NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This study was supported by Lawrence Berkeley National Laboratory; Lawrence Livermore National Laboratory; Los Alamos National Laboratory; Pacific Northwest National Laboratory; Sandia National Laboratories; University of California, Berkeley; and University of California, Office of the President; and by Contract No. DE-AT01-04ER30319, between the National Academies and the Department of Energy. The views presented in this report are those of the authoring committee and are not necessarily those of the funding agencies.