1. a Department of Mathematics , Southeast University , Nanjing, 210096, People's Republic of China
2. b Department of Mathematics , Hong Kong Baptist University , People's Republic of China
3. c College of Math & Physics , University of Information Science & Technology , Nanjing, 210044, People's Republic of China
4. d School of Business , Sun Yat-Sen University , Guangzhou, 510275, People's Republic of China