Received: 29 September 2017
Revised: 8 December 2017
Accepted: 12 December 2017
First Online: 5 February 2018
: Not applicable.
: The study was performed with approval of the ethical committee at Yokohama City University (No. A100903011).
: Not applicable since the manuscript is entirely original; the tables and figures presented are original for this article and have neither been published nor are currently under consideration for publication by any other journal.
: The authors declare that they have no competing interests.
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