Séminaires café 2016

Archive pour les séminaires café de 2016

–  22 & 29 décembre 2016 - Pas de séminaire : vacances de Noël

–  15 décembre 2016 - Présentation des sujets de thèse : 2ème année

–  08 décembre 2016 - Pas de séminaire : soutenance de thèse de Pan Jia

–  01 décembre 2016 - Pas de séminaire : apéro-foie gras

–  30 novembre 2016 - Important : Benoît Semin (agrégé-préparateur à l’ENS Paris)
Quasi-biennial oscillation : a model experiment
(Abstract)
The quasi-biennial oscillation is the periodic reversal of the wind in the
lower equatorial stratosphere. The period of the oscillation is 28 months on average, and is not linked to the year duration. This wind is known to be generated by atmospheric waves, in particular internal gravity waves.

In a second set of experiments, two successive membranes are oscillating in opposition of phase : the wave is stationary in the azimuthal direction. When the amplitude of the forcing is large enough, a mean flow is generated, and oscillates with a period which is much larger than the wave period. This oscillation of the mean flow is similar to the one observed in the atmosphere.

–  24 novembre 2016 - Thomas Humbert (post-doctorant au PMMH)
Wave-induced vortex recoil and nonlinear refraction
(Abstract)
When a vortex refracts surface waves, it exerts a force on the wave field, and the waves exert a reaction force on the vortex. We study experimentally the resulting vortex recoil.

I will also present briefly some experiments that consider the refraction of surface waves by an array of vortices.

–  17 novembre 2016 - Présentations APS (2) : Marine Borocco, Pierre Chantelot et Yanan Liu

–  10 novembre 2016 - Présentations APS (1) : Daniel Beilharz, Martin Coux et Intesaaf Ashraf

–  03 novembre 2016 - Présentation des sujets de thèse : 3ème année

–  27 octobre 2016 - Matthieu Labousse (post-doctorant au MPQ, Université Paris Diderot)
Du contrôle à l’auto-organisation ondulatoire : une expérimentation théorique.
(Abstract)
Les marcheurs sont un cas original de dualité onde-corpuscule à l’échelle macroscopique. La goutte est autopropulsée, guidée sur la surface du liquide vibré par l’onde qu’elle a elle-même créée lors des rebonds précédents. Ces objets possèdent une dynamique originale dominée par le concept de mémoire de chemin, où la structure du champ d’onde dépend de la trajectoire passée. Pour ce faire, nous étudions l’évolution d’un marcheur numérique en potentiel harmonique. Un ensemble restreint de trajectoires stables est obtenu, quantifiées en extension moyenne et en moment angulaire moyen. Nous analysons comment s’imbriquent les différentes échelles de temps de la dynamique et étudions en quoi l’expression du caractère non-local d’un marcheur permet d’en révéler les symétries internes et d’assurer la convergence du système dynamique vers un jeu d’états propres de basse dimension. Une réflexion autour de cette thématique a permis de concevoir une méthode tout à fait originale de contrôle ondulatoire que je décrierai brièvement.

–  20 octobre 2016 - Eliott Varon (doctorant au PMMH)
Feedback control of a bi-modal Ahmed body wake (or on the way to energy saving when driving).
(Abstract)
The design of efficient vehicles requires to identify and reduce the main sources of energy consumption, such as the aerodynamic drag. The studies of the flow around the road vehicle model proposed by Ahmed et al. (1984) reveal the different behaviors of the wake, depending on the slant angle. The presented case is a square-back body from which, especially, a bi-modal wake arises at high Reynolds number. The wake dynamics and its control through real-time PIV will be discussed.

–  13 octobre 2016 - Pas de séminaire Fête de la science

–  06 octobre 2016 - Pas de séminaire Journée "Physique et Mécanique à Paris, une rencontre célébrant la médaille Boltzmann d’Yves Pomeau"

–  29 septembre 2016 - Guangyin Jing (professeur invité au PMMH)
Drying problems in colloidal suspension
(Abstract)
Drying is ubiquitous in industry and our daily life. On the one hand, stress is accumulated during the drying of the suspensions, and inevitably results in the cracks in the dry deposit. On the other hand, the controllable drying is employed to assemble unique nano/micro structured materials, which however suffers from the diverse heterogeneous patterns due to the complicated drying dynamics. In this talk, I would like to discuss the drying from the both dilute and concentrated colloidal suspensions, to understand the hydrodynamics, crack pattern formation, and the interactions between the colloidal particles. The phase separation model is proposed to explain the pattern formation, and finally the diffusion reduction by the coupling motion of the colloidal particles in confined geometry, is also demonstrated as well.

–  22 septembre 2016 - Nicolas Lavielle (post-doctorant au PMMH)
Role of a liquid interface to prevent bacterial adhesion on silicone gels
(Abstract)
Silicone gels, displaying a dynamic liquid interface, can prevent bacterial attachment. Formation, topographic evolution and release kinetics of the liquid layer wetting the air-gel interface were studied. The formed liquid interface acts as a non-adhesive layer preventing bacterial attachment over long term bacterial exposure.

Keywords : silicone gel, liquid-infused, film formation, bacterial adhesion.

–  15 septembre 2016 - Lucie Domino (doctorante au PMMH)
Controlling the propagation of hydroelastic waves :
(Abstract)
Understanding and mastering wave propagation in complex and/or active media is a key issue in numerous fields. Nevertheless, the scales (frequency domains and wavelengths) at which these waves occur make direct observations and experimentation difficult to achieve. The complete knowledge of the properties of the complex media is extremely difficult to obtain and the design and fabrication of media with given properties is most of the time out of range due to size limitations.

We developed an experimental approach using hydroelastic surface waves that allows for direct observation with accurate space and time resolution at the laboratory scale. Hydroelastic waves propagate at the surface of water covered by a thin elastic sheet (here we use silicon rubber). By varying the elastic properties of the polymer cover, we can tune the propagation velocity of the waves, which means that we can define an effective refractive index for our waves. This technique allows us to modulate the media properties to the sub-wavelength scale. We can thus achieve broadband focusing, reflecting and deviation of the waves.

–  08 septembre 2016 - Julien Chopin (Post-doctorant au SIMM/PPMD) Adhesion on functionalized surfaces

–  01 septembre 2016 - Daniel Beilharz

–  PAUSE D’ETE

–  21 juillet 2016 - Adeline Favier (doctorante PMMH) elasto-kinetic transition in sheared granular flow :

The mechanism controlling the rheology of dense granular flows is investigated trough discrete element simulations, by varying their softness relative to the confining pressure. We show that the dynamics exhibits a transition from an intermittent elasto-plastic regime, to a liquid regime controlled by the geometry of the contact network and characterized by permanent delocalized fluctuations. This transition is located at the generalized isostatic point, defined using the coordination number and the fraction of sliding contacts. In the elasto-plastic regime, the power injected is stored in elastic energy and dissipated during localized plastic events [1,2]. By contrast, above the transition, geometrical constrains lead to coherent non-affine displacements along floppy modes, inherently non-local, and energy is permanently dissipated during collisions [3]. The nature of the critical point reached at vanishing shear rate and diverging grain rigidity is finally discussed.

–  07 juillet 2016 - Yanan Liu (doctorante PMMH) The dynamics of semi-flexible actin filament in simple shear flow :
The rheological properties of complex fluids made of particles in a suspended fluid depend on the behavior of microscopic particles in flow [1,2]. A first step to understand this link is to investigate the individual particle dynamics in simple shear flows. A rigid rod will perform so-called Jeffery orbits [3], however when the rod becomes flexible and Brownian, the behavior in terms of deformation and migration is still to be fully understood[4]. We chose here to address this situation by studying experimentally the behavior of semiflexible polymers. We use actin filaments and combine fluorescent labeling techniques, microfluidic devices and an automated stage to carry out controlled systematical experiments and statistic analysis. Different dynamics are observed as a function of the elasto-viscous number, comparing viscous forces to elastic restoring forces. The bending modulus of the actin filaments is given by the persistence length Lp that we measured to be 17±1µm[5]. When increasing the elasto-visous number by increasing either the shear rate or the length of the actin filament we subsequently observe tumbling, buckling, and bending under flow. Those observations seem to be in good agreement with recent numerical simulations [6]. At the same time, actin filaments fluctuate due to Brownian motion and these fluctuations can modify the individual dynamics of actin filaments compared to non-Brownian particles. The effect of these fluctuations increases with decreasing shear rate or viscosity.

References
[1] Bird, R. B., Curtiss, C. F., Armstrong, R. C., and Hassager, O. (1994). Dynamics of Polymeric Liquids. Wiley InterScience New York.
[2] Becker, L. E., Shelley, M. J. (2001). Instability of Elastic Filaments in Shear Flow Yields First-Normal-Stress Differences PRL, 87, 198301.
[3] Jeffery G. B. (1922). The Motion of Ellipsoidal Particles Immersed in a Viscous Fluid. Proceedings of the Royal Society A : Mathematical,
Physical and Engineering Sciences, 102(715), 161Ð179.
[4] M. Harasim, B. Wunderlich, Direct Observation of the Dynamics of Semiflexible Polymers in Shear Flow, PRL110, 108302 (2013).
[5] H. Isambert, P. Venier, Flexibility of Actin Filaments Derived from Thermal Fluctuations, J. of Biological Chemistry 270, 11437 (1995).
[6] Nguyen, H., and Fauci, L. (2014). Hydrodynamics of diatom chains and semiflexible fibres. J. of The Royal Society Interface, 11(96), 20140314.

–  30 juin 2016 - Laurette Tuckerman la Theorie des Elections

–  23 juin 2016 - Idalia Frontczak et Mikołaj Krutnik

–  16 juin 2016 - Marine Daïeff (doctorante PMMH)

–  9 juin 2016 - Joana Fidalgo (doctorante PMMH)

–  2 juin 2016 - Eline Dehandschoewercker (doctorante PMMH)

–  26 mai 2016 - Ludovic Keiser (doctorant PMMH)

–  19 mai 2016 - Intesaaf Ashraf (doctorant PMMH)

–  12 mai 2016 - Théau Conte (doctorant en Génie Civil au LMT, ENS Cachan) (Abstract)

–  05 mai 2016 - ASCENSION

–  28 avril 2016 - Pas de séminaire

–  21 avril 2016 - Martin Coux (doctorant PMMH) : Elastic superhydrophobic surfaces

–  14 avril 2016 - Séminaire exceptionnel en l’honneur d’Etienne Guyon : débute à 11h (programme)

–  07 avril 2016 - Athanasia Christakou (PostDoc PMMH) Thesis short-version : Ultrasound-assisted Interactions of Natural Killer Cells with Cancer Cells and Solid (Abstract)

–  31 mars 2016 - Justine Laurent (Ingénieur PMMH) : Instrumental development : from pN measurements to LIF (laser induced fluoresence) in plasma.

–  24 mars 2016 - Canceled

–  17 mars 2016 - No seminar (Rencontres du Non-Linéaire 2016)

–  10 mars 2016 - Vincent Martinez (Edimburg Univ.) : Spatially-controlled activity of light-driven bacteria (Abstract)

–  3 mars 2016 - Marion Segall (PhD student at PMMH/MNHN) : Water as a driver of evolution : the example of aquatic snakes (Abstract)

–  25 février 2016 - Florence Haudin (PostDoc PMMH) : Croissance de jardins chimiques en milieu confiné / Growth of confined chemical gardens

–  18 février 2016 - Pas de séminaire : Journée PC Focus

–  11 février 2016 - Alexandre Vilquin (PostDoc PMMH) Thesis short-version :
Shock wave structure in granular gases :
In different materials such as gases, plasmas and granular material, an object, moving at supersonic speed, compresses and heats the fluid ahead. The shock front is the out-of-equilibrium area, where violent changes in temperature, pressure and density occur. It has a particular structure with notably strongly non-Gaussian particle velocity distributions, which are difficult to observe. In an important breakthrough in 1951, Mott-Smith describes the shock front as a superposition of two states : the initial supersonic gas and the compressed and heated subsonic gas, implying existence of bimodal velocity distributions. Several experiences at high Mach numbers show this overall bimodal structure. However this model does not explain the existence of a surplus of particles with intermediate velocities, between the supersonic and the subsonic gas. This thesis focuses on shock waves in granular gases, where particles undergo only inelastic binary collisions. In these dissipative gases, the granular temperature, reflecting the particle random motion, allows to define the equivalent to the speed of sound by analogy with molecular gases. The low values of this speed of sound permit to generate easily shock waves in which each particle can be tracked, unlike molecular gases. The first part of this work focuses on the effect of the energy dissipation, due to inelastic collisions, on the shock front structure in granular gases. Modifications induced on temperature, density and mean velocity, are captured by a model based on the bimodal hypothesis of Mott-Smith and including energy dissipation. The second part is devoted to the study of velocity distributions in the shock front. From experiences in granular gases, a trimodal description, including an additional intermediate state, is proposed and successfully extended to the velocity distributions in molecular gases.

–  04 février 2016 - Danilo Carvajal (Centrode Investigación Tecnológica del Agua y el Desierto (Ceitsaza), Universidad Católica del Norte) :
Dew water harvesting in Chile :
In this seminar, the results of the first year of the project entitled Experimental assessment and predictive modeling of rooftop dew collection for water supply in Chile ; (Fondecyt 11140863, CONICYT, Chile) will be presented. The general objective of this project is to assess the dew water collection by passive radiative cooling at eight locations in the north and central area of Chile. A dew potential map based on mathematical models (theoretical and statistical) and experimental data obtained from
on-site dew condensers will be constructed. The chemical characteristics of the dew water collected in every place will be analyzed. The project’s first year was focused in the construction and installation of dew condensers (1 m2 units), including instrumentation for recording dew yields, condenser surface temperature and meteorological data. Two large
scale dew collectors (based on building rooftops) were also implemented. The implementation works and the first results from the condensers which are in operation will be presented and discussed.

–  28 janvier 2016 - Journées de la Physique Statistique 2016 (28-29/01)

–  21 janvier 2016 - Hadrien Bense (PhD student at PMMH) : Crushed hemispherical shells

–  14 janvier 2016 - Hugo Perrin (PhD student at PMMH) : A dynamic view of contact angle hysteresis

–  07 Janvier 2016 - Galette des Rois ;)