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An Experimental Investigation Of Liquid Hydrocarbons In A Simulated Titan Environment, Kendra Farnsworth

Graduate Theses and Dissertations

Saturn’s moon, Titan, has surface conditions (89–94 K, 1.5-bar atmosphere) that permit lakes of methane, ethane, and dissolved atmospheric nitrogen. The effects of atmospheric nitrogen on methane-ethane liquid properties is poorly understood, leading to uncertainty in Titan modeling. I address this question by experimentally investigating the physical properties of methane-ethane liquids under a 1.5-bar nitrogen atmosphere in a simulated Titan environmental chamber.

Chapter 1 addresses nitrogen dissolution kinetics in Titan’s liquid hydrocarbons. I found an exponential increase in nitrogen quantity and diffusion coefficients with increasing methane mol%. I find that Titan’s liquids are likely not saturated in nitrogen, with dissolution …

Increasing Female Enrollment In High School Computer Science Education, Zenovia Brown Frazier

Graduate Theses and Dissertations

“Women have played a vital role in the field of computer science and information technology (IT), developing some of the most essential components of modern IT” (Purdue University Global, 2018). Despite their prominence and achievements in these career fields, computer science has experienced a noticeable decline in the representation of females in industry and in programs of study. This is not a phenomenon reserved for the college classroom and/or the world of work, but is a situation present across schools in the P-12 arena, to include ZBF High School. As such, the purpose of this work was to examine the …

Far-Right Extremism In America: A Geospatial Analysis Of Incident Distribution, Meredith Leann Lerma

Graduate Theses and Dissertations

There has been little empirical research on the spatial relationship of violent far-right extremism. Previous studies have only focused on portions of far-right violent incidents, such as homicides, or amalgamated all far-right extremist activity, including legal incidents. This study uses data from the Extremist Crime Database (ECDB) and Southern Poverty Law Center (SPLC) in a temporal frame of 2000 to 2018 to test the relationship of violent incidents against geographic and social factors. The goal is to explore the relationships between macro-level factors and violent far-right extremist incident. The research determines that the presence of hate groups, higher immigrant populations, …

Earthworm Dynamics In Tallgrass Prairies In The Ozark Highlands Region Of Northwest Arkansas, Carlee Hensley

Graduate Theses and Dissertations

Tallgrass prairie was a historic and is presently a unique and endangered natural ecosystem throughout the Ozark Highlands region in the mid-southern United States. Tallgrass prairies have been disturbed for agricultural production and/or urban expansion; thus, as a result, efforts have been undertaken to reclaim areas previously used for agricultural production to mitigate the loss of tallgrass prairies. Limited research exists on earthworm dynamics in mounded tallgrass prairies or prairie restorations, particularly in the Ozark Highlands region of northwest Arkansas. The objectives of this study were to i) evaluate the effects of soil moisture regime (SMR; aquic and udic), landscape …

Developing A High-Throughput Method To Screen Soybean Germplasm For Hypoxia Tolerance In Hydroponic Systems, Derrick Harrison

Graduate Theses and Dissertations

Soybean [Glycine max (Merr.)], the second most planted crop in the United States, is sensitive to field flooding due to depletion of oxygen and accumulation of CO2 in the rhizosphere. There is a need to breed cultivars that are adapted to areas prone to flooding, but field evaluations in the U.S. are limited because of time (one generation per year) and availability of resources (impermeable soils, irrigation, equipment to build levees). The purpose of this study was to develop and execute a protocol of germplasm screening for hypoxia tolerance using hydroponics in a controlled greenhouse environment. Germination rates and vigor …

Relationship Marketing And Intercollegiate Sport Promotion, Alison Fridley

Graduate Theses and Dissertations

The first article, a case study on a NCAA Division I Power Five university in the southeastern United States, employed a case study framework, explored target markets and exposure techniques through both the planned behavior theory and social identity theory theoretical lenses. This study aimed to better understand how university students and booster club members identify as a social group. The data emerged into four distinct themes, including communication, social interaction, connection, and hospitality. The findings suggested booster club members are primary fans and help the team generate fan interest. The importance of sociability was clear and the implications for …

Visualizing Interdisciplinary Collaborations Within Exercise Science: A Pilot Study, Elizabeth Bjornsen

Graduate Theses and Dissertations

Exercise science is a growing field with sub-disciplines exploring various aspects of physical activity. Diverse perspectives allow the field to answer complex research questions, but little is known about the collaborative nature of exercise science today. Research practices have implications on undergraduate curriculum, likely incorporating experiential knowledge into course subject matter and providing diverse experiences for students entering the workforce. Therefore, the purpose of the pilot study is to visualize and quantify interdisciplinary collaborations within exercise science. Journal citation analysis and an adaptation of social networking theory were utilized to examine collaborative practices of exercise science faculty at the University …

The Attracting Intelligent Minds Conference: An Assessment Of Graduate Diversity Recruitment, Alfred T. Dowe

Graduate Theses and Dissertations

Graduate student recruitment is one of the most important factors in growing university enrollment. Unlike undergraduate recruitment, graduate recruitment is a coordinated effort facilitated between graduate faculty and program coordinators and graduate recruiters who often work outside of the department. An essential element in graduate recruitment is the effectiveness with which underrepresented minorities are identified and recruited. Graduate schools are commonly using initiatives known as intervention strategies to help enhance their traditional recruitment strategies and campus visitation programs have become a popular recruitment tool within those strategies.

Since the 1990’s, the University of Arkansas (UA) has employed various intervention strategies …

A Study Of The Thermodynamics Of Small Systems And Phase Transition In Bulk Square Well-Hard Disk Binary Mixture, Gulce Kalyoncu

Graduate Theses and Dissertations

Under the umbrella of statistical mechanics and particle-based simulations, two distinct problems have been discussed in this study. The first part included systems of finite clusters of three and 13 particles, where the particles are interacting via Lennard Jones potential. A machine learning technique, Diffusion Maps (DMap), has been employed to the large datasets of thermodynamically small systems from Monte Carlo simulations in order to identify the structural and energetic changes in these systems. DMap suggests at most three dimensions are required to describe and identify the systems with 9 (N = 3) and 39 (N = 13) dimensions. At …

Towards A Cyber-Physical Manufacturing Cloud Through Operable Digital Twins And Virtual Production Lines, Md Rakib Shahriar

Graduate Theses and Dissertations

In last decade, the paradigm of Cyber-Physical Systems (CPS) has integrated industrial manufacturing systems with Cloud Computing technologies for Cloud Manufacturing. Up to 2015, there were many CPS-based manufacturing systems that collected real-time machining data to perform remote monitoring, prognostics and health management, and predictive maintenance. However, these CPS-integrated and network ready machines were not directly connected to the elements of Cloud Manufacturing and required human-in-the-loop. Addressing this gap, we introduced a new paradigm of Cyber-Physical Manufacturing Cloud (CPMC) that bridges a gap between physical machines and virtual space in 2017. CPMC virtualizes machine tools in cloud through web services …

Factors Influencing The Adoption Of Immersive Virtual Reality For Individuals With Autism Spectrum Disorder: Parents Perceptions, Fahad Abdeen

Graduate Theses and Dissertations

The purpose of this qualitative study was to identify factors that affect the adoption of a spherical video virtual reality (SVVR) mobile application among parents of adults with Autism Spectrum Disorder (ASD). The study used the diffusion of innovation theory by Rogers (2003) as a framework to explore parents’ perceptions of an SVVR transportation model designed to improve the quality of life of adults with ASD. In addition, the study sought to learn what might increase adoption of VR technology among other parents of individuals with ASD and what life skills that might be addressed using VR technology in the …

Synthesis And Application Of Ceramic Paste For High-Temperature Electronic Packaging, Ardalan Nasiri

Graduate Theses and Dissertations

This dissertation research focused on the synthesis and application of ceramic paste for high-temperature applications. An alumina paste material comprising aluminum dihydric phosphate and alumina powder was developed for high-temperature electronic packaging. Nano aluminum nitride and nano-silica powders were embedded to promote the paste curing process, limit the grain growth, and increase its bond shear strength. The chip-to-substrate bond strength was enhanced and met the MIL-STD requirements for die-attach assembly. Its encapsulation property was improved with fewer cracks compared to similar commercial ceramic encapsulants. The die-attach material and encapsulation properties tested at 500°C showed no defect or additional cracks. Thermal …

Elucidating Collagen Degradation Synergy Between Col G And Col H From Hathewaya (Clostridium) Histolytica And Identifying Novel Structural Features In Hpt And Rec Domains From Vars Histidine Kinase In V. Alginolyticus, Perry Caviness

Graduate Theses and Dissertations

In this research the mechanisms by which Hathewaya (Clostridia) histolytica collagenases are secreted and work together to degrade collagens are investigated. While H. histolytica collagenases Col G and Col H have similar multi-domain structures the difference in number of and orientation of the domains hint that the two target different regions in collagen. Study small angle x-ray scattering (SAXS) was used to give a low-resolution envelope of full-length Col G and Col H and Col G/Col H non-catalytic domains bound to a collagen-like peptide (mini-collagen). SAXS derived envelopes along with structural information was used to tease out the mechanisms by …

Thiophene Derivative Monomers Co-Electropolymerized On Microelectrodes Within Arrays For Tailored Surface Chemistry And Electrochemical Properties, Benjamin J. Jones

Graduate Theses and Dissertations

Potentiodynamic co-electropolymerization of two thiophene derivatives, (2,3-dihydrothieno[3,4-b]dioxin-2-yl)methanol (1) and 4-((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)-methoxy)-4-oxobutanoic acid (2), in aqueous solutions (0.02 M total monomer, 0.05 M sodium dodecyl sulfate (SDS) and 0.1 M LiClO4) on gold microband electrodes in an array was investigated. A modified Steglich esterification reaction between monomer 1 and succinic anhydride produced monomer 2 at 93.6% yield. Seven deposition solutions of the two monomers, defined by mol% of monomer 2 (0, 25, 34, 50, 66, 75, 100) generated seven sets of polymer films by cyclic voltammetry in a specially designed cell to conserve monomer. The onset potential for monomer oxidation and total …

The Emotional Toil Of Paying For College: Lower Socioeconomic Status White Women’S College Experiences, 1880-1920, Heidi A. Jaeckle

Graduate Theses and Dissertations

Typically historical inquiries in higher education have been centered on privileged individuals from wealthier backgrounds who had the opportunity of attending primarily prestigious institutions. The experiences of college women from lower to middle class socioeconomic backgrounds have been for the most part ignored. This dissertation explores how socioeconomic backgrounds shaped the experiences of college women from the late nineteenth century to the early twentieth century, focusing on lower class students. With no universal financial aid program, the majority of these women were from families who could afford to pay tuition. Women from lower socioeconomic backgrounds did attend college, but their …

Rice Fortification By Parboiling In Limited-Water Soaking To Alleviate Mineral And Vitamin Deficiency, Annegret Jannasch

Graduate Theses and Dissertations

Fortification of rice by parboiling is considered a potential alternative to currently available fortification technologies to produce rice with higher mineral and vitamin content significantly contributing to nutrient intake in populations with high prevalence of micronutrient deficiencies. Higher nutrient retention rates and improved sensory characteristics are advantages of fortified parboiled rice compared to fortified rice obtained by currently used fortification technologies including dusting, coating, and extrusion. However, conventional parboiling processes employ excess water that presents an environmental hazard if discarded without treatment. Thus, the objective of this study was to evaluate a limited-water soaking method for the fortification of rice …

Converter- And Module-Level Packaging For High Power Density And High Efficiency Power Conversion, Amol Rajendrakumar Deshpande

Graduate Theses and Dissertations

Advancements in the converter- and module-level packaging will be the key for the development of the emerging high-power, high power-density, high-eciency power conversion applications, such as traction, shipboards, more-electric-aircraft, and locomotive. Wide bandgap (WBG) devices such as silicon carbide (SiC) MOSFET attract much attention in these applications for their fast switching speeds, resulting in low loss and a consequent possibility for high switching frequency to increase the power density. However, for high-current, high power implementations, WBG devices are still available in small die sizes. Multiple SiC devices need to be connected in parallel to replace a large IGBT die. It …

Design And Optimization Of Multichip Gan Module Enabling Improved Switching Performance, Asif Imran Emon

Graduate Theses and Dissertations

Wide bandgap semiconductors (SiC & GaN) due to their enhanced performance and superior material properties compared to traditional silicon power devices have become the ultimate choice for future high-performance power electronics energy conversion. GaN high electron mobility transistor (HEMT) offers very fast switching capability enabling the designer to push switching frequency to the MHz range. Traditional device packaging becomes a limiting factor in fully harnessing the benefits offered by these advanced power devices, and thus, improved and advanced packaging structures are a must to bridge the gap between GaN devices and their applications. A co-design, co-optimization method has been followed …

Conducted Emi Mitigation In Power Converters Using Active Emi Filters, Balaji Narayanasamy

Graduate Theses and Dissertations

Wide bandgap devices enable high power density power converters. Despite the advantages of increased switching frequency, the passive components are still a major bottleneck towards enabling high power density. Among the passive components in the converter, the passive EMI filters are unavoidable to ensure compliance with conducted EMI standards. Active EMI filters help reduce the volume of the passive components and have been around for three decades now. Firstly, this work presents a summary of all the different active EMI filters based on the type of noise-sensing, noise-processing, the type of active circuits used and the type of control methods. …

Towards High Efficiency And High Power Density Converter: System Level Design, Modulation, And Active Emi Filters, Hongwu Peng

Graduate Theses and Dissertations

Power converter exposes strong challenges to its efficiency, power density and reliability. For the grid-connected inverter application, three-level (3-L) T-type neutral-point-clamped (TNPC) inverters has higher efficiency and lower total harmonic distortion (THD) compared to two-level inverter. Hybrid switch concept combines the benefit of both silicon carbide (SiC) MOSFET and Si IGBT. By applying hybrid switch structure in 3-L T-type inverter, the total power density of 3-L TNPC inverter will be higher while the cost will be lower than that of all-SiC 3-L T-type inverter. The hybrid switch based 3-L TNPC inverter also imposes challenge to its modulation and control, a …

Investigation Of The Structural, Electronic, And Thermoelectric Properties Of Mono- Chalcogenides, Aida Sheibani

Graduate Theses and Dissertations

The structural, electronic, and thermoelectric properties of GeTe are studied using density functional theory and Boltzmann transport equations. This material has a rhombohedral crystal structure in ambient temperature with a ferroelectric behavior due to lack of inversion symmetry. This study suggests that the presence of asymmetry in GeTe can lead to an improvement in the thermoelectric properties of this material. In addition, studies on introducing Group III, IV, and V dopants to GeSe show that while these impurities can improve the power factor and decrease the lattice thermal conductivity, they cannot enhance the figure of merit.

Flourishing Through Communicative Language Learning: An Exploration Of University Learners’ Basic Needs, Well-Doing, And Well-Being, William S. Davis

Graduate Theses and Dissertations

In the last 25 years, world language education (i.e., “foreign” or “second” language education) in the United States has seen a meaningful turn toward pedagogical approaches emphasizing communication, contextualization, and culture. This has coincided with the blossoming of recent theoretical perspectives and empirical research centered on language learners’ emotions, beliefs, and well-being. Two frameworks, self-determination theory (SDT) and positive psychology, are leading this exploration. Although these two perspectives have enhanced the discussion around language learning, each has its gaps; positive psychology research and its recommendations for practice do not often agree on what constitutes well-being and flourishing, while SDT, which …

Nonlinear Dimensionality Reduction For The Thermodynamics Of Small Clusters Of Particles, Aditya Dendukuri

Graduate Theses and Dissertations

This work employs tools and methods from computer science to study clusters comprising a small number N of interacting particles, which are of interest in science, engineering, and nanotechnology. Specifically, the thermodynamics of such clusters is studied using techniques from spectral graph theory (SGT) and machine learning (ML). SGT is used to define the structure of the clusters and ML is used on ensembles of cluster configurations to detect state variables that can be used to model the thermodynamic properties of the system. While the most fundamental description of a cluster is in 3N dimensions, i.e., the Cartesian coordinates of …

Heat And Mass Transfer In Parboiled Rice During Heating With 915 Mhz Microwave Energy And Impacts On Milled Rice Properties, Deandrae L.W. Smith

Graduate Theses and Dissertations

Microwave (MW) heating offers an energy-efficient, fast method to dry high moisture content (MC) parboiled rice to safe storage MC. However, there is limited research that describes the fundamentals of heat and mass transport in rice kernels exposed to MW energy at 915 MHz, the most promising heating frequency for industrialized processing. This information is vital to explain the implications of MW technology on dried rice quality. The overall objective of this study was to develop a microwave heating technology that can sufficiently dry high MC parboiled rough rice kernels in one pass using a 915-MHz industrial microwave system. An …

Development Of High-Density Propulsion System Technologies For Interplanetary Small Satellites And Cubesats, Morgan Andrew Roddy

Graduate Theses and Dissertations

The goal of this research was to support the development of a novel propulsion system for small satellites (<180 kg) and CubeSats. This was pursued by conducting a collection of studies that were designed to provide engineering data that would be critical in designing a functional prototype. The novel propulsion system was conceived by the author to provide best-in-class performance for the small satellite and CubeSat families of spacecraft. This context presents specific design requirements that the presented technology attempts to satisfy. The most critical among these is high density; the propellant was designed to be stored with high density and the thruster was designed to be as compact as possible. The propulsion system is composed of two primary elements, a propellant generator and a thruster. The propellant generator works by sublimating a solid crystal into vapor and then using this vapor to etch a dense metal. The resulting gaseous byproducts of this reaction are the propellant. This dissertation used xenon difluoride (XeF2) vapor to etch tungsten (W) which react to form xenon gas (Xe) and tungsten hexafluoride (WF6). This approach gave a theoretical propellant storage density 5.40 g/cm3; and 5.17 g/cm3 was demonstrated. The sublimation dynamics of the XeF2 were studied as a function of surface area and temperature and it was found to be suitable for the intended application due to its high effluence rate; that is, it sublimates fast enough to be useful. The sublimation rates are on the order of 10’s of µg/s. The etch rate of XeF2 on W was also studied and found to be suitably fast to provide useful amounts of reactants for use as a propellant, again on the order of 1’s of µg/s. The thruster is an electrostatic radio frequency (RF) ion thruster design and is manufactured with Low Temperature Co-Fired Ceramic (LTCC) materials system and manufacturing technology. Manufacturing samples of the thruster were built at the University of Arkansas in July 2015 and tested at NASA’s Marshall Space Flight Center in May 2018. Testing validated the viability of the LTCC thruster and provided valuable information on how to improve the thruster’s design.

On The Seismic Performance Of Skewed Special Moment Frame Reduced Beam Section Connections, Damaso Daniel Dominguez

Graduate Theses and Dissertations

Special Moment Frames (SMFs) are frequently used in high seismic areas for architecturally constrained designs, as they provide lateral system stiffness without the use of braces which often obstruct views and architectural features. Reduced beam section (RBS) connections are popular SMF connection details developed following the Northridge earthquake to limit brittle fractures within connection welds. Current American Institute of Steel Construction (ASIC) provisions (i.e. AISC 341-16) provide prequalified SMF RBS connection details (including welding requirements); however, all prequalified details only consider orthogonal connections between the beam and column. This dissertation investigates the effect of adding skew within SMF RBS connections …

Development Of Vs Profiles And Site Periods In The Mexico City Basin, Landon Joel Woodfield

Graduate Theses and Dissertations

This study presents dynamic site characterization measurements at 25 sites within the Mexico City Basin. The primary focus of the testing was along the western edge of the Mexico City Basin. At each site, active source Multi-channel Analysis of Surface Waves (MASW) arrays and passive source Microtremor Array Measurements (MAM) L-arrays and circular arrays were used to acquire dispersion data. Horizontal to Vertical Spectral Ratio (HVSR) data was collected to determine site periods at each location. These experimental dispersion data and site periods were fit using a joint inversion of Rayleigh and Love wave dispersion data and HVSR site period …

Numerically Modeling Steel Continuous Bridges For Early Age Concrete Deck Cracking, Abdul Aziz Nabil Salah

Graduate Theses and Dissertations

Early age bridge deck cracking is a common problem throughout the United States. Early age cracking develops shortly after the deck is poured. It reduces the serviceability and lifespan of bridges. Early age cracking can be typically attributed to either of two factors, 1) construction practices, and 2) shrinkage. The Arkansas Department of Transportation (ARDOT) has experienced early age bridge deck cracking. ARDOT currently specifies a sequence deck pour on most of their bridges; however, contractors prefer continuous deck pours because of ease and construction time. During the period of this TRC1903 research project, ARDOT has only approved a few …

Numerical Simulations Of Spread Foundations Supported On Stone Columns Using The Discrete Element Method, Anibal Enrique Santos Marin

Graduate Theses and Dissertations

The implementation of stone columns as a ground improvement technique has become more popular in geotechnical construction practice as a result of their ability to improve strength, stiffness and permeability characteristics of weak clayey soil deposits. There are several analytical and empirical approaches to estimate the bearing capacity of stone column foundation systems; however, there is notable variation in the performance of these existing methods when compared with full-scale experimental results. For very weak cohesive soils (i.e., undrained shear strength less than 15 kPa), the use of conventional stone columns becomes restricted because of the insufficient confinement that these types …

Best Practices For Asphalt Emulsion Particle Size Analyses Using A Coulter Counter, Logan P. Kiihnl

Graduate Theses and Dissertations

As asphalt pavements develop distresses, pavement preservation, maintenance, and rehabilitation treatments are used to mitigate distresses and extend the life of the pavement. Many of these treatments utilize asphalt emulsion. Previous research has linked particle size to material properties including viscosity and storage stability. General statements have also been made about particle size influencing emulsion performance while other researchers have identified a trend between particle size and prime coat penetration. Even though literature discusses the importance of particle size, there is little guidance on the best practices of asphalt emulsion particle size analyses, specifically with a Coulter counter.

Data collected …