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Adjoint-based data assimilation in a stochastically parametrized Lorenz 96 two-scale system
Get PDFThe success of stochastic parametrization in weather forecasting and subgrid-scale parametrization of ocean eddies shows great promise for its use in modeling the climate of the ocean and atmosphere. These kinds of parametrizations have yet to be employed, however, in full-scale ocean state estimation. I demonstrate the use of stochastic parametrization within a data assimilation context using adjoints by investigating these ideas in a simple toy model, the Lorenz 96 two-scale system (L96).
L96 is used as a proxy for highly resolved ocean dynamics, while a truncated version is used to compare the effectiveness of deterministic and stochastic parametrization schemes in analogy with subgrid-scale parametrization. I show that, in addition to deterministic models, stochastically parametrized models can be tuned via the adjoint method to more closely match the dynamics of a highly resolved model. The stochastic model shows additional promise by capturing a more realistic variability across frequencies. This plays an important role in uncertainty quantification, as shown by comparing an ensemble of stochastic model runs with a deterministic perturbed-parameter ensemble. This demonstrates significant promise for both the practicality and effectiveness of stochastic parametrization in ocean state estimation.Physic
Development of a radioisotope production facility using a cryogenic cooling system
Get PDFThis dissertation details the development of a Cryogenic Tracer Irradiation Facility (CTIF) at The University of Texas at Austin (UT). Radioisotopes are an important tool in the world of nuclear explosion monitoring, as they allow researchers to test detection equipment and simulate underground nuclear explosions before the real thing occurs. At UT, gaseous radioisotopes are typically produced using in-core irradiation procedures that take up time, are expensive, restrict research access, leave equipment contaminated and unable to be used for long periods of time, and their temporary nature poses an increased risk of accidentally releasing the radionuclides. One solution is a beam port based irradiation system, which is less intrusive on reactor operations but has a lower neutron flux than in-core based systems. To compensate for this, a liquid helium compressor is used to freeze a target gaseous isotope and increase the reaction rate to comparable levels with the in-core irradiation. Initial tests for this facility were promising, but equipment failure and incorrect flux measurements towards the end of the experiment resulted in only 0.043 Ci of ¹²⁷Xe being produced after a roughly one month irradiation despite the aim being 2 Ci. Issues with gas leaks and water pump failures were the expected culprit, and were fixed along with a change in methodology to measure short term irradiations using natural xenon. After a sample of natural xenon was irradiated for an hour at 50 kW of reactor power and counted using an high purity germanium (HPGe), a neutron flux and activation rate were determined. The neutron flux was calculated to be 5.13 ∗ 10¹¹ ± 3.94% neutrons/cm²/s for a reactor power of 900 kW. Assuming a one hour irradiation at the same reactor power with one liter of ¹²⁶Xe, the CTIF produced 3.62 ∗ 10⁷ ± 3.94% Bq of ¹²⁷Xe at the end of irradiation. In 2023, an irradiation of ¹²⁶Xe using the in-core facilities produced an activity of 3.81 ∗ 10⁸ ± 3.3% Bq under the same conditions and had an average flux of 1.57 ∗ 10¹³ ± 3.82% neutrons/cm²/s. The production rate for xenon isotopes in the cryogenic irradiation facility in the reactor beam port is found to be approximately 10% of the reaction rate in the previously demonstrated in-core irradiation facility. The cryogenic facility will be an excellent candidate for producing radioxenon isotopes on the order of 100 mCi (3.7x10⁹ Bq), but will not match the production rate of the in-core production method. Placing such a facility in a beam port with a higher flux provides a promising path forward.Mechanical Engineerin
Visions of migration : news images and the production of visual knowledge on the U.S. southern border
Get PDFMigration is a natural and ever-present human process that affects nearly every single country in the contemporary globalized world. Migration is also the most consistently politicized, denigrated and demonized social process in many societies. In the United States, migration exists as a political and social conflict that produces prejudices, stokes nationalistic fervor and influences acts of violence. Without direct experience, much of the knowledge of migration in American life is constructed by news media and especially news images, which are positioned as documentary evidence of these social processes. But news images are not natural, disinterested reflections of reality, they are motivated symbolic constructions that have the capacity to influence material conditions for migrating people. Photographs influence subsequent social practices through their ability to reflect discourses while obscuring their origins; they have the ability to harm and the ability to heal. Through poststructural theories of representation, this dissertation explores the nature of the visual construction of migration in the U.S. news industry. This dissertation employs visual analyses, interviews and ethnographic observation on the U.S.-Mexico border to illuminate the complex social practice of visual news work, the conventions of representation and their knowledge potential. The visual construction of migration is a product of competing interests that influence how photographers work in the field. Multiple stakeholders apply physical, social and temporal pressures, which act as discursive and embodied barriers that divide photographers and migrants during the photographic encounter. This ultimately results in visual conventions such as a priority on moments of enforcement, asymmetrical power relations between symbols of authority and migrating people, and a separation between the viewer and depicted migrants. These conventionalized images reflect beneficial discourses for powerful entities’ distinct agendas—an example of hegemony in action. Though photographers are often bound by these influences, they still retain the ability to change these representations. When conflicts fracture this hegemonic influence, photographers can break conventions and make images that don’t benefit the most powerful stakeholders, but benefit the migrants themselves.Journalism and Medi
Towards robust deep neural networks via synthesizing task-driven adversarial scenarios
Get PDFDeep neural networks (DNNs) have become indispensable in autonomous systems such as robotics and self-driving vehicles, enabling advanced perception, forecasting, and control. Yet their reliability is often undermined by vulnerabilities to out-of-distribution (OoD) inputs and adversarial perturbations. Current robustness methods are predominantly task-agnostic, applying random augmentations or adversarial examples that improve vision models in isolation but may not affect downstream decision-making. As a result, autonomous systems remain susceptible to control-critical failures. This dissertation develops task-specific and game-theoretic approaches to enhance robustness and generalization across three key domains: perception, forecasting, and black-box control. First, I propose a framework for synthesizing adversarial visual scenarios explicitly tailored to multi-step, model-based robotic control. Leveraging the end-to-end differentiability of perception–planning–MPC pipelines and generative models, the method perturbs latent scene parameters in ways that directly degrade control cost. Retraining on these adversarial scenarios improves control robustness on OoD data by up to 36.2%, significantly outperforming conventional task-agnostic data augmentation. This result highlights the importance of aligning robustness interventions with the ultimate control objective. Second, I introduce a game-theoretic framework for robust time-series forecasting in dynamic environments. In this two-player, zero-sum formulation, a forecaster predicts future trajectories while an adversary strategically perturbs historical inputs to maximize control cost. Training against such adversaries compels the forecaster to learn policies that minimize cost under worst-case perturbations. This approach, which converges to local Nash equilibria, yields a 30.1% improvement on OoD real-world lane-change data relative to baseline forecasters. The framework demonstrates how game theory can be used to systematically model and counteract distributional shifts in safety-critical decision-making. Finally, to address settings where gradient-based methods are infeasible, I develop a Bayesian optimization framework for finding local saddle points in two-player zero-sum black-box games. By constructing Gaussian process surrogates and embedding them within a bilevel optimization loop, the method identifies local Nash points using only zeroth-order samples. Strategic sampling of the true objective refines the surrogate and enables efficient discovery of equilibria in nonconvex–nonconcave landscapes. Applied to robust MPC, this approach achieves a 27.6% reduction in mean control cost on OoD data compared to nominal controllers. Together, these contributions form a comprehensive framework for task-aware robustness in machine learning systems. By bridging adversarial scenario synthesis, game-theoretic forecasting, and black-box optimization, this work advances both theoretical understanding and practical tools for ensuring safe, reliable operation of AI in uncertain, real-world environments.Electrical and Computer Engineerin
The influence of social organization on sperm competition in Verreaux's sifaka (Propithecus verreauxi) and the ontogeny of sexual size monomorphism in Verreaux's sifaka (Propithecus verreauxi)
Get PDFThis master’s report is a compilation of two papers. Each abstract is presented below. Chapter 1: Sexual selection predicts that males invest in sperm competition when females mate with multiple males. Because group composition facilitates access to mates, I hypothesized that variation in within-group mate competition influences investment in sperm competition. In a population of wild Verreaux’s sifaka (Propithecus verreauxi), which live in both single and multimale groups, I tested the predictions that (1) dominant males living in multimale groups have larger testes than males in single-male groups, and (2) within multimale groups, dominant males have larger testes than subordinates. Consistent with expectations, I found that dominant males in multimale groups had significantly larger testes mass than males in single-male groups. Within multimale groups, dominant males had significantly larger testes mass than subordinate males. These results demonstrate that (1) males flexibly respond to the current level of within-group sperm competition, and (2) through dominance, within-group contest competition impacts male investment in sperm competition. Chapter 2: Due to variation in life history trajectories, adult body size and age at physical maturation have different determinants and implications for male and female primates. Unlike many other primates, Verreaux’s sifaka (Propithecus verreauxi) exhibit sexual size monomorphism at adulthood, but it is unknown if male and female sifaka experience the same developmental trajectory to reach this same adult body size. I examined the growth rate and duration of 14 morphometric variables collected from a population of wild Verreaux’s sifaka at Kirindy Mitea National Park in Madagascar between 2006 and 2019. Females exhibited longer duration and rate of growth in several skeletal measurements, while males exhibited longer duration and rate of growth in muscular measurements. Adult females had significantly longer hindlimb length than adult males, while adult males had significantly larger thigh circumference, bicep circumference, and a higher intermembral index than adult females. Because most of the differences are only apparent and significant in adulthood, I suggest that these adaptations are tailored for adult behaviors such as infant carrying and intrasexual competition, and that the path to adulthood varies greatly depending on sex and life history.Anthropolog
Pathways to belonging : shared culture, intergroup conflict reduction, and political inclusion of minorities
Get PDFThis dissertation examines how culturally legible practices shape intergroup attitudes and minority political engagement. I focus on low-barrier, repeatedly observable cues—visible appreciation for a locally iconic culture and participation in widely recognized national rituals—and examine whether these practices reduce backlash and if they invite political engagement among minority populations.
Chapter 1 reports findings from a survey experiment where an Asian immigrant’s expressed appreciation for an important local culture exacerbates White backlash to Asian immigration when it appears alongside familiar demographic and economic threat language. In this bundled message context, where positive cultural appreciation signals co-exist with negative immigration threat messages, respondents appear to recode cultural appreciation as appropriation or encroachment, and evaluations move in a more exclusionary direction; the design therefore provides implications for threat-bundling and cue–context mismatch as mechanisms behind White backlash to immigration.
Based on bundled message implications from chapter 1, chapter 2 tests cultural appreciation cue delivered cleanly—without threat message content—using a field experiment (with brief interviews) and a complementary online survey experiment. In chapter 2, a clean cultural appreciation signal reduces perceived cultural threat and lowers restrictive policy support, and follow-up qualitative interviews clarify why respondents interpret appreciation as local norm recognition rather than appropriation.
Then, chapter 3 shifts the focus of local cultural involvement to minority political engagement. Using a Multilingual Asian American Survey, I show that Asian American participation in Thanksgiving, the Super Bowl, and the Fourth of July is positively associated with their political interest, political media use, political discussion, and voting intention; mediation analyses indicate that American national identity carries a meaningful share of these associations. Across chapters, the mixed-method design—experiments, observational analysis, and interviews—specifies when cultural cues can backfire, when these signals can reduce perceived immigrant threat under a clean message delivery, and how ordinary cultural event participation can provide a low-barrier route into civic and political engagement among minority populations.Governmen
Threading the Needle: The Logic of Conventional Coercion in Nuclear Crises
Get PDFCan conventional military success lead to coercive success in a nuclear crisis? Some scholars argue that achieving limited conventional success can be used to coerce nuclear adversaries. Others argue that conventional capabilities coerce by manipulating nuclear risk. I intervene in this debate by arguing that conventional coercion in a nuclear crisis succeeds under two conditions. First, the challenger must possess an effective limited conventional option, or a conventional option that can achieve operational success while also respecting certain escalation thresholds. Second, the challenger must possess a strong nuclear retaliatory capability. Successful conventional coercion is therefore possible, but requires the challenger to thread a fine needle: It needs to restrain itself enough to avoid escalation, while also bringing enough force to bear to inflict a defeat. Achieving both aims simultaneously is difficult to do. One major implication of this argument is that US military and political leaders wanting to use conventional force effectively against a nuclear rival should work in peacetime to develop operational plans that respect geographic boundaries or refrain from targeting certain dual-use adversary platforms.LBJ School of Public Affair
Enhancing intratumoral drug transport by optimizing the surface physicochemical properties of nanotherapeutics
Get PDFCurrent therapies against solid cancers fail in part due to their inability to penetrate through the extracellular matrix (ECM) of tumors and reach the cancer cells at therapeutic doses. Increasing penetration promotes tumor regression and improves the therapeutic index of compounds. To achieve distribution and penetration through tumors, molecules must achieve unhindered diffusion through the size and interaction barriers presented by the heterogeneous ECM network. The interactions between the molecules and the ECM are driven by the surface physicochemical properties of the therapeutics. To address the challenges presented by current surface chemistries, we used peptide-presenting phage libraries as a high-throughput approach to screen and identify peptide coatings with physicochemical properties able to facilitate improved diffusive transport through the tumor microenvironment. Through iterative screening of these phage libraries against tumor ECM and identification through next-generation DNA sequencing and analysis, we identified a peptide that enhanced the diffusivity of both biological and synthetic nanoparticles. Interestingly, in contrast to most studies, we found that a positively charged peptide “surface” enhanced penetration, uptake, and the retention of particles in tumor tissue when compared to neutrally charged peptides. Mechanistically, we demonstrated that the positively charged particle partitioned into the net negative tumor tissue due to electrostatic interactions. Further, weak and reversible binding of the particles with the tumor bed allowed for deep penetration within the tissue. Additionally, the particle had a high number of intra-tissue binding sites in the tumor ECM that enabled longer retention in the tissue. Conjugating these peptides to immune checkpoint inhibitor antibodies improved the binding of the antibodies in a murine melanoma tumor environment. The longer retention of peptide-antibody conjugates recruited a higher number of activated tumor-infiltrating T-cells, resulting in a delayed tumor growth. This study indicates that net negative tumor ECM acts as a drug delivery depot for positively charged solutes toward improved intratumoral drug penetration and retention. Leveraging favorable interactions between the tumor ECM with therapeutics results in improved drug accumulation and retention for improved antitumor efficacy. As a result, this work can upend the current dogma of designing inert drug delivery systems and exploit electrostatic interactions to significantly improve therapeutic index of drugs and in the long-term, improve therapeutic outcomes in solid cancers.Pharmaceutical Science
Advancing water distribution systems modeling and management through high-performance computing
Get PDFWater distribution systems (WDSs) form a critical infrastructure that ensures communities’ reliable supply of clean and safe water. However, these systems face various challenges, including aging infrastructure, population growth, and the potential for water contamination events. To effectively manage and secure WDSs, developing advanced computational methods that can accurately model system dynamics, specifically focusing on transient behaviors, and detect and localize contamination incidents to minimize their impact is imperative. This Ph.D. dissertation focuses on utilizing parallel computational methods and heuristics to advance transient modeling in water distribution systems and develop effective contamination localization techniques. Transients, which are characterized by rapidly changing flow rates and pressures, can occur due to sudden valve operations, pump failures, or other system disturbances. Understanding and predicting transient behaviors is crucial for system design, operation, and maintenance, as well as addressing issues such as pipe bursts, water hammer, and water quality deterioration. Additionally, the dissertation develops water quality modeling tools specifically tailored for contamination detection and localization. Rapid identification and response to water contamination incidents are essential to safeguard public health and prevent widespread contamination. By leveraging advanced computational techniques, we can enhance our ability to detect, locate, and mitigate the impacts of both transients and contamination events, thereby improving the resilience and safety of WDSs.Civil, Architectural, and Environmental Engineerin
Influence of adverse childhood experiences and protective and compensatory experiences on teacher absenteeism
Get PDFTeacher absenteeism continues to present a significant challenge for school leaders and policymakers, particularly in educational settings that serve high-need student populations. This study aimed to examine how adverse childhood experiences (ACEs), protective and compensatory experiences (PACEs), and resilience might influence patterns of teacher absenteeism in a public school district that serves economically disadvantaged communities. This research was grounded in Bolman and Deal’s four-frame model of organizational leadership as a multidimensional lens for analyzing complex issues within school systems.
A quantitative case study design was employed using a structured survey instrument distributed to teachers within the district. The survey gathered self-reported data from 340 teachers on exposure to ACEs, the presence of resilience-building experiences of PACEs, current levels of teacher resilience, and reported frequencies of professional absences. To strengthen the validity of the findings and reduce limitations associated with self-report bias, I incorporated archival absenteeism records provided by the district’s administrative database. This cross-verification allowed for a more accurate depiction of actual attendance patterns and increased the reliability of the analysis. Descriptive statistics were used to summarize the central tendencies within the data, and nonparametric correlational analyses were conducted to explore the relationships between variables measuring ACE, PACE, and resilience and teachers’ self-reported absenteeism. The results demonstrated statistically significant associations between higher ACE scores and increased absenteeism. In contrast, higher PACE scores were positively associated with greater resilience and lower reported absence rates. These findings suggest that a comprehensive understanding of teacher absenteeism requires attention not only to institutional or organizational factors but also to the developmental experiences that educators carry with them. The findings emphasize the importance of trauma-informed leadership approaches and the implementation of staff support systems that are both preventative and responsive in nature. The recommendations and implications might ultimately contribute to improved teacher retention and sustained engagement in classrooms that serve the most vulnerable student populations.Educational Leadership and Polic