Submitted on: 16 September 2007.
Revised on: 05 October 2007.
Accepted on: 10 October 2007.
NULL
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http://reply.papertrans.cn/3/220/21914/21914-33.png
Submitted on: 02 December 2008.
Revised on: 09 December 2008.
Accepted on: 02 January 2009.
NULL
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