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 no. OCE-9729508), the National Institutes of Health (under purchase order no. 467-MZ-801699), the National Institute of Standards and Technology (under contract no. 43NANB909028), the National Aeronautics and Space Administration, the National Oceanic and Atmospheric Administration, and the United States Geological Survey (through the aforementioned National Science Foundation grant no. OCE-9729508), and the Department of Energy (under contract no. DE-FG02-96ER30277).

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