Funding for this research was provided by:
Ministry of Education (2016R1D1A1B03930193)
Text and Data Mining valid from 2019-08-06
Received: 20 February 2019
Accepted: 24 July 2019
First Online: 6 August 2019
Compliance with ethical standards
: Sung-Hee Hwang, Hun-Ho Ahn & Michael Lee declares that they have no conflict of interest.