Acknowledgment
- The work of Yin Zhang was supported in part by NSF DMS-0811188 and ONR N00014-08-1-1101.
- The work of Junfeng Yang was supported in part by the Natural Science Foundation of China grant NSFC-10971095 and the Natural Science Foundation of Jiangsu Province BK2008255.
- The work of W. Yin was supported in part by NSF CAREER Award DMS-07-48839, NSF ECCS-1028790, ONR Grant N00014-08-1-1101, the U. S. ARO and ARL grant W911NF-09-1-0383, and an Alfred P. Sloan Research Fellowship.