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Seminars

Contact :
Matthieu Labousse
matthieu.labousse (arobase) espci.psl.eu
Tel : +33 (0) 1 40 79 45 97

Joshua McGraw
joshua.mcgraw (arobase) espci.fr
Tel : +33 (0) 1 40 79 59 62

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Gulliver seminars take place on Mondays at 11:30 AM in the F304 room, and typically last one hour including questions. The seminars are in English, and the scientific topics are mainly those studied in the laboratory.



Fernando Peruani (Universite de Nice Sophia Antipolis)

Lundi 29 octobre 2012 11:15-12:15 - Bibliothèque PCT - F3.04

From bacteria to collective motion in heterogeneous media

First part - I will show some recent experimental results with three mutants of the gliding bacterium Myxococcus xanthus. We found that mutants lacking biochemical signaling and moving unidirectionally exhibit collective motion in the form of large moving clusters at intermediate densities, while self-organize into vortices at very high densities. Our measurements indicate that there is a critical density at which arbitrary large clusters and giant number fluctuations are observed. These findings are consistent with what is known from self-propelled rod models which strongly suggests that the combined effect of self-propulsion and volume exclusion interactions is the pattern formation mechanism leading to the observed phenomena. On the other hand, if mutants reverse periodically their moving direction — as the wild-type does — the emerging macroscopic patterns are remarkably different, particularly at high density where the bacteria self-organize into a mesh-like structure.

Second part - Most bacteria do not leave in clean and homogeneous media, but rather in highly heterogeneous environments. Despite of this evident fact, little is known about collective motion on heterogeneous media and most, if not all, theoretical efforts have focused on homogeneous media. In the second part of the talk, I will show through a simple model that due to the presence of few heterogeneities the transition to collective motion is radically different from what we know from homogeneous media. For instance, our “homogeneous-based” intuition tells us that low noise intensities should favor collective motion. However, we found that in heterogeneous media this is no longer true. There is a optimal noise amplitude that maximizes collective motion. Counterintuitively, at vanishing noise intensities the system becomes disordered again. These results may shed light on bacterial adaptation and evolution, particularly concerning the bacterial tumbling rate.

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Séminaires  (519)

  • Fernando Peruani (Universite de Nice Sophia Antipolis)
    Lundi 29 octobre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    From bacteria to collective motion in heterogeneous media
    First part - I will show some recent experimental results with three mutants of the gliding bacterium Myxococcus xanthus. We found that mutants lacking biochemical signaling and moving unidirectionally exhibit collective motion in the form of large moving clusters at intermediate densities, while self-organize (...)
  • Oliver Baeumchen (McMaster University,Hamilton, Canada)
    Lundi 5 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Can Polymers Slide ? New Insights from Capillary-Driven Flows in Thin Films
    The motion of small amounts of liquid on the micro- and nanoscale is of enormous scientific interest and additionally holds great technological potential, e.g. in lab-on-a-chip applications for pharmaceuticals, biological analysis or chemical reactions. When downsizing devices, interfacial and confinement (...)
  • Oliver Baeumchen (McMaster University,Hamilton, Canada)
    Lundi 5 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Can Polymers Slide ? New Insights from Capillary-Driven Flows in Thin Films
    The motion of small amounts of liquid on the micro- and nanoscale is of enormous scientific interest and additionally holds great technological potential, e.g. in lab-on-a-chip applications for pharmaceuticals, biological analysis or chemical reactions. When downsizing devices, interfacial and confinement (...)
  • Lev Truskinovsky (Ecole Polytechnique, Palaiseau, France)
    Lundi 12 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Equilibrium and non-equilibrium statistical physics of the power stroke in skeletal muscles
    The classical Huxley-Simmons model of muscle contractions exhibits unusual statistical properties due to the presence of long range elastic interactions. Those include non-equivalence of the soft and hard device ensembles, negative equilibrium stiffness and anomalously slow kinetics in the soft device. Our (...)
  • Lev Truskinovsky (Ecole Polytechnique, Palaiseau, France)
    Lundi 12 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Equilibrium and non-equilibrium statistical physics of the power stroke in skeletal muscles
    The classical Huxley-Simmons model of muscle contractions exhibits unusual statistical properties due to the presence of long range elastic interactions. Those include non-equivalence of the soft and hard device ensembles, negative equilibrium stiffness and anomalously slow kinetics in the soft device. Our (...)
  • James R. Rice (Harvard University)
    Lundi 19 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Dynamics and hydrology of rapid ice sheet motion
    Two questions are discussed which arise in evaluating possible scenarios of accelerated deglaciation in Greenland and Antarctica. A first question is, how fast can a glacier imbibe a meltwater lake, and what are the aftereffects ? It focuses on Greenland where, as spring commences, a broad swath of more (...)
  • James R. Rice (Harvard University)
    Lundi 19 novembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Dynamics and hydrology of rapid ice sheet motion
    Two questions are discussed which arise in evaluating possible scenarios of accelerated deglaciation in Greenland and Antarctica. A first question is, how fast can a glacier imbibe a meltwater lake, and what are the aftereffects ? It focuses on Greenland where, as spring commences, a broad swath of more (...)
  • John F. Brady (California Institute of Technology, USA)
    Lundi 3 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Chemical Swimming
    The design of nanoengines that can convert stored chemical energy into motion is an important challenge of nanotechnology, especially for engines that can operate autonomously. Recent experiments have demonstrated that it is possible to power the motion of nanoscale and microscale objects by using surface (...)
  • John F. Brady (California Institute of Technology, USA)
    Lundi 3 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Chemical Swimming
    The design of nanoengines that can convert stored chemical energy into motion is an important challenge of nanotechnology, especially for engines that can operate autonomously. Recent experiments have demonstrated that it is possible to power the motion of nanoscale and microscale objects by using surface (...)
  • Séminaire : Karim Benchenane (Laboratoire de neurobiologie, ESPCI)
    Lundi 10 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Role of sleep in memory processes
    The two-stage model of memory consolidation developed by Gyorgy Buzsaki proposed that encoding occurs during awake hippocampal theta oscillations (5-10Hz) and consolidation during slow wave sleep (SWS), involving reactivations that occur during hippocampal 200Hz oscillations called the sharp-waves-ripples (...)
  • Séminaire : Karim Benchenane (Laboratoire de neurobiologie, ESPCI)
    Lundi 10 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    Role of sleep in memory processes
    The two-stage model of memory consolidation developed by Gyorgy Buzsaki proposed that encoding occurs during awake hippocampal theta oscillations (5-10Hz) and consolidation during slow wave sleep (SWS), involving reactivations that occur during hippocampal 200Hz oscillations called the sharp-waves-ripples (...)
  • Hirokazu Tanimoto (Institut Curie)
    Lundi 17 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    A simple force-motion relationship of migrating cells
    In this talk, we would discuss about a force-motion relationship of migrating eukaryotic adherent cells. Biological cells migrate without net forces, which is a consequence of force-free and negligible inertia conditions (Purcell, 1977). This indicates that to elucidate a force-motion relationship, unlike in cases (...)
  • Hirokazu Tanimoto (Institut Curie)
    Lundi 17 décembre 2012 11:15-12:15 - Bibliothèque PCT - F3.04
    A simple force-motion relationship of migrating cells
    In this talk, we would discuss about a force-motion relationship of migrating eukaryotic adherent cells. Biological cells migrate without net forces, which is a consequence of force-free and negligible inertia conditions (Purcell, 1977). This indicates that to elucidate a force-motion relationship, unlike in cases (...)
  • Sascha Hilgenfeldt (University of Illinois at Urbana Champaign, USA)
    Lundi 7 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Understanding and manipulating microbubble streaming flows : size-sensitive sorting and mixing
    Ultrasound-induced oscillation of microbubbles gives rise to intense, steady streaming flows. We show that the flow patterns can be flexibly and interactively shaped by the superposition of a transport flow and adjustment of driving amplitude and/or frequency. In this way, sensitive selection, focusing, and (...)
  • Sascha Hilgenfeldt (University of Illinois at Urbana Champaign, USA)
    Lundi 7 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Understanding and manipulating microbubble streaming flows : size-sensitive sorting and mixing
    Ultrasound-induced oscillation of microbubbles gives rise to intense, steady streaming flows. We show that the flow patterns can be flexibly and interactively shaped by the superposition of a transport flow and adjustment of driving amplitude and/or frequency. In this way, sensitive selection, focusing, and (...)
  • Jean-Louis Barrat (Université Joseph Fourier, Grenoble)
    Lundi 14 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Investigating mechanical properties of disordered solids with computer simulations
    Many solids around us are disordered : glassy or semi crystalline polymers, oxide or metallic glasses, nanocomposites, are common examples. In disordered systems, the link between macroscopic mechanical properties and the nanostructure of the materials is far from being understood. I will describe some of the (...)
  • Jean-Louis Barrat (Université Joseph Fourier, Grenoble)
    Lundi 14 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Investigating mechanical properties of disordered solids with computer simulations
    Many solids around us are disordered : glassy or semi crystalline polymers, oxide or metallic glasses, nanocomposites, are common examples. In disordered systems, the link between macroscopic mechanical properties and the nanostructure of the materials is far from being understood. I will describe some of the (...)
  • Alba Marcellan (PPDM-SIMM, ESPCI)
    Lundi 21 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Nano-hybrid gels : from pure chemical to hybrid networks
    Nano-hybrid hydrogels combine a poly(N,N-dimethylacrylamide) covalent network and physical interactions by strong adsorption of polymer chains at the nanoparticle surface. The resulting mechanical behavior of such highly stretchable nano-hybrid hydrogels highlighted a very unusual combination of properties induced (...)
  • Alba Marcellan (PPDM-SIMM, ESPCI)
    Lundi 21 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Nano-hybrid gels : from pure chemical to hybrid networks
    Nano-hybrid hydrogels combine a poly(N,N-dimethylacrylamide) covalent network and physical interactions by strong adsorption of polymer chains at the nanoparticle surface. The resulting mechanical behavior of such highly stretchable nano-hybrid hydrogels highlighted a very unusual combination of properties induced (...)
  • Jean-François Allemand (LPS, ENS, Paris)
    Lundi 28 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Some single molecule approaches to DNA replication
    DNA replication is an essential step of the cell cycle. Despite many biochemical studies, physical approaches can still bring new informations on some process of DNA replication. In vitro, using micromanipulation tools, we have shown that force can trigger some DNA polymerases into an exonuclease mode where (...)
  • Jean-François Allemand (LPS, ENS, Paris)
    Lundi 28 janvier 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Some single molecule approaches to DNA replication
    DNA replication is an essential step of the cell cycle. Despite many biochemical studies, physical approaches can still bring new informations on some process of DNA replication. In vitro, using micromanipulation tools, we have shown that force can trigger some DNA polymerases into an exonuclease mode where (...)
  • Dominique Langevin (LPS, Orsay)
    Lundi 4 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Shear rheology of two-dimensional solids
    Many soft solids, such as concentrated suspensions, emulsions, foams, behave in a similar way under an applied shear : they exhibit a Maxwell-type relaxation with a characteristic relaxation time that varies inversely with the applied shear rate. When the storage and loss moduli are measured at different (...)
  • Dominique Langevin (LPS, Orsay)
    Lundi 4 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Shear rheology of two-dimensional solids
    Many soft solids, such as concentrated suspensions, emulsions, foams, behave in a similar way under an applied shear : they exhibit a Maxwell-type relaxation with a characteristic relaxation time that varies inversely with the applied shear rate. When the storage and loss moduli are measured at different (...)
  • Maxime Clusel (Laboratoire Charles Coulomb, Montpellier)
    Lundi 11 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    A Granocentric viewpoint on random packing of spheres
    I will present and discuss a simple statistical model for the random packing of frictionless, originally introduced to find the link between polydispersity and packing structure. We simplify the problem by considering the “granocentric” point of view of a single particle in the bulk, thereby reducing random packing (...)
  • Maxime Clusel (Laboratoire Charles Coulomb, Montpellier)
    Lundi 11 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    A Granocentric viewpoint on random packing of spheres
    I will present and discuss a simple statistical model for the random packing of frictionless, originally introduced to find the link between polydispersity and packing structure. We simplify the problem by considering the “granocentric” point of view of a single particle in the bulk, thereby reducing random packing (...)
  • Stephan Fauve (LPS, ENS, Paris)
    Lundi 18 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Reversals of a magnetic field generated by a dynamo process
    Magnetic fields of many planets and stars are generated by a dynamo process, i.e. by electromagnetic induction due to the motion of an electrically conducting fluid. They often display reversals : the magnetic field flips between two states of opposite polarities. This occurs roughly periodically for the solar (...)
  • Stephan Fauve (LPS, ENS, Paris)
    Lundi 18 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Reversals of a magnetic field generated by a dynamo process
    Magnetic fields of many planets and stars are generated by a dynamo process, i.e. by electromagnetic induction due to the motion of an electrically conducting fluid. They often display reversals : the magnetic field flips between two states of opposite polarities. This occurs roughly periodically for the solar (...)
  • Julien Deseigne (ENS Lyon)
    Lundi 25 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Molecular transport phenomenon of particles and mixing : building blocks of experimental ecology in oceans ?
    The chaotic laminar advection of colloids in presence of salt is investigated experimentally with microfluidic technology. As long as salt contrasts hold, colloids are carried along saline gradients much faster than the brownian motion. At larger scale, such synergy between salt and colloids give non trivial (...)
  • Julien Deseigne (ENS Lyon)
    Lundi 25 février 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Molecular transport phenomenon of particles and mixing : building blocks of experimental ecology in oceans ?
    The chaotic laminar advection of colloids in presence of salt is investigated experimentally with microfluidic technology. As long as salt contrasts hold, colloids are carried along saline gradients much faster than the brownian motion. At larger scale, such synergy between salt and colloids give non trivial (...)
  • Christophe Josserand (Institut d'Alembert)
    Lundi 18 mars 2013 11:15-12:15 - Bibliothèque PCT - F3.04
    Wave turbulence in vibrating plates
    The concept of wave turbulence has been introduced about 50 years ago in the context of water waves. It consists in an asymptotic expansion of the cumulant terms of the dynamics that leads eventually to a kinetic equation. Beside the thermodynamical equilibrium solutions, this kinetic equation exhibits the (...)

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General recommendations for the speakers

The audience is often heterogeneous - because of the wide range of scientific topics covered in the lab - so planning a talk for a broader audience would be preferred. The seminar is in English, and speakers are thus invited to prepare their slides in English.

The seminar starts at 11:30 AM. The speaker is asked to arrive in the lab at least 15 minutes in advance to set up their computer. The talks last typically 45 minutes, and are followed by a discussion time.

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