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 Dust To Dust: Embracing Entropy Through Organic Building Materials(2022) Muir, Ryan; Williams, Brittany; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Architecture has had a complicated relationship with time. Some architects have chosen to embrace time, while many have chosen to oppose it. Fearful that passing time would overcome their work, many modern architects attempted to suppress its effects. In the commercial realm of today, that fear can largely be characterized by not wanting to be “behind the times”. Commercialism has bred a practice of planned obsolescence that reflects the dynamic, living organism of society, but fails to see buildings themselves as organisms. Our building practices have contributed to an immense amount of waste that is detrimental to our environment. This thesis will test architecture’s ability to embrace the process of entropy through organic building materials and explore the scalability of these methods in the “res-economica” of Washington, DC. This will be applied to three different affordable housing and homeless supportive housing typologies.Item Experimental study of entropy generation and synchronization in networks of coupled dynamical systems(2015) Hagerstrom, Aaron Morgan; Roy, Rajarshi; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis describes work in two areas: unpredictability in a system with both single photon detection and chaos, and synchronization in networks of coupled systems. The unpredictability of physical systems can depend on the scale at which they are observed. For example, single photons incident on a detector arrive at random times, but slow intensity variations can be observed by counting many photons over large time windows. We describe an experiment in which a weak optical signal is modulated by feedback from a single-photon detector. We demonstrate that at low photon rates, the photon arrivals are described by Poisson noise, while at high photon rates, the intensity of the light shows a deterministic chaotic modulation. Furthermore, we show that measurements of the entropy rate can resolve both noise and chaos, and describe the relevance of this observation to random number generation. We also describe an experimental system that allows for the study of large networks of coupled dynamical systems. This system uses a spatial light modulator (SLM) and a camera in a feedback configuration, and has an optical nonlinearity due to the relationship between a spatially-dependent phase shift applied by the modulator, and the intensity measured by the camera. This system is a powerful platform for studying synchronization in large networks of coupled systems, because it can iterate many (~1000) maps in parallel, and can be configured with any desired coupling matrix. We use this system to study cluster synchronization. It is often observed that networks synchronize in clusters. We show that the clusters that form can be predicted based on the symmetries of the network, and their stability can be analyzed. This analysis is supported by experimental measurements. The SLM feedback system can also exhibit chimera states. These states were first seen in models of large populations of coupled phase oscillators. Their defining feature is the coexistence of large populations of synchronized and unsynchronized oscillators in spite of symmetrical coupling configurations and homogeneous oscillators. Our SLM feedback system provided one of the first two experimental examples of chimera states. We observed chimeras in coupled map lattices. These states evolve in discrete time, and in this context, ``coherence'' and ``incoherence'' refer to smooth and discontinuous regions of a spatial pattern.Item ENTROPY CONSIDERATIONS APPLIED TO SHOCK UNSTEADINESS IN HYPERSONIC INLETS.(2012) Bussey, Gillian Mary Harding; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The stability of curved or rectangular shocks in hypersonic inlets in reponse to flow perturbations can be determined analytically from the principle of minimum entropy. Unsteady shock wave motion can have a significant effect on the flow in a hypersonic inlet or combustor. According to the principle of minimum entropy, a stable thermodynamic state is one with the lowest entropy gain. A model based on piston theory and its limits has been developed for applying the principle of minimum entropy to quasi-steady flow. Relations are derived for analyzing the time-averaged entropy gain flux across a shock for quasi-steady perturbations in atmospheric conditions and angle as a perturbation in entropy gain flux from the steady state. Initial results from sweeping a wedge at Mach 10 through several degrees in AEDC's Tunnel 9 indicates the bow shock becomes unsteady near the predicted normal Mach number. Several curved shocks of varying curvature are compared to a straight shock with the same mean normal Mach number, pressure ratio, or temperature ratio. The present work provides analysis and guidelines for designing an inlet robust to off- design flight or perturbations in flow conditions an inlet is likely to face. It also suggests that inlets with curved shocks are less robust to off-design flight than those with straight shocks such as rectangular inlets. Relations for evaluating entropy perturbations for highly unsteady flow across a shock and limits on their use were also developed. The normal Mach number at which a shock could be stable to high frequency upstream perturbations increases as the speed of the shock motion increases and slightly decreases as the perturbation size increases. The present work advances the principle of minimum entropy theory by providing additional validity for using the theory for time-varying flows and applying it to shocks, specifically those in inlets. While this analytic tool is applied in the present work for evaluating the stability of shocks in hypersonic inlets, it can be used for an arbitrary application with a shock.Item Thermodynamics, Reversibility and Jaynes' Approach to Statistical Mechanics(2006-07-25) Parker, Daniel; Bub, Jeffrey; Philosophy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation contests David Albert's recent arguments that the proposition that the universe began in a particularly low entropy state (the "past hypothesis") is necessary and sufficient to ground the thermodynamic asymmetry against the reversibility objection, which states that the entropy of thermodynamic systems was previously larger than it is now. In turn, it argues that this undermines Albert's suggestion that the past hypothesis can underwrite other temporal asymmetries such as those of records and causation. This thesis thus concerns the broader philosophical problem of understanding the interrelationships among the various temporal asymmetries that we find in the world, such as those of thermodynamic phenomena, causation, human agency and inference. The position argued for is that the thermodynamic asymmetry is nothing more than an inferential asymmetry, reflecting a distinction between the inferences made towards the past and the future. As such, it cannot be used to derive a genuine physical asymmetry. At most, an inferential asymmetry can provide evidence for an asymmetry not itself forthcoming from the formalism of statistical mechanics. The approach offered here utilises an epistemic, information-theoretic interpretation of thermodynamics applied to individual "branch" systems in order to ground irreversible thermodynamic behaviour (Branch systems are thermodynamic systems quasi-isolated from their environments for short periods of time). I argue that such an interpretation solves the reversibility objection by treating thermodynamics as part of a more general theory of statistical inference supported by information theory and developed in the context of thermodynamics by E.T. Jaynes. It is maintained that by using an epistemic interpretation of probability (where the probabilities reflect one's knowledge about a thermodynamic system rather than a property of the system itself), the reversibility objection can be disarmed by severing the link between the actual history of a thermodynamic system and its statistical mechanical description. Further, novel and independent arguments to ground the veracity of records in the face of the reversibility objection are developed. Additionally, it is argued that the information-theoretic approach offered here provides a clearer picture of the reduction of the thermodynamic entropy to its statistical mechanical basis than other extant proposals.