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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 under grant EIA-9809120. Any opinions, findings,
conclusions, or recommendations expressed in this material are
those of the authors and do not necessarily reflect the views of
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