This thesis presents new configurations for three-phase AC-to-DC single-stage, softswitched, high frequency (HF) transformer isolated converters with power factor correction (PFC) and low harmonic distortion. Four different configurations are presented. Topology of all these four configurations is based on integration of a front-end DCM boost with a soft switching HF transformer isolated DC-to-DC PWM converter with fixed frequency. DCM operation of the front-end boost provides natural PFC with low total harmonic distortion (THD) and the DC-to-DC HF transformer isolated soft switching PWM converter with an appropriate gating scheme provides output voltage regulation. A double switch AC-to-DC converter is presented in Chapter 2. Due to unsymmetrical gating scheme, DC blocking capacitors are required to avoid transformer saturation. To reduce this problem, a new gating scheme is proposed in Chapter 3, which can be used in full bridge converters providing ZVS. This gating scheme is first used in a DC-to-DC bridge converter. In the next three chapters, this new gating scheme is applied to three different types of single-stage AC-to-DC boost integrated fixed-frequency bridge converters. These configurations are: (i) boost integrated single inductor linear current DC-to-DC PWM bridge converter, (ii) boost integrated series resonant DC-to-DC bridge converter and (iii) boost integrated parallel resonant DC-to-DC bridge converter. The steady state operation of each converter and modes of operation are explained with equivalent circuits for each interval of HF cycle. The general solutions for all the intervals are derived and design curves are obtained based on steady state relations. The design procedure is illustrated with a design example. Detailed PSPICE simulation results and experimental results obtained from a laboratory prototype model are given for all the converters to verify the theory and analysis. THD of the line current without any complex control circuit remains in a reasonable range of 8% to 13% for the total range of operation. Input line current waveforms for all suggested converters shows a low harmonic distortion similar to a single 3-Φ DCM boost. The difference would be in increase or decrease of DC bus voltage in each case, which can affect THD of the boost converter. Three switches in the full bridge converter operate with zero-voltage switching (ZVS) while the main switch operates with ZVS at full load, minimum line voltage and with ZVT at lower loads conditions. Soft switching of all the switches helps in lower loss. Chapter 6 presents the contributions of this thesis, summarizes the advantages and disadvantages of each configuration and gives some suggestions for future work. / Graduate

To date, measurements of tunnel diode noise have dealt mainly with the negative conductance region, because the tunnel diode is an active circuit element only in this region. The noise has not been measured for reverse or near-forward biases due to the difficulties involving excessively low diode impedances in these regions. The purpose of this thesis is to show that, from the Esaki formulation for the direct-tunneling currents of a tunnel diode, in the bias regions where the electronic bands overlap, a simple theory can be developed relating the power spectrum associated with the direct-tunneling current noise to the direct current passing through the diode. This theory assumes that the two oppositely-flowing direct-tunneling currents in the Esaki junction are uncorrected and that both contribute full shot noise. The theory can be critically tested only in the bias regions where the noise is yet unstudied, and at sufficiently high frequencies that no contaminating 1/f noise exists. These conditions have been met experimentally and the noise measured quantitatively over the entire reverse and near-forward regions at a frequency of 4 Mc/s. Impedance-transforming networks and a very low-noise preamplifier suitable to the particular source strengths and impedances presented by the tunnel diode are developed for these measurements. A noise measurement technique is chosen from among several possible ones for the high degree of accuracy and smallest dependence on a good noise figure required for the tunnel diode source. The experimental results agree with the theory and vindicate the usual assumption that the two oppositely flowing direct-tunneling electron currents between two bands of a degenerately-doped semiconductor are uncorrelated. Noise measurements in the "valley" and far-forward region of the tunnel diode characteristic, where the diode current is not due to direct tunneling, do not agree with the simple two-current shot noise theory for direct-tunneling electron currents. Possible reasons for the enhanced noise measured in this region are advanced in the form of two models based on indirect-tunneling electrons via traps as the most important mechanism describing the excess or valley current. These models offer a possible explanation of the observed phenomena, but noise measurements alone appear insufficient to demonstrate unambiguously the detailed mechanisms producing either the excess current or the associated enhanced noise found throughout the valley and far-forward regions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This thesis presents the design and construction details of a physical model of a six-pulse HVDC converter suitable for steady-state studies. The converter rack has been built to facilitate simple testing and breadboarding. A digital equidistant firing angle controller has been constructed for the converter-rectifier current control. An electronic phase-locked loop has been used to generate an accurate control frequency. Modifications have been suggested to make the rectifier, fully operational. The control system has been constructed for future inverter control circuits and possible computer control. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

D.Ing. (Electrical & Electronic Engineering) / Please refer to full text to view abstract

In this work, nickel-gold multi-segmented magnetic nanowires were grown by electrodeposition in anodized alumina templates. The templates were fabricated by a two step anodization process of aluminum disks in an aqueous solution of oxalic acid. In this process, ordered pores grew in an alumina oxide layer at the exposed aluminum area. Each disk was electropolished before the anodization process and the features at its surface were characterized to assess the effect on the pore ordering. Nickel Watts and gold cyanide electrolyte baths were prepared to electrodeposit pure nickel and gold in the templates. Both solutions response to a range of externally applied voltages was characterized and a threshold voltage above which deposition occurs is reported. Single nanowires were isolated by chemically dissolving the template and dispersed in ethanol. Devices were fabricated with these isolated nanowires in which gold contacts were deposited to measure the resistance. A current pulse setup was implemented in a magnetoresistance system allowing to send current pulses with amplitude as low as 2nA and 50μs width. Magneto resistance measurement were carried out on the single nanowires devices and the effect of current pulses was studied. It was found that distinct resistance states can be achieved by applying a determined current pulse at a constant applied field and that the initial state can be recovered by removing excess charge from the nanowire. Finally, the effect of annealing the nanowires in an air atmosphere at 150°C for 24 hours is studied showing that the nickel sections oxidize and the gold sections remain unchanged.

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As an alternative to current trends in literary criticism, this thesis argues that the rigorous methods of obtaining knowledge as well as the concepts and insights developed in systematic psychology and psychoanalysis can and should be applied to both creative writers and their texts. Though the relationship between writer and text is a complicated one, a synthesis of well documented evidence from psychology can illuminate confusing aspects of the personality infused in the work and can thus move the critic closer to scientific literary truth, without dehumanizing literature. The introduction outlines some of the reasons why psychological findings and insights should be useful and why there has not been widespread application of them in the humanities. Biography in particular, as an art form, can benefit from being psychologically informed. Conversely, the discipline of psychology has much to learn from the in-depth study of extraordinary individual lives" The first chapter provides a more detailed inquiry into the methodological problems associated with psychobiography and suggests some applications of scientific method to biography. The example of Virginia Woolf, whose life and works are particularly intricately connected, will be foremost amongst those used to demonstrate the specific problem of hypothesis testing. Some of the proposed strategies will be executed in the second chapter through a case study of the early life of Bertrand Russell, who provides a good example of some of the difficulties likely to be encountered, as well as the advantages of a psychological approach, especially since his life spans the entire development of modern psychology. The hypothesis about the origins cf Russell's creative impulse will be subsequently tested in the light of his creative works in the period from 1904 to 1914. / Thesis / Master of Arts (MA)

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