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17 results on '"Shiwa Y"'

1. Ordering Dynamics of Lamellar Patterns in Cooperative Systems with a Small-World Topology.

Author

Imayama, R. and Shiwa, Y.

Subjects
DYNAMICS, TOPOLOGY, DENSITY, INTEGRAL domains, CONFIGURATIONS (Geometry)
Abstract

We have studied numerically the ordering dynamics of lamellar patterns in two-dimensional small-world media. It is found that increase of the density of random shortcuts causes the coarsening of lamellar domains to become slower and eventually get stuck in a frozen configuration. We discuss the underlying mechanism responsible for this frozen state. [ABSTRACT FROM AUTHOR]

Published
2008
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2. Spirals, Hexagons, and All That through Hydrodynamic Coupling with a Zero Mode.

Author

Shiwa, Y.

Subjects
CONSERVATION laws (Physics), DYNAMICS, BEHAVIOR, INSTABILITY strip (Astrophysics), HEXAGONS, HYDRODYNAMICS
Abstract

We consider the simplest model that allows the investigation of the role of conservation law and its interplay with a striped-pattern dynamics in determining the overall behavior of the system. We observed in numerical simulations that the interaction of striped-pattern forming instability and a neutrally stable zero mode induces patterns of domains of upflow hexagons coexisting with domains of downflow hexagons. They appear only when hydrodynamic flow is present. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2006
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3. Phase separation dynamics in small-world media.

Author

Imayama, R. and Shiwa, Y.

Subjects
TOPOLOGY, PROPERTIES of matter, CRYOBIOLOGY, LOW temperatures, ANALYTICAL mechanics
Abstract

We present results of a numerical study of phase separation dynamics of a two-dimensional quenched system which has a small-world topology, both with and without the conserved order parameter. We examine how the domain coarsening changes with the density of long-range connections (shortcuts). It is demonstrated that the shortcuts have directly opposite effects, i.e., a speeding up of the coarsening process of reaching a fully uniform state, and a freezing of the system in a disordered metastable state. [ABSTRACT FROM AUTHOR]

Published
2007
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4. Exact Renormalization Group for the Brazovskii Model of Striped Patterns.

Author

Shiwa, Y.

Subjects
RENORMALIZATION group, STRIPES, PHASE transitions, QUANTUM perturbations, FUNCTIONAL differential equations, SCALAR field theory, PHASE equilibrium, FERMI liquids
Abstract

We consider the coarse graining of the generalized Brazovskii free energy functional for striped patterns. The technique developed by Shankar for the Fermi liquids is combined with the irreducible version of the exact renormalization group to calculate the recursion relations for interaction vertices. We perform the one-loop calculations from this method taking the eight-point vertex into account. [ABSTRACT FROM AUTHOR]

Published
2006
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9. On the scattering properties of a weakly charged polymer gel.

Author

Shiwa, Y.

Abstract

A phenomenological model is presented to describe weakly charged polymer gels based on the classical elasticity theory. The structure factor of the gel is calculated considering both thermal and frozen concentration fluctuations as well as the screened Coulomb interaction. In agreement with the recent experimental finding the result shows anomalous crosslink-density dependence of the scattering profiles. [ABSTRACT FROM AUTHOR]

Published
1998
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11. Cooperative diffusion in weakly charged polyelectrolyte gels.

Author

Shiwa, Y.

Abstract

A general expression for the cooperative diffusion constant of weakly charged gels is derived as a function of the thermodynamic parameters such as polyelectrolyte concentration, salt concentration, ionic strength, and the degree of crosslinking. In the low concentration range it decreases with the monomer concentration. [ABSTRACT FROM AUTHOR]

Published
1998
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12. Hydrodynamic Coarsening and Pattern Selection in Two-dimensional Quenched Diblock Copolymers.

Author

Yokojima, Y. and Shiwa, Y.

Subjects
HYDRODYNAMICS, COPOLYMERS, POLYMERS, SIMULATION methods & models, MECHANICS (Physics), STATICS
Abstract

We investigate the hydrodynamic coarsening of microphase separation in two-dimensional diblock copolymers using a model set of equations which incorporates the coupling of the flow velocity field to the order parameter. Cell-dynamical-system simulations are carried out to study how the hydrodynamic flow controls the coarsening dynamics of lamellar structures. We extract the growth exponent for the characteristic length scale by measuring the orientational correlation function. Moreover, a global wave number attained after a long time as a function of the strength of hydrodynamic coupling is determined analytically by means of a random phase approximation. The result is compared with the simulation results. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
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13. Exact Renormalization Group for the Brazovskii Model.

Author

Shiwa, Y.

Subjects
QUANTUM field theory, STATISTICAL mechanics, FLUIDS, HYDROSTATICS, PHYSICS, FERMI liquids
Abstract

We consider the coarse graining of the generalized Brazovskii free energy functional for striped patterns. The technique developed by Shankar for the Fermi liquids is combined with the irreducible version of the exact renormalization group to calculate the recursion relations for interaction vertices. We perform the one-loop calculations from this method taking the eight-point vertex into account. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
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