Qunying Wu College of Science, Guilin University of Technology, Guilin 541004, China Correspondence should be addressed to Qunying Wu, [email protected] Received 11 March 2010; Revised 21 June 2010; Accepted 3 August 2010 Academic Editor: Soo Hak Sung Copyright q 2010 Qunying Wu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestric...