1. School of Information Science and Technology, Northwest University, Xi’an 710127, China
2. Network Center, Shijiazhuang Posts and Telecommunications Technical College, Shijiazhuang 050021, China
3. Computer School, Hubei University of Arts and Science, Xiangyang 441000, China
4. School of Fundamental Science and Engineering, Waseda University, Tokyo 1698050, Japan
5. Capinfo Company Ltd, Beijing 100010, China