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Typographical error

Posted by birkdiedenhofen on 10 Apr 2015 at 08:03 GMT

We are grateful to a careful reader who spotted a typographical error in the pdf including supporting information to our article. In the three formulae 4, 32, and 51, there should be a plus sign in front of the square root instead of a minus sign (there is no such error in the main article, though).

No competing interests declared.