1. a Department of Information systems Engineering, Faculty of Engineering , Osaka Sangyo University , 3-1-1 Nakagaito, Daito-shi, Osaka , 574 , Japan
2. b Department of Physics and Electronics, Faculty of Engineering , University of Osaka Prefecture , 1-1 Gakuen-cho, Sakai-shi, Osaka , 593 , Japan
3. c Institute of Theoretical Physics, Academia Sinica , P.O. Box 2735, Beijing , 100080 , China