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      • Analysis of a Water Vapor Helicon Thruster Using Emission Spectroscopy

        Faust, Adriane J University of Maryland, College Park ProQuest Diss 2019 해외박사(DDOD)

        RANK : 247343

        A helicon thruster was developed to research the use of emission spectroscopy diagnostics. Helicon thrusters differ from conventional electric propulsion systems in that the conductive components that power the thruster do not contact the plasma propellant. Because of this design, propellants that would be corrosive in conventional thrusters can be used in the helicon thruster. Water vapor is a possible propellant option because it is cheap, easy to store, and available in space for refueling, making it an attractive choice for deep space missions. Conventional invasive plasma diagnostics do not work reliably with water vapor plasma because it is corrosive and contains multiple species of positively and negatively charged particles, which probes that measure only plasma current are unable to distinguish. These probes can also have measurement errors in the presence of radio frequency, electric, or magnetic fields, making analysis of thruster performance difficult. This research explores the validity of a non-invasive diagnostic technique using emission spectroscopy with a helium seed gas to determine the plasma parameters for any propellant. A helium collisional radiative model was developed to estimate electron temperature and density from helium emission line ratios measured experimentally. Thruster tests conducted with pure helium were used to compare the collisional radiative model to existing models. Tests with pure argon and an argon/helium mix allow for a comparison of Langmuir probe measurements to the emission spectroscopy results and verification that the helium gas seeding does not significantly affect the thruster performance. The diagnostic technique is then tested on a water vapor/helium mix. The estimates for the electron density predicted those measured by the conventional probes well, but the diagnostic technique is less reliable for electron temperature at the experimental conditions.

      • On the Splitting of a Quantum Degenerate Gas of Identical Bosons

        Faust, Douglas Karl University of Washington 2011 해외박사(DDOD)

        RANK : 247343

        The observation of Bose-Einstein condensation in dilute clouds of trapped atoms has stimulated a great deal of research in the last 15 years. Since the basic description of a single Bose-Einstein condensate (BEC) is that of a single macroscopic condensate wavefunction, or condensate order parameter, which displays all of the interference and non-local phenomena associated with the typical quantum mechanical wavefunction, yet describes up to millions of particles, these systems have the potential to bridge the quantum mechanical and visible classical worlds. Many basic scientific questions can be addressed by examining what happens when a single such system is split into multiple entities, independently manipulated and then recombined as has been done experimentally in the case of two potential welts [1] and many potential wells [2], [3]. This thesis shows that these experiments can operate in both a classical and quantum mechanical splitting regime and demarcates the boundary in between the two. By analyzing two specific BEC splitting experiments, it is shown that splitting experiments operating in the limit of a large number of particles per well can exhibit a phenomenon analogous to supercooling in classical phase transitions. In order to perform these simulations, a novel method, extending earlier theoretical work on the splitting problem is presented, computationally implemented, and supported by analytic calculations when possible.

      • Transforming growth factor beta, allograft acceptance and chronic allograft rejection

        Faust, Susan Marie University of Michigan 2009 해외박사(DDOD)

        RANK : 247343

        Chronic allograft rejection (CR) is the main barrier to long-term transplant survival. CR is a progressive disease defined by interstitial fibrosis, vascular neointimal development, and graft dysfunction. The underlying mechanisms responsible for CR remain poorly defined, although transforming growth factor beta (TGFbeta) has been strongly implicated in promoting fibrotic diseases and CR. However, TGFbeta is a suppressive cytokine, which may be beneficial in the transplant setting; Hence, an in depth assessment of the fibrotic and anti-inflammatory activities of TGFbeta in cardiac transplant was performed. In this study, the role of TGFbeta on graft-reactive cellular and humoral responses, T regulatory cell (Treg) function, allograft acceptance and the progression of CR are assessed. These studies identify TGFbeta dependent and independent pathways to allograft acceptance, and investigate the contribution of TGFbeta-induced IL-17 in the progression of CR. Since TGFbeta exhibits exacerbating or ameliorating characteristics depending on the site of action, TGFbeta neutralization within the allograft addresses local TGFbeta inhibition on fibrosis and graft-reactive T and B cell responses. Studies in this dissertation provide insight into the underlying causes of CR and identify therapeutic targets for treatment of this disease.

      • Factors associated with participation of learners in college freshman multi-age classes

        Faust, Debra Fair University of Georgia 2000 해외박사(DDOD)

        RANK : 247343

        The purpose of this study was to identify and describe factors associated with participation of learners in the multi-age college classroom. Besides the multi-age component, I was interested in the perspectives of first-time freshmen because of the lack of research on participation for first-time freshmen in multi-age classrooms. Consequently, a Freshman English course was chosen for the study. Twenty students were in this class—30 percent adult students and 70 percent traditional-age students. Fifty-five percent were first time freshmen. The predominant means of data collection were semi-structured interviews with ten students who were first-time freshmen—six traditional-age and four adult students—and participant observations. All participants were interviewed twice individually and once in a group interview. Their ages ranged from 18 to 39 years of age. Observations took place on a weekly basis throughout the semester. Field notes were taken from observations. The constant comparative method of data analysis was applied to the in-depth interviews. Three areas of inquiry were examined: (1) learners perceptions of each other as students; (2) interactions in a multi-age undergraduate class; and (3) classroom environment. Two major themes associated with participation emerged from the data analysis, both of which were not related to age. The first, <italic>Classroom Environment</italic>, described how the classroom environment influenced participation. Three categories emerged from the data on the Classroom Environment: physical structure of the classroom, social climate, and instructor influence. The second theme, <italic>Nature of Interactions</italic>, described how different types of interactions influenced participation. Two categories emerged from the data on the Nature of Interactions: social interactions and course-focused interactions. Four conclusions were reached based on these findings: (1) the physical structure of the classroom influences student participation and student-to-student interaction; (2) the expectations and teaching style of the instructor influences participation; (3) discussion patterns are established early in the semester and hinders some students' participation; and (4) the social climate affects participation. Overall, findings yielded the same results for traditional-age and adult students. Implications for adult and higher education are presented, and recommendations were made for future research.

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