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No description available.

This thesis is concerned with a 3-phase multistage high frequency link DC to AC power conversion with a novel inverter-cycloconverter circuitry. The conversion system is composed of a high frequency PWM inverter, step-up high frequency transformer and cycloconverter with bidirectional switching devices. In first stage the DC voltage of the power source , say a submarine battery, is inverted to a system of 3-phase sinusoidally modulated I kHz alternative wave forms. For this purpose a suggested optimized PWM technique for 3-phase inverter operation is adopted, in which harmonic components up to 17 th ( 17 kHz) are eliminated from the inverter output voltages. In the second stage, for DC input isolation from AC output and also for a voltage transformation ( here stepping-up )a high frequency ( size reduced ) transformer is employed. Generalized high frequency operation, influence and side effects of the transformer on overall system design & performance is investigated. In the final stage the 1 kHz -to- 50 Hz conversion process is accomplished by a 3-phase cycloconverter. The proposed "nonlinear modulation strategy" for cycloconverter output voltage and associated harmonic analysis is demonstrated, in which the harmonic components up to 38th (1.9 kHz ) are eliminated from the conversion system output voltage. To assess the suggested functioning principles for the inverter & cycloconverter , the prototype conversion system was developed. Some design criteria and switching device selection are presented, together with different voltage & current wave forms of the prototype system under resistive & inductive load (induction motor) and their respective spectra.

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This thesis is concerned with the change in charge on a silicon MOS capacitor (MOS-C) subjected to a voltage step. The transient charge (Q-t) is controlled by the generation and recombination processes in the silicon. A review of these processes in the MOS-C, and of Q-t and other methods of measuring generation lifetime (T(_g)) is given. A thorough experimental investigation of Q-t transients is given including the effects of the guard ring voltage, applied bias, voltage step magnitude, and voltage step polarity. The measurements were performed with an automated apparatus, using a micro computer controlled measuring system developed for the purpose. An improved theory for the Q-t transient has been developed for determining the lifetime. This is midway between the simple theory of Hofstein and the more elaborate computer method of Collins and Churchill. Both the generation and recombination cases of the Q-t transient are covered for the first time and the theoretical results compare well with the experiments. The present Q-t method of determining lifetime is also compared to other Q-t analyses and with the C-t, C-V, and fast ramp methods. Good agreement is obtained with other Q-t and C-t methods, but not with the C-V and fast ramp methods. More than one hundred samples were used in this work but detailed results are presented for typical ones only. This investigation gives confidence in the use of the Q-t method for measuring the minority carrier lifetime easily and accurately.

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Software development is beset with problems relating to development productivity, resulting in projects delivered late and over budget. While the term software engineering was first introduced in the late sixties, its current state reflects no other engineering discipline. Component-orientation has been proposed as a technique to address the problems of development productivity and much industrial literature extols the benefits of a component-oriented approach to software development. This research programme assesses the use of component technologies within industrial software development. From this assessment, consideration is given to how organisations can best adopt such techniques. Initial work focuses upon the nature of component-orientation, drawing from the considerable body of industrial literature in the area. Conventional wisdom regarding componentorientation is identified from the review. Academic literature relevant to the research programme focuses upon knowledge regarding the assessment of software technologies and models for the adoption of emergent technologies. The method pays particular attention to literature concerning practitioner focussed research, in particular case studies. The application of the case study method is demonstrated. The study of two industrial software development projects enables an examination of specific propositions related to the effect of using component technologies. Each case study is presented, and the impact of component-orientation is each case is demonstrated. Theories regarding the impact of component technologies upon software development are drawn from case study results. These theories are validated through a survey of practitioners. This enabled further examination of experience in component-based development and also understanding how developers learn about the techniques. A strategy for the transfer of research findings into organisational knowledge focuses upon the packaging of previous experience in the use of component-orientation in such a way that it was usable by other developers. This strategy returns to adoption theories in light of the research findings and identifies a pattern-based approach as the most suitable for the research aims. A pattern language, placed in the context of the research programme, is developed from this strategy. Research demonstrates that component-orientation undoubtedly does affect the development process, and it is necessary to challenge conventional wisdom regarding their use. While component-orientation provides the mechanisms for increased productivity in software development, these benefits cannot be exploited without a sound knowledge base around the domain.

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No description available.