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First Online: 14 May 2018

Compliance with Ethical Standards

:

: Jung-Kwang Ahn and Jung-Hye Kwon declare that they have no conflict of interest.

: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

: Informed consent was obtained from all individual participants included in the study.

: This article does not contain any studies with animals performed by any of the authors.