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Modeling and Design Optimization of Thermal Hydraulic Systems for Advanced Reactor Applications
No full textThis study presents the thermal���hydraulic phenomena within advanced reactor applications for design and modeling. It is organized into three main sections, each tackling distinct yet interconnected aspects of thermal���hydraulic applications in advanced nuclear reactors.
In the second main section of this dissertation, artificial neural networks (ANNs) and advanced machine learning algorithms are used to predict the friction factors and flow regimes that change from laminar���to���transition and transition���to���turbulent in wire-wrapped fuel assemblies. The ensemble methods showed superior performance for classification of the flow regimes, with accuracies exceeding 95%. The ANN model for friction factor outperformed traditional correlations, with a mean error of 0.10%. This study represents a significant advance in understanding and predicting hydrodynamics in wire-wrapped fuel assemblies.
The third main section identifies the most promising phase change materials for latent heat thermal energy storage in high-temperature applications for heat pipe���cooled microreactors. Twenty-one eutectic salts were studied based on their thermophysical properties and performance metrics. The most promising candidates were MgCl2���NaCl and CaCl2���NaCl. In addition, copper and aluminum foams were investigated for compatibility and durability under extreme conditions. The mixture of copper foam and CaCl2���NaCl exhibited the least corrosion. After a 300-hour melting/solidification cycle, the melting temperature of CaCl2���NaCl remained stable, confirming its reliability for high-temperature thermal energy storage (TES) applications.
The fourth main section of the research delves into a new concept of a tree-shaped fin design for a latent heat thermal energy storage system. The research has made significant progress by utilizing a novel approach that goes beyond the traditional focus on (i) multi���objective considering both power density and energy density, (ii) investigating all variables freely varying using global searching optimization, and (iii) the constraint of the evenly distributed last branch. The study used surrogate���based multi���objective optimization, specifically the Random Forest model, to explore energy density in volume fractions ranging from 9% to 44%. The study achieved a 33% optimal volume fraction for the fin design, resulting in a 61.6% increase in power density and a 38.18% reduction in melting time compared to conventional plate fin designs.
In essence, the overall objective of this dissertation is to contribute valuable insights and methodologies to the ongoing research targeted at enhancing thermal efficiency, safety, and cost��� effectiveness in advanced reactor designs using computational techniques
Biogas Processing and Safety Challenges: Improving Process Components Functionality Through Reliability Engineering Approach
No full textTo achieve the objectives of carbon neutrality, energy security, and sustainability, biogas is increasingly used as fuel in the transportation and power generation sectors. Due to the support strategies for the reduction of greenhouse gases and air pollution implemented by several governments around the world, biogas production has tripled recently, leading to an increase in the number of related facilities. The forecast indicates a further increase in biogas facilities up to 2035. The number of incidents in the biogas industry has increased more than five times from 2001-2012; this trend outpaces the number of biogas facilities. The following categories of causes can be categorized (in order of quantitative relevance) in the analysis of accident causes and consequences: Failures of the entire piece of equipment, component failures, operational errors, design flaws, and maintenance errors.
The aim of this study is to address safety issues of biogas processing activities based on the process components��� failure analysis and reliability studies. Because of the scarce number of documented biogas processing components��� failure rates and the limited details available, biogas processing plants can benefit from the technologies already used for the processing of conventional natural gas, but due to the modest amounts of biogas produced by production and upgrading plants, the size of biogas processing plants must be substantially smaller. On this basis, this work sourced the existing reliability data from conventional natural gas components��� failure rates databases such as: Industrial database (e.g., Offshore and Onshore Reliability Equipment Database-OREDA), manufacturer���s field failure studies and end-user field failure studies. Selected biogas processing components��� unit(s) from active biogas piping and instrumentation diagram P&ID were utilized and data sourced from industrial database was used to perform series of failure analysis and reliability studies; results obtained from this study can be used to analyze the reliability of biogas processing units.
Enhancing the quality of failure data is critical to decreasing the uncertainties associated with biogas processing system reliability estimates to improve the system availability and maintainability and reduce the increasing number of accidents related to biogas processing. Consequentially, improve system availability and maintainability substantially, hence leading to improved productivit
John Bickham field notebook: AK13501-AK14000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK14001-AK14500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
Border Commuting Student Experiences: Developing Transborder/Transfronterize Identities
No full textOscar Martinez argues that an international border is a ���line that separates one nation from another��� to keep the people in the poor country out of the rich country (1994:5). Border commuters cross international borders daily/weekly and participate in each country's society, straddling both physical and non-physical boundaries in the borderlands (Anzaldua 1987; Carter 2006). This thesis focuses on the identity development of high school border commuters, referred to as transfronterize/transborder students (Stephen 2007; Iglesias-Prieto 2011). In addition to the analysis of transborder complex identities and Prudence Carter���s (2006) concept of student ���boundary straddling,��� this study uses Falc��n Orta & Orta Falc��n���s (2018) Transborder Identity Formation Framework to examine how the experiences of border commuter high school students develop transfronterize/transborder identities. The guiding question in this study is: ���In what ways does border commuting for educational purposes shape the identity development of high school transborder/transfronterize students?��� Two specifying questions follow: ���How well do Falcon Orta and Orta Falcon���s Identity Formation Framework apply to transborder high school students?��� and ���How are the identity development experiences of high school transborder students similar/different to that of transborder college students based on the existing theory?��� To answer these questions, qualitative methods were used to explore transborder students��� self-perception, educational aspirations, and border commuting experiences. The findings indicate that the existing framework for transborder college students applies to the experiences of transborder high school students; however, younger students have influential factors that do not apply to college students and vice versa in developing their complex transborder identities
A Guarantee for Confusion: The Impact of Texas��� Guaranteed Tuition Legislation on Tuition and Fees
No full textIncreases in tuition and fees annually charged to students have resulted in public universities and colleges under scrutiny from state legislators. There are as many approaches to increases in tuition as there are states. States like Texas, Illinois, and Oklahoma have implemented legislation requiring public institutions in their respective states to freeze tuition for students. Unlike other states, Texas has placed the requirement on institutions vs. a requirement placed upon students. This research examines the impact on average tuition and average enrollment for Texas public four-year institutions subjected to that state���s guaranteed tuition legislation, using difference-in-differences, a quasi-experimental method. Panel data from 2008 to 2019 obtained from 531 public four-year universities in the United States via the Integrated Postsecondary Education Data System (IPEDS) were used to address two research questions: (1) At public four-year institutions, does the implementation of a required state-level guaranteed tuition policy option for students lead to changes in annual tuition charges of the aggregate amount of tuition paid by students over four years? (2) At public four-year institutions, does the implementation of a state-level guaranteed tuition policy option lead to changes in enrollment for students?
The analysis found the Texas legislation did not significantly increase the average annual tuition charged to in-state students. On average, the legislation did result in a .96 decrease in the average required fees. The analysis also found there were positive changes in enrollment after the imposition of the guaranteed tuition plan legislation. The findings of this study provide insight into the consequences associated Texas��� guaranteed tuition plan legislation. For state policymakers, this study suggests the way in which a guaranteed tuition plan is structured is impactful. For institutional leadership, this study suggests room for improvement in how these plans are described and marketed to students and their families
Triple-Tuned Radiofrequency Coil Designs for Magnetic Resonance Imaging and Spectroscopy
No full textMulti-nuclear MRI/S has been shown to be a powerful tool for both diagnostics and the study of disease. While the potential of this technology has been recognized for decades, widespread clinical adoption of these techniques has been limited in large part due to the continued inaccessibility of multi-nuclear hardware. The work presented here aims to address the many design considerations of multi-nuclear RF coil designs, which are necessary to support biomarker development for Duchenne muscular dystrophy (DMD).
This work specifically details the design, construction, and characterization of several triple-tuned coil designs. First, a triple-tuned nested volume coil design composed of a pair of nine-leg birdcages designed to create parallel fields and an orthogonal saddle coil insert at 4.7T. The nine-leg birdcage pair was designed such that it could geometrically decouple from any orthogonal insert coil, either a dedicated planar receive coil or an orthogonal volume coil to operate in either the double- or triple-tuned configurations. SNR comparisons were specifically drawn between geometric decoupling design and active detuning.
Next, a truly simultaneous triple-tuned trap design was investigated for the use in scalable receiver arrays. This design proposes a parallel trap network in place of a more conventional series design to theoretically decrease the equivalent series resistance of the resultant trap network. A roughly 20% improvement in SNR was seen for 1H, but the theoretical sensitivity gains for the X-nuclei frequencies could not be fully resolved. The parallel trap network was compared to both a double- and triple-tuned series trap designs. X-nuclei sensitivities were close in both the double- and triple-tuned reference coils, indicating the additional losses from triple-tuning are minimal in comparison.
Finally, a modular multi-nuclear array was designed and characterized to enable a biomarker study on canine models of DMD. This design used a series PIN diode as a broadband active detuning network to enable decoupling independent of both position and frequency for stacked receive coils. Comparisons were specifically made between this broadband network and a conventional narrow band trap detuning mechanism. Comparisons were also made between a single larger loop and an inscribed array for 1H, 31P, and 23Na
BATF3 and IRF4 Control iTreg Cell Fate Decisions
No full textFOXP3 is the lineage-defining transcription factor for Tregs, a cell type critical to immune tolerance, but the mechanisms that control FOXP3 expression in Tregs remain incompletely defined- particularly as it relates to signals downstream of TCR and CD28 signaling. In this dissertation, I studied the role of IRF4 and BATF3, two transcription factors upregulated upon T cell activation, to the conversion of conventional CD4+ T cells to FOXP3+ T cells (iTregs) in vitro. I found that BATF3 is a potent inhibitor of FOXP3 expression and iTreg differentiation but is dependent on interactions with IRF4 to mediate this inhibition. BATF3 allows IRF4 to bind an upstream regulatory region within the Foxp3 super enhancer. I further demonstrate that interactions of these transcription factors are necessary for glycolytic reprogramming of activated T cells that is antagonistic to FOXP3 expression and stability. However, I also show that BATF3 and IRF4 play critical roles to iTreg function, demonstrating unique roles for these transcription factors in FOXP3 induction vs. in differentiated iTregs. Thus, my findings highlight how BATF3/IRF4 interactions contribute to the complex interplay between TCR signaling, FOXP3 expression and stability, and iTreg function while providing important insights to cellular mechanisms that govern expression of the Foxp3 locus
John Bickham field notebook: AK10501-AK11000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK11001-AK11500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
D-modules and the Cauchy-Kovlevskaya Theorem
No full textThis is an expository article served as an elementary introduction to the theory of algebraic D-modules. For the first part, we give the definition and basic properties of D-modules. We take advantage of the sheaf theory and compare the results of complex manifolds with those on affine spaces. We particularly focus on introducing the characteristic varieties of D-modules. For the second part, we introduce the classical Cauchy-Kovalevskaya theorem. Using the languages of category theory and homological algebra, we give a generalized version on affine spaces, which is a simplified version of the Cauchy-Kovalevskaya-Kashiwara theorem
Thalamic Modulation of Hippocampal Context Memories During Conditioned Fear Learning
No full textMaladaptive fear poses a significant public health burden, particularly in the forms of anxiety and stress-related disorders such as posttraumatic stress disorder (PTSD), anxiety disorders, and phobias. A popular treatment for these disorders is exposure therapy, which utilizes the 'extinction' of fear through repeated, unreinforced presentation of a stressful cue. However, while effective, these therapies are still susceptible to relapse, in part because extinction memories are highly context dependent. Understanding the neural mechanisms underlying the contextual control of fear suppression becomes particularly important. Recent work has implicated the thalamic nucleus reuniens (RE) in extinction by allowing for bidirectional communication between the prefrontal cortex (PFC), involved in higher-order cognition, and the hippocamps (HPC), which encodes context information. This dissertation examines the specific role of the RE in modulating HPC context information. I first show that the RE is not involved in the storage of extinction memories, and then show that context representations in the HPC can be used to determine appropriate responding to fearful cues. Finally, utilizing selective interference of context memory formation, I illustrate that the RE relies on HPC context memories in order to exert control over contextual processes. Collectively, these data reveal a role of the RE in the suppression of context-inappropriate behavior and, therefore, in encouraging context-appropriate responses to ambiguous cues