The outstanding features of modular multilevel converters (MMC) have recently gained much attention in the high-voltage direct-current (HVDC) transmission field. Power quality, converter cost and system performance are three crucial aspects of HVDC MMCs which are directly linked to the converter modulation and switching schemes. High power quality and performance require high switching frequency and large cell capacitor whereas low switching frequency and small cell capacitor are needed to reduce the converter cost. The main objective of this thesis is to propose a practical switching method for HVDC MMCs which balances the aforementioned contradictory requirements. A mathematical analysis of the converter switching pattern, against the power quality and converter cost, has been conducted to formulate an optimization problem for MMCs. Different objective functions are studied for the formulated optimization problem such as converter loss minimization, voltage imbalance minimization and computational burden minimization. This thesis proposes three methods to address different objective functions. Ultimately, a real-time simulator has been built to practically verify and investigate the performance of the proposed methods in a realistic point-to-point HVDC link. The most significant outcome of this thesis is the tolerance band-based switching scheme which offers a direct control of the cell capacitor voltage, low power losses, and robust dynamic performance. As a result, the converter switching frequency can reach frequencies as low as 70 Hz (with the proposed cell tolerance band (CTB) method). A modified optimized CTB method is proposed to minimize the converter switching losses and it could reduce the converter switching losses by 60% in comparison to the conventional phase shifted carrier modulation method. It is concluded intelligent utilization of sorting algorithm can enable efficient HVDC station operation by reducing the converter cost. / <p>QC 20160916</p>

The purpose of this study is to examine young people’s attitudes towards multiethnic youth language and standard Swedish. The aim is also to examine the situations in which code- switching between different language varieties appears. Semi-structured interviews were performed with eight students to gather empirical material for the study questions. The analysis of the interviews shows that the multiethnic youth language is an artistic and vibrant language that expresses young people's creativity and humor. The analysis also show that the multiethnic youth language is a culture, an own language, which shows where the youth of the suburbs belong.

M.Ing. / In this investigation charge balancing will be investigated from an Electro-Magnetic- Compatibility perspective. The primary sources of common mode Electro-Magnetic- Interference in switching converters are the switching nodes. This is mainly due to the parasitic capacitance between the switching node and the reference earth. Filtering components that are currently used take up a lot of valuable space resulting in the products overall size and cost to increase. Combating common mode current at the source will drastically reduce the size or the need for these large filters. This investigation will focus on a simple method of reducing common mode noise (produced by the switching node), of a two wire system, at the source by making use of a compensating winding which requires very little or no additional space; a buck converter will be used to illustrate the concept. The investigation will start with an overview of Electro-Magnetic-Interference and its components (common and differential mode noise). This investigation will deal with the measurement of common and differential mode noise as well as general Electro-Magnetic-Interference measurement. A design of the buck converter and its drive circuit will also be presented. Reducing the common mode noise by making use of charge balancing using planar inductors will then be presented. This investigation contains the theoretical analysis as well as experimental results to validate the theory. The experiments show encouraging results in using this technique to minimise common mode noise in switched-mode-power-supplies.

The high-frequency properties of coupled magnetic systems have been investigated using vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy. SAF structures consist of two ferromagnetic layers separated by a non-magnetic spacer, coupled through the indirect exchange interaction. The ferromagnetic layers of our samples were composed of FeCoB separated by a layer of Ru. The thickness of Ru was varied in the range of 8 to 18 Å among the samples studied. Antiferromagnetic coupling can be quickly identified by the major hysteresis loop (MHL). A new way of displaying FMR data for these trilayer samples is presented which completely preserves the anisotropy effects while fully characterizing the angular dependence of FMR. The advantage of our representation is that the high-frequency data can be easily compared to the static switching behavior at any angle obtained through susceptibility measurements. Ferromagnetic resonance; Coupled; Synthetic antiferromagnet; Magnetization switching

<p>Nature is challenged to move charge efficiently over many length scales. From sub-nm to μm distances, electron-transfer proteins orchestrate energy conversion, storage, and release both inside and outside the cell. Uncovering the detailed mechanisms of biological electron-transfer reactions, which are often coupled to bond-breaking and bond-making events, is essential to designing durable, artificial energy conversion systems that mimic the specificity and efficiency of their natural counterparts. Here, we use theoretical modeling of long-distance charge hopping (Chapter 3), synthetic donor-bridge-acceptor molecules (Chapters 4, 5, and 6), and de novo protein design (Chapters 5 and 6) to investigate general principles that govern light-driven and electrochemically driven electron-transfer reactions in biology. We show that fast, μm-distance charge hopping along bacterial nanowires requires closely packed charge carriers with low reorganization energies (Chapter 3); singlet excited-state electronic polarization of supermolecular electron donors can attenuate intersystem crossing yields to lower-energy, oppositely polarized, donor triplet states (Chapter 4); the effective static dielectric constant of a small (~100 residue) de novo designed 4-helical protein bundle can change upon phototriggering an electron transfer event in the protein interior, providing a means to slow the charge-recombination reaction (Chapter 5); and a tightly-packed de novo designed 4-helix protein bundle can drastically alter charge-transfer driving forces of photo-induced amino acid radical formation in the bundle interior, effectively turning off a light-driven oxidation reaction that occurs in organic solvent (Chapter 6). This work leverages unique insights gleaned from proteins designed from scratch that bind synthetic donor-bridge-acceptor molecules that can also be studied in organic solvents, opening new avenues of exploration into the factors critical for protein control of charge flow in biology.</p> / Dissertation

The majority of scholars’ work on code-switching within the sociolinguistic approach of Arabic has been mainly concentrated on the interaction of the Standard variety with other regional dialects in indigenous communities (Albirini, 2011; Bassiouney, 2006; Saeed, 1997; Soliman, 2008). Their work also extends to include the interaction of Arabic with other languages in informal and highly interactional settings (Abalhassan and Alshalawi, 2000; Safi, 1992; Sayahi, 2014). When it comes to the religious settings, their work has been solely devoted to Standard Arabic and Dialectal Arabic in Arabic countries and among Arabic native speakers (Albirini, 2011; Bassiouney, 2006; Saeed, 1997; Soliman, 2008). This thesis, in turn, investigates CS between Arabic and English in highly formal religious settings in the United States and among American Islamic preachers, non-native speakers of Arabic. It aims to enumerate the social functions of CS between English and Arabic and provides the internal optimal bilingual grammar of these speakers. To achieve these goals, two analyses have been conducted, the functional analysis and the optimality-theoretic analysis. The results of the first analysis revealed that preachers chiefly switch from English to Arabic for eight functions: (1) to use formulaic expressions; (2) to introduce direct quotations; (3) to show a level of education in the Islamic studies; (4) to show a level of education in the Arabic language; (5) to evoke Muslimness and Islamic affiliation; (6) to mark emphasis; (7) to stress the importance of a speech segment; and (8) to introduce rhyming stretches. On the other hand, they switch from Arabic to English mainly to fulfill two functions: (1) to translate the previous Arabic stretch; and (2) to simplify, explain, and clarify a segment that was previously mentioned in Arabic. The result of the optimality-theoretic analysis showed that the internal optimal bilingual grammar of American preachers is {FAITH, FACE} >> PERSPECTIVE >> {SOLIDARITY, POWER}.

Thesis (M.Com. (Marketing Management and Information Systems))--University of the Witwatersrand, Faculty of Commerce, Law and Management, School of Economic and Business Sciences, 2016. / It was realised that there are inefficiencies at Company X’s plant K shunting yard; service time was long and the idling time of the locomotives was long. Locomotives can be utilised for other purposes in the plant. This has implication in resource planning and productivity in the company. The study deals with the simulation of the Company X rail network in plant K. The focus is on how shunting and product transportation takes place. A background on the study is given, taking into consideration elements which have been included in the study. These include the locomotives and the Block Train Rail Tanker Cars (RTCs). These containers transport different products from Town L to Town M. The study focuses on the transportation of five products. The study also includes the domestic and international Product E trains arriving at the Product E loading and offloading zone. Simulation model which represents the current-state situation was developed, using SIMIO software package. The study examined how service speed during the process of loading and offloading of products in the plant can be improved. The study also focused on locomotives travelling speed and idling time. Conclusions and recommendations have been made on the model developed. The results obtained were also discussed and analysed. / DH2016

M.A., Faculty of Arts, University of the Witwatersrand, 1995

O objetivo deste trabalho é analisar uma topologia de controle para a malha de tensão de um inversor para fontes de alimentação ininterruptas (UPS) com forma de onda senoidal na saída. É proposto um sistema de controle com duas malhas, uma de tensão com controlador ressonante e outra do tipo PI de corrente no qual a variável de controle é a corrente do capacitor de filtro de saída. Mais especificamente pretende-se estudar o problema de rastreamento de tensão nos inversores de UPS monofásicos, apresentando o estado da arte e uma classificação dos controladores que servem de solução para este problema específico. / This work analyses a uninterruptible power supply (UPS) inverter control scheme with sinusoidal output voltage. A two-loop control scheme is proposed; one voltage loop using a resonant controller and a PI current controller with the output capacitor filter current as control variable. A review on voltage tracking control in one-phase voltage source inverter is presented, showing the state of the art and a controller classification for this specific problem.

Leung, Yiu-Wing. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 150-157). / Acknowledgments / Abstract / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Broadband Video Services --- p.1 / Chapter 1.3 --- Videoconference Services --- p.7 / Chapter 1.4 --- Videoconference Systems --- p.8 / Chapter 1.5 --- Chapter Summary and Thesis Organization --- p.18 / Chapter Chapter 2 --- Efficient Algorithms for Multiple Destinations Routing --- p.20 / Chapter 2.1 --- Background --- p.20 / Chapter 2.2 --- Integer Programming Formulation of the MDR Problem --- p.26 / Chapter 2.3 --- Heuristics for Multiple Destinations Routing --- p.27 / Chapter 2.4 --- Performance Comparisons --- p.40 / Chapter 2.5 --- Chapter Summary --- p.50 / Chapter Chapter 3 --- Connection Optimization for Two Types of Videoconferences --- p.51 / Chapter 3.1 --- Background --- p.51 / Chapter 3.2 --- The Videoconference Services --- p.52 / Chapter 3.3 --- Connection Optimization --- p.54 / Chapter 3.4 --- Performance Analysis --- p.62 / Chapter 3.5 --- Chapter Summary --- p.80 / Chapter Chapter 4 --- A TDM-based Multibus Packet Switch --- p.81 / Chapter 4.1 --- Background --- p.81 / Chapter 4.2 --- Architecture of the Multibus Switch --- p.89 / Chapter 4.3 --- Operation of the Multibus Switch --- p.93 / Chapter 4.4 --- Performance Analysis --- p.95 / Chapter 4.5 --- Numerical Results --- p.106 / Chapter 4.6 --- Discussions --- p.109 / Chapter 4.7 --- Chapter Summary --- p.113 / Chapter Chapter 5 --- A Modular Shared Media Video Switch --- p.114 / Chapter 5.1 --- System Architecture and Operation --- p.114 / Chapter 5.2 --- Slot Assignment for Point-to-Point Transmissions --- p.129 / Chapter 5.3 --- Slot Assignment for Point-to-Multipoint Transmissions --- p.132 / Chapter 5.4 --- Network Design Example --- p.136 / Chapter 5.5 --- Chapter Summary --- p.143 / Appendix --- p.144 / Chapter Chapter 6 --- Conclusions --- p.147 / References --- p.150