Séminaires café 2019

12 Décembre Faustine Gomand (Post-doctorante au PMMH)
Bacterial adhesion to food components : extent, characterization, and sensitivity to shear stress
14 novembre Barbara Bouteille (Doctorante chez Saint-Gobain recherche / PMMH )
Phase separation in glass thin films for surface nanostructuration (English)
21 novembre Soutenance de Gaspard Junot
28 novembre Pas de séminaire (plusieurs soutenances )
7 novembre Vinod Saranathan (Professor at Yale-NUS )
Evolutionary Photonics of Self-Assembled Biophotonic Nanostructures
24 octobre Justine Laurent (Ingénieur au PMMH )
Comment fonctionne le concours ingénieur de recherche
17 octobre Martin Brandenbourger (Post-doctorant à l’Université d’Amsterdam)
Tuning flow asymmetry with bio-inspired soft leaflets
10 octobre Marc Fermigier (Professeur à l’ESPCI)
Un Mooke sur les interfaces
3 octobre Ernesto Altshuler (Group of Complex Systems and Statistical Physics Physics Faculty University of Havana)
PENETRATION INTO CONFINED GRANULAR MATTER
I’ll first talk about how a spherical intruder penetrates into light granular matter confined into a cylindrical container. If the intruder is heavier than a critical mass, "infinite penetration" takes place, which can be understood based on an equation of motion including a "Janssen-like" stopping force. Then, by using a device nicknamed "Lab-in-a-bucket", the influence of theeffective gravity on the penetration is evaluated : the total penetration time scales as the inverse of the square root of the effective gravity, but the total penetration depth is independent from gravity. In an effort to understand deeper the intruder-wall interaction, we release a quasi-2D cylindrical intruder near a vertical wall. We find two effects : (a) the intruder is repelled by the wall (b) The intruder rotates as it separates from the wall. Finally, our experiments strongly suggest that the effect of the wall is equivalent to the effect of an "image intruder" with no wall.
19 septembre Shunsuke Yabunak (Department of Physics, Kyushu University, Fukuoka (Japon))
Drag Coefficient of a Rigid Spherical Particle in a Near-Critical Binary Fluid Mixture beyond the Regime of the Gaussian Model
11 juillet Antonios Giannopoulos (Doctorant au PMMH) Neural Network System identification in noise amplifier flows : an experimental study using optical flow PIV
27 juin Pierre-Henri Delville (Doctorant au PMMH) Collective motion with bacteria swimming
6 juin David Wilgenbus (Responsable du programme de la COP, le OCE (office for Climate éducation), et notre voisin chez J.Jouzel ). Il nous parlera des enjeux éducatifs et concrets pour associer les problèmes généraux du réchauffement climatique et évolution dans le système d’éducation. Ceci peut concerner plus directement des équipes de notre laboratoire
23 mai Mengfei He (Doctorant à l’université de Chicago)
Characteristic interfacial structure behind a rapidly moving contact line
When a spatula is quickly inserted into a honey jar, its moving surface drags a thin layer of air into the honey. We discovered that such a simple process produces a remarkable structure in the air layer. This structure is ubiquitous, robust, and is suggestive of a new fluid-mechanical instability. I will show our measurements using new interferometric techniques and describe a new analytic understanding of the flows.
16 mai Daniel Nagy (PostDoctorant au PMMH)
Numerical simulation of the rheology of frictional spherocylinders
The dissipation during granular flow is characterized by the so-called effective friction coefficient, which is defined as the ratio of shear stress and confining pressure. This is in contrast to fluid flows, where dissipation is described by the viscosity. In the case of granular flows, the effective friction originates from microscopic contacts between the particles. Describing the rheology, one needs to measure the effective friction as a function of the dimensionless shear rate (the inertial number), which can be interpreted as the ratio of the macroscopic timescale of the shear flow and the timescale of the microscopic rearrangements of the flowing particles. The rheology of spherical particles has been studied previously by several authors. In our work, we focus on elongated particles, which are ubiquitous in industry and agriculture. They show more complex rheological properties, since elongated particles are rotating in the shear flow and hinder each other’s movement. In our simulations, we quantified how this complex dynamics changes the rheological properties of the system. We also study the origin of a unique behavior, the appearance of a secondary flow in certain geometries.
9 mai Armand Barbot (Doctorant au PMMH)
2 mai Gustavo Martins (Doctorant au PMMH)
Numerical study of transients in bedload transportation
Sediment transport is an important process for the formation of patterns in nature. The reference case of steady and homogeneous transport has been much studied, with calibrated transport laws for the different modes of transport. In comparison, transients, both in time and space, which are crucial for the development of instabilities leading to those patterns, have been overlooked and their characteristics are much less known. This is especially true in the case of bedload, for which time and length scales associated with these transients are too small to be easily measured in experiments. Here, we investigate bedload by means of numerical simulations where a discrete element method (DEM) for the grains is coupled to a continuum description of the water flow using finite difference method (FDM). We specifically address the temporal response of the transport in the transition between two close steady states.
25 avril Matthias Lerbinger (Doctorant au PMMH) Thermal behavior of glassy materials
18 avril John Hinch (Professeur à l’université de Cambridge)
11 avril Cesar Valencia Gallardo (Post-doctorant au PMMH) Shigella IpaA Binding to Talin Stimulates Filopodial Capture and Cell Adhesion
The Shigella type III effector IpaA contains three binding sites for the focal adhesion protein vinculin (VBSs), which are involved in bacterial invasion of host cells. Here, we report that IpaA VBS3 unexpectedly binds to talin. The 2.5 Å resolution crystal structure of IpaA VBS3 in complex with the talin H1-H4 helices shows a tightly folded α-helical bundle, which is in contrast to the bundle unraveling upon vinculin interaction. High-affinity binding to talin H1-H4 requires a core of hydrophobic residues and electrostatic interactions conserved in talin VBS H46. Remarkably, IpaA VBS3 localizes to filopodial distal adhesions enriched in talin, but not vinculin. In addition, IpaA VBS3 binding to talin was required for filopodial adhesions and efficient capture of Shigella. These results point to the functional diversity of VBSs and support a specific role for talin binding by a subset of VBSs in the formation of filopodial adhesions.
4 avril Emmanuel Siefert (Doctorant au PMMH) Inflating to shape
7 mars Bill François (Doctorant au PMMH)
28 février Vincent Cognet (Post doctorant au PMMH)
Using flexible blades to improve wind turbine versatility
L’énergie éolienne joue un rôle croissant dans le mélange énergétique mondial depuis plusieurs décennies. Cependant ces machines manquent cruellement de versatilité. Par exemple, lorsque la vitesse du vent est trop forte ou trop faible, le rendement chute fortement. Pour palier à ce problème, la technique actuellement en place est de modifier continument l’angle d’inclinaison des pales (angle de calage) à l’aide de moteurs situés au pied de chaque pale. Cette technique est néanmoins coûteuse et énergivore.
Depuis quelques années, nous étudions l’intérêt d’utiliser des pales légèrement flexibles, qui adaptent l’angle de calage passivement, sans consommation supplémentaire d’énergie. Après avoir validé théoriquement et expérimentalement l’idée sur un petit modèle, nous proposons ici une procédure qui permet de trouver, pour n’importe quelle éolienne de géométrie donnée, le matériau flexible optimal. La procédure est testée sur une éolienne industrielle, pour différents modes d’opération, et pour différentes tailles. Les résultats montrent une amélioration significative de la puissance récupérée par rapport au cas rigide : de +4% à +25%.
17 janvier Grace Pappas (Royal College of Arts)
10 janvier Wilbert Smit ( Post-doc à l’Institut Chimie Biologie Innovation - ESPCI)
Confinement Determines Dip Coating of Yield-Stress Fluids
Dip-coating is a widely-used industrial process in which surfaces of solid objects are covered by a
thin layer of liquid. The thickness of the coating generally depends on both fluid and geometrical
properties and its mastery is of major interest. Albeit the problem is well-studied for simple liquids,
it remains largely elusive for yield-stress liquids—in spite of the industrial relevance. We study the
effect of geometry by withdrawing rods from cylindrically-shaped baths filled with a Carbopol gel,
which behaves as a model yield-stress fluid. A smaller rod is observed to result in thinner coatings.
When the yield-stress is large in comparison with the capillary pressure, the proximity of the
stationary wall of the liquid reservoir has a profound effect on the coating thickness. We have solved
the fluid flow inside the reservoir and a good agreement between experiment and theory has been
obtained. I will discuss and interpret these results.

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Informations Pratiques

Laboratoire : 01 40 79 45 22
Directeur : Damien Vandembroucq
Codirecteur : Philippe Petitjeans
Administratrice : Frédérique Auger (01 40 79 45 22)
Gestionnaire : Claudette Barez (01 40 79 58 53)
Courriel : dir (arobase) pmmh.espci.fr

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