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Multi-Physics Modeling and Simulations of Heat Pipe Cooled Graphite Moderated Micro Reactor
No full textHeat pipe micro reactors are compact, innovative nuclear reactors that utilize heat pipe technology to manage heat transfer efficiently. The advantage of heat pipe micro reactors lies in their reduced complexity, high efficiency, and ability to provide stable power in various scenarios where traditional, larger reactors are not feasible or practical. This research presents a multi-physics analysis focusing on a proposed design of 0.5 MWth heat pipe cooled, graphite moderated nuclear micro reactor. The main driver of the design study was to achieve enhanced safety characteristics, while maintaining long core lifetime and excellent power producing capabilities. The envisioned outcome was a versatile design adaptable to various purposes including remote locations and space applications.
In order to assess the safety characteristics of the design, investigations of the main reactor parameters were performed through developing a multi-physics tool, that included a neutronic model, point kinetics model, thermal conduction model, heat pipe model, and mechanical model. All models were coupled through a python wrapper to allow for appropriate data exchange. The neutronic model of the design was developed using MCNP and Serpent Monte Carlo codes, in order to calculate important parameters including criticality, control devices worth, power distribution, and temperature reactivity coefficients. The thermal conduction model of the solid-state core was developed and coupled to a heat pipe model using Ansys Fluent, to calculate the temperature distribution in the reactor, while Ansys Mechanical was employed to conduct structural mechanical analysis through performing calculations of the stress, strain, and total deformation of the core. Multi-physics simulations of the design were carried out to provide analysis of both steady-state normal operating conditions and transient scenarios, including accidents related to heat pipe and control drum failures. The obtained results were used to assess the safety aspects of the proposed design and provide valuable insights necessary for the development of heat pipe micro reactors in the near future
Impacts of Hurricanes and Algae-Based Jet Fuel on Energy Production Economics and Markets
No full textThis thesis addresses energy economics aspects involving industry disruptions, low carbon technology, and market responses. The first essay explores the impacts of hurricanes on US refineries and fuel markets. Namely we examine hurricane effects on refinery input and output, crude oil imports, gasoline, diesel, and crude oil stocks, as well as pricing dynamics for gasoline and diesel. In terms of findings this study sheds light on disruptions caused by hurricanes and the resultant welfare implications. Findings reveal that hurricane landfall in the Gulf Coast is associated with decreased refinery production for up to six weeks thereafter, with varied effects beyond the Gulf Coast region across the US. Also, hurricanes lead to regional price increases. Overall, we find hurricane strikes decrease total US social welfare, but with differing effects on producers and consumers.
The second essay reports on life cycle assessment and techno-economic analysis of direct air capture supported algae cultivation systems. The analysis focuses on prospects for generating algae-based limonene that is transformed into aviation fuel and biomass for animal feed. The analysis examines the greenhouse gas and economic consequences of a potential technology that integrates CO2 capture to algae growth to limonene and animal feed productions. Challenges of CO2 source, integrating sorbent production and manufacturing, and nutrient recovery processes associated with algae cultivation are explored. The analysis reveals that achieving environmental and economic feasibility requires more than a hundredfold reuse of the CO2 sorbent and hydrogel, currently deemed unreachable. Additionally, the study underscores that utilization of renewable electricity could further diminish the carbon footprint.
In the third essay, we extend the second essay into the strategic domains of product mix and market penetration. We consider multiple limonene applications and algae biomass markets. We find that prioritizing limonene for cleaning and fragrance is superior to using it to produce jet fuel. We also find substantial penetration of the remaining algae-based biomass as animal feed and as a feedstock for electricity generation. Scenarios involving carbon credits and technology subsidies reinforce these findings. Furthermore, we investigate the influence of enhanced limonene yield which is needed for entry into the jet fuel market
From Syntheses to Applications of Cyclized Conjugated Molecules and Macromolecules
No full textThis dissertation delves into conjugated molecules and macromolecules featuring cyclized constitutional structures, including conjugated ladder molecules, polymers, and macrocycles. These materials offer unique optical and electronic properties due to their extended ��delocalization and strong intermolecular coupling, stemming from their rigid structures. The dissertation explores how these structures can be integrated into conjugated molecules and polymers to address challenges such as instability and limited state delocalization, paving the way for practical applications.
The introduction provides an overview of conductive organic molecules and discusses conjugated macrocycles and ladder molecules, along with the processing of conjugated ladder polymers.
Chapter II presents the synthesis of conjugated ladder polymers with isotopic substitutions, such as deuterium and carbon-13 labels. Deuterium labeling enhances neutron scattering contrast, aiding structural analysis, while carbon-13 labeling assists in defect quantification. Two such polymers are synthesized.
Chapter III introduces the synthesis of a ladder-type structure in polyaniline-inspired polymers. A low-defect conjugated ladder polymer is synthesized, achieving high conductivity (7 mS cm^���1 ) through oxidation and acid doping. It demonstrates exceptional stability against acids and UV irradiation, surpassing commercial standards, and excels in electrochromic devices and supercapacitors.
Chapter IV describes a self-doping ladder-type cyclohexadiene-1,4-diiminium-based system, offering stability and homogeneity, with a conductivity of 1��10^���3 S cm^���1 , surpassing traditional p-type molecules.
Chapter V discusses the synthesis and iodine doping of conjugated macrocycles with different side chains, forming single-crystal structures when doped with iodine, with conductivity ranging from 2.6��10^���3 to 0.65 S cm^���1 . The chapter also explores crystal packing and doping mechanisms.
The dissertation concludes with an outlook on future research into conjugated ladder molecules and cyclic macrocycles, showcasing how cyclized structures in conjugated molecules and macromolecules address challenges in organic electronics, revealing their potential as next-generation electronic materials
Discovering Global False Negatives on the Fly for Self-supervised Contrastive Learning
No full textIn self-supervised contrastive learning, negative pairs are typically constructed using an anchor image and a sample drawn from the entire dataset, excluding the anchor. However, this approach can result in the creation of negative pairs with similar semantics, referred to as ���false negatives���, leading to their embeddings being falsely pushed apart. To address this issue, we introduce GLOFND, an optimization-based approach that automatically learns on the fly the threshold for each anchor data to identify its false negatives during training. In contrast to previous methods for false negative discovery, our approach globally detects false negatives across the entire dataset rather than locally within the mini-batch. Moreover, the per-iteration computation cost of our approach remains independent of the dataset size. Experimental results on image and image-text data demonstrate the effectiveness of the proposed method
Effect of Sample Size on Linear Elastic Fracture Toughness of FFF-Processed PLA Compact Tension Specimens
No full textThe "Effect of Sample Size on Linear Elastic Fracture Toughness of FFF-Processed PLA Compact Tension Specimens" investigates the impact of sample size on the fracture toughness of 3D printed Polylactic Acid (PLA) using Fused Filament Fabrication (FFF) technology. ASTM D5045 standard is widely recognized and employed as a benchmark for evaluating the fracture toughness of materials within the linear-elastic fracture mechanics (LEFM) domain. This research aims to assess the applicability of this standard for evaluating fracture toughness in additive manufacturing thermoplastic materials focusing on the influence of specimen size, among other parameters, on the material's mechanical properties. Through a comprehensive experimental setup involving various sample sizes, infill sizes, and layout patterns, the study provides a detailed analysis of fracture toughness behavior through numerous tests. The findings reveal significant dependencies of fracture toughness on the sample size, indicating a deviation from true plane strain conditions and highlighting the necessity of reporting conditional stress intensity factors (����_����) for this particular case. The research contributes valuable insights into the mechanical characterization of 3D-printed thermoplastic materials and suggests practical implications for improving additive manufacturing testing and evaluation practices
Essays in Climate Risk, Residential Mobility, and Housing Security
No full textThe combination of climate change and economic growth in disaster-prone regions increasingly exposes the population to extreme weather events. In Chapter 1, I use property-level data to quantify the magnitude of climate risk across Texas, highlighting regional variation in exposure that challenges individuals, businesses, and industries across the state.
While the aggregate impacts of natural disasters are well documented, much less is known about the individual responses to these environmental shocks. In Chapter 2, I estimate the average treatment effects of flood damage using a fuzzy regression discontinuity design in the context of Hurricane Harvey, which damaged more than 200,000 homes in Houston, Texas in 2017. I leverage the relationship between flooding and a home���s elevation, exploiting a discontinuous increase in damage from 48,000 once water reaches the first floor. I provide evidence that disaster damage induces homeowners to relocate from their pre-storm residence while simultaneously preventing their decision to sell their property. The impacts on residential mobility attenuate over time, but I document a persistent divergence in the location and type of housing selected by damage-induced movers. My results indicate that flood damage makes people more likely to move shorter distances, and damage-induced movers are more likely to transition out of homeownership. Despite the combined shock to shelter and wealth, I find that flooded households are more likely to sort into higher-income census tracts in the aftermath of Hurricane Harvey.
Housing security is a critical component to wellbeing that extends beyond the context of environmental shocks. In Chapter 3, I explore how housing security relates to tenants��� criminal activity by analyzing the final stage of the eviction process. In particular, I exploit quasi-random variation in eviction executions to identify the impact of extending or shortening the enforcement process on tenants��� arrest propensity. I find no evidence that extending this process affects the likelihood of arrest, but statistical noise from data constraints may contribute to the uncertainty
In Tlilli, in Tlapalli ���The Black Ink, The Red Ink���: Indigenous Experiences in Society and Healthcare from an Indigenous Philosophy
No full textThis dissertation consists of three articles that will address aspects of the Indigenous social and medical experience within United States society. Elevating Indigenous epistemologies and criticisms of standard epistemological traditions in concert with an Indigenous focused and crafted research method informs the overall methodology and analysis of the project. This focuses the paper to be an explicitly Indigenous focused research project created by an Indigenous person utilizing Indigenous millennia knowledge.
Indigenous peoples interact with healthcare systems just as much as any other social or ethnic group in the U.S., however they are unique since the U.S. government is obligated by treaty to provide healthcare for Indigenous communities through the Indian Health Service (IHS). Indigenous people are the only racialized ethnic group in the U.S. to be guaranteed such healthcare which creates a complex system where a colonial government and bureaucracy are directly responsible for some of the most important, sensitive, and life-threatening aspects of a racialized group���s lives. The first section will provide a discussion of the white racial framing and anti-Indigenous subframing of Indigenous people in the U.S. The second section will provide a brief tee-up for the third section by providing an overview and discussion of Indigenous history in the U.S., the scholarly defined eras of Indigenous history, and a comparison of Indigenous and Western bioethics. The final section will address how the history of anti-Indigenous framing has impacted the Indian Health Service and the federal government���s shocking mismanagement of the IHS, however it will also highlight how Indigenous nations are taking back their healthcare and fulfilling hard-fought principles of sovereignty
Unraveling the Role of TET-Mediated Epigenetic Regulation in Heart
No full textDifferent types of DNA modifications play a crucial role in the epigenetic control of gene expression in organisms. Traditionally, the major attention has been focused on 5-methylcytosine (5mC), a major form of DNA modification. However, the discovery of the TET enzymes has sparked new research on their major catalytic product, 5-hydroxymethylcytosine (5hmC). The enzymatic activity of TET proteins is intricately regulated by metabolites under physiology or pathological conditions. In addition, metabolic reprogramming plays an essential role in regulating the development and regeneration of heart tissues. However, how TET enzymes regulate cardiac metabolism in response to external stresses still remain poorly understood.
In this study, we investigated the consequences of Tet triple knockout (Tet-TKO) in mouse embryonic stem cells (ESCs) and observed notable alterations in glucose metabolism. These changes were marked by enhanced glucose uptake and glycolysis, likely owing to the upregulation of genes critical for glucose metabolism. Furthermore, these cells exhibited defects in glucose-dependent differentiation, suggesting that cells with epigenetic defects might display metabolic vulnerability when exposed to external nutritional cues.
Maternal exposure to balanced nutrition is critical for supporting embryonic development. We observed that maternal exposure to a high-fat diet led to noncompaction cardiomyopathy (NCC) in embryos at E15.5. At the molecular level, maternal HFD exposure resulted in significantly reduced 5hmC production and chromatin remodeling in embryonic heart tissues collected from E15.5 embryos. Interestingly, maternal vitamin C treatment countered the negative impact of HFD exposure and restored the metabolic changes observed in pregnant mice, as well as the NCC phenotype observed in E15.5 embryos. This restoration is possibly due to the replenishment of iron, a co-factor of the Tet enzyme, in its reduced form. We further used a cardiac-specific Tet-triple knockout mouse model to confirm that the cardioprotective outcome of maternal vitamin C treatment in HFD conditions is attributable to the enhanced activity of TET enzymes.
There is a mutual influence between obesity and myocardium dysfunction. We report herein abnormal systemic energy homeostasis and obesity phenotypes in adult mice upon disrupting DNA methylation and demethylation balance in heart tissues. We observed that myocardium-specific Tet deletion had minor effects on heart size, structure, and function. By contrast, Tet ablation in heart resulted in increased whole-body weight, accompanied with higher blood glucose and lipid levels. In parallel, Tet-TKO mice exhibited increased glucose intolerance, insulin insensitivity and body fat, which mimicked the obesity phenotype.
Collectively, our findings establish the pivotal role of the TET family of dioxygenases in maintaining proper systemic hemostasis, thus enhancing our understanding of the intricate interplay between epigenetic modifications and cellular metabolism
Helmcick field notebook: GEN1-GEN500.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for GEN1-GEN500 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
The Joppa Environmental Health Project: Evaluating Local Air Quality and Respiratory Health in Dallas' Environmental Justice Neighborhoods
No full textDue to historical racial segregation, People of Color (POC) and low socioeconomic status groups experience disproportionate exposure to particulate matter (PM) air pollution. Fine PM (PM2.5) pollution is associated with several health effects, including cardiovascular and lung disease, respiratory mortality, and adverse birth outcomes. There is a need to characterize environmental and health disparities in susceptible populations like environmental justice (EJ) communities. In Dallas, Texas, EJ communities such as Joppa and ���Singleton��� are POC neighborhoods that are surrounded by multiple pollutant sources. Using a community-based participatory research (CBPR) approach, the Joppa Environmental Health Project (JEHP) was formed in 2020 with the primary objective to assess residents��� perceptions of air pollution and other health concerns through a community household health survey and to evaluate PM pollution through the installation of a local air monitoring network. To carry out these objectives, the following aims are addressed in this dissertation: 1) apply a CBPR approach to facilitate community engagement and action-oriented research on PM pollution and respiratory health in Joppa; 2) quantify daily and monthly PM2.5 concentrations in Joppa and ���Singleton��� using low-cost sensors, PurpleAir and SharedAirDFW; and 3) examine the association between daily PM2.5 exposure and airway inflammation in children residing in Joppa.
Strong community engagement activities and efforts from our steering committee yielded a high neighborhood survey response rate (51%). A high lifetime asthma rate (18%) was also observed among survey respondents. Monitor data demonstrated elevated levels of PM2.5 concentrations in Joppa. Last, active airway inflammation was observed in children who were not diagnosed with asthma. Overall, the application of this research facilitated robust community engagement and resident-led research to address critical neighborhood concerns. Subsequently, an asphalt batch plant in Joppa voluntarily relocated operations in June of 2023. The steering committee organized a new group known as Justice for Joppa/Justicia para Joppa to sustain momentum created by this work, targeting local zoning and land use policies. Future work from this research will involve the placement of a permanent medical clinic in Joppa where residents will have access to long-term health support (i.e., chronic disease diagnosis and management)