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The first two authors, Cheng-jie Xiong and Bo Huang, should be noted as contributing equally to this work.
Author Bo Huang should also be listed as a corresponding author, and can be contacted at the following email address: fmmuhb@126.com
The following information was missing from the Funding section: This work was also supported by the National Natural Science Foundation of China (81101364 and 81071498).
Competing Interests: No competing interests declared.
