Physics Commons^™

Multi-Agent Deep Reinforcement Learning For Radiation Localization, Benjamin Scott Totten

Dissertations and Theses

For the safety of both equipment and human life, it is important to identify the location of orphaned radioactive material as quickly and accurately as possible. There are many factors that make radiation localization a challenging task, such as low gamma radiation signal strength and the need to search in unknown environments without prior information. The inverse-square relationship between the intensity of radiation and the source location, the probabilistic nature of nuclear decay and gamma ray detection, and the pervasive presence of naturally occurring environmental radiation complicates localization tasks. The presence of obstructions in complex environments can further attenuate the …

Possibilities For Inertial Electrostatic Confinement Fusion, Jeffrey Edward Black

Dissertations and Theses

While most of the fusion energy research is focused on magnetic confinement, there have been several alternative confinement methods aimed at the development of smaller and less expensive reactors. A number of these devices utilize a spherically convergent beam of recirculating ions, a technique known as inertial electrostatic confinement (IEC). This study looks at several aspects of IEC devices, including measurements of the fusion rate of an IEC device with a wire mesh electrode cathode, and a solid titanium cathode. In addition, several computational studies were performed to explore the possibilities for IEC fusion. These include development of a 1D-1P …

System Design For The Quantification Of Microbial Motility In Extreme Environments, Megan Marie Dubay

Dissertations and Theses

Motility of microorganisms is understudied but provides useful insights into their behavior. Organisms' ability to move autonomously changes how they interact with their environment--finding nutrients, interacting with other organisms, and avoiding unfavorable conditions. Understanding motility features can also be used to identify specific species, such as the identification of Vibrio cholerae in human samples. Motility might also be used as evidence of life existing in even the most extreme environments on Earth, and possibly beyond. Specialized microscopy systems can be required to examine the motility of microorganisms due to the nature of the environments to which the instruments are exposed. …

Methodologies For Quantum Circuit And Algorithm Design At Low And High Levels, Edison Tsai

Dissertations and Theses

Although the concept of quantum computing has existed for decades, the technology needed to successfully implement a quantum computing system has not yet reached the level of sophistication, reliability, and scalability necessary for commercial viability until very recently. Significant progress on this front was made in the past few years, with IBM planning to create a 1000-qubit chip by the end of 2023, and Google already claiming to have achieved quantum supremacy. Other major industry players such as Intel and Microsoft have also invested significant amounts of resources into quantum computing research.

Any viable computing system requires both hardware and …

Observation And Control Of Photoemission And Electric Field Enhancement Of Plasmonic Antennas Through Photoemission Electron Microscopy, Christopher M. Scheffler

Dissertations and Theses

Photoemission electron microscopy (PEEM) is an imaging method which uses electrons excited through the photoelectric effect to characterize a sample surface with nanometer-level resolution. In PEEM, a high intensity laser excites electrons from the surface of the material and electron optics are used to form an image from the intensity and spatial distribution of the photoemission from the sample. The goal of this research was to study and maximize light confinement, which was accomplished using plasmonic nanostructures. Surface plasmons represent oscillations in the electron density of a material and can occur along the transition interface between a metal and a …

Characterization Of High Mobility Channels For Use In Quantum Computing Devices, Payam Amin

Dissertations and Theses

Quantum computing promises computation that is fundamentally beyond the reach of classical computers. For the realization of a full-scale quantum computer, millions of quantum bits need to be fabricated on an integrated circuit and operated at cryogenic temperatures. Silicon and silicon-germanium based electron spin quantum bits have the advantage of leveraging decades of semiconductor industry knowledge for high volume manufacturability.

During the process development of any semiconductor device, material characterization is essential to understand and improve the process. Transmission electron microscopy is the only technique that could offer localized high spatial resolution characterization. In this work we have introduced two …

Effects Of Pore-Forming Peptides (Melittin And Magainin 2) On The Phospholipid Bilayer Interior, Elmukhtar Ehmed Alhatmi

Dissertations and Theses

Antimicrobial peptides (AMPs) are one of the most promising solutions to drug-resistant bacteria. Melittin and magainin 2 are two of the most representative and extensively studied AMPs. In this research, I investigated the interaction of these two AMPs with three models of cell membranes: 80% POPC 20% POPG, 40%POPC 40% POPE and 20% POPG, and 80%POPC 20%POPG plus 30% mole fraction of cholesterol. Time-resolved fluorescence emission and fluorescence anisotropy decays of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) were analyzed to determine the effects of AMPs on the bilayer headgroup packing and changes in the interior of the phospholipid bilayer during the …

Quantum Field Theories, Topological Materials, And Topological Quantum Computing, Muhammad Ilyas

Dissertations and Theses

A quantum computer can perform exponentially faster than its classical counterpart. It works on the principle of superposition. But due to the decoherence effect, the superposition of a quantum state gets destroyed by the interaction with the environment. It is a real challenge to completely isolate a quantum system to make it free of decoherence. This problem can be circumvented by the use of topological quantum phases of matter. These phases have quasiparticles excitations called anyons. The anyons are charge-flux composites and show exotic fractional statistics. When the order of exchange matters, then the anyons are called non-Abelian anyons. Majorana …

The Return To Anisotropy Across A Jet In Crossflow, Gregory P. Sakradse

Dissertations and Theses

With data from experiments on a jet of air emitting from an orifice flush with the floor of a wind tunnel providing a transverse flow, analysis is conducted to extract information about the state of anisotropy in the Reynolds stress tensor. Inflow velocities are modulated across two distinct turbulence intensity regimes while holding jet exit conditions constant, providing an opportunity to isolate effects of both jet to crossflow velocity ratio, r and the effects of the turbulence carried by the crossflow. Anisotropy in the Reynolds stress tensor is examined through anisotropy invariant maps and evolution of the function F, …

Efficient Neuromorphic Algorithms For Gamma-Ray Spectrum Denoising And Radionuclide Identification, Merlin Phillip Carson

Dissertations and Theses

Radionuclide detection and identification are important tasks for deterring a potentially catastrophic nuclear event. Due to high levels of background radiation from both terrestrial and extraterrestrial sources, some form of noise reduction pre-processing is required for a gamma-ray spectrum prior to being analyzed by an identification algorithm so as to determine the identity of anomalous sources. This research focuses on the use of neuromorphic algorithms for the purpose of developing low power, accurate radionuclide identification devices that can filter out non-anomalous background radiation and other artifacts created by gamma-ray detector measurement equipment, along with identifying clandestine, radioactive material.

A sparse …

Investigation Of Environmental-Friendly, Membraneless Hydrogen Peroxide Fuel Cells, Bao Nguyen

Dissertations and Theses

Human-induced climate change is one of the biggest threats to humanity in the 21^st century. This is caused by the increase in greenhouse gas concentrations in the Earth's atmosphere. The burning of fossil fuels is the primary cause of climate change. This problem can be addressed by replacing fossil fuels with fuel sources that have clean by-products and are cost-effective. For the last few decades, hydrogen (H₂) has been extensively studied as an alternative to carbon-based fossil fuels. Currently, H₂ still has many shortcomings for commercial applications. The photocatalytic production of H₂ still suffers from …

Proximal Policy Optimization For Radiation Source Search, Philippe Erol Proctor

Dissertations and Theses

Rapid localization and search for lost nuclear sources in a given area of interest is an important task for the safety of society and the reduction of human harm. Detection, localization and identification are based upon the measured gamma radiation spectrum from a radiation detector. The nonlinear relationship of electromagnetic wave propagation paired with the probabilistic nature of gamma ray emission and background radiation from the environment leads to ambiguity in the estimation of a source's location. In the case of a single mobile detector, there are numerous challenges to overcome such as weak source activity, multiple sources, or the …

Simulation Of Light Propagation Captured By Photoemission Electron Microscopy (Peem), Nabila Islam

Dissertations and Theses

The Photoemission electron microscopes (PEEM) is a powerful tool capable of synchronously imaging wave nature of light manifested by interference patterns as well as its particle nature through the energy exchange between the incident photons and the photoemitted imaging electrons. PEEM offers a non-invasive high-resolution approach for studying light propagation and interaction phenomena within a nanophotonic waveguide [7,8]. The electric field intensity variation of the interference pattern yielded by the interaction between the incident light and the guided mode coupled into the waveguide produces varying photoemission yields creating contrast in PEEM image. The guided modes cannot be excited simply by …

Photoemission Electron Microscopy For Direct Observation Of Photonic And Plasmonic Phenomena, Theodore Stenmark

Dissertations and Theses

Photoemission electron microscopy (PEEM) is a high-resolution microscopy technique that collects photoemitted electrons from the sample surface to form an image. PEEM offers a non-scanning imaging method with a spatial resolution in the range of 5-100nm by combining the advantages of light excitation and electron imaging. Our work looks at PEEM as an analysis tool for photonic and plasmonic phenomena. Photonic wave guiding structures exhibiting a strong dispersion relation have attracted considerable attention for applications in integrated optics, communications and sensing devices. Line defects in a photonic crystal (PC) slab offer a highly efficient way to create light with group …

Complex Fluid Dynamics: Chemo-Hydrodynamics Driven By Autocatalytic Reaction Fronts, Matthew Walter Eskew

Dissertations and Theses

Chemo-hydrodynamics generated from reaction-diffusion-convection processes of autocatalytic chemical systems are extensively studied for their applications in modeling complex systems. Compared to the more extensively studied autocatalytic systems, chlorite-tetrathionate and chlorite-trithionate, the chlorite-thiourea systems is relatively unexplored. Compared to the two previous systems, chlorite-thiourea has more straightforward chemical kinetics. To narrow the gap between chlorite-thiourea and the other systems a combination of experimental study and numerical simulation were employed to quantify this system.

Compared to established literature, experiments were performed at five orders of magnitude lower concentration of indicator, minimizing confounding effects of indicator on hydrodynamic motion. To accurately image the …

Investigation Of Prussian Blue Analogues As Cathode Materials For Next Generation Batteries, Neal Walters Kuperman

Dissertations and Theses

Since the beginning of the industrial revolution, the average global temperature has risen about 1 °C due increases in anthropogenic greenhouse gases emitted into the atmosphere. Of all human produced greenhouse gases, carbon dioxide is the most prevalent, with the production of electricity from fossil fuels being the major contributor.

Solar and wind power are promising net zero emission energy sources but only accounted for ~5% of global electricity generation in 2016. The most significant hurdle hindering their widespread adoption is the intermittent nature of the electricity generation. To overcome this limitation, significant resources need to be put into the …

Investigation Of Magnetism In Transition Metal Chalcogenide Thin Films, Michael Adventure Hopkins

Dissertations and Theses

Layered two dimensional films have been a topic of interest in the materials science community driven by the intriguing properties demonstrated in graphene. Tunable layer dependent electrical and magnetic properties have been shown in these materials and the ability to grow in the hexagonal phase provides opportunities to grow isostructural stacked heterostructures. In this investigation, cobalt selenide (CoSe) and nickel selenide (NiSe) were grown in the hexagonal phase, which consist of central metal atoms that are natively ferromagnetic in bulk, hence providing the potential for interesting magnetic phases in thin film arrangements as well. These structures may play a role …

Measurements Of N₂O And Sf₆ Mole Fraction And N₂O Isotopic Composition Between 1978 And 1997 In Archived Air Samples From Cape Meares, Oregon, Terry Clinton Rolfe

Dissertations and Theses

Nitrous oxide (N₂O) is the third most important greenhouse gas (GHG) behind carbon dioxide (CO₂) and methane (CH₄). Sulfur hexafluoride (SF₆) does not add significantly to climate forcing by itself due to the low concentration in the atmosphere; however, it is one of the most powerful GHG known. Measurements of atmospheric N₂O made prior to mid-1990 have larger uncertainties than later periods due to advancements made in gas chromatography (GC) methods. Few atmospheric SF₆ measurements pre-1990 exist, especially in the northern hemisphere. Archived samples may be analyzed using updated …

Sensors And Portable Instruments For Postharvest Agriculture, Ryan M. Lerud

Dissertations and Theses

The sensing needs for the fresh produce industry can be split into two primary stages: during maturation in the field, also referred to as Precision Farming, and during storage and transport of the produce, or Postharvest Storage. This work seeks to improve the accuracy and reliability of commercially available electrochemical and spectroscopic sensors tailored to the sensing needs of the fresh produce industry. For electrochemical sensing, this study proposes the use of an inline filter to remove polar organic compounds, which can interfere with the readings of a platinum-based electrochemical sensor. A 50% improvement in measurement accuracy was achieved when …

Capillary Migration Of Large Confined Drops In Non-Wetting Wedges, Logan John Torres

Dissertations and Theses

When confined within containers or conduits, drops and bubbles migrate to regions of minimum energy by the combined effects of surface tension, surface wetting, system geometry, and initial conditions. Such capillary phenomena are exploited for passive phase separation operations in micro-fluidic devices on earth and macro-fluidic devices aboard spacecraft. Our study focuses on the migration and ejection of large inertial-capillary drops confined between tilted planar hydrophobic substrates. In our experiments, the brief nearly weightless environment of a drop tower allows for the study of such capillary dominated behavior for up to 10 mL water drops with migration velocities up to …

Localized Photoemission In Triangular Gold Antennas, Christopher M. Scheffler

Dissertations and Theses

With the development of ultra-fast laser technology, several new imaging techniques have pushed optical resolution past the diffraction limit for traditional light-based optics. Advancements in lithography have enabled the straightforward creation of micron- and nanometer-sized optical devices. Exposing metal-dielectric structures to light can result in surface plasmon excitation and propagation along the transition interface, creating a surface plasmon polariton (SPP) response. Varying the materials or geometry of the structures, the plasmonic response can be tailored for a wide range of applications.

Photoemission electron microscopy (PEEM) has been used to image excitations in micron-sized plasmonic devices. With PEEM, optical responses can …

Jet Rebound From Hydrophobic Substrates In Microgravity, Karl Jeffrey Theodore Cardin

Dissertations and Theses

We experimentally investigate the phenomena of large jet rebound, a mode of fluid transfer following oblique jet impacts on hydrophobic substrates. We initially seek to describe the jet rebound regimes in tests conducted in the weightless environment of a drop tower. A parametric study reveals the dependence of the flow structure on the relevant dimensionless groups such as Reynolds number and Weber number defined on the velocity component perpendicular to the substrate. We show that significantly larger diameter jets behave similarly as much smaller jets demonstrated during previous terrestrial investigations is some parameter ranges while the flow is fundamentally different …

Dc-Rts Noise: Observation And Analysis, Benjamin William Hendrickson

Dissertations and Theses

Dark current random telegraph signal (DC-RTS) is a physical phenomenon that effects the performance of solid state image sensors. Identified by meta-stable stochastic switching between two or more dark current levels, DC-RTS is an emerging concern for device scientists and manufacturers as a limiting noise source. Observed and studied in both charge coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) image sensors, the metastable defects inside the device structure that give rise to this switching phenomenon are known to be derived from radiation damage. An examination of the relationship between high energy photon damage and these RTS defects is presented and …

Shear-Force Acoustic Near-Field Microscopy And Its Implementation In The Study Of Confined Mesoscopic Fluids, Theodore Alex Brockman

Dissertations and Theses

The recently developed Shear-Force Acoustic Near-Field Microscope (SANM) is used to investigate the viscoelastic properties of a mesoscopic fluid layer confined between two trapping boundaries, one being a stationary substrate and the other the apex of a laterally oscillating tapered probe. Hardware improvements and evaluation of the SANM-probe robustness will be a major focus of this thesis. The investigation first discusses characterization and recent developments made to the microscope, including: modifications to the sensor head, conditioning of the Nano positioners electrical drive signal, and the assessment of the probe against eventual plastic deformation or compliance against interactions with samples (the …

Using Strong Laser Fields To Produce Antihydrogen Ions, Christopher Michael Keating

Dissertations and Theses

We provide estimates of both cross section and rate for the stimulated attachment of a second positron into the (1s^{2 1}S^e) state of the H+ ion using Ohmura and Ohmura's (1960 Phys. Rev. 118 154) effective range theory, Reiss's strong field approximation (1980 Phys. Rev. A 22, 1786), and the principle of detailed balancing. Our motivation for producing H+ ion include its potential to be used as an intermediate state in bringing antihydrogen to ultra-cold (sub-mK) temperatures required for a variety of studies, which include both spectroscopy and the probing of the gravitational interaction of …

Investigation Of The Acoustic Response Of A Confined Mesoscopic Water Film Utilizing A Combined Atomic Force Microscope And Shear Force Microscope Technique, Monte Allen Kozell

Dissertations and Theses

An atomic force microscopy beam-like cantilever is combined with an electrical tuning fork to form a shear force probe that is capable of generating an acoustic response from the mesoscopic water layer under ambient conditions while simultaneously monitoring force applied in the normal direction and the electrical response of the tuning fork shear force probe. Two shear force probes were designed and fabricated. A gallium ion beam was used to deposit carbon as a probe material. The carbon probe material was characterized using energy dispersive x-ray spectroscopy and scanning transmission electron microscopy. The probes were experimentally validated by demonstrating the …

Electro-Drop Bouncing In Low-Gravity, Erin Stivers Schmidt

Dissertations and Theses

We investigate the dynamics of spontaneous jumps of water drops from electrically charged superhydrophobic dielectric substrates during a sudden step reduction in gravity level. In the brief free-fall environment of a drop tower, with a non-homogeneous external electric field arising due to dielectric surface charges (with surface potentials 0.4-1.8 kV), body forces acting on the jumped drops are primarily supplied by polarization stress and Coulombic attraction instead of gravity. This electric body force leads to a drop bouncing behavior similar to well-known phenomena in 1-g₀, though occurring for much larger drops (~0.5 mL). We show a simple …

Dark Current Rts-Noise In Silicon Image Sensors, Benjamin William Hendrickson

Dissertations and Theses

Random Telegraph Signal (RTS) noise is a random noise source defined by discrete and metastable changes in the magnitude of a signal. Though observed in a variety of physical processes, RTS is of particular interest to image sensor fabrication where progress in the suppression of other noise sources has elevated its noise contribution to the point of approaching the limiting noise source in scientific applications.

There have been two basic physical sources of RTS noise reported in image sensors. The first involves a charge trap in the oxide layer of the source follower in a CMOS image sensor. The capture …

Wind Energy And Wind-Energy-Inspired Turbulent Wakes: Modulation Of Structures, Mechanisms And Flow Regimes, Elizabeth H. Camp

Dissertations and Theses

The interaction of turbulent wakes with one another and with the adjacent fluid directly impacts the generation of electricity in wind turbine arrays. Computational modeling is well suited to the repeated iterations of data generation that may be required to inform understanding of the function of wind farms as well as to develop control schemes for plant function. In order to perform such computational studies, a simplified model of the turbine must be implemented. One of the most computationally efficient parametrizations of the blade utilizes a stationary disk which has a prescribed drag and produces a wake. However, since accurate …

Clock Jitter In Communication Systems, Andrew Wayne Martwick

Dissertations and Theses

For reliable digital communication between devices, the sources that contribute to data sampling errors must be properly modeled and understood. Clock jitter is one such error source occurring during data transfer between integrated circuits. Clock jitter is a noise source in a communication link similar to electrical noise, but is a time domain noise variable affecting many different parts of the sampling process. Presented in this dissertation, the clock jitter effect on sampling is modeled for communication systems with the degree of accuracy needed for modern high speed data communication. The models developed and presented here have been used to …