Funding for this research was provided by:
Directorate for Mathematical and Physical Sciences (DMS-1418689)
Hong Kong Research Council GRF (15300417, 15325816)
Longshan Talent Project of SWUST (18LZX529)
Article History
Received: 21 November 2018
Revised: 7 July 2019
Accepted: 8 July 2019
First Online: 12 July 2019