1. Professor, College of Management and Economics, Tianjin Univ., No. 92 Nankai District, Tianjin 300072, P.R. China.
2. Ph.D. Candidate, College of Management and Economics, Tianjin Univ., No. 92 Nankai District, Tianjin 300072, P.R. China.
3. Ph.D. Candidate, College of Management and Economics, Tianjin Univ., No. 92 Nankai District, Tianjin 300072, P.R. China (corresponding author).
4. Lecturer, School of Economics and Management, Beihang Univ., Haidian District, Beijing 100191, P.R. China.
5. Associate Professor, College of Management and Economics, Tianjin Univ., No. 92 Nankai District, Tianjin 300072, P.R. China.