1. a Graduate School of NID Fusion Technology , Seoul National University of Science and Technology , 172, Gongreung-dong, Nowon-gu, Seoul , 139-743 , Korea E-mail:
2. b Department of Mechanical Engineering , Seoul National University of Science and Technology , 172, Gongreung-dong, Nowon-gu, Seoul , 139-743 , Korea
3. c Department of Mechanical Engineering , Seoul National University of Science and Technology , 172, Gongreung-dong, Nowon-gu, Seoul , 139-743 , Korea E-mail: