published_or_final_version / Physics / Master / Master of Philosophy

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The electrical synapse was first described over 50 years ago. Since that time appreciation of its complexity and importance has grown, including the hypothesis that early transient formation of these synapses is important to adult patterns of connectivity in neural networks. Presented in this dissertation are studies utilizing identified neurons in cell culture from the snail Helisoma trivolvis to examine discrete periods of electrical synapse formation during regeneration with sustained or transient expression. Extensive knowledge of connectivity patterns of the buccal neurons of Helisoma in cell culture and the ganglia, provide a useful framework for looking at modulation and manipulation of electrical synapses and their impact and emerging connectivity in a simple neuronal network. Two types of electrical connections were observed those that were transient, between a B19 and a B110 and those that were sustained, between a B19 and another B19. Dopamine (DA) modulation of forming electrical synapses (FES) produces a synapse specific effect at those either destined to be transient (TES) or sustained (SES) and may be a direct effect on the gap junctions at the synapses, as is the case at TES, or an indirect effect on other membrane currents, as seen in SES. DA modulation produces different outcomes at SES-centered networks and TES-centered networks with respect to new chemical synapse formation, demonstrating network-dependent effects of electrical synapse modulation. Pharmacological blockade of chemical and electrical components at forming mixed synapses in some cases alters subsequent synapse formation although due to the variable nature does not appear to be a direct interaction between chemical and electrical synapses. Three-cell networks appear to display a balancing mechanism for overall electrical coupling when electrical synapses are blocked suggesting a competition for some resource in the construction or trafficking of gap junctions. In addition to electrophysiological examinations, network coupling can be assessed utilizing fluorescent calcium imaging to look at coincidence of calcium changes as an output for coupling between cells. This technique provides a useful tool for less invasive studies of neuronal networks and the impact of coupling at mixed synapses.

We numerically solve the Gross-Pitaevskii equation and the Bogoliubov de Gennes equations for a double well potential in order to model the dynamics of a Bose-Einstein condensate in a Josephson junction. First, the two dynamical regimes of the Josephson junction, that is, Josephson oscillations and self-trapping, are investigated under the application of a large sudden perturbation. It is found that the Josephson dynamics have a strong dependence on the strength of the interatomic interaction, and we observe the breakdown of the two-mode approximation. Second, we study the control of the dynamics through the use of a time-dependent, tilted double well potential. In the context of complete population transfer, the effect of the interactions on the adiabaticity and self-trapping is discussed in terms of a Landau-Zener-like model. We then explore the splitting of the condensate and the resulting dynamical behaviour by keeping the interaction strength constant, but changing the rate of the tilt sweep. Lastly, we examine the effect of the tilt sweep rate on the dynamics of population transfer. We observe a dependence of the self-trapping on the adiabaticity. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-10 16:31:43.127

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We derive an analytical model for the depletion capacitance of silicon-on-insulator (SOI) optical modulation diodes. This model accurately describes the parasitic fringe capacitances due to a lateral pn junction and can be extended to other geometries, such as vertical and interleaved junctions. Analytical results show excellent agreement with numerical simulations. The model is used to identify the waveguide slab to rib height ratio as a key geometric scaling parameter for the modulation e ciency and bandwidth for lateral diodes. We characterise the fringe capacitance as a parasitic e ffect that leads to a decrease of about 20% in modulation bandwidth of typical SOI diodes without a corresponding increase in modulation effi ciency. From the scaling relations, the most e ffective way to increase the modulation bandwidth is to reduce the series resistance of the diode. In the light of our analysis, we propose high-speed and low power microdisk structures for future SOI modulators.

We derive an analytical model for the depletion capacitance of silicon-on-insulator (SOI) optical modulation diodes. This model accurately describes the parasitic fringe capacitances due to a lateral pn junction and can be extended to other geometries, such as vertical and interleaved junctions. Analytical results show excellent agreement with numerical simulations. The model is used to identify the waveguide slab to rib height ratio as a key geometric scaling parameter for the modulation e ciency and bandwidth for lateral diodes. We characterise the fringe capacitance as a parasitic e ffect that leads to a decrease of about 20% in modulation bandwidth of typical SOI diodes without a corresponding increase in modulation effi ciency. From the scaling relations, the most e ffective way to increase the modulation bandwidth is to reduce the series resistance of the diode. In the light of our analysis, we propose high-speed and low power microdisk structures for future SOI modulators.

No description available.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1991. / Includes bibliographical references (leaves 177-207) / Microfiche. / xiii, 207 leaves, bound ill. 29 cm

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.