1. Ph.D. Candidate, College of Management and Economics, Tianjin Univ., Tianjin 300072, P.R. China.
2. Professor, College of Management and Economics, Tianjin Univ., Tianjin 300072, P.R. China.
3. Postgraduate, College of Management and Economics, Tianjin Univ., Tianjin 300072, P.R. China (corresponding author).
4. Postgraduate, College of Management and Economics, Tianjin Univ., Tianjin 300072, P.R. China.