On the Short-Time Compositional Stability of Periodic Multilayers

The short-time stability of concentration profiles in coherent periodic multilayers consisting of two components with large miscibility gap is investigated by analysing stationary solutions of the Cahn-Hilliard diffusion equation. The limits of the existence and stability of periodic concentration profiles are discussed as a function of the average composition for given multilayer period length. The minimal average composition and the corresponding layer thickness below which artificially prepared layers dissolve at elevated temperatures are calculated as a function of the multilayer period length for a special model of the composition dependence of the Gibbs free energy. For period lengths exceeding a critical value, layered structures can exist as metastable states in a certain region of the average composition. The phase composition in very thin individual layers, comparable with the interphase boundary width, deviates from that of the corresponding bulk phase.Comment: 29 pages including 7 figures, to be published in Thin Solid Film

Caractérisation expérimentale de l'endommagement dans les minicomposites SiC/SiC

National audienceLes composites SiC/SiC sont étudiés pour leur usage potentiel comme matériau de gainage dans les réacteurs nucléaires de génération future. Afin de valider un modèle multiéchelle d'endommagement à l'échelle microscopique, une caractérisation expérimentale de l'endommagement à l'échelle du toron est mise en œuvre. Des essais de traction in-situ sur minicomposite permettent d'obtenir des données statistiques sur la cinétique d'apparition des fissures matricielles et l'évolution de leur ouverture en fonction de la contrainte. Ces observations de surface sont complétées par des observations microtomographiques réalisées à l'ESRF sur un minicomposite en traction. L'analyse des images 3D permet alors d'étudier la propagation des fissures matricielles au sein du minicomposite. Les ruptures de fibres sont également observables grâce à cette technique d'observation

BCG Induced Necrosis of the Entire Bladder Urothelium

AbstractInstillation therapy with attenuated tuberculosis bacteria (BCG) can significantly reduce rates of recurrence of non-muscle invasive bladder cancer. Local and systemic side effects such as dysuria, irritative voiding symptoms or partial bladder contracture and systemic inflammation were reported. A 75 year-old male patient with recurrent non muscle invasive bladder cancer developed necrosis of the entire bladder urothelium more than six years after BCG instillation immunotherapy. The resulting irritative voiding symptoms and low bladder capacity required radical cystectomy. BCG instillation can cause severe side effects, which develop gradually and eventually need radical surgical therapy such as cystectomy without tumor recurrence