THE NATIONAL ACADEMIES PRESS
500 Fifth Street, NW Washington, DC 20001
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 material is based on work supported by the National Science Foundation under Grant No. DBI–0633909. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. government.
International Standard Book Number-13: 978-0-309-11249-9 (Book)
International Standard Book Number-10: 0-309-11249-4 (Book)
International Standard Book Number-13: 978-0-309-11250-5 (PDF)
International Standard Book Number-10: 0-309-11250-8 (PDF)
Library of Congress Control Number: 2007940783
Additional copies of this report are available from the
National Academies Press,
500 Fifth Street, NW, Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu.
Cover: Design by Francesca Moghari; artwork by Nicolle Rager Fuller (www.sayo-art.com).
Copyright 2008 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America