This research is supported by the National Natural Science Foundation of China (Grant number 51276057, and 51676209), and is also supported by Hunan Provincial Innovation Foundation for Postgraduate (Grant No. CX2014B065). Great thanks to the colleges Li Chengjun, Zhou Zhenyu, Li Kunxiang and Wang Tingting for their contribution to the field experiment and survey. Special thanks to all the subjects who volunteered to participate in the experiment.