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Poliomyelitis is a foremost cause of paralysis among preventable diseases among children and adolescents globally. It is caused by persistent infection with poliovirus (PV). The PV infection does not always cause paralysis. A lack of immunization always increases the risk of paralytic polio. Genetic factors also been shown to affect the risk of developing the disease. The aim of this thesis is to investigate whether there are any genetic associations to paralytic poliomyelitis. This is based on a model for understanding its nature as a complex disease, where many genes are involved in contributing to the disease state. This is a population-based case-control study to identify genetic loci that influence disease risk. The study examined the association of genetic variation in single nucleotide polymorphisms (SNPs) across the genome with paralytic poliomyelitis susceptibility in the United States and Canadian survivors of poliomyelitis population, using a genome-wide association study (GWAS) approach. No association was observed. Loci that have been previously implicated were not found to affect the susceptibility to poliomyelitis in this study. The thesis consists of four chapters. Chapter 1 describes the epidemiology, pathogenesis and management of poliomyelitis. Chapter 2 gives an overview of the genomics of infectious diseases in general. Chapter 3 introduces the study population and presents the genome-wide analysis and associations with logistic regression to identify loci explore genes that might be associated with paralytic poliomyelitis and presents results. Chapter 4 discusses the implications of the results and explains future directions. / Thesis / Master of Science (MSc)

Yes / What has generated the unprecedented fascination with the Internet? What future lies ahead for computing as the Internet and its associated infrastructure expand? Will the network be able to cope with rising demands for carrying capacity and response speed? Will it change the way scientists, designers, artists, computer professionals, and home users work in the future? These are some of the wideranging questions being asked about the Internet and World Wide Web.

Substantial resources are being directed towards use of the Internet in K-12 Education with over $2.25 billion annually distributed to K-12 schools from the Federal government alone (Maiden & Beckham, 1999). In 1998, 90% of schools had Internet access while only 2% of funds spent on software in K-12 schools were directed towards Web-based courseware (Jerald & Orlofsky, 1999). The Web-based instructional module Healthy Hearts was developed as a self-contained instructional unit delivered over the Internet, popularly referred to as "e-Learning", for fifth grade students to use as part of the classroom curriculum. Healthy Hearts teaches children about risk factors associated with heart disease, including physical activity, tobacco, and nutrition. After piloting and formatively evaluating Healthy Hearts in two fifth grade classrooms, Elliott (1997) made recommendations for future modification and implementation. No research regarding effects the Web-based instructional unit Healthy Hearts has on fifth grade children exists. The purpose of this study is to evaluate the impact Healthy Hearts has on fifth grade children's physical activity knowledge, attitudes, and behavior. Participants included 233 fifth grade boys and girls and 11 teachers who implemented Healthy Hearts during Spring 2001. A repeated measures experimental-control design was employed to measure Healthy Hearts effects on physical activity knowledge, attitudes, and behavior. The questionnaire used for this study included three attitude items adapted from Sport, Play, and Active Recreation for Kids (SPARK) (Sallis, Alcaraz, McKenzie, & Hovell, 1999a), six criterion referenced knowledge items developed from Healthy Hearts objectives, and a Weekly Activity Checklist to assess physical activity behavior, which was developed and validated for SPARK (Sallis et. al., 1993a). Classroom teachers administered the baseline test before students began using the module. For five weeks following the baseline test, the group 1 engaged in Healthy Hearts lessons by going to a computer lab for 45 minutes twice a week while group 2 participated in regularly scheduled classroom activities. After group 1 finished Healthy Hearts, both groups completed test 1 and then teachers from group 2 implemented Healthy Hearts with their classes. When group 2 finished using Healthy Hearts, both groups completed test 2. Dependent variables were physical activity knowledge, attitude, and behavior with group as independent variables. Other independent variables included school socioeconomic status, time allocated to Healthy Hearts, non-Healthy Hearts instruction time for related objectives, and speed of Internet connection. Repeated measures ANOVA revealed significant effects of Healthy Hearts on physical activity knowledge and attitude, however Healthy Hearts had no significant effects on behavior. Results of this study indicate Healthy Hearts could be an effective means of using the Internet to deliver health and physical activity instruction to fifth grade children, and suggest a need for further design, development, and evaluation of Healthy Hearts. / Ph. D.

The Internet presents a new phenomenon to educators and students in the K-12 environment. It's ease of use and ready access to material provides an overwhelming resource for use in the K-12 classroom. This study looked at content management of Internet resources in the K-12 school environment. Content management is defined as the methods of organizing access to the information available on the Internet allowing the teacher to effectively use resources in a classroom setting. Teachers have managed the material, or content, that they present to students for over a decade. Now that resources available on the Internet are also open to K-12 students, teachers must be aware of the need to manage Internet content, just as they would do for any other content being used in their classroom. This study looked at middle school students in 6th and 7th grades. An experimental design was used to determine if K-12 access to Internet resources provides a higher degree of results when students are presented with managed resources, or when students have open access to Internet resources. Analysis of the results of the study show that there is a significant difference in both the amount and the quality of material that was identified by the group with managed access to Internet content. / Ph. D.

The power system has long been operated in a shroud of introspection. Only recently have dynamic, wide-area time synchronized grid measurements brought to light the complex relationships between large machines thousands of miles apart. These measurements are invaluable to understanding the health of the system in real time, for disturbances to the balance between generation and load are manifest in the propagation of electromechanical waves throughout the grid. The global perspective of wide-area measurements provides a platform from which the destructive effects of these disturbances can be avoided. Virginia Tech's distributed network of low voltage frequency monitors, FNET, is able to track these waves as they travel throughout the North American interconnected grids. In contrast to other wide-area measurement systems, the ability to easily measure frequency throughout the grid provides a way to identify, locate, and analyze disturbances with high dynamic accuracy. The unique statistical properties of wide-area measurements require robust tools in order to accurately understand the nature of these events. Expert systems and data conditioning can then be used to quantify the magnitude and location of these disturbances without requiring any knowledge of the system state or topology. Adaptive application of these robust methods form the basis for real-time situational awareness and control. While automated control of the power system rarely utilize wide-area measurements, global insight into grid behavior can only improve disturbance rejection. / Ph. D.

Because of the increasing emphasis on environmental concerns, there has been a growing demand for lower fuel consumption in modern transportation applications. To reduce fuel comsumption, higher efficiency, higher power density power converters are desired. The new generation of wide bandgap (WBG) power semiconductor devices pushs the switching frequency and output power of the electric system in transportation to a higher level thanks to their higher blocking voltage, higher operating frequency, and smaller parasitic elements. With benefits such as size reudcetion, costs saving, and reliability improvement, integration technologies have been widely adopted in power electronic systems, especially with the emergence of WBG semiconductor devices. These improvements will futher translate into reduced fuel consumption, extended operating range, and increased passenger compartment. Transportation applications pose a challenging environment for converter integration. The fast switching speed and the high blocking voltage of WBG semiconductor devices also put forward higher requirements for converter integration. First, the power converters used in transportation applications are often powered from the batteries that support multiple loads. During load changes, crank, or jump-start, undesired transients exist, which requires the power converters to be capable of operating under a wide-input-voltage range. This requirement results in a very limited design region of acceptance, making the converter hard to handle uncertainties. However, the integration process might bring large uncertainties, such as material property changes. This phenomenon can degrade converter performance or even cause design failures. Besides, the power converters for transporation applications often work in harsh environment, such as high ambient temperature or low air density. The former can lead to overheated and the latter degrades insulation strength, both of which hinder high power density design. Moreover, with the advent of all kinds of portable devices, converters are required to deliver more power. The introduction of universal serial bus (USB) power delivery (PD) extends the delivered power. To meet the specification, the power converters should provide a wide-output-voltage range, which brings challenges to the converter design. Furthermore, the charger is usually fed by an ac voltage of more than 100 V, which is then stepped down to 5 V – 20 V. The high step-down ratio increases the converter loss. To address the wide-input-voltage and high-temperature challenges, a dual-output, PCB-embedded transformer based active-clamp Flyback (ACF) gate-drive power supply (GDPS) for automotive applications is proposed. It has been demonstrated that the PCB-embedding technique effectively improves converter power density. The final prototype achieves a power density of 53.2 W/in3, a peak efficiency of 89.7 %, a transformer input-output capacitance of 9.7 pF, an input-voltage range of 9.9 V – 28 V, and a maximum operating temperature at low-line (LL) voltage of 105 °C and 115 °C at high-line (HL) voltage. Yet the above unit failed to meet all of the design targets due to the material property degradation in transformer. This degradation is caused by the mechanical stress induced in the integration process. To investigate its impact on wide-input-voltage converter design, several PCB-embedded magnetic boards are fabricated with different core materials and stress levels. Based on the analysis, experimentally derived correction factors are proposed and applied to the models used in the multi-objective optimization (MDO) process. The improved design successfully achieves the targeted wide-input-votlage range. When aircrafts climb during flight, air density reduces and the breakdown voltage decreases correspondingly. The insulation design becomes a challenge for the gate driver for SiC-based airborne applications. To provide sufficient insulation strength and achieve high power density simultaneously, a Paschen curve based insulation co-ordination is proposed. Electric-field control methodology is applied to the layout design. By properly designing the field control plates, the peak electric field has been shifted from the air to fr4 material that features much higher dielectric strength. The proposed gate driver attains a small size of 128.7 mm × 61.2 mm × 23.8 mm. Partial discharging tests are conducted in an altitude chamber. The experimental result shows that the proposed gate driver provides sufficient insulation strength at 50, 000 ft. To tackle the wide-output-voltage range and high-step-down ratio challenges in the USB-C PD charger in airborne applications, a LLC converter with PCB-winding based transformer with built-in leakage inductance is presented. A flying-capacitor based voltage divider (FCVD) switching bridge is proposed to replace the conventional half-bridge or full-bridge switching bridge. The propsed FCVD shows a current reduction of over 50 % than the conventional half-bridge with the same circuit elements. The prototype achieves a high efficiency of 90.3 % to 93.2 % over 5 V to 20 V outputs, and a high power density of 73.2 W/ in³, which is almost two time larger than the state-of-the-art power density. Partial discharging tests are also conducted in an altitude chamber. A partial discharing inspection voltage of 800 V is found at 10, 000 ft, which is much higher than the requirement. / Doctor of Philosophy / Because of the increasing emphasis on environmental concerns, there has been a growing demand for lower fuel consumption in modern transportation applications. The new generation of wide bandgap (WBG) power semiconductor devices and various integration technologies enable electronic systems in transportation to achieve higher efficiency and higher power density. These improvement will futher translate into reduced fuel consumption, extended operating range, and increased passenger compartment. However, transportation applications put more requirements on power converter designs. This dissertation, therefore, focusing on addressing the integration challenges in high power density WBG-based circuits for transportation applications from the aspects of wide-input-voltage range, material properties degradation, harsh environment, and wide-output-voltage range together with high step-down ratio. To meet the wide-input-voltage and high temperature requirements in automotive applications, a dual-output, PCB-embedded transformer based active-clamp Flyback (ACF) dc-dc converter is proposed. The final prototype achieves a power density of 53.2 W/in3, a peak efficiency of 89.7 %, a transformer input-output capacitance of 9.7 pF, an input-voltage range of 9.7 V â€" 28 V, and a maximum operating temperature at low-line (LL) voltage of 105 °C and 115 °C at high-line (HL) voltage. Yet the above unit failed to meet all of the design targets due to the material property degration in PCB-embedded transformer. This degradation is caused by the mechanical stress during integration process. To investigate its impact on automotive converter, several PCB-embedded magnetic boards are fabricated with different core materials and stress levels. Based on the analysis, experimentally derived correction factors are proposed and applied to the models used in the multiobjective optimization process. The improved design successfully achieves the targeted wide-input-votlage range. When aircrafts climb during flight, air density reduces and thus insulation strength decreases correspondingly. Instead of using oversized altitude correction factors provided by IEC standards, a Paschen curve based insulation co-ordination is proposed. Electric-field control methodology is applied to the gate driver layout. The proposed gate driver attains a small size of 128.7 mm × 61.2 mm × 23.8 mm. Partial discharging test is conducted in an altitude chamber. The experimental result shows that the proposed gate driver provide sufficient insulation strength at 50, 000 ft. To tackle the wide-output-voltage range and high-step-down ratio challenges in the USB-C PD charger in airborne applications, a LLC converter with PCB-winding based transformer with built-in leakage inductance is presented. A flying-capacitor-based voltage divider (FCVD) switching bridge is proposed to replace the conventional half-bridge or full-bridge switching bridge. The propsed FCVD shows a current reduction of over 50 % than the conventional half-bridge with the same circuit design. The prototype achieves a high efficiency of 90.3 % to 93.2 % over 5 V to 20 V outputs, and a high power density of 73.2 W/ in3, which is more than two time larger than the state-of-the-art power density. Partial discharging tests are also conducted in an altitude chamber. A partial discharing inspection voltage (PDIV) of 800 V is found at 10, 000 ft, which is much higher than the requirement.