http://reply.papertrans.cn/3/257/25618/25618-11.png
http://reply.papertrans.cn/3/257/25618/25618-12.png
Submitted on: 24 July 2000.
Revised on: 16 August 2000.
Accepted on: 12 September 2000.
NULL
Submitted on: 21 July 2008.
Revised on: 29 July 2008.
Accepted on: 23 August 2008.
NULL
http://reply.papertrans.cn/3/257/25618/25618-15.png
http://reply.papertrans.cn/3/257/25618/25618-16.png
http://reply.papertrans.cn/3/257/25618/25618-17.png
http://reply.papertrans.cn/3/257/25618/25618-18.png
Submitted on: 04 October 2001.
Revised on: 11 October 2001.
Accepted on: 31 October 2001.
NULL
http://reply.papertrans.cn/3/257/25618/25618-20.png