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2020 June 5 CAP AND ITS PARTNERS ARE HOSTING SOME VIRTUAL SESSIONS STARTING MONDAY JUNE 8 The Program Committee for the 2020 CAP Congress has developed a reduced program from the originally planned in-person Congress that was cancelled due to COVID-19. An exciting series of presentations, talks, and meetings will be offered during the week of 2020 June 8-12, followed later by the CAP Best Oral Presentation final on 2020 June 25th, CINP Townhall meetings on June 22-23, the IPP Townhall meetings on July 15-16, DPE Workshops on June 15, one day of the Soft Matter Conference on June 17, CEWIP Business Meeting on June 23. In an effort to ensure that all presentations and meetings are accessible at reasonable times across Canada, they are all being offered between 10h00 and 17h00 EST. Click on the Timetable link on the left to see the current planning. Contacting the CAP Office: At this time, the CAP office staff are working remotely from home in accordance with the current provincial recommended best practices, therefore, should you have any questions, please contact Chantal Éthève-Meek in the CAP office by e-mail at programs@cap.ca. Shohini Ghose, CAP President
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The COVID-19 pandemic has touched everyone’s lives, but it has not affected everyone equally. Madonna called COVID-19 “the great equalizer,” but she was wrong: the risk and severity of the disease itself, and the pandemic’s economic and social impacts, vary with age, income, race, and gender. The pandemic has laid bare and often worsened many pre-existing inequalities in our world. One issue of longstanding concern is gender equality, and I will discuss why the pandemic has the potential to worsen gender gaps in STEM fields. Data from several sources, including my own preliminary analysis of preprint submissions to arXiv and bioRxiv broken down by gender, suggest that women are getting less research done than men during the pandemic. I will explore several possible explanations for this trend, including an increased child care burden, and lead the group in a discussion of possible solutions.
During this plenary session, you will hear updates about NSERC activities from Dr. Elizabeth Boston, Director, Mathematical, Environmental, and Physical Sciences, and Dr. Sara Ellison, Physics Evaluation Group Chair.
Au cours de cette session plénière, vous serez mise-à-jour sur les activités de la CRSNG par la Dre Elizabeth Boston, Directrice, sciences mathématiques, environnementales et physiques, et la Dr. Sara Ellison, le présidente du groupe d'évaluation de la physique.
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PPD Chair (M.-C. Piro) and Vice-Chair (M. Danninger) welcome participants
The fact that neutrinos have mass and oscillate means that we can learn a great deal about them by studying what are effectively interference patterns that arise after neutrinos propagate over hundreds of kilometers. These patterns may tell us the reason that our universe is dominated by matter and not simply light, and they can also tell us if neutrinos acquired their mass in the same way that other charged particles have acquired theirs. The DUNE experiment will measure these interference patterns over a broad range of neutrino energies after the neutrinos have propagated 1300km, to a laboratory located 765km south of Regina. In addition, DUNE will use a detector technology that provides exquisite detail about the interactions that make up the interference pattern. In order to measure these patterns, however, we need to not only build enormous detectors and create intense neutrino beams, we also have to understand in fine detail what happens inside the nucleus when a neutrino interacts there.
This talk will present the current state of neutrino oscillation measurements and how the field is preparing for the next big jump in our understanding of neutrinos and the role they play in the universe.
The Deep Underground Neutrino Experiment (DUNE) represents a bold step forward with a new detector technology and the ability to measure neutrinos over an extremely broad energy range. DUNE will consist of two massive detectors: one located at Fermilab in Illinois, and one located 1300 km away in South Dakota. DUNE will use neutrino beams with energy spectra broader than any other experiment. This spectrum offers a unique opportunity to measure the nature of the neutrino masses, to quantify the matter-antimatter symmetry violation, and to potentially discover additional neutrinos. This talk gives an overview of the LBNF-DUNE facility with an emphasis on sensitivity to exotic signatures such as sterile neutrinos and non-standard interactions. The talk also gives an overview of planned Canadian contributions including the data acquisition system, the calibration system and beam line monitor.
Stanley Yen (TRIUMF) for the HALO and HALO-1kT collaborations
Neutrinos provide a nearly-prompt view of the nuclear and particle processes that occur in the bowels of a core-collapse supernova. Most existing detectors are primarily sensitive to electron anti-neutrinos, but a complete picture requires complementary detectors to observe all flavours of neutrinos and antineutrino emitted in the different phases of the explosion. The lead-based HALO detector at SNOLAB is the first and so-far only operational detector in the world primarily sensitive to electron neutrinos. It has been taking data since 2012 and has been a member of the global SuperNova Early Warning System since 2015. Plans are underway for HALO-1kT, a larger lead detector at Gran Sasso. The unexpected and still-contentious early burst of neutrinos related to SN1987A, observed only at the Mont Blanc detector, may be an indication that our understanding of the explosion mechanism is incomplete, and the next galactic supernova may yet yield surprises.
The SNO+ experiment is a multi-purpose neutrino detector located 2 km underground at SNOLAB in Vale’s Creighton Mine in Sudbury, Ontario. The centerpiece of SNO+ is a 12-m diameter acrylic vessel, containing the target medium. The acrylic vessel is surrounded by 7 kilotonnes of ultrapure water shielding and about 9300 photomultiplier tubes. SNO+ is operating in three phases, defined by the target medium: water, scintillator, and scintillator loaded with tellurium. In the water phase, SNO+ has collected ultra-low background data, confirmed previous measurements of solar neutrino flux, and set world-leading limit on invisible modes of proton decay of 3.6×1029 years. Utilizing an Americium-Beryllium neutron calibration source, SNO+ has measured the highest neutron detection efficiency for pure water Cherenkov detectors and this rate will inform physics analyses, such as the antineutrino search.
The Scintillating Bubble Chamber (SBC) is a novel technology currently being developed for sub-keV nuclear recoil detection. This technique combines the event-by-event energy recoil of a liquid-noble scintillation detector with the world-leading electron recoil discrimination of a bubble chamber while significantly lowering the detection threshold. Unambiguous identification of sub-keV nuclear recoils in a scalable detector makes this an ideal technology for both low-mass WIMP searches and CE$ν$NS detection at reactor sites. Progress will be presented as the SBC collaboration works towards the construction of a pari of 10 kg argon bubble chambers at Fermilab and SNOLAB.
In the search for astrophysical neutrinos, neutrino telescopes instrument large volumes of clear natural water. Photomultiplier tubes placed along mooring lines detect the Cherenkov light of secondary particles produced in neutrino interactions, and allow us to search for possible neutrino sources in the sky. The P-ONE experiment proposes a new neutrino telescope off the shore of British Columbia.
To overcome the challenges of a deep-sea installation, we are developing prototype mooring lines in collaboration with Ocean Networks Canada, an initiative of the University of Victoria, which provides the infrastructure for many Oceanographic instruments.
The STRAW mooring lines were deployed in June 2018, and provide continuous monitoring of optical water properties at a new possible detector site in the Pacific.
Their successor STRAW-b, to be deployed in summer 2020, will complement the measurements of STRAW, and test new engineering and deployment strategies, scaleable for larger setups with up to one hundred mooring lines.
We will give an overview over the two pathfinder missions, their construction, deployment, and first results.
King plots have long been used to extract information about relative nuclear charge radii from observed transition frequencies for three or more isotopes of the same element. They have also recently been proposed as a method to search for anomalies that may indicate new physics beyond the standard model [1]. However, an underlying assumption is that the normal and specific isotope shifts vary linearly with $\mu/M$, where $\mu$ is the electron reduced mass and $M$ is the nuclear mass. To test this assumption, we constructed synthetic King plots using as input high-precision theoretical atomic energy levels [2] for the isotopes of helium: He-3, He-4, He-6 and He-8. The results indicate that second-order mass polarization terms proportional to $(\mu/M)^2$ make a significant contribution and must be taken into account in the analysis of high precision spectroscopic data. Otherwise, they could masquerade as a signal for new physics. We propose a modified method of analysis (a super-King plot) that takes into account second-order mass polarization effects.
[1] V. V. Flambaum, A. J. Geddes and A.V. Viatkina, Phys. Rev. A 97, 032510 (2018).
[2] G. W. F. Drake and Z.-C. Yan, Phys. Rev. A 46, 2378 (1992).
Helically sculptured thin films have been an interesting topic in applied optics; mainly because of their controlled optical properties such as optical activity and they can be fabricated by almost any material. These thin films were made by glancing angle deposition (GLAD) which allows us to control the orientation of the substrate during the deposition allowing the helical nanostructure. If the incident light’s wavelength is the same as the helix pitch of the film, due to their chiral structure, these films reflect circularly polarized light with the same spatial handedness of the film’s helix at a fixed time. This well-known phenomenon is called the circular Bragg resonance and it can be observed at any angle of incidence.
When the incidence angle is different than $0^{\circ}$, we have found a second peak at twice the circular Bragg resonance wavelength and it has been confirmed with simulations. We have analysed the optical properties of the film by calculating the eigenvalues and eigenvectors of the Jones matrix of the reflection spectrum in the visible and near IR spectrum for various incidence angles and azimuth angles. We were able to conclude that the eigenmodes around the wave band of the second peak are almost linearly polarized with diagonal and anti-diagonal polarization states with respect to the plane of incidence. When the number of periods is increased, the reflectance approaches unity for both orthogonal polarization states in the neighbourhood of this resonance. However, the phase shift at reflection is different for each eigen polarization. This suggests that the second peak is a linear Bragg resonance. The inclination of the biaxial index ellipsoid of each monolayer lifts the degeneracy that exists between the layers rotated by $180^{\circ}$ when the incidence angle is different from $0^{\circ}$: the periodicity thus becomes twice as large as at normal incidence, and this creates a second resonance at twice the wavelength.blank
Beta decay of the $^6$He halo nucleus to form $^6$Li$^+$ may provide evidence for new physics beyond the standard model [1]. After the decay occurs, the two atomic electrons become redistributed over all possible states of the daughter $^6$Li nucleus, including single- and double-electron emission (shake-off). The present study focuses on the probability for double electron emission to form Li$^{3+}$, where there is a substantial disagreement between theory [2] and experiment [1]. We use pseudospectral representations together with Stieltjes imaging to separate the Li$^{3+} + 2$e$^-$ channel from the energetically overlapping Li$^{2+} + $e$^-$ single ionization channel. We find that the formation of Li$^{3+}$ is strongly suppressed near threshold relative to Li$^{2+}$, thereby accounting for part of the disagreement with experiment. However, there still remains a substantial disagreement in the total probability.
[1] R. Hong et al., Phys. Rev. A 96, 053411 (2017).
[2] E. E. Schulhoff and G. W. F. Drake, Phys. Rev. A 92, R050701 (2015).
We describe the theory of black hole analogues in atomic Bose-Einstein condensates (BECs). An event horizon can occur in such systems if there is a region where the flow speed of the gas exceeds the speed of sound. Such sonic black holes create negative frequency modes that have a positive norm, resulting in negative energies within the Hamiltonian of elementary excitations. An analogue of Hawking radiation then occurs due to the excitation of pairs of atoms out of the condensate. In the vicinity of the event horizon the mode function also suffers a logarithmic phase divergence which heralds the breakdown of the classical wave description [Leonhardt et al., J. Opt. B: Quantum Semiclass. Opt. 5 S42 (2003)]. We examine the connection of this problem to that of caustics in optics in an effort to develop a theory of quantum caustics.
Engineering light absorption in GeSn structures is crucial to enhance their basic device performance for a variety of applications such as MIR photodetectors and solar cells. Surface texturing to reduce the reflectivity is a key strategy to tune the optical properties. Since Group IV semiconductors typically have large refractive indices compared to air (between 3.4 and 4.2), planar opto-electronic devices are plagued by this refractive index mismatch. A promising method to circumvent this limitation is the use of semiconductor nanowires arranged in arrays covering an area of macroscopic dimensions. Top-down etched GeSn nanopillar arrays were microfabricated with varying geometrical configuration. Visible and near IR spectroscopic ellipsometry measurement was undertaken in the spectral range from 900 nm to 2500 nm to evaluate the complex optical constant (n and k) for a 10% GeSn material to allow for an accurate finite-difference time-domain (FDTD) theoretical investigation of the absorptance of GeSn-based nanopillar arrays with different key geometrical parameters (diameter, pillar height, tapering, incidence angle). Additionally, spectral transmittance, reflectance and absorptance of the nanopillar arrays were measured using an integrating sphere in the SWIR spectral range. The presence of absorption enhancement modes in the vertical cavity are explained by the interplay between the HE1m waveguide modes which lead to optimized absorption due to light propagation along the nanopillars axis and the leaky resonance mode. The ability to manipulate light-matter interactions at the nanometer scale with GeSn is opening up new opportunities for spectral tunability in the SWIR range.
Inhaled hyperpolarized (HP) 129Xe MRI is a non-invasive and radiation-risk-free lung imaging method. Simultaneous ventilation/perfusion lung measurements of functional gas exchange within the lungs are possible due to the natural solubility of xenon in lung tissue compared to other imaging gases. Therefore, 129Xe is a unique probe for exploring xenon within and beyond the lung, such as lung parenchyma, red-blood-cells (RBC), and even other organs such as the brain, heart & kidney. This measurement is possible due to the distinct and large range of chemical-shifts ((CS)=200ppm) of 129Xe when residing within parenchyma & RBC compared to the gas phase.
We've conducted CS measurements of HP 129Xe dissolved in ethanol-water mixtures in interval of 0-100% ethanol concentration in order to make a 129Xe MRI phantom mimicking CS (~19ppm) specific for 129Xe residing in parenchyma & RBC. For each concentration, a 20ml of mixture was shaken with 20ml of 129Xe gas then scanned using 3T GE MRI750 scanner. A FID acquisition (flip angle=33o, TE/TR=0.4ms/1.5s, BW=17kHz, 1024 points) was used to resolve the gas & dissolved-phase peaks. The 129Xe frequency obtained for xenon dissolved in a deionized water (0% mixture) was our reference frequency, i.e., zero-CS (0ppm or 0Hz). We've observed a linear increase of the CS values in Hz on the concentration interval of 0-30% (0 to +116Hz). However, at 40% ethanol concentration, the relative CS became negative (-50Hz, i.e., zero-crossing occurred at ~38%) and it continued to decrease on the interval of 40-100% (up to -1031Hz). A significant decrease of the 129Xe gas peak signal was observed for high ethanol concentrations (>60%).
To our knowledge, a zero-crossing effect observed near 40% concentration was not previously reported in a literature. We expected to see a gradual increase in CS with the ethanol concentration increase; However, this was true only for the low concentrations (<30%). We hypothesize that the electron density surrounding 129Xe became similar to that in the pure water case (0Hz at ~38%) and after this, becomes even weaker. The structure of ethanol-water mixtures is a longstanding scientific issue but, the use of HP 129Xe MRI may help to understand these structures better.
We found that the relative frequency shifts obtained at 30% (+116Hz) and 80% (-531Hz) mimic well CS of 129Xe when residing within parenchyma & RBC.
Purpose: Targeting small, breast lesions with high accuracy is critical for early stage diagnosis, treatment planning, and improving patient prognosis. Current imaging methods to target and sample breast lesions are limited in sensitivity and targeting accuracy. We propose using a breast-specific nuclear medicine imaging technique, positron emission mammography (PEM) to improve detection and target localization of breast lesions. To be useful for biopsy, anatomical detail and needle visualization are necessary, but not possible with nuclear imaging. We present a mechatronic guidance system integrating an ultrasound (US) guided biopsy method for improved visualization to target and sample breast lesions detected with PEM.
Methods: A mechatronic guidance system was developed to operate with an advanced PEM and US system. The system features a manually actuated, mechatronic arm with ability to access the breast between PEM detector plates. The end-effector biopsy device contains an US transducer and biopsy gun with its needle focused on a remote-center-of-motion. Kinematics of motion were implemented, and custom software modules were developed to dynamically track, display, and guide the biopsy device. Guiding the needle to calibration fiducials on a simulated PEM detector plate registered the world coordinate system to PEM using landmark-based registration. Validation was performed with fiducials at various locations within the targeting volume of a breast, simulating PEM detected breast lesions. Fiducial Registration Error (FRE) and Target Registration Error (TRE) was quantified to evaluate accuracy. Within 95% confidence intervals, 3D principal component analysis assessed directional trends.
Results: Registration and validation resulted in an FRE of 0.23±0.20mm (N=8) and TRE of 0.70±0.20mm (N=72). Tracking accuracy is <1mm in each axis. A 3D prediction ellipsoid centered on the mean error, such that any future observation has 95% probability of targeting within the volume was determined.
Conclusions: We demonstrate a novel system with the ability to guide with sub-millimeter accuracy in 3D space within targeting region of a breast between simulated PEM detector plates. When a lesion is detected with PEM, this accuracy is within the resolution and imaging uncertainty, demonstrating feasibility to improve targeting accuracy during image-guided breast biopsy.
Introduction: The non-invasive chemical exchange saturation transfer (CEST) MRI method measures pHi with high spatial and temporal resolution. In CEST, exchangeable protons on proteins can be selectively excited and detected through the transfer of magnetization to bulk water; the rate of which is pH-dependent. We have previously developed a CEST-MRI technique, amine and amide concentration-independent detection (AACID), to measure absolute tissue pH that is heavily weighted to the intracellular compartment. The AACID value is inversely related to tissue pH. This study is focused on the change in tumour pHi over time in a rat C6 glioma model.
Methods: C6 glioma cells were injected into the right frontal lobe of fifteen rats. CEST-MRI was performed at baseline, 7-11 days, and 14-16 days post-implantation on a 9.4T MRI. CEST images were acquired at saturation frequencies from 1.2-6.6 ppm to create CEST spectra for each pixel in the image, AACID maps were then produced.
Results: The average AACID values at day 0 were similar to the values in contralateral tissue at days 7-11 and days 14-16 post-implantation. The AACID value was significantly lower in the tumour compared to the contralateral region at day 7-11. At day 7-11, the average AACID value was 4.8% lower in the tumour compared to the contralateral side indicating a 0.24 higher pH. Surprisingly, at day 14-16 the average tumour AACID value was no longer significantly different than the contralateral region.
Discussion: The difference between tumour pH and contralateral pH is expected to increase over time in this model. However, this was not observed. One potential explanation is the temporal stability of the AACID CEST measurement and the emergence of an altered physiological state within the contralateral tissue as tumours increase. Future work will explore different MRI acquisition sequences and coils to improve temporal stability.
Solid-state nanopores can be used as single-molecule detection devices. Since the rate of passage through a nanopore is proportional to the polyeletrolyte concentration, solid-state nanopores can be used to precisely quantify dilute concentrations (nM/pM) of disease-relevant biomarkers. Accurate concentration measurements require statistically significant sample sizes of translocation events, meaning that low abundance biomarkers require significantly longer experiments. A difference in salt concentration on either side of the nanopore (salt asymmetry) can be used to offset this effect by increasing the capture rate without increasing translocation speed (current trace resolution does not suffer), effectively lowering the concentration limit of detection. Therefore, it is of great interest to study the kinetics of capture and translocation by solid-state nanopores in salt asymmetry. The capture rate dependence on the salt concentration ratio, on applied voltage, and on DNA length, is used to infer a transition between two distinct capture rate scaling regimes in salt asymmetry. In the diffusion-limited regime capture rate increases linearly with the salt concentration ratio while in the barrier-limited regime capture rate increases super-linearly with the salt concentration ratio. We show that salt concentration ratios promoting capture shift the transition points dividing regimes, further increasing the range of diffusion-limited capture, a requirement for precise nanopore concentration measurements via Controlled Counting (https://doi.org/10.1021/acs.analchem.9b01900). In terms of translocation kinetics, we report a smaller scaling exponent relating DNA length to translocation event duration in salt asymmetry compared to the analogous exponent in symmetric salt, and show that salt asymmetry promotes folded translocations. Finally, we provide experimental evidence which supports tension propagation theory, providing insight into the sampled polymer conformations during the non-equilibrium translocation process.
Our lab has been investigating the use of laser-induced breakdown spectroscopy (LIBS) for the rapid identification of bacteria in simulated clinical specimens. LIBS is a laser-based spectrochemical technique that allows a near-instantaneous measurement of the elemental composition of a target. Subtle yet reproducible differences in the concentration of inorganic elements like phosphorous, magnesium, calcium, and sodium in the bacterial cell allow a differentiation of the bacteria on the basis of their atomic emission spectrum alone. This can be used for the rapid identification of unknown specimens.
The current testing protocol involves the collection of bacteria using disposable pathology swabs, shaking off the cells into a water suspension, and centrifuging the suspension through a custom-fabricated cone device that concentrates the cells into a 1 mm diameter circular area on a nitrocellulose filter medium. A 10 ns 1064 nm laser pulse focused onto the deposition creates a high-temperature microplasma allowing a measurement of the elemental composition of the cells after dispersion and recording of the atomic emission spectrum with an Echelle spectrometer.
Currently, the construction of a spectral library database containing the LIBS emission spectra from hundreds of spectra obtained from 5 different bacterial species and sterile water control specimens is ongoing. The spectra are analyzed using discriminant function analysis and partial least-squares discriminant analysis to classify unknown samples and to determine the method’s sensitivity and specificity. The limit of identification is also being investigated by improving the external validation accuracy of highly diluted specimens.
Manipulation of the library with outlier elimination techniques, reduction of elemental contaminants contributing to extraneous background signals, and the addition of silver microparticles to enhance signal intensities are all being investigated to produce a standardized protocol that minimizes the bacterial limit of detection while maximizing classification accuracy.
Magnetic resonance imaging requires the sample to be stationary and centered in the magnetic field in order to have the best quality image. After a recent construction period, many pieces of equipment in the lab were lost. Thus we had difficulty imaging live mouse brain with their heads remaining stationary and centered in the magnet. A 3D printed radiofrequency (RF) coil holder attached to a mouse bed was created to center the RF coil, and thus the mouse brain, while keeping the mouse stationary and allowing for the physiological monitoring devices and water warming bed to rest in proper locations to allow for live imaging. The bed was printed with EcoTough PLA. Images of tubes of water were created with and without the mouse bed to assess for artifacts from motion and due to magnetic susceptibility differences. In these images, the signal from all voxels in the water tubes were measured and plotted in a histogram. These signal data were then fitted to a Gaussian. The average signal intensity in arbitrary units for both images were comparable at 0.6 and 0.5. The full width at half maximum (FWHM) for the images using the 3D printed water bed and the image without the water bed was at 1.1 and 1.5, respectively. Both were comparable, with the 3D printed bed being slightly better indicating a more uniform image. Less uniformity could be due to motion, given that the RF coil was not secured as well without the printed mouse bed. With the bed created we are now able to begin live mouse imaging with the mouse brain and coil better secured.
The authors wish to thank NSERC and Mitacs for funding and David Ostapchuk for technical help.
Purpose
Micrometer-scale spatial resolution and sensitivity to low doses remain a challenge for radiation dosimetry, however, these are essential to advancing areas of radiation therapy and understanding health risks from low dose radiation exposures. The purpose of this work is to develop a new approach for high spatial resolution dosimetry based on Raman micro-spectroscopy scanning of radiochromic film that provides improved sensitivity to low doses, an extended range for the dose-response curve in addition to high dose uniformity.
Methods
Samples of EBT3 radiochromic film (RCF), were irradiated at a broad dose-range of 0.03-50 Gy using an Elekta Precise clinical linear accelerator. Raman spectra were acquired with a lab-built Raman micro-spectroscopy setup involving a 500 mW, multimode 785 nm laser. The custom optical design enabled the concurrent collection of Raman spectra from the RCF active layer and the polyester laminate. Raman spectra were corrected for background noise and instrument spectral deviations. Spectra were normalized to the intensity of the 1614 cm-1 Raman peak corresponding to the polyester laminate which was shown to be unaltered by radiation. The peak intensities at 1445 and 2060 cm-1 Raman bands in the active layer of the RCF were used to generate a dose-response curve. Dose uniformity was assessed by taking the ratio of two Raman peak intensities in the active layer.
Results
Radiation induced changes in the RCF were measured for a wide range of doses from 0 to 50 Gy. The generated dose-response curve followed a linear trend until ~10 Gy. The dose non-uniformity determined from averaging spectra over a pixel size of 15 µm was determined to be less than 2% for doses greater than 0.15 Gy.
Conclusions
This work highlights the potential of Raman micro-spectroscopy to produce meaningful dose-estimates that could support applications that require high spatial resolution dosimetry.
Populations of genetically identical cells exhibit significant variability even when grown in constant conditions. This cell-to-cell variability is the result of a varying intracellular milieu, as well as noise arising from probabilistic birth and death events of any molecule of interest. Because the network of molecular interactions within a cell is only sparsely characterized, it is difficult to make rigorous predictions about the variability of any given cellular component. Here we show that non-identical but co-regulated reporters can be used to rigorously infer properties of their upstream dynamics from static snapshots of naturally varying cells. Analytically proving covariance relations for classes of systems, we derive correlation constraints that can be used to detect the presence of feedback. Furthermore, we demonstrate how the variability of co-regulated fluorescent proteins with unequal maturation times can be used to identify genes with cell-cycle dependent transcription rates or detect oscillating genes. Finally, we show that such correlation constraints can be rigorously exploited even in the presence of experimental artifacts, such as molecular undercounting, making our theoretical results directly applicable to commonly used experimental techniques like fluorescent in-situ hybridization.
Abstract
Particle neutron gamma-x detection (PNGXD) is a novel imaging concept proposed for tumor localization during proton therapy. The premise is to use secondary neutron interactions with a gadolinium contrast agent (GDCA) to produce photons within the 40–200 keV energy region that can be used for spectroscopic detection [1]. Previous work has investigated the experimental measurement of photons resulting from gadolinium neutron capture (GdNC) using a passive double scattering proton therapy treatment unit [2]. This research expands on these results by investigating the application of PNGXD for other ions (protons, helium ions and carbon ions). To investigate these additional ions, Monte Carlo (MC) simulations were performed using a 15-25 cm spread out-Bragg peak (SOBP) centered on a 2 cm3, 3 mg/g Gd infused tumor. It was determined that 3.9×1011, 7.4×1011 and 3.0×1011 neutron captures per Gy of dose (captures/Gy) occur for protons, helium ions, and carbon ions, respectively. As a result of this study, helium ions would produce nearly two times more GdNC than protons for the same administered dose. When normalizing to an estimate of RBE weighted dose (Gray Equivalent: GyE) this ratio reduces to 1.4. A total of 3.9×106 Gd photons of energies 43, 79.5 and 181.9 keV would be produced per GyE of administered dose from helium particles. This research indicates that the secondary neutron production from helium ions would be more beneficial than protons for the application of PNGXD or gadolinium dose enhancement from neutron capture.
[1] Gräfe JL. Proton Neutron Gamma-X Detection (PNGXD): An introduction to contrast agent detection during proton therapy via prompt gamma neutron activation. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 2017; 407:20-4.
[2] Van Delinder KW, Crawford D, Zhang T, Khan R, Gräfe JL. Investigating neutron activated contrast agent imaging for tumor localization in proton therapy: a feasibility study for proton neutron gamma-x detection (PNGXD). Physics in Medicine & Biology. 2020 Jan 24;65(3): 035005.
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The NEWS-G direct dark matter search experiment employs spherical proportional counters (SPCs) with light noble gases as target media to search for low-mass Dark Matter (DM). The next generation of the experiment is a 140 cm diameter SPC with a new sensor design and improved shielding, and will profit from a single-electron energy threshold to be sensitive to particle DM with a mass as low as 100 MeV/c2. Before its upcoming installation at SNOLAB, the detector was commissioned at the Laboratoire Souterrain de Modane in France, with a temporary water shield. During this time a short physics campaign with pure methane gas was undertaken, proffering a hydrogen-rich target and reduced backgrounds compared to the neon mixture planned for future measurements. Preliminary results of this campaign are shown, including UV laser and Ar-37 calibration data. The electron-drift properties of this detector allows for the identification of single primary electrons within an event, prompting a new analysis methodology to characterize the single-electrons response of the SPC. The unique two-hemisphere configuration of the sensor also allows for fiducialization.
As part of the ongoing search for dark matter, the NEWS-G collaboration uses a spherical proportional counter to detect WIMP interaction. The detector consists of a grounded spherical vessel filled with gas. A positive voltage is applied on a central anode, inducing a radial electric field. Energy deposited by a WIMP can cause ionization. Under the influence of the electric field, primary electrons drift towards the central anode. Within a few hundred μm around the anode, where the electric field is strong enough, primary electrons acquire sufficient kinetic energy to ionize other gas atoms, producing a large quantity of secondary ion-electron pairs by Townsend avalanche. The time taken for the primary electrons to drift from the sphere’s volume to the central anode is constantly being calibrated by a laser using the photoelectric effect. However, that drift time varies significantly depending on the field conditions. Moreover, it has been found to fluctuate substantially with time and is strongly correlated to other events happening inside the sphere that modify the charges distribution and the electric field. The purpose of this talk is to discuss laser calibration of the detector, causes and consequences of the drift time fluctuations, how it can influence the pulse formations and the overall data analysis as well as how problems arising from this effect can be mitigated.
The NEWS-G experiment aims for the direct detection of low mass Weakly Interacting Massive Particle (WIMP) dark matter using Spherical Proportional Counters (SPC). At the center of the SPC, a small sensor held at high voltage drives the drift of the primary ionization and provide the amplification needed to detect sub-keV nuclear recoils down to single electrons. The ACHINOS is a novel multi-channel sensor at the center of the SPC that allows for high amplification and better primary ionization collection thanks to enhanced electric fields at larger radius. The current implementation of ACHINOS in the NEWS-G SPC has two channels that separate the active volume in a north and south hemisphere. Future implementation of ACHINOS with multi-channel readout could allow for the directional measurement of dark matter in a large, low-pressure SPC. In this talk, the operating principle of the ACHINOS sensor will be presented along with recent experimental data highlighting the features of a two-channel readout in the NEWS-G SPC.
NEWS-G (New Experiments With Spheres-Gas) is a rare event search experiment using Spherical Proportional Counters (SPCs). Primarily designed for the direct detection of dark matter, this technology also has appealing features for Coherent Neutrino-Nucleus Scattering (CE$\nu$NS) studies using nuclear power plants as a neutrino source.
For both applications, an important property of the gas to characterize is the ionization yield, or quenching factor, defined as the ratio of the measured energy induced by a nuclear recoil and an electronic recoil of the same energy. Quenching factor measurements in Neon based gas mixtures are being performed at TUNL (Triangle Universities Nuclear Laboratory) using a neutron beam and an array of backing detectors. We will present the set-up and techniques for quenching factor measurements and the most recent results obtained.
DEAP-3600 is a single-phase liquid argon direct dark matter search experiment located at SNOLAB in Sudbury, Ontario. DEAP-3600 is designed to detect the nuclear recoil signal of a Weakly Interacting Massive Particle (WIMP), while using pulse-shape discrimination to remove backgrounds from argon-39 beta decay. Other sources of background include alpha decays, neutrons, and Cherenkov light. This presentation will summarize the latest results from DEAP-3600: the latest dark matter search results including a detailed background model, a measurement of electromagnetic backgrounds and potassium-42 activity in the detector, and a characterization of the liquid argon pulse-shape. The expected sensitivity of new machine-learning algorithm to suppress alpha particle events occurring in the detector neck, strongly reducing the largest contribution to the background estimates in the dark matter search, will also be presented.
DEAP-3600 is a liquid argon (LAr) based spin-independent direct dark matter search experiment. It is designed to detect nuclear recoils induced by the elastic scattering of weakly interacting massive particles (WIMPs) on argon nuclei. In addition, its large target mass and excellent ability to distinguish between electronic and nuclear recoils makes it well-suited for the detection of 5.5 MeV solar axions, which would produce electronic recoils in the LAr, at higher energy than most backgrounds. In this talk I will discuss the various components of the 5.5 MeV solar axion search analysis, including the calibration of the energy response function on AmBe neutron calibration data, development of the Monte Carlo based background and signal models, the algorithm developed to fit the MC model to the data, the methods used to evaluate the sources of uncertainty, and the approach that will be used to calculate the final result. The projected sensitivity for various axion interaction channels will also be shown.
Astrophysical and cosmological observations support that dark matter constitutes more than 80% of the matter in the universe. Understanding the nature of DM will make possible to reconstruct the early universe history since all the experimental data that we have related to universe evolution comes from Big Bang nucleosynthesis era onwards.
The current Standard Model of particle physics is not able to explain the nature of DM therefore extensions seem necessary to account for new particles that predict be viable dark matter candidates. Currently the QCD axion is an attractive candidate to explain the origin of DM, although axions are extremely light, there are mechanisms corresponding to non-thermal production of axions able to produce axion dark matter in the early universe in such a way that it accounts the total dark matter density currently measured ($\Omega_{𝑐𝑑𝑚}$=0.26 ).
A mechanism corresponds to misalignment mechanism, which consists in the fact that after the PQ phase transition the axion evolves like a massless scalar field, but close to the QCD era ($\Lambda_{𝑄𝐶𝐷}$), the axion acquires an effective potential due to instanton effects. The equation of motion for the field corresponds to
$\dot \theta+ 3𝐻(𝑡)\theta+ 𝑚_𝑎^2(𝑡)𝑠𝑖𝑛\theta=0, \qquad(1) $,
At high temperatures ($𝑇≫\Lambda_{𝑄𝐶𝐷}$), the field is stuck on a constant value, corresponding to the initial misalignment angle of the axion . But, when expansion rate H(t) becomes comparable to the axion mass, the axion field begins to oscillate around the minimum and coherent oscillations are generated, which behave like cold dark matter, i.e. their energy density evolves as $\rho\sim R^{-3}$.
The standard cosmology establishes that before Big Bang Nucleosynthesis (BBN) there was a radiation-dominated era, where its expansion rate of the universe generates a parameters space where axion QCD could be dark matter.
In this work, we assume the scenario of a new period before BBN where extra field $\phi$ present at the early universes (After Inflation) and that eventually, due to its equation of state,$P_\phi=\omega \rho_\phi$, dominates the energy density of the universe. Prior to BBN the field decays with a decay rate $\Gamma_\phi$ and the universe is radiation dominated as hinted by observations.
Finally, we have different compatible cosmologies with the axion being the total CDM content of the universe, providing in a window for axion parameters according to the cosmology used.
We study a model of fermionic dark matter (DM) interacting with the standard model (SM) through a Z’ mediator, the gauge boson of a U(1) extension to the SM symmetry group, to understand the mechanism responsible for the DM relic abundance in different regions of parameter space. We compare two different mechanisms for the DM production in the early universe, freeze-out and freeze-in. For production through freeze-out, DM particles were in thermal equilibrium with the cosmic plasma until the expansion of the universe dominated over the frequency of interactions when the DM decoupled from the thermal bath. For freeze-in, DM was never in thermal equilibrium with the visible sector since it couples so weakly to it. In this work we take into account all processes that change the amount of DM (annihilation and production). The boundary between different production regimes is explored by considering the parameter space of this model namely the DM candidate mass, mediator mass, and DM couplings. Properly taking into account the boundary region between freeze-in and freeze-out could have implications for DM searches.
Magnetic reconnection [1] is a physical non-ideal process involving conductive plasma flows. It converts magnetic energy into kinetic energy and heat by a topology modification of the magnetic field line. In presence of magnetic instabilities, the structures resulting from reconnection processes can then grow into “magnetic island(s)”.
In tokamaks, due to the high temperature required to reach the ignition condition, it is usually thought that resistivity is to weak and the magnetic field should remain “frozen-in” within the plasma. However, in such devices, magnetic islands can be observed at various spatial scales (from millimeters to a few tens of centimeters) with different impacts on the confinement. Indeed, various non-ideal physical mechanisms can allow magnetic reconnection and be at the origin of an instability letting an island to grow.
By means of theoretical calculations and numerical simulations, we propose, here, to examine 3 physical examples leading to the growth of magnetic island(s) in magnetized hot plasma. First, we will consider the “classical” tearing instability [1] where resistivity plays an important role both to allow reconnection and for the growth at large scale of a magnetic island. Then, we will study the generation of Turbulent Driven Magnetic Island (TDMI) [2,3]. In that example, a large magnetic island draws its energy in a nonlinear beating of turbulent modes. Such TDMI can then by amplified nonlinearly and destroys the confinement. Finally, we will investigate the destabilization at small-scales of a thin current sheet by an electronic temperature gradient leading to the formation of islands (in a millimeter range) that can affect the electronic heat transport [4].
References:
1. D. Biskamp, “Magnetic Reconnection in Plasmas”, Cambridge University Press (2010).
2. M. Muraglia et al., Phys. Rev. Lett., 107, 095003 (2011).
3. J. Frank et al., Phys. Plasmas, 27, 022119 (2020).
4. M. Hamed et al., Phys. Plasmas, 26, 092506 (2019).
The formation of soot particles in combustion, of cosmic dusts in the interstellar medium or of carbon nanoparticles in nonthermal plasmas, laser plumes, electric arcs or fusion devices is generally described by successive steps of nucleation, coagulation, processing and surface growth.
Nucleation is the crucial stage. Nevertheless, it is not well defined except in flames where polycyclic aromatic hydrocarbons (PAHs), evidenced as the precursors of soot particles, are formed through successive reactions of hydrogen abstraction and carbon addition.
Based on these models, PAHs have been suspected as precursors of dust particles in nonthermal plasmas. However, only aromatic molecules smaller than naphthalene (C10H8) were identified in acetylene RF capacitively-coupled plasmas. Indeed, though the numerous species (radicals, cations and anions) formed in the plasma through acetylene-electron collisions yields to really efficient dust particle growth, the thermodynamic parameters (pressure, temperature) was considered unsuitable to efficiently produce large PAHs.
Hence, nucleation pathways in nonthermal dusty plasmas still remain open issues, especially at very low pressure as in the case of plasmas excited at electron cyclotron resonance (ECR), where nucleation was generally considered negligible before we reported dust particles formation in pure acetylene. By combining transmission electron microscopy with the analytical experimental setup AROMA, we observed that those dust particles are with a really rich molecular composition. Notably, PAHs such as pyrene (C16H10) or coronene (C24H12) are found in abundance. It also includes carbon clusters (Cn, n < 30) and, more surprisingly in nonthermal plasmas, buckyballs such as C60. The presentation will report some of these results obtained in the ERC Synergy project Nanocosmos.
The amplification of cosmic magnetic fields by chaotic fluid motions is hampered by the adiabatic production of magnetic-field-aligned pressure anisotropy. This anisotropy drives a viscous stress parallel to the field that inhibits the plasma's ability to stretch magnetic-field lines. However, in high-$\beta$ plasmas, kinetic ion-Larmor scale instabilities---namely, firehose and mirror---sever the adiabatic link between the thermal and magnetic pressures, reducing this viscous stress and thereby allowing the dynamo to operate. We identify two distinct regimes of the fluctuation dynamo in a magnetized plasma: one in which these instabilities efficiently regulate the pressure anisotropy so that it does not venture much beyond the firehose and mirror instability thresholds, and one in which this regulation is imperfect. Using kinetic and Braginskii-MHD simulations and analytic theory, we elucidate the role of these kinetic instabilities and determine how the fields and flows self-organize to allow the dynamo to operate in the face of parallel viscous stresses. In the case of efficient pressure-anisotropy regulation, the plasma dynamo closely resembles its more traditional ${\rm Pm}\sim 1 $ MHD counterpart. When the regulation is imperfect, the dynamo exhibits characteristics remarkably similar to those found in the saturated state of the MHD dynamo. An analytical model for the latter regime is developed that exploits this similarity. The model predicts that the plasma dynamo ceases to operate if the ratio of field-aligned to field-perpendicular viscosities is too large, a behavior confirmed by numerical simulation. Leveraging these results, we construct a novel set of microphysical closures for fluid simulations that bridges these two regimes---one that exhibits explosive magnetic-field growth caused by a field-strength-dependent viscosity set by the firehose and mirror instabilities.
The success of next-generation tokamaks such as ITER relies on minimizing the turbulent heat transport that limits confinement and on avoiding macroscopic instabilities that can lead to disruptions. Toroidal plasma rotation is known to be beneficial in both regards: It stabilizes the resistive wall mode and suppresses turbulence. Many current experiments induce rotation by applying an external torque, but this will be less efficient in large, dense plasmas such as ITER. However, even in the absence of external torque, tokamak plasmas spontaneously rotate. This `intrinsic' rotation is a generic feature of tokamak plasmas, but it is not understood well enough to predict reliably the rotation in experiment. A major reason for this uncertainty is that the models used to simulate fusion plasmas are not of a sufficient physical fidelity in order to capture the effects---such as large-scale variations in the pressure and magnetic geometry profiles---needed to describe intrinsic rotation correctly.
To that end, we develop a novel approach to gyrokinetics where multiple flux-tube simulations are coupled together in a way that consistently incorporates global profile variation while retaining spectral accuracy. By doing so, the need for Dirichlet boundary conditions, where fluctuations are nullified at the simulation boundaries, is obviated. These conditions, which are typically employed in global gyrokinetic simulation, prevent convergence to the local periodic limit unless large simulation domains are utilized. Thus, our method of global-local gyrokinetics is appropriate for simulations of the pedestal region where the generation of intrinsic momentum is expected to commence and the details of boundary physics are important. Preliminary results from simulations with equilibrium flow shear using this approach are compared to simulations using conventional global methods and to local flux-tube simulations with wavenumber-remapped flow shear. Progress is also reported on implementing profile variation in both the plasma pressure and magnetic geometry.
to be posted later.
Plasma streamers produced by nanosecond discharges in dielectric media are known to be stochastic in nature. The dynamic of a streamer is highly sensitive to the electric field, among others. Streamer filamentation, produced by the communication of multiple streamers via electric fields and energetic photons, is always described as a stochastic phenomenon that depends on the propagation medium and on the physical and chemical properties of the streamer.
In this contribution, we will discuss the spatiotemporal dynamics of positive and negative streamers produced at the water surface. Temporal resolved ICCD imaging, resolution of 1 nanosecond, has revealed that the positive streamers are not stochastic but highly organised, and the negative streamers are rather homogeneous. The discharges behaviour is investigated under different of high voltage pulse, namely the amplitude and the width of the pulse. Results will be shown and discussed during this presentation.
In this work, the non-equilibrium nature of argon-based radiofrequency (RF) and microwave plasmas at atmospheric pressure is evidenced. In particular, rotational temperature ($T_{rot}$) and neural gas temperature ($T_{g}$) are found to be unequal in every condition tested, even though they are often assumed equal in such plasmas in the literature. Such a finding was made possible through the use of a hyperfine spectrometer developed and commercialized by LightMachinery Inc. Offering a 2 pm resolution over a simultaneous range of 25 nm, it was tuned to the 820-845 nm range in which the broadening of the Ar $2p_{2}-1s_{2}$ and Ar $2p_{3}-1s_{2}$ (Pashen notation) transitions is strongly affected by the neutral gas temperature. Therefore, for these emission lines, the experimental broadening was much smaller than the other broadening sources, ensuring a precise and accurate determination of $T_{g}$.
The microwave plasmas were produced inside a fused silica tube using a surfaguide-type wave launcher, while the RF plasmas were produced inside a fused silica tube placed between two electrodes. In both cases, an admixture of $H_{2}O$ or $N_{2}$ were added to the argon flow in order to observe either the OH ($A^{2}Σ^{+}- X^{2}Π_{i}$) or the $N_{2}^{+}$ ($B_{2}Σ_{u}^{+}- X_{2}Σ_{g}^{+}$) molecular systems. A rotational temperature was then calculated using the Boltzmann plot method. $T_{rot}$ and $T_{g}$ values were obtained every centimeter along the plasma columns. For the microwave plasma with an admixture of $H_{2}O$, $T_{g}$ values of over 2000 K were obtained while $T_{rot}$ values were in the 1400 K range. For the microwave plasma with an admixture of $N_{2}$, $T_{rot}$ values were found to rise to ~3200 K whereas $T_{g}$ values only increased to ~2400 K. The same discrepancies were found in the much colder RF plasmas ($T_{g}$~400 K while $T_{rot}$~515 K). Therefore, since the rotational temperatures did not equal the gas temperature in every condition tested, it is concluded that the rotational-translational equilibrium cannot not be assumed for RF and microwave argon-based plasmas at atmospheric pressure.
to be posted later
For the first time, ultra-high-resolution optical absorption spectroscopy using a supercontinuum laser combined with a widely tunable filter and a hyperfine spectrometer is reported. The measurements were taken in a reduced pressure, nominally pure argon DC plasma. Such measurements allowed the determination of the number density of absorbing species (Ar 1s$_2$ and 1s$_4$ levels (Paschen notation) in this case) while overcoming many of the drawbacks associated with absorption spectroscopy. On the one side, the supercontinuum laser (SuperK EXTREME/FIANIUM, NKT Photonics) paired with a widely tunable filter (Laser Line Tunable Filter, Photon etc.) made it possible to probe any wavelength in the visible/near IR spectrum without altering the plasma properties. This would not have been possible with a spectral lamp emitting at only discrete wavelength or with a strong white light emitting a broad spectrum. On the other side, the ultra-high-resolution (Hyperfine spectrometer, LightMachinery Inc.,), with its 2 pm resolution over a simultaneous range of 25 nm, allowed the detection of the absorbed laser signal through the plasma, an accomplishment that could not be achieved with a typical high-resolution spectrometer (78 pm, Princeton Instruments, IsoPlane-320 spectrometer with a 2400 g/mm holographic grating and a PI-MAX4 iCCD camera). The results obtained were from analysing the absorption profile of the Ar 2p$_3$-1s$_2$ and Ar 2p$_8$-1s$_4$ emission lines at 840 nm and 842 nm respectively. At a pressure of 1 Torr, a discharge current of 20 mA and an absorption length of 18 cm, number densities of 1.3×10$^{16}$ m$^{-3}$ and 2.5×10$^{16}$ m$^{-3}$ were respectively found for the Ar 1s$_2$ and Ar 1s$_4$ levels. These values are typical of DC discharges under similar conditions. The 1s$_2$ level is found to be less populated than the 1s$_4$ level, a result ascribed to its energy being higher in the energy diagram, thus less easily populated. Moreover, the absorption of both lines was found to decrease when decreasing the optical absorption path, without actually resulting in smaller number densities, as expected. Finally, the number densities were found to increase with an increase of the discharge current, a result also coherent with the literature.
Wood components made of cellulose, hemicellulose, lignin, extractives, etc. have been used as a building material for centuries. In light of the growing concern over the environmental impact of human industrial activity, wood has taken on a new importance worldwide. The main advantages of this widely-distributed and renewable resource lie in its versatility, strength-to-weight characteristics, ease of processing, aesthetics, and its sustainability as a green-material. Its bio-polymeric structure, however, renders it susceptible to degradation due to moisture, microorganisms, insects, fire, and ultraviolet radiation. In this context, important research efforts have been devoted to the further development of existing wood protection systems either through the application of paints, varnishes, stains, and water repellents or through direct modification by thermal, chemical, and impregnation methods. In recent years, we have shown that non-thermal plasmas represent a very promising approach for tailoring the surface properties of wood-based materials for both improvement of existing protection systems or as standalone treatment for the growth of functional coatings. In this presentation, the scientific and technological accomplishments associated with the use of plane-to-plane dielectric barrier discharges at atmospheric pressure for plasma activation [1,2] and plasma-enhanced chemical vapor deposition (PECVD) of various barrier coatings on wood surfaces are reviewed [3]. These aspects cover the effects of wood conditions and properties, such as wood inhomogeneities and wood outgassing, on the plasma deposition dynamics of SiOCH barrier layers using organosilicon precursors. This description is extended to more complex systems such as the plasma-assisted growth of nanocomposite coatings (for example TiO2 or ZnO nanoparticles embedded into a SiOCH matrix) using colloidal solutions as the growth precursor for PECVD [5]. For such applications, a combined low-frequency-high-frequency voltage waveform is used to achieve significant and spatially uniform deposition of nanoparticles across the whole substrate surface [6]. Finally, inspired by the development of advanced methods for deconstructing the de-lignified wood tracheids (fibres) into micro and nano fibres on an industrial scale, very recent studies on the plasma-assisted functionalization of highly porous microfibrillated cellulose (MFC) materials derived from the wood biomass are presented. This includes plasma deposition of functional, nanostructured coatings on films and foams made of MFC with the objective of establishing barrier properties to water, vapor, or gases for packaging and energy applications.
Electron transport driven by instabilities is a universal feature in high- and low-temperature magnetized plasmas. Only fairly recently has it become feasible to simulate large-scale plasma transport within the framework of kinetic theory of gases and only the latest additions to computing power have enabled this to be done up to electron scales in tokamak plasmas and system size in Hall-effect thruster plasmas. Emerging evidence shows that complicated interplay over vastly different scales of physics affects transport, making both multi-scale gyrokinetic continuum simulations of tokamak transport and particle-in-cell simulations of Hall-effect thrusters a very interesting prospect indeed.
A lot of indirect evidence suggests that electron temperature gradient (ETG) turbulence is a key player in magnetized fusion plasmas. ETG turbulence is considered to contribute to the overall electron heat flux and to affect ion-scale turbulence by reducing the effectiveness of shear-flow stabilization. Interestingly, ETG turbulence in our simulations exhibits a symmetry breaking as a result of the presence of a low-Z impurity species at significant density. We will elaborate on this point via continuum gyrokinetic simulations.
Anomalous conductivity due to instabilities is an important feature of $E\times B$ driven plasmas (see Refs 1,2). Kinetic simulations show that cascades to large scales occur in density fluctuations as well as the anomalous current. Long term behavior of the system has proven to be surprisingly challenging to simulate numerically with sufficient accuracy. We discuss recent simulations of fluctuations in Hall-effect thrusters and associated heating observed in simulations, as well as analytical theory behind these phenomena.
[1] S. Janhunen et al., Physics of Plasmas 25 (1), 011608 (2018)
[2] S. Janhunen et al., Physics of Plasmas 25 (8), 082308 (2018)
The nonlinear evolution of the The Electron Cyclotron Drift Instability (ECDI)
driven by the electron EB drift in partially magnetized plasmas and anomalous
electron transport in two dimensions are studied using particle-in-cell (PIC) simula-
tions. PIC simulations were performed for the parameters typical of the Hall-e?ect
thruster in the two-dimensional azimuthal-radial geometry to investigate the role
of the boundaries conditions, electric and magnetic ?eld magnitudes, sheath losses
and ?nite-length on the mode development and anomalous electron current. The
saturated state of turbulence and resulting anomalous electron current are studied.
Nature of the anomalous current and contribution of di?erent wavelength are inves-
tigated. It is shown that the magnitude of the anomalous current can be explained
as a EB drift of magnetized electrons in
uctuating ?elds.
a)Electronic mail: maj443@mail.usask.ca
1
Fusion reactors such as the tokamak, represent an attractive means of energy
production in terms of high power output, low emissions, few waste products and
safe operation. Unfortunately, multiple fundamental problems still need to be
addressed for a working reactor. The plasma wall interaction (PSI) is one of these crucial problems.
In a tokamak, a region known as the scrape off layer (SOL) exists between the
plasma and the plasma facing material of the reactor wall. In an effort to remove
heat, accumulated fusion products and impurities from the reactor, divertor plates primarily made of tungsten have been placed in the high heat flux region of the SOL.
The goal of our research is to simulate the behaviour of the sputtered
chamber wall particles (in particular those from the divertor plates) inside of
STOR-M (Saskatchewan Torus Modified). An injector was designed and built which
could introduce tungsten micro particles (dust) into the reactor in a controlled and precisely timed manner. As Tungsten is a high Z material, it is particularly
interesting to study Bremsstrahlung effects and potential disruptions which could
be detrimental to the plasma. The dust dispenser is being tested in an apparatus
specifically devised for injector calibration and dust characterization, before
installation on STOR-M.
STOR-M is equipped with a compact-torus injector, a promising device for
reactor fueling. The dust dispenser will be used to both embed tungsten particles in the STOR-M plasma and introduce tungsten impurity into STOR‑M discharge during
CT Injection. The resulting effects of tungsten dust in the plasma will be analysed.
The acceleration of plasma in a magnetic nozzle has many important applications including nuclear fusion in magnetic mirrors, helicon thrusters for space propulsion and plasma based etching of semiconductors. The goal is to study the acceleration mechanism, determine what factors give rise to larger plasma acceleration and how plasma parameters such as density, pressure, electrostatic potential are affected.
The flow of plasma is described in the paraxial approximation using a two fluid MHD model. Electrons are assumed to be isothermal while ions are fully magnetized, have anisotropic pressures and follow CGL model where heat fluxes are neglected. The magnetic field of the nozzle has no time-dependence, is constant at the left end, increases until it reaches a maximum near the middle of the nozzle and then decreases again and becomes constant at the right end. The flow of plasma is studied in both the absence and presence of ionization and charge-exchange.
From the continuity and CGL equations, the equations that describe ion dynamics were derived. \begin{equation}
\left(M^2-1-\frac{3 p_\parallel }{n T_e}\right)\frac{\partial M}{\partial z}= -\left(1+\frac{p_\perp}{n T_e}\right) M \frac{\partial\log B}{\partial z}
\end{equation}
A singularity occurs for values of $M=\sqrt{1+\frac{3 p_\parallel}{n T_e}}$. Stationary solutions for ion dynamics are obtained using the Shooting Method and time-dependent solutions are obtained using the PDE solver BOUT++. In the Shooting Method differential equations are integrated numerically from the singular point, occurring in the middle of the nozzle where $\frac{\partial\log B}{\partial z} = 0$, in both directions. Initial values of $T_{i\parallel}$ and $T_{i\perp}$ are chosen at the singular point such that when integrated to the left the will result in $T_{i\parallel} = T_{i\perp} = 200 eV$ at the left end of the nozzle where the plasma is completely thermalized. Time-dependent solution are then compared to stationary solutions for large time intervals. Ionization and charge-exchange are added to the model to investigate their effects on plasma acceleration and the shift of the sonic point
Plasma instabilities known as spokes have long been known to exist in ExB devices such as magnetrons and Hall Thrusters. The study of these spokes gives important insight into the ionization efficiencies and transport processes in these devices. However, spokes instabilities vary on small time scales, making characterization difficult. In this study we present results from the combined measurements of a highspeed camera, time-resolved Langmuir probe and floating probe array, for the characterization of spokes in a high-power impulse magnetron sputtering system. Spoke location and mode was determined by highspeed camera and compared to measurements from probes, the oscillating floating potentials was used to estimate the velocity of the spokes. Finally, Langmuir analysis was performed on the time-resolved Langmuir probe measurement to provide information on the evolution of plasma characteristics during the pulsed discharge.
Materials under high intensity femtosecond laser irradiation yield extreme material conditions called warm dense matter (WDM) with thermal energy comparable with the Fermi energy and the ion-ion coupling parameter exceeding unity. The WDM state exists in a variety of processes ranging from laser micromachining to inertial confinement fusion experiments. The WDM exists as transient states including as nonthermal WDM in the first few hundred femtoseconds when the electron thermalization is important and as two temperature WDM with high electron temperature and relatively low ion temperature in the first few picoseconds. The WDM subsequently transits into the plasma state. We have used pump-probe techniques [1-5] to study WDM produced by irradiating few ten's of nanometers thick free-standing metal foils with high intensity femtosecond laser pulses. In this talk I will focus on our studies using ultrafast optical Frequency Domain Interferometry to study the dissemble processes [2] and ultrafast electron diffraction technique to study the structural changes [1] of the laser heated foils. I will also present the results of broadband AC conductivity measurements of the warm dense gold generated with 245eV, 70fs pulses to selectively excite 4f electrons using the XUV-FEL at FLASH. The AC conductivity was measured at different wavelengths (485nm, 520nm, 585nm, 640nm and 720nm) to cover the range from 5d-6s/p interband transitions to 6s/p intraband transitions.
It has only recently become possible to experimentally test our understanding of laser-plasma interaction processes in fusion scale plasmas relevant to directly-driven and indirectly-driven inertial confinement fusion. It is seen that seeded stimulated Brillouin scattering and Raman side-scatter are particularly important processes and pose significant constraints on allowable peak laser powers. Examples will be shown from recent experiments on the National Ignition Facility to support these conclusions. It is suggested that successful fusion schemes will require such instabilities to be mitigated. Two approaches to mitigation will be described: mitigation by the introduction of enhanced laser bandwidth, and the use of structured light beams (e.g., light carrying orbital angular momentum). Simulation results will be presented that show the potential effectiveness of each scheme as will proposals for experimental verification on MJ-class laser facilities.
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Searching for low-mass WIMPs typically relies on ionization from a nuclear recoil in a detector. Calibration of the detector response at different energies can easily be done with charged particles with radioactive sources, but in this case the charged particles give energy directly to the detector material's electrons, not via a nuclear recoil. The ratio of detector response to nuclear and electronic recoils at a given kinetic energy is called the quenching factor.
Neutrons do induce nuclear recoils, but easy-to-get neutron sources produce high-energy (~MeV) neutrons from nuclear reactions. Intermediate and low-energy neutrons can be obtained from reactors or accelerators.
At the Reactor Materials Testing Laboratory (RMTL)[1] at Queen's University, there is a 4 MV tandem accelerator which can deliver proton currents up to 45μA with a maximum energy of 8 MeV. Using nuclear targets such as Lithium Fluoride or Vanadium, one can produce neutrons of various energies. Producing lower-energy neutrons is rather inefficient, but due to its role as a nuclear irradiation facility, RMTL has high enough beam current to overcome this problem.
In 2019 we performed several neutron production tests at RMTL and were able to roughly characterize the proton beam. A significant challenge is the energy width of the proton beam, moderation of the neutrons from excess material in the target chambers, and reflections from the walls.
This poster will introduce the WIMP detector we wish to calibrate, the RMTL facility itself, the technique to produce neutrons, results from the tests in 2019 and the latest progress towards our goals.
[1] Queen's University https://rmtl.engineering.queensu.ca/
The Scintillating Bubble Chamber (SBC) experiment is a novel low-background technique used to directly detect low-mass WIMPs and coherent elastic neutrino nuclear scattering of reactor neutrinos (CEvNS). The detector combines the strengths of bubble chambers with those of scintillation detectors. Nucleation of bubbles due to nuclear recoil of target fluid atoms provide information about the interaction between WIMP-like particles and target fluid. Imaging of the bubbles growth is an essential criteria in this type of detector. A CMOS sensor type camera from BASLER is used with high frame per second (164 fps) and 2.3 MP resolution to image these bubbles. Radioactive backgrounds from the cameras enhance the number of background events, decreasing the WIMP detection sensitivity. It is therefore critical to move the cameras away from the detector while maintaining the bubble imaging parameters (resolution, light collection efficient, field of view). Several options are currently being explored, such as videoscope, rigid borescope, lens system, and lens with nano guide, at the Univ. of Alberta. Background counting of these various setups, and ongoing research activity will be presented.
P-type Point Contact (PPC) germanium detectors are used in rare-event searches, such as neutrinoless double-beta decay and dark matter, due to their low radioactive backgrounds and low energy thresholds. We describe our work to determine the location of energy depositions in PPC detectors using the charge signal that is collected from the single point contact electrode. By comparing charge signals to a library of simulated signals, events can be localized, in some cases, with a resolution of 1mm. This is of interest in localizing low energy backgrounds in these types of detectors.
nEXO aims to search for neutrinoless double-beta decay of Xe-136. Detection of such an event significantly improves our understanding of the nature of the elusive neutrinos, showing that they are Majorana particles (their own antiparticle). Additionally, this would mean the violation of lepton number conservation, opening new avenues for physics beyond the Standard model. To facilitate this, nEXO aims to implement Ba-tagging for explicit detection of Ba-136 ions present in the detector volume resulting from the double beta of Xe-136 as a potential future upgrade. Ions traps are of great importance in particle physics research for filtering, cooling, channeling and detection of charged particles. The Nobel prize winning Paul Ion Trap uses rapidly oscillating electric fields for ion confinement. The Linear Paul Trap, to be used in Ba-tagging uses quadrupole electrodes for applying hyperbolic potential for radial confinement and axial DC field at the end for trapping. The stream of particles being injected will be filtered by passing them through the first section which is a quadrupole mass filter based on the charge to mass ratio of expected barium ions. They would then be cooled using helium as buffer gas, collected and trapped briefly in an ion buncher for performing laser spectroscopy. The bunched ions would then be injected into an MR-TOF (multiple reflection time-of-flight mass spectrometer) for precise identification of barium ions.
Located within the SNOLAB facility at VALE’s Creighton mine in Sudbury, Ontario, SNO+ is an experiment that studies the properties and behaviour of neutrinos. With a radius of 6m, the detector is composed of a spherical acrylic shell that has been filled with ultrapure water, which is now being replaced with linear alkylbenzene (LAB) and poly(p-phenylene oxide) (PPO), and finally with LAB and PPO along with Tellurium. The acrylic vessel (AV) is contained within a cavity filled with ultrapure water, and is held in position so that it is centered within a shell of photomultiplier tubes (PMTs) that capture traces of scintillation light produced by particle interactions with LAB.
The primary goal of SNO+ is to search for neutrinoless double beta decay, however its additional goals include the search for nucleons possibly decaying into neutrinos, to study proton-electron-proton (pep) and carbon-nitrogen-oxygen (CNO) cycles within the sun, to study oscillation parameters of of geo- and reactor- antineutrinos, and to detect and study neutrinos from supernova explosions.
Currently, SNO+ is undergoing the scintillator (LAB & PPO) fill and is continuing to record physics data, even though it contains both ultrapure water and LAB in the AV. In this presentation, I will introduce the SNO+ experiment and its physics program. I will then report on the process and status of filling operations, and discuss how to interpret and utilize the information collected during this period for future phases.
The nEXO experiment is being designed to search for neutrinoless double beta decays in 5 tonnes of liquid xenon enriched in Xe-136. Events in the detector will result in the observation of both charge signals and scintillation light. This light at 175 nm will be detected using UV-sensitive silicon photomultipliers (SiPM) covering an area of about 4.5 m^2. To achieve better than 1% energy resolution, an overall light detection efficiency higher than 3% is required, which implies an SiPM photodetector efficiency of at least 15%. A dark noise rate of less than 50 Hz/mm^2 and a correlated avalanche rate under 0.2 are also required. Recent results on SiPM device qualification from FBK and Hamamatsu, the development of Photon to Digital Converters (also known as 3D digital SiPM), and plans for large-scale SiPM integration will be presented.
Long baseline neutrino experiments, such as the Tokai-to-Kamioka experiment (T2K), study the phenomenon of neutrino oscillations using beams of accelerator produced muon neutrinos or muon antineutrinos. With the discovery of the muon neutrino to electron neutrino oscillation channel in 2014, the T2K experiment established the possibility to search for CP violation in neutrino oscillations. Since that time, T2K has collected data with neutrino and antineutrino beams to probe potential CP asymmetry. I will present the most recent measurements from T2K. Hyper-Kamiokande (Hyper-K), approved in 2020, is the next-generation successor of the T2K and Super-Kamiokande experiments, with an 8 times larger detector and 2.5 times higher intensity beam. In this presentation, I will describe the measurement program of the Hyper-K project, the strategy for controlling systematic uncertainties in precision measurements at Hyper-K, and the status of the project. I will focus on planned Canadian contributions to the Hyper-K experiment, including the Intermediate Water Cherenkov Detector, and multi-PMT photosensors.
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The Monopole and Exotics Detector at the LHC (MoEDAL) experiment is the 7th LHC experiment; a pioneering experiment specifically dedicated to investigating beyond The Standard Model (SM) scenarios by searching for highly ionizing particles, such as magnetic monopoles or massive pseudo-stable charged particles and multiply electrically charged particles as avatars of new physics. Currently, MoEDAL has taken data at center-of-mass energies of 8 and 13 TeV and provides the world's best laboratory constraints on monopoles with magnetic charges ranging from two to five times the Dirac charge. The MoEDAL experiment's ground-breaking physics program of over 40 scenarios complements the larger ATLAS and CMS experiments. During the ongoing shutdown, MoEDAL has been planning and preparing several upgrades for Run-3, including the new MoEDAL-MAPP detector (MoEDAL Apparatus for Penetrating Particles) which is currently being planned and constructed. The aim of the MAPP detector is to expand MoEDAL's physics program by including searches for new mini-ionizing particles (mIPs) as well as new long-lived neutrals (LLPs), both of which are predicted by many well-motivated extensions of the SM. In particular, these particles arise in hidden sector models of dark matter. The goal of this talk is to summarize the new MoEDAL-MAPP detector and introduce its physics program through studies of its potential reach for mIPs and LLPs during Run-3 using two bench-marking models: mini-charged particles in dark QED and new LL scalar & vector portals to dark matter.
A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino ($\tilde\chi^0_1$) is performed. The final state contains large missing transverse momentum, leptons, and several energetic jets (including at least three b-tagged jets). This presentation summarizes the recent ATLAS result on this search which was performed with the LHC $pp$ collision data at a center-of-mass energy $\sqrt{s}=$ 13 TeV, with an integrated luminosity of 139 fb$^{-1}$. No significant excess of events above the Standard Model expectation is observed in any of the search regions, and the results are used to set upper limits on the production of supersymmetric particles. The search excludes at 95% confidence level gluino masses up to 2.5 TeV and neutralino masses below 800 GeV.
Multivariate analysis techniques have found widespread use in high energy physics for their ability to identify complex correlations and nonlinear behaviour within large, high-dimensional datasets. Machine learning (ML) is one such example whereby events of some known classification are input to a map with many free parameters. Determining the values of these free parameters which best recreate the known classification of the inputs at the map’s output is the “learning” or “training” aspect of ML. In Large Hadron Collider (LHC) physics, ML may be used to filter rare processes such as Higgs boson decays from dominant background processes. The Higgs boson process we are interested in involves Higgs boson production in association with a vector boson V (VH) decaying to pairs of W bosons (HWW) in the 2-lepton final state. We have investigated the use of neural networks (NNs), a flavour of nonlinear ML, for classifying input events into six categories. NNs which classify events into more than two categories are referred to as multiclassifiers. Our categories include the signal process: VH(WW); competing Higgs processes: gluon-gluon fusion and vector boson fusion; and leading background processes: top quark production, Z boson production in association with jets, and diboson production. The training was performed using reconstructed ATLAS Run 2 Monte Carlo (MC) samples for the processes of interest. The inputs to the NN included kinematic variables based on leptons, jets, and missing transverse energy. At the level of the inputs, we verified that our MC samples accurately modelled the shape and normalization of data as well as the correlations between inputs. The output of our NN describing how likely an event is to be VH(WW) was used as a discriminant to build a measurement region for VH(WW) which maximized the statistical significance of discovery while protecting against statistical fluctuations. We have shown that the NN discriminant offers substantial improvements in the significance of the measurement over a traditional analysis relying on rectangular cuts on the same inputs. Our NN has yet to be deployed on LHC data, but it shows promising results for improving measurements in these difficult channels.
Precise measurements of jet cross-sections are crucial in understanding physics at hadron colliders. They probe quantum chromodynamics (QCD), where jets are interpreted as resulting from the fragmentation of quarks and gluons produced in a short-distance scattering process. Jet cross-sections provide valuable information about the strong coupling constant, alpha_s, and the structure of the proton. In addition, final states with only jets represent a background to many other processes at hadron colliders. The predictive power of fixed-order QCD calculations is therefore relevant in many searches for new physics. The most recent QCD results from the ATLAS Collaboration in proton-proton collisions involving jets in the final state will be summarized. Among others, the measurement of key differential distributions related to gluon splitting to b-quark pairs is presented, along with other measurements that probe a wide range of QCD phenomena and the structure of a jet.
The ATLAS experiment is currently analysing the proton-proton collision dataset collected from 2015 - 2018. This talk will highlight some of the newest results from ATLAS, focusing on results that are only now possible with 139/fb of 13 TeV data. Both new observations of rare standard model processes and searches for beyond the standard model physics will be discussed.
The Belle II experiment at the SuperKEKB collider in Tsukuba, Japan began physics data taking in 2019. With a target integrated luminosity of 50 ab-1, Belle II aims to record a data sample which is roughly 40 times larger than the combined samples of the preceding BABAR and Belle B factory experiments, enabling studies of b and c quark and tau lepton physics with unprecedented precision. The experimentally clean B factory environment also provides an interesting environment for searches for exotic signatures, including hadron spectroscopy and dark sector / missing energy states. In this talk, I will summarize recent Belle II physics result based on initial data taking, and discuss future prospects for the experiment.
From light-emitting diodes (LEDs) to solar cells, there is a large demand for developing new materials towards more efficient, cost-effective and sustainable optoelectronic devices. [1] Critical to all of these devices is an extensive knowledge on exciton photo-generation and carrier recombination processes. Electroluminescence (EL) imaging is a well-established tool that can used to evaluate the exciton diffusivity [2] on the surface of a device with micrometric resolution. To date, submicron resolution EL imaging is accomplished primarily with the assistance of scanning tunneling microscopy (STM) [3]. However, controversies on the genuineness of EL signal from STM based methods exist, as this has been often attributed to field emission [4]. In this presentation, we present scanning near-field electroluminescence (SNEL) imaging a novel analytical technique developed in our lab, in which EL is recorded in through an aperture-type scanning near-field optical microscope (SNOM) coupled with additional light excitation and AC external bias. The submicron resolution of SNOM is anticipated to be essential to capture the EL signal, as well as the local sample morphology. Preliminary experiments with organic EL devices of P3HT (poly(3-hexylthiophene-2,5 diyl) and PCBM ([6,6]-Phenyl C61 butyric acid methyl ester) with graphene top electrode have been imaged, demonstrating the specific conditions in which genuine EL can be decoupled from field-emission.
[1] O. Ostroverkhova, Chem. Rev. 2016, 116, 13279
[2] I Pelant. & Valenta, J. Luminescence Spectroscopy of Semiconductors. (OUP Oxford, 2012).
[3] S F Alvarado et al IBM J. Res. Dev. 45, 89–100 (2001).
[4] H M Benia, et al., New J. Phys. 10, (2008).
Self-assembled monolayers (SAMs) of organic molecules are extensively used to functionalize surfaces for a wide range of applications from medicine to nanophotonics. However, creating a SAM that is sufficiently stable has been a persistent problem. Although thiols have been the gold-standard for thirty years, N-heterocyclic carbenes (NHCs) have recently been used to create SAMs that are more thermally and chemically stable [1]. NHCs based on diisopropyl benzimidazolylidene (NHCiPr) have also been integrated into biosensors [2]. The field of NHC-based material science is very new and the self-assembly mechanisms are still not well understood.
To provide a molecular-level perspective, we combine density functional theory (DFT) with scanning tunneling microscopy (STM) to study the self assembly of NHCiPr on Au(111) at temperatures as low as 5K in ultra high vacuum (UHV). The isopropyl wing-tip groups of NHCiPr play an important role in the self-assembly. They are responsible for both steric interaction with the surface and for stabilizing an ordered zig-zag lattice via intermolecular CH-pi hydrogen bonds. These NHCs are bound to adsorbed gold atoms (adatoms) extracted from terraces and from step edges, but unlike other systems that have been reported they are relatively immobile at 77K and their surface transport mechanism is largely dominated by a second phase. Through thermal annealing we induced conversion of the zig-zag lattice into flat-lying (NHCiPr)2Au complexes. These complexes interact weakly with the surface and are highly mobile, yet they self-assemble into an ordered lattice when spatially constrained.
The discovery of two different NHC surface phases in this system is completely new. The first upright zig-zag phase can be readily functionalized and used in biosensors. The second phase of (NHCiPr)2Au complexes exhibits intriguing instabilities that will be discussed. These results are a major step forward in understanding the mechanism for self-assembly of NHCs, a process which for thiols has taken thirty years to understand.
[1] C. M. Crudden, et. al, Nature Chemistry 6, 409 (2014).
[2] C. M. Crudden, et. al, Nature Communications 7, 12654 (2016).
Phytoglycogen is a highly branched polymer of glucose produced as soft, compact nanoparticles by sweet corn. Properties such as softness, porosity and mechanical integrity, combined with nontoxicity and biodegradability, make phytoglycogen nanoparticles ideal for applications involving the human body. Many of these applications rely on the binding of small molecules onto phytoglycogen nanoparticles. Surface Plasmon Resonance (SPR) is a sensitive experimental technique, based on the resonant absorption of light within an ultrathin gold film, that can be used to measure the binding kinetics and affinities of small molecules. We have successfully created a stable phytoglycogen-functionalized SPR sensor surface, using 4-mercaptophenylboronic acid as a linker between the gold layer and phytoglycogen. This has allowed us to use SPR to measure the association constant between phytoglycogen and Concanavalin A (ConA) to be $2.87$ $+-$ $0.44$ x $10^5$ $M^-$$^1$ by fitting the data to the Langmuir adsorption model. By measuring the amide bands of ConA bound to phytoglycogen using infrared spectroscopy, we find that ConA maintains a large amount of its native beta-sheet content, suggesting that phytoglycogen helps to preserve its bioactivity.
Quantum systems in gravitational fields (particularly with horizons) are often plagued by paradoxical predictions at very late times. Examples include predictions for information loss in black holes and for properties of eternal inflation. This talk argues that generic problems exist making such predictions because perturbative methods generically fail at very late times. Similar issues arise in other areas of physics (like optics) and the tools there also work in a gravitational context. The talk describes a simple illustrative application of these tools to a qubit in Rindler space (ie an Unruh observer), and to a qubit in an inflationary (de Sitter) universe. The tools are shown to correct earlier results by Candelas and Sciama and show in detail how, when and why these techniques work.
A key challenge to the standard cosmological model is the observation
of very massive (M > 10^9 Msun) and luminous (L > 10^{13} Lsun)
quasars already in place by z~7, when the age of the universe was
just ~800 Myr. The formation of such supermassive black holes (SMBH)
cannot generally occur in the time available if starting from
stellar mass black holes. We explore implications of the
idea of direct collapse black holes (DCBH) emerging from the collapse
of a special class of supermassive stars (~ 10^5 Msun) that could only
form at high redshift in so-called atomic cooling halos. Both numerical
and semi-analytic modeling implies a brief period of rapidly growing
production of supermassive stars, in the approximate redshift range of
z~20 to z~13. Our work shows that the mass function of SMBHs after a
limited time period of rapid formation of DCBH, coupled with a
super-Eddington accretion from their host halos, can be described
as a tapered power law function. The power law at intermediate
masses has an index that is the dimensionless ratio alpha = lambda/gamma,
where lambda is the growth rate of the number density of DCBHs during
their formation era, and gamma is the growth rate of DCBH masses by
super-Eddington accretion during the same growth era. A second feature
is a break in the power-law profile at high masses, above which
the mass function declines rapidly. This mass distribution is largely
set during this early growth era, and subsequent mass growth may be more
limited. We also calculate the implied luminosity function of the
resulting SMBH, which is in remarkable agreement with the broken power
law quasar luminosity function that has been observed at high redshift.
A new generalization of the Hawking-Hayward quasilocal mass to scalar-tensor gravity is compared, for vacum asymptotically flat stationary geometries, with multipole expansion of the gravitational field in this class of theories. The quasilocal mass at spatial infinity coincides with the monopole term, a necessary check lending credibility to this construct.
[Based on V. Faraoni & J. Côté, Phys. Rev. D 100, 084015 (2019)]
At TRIUMF, Canada’s particle accelerator centre, the TIGRESS Integrated Plunger and its configurable detector systems have been used for charged-particle tagging and light-ion identification in Doppler-shift lifetime measurements employing gamma-ray spectroscopy using TIGRESS, an array of HPGe detectors. An experiment using these devices to measure the lifetime of the first $2^+$ ($2^{+}_{1}$) state of $^{40}$Ca has been performed by projecting an $^{36}$Ar beam onto a $^\text{nat.}$C target. Analysis of the experimental gamma-ray spectra confirmed the direct population of the $2^+_1$ state. Event-by-event relativistic kinematic reconstruction of the invariant mass of the two-alpha system indicated that fold-two alpha particle events, detected in the PIN array, came from the decay of a single $^8$Be, rather than fusion-evaporation from a compound $^{48}$Cr nucleus. Since the centre-of-mass energy in the entrance channel was below the Coulomb barrier, the reaction mechanism is believed to be the transfer of one alpha particle from the $^{12}$C target to $^{36}$Ar beam nucleus. The low centre-of-mass energy resulted in the direct population of the 2$^+_1$ state of $^{40}$Ca, which eliminated feeding cascades, and therefore the decay kinetics were predominantly first order. Verification of this alpha-transfer reaction mechanism is being performed using GEANT4 Monte Carlo simulations. Simulations with the correct reaction mechanism are expected to reproduce the experimental energy spectra and angular distributions of alpha particles while providing a Doppler Shift Attenuation Method measurement of the lifetime of the 2$^+_1$ state in $^{40}$Ca. In the future, the observed reaction mechanism can be applied to N=Z radioactive beams to provide direct access to low-lying excited states of nuclei with (N+2) and (Z+2), enabling transition rate studies at the N=Z line far from stability. Results of the analysis of the experimental data and simulations will be presented and discussed.
The universe, shortly after the Big Bang, was at temperatures much higher than the confinement scale of Quantum Chromodynamics (QCD) and was filled by a plasma of quarks and gluons (QGP). We can now study the properties of the QGP at major experimental facilities such as the Relativistic Heavy Ion Collider (RHIC, New York, USA) or the Large Hadron Collider (LHC, CERN, Switzerland) by colliding heavy ions together at very high energies and observing the spectra of the resulting particles from the collision. From these spectra, we can then deduce important information about the strongly interacting medium such as its transport coefficients, and also study the phase diagram of QCD.
Direct photons have proven themselves as enticing probes of the medium. These photons do not originate from a hadronic decay and are produced at all stages of the evolution, giving access to information such as shear and bulk viscosities. Moreover, since photons interact exclusively via electromagnetism, they experience no final state interactions in the QCD plasma once created and escape the system unscathed. Thus, they can faithfully carry information about the local conditions at the moment of their creation. However, it is difficult if not impossible to experimentally separate different production mechanisms of direct photons. As such we have to rely on models and aim for solid theoretical calculations to understand photon emission processes involved at all different stages of evolution.
Here we present the first modern calculation of direct photons, probing the early evolution of the medium. We consider the dynamics of QCD jets, and account for realistic hydrodynamic evolution of the medium as well as jet energy loss. These results include the first systematic calculation of jet-medium photons, arising from the interaction of a jet with the thermal medium, which results in the conversion of the jet to a photon. We will compare our results to current experimental observations as well as make predictions for future runs of the LHC.
The study of neutron rich nuclei far from the valley of stability has become an increasingly important field of research within nuclear physics. One of the decay mechanisms that opens when the decay $Q$ value becomes sufficiently large is $\beta$-delayed neutron emission. This decay mode is important when studying the astrophysical r-process as it can have a direct effect on theoretical solar abundance calculations [1]. The utilization of large-scale neutron detector arrays in future experiments is therefore imperative in order to study these $\beta$-delayed neutron emitters and gain more insight into these astrophysical processes.
At the TRIUMF ISAC facility, $\beta$-delayed neutron spectroscopy experiments are being performed. This is done using the GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigation of Nuclei) spectrometer [2] coupled to DESCANT (DEuterated SCintillator Array for Neutron Tagging) [3]. Since DESCANT was originally intended to be a neutron-tagging array for fusion evaporation reactions, a precise measurement of the neutron energy was not considered a priority over the neutron detection efficiency. Therefore, the use of thin plastic scintillators is being investigated to improve the current obtainable precision on the neutron energy, allowing a more in-depth analysis of $\beta$-delayed neutron emitters at the GRIFFIN decay station. Plastic scintillators are ideal for this enhancement due to their timing properties, customizability, and overall cost effectiveness. The energy of the neutrons can then be determined via the time-of-flight technique. To investigate the viability of this augmentation, GEANT4 is being used to simulate and optimize the experimental design, the progress of which will be discussed.
[1] Mumpower, M. et al., Prog Part Nucl Phys 86 (2016), 86-126.
[2] Garnsworthy, A. B., Svensson, C. E., et al., Nucl Instrum Meth A, 918 (2019) 9-29.
[3] Garrett, P.E., Hyperfine Interact, 225 (2014) 137-141.
In-beam reaction experiments performed at TRIUMF, Canada's particle accelerator centre, allow for precision measurements of nuclei far from stability. Using TIGRESS in conjunction with the TIGRESS Integrated Plunger for charged particle detection, electromagnetic transition rate studies of these nuclei can be performed. These measurements provide a probe of nuclear wavefunctions and tests of theoretical models using the well understood electromagnetic interaction. Of particular interest are neutron rich Mg isotopes far from stability as the shell model's single particle energy state description breaks down, closing the $N=20$ shell gap. In this region, occupation of single particle energy states is \textit{inverted} with respect to the predicted configuration of the shell model and that near stability, motivating this region to be called the \textit{island of inversion}.
Nuclei in the island of inversion also exhibit collective behaviour, in which multiple particle transitions and interactions play a significant role in the nuclear wavefunction. This collectivity is also seen in highly excited states of nuclei approaching the island of inversion, and can be observed through electromagnetic transition strength measurements. By performing measurements on $^{28-32}$Mg, the degree to which nucleons display collective behaviour can be observed both in and approaching the island of inversion. This allows for the evolution of single particle energy states of the nucleus to be studied, providing an avenue for deepening the fundamental understanding of the nuclear interaction.
In this talk, I will discuss our experimental approach to studying the island of inversion, focusing on the approved experiment for measuring the lifetime of the first excited state in $^{28}$Mg. This experiment will use the Recoil Distance Method to exploit the Doppler shift of gamma rays emitted in flight along with Monte Carlo simulations using the \textsc{Geant4} simulation framework to determine the best fit lifetime of the state. I will also discuss future experiments to probe lifetimes in excited states of $^{30-32}$Mg.
Gamma ray spectroscopy in the Nuclear Science Laboratory (NSL) at Simon Fraser University (SFU) is used for nuclear structure studies, neutron activation analysis, and environmental radioactivity monitoring. All non-environmental sources are produced using the in-house Thermo Fisher Scientific P-385 Neutron Generator (NG), which allows for a diverse experimental program. The current detection system is the Germanium detector for Elemental Analysis and Radioactivity Studies (GEARS), and consists of a single high purity germanium (HPGe) detector which is housed in a lead box for passive shielding. Sensitivity is limited especially at low energies due to background radiation and Compton scattering. In order to take full advantage of the NG, improved detection capabilities are required. This can be achieved through the use of Compton suppression and time coincidence measurements which will allow for the possibility of gamma-gamma, beta-gamma, and alpha-gamma measurements that will help distinguish between events of interest, and background radiation or events caused by contaminant induced reactions. However a multi-detector system is required to take advantage of this method. For this purpose, the 8-Pi spectrometer, recently acquired by SFU from the ISAC-1 facility at TRIUMF, is being rebuilt to its original design, consisting of 20 HPGe Compton Suppressed Spectrometers (CSS). The 8Pi consists of 4Pi coverage from an inner layer of Bismuth Germanium Oxide (BGO), as well as 4Pi coverage from an outer later of CSS's. Operation of the 8-Pi requires a 352 channel data acquisition (DAQ) system which is under development, based on the TIG-10 and VF-48 digitizers. A subset of six of the 8Pi CSS’s have been arranged in a cubic array as a testing ground for the 8Pi CSS layer. The development and application of the cubic array will be presented and discussed.
Zinc-65 ($^{65}$Zn) is a radionuclide of interest in the fields of medicine and gamma-ray spectroscopy, within which its continued use as a tracer and common calibration source necessitates increasingly-precise nuclear decay data. A $^{65}$Zn dataset was obtained as part of the KDK ("potassium decay") experiment, whose apparatus consists of an inner X-ray detector and an efficient outer detector, the Modular Total Absorption Spectrometer (MTAS), to tag gamma rays. This setup allows for the discrimination of the electron-capture decays of Zn-65 to the ground (EC) and excited (EC) states of Copper-65 using a novel technique for such a measurement, exploiting the high efficiency ($>$98%) of MTAS. Techniques used to obtain the ratio of EC to EC decays ($\equiv\rho$) of $^{65}$Zn are applicable to the main KDK analysis, which is making the first measurement of $\rho$ for Potassium-40, a common background in rare-event searches such as those for dark matter. We present our current methodology and analysis procedures developed to obtain a neoteric measurement of the electron-capture decays of Zinc-65.
A remarkable achievement of the relativistic heavy-ion program is the realization that relativistic fluid dynamics can describe the evolving system of quark-gluon plasma (QGP) from its early moments to a time when the growing mean-free-paths drive the system out of equilibrium. The effectiveness of this hydrodynamic description is judged by comparing calculated hadronic observables with experimental measurements. Alternatively, electromagnetic radiation could be considered a more distinguishing signal as it is emitted throughout the evolution of the hadronic system. Considerable work has gone into the calculation of photons and dileptons using modern hydrodynamic approaches, however, the calculation of the electromagnetic emissivity of the pre-hydro stage is currently less advanced.
In this talk, we use a transport approach that models the time-evolution of gluons and fermions by solving the Boltzmann transport equation in the diffusion approximation. The initial state is a gluon distribution of a form inspired by the colour glass picture, where quarks and anti-quarks are then generated through interactions. The early stage evolution is modelled by a 1D expansion, during which non-equilibrium parton interactions can also produce real and virtual photons. We show how reliably these Glasma photons can report on the initial momentum anisotropy of the early parton distribution as well as the final net anisotropic emission of photons measured at RHIC and at the LHC (i.e. the “photon $v_2$ puzzle”). We show that the non-equilibrium photons can, in fact, leave an imprint on the final low $p_T$ spectra. This opens the exciting possibility that a measurement of the electromagnetic signal can access the very first instants of heavy-ion collisions.
The rapid neutron-capture process (r-process) is an explosive astrophysical process thought to be responsible for producing half of the elements in the universe that are heavier than iron [1]. However, theoretical calculations have yet to reproduce the observed solar abundances of nuclei. Measuring 𝛽-delayed neutron emission probabilities and neutron-capture rates of neutron-rich nuclei can help to significantly constrain theoretical r-process models. Currently, the 𝛽-delayed neutron emission of very few r-process nuclei have been characterized. TRIUMF, Canada’s particle accelerator centre, can synthesize many isotopes involved in the r-process. Measuring the energies of emitted neutrons can provide complementary information on neutron-capture rates, as well as unveiling the nuclear structure of these exotic species.
The DESCANT (Deuterated Scintillator Array for Neutron Tagging) array coupled to the GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei) γ-ray spectrometer can simultaneously detect γ-rays and neutrons [2]. Although DESCANT has a very high neutron detection efficiency, the array was not designed to measure neutron energies to a high degree of precision. To account for this, an ancillary neutron detector array capable of performing high resolution neutron energy measurements has been proposed. The array will be composed of thin plastic scintillation detectors and will complement the functionality of the detectors currently in use. The time-of-flight (TOF) method will be used to determine neutron energies. Prototype construction has begun in which the optimal scintillator material, thickness and geometry are being explored. We are investigating the use of silicon photomultipliers (SiPM’s) for light collection as an alternative to standard photomultiplier tubes. Tests are planned to characterize neutron back-scattering that may occur from the nearby DESCANT detectors. These results and current progress on detector development will be presented.
[1] M.R. Mumpower, et al. Prog. Part. Nucl. Phys. 86 (2016) 86 – 126.
[2] V. Bildstein et al. Nucl. Instrum. Meth. A 729 (2013) 188 – 197.
High-precision measurements of the $ft$ values for superallowed Fermi beta decays between 0$^+$ isobaric analogue states have provided invaluable probes of the Standard Model description of the electroweak interaction. Theoretical corrections must be applied to the experimentally determined $ft$ values obtained from precise measurements of the half-lives, branching ratios, and $Q$ values of the decays. Of particular interest is the isospin symmetry-breaking correction, $\delta_C$, which is nuclear-structure-model dependent; several theoretical approaches can and have been used to calculate these corrections with varying results. In the most recent survey of superallowed Fermi $\beta$ emitters [1] the selection of a particular $\delta_C$ model depended significantly on four of the least precisely determined corrected-$ft$ values: $^{22}$Mg, $^{38}$Ca, $^{62}$Ga, and $^{74}$Rb for the well-measured cases.
Recently, updated calculations of the universal ``inner'' electroweak radiative correction, $\Delta^V_R$, have been performed [2-4]. This value is used in combination with the corrected superallowed $\mathcal{F}t$ values to extract such quantities as $G_V$, the vector coupling constant, and $\vert V_{ud}\vert$, the most precisely determined element of the CKM quark mixing matrix. With the updated value of $\Delta^V_R$, the first row of the CKM quark mixing matrix now disagrees with unitarity at the 2-4$\sigma$ level, prompting an increased interest in re-investigating the model-dependent nuclear structure corrections, especially those which can be directly constrained experimentally.
We have performed a high-statistics experiment for the superallowed Fermi $\beta^+$ emitter $^{62}$Ga at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF using the high-efficiency Gamma-Ray Infrastructure for Fundamental Investigations of Nuclei (GRIFFIN) spectrometer. The high coincidence efficiency of the GRIFFIN spectrometer allowed for a significant expansion of the level scheme, more than doubling the known $\gamma$-ray transitions in the daughter nucleus, $^{62}$Zn. This allowed a new measurement of the superallowed branching ratio with a precision of $\pm$0.0012\%, $\sim$6 times more precise than previously achieved [5]. Gamma-ray intensities were measured down to the 1 ppm level, effectively solving the Pandemonium problem [6] for $^{62}$Ga. For one particularly important cascade, sufficient statistics were obtained to perform a $\gamma-\gamma$ angular correlation measurement. This allowed the previously-conflicting spin-assignments for the 2.34~MeV excited state in $^{62}$Zn [7,8] to be resolved and firmly established this state to have $J^\pi = 0^+$. The assignment of the spin of this state has important implications for the isospin symmetry breaking correction, $\delta_{C1}$. Final results from this analysis will be presented.
[1] J.C. Hardy and I.S. Towner, Phys. Rev. C 91, 025501 (2015).
[2] C. Seng, M. Gorchtein, H.H. Patel, and M.J. Ramsey-Musolf, Phys. Rev. Lett. 121, 241804 (2018).
[3] C. Seng, M. Gorchtein, and M.J. Ramsey-Musolf, Phys. Rev. D 100 , 013001 (2019).
[4] A. Czarnecki, W.J. Marciano, and A. Sirlin, Phys. Rev. D 100, 073008 (2019).
[5] P. Finlay et al., Phys. Rev. C 78, 025502 (2008).
[6] J.C. Hardy, L.C. Carraz, B. Jonson, and P.G. Hansen, Phys. Lett. B 71, 307 (1977).
[7] M. Albers et al., Nucl. Phys. A 847, 180 (2010).
[8] K.G. Leach et al., Phys. Rev. C 88, 031306 (2013).
I present a theory where neutrinos have much stronger self-interaction among themselves than in the Standard Model. An intriguing connection is pointed out to sterile neutrino dark matter. The presence of the new interaction allows the dark matter relic density to be successfully produced in the early universe while remain in tact with the present indirect detection constraints. I will show that this connection predicts a light, neutrino-philic boson which serves as a well motivated target for our laboratory searches, in particular at dark matter direct detection experiments, as well as near future accelerator neutrino facilities.
NONLOCALITY: Despite numerous exquisite experimental verifications of quantum (Bell) nonlocality (1), Bell’s insights have not led to any new consensus for the ontology of spacetime. This is problematic because there are serious conceptual difficulties in reconciling nonlocal EPR correlations with the metric properties of Minkowskian 4D spacetime. Simply, how is nonlocality sustainable within a local spacetime? I address this conflict by arguing for a series of remarkable parallels between the `Relativity of Colocality’ (2) and quantum nonlocality (QNL). These parallels point to a quantum-friendly spacetime ontology.
RELATIVITY OF COLOCALITY (RoC): This encapsulates the simple fact that inertial observers disagree on the colocality of events. The relativity of colocality (2) is the dual phenomenon to the relativity of simultaneity. This duality arises from the x <--> ct symmetry of the Lorentz boost transformation.
PARALLELS: Let us consider two scenarios: A) an entangled pair of EPR particles, subject to Bell; B) an ensemble of classical inertial observers, subject to the RoC. On the surface, these are quite different systems, yet there are remarkable parallels. The key step is to analyze the ensemble of all observers, not isolated individuals. I will show the following: both scenarios involve a form of spatial correlation (unattenuated by spatial separation); both forms of correlation are no-signalling and avoid causality violation; both involve inseparable events which (in suitable senses) are not localized; and both find a means to render the spacetime interval irrelevant. Such unprecedented kinship with Bell nonlocality demands explanation.
CONCLUSION: The primary purpose of this presentation is to argue that for an ensemble of classical inertial observers, Einstein’s special relativity contains unmistakable echoes of quantum nonlocality. This correspondence opens the door to a new approach to quantum spacetime.
[1] Nicolas Brunner et al. “Bell nonlocality”. In: Rev. Mod. Phys. 86 (2 Apr. 2014), pp. 419–478. DOI: 10.1103/RevModPhys.86.419.
[2] J. C. Sharp. “Symmetry of the Lorentz boost: the relativity of colocality and Lorentz time contraction”. In: European Journal of Physics 37.5 (2016), p. 055606.
Agenda:
● 2020 CAP PPD Virtual
○ Lessons learned
○ Organization of the congress in general
○ Importance of being a member
● Finances
○ Thesis awards
○ Other conferences sponsorship
● PPD Executive and Vote results
● PPD Structure: New proposals
● How can we improve the current way of communication
○ Between us
○ Between CAP
The flat space limit of the AdS/CFT correspondence allows to relate S-matrix elements of flat space scattering to CFT correlation functions. In this talk I will discuss this construction and its implications for the case of Quantum Electrodynamics.
To obtain the precise dictionary between CFT operators and the S-matrix, one reconstructs the Maxwell field close to the center of AdS in terms of CFT operators. One then takes the flat space limit and uses the LSZ prescription to extract creation/annihilation operators, whose correlation functions yield S-matrix elements.
In the infrared, QED has a rich structure which is exemplified by the existence of soft theorems. Soft theorems describe the universal behavior of scattering amplitudes under addition of soft photons. I will argue that they arise as a consequence of Ward identities of the U(1) current dual to the Maxwell field in AdS. In four dimensions, there is also the possibility of quantizing fields on AdS with a different boundary condition at infinity. This is related to electric-magnetic duality and repeating the above argument yields “magnetic” soft theorems.
Thermoelectric materials can convert waste energy back to useful electricity and hence, can significantly contribute to the generation of clean energy. However, thermoelectric materials are currently limited by high cost and low efficiencies. The search for high-efficient thermoelectric materials is hindered by the interrelated electrical and thermal transport properties. High-throughput screenings based on density functional theory (DFT) can accelerate the search and discover novel high-performance thermoelectric candidates. In a recent screening of 48,000 compounds, enhanced electronic properties were observed for various RECuZnP$_2$ compounds. The thermoelectric transport properties were measured for three different RECuZnP$_2$ compounds indicating high thermoelectric efficiencies. Advanced DFT calculations (i.e., AMSET and compressive sensing lattice dynamics) were performed confirming the high thermoelectric performance. These methods can compute the scattering rates of electrons and phonons (even with strong anharmonicity) and provide unique insights of the underlying physics in thermoelectric compounds.
Complexity is a measure of the resources required to perform certain computations. Quantum complexity is an important concept with applications spanning quantum information, condensed matter systems, and quantum field theories. It is defined as the minimum number of fundamental gates in a circuit required to construct a given quantum state. Surprisingly, it was found also to be connected to gravity within the context of AdS/CFT correspondence, with the connection more specifically defined in the complexity=volume (CV) and complexity=action (CA) conjectures. In the CV prescription, the quantum complexity of the boundary state is given by the volume of the Einstein-Rosen bridge behind the horizon of the dual black hole. In the CA prescription, it is given by the gravitational action of the Wheeler-de-Witt patch dual to the boundary state. From purely gravity calculations, these prescriptions were shown to reproduce properties of quantum complexity, such as: linear growth at early-times, exponential scaling with the system size, and growth under perturbations.
I will discuss the quantum complexity of rotation through gravity calculations on rotating spacetimes of arbitrary dimensions with anti-de-Sitter boundaries, and compare the results with known properties of non-spinning black holes.
The dynamical effects of general relativity which go past Newtonian gravity,
especially the expectation that gravitational effects propagate with a finite velocity, have not been directly verified.
The formalism of gravitoelectromagnetism will be applied to compute the
first dynamical corrections to Newtonian gravity due to general relativity.
We consider a system with multiple sources of dynamical gravitational
effects where the main problem arising is that there are different retarded
times for the different sources. The Lagrange inversion theorem can then be used to express all dynamical effects in terms of the instantaneous time and then simply superpose them.
We apply our results to a proposed, realizable experimental set up and find a dynamical effect that could be observed in a LIGO type experiment.
The properties of neutron matter are integral to the correct description of neutron stars and the extraction of their observables as well as the description of neutron-rich nuclei. One key property of neutron matter is its superfluid behaviour in a range of densities relevant to the inner crust of neutron stars. This talk will be centred around the finite size effects in the pairing gap of a pure neutron matter superfluid system at densities found in the inner crust of cold neutron stars. The BCS (Bardeen-Cooper-Schrieffer) treatment of superfluidity gives rise to the mean-field pairing gap, while a projection after variation leads to a beyond-mean-field pairing gap through an odd-even staggering formula. While these two pairing gap results should agree in the thermodynamic limit, we will show that this is the case for systems far from the thermodynamic limit as well. This aims in taking the first step towards a model-independent extraction of the pairing gap in neutron matter.
With the recent direct observation of gravitational waves, a new avenue of observing the Universe has become available. As a result, much effort is being devoted to the design of new detectors sensitive to different gravitational wave sources. One unique proposal is to detect gravitational waves using a Bose-Einstein Condensate (BEC). In this talk, I will show that transient gravitational wave detection using BECs is limited at lower frequencies by methods in quantum optics and by damping at higher frequencies. For continuous sources, the application of an external oscillating magnetic field is considered as a means to amplify sensitivity. I will discuss the prospects and challenges for such detectors to be competitive or even superior in sensitivity to existing gravity wave detectors.
We analyse how zero modes of a quantum field, whenever they arise, have significant impact on the phenomenology of light-matter interactions. Since a zero mode has no physical ground state, several studies in the literature opt to ignore the zero mode and argue that it has negligible impact on the physics. We show that (1) ignoring such modes directly leads to causality violation, in the sense that two atomic detectors can signal faster than light, and (2) how much two detectors can extract entanglement from the quantum vacuum depends strongly on the choice of the zero mode state. Finally, the zero mode provides an explicit example of how the usual wisdom that “quantum field in a large cavity is the same as in free space” does not hold in presence of a particle detector.
We look for evidence of recognisably 'scientific' astronomy three to four thousand years ago, in ancient Egypt. In this talk we will present some texts, objects, and instruments that demonstrate ancient Egyptian interest in the way the night sky functions. We will start by discussing an autobiographical text that recounts the invention process of a new time-keeping instrument, a seasonally-adjusted water clock. The process began with research in a temple library and ended with presentation to the pharaoh, closely following what we call the Scientific Method. Moving from texts to tabular information, diagonal star tables appear on the underside of coffin lids as a representation of how stars move across the night sky depending on the time of year. Of particular interest are the end of these tables that show the final five days of the year. Finally, we will describe a very clearly observationally-based set of texts which map stars in more detail over the course of the year. Together, these texts and tables represent a moving picture of the ancient Egyptian night sky. However, questions remain about the way the observations were conducted and, hence, the identifications of the stars used.