Search

Abstract: Geotextile sand filled containers (GSC) have rapidly become the preferred coastal defence on the east coast of South Africa. Their growth can be attributed to political, social and environmental factors. This paper details South African experiences and the observed performance of GSCs. The main failure mechanism of geotextile sand bag seawalls is identified to be the movement of sand within the bags. This movement is observed to be a result of insufficient filling, bag elongation and sand leaking. Through a review of local and international manufacturing and construction techniques we identify methods of reducing the internal movements of sediment. The observed performance of local bags provide a practical full scale validation of the physical model findings of Hornsey et al. (2011); Recio and Oumeraci (2007). [Copyright &y& Elsevier]

Abstract: The paper investigates how renewable technologies could promote the transition towards a sustainable energy production in developing nations. Based on two different developing nations in terms of economic, technological and institutional structure: South Africa and Senegal, we implemented scenarios in a bottom-up PowerPlan model in order to analyze the transition toward a sustainable electric production. Two scenarios have been considered: a business-as-usual (BAU) and a hybrid renewable energy (HRE) scenario. In the first scenario (BAU) we assume that the electricity demand is entirely satisfied by an increase of the investment in the current supply structure based on fossil-fuel energy source. Whereas in the renewable energy scenario, we assume 20% and 30% of the electricity supply being generated from renewable resources by 2020 and 2030 respectively. Focusing on wind and solar photovoltaic technologies, our results show the cost-competitiveness of renewable energy deployment in South Africa. In the case of Senegal, our results show that fossil-fuel resource remains the most competitive to generate electricity in the nation during the next coming years as long as environmental advantages of renewable resource are not considered. Our research indicates that in the case of a centralized electricity supply option, both a scale effect and a learning improvement could eventually strengthen the competitiveness of renewable technology deployment in developing nations. [Copyright &y& Elsevier]

Abstract: Potential field semiautomatic interpretation techniques can significantly decrease the interpretation workload of a geophysicist and are widely used. This paper generalises the tilt-depth method to gravity data using the horizontal cylinder and the buried sphere models. The method is compared to the Euler deconvolution and is applied to gravity data from South Africa. Matlab source code can be downloaded from the IAMG server at www.iamg.org. [Copyright &y& Elsevier]

Abstract: The HIV/AIDS epidemic is a serious public health challenge in South Africa. In this paper, a simple deterministic HIV/AIDS model incorporating condom use, sexual partner acquisition, behavior change and treatment as HIV/AIDS control strategies is formulated using a system of ordinary differential equations with the object of applying it to the current South African situation. Firstly, a theoretical analysis of the model is presented. The analysis of the model shows that the disease free equilibrium point is globally asymptotically stable for the epidemic threshold (the model reproduction number) less than unit and unstable when this threshold is greater than unit. A unique endemic equilibrium, whose local stability near the threshold , is determined using the center manifold theory, is shown to be locally asymptotically stable for . Global stability of the endemic equilibrium is shown for a special case whenever . Secondly, the model is fitted to data from UNAIDS/WHO on HIV/AIDS in South Africa. Based on the fit to the prevalence data, projections are made beyond 2007 on the course of the epidemic for various levels of interventions. The results compare very well with other research outcomes on the HIV/AIDS epidemic in South Africa. Projections are made to track the changes in the number of individuals who will be under treatment, an important group as far as public health planning is concerned. The epidemiological implications of such projections on public health planning and management are discussed. [Copyright &y& Elsevier]

Abstract: A drug use epidemic can be represented by a finite number of states and transition rules that govern the dynamics of drug use in each discrete time step. This paper investigates the spread of drug use in a community where some users are in treatment and others are not in treatment, citing South Africa as an example. In our analysis, we consider the neighbourhood prevalence of each individual, i.e., the proportion of the individual’s drug user contacts who are not in treatment amongst all of his or her contacts. We introduce parameters and , depending on the neighbourhood prevalence, which govern the spread of drug use. We examine how changes in , and affect the system dynamics. Simulations presented support the theoretical results. [Copyright &y& Elsevier]

Abstract: Mill discharge temperature and differential pressure have a strong effect on efficiency and safety of a coal fired power plant. Therefore, it is imperative that they are closely monitored and controlled during mill operation to keep their levels within a predetermined safe and efficient operating range regardless of the rate at which the raw coal is fed to the mill. One way to achieve this is through a control schedule that compares the value obtained from the process to the stored set-point value to determine if there is any deviation that requires correction. This paper describes a steady state model that could be used alongside conventional controllers as an on-line shadow that provides inferential estimates of desired temperatures and pressure drops in the mill circuit which can be continuously compared with the actual values for adjustment. This would not only help to avoid the difficulties associated with direct measurement but also provide a means for early detection of drifts and failing sensors and serve as a temporal back-up for the out-of-order sensors. The model was tested using industrial data collected from four ball mills at a coal fired power plant in South Africa and the results show a reasonable agreement between the measured data and model predictions both qualitatively and quantitatively within a 5% error margin. The model outputs were found to be highly sensitive to the variation in mill loading, the primary air (PA) flow and the mill channel dimensions. Therefore, for validity of this model, accurate determination of all significant parameters is essential. For now, the model is only valid for the ball mills involved in the current study, but with availability of data it can be reproduced elsewhere. [Copyright &y& Elsevier]