Biomedical subjects

Katsuya Ouchi

Publications and source records attributed to Katsuya Ouchi.

3 recordsLinked to original sources

PubMed2006

Critical dynamics of phase transition driven by dichotomous Markov noise.

An Ising spin system under the critical temperature driven by a dichotomous Markov noise (magnetic field) with a finite correlation time is studied both numerically and theoretically. The order parameter exhibits a transition between two kinds of qualitatively different dynamics, symmetry-restoring and symmetry-breaking motions, as the noise intensity is changed. There exist regions called channels where the order parameter stays for a long time slightly above its critical noise intensity. Developing a phenomenological analysis of the dynamics, we investigate the distribution of the passage time through the channels and the power spectrum of the order parameter evolution. The results based on the phenomenological analysis turn out to be in quite good agreement with those of the numerical simulation.

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PubMed2004

Domain dynamics in the anisotropic Swift-Hohenberg equation.

Two types of asymptotic ordering processes in the anisotropic Swift-Hohenberg equation are studied, paying particular attention to the interaction between domain walls. For the first type, we will discuss the time evolution in which the spatially oscillatory patterns are formed, and show that two kinds of patterns exist depending on whether or not the imaginary part of the field vanishes. When the imaginary part is present, the equation has two distinct states which are regarded as kinds of domains, so the dynamics between two domain walls is established. We then discuss, for the second type, the dynamics when nontrivial uniform states are constructed. There exist two different domain walls, the Ne el type wall and the Bloch type wall, in a similar way to the anisotropic Ginzburg-Landau equation. The equation of motion for two domain walls is derived, and it is shown that the distance between the two domain walls eventually approaches a finite length. The theoretical result is confirmed by numerical simulations. This fact proves the validity of the prediction on the temporal development of the distance between two domain walls.

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PubMed2003

Pattern dynamics associated with on-off convection in a one-dimensional system.

A numerical and theoretical analysis of the phenomenologically constructed nonlinear stochastic model of on-off intermittency experimentally observed by John et al. in the electrohydrodynamic convection in nematic liquid crystal under applied dichotomous electric field is carried out. The model has the structure of the one-dimensional Swift-Hohenberg equation with a fluctuating threshold which represents an applied electric field and either with or without additive noise which corresponds to thermal noise. It is found that the fundamental statistics of pattern dynamics without additive noise agree with those experimentally observed, and also with those reported previously in two-dimensional system. In contrast to that the presence of multiplicative noise generates an intermittent evolution of pattern intensity, whose statistics are in agreement with those of on-off intermittency so far known, the additive noise gives rise to the change of position of the convective pattern. It is found that the temporal evolution of the phase suitably introduced to describe the global convective pattern also shows an intermittent evolution. Its statistics are studied in a detailed way with numerical simulation and stochastic analysis. The comparison of these results turn out to be in good agreement with each other.

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