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Home > Research > Talks & Conferences > Talks Given at LIPhy

Invited Talks

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These talks are given by invited speakers at LIPhy. The intended audience is the whole LIPhy. A large general introduction intended for non-specialist is usually provided.

Typical talk duration is around one hour and includes about 15 mn of questions. The talks are scheduled usually every Monday at 2PM. The place is at the conference room, second floor.

Access to the lab can be obtained by calling Nadine D’Andréa or Chantal Reignier through the intercom at the main entrance.

Agenda

  • Friday 6 November 2015 14:00-15:30 - Roberto RUSCONI - Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, USA

    Nonlinear Dynamics and Spatial Heterogeneity in Flowing Suspensions of Swimming Microorganisms

    Résumé : The vast majority of microorganisms experience fluid flow [1], whether turbulent flow in aquatic and industrial systems, or laminar flow in the human body and medical devices. Common to all flow regimes is hydrodynamic shear, which generates forces and torques on cells. In the absence of shear, motile microorganisms explore their environment with random-walk swimming patterns, resulting in diffusive transport, but little is known about the effects of fluid flow on their navigation and spatial distribution. Using microfluidics, I will show that swimming microorganisms can be trapped in regions of high shear, where the hydrodynamic torque preferentially aligns them in the flow direction, quenching their migration across streamlines [2]. This is a robust phenomenon, which can result in depletion of cells from the low-shear regions of the flow within only a few seconds and which does not require any cell-surface interaction to induce the observed heterogeneous distributions. A shear flow can have even more unpredictable effects on motile phytoplankton cells, as the spatial distribution of these microorganisms is also governed by their swimming style. These observations encompass a rich set of dynamics that emerges from the interaction of microbial motility, morphology and fluid flow and that can affect the microscale distribution of microorganisms in the environment.
    [1] Rusconi R, Stocker R, “Microbes in flow”, Curr. Op. Microbiol. 25, 1–8 (2015).
    [2] Rusconi R, Guasto JS, Stocker R, “Bacterial transport suppressed by fluid shear”, Nature Physics 10, 212–217 (2014).



    contact : Sigolene Lecuyer

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


  • Monday 16 November 2015 14:00-15:30 - Baptiste DEPALLE - Wellcome Trust/MIT Research Fellow, Department of Materials, Imperial College, London, UK

    Nano-Deformation Mechanisms in Bone Collagen Fibrils

    Résumé : The remarkable mechanical properties of bone are dependent upon its complex hierarchical structure made up of an organic matrix, filled with a mineral phase and water. However, the interactions between mineral and organic matter that endow bone with its toughness at the nanoscale have thus far been elusive. Identifying these mechanisms is critical to unlocking the nanoscale underpinning of diseases such as osteoporosis and to developing guidelines for engineering of bone and partially mineralized tissues.
    We explore the intricate relationship between the nanostructure of bone collagen fibrils and their mechanical behavior using coarse-grained molecular dynamics. Here, we focus specifically on the role of enzymatic cross-links and intrafibrillar mineralization in a single collagen fibril. These represent two different ways to improve intermolecular interaction and improve the fibrils mechanics by taking advantage of the full mechanical potential of every collagen molecule in the structure. Cross-linked and mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy which include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage and crystal dissociation.
    By multiplying its sources of energy dissipation and deformation mechanisms, collagen fibrils can reach impressive strength and toughness and give bone its remarkable mechanical properties.



    contact: Aurélien Gourrier

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


  • Monday 23 November 2015 14:00-15:30 - Romain Mari - Dpt of Applied Mathematics and Theoretical Physics (DAMTP), Univ. Cambridge, UK

    Dense Suspensions, Shear Thickening and Shear Jamming

    Résumé : Dense suspensions can thicken or even jam under shear if the volume fraction of solid material is large enough. It has been recently suggested that these behaviors are the consequence of stress-induced frictional contacts between particles in suspension. I will show that numerical simulations using this idea reach a quantitative agreement with experimental results on shear-thickening suspensions. From a theoretical standpoint, this scenario also unveils the relation between shear thickening and shear jamming. I will also discuss the concept of fragility for shear jammed suspension.



    contact: Eric Bertin

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


  • Monday 30 November 2015 14:00-15:30 - Marie-Antoinette Mélières - LTHE, Grenoble

    Climate, Past, Present and Future.

    Résumé : This talk will concentrate on two questions. The Earth’s climate has changed incessantly throughout the ages. Why? The warming that is likely to take place in the course of the 21st century has caused the scientific community to sound the alarm. Why?
    In answer to these two questions a brief outline will be given of how the present climate on Earth can be described in terms of energy, and of the principal causes of climate change. The example of the large glacial oscillations of the last few million years, and the small fluctuations of the last millennia, puts the origin of the recent warming into context, as well as its consequences for the physical and biological world. As human activity continues to emit greenhouse gases, the climate of 2100 will depend on the scenario adopted. If an average warming by 2ºC (low scenario) of the Earth’s surface could be “manageable”, at the cost of adapting, it is not the case for 5ºC (high scenario). That would return us to a climate that prevailed more than 10 million years ago, before the species homo existed, and would be very different from the climates to which our ecosystems have adapted over the last few million years. It is, for example, profoundly doubtful that the planet would be able to feed ten billion inhabitants.



    This seminar is intended for a broad audience and will be given in French.
    contact: Erik Geissler

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


  • Monday 7 December 2015 14:00-15:30 - Bloen Metzger - IUSTI-CNRS, Aix-Marseille University, France

    Microscopic Origin of Hydrodynamic Diffusion?

    Résumé : Torus formation, destabilization into droplets, then self-similar cascade: the sedimentation of a cloud of particles in a viscous fluid is spectacular. How can such a conceptually simple system develop such a rich phenomenology ? The long range nature of the hydrodynamic interactions between particles and their collective aspect (N-body problem) are the essential ingredients to understand this dynamic. We will discuss in particular the phenomenon called “hydrodynamic diffusion” and will show that, despite a similar phenomenology, its origin is very different in sedimenting and in sheared suspensions.



    contact: Thomas Podgorski

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


  • Monday 14 December 2015 14:00-15:30 - Olivier BLANC-BRUDE - ParCC - Paris Cardiovascular Center @ HEGP – INSERM U970

    Red Blood Cells Emit Microparticles Which Attack Blood Vessels: The Case of Sickle Cell Anemia

    Résumé : Abnormal red blood cells (RBCs) persist in blood circulation during certain diseases. They eventually rupture and release their contents, a process called intravascular hemolysis. Do RBCs disappear? Not exactly... During hemolysis, RBCs release membrane fragments, called microparticles, which are not harmless. Our observations conducted on RBCs of patients with sickle cell anemia, the most common genetic disease in France, show that RBC microparticles carry hemoglobin in a degraded and toxic form: Heme previously contained in hemoglobin ends up associated with microparticle membranes or exposed on their surface. This feature makes microparticles dangerous. The heme-loaded microparticles are deposited in sensitive areas of the vascular network and promote the occurrence of cardiovascular damage. While the understanding of the influence of RBC microparticles begins to emerge, the exact mechanisms of their release in the circulation remain to be explored.



    contact: Thomas Podgorski

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


  • Monday 4 January 2016 14:00-15:30 - Benjamin DOLLET - Institut de Physique, Université de Rennes

    Acoustics and Mechanics of Liquid Foam

    Résumé : In spite of their beauty and numerous applications, liquid foams remain poorly understood in some fundamental aspects, like their acoustical and mechanical behavior.
    Liquid foams are known to be efficient to absorb the energy of pressure waves, and are used as such to mitigate blast waves, but the underlying mechanisms are still obscure. We investigate their linear acoustic properties: speed of sound and attenuation, as functions of the frequency and bubble radius. We show that at given frequency, they display a maximum of attenuation for a certain bubble radius, and a strong acoustic dispersion. These results are quantitatively captured by a model based on the acoustical response of the elementary building blocks of aqueous foams: thin soap films supported by thick liquid channels. In particular, we show that foams are natural acoustic metamaterials, displaying effective negative density over extended ranges of frequency and size.
    In mechanics, liquid foams belong to the vast class of complex fluids, displaying elastic, plastic and viscous responses. Bubbles being easy to image, they are a well suited material to address fundamental issues in soft glassy rheology. Our recent experiments will be presented, which illustrate the elastoplastic flow of foams in straight and convergent channels, and the influence of dissipation, nonlocality, and delayed relaxation. We will also show our recent, and unprecedented, time- and space-resolved foam flow measurements in 3D, using fast X-ray tomography.



    contact: Kirsten Martens

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


  • Monday 11 January 2016 14:00-15:30 - Timm Krüger - University of Edinburg, United Kingdom

    Platelet Margination in Tubular Blood Flow

    Résumé : I will talk about platelet margination in tubular blood flow with a special emphasis on the effects of tube diameter and the red blood cell capillary number Ca (i.e. the ratio of viscous fluid to elastic membrane forces). Platelet margination is important for blood clotting: the healing process of damaged blood vessel walls is initiated by nearby platelets. Platelets should therefore be located close to the vessel wall, ideally within the layer that is free of red blood cells (cell-free layer). The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods.
    It turns out that a non-diffusive radial platelet transport facilitates margination. This non-diffusive effect is important near the edge of the cell-free layer, but only for Ca > 0.2, when red blood cells are tank-treading. Platelets at Ca > 0.2 eventually reach the cell-free layer where they are effectively captured. However, platelets can escape again for Ca < 0.2. Furthermore, I will talk about the platelet dynamics once they have reached the cell-free layer.
    contact: Chaouqi Misbah

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


  • Monday 18 January 2016 14:00-15:30 - Romaric VINCENT - CEA/Leti/DTBS, Grenoble

    Adherent Cells as Self-Propelled Particles

    Résumé : Animal cell colonies display a very broad variety of morphologies, ranging from single cell distributions to 3D agglomerates. In-vivo, most structural cells are organized in epithelia. Drastic changes of organization, such as the formation of 3D agglomerates or epithelial-to-mesenchymal transitions, are often associated either to morphogenetic events or to malfunctions such as tumorigenesis or metastasis.
    Here, we study the organization of cell colonies by means of simulations of self-propelled particles with generic cell-like interactions. Varying cell-cell adhesion and contact inhibition of locomotion (CIL), we obtain a rich phase diagram that reproduces several of the existing phenotypes of cell colonies. These include ordered grid-like distributions of cells, collectively migrating epithelia or 3D aggregates formed via dewetting of cells from the substrate. At last, we find that CIL hinders cell extrusion by ensuring tensile intercellular stresses, a ubiquitous but unclear trait of epithelia.



    contact: Philippe Marmottant

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


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  • Wednesday 16 December 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


  • Wednesday 6 July 2016 08:30-18:00 -

    Workshop depinning vs yielding

  • Friday 24 June 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


  • Wednesday 10 November 2021 14:00-17:30 - Nicolas Cuny

    PhD Nicolas Cuny

    Résumé : Dérivations de modèles constitutifs: de la microstructure à la rhéologie des suspensions denses molles
    Jury:

    • Madame Catherine Barentin, Professeur Université Lyon 1
    • Monsieur Ludovic Berthier, Directeur de Recherche CNRS, Université de Montpellier
    • Monsieur Michel Cloitre, Directeur de Recherche CNRS, ESPCI Paris
    • Monsieur Vincent Démery, Maître de conférence, ESPCI Paris
    • Monsieur Pierre Saramito, Directeur de Recherche CNRS, Université Grenoble-Alpes
    • Monsieur Gilles Tarjus, Directeur de Recherche CNRS, Sorbonne Université

    Lieu : Salle de conférence LIPhy


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