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Ultra-High Strain Rate Impact Behavior in High Molecular Weight Thermoplastics
No full textThe advent of commercial and military hypersonic vehicles introduces formidable challenges to existing thermal protection systems and ballistic armor. Concurrently, all spacecraft face escalating threats from hypervelocity impacts (HVIs) by micrometeoroids and orbital debris (MMOD). Overcoming these obstacles requires materials/structures capable of withstanding extreme conditions. Yet, a clear knowledge gap exists in the fundamental understanding of the complex multiphysics phenomena generated when materials are subjected to ultra-high strain rate (>10^6 s^ ���1 ) collisions. This is especially true for polymers, despite their capacity for energy absorption and tailorability. This dissertation endeavors to bridge this knowledge gap by exploring the ultra-high strain rate impact behavior of three high molecular weight thermoplastics, ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and polycarbonate (PC). The primary objective is to help answer fundamental questions about their behavior and illuminate their applications. This goal necessitated a four-pronged strategy: (i) the establishment of an impact testing facility; (ii) the execution of HVI experiments; (iii) the application of numerical simulations to infer impacted target conditions; and (iv) the integration of these findings with existing literature to explain the role a polymer���s microstructure plays in its macroscopic energy absorption. The ensuing findings (i) revealed the difference in UHMWPE and HDPE���s HVI deformation, failure, and energy absorption was governed by an interplay between strain rates and rates of polymer chain disentanglement and reorientation and (ii) demonstrated the viability of threat-optimized protective structures. The dissertation also includes a novel study on similar impact phenomena, generated by decreasing spatial scale instead of increasing velocity. A Laser Induced Projectile Impact Test (LIPIT) apparatus and gas gun were used to launch alumina spheres ranging five orders of magnitude in diameter (3 ��m���10 mm) into scaled PC targets at 550 m/s. Length scale reduction set in motion a remarkable 230% amplification in specific energy absorption and a 240% increase in relative impact deformation area. In all, the dissertation leads to an irrefutable conclusion: while the behavior of polymers at lower rates (<10^3 s^ ���1 ) is well understood, there remains much to discover about their behavior as loading conditions become extreme. Data from lower rates and smaller scales cannot be extrapolated to higher rates and larger scales
The BAZ Family of Chromatin Remodelers in Colorectal Cancer: Insights into Oncogenesis, Alternative Splicing and Chemosensitization
No full textColorectal cancer (CRC) poses a significant healthcare challenge worldwide, necessitating a deeper understanding of the molecular mechanisms underlying its pathogenesis for improved therapeutic interventions. This thesis investigates the BAZ (Bromodomain Adjacent to Zinc finger) family of chromatin remodelers and their intricate involvement in CRC. The BAZ family members, including BAZ1A, BAZ1B, BAZ2A, and BAZ2B, exert critical regulatory functions in chromatin architecture and transcription, impacting various cellular processes from development to disease.
In colorectal cancer, BAZ1A is overexpressed, and its depletion resulted in diminished cell viability, increased apoptosis, augmented DNA damage, and cellular senescence, concomitant with the downregulation of components within the Wnt/��-catenin signaling pathway. In vivo studies corroborated these findings, revealing that knockdown of BAZ1A leads to diminished tumor growth and alterations in chromatin regulation. Interestingly, BAZ1A undergoes alternative splicing, which is promoted by treatment with histone deacetylase inhibitors, thereby highlighting its therapeutic potential. Remarkably, the full-length form of BAZ1A is implicated in DNA repair mechanisms, while its alternatively spliced counterpart is susceptible to increased DNA damage and sensitivity to DNA-damaging agents. These observations underscored the oncogenic role of BAZ1A in colorectal cancer and the importance of considering an oncogene���s alternative splicing patterns.
Similar to BAZ1A, BAZ2A is also upregulated in CRC and associated with reduced patient survival. Functional studies demonstrated their roles in inhibiting cell viability, colony formation, and modulating Wnt/��-catenin signaling. Inhibition of BAZ2A led to reduced tumor growth rates in mouse models, where it also affected histone modification patterns, favoring a less repressive chromatin state, and influencing major histocompatibility complex (MHC) regulation.
In contrast to BAZ1A and BAZ2A, BAZ1B knockdown enhanced cell viability, colony formation, and altered cell cycle progression, suggesting a tumor-suppressive role in metastatic CRC. BAZ1B impacted c-MYC expression independently of the Wnt/��-catenin pathway, and influenced p53 and p21 levels, implicating its involvement in tumor suppressive pathways.
Overall, the study underscores the potential of BAZ family members as therapeutic targets in CRC. Future research should focus on elucidating their molecular mechanisms, translating findings into clinical applications, and exploring combination therapies to improve treatment outcomes for CRC patients, thus advancing more personalized therapeutic approaches for CRC
Sequence Stratigraphy and Chemostratigraphy of the Middle Cretaceous Woodbine and Eagle Ford Groups on the Southeastern Margin of the East Texas Basin and East Texas Submarine Plateau
No full textWithin the East Texas Basin (ETB), the Woodbine and Eagle Ford groups are important hydrocarbon reservoirs. However, little work was done within the southeast margin of the ETB, and adjacent East Texas Submarine Plateau (ETSP) region, to properly differentiate these units. In fact, the entire succession between the Buda Formation and Austin Groups often is referred to as the ���Eaglebine���. When defined, sandstone beds, as well as underlying mudstone beds, within it, are simply lithologically assigned to the Woodbine Group. This study takes a surface-based, or sequence stratigraphic, approach using: 1) a grid of well log cross sections, 2) x-ray fluorescence (XRF) data from cuttings and cores, and 3) previously published seismic data, to chronostratigraphically define and differentiate the Woodbine and Eagle Ford Groups across the study area.
Across much of the western portions of the study area, in Grimes and Madison Counties, a regional unconformity at the base of the Lower Eagle Ford Formation (K630sb) separates the Woodbine Group below from the Eagle Ford Group above. In this area, TOC- and Ca-rich, high-resistivity mudstone of the Lower Eagle Ford Formation unconformably overlie Al-rich, moderate resistivity mudstones of the Pepper Shale, which represent the distal downdip (basinal) equivalents of the Woodbine Group Freestone Delta.
In the western portions of the study area, in Houston and Walker Counties, a regional unconformity at the base of the Upper Eagle Ford Formation (K650sb), truncates the Lower Eagle Ford Formation near the interpreted K630 depositional shelf break. In this area, Al-rich, low-resistivity mudstone, and overlying sandstone, of the Upper Eagle Ford Formation Harris Delta, unconformably overlie Al-rich, low-resistivity mudstones, and overlying sandstones, of the Woodbine Group Freestone Delta. Fortunately, a low-resistivity marker, interpreted as regional flooding surface (K650mfs), near the base of the Upper Eagle Ford Formation can be defined, mapped, and used to differentiate strata of the Upper Eagle Ford Formation Harris Delta from the underlying Woodbine Group Freestone Delta in this area.
Finally, in the southeastern portions of the study area in Polk County, a regional unconformity at the base of the Austin Group (K720sb) truncates most, or all, of the Eagle Ford Group, and the Austin Group, or the lowermost portion of the Upper Eagle Ford Formation unconformably overlie the Woodbine Group Freestone Delta. A thick succession of the Eagle Ford Group was deposited downdip of the interpreted K630sb depositional shelf break in this region
Multi-coil Wireless Power Transfer Systems Analysis and Design
No full textWireless power transfer (WPT) technology is growing fast and has been used for various applications. experiencing rapid growth and finding applications across various sectors. Emerging markets, such as consumer electronics, electric vehicles, and medical implants, are actively exploring the integration of wireless power transfer as an energy solution. Numerous studies have advanced proposals for WPT coil designs, resonant circuit designs, and the incorporation of wide bandgap devices into WPT systems. Concurrently, multi-coil WPT systems, employing more than one coil on either the transmitter or the receiver, have gained prominence. Among these, three-phase wireless power transfer systems have demonstrated several advantages and exhibit potential as viable solutions for technical challenges encountered in the industry.
The first research topic revolves around wireless lithium battery charging, a critical component of electric vehicles. The charging process for lithium batteries requires a sequential application of constant current (CC) charging succeeded by constant voltage (CV) charging. This paper presents a novel reconfigurable compensation topology designed for three-phase wireless charging systems. The reconfigurable compensation topology facilitates a seamless transition between the inductor-capacitor-capacitor-parallel (LCC-P) configuration and the inductor-capacitor-capacitor-series (LCC-S) configuration. This enables the output to exhibit CC and CV characteristics, respectively.
The second research topic delves into wireless power transfer for autonomous underwater vehicles (AUVs). Charging AUVs presents unique challenges due to insulation and water leakage issues when submerged. The application of three-phase wireless power transfer encounters complexities, primarily stemming from uncontrollable docking angles leading to rotational misalignment issues. In response to these challenges, a three-phase wireless power transfer coil resistant to rotational misalignment has been proposed, simulated, and tested
An Epidemiologic Investigation on Arsenic Exposure and Its Association with Mental Health Outcomes
No full textMental health problems, characterized by a clinically important disturbance in cognitive, emotional, or behavioral aspects of an individual���s life, have garnered growing interest in the field of epidemiology due to their complex causal mechanisms, increasing prevalence, and substantial burden on modern populations. There are many causal factors suspected to impact mental health, mental illness, and emotional wellbeing including certain environmental toxins, like arsenic, although these associations are not well established. Arsenic has been shown to be a globally toxic substance that is associated with numerous health problems. Recent studies suggest that arsenic may have an impact on mental health due to its neurotoxicity.
The present research investigates the possible association between arsenic and mental health problems through a systematic review, geographically weighted regression on a county level for the 48 contiguous states with soil arsenic, and a geographically weighted regression on a county level for Texas with water arsenic exposure estimates. The systematic review demonstrated associations between Arsenic and multiple mental disorders as well as generally poor mental health. The first geographically weighted regression of the contiguous 48 states found that soil arsenic was a significant predictor of both county suicide rates and the years of potential life lost due to suicide rate. The second geographically weighted regression found that estimated water arsenic exposure was a significant predictor of both county suicide rates and number of days reported with poor mental health.
The present research suggests that arsenic may be a potential environmental risk factor for mental health outcomes. Further prospective studies with individual-level data are necessary to confirm causality and explore the interactions with other risk factors
SMC-M1 Connectivity and Motor Sequence Learning: A TMS Study
No full textWe experience various types of motor learning throughout our lives. As children, we learned to walk unconsciously. As we grow older, we continue to learn skills like sports or musical instruments. In this study, the primary motor cortex (M1) and the supplementary motor complex (SMC), which are brain regions involved in motor sequence learning but where many aspects still remain unclear, were mainly investigated, and the connectivity of these two regions was measured using the paired-pulse transcranial magnetic stimulation (ppTMS) technique. In Experiment I, sixty-three right-handed undergraduate students participated. Conditioning stimulus (CS) was administered at SMC (i.e., 4 cm anterior to Cz), and test stimulus (TS) was applied at M1. As a result, consistent with the previous ppTMS studies, a facilitatory influence was observed between SMC and M1. In Experiment II, fifty-one right-handed undergraduate students participated. After measuring baseline SMC-M1 connectivity in the same way as in Experiment I, individuals practiced one of three motor sequential tasks (i.e., implicit, explicit, or random sequence task). After practice, ppTMS as post-training stimulation was administered in the same way as the baseline stimulation to investigate the changes in the connectivity between SMC and M1. As a result, it was found that the facilitatory influence decreased after the explicit sequence task that involved motor chunking. This may be because SMC plays a role in motor chunking. In Experiment III, instead of a motor task, intermittent theta-burst stimulation (iTBS) was administered at SMC between two ppTMS sessions, and the connectivity changes were investigated. Similar to the influence of the explicit sequence task in Experiment II, the facilitatory influence decreased in the iTBS group. Although the mechanisms are different from each other, iTBS appears to induce post-synaptic plasticity in the cortico-basal ganglia-thalamic network. After post-stimulation of ppTMS, participants performed the explicit sequence task used in Experiment II twice (i.e., practice and retention test) to reveal the effect of iTBS on motor sequence learning. In the iTBS group, the offline improvement was disturbed at concatenation points compared to the Rest group. In the future, follow-up research that dissociates motor chunking conditions using neuroimaging techniques seems necessary
Shaping Human Capital and Socioeconomic Outcomes: The Impacts of Grade Retention, Lead Exposure, and Social Media Rhetoric
No full textMy dissertation consists of three essays on the topics of grade retention, lead exposure, and social media rhetoric. In the first chapter, I provide the first causal evidence of the effects of grade retention on the labor market outcomes using Texas��� policy of retaining third graders who fail a reading test. The fuzzy regression discontinuity design estimates show that third-grade retention significantly reduces adult earnings. Although the policy aims to improve academic achievement, the results demonstrate that third-grade retention lowers high school graduation rates without improving college outcomes and aggravates absenteeism and violent behavior.
In the second chapter, coauthored with Andy Cao and Jason Lindo, we investigate whether Donald Trump���s "Chinese Virus" tweets contributed to the rise of anti-Asian incidents. We find that the number of incidents spiked following Trump���s initial ���Chinese Virus��� tweets and the subsequent dramatic rise in internet search activity for the phrase. Difference-in-differences and event-study analyses leveraging spatial variation indicate that this spike in anti-Asian incidents was significantly more pronounced in counties that supported Donald Trump in the 2016 presidential election relative to those that supported Hillary Clinton. We estimate that anti-Asian incidents spiked by 4000 percent in Trump-supporting counties, over and above the spike observed in Clinton-supporting counties.
In the third chapter, coauthored with Thao Duong, we analyze the long-term effects of low-level lead exposure during early childhood from Kindergarten through grade three on educational achievement and earnings. Utilizing the unexpected decline in lead emissions following the reduced operation of piston-engine aircraft after the 9/11 attacks as a natural experiment, combined with detailed individual-level administrative data from Texas ERC, we employ both difference-in-differences and instrumental variable techniques to identify the causal impact of lead exposure on various student outcomes. Our findings reveal that even minimal increases in lead exposure, measured in micrograms per cubic meter, are associated with significantly decreased probabilities of high school graduation and post-secondary enrollment in public universities or community colleges. Moreover, we observe that lead exposure adversely affects children by diminishing their future earnings in the labor market
Genetic Architecture of Nodule Traits in Guar
No full textGuar (Cyamopsis tetragonoloba L.) is an annual, diploid legume crop cultivated primarily for the galactomannan gum contained in the seed endosperm, which is used widely in foods, pharmaceuticals, and other industrial applications. As a legume, guar forms root nodules to fix atmospheric nitrogen, but nodulation has been noted to be poor in the field. Phenotypic evaluation of 225 diverse guar accessions from the United States Department of Agriculture germplasm collection revealed significant variation among genotypes for plant height, nodule diameter, fresh and dry nodule weight and dry aboveground plant biomass. However, no significant differences were found for fresh aboveground plant biomass. Broad-sense heritability was highest for nodule diameter (92%) indicating potential for genetic gain through selection. Significant positive correlations occurred between nodule number and weight, and between plant biomass and nodule weight, revealing increased plant growth with greater nodule mass. Several promising genotypes such as PI 288747 were identified that can serve as parents in breeding initiatives to improve nodulation capacity. Population structure analysis on 225 accessions from India, Pakistan, and the United States genotyped with 7,000 SNPs revealed three main genetic clusters largely corresponding to geographic origin. In which Q1 included genotypes from all three countries while Q2 and Q3 included genotypes only from India. Genome-wide association studies using 19,007 filtered SNPs identified SNP markers associated with plant height, nodule number and diameter, nodule weight, and plant biomass across multiple models. Several SNPs were shown to be connected to various guar nodulation traits. SNP Chr6_56449898 showed a strong correlation with the weight and number of nodules. Chr2_51078296 and Chr2_51010513 SNPs showed a strong correlation with nodule characteristics as well as other variables including biomass and plant height. Together, these results further scientific understanding of guar genetic diversity, nodulation traits, and potential genomic regions controlling nodulation. This knowledge and germplasm can aid guar breeding programs seeking to improve nitrogen fixation and yields through enhanced nodulation, which would also increase ecological services. This research provides an important foundation and resources to enable marker-assisted breeding and selection for superior nodulation capacity and associated increased productivity in this economically important legume crop
How Likely Is a Repeat of the February 2021 Winter Storm Event in Texas, Really? An Impact-Driven Analysis of Compound Cold-Weather Variables in the Context of the Changing Climate
No full textThe extreme cold that led to the failure of the Texas electrical grid in February 2021 has been extensively analyzed in terms of both its likelihood and its predictability. Other authors have pointed out that the severity of its impact ��� power lost to 4.5 million households representing 10 million people for roughly 3 full days ��� is disproportionate to the severity of the cold. Because the return periods of individual extreme weather variables did not correlate with the extreme impacts experienced, we analyzed combinations of cold-weather variables known to affect residential heating demand, electrical generation, and fuel supply. We evaluated these combinations using cold-weather indices which include multiple variables and copulas which combine individual variables.
We weighted temperatures by the population of the metropolitan area in which they occurred to reflect their impact on the electrical grid and adjusted these temperatures to reflect the changing climate of Texas. We found that the conditions experienced at the time of failure, February 15th, 2021, at 2am Central Time, could reasonably be expected between every 3 and 18 years, with the most extreme combination being low temperatures and time spent at or below freezing. After scaling past temperatures to reflect a warming climate, this combination has been more extreme in Texas four or more times over the past 80 years than what was experienced when the electrical grid was not able to produce enough electricity to meet demand for it.
Cold-weather conditions were additionally analyzed over the locations where these generation resources and their fuel supply had the highest failure rates. We found significant differences in the likelihood of the February 2021 conditions both in individual variables and combinations.
Wind power was reduced by turbine icing and was unable to restart for over a week. Using freezing duration following icing conditions for most stations in a cluster resulted in return periods which seemed to align with the impacts of this storm, yet still resulted in the turbine icing component of this interconnected failure being the least likely aspect to occur again
De-Equivariantization in Fusion Categories from Quantum Groups at Roots of Unity
No full textThe representations of quantum groups at roots of unity lead to an important class of premodular tensor categories. We will discuss the construction and important properties of these categories. Then we will consider the categories of this kind associated to type D Lie Algebras and present explicit computations to demonstrate the fusion rules, grading and pointed subcategory. We will also discuss and provide examples of de-equivariantization. This process involves creating a new category by taking the category of modules over an algebra object, in some sense taking a ���quotient��� based on the tensor product with this object. More specifically, we identify a subcategory equivalent to Rep(G) for some finite group G and take the algebra object of functions on G in this subcategory. Then we take the modules over this algebra object in the centralizer of Rep(G), which ensures that the resulting category of modules retains the structure of a braided fusion category. Examples of de-equivariantization in the literature primarily consist of performing de-equivariantization with a cyclic group G. We provide an example of de-equivariantization by a non-cyclic group Z2 �� Z2 and discuss strategies to approach de-equivariantization by non-cyclic groups. Specifically, we show that the boson condensation of C(so(8), 10, q) by the full pointed subcategory Rep(Z2��Z2) is isomorphic to four copies of the integral subcategory of C(su(2), 5, q)