doped (GDC) solid solutions have been considered as a promising materials for electrolytes in intermediate-temperature solid oxide fuel cells. In this study, the nano-sized GDC powder with average panicle size of 69nm was prepared by a high energy ball milling process and its sintering behavior was investigated. Heat-treatment at of nano-sized GDC powder mixture led to GDC solid-solution. The enhanced densification over 96% of relative density was obtained after sintering at for 2h. It was found that the sinterability of GDC powder could be significantly improved by the introduction of a high energy ball milling process

대공간구조에서 접합부의 신뢰도는 매우 중요하다. 접합부에 사용되는 고력볼트의 나사부 유효단면적은 축부단면적보다 작고 볼트 축부에 락핀용 구멍이 있기 때문에 볼트 나사부 또는 락핀용 구멍에 응력집중 현상이 발생하여 취성 파단이 발생할 우려가 높다. 특히 접합부는 직렬형 구조로 이루어져 있다. 따라서 접합부에서의 극한상황시 파괴유형은 필히 취성파괴를 피해야 하며 연성파손으로 유도해야 한다. 따라서 본 연구에서는 볼 조인트 접합부의 소성변형능력을 향상시키고 현장에서 발생할 수 있는 시공오차의 흡수가 가능하도록, 볼트의 나사부나 핀부의 취성파단 없이 소성변형능력 향상을 목표로 하였다. 에너지흡수형 볼트를 사용함으로써 소성변형능력이 향상된 스페이스 프레임의 접합상세를 제안하였다.

This Study is about structural analysis of ball valve for controlling cryogenic LNG's flow or stop in normal temperature. The used valve is demanded safety resistance for inner pressure and temperature variation caused by using it in cryogenic, high pressure surrounding. This study evaluates for safety resistance for inner pressure and temperature variation by heat transfer analysis in cryogenic surrounding, heat stress analysis in temperature variation and deformation analysis in high pressure.

This study was designed 10 investigate the effects of therapeutic gymnastic ball exercise on pain, flexibility, lumbar disability level and daily activity levels in male patients of the armed forces medical hospital who complain of chronic low back pain. Twenty-three males were placed in the experimental group and twenty-nine males were placed in the control group. All of the subjects were chosen on the basis of availability among in-patients who were diagnosed with low back pain. The control patients were matched to the experimental group and they were selected considering gender, pain duration and age. Gymnastic ball exercise therapy was developed by the author with the assistance of a rehabilitation specialist. Gymnastic ball exercise therapy includes muscle relaxation, flexibility, muscle strength and posture development exercises. The gymnastic ball exercise therapy was carried out by the experimental group three times a week for eight weeks. Before and after the experiments, the intensity of pain, the lumbar joint mobility (flexibility), the lumbar disability levels, and the daily activity levels of the subjects were measured, respectively. The intensity of pain and the lumbar disability levels were measured by the Visual Analogue Scale, the level of flexibility by a measurement ruler, and the level of disability by the Oswestry Low Back Pain Disability Scale. Data were analysed using a t-test, a paired t-test and an unpaired t-test. The results were as follows: 1. The intensity of pain in the lumbar spine in the experimental group was significantly decreased compared with that of the control group during the 4th week and 8th week. 2. The flexibility of the lumbar spine in the experimental group was significantly increased compared with that of the control group during the 4th week and 8 week. 3. The level of pain caused by anterior, posterior, left lateral and right lateral bending and by rotation in experimental group was significantly decreased compared with that of the control group. 4. The Oswestry Disability score of the experimental group was significantly increased compared with that of control group. These findings indicate that gymnastic ball exercise therapy could be effective in decreasing pain and lumbar disability, and increasing the daily activity levels and lumbar flexibility in patients with chronic low back pain. The study also suggests that gymnastic ball exercise therapy could be an essential factor for effective nursing intervention for patients suffering from chronic low back pain.

The purpose of this study is to analyze the characteristics of the connector having an influence on the elasto-plastic buckling load of ball-jointed single layer latticed domes. As an analytic model, domes are composed of tubular member elements, balls and connectors. The joint system of members in single layer latticed domes has influence on the buckling load. Therefore, in this paper, the variation of the elasto-plastic buckling load by effects of the connectors characteristics is analyzed. The structural behavior of the connector is investigated by following points: (1) the length of rigid zone, (2) looseness of screw and (3) the diameter of connector. In addition, the elasto-plastic buckling analysis is carried out through the variation of the connectors section of yielding part, and then the buckling mode of the dome is examined. As a result, it is emphasized that the characteristics of the connector have significant effects on the buckling load of latticed domes.

Effect of ball filling ratio on the behavior of balls motion and their collision characteristic in a tumbler-ball milling of metal powder are investigated by a computer simulation. The discrete element method and the extended Kelvin model composed of nonlinear spring and nonlinear dashpot were employed in the simulation. It can be possible that analysis of the individual balls motion in a three-dimensional actual mill by the two-dimensional model simulation, since the simulated trajectories of ball paths are in relatively good agreement with the actual ones. It knows that the balls motion in the tumbler-ball mill is strongly influenced by the surface conditions of the balls and mill container wall. The energy consumption of the individual balls during impact and the impact frequency of the individual balls increased with an increase in the ball filling ratio and showed maximum values at about 50-60% ball filling ratio, and then decreased.

Three mixtures of elemental powders of Al-25at.%Ti, 48at.%Ti and 70at.%Ti were offered to ball milling process for the formation of intermetallic compounds of , AlTi and . Ballmilling or attrition process were carried out at the condition of rotaing speed of 110 or 350 rpm at torr vacuum or argon atmospheres. phases were fully obtained by heat treatment for 1 hors at with Al-25at.%Ti composition mixtures milled by 100 hours. The amorphous phase was completely formed at the composition of Al-48at.%Ti mixed powders by milling 100hours at the 50 to 1 weight ratio of ball to powder, and AlTi compounds were obtained by heat treament. In the case of Al-70at%Ti mixed powders milled for 100 hours, and intermetallic compounds were formed by heat treatment for 1 hour at . By attrition milling of 350rpm for 10 hours, phase was formed completley after heat treatment for 1 hour at .