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Stress and temperature dependence of the avalanche dynamics during creep deformation of metallic glasses.

The understanding of the mesoscopic origin of plasticity in metallic glasses remains still an open issue. At the microscopic level, Shear Transformation Zones (STZ), composed by dozens of atoms, have been identified as the basic unit of the deformation process. Macroscopically, metallic glasses perform either homogeneous or inhomogeneous flow depending on the experimental conditions. However, the emergence of macroscopic behavior resulting from STZ interactions is still an open issue and is of great interest. In the current work we present an approach to analyze the different interaction mechanisms of STZ's by studying the statistics of the avalanches produced by a metallic glass during tensile creep deformation. We identified a crossover between different regimes of avalanches, and we analyzed the dependence of such crossover on the experimental conditions, namely stress and temperature. We interpret such crossover as a transition from 3D random STZ activity to localized 2D nano-shear bands. The experimental time at which the crossover takes place seems to depend on the overall strain and strain rate in the sample.peerReviewe

Aberrant expression of costimulatory molecules in splenocytes of the mevalonate kinase‐deficient mouse model of human hyper‐IgD syndrome (HIDS)

Objective We sought to determine the activation status and proliferative capacities of splenic lymphocyte populations from a mevalonate kinase‐deficient mouse model of hyper‐IgD syndrome (HIDS). We previously reported that murine mevalonate kinase gene ablation was embryonic lethal for homozygous mutants while heterozygotes (Mvk+/−) demonstrated several phenotypic features of human HIDS including increased serum levels of IgD, IgA, and TNFα, temperature dysregulation, hematological abnormalities, and splenomegaly. Methods and results Flow cytometric analysis of cell surface activation markers on T and B lymphocytes, and macrophage populations, demonstrated aberrant expression of B7 glycoproteins in all splenic cell types studied. Differences in expression levels between Mvk+/− and Mvk+/+ littermate controls were observed in both the basal state (unstimulated) and after Concanavalin A (Con‐A) stimulation in vitro of whole splenocyte cultures. In Mvk+/− CD4 and CD8 T cells, alterations in expression of CD25, CD80, CD152, and CD28 were observed. Mvk+/− splenic macrophages expressed altered levels of CD80, CD86, CD40, and CD11c while Mvk+/− B lymphocytes had differential expression of CD40, CD80, and CD86. Mvk+/− splenocyte subpopulations also exhibited altered proliferative capacities in response to in vitro stimulation. Conclusion We postulate that imbalances in the expression of cell surface proteins necessary for activation, proliferation, and regulation of the intensity and duration of an immune response may result in defective T cell activation, proliferation, and effector functions in our model and potentially in human HIDS