Comparison between different approaches for the evaluation of the hot spot structural stress in welded pressure vessel components

Fatigue cracks in welds often occur at the toe of a weld where stresses are difficult to calculate at the design stage. To circumvent this problem the ASME Boiler and PV code Section VIII Division 2 Part 5 [1] uses the structural stress normal to the expected crack to predict fatigue life using elastic analysis and as welded fatigue curves. The European Unfired Pressure Vessel Code [2] uses a similar approach. The structural stress excludes the notch stress at the weld toe itself. The predicted fatigue life has a strong dependency on the calculated value of structural stress. This emphasizes the importance of having a unique and robust way of extracting the structural stress from elastic finite element results. Different methods are available for the computation of the structural hotspotstress at welded joints. These are based on the extrapolation of surface stresses close to the weld toe, on the linearisation of stresses in the through-thickness direction or on the equilibrium of nodal forces. This paper takes a critical view on the various methods and investigates the effects of the mesh quality on the value of the structural stress. T-shaped welded plates under bending are considered as a means for illustration

Modèles photométriques multi-échelles des surfaces planétaires: Applications au Satellite Encelade et aux anneaux de Saturne

Owing to its very dense and extended rings as well as the diversity of its satellites, the Saturnian system is a peculiar object in the solar system. However, although Cassini spacecraft, in orbit around Saturn since July 2004, has provided an impressive amount of data, the origin of the entire system (planet-rings-satellites) still remains largely unknown. The lack of constraints on ring's mass and age, coupled with the poor knowledge of rheological properties of satellites ground, in particular Enceladus, do not allow to disentangle between formation models.Mains remote sensing instruments on board the Cassini spacecraft give access to the photometrical behavior of observed bodies, mainly controlled by the regolith that blanket them as well as their macroscopic structure (e.g. ring's thickness and density, satellite's surface topography…). Hence, during my PhD I have developed planetary surfacephotometrical models, which take into account multi-scale effects. Comparison between these models and Cassini spectro-photometrical data leads to the first determination of Saturn's rings structure as a function of its distance to Saturn as well as their chemical composition. A similar work based on shadow measurements of Enceladus's craters gave access to its ground rheological properties.After a brief introduction on the general context of Saturn's formation models and the photometrical multi-scale models I built, I will detail the final results on these two objects and will discuss how this knew knowledge helps us to better understand how this unique system has formed.Le système de Saturne se singularise dans le système solaire de par l'importance de son système d'anneau, extrêmement massif et étalé ainsi que par la grande diversité de ses satellites naturels. Néanmoins, malgré la grande quantité de données recueillies par la sonde Cassini, en orbite autour de Saturne depuis Juillet 2004, le mode de formation du système dans son ensemble (planète-satellites-anneaux) reste une énigme. Le manque de contraintes sur la masse et l'âge des anneaux, couplé à la mauvaise connaissance des propriétés rhéologiques de la surface des satellites, en particulier d'Encelade, ne permettent pas à l'heure actuelle de trancher entre les différents scénarios de formations.Les principaux instruments de la sonde Cassini donnent accès au comportement photométrique des corps observés, contrôlé aussi bien par le régolithe microscopique les recouvrant que par leur structure macroscopique (épaisseur et densité des anneaux, topographie des surfaces des satellites par exemple). C'est pourquoi, au cours de ma thèse je me suis intéressé à modéliser la photométrie des surfaces planétaires en distinguant ces effets multi-échelles. La comparaison de ces modèles aux données spectro-photométriques de la sonde Cassini a permis, après inversion, de remonter à la structure et la composition des anneaux de Saturne d'une part, ainsi qu'aux propriétés rhéologiques du satellite Encelade d'autre part, ce qui, dans les deux cas, est une première à ce jour.Après avoir introduit le contexte général de formation du système de Saturne et les différents modèles photométriques que j'ai construits, je détaillerais les résultats obtenus sur ces deux objets et discuterai l'impact de ces nouvelles données sur notre compréhension des mécanismes de formation d'un système si unique

Vitamin D for the Treatment of Epilepsy: Basic Mechanisms, Animal Models and Clinical Trials

There is increasing evidence supporting dietary and alternative therapies for epilepsy, including the ketogenic diet, modified Atkins diet, and omega-3 fatty acids. Vitamin D is actively under investigation as a potential intervention for epilepsy. Vitamin D is fat soluble steroid which shows promise in animal models of epilepsy. Basic research has shed light on the possible mechanisms by which Vitamin D may reduce seizures, and animal data support the efficacy of Vitamin D in rat and mouse models of epilepsy. Very little clinical data exists to support the treatment of human epilepsy with Vitamin D, but positive findings from preliminary clinical trials warrant larger Phase I and II clinical trials in order to more rigorously determine the potential therapeutic value of Vitamin D as a treatment for human epilepsy