Theses and Dissertations

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    The Birth of Southern Living in the 1960s
    (University of Alabama Libraries, 2004) Lauder, Tracy; McKinnon, Lori Melton
    This study provides a historical snapshot of Southern Living magazine's creation in 1960s Birmingham, Alabama, by The Progressive Farmer Company (now Southern Progress Corporation, an AOL-Time Warner subsidiary). A mixed-method design employed three methods: (1) historical, through analysis of archival data; (2) critical, through a fantasy-theme analysis of the editor's letters; and (3) quantitative content analysis, to further describe the magazine's early editorial content. The dissertation focused on the period 1959 to 1969, providing an exploration of events preceding the magazine's conception and launch in 1966 through the first several years of the publication's initial success. The dissertation chronicles how the editorial philosophy was envisioned, developed, and implemented as a solution to remedy declining readership of The Progressive Farmer Company and to ensure company growth. The launch of Southern Living followed trends in the magazine industry in terms of specialization and targeting women as consumers. Growing suburbs in the region were the heart of the magazine's target market, and the flourishing consumer interest in products for home and leisure provided a strong advertising base for the new magazine. Fantasy theme analysis of the editor's letters showed that the editors reinforced Southern identity by focusing articles on the people, places, and pursuits that represented the regional personality as well as promoting a New-South vision of progress and promise. In addition, the publishers served Southern readers who sought a more positive portrayal of the region in light of the benighted image portrayed by civil rights coverage in national media. Archival evidence and content analysis showed that the magazine consciously chose to ignore the racial unrest around them. In terms of the way the magazine portrayed women, this study found that, for the most part, Southern Living reinforced the traditional roles of women as wives, mothers, and homemakers much like other media of the time. Further study is warranted to explore how the magazine has accommodated change and/or perpetuated archetypes such as the happy homemaker and the Southern belle as well as to what extent the company has strived to portray a more accurate picture of racial diversity in the region.
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    A Survey of the Criticism of Richard Wright's Fiction
    (University of Alabama Libraries, 1979) Hurst, Catherine Daniels; Boyd, Dock; Hobson, Fred; Salem, James; Watson, Charles; Emerson, O.B.
    Richard Wright was a prolific and controversial writer whose literary career spanned a period of more than two and a half decades, in America and abroad. During this time he emerged as the foremost black American writer and one of the most important American writers of the twentieth century. Critics in fact are in general agreement that had he written no more than one novel (Native Son, 1940), an autobiography (Black Boy, 1945), and a few short stories (Uncle Tom's Children, 1938) his place as a first rank writer would be secure. In addition to his personal achievement, Wright's influence on his contemporaries and the generation of young black writers who have come after him will be a lasting testament of his contribution to the development of Black American literature and American culture in general.
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    On the Design of a High-Power Medium-Voltage Converter for Transportation Applications
    (University of Alabama Libraries, 2023) Flack, Calvin Alexander; Lemmon, Andrew N
    In transportation applications, the size and weight of power converters and associated cabling is of paramount importance, as this bulk contributes to the "overhead" that must be carried about by the transportation system. Thus, improvements to the power density of such systems, as well as the possibility of reducing ampacity requirements, is of intense interest. Medium-voltage dc systems provide significant improvements to power density compared to ac systems, and wide-bandgap devices enable operation at sufficiently high switching frequencies to make medium-voltage dc systems attractive. On the other hand, the sparse institutional and industrial support that presently exists for medium-voltage wide-bandgap devices means that additional de-risking is needed prior to implementation in the transportation sector. Additionally, the voltage ratings of commercialized silicon-carbide MOSFETs are below the levels projected for medium-voltage applications. Thus, research into more advanced converter topologies, such as multi-level converters, using wide-bandgap devices is necessary to support the required voltage levels of medium-voltage dc. This thesis provides insight into the design and implementation of a multi-level isolated dc-dc converter for medium-voltage applications to accelerate the adoption of medium-voltage dc systems.
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    Addressing Insect Declines Via Biodiversity Monitoring, Ecological Restoration, and Population Genetics
    (University of Alabama Libraries, 2023) Franzem, Thomas P.; Ferguson, Paige
    Insects are influential in all terrestrial and freshwater ecosystems and are the most diverse and abundant animal group. Yet there are major knowledge gaps concerning ecology, population genetics, and responses to management practices. Recently reported global declines in insect abundance, biomass, and diversity suggest a pressing need to fill these knowledge gaps. Here, I present work that address these knowledge gaps by exploring ways to generate more insect records for biodiversity datasets, investigating how ecological restoration practices influence beetle occurrence, and defining the population genetics of a habitat-specialist beetle. First, I present a novel biodiversity monitoring approach, the Rapid, Recurring, Structured Survey (RRSS). The RRSS can be flexibly applied to meet diverse objectives and can generate data for different taxonomic groups that can be statistically analyzed. Comparison of an insect and avian dataset generated by the RRSS to an insect and avian dataset generated via a community-science biodiversity survey (bioblitz) shows the RRSS was less taxonomically, spatially, and temporally biased than the bioblitz dataset. Moreover, RRSS data was able to be analyzed in statistical models, while bioblitz data could not be tested appropriately. Next, I investigated how grassland restoration practices and fine-scale habitat characteristics influence occupancy and abundance of beetles in the families Scarabaeidae and Carabidae. Insects are often not included in restoration planning, and elucidating insect responses to restoration can enhance insect conservation. We found restoration practices that increase vegetation diversity and habitat heterogeneity were positively associated with occupancy probability of a variety of species across families. Further, similar levels of family-level abundance were estimated across our study area and there was a negative relationship between Scarabaeidae abundance and basal area of woody plants. Finally, I define the population genetics of Tetraopes texanus by sampling populations across its range. Tetraopes texanus occurs primarily in Texas and Oklahoma, but also occurs in Black Belt prairies of Mississippi and Alabama. Mitochondrial and nuclear DNA analysis identified two distinct population clusters of T. texanus corresponding to the Texas and Oklahoma population and the Mississippi and Alabama population. Further, results indicate ongoing isolation of the two populations and suggest a unique biogeographic history.
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    Equivalent Modeling of Medium-Voltage Gate Drive Circuitry
    (University of Alabama Libraries, 2023) Helton, Jared; Lemmon, Andrew N
    There has been a recent increase in the utilization of wide bandgap (WBG) devices in power electronic converter designs. Designs leveraging these devices are capable of achieving high efficiencies and increased power density as compared to more traditional Silicon (Si) based converters. The same behaviors responsible for the increase in utilization of WBG devices also cause an increase in electromagnetic interference (EMI) and potential false turn-on events. The high edge rates for the devices can induce significant current through the gate-to-drain capacitor, causing disturbance voltages across the gate-to-source nodes. The gate-to-source voltage controls whether the device turns on or off, and the disturbance voltages can be severe enough to cause shoot through or even cause the device to fail. Additionally, the more spectrally rich profiles for WBG devices creates challenges for common-mode (CM) conducted emissions behavior that can also negatively affect the gate drive design. This dissertation leverages a decomposition technique to derive equivalent models for the differential-mode (DM) and CM behavior for a medium voltage gate driver. A set of DM and CM templates for a generalized two-line system are leveraged with a design procedure to resolve the equivalent models. These models are then mathematically validated in a state-space simulation environment across a wide range of parameter values. Once validated, the models are then analyzed to identify influential parameters that can potentially disrupt the gate-to-source voltage for the high-side switching device. Specifically, the device capacitor network and gate resistor asymmetry are shown to be highly sensitive parameters for the gate-to-source voltage disturbance. The equivalent models are then validated on an empirical evaluation platform across a broad range of configurations. Additionally, a set of empirical studies are carried out to validate the predicted behavior provided in the analysis. The device capacitor ratio has been previously shown to be a sensitive parameter for the gate-to-source voltage, and this is reaffirmed in the empirical studies. The influence of the gate resistors is a unique behavior solely identified by leveraging the DM and CM equivalent models. The gate resistor asymmetry is shown to be a parameter that can be leveraged to increase the reliability of a gate drive design in an otherwise susceptible configuration. Specifically, placing all or most of the gate resistance at the gate node significantly improves the reliability of the gate drive design.
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    Factors Controlling the Abundance and Distribution of Microplastic Particles in Surface Sediments of Mobile Bay, Alabama
    (University of Alabama Libraries, 2023) Kandow, Alyssa Noel; Donahoe, Rona J.
    Microplastic particles are an environmental concern due to their ability to leach and adsorb pollutants while being small enough to be ingested by aquatic organisms. This study provides the first results of microplastic particle abundance and distribution in the sediments of Mobile Bay, Alabama. Results provide insight into areas of coastal Alabama at greatest risk for anthropogenic plastic pollution which can help guide coastal management practices and assessments of ecosystem health.Microplastic particle abundances were analyzed in fifteen surface sediment samples within Mobile Bay. Density separation with a saturated sodium chloride solution removed microplastic particles from sediments and particles were characterized and quantified using optical microscopy. Fibers are the most common particle shape representing 87.1% of all identified microplastic particles. Particles are commonly red, blue, or colorless. Most of the identified microplastic particles are <100 μm. The mean microplastic particle length is 180.6 ± 273.4, with a range of 45 μm to 2095.9 μm. Microplastic particle abundances in sediments range from 300.4 to 2967.4 particles/kg dry sediment, with an average of 1675.8 ± 721.0 particles/kg dry sediment. The greatest microplastic particle abundances are on the eastern side of Mobile Bay, where potential sources of microplastic particles include residential runoff, wastewater treatment plant effluents, and runoff from biosolid-amended agricultural fields. The sediment grain size distribution in Mobile Bay and the eastern Mississippi Sound is also identified in this study by analyzing 679 surface sediment samples with a laser particle size analyzer. Sediments are classified mostly as silt and sandy silt and range from mud to sand. Sediments are coarser near the shorelines of Mobile Bay and the eastern Mississippi Sound and become finer grained towards the centers of the estuaries. Sediment grain size, total organic carbon, and loss on ignition values are compared to microplastic particle abundances, but no correlations are found. There are also no correlations between microplastic particle abundance and bottom water parameters (temperature, pH, dissolved oxygen, conductivity, and salinity). Sediment microplastic abundances and phthalate concentrations are greatest in northern Mobile Bay suggesting that both pollutants may be primarily transported into the bay by rivers.
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    Transportation Digital Twin Framework and its Vulnerabilities Against Cyber-Attacks
    (University of Alabama Libraries, 2023) Irfan, Muhammad Sami; Rahman, Mizanur
    Digital twin (DT) systems aim to create virtual replicas of physical objects that are updated in real-time with their physical counterparts and evolve alongside the physical assets throughout their lifecycle. Transportation systems are poised to significantly benefit from this new paradigm. In particular, DT technology can augment the capabilities of intelligent transportation systems. However, the development and deployment of networkwide transportation DT systems need to take into consideration the scale and dynamic nature of future connected and automated transportation systems. Therefore, there is a need to understand the requirements and challenges involved in developing and implementing such systems.This thesis investigates the development of a Transportation DT (TDT) system framework and all related components alongside an assessment of the vulnerabilities of such a system against cyber-attacks. Accordingly, the concept of DT and its relationship with the transportation system is investigated. Current studies on the safety and mobility enhancement applications using DT are surveyed. A hierarchical concept for a TDT system starting from individual transportation assets and building up to the entire networkwide TDT is presented. A reference architecture is also presented for TDT systems that could be used as a guide in developing TDT systems at any scale within the presented hierarchical concept. The study also investigates the vulnerabilities of the system against cyber-attacks with respect to each part of the architecture. Based on the vulnerability assessment of the system, an intelligent attack model is developed that uses a Reinforcement Learning (RL) based attack agent to execute a sybil attack on the system. This attack model is implemented in a simulation scenario using a microscopic traffic simulation software with the goal of creating congestion within a TDT system. The analyses revealed that the RL agent can learn an optimal policy for creating an intelligent attack.
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    Exploring the Legacy of Three Colombian Women Composers: Amparo Angel, Alba Potes and Natalia Valencia Zuluaga: Historical Background and Compositions
    (University of Alabama Libraries, 2023) Aldana Porras, Lina Alejandra; Molina, Moises Dr.
    For the final project, I have selected three living composers: Amparo Angel, Alba Potes, and Natalia Valencia Zuluaga, known for their different styles, whose music has been successfully played in Colombia and outside the country. In this research, I will discuss three pieces: "Trio Op. 32 for Violin, Cello, and Piano" by Amparo Angel, "Toque de Arrullos" for Cello Solo by Alba Potes, and "Hilos" for Cello and Piano by Natalia Valencia Zuluaga. I will provide historical background for each of the composers and their respective pieces, explore the context in which they were created, and give an overview of each piece. My aim is to showcase these three very important Colombian women composers and their cello compositions.
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    The Lived Experiences of Black Women with PCOS from Diagnosis to Treatment: a Narrative Approach
    (University of Alabama Libraries, 2023) Opoku, Annabella Achiaamah; Bradley, Lilanta J
    Polycystic ovary syndrome or polycystic ovarian syndrome (PCOS) is a hormonal and reproductive health condition that affects women of reproductive age. PCOS is quite common among women of all races/ethnicities between the ages of 15-44, with 5-10% of them having the condition. Although PCOS affects all women of childbearing age, regardless of race/ethnicity, the literature has found that Black women have a higher risk of suffering from complications like MetSyn. There is limited data on this phenomenon, but it poses the question of what factors play a role and how that can impact diagnosis and treatment plans for Black women. The goal of this study is to better understand Black women's experiences when seeking diagnosis and treatment for PCOS from the moment they suspect having the condition to receiving treatment recommendations. The participants recruited for this study included seven adult females in the age range 18-34. Eligible participants are women who self-identify as Black or African-American (non-Hispanic/Latino) and live in the U.S. Inductive thematic analysis to analyze the data by patterns and themes that arise from the data. The interviews were held virtually through Zoom to comply with COVID-19 guidelines and allow participants who otherwise could not participate because of distance to be included in the study. A phone screening process was conducted to pre-screen participants to determine whether they were eligible. Once eligible, participants had the opportunity to consent to participate and be audio-recorded for the study verbally. Participants were instructed to complete a brief survey on Qualtrics that collected demographic information. Within the interviews, subthemes were identified in various aspects of participants' experience with PCOS. The interviewees expressed their thoughts regarding steps that led to diagnosis, their interactions with their providers, receiving support, and the impact PCOS has had on them. Having Black woman share their stories surrounding PCOS is important in understanding what health disparities impact their health outcome and how PCOS exacerbates that and also spreading awareness on the condition for both them and their providers.
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    Effective Mitigation of Polysulfide Shuttle Effect Through Surface-Engineered and Hetero-Structure-Engineered Cathodes for Metal-Sulfur Batteries
    (University of Alabama Libraries, 2023) Wei, Zhen; Wang, Ruigang
    Environmental pollution caused by the continuous consumption and burning of fossilfuels is harmful to human health. Wind energy and solar energy cannot be extensively applieddue to their intermittent nature. Therefore, renewable, clean, and sustainable energy storagesystems such as rechargeable batteries are in urgent need in order to meet the increasingrequirements of the large-scale production of portable electronic devices and electric vehicles. Inaddition to lithium-ion batteries, lithium–sulfur (Li-S) batteries are an important focus ofacademic and industrial energy storage research owing to their higher theoretical energy density(2,600 Wh kg−1) and the use of low-cost materials. The sulfur cathode with favorablecharacteristics such as natural abundance and environmental friendliness makes Li-S batteries apromising next-generation energy storage technology. According to similar electrochemicalconversion mechanisms, the low-cost sulfur cathode can also be coupled with a wide range ofmetallic anodes, such as sodium (Na), potassium (K), magnesium (Mg), and aluminum (Al).These new "metal–sulfur" battery systems have demonstrated promising potential in loweringthe production cost and/or producing high energy density. The current state of the researchdemonstrates that metal–sulfur batteries are now at the transitioning point from laboratory-scaledevices to a more practical energy-storage application. However, practical commercialization isgreatly hindered by the notorious technical challenge known as the polysulfide shuttle effectinducing a huge loss of active material and rapid capacity decay. The overall objective of thisdissertation aims to effectively mitigate polysulfide shuttling and improve the long-termelectrochemical performances of rechargeable metal-sulfur batteries. To achieve that, we proposetwo effective technical concepts, which are surface engineering and heterostructure engineeringof sulfur-based cathodes in metal-sulfur batteries.
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    Investigating Specific Aspects of Adjudicative Competence in Adults with Autism Spectrum Disorder
    (University of Alabama Libraries, 2024) Hayes, Jenna K.; Salekin, Karen
    Given the United States' high incarceration rate and rising prevalence of diagnosed autism, it is important to explore the unique challenges that people with autism experience in navigating the criminal legal system (Centers for Disease Control and Prevention [CDC], 2023; Chester et al., 2022; Collins et al., 2022; King & Murphy, 2014; The Sentencing Project, 2023; Walmsley, 2013). The primary aims of the present study were to: (1) investigate whether adults with autism experience particular difficulties in meeting the criteria for adjudicative competence, and (2) assess the impact that measured intelligence and theory of mind may have on competence-related abilities. These aims were accomplished using a sample of 34 adults with autism from across the country to compare their scores on the Understanding and Reasoning scales of the MacArthur Competence Assessment Tool–Criminal Adjudication (MacCAT-CA; Hoge et al., 1999) and determine whether IQ and/or theory of mind were able to predict outcomes on the MacCAT-CA. Participants completed a demographic questionnaire, measures of IQ and theory of mind, and the MacCAT-CA. Results indicated that participants demonstrated a unique response pattern on the MacCAT-CA such that their scores on the measure may have been influenced by traits of autism rather than an actual lack of competence-related abilities. Neither IQ nor theory of mind were able to explain the differences observed between participants' Understanding and Reasoning scores. This study's results highlight the importance of forensic evaluators affording particular attention to potential indicators of autism in the defendants they evaluate, as these individuals may possess traits that interfere with their adjudicative competence but are not captured by traditional competence measures.
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    Success of Undergraduate African American Nursing Students in a Clinical Setting
    (University of Alabama Libraries, 2023) Reed, Valerie L; Atkinson, Becky
    This study examined the clinical experiences of African American nurses who graduated from a Bachelor of Science in Nursing (BSN) program at a predominantly White institution (PWI) in the previous 5 years. Currently, African American registered nurses are underrepresented in nursing practice. According to the literature, African American nurses have a higher attrition rate in baccalaureate schools of nursing than other minority groups, a trend that contributes to this underrepresentation. The literature identifies several contributors to the high attrition rates, including stereotype threat persisting throughout the students' matriculation in PWIs and barriers within the clinical environment. The literature also identifies contributors to successful matriculation in nursing schools, such as a positive clinical experience that serves as a significant contributor to African American academic success, perseverance, and the feeling of inclusion as enablers. Questions arise about what specifically constitutes a successful clinical experience for African American nursing students (AANS). This study used a qualitative approach to investigate the experiences of African American nurses in a clinical setting who attended a BSN program at a PWI in the previous 5 years. Participants used counterstories as semistructured face-to-face or Zoom video interviews. I analyzed the data using the constant comparative data methodology. Critical race theory and minority stress theory informed the data. The qualitative study findings identified former AANS' barriers and enablers in addition to their successful experiences in the clinical setting. I categorized the themes emerging from the data to provide information for nursing programs to support the needs of undergraduate AANS to reduce attrition.
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    A Home in the Village: a Constructivist Grounded Theory Inquiry on the Adoption of Older African American Foster Youth with Severe Emotional and Behavioral Challenges
    (University of Alabama Libraries, 2023) Pressley, Tracy Denise; Nelson-Gardell, Debra
    ABSTRACT This qualitative study used constructivist grounded theory to understand the experiences of African American adoptive parents who adopted their teenage African American foster children with severe emotional and behavioral challenges. It also theorized the successful adoption of these children, often deemed "unadoptable". According to the 2022 Adoption and Foster Care Analysis and Reporting Systems (AFCARS) from the U.S. Department of Health and Human Services, adoption outcomes for children over the age of 13 years, were bleak, with only 12% of them being adopted in 2021.Bhattacharyya's (2004) Community Development Theory was used as the theoretical framework for this inquiry, with five research questions guiding the study: (1) How can we theorize successful adoptions of older African American foster youth with emotional and behavioral challenges? (2) How do current and former foster parents who have adopted older African American youth with severe emotional and behavioral challenges explain their motivations for doing so? (3) How would adoptive parents describe their adoption experience(s) with the private child-placing agency? (4) How would adoptive parents describe their adoption experience(s) with the state's public child welfare department? (5) What steps have adoptive parents taken to feel prepared to parent older children with emotional and behavioral challenges? Purposive sampling was used to identify the five participants and the "best" initial interviewee, ending with the theoretical saturation of themes and the elucidation of the related categories. Data gathering strategies included semi-structured interviews, reviews of agency databases, records, and state and federal foster care and adoption data.This study resulted in the development of a new social work practice theory, the Afrocentric Village Theory for the successful adoption of older African American foster youth with severe emotional and behavioral challenges, which includes three key contributors and their corresponding sub-contributors: 1) key contributor - motivation, sub-contributors: community self-help, religion/spirituality, love, fostered their adopted child; 2) key contributor - preparedness to adopt, sub-contributors: specialized preservice training, specialized in-service training, human services work experience, belief in Strong Black Woman (SBW) ideology; and 3) key contributor – support, sub-contributors: agency support, child Protective Services (CPS) support, family support, community support.
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    Zinc and Cobalt Electrodeposition Using Eutectic Mixture of Urea and Choline Chloride Ionic Liquids
    (University of Alabama Libraries, 2023) Lenka, Rajyashree; Reddy, Ramana G.
    In this study, the electrodeposition of critical base metals like zinc and cobalt using a eutectic mixture of urea and choline chloride (molar ratio 2:1) ionic liquid was discussed. The experimental variables namely temperature, cell voltage and concentration were considered for the deposition process. A two-electrode set-up was used for the electrodeposition with copper sheet as working electrode and platinum wire as a counter electrode. XRD and SEM analysis were done to study the crystalline orientation and surface morphology of the surface deposits. The critical parameters in the electrodeposition processes were identified . Zinc was deposited from zinc oxide on copper cathode using urea/choline chloride ionic liquid. The dissolution of zinc oxide in ionic liquid was studied using FTIR spectrum. An additional peak at 2150cm-1in the spectrum confirmed the dissolution of 0.82M ZnO in 2:1 Urea/ChCl. Temperature was varied between 363-373K and potential between 3.0-3.3V to obtain higher current efficiency and low energy consumption . At a fixed concentration of 0.82 M of ZnO, 373 K and 3.3 V, the highest current efficiency of 96.85% and the low energy consumption of 2.79 kWh/kg was recorded. XRD and EDS analysis confirmed the presence of zinc layer of high purity. The parameters for cobalt electrodeposition were temperatures (343-383K),cell voltage (2.7-3.3V) and concentration of cobalt chloride (0.2-0.6 mol/L).Pure cobalt was deposited from cobalt chlorides in a 2:1 urea/ChCl solvent and conditions to obtain maximum current density was investigated. At 0.2M CoCl2 and 3.0V, a current density of 140A/m2 was measured at 383K due to increased conductivity of electrolyte at higher temperature. Further at 383K, 0.2M CoCl2 and 3.3V, a higher current density of 157 A/m2 was obtained due to better ionic mobility at high potential. Fixing the parameters at 383K and 3.3V, the concentration of CoCl2 was varied to obtain a highest current density of 171 A/m2 at 0.4 mol/L. Beyond 0.4M CoCl2,the current density decreased. SEM and EDS analysis confirmed the deposition of cobalt on the cathode surface.
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    Assessing the Crustal Source Depth and Cause of Magnetization North of Caloris Planitia, Mercury
    (University of Alabama Libraries, 2023) Richardson, Ramon Antonio; Plattner, Alain M.
    The Mercury Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) spacecraft made history as the first to orbit Mercury, the innermost planet of our solar system. During its low-altitude orbits, MESSENGER recorded magnetic signals originating from the crust of Mercury. Initial analysis of these measurements revealed short-scale features that were consistent across orbits. However, the underlying geological processes responsible for these observed crustal magnetic field features remain uncertain. One hypothesis is that the magnetic features were formed in the ejecta blankets of impactors. According to this hypothesis, the impactor material would mix with the crustal material, settle as the ejecta blanket, cool, and then become magnetized in an active core magnetic field. As Mercury's crust typically contains a low amount of magnetic carriers, the introduction of impactor material could locally enhance the presence of magnetic minerals. In this study, I aim to test this hypothesis by investigating the depth of the magnetic sources within a specific region in Mercury's northern hemisphere. The chosen region spans latitudes 48° N to 70° N, and longitudes 115° E to 225° E. This region is north of Caloris Planitia, the largest impact crater on Mercury. My findings reveal that the depth to magnetization in the study region is between 50 km to 60 km and thus significantly exceeds the estimated maximum thickness of the ejecta blanket, which is less than one km. This outcome suggests that the original hypothesis may be incomplete. Whereas the magnetic field observed in the study region may still be associated with the Caloris impact, it is likely influenced by the impact's effects at greater depths rather than solely being caused by the ejecta blanket near the surface.
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    Higgs-Portal and Z'-Portal Dark Matters in Brane-World Cosmologies
    (University of Alabama Libraries, 2023) Liu, Taoli; Okada, Nobuchika
    According to various astrophysical and cosmological observations, Dark Matter (DM) accounts for approximately 27% of the Universe's total energy density. However, no viable DM particle candidate exists within the framework of the Standard Model (SM) of particle physics. An electrically neutral, weakly interacting massive particle (WIMP) from physics beyond theSM emerges as an appealing candidate for DM. In this dissertation research, we consider the WIMP DM model within the framework of 5-dimensional brane-world cosmology. In this setup, our familiar 3-dimensional space is realized as a hyper-surface embedded in a 4-dimensional space. Within this context, all SM and DM fields are confined to the hyper-surface, while the graviton resides in the bulk. We explore two well-established brane-world cosmologies: the Randall-Sundrum (RS) and the Gauss-Bonnet (GB)brane-world cosmologies. These models reproduce the standard Big Bang cosmology at temperatures below the so-called "transition temperature." However, at higher temperatures, they introduce significant modifications to the universe's expansion dynamics. This non-standard expansion law directly influences the predictions related to WIMP DM physics.In our investigation, we consider two well-founded WIMP DM models: the Higgs-portal scalar DM model and the Z′-portal DM model. We analyze the effects of brane-world cosmology and identify the allowed parameter space by incorporating constraints from the observed DM relic density, as well as data from direct and indirect DM detection experiments. It is worth noting that for both DM models, the allowed parameter regions are severely restricted within the conventional Big Bang cosmological framework. Our findings reveal that these allowed parameter regions face even more stringent limitations in the RS cosmology, and in some cases, they may even disappear entirely. Conversely, the GB cosmological effects significantly expand the regions of parameter space that are allowed. Furthermore, the discovery of Higgs-portal or Z′-portal DM within the GB brane-worldcosmology would enable us to determine the transition temperature.
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    Growth Characterization of Mesophotic Rhodoliths in the Northern Gulf of Mexico Using Radiocarbon Dating
    (University of Alabama Libraries, 2023) Olmstead, Sarah A; Andrus, C. Fred T
    Boxwork rhodoliths are characterized by a multitaxonomic composition and excessive void spaces, and they are distributed from the intertidal zone to the lower limits of the photic zone. While growth rates and patterns in rhodoliths from shallower depths and simpler morphologies have been assessed using incremental and geochemical analyses, rhodoliths from mesophotic depths have rarely been studied. Furthermore, boxwork rhodoliths have proved too structurally complex for age and growth rate assessment techniques such as stable oxygen isotopes profiling or elemental mapping. Therefore, we utilized sequential radiocarbon analysis for growth characterization of mesophotic boxwork rhodoliths. Rhodoliths were collected from the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico from one location at 48 – 72 m and another at 200 m, spanning the range of the mesophotic zone. Specimens were extensively sampled for radiocarbon concentrations from predicted nucleation points and along growth axes. From depths of 48 – 72 m, nucleation ages ranged from 795 ± 20 to 3270 ± 25 14C ybp. From depths of 200 m, nucleation ages ranged from 8960 ± 110 to 13050 ± 150 14C ybp, dating back to the end of the Pleistocene in some cases. Several rhodoliths contained evidence of growth hiatuses, with deeper samples displaying age reversals that complicated the apparent growth history. We define age reversals to be non-sequential ages within a sampling sequence, typically a singular age before the return to normal age sequence. The research presented here includes the oldest known living rhodoliths, with the oldest rhodoliths grown before and after Holocene sea-level stabilization. These results have implications for the use of rhodoliths as paleoenvironmental indicators, and provide better understanding of the range and volume of carbonate production in these habitats.
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    Mechanisms, Microstructures, and Mechanical Behavior in Cold Spray Refractory Metals
    (University of Alabama Libraries, 2023) Roper, Brett Elizabeth Tucker; Brewer, Luke N
    This dissertation provides the first investigation of laser assisted cold spray (LACS) and laser heated cold spray (LHCS) for the refractory materials tantalum and niobium. Refractory metals possess many desirable material properties, such as high melting temperatures (generally over 2,000℃) and excellent wear resistance. Traditional melt-based additive manufacturing (AM) processes can achieve things like near-net-shaped components but can face particular challenges in creating depositions of refractory materials. The high melting temperatures of refractory metals make melt-based additive manufacturing difficult, necessitating a heat source capable of reaching such temperatures, which also poses challenges in using dissimilar metals for coating or repair due to potential issues like porosity, oxidation, tensile residual stresses, and excessive heat input during the re-solidification process. A solid-state AM process such as CS could allow for the deposition of refractory materials without the challenges associated with melting. This work shows the potential for in situ laser heating applied to cold sprayed refractory metals. The dissertation also provides a detailed, nanoscale examination of the fundamental mechanisms that control deposition and bonding during HPCS of these materials. Precession electron diffraction (PED) experiments revealed that a distinct network of local misorientation was formed in spherical tantalum particles after impact on tantalum and SS304L substrates. While cold gas dynamic spray (CS) is capable of depositing niobium and tantalum, in situ laser-heating can improve the mechanical properties and deposition characteristics of cold sprayed material. In compression, the cold-sprayed material exhibited increased yield stress over wrought due to the work hardening aspect of the cold spray process, and, if needed, an annealing process can restore the mechanical properties of the coating in compression to that of the wrought condition. LHCS showed complete recrystallization of the coating at 1.5 kW of laser heat input for tantalum and 1.0 kW of laser heat input for niobium. The high temperature mechanical behavior and microstructural evolution of cold sprayed niobium and tantalum are also examined and compared with laser annealed materials.
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    Employing a One Health Perspective to Investigate Naegleria Fowleri and Antibiotic Resistance
    (University of Alabama Libraries, 2023) Stahl, Leigha M.; Olson, Julie B.
    The "One Health" concept recognizes that the health of people, animals, and the environment are connected. Under this umbrella of potential intersections, I investigated the microbial ecology of Naegleria fowleri, known as the "brain eating" amoebae, and patterns of antibiotic resistance in bacteria isolated from animals at a zoo and wildlife rehabilitation center. N. fowleri thrives in freshwater and can infect humans during recreational water activities, often leading to fatal primary amoebic meningoencephalitis (PAM), emphasizing the need to understand how this amoeba persists in the environment to decrease human exposure. In my second chapter, I reviewed the abiotic and biotic factors affecting the distribution of N. fowleri within the environment. In chapter three, I studied the interactive effects of three abiotic factors (temperature, salinity, and pH) on N. fowleri growth in deionized water and environmental water. Results indicated that N. fowleri growth was highest at 25° C, and multiple interactive effects occurred between the abiotic factors. My fourth chapter investigated the habitat suitability of N. fowleri across the contiguous United States for the present-day and future using ecological niche modeling using occurrence data from three datasets. Outcomes were used to project habitat suitability up to the year 2060 for three climate change scenarios. Results suggested suitable and unsuitable habitats for N. fowleri exist across the country, where the highest suitable habitat was in the southern half of the US and habitat suitability for N. fowleri generally decreased across time and future climate change scenarios. To address antibiotic resistance, I investigated patterns of antibiotic resistance in bacteria isolated from the feces of zoo mammals (Chapter 5) and raptors admitted to a rehabilitation center (Chapter 6). Using fecal samples from raptors, antibiotic resistance of bacterial isolates was evaluated using phenotypic susceptibility screening. Results suggested antibiotic resistant phenotypes occurred in raptor fecal bacteria prior to rehabilitation and upon release. Ampicillin and tetracycline resistance were common in isolates, and trimethoprim and trimethoprim-sulfamethoxazole resistance occurred after birds were housed at the rehabilitation center. This research is a necessary step to assess antibiotic resistance in wild raptors and determine what factors contribute to antibiotic resistance.
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    Envisioning Urban Air Mobility in Small and Medium-Sized Urban Areas in the United States
    (University of Alabama Libraries, 2023) Yang, Chenxuan; Liu, Jun
    Urban Air Mobility (UAM) represents a revolutionary innovation that utilizes low-altitude urban space to provide air transportation. While UAM offers numerous advantages and holds promise as a solution to traffic congestion, it faces various constraints, including public acceptance, economic considerations, and management challenges. While extensive research has explored the integration of UAM into mobility systems for large metropolitan areas, the potential benefits it could bring to smaller urban areas with populations under 350,000 have been under-discussed. This dissertation research aims to assess the feasibility and viability of implementing UAM in small and medium-sized urban areas. The first major study in this dissertation involves a national survey to investigate Americans' willingness to pay for URAM services and their preferences when faced with commutes that exceed a certain duration. The second study evaluates the impact of UAM on over 300 small and medium-sized urban areas by comparing the travel accessibility of existing road-based regional transportation systems with hypothetical UAM-integrated systems. These hypothetical UAM networks interconnect vertiports within regions, enabling travelers to reach their destinations via Vertical Take-Off and Landing (VTOL) aircrafts after reaching the nearest vertiport by ground transportation. The third study explores an innovative intermodal mobility system that integrates Shared Autonomous Vehicles (SAVs) and VTOLs within the UAM framework. Agent-based simulations are employed to assess the feasibility and viability of this system in small and medium-sized urban areas. This dissertation sheds light on the benefits and trade-offs associated with UAM in small and medium-sized urban areas. It serves as a valuable resource for evaluating the practicality of intermodal UAM services and informs policies related to the planning and implementation of UAM services in the United States.