1. Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University, 12480 Xi'an, Shaanxi, China, (e-mail: yuanhaozhai@gmail.com)
2. Institute of Aritificial Intelligence and Robotics, Xi'an Jiaotong University, 12480 Xi'an, Shaanxi, China, (e-mail: lewang@mail.xjtu.edu.cn)
3. Department of Computer Science, University of Illinois at Chicago, 14681 Chicago, Illinois, United States, (e-mail: tangw@uic.edu)
4. Artificial Intelligence, ABB Corporate Research Center, Raleigh, North Carolina, United States, (e-mail: samqzhang@gmail.com)
5. Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University, 12480 Xi'an, Shaanxi, China, (e-mail: nnzheng@mail.xjtu.edu.cn)
6. Artificial Intelligence, Wormpex AI Research, Bellevue, Washington, United States, (e-mail: ganghua@gmail.com)