Copyright © The Author(s) 2019. Published by Baishideng Publishing Group Inc. This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license.
Except where otherwise noted, this item's license is described as Copyright © The Author(s) 2019. Published by Baishideng Publishing Group Inc. This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license.