Li, Nan
Qi, Xiaoguang
Yang, Lianzhong
Funding for this research was provided by:
the NSF of Shandong Province (ZR2016AQ20)
the NSFC Tianyuan Mathematics Youth Fund (1162611)
the NNSF of China (No.11371225)
the Fund of Doctoral Program Research of University of Jinan (XBS1630)
Article History
Received: 12 December 2017
Revised: 21 April 2018
First Online: 9 May 2018