NOTICE: This publication has been reviewed according to procedures approved by a National Academy of Engineering report review process. Publication of signed work signifies that it is judged a competent and useful contribution worthy of public consideration, but it does not imply endorsement of conclusions or recommendations by the NAE. The interpretations and conclusions in such publications are those of the authors and do not purport to represent the views of the council, officers, or staff of the National Academy of Engineering.

Funding for the activity that led to this publication was provided by the Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Department of Defense–DDR&E-Research, National Science Foundation, Department of Homeland Security, General Electric, Microsoft Corporation, Cummins, Inc., John A. Armstrong, and other individual donors.