Browsing by Author "Wang, Qiong"
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- The activity and content of calpains in maturing dystrophic muscle membranesWang, Qiong (Virginia Tech, 2005-05-11)Increased calcium-activated calpain proteolysis in the sarcolemma membrane is thought to be a primary mechanism in the pathophysiology of Duchenne Muscular Dystrophy (DMD). However, few studies have tested this possibility prior to the overt signs of the dystrophy. The purpose of this study was to test the hypothesis that there is greater calpain content and total relative calpain activity in membranes obtained from dystrophic (mdx; mdx:utrophin-deficient (mdx:utrn-/-)) compared to wildtype (wt) mouse skeletal muscles during maturation at ages 7- and 21-d,and at a post-maturation age of 35-d. Calpain activity was determined as the calcium-dependent cleavage of the flurogenic substrate SLY-AMC, and content was determined by Western analysis with an anti-calpain antibody. There were several intriguing findings: 1. There was an inverse relationship between calpain content and relative activity in the whole muscle in both wt and mdx mice from age 7- to 35-d: calpain content decreased, and relative calpain activity increased as the mice aged. This suggests a similar role for calpain in both genotypes, which might relate to specific maturation processes, possibly up to age 21-d. Although the inverse relation was evident at 35-d, the targets for calpain in mdx compared to wt likely differed. 2. The increased relative calpain activity in the membrane fraction of mdx mice at age 35-d (26.73 Arbitrary Units, (AU)) compared to that of age 7- (4.9AU; p<0.05) and 21-d (8.74AU; p<0.05) is temporally related to degeneration and regeneration processes, and may also indicate activation of apoptosis, in mdx muscles at this age. 3. At age 7-d, there were no significant differences in either calpain content or relative calpain activity in all subcellular fractions for wt and mdx mice. This result might suggest similar calpain distribution and activities that are related to the regulation of muscle maturation and differentiation in both genotypes. (Note:data were not obtained for the mdx:utrn-/- mice at age 7-d because of insufficient animals). 4. At age 21-d, there was greater relative calpain activity in the myofibrillar supernatant fraction in mdx (15.13AU) than wt mice (1.18AU; p<0.05). This could indicate calpain's role in the initiation of myofibrillar protein turnover and the proteolysis of submembranous networks in the mdx muscles. 5. At age 21-d, greater calpain content in the mdx (1.40ìg) compared to wt (0.23 ìg; p<0.05) membrane fraction might suggest a broader distribution of calpain along membranes that contributes to the onset of dystrophy in the mdx muscles. 6. At age 35-d, there was greater calpain content in the mdx:utrn-/- compared to the wt membrane (0.48ìg vs 0.13 ìg), cytosolic (0.88ìg vs 0.30ìg), and myofibrillar supernatant (0.49ìg vs 0.17ìg; p<0.05 ) fractions This increased content and broad distribution across several subcellular fractions may reflect degeneration and regeneration processes, and potentially activation of apoptosis, in the mdx:utrn-/- muscles. These data suggest that calpain activity contributes to dystrophic pathophysiology mainly in the membrane fraction of mdx skeletal muscles at age ~21-d, but appears to contribute later at 35-d and in more subcellular fractions in mdx:utrn-/- skeletal muscles.
- Design of Extreme Efficiency Active Rectifier for More-electric AircraftsWang, Qiong (Virginia Tech, 2015-05-12)The More-electric aircraft (MEA) concept has been raised since 1990s in order to increase fuel economy and reduce environmental impact of aircrafts. The fundamental of the concept is to replace pneumatic, hydraulic and mechanical systems in conventional aircrafts with its electrical equivalent that is lighter and more reliable. In this movement, power electronics technology plays a key role in interfacing the new types of electrical loads to the new aircraft electrical power system. One of the major tasks for power electronics circuits in MEA is to transfer aircraft variable frequency AC voltage into DC voltage, which could be conveniently utilized by different types of loads or power buses. The converters carrying out the task is commonly known as "rectifiers". This work aims at designing and constructing rectifiers that can work efficiently and reliably in more-electric aircrafts. One of the major challenge for these rectifiers comes from the complex aircraft environment. The ambient temperature could be as high as 70 ºC. Moreover, active cooling for converters may not be desirable. To deal with this, rectifiers should achieve extreme efficiency (especially at full load) so that all the components are not overheated without active cooling. This work aims at achieving extreme converter efficiency through advanced converter topologies and design. Both single-phase and three-phase rectifiers are discussed in this work. For single-phase rectifiers, this work focused on boost-type power factor correction (PFC) converters due to the promising efficiency and good PFC characteristics. The well-known two-level semi-bridgeless PFC boost rectifier, together with its interleaved and three-level counterparts, are studied and compared in this work. The operation principles of the converters are analyzed. Models and methods for converter efficiency evaluation are discussed. The efficiency evaluation of the topologies shows the advantage of three-level topologies and interleaved topologies in achieving higher efficiency and better thermal management. For three-phase rectifiers, two-level boost rectifier, three-level neutral point clamped (NPC) rectifier and Vienna rectifier are investigated. The evaluation shows the advantage of Vienna rectifier in achieving high efficiency due to reduced switching loss. Based on the evaluation of single-phase and three-phase active rectifiers, the author selected interleaved Vienna rectifier to achieve extreme efficiency and avoid overheating problem. The operation principle of the interleaved Vienna rectifier is introduced, with particular attention paid to the circulating current generated by interleaving operation. The design procedure for achieving maximum efficiency is described. Finally, a prototype of the proposed converter is constructed, which achieves 99.26% efficiency at nominal load.
- Form-Factor-Constrained, High Power Density, Extreme Efficiency and Modular Power ConvertersWang, Qiong (Virginia Tech, 2018-12-18)Enhancing performance of power electronics converters has always been an interesting topic in the power electronics community. Over the years, researchers and engineers are developing new high performance component, novel converter topologies, smart control methods and optimal design procedures to improve the efficiency, power density, reliability and reducing the cost. Besides pursuing high performance, researchers and engineers are striving to modularize the power electronics converters, which provides redundancy, flexibility and standardization to the end users. The trend of modularization has been seen in photovoltaic inverters, telecommunication power supplies, and recently, HVDC applications. A systematic optimal design approach for modular power converters is developed in this dissertation. The converters are developed for aerospace applications where there are stringent requirement on converter form factor, loss dissipation, thermal management and electromagnetic interference (EMI) performance. This work proposed an optimal design approach to maximize the nominal power of the power converters considering all the constraints, which fully reveals the power processing potential. Specifically, this work studied three-phase active front-end converter, three-phase isolated ac/dc converter and inverter. The key models (with special attention paid to semiconductor switching loss model), detailed design procedures and key design considerations are elaborated. With the proposed design framework, influence of key design variables, e.g. converter topology, switching frequency, etc. is thoroughly studied. Besides optimal design procedure, control issues in paralleling modular converters are discussed. A master-slave control architecture is used. The slave controllers not only follow the command broadcasted by the master controller, but also synchronize the high frequency clock to the master controller. The control architecture eliminates the communication between the slave controllers but keeps paralleled modules well synchronized, enabling a fully modularized design. Furthermore, the implementation issues of modularity are discussed. Although modularizing converters under form factor constraints adds flexibility to the system, it limits the design space by forbidding oversized components. This work studies the influence of the form factor by exploring the maximal nominal power of a double-sized converter module and comparing it with that of two paralleled modules. The tradeoff between modularity and performance is revealed by this study. Another implementation issue is related to EMI. Scaling up system capacity by paralleling converter modules induces EMI issues in both signal level and system level. This work investigates the mechanisms and provides solutions to the EMI problems.
- From Ideas to Actions: Hazard Mitigation Policy Adoption—Analysis of Floodplain Property Buyout ProgramWang, Qiong (Virginia Tech, 2023-08-23)Climate change is exerting a profound influence on natural hazards, resulting in increased frequency, intensity, and altered patterns of extreme weather events. These changes pose significant risks to vulnerable populations worldwide. Consequently, it is imperative to adopt hazard mitigation policies to address the impacts of climate change on natural hazards and communities. The adoption of such policies is a complex and dynamic process that requires a thorough understanding of the key factors influencing policy adoption. The United States has experienced a rise in the severity and frequency of floods, necessitating the implementation of comprehensive flood mitigation policies. These policies aim to protect vulnerable communities, safeguard critical infrastructure, and reduce the economic and human costs associated with these natural disasters. Among the various flood mitigation strategies, floodplain property buyout programs have garnered attention. However, there is limited research that examines the factors influencing the adoption of buyout programs at the local government level from a government perspective. This dissertation provides a comprehensive analysis of the adoption process of floodplain property buyout programs at the local level in the United States. The study employs a mixed methods approach to examine the mechanism behind policy adoption and identify the key factors that influence this process. Chapter 1 lays the foundation for the research by defining relevant terms and outlining the characteristics of floodplain property buyout programs in the U.S. Chapter 2 presents a theoretical framework that enhances our understanding of hazard mitigation policy adoption at the local level. The framework is exemplified through case studies of property buyout programs in North Carolina and New Jersey. The case studies conducted in these states offer compelling evidence that supports the proposed framework, which encompasses five-factor categories: hazard problem, social context, institutional capacity, cross-sector collaboration, and policy diffusion. Notably, institutional capacity plays a crucial role in buyout adoption, encompassing individual, organizational, and system capacity. These factors influence the uptake of buyouts and contribute to their success or failure. This exercise gives us valuable insights into the buyout decision making process and suggests avenues for research in the subsequent chapters. Chapter 3 conducts a quantitative analysis to validate the hazard mitigation policy adoption framework. Specifically, it focuses on investigating the factors that influence the adoption of Federal Emergency Management Agency (FEMA) property buyout programs by local governments in Virginia counties. Utilizing logistic regression models and a survey dataset collected from local floodplain managers in the Commonwealth of Virginia, the study reveals that floodplain managers' perception of repetitive flood loss and economic spillovers in neighboring areas significantly impact the adoption of buyout programs. In Chapter 4, we conduct a qualitative approach to delve into the decision-making dynamics in the adoption of floodplain property buyout programs from a government perspective in Virginia. Through semi-structured interviews with 12 experts representing various stakeholders involved in floodplain management, this study demonstrates the variations in the adoption processes among different local governments. The findings underscore the importance of leadership, community population size, floodplain managers' perception of repetitive flood loss, organizational staff capacity, and tax revenue considerations in shaping buyout decisions. It highlights the need for local leadership commitment, empowerment of floodplain managers, and comprehensive approaches to address challenges faced by small communities. The research provides practical guidance to enhance flood risk management practices and promote resilient and sustainable communities. In conclusion, this dissertation contributes to the understanding of hazard mitigation policy adoption at the local level by proposing a theoretical framework and providing empirical evidence through case studies, surveys, and interviews. The findings emphasize the importance of various factors, such as hazard problem, social context, institutional capacity, and policy diffusion, in shaping buyout policy adoption. The implications of this research extend to policymakers, practitioners, and researchers, providing insights into the motivations, obstacles, and strategies surrounding the adoption and implementation of hazard mitigation policies. By considering these factors and employing comprehensive approaches, communities can enhance their resilience and effectively mitigate the impacts of natural hazards.
- Optimal Investment Strategies for Flexible Resources, Considering Pricing and Correlated DemandsWang, Qiong (Virginia Tech, 2002-12-05)We study the resource investment decision faced by a firm that offers two demand-classes (i.e., products, services), while incorporating the firm's pricing decision into the investment decision. For this purpose, we consider a monopolistic situation and model the demand curve of each demand-class as a downward sloping linear function of its own price. The firm can invest in dedicated resources, which can only satisfy a specific demand-class, and/or in a more expensive, flexible resource, which can satisfy both demand-classes. We consider a two-stage stochastic decision model: In the first stage, the firm determines the dedicated and flexible resource capacities to invest in under demand uncertainty. In the second stage, demand curves are realized and the firm optimizes its revenue through pricing and resource allocation decisions, constrained by its capacity investment decision in the first stage. Our analysis provides the structure of the firm's optimal resource investment strategy as a function of price elasticities and investment costs, and shows how the value of resource flexibility depends on these parameters and demand correlations. Based on our analysis, we provide principles on the firm's optimal resource investment strategy under uncertainty. We show that it can be optimal for the firm to invest in the flexible resource when demand patterns are perfectly positively correlated, while it is not always optimal to invest in the flexible resource when demand patterns are perfectly negatively correlated.