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Article History

Received: 29 January 2016

Accepted: 15 June 2016

First Online: 7 July 2016

Change Date: 4 August 2016

Change Type: Update

Change Details: The version of this Article previously published omitted Zhaohua Jiang as a corresponding author. Correspondence and request for materials should also be addressed to jiangzhaohua@hit.edu.cn. This has now been corrected in the HTML and PDF versions of the Article.

Competing interests

: The authors declare no competing financial interests.