X-ray CT based baggage scanners are widely used in security applications. Recently, there has been increased interest in view-limited systems which can improve the scanning throughput while maintaining the threat detection performance. However as very few view angles are acquired in these systems, the image reconstruction problem is challenging. Standard reconstruction algorithms such as the filtered backprojection create strong artifacts when working with view-limited data. In this work, we study the performance of a variety of reconstruction algorithms for both single and multi-energy view-limited systems.

Magister Artium - MA / This mini-thesis seeks to interrogate the interplay between memory and documentation in the process of exhibition-making by a looking at the preparation for and mounting of the exhibition, Museum. This will be achieved by looking at the institutional methodologies employed by the Museum in dealing with ex-residents of District Six, their memories and artefacts in the heritage practice of a Museum as a forum. This practice was put into effect as the District Six Museum engaged ex-residents of other locations of removal.

The dawn of democracy in 1994 brought hope to South Africans particularly those who had been previously disadvantaged as a result of apartheid policies. This new hope was premised on a vision of creating a people-centred society and a better life for all expressed in the Reconstruction and Development Programme (RDP) whose goals were to eliminate poverty and inequalities of the decades of apartheid. In order to meet this vision the RDP made explicit reference to building the capacity of civil society through extensive development of human resource. It provided a central role for nonprofit organizations. A vibrant and diverse civil society is important in consolidating and sustaining democracy as well as in holding government accountable. Since 1994 government has involved civil society in various stages of policy development aimed at alleviating poverty. This study therefore evaluates the extent to which programmes implemented by civil society, particularly in partnership with Social Development, are participative, empowering, effective and sustainable. This research indicates that civil society, have succeeded in mobilizing communities to take charge of their own development. This has been achieved through activities like needs and beneficiary identification, project implementation and fund raising. Despite this success the study shows that civil society experience challenges in ensuring that their programmes are effective and sustainable. These challenges include limited funding, lack of various skills including management skills, organizational skills, resource mobilization and accountability. The study contends that civil society has a critical role in implementing poverty alleviation programmes and in occupying space between the state and the community. In order to ensure long lasting impact of programmes, there is a great need for strengthening the organizational, management and administrative capacity of civil society. It is generally accepted that local organization capacity is recognized as key for development effectiveness and empowerment of the poor. / Thesis (PhD)--University of Pretoria, 2012. / School of Public Management and Administration (SPMA) / unrestricted

Concussions occur at an unacceptable rate in the sport of ice hockey. Efforts are made to improve its prevention by modifying protective equipment and implementing rules of conduct; yet the effectiveness of these methods remains unknown as there is a lack of evidence pointing to a mechanical metric able to adequately predict concussion. The purpose of this thesis was to identify metrics which best characterize concussion following ice hockey collisions and provide values reflecting concussion risk. The first study reported effective mass of shoulder checks, extended elbow strikes, and tucked-in elbow strikes using 15 competitive ice hockey players as subjects. The results were used to guide the impact mass and compliance of laboratory reconstructions of real-world ice hockey collisions done in the second study. Analysis of these reconstruction showed that concussions following shoulder and elbow to head collisions in ice hockey occurred at low peak linear and angular accelerations and that impulse duration played a large role in the mechanism of injury. The results also indicated that concussion risk estimations are specific to the mechanism of loading. A 50% likelihood of concussion following a shoulder check to the head was established for peak angular accelerations of 9.2, 6.9, 4.6, and 2.2 krad/s^2 for impulse durations of 15, 20, 25, and 30 ms, respectively. A 50% likelihood of concussion following an extended elbow to the head was established for peak linear accelerations of 23, 15, and 7 g for impulse durations of 15, 20, and 25 ms, respectively. Finally, the third study reported brain tissue stress and strain comparable to the ones obtained reconstructing concussive impacts in American football, rugby, and Australian rules football despite having lower peak linear and angular acceleration values. This thesis has provided a new sport concussion data set acquired using a methodology guided by the biomechanics of ice hockey player volunteer testing, has identified metrics which can adequately predict concussion, and has established concussion risk levels. This information will be of use to helmet manufacturing companies, companies developing concussion detection sensors, and governing bodies in their efforts to eliminate concussion from the sport of ice hockey.

A user using a Web application generates HTTP traffic which can be captured and logged to be used for further analysis such as finding potential security holes. This document provides a method to reconstruct user-interactions from HTTP network traffic with a specific focus on RIAs. The only input provided is the full, unaltered HTTP network traffic of the original user-session. This thesis presents a system to replay HTTP trace for reconstructing the user-interactions using a programmable Web browser that is used to simulate user's actions and to execute client-side scripts. The experimental results show that the proposed solution in this thesis leads to a system which has a good performance in reconstructing user-interactions. The system performs an automated reconstruction of the user-interactions which reconstructs every DOM state that has been visited by the user during the user-session and the actions taken by the user, including user-inputs provided by the user.

Dans le domaine de la vision par ordinateur, l’estimation de la structure d’une scène 3D à partir d’images 2D constitue un problème fondamental. Parmi les applications concernées par cette problématique, nous nous sommes intéressés dans le cadre de cette thèse à la modélisation d’un environnement urbain. Nous nous sommes intéressés à la reconstruction de scènes 3D à partir d’images monoculaires générées par un véhicule en mouvement. Ici, plusieurs défis se posent à travers les différentes étapes de la chaine de traitement inhérente à la reconstruction 3D. L’un de ces défis vient du fait de l’absence de zones suffisamment texturées dans certaines scènes urbaines, d’où une reconstruction 3D (un nuage de points 3D) trop éparse. De plus, du fait du mouvement du véhicule, d’une image à l’autre il n’y a pas toujours un recouvrement suffisant entre différentes vues consécutives d’une même scène. Dans ce contexte, et ce afin de lever les verrous ci-dessus mentionnés, nous proposons d’estimer, de reconstruire, la structure d’une scène 3D par morceaux en se basant sur une hypothèse de planéité. Nous proposons plusieurs améliorations à la chaine de traitement associée à la reconstruction 3D. D’abord, afin de structurer, de représenter, la scène sous la forme d’entités planes nous proposons une nouvelle méthode de reconstruction 3D, basée sur le regroupement de pixels similaires (superpixel segmentation), qui à travers une représentation multi-échelle pondérée fusionne les informations de couleur et de mouvement. Cette méthode est basée sur l’estimation de la probabilité de discontinuités locales aux frontières des régions calculées à partir du gradient (gradientbased boundary probability estimation). Afin de prendre en compte l’incertitude liée à l’estimation du mouvement, une pondération par morceaux est appliquée à chaque pixel en fonction de cette incertitude. Cette méthode génère des regroupements de pixels (superpixels) non contraints en termes de taille et de forme. Pour certaines applications, telle que la reconstruction 3D à partir d’une séquence d’images, des contraintes de taille sont nécessaires. Nous avons donc proposé une méthode qui intègre à l’algorithme SLIC (Simple Linear Iterative Clustering) l’information de mouvement. L’objectif étant d’obtenir une reconstruction 3D plus dense qui estime mieux la structure de la scène. Pour atteindre cet objectif, nous avons aussi introduit une nouvelle distance qui, en complément de l’information de mouvement et de données images, prend en compte la densité du nuage de points. Afin d’augmenter la densité du nuage de points utilisé pour reconstruire la structure de la scène sous la forme de surfaces planes, nous proposons une nouvelle approche qui mixte plusieurs méthodes d’appariement et une méthode de flot optique dense. Cette méthode est basée sur un système de pondération qui attribue un poids pré-calculé par apprentissage à chaque point reconstruit. L’objectif est de contrôler l’impact de ce système de pondération, autrement dit la qualité de la reconstruction, en fonction de la précision de la méthode d’appariement utilisée. Pour atteindre cet objectif, nous avons appliqué un processus des moindres carrés pondérés aux données reconstruites pondérées par les calculés par apprentissage, qui en complément de la segmentation par morceaux de la séquence d’images, permet une meilleure reconstruction de la structure de la scène sous la forme de surfaces planes. Nous avons également proposé un processus de gestion des discontinuités locales aux frontières de régions voisines dues à des occlusions (occlusion boundaries) qui favorise la coplanarité et la connectivité des régions connexes. L’ensemble des modèles proposés permet de générer une reconstruction 3D dense représentative à la réalité de la scène. La pertinence des modèles proposés a été étudiée et comparée à l’état de l’art. Plusieurs expérimentations ont été réalisées afin de démontrer, d’étayer, la validité de notre approche / In computer vision, the 3D structure estimation from 2D images remains a fundamental problem. One of the emergent applications is 3D urban modelling and mapping. Here, we are interested in street-level monocular 3D reconstruction from mobile vehicle. In this particular case, several challenges arise at different stages of the 3D reconstruction pipeline. Mainly, lacking textured areas in urban scenes produces low density reconstructed point cloud. Also, the continuous motion of the vehicle prevents having redundant views of the scene with short feature points lifetime. In this context, we adopt the piecewise planar 3D reconstruction where the planarity assumption overcomes the aforementioned challenges.In this thesis, we introduce several improvements to the 3D structure estimation pipeline. In particular, the planar piecewise scene representation and modelling. First, we propose a novel approach that aims at creating 3D geometry respecting superpixel segmentation, which is a gradient-based boundary probability estimation by fusing colour and flow information using weighted multi-layered model. A pixel-wise weighting is used in the fusion process which takes into account the uncertainty of the computed flow. This method produces non-constrained superpixels in terms of size and shape. For the applications that imply a constrained size superpixels, such as 3D reconstruction from an image sequence, we develop a flow based SLIC method to produce superpixels that are adapted to reconstructed points density for better planar structure fitting. This is achieved by the mean of new distance measure that takes into account an input density map, in addition to the flow and spatial information. To increase the density of the reconstructed point cloud used to performthe planar structure fitting, we propose a new approach that uses several matching methods and dense optical flow. A weighting scheme assigns a learned weight to each reconstructed point to control its impact to fitting the structure relative to the accuracy of the used matching method. Then, a weighted total least square model uses the reconstructed points and learned weights to fit a planar structure with the help of superpixel segmentation of the input image sequence. Moreover, themodel handles the occlusion boundaries between neighbouring scene patches to encourage connectivity and co-planarity to produce more realistic models. The final output is a complete dense visually appealing 3Dmodels. The validity of the proposed approaches has been substantiated by comprehensive experiments and comparisons with state-of-the-art methods

Cette thèse présente des outils de vidéo inpainting permettant de reconstruire de manière efficace les zones perdues d'une séquence vidéo. Deux catégories d'approches sont particulièrement étudiées. Dans une première étape les approches basées sur l'exemple sont considérées. Différentes contributions ont été proposées. Une application des méthodes de neighbor embedding pour l'approximation des pixels perdus dans un exemple est d'abord considérée en utilisant deux méthodes de réduction de dimensionnalité: la factorisation de matrice non négative (FMN) et le locally linear embedding (LLE). La méthode d'inpainting proposée a été ensuite adaptée à l'application de dissimulation d'erreurs en utilisant une étape de pré-traitement d'estimation des vecteurs de mouvement perdus. Une approche multisolution a également été considérée pour réduire la complexité. Les évaluations expérimentales de cette approche démontrent son efficacité dans les applications de suppression d'objets et de dissimulation des erreurs. Une deuxième catégorie de méthodes de vidéo inpaintinting a été par la suite étudiée en utilisant une approche basée sur l'optimisation globale d'une fonction d'énergie exprimant la cohérence spatio-temporelle de la région reconstruite. Enfin, le problème d'inpainting des vidéos capturées par des caméras en mouvement a été étudié. L'alignement des images en utilisant une homographie par région montre de meilleure performances que les méthodes classiques d'alignement par optimisation d'une homography par pixel. / This thesis presents video inpainting tools to efficiently recover space-time holes in different kinds of video sequences. Two categories of video inpainting approaches are particularly studied. The first category concerns exemplar-based approach. Several contributions have been proposed for this approach. Neighbor embedding techniques have been proposed for patch sampling using two data dimensionality reductions methods: non-negative matrix factorization (NMF) and locally linear embedding (LLE). An analysis of similarity metrics for patches matching have then been proposed based on both subjective and objective tests. The proposed framework have been also adapted to the error concealment application by using a preprocessing step of motion estimation. A multiresolution approach has been considered to reduce the computational time of the method. The experimental evaluations demonstrate the effectiveness of the proposed video inpainting approach in both object removal and error concealment applications. The video inpainting problem has been also solved using a second approach based on the optimization of a well-defined cost function expressing the global consistency of the recovered regions. The camera moving videos has later been takled by using a region-based homography. The neighboring frames in the sequence are aligned based on segmented planar regions. This method has been shown to give better performance compared to classical optimization-based homography.

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The Democratic Republic of Congo experienced a merciless war from 1998 to 2002 that seriously affected its labour market, as it did all other aspects of society. The effects on the labour market have aroused various debates. This thesis offers a first analysis of the reconstruction process of the labour market in post-war Congo, and of the roles that key actors involved played in it. It asks the following fundamental question: what are the processes involved in the reconstruction of the post-war Congolese labour market, and how did the main actors affect these processes? The research used a constructivist methodological approach and the extended case method to collect detailed data through field interviews conducted with 109 people in Kinshasa. The data suggest that the past of the Congolese labour market is clearly visible in its post-war recovery processes (2003–2018). While the past weighed heavily on the present, from 2003 to 2011 the Congolese government nevertheless delayed the implementation of reform policies aimed at achieving a functioning labour market. Reforms introduced since then have been blunted by poor implementation processes. Moreover, the inherent weakness of Congo’s labour market institutions deepened the lack of impact of the reconstruction attempts. Likewise, the private sector did not contribute substantially to efforts at creating an effective labour market. Entering this landscape, many Congolese employees struggled to achieve integration into the formal labour market. The main argument of this thesis is that the post-war Congolese labour market has experienced an extended reconstruction due to delayed and poorly implemented labour market policies. On a more positive note, this study demonstrates the usefulness of Peck’s theory of labour market social regulation as an efficient theoretical tool in evaluating a problematic transition such as that experienced in the Democratic Republic of Congo. / Thesis (PhD (Sociology))--University of Pretoria, 2020. / the Andrew J. Mellon Foundation / The University of Pretoria, the Faculty of Humanities / Sociology / PhD (Sociology) / Unrestricted

Philosophiae Doctor - PhD / South Africa's health transformation blueprint is designed to replace apartheid's inequities and instill instead a new utilitarian approach by the health care sector. This study gives attention to the medical gaze and the body in hospitalisation. At macropolitical level the study focuses on the ways in which the new health policy impacted on power relations and multi-levelled subject positions of medical and nursing staff, as well as on patients in a hierarchy of spaces such as in the wards, in the institution and at a national level, in terms of policy implementation and the reconstruction of the health care services. It shows that policy and institutional discourses and arrangements were embedded in a regime of visuality which discursively homogenised people from different cultural realities. Yet, at the same time biases related to constructions of bodies in relation to class, age, gender and 'value' continued to exist. At the level of hospital protocols and structure the thesis examines the social, political and conceptual frameworks that conveyed, allowed or disallowed particular meaning to the institution. It describes the formal, dominant discourses and processes in the wards and show how these impacted on everyday interaction and relations of power, autonomy, authority, conflict and resistance. The study shows that for patients there often was a disjuncture between policy and practice, as biomedical practitioners and policy makers struggled to define the scope and implementation of health care services in response to pressures for change and concomitant fluctuation. By problematising the notion of the medical gaze and by giving attention to discourses and practices, which were not legitimated by it, the study draws attention to realities that were deemed largely irrelevant by western medical epistemology, such as subjective experiences and knowledge, which, though lacking the same legitimation as the gaze, did not disappear but only become less visible. In this way the study widens the social context in which medical practice can be perceived and understood within a transforming South African health care system.