The trend towards more and all-electric apparatuses and more electrification will lead to higher electrical demand. Increases in electrical power demand can be provided by either higher currents or higher voltages. Due to "weight" and "voltage" drop, a raise in the current is not preferred; so, "higher voltages" are being considered. Another trend is to reduce the size and weight of apparatuses. Combined, these two trends result in the high voltage, high power density concept. It is expected that by 2030, 80% of all electric power will flow through "power electronics systems". In regards to the high voltage, high power density concept described above, "wide bandgap (WBG) power modules" made from materials such as "SiC and GaN (and, soon, Ga2O3 and diamond)", which can endure "higher voltages" and "currents" rather than "Si-based modules", are considered to be the most promising solution to reducing the size and weight of "power conversion systems". In addition to the trend towards higher "blocking voltage", volume reduction has been targeted for WBG devices. The blocking voltage is the breakdown voltage capability of the device, and volume reduction translates into power density increase. This leads to extremely high electric field stress, E, of extremely nonuniform type within the module, leading to a higher possibility of "partial discharge (PD)" and, in turn, insulation degradation and, eventually, breakdown of the module. Unless the discussed high E issue is satisfactorily addressed and solved, realizing next-generation high power density WBG power modules that can properly operate will not be possible. Contributions and innovations of this Ph.D. work are as follows. i) Novel electric field grading techniques including (a) various geometrical techniques, (b) applying "nonlinear field-dependent conductivity (FDC) materials" to high E regions, and (c) combination of (a) and (b), are developed; ii) A criterion for the electric stress intensity based upon accurate dimensions of a power device package and its "PD measurement" is presented; iii) Guidelines for the electrical insulation design of next-generation high voltage (up to 30 kV), high power density "WBG power modules" as both the "one-minute insulation" and PD tests according to the standard IEC 61287-1 are introduced; iv) Influence of temperature up to 250°C and frequency up to 1 MHz on E distribution and electric field grading methods mentioned in i) is studied; and v) A coupled thermal and electrical (electrothermal) model is developed to obtain thermal distribution within the module precisely. All models and simulations are developed and carried out in COMSOL Multiphysics. / Doctor of Philosophy / In power engineering, power conversion term means converting electric energy from one form to another such as converting between AC and DC, changing the magnitude or frequency of AC or DC voltage or current, or some combination of these. The main components of a power electronic conversion system are power semiconductor devices acted as switches. A power module provides the physical containment and package for several power semiconductor devices. There is a trend towards the manufacturing of electrification apparatuses with higher power density, which means handling higher power per unit volume, leading to less weight and size of apparatuses for a given power. This is the case for power modules as well. Conventional "silicon (Si)-based semiconductor technology" cannot handle the power levels and switching frequencies required by "next-generation" utility applications. In this regard, "wide bandgap (WBG) semiconductor materials", such as "silicon carbide (SiC)"," gallium nitride (GaN)", and, soon, "gallium oxide" and "diamond" are capable of higher switching frequencies and higher voltages, while providing for lower switching losses, better thermal conductivities, and the ability to withstand higher operating temperatures. Regarding the high power density concept mentioned above, the challenge here, now and in the future, is to design compact WBG-based modules. To this end, the extremely nonuniform high electric field stress within the power module caused by the aforementioned trend and emerging WBG semiconductor switches should be graded and mitigated to prevent partial discharges that can eventually lead to breakdown of the module. In this Ph.D. work, new electric field grading methods including various geometrical techniques combined with applying nonlinear field-dependent conductivity (FDC) materials to high field regions are introduced and developed through simulation results obtained from the models developed in this thesis.

The task of detecting human faces within either a still image or a video frame is one of the most popular object detection problems. For the last twenty years researchers have shown great interest in this problem because it is an essential pre-processing stage for computing systems that process human faces as input data. Example applications include face recognition systems, vision systems for autonomous robots, human computer interaction systems (HCI), surveillance systems, biometric based authentication systems, video transmission and video compression systems, and content based image retrieval systems. In this thesis, non-traditional methods are investigated for detecting human faces within color images or video frames. The attempted methods are chosen such that the required computing power and memory consumption are adequate for real-time hardware implementation. First, a standard color image database is introduced in order to accomplish fair evaluation and benchmarking of face detection and skin segmentation approaches. Next, a new pre-processing scheme based on skin segmentation is presented to prepare the input image for feature extraction. The presented pre-processing scheme requires relatively low computing power and memory needs. Then, several feature extraction techniques are evaluated. This thesis introduces feature extraction based on Two Dimensional Discrete Cosine Transform (2D-DCT), Two Dimensional Discrete Wavelet Transform (2D-DWT), geometrical moment invariants, and edge detection. It also attempts to construct a hybrid feature vector by the fusion between 2D-DCT coefficients and edge information, as well as the fusion between 2D-DWT coefficients and geometrical moments. A self organizing map (SOM) based classifier is used within all the experiments to distinguish between facial and non-facial samples. Two strategies are tried to make the final decision from the output of a single SOM or multiple SOM. Finally, an FPGA based framework that implements the presented techniques, is presented as well as a partial implementation. Every presented technique has been evaluated consistently using the same dataset. The experiments show very promising results. The highest detection rate of 89.2% was obtained when using a fusion between DCT coefficients and edge information to construct the feature vector. A second highest rate of 88.7% was achieved by using a fusion between DWT coefficients and geometrical moments. Finally, a third highest rate of 85.2% was obtained by calculating the moments of edges. / Master of Science

The aim of the study is to survey the usage of closure as it is reflected in Northern Sotho Narratives. Chapter one This chapter introduces the objectives of the research and definition of the concepts narrative and closure. Reference is made to different scholars to substantiate the argument. Chapter two Plot serves as the basis of the study of closure in a novel. The interconnectedness of the elements of plot expressed by the presence of different closural patterns supports this. Major mutual relationships are distinguished, namely between author and reader as well as between author, reader and text. Chapter three The principles of brevity and single effect which differentiate a short story from other narratives play a major role in the study of closure. The five signals of closure and the mode of approaching the end also influence how closure is approached in this genre. Chapter four The study of folktales is divided into traditional and modern approaches. Despite their difference, opening and closing are commonly based on the syntactical position occupied by the opening and closing phrases. In the traditional approach the position is fixed while in the modern approach it is controlled by the presence of motifemes. This chapter embarks on the usage of closure in narrative poetry. The ending is doubly determined, based on structural elements and linguistic principles. Repetition and cessation of the idea expressed in a verse llne, are major poetic devises to illustrate closure. Chapter six This chapter summarizes the findings of the previous chapters and proposals for future research. / African Languages / D.Litt. et Phil. (African Languages)

<p>Detta examensarbete har utförts på Fläktwoods AB i Växjö, som producerar stora axialfläktar för olika industriapplikationer. Syftet är att öka kunskapen om fettsmorda axiella kullager genom FE analyser.</p><p>Projektet har genomförts i fem delsteg för att avgöra påverkan av en eller några få parametrar i taget. De studerade parametrarna är: elementstorlek, kontaktstyvhet, last, lagergeometri (dvs. oskulation), ickelinjär geometri och ickelinjära materialegenskaper (dvs. plasticitet).</p><p>Slutsatsen är att elementstorleken bör väljas fint nog för att ge ett jämnt resultat men grovt nog för att beräkningstiden skal vara rimlig. Kontaktstyvheten har inte stor, men tydlig, inverkan på kontakttrycket och penetrationen. Förändringar av oskulationen leder till förändringar i kontaktellipsens form medan olika laster inte påverkar formen på ellipsen, utan snarare storleken. När det handlar om plasticitet är sträckgränsen den viktigaste faktorn att beakta.</p> / <p>This thesis project was carried out at Fläktwoods AB in Växjö who produces large axial fans for different industry applications. The purpose is to increase the knowledge of grease lubricated axial ball bearings through FE analyses.</p><p>The project was executed into five sub steps to determine the influence of one or few parameters at a time. The studied parameters are: mesh density, contact stiffness, load, bearing geometry (i.e. osculation), geometrical nonlinearity and material nonlinearity (i.e. plasticity).</p><p>It is concluded that the mesh density should be selected fine enough to give a smooth result but course enough to give a reasonable calculation time. The contact stiffness has not a major, but a clear, impact on the contact pressure and penetration. Changes of the osculation lead to changes of the contact ellipse shape and applying different load level does not affect the shape of the ellipse but rather the size. When dealing with plasticity the yield strength is the most important factor to take in consideration.</p>

Travaux d'études doctorales réalisées conjointement avec les travaux de recherches doctorales de Nicolas Leduc, étudiant au doctorat en génie informatique à l'École Polytechnique de Montréal. / Cette thèse vise le développement de GeoGebraTUTOR (GGBT), un espace de travail géométrique (ETG) qui intègre un système tutoriel pour l’obtention d’un milieu respectueux du raisonnement idiosyncratique de l’élève. Le raisonnement mathématique, comme l’apprentissage, ne s’exerce pas de manière linéaire, il repose sur un remaniement conceptuel continu. Il est donc peu étonnant qu’une approche séquentielle inflexible pour l’exercice de la démonstration en géométrie soit source d’embûches. Les systèmes tutoriels existants pour l’exercice de la démonstration en géométrie offrent une variété d’outils sans pour autant soulager l’élève de cette rigidité. Le design multidisciplinaire de GGBT repose sur une conception dans l’usage qui articule plusieurs cycles de recherche et de développement successifs. Cette méthodologie itérative et anthropocentrique confère à GGBT une intelligence qui nait d’une convergence d’analyses a priori et a posteriori successives. Cette thèse concerne les deux premiers cycles du développement de GGBT. La première phase du développement implique l’élaboration a priori d’un système capable de recevoir et d’analyser les démarches singulières de démonstration des élèves en fonction de solutions expertes préalablement identifiées. Ce premier prototype de GGBT est conçu en fonction d’une analyse de la relation didactique entre un enseignant réel et l’élève, et la relation didactique simulée entre un agent tuteur virtuel et ce même élève. Cette analyse théorique a priori établit un cadre conceptuel liminaire qui vise à encadrer la création d’un ETG idoine permettant à l’apprenti géomètre de se livrer à son travail mathématique. Cette version initiale de GGBT est mise à l’essai par des élèves réels guidés par leur enseignant ordinaire. Leurs interactions sont ensuite étudiées pour modéliser et implémenter un premier système tutoriel autonome à l’image des échanges témoignant du contrat didactique observé. Le second cycle de développement s’amorce avec la modélisation et la programmation d’une structure tutorielle autonome et d’une interface renouvelée, qui contribuent conjointement au design a priori d’un espace de travail géométrique. La deuxième version ainsi obtenue est également testée en contexte de classe réel. Cette fois, l’exercice empirique vise la validation de la gestion des messages par le système tutoriel et l’exploration des raisonnements instrumentés dans une perspective de précision du travail géométrique possible à l’interface de l’ETG qu’est GGBT. Ce parcours doctoral se clôt par l’exploration d’avenues de recherche potentielles pour la poursuite du développement et du raffinement de GGBT. / This thesis aims at modeling GeoGebraTUTOR, a geometrical workspace that relies on the works of a tutorial system for the definition of a milieu respectful of the student’s idiosyncratic reasoning. Mathematical reasoning, like learning, does not evolve in a linear fashion. It relies on continuous conceptual reorganizations. Therefore, it is little wonder that a linear and inflexible approach for the exercise of geometrical proof creates difficulties. Existing tutorial systems for the solving of geometrical proof problems offer a variety of tools without relieving the student of this rigidity. GGBT’s multidisciplinary design relies on a design in use approach that articulates a series of research and development cycles. This iterative anthropocentric methodology provides GGBT with an intelligence resulting from the confrontation of successive a priori and a posteriori analyses. This thesis is rooted in GGBT’s two first development cycles. The first phase of design implies the planning of a system able to take in singular student proofs and analyze their value compared to previously implemented expert answers. This first GGBT prototype is designed according to an analysis of the didactical relationship between the teacher and the student as well as the relationship that takes place between the student and the tutor agent who evolves within the didactical milieu. This a priori analysis establishes theoretical guidelines, which will steer the design of a geometrical workspace that enables the learning geometer to accomplish his mathematical work. A first GGBT prototype is put to the test with real students assisted by their regular teacher. Their interactions are then studied in order to model and implement a first self-governing tutorial system according to the dialogues reflecting the observed didactical contract. The second design cycle begins with the modeling and programming of a tutorial structure and of a renewed interface, both of which contribute to the planning of a geometrical workspace. This second prototype is also tested in a real class environment, although this time the empirical exercise aims, on the one hand, at validating the management of the tutor’s help messages, and on the other hand at exploring the student’s instrumented reasoning to specify the mathematical activity made possible by the GGBT geometrical workspace. This doctoral endeavor ends with the exploration of potential research avenues for the ongoing design and refining of GGBT.

La cristallisation en solution est un procédé largement utilisé dans l'industrie comme opération de séparation et de purification qui a pour but de produire des solides avec des propriétés spécifiques. Les propriétés concernant la taille et la forme ont un impact considérable sur la qualité finale des produits. Il est donc primordial de pouvoir déterminer la distribution granulométrique (DG) des cristaux en formation. En utilisant une caméra in situ, il est possible de visualiser en temps réel les projections 2D des particules 3D présentes dans la suspension. La projection d'un objet 3D sur un plan 2D entraîne nécessairement une perte d'informations : déterminer sa taille et sa forme à partir de ses projections 2D n’est donc pas aisé. C'est tout l'enjeu de ce travail: caractériser géométriquement et morphométriquement des objets 3D à partir de leurs projections 2D. Tout d'abord, une méthode basée sur le maximum de vraisemblance des fonctions de densité de probabilité de mesures géométriques projetées a été développée pour déterminer la taille d'objets 3D convexes. Ensuite, un descripteur de forme stéréologique basé sur les diagrammes de forme a été proposé. Il permet de caractériser la forme d'un objet 3D convexe indépendamment de sa taille et a notamment été utilisé pour déterminer les facteurs d'anisotropie des objets 3D convexes considérés. Enfin, une combinaison des deux études précédentes a permis d'estimer à la fois la taille et la forme des objets 3D convexes. Cette méthode a été validée grâce à des simulations, comparée à une méthode de la littérature et utilisée pour estimer des DGs d'oxalate d'ammonium qui ont été comparées à d’autres méthodes granulométriques. / Solution crystallization processes are widely used in the process industry as separation and purification operations and are expected to produce solids with desirable properties. The properties concerning the size and the shape are known to have a considerable impact on the final quality of products. Hence, it is of main importance to be able to determine the granulometry of the crystals (CSD) in formation. By using an in situ camera, it is possible to visualize in real time the 2D projections of the 3D particles in the suspension.The projection of a 3D object on a 2D plane necessarily involves a loss of information. Determining the size and the shape of a 3D object from its 2D projections is therefore not easy. This is the main goal of this work: to characterize geometrically and morphometrically 3D objects from their 2D projections. First of all, a method based on the maximum likelihood estimation of the probability density functions of projected geometrical measurements has been developed to estimate the size of 3D convex objects. Then, a stereological shape descriptor based on shape diagrams has been proposed. It enables to characterize the shape of a 3D convex object independently of its size and has notably been used to estimate the value of the anisotropy factors of the 3D convex objects. At last, a combination of the two previous studies has allowed to estimate both the size and the shape of the 3D convex objects. This method has been validated with simulated data, has been compared to a method from the literature and has been used to estimate size distributions of ammonium oxalate particles crystallizing in water that have been compared to other CSD methods.

Synopsis The thesis is concerned to cube solids and their use in primary school geometry. The main direction of the thesis is the development of children's spatial visualisation. The first part contains the explanation of key words in connected to spatial vizualization. I describe the environment of cube solids and work with them in various tasks. The second part includes records and analyses of my experiments, which were realized at two fourth grade classes within several months. First experiments were realized within regular lessons, later experiments in individual meetings. Analysing the experiments I identified and described several cognitive phenomena which I tried to explain in the conclusion.

OF THE THESIS The topic of this thesis is to study the cognitive processes (especially perception, imagination and thinking) of blind pupils through experiments with geometric objects. Tools of the experiment are four tasks (two for one pupil, two for a pair of pupils) that are recorded, transcribed into written protocols and analysed. An overview of the involved cognitive functions or naming of missing cognitive functions has been complied on basis of the specialised literature as a theoretical solution of analysis. Findings of psychology of mathematics didactic were other important theoretical starting points. The ones which are devoted to the tactile perception (of geometrical objects), stages of Piaget operation developments, cognitive mechanisms in mathematics and importance of communication in mathematics or geometry teaching are involved in the theses. Analysis of the experiments involves observations of the tactile perception, imaginations, thinking, cognitive processes, speech and communication, and other occurrences essential for specific tasks.

Le CEA développe et utilise des logiciels de calcul, également appelés codes de calcul, dans différentes disciplines physiques pour optimiser les coûts de ses installations et de ses expérimentations. Lors d'une étude, plusieurs phénomènes physiques interagissent. Un couplage et des échanges de données entre plusieurs codes sont nécessaires.Chaque code réalise ses calculs sur une géométrie, généralement représentée sous forme d'un maillage contenant des milliers voire des millions de mailles. Cette thèse se focalise sur le transfert de déformations géométriques entre les maillages spécifiques de chacun des codes de calcul couplés. Pour cela, elle présente une méthode de couplage de plusieurs codes, dont le calcul des déformations est réalisé par l'un d'entre eux. Elle traite également de la mise en place d'un modèle commun aux différents codes de l'étude regroupant l'ensemble des données partagées. Enfin, elle porte sur les transferts de déformations entre des maillages représentant une même géométrie ou des géométries adjacentes. Les modifications géométriques sont de nature discrète car elles s'appuient sur un maillage. Afin de les rendre accessible à l'ensemble des codes de l'étude et pour permettre leur transfert, une représentation continue est calculée. Pour cela, deux fonctions sont développées : l'une à support global, l'autre à support local. Toutes deux combinent une méthode de simplification et un réseau de fonctions de base radiale. Un cas d'application complet est traité dans le cadre du réacteur Jules Horowitz. L'effet des dilatations différentielles sur le refroidissement d'un dispositif expérimental est étudié. / The CEA develops and uses scientific software, called physical codes, in various physical disciplines to optimize installation and experimentation costs. During a study, several physical phenomena interact, so a code coupling and some data exchanges between different physical codes are required.Each physical code computes on a particular geometry, usually represented by a mesh composed of thousands to millions of elements. This PhD Thesis focuses on the geometrical modification transfer between specific meshes of each coupled physical code. First, it presents a physical code coupling method where deformations are computed by one of these codes. Next, it discusses the establishment of a model, common to different physical codes, grouping all the shared data. Finally, it covers the deformation transfers between meshes of the same geometry or adjacent geometries. Geometrical modifications are discrete data because they are based on a mesh. In order to permit every code to access deformations and to transfer them, a continuous representation is computed. Two functions are developed, one with a global support, and the other with a local support. Both functions combine a simplification method and a radial basis function network. A whole use case is dedicated to the Jules Horowitz reactor. The effect of differential dilatations on experimental device cooling is studied.

Les travaux présentés dans cette thèse portent sur l’étude et la conception de lentilles continues en guide d’ondes à plans parallèles (PPW) pour des applications multi-faisceaux. La conversion du front d'onde est assurée par une lentille formée d’une lame et d'une cavité transversale. Ce concept, proposant une approche mécanique simplifiée et possiblement purement métallique, est particulièrement attractif pour les futurs systèmes de communications par satellites (GEO/LEO) requérants des solutions à moindre coût tout en maintenant de hautes performances. La première partie de cette thèse présente la réalisation d’un outil d’analyse numérique basée sur l’optique géométrique (GO). Une prédiction rapide et précise des performances en rayonnement est obtenue. En combinant cet outil avec des processus d’optimisation, des performances en dépointage sur un large secteur angulaire sont ensuite démontrées, incluant une stabilité des diagrammes en rayonnement (ouverture à mi-puissance, niveaux de lobes secondaires et pertes en dépointage). Un prototype fonctionnant dans la bande Ka est réalisé, validant les performances précédemment obtenues. De hautes efficacités de rayonnement sont également mises en avant sur l’ensemble de la plage de fréquence. Enfin un second prototype plus compact basé sur de multiples lentilles est proposé et étudié, démontrant des performances similaires à la première solution fabriquée et mesurée. / The activities presented in this PhD focus on the study and development of continuous parallel plate waveguide (PPW) lenses for multiple beam applications. The wave front conversion is ensured by a PPW transversal ridge and cavity. The proposed concept, based on a simplified mechanical approach and possibly full-metal, is particularly suitable for future satellite communication systems (GO/LEO) requiring low-cost antennas while maintaining high performances. The first part of the thesis deals with the development of a numerical analysis tool based on geometrical optics (GO). A fast and accurate prediction of the radiation performance is provided.Combining the tool with optimization processes, large scanning performances have been demonstrated, including a stability of the radiation pattern performance (HPBW, SLL, scan loss). A prototype working at Ka band has been manufactured, validating the performances demonstrated previously. High radiation efficiencies are also proved over the entire frequency range. Finally, a second prototype targeting performances in compactness and based on multiple lenses is proposed and studied, showing similar performances as the first solution fabricated and measured.