The DIRECT (DIviding RECTangles) algorithm JONESJOTi, a variant of Lipschitzian methods for bound constrained global optimization, has been applied to the optimal transmitter placement for indoor wireless systems. Power coverage and BER (bit error rate) are considered as two criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. The performance of a DIRECT implementation in such applications depends on the characteristics of the objective function, the problem dimension, and the desired solution accuracy. Implementations with static data structures often fail in practice because of unpredictable memory requirements. This is especially critical in S⁴W (Site-Specific System Simulator for Wireless communication systems), where the DIRECT optimization is just one small component connected to a parallel 3D propagation ray tracing modeler running on a 200-node Beowulf cluster of Linux workstations, and surrogate functions for a WCDMA (wideband code division multiple access) simulator are also used to estimate the channel performance. Any component failure of this large computation would abort the entire design process. To make the DIRECT global optimization algorithm efficient and robust, a set of dynamic data structures is proposed here to balance the memory requirements with execution time, while simultaneously adapting to arbitrary problem size. The focus is on design issues of the dynamic data structures, related memory management strategies, and application issues of the DIRECT algorithm to the transmitter placement optimization for wireless communication systems. Results for two indoor systems are presented to demonstrate the effectiveness of the present work. / Master of Science

Permanent magnet brushless DC motors that have found wide application in high performance servo drives need absolute rotor position sensors. However, the cost of the position sensor limits the use of brush less DC motors for low performance applications such as automotive and home appliances. A sensorless starting scheme for brushless DC motors is studied in this thesis. A hardware implementation of the starting scheme has been instrumented. The modeling and simulation of the sensorless starting performance of brushless DC motors have been accomplished to gain the insight into the process. The experimental results confirm the theoretical prediction that the permanent magnet brush less DC motor can be started without a position sensor. The experimental setup with individual subsystems are described in detail. / Master of Science

No description available.

A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. Fuel cells bear similarity to batteries, with which they share the electrochemical nature of the power generation process and to the engines that, unlike batteries, will work continuously consuming a fuel of some sort. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in the laboratory but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid Polymer Electrolyte Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen contaminated with carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed/liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol and diethyl ether have been considered for fueling PEFCs directly. Among these, methanol with hydrogen content of about 12.8 wt.% (specific energy = 6.1kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the fuel cell during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride (specific energy = 12kWh kg-1), which has a capacity value of 5.67Ah g-1 and a hydrogen content of about 11wt.%. Such fuel cells are called direct borohydride fuel cells (DBFCs). This thesis is directed to studies on SPE-DMFCs and DBFCs

Pendant les dernières décennies, le travail d'une partie toujours croissante de chercheurs qui s'occupent de robotique s'est focalisé sur un groupe spécifique de robots qui fait partie de la famille des manipulateurs parallèles: les robots à câbles. Malgré les nombreuses études que l'on a consacrées à ce sujet, ces robots présentent encore aujourd'hui plusieurs problématiques complètement ou partiellement irrésolues. En particulier l'étude de leur cinématique, qui se révèle déjà complexe pour les manipulateurs parallèles traditionnels, est rendu encore plus compliqué par la nature non linéaire des câbles qui peuvent seulement exercer des efforts de traction. Le travail présenté dans cette thèse concentre donc son attention sur l'étude de la cinématique des robots à câbles et sur la mise au point de techniques numériques capables d'aborder une partie des problématiques liées à cela. La plupart du travail se concentre sur l'élaboration d'un algorithme pour la résolution du problème géométrique direct pour n'importe quel manipulateur à câbles qui se fonde sur l'analyse par intervalles. Cette technique d'analyse permet non seulement de résoudre rapidement le problème mais également de garantir les résultats obtenus en cas d'erreurs d'élimination et d'arrondi et de prendre en considération les incertitudes éventuellement présentes dans le modèle du problème. Le code développé a été testé grâce à un petit prototype de manipulateur à câbles dont la réalisation, qui a eu lieu pendant le parcours de doctorat, est décrite à l'intérieur du mémoire en accord avec la phase de conception du projet et de simulation. / In the past two decades the work of a growing portion of researchers in robotics focused on a particular group of machines, belonging to the family of parallel manipulators: the cable robots. Although these robots share several theoretical elements with the better known parallel robots, they still present completely (or partly) unsolved issues. In particular, the study of their kinematic, already a difficult subject for conventional parallel manipulators, is further complicated by the non-linear nature of cables, which can transmit forces only when they are taut. The work presented in this thesis therefore focuses on the study of the kinematics of these robots and on the development of numerical techniques able to address some of the problems related to it. Most of the work is focused on the development of an interval-analysis-based procedure for the solution of the direct geometric problem (DGP) of a generic cable manipulator. This technique, as well as allowing for a rapid solution of the problem, also guarantees the results obtained against rounding and elimination errors and can take into account any uncertainties in the model of the problem. The developed code has been tested with the help of a small manipulator whose realization is described in this dissertation together with its design and simulation phases.

Doctor of Philosophy / Department of Economics / Yang-Ming Chang / This dissertation comprises three chapters in international trade and the economics of conflict. These chapters are put together according to two dimensions. From the international relations dimension, Chapter 1 analyzes free trade, which is the most “liberal” form of international relation; Chapter 2 analyzes different types of trade agreements, which is the most common and “moderate” form of international relation; and Chapter 3 analyzes conflict, which is the most violent and “extreme” form of international relation. From the proximity dimension, free trade usually occurs between countries that are far from each other, trade agreements usually signed by countries with in a region, and conflict usually happens between two very close countries. Chapter 1 develops a novel model of international trade in which transportation costs are driven by trade imbalance of an individual country. This task is accomplished by assuming a representative transportation firm in each country that competes with its counterparts from other countries for international operation. The model of trade imbalance driven costs complements results from traditional international trade model in that it sheds light on how trade costs are affected by country size. With multiple countries and a continuum of production firms in each country under monopolistic competition, we derive an index of transportation costs to capture bilateral trade barriers for country pairs. This index is time-variant, which makes it suitable for panel data studies. Based on the index, simulation and simplified three-country free trade model show that countries with a relatively larger size incur a trade deficit while smaller size implies a trade surplus under free trade. A gravity equation is derived and estimated using Poisson Pseudo Maximum Likelihood. Estimation results support the fitness and robustness of the theoretical model of trade using the constructed transportation cost index. Further, statistical test shows that this transportation cost index is a better approximation of bilateral trade cost than distance. A growing number of recent regional trade agreements (RTAs) have introduced provisions concerning cross-border investments. Likewise, a substantial number of RTAs have been preceded by agreements regarding cross-border investments. In Chapter 2, we develop a partial equilibrium three-country model to examine the relationship between RTAs and FDI while also allowing for double taxation. Our analysis shows that the formation of an RTA between two regional countries with wage asymmetry is welfare-improving for the low-wage country and the region, but can be welfare-deteriorating for the high-wage country. We extend our analysis to examine the role of repatriation taxes in the determination of firm location when an RTA is and is not established. Our final result suggests that the signing of an RTA would not induce the relocation of a plant from the high-wage country to the low-wage country unless a reduction of the repatriation tax rate also occurs. In Chapter 3, we attempt to resolve the “inefficiency puzzle of war” by developing a general equilibrium model of bargaining and fighting with endogenous destruction. In the analysis, we consider the scenario that two contending parties engage in bargaining to avoid fighting when there are direct costs (e.g., arms buildups) and indirect costs (e.g., destruction to consumable resources) of conflict. Taking into account different modes of “destruction technology” (in terms of weapons’ destructiveness) without imposing specific functional form restrictions on conflict technology and production technology, we characterize their interactions in determining the Nash equilibrium choice between fighting and bargaining. We find that bargaining is costly as the contending parties always allocate more resources to arming for guarding their settlement through bargaining (but under the shadow of conflict) than in the event of fighting. Contrary to conventional thinking that bargaining is Pareto superior over fighting, we show conditions under which fighting dominates bargaining as the Nash equilibrium choice. The positive analysis may help explain the general causes of fighting, strikes, international conflict, and wars without incomplete information or misperceptions.

Direct Metal Laser Sintering (DMLS) is a rapid prototyping technique that allows for direct and rapid manufacturing of complex components. DMLS is however an intricate process and the quality of the final product is influenced by multiple manufacturing parameters (or DMLS settings) and powder characteristics. The effect which each of these manufacturing parameters and powder characteristics has on the final parts is not well understood and the success of process manufacturing mainly relies on empirical knowledge. Consequently high dimensional deformation and relatively poor mechanical properties are still experienced in many DMLS products, in particular in copper-based laser sintered parts. A need therefore exists to systematically examine the effect of process parameters on the quality of final parts in order to determine the most appropriate manufacturing parameters for specific applications of copper-based laser sintered parts. This document summarises the effect of different process parameters on the quality of Direct Metal 20 laser sintered parts produced with a EOSINT M250 Xtended laser sintering machine from powder consisting of Ni5Cu, Cu15Sn – Cu5Sn and Cu8P – Cu2P material grains. The quality of the sintered parts is defined in terms of the microstructures, porosities and dimensional deformations obtained. The effects of three different geometric sintering strategies currently in standard use namely Solid Skin, Skin Stripes and Skin Chess were examined, and the more appropriate process parameters and scanning technique for the available set-up is presented. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

This study focuses on Multinational Corporations (MNCs) and their importance in the economic development of Third World Countries. Recogni sing that. MNCs can contribute to economic growth and development, most Third World Countries are constantly working to attract them. hence their demand has become highly competiti ve. However, MNCs do not go without some negative effects. such as conflicts between host and investor countries. and the creation of damaging competition to local firms. These negative effects could be minimised if policies and strategies for the promotion and attraction of MNCs are part of. and integrated into. general economic development and economic reform policies and not seen in isolation. Although Third World Countries have implemented strategies to attract more MNCs. a refinement of some of these policies is needed if a country is to be successful in this regard. / Thesis (M.A (International Relations) North-West University, Mafikeng Campus, 2014

Direct Metal Laser Sintering (DMLS) is a rapid prototyping technique that allows for direct and rapid manufacturing of complex components. DMLS is however an intricate process and the quality of the final product is influenced by multiple manufacturing parameters (or DMLS settings) and powder characteristics. The effect which each of these manufacturing parameters and powder characteristics has on the final parts is not well understood and the success of process manufacturing mainly relies on empirical knowledge. Consequently high dimensional deformation and relatively poor mechanical properties are still experienced in many DMLS products, in particular in copper-based laser sintered parts. A need therefore exists to systematically examine the effect of process parameters on the quality of final parts in order to determine the most appropriate manufacturing parameters for specific applications of copper-based laser sintered parts. This document summarises the effect of different process parameters on the quality of Direct Metal 20 laser sintered parts produced with a EOSINT M250 Xtended laser sintering machine from powder consisting of Ni5Cu, Cu15Sn – Cu5Sn and Cu8P – Cu2P material grains. The quality of the sintered parts is defined in terms of the microstructures, porosities and dimensional deformations obtained. The effects of three different geometric sintering strategies currently in standard use namely Solid Skin, Skin Stripes and Skin Chess were examined, and the more appropriate process parameters and scanning technique for the available set-up is presented. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Urinary tract infection (UTI) is a very common infection in humans and a majority is caused by Escherichia coli. UTI are commonly treated empirically. However, empiric treatment has become more problematic due to increased antibiotic resistance to commonly used antibiotic agents. It is therefore desirable with short turnover times for antimicrobial susceptibility testing and species identification to improve antibiotic treatment at an early stage. Matrix Assisted Laser Desorption/Ionisation Time of Flight (MALDI-TOF) can provide species identification faster than former routine methods. This study compared direct and standard susceptibility testing using disk diffusion on Enterobacteriaceae (EB) from urine samples. The possibility to standardise the inoculum for direct susceptibility testing via a pellet obtained by a series of centrifugations was also evaluated, as well as direct species identification with MALDI-TOF from the pellet. Results from direct susceptibility testing from urine samples with EB, performed either directly from the urine or with a standardised inoculum, correlated well to those obtained with standardised susceptibility testing using EUCAST disk diffusion methodology with few errors, of which most were associated with Proteus mirabilis. The concept of standardising the inoculum for direct susceptibility testing to 0.5 McFarland was labour intensive and did not improve the results further. However, direct species identification from the urine pellet using MALDI-TOF showed good correlation to routine identification. Of 238 samples, an EB was correctly identified in 148 samples using MALDI-TOF.