National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21202138, 21302051]; Xiangtan University "Academic Leader Program" [11QDZ20]; New Teachers' Fund for Doctor Stations, Ministry of Education [20124301120007]; Hunan Provincial Natural Science FoundationNatural Science Foundation of Hunan Province [13JJ4047]; Hunan Provincial Excellent Young Scientist Foundation [13B114]