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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.

Support for this project was provided by the National Science Foundation and the National Security Agency under sponsor award number CCR-0236725; the Office of Naval Research under sponsor award number N00014-03-1-0915; and the National Science Foundation, the National Security Agency, and the Federal Aviation Administration under sponsor award number CNS-0342801. Any opinions, findings, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the agencies and organizations that provided support for the project.

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