1. Department of Electrical and Computer Engineering; National University of Singapore; 4 Engineering Drive 3 Singapore 117576 Singapore
2. Data Storage Institute; (A*STAR) Agency for Science Technology and Research; 2 Fusionopolis Way Singapore 138634 Singapore
3. School of Aerospace Engineering; Xiamen University; 422 Siming South Road Xiamen 361005 P. R. China
4. Department of Chemistry; National University of Singapore; 3 Science Drive 3 Singapore 117543 Singapore