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Functional Characterization of Induced and Natural Variations in Sorghum Water Transport and Grain Quality
No full textAbstract
Sorghum (Sorghum bicolor), a resilient cereal crop from grass family, exhibits strong tolerance to abiotic stresses such as heat and drought, making it an excellent model for stress biology. However, the genetic mechanisms underlying these traits remain insufficiently understood. In this study, we characterize hs1, a heat-sensitive EMS-induced mutant that displays a pronounced leaf scorching phenotype under elevated field temperatures. Physiological analyses and anatomical observations reveal that this phenotype arises from defective protoxylem development at the leaf base, impairing water transport and reducing water use efficiency. Using Bulk Segregant Analysis (BSA), we identified hs1 as a gene encoding a myosin protein, which further confirmed by the complementation tests with an allelic mutant. This discovery highlights a novel link between cytoskeletal regulation, xylem development, and abiotic stress responses in sorghum. Ongoing work focuses on dissecting the gene’s regulatory network and exploring its potential for improving stress resilience in other crops like maize.
In addition to induced mutants, we also explored natural genetic variations at the GRANULE-BOUND STARCH SYNTHASE (GBSS) locus, which governs the waxy endosperm trait characterized by low amylose content and a glutinous starch profile. While waxy sorghum is valued for its enhanced starch digestibility in food, feed, and biofuel applications, conventional breeding has been limited by the need to phenotype mature grain and the dependence on PCR-based markers not optimized for high-throughput genotyping. To address this limitation, we identified and validated the competitive allelic PCR markers for the two most prevalent wx alleles and fully resolved a previously uncharacterized 5.6 kb Copia retrotransposon insertion. These resources enable accurate genotyping of Wx alleles via short-read sequencing and support early-generation selection. Functional markers were developed and validated across public and private breeding programs, enhancing the efficiency of waxy sorghum hybrid development.
Together, this work demonstrates the value of integrating induced and natural genetic diversity in sorghum to uncover gene function, elucidate developmental mechanisms, and develop scalable molecular tools that accelerate genomics-assisted breeding
Controlled Feeding with 24 Hour Recall
No full textBackground: Self-reported 24-hour dietary recalls systematically underestimate true
energy intake, yet existing validation methods such as doubly labeled water (DLW) only quantify
total intake error without identifying which foods or meals are misreported.
Objective: To evaluate the accuracy and reproducibility of ASA24-administered 24-hour
recalls against precisely weighed ad libitum meals.
Methods: In this observational controlled-feeding study, 41 adults completed two clinic
visits at Texas Tech University’s Nutrition Metabolic Health Initiative. At each visit, participants
consumed a standardized meal (four single-item foods and two mixed dishes) weighed to the
nearest 0.01 g. Visit 1 recalls were conducted covertly (without participants’ prior knowledge of
the forthcoming recall) and Visit 2 recalls followed one week later with full awareness. Recall
accuracy (weighed vs reported calories), proportion of items recalled within ±10%, and effects of
meal type, recall anticipation, and participant characteristics (BMI, gender, race) were analyzed
using paired tests, mixed-effects models, and nonparametric methods as appropriate.
Results: 41 participants enrolled; 38 provided valid unanticipated (Visit 1) recalls and 34
provided valid anticipated (Visit 2) recalls. At Visit 1, there was a non‐significant over‐reporting
bias of 56 ± 374 kcal (median 137; paired t(37)=–0.92, p=0.364), whereas at Visit 2
over‐reporting increased significantly to 234 ± 357 kcal (median 223; paired t(33)=–3.82,
p<0.001). Item‐level recall accuracy within ±10% of true intake differed significantly by food
type. At Visit 1, accuracy was 21 of 89 discrete items (23.6%) versus 4 of 75 mixed dishes
(5.3%) (Fisher’s exact p=0.001; OR=5.43). At Visit 2, 16 of 80 discrete items (20.0%) and 6 of
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Texas Tech University. Casen Bigham, July 2025
65 mixed dishes (9.2%) met the ±10% criteria (p=0.102). Although the median misreport
magnitude increased significantly from Visit 1 to Visit 2 (Wilcoxon V=417, p=0.042).
Exploratory analyses found no significant associations between misreport magnitude and
BMI category (all p>0.2). At Visit 1, men over‐reported more than women (W = 223, p = 0.037),
and at Visit 2, Caucasians over-reported more than Other races (W = 53, p = 0.040). Spearman
correlations showed no relationship between water intake and either total reported calories or
misreporting at Visit 1 or Visit 2 (all |ρ|0.05).
Conclusions: Anticipation of dietary assessment paradoxically exacerbates misreporting,
and mixed-ingredient meals pose greater challenges than single-item foods. Demographic factors
(BMI, gender, race) exert minimal influence on recall bias under controlled feeding, apart from a
sex and gender difference under unanticipated conditions (V2). Water consumption did not
predict accuracy or consumption
Using Interpretable Machine Learning and Event Studies in Analyzing Health Policy and Outcomes
No full textThis dissertation consists of three essays. In the first essay, the impact of Medicaid expansion on mortality is evaluated. A key goal of Medicaid expansion was to improve mortality outcomes in the United States. However, different states adopted the policy at different times. An innovative approach of evaluating the policy expansion is employed. This involves a Staggered Difference-in-Difference (DiD) with Doubly Robust Inverse Probability Weighting (DRIPW) that enables the estimation and inference of interpretable causal parameters, adapting arbitrary treatment effect heterogeneity and dynamic effects. The goal is to examine the impact of the policy expansion on various expansion groups that adopted the policy between 2014 and 2016. Also, the overall policy impact between expansion and non-expansion states is estimated and compared with TWFE.
The second essay applies machine learning (ML) algorithm to predict the contribution of vaping to health outcomes. There has been a consistent rise in the use of electronic cigarettes. Vaping, or using an electronic cigarette, has emerged as the new method for getting nicotine fixation without smoking. The first object is to build a prediction model to classify and distinguish the associated contribution of vaping to good and bad health status. Another objective is to determine how individual characteristics and behavior contribute to the prospects of vaping. In addition, the Shapley Additive explanation method is used to predict the contribution of the features to our outcome.
The third essay is my job market paper, and it examines the association between vaping and two health outcomes: arthritis and poor health status. The purpose of the study is to determine if vaping is indeed safer than smoking based on the data and to further estimate the economic burden of arthritis linked to vaping and smoking. The study employs the Double Machine Learning (DML) technique to independently assess the associated effects of vaping and smoking behaviors on arthritis and bad health. The study further derives the associated effect of vaping as influenced by smoking, as well as the association of smoking as influenced by vaping on arthritis and bad health. The study also derived the healthcare cost per arthritis patient linked to vaping and smoking behaviors. In addition, the Shapley Additive Explanations (SHAP) values are used to predict the marginal contribution of each predictor of the response variable
Yeary, Dan B. III-108 HL1473.
No full textMaterials related to Dan Yeary, who served as college minister at First Baptist Church Lubbock from 1967-1972
Hybridization and sex chromosomes in Salicaceae
No full textAngiosperms, or flowering plants, are the most numerous and diverse group of land plants, and they have dominated the terrestrial ecosystem (Benton et al., 2022). Hybridization is one of the major drivers in adaptation and diversification of angiosperms (Soltis and Soltis, 2009; Whitney et al., 2010; Mitchell et al., 2019). Hybrid zones, areas where species or populations hybridize, play an important role in understanding evolution of reproductive barriers and impact of evolutionary forces in speciation (Rieseberg et al., 1999). Hybridization followed by repeated backcrossing with one of the parental species can also introgress beneficial alleles from one species into the gene pool of other species (Anderson, 1949; Harrison and Larson, 2014). In two chapters of my dissertation (chapters 2 & 3), I explore the impacts of hybridization and introgression on diversification in poplars and willows. Hybridization is often difficult to identify. In addition to their extensive hybridization, angiosperms also exhibit diverse sexual systems. Understanding the evolution of sex determination in plants is an overarching question in my dissertation. While a bulk of angiosperms (90 percent) are hermaphrodites, with bisexual flowers bearing both male and female reproductive structures, 5% -6% percent of angiosperms are dioecious, having male and female flowers on different individuals. I am also interested in whether genes with sex biased gene expression may be important for controlling sexual dimorphism that could be sexually antagonistic. Using the chloroplast and species tree, I first investigated multiple chloroplast captures in willows. Then, using association mapping, I identified the sex determining region in P. mexicana and show that it did not arise via introgression from another Populus species Lastly, I used sex-biased gene expression to explore sex-biased gene expression genes at the early-, mid-, and late-flowering stages of S. nigra with the goals of understanding which genes control sex determination and which are important for contributing to sexual dimorphisms
The Failure of the Stuart Empire in America, c. 1660-1691
No full textAn examination of the aftermath of the Glorious Revolution in England's North American colonies, focusing primarily on New England and Maryland and arguing that Maryland navigated a unique experience through the Glorious Revolution
Developing a Novel Method for Detecting the Astrophysical Gravitational-Wave Background in the LIGO-Virgo-KAGRA Frequency Band
No full textGravitational waves (GWs) were first directly detected by the LIGO and Virgo Collaborations nearly a century after Albert Einstein predicted their existence in his theory of general relativity. Since then, the LIGO-Virgo-KAGRA (LVK) Collaboration has made 90 confident detections of GWs during the first three observing runs (O1-O3), with many more candidate events emerging during the ongoing fourth run (O4). However, a substantial number of weaker signals remain undetected, as they fall below the current sensitivity limits of the detectors. These signals make up the gravitational-wave background (GWB), a background GW signal composed of a large number of weak, independent, and unresolved sources, which can be produced by signals of astrophysical or cosmological origin. An expected astrophysical source of a GWB in the frequency band of the LVK detectors arises from stellar-mass binary black hole (BBH) mergers throughout the Universe. Rate estimates based on observed events suggest that BBH mergers occur in the observable universe approximately once every 5 to 10 minutes, on average. These events, which are short in duration (), are expected to produce an intermittent GWB. However, the current search methods employed by the LVK Collaboration assume a continuous background and do not account for the signal’s intermittent nature. A major focus of this dissertation is the development of a novel detection approach that explicitly incorporates this characteristic of the background. This method is expected to reduce the time to detection for an intermittent background compared to standard search techniques.
Furthermore, to confidently detect the GWB, it is essential to develop techniques for mitigating correlated noise between detector sites. One likely source of such noise is Schumann resonances--global electromagnetic resonances in the cavity of the Earth's surface and the ionosphere, excited by lightning strikes. These resonances can couple to the detectors and, if not properly accounted for, may lead to a false detection of a GWB signal. This dissertation includes a study of the impact of Schumann resonances on GWB searches.
With ongoing improvements in detector sensitivity, the detection of the GWB by the LVK Collaboration is likely only a matter of time. The advanced search methods developed in this dissertation may help accelerate that discovery and contribute to the next breakthrough in gravitational-wave astronomy
Comprehensive Evaluation of Per- And Polyfluoroalkyl Substances (PFAS) Sorption in Soils
No full textPer- and polyfluoroalkyl substances (PFAS) are a diverse class of persistent chemicals that are frequently detected in the environment. The mechanisms governing PFAS retention and mobility in soils remain poorly understood for many PFAS, particularly emerging PFAS such as bis-perfluoroalkyl sulfonimides (bis-FASI) and numerous PFAS present in aqueous film-forming foams (AFFF) impacted sites for which analytical standards are unavailable to date. This dissertation reports the extensive experimentally derived sorption coefficient (Kd) from a single laboratory for 82 PFAS across >20 geochemically diverse soils. Results demonstrate that sorption behavior is strongly influenced by both chemical features and soil properties. Sorption of long chain PFAS increased with -CF2- chain length, reflecting hydrophobicity dominant partitioning. In contrast, short chain PFAS showed weaker sorption and lacked a chain length dependent trend, suggesting influence of electrostatic interactions. A thermodynamic free energy framework revealed a transition zone between electrostatic and hydrophobic dominance near 6 to 8 -CF2- units that are aligned with the observed sorption behavior. Desorption experiments indicated that the release of short chain PFAS are kinetically restricted, and slower release in field aged soils highlights the importance of long-term aging effects on PFAS retention. Sorption behavior of previously unexplored 50 anionic and zwitterionic AFFF PFAS showed influence of structural properties. The n-substituted and unsaturated perfluoroalkyl sulfonates (PFSAs) demonstrated sorption behavior comparable to PFSAs of the same chain length. Zwitterionic PFAS exhibited variable sorption behavior based on net charge and charge position. Net neutral zwitterions showed >2 log units higher sorption than anionic PFAS of same chain length. Zwitterions with two terminal negative charges demonstrated sorption behavior close to anionic PFSAs. The influence of PFAS charge and charge position was validated using hydrophilic interaction liquid chromatography (HILIC) retention times determined under conditions that isolated PFAS electrostatic interactions. These findings provide a conceptual model for zwitterionic PFAS sorption that demonstrates a range of expected sorption behavior. In addition to the experimental work, a thermodynamic model was developed that incorporates hydrophobic and electrostatic free energy components. While the model performed well with internal dataset, its predictive accuracy with external dataset was limited, underscoring the need for expanded datasets to capture a broader range of soil types. Overall, this work provides new insights on the sorption behavior of a broad suite of PFAS and highlights the importance of interactions influenced by both PFAS and soil properties