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Articles 1 - 30 of 34
Full-Text Articles in Physical Sciences and Mathematics
Multidimensional Methods: Applications In Drug-Enzyme Intrinsic Clearance Determination And Comprehensive Two-Dimensional Liquid Chromatography Peak Volume Determination, Dennis Thekkudan
Theses and Dissertations
The goal of the first project was to evaluate strategies for determining the in vitro intrinsic clearance (CLint) of dextrorphan (DR) as metabolized by the UGT2B7 enzyme to obtain dextrorphan glucuronide (DR-G). A direct injection liquid chromatography-mass spectrometry (LC-MS) method was used to monitor products using the pseudo-first-order (PFO) model. Standard enzymatic incubations were also quantified using LC-MS. These data were fit utilizing both PFO and Michaelis-Menten (MM) models to determine estimates of kinetic parameters. The CLint was determined to be 0.28 (± 0.08) µL/min/mg protein for a baculovirus insect cell-expressed UGT2B7 enzyme. This is the first confirmation that dextrorphan …
An Isomorphism Theorem For Graphs, Laura Culp
An Isomorphism Theorem For Graphs, Laura Culp
Theses and Dissertations
In the 1970’s, L. Lovász proved that two graphs G and H are isomorphic if and only if for every graph X , the number of homomorphisms from X → G equals the number of homomorphisms from X → H . He used this result to deduce cancellation properties of the direct product of graphs. We develop a result analogous to Lovász’s theorem, but in the class of graphs without loops and with weak homomorphisms. We apply it prove a general cancellation property for the strong product of graphs.
Preparation And Characterization Of Stable Macroporous Titania Nano-Wells, Hema Santhi Aluri
Preparation And Characterization Of Stable Macroporous Titania Nano-Wells, Hema Santhi Aluri
Theses and Dissertations
Silica based sol-gel thin films have been extensively studied because of their advantages that include optical transparency, high biodegradability and low intrinsic fluorescence. However, one concern with silica based sol-gel derived materials is their long term stability in aqueous solutions. Another concern is their limited porosity. These two concerns limit the application of these materials in catalysis and separations. The main objective of this study is to prepare porous, thin films using titanium alkoxides as precursors and evaluate their long term stability in aqueous solutions. Colloidal crystal templating will be used to introduce macrosized pores into the titania network. The …
Nonlinear Models In Multivariate Population Bioequivalence Testing, Bassam Dahman
Nonlinear Models In Multivariate Population Bioequivalence Testing, Bassam Dahman
Theses and Dissertations
In this dissertation a methodology is proposed for simultaneously evaluating the population bioequivalence (PBE) of a generic drug to a pre-licensed drug, or the bioequivalence of two formulations of a drug using multiple correlated pharmacokinetic metrics. The univariate criterion that is accepted by the food and drug administration (FDA) for testing population bioequivalence is generalized. Very few approaches for testing multivariate extensions of PBE have appeared in the literature. One method uses the trace of the covariance matrix as a measure of total variability, and another uses a pooled variance instead of the reference variance. The former ignores the correlation …
Joint Mixed-Effects Models For Longitudinal Data Analysis: An Application For The Metabolic Syndrome, John Thorp Iii
Joint Mixed-Effects Models For Longitudinal Data Analysis: An Application For The Metabolic Syndrome, John Thorp Iii
Theses and Dissertations
Mixed-effects models are commonly used to model longitudinal data as they can appropriately account for within and between subject sources of variability. Univariate mixed effect modeling strategies are well developed for a single outcome (response) variable that may be continuous (e.g. Gaussian) or categorical (e.g. binary, Poisson) in nature. Only recently have extensions been discussed for jointly modeling multiple outcome variables measures longitudinally. Many diseases processes are a function of several factors that are correlated. For example, the metabolic syndrome, a constellation of cardiovascular risk factors associated with an increased risk of cardiovascular disease and type 2 diabetes, is often …
Deriving Optimal Composite Scores: Relating Observational/Longitudinal Data With A Primary Endpoint, Rhonda Ellis
Deriving Optimal Composite Scores: Relating Observational/Longitudinal Data With A Primary Endpoint, Rhonda Ellis
Theses and Dissertations
In numerous clinical/experimental studies, multiple endpoints are measured on each subject. It is often not clear which of these endpoints should be designated as of primary importance. The desirability function approach is a way of combining multiple responses into a single unitless composite score. The response variables may include multiple types of data: binary, ordinal, count, interval data. Each response variable is transformed to a 0 to1 unitless scale with zero representing a completely undesirable response and one representing the ideal value. In desirability function methodology, weights on individual components can be incorporated to allow different levels of importance to …
An Examination Of The Decision Analysis Approach To R&D Portfolios, Kelly Duncan
An Examination Of The Decision Analysis Approach To R&D Portfolios, Kelly Duncan
Theses and Dissertations
A portfolio can be defined as “a purposeful combination of items” (Chien and Sainfort 1998). As the topic relates to research and development (R&D) the items in question are technologies, projects or products under consideration for inclusion in a given portfolio. As described by surveys from Cooper et al (1998), companies have widely varying practices for portfolio selection. This thesis examines existing literature to determine the key characteristics of good portfolio and portfolio method. The approach needs to handle multiple objectives, account for project interactions, and address the social aspect of decision making. The resulting portfolio should be aligned with …
A Graphical Analysis Of Simultaneously Choosing The Bandwidth And Mixing Parameter For Semiparametric Regression Techniques, Derick L. Rivers
A Graphical Analysis Of Simultaneously Choosing The Bandwidth And Mixing Parameter For Semiparametric Regression Techniques, Derick L. Rivers
Theses and Dissertations
There has been extensive research done in the area of Semiparametric Regression. These techniques deliver substantial improvements over previously developed methods, such as Ordinary Least Squares and Kernel Regression. Two of these hybrid techniques: Model Robust Regression 1 (MRR1) and Model Robust Regression 2 (MRR2) require the choice of an appropriate bandwidth for smoothing and a mixing parameter that allows a portion of a nonparametric fit to be used in fitting a model that may be misspecifed by other regression methods. The current method of choosing the bandwidth and mixing parameter does not guarantee the optimal choices in either case. …
A Sequential Algorithm To Identify The Mixing Endpoints In Liquids In Pharmaceutical Applications, Akriti Saxena
A Sequential Algorithm To Identify The Mixing Endpoints In Liquids In Pharmaceutical Applications, Akriti Saxena
Theses and Dissertations
The objective of this thesis is to develop a sequential algorithm to determine accurately and quickly, at which point in time a product is well mixed or reaches a steady state plateau, in terms of the Refractive Index (RI). An algorithm using sequential non-linear model fitting and prediction is proposed. A simulation study representing typical scenarios in a liquid manufacturing process in pharmaceutical industries was performed to evaluate the proposed algorithm. The data simulated included autocorrelated normal errors and used the Gompertz model. A set of 27 different combinations of the parameters of the Gompertz function were considered. The results …
Factors Limiting Benthic Algal Abundance In Virginia Streams Of The Coastal Plain, Michael Brandt
Factors Limiting Benthic Algal Abundance In Virginia Streams Of The Coastal Plain, Michael Brandt
Theses and Dissertations
Algae are important components of stream food webs and often used in biomonitoring assessments. Little is known regarding the factors that limit their abundance in streams of the VA Coastal Plain. The surficial geology of the Coastal Plain is predominately sandy deposits which comprise the dominant substrate in streams of this region. In a comparative study of five streams located near the VCU Rice Center, we quantified substrate composition, light availability, and nutrient concentrations to assess their relative importance in determining benthic algal abundance. The proportion of stream area comprised of hard substrates was a significant predictor of variation in …
Modeling The Problem Of Assigning Virginia’S Localities To Dcr’S Regional Offices, Sudharshana Srinivasan
Modeling The Problem Of Assigning Virginia’S Localities To Dcr’S Regional Offices, Sudharshana Srinivasan
Theses and Dissertations
Virginia’s Department of Conservation and Recreation (DCR) assigns all of Virginia localities to Regional Offices to help conserve the natural resources in a certain region. In this paper, we present a mathematical model for optimizing such assignments by minimizing the travel time and cost of these assignments. With the growing increase in fuel costs and tighter budgets, our solution finds alternate assignments that will help cut costs by 14% annually. We have used integer programming techniques to find optimal assignments which satisfy requirements, respect limitations and minimize cost. Several plans are suggested, some keeping soil and water conservation districts together …
Comparing Bootstrap And Jackknife Variance Estimation Methods For Area Under The Roc Curve Using One-Stage Cluster Survey Data, Allison Dunning
Comparing Bootstrap And Jackknife Variance Estimation Methods For Area Under The Roc Curve Using One-Stage Cluster Survey Data, Allison Dunning
Theses and Dissertations
The purpose of this research is to examine the bootstrap and jackknife as methods for estimating the variance of the AUC from a study using a complex sampling design and to determine which characteristics of the sampling design effects this estimation. Data from a one-stage cluster sampling design of 10 clusters was examined. Factors included three true AUCs (.60, .75, and .90), three prevalence levels (50/50, 70/30, 90/10) (non-disease/disease), and finally three number of clusters sampled (2, 5, or 7). A simulated sample was constructed for each of the 27 combinations of AUC, prevalence and number of clusters. Estimates of …
Video Scene Detection Using Closed Caption Text, Gregory Smith
Video Scene Detection Using Closed Caption Text, Gregory Smith
Theses and Dissertations
Issues in Automatic Video Biography Editing are similar to those in Video Scene Detection and Topic Detection and Tracking (TDT). The techniques of Video Scene Detection and TDT can be applied to interviews to reduce the time necessary to edit a video biography. The system has attacked the problems of extraction of video text, story segmentation, and correlation. This thesis project was divided into three parts: extraction, scene detection, and correlation. The project successfully detected scene breaks in series television episodes and displayed scenes that had similar content.
Development And Investigation Of Intensity-Modulated Radiation Therapy Treatment Planning For Four-Dimensional Anatomy, Yelin Suh
Theses and Dissertations
Lung cancer is the leading cause of cancer-related deaths worldwide. Radiotherapy is one of the main treatment modalities of lung cancer. However, the achievable accuracy of radiotherapy treatment is limited for lung-based tumors due to respiratory motion. Four-dimensional radiotherapy explicitly accounts for anatomic motion by characterizing the motion, creating a treatment plan that accounts for this motion, and delivering this plan to the moving anatomy. This thesis focuses on the current problems and solutions throughout the course of four-dimensional radiotherapy. For characterization of respiratory-induced motion, patient tumor motion data were analyzed. It is shown that tumor motion can be significant …
Cancellation Properties Of Direct Products Of Digraphs, Katherine Toman
Cancellation Properties Of Direct Products Of Digraphs, Katherine Toman
Theses and Dissertations
This paper discusses the direct product cancellation of digraphs. We define the exact conditions on G such that GxK=HxK implies G=H. We focus first on simple equations such as GxK_2=HxK_2 where K_2 denotes a single arc and then extend this to the more general situation, GxK = HxK. Our results are achieved by using a “factorial” operation on graphs, which is in some sense analogous to the factorial of an integer.
Density Functional Investigations Of Pure And Ligated Clusters, Kristen Casalenuovo
Density Functional Investigations Of Pure And Ligated Clusters, Kristen Casalenuovo
Theses and Dissertations
Atomic clusters are attractive candidates for building motifs for new nano-assembled materials with desirable properties. At this nano-regime of matter, the size, shape, and composition of clusters changes their electronic structure and hence their properties. Computational modeling must work hand in hand with experiment to provide robust descriptions of the geometries and energetics of atomic clusters and how they might behave in a nano-assembled material. To this end, we have investigated three distinct species as model systems: antimony oxides SbxOy (x = 1, 2; y = 0 - 3), metal ion-solvent complexes Mm(NH3)n (M = Bi, Pb; m = 1 …
Shrinking The Janzen-Connell Doughnut: Consequences Of An Invasive Multiplier (Microstegium Vimineum) On The Mid-Canopy In A Mixed Pine-Oak Forest, Rebekha Shaw
Theses and Dissertations
Introduction of invasive species can alter seed fate predictions made by the Janzen-Connell Escape Hypothesis (JCEH). The JCEH states that there is a suitable region around a plant that is ideal for seed germination, growth, and recruitment. Seeds dispersed too close to the maternal plant are subject to competition from the maternal individual and perhaps density-dependent predation, whereas seeds dispersed further away may end up in suboptimal habitats. Invasive species may change the amount of these suitable habitats for native plants by creating unsuitable light environments and as a result, may influence the size of the ideal recruitment zone surrounding …
Haar Measures For Groupoids, Benjamin Grannan
Haar Measures For Groupoids, Benjamin Grannan
Theses and Dissertations
The definition of a groupoid is presented as well as examples of common structures from which a groupoid can be formed. Haar measure existence and uniqueness theorems for topological groups are used for the construction of Haar systems on groupoids. Some Haar systems are presented in addition to an example of a groupoid which admits no Haar system.
Ordinal Indexing Of The Class Of Strictly Singular Operators, Craig Stevenson
Ordinal Indexing Of The Class Of Strictly Singular Operators, Craig Stevenson
Theses and Dissertations
The Schreier families are a collection of finite subsets of N and have been used to provide refinements of the following Banach space notions: unconditional basic sequences, convergent sequences, spreading model and strictly singular operators to name a few. We use the Schreier families to study subclasses of strictly singular operators on Banach spaces. We also provide a sufficient condition on the strictly singular operators implying every operator falls into one of these subclasses.
An Agent Based Gene Flow Model, Erich Foster
An Agent Based Gene Flow Model, Erich Foster
Theses and Dissertations
The understanding of gene movement in plant species is critical to the management of both plant and animal species reliant on that plant. Pollen is the mechanism by which plants pass their genetic material from one generation to the next. Pollen dispersal studies have focused primarily on purely random diffusion processes, while this may be a good assumption for species pollinated mainly by abiotic means, such as wind, it is most likely an over simplification for species that are pollinated by biotic means, such as insects [3]. Correlated random walk (CRW) models are a model of animal movement [10] and …
Spectroscopic Characterizations Of The Compound Ii Intermediate Of Soybean Peroxidase From Soybean Seed Coatings, Andoh-Baidoo Rosemarie Agyepong
Spectroscopic Characterizations Of The Compound Ii Intermediate Of Soybean Peroxidase From Soybean Seed Coatings, Andoh-Baidoo Rosemarie Agyepong
Theses and Dissertations
Spectroscopic characterization of ferric soybean peroxidase with peroxides were studied to determine the ligand coordination and to characterize the structure of the heme active site and its intermediates (ferryl species). The lifetime, chemical reactivity and distinctive colors of the ferryl species (FeIV) formed during the oxidation of peroxidase (FeIII) by peroxides enabled structure, dynamics and reaction mechanisms to be studied. Resonance Raman spectroscopy was used as a means of characterizing the structure of the soybean peroxidase and its intermediates. Excitation in the Soret absorption band at 406.7nm with 2-5mW laser power was used for this study. Resonance Raman spectra in …
Probability Elicitation Methods For Avoiding Biases: An Exposition, Bethany Mihajlovits
Probability Elicitation Methods For Avoiding Biases: An Exposition, Bethany Mihajlovits
Theses and Dissertations
A large portion of decision analysis lies in a decision maker’s uncertainty about an outcome and what they perceive is the chance (probability) of that outcome occurring (in other words, an individual’s “degree of belief” that an outcome will occur). However, thinking probabilistically can be difficult and we rely on “rather primitive cognitive techniques to make” such assessments (these techniques are termed heuristics) (Clemen & Reilly, 2001 p.311). Heuristics are simple and intuitive but tend to result in probabilities that are biased. This thesis will connect the literature available from both the psychology behind the biases and the mathematical problems …
Habitat Suitability Criteria For Fishes Of The South Fork Of The Shenandoah River And An Investigation Into Observer Effects Associated With Two Techniques Of Direct Underwater Observation, Robert Clayton Ramey
Habitat Suitability Criteria For Fishes Of The South Fork Of The Shenandoah River And An Investigation Into Observer Effects Associated With Two Techniques Of Direct Underwater Observation, Robert Clayton Ramey
Theses and Dissertations
This study constructed habitat suitability criteria for fishes of the South Fork of the Shenandoah River, in Virginia. The criteria will be used in an IFIM study to produce estimates of the discharge required by fishes in the South Fork. Chi-square tests were used to evaluate whether criteria described habitat use to a statistically significant degree. Secondly, chi-square tests were used to test transferability. The criteria described the habitat use of seven taxa commonly found in the South Fork to a statistically significant degree. Habitat criteria for two taxa did not describe their habitat use to a statistically significant degree. …
A Mathematical Model For Anti-Malarial Drug Resistance, Amanda Matthews
A Mathematical Model For Anti-Malarial Drug Resistance, Amanda Matthews
Theses and Dissertations
Despite the array of medical advances of our modern day society, infectious diseases still plague millions of people worldwide. Malaria, in particular, causes substantial suffering and death throughout both developed and developing countries. Aside from the socioeconomic challenges presented by the disease's prevalence in impoverished nations, one of the major difficulties scientists have encountered while attempting to eradicate the disease is the parasite's ability to become resistant to new drugs and methods of treatment. In an effort to better understand the dynamics of malaria, we analyze a mathematical model that accounts for both the treatment aspect as well as the …
An Environmental And Economic Assessment Of Future Municipal Solid Waste Disposal: A Case Study Of Select High Growth Regions Of Virginia., Joseph Krouse
Theses and Dissertations
This research analyzed environmental and economic factors associated with municipal solid waste (MSW) management of select high growth Planning District Commissions (PDCs) of Virginia. Current MSW management scenarios were compared to future hypothetical scenarios utilizing a regional landfill or waste-to-energy (WTE) combustion facility. Life-cycle inventory and full cost accounting methods of the Municipal Solid Waste Decision Support Tool, developed by the Environmental Protection Agency (EPA), were utilized to estimate annualized environmental emissions and economic costs. Model results and analysis indicate that a regional landfill would be the least cost intensive MSW management strategy in comparison to current management methods; however …
Hyperspectral Reflectance For Rapid Viability Assessment Of Bacillus Endospores, Jarrod Edwards
Hyperspectral Reflectance For Rapid Viability Assessment Of Bacillus Endospores, Jarrod Edwards
Theses and Dissertations
A study was conducted to optically determine the viability of the Gram +, endospore-forming bacterial genera Bacillus using a hyperspectral reflectance spectrometer. Endospores are a dormant, differentiated cellular capsule form taken by select bacteria to ensure survival when environmental conditions become unfavorable. Two species of Bacillus were used for this study, Bacillus megaterium and Bacillus subtilis. These endospores were killed using a chemical treatment of sodium hypochlorite or a physical treatment of heat and pressure in an autoclave. The treated samples along with viable samples were lyophilized to form a powder. A reflectance spectrometer measuring 350 nm to 2500 nm …
Band Bending In Gan, Michael Foussekis
Band Bending In Gan, Michael Foussekis
Theses and Dissertations
Steady-state and transient surface photovoltages in undoped GaN are studied in various environments (air, nitrogen, oxygen, vacuum) at room temperature and 400 K with a Kelvin probe attached to an optical cryostat. The results are explained within a phenomenological model accounting for the accumulation of photo-generated holes at the surface, capture of free electrons from the bulk over the near-surface potential barrier, and emission of electrons from surface states into the bulk. Mechanisms of surface photovoltage are discussed in detail. Photoadsorption and photodesorption of negatively charged species will either increase or decrease the surface potential and thus band bending. Oxygen …
Elemental Composition And Nutrient Effect On The Uptake And Metabolism Of Dissolved Organic Carbon By Bacteria From A Temperate Region River, Anne Stuart
Theses and Dissertations
Rivers are arteries that connect land and sea, and provide a conduit and reactor for allochthonous and autochthonous organic carbon sources (OC) delivered to the coastal ocean. In comparison to marine waters, inland waters quantitatively represent only a fraction of the marine system; however, their importance to global C cycling maybe disproportional to its actual size. Inland systems are subject to multiple sources of OC (autochthonous and allochthonous) that vary individually in space and time with respect to their concentration and potential bacterial bioavailability. This study investigates the impact of high and ambient inorganic nutrient concentrations on the bacterial bioavailability …
The Responses Of Blue Crabs (Callinectes Sapidus) To Hypoxia/Hypercapnia In Freshwater, James Martin
The Responses Of Blue Crabs (Callinectes Sapidus) To Hypoxia/Hypercapnia In Freshwater, James Martin
Theses and Dissertations
The present research examined respiratory responses of blue crabs to long term (4, 13, and 21 days) hypercapnic hypoxia in freshwater at 23 C. Hypoxic conditions (50-60 & 75-85 mmHg O2) were induced by allowing the crabs to consume their oxygen supply, resulting in a hypercapnic induced decrease in pH that remained through the exposure. Postbranchial hemolymph responses to hypoxia/hypercapnia in freshwater demonstrate decreases in PO2, increases in PCO2, and decreases in pH. Lactate levels decreased over time, but hemocyanin concentration was highly variable with no trends. PH, lactate, and hemocyanin observations also demonstrated high variability and a variety of …
Role Of Bcl-2 Family Members To Promote Glucocorticoid –Induced Apoptosis By Mek Inhibitors In Leukemic Cells, Anila Rambal
Role Of Bcl-2 Family Members To Promote Glucocorticoid –Induced Apoptosis By Mek Inhibitors In Leukemic Cells, Anila Rambal
Theses and Dissertations
Glucocorticoids (GC) are common components of many chemotherapeutic regimens for lymphoid malignancies. GC-induced apoptosis involves an intrinsic BCL-2 family-regulated pathway. It has been shown that BIM (BCL-2 interacting mediator of cell death), a BH3-only pro-apoptotic protein, is up-regulated by dexamethasone (Dex) treatment in acute lymphoblastic leukemia (ALL) cells. Furthermore, BIM is inactivated by extracellular signal-regulated kinase (ERK)-mediated phosphorylation. We therefore hypothesized co-treatment with Dex and MEK/ERK inhibitors would promote apoptosis in ALL cells through BIM up-regulation and activation. We show here that a MEK inhibitor, PD184352 synergistically enhances Dex lethality in CCRF-CEM (T-ALL) cells. Co-treatment with Dex and PD184352 results …