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 National Academy of Engineering. The interpretations and conclusion 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 National Science Foundation, NEC Foundation of America, SBC Foundation, and Honeywell International, and the National Academy of Engineering Fund.