Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2018 / Newly developed mandarin selection ―M37‖ has the potential to become a future export soft citrus cultivar. However, the selection is highly susceptible to chilling injury, which normally reduces post-storage quality and marketability of citrus fruit. Silicon (Si), applied at post-harvest as potassium silicate (K2SiO3), has potential to mitigate against chilling injury. So far, the effect of Si on ―M37‖ mandarin chilling susceptibility is unknown. Therefore, the aim of the study was to investigate the effect of cold storage temperature and postharvest potassium silicate dips on the chilling susceptibility and physico-chemical properties of new mandarin selection ―M37‖ fruit. The experiment was carried out in a factorial, arranged in a completely randomised design (CRD) with three replicates. Treatment factors were: 2 x cold storage temperature (-0.6±1 and 4.5 ±1°C) and 4 x potassium silicate concentration (0, 50, 100 and 150 mL L-1 K2SiO3). Fruit were dipped in different potassium silicate solutions (0, 50, 100 and 150 mL L-1) for 30 minutes, air dried, waxed; and thereafter, stored for 28 days at -0.6 and 4.5°C with 85-90% relative humidity. After withdrawal from cold storage, fruit were held at ambient temperature (±23°C) for 7 days (shelf-life); during shelf-life fruit were evaluated for chilling injury, physical properties (weight loss and firmness loss) and biochemical properties (electrolyte leakage, total soluble acids (TSS), titratable acids (TA) and TSS: TA ratio). The results showed that fruit were highly susceptible to chilling injury after storage at 0.6°C when compared with 4.5°C. However, treating fruit with postharvest potassium silicate dips improved their chilling susceptibility, especially with 50 and 100 mL L-1 K2SiO3 concentrations. Electrolyte leakage was lower for fruit treated with K2SiO3 compared to the control across all the storage temperatures. Although, ―M37‖ fruit stored at 4.5°C showed higher weight loss, firmness loss, TSS and TSS: TA ratio when compared with -0.6°C storage. Fruit firmness increased with the increase in potassium silicate concentrations during storage at -0.6 and 4.5°C; with the highest firmness loss occurring on fruit treated with 150 mL L-1 than control. Similarly, TSS increased concomitant with K2SiO3 concentration. Although, TA decreased with increasing K2SiO3 concentrations for fruit stored at 4.5°C; resulting in higher TSS: TA ratio. In conclusion, postharvest silicon dips effectively improved the storability of ―M37‖ mandarin fruit, preserved quality and extended the cold storage period. xi Keywords: Biochemical properties; Chilling injury; Firmness loss; Potassium silicate dips; Weight loss / Agricultural Research Council (ARC-LNR) and National Research Fund (NRF)

La tesis doctoral presenta un nuevo método de detección y análisis de eventos en la tensión de suministro de energía eléctrica que utiliza simultáneamente el análisis wavelet y un filtro de Kalman extendido actuando en paralelo sobre las muestras de la tensión. El análisis wavelet proporciona la mejor precisión en la determinación de las características temporales del evento y el filtro de Kalman extendido permite, por un lado confirmar la existencia del evento, descartando aquellas detecciones erróneas que puede producir el análisis wavelet debido a su muy alta sensibilidad, así como determinar con la mayor exactitud la magnitud y fase de la tensión durante el evento.El método desarrollado se ha implementado un tiempo real sobre un sistema DSP, de forma que se adquieren las muestras de la tensión y se analizan sus valores dentro del intervalo de muestreo, para poder detectar y analizar eventos en el menor tiempo posible y poder desarrollar estrategias de protección de los distintos equipos conectados a la red de distribución / The thesis presents a new method for detection and analysis of voltage events in power systems using wavelet analysis and an extended Kalman filter acting in parallel on the voltage samples. The wavelet analysis provides the best estimation of the time-related parameters of the voltage event and the extended Kalman filter enables, on the one hand the confirmation of the beginning and the end of the voltage event, avoiding the erroneous detections that can be produced due to the very high sensitivity of the wavelet analysis, and on the other hand, the estimation of the magnitude and phase angle of voltage supply during the event. The method proposed has been implemented in a DSP-based system, where the voltage samples are analyzed within the sampling period for real-time detection of voltage events.

Study of Production Drifts Stability and Assessment of Reinforcement Requirements at LKAB Konsuln Test-Mine Levels 436 and 486 Using Geologic Structures Data, and Modelling Software - Dips and Unwedge:  a Part of dp1 Project (Mine Layout and Technology) of the Sustainable Underground Mining (Sum) Project Oludare Joseph Olufe Global population has been on exponential increase over the past half century. The population explosion is driving massive urbanization and infrastructure developments across the globe, which result in huge demand for metals, especially steel. The trend is forecasted to continue to rise steeply in for the next two decades. This is putting enormous strain on metals mining, especially because new surface economic deposits are rare to come by. Therefore, mining is steadily going deeper in many of the mining destinations across the world.     Mining at great depths present unique challenges, particularly regarding stability of excavations at depths. Rock falls, rock burst, excavation collapse are common occurrences associated with deep mining. In regions with high seismicity potentials the frequency and consequences could be very high. Over the past decade ground instability has become a significant challenge confronting mining at LKAB deep mines. There had been incidents that resulted in long term closure of sections of the mines, with resultant adverse economic impacts. More undesirable is loss of live of personnel.     The study was conducted at the Konsuln test mine levels 436 and 486, aimed to investigate the impacts of geologic structures on excavations instability at depths, at the Kiruna iron ore mines, on one hand.  And on the other hand, evaluate the influence of geologic structures on ground reinforcements at the mine. Structural data were collected and analysed using Dips program to define orientation of major structures. The results were used for wedge analysis and excavations stability modelling using Unwedge program. Important rock mechanical parameters were defined based on data provided, and others based on literatures. A design factor of safety of 1.5 was used.     Results from the study established that structures have significant impact on excavations instability at the Konsuln mine. 100% of the production drifts studied has minimum of four wedges formed in its perimeters. Out of this approximately 37% has factor of safety lower than 1.5. Evaluation of reinforcements (shotcrete and rock bolts) implemented in the mine found that approximately 15% of the total wedges formed in the production drifts has factor of safety less that 1.5 after both shotcrete and rock bolt reinforcements had been implement. Also, approximately 5% of the total wedges has apex height longer the rock bolt length.     It was therefore concluded that structurally induced instability is a major contributor to excavations instability at the Kiruna mine. The study approach presented a new methodology to understand and provide robust solution to ground instability problem at the mine.

This diploma thesis deals with evaluation of voltage events regarding to immunity of electric appliances. This thesis is divided into three logical sections. In the first part are shown the voltage events, their definitions, causes and spreading in the mains. The second part deals with measurements and existing possibilities of evaluation of voltage events. The third part deals with suggestion of new evaluation of voltage events regarding to immunity of electric appliances and verification in practice.

Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / Cold storage is commonly used to prolong papaya fruit storability. Furthermore, the optimal recommended storage temperature is below 10℃ for export and distant market. However, chilling injury (CI) occurs at 10℃ or lower during prolonged cold storage. This condition hampered consumer acceptance, resulting in economic losses for producers and exporters. Therefore, the study aimed to investigate the potential of postharvest polyamine dips and storage conditions to improve the quality and shelf life of ‘Solo’ papaya fruit. The experiment was conducted as 4 x 2 factorial arranged in a completely randomised design (CRD) with eight replications. The fruits were treated with putrescine (PUT) (0 (control), 1, 2 and 3 mM) before storage for 21 days at 7.5 and 13℃ plus 5 days storage at ambient temperature. Additionally, the PUT effect on quality attributes and shelf-life were studied. The results showed that physiological and pathological disorders increased with progressive storage, irrespective of storage temperature. However, PUT treatment reduced the incidence of chilling injury and anthracnose at both 7.5 and 13℃. Additionally, the interaction of treatment and cold storage temperature significantly affected ‘Solo’ papaya fruit physical and biochemical quality attributes. Furthermore, treatment with 2 and 3 mM PUT concentration reduced changes in colour, mass, firmness, TA, and TSS compared to control. In conclusion, postharvest PUT improved ‘Solo’ papaya fruit quality and prolonged shelf-life. / AgriSETA (Agricultural Sector Training Authority)

This thesis explores the feasibility of developing an affordable and easy-to-use feed- back system that leverages information from multiple inertial measurement units (IMUs) to identify mistakes during upper body bodyweight training and provide real-time feedback to the user. To develop the system, a human-centered approach was used, which involved conducting semi-structured interviews with movement ex- perts and a workshop with targeted end-users to understand their needs. The study also involved 12 volunteers who performed push-ups, tricep dips, and planks cor- rectly and then made specific mistakes intentionally while wearing five IMUs. Binary and multiclass classifiers were developed to classify the exercise technique. The re- sults showed that personalized multiclass classifiers produced good to excellent quality results, while global classification techniques performed poorly. Additionally, an increased number of sensors did not always lead to improved classification re- sults, and the placement of the sensors could have a significant impact. The user in- put and evaluation of the feedback system pinpointed the need for customization and accessibility in the design. This thesis contributes to the development of a feedback system that can help users identify mistakes in their upper body bodyweight exer- cises and improve their form and technique. / Denna avhandling utforskar genomförbarheten att utveckla ett prisvärt och lättan- vänt feedbacksystem som utnyttjar information från flera inertiella mätenheter (IMU: er) för att identifiera misstag under överkroppsövningar med egen kroppsvikt och ge användaren realtidsfeedback. För att utveckla systemet användes en human- centrerad metod, som innefattade semistrukturerade intervjuer med rörelseexperter och en workshop med målinriktade slutanvändare för att förstå deras behov. Studien inkluderade också 12 frivilliga som utförde armhävningar, tricep dips och plankor korrekt och sedan medvetet gjorde specifika misstag medan de bar på fem IMU: er. Binära och flerklassklassificerare utvecklades för att klassificera övningstekniken. Resultaten visade att personliga flerklassklassificerare producerade bra till utmärkta resultat, medan globala klassificeringstekniker presterade dåligt. Dessutom ledde ett ökat antal sensorer inte alltid till förbättrade klassificeringsresultat, och placeringen av sensorerna kunde ha en betydande påverkan. Användarinput och utvärdering av feedbacksystemet pekade på behovet av anpassning och tillgänglighet i designen. Denna avhandling bidrar till utvecklingen av ett feedbacksystem som kan hjälpa an- vändare att identifiera misstag i sina överkroppsövningar med egen kroppsvikt och förbättra sin form och teknik.

Esta pesquisa apresenta um estudo da resposta dinâmica dos motores de indução trifásicos submetidos a afundamentos de tensão. As simulações computacionais sobre um sistema de distribuição, assim como a modelagem dos motores de indução trifásicos baseada em dados reais, foram realizadas utilizando-se do software ATP (Alternative Transients Program). Estas tiveram por objetivo gerar situações representativas da operação do sistema elétrico de potência (SEP), caracterizando afundamentos de tensão, fenômenos estes pertencentes à classe de variações de tensão de curta duração (VTCD), no contexto da qualidade da energia elétrica (QEE). Da observação destes afundamentos, verificaram-se as situações que vieram ou não, a comprometer a alimentação do equipamento analisado e, conseqüentemente, seu desempenho. Pelos resultados observados, evidencia-se que a metodologia de análise aplicada é satisfatória e condizente com o encontrado em situações reais de operação dos motores de indução trifásicos, denotando certas características intrínsecas no contexto das VTCDs. / This research shows a study on the dynamic response of three-phase induction motors submitted to voltage sags. Computer simulations about a distribution system, as well as the modeling of three-phase induction motors based on actual data, were made using ATP (Alternative Transients Program) software. These simulations intended to generate representative situations of the electrical power system (EPS) operation, characterizing voltage sags, which is a phenomenon belonging to the class of short duration voltage variations (SDVV), in the electrical power quality context (EPQ). From the observation of these sags, we verified the situations that jeopardized or not the supply of the analyzed equipment and, consequently, its performance. From the observed results, it becomes evident that the methodology of the applied analysis is satisfactory and in agreement with the one found in actual situations of three-phase induction motors operations, indicating certain characteristics intrinsic to the SDVV context.

Esta pesquisa apresenta um estudo da resposta dinâmica dos motores de indução trifásicos submetidos a afundamentos de tensão. As simulações computacionais sobre um sistema de distribuição, assim como a modelagem dos motores de indução trifásicos baseada em dados reais, foram realizadas utilizando-se do software ATP (Alternative Transients Program). Estas tiveram por objetivo gerar situações representativas da operação do sistema elétrico de potência (SEP), caracterizando afundamentos de tensão, fenômenos estes pertencentes à classe de variações de tensão de curta duração (VTCD), no contexto da qualidade da energia elétrica (QEE). Da observação destes afundamentos, verificaram-se as situações que vieram ou não, a comprometer a alimentação do equipamento analisado e, conseqüentemente, seu desempenho. Pelos resultados observados, evidencia-se que a metodologia de análise aplicada é satisfatória e condizente com o encontrado em situações reais de operação dos motores de indução trifásicos, denotando certas características intrínsecas no contexto das VTCDs. / This research shows a study on the dynamic response of three-phase induction motors submitted to voltage sags. Computer simulations about a distribution system, as well as the modeling of three-phase induction motors based on actual data, were made using ATP (Alternative Transients Program) software. These simulations intended to generate representative situations of the electrical power system (EPS) operation, characterizing voltage sags, which is a phenomenon belonging to the class of short duration voltage variations (SDVV), in the electrical power quality context (EPQ). From the observation of these sags, we verified the situations that jeopardized or not the supply of the analyzed equipment and, consequently, its performance. From the observed results, it becomes evident that the methodology of the applied analysis is satisfactory and in agreement with the one found in actual situations of three-phase induction motors operations, indicating certain characteristics intrinsic to the SDVV context.

Recognition that the bioavailability of soil As (As) is influenced by its soil dynamics has initiated research into development of more accurate, site-specific soil guideline values, departing from the assumption that the total soil As content is bioavailable. With the aim of deriving predictive models, the relationship between soil properties and As bioavailability (bioaccessibility and phytotoxicity) was examined on a set of naturally contaminated sheep dip soils (n = 30). Sampled soils were extensively characterised, bioaccessibility was estimated through an in vitro procedure, and soil As toxicity and availability to plants were evaluated using an early growth wheat bioassay. The in vitro bioaccessibility was consistently less than the total soil As content. Arsenic bioaccessibility was negatively correlated to soil iron (Fe), manganese (Mn) and aluminium (Al) contents, and it was positively related to the soil As loading. The in vitro extractable soil As concentrations were successfully modelled using linear combinations of soil As content, soil Fe and Mn determinations and soil pH. Differences in As phytotoxicity, expressed in terms of effective toxic concentration (EC50), between soils were directly related to soil Fe, Mn and Al contents. Available soil phosphorous (P) exerted an ameliorating effect on As toxicity, with the available soil As/P ratio representing the single best predictor of plant growth suppression. Plant P nutrition appeared to influence the relative selectivity for As and P by wheat, with greater selectivity for P demonstrated under P deficient conditions. Plant As uptake, its distribution, and also the plant nutrient status were all adversely affected by increasing soil As exposure. Co-contamination by Zn corresponded to a substantial elevation in proportion of the plant As allocated in shoots. Plant As levels exhibited a saturation-dependent relationship with increasing soil As. The best linear predictors of plant As levels in the non-toxic range were RHIZO-extractable and effective soil As concentrations, the latter based on the diffusive gradients in thin films (DGT) technique. Despite the complexity of soil As dynamics, large proportions in the variances exhibited by the two measures of bioavailability were explained using a small set of readily-available soil properties.

This thesis describes an investigation into the influences of arcing and conductor deflection due to magnetic forces on the accuracy of fault locator algorithms in electrical distribution networks. The work also explores the possibilities of using the properties of an arc to identify two specific types of faults that may occur on an overhead distribution line. A new technique using the convolution operator is introduced for deriving differential equation algorithms. The first algorithm was derived by estimating the voltage as an array of impulse functions while the second algorithm was derived using a piecewise linear voltage signal. These algorithms were tested on a simulated single-phase circuit using a PI-model line. It was shown that the second algorithm gave identical results as the existing dynamic integration operator type algorithm. The first algorithm used a transformation to a three-phase circuit that did not require any matrix calculations as an equivalent sequence component circuit is utilised for a single-phase to ground fault. A simulated arc was used to test the influence of the non-linearity of an arc on the accuracy of this algorithm. The simulations showed that the variation in the resistance due to arcing causes large oscillations of the algorithm output and a 40th order mean filter was used to increase the accuracy and stability of the algorithm. The same tests were performed on a previously developed fault locator algorithm that includes a square-wave power frequency proximation of the fault arc. This algorithm gave more accurate and stable results even with large arc length variations. During phase-to-phase fault conditions, two opposing magnetic fields force the conductors outwards away from each other and this movement causes a change in the total inductance of the line. A three dimensional finite element line model based on standard wave equations but incorporating magnetic forces was used to evaluate this phenomenon. The results show that appreciable errors in the distance estimations can be expected especially on poorly tensioned di stribution lines.New techniques were also explored that are based on identification of the fault arc. Two methods were successfully tested on simulated networks to identify a breakingconductor. The methods are based on the rate of increase in arc length during the breaking of the conductor. The first method uses arc voltage increase as the basis of the detection while the second method make use of the increase in the non-linearity of the network resistance to identify a breaking conductor. An unsuccessful attempt was made to identifying conductor clashing caused by high winds: it was found that too many parameters influence the separation speed of the two conductors. No unique characteristic could be found to identify the conductor clashing using the speed of conductor separation. The existing algorithm was also used to estimate the voltage in a distribution network during a fault for power quality monitoring purposes.