Department of Applied Mathematics, Sejong University, 98 Gunja-Dong Kwangjin-Gu, Seoul 143-747, Korea.|Department of Applied Mathematics, Sejong University, 98 Gunja-Dong Kwangjin-Gu, Seoul 143-747, Korea.|Department of Applied Mathematics, Sejong University, 98 Gunja-Dong Kwangjin-Gu, Seoul 143-747, Korea.|Department of Applied Mathematics, Sejong University, 98 Gunja-Dong Kwangjin-Gu, Seoul 143-747, Korea.|Department of Applied Mathematics, Sejong University, 98 Gunja-Dong Kwangjin-Gu, Seoul 143-747, Korea.