1. School of Economics and Management, North China Electric Power Univ., Beijing China; and School of Economics and Management, Shanghai Univ. of Electric Power, Shanghai, China.
2. School of Economics and Management, North China Electric Power Univ., Beijing, China (corresponding author).
3. School of Economics and Management, North China Electric Power Univ., Beijing, China.
4. Argonne National Laboratory, Argonne, IL; and School of Economics and Management, Shanghai Univ. of Electric Power, Shanghai, China.