L'application des problèmes inverses de diffraction à la détection de fissures via l'utilisation d'ondes acoustiques, électromagnétiques ou élastiques s'élargit dans de nombreux domaines. Des exemples d'application incluent le contrôle non destructif, la prospection géophysique... Cette thèse a pour objectif d'identifier des fissures en utilisant des méthodes d'échantillonnage bien connues. Dans ce travail, nous utilisons la Linear Sampling Method et la méthode de Factorisation pour reconstruire la géométrie de fissures à partir de plusieurs données statiques de champs lointains dans le cas de conditions d'impédance sur les deux bords de la fissure se trouvant dans un domaine homogène. Par ailleurs, une application de la méthode de la Reciprocity Gap Linear Sampling Method est proposée pour la reconstruction de la géométrie de fissures dans un domaine hétérogène avec les mêmes conditions au bord. Dans le but d'élargir l'application de cette dernière méthode, une méthode de complétion de données pour le problème de Cauchy associé à l'équation de Helmholtz a été proposée. La performance des méthodes proposées est montrée à travers de tests numériques pour différentes formes de fissures et pour différentes valeurs de l'impédance.

L'application des problèmes inverses de diffraction à la détection de fissures via l'utilisation d'ondes acoustiques, électromagnétiques ou élastiques s'élargit dans de nombreux domaines. Des exemples d'application incluent le contrôle non destructif, la prospection géophysique... Cette thèse a pour objectif d'identifier des fissures en utilisant des méthodes d'échantillonnage bien connues. Dans ce travail, nous utilisons la Linear Sampling Method et la méthode de Factorisation pour reconstruire la géométrie de fissures à partir de plusieurs données statiques de champs lointains dans le cas de conditions d'impédance sur les deux bords de la fissure se trouvant dans un domaine homogène. Par ailleurs, une application de la méthode de la Reciprocity Gap Linear Sampling Method est proposée pour la reconstruction de la géométrie de fissures dans un domaine hétérogène avec les mêmes conditions au bord. Dans le but d'élargir l'application de cette dernière méthode, une méthode de complétion de données pour le problème de Cauchy associé à l'équation de Helmholtz a été proposée. La performance des méthodes proposées est montrée à travers de tests numériques pour différentes formes de fissures et pour différentes valeurs de l'impédance.

Nous nous intéressons dans un premier temps à l'étude des propriétés spectrale de localisation dynamique pour des opérateurs de Schrödinger ainsi qu'a leurs classifications. Nous introduirons trois classes de propriétés équivalentes en cherchant à établir le lien entre elles d'une façon optimale et illustrée par des contre-exemples. Certaines de ces propriétés s'avèrent jouer un rôle crucial dans l'étude mathématique de plusieurs phénomènes issus de la physique, notamment la quantifi cation de la conductance de Hall et l'apparition des plateaux dûs aux états localisés. Nous nous intéressons ainsi dans la seconde partie, aux conductances de Hall et de bord pour des modèles désordonnés continus et en présence d'un mur électrique aussi bien que magnétique. Nous expliquons comment les murs entrent en jeu pour pouvoir définir la conductance de bord, en tenant compte de la contribution des états localisés et la régularisation que les systèmes désordonnés requièrent. Nous établissons l'égalité de ces deux conductances directement et non par quantification séparée.

The Large Eddy Simulation (LES) technique with the Smagorinsky-Lilly dynamic subgrid model and two-equation Standard k-ω Transitional turbulence model are applied to investigate non-spiral and spiral blood flow through three dimensional models of arterial stenosis and aneurysm. A spiral pattern of blood flow is thought to have many beneficial effects on hemodynamics. Previous computational studies on spiral blood flow involve only steady spiral flow in a straight stenosed pipe without considering an upstream curved section of the artery. But a spiral pattern in the blood flow may exist due to the presence of an upstream curved section in the artery. On the other hand, pressure is generally considered a constant quantity in studies on pulsatile flow through either arterial stenosis or aneurysm; however, blood pressure is a waveform in a physiological flow. Although cosine-type or smooth regular stenoses are generally taken in investigations of blood flow in a three-dimensional model of arterial stenosis, in reality, stenoses are of irregular shape. Besides stenosis and aneurysm, another abnormal condition of the artery is the presence of stenosis with an adjacent aneurysm in the same arterial segment, especially in the posterior circulation. A study on (steady or pulsatile) flow through such arterial stenosis with an adjacent aneurysm in the same arterial segment is not available so far. Therefore, taking above things into consideration, thorough investigations of steady and unsteady pulsatile non-spiral and spiral blood flow in three-dimensional models of stenosis and aneurysm are needed to give a sound understanding of the transition-to-turbulence of blood flow due to stenosis and aneurysm and to study the the effects of spiral velocity on the transition-to-turbulence. The LES technique has mostly been used to investigate turbulent flow in engineering fields other than bio-fluid mechanics. In the last decade, LES has seen its excellent potential for studying the transition-to-turbulence of physiological flow in bio-fluid mechanics. Though the k-ω Transitional model is used in few instances, mainly LES is applied in this study. Firstly, investigations of steady non-spiral and spiral blood flow through threedimensionalmodels of cosine-type regular stenosed tube without and with upstream curved segment of varying angles of curvature are performed by using the k-ω Transitional model and LES. A fully developed Poiseuille velocity profile for blood is introduced at the inlets of the models. To introduce a spiral effect at the inlet, onesixth of the bulk velocity is taken as the tangential velocity at the inlet along with the axial velocity profile there. Secondly, physiological pulsatile non-spiral and spiral blood flow through a three-dimensional model of a straight tube having cosine-type regular stenosis are investigated by using mainly LES. A two-equation k-ω Transitional model is also used in one non-spiral flow case. The first four harmonics of the Fourier series of pressure pulse are used to generate physiological velocity profiles at the inlet. At the outlet, a pressure waveform is introduced. The effects of percentage of area reduction in the stenosis, length of the stenosis, amplitude of pulsation and Womersley number are also examined. Thirdly, transient pulsatile non-spiral and spiral blood flow through a threedimensional model of irregular stenosis are investigated by applying LES and comparison is drawn between non-spiral flow through a regular stenosis and that through an irregular stenosis. Lastly, pulsatile non-spiral and spiral blood flow through a three-dimensional model of irregular stenosis with an adjacent post-stenotic irregular aneurysm in the same arterial segment are studied by applying LES and the k-ω Transitional model. The effects of variation in spiral velocity are also examined. The results presented in this thesis are analysed with relevant pathophysioloical consequences. In steady flow through the straight stenosed tube, excellent agreement between LES results for Re = 1000 and 2000 and the corresponding experimental results are found when the appropriate inlet perturbations are introduced. In the models with an upstream curved segment, no significant effect of spiral flow on any flow property is found for the investigated Reynolds numbers; spiral pattern disappears before the stenosis – which may be due the rigid wall used in the models and/or a steady flow at the inlet. The effects of the curved upstream model can be seen mainly in the maximum turbulent kinetic energy (TKE), the maximum pressure drop and the maximum wall shear stress (WSS), which in the curved upstream models generally increase significantly compared with the corresponding results in the straight stenosed tube. The maximumcontributions of the SGS motion to the large-scale motion in both non-spiral and spiral flow through a regular stenosis, an irregular stenosis and an irregular stenosis with an adjacent post-stenotic irregular aneurysm are 50%, 55%and 25%, respectively, for the highest Reynolds number investigated in each model. Although the wall pressure and shear stress obtained from the k-ω Transitional model agree quite well with the corresponding LES results, the turbulent results obtained from the k-ω Transitional model differ significantly from the corresponding LES results – this shows unsuitability of the k-ω model for pulsatile flow simulation. Large permanent recirculation regions are observed right after the stenosis throat in both non-spiral and spiral flow, which in the model of a stenosis with an adjacent post-stenotic aneurysm are stretched beyond the aneurysm and the length of the recirculation regions increases with spiral velocity. This study shows that, in both steady and unsteady pulsatile flow through the straight tube model having either a stenosis (regular or irregular) or an irregular stenosis with an adjacent post-stenotic irregular aneurysm, the TKE rises significantly at some locations and phases if a spiral effect is introduced at the inlet of the model. However, the maximum value of the TKE in a high spiral flow drops considerably compared with that in a low spiral flow. The maximum wall pressure drop and shear stress occur around the stenosis throat during all the phases of the pulsatile cycle. In the model of a stenosis only, the wall pressure rises in the immediate post-stenotic region after its drop at the stenosis throat. However, in the model of a stenosis with an adjacent aneurysm, the wall pressure does not rise to regain its undisturbed value before the start of the last quarter of the aneurysm. The effects of the spiral flow on the wall pressure and WSS are visible only in the downstream region where they take oscillatory pattern. The break frequencies of energy spectra for velocity and pressure fluctuations from −5/3 power slope to −10/3 power slope and −7/3 power slope, respectively, are observed in the downstream transition-to-turbulence region in both the non-spiral and spiral flow. At some locations in the transition region, the velocity spectra in the spiral flow has larger inertial subrange region than that in non-spiral flow. The effects of the spiral flow on the pressure spectra is insignificant. Also, the maximum wall pressure drop, the maximum WSS and the maximum TKE in the non-spiral flow through the irregular stenosis rise significantly compared with the corresponding results in the non-spiral flow through the regular stenosis. When the area reduction in the stenosis is increased, the maximum pressure drop, the maximumWSS and the TKE rise sharply. As for the effects of the length of the stenosis, the maximum WSS falls significantly and the maximum TKE rises sharply due to the increase in the length of the stenosis; but the maximum pressure drop is almost unaffected by the increase in the stenosis length.

Current grid computing architectures have been based on cluster management and batch queuing systems, extended to a distributed, federated domain. These have shown shortcomings in terms of scalability, stability, and modularity. To address these problems, this dissertation applies architectural styles from the Internet and Web to the domain of generic computational grids. Using the REST style, a flexible model for grid resource interaction is developed which removes the need for any centralised services or specific protocols, thereby allowing a range of implementations and layering of further functionality. The context for resource interaction is a generalisation and formalisation of the Condor ClassAd match-making mechanism. This set theoretic model is described in depth, including the advantages and features which it realises. This RESTful style is also motivated by operational experience with existing grid infrastructures, and the design, operation, and performance of a proto-RESTful grid middleware package named DIRAC. This package was designed to provide for the LHCb particle physics experiment’s “off-line” computational infrastructure, and was first exercised during a 6 month data challenge which utilised over 670 years of CPU time and produced 98 TB of data through 300,000 tasks executed at computing centres around the world. The design of DIRAC and performance measures from the data challenge are reported. The main contribution of this work is the development of a REST model for grid resource interaction. In particular, it allows resource templating for scheduling queues which provide a novel distributed and scalable approach to resource scheduling on the grid.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 27-29). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 27-29). Also available on the Internet.

Life-extension of EDF Energy's existing nuclear fleet is based on an assumption of continued safe operation. Potential fracture of graphite bricks in the nuclear reactor core of a power station represents an unknown variable in the equation. An understanding of the nature of this phenomenon and the impact on operation of the power station is desired. This work prepares the way for the future study of fracture in graphite bricks in a reactor core subject to dynamic excitation. Methodology to couple a multi-body finite element contact code to a crack propagation code is thus developed. Three important scientific contributions have been made: (i) An optimisation problem formulated on a smooth manifold to yield the rotation responsible for infinitesimal rigid body motion. This involves an iterative scheme in the form of Newton's method that takes into account the geometry of the underlying parameter space. There are no issues with singularities or additional computations in each iteration to scale the solution onto the manifold. (ii) An energy consistent crack initiation criterion for brittle material where nucleation is treated as a sudden and discrete rupture event at the macroscopic level. At the heart of the criterion is the finite difference form of the energy release rate; an expression for the characteristic length is derived and the change in total potential energy is obtained from an asymptotic argument involving the topological derivative. The criterion can predict crack onset at a sharp or blunt notch. Fracture toughness and material strength are the only input requirements. (iii) Algorithms related to the detection of sharp notches in a tetrahedral finite element mesh and a general computational procedure for evaluation of non-local crack initiation criteria. The only tool in the implementation of these algorithms is C++11. There is no need for a complex data structure storing all incidence information. Unordered associative containers in the standard library are exploited in the design of these rather efficient algorithms, which cover surface extraction and provide connectivity of the edges representing a sharp notch tip. A mesh re-generation routine for purposes of refinement at the sharp notch tips has also been developed.

The thesis explores the potential of Genetic Algorithms (GAs) for optimising the operation of electric power systems. It discusses methods which have resulted in significant direct cost saving in operating an electric power system. In particular, the thesis demonstrates the simple search procedure and the powerful search ability of Gas in multi-modal, multi-objective problems, which are resisted by the most well known conventional techniques. Special emphasis has been given to the effectiveness of the enhanced genetic based algorithms and the importance of sophisticated problem structures. Finally, the feasibility and suitability of genetic based algorithms for power system optimisations are verified on a real power supply system. The basic requirement in operating a power system is to ensure that the whole system is run at the minimum possible cost, and the lowest possible pollution level, while reliability and security are maintained. These requirements have resulted in a wide range of power system optimisation problems. In this work, a selection of problems concerning operation economy, security and environmental impact have been dealt with by Genetic Algorithms. These problems are in order of increasing complexity as the project progresses: they range from static problems to dynamic problems, single objective to multi-objectives, softly constrained problems to harshly constrained problems, simple problem structure to more rigorous problem structure. Despite the diversity, GAs consistently produce solutions comparable to conventional techniques over the wide range of problem spectrum. It has been clearly demonstrated that a sophisticated problem structure can bring significant financial benefits in system operation, it has however added further complexity to the problem, where the best result may only be sought from the genetic based algorithms. The enhancements of Genetic Algorithms have been investigated with the aim of further improving the quality and speed of the solution. They have been enhanced in two levels: the first is to develop advanced genetic strategies, and this is subsequently refined by choosing optimal parameter values to further improve the strategies. The outcome of the study clearly indicates that genetic based algorithms are very attractive techniques for solving the ever more complicated optimisations of electric power systems. The basic requirement in operating a power system is to ensure that the whole system is run at the minimum possible cost, and the lowest possible pollution level, while reliability and security are maintained. These requirements have resulted in a wide range of power system optimisation problems. In this work, a selection of problems concerning operation economy, security and environmental impact have been dealt with by Genetic Algorithms. These problems are in order of increasing complexity as the project progresses: they range from static problems to dynamic problems, single objective to multi-objectives, softly constrained problems to harshly constrained problems, simple problem structure to more rigorous problem structure. Despite the diversity, GAs consistently produce solutions comparable to conventional techniques over the wide range of problem spectrum. It has been clearly demonstrated that a sophisticated problem structure can bring significant financial benefits in system operation, it has however added further complexity to the problem, where the best result may only be sought from the genetic based algorithms. The enhancements of Genetic Algorithms have been investigated with the aim of further improving the quality and speed of the solution. They have been enhanced in two levels: the first is to develop advanced genetic strategies, and this is subsequently refined by choosing optimal parameter values to further improve the strategies. The outcome of the study clearly indicates that genetic based algorithms are very attractive techniques for solving the ever more complicated optimisations of electric power systems.

A física se relaciona intimamente com a matemática, e essa relação pode ser refletida com olhares distintos e complementares. A respeito dessa temática, existem trabalhos que discutem o papel técnico e operacional que a matemática exerce em diferentes níveis de ensino de física, assim como existem trabalhos que refletem sobre o caráter organizacional e estrutural que ela possui no ensino, construção e aprendizagem da ciência. Esse trabalho tem como principal objetivo observar esses dois tipos de relações em um curso introdutório de mecânica na licenciatura em física da Universidade de São Paulo e refletir sobre como as relações da física com a matemática podem ser apresentadas no contato inicial na graduação que o futuro professor de física tem com os conceitos da mecânica. Para isso, foi realizado um estudo de caso na disciplina Fundamentos de Mecânica em duas turmas com professores distintos. Nesse estudo, foram gravados áudios das explicações dos professores e anotadas as formulações matemáticas utilizadas nas aulas, como equações, resolução de exercícios e/ou esboços de gráficos. Em um primeiro momento, foram analisadas as representações matemáticas utilizadas pelos professores em trechos das aulas denominados episódios de ensino. Nesses episódios, se observaram aspectos como a transitividade de representações matemáticas, o aspecto operacional da matemática e as relações explícitas com outros cursos da licenciatura, como o cálculo e a geometria analítica. Em um segundo momento, foram analisados os aspectos organizacionais da matemática na física presentes no estudo de caso que permitem pensar a matemática como estruturante do pensamento físico (PIETROCOLA, 2002): interpretação, significação, abstração e linguagem matemática. Com essas análises, foi possível concluir que a relação da física com a matemática pode ser explorada no início da formação do professor em aspectos que extrapolam o uso técnico e mecânico das operações: a reflexão sobre a utilização das representações, a extração de informações físicas a partir de formulações e o exercício de pensar e ouvir questionamentos sobre o uso da matemática na física. A partir dessas apresentações, emergem outros questionamentos para a área de ensino de física: quando o futuro professor começa a pensar sobre a relação da física com a matemática? Quais as implicações de um curso introdutório em mecânica ser oferecido concomitantemente com um curso matemático de cálculo, por exemplo? Essa dissertação busca oferecer explanações que permitam levantar questões para futuras pesquisas na área e contribuir para a discussão sobre o tema. / Physics is closely related to mathematics, and this relationship can be seen with different and complementary points of view. Regarding this issue, there are studies that discuss the technical and operational role that mathematics plays in different levels of the education of physics, and there are works that focus on the organizational and structural nature that it has in education, construction and learning of science. This work is aimed at evaluate these two types of relationships in an introductory course in the degree in Physics from the University of Sao Paulo and think about on how the relations of Physics and Mathematics can be presented in the initial contact at the beginning of the university studies that the future teachers of Physics with the concepts of mechanics. For this, a case study in Mechanical Fundamentals course was conducted in two classes with different teachers. In this study, the audio recordings of the teachers explanations were made and noted the mathematical formulations, used in class were noted, as equations, problem solving and/or graphic sketches. At first, we analyzed the mathematical representations used by teachers in parts of classes called episodes of education. In those episodes, aspects such as transitivity mathematical representations, the operational aspect of mathematics and relationships with other courses of degree, such as calculus and analytic geometry, were as noted a second step; the organizational aspects of mathematics in Physics were analyzed to consider Mathematics as a structure for the physical thought (PIETROCOLA, 2002): interpretation, meaning, abstraction and mathematical language. With these analyzes, it was concluded that the physical relationship with mathematics can be explored at the beginning of a teacher training in aspects that go beyond the technical and mechanical use of the operations: a reflection on the use of representations, extraction of physical information from formulations and the exercise of thinking and hearing questions about the use of Mathematics in Physics. From these presentations, other questions emerge for the area of physical education: when the future teacher begins think about the physical relationship with Mathematics? What are the implications if an introductory course in Mechanics is offered concurrently with a Mathematical Calculus course, for example? This dissertation seeks to offer explanations that enable the raise of questions for future researches in the area and contribute to discussion on the topic.