Submitted on: 08 December 1998.
Revised on: 28 March 1999.
Accepted on: 25 April 1999.
___________________Journal of Ocean University of China
http://reply.papertrans.cn/2/185/18434/18434-32.png
http://reply.papertrans.cn/2/185/18434/18434-33.png
http://reply.papertrans.cn/2/185/18434/18434-34.png
http://reply.papertrans.cn/2/185/18434/18434-35.png
http://reply.papertrans.cn/2/185/18434/18434-36.png