Biomedical subjects

Kumiko Hayashi

Publications and source records attributed to Kumiko Hayashi.

5 recordsLinked to original sources

PubMed2005

Fluctuation-dissipation relations outside the linear response regime in a two-dimensional driven lattice gas along the direction transverse to the driving force.

We performed numerical experiments on a two-dimensional driven lattice gas, which constitutes a simple stochastic nonequilibrium many-body model. In this model, focusing on the behavior along the direction transverse to the external driving force, we numerically measure transport coefficients and dynamical fluctuations outside the linear response regime far from equilibrium. Using these quantities, we find the validity of the Einstein relation, the Green-Kubo relation and the fluctuation-response relation.

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PubMed2005

Extended Einstein relations with a complex effective temperature in a one-dimensional driven lattice gas.

We carry out numerical experiments on a one-dimensional driven lattice gas to elucidate the statistical properties of steady states far from equilibrium. By measuring the bulk density diffusion constant D, the conductivity sigma, and the intensity of density fluctuations, chi, we confirm that the Einstein relation Dchi=sigmaT, which is valid in the linear response regime about equilibrium, does not hold in such steady states. Here, T is the environment temperature and the Boltzmann constant is set to unity. Recalling that the Einstein relation provided the first step in the construction of linear response theory, we attempt to extend it to a generalized form valid in steady states far from equilibrium. In order to obtain new relations among measurable quantities, we define a complex effective temperature theta-iphi from studying the static response of the system to a slowly varying potential in space. Replacing T in the Einstein relation by the real part of the effective temperature Theta , we numerically confirm that the relation Dchi=sigmatheta holds in the nonequilibrium steady states far from equilibrium that we study. In addition to this extended form, we find the relation (L/2pi)cchi=sigmaphi , where c represents the propagation velocity of density fluctuations.

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PubMed2005

Decomposition of force fluctuations far from equilibrium.

By studying a nonequilibrium Langevin system, we find that a simple condition determines the decomposition of the coarse-grained force into a dissipative force, an effective driving force and noise. From this condition, we derive a universal inequality, D > or = gamma mu2(d)T , relating the diffusion constant D , the differential mobility mu(d) , the bare friction constant gamma and the temperature T . Due to the general nature of the argument we present, we believe that our idea concerning this decomposition can be applied to a wide class of systems far from equilibrium.

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PubMed2004

Effective temperature in nonequilibrium steady states of Langevin systems with a tilted periodic potential.

We theoretically study Langevin systems with a tilted periodic potential. It is known that the ratio Theta of the diffusion constant D to the differential mobility mu(d) is not equal to the temperature of the environment (multiplied by the Boltzmann constant), except in the linear response regime, where the fluctuation dissipation theorem holds. In order to elucidate the physical meaning of Theta far from equilibrium, we analyze a modulated system with a slowly varying potential. We derive a large scale description of the probability density for the modulated system by use of a perturbation method. The expressions we obtain show that Theta plays the role of the temperature in the large scale description of the system and that Theta can be determined directly in experiments, without measurements of the diffusion constant and the differential mobility. Hence the relation D= mu(d) Theta among the independent measurable quantities D, mu(d), and Theta can be interpreted as an extension of the Einstein relation.

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PubMed2003

Thermodynamic relations in a driven lattice gas: numerical experiments.

We explore thermodynamic relations in nonequilibrium steady states with numerical experiments on a driven lattice gas. After operationally defining the pressure and chemical potential in the driven lattice gas, we confirm numerically the validity of the integrability condition (the Maxwell relation) for the two quantities whose values differ from those for an equilibrium system. This implies that a free-energy function can be constructed for the nonequilibrium steady state that we consider. We also investigate a fluctuation relation associated with this free-energy function. Our result suggests that the compressibility can be expressed in terms of density fluctuations even in nonequilibrium steady states.

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