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Séminaires Invités

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Séminaires donnés par des invités extérieurs au LIPhy.

Ce sont des séminaires généraux qui s’adressent à tous les membres du LIPhy. Par conséquent, l’introduction, la plus large possible, y joue un rôle important.

Les séminaires durent environ 1heure dont 15mn accordées aux questions. Ils ont lieu les lundis à 14h, en salle de conférence du laboratoire au deuxième étage. La langue des séminaires est en général l’anglais.

L’accès au laboratoire peut-être obtenu en contactant le secrétariat.


  • Lundi 3 février 2014 14:00-15:00 - Cécile Monteux - Laboratoire Science et Ingénierie de la Matière Molle, ESPCI, Paris


    Résumé : Our goal is to control the propoerties of liquid interfaces (stability of a foam, spreading of a liquid on a surface) by using ‘reactive’ amphiphilic molecules. I will give two examples
    - Photo-responsive bubbles, films and foams. We use surfactants which change their shape under UV light. Le light intensity enables to control the number of adsorbed surfactants at the air-water interface hence to obtain a remote control of surface flows as well as foam destabilization.
    - Assembly of polymer multi-layers at the oil-water interface for encapsulation
    We study the self-assembly of polymer multi-layers at the oil-water interface to form a rigid membrane. We show that the type and strength of interactions between the polymer layers (electrostatic, hydrogen bonds as well as hydrophobic interactions) enables to control the rheological properties of the membranes.

    Lieu : Salle de conf. 224

    Notes de dernières minutes : contact : Salima Rafaï

  • Lundi 10 février 2014 14:00-15:00 - Sébastien Balibar - LPS ENS

    Quantum crystals : how the supersolid fever led to the discovery of a giant plasticity Cliquer pour télécharger l’affiche

    Résumé : Sometimes one looks for something and one finds something else.
    The 2004 experiments by Kim and Chan triggered an intense activity on a paradoxical question : could solid helium-4 be elastic and superfluid at the same time ?
    9 years later, we have discovered that helium-4 crystals present a giant plasticity in the zero temperature limit if all their impurities are suppressed.
    Ultrapure helium crystals do not resist to an applied shear stress in one particular direction, like a pile of paper sheets that can glide over each other when submitted to a horizontal shear.
    This phenomenon is a spectacular example of "plasticity" because it is a consequence of the motion of crystalline defects called dislocations. It is "giant" because these dislocations move without friction like little violin strings. It disappears if traces of impurities bind to dislocations or if the temperature increases above 0.2 Kelvin and introduces disorder.
    Plasticity is of great importance in Materials Science.
    In solid helium where quantum fluctuations are large, it has unprecedented properties : it occurs with a very large amplitude even under the application of extremely small stresses (nanobars), and it is reversible. In classical crystals, rather large stresses are necessary to produce small irreversible strains.
    Measurements of the damping of the dislocation motion also allowed us to measure the dislocation density and their typical length so that we could rule out the few existing models of supersolidity in solid helium 4.
    Finally we have understood how our results explain the original experiments by Kim and Chan without invoking supersolidity.

    Notes de dernières minutes : Séminaire Dysco contact : S. Rafaï

  • Mardi 11 février 2014 14:00-15:00 - Nicolas Bertin

    Cisaillement de spheroides

  • Lundi 24 mars 2014 14:00-15:00 - Holger Stark - Technische Universitaet Berlin Institut fuer Theoretische Physik

    Prof. Dr. Holger Stark

    Résumé : Active motion of microorganisms or artificial microswimmers in a fluid at low Reynolds number is an appealing subject which has attracted much attention recently. Since these swimmers move constantly in nonequilibrium, they give rise to novel phenomena which, in
    particular, occur when external fields are applied or when they move collectively. The talk reviews three situations how active motion manifests itself. First, a swimmer under Poiseuille flow shows nonlinear dynamics reminiscent of the nonlinear pendulum Bounding
    walls introduce "dissipation" [1] and an elliptical cross section of the microchannel leads to chaotic motion. Secondly, I discuss the collective motion of model swimmers, so-called squirmers, in a quasi 2D geometry by means of multi-particle collision dynamics.
    This is a particle based method to solve the Navier-Stokes equations and helps to elucidate the role of hydrodynamics in collective phenomena. Indeed, we find gas-like and cluster phases as well as phase separation which is strongly influenced by hydrodynamic near-field interactions and the swimmer type. Thirdly, I discuss dynamic clustering of active or self-propelling colloids that interact by diffusiophoresis reminiscent of chemotaxis in bacterial systems.

  • Lundi 19 janvier 2015 14:00-15:00 - Falko Ziebert

    Séminaire Matière Molle Matière Grise

  • Lundi 26 janvier 2015 14:00-15:00 - Christophe Tribet - Pôle de Chimie Biophysique. ENS-UPMC-CNRS UMR 8640 Paris

    Séminaire Matière Molle Matière Grise

    Résumé : Water-soluble amphiphilic copolymers spontaneously form self-assemblies or assemblies with micelles of detergents or lipid membranes, that can be tailored to optimize properties of complex fluids. Applications to biologically relevant systems include controlled activity of proteins (encapsulation, protection), permeabilization of membranes (e.g. biocide agents, or drug cargoes), or triggering cell adhesion. In this context, clean, non toxic, and remote control of hydrophobicity is highly in demand. Exposure to visible light or weak temperature shifts are compatible with a control at spatial and temporal resolutions matching with biological scales. Here we illustrate i) cell-repellent polymer coatings that can present on demand cell-adherent (e.g. RGD) patterns [1], and ii) photopermeabilization by artificial polymers of model giant liposomes and mammalian cell membranes [2]. We evidenced polymer-triggered and light-triggered lipid scrambling, release of encapsulated Dextran, formation of transient channels in black lipid membranes.
    [1] F. Dallier, unpublished data, and Stijn F. M. van Dongen, P. Maiuri, E. Marie, C. Tribet and M. Piel, Adv. Mater. 2013, 25(12):1687-91.
    [2] S. Sebai, et al., Angewandte Chemie Int Ed., 2012, 51, 2132-2136.

    Notes de dernières minutes : contact : Lionel Bureau

  • Lundi 9 février 2015 14:00-15:00 - Modeste NGUIMDO - Applied Physics Research Group, Vrije Universiteit Brussel, Belgium

    Opto-electronic delay systems and their applications

    Résumé : Opto-electronic systems subject to delayed feedback can generate very rich dynamics which are desired for many applications. These systems offer reliability, high bandwidths, high power efficiency and integration facility on networks or optics. Typically, they consist of semiconductor lasers subject to optical delayed feedback or electro-optical delayed feedback. In this seminar, I will discuss the versatile use of opto-electronic systems for some real-world
    applications : One one hand, I will discuss the security issues in chaos cryptosystems based on opto-electronic delay systems. Then, I will deepen these discussions on the generation of high-quality non-deterministic random bits using broadband chaotic signals. On the other hand, I will show that stable periodic regimes generated in these systems are useful for generating ultra-pure microwaves with very low phase noise while the stable steady state regime can be suited for the newly introduced brain-inspired computational paradigm, namely reservoir computing.
    Contact E. Lacot

    Lieu : LIPHY-Salle de conférence - 140 rue de la Physique, St-Martin d’Hères

  • Jeudi 12 février 2015 14:00-15:00 - Nick Hill - School of Mathematics & Statistics, University of Glasgow, U.K.

    Bioconvection Patterns

    Résumé : Fourier analysis [1] has been used successfully to measure pattern wavelengths generated by suspensions of swimming micro-­‐organisms (bioconvection) and thus to quantify the changes that are seen as the patterns evolve in time. This approach gives a global average of the wavelengths over the entire field of view. However, many bioconvection patterns are not spatially uniform, but exhibit different types of patterns such as roles and hexagons in different spatial regions. To identify and analyse such local variation, we have developed techniques from wavelet theory that give measures of the local pattern wavelengths and the principal directions of the lines of symmetry. Results are given from the analysis of bioconvection patterns in suspensions of algae and of bacteria, and also chemoconvection.
    Secondly, computational fluid dynamics is used to investigate pattern formation by swimming microorganisms, when their orientation is determined by balance between gravitational and viscous torques (gyrotaxis), due to being bottom-heavy. The governing equations, which consist of the Navier–Stokes equations for an incompressible fluid coupled with a micro-organism conservation equation, are solved numerically in a large cross-section chamber with periodic boundary conditions in the horizontal directions. The influence of key parameters on wavelength selection in bioconvection patterns is investigated. For realistic ranges of parameter values, the computed wavelengths are in good agreement with the experimental observations provided that the diffusion due randomness in cell swimming behaviour is small, refuting a recently published claim that the mathematical model becomes inaccurate at long times. We also provide the first computational evidence of “bottom-standing” plumes in a three-dimensional simulation.
    [1] Bees, M.A. & Hill, N.A. Wavelengths of Bioconvection Patterns. Journal of Experimental Biology, 200, 1515-­‐1526, (1997).

    Lieu : Conference room, LIPhy

    Notes de dernières minutes : contact : Philippe Peyla

  • Lundi 16 février 2015 14:00-15:00 - Rosario Capozza - International School for Advanced Studies (SISSA), Trieste, Italy

    Electrical charging effects on lubrication properties of a model confined ionic liquid

    Résumé : Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. By means of molecular dynamics simulations, I explore this variety of phenomena using a simple charged coarse-grained model of ionic liquid. With grand-canonical-like conditions to allow the flow of ions in and out of the interplate gap, I simulate the liquid squeezout and obtain effective enthalpy curves showing the local minima that correspond to layering, and predict the switching between one and another under squeezing and charging.
    In view of a possible electrical control of friction, I also explore the dependence of friction upon successive squeezout and charging of plates.
    The actual frictional behavior obtained does depend upon the assumed features and parameters of the model liquid and its interaction with the plates, yet, the broader scenario obtained for charging effects upon boundary lubrication, appear of general value.
    contact : Cyril Picard

    Lieu : LIPHY-Conference Room

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  • Mercredi 16 décembre 2015 10:00-17:00 - plusieurs intervenants

    Journée speckle

    Résumé : *Erik Geissler (DLS et diffusion cohérente des X) ;
    *Romain Pierrat - ESPCI (diffusion optique simple/multiple dans les milieux désordonnés + aspects dynamiques) ;
    *Vincent Favre Niccolin - I.Néel (imagerie par diffraction cohérente des X)

    Lieu : salle de lecture

  • Mercredi 6 juillet 2016 08:30-18:00 -

    Workshop depinning vs yielding

  • Vendredi 24 juin 2016 14:00-15:30 - Emanuela Del Gado - Georgetown University, Washington DC, USA

    Gelation and Densification of Cement Hydrates : A Soft Matter in Construction

    Résumé : Abstract : 5-8 % of the global human CO2 production comes from the production of cement, concrete main binder. The material strength emerges through the development, once in contact with water, of calcium-silicate-hydrate (C-S-H) gels that literally glue together the final compound. Current industrial research aims at exploring alternative and more environmentally friendly chemical compositions while enhancing rheology and mechanics, to overcome the many technological challenges and guarantee concrete standards. Identifying the fundamental mechanisms that control the gel properties at the early stages of hydration and setting is crucial, although challenging, because of far-from-equilibrium conditions, closely intertwined to the evolution of the chemical environment, that are a hallmark of cement hydration.
    I will discuss a recently developed statistical physics approach, which allows us to investigate the gel formation under the out-of-equilibrium conditions typical of cement hydration and the role of the nano-scale structure in C-S-H mechanics upon hardening. Our approach, combining Monte Carlo and Molecular Dynamics simulations, unveils for the first time how some distinctive features of the kinetics of cement hydration can be related to the nano-scale effective interactions and to the changes in the morphology of the gels. The novel emerging picture is that the changes of the physico-chemical environment, which dictate the evolution of the effective interactions, specifically favor the gel formation and its continuous densification. Our findings provide new handles to design properties of this complex material and an extensive comparison of numerical findings for the hardened paste with experiments ranging from SANS, SEM, adsorption/desorption of N2 and water to nano-indentation provide new, fundamental insights into the microscopic origin of the properties measured.
    K. Ioannidou, R.J.-M. Pellenq and E. Del Gado, Controlling local packing and growth in calcium-silicate-hydrate gels, Soft Matter 10, 1121 (2014)
    E. Del Gado, K. Ioannidou, E. Masoero, A. Baronnet, R. J.-M. Pellenq, F. J. Ulm and S. Yip, A soft matter in construction - Statistical physics approach for formation and mechanics of C—S—H gels in cement, Eur. Phys. J. - ST 223, 2285 (2014).
    K. Ioannidou, K.J. Krakowiak, M. Bauchy, C.G. Hoover, E. Masoero, S. Yip, F.-J. Ulm, P. Levitz, R.J.-M. Pellenq and E. Del Gado, The mesoscale texture of cement hydrates , PNAS 113, 2029 (2016)
    K. Ioannidou, M. Kanduc, L. Li, D. Frenkel, J. Dobnikar and E. Del Gado, The crucial effect of early-stage gelation on the mechanical properties of cement hydrates, Nature Communications (2016), to appear.

    contact : Kirsten Martens

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères

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