1. School of Computer Science, Shaanxi Normal University, Xi’an, China
2. Department of Computer Science, Georgia State University, Atlanta, GA 30302, USA
3. School of Computer, Electronics and Information at Guangxi University, Nanning, China
4. Department of Computing Sciences at the College at Brockport, State University of New York, Rochester, NY, USA
5. Computer Science Department at Georgia State University, Atlanta, GA, USA