In this investigation, the resistivity of vanadium nitride at elevated temperatures has been measured using a resistance bridge based on the Dauphinée/Mooser (1955) chopper system. In general, an almost linear increase of resistivity with temperature was observed for VN, but at certain temperatures, deviations from linearity (anomalies) were observed, these have been classified into three types. Attempts have been made to correlate the anomalous behaviour and temperature coefficients of resistivity with the ambient atmospheres and with the impurities, (especially oxygen), stoichiotmetry and density of this material. Oxygen and excess nitrogen appear to be electron donors in their effects on VN and result in a decrease in the slope of resistivity vs temperature curves. Oxygen and excess nitrogen also appear to increase the overall resistivity due to an increase in defect concentration. No effects due to the ambient atmosphere have been observed in the case of hot-pressed samples. lndicating that reaction can only occur if the reacting gases can reach the interior of the samples.

Master of Science / Department of Grain Science and Industry / Yong Cheng Shi / Resistant starch (RS) is notable for having several health benefits in humans, including glucose control and intestinal well-being. Pullulanase is able to debranch amylopectin and result in higher RS content. Different levels of pullulanase have been used to debranch waxy maize starch in the literature, but the changes of structure during debranching are well documented. In this study, waxy maize starch was cooked and debranched by pullulanase with 80, 160 and 240 New Pullulanase Unit Novo (NPUN)/g starch pullulanase. One NPUN was defined as the amount of enzyme, which, under standard conditions, hydrolyzes pullulan, liberating reducing carbohydrate with reducing power equivalent to 1 µmole glucose per minute. The structure of waxy maize starch during debranching was investigated and the digestibility of the debranched products was measured. When pullulanase was increased from 80 to 240 NPUN/g, more amylopectin was debranched in the same debranching time, and the degree of crystallinity and the RS content increased. After the debranched starches were crystallized at 25°C for 24 hours, the RS contents were greater than 63%. When heated and recrystallized under highly regulated conditions, the linear material formed crystallites of a range of geometries, including spherulites of a highly organized structure. Debranched waxy maize starches were used to produce crystalline structure under four conditions: spherulites formed by adding ethanol and crystallized at 4°C (ES4); spherulites formed in water (WS4) at 4°C; particles formed at 50°C (WS50); and spherulites formed at 50°C then further precipitated at 4°C (WS50-4). Spherulites formed at 50°C (WS50) had a higher proportion of smaller molecules than existed in the parent starch (Rh<15nm). ES4 and WS4 were B-type crystalline structure; whereasWS50 and WS50-4 were A-type crystalline structure. ES4 had a larger proportion of molecules with a low degree of polymerization and the RS content was also the lowest of the four samples. With cooling from 50°C to 4°C (WS50-4), the RS content was increased from 60% to 73%. ES4 and WS50-4 contained particles with spherical symmetry and WS4 had partial radial symmetry with some distortions, whereas WS50 displayed oblate particles with a parallel crystal structure.

Pancreatic cancer (PC) is known to be highly resistant to chemotherapy. Transporters, which regulate the influx and efflux of substrates across the plasma membrane, may play a role in PC drug resistance. ABC transporters are a large family of transmembrane proteins with diverse physiological functions, several of which play major roles in cancer drug resistance. Given that 90% of PC express a mutant K-ras oncogene and that PC are highly hypoxic, I postulated that constitutive K-ras activation and/or hypoxia may correlate with ABC transporter expression, which in turn may promote drug resistance in PC. Using normal and PC cell lines either overexpressing mutant K-ras or subjected to hypoxic treatment, mRNA expression was profiled for 48 ABC transporters. My findings indicate that expression of mutant K-ras and hypoxic treatment, as well as long-term exposure to chemotherapy, may contribute to the development of drug resistance in PC cells in part by inducing the expression of ABC transporters. Similar to ABC transporters, I investigated whether amino acid transporters would mediate drug resistance in PC. The Xc⁻ amino acid transporter (Xc⁻) mediates cellular uptake of cystine for the biosynthesis of glutathione, a major detoxifying agent. Because the Xc⁻ has been regulates the growth of various cancer cell types, and Xc⁻ is expressed in the pancreas, I postulated that the Xc⁻ may be involved in growth and drug resistance in PC. The Xc⁻ transporter is differentially expressed in normal pancreatic tissues and is overexpressed in PC in vivo. Using PC cell lines, I found that cystine uptake via the Xc⁻ was required for growth and survival in response to oxidative stress, and that expression of the Xc⁻ correlated with gemcitabine resistance. Accordingly, inhibition of Xc⁻ expression via siRNA reduced PC cell proliferation and restored sensitivity to gemcitabine. I also identified the anti-inflammatory drug sulfasalazine as a mixed inhibitor of the Xc⁻, which acts to inhibit cell proliferation via reducing Xc⁻ activity and not by reducing NFKB activity. My findings thus indicate that the Xc⁻ plays a role in PC growth in partby contributing to glutathione synthesis to promote PC cell proliferation, survival, and drug resistance. / Medicine, Faculty of / Medicine, Department of / Experimental Medicine, Division of / Graduate

The problem of finding an efficient antibiotic against Pseudomonas aeruginosa which can be used in the clinical treatment of genito-urinary tract infections resistant to treatment by streptomycin has not yet been solved. Therefore, this problem has consisted of first, the acquisition of possible inhibitors of the streptomycin resistant strain of Pseudomonas aeruginosa; second, the selection and identification of those which show a marked antagonism toward this organism; third, the determination of the antibiotic spectra of the inhibitors; fourth, the determination of whether the streptomycin resistant strain could also acquire a resistance to the antibiotic produced by its inhibitors; and last, an attempt to evaluate the therapeutic possibilities of the antibiotics demonstrated.

Background: Even with newer and repurposed anti-TB drugs almost a third of patients with XDR-TB have unfavourable outcomes. In patients with localised disease and adequate pulmonary reserve, surgery is an important adjunctive treatment. However, there are no outcome data from TB endemic countries, and the prognostic significance of pre-operative PET-CT findings remains unknown. Objectives: To report outcomes for resectional surgery in our setting, and to study whether PET activity outside of the resection influences treatment outcomes. Methods: A retrospective study of all XDR-TB patients undergoing surgery at Groote Schuur Hospital (GSH) between July 2010 and December 2016 was performed. PET-CT was performed in a subgroup. Patients were followed up to determine treatment outcomes at 24-months post- surgery. Treatment success and failure, including all-cause mortality, was determined. Results: In total, 35 patients underwent surgery. The mean age was 36, 49% were male and 26% were HIV-infected. Pneumonectomy was the most common procedure (57%). Three patients (9%) were lost to follow up by 24 months. Total all-cause mortality was 34%. Treatment success was achieved in 15/35 (43%). In patients who underwent pre-operative PET-CT, there were no overall radiological features or PET parameters that were found to be prognostic for treatment failure. Conclusion: Resectional surgery for DR-TB in combination with chemotherapy resulted in cure in less than half of patients. Our data do not support the use of PET-CT to preselect patients or prognosticate about their outcome. These data inform clinical practice and underscore the need to support antibiotic stewardship strategies in TB-endemic settings.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the Degree of Master of Science / A simple three-dimensional model of a high y' volume fraction Ni-based alloy is developed. The model is based on the idea that a unit volume in the superalloy can be represented by a cuboidal precipitate with thin 'slabs' of matrix material 'stuck' onto its faces in such a way that coherency is maintained. Rafting is investigated by considering the changes in total energy whon the cuboidal precipitates start to flatten into plate shapes or lengthen into rod shapes. It is assumed that inelastic effects are negligible. Internal and external stresses and strains are determined. Expressions for the derivative of the total energy with respect to a shape parameter are then calculated in the absence of applied stress and in the presence of applied stress. Predictions of rafting behaviour are made for six alloys. Excellent agreement is found with experimental evidence but it is suggested that the agreement is fortuitous. / AC 2018

Rotylenchulus reniformis (RN) nematode infection has been identified as a major biotic factor limiting cotton yield (~8%) in Mississippi. Cotton researchers are striving to develop resistance to RN and develop management practices to mitigate the problem. Reniform nematode and soil nitrogen (N) directly affect cotton growth and physiology, however, responses to RN and N may vary across a wide genetic background. The overall objective of this research was to determine the role that host plant resistance to reniform nematode and soil nitrogen plays in cotton growth, physiology, and yield and controlling RN populations. In experiment 1, the effect of RN on resistant (Gossypium barbadense introgressions; 08SS110-NE06.OP and 08SS100) along with a susceptible genetic standard (Deltapine 16) and a commercially, susceptible cultivar (PHY 490 W3FE) was studied based on growth, development, and yield characteristics under field conditions. In experiment 2, the effect of N application rates, ranging from 0-150%, with 100% being recommended rate, on early season morphological and physiological traits of the resistant and susceptible genotypes were studied in the presence and absence of RN under greenhouse conditions. In the field project, agronomic traits varied among genotypes at a given sampling time but growth rates, described by three-parameter sigmoidal function (r2 = 0.95 to 0.99), were not different among genotypes. Further, genotypes exhibited higher agronomic and physiological traits, including plant height, main stem nodes, leaf area, net photosynthetic rates, and hand-picked lint yields in 2018 than 2017. In the greenhouse study, 08SS110-NE06.OP performed physiologically better across RN environments than other genotypes, but growth rates with respect to soil N treatments, described by linear or quadratic function (r2 = 0.72 to 0.99), were not different among genotypes. No interactions between soil N treatments and RN based on physiological and growth traits were observed at the time of harvesting. In both projects, resistant genotypes suppressed reniform nematode population at the time of harvesting. RN resistant lines have no biological significant effect on plant growth, development, or yield but do suppress RN populations.

Class II malocclusions affect over twenty percent of the population. Over the years numerous appliances have been invented and modified in order to treat this type of maloclussion. Functional appliances have been advocated for their ability to assist in mandibular growth along with restraint of maxillary growth, as two-thirds of Class II malocclusions are classified with retrognathic. Publications from the following electronic databases were searched: PubMed, Web of Science, Cochrane Library and Science Direct. Searches included any article published until July 13, 2012. Searches were performed under the term "ForsusTM." These searches yielded sixty-one (61) articles. These were reviewed for relevance based on inclusion and exclusion criteria. Articles were excluded if they did not measure the effectiveness of ForsusTM treatment or were not written in English. Seven (7) articles were deemed of relevance with a high quality study design and were included in this study for evaluation. The current literature suggests that Class II treatment with the ForsusTM appliance is an effective and efficient method to treat Class II maloclussions in six months. It produces mainly a restraining effect on maxillary growth, while the Class II molar correction is derived primarily from dentoalveolar changes. Overjet and overbite is reduced through proclination, mesialization and intrusion of the mandibular incisors and retrusion and extrusion of the maxillary incisors. There is also a distalizing and intrusive force on the maxillary first molars which make this appliance ideal for high angle and open bite cases. Some other noted effects are palatal and occlusal plane clockwise rotation and slight expansion of the intermolar widths after treatment. The other obvious advantage is the continuous wear guaranteed by this non compliance method of treatment. / Oral Biology

Thesis (M. Sc. (Chemistry)) -- University of Limpopo, 2021 / Tuberculosis is one of the top 10 leading causes of death in the world. The development of drug resistant strains of Mycobacterium tuberculosis such as Multidrug resistant (MDR) and Extensively drug resistant (XDR) strains further complicate the TB control. Medicinal plants present a possible source for new potential antitubercular drugs. They have played an important role in drug discovery, with many pharmaceutical products originating from them. Isolation and characterisation of new antitubercular compounds from plant extracts is relevant today because of the development of resistant strains. The aim of the study was to evaluate the antimycobacterial activity of the leave extracts of Croton gratissimus and Leonotis leonorus. The first step was to extract fine powder leaves of the two plant species using four (dichloromethane, acetone, hexane and ethanol/water) different solvent systems. Isolation of the fractions was done using column chromatography and preparative thin layer chromatography. Minimum inhibitory concentrations were determined using the broth dilution method and the values were recorded in μg/mL. All the isolated fractions from both plant species were evaluated for preliminary in-vitro antimycobacterial activity. Some of the isolated fractions showed an increased activity against the pathogen as compared to the crude extracts. All the crude extracts of the two plants had activity with MIC90 values greater than 125 μg/mL. Seven fractions obtained from Croton gratissimus showed potential activity against the pathogen with MIC90 values ranging from 30.61 to 64.88 μg/mL. Leonotis leonurus had three fractions with promising activity with MICs ranging from 1.963 to 62.51 μg/mL. The crude extracts of the two plant species showed that the two plant species have antioxidant properties. The qualitative antioxidant assay showed that DCM crude extracts had more antioxidants than all other extracts because of more clear zones against the purple background colour on the TLC plates. These was confirmed by the qualitative antioxidant assay where DCM crude extracts was able to inhibit the highest percentage of DPPH at different concentrations than all other solvent extracts. The DCM crude extracts of L. leonurus and Croton gratissimus inhibited 87 and 93 % of DPPH respectively at 250 μg/mL. The structures of the compounds within the isolated fractions were elucidated using NMR and confirmed by MS and FTIR spectroscopies. The NMR data showed that the isolated fractions were not pure compounds but mixtures of closely related compounds. The compounds whose structures were elucidated included two labdane diterpenoids (Croton A and Croton B) and a Cembranolide ((5E,10E,13R)-4-isopropyl-7,11-dimethyl-15-oxo-14-oxa-bicyclo [11.2.1] hexadeca-5,10-dien-7-yl acetate) from Croton gratissimus and a phenol (4-(3,3,4,4-tetramethylheptyl) benzene-1,2-diol)) from Leonotis leonurus. / National Research Foundation (NRF) and Sasol Foundation

The study aimed to explore and describe the experiences of people treated for multidrug resistant tuberculosis (MDR-TB) in Omaheke region, Namibia in order to make relevant recommendations regarding their management. A descriptive qualitative design approach was used. Data was collected using in-depth individual interviews with six participants. The interview transcripts were analysed using thematic content analysis. Three themes emerged namely (1) Stressors related to MDR-TB diagnosis and treatment which involved nature of disease and compulsory hospitalisation (2) Impact of being treated for MDR-TB which related to emotional , social , spiritual and financial impact (3) Support structures for people treated for MDR-TB which included family members, health care professionals and friends. Systemic practical patient-centred, staff-centred and community-centred recommendations are suggested as well as recommendations for future research and an appraisal of the limitations of this study. / Health Studies / M.A. (Public Health)