Modélisation multiéchelle du comportement thermo-mécanique des CMO et prise en compte des effets du vieillissement thermique

L'utilisation des Composites à Matrice Organique sur de longues durées, nécessite de prendre en compte les effets du vieillissement qui peuvent considérablement modifier les propriétés mécaniques au cours du temps et réduire la durée de vie. L'objectif de ce travail est de développer un modèle macroscopique utilisable dans le contexte du calcul de structures par Eléments Finis, couplant les différents aspects : viscoélasticité, endommagement et vieillissement thermique. Nous proposons une démarche multiéchelle s'appuyant sur les différentes échelles du composite. Le comportement du pli est obtenu à partir du comportement de ses constituants (fibre et matrice) par la méthode appelée Transformation Fied Analysis. Afin d'analyser les effets du vieillissement thermique, une importante campagne expérimentale a été menée comprenant une caractérisation de type mécanique et physico-chimique. Les effets du vieillissement sont intégrés dans le modèle par l'intermédiaires de variables internesThe use of organic matrix composites for long-term applications leads to take into account the effects of thermal ageing which can considerably modify the mechanical properties and reduce the composite lifetime. The aim of this study is to develop a macroscopic model for structural computation using the finite Element method and to couple different aspects such as : viscoelasticity, damage and thermal ageing. We suggest a multiscale approach laying on the different scales of a composite. The ply behaviour is deduced from the behaviour of the constituents (fibre and matrix) by using Transformation Field Analysis method. In order to analyse the effects of thermal ageing, an important experimental part has been carried out, including mechanical and chemical measurements. Ageing effects are introduced in the model using internal parametersTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Hétéro-épitaxie III-V/Si : contrôle des propriétés des surfaces et interfaces pour la photo-électrochimie

National audienceL’intégration monolithique de semi-conducteurs III-V sur substrat de Si a de nombreux avantages dans le domaine de la photonique, de l’électronique, ou de l’énergie. Dans cet exposé, nous montrerons tout d’abord le rôle fondamental des surfaces et interfaces et de leur structure atomique lors de la croissance III-V sur Si. Nous montrerons ensuite que les parois d’antiphase créées lors de la croissance cristalline se comportent comme des singularités 2D avec des propriétés de confinement de porteurs et de phonons originales. Enfin, nous montrerons comment ces singularités peuvent dans certains cas se comporter comme des inclusions semi-métalliques, et comment il est possible de s’en servir pour la production d’hydrogène solaire

Hétéro-épitaxie III-V/Si : contrôle des propriétés des surfaces et interfaces pour la photo-électrochimie

National audienceL’intégration monolithique de semi-conducteurs III-V sur substrat de Si a de nombreux avantages dans le domaine de la photonique, de l’électronique, ou de l’énergie. Dans cet exposé, nous montrerons tout d’abord le rôle fondamental des surfaces et interfaces et de leur structure atomique lors de la croissance III-V sur Si. Nous montrerons ensuite que les parois d’antiphase créées lors de la croissance cristalline se comportent comme des singularités 2D avec des propriétés de confinement de porteurs et de phonons originales. Enfin, nous montrerons comment ces singularités peuvent dans certains cas se comporter comme des inclusions semi-métalliques, et comment il est possible de s’en servir pour la production d’hydrogène solaire

MAP-Kinase Activated Protein Kinase 2 Links Endothelial Activation and Monocyte/macrophage Recruitment in Arteriogenesis

<div><p>Arteriogenesis, the growth of natural bypass arteries, is triggered by hemodynamic forces within vessels and requires a balanced inflammatory response, involving induction of the chemokine MCP-1 and recruitment of leukocytes. However, little is known how these processes are coordinated. The MAP-kinase-activated-proteinkinase-2 (MK2) is a critical regulator of inflammatory processes and might represent an important link between cytokine production and cell recruitment during postnatal arteriogenesis. Therefore, the present study investigated the functional role of MK2 during postnatal arteriogenesis. In a mouse model of hindlimb ischemia (HLI) MK2-deficiency (MK2KO) significantly impaired ischemic blood flow recovery and growth of collateral arteries as well as perivascular recruitment of mononuclear cells and macrophages. This was accompanied by induction of endothelial MCP-1 expression in wildtype (WT) but not in MK2KO collateral arteries. Following HLI, MK2 activation rapidly occured in the endothelium of growing WT arteries <i>in vivo</i>. <i>In vitro</i>, inflammatory cytokines and cyclic stretch activated MK2 in endothelial cells, which was required for stretch- and cytokine-induced release of MCP-1. In addition, a monocyte cell autonomous function of MK2 was uncovered potentially regulating MCP-1-dependent monocyte recruitment to vessels: MCP-1 stimulation of WT monocytes induced MK2 activation and monocyte migration <i>in vitro</i>. The latter was reduced in MK2KO monocytes, while <i>in vivo</i> MK2 was activated in monocytes recruited to collateral arteries. In conclusion, MK2 regulates postnatal arteriogenesis by controlling vascular recruitment of monocytes/macrophages in a dual manner: regulation of endothelial MCP-1 expression in response to hemodynamic and inflammatory forces as well as MCP-1 dependent monocyte migration.</p></div

MK2 essentially regulates blood flow recovery after hind limb ischemia and growth of collateral arteries during postnatal arteriogenesis.

<p>A, blood flow was determined by laser-doppler-blood flow analysis in wildtype (WT) and MK2-deficient (MK2KO) mice after HLI at the indicated times (day 0 to 21 after arterial ligation). Perfusion is given as relative ischemic perfusion compared to blood flow before arterial ligation (*<i>p</i>< 0.01 WT vs. MK2KO, n = 11). B-E, after HLI (day 21 post arterial ligation) sections (B, H & E staining) of collateral arteries of the ischemic (HLI) and contralateral non-ischemic limb (CTRL) from WT and MK2KO were analyzed by histomorphometry for diameter (C), wall area (D) and number of perivascular mononuclear cells (E). (C-E), #<i>p</i>< 0.05 control vs. HLI, *<i>p</i>< 0.01 WT vs. MK2KO, n = 6).</p

MK2 is activated in monocytes recruited to collateral arteries and mediates MCP-1 induced monocyte migration.

<p>A, Primary murine monocytes isolated from WT mice were stimulated with MCP-1 (10 ng/ml) or LPS (100ng/ml) for the indicated times and activation of MK2 was determined by immunoblotting for phospho-MK2. Representative blots of two independent experiments each employing monocyte isolations from 3 different mice are shown. B, Primary murine monocytes isolated from WT and MK2KO were given into the upper chamber of a transwell cell culture dish and number of cells migrated towards MCP-1 (10 ng/ml) in the lower chamber was quantified after 24 h and normalized to the total number of cells given into the upper chamber (migration-index). #<i>p</i>< 0.05 control vs. MCP-1, *<i>p</i>< 0.05 WT vs. MK2KO, n = 5). C, after hind limb ischemia (6 h after arterial ligation) sections of collateral arteries from the ischemic limb of WT mice were stained for activated phospho-MK2 and analyzed by fluorescence laser scanning confocal microscopy (phospho-MK2, green; endothelial cells, red, CD31; nuclear staining, blue, DAPI). Representative stainings of at least 3 different experiments are shown.</p

MK2 is essential for the vascular recruitment of macrophages and expression of MCP-1 during postnatal arteriogenesis.

<p>A-B, after hind limb ischemia sections of collateral arteries from the ischemic limb from WT and MK2KO were stained for macrophages (A) or MCP-1 (B) (red, F4/80 or MCP-1), α-smooth muscle cell actin (green, SMA) and cell nuclei (blue, DAPI) and analyzed by fluorescence laser scanning confocal microscopy. Representative staining of at least 3 different experiments (day 3 post arterial ligation) are shown. C, mRNA-expression of MCP-1 was determined in hind limb muscle from wildtype (WT) mice at baseline (bsl) and 6 h, day 1 (d1), days 3 (d3), and day 7 (d7) after HLI. Relative mRNA-expression determined by qRT-PCR is shown (*p< 0.05 baseline vs. day 1, n = 4–5). D, mRNA-expression of MCP-1 was determined in hind limb tissue from wildtype (WT) and MK2-deficient mice (MK2KO) at day 1 (d1) after HLI (*p< 0.01 WT vs. MK2KO, n = 6).</p

Model of MK2-regulated postnatal arteriogenesis.

<p>MK2 controls vascular recruitment of monocytes/macrophages during postnatal arteriogenesis in a dual manner: regulation of endothelial MCP-1 expression in response to hemodynamic and inflammatory forces as well as MCP-1-dependent monocyte migration.</p