Physics and Astronomy

Permanent URI for this collectionhttps://hdl.handle.net/10315/28582

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Access status: Open Access ,
Quantum Chemistry, Machine Learning and Atomistic Monte Carlo to Study Melting-Like Transitions in Small Clusters
(2025-11-11) Krishnadas, Anirudh; Fournier, Rene Andre
This thesis develops computational methods for efficiently predicting melting-like transitions in clusters. Four criteria are introduced to characterize these transitions: (i) the width of the potential energy distribution (W_U), which broadens near the melting point; (ii) a dissimilarity measure relative to the ground-state configuration, defined from the ordered interatomic distances r_ij; (iii) the effective count of r_ij values near the mean of the first two peaks of the pair distribution function; and (iv) the degree of non-uniformity in the r_ij distribution. Together with an artificial neural network classifier for estimating solid fractions, these measures identify melting transitions with two- to threefold reductions in computational effort compared to conventional heat-capacity-based (C(T)) analyses. Parallel Tempering Monte Carlo (PTMC) was combined with an E(3)-equivariant neural network potential (Allegro) trained to reproduce density functional theory (DFT) energies. The framework was validated on sodium clusters and applied to aluminum clusters containing up to 16 atoms in both neutral and charged states. Predicted melting temperatures ranged from 305 K to above 1200 K, exhibiting size- and charge-dependent nonmonotonic variations consistent with experimental and theoretical data. The methodology was further extended to global optimization, where tens of millions of candidate geometries were screened using the neural network, refined through local optimization, and classified by topological fingerprints and bond-orientational order. This reduced computational cost by three to four orders of magnitude compared to DFT-based sampling while maintaining near-DFT accuracy. The same approach was applied to heteroatomic icosahedral clusters AB_2C_10 chosen for their superatomic potential. Among them, ZrRb_2Au_10 and Sn_3Y_10 were prioritized based on atomization energies and electronic simplicity. Estimated melting temperatures 1263 K and 2061 K, respectively, exceeded the weighted average of their elemental melting points. Overall, this work provides new insights into cluster melting, revealing size-dependent trends, enhanced thermal stability in superatomic systems, and non-melting behaviour in certain aluminum clusters. By integrating multiple indicators and scalable algorithms, it advances the understanding of phase-like transitions at the nanoscale.
Access status: Open Access ,
Measurements of Diffusion Coefficients for Rubidium Atoms in Inert Gas Mixtures Using Coherent Scattering From Optically Pumped Population Gratings
(2025-11-11) Pouliot, Alexander Peter Armand; Kumarakrishnan, Anantharaman
We present comprehensive determinations of the diffusion coefficients for rubidium atoms in six commonly used buffer gases using a newly developed coherent transient technique. The experiments are carried out by establishing a spatially periodic rubidium population grating using two laser beams intersecting at an angle of a few milliradians. The grating decays exponentially in time due to diffusive motion induced by momentum-changing elastic collisions with buffer gas atoms. The decay can be monitored over a large dynamic range using a heterodyne detection system that records the coherently scattered light from the grating. We are able to distinguish the contribution of diffusion from other collisional processes by measuring the characteristic dependence of the decay rate on the angle between excitation beams. These experiments are carried out in a non-magnetic atomic vapour cell manifold that allows magnetic fields and magnetic field gradients to be cancelled so that rubidium atoms can be manipulated in targeted internal ground states in the presence of different inert gases that can be maintained at pressures ranging from a few hundred pascals to one atmosphere. Our measurements agree with theoretical calculations of diffusion coefficients after reconciling key systematic effects, and this agreement appears to resolve both the widespread scatter in the values of diffusion coefficients using other techniques obtained over several decades and their disagreement with theory. Our measurements lay the groundwork for the development of a quantum pressure sensor that will rely on the intrinsic properties of atoms to calibrate commercial pressure gauges and impact emerging quantum technologies such as magnetometry, spin polarized imaging, and quantum memory that rely on accurate knowledge of diffusion coefficients. We also describe preliminary, comparative studies of a traditional population magnetometer and a unique coherence magnetometer developed by our group, which led to the development of the technique for measuring diffusion. All our experiments were carried out using a low-cost, home-built diode laser system. We present a detailed characterization of this system, which has supported wide-ranging experiments in precision metrology such as optical tweezers-based determination of micro-particle masses, measurements of atomic lifetimes, and atom interferometric measurements of velocity and gravitational acceleration.
Access status: Open Access ,
A Family Album: The Growth and Evolution of Milky Way Analogues from Z=5 to the Local Universe
(2025-11-11) Vivian Yun Yan Tan; Muzzin, Adam
We present a breakdown of the evolutionary history of Milky Way-like galaxies up to redshift z=5, using multi-wavelength optical and NIR photometry from the Hubble Space Telescope and the James Webb Space Telescope. We use abundance matching to find progenitors of Milky Way Analogs (MWAs) by evolving the cumulative number density of the current Milky Way backwards through time, and matching the stellar mass to the expected number density with stellar mass functions obtained from large-scale galaxy surveys. We determine resolved physical properties of MWA progenitors such as stellar mass density, star-formation rate (SFR), age, and metallicity, via SED-fitting to spatially resolved pixel bins of their photometry. In the first part of this thesis, we use photometric data from the Hubble Frontier Fields DeepSpace catalog, a survey of six lensing clusters and their flanking fields in order to chart the mass assembly of MWA progenitors up to z=2. In the second part of this thesis, we extend the study of the mass assembly of MWA progenitors to z=5 with the data from the Canadian NIRISS Unbiased Cluster Survey (CANUCS), using JWST NIRCam and NIRISS imaging. In the early universe, MWA progenitors show clear inside-out mass assembly with specific star-formation rates more enhanced on the outskirts than the inner regions, and more stellar mass added to the outskirts. They are also increasing in size but morphologically remain disk-dominated. Merger fractions increase with increasing redshift, pointing to hierarchical assembly at early times. In the third part of this thesis, we examine the resolved age and stellar metallicities of the MWA progenitors in CANUCS to uncover details of their star-formation history. The slopes of the radial gradients of non-merging galaxies are in line with inside-out growth. The slopes of the radial gradients for ongoing and late stage mergers show enhanced star-formation across the entire galaxy. Metallicity evolves slowly with redshift for MWA progenitors, and mergers contribute to overall mass growth both through their added mass and their enhancement of star-formation, but do not meaningfully alter the chemical evolution history of the galaxy until z~1.5.
Access status: Open Access ,
Progress Towards A Measurement Of The Electron's Electric Dipole Moment Using The EDM3 Method
(2025-07-23) Corriveau, Zachary Adam; Hessels, Eric A.
This dissertation reports the progress made towards measuring the electron's electric dipole moment (de) using a novel method dubbed the Electric Dipole Measurements using Molecules within a Matrix (EDM3) method, first proposed by the EDM3 collaboration. The measurement of a non-zero value of de has long been sought after as a measure of charge-parity violation, a phenomenon necessary to explain the observed asymmetry of matter and antimatter in the universe. This work presents the production of a beam of cold barium monofluoride (BaF) molecules using a buffer-gas-cooled laser-ablation source and the subsequent implantation of BaF molecules into neon solids suitable for use in a measurement of de. Identification of several electronic and vibrational excited states of BaF within a neon matrix is demonstrated and the characteristics of these states are studied. The rate of the excitation for BaF molecules excited to the B state is determined and this result is used to estimate a density of BaF molecules near the targeted value for a first measurement of de. Preliminary experiments demonstrate optical pumping of the embedded BaF molecules with circularly-polarized light. Further experiments show that the hyperfine structure of the ground state can be directly targeted using radio-frequency (RF) pulses that transfer population between the hyperfine states of the electronic ground state. These RF experiments show that population in the F=0, m=0 sublevel of the ground state can be maintained for times on the order of 3 ms in a neon matrix held at 5.8 K. With the results demonstrated in this work, the remaining task prior to a measurement of the electron's electric dipole moment using the EDM3 method will be to demonstrate precession and observe the coherence time associated with the solids produced. Further purification of the molecular beam will be necessary to reach the desired precession times of approximately 10 ms. Improvements to the apparatus are underway by the EDM3 group and their completion could remove the last barriers to a measurement of de.
Access status: Open Access ,
Understanding And Tuning The Heat Transport At Interfaces Between Metals And Highly Anisotropic Semiconductors.
(2025-07-23) Shany Mary Oommen; Pisana, Simone
A complete and accurate description of nanoscale heat transport processes is essential for understanding energy transfer mechanisms and advancing thermal management technologies. This dissertation explores, both theoretically and experimentally, the fundamental heat transport mechanisms in anisotropic semiconductors and investigates how ultrathin metallic interlayers influence thermal boundary conductance at metal-semiconductor interfaces. We first examined metal-isotropic semiconductor systems and introduced a hybrid diffuse mismatch model to describe phonon-mediated interfacial heat transfer. Our thermal model, which incorporates multiple scattering pathways was validated using existing experimental data. It successfully captures how interfacial conductance can be tuned by interlayer thickness, even with films as thin as 1 nm. To accurately characterize the metal-anisotropic semiconductor interface, we studied how in-plane thermal conductivity evolves with thickness in graphite, MoS₂, and hBN. Results showed that conductivity increases with thickness and plateaus at ~5 µm for graphite and ~500 nm for MoS₂ and hBN, reaching bulk values of 2000 W/mK, 114 W/mK, and 490 W/mK, respectively. These findings were interpreted using Boltzmann transport modeling. We then extended the hybrid model to metal–anisotropic semiconductor interfaces and validated its predictions experimentally. The results emphasize the importance of accounting for full phonon dispersion, optical phonons, and electron-phonon coupling in accurately modeling interfacial heat transport. Our results provide a new insight into the fundamental physics of heat transport as well as offer ways to design materials and devices with tailored thermal properties for applications in nano- and micro-electronics, thermoelectrics and nanotechnology.
Access status: Open Access ,
Precision Measurement Of The 2^3P_1-to-2^3P_0 Fine Structure Of Atomic Helium Using Frequency-Offset Separated Oscillatory Fields
(2025-07-23) Heydarizadmotlagh, Farshad; Hessels, Eric A.; George, Matthew C.
Increasing accuracy of the theory and experiment of the 2^3 P fine structure of helium has allowed for increasingly precise tests of quantum electrodynamics (QED), determinations of the fine-structure constant 𝛼, and limitations on possible beyond-the-Standard-Model physics. The work presented is a 2-part-per-billion (ppb) measurement of the 𝐽=1-to-𝐽=0 interval. The measurement is performed using the frequency-offset separated-oscillatory-fields (FOSOF) method. The result of 29 616 955 018(60) Hz represents a landmark for helium fine-structure measurements, and, for the first time, will allow for a 1-ppb determination of the fine-structure constant when QED theory for the interval is improved.
Access status: Open Access ,
Autonomous Sensor Tasking And Object Detection For Space Situational Awareness Using Machine Learning
(2025-04-10) Fairbrother, Michael Christopher; Lee, Regina S. K.
The space domain is becoming increasingly crowded due to the proliferation of man-made resident space objects. Our limited number of object-tracking resources is becoming overburdened by a growing catalog of space debris and active satellites. This problem necessitates the most effective use of available sensors and observatories for catalog maintenance through the optimization of sensor tasking schedules. Given the complexity of the tasking problem, autonomous scheduling is essential and creates a need for increasingly powerful computational optimization algorithms. This research explores one such optimization approach, deep reinforcement learning, as an effective solution for autonomous sensor tasking. In addition to scheduling, improved object detection algorithms are in constant demand in order to more accurately identify resident space objects in images produced by optical sensors. This research additionally explores region-based convolutional neural networks as a potential considerable improvement over traditional detection algorithms.
Access status: Open Access ,
The Past, Present And Future Of Neutrino Near Detectors
(2025-04-10) Zaki, Rowan; Harris, Deborah
This thesis covers two accelerator-driven long-baseline neutrino experiments. The Tokai-to-Kamioka (T2K) experiment uses a 0.6 GeV neutrino beam produced at the J-PARC beamline in Tokai, Japan to measure neutrino oscillation parameters. These parameters can be found by comparing the neutrino interaction rates at the ND280 near detector and the Super-Kamiokande far detector at 280 meters and 295 kilometers from the neutrino beam source, respectively. Accurately measuring these interaction rates and subsequently the oscillation probability is limited by the systematic uncertainties associated with the neutrino-nucleus interaction cross-sections. Hence, these interactions are studied in the high event rate environment of the ND280 near detector. In muon-neutrino-induced charged-current single positive pion production on hydrocarbon, both a muon and a positively charged pion are produced in the final state. The four dimensional differential cross-section for this process has been measured in muon and pion kinematic parameters for the full solid angle in the past, but has always been statistically limited. Here it is presented with the full available statistics including the use of pion properties derived from Michel electrons of their subsequent decay, which improved the statistics for pion momenta between 50-400 MeV by 50\%. The cross-section extraction is done with a binned log-likelihood minimization returning a $\chi^{2}/\text{Ndf}$ of 1.25, showing good agreement with the nominal Monte Carlo models. The future Deep Underground Neutrino Experiment (DUNE) relies on liquid argon as target material for the neutrino interactions in the near and far sites. The liquid argon near detector (NDLAr) has been given a modular design consisting of 35 modules (70 time-projection chambers) in a 7 by 5 array with novel pixelated charge readout systems in order to deal with the high interaction rates in the world's most intense neutrino beam. To understand the behavior of the drift fields and the pixel charge collection efficiencies inside these time-projection chambers, a series of prototypes have been studied. These studies ultimately converged into a diagnostic tool capable of identifying misbehavior in pixel trigger rates during operation.
Access status: Open Access ,
Optical Polarization Studies Of Latex Beads In Aqueous Solution: An Analog For Radar Scattering In Water-Ice Medium
(2025-04-10) Bourget, Antoine Vincent; Daly, Mike
This study presents low phase angle 0◦−5◦ measurements of polarimetric properties of icy planetary regolith analog materials acquired using the custom-built Multi-Axis-Goniometer-Instrument (MAGI). We present same sense (SC), and opposite sense (OC) backscatter circular polarization coefficients, circular polarization ratio (CPR), and degree of linear polarization (DLP) of spherical latex (non-dye) beads of varying sizes and volume concentrations (v/v) in aqueous solutions (λ=0.8μm) in water. We leverage Mie scattering calculations to accurately simulate the polarization behavior of light in an aqueous solution of latex beads. We also present measurements of alumina powder in air at λ=1.064μm. Measurements showed that at a low incidence angle (i=0◦), backscatter is dominated by surface specular single-bounce scattering, which hides other scattering processes. At high (i=15◦) incidence angle, surface single-bounce surface scattering becomes negligible, allowing for the detection of diffuse, dihedral (multiple bounces) scattering. We find that classical Mie alumina particles (2.1μm, 4.0μm) enhance subsurface scattering due to a larger void space relative to larger Mie particles (30μm), which cause the radar signal to scatter forward off small imperfections, maintaining the polarization properties of the signal and generating high >1 CPR. Latex beads, representing impurities, demonstrate the impact of isotropic and anisotropic scattering on radar signatures. Experiment and model found that the scattering medium’s anisotropy correlates to the size of the beads, while the void space of the medium inversely correlates with the bead size and the volume concentration (v/v) of the beads. Model and measurements show that Rayleigh-sized beads (impurities), due to isotropic scattering from the reduced scattering cross-section and higher transparency relative to larger impurities, generate subsurface single bounce scattering, producing OC≫SC and a low (<0.5) CPR and across all v/v with SC, and CPR proportional to v/v, but with OC, and DLP inversely proportional to v/v. Model of Rayleigh-sized beads (impurities) has increased modeled transparency that results in more simulated single-bounce scattering relative to experiment. Conversely, model and measurements of classical and large Mie beads show anisotropic scattering that intensifies scattering in the forward direction with high CPR, inversely proportional to the volume concentration with discrepancies between 4◦−5◦ relative to model.
Access status: Open Access ,
Measurement Of Inclusive Anti Neutrino Cross Section And Ration To Neutrino Cross Section As A Function Of Muon Kinematics
(2025-04-10) Mehmood, Maria; Harris, Deborah
Measurement of inclusive anti neutrino cross section and ratio to neutrino cross section as a function of muon kinematics The MINERvA experiment delves deep into the world of neutrino nucleus interactions to piece together a guidebook of measurements essential to advancing cross section models. The next generation of long baseline neutrino experiments require a high precision understanding of neutrino nucleus interactions to measure oscillation parameters. The MINERvA experiment uses an on-axis flux peaking at 6 GeV from the NuMI beamline at Fermilab. This talk will present a measurement of the inclusive anti neutrino cross section, in terms of muon kinematics, on the hydrocarbon tracker region of the MINERvA detector. An inclusive measurement in terms of muon kinematics will make for a comparatively easier comparison to model predictions, as such a measurement reduces the need for an accurate prediction of hadronic activity, which is harder to model. Furthermore, muon kinematics are easier to reconstruct in the detector and a two-dimensional measurement yields a more detailed view of the phase space being explored. Moreover, the measured cross section can be compared to the baseline model broken down by the predicted interaction channel. Some channels dominate in certain parts of phase space and will motivate which aspects of the model require more improvement. This measurement is extracted in anti-neutrino mode as long-baseline neutrino oscillation experiments rely on a high precision understanding of both neutrino and anti-neutrino nucleus interactions. The neutrino counterpart of this measurement has already been published [1]. Model comparisons are presented for the extracted cross section measurement and its ratio to the neutrino cross section. [1] D. Ruterbories et al. (MINERvA), Measurement of inclusive charged-current νμ cross sections as a function of muon kinematics at < Eν >∼ 6 GeV on hydrocarbon, Phys. Rev. D 104, 092007 (2021), arXiv:2106.16210 [hep-ex].
Access status: Open Access ,
Observing Ultra-Low Surface Brightness Objects In A Bright Sky Environment
(2025-04-10) Skrinnik, Anna; MCCall, Marshall
An array of $\mathrm{n}$ identical lenses operating simultaneously acts as an optical system that has an effective focal ratio that is faster than that of an individual lens by a factor of $\mathrm{\sqrt{n}}$, which enables imaging ultra-low surface brightness objects. Such optical system, when coupled to narrow-band line filters, offers the opportunity to isolate emission from targets while suppressing light from other sources, such as the sky. In this work, we report on the development of a fast focal ratio system consisting of two 400 mm f/2.8 lenses coupled with CCD cameras to observe ultra-low surface brightness objects in the light of H$\mathrm{\alpha}$ and [OI]. The system was used to search for missing gas around a dwarf spheroidal satellite of the Andromeda Galaxy M31 and to locate the transition zones of nebulae. This system was successfully used to observe ultra-low surface brightness objects in the severely light polluted environment of Toronto.
Access status: Open Access ,
Characterizing the Martian Environment Through Surface Spacecraft Observations
(2024-07-18) Campbell, Charissa; Moores, John
Over the course of a Mars Year (MY) atmospheric temperatures vary enough between the furthest (Aphelion) and closest (Perihelion) points in Mars' orbit due to an Earth-like obliquity and elliptical orbit, creating two distinct seasons. Aphelion has cooler temperatures and a cross-equatorial Hadley cell revealing equatorial water-ice clouds. Perihelion has warmer temperatures that support increased dust activity such as dust-devils or dust storms. These two seasons have been observed from orbit and surface, with surface vehicles crucially important for understanding surface-to-atmosphere interactions. Aerosols were examined for wind direction and speed using movies from the Mars Science Laboratory (MSL) rover and InSight lander due to their proximity. Similar Easterly wind directions during the Aphelion season for both landing sites helped pinpoint that observed aerosols were most likely aloft in the middle atmosphere, affected by the same large-scale circulation via Hadley cells. However, mission constraints such as power and data volume limit the amount of returnable data and the ability to fully understand these aerosols. Automated methods appear to show promising results based on an algorithm developed by a team from Curtin university and tested with known wind directions from MSL atmospheric movies. The Onboard Rover Cloud Algorithm (ORCA) could be used on future missions to significantly decrease data volume by simply returning a set of wind parameters without first downlinking images. To further expand low-cost options, an optical meteorological station was created based on the Phoenix Mars mission experiment that imaged the lidar beam shining within aerosols to calculate ice-water content. The Mars Atmospheric Panoramic camera and Laser Experiment (MAPLE) has a panoramic camera and multiple class 3R lasers to maximize returnable science in a minimal way. Field testing in dense fog in Newfoundland showed that MAPLE's lasers could detect fog decks up to 100 m above the camera during nighttime conditions. The lasers were unable to be resolved during the day, but a power calculation determined that all three lasers on MAPLE could be suitable for Martian polar conditions. Understanding the constraints of obtaining Martian atmospheric data enables low-cost options such as MAPLE to further our knowledge of these aerosols.
Access status: Open Access ,
The Morphology-Density Relation of Galaxies at z~1.6
(2024-07-18) Brown, Westley Andrew Louise; Muzzin, Adam
The relationship between galaxy morphology and environment has been well-studied in the local universe and at low redshift, showing that galaxies in dense clusters tend to be elliptical and bulge-like while galaxies in low-density fields tend to be spiral and disk-like. However, this relationship is less understood at higher redshifts, and the few studies at high-z rely on samples with incomplete redshift measurements and poorly constrained stellar masses. We explore the morphology-density relation at z~1.6, the tail end of cosmic noon, using a sample of 3 SpARCS clusters and 2 fields from 3D-HST/CANDELS. Using Sersic index as a proxy for galaxy morphology, we find that the morphology-density relation is already in place in clusters at this epoch. Additionally, we find a significant difference in the relationship between galaxy morphology and stellar mass in clusters compared to field environments. This suggests that the morphology-density relation may be driven by mass-dependent environmental processes.
Access status: Open Access ,
Progress Towards a Precision Measurement of the n = 2 Triplet P0-to-n = 2 Triplet P1 Transition in Atomic Helium
(2024-03-16) Skinner, Taylor David Grant; Hessels, Eric
Significant progress towards a high-precision measurement of the 29.6 GHz 2^3P_1-to-2^3P_0 fine-structure interval in helium at an intended precision of 20 Hz is presented. The measurement is performed using a thermal beam of metastable helium atoms, and the transition is measured using the frequency-offset separated oscillatory fields (FOSOF) method, where the transition is driven by a pair of temporally separated microwave pulses. The two pulses are at slightly different frequencies, which can be viewed as a continuously advancing phase difference between the pulses. The advancing phase difference leads to a sinusoidally varying atomic signal due to quantum interference between atoms excited during the two pulses. The phase difference between the sinusoidal atomic signal and a reference signal generated by combining the two microwave frequencies is zero at resonance and approximately proportional to the difference between the applied microwave frequency and the centre frequency of the transition. A large number of experiment parameters which could lead to systematic effects have been investigated and shown to be sufficiently well-managed at the intended precision level of the intended measurement. One effect which causes the measured linecentre to depend on the range of microwave frequencies at which data is taken has been thoroughly investigated in both experiments and in a numerical simulation developed to investigate systematic effects. This effect is still not sufficiently well-understood or controlled to allow completion of a measurement at the 20 Hz level of precision. A completed measurement, at a precision of 20 Hz, would be able to be combined with our previous 25 Hz measurement of the 2.3 GHz 2^3P_2-to-2^3P_1 interval to obtain a part-per-billion (ppb) determination of the combined 31.9 GHz 2^3P_2-to-2^3P_0 interval. When compared to a sufficiently-precise theoretical calculation, the combined interval would allow a 0.5 ppb determination of the fine-structure constant, the most precise determination of the fine-structure constant in a two-electron system and within an order of magnitude of the most precise determinations of the fine-structure constant. This 0.5 ppb determination could be compared with other fine-structure constant determinations to test beyond-the-Standard-Model physics.
Access status: Open Access ,
Self-Similar Models of Quasar Outflow Shock Structures
(2024-03-16) Weiss, Erik Adam; Hall, Patrick B.
Supersonic winds of outflowing material are observed and/or predicted in a number of astrophysical systems; such winds may drive an expanding shock structure that shocks and pushes the ambient interstellar medium (ISM) outward. This thesis analyses, combines and expands on existing analytic self-similar models of these structures in the context of quasar accretion disk winds; we then search for the bulk acceleration (positive or negative) of low-velocity Ca II in the quasar SDSS J030000.0+004828.0 (J0300) and compare our results to model predictions. We find a strong upper limit on the acceleration magnitude, yielding plausible model constraints, but the observed range of gas velocities implies that the Ca II velocity profile does not coincide with that of the shocked ISM. We conclude with a discussion of recent results regarding J0300's outflow properties and briefly investigate the possibility of pre-existing ISM cloud disruption as an explanation for the observed Ca II velocity profile.
Access status: Open Access ,
Time-evolution of SU(2) lattice gauge theory on a quantum computer
(2024-03-16) Rahman, Sarmed A.; Lewis, Randy
Lattice Gauge Theory is a mathematical tool used to study the forces of nature, like Quantum Electrodynamics and Quantum Chromodynamics. Quantum computers offer an alternative to classical computers in studying these forces. In my thesis, a gate-based quantum computer was used to perform calculations of the propagation of an excitation in real-time. A new error mitigation method was developed to greatly extend the range of comprehensible data over time by using the physics circuits to estimate the accumulated error. I also developed the theoretical foundation for higher energy systems, as well as higher dimensional geometry.
Access status: Open Access ,
Structure and Local Properties of Dark Matter Halos
(2024-03-16) Smith-Orlik, Adam Jacob Ross; Tulin, Sean; Bozorgnia, Nassim
The structure and local properties of dark matter (DM) are important input variables for both direct and indirect detection experiments. Common assumptions about DM, such as, its particle nature being cold and collisionless–CDM–and its distribution in halos being isothermal and spherical, and well-modeled by an isotopic Maxwell-Boltzmann velocity distribution–the Standard Halo Model (SHM)–prove to be at odds with astrophysical observations. In this thesis I present work towards elucidating two areas of refinement to the above-mentioned assumptions regarding DM: 1) allowing moderate self-interactions between DM particles (SIDM), extending the semi-analytic Jeans modeling technique for SIDM halos to multiple dimensions and including baryons and nonspherical effects to study the resulting change in the DM halo structure; 2) quantifying the departure from the SHM by analyzing hydrodynamical simulations of Milky Way (MW) like halos to characterize the impact on local properties of DM induced by satellite galaxies like the Large Magellanic Cloud (LMC) and their implications for direct detection experiments.
Access status: Open Access ,
Extreme Emission Line Galaxies Observed with the James Webb Space Telescope's Medium-Band Filters
(2024-03-16) Withers, Cassandra Carol; Muzzin, Adam; Ravindranath, Swara
Since the beginning of the James Webb Space Telescope's science operations, there have been many observations dedicated to characterizing galaxies during the Epoch of Reionization (EoR). This thesis uses medium-band photometry from the JWST to search for Extreme Emission Line Galaxies (EELGs) in the EoR and analogues at lower redshifts. We present a sample of EELGs over 1.7 < z < 6.7 selected on their strong Halpha and [OIII] + Hbeta emission lines. We measure the equivalent widths (EWs) and physical properties of the galaxies in our sample, finding high EWs (median EW(Halpha) = 893 Angstroms, EW([OIII] + Hbeta) = 1255 Angstroms) and properties typical of EELGs: mostly compact with low stellar mass, low metallicity, little dust, and high specific star formation rates. Follow-up NIRSpec spectroscopy of 15 of the EELGs in our sample confirm the nature and EWs of the EELGs measured from medium-band photometry, demonstrating the accuracy of our colour selections.
Access status: Open Access ,
Cellular Cooperativity
(2023-12-08) Fedoryk, Olha; Bergevin, Christopher
The ear is sound detector that is remarkably sensitive and selective. As a nonlinear and active system, ears also emit sound, known as otoacoustic emission (OAEs). We investigated the theoretical origins of spontaneous emissions (SOAEs), which appear as idiosyncratic peaks unique to a given ear. Using an established model of locally coupled limit cycle oscillators, we adapted and extended the framework for describing an Anolis lizard ear and explored several specific hypotheses. We observed that depending on the set of parameters and number of oscillators, the system could become sensitive to initial conditions and stay either stable or unstable. We also conclude that embedding only morphological differences (via frequency or hair cell bundle height) is not enough to generate "unique ears". Finally, we achieved a peak broadening by presenting additive noise to the system both as external and local thermal noise.
Access status: Open Access ,
Surface Water Investigations on Mars
(2023-12-08) Saive, Elliot Edward; Whiteway, James A.
Experiments are presented which explore whether a layer of liquid water forms at the ice table in the shallow subsurface due to contact between perchlorate and water ice on Mars. Samples of regolith simulant were mixed with varying concentrations of magnesium perchlorate and deposited over ice to simulate the ice-regolith interface as was seen on Mars. Over multiple temperature cycles, the temperatures of melting of the ice and full freezing of the resulting brine were recorded using an embedded moisture sensing device. Based on temperatures simulated to constrain the ice table at the Phoenix landing site, a perchlorate concentration of 5% is sufficient for a layer of liquid water to form which can persist for days at a time, while no liquid forms for a Mars-measured concentration of 0.6%. Other concentrations are also explored.

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