Liu, Feng
Funding for this research was provided by:
the NNSF of China (11701333)
Support Program for Outstanding Young Scientific and Technological Top-notch Talents of College of Mathematics and Systems Science (Sxy2016K01)
Article History
Received: 24 November 2017
Accepted: 29 January 2018
First Online: 6 February 2018
Competing interests
: The author declares that they have no competing interests.