Human movement is a controlled result of the sensory-motor system, and the motor control mechanism has been studied through diverse movements. The present study examined control characteristics of dominant and non-dominant hands by analyzing the transient responses of circular tracking movements in 3D virtual reality space. A visual target rotated in a circular trajectory at four different speeds, and 29 participants tracked the target with their hands. The position of each subject’s hand was measured, and the following three parameters were investigated: normalized initial peak velocity (IPV2), initial peak time (IPT2), and time delay (TD2). The IPV2 of both hands decreased as target speed increased. The results of IPT2 revealed that the dominant hand reached its peak velocity 0.0423 s earlier than the non-dominant hand, regardless of target speed. The TD2 of the hands diminished by 0.0218 s on average as target speed increased, but the dominant hand statistically revealed a 0.0417-s shorter TD2 than the non-dominant hand. Velocity-control performances from the IPV2 and IPT2 suggested that an identical internal model controls movement in both hands, whereas the dominant hand is likely more experienced than the non-dominant hand in reacting to neural commands, resulting in better reactivity in the movement task.

We aim to investigate a control strategy for the circular tracking movement in a three-dimensional (3D) space based on the accuracy of the visual information. After setting the circular orbits for the frontal and sagittal planes in the 3D virtual space, the subjects track a target moving at a constant velocity. The analysis is applied to two parameters of the polar coordinates, namely, ΔR (the difference in the distance from the center of a circular orbit) and Δω (the difference in the angular velocity). The movement in the sagittal plane provides different depth information depending on the position of the target in orbit, unlike the task of the frontal plane. Therefore, the circular orbit is divided into four quadrants for a statistical analysis of ΔR. In the sagittal plane, the error was two to three times larger in quadrants 1 and 4 than in quadrants 2 and 3 close to the subject. Here, Δω is estimated using a frequency analysis; the lower the accuracy of the visual information, the greater the periodicity. When comparing two different planes, the periodicity in the sagittal plane was approximately 1.7 to 2 times larger than that of the frontal plane. In addition, the average angular velocity of the target and tracer was within 0.6% during a single cycle. We found that if the amount of visual information is reduced, an optimal feedback control strategy can be used to reduce the positional error within a specific area.

This study introduces laser surface modification technology using a 532 nm Nd:YAG nanosecond laser. A laser beam homogenizer was used to spatially homogenize the laser beam into a square shape with an interference pattern of 30 μm. For laser surface modification processing, primary processing under 110 conditions was first performed, and then, 15 types of main processing conditions were determined based on the three-dimensional surface structure of laser surface modified zircaloy-4. Subsequently, the specimen was post-processed using three methods: left in the air (25 ℃), heated in the oven (200 ℃ for 2 h), and boiled in water (100 ℃ for 2 h). In the absence of post-processing or with heat post-processing, the laser surface modified zircaloy-4 showed super hydrophobicity with a contact angle of 150° or higher for specific laser surface processing parameters. Under specific laser surface processing conditions, the laser surface modified zircaloy-4 with boiling water post-processing exhibited properties close to super hydrophilic with a contact angle of less than 5°. It was confirmed that the surface wettability of zircaloy-4 can be controlled using a spatially shaped nanosecond laser beam.

We introduce the laser-induced surface processing (LISP) method that imparts hydrophilicity and hydrophobicity using a Nd:YAG nanosecond laser, especially the high-fluence (HF) condition for fast processing and the low-fluence (LF) condition to control the surface wettability. A prime example of HF processing is laser shock peening, where we show the potential to achieve both strength enhancement and wettability in materials. This could be a new advantageous feature in areas such as reactor maintenance. We combined a beam homogenizer with LISP to increase processing efficiency. The beam homogenizer realizes a uniform fluorescence distribution in the beam area and, at the same time, makes the beam rectangular to increase work efficiency. The maximum contact angle was 123.8° for the zircaloy-4 specimen through HF processing with the beam homogenizer. We also showed that nanosecond laser-induced periodic surface structures could be generated by combining LF processing with specific conditions of a beam homogenizer. This could produce a superhydrophobic surface with contact angles up to 166° on zircaloy-4 or achieve a near superhydrophilic surface with a contact angle of 17.9° depending on the processing conditions.

We developed a theoretical model for the relationship between the input and amplified laser beams of energy stability and spatial uniformity in the amplification process. 10 Hz, 8 ns, 1064 nm Nd:YAG Q-switched resonator with Nd:YAG main amplifier was employed for the experiment. The theoretical model simulation and Frantz-Nodvik simulation were performed by utilizing the obtained beam image, acquired energy from the experiment, and stored fluence from the gain medium. The result indicated that the fluctuation of the spatial distribution in a single beam influences the stability of temporally distributed energy during the amplification process of the laser beam, thereby improving energy stability.