Note: According to copyright law, author's always retain the right to create derivative works, regardless of copyright ownership, under the fair use policy. For an entertaining explanation see this Fair(y) Use video.
Editorial: APS now leaves copyright with authors for derivative works
"When you submit an article to an APS journal, we ask you to sign our copyright form. It transfers copyright for the article to APS, but keeps certain rights for you, the author. We have recently changed the form to add the right to make 'derivative works' that reuse parts of the article in a new work. The importance of this change is discussed below."
To learn more about publisher policies that allow authors to rights such as posting their work to a web site or Digital Conservancy, visit the SHERPA reporting site http://www.sherpa.ac.uk/romeo/PDFandIR.html