This dissertation focuses on the modelling, identification and the parameter estimation for the co-infection of HIV-1 and M. tuberculosis. Many research papers in this field focus primarily on HIV, but multiple infections are explored here, as it is common in many individuals infected by HIV. Tuberculosis is also responsible for the highest number of casualties per year in the group of HIV-infected individuals. A model is proposed to indicate the populations of both pathogen as well as key information factors, such as the overall infected cell population and antigen-presenting cells. Simulations are made to indicate the growth and decline in cell-type numbers for a specific individual. Such simulations would provide a means for further, well-founded investigation into appropriate treatment strategies. One previous such model developed by Kirschner is used to obtain a nominal parameter set. Furthermore, the nominal set is then used in conjunction with real-world samples provided by the National Institute for Communicable Diseases in South Africa, to solidify the credibility of the model in the practical case. This is achieved via simulations and employs parameter estimation techniques, namely the Nelder-Mead cost-function method. An identifiability study of the model is also done. Conclusions drawn from this study include the result that the treatment of M. tuberculosis does not affect the course of HIV-1 progression in a notable way, and that the model can indeed be used in the process of better understanding the disease profile over time of infected individuals. / Dissertation (MEng)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / MEng / unrestricted

Numerical simulations of current-voltage characteristics of nanowire CdS/CdTe solar cells are performed as a function of temperature using SCAPS-1D. This research compares the experimental current-voltage (I-V) characteristics with the numerical (I-V) simulations obtained from SCAPS-1D at various temperatures. Various device parameters were studied which can affect the efficiency of the nanowire-CdS/CdTe solar cell. It was observed that the present simulated model explains the important effects of these solar cell devices, such as the crossover and the rollover effect. It was shown that the removal of defect in i-SnO2 is responsible for producing the crossover effect. In the past, the rollover effect has been explained by using back to back diode model in the literature. In this work, simulations were performed in order to validate this theory. At the back electrode, the majority carrier barrier height was varied from 0.4 to 0.5 eV, the curve corresponding to the 0.5 eV barrier showed a strong rollover effect, while this effect disappeared when the barrier was reduced to 0.4 eV. Thus, it was shown that the change of barrier height at the contact is a critical parameter in the rollover effect.

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