1. a Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
2. b Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
3. c Department of Mechanical Engineering, Chungju National University, 72 Daehak-ro, Chungju-si, Chungbuk 380-702, South Korea;, Email: sychung@cjnu.ac.kr