11 research outputs found

    Interfacial Stresses of Thermal Barrier Coating with Film Cooling Holes Induced by CMAS Infiltration

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    To obtain high gas turbine efficiency, a film cooling hole is introduced to prevent the destruction of thermal barrier coating systems (TBCs) due to hot gases. Furthermore, environmental calcium-magnesium-aluminum-silicate (CMAS) particulates plug the film cooling hole and infiltrate the TBCs to form a CMAS-rich layer, which results in phase transformations and significant modifications in the thermomechanical properties that impact the TBCs during cooling. This study aimed to establish a three-dimensional thermo-fluid-solid coupling TBCs model with film cooling holes and CMAS infiltration to analyze the temperature and residual stress distribution via simulations. For the interfacial stress around the cooling hole at the TC/BC interface, the film cooling holes alleviated the interfacial residual stress by 60% due to the reduction in temperature by 40%. In addition, CMAS infiltration intensified the interfacial residual stress via phase transformation. As a result of the influence of larger penetration depths and expansion rates of phase transformation, a significant increase in residual stress was observed. At the beginning of CMAS infiltration, the interfacial stress would be more dominated by the effect of infiltration depth. In addition, the failure due to interfacial normal and tangential stresses was more likely to be found at the infiltration zone near the cooling hole

    Involvement of the GP63 protease in infection of Trichomonas vaginalis

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    Co-capping of ras proteins with surface immunoglobulins in B lymphocytes

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    Cellular ras genes encode a family of membrane-associated proteins (p21ras) that bind guanine nucleotide and possess a low intrinsic GTPase activity. The p21ras proteins are ubiquitously expressed in mammalian cells and are thought to be involved in a growth-promoting signal transduction pathway; their mode of action, however, remains unknown. The ligand-induced movement of cell-surface receptors seems to be a primary event in the transduction of several extracellular signals that control cell growth and differentiation. In B lymphocytes, surface immunoglobulin receptors crosslinked by antibody or other multivalent ligands form aggregates called patches, which then collect into a single assembly, a cap, at one pole of the cell. This process constitutes the initial signal for the activation of a B cell. Here we show by immunofluorescence microscopy that p21ras co-caps with surface immunoglobulin molecules in mouse splenic B lymphocytes. In contrast, no apparent change in the distribution of p21ras occurs during the capping of concanavalin A receptors. The redistribution of p21ras is apparent at the early stages (patching) of immunoglobulin capping and is inhibited by metabolic inhibitors and the cytoskeleton-disrupting agents colchicine and cytochalasin D. The distribution of another membrane-associated guanine nucleotide-binding regulatory protein, the Gi alpha subunit, is not affected by surface immunoglobulin capping. These findings demonstrate that p21ras can migrate in a directed manner along the plasma membrane and suggest that p21ras may be a component of the signalling pathway initiated by the capping of surface immunoglobulin in B lymphocytes
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