Simulations numériques d'écoulements de fluides complexes à l'échelle microscopique : un nouvel outil de rhéologie

National audienceUne méthode de simulation numérique directe a été développée pour l'écoulement de fluides fortement chargés, avec plusieurs populations de particules (fibres et sphères), pouvant entrer en collision. Ce fluide complexe modélise les écoulements de BMC (Bulk Molding Compound) utilisés par Schneider Electric. Une approche par domaines fictifs, avec des conditions limites périodiques, a été utilisée

Numerical and Experimental Studies of Suspensions of Fiber and Spherical Solid Particles

Coupled Problems 2009 is one of the Thematic Conferences of the European Community in Computational Methods in Applied Sciences (ECCOMAS).International audienceThis paper is devoted the behavior of suspension of fiber-spheres particles. We pointed out by experimental and numerical observations that the Jeferry approximation is no more valid as the sphere particle concentration increases

Etudes numériques et expérimentales sur les suspensions de fibres et de sphères solides

International audienceUne méthode numérique a été développé afin de permettre le calcul du mouvement de particules solides dans un fluide en cisaillement. Les calculs sur un volume élémentaire permettent d'étudier l'évolution de l'orientation de particules allongées pour un fluide chargés en particules sphériques. Finalement, des observations expérimentales sont faites en utilisant des outils de rhéooptique

Modélisation et simulation de l'écoulement d'un fluide complexe

PARIS-MINES ParisTech (751062310) / SudocSudocFranceF

Numerical methods for solid particles in particulate flow simulations

International audienceLes écoulements de fluides chargés de particules interviennent dans de nombreux procédés industriels. Le champ de vitesse dans un tel système est donné par une méthode éléments finis associée à une formulation multidomaine (le fluide visqueux et les particules solides). Puis le déplacement des particules est effectué par une méthode particulaire. Cette approche est ici testée sur un écoulement de cisaillement simple = The flow motion of solid particle suspensions is a fundamental issue in many problems of practical interest. The velocity field of a such system is computed by a finite element method with a multi-domain approach of two phases (namely a viscous fluid and rigid bodies), whereas the particle displacement is made by a particulate method. We focus our paper on a simple shear flow of Newtonian flui

Electromagnetic modelling/Modélisation électromagnétique

Realistic numerical modelling of human head tissue exposure to electromagnetic waves from cellular phone

Realistic numerical modeling of human head tissues exposure to electromagnetic waves from mobiles phones

International audienceThe ever-rising diffusion of cellular phones has brought about an increased concern for the possible consequences of electromagnetic radiation on human health. Possible thermal effects have been investigated, via experimentation or simulation, by several research projects in the last decade. Concerning numerical modeling, the power absorption in a user's head is generally computed using discretized models built from clinical MRI data. The vast majority of such numerical studies have been conducted using Finite Differences Time Domain methods, although strong limitations of their accuracy are due to heterogeneity, poor definition of the detailed structures of head tissues (staircasing effects), etc. In order to propose numerical modeling using Finite Element or Discontinuous Galerkin Time Domain methods, reliable automated tools for the unstructured discretization of human heads are also needed. Results presented in this article aim at filling the gap between human head MRI images and the accurate numerical modeling of wave propagation in biological tissues and its thermal effects

Proteomic and transcriptomic profiling of Staphylococcus aureus surface LPXTG-proteins: correlation with agr genotypes and adherence phenotypes.

Staphylococcus aureus infections involve numerous adhesins and toxins, which expression depends on complex regulatory networks. Adhesins include a family of surface proteins covalently attached to the peptidoglycan via a conserved LPXTG motif. Here we determined the protein and mRNA expression of LPXTG-proteins of S. aureus Newman in time-course experiments, and their relation to fibrinogen adherence in vitro. Experiments were performed with mutants in the global accessory-gene regulator (agr), surface protein A (Spa), and fibrinogen-binding protein A (ClfA), as well as during growth in iron-rich or iron-poor media. Surface proteins were recovered by trypsin-shaving of live bacteria. Released peptides were analyzed by liquid chromatography coupled to tandem mass-spectrometry. To unambiguously identify peptides unique to LPXTG-proteins, the analytical conditions were refined using a reference library of S. aureus LPXTG-proteins heterogeneously expressed in surrogate Lactococcus lactis. Transcriptomes were determined by microarrays. Sixteen of the 18 LPXTG-proteins present in S. aureus Newman were detected by proteomics. Nine LPXTG-proteins showed a bell-shape agr-like expression that was abrogated in agr-negative mutants including Spa, fibronectin-binding protein A (FnBPA), ClfA, iron-binding IsdA, and IsdB, immunomodulator SasH, functionally uncharacterized SasD, biofilm-related SasG and methicillin resistance-related FmtB. However, only Spa and SasH modified their proteomic and mRNA profiles in parallel in the parent and its agr- mutant, whereas all other LPXTG-proteins modified their proteomic profiles independently of their mRNA. Moreover, ClfA became highly transcribed and active in fibrinogen-adherence tests during late growth (24 h), whereas it remained poorly detected by proteomics. On the other hand, iron-regulated IsdA-B-C increased their protein expression by >10-times in iron-poor conditions. Thus, proteomic, transcriptomic, and adherence-phenotype demonstrated differential profiles in S. aureus. Moreover, trypsin peptide signatures suggested differential protein domain exposures in various environments, which might be relevant for anti-adhesin vaccines. A comprehensive understanding of the S. aureus physiology should integrate all three approaches