The following license files are associated with this item:

    © 2017 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
    Except where otherwise noted, this item's license is described as https://creativecommons.org/licenses/by-nc-nd/4.0/