Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item PERFORMANCE OF ELECTRIC MEDIUM-SIZED VARIABLE-RPM ROTOR AND SHROUDED ROTOR(2022) Ryseck, Peter Christian; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electric variable RPM rotors are increasingly being used for propulsion and control of unmanned air vehicles. As these vehicles scale to carry heavier payloads of 50 to 400 lbs (20 to 180 kgs) in the group 2 and 3 UAS category, there are concerns about their aerodynamic performance and handling quality degradation. Therefore, there is a need to develop a systematic experimental testing procedure to measure loads on these systems to evaluate performance and augment Computational Fluid Dynamic (CFD) validation tools. In this work, a universal electric powered test rig is designed and fabricated for hover and wind tunnel tests of open and shrouded rotors. Steady hover results are validated using blade element momentum theory. These predictions incorporate an empirical correction approach in conjunction with an interpolation scheme to capture Reynolds number variation along the span of the blade and variation with RPM. Results show good agreement with the interpolation method for the low Reynolds number rotor tested (Re_tip<500,000). For the variable RPM rotor, transient step and chirp inputs are also presented. System identification showed linear frequency responses between thrust and torque with RPM and RPM-square in hover. Therefore, when modeling this rotor, steady inflow appears adequate in the frequency range of interest (0.4 to 60 rad/sec). In addition to an open rotor, the electric motor-rotor test stand was used to test a shrouded rotor in hover and forward flight to systematically compare performance results. Test data showed the shrouded rotor gained 15% thrust for the same power in hover with the best configuration. For low speed forward flight, lift-to-drag ratio was found to increase by 8 to 10% for the shrouded rotor system over the isolated rotor.Item The effects of classroom autonomy, staff collegiality, and administrative support on teachers' job satisfaction(2013) Lasseter, Austin; Lasseter, Austin; Education Policy, and Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of my dissertation is to determine which job-related factors are most likely to explain teachers' sense of satisfaction with their current job. Based on previous research (Fairchild et al., 2012; Lee, Dedrick, & Smith, 1991; Perie & Baker, 1997), I hypothesized that teachers' perceptions of classroom autonomy, staff collegiality, and administrative support would have a greater impact on teachers' job satisfaction than demographic characteristics of either teachers or schools. My study used a dataset of 19,130 teachers in 2,420 schools drawn from the 2007-08 Schools and Staffing Survey (SASS). The study employed a two-level hierarchical linear modeling (HLM) technique. I modeled the key constructs at both the individual and collective levels by conceptualizing autonomy, collegiality, and support as individual teachers' perceptions and as the average of all teachers' perceptions in the school. My dissertation found that individual teachers' perceptions of classroom autonomy, staff collegiality, and administrative support had a greater impact on teachers' job satisfaction than demographic characteristics of schools and teachers. In addition, my study found that school-wide perceptions of classroom autonomy, staff collegiality, and administrative support had a significant effect on teachers' job satisfaction over and above the effects of individual teachers' perceptions. The study found significant negative effects on job satisfaction for teachers working in Catholic schools and for teachers working in schools where poverty was perceived to be a school-wide problem. Finally, my study determined that sufficient between-school variance existed in the outcome to justify future school-level policy interventions aimed at improving teachers' job satisfaction. Based on my findings, I recommend that policy makers who are concerned about addressing low levels of job satisfaction among teachers should begin by improving factors related to classroom autonomy, staff collegiality, and administrative support, since these are likely to have a meaningful impact. I also recommend that future research should employ a narrow definition of the outcome focusing on teachers' satisfaction with their job rather than their satisfaction with teaching in general.Item Rejuvenating the Developmental State in Taiwan: the Impacts of the EIA as an Environmental Governance (2006-2011)(2011) Chen, Ying-Feng; Kastner, Scott; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Asian Tigers were sometimes referred to "developmental states" for they were capable of designing successful development agendas and implementing these plans with the compliance of private capital instead of simply regulating the market. However, with the fast democratic transition during the 1990s, the developmental state encountered serious challenges from business sectors, opposition parties and civil groups. Some literature suggested that this infiltration of private sector jeopardized the state's autonomy in formulating long-term plans. The chaotic policy process at the early stage of democratic transition revealed Taiwan state's capability in controlling developmental agendas has been weakened. If the developmental state of Taiwan ceased to function, in what way did it evolve? This dissertation aimed to answer this question by examining the role of the Taiwan state in promoting three major investments, the Formosa Steel-making Plant, the Central Taiwan Science Park in Holi-Chixing and Erlin, and the Eighth Petrochemical Plant, from 2006 to 2010. While developmental states were often argued incompatible with democratic regimes, this dissertation demonstrated that the status of Taiwan's developmental state remained firm after democratic transition given that the state was still autonomous in terms of defining and preserving national interests. Furthermore, it WAS the public participation and environmental institutional monitoring brought by democratic transition that reinforced the developmental state in Taiwan by correcting the state's errors in promoting those inefficient projects. Through the interdependent governance in the review mechanisms, these industrial programs based on outdated development agendas were smoothly postponed. Some programs were even called off by the corporations themselves. The democratic transition did not lessen politicians' pursuit of constant national economic development; moreover, it brought in correcting mechanisms and thus further reinforced the capacity of the developmental state in choosing developmental agendas.Item A Mixed-Methods Study of Perceived Academic Autonomy in Japanese Students and Its Relations to Their Motivation(2006-08-04) Tonks, Stephen; Wigfield, Allan; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Numerous studies link intrinsic motivation to positive outcomes such as increased cognitive engagement, task persistence, achievement, and creativity (Ryan & Deci, 2000a). In Self-Determination Theory (SDT), Ryan and Deci (2002) propose that high autonomy, or perceiving that one is the origin of one's own behavior, is a necessary component of high intrinsic motivation. Significantly, in SDT, this relation is claimed to be universal. Studies in Western cultures show that when teachers support students' autonomy, the students show higher intrinsic motivation and achievement (Reeve, 2002). This study investigated academic autonomy in Japanese children, as little work has been done in different cultures to test the claim that autonomy is universal. Some research contradicts the universality notion by suggesting that in Japan autonomy may not be an important factor in students' motivation (e.g., Markus & Kitayama, 1991). The current study uses a mixed-methods design to address this issue. Initially, interviews were conducted with 30 5th and 6th grade Japanese students to address the validity of the Self-Regulation Questionnaire-Academic Domain (SRQ-A; Ryan & Connell, 1989), a frequently used measure of perceived autonomy that asks students why they do academic activities. Japanese students mentioned several reasons that were not on the SRQ-A. Therefore, new items were developed to create the Japanese SRQ-A (J-SRQ-A). Next, 179 Japanese 5th and 6th grade students completed the SRQ-A and 208 completed the J-SRQ-A. Exploratory factor analyses showed that the degree of autonomy associated with reasons for certain academic behaviors may be different for Japanese than western students, raising questions about the universality of autonomy. Confirmatory factor analyses showed that a respecified model using the J-SRQ-A provided the best model fit when compared to models using the original SRQ-A, providing further evidence that the structure of autonomy is not universal. Correlations among scales representing differing levels of autonomy were similar to those found in previous research. Positive correlations between autonomy and intrinsic motivation were similar in strength to those in previous research, indicating some support for the SDT claim that autonomy's benefits are universal.