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This dissertation includes theoretical and applied components that address the effect of coatings on rates of mineral reactions that occur in acid mine drainage (AMD) environments. The two major projects investigated how diffusion-limited transport of reactants through pore spaces in coatings on mineral grains affects the reaction rate of the underlying mineral. The first project considered the growth of gypsum coatings on the surface of dissolving limestone in anoxic limestone drains (ALD), which reduces the neutralization rate of the dissolving limestone and the subsequent effectiveness of this treatment. The second project investigated the conditions where iron oxyhydroxide coatings form on oxidizing pyrite and the potential strategies to prevent "runaway" AMD by reducing the rate of acid production to the point that the acid can be neutralized by the surrounding rocks. In both studies, experiments were conducted to measure reaction rates for the underlying minerals, as coatings grew thicker. These experimental data were fit to a diffusion model to estimate diffusion coefficients of reactants through pore spaces in coatings. These models are extrapolated to longer times to predict the behavior of the coated grains under field conditions. The experimental results indicate that management practices can be improved for ALDs and mine waste piles. For example, supersaturation with respect to gypsum, leading to coating formation, can be avoided by diluting the ALD feed solution or by replacing limestone with dolomite. AMD can be prevented if the rate of alkalinity addition to mine waste piles is faster than acid is produced by pyrite oxidation. The diffusion model developed in this study predicts when iron oxyhydroxide coatings will become thick enough that alkalinity from the surroundings is sufficient to neutralize acid produced by coated pyrite oxidation and additional alkalinity is no longer required. / Ph. D.

The advent of wide band-gap semiconductors in power electronics has led to the scope of efficient power conversion being pushed further than ever before. This development has allowed for systems to operate at higher and higher voltages than previously achieved. One area of consideration during this high voltage transition is the synchronous rectifier, which is traditionally designed as an afterthought. Prior research in synchronous rectifiers have been limited to low voltage, high current converters. There is practically no research in high voltage synchronous rectification. Therefore, this dissertation focuses on discovering the unknown nuances behind high voltage synchronous rectifier design, and ultimately developing a practical, scalable solution. There are three main issues that must be addressed when designing a high voltage synchronous rectifier: (1) high voltage sensing; (2) light load effects; (3) accuracy. The first hurdle to designing a high voltage SR system is the high voltage itself. Traditional methods of synchronous rectification (SR) attempt to directly sense voltage or current, which is not possible with high voltage. Therefore, a solution must be designed to limit the voltage seen by the sensing mechanism without sacrificing accuracy. In this dissertation, a novel blocking solution is proposed, analyzed, and tested to over 1-kV. The solution is practical enough to be implemented on practically any commercial drain-source SR controller. The second hurdle is the light load effect of the SR system on the converter. A large amount of high voltage systems utilize a LLC-based DC transformers (DCX) to provide an efficient means of energy conversion. The LLC-DCX's attractive attributes of soft-switching and high efficiency allure many architects to combine it with an SR system. However, direct implementation of SR on a LLC-DCX will result in a variety of light load oscillation issues, since the rectifier circuitry can excite the resonant tank through a false load transient phenomena. A universal limiting solution is proposed and analyzed, and is validated with a commercial SR controller. The final hurdle is in optimizing the SR system itself. There is an inherent flaw with drain-source sensing, namely parasitic inductance in the drain-source sense loop. This parasitic inductance causes an error in the sensed voltage, resulting in early SR turn-off and increased losses through the parallel diode. The parasitic will always be present in the circuit, and current solutions are too complex to be implemented. Two solutions are proposed depending on the rectifier architecture: (1) multilevel gate driving for single switch rectifiers; (2) sequential parallel switching for parallel switch rectifiers. In summary, this dissertation focuses on developing a practical and reliable high voltage SR solution for LLC-DCX converters. Three main issues are addressed: (1) high voltage sensing; (2) light load effects; (3) accuracy. Novel solutions are proposed for all three issues, and validated with commercial controllers. / Doctor of Philosophy / High voltage power electronics are becoming increasing popular in the electronics industry with the help of wide band-gap semiconductors. While high voltage power electronics research is prevalent, a key component of high voltage power converters, the synchronous rectifier, remains unexplored. Conventional synchronous rectifiers are implemented on high current circuits where diode losses are high. However, high voltage power electronics operate at much lower current levels, necessitating changes in current synchronous rectifier methods. This research aims to identify and tackle issues that will be faced by both systems and IC designers when attempting to implement high voltage synchronous rectifiers on LLC-DCXs. While development takes planes on a LLC-DCX, the research is applicable to most resonant converters and applications utilizing drain-source synchronous rectifier technology. This dissertation focuses primarily on three areas of synchronous rectifier developments: (1) high voltage compatibility; (2) light load effects; (3) accuracy. The first issue opens the gate to high voltage synchronous rectifier research, by allowing high voltage sensing. The second issue explores issues that high voltage synchronous rectifiers can inadvertently influence on the LLC-DCX itself - a light load oscillation issue. The third issue explores novel methods of improving the sensing accuracy to further reduce losses for a single and parallel switch rectifier. In each of these areas, the underlying problem is root-caused, analyzed, and a solution proposed. The overarching goal of this dissertation is to develop a practical, low-cost, universal synchronous rectifier system that can be scaled for commercial use.

Cette thèse examine la relation complexe et la causalité entre la migration et le développement, sujet d'actualité vus les flux croissants de migrants et les transferts de fonds privés. La revue de la littérature théorique et empirique montre la complexité de cette relation, et l’absence de consensus dégagé par les travaux menés sur les causes et les effets de la migration sur le développement. Sur les causes de migration, une première estimation empirique montre qu’elle fait partie intégrante du processus de développement et n’est donc pas une simple conséquence de faibles niveaux de développement: le niveau de développement des pays d'origine s’accroissant, les aspirations et les capabilités des populations augmentent et si celles-ci font face à l'absence d’opportunités, elles vont migrer à condition d’en avoir les capabilités (compétences requises, moyens financiers, politiques de migration, etc.). Concernant l’impact de la migration, une deuxième estimation empirique montre un effet positif sur le développement via les transferts privés. Les modèles indiquent que leur contribution se fait à travers deux principaux canaux, l'investissement en capital et le capital humain (éducation et santé), lesquels sont susceptibles de permettre un développement à long terme des pays d'origine. Au niveau micro, une troisième série de modèles étudie le mécanisme de cet impact au niveau de ménages, à partir du cas de l'Egypte. Ces modèles confirment l'importance des transferts privés sur les niveaux d'éducation et de santé dans les ménages qui les reçoivent. Ces résultats sont censés contribuer à la compréhension de cette relation complexe entre migration et développement. / This thesis is concerned with the causal and complex relation between migration and development. A timely subject, especially with increasing flows of migrants and the remittances these migrants send home. Both the theoretical and empirical literature reviews address the complexity of this relation but consensuses on the causes and impacts of migration on development are generally inconclusive. On the causes of migration, our first empirical estimation shows that migration is part of the development process and not a simple result of its low levels: the increasing development level of the home countries increase the aspirations and capabilities of their populations and if these are faced with lack of opportunities at home, individuals seek migration provided they have the right capabilities (skills required, financial means, migration policies, etc.). On the impact of migration, our second empirical estimation gives evidence of a positive impact through remittances on the development of the home countries. The models show the positive contributions of remittances towards development through two main channels: capital investment and human capital (education and health). These two channels are believed to achieve long-term development of the home countries. At the micro level, we look at the mechanism of this impact at the household level, addressing the case study of Egypt. Our third models give evidence of the importance of these remittances in increasing both education and health status of the recipients’ households’. These findings are believed to make a contribution towards the understanding of this complex relation between migration and development.

La capacité d’un émetteur radar à assurer la bonne détection des cibles mouvantes sans générer de fausses alertes dépend principalement de sa stabilité pulse à pulse qui est affectée par de nombreux facteurs tels que les effets mécaniques, thermiques et électriques. Cependant, la stabilité pulse à pulse d’un émetteur radar à impulsions est liée à celle de ses amplificateurs de puissance, et plus particulièrement à la technologie des dispositifs actifs. Dans ce sens, ce travail présente une analyse de ce critère radar au plus près du composant (au niveau d’un transistor HEMT GaN) dans le cas d’une rafale radar d’impulsions irrégulières. Un nouveau banc de mesure temporelle d’enveloppe 4-canaux à base de THA a été développé pour les besoins de mesure de stabilité pulse à pulse. Ce système de mesure permet aussi d’extraire la réponse temporelle de courant basse fréquence à des rafales irrégulières d’impulsions RF. Bien que cette configuration ait été initialement développée pour caractériser la spécification critique de la stabilité pulse à pulse pour les applications radar, elle a montré un énorme potentiel pour la modélisation des pièges lors des simulations temporelles d’enveloppe, en complément des différentes techniques de caractérisation des pièges (I-V impulsionnelle, dispersion basse-fréquence de l’admittance de sortie Y22). / The capability of a radar transmitter to ensure clutter rejection depends mainly on its pulse-to-pulse stability, which is affected by many factors such as mechanical, thermal, and electrical effects. However, the P2P stability of a pulsed radar transmitter is linked to that of its power amplifiers, and more specifically on the active device technology. In this context, thiswork presents the analysis of this radar criterion at device level (GaNHEMTtransistor) in the case of a radar burst of RF pulses. A new on-wafer time-domain envelope measurement setup based on a 4-channel THA receiver has been developed to characterize pulse-to-pulse stability and the low-frequency drain current. While this setup was originally developed to characterize the critical specification of pulse-to-pulse stability for radar applications, it demonstrated a great potential for trap modeling in addition to the different characterization techniques of traps (pulsed I-V, low-frequency dispersion of Y22).

Shire of Murray has concerns regarding the negative impact that a 100 year flood could have on existing structures built before 1997. The increase cost in construction due to landfill has an adverse effect on development in Pinjarra. Feasibility of constructing a diversion channel at upstream of Murray River to attenuate the flood level from 1 in 100 year ARI to 1 in 50 year ARI, was investigated by Kiong (2003). The Murray River Water Surface Profile along three kilometres south of Greenlands Road was modelled. Flood damages on each flood occurrence were assessed and Average Annual Damage (AAD) was calculated. The AAD is used to estimate the monetary benefit against the construction cost of the diversion channel. Groundwater along Greenlands and Fauntleroy Drains was also modelled to determine the viable depth of the designed channel, as well as the analysis of backwater. The proposed channel is designed at different scenarios (invert level at breakout point, culvert or causeway design, and diversion channel variations). The benefit cost ratio of the proposed diversion channel is calculated. Other mitigation options are suggested including detention basins for structural measure, or building a new flood-proof township for non-structural measure.

Over the past 30 years South Africa has lost valuable human capital due to high volumes of emigration. South Africa has also seen numerous changes in its political, economic and social structure specifically in these decades, but little investigation has been done into the possibility of an association between political, economic and social, as well as personal factors, and the decision to leave South Africa. This study refers to Lee’s Migration Model (1966) that was used as a broad theory for migration. The model involves four sets of factors: factors associated with the area of origin, factors associated with the area of destination, intervening obstacles and personal factors. Maslow’s Hierarchy of Needs Theory also explains the personal motivational theory for migration. Lee’s Model of Migration is used to investigate which political, economic, social and personal factors in the area of origin (South Africa) pushed South African emigrants to leave the country. It also investigates which political, economic, social and personal factors in the area of destination (Australia and New Zealand) pulled South African emigrants toward these countries. This study involved mixed-methods research (Creswell, 2009), thus the data collection methods were both qualitative and quantitative. The study followed a sequential exploratory strategy in two stages with the qualitative data collection occurring first, followed by a quantitative study – ‘QUALquan’ study. The data are mixed between analysis of the qualitative data and the quantitative data collection (Creswell, 2009:211). The qualitative data collection instruments used in the first stage of the study in 2009, were face-to-face interviews consisting of one focus group and six personal interviews in New Zealand, as well as twelve personal interviews in Australia. In the second stage of the study in 2015, namely the quantitative research, respondents were selected by contacting 17 closed (secured) Facebook groups that were formed for South Africans living either in Australia or New Zealand. There is no alternative sampling frame available since emigrants do not need to declare themselves as migrants on a work visa, furthermore, official documentation is not accessible to the public. A quantitative data collection instrument was administered with an online questionnaire. In the Australian Facebook groups, 137 respondents completed the questionnaire, and in New Zealand Facebook groups, 118 respondents, which adds up to a total of 255 respondents who completed the questionnaire. The results concluded that South Africa’s governance framework, its infrastructure and legislation acted as political push factors motivating South Africans to emigrate, while an uncertain economy contributed as an economic push factor. Socially, a perception of a limited future and a narcissistic society is what pushed South Africans to emigrate. Personal push factors that drove the emigration decision included, unmet physical, safety, belonging and esteem needs. The political factors that pulled South African emigrants to Australia and New Zealand involved effective government services and governmental aid. Economic pull factors included economic certainty and a lower cost of living. Social pull factors proved to be familiar circumstances and a better future. Personal pull factors were safety, belonging and self-actualisation needs. This mixed-method approach focussed on the gap to a followup study that was identified in previous individual qualitative and quantitative studies. These results may assist the South African government to take measures that ensures the retention of highly skilled citizens. / Business Management / M. Com. (Business Management)

The thesis deals with the back analysis of the instrumentated embankment on the subsoil, improved by prefabricated vertical drains. The first part is devoted to the theory of consolidation calculation. Furthermore, the author deals with a parametric study of the analytical calculation of prefabricated drains and the comparsion of the analytical and numerical solution. The last and the largest part of the work is a back analysis of the embankment which was built as a part of the subsoil improvement near the Suez Canal in Egypt by Keller GmbH.

Thesis (MBA)--University of Stellenbosch, 2011. / Healthcare systems of the world’s poorer nations have been heavily impacted by economic globalisation. This has resulted in a steady deterioration of working conditions, resulted in less job security and has led to an increase in the spread of communicable diseases in developing countries such as South Africa. It is factors such as these, against the backdrop of a global recession, that have contributed to the escalation in global healthcare costs which has itself augmented the strain on already strained hospital resources in developing economies (Issues paper: Economic Globalisation, 2009). The current workplace faces complicated challenges which extend beyond the effects of the global recession. One of these challenges is the task of managing the diversity of the modern day workforce. This includes differences in gender, race, religion, culture, language, physical and mental ability, sexual orientation as well as generational differences. As a result, organisations that choose to exploit these differences are able to leverage a competitive advantage from them. This ability is however determined by the flexibility of organisations’ policies and practices. Furthermore, adapting an organisation’s human resource policies and practices pertaining to attracting, retaining, developing, promoting and managing a generational diverse workforce is only possible once these cohorts have been clearly identified, analysed and understood (Manion, 2009). Nurses are the pillar of healthcare systems throughout the world. In South Africa, however, the high staff turnover of nurses compared to the relatively small number of new recruits is of great concern due to its impact on the South African government’s capacity to provide a healthcare model of sustainable service delivery (Mokoka, 2007). The reality of the decline in the number of newly qualified nurses was clearly evident in the results of this study. Twenty-eight percent of the current community service nurses had previously considered leaving the profession, eight percent reported that they were considering leaving the profession within the next year and 20 percent intended leaving the public health sector after completing community service. The purpose of this qualitative study was to determine factors that preclude better remuneration that would influence community service nurses’ decision to remain employed in the public health sector. According to the Western Cape Nursing directorate, 270 nurses were registered to complete community service in the Western Cape in 2010. The 25 registered nurses who were scheduled to complete community service at Groote Schuur Hospital at the end of 2010 constituted the study sample. A self-administered questionnaire was used as the instrument for data collection from this fixed, convenient sample. Confidentiality of the participants was assured throughout the study and findings were reported as combined facts and figures using histograms. The majority of the participants were between the age of 20 and 25 years (48%). Furthermore, 88 percent of the participants were below the age of 35 years, largely representative of Generation X and the Millennials, Generation Y. The results of this study suggested an extremely complex interplay between intrinsic and extrinsic motivators, in influencing the decision of whether or not to remain employed in the public health sector. It was further evident that most of the factors that were rated to be of high importance were strongly self-centred, largely geared at personal reward and recognition. This finding is in clear agreement with literature published by Manion (2009) who supports the thinking that generations representative of Generation X and Y have a strong need for personal achievement and reward. Eighty percent of participants indicated a dire need for hospital management to recognise and manage generational diversity in the current workforce as this presented a daily challenge in the workplace. It was perceived that fundamental differences in needs, work ethic and values exist between Generations X and Y, compared to those of nurse and hospital managers who were representative of Baby Boomers. Consequently, there appeared to be a mismatch in the expectations and opportunities presented in the current workplace among the three generations. These findings merit further discussion on whether the permanent multi-disciplinary team at hospitals understand the influential role that they have on the complex task of retaining community service nurses in the public health service. Furthermore, 92 percent of community service nurses highlighted the need for mandatory orientation and induction programmes in each ward prior to commencing duty. This in itself was identified as a huge cause for anxiety and discord. In conclusion, even though this study was designed to establish factors that preclude better remuneration which could influence the decision of community service nurses to remain employed in the public health sector, it found that more than half the participants of this study recommended that receiving a more competitive salary was still an important issue for government to prioritise. However, it did not appear to be the overshadowing theme of dissatisfaction amongst community service nurses.

Thesis (MBA)--University of Stellenbosch, 2011. / There is a global scarcity of health care workers (Boseley, 2011: 1). There has been global competition for the scarce resource, with developing countries competing for their own health care workers (Padarath et al., 2004: 5). The health outcomes of a country have been directly correlated with the quantity and quality of its health human resources (Dolea et al., 2005: 3). Pharmacists, who were ranked as the third scarcest professional group in the world, are the most accessible of all health workers (Chan & Wuliji, 2006: 7). The shortage of pharmacists has resulted in inaccessibility to drug treatment, prevention and care, resulting in an insurmountable number of preventable deaths and disease. The number of pharmacists in KwaZulu-Natal province is currently 383, with a 76% vacancy rate (Avery, 2011). The aim of the present study was to define a retention strategy for public sector pharmacists in KwaZulu-Natal province. This self-administered questionnaire survey was participated in by 103 pharmacists. Pharmaceutical services were found predominantly to have been rendered by young (with 32% falling in the age group 22–29 years of age and 36% falling in the age group 30–39 years), Indian (74%), female (82%) pharmacists. Many (68%) of the pharmacists concerned were new entrants (having been in employ for a period of 0–5 years) in the public sector, with just over half (36%) being new entrants into the pharmacy profession, meaning that two-thirds of the public sector pharmaceutical workforce lacked the experience and expertise to make the desired service delivery changes in said environment. The top three motivations for job changes were found to be financial (27%), working conditions (26%) and career advancement opportunities (22%). A third of the respondents were found to be satisfied with the Occupation-specific Dispensation. The remainder of the pharmacists were equally divided about whether they regarded the payout to be inadequate or fair. Nonetheless, 20 per cent had definite intentions to leave, with 40 per cent having no intention to leave, and 40 per cent being uncertain about doing so. Such a finding correlated well with the fact that 24% of the respondents indicated that they felt that they were earning inadequate salaries. The finding did not correlate with the overwhelming response (83%) that money was not the most important consideration in making the choice. The pharmacists were divided regarding career-advancing opportunities in the public sector. Such a finding was echoed in a comparable division of who had access to information on career-advancing opportunities. Two-thirds of the respondents neither shared their goals regarding career progression with their supervisors, nor applied for any such posts. The top three factors that pharmacists liked about their jobs were financial, resources and congenial working conditions. Resources, working conditions and lack of career progression factors were disliked; resources, career progression and financial factors could result in turnover. In summary, money, career progression and resources matter. The pharmacists in the province were found to be satisfied with their earnings. They wanted to be rewarded on merit and were prepared to move to receive this and support in career progression. The National Department of Health (KwaZulu-Natal) must drive recruitment efforts to address the skills shortage, improve working conditions and ensure that salaries keep pace with inflation to create long-term wins for the public health sector.