School of Computer, Wuhan University, Wuhan 430072, China. Tel.: +86-27-6877-5711, Fax: +86-27-6877-5711, liujuan@whu.edu.cn, Fang-Xiang Wu, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Tel.: +1-306-966-5280, Fax: +1-306-966-5427, E-mail: faw341@mail.usask.ca.|School of Computer, Wuhan University, Wuhan 430072, China. Tel.: +86-27-6877-5711, Fax: +86-27-6877-5711, liujuan@whu.edu.cn, Fang-Xiang Wu, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Tel.: +1-306-966-5280, Fax: +1-306-966-5427, E-mail: faw341@mail.usask.ca.|School of Computer, Wuhan University, Wuhan 430072, China. Tel.: +86-27-6877-5711, Fax: +86-27-6877-5711, liujuan@whu.edu.cn, Fang-Xiang Wu, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Tel.: +1-306-966-5280, Fax: +1-306-966-5427, E-mail: faw341@mail.usask.ca.|School of Computer, Wuhan University, Wuhan 430072, China. Tel.: +86-27-6877-5711, Fax: +86-27-6877-5711, liujuan@whu.edu.cn, Fang-Xiang Wu, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Tel.: +1-306-966-5280, Fax: +1-306-966-5427, E-mail: faw341@mail.usask.ca.