Thesis (M.Sc.)--York University, 2005. Graduate Programme in Computer Science. / Typescript. Includes bibliographical references (leaves 146-148). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11740

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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The purpose -of this work is to discuss the symmetry, or lack of it, under reversal of motion in physical objects, states and processes. Considerations of such symmetry are made in both classical and quantum physics, notably in the problem of reconciling the assumed time-reversal symmetry of microscopic processes with the observed asymmetry of macroscopic processes. In the case of classical mechanics, a simple model of a free particle colliding with a series of almost stationary or stationary particles of smaller mass is introduced in order to show how a friction-like phenomenon can arise from processes all of which have symmetry under reversal of motion. It is maintained throughout that symmetry under reversal of motion is a property of all fundamental states and processes in nature. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Thesis (Ph D.)--University of Nevada, Reno, 2007. / "May 2007." Includes bibliographical references (leaves 61-63). Online version available on the World Wide Web.

Please read the abstract in the front of the document. / Dissertation (MSc)--University of Pretoria, 2009. / Physics / unrestricted

There are two classes of phononic structures that can support elastic waves with non-conventional topology, namely intrinsic and extrinsic systems. The non-conventional topology of elastic wave results from breaking time reversal symmetry (T-symmetry) of wave propagation. In extrinsic systems, energy is injected into the phononic structure to break T-symmetry. In intrinsic systems symmetry is broken through the medium microstructure that may lead to internal resonances. Mass-spring composite structures are introduced as metaphors for more complex phononic crystals with non-conventional topology. The elastic wave equation of motion of an intrinsic phononic structure composed of two coupled one-dimensional (1D) harmonic chains can be factored into a Dirac-like equation, leading to antisymmetric modes that have spinor character and therefore non-conventional topology in wave number space. The topology of the elastic waves can be further modified by subjecting phononic structures to externally-induced spatio-temporal modulation of their elastic properties. Such modulations can be actuated through photo-elastic effects, magneto-elastic effects, piezo-electric effects or external mechanical effects. We also uncover an analogy between a combined intrinsic-extrinsic systems composed of a simple one-dimensional harmonic chain coupled to a rigid substrate subjected to a spatio-temporal modulation of the side spring stiffness and the Dirac equation in the presence of an electromagnetic field. The modulation is shown to be able to tune the spinor part of the elastic wave function and therefore its topology. This analogy between classical mechanics and quantum phenomena offers new modalities for developing more complex functions of phononic crystals and acoustic metamaterials.