Identification of crystalline behavior on macroscopic response and local strain field analysis: application to alpha zirconium alloys

The purpose of this paper is to present an identification method of the crystalline behavior of a material from a mechanical test performed on a polycrystalline sample. Because of the lack of knowledge about its crystalline behavior, this method is applied to a Zirconium alloy. This identification is based on a finite element modeling of the microstructure, and the results are compared to both the macroscopic and the microscopic experimental results. On the microscopic scale, the plastic strains are obtained using a micro-extensometry technique and the crystalline orientation using an EBSD technique. In order to validate the method, an identification is performed with only two free parameters: the evolutions of the macroscopic and microscopic errors appear to be regular and exhibit a well-defined minimum so that the parameters can be clearly identified

Decrease of breast cancer cell invasiveness by sodium phenylacetate (NaPa) is associated with an increased expression of adhesive molecules

Sodium phenylacetate (NaPa), a non-toxic phenylalanine metabolite, has been shown to induce in vivo and in vitro cytostatic and antiproliferative effects on various cell types. In this work, we analysed the effect of NaPa on the invasiveness of breast cancer cell (MDA-MB-231, MCF-7 and MCF-7 ras). Using the highly invasive breast cancer cell line MDA-MB-231, we demonstrated that an 18-hour incubation with NaPa strongly inhibits the cell invasiveness through Matrigel (86% inhibition at 20 mM of NaPa). As cell invasiveness is greatly influenced by the expression of urokinase (u-PA) and its cell surface receptor (u-PAR) as well as the secretion of matrix metalloproteinases (MMP), we tested the effect of NaPa on these parameters. An 18-hour incubation with NaPa did not modify u-PA expression, either on MDA-MB-231 or on MCF-7 and MCF-7 ras cell lines, and induced a small u-PA decrease after 3 days of treatment of MDA-MB-321 with NaPa. In contrast, an 18 h incubation of MDA-MB-231 increased the expression of u-PAR and the secretion of MMP-9. As u-PAR is a ligand for vitronectin, a composant of the extracellular matrix, these data could explain the increased adhesion of MDA-MB-231 to vitronectin, while cell adhesivity of MCF-7 and MCF-7 ras was unmodified by NaPa treatment. NaPa induced also an increased expression of both Lymphocyte Function-Associated-1 (LFA-1) and Intercellular Adhesion Molecule-1 (ICAM-1), which was obvious from 18 hour incubation with NaPa for the MDA-MB-231 cells, but was delayed (3 days) for MCF-7 and MCF-7 ras. Only neutralizing antibodies against LFA-1 reversed the decreased invasiveness of NaPa-treated cells. Therefore we can conclude that the strong inhibition of MDA-MB-231 invasiveness is not due to a decrease in proteases involved in cell migration (u-PA and MMP) but could be related both to the modification of cell structure and an increased expression of adhesion molecules such as u-PAR and LFA-1. © 2001 Cancer Research Campaign http://www.bjcancer.co

Multiscale approach of mechanical behaviour of SiC/SiC composites: Elastic behaviour at the scale of the tow

SiC/SiC composites are candidates for structural applications at elevated temperatures in the context of the development of the 4th generation of nuclear reactors. A multiscale approach is under development to construct a predictive modelling of their complex mechanical behaviour due to their heterogeneous microstructure. This approach is based on two scale transitions: from the fibres/matrix microstructure to the tow and from the tow to the woven composite, each scale presenting a significant residual porosity. This paper focuses on the first scale transition and on the modelling of the elastic behaviour of the tow at room temperature. A microstructural investigation of several tows in a 2D SiC/SiC specimen has been conducted using scanning electron microscopy to get statistical data on microstructural characteristics by image analysis in order to generate a virtual microstructure. The elastic problem of homogenisation is numerically solved by means of finite element techniques. The simulations performed on various volumes show noticeable fluctuations of the apparent behaviour: so separation of length scales is not satisfied in this material. Nevertheless, this problem is neglected in a first approximation and the homogeneous equivalent behaviour is evaluated by averaging the apparent behaviours of several volume elements – smaller than the Representative Volume Element (RVE) – called Statistical Volume Elements (SVEs). Finally, influence of porosity and pores’ morphology is quantified

Mixtures of ultracold atoms in one-dimensional disordered potentials

We study interacting one-dimensional two-component mixtures of cold atoms in a random potential, and extend the results reported earlier [Phys. Rev. Lett. 105, 115301 (2010)]. We construct the phase diagram of a disordered Bose-Fermi mixture as a function of the strength of the Bose-Bose and Bose-Fermi interactions, and the ratio of the bosonic sound velocity and the Fermi velocity. Performing renormalization group and variational calculations, three phases are identified: (i) a fully delocalized two-component Luttinger liquid with superfluid bosons and fermions, (ii) a fully localized phase with both components pinned by disorder, and (iii) an intermediate phase where fermions are localized but bosons are superfluid. Within the variational approach, each phase corresponds to a different level of replica symmetry breaking. In the fully localized phase we find that the bosonic and fermionic localization lengths can largely differ. We also compute the long-wavelength asymptotic behavior of the momentum distribution as well as that of the structure factor of the atoms (both experimentally accessible), and discuss how the three phases can be experimentally distinguished

Photochemistry of glycolaldehyde in cryogenic matrices

International audienceThe photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization and fragmentation processes are found to compete. The hydrogen-bonded Cis-Cis form of GA is transformed mainly to the open Trans-Trans conformer and to CO and CH3OH fragments and their mixed complexes. Different photo-induced behaviours appear depending on the matrix. In nitrogen, small amounts of Trans-Gauche and Trans-Trans conformers are detected after deposition and grow together upon irradiation. The Trans-Gauche conformer is characterized for the first time. In para-hydrogen due to a weaker cage effect additional H2CO and HCO fragments are seen. Calculations of the potential energy surfaces of S0, S1, and T1 states – to analyse the torsional deformations which are involved in the isomerization process – and a kinetic analysis are presented to investigate the different relaxation pathways of GA. Fragmentation of GA under UV irradiation through the CO+CH3OH molecular channel is a minor process, as in the gas phase

Genome-wide transcriptional response of an avian pathogenic Escherichia coli (APEC) pst mutant

<p>Abstract</p> <p>Background</p> <p>Avian pathogenic <it>E</it>. <it>coli </it>(APEC) are associated with extraintestinal diseases in poultry. The <it>pstSCAB</it>-<it>phoU </it>operon belongs to the Pho regulon and encodes the phosphate specific transport (Pst) system. A functional Pst system is required for full virulence in APEC and other bacteria and contributes to resistance of APEC to serum, to cationic antimicrobial peptides and acid shock. The global mechanisms contributing to the attenuation and decreased resistance of the APEC <it>pst </it>mutant to environmental stresses have not been investigated at the transcriptional level. To determine the global effect of a <it>pst </it>mutation on gene expression, we compared the transcriptomes of APEC strain χ7122 and its isogenic <it>pst </it>mutant (K3) grown in phosphate-rich medium.</p> <p>Results</p> <p>Overall, 470 genes were differentially expressed by at least 1.5-fold. Interestingly, the <it>pst </it>mutant not only induced systems involved in phosphate acquisition and metabolism, despite phosphate availability, but also modulated stress response mechanisms. Indeed, transcriptional changes in genes associated with the general stress responses, including the oxidative stress response were among the major differences observed. Accordingly, the K3 strain was less resistant to reactive oxygen species (ROS) than the wild-type strain. In addition, the <it>pst </it>mutant demonstrated reduced expression of genes involved in lipopolysaccharide modifications and coding for cell surface components such as type 1 and F9 fimbriae. Phenotypic tests also established that the <it>pst </it>mutant was impaired in its capacity to produce type 1 fimbriae, as demonstrated by western blotting and agglutination of yeast cells, when compared to wild-type APEC strain χ7122.</p> <p>Conclusion</p> <p>Overall, our data elucidated the effects of a <it>pst </it>mutation on the transcriptional response, and further support the role of the Pho regulon as part of a complex network contributing to phosphate homeostasis, adaptive stress responses, and <it>E. coli </it>virulence.</p