1. School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, P. R. China
2. School of Nanjing Forestry University, Nanjing 210018, P. R. China
3. Zhongguancun Sub-Branch, PSBC, Beijing 100080, P. R. China
4. School of Engineering, University of Lincoln, Lincoln LN67TS, UK
5. Department of Business Studies, Air University Islamabad, Pakistan