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- ItemA whistle-stop tour of automatic speech recognition(Stellenbosch : Stellenbosch University, 2013-11) Niesler, ThomasThomas Niesler’s academic career began at the University of Stellenbosch where he obtained the BEng and MEng degrees in Electronic Engineering in 1991 and 1993 respectively. He moved to St John’s College, Cambridge, in 1994 as a Benefactor’s Scholar and obtained his PhD from the University of Cambridge in 1998 on the subject of statistical language modelling for large vocabulary speech recognition. He was employed first as a research associate (1997) and subsequently as a lecturer (1998–2000) by the University of Cambridge, where he taught undergraduate and master’s-level courses as part of the MPhil in Computer Speech and Language Processing. He joined the Department of Electrical and Electronic Engineering at the University of Stellenbosch in November 2000, where he teaches undergraduate and postgraduate students in signal and speech processing. In 2002 he was an invited researcher at the NTT Speech Open Laboratory in Kyoto, Japan. He has authored 22 journal publications, as well as 24 refereed international and a further 19 national conference publications. He holds a C2 rating with the South African National Research Foundation, and has supervised 16 postgraduate students to graduation. His research interests lie in signal and pattern recognition, with a particular emphasis on human language technology. He is a member of the International Speech Communication Association.
- ItemUnderstanding the pwm non-linearity(Stellenbosch : Stellenbosch University, 2012-03) Mouton, ToitHendrik du Toit Mouton was born in Somerset-West in 1965. In 1976 his family moved from Stellenbosch to Bloemfontein where he matriculated in 1983. He started his B.Sc. at the University of the Orange Free State in 1984 and majored in Mathematics and Physics. After completing a B.Sc.(Hons) and M.Sc. in Mathematics he was appointed as lecturer in Mathematics at the University of the Orange Free State in 1990. He completed his Ph.D. in Mathematics, on Fredholm theory relative to Banach Algebra homomorphisms, under the supervision of Prof. Heinrich Raubenheimer in 1991. During the second semester of 1992 he spent a six month sabbatical, during which time he collaborated with Prof. Sandy Grabiner from Pomona College in the USA and Prof. Bernard Aupetit from Laval University in Canada. In 1995 he moved to Stellenbosch and enrolled for the degree Bachelor in Electrical and Electronic Engineering, which he received in 1996. In 1997 he enrolled for a Ph.D. in Electrical Engineering under the supervision of Prof. Johan Enslin on a high power converter for a superconducting magnet. He was appointed as senior lecturer in Power Electronics in October 1997 and completed his Ph.D. in Electrical Engineering in 2000. In 2001 he was promoted to associate professor in Power Electronics. In 2003 he spent a sabbatical at the University of Toulouse, where he collaborated with Dr Thierry Meynard, and the University of Wuppertal, where he collaborated with Prof. Ralph Kennel. His research team collaborates closely with industry and generates the majority of its research funding through contract research for ESKOM. He currently collaborates on research projects with the Technical University of Munich, The Royal Melbourne Institute of Technology and Hypex Electronics in Groningen. His research interests include high power converters, multilevel converters, modulation theory and class-D audio amplifiers.
- ItemA comparative study of insulator materials exposed to high voltage AC and DC surface discharges(Stellenbosch : University of Stellenbosch, 2009-03) Heger, Gernot; Vermeulen, H. J.; Vosloo, W. L.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.The rising worldwide popularity of HVDC applications for power transmission purposes increases the need to study the performance of commonly used insulation materials when exposed to this voltage type. The aim of this study is thus to compare several insulation materials according to their resistance to erosion and tracking when exposed to surface discharges of HVAC and HVDC voltages of both polarities. The materials are tested according to the Incline Plane Test method described in the IEC 60587 standard, using a test voltage of 4.0 kV (rms). An important aspect of this project is the development of a bipolar DC source capable of delivering the required test voltage and current for both positive and negative polarities, while performing in accordance with the specifications set down in the standard. The design is intentionally kept modular in order to make it adaptable for future installations. Since the standard describes two different test methods, i.e. the constant tracking voltage method and the stepwise tracking voltage method, a comparison is done between the two methods in order to determine which one delivers best results for the test samples. The comparison shows that the methods deliver comparable results, but the constant tracking voltage method is preferred due to its superior test procedure. Finally, four different polymer insulator materials are tested and successfully compared under the effects of HVAC and HVDC of both polarities. The test materials include a RTV silicone rubber coated ceramic, two different HTV silicone rubbers and an EPDM rubber. The comparison is done according to the results obtained for a number of evaluation criteria. The results show that the RTV silicone rubber coating exhibits the least erosion for an AC voltage, but shows extensive erosion for a negative DC voltage. The HTV silicone rubbers exhibit only minimal erosion when exposed to an AC test voltage, but develop strong erosion under a positive DC voltage which can result in sample failure. The EPDM experiences its least erosion for a negative DC voltage, but shows maximum erosion severity for the AC voltage.