Supported by the National Natural Science Foundation of China under Grant No.60703089 (国家自然科学基金); the Shandong Provincial Natural Science Foundation of China under Grant Nos.ZR2009GQ008, ZR2010FQ019 (山东省自然科学基金); the Science and Technology Project of Provincial Education Department of Shandong Province of China under Grant No.J08LJ02 (山东省教育厅科技计划); the Scientific Research Foundation for the Excellent Middle-Aged and Youth Scientists of Shandong Province of China under Grant No.2008BS01011 (山东省优秀中青年科学家科研奖励基金)