Digital Commons Network^™

Dynamics Modeling Of Molten Salt Reactors, Visura Umesh Pathirana

Doctoral Dissertations

The abundance of energy is a necessity for the prosperity of humans. The rise in energy demand has created energy shortages and issues related to energy security. Nuclear energy can produce vast amounts of reliable energy without many of the negative externalities associated with other competing energy sources, such as coal and natural gas. As a result, public interest in nuclear power has increased in the past decade. Many new types of nuclear reactor are proposed. These nuclear reactor designs feature many passive technologies that can operate without external influence. Reactors that feature advanced passive safety features are catagorized as …

Effects Of The U.S. Veterinary Feed Directive Final Rule On The Prevalence Of Violative Antibiotic Residues And Antibiotic-Resistant Bacteria In Animal Products, Md Shamim Sarkar

Doctoral Dissertations

Antibiotic-resistant is a public health concern. The dissertation objective was to assess the effect of the implementation of the Veterinary Feed Directive (VFD) rule changes on the prevalence of violative antibiotic residues and antibiotic-resistant bacteria in food-animal tissues, retail meats, and cecal samples from food animals compared to the pre-VFD rule change period in the U.S. To understand the effect of implemented VFD rule changes on violative antibiotic residues in food-animal tissues, inspector-generated sampling (IGS) data from the U.S. National Residue Surveillance Program (NRP) was analyzed. An important observation was that implementing VFD rule changes was associated with the decreased …

Factors Associated With The Success Of An African American College President, Tyvi T. Small

Doctoral Dissertations

This narrative study examines the experiences of Dr. George Wright, a successful African American college president. Dr. Wright had 14-year career at the helm of Prairie View A&M University, an Historically Black College or University (HBCU), where he changed the trajectory of the institution. His story begins with seminal experiences in the segregated schools of Lexington, Kentucky and continues to Duke University, where he became the first African American to receive a Ph.D. in History. In this study, Dr. Wright relates critical moments in his childhood, educational, and career experiences that put him on a path to success. This narrative …

Stress Relaxation Cracking In 347h Austenitic Steel Weldments Under Various Heat Treatments: Experiments And Modeling, Yi Yang

Doctoral Dissertations

347H austenitic stainless steel exhibits exceptional creep and corrosion resistance, rendering it an exemplary candidate for pipeline materials, particularly in mid- to high-temperature working conditions. However, due to constraints in component dimensions, welding has been chosen as the preferred method for joining pipeline systems extensively employed in nuclear power plants, fossil fuel plants, and petrochemical companies. The welding process entails the accumulation of residual stress during the cooling stage, along with the introduction of microstructure evolution. Moreover, the residual stress field and microstructure continuously evolve under service conditions, thereby intensifying the susceptibility of crack initiation and propagation. The initial residual …

Generalized Differentiable Neural Architecture Search With Performance And Stability Improvements, Emily J. Herron

Doctoral Dissertations

This work introduces improvements to the stability and generalizability of Cyclic DARTS (CDARTS). CDARTS is a Differentiable Architecture Search (DARTS)-based approach to neural architecture search (NAS) that uses a cyclic feedback mechanism to train search and evaluation networks concurrently, thereby optimizing the search process by enforcing that the networks produce similar outputs. However, the dissimilarity between the loss functions used by the evaluation networks during the search and retraining phases results in a search-phase evaluation network, a sub-optimal proxy for the final evaluation network utilized during retraining. ICDARTS, a revised algorithm that reformulates the search phase loss functions to ensure …

Development Of A Portable, Tileable, Dual-Particle Radiography System, Christian Xavier Young

Doctoral Dissertations

A scalable, portable, multi-particle neutron radiography device has been developed using commercial-off-the-shelf-parts. The IDEAS ROSSPAD readout module was selected for use in developing the radiography panel due to its single-wire Power-over-Ethernet (PoE) connectivity and its tileable form factor. Each ROSSPAD detector is paired with an 8 by 8 array of 6-mm-pitch Sensl J-Series silicon photomultipliers (SiPMs). With both single and multi-ROSSPAD testing, a detection package consisting of a 3-mm-thick sheet of EJ-200 plastic scintillator and a 3-mm-thick sheet of acrylic light spreader was coupled to the SiPM board face. After both quality assurance of the detector packages and the calibration …

A Two-Diameter Helical Endmill Beam Model For Tool Tip Dynamics Prediction With Application To Milling, Emma D. Betters

Doctoral Dissertations

The aim of this dissertation is to describe the dynamic response of helical endmill geometries to enable the use of receptance coupling substructure analysis (RCSA) to predict the tool tip vibration response of arbitrary tool-holder-spindle-machine combinations. The tool tip vibration response, or receptance, is a key input for milling stability prediction. Currently, a measurement is required to determine the tool tip receptance for each tool-holder-spindle-machine combination, which may not be possible in production environments. In the RCSA approach, the spindle receptances are measured once and archived, while the tool and holder are modeled. Tool tip receptances are predicted by analytically …

Material Formulation And Process Optimization Towards Fabricating Robust 3d Printed Structures, Austin Riggins

Doctoral Dissertations

This dissertation focuses on understanding and addressing the fundamental physicochemical phenomena that lead to weak interfaces and structural warpage in material extrusion 3D printing. Polymeric feedstocks used for this manufacturing technique were manipulated through the incorporation of additives that alter the dynamics of the matrix during and after printing. In Chapter II, adhesion between layers of structures printed from PEEK was strengthened through a combination of low-molecular weight additive incorporation and post-printing thermal annealing. Chapter III reports a method for decreasing the irreversible thermal strain of structures printed from poly(lactic acid) by introducing nanographene and photoinitiator additives into the feedstock …

Enhanced Bioretention Modeling At The Catchment-Scale: An Integrated Drainmod-Urban And Swmm Approach, Ghada Diab

Doctoral Dissertations

Bioretention systems are increasingly being adopted in stormwater management as an effective measure to promote infiltration and restore more natural hydrology in urbanized watersheds. Given the significant financial investment in these practices, reliable bioretention models are necessary to predict the effectiveness of these practices prior to installation. One such model, DRAINMOD-Urban (DM-Urban), was recently developed to produce hydrographs with a high temporal resolution at the site-scale, showing substantial promise during initial testing. However, the dataset used for initial testing was limited, consisting of one bioretention area with minimal occasions of overflow. Additionally, DM-Urban is an input-heavy model and there is …

Static And Dynamic State Estimation Applications In Power Systems Protection And Control Engineering, Ibukunoluwa Olayemi Korede

Doctoral Dissertations

The developed methodologies are proposed to serve as support for control centers and fault analysis engineers. These approaches provide a dependable and effective means of pinpointing and resolving faults, which ultimately enhances power grid reliability. The algorithm uses the Least Absolute Value (LAV) method to estimate the augmented states of the PCB, enabling supervisory monitoring of the system. In addition, the application of statistical analysis based on projection statistics of the system Jacobian as a virtual sensor to detect faults on transmission lines. This approach is particularly valuable for detecting anomalies in transmission line data, such as bad data or …

Atomic-Level Mechanisms Of Fast Relaxation In Metallic Glasses, Leo W. Zella

Doctoral Dissertations

Glasses are ubiquitous in daily life and have unique properties which are a consequence of the underlying disordered structure. By understanding the fundamental processes that govern these properties, we can modify glasses for desired applications. Key to understanding the structure-dynamics relationship in glasses is the variety of relaxation processes that exist below the glass transition temperature. Though these relaxations are well characterized with macroscopic experimental techniques, the microscopic nature of these relaxations is difficult to elucidate with experimental tools due to the requirements of timescale and spatial resolution. There remain many questions regarding the microscopic nature of relaxation in glass …

Ethyl Pyruvate Failed To Reduce Pro-Inflammatory Cytokines Release Following In Vitro Stimulation In Dairy Calves' Whole Blood., Vincent Dore

Doctoral Dissertations

Recent developments in sepsis treatment showed that control of the late mediator of inflammation, High Mobility Box group-1 (HMGB1), improves survival in animal models of endotoxemia. Ethyl pyruvate is a small-molecule inhibitor that has been shown to reduce the systemic release of HMGB1 during experimental treatment of systemic inflammation in different species. The objectives of this body of work were 1) to explore ethyl pyruvate's ability to modulate early pro-inflammatory cytokines production and immune effector function in treated calves, 2) to evaluate the safety of an administration of ethyl pyruvate infusion in neonatal calves, and 3) to explore ethyl pyruvate's …

Transportation System Performance And Traveler Behavior In The Context Of A Systemwide Shock: Applications Of Data Science Toward A Sustainable Future, A. Latif Patwary

Doctoral Dissertations

The COVID-19 pandemic, a systemwide shock, has left a long-lasting and significant impact on transportation systems. It has contributed to a shift in travel behavior, with many people turning to work from home (WFH) and online shopping. This shift has led to a reduction in vehicular travel. However, the pandemic witnessed increased crash fatalities despite a reduction in overall crashes, disproportionately affecting disadvantaged communities (DACs). The main question arising from these pandemic-related issues is what we can learn to improve transportation systems and shape future travel behavior. Therefore, this dissertation aims to investigate how the transportation system changed during COVID-19 …

Exploring Soil Microbial Dynamics In Southern Appalachian Forests: A Systems Biology Approach To Prescribed Fire Impacts, Saad Abd Ar Rafie

Doctoral Dissertations

Prescribed fires in Southern Appalachian forests are vital in ecosystem management and wildfire risk mitigation. However, understanding the intricate dynamics between these fires, soil microbial communities, and overall ecosystem health remains challenging. This dissertation addresses this knowledge gap by exploring selected aspects of this complex relationship across three interconnected chapters.

The first chapter investigates the immediate effects of prescribed fires on soil microbial communities. It reveals subtle shifts in porewater chemistry and significant increases in microbial species richness. These findings offer valuable insights into the interplay between soil properties and microbial responses during the early stages following a prescribed fire. …

The Identification Of Small Molecule Inhibitors To Candida Albicans Phosphatidylserine Synthase, Yue Zhou

Doctoral Dissertations

Candida albicans phosphatidylserine (PS) synthase, encoded by the CHO1 gene, has been identified as a potential drug target for new antifungals against systemic candidiasis due to its importance in virulence, absence in the host and conservation among fungal pathogens. This dissertation is focused on the identification of inhibitors for this membrane enzyme. Cho1 has two substrates: cytidyldiphosphate-diacylglycerol (CDP-DAG) and serine. Previous studies identified a conserved CDP-alcohol phosphotransferase (CAPT) binding motif present within Cho1, and here we revealed that mutations in all but one conserved amino acid within the CAPT motif resulted in decreased Cho1. For serine, we have predicted a …

Design And Evaluation Of An Elevated Temperature Cutting Force Dynamometer For Hybrid Manufacturing, Justin West

Doctoral Dissertations

Cutting force coefficients, workpiece dynamics, and uncut chip area all change as a function of temperature during machining processes at elevated temperatures. In a traditional milling process, these parameters are nearly constant. The bulk workpiece temperature remains well below the working limit of the material, generally near room temperature. However, workpiece temperatures in hybrid manufacturing, where additive deposition precedes machining, are spatially and temporally variable. A milling force model that does not incorporate temperature effects will generally overestimate the cutting force and workpiece dynamic stiffness and underestimate the chip area. Milling parameters that are stable at room temperature may be …

A Measurement Of Neutron Polarization And Transmission For The Nedm@Sns Experiment, Kavish Imam

Doctoral Dissertations

The D.O.E Nuclear Science Advisory Committee Long Range Plan has called for experimental programs to explore fundamental symmetry violations and their implications in nuclear, particle and cosmological physics. The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) aims to search for new physics in the Time-reversal (T) and Charge-Parity (CP) symmetry violating sector by setting a new limit on the nEDM down to a few x 10^-28 e·cm using a novel cryogenic technique, which combines the unique properties of polarized Ultracold Neutrons (UCN), polarized ³He, and superfluid ⁴He. The experiment will employ a cryogenic …

3d Experimental Studies Of Temperature And Crystallographic Effects On Creep And Strength In Rock Salt, Amirsalar Moslehy

Doctoral Dissertations

Salt domes utilization as storage reservoirs in the energy sector has led to extensive studies on rock salt’s mechanical and geothermal behavior. These important facilities’ safety and serviceability rely on understanding rock salt’s compressive strength and creep behavior under various loading directions, water contents, in-situ stresses, and temperatures. Despite numerous studies on rock salt’s mechanical behavior in the literature, there are still many unanswered questions about rock salt’s behavior. This dissertation was aimed at utilizing state-of-the-art experimental techniques such as 3D synchrotron micro-computed tomography (SMT) and 3D x-ray diffraction (3DXRD) along with hundreds of compression and creep experiments to enhance …

Opioid Use And Borderline Personality Disorder Features: Implications For Postpartum Maternal Self-Efficacy, Andrea Gorrondona

Doctoral Dissertations

The current study sought to understand and explore the experiences of pregnant individuals who use opioids as previous research has mainly focused on identifying potential negative implications (Ryan, Marsh, Testa, & Louderman, 2006; Choi & Ryan, 2007; Grella, Needell, Shi, & Hser, 2009; de Bernabe et al., 2004). The initial sample included 178 total participants recruited from a high-risk pregnancy clinic during their pregnancy. Borderline features, approximation of borderline personality disorder (BPD) diagnosis (determined using a cutoff score of self-reported features, Kurt & Morey, 2001), opioid use status in pregnancy, and postpartum opioid use status were evaluated as potential predictors …

Fourier Analysis And Optimization Of Inductive Wireless Power Transfer For Electric Vehicle Charging, Andrew P. Foote

Doctoral Dissertations

With the growth of electric vehicle (EV) popularity, different charging options to increase user convenience and reduce charging time such as high power wireless charging are increasingly being developed and researched. Inductive wireless power transfer (WPT) systems for EVs must meet specifications such as stray field, battery power and voltage operating range, efficiency, and ground clearance. The coil geometry and design have a large impact in meeting these constraints. Typical design approaches include iterative analysis of predetermined coil geometries to identify candidates that meet these constraints.

This work instead directly generates WPT coil shapes and magnetic fields to meet specifications …

Economics In Transition: Issues Applicable To Climate Change, Odysseus Bostick

Doctoral Dissertations

This dissertation presents three essays on topics that characterize the challenges of the energy transition. The first two focus on mitigating the worst impacts of climate change while the final hones in on adapting to climate change.

The first essay estimates willingness-to-pay (WTP) of electricity customers for rooftop solar within the Tennessee Valley Authority. Applying a conditional logit model, the probability of adoption rises with utility rates and emissions-reductions and declines with costs. Evidence of social contagion exists with adoption probabilities increasing 55 − 57% when respondents know someone with panels. WTP also rises. Comparing aggregated to regional WTPs confirms …

Characterization Of Radiotolerance In Potato And Development Of A Gamma Radiation Phytosensor., Robert Graham Sears

Doctoral Dissertations

As humans pursue space travel and nuclear energy, the risk of harm from ionizing radiation increases. On Earth or in space, plants are essential to our personal and environmental health. Plants serve as sentinels, bioremediators and food sources in areas of high ionizing radiation, therefore it is essential to understand how ionizing radiation affects plant biology. This work aimed to understand plant responses to ionizing radiation in the potato chassis and apply that knowledge to generate novel phenotypes for nuclear energy and space applications. The first gamma radiation phytosensor was developed for monitoring at standoff distances greater than three meters. …

Effect Of Seawater And Temperature Upon Carbon Fiber/Vinyl Ester (Cfve) Composites And Its Constituents, Vivek Chawla

Doctoral Dissertations

An experimental and computational investigation has been carried out to: (1) develop micromechanical characterization techniques for polymeric composites and (2) evaluate the effects of seawater and temperature upon the micro- and macro-response of the carbon fiber vinyl ester composites (CF/VE). Compression properties degradation due to short-term and long-term exposure to seawater is evaluated. A 12-16 % reduction in compression strength is observed due to long-term exposure to seawater, which is attributed to a decrease in interfacial shear strength (IFSS) due to long-term exposure to seawater. The developed Push-out methodology is used to characterize the IFSS. The presented approach consistently yields …

Impact Of Cadmium Stress On Soil Virus Reproduction And The Persistence Of Viruses Under Abiotic Conditions, Zhibo Cheng

Doctoral Dissertations

Soil viruses are ubiquitous and greatly impact the structure and function of soil microbial communities, with their effects modulated by various environmental factors. This study investigates the inactivation of naturally occurring soil viruses in sterilized soil, as well as the effects of cadmium (Cd) exposure and carbon (C) and nitrogen (N) nutrient availability on the population dynamics of virus-host communities in agricultural soil.

Lab-scale slurry and unsaturated experiments were performed to examine virus inactivation in the absence of host bacteria in sterilized soil. In slurry experiments, virus abundance declined by over 90% after 10 days of incubation. The addition of …

Essays In Microeconomics, Michael Charysh

Doctoral Dissertations

\chapter*{Abstract}\label{ch:abstract} The first chapter evaluates the effect of the passage of the Campus Save Act (as part of the Violence Against Women Act (VAWA) Reauthorization in 2013) on reported incidents of crime on college campuses in the United States. This piece of legislation required colleges and universities to provide sexual assault awareness training and preventive education programs for all new students, faculty, and staff. I collect survey data from colleges and universities on their historical training efforts and available resources from 2010 to 2020. While previous studies have examined the relationship between sexual violence and future earnings or labor market …

I Read To You, And You Relax: Interactive Teacher Read-Alouds Of Picture Books In The Undergraduate Foreign Language Classroom, Mareike Geyer

Doctoral Dissertations

Research Area: This dissertation investigates interactive teacher read-alouds of picture books in the undergraduate foreign language classroom. It focused on reading comprehension and read-aloud enjoyment.

Study Design: The study was conducted in four in-person German language classes at a U.S. university. It consisted of six weekly read-alouds interventions that took place over the time span of 7 weeks. During the interventions, one German picture book was read interactively to the students.

Data Collection Instruments: Reading comprehension was measured with a pre-test and a post-test and read-aloud enjoyment was measured with a pre-intervention survey and a post-intervention survey.

Results: The findings …

A Narrative Inquiry On Chinese International Doctoral Students’ Perspectives On Developing Critical Thinking In The U.S., Shuaipu Jiang

Doctoral Dissertations

Guided by transformative learning theory and Perry's scheme of intellectual and ethical development, this dissertation study examines Chinese international doctoral students' critical thinking development process in the US. The two research questions that guided this study are: (1) How do Chinese international doctoral students understand and conceptualize critical thinking? and (2) How have Chinese international doctoral students developed critical thinking during their doctoral studies in the U.S.? Narrative method design is applied to the study, which interviews eight participants. Using narrative thematic analysis of data, four key themes emerged from the study: a) awareness of critical thinking in Western versus …

Towards Safer Code Reuse: Investigating And Mitigating Security Vulnerabilities And License Violations In Copy-Based Reuse Scenarios, David Reid

Doctoral Dissertations

Background: A key benefit of open source software is the ability to copy code to reuse in other projects. Code reuse provides benefits such as faster development time, lower cost, and improved quality. There are several ways to reuse open source software in new projects including copy-based reuse, library reuse, and the use of package managers. This work specifically looks at copy-based code reuse.

Motivation: Code reuse has many benefits, but also has inherent risks, including security and legal risks. The reused code may contain security vulnerabilities, license violations, or other issues. Security vulnerabilities may persist in projects that copy …

Additively Manufactured Nature Inspired Morphology For Redesign: Advancing Next Generation Energy Systems, Vanshika Singh

Doctoral Dissertations

To meet cleaner energy goals and increasing demand, energy systems such as gas turbines and power plants are required to be operated under harsh loading conditions like higher temperatures and pressures, fluctuating loads, and corrosive environments. Advanced manufacturing techniques such as additive manufacturing (AM) have put us on the trajectory for next-generation system designs, allowing complex geometries and high-temperature alloys with tailored material properties. We need new and systematic design philosophies to use AM's unique characteristics prudently. For a given functionality, nature tends to provide similar solutions in animate and inanimate structures. We propose to take inspiration from nature's repetitive …

The Other Side Of The Story: An Exploratory Case Study Of Barriers Experienced By Tennessee Transfer Pathways Students, Alexis Hartley

Doctoral Dissertations

The vital topic of improving the experiences of transfer students is investigated comprehensively in this research. A qualitative method was used in the design of the case study to explore the experiences that transfer students had while participating in a state transfer pathway program. In particular, this approach focused on the barriers that transfer students faced and the knowledge and actions that were required to overcome these barriers. After completion of an accredited associate's degree, students who have participated in the Tennessee Transfer Pathway (TTP) are eligible to transfer into a four-year program at one of the state's participating four-year …