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 Follow the Leaders: Policy Presentation in the U.S. Congress(2022) Gaynor, SoRelle Wyckoff; Miler, Kristina; Government and Politics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents a theory of policy presentation in the U.S. Congress. I define policy presentation as the strategic development and distribution of partisan information to explain major legislative decisions by congressional leaders. Today, rank-and-file members, increasingly removed from the legislative process, rely on guidance from congressional leaders to discuss major legislative decisions with their constituents. As a result, preparing constituent communication materials has become an institutionalized responsibility for party and committee leaders, particularly for House Republicans. I also argue that policy presentation is an undocumented source of partisan polarization, as it incentivizes a partisan presentation of legislative activity—even in cases of bipartisanship and compromise. Using interviews with members of Congress and staff, computational text analysis, and social network analysis, I demonstrate how congressional leaders develop and distribute partisan messages for constituent use. I also document the conditions under which policy presentation occurs, and the members most likely to rely on party and committee leaders for assistance with constituent communication.Item POLARIZATION-PRESERVING WAVEGUIDE FILTER FOR ASTRONOMICAL APPLICATIONS(2005-11-29) Vanin, Felice Maria; Zaki, Kawthar; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As part of NASA's Beyond Einstein Program, the characterization of the Cosmic Background polarization has become a high priority for NASA. Since 2002, the efforts in which NASA is engaged are the first steps in the development of the instrumentation to achieve this vision. The critical systems that have previously caused the most losses have to be replaced. Microwave waveguide components are ideal to replaces old systems, improving accuracy of measurement and reducing the losses. In this work, a novel microwave waveguide filter and transformer are presented and discussed. The filter has been designed with 30% fractional bandwidth, guaranteeing extreme stop-band performances by using a quadruple ridge waveguide cross section. The waveguide component exhibits four-fold-symmetry preserving the dual polarization state of the electromagnetic field and resulting ideal for astronomical detections. Moreover, the important suppression of the fundamental mode re-resonance by using attenuation zeros is also discussed.Item Spin injection and detection in copper spin valve structures(2005-01-25) Garzon, Samir Y; Webb, Richard A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We report measurements of spin injection and detection in a mesoscopic copper wire from which the electron spin relaxation time and the spin current polarization in copper can be found. Spin injection is realized by applying a voltage to drive a current from a ferromagnet into the normal metal, while spin detection is done using transport measurements. Precession of the spin of the injected electrons due to an external magnetic field is also studied. The existence of a previously unobserved spin signal which vanishes at low temperatures but increases nonlinearly above 100K is reported and a possible explanation for its origin, based on interfacial spin-flip scattering, is suggested. Multiple cross checks to test the possibility of artifacts as an origin of this signal are discussed. An alternative spin detection method using magnetic force microscopy (MFM) is also studied. This method measures the magnetic field produced by the injected spins directly, so the spin coherence length and the spin current polarization can be extracted directly without the need of a particular transport model, avoiding issues like contact resistance and interface scattering. The MFM method can also be useful for measuring the spin polarization of currents in semiconductors and semiconductor heterostructures, which is important for the development of spintronics.