Browsing by Author "Leech, Irene E."
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- Analysis and Design of Paralleled Three-Phase Voltage Source Converters with InterleavingZhang, Di (Virginia Tech, 2010-04-26)Three-phase voltage source converters(VSCs) have become the converter of choice in many ac medium and high power applications due to their many advantages, including low harmonics, high power factor, and high efficiency. Modular VSCs have also been a popular choice as building blocks to achieve even higher power, primarily through converter paralleling. In addition to high power ratings, paralleling converters can also provide system redundancy through the so-called (N+1) configuration for improved availability, as well as allow easy implementation of converter power management. Interleaving can further improve the benefit of paralleling VSCs by reducing system harmonic currents, which potentially can increase system power density. There are many challenges to implement interleaving in paralleled VSCs system due to the complicated relationships in a three-phase power converter system. In addition, to maximize the benefit of interleaving, current knowledge of symmetric interleaving is not enough. More insightful understanding of this PWM technology is necessary before implement interleaving in a real paralleled VSCs system. In this dissertation, a systematic methodology to analyze and design a paralleled three-phase voltage source converters with interleaving is developed. All the analysis and proposed control methods are investigated with the goal of maximizing the benefit of interleaving based on system requirement. The dissertation is divided into five sections. Firstly, a complete analysis studying the impact of interleaving on harmonic currents in ac and dc side passive components for paralleled VSCs is presented. The analysis performed considers the effects of modulation index, pulse-width-modulation (PWM) schemes, interleaving angle and displacement angle. Based on the analysis the method to optimize interleaving angle is proposed. Secondly, the control methods for the common mode (CM) circulating current of paralleled three-phase VSCs with discontinuous space-vector modulation (DPWM) and interleaving are proposed. With the control methods, DPWM and interleaving, which is a desirable combination, but not considered possible, can be implemented together. In addition, the total flux of integrated inter-phase inductor to limit circulating current can be minimized. Thirdly, a 15 kW three phase ac-dc rectifier is built with SiC devices. With the technologies presented in this dissertation, the specific power density can be pushed more than 2kW/lb. Fourthly, the converter system with low switching frequency is studied. Special issues such as beat phenomenon and system unbalance due to non-triplen carrier ratio is explained and solved by control methods. Other than that, an improved asymmetric space vector modulation is proposed, which can significantly reduce output current total harmonic distortion (THD) for single and interleaved VSCs system. Finally, the method to protect a system with paralleled VSCs under the occurrence of internal faults is studied. After the internal fault is detected and isolated, the paralleled VSCs system can continue work. So system reliability can be increased.
- Career choice decisions of Family and Consumer Sciences education recent graduates: implications for recruitment to address the teacher shortageMimbs, Cheryl A. (Virginia Tech, 1996)A national teacher shortage in Family and Consumer Sciences (FCS) prompted the development of this study. This study examined career motivations of recent graduates of FCS to determine target audiences and marketing strategies for recruitment to address the teacher shortage. Personal, educational, and employment demographics, career choice decisions, and contextual factors of recent graduates of FCS teacher licensure programs in 14 southern states were examined. The study also examined differences between first and second career graduates. A survey instrument developed by Serow (1994) was adapted for use in this study. Subjects were asked to indicate which of 35 career choice factors and personal values influenced their decision to become a teacher and to choose FCS as a field of study. The instrument was mailed in May 1996 to 494 graduates, whose names were obtained from teacher educators. The final sample consisted of 396 graduates. A total of 262 respondents completed the survey for a return rate of 66%. All but five of the respondents were female. The average age was 30 years. Ten percent were from minority groups. Over 40% lived and worked in rural areas or towns with under 10,000 population. Eighty-eight percent completed their teacher licensure through a bachelor's degree program. Most made their career choice decision while in college. Employment demographics indicated 43% of respondents were second career graduates, who indicated they had various first careers before seeking teacher certification. A total of 31% of respondents, although certified, were not teaching. Reasons given included not being able to find a job in the geographical area where they wanted to live or being employed in another field. Interest in FCS subject matter, enjoyment of working with young people, interest in families, helping people, professional satisfaction, and creativity were the reasons most often given as influencing career choice decisions. Cluster analysis of graduates responses on career choice factors revealed five groupings. These are (1) altruistically motivated, (2) interest, flexibility, and variety of career, (3) secondary school experience influenced, (4) socially conscious and friend influenced, and (5) college experience influenced.
- Characteristics and practices of financially-stressed homeowners in Prince William County, VirginiaO'Neill, Barbara Mary (Virginia Tech, 1995)This study was designed to examine characteristics of overextended homeowners and to determine to what extent financial difficulty, as measured by the back-end financial ratio (principal, interest, taxes, and insurance, plus consumer credit payments, divided by gross monthly income), can be explained by a combination of affective and objective attributes and precipitating life events. The Parrott and Lytton (1993) Model of Family Housing Stability was used as the theoretical basis of this investigation. Demographic characteristics; financial characteristics, including net worth and financial ratios; money management characteristics and practices; recently-experienced life events; and psychological characteristics of the sample were reported. Data were obtained from a convenience sample of Prince William County, Virginia residents who were clients of a Cooperative Extension financial counseling program. Two sources of data were used: a 169-item survey instrument and a financial profile. Of the 519 cases where both a financial profile and a survey were completed, 245 were homeowners and comprised the sample. Demographic characteristics of the sample were found to be dissimilar to those of Virginia and U.S. citizens. Respondents had lower median incomes, and a higher percentage of ethnic minorities and households with children living at home. Descriptive statistics were used to profile sample households. A quarter of the sample had a negative net worth and the mean amount of liquid assets covered one week’s expenses. Almost three-quarters of sample households had monthly household expenses that exceeded income. Over 80% experienced three or more life events that affected their finances. The most frequently-reported event was unemployment. Seventeen independent variables were regressed on the dependent variable to produce a statistically significant R² of .3138 (p <.0001). Objective and affective attributes and precipitating life events were also regressed as blocks on the dependent variable. Only the objective attribute group was significant, accounting for approximately a quarter of the variance in financial difficulty. Only one individual variable, the number of household earners, was significant in explaining variance in the dependent variable. A negative coefficient indicated that, as the number of wage earners was reduced, the back-end ratio of sample households increased.
- A comparison of the financial situations and practices of remarried and first-married familiesLinzey, Juanita Bird (Virginia Tech, 1993-08-05)This study was designed to compare the financial situation of both remarried and first-married families from a large randomly selected sample. An adaptation of Campbell, Converse, and Rogers' "Model of Life Satisfaction" was used as the theoretical basis for this investigation. Data were compared to assess differences in (a) personal characteristics; (b) objective attributes, the personal resources of homeowners hip, income, education, employment status, and occupation; (c) perceived attributes, financial attitudes and management behaviors of respondents; (d) evaluated attributes, an assessment of financial situation; and (e) satisfaction level with financial situation. The respondents were a sub-set from pre-collected data sets entitled Financial Attitudes and Practices of Virginia Citizens, Form A and Form B, (N=1098). Responses to items identical in both survey forms were merged to create a new data base which was used in this study. A sample of 173 remarried and 173 first-married respondents was used. Descriptive statistics were used to profile the two respondent groups. Independent t test and chi-square analyses were used to compare responses by marital status. Remarried and first-married respondents were similar in personal characteristics except in ethnicity and gender role philosophy with the remarrieds having a more egalitarian than traditional philosophy. The two groups were similar in objective attributes except in educational attainment. The remarried spouses were not as well educated as their counterparts. Financial management behavior and attitudes were similar for both groups except in the area of risk management and capital accumulation. Both groups reported a positive net worth and adequate income, however, remarrieds were less satisfied with their financial situation than first-marrieds. The results of this study demonstrated differences in the financial domain of remarried and first-married households and pointed to areas of concern for educators and family life specialists.
- Consumer Knowledge of Middlesex, Virginia High School StudentsKyle, Kendra J. (Virginia Tech, 1998-07-17)This study was designed to help those persons developing and delivering consumer education curriculum understand the needs of Middlesex, Virginia High School Students. The instrument used was a consumer knowledge survey developed by a partnership between the Consumer Federation of American and American Express. The 52 item questionnaire was designed to measure knowledge in six key areas of consumption-consumer credit, checking/savings accounts, automobile insurance, housing rental, food purchase, and automobile purchase. The respondents were students attending Middlesex High School from the four grade levels with completed Informed Consent forms. There were 55 respondents from a total pool of 375 (freshmen, 44%; sophomores, 27%; juniors, 13%; and seniors, 16%). Descriptive statistics were used for demographic items. Non-statistical comparisons were made between grade levels, descriptive demographic characteristics, and consumer categories. Comparisons were also made between the data collected and the data of the national consumer knowledge survey by the Consumer Federation of America and American Express Company. The results indicate that Middlesex High School students were not well prepared for the world of consumption. Overall, the students who responded had limited understanding of consumer knowledge in the six specific areas. The average score was 39%. Students had the poorest understanding of consumer credit, auto insurance, and food purchases. Scores for these category areas averaged less than 40%. The students scored highest on housing rental (45%) and checking/savings accounts (44%). The seniors scored the highest overall score (48%), which was higher than the national average of high school seniors (42%).
- Consumers' knowledge, practices, and satisfaction with cooking systems' interactionDeMerchant, Elizabeth Ann (Virginia Tech, 1993-12-05)The purpose of this research was to determine consumers’ satisfaction with cooking systems commonly available in the United States. Five types of cooktops (conventional electric coil, gas flame, solid element, and halogen and electric coil under glass ceramic) and six types of cookware (glass ceramic, porcelain enamel-on-aluminum nonstick, stainless steel with an aluminum disk, heavy gauge aluminum, thin gauge aluminum, and heavy gauge aluminum with non-stick finish) formed 30 cooking systems. Fifteen consumers prepared one menu that represented four cooking operations (frying, boiling, thermalization, and waterless) with each of the 30 cooking systems. They also completed a three-part questionnaire to determine their knowledge and practices regarding the interaction between cooktops and cookware at the beginning, to assess their satisfaction with each cooking system, and to test their knowledge and preferences after completing the 30 cooking systems. Statistical analysis included repeated measures ANOVA, T-test, and General Linear Model (GLM). Statistically significant findings include: (1) Knowledge was different before and after completing the 30 cooking systems; (2) There was a relationship between consumers’ knowledge and overall satisfaction; (3) There was a relationship between optimum compatibility and consumers’ satisfaction; (4) There were differences among cookware of different gauges with respect to evenness of heating; (5) The cooking systems required different levels of user interaction; (6) There were differences in consumers’ satisfaction with cookware cleaning and frying due to the interior finish of the cookware. However, there was no significant difference in consumers’ overall satisfaction with the cooking systems.
- The Contributions of Veterans in Business and Economy: Africa as a Case StudyOshigbo, Taiwo Oluwaseyi (2014-04)This paper discusses the growing influence retired military men and women are now exacting in African society based on their business franchises, which cut across telecoms, agriculture, mining, shipping, oil and gas, broadcasting, small medium enterprise, and more. These are mass-oriented and beneficial investments not only to the society but to the economic growth of their respective nations, which will be advantageous to the collective development of the society and the continent at large. This paper shows a relationship between the period spent as service members and in business careers after retirement, which is a positive indicator and a palliative to stem the idea of young military officers nursing the nocturnal ambition of coup d'etat, since life after service years are no longer an armageddon. This paper takes a periscopic view of how these veterans’ impacts and successes in their new chosen careers have positively affected their immediate communities and beyond in the areas of youth employment and empowerment; capacity building; and re-focusing, re-engineering, and social development indicative of a transformation that underscores a paradigm shift in people’s perception of the men and women in khaki.
- Cutting CostsLeech, Irene E.; Scott, Elaine D. (Virginia Cooperative Extension, 2009-05-01)If a family wishes to cut expenses, there are usually many ways in which to do this. Most of the following suggestions will not save a huge amount of money by themselves. But, if you begin practicing several of them, you should be able to experience a significant reduction in day-to-day living expenses.
- Differences in income and consumer expenditure patterns between foreign and American graduate students at Virginia Polytechnic Institute and State UniversityGuo, Ting (Virginia Tech, 1991-01-05)The purpose of the study was to determine the differences in the total annual income, total annual and monthly expenditures, and consumer expenditure patterns between American and foreign graduate students at Virginia Polytechnic Institute and State University (VPI & SU). The study was based on a survey entitled "Virginia Polytechnic Institute and State University Graduate Students Demographic and Economic Impact Study" conducted in April, 1989. The sample size used in the analysis was 442, including 373 American and 69 foreign students. The findings from the study showed that (1) the American students had significantly higher total monthly expenditures than did the foreign students; (2) the American students had significantly higher absolute expenditures on tax, auto insurance, gasoline and auto repair, medical, laundry, and gifts and contributions, while the foreign students had significantly higher expenditures for telephone calls~ and (3) the American students had significantly larger percentage expenditure on tax, auto insurance, gasoline and auto repair, and entertainment, while the foreign students had significantly larger percentage expenditures on food, utilities, telephone, and travel.
- The Effect of Current and Perceived Economic Conditions on Consumer Apparel Purchase ExpendituresWoods, Adria M. (Virginia Tech, 2005-05-13)Consumer spending accounts for over sixty-five percent of the Gross Domestic Product in the United States, greatly affecting the economy, as well as the retail sector. The consumer, rather than business or government, has become the dominant factor in shaping the course of the aggregate U.S. economy (Curtin, 1982). The purpose of this study is to examine whether the economy, as perceived by consumers, has any effect on the apparel purchase expenditures of consumers, and if so, how personal factors such as gender, age, income, educational attainment, race, and marital status contribute to their perceptions and decisions. A research model was created using consumers' current economic perceptions, future economic perceptions, and importance of fashion as predictors of apparel expenditures. Demographic variables were included to see if demographics had any significant influence on current and future perceptions, importance of fashion, and/or apparel expenditures. Data for this study was obtained by administering a paper and internet survey to 166 consumers in the stratified market of Roanoke, VA. One-way ANOVA analysis findings indicate that age had an influence on consumers' future economic expenditures. Age and education had an influence on consumers' importance of fashion, while marital status had an influence on apparel expenditures. Regression analysis indicated that consumers' perceptions of current and future economic conditions and importance of fashion were significant predictors of consumers' apparel expenditures. Recommendations include collecting real expenditure amounts, comparing perceived economic conditions data to real economic indicators, and comparing Consumer Expenditure Survey data with real economic indicators.
- The Efffects of Workplace Financial Education on Personal Finances and Work OutcomesKim, Jinhee (Virginia Tech, 2000-04-14)The purpose of this research was to examine the effects of workplace financial education on workers' personal finances and work outcomes and determine relationships among financial management (attitudes, knowledge and behaviors), financial well-being, personal finance-work conflict, and work outcomes with data of white-collar workers in an insurance company in mid-western states. Research questions were (1) What are the profiles of financial attitudes, financial knowledge, financial behaviors, financial well-being, personal finance-work conflict, productivity, absenteeism, work time use, organizational commitment, pay satisfaction, loyalty, and intention to leave?, (2) Do the profiles of financial attitudes, financial knowledge, financial behaviors, and financial well-being differ by the individual characteristics?, (3) Do the profiles of personal finance-work conflict, productivity, absenteeism, work time use, organizational commitment, and pay satisfaction differ by the individual characteristics?, (4) What are the relationships among financial attitudes, financial knowledge, financial behaviors, financial well-being, and work outcomes (productivity, absenteeism, organizational commitment, and pay satisfaction)?, (5) What are the effects of workplace financial education on financial attitudes, financial knowledge, financial behaviors, financial well-being, and work outcomes?, and (6) What are the individual profiles of workplace financial education including participation, value of workplace financial education, reasons for participation and non-participation, desire for financial check-up, and desired topics of workplace financial education? The research design was a pre- and post-assessment survey. A pre-assessment survey was conducted in February and March 1999 before workplace financial education was provided during March 1999. One-and one-half hour workplace financial education workshops were provided at no cost to employer or employees in March 1999. Three months after the workplace financial education was provided, a post-assessment survey was conducted from June through August 1999. A pre-assessment questionnaire was mailed to all 476 workers (five were undeliverable) and 262 responses were utilized for data analysis. In the post-assessment, 482 questionnaires were mailed to workers and five were undeliverable. Usable return rates for the data analysis were 56.0% in the pre-assessment (262/471) and 40.0% in the post-assessment (189/477). Overall, the respondents in this study were somewhat positive toward financial management, were not knowledgeable on financial matters, and were practicing their financial behaviors fairly well. Objective financial well-being measures showed that workers were in fairly good financial condition but the levels of subjective financial well-being were about the mid-point on a scale, when each score was converted into a percentage. The workers reported that they were very productive, did not miss work days frequently, were highly committed to their organization, and they showed fairly high levels of pay satisfaction. Workers were very hesitant to admit to direct questions asking about whether or not their financial concerns interfered with their responsibilities at the workplace while they were not always able to do normal work even though they were present in the office and spent some work time handling financial matters. Some of individual characteristics influenced financial attitude, financial knowledge, financial behavior, financial well-being, personal finance-work outcomes, and work outcomes. The tests of the structural equation model showed that worker's personal finances had direct and indirect effects on work outcomes. The financial well-being had a negative effect on personal finance-work conflict. The financial well-being had direct effects on negative work time use and pay satisfaction. The financial well-being had indirect effects through personal finance-work conflict on absenteeism, negative work time use, and organizational commitment. The t-test results did not show the significant effects of workplace financial education on personal finances and work outcomes between the pre- and the post-assessment.
- Families Taking Charge. Taking InventoryLeech, Irene E. (Virginia Cooperative Extension, 2009-05-01)Families Taking Charge is a multi-part series for individuals and families experiencing financial stress as a result of difficult economic times. This publication focuses on taking inventory of assets you have that could be used to meet your obligations.
- Families Taking Charge. Talking With CreditorsLeech, Irene E. (Virginia Cooperative Extension, 2009-05-01)Families Taking Charge is a multi-part series for individuals and families experiencing financial stress as a result of difficult economic times. This publication focuses on talking with creditors.
- Families Taking Charge. What's Next?Leech, Irene E.; Sporakowski, Michael J. (Virginia Cooperative Extension, 2009-05-01)Families Taking Charge is a multi-part series for individuals and families experiencing financial stress as a result of difficult economic times. This publication focuses on what's next after financial problems.
- Frequency Monitoring Network (FNET) Algorithm Improvements and Application DevelopmentXia, Tao (Virginia Tech, 2009-12-07)The Internet Based real-time GPS synchronized wide-area Frequency Monitoring Network (FNET) is an extremely low cost and quickly deployable wide-area frequency measurement system with high dynamic accuracy which consists of Frequency Disturbance Recorder (FDR) distributed to more than 100 places around North America and an Information Management System situated at Virginia Tech. Since its first FDR deployment in 2003, the FNET system has been proved to be able to reliably receive phasor data accurately measured at and instantaneously sent via the Internet from different locations of interest, and efficiently run the analyzing program to detect and record significant system disturbances and subsequently estimate the location of disturbance center, namely the event location, in the electric grid based on the information gathered. The excellent performance of the FNET system so far has made power grid situation awareness and monitoring based on distribution level frequency measurements a reality, and thus advances our understanding of power system dynamics to a higher level and in a broader dimensionality. Chapter 1 and Chapter 2 of this dissertation briefly introduce the genesis and the architecture of the FNET system, followed by a summary of its concrete implementations. Chapter 3 and Chapter 4 outline FNET frequency estimation algorithm and phase angle estimation algorithm, including their attributes and the new methodologies to enhance them. In Chapter 5, the report discusses the algorithms developed at FNET to detect the frequency disturbance and estimate the disturbance location by the triangulation procedure using real-time frequency data and geographic topology of the FNET units in the power grid where the disturbance occurs. Then, the dissertation proceeds to introduce the FNET angle-based power system oscillation detection and present some research about Matrix Pencil Modal Analysis of FNET phase angle oscillation data in the following two chapters. Lastly, the content of this report is summarized and the future work envisioned in Chapter 8.
- Getting Out of DebtLeech, Irene E.; Scott, Elaine D.; Hayhoe, Celia Ray (Virginia Cooperative Extension, 2009-05-01)If making credit repayments has become difficult, there are steps you may take to improve the situation. This publication focuses on those steps and includes worksheets and a sample letter.
- High Power Density and High Temperature Converter Design for Transportation ApplicationsWang, Ruxi (Virginia Tech, 2012-06-25)The continual development of high-power-density power electronic converters is driven particularly by modern transportation applications like electrical vehicles and more electric aircraft where the space and carrier capability is limited. However, there are several challenges related to transportation applications such as fault tolerance for safety concern, high temperature operation in extreme environments and more strict electromagnetic compatibility requirement. These challenges will increase difficulties for more electrical system adoption in the transportation applications. In this dissertation, comprehensive methodologies including more efficient energy storage solution, better power electronics devices capability, better packaging performance and more compact EMI filter design are analyzed and proposed for the goal of high power density converter design in transportation applications.
- Home Repair Experiences of Older Consumers in Montgomery County, VirginiaCampbell, Cristin L. (Virginia Tech, 1998-10-13)This study was designed to explore the offers for home repair received at their door by older consumers and the decisions that were made regarding these offers. Deacon and Firebaugh's decision making process was used as the theoretical model for this study. Participants were asked questions about their experiences with door-to-door solicitations for home repair and how they made the decision to accept or reject the offer. The participants in this study were twenty-five older consumers involved in senior groups in Montgomery County, Virginia. Participants were obtained by the researcher at meetings in different parts of the county. A telephone interview was used to collect the data. Demographic data is reported using descriptive statistics. Qualitative analysis of anecdotal data was used to determine themes and patterns in the interview data. Questions about uses of the media and knowledge of the Virginia Consumer Protection Hotline were asked. The results of this study support the idea that older consumers in this county are being approached at their door by people offering them home repair services. Two of the six participants who had received an offer for home repair (specifically driveway sealing), accepted the offer. One participant was unhappy with the outcome of the repair, while the other was satisfied with the service.
- Household filing system : what do I keep and for how long?Scott, Elaine D.; Leech, Irene E.; Porter, Nancy M. (Virginia Cooperative Extension, 1991)Discusses which household records to keep and how to organize and file them.
- Housing Market Choice Patterns of Single Women HomeownersWood, Rebecca S. Jr. (Virginia Tech, 1998-05-21)Housing researchers are aware of the lower homeownership rates and other housing problems of single women but there is very little research focusing on single women homeowners or the characteristics of the housing they buy. Also, since a wide body of research can be found that examines determinants of homeownership for various population groups, the importance of this study was in its focus on single women homeowners and the characteristics of their housing rather than the determinants of ownership for this group. Using data from the 1993 American Housing Survey (AHS), the study sample consisted of 639 women homeowners who were either widowed, divorced, separated, or never-married, and who did not own their previous residence. The study's purpose was to construct a profile of single women home- owners that included a description of their demographic and housing characteristics, the means by which they acquired their homes, and the changes made in their housing when they became homeowners. Additionally, this study examined which demographic and previous housing characteristics of this group were related to the housing characteristics of their present homes. Descriptive results from this study suggested that single women homeowners are primarily middle aged without young children at home, earn moderate incomes, and that the largest proportion of them live in the South and metropolitan areas. When compared to homeowners in general, single women homeowners' homes cost less and represented a higher proportion of attached and mobile home units. The results also showed that single women used low-down payment financing instruments to a lesser degree than did all homeowners. Results from statistical analyses suggested that significant relationships exist between single women homeowners' housing characteristics, and a) their demographic characteristics, b) their previous housing characteristics, and c) their reasons for moving and selecting their current homes and neighborhoods. Another key finding was that single women homeowners of varying marital status differed in their present and previous housing characteristics and their reasons for selecting the current home. The results of this study support suggestions made by other researchers that examining differences not only by gender but also by the variations in marital status will help to clarify and add to the knowledge of housing and its relevance to populations of varying social composition.
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