1. School of Mechanical Engineering; Kyungpook National University; 1370 Sankyuk-Dong Buk-gu Daegu 702-701 Korea
2. Department of Biology and Advanced Bio-Resource Research Center; Kyungpook National University; Buk-gu Daegu Korea
3. Department of Mathematics and KNU-Center for Nonlinear Dynamics; Kyungpook National University; Buk-gu Daegu Korea