Includes abstract. Includes bibliographical references.

Includes abstract. / Includes bibliographical references. / This dissertation investigates methods for improving the image quality of a digital radiography system. The Lodox Statscan™ X-ray system provides a full-body scanned image for initial diagnosis. The system is driven by a permanent magnet linear motor (PMLM) controlled by a cascaded proportional-proportional integral controller (P-PI). Transient errors in the trapezoidal motion profile of the scanning C-arm may cause mismatches between the detector and the collimated beams from the X-ray source. This results in a partial degradation of image quality. The Statscan™ X-ray system was investigated and the following constraints were identified: The scanning time is limited to 13 seconds and the maximum scan length is limited to 1.8 m. Since it was not possible to obtain the Lodox Statscan™ dynamics model, because of the similarity, a characteristic model was then developed using a DC motor in order to investigate the control dynamics. It is not advisable for a designer to manipulate the controllers on commercial machines except for changing the parameters for tuning. Therefore, a P-PI controller and a proportional-integral sliding mode controller (P-ISMC) as well as a Boundary Layer variant (P-ISMC+BD) were designed for fair comparison purposes. Root locus, Bode diagrams and integral sliding mode control methods, respectively, were used to design the P-PI and P-ISMC controller groups. Each controller consists of an inner loop and an outer position loop. Proportional integral (PI) and integral sliding mode controllers (ISMC) were used for the inner loop. The two inner loop controllers were tuned, and then tested, before cascading them with the outer position loop. The simulation and experiments were conducted to compare each controller’s performance on step set-point tracking, trapezoidal motion profile tracking, the time transient’s specifications and robustness against disturbances. In order to test image quality, 27 distance profiles were generated from P-PI, P-ISMC and P-ISMC+BD. In addition, four images captured by the Statscan™ were also selected. A time delay integrator (TDI) simulator was used on the distance profiles and the four images to generate 108 distorted image profiles.

Includes bibliographical references. / Acute inferior myocardial infarction is generally associated with a benign course and low in-hospital mortality. However, a group of patients with high degree atrioventricular block has significantly increased mortality. Although some of the prognostic factors associated with increased mortality have been identified, the explanations for these remain less than satisfactory.

Includes bibliographical references (leaves 73-89). / Tumour necrosis factor alpha (TNFa) is a pleiotropic cytokine which has both beneficial and deleterious effects. It has previously been shown in our laboratory that TNFa can mimic ischemic preconditioning (IPC). However, the signalling pathways involved in this protection remain incompletely understood. One potential protective pathway involves the generation of reactive oxygen species (ROS), which are known to be activated by TNFa. It was therefore hypothesized that TNFa-induced cytoprotection requires the generation of ROS. In addition, it was postulated that this ROS generation originates in the mitochondria.

Includes abstract. / Includes bibliographical references. / Peripartum cardiomyopathy (PPCM) is a heart disease of unknown aetiology emerging in previously healthy women towards the end of pregnancy or first postpartum months. Previous studies have suggested that oxidative stress contributes to the pathogenesis of PPCM. Melatonin is a powerful endogenous antioxidant that can limit the damaging effect of oxidative stress. Melatonin levels are known to be altered in sleep disruption, depression and other cardiac diseases. The aim of this study was to determine if melatonin levels are disrupted in women with PPCM compared to healthy patients. We hypothesised that sleep disruption and depression may contribute to a disruption in their melatonin levels.

Includes abstract. / Includes bibliographical references. / Aseptic loosening of artificial joints occurs due to the loss of implant fixation. By implementing a 3D porous structure at the bone-implant interface, the ingrowth of bone will permit better and stronger interlocking of the implant to prevent loosening. In this study, it is hypothesized that the seeding of 3D scaffolding structures with mesenchymal stem cells (MSCs) will improve the potential for osseointegration of the implants, as the existing bone may be more inclined to unite with developing bone than with the implant substrate. Titanium-6 Aluminium-4 Vanadium (Ti64) is one of the most commonly used implant materials. Heat treatment of Ti64 was seen in tests done at the University of Cape Town to further improve against implant failure by vastly improving the materials strength and reducing debris formation. Thus the aim of this study was to investigate the effects the heat treatment of Ti64 would have on the capabilities of seeded MSCs in vitro.

Includes bibliographical references. / Sub- Saharan Africa is the world's worst HIV-AIDS affected region. More interventions to manage this pandemic are urgently required. Transmission of the virus through an exchange of saliva is rarely known to occur. The role of saliva and its mucus in this inhibition requires clarification. This project sought to verify the previous findings in our laboratory (Habte et al. , 2006; Peacocked et al. (manuscript under revision)), that crude saliva from uninfected individuals together with its purified mucin components inhibited HIV-1 in an in vitro assay. Mucins from infected saliva did not show inhibition in this assay. Mucus was extracted in 6M guanidinium hydrochloride and a cocktail of protease inhibitors, pH 6.5. Sepharose CL-4B gel filtration separated MUC5B and MUC7 in saliva. Mucins were purified by density gradient ultra-centrifugation in caesium chloride. Western blotting and amino acid analysis determined the size, charge and identity of the mucins. The inhibitory activity of crude saliva, salivary mucin components MUC5B and MUC7 from HIV-negative and HIV-positive donors, was tested by their incubation in an in vitro HIV-neutralisation assay using a pseudovirus of Subtypes A and C, and infection of susceptible epithelial tumour cells (genetically modified TZM- bl cells). Glycosylation analysis by HPLC was also performed on each group. The presence of MUC5B and MUC7 in saliva was confirmed and it was shown that there was inter-individual variation in their amounts and electrophoretic behaviour between and within groups. Crude HIV-negative and HIV-positive saliva and its purified mucins MUC5B and MUC7 significantly inhibited the infection of HIV-1 in an in vitro pseudoviral assay in a dose-response manner. HPLC revealed two glycoforms of salivary MUC5B.

Both human immunodeficiency virus (HIV) infection and tuberculosis (TB) are complicated by a painful distal sensory polyneuropathy (DSP) that may be due to virus-related HIV-DSP, antiretroviral toxic neuropathy (ATN) or isoniazid-induced peripheral neuropathy (INH-PN). In co-infection with and co-treatment for HIV/TB, DSP risk is increased. Factors driving this risk may be vitamin B6 deficiency and slow metabolism of INH mediated by N-acetyltransferase 2 (NAT2) acetylation, both known risk

This work details the method of Simultaneous Model-based Clustering. It also presents an extension to this method by reformulating it as a model with a mixture of factor analysers. This allows for the technique, known as Simultaneous Model-Based Clustering with a Mixture of Factor Analysers, to be able to cluster high dimensional gene-expression data. A new table of allowable and non-allowable models is formulated, along with a parameter estimation scheme for one such allowable model. Several numerical procedures are tested and various datasets, both real and generated, are clustered. The results of clustering the Iris data find a 3 component VEV model to have the lowest misclassification rate with comparable BIC values to the best scoring model. The clustering of Genetic data was less successful, where the 2-component model could successfully uncover the healthy tissue, but partitioned the cancerous tissue in half.

Includes bibliographical references (leaves 109-122 ). / This study investigated four indigenous South African medicinal plants that are commonly used in traditional medicine for their bioactivity against Mycobacterium tuberculosis. Crude plant extracts were prepared and characterized using HPLC analysis. The crude rhizome extracts of Agapanthus praecox, leaf extracts of Olea europaea subsp.