Tatsuhiro Ueki

Transient Mode Selections in Soft-Mode Turbulence by Controlling the Nambu–Goldstone Modes

We have studied the soft-mode turbulence (SMT), a type of spatiotemporal chaos observed in the electroconvection of the homeotropic nematic liquid crystals, induced by nonlinear interaction between the long-wave length Nambu–Goldstone modes and the short-wave length convective modes. By applying an external magnetic field H, the NG mode can be controlled and as a result an ordered pattern may be observed. Transiently it is achieved by the dynamical changes of the many domains consisting of regular rolls. Removing the magnetic field, then, the ordered state relaxes to its original SMT pattern. The transient dynamics of such a relaxation process is also investigated. An order parameter called as M p is used as a quantitative indicator for the transient process. We reveal two regimes of relaxation process: regime I and regime II correspond to the superposition of the modes and the free rotation of wavevector q ( r ) of the electroconvective pattern, respectively.

Magnetic Field Dependence of Spatiotemporal Chaos in a Homeotropic Nematic System

We investigate the response of electroconvective patterns to an external magnetic field H in a homeotropic nematic system where spatiotemporal chaos called soft-mode turbulence (SMT) occurs. The pattern ordering M p , which shows pattern regularity in SMT, increases with the magnetic field H due to the suppression of the azimuthal rotational freedom. Three regions in the H -dependence of M p are found: the zero regime, the steep increase regime and the saturated regime. In the steep increase regime, M p shows a linear relation with \bar H 2 , from which the susceptibility χ p for the pattern ordering is obtained.

New measure of chaos of convective pattern in soft-mode turbulence

We investigate the response of electroconvective patterns to an external magnetic field H in a homeotropic nematic system where spatiotemporal chaos called the soft‐mode turbulence (SMT) occurs. We introduce new order parameter Op, obtained directly from the amplitude spectrum of the patterns. We measure the degree of regularity of patterns under influence of H using Op and compare with the pattern ordering Mp obtained from analogy with the magnetization in 2D XY model. Our new order parameter Op is well proportional to Mp.