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Superconductivity Near a Quantum-Critical Point: Analysis of the Discrete ��-Model at Finite Temperatures
No full textNear a Quantum-Critical Point (QCP) in a metal, strong Fermion-Fermion interaction mediated by a soft collective Boson gives rise to two competing tendencies, non-Fermi Liquid behaviour and Superconductivity which differs from the standard BCS theory. In this thesis, we consider a class of models, known as ����� Model, in which the effective interaction potential takes the form V (���) ��� 1/|���| �� . We introduce some numerical and semi-analytical techniques to analyze the behaviour near QCP. Based on the mapping between Eliashberg theory and the classical spin chain, we get a discrete Hamiltonian in terms of the angles made by individual spins. 2 different numerical approaches are introduced to solve the infinite number of coupled non-linear equations resulting from minimizing the Hamiltonian, which will yield the topologically distinct minima and saddle points. We find that the minimum energy state is always a superconducting state with winding number n = 0. Other superconducting states were also found, they represent topologically different pairings with different winding numbers. These states represent the saddle points of the free energy functional. We focus our analysis mainly on the case 1 < �� < 2 at finite temperatures
Nanoscale Functionalization of Graphene-Based and Molybdenum Disulphide Samples via Electrochemical and Thermochemical Methods
No full textOur primary objective was to try to functionalize Graphene-based and Molybdenum Disulphide samples through electrochemical and thermochemical methods. The samples that we experimented with were Graphene, Graphene Oxide, and Molybdenum Disulphide on gold substrates. We chemically functionalized Graphene Oxide with Cyanuric Chloride (2,4,6- trichloro-1,3,5-triazine), assisted by an external heater source to covalently bond the compounds (thermochemical means), which was confirmed by X-ray Photoelectron Spectroscopy (XPS) results.
In the electrochemical method, we attempted to locally functionalize Graphene and Molybdenum Disulphide (MoS2) samples fabricated on a gold substrate via tip-based Local Anodic Oxidation (LAO) using a Conductive Atomic Force Microscope, where the AFM tip is connected to the positive terminal of the source meter and sample connected to the negative terminal. The local chemical changes were analyzed by measuring and comparing scan heights before the LAO. Platinum-coated Silicon tips were used due to their hardness and local corrosion resistance to pattern the 2D materials. Analysis of results and a proposed future work on the chemical functionalization of Molybdenum Disulphide were also discussed due to its surface properties akin to Graphene samples
Essays in Law and Economics
No full textMy dissertation focuses on issues related to the criminal justice system in the United States, especially with respect to indigent defense and policing.
First, I ask whether indigent defense attorneys secure better deals for same-race defendants. This is important since 80 percent of criminal defendants rely on assigned counsel for legal defense. To do this, I employ a difference-in-differences approach, exploiting the quasi-random assignment of court-appointed attorneys to cases in Travis County, Texas. Results indicate that while Black and White attorneys are similarly effective at securing dismissals for White defendants, Black attorneys are less effective than White attorneys at securing dismissals for Black defendants. Specifically, Black defendants who are represented by White rather than Black attorneys are 20-22 percent more likely to have their charges dismissed and 17-27 percent less likely to be incarcerated. Moreover, Black defendants who are represented by White attorneys are not more likely to re-offend in the future.
Second, I study the effect of police-involved shootings on gun violence and civilian cooperation with police. To distinguish between crime reporting and crime incidence, I use administrative data on 911 calls and ShotSpotter data from Minneapolis. Exploiting the variation in the timing and the distance to these incidents, I show that exposure to a police shooting increases gun-related crimes by 3-6 percent and reduces civilian crime reports to police by 4-6 percent.
Finally, I study the impact of internal affair investigations, the most common accountability system in policing, on police behavior. Using data from a large city where there is conditionally random assignment of officers to 911 calls, I employ regression discontinuity and difference-indifferences methods to distinguish the impact of investigations from confounding factors. Results indicate that increased oversight from internal investigations does not change an officer���s likelihood of making an arrest or using force. This is true across different types of allegations, including those that are sustained
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
Application of Image-based Techniques to Analyze Coastal Flows and to Evaluate Temporal Wetland Changes
No full textCoastal transport processes occurring at the landward edge of tidal and wave action are important for the diversity of coastal ecosystems, determining nutrient fluxes, the dynamics of sediment and marine pollution during tidal mixing, and controlling coastal geomorphology. Understanding these processes requires large-scale field observations over modest spatial domains to fully resolve their governing mechanisms and to validate and update algorithms in existing numerical and laboratory simulations. This dissertation investigates the application of remote sensing techniques based on UAS and satellite imagery to monitor large-scale coastal processes along the Texas coast, particularly focusing on Galveston Bay, TX. First, surface current mapping methods using UAS video sequences are presented to provide a means of practical measurements of ocean surface currents for the effective prediction of tidal mixing exchange dynamics. The main method, introduced by Stre��er et al. (2017), utilizes a two-dimensional space-plus-time Fourier transform of UAS imagery, linked to the Doppler-shifted dispersion relation fitting technique for surface gravity waves. The resulting current fields reveal the flow structures of tidal currents through inlets at Freeport Harbor and Galveston Bay entrance in flexible spatial resolution. Second, satellite images from Sentinel-2 near Galveston Bay inlet are utilized to bridge the knowledge gap between a series of laboratory, numerical, and limited field studies on tidal vortices to observe their large-scale formation and the influence of coastal currents. A classification scheme is introduced to identify two types of vortex flow patterns observed in the satellite imagery. This classification scheme is validated at Galveston Bay using different satellite images from MODIS with a larger dataset. Lastly, shoreline change monitoring at coastal wetlands in Galveston Bay is explored, leveraging geospatial mapping from UAS imagery enhanced by a new georectification technique adapting the particle image velocimetry (PIV) algorithm. A time series of wetland maps, generated using a Structure-from-Motion (SfM) technique, facilitates the computation of shoreline change rates along the observed wetland boundaries. Subsequent statistical analysis of these rates allows for an assessment of the impact of seasonal variations and storm events on short-term wetland evolution
A Primate Model for Studying the Importance of Environment and Family Lineage on Development, Health, and Aging
No full textThe Cayo Santiago rhesus macaques are one of the most intensely studied primate colonies in the world. They are associated with a rare skeletal collection that is contextualized with known sex, age, and familial information. The purpose of this dissertation is to elucidate environmental and genetic contributions of bone health, evolution, and development. In doing so, this will become a translational resource for human disease and variation. This study departs from previous endeavors by extracting almost all development and pathological data from the derived skeletal collection and stratifying it with known life-history and demographic information to produce reliable biomedical models of health. The backbone of the proposed model is derived from the skeletal collections housed at the Caribbean Primate Research Center University of Puerto Rico, Medical Sciences Campus and New York University, Department of Anthropology. Statistical analysis such as relative risk ratios, and multivariate regression were employed to test for the relative roles of environment and genetics on bone health in the population. The Cayo Santiago population were found to exhibit secular trends in congruence with ecogeographic rules. Specifically, body weights declined, and limb dimensions became slenderer, increasing surface area/volume ratios of individuals and heightening heat expenditure in a more homogeneously warm climate than the one they were adapted to over evolutionary timescales. In contrast to the gradual impacts of climate, major hurricane events precipitated increased levels of systemic disease, bone mineral density (BMD) reductions, and delayed dental eruption timings. Greater rheumatic disease, lower BMD, and delayed dental eruption are believed to relate to immune dysregulation, low grade chronic inflammation, and early-adversity. Further analysis indicated that disease is also patterned across families indicating that a genetic susceptibility to disease can be observed within the matrilines of the Cayo population. Lastly, the neurosurgical landmark, the pterion, exhibited strong support for inheritance of pattern. This work suggests craniotomies using the pterional approach may benefit from taking or making use of family history of pterion type and subsequently benefit from aspects of its variatio
Essays on Microeconometrics
No full textThis dissertation consists of three essays on Microeconometrics and Applied Econometrics.
Chapter 2 provides nonparametric identification results in first-price auctions with unknown collusion schemes. This chapter shows that regardless of the unknown collusion scheme, collusive bidders in a partial cartel can be identified from winning bids, identities of winners, and auction-specific covariates satisfying an exclusion restriction. It can be shown that the value distributions of collusive bidders are identified under two types of cartels characterized by McAfee and McMillan (1992). This chapter proposes a test procedure to recover the identities of collusive bidders. The test method is applied to California highway procurement auctions.
Chapter 3, a joint work with Yonghong An, Matthew Gentry, and Daiqiang Zhang, examines the economic impacts of anti-bid-shopping legislation. We exploit the policy changes in Washington state to evaluate the impacts of anti-bid-shopping legislation on both ex-ante and ex-post procurement auction outcomes. With the engineer���s estimate of the cost and work types of projects, we can classify the contracts affected or not affected by anti-bid-shopping legislation. We estimate the effects of the policy using Regression Discontinuity Design (RDD) or Difference-in-Difference (DID). Findings indicate that the requirement for subcontractor listing can increase the winning bid while reducing the final total payment to the primary contractor. Moreover, disallowing substitutions may expedite project completion time and reduce the final total payment.
Chapter 4 proposes nonparametric estimation and uniform inference on counterfactual distributions in the presence of proxy variables. A two-step series estimator is developed to consistently estimate counterfactual distributions and their functionals under a general framework with latent variables. The uniform asymptotic theory is built on strong approximations of Gaussian processes introduced in Chernozhukov et al. (2013). The two-sample series counterfactual distribution estimator is applied to both simulations and an empirical study of the wage gap, in which the Armed Forces Qualifying Test (AFQT) score is used as a proxy variable for premarket human capital. The difference in the distribution of premarket human capital explains the racial wage ga
Astrocytic Nik Regulates Local and Systemic Inflammatory and Metabolic Responses
No full textThough NF-��B-inducing kinase (NIK) has well-established roles in inflammatory, immune, and
metabolic regulation on a systemic level, its specific roles in the central nervous system (CNS)
are not well-defined. NIK���s tumor-intrinsic roles in glioblastoma multiforme (GBM) promoting
tumor invasion and growth suggest it could be involved in other neuroinflammatory conditions,
such as stroke and traumatic brain injury, as well as maintain tumor-extrinsic functions in GBM.
Critical in each of these conditions are astrocytes, glial cells of the CNS with diverse immune
and metabolic functions. No study has characterized the function of NIK in astrocytes. Thus, this
thesis aims to examine NIK���s roles in inflammation, immunity, and metabolism within 1) the
CNS overall and 2) specifically through astrocytes ��� critical CNS support cells.
The impact of NIK on GBM survival was investigated via orthotopic implantation of the
syngeneic GL261 GBM model in a total NIK knockout (KO) mouse model. The function of NIK
in astrocytes under basal and lipopolysaccharide-induced inflammatory conditions was explored
with a GFAP-Cre NIK KO mouse model. Output from metabolic cages, transcriptional
regulation of cytokines and metabolic markers in harvested liver and brain tissue, and protein
expression of cytokines in tissue and serum was analyzed in GFAP-Cre NIK KO and control
mice.
Loss of NIK in the GBM tumor microenvironment (TME) increased male mouse survival. With loss of NIK in astrocytes, increased signaling and decreased metabolism was noted both locally and systemically, specific to male mice. After induction of inflammation with LPS, increased astrocytic response and cytokine signaling was identified locally, and decreased tissue inflammation and metabolism systemically, again in male mice.
NIK plays a critical, pro-tumor role within the GBM TME, resulting in increased survival when knocked out. With loss of NIK in astrocytes, systemic homeostasis is impacted, specifically in signaling and metabolic regulation. These effects are significantly more pronounced in males, suggesting a critical sex-specific role of NIK in the CNS and in inflammatory CNS pathologies such as GBM
Development of a Finite Element Analysis (FEA) Model for Predicting Elbow Torque of the Apollo A7LB Extravehicular Activity (EVA) Spacesuit Pressurized Sleeve
No full textEVA spacesuits are critical to human survivability in the hostile environment of space, which consists of low atmospheric pressures (e.g., vacuum in LEO and on the lunar surface) and temperature extremes (e.g., ���65��C to 125��C in LEO). While spacesuits must protect humans against these conditions, maintaining an astronaut���s mobility is also crucial to achieve mission objectives such as in a return to the Moon as defined by the Artemis architectures. Spacesuit mobility is largely driven by the design of joints such as in the knees, shoulders, ankles, waist, and elbows. In the Apollo A7L/A7LB spacesuits, full circumferential rubber-dipped nylon convolutes were utilized in these joint locations. Understanding the Apollo elbow joint design���s mobility, in comparison to the Extravehicular Mobility Unit���s (EMU) flat pattern gore design, could provide new insights for the development of future spacesuits. In this research, an Abaqus FEA model was developed to predict elbow joint torques during pressurized bends using the A7L/A7LB pressure garment assembly arm configuration. The model was scripted to allow for simple adjustment of numerous design variables, such as the number and size of the convolutes. Through DOE studies, it was found that sleeve radius had the largest proportional effect on joint torque, while sleeve thickness and fabric bias direction Young���s modulus had smaller effects. Increasing number of convolutes reduced joint torque, but this effect diminished at larger numbers. Increasing operating pressure significantly increased joint torque, especially at high bend angles (such as 120 degrees). The results showed that lowest torque designs from these DOE studies required less joint torque than an Aerospace Human Systems Laboratory (AHSL) EMU FEA elbow model up to 55-60 degrees, and after 105 degrees. The model was also adjusted to available Apollo sleeve dimensions, and the material properties were approximated to yield joint torque data closely aligned with an A7LB empirical measurement in literature. Results showed this Apollo sleeve required less joint torque than the AHSL EMU model from 0-40 degrees. Lastly, the model was adjusted to an alternative convolute joint used in empirical joint testing, and joint torque results were the same order of magnitude as reported data
Improving the Accuracy, Reliability, and Throughput of Nanoindentation Hardness and Modulus
No full textInstrumented nanoindentation is a form of load and depth sensing indentation that characterizes material properties on the micro- and nanoscale. This form of indentation is widely used for its ability to measure a variety of material properties on very small scales in a high-throughput manner without extensive sample preparation and with minimal sample damage after testing. However, this versatility introduces a level of complexity, and due to the various methods for performing nanoindentation tests and collecting data, there are inevitably opportunities to encounter and cause experimental errors. Common sources of error include not accounting for pile-up or other area-related issues, frame stiffness and sample mounting issues, and using improper sample preparation and testing parameters as well as testing non-ideal samples. This thesis provides a background for these sources of error and expands on best practices from research and literature to overcome or avoid these sources of error. To this end, a highly ordered pyrolytic graphite sample was tested and the lack of residual indent impression and sample anisotropy was examined in detail, with methods used to account for such sample non-idealities and provide more reliable data presented. This thesis further investigates how sample mounting conditions affect and can sometimes produce error in the compliance of the nanoindentation system. Such research expands and improves the minimal research that currently exists in the literature by providing concrete methods for avoiding issues caused by sample mounting in order to produce accurate and reliable data