1. Department of Economics, Chongqing Technology and Business University, No. 19 Xuefu Avenue, Nanan District, Chongqing 400067, P. R. China
2. College of Aerospace and Civil Engineering, Harbin Engineering University, No. 145 Nantong Street, Nangang District, Harbin 150001, P. R. China
3. Department of Economics, Jinan University, No. 601 West Huangpu Road, Guangzhou 510632, P. R. China