Digital Commons Network^™

Microstructure Control Through The Use Of Gas Tungsten Arc Welding Based Additive Manufacturing, Benjamin M. Beeker

Dissertations

Additively manufactured (AM) parts are subjected to rapid and repeated localized melting, solidification, and reheating, which produces a heterogeneous microstructure. To homogenize the resulting heterogeneous microstructure that results from this non-equilibrium thermal cycling, ex-situ heat treatments can be used. However, this is intended to provide homogenous properties to the printed part, thereby not realizing one of the potential benefits of AM in providing site-specific properties such as fatigue resistance, wear resistance or high strength. This study explores the use of in-situ heat treatments to spatially control microstructure evolution, thereby controlling the location of specific mechanical properties. To guide the processing …

Design, Modeling, And Experimental Realization Of Tunable Fabry-Perot Nanocavities For Broadband And Narrow-Band Applications, Kirtankumar Pravin Dixit

Dissertations

Efficient control of light absorption at the nanoscale has become a popular area of research, leveraging metal, semiconductor, and dielectric thin film technologies to engineer multilayer structures that modulate light through interference. A Fabry-Perot nanocavity can be configured with a dielectric or semiconductor layer sandwiched between two metal layers to exploit interference. This necessarily involves multiple optical paths through a spacer medium. The ensemble structures can be configured for anti-reflection, high-reflection, and dichroism. This dissertation is structured around four main objectives, each aimed at demonstrating the advanced capabilities of these nanocavities in manipulating light. The goals specifically focus on showcasing …

A Computational Investigation Of Firebrand Dispersion And Deposition In Areas With Cubic Structures, Aditya Prakash Mankame

Dissertations

The spread of wildland and wildland urban interface (WUI) fires can be caused by spotting, where embers from a primary fire ignite spot fires. This study investigates the dispersion and deposition of firebrands over cubic structures in WUI regions under wind condition. Large eddy simulation was used for turbulence while tracing firebrands in Lagrangian framework, employing the open source software Fire Dynamics Simulator (FDS). The software program was revised to include a firebrand model where the rotational motion and thermal degradation of firebrands were taken into account in addition to the translation motion. This was used for simulation of cylindrical. …

Liner Implosion Of Magneto-Inertial Fusion Plasmas Across The Periodic Table, Brian Dale Taylor

Dissertations

The goal of achieving net energy production from fusion reactions would have many positive and transformational impacts upon society and is therefore of great interest. Magneto-Inertial Fusion may be a path to achieving the high energy density requirements. One possible method for reaching the necessary plasma conditions is through a z-pinch driving a magnetized liner to compress and heat the fusion fuel. Progress has been made through both modeling and experiment, largely through Sandia National Laboratories, in recent years in developing this process and achieving neutron yields in the range of 1013 neutrons per pulse. Magnetized liner z-pinch experiments have …

Unveiling The Mechanisms Of Bromate Formation And Nom Treatment In Drinking Water Via Plasmon-Enhanced Catalytic Ozonation, Amir Ahmadi Zahrani

Dissertations

High energy consumption and the formation of harmful byproducts are significant challenges in advanced oxidation processes (AOPs). While much research has focused on improving treatment efficiency, controlling byproduct formation requires more attention. The focus of this dissertation is divided into three main focuses: Firstly, the underlying mechanism of bromate formation inhibition during a plasmon-enhanced catalytic ozonation (PE catalytic ozonation) process using silver-doped spinel ferrite (0.5wt%Ag/MnFe2O4) as the catalyst was investigated by scrutinizing the effects of each factors involved in PE catalytic ozonation including irradiation, catalyst, and ozone, both individually and in combination, on major bromine species involved in bromate formation. …

Understanding Battery Degradation And Failure With Impedance And Imaging Techniques, Megan F. Gober

Dissertations

With the increasing desire for fast charging capabilities in lithium-ion batteries due to the popularity of electric vehicles, research has recently been focused on increasing energy and power density while simultaneously revealing the need for improved understanding of degradation mechanisms to achieve the desired safety and fast charge performance. The work presented seeks to further understanding of mechanical, temperature, and electrochemical degradation mechanisms within varying battery chemistries and geometries through evaluation of impedance response and multiscale imaging techniques. First, in order to understand the limitations of mechanical and electrical integrity of battery systems, a combined application of impedance characterization and …

Simulation Of Atmospheric Pressure Dielectric Barrier Discharges At Low Driving Frequencies, Shanti K. Thagunna

Dissertations

This dissertation investigates the self-pulsing of Dielectric Barrier Discharges (DBDs) at low driving frequencies, in particular, (a) the dependence of current on the product pd of gas pressure p and the gas gap length d, (b) the effects of lossy dielectrics (in resistive discharges) and large dielectric permittivity (in ferroelectrics) on current dynamics, (c) the transition from Townsend to a dynamic Capacitively Coupled Plasma (CCP) discharge with changing pd values, and (d) the transition from Townsend to a high-frequency CCP regime with increasing the driving frequency. A one-dimensional fluid model of Argon plasma is coupled to an equivalent RC circuit …

Mitigation Of Inflammation In Early Post-Traumatic Osteoarthritis Through Low-Intensity Ultrasound, Shahid Khan

Dissertations

Post-traumatic osteoarthritis (PTOA), a subset of OA caused by direct injury or repetitive microtrauma, results in a robust release of inflammatory mediators. If inadequately controlled, this pro-inflammatory phase leads to early tissue damage. The biomedical burden of PTOA is significant and inadequately addressed due to difficulties in identifying the disease onset, slow progression, and incomplete understanding of its etiology and pathogenesis. However, PTOA's distinct initiating events allow for early intervention. This thesis investigates whether fibronectin fragments (FnFs) can induce an early inflammatory response in a triple cellular in vitro model of early PTOA and whether continuous low-intensity ultrasound (cLIUS) can …

Nuclear Fission Rovers For Martian Exploration, Alexander Constantine Bendoyro

Dissertations

A comprehensive analysis was performed on the impact of embedding a Kilopower-style fission reactor into a pressurized rover on architectural performance for a sample lunar, Mars opposition, and Mars conjunction mission. The high gamma ray flux necessitated the addition of substantial shielding for the crew. A single material shielding analysis using the Taylor formulation revealed that varying the distance between the crew and the reactor core from 3 m to 6 m reduced the required shielding thickness by 7%. Increasing the power output of the reactor from 3.4 kWe (comparable to radioisotope power capability) up to 10 kWe (Kilopower design …

Assembly And Analysis Of Space Biofilm-Forming Bacterial Model Organisms Towards The Treatment Of Water System Biofilms, Yo-Ann VéLez Justiniano

Dissertations

Space exploration imposes unique challenges on the human body and engineered systems alike. One such challenge is the control of microbial life, specifically biofilms, within the water processor assembly of the International Space Station (ISS). This investigation aimed to determine the feasibility of using an innovative bioremediation approach to mitigate biofilm growth in the water processor assembly. This approach entails the dissemination of a desired anti-biofilm gene across the microbial population of the water processor assembly through horizontal gene transfer via conjugation. To ascertain the viability of this method, the research was divided into two primary focuses. The first part …

Experimental Investigation Of Steady And Unsteady Effects Of A Circulation Control Wing With Spanwise Segmented Blowing, Tulasi Ram Vechalapu

Dissertations

Active Flow Control (AFC) techniques are a class of methods that improve aerodynamic efficiency by affecting the flow field through actuation or interaction to produce a desired change in flow behavior. Circulation control (CC), which is considered one of the most effective AFC methods, holds significant potential to enhance aircraft efficiency and has been researched for lift enhancement and boundary layer control, among other applications. However, its practical application has been constrained by high mass flow requirements and several unanswered questions in current research. A critical area of investigation is the interaction between trailing-edge blowing and 3D unsteady effects under …

The Structural Basis Of Inflammation : Computational Characterization Of Molecular Mechanisms, Sara W. Jackson

Dissertations

Computational tools are useful in the interpretation and analysis of experimental data. In the world of structural biophysics, computational tools go a bit further: they can simulate atomic motions and molecular interactions based on experimentally-determined biomolecule structures, therein describing natural phenomena, and inspiring the formulation of new hypotheses. In this work, computational structural biology tools are used to answer questions about molecules of inflammatory importance. Quantum chemistry computational tools are used to determine the electronic structure of sesamin, a component of many diets which may be a modulator of an enzyme involved in the metabolism of inflammation mediators. Virtual docking …

How The Extraction Of Free Ligands From Nanoparticle Dispersions Affects Their Langmuir Films, Jimmie Mitchell

Dissertations

When nanoparticles are used as coatings on displays, solar cells, or devices, a thin, closely packed, uniform film is desired to enhance performance. Organic ligands are commonly used during the synthesis of metal or semiconductor nanoparticles. The ligands bind to the surface of the nanoparticle to control size, stability, or functionality. Commercially available nanoparticles have excess (free), ligands in their dispersions. Removal of the free ligands can potentially improve the performance of the system, especially when the dispersion is subsequently coated on a surface. Current methods to remove free ligands from nanoparticle dispersions result in mass loss, reduced performance, or …

A Framework For Identifying Transit Deserts In Rural Areas With Demand-Response Transit Services, Agnes L. Barnwell

Dissertations

The primary objective of this research is to develop a comprehensive framework for identifying transit deserts in rural areas with Demand Response Transit (DRT) services. This framework will focus on marginalized rural areas in Alabama, providing a foundation for better understanding their transportation needs. The research gap regarding transit deserts in rural areas is significant. While the concept of transit deserts has been explored in urban settings, rural areas with DRT services remain largely under-researched. Addressing this gap is vital for establishing equitable access to transit services across rural areas. This research contributes to the existing body of literature in …

Variability In Semidiurnal Surface And Internal Tides In Global Ocean Model Simulations, Harpreet Kaur

Dissertations

This dissertation focuses on semidiurnal (D2) surface and internal tides. Chapter 2 investigates the transition of M₂ barotropic Kelvin waves into Hybrid Kelvin-Edge (HKE) waves and the associated generation of internal tides at widening shelves using theory and a realistic global baroclinic Hybrid Coordinate Ocean Model (HYCOM) simulation. To understand the effect of complex, realistic bathymetry on the HKE wave transition, we perform quasi-realistic barotropic HYCOM simulations of the Celtic Sea/Bay of Biscay shelf areas. We conclude that the HKE wave transition is most likely masked by the effects of complex bathymetry and offshelf baroclinic fluxes cannot be exclusively …

A Quantitative Study Of Perceived Factors That Influence Enrollment Within A Regional Conference Seventh-Day Adventist School System, John Calvin Alberty Jr.

Dissertations

Problem

A significant challenge confronting Seventh-day Adventist schools is declining enrollment, with schools in the North America Division of the Seventh-day Adventist Church either closing or experiencing a substantial reduction in enrollment over the years. The purpose of this study is to identify the perceived factors influencing enrollment within the Allegheny East Conference school system, ultimately explaining the enrollment shift from 1277 students to 635 students over a twenty-year period within the Allegheny East Conference school system. The study also determined if there are significant differences in perceptions of the importance of these observed enrollment-related factors among participants who hold …

Jointly Operating A Merged Junior Academy: A Case Study Of Interracial Cooperation In Seventh-Day Adventist Education In North America, Fabian S. Reid

Dissertations

Problem

Despite the landmark 1954 US Supreme Court decision in Brown v. Board of Education that rules segregated schools unconstitutional, the Seventh-day Adventist Church in North America continues to operate segregated schools in close proximity, a practice rooted in a 1944 General Conference vote that allowed the establishment of separate regional (predominantly Black) and state (predominantly White) conferences within the same geographical regions (a conference is a group of churches, schools, and other institutions within a specified geographic region with one central administrative body). This dual system persists even as declining enrollments and frequent school closures prompt consideration of school …

The Andrews University Mba Program In Vietnam: Assessing The Experience And The Career Advancement Of Its Students, Masazumi Mark Sugi

Dissertations

Problem

The demand to recruit highly skilled managers and laborers in Vietnam has encouraged educational institutions to upgrade the quality of their higher education programs and to evaluate their effectiveness. Andrew University’s MBA program did not have an assessment developed to evaluate the program’s effectiveness in Vietnam. It required an assessment of students’ experiences as a major predictor of evaluating how the Andrews University MBA program in Vietnam has impacted their career path and the extent to which it has benefited students.

Method

This study investigated the motivations, expectations, actual experiences, and career advancement opportunities of graduated students and current …

Teachers' Perceptions Of Play-Based Learning In Early Childhood Classrooms, Laura B. Rushatz

Dissertations

Play-based learning is an important part of developing the whole child emotionally, socially, physically, cognitively, and communicatively. Through play, children are allowed to explore, investigate, discover, think, solve problems, and communicate. The purpose of this study was to determine what early childhood teachers in public schools know and believe about the use of play-based learning in their classrooms and how these teachers perceive their administrator’s role in the use of play-based learning. This study used a mixed method approach to gather the perceptions of early childhood educators in seven different school districts through four counties. The sample included responses from …

How Can A Cloud Computing It Framework Be Created And Applied Effectively In The Online Printing Industry?, Stefan Meissner

Dissertations

This research aims to design a cloud computing IT framework for the online printing industry based on a detailed literature review, the development of proof of concepts (PoC), and the conduction of a focus group. The framework can be adopted by the online printing industry or by vendors of print-specific applications to optimize their products for the online printing industry. The author has been working in the online printing process optimization and automation since 2007. During this time, he got deep insight into many industry-specific applications, their architectural design, and their challenges being used in the context of online printing. …

The Relationship Between Secondary Ela Teacher Pedagogical Practices, Student Self-Regulated Learning And Digital Self-Efficacy In A Blended Learning Environment, Melissa K. Miller

Dissertations

In the era of emerging technologies in the 21st Century classroom, secondary English Language Arts (ELA) students may exhibit complications in navigating literacy in blended learning environments. The purpose of this research study focused on addressing a gap in the current literature in these specific areas to investigate the relationship between ELA teachers’ pedagogical practices and elements of secondary students’ learning motivation for ELA. Specifically, this study explored secondary ELA students’ perception of teachers’ classroom practices, self-regulated learning, and digital self-efficacy. The overarching research question in this study examined: What relationship exists between (a) the pedagogical practices of secondary ELA …

Quantitative Characterization Of Non-Bonded Interactions In Proteins Affecting Human Health And Disease, Maher Mansur

Dissertations

Non-bonded interactions are fundamental forces that govern molecular relationships between two or more molecules. These interactions contribute to the stability of complex biological structures like DNA, RNA, and proteins, and control various biological processes. Almost all of these processes are significantly influenced by protein-protein and protein-ligand intermolecular interactions. Here, the interactions of various proteins with other proteins, peptides, and/or ligands were quantified computationally to tackle human health-related problems. For estimating the intermolecular interactions, a number of computational approaches including protein structure modeling, molecular dynamics simulations, molecular docking, ensemble docking, semi-empirical methods, etc., were used. The basics of Molecular Mechanics and …

Benefits Of Quadratically Tapered Flexures For Mems Resonators And Gyroscopes, Brian Grantham

Dissertations

An investigation into the benefits of quadratically tapered flexures for MEMS resonators and gyroscopes is performed and compared to the traditional non-tapered flexure design. Quadratically tapered flexures exhibit constant strain along the outer edge of the flexure whereas non-tapered flexures have significant stress concentration near the base of the flexure. The investigation considers peak stress, thermoelastic damping (TED), nonlinearity, and sensitivity to manufacturing variations. The impact of inside corner fillets on peak stress, TED, and resonant frequency is also investigated. Five new anti-phase lever mechanism (APLM) configurations for resonators and gyroscopes are designed and analyzed using CoventorWare 10. Fabrication experiment …

Developing Geopolymer-Based Adsorptive Materials For Nutrient Removal From Agricultural Runoff And Drainage, Gabrielle Jacquelle Savoir

Dissertations

With the rise of population placing strain on food supplies and the failure of current prevention strategies to mitigate effects of agricultural pollution, research is needed to develop new technologies for the removal and recovery of nutrients from agricultural runoff and drainage. Geopolymer, an alkali-silicate material polymerized within an acidic or alkaline medium, is promising as an adsorptive substrate due to its multifaceted customizability, cost effectiveness, and adsorptive properties. Hence, the objective of this research was to develop porous metakaolin (MK) geopolymer based adsorptive materials with high affinities for phosphate and ammonium/ammonia to act as nutrient control within agricultural runoff …

Nonlinear Dynamics Of Acoustic Fluctuations In One-Dimensional Ducts With And Without Unsteady Combustion, Swarnalatha Kathalagiri Vasantha Kumar

Dissertations

The overall objective of this research is to analyze the nonlinear dynamics of combustors in one dimensional Cartesian coordinate. This research was carried out in four parts, with each successive part building on the previous one. The first part begins with investigation of the coupled nonlinear evolution of acoustic modes in a quasi 1-D duct with axially inhomogeneous mean velocity and mean thermodynamic properties. A novel modification of the Krylov--Bogoliubov method of averaging (KBMA) is developed to analytically solve the modal-amplitude equations that are linearly and nonlinearly coupled with both quadratic and cubic nonlinearities. Approximate analytical solutions based on the …

Perception Of The Elementary Education Profession And Levels Of Job Satisfaction: Is There A Correlation?, Alexis H. Redman

Dissertations

The purpose of this dissertation was to introduce the context and purpose of the research study. The study’s focus was on the perception of the elementary education profession and the prestige ascribed to classroom teachers working in public education by individuals outside the education system. The research questions were as follows: (1) What level of prestige is afforded to the elementary public school classroom teacher from the noneducator perspective? (2) To what extent do noneducators’ perceptions affect the level of job satisfaction among elementary public school classroom teachers? Themes found in literature supporting the research questions included the perceived devaluation …

An Empirical Study Of The Relationship Between Automation And Aircrew Accident Performance In High Performance Aircraft Operating In The U.S. Naval Shipboard, Richard Matthew Gensley

Dissertations

The research described in this dissertation was an empirical study of cockpit automation and aircrew accident performance in high performance aircraft. The data set consisted of 3,249 accident records released by the U.S. Naval Safety Center and publicly available information for high performance aircraft based aboard U.S. aircraft carriers between the years of 1980 and 2013. Five conclusions resulted from this study. The first result was a demonstration that through statistical analysis, it is possible to assess if different aircraft over a prolonged period of time have been exposed to a common operating environment. The second result was that while …

Characterization Of Size Effects In Additively Manufactured Grcop-42 And Their Influence On Mechanical Response, Gabriel Demeneghi

Dissertations

This study investigates size effects on microstructure, mechanical behavior, and fatigue performance of additively manufactured GRCop-42. Systematic analyses, encompassing changes on powder composition, wall thickness, and heat treatment, was conducted on specimens produced through laser powder bed fusion (L-PBF) and laser powder direct energy deposition (DED) techniques. L-PBF specimens exhibited a reduction in strength and elongation with decreasing thickness, attributed to increasing porosity as specimen’s thickness decreases. Conversely, in DED specimens, decreasing mechanical properties with thickness were associated to surface topography. Emphasizing the non-generalizability of size effects across AM methods. Size effects were also investigated on high cycle fatigue, as …

Exploring The Impact Of Ionizing Radiation On Security And Reliability In Modern Semiconductor Memories, Umeshwarnath Surendranathan

Dissertations

Radiation effects in semiconductor devices have gained great traction in recent years due to an exponential growth in space exploration. The harsh conditions of space, devoid of the atmosphere and Earth's magnetic field, pose considerable challenges to electronic systems due to ionizing radiation exposure. While radiation-hardened (rad-hard) components are continually under development, they often lag several technology generations compared to commercial off-the-shelf (COTS) parts. Notably, rad-hard memories, particularly in terms of capacity (megabytes vs. terabytes) and cost, fall short compared to regular COTS memories. This underscores the compelling need to evaluate the radiation tolerance of COTS memories. This dissertation focuses …

Online Learning For Adaptive Control : Stable Learning And Control For Aerospace And Robotics, Jacob G. Elkins

Dissertations

Aerospace and robotic systems perform various tasks in uncertain, dynamic environments. Further, the data that a system encounters in the real-world is often the most valuable. The most advanced aerospace and robotic systems of the future will be able to learn online, during operation, from this real-world data. Aerospace and robotic systems are often expensive and difficult to model, and the controllers of these systems thus require rigorous control proofs and safety guarantees. Recently, general research in artificial intelligence and machine learning (AI/ML) has made significant strides in developing learning-based systems and controllers. However, much of this research has focused …