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The host potential of wheel-and-axle polyaromatic compounds
Get PDFIn this work, wheel-and-axle compounds 1,4-phenylene-bis(diphenylmethanol) (H1), 1,4-phenylene-bis(di-p-tolylmethanol) (H2) and 1,4-phenylene-bis(di-p-fluorophenylmethanol) (H3) were investigated for their host behaviour in various pyridyl and heterocyclic guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on dimethyl terephthalate, employing the aryl halides bromobenzene for H1 (73% yield), p-bromotoluene for H2 (69%) and p-bromofluorobenzene for H3 (70%). Molecular modelling calculations demonstrated that the various C-C-C angles differed between the computed low energy host conformers and those in the host molecules from their PYR-containing crystal structures. However, specified ‘torsion’ angles were in close agreement. Compound 1,4-phenylene-bis(diphenylmethanol) (H1) possessed the ability to form 1:2 host-guest (H:G) complexes with each of pyridine (PYR) and 2-, 3- and 4-methylpyridine (2MP, 3MP and 4MP). Furthermore, H1 showed preferential behaviour towards PYR and 4MP when presented with various mixtures of these four pyridines. Due to the high selectivity coefficients calculated in many instances (the selectivity coefficient, K, is a measure of the selectivity of a host compound for one particular guest in a mixture), it was demonstrated that H1 would be suitable for separations/purifications for many of the mixtures investigated in this work through host-guest chemistry strategies. (These pyridines are difficult to separate by means of the more conventional fractional distillations because of very similar boiling points.) Single crystal X-ray diffraction (SCXRD) analyses revealed that 4MP and 3MP experienced hydrogen bonds with the host molecule which were similar in distance, while the hydrogen bond distance between H1 and 4MP was shorter than that between H1 and 2MP. Furthermore, the hydrogen bond angles in complexes with the preferred PYR and 4MP guest species were more linear than in those having 2MP and 3MP. Additionally, preferred PYR and 4MP experienced significant π‧‧‧π contacts with nearby guest molecules, while disfavoured 2MP and 3MP did not interact in this fashion. Hirshfeld surface analyses demonstrated that PYR and 4MP (favoured) were involved in a greater percentage of (guest)N‧‧H(host)Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 202
The value-added tax implications in respect of the supply of services by foreign companies in South Africa
Get PDFA foreign company providing services in South Africa may, depending on the nature of the services rendered, do so directly or through its branch. Where the foreign company or its branch in providing such services falls within the ambit of the compulsory registration requirements set out in section 23, the foreign company or its branch is obliged to register as a vendor and the provisions of the VAT Act thereafter apply to such foreign company or its branch. The nature of the services rendered determine whether it is the foreign company or its branch which is obliged to register as a vendor. Where the services rendered constitute 'electronic services' falling within the scope of paragraph (vi) of the enterprise definition, it is the foreign company which must register as a vendor and not its branch. In all other cases (apart from the supply of 'imported services'), where services are rendered in South Africa, it is the branch which must register as a vendor, unless it is a 'dependent agent' of the foreign company as envisaged in the Wenco case 1, in the sense that it has no clients of its own in South Africa and supplies only services on behalf of the foreign company. In such a case the branch does not conduct an 'enterprise' and its foreign company must register as a vendor. Where a dependent branch supplies services to the foreign company's main business abroad, the supply is not zero-rated in terms of section 11 (2)(o) as, on the authority of the Wenco case, the provisions of section 8(9) have no application in such a case. Generally, where a foreign company or its branch supplies services in South Africa and is obliged to register as a vendor, output tax is levied in terms of section 7(1 )(a) and an input tax deduction may, in certain circumstances, be claimed provided that the foreign company or its branch is actually registered for VAT. In the case of 'imported services' it is the recipient which is liable for VAT thereon in certain circumstances.Thesis (LLM) -- Faculty of Law, 202
The on-demand continuous flow generation, separation, and utilization of monosilane gas, a feedstock for solar-grade silicon
Get PDFThis research is dedicated to the development of a continuous flow process for the production and utilization of monosilane gas. The utilization of continuous flow techniques was instrumental in addressing the challenges and conditions associated with the handling of monosilane gas. Furthermore, the integration of Process Analytical Technologies (PAT) facilitated in-process monitoring and analysis. Chapter one of this research provides an extensive background and literature review encompassing the purification methods of silicon, the latest advancements in the direct synthesis of alkoxysilanes, current synthesis methods for monosilane, the various applications of monosilane, as well as the utilization of continuous flow technology and process analytical technologies. In chapter two, a detailed account of the experimental procedures employed in this research is presented. Chapter three delves into the results derived from each section of the research. The first section discusses an attempt to upscale the continuous flow synthesis of triethoxysilane, based on previous group research. Process Analytical Technologies (PAT), specifically thermocouples, were utilized in this endeavor. The study revealed temperature inconsistencies along the packed bed reactor, which had a notable impact on the reaction capabilities. The subsequent section explores the continuous flow synthesis of monosilane from triethoxysilane. A Design of Experiment (DoE) approach was employed to identify the optimal reaction conditions and compare the effectiveness of two catalysts. The study determined that Amberlyst-A26 emerged as the superior catalyst, offering stability and reasonable conversions over a 24-hour period. In a residence time of 6 minutes and at a temperature of 55 °C, the maximum triethoxysilane conversion of 100% was achieved. PAT, particularly inline FT-IR, was instrumental in monitoring catalyst activity, while continuous flow gas separation techniques facilitated the separation of monosilane. The research also demonstrated further applications of continuous flow techniques in the synthesis of monosilane from tetraethoxysilane and magnesium silicide. The former aimed toThesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 202
The perception of pharmacists’ assistants (post-basic) in Gauteng on the appropriateness of the training received to their roles in pharmaceutical manufacturing
Get PDFThe concept of pharmacists as key providers of pharmaceutical services with supporting personnel is quite uniform across the world with differences in the requirements for the registration, scope of practice, and training approach. Pharmacy support personnel have been part of the workforce for many decades in South Africa, practicing in all pharmacy categories. Pharmacy support personnel are required to undergo training in the category in which they are employed and registered. There is limited literature on the scope of practice and training of pharmacy support personnel in pharmaceutical manufacturing. This research project was undertaken to determine the perceptions of pharmacists’ assistants (post-basic) in Gauteng on the appropriateness of the training received to their roles in pharmaceutical manufacturing. A descriptive qualitative design was employed for the study which involved pharmacists’ assistants (post-basic) who were trained and employed in pharmaceutical manufacturing. Semi-structured virtual interviews were conducted with the participants to gain their understanding regarding their experiences and perceptions of the training they received. The perception of participants on whether the training prepared them to their role was interpreted through thematic analysis. Pharmacists’ assistants (post-basic) perceptions regarding the training they have received to support their roles was generally positive, with an emphasis on the comprehensiveness and appropriateness of training. Participants supported their perceptions by providing scenarios in their workplace on how the training has improved their knowledge in performing their job functions and confidence in carrying out their duties. Differences in perceptions regarding preparedness of PAPBs to carry out their roles and responsibilities in pharmaceutical manufacturing were noted and appeared to be dependent on the nature of the role and the activities involved where further on-the-job training might be required. Participants also demonstrated an interest in the expansion of the curriculum to cover more specialised other aspects of the pharmaceutical manufacturing such as quality and regulatory. Participants perceived the education and training to prepare them for the roles and responsibilities in pharmaceutical manufacturing and recommendations for future research studies on training programmes and job functions for PSP were identified.Thesis (MPharm) -- Faculty of Health Science, School of Clinical Care and Medicinal Sciences, 202
Synthesis and applications of hydroxyl-functionalized chemosensors for selective detection of ions in aqueous systems
Get PDFFluorescent molecular chemosensors are crucial tools for monitoring toxic metal ions and environmental compounds that pose risks to both humans and wildlife. Continuous sensing is essential for early detection, and chemosensors offer a sensitive and straightforward approach by detecting challenging analyte’s through optical absorption and fluorescence. Current detection methods, such as flame photometry and mass spectrometry, can be expensive, destructive, and impractical for continuous monitoring. Consequently, fluorescent-based methods present a promising, simple, and highly sensitive alternative for chemical recognition and monitoring. In this project, we successfully synthesized ten highly selective small hydroxyl containing molecule fluorescent and colorimetric sensors; Oxime Dye (OD), Small Sensor 1 (SS1), Small Sensor 2 (SS2), Quinoline Dye 1 (QD1), Quinoline Dye 2 (QD2), Quinoline Dye 3 (QD3), Coumarin Dye 1 (CD1), Coumarin Dye 2 (CD2), Naphthalene Dye 1 (ND1), Naphthalene Dye 2 (ND2). These chemosensors contained benzothiazole, naphthalene, quinoline, and coumarin fluorophores. These sensors facilitate both quantitative and qualitative assessment of cationic and anionic species in aqueous organic media. The chemosensors were synthesized using modified Schiff base, azo dye, and oxime-based reactions, enhancing binding and selectivity with analyte’s. They exhibited selectivity towards various metal ions (Cu2+, Fe2+, Ni2+, and Hg2+) and anions (hydroxyl and cyanate), characterized by distinct absorption bands and significant fluorescent quenching and enhancement. While some sensors were selective towards both cations and anions, others exclusively targeted cations, showing lower selectivity or sensitivity towards anions upon further testing. Conversely, certain sensors were selective towards anions, demonstrating reduced sensitivity or selectivity towards the tested cations. The oxime-based chemosensor, OD, was obtained through an oxime-based reaction. The sensor demonstrates remarkable selectivity for Cu2+ and cyanate ions. During titration experiments, the interaction of Cu2+ with OD resulted in a noticeable fluorescence quenching effect, while the presence of OCN ions led to fluorescence enhancement. These distinct behaviors strongly suggest the formation of specific 1:1 complexes between OD and Cu2+ or OCN ions, a conclusion supported by detailed analysis using the Jobs plot technique. In addition to the fluorescence studies, investigations into the influence of pH on the sensor OD, as well as its complexes with Cu2+ and OCN, were conducted to determine the optimum pH conditions for their operation. Moreover, reversible behavior of the complexes was explored in the presence of EDTA, revealing that only the OD-OCN complex displayed reversibility. Furthermore, molecular modeling studies were performed to validate the binding units and calculate the energy differences between the sensor and its respective complexes. Additionally, four chemosensors (SS1, SS2, CD2, and QD2) were synthesized and characterized using Schiff-based reactions, showcasing their unique absorption behaviors. SS1 and SS2, characterized by benzothiazole fluorophores, demonstrated high sensitivity to hydroxyl anions. Jobs plot studies revealed a stable 1:1 binding stoichiometry. Chemosensor CD2, incorporating a coumarin fluorophore, was structurally confirmed but showed no significant spectral changes when screened with various ions. Chemosensor QD2 exhibited remarkable selectivity for Fe2+ ions, and stable 1:1 complexes were confirmed. Further molecular modeling studies were conducted to identify potential binding sites. Furthermore, five chemosensors (CD1, CD3, QD1, ND1, and ND2) were synthesized and characterized using azo dye reactions, revealing their unique absorption behaviors. Chemosensor CD1 showed high selectivity towards Hg2+ under both absorption and emission spectroscopy. Job's plot studies confirmed a stable 1:1 complex formation. The presence of competing cations did not affect complex formation, emphasizing its stability and selectivity. Another coumarin-containing dye chemosensor, CD3, was synthesized as a novel chemosensor. In the presence of TBA anionic solutions, CD3 exhibited strong absorption bands and selectivity for OH- ions, forming a stable complex with them. Quantitative studies, including the determination of LOD and LOQ, were also conducted. The binding stoichiometry of 1:1 between CD3 and OH- was established through Job's plot analysis. Lastly, two naphthalene dyes were synthesized. However, they did not exhibit selectivity towards cations or anions. Interestingly, their absorption spectra were affected by the change in solvent system, a concept worth exploring in future work. Chemosensor ND1 and ND2 did not show any cation or anion selectivity. However, they demonstrated different spectra and colour responses to cations and anions in different water-DMSO solvent systems.Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 202
Evaluating elephant, Loxodonta africana, space-use and elephant-linked vegetation change in Liwonde National Park, Malawi
Get PDFHeterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202
The demographic-specific prey preferences of lions and cheetahs, and potential impacts on prey populations
Get PDFUnderstanding prey selection offers predictive insights into predator-prey interactions, which can be extended to explore the impacts of predators on prey populations. Prey availability and vulnerability vary across species, demographic classes, body sizes, and seasons. Traditional prey selection models for large carnivores, based on estimates of prey body size, assume uniform vulnerability across prey demographic classes and seasons, failing to account for these variations. This study aims to contrast seasonal shifts in demographic-specific prey preferences between lions and cheetahs and examine the potential impact of their demographic-specific predation patterns on a range of prey species across a body size spectrum. It was predicted that cheetahs would shift their selection from adults and juveniles of smaller prey species in the dry season to neonates and juveniles of both smaller and larger prey species in the wet season, while lions would select adults irrespective of the season. Additionally, predation focusing on adults would have a greater impact on prey populations compared to predation focusing on non-adults. Furthermore, it was predicted that prey populations experiencing demographic-specific selection from both lions and cheetahs would be impacted more than species selected by only one predator. Degrees of preference (DOP) were estimated based on prey availability (camera traps) and prey use (GPS clusters) for lion and cheetah populations in Lapalala Wilderness Reserve. Generalized Additive Models for Location, Scale, and Shape (GAMLSS) were used to determine seasonal shifts in demographic-specific prey preferences. The seasonal-demographic specific predation patterns of lion and cheetah, along with prey vital rates extracted from the literature, were then used to model potential predation impacts on prey populations using both Leslie-Usher and Lefkovitch matrix models. Lions preferred larger adult prey such as blue wildebeest, eland, and buffalo, while cheetahs preferred smaller prey, particularly juveniles of small to intermediate-sized species like impala, kudu, blue wildebeest, and zebra. Both predators showed seasonal shifts in demographic-specific prey preferences, with lions selecting adult buffalo during the dry season and juvenile buffalo in the wet season, and cheetahs selecting juveniles in the dry season and neonates and juveniles during the wet season. Lions and cheetahs exerted the highest degree of top-down limitations on their preferred prey. Predation on adult prey had a greater effect on prey population growth rates than predation on non-adults, especially in the dry season. Intermediate-sized prey species experienced the highest predation pressures, while larger prey species were more affected than smaller ones, contrary to the size-nested predation hypothesis. My study represents a first effort in the southern hemisphere to model the demographic impacts of multiple predators on diverse prey species, incorporating seasonal and demographic-specific prey preferences. The findings emphasise the importance of incorporating prey demographics and seasonality in predator-prey studies as these refined studies have implications for the management and conservation of both predator and prey populations.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202
Co-occurrence of Sympatric Poroderma Species
Get PDFSpecies exploiting similar ecological niches are expected to adapt their behaviour, which can either promote or hinder coexistence. This study examined the ecological (dis)similarity between the endemic Poroderma africanum (pyjama catshark) and Poroderma pantherinum (leopard catshark) in Mossel Bay, South Africa. The co-occurrence of these species was examined along the ecological axes of time, trophic position and space, between October 2015 and April 2018, through the use of Baited Remote Underwater Videos (BRUV), gastric lavage, and acoustic telemetry. Through the deployment of 197 BRUVs, P. africanum showed a seasonal, higher Relative Abundance (RA = 0.52), occurring more frequently during winter months, while showing an overall decline in RA over the course of the study period. Poroderma pantherinum on the other hand, showed a lower, unseasonal RA (0.20), remaining relatively stable throughout the study period. The BRUV deployments indicated that the two species showed a positive co-occurrence with one other, being sighted in BRUV deployments more frequently together as opposed to in isolation/at random. Acoustic telemetry indicated that the two species were active during different diel periods, influenced by a complex combination of tidal and diel rhythms, while P. pantherinum showed a higher residency compared to P. africanum (P. pantherinum: Continuous Residency Time (CRT)24 = 3.32 days (mean), 95% CI: 2.53–4.11 days; P. africanum: CRT24 = 2.01 days, 95% CI: 1.66–2.36 days). While the two species are sympatric in nature, and have an overlapping, endemic, distribution, acoustic telemetry indicated that 1 ABSTRACT P. africanum showed higher degrees of movement throughout the acoustic receiver array (P. africanum: edge density (ED) = 0.25; P. pantherinum: ED = 0.12); however, certain areas of the bay showed to be of high importance for both species. Both species revealed high levels of intra- and inter-specific variation in both residency and movement behaviour. Gastric lavage indicated partially overlapping trophic niches, between the two Poroderma spp. Poroderma africanum had a generalist diet, dominated by teleosts (Index of Relative Importance (IRI)% = 22.69), octopus (IRI% = 11.48) and discarded bait (IRI% = 64.54), while P. pantherinum showed indications of being a specialist predator, with a diet dominated by cephalopods (IRI% = 83.68). The two Poroderma spp. showed a partially overlapping, but separate trophic niches, while displaying spatial dissimilarity in diet. The study suggests that the two species are able to coexist within the same geographical area through niche differentiation across trophic and temporal ecological axes, with varying spatial use. The intra- and inter-specific differences between the two species may complicate elasmobranch management efforts for these co-occurring endemic catsharks, and as such, efforts should follow either an individual species approach, which is often not feasible, or an ecosystem-based approach, as opposed to considering the genus as a whole.Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 202
Exploring grade 11 learners’ mathematical problem-solving skills using Polka’s model during the learning of Euclidean geometry
Get PDFThe skill of Problem-solving in Mathematics is very imperative. Poor performance by most South African learners in schools and international tests such as the Trends in International Mathematics and Science, calls for emphasis to be placed on problem-solving in the teaching and learning of Mathematics. Euclidean Geometry is perceived, especially by learners, to be one of the difficult components of Mathematics. Thus, the aim of this study was to explore and develop the mathematical problem-solving and geometric skills of Grade 11 learners in Euclidean Geometry. Polya’s model of problem-solving was employed in geometric skills development as a tool for intervention. The concepts Geometry and problem-solving formed the conceptual framework of the study, while the social cognitive theory constituted the theoretical framework. A case study was used as the main research method following a mixed method approach within an interpretivist paradigm. Purposive and convenience sampling methods were used in the selection of both the Mathematics class and the six learners whose work was further observed and analysed. Data about the geometric skills displayed by the learners was gathered using a moderated pre-intervention test; observations; document analysis; a moderated post-intervention test; and focus group interviews. Data was analysed quantitatively using descriptive statistics and qualitatively using thematic analysis. In the pre-intervention test, learners did not bring with them expected geometric skills to the classroom before they were introduced to grade11 Geometry content and when doing problem-solving during intervention, the four stages of model used were not necessarily following each other in a linear sequence with most of the learners not applying the fourth stage “look back”. In the post intervention test, the frequency of use and application of most geometric skills improved in comparison to the pre-intervention test; the frequency of correct and inappropriate application of the skills increased at the expense of incorrect application. Learners appreciated the four stages model and gave their views related to the challenged faced during the use of the four stages model and the challenges revealed include: practice related challenges, challenges specific to certain learners, concept related challenges, curriculum-related challenges, model application challenge, and context related challenges. The study concludes that the effective use of Polyas’ four stages model can yield great results in developing learners’ geometric and problem-solving skills. The study recommends that teachers give more attention to prior geometric knowledge, teaching of geometric theorems, teaching of geometric problem-solving, and the learning environment.Thesis (MEd) -- Faculty of Education, Secondary and Post School Education, 202
Risk Management as a nexus to Ameliorate Citizen Centricity in the Western Cape Provincial Government
Get PDFThis study aims to explore how risk management can be applied by the Western Cape Provincial Government to enhance citizen centricity in the Province. The Provincial Departments and Public Entities in this province are applauded for achieving satisfactory audit results in recent financial years from the Auditor-General South Africa. Despite the aforementioned, service delivery protests remain ongoing, which is indicative of citizen dissatisfaction and distress. Ensuring an effective, efficient, and transparent risk management system is mandatory, as prescribed by relevant legislation in South Africa and citizens are entitled to specific rights articulated in the Bill of Rights chapter of the Constitution. Therefore, it is essential that risk management – which forms part of good governance – be embedded by leadership and in processes to ultimately constrain risks which may hinder citizen centricity. Six chapters are included in this research paper. A qualitative approach was adopted, which considered a comprehensive review of literature, and a desktop analysis was performed. Secondary data and information sources were consulted and applied, without the participation of human subjects, for the purposes of primary data collection. Research findings were presented utilising thematic content analysis. It was found during the study that the Western Cape Government risk management framework is flexible to constrain various categories of risk and embraces local and global best practices in the risk management and citizen-focused governments arenas. Furthermore, the framework advocates and drives collaboration between a myriad of role-players, both internal and external to the organisation, to collectively manage risks posed to the achievement of the defined goals, objectives and priorities. To this end, the study was pursued through the lenses of a New Public Management (NPM) paradigm as well as deliberative democracy theory and public governance theories and administrative practices.Thesis (MPA) -- Faculty of Humanities, School of Governmental and Social Sciences, 202