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Articles 1 - 28 of 28
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A Time-Efficient Method For Accurate T1 Mapping Of The Human Brain, Yung-Yeh Chang
A Time-Efficient Method For Accurate T1 Mapping Of The Human Brain, Yung-Yeh Chang
Theses and Dissertations
The signal resulting from the IR-FSE sequence has been thoroughly analyzed in order to improve the accuracy of quantitative T1 mapping of the human brain. Several optimized post-processing algorithms have been studied and compared in terms of their T1 mapping accuracy. The modified multipoint two-parameter fitting method was found to produce less underestimation compared to the traditional multipoint three-parameter fitting method, and therefore, to result in a smaller T1 estimation error. Two correction methods were proposed to reduce the underestimation problem which is commonly seen in IR-FSE sequences used for measuring T1, especially when a large turbo factor is used. …
Investigation Of Biomolecular Interactions For Development Of Sensors And Diagnostics, Xiaojuan Zhang
Investigation Of Biomolecular Interactions For Development Of Sensors And Diagnostics, Xiaojuan Zhang
Theses and Dissertations
The highly specific recognition processes between biomolecules mediate various crucial biological processes. Uncovering the molecular basis of these interactions is of great fundamental and applied importance. This research work focuses on understanding the interactions of several biomolecular recognition systems and processes that can provide fundamental information to aid in the rational design of sensing and molecular recognition tools. Initially, a reliable and versatile platform was developed to investigate biomolecular interactions at a molecular level. This involved several techniques, including biomolecule functionalization to enable attachment to self-assembled monolayers as well as atomic force microscopy (AFM) based force spectroscopy to uncover the …
Tissue Engineering An Acellular Bioresorbable Vascular Graft To Promote Regeneration, Patricia Wolfe
Tissue Engineering An Acellular Bioresorbable Vascular Graft To Promote Regeneration, Patricia Wolfe
Theses and Dissertations
Tissue engineering is an interdisciplinary field that aims to restore, maintain, or improve diseased or damaged tissues. Electrospinning has become one of the most popular means to fabricate a scaffold for various tissue engineering applications as the process is extremely versatile and inexpensive. The ability for electrospinning to consistently create nanofibrous structures capable of mimicking the native extracellular matrix (ECM) is the basis behind why this technique is so successful in tissue engineering. Cardiovascular disease has been the leading cause of death in the United States for over 100 years, and because of this, the need for coronary artery replacements …
Investigations On The Corrosion Resistance Of Metallic Bipolar Plates (Bpp) In Proton Exchange Membrane Fuel Cells (Pemfc) - Understanding Of The Effects Of Material, Coating And Manufacturing, Ender Dur
Theses and Dissertations
Polymer Electrolyte Membrane Fuel Cell (PEMFC) systems are promising technology for contributing to meet the deficiency of world`s clean and sustainable energy requirements in the near future. Metallic bipolar plate (BPP) as one of the most significant components of PEMFC device accounts for the largest part of the fuel cell`s stack. Corrosion for metallic bipolar plates is a critical issue, which influences the performance and durability of PEMFC. Corrosion causes adverse impacts on the PEMFC`s performance jeopardizing commercialization. This research is aimed at determining the corrosion resistance of metallic BPPs, particularly stainless steels, used in PEMFC from different aspects. Material …
Synthesis Of Crosslinked Polyurethane And Network Constrained Surface Phase Separation, Chenyu Wang Jr.
Synthesis Of Crosslinked Polyurethane And Network Constrained Surface Phase Separation, Chenyu Wang Jr.
Theses and Dissertations
To create functional surfaces for soft materials, such as polyurethanes, our approach is to use a semifluorinated surface modifier as minor component to the matrix material. The surface modifier, driving by reduction in surface energy, surface-concentrates to form a functionalized surface layer at the air-polymer interface. In our previous studies, linear PTMO-based polyurethanes were used as the matrix material. These systems undergo slow surface phase separation at room temperature due to the thermodynamically immiscibility of the soft blocks. In this study, chemically crosslinked matrix was developed to provides a steric hindrance to constrain the mobility of surface modifier and to …
Simulation, Measurement And Image Analysis Of Corrosion Initiation And Growth Rate For Aluminum 2024 And Steel 304, Yan Fang
Theses and Dissertations
Abstract SIMULATION, MEASUREMENT AND IMAGE ANALYSIS OF CORROSION INITIATION AND GROWTH RATE OF ALUMIUM 2024 AND STEEL 304 By Yan Fang, MS A thesis submitted in partial fulfillment of the requirements for the degree of M.S. of Mechanical and Nuclear Engineering at Virginia Commonwealth University. Virginia Commonwealth University, 2011 Major Director: Dr. Brian Hinderliter, Ph. D Associate professor, Mechanical and Nuclear Engineering Time: 11 a.m. Place: Room E3210 Engineering East Hall Date: Friday August 12, 2011 Corrosion initiation and growth rate are important properties in maintaining structural integrity, especially for surface and pit corrosion of common infrastructure and transportation metals. …
Electrospun Polymer-Fiber Solar Cell, Shinobu Nagata
Electrospun Polymer-Fiber Solar Cell, Shinobu Nagata
Theses and Dissertations
A study of fabricating the first electrospun polymer-fiber solar cell with MEHPPV is presented. Motivation for the work and a brief history of solar cell is given. Limiting factors to improvement of polymer solar cell efficiency are illustrated. Electrospinning is introduced as a technique that may increase polymer solar cell efficiency, and a list of advantages in the technique applied to solar cell is discussed. Results of electrospun polymer-fiber solar cell, absorption, and its device parameter diagnosis through an equivalent circuit analysis are presented.
Performance Comparison Of Layered Composite Bimodal Fiber Mats With Unimodal Fiber Mats, Sukhada Sanjay Kulkarni
Performance Comparison Of Layered Composite Bimodal Fiber Mats With Unimodal Fiber Mats, Sukhada Sanjay Kulkarni
Theses and Dissertations
The study was conducted to evaluate and compare performance of unimodal and bimodal mats with approximately same mass. 10% and 18% Nylon 4, 6 polymer solution were used for electrospinning the fibers. A negative ion source was used to neutralize the surface charge. The fiber diameters were measured with SEM and were <500 nm thus incorporating the slip effect. Bimodal mats were prepared from different deposition modes. Optimal mode was selected on analyzing the performance factors. The bimodal mats were then compared with unimodal mats. For their performance the fiber mass for these mats was approximately the same. It was observed that the unimodal mats had higher efficiencies and higher pressure drop giving a lower FOM. Bimodal mats showed lower efficiencies and pressure drop compared to unimodal mats. However, the FOM for bimodal mats was approximately 200% higher than unimodal mats
Development Of A Multiple Vehicle Collaborative Unmanned Aerial System, Lloyd B. Mize Iv
Development Of A Multiple Vehicle Collaborative Unmanned Aerial System, Lloyd B. Mize Iv
Theses and Dissertations
The purpose of this research was to design a multiple UAV system with collaborative operation. This project is built on work that has been done in the field of Unmanned Systems at VCU and is aimed at providing a starting point for research into collaborative control of multiple UAVs. The current GCS software was extended to include multiple vehicles per single controller via a new communication protocol. Many changes were made to the user interface to facilitate controlling multiple vehicles with a single operator. A second processor, called an MCS, was added to each vehicle to allow for greater flexibility …
Silk Fibroin-Based Scaffolds For Tissue Engineering Applications, Jennifer Mccool
Silk Fibroin-Based Scaffolds For Tissue Engineering Applications, Jennifer Mccool
Theses and Dissertations
This study focused on the comparison of the electrospun silk scaffolds to the electrospun silk fibroin gel scaffolds. Moreover, this study examined the differences in cross-linking effects of genipin and methanol as well as solvents on the mechanical properties and cell compatibility of the scaffolds. Silk scaffolds were electrospun from an aqueous solution or 1,1,1,3,3-hexafluoro-2-propanol (HFIP) without genipin, immediately after 8 % (wt) genipin was added to the solution, and 18 hours after genipin blended with the solution. Uniaxial tensile testing determined that the silk scaffolds electrospun from water exhibit a higher modulus and peak stress than that of the …
Theoretical And Experimental Studies Of Noise Limited Phenomena In Nanowires, Pratik Agnihotri
Theoretical And Experimental Studies Of Noise Limited Phenomena In Nanowires, Pratik Agnihotri
Theses and Dissertations
Electronic noise is an area of fundamental importance that reveals information about the system that transport or optical measurements cannot. The present work focuses on recent advances made in the area of noise in nanodevices. This area is attracting increasing attention because noise in nanostructures is qualitatively and quantitatively different from that in bulk systems. Chapter 1 discusses different kinds of noise in nanostructures with a focus on 1/f noise. Monte-Carlo simulation is used to find velocity as a function of time to calculate velocity autocorrelation function and noise spectral density. The spectrum has 1/f^2 dependence which is universal irrespective …
Modeling Particle Filtration And Caking In Fibrous Filter Media, Seyed Alireza Hosseini
Modeling Particle Filtration And Caking In Fibrous Filter Media, Seyed Alireza Hosseini
Theses and Dissertations
This study is aimed at developing modeling methodologies for simulating the flow of air and aerosol particles through fibrous filter media made up of micro- or nano-fibers. The study also deals with modeling particle deposition (due to Brownian diffusion, interception, and inertial impaction) and particle cake formation, on or inside fibrous filters. By computing the air flow field and the trajectory of airborne particles in 3-D virtual geometries that resemble the internal microstructure of fibrous filter media, pressure drop and collection efficiency of micro- or nano-fiber filters are simulated and compared with the available experimental studies. It was demonstrated that …
Developing A Hybrid Model To Predict Student First Year Retention And Academic Success In Stem Disciplines Using Neural Networks, Ruba Alkhasawneh
Developing A Hybrid Model To Predict Student First Year Retention And Academic Success In Stem Disciplines Using Neural Networks, Ruba Alkhasawneh
Theses and Dissertations
Understanding the reasoning behind the low enrollment and retention rates of Underrepresented Minority (URM) students (African Americans, Hispanic Americans, and Native Americans) in the disciplines of science, technology, engineering, and mathematics (STEM) has concerned many researchers for decades. Numerous studies have used traditional statistical methods to identify factors that affect and predict student retention. Recently, researchers have relied on using data mining techniques for modeling student retention in higher education [1]. This research has used neural networks for performance modeling in order to obtain an adequate understanding of factors related to first year academic success and retention of URM at …
Optimization Of A Tri-Layered Vascular Graft: The Influence Of Cellular And Mechanical Properties, Michael Mcclure
Optimization Of A Tri-Layered Vascular Graft: The Influence Of Cellular And Mechanical Properties, Michael Mcclure
Theses and Dissertations
Electrospinning is a polymer processing technique which allows for the production of nano to micro size fibers and scaffolds which can be composed of numerous synthetic biodegradable materials and natural biopolymers. Natively, elastin and collagen are the main components of vascular tissue. Arranged in a tri-layered structure, they create a specific mechanical environment that can withstand the rigors of circulation. The goal of this study was to develop a mechanically ‘biomimicking’ vascular graft composed of three distinct layers through the process of electrospinning. We hypothesize that the use of bioactive agents such as elastin, collagen, and silk to supplement poly(caprolactone) …
Model-Guided Systems Metabolic Engineering Of Clostridium Thermocellum, Christopher Gowen
Model-Guided Systems Metabolic Engineering Of Clostridium Thermocellum, Christopher Gowen
Theses and Dissertations
Metabolic engineering of microorganisms for chemical production involves the coordination of regulatory, kinetic, and thermodynamic parameters within the context of the entire network, as well as the careful allocation of energetic and structural resources such as ATP, redox potential, and amino acids. The exponential progression of “omics” technologies over the past few decades has transformed our ability to understand these network interactions by generating enormous amounts of data about cell behavior. The great challenge of the new biological era is in processing, integrating, and rationally interpreting all of this information, leading to testable hypotheses. In silico metabolic reconstructions are versatile …
The Presentation And Perception Of Virtual Textures Through A Haptic Matrix Display Device, Patrick Headley
The Presentation And Perception Of Virtual Textures Through A Haptic Matrix Display Device, Patrick Headley
Theses and Dissertations
Dynamic, refreshable tactile displays offer a method of displaying graphical information to people who are blind or visually impaired. Texture, which is already used as an effective method to present graphical information in physical tactile diagrams, conceivably constitutes the best way to present graphics through a tactile display. This thesis presents the design of a new low-cost haptic matrix display device capable of displaying graphical information through virtual textures. The perception of virtual textures through the display is examined through three main experiments. The first two experiments examine the perception of square wave gratings through the device. The final experiment …
Development Of Physiologic Contact Models For Articular Surfaces, John Owen
Development Of Physiologic Contact Models For Articular Surfaces, John Owen
Theses and Dissertations
The superficial tangential zone (STZ) plays a significant role in normal articular cartilage’s ability to support loads and retain fluids. To date, tissue engineering efforts have not replicated normal STZ function in cartilage repairs. Finite element models were developed to examine the STZ’s role in normal and repaired articular surfaces under different contact conditions. Models were developed by incrementally adding improvements which culminated in contact loading of curved models by permeable and impermeable rigid surfaces and a normal cartilage layer. In the normal STZ, permeability was strain-dependent on volumetric strain; tension-compression nonlinearity modeled collagen behavior. Nonlinear geometry accounted for finite …
A Parallel Genetic Algorithm For Placement And Routing On Cloud Computing Platforms, Jacob A. Berlier
A Parallel Genetic Algorithm For Placement And Routing On Cloud Computing Platforms, Jacob A. Berlier
Theses and Dissertations
The design and implementation of today's most advanced VLSI circuits and multi-layer printed circuit boards would not be possible without automated design tools that assist with the placement of components and the routing of connections between these components. In this work, we investigate how placement and routing can be implemented and accelerated using cloud computing resources. A parallel genetic algorithm approach is used to optimize component placement and the routing order supplied to a Lee's algorithm maze router. A study of mutation rate, dominance rate, and population size is presented to suggest favorable parameter values for arbitrary-sized printed circuit board …
Vapor Transport And Aerosol Dynamics In The Respiratory Airways, Geng Tian
Vapor Transport And Aerosol Dynamics In The Respiratory Airways, Geng Tian
Theses and Dissertations
Predicting vapor transport and aerosol dynamics in the respiratory airways is important for analyzing both environmental exposure and respiratory drug delivery. A large number of analytical models, computational studies, and experiments on vapor and aerosol transport in the respiratory tract have been conducted previously. However, a number of critical questions remain unanswered. In this study, computational fluid dynamics (CFD) is primarily employed with frequent comparisons to existing and new experimental data sets to address previously unanswered issues related to the transport of vapors and aerosol in the respiratory tract. The three objectives of this study are further described below. Objective …
A Novel P300 Speller With Motor Imagery Embedded In A Traditional Oddball Paradigm., Vaishnavi Karnad
A Novel P300 Speller With Motor Imagery Embedded In A Traditional Oddball Paradigm., Vaishnavi Karnad
Theses and Dissertations
A Brain Computer Interface (BCI) provides a means, to control external devices, through the electrical activity of the brain, bypassing motor movement. Recent years have seen an increase in the application of P300 cognitive potential as a control and/or communication signal for the motor restoration in paralyzed patients, such as those in the later stages of ALS (Amyotrophic lateral sclerosis). Although many of these patients are in locked-in state i.e. where motor control is not possible, their cognition is known to remain intact. The P300 speller paradigm explored in this study relying on this cognition represented by the P300 peak …
Investigations On The Effect Of Manufacturing On The Contact Resistance Behavior Of Metallic Bipolar Plates For Polymer Electrolyte Membrane Fuel Cells, Cabir Turan
Theses and Dissertations
Polymer electrolyte membrane fuel cells (PEMFCs) have emerged as a strong and promising candidate to replace internal combustion engines (ICE) due their high efficiency, high power density and near-zero hazardous emissions. However, their commercialization waits for solutions to bring about significant cost-reductions and significant durability for given power densities. Bipolar plate (BPP) with its multi-faceted functions is one of the essential components of the PEMFC stacks. Stainless steel alloys are considered promising materials of choice for bipolar plate (BPP) applications in polymer electrolyte membrane fuel cells (PEMFC) due to their relatively low cost and commercial availability in thin sheets. Stainless …
Investigations On The Micro-Scale Surface Interactions At The Tool And Workpiece Interface In Micro-Manufacturing Of Bipolar Plates For Proton Exchange Membrane Fuel Cells, Mevlut Fatih Peker
Investigations On The Micro-Scale Surface Interactions At The Tool And Workpiece Interface In Micro-Manufacturing Of Bipolar Plates For Proton Exchange Membrane Fuel Cells, Mevlut Fatih Peker
Theses and Dissertations
Micro-forming studies have been more attractive in recent years because of miniaturization trend. One of the promising metal forming processes, micro-stamping, provides durability, strength, surface finish, and low cost for metal products. Hence, it is considered a prominent method for fabricating bipolar plates (BPP) with micro-channel arrays on large metallic surfaces to be used in Proton Exchange Membrane Fuel Cells (PEMFC). Major concerns in micro-stamping of high volume BPPs are surface interactions between micro-stamping dies and blank metal plates, and tribological changes. These concerns play a critical role in determining the surface quality, channel formation, and dimensional precision of bipolar …
Design And Implementation Of An Eye Blink Controlled Human Computer Interface, Poonam Gwalani
Design And Implementation Of An Eye Blink Controlled Human Computer Interface, Poonam Gwalani
Theses and Dissertations
Advances in Human Computer Interface (HCI) have made this area of research important for improving the standard of living for people with disabilities. An eye blink system is presented to allow people with disabilities to control a standard computer mouse. This system is designed for people who are paralytic with no control over their arms, speech, and anyone who is restricted to only the control of eye and head movements. This system is based on infrared reflectivity to capture and analyze real time eye blink signal of the user. It uses simple economical hardware electronics to emulate the functionality of …
The Program Pathing Trust Model For Critical System Process Authorization, Robert Dahlberg
The Program Pathing Trust Model For Critical System Process Authorization, Robert Dahlberg
Theses and Dissertations
Since computers are relied upon to run critical infrastructures – from nuclear power plants to electronic battlefield simulations – the concept of a “trusted” or tamperproof system has become even more important. Some applications have become so critical that it is imperative that they run as intended, without interference. The consequences of these systems not running as intended could be catastrophic. This research offers a solution for a key element for protecting these critical servers – validating process invocation sequences. The purpose of this research is to increase operating system security by detecting, validating, and enforcing process invocation sequences within …
3d Functional Modeling Of Dbs Efficacy And Development Of Analytical Tools To Explore Functional Stn, Deepak Kumbhare
3d Functional Modeling Of Dbs Efficacy And Development Of Analytical Tools To Explore Functional Stn, Deepak Kumbhare
Theses and Dissertations
Introduction: Exploring the brain for optimal locations for deep brain stimulation (DBS) therapy is a challenging task, which can be facilitated by analysis of DBS efficacy in a large number of patients with Parkinson’s disease (PD). The Unified Parkinson's Disease Rating Scale (UPDRS) scores indicate the DBS efficacy of the corresponding stimulation location in a particular patient. The spatial distribution of these clinical scores can be used to construct a functional model which closely models the expected efficacy of stimulation in the region. Designs and Methods: In this study, different interpolation techniques were investigated that can appropriately model the DBS …
Accelerating Finite State Projection Through General Purpose Graphics Processing, Thomas Trimeloni
Accelerating Finite State Projection Through General Purpose Graphics Processing, Thomas Trimeloni
Theses and Dissertations
The finite state projection algorithm provides modelers a new way of directly solving the chemical master equation. The algorithm utilizes the matrix exponential function, and so the algorithm’s performance suffers when it is applied to large problems. Other work has been done to reduce the size of the exponentiation through mathematical simplifications, but efficiently exponentiating a large matrix has not been explored. This work explores implementing the finite state projection algorithm on several different high-performance computing platforms as a means of efficiently calculating the matrix exponential function for large systems. This work finds that general purpose graphics processing can accelerate …
Characterization And Genetic Analysis Of The Cellulolytic Microorganism Thermobifida Fusca, Yu Deng
Characterization And Genetic Analysis Of The Cellulolytic Microorganism Thermobifida Fusca, Yu Deng
Theses and Dissertations
Currently, one of the hurdles hindering efficient production of cellulosic biofuel is the recalcitrant nature of cellulose to hydrolysis. A wide variety of cellulase enzymes are found natively in microorganisms that can potentially be used to effectively hydrolyze cellulose to fermentable sugars. Thermobifida fusca is a high G-C content, thermophilic, gram-positive soil actinobacterium with high cellulolytic activity. The phenomenological and mechanistic parameters affecting cellulase activity were studied in T. fusca and two mechanisms have been found: 1) transcriptions of cellulase-related genes were not closely associated with measured differences in cellulase activity and 2) cellular energetics (intracellular ATP) correlated more closely …
Development Of Novel Copolyoxetanes: Antimicrobial Agents, Allison King
Development Of Novel Copolyoxetanes: Antimicrobial Agents, Allison King
Theses and Dissertations
This thesis focuses on solution antimicrobial effectiveness for copolyoxetanes with quaternary ammonium and PEG-like side chains. Ring opening copolymerization of 3-((4-bromobutoxy)methyl)-3-methyloxetane (BBOx) and 3-((2-(2-methoxyethoxy) ethoxy) methyl)-3-methyloxetane (ME2Ox) yielded random copolymers with 14-100 (m) mole% BBOx designated P[(BBOx-m)(ME2Ox)]. Reaction of P[(BBOx-m)(ME2Ox)] with dodecyl dimethylamine gave the corresponding quaternary P[(C12-m)(ME2Ox)] polycation salts, designated C12-m. Mole ratios and molecular weights were obtained from 1H-NMR and end group analysis. Differential scanning calorimetry (DSC) studies showed Tg’s between 69 and -34 °C. Minimum inhibitory concentrations (MIC) against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa showed MIC decreasing with increasing C12 mole% reaching a minimum between …