Acoustique d'un fluide au voisinage du point d'ébullition

International audienceDans une étude précédente (Boutin et Auriault 1993), la propagation d'ondes acoustiques dans un fluide à bulles en concentration finie était analysée au moyen de la méthode des échelles multiples. Trois comportements différents étaient mis en évidence suivant la taille des bulles, grande, moyenne ou petite. Dans la présente note, nous étendons cette étude par la prise en compte d'un possible changement de phase. Nous montrons que les effets de celui-ci sont négligeables dans le cas de grandes bulles, et modifient fortement le comportement des bulles moyennes en diminuant de plusieurs orders de grandeur la rigidité effective. Pour les petites bulles la capillarité devient le phénomène prépondérent

Waves in bubbly liquids with phase change

International audienceIn a previous paper (C. Boutin, J.-L. Auriault, Acoustics of a bubbly fluid at large bubble concentration, Eur. J. Mech. B/Fluids, 12(3) (1993) 367-399), the homogenization technique was used to investigate how acoustic waves propagate in a bubbly fluid at finite concentration. Three different equivalent macroscopic behaviours were shown to exist, for "large"-, "medium"- and "small"-size bubble systems, respectively. In the present paper, we extend the analysis by taking into consideration possible phase change effects. We show that phase change effects are negligible in the case of large-size bubbles, whereas they strongly modify the medium-size bubble system behaviour. For small-size bubbles capillarity dominates the process

Long wavelenght inner-resonance cut-off frequencies in elastic composite materials

International audienceWe revisit an ancient paper (Auriault and Bonnet, 1985) which points out the existence of cut-off frequencies for long acoustic wavelength in high-contrast elastic composite materials, i.e. when the wavelength is large with respect to the characteristic heterogeneity length. The separation of scales enables the use of the method of multiple scale expansions for periodic structures, a powerful upscaling technique from the heterogeneity scale to the wavelength scale. However, the results remain valid for non-periodic composite materials which show a Representative Elementary Volume (REV). The paper extends the previous investigations to three-component composite materials made of hard inclusions, coated with a soft material, both of arbitrary geometry, and embedded in a connected stiff material. The equivalent macroscopic models are rigorously established as well as their domains of validity. Provided that the stiffness contrast within the soft and the connected stiff materials is of the order of the squared separation of scales parameter, it is demonstrated (i) that the propagation of long wave may coincide with the resonance frequencies of the hard inclusions/soft material system and (ii) that the macroscopic model presents a series of cut-off frequencies given by an eigenvalue problem for the resonating domain in the cell. These results are illustrated in the case of stratified composites and the possible microstructures of heterogeneous media in which the inner dynamics phenomena may occur are discussed

Acoustics of a porous medium saturated by a bubbly fluid undergoing phase change

International audienceThe objective of this work is the derivation of the wave equations for describing acoustics in a deformable porous medium saturated by a bubbly fluid, when capillary, thermal and phase change effects are accounted for. This is performed using an homogenisation technique: the macroscopic model is obtained by upscaling the bubble-scale and the pore-scale descriptions. For convenience a bubbly fluid near the bubble point, in the bulk of which a small perturbation can generate small bubbles is considered. Although the derived macroscopic wave equations are similar in their structure to Biot's equations that describe wave propagation in saturated porous media, important differences appear as a result of the presence of bubbles. In effect, gas-liquid phase change considerably decreases the apparent rigidity of the bubbly fluid, and consequently decreases the wave velocity in the porous medium. Moreover, this phenomenon is amplified for very small bubbles, for which the apparent rigidity of the bubbly fluid can be negative. The influence of the bubbly liquid apparent rigidity on the wave velocity and attenuation is highlighted on an illustrative example: it is shown that they strongly differ from wave velocities and attenuations in porous media saturated by a liquid or by a gas

Acoustics of a bubbly fluid at large bubble concentration

International audienceThe homogenization process is used to investigate how acoustic waves propagate in a bubbly fluid at finite concentration. This method involves the consideration of waves whose lengths are large compared with the bubble size. We focus on the linear domain, with viscous, thermal and capillary effects. It is shown that this medium displays three different macroscopic descriptions according to bubble diameter and wave frequency. For bubbles of small size, the capillary effect leads to a model where in acoustic waves are either propagative with low celerity or diffusive. On increasing the bubble diameter we obtain waves which are damped and dispersed by both viscous and thermal effects. Finally for large bubbles, we get biphasic undamped and dispersed waves. Moreover, the homogenization method allows us to predict the kind of behaviour and the accuracy of the model from a knowledge of the physical characteristics of the mixture. Applications of these results are presented in the case of water containing air bubbles in equal proportion

Nonlocal boundary conditions for corrugated acoustic metasurface with strong near field interactions

The propagation of long-wavelength sound in the presence of a metasurface made by arranging acoustic resonators periodically upon or slightly above an impervious substrate is studied. The method of two-scale asymptotic homogenization is used to derive effective boundary conditions, which account for both the surface corrugation and the low-frequency resonance. This method is applied to periodic arrays of resonators of any shape operating in the long-wavelength regime. The approach relies on the existence of a locally periodic boundary layer developed in the vicinity of the metasurface, where strong near-field interactions of the resonators with each other and with the substrate take place. These local effects give rise to an effective surface admittance supplemented by nonlocal contributions from the simple and double gradients of the pressure at the surface. These phenomena are illustrated for the periodic array of cylindrical Helmholtz resonators with an extended inner duct. Effects of the centre-to-centre spacing and orientation of the resonators' opening on the nonlocality and apparent resonance frequency are studied. The model could be used to design metasurfaces with specific effective boundary conditions required for particular applications

Interleukin-7 Regulates Adipose Tissue Mass and Insulin Sensitivity in High-Fat Diet-Fed Mice through Lymphocyte-Dependent and Independent Mechanisms

Although interleukin (IL)-7 is mostly known as a key regulator of lymphocyte homeostasis, we recently demonstrated that it also contributes to body weight regulation through a hypothalamic control. Previous studies have shown that IL-7 is produced by the human obese white adipose tissue (WAT) yet its potential role on WAT development and function in obesity remains unknown. Here, we first show that transgenic mice overexpressing IL-7 have reduced adipose tissue mass associated with glucose and insulin resistance. Moreover, in the high-fat diet (HFD)-induced obesity model, a single administration of IL-7 to C57BL/6 mice is sufficient to prevent HFD-induced WAT mass increase and glucose intolerance. This metabolic protective effect is accompanied by a significant decreased inflammation in WAT. In lymphocyte-deficient HFD-fed SCID mice, IL-7 injection still protects from WAT mass gain. However, IL-7-triggered resistance against WAT inflammation and glucose intolerance is lost in SCID mice. These results suggest that IL-7 regulates adipose tissue mass through a lymphocyte-independent mechanism while its protective role on glucose homeostasis would be relayed by immune cells that participate to WAT inflammation. Our observations establish a key role for IL-7 in the complex mechanisms by which immune mediators modulate metabolic functions

Stratégie de vaccination peptidique dans les tumeurs associées à une latence de type II du virus d'Epstein-Barr

Le virus d'Epstein-Barr (EBV) est impliqué dans différentes pathologies tumorales que l'on peut distinguer par le type de latence virale exprimée. La latence de type II est retrouvée dans la maladie de Hodgkin, les lymphomes T/NK et le carcinome indifférencié du nasopharynx. Elle se caractérise par une expression limitée aux antigènes EBNA1, LMP1 et LMP2. Le contrôle immunitaire de cibles exprimant ces antigènes passe prioritairement par une réponse T CD4+. Nous avons cherché à déterminer un mélange de peptides contenant des épitopes T CD4+ dérivés des antigènes de latence de type II d'EBV et potentiellement reconnus par une grande majorité de la population (peptides HLA II promiscuous). Nous avons dans un premier temps proposé une méthode de sélection de peptides HLA II promiscuous, reposant sur la combinaison de tests de liaison in vitro sur molécules HLA II purifiées et l'immunisation de souris transgéniques pour les molécules du CMH de classe II humaines, réalisés sur des peptides préalablement sélectionnés par des logiciels de prédiction. Nous avons démontré la cohérence de cette approche en utilisant comme modèles 2 peptides d'intérêt vaccinal, le peptide Nef 56-68 dérivé de la protéine Nef de HIV et le peptide Sm28GST 190-211 dérivé de la Glutathion-S-transférase de 28-kDa de Schistosoma mansoni. Nous avons ensuite utilisé cette méthode pour déterminer un cocktail de peptides HLA II promiscuous dérivés des protéines EBNA1, LMP1 et LMP2 d'EBV. Vingt-quatre séquences peptidiques susceptibles de contenir chacune plusieurs épitopes T CD4+ HLA II promiscuous ont été déterminées grâce à l'utilisation du logiciel de prédiction TEPITOPE. Les tests de liaison ont permis de sélectionner 6 peptides possédant une bonne affinité pour au moins 7 des 12 allèles HLA II testés (3 peptides dérivés de EBNA1, 2 dérivés de LMP2 et un de LMP1). L'immunogénicité des peptides a ensuite été évaluée en immunisant des souris transgéniques pour la molécule HLA-DR1. Ceci a permis de mettre en évidence une réponse cellulaire et humorale spécifique de type Th1. Nous avons également montré que ces peptides contenaient des épitopes T CD4+ naturellement présentés au cours de l'infection virale et reconnus par des lymphocytes T CD4+ humains issus de donneurs exprimant des génotypes HLA II variés. Ce cocktail peptidique pourrait être utilisé dans des approches d'immunothérapie (vaccination ou thérapie cellulaire) dans le traitement de tumeurs associées à l'EBV.The Epstein-Barr virus (EBV) is associated with several malignant diseases which can be distinguished by their patterns of viral latent gene expression. The latency II program is limited to the expression of the non-immunodominant antigens EBNA1, LMP1 and LMP2 and is seen in EBV-positive Hodgkin's disease, nasopharyngeal carcinomas and peripheral T/NK-cell lymphomas. CD4+ T cells may play a crucial role in controlling these EBV latency II malignancies. The aim of this study was to determine an HLA II promiscuous peptide cocktail containing epitopes from EBV latency II antigens. As a first step, we determined a rational method for selecting HLA II promiscuous peptides, based on the combination of peptide-binding assays on HLA II purified molecules and HLA II transgenic mice experiments, performed with peptides previously selected by prediction software. The coherence of this approach was demonstrated by using as models 2 MHC class II-restricted peptides, one derived from the HIV Nef regulatory protein (Nef 56-68) and the other from the Schistosoma mansoni 28-kDa glutathione-S-transferase (Sm28GST 190-211). We used the prediction software TEPITOPE to predict promiscuous MHC class II epitopes derived from the latency II antigens EBNA1, LMP1 and LMP2. The predicted peptides were then submitted to peptide-binding assays on HLA II purified molecules, which allowed the selection of 6 peptides (EBNA1: 3; LMP1: 1; LMP2: 2) with a highly promiscuous capability of binding. This peptide cocktail was immunogenic in HLA-DR1 transgenic mice, leading to a specific cellular and humoral Th1 response. We also showed that the peptide cocktail contains naturally-processed epitopes recognized by human CD4+ T cells from individuals expressing various HLA II genotypes. This promiscuous peptide cocktail could be used in immunotherapeutic approaches (as peptide-based vaccine or cellular therapy) against EBV latency II malignancies.LILLE2-BU Santé-Recherche (593502101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Contribution à l'étude de la présentation des peptides synthétiques par les molécules du complexe majeur d'histocompatibilité de classe II

La comprehension des mecanismes regissant la presentation des peptides antigeniques par les molecules du complexe majeur d'histocompatibilite (cmh) de classe ii est essentielle pour la caracterisation d'epitopes t en vue du developpement de vaccins peptidiques. La conformation adoptee par les molecules de cmh de classe ii constitue un des parametres importants susceptibles d'influencer la presentation d'antigenes et par consequent la reactivite des cellules t. Dans un premier temps, nous avons analyse l'influence des ligands peptidiques sur la conformation des molecules du cmh ii, en utilisant comme modele la molecule recombinante hla-dr1 (1*0101) soluble, produite en cellules d'insectes. Par une approche moleculaire, nous avons montre que la liaison de differents epitopes peptidiques induit de multiples conformations des complexes hla-dr1. La nature du peptide ligant apparait directement impliquee dans la modulation de la conformation du dimere de classe ii, non seulement par le biais des residus ancres dans le sillon de fixation des peptides, mais egalement via ses extremites n- et c-terminales. L'influence des residus flanquants n- et c-terminaux nous a amene a supposer l'existence de sites de fixation sur la molecule de cmh ii distincts du sillon principal de liaison des peptides et capables de gouverner certaines transitions structurales.LILLE1-BU (590092102) / SudocSudocFranceF

Modèles d'études d'induction et d'optimisation de la réponse immune à des constructions peptidiques d'intérêt vaccinal

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF