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N Fuchikami

Publications and source records attributed to N Fuchikami.

4 recordsLinked to original sources
PubMed1999

Randomly amplified discrete Langevin systems.

A discrete stochastic process involving random amplification with additive noise is studied analytically. If the non-negative random amplification factor b is such that =1, where beta is any positive noninteger, then the steady state probability density function for the process will have power law tails of the form p(x) approximately 1/x(beta+1). This is a generalization of recent results for 0<beta<2 obtained by Takayasu, Sato, and Takayasu [Phys. Rev. Lett. 79, 966 (1997)]. It is shown that the power spectrum of the time series x becomes Lorentzian, even when 1<beta<2, i.e., in the case of divergent variance.

Journal Article↗
PubMed1993

Model of chemically excitable membranes generating autonomous chaotic oscillations.

A simple mathematical model of the chemically excitable membranes leading to autonomous chaotic oscillations is presented. The model assumes two kinds of autocatalytic ion channels, one is for cations and the other is for anions. Self-consistency between the ion distributions and the electric potentials is taken into account by including the counter ions explicitly. Cations and anions pass through their own channels with their permeabilities changing nonlinearly with the densities of ions at the surfaces of the membrane. Cation and anion transport systems then form two subsystems that oscillate and interact with each other through the membrane potential. When the coupling strength between the two ion systems and adsorption rate of ions to channels are varied, various types of chaotic oscillations are generated autonomously, i.e., without a stimulating periodic force. Experimental evidence to the present model is discussed. It is suggested that endogenous chaos in biological systems may appear from the electric coupling among different kinds of ion transport systems.

Catalysis↗
PubMed1991

Model for the dynamic responses of taste receptor cells to salty stimuli. I. Function of lipid bilayer membranes.

The dynamic response of the lipid bilayer membrane is studied theoretically using a microscopic model of the membrane. The time courses of membrane potential variations due to monovalent salt stimulation are calculated explicitly under various conditions. A set of equations describing the time evolution of membrane surface potential and diffusion potential is derived and solved numerically. It is shown that a rather simple membrane such as lipid bilayer has functions capable of reproducing the following properties of dynamic response observed in gustatory receptor potential. Initial transient depolarization does not occur under Ringer adaptation but does under water. It appears only for comparatively rapid flows of stimuli, the peak height of transient response is expressed by a power function of the flow rate, and the membrane potential gradually decreases after reaching its peak under long and strong stimulation. The dynamic responses in the present model arise from the differences between the time dependences in the surface potential phi s and the diffusion potential phi d across a membrane. Under salt stimulation phi d cannot immediately follow the variation in phi s because of the delay due to the charging up of membrane capacitance. It is suggested that lipid bilayer in the apical membrane is the most probable agency producing the initial phasic response to the stimulation.

Animals↗