1. Department of Astronautic Science and Mechanics; Harbin Institute of Technology; Harbin 150001 China
2. LSEC, ICMSEC, Academy of Mathematics and Systems Sciences, Chinese Academy of Sciences; Beijing 100190 China
3. Department of Mathematics; College of Science, Guizhou Minzu University; Guiyang 550025 China
4. Department of Applied Mathematics; Northwestern Polytechnical University; Xi'an 710129 China