The authors appreciate Dr Deene Manik Prabhu’s kind help and
advices to the manuscript. This work was financially supported by
the National Natural Science Foundation of China (NSFC, No.
41361075), Key Foundation Program of Yunnan Province of China
(No. 2013FA015), Major Program of Educational Commission of
Yunnan Province of China (No. ZD2013008), and the Basic Research
Foundation of Yunnan University (2013S204).