Funding for this research was provided by:
National Natural Science Foundation of China (11722112, 91630207)
Division of Mathematical Sciences (DMS-1453661, DMS-1720023)
Division of Mathematical Sciences (DMS-1719942)
Article History
Received: 21 March 2018
Revised: 20 June 2018
Accepted: 17 July 2018
First Online: 24 July 2018