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EVOLUTION OF FERROMAGNETISM IN SELF-INTERCALATED CHROMIUM TELLURIDES
No full textIn this thesis chromium-tellurides were synthesized via solid state reaction and single crystals were grown via chemical vapor transport reactions. Both monoclinic and hexagonal Cr7Te8 phases were synthesized and magnetic susceptibility measurements and field sweeps were preformed. Arrott plots were generated to determine the exact Curie temperature of the monoclinic and hexagonal phases of 328K and 342K respectively. The disordered phase sample shows a unique meta-magnetic transition around 70K. Neutron diffraction was taken on the meta-stable hexagonal phase and magnetic structures were solved showing a simple ferromagnetic arrangement at room temperature followed by a change in easy axis at 150K, and finally a spin-recant to the c-axis at 5K. The addition of an anti-ferromagnetic component and a magnetic propagation vector of k= (1/2, 1/2, 0) was also observed at 5K. Single crystals were then grown via chemical vapor transport and macro-magnetic properties were measured utilizing a SQUID magnetometer. Several samples showed the same meta-magnetic transition around 70~K with exotic susceptibility data between in and out of plane measurements. Finally, this works next steps should include single crystal neutron diffraction of the monoclinic, trigonal, and hexagonal phase single crystal samples to elucidate the exotic magnetic structures hinted at by the susceptibility data
ON THE SMOLUCHOWSKI-KRAMERS APPROXIMATION OF STOCHASTIC DAMPED WAVE EQUATIONS
No full textIn this thesis, we study three problems related to the small mass limit, also known as the Smoluchowski-Kramers diffusion approximation for stochastic damped wave equations. In the first part, we study the validity of a large deviation principle for a class of stochastic nonlinear damped wave equations, including equations of Klein-Gordon type, in the joint small mass and small noise limit. Additionally, we provide a proof of the Smoluchowski-Kramers approximation in the case of variable friction, non-Lipschitz nonlinear term, and unbounded diffusion.
In the second part, we investigate the convergence, in the small mass limit, of the stationary solutions of a class of stochastic damped wave equations, where the friction coefficient depends on the state and the noisy perturbation is of multiplicative type. We demonstrate that the Smoluchowski-Kramers approximation, previously shown to hold for any fixed time interval, remains valid in the long-time regime. Specifically, we prove that the first marginals of any sequence of stationary solutions for the damped wave equation converge to the unique invariant measure of the limiting stochastic quasilinear parabolic equation.
The final result of this thesis concerns the Smoluchowski-Kramers approximation for a system of stochastic damped wave equations, whose solution is constrained to live on the unitary sphere in the space of square-integrable functions on any fixed interval. The stochastic perturbation is a nonlinear multiplicative Gaussian noise, with the stochastic differential interpreted in Stratonovich sense. Due to its particular structure, this noise not only conserves almost surely the constraint, but also preserves a suitable energy functional. In the small-mass limit, we derive a deterministic system, that remains confined to the unit sphere, but includes additional terms. These terms depend on the reproducing kernel of the noise and account for the interaction between the constraint and the conservative noise
NATURAL AND EXPERIMENTAL CONSTRAINTS ON LITHIUM INCORPORATION AND DIFFUSION IN GARNET AS AN INDICATOR OF FLUID ROCK INTERACTION
No full textFluid flow in the deep crust is a major avenue of mass transport and impacts rheology, the generation of arc magmas, and contributes to the formation of ore deposits. Evidence for fluid infiltration events can be recorded by elemental zoning within garnet. One example is lithium, a fluid-mobile element that diffuses rapidly and can act as a tracer of fluid-rock interactions in metamorphic terrains. While whole-rock lithium concentrations have been used to determine the timescales of short-lived events including time-integrated fluid event durations in metamorphic settings, resolving individual fluid pulses requires detailed in situ measurements of lithium concentrations across metamorphic minerals. Interpreting timescales of fluid infiltration in metamorphic rocks on the basis of variations in lithium concentration in garnet requires exploration of lithium in metamorphic garnet as well as quantitative knowledge of lithium in garnet diffusion coefficients (D) that have not yet been experimentally determined. This study takes a two-pronged approach at (1) deciphering the distribution of lithium in garnets from metamorphic terrains that have experienced fluid-rock interaction and (2) constraining the diffusivity of lithium in garnets of varying composition at different temperature and oxygen fugacity conditions. For the natural rock record, four metamorphic localities were selected to represent a range of pressure and temperature conditions, tectonic settings, and fluid histories: Waits River, VT; Monviso, Italy; Erzgebirge, Germany; and Catalina, CA. Lithium concentration data were collected on garnets from these localities via LA-ICP-MS, in the form of traverses and quantitative mapping. The results of those analyses reveal supporting evidence of fluid infiltration events and show correlations between lithium and other trace and rare earth elements. To determine the diffusivity of lithium in garnet, two types of powder source diffusion experiments were performed; box furnace experiments using a sealed silica tube method, and gas mixing furnace experiments using a suspended, open platinum capsule. Garnet starting material and experimental run products were analyzed for their lithium concentration using LA-ICP-MS and SIMS depth profiling. The sealed silica tube experiments used polished almandine-pyrope, grossular, and spessartine grains surrounded by a lithium rich powder (spodumene or Li-doped crushed garnet) at temperatures ranging from 600 to 800 °C for durations of 1 to 8 weeks. The garnet starting material (control) displayed a uniform lithium concentration from surface to interior. The experimental run-product garnets exhibited an enrichment in lithium of up to 100s ppm at the rim followed by a smooth decrease towards the interior over length scales on the order of 1-8 μm, indicative of diffusive uptake. One-dimensional diffusion modeling was performed to calculate a best-fit D for each temperature. The data were best fit by a model with two independent mechanisms, which has been postulated for Li in olivine and pyroxene and theorized for lithium in garnet. The diffusivities of both mechanisms are slower than lithium diffusion in olivine along interstitial sites, comparable to diffusion in olivine through metal vacancies, and faster than lithium+REE coupled substitution into garnet. The gas mixing furnace experiments were conducted at 800 °C with ratios of CO:CO2 that correspond to FMQ+2 and FMQ-2, as well as in air (FMQ+13). The FMQ+13 run products display a typical, exponentially decreasing diffusion profile that can be modeled using the same two-mechanism model as the box furnace experiments. Results from the FMQ+2 and FMQ-2 experiments show a more complex diffusion behavior, where the lithium concentration is elevated at the surface of the grain, increases until it reaches a local maximum and then decreases until it reaches the internal lithium concentration of the garnet. This “peaked” curve can best be explained by a “lithium incorporation and loss” model, where lithium is moving both in and out of the garnet along different pathways activated at reduced fO2 conditions. These results appear to be the first experimentally derived diffusion coefficients for lithium in garnet and can be used to constrain the duration of individual fluid flow events in metamorphic settings
¡ILEGAL!: THE RACIAL POLITICS OF UNDOCUMENTED MEXICAN IMMIGRATION IN CALIFORNIA, 1970-1999
No full textThis dissertation examines how undocumented Mexican immigrants were alternately constructed as both threats and economic necessities between 1970 and 1999. This study uses legislative debates, newspaper articles, and political rhetoric, to explore how exclusionary discourses shaped immigration policies and reinforced racial hierarchies. It argues that the category of the “illegal alien” was not just a legal designation but a racialized one used to justify exclusion, economic exploitation, and shifting definitions of national belonging. Focusing on three key immigration policies—the Dixon Arnett Law (1971), the Immigration Reform and Control Act (IRCA, 1986), and Proposition 187 (1994)—this dissertation traces how undocumented Mexican immigrants were framed in moments of political and economic uncertainty. In particular, it looks at how the economic anxieties of the 1970s transformed Mexican migration into a crisis, reinforcing narratives of invasion and displacement. By the 1980s, immigration policies like the Immigration Reform and Control Act (IRCA) balanced selective inclusion—offering amnesty to some while expanding workplace surveillance and employer sanctions that deepened labor precarity. While IRCA introduced limited avenues to legalization, it also reinforced surveillance and labor control, paving the way for what takes place in the 1990s: a shift in the discourse from economic concerns to moralized and racialized preservationist rhetoric, culminating in Proposition 187’s attempt to criminalize undocumented immigrants’ presence in public life.
Using the Manufacturing Danger / Manufacturing Possibility framework, this dissertation demonstrates how narratives of crisis, control, and conditional inclusion actively shaped immigration policy to sustain racial and economic hierarchies. Rather than viewing exclusionary laws as inevitable responses to migration, this study reveals how they were strategically produced to sustain white dominance and economic precarity. By historicizing these shifts, this project challenges the idea that exclusionary immigration policies naturally respond to migration. Instead, it reveals how discourse has historically and strategically been deployed to justify exclusion, reinforce racial and economic hierarchies, and sustain cycles of criminalization. Understanding these historical patterns is essential for resisting contemporary efforts to criminalize and marginalize immigrant communities
Mathematics Models of Tumor-Immune Interactions And Immunotherapy
No full textImmunotherapy is rapidly becoming a standard treatment in cancer, alongside surgery,chemotherapy, and radiotherapy. As T cells are key players in anti-tumor immune response,
strategies to modify T cells and then re-inject them to enhance anti-cancer immunity are at the
forefront of cancer immunotherapy. Engineered T cell receptor (TCR)-expressing T (TCR-T)
cells are intended to drive strong anti-tumor responses upon recognition of the specific cancer
antigen, resulting in rapid expansion in the number of TCR-T cells and enhanced cytotoxic
functions, causing cancer cell death. However, although TCR-T cell therapy against cancers has
shown promising results, it remains challenging to predict which patients will benefit from such
therapy. In this dissertation, we look specifically at TCR-T cell therapy, explore the mechanisms
by which this living product grows and changes inside the body, explore how and why this process
differs so dramatically between patients, and explore how quantity and quality must be optimized
for maximal effectiveness of this therapy.
We developed two ordinary differential equation models: one focusing on TCR-T cell
therapy for cervical cancer, and another that expands this framework to evaluate TCR-T cell
therapy as a dynamic system involving effector TCR-T cells, regulatory T cells (Tregs), and
“non-cancer-killing” TCR-T cells. Our results provide a plausible mechanistic explanation for
the wide variability in clinical responses to TCR-T cell therapy and suggest strategies to enhance
patient outcomes, particularly for highly heterogeneous patient populations. Specifically, our
findings indicate the existence of an optimal dosage window for TCR-T cells, dependent on the
initial tumor size, to achieve successful cancer elimination. Furthermore, we demonstrate that
a significant proportion of TCR-T cells within the tumor microenvironment (TME) are ”noncancer-
killing” cells, such as exhausted T cells, contributing little or no direct cytotoxicity. We
also identify two critical factors influencing tumor regression: the reversal of the immunosuppressive
TME following Treg depletion and the increased presence of effector TCR-T cells with antitumor
activity. Finally, we show that parameters such as enhancing the cytotoxicity of effector TCR-T
cells and increasing their numbers are crucial in determining treatment outcomes
Bridge Hazard Analysis and Evaluation Considering the Combined Effects of Pier Scour and Seismic Action
No full textBridges are critical components of transportation infrastructure, and their safety and resilience are significant to ensure public welfare. This study presents a comprehensive analysis and evaluation of bridges under multi-hazards, focusing on the interplay between two significant factors: pier scour and seismic action. The joint effects of these natural hazards present a substantial challenge for bridge engineers and require further analysis and assessment.This study presents a framework for assessing the vulnerability of bridges under combined seismic and scour hazards. It employs nine bridge categories, defined by the NCHRP 24-34 project, based on bridge lengths and pier sizes. A probabilistic approach was introduced for hazard curve development, focusing on local pier scour depth as the intensity measure. The probability distribution of scour depth was derived from nominal values of the HEC-18 scour equation and uncertainties evaluated in the NCHRP 24-34. Key random variables, including Manning’s n value, channel bed slope, discharge, and cross-section area, were analyzed for uncertainty, leading to their respective probability distributions. Monte Carlo simulations were then used to generate generalized scour hazard curves for each bridge category, allowing for the estimation of the probability of scour exceeding a given depth at any given day or during extreme events.
Seismic fragility analysis was conducted using nonlinear dynamic analysis to evaluate the probability of bridge failure under seismic loading, with the limit states of bridge components like piles and bearings. The study further integrates seismic fragility with scour hazard curves to assess the joint probability of failure due to both hazards. A case study is included, applying the proposed methods to a specific bridge, demonstrating how site-specific ground motions, finite element modeling, and dynamic characteristics are considered in evaluating the bridge's response to these combined hazards.
This work provides a comprehensive approach for improving bridge risk assessments and prioritizing mitigation strategies, offering valuable insights into the interaction between scour and seismic vulnerabilities
Charting New Courses: Navigating, Designing, and Facilitating Archival Instruction
No full textThis presentation was given as part of Session 7 "Archival Educators in MARAC: Building the Bridges Between Theory & Practice" at the Spring 2025 MARAC conference in Harrisburg, PA
Cognitive Measures Explain Variance in Speech-in-Noise Among Older Adults
No full textBinaural hearing, the ability to hear with two ears, helps individuals localize sound and understand speech in noisy environments. As individuals age, speech-in-noise understanding becomes more difficult, and this decline has been linked to both auditory and cognitive changes. This study investigates how processing speed, the rate at which the brain processes and receives stimuli, affects speech-in-noise understanding. The Coordinate Response Measure (CRM) evaluates how well a person separates speech from background noise. We hypothesized that individuals with higher processing speed would exhibit better speech-in-noise ability, with age acting as a moderator. Processing speed was measured with the NIH Pattern Comparison test, and binaural hearing abilities were assessed with CRM.
Results revealed that higher Pattern Comparison scores significantly predicted better speech-in-noise recognition at 45° (p = 0.00026, R² = 0.478), suggesting that processing speed plays a role in spatial listening ability. However, when age was added to the model, Pattern Comparison was no longer a significant predictor (p = 0.5675), and age itself became the dominant predictor of performance (p = 0.0129). This indicates that age may act as a confounding factor in cognitive influences on speech-in-noise recognition.
These findings highlight the role of cognitive factors in spatial and speech processing, particularly in more complex listening environments. Future research should explore how cognitive training can enhance binaural hearing, particularly in older individuals, and whether targeted interventions can improve spatial listening abilities.National Institute On Deafness And Other Communication Disorders of the National Institutes of Health under Award Number R21DC02182