Takayuki Hirata

Chaotic Dynamics During Slow Relaxation Process in Magnon Systems

Experimental evidence of chaotic dynamics during a slow relaxation process with very low frequency magnetization auto-oscillations in magnon systems is presented. A ferromagnetic resonance experiment using a sphere of pure yttrium iron garnet (YIG) at the X-band pumping frequency within the coincidence regime reveals a slow relaxation process with a long tail after a stepwise drop in external pumping power. The relaxation process is found to follow a power-law with time as a transient process involving a transition of local dynamics from a quasi-periodic state to a chaotic state as the collapse of torus.

1/f Fluctuation and a Many-Body Disk Model of Slip Phenomena

A many-body disk system was investigated as a model of slip phenomena. A two-dimensional many-body disk system was used as a model of the boundary layer between slip surfaces. Frustrated states occurred in this system depending on the disk configuration. Experiments with this were carried out using a random packing configuration (packing fraction: 0.74 ∼0.76). Acrylic resin disks were packed between a co-axial outer rotating cylinder and an inner fixed cylinder. The outer cylinder was rotated by a motor and the torque at the fixed inner cylinder was measured in a time series. Stick-slip and 1/ f fluctuation were observed in the time series.

Intermittency in Magnon Systems near the Onset of the Second-Order Suhl Instability

Intermittent behavior in magnon systems is studied through ferromagnetic resonance experiments using a sphere of yttrium–iron–garnet (YIG) under X-band microwave pumping. Intermittency is observed ...

Visualization system for the information measured by motion capture system

This study aims to propose a system to visualize the velocity of motion, velocity/change of acceleration, and shape of trajectory based on the information measured by optical motion capture systems. It is difficult to figure out the above-mentioned information only by physical movements. The system uses various sizes of spheres and trigonal pyramids as well as colors and line segments to express velocity of motion, acceleration of motion, and changes in direction by showing them in a three-dimensional space following the motion trajectories. We conducted a questionnaire survey on the 20 participants of the study, asking them to evaluate whether or not the proposed system was easy to perceive the velocity of motion, acceleration and the change in direction. As a result, we found the system appropriate enough to show velocity and acceleration, and to show a detailed direction.

Stability of systems to control upright postures of young people

Stabilometry, which is useful for quantitative evaluation of equilibrium function, is generally performed using Rombergs posture. However, there is a risk of falls in diagnosing diseases such as Meniere disease, sudden deafness accompanied by vertigo, and vestibular neuronitis, measurement of body sway, and course observation of vertigo and balance dysfunction using stabilometry. The aim of this study was to compare the mathematical model in Rombergs posture with that in a posture in which the heels are together and feet are parallel. Stabilograms of the young were recorded with each posture. The distribution of stabilograms in the 2 postures did not also differ significantly. Therefore, we considered that there was no effect of the postural difference on their stability.

Evaluation of Body Sway in a Seated Posture after Alcohol Ingestion with an Aim to Evaluate Motion Sickness Caused by Three-Dimensional Images

A few studies have evaluated swaying motion of the body in the seated posture; however, these studies did not evaluate motion sickness caused by watching movies, traveling, etc. This study aimed to analyze stabilograms recorded while the individuals were seated. Stabilometry was performed on 7 healthy male subjects (age, 21–22 years) in the seated position 5 min before, and at 5-min intervals from 5 to 60 min after alcohol load. Alcohol caused a decrease in the cerebellar equilibrium function that controls the vestibulospinal reflex. We adjusted the degree of simulative effect on the human equilibrium function. The stabilograms of the test subjects were analyzed according to the area of sway, total locus length, and total locus length per unit area. We found that significant alcohol-induced changes in the sway values in the seated posture were similar to those in the upright posture.

Self-organized Path Formation by Ant Robots - An Approach to Understanding Ant’s Acts by Autonomous Distributed Systems -

A formation of path from a nest to a feeding area by ants was investigated by using small robots. An ant communicates the route from the nest to feeding area to the other ants by a pheromone. When an ant discovers food, it goes back marking a pheromone on its way to the nest. Its fellows follow the trace of the pheromone and then they also mark the pheromone on their way to the nest after arriving at the feeding area. At the early stage, the route is a complicated line. A lot of ants’ coming and going optimize the route from the nest to the feeding area. We observed the behavior of ants. Based on the observation we designed an ant type robot. Then we investigated the formation process of the route from the nest to the feeding area by artificial ants.