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Search Results: 1 - 10 of 4199 matches for " Christophe Josserand "
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Stability of giant vortices in quantum liquids
Christophe Josserand
Physics , 2004, DOI: 10.1063/1.1785892
Abstract: We show how giant vortices can be stabilized in strong external potential Bose-Einstein condensates. We illustrate the formation of these vortices thanks to the relaxation Ginzburg-Landau dynamics for two typical potentials in two spatial dimensions. The giant vortex stability is studied for the particular case of the rotating cylindrical hard wall. The minimization of the perturbed energy is simplified into a one dimensional relaxation dynamics. The giant vortices can be stabilized only in a finite frequency range. Finally we obtain a curve for the minimum frequency needed to observe a giant vortex for a given nonlinearity.
Cavitation induced by explosion in a model of ideal fluid
Christophe Josserand
Physics , 1998, DOI: 10.1103/PhysRevE.60.482
Abstract: We discuss the problem of an explosion in the cubic-quintic superfluid model, in relation to some experimental observations. We show numerically that an explosion in such a model might induce a cavitation bubble for large enough energy. This gives a consistent view for rebound bubbles in superfluid and we indentify the loss of energy between the successive rebounds as radiated waves. We compute self-similar solution of the explosion for the early stage, when no bubbles have been nucleated. The solution also gives the wave number of the excitations emitted through the shock wave.
Wave turbulence and Bose-Einstein condensates
Christophe Josserand
Physics , 2004, DOI: 10.1016/j.crhy.2004.01.004
Abstract: Asymptotic behavior of a class of nonlinear Schr\"odinger equations are studied. Particular cases of 1D weakly focusing and Bose-Einstein condensates are considered. A statistical approach is presented to describe the stationary probability density of a discretized finite system. Using a maximum entropy argument, the theory predicts that the statistical equilibrium is described by energy equivalued fluctuation modes around the coherent structure minimizing the Hamiltonian of the system. Good quantitative agreement is found with numerical simulations. In particular, the particle number spectral density follows an effective $1/k^2$ law for the asymptotic large time averaged solutions. Transient dynamics from a given initial condition to the statistically steady regime shows rapid oscillation of the condensate.
Curvature singularity and film-skating during drop impact
Laurent Duchemin,Christophe Josserand
Physics , 2010, DOI: 10.1063/1.3640028
Abstract: We study the influence of the surrounding gas in the dynamics of drop impact on a smooth surface. We use an axisymmetric 3D model for which both the gas and the liquid are incompressible; lubrication regime applies for the gas film dynamics and the liquid viscosity is neglected. In the absence of surface tension a finite time singularity whose properties are analysed is formed and the liquid touches the solid on a circle. When surface tension is taken into account, a thin jet emerges from the zone of impact, skating above a thin gas layer. The thickness of the air film underneath this jet is always smaller than the mean free path in the gas suggesting that the liquid film eventually wets the surface. We finally suggest an aerodynamical instability mechanism for the splash.
Vortices in condensate mixtures
Christophe Josserand,Yves Pomeau
Physics , 2004, DOI: 10.1103/PhysRevA.72.023618
Abstract: In a condensate made of two different atomic molecular species, Onsager's quantization condition implies that around a vortex the velocity field cannot be the same for the two species. We explore some simple consequences of this observation. Thus if the two condensates are in slow relative translation one over the other, the composite vortices are carried at a velocity that is a fraction of the single species velocity. This property is valid for attractive interaction and below a critical velocity which corresponds to a saddle-node bifurcation.
Self-organization in nonlinear wave turbulence
Richard Jordan,Christophe Josserand
Physics , 1999, DOI: 10.1103/PhysRevE.61.1527
Abstract: We present a statistical equilibrium model of self-organization in a class of focusing, nonintegrable nonlinear Schrodinger (NLS) equations. The theory predicts that the asymptotic-time behavior of the NLS system is characterized by the formation and persistence ofa large-scale coherent solitary wave, which minimizes the Hamiltonian given the conserved particle number,coupled with small-scale random fluctuations, or radiation. The fluctuations account for the difference between the conserved value of the Hamiltonian and the Hamiltonian of the coherent state. The predictions of the statistical theory are tested against the results of direct numerical simulations of NLS, and excellent qualitative and quantitative agreement is demonstrated. In addition, a careful inspection of the numerical simulations reveals interesting features of the transitory dynamics leading up to the to the long-time statistical equilibrium state starting from a given initial condition. As time increases, the system investigates smaller and smaller scales, and it appears that at a given intermediate time after the coalescense of the soliton structures has ended, the system is nearly in statistical equilibrium over the modes that it has investigated up to that time.
Elastic wave-turbulence and intermittency
Sergio Chibbaro,Christophe Josserand
Physics , 2015,
Abstract: Weak Wave Turbulence is a powerful theory to predict statistical observables of diverse relevant physical phenomena, such as ocean waves, magnetohydrodynamics and nonlinear optics. The theory is based upon an asymptotic closure permitted in the limit of small nonlinearity. Here, we explore the possible deviations from this mean-field framework, in terms of anomalous scaling, focusing on the case of elastic plates. We establish the picture of the possible behaviors at varying the extent of nonlinearity, and we show that the mean-field theory is appropriate when all excited scales remain dominated by linear dynamics. The other picture is non-trivial and our results suggest that, when large scales contain much energy, the cascade sustains extreme events at small scales and the system displays intermittency.
Rarefied gas correction for the bubble entrapment singularity in drop impacts
Laurent Duchemin,Christophe Josserand
Physics , 2012, DOI: 10.1016/j.crme.2012.10.028
Abstract: We study the non-continuous correction in the dynamics of drop impact on a solid substrate. Close to impact, a thin film of gas is formed beneath the drop so that the local Knudsen number is of order one. We consider the first correction to the dynamics which consists of allowing slip of the gas along the substrate and the interface. We focus on the singular dynamics of entrapment that can be seen when surface tension and liquid viscosity can be neglected. There we show that different dynamical regimes are present that tend to lower the singularity strength. We finally suggest how these effects might be connected to the influence of the gas pressure in the impact dynamics observed in recent experiments.
Coexisting ordinary elasticity and superfluidity in a model of defect-free supersolid
Christophe Josserand,Yves Pomeau,Sergio Rica
Physics , 2006, DOI: 10.1103/PhysRevLett.98.195301
Abstract: We present the mechanics of a model of supersolid in the frame of the Gross-Pitaevskii equation at $T=0K$ that do not require defects nor vacancies. A set of coupled nonlinear partial differential equations plus boundary conditions is derived. The mechanical equilibrium is studied under external constrains as steady rotation or external stress. Our model displays a paradoxical behavior: the existence of a non classical rotational inertia fraction in the limit of small rotation speed and no superflow under small (but finite) stress nor external force. The only matter flow for finite stress is due to plasticity.
Can we hear Kolmogorov spectra?
Gustavo During,Christophe Josserand,Sergio Rica
Physics , 2005,
Abstract: We study the long-time evolution of waves of a thin elastic plate in the limit of small deformation so that modes of oscillations interact weakly. According to the theory of weak turbulence a nonlinear wave system evolves in long-time creating a slow transfer of energy from one mode to another. We derive this kinetic equation for the spectral transfer in terms of the second order moment. We show explicitly that such a non-equilibrium theory describes the approach to an equilibrium wave spectrum, and describes also an energy cascade, often called the Kolmogorov-Zakharov spectrum. We perform numerical simulations confirming this scenario.
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