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The 2018 CAP Congress is being hosted by the Dalhousie University (Halifax, NS), June 10 - 16, 2018. 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.
Our system is now open for post-deadline abstracts for the 2018 CAP Congress as well as for Soft Matter Canada 2018. Oral abstracts will only be accepted if space permits; otherwise, they are subject to acceptance as poster contributions.
Registration for the 2018 CAP Congress is now open. For more information about registration fees, click here.
Le Congrès 2018 de l'ACP se tiendra à l'université Dalhousie (Halifax, N-É) du 10 au 16 juin 2018. 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.
Le système de soumission des résumés est maintenant ouvert pour la soumission de résumés « après la date d’echéance » pour le congrès de l’ACP 2018 ainsi que pour la conférence sur la matière molle 2018. Les présentations orale sera accepté seulement s’il y a d’espace; sinon, ils peuvent être acceptées comme présentations par affiche.
L’inscription au Congrès de l’ACP 2018 est en cours. Pour de plus amples renseignements à propos des rais d'inscription appuyez ici.
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.
Traditionally, the wetting of a solid surface by the drop of an emulsion has been thought to be mediated by the formation of a liquid bridge that connects the drop and the surface. In the current work, we experimentally show the spreading of a drop on a surface follows a different, new mechanism. Experiments were conducted for liquid-liquid systems, wherein drops of higher density (glycerol) were allowed to settle under gravity in a lighter polymeric liquid phase (silicone oil) under conditions of small Bond numbers. The approach of the drop towards the substrate was visualized using Reflection Interference Contrast Microscopy (RICM), and the details of the film drainage dynamics and the spreading process of the drop on the surface were recorded. The film shapes obtained were compared with predictions from scaling analysis. The temporal variation of the minimum film heights matched theoretical expectations, until the height reached few tens of nanometers, at which point a stable film was formed. Following this, deformable islands were observed to grow on the substrate, one of which eventually merged with the parent drop to complete spreading. The reasons for the arrest of film drainage and the appearance of the islands will be discussed. The fundamental mechanism discovered here will ultimately guide the tailoring of emulsion-based coatings or paints to have predefined spreading times.
In a crowded space, a long chain molecule can be phase-separated into a condensed state, redistributing the surrounding crowders. Here we discuss how crowding influences the spatial organization of a ring polymer, consisting of two “arms," in a cylindrical space. In a parameter space of biological relevance, the distributions of monomers and crowders follow a simple relationship: the sum of their volume fractions rescaled by their size remains constant. Beyond a physical picture of molecular crowding it offers, this finding explains a few key features of what has been known about chromosome organization in an E. coli cell. For instance, it is consistent with the observation that crowding promotes clustering of transcription-active sites into transcription foci. Finally, crowding is essential for distributing the two arms in the way observed with E. coli chromosomes.
The internal structure of porous materials and membranes plays a critical role in their mechanical and biochemical properties, especially if they are targeted for cell growth in tissue healing and regeneration applications. Collagenous membranes are a class of proteinaceous materials that has been targeted for cell scaffolding studies because collagen is a structural protein found in many tissues. Collagen’s aggregation in a hierarchical fibrillar structure can be stimulated and controlled in vitro to create products that function similarly to those produced in vivo. This can be accomplished merely by changing pH and temperature, even in the absence of growth factors and enzymes that are present during in vivo growth.
Scaffolds can interact with cells by serving as a structure for their attachment, or as a matrix for introducing nutrients, antibiotics, and other molecules to the cells. In this way, the 3D structure and mechanical properties of a scaffold can influence how cells move within and interact with it. In earlier work, we showed that electrochemically produced type I collagenous membranes can control cell proliferation to mimic their behaviour in vivo, unlike collagen fibrilized by standard thermal methods.[1,2] Furthermore, the electrochemically assembled collagen has proven to be a better matrix for osteoblast differentiation relative to other types of common scaffold materials. Since these findings show that matrix composition alone does not explain cell response, we continue to study the 3D structure of the electrochemically produced collagen scaffold prepared under different conditions.
It is challenging to assess the internal structure of a membrane, such as the sizes and connectivity of its pores, since traditional optical or scanning probe imaging methods do not allow access to internal voids within the material. SPT is a passive microrheological technique [3] that we used to follow the diffusion of individual fluorescent particles that were suspended in the collagen membrane during its electrochemical formation. Each sphere samples its local rheological environment, which makes SPT well-suited for assessing the degree of heterogeneity in a system. While there have been bulk rheological studies of collagen-based matrices and at least one diffusion study within individual collagen fibrils, there is a surprising absence of microrheological studies of collagen-based scaffolds.
Earlier work from our group showed that preparing these membranes in the presence of different cations led to different degrees of collagen fibrillation and aggregation as well as differences in membrane stiffness.[4] Our preliminary SPT results show that all of these electrochemically produced collagen membranes have a very compartmentalized structure, regardless of their stiffness. Our findings suggest that electrochemically induced aggregation can independently affect the structure, stiffness, and fluid viscosity of collagen membranes, which offers interesting future opportunities in cell scaffold design.
[1] Gendron, R.; Kumar, M. R.; Paradis, H.; Martin, D.; Ho, N.; Gardiner, D.; Merschrod S., E. F.; Poduska, K. M. Controlled cell proliferation on an electrochemically engineered collagen scaffold. Macromol. Biosci. 2012, 12, 360–366.
[2] Nino-Fong, R.; McDuffee, L. A.; Esparza Gonzalez, B. P.; Kumar, M. R.; Merschrod S., E. F.; Poduska, K. M. Scaffold Effects on Osteogenic Differentiation of Equine Mesenchymal Stem Cells: An In Vitro Comparative Study. Macromol. Biosci. 2013, 13, 348–355.
[3] Oppong, F. K.; Rubatat, L.; Frisken, B. J.; Bailey, A. E.; de Bruyn, J. R. Microrheology and structure of a yield-stress polymer gel. Phys. Rev. E 2006, 73, 041405.
[4] Kumar, M. R.; Merschrod S., E. F.; Poduska, K. M. Correlating Mechanical Properties with Aggregation Processes in Electrochemically Fabricated Collagen Membranes. Biomacromol. 2009, 10, 1970–1975.
MacSANS is a new small angle neutron scattering (SANS) beamline currently under construction at the McMaster Nuclear Reactor, a 5 MW research reactor based at McMaster University in Hamilton, Ontario. This beamline is designed to study a broad range of nanostructured materials, including biological membranes, polymers, superconductors, and novel magnets. In particular, MacSANS will allow users to probe the structure and magnetism of materials on length scales ranging from ~0.5 to 125 nm. MacSANS will be the only instrument of its kind in Canada, and is scheduled to begin commissioning experiments in the spring of 2019. In this presentation we will provide an overview of the instrument design and technical specifications, and discuss several potential applications in the field of soft matter physics.
We study the structure of novel polymers for proton and anion exchange membranes through a combination of experiment and simulations. X-ray and neutron scattering experiments reveal microphase separation and intermolecular order, and interpretation is validated by molecular dynamics (MD) simulations. These studies help us understand the conductivity and swelling of the materials, and inform development of new polymers.
Living cells are composed of a complex mixture of macromolecules. To regulate their activity, cells partition these molecules into specialized compartments called organelles. Typically, membranes form a selective barrier between organelles and the cytoplasm, allowing each compartment to maintain a distinct biochemical composition that is tailored to its function. However, cells also contain a variety of organelles that are not enclosed by membranes. For example, germ granules, stress granules and the nucleolus consist of local concentrations of protein and nucleic acid that rapidly exchange with the surrounding cytoplasm or nucleoplasm. Recent progress suggests that these membraneless organelles assemble through phase separation, whereby soluble components condense from the cytoplasm to form dynamic droplets. Intracellular phase transitions appear to be widespread in eukaryotes and we hypothesize that they may contribute to spatiotemporal organization in bacteria as well. Nevertheless, the molecular forces that drive such phase transitions, and how they are regulated in response to environmental and/or developmental conditions, remain poorly understood. Here, I describe our efforts to answer these questions using quantitative live-cell imaging and physical modeling.
Ideally, we would like to have first-principles simulations capable of quantitatively accurate predictions for any block copolymer system. Usually, our choice of model involves balancing the complexity needed to faithfully represent an actual experimental system and the simplicity required to make the simulation tractable. Fortunately, block copolymer phase behavior is believed to become universal in the high molecular-weight limit, which foregoes the need for detailed models. We illustrate how this universality can be used to make accurate predictions for a diblock copolymer melt from simulations using a simple lattice model. Nevertheless, simulations of blends and/or complex architectures are still extremely challenging even with the simplest of models. We conclude by discussing how this last obstacle could be overcome with field-theoretic simulations.
Biomaterial fabrics have numerous biomedical applications ranging from drug delivery to tissue engineering. A variety of approaches are available for generating biomaterial fibers from various precursor polymer solutions. Approaches such as wet-spinning, electrospinning, and extrusion have been exploited in the past to generate extremely long fibers ranging in diameter from tens of nanometers to hundreds of microns. An alternative approach for manufacturing polymer fibers is to utilize a dry-spinning approach that generates fibers by balancing the cohesive forces within a highly-concentrated and highly-viscous polymer solution with the adhesive forces of this fluid with a solid substrate applicator. This approach can be used to generate a multitude of fibers that can be arranged on a collector to generate large scale fabrics from a variety of polymer precursor solutions. This presentation will describe the working principals underlying this approach to biomaterial fabric production, along with preliminary material characterization data. Applications in the release of drugs and the templating of protein networks for directing cell growth will also be described. The versatility and potential of these materials for wound reconstruction, as well as in non-biomedical industrial applications will also be highlighted.
Collagen is the protein building block of most mammalian tissues such as tendon, arteries, skin and bone. In its triple helical form, collagen assembles into fibrils with tensile properties comparable to the strongest man-made polymer materials. Structural characterization of collagen fibrils using X-ray scattering and electron microscopy led to a picture where long triple helices form a paracrystalline array with a distorted hexagonal radial packing, a slightly lower density of molecules in the fibril centre, and some moderate molecular tilt at the fibril surface. Here I will present some recent single collagen fibril mechanical testing experiments that highlight both their rope-like and tube-like nature. I will also discuss how this rope-tube duality may be modulated by intermolecular crosslinks.
The extracellular matrix (ECM), a complex network of proteins including collagen (COL) and fibronectin (FN) couples a cell with its environment and directly regulates the cell’s fate via physical and biochemical signals. Although the ECM was often considered a static structure providing cohesion and mechanical integrity to tissues, it has recently been shown that (i) the nano-structure, (ii) the nano/micro mechanics, and (iii) the signaling capacity of the ECM are affected by cell-generated forces. Our work has focused on investigating and controlling the material properties of ECM networks and the synergistic roles of FN and COL in 3D environments. In a first example, I will show how the integrated method used in our lab allows us to diagnose early dysregulation of the ECM materials properties in tumors. In a second example, I will present 3D matrix-mimicking polymeric platforms we developed to control both COL and FN properties over macroscopic volumes. These platforms enable a better understanding of the critical link between protein structure and function, with the ultimate goal of controlling cellular functions through cell-matrix interactions. As such, they represent a new tool for biological research with many potential applications in basic research, medical diagnostics, and tissue engineering.
Amphiphilic secondary structures are ubiquitous in native proteins, where they serve a wide variety of functions from specific binding ligands to structural elements in supramolecular assemblies. This talk describes the use of amphiphilic coiled-coil motifs in modular protein polymers as a strategy to achieve electrochemical gelation capabilities. Our de novo electrogelation protein is a telechelic, triblock design comprised of a central spider silk glue motif flanked by terminal pH-triggered coiled-coil domains. The coiled-coiled domains were designed to form intramolecular helix bundles below a sharply-defined pH-trigger point, while the pH-responsive spider silk glue sequence serves both as an anionic electrophoretic transport element at neutral and elevated pH and as a disordered linker chain between the associated helix bundles at reduced pH. In an electrochemical cell, a solution of these telechelic proteins migrates toward the anode where the terminal coiled-coil domains are triggered to form coiled-coil assemblies that act as transient crosslinks for the e-gel state. Upon cessation of the current, the coiled-coil domains denature gradually and the e-gel transforms back into a fluid solution of polypeptides in a fully reversible manner. This simplified triblock protein design mimics many of the characteristics of more complex electrogelation proteins, such as silk fibroin. We discuss experimental and computational studies the physical properties of this protein and the potential for biomedical applications of electrochemically triggered gelation.
Hydrophobins are low molecular weight (5-20 kDa) self-assembling proteins secreted by fungi that accumulate at hydrophobic-hydrophilic interfaces and are extremely surface-active. Hydrophobins can also undergo a structural rearrangement and oligomerize to form rodlets, which are an insoluble functional amyloid that coats fungal spores to act as a water repellent, facilitate dispersal into the air, and prevent immune recognition. Rodlets are extremely durable and due to their biochemical properties they are a target for commercial application. To better understand what protein sequence characteristics determine hydrophobin properties, we are characterizing the structure and properties of diverse class IB hydrophobins from various fungal sources. We have expressed hydrophobins in E. coli and purified them to homogeneity using immobilized metal ion affinity and ion exchange chromatography. We then used nuclear magnetic resonance spectroscopy to characterize the high-resolution molecular structures of hydrophobins and are comparing their self-assembly properties with thioflavin-T fluorescence assays and atomic force microscopy. These experiments will form the basis of future mutagenesis experiments to develop new hydrophobins with desired properties.
Monte Carlo simulations are used to study the conformational properties of a folded semiflexible polymer confined to a long channel. We measure the variation in the conformational free energy with respect to the end-to-end distance of the polymer, and from these functions we extract the free energy of the hairpin fold as well as the entropic force arising from interactions between the portions of the polymer that overlap along the channel. We consider the scaling of the free energies with respect to varying the persistence length of the polymer and the channel dimensions for confinement in cylindrical, rectangular and triangular channels. We focus on polymer behaviour in both the classic Odijk and backfolded Odijk regimes. We find the scaling of the entropic force to be close to that predicted from a scaling argument that treats interactions between deflection segments at the second virial level. In addition, the measured hairpin fold free energy is consistent with that obtained directly from a recent theoretical calculation for cylindrical channels. It is also consistent with values determined from measurements of the global persistence length of a polymer in the backfolded Odijk regime in recent simulation studies.
Natural and engineered proteins have recently been discovered with a unique ability to reversibly switch between entirely different 3-dimensional structures, with accompanying major changes in their secondary structure contents, hydrophobic sidechain packing and overall shape. The major conformational changes in these shape-shifting proteins are triggered by, for example, ligand binding, changes in pH, or — as in evolutionary processes — mutations. Using a coarse-grained model for protein folding with 7 atoms per amino acid and 3 amino acid types (polar, hydrophobic and turn-type), we investigate the character of fold switching transitions. We determine the folding thermodynamics of several “single-ground state” sequences that fold spontaneously into a unique structure, including all-alpha, mixed alpha-beta, and beta barrel folds. We then apply a generalized-ensemble Monte Carlo algorithm to explore sequences that lie in the space between folds. We find that proteins in our model can be driven to switch folds through a series of mutations without needing to pass through unstable “non-folding” sequences, in line with recent protein design experiments. At the border between folds, some sequences exhibit an ability to populate more than one fold. Such sequences are relatively rare, however, and fold changes are therefore typically accomplished in just a few mutational steps. We comment on potential evolutionary implications.
Water is the most important solvent in biological systems. Yet majority of its properties are poorly reproduced by the most commonly used models. An ideal water model needs to accurately capture both structure and dynamics over a wide range of thermodynamic conditions.
To create such a model we attempted both coarse grained1 and atomistic parametrizations. Our experience shows the need for fitting to multiple target properities at different state points for the model to be both accurate and transferable.
Introduction: The three-dimensional (3D) culture of neural cells in extracellular matrix (ECM) gels holds promise for modeling neurodegenerative diseases. However, air-liquid interfacial tension and evaporation can result in inconsistent 3D cultures at low volumes. Thick-layer hydrogels can counter these factors, but large diffusion distances, high cost, and incompatibility with standard imaging tools, plate readers and assays limit their use. To address these limitations, we have developed a thin-layer, 3D culture technique using a commonly used self-assembling ECM hydrogel (Matrigel) combined with an aqueous two-phase system (ATPS).
Methods: A dextran T10 (D10) and hydroxypropyl methylcellulose 4000 cPs (HPMC) ATPS was used to confine small volumes of Matrigel containing the model neural cell line, SH-SY5Y, into thin layers in a 96-well plate format. SH-SY5Y cells were differentiated and cell viability and morphology were observed under epifluorescence microscopy. The ATPS-Matrigel 3D culture method was characterized by monitoring the distribution of 3.0 µm microbeads within gel constructs without cells.
Results: Matrigel evaporation was eliminated in the ATPS-Matrigel 3D culture method, and small volumes (20 µl and lower) formed evenly thin gels. SH-SY5Y cells were observed to extend neurite-like processes in three-dimensions when differentiated, and cell viability remained high, suggesting minimal negative impact of the protocol on cell growth.
Conclusion: We demonstrate a low cost, simple, high-throughput, 3D neuronal cell culture system that is compatible with well-established equipment and commercially available materials.
The production of functional skin equivalents derived from human cells holds promise for reconstruction of severe wounds and for modeling various skin pathologies. Although epidermal cells have the capacity to self-organize and form stratified structures in culture, it is often difficult to integrate these structures with dermal components. In recent years, cellular bioprinting has emerged as an efficient strategy for fabricating functional skin equivalents comprising both dermal and epidermal cells. Examples of bioprinting methods used for fabrication of functional skin equivalents include extrusion-based bioprinting, laser-assisted bioprinting, and inkjet printing. Here, we investigated the use of a layer-by-layer lab-on-a-printer technology for generating multi-cellular three-dimensional skin constructs. To efficiently print sheets of cells using this approach, we first examined the performance of several cross-linkable bio-ink formulations (e.g., alginate and chitosan) containing key extracellular matrix proteins hypothesized to improve cell attachment and growth (e.g., collagen I, collagen IV, fibronectin and laminin). Using these bio-inks, we demonstrate bioprinting of cell-laden sheets in various geometries such as squares and disks containing multiple layers of cells. We also demonstrate that it is possible to print cell-laden sheets using various fill patterns including rectilinear, concentric, and a combination of rectilinear and concentric. Furthermore, we demonstrate that it is possible to produce co-culture sheets consisting of dermal and epidermal cells using the lab-on-a-printer approach. Preliminary analysis of cell viability and organization within these bioprinted skin constructs is presented. Future work will optimize this approach to rapidly generate constructs that closely resembled the natural structure of skin.
The collagen fibrils are the main building block of connective tissues in mammals where they fulfill both structural and mechanical roles. The structure of a fibril is based on collagen molecules that self-assemble into micro-fibrils and sub-fibrils stabilized by hydrogen bonds and covalent crosslinks. The non-integer staggering of collagen molecules results in a characteristic D-band pattern along the fibril with a periodicity of 67nm. Besides this natural variation, localized damaged sites have been observed along the length of mechanically overloaded fibrils [1], which suggests the inherent existence of structural inhomogeneity along collagen fibrils. To explore this further we are using an atomic force microscopy (AFM)-based manipulation technique that allows us to perform tensile tests on a single fibril in bowstring geometry [2]. In this work, we are investigating the potential impact of structural inhomogeneity on the viscoelastic properties of single fibrils. Fibrils were extracted from bovine extensor tendons, around 50 microns long segments were isolated (n=20), imaged with AFM before manipulation and then stretched to the range of strain between 5% and 20%, held at that strain for 150 seconds(n=13), 1 second (n=3), and 1500 seconds(n=3) then released. There was also one fibril that has been pulled and released very slowly in controlled way for comparison. Comparison between AFM image of the manipulated fibrils and pre-manipulated fibrils demonstrated height fluctuations occurring along the fibril length in the micrometer range. We propose that the inherent structural heterogeneity along the length of the fibril becomes a prominent feature after stress relaxation providing a new mechanism for probing morphological changes in fibril level after stress relaxation.
[1] Veres, S.P. and Lee, J.M. Biophys. J. 2012, 102: 2876-2884.
[2] Quigley, A. S. et al. PLoS One. 2016, 11: e0161951.
Many biologically motivated problems naturally call for the investigation and comparison of molecular variants, such as determining the mechanisms of specificity in biomolecular interactions or the mechanisms of molecular evolution. We consider a generalized ensemble algorithm for coarse-grained simulations of biomolecules which allows the thermodynamic behavior of two or more sequences to be determined in a single multisequence run. By carrying out a random walk in sequence space, the method also enhances conformational sampling. Escape from local energy minima is accelerated by visiting sequences for which the minima are shallower or absent. We test the method on an intermediate-resolution coarse-grained model for protein folding with 3 amino acid types and explore the potential for large-scale coverage of sequence space by applying it to sets of more than 1,000 sequences each. The resulting thermodynamic data is used to analyze the structures and stability properties of sequences covering the space between folds with different secondary structures. Besides demonstrating that the method can be applied to a large number of sequences, the results allow us to carry out a more systematic analysis of the biophysical properties of sequences along mutational pathways connecting pairs of different folds than has been previously possible.
We explore a variety of thermodynamically stable molecular configurations of collagen fibrils. Using a liquid crystal model of radial fibril structure with a double-twist director field, we show that two dimensionless parameters, the ratio of saddle-splay to twist elastic constants $ k_{24}/K_{22}$ and the ratio of surface tension to chiral strength $\tilde{\gamma} \equiv \gamma/(K_{22}q)$, largely specify both the scaled fibril radius and the associated surface twist of equilibrium fibrils. We find that collagen fibrils are the stable phase with respect to the cholesteric phase only when the reduced surface tension is small. Within this stable regime, collagen fibrils can access a wide range of radii and associated surface twists. Remarkably, we find a maximal equilibrium surface twist which is compatible with corneal collagen fibrils, and we show how the large surface twist is needed to explain the narrow distribution of corneal fibril radii. Conversely, we show how small surface twist is required for the thermodynamic stability of tendon fibrils in the face of considerable polydispersity of radius.
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
Sixty years ago, Canadian Physicist Bertram Brockhouse pioneered inelastic neutron scattering. His invention, the triple axis spectrometer, enabled direct measurements of phonons, magnons, and other collective elementary excitations in materials. In more recent times the practice of inelastic neutron scattering has been revolutionized by pulsed neutron time-of-flight spectroscopy, enabled in part by the vast increase in available computational power. This has allowed detailed investigations of exotic phenomena including fractionalized magnetic excitations. This talk will begin by surveying some relevant developments in neutron instrumentation, primarily at the accelerator-based Spallation Neutron Source at Oak Ridge. The focus will then shift to the physics of quantum magnets and fractionalized excitations, showing how these are probed by neutron scattering. Next will be a look at the exactly solvable model on a honeycomb lattice proposed by Alexei Kitaev, that exhibits a quantum spin liquid ground state. The talk will conclude with an examination of recent experiments on materials that exhibit mutually competing interactions like those postulated by Kitaev, showing evidence for fractional excitations associated with his eponymous quantum spin liquid.
Speakers: Dr. Nergis Mavalvala and Dr. Edmund Bertschinger, MIT. Organized by S. Ghose, A.W. Peet, and K. Hewitt.
Creative, collaborative effort to advance a respectful and caring community can make a big difference to students, staff and faculty in physics departments, improving their ability to thrive. Data on demography and the climate for inclusion at MIT show the effects of inclusive leadership based on community, culture and values. This short talk will provide both data and tips on how you can strengthen your department for everyone.
We create and control intense transient waveforms by compressing in space and time optical pulses down to a single half-cycle, nearly 1 femtosecond (1 fs = $10^{-15}$ s) in duration. By measuring the optical waveform using an in-situ attosecond (1 as = $10^{-18}$ s) technique we confirm the pulse reshaping. We use the intense transient as a source for generating isolated attosecond pulses from both gases and condensed matter. Furthermore, we develop a general single-shot technique to directly and in real-time measure electric field waveforms.
Attosecond Physics explores ways to follow and control matter with unprecedented temporal resolution (1 attosecond= 10-18 s.). Strong laser fields used to apply forces on the sub-cycle timescale, together with the availability of tabletop attosecond soft x-ray pulses, now open avenues for time-resolving ultrafast dynamics on the unexplored attosecond timescale [1, 2]. In this first attosecond pump - attosecond probe experiment, an isolated 100 eV attosecond pulse initiates an Auger decay followed by an attosecond broadband (250-1100nm) optical pulse. The observable is the soft x-ray absorption spectrum as a function of pump-probe delay. A first experiment in krypton atoms allows us to model the effect of the optical probe as a gate of the Auger electronic dipole, a universal analog to the frequency-resolved optical gating technique [3]. Applying our attosecond x-ray absorption near-edge spectroscopy (AXANES) to the L-edge of fused silica enables us to directly observe and control sub-femtosecond core-excitons in solids, laying the foundation of soft x-ray excitonics.
[1] J. B. Bertrand et al., Nature Physics 9, 174 (2013).
[2] S. R. Leone et al., Nature Photonics 8, 162 (2014).
[3] R. Trebino, FROG, Kluwer Academic Publishers, Boston (2002).
[4] A. Moulet, J. B. Bertrand, T. Klostermann, A. Guggenmos, N. Karpowicz, E. Goulielmakis, Science 357, 1134-1138 (2017).
The initialization and control of the quantum states of excitons in semiconductor quantum dots (QDs) may be achieved using coherent optical pulses, making these systems of interest for solid state approaches to quantum simulators [1] and single photon sources [2]. Quantum state control via adiabatic rapid passage (ARP), which is insensitive to variations in the QD parameters (dipole moment, transition energy) provides an effective strategy for achieving robust quantum state inversion, and has been the subject of intensive study in recent years [3,4]. Robust state inversion is essential for the development of triggered single and entangled photon sources [2,5] and all optical switches utilizing quantum dot states [6]. The extension of ARP to the control of ensembles of QDs would be beneficial for parallel state initialization [7], and may enable the formation of a Bose-Einstein condensate in a quantum dot ensemble [8]. Building on previous demonstrations of ARP in a single quantum dot using subpicosecond pulses [9] and simultaneous deterministic control of excitons in multiple quantum dots [10,11], we demonstrate simultaneous adiabatic rapid passage in multiple quantum dots and evaluate the inversion efficiency of ARP for a range of control pulse parameters.
[1] Ramsay, Semicond. Sci. Technol. 25 (2010) 103001
[2] Michler et al Science, 290(5500):2282–2285, 2000.
[3] Simon et al Phys.Rev.Lett. 106, 166801 (2011).
[4] Kaldewey et al Phys.Rev B 95, 161302(R) (2017).
[5] Dousse et al Nature,466(7303):217–220, Jul 2010.
[6] Schuh et al Applied Physics Letters,99(1):011105, 2011.
[7] Schmidgall et al Physical Review B, 81(19):1–5, May 2010.
[8] Eastham et al Phys. Rev. B 79, 165303 (2009).
[9] Mathew et al, PRB 90, 035316 (2014).
[10] Gamouras et al Nano Lett., 2013, 13 (10), pp 4666–4670.
[11] Mathew et al Phys.Rev B 92, 155306 (2015).
Standard Model processes are at the core of the physics programme of the ATLAS Experiment. In this talk, a review of recent measurements is presented: the production cross-sections of vector bosons in association with jets; the mass of the $W$ boson; processes yielding jets of hadrons in the final state; strong and electroweak production modes of the top quark and its properties; the production cross-section of the Higgs boson and of its couplings to other particles.
The PIENU experiment at TRIUMF aims to make a high-precision measurement of the $ \pi \rightarrow e \nu $ branching ratio: $ R_{\pi} = \frac{\Gamma\left(\pi \rightarrow e \nu \hspace{1 mm} + \hspace{1 mm} \pi \rightarrow e \nu \gamma \right)}{\Gamma\left(\pi \rightarrow \mu \nu \hspace{1 mm} + \hspace{1 mm} \pi \rightarrow \mu \nu \gamma \right)}. $ Measurement of $R_{\pi}$ provides a sensitive test of lepton universality and tight constraints on many new physics scenarios. In addition, a heavy neutrino lighter than the pion could be detected through its effect on the $\pi \rightarrow e \nu$ energy spectrum.
New results will be presented, using the full PIENU dataset, placing limits on the mixing of a neutrino of mass 60-135 MeV/$c^2$ with the electron neutrino. These limits are improved by up to an order of magnitude over previous results. The status of the branching ratio analysis will be presented as well.
NEWS-G (New Experiments With Spheres-Gas) is a direct dark matter detection experiment using Spherical Proportional Counters (SPCs). SPCs are gaseous detectors, where different gases can be use to optimise sensitivity for different dark matter masses. First results using Neon in the prototype SEDINE at Laboratoire Sousterrain de Modane (LSM) were presented at the 2017 CAP Congress.
I will describe the development work performed at Queen’s University to improve this technology. The improvement will be implemented at a larger experiment planned to run at SNOLAB at the end of 2018. I will show how we improved the electric field with new sensors. I will show how we purify the gas and precisely monitor its composition. I will also show how we improved our understanding of the detector using radioactive sources and a calibration laser.
New Experiments With Spheres-Gas (NEWS-G) is a dark matter direct-detection experiment using spherical proportional counters (SPCs) with light noble gases. First results obtained with a SPC prototype operated with Ne gas at the Laboratoire Souterrain de Modane (LSM) have already placed NEWS-G as a leader in the search for low-mass WIMPs. The forthcoming next phase of the experiment consists of a large 140 cm diameter SPC to be operated at SNOLAB with H and He gas. The use of lighter targets, improved thresholds and detector performance together with a significant reduction of the background levels will allow for unprecedented sensitivity to sub-GeV WIMPs down to 0.1 GeV. A status report on the research project at SNOLAB is given. Recent improvements in detector performance and data quality with the experiment at the LSM are also discussed.
Ionospheric physics is rich with anomalies that are typically taking place on short temporal and/or spatial scales. Finding suitable explanations for these anomalies is one thing that keeps the field alive, as they lead to new discoveries into the rich ways by which the ionosphe couples with the atmosphere and magnetosphere, particularly when there are large departures of the system from equilibrium. These localized phenomena may play a key role in the way by which turbulence (or perhaps stochasticity/intermittency?) regulates the exchange of particles, momentum and energy between the subsystems. Given the limited amount of time for a presentation such as this, the talk will be limited to only a few noteworthy items, namely, some neutral atmospheric anomalies, hot ionospheric electron temperatures episodes, unexpected/unusual ion velocity and spectral signatures, and the connection of the latter (or lack thereof) with ion upflows and outflows.
We present first results from a comprehensive three-dimensional model of magnetosphereionosphere coupling. The model describes plasma flow produced by global scale (Volland-Stern) convection electric fields that are coupled with a physical model of the ionosphere. The initial
magnetospheric plasma density is specified using the Global Core Plasma Model (GCPM), while initial density and temperature profiles of electrons and various species of ions and neutrals are taken from the IRI and MSIS models, respectively. The interaction of magnetospheric plasma with the ionosphere is self-consistent and includes effects of sunlight,ionization and recombination,heating and cooling processes,Hall and Pedersen conductivity altitude dependence,and chemistry.The model has already been used to study the development and erosion of plasmaspheric plumes that exert influence over energetic particle dynamics in the inner magnetosphere. It also describes plasma flow over the entire polar cap, which, when combined with data-assimilation of,for example, SuperDARN data, will eventually lead to improved accuracy of space weather forecasting. The main application of the new model is focused on interpreting measurements from the ePOP/CASSIOPE and SWARM satellite missions, which have combined their operations. First modelling results utilizing observations from this new ESA-Canada joint mission will be presented. The novel Yin-Yang overset grid and flexibility of the model to describe non-dipolar magnetic fields will be briefly described, as well as methodology needed to combine the model with more global models such as the LFM MHD model.
CubeSats are increasingly popular among the space physics commuinty, as an afordable means of deploying large numbers of instruments in space, thus providing better monitoring and coverage of space environment. Needle probes consisting of thin cylindrical probes of length ranging from a few to several centimeters, have been used on a number of cubeSats, because of the relative simplicity with which they can be used to infer plasma density. The interest in this type of probes is motivated by the dependence of their characteristic on plasma density and temperature, whereby the collected current in the electron saturation region is approximately proportional to the density and the square root of the potential, with only a week dependence on temperature. As a result, when operated in fixed-bias mode, these probes can provide the electron density from the slope of the current square as a function of bias voltage. One concern with the use of such probes on cubeSats, however, has to do with their impact on the satellite bus (the ground) potential. Indeed with probes mounted on larger spacecraft, the probe bias and collected current generally has negligible effect on the bus floating potential. With the much smaller CubeSats, however, the ion collection capacity of the bus is limited. The relatively large positive biases and resulting collection of negative current, have to be balanced with an equal positive collected current from the rest of the satellite. The concern that this may only be possible by reducing the spacecraft potential to the point that positively biased probes with respect to the bus, may have a potential comparable to, or less than that of surrounding plasma. In this talk simulation results are presented, showing the effect on the bus floating potential, associated with needle probes operating in the electron saturation region. It is shown that under certain conditions, the bus floating potential can become significantly more negative than it would be in the absence of probes, and that active means of controlling the bus floating potential may be required.
We identify the light-cone-like structures present following quenches in spin-chains as quantum caustics. These are discrete versions of the singularities classified by catastrophe theory. From this identification follows: local universality
Imagine a quantum system placed within a thermal gas, which is itself composed of many quantum systems e.g. atoms/molecules. As the constituents of the environment scatter off of the system, it is natural to expect that the system will reach a thermal equilibrium with its environment. Moreover one may expect that the ultimate thermalization of the system is largely independent of the coupling between the system and its environment, $H_{SE}$, and of the time scale of the scattering.
We show that if the scattering time scale is sufficiently small, then the final temperature of the system is generically not the temperature of its environment, $\beta_S(\infty)\neq\beta_E$. Instead we find equilibrium of the form $E_S \beta_S(\infty)=f(H_{SE},E_E\beta_E)$ where $E_S$ and $E_E$ are the energy scales of the free system and environment respectively.
The goal of this project is to make progress in quantum gravity by studying gravity in quantum mechanical systems at atomic scales. We compare approaches to the generation of gravitational waves and gravitons from quantum mechanical systems such as the ammonia molecule. The approach is guided by the strong analogy between classical electromagnetism and classical general relativity. We evaluate the semi-classical Einstein equations based upon their predictions for gravitational wave generation.
When a charged particle moves in a plane perpendicular to a constant magnetic field (z-direction) the discrete energy levels are called Landau levels. The energies resemble those of the harmonic oscillator with $\omega$ the cyclotron frequency $\omega_c$. The energies are highly degenerate, with the degeneracy being independent of the energy. We now add a linear electric field parallel to the magnetic field above the plane and anti-parallel below the plane. This introduces a second frequency $\omega_z$ associated with oscillations along the z-direction. We show how the Landau levels get modified, but more crucially show that the degeneracy increases with energy, with critical jumps when $\omega_z$/$\omega_c$ is a rational number.
Gaining insight into the astrophysical processes that govern nucleosynthesis in stellar scenarios requires a detailed understanding of the involved nuclear reactions. Radiative capture cross sections at typical temperatures of environments like novae, X-ray burst or supernovae are in many cases vanishingly small, thus making the reaction rates extremely challenging to access experimentally.
The DRAGON ({\bf D}etector of {\bf R}ecoils {\bf A}nd {\bf G}ammas {\bf O}f {\bf N}uclear reactions) recoil separator has been designed to recreate nuclear fusion reactions on radioactive as well as on stable nuclei of astrophysical interest in the laboratory, and to directly measure absolute cross sections of radiative capture reactions on protons and alpha particles.
In order to take advantage of the radioactive beams delivered by the TRIUMF-ISAC facility, which are often too short-lived to be used as target material for normal kinematics measurements, the reaction rates require to be studied in inverse kinematics. Ion beams at energies of 0.15 to 1.5 MeV/u impinge on the windowless gas target and $\gamma$-rays from the de-excitation of the compound nucleus are detected in the high-efficiency BGO array surrounding the target.
With 8 out of 10 radioactive beam experiments performed over the last one and a half decades, DRAGON still holds the record for the number of direct radioactive beam measurements of radiative capture.
In this presentation I will give an overview of the DRAGON recoil separator and outline its capabilities before presenting results of the most recent experiments; among them the direct measurement of the long debated strength of the E$_{c.m.}$ = 456 keV key astrophysical resonance in the $^{19}$Ne(p,$\gamma$)$^{20}$Na reaction. The latter bypasses the production of $^{19}$F observed in the ejected shells of oxygen-neon novae, and is further expected to play an important role in Type-I X-ray bursts during the "breakout" from the hot CNO cycles into a new set of thermonuclear reactions, known as the rp process.
In asymptotic giant branch (AGB) stars, 22Ne plays an important role in several nucleosynthesis processes, with its production competing with the synthesis of 19F through the so called ‘poisoning reaction’, and the following transfer into 25Mg acting as one of the main neutron sources for the s-process, affecting the reaction rates of numerous isotopes.
In this contribution, we present a preliminary look into a recent neutron transfer experiment done at TRIUMF in July 2017, studying the high-lying resonances of the 22Ne nucleus. Using TIGRESS, we can accurately determine these resonance energies, utilizing the precision of the HPGe detectors. Alongside this, we can use data taken simultaneously with the SHARC silicon detector to determine the spins for these resonances, and finally, apply Doppler shift attenuation method to constrain the lifetimes of resonances down to femtoseconds.
A striking example of quantum behaviour in the nucleus are the nuclear shells, analogous to the electron shell system in atomic physics, at well-known magic numbers of protons/neutrons. Nuclear shells can evolve with changing proton and neutron count as shown in the emergence of the N = 32 shell closure. This changing nuclear structure can directly affect nuclear properties like masses (separation energies) and half-lives. Investigations of neutron-rich 51-55V and 51-55Ti isotopes were performed at TRIUMF. Half-lives were measured with the ISAC Yield Station and high precision mass measurements were performed with TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN), employing for the first time the TITAN Multiple-Reflection Time-Of-Flight Mass Spectrometer (MR-TOF-MS). In the results, weak shell effects were observed in Ti isotopes. In this talk, these observed shell effects will be discussed in context of the evolution the N = 32 shell closure.
Half-lives of $N=82$ nuclei below doubly-magic $^{132}$Sn are key input parameters for calculations of any astrophysical $r$-process scenario and play an important role in the formation and shape of the second $r$-process abundance peak. In the past, shell-model calculations of neutron-rich nuclei near the $N=82$ neutron shell closure that are not yet experimentally accessible have been performed by adjusting the quenching of the Gamow-Teller (GT) operator to reproduce the $^{130}$Cd half-life reported in Ref. [1]. The calculated half-lives of other nuclei in the region are known to be systematically too long. Recently, a shorter half-life for $^{130}$Cd was reported [2,3]. A re-scaling of the GT quenching to the new $^{130}$Cd half-life by a constant factor for all nuclei in the region resolved the discrepancy. However, the reduced quenching of the GT operator creates a new discrepancy in the calculated half-life of $^{131}$In. The measurement of $^{131}$In is complicated due to the presence of three known $\beta$-decaying states with roughly the same half-life, making photopeak gating an ideal method to measure each of these half-lives. In this talk, the half-lives of $^{128-130}$Cd and $^{131}$In, as well as the spectroscopy of $^{131}$Sn, measured using the GRIFFIN $\gamma$-ray spectrometer at TRIUMF will be presented.
[1] M. Hannawald et al., Nucl. Phys. A 688, 578 (2001).
[2] R. Dunlop et al., Phys. Rev. C 93, 062801(R)
[3] G. Lorusso et al., Phys. Rev. Lett. 114, 192501 (2015).
Sic1 is a disordered kinase inhibitor, which must be phosphorylated on at least six sites to allow its recognition by the WD40 binding domain of the Cdc4 protein in the yeast cell cycle. The highly-cooperative, switch-like dependence on the number of phosphorylated sites on Sic1 cannot be accounted for by traditional thermodynamic models of cooperativity. We used single-molecule fluorescence techniques to study the dimensions and dynamics of Sic1’s N-terminal targeting region (residues 1-90, henceforth Sic1) and phosphorylated Sic1 (pSic1). A quantitative relationship between sequence properties and ensemble properties is a prerequisite for understanding IDP phosphorylation and its role in highly cooperative binding.
Single-molecule Fӧrster Resonance Energy Transfer (smFRET) data obtained for dye-labelled Sic1, pSic1, and the pSic1-WD40 complex were used to infer the dimensions of disordered ensembles for different states of Sic1. In a refinement to the conventional approaches for inferring IDP dimensions from smFRET experiments, we use distance distributions from Monte Carlo simulations, which extensively sample coarse-grained protein conformations. The application of polymer physics theory/simulations towards smFRET data interpretation, and towards IDP binding, contributes to the growing toolkit for understanding how IDPs function in the absence of a stable 3D structure.
The retina, with its neural tissue, also acts as a window on the brain. Alzheimer’s disease is currently only definitively diagnosed after death from an analysis of deposits of amyloid beta (plaques) in the brain. Retinal function has been reported to be directly affected by the disease and neurotoxic effects of amyloid beta have been demonstrated in the retina. We were one of the first groups to find amyloid deposits in association with neural cells in ex vivo retinas of those with Alzheimer's disease. Using Mueller matrix polarimetry, and taking 16 images as we rotate quarter wave plates with respect to linear polarizers within a polarization state generator and analyzer, we can identify the presence of the disease with high sensitivity and specificity without the use of a dye. A number of interactions of the deposits with polarized light differ from those of the surrounding tissue. One of the largest differences is in the birefringence of the amyloid deposits. This gives rise to relative retardation of two perpendicular linear polarizations and contrast in cross polarization. In our hands, polarization imaging of the retina provides a noninvasive, less expensive and simple method of detecting and tracking amyloid deposits. In addition, we have shown that the number of deposits can predict the severity of Alzheimer’s disease. Here we will describe the similarity of polarimetry measurements on pure amyloid beta and deposits in retinal tissue. We will then describe our intended instrument configuration for imaging these deposits in the living eye.
Alzheimer’s disease (AD) is a neurodegenerative disease characterized by dementia and memory loss for which no cure or prevention is available. Amyloid toxicity is a result of the non-specific interaction of toxic amyloid oligomers with the plasma membrane.
We studied amyloid aggregation and interaction of amyloid beta (1-42) peptide with lipid membrane using atomic force microscopy (AFM), Kelvin probe force microscopy and surface Plasmon resonance (SPR). Using AFM-based atomic force spectroscopy (AFS) we measured the binging forces between two single amyloid peptide molecules. Using AFM imaging we showed that oligomer and fibril formation is affected by surfaces, presence of metals and inhibitors. We demonstrated that lipid membrane plays an active role in amyloid binding and toxicity: changes in membrane composition and properties increase amyloid binding and toxicity. Effect of lipid composition, the presence of cholesterol and melatonin are discussed. We discovered that membrane cholesterol creates nanoscale electrostatic domains which induce preferential binding of amyloid peptide, while membrane melatonin reduces amyloid-membrane interactions, protecting the membrane from amyloid attack. Using AFS we that novel pseudo-peptide inhibitors effectively prevent amyloid-amyloid binding on a single molecule level, to prevent amyloid toxicity. These findings contribute to better understanding of the molecular mechanisms of Alzheimer's disease and aid to the developments of novel strategies for cure and prevention of AD.
References:
Counting photobleach steps lets us infer the number of oligomeric subunits of fluorescently-labelled protein complexes. While ad hoc step-counting algorithms are adequate for low noise imaging with small numbers of steps, noise increases with the number of fluorophores and introduces bias when the intensity trace is filtered to reduce noise. We present a principled Bayesian approach with a prior distribution that incorporates the statistics of photobleaching and that does not require filtering. Our physics-based prior leads to a simple and efficient numerical scheme for maximum a posteriori probability (MAP) estimates of the initial fluorophore number n0. We illustrate how experimental data can be used to calibrate the photophysics. Using simulated data where n0 is known, we show that the bias of our MAP estimate remains minimal as the number of fluorophores increase. We investigate how our errors scale with n0, with the signal-to-noise ratio (SNR), and with the cam- era exposure time t or, equivalently, the illumination intensity. We find that the dimensionless ratio of camera exposure time to the average time to the first bleach step controls the imprecision of the MAP estimation. Many short exposures are recommended with our approach.
Many hypotheses have been posed about the reasons why there are fewer women than men identified as physicists, although most have not been rigorously tested (and some could not be in an ethical way.) Over time these hypotheses have shifted in nature. I will use the Halpern, Wai and Saw (2005) psycho-bio-social framework for analyzing gender differences to review recent findings that shed light on reasons why we might find fewer women in our physics classrooms and laboratories. I will present suggestions from this body of research about measures we might take to address the gender gap in physics, should we choose to. Finally, I will highlight resources available from AAPT, APS, and AIP- and hope to learn more about the efforts of the CAP.
Phase-locked, few cycle pulses of THz light are powerful tools for both probing and controlling charge carriers in condensed matter. Used as time-resolved spectroscopic probes, meV scale excitations can be monitored with sub-picosecond temporal resolution. In this talk, I discuss recent multi-THz measurements on organometallic metal halide perovskites revealing exciton energetics, screening dynamics and the effects of strong spin-orbit interactions. In addition to probing dynamics, strong field THz pulses can be used to control the motion of charged particles on sub-cycle time scales. I will discuss our recent work on sub-cycle THz field emission of femtosecond electron wavepackets from metal nanotips. Electrons are accelerated in the local THz fields to keV energies with femtoCoulomb bunch charges, a step towards a light field-driven ultrafast electron microscope. Finally, a new method for arbitrarily shaping THz fields in time will be presented, based on an optically addressable dynamic waveguide. The ability to create multiple pulse sequences from a single THz pulse opens the door to advanced forms of multi-dimensional THz spectroscopy.
The ability to directly probe ultrafast phenomena on the nanoscale is essential to our understanding of excitation dynamics on surfaces and in nanomaterials. Recently, a new ultrafast scanning tunneling microscope (STM) technique that couples terahertz (THz) pulses to the scanning probe tip of an STM was demonstrated (THz-STM), showing photoexcitation dynamics of a single InAs nanodot with simultaneous 0.5 ps time resolution and 2 nm spatial resolution under ambient conditions. Operation of THz-STM in ultrahigh vacuum now makes it possible to spatially-resolve subpicosecond dynamics of single molecules and silicon surfaces with atomic precision. This talk will discuss how THz-STM works and how it can provide new insight into ultrafast dynamics on the atomic scale, which is essential for the development of novel silicon nanoelectronics and molecular-scale devices operating at terahertz frequencies.
Research into organo-halide perovskites has flourished due to their unprecedented success as an absorbing layer in solution processed solar cells. Theoretical studies have shown these materials exhibit intriguing optical properties such as large spin-orbit coupling, photo-induced magnetization, and spin-dependent optical Stark effect, leading to potential spintronic applications. However; very few spin-related experimental studies have been reported. Here we report circular-polarized pump-probe studies of the 2D perovskite butylammonium methylammonium lead iodide. These results indicate a strong influence of Rashba spin-splitting on the carrier kinetics, consistent with our recent four-wave mixing studies of bulk $\text{CH}_3\text{NH}_3\text{PbI}_3$.
Solar cells based on CH3NH3PbI3 (MAPI) have reached efficiencies comparable to the best polycrystalline silicon solar cells in just 9 short years [1]. Despite the unparalleled increase in efficiency, the fundamental photo physical properties in this archetypical perovskite material system are not yet well understood. In order to further optimize device performance, it is essential to determine the fundamental processes that govern carrier generation, and transport. Here we have utilized four-wave mixing spectroscopy to study the optical response of MAPI thin films with excitation densities comparable to solar cell operating conditions, revealing weaker carrier-carrier and exciton-carrier scattering in the perovskite system compared to GaAs [2], exciton binding energies for bound and unbound excitons in the low temperature phase [3], and a measurement of the carrier diffusion length at room temperature by implementing the transient grating four-wave mixing technique [4].
References
[1] http://www.nrel.gov./ncpv/images/efficiency_chart.jpg.
[2] S. A. March, C. Clegg, D. B. Riley, D. Webber,, I. G. Hill, and K. C. Hall, Simultaneous observation offree and defect-bound excitons in CH3NH3PbI3 using four-wave mixing spectroscopy, Scientific Reports 6, 39139 (2016)
[3] S. A. March, DB Riley, C Clegg, D Webber, X Liu, M Dobrowolska, Jacek K Furdyna, Ian G Hill, Kimberley C Hall, Four-wave mixing in perovskite photovoltaic materials reveals long dephasing times and weaker many-body interactions than GaAs, ACS Photonics 4 (6), 1515-1521 (2017)
[4] D. Webber, C. Clegg, A. W. Mason, S. A. March, I. G. Hill, K. C. Hall, Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing, Applied Physics Letters 111 (12), 121905 (2017)
This presentation will discuss Hydro-Quebec’s historical records and observations of geomagnetic disturbance. We will show how data/forecasts are used and integrated in control room operation. A real event will be presented in detail. Looking at the future, we will illustrate some gaps and research needs. The main idea of the presentation is that electricity provides relevant feedbacks to space weather physics.
La présentation discutera des perturbations géomagnétiques historiques enregistrées et observées à Hydro-Québec. Nous montrerons comment les données/prévisions sont intégrées dans les opérations du centre de contrôle. Un événement réel sera présenté en détails. Au niveau du futur, nous illustrerons des pistes de recherche à combler. L’idée majeure de la présentation est que l’électricité fournit des informations pertinentes sur la physique de la météorologie spatiale.
Bursts of enhanced electron density in the ionospheric D-region due to photoionization by X-ray radiation from solar X-ray flares leads to a fadeout of short wave signals, potentially causing a loss of high frequency radio communication in affected regions. D-region absorption is typically monitored using riometer instruments which typically operate at 30 MHz. There are well established relationships for modelling the absorption anticipated during a SWF event based on the energetic electron flux. These relationships are examined using the Natural Resources Canada riometer network which provides a unique opportunity to study SWF over a wide spread in latitude (45.4° to 82.5°) for a 90° band of longitude. Based on observations from an event on 11 March 2015, current methods for modelling SWF are shown to severely underestimate absorption. We devise an improved SWF model which corrects this underestimation. Improved modelling provides a better estimate of the peak absorption and its duration above threshold levels anticipated to impact HF radio communication.
In this study, we begin by presenting an overview of the methodology behind existing empirical ionospheric electron density models, including the E-CHAIM and International Reference Ionosphere (IRI). Several limitations have been identified in the methodology used to parameterize the IRI (Themens et al., 2014, 2016, and 2017a), particularly in its application at high latitudes. Using these validation studies to inform the approach used in E-CHAIM, we managed to avoid several of the IRI’s short comings and have demonstrated substantial quantitative improvements in performance over the IRI (Themens et al., 2017b, and 2018). We will here explore those improvements and examine the limits of empirical approaches in their ability to represent “weather-like” time scales. To this end, we have manual scaled a year of ionosonde data from several Canadian High Arctic Ionospheric Network (CHAIN) ionosondes and will assess the representativeness of climatologies at high latitudes. In so doing, we will demonstrate that, while empirical models struggle appreciably in the representation of smaller time scales (two hours or less), it is well within their capacity to capture variabilities on 2-7 day timescales using measured geomagnetic indices as drivers. We also demonstrate that in the absence of a storm-time correction, empirical models may exhibit biases in their representation of monthly median variability at high latitudes due to the dominance of negative storm responses in these regions.
SuperCDMS SNOLAB is a dark matter experiment currently under
construction and slated for installation in SNOLAB in 2019. SuperCDMS
SNOLAB will use cryogenic silicon and germanium detectors to search
for nuclear recoils produced by dark matter particles interacting in
the detectors. These nuclear recoils will produce both phonon
excitations and ionization (electron/hole pairs) in the detector,
which can be read out by sensitive elements on the surface of the
detector. Applying a voltage across the detector can amplify the
ionization signal into a large phonon signal through the conversion of
the charge carriers' kinetic energies into phonon vibrations, greatly
lowering the energy threshold of the experiment. This low energy
threshold will give SuperCDMS SNOLAB world-leading sensitivity for
dark matter particles with masses below ~10 GeV/c^2. SuperCDMS SNOLAB
can also search for hypothesized dark photons that produce electrons
in the detectors through an analog of the photoelectric effect. In
this talk I will review the scientific program of SuperCDMS SNOLAB,
its current status, and the latest science results from this unique
detection technology.
In 2024 the Large Hadron Collider at CERN will enter its High Luminosity phase, which will see its instantaneous luminosity reach seven times its design value and will produce pp collisions at 14 TeV with an average of 200 interactions per bunch crossing.
These challenging conditions are beyond the ATLAS design and require an upgrade of the ATLAS tracking system. The ATLAS new Inner Tracker (ITk) will be an all-silicon tracking detector composed of pixel and strip sensors arranged in barrel and end-cap discs.
ATLAS Canada is participating as a whole in the building process of the ITk strip end-cap discs.
As we move towards the production phase of the ITk, a lot of effort has been put in the designing, prototyping and testing of the ITk components.
This talk presents the ITk activities involving the SFU, TRIUMF and UBC ATLAS groups, focusing on the building of the modules, the loading on the supporting structures, the electrical tests and the data taking at testbeam facilities.
The High-Energy Light-Ion eXperiment (HELIX) is designed to measure the
fluxes of light cosmic-ray nuclei at energies of a few GeV per nucleon.
The primary goal is to study the evolution of the ratio of Be-10
to Be-9 between 0.2 GeV/n and 3 GeV/n. The former is a radioactive 'clock
isotope' while the latter is stable, so the ratio contains information about
how far and through what the cosmic rays have been propagating. Better
knowledge of our local environment within the Galaxy has become important
in understanding the increase with energy of the positron flux seen in
new data from the AMS-02 detector installed on the International Space
Station. Is it from dark-matter annihilation or from more conventional
astrophysical phenenomena?
HELIX is a balloon-borne detector based on a 1 T superconducting solenoid.
A drift chamber will be used to measure particle momenta while time-of-flight
counters will determine the velocities at low energies. At higher energies
a ring-imaging Cherenkov counter based on aerogel tiles and silicon
photomultipliers will take over. A 14-day circumpolar flight launched
from McMurdo Station on the coast of Antarctica has been scheduled for
the 2019/20 season.
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 data taking.
Computed Tomography (CT) is considered a mature technology as it did not change significantly since the advent of multislice devices (2000s) and helical acquisitions (1990s). However, innovations in CT are still happening. After a brief history of CT, the evolution of this imaging modality during the last few years will be reviewed from technological, social and medical perspectives. On the technological front, CT can nowadays rely on unprecedented computing power, allowing the execution of advanced reconstruction algorithms in a reasonable time. Massively parallel Graphics Processing Units (GPUs), for instance, allow the used of complex physical models in iterative reconstruction schemes. These approaches can yield better images acquired at lower patient doses. From a health physics perspective, the steadily increasing number of CT studies performed each year has drawn the attention of the media and radiation safety authorities. CT manufacturers, well aware of this situation, nowadays propose technologies aiming at reducing the radiation dose to the patient. These technologies will be reviewed and discussed. From a medical perspective, CT nowadays allow new applications thanks to technological developments. The case of dual-energy imaging will be reviewed and discussed. Finally, current research avenues in CT will be reviewed, from technological and medical perspectives.
As part of the 2018 Congress for the Canadian Association of Physicists (CAP), the Division of Physics in Medicine and Biology (DPMB) is hosting a "DPMB 101" session. The purpose is to present "primer" talks that provide an overview of salient topics broadly relevant to the meeting. The intended audience is expected to be diverse, ranging from the relative novice (e.g., a curious undergraduate or graduate student) to experts. This particular talk will focus on the notion of biological transport, chiefly the concepts of diffusion and the movement of charged particles across cell membranes. Specific topics include: Fick's law, ensembles of random walkers, derivation of the diffusion equation, the Nernst-Plank equation, steady-state electrodiffusion, the generation of the membrane resting potential, circuit models for the cell membrane, and the Hodgkin-Huxley model for action potentials in neurons.
TRIUMF’s Ion Trap for Atomic and Nuclear science (TITAN) is located at the Isotope Separator and Accelerator (ISAC) facility, Vancouver. Titan is a multiple ion trap system capable of performing high-precision mass measurements and in-trap decay spectroscopy. In particular TITAN has specialised in fast Penning trap mass spectrometry of short-lived exotic nuclei using its Measurement Penning Trap (MPET). In order to reach the highest possible precision, ions can be charge bred into higher charge states by an Electron Beam Ion Trap (EBIT), reducing the required excitation time for a needed precision. Thus using highly charged ions, TITAN is capable of performing mass measurements of short lived heavy species with high precision. Although ISAC can deliver high yields for some of the most exotic species, many measurements suffer from a strong isobaric background. This background often prevents the high precision measurement of the exotic species of interest. To overcome this limitation an isobar separator based on the Multiple-Reflection Time-Of-Flight Mass Spectrometry (MR-TOF-MS) technique has been installed recently at TITAN, similar to other ion trap on-line facilities. At TITAN the mass selection is achieved using dynamic re-trapping of the species of interest after a time-of-flight analysis in an electrostatic isochronous reflector system. Additionally the MR-TOF-MS enables mass measurements of very short-lived nuclides that are weakly produced, complementing TITAN’s existing mass measurement program of short-lived exotic nuclei.
In this way TITAN is able to expand its mass measurements towards even more exotic isotopes produced at very low production yields. Results from recent high-precision mass measurements of super-allowed beta decays emitters, as well as mass measurements for nuclear structure and nuclear astrophysics will be shown employing singly and highly charged ions with MPET and the new MR-TOF-MS.
Shape coexistence is associated with nuclear deformations at low excitation energies and has been a topic of extensive research in nuclear physics over the past 60 years. Shape coexistence is driven by two opposing forces. One is the stabilizing effect of closed shells causing the nucleus to have a spherical shape, while the other is the residual interaction between proton and neutrons, the correlation energy gain, in which the proton-neutron interaction energy is a major contribution [1]. A region of particular interest is the neutron deficient Hg isotopes, which is a well-known region of shape coexistence. A large isotope shift in the neutron deficient Hg isotopes was reported in the 1970's and is interpreted as differently shaped potentials along the isotopic chain causing differences in deformation [2]. Using the high efficiency GRIFFIN spectrometer, a detailed study of the excited states populated in $^{188}$Hg following the $\beta^{+}$/EC decay of $^{188}$Tl was preformed as part of an experimental campaign to help further a comprehensive understanding of nuclear structure evolution in this region.
[1] Kris Heyde and John L. Wood. Shape coexistence in atomic nuclei. Rev. Mod. Phys., 83, 1467-1521, Nov 2011.
[2] J. Bohn et. al.. Sudden change in the nuclear charge distribution of very light mercury isotopes. Physics Letters B, 38, 308 – 311, 1972.
The neutron-rich Cadmium isotopes around the well-known magic numbers at $Z=50$ and $N=82$ are prime candidates to study the evolving shell structure observed in exotic nuclei. Additionally, the extra binding energy observed around the nearby doubly-magic $^{132}$Sn has direct correlations in astrophysical models, leading to the second r-process abundance peak at $A\approx130$ and the corresponding waiting-point nuclei around $N=82$. The $\beta$-decay of the $N=82$ isotope $^{130}$Cd into $^{130}$In was first studied a decade ago [1], but the information for states of the lighter indium isotope ($^{128}$In) is still limited. Detailed $\beta\gamma$-spectroscopy of $^{128}$Cd was accomplished using the GRIFFIN [2] facility at TRIUMF, which is capable of performing spectroscopy down to rates of 0.1 pps.
The ongoing analysis of the $^{128,131,132}$Cd will be presented. Already in
$^{128}$Cd, 28 new transitions and 11 new states have been observed in addition to the 4 previously observed excited states [3]. These new results are compared with recent Shell Model calculations. For $^{131}$Cd, results will be compared with the recent EURICA data. These data highlight the unique capabilities of GRIFFIN for decay spectroscopy on the most exotic, short-lived isotopes, and the necessity to re-investigate even "well-known" decay schemes for missing transitions.
[1] I. Dillmann $et \ al.$, Phys. Rev. Let. 91, 162503 (2003)
[2] C.E. Svensson and A.B. Garnsworthy, Hyperfine Int. 225, 127 (2014)
[3] B. Fogelberg, Proc. Intern. Conf. Nuclear Data for Science and Technology, Mito, Japan, p.837 (1988)
High precision measurements of the $\mathcal{F}t$ values for superallowed Fermi beta transitions between $J^\pi = 0^+$ and isospin $T=1$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the Conserved-Vector-Current hypothesis, the most precise determination of the up-down element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, $V_{ud}$, and set stringent limits on the existence of scalar currents in the weak interaction. In order to use the superallowed decays to perform such tests, however, several theoretical corrections must be applied to the experimental data. In particular, many studies of the isospin symmetry breaking correction, $\delta_C$, have been performed with large model dependent variations. Precise experimental determinations of the $ft$ values can be used to help constrain the different models used in the calculation of $\delta_C$.
The uncertainty in the $^{22}$Mg superallowed $\mathcal{F}t$ value is dominated by the uncertainty in the experimental $ft$ value. Prior to this work, the adopted half-life of $^{22}$Mg was dominated by a single high-precision measurement ($T_{1/2} = 3.8755\pm0.0012$ s [1]) which disagrees with the only other, and less precise, measurement ($T_{1/2} = 3.857\pm0.009$ s [2]) which yielded a $\chi^2/\nu = 4.0$ and resulted in the inflation of the weighted-average half-life by a factor of 2. The discrepancy between these two measurements was addressed through a high-precision half-life measurement for $^{22}$Mg which was carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) facility. This experiment was performed using a 4$\pi$ continuous-flow gas proportional counter to detect the $\beta$ particles with near 100\% efficiency. The result of $T_{1/2} = 3.87400 \pm 0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published $^{22}$Mg half-life measurements [3]. In this presentation, the new high-precision half-life measurement for $^{22}$Mg and its implications for testing the isospin symmetry breaking corrections in superallowed Fermi $\beta$ decays will be discussed.
[1] J. C. Hardy et al., Phys. Rev. Lett. 91, 082501 (2003).
[2] J. C. Hardy et al., Nucl. Phys. A 246, 61 (1975).
[3] M. R. Dunlop et al., Phys. Rev. C 96, 045502 (2017).
Charge radius is an important bulk property of the nucleus for investigating nuclear structure. The nuclei lying close to the boundaries of the nuclear chart (the drip lines) have revealed new features like halo and skin. Another new phenomenon that has emerged in the neutron-rich region is the changing or vanishing of magic numbers [1,2]. The knowledge of proton radii is crucial for understanding the halo and skin formation and also the shell evolution in unstable nuclei. The systematic study of proton radii along an isotope chain, together with knowledge of the matter radii is important to deduce the neutron skin thickness in the neutron-rich nuclei. Furthermore, the proton radii are crucial to understand the spatial correlation between halo neutrons and its core nucleus. Proton radii also serve as a test of newly developed structure models including those based on $ab$ $initio$ theory. Charge-changing cross section ($\sigma_{cc}$) is the total cross section for the change of the atomic number of the projectile nucleus. It is a new method to extract the proton radii of neutron-rich nuclei using the Glauber model analysis. The proton radii of \textsuperscript{12-17}B [3] and \textsuperscript{12-19}C [4] have been successfully determined using the charge-changing cross section measurements. The neutron-rich oxygen isotopes are particularly interesting nuclei, with a new magic number (N=16) at the neutron drip line [5]. The proton radii of neutron-rich oxygen isotopes have not been measured til date. We, therefore, performed an experiment at Fragment Separator (FRS) in Germany using relativistic beams of \textsuperscript{16-24}O with energy around 900 MeV/u. In this talk, I will present the preliminary results of $\sigma_{cc}$ measurements of \textsuperscript{16-24}O.
References
[1] A. Ozawa et al., Phys. Rev. Lett. 84, 5493 (2000).
[2] R. Kanungo et al., Phys. Lett. B 528, 58 (2002).
[3] A. Estrade ́ et al., Phys. Rev. Lett. 113, 132501 (2014).
[4] R. Kanungo et al. Phys. Rev. Lett. 117, 102501 (2016).
[5] C. R. Hoffman et al., Phys. Rev. Lett. 100, 152502 (2008).
Representation of women and racialized people in Canadian/US physics is still disappointingly low. In this session, panellists will discuss why it is important to address both of these problems together rather than separately. How can we best challenge myths about excellence, foster a culture of equity/diversity/inclusion (EDI) work being done by everyone, learn how to mentor younger physicists different from us, and negotiate EDI controversies on campus/in the workplace? There will be an audience Q&A at the end.
Many biological processes in cells are complex yet sparsely characterized. Constructing physical models of such systems then often requires making many assumptions based on guesswork. Instead of ignoring or guessing unknown details in complex processes we have derived universal balance relations to rigorously characterize stochastic fluctuations in incompletely specified systems. Specifying some features of a system while leaving everything else unspecified then allows us to establish physical performance bounds for classes of intracellular processes. Additionally, we can turn general network invariants into experimental data analysis tools. For example, exploiting naturally occurring cell-to-cell variability allowed us to test specific hypotheses about gene expression, showing that observed fluctuations in E. coli contradict the majority of published models of stochastic gene expression.
The development of drug resistance is a serious problem that reduces therapeutic susceptibility and complicates the treatment of infectious disease and cancer. To explore non-genetic causes of spontaneous drug resistance in rapidly proliferating cell populations, we constructed a set of synthetic transcriptional regulatory networks in yeast Saccharomyces cerevisiae to control the expression of the pleiotropic drug resistance gene PDR5. This gene is a conserved homologue of a human multidrug resistance gene (MDR1) that protects cells from many first line chemotherapies and implicated in the development of drug resistant cancers. For this reason, we hypothesized that transcriptional regulation may contribute to drug resistance and examined how certain transcriptional regulatory network features, or motifs, contribute to cell survival in the presence of a cytotoxic drug. Our results reveal that the coherent feedforward motif can enhance cell survival in the presence of the drug by allowing rapid and prolonged activation of gene expression, and that combining coherent feedforward and positive feedback motifs leads to increased drug resistance. These observations provide direct evidence that certain gene network motifs cause reduced susceptibility to drug treatment and underscore the importance of regulatory network interactions in the development of non-genetic drug resistance.
Human aging leads to the stochastic accumulation of damage. We model an aging population using a stochastic network model. Individuals are modeled as a network of interacting nodes, representing health attributes. Nodes in the network stochastically damage and repair, with rates dependent on the state of their neighbors. Damaged nodes represent health deficits. Overall damage in the network is measured with the Frailty Index (FI), a quantitative measure of deficit accumulation used in observational studies of aging to assess health and predict mortality. We use our understanding of the mechanisms of aging in our model to understand observational health data where the mechanisms are unknown. With stochastic simulations and mean-field theory we show how the underlying network structure controls the behaviour of the FI and how damage propagates within the network, leading to individual mortality.
Dendrites are often excitable structures involved in the signal processing of almost all neurons.
We find that when an active dendrite has a greater intrinsic variability and a longer refractory period
than the soma, it will determine spike times for weak inputs but be entrained by somatic spikes for
strong inputs. This produces an input-dependent gating of dendritic noise. As a result, populations
of dendrite-soma systems improve transmission of sub- and suprathreshold signals for a large range
of intrinsic dendritic noise. This novel mechanism suggests a functional role for active dendrites.
link.aps.org/pdf/10.1103/PhysRevX.7.031045
It is well-known that the atmosphere in the polar regions of this planet is considerably different from the more temperate regions due to a variety of factors including the planetary rotation, the magnetic field and the fact that the extreme polar regions undergo an annual cycle of light and darkness which overwhelms the 24-hour cycle that characterises the lower latitudes.
For the last decade a group of university and government researchers operating as an informal group called the Canadian Network for the Detection of Atmospheric Change (CANDAC) have operated a year-round observatory at Eureka, Nunavut on the 80N latitude line. This observatory has been dubbed the Polar Environment Atmospheric Research Laboratory (PEARL).
Research at PEARL spans the atmosphere from the surface at about 100km and teams from many Canadian universities as well as international groups are engaged in research at the site.
One talk cannot suffice to show the entire range of the research currently underway at PEARL and so highlights, perhaps of more interest to a physics community, will be presented along with some account of the history and speculation about the future of research at PEARL.
PEARL is currently supported by Natural Sciences and Engineering Research Council (NSERC), Environment and Climate Change Canada (ECCC) and the Canadian Space Agency.
Observations of aerosol scattering and absorption offer valuable information about aerosol composition. We apply a simulation of the Ultraviolet Aerosol Index (UVAI), a method of detecting aerosol absorption from satellite observations, to interpret UVAI values observed by the Ozone Monitoring Instrument (OMI) over 2005–2015 to understand global trends in aerosol composition. We conduct our simulation using the vector radiative transfer model VLIDORT with aerosol fields from the global chemical transport model GEOS-Chem. We examine the 2005–2015 trends in individual aerosol species from GEOS-Chem, and apply these trends to the UVAI simulation to calculate the change in simulated UVAI due to the trends in individual aerosol species. We find that global trends in the UVAI are largely explained by trends in absorption by mineral dust, absorption by brown carbon, and scattering by secondary inorganic aerosol. Trends in absorption by mineral dust dominate the simulated UVAI trends over North Africa, the Middle-East, East Asia, and Australia. The UVAI simulation well resolves observed negative UVAI trends over Australia, but underestimates positive UVAI trends over North Africa and Central Asia near the Aral Sea, and underestimates negative UVAI trends over East Asia. We find evidence of an increasing dust source from the desiccating Aral Sea, that may not be well represented by the current generation of models. Trends in absorption by brown carbon dominate the simulated UVAI trends over biomass burning regions. The UVAI simulation reproduces observed negative trends over central South America and West Africa, but underestimates observed UVAI trends over boreal forests. Trends in scattering by secondary inorganic aerosol dominate the simulated UVAI trends over the eastern United States and eastern India. The UVAI simulation slightly overestimates the observed positive UVAI trends over the eastern United States, and underestimates the observed negative UVAI trends over India. Quantitative simulation of the OMI UVAI offers new insight into global trends in aerosol composition.
Accurate characterization of the ionosphere in response to thunderstorms has important implications for the effective use of high frequency (HF) communications in civilian and military operations, to include emergency services, amateur radio, aviation, and over-the-horizon radar. This study investigates changes in the structure of the ionosphere due to strong convective activity and cloud electrification associated with thunderstorms over North America. Superposed Epoch Analysis (SEA) is applied to surface weather observations and ionosonde data at Eglin Air Force Base, Boulder, and Millstone Hill from 2010 to 2017. Initial findings indicate that lightning significantly modifies the structure of the ionosphere, generating statistically different measurements of several key parameters compared to clear-sky observations. The influence of seasonal and diurnal variations is also presented. Results of this research may eventually lead to the development of a parameterization scheme to incorporate thunderstorm and cloud electrification effects into global and regional ionosphere models. Because troposphere-ionosphere coupling has been poorly addressed, analysis of the electrodynamic connection between the lower and upper atmospheres has important implications for both space physics and atmospheric science communities.
Fog reduces visibility, causing delays in transportation by land, sea and air. It is also a safety hazard that results in accidents and sometimes even death. Like cloud droplets, fog droplets form on cloud condensation nuclei, existing aerosol particles in the atmosphere that have the ability to activate into droplets. As such, fog droplets provide a unique, in situ method of studying the process of aerosol activation. The interactions between aerosols and water vapour can determine the formation and persistence of fog, which makes fog forecasting challenging. Current parameterizations within models suffer notably from unresolved microphysical problems such as neglecting droplet concentration, which leads to large errors in droplet density predictions and therefore visibility. This study presents results from fog studies conducted on the eastern coast of Canada in Nova Scotia. Observations of aerosol size distributions and chemical composition were conducted using a ground-based counter flow virtual impactor, which allowed the droplet residuals to be measured directly. Fog droplet size distributions, visibility and other meteorological variables were also measured at the same time. Aerosol and droplet microphysical parameters will be presented including the influence of air mass history. Preliminary results show that aerosol growth may be contributing to the dissipation of fog under some conditions, suggesting that despite the importance of atmospheric dynamics on fog formation and dissipation, aerosols can also play an important role in the life cycle of fog.
The proposed ionising influence of cosmic rays on atmospheric aerosols, clouds and atmospheric electrical properties has resulted in several attempts to obtain convincing correlations. Several theoretical studies on such possible indirect influence is still poorly understood while the observational evidence remains controversial and incomplete. This study examines the Heliospheric-Magnetospheric-Atmospheric responses during a recent fortuitous cosmic rays Forbush decrease (FD) that occurred on 16-17 July 2017. The varied instrumentation located on SANAE IV in Antarctica provided us an opportunity to test the different theories applied to cosmic ray influence. Various ground based instruments located in South Africa, belonging to South Africa National Space agency, are used to coordinate FD-atmospheric connection hypothesis. A synthesis of multiple observations indicates that there is a plausible link between cosmic ray ionisation and polar aerosols, but clouds.
We find the explicit form of two-point functions for the conformal energy momentum operators as well as conformal spin-one operators on the near horizon of a near extremal Kerr black hole. We introduce the appropriate boundary actions for the spin-two and the vector fields near the horizon of near extremal Kerr black hole. We find the two-point function for the conformal energy-momentum operators and the spin-one operators in Kerr/CFT correspondence by finding the variation of the proper boundary actions. We find agreement between the two-point functions and the correlators of the dual conformal field theory to the Kerr black hole.
One of the more intriguing solutions of General Relativity is the C-metric, which can be interpreted as describing the spacetime of an accelerating black hole. Little is known about the thermodynamics of these objects. Here I present a consistent formulation of the thermodynamics of accelerated black holes, resolving inconsistencies and discrepancies that have appeared in previous investigations of this subject. Their thermodynamic volume obeys the reverse isoperimetric inequality for all values of the parameters. The dual stress-energy tensor for the spacetime corresponds to a relativistic fluid with a non-trivial viscous shear tensor.
We present a no-hair theorem for spherical black holes in scalar-tensor gravity. Contrary to the existing theorems, which are all proved in the Einstein conformal frame, this proof is performed entirely in the Jordan frame. The theorem is limited to spherical symmetry (instead of axisymmetry), but it holds for non-constant Brans-Dicke coupling.
[Based on V. Faraoni, Phys. Rev. D 95, 124013 (2017)]
Brans-Dicke gravity, enriched by the possibility of an arbitrary potential V (ϕ) for the Brans-Dicke scalar field, and in the presence of conformally invariant matter admits a 1-parameter symmetry group. We explore the use of these symmetries as a solution-generating technique using known solutions as seeds. We apply this technique to generate, as examples, new spatially homogeneous and isotropic cosmologies, a 3-parameter family of spherical and time-dependent spacetimes conformal to a Campanelli-Lousto geometry, and a new family of cylindrically symmetric geometries
In the context of black hole chemistry, we study the thermodynamics of asymptotically de Sitter black holes with conformal scalar hair in Einstein gravity. The hair parameter allows us to reach thermodynamic equilibrium between the event horizon and the cosmological horizon. We find that the system of the black hole and the de Sitter space surrounding it undergo a phase transition that resembles the Hawking-Page phase transition provided we consider the micro-canonical ensemble.
The QWeak collaboration completed a two year long, high precision measurement of the parity violating asymmetry in the elastic scattering of 1.1 GeV, longitudinally polarized electrons from protons. At low momentum transfer the measured asymmetry is directly related to the Weak charge of the proton $Q^p_W = 1 - 4 sin^2 \theta_W$. The Standard Model makes a firm prediction for the size of the Weak charge, based on the "running" of the Weak mixing angle $sin^2\theta_W$, away from the $Z^0$-pole, toward lower energies. The QWeak measurement provides a sensitive test for new physics beyond the Standard Model, with a mass scale sensitivity up $\Lambda/g = 7.5$ TeV. I will provide an overview of the experiment, including the measurement methodology and associated systematic effects. I will then present our final results for the proton Weak charge, the Weak mixing angle, and an extraction of the vector Weak quark couplings $C_{1u}$ and $C_{1d}$, using a combination of the $^{133}Cs$ APV and QWeak measurements. I will also discuss the QWeak mass reach for new beyond-the-Standard-Model physics and briefly discuss our sensitivity to a few models.
The proton radius puzzle is the difference between the radius of the proton as measured with electron scattering and atomic hydrogen spectroscopy, and that measured in muonic hydrogen. In 2010, the CREMA Collaboration published their measurement of the proton radius $R_p=0.8409(4)$ fm, which was made by studying the Lamb shift in muonic hydrogen. Although ten times more precise than the 2010 PDG value of $R_p=(0.877 \pm 0.007)$ fm, the CREMA result is completely incompatible with it. Until that point, the PDG value had been in good agreement with both scattering and spectroscopy results.
Since 2010, there have been many theoretical and experimental efforts to try to resolve the puzzle: the CREMA collaboration have made a series of measurements in light nuclei, the PRad experiment at JLab and Intial State Radiation experiment in Mainz have sought to measure the radius at lower momentum transfer, there have been efforts at the Max Planck Institute for Quantum Optics in Munich to re-measure the hydrogen spectroscopy lines, and meanwhile many theorists have been trying to analyze the issue from multiple perspectives. A future experiment on Muon Scattering has also been funded by NSF and is under construction (the MUon proton Scattering Experiment, MUSE).
We will review the current status of the Proton Radius Puzzle, and give an overview of the ongoing efforts to resolve the puzzle.
The precise measurement of the 1S-2S transition in atomic hydrogen via 2-photon spectroscopy determines the value of the Rydberg and constrains our knowledge of the fundamental constants. The prospect of such a measurement in antihydrogen to test CPT motivated the construction two decades ago of the CERN AD and its initial program . The ALPHA collaboration has now measured this transition in antihydrogen with a precision of a few parts per trillion. Its comparison with the hydrogen value is a strong test of CPT symmetry. This talk will discuss the considerable challenges we were faced with, both in the production of the antihydrogen and in spectroscopy in the environment containing the trapped particles. Prospects for improved precision will be presented.
$^2$ALPHA collaboration http://alpha-new.web.cern.ch: M. Ahmadi, B.X.R Alves, C.J.Baker, W. Bertsche, A. Capra, C. Carruth, C.L. Cesar, M. Charlton, S. Cohen, S. Eriksson, A.L. Evans, N. Evetts, A. Evans, J. Fajans, T. Friesen, M.C. Fujiwara, D.R. Gill, J.S. Hangst, W.N. Hardy, M.E. Hayden,, C.A. Isaac, M.A. Johnson, J.M. Jones, S.A. Jones, S. Jonsell, A. Khramov, P. Knapp, L. Kurchaninov, N. Madsen, D. Maxwell, J.T.K. McKenna, S. Menary, T. Momose, J.J. Munich, K. Olchanski, A. Olin, P. Pusa, C. Ø. Rasmussen, F. Robicheaux, R.L. Sacramento, M. Sameed, E. Sarid, D.M. Silveira, C. So, T. D. Tharp. R.I. Thompson, D.P. van der Werf, J.S. Wurtele.
The weight of antimatter is a crucial missing measurement in our picture of the natural world. It is important in two ways: 1. The predominance of matter created in the Big Bang demands some form of mismatch in properties between matter and antimatter. Many experiments have sensitively compared their charge, magnetic moment, nuclear bonding and decay behaviour, yet no significant mismatch has been found to date to explain the cosmic matter dominance. One of the last unexplored domains is gravitational behaviour. 2. Our understanding of the subatomic world is wholly incompatible with General Relativity, the dominant phenomenon on astronomical scales. New ideas on a unified theory on atomic and gravitational interactions may require antimatter to respond uniquely to gravity. Measuring such behaviour experimentally will provide vital evidence to accept or reject these ideas, and further the development of a unified view of nature.
Experimentally, weighing antimatter has been difficult because electrical influences on the charged, energetic antiparticles commonly created in accelerators massively overwhelm their gravitational response. Their short life in these machines also leaves no time for observation. The antihydrogen trapping technology developed by the world-leading ALPHA collaboration has, however, completely altered this picture, by generating antimatter that has low energy, long lifetime and immunity to electric forces. The new ALPHA-g experiment is designed to leverage this new technology, and weigh antimatter by letting antiatoms escape through the bottom and top of a tall magnetic confinement system. By precisely controlling the magnetic field of the openings, the escape bias induced by gravity can infer antihydrogen weight to within 1%. This constitutes the most sensitive antimatter gravity measurement ever made, and a significant breakthrough in subatomic and fundamental physics. Its results have potential to revolutionise our understanding of matter and antimatter, natural forces and the process of creation.
In this presentation, we outline the basic principles and experimental design of the ALPHA-g experiment, with emphasis on technical challenges involved in the experiment.
We report direct spectroscopic evidence of correlations between monopoles in a quantum spin ice. A hierarchy of unequally spaced magnetic excitations has been observed via low energy inelastic neutron spectroscopy in Pr2Sn2O7, resembling the confinement of spin defects in low-dimensional quantum magnets.[1],[2] Using a simple linear potential model to fit the excitations, we have estimated the monopole pair creation energy, and calculated a lower bound for the tension between monopole-like quasiparticles. The linear potential model provides a natural explanation as to why detection of these correlations have been so elusive in the canonical dipolar spin ices. This is the first spectroscopic measurement of an effective “Dirac string” between magnetic monopoles.
References
[1] P. M. Sarte et al 2017 Journal of Physics: Condensed Matter Vol. 29, 45LT01.
[2] P. M. Sarte et al 2018, submitted to Physical Review Letters.
Chiral interactions in magnetic materials are unique in their ability to stabilize static magnetic solitons, known as skyrmions. At surfaces and interfaces, the chiral interaction results in novel magnetic surface states [1]. These surface twists help to further stabilize skyrmions in thin films [2], together with the influence of epitaxy induced magnetocrystalline anisotropy. These interactions play a crucial role in determining the observed magnetic textures, and lead to dramatically different behaviour in films as compared to bulk crystals.
The magnetic structure of MnSi thin films has been highly controversial. Our group was the first to report in-plane skyrmions [4], and the suppression of skyrmions out of plane [5], in contrast to reports from other groups. To resolve the controversy, we measured the magnetic structure of the in-plane skyrmions in epitaxial MnSi/Si(111) thin films, probed in three dimensions by the combination of polarized neutron reflectometry (PNR) and small angle neutron scattering (SANS) [6]. We demonstrate that skyrmions exist in a region of the phase diagram above a temperature of 10 K. PNR shows the skyrmions are confined to the middle of the film due to the potential well formed by the surface twists.
More than half of the energy produced worldwide is currently lost as heat and recovering even a fraction of that would be beneficial for global climate change. Toward this aim, thermoelectric materials can recover waste heat and convert it to useful energy. However, thermoelectrics are not widely commercially applied due to high cost and low efficiency. The search for new high-performance thermoelectric materials is challenging because they require enhanced electrical properties and low thermal conductivity. A potential route to discover novel high-performance thermoelectric materials can be provided by first-principles calculations [Chen, Pöhls et al. JMCC, 2016].
While the electronic properties can be predicted with a high accuracy, accurate prediction of the heat transport is currently not feasible. However, insight of the heat transport can be provided by computing the minimum thermal conductivity. In this study, a new model of minimum thermal conductivity was developed in which the thermal energy is transported between entities of phonons vibrating in a range of frequencies and limited by the phonon mean speed. This model was motivated by understanding the lowest experimental thermal conductivity to date for a fully dense solid (PCBM, κ = 0.07 W K$^{-1}$ m$^{-1}$ at 300 K), which agrees with the present model [Pöhls et al. PCCP, 20161].
In a high-throughput screening within ‘The Materials Project’ the electronic properties of ~48,000 compounds were calculated and two novel high-performance thermoelectric classes, XYZ$_2$ (X,Y: rare earth or transition metals, Z: Group VI element) and metal phosphides, show promise. A variable relaxation time was developed using a semi-empirical approach to accurately calculate the temperature-dependent electronic properties.
Three compounds of the XYZ$_2$ class were synthesized and their computed thermoelectric properties were compared to experiments [Zhu et al. JMCC, 2015; Aydemir, Pöhls et al. JMCA, 2016]. All compounds exhibited extremely low thermal conductivity and a maximum figure of merit of ~0.73 was found. Enhanced electronic properties and low heat transport were also predicted for metal phosphides. As an example, NiP$_2$ was synthesized indicating good agreement with computation and the present model of minimum thermal conductivity [Pöhls et al. JMCC, 2017].
High entropy materials are a group of materials that can be potentially used in extreme temperature applications and have interesting properties such as hardness, toughness, and corrosion resistance. In particular, high entropy oxides have attracted attention due to intriguing properties such as colossal permittivity and superionic conductivity. Since high entropy oxides are achieved from entropy driven reaction so they undergo reversible phase transition from multiphase to single phase by sintering at high temperature. In this experimental work, we have shown that this is not the case for their magnetic properties. The magnetization of a sample resintered at 700oC after sintering at 1100oC was entirely different from the sample sintered at 700oC, but not sintered at 1100oC. The multiphase resintered sample's magnetization was very similar to the single-phase sample’s magnetization. We have found that there is a close connection between the structural and magnetic properties which can explain the difference in magnetic behavior of multiphase samples.
Motivated by the recent experimental realizations of pyrochlore thin films, I will explore in this talk some of the promising facets offered by the slab geometry. Thin films are a natural platform to study the confinement of spin-liquid gauge fields and the evolution from three to two dimensional spin textures. In spin ice films for example, monopole excitations may crystallize on the surfaces, thanks to the long-range Coulomb potential between them. Depending on the type of substrate, interactions on the surfaces can be varied away from their bulk values. This offers a tuning parameter allowing for a new degree of frustration when spatial invariance is lost. More generally, I will discuss a sample of models and materials to illustrate how the mechanism ordering changes from the surfaces to the bulk and over what length scale this happens. Beyond the physics of films, the results of this research may apply to surface effects in single crystals.
This talk will present the current status of the PICO dark matter experimental program. The PICO detectors are based on the bubble chamber technology and record potential interactions of WIMPs in the target fluid through phase transitions induced by the energy depositions of recoiling nuclei. The technique is complementary to other dark matter search methods and has lead to several world-leading results for spin-dependent WIMP interactions. The current state of the results from PICO operations will be presented, as well as an update on the status and prognosis for the new detector configuration PICO-40, currently being installed at SNOLAB. The future prospects for a tonne scale “PICO-500” will also be described.
The Super Cryogenic Dark Matter Search experiment (SuperCDMS) seeks direct evidence of Weakly Interacting Massive Particle (WIMP) dark matter through interactions with cryogenic germanium crystals. Particle interactions in the germanium produce phonons and electron-hole pairs. The CDMS low ionization threshold experiment (CDMSlite) is an operating mode of SuperCDMS that applies a high voltage bias of ~70 V across the detector. This creates a phonon amplification of the charges through the Neganov-Luke effect, and thus opens a window to search for lower mass WIMPs, though at the expense of discrimination between electron and nuclear recoils. CDMSlite Run 3 is the final iteration of the experiment, using data collected at the SuperCDMS location at the Soudan Underground laboratory in 2015. In the analysis of Run 3 we are introducing advanced techniques that we did not use in earlier analyses, with the goals to improve the sensitivity in spite of a shorter exposure compared to Run 2, and to prepare our analysis toolbox for the upcoming SuperCDMS SNOLAB experiment, where half the detectors will be operated in this high voltage mode. Examples for these improvements are modelling the background to be used in a profile likelihood analysis, and salting the dataset as a method of blinding to reduce potential bias in the analysis. My presentation will discuss how we implement these techniques, as well as the status of the analysis and the expected improvements in sensitivity.
The Super Cryogenic Dark Matter Search (SuperCDMS) uses cryogenic semiconductor detectors to search for Weakly Interacting Massive Particles (WIMPs), a well-motivated class of candidate particles for the dark matter that constitutes 27% of the energy density of the universe. The CDMS Low Ionization Threshold Experiment (CDMSlite) probes the low mass WIMP region (<10 GeV/c2) by applying a high voltage (HV) across the SuperCDMS detectors, utilizing the Neganov-Trofimov-Luke effect to amplify small energy deposits. While this results in a very low energy threshold (<60 eV has been achieved), it is no longer possible to discriminate the electron recoil background from a potential nuclear recoil WIMP signal. In the SuperCDMS Soudan experiment (completed in 2015), two germanium detectors were operated in the CDMSlite mode.
In the next phase of SuperCDMS at SNOLAB, half of the detectors will be operated in HV mode. The limiting background is expected to result from cosmogenic activation of the detector material itself; 3H dominates in germanium (and is also significant in silicon). However, with a wide spread in the results of theoretical calculations and only one experimental data point with large uncertainty, the cosmogenic production rate of 3H in germanium is not well known. Using data from the second run of CDMSlite at Soudan and the location history of the detector, cosmogenic production rates are extracted for 3H and several other cosmogenically produced isotopes.
The existence of a non-zero neutron electric dipole moment (nEDM) would violate parity and time-reversal symmetry. Extensions to the Standard Model predict the nEDM to be $10^{-26}$ -- $10^{-28}$ e-cm. The current best upper limit set by Sussex/RAL/ILL nEDM experiment is $3.0 \times 10^{-26}$ e-cm. The nEDM experiment at TRIUMF is aiming at the $10^{-27}$ e-cm sensitivity level. We are developing the world’s highest density source of UCN. The experiment requires a very stable ($<$~pT) and homogeneous ($<$~nT/m) magnetic field (B0) within the measurement cell. My involvement in the nEDM experiment is the development of active magnetic shielding to stabilize the external magnetic field by compensation coils. A prototype active magnetic shield has been tested at The University of Winnipeg. I will report on experimental results from this prototype and its performance compared to simulation studies. I will also discuss the greater challenges expected at TRIUMF, due to the large cyclotron field (almost an order of magnitude larger than in our lab in Winnipeg) and the changing magnetic environment from large iron structures. Simulation studies of the implementation at TRIUMF will also be reported.
The recent announcements of the first ever detections of gravitational waves from colliding black holes and neutron stars have launched a new era of gravitational wave astrophysics. Gravitational waves were predicted by Einstein a hundred years earlier. I will describe the science, technology, and human story behind these discoveries that provide a completely new window into some of the most violent and warped events in the Universe.
We have recently determined a correlation between the acoustic response, state of charge and state of health of closed system electrochemical energy storage systems. Because a closed cell is a mass redistribution reactor, and in a standard cell the volume is effectively fixed, the distribution of density within a battery must change as a function of state of charge and, along with density, the elastic moduli of the anode and cathode changes as well. Since
cs = sqrt(E/rho)
This basic relation establishes a link between acoustic behavior and battery state. In this presentation we will review the physical basis of our hypothesis and present progress in
One of the Grand Challenges for humanity in the 21st Century is sustainable energy generation and storage. This translates to major opportunities for AFM to help addressed relevant materials issues if ultrafast time resolution in the localized measurement of electronic properties can be achieved. In this presentation, I will give an overview of our recent successes at characterizing surface potentials using AFM-based techniques on time scales down to ps. The high spatial resolution of AFM in principle then allows the identification of rate limiting structures/defects, allowing the fundamentally important correlation of structure and processing with properties.
We have combined a UHV AFM system with a fs laser excitation system tunable in the optical spectrum. By developing a new pump-probe method we can measure ultrafast decay times using AFM/EFM as a spatial detector. We have applied this technique to organic and organometallic perovskite as well as GaAs to measure ultrafast charge carrier decay times as well as mobility. We will also discuss the fundamental time limits achievable using the AFM probe as a detector in pump-probe experiments. [see DOI: 10.1063/1.4975629]
A major challenge in the widespread deployment of sustainable energy sources such as solar and wind is maintaining grid stability. Distributed energy storage in electrical vehicle batteries connected to the grid is an option. A major issue inhibiting wide spread deployment is low charging rates. This is related to the poor current understanding of what determines mobility of Li ions in cathode materials. We have used a newly developed AFM/EFM technique to spatially determine variations in Li transport mechanism in LiFePO4, a model cathode material. We applied voltage pulses to the sample and observed the resultant fast time decay of the electrostatic forces due to the mobility of Li ions using a time averaging technique. By performing these experiments as a function of temperature we obtain spatially resolved activation barriers for Li transport. By combining our ultrafast AFM techniques with SEM, TOF-SIMS and EBSD as well as comparison to DFT calculations we show that ionic transport in these materials must be regarded as a collective effect due to the significant contributions by ion-ion and ion-polaron interactions to the measured activation energies. (Collaborators: A. Mascaro, Z. Wang, P. Hovington, Y. Miyahara, A. Paollela, V. Gariepy, Z. Feng,T. Enright, C. Aiken, K. Zaghib, K. Bevan)
In memory of Prof. Akira Hirose, a long-time DPP member and major force in Canadian Plasma Physics for many years.
Owing to their relative simplicity, Langmuir probes are the instrument of choice to infer the density and temperature in space and laboratory plasma experiments. The interpretation of probe characteristics, that is, the collected current as a function of bias voltage, is practically always based on theoretical models amenable to analytic solutions, and capable of producing fast solutions under real-time experimental conditions. Several theoretical probe models have been developed over the years corresponding to plasma conditions under various limiting cases including collisionless unmagnetized plasma, low or high density plasma, strongly collisional plasma, and strongly magnetized plasma. Analytic models also assume isolated probes in a spatially uniform background, far from any other material object. Unfortunately these analytic models, while useful as fast and effective interpretation tools, cannot account for physical processes or experimental conditions which affect the measurements of characteristics in actual experimental conditions. Ideally, a preferred solution would rely on computer models capable of accounting for actual non-ideal measurement conditions, such as weakly magnetized plasma, Debye lengths comparable to size of the probe, plasma inhomogeneity, and the proximity of objects responsible for deflecting or obstructing particle to be collected. Such numerical models however, require considerable computing resources, which renders them inapplicable under real-time experimental conditions. This is the case in laboratory experiments, as well as in satellite on-orbit conditions. A solution would consist of using computer models, capable of accounting for the actual conditions under which lab or space measurements are made, to compute probe characteristics, and create a library of solutions over expected ranges of plasma parameters. Given this solution library, it would be possible to infer plasma parameters such as the density and temperature, directly from measured characteristics by using an adapted multivariate regression algorithm. In this talk, preliminary results are presented using solution libraries constructed from a combination of synthetic results obtained analytically, and numerically from kinetic simulations. The applicability of the method is discussed, with a particular attention to space-borne Langmuir probe measurements.
In a magnetically confined fusion reactor, the density and the temperature profiles are highly peaked at the core of the reactor and the fusion reactions occur mostly at the center. Unlike the fission reactors with the fuel bundle inserted in the reactor core, the fusion fuels have to be continuously injected from the outside to maintain the desired density in the reactor. The primary objective of the study of compact torus injector at the University of Saskatchewan is to investigate the feasibility of direct central fueling of a tokamak by CT injection and to study its effects on the tokamak discharge in our STOR-M tokamak, the only operating tokamak in Canada today. Compact torus is formed in a magnetized coaxial gun and is confined by the magnetic field self-induced by the current in CT. CTs can be accelerated to velocities 1-2 orders of magnitude higher than the fuel velocities currently achievable by any other fuel delivery technologies. In addition, CTs can be formed only one at a time. To maintain steady-state operation of a fusion reactor, repetitive CT operation is needed. In this talk, recent experimental results on repetitive and reproducible CT operation and momentum injection into the STOR-M tokamak by CT injection will be presented.
On 12 September 2014 the IMF turned very strongly northward for a prolonged period of time, reaching up to 28 nT at some point. Clauer et al (JGR, Space Physics, 121, 5422, 2016) showed from RISR-N Incoherent Scatter Radar (ISR) data at Resolute Bay that the convection on the sunward side of the polar cap was very strong and sunward during this exceptional event, with a convection electric field exceeding 150 mV/m at the peak of the event. The very strong electric fields were sustained for so long that we could determine from the ISR observations the anisotropy of the ion temperature in the F region. In particular, the perpendicular to parallel (to the geomagnetic field) temperature ratio for O+ ions undergoing resonant charge exchange with atomic oxygen could be derived. Preliminary results at the time of abstract submission indicate that this ratio was actually larger than expected from theoretical calculations involving published cross sections, with important implications for transport calculations involving collisions between ions and neutrals. The unique data set from the event also produced several large E region electron temperature (Te) measurements reaching up to almost 4000K through plasma wave heating. This temperature is one order of magnitude greater than found for electric fields weaker than 40 mV/m. Foster and Erikson (GRL, 27, 3177, 2000) have suggested that Te could be used to infer the electric field strength, based on rare electric field observations going up to 125 mV/m. The Sept 2014 data set allowed us to (1) make an alternate determination of the electric field from simultaneous E and F region ion drift measurements on nearby magnetic field lines to confirm the validity of other electric field determinations and (2) to make a substantial addition to the number of observations of Te as a function of electric field strength under very strongly disturbed conditions. We have found no evidence for a limit in the wave-induced electron heating, with an electron temperature that increased basically linearly with electric field strength all the way to 150 mV/m.
Plasma flow patterns at northward-oriented IMF are not well defined. For example, near noon sunward flows (reverse flows) often deviate from the midnight-noon meridian and the amount of deviation can be as large as several hours of magnetic local time. Over the last several years, significant data on reverse flows have been accumulated in the Canadian sector of Arctic where three PolarDARN radars routinely produce global-scale plasma flow maps while the RISR incoherent scatter radars at Resolute Bay provide more localized information. In addition, polar cap SuperDARN radars in the southern hemisphere monitor plasma flows in about the same magnetic local time sector. In this study, we investigate the meridional sunward flows in both hemispheres, their response to IMF turnings as well as the shape and location of the reverse convection cells.
The European Space Agency’s trio of Swarm were launched in November 2013 to measure the environment around Earth using a suite of instruments. Each satellite is equipped with two Langmuir probes that run in parallel and have different coatings. One is gold plated and the other has a titanium nitrate coating. This configuration on each satellite provides an opportunity to study if and how coatings on Langmuir probes may affect plasma density and temperature measurements.
In this study, data are selected from each probe pair to control for solar illumination, magnetic field orientation, and operative mode to assess the extent to which differences in measurements are present. Any differences from the two probes can be attributed to the surface coatings. Preliminary results will be presented and discussed.
Studies on scattering of longitudinally and transversely incident beam of electrons by hollow cylindrical potential and coaxial cylindrical potentials have shown the presence of quasi bound “whispering” modes [1,2]. The realization of Levinson’s theorem [3,4] has been studied for some scattering potentials and results are widely available.
Roberts and Valluri [5] presented a geometric analytic technique, which utilizes conformal mapping W->Z=We^W between two complex domains to solve the 1-dimensional finite square well potential. The symmetry of the hollow cylindrical potential can be used to solve the Schrodinger equation as a 1-dimensional finite square well potential in the radial direction. This leads to the possible generalization to a concentric double walled cylindrical potential by considering it as a double well finite potential in the radial direction. The number of bound states of such a potential can be counted using the Lambert W formalism, as it is a geometric method, and the relation to the scattering phase shift can be established.
References:
1) Vivishek Sudhir and P. C. Deshmukh
Scattering of electrons off hollow cylindrical potentials
J. Comput. Theor. Nanosci. 7, 2036 (2010)
2) Vivishek Sudhir and P. C. Deshmukh
Scattering of electrons by multi-walled cylindrical potentials
J. Comput. Theor. Nanosci. 8, 2321 - 2326 (2011)
3) N. Levinson
On the uniqueness of the potential in a Schrodinger equation for a given asymptotic phase
Danske Vid. Selsk. Mat.-Fys. Medd. 25:9 (1949)
4) C.J.Joachain
Quantum Collision Theory
North Holland, Amsterdam (1975)
5) Roberts and S.R. Valluri
The quantum finite square well and the Lambert W Function
Can. J. Phys. 95: 105-110 (2017)
I highlight how the problem of obtaining correspondence rules for SU3 Wigner function differs from that of the SU2 problem. I show how these rules are easily obtained for the Q-functions but how the transition from Q to Wigner functions for SU3 brings about novel features not present in SU2. A path to solution will be proposed.
We have proposed, in a previous CAP conference, an erfc potential that can be integrated in a symmetric metric to define the space-time surrounding a static symmetric massive object. The geometry described by this metric provides a unique representation of a static symmetric stellar system that is continuous over all the coordinate ranges. No discontinuities and no singularities, coordinate or intrinsic, come into play. A first attempt to extend this analysis would be to interpret the resulting space-time equations in terms of an isotropic stellar interior, considering the corresponding Tµµ as describing a perfect fluid under an isotropic pressure P. Such an approach leads to inconsistencies, because the pressure cannot be assumed to be equal in all directions in the present model. A more realistic solution is obtained using the Pµµ and associating these to the field equations. Solving this system for the Pµµ provides relationships between the different components as well as analytical expressions for each one of these. As it can be seen with computer simulations, the erfc potential generates supplementary principal radial constraints and the Rµµ are directly linked to the pressure components. The energy momentum components generate internal pressure in the system and these pressure components generate space-time curvature. The energy density ρc2 produces an inward attractive pressure P11 and the two pressures P22 and P33 are equal and negative to maintain the equilibrium of this static model
In this work, we consider the Korteweg-de Vries equation and its variants which are third order nonlinear partial differential equations. It originates from many physical phenomena, for example, the flow of liquids containing gas bubbles, in the study of the propagation of waves in an elastic tube filled with a viscous fluid and also for the description of shallow water waves on viscous fluid.
We start by designing implicit finite difference schemes that conserve the first three integrals: mass, momentum and energy. The derived schemes being implicit are difficult to implement and consume more computer time, hence quest for explicit finite difference schemes is highlighted since they are easy to implement and consume less computer time. Here we investigate explicit schemes for the Korteweg de Vries equations and it’s variant.
With regards to these schemes, several numerical experiments are carried out to analyse their spectral properties. Their performance is compared with regards to dispersive and dissipative errors and their ability to conserve the first three integrals. In addition, an optimisation procedure is carried out to determine the optimum spatial step size that produces the minimum error. Graphical presentation of results obtained shed more light.
$B\to K^*\nu\bar \nu$ is an excellent venue to test various model predictions for $B\to K^*$ transition form factors. Here we compare predictions for the differential branching ratio, as well as the longitudinal polarization fraction obtained from AdS/QCD holographic light-front wavefunction and QCD sum rules.
In a recent paper, we have shown that dynamical spin effects are important to describe pion observables within holographic light-front QCD. The relative importance of such effects was freely chosen to fit the data. We now show that these dynamical spin effects can actually be theoretically constrained if we dare to extrapolate the use of an exact QCD relation away from the chiral limit. Despite this new theoretical constraint, we find that the dynamical spin effects still bring a significant improvement to describe the pion observables.
We compute masses of light quarkonium and strangeonium $0^{+-}$ hybrids using Gaussian sum-rules. Correlation functions account for condensates up to dimension-six and are calculated at leading-order in $\alpha_s$. Our analysis indicates that the resonance signal strength in this channel is distributed over a wide range, inconsistent with a single narrow resonance. A single wide resonance is also disfavoured as the resonance width would have to be extremely large. Using a double narrow resonance model, we find excellent agreement between QCD and hadron phenomenology, and extract mass predictions of $2.6~\text{GeV}$ and $3.6~\text{GeV}$.
Advances in medical imaging and demands for better diagnoses brought up the idea to combine complementary image modalities with the aim to provide better image quality and more information. Many combined PET/MRI scanners designed for truly simultaneous operation are still in the developing stage. One of the main interferences between PET and MRI arises from the different material magnetic susceptibilities and the presence of metal inside the MRI field of view that could produce eddy current and increase the temperature of PET electronics. In this report, we discuss the effect of MRI gradient on the PET electronics.
We consider a 3 T MRI with an open bore diameter of 50 cm, gradient with slew rate of 200 mT/m/s and RF coil with outer diameter of 30 cm with an avalanche photodiode (APD)-based PET detector located at outer surface of the RF coil. Sensitive materials in PET detectors include application-specific integrated circuits (ASICs) (mainly silicon and copper wiring) of 23.5 × 11.5 mm2 with 0.650 mm diameter ball grid arrays (BGAs) made of SAC305 (Sn96.5Ag3Cu0.5).
Since APD performance is sensitive to temperature and the PET detector electronics are designed in a way that low frequency RF could not disturb its biasing and signaling, the induced eddy current and the associated heat loss in the PET detector have been evaluated using the COMSOL magnetic field module. To model the eddy current and heat loss, we used magnetic vector potential and the skin depth (δ) of materials. The skin depth of copper and SAC305 are 652.3 µm and 1636 µm at 10 kHz, respectively.
The induced current density was simulated in one individual SAC305 sphere and in a detector with 116 spheres as BGAs along with two ASICs in presence of the gradient field. By volumetric integration of current, the induced current density in one BGA was calculated as 0.3 µA.m and the heat loss was 37.3 pW. The total eddy current density norm and heat dissipation for one detector would then be 1.7 mA.m and 0.6 µW, respectively.
Our results show that by using non-ferromagnetic materials in small quantity and low distribution, the induced current and heat dissipation due to gradient changes are so small that they would not raise the detector temperature to a level that would affect the PET performance.
Accurate, quantitative measurements of radiation fields are essential prerequisites for the safe and effective use of ionizing radiation in diagnostic and therapeutic medical applications. Common examples of radiation detectors include: ionization chambers, thermoluminescent dosimeters (TLDs), films and various electronic devices. Semiconductor dosimeters such as p/n type silicon diodes and MOSFETs have found widespread adoption due to their high sensitivity and easy processing. A significant limitation of these devices, however, is their lack of tissue equivalence. The high atomic number (relative to soft tissue) of silicon causes these devices to over-respond to photon beams that include a significant low energy (e.g. kilovoltage) component due to an enhanced photoelectric interaction coefficient.
This work presents preliminary measurements with organic semiconductor diodes and organic floating gate (FG) transistors as dosimeters capable of providing a tissue equivalent response to ionizing radiation. The direct detection of X-rays from a medical linear accelerator using Phthalocyanine/C60 based organic planar heterojunction diodes is presented. The diodes produce a linear increase in current with increasing dose rate and show a stable response after exposure to doses up to 5000 cGy. The Pentacene-based organic floating gate transistors have also been investigated for dosimetry applications. The possibility of resetting the transistors for repeated use and sensitivity optimization by electrical charging of floating gate through Fowler-Nordheim tunneling is currently being investigated. The sensitivity of these devices has been determined from the transistor threshold voltage shift as a function of accumulated dose. After negative or positive pre-charge of floating gate the average sensitivity was 0.09V/Gy, 0.045V/Gy, 0.02 V/Gy, 0.01 V/Gy at 10 Gy, 20Gy, 30 Gy, 40 Gy, 50 Gy, 60 Gy, respectively. The sensitivity of FG pentacene transistors was stable after two pre – charge cycles of the FG.
Stable isotope abundances vary in nature due to differences in zero-point energies of the binding site of a molecule upon isotopic substitution. This causes isotopes of an element to participate in reactions with different rates resulting in a redistribution of the isotopes in a system. Although the range in relative isotopic abundance of copper in natural materials is narrow, < 1.0%, current measurement techniques allow for quantification of changes as small as 0.01%. Recent attention is focussing on the redistribution of copper isotopes in biological systems.
The present study investigated the influence of gut bacteria on the redistribution of stable copper isotopes in the gastrointestinal tract of mice. Trillions of bacteria reside in our gastrointestinal tract and play an important role in energy homeostasis, protection against pathogens, nutrient metabolism, host immunity and intestinal barrier function. Here we compared the isotopic redistribution of copper isotopes in mice with gut bacteria significantly impacted by antibiotic consumption. A significant difference, ~0.1%, in copper isotope abundances was measured in the proximal colons of the gastrointestinal tracts of antibiotic-treated mice, indicating a drastic change in copper processing in this region when bacteria were eliminated. In order to investigate the mechanism of these changes we examined copper transporters in the epithelium as they have been shown to modulate the extent of isotopic redistribution$^1$. Both CTR1, responsible for copper import, and ATP7A, responsible for copper efflux, were significantly down-regulated in antibiotic-treated mice. Down-regulation of these proteins in intestinal epithelial cells is associated with increased extracellular copper$^{2,3}$ and suggest that gut bacteria are influencing the amount of bioavailable copper to cells. These results highlight the relationship between gut bacteria and copper, both identified as having an important role in health.
References:
1 Cadiou, J., et al. (2017) Scientific reports 7, p. 44533.
2 Petris, M. J., et al. (2003) Journal of Biological Chemistry 278, p. 9639
3 Chun, H., et al. (2017) Scientific reports 7, p. 12001.
Cellular reprogramming is a source of induced pluripotent stem cells, but this process remains incompletely understood. The current theory of equipotency during reprogramming, in which all cells are equally inducible, argues that clone size distributions arise only from stochasticity in the system. However, large variability is seen in experiments. Our null, stochastic model, does not agree with barcoding experiments and shows that the equipotency theory may not be correct. To better explain these distributions we introduce multiple populations with different reprogramming parameters. Reprogramming is driven by a few dominant clones, a feature that will be captured by this mixed population model. Furthermore, barcoding experiments show correlation in clone sizes in repeated trails, indicating that there is heterogeneity in the reprogramming potential of clones. We will develop a stochastic model informed by experimental evidence that the cells that are derived from the neural crest have a proliferative advantage. This approach also introduces heritable reprogramming potential into our model. An accurate model of the reprogramming process can inform our understanding of the path to pluripotency, and increase the yield of reprogramming protocols.
If you are planning to apply for a faculty position, or for a promotion, or if you are up for tenure, you will likely have to submit your teaching dossier (also known as teaching portfolio) in addition to your CV and research statement. This one-hour workshop will get you started on preparing your dossier. You will learn what information it should include, how to collect and organize evidence for your teaching practice and effectiveness, and how to approach writing your teaching philosophy statement. You will have an opportunity to look at examples – good and not so good – and learn about the criteria committees typically use when reviewing teaching dossiers.
Colloids are small particles with diameters that lie within the nanoscopic and microscopic domains. Recently, research has focused on deformable or soft colloidal particles, such as microgels and star polymers, which show fascinating behaviour such as jamming and glass formation in dense dispersions. I will describe a new type of soft colloidal particle, phytoglycogen, which is produced in the form of highly branched, monodisperse nanoparticles in sweet corn [1]. The particles are chemically simple, but it is their dendrimeric or tree-like physical 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 promising 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 unusually strong interaction with water [2]. I will describe our journey from our initial serendipitous discovery of the particles to our detailed analysis of their structure, hydration and soft mechanical properties to the commercialization of this natural, sustainable nanotechnology in our Guelph-based spinoff company Mirexus.
[1] J.D. Nickels, J. Atkinson, E. Papp-Szabo, C. Stanley, S.O. Diallo, S. Perticaroli, B. Baylis, P. Mahon, G. Ehlers, J. Katsaras and J.R. Dutcher. Structure and Hydration of Highly-Branched, Monodisperse Phytoglycogen Nanoparticles, Biomacromolecules 17, 735-743 (2016).
[2] M. Grossutti and J.R. Dutcher. Correlation Between Chain Architecture and Hydration Water Structure in Polysaccharides, Biomacromolecules 17, 1198-1204 (2016).
NSERC EG Chair Report | Rapport de la présidente du GE
CAP-NSERC Liaison Committee Report | Rapport du Comité de liaison ACP-CRSNG
In the strong light-matter coupling regime, energy is reversibly exchanged between the electromagnetic field and the polarization field. A microscopic description of this regime is usually presented in terms of hybrid light-matter quasiparticles called polaritons. These quasiparticles have a number of fascinating properties such as an ability to undergo Bose-Einstein condensation at high densities and possess very strong optical nonlinearities due to their matter component. For nearly two decades, the platform of choice for studying polaritons has been planar semiconductor microcavities composed of group III-V quantum wells. Unfortunately in these materials, exciton binding energies are well below kT and most polaritonic phenomena can only survive at low-temperatures.
We will describe semiconductor microcavities composed of organic semiconductors and two-dimensional (2D) materials where polaritonic phenomena can survive at room-temperature. Using these, we have recently demonstrated a broad range of nonlinear phenomena such as Bose-Einstein condensation of polaritons, room-temperature superfluidity, tunable third harmonic generation and polariton diodes. We will showcase some of the recent demonstrations and outline future steps for realizing polariton devices based on a room-temperature semiconductor platform.
Three-pulse multidimensional coherent spectroscopy allows for isolation of zero-, one- and two-quantum pathways for separate and coupled, as well as their homogeneous and inhomogeneous linewidths [1]. Excitons and biexcitons are examined in semiconductor quantum wells to determine the lineshapes and quantum pathways associated with the optical excitation. These result are compared and contrasted with those from a semiconductor microcavity where the excitons form polaritonic modes due to normal-mode splitting [2]. One-quantum rephrasing spectroscopy maps the detuning dependence of the exciton-polariton branches. Increasing detuning moves all features to higher energy and the expected anti-crossing is observed. An isolated biexciton is seen only at negative detuning, separated by a binding energy of approximately 2 meV. For positive detuning, the spectral weight of the off-diagonal features swap, as the lower polariton branch and biexciton come into resonance. This indicates that the off-diagonal features are sensitive to the interactions including two-quantum contributions and that a situation similar to a Feshbach resonance exists. Polarization dependence of two-quantum contributions show spin sensitive two-polariton and new biexciton correlations. The latter likely influence the Feshbach resonance between biexcitons and two-polariton states. The two-quantum signatures also demonstrate that biexcitons perturb the light-matter coupling in the microcavity to reduce the mixed two-polariton contributions. Detuning dependence of zero-quantum contributions show Raman-like coherences that are enhanced near zero detuning. Asymmetry of the Raman coherences are indicative of many-body interactions, which also grow stronger as the light-matter interactions are enhanced near zero detuning.
[1] Bristow et al, Rev Sci Instrum 80, 073108–8 (2009).
[2] Wilmer et al, Phys. Rev. B 91, 201304(R) (2015).
Most departments rely on student evaluations of teaching (SET) when trying to determine an instructor's teaching effectiveness. Some even focus on a single number, the "overall mark" given by students. How can we do better? We want to know which methods you use and why, and if you are satisfied with the information they provide. We especially want to hear from you if you are using Peer Evaluation of Teaching - how do you keep the workload manageable? How do you handle issues of trust? We look forward to having an inspiring conversation with you.
There has been an exciting recent development in auroral research associated with the discovery of a new subauroral phenomenon called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is a new upper atmosphere phenomenon. Observed first by amateur auroral photographers, STEVE appears as a narrow luminous structure across the night sky over thousands of kilometers in the east-west direction. In this paper, we present the first statistical analysis of the properties of 28 STEVE events identified using THEMIS ASI and the REGO database. We found that STEVE occurs about one hour after substorm onset at the end of a prolonged expansion phase. On average, the AL index magnitude is larger and the expansion phase has longer duration for STEVE events compared to SAIDs or Substorm. The average duration for STEVE was about one hour and its latitudinal width was ~20km, which corresponds to ~ ¼ of the width of narrow auroral structures like streamers. STEVE typically has an equatorward displacement from its initial location of about 50 km and a longitudinal extent of 2145 km. We also analyzed STEVE’s seasonal dependence and found that more events were observed during equinox. Finally, we did not find evidence of solar cycle dependence for the events of STEVE analyzed in this study.
In addition, we use data from Meridian Scanning Photometers (MSP, NORSTAR and FESO) that measure brightness of H-β proton auroral emission at 4861Å. This dataset help us to locate STEVE relative to typical auroral arcs. We analyzed in total 12 events in which THEMIS or REGO have a good conjunction with MSP instruments from December 2007 up to May 2017. Our observations suggests that Steve is always located equatorward of the proton aurora (~5˚mlat on average), and thus is not a traditional electron auroral arc, a feature which is always poleward of the peak in proton auroral brightness.
After four years in orbit, the Swarm Electric Field Instruments have contributed to dozens of scientific studies on topics that include the electrodynamics of auroral arcs, supersonic flow channels associated with region 1/2 currents and sub-auroral ion drifts, polar cap patch dynamics, Poynting flux, and magnetosphere-ionosphere coupling via Alfven waves. This talk will overview capabilities and accomplishments of these instruments and highlight future opportunities as the Swarm mission is extended into the next four years.
We present recent results from a preliminary inter-satellite comparison of ionospheric flow measurements from the European Space Agency Swarm mission. Swarm consists of three identical satellites in near-polar circular orbits in the topside F region ionosphere. Each spacecraft carries a set of two orthogonal thermal ion imagers designed to measure full ion flow vectors twice per second. The thermal ion imagers are beset by a measurement anomaly caused by water contamination, which has precluded routine automated determination of ion flows. An extensive experimental campaign to understand and fix the anomaly has revealed several mitigation strategies that enable daily operations that return high quality scientific flow data. The aim of the present work is to assess the validity of these flows by comparing similar measurements from the different satellites. Preliminary results reveal both highly correlated ion flows, as well as intriguing differences suggestive of spatial-temporal inhomogeneities, as determined with pairs of the Swarm satellites.
Proton therapy is gaining popularity as a tumor irradiation method due to the superior dose distribution offered by heavy charged particles. The subject of range and dose verification has been approached from several angles and fields.
Upon interaction with low-energy protons, certain nuclei undergo fusion-evaporation reactions. The resulting reaction products emit a cascade of characteristic gamma rays as they decay to their ground state. The product of these fusion-evaporation reactions is highly dependent on the energy of the incident proton. This means that the relative intensity of the competing fusion-evaporation channels can be correlated with the energy of the proton beam, and, by extension, its range. By administering an appropriate contrast agent to the tumor being irradiated, we are able to measure the intensity of characteristic prompt gamma rays resulting from fusion-evaporation reactions occurring inside the tumour.
We propose to take advantage of the timing and energy resolutions of a fast scintillator detector to measure beam range and dose administered in proton radiation therapy. Fast scintillator detectors are used frequently in nuclear research due to their good timing resolution and reasonable energy resolution, and have begun to make their way into the medical field.
Our Geant4 simulation results show that this technique would allow for accurate measurement of beam range relative to the position of the tumour within the body, as well as dose administered to the tumour. Additionally, the excited states resulting from the reactions of interest are very short-lived and as such this measurement is taken while the beam is online. This is advantageous because it allows for dose monitoring during the treatment as opposed to afterwards.
The presented approach combines the unique expertise at TRIUMF in the fields of both gamma ray spectroscopy in nuclear physics research and proton therapy in order to strive towards improved cancer radiation therapy.
Plastic scintillation detectors (PSD) are excellent candidates for in-vivo dosimetry due to their small size, sensitivity and potential for real time readout. One challenge associated with PSD dosimetry is the contamination of the scintillation signal with Cerenkov radiation and fluorescence. An implicit assumption made with PSDs is that the spectral components of the scintillator and fiber response are invariant between calibration and measurement conditions. In this study this assumption was tested by measuring the spectral content of the emissions of the scintillator and the optical fiber as a function of the angle of incidence of a radiation beam on a PSD. We studied two different Kuraray plastic scintillators coupled to Mitsubishi Eska optical fiber. The spectral content of the PSD emissions was measured with a spectrophotometer. The PSDs were placed both at the surface and at depth in a solid water phantom in different orientations in the beam. The gantry angle was varied between 0⁰ and 45⁰. The normalized emission spectra of the scintillators and the fibre were compared for different orientations and gantry angles. Photons of energy 6 MV and electrons of energies 6 MeV and16 MeV were investigated. On the surface, the relative contributions of Cerenkov and fluorescence vary as a function of gantry angle when the PSD is oriented in the plane of gantry rotation. For 6 MV, 6MeV and 16MeV, we found a variation of 2.5, 4.5 and 5.5 % in the peak emission of optical fiber and 2.5, 7.3, and 9.3 % in the emission of the scintillator respectively. The variability in decreased with depth. The effect of this variability on dose prediction (with assumption of spectral composition invariability) was studied.
A prototype clinical study is being developed to assess pre-adult patients with hemophilic arthropathy. Patients with this condition experience pain in ankle, knee, wrist, or elbow joints due to joint bleeds. Typical ultrasound exams involve probe to skin contact to generate an image, which places a moderate to high level of pain on the effected joint. To overcome the physical touch of an ultrasound probe to the skin, a prototype has been built that consists of a three-dimensional (3D) ultrasound (US) system, and a water filled plastic cylindrical tub. The latter is able to freely rotate about a base plate, while an off-the-shelf electromagnetic encoder, attached to the rotational shaft of the tub, provides the rotational position of the device. Moreover, software running on a Microsoft Windows computer, written by developers at The Robarts Research Institute, takes the encoder position from a USB interface along with conventional two-dimensional (2D) ultrasound images to create a 3D volume. The 2D US images are recorded with a given angular sampling and reconstructed into the 3D volume in an inverse fan geometry. The 3D image is able to provide a viewpoint that is unreachable in conventional 2D ultrasonography, since a manipulation through all planes is possible. Preliminary testing of the device has shown favorable image quality and level of details in two health human wrist and ankle pairs. The prototype design, study protocol workflow, and preliminary results will be presented; specifically showing corresponding anatomical landmarks between 3D ultrasound and MR images. The future work for the study is a clinical trial at Sick Kids hospital in Toronto; whereby, ultrasound / MRI data from each subject will be viewed by two radiologists who are separated from the other aspects of the study. Interpretations from both modalities will gauge the feasibility of this approach for use in imaging hemophilic arthropathy in limb joints.
TRansmit Array Spatial Encoding (TRASE) is a Magnetic Resonance Imaging (MRI) method which uses phase gradients of the $B_1$ field – rather than magnitude gradients of the $B_0$ field – to achieve spatial encoding. The potential benefits and limitations of this technique are still being explored in both conventional and low-field magnets. This work designs a highly homogeneous, low-field magnet (<10 mT) to further studies of TRASE in this regime. The design method is novel and allows for ostensibly perfect field homogeneity. Furthermore, given that TRASE does not require the application of switched $B_0$ gradients, we propose to build the magnet on an aluminum housing which acts both as a heat sink and an effective low-frequency RF shield.
This talk will present the design method, convergence tests of this method, and the final design. The method is founded upon consideration of two coaxial cylindrical surfaces of finite lengths with surface currents on their bodies and end caps. Boundary conditions are set such that the outer surface perfectly shields the field created. Using finite element methods, the Laplacian of the magnetic scalar potential $Φ$, and hence magnetic field $B$, is found in the region between the cylinders. One is free to specify any solution to the Laplace equation in the inner region, including $Φ=-Bz/μ_o$, which gives a uniform field. By moving the outer surface farther and farther away, we are able to converge to a solution for a single, finite-length cylinder in free space with the perfectly uniform internal field of an infinitely long solenoid. The discontinuity of the scalar potential across the cylinder boundary is, in fact, equivalent to the stream function, and, as a result, evenly spaced contours of $ΔΦ$ give the coil winding pattern. Because no current flows at the center of the end caps, access holes can be created in these regions.
Fluid turbulence has been called the “last unsolved problem of classical physics” and the measurement of this phenomenon presents a formidable challenge. Turbulent systems are highly sensitive to perturbations, and so a non-invasive technique is needed to probe their properties. Turbulence is also difficult to fully characterize, particularly in the case of anisotropic turbulence. Magnetic Resonance Imaging (MRI) is a useful and versatile tool in this regard, because with the application of magnetic field gradients, MRI can be sensitized to various flow characteristics. The particular version of MRI used to measure turbulent gases is the motion-encoded Single Point Ramped Imaging with T1 Enhancement (SPRITE) technique developed at the University of New Brunswick. With the application of motion-sensitizing magnetic field gradients, SPRITE can be used to measure the three-dimensional time-averaged velocity field. This information is contained within the phase of the detected signal. Results of this type of measurement will be presented with a recorder as a turbulent flow system, which is often used as an example wind-instrument in musical acoustics. SPRITE can also be used to measure the anisotropy in mean-squared displacements caused by turbulent fluctuations. This information is contained within the signal amplitude of the detected signal. Results from measurements on gas flow through a cylindrical pipe with a hemi-cylindrical obstruction will be presented. These results show that at the time scale probed by this measurement, turbulence is anisotropic.
Since the first demonstration of atomic resolution in ultra-high vacuum more than twenty years ago, frequency modulation-based noncontact atomic force microscopy (FM-NC-AFM) has significantly matured and is now routinely applied to study problems that benefit from high-resolution surface imaging. In FM-NC-AFM, control of the tip’s vertical position is accomplished by detecting a shift in the cantilever’s resonance frequency upon approach to the sample. Consistently ensuring reliable distance control during extended data acquisition periods has nevertheless remained challenging, as most FM-mode-based control schemes employ three feedback loops that may interfere. As a consequence, sample throughput in FM-NC-AFM is often low compared to ambient condition AFM, where the easy-to-implement amplitude-modulation (AM) control scheme is predominantly used. Transfer of the AM methodology to high-resolution measurements in vacuum is, however, difficult as with AM-AFM, instabilities during approach are common; in addition, the lack of viscous air damping and the related significant increase of the cantilever’s quality factor generates prolonged settling times that cause the system’s bandwidth to become impractical for many applications. Here we introduce a greatly simplified approach to NC-AFM imaging and quantitative tip-sample interaction force measurement that prevents instabilities while simultaneously enabling data acquisition with customary scan speeds by externally tuning the oscillator’s response characteristics [1]. After discussing background and basic measurement principle, examples for its application to characterize layered materials, thin-films, and topological crystalline insulators are provided [2-4].A major advantage of this operational scheme is that it delivers robust position control in both the attractive and repulsive regimes with only one feedback loop, thereby carrying the potential to boost the method’s usability.
[1] O. E. Dagdeviren et al., Nanotechnology 27, 065703 (2016).
[2] O. E. Dagdeviren et al., Nanotechnology 27, 485708 (2016).
[3] O. E. Dagdeviren et al., Physical Review B 93, 195303 (2016).
[4] O. E. Dagdeviren et al., Advanced Materials Interfaces 4, 1601011 (2017).
Light incident on nanoscale metal-insulator-metal (MIM) plasmonic gratings generates surface plasmon polaritons (SPPs) which resonate and propagate within the grating structure. A variation in the SPP resonant wavelength is achieved by gradually increasing the width of the MIM grooves symmetrically about a central groove to create a graded grating, which leads to a gradient in the effective refractive index wherein the index increases in the direction of the central groove. The index gradient guides non-localized SPP waves towards the grating center which, in combination with localized SPP modes within the narrowest central grooves, produce multi-wavelength electric field enhancement at the center of the grating.
Central grooves with sub-50 nm widths enable enhanced localization of multiple wavelengths of light. Therefore, these structures can be used as unique substrates for surface enhanced Raman spectroscopy (SERS), having the potential to achieve unprecedented detection sensitivity, specificity and rapidity. However, large scale fabrication of such narrow gratings using standard nanofabrication techniques is not cost effective and limits the minimum groove width to approximately 50 nm. Herein we report on the development of a novel nanoplasmonic graded grating with a sub-10 nm central groove flanked by increasingly wider grooves on either side, which are fabricated economically using state-of-the-art, thin film sputter deposition.
These structures are also studied using COMSOL Multiphysics modelling where we vary the minimum groove width, groove-to-groove separation and groove depth, and thus demonstrate localization of broadband incident light with intensity enhancements of over five orders of magnitude. Additionally, we explore the effect of the number of grooves and the material composition of the structure on the near-field optical response. Experimental results from confocal fluorescence microscopy demonstrate multi-wavelength localization within the grating structures. In addition, SERS characterization of low concentration biomolecules using the gratings reveal the potential of these nanoplasmonic graded gratings as a rapid and highly sensitive platform for the detection of a variety of molecular species amenable to a wide range of applications including health, environment and security.
Traditional point sources of neutrons produce free neutrons in isotropic directions and with kinetic energy in the MeV energy domain. These neutrons are too fast for many applications as the probability of interaction between neutrons and surrounding matter is often higher at low neutron energies. Therefore, to optimize interaction between neutrons and its environment, these neutrons are slowed down in the eV or meV energy domain with a moderator.
This presentation describes a novel method for neutron moderation from an isotropic source by utilizing a rotating moderator to provide a versatile source of neutrons. The source of primary neutrons, the rotation speed of the moderator, the physical properties of the moderator and neutron scattering instruments surrounding the moderator are all adjustable parameters impacting the final neutron spectrum. A GEANT4 (toolkit for the simulation of the passage of particles through matter) simulation was built and shows that this rotating neutron moderator can partially focus neutrons in space; neutrons are emitted preferentially in the rotation plane, but throughout the longitudinal domain because of its circular configuration. To further increase neutron flux, it is desirable to consolidate the emitting neutrons to a narrower longitudinal domain. Fortunately, the direction of emission of the neutrons, relative to the moderator, is known as it depends on the rotation speed. This important detail allows use of neutron supermirrors to achieve longitudinal consolidation, since alignment of supermirrors requires accurate control. Therefore, McStas (Monte Carlo code) was used to evaluate the possibility of using supermirrors to collect neutrons from the rotating moderator into a beam. Unfortunately, constructing such a device is limited by material strength to withstand the rotational forces and temperatures required.
In this presentation, I will present the many-body interactions in solids studies by high resolution ARPES. High-resolution angle-resolved photoemission spectroscopy studies of Fe (1 1 0)；Ni(110) and other 3d single crystals have been conducted to clarify the role of many-body interactions acting on the quasi-particles at the Fermi level at low temperatures.
The Canadian Light Source (CLS) located in Saskatoon on the campus of the University of Saskatchewan has been in operation since 2005. Upon completion of the Phase III beamlines in 2019, the total number of end-station will be over 25, leaving space for only one last beamline. In light of the growing demand for synchrotron light and the advances in accelerator physics in the past 20 years since the CLS was designed, a new Conceptual Design Report is being prepared to explore how the needs of Canadian scientists can be met. This talk will cover the trends in synchrotron light sources, the state-of-the-art technology and the present status of the CLD 2.0 design study.
When orbitals are already occupied by one electron, the addition of a second charge to that position in space entails overcoming the Coulomb repulsion between the charges. This on-site Coulomb repulsion is often characterized by the so-called Hubbard U: the energy difference between the doubly negative and charge neutral state. As charges move from site to site in a material they must overcome this interaction, and when U is large compared to hopping parameters these effects influence transport, breakdown single particle theories, and lead to low temperature phase transitions into distinct electronic states. As these effects are inherently local, and orbital dependent, a real-space tool to measure this on-site Coulomb interaction has the potential to offer new insight into interaction-driven and correlated electron behavior.
Here we provide a new sub-nanometer scale view into this old problem via noncontact atomic force microscopy. Our observations of singly charged 3,4,9,10-peryelene tetracarboxylic dianhydride (PTCDA) molecules on bilayer NaCl on an Ag(111) surface show bias-dependent transient charging behavior. Electrostatic force spectroscopy (EFS) shows distinct jumps at the energies corresponding to Hubbard states previously identified by scanning tunneling spectroscopy (STS) [1] and are indicative of transitions between the 0, 1-, and 2- states. Using pixel-by-pixel EFS in tandem with STS we can locally map this charging energy required to overcome the on-site Coulomb repulsion providing a direct characterization of the Hubbard interaction. Our measurements indicate that the Hubbard U varies spatially depending on the local environment of 2-dimensional clusters of PTCDA molecules and even on submolecular length scales associated with the spatial extent of the half-filled orbital. This new visualization tool has the potential to be applied to a wide range of materials providing opportunities open up new perspectives in this key underpinning of correlated electron behavior.
[1] K. A. Cochrane, A. Schiffrin, T. S. Roussy, M. Capsoni & S. A. Burke, Nat Commun, 8, 8312 (2015)
MacSANS is a new small angle neutron scattering (SANS) beamline currently under construction at the McMaster Nuclear Reactor, a 5 MW research reactor based at McMaster University in Hamilton, Ontario. This beamline is designed to study a broad range of materials, including biological membranes, polymers, superconductors, and novel magnets, by probing structure and magnetism on length scales ranging from ~0.5 to 125 nm. MacSANS will be the only instrument of its kind in Canada, and is scheduled to begin commissioning experiments in the spring of 2019. In this poster we will provide an overview of the instrument design, a description of the major components, and a discussion of potential scientific applications.
Precision low-energy experiments in electroweak electron-proton interactions are a vital complement to direct tests of the Standard Model. They also give information about the structure of the proton. In parity-violating electron-proton scattering, recent results reported by the Qweak collaboration, and the proposed Møller experiment at Jefferson Lab, have the potential to give constraints on physics beyond the Standard Model, provided that critical hadronic radiative corrections involving the strong interaction are under control. In this talk I will give an overview of recent theoretical progress in our understanding of these important corrections, and of the future opportunities to exploit measurements to calibrate the theoretical predictions.
We know that the Standard Model of Particle Physics is incomplete - for example, we still do not understand the nature of dark matter, matter- antimatter asymmetry or hierarchy of the three generations of elementary particles. There is a wide spectrum of experiments searching for new particles beyond the Standard Model (BSM), broadly defined by three domains - Energy, Cosmic and Precision frontiers. The Energy frontier concentrates on the high-energy production of BSM particles, the experiments at the Cosmic frontier are dedicated to astrophysical searches of the products of the decays of BSM particles, and the Precision frontier is focused on low-energy but high-precision searches mostly in parity-violating high-intensity scattering. At the Precision frontier, we look for the BSM particles acting as the interaction carriers, having a small, but potentially detectable impact on the scattering observables. The talk will outline the latest advances in the precision parity-violating BSM physics searches in both theory and experiment.
We describe a monolithic thin-film buckling process used to fabricate arrays of high-finesse, tunable, curved-mirror Fabry-Perot cavities on a chip. Arrays of small-mode-volume cavities exhibit good uniformity and nearly reflectance-limited finesse. The process has been adapted to a variety of thin film material combinations, for operation throughout the visible and near-infrared regions. Ongoing efforts to integrate gas-phase, liquid-phase and solid-state light emitters, and to integrate cavity resonance tuning mechanisms, will also be described.
For cavity QED applications, these cavities offer an intriguing mix of potential advantages. Their monolithic fabrication by buckling self-assembly results in smoothly curved mirrors forming a ‘self-aligned’ cavity with highly predictable Gaussian mode properties. Furthermore, the cavities have a hollow core which is effectively enclosed by upper and lower Bragg mirrors. This can lead to significant inhibition of background emission for emitters embedded within the air core, particularly if the Bragg mirrors have sufficiently high index contrast to provide an omnidirectional reflection band. Preliminary results from a theoretical study of dipole emission inside cavities with Si/SiO2-based omnidirectional Bragg mirrors will be presented. Using parameters extracted from previously fabricated cavities (operating in a fundamental spatial mode regime at ~ 1550 nm with modest Q ~2000 and low mode volume on the order of one cubic wavelength), and an optimally located emitter, we predict simultaneous Purcell enhancement of emission into the cavity mode by ~120 and suppression of background emission by ~25. These results imply a potential for high cooperativity and a near-unity spontaneous emission coupling factor, even for a relatively broad line-width emitter.
While quantum properties of light promise much-needed enhancements to metrology, further development of quantum light sources are needed to readily harness energy-time correlations for applications in imaging and spectroscopy. Spectrally broadband photon pairs, generated from the process of spontaneous parametric down-conversion (SPDC), require tight energy-time anti-correlations in order to achieve appreciable quantum frequency conversion rates needed in many of these applications. Such photon pair sources with Type-0 (eee) wave interactions have been characterized for periodically poled potassium titanyl phosphate (PPKTP) but not for periodically poled lithium niobate (PPLN), a more nonlinear, or efficient, crystal. Here, we demonstrate an easier method of (indirectly) characterizing the “x-spectrum”, or coupled spatial and spectral photon emission properties, in a simpler, single-shot method of SPDC spatial mode measurement. A high brightness photon pair source, operating at 532 nm → 1064 nm + 1064 nm, is characterized with this method using a ubiquitous silicon CCD beam profiling camera and spectral filters and compared with a theoretical model. Such a method and a model can allow for tailored control of spatial and spectral entangled photon pair properties and is adaptable to other photon pair source brightnesses and camera efficiencies. This can be especially useful in quantum optical experiment design.
Single photons play an important role in several quantum technologies, acting as flying qubits to transfer quantum information for both computing and communication applications. In many cases, it is acceptable for these single photons to be produced randomly, as long as they are accompanied by heralding signals announcing their creation. Such heralded single photons sources are straightforward to implement with pairs of photons produced by spontaneous parametric downconversion, by detecting one photon from a pair to announce the presence of its partner. However, the quality of single photons produced in this way is limited. Detector dark counts and multi-pairs events inevitably lead to cases where, instead of preparing a state with one photon, several photons or no photons at all are produced. To address this issue, we propose the use of a second downconversion stage to precertify the presence of a heralded single photon. We show the additional heralding signal provided by this scheme leads to sources with improved single-photon properties, as quantified by the heralded second-order correlation function, g(2). Significantly, we find that this improvement is present even at equal single-photon production rates, and can be achieved with current detectors and downconversion crystal. Our results are most relevant to applications in which single photon with high number purity are essential.
A trace gas detection device has applications in environmental monitoring and healthcare. Authors will present the working principle of a trace gas sensor operating at room temperature, which was developed using the intracavity absorption spectroscopy method. In the system, a gas cell based on hollow core photonic crystal fiber (PCF) was used as an intracavity cell. The experiments were repeated using a multi-pass gas cell and compared with the results from the PCF based gas cell. The laser wavelength was selected by a fiber Bragg grating (FBG) with a peak wavelength close to one of the absorption lines of the gas sample to be detected. The presentation will include results based on the greenhouse gas, nitrous oxide (N2O), and acetylene (C2H2). The effect of off-resonance laser wavelength, response time and the detection limit of the device will be discussed. Finally, authors will present the application of the device for the measurement of N2O flux. The system can be made to operate in the detection of other gases by using a tunable FBG.
The research was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Foundations for Innovations.
The strong interactions between Rydberg atoms provides an exciting platform for quantum nonlinear optics. Rydberg blockade (where a cloud of many atoms is unable to support more than a single excitation due to dipole interactions) combined with electromagnetically induced transparency (EIT) (where on-resonant absorption is suppressed due to the presence of a second coupling field) has been used to demonstrate single photon generation, strong photon-photon interactions, and quantum memory. Despite these advances, Rydberg blockade is unsuited for other important applications in quantum nonlinear optics, like quantum non-demolition measurements of photon number, and photon-number squeezing. This is because Rydberg blockade treats all photons after the first photon (which caused the blockade) indistinguishably. Here, we report on an experiment far from the blockade regime where weak Rydberg interactions enable an optical pulse propagating through a cloud of atoms to acquire a phase shift proportional to the number of photons in a second optical pulse. We present preliminary observations of the phase shift as a function of photon number and Rydberg principal quantum number. We discuss possible next steps towards harnessing this enhanced Kerr nonlinearity for photon-number squeezing and non-demolition measurement.
Revealing the local electronic properties of surfaces and their link to structural properties is an important problem for topological crystalline insulators (TCI) in which metallic surface states are protected by crystal symmetry. As a first step toward this goal, we have studied the epitaxial growth of SnTe films and characterized their structural and electronic properties by molecular beam epitaxy using scanning probe microscopy, non-contact atomic force microscopy, low-energy and reflection high-energy electron diffraction, X-ray diffraction, Auger electron spectroscopy, and density functional theory [1,2]. Initially, SnTe (111) and (001) surfaces are observed; however, the (001) surface dominates with increasing film thickness. The films grow island-by-island with the [011] direction of SnTe (001) islands rotated up to 7.5° from SrTiO3 [010]. Although films with a mosaic spread in the epitaxial alignment are generally undesirable, in this case they provide a route to creating periodic symmetry breaking defects that may be used to pattern topological states. Microscopy reveals that defects on different length scales and dimensions that affect the electronic properties, including point defects (0D); step edges (1D); grain boundaries between islands rotated up to several degrees; edge-dislocation arrays (2D out-of-plane) that serve as periodic nucleation sites for pit growth (2D in-plane); and screw dislocations (3D). These features cause variations in the surface electronic structure that appear in STM images as standing wave patterns and a non-uniform background superimposed on atomic features. The results indicate that both the growth process and the scanning probe tip can be used to induce symmetry breaking defects that may disrupt the topological states in a controlled way.
[1] O. E. Dagdeviren et al., Advanced Materials Interfaces 4, 1601011 (2017).
[2] O. E. Dagdeviren et al., Physical Review B 93, 195303 (2016).
Percolation is a geometric condition that occurs naturally in the growth of two-dimensional (2D) films (and in many other contexts). Atoms that are deposited on a substrate aggregate to form isolated islands whose size bounds the range of correlated behavior, or correlation length, of the system. At greater deposition the islands coalesce, and at a critical fractional coverage of the substrate, p=p_c, at least one island forms a connected path throughout the entire sample. Then the correlation length has diverged and the system has “percolated”. The percolation transition is a second order phase transition. When the deposited atoms normally support magnetic phases, the percolation transition is often accompanied by a second order magnetic transition, and can be studied using the magnetization M or susceptibility χ. Most experimental studies of percolation measure the properties of a series of samples, each with a fixed coverage, as a function of temperature or an applied field to determine whether or not it has percolated. This method cannot record and investigate percolation as it occurs. Our recent experiments on Fe/W(110) take the unusual approach of measuring χ(p) as the film grows at constant temperature and percolation occurs.
We have detected a sharp, narrow peak in χ(p) near a Fe coverage of one atomic layer on W(110) that is consistent with a second order phase transition. Using measurements at a series of constant temperatures, we have constructed the phase transition line in the (p,T) plane, and compared it quantitatively to the predictions of scaling theory as applied to the bicritical point (p_c , T=0). We have also made quantitative comparisons of measurements of χ(p≈p_c , T) and χ(p, T=255 K) to scaling theory and found that the phase transition is in agreement with the predictions for the 2D percolation of a 2D Ising system. In particular, we measure the percolation critical exponent of the susceptibility (or mean island size) to be γ_p=2.39±0.04, in excellent agreement with the theoretical value of 43/18.
The molybdenum oxide bronzes are a family of low-dimensional materials exhibiting interesting behavior including superconductivity, charge-density wave states, and metal-insulator transitions. After considerable study, there is still no firm consensus regarding a theory to explain their unique features. We have synthesized single crystals of blue bronzes A0.3MoO3 (A=K, Rb) and purple bronzes A0.9Mo6O17 (A=Li, Na, K) using a gradient flux technique and have investigated the optical properties of these materials along different crystallographic axes using optical reflectance spectroscopy. We have taken advantage of annealing the single crystals in various gas flows to analyze changes in their properties after annealing in hopes of contributing to the understanding of the mechanisms at play in these low-dimensional materials. Changes in their structural and magnetic properties upon annealing were investigated via X-ray diffraction and magnetization measurements and will also be reported.
The intent of this project was to compare the electrical outputs of two types of solar cells under different treatments in a high altitude and low atmosphere environment. Four cells were compared: a standard photovoltaic (PV) cell, a Gallium Antimonide (GaSb) thermophotovoltaic (TPV) cell sensitive to infrared radiation, and another pair of PV and TPV cells under Fresnel lenses treatment (PV-F, TPV-F). The cells were mounted on a custom-designed scientific payload, which was integrated on a high altitude balloon launched at NASA’s Columbia Scientific Balloon Facility location in Fort Sumner, New Mexico. The payload data were collected throughout the balloon’s ascent, and at the balloon’s float altitude of approximately 33km. Analysis of the results, when normalized for difference in surface area between cells, suggest that the PV cells consistently produced more current than the TPV cells, both with and without Fresnel lenses. The PV cell produced an average of 1.498 times more current than the TPV cell, while the PV-F cell produced an average of 1.611 times more current than the TPV-F cell. Additionally, the PV cell produced an average of 1.574 times more current than the PV-F cell, while the TPV cell produced an average of 1.693 times more current than the TPV-F cell. Therefore, the data suggest that PV cells perform better than TPV cells, and that Fresnel lenses decrease the output of both cell types. Further exploration of the results in a current/time analysis showed a strong correlation between the PV and TPV cells, and a strong correlation between the PV-F and TPV-F cells, with different trends appearing in each pair of data comparisons. Analysis of the variation in trends in data between the PV and TPV cells and the PV-F and TPV-F cells allowed for conclusions regarding the reasons for the overall hindrance caused by the Fresnel lenses during flight. Comparing the performance of PV cells and TPV cells, it is clear that the current technology used in TPV cells do not make them viable for high altitude applications.
Many extensions to the Standard Model predict new particles at the TeV scale which decay to pairs of electro-weak gauge bosons. The ATLAS detector is one the most sensitive probes for these scenarios because it studies the LHC collisions which have unprecedented center of mass energies and luminosity. In conjunction with new experimental techniques for identifying the hadronic decays of weak bosons, searches have been able to greatly increase the sensitivity for these TeV scale resonances. In this talk I will summarize recent results from diboson resonance searches with the 36.1fb-1 of 13TeV pp collision data with ATLAS.
The recent discovery of the Higgs boson (h) is an affirmation of the
Standard Model (SM) of particle physics and concludes several decades of
experimental searches. However, the experimental investigation of its
properties has just begun. Current measurements of h properties permit
the fraction of h decays to Beyond-Standard-Model (BSM) particles to be
as high as approximately 30%. These exotic decays are also
well-motivated theoretically. Of particular interest is the decay of h
to two dark sector particles each called Zd. This decay occurs in models
where h interacts with a dark sector which could have a rich and
interesting phenomenology like the SM. A dark sector could naturally
address many of the questions left unanswered by the SM. The higher rate
of h production resulting from the increased proton beam intensity and
energy of the Large Hadron Collider (LHC) in the 2015-2018 data-taking
run – combined with strong theoretical motivation and tantalizing hints
seen in past searches – makes this decay a promising avenue for the
discovery of new physics. I will present current results of this search, and prospects for the full 2015-2018 dataset.
As first discussed by U. Fano in the 1940’s, the statistical fluctuation of the number of e-/ion pairs produced in an ionizing interaction is known to be sub-Poissonian, the dispersion being reduced by the so-called “Fano Factor”. Despite this knowledge, the Poisson distribution is commonly used to model the quantization of ionizing processes while the effect of the reduced dispersion is folded in with other processes affecting energy resolution. While this approximate treatment is valid down to relatively low energies, experiments now have energy thresholds low enough such that more accurate modeling on the order of a few pairs has become necessary.
We propose a new approach to this problem using a novel discrete probability distribution not well-known in the field of particle physics. The validity of this treatment is supported with calibration data obtained with a spherical proportional counter from the NEWS-G dark matter search experiment. As an application of this, the potential impact of the Fano Factor on sensitivity to low mass WIMPs is discussed as well.
Throughout Run II ATLAS has maintained an extensive, varied program of searches for physics beyond the Standard Model. Searches for supersymmetry cover strong and electroweak production as well as R-parity violating scenarios, while Exotic analyses search for heavy bosons, dark matter mediators, exotic Higgs production, and much more. This talk will show highlights of the Run II search results so far and lay out plans for analyses in the full dataset and beyond.
It is now 100 years since Planck received a Nobel Prize for describing blackbody radiation. It is 75 years since McKellar found a background temperature of molecules in space and 55 years from the recognized discovery of the cosmic microwave background. Measurements of the spectrum, and the the anisotropy of the intensity and polarization patterns of the CMB have told us about thermal equilibrium in the first weeks of the Universe, the geometry, baryon fraction and expansion history of the Universe and constrain neutrino masses, among many other things. I will describe these measurements and also the current experimental efforts to measure large angular scale odd-parity polarization patterns in a hope to understand cosmic inflation and perhaps GUT-scale physics.
I will explain how observations of the cosmic microwave background constrain theories of the early universe. I will then present some cosmological models whose predictions are in agreement with current observations, and explain how future observations may be able to differentiate between these models.
It is well established that the near singularity dynamics of a Bianchi IX spacetime can be characterized as a series of transitions between Kasner solutions (BKL map). The majority of results obtained in this limit rely on an (intrinsic) geometric time variable (f(g)). This time variable is not suitable to determine the intermediate regime dynamics of Bianchi IX with matter. We study Bianchi IX with dust and show that using dust as time can give us a handle on the intermediate dynamics; a transition map involving a degree of freedom from the matter sector, which reduces to the BKL map near the singularity. Moreover, the analysis gives us a new physical picture in which the dynamics is characterized by a series of transitions between Bianchi I solutions with dust.
The cosmological constant problem is described as one of the greatest crises of modern physics. The conventional problem is posed in the framework of quantum fields on a fixed background and their semiclassical backreaction on gravity. In this talk, expanding on a recent proposal, I will argue that this problem does not arise in a fully non-perturbative gravity-matter framework. I will show how vacuum energy density depends on a choice of global time and physical Hamiltonian, and how it varies from one choice to another.
The GlueX experiment is located in the recently constructed experimental Hall D at Jefferson Lab (JLab), and provides a unique capability to search for hybrid mesons in high-energy photoproduction, utilizing a 9 GeV linearly polarized photon beam. Commissioning of the Hall D beamline and GlueX detector was recently completed and the data collected in the spring of 2017 officially began the GlueX physics program. The statistical precision of this initial dataset surpasses the previous world data on polarized photoproduction in this energy domain by orders of magnitude. First results from this dataset will be presented along with the plan for acquiring higher statistics datasets to begin the search for hybrid mesons at GlueX.
Quantum chromodynamics (QCD), the fundamental theory of the strong interaction, tells us that when quarks are close together (high energy) the interaction is feeble but when they are far apart (low energy) the strong force is intense. Currently, QCD can accurately describe the high energy regime, but calculations are difficult in the non-perturbative, low energy regime. At Jefferson Lab (JLab), 12 GeV electrons impinge upon a variety of targets in experimental Hall C, making it a prime location to probe how QCD transitions from the high energy to low energy regime.
There are two spectrometers in Hall C called the High Momentum Spectrometer and the Super High Momentum Spectrometer (SHMS). The SHMS features a suite of detectors used to track and identify particles to extract meaningful quantities from the experiment. One such detector is a gas Cherenkov used for identification of charged particles based off their velocity. If a particle passes through the detector faster than the speed of light in the media, characteristic Cherenkov radiation (photons) will be produced. The detector is outfitted with photomultiplier tubes which collect this light and convert it to an electrical signal, which is measured. Lighter particles of equal momenta produce more light, allowing us to distinguish between different species.
In this presentation I give a general overview of the JLab accelerator facility and the experimental Hall C. This will include a description of the detector stack in the SHMS and the role the HGC plays. I will then talk about the HGC specifically, how it was designed and the theory behind Cherenkov radiation. Next the calibration procedure will be shown, demonstrating how the detector is gain-matched and capable of performing particle separations. Afterwards I will show how the efficiency of the HGC is determined. Lastly I will show some simulations of the HGC and how they compare to the experimental data.
Exclusive meson electroproduction at different squared four-momenta of the exchanged virtual photon, $Q^2$, and at different four-momentum transfers, $t$ and $u$, can be used to probe QCD's transition from hadronic degrees of freedom at long distance scale to quark-gluon degrees of freedom at short distance scale. Backward-angle meson electroproduction was previously ignored, but is anticipated to offer complimentary information to conventional forward-angle meson electroproduction studies on nucleon structure. The results of our pioneering study of backward-angle $\omega$ cross sections through the exclusive $p(e,e'p)\omega$ reaction will be presented. The experiment was performed as part of E01-004 in Jefferson Lab Hall C, with central $Q^2$ values of 1.60 and 2.45 GeV$^2$, and $W$=2.21 GeV. The extracted cross sections were separated into transverse (T), longitudinal (L), and LT, TT interference terms. The data set has a unique coverage of $u\sim$ 0, opening up a new means to study the transition of the nucleon wave function through backward-angle experimental observables. Plans to extend these studies to the $\pi^0$ and $\phi$ channels will also be presented.
The Solenoidal Large Intensity Device (SoLID) is a new detector planned for installation at Jefferson Lab's (JLab) Hall A, as part of the 12 GeV era of JLab physics. This detector will have a large acceptance, and be capable of operating at high luminosity, enabling multiple new experiments probing the inner structure of nucleons. We have received funding from CFI and Fedoruk Institute to build a prototype segment of SoLID's Heavy Gas Cherenkov detector (HGC) at University of Regina, in conjunction with Duke University. This detector will contain $C_4F_{10}$ gas at a pressure of 1.5 atm, and will be used in identification of both positive and negative pions. In this talk we discuss the design challenges of the SoLID HGC, which must be strong enough to hold the pressure without bursting or leaking the expensive gas, and must have an entry window as thin as possible, to minimize impact on the data.
Double-beta (ββ) decay measurements are a class of nuclear studies with the objective of detecting the neutrinoless (0ν) decay variants. $^{96}$Zr is of particular interest as a ββ decay candidate as it has one of the shortest ββ decay half-lives and largest Q-values. A geochemical measurement of its ββ decay half-life was previously performed by measuring an isotopic anomaly of the $^{96}$Mo daughter in ancient zircons. This measurement yielded a value of 0.94(32)x10$^{19}$ a [1]. More recently, the NEMO collaboration measured the half-life by a direct count rate measurement to be 2.4(3)x10$^{19}$ a [2], twice as long as the geochemical measurement. $^{96}$Zr is also distinctive in that it can undergo a highly forbidden single β decay to $^{96}$Nb, which then immediately decays to $^{96}$Mo, with a theoretical half-life > 10$^{20}$ a. The geochemical measurement of the $^{96}$Zr half-life does not discriminate between these two decay channels, and thus could provide a way to measure the single-beta decay rate.
We aim to study this system through a series of experiments combining nuclear physics and geochemical techniques. We are measuring the amount of daughter product of the decay of $^{96}$Zr→$^{96}$Mo in 2.72 Ga zircons (ZrSiO$_4$). The zircons, which have remained a closed system over their lifetimes, are especially suitable for this investigation due to their high Zr content and low natural Mo content. This makes it possible to detect the small amount of accumulated decay product as an excess compared to the natural Mo isotopic composition.
A discussion of advances in the techniques required for the geochemical measurement will be presented. These advancements have enabled us to produce the first measurements of Mo isotope composition from 2.76 Ga zircons using MC-ICP-MS. The implications for the single and double β decay half-life will be discussed along with future directions.
[1] Wieser and De Laeter (2001), Phys. Rev. C 64, 024308.
[2] NEMO-3 Collaboration (2010) Nucl. Phys. A 847, 168-179.
Recent studies have suggested that structured laboratory activities may not be the most effective way of teaching content and concepts to first year physics majors. We examine and extend that investigation to a high-enrollment Introductory Physics for the Life Sciences course. Using a varied laboratory curriculum, we correlate quiz marks, exam marks, and student attitudinal data to determine whether specific concepts were reinforced by laboratory activities. We also attempt to ascertain what additional skills are delivered by labs; whether they should be considered conceptual instruction tools, focused on practical skills, research or data analysis skills, a hybrid of all, or something else entirely. Initial results suggest that a highly scaffolded lab that limits inquiry in favour of specific content instruction may not be the most effective tool for content reinforcement.
Physics is an empirical science. Therefore, learning physics must include learning how to design and conduct experiments, analyze and interpret data, and revise models and apparatus. Physics lab courses at the introductory and upper-division levels are one of only a few opportunities for students to engage in these authentic physics practices. For many students, instructional labs are the only opportunity. However, these courses do not always have the students reach the desired learning goals. Our work looks to improve lab experiences by improving students' competency with modeling of physical and measurment systems, troubleshooting skills, documentation practices, and views of the nature of experimental physics.
Undergraduate students are typically introduced to advanced optical instrumentation during their senior physics and chemistry courses. Experiments available from educational companies typically use low end optics in customized formats, beneficial for younger students eager to explore the physical and chemical phenomena under study. However, these setups prevent senior students from learning more advanced optical techniques increasingly desired by employers, such as experience with laser beam alignment, laser beam quality and divergence, the function of real (imperfect) optics, and limitations of photodetectors. Therefore, senior students would benefit from experience with the same professional equipment used in advanced research and development laboratories.
Consequently, we have developed three laboratory modules that provide students with the opportunity to build their own advanced instrumentation, allowing them to learn laser-based instrumental procedures while simultaneously determining the function of advanced optical components. In one experiment, students build a laser interferometer with which they study the temperature dependency of the refractive index of solutions. In a second module, students develop their own laser-beam profiler. In a third experiment, students develop their own laser-based polarimeter to measure polarization scattering and optical rotation by incorporating Stokes-based measurements.
The experiments consist of standard laboratory optics and optomechanics, more expensive than the low-cost versions of these instruments, but less expensive than the instruments sold by educational companies. Further, these parts are of high quality, and by choosing standard optics, compatibility issues are nonexistent. Optical components can be easily re-combined to produce alternative arrangements, allowing senior students to perform novel proof of principle optical techniques in literature. As a result, students gain understanding, confidence, and excitement for science, as well as practical experience by assembling, operating, and troubleshooting their devices. Furthermore, because students use the same equipment found in professional optics labs, they are more prepared for the workplaces of tomorrow.
A common complaint from students in undergraduate physics laboratories is that they spend too much time propagating uncertainties and not enough time understanding the physics. We have worked with students at Queen's University to develop QExpy, a python package designed to facilitate undergraduate physics laboratories, while easing students into learning to program in python. The open source package can be downloaded by anyone and allows students to easily propagate uncertainties using a variety of methods including Monte Carlo, as well as to make interactive plots and fit arbitrary models to the their data. The package was specifically designed to be easy to use, pedagogic, and well-integrated with the Jupyter Notebooks framework. QExpy has been used by several hundred students at Queen's University, including first year students, and this presentation will highlight some of its features.
Electroless copper films are used in printed circuit board industry to establish a conductive layer on insulating substrates. These films may have failures (voids, blisters) related to stress and/or hydrogen co-deposition in Cu films. Typical methods to determine amount of hydrogen are destructive and indirect. We have developed a time-resolved method to measure amount of hydrogen released from Cu deposits after plating. At ambient conditions, films with high initial hydrogen loading release hydrogen for several days. Hydrogen content and hydrogen-related compressive film stress component in copper are proportional with a slope of (3.2±0.3) MPa/at.% H. Nickel, as an additive, promotes adhesion and changes stress in electroless copper film from compressive to tensile. The present work shows that nickel suppresses hydrogen incorporation into the Cu film from typically 25 to 0.01 at.% (thus explaining the stress effect), while hydrogen release during plating remains almost unchanged.
The way that water wets a surface can be controlled by manipulating surface energies and/or surface topography. Although these factors can be controlled very well on the lab scale for certain kinds of materials, it is very challenging to achieve good control on compositionally heterogeneous surfaces such as stainless steel. Here, we show that mildly alkaline electrolytes can be used to produce zinc electrodeposits that, when capped with stearic acid to prevent oxidation, can improve the water repellent properties of stainless steel. The electrolyte composition and the applied potential during deposition influence the growth morphologies of crystallites within the electrodeposit. The capped electrodeposits display an impressive degree of water repellency, including extremely poor water droplet adhesion. We discuss physical and chemical factors that contribute to the water-repellent behaviours of these electrodeposits, and describe their potential applications to mitigate icing and corrosion in harsh offshore environments.
Advances in THz generation have enabled a wide range of new scientific tools that probe previously inaccessible dynamics in materials. In the area of scanning tunneling microscopy the capability of generating large amplitude THz pulses have enabled practical ultrafast scanning tunneling microscopy experiments. In a THz-coupled scanning tunneling microscope (THz-STM), THz pulses couple to the tip of the microscope and provide a means to modulate the electric field at the microscope’s tunnel junction thus allowing ultrafast control of the tunnel current. Using a THz time domain spectrometer, THz pulses can then be used to achieve stroboscopic ultrafast time resolution in STM experiments. The operating principles of a THz-STM will be introduced along with the results of a recent experiment on charge density wave (CDW) state supported by niobium diselenide. In this experiment the response of the CDW state to strong electric field pulses was examined using a THz-STM to extract the response of individual atomic site. This allowed a measurement of the impact a single individual atomic defect has on the dynamic modes of the CDW state.
Roll-annealed (RA) copper foils are commonly used in the printed circuit industry as flexible conductive base materials. The RA process produces foils with the crystallites aligned in particular directions. RA foils used in applications have either {100}<001> “cube” texture, or a mixture of {112}<111> “copper”, {123}<634> “s” and “cube” textures. Manufacturing circuits requires the deposition of electroless and galvanic Cu layers on the RA foils. The substrate texture can lead to growth of large epitaxial crystals with a rough surface, which causes problems in subsequent processing steps. We show that with an appropriately designed electroless Cu interlayer, the deposit texture is sufficiently suppressed and a smooth galvanic layer is obtained. We present XRD pole figure based analysis of substrates and electroless/galvanic deposits.
The structure and properties of perovskite substrates have attracted substantial interest due to material’s popularity as a substrate for complex oxide epitaxy [1,2]. Strontium titanate (SrTiO3) is among the most popular perovskites, with film quality dependent on the structure of the substrate at the beginning of the growth process. Here, we examined the surface structure of SrTiO3 (100) single crystals as a function of annealing time and temperature in either oxygen atmosphere or ultra-high vacuum (UHV) for a variety of different preparation schemes using scanning probe microscopy, auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) [1]. We find that the SrTiO3 surface evolves depending on the preparation scheme with respect to surface roughness, surface terminations, and surface reconstruction. Non-contact atomic force microscopy (NC-AFM) images, e.g., reveal a non-monotonic trend of surface roughness with respect to UHV annealing temperature. Interestingly, the surface roughness changes also as a function of the bias voltage applied to the surface. This can be explained by the effect of the electrostatic field induced by both the Nb-doping and oxygen deficiencies in the bulk or on the surface, with the latter being a function of the preparation history. As for surface termination, we observe for initially TiO2-terminated crystals the formation of terraces with half unit cell step heights between them with increasing UHV annealing temperatures, implying that multiple terminations are forming. This conclusion is corroborated by AES data, which expose an increase in Sr amount relative to Ti and O. Complementary LEED data reveals a structural phase transition from (1x1) termination to an intermediate c(4x2) surface reconstruction to ultimately a sqrt(13) x sqrt(13)-R33.7° surface phase by annealing the sample with oxygen flux, while the inverse structural phase transition from sqrt(13) x sqrt(13)-R33.7° to c(4×2) is observed when annealing in UHV. As a result, we suggest that careful selection of preparation procedure combined with applying an appropriate bias voltage during growth may be used to control outcomes of thin film growth.
[1] O. E. Dagdeviren et al., Physical Review B 93, 195303 (2016).
[2] O. E. Dagdeviren et al., Advanced Materials Interfaces 4, 1601011 (2017).
** this session needs to be on Monday or Tuesday
Superpositions of macroscopically distinct quantum states, introduced in Schrödinger's famous Gedankenexperiment, are an epitome of quantum ``strangeness" and a natural tool for determining the validity limits of quantum physics. The optical incarnation of Schrödinger's cat – the superposition of two opposite-amplitude coherent states – is also the backbone of quantum information processing in the continuous-variable domain. The talk will cover recent experimental progress on preparing such states, applying them in quantum technology and communications, and increasing their amplitudes.
Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. However, computing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods. In the spirit of Feynman's vision of a quantum simulator, this has recently stimulated theoretical effort to devise schemes for simulating such theories on engineered quantum-mechanical devices, with the difficulty that gauge invariance and the associated local conservation laws (Gauss laws) need to be implemented. Here we report the first experimental demonstration of a digital quantum simulation of a lattice gauge theory, by realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a few-qubit trapped-ion quantum computer. We are interested in the real-time evolution of the Schwinger mechanism, describing the instability of the bare vacuum due to quantum fluctuations, which manifests itself in the spontaneous creation of electron-positron pairs. To make efficient use of our quantum resources, we map the original problem to a spin model by eliminating the gauge fields in favour of exotic long-range interactions, which have a direct and efficient implementation on an ion trap architecture. We explore the Schwinger mechanism of particle-antiparticle generation by monitoring the mass production and the vacuum persistence amplitude. Moreover, we track the real-time evolution of entanglement in the system, which illustrates how particle creation and entanglement generation are directly related. Our work represents a first step towards quantum simulating high-energy theories with atomic physics experiments, the long-term vision being the extension to real-time quantum simulations of non-Abelian lattice gauge theories.
The best trapped-ion atomic clocks today are accurate to better than one part in $10^{18}$ [1]. To improve their accuracy even further, we must consider small perturbations of the clock frequency due to collisions between the clock ion and background gas atoms. Our group has recently developed a simple analytic formulation [2] to evaluate the collisional frequency shift (CFS) based on a quantum-channel description of the ion-atom scattering process. In this talk, I will present an extension of this formalism. The extended formalism estimates the CFS more accurately by considering effects such as inelastic scattering due to spin-orbit mixing, and the quantized motion of the trapped ion. Improved estimates of the CFS systematic error could lead to ion clocks that are more accurate by an order of magnitude.
References
[1] Nisbet-Jones, P. B. R., et al. "A single-ion trap with minimized ion–environment interactions." Applied Physics B 122.3 (2016): 57.
[2] Vutha, Amar C., Tom Kirchner, and Pierre Dubé. "Collisional frequency shift of a trapped-ion optical clock." Physical Review A 96.2 (2017): 022704.
Development of Utility Friendly Safe Olivine Based ESS in Esstalion Technologies.
K. Zaghiba, Y. Asakawa, J. C. Daigle, M. Yasudab, and S. Uesaka*b
§ Esstalion Technologies Incorporated, 1804 Lionel-Boulet Blvd., Varennes, Quebec, Canada, J3X 1S1
a) Center of Excellence I Transportation Electrification and Energy Storage (CETEES), Hydro-Québec, 1800 Lionel-Boulet Blvd., Varennes, Quebec, Canada, J3X 1S1
b) Tohoku Murata Manufacturing Co., Ltd., 2 Toinokuchi Motomiya, Motomiya-shi, Fukushima 969-1180 Japan
One of the promising approaches for striking a balance of realizing sustainable society and maximizing utility’s profit is to apply energy storage system (ESS). There’re many use cases proposed (1), such as reserve, regulation, peak shaving, time shift, load following, smoothing, and minimum emission. To answer these demands, the development of a battery with high rate of charging and discharging, a longer cycle life and safe is imperative.
Esstalion Technologies Inc. was established in 2014 as a joint venture company between Sony Corporation and Hydro-Québec.(2) . By September 2017, Sony Corp. has sale of its battery business to electronic parts maker Murata Manufacturing Co.
We are the first corporate joint venture between battery manufacturer and utility.
Since then, we’ve developed utility friendly ESS based on lithium ion battery technology for grid scale utilization.
Since we put our importance on safety and long-life, our core technology is olivine based material which is patented by Hydro Québec and commercialise by Sony as Fortelion. (3)
We’ve started in field testing using 1.2 MWh ESS in 2016.
In Esstalion, we try to bring innovation by gathering “multi-wisdom” in ONE ESSTALION team, doing the new material research, BMS/EMS development and ROI calculation etc.
We propose a brief review of our technologies and we will show an example of our efforts to enhance the key properties of the Li-ion battery.
(1) Pacific Northwest National Laboratory, Protocol for Uniformly Measuring and Expressing the Performance of Energy Storage Systems
(2) Press Release, Establishment of Esstalion Technologies, Inc., a joint venture between Hydro-Québec and Sony, 2014
(3) News Release, Sony Launches High-power, Long-life Lithium Ion Secondary Battery
Using Olivine-type Lithium Iron Phosphate as the Cathode Material, 2009
Tuning positive electrode materials in lithium-ion cells provides a promising means for lowering cost of materials while maintaining safety and energy density standards. Due to the rising cost of cobalt, it is important to find less expensive alternatives. Here we present results from first-principles computations within the formalism of density functional theory examining changes in electronic properties and thermodynamic stability of Li$_{x}$Ni$_{1-y-z}$Al$_{y}$Co$_{z}$, where $0\lt x \lt 1$ and $0\lt y,z \lt 0.2$, positive electrode materials as a function of cobalt, aluminum, and lithium content. Results using a new exchange-correlation functional (SCAN) [1,2] within the class of meta-GGAs are compared with the traditionally employed empirical GGA+U. Fundamental understanding of these properties may help in designing less expensive positive electrode materials.
[1] Strongly Constrained and Appropriately Normed Semilocal Density Functional, J. Sun, A. Ruzsinszky, and J. P. Perdew, Phys. Rev. Lett. 115, 036402 (2015)
[2] Accurate first-principles structures and energies of diversely bonded systems from an efficient density functional, J. Sun et al., Nature Chemistry 8, 831–836 (2016)
Lithium ion batteries are used in consumer electronics, electric vehicles and grid energy storage.1 New positive electrode materials like LiNi1-x-yMnxCoyO2 (NMC) are required to increase energy density, lower cost and increase lifetime. Conventional NMC has large secondary particles (10 - 15 µm) made of agglomerates of small grains (~ 200 - 500 nm) and is thus called polycrystalline NMC.2 Commercially available single crystal NMC532 materials show particles that are about ~3 µm in size, and were shown to have superior stability at high voltages and elevated temperatures compared to conventional polycrystalline NMC532 by the authors.2 Conventional LiNi0.6Mn0.2Co0.2O2 (NMC622) usually offers more capacity than NMC532 when charged to the same upper cut-off voltage so NMC622 is attractive.3 It is expected that single crystal NMC622 could also provide better performance than typical polycrystalline NMC622 materials. This work explores the synthesis of single crystal LiNi0.6Mn0.2Co0.2O2 and preferred synthesis conditions were found. A washing and reheating method was used to remove residual lithium carbonate after sintering. The synthesized single crystal NMC622 material worked poorly without the use of electrolyte additives in the electrolyte. However, with selected additives, single crystal cells outperformed the polycrystalline reference cells in cycling tests. It is our opinion that single crystal NMC622 has a bright future in the Li-ion battery field.
To further progress the adoption of electric vehicles and other high power energy storage applications, it is desirable to develop lithium-ion cell chemistries that offer longer lifetimes at high temperatures and cell voltages, without significantly increasing the cost. The introduction of sacrificial electrolyte additives on the order of a few weight percent is a practical method to form protective solid-electrolyte interphase (SEI) layers that limit electrolyte decomposition during cell storage and operation. In recent years, significant efforts have provided new understanding of the underlying chemistry of several such additives, including sulfur-containing heterocyclic compounds and species that contain a Lewis acid-base adduct.
This work will present how density functional theory (DFT) calculations have been used to explore the underlying chemical reactions leading to SEI formation. Two sulfur-containing additives, prop-1-ene-1,3-sultone (PES) and ethylene sulfate (DTD), and two Lewis adducts, pyridine boron trifluoride (PBF) and pyridine phosphorus pentafluorophosphate (PPF), will be discussed. The DFT results offer new insight into the onset potential and reaction products of electrochemical reduction. By pairing DFT with a diverse set of experimental techniques, including X-ray photoelectron spectroscopy, isothermal microcalorimetry, solid-state nuclear magnetic resonance spectroscopy, gas volume measurements, and electrochemical techniques, new SEI components are proposed for each additive.
In general, the results in this work confirm previous recommendations that a wide variety of experimental techniques, coupled with computational methods such as density functional theory, can offer new insights into the underlying chemistry of SEI formation in lithium-ion cells. It is hoped that future work can apply the results of this work to understand what makes a ‘good’ electrolyte additive and, ultimately, to design new and improved electrolyte cell chemistries.
The Belle II electron-positron collider experiment at the KEK laboratory in Japan is undergoing detector commissioning this year, with first data taking using the full detector planned for early 2019. I will present the physics goals and current status of the project with a summary of recent activities relating to detector construction and the commissioning of the SuperKEKB accelerator. I will also report on the activities of Canadian groups that contribute to Belle II, as we commence the operational phase of the project.
We study the potential for using CsI(Tl) pulse shape discrimination in order to improve particle identification at high energy electron-positron collider experiments such as the Belle II experiment. Using neutron and proton testbeam data collected at the TRIUMF Proton Irradiation Facility we analyze the scintillation pulse shape differences between photon and hadron energy deposits and demonstrate that the pulse shape variations in CsI(Tl) for hadronic energy deposits can be characterized using an additional scintillation component for CsI(Tl) [1]. Using this new pulse shape characterization techniques for computing the pulse shapes for CsI(Tl) are develop and applied to GEANT4 simulations. With these simulations comparisons are made with testbeam data and predictions for the performance of CsI(Tl) pulse shape discrimination for separating high energy electromagnetic and hadronic showers will be presented. Ongoing work to incorporate pulse shape discrimination into the Belle II experiment will also be discussed.
[1] S . Longo and J . M . Roney, "Hadronic vs Electromagnetic Pulse Shape Discrimination in CsI(Tl) for High Energy Physics Experiments", arXiv: 1801.07774
Our current knowledge of particle physics is best described by the standard model (SM). Despite this, astronomical observations of dark matter made over the past few decades mean that the SM must be incomplete. New models are now motivating the possibility of dark matter being governed by the an extended $SU(3)$ gauge theory resembling Quantum Chromodynamics (QCD) for the strong force. This model includes a stable dark baryon, similar to the proton, as a possible dark matter candidate. If these dark hadrons are accessible at the LHC the dark analogue to the quark will produce a parton shower throughout the detector volume, eventually fragmenting into jets of invisible (dark) colour singlet hadrons. When the unstable particles eventually decay into visible quarks/leptons, a novel jet structure will be seen displaced from the proton-proton collision vertex, termed an 'emerging jet'. With the experiments at CERN producing enormous amounts of data per collision, triggers are implemented for reducing the data by means of vetoing events that deviate from a set of pre-defined criteria. These triggers could potentially throw away an interesting signal if not properly optimized. We use existing triggers, alone and in combination, in obtaining the maximum detected efficiency of an emerging jets signal. The same tools that are familiar for QCD are used to simulate these processes under identical conditions at the ATLAS $\&$ CMS experiments. Alongside simulating highly energetic, simple 'toy' processes, interactions with added particle radiation give a better gauge to the complicated dynamics of the theory. The extracted efficiencies corresponding to various triggers will be presented. Finally, new methods of signal discrimination will be discussed for a variety of models.
At the large hadron collider, most Z bosons are produced in a qqZ vertex, sometimes in association with jets produced via the strong interaction. A more rare production mode for Z bosons is through a triple gauge coupling via a process called vector boson fusion (VBF). This VBF Z process is similar in nature to VBF Higgs production, which is of great interest and is being studied by large groups of physicists on the ATLAS and CMS experiments. VBF Z production is interesting in its own right as a probe for new physics via the triple gauge coupling. Measurements of the cross section and kinematic distributions of VBF Z production can also be used to constrain new physics scenarios, such as fits to an effective field theory extension of the Standard Model Lagrangian. An analysis of the standard model VBF Z process is ongoing, the general structure of the analysis will be discussed along with details of the systematic variations and pileup contamination of the Monte Carlo (MC) simulation. The VBF signal is measured by extrapolating between carefully chosen regions of phase space to best model signal and background distributions. Understanding the MC simulation is crucial to making an accurate final measure of the VBF Z cross section.
Molybdenum disulfide was produced in an exfoliated state by combining molybdic acid with an excess of thiourea at 500°C under nitrogen. Nanocomposites of the conducting polymer polyaniline (PANI) and exfoliated MoS2 were then synthesized. The nanocomposites with varying percentage by weight of exfoliated MoS2 were characterized using powder X-Ray diffraction, electrical conductivity measurements, Seebeck coefficient measurements, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. An intriguing result was seen in the conductivity data, where several of the nanocomposites containing relatively small percentages of exfoliated MoS2 yielded higher conductivity overall in comparison to a sample of pure PANI. The exfoliated MoS2 used in this work is highly disordered, and is expected to be predominantly the 2H polytype. This form of MoS2 has very low conductivity, thus the increased conductivity of the nanocomposite suggests that PANI is most likely stabilizing MoS2 in its 1T metallic form, which is higher in conductivity.
This talk will look at cost effective and environmentally friendly surface treatments to improve the corrosion resistance of SS 316. Mechanically polished samples were treated by heating in deionized water, a hydrogen peroxide solution, electropolishing and heat treating in an oven. Cyclic voltammetry and optical microscopy were used to measure corrosion on the samples in a 0.9% NaCl solution. X-ray photoelectron spectroscopy was also used to analyze the composition of the different oxide layers. The greatest improvement in corrosion resistance was observed after treating the steel in a hydrogen peroxide solution. However, electropolishing also showed a large improvement while having other practical advantages.
Nitinol (nickel-titanium) alloys have a unique property, superelasticity, which allows the manufacture of minimally invasive self-expanding stents. Nitinol is approximately composed of 50% nickel, which is known to be toxic. Therefore, corrosion resistance is key to the good biocompatibility of this material, especially considering the aggressive environment of the body. We tested the effects of the surface roughness and different passivation techniques on the corrosion resistance of nitinol using potentiodynamic measurements. Furthermore, we applied environmentally friendly treatments to nitinol, boiling in hydrogen peroxide and boiling in distilled water, which substantially improved the corrosion resistance. The effects of these treatments on the oxide layer composition and morphology was investigated using x-ray photoelectron spectroscopy, grazing incidence x-ray diffraction, and scanning electron microscopy. We found that due to these treatments a more homogeneous titanium dioxide oxide layer was formed. The pitting corrosion of nitinol was also observed in real time using a microscope. This gave us novel information about the spatial distribution of corrosion.
Periodic wrinkling of a rigid capping layer on a deformable substrate is a ubiquitous example of pattern formation in nature. Many experiments have studied wrinkle formation during the compression of thin rigid films on relatively thick pre-strained elastic substrates. The resulting wrinkling wavelength and amplitude can be predicted by minimizing the bending energy of the rigid film and the deformation energy of the soft substrate. To date, most wrinkling studies have focused on the regime where the substrate thickness can be considered semi-infinite relative to that of the rigid film. In this work we use optical and atomic force microscopy to study the wrinkling behaviour of thin rigid films upon compression by a pre-strained freestanding elastic substrate which cannot be considered semi-infinite. As the ratio of substrate to rigid film thickness is decreased, the system transitions from the semi-infinite wrinkling regime to one in which the entire bilayer film buckles upon compression. This transition is found to be strongly dependent on the pre-strain in the elastic film.
Vanadium oxide (VO2) thin films have been studied extensively because of their thermochromic properties, i.e. reversible optical change as a function of temperature. These reversible optical changes, also accompanied by electrical changes make these films interesting from application point of view. Many applications such as smart windows, sensing devices, variable reflectance mirrors and many others can be envisiioned. VO2 undergoes a reversible insulator-to-metallic (MIT) phase transition at a temperature of ~ 68° C. This phase change is accompanied by a change of the optical and electrical properties. The electric resistance decreases to a few ohms and the film changes from transparent to opaque in the IR region after a phase transition occurs.
Sputtering technique was used to deposit pure vanadium thin films on glass and quartz substrates. Subsequently, the films were annealed at 500°C in a vacuum chamber in the presence of oxygen gas for 1 hour to oxidize the films to obtain stoichiometric VO2. Both electrical and optical changes during the transition insulator to metal (MIT) were studied. All the fabricated films exhibit efficient thermochromic changes. The films deposited on quartz substrates were found to show an unusual hysteresis in their resistivity in the first few cycles. XRD and XPS studies were done to understand this unusual behaviour of VO2 films on quartz substrates.
The use of enriched liquid Xe-136 (LXe) offers significant advantages to search for double beta decay processes. A discovery of the neutrinoless mode (0vbb) would reveal new properties of neutrinos including first measurement of its mass scale, evidence that they are their own antiparticles, and a first observation of lepton number violation.
The Enriched Xenon Observatory (EXO) employs a time projection chamber filled with LXe to search for 0vbb, which allows an efficient and monolithic detector, ideal to identify and separate background arising from gamma rays. The EXO-200 is a 100-kg class detector in operation at the WIPP mine in New Mexico, USA. Its latest search for 0vbb is among the world’s best, with sensitivity to the 0vbb half-life of 3.7x10^25 yr at the 90% confidence level. To further reject backgrounds, this search introduced a boosted decision tree trained on multiple topological variables. Rooted in the success of EXO-200, nEXO is a tonne-scale detector being designed to reach a sensitivity near 10^28 yr.
In this talk, the latest results with EXO-200 as well as projections for nEXO, the next generation experiment, will be discussed.
The nEXO Collaboration is developing a proposal for a 5-tonne experiment with initial neutrinoless double-beta decay sensitivity approaching to $10^{28}$ years. The nEXO detector will be a homogeneous liquid xenon (enriched to 90% in $^{136}$Xe) time projection chamber inspired by the highly successful EXO-200 detector. Energy resolution, event topology, and event localization in the large homogeneous detector will work in concert to simultaneously minimize and characterize backgrounds. In this talk we will describe the detector design choices and show the sensitivity that the detector can reach using only materials for which radiopurity has already been demonstrated.
The hydrogen atom has played a fundamental role in the development of our understanding of the universe and of quantum mechanics. This makes antihydrogen a natural candidate for testing symmetries between matter and antimatter. The goal of the ALPHA (Antihydrogen Laser PHysics Apparatus) collaboration is to synthesize, trap, and study antihydrogen atoms. ALPHA has made significant progress recently in measuring the 1S - 2S transition in antihydrogen [1], exciting the 1S - 2P transition (a laser cooling transition), and is currently constructing a new apparatus designed to measure the gravitational free fall of antihydrogen.
In addition, ALPHA is working towards high precision measurements of antihydrogen's ground-state hyperfine splitting frequency. Following an initial proof-of-principle experiment in 2012 [2], ALPHA has recently measured the hyperfine splitting in antihydrogen to be 1420.4 +/- 0.5 MHz [3]. In this talk, I will present a brief overview of ALPHA's physics program and a detailed summary of our hyperfine splitting experiments.
[1] M. Ahmadi et al. (ALPHA collaboration), Nature 541, 506 (2017).
[2] C. Amole et al. (ALPHA collaboration), Nature 483, 439 (2012).
[3] M. Ahmadi et al. (ALPHA collaboration), Nature 548, 66 (2017).
The Martian atmosphere exhibits more dynamical variability than the terrestrial atmosphere with large amplitude tides and gravity waves in addition to the seasonal dust storms. To date, there have not been dedicated wind measurements from orbit around Mars and there is some evidence that the winds do not match expectations from models. As with the terrestrial atmosphere, airglow is one means to observe Martian atmospheric dynamics. The field-widened Michelson imaging interferometer is one technique with which wind and temperature measurements can be made. The O2 IR atmospheric band is an extremely bright emission in the Martian dayglow and allows observations to be made from close to the surface to ~50 km. In this paper, our current understanding of the dynamics of the Martian atmosphere will be reviewed and the ability of an imaging Michelson interferometer to probe the dynamics of the atmosphere presented.
The Waves Michelson Interferometer (WaMI) is designed to make wind measurements of the atomic oxygen green line (557.7 nm) emission, a molecular oxygen line at 1264 nm, and a hydroxyl line at 1315 nm. These emissions provide a capability for probing the dynamics of the middle atmospheres of the terrestrial planets. The special feature of the design of this instrument is that the back mirror is a quad mirror configuration. As a result four fringe phase images can be generated simultaneously thereby eliminating the effects of irradiance variations during the integration time. The WaMI is currently set-up in a laboratory environment, with a retro-reflective wheel used to simulate Doppler winds. Results of the step size calculations, as well as, wind wheel measurements will be presented. These validate the use of this instrument as a monolithic instrument capable of measuring winds without mirror scanning for ground based and satellite applications.
A portion of upper main-sequence stars, called chemically peculiar (CP) stars, show significant abundance anomalies mainly due to atomic diffusion of chemical elements within the stellar atmospheres of these stars. Slowly rotating CP stars may have hydrodynamically stable atmospheres where a competition between the gravitational and radiative forces launches the mechanism of atomic diffusion that can be responsible for the abundance peculiarities observed in CP stars. Recently, Project VeSElkA (Vertical Stratification of Elements Abundance) was initiated with the aim to detect and study the vertical stratification of element abundances in atmospheres of CP stars. The first results from abundance analysis of several slowly rotating (Vsin(i)<40 km/s) CP stars observed recently with ESPaDOnS are presented here. Signatures of vertical abundance stratification for several chemical elements have been found in stellar atmospheres of HD22920, HD41076, HD95608, HD116235, HD148330 and HD157087.
Two high resolution and high signal to noise ratio spectra of HD176232 have been analyzed to study the chemical abundances in atmosphere of this star using the ZEEMAN2 code. These spectra were recently obtained with the spectropolarimeter ESPaDOnS at the Canada-France-Hawaii telescope (CFHT) in the frame of the project VeSElkA. The project’s objective is the search for signatures of vertical stratification of chemical element abundance within chemically particular (CP) stars. The surface gravity and effective temperature of HD176232 were derived from the fitting of nine Balmer line profiles through the FITSB2 code. Over one hundred line profiles were analyzed in each spectrum and the average abundance of 32 chemical elements were measured. Some of them, for example, cobalt, neodymium, samarium and gadolinium show a significantly enriched abundance in the stellar atmosphere of HD176232, while carbon and molybdenum seem to be in deficit. Also, our analysis reveals an abundance stratification with optical depth for calcium, cobalt, iron, manganese and nickel.
Miniaturized biosensors are essential components of continuous health monitoring systems, which are expected to significantly impact human health management. Biosensors integrate biorecognition elements with transducers to detect the presence, absence, and quantity of biologically-relevant elements. Nanoscale materials play a critical role in enhancing the sensitivity and specificity of these devices.
In this work, we have developed a fabrication toolbox for creating interfaces that combine biorecognition and signal transduction. More specifically, we use multiple tunable materials building blocks to create electrochemical or photoelectrochemical biosensors. A wrinkled scaffold with tunable feature sizes is used to create a high density network of nanoparticles. A biofunctionalized network of semiconductive or metallic nanoparticles is used to create integrated biorecognition/signal transduction interfaces. Furthermore, a network of nanoparticles featuring molecular linkers is used to reduce biofouling and non-specific adsorption in biosensors. By combining the materials strategies developed in this work, we demonstrate multiple biosensor examples for detecting specific nucleic acid sequences and protein targets. Finally, a clinically-relevant biosensor for the detection of Brain Derived Neurotrophic Factor is demonstrated.
Antimicrobial Peptides (AMPs) are small chains of between 10 and 50 amino acids with the ability to kill pathogens such as bacteria, fungus, viruses, and even cancer cells. AMPs are one of many mechanisms that living organism have developed to protect themselves from pathogenic microorganisms. Most research in AMPs is focused on understanding the mechanism or mechanisms that AMPs use to kill pathogens. In the case of bacteria, it is widely accepted that AMPs are able to disrupt the bacterial cell membrane more specifically, the lipid bilayer. In order to fully understand how AMPs are able to kill bacteria, it is also important to understand the role of other components of the bacterial cell envelope such as the lipopolysaccharides and the peptidoglycan (PGN) layer. 2H NMR is a technique that can be used to study the fluidity of lipid bilayers assemblies. In particular, 2H NMR can be used to identify order parameter changes resulting from the interaction between lipid vesicles with AMPs. Our group and others have developed methods to grow 2H-membrane-enriched bacteria. In this research, We observe the changes in the 2H NMR spectrum of different bacterial strains (E .coli LA8, E. coli JM109 and B. subtillis) in the presence and absence of different AMPs (MSI-78, CAME and BP100). Additionally, exploring the importance of the PNG layer in the interaction between the MSI-78 and BP100 with the lipids in the bacterial cell membrane of B. subtillis, we discovered that the removal of the PGN layer does not generate changes in the 2H NMR spectrum of B. subtillis. Moreover, the level of disruption observed on the lipid bilayer of B. subtillis caused by MSI-78 and BP100 does not change after the partial removal of the PGN layer.
Funded by grants to VB and MRM from the Natural Sciences and Engineering Research Council of Canada and a grant to NPS from the alliance Colciencias-Colfuturo.
Bacterial pathogens can be differentiated via an elemental analysis technique known as laser-induced breakdown spectroscopy (LIBS). This technique can be of use in the rapid identification of bacterial pathogens, for which there is a high demand, particularly in a clinical setting. The identification of bacteria with LIBS must therefore be possible with the types and numbers of bacterial cells that would be obtained from a clinical diagnostic test. This talk will introduce the underlying principles behind the technique, summarize our current progress to date, and present our efforts to advance the use of LIBS for bacterial identification in a clinical setting.
Specifically, we will describe how the laser-induced plasma is created on our bacterial targets utilizing a nanosecond pulsed laser; how the time-resolved emission spectra are collected and analyzed using a high-resolution Echelle spectrometer; and how computerized chemometric algorithms are used to differentiate the highly-similar LIBS emission spectra from different bacterial species and genera. A sample preparation method for separating the bacteria from the other unwanted biological matter that could be present in a clinical specimen will be presented. A method for mounting the bacteria that improves our bacterial limit of detection compared to previous mounting procedures will also be presented. Lastly, we will report on our efforts to detect bacteria that have been collected using pathology swabs currently in use in the clinical setting.
G protein coupled receptors (GPCRs) are a superfamily of membrane receptors known for high signal transduction efficiencies. One of the key aspects of the GPCR signaling mechanism is the coupling interaction between the receptor and the G protein in response to external stimuli. We examined the pre-stimulus receptor-G protein coupling state by single-particle tracking (SPT) of M$_2$ muscarinic receptors and G$_i$ proteins in live cells.
M$_2$ receptors and G$_i$ proteins were genetically fused with fluorescent proteins (GFP and/or mCherry), expressed in CHO cells, and imaged on a Total Internal Reflection Fluorescence (TIRF) microscope. Single particles were identified in each frame of the TIRF movies and tracked using the TrackMate software. Mean-squared displacement (MSD) functions were computed for each single-particle trajectory. The diffusion parameters for receptors and G proteins were obtained by fitting their MSD functions to appropriate diffusion models.
Both the M$_2$ receptors and the G$_i$ proteins exhibited significant fractions of confined diffusion (compatible with the membrane compartment formed by actin microfilament-based meshwork) and active transportation (compatible with the rate of myosin trafficking along actin microfilaments). The motions of the M$_2$ receptors and of the G$_i$ proteins were distinctive from each other in the basal state of receptors, but they became similar when the receptors were activated by the agonist. Corroborated with dual-color fluorescence correlation spectroscopy measurements performed on the same samples, the SPT results supported a transient recruitment model without a stable pre-stimulus coupled complex.
One way to motivate students to learn physics is to use examples of daily life where it applies, and sports are a good example. Ice hockey is particularly rich in the variety of physics elements it contains, from the biomechanics of skating, to shooting and puck aerodynamics, to player collisions. With the help of physics and statistics, I will tackle fun questions like Can a hockey puck become airborne? Why is ice so slippery? From how far away can goalies stop pucks travelling at 160 km/h? Why are NHL goalies becoming taller? Are collisions at mid-ice more dangerous than against the board? and Do NHL teams tend to play better or worse after losing several games? These questions and others will be taken from my books Slap Shot Science and The Physics of Hockey.
I will present my perspective on using physlets and physclips in introductory physics courses. The physclips have been developed at the School of Physics, University of South Wales, Australia, along with other multimedia resources. The physclips were downloaded from open sources such as: http://www.compadre.org/physlets/ or were available as PhET simulations in textbooks' online resources. Observed changes in students' performance and in the type of skills that they developed will be discussed. I will also comment on ways in which such resources could be incorporated in "scale-up" or project-based teaching environments.
Problem solving is a major stumbling block in the introductory physics courses in both STEM and life science programs. Our students have been provided with an optional tool to supplement and reinforce lecture and in-class tutorial instruction. A series of video tutorials were created to address curriculum topics covered in first year physics courses. The tutorials target the topics that are known to be particularly challenging for first year students. The video tutorials consist of a theoretical introduction - review of the main concepts in the topic the video addresses - followed by problem solving tips and examples of applications. The tutorials were screen-captured using Camtasia, with voice track added to the presentations. The tutorials were made available to Ryerson University students through D2L Brightspace course management system and/or Google Drive. The video tutorials support student engagement inside and outside the classroom, by enabling students to access on demand, at their own pace and time, specific instructions, which relate directly to the material they learn in the course. Initial students’ response to the resource has been very positive, and we plan to expand the project to include other topics from the first year curriculum as well as create videos for selected upper year courses. Session participants will learn about the process of creating the tutorials. Examples of video tutorials will be provided.
ChromaStar is a responsive physical model star and exo-planet life zone equipped with a suite of virtual astronomical instruments. It runs in a web-browser on any commonplace personal computing device and allows for PER-based methods and lab assignments when teaching astronomy from the High School to the upper University level. Advanced students can access the code through the browser’s developer console. I will provide sample demonstrations with the apparatus. See www.ap.smu.ca/OpenStars .
We think that black holes are ordinary quantum systems with a finite number of microstates, when we view them from the outside.
A pair of black holes can then be entangled with each other. A special entangled state of this kind can be described by a geometry similar to the maximally extended Schwarzschild black hole. This geometry is a non-traversable wormhole.
We will discuss how to make the wormhole traversable, viewing the process as an example of quantum teleportation.
(18h00-19h30) Poster Session & Finals
(19h30-20h00) Mingle session
(18h00-19h30) Poster Session & Finals
(19h30-20h00) Mingle session
Laser-induced breakdown spectroscopy (LIBS) is an elemental analysis technique in which a high powered laser is used to create a plasma on the surface of a sample. The light emitted from this plasma through a de-excitation process is then collected and used to spectrally analyze the sample. Two techniques that can improve the signal-to-noise ratio of LIBS spectra are dual-pulse LIBS, which utilizes a second laser that couples into the plasma created by the first laser pulse; and resonance-enhanced LIBS, which is similar to dual-pulse LIBS except that the second laser pulse has its wavelength tuned to match a known atomic transition in the sample in order to improve the coupling to the plasma. This enhancement can be useful for applications where a single pulse LIBS signal would be too weak to produce accurate or even detectable measurements, such as in handheld LIBS.
Presented here are measurements utilizing these two techniques on steel and neodymium samples. The first pulse was provided by a 1064 nm Nd:YAG laser and the second pulse was provided by a tunable OPO laser (both having 10 ns pulse duration). Time resolved LIBS spectra were acquired using an echelle spectrometer with a time-gated intensified CCD providing sub-nanosecond timing resolution. LIBS emission enhancement due to the second laser pulse was measured as a function of laser power, OPO wavelength, interpulse delay time, and gaseous environment present in the chamber. These tests were conducted to determine optimal parameters for signal enhancement. Additionally, attempts to replicate these measurements in a vacuum chamber will be discussed.
Dissociative excitation of adenine (C5H5N5) into excited atomic fragments has been studied in the electron impact energy range from threshold to 400 eV. A crossed beam system coupled to a vacuum ultraviolet (VUV) monochromator is used to study emissions in the wavelength range from 90 to 200 nm. The beam of adenine vapor from a stainless steel oven is crossed at right angles by the electron beam and the resultant VUV radiation is detected in a mutually orthogonal direction. Excitation of the H Lyman series, the strongest features in the spectrum, is considered in detail.
Financial support from NSERC, Canada, is gratefully acknowledged.
Pyrrole and furan, two aromatic five-membered ring molecules, have been the subject of extensive ab initio and experimental studies. We have taken Fourier transform far-infrared spectra of these molecules at the Canadian Light Source. Two fully-entangled vibrational bands of furan, n8 and n21 at ~ 870 and 873 cm-1, that are present in the spectra show some perturbations and interact with each other via Coriolis coupling. In pyrrole, a weak c-type band, n13 at ~ 830 cm-1, is observed, in addition to two other vibrational modes of pyrrole, n9 and n10 at ~ 880 and 864 cm-1, that experience the same perturbation as do the bands of furan. We will discuss our analysis and attempts at deperturbation of these bands.
A larger related molecular system, Catechol, consists of a six-membered ring and two OH groups. The high-resolution rotation-vibration spectra of this molecule have never been taken. However, low-resolution data [1]show some vibrational transitions between ~ 450-4000 cm-1. Motivated by the potential applications of ring molecules in the field of molecular electronics, we decided to take high resolution spectra of Catechol at the Canadian Light source in Saskatchewan. Our progress in obtaining rotationally resolved vibrational spectra of Catechol will also be discussed.
References:
[1] http://webbook.nist.gov/cgi/cbook.cgi?ID=C120809&Mask=80
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 first, 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 second, 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.
Integrity of digital security is crucial for maintaining the secrecy of banking data, personal information, company trade secrets, governmental records, and more. A perfectly implemented quantum cryptographic scheme, such as quantum key distribution (QKD), would be impossible to break. Freespace QKD systems commonly rely on polarization encoded single-photons. However, the optics required to manipulate photons can perturb the polarization, reducing the encoded state’s integrity thus, decreasing the quality of the quantum channel. Here I present a method for characterizing the effects of optical elements on photon polarization with respect to QKD performance. This computational model describes polarization effects by tracing light propagation paths through many individual optical elements. This research will forward for the development of freespace QKD reliability.
Second harmonic generation (SHG) is a non-linear optical process where two photons from the pump wave interacting with a non-linear material are combined to generate a new photon, with twice the frequency of the initial ones. The use of organic crystals for SHG is appealing, as the nonlinear coefficients of these crystals are much greater than those of standard inorganic materials, especially when the pump wavelength is close to an optical resonance. However, in such a case, chromatic dispersion must be properly treated.
Indeed, standard formalism for describing the wave equation of SHG in a material has been shown to be flawed in the case of materials with high dispersion. The slowly varying amplitude approximation which is made in the development is not always justified for organic crystals. Solving the equation without this approximation leads to a result with a different amplitude and an additional term, which we refer to as the “zeta term”. This term adds an oscillating component in the intensity profile of the second harmonic signal which is not present in standard theory.
Here we experimentally measure the dependence of second harmonic intensity versus pathlength and wavelength in 2-methyl-4-nitroaniline (MNA). Working in photon counting mode, with a motorised translator that allows the sample to be scanned with high reproducibility, we observe what we believe to be a combination of the zeta fringes and an effect caused by multiple reflections, since we are working with thin films. Qualitatively, this agrees with our theoretical predictions and leads us to believe that the standard formalism might lead to significant inaccuracies in the case of highly dispersive materials.
Our results have implications for implementations of non-linear optics in dispersive media, and in the determination of non-linear coefficient with the Maker fringes technique, which relies on the intensity profile of the material.
Il s’agit de concevoir et de fabriquer un laser à l’état solide aux dimensions réduites pouvant émettre dans un seul mode aux hautes puissances. Nous fabriquons nos miroirs lasers polarisants en déposant sur un miroir laser commercial une couche anisotrope servant de lame quart d'onde par la méthode de déposition par incidence oblique. Le matériau utilisé est le dioxyde de titane. Une caractérisation par microscopie à force atomique est faite de même que des mesures ellipsométriques afin de déterminer l’épaisseur et les propriétés optiques de nos revêtements. Ces miroirs sont utilisés pour construire un laser de sorte que les polarisations des deux ondes contra-propagatives soient orthogonales pour éliminer le brûlage spatial de trous. Le milieu actif utilisé est le YAG dopé avec de l’ytterbium trivalent pompé avec une diode laser. Les tests lasers sont faits en régime continu puis pulsé.
In this project, we design and manufacture a solid-state microchip laser with single transverse and longitudinal mode emission at high power. We manufacture our polarizing laser mirrors by depositing an anisotropic quarter-wave plate on a commercial laser mirror using the Glancing Angle Deposition. The material used is titanium dioxide. Characterization by atomic force microscopy is done as well as ellipsometric measurements to determine the thickness and optical properties of our deposited coatings. These mirrors are used to construct a laser so that the polarizations of the two counter-propagating waves are orthogonal to eliminate the spatial hole burning. The active medium is YAG doped with trivalent ytterbium pumped with a fiber-coupler laser diode. Laser experiments are performed in both continuous and pulsed modes.
An exciting frontier in quantum information science is the realization of complex many-body systems whose interactions are designed quanta by quanta. Hybrid nanophotonic system with cold atoms has emerged as the paradigmatic platform for engineering long-range spin models from the bottom up with unprecedented complexities. Here, we develop a toolbox for realizing fully programmable complex spin-network with neutral atoms in the vicinity of 1D photonic crystal waveguides. The enabling platform synthesizes strongly interacting quantum materials mediated by Bogoliubov phonons from the underlying collective motion of the atoms. In a complementary fashion, phononic quantum magnets can be designed through the coupling to the magnonic excitation of the atomic medium. We generalize our approach to long-range lattice models for interacting SU(n)-magnons mediated by local gauge constraints. Universal open q-body dynamics with q > 2 can be built from floquet driven-dissipation, and the dynamics of arbitrary quantum materials can be constructed with minimal overheads.
(18h00-19h30) Poster Session & Finals
(19h30-20h00) Mingle session
This investigation reports on the 2016 Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the Galactic Center (GC). Two new transients were identified within the Galactic Center, Swift J174540.7-290015 (Transient 15) and Swift J174540.2-290037 (Transient 37). Having observed the GC for 10 years and detected no prior outburst, it can be concluded that the time between outburst (recurrence time) is longer than 10 years. The recurrence time of a neutron star is less than 10 years, while that of a black hole is assumed to be approximately 100 years. Therefore, it can be concluded that these transients are very likely black hole binaries. Through both spectral fitting and timing analysis, Transients 15 and 37 were identified as black hole candidates. The observed number of transients were used to estimate the existence of 30 black hole binaries within the Galactic Center, 27 still unobserved, indicating the likelihood of a substantive population of black holes within the Galactic Center.
High resolution and high signal to noise spectra of two HgMn stars, HD53929 and HD63975, were analysed in the frame of Project VeSElkA (Vertical Stratification of Element Abundances) to search for vertical stratification of element abundances in their stellar atmospheres. These stars show signatures of a slow axial rotation and most probably possess hydrodynamically stable stellar atmospheres, where the atomic diffusion mechanism can cause abundance accumulation or depreciation of particular chemical elements at the certain atmospheric depths. With the help of the ZEEMAN2 code, we were able to determine average abundance of analysed chemical species and to detect in both studied stars an increase of phosphorus abundance towards the upper atmospheric layers. The strong overabundances of Mn derived in the stellar atmospheres of HD53929 and HD63975 confirms that they are HgMn type stars.
The results of analysing of the chemical abundance in stellar atmosphere of Sirius are presented as a part of the project VeSElkA that aims to search for evidence of vertical stratification of elements’ abundance in chemically peculiar (CP) stars. Using the high resolution and high signal to noise spectra obtained with the spectropolarimeter NARVAL, we have analysed hundreds of line profiles with the help of the code ZEEMAN2. The estimates of average abundance for 39 chemical elements were obtained for two phases of orbital rotation of Sirius in binary system. We were able to find a significant overabundance of argon, scandium, manganese, cobalt and some rare-earth elements, and an under-abundance of molybdenum for two phases of Sirius orbital motion in binary system.
In order to adequately understand the effects that energetic particle precipitation bears on radio wave absorption, we have analysed cosmic noise absorption (CNA) measured by the imaging riometer at Kilpisjarvi, Finland (IRIS) during 1996-2011. We analysed periods of co-rotating interaction regions(CIR) occurring as a result of the interaction of high speed solar wind streams emanating from coronal holes. We utilised the superposed epoch analysis method to investigate the absorption signature during these events. We identified periods of maximum CNA enhancement for each of these events and the duration of elevated CNA. Each of these events show differing CNA enhancement periods and elevation thresholds.
A plane polarized electromagnetic (EM) wave that propagates through a plasma, (anti-)parallel to a magnetic field, experiences a gradual rotation of its plane of polarization called Faraday rotation (FR). Automatic Dependent Surveillance Broadcast (ADS-B) signals are linearly plane polarized and therefore are susceptible to FR as they traverse the ionospheric plasma, where they encounter a field-aligned component of the geomagnetic field and anisotropies in the ionospheric medium. An EM-wave ray tracing model was used to generate simulated ADS-B data to determine the wave path and the polarization state at incremental distances along the ray path resulting in estimates for the total electron content (TEC) and FR received at the satellite receiver position. Results will be discussed that use the TEC and FR values from multiple aircraft at different latitudes transmitting ADS-B signals to a satellite receiver to infer the effective parallel component of the geomagnetic field along the path.
The Michelson Interferometer for Airglow Dynamics Imaging (MIADI) is a field widened Michelson interferometer which provides images of wind using Doppler shifts in interference fringes from terrestrial airglow emissions. Although it is thermally compensated by using different glasses, some residual temperature dependence remains. Close examination of the interference fringes using a fixed source reveals details about the path difference and its dependence on temperature and pressure. The phase of the interference patterns should remain constant over time in an ideal environment. By monitoring the phase of the interference pattern along with the environmental temperature and pressure the sensitivity of the instrument to temperature, pressure, and humidity can be determined. Several time series of the interferometer phase as a function of vary conditions have been undertaken in our lab at the University of New Brunswick. Multiple regression analyses of the dependencies of phase on environmental conditions were calculated. In this paper, an overview of the process to determine the temperature, pressure, and humidity dependencies of the Michelson Interferometer for Airglow Dynamics Imaging (MIADI) and their implications are presented. Since the observed dependencies do not match theoretical expectations determining the different environmental dependencies will allow for corrections to be made in the design of new wind imaging instruments.
(18h00-19h30) Poster Session & Finals
(19h30-20h00) Mingle session
In a real-world situation, a battery is not cycled continuously until death nor stored endlessly at top of charge. Test conditions should mimic real-world situations to better understand different failure mechanisms occurring within cells of the same build and electrolyte. Three complimentary tests are proposed to probe cycle-dependent and time-dependent aging under a spectrum of voltage and temperature stresses.
First, single crystal LiNi0.5Mn0.3Co0.2O2 (NMC)/graphite cells were evaluated under continuous cycling conditions. Cells were charged and discharged continuously (3 hour charge and 3 hour discharge) between 3.0 and 4.2 or 4.3V at 20, 40, or 55oC. Every 50 cycles there was a slow (20 hour charge and 20 hour discharge) cycle to monitor capacity loss. The slow cycle is assumed to be unaffected by decrease in cell rate capability. The capacity loss of the slow cycles was well described by an expression following the square root of time, and that this expression followed Arhennius’ law to describe the acceleration of failure due to increased temperature.
Next, cells were evaluated under storage conditions. Cells were stored at “shipping voltage”, 4.0, 4.1, 4.2, and 4.3V at 20, 40, and 55oC with regular (two week diminishing to five month frequency) reference performance tests (RPTs). A RPT includes 3 hour and 20 hour cycles (as above) from 3.0-4.1V at 20oC. Standardized conditions allowed absolute capacity loss and impedance growth to be compared directly across temperatures and voltages. Similar to cycling, C/20 capacity loss is proportional to the square root of time. Increased temperature has a stronger detrimental effect on cells stored at high potential than on cycled cells.
Finally, cells were evaluated using a hybrid cycle-store protocol. Cells cycling with 3 hour charge and discharges were allowed to rest open circuit at top of charge for 0, 12, 84, or 180h. Cells were tested to 4.1, 4.2, and 4.3V at 40oC. Capacity retention and impedance growth is worst for cells with the 12h storage condition. This observation can be explained based on the results of the previous two experiments as will be demonstrated.
Metallic Li is considered as the promising anodes for next generation Li-metal batteries including Li-S, Li-air and all solid-state batteries. However, it is still a crucial problem of Li dendrite growth and large volume change during the stripping/plating process. In our study, the advanced atomic/molecular layer deposition (ALD/MLD) is used to deposit protective coatings on Li metal with excellent coverage and controllable thickness to stabilize the SEI layer and longer the life time [1].
Herein, we demonstrated MLD alucone (Al-EG and Al-GLY) as protective layers for Li metal anode with improved stability and life time, leading to the better performances than ALD Al2O3 [2]. Furthermore, the conductive carbon paper (CP) is proposed as an “interlayer” for Li metal anode with super long-life time under high current density [3].
Na metal anode also shows the great potential for the Na metal batteries [4], which facing the similar problems of dendritic Na growth. Here, we demonstrated the successful application of both ALD Al2O3 and MLD alucone protective coatings on Na metal anode in ether and carbonate-based electrolyte, respectively, to achieve long lifetime Na metal anode with suppressed dendrite growth [5]. To further reduce the dendrite growth and minimize the volume change, the 3D skeleton (carbon paper with N doped carbon nanotube) has been design with excellent electrochemical performance under high current density and high capacity [6]. To address the practical problems in Na-O2 batteries, the CP is used as “interlayer” to avoid the corrosion of Na metal and reduce the dendritic Na growth [7].
In conclusion, we developed the different approaches, including ALD and MLD protective layers, interlayers, and 3D skeleton design, for Li and Na metal anodes with enhanced electrochemical performances and reduced dendrite growth. Meanwhile, the ideas have been also applied to solve the practical issues for testing Li and Na metal batteries.
[1] X. Meng, X. Sun, Advanced Materials, 2012, 24, 1017; Y. Zhao, X. Sun, ACS Energy Letters, 2018, in press (review paper)
[2] Y. Zhao, X. Sun, Small Methods, 2018, DOI: 10.1002/smll.201703717; A. Lushington, X. Sun, submitted
[3] Y. Zhao, X. Sun, Nano Energy, 2018, 43, 368
[4] H. Yadegari, X. Sun, Advanced Materials, 2016, 28, 7065
[5] Y. Zhao, X. Sun, Advanced Materials, 2017, 29, 1606663; Y. Zhao, X. Sun, Nano Letters, 2017, 17, 5653
[6] Y. Zhao, X. Sun, Small, 2018, DOI: 10.1002/smll.201703717
[7] X. Lin, X. Sun, submitted
Instability of GaAs and AlGaAs in an aqueous environment increases drastically following illumination with photons of energy exceeding bandgap of these materials. We have investigated the dynamics of photon-induced dissolution of GaAs/AlGaAs nano-heterostructures in deionized water (DI H2O) and ammonium hydroxide (NH4OH) environments by employing inductively coupled plasma mass spectrometry (ICP-MS). The samples were irradiated with a 660 nm light-emitting diode delivering 16 or 20 mW/cm2 of a uniform radiation and their photocorrosion was monitored in situ with the photoluminescence effect. Consistent with the calculated concentrations of ions released by dissolving GaAs/Al0.35Ga0.65As nano-heterostructures up to approximately 60 nm thick, the ICP-MS results confirmed the expected presence of As3+ ions in the photocorrosion products. Some accretion of Ga2O3, Al2O3 and Al(OH)3 has been observed on the surface of thicker samples, as evidenced by the Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy data. These results have been corroborated by the ICP-MS analysis that revealed reduced concentrations of As3+ and Ga3+ ions released to the photocorrosion product by nano-heterostructures thicker than ~ 60 nm. The photocorrosion in NH4OH environment allowed to alleviate, partially at least, the problem of an excessive accumulation of oxides. We discuss the conditions that needs to be met to allow digital photocorrosion of GaAs/Al0.35Ga0.65As nano-heterostructures thicker than 100 nm.
In the quest for high performance materials for energy storage, a comprehensive toolbox of characterization techniques - both experimental and theoretical - is an absolute necessity. In recent years, many techniques have been increasingly focussed on combining observations of material structure, composition, and dynamics to develop a complete picture on how various material properties affect overall performance. This is generally achieved either by custom built hardware that incorporates several characterization techniques that can be performed consecutively, or by successive ex-situ measurements that each capture different information. There do exist, however, some emerging techniques that can capture both dynamic and structural information simultaneously, one of which is atomic force microscopy (AFM). The operating principle of AFM employs an extremely sensitive and highly localized force sensor (probe), which makes it a very good candidate for measuring local dynamic processes. Here we will present some of the leading work on various implementations of AFM and how they are applied to energy materials, including time-resolved electrostatic force microscopy (EFM), which enable the direct probing of charge transport processes with high spatial resolution.
In EFM-based techniques, the probe is used to detect changes in the local electric field, which can arise from a variety of processes including the movement of ions. By driving ionic transport with an applied potential and acquiring the response signal over time, it can be used to directly measure the bulk ionic conductivity of a substrate and - if done at varying temperatures - the local activation energy and hopping barriers. Using this time-resolved technique on a heterogeneous sample, we have observed spatial variations in the response signal on the order of 50nm, demonstrating the true power of this technique. The topographic images obtained also allow for further characterization on the exact same physical regions of the sample, which eliminates the effects of averaging over large macroscopic areas.
These measurements allow us to directly peer into the relationship between local structure and dynamics with the spatial and temporal resolution not previously available with many standard approaches. This has lead to the maturation of AFM into a staple in the characterization toolbox for energy materials.
Sometimes lithium-ion cells show a very insidious type of failure where they display close to 100% of their capacity for about 1000 charge-discharge cycles and then lose most of their capacity in only 100 cycles or so with very little warning to the user. This is called “rollover failure”. Experimental observations show that the likelihood of rollover failure increases with upper cutoff potential of lithium-ion cells. Since increasing the upper cutoff potential is essential to increase the energy density of lithium-ion cells, a full understanding of the causes of rollover failure is essential, but this is proving very difficult to attain.
In this presentation, the phenomenon of rollover failure during long-term cycling will be discussed based on a comparison among Li(Ni0.5Mn0.3Co0.2)O2/graphite pouch cells with different electrolyte and electrode designs undergoing different testing protocols. A few facts can be gleaned from the data:
1. For cells charged to the same upper cutoff potential, those showing the highest rates of electrolyte oxidation at the positive electrode (due to electrolyte or cell chemistry changes) are most prone to rollover failure.
2. Any cell is more prone to rollover failure if charged to higher potential. This increases the rate of electrolyte oxidation at the positive electrode.
3. When cells are disassembled after rollover failure, they invariably show unexpected and unwanted lithium metal plating on the surface of the graphite negative electrode.
Based on these and other observations some simple handwaving models of rollover failure can be postulated but serious experimental studies using a variety of methods are required for full understanding. It is hoped that this lecture can spur other researchers to help tackle this critical problem!
Lithium Ion Batteries are widely used in a large variety of consumer products. With the rise in use in electric vehicles, increasing the energy density of LIBs is a priority. One way of accomplishing this is to increase the charge cutoff potential. However, this results in significant deterioration of the LIBs caused by side reactions between the electrolyte and the electrode. A possible solution to this is to use a coating to protect the positive electrode material. Al2O3 is currently being studied as a possible protective coating.
The Al2O3 is deposited through atomic layer deposition, which creates a thinner more even coating than the alternative wet-chemistry method. Two thicknesses of Al2O3 coatings are being investigated on two different types of positive electrode material, Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Cobalt Aluminum Oxide (NCA). Samples from each material and coating type are heat treated to different temperatures ranging from 400˚C to 900˚C. To study the effects of the heat treatment temperature on the Al2O3 coating the samples underwent a range of different types of characterization testing. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and aluminum solid state nuclear magnetic resonance (Al NMR) have been used to study the heat-treated samples.
Results of the Al NMR on the thick coated NMC series suggests diffusion of the Al2O3 coating into the NMC begins with 400˚C heat treatment. XPS results differ from this, suggesting that diffusion begins at 600˚C for the thin coated material and 700˚C for the thick coated material. This suggests that the Al2O3 coating is thicker than the XPS measurement depth and the initial diffusion from the coating isn’t visible to XPS while it is to NMR. As the heat treatment temperature increases, so does the diffusion of the Al2O3 layer into the NMC until the layer is reduced enough that the underlying NMC becomes visible to XPS measurement.
All electrode material powder samples were used to form electrodes and coin cell batteries were made from these for thorough electrochemical testing to evaluate the high voltage performance of the various coatings and heat treatment temperatures.
Carbon-based nanomaterials are key components in energy storage devices. Their functions can be tailored by adjusting or developing new synthesis pathways. In this study, two living radical polymerization techniques, an electrochemically-aided atom transfer radical polymerization (e-ATRP) and reversible addition chain transfer polymerization (RAFT), were applied for grafting of carbon allotropes such as multi-walled carbon nanotubes (MWCNT), graphene and single-walled carbon nanohorns (SWCNH) with a 2-(1H-pyrrol-1-yl)ethyl methacrylate. The functionalized carbons were examined as polymerization initiators in the RAFT and e-ATRP synthesis. The Fourier-transform infrared and Raman spectroscopies were used to identify the reaction products at each phase and for the final composites. TEM imaging showed that the morphology of composites made from the same carbon allotrope are not significantly different for RAFT and e-ATRP products; and the structure of the ultimate product strongly depends on the type of carbon. Also, the poly(pyrrole) film or the particle size was very small (in all cases less than 30 nm), demonstrating the control over the polymer morphology in living polymerization techniques. The high specific gravimetric capacitances over 456 F g-1 and electrochemical stability up to 7500 cycles were obtained for MWCNT-grafted-poly(pyrrole), and slightly less for Graphene-based composites synthetized by e-ATRP, showing the advantages of this method over RAFT. The electrode voltages for all composites were higher as compared to the pure polymer electrodes, with some benefit of RAFT over e-ATRP product, and with significant improvement observed for the MWCNT- and Graphene-based systems. Regardless of the synthesis method, all composites demonstrated enhanced specific capacitance as compared to their individual components, revealing the synergy of double-layer capacitance from the carbon and the pseudo-capacitance generated by the polymer fraction.
Nickle-rich LiNixMnyCozO2 (x + y +z = 1) (NMC) (Ni content higher than 60% of the total transition metals) is one of the most promising positive electrode materials for lithium-ion cells due to its high specific capacity of up to 220 mAh/g. Conventional NMC materials such as LiNi0.4Mn0.4Co0.2O2, LiNi0.5Mn0.3Co0.2O2, LiNi0.6Mn0.2Co0.2O2 etc. have more than 20% Co among the transition metal atoms. However, the high price of Co prevents the development of lithium ion batteries with low cost and high energy density for grid energy storage and electric vehicles. To lower the Co content while still maintaining good electrochemical performance, herein, the authors studied three series of materials with different transition metal ratios, which are LiNi0.6Mn(0.4-x)CoxO2 (x=0, 0.1, 0.2), LiNi(0.9-x)MnxCo0.1O2 (x=0.1, 0.2, 0.25) and LiNi0.8Mn(0.2-x)CoxO2 (x=0, 0.1, 0.2). The materials were synthesized via a co-precipitation-solid state sintering method [1, 2]. Powder X-ray diffraction and Rietveld refinement were carried out to investigate the structural properties of the materials. Coin-type cells were made to measure the electrochemical properties of the materials. In addition, accelerating rate calorimetry (ARC) was used to study the safety of charged NMC cathode materials in the presence of electrolyte. It was found that LiNi0.6Mn0.3Co0.1O2 and LiNi0.7Mn0.2Co0.1O2, which have 50% less Co content than current commercialized materials, exhibited excellent capacity and thermal stability, and therefore deserve careful consideration as next generation materials.
[1] van Bommel, Andrew, and J. R. Dahn. "Analysis of the growth mechanism of coprecipitated spherical and dense nickel, manganese, and cobalt-containing hydroxides in the presence of aqueous ammonia." Chemistry of Materials 21.8 (2009): 1500-1503.
[2] Li, Jing, et al. "Synthesis of Single Crystal LiNi0.5Mn0.3Co0.2O2 for Lithium Ion Batteries." Journal of The Electrochemical Society 16a4.14 (2017): A3529-A3537.
Improving the cost, lifetime, and energy density of lithium-ion cells is critical in the transition away from fossil fuels for energy production and transportation. Increasing the operational voltage of a lithium ion cell is one way to increase energy density and decrease cost. However, traditional solvents used in lithium-ion electrolytes are not stable at these potentials, causing what are termed ‘parasitic reactions’ – or the decomposition of electrolyte species into unwanted products. These reactions consume lithium content and electrolyte species, decreasing the available capacity of the cell, and can create films of reaction products on the electrodes which mitigate ion transfer, ultimately leading to cell death [1]. Due to the complexity of the electrochemical system, the exact mechanisms of parasitic reactions are often unknown and vary depending on electrode materials and coatings, electrolyte solvents, lithium salts, electrolyte additives, etc.
Isothermal microcalorimetry offers a unique way to probe parasitic reactions in-situ and non-destructively. The heat flow of a lithium-ion cell during operation has contributions from entropy changes in the electrode materials, the internal resistances in the cell (joule heating), and parasitic reactions. The heat flow from parasitic reactions can be found using a careful analysis during charge and discharge cycling of a cell. Using this analysis method, the parasitic heat flow has been found to directly correlate to cell lifetime [2, 3]. This presentation will highlight the advantages of this technique and how isothermal microcalorimetry has be used to aid in the design and understanding of electrolyte systems for high energy density, long lifetime lithium-ion cells.
[1] Xu, K. Chem. Rev. 2014, 114, 11503–11618.
[2] Glazier, S.L. et al. J. Electrochem. Soc. 2017, 164, A567–A573
[3] Glazier, S.L. et al. J. Electrochem. Soc. 2017, 164, A3545-A3555
Normal Li-ion cells with a positive electrode and a negative electrode normally have a voltage near 4.0 V. There are many surprising things about lithium-ion cells. One of these is that unwanted chemical reactions between one charged electrode (say the positive) and the electrolyte can create reaction products that migrate to the other electrode (say the negative) and affect it dramatically [1,2]. In order to eliminate this “cross-talk”, “symmetric” cells, which have two positive (or two negative electrodes) electrodes and hence an average voltage of zero, are used [3,4]. The charge discharge cycle performance of a symmetric cell is exclusively determined by the compatibility of the electrode of interest with the electrolyte of choice.
In this study, the compatibility of various electrolyte additives with Li[Ni0.6Mn0.2Co0.2]O2 positive electrodes were studied using positive-positive symmetric cells built in-house. Symmetric cell testing is a method to effectively evaluate materials made in an academic laboratory when machine-made electrodes and full Li-ion cells are not readily available.
Michael Bauera, Eric Logana, Lauren Thompsonb, J.R. Dahna,b
aDepartment of Physics and Atmospheric Science, Dalhousie University, Halifax B3H 3J5, Canada
bDepartment of Chemistry, Dalhousie University, Halifax B3H 4R2, Canada
Li-ion cells contain liquid electrolyte that degrades over the course of their lifetime. High temperatures, high charging currents, and high voltage exposure can all accelerate electrolyte degradation. This degradation will eventually contribute to the death of the cell. As the electrolyte degradation pathways are not currently well understood, tools for careful probing of the electrolyte are required to further develop cell chemistries for longer lasting cells, which is especially important for long term grid level storage.
Li-ion differential thermal analysis (Li-ion DTA) is a non-destructive in-situ method for probing the state of an electrolyte in a liquid electrolyte cell. Various methods of studying electrolyte ex-situ, by opening a Li-ion cell, have been developed, but these destroy the cell of interest. Using Li-ion DTA methods, which do not damage the cell, the degradation to the electrolyte of a single cell can be tracked throughout its lifetime. The DTA method functions by cooling a sample cell to below the electrolyte freezing point using a temperature controlled cryostat, and heating the cell linearly in time back to room temperature where the electrolyte is liquid again. By comparing the resultant temperature-time signal of the sample cell to that of a reference cell that did not undergo a phase change in the same temperature range, the phase changes of the electrolyte in the sample cell can be determined. By comparing these phase change temperatures to known electrolyte compositional phase diagrams, the state of the electrolyte can be determined qualitatively, and, in future, quantitatively. The method will be explained and results from several long term experiments on aged Li-ion cells will be described.
Lithium-ion cells are complex electrochemical system and various physical properties can be measured, giving valuable insights into their behavior, state-of-health, degradation mechanisms, etc.. However, many such insights remain unexploited because of the difficulty of relating the raw data to the variables of interest. This is a setting well suited to Machine Learning. This talk will take as example the task of determining the composition of an unknown electrolyte, simply by using the Fourier-Transform Infrared (FTIR) spectrum. Some samples of known composition were measured, to build a calibration set, which was used to approximate the relationship between FTIR spectrum and electrolyte concentration.
Machine Learning methods have made significant leaps forward in recent years, achieving impressing results in image recognition, audio signal analysis, natural language processing, and even video game artificial intelligence. State-of-the-art methods in this emerging field of “deep learning” are however known to require huge amounts of data to achieve good results. This talk will demonstrate that this need not be so, by presenting a successful application of state-of-the-art complex neural networks to the problem of electrolyte analysis. A special emphasis will be given to the techniques developed to ensure the robustness of the resulting model, allowing the application of these techniques to more problems in the future. The resulting model will be compared to alternative techniques such as inductively coupled plasma optical emission spectrometry (ICP-OES) and Gas chromatography–mass spectrometry (GC-MS), thus validating it as a tool for the analysis of electrolytes from aged Lithium-ion cells, requiring no special sample preparation and using no harsh or expensive solutions.
The widespread adoption of electric vehicles over gas-powered transport is essential to our sustainable future. Consequently, the lithium-ion batteries used for electric cars are receiving more and more attention. Lithium-ion cells with LiNi0.8Co0.15Al0.05O2 (NCA) positive electrodes have been observed to lose capacity during their lifetime as a result of impedance growth.1,2 Understanding the origin of the impedance growth is important to improving the lifetime of these cells, which in turn can help make electric vehicles more desirable to consumers and speed the adoption of sustainable transport.
In this study impedance growth was observed to contribute to capacity loss in pouch cells with NCA positive electrodes and graphite, graphite-SiO, or graphite-SiC negative electrodes. The positive electrode was observed to have drastic impedance growth during cycling while the negative electrode impedance was small in comparison. The impedance growth for NCA pouch cells was controlled by cycling in the limited voltage range of 3.0 V – 3.8 V, while impedance growth was still observed for cells cycled only at high voltage (3.8 V – 4.2 V). Additionally, the magnitude of impedance was highest near 4.2 V. The cathode material undergoes irreversible impedance growth in the high voltage region. Differential capacity vs. voltage (dQ/dV) for the NCA material shows a peak at 4.2 V vs Li/Li+, which may correspond to the i