Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 4 )

2019 ( 212 )

2018 ( 241 )

2017 ( 242 )

Custom range...

Search Results: 1 - 10 of 144368 matches for " B. Dollet "
All listed articles are free for downloading (OA Articles)
Page 1 /144368
Display every page Item
Plastic flow of foams and emulsions in a channel
B. Dollet,A. Scagliarini,M. Sbragaglia
Physics , 2014,
Abstract: In order to understand the flow profiles of complex fluids, a crucial issue concerns the emergence of spatial correlations among plastic rearrangements exhibiting cooperativity flow behaviour at the macroscopic level. In this paper, the rate of plastic events in a Poiseuille flow is experimentally measured on a confined foam in a Hele-Shaw geometry. The correlation with independently measured velocity profiles is quantified. To go beyond a limitation of the experiments, namely the presence of wall friction which complicates the relation between shear stress and shear rate, we compare the experiments with simulations of emulsion droplets based on the lattice-Boltzmann method, which are performed both with, and without, wall friction. Our results indicate a correlation between the localisation length of the velocity profiles and the localisation length of the number of plastic events. Finally, unprecedented results on the distribution of the orientation of plastic events show that there is a non-trivial correlation with the underlying local shear strain. These features, not previously reported for a confined foam, lend further support to the idea that cooperativity mechanisms, originally invoked for concentrated emulsions (Goyon et al. 2008), have parallels in the behaviour of other soft-glassy materials.
Discrete rearranging disordered patterns, part I: Robust statistical tools in two or three dimensions
Fran?ois Graner,B. Dollet,Christophe Raufaste,Philippe Marmottant
Physics , 2007, DOI: 10.1140/epje/i2007-10298-8
Abstract: Discrete rearranging patterns include cellular patterns, for instance liquid foams, biological tissues, grains in polycrystals; assemblies of particles such as beads, granular materials, colloids, molecules, atoms; and interconnected networks. Such a pattern can be described as a list of links between neighbouring sites. Performing statistics on the links between neighbouring sites yields average quantities (hereafter "tools") as the result of direct measurements on images. These descriptive tools are flexible and suitable for various problems where quantitative measurements are required, whether in two or in three dimensions. Here, we present a coherent set of robust tools, in three steps. First, we revisit the definitions of three existing tools based on the texture matrix. Second, thanks to their more general definition, we embed these three tools in a self-consistent formalism, which includes three additional ones. Third, we show that the six tools together provide a direct correspondence between a small scale, where they quantify the discrete pattern's local distortion and rearrangements, and a large scale, where they help describe a material as a continuous medium. This enables to formulate elastic, plastic, fluid behaviours in a common, self-consistent modelling using continuous mechanics. Experiments, simulations and models can be expressed in the same language and directly compared. As an example, a companion paper (Marmottant, Raufaste and Graner, joint paper) provides an application to foam plasticity.
Two-dimensional shear modulus of a Langmuir foam
S. Courty,B. Dollet,F. Elias,P. Heinig,F. Graner
Physics , 2003, DOI: 10.1209/epl/i2003-00283-5
Abstract: We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by applying a mechanical perturbation, and simultaneously image it by Brewster angle microscopy. We determine the foam stress tensor (through a determination of the 2D gas-liquid line tension, 2.35 $\pm$ 0.4 pJ$\cdot$m$^{-1}$) and the statistical strain tensor, by analyzing the images of the deformed structure. We deduce the 2D shear modulus of the foam, $\mu= 38 \pm 3 \mathrm{nN}\cdot \mathrm{m}^{-1}$. The foam effective rigidity is predicted to be $ 35 \pm 3 \mathrm {nN}\cdot \mathrm {m}^{- 1}$, which agrees with the value $37.5 \pm 0.8 \mathrm {nN}\cdot \mathrm {m}^{-1}$ obtained in an independent mechanical measurement.
Local description of the two-dimensional flow of foam through a contraction
Benjamin Dollet
Physics , 2009, DOI: 10.1122/1.3380852
Abstract: The 2D flow of a foam confined in a Hele-Shaw cell through a contraction is investigated. Its rheological features are quantified using image analysis, with measurements of the elastic stress, rate of plasticity, and velocity. The behavior of the velocity strongly differs at the contraction entrance, where the flow is purely convergent, and at the contraction exit, where a velocity undershoot and a re-focussing of the streamlines are unraveled. The yielded region, characterized by a significant rate of plasticity and a maximal stress amplitude, is concentrated close to the contraction. These qualitative generic trends do not vary significantly with the flow rate, bubble area and contraction geometry, which is characteristic of a robust quasistatic regime. Using surfactants with a high surface viscoelasticity, a marked dependence of the elastic stress on the velocity is exhibited. The results show that the rate of plasticity does not only depend on the local magnitude of the deformation rate, but also crucially on the orientation of both elastic stresses and deformation rate. It is also discussed how the viscous friction controls the departure from the quasistatic regime.
Yield drag in a two-dimensional foam flow around a circular obstacle: Effect of liquid fraction
Christophe Raufaste,B. Dollet,Simon Cox,Yi Jiang,Fran?ois Graner
Physics , 2006, DOI: 10.1140/epje/i2006-10178-9
Abstract: We study the two-dimensional flow of foams around a circular obstacle within a long channel. In experiments, we confine the foam between liquid and glass surfaces. In simulations, we use a deterministic software, the Surface Evolver, for bubble details and a stochastic one, the extended Potts model, for statistics. We adopt a coherent definition of liquid fraction for all studied systems. We vary it in both experiments and simulations, and determine the yield drag of the foam, that is, the force exerted on the obstacle by the foam flowing at very low velocity. We find that the yield drag is linear over a large range of the ratio of obstacle to bubble size, and is independent of the channel width over a large range. Decreasing the liquid fraction, however, strongly increases the yield drag; we discuss and interpret this dependence.
Bubbles in sheared two-dimensional foams
C. Quilliet,M. A. P. Idiart,B. Dollet,L. Berthier,A. Yekini
Physics , 2005,
Abstract: Oscillatory shear on two-dimensional monodisperse liquid foams was performed. We show that the effect of the oscillatory shear is to cause the migration of bubbles which size is greater than that of a typical bubble of the foam. These so-called flaws move towards the periphery of the foam in a non random motion, thus realizing size segregation in a system which is by construction gravity insensitive. We also show that elongated cavities in the foam could be relaxed towards a more isotropic form with oscillatory shear, and we discuss the pertinent parameters of this relaxation.
Two-dimensional flow of foam around a circular obstacle: local measurements of elasticity, plasticity and flow
Benjamin Dollet,Francois Graner
Physics , 2006, DOI: 10.1017/S0022112007006830
Abstract: We investigate the two-dimensional flow of a liquid foam around circular obstacles by measuring all the local fields necessary to describe this flow: velocity, pressure, bubble deformations and rearrangements. We show how our experimental setup, a quasi-2D "liquid pool" system, is adapted to the determination of these fields: the velocity and bubble deformations are easy to measure from 2D movies, and the pressure can be measured by exploiting a specific feature of this system, a 2D effective compressibility. To describe accurately bubble rearrangements, we propose a new, tensorial descriptor. All these quantities are evaluated via an averaging procedure that we justify showing that the fluctuations of the fields are essentially random. The flow is extensively studied in a reference experimental case; the velocity presents an overshoot in the wake of the obstacle, the pressure is maximum at the leading side and minimal at the trailing side. The study of the elastic deformations and of the velocity gradients shows that the transition between plug flow and yielded regions is smooth. Our tensorial description of T1s highlight their correlation both with the bubble deformations and the velocity gradients. A salient feature of the flow, notably on the velocity and T1 repartition, is a marked asymmetry upstream/downstream, signature of the elastic behaviour of the foam. We show that the results do not change qualitatively when various control parameters vary, identifying a robust quasistatic regime. These results are discussed in the frame of the actual foam rheology literature, and we argue that they constitute a severe test for existing rheological models, since they capture both the elastic, plastic and fluid behaviour of the foam.
Liquid films with high surface modulus moving in tubes: dynamic wetting film and jumpy motion
Isabelle Cantat,Benjamin Dollet
Physics , 2011,
Abstract: We investigate the motion through a wet tube of transverse soap films, or lamellae, of high surface dilatationnal modulus. Combining local thickness and velocity measurements in the wetting film, we reveal a zone of several centimeters in length, the dynamic wetting film, which is significantly influenced by a moving lamella. The dependence of this influence length on lamella velocity and wetting film thickness provides a discrimination among several possible surfactant minimal models. A spectacular jumpy mode of unsteady motion of a lamella is also evidenced.
Mobilisations collectives et femmes immigrées en France
Sylvie Thiéblemont-Dollet
Amnis , 2008, DOI: 10.4000/amnis.550
Abstract: Si nombreuses que soient les études ayant trait à l’immigration en France (et plus particulièrement masculine), aborder l’immigration sous l’angle des femmes immigrées et des processus communicationnels qu'elles ont développés en terre d’accueil est un apport essentiel aux sciences humaines. C’est pourquoi, cet article traite du thème de la mobilisation collective entre 2000 et 2008, par le biais des actions et des processus communicationnels mis en uvre par des femmes immigrées ou issues de l’immigration, originaires du Maghreb et de l’Afrique de l’Ouest, plus particulièrement à partir de l’exemple du mouvement Ni Putes Ni Soumises. Analyser les réseaux d’interdépendance et de contagion entre ces actrices aux origines sociales identiques, faisant que ces femmes expriment un sentiment d’exclusion et associent leur statut social (ch mage, profession sous-qualifiée), ethnique (origine maghrébine ou africaine) et spatial (cité, banlieue, quartier dit difficile), à un même stigmate les reléguant à un univers discriminatoire, dégager les spécificités de leurs paroles selon les espaces et les temporalités où elles ont été délivrées, saisir leurs manières de s’organiser et leurs possibilités de mobilisation, sont les grands axes de cette réflexion. Suggérer enfin que ces femmes constituent un corps social émergent et mutant est une autre manière de lire ce texte. émergent, parce qu’il est relativement récent du point de vue de sa visibilité dans la sphère publique et mutant, parce qu’il intègre des femmes qui participent d’un changement en train de se faire dans la société fran aise et qui donnent une nouvelle image d’elles : non pas celle de féministes au sens classique du terme et de ce qui peut s’y rattacher, mais celle qui s’inscrit dans la perspective de comportement de genre à entendre comme mixité et modalités d’interaction entre femmes et hommes. Enfin, parce que longtemps exclu de la représentation sociale et militante par les institutions fran aises et cantonné dans la représentation de femmes d’immigrés, ce corps social émergent et mutant a sans doute cette particularité de réunir des femmes ayant le souci de l’Autre et la volonté d’une participation active aux actions publiques de la cité. Por muy numerosos que sean los estudios que tengan relación con la inmigración en Francia (y más particularmente masculina), abordar la inmigración, bajo el ángulo de las mujeres inmigradas y de los procesos comunicacionales que desarrollaron en tierra de acogida, es una aportación esencial a las ciencias humanas. Es por eso que, este artículo trata el tema d
Th1 Disabled Function in Response to TLR4 Stimulation of Monocyte-Derived DC from Patients Chronically-Infected by Hepatitis C Virus
Laure Perrin-Cocon, Sophie Agaugué, Olivier Diaz, Béatrice Vanbervliet, Sandra Dollet, Aurélie Guironnet-Paquet, Patrice André, Vincent Lotteau
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002260
Abstract: Background Lack of protective antibodies and inefficient cytotoxic responses are characteristics of chronic hepatitis C infection. A defect in dendritic cell (DC) function has thus been suspected, but this remains a controversial issue. Methods and Findings Here we show that monocyte-derived DC (MoDC) from chronically-infected patients can mature in response to TLR1/2, TLR2/6 or TLR3 ligands. In contrast, when stimulated with the TLR4 ligand LPS, MoDC from patients show a profound defect in inducing IFNγ secretion by allogeneic T cells. This defect is not due to defective phenotypic maturation or to the presence of HCV-RNA in DC or monocytes but is correlated to reduced IL-12 secretion by DC. Restoration of DC ability to stimulate IFNγ secretion can be obtained by blocking MEK activation in DC, indicating that MEK/ERK pathway is involved in the Th1 defect of MoDC. Monocytes from HCV patients present increased spontaneous secretion of cytokines and chemokines, especially MIP-1β. Addition of MIP-1β on healthy monocytes during differentiation results in DC that have Th1 defect characteristic of MoDC from HCV patients, suggesting that MIP-1β secretion by HCV monocytes participates in the Th1 defect of DC. Conclusions Our data indicate that monocytes from HCV patients are activated in vivo. This interferes with their differentiation into DC, leading to deficient TLR4 signaling in these cells that are enable to induce a Th1 response. This specific defect is linked to the activation of the MEK/ERK pathway.
Page 1 /144368
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.