M.Com. (Business Economics) / Please refer to full text to view abstract

Le nombre de cancers et notamment de cancers photoinduits étant en augmentation, il est indispensable d’identifier de nouvelles molécules protectrices de type filtres UV, réparatrices vis-à-vis des altérations de l’ADN mais également favorisant la réponse pigmentaire. Les lichens sont des organismes originaux qui possèdent des qualités de résistance remarquables aux rayonnements solaires dues notamment à la production de métabolites photoprotecteurs tels que les mycosporines. A partir de ce motif structural original, nous avons synthétisé divers analogues par catalyse à l’or en utilisant un outil de la chimie théorique (TD-DFT) pour orienter les synthèses. Les premières évaluations de leurs propriétés physico-chimiques des molécules ont montré des activités prometteuses. / For several years, melanoma is the cancer with 84,000 new cases per year in Europe, including over 7000 cases in France, in 2010. One of the major causes of this cancer is the excessive exposure to UV radiations and it has been suggested that UV-A may be the primary cause of sunlight-induced melanoma. Hence, sunscreens with a good absorption in the UV-A spectral range need to be developed with a good efficacy and photostability. Lichens are original sources for the development of new UV filters because they possess ability to absorb UV due to the presence of metabolites such as mycosporines or MAAs (mycosporines like aminoacid). Based on the general structure of mycosporines, we have synthesized various analogues of mycosporines using a gold-catalyzed strategy. To orientate the synthesis, we used the method of the quantum chemistry: TD-DFT (Time-dependent density functional theory). These products were analyzed for their UV profiles and some of them showed good absorbing properties in UVA range. The cytotoxicity assay showed no toxicity of all products evaluated.

>Magister Scientiae - MSc / Nanotechnology has emerged as a promising field in the quest to address health conditions. Green nanotechnology is a fairly new branch of nanotechnology, which aims to produce and utilize nanomaterials in a way that is safe for living organisms and their environment. Plant extracts are increasingly used in the green synthesis of gold nanoparticles (AuNPs), which involves the reduction of sodium tetrachloroaurate (III) dehydrate by phytochemicals present in the plant extract. It is probable that the green synthesised AuNPs are more biocompatible than chemically synthesised AuNPs as biomolecules of plant origin are involved in the synthesis process. Therefore, this study aimed to explore various water extracts from indigenous South African plants, which included Perlagonium capitatum, Otholobium bracteolatum, Gerbera linnae, Morrella quercifolia, Searsia lucida, Phylica bubescens, Euclea racemosa, Tetragonia fruticosa, and Searsia glauca for their potential to synthesize AuNPs and to investigate their toxicity towards several microorganisms known to cause skin infections. These organisms play a significant role in delaying the healing of wounds. The antimicrobial properties of nanoparticles are increasing exploited in the production of wound treatments.

The harvesting of solar light is one of the main challenges in science. The outstanding optical properties of plasmonic in the visible and near-infrared ranges due to the localized surface plasmon resonance (SPR) has emerged as a promising approach for the solar-tochemical energy conversion. Specifically, it has been demonstrated that the SPR excitation in the visible range in silver (Ag) and gold (Au) nanoparticles can drive and accelerate chemical transformations. This field, coined plasmonic catalysis, enables one to merge catalytic and optical properties in the nanoscale and use visible or near-infrared light as a sustainable energy input to accelerate molecular transformations. In the first part of this thesis. we developed Au branched nanostructures to be employed as plasmonic catalysts. In this case, we aimed at investigating the effect of the sharp tips at their surface over their plasmonic catalytic performance, as it is established that tips can concentrate higher electric field enhancements relative to rounded surfaces as a result of the lightning rod effect, which, in turn, can translate into higher plasmonic catalytic performances. Here, the plasmonic-catalytic performances were tested using the SPR mediated oxidation of paminothiophenol and benzylamine as model transformations. While the Ag and Au nanoparticles support LSPR excitation in the visible and near-infrared ranges, their catalytic properties are limited in terms of versatility. Conversely, metals that are important in catalysis, such as palladium Pd, do not support SPR excitation in the visible or near-infrared range. In the second part of this thesis, we developed multimetallic nanoparticle morphologies, composed of both Au and Pd, that enabled us to marry catalytic and plasmonic component in order to address this challenge. We focused on plasmonic core-catalytic shell structures, in which the shell displayed a branched morphology. Parameters such as shell thickness could be controlled, and structure performance relationships were established towards the methanol electro-oxidation under plasmonic excitation. / O aproveitamento da luz solar é um dos principais desafios da ciência. As excepcionais propriedades óticas plasmônicas nas regiões do visível e do infravermelho próximo, devido a ressonância plasmônica de superfície localizada (SPR), surgiram como uma abordagem promissora para conversão de energia solar em energia química. De maneira mais específica, vem sendo demonstrado que a excitação SPR na região do visível em nanopartículas de prata (Ag) e ouro (Au) podem conduzir e acelerar transformações químicas. Esse campo, chamado catálise plasmônica, permite a fusão de propriedades óticas e catalíticas na nanoescala e a utilização de luz visível ou infravermelha próxima como uma fonte de energia para acelerar transformações moleculares. Na primeira parte desta dissertação, nós desenvolvemos nanoestruturas de ouro ramificadas para serem empregadas em catálise plasmônica. Neste caso, nosso foco era investigar o efeito de pontas afiadas em sua superfície sobre seu desempenho catalítico plasmônico, visto que está bem estabelecido que pontas podem concentrar maiores intensificações de campo elétrico em relação a superfícies arredondadas como resultado do \"efeito para-raios\" o que, por sua vez, pode se traduzir em maiores desempenhos em catálise plasmônica. O desempenho da catálise plasmônica foi testado através da oxidação mediada por SPR do p-aminotiofenol e da benzilamina como reações modelo. Contudo, enquanto nanopartículas de prata e ouro apresentam excitação SPR nas regiões do visível e infravermelho próximo, suas propriedades catalíticas são limitadas em termos de versatilidade. Por outro lado, metais que são importantes em catálise, como o paládio, não apresentam excitação SPR no visível e infravermelho próximo. Por isso, na segunda parte desta dissertação, nós desenvolvemos nanopartículas multimetálicas, compostas de Au e Pd, que nos permitem unir os componentes catalíticos e plasmônicos com o objetivo de enfrentar este desafio. Nós focamos em estruturas do tipo core-shell, com núcleos plasmônicos e cascas catalíticas, na qual a casca apresenta morfologia ramificada. Paramêtros como a espessura da casca puderam ser controlados, e a relação estruturaperformance foi estabelecida através da eletro-oxidação do metanol sobre excitação plasmônica.

TESIS PARA OPTAR AL GRADO DE MAGÍSTER EN FINANZAS / El presente trabajo corresponde a la valoración de la multinacional empresa de Oro Kinross Gold Corporation (KGC) al 30 de junio del 2016 a través del método de flujos de caja descontados. También se realiza una comparación con el método de múltiplos. En primer lugar, se realiza un análisis de la empresa y minería del Oro. Se tomaron criterios base de acuerdo a la realidad actual que muestra la empresa y su carácter multinacional para poder realizar la valoración de la tasa de costo promedio ponderado y los flujos proyectados. El resultado de su tasa de costo promedio ponderado WACC es 5,94%. Luego se realiza un análisis de las ventas históricas a nivel de empresa y las estimaciones de la industria del Oro, análisis de costos, activos y una proyección de sus resultados. Finalmente, a partir de los ajustes al Estado de Resultados proyectado se obtienen los flujos de caja libre, los que se descuentan a la tasa de costo promedio ponderado para obtener el valor de la empresa. Bajo los supuestos base realizados en el presente trabajo donde se definió también una prima por liquidez de 3%, los resultados del método de flujos de caja descontados muestran que la empresa multinacional Kinross Gold Corporation, al 30 de Junio del 2016, se encuentra valorizada en 6.008 MM US$. Al 30 de Junio del 2016, el valor de mercado de las acciones es 4,89 US$/acción versus el precio valorizado en el presente estudio de 4,83 US$/acción (+1,3%). Al sensibilizar resultados de la valorización y retirar la prima por liquidez de 3%, el resultado de la valorización de la compañía KGC es 7.608 MM US$. Se recomienda continuar con posteriores estudios con el objetivo de analizar nuevos métodos de valoración para empresas mineras Auríferas multinacionales.

Cette thèse visait à développer des techniques d'ablation au laser et de fragmentation dans des liquides pour la synthèse de nouveaux NPs ayant des fonctionnalités utiles. L’approche de la thèse est axée sur l’élaboration de la technique ablative au laser pour la synthèse de matériaux conventionnels avec des paramètres pour des applications biomédicales sélectionnées, ainsi que sur le développement de cette technique pour la synthèse de nouveaux nanomatériaux destinés à des applications biomédicales. En particulier, il comprend:1. Nous avons élaboré un régime de fragmentation laser fs à partir de colloïdes de Si pour la synthèse de NPs de Si ayant une taille, une cristallinité et un état d'oxydation contrôlables.Nous avons testé un certain nombre d’applications biomédiales particulières de Si Si préparés de cette manière.2. Nous avons développé une technique d'ablation et de fragmentation au laser fs pour fabriquer des noyaux Au NPs et des carottes en Au-Si nus pour SERSapplications. Une approche est basée sur l'ablation au laser de la cible Au dans une solution colloïdale de NP Si.3. Pour la première fois, nous avons synthétisé de nouveaux NP plasmoniques à base de nitrure de titane. Nous avons également montré qu’une étape supplémentaire de fragmentation du laser fs entraînait une diminution de la taille des NP à 5 nm. En outre, nous avons constaté que ces NP ont un très large pic d'extinction dans le proche IR.4. Pour la première fois, nous avons démontré la synthèse de NPs organiques fluorescentes d'un luminophore à émission induite par agrégation spécialement conçu (AIE LP). La luminosité de ces NP a été jugée comparable à celle des points quantiques. / This thesis as aimed at the development of techniques of fs laser ablation and fragmentation in liquids for the synthesis of novel NPs having useful functionalities. The approach of the thesis is focused on the elaboration of the laser ablative technique for the synthesis of conventional materials with parameters for selected biomedical applications, as well as the development of this technique for the synthesis of novel nanomaterials for biomedical applications. In particular it includes:1. We elaborated a regime of fs laser fragmentation from Si colloids for the synthesis of Si NPs having controllable size, crystallinity and oxidation state. We tested so-prepared Si NPs a number of particular biomedial applications.2. We elaborated a technique of fs laser ablation and fragmentation to fabricate bare Au NPs and Au-Si core-shells for SERSapplications. One approache is based on laser ablation of Au target in colloidal solution of Si NPs. 3. For the first time we synthesized novel plasmonic NPs based on titanium nitride. We also showed that an additional fs laser fragmentation step leads to the decrease of NPs size to 5 nm. Besides, we found that such NPs have a very broad extinction peak in the near IR.4. For the first time we demonstrated the synthesis of fluorescent organic NPs of specially designed aggregation-induced emission luminophore (AIE LP). The brightness of such NPs was determined to be comparable to that of quantum dots.

A research report submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Master of Science, Johannesburg, August, 2014. / Efflorescent minerals are a common feature of the soil surface in seasonal environments where evapotranspiration (ET) exceeds precipitation (P), and are formed by the evaporation of salt solutions from the soil during periods of drying. On the Highveld gold fields, ET exceeds rainfall by approximately two-and-a-half times during the dry season, and soils overlying acid mine drainage and along polluted stream banks can become covered by distinctively coloured mineral efflorescent crusts. Whereas some efflorescent minerals are relatively insoluble and present a negligible environmental hazard (for example, gypsum), others may be readily soluble and contain high concentrations of potentially toxic metals (for example, copiapite, jarosite and uranyl sulphate). During periods of rainfall, such salts are washed further afield and into surface water bodies and act as sources of episodic pollution. The presence of some efflorescent minerals can be detected from their characteristic reflectance signatures using remote-sensing (RS) of the electromagnetic spectrum. The species of efflorescent minerals present is a useful indication of the spatial extent of sub-surface contamination, and also of the chemical conditions of the substrate, in particular the concentration of total dissolved solids, pH and redox conditions. The aim of this study was therefore to assess the use of remote-sensing on indicator efflorescent minerals as a cost-effective aid in the spatial mapping of acid rock-drainage polluted soils and water-bodies. This study describes the range of efflorescent crusts identified on different land-use areas and soil classes in a Highveld gold-mining region. Crusts were first measured in-situ under natural sunlight using a portable analytical spectral radiometer (ASD) as well as using X-ray diffraction (XRD). They were then dissolved in deionized water and the resulting salt solutions allowed to evaporate prior to analysis under controlled lighting conditions. Spectra were post-processed and compared with iv geological spectral reference libraries. The salt solutions were also analyzed for metal and sulphate content and the results were used to establish evaporation models from which mineral precipitation could be predicted. Minerals identified in the visible near-infra red (VNIR) region included iron oxides (hematite and goethite), and the sulphate mineral jarosite. In the short wave infra-red (SWIR) region clay minerals of the smectite group were dominant. Gypsum and Al-Mn-Mg-Na sulphate salts were identified in the SWIR region as mixtures occurring with clay minerals. Minerals identified in the VNIR-SWIR region were all confirmed by X-Ray diffraction (XRD). Upon dissolution, geochemical modeling revealed that gypsum and jarosite are the most common minerals expected to precipitate. The precipitation of gypsum and jarosite indicates persistent acidic conditions after dissolution of mineral salts. Gypsum and jarosite were also accurately identified by hyper-spectral spectroscopy and confirmed by XRD and geochemical modeling. Agreement between spectral interpreted minerals and geochemically precipitated mineral phases demonstrated the ability of hyper-spectral data in detecting efflorescence minerals on the soil surface. Using partial least squares regression (PLSR) combined with bootstrapping, reflectance spectrum was significantly correlated with geochemical variables.

A project report submitted to the Faculty of Engineering, University, of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1991 / As mining proceeds deeper on Elandsrand Gold Mine scattered mining will no longer be viable due to the excessive stress levels which would occur during mining of the final remnants between raises. Longwall mining with strike stabilizing pillars would eliminate this need for remnant mining. However, since the Ventersdorp contact Reef on Elandsrand has a relatively large number of faults and dykes and highly variable grade, longwall mining would result in a excessive amount of off-reef mining and mining of unpayable reef. / GR 2017

Highly dispersed gold nanoparticles on metal oxide surfaces have recently been reported to exhibit high catalytic activity for low-temperature carbon monoxide oxidation. Amongst the metal oxides, titanium dioxide, more often the commercial form Degussa P25, has been the most studied support for gold as a catalyst for CO oxidation because it yields some of the most active and stable catalysts. Physical and chemical modification of catalysts supports has been shown to affect their catalytic properties. In this research, modified gold supported catalysts have been prepared, characterized and tested for CO oxidation. Their properties have been compared with those of the unmodified catalysts. Catalysts containing1wt% Au supported on MxOy and TiO2/MxOy mixed oxide (M = Zn, Mg, Ni, Fe, Cr, Cu, Mn and Co; TiO2:MxOy mole ratio of 5:1; TiO2 = Degussa P25) were prepared by the single step borohydride reduction method and it was found that TiO2 gave the most superior activity as support for gold for CO oxidation, followed by TiO2/MxOy and the corresponding MxOy. The specific activities for CO oxidation of Au/TiO2 catalysts per unit of prepared in the range 0.05 to 1 wt% of Au indicates that for catalysts prepared by deposition precipitation, there is a significant decrease in specific activities with an increase with gold loading. For the single step borohydride reduction procedure, specific activities decrease less significantly with increasing gold content, implying that for economic and practical reasons, it would be advantageous to prepare gold catalysts with low gold loadings. Cyanide leaching of 1 wt% Au/TiO2 catalysts at different Au:CN- ratios, to selectively remove some of the gold in the catalysts, shows the activity per unit mass of gold to increases as more gold is removed from the catalyst. This is consistent with the idea that gold exists in more than one oxidation state in the systems and a significant fraction of the gold present in the catalysts do not contribute to catalytic activity. A number of anions and cations have been incorporated into TiO2 as support for gold catalysts and also into as-prepared Au/TiO2 catalysts at levels ranging from 0.05 mol% to 2.5 mol% with respect to the support. The activities of the catalysts for CO oxidation reveal that at the highest concentration levels of the ions, in all cases, a decrease in activity compared with unmodified Au/TiO2 is observed. However, addition of 0.05 to 0.4 mol% of the ions with respect to the support, prior to gold addition, in most cases, resulted in activity enhancement which increased with a decrease in the ion content. Similar addition of 0.05 to 0.4 mol% of the ions with respect to TiO2 to Au/TiO2 resulted in a decrease in activity. Attempts to understand the origins of these effects show that there is a degree of chemical interaction between the added ions and gold.

A thesis submitted for the degree of Doctor of Philosophy in the Faculty of Science at the University of the Witwatersrand. / The present thesis is divided into three parts. The study described in Part I arose out of a request by the Chamber of Mines Mining Research Laboratory to the National Institute for Metallurgy to undertake a preliminary study of whether it would be feasible, in Witwatersrand conglomerates, to carry out rapid delimitation of areas rich in gold and/or uranium at the rock face, a procedure which would permit areas of rich ore to be removed selectively by means of the "rock-cutter". The approach adopted in this study was essentially geochemical, while conventional mineralogical techniques (macro-auto radiographs , thin section and polished section analyses) provided a control. The samples were drawn from the Vaal Reef at Hartebeestfontein and Zandpan and from the Ventersdorp Contact Reef at Venterspost, and were analysed quantitatively for gold, silver, uranium, pyrite, muscovite, pyrophyllite, chlorite, quartz, iron, potassium, nickel, titanium, zirconium and chromium. The intensity of the interrelationships between the elements and minerals analysed for was examined statistically by means of correlation covariance and factor analysis programmes written for an IBM 360/50 digital computer. A sympathetic relationship -- defined as significant positive correlation (with a correlation coefficient r> 0. 7) -- was found to exist between gold and uranium in both the Vaal Reef and Ventersdorp Contact Reef samples. These findings suggest that gold and uranium can be removed Simultaneously by means of the rock-cutter, and that radioactivity can be used as an indicator for on-site delimitation of areas rich in gold. In the course of the study described in Part I, it became evident that little detailed mineralogical work had ever been done on the phyllosilicates occurring in the Witwatersrand System. Accordingly, certain phyllosilicates from Witwatersrand conglomerate bands and other sources were examined in detail, this study being described in Part II of the present thesis. This study called for detailed chemical, optical, X-ray crystallographic, infra-red, differential thermal and thermogravimetric analyses, the results of which are presented. The findings were examined in the light of variolls classification schemes that have bep proposed for the phyllosilicates. This investigation revealed the need for a universally acceptable system of classification for the phyllosilicates, which should preferably be drawn up under the auspices of the International Mineralogical Association to avoid the confusion that exists at present. Part III of the present thesis is devoted to a discussion and description of various analytical techniques that had to be modified or developed to meet th8 requirements of the studies described in Parts I and II. The techniques described include: (1) An X-ray diffraction method which was developed for the quantitative analysis of pyrite, muscovite, pyrophyllite, chlorite and quartz in crushed ore from Witwatersrand conglomerates. This method makes use of novacul iie as an external standard and of binary mixtures as analytical standards, and had a mean absolute error of 1. 1 %. This method may be expanded to permit analysis of an n-component mixture. (2) A whole rock pressed powder technique of X-ray fluorescence analysis which was used for the quantitative determination of iron, potassium, nickel, titanium, zirconium and chromium. This method makes use of internstional rock standards as external standards. Six computer programmes used for the computation of the analytical results and in the statistical and crystallographic calculations are also presented in Part III. / AC2017