio signals to determine the level of radio-wave attenuation in the D-region. In this presentation, the results of an exploratory spectrum analysis will be reviewed, where it is revealed that solar modes likely constitute a significant fraction of the drivers of perturbations in the D-region radio-frequency opacity. The analyzed dataset was a one-second voltage series from the riometer at the Geomagnetic Laboratory in Ottawa. Voltages in this series were recorded over the duration of 2011. The analysis involved implementation of a mode-detection test, whose test statistic is a transfer-function. An interesting problem was the identification of transfer functions which smear the spectral peaks of interest.
It is now well-known that under the action of a strong electric field, ions in the high latitude F region acquire a toroidal (doughnut shape) velocity distribution as a result of collisions with neutral particles. As defined by the second moment of the velocity distribution, the resulting velocity distributions have different temperatures along and perpendicular to the magnetic field. An exact determination of the shape of the velocity distribution and associated anisotropy is, however, not a straightforward exercise because the ion-neutral collisional cross-section is not known with precision, and also because collisions between charged particles modify the velocity distribution and its velocity moments. Unfortunately, as just stated, it's not just the anisotropy that is affected by collisions, but also the velocity distribution itself, which means that spectral shapes obtained by Incoherent Scatter Radars (ISR) and satellite images of the velocity distribution must be handled with care. To that goal we have used a state-of-the-art Monte-Carlo simulation of the ion velocity distribution and its dependence on scattering cross sections between ions and neutrals to reconstruct spectra observed by ISR's. We have found that the interpretation of the radar spectra can be seriously affected by the shape of the velocity distribution during strong frictional heating events, not just in directions perpendicular to the magnetic field (as has been well-known for some time) but also along the magnetic field direction. This new result has been found to be due to the influence of a hot subpopulation in the tail of the velocity distribution along the magnetic field direction during heating events. We have reconstructed ISR spectra for a wide variety of cases, and have carried a systematic comparison with several observations, including some ran with special experiments on RISR-N and RISR-C. Among other things, we found that for small to moderate electric field strengths, a proper interpretation of the radar experiments requires the inclusion of ion-ion collisions, particularly if the line of sight is close the the magnetic field direction. We have also modeled the evolution of the velocity distribution above the collisional region, which introduces additional changes to the ion velocity distribution that depend on the time-history of a particular magnetic field tube. This, in turn, affects the values observed for the temperature anisotropy and for the vertical mean ion drift velocities, among other things. A comparison with Swarm observations is currently under way and progress on that subject will be reported on.
The three Swarm satellites were launched from Plesetsk, Russia in November 2013, with the mission to measure the goemagnetic field with unprecedented accuracy. These measurements in turn will help us better understand of the many contributions to the near-Earth magnetic field, from the Earth core, up to the ionosphere and magnetosphere. Each of the three satellites is equipped with a vector magnetometer, and an absolute scalar magnetometer located approximately 1.5 m apart. Ideally a consistency of order 20 to 50 pT, corresponding to the sensitivity of the instruments, is expected. Yet, it is found that, depending on the location and flying attitude, systematic discrepancies of order 1 nT or more can be found. Several models have been proposed to explain these differences, but some persist and remain elusive. One possible explanation for some of the differences has to do with the interaction between the Swarm satellites and nearby space environment, which would lead to a) perturbed plasma current densities, and induced currents in the satellites themselves, which would then be responsible for perturbed magnetic fields at the magnetometers. This hypothesis is tested with fully kinetic PTetra simulations of the interaction between Swarm and ionospheric plasma, under the conditions in which these unexplained discrepancies are observed. The simulations account for the full ~10m length of the satellite, and realistic ionospheric plasma parameters. Simulation results are then used to assess satellite-plasma interaction induced magnetic perturbations at the magnetometers, as a possible explanation for observed discrepancies.
Nearly two decades of auroral zone magnetometer observations are used to develop statistical predictions of geomagnetic field time derivatives.
Distributions of differences between successive 5-second vector field measurements are approximately lognormal, motivating a parametrization in terms of the first and second log-moments which are nearly uncorrelated and exhibit very different properties. Log-mean ranges over several orders of magnitude, with typicall autocorrelation time scales longer than 30 minutes. Log-variance correlation time is usually less than 5 minutes, with small amplitude noise-like fluctuations. Both log-moments depend on local time and magnetic latitude, but these factors predict less than 10% of observed variance. Simple combinations of solar wind parameters can be used to predict nearly 50% of log-mean but almost none of log-variance.
Including information about recent local activity significantly improves log-mean predictability to 70% but only accounts for 10% of log-variance.
Empirical models for these two parameters provide lognormal distribution forecasts which can be used to obtain point and range estimates of upcoming geomagnetic activity.
Prediction accuracy is highest during the day and lowest before midnight.
Hourly predictions of typical (median) and disturbed (90th percentile) events are unbiased, with roughly 90\% of cases falling between half and twice the predicted value.
Extreme (99th percentile) event magnitudes are consistently lower than predicted, by about 20%, possibly due to deviations from lognormality in the tail of the distribution.
TBA
Much of complex biology results from interactions among a large number of individually simpler elements. Behavior of large collection of cells from microbes to stem cells are no different. In this talk I will describe how theoretical ideas from statistical mechanics are being used to understand behavior of such heterogeneous populations, focusing on two examples. In first, I will present a coarse-grained model of blood regeneration, which provides a framework to understand large variations (~3 orders of magnitude) among contributions from individual stem cells without active competition. In contrast, the second describes how competition plays a central role in understanding dynamics of reprogramming population of somatic cells.
The roundworm, C. elegans is a relatively simple organism with only 300 neurons but can generate complex adaptive behavioral responses to a wide range of sensations including taste, touch, and temperature. One of the grand goals in neuroscience is to understand how neural, genetic, and biochemical circuits produce these behaviors. While a great deal of work has been done on developing tools to perturb and measure circuits underlying sensory behavior, advances in the study of behavior itself has lagged behind. Here I will describe some attempts to close this gap with focus on C. elegans locomotion and its response to thermal stimuli. We’ve developed simple desktop experiments to programmatically stimulate C. elegans and quantitatively capture its behavioral response. Using these data we have shown that C. elegans moves through a “shape space” that is low dimensional in which four dimensions capture approximately 95% of the variance in body shape. Here I will give two examples of modeling that take advantage of this low dimensionality and stereotypy. In the first we show that stochastic dynamics within this shape space predicts transitions between attractors corresponding to abrupt reversals in crawling direction. With no free parameters, our inferred stochastic dynamical system generates reversal timescales and stereotyped trajectories in close agreement with experimental observations. In the second we model the worm’s perception to “thermal pain” allowing us to infer perceived stimulus from careful measurement of the worm’s “body language.”
The continuous electric organ discharge (EOD) of the weakly electric fish, Eigenmannia, reflects action potentials (APs) fired by the EO’s muscle-derived electrocytes. EODs enable electrosensing and communication. AP frequency is neurally controlled, with acetylcholine-gated channels (AChRs) mediating synaptic transmission. According to EOD-linked whole-fish O2 consumption (for fish with EODs between ~300-500 Hz) ATP demand per AP grows exponentially with frequency. The unimodal task, continual firing, and simple homogeneous structure of the EO render it especially suitable for probing excitable system energetics in relation to molecular, cellular and tissue features. We develop a model, Epm, to depict currents at the electrocyte’s energy-dissipating Excitable posterior membrane. In situ, 3Na/2K-ATPases (pumps) counteract the dissipation of electrocyte ENa (and EK). Using Epm we calculate AP frequency-dependent “Na+ -entry budgets” for synaptic activation (pulsatile and/or steady-state, with/without noise). Comparison of Epm-calculated ATP consumption (inferred from total Na+ -entry) against published EOD-linked whole-fish O2 consumption suggests that EOD-linked energy demands external to electrocytes (neuronal, circulatory etc) exceed, several-fold, those of electrocyte excitability per se. Well-understood conductance processes (as modeled by Epm) proved fully adequate for generating sustained APs (including during jamming avoidance responses) from 200-600 Hz. By contrast, although we computationally impose the equivalent of fast stimulatory variations in [ACh], even at the bottom of this frequency range the means by which synaptic transmission machinery so reliably achieves the requisite fast variations is a mystery. The simple Eigenmannia EO therefore continues to emerge as a fascinating model system for studying not only the energetics but the subcellular and broader-level dynamics of high frequency excitability.
This study examines the biomechanics of a unique style of phonation, commonly referred to as "Tuvan throat singing" (Tuva is part of Russia close to Mongolia). It is characterized by overtones (i.e., harmonics) of the the source (i.e., vibrating vocal folds) being "focused" into a single concentrated formant, which can then be manipulated in frequency. The underlying biomechanical mechanisms are not well understood. Here, data were collected from a group of Tuvan singers (Huun Huur Tu) in two different forms. First, audio recordings were made in an acoustic isolation booth for detailed spectral analysis. Spectrograms revealed dynamical properties going into and out of the focused state, with relatively rapid transitions (~100-200 ms). Second, one of the singers was scanned by MRI during phonation. Images (and associated audio) of two types were made: volumetric (3-D volume scan during steady-state phonation) and dynamic (single sagittal slice with a frame rate of ~3.6 Hz). From these, area functions and articulator positions could be extracted and used in a computational model of sound production. Initial modeling efforts have successfully reproduced the steady-state condition, with a further goal to now characterize how articulator position affect the rapid transitions and frequency shifts of the focused state.
We’re all going to die, and our collective mortality rate increases exponentially with age. As we get older, we also become more frail --- which explains much of the increased mortality rate. Frailty involves multiple interacting health deficits, but can be quantitatively characterized. This has been done with traditional studies of human aging using cohorts of up to 10 000 individuals, as well as in new studies with electronic health records that are 10-100x larger. Our computational cohorts are even larger, and are helping us to explore aging with big data. I will tell you what we have done so far (a network model of aging), what we have learned (about the frailty maximum and about the effects of repair), and what we are doing now (using information measures in aging). I will also tell you a bit about the foundations of our work: information entropy, scale-free networks, and stochastic simulation algorithms (SSA).
In the absence of extraneous and stochastic data artifacts, differences between X-ray diffraction snapshots of a biomolecule arise from changes in object orientation and conformation. Using the X-ray Free Electron Laser data from the PR772 virus, collected at SLAC National Laboratory, we show that a manifold embedding technique can extract the structure and map the conformational spectrum of this virus. The ability to determine and sort conformational heterogeneity is thus essential for a reliable determination of the three-dimensional structure in single-particle experiments.
Following the success of SNO, recognized internationally with the award of the 2015 Noble Prize in Physics, the underground laboratory has been expanded to the new SNOLab facility which is designed to house a variety of experiments that will investigate the properties of neutrinos and dark matter. The EXO collaboration is developing detection techniques that will enable a precision search for the neutrino-less double beta decay. A definitive discovery of this process would provide new information on the properties of neutrinos, helping to determine the absolute mass scale. The double beta decay of Xe-136 produces a Ba-136 ion that is the only element for which there is experimentally demonstrated single-ion detection and identification capability aka tagging. However, applying efficiently the Ba ion tagging technique to a massive cryogenic TPC remains a challenge. EXO-Carleton focuses on a R&D program aimed at developing, optimizing and characterizing a probe for ion collection from a LXe TPC. The talk will present the challenges that the next generation neutrino-less double beta decay experiments are facing as well as the discovery potential of nEXO. It will also review the progress toward an efficient Ba ion tagging technique, with emphasis on future Canadian contributions.
The SNO+ experiment is a large-scale liquid scintillator detector re-using the major infrastructure from the completed Sudbury Neutrino Observatory experiment (SNO) at Vale’s Creighton Mine near Sudbury, Canada. The original SNO 12 m diameter acrylic vessel has a hold-down net installed to counter the buoyancy of filling the detector with 780 tonnes of Linear Alkyl Benzene (LAB) within the water-shielded cavity 2 km underground. The experiment re-uses the original 9500 spherically mounted PMTs with refurbished electronics and trigger system and a new DAQ. The high light-yield of LAB, together with a state of the art scintillator purification plant, will realise a multipurpose neutrino detector with low background and low energy threshold. The primary physics goal is the search for neutrinoless double beta decay ($0\nu\beta\beta$) of $^{130}$Te to investigate the Majorana nature of neutrinos and the neutrino mass. Tellurium has a large 34% isotopic abundance of $^{130}$Te, and using novel metal loading chemistry, about seven tonnes of telluric acid will be added to achieve an initial detector loading of almost 0.5% tellurium, with about 1330 kg of $^{130}$Te. With several years of data taking it is then expected to reach a Majorana mass sensitivity between 36-90 meV, and recent R&D provide methods for higher loadings of several percent Te for future phases of SNO+ to reach the bottom of the inverted mass hierarchy. Both before and after the $0\nu\beta\beta$ phase the pure scintillator fill has a rich program in physics, including the measurement of solar $^{8}$B, pep and CNO neutrinos, reactor anti-neutrinos, and geological anti-neutrinos, in addition to continuous supernovae sensitivity. Currently the detector is filled with water and taking interesting water-fill physics data. I will present an update on the detector status and current commissioning activities and the scintillator filling schedule for the detector.
The Enriched Xenon Observatory (EXO) is a particle physics experiment searching for neutrinoless double-beta decay in xenon-136 with a 200-kg time projection chamber. Efforts are currently being made to enhance the experiment’s sensitivity with the development of a 5 tonne-scale detector, the next Enriched Xenon Observatory (nEXO). Major experimental improvements include the use of low noise silicon photomultipliers (SiPM) for the detection of liquid Xenon scintillation light. While the baseline of the experiment is to use SiPM, the Sherbrooke’s radiation instrumentation team is proposing a vertically integrated and digitally controlled SiPM that is expected to achieve excellent performances with minimum power dissipation, a critical element to avoid the formation of bubbles in liquid Xenon. Using a digital readout takes advantage of the inherently binary nature of the device, provides fast in-chip processing and significantly lowers the output capacitance of the detector. Moreover, by having the readout electronics under the SiPM, both tiers can be optimally and independently fabricated; a very dense CMOS bottom tier and a dedicated custom SiPM top tier with an improved photosensitive fill factor. This talk presents Sherbrooke’s first functional 3D digital SiPM. The motivation of this work was to establish a proof of concept and consequently did not aim at ultimate performance. The work done shows that 3D integration of SPAD arrays on standard CMOS electronics is not significantly affecting the Single Photon Avalanche Diode array performances. Work is underway to develop a 3D integration process with industrial partners to be able to produce the required 4-5 m2 of detectors and to improve sensitivity at 170-180 nm.
SNO+ will be an organic liquid scintillator experiment, a successor of the Sudbury Neutrino Observatory (SNO). It has been designed and optimized to maximize sensitivity to neutrinoless double beta decay when the organic scintillator, a mineral oil, will be loaded with the isotope of tellurium-130. The first phase of this competitive search is anticipated to begin as early as 2018.
In this presentation, I will cover some of the fundamentals of the unique metal loading technique developed by the SNO+ collaboration, characteristics and long term stability and compatibility properties of the scintillator cocktail.
SNO+ is a multi-purpose neutrino experiment aiming to explore the unknown properties of neutrinos. The main physics goal of SNO+ is to explore whether the neutrinos are Majorana-type particles by searching for neutrinoless double beta decay of $^{130}$Te. The whole experiment can be divided into three stages: first the water phase, then the scintillator phase and finally the tellurium-loaded scintillator phase searching for neutrinoless double-beta decay.
The SNO+ detector is currently filled with water and has been turned on for the water phase operation for months. In order to calibrate the detector, an $^{16}$N calibration source inherited from the SNO experiment is scheduled to be deployed. The $^{16}$N source mainly emits 6.1 MeV $\gamma$-rays which interact with the water in the detector. The tagged $^{16}$N events can be used to optimize the position and direction reconstruction algorithms and to estimate the energy response of the detector.
We apply the current SNO+ reconstruction algorithms to the old SNO $^{16}$N calibration data and the corresponding Monte Carlo simulations to check the position reconstruction and direction resolutions of the SNO+ algorithms. The results are comparable to those from SNO. A SNO+ energy response processor is also tested by using the old SNO data and the simulations.
By comparing the simulation results with the SNO data, we can estimate the systematic certainties given by the current SNO+ algorithms.
(Brockhouse Medal Recipient / Récipiendaire de la médaille Brockhouse)
We discuss recent theoretical development in understanding emergent quantum phases of matter in correlated materials with strong spin-orbit coupling, especially in 4d and 5d transition metal oxides. In particular, we explain what kind of material platforms may be promising for discoveries of exotic quantum states such as quantum spin liquid and Weyl semimetal phases. Experimental signatures and possible applications of these phases will also be discussed.
Medal for Lifetime Achievement in Physics / Médaille pour contributions exceptionnelles à la physique
TBA
We study the spontaneous breaking of rotational symmetry in the helical surface state of three-dimensional topological insulators due to strong electron-electron interactions, focusing on time-reversal invariant nematic order. Owing to the strongly spin-orbit coupled nature of the surface state, the nematic order parameter is linear in the electron momentum and necessarily involves the electron spin, in contrast with spin-degenerate nematic Fermi liquids. For a chemical potential at the Dirac point (zero doping), we find a first-order phase transition at zero temperature between isotropic and nematic Dirac semimetals. This extends to a thermal phase transition that changes from first to second order at a finite-temperature tricritical point. At finite doping, we find a transition between isotropic and nematic helical Fermi liquids that is second order even at zero temperature. Focusing on finite doping, we discuss various observable consequences of nematic order, such as anisotropies in transport and the spin susceptibility, the partial breakdown of spin-momentum locking, collective modes and induced spin fluctuations, and non-Fermi liquid behavior at the quantum critical point and in the nematic phase.
Time-reversal symmetry (TRS) and topological phenomena associated with it are hot topics in condensed matter physics. The existence of the gapless Andreev bound states on [110] surfaces of a high-Tc cuprate superconductor is guaranteed by the bulk-edge correspondence to a topological invariant protected by TRS. Recent experiment on a nanoscale cuprate island
has detected a full gap that is consistent with broken TRS [1]. By solving the Bogoliubov-de Gennes equations self-consistently for d-wave nanoislands and nanoribbons with [110] surfaces, we show that TRS is spontaneously broken at low temperatures with spontaneous emergence of a new complex order parameter along the [110] surfaces. This new order parameter has extended s-wave symmetry and its magnitude determines the splitting of the Andreev bound states, which are gapped due to the loss of topological protection by TRS. We find this phase transition within the TRS-preserved d-wave phase to be of second order and a generic feature of [110] surfaces. Furthermore, when the side length of a nanoisland or the width of a nanoribbon is relatively large, vortex-antivortex pairs appear along the surfaces, each of which contains Andreev bound states. The TRS-broken phase, with or without vortex-antivortex pairs, can be distinguished from the TRS-preserved phase by means of surface-sensitive probes [2].
[1] D. Gustafsson et al., Nat. Nano. 8, 25 (2013).
[2] Y. Nagai, Y. Ota, and K. Tanaka, arXiv :1610.05501.
The Institut Quantique (IQ) at the Université de Sherbrooke is an open and collaborative research environment with expertise ranging from fundamental to applied at the interface of quantum information, quantum materials and quantum engineering. In this talk, an overview of the main research directions at IQ will be presented.
Microcavity exciton-polaritons are hybrid quantum quasi-particles as an admixture of cavity photons
and quantum well excitons. The inherent light-matter duality provides experimental advantages to form
coherent condensates at high temperatures (e.g. 4 K in GaAs and room temperature in GaN materials) and
to access the dynamics of exciton-polaritons. I present engineered exciton-polariton-lattice systems,
where we seek the beauty of non-zero momentum boson order arising from the intrinsic open-dissipative
nature of the condensate as well as the topology of lattices. I envision that the dynamical polariton-lattice
systems will be an intellectual interface, where we may address wondrous quantum many-body problems
in the light-matter domain.
Quantum networks are composed of quantum nodes that interact coherently through quantum channels, and open a broad frontier of scientific opportunities. An exciting frontier in this endeavor is the integration of otherwise ‘simple’ quantum elements into complex quantum networks. In this context, there is active research to achieve lithographic quantum optical circuits, for which atoms are trapped in nanoscopic dielectric structures and ‘wired’ together by photons propagating through circuit elements. Exemplary experimental platforms include photonic crystal waveguides and cavities. Owing to their small optical loss and tight field confinement, these nanoscale dielectric devices are capable of mediating long-range atom-atom interactions using photons propagating in their guided modes. In a complimentary fashion, long-range interactions between photons can be mediated by an underlying lattice of atoms. Such systems have the potential to provide new tools for scalable quantum networks, quantum phases of light and matter, and quantum metrology. I will discuss the designers’ approach to “few-body physics” of ultracold atoms interfaced with nanophotonic waveguides, and a recent experimental demonstration of collective band-edge nonlinearity with localized atoms in 1D photonic crystal waveguides. By trapping single atoms within vacuum spaces of a photonic crystal, tantalizing opportunities emerge for novel quantum transport phenomena, tunable long-range atomic interactions, and control of quantum vacuum forces. By extension, I will describe the theoretical aspects of novel “many-body” phenomena with Rydberg-dressed spin models.
The neutrino is an incredibly small and light particle that rarely interacts with any materials: 10 billion cosmic neutrinos pass through each square centimetre of Earth every second with no effect. This makes them extremely difficult to study. As a result, experiments designed to detect neutrinos must be very large.
Following upgrades to the Nobel Prize-winning SNO (Sudbury Neutrino Observatory) detector, the SNO+ detector aims to accomplish this challenging task. Located 2 kilometres underground in Sudbury, Ontario, the SNO+ detector is an acrylic sphere, 12 metres in diameter, filled with a kilotonne of liquid scintillator (fluid that gives off a measurable light signal when struck by radiation).
The primary goal of the SNO+ experiment is to look for a very rare form of radioactive decay (neutrinoless double beta decay) to see if the neutrino can be the first particle known to also be its own antiparticle. This large-scale liquid scintillator detector will also be used for a number of other measurements--one such measurement is the detection of antineutrinos.
Antineutrinos--produced in large quantities from nearby nuclear reactors--will interact in the detector through the inverse beta decay (IBD) reaction. Along the way to the detector, some of these antineutrinos will oscillate, escaping detection. Due to its geographical proximity to these reactors, SNO+ is very well suited to measure the parameters that govern this neutrino oscillation.
We have used Monte Carlo simulations to show what the IBD signal from antineutrinos will look like in the SNO+ detector. We have also developed techniques that will distinguish this signal from naturally occurring radioactive backgrounds. The next step is to implement this antineutrino search while the detector is filled with water (the current intermediate phase before scintillator is added).
By performing the search in the water phase of the experiment, we will further develop the efficacy of the tools necessary to sift through the detector data for this rare signal. This also enables us to identify and evaluate possible backgrounds that could mask IBD interactions. Following this, we will be well positioned to measure antineutrino signals once the detector is fully commissioned.
SHiP and DUNE are future high intensity neutrino experiments, both of which generate a very large flux of neutrinos and anti-neutrinos of all 3 flavours. Combined with improved detector technology, their high luminosity means that these experiments are sensitive to subdominant neutrino physics. Neutrino trident production is one such process, which sees an incoming neutrino incident on a nucleus produce an outgoing neutrino and two oppositely charged leptons. In this talk we will show that the standard model rates at SHiP and DUNE allow for a number of trident mixed-flavour modes, most of which have never been observed. Some of these mixed-flavour modes have production cross sections as high as 35 times those previously considered by CHARM-II and CCFR, the latter of which currently provides the most stringent bound on certain $Z’$ models. This suggests that with future experiments trident can serve as a useful tool in the study of BSM physics. As an example we study the constraints to generic leptophilic scalar extensions of the standard model.
The IceCube Neutrino Observatory instruments more than a cubic kilometre of the deep glacial ice below South Pole Station, Antarctica, creating the largest water Cherenkov detector. With the addition of a low energy detection array, DeepCore, completed in 2010, the observatory is sensitive to neutrinos with energies between 10 GeV and the EeV scale. IceCube has now accumulated the world’s largest sample of atmospheric neutrinos, providing the ability to perform precision studies of the flux over the full energy range of the detector. We present results of atmospheric neutrino flux measurements with particular attention to the low-energy regime.
The IceCube Neutrino Observatory was designed with the primary goal of detecting very high energy neutrino events beyond the TeV scale from astrophysical sources. A low-energy infill array, DeepCore, was designed to extend the reach of IceCube to events with energies of ~10 GeV. At these low energies, there is less recorded event information that introduces challenges for the reconstruction of event properties, including energy and incoming angle. Further, to accurately resolve these quantities requires the ability to incorporate complex models of the natural ice medium. By simulating events in real time in place of approximated tabulated templates, it is possible to include the full description of the glacial detector medium from calibration data. This method of direct reconstruction thus provides the ability to reduce some of our leading, ice-related, systematic uncertainties. A full description of the algorithm, as well as an estimation of its effects on event reconstruction and corresponding impact on DeepCore analyses will be presented.
I review applications of holographic framework to out of equilibrium dynamics in strong coupled gauge theories. Potential applications range from physics of heavy-ion collisions to properties of primordial quark-gluon plasma in early Universe.
Non-perturbative techniques are needed to study strongly coupled systems.
One popular method is the 2 particle irreducible (2pi) effective theory.
For scalar theories, calculations at the 3 loop level show improved convergence, relative to perturbative results.
We present results in $\phi^4$ theory at the 4 loop level which show that convergence breaks down at large coupling.
This indicates the need for higher order effective theories.
4pi calculations in 4 dimensions have never been attempted, because no method is known to deal with the overlapping sub-divergences that appear in these theories. We present a new technique to renormalize the 4pi effective theory, based on a renormalization group approach.
For phases like quark-gluon plasmas, the strong-coupling nature of the system means that perturbative approximations are invalid, and therefore conventional solution methods break down. However, using a duality first established by string theory, we are able to relate strongly coupled quantum field theories to weakly coupled gravitational systems (in one higher dimension). The most common use of this hidden relationship is to map between special quantum field theories — known as Conformal Field Theories (CFTs) — and general relativity in anti-de Sitter (AdS) space. As a consequence of the AdS/CFT correspondence, the more strongly coupled a CFTs is, the more weakly curved (i.e., classically solvable) the gravitational dual is.
Motivated by the AdS/CFT correspondence, we examine the conditions that lead to the formation of a black hole in 4D AdS as a dual to the thermalization of a 3D CFT under an initial energy perturbation. We numerically evolve the full Einstein equations in the presence of both massless and massive scalar fields for a variety of initial momentum profiles. The curvature of AdS is such that massless fields are able to travel to spatial infinity and back in finite time, and therefore these fields have multiple opportunities to collapse. Massive fields do not travel to infinity, but do undergo periodic motion that may lead to horizon formation at long times.
The interplay between the initial conditions and the geometry of the space lead to a landscape of collapse behaviour that will be explored in this talk. Using the highest resolution available, we are able to extend our numerical results into amplitude regimes that are described by a perturbative theory. For certain initial profiles, the prediction of the perturbative theory — that AdS space is stable to black hole formation in this regime — is at odds with the numerical data. We will make preliminary comments on how this discrepancy may be resolved, and how the resolution could bring about significant improvements in modelling the formation of black holes from massless and massive scalar fields.
There is a long tradition of using applied physics to improve medicine. Over the years, several new treatments and new diagnostic tools have been developed by physicists. However the clinical world is much different from the laboratory. Thus, even if there are numerous opportunities for physicists in the field of medicine it can sometimes be challenging to seize them.
In this context, this paper will present how physicists can make a meaningful contribution in the clinic by illustrating the feasibility by focussing on a single clinical challenge: the precise monitoring of radiation doses delivered to cancer patients. Radiation treatments have substantially improved in recent years. It is now technically possible to irradiate a small tumor to high doses while preserving healthy tissues surrounding the tumor. However, these high conformity treatments can be taxing for the delivery equipment. Furthermore, patients are rarely static; a patient's movement or anatomical changes could cause a treatment to miss its intended target. Thus, there is a need to verify that doses are delivered accurately and exactly as planned. Three strategies for monitoring dose received by patients will be presented: (1) development of a new instrument (a multipoint scintillation dosimeter) to measure radiation on the patient; (2) an image processing and data analysis workflow to track the evolution of a patient’s morphology during treatments and (3) a purely clinical, retrospective analysis to assess potential side effects of radiation treatments. In each case, the physicist's role varies greatly. However, in all three strategies, a close collaboration between physicists and clinicians, as well as industrial partners, is necessary for success.
By looking at concrete examples of applied physics for medical applications, I hope to help demystify the clinical world and show how physicists can work to improve patient care.
Purpose Emmetropization is an active process of reduction of defocus, regulated by the optical image on the retina. Rather than the value of defocus approaching zero, a non-zero error has been reported in humans and by us in an animal models. Here we explore the relationship between optical blur and cone photoreceptor sampling in the growing chick eye with and without imposed defocus blur.
Methods The right eyes of fifteen Ross Ross chicks were goggled with -15D lenses on the day of hatching and the left eye grew normally. All measurements were performed from day 9 to 21. Measurements of axial length, using A-scan ultrasound and aberrations and defocus, using a Hartmann-Shack aberrometer were made. The total optical blur and the portion due to spherical defocus and total defocus were estimated from the equivalent blur. Cone photoreceptors were imaged close to the area centralis using adaptive-optics. Angular cone density and angular cone row spacing (RS) were calculated from the images. Point spread functions (PSF) were calculated using Matlab. Data from previous measurements on chick eyes unilaterally googled with a -15D lens were also analyzed.
Results Cone row spacing decreases exponentially to threshold values in both eyes at a slower rate than blur and the decrease was not significantly different between eyes. Optical blur reduces exponentially to threshold values in both control and goggled eyes which did not differ significantly. Cone row spacing changed little after day 14. The estimate of the threshold value of total blur was not significantly different from the cone resolution (2X cone row spacing) in either the goggled or control eyes. After day 14, the estimate of total blur did not differ significantly from the cone resolution in the control eye but optical blur appeared slightly higher than cone resolution in the goggled eye. There was a significant difference in astigmatism between control and goggled eyes on every day (P<0.001).
Conclusions Defocus from the goggle does not affect the change with age of cone density. Optical blur reduces to a value above zero, indicating a small amount of residual defocus. This value of optical blur matches or slightly exceeds the amount that can be resolved by the photoreceptor array, indicating that cone photoreceptor density determines the minimum blur achieved.
Amyloid-beta (A$\beta$ ) peptides are 36 to 43 amino acid residues, implicated by the amyloid cascade hypothesis as one of the cause of Alzheimer’s disease (AD). In the brain, A$\beta$ forms small peptide aggregates, called oligomers, leading to $\beta$-sheet fibrils that, with time, forms the 3D amyloid plaque that is the hallmark of AD. The structure of fibrils consists of parallel and/or anti-parallel sheets wound in a wide array of complex three-dimensional structures. Though parallel $\beta$-sheets are more common in AD, anti-parallel sheets are believed by some researchers to be associated with early onset AD.
This paper presents our effort in building a coarse-grained model of the formation of micro-crystal fibril of fragments of A$\beta$. For computational efficiency, an amino acid is represented as a spherical bead, located at the center of its C$_\alpha$ carbon.This allows the study of systems of up to 200 peptides. In the spirit of Go models, the intra-peptide dihedral and van der Waals interactions, as well as inter-peptide interactions are biased to the experimental crystal structures. Two C$_\alpha$ beads on different peptides can also interact by a Mercedes-Benz-type hydrogen bond,which stabilizes $\beta$-sheet. MD simulations observed that A$\beta$ fragment models that are biased to anti-parallel $\beta$-sheets condensed to fibrils at lower temperature than models biased to parallel $\beta$-sheets. Finally the kinetics of fibril formations are presented, and the implication to AD are discussed.
A persistent gender gap in physics—particularly in both conceptual understanding and retention in programs—has concerned educators and policy makers for decades. Though women make up the majority of undergraduate students, they represent only 20% of physics undergraduates. We found that in a study of 790 students from our institution, physics identity plays a significant role, distinct from prior knowledge, in mediating the gender gap in conceptual understanding and intention to continue in a physics program. This suggests that teaching techniques that target identity growth could help close the gap. Examples of techniques used in the classroom that correlate with identity growth (and some that seem to stifle it) will be discussed.
Research into education strategies has repeatedly shown that actively engaging students results in stronger learning of core concepts (Korff, 2016). Calls to include experiential, inquiry-based strategies, particularly in STEM (Science, Technology, Engineering and Math) education have been persistent (Zhang, 2016). Many institutions are searching for ways to accomplish this, and research institutions are searching for ways to showcase their accomplishments and attract potential new researchers. The Canadian Light Source (CLS) has developed successful education programs for high school students that focus on the process of research and provide as close to an authentic research experience as possible (Walker, 2013). This presentation will describe how the CLS collaborated with faculty at the University of Saskatchewan to pilot several methods of including authentic research experiences for undergraduate students at the first and upper years. Keeping student driven research utilizing synchrotron techniques as the core of the experience, we have explored the following methods: 1) a tutorial in a first year Environmental Science course, 2) a course centered around a collaboration between third year students from the departments of Chemistry and Classical, Medieval, & Renaissance Studies, and 3) a course centered around a concurrent experience in scientific inquiry and the pedagogy of inquiry for curriculum studies students in the college of education. Elements of success and areas where improvement is required will be shared from the perspective of student engagement and learning, faculty involvement and resources, and working with research laboratories. While using Canada’s only synchrotron is a hook to attract students, we propose the methods we explored could be successful using any research technique.
Several provinces have now included quantum mechanics in their physics curriculum for grades 11 and 12. While certainly well intended, this is expected to cause problems due to the students’ lack of mathematical proficiency, the fact that many physics teachers do not have a physics background, and the inadequate selection of specific topics that are suggested in the curriculum.
In this talk, I will give an overview of a professional development workshop I gave to BC high school teachers earlier this year. It includes a brief history of quantum mechanics that addresses the BC curriculum requirements, plus suggestions on how to make this content meaningful to the students. The next part is a summary of how we understand quantum mechanics today and addresses common misconceptions found in the media and even in textbooks, with suggestions for student activities and useful resources. The last part focuses on current research, mainly quantum computing, to inspire students to learn more and perhaps even consider a career in physics.
In order to create a scientifically literate society, and to keep up with the rapid pace of technological change around the world, more students must be encouraged to pursue degrees in physics and related fields (President’s Council of Advisors, 2012). This study invited students taking introductory physics at a university in Atlantic Canada to participate in an anonymous, mainly short answer survey regarding their physics experiences both before and during their first year at university, and to discuss what influenced their choice of major. The course professor and lab technician were also interviewed to get their perspectives.
The results of our grounded theory analysis showed that interest in the “fascinating” subject matter of physics, or in their chosen field, was the primary factor affecting students’ choice of major. Interest in the field was followed by their perceptions of the teaching in the introductory physics courses, their impressions of what careers would be available to them after university, and their feelings of competence to succeed in a physics degree. The new physics education research-based laboratory curriculum that had been implemented during the academic year in question was perceived as more interesting and stimulating than traditional laboratories, especially for female students. This talk will summarize the results of the study and illustrate how they may be useful for physics professors, lab instructors, support staff, and administrators.
The fourth edition of the Canadian Conference for
Undergraduate Women in Physics (CUWiP) series was held at McMaster
University on 13-15 January 2017. A conference report for this 2017
edition will be presented along with historical statistics from the past
conferences held in Canada so far. The second part of this talk
will report on the developing partnership between CAP and the US
American Physical Society CUWiP organization.
Quantum communication allows the provably secure distribution of cryptographic keys, and the teleportation of quantum states between distant particles. Applications of these two key concepts of quantum information processing generally require sender and receiver to be at distant locations.
I will discuss our recent advances in quantum key distribution (QKD) and quantum teleportation using the City of Calgary’s standard fibre network. More precisely, I will comment on our work towards the implementation of so-called measurement-device-independent QKD [1,2] – a recently proposed QKD protocol that is immune to side-channel attacks that exploit vulnerabilities of single-photon detectors – in a star-type network topology. Furthermore, I will discuss quantum teleportation from a photon, interacting with another photon after both have travelled several kilometres over deployed fibre and over a combined beeline distance of 8.2 km, onto a third photon 6.2 km away [3]. Both investigations constitute important steps on the path towards a large scale quantum communication network, and ultimately a quantum computer network.
[1] H.-K. Lo, M. Curty and B. Qi, Measurement-Device-Independent quantum key distribution, Phys. Rev. Lett. 108, 130503 (2012) .
[2] A. Rubenok et al., Real-World two-photon interference and proof-of-principle quantum key distribution immune to detector attacks, Phys. Rev. Lett. 111, 130501 (2013).
[3] R. Valivarthi et al., Quantum teleportation across a metropolitan fibre network, Nature Photonics 10, 676–680 (2016).
We investigate the open dynamics of a quantum system undergoing short discrete repeated interactions. We assume the joint dynamics of the system and the ancilla are unitary and the interaction is of brief duration $\delta t$. We then take the unique Markovian interpolation between the discrete post-interaction states and find its Master Equation. To zeroth order in $\delta t$ we find the evolution is unitary and maintains the purity of the state. To first order in $\delta t$ we see the leading dissipative effects.
In order for these dynamics to cause equillibration, they must be able to purify some state. We analyze exactly when these dynamics can purify finding that only interactions with a certain degree of complexity can purify. Restricing our attention to Gaussian states and Transformations we find that thermalizing interactions are given by a two parameter family of interaction Hamiltonians.
We analyze the entanglement harvested from a quantum field through local interactions of a pair of identical Unruh-DeWitt detectors that are moving with relative constant velocity. These detectors are taken to be point-like and have Gaussian switching. For detectors moving in opposite directions we find that the entanglement harvested has a complicated dependence on the detectors’ velocities, energy gap, and their cross-over time relative to the peak of their switching. Additionally, we find that for any combination of parameters there is a velocity that globally maximizes entanglement harvesting, and there may be more than one local maximum. Finally, we find that for small time differences and a large enough detector gap, entanglement harvesting is always possible.
Demonstrations of quantum key distribution (QKD) with moving platforms are important to prove the viability of future satellite implementations. Thus far, however, demonstrations of QKD to aircraft have operated exclusively in the downlink configuration where the quantum source and transmitter are placed on the airborne platform. While this approach ultimately has the potential for higher key rate, it is more complex and is not as flexible as an uplink configuration, which places the quantum receiver on the airborne platform while keeping the quantum source at the ground station. Here we present the first successful demonstration of QKD to a receiver on a moving aircraft.
The apparatuses for our demonstration consist of a QKD source and transmitter located at a ground station at Smiths Falls-Montague Airport, and a QKD receiver located on a Twin Otter research aircraft from the National Research Council of Canada. Optical links were established using strong beacon lasers (at a wavelength different from the quantum signal), an imaging camera, and tracking feedback to 2-axis motors at each of the two sites. Once at the aircraft, the QKD signals were recorded for later processing to complete the QKD protocol and extract secure key.
The airplane flew two path types: circular arcs around the ground station, and lines past the ground station. The distances for each type of pass varied from 3-10 km. The flight paths were prepared in advance of the flight and integrated with the flight software.
In total, we had successful quantum links in seven of 14 passes of the airplane over the ground station, generating asymptotic key in one pass and finite-size secure key in 5 passes, with one showing over 800 kb. The circular passes allowed the demonstration of longer link times, whereas the line passes were more representative of a satellite pass over a ground station. Angular speeds (at the transmitter) between 0.4 degree/s and 1.28 degree/s were achieved.
We have measured the beta asymmetry with respect to the nuclear spin in 37K decay to be -0.5706+-0.0018. Ours is the most accurate beta asymmetry measurement in any nucleus or the neutron, and is in agreement with the Standard Model of particle physics. I will show our constraints on beyond-Standard Model physics complementary to other beta decay measurements. I will also describe our planned improvements to TRIUMF's laser-cooled atom trap for beta decay (TRINAT), including measurement of the asymmetry of the low-energy nuclear recoils. We hope to reach accuracy sufficient to complement pion decay and high-energy experiments, probing coupling strengths of possible new bosons to first-generation particles.
The ALPHA experiment at CERN was designed to test CPT symmetry through
comparisons of measurements of antihydrogen transition frequencies to those of
hydrogen. I will describe our recent result on the 1S to 2S transition in
antihydrogen. Then I will discuss a new experiment - ALPHA-g - which aims to
study the gravitational interaction between antihydrogen and the Earth.
The goal of the CERN-based ALPHA Collaboration is to examine the properties of the antihydrogen atom at the highest levels of precision possible [1], and thereby place constraints on any differences that might exist between antihydrogen and normal matter counterpart, hydrogen. These comparisons are expected to provide stringent tests of CPT symmetry, which is one of the cornerstones upon which quantum field theory is built. In 2012 we reported on an experiment in which transitions were induced between hyperfine levels of ground state antihydrogen atoms held in a magnetic trap [2]. We have made significant progress with that experiment during the interim, and anticipate that we will soon be able to report a measurement of the hyperfine splitting of the antihydrogen atom. That work, as well as future prospects for precision microwave spectroscopy of antihydrogen, will be described.
[1] ALPHA Collaboration, Nature 541, 506 (2017).
[2] ALPHA Collaboration, Nature 483, 439 (2012).
During the fall of 2016, the ultracold neutron (UCN) collaboration at TRIUMF conducted a number of tests for the cold neutron (CN) source commissioning. Maximizing the resultant CN flux through this source is imperative to producing the world’s highest density of UCN. This is necessary in order to increase the sensitivity of the measured neutron electric dipole moment (nEDM) by an order of magnitude over current measurements (<3e-26 e.cm) and thus search for new sources of CP-violation to explain the baryon asymmetry of the universe. The commissioning tests included determining the thermal neutron flux outside the source via 197Au(n,γ)198Au process and determining the CN flux inside the source by activating a number of different metals through neutron capture and analyzing the respective flux energies. This talk covers the theory, method, and results of the neutron activation measurements.
The TRIUMF nEDM experiment aims to constrain the neutron’s electric dipole moment by an order magnitude over the current sensitivity. The experiment employs a magnetically shielded Ramsey Resonance based EDM apparatus employing ultracold neutrons from a spallation based superfluid helium UCN source, currently under construction at TRIUMF. In our experiment, inhomogeneities (gradients) and instability of the applied magnetic fields are expected to be one of the leading sources of systematic errors in the measurement. The magnetic holding field is typically created by coils that are coupled to the passive magnetic shield surrounding the experiment. The innermost layer of the shield acts as a return yoke. This couples the stability of the holding field to the stability of the magnetic shield material which limits the sensitivity reach of the experiment. An alternative to the shield coupled holding field coil is a self-shielded holding field coil. Here, two coils of different sizes with counter-propagating currents work together to provide the holding field inside the EDM cell while canceling each other at distances greater than both coil shells. One primary concern with employing self-shielded coils is to how precisely one needs to place the individual wires of the two coils. To this end, we have been developing a self-shielded holding field coil using the 3D finite element analysis program COMSOL to investigate how misplacements of the coil locations affect the overall homogeneity over the EDM cell. This presentation will discuss our study into this aspect using a box-shaped self-shielded coil.
Radiation therapy (RT) is one of the primary modalities for the treatment of cancer with approximately 50% of the cancer patients having some form of RT during their care. RT treatment has advanced considerably in the last decade through the development of improved imaging and radiation modelling to predict dose delivery to individual patients, and of advanced equipment operating dynamically under computer control to better deliver the radiation to the patient. The progress has enabled complex intensity modulated and volumetric radiation delivery techniques (IMRT and VMAT) that provide precise dose sculpting so that treatment targets receive the high doses required for tumour control while healthy tissue toxicity and damage is minimized. But the individual steps in patient treatment are complex, driving a clinical need for extensive quality assurance including the validation of the dose delivery at various levels. For example, the integrity of the dose delivery must be verified initially when a new treatment technique is commissioned and implemented, and then, perhaps again, immediately prior to an individual patient’s treatment. There are considerable technical challenges in making sure that the intended dose delivery is achieved since conventional point and planar dosimetry techniques do not provide full three dimensional (3D) dose data. In Kingston this clinical requirement has driven an interdisciplinary research effort involving clinical medical physicists, chemical engineers and computer scientists to advance three dimensional dosimetry techniques. In this talk I will review the clinical demands associated with modern RT dose delivery validation, describe the development of 3D dosimetry particularly using gel dosimeters, describe the fundamental science that informs the development of these new dosimeters and makes their use clinically practical, and, finally, present how new 3D dosimetry systems can be used with other dosimetry techniques to guide clinical practice.
Injections of gold nanoparticles (Au-NPs) at the vicinity of low-dose radioactive implants (containing 103Pd or 125I) could enhance the efficiency of prostate cancer brachytherapy. The interaction of low-energy photons with gold produces a large number of photoelectric events that are expected to lead to higher energy deposition. Understanding the impact of intracellular Au-NPs concentration and diffusion on the deposition of dose at the subcellular level is essential to achieve a good control of this emerging treatment. Here we report on the first microdosimetric study based on the microscopic mapping of radioactive Au-NPs injected in prostate cancer tumors.103Pd-doped Au-NPs were synthesized (50 nm diam.) and stabilised with biocompatible polyethylene glycol. The Au-NPs were injected intratumorally in a murine prostate cancer (PC3) xenograft model. CT imaging, transmission electron microscopy (TEM) and optical microscopy were used to follow-up the diffusion and the cell internalization of the Au-NPs. TEM histology maps were used to generate a microdosimetric Monte Carlo dose deposition study. The macroscopic distribution volume of Au-NPs after injection (2mm3), was estimated to 4.1 ± 1.6 mm3 (2h), 3.0 ± 0.9 mm3 (4 days), and 3.1 ± 1.2 mm3 (8 days). TEM and optical microscopy images confirmed the rapid uptake of the Au-NPs by the cells. After 2h, accumulations of Au-NPs were visible in vesicles. The activity in tumors was also measured, which confirmed the retention (80 %) of Au-NPs after 8 days. The microdosimetry assessment showed that energy deposition gradient is very steep and mostly confined inside the vesicles, which indicates that Au-NPs need to get closer of the nucleus to deliver the dose. In conclusion, radioactive nanoparticles were efficiently synthesized and showed good retention in tumors. Energy deposition from radioactive nanoparticles was calculated for the first time according to in vivo conditions and showed that the dose decreases dramatically at the edge of the vesicles.
Recent findings in populations exposed to radiation indicate dose-related lens opacification occurs at much lower doses (< 2Gy) than indicated in radiation protection guidelines. As a result, research efforts are now being directed towards identifying early predictors of lens degeneration resulting in cataractogenesis. In this study, Raman microspectroscopy was used to investigate the effects of varying doses of radiation on human lens epithelial (HLE) cells. Samples of live cells adhered to quartz coverslips were irradiated utilizing a 120 kV, 12.5 mA X-ray source at six dose levels, ranging from 0.01 Gy to 5 Gy. The cells were incubated for 24 hours post exposure and then fixed with 10% formalin. Raman spectra were acquired from the nucleus, cytoplasm, and membrane of the chemically fixed HLE cells using a custom-built confocal Raman microscope equipped with a 785 nm laser. For nucleus and cytoplasm targets, spectra were collected from points in a 3x3 grid pattern and then averaged. The raw spectra were background subtracted to remove contribution from the quartz substrate and vector-normalized. Distinct differences between spectra collected from the cytoplasm of the unirradiated HLE cells and those irradiated at 5 Gy were seen after this processing. Principal component analysis and multiclass linear discriminant analysis (PCA-LDA) was used to discriminate by dose. A high classification accuracy (> 95%) was obtained for the leave-one-out classification of cells exposed to 0, 1, 5, 50, and 500 cGy. These initial findings are promising and suggest that Raman spectroscopy may be able to support the early identification of cataract formation.
Single photon emission tomography (SPECT) is the gold standard and well- established clinical diagnostic imaging technique using designated Tc-99m or I-123 pharmaceuticals for cardiac diseases, bone diseases, and thyroid diseases. The conventional method of producing Tc-99m pharmaceuticals is to use the parent nucleus Mo-99 produced in a nuclear power reactor by a fission reaction of U-235. In recent years, due to shut down of Chalk River power reactor in Canada, one of the major suppliers of the Tc-99m, the continuous supply of the pharmaceuticals was adversely interrupted. Therefore, new techniques are being developed to use other techniques to produce the Tc-99m pharmaceuticals. The irradiated enriched Mo discs were received from Missouri University Research Reactor (MURR), which uses neutron activation processes, in which Mo-99 is obtained by the neutron activation (n,gamma reaction) of Mo-98 in a high neutron flux reactor. The radiochemistry lab, at the Winnipeg Health Sciences Centre (HSC), processed the Mo-99 pallets and produced the Tc-99m pharmaceuticals, using some of the instruments and setup used for their clinical productions. Three Tc-99m pharmaceuticals, for brain, cardiac, and bone SPECT imaging were produced and injected intravenously into healthy CD1 mice. The animals were imaged with a hybrid SPECT/CT scanner (NanoScan, Mediso Medical Imaging Systems- Budapest, Hungary). In the control groups, the animals were injected with the same pharmaceuticals produced using the conventional Mo sources. After imaging, the animals were euthanized, and the radioactivity in vital organs, such as heart, lungs, kidneys, intestines, etc., was measured using a well counter. The images were quantified using region of interest analysis on VivoQuant software, provided by the manufacturer. Preliminary quantification results demonstrate agreement between the in-vivo and ex-vivo quantification. The results of the image quantification will be compared to those obtained in the control group, to validate the equivalency of the Tc-99m pharmaceuticals produced by the two techniques.
In rare event searches, minimizing backgrounds is essential to obtaining high sensitivity. Many Weakly Interacting Massive Particle (WIMP) detectors employ powerful tools such as pulse shape discrimination to differeniate between electronic recoils and nuclear recoils; since WIMPs are expected to produce nuclear recoils, the total background rate can be drastically reduced. Liquid argon-based detectors such as DEAP-3600 use pulse shape discrimination to efficiently reject electronic recoils. However, radon is naturally occuring in the air, and it may deposit its progeny on the inner surfaces of detector materials. When these isotopes alpha decay, they may send either an alpha particle or a recoiling nucleus into the sensitive volume of the detector to produce a nuclear recoil, which can mimic a WIMP event near the surface. Extremely long-lived scintillation light tail in TPB--a wavelength shifter commonly evaporated onto the inner surfaces of argon-based detectors--may provide a powerful signature for tagging such surface backgrounds. I will discuss the in-situ observation of this signature in the DEAP-3600 detector, compare with a set of a set of ex-situ measurements and show how we can use it to help characterize the surface backgrounds in the experiment.
The SNOLAB facility is located within an active mine, and as such the experiments housed there are subject to daily seismic activity, both planned and unplanned. For this reason, A hydrophone has been installed within the water shielding tank of DEAP-3600, an ultra-low background dark matter experiment, to act as a seismograph and to identify and timestamp seismic activity. This presentation outlines the reasons for installing a seismograph, and documents the installation and integration of the hydrophone into the existing data acquisition system.
This talk won the SNOLAB summer student competition.
For many years now, terahertz imaging has been applied to many fields. In this work, we experimentally demonstrate THz Fourier imaging. We use a lens to generate the Fourier transform of a transmission object. Then, we measure the Fourier plane using a THz detector mounted on a 3D stage. First, we demonstrate that using the conventional inverse Fourier transform the image can be reconstructed for a single THz frequency. Temporal THz electric waveforms are detected by raster scanning of the Fourier plane. Then, temporal Fourier transform is applied to those points resulting in an image per THz frequency. Using the inverse Fourier transform algorithm, we can reconstruct the object at each THz frequency. Second, we show that using less than 2% of the original pixels, we can still reconstruct the object. The spatial frequencies being directly proportional to the THz frequency, the measurement of a THz spectrum creates a line in the k-space. Therefore, instead of measuring on a 2D grid, it is possible to measure only a 1D path along a circle to reconstruct the k-space. Here, we demonstrate that using only 1.6% of the points, we can reconstruct the object. This is a considerable improvement to reduction of the data points using compressive sensing theory.
Weak-value amplification (WVA) is a technique that has been used in a variety of experimental settings to permit the precise measurement of small parameters. WVA is a special instance of a more general measurement strategy that involves sorting data into separate subsets based on the outcome of a second ``partitioning'' measurement. Whether or not WVA has an actual advantage in terms of the resulting measurement precision has been the subject of an ongoing debate over the past few years. In this paper we analytically and numerically investigate the performance of weak-value amplification (WVA) and related parameter estimation methods in the presence of temporally correlated noise. Using a simplified noise model that can be analyzed exactly we compare WVA to a conventional measurement method. We find that introducing WVA indeed yields a much lower variance of the parameter of interest than does the conventional technique, optimized in the absence of any partitioning measurements. In contrast, a statistically optimal analysis that employs partitioning measurements, incorporating all partitioned results and their known correlations, is found to yield an improvement -- typically slight -- over the noise reduction achieved by WVA. This is because the simple WVA technique is not tailored to a given noise environment and therefore does not make use of correlations between the different partitions. We also compare WVA to traditional background subtraction, a familiar technique where measurement outcomes are partitioned to eliminate unknown offsets or errors in calibration. Surprisingly, in our model background subtraction turns out to be a special case of the optimal partitioning approach in the balanced case, possessing a similar typically slight advantage over WVA. These results give deeper insight into the role of partitioning measurements, with or without post-selection, in enhancing measurement precision, which some have found puzzling. We finish by presenting numerical results to model a more realistic laboratory situation of time-decaying correlations, showing our conclusions hold for a wide range of statistical models.
Medical imaging such as positron emission tomography (PET) and high energy physics experiments such as time imaging calorimetry are among examples that would benefit from better timing resolution and use time-of-flight (ToF) measurements to improve image contrast or mitigate pileup. The single photon timing resolution (SPTR) is the timing resolution of the photodetector and readout electronics when triggered by a single photon. This performance is an important feature for ToF PET in order to take advantage of the timing information of the first emitted scintillation photons. One of the biggest challenges in the development of photodetectors for these applications is combining high photodetection efficiency (PDE) with high SPTR. Current SiPMs have a high PDE, but are limited in SPTR by two factors. First, the photodetector has a high output capacitance which affects the rise time and thus the SPTR. Second, the SPAD position in the array has different timing skew generating a time jitter according to geographical light detection. The solution proposed to obtain ToF capabilities with high SPTR and high PDE is a 3D digital SiPM in which every SPAD are individually connected to a readout circuit and a Time-to-Digital Converter (TDC). This approach will minimize the aforementioned limitations of current SiPMs and will offer additional functionalities. While the 3D integration process with an industrial partner is underway, we realized a 2D version of the different components of the detector such as SPAD, readout circuit, TDC, array readout and on-chip post-processing. This presentation will be an overview of the implemented architecture and the different features that can be added for specific applications such as dark noise suppression, energy estimation, timing estimation and photon counting. Furthermore, prototypes’ measurements demonstrating sub 10 ps timing resolution for a SPAD and its readout in TSMC CMOS 65 nm will be presented (current measurement 8 ps FWHM). This will change the paradigm and approach to many physics experiments.
Gamma-ray spectroscopy is a powerful tool used in a variety of fields including nuclear and analytical chemistry, environmental science, and health risk management. At Simon Fraser University Nuclear Science Laboratory (SFU NSL), the Germanium detector for Elemental Analysis and Radiation Studies (GEARS), a low-background shielded high-purity germanium gamma-ray detector, has been used recently in all of the above fields.
The environmental radioisotope monitoring program at SFU NSL has formed into many working collaborations both within and outside the university community. The primary focus of the majority of these collaborations has been towards monitoring the fallout and spread of Fukushima-derived radioisotopes such as cesium-134 and cesium-137 in Pacific marine life. These measurements often focus on measuring trace quantities of radionuclides in extended environmental samples using low-background gamma-ray spectroscopy with GEARS.
A recent addition to the SFU NSL is the Thermo Scientific P 385 neutron generator. This device provides a nominal yield of 3$\times$10$^8$ neutrons/s providing the capacity for neutron activation analysis (NAA), a major avenue of research which was previously not possible at SFU NSL. To measure and study a larger quantity of isotopes produced via NAA, a new analog data acquisition (DAQ) system has been installed on GEARS to do time-resolved gamma-ray spectroscopy with the purpose of measuring nuclear decay kinetics of activated samples. This DAQ allowed GEARS to do precise measurements of the decay kinetics of a meta stable state in tin-117, a candidate radionuclide for diagnostic and therapeutic applications in nuclear medicine, which was produced via NAA at SFU NSL.
An overview and recent results of SFU NSL’s environmental radioisotope monitoring program and the neutron generator facility will be presented.
One of the many challenges for nanoscale engineering is to purposely direct the self-assembly of nano-materials into desired patterns. Easy deposition methods (such as drop-casting) are preferable over ones that require high-vacuum (such as thermal deposition), as the latter has a high cost and requires long processing time; both of which renders the method infeasible for mass production. The trade-off for ease-of-use fabrication is that intermolecular morphology of the nano-objects are likely to have some uncontrollable variation between experimental outcomes, resulting in disordered states. To achieve desired patterns, researchers rely on trial-and-error methods to understand which experimental parameters have the necessary influence on morphology. However, in systems of similar density, human perception is unable to detect subtile differences in the localized structure, which can lead to misclassifications in the amount and type of disorder in the system. In this talk, we’ll explore numerical methods where in which these disordered states can be quantified and ranked between each other when the preparation method for nanoparticle deposition at the interface is varied. This allows researchers to quickly and confidently decide the next variation in methodological refinement by rejecting unnecessary experiments. These analysis tools have been developed as a Mathematica package and are made freely available to use. The only requirement for using these tools is knowing the relative positions of the objects, which can be extracted from imaging techniques (such as AFM or SEM).
The addition of a qPlus sensor to a tunneling microscope (STM) allows measurement modalities from the world of force microscopy, such as non-contact atomic force (NC-AFM) and Kelvin probe force microscopy (KPFM), to be performed ‘alongside’ STM and STM spectroscopy with a metal tip or a metal tip functionalized with a well defined probe species such as CO or Xe. This approach is illustrated using two different systems. The near surface defects in the delta-doped B:Si(111) system have been studied using a combination of STM, KPFM, total energy DFT and STM theoretical simulations. This allowed defect configurations to be identified and the chemical activity of commonly found configurations to be compared. Also, it has previously been found that the large dipole moment of Ir(ppy)3 results in a repulsive dipole-dipole interaction in addition to the long-range interaction mediated by the Shockley surface states when it is adsorbed on Cu(111). These interactions lead to a model system with highly dispersed superstructures. The conformations of this large dipolar molecule on Cu(111) have been identified with STM, DFT total energy and STM simulation. In addition to these two studies, new experimental facilities will be described that will allow combined STM/AFM to be performed at Queen’s University with a qPlus sensor for the first time.
The development of organic analogues of graphene, the only known 2-d conjugated polymer, would represent a new class of materials [1]. One approach to the formation of covalent organic frameworks (COF) is the adsorption of halogenated aromatic precursors onto atomically ordered surfaces, followed by de-halogenation, and subsequent covalent coupling. Although examples of COF formation on single crystal metal surfaces have been described, very limited work has been done to explore formation on semiconducting surfaces. Recently, we have reported that the Si(111) √3×√3-Ag can provide an inert, high-mobility template suitable for the adsorption of halogenated organic molecules [2].
In this presentation we discuss the room temperature adsorption of a halogenated organic molecule, 2,4,6-tris(4-iodophenyl)-1,3,5-triazine (TIPT), onto the Si(111)-√3×√3-Ag surface studied by scanning tunneling microscopy (STM) in ultrahigh vacuum. We find that at low coverage TIPT monomers remain intact and display high mobility on the √3-Ag surface. At low coverage many STM images show evidence of diffusing species on the surface. In fact, this evidence is often manifest as parallel “fuzzy” lines on the √3-Ag terraces. With increasing molecular dose the monomers form supramolecular domains defined by a 2.0 nm by 1.8 nm rectangular cell. The size and symmetry of the unit cell provides strong evidence that the monomers do not undergo de-halogenation, and that the dominant interaction within the domains is intermolecular I···H hydrogen-bonding. As the coverage approaches one monolayer, the molecular film is a mixture of supramolecular domains separated by disordered regions. In addition to our results at room temperature, we will discuss preliminary experiments on the affect of annealing.
Antiferromagnetic coupling (AFC) has plays an important role in many magnetic thin film structures used in applications such as sensors, hard drives, and solid state memories. AFC is achieved in FM/NM/FM structures where two ferromagnetic layers (FM) are separated by a non magnetic (NM) spacer layer. Coupling of FM films across NM is RKKY like and oscillates between antiferromagnetic and ferromagnetic (FC) with the change of NM layer thickness. Here we investigate the coupling strength in Co/XRu/Co (X= Ni, Co, and Fe) trilayer structures as a function of the XRu layer thickness. Ru spacer layer is known to generate the largest AFC between Co films. Our result found that the coupling strength in Co/XRu/Co depends on the magnetic element added into the Ru. Furthermore. AFC increases 1.3 times in respect to AFC in Co/Ru/Co if the optimal concentration of Fe is added to Ru.
Our sample structure consisted of a Ta(3 nm)/Ru(10 nm) seed layer to obtain proper [0001] growth orientation, followed by the Co(2 nm)/XRu(d)/Co(2 nm) trilayer, where d is the XRu thickness, and Ru(3 nm) capping layer is used to minimize oxidation of the magnetic layers. All samples were deposited on Si substrates at room temperature using magnetron sputtering in 1.8mTorr of Argon. Out of plane X-ray diffraction measurements show that Co, Ru and XRu films are highly textured with full-width- at- half- maximum (FWHM) of rocking curve below 3.5 degrees. The coupling strength of these trilayer structures were determined from magnetization versus field dependence, M(H), in fields up to 7 T, using SQUID magnetometer. In Co(2 nm)/XRu(d)/Co(2 nm) demagnetizing dipolar field in Co films is much larger than the uniaxial magnetocrystalline anisotropy field forcing the magnetization to lie in plane. Thus, in our M(H) measurements the magnetic field was applied parallel to the film surface. The M(H) data are fit using a micromagnetic model. The model has only two fitting parameters the exchange stiffness within each Co layer that was kept constant, and RKKY coupling strength, JRKKY, across XRu spacer layer.
Spin transfer torque is mostly studied in nanopillars that consist of two ferromagnetic (FM) layers (reference and free, respectively), separated by a thin non-magnetic spacer. Spin polarized current is used to switch the magnetization of the free FM layer. The main challenge for implementing the spin transfer torque-random access memory (STT-RAM) devices is the reduction of the critical current (IC) required for switching, while maintaining a suitable thermal stability. To minimize IC, we propose a unique design of nanopillars for STT-RAM devices, consisting solely of Co/Ni multilayers (MLs) with the total magnetic anisotropy perpendicular to the film surface. A synthetic anti-ferromagnet (SAF), consisting of two Co/Ni MLs coupled anti-ferromagnetically through a Ru layer, is used as a reference layer in order to minimize the dipolar field on the free layer, FL. FL is a single 4x[Co/Ni] multilayer separated from SAF by a thin Cu layer. The Co/Ni thickness ratio is optimized to have low damping. Adding Pt and Pd was avoided in order to lower the spin orbit scattering in magnetic layers and intrinsic damping in the FL [1]. The intrinsic Gilbert damping of a continuous 4x[Co/Ni] multilayer film was measured by FMR to be α = 0.022, which is significantly lower than in Pt and Pd based magnetic MLs with perpendicular anisotropy. Resistance versus current at fixed applied fields and magnetoresistance curves for different applied currents of circularly shaped 200nm diameter nanopillars were measured at room temperature. The minor loops for the FL exhibit an average offset of 0.038 T, reflecting a small dipolar interaction between the SAF and the FL. We also characterized STT-driven switching in our nanopillars. The critical current, IC, required to reverse the magnetization of the FL from parallel (P) to anti-parallel (AP) alignment is 6.1 mA (1.94×10^11 Am−2) and from AP to P is 4.3 mA (1.37×10^11 Am−2) in zero magnetic field. With volume of the FL, VFL = 1x10-22 m3, we find that Ic/(VFLHc) is 6.25x 1020 A/Tm3. This indicates that our device is almost twice as efficient as any previously reported device with SAF as a reference layer [2].
[1] S. Mangin, D. Ravelosona, J. A. Katine, M. J. Carey, B. D. Terris, and E. E. Fullerton, Nature Materials, 5, 210 (2006).
[2] I. Tudosa, J. A. Katine, S. Mangin, E. E. Fullerton, Applied Physics Letters, 96, 212504 (2010).
Graphene, a two-dimensional carbon material discovered in 2004, is the hallmark relativistic material. Its charge carriers, although moving at less than one percent the speed of light, are described by the massless Dirac equation (derived in 1928 for ultrarelativistic fermions). These Dirac fermionic quasiparticles carry not only the intrinsic spin-1/2 of the electron, but are imbued with an additional emergent spin-1/2, referred to as pseudospin. It is no stretch of the imagination then to consider the existence of relativistic condensed matter systems with particles of pseudospin higher than 1/2. This thesis details some of the optical and electronic properties of such systems, exhibiting individual characteristic signatures. These experimentally accessible signatures may then lend to the discovery of novel materials that are similar to graphene, but enjoy their own fascinating properties as well.
Neutrons are important probes of matter and they are particularly powerful at characterizing magnetic structures. In order to extend the applications of neutron physics we have developed methods for preparing orbital and spin-orbit states of neutrons. Such states may be prepared for the beam as a whole, or with reference to the coherence length of the neutron wavepacket, which is much smaller than the width of useful beams. I will describe experiments to prepare and characterize neutron beams with specific orbital and spin-orbit structure based on neutron interferometry. The preparation methods of the neutron spin-orbit states induce orbital angular momentum via spin-orbit coupling. The characterization of the spin orbit states is done by directly measuring the correlation between spin and linear momenta.
The recent establishment of the Stewart Blusson Quantum Materials Institute (SBQMI) is the latest step in a sustained effort to expand this area of research at the University of British Columbia and move to a global level. The founding principle is to balance strengths in materials, theory, and a diverse range of experimental techniques. Above all though, SBQMI is built on collaboration, within the institute, across related initiatives in Canada, and internationally. This overview will offer some insights into the stages taken to get to this point, the vision for taking quantum materials from the laboratory to applications, and the challenges of making rapid progress forwards on this path.
Coupling single quantum emitters such as atoms and quantum dots (QDs) to structured photonic reservoir structures is usually assumed to depend on the local density of photon states (LDOS). However, in nanophotonic cavity structures, there is a much richer coupling that can take place - in particular, by controlling the anisotropic vacuum. Photonic crystal waveguides, for example, are periodic semiconductors for light that can control and mold the flow of photons in ways that are not possible in conventional optical structures.
This talk will first introduce the motivation and theory of light-matter interactions and quantum
optics control that is possible in slow-light photonic crystal waveguides, with a focus on hybrid
QD (artificial atom) photonic-crystal systems. I will discuss the underlying physics of enhanced
light-matter interactions and light propagation in these open cavity structures, and give examples
where one can controllably emit single photons on a chip and create spin photon entanglers using
the remarkable chiral properties of the nanoconfined light fields [1]. I will show why one needs
more than just the LDOS to describe light-dipole interactions, and demonstrate a drastic
failure of semiclassical theory for light propagation even at the level of a single quantum excitation. Second, I will show how one can exploit anisotropy-induced quantum interference [2] to eliminate single photon spontaneous emission and create population trapping between orthogonal QD exciton states in photonic crystal waveguides and microcavity systems.
[1] A. B. Young, A. Thijssen, D. M. Beggs, P. Androvitsaneas, L. Kuipers, J. G. Rarity, S.
Hughes, and R. Oulton, Polarization engineering in photonic crystal waveguides for spin-photon entanglers, Phys. Rev. Lett. 115, 153901 (2015).
[2] S. Hughes and G. S. Agarwal, Anisotropy-induced quantum interference and population trapping between orthogonal quantum dot exciton states in semiconductor cavity systems, Phys. Rev. Lett. 118, 063601 (2017).
The potential applications of metallic nanoparticles, such as gold nanorods (GNRs), in sensing are very promising due to their unique optical properties. More specifically, Surface-Enhanced Raman Spectroscopy (SERS) is an area of sensing which has been able to utilize the unique properties of metallic nanoparticles as a substrate for Raman signal enhancement. The Photonics Research Group at Lakehead University has developed a unique method to prepare a plasmonic structure on the surface of a multimode tapered optical fiber, referred to as a fiber nano-probe, which can be used as a SERS substrate. This plasmonic structure is based on GNRs which are distributed in a unique pattern on the surface of the tapered multimode fiber, which was achieved by optical tweezing. The fiber probe can be used for the detection of chemicals, ideally down to the molecular level. We will present our recent progress on the application of the developed nano-probe for the detection of chemicals. The effect of excitation wavelength on the SERS spectra will also be discussed. We will also describe techniques which can be used in conjunction with the nano-probe in order to collect scattered light from the sample. Finally, we will present the preliminary SERS spectra collected for the chemical Rhodamine 6G (R6G).
The research was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Foundations for Innovation.
The on-demand generation of bright entangled photon pairs is highly needed in quantum optics experiments and emerging quantum technologies. However, a quantum light source combining both high fidelity and on-demand bright emission has proven elusive with current leading photon technologies. In this work we present a new bright nanoscale source of strongly entangled photon pairs generated with a quantum dot in a nanowire waveguide. Owing to the shaped nanowire waveguide structure, which serves to direct the quantum dot emission, we detect photon pair rates that are more than two orders of magnitude brighter than a bare quantum dot without photonic nanostructure. The major breakthrough in the nanowire growth to reach entanglement fidelities close to 90% while maintaining high efficiencies will also be discussed. These results will be put in perspective with state-of-the-art entangled photon sources. This is the first bright quantum dot source of entangled photon pairs capable of violating Bell`s inequalities, opening up future experiments in quantum optics and developments in quantum communication.
The holographic Schrodinger Equation is to hadron physics what the ordinary Schrodinger Equation is to atomic physics. The ordinary Schrodinger Equation emerges from Quantum Electrodynamics in the non-relativistic limit while the holographic Schrodinger Equation emerges from Quantum Chromodynamics, quantized at equal light-front (not ordinary) time, in the so-called semi-classical approximation. Unlike the ordinary Schrodinger Equation, the holographic Schrodinger Equation is Lorentz invariant and remarkably it maps exactly onto the classical wave equation for string modes in an anti-de Sitter 5-dimensional space (and this is why we call it 'holographic'). This is an example of a gauge-gravity duality in which the deformation of the pure anti-de Sitter space drives the interacting potential in ordinary 4 dimensional spacetime. The holographic Schrodinger Equation provides a first approximation to the physics of QCD bound states. Just as for the ordinary Schrodinger Equation, phenomenological corrections, like the spin-orbit interaction, are important to make contact with data and these have been implemented with success. The development of the holographic Schrodinger Equation, which we review here, helps to achieve a better understanding of QCD bound state effects. A quantitative assessment of these effects is crucial when interpreting the recent LHC data on exclusive B meson decays, in the hope to detect New Physics.
Hybrids are hypothesized hadrons containing explicit quark, antiquark, and gluon degrees of freedom. D-hybrids are hybrids containing a charm quark and a light quark (i.e., up, down, or strange). We use QCD sum-rules to predict masses of spin-0,1 D-hybrids of both positive and negative parity. Our correlator calculations take into account condensates up to and including those of dimension-six. In addition, we investigate possible mixing between hybrids and conventional mesons.
We study the phenomenology of a supersymmetric extension of the Standard Model with an $R$-symmetry under which $R$-charges correspond to the baryon number. This identification allows for the presence in the superpotential of the $R$-parity violating term $\lambda''U^c D^c D^c$ without breaking baryon number, which loosens several bounds on this operator while changing considerably the phenomenology. However, the $R$-symmetry cannot remain exact as it is at least broken by anomaly mediation. Under these conditions, we investigate the constraints coming from recent ATLAS and CMS experimental searches and use these to place limits on the parameter space of the model. This is done for both stop production, which now features both pair and resonant production, and pair production of the first two generations of squarks.
We present our predictions for pion mean charge radius, decay constant, spacelike electromagnetic form factor, twist-2 Distribution Amplitude and the photon-to-pion transition form factor when a dynamical spin structure for the pseudoscalar particle is considered along with a holographic light-front wavefunction. Our results show significant improvement in agreement with available data.
Purpose: High-dose-rate brachytherapy (HDR-BT) is a radiation therapy technique for prostate cancer involving the temporary placement of a radioactive source within the gland to deliver a prescribed dose. The radiation source is delivered through hollow needles, which are positioned using ultrasound images. Conventional ultrasound images have limited spatial resolution and cannot distinguish between cancerous and normal prostate tissue, so the entire prostate is prescribed a uniform dose regardless of cancer location. Our group has been working to implement an HDR-BT technique combining 3D ultrasound and dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) to deliver a higher dose to the tumour and lower dose to normal prostate tissue.
Methods: We will report the results from two studies validating the 3D ultrasound and DCE-MRI techniques for tumour-targeted HDR-BT. 10 patients underwent HDR-BT using a custom robotic device to acquire both conventional and 3D ultrasound images, enabling the comparison of needle localization accuracy between techniques. Two cohorts of patients underwent DCE-MRI using either a “fast, low spatial-resolution” pulse sequence (n=16) or a “slow, high spatial-resolution” pulse sequence (n=18). The patients’ prostates were then removed for histological analysis, enabling comparison of imaging data with cancer location indicated by histology.
Results: The 3D ultrasound imaging technique demonstrated a significant improvement in needle segmentation accuracy, providing 84% of needle tips within 3 mm error versus 57% using conventional ultrasound. Preliminary results suggest that the increasing DCE-MRI acquisition time to achieve higher spatial resolution leads to systematic biases in measured tissue permeability, but these biases may be mitigated by normalizing values in the prostate to those of nearby muscle.
Conclusions: Robotically-assisted 3D ultrasound imaging significantly improves HDR-BT needle tip localization accuracy relative to the clinical standard. High spatial-resolution DCE-MRI shows promise in providing tissue permeability measurements for tumour localization. We will present these results in the context of tumour-targeted HDR-BT, as well as the comparison of DCE-MRI with co-registered histology.
Prostate cancer (PCa) is one of the leading causes of death among men, and brachytherapy is widely used to treat this type of cancer. Low-dose brachytherapy for instance, requires the implantation of tens of radioactive seeds per organ. This treatment causes discomfort, and the implants cannot be removed. They usually generate image artefacts impeding the delineation of recurrent cancers. Our research group has focused on the development of gold nanoparticles used as radiosensitizers and as radioactive seeds, for the treatment of PCa. This presentation will review the principles of radiosensitization, as well as the topic of radioactive gold nanoparticles containing low-energy gamma emitters (103Pd, 125I) for low-dose rate brachytherapy. In particular, a new class of products made of core-shell 103Pd@Au nanoparticles, will be presented as an alternative to the current implantation of massive seeds. The particles are synthesized by a rapid one-pot process, and they have a diameter of 36 – 48 nm. Low volume (2 - 4 µL), single dose injections (1.6 - 1.7 mCi) were administrated in xenograft tumours of PCa (a murine model). After 4 weeks, a tumor volume inhibition of 56% was observed, and this confirmed the strong potential of radioactive gold nanoparticles for low-dose brachytherapy treatments. A comprehensive histological study, coupled to microdosimetric calculations, will allow a better understanding of the optimal intratumoral and pericellular distribution to be achieved in future brachytherapy treatments relying on this technology. Overall, this presentation will describe the strengths, advantages and potential pitfalls of gold nanoparticles as substitutes for the current radioactive seeds in brachytherapy.
The mining industry is often viewed as comprised of rough and tough characters, but in the rapidly changing environment of modern mining such innovations robotics and the advent of other highly technological solutions are revolutionising the industry and consequently the demand for highly qualified staff such as physicists. In this communication three career physicists outline their experiences with Physics in Mining.
Daniel Cluff will discuss are his work at SNO such as the construction of an underground clean room at Creighton mine to perform gamma spectroscopy and other experimental work in support of the development on the 6800´ L. He also provided thermodynamics support on the Frozen backfill project with Glencore. As a member of the LOWCARB project in the UK he developed the VamTurBurner© to mitigate methane at operating coal mines. He is currently working on the physics of cooling and energy storage for deep mines.
Steffon Luoma has designed technologies that have been used for sensor, control and communications systems for telerobotics. The basis of these technologies span from inertial navigation systems for geolocation in the GPS denied underground environment of mining to vision and LIDAR systems for 3D asbuilt representation. In addition he has devised algorithms for semiautonomous driving of mining robots. Currently Mr. Luoma is developing wearable technology to both monitor and augment the body’s natural thermoregulation for miners working in the high heat of ultra-deep mines.
Naeem Ahmed will discuss some of the industrial projects he has been involved in including development of through-air and underwater telecommunication systems, LiDAR based scanning and mapping systems for underground mines and convergence monitoring system for underground mine openings. Naeem currently runs a Sudbury-based company, Clickmox Solutions, that provides consultancy services and works on development of cutting-edge technologies for the mining sector in the areas of 3D laser scanning and mapping, controls and automation.
Cryogenics is a mature industry serving a wide spectrum of industries from welding to space. In this paper a cryogenics concept, capable of providing chilling and ancillary services for deep mining is described.
As mining projects get deeper they also get hotter, a Cryogenic Energy Storage system provides the economies of scale infrastructure that allows for the cryogen supply for chilling delivered to the depth via a liquid flow. Modular compressed air supply or electrical systems are able to provide mobile on-demand services and a recent development suggests that cryogenic engines can simultaneously power large vehicles while providing chilling power; thus, large underground equipment becomes a source of cool air. By introducing a cryogenic liquid with an expansion factor of about 700 and replacing Diesel engines with Liquid Air (LA) or electric motors a substantial reduction in the ventilation required the surface is realised because the dilution of diesel and removal of heat generated by equipment is no longer part of the ventilation calculation, which accounts for a substantial energy saving as ventilation can account for more than 50% of the energy costs. An on demand modular LA based compressed air system would also absorb heat locally. Electricity generation is accomplished by expanding the cryogen through a turbine coupled to a generator; a modular system with battery storage could supply power, reducing the infrastructure from the surface. The technology prototyping, results of computer modelling and a broader discussion on the progress of the economic evaluation and technology development will be provided.
The implementation of these systems in mining relies on the physics of psychrometrics to determine chilling demand under varying atmospheric conditions; thermodynamics of heat flow and transfer from, the surrounding rock to the ventilation air flow, equipment operating at depth or various operations such as blasting; computational fluid dynamics to model the numerous thermal interactions and design new technologies; and computer coding or numerical modelling. These topics will be covered with examples from ongoing projects.
Mines, especially deep underground mines, are engaged in producing the metals that feed the global economy. With a continuously increasing global population and expanding material aspirations of this population, the long-term demand for metals is strong. But the resources that were easy to access have been extracted, and remaining ore grades are declining. Ore is either deeper and more expensive to extract, or is found in locations that are more remote from the market that will consume it, and so require more capital infrastructure. The logical extension of this factor - mining asteroids - reveals its absurdity.
Mining at greater depth means managing more geothermal heat as well as more hoisting capacity. The primary purpose of mine ventilation is to remove heat, not to provide breathable air. Conventional hoisting from below 2.5km is not feasible because modern equipment cannot hoist the steel cable, far less a load of ore. Hoisting systems are typically at capacity so that if a logistical failure prevents a tonne of ore from being hoisted on schedule, it can never be hoisted; hoisting it tomorrow simply displaces a tonne of ore from tomorrow's schedule. For hundreds of years mining has been thought of as a mundane and uninspiring activity but the creativity of miners drove the development of steam engines, ventilation systems, elevator systems and breathing apparatus. Mining confronts the challenges of time, gravity and heat every single day - and for all our sakes we have to be successful. Improving the better application of physics to the mining problems of tomorrow is essential for our survival.
As part of a larger goal in revamping the physics undergraduate laboratory curriculum at Queen’s University, we have started implementing small changes to some lab courses and are measuring their effects to guide further transformation. For our second-year physics lab course, we have transformed an experiment previously given with a set procedure into an activity where students design the lab. This is the compact disk diffraction experiment where laser light is diffracted from the surface of a compact disk and an estimate of the groove spacing is obtained from measurements of the diffracted light. In the design lab, the students are provided with question prompts and they have to come up with their own experimental procedures. We record the students’ voices when they perform the experiment. The audio recordings are transcribed and student behaviors are studied. They are compared to student behaviors in the non-design labs where the students are provided with a detailed procedure. Students’ data analysis and reports are also examined to evaluate their learning. We will report our findings in this talk and discuss our plan to implement similar activities over the whole laboratory curriculum, and how to assess its success.
In a multi-year study at the University of British Columbia, first year physics labs are used primarily to teach students about the tools used to analyze and interpret data. Within this context, we have developed a simple form of scaffolding that dramatically enhances the quality of student reasoning. Students are asked to make comparisons after completing some measurements, to reflect on the comparison, make a plan based on their reflection, then execute the new plan. The experiments are simple enough that they can do this cycle more than once, modeling a more authentic, iterative approach to experimentation. We find that after several weeks, when the scaffolding has been removed, students continue with this more expert-like behavior and show improvements in the quality of their reasoning. Further refinements to this approach indicate that students benefit from an opportunity to do an experiment, without being taught any analysis techniques, allowing them to more freely explore the tools that they have learned.
Designing and improving laboratories, particularly at the advanced level, is critical for preparing physics major students for professional work or graduate school. Planning a laboratory curriculum has to follow a vision for the new generation of graduates that establishes a set of learning outcomes for deeper understanding and student engagement. Selecting effective experiments that create the framework for achieving this goal has been a collective effort of the Physics department laboratory staff, students and faculty at Carleton University. For many students, the advanced laboratory becomes a turning point in their interests since it creates the bridge between the theory and physics phenomena learnt in lectures and the experimental techniques they need to observe them. The skills and expertise gained in the physics advanced laboratory are the greatest strengths of constructive knowledge physics graduates bring to their future research or work. The selection of a broad range of physics laboratory experiments has allowed students to follow their interests and gain this valuable expertise.
The talk is devoted to one of the most challenging parts of the physics laboratory curriculum: data analysis and uncertainty calculation. We expect students to know a lot about their experiment data analysis starting their first lab session in their 1st-year physics course, while the students have zero background in this area. Recommended readings are very little helpful. Instead of evaluating very poor results of students’ self-preparation, it seems reasonable to include teaching elements of data analysis into teaching the experiment methods in the labs regardless the labs format. Report is based on the 8-year experience in teaching data analysis for the 1st and the 2nd year Engineering Science students and more than 10 years teaching Physics Majors and Engineering Science students in Advanced Physics Laboratory (3rd and 4th year of undergraduate physics course). For juniors, the technique utilizes analysis of the currently run laboratory experiments to explain general concepts of measurements and calculating uncertainties along with their application to specific data and data collection method.
In living systems thermal motions become dominant at the nanometre scale, thus protein diffusion must play an important role in cells. But how can stochastic motions at the molecular scale add up to create the exquisite order observed at the cellular scale? I will present the case of Bicoid, a protein whose concentration acts as a postal code in the fly embryo, by letting cells know what is their exact location. The diffusion of Bicoid across the embryo drives the robust and precise formation of a large-scale concentration gradient, as envisioned by Francis Crick in 1970. Further, the diffusion of Bicoid while searching for its binding sites on the DNA controls how quickly and precisely each cell in the embryo can “read” the gradient concentration. Bicoid is thus a perfect example of how protein diffusion in cells can both drive exquisitely precise pattern formation and support the very rapid transmission of information.
A unique detector which is selectively sensitive to low energy metastable atoms, is used to study the production of ground configuration N(2P) atoms following collisions of low energy (0-300 eV) electrons with molecular nitrogen. Time-of-flight detection has allowed identification of at least two dissociation channels with significant differences in released kinetic energy of the fragments. Excitation probability measurements will be presented as a function of incident electron energy and near-threshold data will be used to help identify possible excitation channels.
Support of NSERC and CFI, Canada, is gratefully acknowledged.
Hollow-core photonic-crystal fibers (HCPCF) provide avenues to study light-matter interactions under tight transverse confinement of both atoms and photons. We implement a novel type of cavity by attaching a pair of photonic crystal (PC) slabs acting as high reflectivity dielectric metasurface mirrors onto the ends of a piece of a HCPCF. These mirrors, which can reflect perpendicularly incident light, consist of a dielectric membrane with sub-micrometer thickness and periodically arranged holes with diameter and spacing of approximately 700nm. The cavity further enhances the atom-photon interactions by longitudinally confining light in the fiber. Introduction of laser-cooled atoms into the fiber core through the holes of the PC mirrors should be possible when a red detuned laser, diverging from the fiber, guides the free falling atoms from a magneto-optical trap (MOT) toward the fiber tip using optical dipole forces.
We present calculations for the loading efficiency of atoms into our fiber-integrated cavities, considering perturbations to the dipole potential due to the presence of the PC membranes, as well as atom-dielectric interactions. An overall potential landscape is obtained through simulations, leading to statistical simulations of atom-trajectories from which the loading efficiencies can be found. We discuss the potential uses of the resulting fiber-integrated cavity loaded with laser-cooled atoms for applications such as single-photon all-optical transistors and superradiant lasers.
This work focuses on two Ru-bearing molecules: RuF and RuCl. Both molecules were created in a molecular beam apparatus at UNB. Their spectra were detected by laser-induced fluorescence. In the low-resolution survey of RuF from 400 to 770 nm , five bands were detected in the blue, green and infrared regions of the electromagnetic spectrum. Four of them were rotationally analyzed from high-resolution data. Three bands in the green region are associated with the $^4\Gamma-X ^4\Phi_{4.5}$ system first observed by Steimle et al. (J. Chem. Phys. 124, 024309 (2006)). A new $^4\Delta_{3.5}-X ^4\Phi_{4.5}$ transition in the blue region was also detected. The related molecule, RuCl was also created and spectroscopically detected for the first time. Two high-resolution bands of RuCl were rotationally analyzed, and the ground state was also found to be $ X^4\Phi_{4.5}$. The data provide detailed structural information about the molecules, such as bond lengths, vibrational frequencies, isotopic structure, spin-orbit interactions and hyperfine interactions.
Modulating the phase of a light field with a single photon is a requirement for many applications related to quantum information processing. Here, we predict large phase shifts induced in a meter field by a probe field at single photon levels in an off-resonant three-level ladder scheme implemented with a laser-cooled ensemble of cesium atoms. The strong optical nonlinearity arises when both photons and laser-cooled atoms are tightly confined inside a hollow-core photonic-crystal fiber (HCPCF). Compared to the previously reported experiments utilizing this scheme with room-temperature atoms [1], the use of laser-cooled atoms suppresses Doppler broadening and thus reduces the absorption of the weak probe field at a given detuning from resonance. This allows the light fields in the ladder scheme to be tuned closer to resonance where stronger nonlinearities become available. We study the effect of the detuning of probe and meter fields, the optical depth of the atomic ensemble, and the power of the meter beam on phase shifts induced by a weak probe. Experimental studies will eventually be performed in our recently built system for loading atoms into a hollow-core fiber.
[1] Venkataraman, Vivek, Kasturi Saha, and Alexander L. Gaeta. "Phase modulation at the few-photon level for weak-nonlinearity-based quantum computing." Nature Photonics 7.2 (2013): 138-141.
Squeezed states have recently attracted attention for use in quantum information as continuous variable entangled systems[1]. Such states can potentially be created in microring resonators and photonic crystal cavities. However, scattering leakage in these nanoscopic systems leads to loss, as it is an inherent feature of these devices. In this work, we show that the states created in lossy cavities via parametric down conversion are squeezed thermal states and we examine the effects of the loss on the squeezing parameter and thermal photon number as a function of time and pump intensity.
We consider a cavity with one leaky signal mode and pump this mode at twice signal-mode frequency. As such, this problem reduces to determining the photon dynamics of an optical parametric oscillator (OPO), where the pump light is treated classically. Although this problem can be solved by employing the Heisenberg-Langevin equations [2] or numerical methods [3], using our approach, we show that the exact solution to the Lindblad master equation for an OPO is the density matrix of a squeezed thermal state: $\rho(t)=S(u,\phi) \rho_{th}(n_{th})S^{\dagger}(u,\phi)$. The problem is therefore reduced to solving the three coupled differential equations for $u$, $\phi$, and $n_{th}$, which are respectively, the squeezing amplitude, squeezing phase, and the thermal photon number in the thermal state that is being squeezed. We solve these equations to yield the time-dependent and steady-state solutions for the quadrature noise, thermal photon number, squeezing parameter, total photon number and second order correlation function under different pumping regimes.
References
[1] J. Fiurášek, "Continuous-variable quantum process tomography with squeezed-state probes," Phys. Rev. A. 92, 022101 (2015)
[2] M. O. Scully and M. S. Zubairy, Quantum optics (Cambridge university press, 1997).
[3] J. Johansson, P. Nation, and F. Nori, Computer Physics Communications 184, 1234 (2013).
Entanglement distribution over long distances enables us to transfer information securely by means of quantum repeaters across quantum networks. Here we present a scheme for generating heralded entanglement between spatially separated single rare-earth ions doped into crystals. We propose to co-dope each crystal with a single Er ion and several Eu ions. Gate operations between nearby ions can be performed using dipole coupling in order to map the quantum states of rare earth ions onto each other and to establish long-lasting entanglement between distant ions. We also describe preparation strategies that allow us to design quantum repeaters using single rare earth ions.
Radiative transition probabilities in atoms are normally calculated from
nonrelativistic wave functions and the electric dipole transition operator.
The theory of relativistic corrections to nonrelativistic energies is well established in terms of the Breit interaction, but the same is not true for relativistic corrections to transition probabilities. Our objectives are (i) to start from operators derived from quantum electrodynamics for the lowest-order relativistic corrections and verify that they yield the same results as from solutions to the Dirac equation for the case of hydrogen, and (ii) apply the same
operators (including two-electron corrections) to the case of electric dipole transitions in heliumlike ions. In both cases, relativistic corrections become increasingly important with increasing nuclear charge. Results from part (i) will be presented at the conference.
We present a home-built Czerny-Turner triple-grating spectrometer with a focal length of 1.5m and a basic of-the-shelf astronomy camera. This spectrometer offers high spectral resolution and good light sensitivity at a relatively low cost compared to commercially available systems with similarly large focal length.
The three gratings are mounted on a turret and can be swapped without recalibrating the system, which allows the user to quickly change the span and resolution of the observed spectrum. A distinct feature, generally not available in commercial spectrometers, is implemented by having two separate axes of rotation -- one for the turret rotation to change between gratings and one to control the angle of the grating in use. Unlike triple-grating systems with a single rotation axis, this feature enables the grating in use to rotate around an axis that passes along the grating's front surface. This allows the grating to remain in the mirrors' focal points as its angle is adjusted and also extends the range of wavelengths over which a given grating can be used. We compare Zemax simulations predicting resolution <10GHz at 852nm with experimental data to evaluate the performance of the spectrometer.
A scheme for an on-demand optical pulse-triggered quantum dot single-photon source which utilizes stimulated Raman adiabatic passage and photonic cavity-coupling is presented. This single photon source is coherently pumped in the presence of a continuous wave drive, allowing for highly efficient indistinguishable single photons to be produced which are of a different polarization than the input pulse, ensuring spectral separability of the outgoing photons. We model this system using an open-system approach at the level of a polaron master equation including both exciton and biexciton states [1]. In addition to zero-phonon Lindblad decoherence processes (including pure dephasing and spontaneous emission), exciton-acoustic-phonon coupling, which degrades the indistinguishability and efficiency of semiconductor photon sources, is rigorously taken into account. Through careful design and analysis, the on-demand source can be minimally affected by phonon coupling, and robust to laser and cavity detuning. We describe how this biexciton-exciton cascade scheme allows for true single photons to be generated with over 90% quantum indistinguishability and efficiency using experimentally realizable parameters.
[1] e.g., see F. Hargart, M. Müller, K. Roy-Choudhury, S. L. Portalupi, C. Schneider, S. Höfling, M. Kamp, S. Hughes, and P. Michler, Cavity-enhanced simultaneous dressing of quantum dot exciton and biexciton states, Phys. Rev. B 93, 115308 (2016).
The miniaturization of optically addressable ion traps for the goal of scalable quantum information processing has led to an increased interest in finding a balance between ion and photon confinement.
We propose a radio-frequency ion trap integrated with an optical cavity in which the needle electrodes consist of a pair of tapered metal-coated optical fibers capped with semiconductor metasurfaces designed to act as high-reflectivity confocal mirrors. We present numerical simulations of the ion-trapping dynamics in this system and discuss the outlooks for achieving the strong-coupling regime for the ion-photon interaction inside the cavity formed by the two metasurface mirrors.
Band pass optical interference filters can be constructed from simpler, stand-alone filter design components. Typically a peak centered in the filter’s free spectral range is combined with low and high pass filters such that only a desired band pass remains over a wavelength range. The component filters can be either interference or absorption filters chosen such that there are no unwanted light leaks outside the band pass. Replacing the low pass filter with an induced transmission filter, one using embedded metal layers, can provide a better approach to suppressing long wavelength light leaks. This paper reports on simulations used to explore the performance of several easily vacuum deposited metals used in induced transmission filters.
Visualization of state determination via weak measurements
Igor D. Ivanovic
Physics Department,
Carleton University
Recently the weak measurement expression A_w=(<ψ|A|φ>)/(<ϕ|φ>) and its modification were used in state determination of an unknown state [e.g. 1,2]. In this note a visualization is given of the weak values of an unknown state ϱ_w=(<ψ|ϱ|φ>)/(<ϕ|φ>) , where ϱ is the unknown state ( ϱ ≥0,tr(ρ)=1 ), following the visualisation presented in [3] . An attempt is made to apply it to the state determination of a two level system ( C2,) comparing the standard state determination and the weak value state determination. Also, an excursion into C3 is made. Assuming that each weak value needs two measurement, for real and imaginary part, and that the measurements are not sequential, it is not clear if any advantages, in weak measurement state determination are present [5,6] .
[1] Dressel J, et al, arXiv 1305.7154 [quant-ph]
[2] Diaz JJ., et al: arXiv 1602.04073 [quant-ph]
[3] Farinholt.,J.M. et al: arXiv 1512.02113 [quant-ph]
[4] Ivanovic I.D. :Phys.LettA, 228 (1997), p329
[5] Haapasalo E., et al : arXiv 1108.3663 [quant-ph]
[6] Gross J.A., et al : arXiv:1506.08892.
Coupled mode theory is applied to the analysis of a microsphere cavity whispering gallery mode excited by amplitude modulated light. Expressions are derived for the transmitted and backscattered modulation frequency dependent intensity and phase-shift of the light on resonance. Using these expressions, the resonance lifetime and cavity coupling parameters can be derived from the experimental data.
According to recent developments in nanotechnology, the fabrication of nanostructures such as nano-particles (NPs), nano-rods (NRs), and nano-tubes (NTs) have been intensified, which have wide range of applications in electronic, magnetic, optical and energy storage devices. Various processing methods are used such as lithography and porous templates among which porous anodic alumina (PAA) membranes are the most widely used templates. PAA template is self-organized nano-channels with a high degree of arranged nano-pores formed by electrochemical anodization, fabricated in acidic electrolyte. Nano-structure synthesis is achieved by filling the pore channels either by soaking the membrane in appropriate precursor solutions or by electrodeposition process. In our project, using a PAA template, which has a barrier layer, to fabricate an array of optical nano-antennas is a big challenge due to its electrical insulation. Moreover, the use of commercial alumina membrane on free-substrates is not efficient due to the lack of controllability on its specifications, such as the pore’s sizes and interconnected channels. So, we made the barrier layer thickness very thin, at the end of the anodization process by controlling the applied voltage. We could also control the depth and radius of pores to match specified requirements. Actually, the aspect ratio of optical nano-antenna is very crucial to have resonation at various light spectrums. Then we could detach the PAA membrane from the bulk Aluminum by dissolving the remaining metal in Mercuric chloride (HgCl2). After opening the bottom of the pores and sputtering a thin layer of gold as an electrode, it used as a template for the nano-rods growth on top of the conductive substrate. An array of Ag or Au nano-antennas will be developed with uniform size and length through this template as an inexpensive and reproducible process to be used in the large-area fabrication of Rectenna (rectifying antenna) solar cells.
Magnetic field perturbations in the auroral zone are produced by a combination of distant ionospheric and local ground induced currents. Spatial and temporal structure of these currents is scientifically interesting and can also have a significant influence on critical infrastructure.
Ground-based magnetometer networks are an essential tool for studying these phenomena, with the existing complement of instruments in Canada providing extended local time coverage. In this study we examine the spatial correlation between magnetic field observations over a range of scale lengths. Principal component and canonical correlation analysis are used to quantify relationships between multiple sites. Results could be used to optimize network configurations, validate computational models, and improve methods for empirical interpolation.
We examine the conditions under which along-track ion flows and the average ion mass can be obtained by combining electric current measurements of the European Space Agency's Swarm Electric Field Instrument (EFI) Langmuir probes. Each EFI is equipped with two spherical probes and a planar probe. Using the orbit-motion limited approximation, we combine the expressions for the electric currents to the spherical and planar probes to determine self consistently the effective ion mass and component of ion bulk velocity parallel to the satellite velocity vector ('along-track'). We compare results with observations from the EFI thermal ion imagers and ground-based radars.
We report the findings of a case study in which in the Enhanced Polar Outflow Probe (e-POP) passed over a stable double-arc system in the pre-midnight sector. The arcs’ near infrared emissions were identified using e-POP’s Fast Auroral Imager (FAI). We have assimilated measurements from e-POP’s highly-resolved contemporaneous dataset in order to provide new and compelling insight into the microphysics of dynamic magnetosphere-ionosphere coupling processes. As e-POP crossed the arc, its magnetic footprint remained within the FAI’s field-of-view, allowing for the interconnection of the optical, plasma, and electromagnetic properties of the arc to be studied in detail. e-POP’s MaGnetic Field instrument (MGF) measured magnetic field perturbations indicative of structures of field-aligned currents collocated with the optical signature of the arc. The Radio Receiver Instrument (RRI) data exhibits a highly structured VLF spectrum and shows that a prominent VLF hiss structure was generated by the arc. Measurements from e-POP’s Imaging and Rapid-Scanning Mass Spectrometer (IRM) show that, in the vicinity of the arc, the ionosphere was dominated by vertically upward plasma flows, and that the flows did not show any significant structuring at the location of the arc. However, approximately 75 km poleward of the arc in a region that was devoid of optical emissions, an ion-energization event was detected by both the IRM and Suprathermal Electron Imager (SEI). The energization is supported Ultra Low Frequency (ULF) radio wave activity as detected by the Radio Receiver Instrument (RRI).
The performance of bulk heterojunction organic solar cells made of conjugated polymers/oligomers and fullerenes has significantly improved in the last few years (with PCE exceeding 10%).1 Experiments suggest that the intermolecular interactions between polymers and fullerenes are critical to the design of (even) more efficient organic photovoltaic cells.2 However, a detailed understanding of these intermolecular interactions is still lacking. In this work, we employ dispersion corrected density functional theory (DFT) methods, wB97xD, B3LYP-D3, B97D3, and PBE1PBE-D3, to investigate the properties of these heterogenous interactions in various promising oligomer/fullerene combinations (e.g. a pair of PC71BM and a copolymer based on thieno[3,4-b]thiophene/benzodithiophene (PTB7)3, PCBM and a copolymer based on 2,7-carbazole/dithienyl-2,1,3-benzothiazole (PCDTBT)4, and PC71BM and a copolymer based on difluorobenzothiadizole/quaterthiophene (PffBT4T-2OD)1). In particular, we determine and analyze the conformational and electronic structures, and binding energies of these combinations. We obtain the most preferred orientations of oligomers with respect to fullerenes and analyze the connection between their electronic structures and device performances. Finally, using binding energies, we assess the strength and stability of the oligomer/fullerene intermolecular interactions.
Keywords: Polymer/Fullerene Interactions, Organic Solar Cells, DFT.
[1] LIU, Y., ZHAO J., LI, Z., et al. 2014. Nature Communications.
[2] HUANG, Y., KRAMER, E., HEEGER, E., et al. 2014. Chemical Reviews.
[3] HE, Z., ZHONG, C., SU, S., et al. 2012. Nature Photonics.
[4] BEAUPR´E, S. & LECLERC, M. 2013. Journals of Materials Chemistry.
Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario, K7L 3N6, Canada
Light-emitting conjugated polymers can be electrochemically p- and n-doped in situ in a device called the polymer light-emitting electrochemical cell (PLEC). [1] Electroluminescence occurs through the injection of minority charge carriers when the doped polymers make contact and form a p-n junction. This doping and junction formation make PLEC fundamentally different from the widely studied organic or polymer light-emitting diodes (PLEDs or OLEDs). [2] Bipolar electrochemistry is an electrochemical phenomenon where a polarized conducting object inside an electric field that will induce redox reactions at its extremities if sufficient potential difference is applied. [3] The conducting object is called bipolar electrode which promotes electrochemical reactions at its extremities even in absence of a direct ohmic contact. Our group first presented a solid-state, polymer-based, light-emitting electrochemical cell incorporating metallic bipolar electrodes positioned between the driving electrodes. [4] The inclusion of bipolar electrodes can lead to more efficient polymer light-emitting when a large number of active junctions are formed. Further study showed that electrochemical phenomenon can be observed to originate from the previously doped regions that are isolated from the driving electrodes. A pair of biased metallic probes is in direct contact with the exposed polymer surface, which cause in situ electrochemical p- and n-doping of the luminescent polymer in the interior of an electrochemical cell. After applying sufficient voltage to the driving electrodes, p- and n-doping were observed from the extremities of doped luminescent conjugated polymer. By analyzing the complex doping patterns generated, we conclude that the doped polymers have functioned as bipolar electrodes, from which electrochemical p- and n-doping are induced wirelessly.
Two-dimensional void inclusion phononic crystal waveguide structures on gallium arsenide (GaAs) can be used to control surface acoustic waves (SAWs). In GaAs, SAWs create a piezoelectric field, providing a dynamic spatial confinement potential of electron/holes, which can then be implemented to transport charge and potentially spin. This work develops the first phononic crystal technology in GaAs with the goal of developing an acoustic charge transport method via phononic crystal waveguide modes. The use of single and double linear defect phononic crystal waveguides is studied both numerically and experimentally. Finite element analysis device simulations are performed in COMSOL to provide the propagation characteristics of SAWs in phononic crystal waveguides. Simulations are conducted for three-dimensional domains, which have an improved accuracy over previous two-dimensional studies. For the experiments, devices are constructed using optical photolithography with the phononic crystals produced using reactive ion etching and the interdigitated transducers (IDTs) fabricated through the lift-off of evaporated aluminum. To experimentally determine the SAW mode frequency, wideband phase modulated SAW transducers are placed in front of the waveguide. The wide bandwidth of the transducers allow for scanning the precise mode frequency. By having the waveguide mode frequency determined, a tuned transducer with focusing capability is placed in front of the waveguide to excite the waveguide mode. The mode resonates sufficiently to generate a moving potential which has the possibility to be utilized for future charge transport studies.
Perovskite Solar Cells Fabricated with Various Buffer Layers: Relationship Between Carrier Lifetime and Observed J-V Hysteresis
William Elcock, Robert Bauer, and Gap Soo Chang
Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon SK S7N 5E2
Perovskite solar cells have been the subject of intensive research efforts over the past 7 years with the highest performing device having a reported efficiency of more than 20%. Despite their rapid advancement, these devices are not without issues. The current density-voltage(J-V) response of these devices has been shown to vary depending on the direction of the voltage during characterization. Voltage scan rate, and device pre-conditioning, such as exposure to light for a set period of time, or biasing the device at a set voltage for a set period of time, have also been shown to affect the J-V response of perovskite solar cells. This J-V hysteresis has posed a challenge in determining the actual efficiency of devices. It has been shown that the use of different buffer layers in perovskite devices can alter the observed hysteresis. This work seeks to investigate the effect of varying buffer layers on hysteresis in perovskite solar cells. Specifically, the relationship between the carrier lifetime and the severity of observed hysteresis is observed. Buffer layer choices which result in reduced levels of hysteresis are highlighted.
Spin current transport generated by spin pumping was investigated in magnetic single py (Ni80Fe20)/Ta and double py/Ta/py/Fe layer structures prepared by magnetron sputtering. Ferromagnetic Resonance (FMR) generates rf pure spin current at the py/Ta interface. This leads to an interface Gilbert damping $\alpha_{sp}$ characterized by the spin mixing conductance parameter $g_{\uparrow \downarrow}$. Spin current propagation in Ta overlayer is governed by spin diffusion of the accumulated spin density in Ta. Ta belongs to heavy metals where the spin diffusion length $\lambda_{sd}$ is very short, ~1 nm, compared to that of other simple metals Pd, Au and Cu. It is comparable to that found in Pt, where a short spin diffusion length by FMR studies was interpreted by interface spin loss due to Rashba interface scattering. X-ray diffraction (XRD) and transmission electron microscope (TEM) studies showed that the sputtered Ta films are amorphous in the thickness region where the spin transport is significant. The parameters describing the spin transport in Ta are the resistivity of Ta layer and spin diffusion length. We found that consistent and unique set of parameters describing spin pumping requires to carry out FMR studies on both the single magnetic structure py/Ta and double magnetic layer py/Ta/py/Fe where py/Fe layer acts as perfect spin sink. For the single magnetic layer the spin pumping Gilbert damping, $\alpha_{sp}$, increases with an increasing Ta thickness $d_{Ta}$ while in magnetic double layer it starts with maximum $\alpha_{sp}$ and then decreases approaching the same asymptotic value when $d_{Ta}$>>$\lambda_{sd}$. We used several models and found that a consistent fit can be reached by using $\rho$=370 $\mu \Omega$ cm, $\lambda_{sd}$=1 nm, and $g_{\uparrow \downarrow}$=1.7$\times 10^{15}$ cm$^{-2}$. The resistivity parameter was in agreement with ex situ four probe resistivity measurements. Our studies show that there is no interface spin loss in py/Ta compared to that found in py/Pt.
Microcavity polaritons are a hybrid photonic system arising from the strong coupling of cavity photons to quantum-well excitons. The light-matter nature of polaritons introduces a Kerr-like nonlinearity while still being easily accessible by standard optical means. The ability to engineer confinement potentials in microcavities makes polaritons a convenient system to study spatially localized bosonic populations, which have great potential for the creation of novel photonic devices.
In this work, we present a polariton Josephson junction which consists of two localized polariton populations coupled via tunneling. Careful engineering of this system was predicted to induce Gaussian squeezing, a phenomenon that lies at a heart of the unconventional photon blockade associated with single photon emission. The squeezing operator originates from the interplay between two entities: the polariton nonlinearity and the coupling strength of the two polariton states. The Josephson oscillations induce dynamics in the population imbalance and relative phase, which therefore varies the squeezing parameters over a wide range of values.
Here, we reveal a manifestation of the predicted squeezing by measuring the ultrafast time-dependent second-order correlation function $g^{(2)}($0) by means of a streak-camera acting as a single photon detector [1]. The light emitted by the microcavity oscillates between Poissonian and super-Poissonian in phase with the Josephson dynamics. We model this behaviour using quantum simulations, which predict a dynamical evolution of the squeezing parameters. We show that a crucial prerequisite for squeezing is presence of a weak, but non-zero nonlinearity [2]. Our results [3] open the way towards generation of nonclassical light in solid-state systems possessing a single particle nonlinearity like microwave Josephson junctions or silicon-on-chip resonators.
References
[1] A. F. Adiyatullin, et al., “Temporally resolved second-order photon correlations of exciton-polariton Bose-Einstein condensate formation”, Appl. Phys. Lett. 107, 221107 (2015).
[2] H. Flayac and V. Savona, “Towards Nonclassical Dynamics in Semiconductor Microcavities”, arXiv:1609.00028 (2016).
[3] A. F. Adiyatullin et al., “Periodic squeezing in a polariton Josephson junction”, arXiv:1612.06906 (2016).
When electronic channels compete to screen a single impurity spin, as in the one- and two-channel Kondo model, a ground state with nontrivial entanglement structure is expected to arise. We exploit a spin-chain representation of both the one- and two-channel Kondo model to probe the ground-state block entropy, negativity, tangle, and Schmidt gap, using a density matrix renormalization group approach. The contribution to the entanglement arising from the impurity is shown to satisfy a characteristic scaling and for the two-channel model we confirm field-theory predictions for the boundary entropy difference.
We propose a dynamic nuclear polarization technique at high field and at cryogenic condition in order to highly polarize a nano-meter ensemble of protons with high efficiency. The proposed experiment is particularly designed as an initialization step for ultra-sensitive magnetic resonance imaging (MRI) and spectroscopy using silicon nanowire mechanical oscillator in order to enhance the image resolution of nanoscale samples. This DNP technique consists of an adiabatic half passage pulse followed by an adiabatic linear sweep of electron Rabi frequency, which can be considered as an adiabatic nuclear orientation via electron spin locking (adiabatic-NOVEL). We study the process of polarization transfer between a parametric center and its nearby nuclei both numerically and analytically to show that the adiabatic-NOVEL is highly efficient and is very robust against field inhomogeneity. We discuss the experimental implementation of the proposed DNP technique using the nanoscale architecture designed for nano-MRI.
Organic semiconductors are quite promising for the field of photovoltaics, light-emitting diodes, flexible electronics and biosensors/electronics. However, poor charge mobility that comes along with their amorphous nature, and/or their susceptibility to photodegradation especially in the presence of oxygen and moisture, and poor repeatability of characteristics have been some of the common issues which yet need better understanding. While there is an ongoing research on improving the stability by modifying the polymer structure and morphology of the film formation, it is also
critical to identify the spatial and energetic location of defects in these materials in order to mitigate them. In this work, we probe the defects by soaking the devices based on two conjugate polymers, P3HT and MDMO:PPV, under UV-visible light using simple current-voltage characteristics, charge extraction technique like CELIV and luminescence studies. A common observation to all the devices that indicate a reduced charge extraction and enhanced electroluminescence efficiency will be given a physical interpretation of the location of the defects in them. The tests were performed on the (un)encapsulated devices and probed at microscopic scale using optical microscope. A comparative tests on the encapsulated and unencapsulated devices helped identify the effects of intrinsic and extrinsic defects on the polymers based devices.
Muon Scattering Tomography (MST) is a well-established method for detecting the presence of high density/high-Z materials for a variety of applications. Canadian Nuclear Laboratories (CNL) is a leading institution in MST research and the Chalk River site is an ideal proving ground for a number of relevant applications. CNL’s Cosmic Ray Inspection and Passive Tomography (CRIPT) detector is a novel muon tomography system currently being used to quantitatively demonstrate improvements to MST by integrating muon momentum information, neutron, and gamma detectors. A series of blind experiments were conducted where unknown targets were passively scanned and the data were analyzed in an unbiased way. In addition to these experiments, on-going development of new image reconstruction algorithms is underway. One such algorithm, a new method for reconstructing 3D images based solely on the absorption of muons by materials with specific applications to imaging large structures, will be presented.
ABSTRACT: In recent years, nanostructured carbon allotropes have received considerable attention for their potential applications in variety of fields, including but not limited to nanoelectronics, flexible electronics, gas and chemical sensors, power conversion and storage devices, just to name a few. Their outstanding physical properties, chemical stability and the ability to engineer their charge mobility are the main drivers for this widespread interest. However, various applications require structures with different building blocs, which necessitates development of specific strategies for their selective growth, with excellent control over the size, electrical, mechanical and optical characteristics. Moreover, some applications, particularly those related to nanoelectronics and NEMS, will require doping of these molecular structures with various dopants in order to modify their electrical properties.
There is variety of techniques used for fabrication of allotropes of carbon nanostructures. Plasma- and vacuum assisted synthesis techniques have been used as a strategy to assist the synthesis at lower temperatures, since plasma-assisted dissociation of precursors, facilitate the nanomaterial growth at lower temperatures [1,2]. Plasma techniques have also been used to dope graphene and CNT with nitrogen [3], an important step for nanoelectronic applications. In this presentation we will discuss various synthesis strategies and their specific advantages. We will also present characteristics of some samples produced from different techniques, and finally will present an example of applications related to energy production using thermionic converters [4].
[1] M. Ionescu, et al. ESC Transactions, 25,8, (2009), 737-748
[2] J-B. Kpetsu, et al. Nanoscale Res. Lett. 4;5,3, (2010), 539-544
[3] G.R. Bigras, et al. Graphene Canada 2015
[4] P. Yaghoobi, et al. AIP Advances, volume 2,(2012) 042139-1 to 12
The SNO+ experiment is a rare event search for neutrinoless double beta decay ($0\nu\beta\beta$) and is located 2km underground at SNOLAB in Sudbury. Discovering $0\nu\beta\beta$ would give us deeper insight into the properties of neutrinos, specifically if neutrinos are Marjorana particles or Dirac particles. Current half-life estimates of the $0\nu\beta\beta$ process are around $10^{24}$ years. Due to the rarity of the process, the backgrounds of the SNO+ experiment have to be well-understood. SNO+ is currently entering the water phase, where the detector is filled with water. During this phase, we will be ascertaining the cleanliness of the water used in the process systems as well as the acrylic vessel. This presentation will focus on work done on in situ analysis of $^{214}$Bi and $^{208}$Tl (daughters of $^{238}$U and $^{232}$Th) in water. Results based on large scale internal background Monte Carlo simulations will be presented.
The notion of a quantum reference frame is needed to adequately describe quantum communication without a shared reference frame or the construction of a relational quantum theory. It was recently shown that when transforming quantum systems that have degrees of freedom referenced with respect to an external frame to that of a quantum reference frame, entanglement can be generated between the transformed degrees of freedom. In the present work we introduce a new quantum reference frame using the so-called $\rho\lambda$ coordinates to explore different types of entanglement properties that can emerge. This is analyzed using a one-dimensional system comprised of three Gaussian states. Additionally, we examine how $1+1$ Newtonian gravity affects this generated entanglement in both the previously considered quantum reference frame and in the $\rho\lambda$ case. It was found that under the $\rho\lambda$ coordinate transformation, the entanglement properties display interesting distributions using the logarithmic negativity as the quantifying measure of entanglement. We show that the interaction Hamiltonian generating the gravitational time evolution does not alter the entanglement properties. The kinetic energy of the particles however does alter the entanglement and evolves the system to an equilibrium state at large $t$ regardless of initial covariance matrix parameters.
We construct a new class of non-stationary exact solutions to five-dimensional Einstein-Gauss-Bonnet gravity based on Atiyah-Hitchin space by finding analytical expression for the unknown metric functions. We investigate the behavior of the solutions numerically since these expressions cannot be written in closed forms. We also consider an extremal limit of the Atiyah-Hitchin metric which it reduces to the Euclidean Taub-NUT metric and discuss about the properties of the reduced solutions.
A complete understanding of classical-quantum correspondence in the chaotic limit is still lacking. We study this correspondence from a quantum information-theoretic perspective in a quantum kicked top model. This is a multiqubit system whose dynamics is governed by successive twists and turns of the collective angular momentum operator. This system is of particular interest because it displays bifurcations, regular behaviour as well as chaotic behaviour in the classical limit, and is one of the few systems that has been experimentally realized in the quantum regime. We analyse the dynamics of different measures of quantum correlations, including Bell correlation functions, entanglement entropy and quantum discord among the qubits in the kicked top system. We find a new correspondence between classical phase space structures and time averaged Bell correlation functions. We also identify signatures of classical bifurcations in the time-averaged entanglement entropy. Our analysis provides new insight into the effects of classical chaos on the dynamics of systems in a deeply quantum regime.
We present all real quantum mechanical potentials in a two-dimensional Euclidean space that have the following properties: 1. They allow separation of variables in polar coordinates, 2. They allow an independent fourth order integral of motion, 3. Their angular component $S(\theta)$ does not satisfy any linear ODE. We show that $S(\theta)$ satisfies a nonlinear ODE that has the Painlevé property. The classical analog, including the generating algebra of the integrals of motion, is considered as well.
Motivated by statements in the literature which contradict two general theorems, the static and spherically symmetric Brans solutions of scalar-tensor gravity are analyzed explicitly in both the Jordan and the Einstein conformal frames. Depending on the parameter range, these solutions describe wormholes or naked singularities but not black holes.
Radon-222 and its daughters are a primary background within SNO+, a large liquid scintillator detector located deep underground at SNOLAB, designed to detect rare neutrino interactions. Therefore it is crucial to determine the remaining trace amounts contributing to the experiments background signal carefully.
A cryogenic radon trapping system is used to monitor the backgrounds observed in both water and scintillator phases of the experiment, this system has been improved and must be tested and then operated frequently. Concentrations up to 8×10-5 Rn atoms/L (1.6 × 10-17 g 238U/g LAB) can be measured within scintillator, and 3.5×10-14 g 238U/g H2O in water.
Some of the data taken so far and the expectations will be shown in this poster.
The DEAP-3600 dark matter experiment is a single phase liquid argon (LAr) based detector located 2km underground at the SNOLAB facility near Sudbury, Ontario. This experiment requires thorough characterization of all expected backgrounds in order to push the current limits on the spin-independent Weakly Interacting Massive Particle (WIMP) scattering cross section. As such, key systematics must be examined in order to fully characterize the detector response. This work examines the detector response through process system related backgrounds induced by thermodynamic changes to the LAr volume and explores methods to suppress such events. Cosmic ray muon events are examined by thorough analysis of the muon veto system data in tandem with detector data within the veto time window.
Although the nature and properties of dark matter (DM) are not well known, it is expected to have some large scale gravitational effects. The DAMA collaboration claims to have made a direct detection of DM through the observation of an annual modulated signal in the 2-6 keV region, which is an expected feature of the currently accepted model for DM. However, the NaI crystals used for this experiment are inherently contaminated by a radioactive isotope: 40K, due to its chemical affinities with Na. 40K decays to the ground state of 40Ar through electron capture (EC) releasing 3.2 keV X-rays and Augers that may appear in the signal observed by DAMA. It also decays to an excited state of 40Ar (EC) releasing an additional 1460 keV gamma-ray that DAMA tags to exclude the contribution of the EC decay. To this day, the contribution of the 40K EC decay to the background in the DAMA experiment remains poorly known, notably because of the uncertainty on the branching ratios of 40K. This issue is addressed by the KDK experiment that will be conducted at Oak Ridge National Laboratories, in Tennessee, USA. This experiment uses two detectors, one for the low-energy Augers and X-rays and the MTAS detector for the higher-energy gamma-rays emitted through the EC* decay. To achieve the needed precision, MTAS will be calibrated using two radioactive isotopes with similar, but well-known decay schemes: 54Mn and 65Zn. This poster will describe the KDK experiment and its motivations, explain the calibration of MTAS and present systematic effects including those introduced by uncertainties on the branching ratios in the decays of 54Mn and 65Zn.
The Super Cryogenic Dark Matter Search (SuperCDMS) hunts for direct evidence of dark matter in the form of WIMPs. Cryogenic Germanium detectors are deployed in a well shielded environment deep underground to minimize interactions from cosmogenic and radiogenic particles. Particle interactions in the detector deposit vibrational energy (phonons) and free electron-hole pairs. Sensors on the surface of the detector measure the phonon signal to extract the energy of the initial particle interaction. In the CDMS low ionization threshold experiment (CDMSlite), an electric potential is applied on one face of the detector. Electrons and holes drift to opposite sides of the detector in the resulting electric field. As they drift apart, they deposit more vibrational energy to the crystal, amplifying the phonon signal in a process called Luke amplification. Determining where in the detector an event occurred is important because the electric field is not perfectly flat, leading to regions of reduced Luke amplification at high radius. The shape of the phonon pulses and the geometry of the detector allow for an approximate radial reconstruction based on the relative sharpness of the rises of pulses in different sensors. This poster discusses the CDMSlite experiment and how the pulse information is used to extract the information necessary to achieve the most sensitive measurement.
The DEAP-3600 spin-independent WIMP search experiment has been taking data since 2016. In order to exclude WIMP-like backgrounds, it is necessary to make a fiducial volume cut. This is only possible through effective event position reconstruction. The results of Monte Carlo studies on the probability of events that occur outside the fiducial volume being reconstructed within the fiducial volume will be presented. Scattering, absorption, and various other aspects of the optical model of the Monte Carlo detector have also been tuned to match that of the physical detector, and the process behind this tuning will be presented.
DEAP-3600 is a direct-detection dark matter experiment using natural liquid argon as its target material. This experiment is located 2km underground in the SNOLAB facility at VALE’s Creighton Mine near Sudbury, Ontario. Natural atmospheric argon has three long-lived radioactive isotopes, one of which ($^{39}$Ar) contributes significantly to the overall rate of background events in DEAP-3600. The isotopes of interest for this work are $^{39}$Ar and $^{42}$Ar which both undergo beta decay with half-lives of roughly 269 years and 32.9 years respectively, and $^{36}$Ar which can decay via double electron capture. $^{36}$Ar may also undergo the lepton number violating process of radiative neutrinoless double electron capture (0νECEC) for which a lower half-life limit on the order of 10$^{21}$ years has previously been established. The specific activities of $^{39}$Ar and $^{42}$Ar in natural argon have been measured, however the activity of $^{42}$Ar has been a subject of debate; this work outlines how these measurements can be made using DEAP-3600, and additionally how a search for the 0νECEC of $^{36}$Ar decay may be performed.
The SNO+ experiment is searching for neutrinoless double beta decay with Tellurium-130 isotope. Tellurium is synthesised from Telluric Acid into Tellurium Butane Diol (TeBD), this is dissolved in 780 tonnes of liquid scintillator (Linear Alkyl Benzene, LAB), and this is then circulated back into the acrylic vessel of the detector. In the first phase of the competitive neutrinoless double beta decay search the SNO+ experiment will use 0.5% Tellurium loading in LAB. As many solvents interact with acrylic the compatibility between the Tellurium complex and acrylic needs to be tested.
Exposing acrylic to the complex and applying constant strain accelerates any chemical effects. Performing tensile testing on the exposed acrylic yields insight into how the complex will affect the acrylic vessel throughout the lifetime of the SNO+ experiment. In the poster, I will present results from tensile testing after different exposure lengths, as well as microscopic images of the acrylic surface post exposure.
The Standard Model in 1967 (Salam 1968, Weinberg 1967) incorporated the theoretical Higgs boson unified theory for the weak and electromagnetic interactions. In 2012 Higgs boson was confirmed as a new particle with characteristics very similar to those first predicted theoretically in 1964 (Higgs 1964). Standard Model is the theory currently accepted by the scientific community to explain the behavior of the Universe at particle scale, including the scale of the Universe and has succeeded in making several predictions experimentally confirmed, decades later. This model includes the Higgs field, fundamental to explain the origin of the mass of the elementary particles. We focused here, on three distributions largely used in the statistical universe. Special importance has been given to the normal distribution, the uniform distribution of continuous and continuous exponential distribution. The normal distribution wanted to illustrate their use through a real case that is at the forefront of scientific knowledge, which is the search for the Higgs boson and its close relationship with the statistics to be able to distinguish what in fact is presented as a new particle of what is just background noise. Examples were given to illustrate, using always the practical presentation of results with the use of R software, several inherent in this distribution parameters as well as practical examples of how these parameters can be used to solve real problems. For uniform distribution we try to emphasize its importance for simulation, that generally all major simulation methods both for continuous and discrete event based on continuous uniform distribution. inally, a new practical example was given in solving a problem using statistical methods of R software applied to this distribution.
The Super Cryogenic Dark Matter Search (SuperCDMS) will be one of the leading efforts to directly search for Weakly Interacting Massive Particles (WIMPs) at the low mass scale (below 10 GeV/$c^{2}$). The SuperCDMS SNOLAB data acquisition (DAQ) and trigger system will use the MIDAS (Maximum Integrated Data Acquisition System) program - a flexible, open source C++-based DAQ framework, with off-the-shelf computers and custom trigger electronics for the SNOLAB project. The DAQ will involve front-end and back-end computers which together retrieve data from the detectors through a three-level triggering process, as well as an additional cluster that performs environmental monitoring, data quality monitoring, and real-time data analysis. The design of the SuperCDMS SNOLAB DAQ is such that there is deadtime-free triggering with very low energy thresholds, and the ability to handle high event rates during calibration by allowing for two different modes of data-taking: normal (WIMP search) and calibration mode. The flexibility and customizability of the MIDAS framework allows for the SuperCDMS SNOLAB DAQ to incorporate a mix of iZIP and high voltage (HV) detectors simultaneously, and provides easy scalability. Thus the SuperCDMS SNOLAB DAQ is a unified system capable of use for small-scale test facility experiments, intermediate-sized experiments such as CUTE and NEXUS, as well as the large-scale SNOLAB project.
The Super Cryogenic Dark Matter Search (SuperCDMS) operates cryogenic detectors to search for a particle candidate constituting approximately 85% of the matter in the universe. The cryogenic system of the previous experimental setup at the underground laboratory in Soudan, Minnesota was shown to introduce vibrations that limited the sensitivity of the experiment. As a first step towards developing specifications for the maximum allowable level of vibrations in the next phase of SuperCDMS at SNOLAB, the dry dilution refrigerator of the detector test facility at Queen's University was equipped with a set of accelerometers to measure the transmission of vibrations. These measurements are used to validate a detailed finite element model of the system. These tools can be used by SuperCDMS in the future to better understand and minimize the impact of vibrations on the detector sensitivity.
Small amphipathic polypeptides that can reduce the viability of bacterial cells are known as antimicrobial polypeptides (AMPs). Permeabilization of lipid bilayers by AMPs has been previously investigated in model lipid systems that mimic aspects of bacterial membrane composition. Model studies, however, do not address the possibility that polypeptide antimicrobial activity might also involve the disruption of non-membrane targets or might be enhanced by interaction with non-membrane cell components. In order to learn how AMPs interact with more complex structures within real bacterial cell envelopes, we have deuterium-labeled membranes of the gram positive bacteria Bacillus subtilis and have used $^2$H NMR to study how lipid acyl chain orientational order in the membranes of these bacteria is affected by the presence of specific AMPs. In the absence of AMP, the $^2$H NMR spectrum of the labeled bacterial membrane is a superposition of doublets characteristic of fast axially symmetric chain reorientation. Prominent shoulders, at +/-12 kHz, reflect an order parameter profile having a plateau near the headgroup end of the chain. In the presence of CAME (a hybrid of cecropin and melattin), intensity shifts from the plateau spectral region to smaller quadrupole splittings suggesting a peptide-induced disordering of the bacterial membrane. Spectra have also been obtained from deuterated B. subtilis in which the peptidoglycan layer has been disrupted using lysozyme. The capacity to observe such spectra will facilitate studies of how the bacterial peptidoglycan layer affects AMP perturbation of the B. subtilis membrane. Supported by NSERC and Colciencias-Colfuturo.
Weakly electric fish produce a high-frequency oscillating electric field that allows them to navigate and communicate in the dark. Their clock-like signal is the least variable of any known biological oscillator, but the mechanisms underlying this extreme precision are not clear. We recorded electric discharges in Apteronotus albifrons (blackghost knifefish) at 50MHz sampling frequency to characterize temporal precision under different conditions, such as a varying temperature. We used three different approaches to analyse cycle-to-cycle variability: the first involved a simple signal threshold; the second was based on the signal envelope using Hilbert transforms; and the third, which was the most accurate, used the phase of the Hilbert transform. One important observation was that under certain conditions, the histogram of cycle periods exhibits two peaks. We hypothesize that the electric organs on the left and right sides of the fish are independent oscillators that normally are synchronized but can also operate separately under some conditions. We will discuss the implications of our results on the neural generation of high-frequency signals and the insight that it provides for brain oscillations in general.
Insertion and deletion mutations are common events in protein evolution but occur much less frequently than point mutations. Due to this, the effects of insertions and deletions on the biophysical properties of proteins are much less studied and understood.
A continuous three-letter protein model was used to study the effects of these mutations on the folding and stability of proteins. Thermodynamic behaviour was calculated using simulated tempering Monte Carlo methods.
As an initial sequence, we used a 35-amino acid sequence that folds into a stable native state with both α- and β-structure. We generated and simulated all 25 unique insertion mutations and all 73 unique deletion mutations for this initial sequence. In particular, this allowed us to assess the effects of the mutations on structure and stability.
The biomedical imaging community has recently seen a tremendous development of novel ultrasound-based tissue characterization techniques. These methods often involve the application of an external stimulus and the measurement of the tissue response, from which tissue properties can be inferred. To further the development of these tissue characterization techniques, one needs to characterize the applied external stimulus and the resultant ultrasound waveforms as they travel through the tissue or the phantom.
To address this need, we developed and characterized a fiber optic vibration sensor with an ultra-wide dynamic sensing range, from a less than 1 Hz to clinical ultrasound frequencies. The vibration sensor consists of a matched pair of fiber Bragg gratings coupled to a custom built signal processing circuit. The wavelength of a laser diode is locked to one of the many cavity resonances using the Pound-Drever-Hall scheme. A calibrated piezoelectric vibration element was used to characterize its strain, temperature, and noise responses. To demonstrate its sensing capability, an ultrasound phantom with built-in low frequency vibration actuation was constructed. The fiber optic senor was shown to simultaneously capture the low frequency vibration and the clinical ultrasound transmission waveforms with nanostrain sensitivity.
The developed miniaturized and sensitive vibration sensor can provide invaluable correlation between the low frequency strain deformation and the ultrasound transmission. This correlation is useful for characterizing strain deformation under an applied external strain. Therefore, this sensor can be applied to study tissue deformation in ultrasound elastography and high intensity focused ultrasound. Laser-locked FBG cavities can also provide useful information regarding ultrasound transmission in tissues or tissue surrogates. The ability to implant a strain sensor of this bandwidth and sensitivity into tissues and tissue surrogates can permit the ready determination of mechanical properties, such as the speed of sound and bulk modulus, which are useful for modeling ultrasound propagation in such media.
The aim of this study was to investigate the effect of femtosecond Laser Induced Periodic Surface Structures (LIPSS) with different periodicities in the range of 300 nm to 800 nm on osteoblast-like cells (i.e., Saos-2, osteosarcoma) growth on titanium. Femtosecond pulses from Yb:KGW laser source were used to synthesize LIPSS on titanium at fundamental wavelength of 1030 nm with a pulse duration of 350 fs at a repetition rate of 1 kHz. Scanning electron microscopy and x-ray photoelectron spectroscopy were used to characterize the surface topography and chemical composition of LIPSS on titanium, respectively. The results of in vitro study of Saos-2 cell metabolism on LIPSS with different periodicities on titanium are presented in this work.
Asfia Soomro and Maikel C. Rheinstädter
Department of Physics and Astronomy, McMaster University
Giant Axonal Neuropathy (GAN) follows an autosomal recessive genetic inheritance and impedes the peripheral and central nervous system due to axonal swellings that are packed with neuro-filaments. The patients display a number of phenotypes, including hypotonia, muscle weakness, decreased reflexes, ataxia, seizures, intellectual disability, pale skin, and often curled hair. We used X-ray diffraction and tensile testing to determine potential changes to the structure of keratin intermediate filaments (IFs) in the hair of patients with GAN. A statistically significant decrease of the 47 Å and the 27Å diffraction signals were observed. Tensile tests determined that the hair was slightly stiffer, stronger, and more extensible in GAN patients. These results suggest that the structure of keratin IFs in hair is altered in GAN, and the findings are compatible with an increased positional disorder of the keratin tetramers within the hair fibres. We present a detailed model how molecular disorder affects the structure of Ifs to describe our scattering data. Our results also support the use of X-ray diffraction and tensile testing as a potential diagnostic method for diseases affecting hair structure allowing for fast and non-invasive screening
Solution-processed nanomaterials offer low-cost alternatives to traditional bulk semiconductors. Recent breakthroughs have demonstrated electron mobilities and trap densities in solution-processed thin films on par with those of crystalline silicon.
In this talk I will discuss the research directions our group is taking using solution-processed nanomaterials for applications in optoelectronics, in particular solar cells, lasers, and LEDs, as well as perspectives and challenges in further improving their properties for specific applications.
Colloidal quantum dots have just reached 12% certified photovoltaic performance by using solution-based ligand exchange that reduces defect densities and improves carrier extraction. Further progress is expected as loss mechanisms are unveiled, and the origin of open circuit voltage deficit is understood.
Past year has seen the first implementation of a CW laser based on colloidal quantum dot thin films after more than a decade since the first gain and lasing were demonstrated in these materials. I will discuss how the understanding of electronic structure of quantum dots and its relation to optical gain motivated new chemical synthetic methods that allowed to bridge the gap between fs, ms and CW lasing.
The search for low-cost technologies that reduces our energy consumption is a priority in our struggle for the well-being of our environment. The BaTiO3 particles were synthesized for this research with the aim of enabling a more efficient use of the electric energy in electroluminescent devices (ELDs). In these devices, BaTiO3 is often used as the dielectric layer. A more efficient dielectric layer would allow a reduction of the thickness of the overall device, which would result in lower production costs and increased brightness. The BaTiO3 was synthesized using a sol-gel method, which allows for the control of particle size and dopant concentration. The material was characterized using scanning electron microscopy, X-ray diffraction analysis and X-Ray photoelectron spectroscopy (XPS). The XPS results showed a large split in the lanthanum's binding energy which was never discussed in the literature. Following this, a hypothesis was advanced about the interaction between the Ti-O strong bond and the lanthanum. The ELDs were screen-printed using inks made from the experimental BaTiO3 and a ZnS commercial powder. The optimal concentration of dopant (0,5 mol% La) was obtained by using impedance spectroscopy and photometry to determine the electric permittivity of the BaTiO3 layer and the luminescence of the ELDs, respectively. The samples made with this concentration exhibited a luminescence more than double the one emitted by samples made with commercial powders of both BaTiO3 and ZnS. Even more remarkably, one of the luminescent samples was found to be 600% brighter than the others. Although these are preliminary results, they could prove to be of great importance for the field of ELD research, provided a verifiable reproducibility with a commercial printer.
It was shown in 2004 that a two-dimensional electron gas may form at the interface between non-polar SrTiO$_3$ and polar cap layers such as LaAlO$_3$. Ongoing interest in these interfaces is sustained by observations of gate-tunable superconductivity, ferromagnetism, and spin-orbit and polaronic effects. This talk will focus on the interfacial electronic structure, which is not well understood even a decade later.
In particular, I will show that the electron distribution at the interface is fundamentally tied to a nearby ferroelectric quantum critical point: energetically, the SrTiO$_3$ lattice favours a ferroelectric transition which, however, is suppressed by quantum fluctuations. Consequently, the SrTiO$_3$ dielectric susceptibility is a strong function of temperature, electric field, and wavevector. As this dielectric susceptibility shapes the confining potential well at the interface, one must expect the electron distribution to also be a strong function of temperature and gate voltage. One of the most striking manifestations of quantum criticality is the prediction that the electron gas becomes deconfined from the interface at low temperatures and densities, opposite to what would be found in conventional semiconductor interfaces.
Queen's University is celebrating its 175th year. Physics and astronomy have been taught here since the early days; an independent department was formed over a century ago; the engineering physics program was started about that time and research became a feature of the Department. We shall begin with a brief chronology and then illustrate the development of physics at Queen's by sketching a few of its memorable characters and by drawing on items from the Department's collection of historical equipment and documents.
I will recount some vignettes from the life, work, and engagements of the late John David Jackson—Western Ontario undergraduate, McGill faculty member, professor emeritus at the University of California, Berkeley— whose magisterial textbook Classical Electrodynamics has shaped graduate education for more than a half century.
In this talk I will discuss several recent trends in Canadian neutron scattering, as determined from a study of neutron publication data. The main goal of this study was to identify: (1) where Canadian scientists have been carrying out their neutron scattering experiments, (2) what type of techniques and instrumentation they have been utilizing, (3) which fields of science they have been working on, and (4) how these trends have evolved over time. Given the planned shutdown of the NRU reactor at Chalk River in 2018, it is particularly instructive to compare bibliographic data from the Canadian neutron scattering community to those of other countries (such as Sweden and Denmark) which have recently closed their own large national neutron sources.
The Belle II experiment at the KEK laboratory in Japan will begin detector commissioning this year, with first data taking for physics planned for 2018. I will present the current status of this project, and describe recent activities relating to detector construction and testing, as well as the commissioning of the SuperKEKB accelerator. I will also report on the activities of Canadian groups that participate in Belle II, as we prepare for the operational phase of the experiment.
T2K is a long baseline neutrino oscillation experiment in Japan. T2K produces neutrinos at the J-PARC accelerator complex and observes them at the ND280 and Super-Kamiokande detectors. T2K continues to accumulate significant new data sets in neutrino and anti-neutrino mode. We will review the overall concept of the T2K experiment and then present our most up-to-date three-flavour results which include world-leading measurements of neutrino oscillation parameters, including the search for leptonic CP violation. We will also briefly introduce plans for future neutrino projects in Japan, namely T2K-II, NuPRISM and Hyper-Kamiokande.
As long-baseline neutrino oscillation parameter measurements arrive at the precision era, future experiments will be dominated by systematic rather than statistical uncertainty. The determination of the incident neutrino energy based on experimental observables relies on theoretical neutrino-nucleus interaction models, which are the dominant uncertainties for the T2K-II and HK experiments. NuPRISM is an experimental solution to constrain this uncertainty.
NuPRISM is a water Cherenkov detector that can be raised/lowered to span a continuous 1-4 degree off-axis range, relative to the neutrino beam centre. Linear combinations of the near detector flux, at different off-axis angle slices, can then be taken to match the far detector flux measurement. Oscillation parameters may then be obtained while largely reducing the neutrino interaction model dependence. NuPRISM also enables a unique measurement of the neutrino cross-section as a function of neutrino energy, as well as probing for sterile neutrinos.
NuPRISM plans to use multi-PMT modules, which are under development in Canada. The experiment will also require a data collection system capable of supporting high bandwidths, as well as an in-situ PMT calibration system. NuPRISM Phase-0 is planned to demonstrate the technology and an understanding of the detector at the 1% level. It will be located between 6 and 12 degrees off-axis where a large electron neutrino flux may be used to make a leading electron to muon flavour neutrino cross-section ratio measurement. Gadolinium doping may be used to measure neutron emissions from neutrino interactions.
Freeman et al. in their landmark 225-study metaanalysis determined that active learning increases student performance in STEM (PNAS 2014). They went so far as to state “If the experiments analyzed here had been conducted as randomized controlled trials of medical interventions, they may have been stopped for benefit“. Did they just conclude (in a paper cited over 1000 times) that smooth and clear (prof-centred) lecturing is not ethical? If so, how do we achieve active learning with 200 or more students? Research-based instructional strategies provide almost too many options. Reading the studies, there is one common factor that rises to the fore: feedback is provided to every student in every class. And the only way to do it is to engage the students as teachers.
The DEAP-3600 experiment is searching for Dark Matter with a 3600 kg single phase liquid argon (LAr) target and a projected exclusion sensitivity to the spin-independent 100 GeV WIMP-nucleon cross-section of 10$^{-46}$ cm$^{2}$ after a background-free exposure of 3000 kg$\cdot$yr.
The experimental signature are keV-scale WIMP recoils producing 128 nm LAr scintillation photons which are wavelength shifted and observed by 255 PMTs. To reach the large background-free exposure, a combination of careful material selection, passive shielding, active vetoes, fiducialization and pulse shape discrimination (PSD) is used. The main concept of the background rejection in DEAP is the powerful PSD, employing the large difference between fast and slow component of LAr scintillation light to achieve an electronic and nuclear recoils separation in the order of $10^{10}$; this can successfully reject $^{39}$Ar beta-decays with an activity of about 1 Bq/kg in argon with natural isotopic composition.
The design background goal for DEAP-3600 are 0.2 events from external neutrons, 0.2 events from surface alphas and 0.2 events from $^{39}$Ar in the WIMP region in a 1 tonne fiducial volume within 3 yr. The experiment was filled in November 2016 and is currently taking data. This talk will present a reevaluation of the background projection with the current run conditions and report on the current understanding of the background in DEAP based on first data.
Experiments currently searching for dark matter, studying properties of neutrinos or searching for neutrinoless double-beta decay require very low levels of radioactive backgrounds both in their own construction materials and in the surrounding environment. These low background levels are required so that the current and next generation experiments can achieve the required sensitivities for their searches. This presentation will describe the low background measurement facilities currently operating at SNOLAB and will discuss plans and options to expand these facilities to allow for the increased sensitivity required by the next generation of experiments.
DEAP-3600 is a liquid argon experiment for direct dark matter detection which is located $2$km underground at the SNOLAB facility in Lively, Ontario. It was designed with a target sensitivity of $10^{-46}$cm$^2$ for the spin-independent scattering cross section of Weakly Interacting Massive Particles (WIMPs) at masses of $100$GeV on the nucleons of the scintillation material. Nuclear recoils from a WIMP signal can be distinguished from electronic recoils by pulse shape discrimination (PSD), utilising the decay times of the different excited states of the liquid argon following the interactions, reducing gamma backgrounds for the WIMP signals. Thus, the intrinsic backgrounds from the $^{39}$Ar beta emitter contained within the liquid argon scintillator, as well as gamma signals originating from isotopes contained in the detector material, can be separated from the expected WIMP signal and used to understand the detectors energy response and position reconstruction in the region of interest. This talk will discuss the methods used to achieve a detailed understanding of the detector response with these non-WIMP signals.
Protection from and rejection of backgrounds are key issues for direct dark matter detection experiments.
The next-generation SuperCDMS SNOLAB experiment will be described, focusing on background strategy and characterization.
The potential of SuperCDMS detectors for achieving very low energy threshold is particularly attractive for searches for WIMPs with masses below 10 GeV/c^2.
Thus, the background at energies below a few tens of keV is of particular interest. Surface contamination from plate-out and implantation of radon daughters can give rise to neutron and gamma-ray backgrounds in the region of interest. Ongoing R&D projects to characterize these backgrounds will be discussed.
Quantum state engineering of ultracold matter and precise control of laser coherence have revolutionized a new generation of atomic clocks with accuracy at the 18th digit. This progress has benefited greatly from microscopic understandings of atomic interactions in the quantum regime. In return, the unified front of precision metrology and quantum physics has enabled exploration of many-body spin systems. Our next clock will have at its core a Sr Fermi degenerate gas configured as a band insulator in a three-dimensional optical lattice. The correlated, high-density atomic system provides a clear path for improving the clock performance to the next decimal point, and sets the stage to advance measurement precision beyond the standard quantum limit. These emerging quantum technologies will allow us to test the fundamental laws of nature and search for new physics.
CAP-CRM Prize in Theoretical and Mathematical Physics | Prix ACP-CRM de physique théorique et mathématique
TBA
Medal for Outstanding Achievement in Industrial and Applied Physics | Médaille pour des réalisations exceptionnelles en physique industrielle et appliquée
Optical to electrical power converting devices are achieved with breakthrough performance using a Vertical Epitaxial HeteroStructure Architecture (VEHSA design). The III-V semiconductor devices allow achieving a near-optimum responsivity, an improved photovoltage output compared to p/n junctions with standard thicknesses. The ultrahigh conversion efficiencies were obtained by monolithically integrating several thin GaAs photovoltaic junctions tailored with submicron absorption thicknesses and grown in a single crystal by epitaxy. Experimental evidence of the significant impact of photon recycling in these photovoltaic devices has been observed. The devices exhibited a near optimum responsivity of up to 0.645A/W, corresponding to an external quantum efficiency of ~94%. Recent progresses include: -The highest optical to electrical efficiency ever achieved; -The highest output powers ever reported for a high-efficiency monolithic PV cell with 5.87W of converted output from a CW laser; -The highest efficiencies ever reported for any types of optical to electrical power conversion devices simultaneously combining high photovoltage and output powers (> 5W at > 7V with > 60% efficiency and > 3W at > 14V with > 60% efficiency); -The highest photovoltage ever reported for monolithic photovoltaic semiconductor heterostructures with measured Voc > 23V; -the thinnest p/n junctions ever implemented successfully with high-performance, with GaAs bases as small as 24nm.
CAP-TRIUMF Vogt Medal for Contributions to Subatomic Physics | ille Vogt de l'ACP-TRIUMF pour l'excellence dans le domaine de la recherche théorique ou expérimentale en physique subatomique
TBA
Polyolefin-based agricultural mulch films are widely used to extend the growing season for fruits and vegetables, improve yields and reduce the need for both irrigation and the application of pesticides. The careful addition of prodegradants and stabilizers to otherwise conventional polyolefin materials allows mulch films to degrade in a predictable way in the presence of oxygen and sunlight, thus eliminating the costs associated with removal and disposal of films at the end of the season.
In this presentation we describe the results of several ongoing research projects aimed at examining the behavior of polyolefin-based agricultural mulch films in both the field and laboratory environments. Three aspects of film performance are investigated. We have characterized the effect of films’ colour on their ability to modify the temperature and moisture in the soil surrounding desirable plants. We have also examined the extent to which film degradation (as measured in both field and accelerated ageing environments using FTIR spectroscopy) can be modified by adjusting the film composition. Finally, we describe how exposure to pesticides may affect the degradation behavior of films.
The infrared Fourier transform spectrum of the S-H stretching fundamental band of CH$_{3}$SH at 2604 cm$^{-1}$ has been recorded using synchrotron radiation at the FIR beamline of the Canadian Light Source in Saskatoon. This band is an order of magnitude weaker than the corresponding O-H stretch of methanol, with a very different structure. It is a hybrid band predominantly of perpendicular $b$-type, with a smaller parallel $a$-component. With both $\Delta$$K$ = +1 and $\Delta$$K$ = -1 sub-bands present, the assignments are well-determined from ground-state combination relations, but are complicated by the presence of many $J$-localized perturbations. Upper-state term values have been determined for $K$ = 0-14, and the substate origins have been fitted to a Fourier model. The oscillation amplitude of the torsional curves is 0.545 cm$^{-1}$ compared to 0.652 cm$^{-1}$ for the ground state, indicating a reduction of the order of 16% in the torsional barrier height $V_{3}$.
Edholm’s law of bandwidth states that the required data rate in the communication industry is doubled every 18 months. To meet the demand in the bandwidth for wireless communications, several experiments has been carried out using Terahertz (THz) waves (0.1 THz – 10 THz). Though the THz waves are being absorbed by the atmosphere, mainly due to the water molecules, the available low loss transmission windows allows us to increase the link distance for outdoor communications. The THz communication link can be established using either electronic or photonics based approach. In this work, we have described the design and demonstration of an error free 5 Gbps transmission over the link distance of 30 cm using photonics based technologies. Two Distributed Feedback (DFB) lasers having slightly different center wavelengths operating in the telecom region is used as the source for difference frequency generation. One of the DFB lasers is intensity modulated using electro-optic modulator with the pseudo random bit sequence (PRBS) data with the pattern length of 29-1 and the data rate of 5 Gbps. The frequency of the DFB lasers is tuned in order to get the difference frequency of 140 GHz by mixing it in the photomixer. A zero bias Schottky detector (ZBD) is used at the receiver end for the detection and direct demodulation. The demodulated baseband signals are pre-amplified using a low noise amplifier and the performance is analyzed by recording the eye pattern. The amplitude of the eye opening is clear, demonstrating the error free operation of the communication link.
Non-destructive and high speed imaging is the requirement of many industrial, medical and scientific applications. The principle of non-destructive imaging using Terahertz (THz) radiation (0.1 THz – 10 THz) has been already demonstrated in many research works. Single pixel imaging is the most commonly used method in obtaining THz image which lacks fast image acquisition. Few works has been carried out to increase the acquisition speed using multichannel detection and advanced algorithms. In this paper, we have shown the proof of concept for high speed acquisition of 2D image with improved resolution by dynamically reconfiguring the optical wavefront using spatial light modulator. An eight channel THz array antenna with an electrode gap of 100 μm and length of 0.5 cm is fabricated using the commercially available Gallium Arsenide (GaAs) semiconductor. By spatially reconfiguring the wavefront of the probe beam using spatial light modulator, we can excite each detector array simultaneously and record the THz electric field using 8 channel lock-in amplifiers. By scanning the probe beam along the length of the dipole array antenna with a small step size, the 2D image can be obtained with higher resolution along with frequency information.
We study a 3D-printed hollow core terahertz (THz) Bragg waveguide for resonant surface sensing applications. We demonstrate theoretically and confirm experimentally that by introducing a defect in the first layer of the Bragg reflector, thereby causing anticrossing between the dispersion relations of the core-guided mode and the defect mode, we can create a sharp transmission dip inside of the waveguide transmission bandgap. By tracking the changes in the spectral position of the narrow transmission dip, one can build a sensor, which is highly sensitive to the optical properties of the defect layer. In order to calibrate our sensor, we use PMMA layers with different thicknesses attached on the waveguide inner surface. Strong frequency shift is observed, and the demonstrated sensitivity is found to be 0.1GHz/μm to changes in the defect layer thickness. Then, an example of THz resonant surface sensing using α-lactose monohydrate powder as the analyte is demonstrated experimentally. The anticrossing phenomenon between the core-guided mode and the defect mode is confirmed by imaging the modes propagated in the Bragg waveguide using a fiber coupled THz microscopy setup. Moreover, both THz time-domain spectroscopy (TDS) and continuous wave (CW) systems are used for comparative study of designing optimal detection systems. Unlike many other photonic bandgap waveguide sensors operating on a more common bulk sensing modality, the one proposed here enables a resonant surface sensing modality.
A novel hollow core waveguide Bragg gratings featuring periodically placed triangular axisymmetric slopes on its inner surface is proposed for the dispersion compensation in the terahertz frequency range. The proposed waveguide Bragg grating is operated in the bandgap of higher order modes and uses the fundamental HE11-like mode for the dispersion compensation. Theoretical results show that the optimized waveguide Bragg grating supports a single mode operation over the 137-141GHz spectral range. Within the single mode guiding range, the dispersion of the fundamental HE11-like mode has large negative values. Specifically, the dispersion of the fundamental HE11-like mode is ~ -130ps/(THz∙cm) at 140GHz, while varying in the -500 ~-100 ps/(THz∙cm) range over 137-141 GHz. In the vicinity of 160GHz, we also obtain a single mode range over the spectral range of 156-162GHz, where the dispersion of the fundamental HE11-mode varies from -1500ps/(THz∙cm) to -60ps/(THz∙cm).
Using numerically optimized waveguide structure, we fabricated the prototype of the waveguide Bragg grating using a 3D stereolithography system, and subsequently metallized it with a silver layer using wet chemistry. The optical properties of the fabricated waveguide Bragg grating were then measured experimentally using a terahertz continuous wave spectroscopy. We also mapped the output electric field of the fabricated waveguide Bragg grating. Experimental findings reproduced well the theoretically predicted modal properties, including spectral positions of high transmission regions and modal dispersion within these regions. From this, we conclude that presented device shows single mode operation, relatively high coupling efficiency, and strong negative dispersion, which is at least one order of magnitude higher than these of typical THz waveguides. This makes the proposed device suitable for dispersion compensation in free-space and fiber links for terahertz communications.
Over the past decade or more, there has been a great deal of interest in the mechanical, electronic and optical properties of graphene. The interest in the optical properties of monolayer graphene stems largely from two key features of the electronic band structure: it is gapless and the dispersion is linear near the Dirac points, where the two bands touch. Both of these features can be uniquely accessed using terahertz radiation, because, under the right conditions, it can strongly drive both interband and intraband transitions. In this talk, I will describe the formalism and computational results of our density-matrix approach to modelling the nonlinear terahertz response of monolayer graphene as well as unbiased and biased bilayer graphene. As I will show, although the linear dispersion of monolayer graphene does result in a relatively strong nonlinearity due to intraband transitions, in undoped graphene, it is the interplay between the intraband and interband transitions that dominates the nonlinear response. Consequently, we find that the nonlinear terahertz response of bilayer graphene can be greater than that of monolayer graphene, even though it’s dispersion is parabolic.
The Super Cryogenic Dark Matter Search (SuperCDMS) experiment is preparing for its next phase to be deployed at SNOLAB. Cryogenic detectors with their excellent resolution and potentially very low energy threshold are particularly suited to search for dark matter particles with masses below about 10 GeV/c2. After a reminder of the basic ideas behind the SuperCDMS detector technology, this presentation will focus on the status and plans for SuperCDMS at SNOLAB. These include a Cryogenic Underground detector TEst facility (CUTE) which is presently under construction, and will allow us to test a number of detector properties that cannot be investigated in the presence of environmental background at the rates found in the existing SuperCDMS detector test facilities above ground.
The nature of the dark matter thought to make up most of the matter in the universe is unknown. It may consist of new particles from beyond the standard model. For close to two decades, the DAMA experiment has claimed to have detected such particles. This claim is controversial, in particular because there is no accepted model for the background radioactivity in DAMA. One major unknown is the contribution of the decay of potassium 40 (40K) by electron capture (EC) to ground state. The KDK (40K decay) experiment at Oak Ridge National Laboratories (ORNL) brings together groups from Queen's, ORNL, the University of Tennessee, the Max Planck Institute and TRIUMF. KDK will measure the EC branching ratio using a 40K source, a small detector to trigger on the 3 keV X-rays from EC, and a large outer detector to veto the 1.4 MeV gamma rays coming from the competing electron capture decays to an excited state. We will present the status of the experiment, including source preparation, efficiency calibrations, blinding procedure, and prospects.
DEAP-3600 is a liquid argon based dark matter experiment located 2km underground in VALE’s Creighton mine, Lively, Ontario. In 2016, DEAP-3600 completed its commissioning phase and began collecting data for the objective physics search; the direct detection of spin-independent dark matter through pulse shape discrimination. In order to achieve the unprecedented levels of sensitivity required for such a measurement, a series of data cleaning procedures are applied to the data in order to remove the degrading effects of anomalous instrumental and environmental effects. Such examples include seismic activity and temperature fluctuations in the systems that maintain the necessary cryogenic conditions of the liquid argon. The identification of such effects in the data is first presented alongside the methods used to remove them. This is followed by a discussion of the signal acceptance and exposure for the first dark matter data set.
The talk will present the instructor’s perspective on course redesign using the National Council for Academic Transformation (NCAT) approach. NCAT is an independent, non-profit US-based organization that provides leadership in using educational technologies to redesign learning environments with the goal of producing better learning outcomes for students at a reduced cost to the institution. In 2014 Ryerson University applied for and received funding from the government of Ontario to carry out a pilot course redesign project. The project pursued two simultaneous goals: improving student learning outcomes and the institution’s capacity to deliver thus enhanced educational experience efficiently (productivity). Large-enrollment (450+ students) introductory physics course for science programs was among the fourteen courses selected for the pilot. The redesigned course can be characterized as active learning blended environment with partially flipped lectures and with a significant online component to extend learning beyond the classroom. The online component of the course provides ongoing automated but highly individualized feedback and ensures that the students can work at their own pace. The role of the tutorial Teaching Assistants shifted from administering and grading toward more tutoring and mentoring roles. The students achieved better mastery of core physics concepts included in the course syllabus. The improvement in retention and successful completion rate was achieved with the existing resources and without increasing the cost of course delivery.
Dual processing theory asserts that there are two modes of thinking: A fast, reflexive "system 1"—which provides unconscious, intuitive judgements—and a slower, more reflective "system 2"—which involves deliberate and conscious effort. We examine the implications of this theory in the context of multiple-choice questions on physics exams by including an "Explain your answer" box for certain problems on the exams in a large-scale calculus-based introductory physics course. Our hypothesis is that slowing students down by asking them to write an explanation may trigger system 2, resulting in increased performance on the question. The propensity of students to engage system 2 was measured using the Cognitive Reflection Test (CRT), and a pre/post concept inventory measured both incoming knowledge and learning through the semester. Preliminary results indicate that an "Explain your answer" box results in a statistically significant increase in the odds of a student answering the corresponding question correctly and that the CRT was a strong predictor of exam performance. Implications for exam design will be discussed.
In September 2014 we launched our significantly revised and updated undergraduate physics program. The redesign process was guided by an extensive curriculum mapping exercise, focusing on the desired graduate attributes of students completing degrees in our department. In the new sequence of courses, all of our students are now required to take our new Science Communication course in their third year, allowing us to take a more intentional approach to the development of communication skills. Through this course students are given the opportunity to share their passion for physics with a wide array of target audiences, ranging from elementary school students to teachers to special interest groups. As they work through a variety of exercises and assignments, students hone their abilities to communicate clearly and engagingly both orally and in writing. The course structure, as well as feedback from students who took the course in its first offering in Winter 2017, will be discussed.
Physics education research shows that improving student engagement increases the retention of material presented in class, but this work has focused on material at the first year level. Far less work has explored increasing engagement at the upper division level. This talk will discuss an innovative method of presenting example derivations and calculations in a third year physics classes on electricity and magnetism for physics and astrophysics majors. The talk will discuss our preliminary observations of student engagement and formative assessment in the classroom and applications to other upper division physics classes.
Interest in atomically-thin transition metal dichalcogenide (TMD) semiconductors such as MoS2 and WSe2 has exploded in the last few years, driven by the new physics of coupled spin/valley degrees of freedom and their potential for new spintronic and ‘valleytronic’ devices. Although robust spin and valley degrees of freedom have been inferred from polarized photoluminescence (PL) studies of excitons, PL timescales are necessarily constrained by short-lived (1–30 ps) recombination timescales of excitons. Direct probes of spin and valley dynamics of the resident electrons and holes in n-type or p-type doped TMD monolayers, which may persist long after recombination ceases, are still at a relatively early stage.
In this work, we directly measure the coupled spin-valley dynamics of resident electrons and resident holes in n-type and p-type monolayer TMD semiconductors using time-resolved Kerr rotation. Very long relaxation timescales in the nanosecond to microsecond range are observed at low temperatures -- orders of magnitude longer than typical exciton lifetimes. In contrast with III-V or II-VI semiconductors, electron spin relaxation in monolayer MoS2 is found to accelerate rapidly in small transverse magnetic fields. This indicates a novel mechanism of electron spin dephasing in monolayer TMDs that is driven by rapidly-fluctuating internal spin-orbit fields that, in turn, are due to fast electron scattering between the K and K’ conduction bands [1]. Additionally, a small but surprisingly long-lived oscillatory signal is also observed, indicating the spin coherence of a small population of localized states [2]. More recent studies of gated TMD monolayers also allow observation of very long spin/valley relaxation of resident holes, a consequence of spin-valley locking [3]. These studies provide direct insight into the physics underpinning the spin and valley dynamics of electrons and holes in the monolayer semiconductors.
[1] L. Yang et al., Nature Physics 11, 830 (2015).
[2] L. Yang et al., Nano Letters 15, 8250 (2015).
[3] P. Dey et al., submitted.
This work demonstrates that, in order for Fourier transform infrared (FTIR) spectroscopy to be an effective materials characterization tool, it is essential to evaluate which bands are affected exclusively by specimen differences, independent of the detection and data analysis methodologies. To do this, we compared standard optical detection with photoacoustic detection of FTIR spectra for two classes of benchmark samples: uniformly sized and shaped particles (silica spheres), and size-fractioned CaCO$_3$ (calcite) powders. Subsequent analyses focused on assessments of peak positions, relative intensities, and widths as a function of different sample and data collection parameters. By comparing these trends with other structural characterization data, we identify which spectrum features are uniquely related to structural disorder in the calcite powders. In doing so, we present a best-practices methodology for extracting specimen-specific features from FTIR spectra.
Laser ablation is the process of material removal from a target surface by intense Laser radiation. The technique is used for the production of nanoparticles (NPs) and associated thin films, micromachining of surfaces, and Laser-induced breakdown spectroscopy (LIBS) for material analysis. The amount of ablated material, sample heating, plasma properties (density, temperature, and luminosity) and properties of the generated NPs (size distribution, shape, crystallinity, and magnetic order) depend on material, Laser fluence, and Laser pulse shape. Using numerical simulations, we study the influence of the delay of ultra-short double Laser pulses on the ablation process elucidating the underlying mechanisms and identifying promising conditions for applications. This work focuses on aluminum as a generic example and a widely investigated material in Laser ablation.
The wide range of time and length scales involved in Laser ablation is challenging for both experiment and simulation. We follow a hybrid two-temperature model (TTM) and embedded atom method (EAM)-based molecular dynamics (MD) approach, which offers a simple but realistic description of metallic interactions and electronic properties for systems containing several million atoms over nanosecond timescales. The TTM is based on the heat equation for electrons with the Laser as a source term. The energy of hot electrons is then transferred to the MD subsystem via an electron-phonon coupling term.
The effect of double pulse delays in the range of 1-200 ps on the mechanisms active during the different stages of ablation is revealed using thermodynamic pathways analysis. Furthermore, the NP size distribution is monitored as a function of pulse delay. This study contributes to an explanation of the trends observed in double pulse ablation with respect to ablation efficiency and NP formation. Validation against available experimental results is also attempted.
In High-order Harmonic Generation (HHG), the electron that tunnel ionize from a given electronic state generally photorecombine onto the same state. We have demonstrated that during a few cycle laser pulse, several Rydberg states can be populated and open a new channels for HHG : the tunnel ionization from excited states and photorecombination onto the ground state. Using the attosecond lighthouse technique to spectro-temporally map the emission, we showed that the high harmonic emission from Rydberg states is temporally delayed by few-femtosecond compared to the usual non-resonant HHG [1].
Moreover, when the laser pulse is over, the coherence between the ground state and the Rydberg states created during the laser pulse leads to narrowband XUV emission at the Rydberg states field-free energies, due to Free Induction Decay (FID). Using a time-delayed IR pulse, this FID emission is probed and controlled, both in amplitude and phase. We directly measure the laser-induced phase on the FID emission by using a simple heterodyne dectection scheme based on two-source interferometry [2]. This technique provides rich information about the interplay between the laser field and the Coulombic potential on the excited electron dynamics.
[1] S. Beaulieu et al., Phys. Rev. Lett. 117, 203001 (2016)
[2] S. Beaulieu et al., arXiv: 1701.06352v1 [physics.atom-ph] (2017)
The goal of the NEWS-G (New Experiments with Spheres filled with Gas) project is to search for galactic Dark Matter particles in the GeV mass region. Used detectors are constituted of spherical metallic vessels equipped with small ball sensors set at high voltage at center of sphere, filled with noble gas mixtures (Ar, Ne, He, H), operated in proportional mode.
Activities performed within the collaboration will be summarised : they include results from data taken with Neon target with a 60 cm diameter prototype detector in the Laboratoire Souterrain de Modane in France, R&D activities on optimisation of sensors, characterisation of gas and running conditions, calibrations scheme, quenching factor measurements, preparation of the 140 cm diameter detector to be installed in SNOLAB by 1 year.
One of the most pressing question in modern physics arises from the growing evidence that dark matter constitutes the vast majority of the universe's content. The PICO collaboration searches for dark matter particles using superheated fluid detectors, or bubble chambers. These detector can be made inherently insensitive to gamma and beta radiation, while the additional background suppression required to obtain sensitivity to the elusive dark matter signal is achieved with the acoustic signature of the bubble nucleation that allows the identification of alpha particles. In this talk I will present recent results obtained with the PICO bubble chambers that operated at SNOLAB, including the latest results of the PICO-60 detector that set the most stringent constraints on the dark matter signal in the spin-dependent sector. I will also present on PICO Collaboration's plans on building at SNOLAB a 40-liter bubble chamber with a novel design, and the design of a ton-scale bubble chamber that will possess a unique potential to probe a vast area of the dark matter phase-space that is predicted by current theories.
Hypothetical dark-matter particles could make up the bulk of the matter in the universe. Spherical gaseous detectors, like the one being planned by the NEWS-G experiment at SNOLAB, could investigate the existence of low-mass dark-matter particles. An important property to characterize is the quenching factor of such detectors, ie the ratio of signal created by the nuclear recoils expected to be induced by dark-matter particles, to that created by strongly-ionizing calibration particles. We report on the status of these measurements carried out at the COMIMAC facility in Grenoble, which allows to send electrons and ions of energy as low as 1 keV and below into a detector.
The IceCube Neutrino Observatory, completed in 2010, is the world's largest neutrino detector, using a cubic kilometer of Antarctic ice as a Cherenkov medium. With the inclusion of the DeepCore low energy extension, the observatory is able to analyze neutrinos down to 6 GeV in energy, enabling a wide variety of particle physics research in addition to the high energy astrophysics for which it was conceived. This talk will discuss recent results in neutrino oscillations, indirect dark matter detection, searches for astrophysical neutrino sources, as well as the outlook for the IceCube-Gen2/PINGU upgrade.
A permanent non-zero electric dipole moment of the free neutron (nEDM) violates CP-symmetry. Beyond Standard Model theories predict nEDMs very close to the current upper limit of 3·10$^{-26}\,e$·cm. Those predictions result from CP-violating processes, which in turn can be related to the matter-antimatter asymmetry observed in our universe. Thus the search for an nEDM contributes to understanding the Baryon asymmetry. It also has a high discovery potential for Beyond Standard Model physics. The tool of choice to investigate the nEDM are ultracold neutrons (UCN), since they have such low energies that they can be stored in traps and allow observation times of hundreds of seconds.
The distinct feature of TRIUMFs UCN facility is the combination of a neutron spallation source with a superfluid helium UCN converter - unique among all existing and planned UCN sources worldwide. The goal of the UCN project at TRIUMF is to provide a density of several hundreds of UCN per cubic cm to experiments at up to two ports: one of them will be dedicated to determine the nEDM to the 10$^{-27}\,e$·cm level of precision.
This presentation shall give an introduction to UCN physics, and update the audience on the current status of the new UCN facility at TRIUMF: the proton beamline and spallation target dedicated to UCN production have been commissioned successfully. Furthermore, we created a significant flux of thermal and cold neutrons - a crucial step towards the production of ultracold neutrons. First results of the commissioning process will be presented.
The Japanese-Canadian Ultracold Neutron (UCN) Source is a new facility under
construction at TRIUMF. The primary physics goal of this facility is a world-leading measurement of the neutron electric dipole moment. In order to achieve this goal, we require the creation of the world's highest UCN density; this is turn requires a high-power spallation target producing neutrons.
Over the last couple years, a new TRIUMF beamline has been constructed that delivers 20kW of 500MeV protons to a high-power water-cooled tungsten target. This work culminated on Nov 22, 2016, when first "protons on target" was achieved. We will describe the details of the UCN beamline construction, including the magnets, vacuum, diagnostics and target systems. A particular focus of the talk will be the design and commissioning of the UCN kicker magnet, which will divert a small fraction of the TRIUMF beamline 1A beam to the UCN target with minimal impact to other users of that beamline.
Ultracold neutrons (UCN) are extremely cold neutrons with energies below ~ 300 neV and can be confined in a material vessel. Toward the neutron fundamental physics experiments like a neutron electric dipole moment (nEDM) measurement, we developed a new intense UCN source using superfluid helium (He-II) at the Research Center for Nuclear Physics (RCNP), in Japan. In He-II, cold neutrons are down-scattered by phonons to the UCN energy range efficiently. We coupled a lead spallation neutron source with 300 K and 10 K heavy water (D$_2$O) moderators to produce cold neutrons. The cold neutrons were then converted to UCN in He-II, and then, extracted from the He-II to an experimental apparatus. At the exit of the UCN source, a UCN density of 26 UCN/cm$^3$ at 90 neV critical energy was achieved with the 400 W proton beam of the ring cyclotron of RCNP in 2011. This was a world competitive value.
In 2016, this He-II UCN source was transported from RCNP to TRIUMF. The UCN source is to be installed above a tungsten spallation target on the beamline 1U in the Meson hall. Before the installation on the beamline 1U, we were doing cold tests of the cryostat.
We have succeeded in cooling down the UCN cryostat to 20 K using a Gifford-McMahon (GM) refrigerator. For the full cooling test using liquid helium planned in March 2017, we are building up the helium-3 circulation system, the isopure helium circulation system, the 4K liquid helium auto-filling system and radiation shielding.
In this talk, the present status of this apparatus will be discussed.
Motivated by a set of compelling cosmological and astrophysical observations giving evidence for the existence of dark matter, the Super Cryogenic Dark Matter Search (SuperCDMS) experiment aims to keep pushing the sensitivity for interactions of Weakly Interacting Massive Particles (WIMPs), one of the most plausible dark matter candidates, and directly detect them with an array of cryogenic detectors.
Due to the low number of expected signal events and the presence of background, the analyzers may be unconsciously biased to fine-tuning for or against a signal-like feature while performing the analysis. To remove such human bias, the region of interest should be blinded until all relevant analysis decisions are taken. The blinding method of restricting access to data within the region of interest, traditionally used in CDMS and SuperCDMS, is well suited for the typical analyses where little or no background is expected in the signal region. However, it does not appear to be the best option for the background limited analysis of the CDMS Low Ionization Threshold Experiment (CDMSlite). Thus, for CDMSlite Run 3, a new blinding approach is adopted where artificial events (“salt”) are injected into the data, only to be removed during the un-blinding step of the analysis.
This talk will mainly focus on the implementation of salting in CDMSlite, while briefly discuss its potential adaptation in the future for SuperCDMS SNOLAB.
Many of the outstanding questions in astroparticle and subatomic physics today require the ultra-quiet environment provided by deep underground research facilities. SNOLAB is one such facility, based at a depth of 2km in the Vale Creighton mine near Sudbury, Ontario. In this environment, cosmic radiation induced backgrounds are minimized to levels allowing the operation of sophisticated experiments. The lab is host to a number of neutrino and dark matter experiments as well as new biology and genomic experiments making use of the unique facility. Investigations to expand the lab for future experiments and near term infrastructure developments will be outlined.
I will present an overview of where we stand in the physics of high energies and ultrasensitive experiments, mentioning developments from Large Hadron Collider experiments and elsewhere, and give an assessment of what comes next. I will bring plenty of questions, and look forward to hearing yours!