Digital Commons Network^™

Analysis Of A Magnetically Enhanced Microwave Powered Split-Ring Resonator Plasma Source For Micropropulsion, Andrew Walsten

Dissertations

This work focuses on better understanding split-ring resonators (SRRs) as plasma devices and exploring their use as a plasma source in a two-stage Hall thruster. This is done by first studying the effect of a single versus a coupled SRR on plasma production. Through the use of simulations in ANSYS HFSS and Langmuir probe measurements, it is found that coupled SRRs result in a more uniform plasma at higher pressures due to the introduction of a secondary ionization point, and the electromagnetic coupling resulting in a slightly stronger electric field being produced at the primary gap. Experiments were also done …

Adaptive Discrete Time Sliding Mode Control For N-Th Order Flapping-Wing Micro Air Vehicles With Unknown Parameters, Joshua Hill

Dissertations

Small aerial systems, such as nature-inspired flapping-wing micro aerial vehicles (FWMAV), operate in uncertain and dynamic environments that are subject to unknown disturbances, e.g., wind gusts. With the proliferation of inexpensive system components, extensive research has been dedicated to improving the operation of these FWMAVS, both in civilian and military applications. Given dynamic environments and variations in individual components, sliding mode control has become an increasingly applied control method for FWMAV. Its robustness proves invaluable to ensure stability in the presence of uncertain system parameters and environmental disturbances. This dissertation presents three discrete-time sliding mode control (DSMC) methods and applies …

Leading From The Middle: Arts Administrators' Beliefs About The Impact Of Arts Education On High-Needs Students, Sofia Fojas

Dissertations

Research on arts education notes the positive impact of arts education on educational outcomes for students, particularly students of color, students in poverty, and students needing additional academic support. Students living in low-income communities receive different educational opportunities than those in high-wealth districts. This disparity is especially true for highly mobile and high-needs students of color. Arts education has made positive differences in student outcomes. This qualitative study examined the beliefs of county arts leads, leaders in the middle, situated between the California Department of Education and their local school districts, and how they can be empowered to be change …

Development Of A Continuum Damage Constitutive Model And Simulation For Brittle Materials In Space Infrastructure Application, Luis Eduardo Deganis

Dissertations

The purpose of this work is to develop a continuum damage constitutive material model and apply it to structural response characterization of brittle materials for in-situ construction of space infrastructure. This research improves and expands the utility of the physics-based dominant crack algorithm (DCA) model in order to account for very low-strain rate phenomena in plain concrete structures. The DCA model is strain-rate dependent and has been effectively utilized for highly dynamic phenomena. The model has a strong basis in micromechanics and is able to capture the strain-softening response of brittle materials. The newly developed constitutive model can be easily …

A New, Intuitive Method For The Design And Analysis Of Multi-Pass Cavities, Adam S. Mansor

Dissertations

This dissertation develops a new analytical approach for designing and analyzing multi-pass cavities like the Herriott cell employing the graphical yӯ diagram approach. The new technique can be deployed in spectroscopy absorption detection, femtoseconds laser cavities, or any off -axis spherical mirror interferometers applications. Such a system can be uniquely designed and evaluated by entering a few parameters that define the required physics for the cell, the packaging size limits for the system and the probe beam size, plus two user selected parameters. The existing design method, developed by Herriott, is discussed and then the yӯ diagram method is presented …

Application Of A New Scale-Resolving Turbulence Model To Supersonic Retropropulsion Flows With Chemistry, Gabriel C. Nastac

Dissertations

Turbulent compressible flows are ubiquitous in many engineering applications of flight and propulsion. Computational fluid dynamics simulations are commonly performed to analyze these flows. Scale-resolving turbulence models inherently better capture various flow phenomena, including separation and mixing, as well as enable predictions of fluctuations, which can be critical for design compared to traditional steady-state turbulence models. In this work, new scale-resolving blended Partially-Averaged Navier-Stokes (BPANS) turbulence models are developed to account for compressibility effects and are employed to efficiently simulate turbulent compressible flows. Specifically, supersonic retropropulsion flows are investigated. Supersonic retropropulsion is a key technology for next-generation rockets. The new …

Modeling On-Demand Meal Delivery With Multi-Modal Couriers: Considering Both Certain And Uncertain Orders, Zohre Noormohamadzade

Dissertations

The on-demand meal delivery sector has experienced significant transformation, reshaping consumer dining habits and operational practices in the food delivery industry. This dissertation explores the changing landscape of on-demand meal delivery services through two interrelated topics, namely Modeling On-demand Meal Delivery in a Link-Node Based stochastic User Equilibrium with certain demand and Modeling On-demand Meal Delivery with different vehicle modes and uncertain demand, aiming to address the evolving challenges and opportunities in this dynamic industry. The rest of this dissertation is composed of two parts. The first part addresses the integration of internal restaurant couriers and third-party platform couriers to …

Thermal Processing Of Al-Zn-Cu-Mg-Zr Laser Powder Bed Fusion Material For Increased Ductility, Jeffrey S. Gaddes

Dissertations

Although the use of wrought high strength aluminum alloys is prevalent throughout aerospace systems, they often have long lead times and become difficult to source throughout the long lifecycle of aviation systems. Laser Powder Bed Fusion (LPBF) Additive Manufacturing (AM) provides opportunity to directly manufacture wrought equivalent aluminum products without forging supply chain challenges. If these LBPF components are made with the same aluminum material system with similar strength and ductility, they can be a direct replacement for traditionally manufactured components. However, existing 7xxx aluminum alloys are prone to cracking during fusion welding and therefore are not readily produced through …

Context-Aware Machine Learning For Low-Burden Brain-Computer Interfaces, T. Warren De Wit

Dissertations

We are interested in the utility that artificially intelligent mobile systems such as drones offer to personnel in fast-paced, high-stakes situations such as disaster relief that demand real-time situational awareness. Ideally, these assistive systems place no additional cognitive or physical burden on their user; rather, they should respond to the user's intent with minimal physical or cognitive impact. Artificial intelligence (AI) and machine learning (ML) are already widely applied in both brain-computer interfaces (BCI) and drone navigation. We propose leveraging the robust computer-vision based AI that exists on modern drones to use objects as waypoints and fly a reconnaissance drone …

Queer A.F.: Queer Educators In Affinity Family Personal-Professional Development, James Egisto Aguirre

Dissertations

Scholarship shows that affinity groups are spaces of support, learning, and healthy career development that are responsive to the needs of a particular marginalized community. The concept of heteroprofessionalism– the implicit or explicit pressure/s queer educators feel to fit within the proverbial cisgender/heterosexual (cishet) box–is but one of a myriad issues and pressures affect queer educators across the nation. This study brings queer educators from one school district together to unpack their experiences through the lens of heteroprofessionalism. Via queer theory, qualitative, written response data was collected and subsequently analyzed in three, half-day sessions offered in spring 2024. Thirty participants …

Addressing Equity Gaps In Stem: A Self-Study, Prabhjeet Kaur Brar

Dissertations

The Hispanic/Latinx population is increasing nationwide and in the state of California; however, the Hispanic/Latinx population remains underrepresented in STEM professions contributing to a lack of diversity in STEM. To increase the academic success of the Hispanic/Latinx student population in STEM majors, high leverage research-based teaching strategies through the lens of historically responsive literacy were applied and examined throughout this research. The purpose of this mixed-methods self-study was to examine the impact of research-based effective strategies/high leverage practices on Latinx students’ success rates in my introductory biology classrooms. The study focused on two biology course sections with a laboratory. Each …

Employees' Perception Of The Management Of The Covid-19 Crisis At Najran University, Saudi Arabia, Noora Nasser Alsuhaibani

Dissertations

Problem

During the COVID-19 crisis, particularly in the context of Saudi education, the ability to physically attend schools and colleges was greatly hindered due to the widespread transmission of the virus and the resulting obstacles. The issues necessitated the use of crisis management strategies. Some Saudi universities are capable of implementing an organized plan both before to and during crisis management, whereas others lack this competence. This is a substantial problem. Several universities in Saudi Arabia effectively managed the COVID-19 epidemic, whereas others did not. Furthermore, prior studies on crisis management indicate that administrators exhibit diverse responses. By participating in …

Reporting And Addressing Sexual Harassment At Four Institutions Of Higher Learning In Zambia: A Quantitative Study Of Related Attitudes And Perceptions, Earlymay Chibende

Dissertations

Problem

Sexual harassment is a social ill that exists across nations, socio-economic backgrounds, races, nationality, ethnicity, age groups, and sex. Although both male and female members of society experience sexual harassment, research shows that a greater percentage of sexual harassment victims are women (Whitley & Page, 2015; CharterJee, 2018). A comparison of the prevalence of sexual harassment at workplaces and educational institutions shows that sexual harassment is more widespread at institutions of learning than at workplaces. Research on the prevalence of attitudes and or perceptions toward sexual harassment in institutions of higher learning shows that between 10%- 68% of female …

A Fully Automated Global Post-Hoc Method Based On Abstract Argumentation For Explainable Artificial Intelligence And Its Application On Fully Connected Dense Deep Neural Networks, Giulia Vilone

Dissertations

Explainable Artificial Intelligence (XAI) has rapidly grown in the past decade due to the prevalence of machine learning, especially deep learning, in fields like healthcare and finance. While these models excel in accuracy, their complexity hampers transparency and interpretability. Ensuring understandable explanations for AI predictions fosters trust, prevents errors, complies with regulations, and enhances model refinement. The research project outlined in this thesis unfolds in phases. It commences with a comprehensive review of existing XAI studies, contributing to the field’s knowledge by proposing a taxonomy that organises theories and notions related to explainability, the evaluation approaches for XAI methods, and …

Depressurization Characteristics Of Steam-Based Reciprocating Vacuum Pump, Hongling Deng

Dissertations

This dissertation introduces a novel vacuum technology that leverages low-pressure saturated steam and cooling-controlled condensation, offering an efficient way to utilize low-grade thermal energy sources like waste heat, steam, or solar energy. At the heart of this technology is a unique duo-chamber vacuum pump system, featuring a reciprocating piston and a heat-conductive wall, designed to generate a vacuum through steam-condensation and cooling processes.

The core of this research lies in developing and validating mechanistic models for the steam-condensation depressurization process, a complex phenomenon involving phase change and transport mechanisms. Prior to this work, these mechanisms were not sufficiently modeled or …

5g New Radio Access And Core Network Slicing For Next-Generation Network Services And Management, Abdullah Ridwan Hossain

Dissertations

In recent years, fifth-generation New Radio (5G NR) has attracted much attention owing to its potential in enhancing mobile access networks and enabling better support for heterogeneous services and applications. Network slicing has garnered substantial focus as it promises to offer a higher degree of isolation between subscribers with diverse quality-of-service requirements. Integrating 5G NR technologies, specifically the mmWave waveform and numerology schemes, with network slicing can unlock unparalleled performance so crucial to meeting the demands of high throughput and sub-millisecond latency constraints.

While conceding that optimizing next-generation access network performance is extremely important, it needs to be acknowledged that …

Model-Based Deep Autoencoders For Clustering Single-Cell Rna Sequencing Data With Side Information, Xiang Lin

Dissertations

Clustering analysis has been conducted extensively in single-cell RNA sequencing (scRNA-seq) studies. scRNA-seq can profile tens of thousands of genes' activities within a single cell. Thousands or tens of thousands of cells can be captured simultaneously in a typical scRNA-seq experiment. Biologists would like to cluster these cells for exploring and elucidating cell types or subtypes. Numerous methods have been designed for clustering scRNA-seq data. Yet, single-cell technologies develop so fast in the past few years that those existing methods do not catch up with these rapid changes and fail to fully fulfil their potential. For instance, besides profiling transcription …

Novel Photobase Generators For Photoinduced Polymerization And Ph Regulation, Shupei Yu

Dissertations

Photochemistry encompasses the investigation of chemical processes instigated by light absorption. As important branches of photochemistry, photosensitive and optical materials have attracted extensive research interests in both academia and industry. Photosensitive and optical materials are composed of polymers / small molecules with photo-responsive properties. These materials not only can absorb light in the desired energy spectrum, but also exhibit chemical / physical reactions, which can be applied to different fields such as photoredox, photo-heat, phototherapy, solar cells, diodes, etc. Among them, photobase generators (PBGs) are a series of photosensitive compounds, which absorb the incident light, then release the basic species …

Assessing The Feasibility And Mechanism Of Destructive Removal Of Per- And Polyfluoroalkyl Substances (Pfas) From Water, Kaushik Vinaykumar Londhe

Dissertations

One of the most pertinent challenges faced by the drinking water community is the widespread contamination of per- and polyfluoroalkyl substances (PFAS). These anthropogenic chemicals have been ubiquitously used in everyday products such as carpets, stain repellents, dyes, shampoos, non-stick cookware as well as in aqueous firefighting foams. PFAS are linked with adverse health effects in humans such as thyroid disease, obesity, immunological and reproductive disorders and linked to cancer in adults and low birth weight and developmental defects in infants.

Conventional water treatment technologies have proven to be largely ineffective in PFAS remediation, due to their extreme stability and …

Distributed Intelligence: Exploring Federated Paradigms Across Computing And Networking On The Edge, Yang Deng

Dissertations

Computer Graphics (CG) revolves around virtual content creation using computational methods, spanning applications from games to visual effects. Typically, the creation of CG content is led by expert practitioners who guide computational algorithms towards satisfactory results. Thus, creating CG content often requires manual iterations encompassing algorithm design, parameter tuning, and aesthetic feedback. This work investigates how to leverage crowd-sourcing to streamline such creation processes, focusing on animation and simulation. In animation, a novel crowd-sourcing framework is proposed for combat animation, enabling users to analyze motion similarities, and retrieve matching motions using novel crowd-sourced motion features. Such features enable quantifying previously …

Quantifying Non-Muscle Myosin 2 Filament Dynamics, Melissa Ann Quintanilla

Dissertations

Non-muscle myosin 2 is a motor protein that, when assembled into filaments, works on the actin cytoskeleton to produce contractile forces within cells. This type of myosin dynamically assembles within cells to exert forces necessary for a wide variety of functions including cell division, migration, and multicellular movement. The ability to dynamically assemble contractile networks, and the ability to control the assembly and placement of these myosin filaments in both space and time, is therefore required throughout cell physiology. We used a suite of dynamic, quantitative imaging approaches to identify deterministic factors that drive myosin filament appearance and amplification as …

Revitalizing The Middle-Skill Talent Pipeline: Exploring The Decision To Enroll In A Postsecondary Career And Technical Education Program, Felicia Hall

Dissertations

A workforce shortage exists within occupations requiring educational training beyond high school but less than a 4-year degree, known as middle-skill occupations. Career and Technical Education (CTE) programs offered at community colleges throughout the United States equip graduates at the middle-skill level. Although affordable CTE programs are readily available, little is currently known about what makes students consider and ultimately enroll in postsecondary CTE programs. This qualitative phenomenological study investigated the decision to enroll in a postsecondary CTE program as experienced by current students at a North Alabama community college to identify enablers and barriers faced during the decision to …

Thermally Rearranging Polyimide Networks For High-Temperature Applications, William Guzman

Dissertations

High-performance polymers can retain functional properties when exposed to long-term or short-term durations of harsh conditions, such as mechanical action, at elevated temperatures (>177 °C). A mixture of intramolecular and intermolecular forces of and between polymer chains provide excellent property retention at elevated temperatures. Specifically, the highly aromatic nature of high-performance polymer backbones provides outstanding thermal stability, which is typically attributed to π-π stacking. However, the interrelationship between thermal stability and high aromaticity creates a challenging structure-processing relationship paradigm, which causes poor polymer processability in most high-performance polymers. Herein, it was demonstrated that rationally designing a crosslinking phenylethynyl imide …

An Analysis Of The Factors That Affect Self-Employment, Stefani Broome

Dissertations

This dissertation research identifies the factors that affect self-employment in a three-essay format. Essay one builds a foundation on analyzing the determinants that affect self-employment in the United States through a country-level time-series analysis. Essay two includes a time-series panel analysis and comparative analysis between the United States and United Kingdom by expanding on Meager’s (1992) study of the relationship between unemployment and self-employment. This analysis focuses on the United Kingdom, an outlier in Meager’s (1992) study, which included a structural change to the motivation to enter self-employment after an economic shock in the late 1970s. Essay three utilizes a …

Using Afm-Ir To Study Nanoscopic Phase Behavior Of Polymer Blends And Photovoltaic Bulk Heterojunctions, Nathaniel L. Prine

Dissertations

Conjugated polymers (CPs) and polymer blends harbor the potential for high-performance organic solar cells (OSCs) due to their short energy payback time, low cost, solution processability, lightweight attributes, and flexibility. However, OSCs suffer from poor thermal stability compared to their inorganic equivalents. This study explores the thermal instability of OSCs, focusing on phase separation of the photoactive layer under heat, resulting in morphology changes and degradation of power conversion efficiency (PCE). Utilizing atomic-force microscopy coupled with infrared spectroscopy (AFM-IR) and differential scanning calorimetry (DSC), we delve into thermal stability-morphology relationships to devise strategies to improve OSC blend durability under thermal …

Timeseries Forecasting Of U.S. Housing Price Index Using Machine Learning And Deep Learning Models, Krishna Chaitanya Nunna

Dissertations

Time series forecasting is a promising technique for various applications which predicts future values or patterns by taking historical data as base. Forecasting future trends is very beneficial for different industries to make valuable decisions and strategies. One such industry is housing market; it has biggest influence on U.S. economy. Housing price index (HPI) is a one of the crucial economic indices published by various government funded and private agency to benefit several industries and individuals for better analysis of future trends of housing market.

Several factors influence the HPI, economical, geographical, and demographic features. Development of traditional time series …

Heterotypic Interaction Of Α-Synuclein And Tdp-43 In Neurodegenerative Diseases, Shailendra Dhakal

Dissertations

Amyloid aggregates of specific proteins form important pathological hallmarks in many neurodegenerative diseases, defining neuronal degeneration and disease onset. Recently, increasing numbers of patients show co-morbidities and exhibit clinical and pathological overlaps between multiple neurodegenerative diseases including α-synucleinopathies and TDP-43 proteinopathies. These overlaps are often accompanied by co-localization of α-synuclein (αS) and TDP-43 enhancing the possibility of direct interactions to generate heterotypic amyloids with distinct cellular consequences. To understand this, we investigate the interaction of α-synuclein (αS) and prion-like domain of TDP-43 (TDP-43 PrLD) in both homogenous and inhomogeneous phases. Firstly, we show that monomeric TDP-43 PrLD and αS interact …

Intelpvt And Opt-Stvit: Advances In Vision Transformers For Object Detection, Classification And Video Recognition, Divya Nimma

Dissertations

Since the advent of Transformers, followed by Vision Transformers (ViTs), great success has been achieved by researchers in the field of computer vision and object detection. The difficult mechanism of splitting images into fixed patches posed a serious challenge in this arena and resulted in the loss of useful information at the time of object detection and classification. We propose an innovative Intelligent-based patching mechanism to overcome the challenges and integrate it seamlessly into the conventional Patch-based ViT framework. The proposed method enables the utilization of patches with flexible sizes to capture and retain essential semantic content from input images, …

An Examination Of Influential Factors Of Academic Dishonesty And Ethical Decision-Making Among Community College Nursing Students, Roshelle L. Lemon-Howard

Dissertations

Academic dishonesty remains a pervasive, multi-discipline dilemma which has been reported as having the propensity of resulting in longstanding consequences beyond academic settings. Previous research has suggested that students who participate in dishonest behaviors while attending institutions of higher education have greater tendencies to engage in dishonest and unethical behaviors within professional settings. Notably, schools of nursing are not exempt from academic dishonesty and the ramifications that have been associated with such misconduct. Although academic dishonesty has been examined from various perspectives, and in numerous contexts, current studies that compare relationships between peer and faculty influences on academic dishonesty and …

Biophysical Factors Affecting Habitat Suitability For Crassostrea Virginica, Jason D. Tilley

Dissertations

Oyster reefs provide a variety of important ecosystem services. However, the mortality rate of eastern oyster, Crassostrea virginica, the dominant species that produces oyster reefs in the northern Gulf of Mexico, is increasing at an alarming rate due to a variety of abiotic and biological factors. I examined how biophysical factors, including the less-studied fatty acid profiles of the suspended particulate matter on which oysters feed, influenced morphometric condition of C. virginica.

I sampled suspended particulate matter (SPM) and oysters in-situ in the western Mississippi Sound, which historically supported the majority of oyster production in Mississippi waters. Sampling …