Generalized modal analysis techniques for the characterization and modeling of dissipationless planar waveguide structures and discontinuities encountered in microwave and optical integrated circuits, as well as of quantum waveguide structures and devices, are presented. The frequency-dependent transmission properties of the curved microstrip bend are derived by utilizing a second-order perturbation analysis of the equivalent modified curved waveguide model and a mode-matching method which includes the higher order modes. An extension of the mode-matching method for characterization of microstrip right-angle bends and T junctions having a rectangular notch is formulated. The modal solutions for an arbitrary graded-index dielectric slab waveguide are derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous parallel-plate waveguide model with electric or magnetic walls. These modal solutions are employed in a mode-matching procedure to calculate the transmission properties of a step discontinuity in typical diffused optical dielectric slab waveguides. Power loss calculations for an abrupt offset in a diffused optical waveguide show a smooth increase in radiation loss whereas a sharp transition from almost zero to nearly total radiation loss is found for an abrupt change in diffusion depth. In the analysis of quantum waveguide structures, the modal expansions of the wave function together with a mode-matching technique are utilized. The computed generalized scattering matrices (GSMs) of junctions and uniform waveguide sections are combined via an extended GSM technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right-angle bends and periodic multi-waveguide structures in a split-gate configuration are presented assuming hard wall confinement. For the multisection structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current-voltage characteristics for a double constriction in GaAs are shown, exhibiting a region of negative differential resistance for temperatures up to approximately 60K with a maximum peak-to-valley ratio of over 80:1. Finally, a uniform narrow constriction with an assumed parabolic - like lateral potential confinement is analyzed by utilizing the modal expansion techniques developed for dielectric waveguides. / Graduation date: 1991

ABSTRACT Fan cooling is a fairly mainstream and well-developed technology. Vibration may make users feel uncomfortable. Assembly system may produce different noises right after the adverse effect components were destroyed, such as computer crashed or vibration or fan structural damage subsequently affects their fan reliability. Therefore, small vibration resonance amplification can not be overlooked. The researcher applied a 40 * 40 * 48mm fan to solve the problem of resonant vibration. He found the similar results of the natural frequencies of the structure of the fan by experimental and finite element analysis. In order to improve the vibration resonance, he changed the structural of the fans. In different structural designs, the natural frequencies did not change a lot. The natural frequency switched from 3000Hz to 3200Hz. To avoid the resonant frequency of the assemble fan, the researcher changed the number of fan blades and simulated the flow field. Compared the data to the experimental results, the results of the analysis were reasonable. The results showed the performance of the assembly fan did not necessarily need more leaves. The leaf numbers were from 7 (Inlet Fan) & 4 (Outlet Fan) into 5 (Inlet Fan) & 4 (Outlet Fan). Operation speed was changed from 14500 rpm (Inlet & Outlet Fan) to 15500 rpm (Inlet Fan) &11600 rpm (Outlet Fan). Using the fluid flow analysis, he found the change of the leaf number and operation speed of the fan could effectively avoid the resonance frequency and reduce vibration. An impact analysis was also helped to verify the capacity of the anti-impact of the fan. The structure of the fan after the preliminary design has been shaped mostly. By only changing the structural design to avoid excitation of the resonant frequency is difficult to achieve the effective function. To ensure the product stability, it is necessary to deal with the inducing vibration of the fluid flow.

Modal logics with possible worlds semantics can be used to represent mental states such as belief, goal, and intention, allowing one to formally describe the rational behavior of agents. Agent??s beliefs and goals are typically represented in these logics by primitive modal operators. However, the representation of agent??s intentions varies greatly between theories. Some logics characterize intention as a primitive operator, while others define intention in terms of more primitive constructs. Taking the latter approach is a theory due to Philip Cohen and Hector Levesque, under which intentions are a special form of commitment or persistent goal. The theory has motivated theories of speech acts and joint intention and innovative applications in multiagent systems and industrial robotics. However, Munindar Singh shows the theory to have certain logical inconsistencies and permit certain absurd scenarios. This thesis presents a modification of the theory that preserves the desirable aspects of the original while addressing the criticism of Singh. This is achieved by the introduction of an additional operator describing the achievement of expectations, refined assumptions, and new defi- nitions of intention. The modified theory gives a cogent account of the rational balance between agents?? action and deliberation, and suggests the use of meansends reasoning in agent implementations. A rule-based reasoner in Jess facilitates evaluation of the predictiveness and intuitiveness of the theory, and provides a prototypical agent based on the theory.

Delivering high bandwidth to the individual household or small business is currently a major bottleneck in the high speed network, a problem referred to as the last mile issue. Multimode fibre is widely deployed in the last mile for cost reasons. Recently, the tremendous high-speed data transport potential of multimode fibre has been demonstrated by utilizing offset launch techniques and a laser source. However, modal noise, caused by interference among the various propagating modes of a multimode fibre in the presence of mode selective loss, is a significant roblem when a laser source is employed. This thesis investigates several aspects of modal noise for what we believe to be the first time. By utilizing single mode fibre launching, modal noise is measured at different transverse offset launching positions with both continuous wave and pulse waveform input at several different fibre lengths. Modal noise is also measured for both waveforms in conjunction with a multimode optical fibre taper in an “in line” configuration, and timing jitter is investigated for the case of pulse waveform input. Performance improvements are found in some offset positions with the fibre taper in line. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-11-15 09:37:44.887

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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 396-400). Also available via the Internet.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 188-191). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 122-123). Also available via the Internet.