1. computer science, The George Washington University, 8367 Washington, District of Columbia, United States, 20052-0086 (e-mail: hljiang0720@gwu.edu)
2. School of Computing Science, Simon Fraser Univeristy, Burnaby, British Columbia, Canada, V5A 1S6 (e-mail: jpei@cs.sfu.ca)
3. School of Computer Science and Technology, Shandong University, 12589 Qingdao, Shandong, China, (e-mail: dxyu@sdu.edu.cn)
4. School of Computer Science and Technology, Qilu University of Technology, 12689 Jinan, Shandong, China, (e-mail: jiguoyu@sina.com)
5. School of Information Technology, Beijing University of Technology, 12496 Beijing, Beijing, China, (e-mail: gongbei@bjut.edu.cn)
6. Computer Science, The George Washington University, Washington, District of Columbia, United States, 20052 (e-mail: cheng@gwu.edu)