Detection of Temper Embrittlement in Steel by Magnetoacoustic Emssion Technique

A bulk ferromagnet possesses two types of domain walls: 180° and non-180° [1]. In the case of iron-like ferromagnets, the latter type of walls are 90° domain walls. As a result of the magnetoelastic interaction, unit cells of a ferromagnet deform slightly in a way that is unique to particular types of domains [2]. Such a spontaneous deformation, called magnetostriction, causes local lattice strains at domain walls with the strain fields being particularly strong for 90° domain walls [3]. The motion of the 90° domain walls is followed by a redistribution of local lattice strain fields. Elastic energy is being released by this process and propagates through material as acoustic waves. Acoustic emission (AE) generated due to magnetic domain wall motion is thus defined as magnetoacoustic emission (MAE)

Arrangement of Annexin A2 tetramer and its impact on the structure and diffusivity of supported lipid bilayers

Annexins are a family of proteins that bind to anionic phospholipid membranes in a Ca2+-dependent manner. Annexin A2 forms heterotetramers (Anx A2t) with the S100A10 (p11) protein dimer. The tetramer is capable of bridging phospholipid membranes and it has been suggested to play a role in Ca2+-dependent exocytosis and cell-cell adhesion of metastatic cells. Here, we employ x-ray reflectivity measurements to resolve the conformation of Anx A2t upon Ca2+-dependent binding to single supported lipid bilayers (SLBs) composed of different mixtures of anionic (POPS) and neutral (POPC) phospholipids. Based on our results we propose that Anx A2t binds in a side-by-side configuration, i.e., both Anx A2 monomers bind to the bilayer with the p11 dimer positioned on top. Furthermore, we observe a strong decrease of lipid mobility upon binding of Anx A2t to SLBs with varying POPS content. X-ray reflectivity measurements indicate that binding of Anx A2t also increases the density of the SLB. Interestingly, in the protein-facing leaflet of the SLB the lipid density is higher than in the substrate-facing leaflet. This asymmetric densification of the lipid bilayer by Anx A2t and Ca2+ might have important implications for the biochemical mechanism of Anx A2t-induced endo- and exocytosis.Comment: 27 pages, 7 figures; supplementary material available upon request from the author