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Essafi K.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Kownacki J.-P.,Cergy-Pontoise University | Mouhanna D.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review Letters | Year: 2011

Anisotropic D-dimensional polymerized phantom membranes are investigated within a nonperturbative renormalization group framework. One focuses on the transition between a high-temperature, crumpled phase and a low-temperature, tubular phase where the membrane is flat along one direction and crumpled along the other ones. While the upper critical dimension-Duc=5/2-is close to D=2, the weak-coupling perturbative approach is qualitatively and quantitatively wrong. We show that our approach is free of the problems encountered within the perturbative framework and provides physically meaningful critical quantities. © 2011 American Physical Society.


Momoi T.,RIKEN | Sindzingre P.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Kubo K.,Aoyama Gakuin University
Physical Review Letters | Year: 2012

We figure out that the ground state of a multiple-spin exchange model applicable to thin films of solid He3 possesses an octahedral spin nematic order. In the presence of a magnetic field, it is deformed into an antiferroquadrupolar order in the perpendicular spin plane, in which lattice Z 3 rotational symmetry is also broken. Furthermore, this system shows a narrow magnetization plateau at half, m/m sat=1/2, which resembles recent magnetization measurements. © 2012 American Physical Society.


Bianca C.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Dogbe C.,University of Caen Lower Normandy
Nonlinearity | Year: 2014

This paper deals with the modelling of complex systems composed of a large number of elements grouped into different functional subsystems. The modelling framework is that of the thermostatted kinetic theory, which consists of a set of nonlinear integro-differential equations. Another source of nonlinearity is the presence of a mathematical thermostat that ensures the control of the global energy of the system. Specifically, this paper is devoted to the derivation of evolution equations for the macroscopic variables (density and momentum) from the underlying description at the microscopic scale delivered by the thermostatted kinetic models. With this as the aim, hyperbolic-type and parabolic-type scalings of the thermostatted kinetics for the active particles model are performed and the resulting macroscopic equations are obtained. Finally, asymptotic methods are applied to the relaxation model. © 2014 IOP Publishing Ltd & London Mathematical Society.


Cammarota C.,CEA Saclay Nuclear Research Center | Biroli G.,CEA Saclay Nuclear Research Center | Tarzia M.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Tarjus G.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review Letters | Year: 2011

We consider the approach describing glass formation in liquids as a progressive trapping in an exponentially large number of metastable states. To go beyond the mean-field setting, we provide a real-space renormalization group (RG) analysis of the associated replica free-energy functional. The present approximation yields in finite dimensions an ideal glass transition similar to that found in the mean field. However, we find that along the RG flow the properties associated with metastable glassy states, such as the configurational entropy, are only defined up to a characteristic length scale that diverges as one approaches the ideal glass transition. The critical exponents characterizing the vicinity of the transition are the usual ones associated with a first-order discontinuity fixed point. © 2011 American Physical Society.


Chupeau M.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Benichou O.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Voituriez R.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Voituriez R.,CNRS Jean Perrin Laboratory
Nature Physics | Year: 2015

How long must one undertake a random search to visit all sites of a given domain? This time, known as the cover time, is a key observable to quantify the efficiency of exhaustive searches, which require a complete exploration of an area and not only the discovery of a single target. Examples range from immune-system cells chasing pathogens to animals harvesting resources, from robotic exploration for cleaning or demining to the task of improving search algorithms. Despite its broad relevance, the cover time has remained elusive and so far explicit results have been scarce and mostly limited to regular random walks. Here we determine the full distribution of the cover time for a broad range of random search processes, including Lévy strategies, intermittent strategies, persistent random walks and random walks on complex networks, and reveal its universal features. We show that for all these examples the mean cover time can be minimized, and that the corresponding optimal strategies also minimize the mean search time for a single target, unambiguously pointing towards their robustness. © 2015 Macmillan Publishers Limited. All rights reserved.


Talbot J.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Wildman R.D.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Wildman R.D.,Loughborough University | Viot P.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review Letters | Year: 2011

Within the framework of a Boltzmann-Lorentz equation, we analyze the dynamics of a granular rotor immersed in a bath of thermalized particles in the presence of a frictional torque on the axis. In numerical simulations of the equation, we observe two scaling regimes at low and high bath temperatures. In the large friction limit, we obtain the exact solution of a model corresponding to asymptotic behavior of the Boltzmann-Lorentz equation. In the limit of large rotor mass and small friction, we derive a Fokker-Planck equation for which the exact solution is also obtained. © 2011 American Physical Society.


Leonard F.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Delamotte B.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review Letters | Year: 2015

We present models where γ+ and γ-, the exponents of the susceptibility in the high- and low-temperature phases, are generically different. In these models, continuous symmetries are explicitly broken down by discrete anisotropies that are irrelevant in the renormalization-group sense. The Zq-invariant models are the simplest examples for two-component order parameters (N=2) and the model with icosahedral symmetry for N=3. We accurately compute γ+-γ- as well as the ratio ν/ν′ of the exponents of the two correlation lengths present for T


Benichou O.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Loverdo C.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Moreau M.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Voituriez R.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Reviews of Modern Physics | Year: 2011

This review examines intermittent target search strategies, which combine phases of slow motion, allowing the searcher to detect the target, and phases of fast motion during which targets cannot be detected. It is first shown that intermittent search strategies are actually widely observed at various scales. At the macroscopic scale, this is, for example, the case of animals looking for food; at the microscopic scale, intermittent transport patterns are involved in a reaction pathway of DNA-binding proteins as well as in intracellular transport. Second, generic stochastic models are introduced, which show that intermittent strategies are efficient strategies that enable the minimization of search time. This suggests that the intrinsic efficiency of intermittent search strategies could justify their frequent observation in nature. Last, beyond these modeling aspects, it is proposed that intermittent strategies could also be used in a broader context to design and accelerate search processes. © 2011 American Physical Society.


Perera A.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Molecular Physics | Year: 2011

The radial distribution function of liquid water, as obtained by the computer simulations of several classical models of water, is re-examined herein and shown to display two intriguing features. These consist of a compact three-peaks structure over three molecular diameters, which is followed by an apparent loss of the packing correlations beyond R c ≈ Å. This is in contrast to simple liquids for which the correlationsdecay continuously with distance. This structure is reproduced for many widely used classical force field models of water and by scattering experiments as well. It is also preserved in aqueous binary mixtures of organic solvents, even up to equimolar mixture in some cases. The analysis of the structure factor highlights the role played by the competition between the packing effect and the hydrogen bonding interactions. This analysis, in terms of competition of two length scales, is also supported by a simple core-soft model, which reproduces the structural features outlined above. © 2011 Copyright Taylor and Francis Group, LLC.


Charbonneau P.,Duke University | Tarjus G.,CNRS Laboratory of Theoretical Physics and Condensed Matter
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

We show that, in the equilibrium phase of glass-forming hard-sphere fluids in three dimensions, the static length scales tentatively associated with the dynamical slowdown and the dynamical length characterizing spatial heterogeneities in the dynamics unambiguously decorrelate. The former grow at a much slower rate than the latter when density increases. This observation is valid for the dynamical range that is accessible to computer simulations, which roughly corresponds to that accessible in colloidal experiments. We also find that, in this same range, no one-to-one correspondence between relaxation time and point-to-set correlation length exists. These results point to the coexistence of several relaxation mechanisms in the dynamically accessible regime of three-dimensional hard-sphere glass formers. © 2013 American Physical Society.

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