Physical Sciences and Mathematics Commons^™

Marginal Structural Cox Model For Survival Data With Treatment-Confounder Feedback, Yanan Zhang

Theses and Dissertations

In an observational longitudinal study, there can be time-varying exposure/treatment and time-varying confounders. When the confounders affect the exposure and prior exposure also has an impact on levels of confounders, there is treatment confounder feedback. To admit estimation of unbiased causal effects, these conditions need to be hold, exchangeability, positivity, consistency. The traditional method of conditioning on potential confounders does not meet these 3 conditions. Therefore, parameter estimates from traditional Cox model are biased casual effect estimates when the treatment confounder feedback exists. The marginal structural Cox model can be used to address this issue. By calculating and including inverse …

Comparison Of Atypical Bacteriophages That Infect Caulobacter Crescentus, Doreen Nguyen

Theses and Dissertations

Several Caulobacter bacterial genomes have been recently sequenced, and all of the genomes contained one or more clusters of genes with phage origins. This observation indicates that bacteriophages contribute to the Caulobacter gene pool, so in order to understand bacteria genomes we will need to understand phage genomes as well. As part of understanding the phage genomes, we want to isolate novel bacteriophages and study their genomics. This study resulted in the isolation of 12 new phages, including four that differ from the well-studied CbKlike phages. Two of these novel phages are Podoviruses with icosahedral heads and small tails, and …

Spatio-Temporal Analysis Of The Occupational Fatal Victimization Of Law Enforcement Officers In The Us, Xueyi Xing

Theses and Dissertations

The models with constant coefficients of the covariates across space and time are commonly used in spatio-temporal analyses. However, the associations between risk factors and the outcome could have locally differential temporal trends in many cases. In this study, a Bayesian latent cluster modeling strategy is employed to identify potential spatial clusters in which locally specific sets of temporally varying coefficients of covariates are allowed. A state-level panel data of police officers occupational fatal victimization for the years 1979-2010 is used. To accommodate overdisperson and excess zeros, a negative binomial model and zero-inflated Poisson/negative binomial models are also utilized. A …

Simulation Based Evaluation Of Multiscale Small Area Health Models, Purbasha Dasgupta

Theses and Dissertations

The effects of scale on the analysis of spatial data, often referred to as the modifiable areal unit problem in spatial studies, is one of the issues often encountered in small area health models. These spatial effects of scale are also seen in the areas of disease mapping where data are usually available in counts. Often there is a need to consider the different scales of aggregation that exist within count data, since inferences based on analyses can vary if we change the definition of the unit of analysis. This thesis provides a framework that describes the distribution of relative …

Characterization Of The Role Of Fro6 In Metal Homeostasis In Arabidopsis Thaliana, Margo Ellen Maynes

Theses and Dissertations

Iron deficiency is the most common human nutritional disorder in the world today, affecting approximately 2 billon people worldwide, almost a third of the world's population. For most of the world's population, plant foods serve as the major source of dietary iron. One approach that may contribute towards the solution of iron deficiency is the development of crop plants that contain higher levels of bioavailable iron. This project focuses on FRO6, a ferric chelate reductase in Arabidopsis thaliana that is thought to reduce apoplastic iron for transport across the plasma membrane in leaf cells. We hypothesize therefore that FRO6 controls …

The Reproductive Ecology Of Plethodontid Salamanders In The South Carolina Inner Coastal Plain, Heather Rena Oswald

Theses and Dissertations

Nest- site selection is a critical process in the life history of amphibians, directly influencing offspring survival and parental fitness. When and where an amphibian chooses to nest is strongly influenced by a range of environmental cues. We monitored plethodontid salamander breeding behavior in seepage wetlands in the South Carolina inner Coastal Plain. Seepage wetlands are ideal for monitoring semiaquatic salamander breeding, because they provide habitat for both larval and adult salamanders while having relatively predictable, constant water temperatures and presence year round. We observed the breeding phenology of three sympatric salamanders (Eurycea cirrigera, Desmognathus auriculatus, and Pseudotriton ruber) in …

Trophic Response To Polycyclic Aromatic Hydrocarbons And Copper In Tidal Flats Of North Inlet, South Carolina, Leslie Lynn Muggelberg

Theses and Dissertations

The trophic link between benthic microalgae (BMA) and fiddler crabs is critical for the ecosystem functioning of estuaries and alterations in this linkage by anthropogenic activities could have cascading impacts on food webs and biogeochemical cycling in these sensitive habitats. Singular and interactive effects of two common pollutants in aquatic ecosystems, polycyclic aromatic hydrocarbons (PAHs) and copper (Cu), were investigated by exposing field collected sediment communities to the contaminants and measuring changes in BMA biomass and community composition in a bioassay design. The consequential impacts on the food web were then explored by examining the effects of PAHs and copper …

Insects As Indicators Of Environmental Stress, De Anna Estella Beasley

Theses and Dissertations

In the face of climate change-related events and anthropogenic disturbances, understanding the impacts of these events on species richness, abundance and distribution is important for us to mitigate biodiversity loss and better predict consequences for the environment and for human life. Insects are excellent models for understanding the consequences of environmental stress due to the sensitivity of their development and behavior. The overall focus of my dissertation research is the investigation of fluctuating asymmetry and oviposition behavior as indicators of environmental stress. My research includes a meta-analysis of published literature, and empirical research that was part of a collaborative initiative …

A Critical Review Of Endometriosis Pathology, Brittany Lauren Cureton

Theses and Dissertations

Endometriosis is a complex, multifactorial, reproductive disorder present in approximately 10-15% of adult women between the ages of 25-35. This disorder occurs when endometrial glands and stroma grow ectopically on the surface of the ovaries, pelvic peritoneum, fallopian tubes, and the uterus. Endometriosis causes varying degrees of painful symptoms and infertility in infected individuals. Three main theories of endometrial accumulation attempt to explain the etiology of this elusive disease. There have been various staging of endometriosis symptoms that attempt to standardize classification as well as predict pain and infertility. Angiogenesis, necessary to the survival of endometrial tissue, along with immune …

The Role Of Reactive Oxygen Species In Cell Death Induced By Thymidylate Synthase Inhibitors, Ufuk Ozer

Theses and Dissertations

Thymidylate synthase (TS) catalyzes the reductive transfer of a methyl group from N5,N10-methylenetetrahydrofolate (CH₂-THF) to dUMP, forming dTMP and dihydrofolate (DHF). It is generally accepted that inhibition of the enzyme leads to a deficiency of dTMP, followed by genome damage and programmed cell death. As such, TS has long been viewed as an important target of anti-neoplastic agents, such as 5-fluorouracil (5-FU) and raltitrexed (RTX), which lead to inhibition of the enzyme. Oxidative stress is well-recognized as having a central role in cellular response to a number of DNA damaging agents, and may be a proximate cause of …

Environmental Pre-Conditioning Of Bacterial Populations And Communities To Extreme Acidity, Gabriel Joseph Swenson

Theses and Dissertations

The ability of opportunistic enteric pathogens to cause disease is effected by their ability to survive the variable and lethal acidity of the mammalian host gastrointestinal milieu. In many of these pathogens, survival is conferred by an acid stress response (ASR). ASR is elicited when bacterial cells are pre-conditioned in sub-lethal acidity (pH 4-6) which induces rapid biochemical and physiological modifications and facilitates survival when extreme acidity (pH 1-3) is encountered. In Vibrio cholerae, the causative agent of the diarrheal disease Cholera, ASR was initially investigated in an effort to determine how this ubiquitous aquatic bacterium is capable of causing …

The Role Of Host-Tumor Interactions In Liver Metastasis Of Colorectal Cancer, Yu Zhang

Theses and Dissertations

Colon cancer is the third most frequent cancer and the second leading cause of cancer deaths in the United States. Liver metastasis is the major cause of death in colon cancer. Successful metastases depend on productive collaborations between tumor cells and host-derived cells in the tumor microenvironment, target organ environments, and cells in the hematopoietic compartment.

To identify the host-tumor interactions promoting liver metastasis and their molecular and cellular mediators, an orthotopic mouse model of liver metastasis of colon cancer was established that recapitulates all stages of tumor growth and metastasis. A highly metastatic mouse carcinoma cell line CT26-FL3 was …