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Articles 1 - 30 of 48
Full-Text Articles in Physical Sciences and Mathematics
Impact Of Post-Synthesis Modification Of Nanoporous Organic Frameworks On Selective Carbon Dioxide Capture, Timur İslamoğlu
Impact Of Post-Synthesis Modification Of Nanoporous Organic Frameworks On Selective Carbon Dioxide Capture, Timur İslamoğlu
Theses and Dissertations
Porous organic polymers containing nitrogen-rich building units are among the most promising materials for selective CO2 capture and separation applications that impact the environment and the quality of methane and hydrogen fuels. The work described herein describes post-synthesis modification of Nanoporous Organic Frameworks (NPOFs) and its impact on gas storage and selective CO2 capture. The synthesis of NPOF-4 was accomplished via a catalysed cyclotrimerization reaction of 1,3,5,7-tetrakis(4-acetylphenyl)adamantane in Ethanol/Xylenes mixture using SiCl4 as a catalyst. NPOF-4 is microporous and has high surface area (SABET = 1249 m2 g-1). Post-synthesis modification of NPOF-4 by nitration afforded (NPOF-4-NO2) and subsequent reduction resulted …
A Lexicographic Product Cancellation Property For Digraphs, Kendall Manion
A Lexicographic Product Cancellation Property For Digraphs, Kendall Manion
Theses and Dissertations
There are four prominent product graphs in graph theory: Cartesian, strong, direct, and lexicographic. Of these four product graphs, the lexicographic product graph is the least studied. Lexicographic products are not commutative but still have some interesting properties. This paper begins with basic definitions of graph theory, including the definition of a graph, that are needed to understand theorems and proofs that come later. The paper then discusses the lexicographic product of digraphs, denoted $G \circ H$, for some digraphs $G$ and $H$. The paper concludes by proving a cancellation property for the lexicographic product of digraphs $G$, $H$, $A$, …
Surreal Numbers, Joshua Hostetler
Surreal Numbers, Joshua Hostetler
Theses and Dissertations
The purpose of this thesis is to explore the Surreal Numbers from an elementary, con- structivist point of view, with the intention of introducing the numbers in a palatable way for a broad audience with minimal background in any specific mathematical field. Created from two recursive definitions, the Surreal Numbers form a class that contains a copy of the real numbers, transfinite ordinals, and infinitesimals, combinations of these, and in- finitely many numbers uniquely Surreal. Together with two binary operations, the surreal numbers form a field. The existence of the Surreal Numbers is proven, and the class is constructed from …
Tuning Parameter Selection In L1 Regularized Logistic Regression, Shujing Shi
Tuning Parameter Selection In L1 Regularized Logistic Regression, Shujing Shi
Theses and Dissertations
Variable selection is an important topic in regression analysis and is intended to select the best subset of predictors. Least absolute shrinkage and selection operator (Lasso) was introduced by Tibshirani in 1996. This method can serve as a tool for variable selection because it shrinks some coefficients to exact zero by a constraint on the sum of absolute values of regression coefficients. For logistic regression, Lasso modifies the traditional parameter estimation method, maximum log likelihood, by adding the L1 norm of the parameters to the negative log likelihood function, so it turns a maximization problem into a minimization one. To …
Acid-Base Catalysis In Proton-Coupled Electron Transfer Reactions (Pcet): The Effects Of Brönsted Bases On The Oxidation Of Glutathione And Hydroquinone, Ramos Jonnathan Medina
Acid-Base Catalysis In Proton-Coupled Electron Transfer Reactions (Pcet): The Effects Of Brönsted Bases On The Oxidation Of Glutathione And Hydroquinone, Ramos Jonnathan Medina
Theses and Dissertations
This thesis presents the results and discussion of the investigation of the effects of Brönsted bases on the kinetics and thermodynamics of two proton-coupled electron transfer processes: the mediated oxidation of glutathione and the electrochemical oxidation of hydroquinone. Proton-coupled electron transfer (PCET) is the name given to reactions that involve the transfer of electron(s) accompanied by the exchange of proton(s). PCETs are found in many chemical and biological processes, some of current technological relevance such as the oxygen reduction reaction in fuel cells, which involves the transfer of four electrons and four protons (4e-, 4H+); or the splitting of water …
The Effects Of River Sediment, Endosulfan, And Moderate Hypoxia On Blue Crabs (Callinectes Sapidus) From The Tidal, Freshwater James River, Laura Williams
The Effects Of River Sediment, Endosulfan, And Moderate Hypoxia On Blue Crabs (Callinectes Sapidus) From The Tidal, Freshwater James River, Laura Williams
Theses and Dissertations
Juvenile male blue crabs move into the tidal, freshwater James River during warmer months to feed and grow by undergoing molting. In crustaceans, growth and molting are hormonally controlled. The physiological effects of a multiple-stressor environment are determined by comparing the blue crab’s oxygen uptake after exposure to pure sand, James River sediment, or endosulfan-spiked sand. The effect of multiple stressors on molting is measured by the activity level of N-acetyl-ß-glucosaminidase (NAG), an enzyme in epidermal tissue important to molting. The oxygen uptake was decreased by exposure to James River sediment but not for exposure to endosulfan for seven days. …
Investigations Into Background Correction And Retention Time Alignment To Enhance Quantitative Chemometric Analysis Of Comprehensive Two-Dimensional Liquid Chromatography-Diode Array Detection Data, Robert Allen
Theses and Dissertations
The focus of the projects presented here was to develop possible solutions to three issues commonly encountered during chemometric analysis of comprehensive two-dimensional liquid chromatography diode array detector (LCxLC-DAD) data. The focus of the first project was to determine a means of performing background correction that removed two background ridges. The methods of simply subtracting out a mean blank sample, singular value decomposition based background correction (SVD-BC) and asymmetrically weighted least squares (AWLS) were compared. AWLS was found to be the only background correction technique to fully remove the ridges. However, AWLS was also found to attenuate the peak intensity …
Chemometric Analysis Of Comprehensive Two-Dimensional Liquid Chromatographic-Diode Array Detection Data: Peak Resolution, Quantification And Rapid Screening, Hope P. Bailey
Theses and Dissertations
This research project sought to explore, compare and develop chemometric methods with the goal of resolving chromatographically overlapped peaks though the use of spectral information gained from the four-way data sets associated with comprehensive two-dimensional liquid chromatography with diode array detection (LC ´ LC-DAD). A chemometric method combining iterative key set factor analysis (IKSFA) and multivariate curve resolution-alternating least squares (MCR-ALS) was developed. In the section of urine data analyzed, over 50 peaks were found, with 18 visually observable and 32 additional compounds found only after application of the chemometric method. Upon successful chemometric resolution of chromatographically overlapped peaks, accurate …
Using Macroinvertebrate Community Composition To Distinguish Between Natural And Anthropogenic Sedimentation, Amanda E. Schutt
Using Macroinvertebrate Community Composition To Distinguish Between Natural And Anthropogenic Sedimentation, Amanda E. Schutt
Theses and Dissertations
Excess fine sediment from human activity is a major pollutant to streams across the U.S.; however, distinguishing human-induced sedimentation from natural fine sediment is complex. The U.S. Environmental Protection Agency recently implemented a protocol for the quantitative field assessment of human-induced sedimentation using measurements of stream geomorphology. Macroinvertebrate community composition, streambed sediment stability, and sediment composition were studied at 49 sites in the James River watershed in central Virginia. Sediment composition was found to be a stronger driver of community composition than sediment stability. Although I was not able to show that macroinvertebrate metrics were related to sediment stability independently …
Mass Spectroscopic Identification And Quantification Of Protein Carbonyls, Zafer Ugur
Mass Spectroscopic Identification And Quantification Of Protein Carbonyls, Zafer Ugur
Theses and Dissertations
It is well established that free radical mediated oxidative stress plays a critical role in aging and age-related diseases. Among the post-translational protein modifications, carbonylation has attracted a great deal of attention due to its irreversible and irreparable nature. Despite the fact that protein carbonylation is associated with a series of physiological and pathological processes, there are still issues to be clarified such as why certain proteins are more vulnerable to modification, what are the locations of the protein modifications, and how does the nature of the oxidant affect the preferred site of modification. In this study, we will seek …
A Water Quality Investigation Of Kimages Creek, Michael Trop
A Water Quality Investigation Of Kimages Creek, Michael Trop
Theses and Dissertations
Analysis of continuous monitoring water quality data (temperature, specific conductivity, depth, pH, dissolved oxygen, and turbidity) at two locations in a tidal freshwater creek (Kimages Creek) characterized seasonal variation and responses to short-term events. Supplemental water quality measurements were collected to describe longitudinal variations in the creek. There were significant differences in water quality between the two continuous monitoring stations (one tidal and unforested, the other non-tidal and forested) over varying time scales. Rain events showed increases in turbidity, depth and dissolved oxygen, and reductions in temperature, conductivity, and pH at both stations. Tides influenced the water quality at the …
Parameter Tuning For Optimization Software, Radhashilpa Koripalli
Parameter Tuning For Optimization Software, Radhashilpa Koripalli
Theses and Dissertations
Mixed integer programming (MIP) problems are highly parameterized, and finding parameter settings that achieve high performance for specific types of MIP instances is challenging. This paper presents a method to find the information about how CPLEX solver parameter settings perform for the different classes of mixed integer linear programs by using designed experiments and statistical models. Fitting a model through design of experiments helps in finding the optimal region across all combinations of parameter settings. The study involves recognizing the best parameter settings that results in the best performance for a specific class of instances. Choosing good setting has a …
The Severity Of Stages Estimation During Hemorrhage Using Error Correcting Output Codes Method, Yurong Luo
The Severity Of Stages Estimation During Hemorrhage Using Error Correcting Output Codes Method, Yurong Luo
Theses and Dissertations
As a beneficial component with critical impact, computer-aided decision making systems have infiltrated many fields, such as economics, medicine, architecture and agriculture. The latent capabilities for facilitating human work propel high-speed development of such systems. Effective decisions provided by such systems greatly reduce the expense of labor, energy, budget, etc. The computer-aided decision making system for traumatic injuries is one type of such systems that supplies suggestive opinions when dealing with the injuries resulted from accidents, battle, or illness. The functions may involve judging the type of illness, allocating the wounded according to battle injuries, deciding the severity of symptoms …
Essential Spawning Habitat For Atlantic Sturgeon In The James River, Virginia., Geoffrey Austin
Essential Spawning Habitat For Atlantic Sturgeon In The James River, Virginia., Geoffrey Austin
Theses and Dissertations
Substrate composition plays a critical role in determining the spawning success of Atlantic sturgeon. A benthic analysis of the tidal freshwater portion of the James River, Virginia, was performed to locate and protect remaining sturgeon spawning habitat within the James River system. I modeled structural habitat, substrate distribution, and river bathymetry from Richmond, Virginia to the Appomattox River confluence. A classification model was developed to describe the dominant substrate type (mud/silt, sand, gravel, bedrock) using side scan sonar data collected from August 2011-Febuary 2012. River depth, bottom imagery, substrate density (hardness), and ground truth substrate samples were interpolated into a …
A Physiological Signal Processing System For Optimal Engagement And Attention Detection., Ashwin Belle
A Physiological Signal Processing System For Optimal Engagement And Attention Detection., Ashwin Belle
Theses and Dissertations
In today’s high paced, hi-tech and high stress environment, with extended work hours, long to-do lists and neglected personal health, sleep deprivation has become common in modern culture. Coupled with these factors is the inherent repetitious and tedious nature of certain occupations and daily routines, which all add up to an undesirable fluctuation in individuals’ cognitive attention and capacity. Given certain critical professions, a momentary or prolonged lapse in attention level can be catastrophic and sometimes deadly. This research proposes to develop a real-time monitoring system which uses fundamental physiological signals such as the Electrocardiograph (ECG), to analyze and predict …
Accurate Methodology For Monitoring Biomembrane Events, Christine A. Winschel
Accurate Methodology For Monitoring Biomembrane Events, Christine A. Winschel
Theses and Dissertations
Abstract ACCURATE METHODOLOGY FOR MONITORING BIOMEMBRANE EVENTS By Christine A. Winschel, Ph.D. A Dissertation submitted in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Chemistry at Virginia Commonwealth University. Virginia Commonwealth University, 2012 Major Director: Dr. Vladimir A. Sidorov ASSOCIATE PROFESSOR, DEPARTMENT OF CHEMISTRY This study describes the synthesis and characterization of a new receptor (cyclen 1) capable of strong selective binding of pyrene-based anionic dyes under near-physiological conditions. This receptor comprises four naphthylthiourea groups tethered to a cyclen core via an ester linkage. The most important finding was the ability of cyclen 1 to …
Development Of Nano-Scale Featured Materials For Electrode Modification And Solid Supports., Amy Rue
Development Of Nano-Scale Featured Materials For Electrode Modification And Solid Supports., Amy Rue
Theses and Dissertations
This work utilized the sol-gel process in two ways. First, macroporous silica thin films were developed using a combination of casting techniques and templating. Macroporsity was introduced to the silica thin films by either doping the silica sol before casting or by ordering the template on a substrate and then casting a sol over it. These techniques were first used to create silica thin films with long microchannel pores (200 nm x 60 µm) from a doped sol with the bacteria, B. Megaterium, as the template for nanomaterial formation. To enable the formation long microchannels, the flexible bacteria chains were …
A Comparison Of Methods Of Analysis To Control For Confounding In A Cohort Study Of A Dietary Intervention, Esinhart Hali
A Comparison Of Methods Of Analysis To Control For Confounding In A Cohort Study Of A Dietary Intervention, Esinhart Hali
Theses and Dissertations
Comparing samples from different populations can be biased by confounding. There are several statistical methods that can be used to control for confounding. These include; multiple linear regression, propensity score matching, propensity score/logit of propensity score as a single covariate in a linear regression model, stratified analysis using propensity score quintiles, weighted analysis using propensity scores or trimmed scores. The data were from two studies of a dietary intervention (FIBERR and RNP). The outcome variable was change from baseline to one month for eight outcome measures; fat, fiber, and fruits/ vegetables behavior, fat, fiber, and fruits/vegetables intentions, fat and fruits/vegetables …
The Effect Of Baseline Cluster Stratification On The Power Of Pre-Post Analysis, Fengjiao Hu
The Effect Of Baseline Cluster Stratification On The Power Of Pre-Post Analysis, Fengjiao Hu
Theses and Dissertations
The purpose of study is to check whether the power of detecting the effect of intervention versus control in a pre- and post-study can be increased by using a stratified randomized controlled design. A stratified randomized controlled design with two study arms and two time points, where strata are determined by clustering on baseline outcomes of the primary measure, is considered. A modified hierarchical clustering algorithm is developed which guarantees optimality as well as requiring each cluster to have at least one subject per study arm. The power is calculated based on simulated bivariate normal distributed primary measures with mixture …
Does Pair-Matching On Ordered Baseline Measures Increase Power: A Simulation Study, Yan Jin
Does Pair-Matching On Ordered Baseline Measures Increase Power: A Simulation Study, Yan Jin
Theses and Dissertations
It has been shown that pair-matching on an ordered baseline with normally distributed measures reduces the variance of the estimated treatment effect (Park and Johnson, 2006). The main objective of this study is to examine if pair-matching improves the power when the distribution is a mixture of two normal distributions. Multiple scenarios with a combination of different sample sizes and parameters are simulated. The power curves are provided for three cases, with and without matching, as follows: analysis of post-intervention data only, adding baseline as a covariate, and classic pre-post comparison. The study shows that the additional variance reduction provided …
Analysis Of The Fish Community On Tidal-Freshwater Constructed Reefs, Briana Langford
Analysis Of The Fish Community On Tidal-Freshwater Constructed Reefs, Briana Langford
Theses and Dissertations
Constructed reefs are used successfully in marine systems to enhance spawning habitat; this study examines the effectiveness of constructed reefs in a tidal-freshwater river. Fish abundance, species diversity and richness, residency, water column position, reproductive guilds, and feeding guilds were analyzed on two constructed reefs in the tidal-freshwater James River and compared to silted regions representing the primary substrate in the river. Reefs were sampled using hydroacoustics, electroshocking, gillnetting, trawling, and egg mats. The constructed reefs had a greater proportion of fish that broadcast spawn over hard substrate and a trend of more overall individual, residential, and demersal fish. The …
An Agent Based Model Of Tumor Growth And Response To Radiotherapy, Nicole O'Neil
An Agent Based Model Of Tumor Growth And Response To Radiotherapy, Nicole O'Neil
Theses and Dissertations
An agent based model was developed to examine the growth of a tumor in a healthy cell population. Response to radiation and impact of mutation and bystander effects were studied. In the growth model, the cancer cells proliferated outward becoming invasive. The mass of cancer cells developed a necrotic core. Various treatment protocols of radiation were compared. Timing of treatments was critical to the success of therapy. The event of mutation was rare. When mutation occurred, either unsuccessful treatment or re-growth could result. Multiple rounds of radiation potentially led to increased mutation. Low levels of the bystander effect had little …
Unbiased Estimation For The Contextual Effect Of Duration Of Adolescent Height Growth On Adulthood Obesity And Health Outcomes Via Hierarchical Linear And Nonlinear Models, Robert Carrico
Theses and Dissertations
This dissertation has multiple aims in studying hierarchical linear models in biomedical data analysis. In Chapter 1, the novel idea of studying the durations of adolescent growth spurts as a predictor of adulthood obesity is defined, established, and illustrated. The concept of contextual effects modeling is introduced in this first section as we study secular trend of adulthood obesity and how this trend is mitigated by the durations of individual adolescent growth spurts and the secular average length of adolescent growth spurts. It is found that individuals with longer periods of fast height growth in adolescence are more prone to …
Unconventional Superhalogens: Design And Applications, Devleena Samanta
Unconventional Superhalogens: Design And Applications, Devleena Samanta
Theses and Dissertations
Electron affinity is one of the most important parameters that guide chemical reactivity. Halogens have the highest electron affinities among all elements. A class of molecules called superhalogens has electron affinities even greater than that of Cl, the element with the largest electron affinity (3.62 eV). Traditionally, these are metal-halogen complexes which need one electron to close their electronic shell. Superhalogens have been known to chemistry for the past 30 years and all superhalogens investigated in this period are either based on the 8-electron rule or the 18-electron rule. In this work, we have studied two classes of unconventional superhalogens: …
An Agent Based Model To Study The Barrier Effect On An Urban Neighborhood, Cheri C. Doucette
An Agent Based Model To Study The Barrier Effect On An Urban Neighborhood, Cheri C. Doucette
Theses and Dissertations
This study asks the question: If we take a small neighborhood and introduce a barrier, how will the neighborhood change? Will it be better protected and flourish, or will it decay and die or perhaps will there be no change at all? What determines the outcome? This work tries to answer these questions by creating an Agent-Based Model (ABM) to test different scenarios and observe the results. Urban environments, both natural and built, are complex systems, containing a multitude of people, landscapes and buildings. Simple changes in street-lighting and sidewalks, the addition of trees and green scapes or the enforcement …
Population Based Model Of Gonorrhea And Interventions Against Increased Antibiotic Resistance, Courtney Henry
Population Based Model Of Gonorrhea And Interventions Against Increased Antibiotic Resistance, Courtney Henry
Theses and Dissertations
Gonnorrhea is an infectious sexually transmitted disease (STD) caused by the bacterium Neisseria gonorrhoeae that commonly reproduces in the reproductive tract.The Centers of Disease Control and Prevention (CDC) estimate that more than 700,000 individuals in the U.S. contract new gonorrheal infections per year. During recent years, there has been a progressive global increase of drug-resistant strains of gonorrhea. Therefore, there exists the necessity for health organizations to encourage the monitoring, research and development of innovative treatment regimens. We have developed multiple mathematical models to explore the gonorrheal disease state. The first objective of model formulation was to fit the model …
Photoluminescence From Bulk Gan Substrates, Marrwa Alrrshedan
Photoluminescence From Bulk Gan Substrates, Marrwa Alrrshedan
Theses and Dissertations
Photoluminescence (PL) has been studied from different types of bulk GaN samples grown by hydride vapor phase epitaxy technique at Kyma Technologies. Point defects in bulk and at the surface affect the electrical and optical properties of GaN and could be analyzed by PL. The surface of the samples was polished with different techniques: one is chemical mechanical polish (CMP) and another is mechanical polish (MP). PL data from MP and CMP surfaces show that PL intensity from the CMP-treated surface is much higher than that from the MP-treated surface. This can be explained by defects formed during the process …
Spatial Patterns Of Herbaceous And Woody Recruitment In A Recently Restored Mixed Tidal Regime Freshwater Wetland, James B. Deemy
Spatial Patterns Of Herbaceous And Woody Recruitment In A Recently Restored Mixed Tidal Regime Freshwater Wetland, James B. Deemy
Theses and Dissertations
Ecological restoration of a converted wetland was characterized within a recently drained impoundment along the James River in Charles City County, Virginia. Colonizing vegetation was assessed over three growing seasons in both tidal and non-tidal environments. Study objectives were to (1) examine geospatial relations of recruitment patterns among colonizing species over three growing seasons, (2) quantify species composition and potential differences between extant species cover and soil seed banks across restored and natural wetland habitats and (3) assess geospatial patterns to develop a GIS model of bald cypress (Taxodium distichum L.) recruitment. The two most common native colonizing species during …
Preferentially Orienting Ag Nanoparticles Using Caf2 Nanorods, Mathias Auer
Preferentially Orienting Ag Nanoparticles Using Caf2 Nanorods, Mathias Auer
Theses and Dissertations
A study was done to examine the effect of surface orientation as well as heterogeneous epitaxy at an interface between two materials with a large lattice mismatch. Silver nanoparticles of different diameters were grown in an effort to study methods of preferentially orienting the geometry of metal nanoparticles. Arrays of calcium fluoride nanorods were grown on silicon substrates using oblique angle thermal vapor deposition. The chamber operated at an ultra high vacuum pressure of 10^-10 Torr during the deposition of the rods and an oblique angle of 75° was kept between the silicon substrate normal and the direction of incident …
Towards An Incentive Compatible Framework Of Secure Cloud Computing, Yulong Zhang
Towards An Incentive Compatible Framework Of Secure Cloud Computing, Yulong Zhang
Theses and Dissertations
Cloud computing has changed how services are provided and supported through the computing infrastructure. It has the advantages such as flexibility , scalability , compatibility and availability . However, the current architecture design also brings in some troublesome problems, like the balance of cooperation benefits and privacy concerns between the cloud provider and the cloud users, and the balance of cooperation benefits and free-rider concerns between different cloud users. Theses two problems together form the incentive problem in cloud environment. The first conflict lies between the reliance of services and the concerns of secrets of cloud users. To solve it, …