Erratum
After publication of the original article [1], it came to the authors’ attention that there were spelling errors in the surnames of two of the authors. The surnames of A. Batticciotto and A. Draghessi were misspelled but appear correctly in this erratum.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.