Modifications mécaniques et biologiques induites dans des cellules en culture par application locale d'une force contrôlée

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Elaboration de matériaux poreux géopolymères à porosité multi-échelle et contrôlée

Ce travail est basé sur l élaboration, la caractérisation, et le contrôle de la porosité d un matériau poreux à matrice géopolymérique, synthétisé à partir du mélange de métakaolin, d une solution de silicate alcaline, d hydroxyde alcalin, et de fumée de silice comme agent porogène. Ce mélange donne lieu à une mousse avec production continue de dihydrogène in-situ au sein d un gel visqueux évolutif. Le contrôle de la porosité à cette valeur élevée de pH est régi par un équilibre entre des cinétiques de réactions de polycondensation (consolidation) et de production de gaz. L influence des différents paramètres est testée par la caractérisation du réseau poreux obtenu. La conductivité thermique d échantillons homogènes est mesurée par fluxmètre et par fil chaud. Ces valeurs sont discutées à partir de l analyse de la microstructure et des différents modèles analytiques issus de la littérature. Une démarche numérique inverse est utilisée pour retrouver la valeur de conductivité thermique du squelette solide s du matériau. En effet il est difficile d obtenir un matériau pseudo-dense pour une même composition. Un calcul par éléments finis, avec une méthode d homogénéisation, est appliqué sur des Volumes Elémentaires Représentatifs construits à partir des données expérimentales. La valeur de s est alors évaluée entre 0,98 et 1,12 W.m-1.K-1. Les mousses ont des taux de porosité compris entre 65 et 85% et des valeurs de conductivités thermiques comprises entre 0,12 et 0,35 W.m-1.K-1, ce qui en fait un matériau isolant.This work is focused on the preparation, the characterization, and the control of the porosity in geopolymer foams, synthesized from the mixing of metakaolin, a alkali silicate solution, alkali hydroxide, and silica fume as the pore forming agent. This mixture results in a foam in which hydrogen gas is produced continuously in an evolutive viscous gel. The control of porosity, in consideration of the very high value of pH, requires the establishment of an equilibrium between the kinetics of polycondensation reactions (hardening) and the kinetics of gassing. The influence of different parameters is studied through the characterization of the obtained porous network. The thermal conductivity of the homogeneous samples is measured with a fluxmeter and also with a hot wire method. The values obtained are then discussed in relation to the microstructure and relevant analytical models of the literature. An inverse numerical approach is used to find the thermal conductivity value of the skeleton of the foam s. In fact, it is difficult to prepare a material with a low pore volume fraction from the same composition. A finite element calculation, coupled with a homogenization method, is applied on Representative Volume Elements constructed in relation with the experimental data. The value of s is then calculated between 0.98 and 1.12 W.m-1.K-1. The foams have pore volume fractions values between 65 and 85% corresponding to thermal conductivity values between 0.12 and 0.35 W.m-1.K-1, yielding a good material for thermal insulation.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

L’outillage de mouture va-et-vient des Feuilly à Saint-Priest (Rhône)

International audiencel’étude des moulins va et vient des Feuilly, à Saint-Priest (Rhône), permet de présenter l’évolution typologique et pétrographique de l’outillage de mouture d’un même site depuis le Néolithique moyen, de culture bourguignonne, jusqu’à la charnière du premier et second âge du Fer en passant par le Bronze final 2b-3a. La réduction de la courbure de la surface active semble se confirmer entre le Néolithique et la Protohistoire. Une molette débordante du Néolithique moyen est identifiée. Alors qu’aucune évolution typologique n’apparaît entre le matériel du Bronze final et celui de l’âge du Fer, des différences pétrographiques dans le choix des matériaux voient le jour, avec une plus grande variété de roches durant la Protohistoire, bien que le granite reste le matériau de prédilection depuis le Néolithique moyen

Analytical estimation of skeleton thermal conductivity of a geopolymer foam from thermal conductivity measurements

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Potassium geopolymer foams made with silica fume pore forming agent for thermal insulation

International audiencePorous potassium based geopolymers with a mutli-scale porosity were synthesized. Silica fume is introduced as an additive to the geopolymer formulation. The free silicon contained inside this silica fume is oxidized in alkaline solution, releasing molecular hydrogen which generates the porosity. Previous work has shown how the porosity can be controlled with temperature, repeated temperature cycles and the mass introduced. Using this protocol, homogeneous foams were made and then studied with scanning electron microscopy. In particular the foam expansion has been followed with time in relation to the microstructure. The thermal conductivity values of the foams were evaluated using a fluxmeter method. The effective thermal conductivities are comprised between 0.12 and 0.35 W m−1 K−1 for apparent densities ranging from 0.40 to 0.85 g cm−3. The corresponding calculated pore volume fractions are in the range of 65–85%. The interest of this material is that it combines the advantages of low bulk density and insulating properties with the characteristics of a geopolymer skeleton. Literature reports a very good fire and acid/base resistance, a low cost of production and the possibility of recycling industrial waste in the form of silica fume

Porosity control of cold consolidated geomaterial foam: Temperature effect

International audiencePorous K-geopolymers with mutli-scale porosity were synthetized, based on the production of molecular hydrogen due to the oxidation of free silicon associated with polycondensation reactions. The various drying steps at low temperatures influencing the foams morphology were evaluated in function of parameters like mass effect, mold dimensions and drying cycles. The results obtained evidenced the possibility to perform reproducible foams with a control of their porosity. These foams are in agreement with the environmental demand with their recycling properties and their low cost of production due to the cheap materials used and the low temperature of synthesis. Some other advantages like their fire resistance, acid/base resistance, their good mechanical properties and their good thermal conductivity is a good point for future applications. As an example a homogeneous foam with a pore size of 1.5 mm at 50 °C (9 days for an achieved drying but consolidated before) can be prepared. Moreover the porosity can be controlled with various temperature cycles decreasing the time of synthesis. From the cycles tested (70–55 °C and 70–23 °C), some homogeneous samples were obtained with pores sizes varying from 0.5 to 1.5 mm. Then the work was extended to larger surfaces exchange, what evidences the importance of drying and mass effects upon the porosity as well as the mechanical properties of the mold used during synthesis

Analytical and numerical identification of the skeleton thermal conductivity of a geopolymer foam using a multi-scale analysis

International audienceThis work focuses on the identification of the thermal conductivity of potassium geopolymer foams by experimental and numerical/analytical approaches. The porous foams, synthesized by a direct foaming process, display pore volume fractions ranging between 65% and 85% with thermal conductivities from 0.35 to 0.12 W m-1 K-1 respectively. A quantitative characterization of the pore volume fractions has been made by image analysis, taking into account the multi-scale aspect of these foams. Motivated by the character of the microstructure, an inverse multi-scale analytical method was applied to find the value of the thermal conductivity of the skeleton λs. In fact, due to the range of pore volume fractions, standard analytical relations describing thermal conductivity were found to be of limited use. In order to take into account the local aspects of the microstructure and to treat the actual pore volume fractions, an inverse numerical approach, based on a finite element calculation coupled with a homogenization method, was used. As a result, the multi-scale analytical approach evaluates the value of λs between 0.95 and 1.19 W m-1 K-1. Numerical results, taking faithfully into account local parameters of the pore network, give λs values within the range 1.09-1.12 W m-1 K-1. The numerical values of λs are in agreement with values obtained in the literature

Lymphocytes can self-steer passively with wind vane uropods

International audienceA wide variety of cells migrate directionally in response to chemical or mechanical cues, however the mechanisms involved in cue detection and translation into directed movement are debatable. Here, we investigate a model of lymphocyte migration on the inner surface of blood vessels. Cells orient their migration against fluid flow, suggesting the existence of an adaptive mechano-tranduction mechanism. We find that flow detection may not require molecular mechano-sensors of shear stress and detection of flow direction can be achieved by the orientation in the flow of the non-adherent cell rear, the uropod. Uropods act as microscopic wind vanes that can transmit detection of flow direction into cell steering via the on-going machinery of polarity maintenance, without need for novel internal guidance signalling triggered by flow. Contrary to chemotaxis, which implies active regulation of cue-dependant signalling, upstream flow mechanotaxis of lymphocytes may only rely on a passive self-steering mechanism

Condé-sur-Suippe : l’oppidum du « Vieux Reims » (Aisne, RD62): Rapport de fouille archéologique 2016

National audienceL’opération de fouilles préventives menée en 2012 au cœur de l’oppidum de Condé-sur-Suippe/Variscourt concernait une surface de 1 200 m² dans l'enceinte de l'ancienne sucrerie. Cette fouille faisait suite à deux diagnostics qui avaient mis en évidence l'existence de secteurs préservés au sein du site industriel. Un des intérêts de cette fouille est d’avoir, malgré la surface restreinte, livré un focus sur un nouveau secteur de cet oppidum, bien connu des protohistoriens. Elle vient compléter les informations acquises lors de fouilles de grande envergure réalisées dans les années 70 et 80 mais dont les résultats n’ont été que partiellement publiés. Ces nouvelles données s’intègrent dans l’axe 5 de la programmation de la recherche archéologique en France, en ce qu’elle concerne l’organisation d’un site fortifié à caractère urbain