OCTOBER 1993 $3.95 Is Los Angeles winning the war on smog? Computers that mimic damaged brains. Vast lava flows that reshaped the earth. Video proofs, such as this one of a sphere being turned inside out, are transforming mathematics. Copyright 1993 Scientific American, Inc. October 1993 Volume 269 Number 4 32 Clearing the Air in Los Angeles James M. Lents and William J. Kelly The caustic brown smog that often veils the San Bernardino Mountains attests that the air quality in Los Angeles is still the worst in the U.S. Yet it obscures a remarkable achievement: during the past two decades, pollution has been cut dramatically—even as the city’s population and the number of automobiles clog- ging freeways soared. The cleanup is one that other cities might emulate. 42 Large Igneous Provinces Millard F. Co¤n and Olav Eldholm Periodically in the earth’s past, massive upwellings of magma have created vast el- evated plains, both on land and beneath the sea. Unlike the comparatively steady volcanism at the margins of continental plates, these powerful spasms occurred extremely rapidly in geologic time. Studies of these ancient lava flows indicate they may have profoundly altered the global climate and the course of evolution. 50 Evolutionarily Mobile Modules in Proteins Russell F. Doolittle and Peer Bork Like necklaces strung from beads, many proteins consist of discrete modules that have distinct structures and functions. Surprisingly, some of these individ- ual domains appear in animal and bacterial cells. Does that imply that they are ancient relics of their common ancestry? Not always, the authors contend; some of them may have jumped across species lines—and done so fairly recently. 58 Electrorheological Fluids Thomas C. Halsey and James E. Martin They are liquid until an electric current is applied; then they ooze like honey or solidify like gelatin—all in less time than the blink of an eye. The unusual properties of electrorheological fluids, first patented in 1947, have suggested applications ranging from automotive clutches to adaptive shock absorbers. Only now are technical impediments to commercialization being overcome. 68 Water-Pollinated Plants Paul Alan Cox With fickle currents and changing tides, water seems a poor vector to disperse the pollen of flowering plants. But some aquatic species have developed strate- gies that the mathematics of search theory proves to be quite e¤cient. These adaptations to exploit the physics of fluids enabled terrestrial plants to return to an aquatic environment and are classic examples of convergent evolution. Copyright 1993 Scientific American, Inc. 4 Scientific American (ISSN 0036-8733), published monthly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright © 1993 by Scientific American, Inc. All rights reserved. No part of this issue may be reproduced by any mechanical, photographic or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. Second-class postage paid at New York, N.Y., and at additional mailing offices. Authorized as second-class mail by the Post Office Department, Ottawa, Canada, and for payment of postage in cash. Canadian GST No. R 127387652. Subscription rates: one year $36 (outside U.S. and possessions add $11 per year for postage). Subscription inquiries: U.S. and Canada 800-333-1199; other 515-247-7631. Postmaster: Send address changes to Scientific American, Box 3187, Harlan, Iowa 51537. Reprints available: write Reprint Department, Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111, or fax: (212) 355-0408. 76 Simulating Brain Damage Geo›rey E. Hinton, David C. Plaut and Tim Shallice Certain injuries of the brain produce bizarre patterns of errors in reading. The same aberrations can be reproduced in computer models by damaging informa- tion pathways. Such simulations add support to current ideas about the nature of dyslexia and the way written language is processed in the brain. 84 Raising the Vasa Lars-Akeº Kvarning On a sunny day in 1628, the proudest addition to the navy of Sweden’s King Gustavus II Adolphus foundered just minutes into her maiden voyage. Today this magnificent, flawed vessel is the centerpiece of a museum in Stockholm. Here is the story of her 30-year-long salvage and painstaking restoration. 92 TRENDS IN MATHEMATICS The Death of Proof John Horgan, senior writer Mathematicians have always measured the progress of their search for truth in the precise language of the proof. But computers are putting a new spin on QED. No mere human can verify the accuracy of the enormous calculations in so-called computer proofs. Will mathematicians be forced to accept that their assertions are, at best, only provisionally true, true only until they are proved false? DEPARTMENTS 14 Science and the Citizen 8 Letters to the Editor The ease of elaboration.... Wealth and health.... Mauled anecdote. The toll of child labor.... A winning strategy.... Gene therapy as a can- 12 50 and 100 Years Ago cer treatment.... Nuclear subs for 1893: A remarkable experiment oceanographers.... Sharks get tu- that only a few could repeat. mors.... Art that evolves.... Jurassic viruses.... PROFILE: Twice Nobelist Frederick Sanger. 112 The Amateur Scientist Fluids that turn solid in a magnetic field. 104 Science and Business 114 Book Reviews Malthusian musings.... The ships Critical of CRADAs.... Is magnetic of Iberia .... Following the flu. resonance really safe?... The battery bottleneck .... Cordless elevators.... Impoverished elderly.... A gas meter 120 Essay : Richard Wassersug that listens to the flow.... THE ANA- The unstoppable human LYTICAL ECONOMIST: Pondering high- pilgrimage to the planets. tech fixes for developing nations. Copyright 1993 Scientific American, Inc. 5 THE COVER shows a scene from a comput- ® er-generated film of a sphere being turned inside out, or everted. The “video Proof,” which was produced at the Geometry Cen- Established 1845 ter in Minneapolis, Minn., is based on a topological theorem by William P. Thurston EDITOR: Jonathan Piel of the Mathematical Sciences Research In- BOARD OF EDITORS: Alan Hall , Executive Editor ; stitute (see “The Death of Proof,” by John Michelle Press, Managing Editor ; John Rennie, Horgan, page 92). The rules of topology al- Russell Ruthen, Associate Editors; Timothy M. low the skin of the sphere to be stretched Beardsley; W. Wayt Gibbs; Marguerite Holloway ; and twisted and even to pass through it- John Horgan, Senior Writer ; Philip Morrison, Book Editor ; Corey S. Powell; Philip E . Ross; Ricki self, but the eversion must be completed L. Rusting; Gary Stix; Paul Wallich; PhiliP M. Yam without the formation of a kink. ART: Joan Starwood, Art Director ; Edward Bell, Art Director, Graphics Systems; Jessie Nathans, Associate Art Director ; Nisa Geller, Photography Editor ; Johnny Johnson, Assistant Art Director, THE ILLUSTRATIONS Graphics Systems Cover illustration by the Geometry Center, University of Minnesota COPY: Maria-Christina Keller, Copy Chief; Nancy L. Freireich; Molly K. Frances; Daniel C. Schleno› Page Source Page Source PRODUCTION: Richard Sasso, Vice President, Production; William Sherman, Production Man- 32–33 Miguel L. Fairbanks (top, 76–77 Courtesy of Tim Shallice ager ; Managers: Carol Albert, Print Production; first six photographs), Ken Janet Cermak, Quality Control; Tanya DeSilva , Biggs/Tony Stone Images 78 Johnny Johnson (top), Prepress; Carol Hansen, Composition; Madelyn (top, last photograph), Boris Starosta (bottom) Keyes, Systems; Eric Marquard, Special Projects; Leo J. Petruzzi , Manufacturing & Makeup; Ad Edwin Maynard/The 79–82 Boris Starosta Tra¤c: Carl Cherebin Environmental Picture CIRCULATION: Lorraine Leib Terlecki, Circulation Library (bottom) 84–85 Courtesy of Vasa Director ; Joanne Guralnick, Circulation Promo- Museum, Stockholm 34–35 Jana Brenning tion Manager ; Rosa Davis, Fulfillment Manager ; Katherine Robold, Newsstand Manager 86–87 Jana Brenning (top), 36 Johnny Johnson Vasa Museum (bottom) ADVERTISING: Robert F. Gregory, Advertising Director. 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