Funding for this research was provided by:
the Science and Technology Research Program of Chongqing Municipal Education Commission (KJ1713330)
Research Foundation of Chongqing University of Science and Technology (ck2017zkyb025)
the National Natural Science Foundation of China (61601068)
Article History
Received: 7 February 2018
Accepted: 16 August 2018
First Online: 5 September 2018
Competing interests
: The authors declare that they have no competing interests.