Biomedical subjects

Toyonori Munakata

Publications and source records attributed to Toyonori Munakata.

7 recordsLinked to original sources

PubMed2006

Ergodic-nonergodic transition in a threshold system with feedback.

A threshold system with feedback is studied from the viewpoint of an ergodic-nonergodic transition, a kind of nonequilibrium phase transition, as the rate of input signal variation is changed. By discussing the time evolution of the distribution function, instead of its lowest moment (an order parameter), we can determine the transition point and make clear the role and limitation of the self-consistent equation for the order parameter. Finally the feedback strength is related to an activation energy from a statistical mechanical viewpoint.

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PubMed2005

Relaxation to equilibrium in few-particle adiabatic piston systems.

A Hamiltonian system with few particles and a heavy adiabatic piston is studied. With ensemble averages based on proper classification of slow and fast variables, a nonequilibrium state is defined and the relaxation from nonequilibrium to equilibrium is investigated. Coherent oscillation, dissipative oscillation damping, and anti-intuition energy transfer of the adiabatic piston are observed by numerical simulations. Noise-driven thermodynamic equations of slow variables are derived, based on the assumption of local equilibrium and the fluctuation-dissipation theorem, to understand and quantitatively reproduce all the above few-body nonequilibrium relaxation features.

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PubMed2004

Signal estimation and threshold optimization using an array of bithreshold elements.

We consider the problem of optimizing signal transmission through multichannel noisy devices. We investigate an array of bithreshold noisy devices which is connected in parallel and convergent on a summing center. Utilizing the concept of noise-induced linearization we derive an analytical approximation of the normalized power norm and clarify the relation between the optimum threshold and the standard deviation of noises. We show that the optimum threshold value is 0.63 times the standard deviation of the noises. This relation is applicable to both subthreshold and suprathreshold inputs.

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PubMed2003

Rectification efficiency of a Brownian motor.

The energy balance of a Brownian motor is discussed based on a Langevin equation without the overdamped approximation. Energetics of the system suggests that the frictional dissipation energy associated with the unidirectional movement should be counted as a part of the useful energy for the rectification process of a Brownian motor. This leads to a new definition of the efficiency, which is applicable, contrary to the conventional one, even if the external load is absent. For the so-called flashing ratchet model, we numerically solve the Langevin equation for various situations and discuss both the temperature and the friction strength dependence of the rectification efficiency and the role of the duty ratio.

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PubMed2003

Glass transition of hard sphere systems: molecular dynamics and density functional theory.

The glass transition of a hard sphere system is investigated within the framework of the density functional theory (DFT). Molecular dynamics (MD) simulations are performed to study the dynamical behavior of the system on the one hand and to provide the data to produce the density field for the DFT on the other hand. Energy landscape analysis based on the DFT shows that there appears a metastable (local) free energy minimum representing an amorphous state as the density is increased. This state turns out to become stable, compared with the uniform liquid, at some density around which we also observe a sharp slowing down of the alpha relaxation in the MD simulations.

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PubMed2003

Markovian approximation and dynamic density functional theory for classical dense liquids.

A kinetic description of dense liquids is one of the-long-standing problems in statistical mechanics. We apply here a well-known Markovian approximation to the Mori-Fujisaka nonlinear generalized Langevin equation. This enables us to derive systematically and without further approximations the Smoluchowski equation for an interacting many-body system and the dynamic density functional theory (DDFT), which are playing important roles for the glass transition and dynamics in supercooled liquids. The free energy functional in our DDFT may be termed microcanonical as compared with the grand-canonical one widely used in the equilibrium theory of liquids.

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PubMed2002

Statistical mechanics of two hard disks in a rectangular box.

A system of two hard disks in a rectangular box is studied based on the exact partition function and equilibrium distribution functions of particles. Box-size dependence of some quantities of interest, such as pressure and the particle distribution functions, is investigated and in particular the negative compressibility of the van der Waals type and the corresponding phase transition are analyzed in detail. This system turns out to have rich structures that are related to the ergode-nonergode transitions in this system.

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