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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

  • Monday 27 March 2017 14:00-15:30 - Céline LABOUESSE - Chalut lab, Stem Cell Institute, University of Cambridge, UK

    Mechanical Signals in Embryonic Stem Cells’ Differentiation

    Résumé : Embryonic stem cells (ESCs) cultured in vitro are functionally equivalent to the pluripotent stem cells of the early pre-implantation embryo. These cells have the potential to differentiate into all embryonic germ layers. The differentiation of ESCs is triggered by the removal of specific kinase inhibitors, which leads to the destabilization of the naïve pluripotency gene network, and the priming of lineage specification genes. The transition from naïve to primed state is characterized by striking morphological changes as cells go from tight round colonies to being flatter and spread out. They also appear to be increasingly sensitive to mechanical forces, as evidenced by the compliance and auxeticity of transition ESC nuclei (Pagliara et al., Nat. Mat., 2014). The actin cytoskeleton is known to have a significant role in determining cell morphology, adhesion strength and mechanosensitivity, yet how these properties are connected to ESC fate determination is unknown. We have developed several systems to test how external mechanical constraints impact cytoskeleton organization in ESCs, nuclear structure and ultimately regulate the exit of pluripotency. We first use compliant substrates with controlled adhesive density to study the crosstalk between mechanical signals and biochemical signaling pathways in naïve ESCs. Preliminary results show that compliant substrates enhance self-renewal of ESCs, through regulation of MAPK pathway. We also are developing a colony compression system to investigate how anisotropic stresses may drive different cell fates in colonies exiting pluripotency.



    contact: Pierre Recho

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


  • Monday 3 April 2017 14:00-15:30 - Marcel A. LAUTERBACH - Max Planck Institute for Brain Research, Dpt of Neural Systems, Frankfurt am Main, Germany

    STED Microscopy and its Applications in Neuroscience

    Résumé : Stimulated Emission Depletion (STED) microscopy overcomes the diffraction barrier of conventional light microscopy, which limits resolution and thus useful magnification. STED microscopy allows using an increased magnification under physiological conditions.
    I will demonstrate how simultaneous holographic photo-stimulation and super-resolution STED imaging can be achieved by incorporating Computer Generated Holography into a STED microscope. This system is applied to study the morphological changes of dendritic spines in neurons after stimulation.
    Furthermore, Fast STED microscopy with 28 frames per second enabling the detailed analysis of the motion of synaptic vesicles in living neurons is shown. Dynamic imaging with up to 200 frames per second is exemplified by the observation of colloidal-crystal formation.
    Whereas STED microscopy resolves nanostructures even in vivo, it is often difficult to relate super-resolved structures to other non-labeled features. Integrating phase contrast into a STED microscope provides a second, label-free contrast channel. This allows for easy correlation of morphological structures with high-resolution fluorescence images. It is demonstrated that Spiral Phase Contrast in scanning confocal configuration yields improved optical contrast and allows quantitative phase measurements. Scanning phase contrast allows for registration with the fluorescence images and for simultaneous recording of phase contrast and STED images. It enables therefore dual imaging and overlay in two contrast modes in fixed and in living specimen.



    contact: Aurélie Dupont

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


  • Monday 10 April 2017 14:00-15:30 - Ludovic PAUCHARD - Laboratoire FAST, Orsay

    Crack Patterns in Drying Colloidal Films: Application to Art Paintings Study

    Résumé : Most coatings are made by depositing a volatile liquid that contains dispersed colloidal particles or dissolved macromolecules.
    The liquid is then evaporated until a dry film is obtained. When the wet film dries, non-uniform shrinkage occurs; this generates tensile stresses that can eventually lead to mechanical instabilities. In particular cracks can form leading to a large variety of morphologies.
    Such structures affect the quality of the final product ; however the presence of cracks can be of great interest in the domain of conservation/restoration of paintings.
    Indeed, the crack patterns can reveal the mechanical properties of the pictorial matter that exhibit a complex system, both from a geometrical and a physicochemical point of views.
    These processes will be presented, and highlighted studying a model system.



    contact: Thomas Podgorski

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


  • Thursday 4 May 2017 11:00-12:30 - Pascal Picart - LAUM CNRS Université du Maine, Le Mans

    Coherent Imaging to Study Traveling Waves

    Résumé : In the domains of acoustics, vibro-acoustics, vibrations of structures or flow-induced vibrations, Laser Doppler Vibrometer is used for dynamics measurements. To get simultaneously a collection of data points at the surface of the inspected vibrating object, multipoint vibrometer was developed. Full-field evaluation can be obtained with coherent imaging based on digital holographic interferometry. Such an approach is well suited because of the high density of measuring points and the reduced measurement time. The use of time-averaging and quasi-time-averaging in digital Fresnel holography was proposed and discussed in the past. However, the stationary regime is a particular case for investigating the structure vibration behavior (propagation of traveling waves), and the characterization of structures under operational or real functioning conditions requires analysis in the time domain. Then, providing a real-time follow-up of the vibration amplitude, whatever the excitation condition, is a challenge for full-field optical metrology. This seminar aims at describing recent advances in high-speed holographic imaging; especially we will focus on the use of such an approach to investigate traveling acoustic waves in mechanical structures. Limits are related to few parameters that will be highlighted so as to establish a wish list for the near future.
    The seminar will be given in French



    contact: Benjamin Cross

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


  • Monday 15 May 2017 14:00-15:30 - Marc BARTHELEMY - Labo. Physique Théorique, CEA, Gif/Yvette

    Characterization of Spatial Networks

    Résumé : Complex systems are very often organized under the form of networks where nodes and edges are embedded in space. Transportation and mobility networks, Internet, mobile phone networks, power grids, social and contact networks, vascular and neural networks, are all examples where space is relevant and where topology alone does not contain all the information. Characterizing and understanding the structure and the evolution of these "spatial networks" is thus crucial for many different fields ranging from urbanism to biology and epidemiology. An important consequence of space on networks is that there is a cost associated to the length of edges which in turn has dramatic effects on their topological structure: due to physical constraints, most standard measures for complex networks are irrelevant for this class of graphs and I will review here some of the most interesting and promising measures for characterizing these graphs and their time evolution. In particular, I will illustrate on various real-world examples the simplicity profile, the spatial distribution of the betweenness centrality and, if time allows, the shape distribution of faces. I will end this talk by discussing briefly interesting directions for modelling these systems.



    contact: Chaouqi Misbah

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


  • Monday 29 May 2017 14:00-15:30 - Maria Consiglia Merola - Stanford University, USA

    Viscoelastic properties of corneal epithelial cells using the “Linear Cell Monolayer Rheometer”

    Résumé : Mechanical properties of cells are determined by complex intracellular structures. In other words, there is a strong connection between biological processes and cellular mechanical response to external stimuli. In fact, cells’ interactions with their living environment are affected by their own mechanical behavior during biological deformations. These interactions, notably adhesion, are crucial to understand the cells adaptation in presence of artificial material such as contact lenses or medical devices.
    During the last decades, different experimental techniques have been used to investigate cell mechanics. Among them, we can mention atomic force microscopy (AFM) and microrheology. While they present a great interest, these techniques are however limited since they can only probe a single cell. In order to overcome the challenges with the biological variation between individual cells, new technologies are thus necessary.
    In this work, we present measurements using a purpose made Linear Cell Monolayer Rheometer (LCMR) that can characterize averaged cell mechanics or averaged cell adhesion. The LCMR enables the investigation of biologically active layers: controlled amounts of live cells with or without artificial materials (e.g., contact lenses). It is used in this study to measure the mechanics of corneal epithelial cells in order to characterize how these cells mechanically deform to external stimuli.
    To simulate physiological conditions, cell mechanics is quantified in experiments in which cells are strained tangential to the cell monolayer. Time-dependent step-strain tests are used to determine the mechanical relaxation of the cell layers.
    The quantification of cell mechanics using the LCMR has the potential for multiple biomedical applications, including disease diagnosis and drug-efficacy screening.



    contact: Claude Verdier

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


  • Thursday 1 June 2017 14:00-15:30 - Silvio FRANZ - LPTMS, CNRS, Univ. Paris-Sud, Universite' Paris-Saclay, 91405 Orsay

    Mean-field avalanches in jammed spheres

    Résumé : Disordered systems are characterized by the existence of many sample-dependent local-energy minima that cause a step-wise response when the system is perturbed. In this talk I will illustrate an approach based on elementary probabilistic methods to compute the complete probability distribution of the jumps (static avalanches) in the response of mean-field systems described by replica symmetry breaking; there is a precise condition for having a power-law behavior in the distribution of avalanches caused by small perturbations, our predictions are in remarkable agreement with simulations of three-dimensional systems of soft spheres, either at jamming or at slightly higher densities.
    Ref: SF and S. Spigler PHYSICAL REVIEW E 95, 022139 (2017)



    contact: Giacomo Gradenigo

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


  • Wednesday 7 June 2017 14:00-15:30 - Stefanos PAPANIKOLAOU - Department of Physics, West Virginia University, USA

    Abrupt Events in Crystal Plasticity: From Uniaxial Compression to Nanoindentation

    Résumé : Crystal plasticity is stochastic and characterized by rare events when there are stiff spatial constraints. In nanopillars under uniaxial compression, size effects are accompanied by plastic deformation that is predominantly stochastic and abrupt with complex probability distributions of rare events.
    In nanoindentation studies of crystalline surfaces, size effects are accompanied by abrupt “pop-in” events that are strongly related to the constrained dislocation dynamics near a surface. The connection and range of the validity and agreement of the character of crystalline stochastic events will be discussed. We will present minimal discrete dislocation plasticity and continuum models that aim to unify observations across crystal plasticity geometries and scales. We will also discuss our experimental efforts towards the statistical understanding of nanoindentation in FCC polycrystals.



    contact: Kirsten Martens

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


  • Monday 12 June 2017 14:00-15:30 - Kaare H. JENSEN - Department of Physics, Technical University of Denmark

    Sap Flow and Gas Exchange in Real and Artificial Plants

    Résumé : The exchange of water for atmospheric CO2 to synthesize sugars in plant leaves is the most fundamental currency of terrestrial life. This exchange occurs via epidermal pores—stomata—that balance the leaf’s need to perform photosynthesis against the dangers of desiccation. Gas fluxes and plant productivity depend on external factors such as light, water, and CO2 availability and on geometric properties of the stomata pores. The link between stomata geometry and environmental factors have informed a wide range of scientific fields - from agriculture to climate science, where observed variations in stomata size and density is used to infer prehistoric atmospheric CO2 content. However, the physical mechanisms and design principles responsible for major trends in stomatal patterning, are not well understood. Here we use a combination of biomimetic experiments and theory to rationalize the observed changes in stomatal geometry. We show that the observed correlations between stomatal size and density are consistent with the hypothesis that plants favor efficient use of space and maximum control of dynamic gas conductivity, and – surprisingly - that the capacity for gas exchange in plants has remained constant over at least the last 325 million years. Our analysis provides a new measure to gauge the relative performance of species based on their stomatal characteristics, and suggests efficient designs for micro engineered systems for gas exchange.



    contact: Jean-François Louf

    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 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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