At the proof stage, we will require you to read, sign, and return the Copyright Agreement. You will receive it from our production office (EDP Sciences). We cannot publish your article without this approval. The agreement should be signed by the corresponding author (who agrees to inform the co-authors, if any). If the corresponding author is a US Government officer or employee and prepared the article as part of their official duties, they do not own any copyright in it. If at least one of their co-authors is not a US Government employee, one of those non-government authors should sign the Copyright Agreement.