laboratoire de physique statistique
laboratoire de physique statistique




Capillary wrinkling of elastic membranes - Vella, D. and Adda-Bedia, M. and Cerda, E.
SOFT MATTER 65778-5782 (2010)

Abstract : We present a physically-based model for the deformation of a floating elastic membrane caused by the presence of a liquid drop. Starting from the equations of membrane theory modified to account for surface energies, we show that the presence of a liquid drop causes an azimuthal compression over a finite region. This explains the origin of the wrinkling of such membranes observed recently (Huang et al., Science, 2007, 317, 650) and suggests a single parameter that determines the extent of the wrinkled region. While experimental data supports the importance of this single parameter, our theory under-predicts the extent of the wrinkled region observed experimentally. We suggest that this discrepancy is likely to be due to the wrinkling observed here being far from the threshold.
Density of states of colloidal glasses and supercooled liquids - Ghosh, Antina and Mari, Romain and Chikkadi, Vijayakumar and Schall, Peter and Kurchan, Jorge and Bonn, Daniel
SOFT MATTER 63082-3090 (2010)

Abstract : The glass transition is perhaps the greatest unsolved problem in condensed matter physics: the main question is how to reconcile the liquid-like structure with solid-like mechanical properties. In solids, structure and mechanics are related directly through the vibrational density of states of the material. Here, we obtain for the first time the density of states of colloidal glasses and supercooled liquids from a normal-mode analysis of particle displacements measured using confocal microscopy. We find that the spectrum of the (non-linear) vibrations has many `soft', low-frequency modes, more abundant and very different in nature from the usual acoustic vibrations of ordinary solids. This results in an anomalous low-frequency peak in the density of states which approaches zero frequency as one goes deeper into the glass. The observed soft modes are due to collective `swirling' particle motions, that extend over surprisingly long length scales.
Super-diffusion around the rigidity transition: Levy and the Lilliputians - Lechenault, F. and Candelier, R. and Dauchot, O. and Bouchaud, J. -P. and Biroli, G.
SOFT MATTER 63059-3064 (2010)

Abstract : By analyzing the displacement statistics of an assembly of horizontally vibrated bi-disperse frictional grains in the vicinity of the jamming transition experimentally studied before (F. Lechenault, O. Dauchot, G. Biroli and J.-P. Bouchard, Europhys. Lett., 2008, 83, 46003), we establish that their superdiffusive motion is a genuine Levy flight, but with a `jump' size that is very small compared to the diameter of the grains. The vibration induces a broad distribution of jumps that are random in time, but correlated in space, and that can be interpreted as micro-crack events at all scales. As the volume fraction departs from the critical jamming density, this distribution is truncated at a smaller and smaller jump size, inducing a crossover towards standard diffusive motion at long times. This interpretation contrasts with the idea of temporally persistent, spatially correlated currents and raises new issues regarding the analysis of the dynamics in terms of vibrational modes.
Evaporation of macroscopic sessile droplets - Cazabat, Anne-Marie and Guena, Geoffroy
SOFT MATTER 62591-2612 (2010)

Abstract : This review is aimed at presenting the evaporation of macroscopic sessile droplets on inert substrates in normal atmosphere in simple cases, as a basis for more complex analyses.
Convergence and coupling for spin glasses and hard spheres - Chanal, Cedric and Krauth, Werner

Abstract : We discuss convergence and coupling of Markov chains, and present general relations between the transfer matrices describing these two processes. We then analyze a recently developed local-patch algorithm, which computes rigorous upper bound for the coupling time of a Markov chain for nontrivial statistical-mechanics models. Using the ``coupling from the past'' protocol, this allows one to exactly sample the underlying equilibrium distribution. For spin glasses in two and three spatial dimensions, the local-patch algorithm works at lower temperatures than previous exact-sampling methods. We discuss variants of the algorithm which might allow one to reach, in three dimensions, the spin-glass transition temperature. The algorithm can be adapted to hard-sphere models. For two-dimensional hard disks, the algorithm allows us to draw exact samples at higher densities than previously possible.
A model for hierarchical patterns under mechanical stresses - Corson, F. and Henry, H. and Adda-Bedia, M.

Abstract : We present a model for mechanically-induced pattern formation in growing biological tissues and discuss its application to the development of leaf venation networks. Drawing an analogy with phase transitions in solids, we use a phase field method to describe the transition between two states of the tissue, e.g. the differentiation of leaf veins, and consider a layered system where mechanical stresses are generated by differential growth. We present analytical and numerical results for one-dimensional systems, showing that a combination of growth and irreversibility gives rise to hierarchical patterns. Two-dimensional simulations suggest that such a mechanism could account for the hierarchical, reticulate structure of leaf venation networks, yet point to the need for a more detailed treatment of the coupling between growth and mechanical stresses.
Visual memory - Ninio, Jacques
PERCEPTION 39140-141 (2010)
MAGNETIC TWEEZERS FOR THE STUDY OF DNA TRACKING MOTORS - Manosas, Maria and Meglio, Adrien and Spiering, Michelle M. and Ding, Fangyuan and Benkovic, Stephen J. and Barre, Francois-Xavier and Saleh, Omar A. and Allemand, Jean Francois and Bensimon, David and Croquette, Vincent

Abstract : Single-molecule manipulation methods have opened a new vista on the study of molecular motors. Here we describe the use of magnetic traps for the investigation of the mechanism of DNA based motors, in particular helicases and translocases.
Experimental validation of a time domain simulation of high frequency ultrasonic propagation in a suspension of rigid particles - Galaz, Belfor and Haiat, Guillaume and Berti, Romain and Taulier, Nicolas and Amman, Jean-Jacques and Urbach, Wladimir

Abstract : Ultrasonic propagation in suspensions of particles is a difficult problem due to the random spatial distribution of the particles. Two-dimensional finite-difference time domain simulations of ultrasonic propagation in suspensions of polystyrene 5.3 mu m diameter microdisks are performed at about 50 MHz. The numerical results are compared with the Faran model, considering an isolated microdisk, leading to a maximum difference of 15\% between the scattering cross-section values obtained analytically and numerically. Experiments are performed with suspensions in through transmission and backscattering modes. The attenuation coefficient at 50 MHz (alpha), the ultrasonic velocity (V), and the relative backscattered intensity (I(B)) are measured for concentrations from 2 to 25 mg/ml, obtained by modifying the number of particles. Each experimental ultrasonic parameter is compared to numerical results obtained by averaging the results derived from 15 spatial distributions of microdisks. alpha increases with the concentration from 1 to 17 dB/cm. IB increases with concentration from 2 to 16 dB. The variation of V versus concentration is compared with the numerical results, as well as with an effective medium model. A good agreement is found between experimental and numerical results (the larger discrepancy is found for alpha with a difference lower than 2.1 dB/cm ). (C) 2010 Acoustical Society of America. [DOI: 10.1121/1.3270399]
Impact dynamics of surfactant laden drops: dynamic surface tension effects - Aytouna, Mounir and Bartolo, Denis and Wegdam, Gerard and Bonn, Daniel and Rafai, Salima

Abstract : We study the impact and subsequent retraction of aqueous surfactant-laden drops upon high-speed impact on hydrophobic surfaces. Without surfactants, a rapid expansion of the drop due to the fluid inertia is followed by a rapid retraction, due to the wetting incompatibility. With surfactants, the retraction can be partly or completely inhibited. We provide quantitative measurements showing that both the expansion and the retraction dynamics depend not only on the equilibrium surface tension (ST) but also on the dynamic tension of the surfactant solutions; the latter varies significantly between different surfactants.
Modulation of the Lateral Mobility of Transmembrane Peptides with Hydrophobic Mismatch - Gambin, Yann and Reffay, Myriam and Sierecki, Emma and Homble, Francois and Genest, Marc and Hodges, Robert S. and Gov, Nir and Taulier, Nicolas and Urbach, Wladimir
Coupling DNA Unwinding Activity With Primer Synthesis in the Bacteriophage T4 Primosome - Croquette, Vincent and Manosas, Maria and Spiering, Michelle M. and Zhuang, Zhihao and Benkovic, Stephen J.
Surfactant Sponge Phase Is a Versatile, Tunable and Biologically Relevant Medium To Study Membrane Protein Interactions - Picard, Martin and Rayan, Gamal and Taulier, Nicolas and Broutin, Isabelle and Ducruix, Arnaud and Urbach, Wladimir
Transmembrane Protein Association in a Biomimetic Medium - Rayan, Gamal and Reffay, Myriam and Picard, Martin and Taulier, Nicolas and Ducruix, Arnaud and Urbach, Wladimir
Stereoscopic memory beyond stimuli persistence: the multiplicative effect of binocular intervals - Rychkova, S. I. and Rabitchev, I. E. and Ninio, J.
PERCEPTION 39161 (2010)
Fluctuations and Redundancy in Optimal Transport Networks - Corson, Francis

Abstract : The structure of networks that provide optimal transport properties has been investigated in a variety of contexts. While many different formulations of this problem have been considered, it is recurrently found that optimal networks are trees. It is shown here that this result is contingent on the assumption of a stationary flow through the network. When time variations or fluctuations are allowed for, a different class of optimal structures is found, which share the hierarchical organization of trees yet contain loops. The transitions between different network topologies as the parameters of the problem vary are examined. These results may have strong implications for the structure and formation of natural networks, as is illustrated by the example of leaf venation networks.
Acoustic Properties of Solid He-4 in the Limit of Zero Impurity - Rojas, X. and Pantalei, C. and Maris, H. J. and Balibar, S.

Abstract : We have studied the elasticity of solid He-4 in relation with its possible supersolidity. For this we have measured acoustic resonance frequencies in a 1 cm(3) cell filled either with polycrystals or with single crystals of He-4. We have observed a large stiffening at low temperature as first observed by Day and Beamish in polycrystals. The He-3 impurity content has been varied from 300 ppb to 0.4 ppb. When kept in equilibrium with liquid helium, single crystals should be impurity free. In these crystals, a large stiffening is observed, which should not be the result of the pinning of dislocations by impurities.
Buckling of Liquid Columns - Habibi, M. and Rahmani, Y. and Bonn, Daniel and Ribe, N. M.

Abstract : Under appropriate conditions, a column of viscous liquid falling onto a rigid surface undergoes a buckling instability. Here we show experimentally and theoretically that liquid buckling exhibits a hitherto unsuspected complexity involving three different modes-viscous, gravitational, and inertial-depending on how the viscous forces that resist bending of the column are balanced. We also find that the nonlinear evolution of the buckling exhibits a surprising multistability with three distinct states: steady stagnation flow, ``liquid rope coiling,'' and a new state in which the column simultaneously folds periodically and rotates about a vertical axis. The transitions among these states are subcritical, leading to a complex phase diagram in which different combinations of states coexist in different regions of the parameter space.
Destabilizing Taylor-Couette flow with suction - Gallet, Basile and Doering, Charles R. and Spiegel, Edward A.

Abstract : We consider the effect of radial fluid injection and suction on Taylor-Couette flow. Injection at the outer cylinder and suction at the inner cylinder generally result in a linearly unstable, steady, spiraling flow, even for cylindrical shears that are linearly stable in the absence of a radial flux. We study nonlinear aspects of the unstable motions with the energy stability method. Our results, though specialized, may have implications for drag reduction by suction, accretion in astrophysical disks, and perhaps even in the flow in Earth's polar vortex. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3319824]
Normal state of highly polarized Fermi gases: The bound state - Combescot, R. and Giraud, S. and Leyronas, X.
LASER PHYSICS 20678-682 (2010)

Abstract : We consider a highly polarized Fermi gas with a single a dagger'' atom within a Fermi sea of a dagger atoms. We extend a preceding many-body analysis to the case where a bound state is formed between the a dagger'' atom and an a dagger atom.