Biomedical subjects

K S Ikeda

Publications and source records attributed to K S Ikeda.

3 recordsLinked to original sources

PubMed2003

Semiclassical study on tunneling processes via complex-domain chaos.

We investigate the semiclassical mechanism of tunneling processes in nonintegrable systems. The significant role of complex-phase-space chaos in the description of the tunneling processes is elucidated by studying a kicked scattering model. Behaviors of tunneling orbits are encoded into symbolic sequences based on the structure of a complex homoclinic tangle. By means of the symbolic coding, the phase space itineraries of tunneling orbits are related with the amounts of imaginary parts of actions gained by the orbits, so that the systematic search of dominant tunneling orbits becomes possible.

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PubMed2001

Tunneling mechanism due to chaos in a complex phase space.

We have revealed that the barrier-tunneling process in nonintegrable systems is strongly linked to chaos in complex phase space by investigating a simple scattering map model. The semiclassical wave function reproduces complicated features of tunneling perfectly and it enables us to solve all the reasons why those features appear in spite of absence of chaos on the real plane. Multigeneration structure of manifolds, which is the manifestation of complex-domain homoclinic entanglement created by complexified classical dynamics, allows a symbolic coding and it is used as a guiding principle to extract dominant complex trajectories from all the semiclassical candidates.

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PubMed1999

Dynamical delocalization in one-dimensional disordered systems with oscillatory perturbation.

The effect of dynamical perturbation on the quantum localization phenomenon in a one-dimensional disordered quantum system (1DDS) is investigated systematically by a numerical method. The dynamical perturbation is modeled by an oscillatory driving force containing M independent (mutually incommensurate) frequency components. For M>or=2 a diffusive behavior emerges and in the presence of the finite localization length of the asymptotic wave packet can no longer be detected numerically. The diffusive motion obeys a subdiffusion law characterized by the exponent alpha as xi(t)(2) proportional t(alpha), where xi(t)(2) is the mean square displacement of the wave packet at time t. With an increase in M and/or the perturbation strength, the exponent alpha rapidly approaches 1, which corresponds to normal diffusion. Moreover, the space-time (x-t) dependence of the distribution function P(x,t) is reduced to a scaled form decided by alpha and another exponent beta such that P(x,t) approximately exp(-constx(x/t(alpha/2))(beta)), which contains the two extreme limits, i.e., the localization limit (alpha=0, beta=1) and the normal-diffusion limit (alpha=1, beta=2) in a unified manner. Some 1DDSs driven by the oscillatory perturbation in different ways are examined and compared.

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