This journal is copyrighted by the American Institute of Physics (AIP). Individual articles in this journal are copyrighted by the AIP, as indicated on each article. Original U.S. Government works are exempt from copyright.

Individual articles may be downloaded for personal use; users are forbidden to reproduce, republish, redistribute, or resell any materials from this journal in either machine-readable form or any other form without permission of the AIP or payment of the appropriate royalty for reuse.