The policy of Separate Development and its forceful implementation by the Nationalist Government from the !960's and into the 1980's resulted in the resettlement of thousands of Africans in the 'homeland' Ciskei in the Eastern Cape. All these changes had a profound and very often a disruptive influence on the lives of those involved. People's ability to survive amidst these circumstances, was tested to the limit. This study looks at the role of the local Christian faith community in supporting its members during these rapid and disruptive socioeconomic and political changes. The study is confined to two congregations of the Uniting Reformed Church in Southern Africa in Ilitha and Ndevana in the Eastern Cape. Following an introductory chapter, Chapter 2 gives a historical outline of developments in the broader Ciskei. Attention is also given to demographic, social and economic conditions. Chapter 3 describes the culture and feeling of despair, powerlessness and mistrust that is deeply entrenched in the minds of many people in the community due to depressive socio-economic situations. Chapter 4 gives an overview of the churches in the area and describes the supportive structures and actions of two churches in the Ilitha-Ndevana area. No instant solutions are offered to members but through mutual support they find a sense of belonging and encouragement in the midst of their hardship. In Chapter 5 a model for the mission of the local church in a context of social and economic change and disruption, is presented. It is shown how the image of Christianity and the Gospel have been distorted and misused in the past through the entanglement of mission and colonialism, a negative attitude towards African culture, and by contributing to the subordination of women in society. A vision that people in Africa can have peace and dignity and become self-reliant is proposed. Within the local faith community this vision is built on an understanding of God as the weak and suffering Lord, on fellowship and mutual support, a new reading of the Bible, a practical community based spirituality, and an emphasis on healing. / Die daarstelling en .kragdadige toepassing van die beleid van Afsonderlike Ontwikkeling vanaf die 1960's tot·die 1980's het tot gevolg_gehad dat duisende Swart Suid-AftilCaners hervestig is in die Ciskei-tuisland in die Oos-Kaap. Al hierdie veranderinge het verreikende en baie dikwels ontwrigtende gevolge op die betrokkenes gehad. Mense se vermoens om binne hierdie omstandighede te oorlee:t: is tot die uiterste beproef. Hierdie studie kyk na die rol van die plaaslike · Cbristelike. geloofsgemeenskap in die ondersteuning van sy lede tydens snelle en ontwrigtende sosiale, ekonomiese en politieke veranderinge. Die studie is beperk tot twee gemeentes van die Verenigende Gereformeerde Kerk in Suider-Aftika in Ilitha en Ndevana in die Oos-Kaap. Na 'n inleidende hoofstuk, gee hoofstuk 2 'n historiese oorsig van ontwikkelinge in die breere Ciskei-gebied. Aandag word ook gegee aan demografriese, sosiale en ekonomiese toestande. Hoofstuk 3 beskryf 'n kultuur en gevoel van moedeloosheid, magteloosheid en wantroue wat, as gevolg van neerdrukkende sosiaal-ekonomiese toestande, diep in menige mense se gemoedere vasgele is. Hoofstuk 4 gee 'n oorsig oor die kerke in die gebied en beskryf die ondersteunende strukture en optrede in twee gemeentes in die Ilitha-Ndevana area. Geen kitsoplossings word aan lede aangebied nie, maar deur onderlinge steun vind hulle geborgenheid en bemoediging te midde van swaarkry. In hoofstuk 5 word 'n model aangebied vir die missie van die plaaslike kerk te midde van sosiale en ekonomiese veranderinge en ontwrigting. Daar word aangetoon hoe die beeld van die Christendom in die verlede verwring en misbruik is deur: die verstrengeling van sending en kolonialisasie; 'n negatiewe houding teenoor kultuur in Afrika; en deur by te dra tot die ondergeskikte posisie van vroue in die samelewing. 'n Visie dat die mense van Afrika vrede en menswaardigheid kan geniet en self onderhoudend kan raak, word voorgestel. Binne die plaaslike geloofsgemeenskap word aan hierdie visie gebou deur 'n begrip van God as die magtelose en lydende Here, deur onderlinge gemeenskap en ondersteuning, 'n nuwe lees en begrip van die Bybel, 'n praktiese gemeenskaps-gerigte spiritualiteit en 'n beklemtoning van heling en herstel. / Christian Spirituality, Church History and Missiology / D.Th. (Missiology)

This thesis presents novel radio frequency microelectromechanical (RF MEMS) circuits based on the three-dimensional (3-D) micromachined coplanar transmission lines whose geometry is re-configured by integrated microelectromechanical actuators. Two types of novel RF MEMS devices are proposed. The first is a concept of MEMS capacitors tuneable in multiple discrete and well-defined steps, implemented by in-plane moving of the ground side-walls of a 3-D micromachined coplanar waveguide transmission line. The MEMS actuators are completely embedded in the ground layer of the transmission line, and fabricated using a single-mask silicon-on-insulator (SOI) RF MEMS fabrication process. The resulting device achieves low insertion loss, a very high quality factor, high reliability, high linearity and high self actuation robustness. The second type introduces two novel concepts of area efficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. The coupling is achieved by tuning both the ground and the signal line coupling, obtaining a large tuneable coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity over a very large bandwidth. This thesis also presents for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. Closed-form analytical formulas for the IIP3 of MEMS multi-device circuit concepts are derived. A nonlinearity analysis, based on these formulas and on  measured device parameters, is performed for different circuit concepts and compared to the simulation results of multi-device  conlinear electromechanical circuit models. The degradation of the overall circuit nonlinearity with increasing number of device stages is investigated. Design rules are presented so that the mechanical parameters and thus the IIP3 of the individual device stages can be optimized to achieve a highest overall IIP3 for the whole circuit.The thesis further investigates un-patterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip inductances. The approach used is to increase the thickness of the ferromagnetic material without increasing its conductivity, by using multilayer NiFe and AlN sandwich structure. This suppresses the induced currents very effectively and at the same time increases the ferromagnetic resonance, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. The so far highest permeability values above 1 GHz for on-chip integrated un-patterned NiFe layers were achieved. / <p>QC 20140328</p>

This thesis aims at an automatic detection of artifacts in optical satellite images such as aliasing, A/D conversion problems, striping, and compression noise; in fact, all blemishes that are unusual in an undistorted image. Artifact detection in Earth observation images becomes increasingly difficult when the resolution of the image improves. For images of low, medium or high resolution, the artifact signatures are sufficiently different from the useful signal, thus allowing their characterization as distortions; however, when the resolution improves, the artifacts have, in terms of signal theory, a similar signature to the interesting objects in an image. Although it is more difficult to detect artifacts in very high resolution images, we need analysis tools that work properly, without impeding the extraction of objects in an image. Furthermore, the detection should be as automatic as possible, given the quantity and ever-increasing volumes of images that make any manual detection illusory. Finally, experience shows that artifacts are not all predictable nor can they be modeled as expected. Thus, any artifact detection shall be as generic as possible, without requiring the modeling of their origin or their impact on an image. Outside the field of Earth observation, similar detection problems have arisen in multimedia image processing. This includes the evaluation of image quality, compression, watermarking, detecting attacks, image tampering, the montage of photographs, steganalysis, etc. In general, the techniques used to address these problems are based on direct or indirect measurement of intrinsic information and mutual information. Therefore, this thesis has the objective to translate these approaches to artifact detection in Earth observation images, based particularly on the theories of Shannon and Kolmogorov, including approaches for measuring rate-distortion and pattern-recognition based compression. The results from these theories are then used to detect too low or too high complexities, or redundant patterns. The test images being used are from the satellite instruments SPOT, MERIS, etc. We propose several methods for artifact detection. The first method is using the Rate-Distortion (RD) function obtained by compressing an image with different compression factors and examines how an artifact can result in a high degree of regularity or irregularity affecting the attainable compression rate. The second method is using the Normalized Compression Distance (NCD) and examines whether artifacts have similar patterns. The third method is using different approaches for RD such as the Kolmogorov Structure Function and the Complexity-to-Error Migration (CEM) for examining how artifacts can be observed in compression-decompression error maps. Finally, we compare our proposed methods with an existing method based on image quality metrics. The results show that the artifact detection depends on the artifact intensity and the type of surface cover contained in the satellite image.

Ein tieffrequenter lauter Suppressorton verlagert das Corti-Organ periodisch in Richtung Scala vestibuli und Scala tympani. Simultan registrierte DPOAE (Distorsionsprodukte otoakustischer Emissionen) werden in beiden Richtungen unterschiedlich supprimiert. Bei Vorliegen eines endolymphatischen Hydrops (EH) ist die Beweglichkeit der Basilarmembran eingeschränkt, so daß keine oder eine nur geringe Modulation des DPOAE-Pegels entstehen kann. In dieser Arbeit wird die diagnostische Aussagekraft von Messungen tieftonmodulierter DPOAE bei zwei Patientenkollektiven mit Verdacht auf EH im Vergleich mit einem Normalkollektiv (n = 22) geprüft: bei Patienten mit M. Menière (n = 23) und Patienten mit Ohrdruckgefühl ohne Schwindelsymptomatik (n = 8). Bei den M. Menière-Patienten sind die ipsilateralen Modulationstiefen (MD) im Median hochsignifikant geringer als die des Normalkollektivs. Dies wird als Hinweis auf einen EH gewertet. Bei Primärtonpegeln mit L2 = 20 dB SL ergibt sich für den Grenzwert der MD mit 6 dB die Sensitivität von 64% und die Spezifität von 90%. Die kontralateralen MD der M. Menière-Patienten sind im Median signifikant geringer als die des Normalkollektivs. Für Primärtonpegel mit L2 = 20 dB SL liegen 33% der Werte unter dem Grenzwert, von diesen Ohren ist die Hälfte symptomfrei. Auch im kontralateralen Ohr kann ein – eventuell asymptomatischer – Hydrops vorliegen. Die Ergebnisse der Patienten mit Ohrdruckgefühl ohne Schwindel zeigen im Median hochsignifikant geringere MD als die der Normalhörenden und unterscheiden sich nicht signifikant von den Werten der ipsilateralen Ohren der M. Menière-Patienten. Das Ohrdruckgefühl kann auf einen cochleären Hydrops hinweisen und die weitere Entwicklung eines EH ankündigen. Bei den Verlaufsuntersuchungen zeigen die MD beider Patientenkollektive, deren Symptomatik sich während dieses Zeitraums änderte, Variabilitäten: mit Zunahme der Heftigkeit der spezifischen Symptome nimmt die MD ab und umgekehrt. Die Tieftonmodulation scheint den Zustand der Cochlea widerspiegeln zu können. Im Vergleich mit den in der Klinik gängigen Verfahren zur Hydropsdiagnostik wie der ECochG oder dem Glyceroltest erweist sich das in dieser Arbeit angewandte objektive Verfahren als vorteilhaft: es ist schnell durchführbar, nicht belastend und nicht invasiv. Es eignet sich als Screeningverfahren und kann zur Verlaufskontrolle eingesetzt werden. / The cochlear partition is moved periodically towards scala vestibuli and scala tympani by a low-frequency high-level suppressor tone. Simultaneously recorded DPOAEs (distortion product otoacoustic emissions) are suppressed differently in both directions. This modulation of the DPOAE level may be reduced or even missing if the displacement of the basilar membrane is inhibited by endolymphatic hydrops (EH). In this thesis the diagnostic significance of the low-frequency modulation of DPOAEs is tested in two patient groups with suspected EH: patients with Menière’s disease (n = 23) and patients with aural fullness without vertigo (n = 8), compared to a control group of normal hearing adults (n = 22). In the patients with Menière’s disease the ipsilateral modulation depths (median) are high significantly lower than in the control group. This can be interpreted as a sign of EH. At primary tone levels with L2 = 20 dB SL and a limiting value of 6 dB modulation depth (MD), a sensitivity of 64% and a specificity of 90% are found. The contralateral MDs of the patients with Menière’s disease (median) are significantly lower than in the control group. At primary tone levels with L2 = 20 dB SL, 33% of the MDs are below the limiting value, half of these ears are symptom-free. So in the contralateral ear a possibly asymptomatic hydrops may be present as well. The patients with aural fullness without vertigo show high significantly lower MDs (median) than the normal hearing adults and no significant difference to the ipsilateral MDs of the patients with Menière’s disease. Aural fullness can be a sign of cochlear hydrops and may indicate the further development of EH. During the course of disease the MDs of both patient groups vary when symptoms change: with increasing intensity of the specific symptoms the MD is reduced and vice versa. Low-frequency modulation seems to reflect the state of the cochlea. Compared to the generally used clinical tests for the assessment of EH like ECochG or the glycerol test, the objective method presented in this thesis is advantageous: it is fast, not straining and non-invasive. It is suitable for screening and can be used to monitor the course of disease.

The growth in the number of wireless devices and applications underscores the need for characterizing and mitigating interference induced problems such as distortion and blocking. A typical interference scenario involves the detection of a small amplitude signal of interest (SOI) in the presence of a large amplitude interfering signal; it is desirable to attenuate the interfering signal while preserving the integrity of SOI and an appropriate dynamic range. If the frequency of the interfering signal varies or is unknown, an adaptive notch function must be applied in order to maintain adequate attenuation. This work explores the performance space of a phase cancellation technique used in implementing the desired notch function for communication systems in the 1-3 GHz frequency range. A system level model constructed with MATLAB and related simulation results assist in building the theoretical foundation for setting performance bounds on the implemented solution and deriving hardware specifications for the RF notch subsystem devices. Simulations and measurements are presented for a Low Noise Amplifer (LNA), voltage variable attenuators, bandpass filters and phase shifters. Ultimately, full system tests provide a measure of merit for this work as well as invaluable lessons learned. The emphasis of this project is the on-wafer LNA measurements, dependence of IC system performance on mismatches and overall system performance tests. Where possible, predictions are plotted alongside measured data. The reasonable match between the two validates system and component models and more than compensates for the painstaking modeling efforts. Most importantly, using the signal to interferer ratio (SIR) as a figure of merit, experimental results demonstrate up to 58 dB of SIR improvement. This number represents a remarkable advancement in interference rejection at RF or microwave frequencies.

Submitted by Maria Aparecida (cidazen@gmail.com) on 2017-04-17T13:14:17Z No. of bitstreams: 1 Elson Moreira.pdf: 7883984 bytes, checksum: cf59b3b0b24a249a7fd9e2390b7f16de (MD5) / Made available in DSpace on 2017-04-17T13:14:17Z (GMT). No. of bitstreams: 1 Elson Moreira.pdf: 7883984 bytes, checksum: cf59b3b0b24a249a7fd9e2390b7f16de (MD5) Previous issue date: 2017-02-10 / CNPQ / A problem of electric power quality that always affects the consumers of the distribution network are the harmonic distortions. Harmonic distortions arise from the presence of socalled harmonic sources, which are nonlinear equipment, i.e., equipment in which the voltage waveform differs from the current. Such equipment injects harmonic currents in the network generating distortions in the voltage waveform. Nowadays, the number of these equipment in the electrical network has increased considerably. However, the increasing use of such equipment over the network makes systems more vulnerable and prone to quality problems in the supply of electricity to consumers. In addition, it is important to note that in the current scenario, the generation of electricity from renewable sources, connected in the secondary distribution network, is increasing rapidly. This is mainly due to shortage and high costs of fossil fuels. In this context, the Photovoltaic Distributed Generation (PVDG), that uses the sun as a primary source for electric energy generation, is the main technology of renewable generation installed in distribution network. However, the PVDG is a potential source of harmonics, because the interface of the PVDG with the CA network is carried out by a CC/CA inverter, that is a highly nonlinear equipment. Thus, the electrical power quality problems associated with harmonic distortion in distribution networks tend to increase and be very frequent. One of the main indicators of harmonic distortion is the total harmonic distortion of voltage ( ) used by distribution utilities to limit the levels of harmonic distortion present in the electrical network. In the literature there are several deterministic techniques to estimate . These techniques have the disadvantage of not considering the uncertainties present in the electric network, such as: change in the network configuration, load variation, intermittence of the power injected by renewable distributed generation. Therefore, in order to provide a more accurate assessment of the harmonic distortions, this dissertation has as main objective to develop a probabilistic methodology to estimate the level of in secondary distribution networks considering the uncertainties present in the network and PVDG connected along the network. The methodology proposed in this dissertation is based on the combination of the following techniques: three-phase harmonic power flow in phase coordinate via method sum of admittance, point estimate method and series expansion of Gram-Charlier. The validation of the methodology was performed using the Monte Carlo Simulation. The methodology was tested in European secondary distribution network with 906 nodes of 416 V. The results were obtained by performing two case studies: without the presence of PVDG and with the PVDG connection. For the case studies, the following statistics for nodal were estimated: mean value, standard deviation and the 95% percentile. The results showed that the probabilistic estimation of is more complete, since it shows the variation of due to the uncertainties associated with harmonic sources and electric network. In addition, they show that the connection of PV-DG in the electric network significantly affects the levels of of the electric network. / Um problema de qualidade de energia elétrica que afeta os consumidores da rede de distribuição secundária são as distorções harmônicas. As distorções harmônicas são provenientes da presença das chamadas fontes de harmônicas que são equipamentos de características não-lineares, ou seja, equipamentos em que a forma de onda da tensão difere da de corrente. Tais equipamentos injetam correntes harmônicas na rede produzindo, portanto distorções na forma de onda da tensão. Nos dias atuais, a quantidade desses equipamentos na rede elétrica tem aumentado consideravelmente. Porém, o uso crescente desse tipo de equipamento ao longo da rede torna os sistemas mais vulneráveis e propensos a apresentarem problemas de qualidade no fornecimento de energia elétrica aos consumidores. Além disso, é importante destacar que no cenário atual, a geração de energia elétrica a partir de fontes renováveis, conectada na rede de distribuição secundária, está aumentando rapidamente. Isso se deve principalmente devido a escassez e altos custos dos combustíveis fosseis. Neste contexto, a Geração Distribuída Fotovoltaica (GDFV), que utiliza o sol como fonte primária para geração de energia elétrica, é a principal tecnologia de geração renovável instalada na rede de distribuição no Brasil. Contudo, a GDFV é uma potencial fonte de harmônica, pois a interface da GDFV com a rede CA é realizada por um inversor CC/CA, que é um equipamento altamente não-linear. Desde modo, os problemas de qualidade de energia elétrica associados à distorção harmônica nas redes de distribuição tendem a aumentar e a serem bem frequentes nos consumidores da rede de distribuição secundárias. Um dos principais indicadores de distorção harmônica é a distorção harmônica total de tensão ( do inglês “Total Harmonic Distortion of Voltage”) utilizada pelas concessionárias de energia elétrica para quantificar os níveis de distorção harmônica presentes na rede elétrica. Na literatura técnica existem várias técnicas determinísticas para estimar a . Essas técnicas possuem a desvantagem de não considerar as incertezas presentes na rede elétrica, tais como: mudança na configuração da rede, variação de carga e intermitência da potência injetada pela geração distribuída renovável. Portanto, a fim de fornecer uma avaliação mais precisa das distorções harmônicas, este trabalho tem como principal objetivo desenvolver uma metodologia probabilística para estimar o nível de em redes de distribuição secundária considerando as incertezas presentes na rede e na GDFV conectada ao longo da rede. A metodologia proposta nesta dissertação se baseia na combinação das seguintes técnicas: fluxo de potência harmônico trifásico em coordenadas de fase via método de soma de admitância, método de estimação por pontos e expansão em série de Gram-Charlier. Além disso, a validação da metodologia foi realizada utilizando a Simulação Monte Carlo. A metodologia desenvolvida foi testada na rede de distribuição secundária europeia com 906 nós de 416 V. Os resultados foram obtidos realizando dois casos de estudos: sem a presença de GDFV e com a conexão de GDFV. Para ambos os casos de estudo as seguintes estatísticas do nodal foram estimadas: valor médio, desvio padrão e o percentil de 95%. Os resultados demonstraram que a estimação probabilística da é mais completa, pois mostra a variação da devido às incertezas associadas com as fontes de harmônicas e as da rede elétrica. Os resultados também mostram que a conexão da GDFV afeta significativamente os níveis de da rede elétrica

The present work is dedicated to the development of high performance integrated circuits for wireless communications, by acting of three different levels: technologies, devices, and circuits. Silicon-on-Insulator (SOI) CMOS technology is used in the frame of this work. Micromachining technologies are also investigated for the fabrication of three-dimensional tunable capacitors. The reliability of micromachined thin-film devices is improved by the coating of silanes in both liquid- and vapor-phases. Since in telecommunication applications, distortion is responsible for the generation of spurious frequency bands, the linearity behavior of different SOI transistors is analyzed. The validity range of the existing low-frequency nonlinear characterization methods is discussed. New simple techniques valid at both low- and high-frequencies, are provided, based on the integral function method and on the Volterra series. Finally, the design of a crucial nonlinear circuit, the voltage-controlled oscillator, is introduced. The describing function formalism is used to evaluate the oscillation amplitude and is embedded in a design methodology. The frequency tuning by SOI varactors is analyzed in both small- and large-signal regimes.

See file appended.

Voltage source inverters (VSI) are popular in variable speed induction motor drive applications. Pulse width modulation (PWM) is employed to achieve variable voltage variable frequency output from a fixed DC bus voltage. The modulation method greatly influences the harmonic distortion in line current and the inverter switching loss. This thesis evaluates a few space vectorbased PWM techniques which reduce the harmonic distortion and/or the inverter switching loss, compared to conventional space vector PWM (CSVPWM), at a given average switching frequency. In space vector-based PWM, the average voltage vector applied over a sub-cycle equals the commanded reference vector, thereby maintaining voltsecond balance. The given average vector can be realized by applying the voltage vectors of the inverter in different sequences. CSVPWM employs a switching sequence in which all the phases switch once in a sub-cycle. Sequences, in which a phase is clamped, while the other two phases switch once in a sub-cycle have been reported in literature. Further, certain special switching sequences have also been reported recently. These special sequences involve switching a phase twice, while switching the second phase once and clamping the third phase in a sub-cycle. This work investigates the use of such special switching sequences to reduce line current distortion and inverter switching loss in an induction motor drive. The influence of various switching sequences on line current ripple and inverter switching loss is discussed in the thesis. Comparison of the sequences in terms of switching loss leads to a hybrid PWM technique, which deploys the best sequence to reduce switching loss under a given operating condition. This technique is referred to as minimum switching loss PWM (MSLPWM). Further, a procedure for design of hybrid PWM techniques to achieve reduced line current distortion as well as inverter switching loss is elaborated. Four such specially designed hybrid PWM techniques are discussed. Analytical methods are presented for the evaluation of total RMS harmonic distortion factor of line current and inverter switching loss corresponding to different PWM techniques. The MSLPWM and the hybrid PWM techniques are evaluated analytically in terms of harmonic distortion and switching loss. It is observed that the switching loss corresponding to MSLPWM is considerably less than that with CSVPWM over the entire range of power factor. The reduction in switching loss with MSLPWM is as high as 36% at high power factors close to unity, while it is not less than 22% at power factors close to zero. MSLPWM also reduces the harmonic distortion for power factors close to unity at high modulation indices. Compared to CSVPWM, the hybrid PWM techniques result in a maximum reduction of about 40% in the harmonic distortion at fundamental frequencies close to 50Hz, and about 30% reduction in switching loss at power factors close to unity. The various PWM techniques are tested on a constant V /f induction motor drive with a digital control platform based on ALTERA Cyclone II field programmable gate array (FPGA) device. With a 10kVA IGBT based inverter feeding a 2.2kW, 415V, 50Hz, three-phase induction motor, the total RMS harmonic distortion factor of line current (IT HD) is measured at different fundamental frequencies for the various PWM techniques. The average switching frequency is 2.44kHz. The measured values of IT HD show a reduction in distortion with the hybrid PWM techniques over CSVPWM at high speeds of the drive. The relative values of IT HD corresponding to different PWM techniques agree with the theoretical predictions. With the 10kVA IGBT based inverter feeding a 6kW, 400V, 50Hz, 4pole, three-phase induction motor, the switching losses corresponding to CSVPWM and MSLPWM are evaluated and compared. This is done by measuring the steady state temperature rise of the heat sink over the ambient for the two techniques under different conditions. The thermal measurements are carried out at different loads with power factor ranging from 0.14 to 0.77. The measurements are also carried out at different fundamental frequencies (or modulation indices). Further, to separate conduction (constant) losses and switching (variable) losses, the heat sink temperatures are measured at two different switching frequencies, namely 2.44kHz and 4.88kHz. It is observed that the temperature rise due to MSLPWM is less than that due to CSVPWM consistently under various operating conditions. The thermal measurements confirm the theoretical prediction of reduction in switching loss with MSLPWM. Measurements of heat sink temperature rise corresponding to CSVPWM, MSLPWM and the hybrid PWM techniques are carried out at a higher power factor of 0.98 (lag) with the inverter feeding an RL load (instead of an induction motor). The hybrid PWM and MSLPWM result in lower switching losses as indicated by the reduction in temperature rise.

Two and three-phase flow processes involving gas, liquid and solid, are common in nature and industry, and include some of the most complex and poorly-understood transport problems. In this research hydrodynamics, heat and mass transfer processes in complex two and three-phase flows were investigated. The interfacial surface area concentration in a short vertical column subject to the through flow of fiber-liquid-gas slurry was experimentally measured using the gas absorption technique. The experimental data were statistically analyzed for parametric effects, and were empirically correlated. The absorption of a gaseous species by a slurry droplet with internal circulation and containing reactive micro-particles was simulated, and parametrically studied. The micro-particles were found to enhance the absorption rate. The absorption rate was sensitive to droplet recirculation, and shrinkage of particles with time resulted in declining absorption rates. The transport of soot particles, suspended in laminar hot gas flowing in a tube, was modeled and parametrically studied. Due to coupled thermal radiation and thermophoresis, a radially-nonuniform temperature profile develops, leading to sharp, non-uniform radial soot-concentration profiles. The assumption of monodisperse particles leads to over-prediction of thermophoresis. The transport and removal of particles suspended in bubbles rising in a stagnant liquid pool were modeled based on a Eulerian – Monte Carlo method. The bubble hydrodynamics were treated in Eulerian frame, using the Volume-of-Fluid (VOF) technique, while particle equations of motion were numerically solved in Lagrangian frame. The bubbles undergo shape change, and have complex internal circulation, all of which influence the particle removal. Model predictions were also compared with experimental data. Using a resemblance between two-phase flow in microchannels, and in large channels at microgravity, a simple Weber number-based two-phase flow regime map was developed for microchannels. Based on the available air-water experimental data, a criterion for the prediction of conditions that lead to flow regime transition out of the stratified-wavy flow pattern in horizontal annular channels was proposed. The thermocapillary effects on liquid-vapor interface shape during heterogeneous bubble ebullition in microchannels were analytically studied.