基金Supported by the National Natural Science Foundation of China under Grant Nos 60678022 and 10704001, the Specialized Research Pund for the Doctoral Program of Higher Education under Grant No 20060357008, the Key Program of the Education Department of Anhui Province under Grant Nos KJ2009A048Z, the Talent Project of the Anhui Province for Outstanding Youth under Grant Nos 2010SQRL153ZD and 2010SQRL187.