National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [81270420, 81470434, 81470435, 81170277]; Hunan Provincial Natural Science Foundation of ChinaNatural Science Foundation of Hunan Province [14JJ3102]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2014M560647]; Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province [2008-244]