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Item Open Access A Search For Warm-Hot Intergalactic Matter in the Local Sheet of Galaxies(2015-12-16) Deneault, Ryan Scott; McCall, Marshall30-40% of all baryons in the Universe are thought to reside in the warm-hot intergalactic medium (WHIM) at temperatures in the range of 10^5-10^7 K. If the oxygen abundance is comparable to expectations, then OVI absorption from the WHIM associated with the Local Sheet of galaxies should have been detected in background sources observed by the Far-Ultraviolet Spectroscopic Explorer (FUSE). FUSE spectra of targets spanning the entire sky have been examined to distinguish the WHIM in the Sheet from other sources. These observations suggest that the Sun is offset from the plane of the Local Sheet WHIM, defining a theoretical framework against which the data was compared. By looking for a correlation of the OVI absorption equivalent widths with latitude and comparing the results to hydrodynamical simulations, strong constraints have been placed on the properties of the WHIM. With a hydrogen number density equal to that predicted by the simulations, the upper limit to the oxygen abundance for the WHIM in the Local Sheet must be 0.05 ± 0.01 Z⊙. If instead a metallicity of 0.1 Z⊙ is adopted for the WHIM, the upper limit to the hydrogen number density must be 0.64 ± 0.02 times that predicted by the simulations.Item Open Access Antihydrogen Via Two-Stage Charge Exchange(2016-09-20) Fitzakerley, Daniel William; Hessels, EricThis thesis describes positron and antihydrogen research performed at CERN in the context of the ATRAP collaboration. Positrons emitted from a radioactive source are moderated in a layer of frozen neon. The rate at which slow positrons exit the moderating material is precisely determined. The slow positrons are trapped in a differentially pumped Penning trap. Large numbers of positrons are accumulated and transferred into a cryogenic Penning trap at a record rate. Plasmas of up to four billion positrons are created --- the largest number of positrons ever held in a single trap. Counting techniques for positron and electron plasmas are compared, validating the charge-counting techniques used for each. Positron plasmas are compressed using rotating electric fields in preparation of antihydrogen production experiments. Antihydrogen atoms are created via laser-controlled, two-stage charge exchange. These antihydrogen atoms, approximately 2000 per trial, should be created with low enough energy so that some of them can be confined in a magnetic quadrupole or octupole trap. The goal of ATRAP is to precisely measure the spectroscopy of these trapped antihydrogen atoms, and compare it to the spectroscopy of hydrogen to test CPT and Lorentz invariance.Item Open Access Apparatus for Inertial Sensing with Cold Atoms(2018-11-21) Carew, Adam Curtis; Kumarakrishnan, AnantharamanA variety of experimental techniques and equipment for the measurement of inertial effects are herein presented. The bulk of the work relates to improvements to an existing local gravitational acceleration "little-g'' measurement apparatus. These improvements are predicted to push the statistical uncertainty in the measurement of g to less than 1 part-per-billion (ppb). To accomplish this goal, several other projects were undertaken. These include a finite-element model of the magnetic field coil setup used in the experimental apparatus, as well as the design and construction of a hermetically-sealed diode laser system with excellent long-term frequency stability. Additionally, a direct digital synthesis-based frequency generator was designed and built for a proposed frequency-domain atom interferometer experiment. Finally, a side-project involving the evaluation of the magnetic field uniformity/stability of a commercial optical isolator was performed, and its results are presented as an appendix.Item Open Access Apparatus for Positronium Production via Rydberg Cesium Charge-Exchange(2021-11-15) Thai, Richard; Storry, Cody H.This dissertation outlines research conducted with positrons towards the production of positronium via charge-exchange with Rydberg cesium atoms. Positronium is a purely leptonic atomic system that is ideal for tests of quantum electrodynamics (QED) theory. A frozen neon crystal moderator produces low-energy positrons from a radioactive source that are magnetically guided towards a buffer-gas accumulator. The buffer-gas accumulator has been optimized to store large numbers of positrons (>40 million in 2 minutes) for a long time to perform a variety of experiments. The 200 meV energy width of the accumulated positrons is suitable for charge-exchange experiments. The positrons are then magnetically guided through a 90 bend towards an apparatus where charge-exchange takes place. The experimental techniques to produce and detect Rydberg positronium are described and the progress is presented. A data acquisition system has been developed to detect positron signatures based on the coincidence-timing of back-to-back annihilations on a single-event basis where time and energy analysis cuts allow strict criteria to distinguish signal from background. The long-term goal of the research program is to perform precision spectroscopy of the internal structure of Rydberg positronium. These measurements can be used to determine fundamental constants of nature and to test QED theory. A deviation from the QED predictions can be an indication of physics beyond the Standard Model. Physics beyond the Standard Model can provide a solution to unsolved problems, such as the matter-antimatter imbalance that is observed today.Item Open Access Atmospheric Temperature Profiling using Rotational Raman Lidar Measurements with a 32-Channel Spectral Detector(2021-07-06) Seth, Kanupria; Whiteway, James A.Atmospheric backscatter measurements with lidar at 355 nm laser wavelength were conducted at York University. The novel combination of the lidar system with a new 32-channel spectral detector made possible detecting photon-counting signals for multiple wavelengths simultaneously. The goal of this research was to derive atmospheric temperature profiles using the rotational Raman backscatter signal. The temperature was derived using the ratio of two wavelength intervals in the rotational Raman backscatter spectrum. A calibration function for the signal ratio and temperature on June 6, 2019 was found using temperature data from radiosonde measurements in Buffalo. The calibration function was used to derive temperature from ground up to 1200 m using lidar measurements on April 18, June 11 and June 12 in 2019. The lidar-calculated temperature profile had a mean deviation of 2.14 K from the radiosonde temperature values. The method requires improvements, such as controlling the temperature of the edge filter to minimize changes in the calibration from day to day.Item Open Access ATRAP Buffer-Gas Positron Accumulator(2015-08-28) Comeau, Daniel Andre; Hessels, EricThe ATRAP collaboration has been creating antihydrogen, the simplest antimatter atom, since 2002 and has a long-term goal of performing precision laser spectroscopy on these antihydrogen atoms. ATRAP has produced antihydrogen by positron cooling of antiprotons and by a laser-controlled charge-exchange process. Both methods require large numbers of antiprotons and positrons (the constituent particles of antihydrogen). This dissertation describes the methods developed to increase the number of positrons available for the ATRAP experiments by a factor of 200. The development of the new positron loading scheme has enabled the ATRAP collaboration to greatly increase the daily rate of antihydrogen production. Positrons originating from a radioactive source travel through a moderating material and are accumulated in a differentially pumped vacuum chamber. When required, the positrons are sent through a complex magnetically-guided beamline to the location where antihydrogen is produced. The system built allows for a reliable, highly-efficient method of providing positrons to the ATRAP experiment.Item Open Access Calibration and Flight of a Balloon-Borne O2 Atmospheric Band Fabry-Perot Spectrometer(2018-03-01) Voutsogiannakis, Michael; Shan, JinjunThe Fabry-Perot spectrometer is an extremely useful tool for retrieving spectral information of the Oxygen A-band at nadir viewing angles, as well as for remote sensing purposes. Testing the performance of this spectrometer will help us determine possible limitations and improvements needed to be carried out for future missions, so that the scientific objectives can be met successfully. For the calibration setup, a narrow line argon source was used and the procedure was carried out by varying the gap spacing between the etalon plates, thus performing step scans that cover the entire free spectral range. Valuable information can be acquired, such as the reflective Finesse of the etalon, the degree of parallelism and flatness of the plates, as well as the temperature coefficient of the etalon. Measurements were also performed on O2 interference filters, making use of a diffraction grating spectrometer, in order to understand their behavior with temperature change.Item Open Access Cellular Cooperativity(2023-12-08) Fedoryk, Olha; Bergevin, ChristopherThe 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.Item Open Access Cosmic Bubble Collisions: Observable Signature of a Classical Transition(2015-08-28) Lin, Wei; Johnson, Matthew C.The theory of inflation was introduced to resolve many existing observational problems in cosmology. Inflation becomes eternal when a region of space continuously spawns non-inflation regions. This process arises from metastable vacua in a potential landscape. Our universe could be a realization of one of these many vacua predicted by the theory. In this thesis, we explored the idea that a universe can be born via a collision between two bubble universes. This process is known as a ``Classical Transition''. In this thesis, the potential observability of relics produced during the collision is studied. If a classical transition did happen in the past, its presence is imprinted on the CMB temperature anisotropy.Item Open Access Development and Characterization of Auto-Locked Laser Systems and Applications to Photon Echo Lifetime Measurements(2020-05-11) Beica, Hermina; Kumarakrishnan, AnantharamanWe have developed and characterized a new class of vacuum-sealed, auto-locking diode laser systems with an auto-locking controller that allows these instruments to be operated with greater ease and control at desired wavelengths in the visible and near-infrared spectral range. These laser systems can be tuned and frequency stabilized with respect to atomic, molecular, and solid-state resonances without human intervention using a variety of control algorithms programmed into the same controller. We show that these lasers have exceptional long-term stability, with an Allan deviation (ADEV) floor of 210^{-12}, and a short-term linewidth of 200 kHz. These performance characteristics are related to reducing current noise and ensuring vacuum sealing. We demonstrate accurate measurements of gravitational acceleration at the level of a few parts-per-billion by incorporating the laser into an industrial gravimeter. We also realize the basis of a LIDAR transmitter that can potentially operate in a spectral range in which frequency references are not readily available. We have also developed a technique for precise measurements of atomic lifetimes using optical photon echoes. We report a measurement of 26.10(3) ns for the 5^2P_{3/2} excited-state in ^{85}Rb vapour that has a statistical uncertainty of 0.11% in 4 hours of data acquisition. We show that the best statistical uncertainty that can be obtained with the current configuration is 0.013%, which has been exceeded by only one other lifetime measurement. An analysis of the technical limitations based on a simple model shows that these limitations can be overcome using a feedback loop with a reference interferometer. Our studies indicate that it should be possible to investigate systematic effects at the level of 0.03% in 10 minutes of data acquisition. Such an outcome could potentially result in the most accurate measurement of any atomic lifetime.Item Open Access Development of Software to Measure the Gravitational Redshift with RadioAstron(2022-03-03) Nunes, Nelson Vitoria; Bartel, Norbert H.The incompatibility of General Relativity (GR) and quantum theory continues to be a stumbling block in the unification of our understanding of the physical world. Tests of the Einstein Equivalence Principle, lying at the core of GR, are vital to constrain new theories that require departures from GR's predictions. One such test is measuring the gravitational redshift using RadioAstron – a space-VLBI mission launched in 2011 into a highly elliptical orbit. Utilizing the onboard H-maser frequency standard along with a Doppler compensation scheme that minimizes systematics, the gravitational redshift is anticipated to be determined with a relative accuracy of 10^-5. A third-order dynamical model has been implemented to predict frequency shifts in the spacecraft's carrier signal needed to conduct the experiment. The theory behind this model is developed, the software implementation described and third-order effects necessary to achieve the desired measurement accuracy are discussed.Item Open Access Differential Absorption Lidar Measurements of Troposheric Ozone in the Arctic(2015-08-28) Seabrook, Jeff Adams; Whiteway, James A.A differential absorption lidar was constructed at the laboratory at York University and deployed in field campaigns to measure vertical profiles of tropospheric ozone. Profiles of ozone concentration were derived from the range-resolved simultaneous detection of backscatter from two or more wavelengths of laser radiation. By analyzing the absorption differences due to ozone between the two lidar returns, an ozone profile along the optical path of the laser was determined. This method is capable of resolving ozone concentrations between a range of 300 m to 8 km from the lidar. During the spring in the polar region, tropospheric ozone depletion events occur due to the presence of inert halide salt ions such as Br- in the atmosphere. After polar sunrise, this Bromine photochemistry can cause ozone concentrations near the ice surface to drop to near zero levels. Outstanding questions addressed by the lidar measurements were (a) whether significant ozone depletion occurs in layers not connected to the surface, and, (b) how local topography can influence ozone concentrations measured at land based locations such as Eureka NU. Measurements were made during three field campaigns. The first was on the Amundsen icebreaker ship of the Canadian Coast Guard as part of the circumpolar Flow Lead study. For the second campaign the lidar was installed on the Polar-5 aircraft for flights over the sea ice north of Barrow Alaska. The third campaign involved ground based measurements from Eureka Weather Station on Ellesmere Island in the Canadian High Arctic. All of the measured ozone depletions were connected to the surface, and no evidence of ozone depleted air detached from the boundary layer was found. The lack of free tropospheric depletions indicate that such events are likely rare, and not a significant ozone sink. While measuring tropospheric ozone from a land based location, the measured depletions were found to be mainly confined to the atmospheric boundary layer except in instances where surrounding topography enabled the transport of ozone depleted air into the free troposphere. This effect was common at the Eureka weather station on Ellesmere Island, which is surrounded by a number of mountain ranges.Item Open Access Disc Winds and Line-Width Distributions in Active Galactic Nuclei(2016-09-20) Chajet, Laura Susana; Hall, Patrick BWe study Active Galactic Nucleus (AGN) emission-line profiles by combining an improved version of the accretion disc-wind model of Murray & Chiang with the magnetohydrodynamic model of Emmering et al. We consider central objects with different masses and/or luminosities. We show how the shape, broadening and shift of the C IV line depend not only on the viewing angle to the object but also on the wind launching angle, especially for small launching angles. We have compared the dispersions in our model C IV line-width distributions to observational upper limits on that dispersion, considering both smooth and clumpy torus models. Following Fine et al., we transform that scatter in the profile line-widths into a constraint on the torus geometry. We show how the half-opening angle of the obscuring structure depends on the mass and luminosity of the central object.Item Open Access Double-Loop Microtrap Array for Ultracold Atoms(2015-01-26) Jian, Bin; Van Wijngaarden, William A.A novel kind of magnetic microtrap is demonstrated for ultracold neutral atoms. It consists of two concentric loops of radii $r_1$ and $r_2$ having oppositely oriented currents. A magnetic field minimum is generated in three dimensions that can be used to trap the atoms with a trap depth of about 1 mK using a current of 2.6 A. The condition $r_2/r_1$ = 2.2 maximizes the restoring force on the atoms toward the trap center. Unlike conventional magnetic microtraps, an external bias field is not required. Moreover, a one dimensional array of double-loop microtraps can be created by daisy chaining single microtrap circuits. A linear array of three microtraps having $r_1$ = 300 $\mu$m was fabricated as part of an atom chip. The following three techniques were developed to load the microtrap array: 1) atoms initially contained in a magneto-optical trap (MOT) were transported to the atom chip by a conventional magnetic trap, 2) atoms were first loaded into a mirror MOT and 3) atoms were initially loaded in a far off resonance optical dipole trap (FORT). Each technique loaded greater than $10^5$ $^{87}$Rb atoms into the microtrap array. The lowest temperature of 30 $\mu$K for the microtrapped atom cloud was achieved using FORT loading. The strength and the position of the microtrap could be precisely adjusted over a range from 300 to 50 $\mu$m above the atom chip surface by applying an external bias magnetic field. The lifetime of the atoms trapped in the microtrap array was measured to be 350 ms which was limited by the collisions with residual background gas.Item Open Access Effects of Ultrathin Interlayers on Thermal Boundary Conductance at Metal-Dielectric Interfaces(2019-11-22) Oommen, Shany Mary; Pisana, SimoneHeat transport in micro- and nano-scale materials have an increasingly important role in thermal management of numerous technologies such as thermoelectric energy conversion, microelectronics, and plasmonic devices. Understanding the heat transport contributions from the interface is crucial when interfacial resistance forms a significant fraction of the total thermal resistance of the device. In this thesis, we analyze the modification of thermal conductance at metal-dielectric interfaces by inserting few-nanometer thick metal interlayers. A thickness-dependent interlayer study suggests that interfacial conductance alters significantly at ultrathin thicknesses before reaching a plateau. Our results reveal that the electron-phonon coupling strength of an interlayer plays a significant role in determining the overall thermal boundary conductance. Analysing heat transport mechanisms across a variety of metal-dielectric interfaces by means of an interlayer indicated that thermal boundary conductance depends on an interplay between the phonon vibrational properties and metal electron-phonon coupling strength overlap.Item Open Access Efficient Detection of Cloud Scenes by a Space-Orbiting Argus 1000 Micro-Spectrometer(2018-03-01) Siddiqui, Rehan; Quine, BrendanThe description, interpretation and imagery of clouds using remote sensing datasets collected by Earth-orbiting satellites have become a great debate spanning several decades. Presently, many models for cloud detection and classification have been reported in the modern literature. However, none of the existing models can efficiently detect clouds within the shortwave upwelling radiative wavelength flux (SWupRF) band. Therefore, in order to detect clouds more efficiently, a method known as radiance enhancement (RE) can be implemented. A satellite remote sensing database is one of the most essential parts of research for monitoring different atmospheric changes. This study proposes an innovative approach using RE and SWupRF to distinguish cloud and non-cloud scenes by using a space-orbiting Argus 1000 spectrometer utilizing the GENSPECT line-by-line radiative transfer simulation tool for space data retrieval and analysis. We apply this approach within the selected wavelength band of the Argus 1000 spectrometer in the range from 1100 nm to 1700 nm to calculate the integrated SWupRF synthetic spectral datasets. We used the collected Argus observations starting from 2009 to investigate radiative flux and its correlation with cloud and non-cloud scenes. Our results show that the RE and SWupRF model can identify most of the cloudy scenes except for some thin clouds that cannot be identified reasonably with high confidence due to complexity of the atmospheric system. Based on our analysis, we suggest that the relative correlation between SWupRF and RE within a small wavelength band can be a promising technique for the efficient detection of cloudy and non-cloudy scenes.Item Open Access Electron Removal Processes in Proton-Methane Collisions(2015-08-28) Salehzadeh, Arash; Kirchner, Tom K. R.We have conducted a quantum-mechanical analysis within the independent elec- tron model to investigate electron removal processes in the proton-methane collision system in the 20 keV to a few MeV energy range. Similar to a previous work, we have used a spectral representation of the molecular Hamiltonian and a single-centre expansion of the initially populated molecular orbitals. The two-centre basis gen- erator method is then used to solve the time-dependent single-particle Schr ̈odinger equations. We have also used the “independent atom model” in which we have treated the collision system with a molecular target as a combination of collision systems with atomic targets. We have also shown that Bragg’s additivity rule is derived from the independent atom model. The results for net capture and ionization cross sections, obtained by the molec- ular method as well as Bragg’s additivity rule, are compared with available ex- perimental studies. We observe good agreement at high energies for both models. At intermediate and lower energies the situation seems to be less clear. For the molecular method the ionization results are improved when we estimate excitation particularly at intermediate energies. Overall, our molecular method outperforms Bragg’s additivity rule for both capture and ionization.Item Open Access Electronic Properties of Anatase TiO2 and Iron (III) Doped TiO2 Nanoparticles(2022-08-08) Gong, Tuochen; Morin, SylvieSince its discovery by Fujishima and Honda in 1972, titanium dioxide (TiO2) has been studied extensively due to its ability to split water and decompose dyes as a photocatalyst. Among all phases, TiO2 in the anatase phase displayed the highest photocatalytic rates for dye decompositions. Iron is selected as a dopant to maximize the efficiency under solar light. In this study, we use structural, morphological, chemical methods to study nanoparticles prepared using the sol-gel method, to confirm their phases, crystallite sizes, appearance, and detailed chemical compositions. To understand the effect of iron doping on photocatalysis, band gaps and valence band structures are obtained using state-of-the -art spectroscopy techniques. Models of electronic band structures of anatase TiO2 with various iron doping percentages are proposed, and effects of iron dopants on photodegradation are discussed using experimental results. Our study will benefit water purification industries, especially for on-site water treatments.Item Open Access Estimating the Altitudes of Clouds at the Mars Science Laboratory Landing Site(2019-03-05) Campbell, Charissa; Moores, JohnUsing the Navigation Camera, the Mars Science Laboratory (Curiosity) Rover images the atmosphere to capture clouds. A Zenith Movie (ZM) consists of eight upward-pointing images taken over five minutes. The angular distance and wind direction are measurable, but without a lidar the altitude is not. Instead, parameters are compared with results modelled by the Mars Regional Atmospheric Modelling System (MRAMS). An altitude is estimated with the half-normal probability distribution to evaluate the probability MRAMS has similar conditions to observational values. Throughout a sol, clouds were predicted below the crater rim and planetary boundary layer, but higher altitude clouds were primarily predicted in the morning. Results are compared to ice extinction data from the Mars Climate Sounder (MCS) and a shadow movement across Aeolis Mons through a Cloud Height Movie (CHM). Pairing a ZM with a CHM allows direct measurement of the altitude of clouds for the first time from the surface.Item Open Access Evaluating the Top-down Emission Rate Retrieval Algorithm (TERRA) Using Virtual Aircraft-based Sampling Within the GEM-MACH Model(2018-05-28) Fathi, Sepehr; Gordon, Mark D.Between August 13th and September 7th of 2013, aircraft-based measurements of air pollutants were collected in support of the Joint Canada-Alberta Implementation Plan on Oil Sands Monitoring (JOSM). The Top-down Emission Rate Retrieval Algorithm (TERRA) was developed by Environment and Climate Change Canada (ECCC) to estimate facility emission rates based on the aircraft measurements. Here, as part of a larger effort on TERRA improvement, ECCC's air quality model, Global Environmental Multiscale-Modeling Air-quality and CHemistry (GEM-MACH), was used as a surrogate source of concentration and meteorology data. The TERRA-calculated emission rates are compared with those input into GEM-MACH, for different TERRA configurations. This work evaluates the combination of TERRA and GEM-MACH as a proxy for testing the downward extrapolation schemes within TERRA and identifies possible avenues for GEM-MACH and/or TERRA improvements. Outcomes from this work can provide useful suggestions for future flight plans for top-down emission rate estimations.