1. Department of Mathematics, Kyonggi University, Suwon 443-760, Republic of Korea
2. Department of Mechanical Engineering, Kyung Hee University, Yongin 446-701, Republic of Korea
3. e-Spine Center, Kyung Hee University, Yongin 446-701, Republic of Korea
4. Department of Computer Science, Yonsei University, Seoul 120-749, Republic of Korea