Modélisation multi-échelle du comportement électrique de nano-composites Cu-Nb

Les fils composites nanostructurés et architecturés cuivre-niobium, qui sont de bons candidats pour la génération de champs magnétiques intenses, allient une limite d’élasticité élevée et une excellente conductivité électrique. Ils sont élaborés par co-déformation d’un assemblage composite Cu-Nb. La microstructure, multi-échelle, est formée de 853 motifs élémentaires de Cu-Nb de taille caractéristique nanométrique. Afin d’étudier le lien entre la conductivité électrique effective et la microstructure, deux méthodes d’homogénéisation sont appliquées : l’une, en champs moyens (modèle auto-cohérent généralisé), dans laquelle une microstructure formée de motifs co-cylindriques répartis aléatoirement est considérée, et l’autre, en champs complets (éléments finis), dans laquelle l’aspect périodique de la microstructure expérimentale est pris en compte. Les effets de la taille des constituants élémentaires (nm), de la température, ainsi que de la densité de dislocations, sur la conductivité locale sont considérés. Le caractère multi-échelle du matériau est pris en compte grâce à un processus itératif. Les conductivités effectives longitudinale et transversale obtenues avec les deux méthodes sont en excellent accord, montrant un moindre effet de la distribution des fibres sur ces propriétés. Ces résultats reproduisent également les données expérimentales disponibles

Anarchism, Utopianism and Hospitality: The Work of René Schérer

René Schérer (born 1922) is lamentably almost unknown to the Anglo-American world as his work has, as yet, not been translated . He is one of the main specialists of the French “utopian socialist”, Charles Fourier (1772-1837), and a major thinker in his own right. He is the author of more than twenty books and co-editor of the journal Chimères. Colleague and friend at Vincennes university (Paris 8) of Michel Foucault, Gilles Deleuze, Félix Guattari, Jacques Derrida, Jacques Rancière, Jean-François Lyotard, François Châletet, Alain Brossat, Georges Navet, Miguel Abensour, Pierre Macherey… he continues to host seminars at Paris 8 (now located at St. Denis). He is a living testimony to a radical past, and a continuing inspiration to a new generation of young thinkers. This article aims to convey the original specificity of his understanding of anarchism. By so doing, it will stress the importance of his work for any thinking concerned with a politicised resistance to social conformity and the supposed “state of things” today

Multiscale modeling of the elasto-plastic behavior of architectured and nanostructured Cu-Nb composite wires and comparison with neutron diffraction experiments

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields ( 100T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shape along the wire axis. This paper presents a comprehensive study of the effective elastoplastic behavior of this composite material by using two different approaches to model the microstructural features: full-field finite elements and mean-field modeling. As the material exhibits several characteristic scales, an original hierarchical strategy is proposed based on iterative scale transition steps from the nanometric grain scale to the millimetric macro-scale. The best modeling strategy is selected to estimate reliably the effective elasto-plastic behavior of Cu-Nb wires with minimum computational time. Finally, for the first time, the models are confronted to tensile tests and in-situ neutron diffraction experimental data with a good agreement

The Parental Non-Equivalence of Imprinting Control Regions during Mammalian Development and Evolution

In mammals, imprinted gene expression results from the sex-specific methylation of imprinted control regions (ICRs) in the parental germlines. Imprinting is linked to therian reproduction, that is, the placenta and imprinting emerged at roughly the same time and potentially co-evolved. We assessed the transcriptome-wide and ontology effect of maternally versus paternally methylated ICRs at the developmental stage of setting of the chorioallantoic placenta in the mouse (8.5dpc), using two models of imprinting deficiency including completely imprint-free embryos. Paternal and maternal imprints have a similar quantitative impact on the embryonic transcriptome. However, transcriptional effects of maternal ICRs are qualitatively focused on the fetal-maternal interface, while paternal ICRs weakly affect non-convergent biological processes, with little consequence for viability at 8.5dpc. Moreover, genes regulated by maternal ICRs indirectly influence genes regulated by paternal ICRs, while the reverse is not observed. The functional dominance of maternal imprints over early embryonic development is potentially linked to selection pressures favoring methylation-dependent control of maternal over paternal ICRs. We previously hypothesized that the different methylation histories of ICRs in the maternal versus the paternal germlines may have put paternal ICRs under higher mutational pressure to lose CpGs by deamination. Using comparative genomics of 17 extant mammalian species, we show here that, while ICRs in general have been constrained to maintain more CpGs than non-imprinted sequences, the rate of CpG loss at paternal ICRs has indeed been higher than at maternal ICRs during evolution. In fact, maternal ICRs, which have the characteristics of CpG-rich promoters, have gained CpGs compared to non-imprinted CpG-rich promoters. Thus, the numerical and, during early embryonic development, functional dominance of maternal ICRs can be explained as the consequence of two orthogonal evolutionary forces: pressure to tightly regulate genes affecting the fetal-maternal interface and pressure to avoid the mutagenic environment of the paternal germline

Human oocyte-derived methylation differences persist in the placenta revealing widespread transient imprinting

Thousands of regions in gametes have opposing methylation profiles that are largely resolved during the post-fertilization epigenetic reprogramming. However some specific sequences associated with imprinted loci survive this demethylation process. Here we present the data describing the fate of germline-derived methylation in humans. With the exception of a few known paternally methylated germline differentially methylated regions (DMRs) associated with known imprinted domains, we demonstrate that sperm-derived methylation is reprogrammed by the blastocyst stage of development. In contrast a large number of oocyte-derived methylation differences survive to the blastocyst stage and uniquely persist as transiently methylated DMRs only in the placenta. Furthermore, we demonstrate that this phenomenon is exclusive to primates, since no placenta-specific maternal methylation was observed in mouse. Utilizing single cell RNA-seq datasets from human preimplantation embryos we show that following embryonic genome activation the maternally methylated transient DMRs can orchestrate imprinted expression. However despite showing widespread imprinted expression of genes in placenta, allele-specific transcriptional profiling revealed that not all placenta-specific DMRs coordinate imprinted expression and that this maternal methylation may be absent in a minority of samples, suggestive of polymorphic imprinted methylation