Characterization of particle distribution in a black carbon-filled elastomer via nanoindentation

A new method to characterize the distribution of hard particles dispersed into a soft elastomer matrix is developed using nanoindentation. It is based on the measurement of the contact stiffness from the continuous stiffness measurement module (CSM). Theoretically, for a homogeneous material, the contact stiffness is directly proportional to the contact depth. However, when indenting a carbon black-filled fluoroelastomer (FKM) this relation is no longer valid and abnormal contact stiffness evolutions are measured (jumps). The tip-particle model developed in this work is simply based on the hypothesis that all the deformation is supported by the elastomer matrix and that black carbon aggregates play the role of hard extensions of the diamond tip, when touching it (grey particles 1,2 & 3, Fig. 1a). As a result, each abnormal variation of contact stiffness is related to a new aggregate in contact with the tip. By knowing the stiffness amplitude of a jump and the relative stiffness where it appeared , the equivalent projected area of a particle can be calculated (Fig. 1d). From this calculation, one can extract the distribution of particles surface density from nanoindentation measurements only. Ten experimental indentation tests have been performed and the results are displayed in Fig. 1e. The distribution of particles surface density extracted from experiments is compared to measurements performed by image analysis of a 100 nm thick slide of the material observed by Transmission Electron Microscopy (TEM) (black squares). Furthermore, the tip-particle model is simulated numerically on the same image analysis (down pointing triangles). The results obtained from this model are in excellent agreement with the TEM observation which is really promising. Indeed, this model is an alternative to microscopy characterization which can be complicated to implement. Please click Additional Files below to see the full abstract

Combined synchrotron X-rays and image correlation analyses of biaxially deformed W/Cu nanocomposite thin films on Kapton

International audienceAbstract In-situ biaxial tensile tests within the elastic domain were conducted with W/Cu nanocomposite thin films deposited on a polyimide cruciform substrate thanks to a biaxial testing machine developed on the DiffAbs beamline at SOLEIL synchrotron. The mechanical behavior of the nanocomposite was characterized at the micro-scale and the macro-scale using simultaneously synchrotron X-ray diffraction and digital image correlation techniques. Strain analyses for equi-biaxial and non equi-biaxial loading paths have been performed. The results show that the two strain measurements match to within 1 × 10-4 in the elastic domain for strain levels less than 0.3% and for both loading paths

Élasticité et endommagement sous chargement bi-axial de nano-composites W/Cuen couches minces sur polyimide (apport des techniques synchrotrons)

Ce travail de thèse porte sur la déformation bi-axiale contrôlée de nano-composites W/Cu en couches minces déposées sur des substrats polyimides. La nano-structuration est obtenue par stratification de deux matériaux immiscibles (W et Cu) par pulvérisation ionique avec contrôle de la taille des grains au sein du film mince par contrôle de l'épaisseur selon la direction decroissance du film. Nous avons développé une procédure permettant de caractériser le comportement mécanique des échantillons à deux échelles différentes. L'essai de traction biaxial est couplé à la diffraction des rayons X (déformation microscopique) et à la corrélation d'images numériques (déformation macroscopique). Nous avons utilisé une machine de tractionbi-axiale développée dans le cadre d un projet ANR sur la ligne de lumière DiffAbs du synchrotron SOLEIL. Elle permet de contrôler les contraintes dans des films minces supportés par des substrats polyimides. La confrontation des résultats obtenus par ces deux techniques dans le domaine d'élasticité a montré que la déformation est intégralement transmise via l interfacefilm - substrat. La seconde étape de notre travail a consisté à étudier les déformations du nanocomposite W/Cu au-delà du domaine d élasticité. Nous avons mis en évidence trois domaines de déformation associés à différents mécanismes de déformation. La limite d'élasticité du nanocomposite W/Cu a été déterminée en comparant la déformation élastique du film mince à la déformation macroscopique du substrat. Enfin, l'étude de la limite d'élasticité du nanocomposite W/Cu pour différents ratios de force a révélé un comportement fragile du nanocomposite W/Cu.This thesis focuses on the biaxial deformation of W/Cu nanocomposite thin films deposited on polyimide substrates. The grain size in the thin film is controlled by stratification of two immiscible materials (W and Cu) employing sputtering techniques. We developed a procedure to characterize the mechanical behavior of samples at two different scales. A biaxial tensile test is coupled to X-ray diffraction (microscopic deformation) and digital image correlation (macroscopic deformation) techniques. We used a biaxial tensile setup developed in the framework of an ANR project on the DiffAbs beamline at synchrotron SOLEIL allowing forthe control of stresses in thin films supported by polyimide substrates. By comparing the strains obtained by these two techniques, the applied strain is determined to be transmitted unchanged in the elastic domain through the film - substrate interface. The second part of our work was to study the deformation of W/Cu nanocomposite beyond the elastic range. We have highlighted three domains of deformation associated with different deformation mechanisms. The elastic limit of the W/Cu nanocomposite was determined by comparing the elastic deformation of the thin film to the macroscopic deformation of the substrate. Finally, the elastic limit of W/Cu nanocomposite was studied for different load ratios. The overall results emphasized the brittle behavior of these nanocomposites.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment

International audienceThe early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations. Lithic vestiges are the only sources that remain of this process and the understanding of the material's properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment. Several models of the structural transformations upon heating have been proposed in the current literature. These models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony. In order to propose a new model, we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy, solid state NMR, X-ray diffraction and electron microscopy. The results show that the major transformation to happen is the loss of silanole (SiOH) and the creation of new Si-O-Si bonds according to the reaction: Si-OH HO-Si -> Si -O-Si + H2O. This reaction starts between 200 degrees C and 300 degrees C and causes an increase in the hardness of the rocks. The maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created H2O and depend on the size of the specimen and the volume of its porosity. These results also show that the annealing duration at maximum temperature can be relatively short (<50 min) for a sufficiently large amount of transformation to be accomplished

Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

International audienceA prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes

Novel Insights into the Bovine Polled Phenotype and Horn Ontogenesis in Bovidae

Despite massive research efforts, the molecular etiology of bovine polledness and the developmental pathways involved in horn ontogenesis are still poorly understood. In a recent article, we provided evidence for the existence of at least two different alleles at the Polled locus and identified candidate mutations for each of them. None of these mutations was located in known coding or regulatory regions, thus adding to the complexity of understanding the molecular basis of polledness. We confirm previous results here and exhaustively identify the causative mutation for the Celtic allele (PC) and four candidate mutations for the Friesian allele (PF). We describe a previously unreported eyelash-and-eyelid phenotype associated with regular polledness, and present unique histological and gene expression data on bovine horn bud differentiation in fetuses affected by three different horn defect syndromes, as well as in wild-type controls. We propose the ectopic expression of a lincRNA in PC/p horn buds as a probable cause of horn bud agenesis. In addition, we provide evidence for an involvement of OLIG2, FOXL2 and RXFP2 in horn bud differentiation, and draw a first link between bovine, ovine and caprine Polled loci. Our results represent a first and important step in understanding the genetic pathways and key process involved in horn bud differentiation in Bovidae

Direct interaction of TrkA/CD44v3 is essential for NGF-promoted aggressiveness of breast cancer cells

Background CD44 is a multifunctional membrane glycoprotein. Through its heparan sulfate chain, CD44 presents growth factors to their receptors. We have shown that CD44 and Tropomyosin kinase A (TrkA) form a complex following nerve growth factor (NGF) induction. Our study aimed to understand how CD44 and TrkA interact and the consequences of inhibiting this interaction regarding the pro-tumoral effect of NGF in breast cancer. Methods After determining which CD44 isoforms (variants) are involved in forming the TrkA/CD44 complex using proximity ligation assays, we investigated the molecular determinants of this interaction. By molecular modeling, we isolated the amino acids involved and confirmed their involvement using mutations. A CD44v3 mimetic peptide was then synthesized to block the TrkA/CD44v3 interaction. The effects of this peptide on the growth, migration and invasion of xenografted triple-negative breast cancer cells were assessed. Finally, we investigated the correlations between the expression of the TrkA/CD44v3 complex in tumors and histo-pronostic parameters. Results We demonstrated that isoform v3 (CD44v3), but not v6, binds to TrkA in response to NGF stimulation. The final 10 amino acids of exon v3 and the TrkA H112 residue are necessary for the association of CD44v3 with TrkA. Functionally, the CD44v3 mimetic peptide impairs not only NGF-induced RhoA activation, clonogenicity, and migration/invasion of breast cancer cells in vitro but also tumor growth and metastasis in a xenograft mouse model. We also detected TrkA/CD44v3 only in cancerous cells, not in normal adjacent tissues. Conclusion Collectively, our results suggest that blocking the CD44v3/TrkA interaction can be a new therapeutic option for triple-negative breast cancers

Des carrières sous le plafond de verre. Les femmes architectes en Lettonie soviétique

International audienceLatvia stands out by the speed and scope at which the profession of architect feminized over the 20th century, whether in Europe or in the Soviet Union, which annexed Latvia during the Second World War. This article focuses on the factors and limits of feminization of this little professional group after 1945. It questions the Soviet and local mechanisms of feminization of this profession and the international transformations of this trade so as to show the discrepancy between, on the one had, training and recruitment, favorable to women, and on the other hand a professional world governed by just as powerful sexist exclusion mechanisms until de 1980s. These mechanisms are interpreted as arrangements after which women’s progression in the profession is used to absorb the constraints inherent to the trade.La Lettonie se distingue par la rapidité et l’ampleur de la féminisation de la profession d’architecte au cours du xxe siècle, aussi bien en Europe qu’au sein de l’Union soviétique qui l’a annexée au cours de la Seconde Guerre mondiale. Cet article se penche sur les facteurs et les limites de la féminisation de ce petit groupe professionnel après 1945. Il interroge les ressorts soviétiques et locaux de la féminisation de cette profession et les transformations internationales du métier pour mettre en valeur les décalages entre la formation et l’embauche, favorables aux femmes, et un monde du travail régi jusque dans les années 1980 par des mécanismes d’exclusion sexiste tout aussi puissants. Ces mécanismes sont interprétés comme des arrangements aux termes desquels la progression des femmes dans la profession sert à absorber les contraintes imposées au métier