published_or_final_version / Physics / Master / Master of Philosophy

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Thesis (M.S.)--Ohio University, August, 1996. / Title from PDF t.p.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 20, 2006) Includes bibliographical references.

Thesis (M.Eng.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 111-113.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / The industrial and population growth of a nation can cause power delivery problems to localized areas of a national grid through their increased demand for electrical energy. One reason for these power shortages is the insufficient current carrying capacity of existing high voltage alternating current, (HVAC), transmission lines supplying the area. High voltage direct current (HVDC) transmission lines are a possible solution as they provide better power delivery than HVAC lines. New or upgraded HVAC lines, or HVDC lines or combinations of HVAC and HVDC lines are possible solutions to improve power delivery. This research investigates the various line possibilities using theory. and cutting edge frequency and time domain software tools. The challenge is how to approach this problem. What methodology or structure should be used? Thus one of the contributions of this work is the development of a strategy (flow chart), for solving power delivery problems to localized areas of a national grid through individual or combinations (e.g. parallel operation) of HVAC and/or HVDC transmission lines. The main contribution is the evaluation of a HVDC system as a solution to overcoming power delivery shortages to a localized area of a national grid. Three different software packages (two industrial and one academic) namely, PSCAD/EMTDC (time domain), DlgSILENT PowerFactory (frequency domain) and MathCAD software are evaluated for their capability to perform the simulation studies necessary to prove the possible solutions given in the developed flow chart. The PSCAD/EMTDC software package is evaluated for integrated HVAC/HVDC load flow analyses, DlgSILENT for individual and parallel combinations of HVAC lines and MathCAD to prove hand calculations to software results. Five case studies are conducted. The first case study demonstrates a healthy system with no delivery shortcomings, the second case study portrays the delivery shortcoming due to increased localized area demand, and the remaining three case studies explore possible solutions to solve the problem. The first possible solution is to construct an identical HVAC line in parallel to the existing line.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017. / This dissertation represents the design and development of a load management system for fixed appliances in a safe direct current (DC) Reconstruction and Development Programme (RDP) house. A combination of valley filling, load shifting and peak clipping load management techniques were employed to assist in reducing the peaks observed in the RDP house load profile during peak hours. A DC RDP house laboratory model was developed. The study is based on the assumption that the normally 220 V alternative current (AC) grid is replaced by a 350 V DC grid. The assumption is thus that 350 V DC is available at the distribution box in the RDP house laboratory model. All theoretical work was based on a 350 V DC system, but due to the lack of a laboratory 350 V DC supply, all physical tests were conducted by making use of a 300 V DC supply which was available. Consequently all calculations were thus based on 300 V DC as well. The geyser was the main fixed appliance focused on since it contributes to a significant portion of the power used. An AC geyser was successfully modified in order to be used in the DC network. Safety of the system was considered in order to interrupt the power in case of overcurrent or to isolate the power. Electronic switches were also developed and implemented to ensure that the DC power could be safely switched on and off and that the low power DC was isolated from the high power DC. LabVIEW allowed all other appliances in the DC RDP house to be virtually represented so that a holistic view of the power use of the house could be represented. This also allowed the system to be successfully simulated before any physical work was conducted. The load management system was successfully implemented by making use of power line communication. This proved to be a cost effective means to apply the load management algorithm. The algorithm consisted mainly of power on / off instructions that were executed during peak and off-peak times. It follows the normal use of timers used in the AC system to help reduce demand. It was found that the load management system successfully reduced the demand during peak hours without compromising the basic needs of the user. The power line communication modem proved to be very reliable in implementing the load management algorithm.

M.Ing. (Electrical and Electronic Engineering) / The possibilities and technology of converters with an alternating voltage link are investigated for high specific power conversion at high frequencies. With a view to the functional description of these power converters, s i muLat i on techniques are considered for both system and circuit analysis. A thorough investigation is made into the design of high frequency power transformers, which play an important role in this class of power circuits. This includes a theoretical analysis in conjunction with the 'practical implementation of a design procedure for minimal eddy current losses in the windings as well as experimental work on losses in ferrite cores. For the remainder of the study, attention is focussed on the two pulse inverter which is responsible for the generation of the alternating voltage in the high frequency link. The suitability of bipolar and field effect transistors for power switching, is critically examined and a voltage compensation on the bipolar Darlington, which reduces on-state losses, yielded good results upon application. A study on the feasibility of non-dissipative snubber techniques on the centre tapped inverter is presented, thus supplying a practical way of reducing switching losses without affecting the efficiency of the system. An additional, yet simple, network is added to the snubber circuits of the two pulse inverter which is operational during low load conditions.' in order also to have low switching losses under these circumstances. Finally a 50 k~v, 10 kHz centre tapped inverter was developed and built.

It was the purpose of this investigation to study the effect of varying the direct to reverse time ratio of periodically-reversed, direct current from 1.0 to 20.0 at an anode current density of 4.5 amperes per square centimeter, and to study the effect of alternating current of 60, 240, and 500 cycles per second, 0.2 to 4.5 amperes per square centimeter, superimposed on direct current on the electrolytic production of peroxydisulfuric acid. Electrolyses of 200 milliliters of sulfuric acid of specific gravity 1.4, at a temperature of 5 to 10 °C were performed with direct current. The anode current density was varied. The surface area of platinum anode and lead cathode was 2.0 and 221.8 square centimeters, respectively. For one hour of electrolysis, the yields were 7.9, 14.0, 20.2, and 22.9 grams of peroxydisulfuric acid at the anode current density of 1.5, 3.0, 4.5, and 6.0 amperes per square centimeter, respectively. The current efficiencies corresponding to these anode current densities were 85.0, 77.0, 61.5, and 53.4 per cent. The results showed that the yield was increased and the current efficiency was decreased with increase in the anode current density. Electrolysis of the same concentration and volume of sulfuric acid using periodically-reversed, direct current yielded 14.2 grams at an anode current density of 4.5 amperes per square centimeter and at a temperature of 5 to 8 °C. The time of electrolysis was one hour and the time ratio of direct to reverse electrolysis was 20. The current efficiency obtained under these conditions was 42.6 per cent. Decreasing the direct to reverse time ratio gave lower yields and current efficiencies. Apparently, there is no advantage in using periodically-reversed, direct current over the use of direct current for this reaction under the above experimental conditions. Electrolyses of 200 milliliters of sulfuric acid of the same concentration were performed with 60 cycles per second, alternating current superimposed on direct current. The direct current density was 4.5 amperes per square centimeter for the ten tests, but the surface area of the platinum anode was changed from two to one square centimeter and the direct current was decreased from 9.0 to 4.5 amperes. The current efficiency decreased sharply from 61.5 to approximately 31.0 per cent as the ratio of peak alternating to direct current increased from zero to 0.2 and then it remained constant until the ratio reached one. The current efficiency decreased suddenly to almost zero when the ratio was greater than one. The same sulfuric acid was electrolyzed under the same experimental conditions with 240 and 500 cycles per second, alternating current superimposed on direct current. Both direct and alternating anode current densities were varied. The direct current density was 2.2 and 4.5 amperes per square centimeter. The current efficiencies obtained during these tests were almost the same as that obtained with 60 cycles per second, alternating current within a specific limit of the ratio of peak alternating to direct current. The ratio of peak alternating current to direct current at which the current efficiencies suddenly dropped to zero was 0.75 for 240 cycles per second, and 0.5 for 500 cycles per second, instead of one for 60 cycles per second, superimposed alternating current. The platinum anode was activated and dissolved into the sulfuric acid when the ratio of peak alternating to direct current was greater than 1.0, 0.75, and 0.5 for 60, 240, and 500 cycles per second, alternating current superimposed on direct current. Apparently, there is no advantage in using alternating current superimposed on direct current over the use of direct current for electrolytic production of peroxydisulfuric acid. / Master of Science

No Brasil 72% dos óbitos são decorrentes de complicações destas doenças. Associado ao alto custo do Sistema Público de Saúde e elevado risco às doenças secundárias, o excesso de peso, pode ocasionar a lipodistrofia localizada, esta, caracterizada pelas poucas alternativas de tratamento, sendo o tratamento cirúrgico o mais realizado. Poucos estudos demonstram a utilização de terapia auxiliar para a redução da lipodistrofia localizada e ainda há maior restrição em pesquisas específicas visando o tratamento da lipodistrofia abdominal. O presente estudo procurou verificar os efeitos de uma terapia não invasiva, em uma região específica predisponente ao acúmulo de gordura, o abdome. Foi realizado um estudo longitudinal, de abordagem quantitativa, do tipo descritiva, composto por 33 mulheres, com acúmulo de adiposidade abdominal, na faixa etária dos 20 a 35 anos. Inicialmente todas assinaram o Termo de Consentimento Livre e Esclarecido (TCLE); sequencialmente, houve uma divisão da amostra em dois grupos: A, que realizou dez sessões seguidas do protocolo fisioterapêutico e B, que realizou cinco sessões, seguida de uma pausa e realizou outras cinco sessões do protocolo. Todas as voluntárias responderam o questionário e realizaram a primeira avaliação corporal que foi repetida após a quinta e décima sessão do protocolo fisioterapêutico além da realização do exame de Densitometria por Absorciometria de Raios X de Dupla Energia (DXA) que foi realizado ao início e término das sessões, que consistiu na aplicação abdominal de um protocolo desenvolvido baseado em associação de duas técnicas fisioterapêuticas: o ultrassom de 3MHz e a corrente alternada de média frequência. Foram analisados inicialmente os dados coletados da amostra geral seguido da análise de comparação entre os grupos A e B, para a verificação da normalidade da distribuição utilizou-se o teste de Shapiro-Wilk e para a comparação dos dados utilizou-se a ANOVA de Friedman. Os resultados encontrados para as variáveis analisadas da amostra geral: massa, perimetria de cintura, perimetria de cicatriz umbilical, perimetria da menor circunferência abdominal, perimetria da maior circunferência abdominal e percentual de gordura de tronco avaliado por meio da DXA, apresentou o valor de p<0,001 verificando uma diferença significativa comparada à avaliação inicial à final. Em relação ao percentual de gordura corporal total avaliado pela DXA, o valor de “p” foi p=0,779, demonstrando uma redução com variação de 0,1% a 2,7% entre as voluntárias. Quando comparados os grupos A e B, observou-se homogeneidade entre os grupos e não foi apresentada diferença estatística entre eles, portanto não houve alteração do resultado final. Sendo assim, este protocolo foi desenvolvido especificamente para o tratamento da lipodistrofia abdominal feminina e durante o estudo se mostrou eficaz no tratamento para redução deste tipo de adiposidade em mulheres jovens. / In Brazil the complications of these illnesses are responsible for 72% of the deaths. Overweight combined with not only the high costs of health service provided by the government, but also with the high risk of secondary diseases, can cause localized lipodystrophy which has few alternatives for treatment, being surgical treatment the most common. Few studies show the usage of adjunctive therapy in order to reduce localized lipodystrophy and still they have greater restriction in specific research aiming at the treatment of localized abdominal lipodystrophy. The objective of this study was to verify the results of a non-invasive therapy in a specific area more predisposed to fat accumulation – the abdomen. A longitudinal study was performed, using a quantitative-descriptive research composed of 33 women with abdominal fat accumulation, with an age range of 20 to 35 years old. All of them signed an informed consent term (TCLE) and the sample was divided in two groups: A, which held ten physiotherapy sessions according to the physiotherapy protocol and B, which held five physiotherapy sessions, followed by a pause, and then held other five sessions according to the protocol. All the volunteers answered a questionnaire and went through their first body evaluation, which was repeated after the fifth and tenth session according to the physiotherapy protocol. They also underwent a Dual-Energy X-ray absorptiometry (DXA) test, repeated in the beginning and in the end of the sessions, which consisted of an application of a protocol, in the abdomen, developed based on the association of two physiotherapy techniques: 3-MHz ultrasound and medium-frequency alternating current. Initially, the general sample data was analyzed, followed by the comparative analysis between groups A and B. A Shapiro- Wilk test was performed to check the normality of the distribution and ANOVA Friedman was used to compare the data. The results for the variables analyzed in general sample were: mass, waist measurement, umbilical scar measurement, narrowest abdominal circumference measurement, widest abdominal circumference measurement and midsection fat percentage p<0,001, evaluated by DXA, showing a considerable difference if compared from the initial evaluation to the final. The percentage of total body fat evaluated by DXA was p=0,779 demonstrating reduction with a variation of 0,1% to 2,7% among all the volunteers. Comparing groups A and B, homogeneity could be observed and there was no statistic difference between them. Therefore, this protocol was developed specifically for the treatment of abdominal lipodystrophy in women and during the present study it demonstrated to be efficient for the treatment of reduction for this type of adiposity in young women.