Crystallography of graphite spheroids in cast iron

To further understand graphite growth mechanisms in cast irons, this study focuses on the crystal structure of a graphite spheroid in the vicinity of its nucleus. A sample of a graphite spheroid from a commercial cast iron was characterised using transmission electron microscopy. The chemical composition of the nucleating particle was studied at the local scale. Crystal orientation maps of the graphite spheroid revealed misorientations and twist boundaries. High resolution lattice fringe images showed that the basal planes of graphite were wavy and distorted close to the nucleus and very straight further away from it. These techniques were complementary and provided new insights on spheroidal graphite nucleation and growth

Medium range structural order in amorphous tantala spatially resolved with changes to atomic structure by thermal annealing

Amorphous tantala (a-Ta2O5) is an important technological material that has wide ranging applications in electronics, optics and the biomedical industry. It is used as the high refractive index layers in the multi-layer dielectric mirror coatings in the latest generation of gravitational wave interferometers, as well as other precision interferometers. One of the current limitations in sensitivity of gravitational wave detectors is Brownian thermal noise that arises from the tantala mirror coatings. Measurements have shown differences in mechanical loss of the mirror coatings, which is directly related to Brownian thermal noise, in response to thermal annealing. We utilise scanning electron diffraction to perform Fluctuation Electron Microscopy (FEM) on Ion Beam Sputtered (IBS) amorphous tantala coatings, definitively showing an increase in the medium range order (MRO), as determined from the variance between the diffraction patterns in the scan, due to thermal annealing at increasing temperatures. Moreover, we employ Virtual Dark-Field Imaging (VDFi) to spatially resolve the FEM signal, enabling investigation of the persistence of the fragments responsible for the medium range order, as well as the extent of the ordering over nm length scales, and show ordered patches larger than 5 nm in the highest temperature annealed sample. These structural changes directly correlate with the observed changes in mechanical loss.Comment: 22 pages, 5 figure

Influence of equal-channel angular pressing on the microstructure and corrosion behaviour of a 6xxx aluminium alloy for automotive conductors

An Al-Mg-Si aluminium alloy was shaped by using a two-pass equal-channel angular pressing (ECAP) process.This led to fragmentation of the coarse Fe-rich intermetallics (IMCs), a decrease in grain size and an increase in the high angle grain boundary (HAGB) density, with overconcentration of HAGBs around the IMCs. Corrosion tests in NaCl solution showed that, before and after ECAP, only pitting corrosion occurred. However, for ECAP samples, pits were more numerous due to the fragmentation of the IMCs; they were also larger and less deep,their propagation being strongly influenced by the presence of very small grains around the IMCs

Architectured duplex stainless steels micro-composite: Elaboration and microstructure characterization

International audienc

Nano-scale orientation mapping of graphite in cast irons

International audienc

Solution structure of NEMO zinc finger and impact of an anhidrotic ectodermal dysplasia with immunodeficiency-related point mutation.

International audienceThe regulatory NEMO (NF-kappaB essential modulator) protein has a crucial role in the canonical NF-kappaB signaling pathway notably involved in immune and inflammatory responses, apoptosis and oncogenesis. The regulatory domain is located in the C-terminal half of NEMO and contains a classical CCHC-type zinc finger (ZF). We have investigated the structural and functional effects of a cysteine to phenylalanine point mutation (C417F) in the ZF motif, identified in patients with anhidrotic ectodermal dysplasia with immunodeficiency. The solution structures of the wild type and mutant ZF were determined by NMR. Remarkably, the mutant adopts a global betabetaalpha fold similar to that of the wild type and retains thermodynamic stability, i.e., the ability to bind zinc with a native-like affinity, although the last zinc-chelating residue is missing. However, the mutation induces enhanced dynamics in the motif and leads to an important loss of stability. A detailed analysis of the wild type solution structure and experimental evidences led to the identification of two possible protein-binding surfaces that are largely destabilized in the mutant. This is sufficient to alter NEMO function, since functional complementation assays using NEMO-deficient pre-B and T lymphocytes show that full-length C417F pathogenic NEMO leads to a partial to strong defect in LPS, IL-1beta and TNF-alpha-induced NF-kappaB activation, respectively, as compared to wild type NEMO. Altogether, these results shed light onto the role of NEMO ZF as a protein-binding motif and show that a precise structural integrity of the ZF should be preserved to lead to a functional protein-recognition motif triggering full NF-kappaB activation

NMR studies on the flexibility of nucleoside diphosphate kinase.

International audienceHuman NDP kinase B, product of the nm23-H2 gene, binds DNA. It has been suggested that a helix hairpin on the protein surface, part of the nucleotide substrate binding site, could accommodate DNA binding by swinging away. The presence of flexible regions was therefore investigated by 1H NMR dynamic filtering. Although TOCSY peaks could be assigned to five residues at the N terminus of Dictyostelium NDP kinase, no flexible region was detected in the human enzyme. These data favor the idea that the protein offers different binding sites to mono- and polynucleotides

Macro and Micro mechanical in-situ characterization using synchrotron diffraction of Architectured micro-composite Duplex Stainless Steels

International audienceThe mechanical behavior of micro-composites Duplex Stainless steels (DSS) produced by Accumulative re-Bundling and Drawing (ABD) has been investigated. We evidenced a systematic increase in the yield strength, as a function of the manufacturing step, independently from the phases' volume fraction. A simple rule of mixture (ROM) successfully predicted the first generation of composites presenting a simple microstructure. However, a modified ROM taking into account the contribution of each component and its grain size could not predict the mechanical response of the composites of higher generation. An in-depth analysis is conducted to investigate the microstructure-mechanical behavior relationship and to rationalize the resultant mechanical behavior from that of each constitutive phase. For this purpose, in-situ synchrotron High Energy X-ray Diffraction measurements during uniaxial tensile experiments have been carried out to calculate the strain partitioning within each phase of the composites

The zinc finger of NEMO is a functional ubiquitin-binding domain.

International audienceNEMO (NF-kappaB essential modulator) is a regulatory protein essential to the canonical NF-kappaB signaling pathway, notably involved in immune and inflammatory responses, apoptosis, and oncogenesis. Here, we report that the zinc finger (ZF) motif, located in the regulatory C-terminal half of NEMO, forms a specific complex with ubiquitin. We have investigated the NEMO ZF-ubiquitin interaction and proposed a structural model of the complex based on NMR, fluorescence, and mutagenesis data and on the sequence homology with the polymerase eta ubiquitin-binding zinc finger involved in DNA repair. Functional complementation assays and in vivo pull-down experiments further show that ZF residues involved in ubiquitin binding are functionally important and required for NF-kappaB signaling in response to tumor necrosis factor-alpha. Thus, our findings indicate that NEMOZFisa bona fide ubiquitin-binding domain of the ubiquitin-binding zinc finger type