Funding for this research was provided by:
Ministry of Education, Culture, Sports, Science and Technology (17H04027, 15H05940)
Text and Data Mining valid from 2018-10-18
Received: 27 July 2018
Accepted: 19 September 2018
First Online: 18 October 2018
Compliance with ethical standards
: The authors declare that they have no conflicts of interest.