4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Low-temperature electronic transport of metal doped carbon nanotube molecular hybrids and Nitrogen-doped nanocrystalline diamond(University of the Witwatersrand, Johannesburg, 2024-08) Sodisetti, Venkateswara Rao; Bhattacharyya, SomnathThis thesis explores the magnetism and spin-related properties in carbon-based molecular hybrid materials, with a focus on expanding our understanding of low-dimensional carbon structures and their potential electronic applications. The investigation spans from one-dimensional systems, such as carbon nanotubes (CNTs) functionalized with single-molecule magnets (SMMs), to three-dimensional systems like nitrogen-doped ultra nanocrystalline diamond (UNCD). In these carbon structures, electronic transport is intricately tied to microstructural features, such as grain boundaries and impurity clusters, which hold significant potential for the development of all-carbon electronic devices. The research begins with a detailed examination of the chemical functionalization of multi-walled carbon nanotubes (MWCNTs) through controlled acid treatment to achieve precise metal doping. Using Raman spectroscopy and complementary techniques like ICP-MS and ToF-SIMS, we successfully demonstrate how functionalization levels influence the magnetic properties of CNT hybrids loaded with magnetic metals from the lanthanide series (Gd, Tb, Dy). The study reveals that low percentages of metal doping (0.5% to 1.0%) preserve the magnetic bistability of SMMs post-grafting, while higher doping levels lead to complex magnetic behaviors including super paramagnetism, quasi-ferromagnetism, and potential Kondo lattice behavior inCNT-heavy metal systems. We also explore the spin-phonon coupling in Gd-filled double-walled CNTs, where the onset of superparamagnetic properties at low temperatures is coupled with phonon mode stiffening observed via Raman spectroscopy. This enhanced coupling offers promising pathways for developing efficient molecular qubits through the modulation of spin-phonon interactions in one-dimensional systems. The second part of the thesis investigates into the microwave plasma-assisted chemical vapor deposition (MWCVD) growth of nitrogen-doped nanocrystalline diamond (NCD) thin films on different substrates. By pioneering upgrades to the MWCVD system, I was able to achieve reliable growth of high-quality nanocrystalline diamond thin films. Notably, I observed a novel nanostructure, termed Diaphite-a previously unreported feature, in these NCD films, consisting of nanodiamond grains coherently linked with graphene-like rings. This structure, along with the non-equilibrium growth conditions induced by nitrogen doping and secondary nucleation, presents unique polymorphic features in artificially grown diamonds. Detailed low-temperature transport measurements on four different samples—ranging from 7.5% to 20% nitrogen doping—uncovered complex transport phenomena such as 3D weak localization (WL), variable-range hopping (VRH), and unusual magnetoresistance (MR) behavior. In particular, the 7.5% N2-doped UNCD film on quartz exhibited 3D weak localization (WL) at low fields and anti-weak localization (AWL) at higher fields, with distinct magnetoresistance characteristics depending on the direction of the applied magnetic field. The 20% N2-doped films on both quartz and silicon showed more metallic-like behavior, with magneto-resistance characterized by a B1/2 dependence at low temperatures, suggesting an intricate relationship between doping level, microstructure, and electron transport. These findings significantly expand our understanding of the role that microstructural and chemical modifications play in determining the electronic and magnetic properties of carbon-based materials. This work provides a foundational platform for future research into carbon electronics, offering potential breakthroughs in spintronics, molecular transistors, quantum computing, and other advanced electronic applications.Item An examination of the legal framework for the governace of public universities in South Africa: The case of the Vaal University of Technology(University of the Witwatersrand, Johannesburg, 2024) Mahlako, Neo; Moyo, KhulekaniItem Digital toolbox for the generation and detection of vectorial structured light(University of the Witwatersrand, Johannesburg, 2023-06) Singh, Keshaan; Dudley, Angela; Forbes, AndrewLight has been an invaluable tool in the development of the modern world, with the myriad of applications increasing along with our degree of control over it. From the development of coherent light sources, to the shaping of amplitude and phase, this development has not ceased for the past half century. The field of structured light, borne out of the necessity and desire for control over light, has been growing steadily in recent years. In the spatial domain, the control over light’s polarization (i.e., the local planes in which the electric and magnetic fields oscillate) has been the most recent avenue of improvement, providing enhancements to a variety of applications ranging form microscopy and communication to materials processing and metrology. This class of light, commonly referred to as vectorial light, often requires specialised equipment in order for its its creation before its numerous benefits can be exploited. These tools often incur high costs and suffer from limitations relating to the diversity of vectorial light they can create, wavelength dependence and slow refresh rates. This thesis follows the development of a series of digital tools for the versatile generation and analysis of vectorial light using low-cost core technologies which can operate at high rates over a broad wavelength range. We follow the development of the generation tool in the context of its application in generating novel accelerating polarization structures, emulating vectorially apertured optics, generating probes to measure birefringence and chirality and creating synthetic spin dynamics. The development of the analysis tool is explored by investigating its application in performing automated digital Stokes polarimetry measurements, completely characterizing the internal degrees of freedom of arbitrary vectorial light and acting as a polarization and wavelength independent wavefront sensor. We then demonstrate how these tools can be used, in conjunction, to investigate the fundamental invariance of vectorial light to perturbing channels and how this invariance can be exploited in a highly robust novel communication scheme. In addition to demonstrating the applicability and versatility of these vectorial light tools, the applications offered a means to highlight areas for the optimization for the design. This culminated in the ongoing prototyping of versatile, fast, broadband devices which operate stably and have a small physical footprint.Item Immunomodulation of the innate immune system: The role of vitamin D in the context of monocytes and macrophages(University of the Witwatersrand, Johannesburg, 2024-07) Mol, Bronwyn Ashleigh; Gentle, Nikki; Meyer, VanessaMacrophages are widely distributed cells of the innate immune system with essential roles in homeostasis and disease. Despite concerted efforts, several aspects of macrophage origin, biology, and functionality remain poorly understood. To gain a deeper understanding of these cells, a physiologically relevant, but practical model is required. In vitro, macrophages are principally generated from primary monocytes and monocyte-like cell lines through a natural process referred to as monocyte-to-macrophage differentiation. Monocyte-like cell lines have several practical advantages over the use of primary monocytes with the most commonly employed monocyte-like cell lines being THP-1 and U937 cells. Despite their frequent use, no standardised protocol is employed in the differentiation of monocyte-like cell lines to macrophages. Naturally, this results in large discrepancies and a lack of comparability between studies. Furthermore, many of these protocols are not physiologically relevant and produce macrophages that are not responsive to downstream stimuli. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the biologically active form of vitamin D3, is a recognised immunomodulator that shows pronounced genomic and non-genomic effects in immune cells. It is also reported as an inducer of monocyte-to-macrophage differentiation, though heavily debated, and a potential macrophage polarisation agent. Despite this, there is relatively little information concerning the role of 1,25(OH)2D3 in monocyte-to-macrophage differentiation and macrophage biology. This study aimed to develop a more physiologically relevant differentiation protocol for the monocyte-like THP-1 and U937 cell lines. This model was then used to investigate the role of 1,25(OH)2D3 in monocyte-to-macrophage differentiation and macrophage biology. Assessment of morphological features and the macrophage markers, CD11b and CD14, indicated that in both THP-1 and U937 cells, differentiation induced using a combination of 5 nM of phorbol 12-myristate 13-acetate (PMA) and 10 nM 1,25(OH)2D3 over 96 hours produced the most mature macrophages. It was observed that 1,25(OH)2D3 alone was not capable of inducing differentiation, yet when combined with PMA, greatly enhanced macrophage features. THP-1 cells are the most widely employed monocyte-like cell line, and are proposed to be the most reflective of primary monocytes. In this study these cells were shown to be more responsive to the effects of 1,25(OH)2D3 than their U937 counterparts. As such, RNA-sequencing was used to explore the efficacy of the proposed differentiation protocols and the influence of 1,25(OH)2D3 on macrophage biology in THP-1 cells. Differential gene expression analysis confirmed that the most effective differentiation protocol was the combination of 5 nM PMA with 10 nM 1,25(OH)2D3 when considering macrophage associated features including transcription factor usage, adhesion, phagocytosis, and cytokine and cytokine receptor expression. This protocol also produced THP-1-derived macrophages that showed increased expression of genes considered to be primary macrophage markers. These results also suggested that THP-1 cells differentiated with neither PMA nor PMA with 1,25(OH)2D3 were likely to represent fully polarised macrophages. 1,25(OH)2D3 treatment of THP-1 monocytes and THP-1-derived macrophages produced distinct gene expression profiles with considerably less overlap than expected. Though 1,25(OH)2D3 treatment often affected similar biological processes in both cell types, the genes within these processes found to be differentially expressed in each cell line were often distinct. For example, in THP-1- derived macrophages, but not THP-1 monocytes, 1,25(OH)2D3 treatment resulted in the increased expression of genes encoding numerous antibacterial peptides, several small GTPases and their regulators. Additionally, several type I interferon response related proteins showed decreased expression, while expression of cytokines and cytokine receptors was variable. This, taken together with the morphological work, indicates two potential roles for 1,25(OH)2D3 in macrophages. Firstly, a protective role as it suggests the potential to prime an antibacterial response, while still balancing inflammatory responses and protecting against autoinflammation induced by aberrant type I interferon response. Secondly, a potential role in determining the morphological features, clearly demonstrated through microscopy, and further suggested by the differential expression of a variety of small GTPases and their regulators.Item How Diversity and Inclusion May Transform South African Commercial Property Organisations at Top Management Level(University of the Witwatersrand, Johannesburg, 2017-08) Motshegare, Reabetswe Regina; Levy, DeborahThe purpose of this report is to outline contemporary transformation frameworks that emphasise diversity and inclusion and how the latter may likely transform Growthpoint Properties South Africa (Growthpoint S.A). The main focus of the consultancy report is to compare and contrast traditional transformation methodologies and contemporary diversity and inclusion methodologies as strategies to assist Growthpoint S.A transform its senior and executive management. The propositions are that; an effective transformation strategy for Growthpoint S.A is one that focuses on identification; inclusion; attraction; diversification and retention of key talent at senior levels. Furthermore, that once diversity and inclusion interventions are implemented, there will be transformation at senior and executive levels. Out of 15 executives in the management team, six representatives were interviewed. The limitations highlight that the majority of participants are South African and may have certain biased perceptions about the topic as opposed to the rest of the participants, who are foreign nationals. The methodology focuses on a thematic analysis and four themes namely: leadership; corporate culture; strategies and communication are identified. Following in-depth discussions, six recommendations are provided. These include 360-degree feedback; diversity and inclusion workshops; introduction of a diversity and inclusion forum; KPI’s that measure diversity and inclusion targets; workplace enhancement programmes that focus on diverse candidates and lastly, robust succession plans. The role of the researcher as a professional Human Resource Business Partner ensured that any work dealt with is approached ethically, and the researcher’s ability to do this ensured quality, reliability, validity and effectiveness of the research.Item 3D Human pose estimation using geometric self-supervision with temporal methods(University of the Witwatersrand, Johannesburg, 2024-09) Bau, Nandi; Klein, RichardThis dissertation explores the enhancement of 3D human pose estimation (HPE) through self-supervised learning methods that reduce reliance on heavily annotated datasets. Recognising the limitations of data acquired in controlled lab settings, the research investigates the potential of geometric self-supervision combined with temporal information to improve model performance in real-world scenarios. A Temporal Dilated Convolutional Network (TDCN) model, employing Kalman filter post-processing, is proposed and evaluated on both ground-truth and in-the-wild data from the Human3.6M dataset. The results demonstrate a competitive Mean Per Joint Position Error (MPJPE) of 62.09mm on unseen data, indicating a promising direction for self-supervised learning in 3D HPE and suggesting a viable pathway towards reducing the gap with fully supervised methods. This study underscores the value of self-supervised temporal dynamics in advancing pose estimation techniques, potentially making them more accessible and broadly applicable in real-world applications.Item Detecting Disease in Citrus Trees using Multispectral UAV Data and Deep Learning Algorithm(University of the Witwatersrand, Johannesburg, 2024-06) Woolfson, Logan Stefan; Adam, ElhadiThere is a high prevalence, in South Africa, of fruit tree related diseases infesting lemon trees, subsequently affecting overall crop yield and quality. Ultimately, the income for the farmers is significantly diminished and limits the supply of nutritional food crops for the South African population, who already suffer from a high incidence of malnutrition. Currently, there are various methods utilized to detect diseases in fruit trees, however they pose limitations in terms of efficiency and accuracy. By employing the use of drones and machine learning methods, fruit tree diseases could be detected at an earlier stage of development and with a much higher level of accuracy. Consequently, the chances of remedying the trees before the disease spreads is greatly improved, and the supply of nutritious fruit within South Africa is increased. This research report’s aim is to investigate the effectiveness of a deep learning algorithm for detecting and classifying diseases in lemon orchards using multispectral drone imagery. This entails assessing the performance of a pretrained ResNet-101 model, fine-tuned with additional sample images, in accurately identifying and classifying diseased lemon trees, specifically those affected by Phytophthora root rot. The methodology involves the utilization of a pretrained ResNet-101 model, a deep learning architecture, and the retraining of its layers with an augmented dataset from multispectral aerial drone images of a lemon orchard. The model is fine-tuned to enhance its ability to discern subtle spectral variations indicative of disease presence. The selection of ResNet-101 is grounded in its proven success in image recognition tasks and transfer learning capabilities. The results obtained demonstrated an impressive accuracy of 80%. The deep learning algorithm exhibited notable performance in distinguishing root rot-affected lemon trees from their healthy counterparts. The findings indicate the promise of utilizing advanced deep learning methods for timely and effective disease detection in agricultural farmlands, facilitating orchard management.Item Knockdown of long non-coding RNA PANDA improves the cytotoxic effects of cisplatin in oesophageal squamous cell carcinoma cell lines(University of the Witwatersrand, Johannesburg, 2024-11) Moonsamy, Sasha Sarasvathee Keshnee; Mavri-Damelin, Demetra; Jivan, RupalOesophageal cancer is one of the leading causes of cancer death worldwide, of which oesophageal squamous cell carcinoma (OSCC) is the major subtype in southern and eastern Africa. Cisplatin is a well-established drug used to treat multiple cancers, including OSCC. Drug resistance is a major impediment to continued cisplatin therapy in numerous cancers. LncRNA P21-associated non-coding RNA DNA damaged activated RNA (PANDA) is known to function in cell cycle regulation in response to DNA damage and is upregulated in OSCC. We aim to determine lncRNA PANDA expression in South African-derived OSCC cells and establish whether down-regulation of this lncRNA can be used to supplement cisplatin therapy. In this study, MTT assays were performed to determine the EC50 concentrations of cisplatin in OSCC (WHCO1, WHCO5, and SNO) cells and HEK293 cells as a non-cancer control. The cytotoxic effects of cisplatin were exerted in all cell lines, with WHCO5 and SNO appearing more responsive to cisplatin than WHCO1 and HEK293. RT-PCR was used to detect if lncRNA PANDA is expressed in untreated and cisplatin-treated cells and was detected in all cell lines. Knockdown of lncRNA PANDA by siRNA was assessed with RT-PCR. Phase contrast microscopy was used to assess whether siRNA reagents altered cell morphology at 5, 24, and 48 hours post treatment. No significant alterations in cell morphology were observed in WHCO1, WHCO5, SNO, and HEK293 cells. MTT assay evaluation after 48 hours of cisplatin exposure, with or without siRNA for lncRNA PANDA, showed a significant reduction in EC50 concentrations in WHCO5, SNO, and HEK293 cell lines, suggesting that knockdown of lncRNA PANDA may improve cisplatin cytotoxicity in some cell lines. However, the EC50 values were higher with lncRNA PANDA knockdown in the WHCO1 cell line, suggesting that not all OSCC cell types may be responsive to this approach. In conclusion, lncRNA PANDA is expressed in response to cisplatin-induced DNA damage, and the down regulation of lncRNA PANDA improves the cytotoxic effects of cisplatin; however, further investigations are warranted in OSCC.Item An exploration of Business Studies Teachers' integration of Information and Communication Technologies to equip Grade 12 learners with critical business skills(University of the Witwatersrand, Johannesburg, 2024) Gcabanshe, Nduduzo Brian; Ndlovu, Nokulunga SithabileBusiness studies is a subject that in South African schools to equip learners with skills that would enable them to operate effectively in contemporary business environment, either as employers or employees. However,there is a general concern that learners who are produced by these schools do not possess skills that are relevant to current business environments. This is partly due to the impact of technological developments that continue to cause a shift in skills needed by businesses. Therefore, there is a need for an exploration on how best business studies teachers integrate ICTs in their classrooms to equip learners with skills that are required by the contemporary business environment. This study explored ICT integration by business studies teachers to equip Grade 12 learners with critical business skills that are required by the contemporary business environment. Social Constructivism Theory and Functional Context Theory were adopted as the theoretical lenses of this study. Social Constructivists emphasize the need for interaction, collaboration, active learning, and autonomous learning in the learning context for meaningful learning to occur. Functional Context Theory, on the other hand, advocates for a learning environment that reflects the world for which learners are being prepared for. The proponents of this theory advise teachers to integrate resources that learners would use upon joining the real world of work. This is a qualitative study underpinned by the interpretive research paradigm. A multi case study research design was deemed suitable for this particular study. Face-to- face individual interviews and classroom observations were adopted to collect data. Six Business Studies teachers who use ICTs to teach were selected from six secondary schools located in Kwa-Zulu Natal province of South Africa were iv purposively sampled. Data that was collected were analyzed using hybrid thematic analysis. Findings of the study were that: i. teachers see value in ICT integration in their business studies pedagogical practices. teachers see ICTs as tools that assist in exposing learners to authentic learning activities that help them to acquire critical business skills needed by the contemporary business environment. business studies teachers adopted various learner-centred teaching methods to create learning environments that promote the acquisition of critical business skills. iv. most teachers integrated different ICTs to nurture learners’ critical business skills. teachers mainly relied on their personal teaching experiences and their generic technological skills. Based on the findings of this study, Technology Integration Model for Business Studies teachers was developed. The developed framework can play a role in helping business studies teachers integrate ICTs in a systematic way that would lead to learners’ acquisition of critical business skills. Based on the key findings highlighted above, the study recommends that the Department of Basic Education (DBE) should develop coherent professional development programmes to expose all business studies teachers to novel pedagogies, learning activities and ICTs that can be used to nurture learners’ critical v business skills. This will help to reduce teachers’ over reliance on their teaching experiences and what they think is suitable for learners to acquire critical business skills, which sometimes can be inconsistent with the objectives of the business studies curriculum.Item Novel antiangiogenic peptide targeted therapeutic nanosystem for non-small-cell lung carcinoma(University of the Witwatersrand, Johannesburg, 2023) Ngema, Lindokuhle Malibongwe; Choonara, Yahya Essop; Marimuthu, Thashree; Adeyemi, AdebawoleLung cancer is the leading cause of cancer deaths globally, with nearly 1.8 million deaths and 2.2 million incidences recorded annually. Primarily, non-small-cell lung carcinoma (NSCLC) is the most commonly diagnosed type of lung cancer, which makes up approximately 85% of all reported lung cancer cases. Currently, the management of NSCLC is a global challenge, and although, various treatment protocols are available, such as surgery, radiotherapy, and chemotherapy, the survival outcomes remain poor. Combination chemotherapy is the current first-line treatment for NSCLC, however, it presents with a myriad of drawbacks, including non-specificity, high dosage, and detrimental side effects, resulting in patients intolerability to the regimen. Consequently, a new therapeutic approach is greatly needed and warrants the design of biocompatible targeted drug delivery nanosystems that can halt tumor proliferation and metastasis by targeting key molecules and deliver drugs directly to tumors, with limited side effects and toxicity to healthy cells. Tumor targeted drug delivery nanosystems such as magnetic nanoparticles (MNPs) modified with biomolecules and functionalized with homing peptides are of great interest for potential application as a potent nanomedicine in NSCLC management. Accordingly, the present study set to develop novel targeted paclitaxel (PTX) delivery nanosystems from the amenable superparamagnetic iron oxide nanoparticles (SPIONs) coated with trans-10,cis-12 conjugated linoleic acid (10E, 12Z) and functionalized with either a vascular endothelial growth factor receptor (VEGFR) binding or a matrix metalloproteinase 2 (MMP-2) binding peptide, for specific delivery of PTX to VEGFR and MMP-2 expressing NSCLC tumors. A preceding nanosystem without the peptides (CLA-coated PTX-SPIONs) was originally fabricated as proof of concept for the application of 10E, 12Z CLA as a surface coating and drug partitioning biomolecule. CLA-coated PTX-SPIONs exhibited a spherical shape, with an average particle size and zeta potential of 96.5 ± 0.6 nm and −27.3 ± 1.9 mV, respectively. The nanosystem had a drug loading efficiency of 98.5% and demonstrated a sustained site-specific in vitro release of PTX over 24 h (i.e., 94% at pH 6.8 mimicking the tumor microenvironment). Enhanced anti-proliferative activity was also observed with the CLA-coated PTX-SPIONs against a lung adenocarcinoma (A549) cell line after 72 h, with a recorded cell viability of 17.1%. Thereafter, the fabricated nanosystem was optimised for direct tumor-targeting by functionalization with HRH or CTT peptides, to give CLA-coated PTX-SPIONs@HRH and CLA-coated PTX-SPIONs@CTT. A new design methodology was established for the tandem surface functionalization of CLA-coated PTX-SPIONs with the antiangiogenic peptides, via coupling reactions. A series of robust nanotechnological techniques were employed for pertinent physicochemical characterization, in vitro evaluation of drug release, anti-proliferative activity, and quantification of VEGF-A and MMP-2 levels. Meanwhile, in vivo testing was carried out on a lung tumor xenograft mouse model. Both nanosystems exhibited a marked cellular uptake and internalization by A549 cells, and CLA-coated PTX-SPIONs@HRH significantly reduced secretion levels of VEGF-A in human dermal microvascular endothelial cells (HMEC-1) from 46.9 pg/mL to 35.6 pg/mL, meanwhile CLA-coated PTX-SPIONs@CTT significantly inhibited MMP-2 secretion by almost 70% , indicating specific anti-MMP-2 activity. A 76.6% and 69.7 % tumor regression was observed in a lung tumor xenograft mouse model treated with CLA-coated PTX SPIONS@HRH and CLA-coated PTX-SPIONs@CTT, respectively, demonstrating tumor targetability and angiogenesis inhibition. Lastly, the pharmacokinetics (PK) evaluation revealed that both nanosystems prolonged the half-life of PTX and circulation time in vivo. In essence, potent antiangiogenic tumor-targeted PTX delivery nanosystems were successfully fabricated, and the obtained results suggest potential application of CLA-coated PTX SPIONs@HRH and CLA-coated PTX-SPIONs@CTT for effective management of NSCLC.