This research has been conducted in order to develop a short-range ensemble numerical weather prediction system over southern Africa using the Conformal-Cubic Atmospheric Model (CCAM). An ensemble prediction system (EPS) combines several individual weather model setups into an average forecast system where each member contributes to the final weather forecast. Four different EPSs were configured and rainfall forecasts simulated for seven days ahead for the summer months of January and February, 2009 and 2010, for high (15 km) and low (50 km) resolution over the southern African domain. Statistical analysis was performed on the forecasts so as to determine which EPS was the most skilful at simulating rainfall. Measurements that were used to determine the skill of the EPSs were: reliability diagrams, relative operating characteristics, the Brier skill score and the root mean square error. The results show that the largest ensemble is consistently the most skilful for all forecasts for both the high and the low resolution cases. The higher resolution forecasts were also seen to be more skilful than the forecasts made at the low resolution. These findings conclude that the largest ensemble at high resolution is the best system to predict rainfall over southern Africa using the CCAM. / Dissertation (MSc)--University of Pretoria, 2014. / gm2014 / Geography, Geoinformatics and Meteorology / unrestricted

Dans le cadre des recherches sur l'aval du cycle du combustible et des projets de transmutation de l'américium, un procédé innovant de fabrication de Couvertures Chargées en Américium (CCAm) a été développé. Ce procédé, intitulé CRMP (Calcined Resin Microsphere Pelletization), vise la fabrication de pastilles d'oxyde mixte uranium-américium par une voie non conventionnelle de métallurgie des sphérules. Il consiste à produire des pastilles par pressage et frittage de précurseurs d'oxyde sous la forme de microsphères millimétriques obtenues par minéralisation de perles de résines échangeuses d'ions chargées en cations uranium et américium. L'avantage d'un tel procédé par rapport à la métallurgie conventionnelle des poudres est de s'affranchir de la problématique des fines particules disséminantes et contaminantes et de faciliter les opérations de transfert de matière lors de la phase de mise en forme. Le procédé a d'abord été optimisé et validé pour la production de pastilles d'oxyde de cérium. Des pastilles d'oxyde d'uranium de microstructure contrôlée, dense ou poreuse, ont ensuite été produites dans le but de répondre aux spécifications envisagées pour les CCAm. Dans une troisième phase, le procédé a été appliqué avec succès à la synthèse de microsphères d'oxydes mixtes monophasés de type U1-xCexO2±δ (0,1≤x≤0,3) qui ont servi à l'élaboration de pastilles de céramiques d'oxydes mixtes. La faisabilité technique du procédé CRMP a été finalement validée à l'échelle d'une pastille U0,9Am0,1O2±δ de microstructure homogène et de densité égale à 95 % de la densité théorique. / In the framework of research on the back-end of the nuclear fuel cycle, and notably projects on transmutation of americium (Am), an innovative manufacturing process of Minor Actinides Bearing Blanket (MABB) has been developed.This process, called CRMP (Calcined Resin Microsphere Pelletization), consists in the production of mixed uranium-americium oxide pellets by a non-conventional route involving microspheres. Pellets are produced by pressing and sintering oxide precursors in the form of millimetric beads obtained by mineralization of ion exchange resin loaded with uranium and americium cations. The advantage of such a process compared to conventional powder metallurgy is to overcome the problem of the handling of very fine powders.The method was first validated and optimized for the production of ceria pellets. Then uranium dioxide pellets with tailored microstructure (dense or porous) were produced in order to reach the required specifications for MABB. In a third phase, the process has been applied to the synthesis of single-phase mixed oxide microspheres composed of U1-xCexO2±δ (0.1 ≤ x ≤ 0.3) and U0;9Am0.1O2±δ. The technical feasibility of CRMP process has been validated for the production of dense mixed oxide pellets by pressing and sintering these microspheres. A U0, 9Am0,1O2±δ pellet with homogeneous microstructure with a density equals to 95 % of theoretical density was successfully produced using CRMP process.

The frightful statistics regarding road accidents draws a dreadful picture for individuals, communities, and nations across the globe. The number of fatalities exceeds a million every year. To address this issue, an initiative called Vision Zero was introduced first in Sweden 1997. The goal is to reach zero road fatalities and severe injuries by 2045. However, to achieve this goal, Vision Zero is being divided in 4 categories, called Days. Day 4 represents fully automated, cooperative, and connected mobility (CCAM). Now, one of the typical cases that causes road accidents is overtaking. CCAM is a way to enhance safety in such cases. Therefore, this thesis proposes a system that is based on Vehicle-to-Vehicle (V2V) communication where vehicles exchange their intentions and cooperatively perform overtaking manoeuvres. The prevalent approach nowadays is depending on the vehicles’ onboard sensors only, blocking it from having knowledge about the intentions of other actors. Thus, it prevents vehicles from cooperation and coordination. We evaluate the performance of our approach and compare it against the sensors only approach. We show that the proposed approach outperforms the prevalent one in performance. Therefore, vehicle communication must be considered in the upcoming mobility for higher accuracy and safety. / Den skrämmande statistiken angående trafikolyckor tecknar en fruktansvärd bild för individer, samhällen och nationer över världen. Antalet dödsfall överstiger en miljon varje år. Ett initiativ som kallas Vision Zero introducerades i Sverige 1997, vars syfte är att ta itu med detta problem. Målet är att nå noll trafik dödsfall, och allvarliga skador år 2045. För att verkställa det målet, Vision Zero delades in i 4 kategorier, som kallas för Dagar. Dag 4 representerar fullt automatiserad, kooperativ och kommunikativ mobilitet (CCAM). Ett av det vanligaste fallen som orsaker trafikolyckor är omkörningar. CCAM är ett sätt att förbättra säkerheten i sådana fall. Därför presenterar denna avhandling ett system som bygger på fordon-till-fordon (Vehicle-to-Vehicle V2V) kommunikation. Detta system tillåter fordon att utbyta avsikter för att samarbeta och utföra säkra omkörningar. Den ledande teknologin nuförtiden beror enbart av fordonens sensorer, vilket hindrar dem från att ha kunskap om andra aktörers avsikter. Därmed hindrar det dem från att samarbeta. Vi utvärderar prestandan av vårt system och jämför det med den ledande teknologin. Vi visar att vårt system är överlägsen det ledande sättet (dvs. enbart sensorer) i prestanda. Därför måste fordon kommunikation tas hänsyn till i kommande mobilitet för högre noggrannhet och säkerhet.

With the growing number of vehicles on the road, improving traffic safety and efficiency has become a major challenge. One of the promising solutions is the implementation of Intelligent Transportation Systems (ITS), which utilizes communication technologies to facilitate real-time information sharing between vehicles and infrastructure. This research aims to contribute to the field of Intelligent Transportation Systems (ITS) improving traffic safety and efficiency achieving the Vision Zero goal. In this thesis, we focus on the performance analysis of two communication protocols used for two signal dissemination techniques for IVI (infrastructure-vehicle-information communication). Periodic, which sends signals at fixed intervals, and On-demand which sends signals upon request from road users. The results of our experiments showed that there are trade-offs between the periodic and on-demand approaches in V2I communications. The on-demand approach performs better in terms of PER (Packet error ratio), but it results in higher latency, even with low congestion. On the other hand, the periodic approach exhibits higher PDR (Packet delivery ratio) but suffers from inefficiencies due to the transmission of redundant messages resulting in higher PER. Our findings have implications for the scalability of V2I communications and can be translatable to other access technologies used in ITS.

MENVSC (Climatology) / Department of Geography and Geo-Information Sciences / Heat waves are warm extreme temperature events that have environmental and socio-economic impacts in many regions across the world. Negative impacts of warm extreme temperatures over South Africa necessitate the need to study the nature of heat waves. Observations and satellite datasets are analysed in the investigation of the nature and trends of heat waves over South Africa in the present (1983-2012) and future (2010-2039, 2040-2069, 2070-2099) climates. Case study and composite analysis of National Centers for Environmental Prediction datasets were done using the Grids Analysis and Display Systems to get an in-depth understanding of the structure of heat waves in South Africa. Future climate model output obtained from the Conformal Cubic Atmospheric Model was used for future heat wave trends in South Africa. The simulations were made using the Representative Concentration Pathways 4.5 and 8.5. Heat waves are unusual events in the present climate (1983-2012) over much of the country, with 20 of the selected 24 stations experiencing an average of less than one heat wave per season. Heat waves are also more frequent and last longer during warm phase of El Niño-Southern Oscillation (ENSO) than in cool phase of ENSO with the north-east being the most prone region. Composite analysis of 500 hPa omega indicates subsidence over the interior of South Africa in both phases of ENSO. Heat waves in South Africa are localized and associated with a middle level high pressure system that persists over the interior inducing anticyclonic flow and subsidence. The anticyclonic circulation over a region experiencing heat wave weakens with decreasing height over land areas which may be due to frictional forces at the surface and the high is placed further south-east at the surface. Advection of dry continental northerly winds also contributes to high maximum temperatures during heat waves in the interior. Maximum temperatures are expected to increase drastically from the present-day climate to the 2070 – 2099 period, with an average increment of about 8°C during DJF in much of the central interior. As a result, heat wave occurrences are expected to be higher in the future warmer climates when climate change signal is higher. Most increases are expected for heat waves lasting for a week than those lasting for over 2 weeks. CCAM outputs also indicated that heat waves in South Africa are expected to last longer and become more intense during the future warmer climates. Longer lasting and more intense heat waves are expected over the Karoo than in other parts of the country.