1. Research Center of Complex Systems Science, University of Shanghai for Science and Technology, Shanghai 200093, P. R. China
2. Department of Modern Physics, University of Science and Technology of China, Hefei 230026, P. R. China
3. Department of Physics, University of Fribourg, Fribourg CH-1700, Switzerland
4. Business School, University of Shanghai for Science and Technology, Shanghai 200093, P. R. China