UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Repositioning Cognitive Kinds(2022) Roige Mas, Aida; Carruthers, Peter; Philosophy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation puts forward a series of theoretical proposals aimed to advance our understanding of cognitive kinds. The first chapter introduces the general debates that provide the philosophical underpinnings for the topics addressed in each of the following chapters. Chapter two compares and distinguishes between modules of the mind and mechanisms-as-causings, arguing that they should not be conflated in cognitive science. Additionally, it provides a novel “toolbox” model of accounts of mechanisms, and discusses what makes any such account adequate. Chapter three addresses the question of whether there is a role within the new mechanistic philosophy of science for representations. It advances a proposal on how to carve working entity types, so that they may include representational explanans. Chapter four offers an account of mental disorders, one that captures the regulative ideal behind psychiatry’s inclusion of certain conditions as psychopathologies. Mental disorders are alterations in the production of some mental outputs (e.g. behaviors, beliefs, emotions, desires), such that their degree of reasons-responsiveness is extremely diminished with respect to what we would folk-psychologically expect it to be.Item RELIABILITY OF CERAMIC ELECTRODES OF SOLID OXIDE FUEL CELLS(2018) Patel, Nripendra Kumar; Pecht, Michael G; Das, Diganta; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid oxide fuel cells (SOFCs) are highly efficient chemical to electrical energy conversion devices that have potential in a global energy strategy. The wide adoption of SOFCs is currently limited by cell durability and manufacturing cost. Ceramic anodes show promise for improved durability and are prominent candidate for electrodes of SOFCs. Ishikawa diagram was developed and a comprehensive failure modes, mechanisms, effects, and criticality analysis (FMMECA) methodology is applied to ceramic anodes of SOFCs to understand possible causes of failure. Despite high conductivity and better performance of conventional ceramic electrodes i.e. strontium-based perovskite electrodes, there is a concern that humidity, especially high humidity and high temperature, during storage can affect the properties prior to installation. Degradation mechanisms which can manifest themselves during storage was found and empirical degradation model was developed to determine the storage specification for strontium-based perovskite electrodes of SOFCs.Item FAILURE MECHANISMS OF ULTRA HIGH MOLAR MASS POLYETHYLENE SINGLE FIBERS AT EXTREME TEMPERATURES AND STRAIN-RATES(2017) Jenket II, Donald Robert; Al-Sheikhly, Mohamad; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of temperature and strain-rate on the mechanical properties of Ultra High Molar Mass Polyethylene (UHMMPE) single fibers was investigated at eleven temperatures from room temperature (20 °C) to the orthorhombic-hexagonal phase transition (148 °C) and at six strain-rates from quasi-static (10-3 s-1) to dynamic (103 s-1). Dimensional analysis of ballistic limit tests using has shown an underperformance of materials comprised of UHMMPE fibers. A possible explanation is the relatively low melting temperature of UHMMPE fibers (~150 °C) in comparison to other fiber materials, such as poly-aramids (~450 °C). The mechanical properties of UHMMPE single fibers were investigated through a series of 437 tensile tests at 66 temperature-strain-rate combinations. Changes in stress-strain curve shapes were observed with respect to temperature and strain-rate. The transition of stress-curve shape with increasing temperature was observed to be pseudo-brittle, plateauing, necking, and non-failure and transitions between these phases were observed within a strain-rate dependent temperature range. For low and intermediate strain rates, a temperature and strain-rate equivalence is observed: a decadal increase of strain-rate is mechanically equivalent to a ~20 °C decrease in temperature. Strain to failure for dynamic strain rates was invariant over the temperature range of this study. Strength and modulus properties were observed to decrease with increasing temperature and increase with increasing strain-rate. An orthorhombic to hexagonal phase transition occurs between 145 °C and 148 °C and a sudden decrease in strength and moduli was observed. The change in dominant stress-relieving mechanism is proposed. Chain slippage is dominant for the majority of conditions in this study except where scission and straightening are the dominant mechanism. At high temperatures for constrained fibers in the hexagonal phase, chain slippage occurs more frequently due to the trans to gauche conformation. Chain scission is only dominant moments before fiber failure and near the failure surface. Chain straightening is dominant at low strain (0 % to 0.5 %) and at temperatures greater than or equal to the necking temperatures for the quasi-static and intermediate strain-rates and at all temperatures for the dynamic strain-rates.