Current Subjects

Bioconvection of Euglena

A group of micro-organisms often generates a macroscopic ordered pattern such as a bacteria colony and bioconvection. The bioconvection is one of fluidic patterns caused by an upward swimming of the micro-organisms. The oriented swimming is induced in response to an external stimulus or force field, e.g., a gradient in oxygen concentration, light illumination, and gravity. We focused on a swimming micro-organism exhibiting phototaxis, Euglena. In contrast to a general bioconvection appearing all over a chamber, Euglena formed a bioconvection in a part of a chamber (figure). In this seminar, we would like to introduce to the characteristic behavior of bioconvection of Euglena, and discuss the mechanism of the pattern formation based on both experimental results and numerical calculation.
Formation and gathering of Euglena clusters. With the light illumination from bottom of the system (3000 Lx), bioconvection like pattern was locally formed. The group of the clusters migrated with keeping the distances between the clusters.

Mode-Swhitching of Self-Motion of A Camphor Boat

We demonstrated mode-switching of self-motion coupled with diffusion of molecules at a solid/liquid interface. A camphor boat moved spontaneously on water and the mode of self-motion depended on the setup of the boat. When a camphor disk was connected to the center of a larger plastic plate, intermittent motion (alternating between rest and rapid motion) was observed. When the position of the camphor disk was changed from the center to one of its edges, the period of intermittent motion decreased, and intermittent motion changed to continuous motion.
Camphor boat

Collective Behavior of Camphor Boats

We propose an inanimate system composed of camphor boats in an annular water channel in order to understand the collective motions. The boats move on the water surface spontaneously and interact with one another through the concentration of the camphor molecules on the water. We observed several modes of collective motion, e.g., behaviors analogous to traffic flow or an ant trail. Our system provides a convenient experimental setup for the investigation of a variety of collective motions.
Camphor jam

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