A Hybrid Deep Learning based Algorithm for Gamma Spectroscopy Analysis

Thesis (PhD)--Stellenbosch University, 2025.Buckton, C. 2025. A Hybrid Deep Learning based Algorithm for Gamma Spectroscopy Analysis. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/8db1d4f0-1872-4d33-87fd-8b3527a44704There exists a select group of unstable nuclei which undergo radioactive decay by emission of highly-energetic photons or γ-rays. An effective tool for analysing γ-emitting radioactive sources, γ spectroscopy is a common experimental technique used in high-energy physics and environmental monitoring of radiation. Analysis of various naturally-occurring radionuclides and their decay products through γ spectroscopy has provided a practice for health and safety regulation. It is a process which has seen a large amount of improvement in efficiency and optimization over the past decade. This has often been partly due to developments in detection and analysis which build upon existing experimental methods. Recently, there have been developments in machine learning based approaches, for automated and efficient detection and radioisotope "fingerprinting". That is, these methods make use of the characteristic spectra measured from radioactive isotopes to identify them. These methods have commonly consisted mostly of a computational component, a deep-learning algorithm known generally as a deep neural network (DNN), which is trained on a representative dataset of energy spectra from different isotopes, often simulation-based. Becoming increasingly more efficient, a type of network called convolutional neural networks (CNNs) are most prominent in this application, due to their ability to effectively learn useful features from high-quality data and being able to classify or recognise radioactive species with very good accuracy. However, a challenge which can occur is when there are multiple sources present in a sample of data, as opposed to just a single source, where the accuracy of the network will often decrease as the number of sources increases. Additionally, developing a CNN model which is computationally efficient, but also accurate and robust to noise and other environmental influences can be difficult.Doctora

Fracture of laser-based powder bed fusion produced Ti6Al4V

Thesis (PhD)--Stellenbosch University, 2025.Louw, D. F. 2025. Fracture of laser-based powder bed fusion produced Ti6Al4V. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/961bff00-ca87-4973-8bb3-2f4c7dac059bThis project seeks to provide insights that enable the design of damage-tolerant, high-performance components produced out of Ti6Al4V by laser-based powder bed fusion (LPBF). By investigating the relationship between fracture toughness, microstructural characteristics, and residual stresses, progress is made to produce more damage-tolerant components. Finally, the capabilities of predicting support breakage, delamination, and in-situ cracking with finite element modeling (FEM) of the process, are evaluated. This capability has the potential to significantly reduce the number of trial-and-error iterations needed to successfully manufacture a component free from such issues. The project starts by establishing a link between the material’s micro- and mesostructure and its fracture toughness. The fracture toughness was measured in various orientations to gain additional insight into the toughening mechanism. It was found that variations in post-process heat treatment can cause fracture toughness to vary between 42 and 95 MPa√m. The differences in fracture toughness are largely due to differences in ductility, which is linked to how the heat treatment affects the hierarchical lath structure. Anisotropy in fracture toughness is attributed to elongated prior- grains, whereby low fracture toughness arises if the crack propagation direction aligns with the elongated boundaries. A heat treatment step above the -transus temperature () removes the anisotropy. The second contribution of this project lies in quantifying the influence of residual stress, a well-known process attribute, on fracture toughness. Fracture toughness in the as-built condition was measured in two orientations with a range between 24 and 37 MPa√m obtained. In each orientation, the residual stress distribution before fatigue pre-cracking in the compact tension specimen on the crack plane was measured with the contour method. Thereafter, the stress intensity factor due to residual stress after fatigue pre-cracking was determined by finite element modeling (FEM). It was found that fracture toughness in the as-built condition is reduced by up to 36 % by residual stresses. This quantitative result cannot be generalized to all fracture toughness measurements performed on as-built material because it is a function of how the specimen is cut from the as-fabricated block. Still, it indicates the importance of residual stress when interpreting fracture toughness. The final contribution of this project lies in evaluating the capability of a FEM of the process. It was found that a FEM based on the inherent strain method can be combined with a criterion based on the stress intensity factor or the volume strain energy density to predict the height at which in-situ cracking occurs accurately to within 12 %.Doctora

Superficial scald on ‘Granny Smith’ – understanding commercial storage protocols and their limitations

Thesis (PhD)--Stellenbosch University, 2025.Gerber, M. 2025. Superficial scald on ‘Granny Smith’ – understanding commercial storage protocols and their limitations. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/e71b5efb-3845-4d1c-b5cd-367bca935b5fSuperficial scald is a major postharvest disorder induced by oxidative stress during the first 7 d after harvest, during short-term storage or shipment in a regular atmosphere (RA). The induction period is associated with ethylene-dependent processes and the accumulation of α-farnesene oxidation products like 6‑methyl‑5‑hepten‑one (MHO). Symptoms develop as bronze patches on the fruit peel on transferring the fruit from regular atmosphere (RA) or low-oxygen storage to shipment and shelf‑life conditions. Incidence of more than 1 % on arrival in the overseas market may lead to claims and significant economic losses. This study assessed the efficacy of storage techniques and their combinations used by the South African export industry to control superficial scald. ‘Granny Smith’ apples were subjected to 12 treatments for 4(6), 8, and 16 weeks (short-term) as well as 24, and 33 weeks (long-term) cold storage followed by a simulated 6‑week RA shipment period at −0.5 °C plus a 10-d shelf-life at 20 °C, for three seasons. The fruit were stored under RA (−0.5 °C), with, or without diphenylamine (DPA) (9.6 mL L-1), or 1‑methylcyclopropene (1-MCP) (1 μL L- 1). Low-oxygen storage treatments included controlled atmosphere (CA; 1.5 % O2 and 1.0 % CO2 at 0 °C), dynamic controlled atmosphere ‑ chlorophyll fluorescence (DCA-CF; 0.5 % O2 and 0.7 % CO2 at 0 °C), and cycles of repeated low oxygen stress (RLOS; 0.5 % O2 for 10 d at 0 °C) + ultra-low oxygen storage (ULOS; 0.9 % O2 and 0.8 % CO2 for 21 days) and 0.5 % O2 for 7d at 0 °C. Subsamples of the 1-MCP+CA treated fruit were subjected to a secondary 1‑MCP or DCA‑CF (0.5 % O2 + 0.7 % CO2 for 7 d) or combination (1-MCP+DCA-CF) treatment after long‑term storage, prior to the simulated shipment period. Results indicated that the RA and RLOS+ULOS stored fruit, with or without 1-MCP or DPA, and untreated CA fruit posed a high superficial scald risk during short-term storage plus simulated shipment and shelf-life. Fruit accumulating even low levels of ethylene often posed a higher risk of developing the defect later in storage or shelf-life. DPA treatment did not reduce internal ethylene but reduced scald by preventing the oxidation of α-farnesene to MHO. CA, DCA-CF and RLOS+ULOS in combination with 1-MCP inhibited internal ethylene accumulation and reduced MHO concentrations during short- and long-term storage, however ethylene inhibition did not last during shelf-life after long-term storage. A 1-MCP treatment at harvest and after long-term storage resulted in complete control of superficial scald for these treatments (1-MCP+CA+1-MCP and 1‑MCP+CA+(1‑MCP+DCA‑CF)), even after shipment and shelf-life, and maintained fruit sensory quality. Only complete inhibition of internal ethylene resulted in the prevention of superficial scald incidence for all the storage treatments, except for RLOS+ULOS. Monitoring exogenous ethylene levels during storage and applying a second 1‑MCP treatment after long-term storage before shipping to overseas markets, is advised. This study provided unique insights into the modes of action of different storage techniques to prevent superficial scald in ‘Granny Smith’ apples during short- and long‑term storage.Doctora

Economic Sharing as a Ministry Model for Poverty Alleviation? Perceptions of Church leaders in the City of Johannesburg

Thesis (MTh)--Stellenbosch University, 2025.Kekana, M. B. A. 2025. Economic Sharing as a Ministry Model for Poverty Alleviation? Perceptions of Church leaders in the City of Johannesburg. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/dae9c36c-7e0f-4127-8173-d264b068b98bThe scourge of poverty and inequality continues to be a devastating reality in South Africa, existing in the context of 80% of the population identifying as Christian. When assessing the normative responses to poverty in the Bible, the principle of economic sharing is prevalent. This study is concerned with determining the perspectives of church leaders on the theological principles of economic sharing and whether or not they could be applied to address poverty and inequality in South Africa. The study assesses the extent and effects of poverty and inequality in South Africa, with a particular focus on the City of Johannesburg, discussed an African theology of poverty, wealth and economic sharing and finally explored the perceptions of Johannesburg church leaders on the principle of economic sharing. The findings indicate that poverty is a complex issue that affects all aspects of life. More than half of the South African population lives in poverty, and based on Gini-coefficient, the nation is considered to be the most unequal in the world. In terms of the church’s response, research indicates that churches’ efforts have been primarily focused on relief centred initiatives. It was also determined that the principle of economic sharing aligns not only with the biblical notion of Shalom, but also with the African ethical values, making it a component of African Christian theology. In the empirical component of the study it became evident that although the clergy are dissatisfied with limited responses to poverty, they also feel overwhelmed by the magnitude of work required to establish alleviation efforts centred on justice and equity, especially without government participation. The study thus concludes that poverty is a multidimensional issue, rather than a simple economic deficit, and that church’s current relief-centred efforts, while helpful in providing immediate relief, do not align with the notion of Shalom.Master

The conceptualisation and centrality of the self of the coach in achieving coaching outcomes

Thesis (MCom)--Stellenbosch University, 2025.Marshall, C. B. 2025. The conceptualisation and centrality of the self of the coach in achieving coaching outcomes. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a356eb31-abc4-40c0-a603-aaa1f1edb7d1The notion of the coach’s “use of self” is becoming more relevant as a factor in establishing a successful coach-client relationship and is essential for achieving desired coaching outcomes in leadership and executive coaching within organisations. While previous research has identified several success factors that contribute to the effectiveness of the coach-client relationship, limited research exists particularly on how coaches use the self. Therefore, this study aimed to explore how coaches apply the self and whether the centrality of the coach’s use of self has an impact on the achievement of coaching outcomes. By using a qualitative research design, this study drew on data collected from 14 semi-structured interviews with experienced executive/leadership coaches, selected through purposive snowball sampling. The information was analysed by the use of thematic analysis, uncovering insights into the subjective and multifaceted nature of the coach’s use of self in the coaching session. Findings from this study led to the development of a conceptual framework illustrating how coaches use the whole self, while also highlighting the importance of self-development. This framework also provides an overview of what the use of self constitutes and delves deeper into the centrality and multiplicity of the self as a diagnostic instrument in coaching. The study’s findings emphasise the importance of the coach’s authentic use of self as a core mechanism for establishing trust, displaying empathy and adapting when necessary to remain a resilient instrument, engaged in the coaching session. This research further contributes to the field of coaching by highlighting the nuanced role of the coach’s use of self in supporting the uniqueness that each coach brings to the coaching process. It is evident that continuous refinement of coaching practices significantly better serves organisational leadership when using the self as an instrument.Master

Modelling the effects of compression of fouling layers on the filtration performance of membrane bioreactors

Thesis (PhD)--Stellenbosch University, 2025.Yala, S. A. 2025. Modelling the effects of compression of fouling layers on the filtration performance of membrane bioreactors. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a524cbdc-94ef-4ce7-ab10-1e2301bc7bb2Membrane fouling is a major operational challenge in membrane bioreactors (MBRs). It reduces membrane productivity and increases the operational cost of the system. Permeation drag due to applied pressure or flux, is one of the major contributors to membrane fouling. High drag force promotes deposition of foulants and compresses fouling layers, which consequently affects the overall performance of membranes in MBRs. Hence, prioir prediction and understanding of the effect of compression of fouling layers due permeation drag is essential for minimizing fouling and optimizing MBR operations. Mathematical models can be employed for such purposes. Therefore, this study developed a model that could predict the filtration performance of MBRs and also provide microscopic insight on membrane fouling under different compressions conditions. First, membrane filtration experiments of yeast suspension were carried at a laboratory scale under constant pressure and constant flux mode to obtain flux and pressure time profiles, respectively. The obtained data, which were inherently consistent and followed normal trend reported in literature, were used for modelling purposes. From the plots, it was observed that applied transmembrane pressure (TMP) and applied flux had a positive effect on the filtration performance of the membrane upto a certain limit, where a further increase did not increase permeate flux for constant pressure operations and resulted to a drastic increase in TMP for constant flux operations. The levelling off of flux at high applied TMPs and the drastic increase in TMP at high applied fluxes was attributed to compression of fouling layers. The second phase of the study involved modelling the effects of compression of fouling layer. A simple model that can predict the flux decline (constant pressure), TMP increase (constant flux) and profiles of fluid flow and fouling layer characteristic, based on filtration and compressibility of a feed, was proposed. The model was derived from conventional cake filtration theory, which involves combining equations that describe the compressibility of fouling layers and the fluid flow equations. The model parameters were estimated through fitting of experimental data of one run into the proposed equations. Thereafter, they were validated by data obtained from runs carried at different applied TMPs (10, 20, 50 & 60 kPa), applied fluxes (15, 25, 45, 55 LMH) and with different feed concentrations (6 & 8 g/L). Finally, the applicability of the model on real wastewater was tested. For all the evaluated conditions, the model satisfactorily predicted the filtration performance of the membranes. The F test, which compares the variances of the experimental data to that of the data predicted by the model, showed that all the F values were less than the F critical value of 2.2719. This indicates that the model predictions were consistent with the experimental data. Subsequently, it was successfully demonstrated how the proposed model can be used to optimize operations in an MBR. From the findings, it was concluded that the proposed model provides a valuable tool for predicting and optimizing the filtration performance of an MBR. However, further validation of the model with data from a full plant would be necessary. In addition, the model should be coupled with other supporting equations that describe other processes within an MBR, for comprehensive predictions and optimization.Doctora

Proton Single-Event Effects Tolerance Testing of a Vision Processing Unit for Satellite Use

Thesis (MEng)--Stellenbosch University, 2025.Badat, S. 2025. Proton Single-Event Effects Tolerance Testing of a Vision Processing Unit for Satellite Use. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ab66f6c1-dc89-48a2-ba4c-37f9d0e09a07This thesis investigates the Single Event Effects (SEE) susceptibility of the Intel Movidius Myriad X Vision Processing Unit (VPU) when exposed to 66 MeV protons. The research makes use of an industry-standard computer vision model and a custom neural network designed specifically for SEE detection to perform testing with only API-level access to the device. Testing was performed using the YOLOv7-tiny object detection model and a custom single-layer network (PlusOne) designed to trace error propagation. The Myriad X exhibited SEE cross-sections in the range of 10−11 to 10−9 cm2, with functional failure occurring at approximately 65.77 krad(Si). While numerous Single Event Upsets (SEUs) were observed, post-processing techniques proved effective at filtering many error- induced predictions. Analysis of recurring errors provided insight into potential firmware vulnerabilities to SEE. The research also reveals opportunities for SEE-aware neural network design, suggesting that architectural modifications to networks could enhance radiation tolerance.Master

Exploring the framing of news by selected specialist beat journalists during the Covid-19 pandemic in 2020

Thesis (MA)--Stellenbosch University, 2025.Jam Jam, Z. 2025. Exploring the framing of news by selected specialist beat journalists during the Covid-19 pandemic in 2020. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/aacf2356-4ce1-4768-a114-704dfc14495fThe South African government instituted regulations during the Covid-19 pandemic lockdown levels five and four (between 26 March 2020 and 31 May 2020) to impose restrictions and curb the spread of the virus. These restrictions were imposed to ensure people adhered to social distancing, no travelling, no events, and no access to public places. Considering that the government-imposed restrictions, journalists fulfilled their journalistic duties by reporting on different activities and related issues during the lockdown. These include the increasing number of Covid infections, closure of schools, universities implementing online learning, as well as the cancellation of events and sporting activities. This study explores how selected specialist beat journalists from selected newspapers framed news during the Covid-19 pandemic. The selected journalists were beat specialists in the areas of politics, education, business, entertainment, sport (cricket), local community news, and sport (rugby). The newspaper articles written by the journalists were sampled from South African-based news organisations that publish daily news in the English language. The newspapers are The Herald, The Sowetan, Cape Times, The Citizen KZN, The Cape Argus, and The Mercury. In employing the beat concept and framing theory, a qualitative framing analysis was applied as the central methodology. Eight frames were identified in the sampled news articles which are: Covid-19 pandemic, education, local community, politics, economic, entertainment and lifestyle, sport, and miscellaneous. Some of the themes that have been identified through the analysis were the consumption of home remedies to cure Covid-19, vandalism, police brutality, implementation of online learning in the education sector and increased mental health issues. The general conclusion of the study is that selected specialist beat journalists framed news according to their beats as well as the Covid-19 pandemic itself. While journalists did adapt their reporting to incorporate Covid-19, most of them continued to focus on their specific beats. Future studies could conduct quantitative research to better understand the number of stories that were written across different media outlets and beats during the Covid-19 lockdowns. In addition, interviews with journalists would also help gain more insight into how they adapted their reporting practices and routines.Master

Teachers’ Experiences of Children’s Participation Rights in Grade One Classrooms

Thesis (MEd)--Stellenbosch University, 2025.de Bruyn, N. 2025. Teachers’ Experiences of Children’s Participation Rights in Grade One Classrooms. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/df2d6cf3-f141-41f1-ac68-0ef7b868f279This study explored teachers’ experiences of children’s participation rights in their Grade One classrooms. The aim was to investigate how South African teachers understand and support children’s participation rights, as outlined in legislation, and the spaces and strategies they create to enable children to exercise these rights within the classroom context. Additionally, it covered the challenges teachers face when involving children in decision-making processes, as well as the types of support they need to overcome these challenges effectively. Children’s participation rights are a well-researched phenomenon that has gained substantial traction in South African research in recent years. However, a discrepancy still exists between research and teachers’ awareness of these rights and, consequently, their implementation. Hart’s Ladder of Participation (Hart, 1992) and Lundy’s Voice Model (Lundy, 2007) were used as the conceptual framework. I used an interpretive, qualitative, multiple-case study approach to examine and understand the experiences of Grade One teachers regarding child participation. To select the six Grade One teachers as participants, I employed a combination of purposive and snowball sampling from three schools in the Western Province. Data collection methods included questionnaires, photovoice, photo-elicitation interview, a focus group, and notes from my research journal. Four themes emerged from the inductive thematic data analysis focused on the outcomes of teachers’ experiences regarding child participation. The four identified themes were consequently, Teachers’ Awareness of Child Participation Rights, Supporting Child Participation in Classroom Contexts, Perceived Benefits of Supporting Child Participation in Classroom Contexts, and lastly, Factors Influencing the Implementation of Child Participation. The study’s findings indicate teachers’ awareness of children's participation rights and related legislation, as well as how these rights are implemented in classroom settings. Additionally, the findings reveal the potential benefits that teachers perceive when children participate, along with the challenges they encounter in attempting to include children in participatory practices. The study has implications for teachers and teacher training institutions.Master

Petrogenesis of Mesoarchean high-K rocks in the Kaapvaal Craton: Investigating the Boesmanskop Alkaline Complex and Salisbury Kop batholith

Thesis (PhD)--Stellenbosch University, 2025.Leandro, M. V. S. 2025. Petrogenesis of Mesoarchean high-K rocks in the Kaapvaal Craton: Investigating the Boesmanskop Alkaline Complex and Salisbury Kop batholith. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/76b804c3-689a-4c34-a14d-a7b7f1a791f1The Boesmanskop Alkaline Complex (BAC) and Salisbury Kop batholith (SB) are two contrasting units of the large ca. 3105 Ma Granodiorite-Monzogranite-Syenogranite (GMS) suite, situated on the eastern margin of the Kaapvaal Craton. The BAC consists of small intrusions at the southern end of the Barberton greenstone belt, recording shear deformation and containing the most potassic and REE-rich rocks of the GMS suite. In contrast, the SB is a homogeneous batholith at the north of the belt with a more sodic character. This study examines the BAC and SB through field observations, petrography, mineral chemistry, whole-rock compositions, and U-Pb zircon geochronology, alongside Rb-Sr and Sm-Nd isotopic data and phase equilibrium modeling for the BAC rocks. The BAC includes coarse-grained syenite, quartz monzonite and leucogranite. Some syenites display porphyritic textures that indicate K-feldspar phenocryst accumulation, with clinopyroxene and Ca-amphibole as intercumulus phases. Field observations indicate that the BAC magmas were emplaced at shallow levels along active shear zones. New U-Pb zircon dating of a quartz monzonite yielded a crystallization age of 3118 ± 9 Ma and inherited cores of ca. 3220 Ma. Zircon, apatite, and titanite compositions reflect high-temperature crystallization from REE-rich felsic magmas, with Ti-in-zircon thermometry recording temperatures up to 915 °C. Additionally, the high K2O+Na2O, low MgO and CaO contents of all the rocks, the presence of inherited zircon cores, and crustal isotopic signatures of the cumulus rocks suggest that they derive from magmas produced by low-degrees of fluid-absent anatexis of the lower crust (including recycled sediments). Phase equilibrium modeling conducted at pressure of 1.5 kbar and temperature range from 800 to 950 °C, consistent with intrusion at shallow depths, demonstrated that a subset of high-alkali content GMS granitic compositions is capable of crystallizing K-feldspar as the first tectosilicate. These experiments support the hypothesis that the syenites and quartz monzonites originated from hot granitic melts that underwent significant crystal accumulation of alkali feldspar. These textural and geochemical features and zircon U-Pb ages advocate that the BAC quartz monzonites and syenites formed earlier than the surrounding granitic bodies, representing the onset of the K-high magmatism responsible for transferring incompatible and heat-producing elements to shallow levels, thereby contributing to the stabilization of the Kaapvaal Craton. Conversely, the leucogranites and granodiorites of the SB lack cumulus textures. U-Pb zircon dating of granodiorites yields a crystallization age of 3094 ± 10 Ma and the titanite dating yields a within error identical age of 3100 ± 11 Ma. The idiomorphic biotite as the only mafic phase suggests that these rocks originated from more evolved and colder magma than the syenites and quartz monzonites. Taken together, the BAC and SB represent two key magmatic complexes that record high-K magmatism associated with the partial melting of the lower crust. The features reported highlight the importance of crustal reworking and lower crustal melting in stabilizing the early cratons, such as the Kaapvaal Craton. The BAC represents the initiation of the magmatic event.Doctora