Yuhei Yamaguchi

Genuine Phase Diagram of Homogeneously Doped CuO2 Plane in High-Tc Cuprate Superconductors

We report a genuine phase diagram for a disorder-free CuO 2 plane based on the precise evaluation of the local hole density ( N h ) by site-selective Cu-NMR studies on five-layered high- T c cuprates. It has been unraveled that (1) the antiferromagnetic metallic state (AFMM) is robust up to N h ≈0.17, (2) the uniformly mixed phase of superconductivity (SC) and AFMM is realized at N h ≤0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM (paramagnetism) phases may be present at N h ≈0.15 and T ≈75 K, (4) T c is maximum close to a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high- T c SC and the AFM order. The results presented here strongly suggest that the AFM interaction plays the vital role as the glue for the Cooper pairs, which will lead us to a genuine understanding of why the T c of cuprate superconductors is so high.

DEVELOPMENT OF HIGH-PERFORMANCE MR ACTUATOR AND ITS APPLICATION TO 2-D FORCE DISPLAY

Force display systems are a kind of robot systems, which share the space with people while they are working, and which directly touch and display force-senses to their users. For such a robot system, it is important to estimate safety quantitatively and to assure mechanically safety. The safety can be assured by using MR actuator because MR actuator is one of clutch type actuators. And, the features of MR actuator are very preferable to those of ER actuator and other clutch type actuators, to improve the performance of force display systems. In this study, we developed an MR actuator with low inertia, high torque/inertia ratio and high responsibility. Then, a 2-D force display system using the MR actuator was developed. The characteristics of the MR actuator that are low inertia, high torque/inertia ratio and high responsibility contribute to improve the performance of force display systems.

Development of a 6-DOF Force Display System with High Safety and its Application to Rehabilitation

Movements of the upper limbs are indispensable for daily activities. Rehabilitation for upper limbs is important for aged people or patients of paralysis caused by stroke. Because of aging of society, the number of stroke patients will increase more in the near future. In recent years, the needs for rehabilitation support systems are increasing, which use robot technology and virtual reality technology. Applying these technologies make efficient rehabilitation possible. This paper presents the development of a 6-DOF rehabilitation system for upper limbs including wrists. This system ensures efficient rehabilitation training which focus on the harmonic movement of the whole upper limb

High-performance 2-D force display system using MR actuators

A force display system is a kind of human-coexistent robot systems, which share the space with people while they are working, and which directly touch and display force-senses to their users. For such a robot system, it is important to estimate safety quantitatively and to ensure mechanical safety. In this paper, it is described that using MR (magneto-rheological) actuators, which is one clutch type actuators, can ensure safety. Moreover, the characteristics of MR actuators that are low inertia, high torque/inertia ratio and high responsibility contribute to improve the performance of force display systems. In this study, we developed an MR actuator with low inertia (2.6/spl times/10/sup -5/[kg/spl middot/ m/sup 2/]), high torque/inertia ratio (3.8/spl times/10/sup 5/[1/s/sup 2/]) and high responsibility. Torque/inertia ratio of this MR actuator is highest among MR actuators developed so far and much higher than those of conventional servo actuators. Then, a high-performance 2-D force display system using the MR actuator was developed. Maximum force displayed is 190 [N] and rigidity of the system is 5.9 [N/mm]. Moreover, backdrivability, dynamic range and collision sense are improved by using MR actuators in comparison with a system using ER actuators.

Genuine phase diagram of high-Tc superconductors based on site-selective Cu-NMR studies on five-layered cuprates

We report a genuine phase diagram for a disorder-free CuO2 plane based on the evaluation of the local hole density (Nh) by site-selective Cu-NMR studies on five-layered cuprates. It has been unraveled that (1) the antiferromagnetic (AFM) metallic state is robust up to Nh ≈ 0.17, (2) the uniformly mixed phase of SC and AFM metal (AFMM) is realized at Nh ≤ 0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM(Paramagnetism) phases may be present at Nh ≈ 0.15 and T ≈ 75 K, (4) Tc is maximum just outside a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high-Tc SC and the AFM order. Our finding experimentally suggests that the AFM interaction plays the vital role as the glue for the Cooper pairs.