Funding for this research was provided by:
National Natural Science Foundation of China (11672231, 11672233)
NPU Foundation for Fundamental Research (3102017AX008)
NSF of Shaanxi Province ((Grant No. 2016JM1010))
National Natural Science Foundation of China (11672230)
Article History
Received: 23 July 2017
Accepted: 23 February 2018
First Online: 16 March 2018