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Item A comparative analysis of classic Geometrical methods and sparse regression methods for linearly unmixing hyperspectral image data(2019) Nicolae, AurelThis research report presents an across-the-board comparative analysis on algorithms for linearly unmixing hyperspectral image data cubes. Convex geometry based endmember extraction algorithms (EEAs) such as the pixel purity index (PPI) algorithm and N-FINDR have been commonly used to derive the material spectral signatures called endmembers from the hyperspectral images. The estimation of their corresponding fractional abundances is done by solving the related inverse problem in a least squares sense. Semi-supervised sparse regression algorithms such as orthogonal matching pursuit (OMP) and sparse unmixing algorithm via variable splitting and augmented Lagrangian (SUnSAL) bypass the endmember extraction process by employing widely available spectral libraries a priori, automatically returning the fractional abundances and sparsity estimates. The main contribution of this work is to serve as a rich resource on hyperspectral image unmixing, providing end-to-end evaluation of a wide variety of algorithms using di erent arti cial data sets.Item Application of integrated methods to assess and characterise the hydrogeology of coastal aquifers in parts of Lagos, Southwest, Nigeria(2020) Yusuf, Mumeen AdebayoThe scope of this Thesis was to apply integrated methods to characterise the groundwater systems of the Lagos Coastal Basin. Like every coastal area in the world, saline intrusion has been the major challenge threatening the fresh groundwater aquifers of the study area over the last couple of decades, and thus, necessitating its assessment. Environmental isotopes, being a reliable and standard tool in hydrological investigation, was employed in combination with geophysical and hydrogeochemical methods to study the coastal aquifer systems. Geophysical probing of the subsurface revealed an alternating sequence of clay and sand, constituting the major lithological units in the study area. The basin aquifers are hosted essentially by sands and clayey sand, while the modes of aquifer occurrences are unconfined to semi-confined and confined for shallow and deep aquifers, respectively. Hydrochemical interpretation identified a surficial thin layer of fresh groundwater overlying the main zone of saline intrusion, which essentially comprises Ca-HCO3 and Ca-Mg-HCO3, Ca-Mg-HCO3 and Ca-Mg-Cl-SO4 hydrochemical facies for both dry and wet seasons, whereas the surface waters are characterised by Mg-Cl and Na-Cl water types for the lagoon and the ocean, respectively. The evaluation of the chemical processes revealed the dominance of carbonate weathering in the shallow aquifer. Hydrochemical, statistical and geochemical model analyses identified that the groundwater chemistry is significantly controlled by water–rock interaction and ion exchange processes as well as anthropogenic activities. Stable isotopes revealed precipitation as the main source of recharge into the basin aquifer systems. Analyses of the 3 H and 14 C activities were in agreement, revealing an interesting fact about the increase in the groundwater residence time from the surface through deeper depths deducible from 3H values range between 0.1 TU and 2.8TU; 0.0 TU and 0.3 TU; and 14 C age range from 4350±10 to 1050±10 years and between 12030±69 and 7400±50 years for the shallow and deep aquifers, respectively. The mean residence time was supported by the aquifer systems‟ recharge which took place in Holocene for the shallow aquifer and Late Pleistocene–early Holocene for the deep aquifers evident from the calculated ambient temperature, 18 O and 14 C plots. The hydrogeological conceptual models showed that saline incursion severely impacted the second aquifer from a depth ≥20m to 170m in the western and central parts of the study. However, the observed local saline occurrence in places <20m was attributed to groundwater overexploitation. Conclusively, the hydrological systems of the Lagos coastal basin is continually being modified by both anthropogenic and natural activities that constitute not only a major threat to the groundwater sustainability of the Lagos coastal basin but can also consume the entire study areaItem Resolvability of groups(University of the Witwatersrand, Johannesburg, 2020) Ndhlalane, MororisengA topological group is called resolvable if it can be partitioned into two dense subsets. A group is absolutely resolvable if it can be partitioned into two subsets dense in any nondescript group topology. The aim of this dissertation is to give a unified exposition of some major results about resolvability of groups. In particular, we show that; 1. Every countable nondescript topological group not containing an open Boolean subgroup is resolvable, 2. Every infinite Abelian group not containing an infinite Boolean subgroup is absolutely resolvable.Item Remote sensing survey of archaeological sites in the Shashi- Limpopo Region(2020) Thabeng, Olaotse LokwaloThe African continent is rich with archaeological heritage, which needs to be preserved for the current and future generations. The majority of archaeological heritage sites in Africa are facing disappearance due to a number of challenges including looting, destruction from developments, expansion of agricultural land and natural hazards. Documentation and monitoring of archaeological heritage sites, therefore, is of paramount importance for effective site management and preservation. However, archaeological heritage sites in the continent are poorly documented and monitored due to a number of factors including lack of funds by heritage management institutions, lack of trained personnel and inaccessibility of some areas due to conflicts or land ownership rights. Traditionally, the documentation and monitoring of archaeological heritage sites in Africa have been done through fieldwork, which is costly, time-consuming and difficult to carry out over large areas. Remote sensing offers a relatively fast, cheap, systematic and reproducible method of surveying and monitoring archaeological sites over large and/or restricted areas. Remote sensing techniques are used to identify earth surface features based on their spectral signature, which is the variation of reflection or emittance of materials’ electromagnetic energy. Spectral signatures for identifying archaeological sites are not universal, and an assessment of the applicability of remote sensing techniques in different archaeological landscapes is needed. The aim of this study, therefore, was to investigate the potential of using remote sensing techniques to document archaeological sites previously occupied by farming communities, which are traditionally associated with the Iron Age period in Southern Africa, using the Shashi-Limpopo case study. The first part of this study gives a review of the use of remote sensing in the African archaeological context. Despite it being a fast, cost-effective and systematic method of survey, the results of this study have demonstrated that remote sensing is not widely used in archaeological applications in Africa. The aforementioned situation calls for studies investigating the potential of using remote sensing techniques to fast track archaeological site survey, documentation and monitoring in the continent. The chemical composition of materials characterising different features have more or less subtle variations that, in turn influence the spectral behaviour of soil. This is an important principle that can be used for distinguishing archaeological soils from non-archaeological soils and can potentially help in discriminating different archaeological signatures. As such, the second part of this study investigated the possibility of using field spectrometer measurements to discriminate middens, non-vitrified dung, vitrified dung and non-sites (natural soils) characterising archaeological landscapes previously occupied by farming communities. It then investigated the presence of differences in the chemical composition of elements between middens, non-sites, vitrified dung and non-vitrified dung. The findings indicated that there is a statistically significant difference in the concentration of soil elements between non-sites, middens, vitrified dung and non-vitrified dung byres. They also indicated that some bands in the visible and shortwave infrared regions of the electromagnetic spectrum important bands for predicting the aforementioned archaeological sites and non-archaeological sites. In the third part of this study, the ability of multispectral sensors to discriminate archaeological and non-archaeological features in Shashi-Limpopo confluence area was investigated using field spectral data resampled to the spectral resolutions of common multispectral satellites namely GeoEye, Landsat 8 OLI, RapidEye, Sentinel-2, SPOT 5 and WorldView-2. This is because the spectral and spatial resolutions of various multispectral sensors determine the size and the type of archaeological data a sensor can detect. As such, another goal of this study was to identify multispectral sensors with the optimum spectral resolutions for detecting middens, non-vitrified dung, vitrified dung and non-sites. Additionally, the performance of advanced classification algorithms (random forest and support vector machines) in discriminating middens, non-vitrified dung, vitrified dung and non-sites was also investigated. The results proved the possibility of using multispectral satellites in mapping middens, non-sites, vitrified dung and non-vitrified dung sites. These results initiated the need to upscale the test to actual satellite images. The fourth part of this study assessed the possibility of prospecting for archaeological sites previously occupied by farming communities in the Shashi-Limpopo Confluence Area, using a very high-resolution satellite WorldView-2 image. The findings have shown that WorldView-2 satellite images and advanced classification algorithms can be used in prospecting for archaeological sites previously occupied by farming communities in Shashi-Limpopo Confluence Area. Finally, the ability of geographic object-based image analysis (GEOBIA) based on random forest and support vector machines, to discriminate archaeological and non-archaeological features on a very high-resolution satellite WorldView-2 image was investigated. The results of this study demonstrated the robust ability of the GEOBIA to integrate spatial attributes into the classification model improves the chances of separating materials with limited spectral contrast. Generally, this study has shown that remote sensing techniques can be used to map archaeological landscapes characterised by middens, non-vitrified dung, vitrified dung and non-sites. This will help archaeological heritage managers and researchers to document and monitor sites in archaeological landscapes characterised by the aforementioned features in a fast, systematic, reproducible and cost-effective mannerItem Climate change and heritage tourism: threats to Makgabeng in a regional context, Limpopo South Africa(2020-11) Mcpherson, Fazlin AhdielahThe Makgabeng area is situated in the north-west corner of the Limpopo province in South Africa. The Makgabeng area is an emerging tourist destination with a variety of activities to offer. The area is rich in ancient rock art sites and, as a result, has great potential for the development of heritage tourism. Extensive research has been conducted on the rock art in this region. However, the impact of climate change on heritage tourism has not yet been explored. The local community of the Makgabeng area is developing a heritage tourism destination within the region and it is important to determine whether the initiative will be sustainable, especially in the context of climate change threats to the region. In a region such as Makgabeng where the primary attraction is natural heritage tourism rather than cultural, this then poses a severe threat to tourism within the region, especially since most of these attractions are outdoors. Hence, this research project is primarily aimed at determining climate change threats to heritage tourism in the Makgabeng region, South Africa. The research has employed a mixed-method approach consisting of interviews done with various stakeholders within the tourism industry and community members in the Makgabeng region. The other methods used are hard-copy and online questionnaires, TripAdvisor reviews, and the Tourism Climatic Index (TCI). What the research has found is that people do not know that Makgabeng exists, and for those who are aware of its existence they have never visited the region. this is because the area is not being marketed effectively. The TCI scores show that winter is the best time of the year for tourism. Consequently, stakeholders and community members should market the area with this in mind. However, tourists have said they enjoy the weather in the region all year round.Item Trimetallic nanoparticles immobilised on polymeric membranes for the degradation of organic pollutants in water(2021) Kgatle, Masako; Moloto, Nosipho; Sikhwivhilu, Keneiloe; Ndlovu, GebhuWater is one of the most essential resources in the world, but its scarcity has become an issue of global concern. The scarcity of water is largely the result of climate change, water pollution and increasing population growth which limits the availability of water resources. Moreover, South Africa has been making headlines since 20 IO due to water shortages experienced. It is, therefore crucial to find cost-effective ways to expand the water supply and address the issue of water pollution. This study seeks to tackle the problem of water pollution emanating from textile industries. Over the last few years, nanotechnology and membrane technology have appeared as some of the most widely used methods for the mitigation of water pollution problems. Particularly, nanoscale zerovalent iron (nZVI) has emerged as one of the most broadly used nanoparticles in wastewater treatment and remediation owing to its low-cost and high effectiveness. However, because of its ease of aggregation and consequent loss of reactivity, nZVI is coupled with one or more transition metals to produce multimetallic systems. Nanoparticles alone quickly agglomerate and form large micro-scale particles owing to the magnetic forces thus losing their mobility and chemical reactivity. To avoid these issues, the nanoparticles are stabilized on polymeric membranes. In this study, two trimetallic nanoparticle systems were synthesized, characterized and tested for catalytic activity. The polyvinylpyrrolidone (PVP)-stabilized Fe/Cu/Ag nanoparticles were synthesized by the sodium borohydride chemical reduction method. These nanoparticles were characterized using XRD, XPS, EDX and TEM. The XRD, EDX and XPS techniques showed the presence of all three metals, including iron oxides due to the oxidation of iron in air. The obtained TEM images showed the characteristic core-shell morphology of the nZVI-based nanoparticles. The evaluation of the catalytic activity of the nanoparticles was conducted using methyl orange (MO) dye as the model pollutant and this showed a remarkable degradation efficiency within few minutes. The effect of parameters such as MO solution pH, initial MO dye concentration and nanoparticle dosage in MO degradation was investigated. The nanoparticles were found to have performed better at lower pH, lower initial MO dye concentration and higher nanoparticle dosage. The degradation of MO dye was monitored using UV-Vis analysis and occurred within 1 min. The degradation was found to follow a pseudo first-order kinetic model and was vastly influenced by the studied parameters. The analysis of by-products and reaction pathway were done using LC-MS and this further confirmed that the degradation of MO was indeed rapid. The Fe/Cu/Ag trimetallic nanoparticles were demonstrated as suitable and effectual alternative for the remediation of textile dye wastewater. For the second trimetallic system, three different trimetallic nanoparticles (Fe/(Zn/Ag), Fe/Zn/Ag and Fe/ Ag/Zn) with different metal addition sequences were synthesized. The prepared nanoparticles were characterized using XRD, EDX and TEM analyses. The techniques proved successful synthesis of the nanoparticles and XRD and EDX showed the presence of the three metals together with the oxides. The evaluation of the catalytic reactivity of the nanoparticles was conducted in a series of batch experiments using MO dye as the model pollutant. About 100% of the MO dye was degraded by Fe/ Ag/Zn trimetallic nanoparticles within 1 min and the second-order rate constant obtained was 0.0744 ppm- 1min-\ the rate of reaction was higher than that of the other trimetallic systems. Using Fe/ Ag/Zn trimetallic nanoparticles, parametric tests were conducted at different MO solution pH, initial MO concentration and nanoparticle dosage. The results showed that the reactivity of the Fe/Ag/Zn trimetallic nanoparticles was highly dependent on the aforementioned parameters. Like the Fe/Cu/Ag system, the Fe/Ag/Zn performed better at lower pH, lower initial MO dye concentration and higher nanoparticle dosage. The overall kinetic study showed the removal of MO using Fe/Ag/Zn system to follow a second-order kinetic model. The elucidation of the degradation pathway and MO by-products identification were done using LC-MS and the mechanism of degradation displayed the degradation of methyl orange to proceed via azo-bond cleavage. Moreover, the Fe/ Ag/Zn nanoparticles proved to be effective at degrading methyl orange dye and can be used to treat azo-dye wastewater from textile industries. The Fe/Cu/ Ag trimetallic nanoparticle system was immobilized on a polymethacrylic acid grafted polyethersulfone (PMAA-g-PES) membrane to minimize the issue of recoverability and nanoparticle agglomeration. The nanocomposite membranes were prepared by loading different quantities of Fe/Cu/Ag trimetallic nanoparticles onto the PMAA-g-PES membrane for optimization purposes. Characterization was performed using FTIR, NMR, XPS, SEM/EDS and AFM analyses. The PMAA g-PES and nanocomposite membranes were found to have a porous top layer and a rough surface. Moreover, the addition of nanoparticles did not cause any significant changes in the membrane structure, however, further addition of nano particles led to the blockage of pores. The performance of the synthesized membranes was tested using pure water flux and MO (anionic dye) and methylene blue (MB) (cationic dye) dye removal capacity. The negatively charged membranes were found to have more affinity for MB dye than the MO dye and this was ascribed to the charge interaction between the membrane surface and the dyes. The nanocomposite with 5% Fe/Cu/Ag trimetallic nanoparticle loading on PMAA-g-PES membrane (M4-5% membrane) was found to have the best adsorption capacity with about 60% MB dye removal efficiency. Furthermore, the effect of process parameters such as pH, temperature and H2O2 concentration on the removal of MB was studied. The removal efficiency was found to be higher at higher pH and lower temperature. About 100% removal efficiency was obtained when the process was performed at pH 9 in the presence of H2O2 via adsorption and Fenton degradation. This showed that a hybrid of processes was convenient for the removal of MB dye by adsorption (primarily) and degradation using the nanocomposite membrane. Adsorption equilibrium data were assessed using the Langmuir, Freundlich and Temkin models; the Temkin model was the most convenient to explain the adsorption of MB onto M4-5% membrane. Moreover, lcinetic studies were performed on four kinetic models: pseudo first-order, pseudo second order, intraparticle diffusion and elovich models. The pseudo second-order was found to be the best suitable to explain the adsorption of MB onto M4-5% membrane. Thus, the adsorption of MB onto the nanocomposite membrane is an exothermic chemical process that occurs on a heterogeneous surface. Therefore, the nanocomposite membrane has the prospective to be applied in the removal of cationic textile dyes in the presence of an oxidiser.Item Synthesis and characterization of nitrogen-doped hollow carbon spheres/ Cu2S composites for potential application as counter electrodes in dye sensitized solar cells(2022) Majola, ThelmaCurrent solar cells have disadvantages that include weather dependency and high manufacturing costs. Dye-sensitized solar cells (DSSCs) have emerged as possible solutions for these drawbacks. Since it is predicted that the global warming effect will result in the sun emitting less energy. DSSCs have the added advantage of working in low-light conditions, and the ability to harness light energy from other devices. Although DSSCs have low production costs, their low efficiency due to the platinum (Pt) electrocatalyst limits their commercial implementation. DSSCs are made up of many components including dye, and counter electrode (CE). Modifications can be made on these components to improve efficiency and make the DSSC more eco-friendly. For instance, CE research has focused on finding substitute electrocatalysts. In this study copper sulfide (Cu2S) and hollow carbon spheres (HCSs) have been considered as viable substitutes for Pt since they exhibit good electrocatalytic properties. Carbon materials have corrosion resistance towards iodine, and Cu2S has superior oxidation resistance. Therefore, they can be used for electrolyte redox reactions at the CE in a DSSC. The properties of HCSs can be enhanced by making the carbon shell porous, increasing the number of carbon shells, or by doping the carbon shell with heteroatoms such as nitrogen (N). These modifications can improve the conductivity, surface area, adsorption, and electronic properties. For this research porous nitrogen doped single-shelled and double-shelled HCSs were synthesized. To prepare the HCSs, a carbon shell was coated on the surface of the mesoporous silica spheres using the chemical vapour deposition method (CVD) with acetylene or toluene as carbon precursors at 900 °C for 1 h. Thereafter, the silica template was etched using 10 % HF at room temperature for 24 h. It was found that toluene produced HCSs with a higher surface area. Unexpectedly, the double-shelled HCSs were found to exhibit low surface areas than the single-shelled HCSs. Nitrogen doping improved the properties of both the single and double-shelled HCSs. The nitrogen-doped, single-shelled mesoporous hollow carbon spheres (N-HCS) showed better properties for electrocatalysis than the double-shelled HCSs. The Cu2S nanoparticles were prepared using colloidal synthesis at 230 °C for 1 h with oleylamine (OLA) as the surfactant and 1-dodecanethiol (1-DDT) as the sulfur source. Different copper precursors were used which gave Cu2S with varying compositions. Both precursors produced particles with a hexagonal morphology, however, copper (II) acetylacetonate (Cu(acac)2) produced smaller particles (30 nm) compared to large particles (479 nm) from copper chloride (CuCl). A time study on the different copper sources showed a variance in nucleation and particle growth. The Cu2S-HCS composites were prepared using OLA as the surfactant, with different percentages of Cu2S and HCSs. The different composition mixtures were heated to 100 °C and then washed to remove the unreacted elements. The synthesized materials were analyzed using various techniques. TEM showed the spherical morphology of HCSs, the hexagonal morphology of Cu2S, and the successful formation of the composites. The surface area and porosity of the materials were measured using the BET technique. Graphitization of carbon and the phase composition of Cu2S was analyzed using PXRD. The successful incorporation of N within the structure of the N-HCSs was confirmed using XPS. The electrocatalytic activities of the composites were investigated using CV,EIS, Tafel polarization, I-V and compared to Pt under similar conditions. The 75 wt% N-HCS: 25 wt% Cu2S composite had higher current density, lower peak-to-peak separation, and high electrochemical double layer capacitive current, good adhesion to the FTO glass and great photovoltaic performance compared to Pt. This suggests that it was the better performing composite and has the potential to substitute Pt- CE in DSSCs.Item The influence of plant phenolic compounds on the host range of Coniatus tamarisci Fabr. (Coleoptera: Curculionidae): a potential biological control agent of invasive Tamarix L. (Caryophyllales: Tamaricaceae) Taxa in South Africa(University of the Witwatersrand, Johannesburg, 2022) Hatile, Sivenathi Luvolwethu; Byrne, Marcus; Mayonde, SamalesuTamarix L. (Caryophyllales: Tamaricaceae) are halophyte species that are native to Eurasia, North Africa, and southwestern Africa. These phreatophyte trees or shrubs have become prominent and widespread invaders in North America, South America, Australia, and South Africa. In South Africa, the Alien and Invasive Species regulations of the National Environmental Management: Biodiversity Act 2014 (NEM:BA) has classified invasive Tamarix as category 1b invader, which require control. Thus, three potential biological control agents have undergone laboratory-based host-specificity trials for the long-term sustainable control of Tamarix. The first two of these biocontrol agents, Diorhabda carinulata (Desbrochers.) (Coleoptera: Chrysomelidae) and Trabutina mannipara (Hemprich & Ehrenberg) (Hemiptera: Pseudococcidae), both failed the laboratory-based host-specificity trials because they completed their life cycle on the indigenous T. usneoides E. Mey ex Bunge. Previously, potential biocontrol agents were selected based on their native distribution and the phylogenetic relatedness of the invasive weed to indigenous nontarget species. However, it has recently been suggested that secondary metabolites also play a major role in insect host selection, and thus should be considered to improve the selection criteria of potential biocontrol agents. The current study is based on the third biocontrol agent that recently underwent laboratory based host-specificity trials in South Africa, Coniatus tamarisci (Fabr.) (Coleoptera: Curculionidae). This was in conjunction with an analysis of the potential influence Tamarix phenolic compounds have on insect host selection. The results show that although C. tamarisci could complete its’ life cycle on T. usneoides, the weevil had a low affiliation/risk associated with the indigenous Tamarix taxon. This advocates for the conduction of open field host-specificity trials, which will allow for a better understanding of C. tamarisci behaviour in a natural setting. Regarding phenolic compounds, three phenolic acids have been identified as being significantly prominent in T. usneoides compared to the invasive Tamarix taxa present in South Africa. These are gallic acid, dehydrodigallic acid, and syringic acid. These compounds are associated with protection from plant herbivory, which could explain the behaviour of C. tamarisci when exposed to and reared on T. usneoides.Item A study of the support effect of carbon dots-derived graphene-like sheets on the autoreduction of cobalt nanoparticles for Fischer–Tropsch synthesis(2022) Mokoloko, Lerato LydiaThe aim of this study was to synthesize and characterize carbon dots (CDs) and to use them as a support material for cobalt (Co) based Fischer-Tropsch synthesis (FTS) reactions. The CDs were chosen for this study due to their small size (< 10 nm), easy surface functionalization and synthesis. The small size of the CDs was required for the study of inverse catalyst support effects. An inverse supported catalyst (in this case, the Co/CDs catalyst) refers to the dispersion of a support material that has a small size (d < 5 nm) onto the surface of a metal catalyst with a similar small size (d > 8 nm). The synthesis of this proposed catalyst was successful. FTS studies on the Co ‘supported’ CDs were attempted. Extremely poor FT activity was observed. Post analysis of the catalyst revealed that the CDs did not retain their quasi-spherical and small particle size morphology under the FTS reaction conditions (temperature 220 °C, 10 bar P; H2:CO ratio = 2:1). Instead, upon exposure to a heat treatment, the CDs were transformed into layered structures with a unique resemblance to graphene-based nanosheets (GNSs). This transformation impacted on the use of these catalysts in the FTS reaction. However, this result indicated an unusual transformation of the CDs into another carbon shape. In light of the fascinating transformation phenomenon, annealing studies were then conducted to investigate the effect of annealing temperatures on the CDs structural changes. The CDs (average d= ~ 2.5 nm) used in this study were obtained from the microwave-assisted carbonization of L-ascorbic acid and subjected to a heat treatment (i.e. annealing) at temperatures between 200 and 700 ℃ in a horizontal CVD apparatus under an inert nitrogen gas. It was observed that annealing transformed the CDs from 0-D qausi-spherical nanoparticles to 3- D multi-layered carbons (at 300-600 ℃) and finally 2-D layered materials (at 700 ℃). Furthermore, annealing at 700 ℃ yielded a 2-D single-layered material with comparable properties to traditionally reduced graphene oxide (rGO). A wide range of characterization techniques were used to gain an insight into the physicochemical properties of these novel CDs-derived allotropes as well as to rationalize their mechanism of formation. After evaluating the properties of these materials, it was clear that the surface oxygen functional groups, observed from XPS, 13C NMR and other studies, were responsible for the CDs to rGO transformation. It was proposed that the CDs are assembled to form rGO (and other CDs-rGO derivatives) by either the Ostwald ripening (in which the carbons agglomerated via a gas phase) or a solid phase reaction (involving reaction of CD edges). To further investigate the effect of annealing on the evolution of CDs to layered carbon structures, N-doped CDs (or NCDs) were also studied. The method used to make the pristine CDs was modified by incorporating urea as a nitrogen source to make the NCDs. Annealing the NCDs at temperatures between 200 and 700 ℃ also transformed the quasi-spherical NCDs (average d = ~ 4.1 nm) to multi-layered carbon sheets at temperature as low as 200 ℃. The CD transformation was also associated with the loss of surface functional groups, with % O and N contents of ca. 17 and 16 % (pristine NCDs) being reduced to ca. 8 and 7 % for NCDs annealed at 700 ℃. A similar mechanism for the formation of these N-doped layered carbon structures by annealing was also proposed here. For these samples, it was also observed that the N-bonds, especially the sp3 type nitrogen bonds found on the edges of the NCDs, also took part in the coalescence of the NCDs to give the layered materials. XPS data suggested that in the process, these sp3 type nitrogen bonds were transformed into sp2 pyrrolic-N, pyridinic-N and GraphiticN groups. The annealed CDs products were used to support Co (called Co3O4/T250, Co3O4/T400 and Co3O4/T700 where T is the temperature at which the CDs were annealed) for use in FT studies. Studies were conducted to evaluate the effect Co hydrogen reduction temperatures verses autoreduction temperature, catalyst thermal stability and performance in the FTS reaction at 220 °C (10 bar P; H2:CO ratio = 2:1). Upon investigation of the reduction behaviour of the Co/CDs derivative catalysts using in situ PXRD, it was found that these materials can successfully facilitate autoreduction of Co3O4 to Co face-centered-cubic (fcc) at temperatures > 400 ℃ by a reduction pathway similar to that observed using conventional H2 reduction conditions. As expected, the reduction under H2 took place at a lower activation temperature (> 250 ℃) than the autoreduction process. It was also noted that these novel carbon support derived from CDs gave reduced FTS performance compared to the unsupported Co, especially towards C5+ yields (< 30 % for all Co supported catalysts). These novel CDs-derived allotropes were found to have limited use as supports in Co-based FTS, due to Co agglomeration. These NCDs-derived allotropes (annealed at 200 ℃, 400 ℃ and 700 ℃) were incorporated as active layers in the fabrication of chemoresistive sensing device detection of volatile organic compounds (VOCs). These layered showed enhanced chemical vapour sensing properties, especially for methanol and ethanol detection at room temperature. Therefore, although there are great limitations for applications of these CDs-derived layered allotropes in FTS reaction, these materials show a much better potential for applications in facile and cost effective VOC sensors. Further studies on this will be conducted.Item Colloidal synthesis and characterization of molybdenum and tungsten-based phosphide electrocatalysts for hydrogen evolution reaction(2022) Nkabinde, Siyabonga Sipho; Moloto , NosiphoThe production of hydrogen gas via hydrogen evolution reaction (HER) in acidic media has become an important area of research in light of the increasing demand for sustainable and environmentally friendly sources of energy. However, its large-scale production is currently being hindered by the lack of inexpensive and highly efficient non-noble electrocatalysts. Transition metal phosphides (TMPs) have transpired as favourable catalysts that can be prepared from cheap and readily available sources. Up to now, TMPs have been commonly prepared using solid-state and solid-gas reactions, which rely on the use of high temperatures and hence generate inhomogeneity in the prepared materials. Inhomogeneous materials are unattractive as catalysts because the correlation between a catalyst and its structural features cannot be systematically studied. For this reason, colloidal synthesis has emerged as a powerful method in the synthesis of TMPs as it allows for control over the resulting physical features (i.e. size, morphology, crystal phase, crystallinity etc.). The ability to tailor these physical properties provides room for improving the catalytic activity. By using the colloidal synthesis method, we have successfully prepared molybdenum and tungsten-based phosphide nanoparticles and studied the effect of their physical features on HER activity. In chapter 3, we report a facile colloidal synthesis method to produce an amorphous phase of molybdenum phosphide (MoP) by using trioctylphosphine (TOP) as a phosphorus source, molybdenum pentachloride (MoCl5) as a metal source and 1-octadecene (1-ODE) as a solvent/reducing agent. The use of the forementioned precursors promoted the formation of very small, shape controlled and well dispersed amorphous molybdenum phosphide (MoP) nanoparticles. Annealing (800 °C) of the amorphous MoP nanoparticles resulted in the formation of a crystalline MoP phase with a slightly bigger size but retained its dispersity and morphology upon exposure to high temperature. The amorphous and crystalline MoP phases were compared as HER electrocatalysts. HER results indicated that the amorphous MoP phase exhibited enhanced catalytic activity in hydrogen evolution reaction compared to the crystalline MoP phase. The high activity displayed by the amorphous MoP was attributed to the small sizes and the high density of unsaturated active sites characteristic of nanoparticles lacking long range crystalline order.Item Fabrication of polyaniline/indium oxide /onion-like carbon ternary nanocomposite for room tempera ture gas sensing applications(University of the Witwatersrand, Johannesburg, 2022-08) Mathe, Boipelo Nicholette; Linganiso, E.C; Tetana, Z; Moma, JMonitoring and documenting chemical stimuli or environmental fluctuations is vital to daily health care and environmental monitoring. This objective can be accomplished through the development of high-performance sensors able to detect toxic gases such as ammonia, volatile organic compounds (VOCs) and many more. The modification of carbon nano-onions with metal oxides/conducting polymer could enhance sensing performances at room temperature. This research focuses on the development of a flexible room temperature gas sensor for ammonia sensing with a sensing layer composed of indium oxide (In2O3)/onion-like carbons (OLCs)/ polyaniline (PANI). The current sensors were tested at a 40-45 percentage humidity. Polyaniline was produced utilizing the rapid polymerization technique with aniline and ammonium persulfate as precursors. Carbon nano-onions were obtained by the flame pyrolysis process with candle wax as the carbon source. The present study compared two microwave-assisted solution-phase methods for the synthesis of indium oxides. The first methods produced indium hydroxide (In(OH)3) followed by its conversion to In2O3 through annealing at 400 oC, and the second used a one-step method where ethanol was used as a solvent instead of water. Different reaction times were used to determine the effect of microwave power on the indium oxide formed through a solution-phase method, and several characterizations techniques were performed to characterize the products, including transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy and Ultraviolet-visible spectroscopy. The ternary In2O3/PANI/OLCs nanocomposite was fabricated using physical mixing by adding varying amounts of In2O3 to fixed quantities of PANI and OLCs. Using gold-plated interdigitated electrodes (IDEs) embedded on a printed circuit board (PCB) substrate, inexpensive and room temperature functional sensors based on plain PANI, OLCs, OLCs/PANI, and OLCs/PANI/In2O3 were developed. The sensors based on ternary composites outperformed of sensors based on pure PANI, OLCs, and PANI/OLCs, due synergic effect of PANI, OLCs and In2O3 when combined. The sensor with the highest response among the sensors with the ternary nanocomposite as the sensing layer, was chosen for further evaluations of recovery time, reaction time, repeatability, and selectivity. The sensor containing (4.6 mg) B-In2O3/PANI/OLCs was particularly responsive to ammonia in comparison to other analytes (hexane, isopropanol, acetone), with the response and recovery durations of 2.2 minutes and 4.3 minutes, respectively, spanning a concentration range of 25 ppm to 125 ppm. Current results showed that In2O3 materials can be successfully applied in room temperature gas sensing application and further enhance the sensing response to levels that cannot be obtained when using PANI or OLC individually.Item Estimating skills in discrete pursuit-evasion games(University of the Witwatersrand, Johannesburg, 2023) Gomes, Byron John; Rosman, BenjaminGame Theory is a well-established field in mathematics, economics, and computer science, with a rich history of studying n-person, zero-sum games. Researchers have utilized the best computational power of their time to create computational players that are able to beat the best human players at complex two-player, zero-sum games such as Chess and Go. In the field of Reinforcement Learning and Robotics, these types of games are considered useful environments to conduct experiments about agent behavior and learning. In this research report we explore a subset of discrete skill-dependent pursuit-evasion games upon which we build a framework to estimate player skills. In this game environment a player’s skill determines the actions available to them in each state and the transition dynamics resulting from the chosen action. The game offers a simplified depresentation of more complex games which often have vast state and action spaces, making it difficult to model and analyze player behavior. In this game environment we find that players with incorrect assumptions about an opponent’s skill perform sub-optimally at winning games. Given that knowledge of an opponent’s skill impacts on player performance, we demonstrate that players can use Bayesian inference to estimate their opponent’s skill, based on the action outcomes of an opponent. We also demonstrate that skill estimation is a valuable exercise for players to undertake and show that the performance of players that estimate their opponent’s skill converges to the performance of players given perfect knowledge of their opponent’s skill. This research contributes to our understanding of Bayesian skill estimation in skill-dependent pursuit-evasion games which may be useful in the fields of Multi-agent Reinforcement Learning and Robotics.Item Comparing the effectiveness of LSTM, ARIMA, and GRU algorithms for forecasting customer charging behavior in the electric mobility industry in Europe(University of the Witwatersrand, Johannesburg, 2023) Pelwan, Robyne ChimereForecasting, a powerful technique for unveiling potential future events, relies on historical data and methodological approaches to provide valuable insights. This dissertation delves into the domain of electric mobility, investigating the effectiveness of three distinct algorithms—Long Short-term Memory (LSTM), Autoregressive Integrated Moving Average (ARIMA), and Gated Recurrent Unit (GRU)—for predicting customer charging behavior. Specifically, it focuses on forecasting the number of charges over a 7-day period using time-series data from European electric mobility customers. In this study, we scrutinize the interplay between algorithmic performance and the intricacies of the dataset. Root mean squared error (RMSE) serves as a metric for gauging predictive accuracy. The findings highlight the supremacy of the ARIMA model in single-variable analysis, surpassing the predictive capabilities of both LSTM and GRU models. Even when additional features are introduced to enhance LSTM and GRU predictions, the superiority of ARIMA remains pronounced. Notably, this research underscores that ARIMA is particularly well-suited for time series data of this nature due to its tailored design. It contributes valuable insights for both researchers and practitioners in the electric mobility industry, aiding in the strategic selection of forecasting methodologies.Item Investigating the regulation of PXDN expression by the early growth response 1(EGR1) transcription factor in the context of human fibrotic diseases(University of the Witwatersrand, Johannesburg, 2023) Makhanya, ThokozilePeroxidasin (PXDN) is a novel member of the peroxidase-cyclooxygenase family of haem containing proteins that catalyze oxidative reactions. It consolidates the extracellular matrix (ECM) by using hydrogen peroxide (H2O2) as a substrate to generate hypohalous acid intermediates, which help catalyze the formation of sulfilimine bonds between collagen IV protomers. The aberrant expression of PXDN has been linked to the development of various diseases where the architecture of the ECM is compromised such as cardiovascular diseases, ocular diseases, cancer, and fibrosis. Fibrosis develops due to repetitive tissue injury which is followed by aberrant wound healing that causes the excessive deposition of ECM proteins such as collagen into the injured tissue. In turn, ECM crosslinking enzymes such as PXDN are upregulated, and the matrix becomes thick and heavily crosslinked. This study aims to elucidate whether early growth response 1 (EGR1), a zinc-finger transcription factor which regulates cell proliferation, differentiation, apoptosis, and a key pro-fibrotic protein, can drive PXDN expression. To address the aim, HEK293 cells were treated with TGF-β1, a master activator of fibrotic genes, and western blot and immunofluorescence microscopy were performed to detect EGR1 and PXDN and their cellular localization, respectively. Chromatin immunoprecipitation (ChIP) was performed to determine if EGR1 binds to the PXDN promoter and the luciferase reporter assay was employed to determine if the interaction resulted in an alteration in gene expression. Our western blot findings showed that for EGR1, there was a statistically insignificant increase in protein expression in response to the TGF-β1 treatment. PXDN expression could not be quantified due to the high background on the blots. Further analysis by immunofluorescence microscopy showed that EGR1 expression was increased and was localised to the nuclei in response to the TGF-β1 treatment. We also observed that PXDN was predominantly expressed extracellularly and showed a significant increase in protein expression with treatment. The bioinformatics analysis has identified two putative EGR1 binding sites in the PXDN promoter and ChIP-PCR showed that binding occurred at one of these sites. This site was cloned into the pGL4.10 vector to determine whether EGR1 drives PXDN expression. Due to unsuccessful transfection optimization, the luciferase assay could not be performed and therefore for future work this assay needs to be performed to verify if EGR1 can drive PXDN expression. In conclusion, we showed that PXDN is a TGF-β1-responsive gene and may be regulated by EGR1. Studying the interaction of EGR1 and PXDN may establish roles for PXDN in fibrosis and further consolidate PXDN as a possible anti-fibrotic therapeutic target.Item On polarity-based semantics for non-distributive modal logics(University of the Witwatersrand, Johannesburg, 2023) Clingman, R.; Conradie, WillemThis masters study builds upon recent research in polarity-based semantics for non-distributive modal logics (NDMLs). Current formulations of polarity-based semantics for NDML impose compatibility requirements on additional relations of polarity-based frames, hindering applicability of the semantics, as arbitrary frames need not be compatible. In this study we develop a polarity-based semantics for NDML with modalites that are, in general, neither normal nor distributive and without the imposition of compatibility requirements. We provide a sound and complete axiomatization of this logic. The second half of the thesis focuses on a special class of enriched polarities, those who are in a sense liftings of Kripke frames. The compatibility of these liftings combined with the intuitive nature of the underlying Kripke frames makes for a useful case study in which to explore p-morphisms between enriched polarities, and enriched polarity-based models, from a relational perspective.Item The political geography of hemp Cannabis in South Africa: A development critique(University of the Witwatersrand, Johannesburg, 2023-06) Moore, Wendell; Wafer, A; Mnwana, SThe discourse on Cannabis that is generally understood in the public domain, revolves mostly around its recreational uses and more recently its medicinal potential. The plants industrial usages and overall worth to society are often framed in relation to these more popular parts of Cannabis. The study focuses its attention on hemp Cannabis to tell a different story but acknowledges that all the uses of Cannabis are interlinked. Using an extensive desktop analysis, Cannabis webinars and conferences, as well as autoethnography, the thesis shows that there is in fact more to the plant than what first meets the eye. It especially illuminates two important dimensions of Cannabis that are often overlooked when discussing the plant. Firstly, by its nature Cannabis is political, which is deeply embedded in how the plant is understood in the geographic diaspora of the Global South. Secondly, it shows that any serious social scientific analysis of contemporary Cannabis development must think through how the ways of knowing, Produced during prohibition, will become a part of the plant’s future. This thesis therefore argues for an appraisal and maintenance of the historical resistances of Cannabis used prior to legalization, if its development in the legal era is to be successful. To be sure, such innovative and alternative models of practical development should become a standard part of the geographies of all work economies. Moreover, making use of these forms of resistance is not about Cannabis gaining the approval from ‘the market’. In fact, the skills learnt while labouring for Cannabis, when it was prohibited, has become such a permanent feature of its development that liberal democratic consent is not an option. Therefore, the thesis proposes that Cannabis development delink from the prohibition narratives inscribed onto the plant. It continues by showing that the current medicalisation of Cannabis only updates gatekeeping models. Hence, an agrarian alternative was suggested that consolidates all the uses of Cannabis without undermining any one part of the plant. Lastly, the thesis documents the possibilities of gaining access into the industry for black people, the poor working class and women. What it argues is that ownership, just employment and leadership of Cannabis industries in South Africa must be repurposed so that ordinary people can also play a part in making sure the plants contemporary development is truly sustainable. Taken together, this is the critique of development that the political geography of hemp Cannabis in South Africa reveals.