Text and Data Mining valid from 2019-06-11
Received: 3 December 2018
Revised: 14 May 2019
Accepted: 26 May 2019
First Online: 11 June 2019
Compliance with ethical standards
: There is no conflict of interest in this manuscript, which has been approved by all authors for publication. On behalf of my co-authors, I declare that this study is an unpublished original study and that it is not considered to be published in whole or in part elsewhere. All the authors listed approved the declaration.
: The study was approved by the local ethics committee in China.