33 research outputs found
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 Ă 10â7 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 cmâ3, 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 MatzenmillerâLublinerâTaylors 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 Ă©vidence un ensemble de configurations multifactorielles et dynamiques parmi lesquelles le phĂ©nomĂšne de concurrence s'est rĂ©vĂ©lĂ© central. En se positionnant comme comme un principe organisateur structurant les modalitĂ©s de pratique, il gĂ©nĂšre un systĂšme de rĂ©partition des capacitĂ©s d'action pour l'ensemble de la population de pratiquants. Cette quĂȘte de pratique, c'est-Ă -dire le dĂ©sir (souvent inassouvi) de faire du surf , associĂ© Ă celui d' ĂȘtre surfeur , se situe au centre de la relation qui lie et/ou dĂ©lie le pratiquant Ă la fĂ©dĂ©ration. Notre rĂ©flexion fait apparaĂźtre que le dĂ©saccord n'est pas dĂ©terminĂ© par un dĂ©sir de libertĂ© ou une recherche d'indĂ©pendance, mais qu'il s'explique par la structure de l'activitĂ© organisĂ©e autour de normes de fonctionnalitĂ© autonomes et contingentes Ă©mergeant d'une culture d'adaptation . C'est au sein de cette rĂ©sistance positive et Ă©mancipatoire, propitiatoire d'une pratique en quĂȘte d'Ă©quilibre et d'Ă©quilibrage des forces en prĂ©sence, que certains pratiquants font le choix de s'opposer , consciemment ou non, Ă l'orthopraxie fĂ©dĂ©rale. Dans ce cadre, la contestation , notamment rĂšglementaire, n'est pas un Ă©tat d'esprit prĂ©alable Ă l'activitĂ© mais un comportement subsĂ©quent Ă la pratique contextuĂ©e. Ce dĂ©saccord participe d'un systĂšme aporĂ©tique faisant Ă©tat d'une contradiction insoluble entre la dĂ©marche fĂ©dĂ©rale indiffĂ©renciatrice relative Ă une conception intĂ©grative de l'ensemble des surfeurs, et la logique diffĂ©renciatrice 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 fĂ©dĂ©ration parviendrait Ă Ă©dicter une forme d'organisation lĂ©gitimĂ©e par tous ses pratiquants. Il s'agit d'une res nullius, la chose de personne ainsi dĂ©voluĂ©e aux pratiquants eux-mĂȘmes. Sujette aux possessions et aux appropriations, elle gĂ©nĂšre un processus continuel de lĂ©gitimation et de dĂ©-lĂ©gitimation structurant la pratique libre du surf et dont l'enjeu premier demeure la quĂȘte praxique, autrement dit, la conquĂȘte de vague.ROUEN-BU Lettres (764512101) / SudocSudocFranceF
Drying of silica gels to obtain aerogels : phenomenology and basic techniques: Review
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Présentation générale du séchage des gels de silice nanostructures
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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