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Matsuda Y.,Hiroshima University | Suematsu N.J.,Meiji University | Suematsu N.J.,Meiji Institute for Advanced Study of Mathematical science MIMS | Nakata S.,Hiroshima University
Physical Chemistry Chemical Physics | Year: 2012

The photo-sensitive self-motion of a benzoquinone (BQ) disk was investigated on a hydroquinone (HQ) aqueous solution. The mode-switching of self-motion, i.e., continuous → intermittent → no motion, was observed with an increase in the concentration of HQ. Upon irradiation with UV light (∼254 nm), the critical concentrations of HQ that were associated with the three modes of motion shifted to lower values, and the average speed of motion decreased. We discuss the mechanism of the photo-sensitive self-motion in relation to the photochemical reaction from BQ to HQ and the driving force of the disk. This journal is © the Owner Societies 2012. Source


Heisler E.,Hiroshima University | Suematsu N.J.,Meiji University | Suematsu N.J.,Meiji Institute for Advanced Study of Mathematical science MIMS | Awazu A.,Hiroshima University | Nishimori H.,Hiroshima University
Journal of the Physical Society of Japan | Year: 2012

The motion of several self-propelled boats in a narrow channel displays spontaneous pattern formation and kinetic phase transitions. In contrast with previous studies on self-propelled particles, this model does not require stochastic fluctuations and it is experimentally accessible. By varying the viscosity in the system, it is possible to form either a stationary state, correlated or uncorrelated oscillations, or unidirectional flow. Here, we describe and analyze these self organized patterns and their transitions. © 2012 The Physical Society of Japan. Source


Ikura Y.S.,Hiroshima University | Tenno R.,Hiroshima University | Kitahata H.,Chiba University | Kitahata H.,Japan Science and Technology Agency | And 3 more authors.
Journal of Physical Chemistry B | Year: 2012

We investigated the Marangoni flow around a camphor disk on water with the addition of sodium dodecyl sulfate (SDS). The flow velocity decreased with an increase in the concentration of SDS in the aqueous phase, and flow was hardly observed around the critical micelle concentration (cmc), because SDS reduced the driving force of Marangoni flow. However, the flow velocity increased with a further increase in the concentration of SDS. Thus, the Marangoni flow is maximally inhibited around the cmc of SDS. In this paper, we concluded that the regeneration of Marangoni flow originates from an increase in the dissolution rate of camphor into the SDS aqueous solution. © 2011 American Chemical Society. Source


Suematsu N.J.,Meiji University | Suematsu N.J.,Meiji Institute for Advanced Study of Mathematical science MIMS | Sato T.,Hiroshima University | Motoike I.N.,Japan Science and Technology Agency | And 3 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

A wave train in an excitable reaction-diffusion medium shows a variety of spatiotemporal patterns as a result of interactions between the individual waves. In this paper, we report a novel spatiotemporal pattern in a wave train in a closed excitable medium. We carried out experiments using a photosensitive Belousov-Zhabotinsky reaction with Ru(bpy)32+ as a catalyst and a numerical calculation using the FitzHugh-Nagumo equation. A wave train was locally distributed as an initial condition and the number of waves was systematically varied. In both the experiment and numerical calculation, density wave propagation was formed in a wave train during relaxation with a large number of waves. Our results suggest that density wave propagation originates from inhibitory interaction between the waves. © 2011 American Physical Society. Source


Suematsu N.J.,Hiroshima University | Suematsu N.J.,Meiji University | Suematsu N.J.,Meiji Institute for Advanced Study of Mathematical science MIMS | Awazu A.,Hiroshima University | And 5 more authors.
Journal of the Physical Society of Japan | Year: 2011

Localized pattern of bioconvection was newly observed in a suspension of Euglena gracilis, which was a photosensitive micro-organism. The suspension was exposed bright illumination from the bottom, in which the cells swam away from the light source. Then high-density spots, i.e., settling the cells, were formed at a part of a sealed chamber. This localized pattern was contrast with a general bioconvection where pattern was generated whole of a chamber. The experimental observations were reproduced by a mathematical model that was based on the phototaxis of individual cells in both vertical and lateral directions. Our results indicate that convection is maintained by upward swimming, as with general bioconvection, and the localization originates from lateral phototaxis. © 2011 The Physical Society of Japan. Source

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