Faculty of Mechanical and Automotive Engineering, Keimyung University,2800 Dalgubeoldaero Dalseo-Gu, Daegu 704-701, Korea;
Division of Mechanical and Automotive Engineering, Kongju National University,1223-24 Cheonan Daero, Seobuk-gu Cheonan-si, Chungnam 331-717, Korea;