Characterisation of the surface damage of X38CrMoV5 (AISI H11) tool steel at room temperature and 600 degrees C

International audienceA novel approach is used to characterise the surface damage of AISI H11 hot work tool steel. The fatigue crack growth rate (FCGR) experiments on thin specimens, considered representative of the surface of tool steels, are carried out. Single edge notched tension specimens of 8mm width and different thicknesses are used in the study. Initially, the effect of thickness (scale) on the FCGR is investigated to establish if there exists a difference between bulk and near surface properties of the tool steel. Then, the effect of R value on the thin specimens is investigated. All the experiments are carried out at room temperature and 600 degrees C. These temperatures represent the limits of use of this steel. Paris curves are established. Effect of R ratio on the threshold value of propagation at elevated temperatures is investigated in detail. A special ascending K experiment for establishing the threshold of propagation at elevated temperatures in small specimens is proposed, and the results are presented. The increase in R ratio increases the FCGR at low temperature, while it has no effect at 600 degrees C. A reduction in thickness shows a reduction in the FCGR. Increase in temperature increases the FCGR and dramatically increases the threshold of crack propagation. The sharp increase in threshold value is studied in detail. Scanning electron microscopy of the specimens is performed to explain some of the characteristics observed in the specimen testing

Protein–Glycolipid Interactions Studied in Vitro Using ESI-MS and Nanodiscs: Insights into the Mechanisms and Energetics of Binding

Electrospray ionization-mass spectrometry (ESI-MS) analysis combined with the use of nanodiscs (NDs) to solubilize glycolipids (GLs) has recently emerged as a promising analytical method for detecting protein–GL interactions <i>in vitro</i> and, when applied to libraries of GLs, ranking their affinities. However, there is uncertainty regarding the mechanism(s) of complex formation in solution and the extent to which the relative abundances of protein–glycolipid complexes observed by ESI-MS reflect the relative concentrations in solution. Here, we describe the results of a systematic ESI-MS study aimed at elucidating the processes that influence binding of water-soluble proteins to GLs incorporated into NDs and to exploit these insights to quantify the binding energetics. The interactions between the cholera toxin B subunit homopentamer (CTB₅) and its native ganglioside receptor, β-D-Gal-(1 → 3)-β-D-GalNAc-(1 → 4)-[α-D-Neu5Ac-(2 → 3)]-β-D-Gal-(1 → 4)-β-D-Glc-ceramide (GM1), and between a recombinant fragment of family 51 carbohydrate-binding module (CBM), originating from <i>S. pneumoniae</i>, with a synthetic B type 2 neoglycolipid, α-D-Gal-(1 → 3)-[α-L-Fuc-(1 → 2)]-β-D-Gal-(1 → 4)-β-D-GlcNAc-1,2-di-O-dodecyl-<i>sn</i>-glycero (B2_NGL) served as model protein–GL complexes for this study. The results of the ESI-MS measurements reveal that proteins bind reversibly to ND-bound GLs and that proteins possessing multiple ligand binding sites are able to interact with GLs originating from different NDs. Experimental evidence suggests that the diffusion of GLs between NDs is rapid and influences the nature of the protein–GL complexes that are detected. Using a newly developed ESI-MS assay, the proxy ligand method, the association constants for the CBM-B2_NGL and CTB₅–GM1 interactions were quantified and found to be slightly smaller than those for the corresponding oligosaccharides in solution

CD22 blockade restores homeostatic microglial phagocytosis in ageing brains.

Microglia maintain homeostasis in the central nervous system through phagocytic clearance of protein aggregates and cellular debris. This function deteriorates during ageing and neurodegenerative disease, concomitant with cognitive decline. However, the mechanisms of impaired microglial homeostatic function and the cognitive effects of restoring this function remain unknown. We combined CRISPR-Cas9 knockout screens with RNA&nbsp;sequencing analysis to discover age-related genetic modifiers of microglial phagocytosis. These screens identified CD22, a canonical B&nbsp;cell receptor, as a negative regulator of phagocytosis that is upregulated on aged microglia. CD22 mediates the anti-phagocytic effect of α2,6-linked sialic acid, and inhibition of CD22 promotes the clearance of myelin debris, amyloid-β oligomers and α-synuclein fibrils in vivo. Long-term central nervous system delivery of an antibody that blocks CD22 function reprograms microglia towards a homeostatic transcriptional state and improves cognitive function in aged mice. These findings elucidate a mechanism of age-related microglial impairment and a strategy to restore homeostasis in the ageing brain