1. School of Computer Science and Technology, Nanjing Normal University, Nanjing, Jiangsu 210023, China
2. School of Computer Science and Technology, Nanjing Normal University, Nanjing, Jiangsu 210023, China. wangshuihua@njnu.edu.cn
3. Jiangsu Key Laboratory of 3D, Printing Equipment and Manufacturing, Nanjing, Jiangsu 210042, China
4. Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
5. School of Natural Sciences and Mathematics, Shepherd University, Shepherdstown, WV 25443, USA
6. Department of Electrical Engineering, The City College of New York, CUNY, New York, NY 10031, USA
7. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA