Funding for this research was provided by:
National Natural Science Foundation of China (61863004)
National Natural Science Foundation of China (61364006)
National Natural Science Foundation of China (61563005)
Natural Science Foundation of Guangxi Province (2017GXNSFAA198179)
Article History
Received: 10 July 2018
Accepted: 10 September 2018
First Online: 25 September 2018
Competing interests
: The authors declare that they have no competing interests.