Measure of combined effects of morphological parameters of inclusions within composite materials via stochastic homogenization to determine effective mechanical properties

In our previous papers we have described efficient and reliable methods of generation of representative volume elements (RVE) perfectly suitable for analysis of composite materials via stochastic homogenization. In this paper we profit from these methods to analyze the influence of the morphology on the effective mechanical properties of the samples. More precisely, we study the dependence of main mechanical characteristics of a composite medium on various parameters of the mixture of inclusions composed of spheres and cylinders. On top of that we introduce various imperfections to inclusions and observe the evolution of effective properties related to that. The main computational approach used throughout the work is the FFT-based homogenization technique, validated however by comparison with the direct finite elements method. We give details on the features of the method and the validation campaign as well. Keywords: Composite materials, Cylindrical and spherical reinforcements, Mechanical properties, Stochastic homogenization.Comment: 23 pages, updated figures, version accepted to Composite Structures 201

Cell-Specific Imd-NF-κB Responses Enable Simultaneous Antibacterial Immunity and Intestinal Epithelial Cell Shedding upon Bacterial Infection

Intestinal infection triggers potent immune responses to combat pathogens and concomitantly drives epithelial renewal to maintain barrier integrity. Current models propose that epithelial renewal is primarily driven by damage caused by reactive oxygen species (ROS). Here we found that in Drosophila, the Imd-NF-κB pathway controlled enterocyte (EC) shedding upon infection, via a mechanism independent of ROS-associated apoptosis. Mechanistically, the Imd pathway synergized with JNK signaling to induce epithelial cell shedding specifically in the context of bacterial infection, requiring also the reduced expression of the transcription factor GATAe. Furthermore, cell-specific NF-κB responses enabled simultaneous production of antimicrobial peptides (AMPs) and epithelial shedding in different EC populations. Thus, the Imd-NF-κB pathway is central to the intestinal antibacterial response by mediating both AMP production and the maintenance of barrier integrity. Considering the similarities between Drosophila Imd signaling and mammalian TNFR pathway, our findings suggest the existence of an evolutionarily conserved genetic program in immunity-induced epithelial sheddin

Polariton-polariton interaction potentials determination by pump-probe degenerate scattering in a multiple microcavity

International audienceWe study the polarisation-dependent polariton-polariton interaction through its effect on a parametric scattering process in a microcavity (MC). The ratio of the anti-circular interaction strength V2 over its co-circular counterpart V1 is involved in defining the regime in which many nonlinear processes arise in MCs, such as parametric conversion or condensation. We measure the ratio V2/V1 using a stimulated energy-degenerate parametric scattering process in a multiple MC. The sample is pumped at normal incidence, probed with a non-zero angle, and the phase-matched idler is observed at the opposite angle. The idler behaviour, both in power and polarisation, is compared to a hamiltonian interaction model that takes into account the two polarisation-dependent parametric scattering channels characterized by V1 and V2. The proposed method to measure the ratio V2/V1 is convenient and precise. The flexibility of the triple MC allows to observe the process and measure this ratio over a large range of detunings, where we find it to be highly dependent on the detuning. These measurements complement the previous study of Vladimirova et al. [Phys. Rev. B 82, 075301 (2010)] with an original approach and for detunings that were unexplored up to now

The antimicrobial peptide Defensin cooperates with tumour necrosis factor to drive tumour cell death in Drosophila

Antimicrobial peptides (AMPs) are small cationic molecules best known as mediators of the innate defence against microbial infection. While in vitro and ex vivo evidence suggest AMPs’ capacity to kill cancer cells, in vivo demonstration of an anti-tumour role of endogenous AMPs is lacking. Using a Drosophila model of tumourigenesis, we demonstrate a role for the AMP Defensin in the control of tumour progression. Our results reveal that Tumour Necrosis Factor mediates exposure of phosphatidylserine (PS), which makes tumour cells selectively sensitive to the action of Defensin remotely secreted from tracheal and fat tissues. Defensin binds tumour cells in PS-enriched areas, provoking cell death and tumour regression. Altogether, our results provide the first in vivo demonstration for a role of an endogenous AMP as an anti-cancer agent, as well as a mechanism that explains tumour cell sensitivity to the action of AMPs

Génération aléatoire de VER à inclusions géométriques modulables inspirée de la dynamique moléculaire

Les matériaux composites sont de plus en plus élaborés pour répondre à des demandes plus exigeantes dans l'industrie aéronautique, automobile,.... L'objectif d'un nouveau matériau est de garantir des caractéristiques supérieures à celles des matériaux déjà existants, selon l'usage qu'on lui destine. Ils sont complexes dans leur mise en ?uvre et leur expérimentation est souvent délicate et onéreuse. Pour étudier un matériau en phase de conception, nous pouvons nous intéresser à ses caractéristiques homogénéisées mécaniques et thermiques. Pour ce faire, nous recourons à des méthodes expérimentales ou bien numériques avec l'utilisation des éléments finis ou de la FFT (Fast Fourier Transform). Dans une simulation numérique en 3D, nous devons disposer d'une représentation en 3D du matériau (maillage ou images). Des images peuvent être obtenues par tomographie, mais cette technique est coûteuse, demande d'avoir accès à des appareils peu accessibles au niveau académique et nécessite un traitement d'image. C'est pourquoi, naturellement, la génération aléatoire permet de répondre à cette problématique. Plus particulièrement, nous nous intéressons à la génération aléatoire d'un matériau composite en 3D de type matrice renforcée. Dans la littérature, nous trouvons la méthode RSA très efficace pour des volumes d'inclusions allant jusqu'à 30 % environ. Toutefois, pour des volumes supérieurs d'inclusions, la méthode RSA devient prohibitive en temps. Nous proposons alors de générer des VER 3D de type matrice renforcée d'inclusions à géométrie sphérique, cylindrique ou elliptique en utilisant une méthode inspirée de la dynamique moléculaire. Cette génération aléatoire garantit des inclusions disjointes deux à deux, pouvant au besoin être déformées, arrachées partiellement, ou pelliculées. L'intérêt de la génération proposée est sa capacité à générer aléatoirement sans recouvrement un VER avec des taux d'inclusions supérieurs à 30 % du volume total. Le taux d'inclusion (à dimensions constantes pour chaque type d'inclusion) peut en effet atteindre 60 % du volume total. De plus, cette méthode basée sur la dynamique moléculaire est capable de générer des VER à des taux d'inclusions supérieurs à 60 % en prenant en compte des tailles variables des géométries choisies pour les inclusions, typiquement cela consiste à faire varier le rayon des sphères et / ou des cylindres et / ou des sphéroïdes. La génération prend alors en compte un grand nombre d'inclusions (de l'ordre de 1000 ou davantage). Les applications de cette génération sont multiples. Elle est modulable : les géométries considérées sont diverses, les inclusions peuvent être post-traitées pour être pelliculées ou déformées. Elle s'adapte aux calculs de coefficients homogénéisés en élasticité et en thermique via des méthodes de type éléments finis ou des méthodes basées sur la FFT (Fast Fourier Transform)

Computation of thermal properties via 3D homogenization of multiphase materials using FFT-based accelerated scheme

In this paper we study the thermal effective behaviour for 3D multiphase composite material consisting of three isotropic phases which are the matrix, the inclusions and the coating media. For this purpose we use an accelerated FFT-based scheme initially proposed in Eyre and Milton (1999) to evaluate the thermal conductivity tensor. Matrix and spherical inclusions media are polymers with similar properties whereas the coating medium is metallic hence better conducting. Thus, the contrast between the coating and the others media is very large. For our study, we use RVEs (Representative volume elements) generated by RSA (Random Sequential Adsorption) method developed in our previous works, then, we compute effective thermal properties using an FFT-based homogenization technique validated by comparison with the direct finite elements method. We study the thermal behaviour of the 3Dmultiphase composite material and we show what features should be taken into account to make the computational approach efficient

Genetic variations within human gained enhancer elements affect human brain sulcal morphology.

The expansion of the cerebral cortex is one of the most distinctive changes in the evolution of the human brain. Cortical expansion and related increases in cortical folding may have contributed to emergence of our capacities for high-order cognitive abilities. Molecular analysis of humans, archaic hominins, and non-human primates has allowed identification of chromosomal regions showing evolutionary changes at different points of our phylogenetic history. In this study, we assessed the contributions of genomic annotations spanning 30 million years to human sulcal morphology measured via MRI in more than 18,000 participants from the UK Biobank. We found that variation within brain-expressed human gained enhancers, regulatory genetic elements that emerged since our last common ancestor with Old World monkeys, explained more trait heritability than expected for the left and right calloso-marginal posterior fissures and the right central sulcus. Intriguingly, these are sulci that have been previously linked to the evolution of locomotion in primates and later on bipedalism in our hominin ancestors

One-dimensional microcavity-based optical parametric oscillator: generation of balanced twin beams in strong and weak coupling regime

International audienceWe report on a detailed experimental investigation of interbranch parametric scattering processes in onedimensional semiconductor microcavities. Band dispersion and corresponding far field emission patterns are studied by polarization resolved and power dependence measurements under resonant and non-resonant excitation at normal incidence. We demonstrate the realization of optical parametric oscillation of balanced twin beams which are degenerate in energy and split in momentum space. This achievement is shown for both the strong and the weak coupling regime highlighting the versatility of this peculiar microcavity system