Fuel inventory and generation of carbon and metal dust in a tokamak are perceived to be serious safety and economy issues for the steady-state operation of a fusion reactor, e.g. ITER. These topics have been explored in this thesis in order to contribute to a better understanding and the development of methods for controlling and curtailing fuel accumulation and dust formation in controlled fusion devices. The work was carried out with material facing fusion plasmas in three tokamaks: TEXTOR in Forschungszentrum Jülich (Germany), Tore Supra in the Nuclear Research Center Cadarache (France) and JET in Culham Centre for Fusion Energy (United Kingdom). Following issues were addressed: (a) properties of material migration products, i.e. co-deposited layers and dust particles; (b) impact of fuel removal methods on dust generation and on modification of plasma-facing components; (c) efficiency of fuel and deposit removal techniques; (d) degradation mechanism of diagnostic components - mirrors - and methods of their regeneration. / <p>QC 20121116</p>

No description available.

Un épithélium est un tissu formé de cellules étroitement juxtaposées dont la fonction est d'isoler des organes entre eux ou vis-à-vis du milieu extérieur. Nous étudions la croissance d'un épithélium en géométrie confinée. En utilisant des techniques de microfabrication, nous avons développé un protocole de traitement de surface permettant de confiner un tissu dans une zone adhésive pendant plusieurs semaines. La résolution spatiale de cette technique est micrométrique, et nous autorise la conception de motifs adhésifs de diverses géométries. Dans notre étude, leurs tailles sont telles que les cellules s'y comportent collectivement. Nous analysons la croissance d'un épithélium de cellules Madine Derby Canine (MDCK) dans des domaines adhésifs circulaires. La migration et la densification du tissu sont étudiées par PIV (Particle image velocimetry) et d'autres techniques d'analyse d'image. Nous caractérisons les champs de vitesse et observons des oscillations de grande amplitude de la vitesse dont la période correspond à l'hypothèse d'une onde de contraintes se propageant dans l'épithélium. Nous caractérisons également l'apparition d'un bourrelet tridimensionnel de cellules à la périphérie de l'épithélium, rappelant les premières étapes de la tubulogénèse. Dans deux autres expériences, en utilisant une géométrie inverse, nous étudions le recouvrement d'un épithélium sur une région anti-adhésive. Nous montrons que ce recouvrement nécessite un câble d'actomyosine supracellulaire, et que la tension de ce câble s'opposant à une tension de surface définit une taille critique au-delà duquel le motif anti-adhésif ne peut pas être recouvert par l'épithélium

Concrete masonry is a multi-component structural system. In the case of reinforced concrete masonry, the system includes the concrete units, the mortar, the reinforcing steel and the grout fill. Placing vertical steel reinforcing bars in the cores of the concrete units enhances the flexural strength of the wall. The vertical steel, when subjected to compression at moderate strain levels, must be confined to improve its resistance to buckling and to improve the effectiveness of the grout around the reinforcing bar. Based on the well established behaviour of reinforced concrete systems, it seems reasonable to presume that the primary means of enhancing ductility is to provide lateral confining steel at closely-spaced intervals to effectively increase the ultimate compressive strain in the grout. It may be assumed that transverse reinforcement in concrete masonry provides lateral confinement to the core so that the axial compressive strength of the grout is enhanced and the ductility improved. <p>The focus of this study was to investigate the effect of vertical reinforcement and lateral confinement on the axial capacity of short partially grouted concrete masonry walls built in running bond. In order to better understand the structural behaviour of both confined and unconfined concrete masonry, it is important to have some knowledge of the load-displacement behaviour, stress-strain behaviour and failure modes of the masonry walls with different configurations of vertical and lateral reinforcement. <p>An experimental study was performed to investigate the behaviour of partially grouted concrete masonry block walls under axial loading. Three types of test specimens of partially grouted concrete block masonry walls were tested: <p>(1) specimens with a grouted core only; <p>(2) specimens with a grouted core and vertical reinforcement (i.e. no confinement); and <p>(3) specimens with a grouted core, vertical reinforcement and spiral confinement in the grouted cores. In total, thirty short wall specimens were tested to failure. <p>The structural behaviour of vertically reinforced, laterally confined walls was compared to vertically reinforced, unconfined walls, as well as to unreinforced, unconfined masonry walls. The test results indicated that vertical reinforcement of the grouted core did not have a significant positive effect on the failure modes and strength of the short masonry walls. Due to problems with adequate compaction, the lateral confinement provided by the spiral reinforcement had a slightly negative effect on the compressive strength of concrete masonry walls built in running bond. Vertical reinforcement and lateral confinement of the grouted core had some positive effect on the ductility. From a comparison of the ductility for all three types of specimens it was found that both the vertical reinforcement and lateral confinement of the core had a beneficial influence on the post-peak ductility. <p>In general, similar crack patterns and failure modes were observed in all three types of specimens. Vertical cracks that progressed through the end faces of the concrete blocks and mortar joints, suggesting that the lateral expansion of the grouted core contributed to tensile splitting stresses in walls. All walls failed in a compression-tension stress state, which featured spalling away of the block shells and vertical tensile splitting on the end faces.

Les domaines scientifiques, nécessitant l'imagerie d'objets de petites dimensions (micrométriques voire nanométriques) et peu émissifs, sont de plus en plus nombreux (physique des plasmas, astrophysique, physique des matériaux, biotechnologies,...) et les challenges posés par l'étude de ces objets en font un axe de recherche et de développement en constante évolution. Le travail présenté dans ce document a un objectif double : présenter les spécificités de l'instrumentation associée à ce domaine de recherche ainsi que les facteurs susceptibles d'améliorer la précision des systèmes d'imagerie ; présenter les techniques numériques d'analyse de données et de reconstruction capables de restituer des résolutions spatiales en adéquation avec les dimensions de l'objet étudié. La similitude des algorithmes d'analyse de données et de reconstruction appliqués à la fusion par confinement inertielle et à l'imagerie moléculaire de fluorescence, deux domaines scientifiques dont les enjeux sont très différents, montre combien l'imagerie d'objets de petites dimensions est un domaine de recherche à la frontière d'un grand nombre de disciplines scientifiques

A two-dimensional axisymmetric implementation of the smoothed particle hydrodynamics (SPH) technique, called for short AxisSPH, has been described in this thesis, along with a number of basic tests and realistic applications. The main goal of this work was to fill a gap on a topic which has been scarcely addressed in the published literature concerning SPH. Although the application of AxisSPH to the simulation of real problems is restricted to those systems which display the appropriate symmetry there are, however, many interesting examples of physical systems which evolve following the axisymmetric premise. These examples belong to a variety of scientific and technological areas such as, for example, astrophysics, laboratory astrophysics or inertial confinement fusion. Additionally AxisSPH can be also useful in convergence studies of the standard 3D-SPH technique because the higher resolution achieved in 2D can be used to benchmark the three-dimensional codes. The main improvements implemented in AxisSPH with respect existing axisymmetric SPH formulations are summarized as follows: 1) We have derived simple analytical expressions for correction factors which largely improves the calculation of density and velocity in the vicinity of the z-axis. These expressions and their derivatives were given as a function of an adimensional parameter and do not increase the computational load of the scheme. 2) We have obtained the appropriate expression of the fluid Euler equations containing the new correction functions and their derivatives. Far enough from the singular axis, the scheme reduces to the standard formulation discussed by Brookshaw (2003). 3) A novel expression for the heat conduction term, which has to be added to the energy equation was devised and checked. This new term improves the description of the heat flux for those particles located at the axis neighborhoods. 4) Until now axisymmetric SPH hydrocodes handle artificial viscosity using a crude approach because it was treated as a simple restriction of the standard 3D Cartesian viscosity to 2D. Here we propose to calculate the viscous pressure as a combination of two terms, the first one is the (standard) Cartesian part and the second is the axis-converging part of the viscosity respectively. As expected this last term is of special relevance to simulate implosions. 5) We have developed an original method to incorporate gravity into AxisSPH. First the direct ring to ring force was found as a function of the Euclidean distance between the 2D particles. In second place the gravitational force on a given particle was obtained by summing the contributions of all N particles. We have also developed a more efficient scheme to obtain the gravitational force calculating the potential of the ring, instead the force because it involves lesser algebraic operations. The scheme has been checked using a large number of tests cases. These tests range from very specific oriented to check a particular algorithm or a piece of physics, to rather complex ones intended to analyze the behavior of the scheme in potential real applications (ICF, jets, astrophysics). At least in one case, the head on collision of a pair of white dwarfs, the result of the simulations carried out using AxisSPH brings new, unpublished, scientific material. / En esta tesis se ha desarrollado un código, que hemos llamado AxisSPH, en dos dimensiones axisimétrico a partir de la técnica conocida como SPH (“smooothed particle hydrodynamics”). AxisSPH ha sido validado después de realizar una serie de tests básicos y algunas simulaciones de situaciones reales. El objetivo principal de este trabajo ha sido llenar, en parte, el vacío existente al respecto en la literatura sobre SPH. Aunque sólo se puede aplicar AxisSPH en problemas reales que presenten la apropiada simetría, existen muchos ejemplos interesantes de sistemas físicos que presentan la simetría axial demandada. Existen ejemplos en campos de aplicación tanto científica como tecnológica, por ejemplo en astrofísica, en el llamado laboratorio de astrofísica o en fusión por confinamiento inercial (ICF). Otra interesante aplicación de AxisSPH puede ser su utilización en estudios de convergencia con otros códigos 3D-SPH debido a su mayor resolución, al tratarse de un código 2D. Las mejoras implementadas en el código AxisSPH en comparación con otros códigos axisimétricos SPH existentes se pueden resumir en los siguientes puntos: 1) Hemos deducido expresiones analíticas simples para unos factores de corrección que mejoran el cálculo de la densidad y la velocidad en las proximidades del eje z. Dichas expresiones y sus derivadas dependen de un parámetro adimensional que no incrementa mucho el peso computacional del esquema propuesto. 2) Hemos obtenido las expresiones adecuadas de las ecuaciones de Euler que contienen estas nuevas funciones correctoras y sus derivadas. Lejos del eje de singularidad estas ecuaciones se transforman en las de la formulación estándar propuesta por Brookshaw (2003). 3) Una expresión novedosa del término de conducción, que debe de añadirse a la ecuación de la energía, se ha propuesto y validado. Este nuevo término mejora la evolución del flujo de calor de las partículas situadas en las proximidades del eje z. 4) Hasta el momento los códigos hidrodinámicos SPH axisimétricos existentes trabajaban con una aproximación poco elaborada de la viscosidad artificial ya que consistían en una restricción a dos dimensiones de la viscosidad estándar 3D. En este trabajo proponemos el cálculo de la presión debida a la viscosidad como combinación de dos términos, el primero reflejo de la parte cartesiana y la segunda da cuenta de la parte relacionada con la convergencia en el eje. Como era de esperar este último término es de relevante importancia en la simulación de implosiones. 5) Hemos desarrollado un método original para incorporar el cálculo de la gravedad en el código AxisSPH. En primer lugar la fuerza directa de anillo a anillo y en segundo lugar la fuerza de la gravedad que sufre una determinada partícula a partir de la contribución del resto de las N partículas existentes. También hemos desarrollado un esquema más eficiente para calcular la gravedad a partir del cálculo del potencial del anillo en lugar del cálculo directo de la fuerza ya que implica un menor número de operaciones algebraicas. El método ha sido verificado con un gran número de test numéricos. Desde los más específicos orientados a comprobar la validez de un algoritmo particular o la capacidad para simular un fenómeno físico en particular, hasta simulaciones bastante más complejas, con la intención de validar la capacidad de simular aplicaciones potencialmente más reales (ICF, jets, astrofísica). Así, en al menos un caso, en la colisión frontal de dos enanas blancas, los resultados de la simulación utilizando AxisSPH pueden aportar material científico publicable.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Bond in a reinforced concrete (RC) structure is the interaction force that transfers force between the steel and concrete. It influences the structural performance and serviceability of a structure under both static and cyclic loading. Corrosion of reinforcing steel in RC structures is the primary reason behind bond loss in RC elements. A loss of bond in concrete results in a decrease in the serviceability strength and eventually causes a brittle and sudden failure. Structures, such as bridges, are vulnerable to corrosion and at the same time are subjected to repeated loading rather than static loading. Nevertheless, little experimental or analytical studies that address the problem of corroded steel-concrete bond under repeated loading exist. This study was aimed at increasing the understanding of the behaviour of bond between corroded reinforcing steel bars and concrete for structures subjected to repeated loading. In addition, the effect of fibre reinforced polymers (FRP) as a rehabilitation method was assessed. Fibre reinforced polymers is considered to be a state-of-the art rehabilitation material due to its advantages, such as high strength, light weight and ease of handling and application. Forty-seven anchorage-beam specimens were cast and tested. The specimens’ dimensions were 152 x 254 x 2000 mm reinforced with two 20M bars. The steel reinforcement in a specimen was unbonded except for 250 mm from each end. This bonded length was selected to ensure a bond failure. The corrosion was induced using an accelerated corrosion process. The parameters investigated were the corrosion level (0, 5 and 9% measured mass loss), whether the specimen was wrapped in the anchorage zone with a U-shaped carbon fibre reinforced polymer (CFRP) sheets or not, and the load range applied. The minimum load applied was 10% of the static bond capacity of the specimen. The maximum load was varied to give the desired range of fatigue lives (103 to 106 cycles). The test frequency for all repeated tests was 1.5 Hz. Results showed that the repeated loading either pushed the bottom concrete cover away from the steel bar by wedge action for unwrapped beams or cracked and crushed the CFRP confined bottom concrete cover for wrapped beams. The concrete damage caused the bond stress to undergo a gradual redistribution, moving the peak bond stress from the loaded end towards the free end, resulting in failure of the specimens by fatigue of bond. Corrosion levels of 5% and 9% decreased the fatigue bond strength on average by 19%. The rate of slip of the steel bar increased as the corrosion level increased. CFRP sheets changed the mechanism by which the concrete resist the bond forces by engaging the bottom cover. This in turn increased the fatigue bond strength at all corrosion levels on average by 31% compared to unwrapped specimens. Based on the test results and observations, a hypothesis of the mechanics of bond under repeated loading was postulated and a fatigue slip-growth analysis (similar to the fracture mechanics crack growth approach) was proposed to calculate the fatigue life of a specimen that fail in bond. The proposed analysis was in reasonable agreement with the experimental results.

Anisotropic molecules confined on a spherical or other curved surface can display coupled positional and orientational orderings, which make possible applications in physics, chemistry, biology, and material science. Therefore, controlling the order of such system has attracted much attention recently. Several distinct conformations of rod-like or chain-like molecules confined on a spherical surface have been predicted, including states such as tennis-ball, rectangle, and cut-and-rotate splay. These conformations have four +1/2 defects and are suggested to dominate over the splay conformation that has two +1 defects. For the purpose of investigating the conformations of 2-fold anisotropic molecules confined on the spherical surface, the author of this thesis utilizes the Onsager model to study the system of rigid rods and conducts Monte Carlo simulations on the bead-bond model to research the system of semiflexible polymer chains. At low surface coverage density, no particular pattern of the molecules would form. However, coupled positional and orientational ordering begins to emerge beyond a transition density. On the basis of the numerical solutions of the Onsager model of rigid rods, the splay conformation is shown to be the only stable state. On the other hand, Monte Carlo simulations on a polymer system indicate that the ordered state always accompanies the tennis-ball symmetry. With comparison to the continuous isotropic-nematic transition of a fluid of hard rods embedded in a flat two-dimensional space, the disorder-order transition for both the system of rigid rods and the system of polymer chains confined on the spherical surface has first-order phase-transition characteristics.

Concrete masonry is a multi-component structural system. In the case of reinforced concrete masonry, the system includes the concrete units, the mortar, the reinforcing steel and the grout fill. Placing vertical steel reinforcing bars in the cores of the concrete units enhances the flexural strength of the wall. The vertical steel, when subjected to compression at moderate strain levels, must be confined to improve its resistance to buckling and to improve the effectiveness of the grout around the reinforcing bar. Based on the well established behaviour of reinforced concrete systems, it seems reasonable to presume that the primary means of enhancing ductility is to provide lateral confining steel at closely-spaced intervals to effectively increase the ultimate compressive strain in the grout. It may be assumed that transverse reinforcement in concrete masonry provides lateral confinement to the core so that the axial compressive strength of the grout is enhanced and the ductility improved. <p>The focus of this study was to investigate the effect of vertical reinforcement and lateral confinement on the axial capacity of short partially grouted concrete masonry walls built in running bond. In order to better understand the structural behaviour of both confined and unconfined concrete masonry, it is important to have some knowledge of the load-displacement behaviour, stress-strain behaviour and failure modes of the masonry walls with different configurations of vertical and lateral reinforcement. <p>An experimental study was performed to investigate the behaviour of partially grouted concrete masonry block walls under axial loading. Three types of test specimens of partially grouted concrete block masonry walls were tested: <p>(1) specimens with a grouted core only; <p>(2) specimens with a grouted core and vertical reinforcement (i.e. no confinement); and <p>(3) specimens with a grouted core, vertical reinforcement and spiral confinement in the grouted cores. In total, thirty short wall specimens were tested to failure. <p>The structural behaviour of vertically reinforced, laterally confined walls was compared to vertically reinforced, unconfined walls, as well as to unreinforced, unconfined masonry walls. The test results indicated that vertical reinforcement of the grouted core did not have a significant positive effect on the failure modes and strength of the short masonry walls. Due to problems with adequate compaction, the lateral confinement provided by the spiral reinforcement had a slightly negative effect on the compressive strength of concrete masonry walls built in running bond. Vertical reinforcement and lateral confinement of the grouted core had some positive effect on the ductility. From a comparison of the ductility for all three types of specimens it was found that both the vertical reinforcement and lateral confinement of the core had a beneficial influence on the post-peak ductility. <p>In general, similar crack patterns and failure modes were observed in all three types of specimens. Vertical cracks that progressed through the end faces of the concrete blocks and mortar joints, suggesting that the lateral expansion of the grouted core contributed to tensile splitting stresses in walls. All walls failed in a compression-tension stress state, which featured spalling away of the block shells and vertical tensile splitting on the end faces.