The production of cereals, especially maize, which is a staple food in sub-Saharan Africa, is challenged by pests and diseases. In addition, climate change will exacerbate the magnitude of these challenges and agriculture in general. Lepidopteran stemborers are major pests of cereal crops in sub-Saharan Africa. Two indigenous noctuids, Busseola fusca and Sesamia calamistis and one exotic crambid, Chilo partellus, occur as single and mixed-species communities infesting cereal crops in East and southern Africa. The composition of these communities however varies with altitude and over seasons. Interactions between the species especially when in combination, can affect the level of damage to cereal crops. The objective of this study was to describe the intraspecific and interspecific interactions between the three stemborer species when they make use of the same resources. This study involved field surveys in maize fields in major agro-ecological zones and also different experiments under greenhouse and laboratory conditions to describe the interactions between the species as well as the effect of temperature, species density and duration of the period of competition on outcomes of these interactions. Results showed that stemborer communities are composed of single and mixed species of B. fusca, S. calamistis and C. partellus, which varied with the different agro-ecological zones and also along altitudinal gradients. Temperature was the most important abiotic factor that influenced the composition of stemborer communities. However, infestation patterns varied with season. This study also showed that female moths of the three species did not avoid oviposition on plants that were previously infested by stemborers. Busseola fusca showed a high preference for heterospecific-infested plants, while C. partellus preferred conspecific-infested plants. Sesamia calamistis did not show a significant preference for one plant over the other. This study further showed that both intra- and interspecific competition characterise communities of these stemborer species which ultilise the same resources. Interspecific competition was stronger between the noctuids and the crambid than between the two noctuid species. Temperature had a significant influence on the competitive outcomes between the three species. Finally the study showed that densitydependent effects and the duration of the interactions are also important factors which influence the level of competitive outcomes between the species. Climate change is likely to influence the interactions and composition of stemborer communities. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

The production of cereals, especially maize, which is a staple food in sub-Saharan Africa, is challenged by pests and diseases. In addition, climate change will exacerbate the magnitude of these challenges and agriculture in general. Lepidopteran stemborers are major pests of cereal crops in sub-Saharan Africa. Two indigenous noctuids, Busseola fusca and Sesamia calamistis and one exotic crambid, Chilo partellus, occur as single and mixed-species communities infesting cereal crops in East and southern Africa. The composition of these communities however varies with altitude and over seasons. Interactions between the species especially when in combination, can affect the level of damage to cereal crops. The objective of this study was to describe the intraspecific and interspecific interactions between the three stemborer species when they make use of the same resources. This study involved field surveys in maize fields in major agro-ecological zones and also different experiments under greenhouse and laboratory conditions to describe the interactions between the species as well as the effect of temperature, species density and duration of the period of competition on outcomes of these interactions. Results showed that stemborer communities are composed of single and mixed species of B. fusca, S. calamistis and C. partellus, which varied with the different agro-ecological zones and also along altitudinal gradients. Temperature was the most important abiotic factor that influenced the composition of stemborer communities. However, infestation patterns varied with season. This study also showed that female moths of the three species did not avoid oviposition on plants that were previously infested by stemborers. Busseola fusca showed a high preference for heterospecific-infested plants, while C. partellus preferred conspecific-infested plants. Sesamia calamistis did not show a significant preference for one plant over the other. This study further showed that both intra- and interspecific competition characterise communities of these stemborer species which ultilise the same resources. Interspecific competition was stronger between the noctuids and the crambid than between the two noctuid species. Temperature had a significant influence on the competitive outcomes between the three species. Finally the study showed that densitydependent effects and the duration of the interactions are also important factors which influence the level of competitive outcomes between the species. Climate change is likely to influence the interactions and composition of stemborer communities. / PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

The rapidly expanding space sector is at the forefront of innovation. New technologies are been continuously developed to allow more availability of space for a multitude of commercial or scientific goals. The same is especially true for the field of Space propulsion, where the focus is towards more compact and greener solutions, for launchers, satellites and landers. One of the most suitable candidates for chemical propulsion is the use of liquid oxygen in combination with liquid hydrogen, which, however, comes with many drawbacks connected primarily to the low energetic density of liquid hydrogen and the complexity of storing cryogenics. An innovative solution to this challenge comes with the use of Metal oxidation or metal combustion reaction. This implies the use of the reaction between air and metals or between water and metals to generate heat, power and hydrogen. This allows for much easier power generation since metal powders are simple to stock and have a much higher density than hydrogen. Therefore, the process is compact and completely renewable. The technology has undoubted potential for space applications too. The high energy density, the lack of cryogenics, the high availability and the re-usability make this technology suitable for power generation purposes and, in this case, for propulsive purposes. This thesis aims to explore the various applications of metal combustion, with a particular focus on space propulsion applications. The gathered literature will be then used to produce a conceptual design of a novel propulsion system which maximises the benefits of metal combustion.

Thesis (MComm (Logistics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Suppose a lottery draw consists of forming a winning ticket by randomly choosing t m distinct numbers from a universal set Um = f1; : : : ;mg. Each lottery participant forms a set of tickets prior to the draw, each ticket consisting of n m distinct numbers from Um, and is awarded a prize if k minfn; tg or more numbers in at least one of his/her tickets matches those of the winning ticket. A lottery of this form is denoted by the quadruple hm; n; t; ki, and the prize is known as a k-prize. The participant's set of tickets is also known as a playing set. The participant may wish to form a playing set in such a way that the probability of winning a k-prize is at least 0 < 1. Naturally, the participant will want to minimise the cost of forming such a playing set, which means that the cardinality of the playing set should be as small as possible. This combinatorial minimisation problem is known as the incomplete lottery problem and was introduced by Gr undlingh [16], who also formulated a related problem called the resource utilisation problem. In this problem one attempts to select a playing set of pre-speci ed cardinality ` in such a way that the probability of winning a k-prize is maximised. Gr undlingh [16] studied the incomplete lottery problem and the resource utilisation problem in the special case where n = t. In this thesis both problems are considered in the general case where n 6= t. Exact and approximate solution methods are presented and compared to each other in terms of solution quality achieved, execution time and practical feasibility. The rst solution method involves a mathematical programming formulation of both problems. Using this solution method, both problems are solved for small lottery instances. An exhaustive enumeration solution method, which uses the concept of overlapping playing set structures [5, 16], is reviewed and used to solve both combinatorial optimisation problems for the same small lottery instances. The concept of an overlapping playing set structure is further explored and incorporated in an attempt to solve both combinatorial optimisation problems approximately by means of various metaheuristic solution approaches, including a simulated annealing algorithm, a tabu search and a genetic algorithm. The focus of the thesis nally shifts to a di erent problem involving lotteries. An investigation is conducted into the probability, P(N; ), of participants sharing a k-prize if a total of N tickets are purchased by participants of the lottery hm; n; t; ki. Special attention is a orded in this problem to the jackpot prize of the South African national lottery, Lotto, represented by the quadruple h49; 6; 6; 6i and how the value of P(N; ) is a ected by the way that participants select their playing sets. / AFRIKAANSE OPSOMMING: Gestel 'n lotery-trekking bestaan uit die ewekansige seleksie van 'n wenkaartjie bestaande uit t m verskillende getalle uit 'n universele versameling Um = f1; : : : ;mg. Elke lotery-deelnemer vorm 'n versameling kaartjies voor die trekking, wat elk uit n m verskillende getalle in Um bestaan, en wen 'n prys indien k minfn; tg of meer getalle in minstens een van sy/haar kaartjies ooreenstem met di e in die wenkaartjie. 'n Lotery van hierdie vorm word deur die viertal hm; n; t; ki aangedui, en die prys staan as 'n k-prys bekend. 'n Deelnemer se kaartjies staan ook as a spelversameling bekend. 'n Lotery-deelnemer mag poog om sy spelversameling s o te selekteer dat die waarskynlikheid om 'n k-prys te wen, minstens 0 < 1 is. Die deelnemer sal natuurlik die koste wat met so 'n spelversameling gepaard gaan, wil minimeer, wat beteken dat die kardinaliteit van sy spelversameling so klein as moontlik moet wees. Hierdie kombinatoriese minimeringsprobleem staan as die onvolledige lottery-probleem bekend en is vir die eerste keer deur Gr undlingh [16] bestudeer, wat ook die verwante hulpbronbenuttingsprobleem geformuleer het. In laasgenoemde probleem word daar gesoek na 'n spelversameling van vooraf-gespesi seerde kardinaliteit wat die waarskynlikheid om 'n k-prys te wen, maksimeer. Gr undlingh [16] het die onvolledige lottery-probleem en die hulpbronbenuttingsprobleem in die spesiale geval oorweeg waar n = t. In hierdie tesis word beide probleme in die algemeen oorweeg waar n 6= t. Eksakte en heuristiese oplossingstegnieke word vir beide probleme daargestel en met mekaar in terme van oplossingskwaliteit, oplossingstyd en praktiese haalbaarheid vergelyk. Die eerste oplossingstegniek behels 'n wiskundige programmeringsformulering van beide probleme. Die probleme word deur middel van hierdie benadering vir klein loterye opgelos. 'n Uitputtende enumerasietegniek, wat gebruik maak van die konsep van spelversameling oorvleuelingstrukture [5, 16], word daarna in o enskou geneem en beide kombinatoriese optimeringsprobleme word vir dieselfde klein loterye met behulp van hierdie tegniek opgelos. Die konsep van 'n spelversameling oorvleuelingstruktuur word verder ondersoek en in 'n benaderde oplossingstegniek vir beide kombinatoriese optimeringsprobleme ge nkorporeer deur gebruik te maak van verskeie metaheuristiese oplossingsbenaderings, insluitende 'n gesimuleerde afkoelingsalgoritme, 'n tabu-soektog en 'n genetiese algoritme. Die fokus in die tesis verskuif laastens na 'n ander probleem oor loterye. 'n Ondersoek word geloots na die waarskynlikheid, P(N; ), dat lottery-deelnemers 'n k-prys sal deel indien 'n totaal van N kaartjies in die lotery hm; n; t; ki gekoop word. Spesiale aandag word aan hierdie probleem geskenk in die geval van die boerpot-prys in die Suid-Afrikaanse nasionale lotery, Lotto, wat deur die viertal h49; 6; 6; 6i voorgestel word, en hoe die waarde van P(N; ) be nvloed word deur die manier waarop deelnmers hul spelversamelings selekteer.

<p dir="ltr">Current mission plans for harvesting lunar resources require further investigation of technological and energy requirements to do so. This paper presents an analysis of the thermodynamics involved in hydrogen (H₂) evolution and liquefaction within this scope. It highlights the use of solar-powered systems for electrolysis and membrane separation as efficient means to produce H₂ on the lunar surface. The study compares energy requirements and logistical considerations of in-situ resource utilization (ISRU) against transporting precursors from Earth, where the energy penalty stands at 540 MJ/kg. It is argued that an ISRU solution stands to present the most energy efficient option, particularly with the use of an active magnetic regenerative refrigeration (AMRR) system for liquefaction. Furthermore, an AMRR system also makes the currently proposed plan of shipping methane (CH₄) from the Earth for H₂ production more favorable than implementing ISRU with the state-of-the-art (SOA) reverse turbo-Brayton cryocoolers (RTBC). This emphasizes the significance of an AMRR system for H₂ production and the need for further research in its development. Additionally, this study underscores the significance of regenerative technologies and advanced life support systems for sustainable off-planet human habitation, particularly in the context of lunar and Martian missions.</p>

L’accès aux interventions de la prévention de la transmission mère-enfant (PTME) est limité en Afrique de l’Ouest et les mères infectées continuent de transmettre le virus à leurs enfants. D’importantes questions sur le diagnostic et traitement antirétroviral (TAR) précoce pour les enfants dans les pays à ressources-limitées restent sans réponses. La simulation est un outil utile qui permet d’intégrer toutes les données disponibles et de projeter à long terme les retombées cliniques et économiques de l’infection à VIH pédiatrique et informer les politiques de santé. Bien que les modèles de simulation soient mathématiquement sophistiqués, l’utilité des études basées sur la simulation dépend de la qualité des données de départ. L’objectif principal de ce travail était de fournir des données originales et récentes sur la mortalité, morbidité sévère et recours aux soins chez les enfants infectés par le VIH suivis dans des programmes de soins, avant et après initiation du TAR, dans le contexte du passage à l’échelle du TAR depuis 2004 en Afrique de l’Ouest. Nos résultats font ressortir un taux de mortalité comparable à d’autres études, atteignant 5.5% après 18 mois de suivi dans une cohorte d’enfants non traités par TAR, inclus à un âge médian de 5 ans. Les taux de morbidité sévère étaient élevés chez les enfants non traités mais aussi traités. Nous avons rapportés qu’une hospitalisation sur trois était provoquée par une morbidité infectieuse, évitable par une prophylaxie par cotrimoxazole, une intervention simple et efficace qui n’est toujours pas accessible à tous en Afrique de l’Ouest. Nous avons également observé un recours aux soins importants associé à la morbidité sévère. Cependant, parmi les enfants non traités, comme les traités, le recours aux soins était plus faible parmi les enfants les plus immunodéprimés. Le principal obstacle aux recours aux soins était le coût associé pour les familles. Enfin, les enfants qui initiaient un TAR l’initiaient trop tard, à un stade trop avancée de la maladie pour une restitution immunitaire pour âge ; la probabilité de rattraper une immunité normale était encore plus faible chez les enfants âgés > 5 ans comparé aux plus jeunes. Globalement, ce travail met en avant la nécessité de la mise en place de stratégies de diagnostic et traitement précoce. Optimiser le parcours de soins ainsi implique des interventions à de nombreux niveaux du système de soins et aucune approche unique ne pourra être efficace. De plus, les coûts liés à une prise en charge à vie devront être estimés dans un contexte où le VIH devient une maladie chronique engendrant un plus gros recours aux soins. Intégrer ces données dans un modèle de simulation permettra d’informer les politiques de santé et les soignants afin d’identifier les stratégies les plus efficaces et coût-efficaces pour le diagnostic, le traitement et le suivi à long terme de l’enfant infecté par le VIH dans les pays à ressources limitées. / Access to prevention of mother-to-child transmission (PMTCT) interventions is limited in West Africa and mothers continue to transmit HIV disease to their children. Important questions on early HIV diagnosis and early antiretroviral therapy (ART) for children in resource-limited settings remain unanswered. Computer simulation models can provide helpful information to project long-term patient outcomes and inform health policy. Although simulation models are computationally sophisticated, the usefulness of the results of modelling studies depends on the quality and accuracy of the data on which they are based. The main objective of the following work was to provide accurate and up-to-date data on mortality, severe morbidity and healthcare resource utilisation in HIV-infected children enrolled in care, before and after ART initiation in the context of the access to ART roll-out since 2004 in West Africa. Our findings suggest mortality rates comparable to those of other studies, reaching 5.5% by 18 months of follow-up in children enrolled in cohorts at a median age of 5 years who had not yet initiated ART. Severe morbidity rates were high, in both ART-treated and untreated children. We found that one hospitalisation in three was caused by an infectious disease, avoidable by cotrimoxazole prophylaxis, a simple and efficient intervention that is still not accessible to all in West Africa. We also reported substantial rates of healthcare resource utilisations associated with this severe morbidity. However, in both untreated and ART-treated children, healthcare resource utilisation was lower in the sickest, most immunodeficient children. Access to healthcare remains limited and one of the explanations we put forward are the costs borne by the families. Finally, children on ART remain initiated at a too late stage to be able to restore normal immunity for age; this is even less likely in those who initiated ART after 5 years compared to younger children. Overall, this work underlines the need for an effective early HIV diagnosis and treatment. Optimising this requires interventions at multiple levels of the healthcare system and no single approach is likely to be effective. Furthermore, lifetime treatment costs will need to be assessed as HIV becomes a chronic disease leading to greater healthcare resource utilisation. Integrating these data in computer simulation models will assist healthcare providers and policy-makers to identify the most effective and cost-effective strategies for diagnosis, treatment and monitoring of paediatric HIV in low income countries.

In this work, the use of a lunar regolith simulant as feedstock for the direct ink writing additive manufacturing process is explored, the purpose of which is to enable future lunar in-situ resource utilisation. The feasibility of this approach is demonstrated in a laboratory setting by manufacturing objects with different geometries using methyl cellulose or sodium alginate as binding agents and water as liquid phase together with the lunar regolith simulant EAC-1A to create a viscous, printable ‘ink’ that is used in combination with a custom three-axis gantry system to produce green bodies for subsequent sintering. The sintered objects are characterised using compressive strength measurements and scanning electron microscopy (SEM). It is proposed that the bioorganic compounds used in this work as additives could be produced at the site for a future lunar base through photosynthesis, utilising carbon dioxide exhaled by astronauts together with the available sunlight, meaning that all the components used for the dispersion – additive, water (in the form of ice) and regolith – are available in-situ. The compressive strength for sintered samples produced with this method was measured to be 2.4 MPa with a standard deviation of 0.2 MPa (n = 4). It is believed, based on the high sample porosity observed during SEM analysis, that the comparatively low mechanical strength of the manufactured samples is due to a non-optimal sintering procedure carried out at a too-low temperature, and that the mechanical strength could be increased by optimising the sintering process further.

The purpose of the research was to recommend a model for strategic human resource management through an effective staff performance appraisal system in Botswana public libraries. Performance appraisal is not a new concept; however the evolution of performance appraisal tools and techniques has been slow compared to that of other management fields. This discrepancy is now being realised; organisations are starting to acknowledge the importance of comprehensive, regular appraisal of staff as part of an effective human resource management policy. Human resources are a scarce and valuable tool in any organisation and it is mainly through performance appraisal that they can be developed and maintained, to ensure organisational success. The theory underlying strategic human resource management and performance management has been studied. Empirical research through a questionnaire was carried out in 23 public libraries. From these it was possible to develop a model entitled "A recommended strategic human resource management model". From empirical investigation the main critical qualities for efficient public library services were revealed as enthusiasm; positive attitude; innovative thinking; capability and commitment; critical competencies as expertise; team-building; and leadership; critical external factors as external environment; global competition; shrinking budget; changing library customers and employees' needs and information technology; strategic management issues organisational culture; transformational leadership; employee recognition and reward systems; performance measurement system; productivity improvement; and customer orientation; critical staff issues as sense of purpose and achievement; feeling of self-worth; job-security; recognition; status; career development; and salary; motivational factors as effective communication; job satisfaction; delegation of authority; clear job description; performance feedback; conducive working environment; human resource strategy issues as motivation building among staff;continuous education and development; generating competitive advantage through human resources; and alignment of human resource strategy with strategic management plan. The study recommends a strategic human resource management model for libraries along with: conducive working environment; adequate IT infrastructure to store, organise and retrieve information; staff training for excellent customer service; objective, reward based staff appraisal; performance feedback; performance appraisal should be aligned with staff selection, library mission, staff motivation and promotion in order to use it strategically; and human resource strategy should be developed immediately. / Information Science / D. Litt. et Phil. (Information Science)

The purpose of the research was to recommend a model for strategic human resource management through an effective staff performance appraisal system in Botswana public libraries. Performance appraisal is not a new concept; however the evolution of performance appraisal tools and techniques has been slow compared to that of other management fields. This discrepancy is now being realised; organisations are starting to acknowledge the importance of comprehensive, regular appraisal of staff as part of an effective human resource management policy. Human resources are a scarce and valuable tool in any organisation and it is mainly through performance appraisal that they can be developed and maintained, to ensure organisational success. The theory underlying strategic human resource management and performance management has been studied. Empirical research through a questionnaire was carried out in 23 public libraries. From these it was possible to develop a model entitled "A recommended strategic human resource management model". From empirical investigation the main critical qualities for efficient public library services were revealed as enthusiasm; positive attitude; innovative thinking; capability and commitment; critical competencies as expertise; team-building; and leadership; critical external factors as external environment; global competition; shrinking budget; changing library customers and employees' needs and information technology; strategic management issues organisational culture; transformational leadership; employee recognition and reward systems; performance measurement system; productivity improvement; and customer orientation; critical staff issues as sense of purpose and achievement; feeling of self-worth; job-security; recognition; status; career development; and salary; motivational factors as effective communication; job satisfaction; delegation of authority; clear job description; performance feedback; conducive working environment; human resource strategy issues as motivation building among staff;continuous education and development; generating competitive advantage through human resources; and alignment of human resource strategy with strategic management plan. The study recommends a strategic human resource management model for libraries along with: conducive working environment; adequate IT infrastructure to store, organise and retrieve information; staff training for excellent customer service; objective, reward based staff appraisal; performance feedback; performance appraisal should be aligned with staff selection, library mission, staff motivation and promotion in order to use it strategically; and human resource strategy should be developed immediately. / Information Science / D. Litt. et Phil. (Information Science)