小平 將裕

An oscillatory system called a plastic bottle oscillator is studied, in which the downflow of water and upflow of air alternate periodically in an upside-down plastic bottle containing water. It is demonstrated that a coupled two-bottle system exhibits in- and antiphase synchronization according to the nature of coupling. A simple ordinary differential equation is deduced to interpret the characteristics of a single oscillator. This model is also extended to coupled oscillators, and the model reproduces the essential features of the experimental observations.

We observed the photophoresis of smoke particles in a small focal laser beam under micro-gravity, exerted in an airplane, to avoid air convectional flow due to buoyancy. We measured the motion of smoke particles and found that the particles exhibit negative photophoresis under the suppression of the convection. Based on the distribution of velocity of negative photophoresis, it is shown that the photophoretic velocity is proportional to the laser power applied for the particle. We discuss the mechanism in terms of the radiometric force. (C) 2011 Elsevier B.V. All rights reserved.

When a plastic bottle with water is placed upside-down with a thin pipe at its head. limit-cycle oscillation call be observed. A simple differential equation can reproduce the properties of this oscillation. In the present study, a three-coupled-oscillator system is investigated experimentally and numerically. The behavior of the three coupled oscillators with frustration is interesting from the viewpoint of mathematical physics, and with all increase in size, this system should be helpful in unconventional computing, such Lis in, for example, optimization problems.

The oscillatory flow of water draining from an upside-down plastic bottle with a thin pipe attached to its head is studied as an example of a dissipative structure generated under far-from-equilibrium conditions. Mode bifurcation was observed in the water/air flow: no flow, oscillatory flow, and counter flow were found when the inner diameter of the thin pipe was changed. The modes are stable against perturbations. A coupled two-bottle system exhibits either in-phase or anti-phase self-synchronization. These characteristic behaviors imply that the essential features of the oscillatory flow in a single bottle system can be described as a limit-cycle oscillation. (c) 2007 American Association of Physics Teachers.

To identify the optimum conditions for the optical trapping of a droplet under microgravity, we theoretically analyzed the efficiency of trapping with counter laser beams. We found that the distance between the two foci is an important parameter for obtaining stable trapping conditions. We also performed an optical trapping experiment with counter laser beams under microgravity. The experimental results correspond well to the theoretical prediction. (c) 2006 Elsevier B.V. All rights reserved.

The optical levitation of a liquid droplet in the gas phase was investigated under a time-dependent change in the gravitational acceleration in an airplane following a specific flight profile. Through multiple trials under a linear increase in effective gravitational acceleration, we performed an experiment on the optical trapping of a droplet from 0.3g0 to 0.9g0, where g0 = 9.8 m/s2. During this change in the effective gravitational acceleration, the trapping position of a droplet with a radius of 14 μm was found to be lowered by ca. 100 μm. The essential feature of the change in the trapping position was reproduced by a theoretical calculation under the framework of ray optics. To the best of our knowledge, this study is the first to report on optical levitation under a time-dependent gravitational change. © 2005 Elsevier B.V. All rights reserved.

A water droplet, which was formed as a nucleation center from an aerosol of ammonium chloride, was trapped by a converged c.w. IR laser (lambda = 1064 nm) using a 100x objective lens, and the successive growth of the droplet was observed under supersaturated water vapor. The size of the droplet increased linearly with time and its maximum radius was 5.7 mum at a laser at 5 mW, indicating that the axial trapping efficiency Q was 0.46. This efficiency is much greater than those reported previously; for example, according to Ashkin and Dziedzic [Science 1975, 187, 1073], Q = 0.08 for a glycerol droplet of radius 6 mum at 40 mW (lambda = 514.5 nm).

The synchronized self-motion of two camphor boats was investigated on a circular water route. Two kinds of synchronization, phase-locking and phase-oscillatory modes, could be produced by changing the temperature, the radius of the circular cell, and the mass of each boat. The nature of the synchronization is discussed in relation to the distribution of the camphor layer, which is an important factor in the driving force of self-motion. The essential features of synchronized motion were reproduced by a numerical calculation regarding the spatial distribution of the camphor layer at the air/water interface. We believe that the present results may be useful for realizing artificial motors or chemomechanical transducers, which mimic motor organs or organelles in living organisms under nonlinear and isothermal conditions.

The mode selection of a camphor boat was investigated. When a camphor boat, confined in a container with a shape of number 8, was floated on the surface of water, one of the three modes of motion (rotation within one cell, outer rotation without passing through the intersection of the two cells, and 8-shaped rotation) was maintained for several tens of cycles. This mode selection depended on the conditions of camphor scrapings attached to the boat. When two camphor boats were floated on the water, a synchronized motion between them was observed. The present system suggests a chemo-mechanical transducer, where the vectorial process is sensitive to the shape of the cell and the surface concentration of the camphor molecule under isothermal conditions. (C) 2000 Elsevier Science B.V. All rights reserved.