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Sens P.,CNRS Gulliver Laboratory | Turner M.S.,University of Warwick
Physical Review Letters | Year: 2011

Compositional heterogeneities of cell membranes are thought to play an important role in many physiological processes. We study how variations in the membrane composition can be driven by nonthermal fluctuating forces and therefore show how these can occur relatively far from any critical point for the membrane. We show that the membrane steady state is not only controlled by the strength of the forces and how they couple to the membrane, but also by their dynamics: In a simple class of models this is captured by a single force correlation time. We conclude that the coupling of membrane composition to normal mechanical forces, such as might be exerted by polymerizing cytoskeleton filaments, could play an important role in controlling the steady state of a cell membrane that exhibits transient lateral modulations of its composition on length scales in the 10-100 nm regime. © 2011 American Physical Society.

Decelle A.,University Paris - Sud | Krzakala F.,CNRS Gulliver Laboratory | Moore C.,Santa Fe Institute | Zdeborova L.,CEA Saclay Nuclear Research Center
Physical Review Letters | Year: 2011

We present an asymptotically exact analysis of the problem of detecting communities in sparse random networks generated by stochastic block models. Using the cavity method of statistical physics and its relationship to belief propagation, we unveil a phase transition from a regime where we can infer the correct group assignments of the nodes to one where these groups are undetectable. Our approach yields an optimal inference algorithm for detecting modules, including both assortative and disassortative functional modules, assessing their significance, and learning the parameters of the underlying block model. Our algorithm is scalable and applicable to real-world networks, as long as they are well described by the block model. © 2011 American Physical Society.

Bocquet L.,University Claude Bernard Lyon 1 | Bocquet L.,Massachusetts Institute of Technology | Tabeling P.,CNRS Gulliver Laboratory
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2014

From a physical perspective, nanofluidics represents an extremely rich domain. It hosts many mechanisms acting on the nanoscale, which combine together or interact with the confinement to generate new phenomena. Superfast flows in carbon nanotubes, nonlinear electrokinetic transport, slippage over smooth surfaces, nanobubble stability, etc. are the most striking phenomena that have been unveiled over the past few years, and some of them are still awaiting an explanation. One may anticipate that new nanofluidic effects will be discovered in the future, but at the moment, the technological barrier is high. Fabrication of nanochannels is most often a tour de force, slow and costly. However, with the accumulation of technological skills along with the use of new nanofluidic materials (like nanotubes), nanofluidics is becoming increasingly accessible to experimentalists. Among the technological challenges faced by the field, fabricating devices mimicking natural nanometric systems, such as aquaporins, ionic pumps or kidney osmotic filtering, seems the most demanding in terms of groundbreaking ideas. Nanoflow characterization remains delicate, although considerable progress has been achieved over the past years. The targeted application of nanofluidics is not only in the field of genomics and membrane science-with disruptive developments to be expected for water purification, desalination, and energy harvesting-but also for oil and gas production from unconventional reservoirs. Today, in view of the markets that are targeted, nanofluidics may well impact the industry more than microfluidics; this would represent an unexpected paradox. These successes rely on using a variety of materials and technologies, using state-of-the-art nanofabrication, or low-tech inexpensive approaches. As a whole, nanofluidics is a fascinating field that is facing considerable challenges today. It possesses a formidable potential and offers much space for creative groundbreaking ideas. © 2014 the Partner Organisations.

Ziebert F.,CNRS Gulliver Laboratory | Lacoste D.,CNRS Gulliver Laboratory
New Journal of Physics | Year: 2010

The behavior of a non-conductive quasi-planar lipid membrane in an electrolyte and in a static (dc) electric field is investigated theoretically in the nonlinear (Poisson-Boltzmann) regime. Electrostatic effects due to charges in the membrane lipids and in the double layers lead to corrections to the membrane elastic moduli, which are analyzed here. We show that, especially in the low salt limit, (i) the electrostatic contribution to the membrane's surface tension due to the Debye layers crosses over from a quadratic behavior in the externally applied voltage to a linear voltage regime, and (ii) the contribution to the membrane's bending modulus due to the Debye layers saturates for high voltages. Nevertheless, the membrane undulation instability due to an effectively negative surface tension predicted by the linear Debye-Hückel theory is shown to persist in the nonlinear, high-voltage regime. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Golestanian R.,University of Sheffield | Golestanian R.,CNRS Gulliver Laboratory
Physical Review Letters | Year: 2010

A minimal design for a molecular swimmer is proposed that is based on a mechanochemical propulsion mechanism. Conformational changes are induced by electrostatic actuation when specific parts of the molecule temporarily acquire net charges through catalyzed chemical reactions involving ionic components. The mechanochemical cycle is designed such that the resulting conformational changes would be sufficient for achieving low Reynolds number propulsion. The system is analyzed within the recently developed framework of stochastic swimmers to take account of the noisy environment at the molecular scale. The swimming velocity of the device is found to depend on the concentration of the fuel molecule according to the Michaelis-Menten rule in enzymatic reactions. © 2010 The American Physical Society.

Lacoste D.,CNRS Gulliver Laboratory | Gaspard P.,Free University of Colombia
Physical Review Letters | Year: 2014

We derive a set of isometric fluctuation relations, which constrain the order parameter fluctuations in finite-size systems at equilibrium and in the presence of a broken symmetry. These relations are exact and should apply generally to many condensed-matter physics systems. Here, we establish these relations for magnetic systems and nematic liquid crystals in a symmetry-breaking external field, and we illustrate them on the Curie-Weiss and the XY models. Our relations also have implications for spontaneous symmetry breaking, which are discussed. © 2014 American Physical Society.

Phillips R.,California Institute of Technology | Phillips R.,CNRS Gulliver Laboratory
Annual Review of Condensed Matter Physics | Year: 2015

It has been said that the cell is the test tube of the twenty-first century. If so, the theoretical tools needed to quantitatively and predictively describe what goes on in such test tubes lag sorely behind the stunning experimental advances in biology seen in the decades since the molecular biology revolution began. Perhaps surprisingly, one of the theoretical tools that has been used with great success on problems ranging from how cells communicate with their environment and each other to the nature of the organization of proteins and lipids within the cell membrane is statistical mechanics. A knee-jerk reaction to the use of statistical mechanics in the description of cellular processes is that living organisms are so far from equilibrium that one has no business even thinking about it. But such reactions are probably too hasty given that there are many regimes in which, because of a separation of timescales, for example, such an approach can be a useful first step. In this article, we explore the power of statistical mechanical thinking in the biological setting, with special emphasis on cell signaling and regulation. We show how such models are used to make predictions and describe some recent experiments designed to test them. We also consider the limits of such models based on the relative timescales of the processes of interest. © 2015 by Annual Reviews.

Verley G.,CNRS Gulliver Laboratory | Chetrite R.,French National Center for Scientific Research | Lacoste D.,CNRS Gulliver Laboratory
Physical Review Letters | Year: 2012

We discuss the consequences of a variant of the Hatano-Sasa relation in which a nonstationary distribution is used in place of the usual stationary one. We first show that this nonstationary distribution is related to a difference of traffic between the direct and dual dynamics. With this formalism, we extend the definition of the adiabatic and nonadiabatic entropies introduced by M. Esposito and C. Van den Broeck in Phys. Rev. Lett. 104, 090601 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.090601 for the stationary case. We also obtain interesting second-law-like inequalities for transitions between nonstationary states. © 2012 American Physical Society.

Schindler M.,CNRS Gulliver Laboratory
Chemical Physics | Year: 2010

The correlations of the fluctuating stress tensor are calculated in an equilibrium molecular dynamics simulation of a Lennard-Jones liquid. We define a coarse-grained local stress tensor which can be calculated numerically and which allows for the first time to determine the stress correlation function both in time and in space. Our findings corroborate the assumptions made in fluctuating hydrodynamics as long as the liquid is isotropic, that is in bulk. In the vicinity of a rigid plate, however, the isotropy is restricted, and major modifications must be done with respect to the usual theory. Among these are the appearance of five different viscosities instead of two and a non-trivial dependence of the distance from the wall. We determine these viscosities from the simulation data and find that their values are very different from the bulk values. We further find much longer relaxation times of the stress correlations than in bulk. © 2010 Elsevier B.V. All rights reserved.

Bapst V.,French National Center for Scientific Research | Foini L.,University Pierre and Marie Curie | Krzakala F.,CNRS Gulliver Laboratory | Semerjian G.,French National Center for Scientific Research | Zamponi F.,French National Center for Scientific Research
Physics Reports | Year: 2013

Among various algorithms designed to exploit the specific properties of quantum computers with respect to classical ones, the quantum adiabatic algorithm is a versatile proposition to find the minimal value of an arbitrary cost function (ground state energy). Random optimization problems provide a natural testbed to compare its efficiency with that of classical algorithms. These problems correspond to mean field spin glasses that have been extensively studied in the classical case. This paper reviews recent analytical works that extended these studies to incorporate the effect of quantum fluctuations, and presents also some original results in this direction. © 2012 Elsevier B.V.

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