900 Works

Improving Response Characteristics of Split Ring Resonators Using Experimental Designs

Omer Faruk Keskin
The purpose of this thesis is to investigate the application of design of experiments approaches in the analysis of split ring resonators, and to compare two different approaches. The design parameters of the meta-material device are examined to study all the main effects, the two factor interactions, and the curvature effects. A full factorial design and a central composite design is utilized for the study. The results in improving split ring resonator design are discussed....

Evaluation of 4h-Sic Photoconductive Switches for Pulsed Power Applications Based on Numerical Simulations

Rajintha Tiskumara
Since the early studies by Auston, photoconductive semiconductor switches (PCSSs) have been investigated intensively for many applications owing to their unique advantages over conventional gas and mechanical switches. These advantages include high speeds, fast rise times, optical isolation, compact geometry, and negligible jitter. Another important requirement is the ability to operate at high repetition rates with long device lifetimes (i.e., good reliability without degradation). Photoconductive semiconductor switches (PCSSs) are low-jitter compact alternatives to traditional gas...

Computational Modeling of Facial Response for Detecting Differential Traits in Autism Spectrum Disorders

Manar D. Samad
This dissertation proposes novel computational modeling and computer vision methods for the analysis and discovery of differential traits in subjects with Autism Spectrum Disorders (ASD) using video and three-dimensional (3D) images of face and facial expressions. ASD is a neurodevelopmental disorder that impairs an individual’s nonverbal communication skills. This work studies ASD from the pathophysiology of facial expressions which may manifest atypical responses in the face. State-of-the-art psychophysical studies mostly employ naive human raters to...

A Study of the Sensitivity of Energy Conversion Efficiency to Load Variation in Class-E Resonant Power Inverter

Richard Samuel Jennings
In this thesis the sensitivity of energy conversion efficiency (ECE) and output power of a class-E resonant inverter under variable resistive and inductive load assignments is examined for wireless power transfer (WPT) applications. By performing simulation and mathematical analysis, it was found that the on-resistance of the switching device has minor effect on the design’s efficiency. Additional comparisons between the simulation and mathematical analysis show reasonable output power and ECE load variation performance for the...

Investigation of Low Cost Substrate Approaches for III-V Solar Cells

Marlene Lydia Lichty
With the need for cleaner energy sources, which can displace fossil fuel, the solar cell industry is of particular interest due to the abundancy of the Sun. Silicon currently dominates terrestrial applications, but efficiency improvements have saturated. III-V based solar cells have reported the highest efficiencies, however, high costs due to substrates and fabrication processes have limited these devices to specialty applications, such as space. In order to reduce the cost associated with fabricating III-V...

Testing and Analysis of an Exergetically Efficient 4 K to 2 K Helium Heat Exchanger

Peter N. Knudsen
Modern experimental nuclear physics programs that utilize advanced superconducting devices require refrigeration below the lambda temperature of helium (2.1768 K) and involve sub-atmospheric helium at some point in the process. They typically operate between 1.8 and 2.1 K (16 to 40 mbar) and can require refrigeration ranging from tens to thousands of watts. These processes are very energy intensive, requiring roughly 850 W/W even for large and well-designed refrigerators, though they can easily require much...

Thermo-Mechanical System Identification of a Shape Memory Alloy Actuated Mechanism

Cody Alexander Wright
Shape memory alloy (SMA) actuators paired in an antagonistic arrangement can be used to produce mechanisms that replicate human biomechanics. To investigate this proposal, the biomechanical articulation of the elbow by means of the biceps brachii muscle is compared with that of a SMA actuated arm. This is accomplished by parametric analysis of a crank-slider kinematic mechanism actuated, first, with an experimentally characterized SMA wire and then an idealized musculotendon actuator based on actuation properties...

Abstracts of Papers, 80th Annual Meeting of the Virginia Academy of Science, May 22-24, 2002, Hampton University, Hampton, Virginia

Virginia Academy Of Science
Abstracts of papers that were presented at the 80th annual meeting of the Virginia Academy of Science.

Reproduction of the Black Drum, Pogonias cromis, from the Chesapeake Bay Region

Brian K. Wells & Cynthia M. Jones
Ovaries of black drum, Pogonias cromis, collected from the Chesapeake Bay region in 1992, were used to describe reproductive strategy and fecundity. Histological examination showed that black drum spawn in the Chesapeake Bay region from April through early June. Distributions of oocyte diameter showed distinct oocyte-developmental groups indicating that Chesapeake Bay black drum are group-synchronous batch spawners. Female black drum are extremely fecund ranging from 414,000 to 3,736,000 hydrated oocytes (mean = 1,389,000) per batch...

Alcohol and Substance Use Knowledge, Attitudes, Subjective Norms, Self-Efficacy, Perceived Behavioral Control, and Behavioral Intentions Among Omani College Students

Muna S. Bait Ajzoon
Alcohol and/or substance use among college students is a serious public health issue. In Oman, studies addressing college student’s alcohol and/or substance use are limited. The purpose of this study was to identify knowledge, attitudes, subjective norms, self-efficacy, and perceived behavioral control associated with alcohol and/or substance usage patterns among Omani college students (OCSs); identify behavioral intentions for alcohol and/or substance use among OCSs; and facilitate the development of culturally relevant evidenced-based interventions for Omani...

A Study of Visible Tattoos in Entry-Level Dental Hygiene Education Programs

Kathryn R. Search
Purpose: The purpose of this study was to survey entry-level dental hygiene program directors in the United States to assess their perceptions of dental hygienists with visible tattoos as well as their satisfaction with current program tattoo polices. Methods: After IRB approval, a 14-item survey was administered online to 340 entry-level dental hygiene programs. Participants used a seven-point Likert type scale ranging from strongly disagree (1) to strongly agree (7), to indicate their opinions of...

Crabbing System for an Electron-Ion Collider

Alejandro Castilla
As high energy and nuclear physicists continue to push further the boundaries of knowledge using colliders, there is an imperative need, not only to increase the colliding beams’ energies, but also to improve the accuracy of the experiments, and to collect a large quantity of events with good statistical sensitivity. To achieve the latter, it is necessary to collect more data by increasing the rate at which these pro- cesses are being produced and detected...

Feeding Habits of Young-of-Year Striped Bass, Morone saxatilis, and White Perch, Morone Americana, in Lower James River, VA.

Paul J. Rudershausen & Joseph G. Loesch
A total of 188 young-of-year (YOY) striped bass, Morone saxatilis, and 199 YOY white perch, Morone americana, were collected by pushnet, seine and trawl during 24-hour periods from June through August, 1992 in lower James River, Virginia. The purpose was to identify prey and temporal and spatial feeding habits. Copepods were the most numerous prey of both species. Fishes and mysids comprised the largest volumetric percentage of diets of striped bass and white perch, respectively....

An Exploration of Ticket Pricing in Intercollegiate Athletics

Craig A. Morehead
Ticket sales represent a significant revenue stream for FBS athletic departments, yet little is known about how administrators determine prices for those tickets. This three-paper format dissertation is an attempt to begin filling this gap in the literature so that we may better understand ticket pricing from a managerial perspective. Paper one is conceptual in nature, and includes a review of extant ticket pricing literature and presents a research agenda for studying pricing in the...

Seasonal Variation in Diet of a Marginal Population of the Hispid Cotton Rat, Sigmodon hispidus

Lynn A. Walker & Robert K. Rose
Cotton rats live in oldfields, habitats with a variety of mostly herbaceous plants. Based on other studies, the hispid cotton rat, Sigmodon hispidus, eats many kinds of herbaceous plants but grasses predominate. In contrast, our population of cotton rats ate many monocots but mostly they were not grasses. Our study sought to determine the diet of the cotton rat in eastern Virginia, near the northern limit of distribution on the Atlantic Coast. Fecal samples, collected...

Graminicolous Fungi of Virginia: Fungi in Collections 2004-2007

Curtis W. Roane
Fungus-grass associations recognized in Virginia from 2004 to 2007 are recorded. Many associations are new to the United States (U), eastern United States (EU) and Virginia (V); other associations extend the known distribution of those previously discovered. These reports contribute further to knowledge of the mycoflora of Virginia.

A Comparative Study of the Effects of External Selection on Settleability and Formation of Aerobic Granular Sludge

Tyler A. Brickles
Aerobic granular sludge (AGS) has shown much promise in the advancement of the wastewater treatment industry. AGS has been studied intensely since the early 1990’s due to highly desirable characteristics of nutrient removal efficiency, low footprint, and abnormally faster settling rates than conventional activated sludge. With the exception of a few on-going research projects, all AGS systems have been studied and implemented through the use of sequencing batch reactors (SBR). Recently, a novel approach to...

Holistic Approach in Microalgae Conversion to Bioproducts and Biofuels Through Flash Hydrolysis

Ali Teymouri
In recent years, the demand for renewable energy, mainly biomass has increased. The U.S. Energy Information Administration reported that more than 13.3% of the total energy production in the first seven months of 2017 was produced from a biomass source. Among all biomass resources, microalgae has brought a lot of attention due to their numerous advantages such as higher growth rate and productivity compared with the conventional energy crops, higher energy conversion efficiency by photosynthesis,...

Sense of Belonging, Emotion Regulation, Perceived Social Support and Mental Health among College Students

Sara Bock Davis
Perceived social support (PSS) is linked to a range of beneficial effects, but the factors that influence the effectiveness of PSS are less well understood. In their Relational Regulation Theory (RRT), Lakey and Orehek (2011) emphasize the importance of distinguishing the role of individual factors from relational influences on PSS. This study tested the RRT by examining whether the association of PSS to three mental health outcomes (i.e., aggression, binge eating, depressive symptoms) varies by...

Numerical Studies and Optimization of Magnetron with Diffraction Output (MDO) Using Particle-in-Cell Simulations

Alireza Majzoobi
The first magnetron as a vacuum-tube device, capable of generating microwaves, was invented in 1913. This thesis research focuses on numerical simulation-based analysis of magnetron performance. The particle-in-cell (PIC) based MAGIC software tool has been utilized to study the A6 and the Rising-Sun magnetron structures, and to obtain the optimized geometry for optimizing the device performance. The A6 magnetron is the more traditional structure and has been studied more often. The Rising-Sun geometry, consists of...

Civilians on the Battlefield: Creating a Realistic Training Aid for the United States Military

Aaron D. Beam
The United States and our allies and partners have adopted a humane approach to warfare based on established principle of the laws of war centered on the principles of Military Necessity, Humanity, Proportionality, Distinction, and Honor. These principles dictate that US Military forces conduct warfare with a careful consideration of our impact on civilian populations with a special duty to protect and limit harm as much as possible given the accomplishment of a mission. Likewise,...

Traditional Student Perceptions and Experiences Contributing to Community College Persistence

Naomi Elizabeth Simpson
An increased effort to improve the retention percentages and number of college graduates must address the unique characteristics and experiences of the traditional-aged community college student population. Models of student departure and attrition seek to explain why a student stops attending a college through the analysis of quantitative data. These data, whether about student demographic characteristics, academic intent, institutional factors, motivational factors, etc. are used abundantly to predict persistence and retention patterns of 4-year college...

Defining the Competencies, Programming Languages, and Assessments for an Introductory Computer Science Course

Simon Sultana
The purpose of this study was to define the competencies, programming languages, and assessments for an introductory computer science course at a small private liberal arts university. Three research questions were addressed that involved identifying the competencies, programming languages, and assessments that academic and industry experts in California’s Central Valley felt most important and appropriate for an introduction to computer science course. The Delphi methodology was used to collect data from the two groups of...

Motivation and Learning in an Online Collaborative Project Using Gamification

Michele L. Hudiburg
In 2012, there were 2.9 million students enrolled in graduate degrees and 22% were taking strictly online courses (Kena et al., 2014). Many students are not motivated to participate in collaborative learning experiences in online courses (Dirkx & Smith, 2004). Gamification, the inclusion of game elements in non-game contexts, has been shown to have a positive impact on motivation (Deterding, 2012; Kapp, 2012). Prior work has focused on structural gamification including elements such as points,...

Education and Post-Release Employment: An Exploratory Study of Offender Perceptions

Frank R. Wood
Employment is an essential component of the reintegration process for returning offenders. As one of the eight criminogenic needs, improving employment opportunities for returning offenders increases the ability of returning offenders to reintegrate back into the community, as well as decreases the potential threat of recidivism. However, further research is needed to examine how an offenders’ prospectus from educational experiences influences their perceptions of finding legal employment after release. The current study contributes to current...

Registration Year

  • 2018

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