Theses and Dissertations (University of Pretoria)

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Die herkoms en die sosiale, ekonomiese en opvoedkundige aspekte van die lewe van die Kleurlinge van Eersterust
(University of Pretoria, 1968-06) Coertze, P.J.; Jacobs, Paul Petrus
Mineralogy of the lower part of the upper zone, eastern Bushveld Complex : implications for ore-forming processes
(University of Pretoria, 1991) Von Gruenewaldt, G. (Gerhard), 1942-; Harney, Dirk M.W.
English: The lower part of the upper zone in the eastern Bushveld Complex was subjected to a detailed mineralogical investigation, aimed at gaining a better understanding of processes that led to the formation of the main magnetite layer (MML), sulfide-enriched horizons and possible concentrations of platinum-group elements (PGE). The most prominent rock types in the investigated stratigraphic sequence are anorthosites, containing variable amounts of magnetite, which are interlayered with gabbronorites, leuco-gabbronorites and magnetite layers. Elevated sulfide concentrations are commonly associated with magnetite layers. The highest values were found in an anorthosite directly below the MML, and the sulfide assemblage typically contains pyrrhotite, chalcopyrite, cubanite and pentlandite in decreasing order of abundance. PGE are not enriched in specific stratigraphic horizons, as in those known from the critical zone. However, a local concentration of Pt and Pd has been encountered in the sulfide-bearing anorthositic footwall of lower magnetite layer 2. Several Pt-Pd-Bi-Te minerals were found, namely michenerite, moncheite, merenskyite and froodite, and textural as well as compositional evidence indicates that these platinum-group minerals are of hydrothermal origin. Post-magmatic hydrothermal processes also affected the mineralogy and composition of sulfides above the MML. Pentlandite, in particular, reflects such hydrothermal activity and displays varying, but considerably elevated, Co concentrations. Changes in the Sr content and the Sr/Al 2o3 ratio of plagioclase, the whole-rock PGE concentration pattern and possibly also the composition of pyroxene at the level of the MML show that the MML formed in response to a magma mixing event between the resident and a less differentiated magma. Magma mixing resulted either from a breakdown of density stratified liquid layers or an influx of a small volume of new magma (up to 30 % of the hybrid). In addition to the formation of the MML, magma mixing is also believed to have caused the segregation of sulfides associated with that layer. It is concluded that the evolution of the upper zone does not reflect simple differentiation, but that it was interrupted by magma mixing events which occurred at the level of the MML and possibly also at other levels during crystallization of the upper zone. Afrikaans: Die onderste gedeelte van die bosone in die oostelike Bosveldkom-pleks is mineralogies noukeurig ondersoek met die doel om 'n beter begrip te vorm van die prosesse wat aanleiding gegee het tot die ontstaan van die hoofmagnetietlaag (HML), sulfied-verrykte lae en konsentrasies van die platinum-groep elemente (PGE). Die mees algemene gesteente tipes in die stratigrafiese suksessiewat ondersoek is, is anortosiete met varierende hoeveelhede magnetiet, wat tussengelaagd is met gabbronoriet, leukogabbronoriet en magnetietlae. Verhoogde sulfiedkonsentrasies is meestal geassosieer met magnetietlae. Die hoogste konsentrasies kom in 'n anortosietlaag direk onderkant die HML voor. Die mees algemene sulfiedassosiasie bevat, in volgorde van afnemende hoeveelheid, pirrhotiet, chalkopiriet, kubaniet en pentlandiet. Die PGE is nie in enige van die sulfiedgemineraliseerde lae verryk nie. Lokale verryking van Pt en Pd is egter teegekom in die sulfied-draende anortosiet net onder die laer magnetietlaag 2. Verskeie Pt-Pd-Bi-Te minerale is teegekom, te wete micheneriet, moncheiet, merenskyiet en froodiet. Tekstuur en samestelling dui daarop dat hierdie platinumminerale van hidrotermale oorsprong is. Na-magmatiese hidrotermale prosesse het ook die sulfied-mineralogie en samestelling bokant die HML geaffekteer. Veral pentlandiet reflekteer sodanige hidrotermale aktiwiteit en toon varierende, maar aansienlik verhoogde, Co konsentrasies. Veranderings in die Sr-inhoud en die Sr/Al 2o3 verhouding van plagioklaas, die heelgesteente PGE konsentrasiepatroon en moontlik ook die samestelling van pirokseen by die posisie van die HML dui daarop dat hierdie laag moontlik ontstaan het as gevolg van magmavermenging tussen die kristalliserende magma en 'n minder gedifferensieerde een. Magmavermenging kan of die gevolg wees van die ineenstorting van digtheidsgestratifiseerde vloeistoflae, of die gevolg van die invloei van 'n klein volume nuwe magma (tot 30 % van die hibriede produk). Bykomstig tot die ontstaan van die HML, word magmavermenging ook beskou as die oorsaak te wees vir die segregasie van sulfiede geassosieer met die laag. Daar word tot die slotsom gekom dat die ontstaan van die bosone nie die gevolg van 'n eenvoudige differensiasie is nie, maar dat dit onderbreek was deur episodes van magmavermenging soos byvoorbeeld by die HML en moontlik ook op ander tye tydens kristallisasie van die bosone.
Evaluering van bestuurstyle van opleiers in nie-formele onderwys : 'n fundamenteel-andragogiese begronding
(University of Pretoria, 1992-10) Moller, T.; Van Aardt, Nicolaas Johannes
Afrikaans: Vanuit 'n fenomenologiese perspektief het die volwassene 'ninherente strewe om toenemend iemand te wil word, dus om te leer. Vanwee sy normatiewe ingesteldheid wil hy sy volle potensiaal binne werkverband ontplooi ten einde die maatskappy te help om gestelde doelwitte te bereik. Die individu-in-indiensopleiding in die bedryfsektor word meer as ooit tevore met die vrae van waardes, lewensdoel en optimale betekenis van die lewe gekonfron-teer. Hulle verkeer in nood en vra leiding. Hoe meer die w~reld se kompleksiteit toeneem, hoe grater die mens se nood. Die werk- nemer raak verward in die nuwe geYndustraliseerde samelewing waarin ans, ans tans in bevind omdat nie genoegsame aandag gegee word aan die essensies van menswees nie. Die gevolg van hierdie verwardheid waarin die werknemer horn tans in bevind, lei daartoe dat produktiwiteit in die slag bly. Die bestuurder gee nie genoegsame aandag aan die menslikheid van sy ondergeskiktes ten einde produktiwi tei t van sy werknemers te bevorder nie. Die andragogiese-essensies van menswees naamlik in-betekenis- wees, medesyn, temporaliteit en self-iemand-wees word nie verwerklik in die sakesektor nie. Die andragogiese-essensies is nie net mensweesessensies nie, maar produktiwiteitessensies. Indien die andragogiese-essensies nie verwerklik word in die sakesektor nie, sal produktiwiteit nooit verbeter word in geindustraliseerde werkomgewing nie. Die fundamentele andrago-giese-essensies moet toegepas word binne 'n maatskappy ten einde verhoogde produktiwiteit mee te bring. Individue-in-indiensopleiding beskik oor die potensiaal om produktief te wees en wil graag hierdie potensiaal tot uiting bring. Die bestuurder as opleier moet die klimaat skep waarbinne hierdie werknemer in die maatskappy kan funksioneer. Indien die bestuurder die andragogiese-essensies ontken, ontken hy menswees. Die werknemer as volwassene strewe inherent na uitnemendheid en het die wil om te presteer. Indien hulle deur deelname gelei word, sal dit lei tot verbondenheid wat op sy beurt lei tot kreatiwiteit. Die werknemer wil 'n betekenisvolle lewe lei en hy wil aan alle aspekte van sy lewe betekenis gee en dus ook in die maatskappy waar hy werk betekenisvol wil funksioneer. Die kernbegrip hoe volwasse leer by die werknemer plaasvind, is dat die volwassene selfrigtend is. Die vo--lwasse leerder wil deur andere gesien word as onafhanklik en selfbepalend. Wanneer die ondergeskikte dus 'n. situasie ervaar waar hy/sy nie toegelaat word om onafhanklik en selfbepalend op te tree nie, kan dit lei tot 'n onderbewuste gevoel van weerstand en woede. Dit kan lei tot onproduktiwiteit deurdat hy nie die geleentheid gegun word om sy potensiaal tot uiting te bring nie. Uit die navorsing het geblyk dat die wyse hoe volwasse leer plaasvind nie net mensge-orienteerde leerteoriee bevat nie, maar byvoorbeeld assosiatiewe, funksionele en kognitiewe leerteoriee. Die werknemer strewe na die transendente. Dit beteken dat hy gedurig in wording is en dat hy op pad is om iemand te word. Die andragogiese-essensies is daarop gemik om vir die werknemer wat ongeborgenheid beleef, vertroue in die eie saak te gee. Die Christelike lewensopvatting in besonder bepaal dat God Drie-Enig, die Skepper, Onderhouer en Regeerder van die ganse werklikheid is en dat die werknemer groepe is om God in al sy aktiwiteite te eer en te verheerlik. Hierdie lewensopvatting soos gehuldig deur 80% van die RSA se bevolking moet dus as basis dien vir 'n gesonde bedryfsektor. English: From a phenomenoligical perspective the adult has an inherent desire to be entertained increasingly; that is, to learn. Because of his normative propensity, he strives to develop his full potential in the working context in order to assist the company in reaching his objectives. The individual in in-service training in the operations sector is more than ever before, being confronted with questions regarding values, the purpose of life and the optimum value of life. They find themselves in distress and seek guidance. The more the world's complexity increases, the greater man's distress. The employee becomes perplexed in the new industrialised society in which we are presently became inadequate attention is being given to the essentials of humanity. The result of this confusion in which the employee finds himself presently, leads to a decline in productivity. The manager does not give sufficient attention to the humanity of his subordinates which could promote the productivity of his in-service training personnel. The andragogical essentials of humanity namely being a part of a meaningful world, fellowship, temporality and self-esteem are not being satisfied in the business sector. The andragogical essentials are not human~ essential, but productivity essentials. If the andragogical essentials do not materialise in the 1:fosiness sector, productivity will never improve in the industrialised working environment. The fundamental andragogical essentials have to be applied within, the company in order to bring about increased productivity. Individuals engaged in in-service training have the potential to be productive and have the need to express this potential. The manager must create the climate in which the employee can function within the company. The manager who denies the andragogical essentials denies humanity. The employee as adult inherently strives toward excellence and has the will to perform. If they are guided through participation, it will lead to commitment which in turn leads to creativity. The employee wishes to lead a meaningful life and wants to add significance to all aspects of his life as well as in the company where he works. The basic concept of how the adult doctrine transpires, is that the adult is self-directed. The adult learner wants others to regard him as independent and self-determined. When the employee therefore, experiences a situation in which he is not allowed to act independently and self-determining, it may lead to unproductivity because he is denied the opportunity to demonstrate his potential. Research revealed that the adult doctrine not only contains human orientated learning theories, but for instance, contains associative, functional and cognitive learning theories. The employee strives towards the transcendental. This means that the employee is constantly in the making and on the way of becoming someone. The andragogical essentials are aimed at giving the employee experiencing insecurity, trust in his own situation. The Christian outlook in particular determines that God triune is Creater, Provider and Ruler of the entire universe and that the employee is destined to honour and glorify God in all his activities. This outlook, recognised by 80 % of the population of the RSA, must therefore serve as basis for a sound operations sector.
Gestaltterapie met die allergiese kind in die middelkinderjare
(University of Pretoria, 1999-08) Joubert, J.M.C.; Yssel, Johanna Maria
Afrikaans: Hierdie studie is gerig op die daarstelling van 'n gestaltspelterapeutiese program wat gebruik kan word om die allergiese kind in die middelkinderjare te begelei om beheer oor sy siekte te verkry en om die invloed daarvan op sy ontwikkelingstaakbemeestering te minimaliseer. In aansluiting hierby is 'n ouerleidingprogram ontwikkel waar gestaltbeginsels benut is om die ouers van die allergiese kinders ter versterking van die doelstellings van die spelterapeutiese program te bemagtig. Vanuit die literatuur en vorige navorsingsbevindinge is dit duidelik dat die voorkoms van 'n allergiese siekte 'n negatiewe invloed op die kind in die middelkinderjare se bemeestering van sy ontwikkelingstake op emosionele, sosiale en akademiese gebied kan uitoefen. Dit kan daartoe lei dat die kind se selfbeeldontwikkeling benadeel word en hy kan angs, frustrasie en aggressie ervaar wat sy gesonde funksionering strem. Op sosiale gebied kan allergiese siektes daartoe lei dat die kind ge"fsoleer word en dat hy nie soos sy maats aan alle aktiwiteite kan deelneem nie - dit kan tot portuurgroepverwerping lei. Op akademiese gebied kan die allergiese kind te siek voel om sy volle aandag aan sy skoolwerk te gee, wat moontlik onderprestasie en verminderde motivering tot gevolg kan he. Die voorkoms van 'n allergiese siekte het verder 'n definitiewe invloed op die gesinsfunksionering en kan negatiewe gevolge vir sowel die ouer-kind verhouding en opvoedingstyl as die sibbeverhoudinge inhou. Die beginsels van die gestaltbenadering fokus op die kind se verhoogde bewustheid van homself in sy situasie, sy verbeterde emosionele hantering van eise wat aan horn gestel word, die verhoging van sy beheer oor sy lewe en die versterking van sy eie verantwoordelikheidneming vir sy gesondheid. Deur die benutting van hierdie beginsels in beide programme kan die kind deur spelterapie en 'n ondersteunende ouerleidingprogram gehelp word om toepaslike beheer oor sy siekte uit te oefen en die moontlike negatiewe invloed van allergiese siektes op sy ontwikkelingstaak bemeestering en totale funksionering te minimaliseer. Ten einde die kennisleemte wat in die hantering van die spesifieke behoeftes van allergiese kinders bestaan te oorbrug, is die gestaltspelterapeutiese- en ouerleidingprogramme ontwikkel. Ses respondente in hul middelkinderjare en hul ouers is by die implementering van beide die spelterapeutiese- en ouerleidingprogramme betrek. Die navorsingsresultate het daarop gedui dat die gestaltspelterapeutiese program suksesvol was in die fasilitering van die kind se verhoogde bewustheid van homself in en verhoogde beheer oor sy situasie, verbeterde emosionele hantering en verhoogde verantwoordelikheidneming vir sy gesondheid. Die gegewens het verder daarop gedui dat die ouerleidingprogram suksesvol was om die ouers van die kinders tot ondersteuning van die spelterapeutiese doelstellings te bemagtig en hul opvoedingstaak te vergemaklik. Die programme is dus suksesvol vir sowel die gestaltterapeutiese begeleiding van allergiese kinders in die middelkinderjare tot optimale funksionering en beheer van allergiese siektes, as die bemagtiging van ouers ter ondersteuning van die spelterapeutiese program. Die gevolgtrekkings en aanbevelings van die studie fokus op die bereiking van die doelstelling en doelwitte van die studie, gevolgtrekkings oor die navorsingsbevindinge, aspekte wat in ag geneem moet word in die gebruik van die programme en verdere navorsingsmoontlikhede wat uit die studie voortspruit.
Occurrence and characterization of Shiga toxin-producing Escherichia coli from goats on communal rangeland in Gauteng South Africa
(University of Pretoria, 2022-05) Karama, Musafiri; Marufu, Munyaradzi Christopher; u28556021@tuks.co.za; Malahlela, Mogaugedi Nancy
Shiga-toxin-producing Escherichia coli is a foodborne pathogen commonly associated with human disease characterized by mild or bloody diarrhoea hemorrhagic colitis and hemolytic uremic syndrome. This study investigated the occurrence of STEC in fecal samples of 289 goats in South Africa using microbiological culture and PCR. Furthermore, 628 goat STEC isolates were characterized by serotype (O:H) and major virulence factors by PCR. STEC was found in 80.2% (232/289) of goat fecal samples. Serotyping of 628 STEC isolates revealed 63 distinct serotypes including four of the major top seven STEC serogroups which were detected in 12.1% (35/289) of goats: O157:H7, 2.7% (8/289); O157:H8, 0.3%, (1/289); O157:H29, 0.3% (1/289); O103:H8, 7.6% (22/289); O103:H56, 0.3% (1/289); O26:H2, 0.3% (1/289); O111:H8, 0.3% (1/289) and 59 non-O157 STEC serotypes. Twenty-four of the sixtythree serotypes were previously associated with human disease. Virulence genes were distributed as follows: stx1, 60.6% (381/628); stx2, 72.7% (457/628); eaeA, 22.1% (139/628) and hlyA, 78.0% (490/628). Both stx1 and stx2 were found in 33.4% (210/628) of isolates. In conclusion, goats in South Africa are a reservoir and potential source of diverse STEC serotypes that are potentially virulent for humans. Further molecular characterization will be needed to fully assess the virulence potential of goat STEC isolates and their capacity to cause disease in humans.
Model predictive static programming control applied to mineral processing plants
(University of Pretoria, 2023-05) Le Roux, Johan Derik; z.noome@gmail.com; Noome, Zander Meindert
In a mineral processing plant, the separation of valuable material from ore has multiple stages. Usually, the ore is crushed or ground into smaller parts through multiple crushers or grinding mills. This is called the communition process. This process is typically the first stage for extracting valuable material and is important for further down-stream processes. The output of the communintion stage is usually regulated to achieve a stable throughput and a specific ore particle size. After the ore is crushed and ground to a specified size, the valuable material in the ore needs to be separated from the undesired materials. The properties of the desired material influence the method used for separation. These methods include froth flotation, gravitational separation, magnetic separation and electrostatic separation. The separation process can include multiple process streams to get a high grade of the desired minerals out of the ore. In froth flotation, the main objective is to extract the desired material from the ore to obtain a large mineral recovery. Because the flotation process relies on the flotation of particles, particle size is extremely important. The use of control systems in mineral processing plants has been adopted to improve throughput, optimize power usage, ensure safe process operation and to running at a stable operating condition. The control of these plants makes use of different advanced process control strategies which include but are not limited to cascaded control, where multiple layers of control systems are applied, and model predictive control. These different control strategies can range from regulatory control to supervisory control. Because of the large number of inputs to these plants, efficient controllers are necessary to obtain desired results. The use of Nonlinear Model Predictive Control (NMPC) is an attractive option for most mineral processing plants because of the constraint management capabilities of the controller. Unfortunately, the NMPC method has a large computational load which requires sufficient resources to make it a viable option. Another model predictive control method known as Model Predictive Static Programming (MPSP) has shown promise to improve the computational time of a standard NMPC controller. The MPSP control philosophy generates a static optimization problem which is less computationally difficult to solve compared to the dynamic optimization problem that is generated through NMPC. In this dissertation, the control of a single-stage grinding mill circuit and a four-cell flotation circuit with an MPSP controller to reduce the computational load is proposed. The computational efficiency and the output performance of MPSP controllers are compared to NMPC controllers as a motivation for the use thereof. The comparison is done by simulating two mineral processing stages, namely the communition phase and the separation phase. The simulations considered different configurations for both the MPSP and NMPC controllers. The comparison of the controllers in the simulations shows that the MPSP controller obtained similar or improved plant results while also having a reduced computational time compared to the NMPC controller. The MPSP controller also displays scalability improvements compared to the NMPC controllers which can be beneficial for supervisory control of large-scale processing plants.
Advancing environmental, social, and governance outcomes through process optimisation and control
(University of Pretoria, 2024-02) Le Roux, Johan Derik; Craig, Ian K.; burchell.john@gmail.com; Burchell, John James
Organisations are compelled to integrate Environmental, Social, and Governance (ESG) considerations into their core strategy, with the tightening of regulatory requirements and the mounting pressure from stakeholders for sustainable practices driving a trend toward socially responsible investing. Advanced process optimisation and control provides innovative solutions to support ESG objectives. This thesis explores two case studies aimed at enhancing the consistency of material flow and composition into metallurgical operations to improve overall processing efficiency. The first case study introduces a (μ+λ)-Evolutionary Strategy (ES) to solve the input blending problem for a base metal refinery (BMR), where variability in the feed of contaminants to the operation impact negatively on plant throughput, product quality, and harmful emissions. The algorithm outperforms baseline blending strategies demonstrating a significant improvement in the blended consistency of contaminant feed. In the second case study, a nonlinear Model Predictive Controller (NMPC) is developed and implemented on a surge tank for level averaging control in an industrial tailings reprocessing circuit. A rigorous dynamic model is derived to describe the rate of change of both the volume and density in these surge tanks. By simulation with industrial data it is demonstrated that the significant input disturbances typical to tailings reprocessing circuits drive a gain inversion in the density model of the surge tank. This gain inversion and the multivariable objectives of both density and flow disturbance attenuation motivates for a NMPC solution. Results presented show significant improvements in both the water recovery and the stability of mass flow of tailings in the circuit. These advanced optimisation and control solutions support ESG objectives across multiple dimensions. Improved input stability with the (μ +λ)-ES enhances the efficiency of downstream processes where contaminants are extracted, resulting in lower emissions, especially when hazardous reagents are involved in the extraction process. By improving the efficiency of contaminant extraction the need for rework of product that fail to meet specifications is minimised, which leads to a reduction in waste generation, conservation of resources, and lower energy consumption. Improved water recovery with the NMPC lowers the overall environmental footprint of the tailings reprocessing circuit by reducing water consumption and energy usage, while stability improvements positively impact recoveries, thereby reducing waste and supporting responsible resource management.
Extremum seeking control of grinding mill circuits based on grind curves
(University of Pretoria, 2023-05) Le Roux, Johan Derik; Craig, Ian K.; lukieski@gmail.com; Ziolkowski, Lukasz
Mineral processing plants include several operations to liberate the valuable minerals within raw ore material to produce a concentrate, which is processed into a usable product by a metallurgical refinery. A mineral processing plant consists of a comminution and a separation stage. During the comminution stage, the raw ore material is processed through a grinding mill circuit to liberate the valuable minerals by grinding the ore to fine particles. The product from the comminution stage is then processed at a separation stage, which separates the valuable minerals (concentrate) from the waste material (tailings). The comminution stage plays a crucial role in the mineral processing industry. It significantly impacts the net revenue generated by a mineral processing plant due to the high operating costs associated with liberating the valuable minerals from the ore material. A grinding stage operates efficiently if it is processing the ore material at its maximum capacity, minimizing power consumption while reducing the amount of valuables lost to the tailings stream. Therefore, the ore material should be sufficiently ground for effective separation in subsequent downstream processes. Ideally, the separation stage requires a consistent stream of fine particles for effective separation. It is challenging for plant operators to manually achieve the above-mentioned operational objectives, which motivates the need to adopt a suitable control framework and ensure an efficiently run process. The performance of a grinding mill circuit is measured by its throughput and grind quality. These performance indicators are inversely related to operational objectives. The challenge in controlling the grinding mill circuit arises in determining the optimal operating conditions to maximize the net revenue generated by the plant. The optimal operating conditions vary with different ore types and unknown disturbances, such as varying ore hardness, which can result in the comminution stage operating at sub-optimal operating conditions. Furthermore, grinding mills rely on the cascading motion of the ore material and grinding media to accelerate ore breakage. The cascading motion is a function of the fraction of the mill volume filled with ore and the mill rotating speed, which influences the breakage forces that occur between rocks. Therefore, selecting optimal operating conditions is a difficult task requiring frequent adjustments as the operating conditions vary. Grind curves are a valuable tool that establishes the relationship between the mill load filling and rotational speed to the grinding mill throughput, grind quality and power consumption for a given ore type. Generally, the curves show parabolic features and the peaks vary with changes in the ore characteristics. A model-free adaptive control strategy is proposed for optimizing the performance of a semi-autogenous grinding (SAG) mill based on grind curves to improve throughput or grind quality. The controller explores an unknown map in search of the extremum of the performance indicators along the grind curves. A perturbation-based (PESC), a time-varying parameter estimation-based (TESC), and a Nelder-Mead simplex-based (SESC) extremum seeking control method are considered to optimize the grinding mill performance. Several optimization strategies are investigated for an open grinding mill configuration and a closed grinding mill circuit, where the closed circuit is equipped with a screen or with a hydrocyclone classifier to recirculate oversized ore material for additional grinding. The challenge lies in implementing an efficient optimization model-free control framework that will effectively maximize the performance measures of the complex, non-linear behaviour of the grinding mill circuit.
Model-based estimation and control of wheel slip in locomotives
(University of Pretoria, 2023-10) Le Roux, Johan Derik ; charlvandemerwe@gmail.com; Van de Merwe, Charl Viljoen
This dissertation investigates wheel slip control of locomotive traction systems in the presence of non-linear wheel surface behaviour and varying adhesion conditions. It is difficult to determine when the maximum point of adhesion has been exceeded since the adhesion coefficient cannot be measured directly during the operation of the locomotive. Therefore, classical slip controllers suppress excessive slip by using predetermined thresholds for the slip velocities and accelerations of the axles. The classical methods are convenient but cannot maximise adhesion utilisation. Modern methods continuously modulate the torque and are expected to produce superior performance if implemented effectively. Most continuous controllers calculate the reaction torque using a generated slip ratio (slip velocity divided by the locomotive velocity) reference and a slip ratio estimate feedback. Computing the estimate depends on an accurate locomotive velocity estimate, which is difficult to obtain when all the wheelsets of a locomotive are driven. Slip ratio reference generation generally requires estimates of the slip ratio and adhesion coefficient or adhesion force. This dissertation focuses on producing accurate estimates to enable effective slip control. Adhesion force is the adhesion coefficient multiplied by the normal force. The adhesion coefficient is dependent on the rail conditions. Under constant rail conditions, it varies only with a wheel load and slip ratio change. Therefore, the normal forces, wheel velocities, and locomotive velocity should be modelled accurately to ensure the model produces realistic adhesion coefficients. A linearised railway vehicle model could be well over the 100th order. Such models are helpful for design and validation, but using such complex models in model-based filter or estimator design is impractical. In this dissertation, a new simulation model is developed that includes the longitudinal, pitch, vertical, and wheelset rotational dynamics. In addition, it includes a unique approach to the coupler force by modelling the wagons using a single-axle wheelset model. This model captured the desired dynamics, including wheelset torsional vibrations and oscillations in the pitch dynamics. A linear state-observable estimator is developed to produce estimates of slip ratios and adhesion coefficients. The estimation model is an adaptation of the simulation model, but the adhesion forces and coupler force are modelled as unknown disturbances. This estimator requires measurements of the locomotive longitudinal acceleration and velocity, body pitch angle and rate, and the motor angular velocities. The rail angle and motor torque estimates should be provided to the estimator. The estimates are used in a novel slip ratio reference adaptation method to provide a reference to an adaptive PI controller. The PI controller is used to compute the reaction torque to prevent unstable slip in the rear/reference wheelset, while a speed differential controller is used to prevent slip in the other wheelsets. The simulation results indicate that the estimator and controller configuration can suppress unstable slip under varying adhesion conditions, thereby preventing damage to the wheels and rail while ensuring maximum adhesion utilisation. Maximum adhesion utilisation allows a locomotive to increase its hauling capacity without increasing its mass.
A one health assessment of a “Herding for Health” project at the wildlife-livestock interface in western Ngamiland, Botswana
(University of Pretoria, 2021-10) Quan, Melvyn; Van Rooyen, Jacques; McNutt, John W.; bheermans@yahoo.com; Heermans, Ben Cooper
This PhD thesis titled, ‘A One Health assessment of a Herding for Health project at the wildlife-livestock interface in western Ngamiland, Botswana’, analyzed data collected from an applied Herding for Health (H4H) project implemented in western Ngamiland, Botswana. The H4H model was first established at the Department of Veterinary Tropical Diseases at the University of Pretoria to apply One Health principles that acknowledge the interconnectedness of human, animal and ecosystem health. The model aims to assist agropastoral communities in the transfrontier conservation areas (TFCAs) of southern Africa with the dual objectives of poverty eradication and biodiversity conservation. A mixed-methods approach was used to investigate some of the key assumptions of the H4H model. The thesis is comprised of five chapters: Chapter 1, an introduction to the H4H model and a literary review of the methodology of subsequent chapters; Chapter 2, ‘One Health profile and farmer’s perceived risk analysis for an agropastoral community in the Khaudum-Ngamiland Wildlife Dispersal Area of the Kavango–Zambezi TFCA’, that used a qualitative and quantitative survey approach to investigate community sentiments on animal and rangeland health, regional constraints to livestock husbandry and human-wildlife conflict; Chapter 3, ‘An environmental template and drivers of functional heterogeneity in communal rangelands of the western Okavango Delta’, which used community survey and rangeland sampling techniques to explore how H4H can address the piospheric nature of rangeland degradation; Chapter 4, ‘Husbandry and Herding: a community-based approach to address illegal wildlife trade’, which used a Theory of Change approach developed with input from relevant stakeholders to guide how H4H could address the current trend of diminishing wildlife populations around the Okavango Delta and Chapter 5, ‘Conclusions’, which summarizes the major findings of the dissertation and provides recommendations for H4H project interventions and for further research. Some of the key results from this thesis illustrate the importance of cattle rearing in western Ngamiland, Botswana which was the main source of household income for 97% of respondents. While most residents were satisfied with the advice supplied by local veterinary extension services, animal diseases continue to be a major challenge to farming, surpassed only by the related factor of constraints to market access due to Foot and Mouth Disease control policies. While diseases account for 7.7% of total cattle losses, the greater loss reported is due to straying animals which account for 60.3% of total losses whereas predation accounts for 22.9%. The herding and kraaling activities promoted by H4H are ideal interventions to address losses to disease, livestock-wildlife conflict as well as stray animals. Stray cattle are a likely threat to animal disease control and may explain regional FMD outbreaks outside of buffalo (Syncerus caffer) ranges, which is a topic outlined for further research. The potential for planned grazing and kraaling to address rangeland health is exemplified in the environmental template which demonstrates higher wildlife utilization in abandoned kraal sites and the effect that high-density grazing has on rangeland species composition including functional attributes such as stem height, tuft basal width, the distance between tufts and grass abundance which are significantly influenced along the grazing gradient. Lastly, the H4H Theory of Change identifies three pathways based on community-level actions to address illegal wildlife trade in the region which include: increasing institutions for local enforcement, developing incentives for ecosystem stewardship and decreasing the costs of living alongside wildlife. The success of the pathways depends on underlying enabling actions related to supporting the development of institutional frameworks, building community capacity and strengthening a Conservation Agreement model to facilitate informed best farming practices targeted to increase community and ecosystem resilience to economic shocks.
Nana's living library : an outdoor South African floral library in Pretoria CBD
(University of Pretoria, 2024-11) Shand, Dayle; mariette.dekock01@gmail.com; De Kock, Maureen
Urbanisation increasingly diminishes the availability of open space in cities, creating a disconnect between people and nature, especially in the heart of the Pretoria Central Business District (CBD), along Nana Sita Street. Here, local communities are restricted to poorly maintained public parks and occasional visits to natural landscapes, outside of the city, for brief interactions with nature. Meanwhile a deep connection with natural elements like flora is an important part of people’s lives. A notable example of lack of engagement is that local floral knowledge is primarily restricted to botanical gardens and nature reserves on the city’s outskirts. This project addresses these challenges by proposing a spatial framework to reintegrate nature within Tshwane’s inner city, emphasising underrepresented floral knowledge exchange. Central to this initiative is exploring methods of knowledge sharing and translating it to landscape architectural elements. Nana Sita Street serves as the primary spine of the precinct development, with improved pedestrian conditions and pathways, creating a network of new and existing green spaces in the CBD as satellite floral gardens. These foster improved human-nature relationships, celebrating authentic interactions with locally indigenous plants by transforming current derelict open spaces into gardens with medicinal, edible, culturally significant and useful plant species. The proposal is further detailed on one site within Nana Sita Street, where leftover space is transformed into an outdoor floral library complete with a discussion pavilion, exhibition walls, herbarium, workshops and demonstration areas. Other proposed development includes the repurposing of a petrol station into a vegetated area, adding residences, play areas and shops. The owner of the site, FABA Properties Ltd is considered to be the primary client and collaborates with the South African National Biodiversity Institute and the Future of the City Centres Network, which focuses on improving city centres. The proposal serves the diverse community, including working professionals, school children, theatre goers, families and visitors from surrounding areas. Overall, this proposal acts as a catalyst to highlight the importance of good quality urban green spaces, advocating for alternative representations of urban nature that integrate floral knowledge and its significance within local human-nature relationships.
'n Kwalitatiewe ondersoek na die emosionele belewenis van enkele Suid-Afrikaanse blanke geskeide mans
(University of Pretoria, 1992-02) Du Preez, M.S.E.; sulette.ferreira@gmail.com; Ferreira, Sulette
Afrikaans: Hierdie ondersoek lewer 'n beskeie bydrae tot die verkryging van wetenskaplike kennis oor mans se ervaring en hantering van egskeiding waaroor weinig, veral in Suid-Afrika, bekend is, asook tot die verskaffing van maatskaplikewerk-hulp aan mans wat in Suid-Afrika hierdie lewenskrisis beleef. Ten einde die ondersoek te kon doen, is die doelstellings van die ondersoek soos volggestel: Om deur middel van 'n verkenning van die bestaande literatuur oor egskeiding die sentrale teoretiese modelle te bepaal en te beskryf wat deur sosiaal-wetenskaplikes gekonstrueer is om egskeiding te begryp, en terapie te verskaf aan diegene wat daardeur geraak word. Om deur middel van 'n plooibare navorsingsbenadering, te wete die kwali tatiewe model, eerstehandse inligting te bekom rakende enkele geskeide blanke Suid-Afrikaanse mans se sosiale werklikheid, dit wil se hoe hulle sin en betekenis aan hul egskeidings gee. Om te let op die behoefte van die geskeide man aan terapeutiese hulpverlening en op grond hiervan aanbevelings te maak aan die Suid-Afrikaanse maatskaplikewerk-praktyk. Om 'n bydrae tot die metodologie van maatskaplikewerknavorsing in Suid-Afrika te lewer deur prakties te illustreer hoe die kwalitatiewe navorsingstyl wat tot nog toe selde in plaaslike maatskaplikewerk-studies onderneem is, aangewend kan word om geskeide mans se definisies van hul situasies, of meer spesifiek, hul subjektiewe ervarings en interpretasies van hul lotgevalle, te peil en te beskryf. Hoewel vandag algemeen aanvaar word dat een uit elke drie huwelike in Suid-Afrika in die egskeidingshof eindig, is wetenskaplike literatuur oor die probleem in die land beperk. Verder blyk dit dat weinig teoretiese en empiriese inligting spesifiek oor die geskeide man hier te lande beskikbaar is. Hoewel aansienlik meer aandag in die buiteland aan egskeiding gegee word, blyk dit dat sosiaal-wetenskaplikes veral in die geskeide vrou geYnteresseerd is en dat haar eweknie, te wete die geskeide man, verwaarloos word. Nogtans is waardevolle inligting uit die beskikbare literatuur onttrek oor die egskeidingsproses en oor sowel die geskeide vrou as die geskeide man. Die insigte wat van die onderskeie teoretici en navorsers verkry is, was nie alleen nuttig om die data te interpreteer wat tydens die empiriese studie ingesamel is nie, maar hou belofte in vir sowel verdere plaaslike studies van geskeide mans as vir hulpverlening aan hulle. Vyftien geskeide blanke mans is met behulp van die sneeubaltegniek opgespoor en tot deelname aan die empiriese studie oorgehaal. Hierbenewens is twee geskeide mans op dieselfde wyse gewerf om die navorsingsresultate te verifieer. Bestaande riglyne vir kwalitatiewe navorsing is sover moontlik in die studie toegepas en daar is daarin geslaag om, hoewel nie uitvoerig nie, 'n getroue prentjie van die lewensituasie van die geskeide blanke man te beskryf. Die data is verkry deur onderhoude (semi-gestruktureerd maar ook ongestruktureerd) met die respondente te voer en deur dokumente te benut wat hulle vir hul eie gebruik of op versoek van navorser opgestel het. Afgesien van die dokumente is van oudiobande gebruik gemaak en die byhou van notas om die verkree data vas te le. Die data is voortdurend bestudeer en is veral aan die einde van die ondersoek in temas en patrone gekategoriseer en geYnterpreteer met behulp van sekere bestaande teoriee wat tydens die literatuurverkenning afgebaken is. Regdeur die ondersoek is sover moontlik gepoog om faktore te neutraliseer wat die resultate nadelig kon beYnvloed. Die slotsom waartoe uiteindelik geraak is, is dat die lewensituasie van die aantal geskeide mans wat as proefpersone benut is, geldig en akkuraat verken en beskryf is. Die belangrikste bevindinge van die empiriese studie is die volgende: Egskeiding is 'n proses met fases wat onderskei maar nie geskei kan word nie; die geskeide man ervaar verskeie emosionele belewenisse voor, tydens en na afloop van die egskeiding; die aanpassing aan die egskeiding word deur verskillende faktore geaffekteer; egskeiding het 'n effek op die verhoudingslewe van die geskeide man; die godsdiensbeskouing van die geskeide man speel 'n kardinale rol in sy verwerking van die egskeiding en ten slotte het die geskeide man behoefte aan terapeutiese intervensie. Dit blyk dat geskeide mans by maatskaplikewerk-hulpverlening kan baat mits sodanige programme in samewerking met hulle opgestel word.
Mathematics teachers' professional noticing as an immanent feature of Lesson Study
(University of Pretoria, 2024-09) Sekao, David; u18229256@tuks.co.za; Moremi, Koketso Clinton
Teachers’ professional noticing is an essential pedagogical skill for the effective teaching and learning of mathematics. Professional noticing is an inherent attribute of Lesson Study (LS). Therefore, LS is the perfect context to explore how mathematics teachers used professional noticing when offering lessons within the LS setting; thereby making instant instructional decisions while the lesson unfolds. My qualitative case study research is situated within the interpretivist paradigm, wherein two LS groups were studied to gain insights into how mathematics teachers’ professional noticing informs their instructional decisions. I used two theoretical lenses, namely, Situated Learning Theory (Lave & Wenger, 1991), to provide a theoretical basis for LS and FOCUS Framework for Productive Noticing (FFPN) (Choy, 2015) to provide a theoretical basis for professional noticing. The two LS groups were purposively selected because of their familiarity with and implementation of LS. Data were collected through observation, document analysis and unstructured interviews to answer the primary research question: How do mathematics teachers use professional noticing to facilitate lessons within LS? The findings of this research have practical implications for mathematics teaching. The study revealed that while teachers noticed learners struggling with specific mathematics ideas, their noticing was only superficial. This led to instructional decisions that were not optimal for enhancing or developing learners’ mathematical thinking. The dominant instructional decision was to, in the same way, re-explain a mathematics idea in the same way when learners were struggling with it. The study also revealed that teachers could reflect on practice cosmetically and suggest alternatives for the future. The recommendations from this research can guide teachers to use purposeful activities when teaching in the LS context to enable them to notice specific issues regarding learners’ mathematical thinking and then make suitable instructional decisions. It also suggests that teachers consult curriculum policy when engaging in post-lesson reflections to enrich their reflection-on-practice.
Visualising M’bona religious beliefs and practices : a visual cultural artistic co-production with the custodians of Khulubvi and Associated Rain Shrines in Nsanje, Malawi
(University of Pretoria, 2025-06) Kriel, Lize; Beyers, Jaco; mamayewo@gmail.com; Chikabadwa, Eva
The study examines the role of the visual in research and documentation by analysing the power relations between the visual, oral, and written forms in the context of heritage preservation, drawing on theories of visual culture. The project aimed to visualise the M’bona beliefs and practices for the adornment of a future museum in a manner that strikes a balance among the three (visual, oral, and written) for heritage sustainability. The vision aligns with the concept of ‘decolonizing heritage for development,’ where development encompasses improvements in both material and non-material aspects, the ability to help others, and a change in individual and collective circumstances. Heritage, on the other hand, comprises skills, knowledge, and practices. In short, heritage development is a consequence of heritage and heritage making. The study organized the data using Ninian Smart’s seven dimensions of religion. It employed Clifford Geertz’s definition of religion, Talal Asad’s critique, the African Traditional Religions framework, and participants’ views to examine the M’bona culture as a religion. The Manganja M’bona advocates asserted that they do not consider the term ‘religion’ applicable in their culture. An experimental research approach, the ‘Meta Picture Data Collection Technique,’ which strikes a balance between textual, oral, and visual elements of heritage while prioritizing community involvement, was developed and used in the study. The technique aims to balance practice and theory in visual culture by emphasizing artmaking as a holistic approach, much like reading and writing texts for deeper studies.
Delinquency of the youth in rural Bisho : a pastoral challenge
(University of Pretoria, 2024) Masango, Maake J.S.; lindelwakumbaca@gmail.com; Kumbaca, Lindelwa
This exploratory study investigates the root causes of youth delinquency in rural Bisho, focusing on the complex interplay of social, educational, and environmental factors influencing adolescent behaviour. Youths in rural communities face challenges stemming from their interactions within schools, religious institutions, and the broader community, as well as from peer and adult relationships. Many young individuals join gangs to establish a shared identity or pursue specific objectives, often rooted in criminal or delinquent activities such as drug trafficking, substance abuse, and other unlawful behaviours. Understanding the underlying causes of youth delinquency is essential for designing effective interventions and operational resolutions to social problems. This research highlights key factors contributing to criminality among rural youth, with a particular focus on the socio-environmental context of Bisho, Kwatyutyu. Addressing this pastoral challenge requires collaboration among clergy, faith communities, and stakeholders, emphasizing their responsibility to nurture children as gifts from God. Delinquent behaviours, including truancy, drug use, violence, property crimes, and interactions with the criminal justice system, were analysed using regression models to assess their impact on educational and occupational outcomes. Findings reveal that youth delinquency significantly hinders educational attainment for both males and females, even after controlling for standard status attainment variables. Furthermore, while delinquency consistently affects male occupational outcomes, its impact on female occupational outcomes is comparatively weaker. The study underscores the importance of examining successful intervention programs from similar contexts to inform strategies aimed at mitigating youth delinquency in rural settings. Insights gained from the study, contribute to a deeper understanding of the factors shaping delinquent behaviour and inform policies aimed at fostering positive youth development.
Clinician and patient views on antiretroviral treatment integration in primary health care clinics, Tshwane, South Africa
(University of Pretoria, 2014) Hendricks, S.J.H. (Stephen); Bergh, Anne-Marie; stephen.hendriks@up.ac.za; Mathibe, Maphuthego Deliah
Background: Primary health care (PHC) clinicians and patients are major role players in the South African antiretroviral treatment programme. Understanding their perceptions of integrated care and the management of people living with HIV/AIDS in PHC facilities is necessary for successful implementation and sustainability. Objective: This study explored clinician and patient perceptions of integration of antiretroviral treatment in PHC clinics. Method: An exploratory, qualitative design was used. Four City of Tshwane PHC facilities were purposively selected, two urban and two rural. A self-administered questionnaire was distributed to 35 clinicians and four focus group interviews were conducted with HIV patients. Results: Models of care implemented were: full integration; partial integration; and separate services. Workload, staff development and support for integration affected clinicians’ performance and viewpoints. Promotion of privacy, reduced discrimination and increased access to comprehensive care were perceived as benefits of service integration and delays, poor patient care and patient dissatisfaction as negative aspects. In three facilities patients were satisfied with integration or semi-integration and felt common queues prevented stigma and discrimination, while the reverse was true in separate services. Single-month issuance of antiretroviral drugs and clinic schedule organisation were viewed negatively, as well as staff attitudes, poor communication and long waiting times. Conclusion: Integration of ART service in primary health services improved accessibility of the comprehensive service packages and coverage. The fully integrated model shared resources and had equitable work distribution amongst clinicians.
Genetic algorithm with temporal logic for automated markers
(University of Pretoria, 2025-07) Bosman, Anna S.; Marshall, Linda; Nils, Timm; u19089296@tuks.co.za; Redelinghuys, Francois Jacobus
Automated assessment is essential for large-scale programming courses, as it addresses the challenges of evaluating correctness and providing feedback efficiently. Traditional methods of automated assessment rely on hand-crafted test cases, which are time-intensive and lack scalability. Automated test generation methods, such as random input generation or genetic algorithms combined with code coverage metrics, offer alternatives, but often fail to capture the complexity required for educational assessments. To address this, a novel approach that integrates genetic algorithms with linear temporal logic (LTL) formulae is proposed. LTL properties, commonly used in model checking, formalise correctness criteria for programming assignments. The proposed method evolves test cases designed to maximise violations of the LTL properties in student submissions, determining correctness and generating personalised feedback by providing examples of failing test cases. Experiments \replaced{were}{are} conducted to evaluate the approach in terms of sensitivity to hyperparameter settings, and effectiveness relative to the established techniques, such as random input generation and code coverage-based genetic algorithms. Results demonstrate that combining genetic algorithms with LTL properties enhances automated assessment accuracy and feedback quality, offering a solution to the problems faced by automated assessment in large educational settings for both students and lecturers.
Peace mediation : the role of John 7:53–8:11 for possible conflict management in reformed churches in northwest region of Cameroon
(University of Pretoria, 2025-04) Hombana, Mphumezi; rogertem1@gmail.com; Tem, Roger M.
No abstract
Sabbatian influences on the Chassidic and Mitnagdic movements : an excursion into messianic Kabbalah and its disseminators in the aftermath of Shabbatai Tzvi
(University of Pretoria, 2024-08-30) Human, Dirk J.; baalshem@global.co.za; Michal, Gavin
This study hypothesises that as a result of a thorough analysis of the context and content of rabbinic texts, including the known associations of their authors − spanning the periods of Shabbatai Tzvi, the Baal Shem Tov and the Vilna Gaon − the conclusion can be reasonably drawn that the Chassidic and Mitnagdic movements had been fundamentally subjected to multiple Sabbatian influences and that a causal doctrinal and rabbinic link between Sabbatianism and both the Chassidic and Mitnagdic movements can be demonstrated.
Redefining the church's mission : towards a contextual and missional ecclesiology in responding to poverty in South Africa
(University of Pretoria, 2024-09) Dreyer, Willem Akkerhuys (Wim); bernardprinsloo@yahoo.com; Prinsloo, Christoffel Bernardus
This research critically examines the transformative potential of adopting a contextual and missional ecclesiology to enhance the Nederduitsch Hervormde Kerk van Afrika's (NHKA) engagement with poverty alleviation in South Africa. Against the country’s severe socio-economic challenges, the study seeks to redefine the church's mission in addressing this pervasive issue more effectively. Central to this investigation is the hypothesis that a shift towards missional ecclesiology – rooted in the Trinitarian mission of God - can significantly empower the NHKA to respond more effectively to poverty. This approach calls for moving beyond traditional ecclesiology models to embrace responsive, contextually informed practices that align with the missio Dei. The research integrates historical reflections on the NHKA's involvement in poverty alleviation, theoretical explorations of missional ecclesiology, and practical considerations for the church's societal engagement. It aims to bridge the gap between ecclesiological theory and the practical realities of addressing socio-economic challenges in contemporary South Africa. Key concepts such as missional ecclesiology, diaconal ministry, and contextual theology are foundational to understanding the proposed shift in the NHKA’s approach to its mission. The study posits that by re-envisioning its mission and practices in light of these concepts, the NHKA—and other ecclesial bodies—can significantly enhance their impact on poverty alleviation. Ultimately, this research contributes to the broader ecclesiology and social engagement discourse in South Africa. It highlights the church's potential as a transformative force in society, emphasising the importance of theological reflection, historical awareness, and actionable strategies in driving its mission forward. This thesis advocates for a missional reorientation of the church’s role in society, suggesting that deeper engagement with the gospel's transformative power can lead to more effective responses to the urgent challenge of poverty in South Africa.

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