Funding for this research was provided by:
National Natural Science Foundation of China (31640061)
Hainan Key Scientific and Technological Projects of China (ZDYF2016096)
Hainan University Start-up Scientific Research Projects of China (kyqd1551, kyqd1630)
Article History
Revised: 1 August 2017
Accepted: 18 December 2017
First Online: 6 February 2018
Compliance with ethical standards
:
: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.