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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Thermal Drilling and Anchoring on Icy Planetary Bodies(2020) Halperin, Adam Hugh; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Europa is of scientific interest because it is made primarily of water, may have subsurface liquid oceans, and has active cryovolcanoes. Despite the cryogenic surface temperatures, ambient vacuum pressure, and high levels of radiation, potential missions to its surface or its subsurface oceans are topics of current research. Exploring Europa’s surface poses an interesting challenge because of these ambient conditions. Furthermore, any regions of crevasses, ridges, penitentes, cryovolcano formations, and other extreme terrains would be inaccessible to existing rover designs. The “thermal pick” proposed here is a novel system to enable a rover to traverse even the most extreme Europan terrains. It is a dual-function system that first uses a thermal drilling process to burrow into Europa’s surface ice and then serves as an anchor, supporting the mobility of the rover to which it is attached. Thermal drilling provides high reliability but can be energetically costly. An intermittent thermal drilling approach was developed that dramatically reduces the primary drivers of energy cost for thermal drilling in cryogenic ices. Since thermal drilling can cause thermally induced ice fracturing, operational conditions that minimize the likelihood of ice failure modes were established. Three test rigs, two end effectors, and over ten thermal picks were prototyped and tested. Testing with dry ice at atmospheric pressure and testing with cryogenic water ice in a vacuum chamber provided an understanding of thermal drilling in the sublimation and melting regimes, respectively. This testing demonstrated efficiencies of up to 90% relative to ideal sublimation with dry ice and efficiencies of up to 50% relative to melting with cryogenic water ice under vacuum. For safe mobility in the toughest icy terrains, a single anchor should be capable of supporting an entire rover’s weight. Anchoring strengths in excess of 130N were demonstrated, which is the full weight of 100kg on Europa. This 130N anchoring force was supported by even the weakest anchor tested, suggesting potentially greater anchoring loads can be supported.Item The Long Shot(2017) Zitta, Anthony; Norman, Howard; Creative Writing; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The following stories sew together parts and characters of Pennsylvania that can be neighbor to any, and with that, the reminder that family is the one thing everybody has to deal with and adapt to in order to survive.Item Thermal activation, long-range ordering, and topological frustration of artificial spin ice(2016) Drisko, Jasper Altman; Cumings, John; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Frustrated systems, typically characterized by competing interactions that cannot all be simultaneously satisfied, are ubiquitous in nature and display many rich phenomena and novel physics. Artificial spin ices (ASIs), arrays of lithographically patterned Ising-like single-domain magnetic nanostructures, are highly tunable systems that have proven to be a novel method for studying the effects of frustration and associated properties. The strength and nature of the frustrated interactions between individual magnets are readily tuned by design and the exact microstate of the system can be determined by a variety of characterization techniques. Recently, thermal activation of ASI systems has been demonstrated, introducing the spontaneous reversal of individual magnets and allowing for new explorations of novel phase transitions and phenomena using these systems. In this work, we introduce a new, robust material with favorable magnetic properties for studying thermally active ASI and use it to investigate a variety of ASI geometries. We reproduce previously reported perfect ground-state ordering in the square geometry and present studies of the kagome lattice showing the highest yet degree of ordering observed in this fully frustrated system. We consider theoretical predictions of long-range order in ASI and use both our experimental studies and kinetic Monte Carlo simulations to evaluate these predictions. Next, we introduce controlled topological defects into our square ASI samples and observe a new, extended frustration effect of the system. When we introduce a dislocation into the lattice, we still see large domains of ground-state order, but, in every sample, a domain wall containing higher energy spin arrangements originates from the dislocation, resolving a discontinuity in the ground-state order parameter. Locally, the magnets are unfrustrated, but frustration of the lattice persists due to its topology. We demonstrate the first direct imaging of spin configurations resulting from topological frustration in any system and make predictions on how dislocations could affect properties in numerous materials systems.