Green in Sherpa: Author's Pre-print: author can archive pre-print (ie pre-refereeing)
Author's Post-print: 	author can archive post-print (ie final draft post-refereeing)
Publisher's Version/PDF: author can archive publisher's version/PDF
General Conditions: Publisher's version/PDF may be used
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17.5.16--MMM. 
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0, license added, LL 8/5/19