Effective Thermal conductivity of divided silica xerogel beds

International audienceApparent thermal conductivity (λ) measurements were made on monolithic silica aerogels and divided low-density xerogels. The objective of the tests on monoliths was to determine the variation of λ with the solid content. Additional compressive tests were also made to follow the evolution of bulk modulus with apparent density, in order to further optimize the solid content of xerogel particles. Divided xerogels were characterized under the following conditions: at ambient conditions (T, P, and relative humidity of water vapor in air), under partial vacuum (from atmospheric pressure to 4 × 10−7 bar) and under different relative humidities. The effect of the divided xerogel granularity on λ has been studied by using different size range and distributions. The results of our studies indicate an optimum particle density at 0.15 g cm−3, and a decrease in λ for samples containing fine particles

Macroscopically consistent non-local modelling of heterogeneous media

International audienceWithin the framework of the homogenization of heterogeneous media, a non local model is proposed. A field of non-local filtered stiffness tensor is introduced by filtering the solution to the homogenization problem. The filtered stiffness tensor, depending on the filter to heterogeneity size ratio, provides a continuous transition from the actual micro-scale heterogeneous stiffness field to the macro-scale homogenized stiffness tensor. For any intermediate filter size, the homogenization of the filtered stiffness yields exactly the homogenized stiffness, therefore it is called macroscopically consistent. The non-local stiffness tensor is intrinsically non symmetric, but its spatial fluctuations are smoothed, allowing for a less refined discretization in numerical methods. As a by-product, a two step heterogeneous multiscale method is proposed to reduce memory and computational time requirements of existing direct schemes while controlling the accuracy of the result. The first step is the estimation of the filtered stiffness at sampling points by means of an oversampling strategy to reduce boundary effects. The second step is the numerical homogenization of the obtained sampled filtered stiffness

Coupling continuous damage and debris fragmentation for energy absorption prediction by cfrp structures during crushing

Energy absorption during crushing is evaluated using a thermodynamic based continuum damage model inspired from the Matzenmiller–Lubliner–Taylors model. It was found that for crash-worthiness applications, it is necessary to couple the progressive ruin of the material to a representation of the matter openings and debris generation. Element kill technique (erosion) and/or cohesive elements are efficient but not predictive. A technique switching finite elements into discrete particles at rupture is used to create debris and accumulated mater during the crushing of the structure. Switching criteria are evaluated using the contribution of the different ruin modes in the damage evolution, energy absorption, and reaction force generation

Genome-wide association analyses identify new Brugada syndrome risk loci and highlight a new mechanism of sodium channel regulation in disease susceptibility

Brugada syndrome (BrS) is a cardiac arrhythmia disorder associated with sudden death in young adults. With the exception of SCN5A, encoding the cardiac sodium channel NaV1.5, susceptibility genes remain largely unknown. Here we performed a genome-wide association meta-analysis comprising 2,820 unrelated cases with BrS and 10,001 controls, and identified 21 association signals at 12 loci (10 new). Single nucleotide polymorphism (SNP)-heritability estimates indicate a strong polygenic influence. Polygenic risk score analyses based on the 21 susceptibility variants demonstrate varying cumulative contribution of common risk alleles among different patient subgroups, as well as genetic associations with cardiac electrical traits and disorders in the general population. The predominance of cardiac transcription factor loci indicates that transcriptional regulation is a key feature of BrS pathogenesis. Furthermore, functional studies conducted on MAPRE2, encoding the microtubule plus-end binding protein EB2, point to microtubule-related trafficking effects on NaV1.5 expression as a new underlying molecular mechanism. Taken together, these findings broaden our understanding of the genetic architecture of BrS and provide new insights into its molecular underpinnings

Genome-wide association analyses identify new Brugada syndrome risk loci and highlight a new mechanism of sodium channel regulation in disease susceptibility.

Brugada syndrome (BrS) is a cardiac arrhythmia disorder associated with sudden death in young adults. With the exception of SCN5A, encoding the cardiac sodium channel Na1.5, susceptibility genes remain largely unknown. Here we performed a genome-wide association meta-analysis comprising 2,820 unrelated cases with BrS and 10,001 controls, and identified 21 association signals at 12 loci (10 new). Single nucleotide polymorphism (SNP)-heritability estimates indicate a strong polygenic influence. Polygenic risk score analyses based on the 21 susceptibility variants demonstrate varying cumulative contribution of common risk alleles among different patient subgroups, as well as genetic associations with cardiac electrical traits and disorders in the general population. The predominance of cardiac transcription factor loci indicates that transcriptional regulation is a key feature of BrS pathogenesis. Furthermore, functional studies conducted on MAPRE2, encoding the microtubule plus-end binding protein EB2, point to microtubule-related trafficking effects on Na1.5 expression as a new underlying molecular mechanism. Taken together, these findings broaden our understanding of the genetic architecture of BrS and provide new insights into its molecular underpinnings

Le pouvoir fédéral face au contexte praxique (le cas du surf et des pratiquants libres)

L'analyse de la pratique libre du surf a permis de mettre en évidence un ensemble de configurations multifactorielles et dynamiques parmi lesquelles le phénomène de concurrence s'est révélé central. En se positionnant comme comme un principe organisateur structurant les modalités de pratique, il génère un système de répartition des capacités d'action pour l'ensemble de la population de pratiquants. Cette quête de pratique, c'est-à-dire le désir (souvent inassouvi) de faire du surf , associé à celui d' être surfeur , se situe au centre de la relation qui lie et/ou délie le pratiquant à la fédération. Notre réflexion fait apparaître que le désaccord n'est pas déterminé par un désir de liberté ou une recherche d'indépendance, mais qu'il s'explique par la structure de l'activité organisée autour de normes de fonctionnalité autonomes et contingentes émergeant d'une culture d'adaptation . C'est au sein de cette résistance positive et émancipatoire, propitiatoire d'une pratique en quête d'équilibre et d'équilibrage des forces en présence, que certains pratiquants font le choix de s'opposer , consciemment ou non, à l'orthopraxie fédérale. Dans ce cadre, la contestation , notamment règlementaire, n'est pas un état d'esprit préalable à l'activité mais un comportement subséquent à la pratique contextuée. Ce désaccord participe d'un système aporétique faisant état d'une contradiction insoluble entre la démarche fédérale indifférenciatrice relative à une conception intégrative de l'ensemble des surfeurs, et la logique différenciatrice des pratiquants en lien direct avec la structure exluante de la pratique. L'univers du surf ne constitue pas une res publica dans laquelle la fédération parviendrait à édicter une forme d'organisation légitimée par tous ses pratiquants. Il s'agit d'une res nullius, la chose de personne ainsi dévoluée aux pratiquants eux-mêmes. Sujette aux possessions et aux appropriations, elle génère un processus continuel de légitimation et de dé-légitimation structurant la pratique libre du surf et dont l'enjeu premier demeure la quête praxique, autrement dit, la conquête de vague.ROUEN-BU Lettres (764512101) / SudocSudocFranceF

Drying of silica gels to obtain aerogels : phenomenology and basic techniques: Review

International audienc

Présentation générale du séchage des gels de silice nanostructures

International audienc

Study of evaporative drying of treated silica gels

Issu de : 7th International symposium on Aerogels (ISA-7), Alexandria, Virginia, USA, 2-5 November, 2003International audienceStudies were performed on silica gels synthesized in isopropanol to determine the parameters necessary to follow evaporative drying quantitatively, particularly during the last drying phase controlled by vapor diffusion in the gel nanostructure. As prepared and silanized gels were compared. Dynamic vapor sorption of isopropanol was used to determine adsorption isotherms and apparent diffusion coefficients in the silica network. A significant effect of surface modification (consisting in capping the silica surface with trimethylsilyl groups) has been observed. The diffusivity of solvent vapors was found to be very low, from 10-9 to 10-10 m2s-1, respectively, for treated and untreated samples, but in agreement with previously published works. Microcalorimetry confirmed a reduction in the affinity between the solid phase and solvent due to the silanization treatment. In parallel, evaporative drying experiments were conducted, recording the sample mass and taking photographs during the entire process of solvent evaporation. Comparison between untreated and treated samples during the last drying step showed how and when spring-back takes place for the latter