1. Department of Mechanical and Control Engineering, Handong Global University, Pohang, Kyung-Buk 375-554, South Korea
2. Department of Mechanical Engineering, KAIST, Daejeon 305-701, South Korea
3. School of Civil and Environmental Engineering, KAIST, Daejeon 305-701, South Korea
4. School of Mechanical Engineering, Chungnam National University, Daejeon 305-764, South Korea