17,696 research outputs found

    Fluctuation theorem applied to the Nos\'e-Hoover thermostated Lorentz gas

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    We present numerical evidence supporting the validity of the Gallavotti-Cohen Fluctuation Theorem applied to the driven Lorentz gas with Nos\'e-Hoover thermostating. It is moreover argued that the asymptotic form of the fluctuation formula is independent of the amplitude of the driving force, in the limit where it is small.Comment: 4 pages, 3 figure

    Heat conduction and the nonequilibrium stationary states of stochastic energy exchange processes

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    I revisit the exactly solvable Kipnis--Marchioro--Presutti model of heat conduction [J. Stat. Phys. 27 65 (1982)] and describe, for one-dimensional systems of arbitrary sizes whose ends are in contact with thermal baths at different temperatures, a systematic characterization of their non-equilibrium stationary states. These arguments avoid resorting to the analysis of a dual process and yield a straightforward derivation of Fourier's law, as well as higher-order static correlations, such as the covariant matrix. The transposition of these results to families of gradient models generalizing the KMP model is established and specific cases are examined.Comment: 26 page

    Statistics of active vs. passive advections in magnetohydrodynamic turbulence

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    Active turbulent advection is considered in the context of magneto-hydrodynamics. In this case, an auxiliary passive field bears no apparent connection to the active field. The scaling properties of the two fields are different. In the framework of a shell model, we show that the two-point structure function of the passive field has a unique zero mode, characterizing the scaling of this field only. In other words, the existence of statistical invariants for the decaying passive field carries no information on the scaling properties of the active field.Comment: 4 pages, 2 figure

    Heat conductivity from molecular chaos hypothesis in locally confined billiard systems

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    We study the transport properties of a large class of locally confined Hamiltonian systems, in which neighboring particles interact through hard core elastic collisions. When these collisions become rare and the systems large, we derive a Boltzmann-like equation for the evolution of the probability densities. We solve this equation in the linear regime and compute the heat conductivity from a Green-Kubo formula. The validity of our approach is demonstated by comparing our predictions to the results of numerical simulations performed on a new class of high-dimensional defocusing chaotic billiards.Comment: 4 pages, 2 color figure

    Does the brain listen to the gut?

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    Transplanting gut bacteria from one mouse strain to another can override genetics and change behavior

    Learning From The Skills Of Others: Experimental Evidence

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    This paper reports an experimental test of how, when observing others' actions, participants learn more than just information that the others have. We use a setting where all information is public and where subjects face two kinds of information sets: (1) the information that is necessary and su±cient for them to payoff-maximize and (2) the decisions of previous players. We show that by observing the second type of information subjects learn how to improve their own decision-making process. Specifically, the accurate players make small errors no matter what information set they face whereas the inaccurate players perform much better when the decisions of others are public.

    A two-stage approach to relaxation in billiard systems of locally confined hard spheres

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    We consider the three-dimensional dynamics of systems of many interacting hard spheres, each individually confined to a dispersive environment, and show that the macroscopic limit of such systems is characterized by a coefficient of heat conduction whose value reduces to a dimensional formula in the limit of vanishingly small rate of interaction. It is argued that this limit arises from an effective loss of memory. Similarities with the diffusion of a tagged particle in binary mixtures are emphasized.Comment: Submitted to Chaos, special issue "Statistical Mechanics and Billiard-Type Dynamical Systems

    Fractality of the non-equilibrium stationary states of open volume-preserving systems: II. Galton boards

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    Galton boards are models of deterministic diffusion in a uniform external field, akin to driven periodic Lorentz gases, here considered in the absence of dissipation mechanism. Assuming a cylindrical geometry with axis along the direction of the external field, the two-dimensional board becomes a model for one-dimensional mass transport along the direction of the external field. This is a purely diffusive process which admits fractal non-equilibrium stationary states under flux boundary conditions. Analytical results are obtained for the statistics of multi-baker maps modeling such a non-uniform diffusion process. A correspondence is established between the local phase-space statistics and their macroscopic counter-parts. The fractality of the invariant state is shown to be responsible for the positiveness of the entropy production rate.Comment: Second of two papers, 17 double column pages, 10 figure
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