First Author:   Qiang Wang College of Economics and Management, Nanjing University of Aeronautics and Astronautics, China. njwqluck@live.cn         Second Author: Yuanyuan He College of Economics and Management, Nanjing University of Aeronautics and Astronautics, China. heyyluck1981@hotmail.com         Third Author: Qi Chen College of Economics and Management, Nanjing University of Aeronautics and Astronautics, China. chenqi_357@163.com