NEWSA Publication of The American Physical Society http://www.aps.org/apsnews

February 2003Volume 12, No. 2

12The BackPage:Meg Urry Speedingup the Long SlowPath to Change

Katepalli Sreenivasan, a distin-guished university professor ofphysics and mechanical engineer-ing at the University of Maryland,College Park, has been appointedas the new director for the AbdusSalam International Center forTheoretical Physics (ICTP) inTrieste, Italy. He succeeds retiringdirector Miguel Virasoro, who hasheld the post since 1993.

Founded in 1964 by Pakistaniphysicist Abdus Salam, the ICTP’smission is to provide opportuni-ties for physicists from developingcountries to interact with thosefrom developed countries, whileencouraging them to remain intheir home countries. Its contribu-tions to the international physicsenterprise include visiting pro-grams for international scholars,

Sreenivasan Is New ICTP Directorscientific workshops and confer-ences, remedial courses in scienceeducation, and distribution to de-veloping countries of scientificjournals, conference proceedings,and electronic databases. The Cen-ter houses a small but excellentpermanent scientific staff in highenergy physics, mathematics, con-densed matter and statisticalphysics, and physics of weatherand climate.

Known as “Sreeni” to friendsand colleagues, Sreenivasan re-ceived his education in India, firstat the University of Bangalore andthen at the Indian Institute of Sci-ence in Bangalore, where he earneda doctorate in aerospace engineer-ing in 1975. After two years ofpostdoctoral study in Sydney andNewcastle, Australia, he came to

See SREENIVASAN on page 2

the U.S. as a researcher at JohnsHopkins University. Later he be-came the Harold W. Cheelprofessor of mechanical engineer-ing and professor of physics,applied physics and mathematicsat Yale University. He moved toMaryland in January 2001, wherehe directs the university’s Institutefor Physical Science and Technol-ogy. His primary fields of researchare fluid dynamics and turbu-lence, and he has publishedextensively on these and otherrelated subjects.

“Sreeni is a world renowned ex-perimental physicist with anappreciation for theory and has adeep understanding of both thefrontier research enterprise andthe potential of intellectual talentin developing countries,” said Irv-ing Lerch, APS director ofinternational scientific affairs ofSreenivasan’s appointment. Itcomes at a particularly critical timein the Center’s 30-year history.Originally the operation of the in-stitute was the responsibility of theInternational Atomic Energy As-sociation (IAEA), with additionalsupport provided by UNESCOand the Italian government. Since1992, governing authority hasbeen transferred to UNESCO, andaccording to Lerch, withVirasoro’s retirement, UNESCO isconsidering the tightening of theICTP management. The implica-tions of the new policy remain tobe seen, but as the new director,Sreenivasan will play an importantrole in the future of the Center.

Furthermore, the Italian gov-

Physics AndTechnologyForefrontsProtein Folding,HIV and Drug Design.

10HHHHHighlightsighlightsighlightsighlightsighlights

Questioned Papers in PhysicalReview Journals Retracted

APS journals are printingretractions of six papers as aresult of the Lucent Technolo-gies/Bell Labs inquiry intomisconduct by Jan HendrikSchön. Two of the papers, pub-lished in Physical Review B, wereimplicated in the Lucent inves-tigation chaired by MalcolmBeasley of Stanford University.They were retracted with theagreement of all authors.

Four additional papers, pub-lished in Physical Review B andPhysical Review Letters, but notstudied by the Lucent investi-gation, were retracted with theagreement of all authors exceptSchön. Two papers, one that in-cluded Schön as a coauthor andthe other with Schön as the soleauthor, remain in the literatureafter the authors indicated thatthey do not wish to retractthem.

According to APS Editor-in-Chief Martin Blume, in view ofthe seriousness of the issue,APS felt it prudent to contactSchön and all of his living co-authors (one is deceased)about articles in APS journals,although only two of the eightarticles were explicitly dis-cussed in the Lucent report.Information from these coau-thor indicates scientificconcerns for all the retractedpapers. “Given the notoriety ofthis case, we felt that peopleought to know the status of all

Incoming ICTP Director Katepalli Sreenivasan (seated, center) meets at APSheadquarters with Executive Officer of APS and Secretary-General of IUPAPJudy Franz (left); Chair of the APS Committee on International ScientificAffairs Peter Barnes (right); and APS Director of International Affairs IrvingLerch (standing).

Photo credit: Laleña Lancaster

of the articles,” Blume says.All coauthors felt the papers

should be retracted. Schön de-clined to join in this statementexcept with regard to the two pa-pers mentioned in the Lucentreport. Given the preponderanceof evidence from the Lucent re-port and the opinions of Schön’scoauthor, the APS decided it wasin the best interests of the com-munity to report the fact thatthese articles are being retractedby most of the authors, while alsoreporting Schön’s contrary view.

Retractions will appear in up-coming print issues of the journalsand online versions will have no-tations to indicate the retractions.The online tables of contents andabstracts of the papers will in-clude a message with links to thefull text retractions.

The editors of the PhysicalReview journals have chosen toleave the retracted papers avail-able online as part of the researchrecord, just as they remain inarchived print copies of the jour-nal. However, online versions willappear with clear statements ofretraction and all papers affectedwill be accompanied by links tothe retractions. These notationswill appear so that researchers willbe able to see them regardless ofhow they navigate to the versionsof the papers online. “We do notwant to tamper with the archiveof published papers,” says Blume.

See RETRACTED on page 3

APS Member Gives MinorityScholarship Fund a Boost

The APS Corporate MinorityScholarship received a financialboost last year with the establish-ment of a trust fund yielding about$5,500 annually. AleksandarSvager, a professor emeritus atCentral State University (CSU) inOhio and long-standing APS mem-ber, had always planned toestablish a trust inhis name upon hisdeath, but financialadvisors at theGreene CommunityFoundation (also inOhio) convincedhim he could do sobefore then. Be-sides, “My doctorassures me I willlive,” he laughs.

Widowed threeand a half years ago,

Svager has also established a schol-arship fund in mathematics throughthe Dayton Foundation in honor ofhis late wife Chrysa, who was the firstfemale African-American to receivea PhD in math. The first three schol-arships were awarded last year. Thecouple worked together to encour-age more African-American students

to major in math andphysics since theyfirst met in 1964 atCSU, an historicallyblack universitywhere Chrysa was amath professor.They married oncommencement dayin 1968.

Svager discov-ered his giftfor teaching earlyon while still a stu-

dent in Sarajevo, Yugoslavia, tutor-ing those who were struggling withmath and science. He spent a littleover two years at the Nuclear Insti-tute of Zagreb, teaching at theuniversity there, and also taught atthe University of Sarajevo beforecoming to the U.S. in 1960 throughthe Institute for International Edu-cation. He earned his master’s degreein physics from Texas Christian Uni-versity. Eager to stay in the U.S. whenthe Yugoslavian government askedhim to return, but unwilling to placehis family and friends back home indanger by requesting political asy-lum, Svager did the next best thing:he took a faculty position with CSUand devoted himself to the teach-ing he loved, becoming chair of thephysics department a year later.

The most rewarding aspect of

For Some APS Prizes and AwardsCompetition Cuts Across All Fields’

Many APS prizes and awardsare given for contributions to spe-cific areas of physics research, buta few are open to all fields of phys-ics across the board. “While theseinclude some of the most presti-gious prizes that the APS awards,they are usually not publicized byindividual units and so it’s prob-ably a good idea to remind ourmembers about them in case theyknow of someone who deservesto be nominated” said Alan

Chodos, APS Associate ExecutiveOfficer.

Leading this list is the GeorgeGeorgeGeorgeGeorgeGeorgeE. VE. VE. VE. VE. Valley Prizealley Prizealley Prizealley Prizealley Prize, which, with a sti-pend of $20,000, carries thelargest monetary award of anyAPS prize. Founded with abequest from the estate of GeorgeE. Valley, Jr., it is given every otheryear, and will be awarded for thesecond time in 2003. Its purposeis “to recognize one individual,

See AWARDS on page 10

Aleksandar SvagerAleksandar SvagerAleksandar SvagerAleksandar SvagerAleksandar Svager See SVAGER on page 3

IN THIS ISSUE:PHYSICS NEWS

in 2002 Pages 4-9

2 February 2003 NEWS

APS News (ISSN: 1058-8132) is published 11Xyearly, monthly, except the August/September issue,by the American Physical Society, One PhysicsEllipse, College Park, MD 20740-3844, (301) 209-3200. It contains news of the Society and of itsDivisions, Topical Groups, Sections and Forums;advance information on meetings of the Society;and reports to the Society by its committees andtask forces, as well as opinions.

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APS COUNCIL 2003PresidentMyriam P. Sarachik*, City College of New York - CUNYPresident-ElectHelen R. Quinn*, Stanford University (SLAC)Vice-PresidentMarvin L. Cohen*, University of California, BerkeleyExecutive OfficerJudy R. Franz*, University of Alabama, Huntsville (on leave)Treasurer

Thomas McIlrath*, University of Maryland (emeritus)Editor-in-ChiefMartin Blume*, Brookhaven National LaboratoryPast-PresidentWilliam F. Brinkman*, Bell Labs-Lucent Technologies (retired)General CouncillorsJonathan A. Bagger*, Janet Conrad, Stuart Freedman*, FrancesHoule, Gerald Mahan, Margaret Murnane*, Cherry AnnMurray*, Philip Phillips*, Laura Smoliar, Jin-Joo Song

International CouncillorT. Maurice Rice

Chair, Nominating CommitteeSusan Seestrom

Chair, Panel on Public AffairsJohn Ahearne

Division, Forum and Section CouncillorsKate Kirby (Atomic, Molecular & Optical Physics), RobertEisenberg (Biological), Sylvia Ceyer (Chemical), AllenGoldman* (Condensed Matter Physics), Steven White(Computational), Harry Swinney (Fluid Dynamics), PeterZimmerman (Forum on Education), Stuart Wolf (Forum onIndustrial and Applied Physics),Gloria Lubkin (Forum onHistory of Physics), James Vary (Forum on International

Physics), Ed Gerjuoy (Forum on Physics and Society),Timothy P. Lodge, (Polymer Physics), J. H. Eberly(Laser Science), G. Slade Cargill*, III (Materials),Bunny C. Clark (Nuclear), Sally Dawson, Peter Meyers(Particles & Fields), Stephen Holmes (Physics ofBeams), James Drake (Plasma), Gian Vidali, (NewYork Section), Joe Hamilton (Southeast Section)ADVISORSRepresentatives from Other SocietiesCharles H. Holbrow, AAPT; Marc Brodsky, AIP

International AdvisorsHéctor O. Murrieta Sánchez, Mexican Physical Society,W. J. McDonald, Canadian Association of Physicists

Staff RepresentativesAlan Chodos, Associate Executive Officer; Irving Lerch,Director of International Affairs; Fredrick Stein, Directorof Education and Outreach; Robert L. Park, Director,Public Information; Michael Lubell, Director, PublicAffairs; Stanley Brown, Editorial Director; CharlesMuller, Director, Journal Operations; Michael Stephens,Controller and Assistant Treasurer

Administrator for Governing CommitteesKen Cole

* Members of the APS Executive Board

This Month in Physics HistoryThis Month in Physics HistoryThis Month in Physics HistoryThis Month in Physics HistoryThis Month in Physics HistoryFebruary 1987: Discovery of Supernova 1987A

On February 23, 1987,Canadian astronomer IanShelton (then with the Univer-sity of Toronto) was engaged inwhat he thought was merelyroutine work at the LasCampanas Observatory in Chile,taking a telescopic photo of asmall galaxy 167,000 light-yearsfrom Earth called the Large Ma-gellanic Cloud. But when hedeveloped the photographicplate, he noticed an extremelybright star that he had not seenin previous observations of thesame area: a star of about thefifth magnitude. He realized thatit was not a new star, but an ag-ing massive star that had blownapart in a supernova explosion.

Data taken by a small tele-scope aboard the InternationalUltraviolet Explorer (IUE) satel-lite helped astronomers identifythe exploding star’s location asSanduleak -69° 202, the formersite of a blue supergiant about20 times the mass of the sun.They named the exploding starSupernova 1987A. Astrono-mers believe the star swelled upto become a red supergiant,puffed away some of its mass,and then contracted andreheated to become a bluesupergiant. In less than a sec-ond, the star’s core collapsed,and a wave of neutrinos heatedthe inner core to 10 billiondegrees. The process triggereda shock wave that ripped the starapart, propelling a burst of neu-trinos into space.

Supernova 1987A is the clos-est supernova to have explodedin modern times, and the bright-est since Johannes Keplerobserved a supernova in 1604in the Milky Way Galaxy; it is alsothe first supernova visible to thenaked eye since 1885. In addi-tion, research over the last 15years has yielded a wealth of newobservational data that hasprovided astronomers with un-precedented insight into theprocesses that govern stellarbodies.

By May 1987, the IUE teamhad discovered an abundanceof chemical elements in the su-pernova debris, indicating thatthe progenitor star had alreadypassed through the red giantphase, and verifying the origi-

nal theory. By July, a Japanese sat-ellite and West German telescopedetected x-rays emanating fromthe debris. And from August toNovember, several other researchmissions detected high-energygamma rays, typically released inthe decay of radioactive elementsformed in nuclear reactions at thecore of a dying star. The data con-firmed a widely held theory thatsupernovas produce the heavychemical elements that make upmost of the matter on Earth.

Two years later, optical obser-vations in La Silla, Chile, showed abright ring around the Supernova,an observation that was con-firmed a year later by the FaintObject Camera aboard the newlydeployed Hubble Space Telescope.Since its discovery, the remnantfrom Supernova 1987A has beenexpanding. Its rings are thought tobe parts of shells of gas ejected bythe star long before the explosion.In May 1997, Hubble’s imagingspectrograph produced a detailedultraviolet image of the inner ring,identifying specific gases such asoxygen, nitrogen, hydrogen andsulfur, which astronomers hopewill help them assemble a pictureof how the ring was created.

Radio waves were detected fortwo weeks after the supernovawas first observed, but in 1990,scientists at the Australia TelescopeNational Facility detected rapidlybrightening radio emissions, whichthey traced to an area that liesbetween the ring and the glowingdebris of the supernova at its cen-ter, where the most rapidly movingdebris is crashing into gas. Twoyears later, the ROSAT satellitedetected rapidly brighteningx-rays from the supernova, com-ing from the same collision area as

the radio waves.In May 1994,

Hubble revealed twoadditional loops ofglowing gas. In Janu-ary 1997, it showedtwo blobs of debrisin the Supernova’scenter racing awayfrom each other atnearly 6 million mph.Later that year, as-tronomers made thefirst measurementsof the fast-movinggas ejected by the su-

pernova explosion—gas thathad been invisible until Hubble’simaging spectrograph enabledscientists to observe it in ultra-violet light.

The collisions were predictedby theory, and expected tooccur sometime between 1995and 2010, as the ring absorbedthe full force of the crash. Whilethe radiation from the originalexplosion traveled out at thespeed of light, material from thestar itself was ejected at a muchlower speed, and was only nowcatching up and colliding withmaterial blown out some 20,000years earlier by the star. The col-lision caused the gases in the ringto glow as they heated to mil-lions of degrees, compressed bya blast wave estimated to bemoving at 40 million mph.

As recently as February2000, Supernova 1987A was stillyielding surprising discoverieson stellar processes. New imagestaken by Hubble revealed fourbright new knots of heated gasin an area that had been fadingslowly for a decade. This was sig-nificant because the hot spotswere not confined to a singlelocation, but distributed aroundthe circumstellar ring, indicatingthat a large fraction of the ejectedmaterial was finally colliding withthe entire ring, marking thebeginning of the formation of aSupernova remnant. Astrono-mers hope that the light from thecollisions will illuminate mattersurrounding the Supernova thatuntil then had been invisible,providing useful information onthe true structure of the gasaround the Supernova, andenabling them to determine howit might have gotten there.

SREENIVASAN from page 1

ernment is by far the largest finan-cial supporter of the ICTP, andLerch believes that “there is a realdanger that the Center will be ab-sorbed into the Italian institutionalsystem and lose its original pur-pose.” Sreenivasan, however, doesnot anticipate such an occurrence,since thus far the ICTP has beenleft autonomous. “Everyone recog-nizes that the Center is trulyscientific in nature,” he says. “It’sworked very well thus far andthere is no reason to change itnow.” His focus will be onimprovements in management, arenewed commitment to theCenter’s original mission, andachieving greater reknown for thequality of the scientific researchdone at the Center.

Sreenivasan also takes the helmin a radically changed internationalclimate in the aftermath of the ter-rorist attacks of September 11,2001, with much harsherrestrictions on travel and more dif-ficulty in acquiring visas to travelto other countries, even forscientific exchange. However,Sreenivasan, a self-described opti-mist at heart, also believes that thetragedy has had a positive impactin terms of fostering the notion ofan international community. “Ithink people have a greater under-standing about why it is importantto engage the rest of the world insome constructive way in order tobe at peace ourselves,” he said.“We recognize better now thatevents occurring on the other side

of the world can affect us here inthe U.S.”

In fact, it was the chance tomake a difference internationallyand give something back to theworld physics community that at-tracted Sreenivasan to the post,despite the personal sacrifices as-sociated with accepting it. It meansnot only a substantial reduction insalary, but also the necessity of leav-ing his wife, a psychiatrist, andteenaged son in New Haven,Connecticut, at least until his soncompletes high school. “I am fromone such developing country andI was received in the U.S. sciencecommunity very well; I spent manyyears on the receiving end,” he said.“I have done my best to createopportunities for others in turn, butthis is an opportunity where thescope is substantially larger.”

“I have always viewed physicsas a unifying feature among themany divisions we have as humanbeings, bringing together physi-cists of different cultures, origin,background and economicprogress,” he said. “And perhapsmany will act as ambassadors forthis grand notion of a unifiedworld.” His belief in, and commit-ment to, the unity of physics is evenreflected in his title: in addition tobeing director, he will also be theAbdus Salam professor. “I thoughtit would be nice to have an Indianwith the title of a Pakistani profes-sorship,” he said. “I hope it is asymbol I can carry forward in mywork with the ICTP.”

NEWSCoden: ANWSEN ISSN: 1058-8132

Series II, Vol. 12, No. 2February 2003

©2003 The American Physical Society

Editor ............................................................................................................ Alan ChodosAssociate Editor .................................................................................... Jennifer OuelletteSpecial Publications Manager .................................................. Elizabeth Buchan-HigginsDesign and Production ..................................................................... Stephanie JankowskiForefronts Editor ..................................................................................... Neville ConnellProofreader ..................................................................................................... Edward Lee

Physicists Honored at Southeastern Section Meeting

From left to right: Paul Cottle, Myron McCay, and Raymond Flannery. Threemembers of the Southeastern Section of the American Physical Society were pre-sented awards for outstanding contributions to physics in the region at the annualmeeting held October 31 – November 2, 2002, at Auburn University. Professor PaulCottle, Florida State University, received the George B. Pegram Award: “For hisoutstanding university teaching, and his untiring efforts and innovative programs tohelp K-12 science teachers.” Professor Emeritus Myron McCay, University of Ten-nessee at Chattanooga received the Francis G. Slack Award: “For his contributionsto the Southeastern Section of the American Physical Society, and physics educationin the South.” Professor Raymond Flannery, Georgia Institute of Technology, re-ceived the Jesse W. Beams Award: “For his pioneering, seminal, influential andenduring contributions to Atomic and Molecular Collision Physics.”

The nebula of SuperNova 1987A photograhed in 2002.

February 2003 3NEWS

Scaling Theory of Localization: Absence of Quantum Diffusionin Two Dimensions(E. Abrahams, P. W. Anderson, D. C. Licciardello, and T. V. Ramakrishnan, Phys. Rev. Lett. 42 (1979) 673), 2446 citations

NUMBER SEVEN

Top 10 (±2) Physics Pick-Up Lines(in randomized order)by the University of Wisconsin-River Falls Society of Physics Students

1). Y1). Y1). Y1). Y1). You x Me = Loveou x Me = Loveou x Me = Loveou x Me = Loveou x Me = Love

2). I want to sum the forces to your heart!2). I want to sum the forces to your heart!2). I want to sum the forces to your heart!2). I want to sum the forces to your heart!2). I want to sum the forces to your heart!

3). What’3). What’3). What’3). What’3). What’s a nice girl/guy like you doing in a n-dimensional space like this?s a nice girl/guy like you doing in a n-dimensional space like this?s a nice girl/guy like you doing in a n-dimensional space like this?s a nice girl/guy like you doing in a n-dimensional space like this?s a nice girl/guy like you doing in a n-dimensional space like this?

4). Let’4). Let’4). Let’4). Let’4). Let’s take a ride down the Quantum Ts take a ride down the Quantum Ts take a ride down the Quantum Ts take a ride down the Quantum Ts take a ride down the Quantum Tunnel of Love!unnel of Love!unnel of Love!unnel of Love!unnel of Love!

5). The reduced 5). The reduced 5). The reduced 5). The reduced 5). The reduced χχχχχ5 of your beauty is zero compared to the theoretical model! of your beauty is zero compared to the theoretical model! of your beauty is zero compared to the theoretical model! of your beauty is zero compared to the theoretical model! of your beauty is zero compared to the theoretical model!

6). I’m trapped in the potential well of your gaze!6). I’m trapped in the potential well of your gaze!6). I’m trapped in the potential well of your gaze!6). I’m trapped in the potential well of your gaze!6). I’m trapped in the potential well of your gaze!

7). love; i 7). love; i 7). love; i 7). love; i 7). love; i ===== me, j me, j me, j me, j me, j ===== you you you you you δ δ δ δ δ

if if if if if =====

0 0 0 0 0 : i : i : i : i : i ===== me, j me, j me, j me, j me, j ===== you you you you you

8). Y8). Y8). Y8). Y8). Your love is at my fundamental frour love is at my fundamental frour love is at my fundamental frour love is at my fundamental frour love is at my fundamental frequency!equency!equency!equency!equency!

9). In the integrated circuit of our relationship, there are no resistors, only capacitors!9). In the integrated circuit of our relationship, there are no resistors, only capacitors!9). In the integrated circuit of our relationship, there are no resistors, only capacitors!9). In the integrated circuit of our relationship, there are no resistors, only capacitors!9). In the integrated circuit of our relationship, there are no resistors, only capacitors!

10). Y10). Y10). Y10). Y10). Your our our our our ΒΒΒΒΒ aligns my spin towar aligns my spin towar aligns my spin towar aligns my spin towar aligns my spin toward you, babe!d you, babe!d you, babe!d you, babe!d you, babe!

11). The size of my love creates a gravitational field that attracts only you!11). The size of my love creates a gravitational field that attracts only you!11). The size of my love creates a gravitational field that attracts only you!11). The size of my love creates a gravitational field that attracts only you!11). The size of my love creates a gravitational field that attracts only you!

12). I want you to diagonalize my inertia tensor!12). I want you to diagonalize my inertia tensor!12). I want you to diagonalize my inertia tensor!12). I want you to diagonalize my inertia tensor!12). I want you to diagonalize my inertia tensor!

The seventh paper in our list of theten most cited Physical Review Let-ters revolutionized understanding ofthe electrical properties of materialsin certain, important regimes. APSNews interviewed three of the paper’sauthors, and some of their thoughtsare reprinted below.

Elihu Abrahams is the BernardSerin Professor of Physics (emeritus)at Rutgers, Nobel Laureate PhilipAnderson is the Joseph Henry Pro-fessor of Physics (emeritus) atPrinceton, and T. V. “Rama”Ramakrishnan is a newly elected Fel-low of the Royal Society and a physicsprofessor at the Indian Institute ofScience in Bangalore. DonaldLicciardello left Princeton shortlyafter the publication of the ScalingTheory of Localization PRL to foundPrinceton Telecom, and was notavailable for an interview.

APS News:APS News:APS News:APS News:APS News: What are the impor-tant findings in your 1979 PRL?

Abrahams:Abrahams:Abrahams:Abrahams:Abrahams: There were two signifi-cant results from our paper. One isthe new conclusion that in a two-dimensional, disordered electronicsystem (i.e. defects are present)where the electrons do not interact

This is the fourth in a seriesof articles by James Riordon.The first article appeared in theNovember 2002 issue. Thearticles will be archived under“Special Features” on the APSNews online web site.

with each other (or the interaction,for some reason, can be neglected)the ground state, which is the stateat zero temperature, is always insu-lating. Thus, there are no truemetallic states in two-dimensions.The other important conclusion isthat in dimensions greater than two,where you could have a metal-insu-lator transition by changing someparameter (such as the degree ofdisorder), the transition is continu-ous. This means that, as you passfrom metal to insulator at zero tem-perature, the conductivity goescontinuously to zero, rather thanjumping from some minimum valueto zero.

APS News:APS News:APS News:APS News:APS News: Why has the paperacquired so many citations?

Ramakrishnan: Ramakrishnan: Ramakrishnan: Ramakrishnan: Ramakrishnan: The initial atten-tion was I think due to the fact thatwe made experimentally testable,unusual predictions based on a newquantum, many-body, interferenceprocess; one which explored theprocess of localization, i.e. thenature of transition from a metal toinsulator. At that time (1978-79), thequestion of the nature of this transi-tion and its experimentalmanifestations was beginning to at-tract a lot of attention, since itrepresents a total change in thenature of electronic states (fromextended to localized) not as aresult of binding to a strong enoughattractive potential as in one-elec-tron quantum mechanics, but as aconsequence of increasing disorder.

Abrahams:Abrahams:Abrahams:Abrahams:Abrahams: In recent years, the ex-perimental discovery of whatappear to be metallic states at zerotemperature in 2-D systems has re-sulted in many experimental andtheoretical papers which also refer-ence our earlier work.

APS News: APS News: APS News: APS News: APS News: What led you to studythis particular problem?

Anderson:Anderson:Anderson:Anderson:Anderson: It was partly a lecture Igave in an advanced course whichset me thinking, plus a lunch tableconversation with Rama andAbrahams, where Rama recalledsome puzzling old work which wegeneralized. We were all aware of SirNeville Mott’s idea [regarding resis-tivity and disorder] and experimentaldata confirming it, and Licciardellohad written a paper with Thoulesswhich kind of foreshadowed scaling.

Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan: . . . Anderson hadshown, in a famous paper publishedin 1957, that if the medium in whichthe electron moves is sufficiently dis-ordered, the electronic state isspatially localized and is not ex-tended throughout the system (freeelectron ).The system is then an in-sulator. For small disorder, oneintuitively feels that the system is ametal with a small residual resistivity.What is the nature of the transitionfrom metal to insulator as disorderis increased? There was a very sig-nificant conjecture with considerableexperimental support, due to SirNeville Mott which went as follows:as disorder increases, the residual re-sistivity continues to increase to a

maximum value (which he estimated)and then, for a slightly larger disor-der, one has an insulator with aninfinite resistivity (at T=0). Thisfocused attention on the fact thatnone of the theories of localizationat that time calculated a physicallymeasured quantity such as resistiv-ity; they concentrated on whetherthe state was localized or not, e.g. bytrying to calculate the localizationlength, or asking whether an elec-tron in the random medium diffusedaway or not.

APS News:APS News:APS News:APS News:APS News: Were you surprisedby the theoretical results of thework?

Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan: Yes, very much so.We had uncovered a new quantummechanical process of interferencebetween paths for the electron start-ing and ending at the same point,diffusing through the randommedium, but in opposite directions.This is the localizing process whichincreases the amplitude for an elec-tron to come back where it started.It leads to a nonclassical scale-dependent resistivity and is behindthe unexpected result that there areno metals in two dimensions, at ab-solute zero.

Anderson: Anderson: Anderson: Anderson: Anderson: No, it seemed to fitright in with what we knew orguessed.

APS News: APS News: APS News: APS News: APS News: How has your careerbeen affected by being the author ofsuch a highly cited paper? Has it lim-ited your options as a researcher?Has it expanded them?

Abrahams:Abrahams:Abrahams:Abrahams:Abrahams: Briefly—it was goodfor the career, hasn’t limited researchoptions and expanded them some-what.

Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan:Ramakrishnan: It was a wonder-ful experience, especially after thediscovery of the localizing process,to take part in the creative interac-tion between theory andexperiment, and to realize the vari-ety of new phenomena which‘emerge’ from a new idea.

Anderson:Anderson:Anderson:Anderson:Anderson: This is my nth highlycited paper so it couldn’t make thatmuch difference. It was a little im-portant to me because it bolsteredmy self-confidence at that particu-lar time. I had read things abouthow the Nobel prize would destroymy productivity, which I now knowis hogwash—it depends on whatyou want to do, and I wanted to goon producing physics. But I alsowrote a highly cited paper, moreimportant than this one, in 1977(TAP, or Thouless-Anderson-Palmer), and continued to doimportant physics until now.

APS News:APS News:APS News:APS News:APS News: Is there anything elseyou’d like to say?

Anderson:Anderson:Anderson:Anderson:Anderson: I was delighted withthe prominence of this paper be-cause El Abrahams had beenimportant in following up my origi-nal localization work and hadn’tbeen recognized for it, and just foralphabetical reasons we put himfirst—he, Rama and I contributedpretty equally. Another nice thingwas that it was followed by a spateof work worldwide which was verycooperative and collegial, with ev-eryone cooperating with everyoneelse - Russians, Japanese, Germans,Americans, Indians and others. Itwas a marvelous contrast to whathas happened with other discov-eries.

“It will say in red ‘retraction.’ It’s likea scarlet letter.”

The retractions also link to thefull text of the Beasley report,which Lucent has given the APSpermission to mirror at a perma-nent web address associated withthe journals. It is available at http:/

/publish.aps.org/reports/. In thepast, Schön has denied committingmisconduct, saying only that hemade “mistakes.”

A full list of the Physical Reviewpapers in question can be foundin the online version of this articleat http://www.aps.org/apsnews .

RETRACTED from page 1

teaching for Svager is the oppor-tunity to make a real differencein students’ lives. Although CSU’sphysics department is small, it hasproduced around 40 physicsmajors since Svager first joinedthe faculty, all but five of themAfrican-American. Of those 40,30 went on to receive master’s de-grees in various fields, and fiveeventually earned PhDs, three inphysics.

But Svager’s favorite storyconcerns a young female studenthe tutored while still at TexasChristian University, the daugh-ter of his next-door neighbors,

SVAGER from page 1

who was majoring in math. Sheended up earning a double de-gree in math and physics,ultimately earning a PhD in phys-ics. On the day she graduated,she presented Svager with twogifts: a set of Cross pens, and asigned form to drop her physicscourse. It turned out she hadbeen planning to drop physicswhen Svager offered to tutor her,“but because of me, she decidedto double major,” he said. “So Iknew I could make a difference.”And he continues to do so todaywith his support of the Society’sMinority Scholarship program.

Physics News in 2002

INTRODUCTION

ASTROPHYSICS

TABLE OF CONTENTSPhysics News in 2002 is a summary of physics highlights compiled from items appearing in theweekly newsletter Physics News Update of the American Institute of Physics (AIP). Many of theentries appearing here were also published in Physics Today magazine, where they were editedfurther by Stephen Benka. Readers should keep in mind that because of the way Physics NewsUpdate itself is prepared (short items aimed primarily at science journalists) and because oflimited space in Physics News in 2002, some fields of physics research might be under-representedin this compendium. Readers can get a much wider view of the year’s top physics research bygoing to the Physics News Update website at http://www.aip.org/physnews/update or APS’s PhysicalReview Focus website at http://focus.aps.org/. The material appearing under the headline “Highlightsof Science Policy and Budget Developments in 2002” on page 9 is a compendium from theelectronic news service FYI produced by the Media and Government Relations Division of theAIP. See http://www.aip.org/enews/fyi/ .

Astrophysics .............................................................. 4

Atomic, Molecular, and Optical Physics .................. 4

Biological Physics ..................................................... 5

Condensed Matter, Materials Physics....................... 6

Particle, Nuclear, and Plasma Physics...................... 7

Other Physics Highlights .......................................... 8

Highlights of Science Policy and Budget ................. 9POLARIZAPOLARIZAPOLARIZAPOLARIZAPOLARIZATION IN THE COSMIC MICROWTION IN THE COSMIC MICROWTION IN THE COSMIC MICROWTION IN THE COSMIC MICROWTION IN THE COSMIC MICROWAAAAAVE BACKGROUNDVE BACKGROUNDVE BACKGROUNDVE BACKGROUNDVE BACKGROUND has been measured.

The most fundamental properties of the CMB — which can reveal conditions in the universewhen it was only about 400,000years old—are its frequencyspectrum and its angular powerspectra of both temperature andpolarization fluctuations.According to the modern theoryof cosmology, the CMBmicrowaves received anorientation (polarization) justbefore the seething plasma thatpervaded the cosmos in that earlyera finally became a neutral,transparent gas. Until now, the lowlevel of polarization had allowedthat quantity to escape detection.Using the Degree Angular ScaleInterferometer detector situatedat the South Pole, a group fromthe University of Chicago and theUniversity of California, Berkeley,has acquired and analyzedenough high-quality data toactually see the CMB polarization. The observed value is consistent with predictions andthus strongly validates the underlying theory. (J. Kovac et al., preprint available at http://arXiv. org/abs/astro_ph/0209478.)

JUPITER’S MAGNETOSPHEREJUPITER’S MAGNETOSPHEREJUPITER’S MAGNETOSPHEREJUPITER’S MAGNETOSPHEREJUPITER’S MAGNETOSPHERE has been simultaneously sampled by two spacecraft,Galileo (already on patrol in the Jupiter system) and Cassini-Huygens (headed toward Saturn).Just as Cassini was approaching Jupiter in January 2001,other Earthbound observatories, including radiotelescopes and the Hubble (optical) and Chandra(x-ray) satellites, were turned to the giant planet. TheSun also cooperated: Three interplanetary shock wavesin the solar wind swept by. The two spacecraft caughtJupiter’s magnetosphere in the act of being compressed.That compression produced strong electric fields andtherefore particle accelerations, which brightenedJupiter’s auroras. Internal magnetospheric dynamicscaused other observed auroral brightenings and a windof neutral atoms—formed from ions spewed by Io’svolcanic eruptions—sent outward against the incomingsolar wind. Such energetic neutral atoms had not beendirectly observed before. The flyby also provided thefirst opportunity to observe electrons above 50 MeVtrapped in Jupiter’s radiation belts. Shown here is thesynchrotron radiation from those electrons, with a superimposed Hubble image of Jupiter.(Seven articles in Nature 415415415415415, 985, 2002.)

A YOUNG EVOLA YOUNG EVOLA YOUNG EVOLA YOUNG EVOLA YOUNG EVOLVING PLANETVING PLANETVING PLANETVING PLANETVING PLANETARARARARARY SYSTEMY SYSTEMY SYSTEMY SYSTEMY SYSTEM has been seen. A star much like our Sunwhen it was only 3 million years old has been winking at astronomers from a distance ofabout 2400 light years for the past five years. Every48.36 days, the star suddenly dims to a smallpercentage of its normal brightness for about 18days. The duration and depth of these periodicoccultations, discovered by William Herbst andhis colleagues at Wesleyan University inConnecticut, had not been seen before. Eighteendays is much too long for occultation by a loneplanet in a 48-day orbit. The observations’ mostlikely explanation, put forth by Herbst at a meetingat the Carnegie Institution of Washington in June2002, is that a collection of dust grains, rocks,and perhaps asteroids is strung out in a clumpyarc of an orbiting circumstellar disk, with a largerobject like a protoplanet shepherding the material.Now, with a worldwide collaboration watching the star continually, the Wesleyan group has

found evidence that the orbital period is, in fact, 96.72 days: The star is being occulted bytwo separate clumpy regions on opposite sides of the disk. Theoretical models indicate thata single shepherding object could account for both clumps. The 97-day period indicates thatthe ringlike disk is about as far away from the star as Mercury is from the Sun. Thecollaboration has also seen the system changing slightly on a scale of months and years, thustantalizing astronomers with the prospect of viewing planetary evolution in real time. (W.Herbst et al., http://www.astro.wesleyan.edu/kh15d/)

SPIRAL ARMS, COSMIC RASPIRAL ARMS, COSMIC RASPIRAL ARMS, COSMIC RASPIRAL ARMS, COSMIC RASPIRAL ARMS, COSMIC RAYS, AND ICE AGESYS, AND ICE AGESYS, AND ICE AGESYS, AND ICE AGESYS, AND ICE AGES. Most cosmic rays (CRs) are thoughtto originate in supernovae, and most supernovae occur in the wake of galactic spiral densitywaves. Nir Shaviv of the University of Toronto and Jerusalem’s Hebrew University has developeda new CR diffusion model that includes the presence of arms. Not surprisingly, he found thatthe CR flux at Earth would vary with time and be correlated with our Solar System’s passagethrough galactic spiral arms as we circumnavigate the Milky Way. He then looked at a historicalrecord of CR flux, in the form of 42 age-dated iron meteorites whose exposures to CRs couldbe determined. He found a periodicity of 143 million years in the CR flux, which he attributesto passages through spiral arms. On the assumption that CRs ionize Earth’s lower atmosphereand can thus influence climate, Shaviv next looked at the geologic record for ice ages andfound “a compelling correlation” of both period and phase between CR flux and glaciationepochs during the past billion years. Between 1 and 2 billion years ago, there is no evidencefor any ice age, consistent with a slowed star-formation rate during that period of ourgalaxy’s history. Shaviv says that the weakest link in his analysis is the uncertainties in theglaciological record. (N. J. Shaviv, Phys. Rev. Lett. 8989898989, 051102, 2002.)

NEW COSMOLOGICAL UPPER LIMIT ON NEUTRINO MASSNEW COSMOLOGICAL UPPER LIMIT ON NEUTRINO MASSNEW COSMOLOGICAL UPPER LIMIT ON NEUTRINO MASSNEW COSMOLOGICAL UPPER LIMIT ON NEUTRINO MASSNEW COSMOLOGICAL UPPER LIMIT ON NEUTRINO MASS. Recent neutrinoresults imply that one or more of the three neutrino flavors (electron, muon, and tau neutrinos)have some mass (see Physics Today, July 2002, page 13). Considering the number of neutrinosloose in the universe, even a small mass means they will have significantly influenced thedevelopment of galaxies. Various physics experiments have established an upper limit of 3eV for the electron neutrino and whopping upper limits in the MeV range for the muon andtau neutrinos. Now, a worldwide collaboration of astronomers has looked at the distributionof 250,000 galaxies in the 2 Degree Field Galaxy Redshift Survey and measured large-scalestructure statistics in the form of a power spectrum. They compared the data with calculatedpower spectra using a model that included baryons, cold dark matter, massive neutrinos(hot dark matter), and a cosmological constant. The model had a few reasonable assumptions—for example, that all three types of neutrinos drop out of thermal equilibrium at the sametemperature and that the spectrum of primordial fluctuations from which galaxies evolved isscale-independent—and an appropriate treatment of previously measured cosmologicalparameters. The group then arrived at two big conclusions: Neutrinos can account for nomore than 13% of the matter in the universe, and the sum of all three neutrino masses is nomore than 2.2 eV. Group members Oystein Elgaroy and Ofer Lahav say that this is the bestupper limit for neutrino mass derived with relatively conservative assumptions on cosmologicalparameters. (Elgaroy et al., Phys. Rev. Lett. 8989898989, 061301, 2002.)

QUAOARQUAOARQUAOARQUAOARQUAOAR is the provisional name for a large, newly discovered planet like inhabitant ofour solar system. First spotted on 4 June 2002, Quaoar (pronounced KWAH-o-wahr) lives inthe Kuiper Belt debris zone beyondNeptune’s orbit. Its diameter of 1250 kmis about half that of Pluto, and its distanceof 42 astronomical units from Earth is farbeyond Pluto’s current distance of about30 AU. (One AU is the mean distance ofEarth from the Sun, about 150 millionkilometers.) Caltech scientists announcedthe finding in October at the meeting ofthe division for planetary sciences of theAmerican Astronomical Society, held inBirmingham, Alabama. (Abstract 9.04, Bull.AAS 3434343434(3), 2002. Also see http://www.gps.caltech.edu/~chad/quaoar.)

Synchrotron radiation around Jupiter.

An artist’s rendition illustrates a possibleconfiguration of a young evolving planetarysystem (Courtesy, Geoffrey Bryden, JPL.)

An image of the intensity and polarization of the cosmicmicrowave background radiation made with the DegreeAngular Scale Interferometer (DASI) telescope. The smalltemperature variations of the cosmic microwave backgroundare shown in false color, with yellow hot and red cold.(Courtesy DASI collaboration.)

ATOMIC, MOLECULAR, AND OPTICAL PHYSICS

STORAGE RING FOR NEUTRAL ASTORAGE RING FOR NEUTRAL ASTORAGE RING FOR NEUTRAL ASTORAGE RING FOR NEUTRAL ASTORAGE RING FOR NEUTRAL ATOMSTOMSTOMSTOMSTOMS. Generally, a storage ring not only storescharged particles but also defines their energy and trajectory; particles with the wrong

4

Physics News in 2002

ELECTRICAL BIOSENSORS FOR INDIVIDUAL LIVING CELLSELECTRICAL BIOSENSORS FOR INDIVIDUAL LIVING CELLSELECTRICAL BIOSENSORS FOR INDIVIDUAL LIVING CELLSELECTRICAL BIOSENSORS FOR INDIVIDUAL LIVING CELLSELECTRICAL BIOSENSORS FOR INDIVIDUAL LIVING CELLS were described at theMarch 2002 meeting of the American Physical Society. Cells are complex networks ofinteracting molecules, and are usually studied with optical techniques. Electricalmeasurements, however, can provide complementary information. Toward that end, LydiaSohn of Princeton University described several new biosensors. With one, she measured theamount of DNA in a single living cell passed through a small fluid chamber between twometal electrodes. The cell changed the system’s capacitance in a way that reflected theamount of the cell’s negatively charged DNA but not its other ions. Sohn reported that thetechnique can identify the stage of a cell’s development (since cells can contain differentamounts of DNA at different stages) and can potentially distinguish cancerous cells fromhealthy ones. Sohn also described a biosensor that can detect small amounts of a specificprotein in live E. coli cells. The eventual goal of Sohn’s lab is to take inventory of a living cell’sprotein contents—something that cannot be done with current protein assay techniques,which require the destruction of cells. (More information at http://www.aps.org/meet/MAR02/baps/vpr/layf7-003.html.)

NOISE CAN IMPROVE HUMAN BALANCE CONTROLNOISE CAN IMPROVE HUMAN BALANCE CONTROLNOISE CAN IMPROVE HUMAN BALANCE CONTROLNOISE CAN IMPROVE HUMAN BALANCE CONTROLNOISE CAN IMPROVE HUMAN BALANCE CONTROL, to the point that it may enableelderly subjects to steady themselves as well as their young counterparts, researchers in NewEngland have demonstrated. Noise, in this case, refers to random mechanical vibrationsapplied to the feet. In physics, noise denotes any random or seemingly useless fluctuation.Static on a radio station, peripheral conversations in a crowded room, and flashing neonlights along a busy thoroughfare all tend to obscure or distract one from receiving the

energy simply fly away from their magneticallyguided route. Neutral atoms don’t have a netcharge for magnets to act on, but they canhave a net magnetic dipole moment. If theatom moves slowly enough, its dipole issufficient for magnetic guidance, and severalsuch neutral atom guides have already beenbuilt. Physicists at Georgia Tech have now builta ring only 2 cm across, consisting of twoconcentric current-carrying wires, separatedby 840 mm. They also built a wire “funnel” totransfer neutral rubidium atoms from amagneto-optic trap to the ring, where theatoms moved at only 85 cm/s, correspondingto kinetic energies of about 100 neV. The researchers thus dubbed their device the “Nevatron.”The image shows an atom cloud after having completed two full circuits between the tworing wires. So far, swarms of 1 million atoms have made as many as 10 circuits around thering. The physicists are extending the work to include ring-based atom interferometry andcold-beam generation. (J. A. Sauer, M. D. Barrett, M. S. Chapman, Phys. Rev. Lett. 8787878787, 270401,2001.)

A DENDRIMER LASERA DENDRIMER LASERA DENDRIMER LASERA DENDRIMER LASERA DENDRIMER LASER has been demonstrated. A conventional dye laser uses fluorescingdye molecules as the active medium. When excited with an external laser, the molecules emita range of wavelengths that are then tuned by the dye-laser cavity. In most dye lasers, the dyeconcentration cannot go above amillimole/liter without quenching thefluorescence. Now, scientists at theCommunications Research Laboratory inJapan and PRESTO Japan Science andTechnology Corp have achieved lasingwith a dye concentration of 9 mmol/l byencapsulating the dye molecules at theheart of hyperstructured, tree-shapedpolymers called dendrimers. As the dyeconcentration increased within the newdendritic high-gain medium, the laseroutput also increased while the lasingthreshold decreased. Furthermore, theresultant spectral linewidth was only 0.1nm. The researchers are now working toincorporate their dendrimers into solid-state waveguides, optical fibers, andphotonic crystals. (S. Yokoyama, A. Otomo, S. Mashiko, Appl. Phys. Lett. 8080808080, 7, 2002.)

LIGHT SLOWED AND STORED IN A SOLIDLIGHT SLOWED AND STORED IN A SOLIDLIGHT SLOWED AND STORED IN A SOLIDLIGHT SLOWED AND STORED IN A SOLIDLIGHT SLOWED AND STORED IN A SOLID. The group velocity of light—the speed atwhich the wave pulse propagates—can be considerably lowered, even to zero, in a mediumhaving an index of refraction that changes dramatically with wavelength. The energy andinformation in the original light pulse can be stored, without any heating, in the form ofcoherent spin excitations in the atoms of the medium. Last year, two different experimentsstopped and stored light in a vapor sample (see Physics Today, March 2001, page 17). Now thefeat has been carried out in a 3-mm-thick crystal-yttrium silicate doped with atoms of therare earth praseodymium-already in common use for high-density optical data storage. Theexperiment was carried out at MIT and at the Air Force Research Laboratory in Hanscom,Massachusetts. The researchers foresee many applications in areas such as quantumcomputing, ultrasensitive magnetometry, and acousto-optics. (A. V. Turukhin et al., Phys. Rev.Lett. 8888888888, 023602, 2001.)

NONLINEAR LASER WITH ULNONLINEAR LASER WITH ULNONLINEAR LASER WITH ULNONLINEAR LASER WITH ULNONLINEAR LASER WITH ULTRALOW THRESHOLDTRALOW THRESHOLDTRALOW THRESHOLDTRALOW THRESHOLDTRALOW THRESHOLD. Physicists at Caltech coupleda 70-micron silica sphere to an optical fiber, which enabled light to race around near thesurface of the sphere in a “whispering gallery” mode. Whispering modes have been producedbefore, for example, in microdroplets, but practical applications seemed remote. The lightbuildup in these modes is characterized by a parameter Q, referred to as the quality factor;for the microsphere, Q exceeded a hundred million. The light can build up to such an extentthat nonlinear interactions take place and engender coherent light emission. The result is aRaman laser, which is tunable and can be used as a pump for other lasers. Typically, Ramanlasers need a highpower input to work at all. But the Caltech result achieved lasing with onlytens of microwatts of input power—1000 times less than other Raman lasers and in a muchsmaller package—although the output was only picowatts. The nonlinear properties of lightin the silica microspheres offer new avenues of exploring quantum optics. (S. M. Spillane etal., Nature 415415415415415, 621, 2002.)

ALL-OPTICAL TRAPPING OF A DEGENERAALL-OPTICAL TRAPPING OF A DEGENERAALL-OPTICAL TRAPPING OF A DEGENERAALL-OPTICAL TRAPPING OF A DEGENERAALL-OPTICAL TRAPPING OF A DEGENERATE FERMI GASTE FERMI GASTE FERMI GASTE FERMI GASTE FERMI GAS has been demonstrated.First created in a magnetic trap (see Physics Today, October 1999, page 17), a degenerateFermi gas consists of fermionic atoms—those with an odd total number of protons, neutrons,and electrons—sufficiently dense and cold that only the lowest trap energy levels areoccupied. An all-optical trap has previously been used to confine a Bose-Einstein condensate(see Physics Today, July 2001, page 20 and September 2001, page 79). Now, using a stable,high-power CO

2 laser, physicists at Duke University have created a kind of “optical bowl” for

lithium-6 atoms: Slowly lowering the bowl’s rim permitted the hottest atoms to evaporate.The researchers then adiabatically recompressed the trap to its full depth, which tightlyconfined the remaining degenerate gas. In this way, an equal mixture of lithium atoms in spin-up and spin-down states was captured, a feat not possible in magnetic traps. According tothe Duke researchers, such equal two-state mixtures are potentially ideal for forming neutrallycharged, quasibound pairs of atoms in Fermi gases—something the researchers hope toobserve soon. Several groups are pursuing such an atomic-gas analog of superconductivityin different ways. (S. R. Granade et al., Phys. Rev. Lett. 8888888888, 120405, 2002.)

BRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSABRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSABRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSABRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSABRIGHT SOLITONS IN A BOSE-EINSTEIN CONDENSATETETETETE. A soliton is a localizedwave that, because of nonlinear effects, can travel for long distances without spreading outor losing its original shape. Solitons can occur in all kinds of waves, including sound andlight. In fact, solitons are regularly used in telecommunications in optical fibers. Essentially amacroscopic matter wave, a BEC can also form solitons. Usually, however, a BEC quicklyspreads after it is released from the trap in which it was created. Now, groups at Rice Universityin Houston and at the Ecole Normale Supérieure in Paris have been able to form BEC solitonswith lithium-7 atoms. Both groups used a tunable magnetic field to adjust the interatomicinteractions from repulsive-necessary to form a stable condensate-to weakly attractive. Theattractive interactions provided a self-focusing nonlinearity that exactly compensated for

A tongue-in-cheek comparison of the TeVatronand the NeVatron (Courtesy Michael Chapman,Georgia Tech.)

A large dendrimer polymer molecule (green) with adye molecule lodged at its center. (Courtesy S.Yokoyama et al.)

wavepacket dispersion. After releasingthe atoms into a 1D potential, bothgroups observed solitons thatpropagated without changing shape formore than a millimeter—a trulymacroscopic distance. The Riceexperimenters formed a train of up to10 individual solitons, which appearedto repel each other as they oscillatedin a weakly harmonic potential. TheParis group set up an open waveguideand accelerated a single soliton.Matter-wave solitons may prove usefulfor eventual technological applicationsof BECs, such as for gyroscopes forultraprecise navigation, very accurateatomic clocks, or other devices thatuse atom interferometry. (K. E. Strecker et al., Nature 417417417417417, 150, 2002; L. Khaykovich et al.,Science 296296296296296, 1290, 2002.)

SONOLUMINESCENCE ENERGY IS MAINLSONOLUMINESCENCE ENERGY IS MAINLSONOLUMINESCENCE ENERGY IS MAINLSONOLUMINESCENCE ENERGY IS MAINLSONOLUMINESCENCE ENERGY IS MAINLY CHEMICALY CHEMICALY CHEMICALY CHEMICALY CHEMICAL, according to a new set ofexperiments at the University of Illinois. Yuri Didenko and Kenneth Suslick quantified theenergy consumption during sonoluminescence, the conversion of ultrasonic waves intopicosecond light pulses via rapid oscillations of bubbles in a liquid. They found that, duringthe compression phase, a bubble’s interior gets hot enough to dissociate many gas moleculesand initiate a furious session of chemical reactions. The researchers carefully monitored thereactant products—mostly nitrite ions (NO

2_), hydroxyl radicals (OH), and light—of a single

bubble of air in a bath of water subjected to ultrasound. They found that about 100 timesmore energy goes into chemical reactions than into light. Their experimental conditionswere very different from those used for the recent claim of “sonofusion” (see Physics Today,April 2002, page 16), and thus their results may not apply to that claim. However, DanShapira and Michael Saltmarsh of Oak Ridge National Laboratory did duplicate the sonofusionconditions. They showed that the earlier coincidence data can be accounted for by randomcoincidences; they also placed an upper limit on the relevant neutron emission that is 104

less than that implied by the earlier claim. (Y. T. Didenko, K. S. Suslick, Nature 418418418418418, 394, 2002.D. Shapira, M. Saltmarsh, Phys. Rev. Lett. 8989898989, 104302 , 2002.)

A MAA MAA MAA MAA MATTER-WTTER-WTTER-WTTER-WTTER-WAAAAAVE INTERFEROMETER FOR LARGE MOLECULESVE INTERFEROMETER FOR LARGE MOLECULESVE INTERFEROMETER FOR LARGE MOLECULESVE INTERFEROMETER FOR LARGE MOLECULESVE INTERFEROMETER FOR LARGE MOLECULES. A matter-waveinterferometer for large molecules has been devised and demonstrated for the first time. Formany yearsscientists havestudied theproposi t ionthat things wenormally thinkof as particles,such ase l e c t r o n s ,should alsohave wavep r o p e r t i e s .Indeed studiesof beams ofe l e c t r o n s ,neutrons, evenwhole atoms,have confirmedthat particlescan be viewed as a series of traveling waves which diffracted when they pass through a grating orthrough slits. These waves could even interfere with ach other, resulting in characteristic patternscaptured by particle detectors. In this way, in 1999 Anton Zeilinger and his colleagues at theUniversity of Vienna demonstrated the wave nature of carbon-60 molecules by diffracting them(in their wave manifestation) from a grating. Now the same group, using a full interferometerconsisting of three gratings with wider grating spacings and a more efficient detector setup,observe a sharp interference pattern. Moreover, because the beam of particles used, carbon-70molecules at a temperature of 900 K, are themselves in an excited state (undergoing 3 rotationaland 204 vibrational modes of internal motion), it should be possible to study the way in which anatom wave, or in this case a macromolecular wave, becomes decoherent (that is, loses its wavelikecharacter) Because of thermal motions and other interactions with its environment. Thus thistype of interferometer experiment will be useful in studying the borderland between the quantumand classical worlds. The researchers are aiming to study the wave properties of even largercomposite objects, mid-sized proteins. (Brezger et al., Physical Review Letters 8888888888, 100404, 2002).

Bright Solitons, composed of Bose-Einstein Conden-sates of lithium-7, have been observed in a single beamoptical trap (Courtesy Randy Hulet and colleagues, RiceUniversity.)

A matter-wave interferometer for large molecules (Courtesy University of Vienna)

BIOLOGICAL PHYSICS

5

Physics News in 2002

desired information. But more and more studies in a wide variety of systems—global climatemodels, electronic circuits and sensory neurons, to name a few—have shown that certainlevels of noise can actually enhance the detection and transmission of weak signals, througha mechanism known as stochastic resonance (SR). Here the authors show that postural sway,the slight movements exhibited by the body when it is erect, can be significantly reduced forboth young and elderly individuals. The authors achieved this by randomly applying subtlemechanical vibrations, just below the threshold of sensory perception, under the subjects’feet. The random vibrations likely act to enhance the sensation of pressure on the soles ofthe feet. The authors further demonstrate a trend in elderly subjects towards reducing theirpostural sway to the level of young subjects, suggesting that noise may be a “fountain ofyouth” for human balance. These results indicate that the random vibrations may ameliorateage-related impairments in balance control. Noise may provide similar beneficial effects inindividuals with marked sensory deficits, such as patients who have suffered a stroke or adisorder in the peripheral nervous system. In the future, the authors speculate, noise-baseddevices, such as randomly vibrating shoe inserts, may enable people to overcome functionaldifficulties due to age- or disease-related sensory loss (Priplata et al., Physical Review Letters,8989898989, 238101, 2002). This paper comes on the heels of another recent finding, that the randomhand motions generated by noise in the human nervous system make it possible for peopleto balance a stick on a finger (Cabrera and Milton, Physical Review Letters 8989898989, 158702, 2002).

VISCOSITY OF TWO-DIMENSIONAL SUSPENSIONSVISCOSITY OF TWO-DIMENSIONAL SUSPENSIONSVISCOSITY OF TWO-DIMENSIONAL SUSPENSIONSVISCOSITY OF TWO-DIMENSIONAL SUSPENSIONSVISCOSITY OF TWO-DIMENSIONAL SUSPENSIONS is similar to that in threedimensions. Many technologically and biologically important interfaces are actuallymonolayers composed of two coexisting phases: solid like crystals of the molecules floatingin a sea of liquid like molecules. Researchers at the University of California, Santa Barbara,measured the viscous drag on a magnetic needle in monolayers of human lung surfactantlipids. They found that if the relative fraction of the layer’s area that contained crystals waslow, the viscosity was also low and the monolayer spread easily. As the crystals’ coverageincreased, so did the viscosity until, at a critical fraction of the total area, the monolayerabruptly became rigid. Moreover, the behavior held for a wide range of surface pressures,temperatures, and monolayer compositions and was the same as that for a 3D dispersion ofhard spheres in a solvent with long-range repulsive interactions. The scientists believe theirwork could lead to better replacement surfactants—for example, for premature infants withrespiratory distress syndrome. Human lung surfactant has an important role in replacing theblood’s carbon dioxide with oxygen. It helps keep the lungs’ tiny air sacs properly inflated bycontrolling their surface tension. (J. Ding et al., Phys. Rev. Lett. 8888888888, 168102, 2002.)

A STRETCH-FIT TEMPLAA STRETCH-FIT TEMPLAA STRETCH-FIT TEMPLAA STRETCH-FIT TEMPLAA STRETCH-FIT TEMPLATE FOR FILMSTE FOR FILMSTE FOR FILMSTE FOR FILMSTE FOR FILMS of organic and inorganic molecules. Manybiological processes, such as bone formation, require hard inorganic materials to grow on asoft macromolecular substrate, although precisely how the two mesh has been something ofa mystery. To examine thatissue, physicists atNorthwestern Universityfloated a two-dimensionalarray of a fatty acid (aLangmuir monolayer) on asupersaturated solution ofbarium fluoride (BaF

2), which

then crystallized at theinterface. Separately, the twolattices are incommensurate.Using x-ray diffraction, theresearchers observed thatboth lattices adapted in orderto register with each other.The lattice of the BaF

2 thin film

contracted by a few percentand the organic latticeexpanded by tilting themolecules. The result was thatthe facial areas of the unit cellsfell into a commensurate ratio of 1.5. BaF

2 is not a biologically important mineral, but Pulak

Dutta says he and his fellow group members expect to look directly at biomineralization inan upcoming phase of their work. (J. Kmetko et al., Phys. Rev. Lett. 8989898989, 186102, 2002.)

SUPERCONDUCTIVITY IS REDUCEDSUPERCONDUCTIVITY IS REDUCEDSUPERCONDUCTIVITY IS REDUCEDSUPERCONDUCTIVITY IS REDUCEDSUPERCONDUCTIVITY IS REDUCED as a system becomes more one-dimensional.Moving through very thin passages, Cooper pairs of electrons, which constitute thesupercurrent, are sensitive to quantum effects not noticeable in larger wires. For example,quantum phase slips-fluctuations in which the superconducting wavefunction spontaneouslytunnels from one state to another-occur well below the critical temperature. The tunnelingproduces a momentary voltage, and therefore a nonzero electrical resistance, even if thetemperature could somehow be reduced to absolute zero. Armed with progressively thinnerwires—down to 10 nm across—of molybdenum-germanium deposited onto carbonnanotubes, Michael Tinkham and his colleagues at Harvard University have definitivelyshown that resistance goes up as the wire diameter goes down. The quantum resistanceeffect only becomes noticeable for wires less than about 30 nm across. By going to lowertemperatures, says Tinkham, one can eliminate resistivity arising from thermal fluctuations,but not from quantum fluctuations. (C. N. Lau et al., Phys. Rev. Lett. 8787878787, 217003, 2001.)

INSLULAINSLULAINSLULAINSLULAINSLULATOR-TO-METTOR-TO-METTOR-TO-METTOR-TO-METTOR-TO-METALALALALAL within a picosecond. A group from the University of California,San Diego, and the University of Quebec studied a 200-nm thick film of vanadium oxide(VO

2). They fired a 50-fs laser pulse at the sample, causing what they believe to be two phase

transitions: a structural one (the unit cell size increases a bit), monitored with short x-raypulses; and an electrical one (insulator-to-metal), monitored by short pulses of visible light.The simultaneous, ultrafast measurement of more than 1 degree of freedom showed thatboth transitions happened essentially all at once. Therefore, the experiment still did notsettle an old question in condensed matter physics: Which comes first, the structural changein the sample or the electrical change? Because the crystalline reordering occurs in a fewhundred femtoseconds and is reversible, and because x rays scatter differently from the twocontrasting crystalline forms, it might be possible to use this whole process as an ultrafast“Bragg switch” to divert subpicosecond portions of a longer x-ray wavetrain. (A. Cavalleri etal., Phys. Rev. Lett. 8787878787, 237401, 2001.)

SOUND WSOUND WSOUND WSOUND WSOUND WAAAAAVES MAKE FILVES MAKE FILVES MAKE FILVES MAKE FILVES MAKE FILTERS FINER.TERS FINER.TERS FINER.TERS FINER.TERS FINER. Generally, the performance of filters thatremove particulates from fluids is limited by their pore sizes: A filter with large pores isn’tlikely to catch many tiny particles. By contrast, a filter with tiny pores will trap small particles

but inhibit fluid flow. Now,Donald Feke (Case WesternReserve University) hastrapped particles up to ahundred times smaller thanthe nominal pore size byapplying a low-poweracoustic signal to the filter.The sound field within aporous material createspatterns of standing wavesassociated with the pores.Rather than wending theirway through the filter,particles headed for thefocal points either formintricate, stable filaments orgather into groups thatorbit in regions of stabilityfor as long as the signal persists. Such an acoustically aided filter offers little resistance to thefluid that flows through it, yet collects particles as efficiently as a much finer filter does. Andonce the filter has done its job, the trapped particles can be released with the flip of a switchthat cuts off the signal. Feke presented his work at the 73rd annual Society of Rheologymeeting in Bethesda, Maryland.

LIGHTLIGHTLIGHTLIGHTLIGHT-ACTIV-ACTIV-ACTIV-ACTIV-ACTIVAAAAATED PLASTIC MAGNETTED PLASTIC MAGNETTED PLASTIC MAGNETTED PLASTIC MAGNETTED PLASTIC MAGNET. . . . . Photoinduced magnetism is of considerableinterest in data storage applications. Over the past six years, the phenomenon has been seen,generated, and studied in several different materials. Now, scientists at Ohio State Universityand the University of Utah have produced light-induced magnetization in an organic-basedmaterial, tetracyanoethylene (TCNE), contained within a manganese compound. When thematerial was exposed to blue light from an argon laser, its magnetization increased by asmuch as 50%. The material was magnetic at temperatures below 75 K and retained itsmagnetism for days, perhaps through the formation of a metastable state in a distortedlattice. The magnetism could be partially undone by green light, and completely undone byheat. The researchers believe that the light can be selectively targeted to domains as small as,or smaller than, the wavelength of the light itself, thus possibly enabling information storage.Magneto-optic effects are currently used only to retrieve information. The new processpromises to offer both reading and writing capabilities. The benefits of plastic electroniccomponents made of plastic include flexibility, low cost, and tunability. (D. A. Pejakovic et al.,Phys. Rev. Lett. 8888888888, 057202, 2002.)

RAPID-RESPONSE HYDROGELSRAPID-RESPONSE HYDROGELSRAPID-RESPONSE HYDROGELSRAPID-RESPONSE HYDROGELSRAPID-RESPONSE HYDROGELS, water-swelled polymers that quickly change theirproperties when triggered by the right stimulus, have been created. A hydrogel is a 3Dcagelike polymer that is relatively sluggish in responding to the application or removal ofstress, light, or a change in acidity. Using a novel design based on artificial protein polymers,a collaboration of scientists from the University of California, Santa Barbara, and the Universityof Delaware has now developed a hydrogel that can recover quickly after the removal ofmechanical stress. The novel hydrogel contains two chemical building blocks: one that ishighly charged and hydrophilic and another that is hydrophobic and has a special shape thatcauses the polymers to link and form a porous hydrogel at very low concentrations insolution. After the gels were shaken vigorously to break down their structure, they recovered80% of their strength in a matter of seconds, even at 90°C. The rapid response and highlyporous nature of the new hydrogel potentially opens up new biotechnological uses for thecompound. Possibilities include an organic scaffolding to hold regenerating tissue within thebody and a drug-delivery capsule to hold large proteins and release them when given theright stimulus. (A. P. Nowak et al., Nature 417417417417417, 424, 2002.)

MICROTESLA NUCLEAR MAGNETIC RESONANCEMICROTESLA NUCLEAR MAGNETIC RESONANCEMICROTESLA NUCLEAR MAGNETIC RESONANCEMICROTESLA NUCLEAR MAGNETIC RESONANCEMICROTESLA NUCLEAR MAGNETIC RESONANCE has been demonstrated. Inconventional NMR, a several-tesla magnetic field is used to orient atomic nuclei in the sample.The polarized nuclei can resonantly absorb a burst of radio waves, and precess around theimposed field. The spectral “chemical shift” information from reemitted radio waves is thenused to identify molecules. NMR also lies at the heart of magnetic resonance imaging (MRI).Now, a team of scientists led by John Clarke and Alexander Pines (Lawrence Berkeley NationalLaboratory and the University of California, Berkeley) have exploited an often overlookedfact: For a homogeneous field, the NMR linewidth scales linearly with the field strength.Thus, a 1000-fold reduction in field strength produces a line both narrower and taller bythat same factor. The researchers placed a small liquid sample of methanol and phosphoricacid in a polarizing field of only 1 mT and a much weaker orthogonal measuring field of 5 mT(Earth’s field is roughly 50 mT). The group then turned off the polarizing field and used aSQUID to detect not chemical shift but “J-coupling,” which can measure an atom’s chemicalenvironment as well as its identity. In that way, they not only identified protons andphosphorous—31, but saw the signature—a doublet split by 10.4 Hz—of the covalentbonds in trimethyl phosphate. These techniques open the possibility for “pure J” spectroscopyand perhaps could form the basis of inexpensive MRI machines. (R. McDermott et al., Science295295295295295, 2247, 2002.)

A SINGLE-PHOTON LIGHTA SINGLE-PHOTON LIGHTA SINGLE-PHOTON LIGHTA SINGLE-PHOTON LIGHTA SINGLE-PHOTON LIGHT-EMITTING DIODE-EMITTING DIODE-EMITTING DIODE-EMITTING DIODE-EMITTING DIODE has been created. At the May 2002CLEO/QELS meeting in Long Beach, California, scientists from Toshiba Research Europe Ltddescribed a nanometer-scale indium arsenide quantum dot integrated into a conventionalgallium arsenide LED structure. Using a pulse of electric current, the researchers couldinduce a single electron and a single hole to recombine in the dot, thus generating a singlephoton. Because the exciton’s lifetime was 1.0 ns and the equipment had subnanosecondtime resolution, the physicists could verify that photons were emitted singly. The researchersbelieve this is the first electrically driven single-photon source. Such single-particle-emittingsources could offer a potentially inexpensive and convenient component for quantumcryptography and other applications. (Paper QTuG1 at the meeting; see also Z.Yuan et al.,Science 295295295295295, 102, 2002.)

A NANOSCALE NONMAGNETIC READ-HEAD SENSORA NANOSCALE NONMAGNETIC READ-HEAD SENSORA NANOSCALE NONMAGNETIC READ-HEAD SENSORA NANOSCALE NONMAGNETIC READ-HEAD SENSORA NANOSCALE NONMAGNETIC READ-HEAD SENSOR, based on extraordinarymagnetoresistance (EMR), has been developed. Today’s state-of-the-art magnetic recordingdelivers about 15 gigabits per square inch of recording medium. To achieve that result, theread head uses magnetic metals in a layered structure with either the giant magnetoresistance(GMR) or tunneling magnetoresistance (TMR) effect to convert the field orientation (up ordown) of tiny magnetic domains into changes in electrical resistance. Both effects make useof electrons’ spin and are subject to magnetic noise. By contrast, EMR makes use of electrons’orbital degrees of freedom; the magnetic fields deflect a current from a conducting shuntattached to the semiconductor and thereby produce resistance changes. A group led by

X rays are used to reveal, in detail for the first time, how aninorganic crystal (barium fluoride) can grow, in registry, upon anorganic material (a fatty acid). (Courtesy, Jan Kmetko, North-western Univ.).

CONDENSED MATTER/MATERIALS PHYSICS

Acoustic filter: when an acoustic signal is turned on, tinyparticles are trapped by a complex pattern of standing soundwaves (Courtesy CWRU)

6

Physics News in 2002

Stuart Solin of NEC ResearchInstitute in Princeton, NewJersey, has now usednonmagnetic, silicon-dopedindium antimonide to builda mesoscopic read head (seethe scanning electronmicrograph) that operateson the EMR principle.According to Solin, GMRand TMR will ultimatelyhave a noise-limited arealdensity of about 150 Gb/in2,whereas EMR could reach 1Tb/in2 and has a fast enoughresponse time to utilize thatdensity. The researchersfabricated their 116-Gb/in2

device using a multistep electron-beam lithography process that required excruciatingaccuracy: Features needed to be aligned to within 10 nm. Although free of magnetic-noiselimitations, the device needs to sense magnetic fields that are 10 times stronger than thosesensed with current technologies, which could limit its practical application for the timebeing. (S. A. Solin et al., Appl. Phys. Lett. 8080808080, 4012, 2002.)

SINGLE-SPIN TRANSISTORSINGLE-SPIN TRANSISTORSINGLE-SPIN TRANSISTORSINGLE-SPIN TRANSISTORSINGLE-SPIN TRANSISTOR. Spintronics is a relatively new field in which an electron’sspin, not just its charge, is exploited in devices and circuits. Physicists at the Institute forMicrostructural Science in Ottawa, Canada, have connected a quantum dot to spin-polarizedleads in an external magnetic field. They emptied the dot of conduction electrons and thenadded them back one at a time. The researchers found that the total spin of the electronsdepended both on the number of electrons in the dot and on the applied magnetic field.With fewer than about 20 electrons in the dot, an even number of spins paired off in singletstates with zero net spin, whereas an odd number had a net spin corresponding to theunpaired electron. Above the critical number, however, the additional electrons all had thesame spin polarization. Furthermore, the single-spin, singlet, and polarized phases of the doteach allowed different currents to flow through the dot. The physicists controlled the spinstate of the dot either by adding electrons or by tuning the magnetic field, and thus produceda prototype single-spin transistor. The group believes their work may play a role in futuresolid-state forms of quantum information. (M. Ciorga et al., Phys. Rev. Lett. 8888888888, 256804,2002.)

BALLISTIC MAGNETORESISTBALLISTIC MAGNETORESISTBALLISTIC MAGNETORESISTBALLISTIC MAGNETORESISTBALLISTIC MAGNETORESISTANCE (BMR)ANCE (BMR)ANCE (BMR)ANCE (BMR)ANCE (BMR) is yet another way in which spin orientationcan modify electrical resistance in a circuit. The sensitive part of the circuit might consist ofsandwiches of alternating magnetic and nonmagnetic layers (giant magnetoresistance andtunnel magnetoresistance) or might have no magnetic materials at all. In BMR, the sensor isa quantum point contact of ferromagnetic atoms between two wires. The contact is narrowerthan the typical scattering path length for electrons, which therefore move ballistically instraight trajectories. Any scattering an electron suffers will be due only to magnetic effects.If the electrons in the circuit are spin polarized then they will scatter more or less (withgreater or lesser resistance) at the contact, depending on the contact’s magnetization stateand on the faint force exerted by any nearby tiny magnetic storage domain. In a new BMRexperiment conducted at SUNY Buffalo, Harsh Chopra and Susan Hua found a remarkablylarge resistance change in nickel nanocontacts at room temperature. For example, they sawa change in resistance of more than a factor of 30 (from 8 to 260 ohms) in an appliedmagnetic field of less than 0.016 T (160 gauss). The researchers say that they can reliablyreproduce the BMR effect in many samples. (H. D. Chopra, S. Z. Hua, Phys. Rev. B 6666666666, 020403(R),2002.)

THE ROLE OF THE NANOSCALE IN THE ROLE OF THE NANOSCALE IN THE ROLE OF THE NANOSCALE IN THE ROLE OF THE NANOSCALE IN THE ROLE OF THE NANOSCALE IN AAAAARRRRRTIFICIAL LEATIFICIAL LEATIFICIAL LEATIFICIAL LEATIFICIAL LEAVESVESVESVESVES has been elucidated.Several semiconductor materials are known to catalyze the removal of excess airbornecarbon dioxide in the presence of light and organic molecules, just like real leaves. Forexample, bulk surfaces of cadmium sulfide and zinc sulfide can photocatalytically fix CO

2

into an organic molecule. Cadmium selenide, however, can only accomplish that task in itsCd-rich nanocrystalline form. Three physicists at Oak Ridge National Laboratory andVanderbilt University believe they have now found out why. In a series of parameter-free,first-principles calculations, they found that CO

2 is adsorbed only at Se vacancies and then

becomes negatively charged and, potentially, more reactive. The CO2 does not react on the

surface; it needs to yank the extra electron out of the semiconductor, desorb, and becomeincorporated into another molecule elsewhere. For this scenario to occur, the extra electronmust first be excited into the semiconductor’s conduction band, for example by shining lighton it. Still, the energy cost is too high for the charged CO

2 to desorb from bulk CdSe. Enter

the nanoscale. As a nanocrystal’s size decreases, its energy gap increases. Thus, electrons canflow freely to desorbing CO

2 molecules if the CdSe crystal is small enough. As a bonus, the

theorists found that n-doping with indium might allow CO2 fixation to take place without the

need for light. (L. J. Wang, S. J. Pennycook, S. T. Pantelides, Phys. Rev. Lett. 8989898989, 075506, 2002.)

NANOTUBE DIAGNOSTIC X RANANOTUBE DIAGNOSTIC X RANANOTUBE DIAGNOSTIC X RANANOTUBE DIAGNOSTIC X RANANOTUBE DIAGNOSTIC X RAYS. YS. YS. YS. YS. The design of the x-ray tubes used in many medicaland dental offices is essentially unchanged from a hundred years ago. A metal filament, thecathode, emits electrons when heated to more than 1000° C. The electrons are acceleratedacross a vacuum tube into a target, where they generate x rays. Now, a team of physicists anddoctors at the University of North Carolina atChapel Hill and the nearby firm of AppliedNanotechnologies Inc has created an x-ray tubeusing a room-temperature array of carbonnanotubes in a field-emission triode. Theydemonstrated a sufficiently large and stable currentfor practical medical imaging, as shown here bythe x ray of a fish. According to the researchers,the device can be much smaller, is expected to lastlonger, and can produce a more focused x-ray beamthan the hot-cathode design. In addition, theresponse time is sharper and the pulse shape and timing can be programmed, all of whichhelp in the tracking of moving objects. (G. Z. Yue et al., Appl. Phys. Lett. 8181818181, 355, 2002.)

A SOLID-STA SOLID-STA SOLID-STA SOLID-STA SOLID-STAAAAATE CATE CATE CATE CATE CATHODE RATHODE RATHODE RATHODE RATHODE RAY TUBEY TUBEY TUBEY TUBEY TUBE has been developed by scientists at the TokyoUniversity of Agriculture and Technology. The CRT used in most television sets and computermonitors consists of a bulky box with a gun that shoots electrons (cathode rays) from a hotcathode through a vacuum toward a phosphor screen. The new vacuumless solid-state

A nanoscale, nonmagnetic read_head sensor, based on extraor-dinary magnetoresistance (EMR). (Courtesy Solin et al..)

equivalent makes use of nanocrystalline porous silicon, in which electrons subjected to anelectric field are accelerated to several eV by a multiple-tunneling cascade through theinterfacial barriers between nanocrystallites. The energetic electrons then ballistically hit aluminescent organic film deposited on the silicon, resulting in uniform planar light emission.Nobuyoshi Koshida argues that the device, unlike other flat-panel luminescent displaycandidates, has all of the desirable technological features: It consumes little power, is silicon-based, produces a sharp picture, is scalable to large areas, responds quickly, is inexpensivebecause of its simple design, and can easily incorporate the three primary colors. (Y. Nakajima,A. Kojima, N. Koshida, Appl. Phys. Lett. 8181818181, 2472, 2002.)

AAAAATOMIC-RESOLUTION NEUTRON HOLOGRAPHYTOMIC-RESOLUTION NEUTRON HOLOGRAPHYTOMIC-RESOLUTION NEUTRON HOLOGRAPHYTOMIC-RESOLUTION NEUTRON HOLOGRAPHYTOMIC-RESOLUTION NEUTRON HOLOGRAPHY. To obtain a holographic image,one must record the interference of two coherent waves emitted by the same source. Onewave must reach a detector directly while the other first scatters off of the object to beimaged. Holography using lasers has been familiar for decades, but better resolution hasbeen achieved in recent years with electron and x-ray holography (see Physics Today, April2001, page 21). Neutrons, however, because theyonly interact with nuclei, may offer a more versatilealternative. Last year, a group led by Laszlo Cser ofthe Central Research Institute for Physics in Budapest,Hungary, proposed two ways to use neutrons forholography. Soon thereafter, a group in Canadarealized one of those methods-the inside-sourcemethod-using hydrogen, a strong neutron scatterer,to act as a point source of neutron waves within asample. Now the second, the inside-detector method,has been demonstrated by Cser and his colleagues.The group placed a single crystal of lead, in whichthey replaced a few Pb atoms with cadmium, into aneutron beam. Because Cd absorbs neutrons 106times more readily than does Pb, the Cd acts as aninternal neutron detector. The number of absorptionsdepends on the total neutron wave field at the Cd,including the interference between the directlyarriving and previously scattered neutron waves.After absorbing a neutron, the new Cd isotope emitsgamma radiation as it drops to the ground state, andthose photons provide the data for the hologram. The physicists not only found the correctlattice parameter (4.93 angstroms) but also determined the sample’s orientation in the neutronbeam. Cser believes that holography with polarized neutron beams will be valuable forstudying the structure of magnetic materials. (L. Cser et al., Phys. Rev. Lett. 8989898989, 175504,2002.)

Pictures of a hand and a fish taken with acarbon-nanotube source of x rays. (Cour-tesy UNC/Applied Technologies)

Neutron hologram of a lead crystal. Thespots represent the positions of 12 leadatoms forming the first neighbors of acadmium nucleus, as displayed on asphere of radius .35 nm. (Courtesy Cen-tral Research Institute for Physics,Budapest)

PARTICLE, NUCLEAR, PLASMA, BEAMS PHYSICS

SOLAR NEUTRINO PROBLEM CLOSEDSOLAR NEUTRINO PROBLEM CLOSEDSOLAR NEUTRINO PROBLEM CLOSEDSOLAR NEUTRINO PROBLEM CLOSEDSOLAR NEUTRINO PROBLEM CLOSED. The solar neutrino problem has been closedand the ability of neutrinos to change from one type, or “flavor,” to another establisheddirectly for the first time by the efforts of the Sudbury Neutrino Observatory (SNO)collaboration. This finding gives physicists new confidence that they understand how energyis produced in the sun’s core and that neutrinos are just as quirky as we thought. Thebenevolent sunlight we receive on Earth has its origin in the sun’s central fusion furnace,whence the light must fight its way outwards in a series of scatterings that takes, on average,hundreds of thousands of years. Solar neutrinos, setting out from the same place, fleeunhindered, thus providing the most unadulterated proxy of activity at the core.Measurements dating back to the 1960’s of this neutrino flux were puzzling: only a fractionof the expected number arrived at detectors on Earth. Suspicion naturally fell on theexperiments and on the standard solar model (SSM) used to calculate the flux.

Soon, however, the neutrinos themselves were implicated. If on their journey to Earthsome of the neutrinos (basically, solar reactions produce electron-neutrinos) had changedinto muonor tauneutrinos, then terrestrial detectors designed only to spot electron neutrinos(e-nu’s) would be cheated of their rightful numbers. SNO scrutinizes a particular reaction inthe sun: the decay of boron-8 into beryllium-8 plus a positron and an e-nu. SNO’s giganticapparatus consists of 1000 tons of heavy water (worth $300 million Canadian) held in anacrylic vessel surrounded by a galaxy of phototubes, the whole residing 2 km beneath theEarth’s surface in an Ontario mine, the better to filter out distracting background interactions.In 2001 SNO reported first results based on reactions in which a solar neutrino enters thedetector and either (1) glances off an electron in one of the water molecules (this so-calledelastic scattering (ES) is only poorly sensitive to muon and tau neutrinos) or (2) combineswith the deuteron to create an electron and two protons, a reaction referred to as a “chargedcurrent” (CC) interaction since it is propagated by the charged W boson. The SNO data,when supplemented with ES data from the Super Kamiokande experiment in Japan, providedpreliminary evidence a year before for the neutrino-oscillation solution for the solar neutrinoproblem.

Now the definitive result has been tendered by SNO scientists at the April 2002 APSmeeting in Albuquerque. The new findings update last year’s CC and ES data and introduce,for the first time, evidence deriving from a reaction in which the incoming neutrino retainsits identity but the deuteron (D) is sundered into a proton and neutron; this is why SNO wentto such trouble and expense of using D

2O-for the weakly bound neutron inside each D. This

interaction, called a neutral-current (NC) reaction because the operative nuclear voltagespreads in the form of a neutral Z boson, is fully egalitarian when it comes to neutrinoscattering; unlike the 2001 ES data, the NC reaction allows e-nu’s, mu-nu’s, and tau-nu’s toscatter on an equal footing.

The upshot: all the nu’s from the sun are directly accounted for. The missing nu-e fluxshows up as an observable mu-nu and tau-nu flux. This conclusion is established with astatistical surety of 5.3 standard deviations, compared to the less robust 3.3 of a year before.(Ahmad et al., Phys. Rev. Lett. 8989898989, 011301, 2002.)

COLD ANTI-HYDROGEN ACOLD ANTI-HYDROGEN ACOLD ANTI-HYDROGEN ACOLD ANTI-HYDROGEN ACOLD ANTI-HYDROGEN ATOMSTOMSTOMSTOMSTOMS have been made and detected, for the first time, bytwo groups at CERN. The ATHENA collaboration makes the anti-H atoms when a swarm ofantiprotons is loosed upon a cloud of positrons held within the same trap. Anti-H atomsannounce their presence when they drift out of the trap region and annihilate with ordinaryatoms in a sort of double suicide. The antiproton perishes when it meets a regular proton,resulting in the creation of a few pi mesons detected in silicon microstrips, a process whichpoints to the annihilation vertex with a precision of 4 mm. Meanwhile the positron partnerfrom each anti-H meets its separate fate when it collides with the nearest electron, producinga telltale pair of 511-keV gamma rays which show up in adjoining CsI crystals. (Amoretti etal., Nature, posted online, 18 Sept 2002.)

7

Physics News in 2002

Meanwhile, the ATRAP collaboration has also detected antihydrogen atoms, but in amore direct way, through a process called field ionization, which works as follows. Havingformed in the center of the enclosure, neutral anti-atoms are free to drift in any direction.Some of them annihilate but others move into an “ionization well,” a region where strongelectric fields tear the H-bar apart and the antiprotons are trapped in place, leaving thepositron to move off and annihilate elsewhere. By counting the number of antiprotons oneknows how many anti-atoms had arrived at the well. Every event represents an anti-atom.Moreover, one can now make a statistical study of the electric field needed to ionize thepositron and deduce from this, in a rudimentary way, some information about the internalenergy states of the H-bar. Thus the internal properties of an anti-atom have been studied forthe first time. The observed range in principal quantum number n (n=1 corresponding to theground state, or lowest level) goes from 43 up to 55. (G. Gabrielse et al., Phys. Rev. Lett. 8989898989,233401, 2002.)

The ultimate goal of these experiments will be to trap neutral cold anti-hydrogen atomsand to study their spectra with the same precision (parts per 1014 for an analysis of thetransition from the n=2 to the n=1 state) as for plain hydrogen. One could then tell whetherthe laws of physics apply the same or differently to atoms and anti-atoms.

CP-VIOLACP-VIOLACP-VIOLACP-VIOLACP-VIOLATION IN B MESON DECATION IN B MESON DECATION IN B MESON DECATION IN B MESON DECATION IN B MESON DECAYS. YS. YS. YS. YS. New reports on this important subject(important since it bears on the fundamental difference between matter and antimatter)were provided this past year by scientists from the Belle experiment at the KEK lab in Japanand the BaBar experiment at SLAC in the US. The standard model, trying to explain theforces of nature through the exchange of particles, consists of the electroweak framework(force exchanged by photons and by Z and W bosons) plus the quantum chromodynamic(QCD) framework for quarks (force exchanged by gluons). The model has been highlysuccessful in accounting for the behavior of electrons in atoms (in the case of some transitionfrequencies, theory and experiment agree at the parts-per-trillion level or better) and does agood job of predicting other phenomena as well, such as CP violation. The new CP violationtests were reported at the International Conference on High Energy Physics in Amsterdam inthe summer of 2002. Both Belle and BaBar observed subtleties in the decays of B mesons andmeasured a parameter called sine two beta. The value measured for both groups, withmuch better precision than ever before, is approaching the value predicted by the standardmodel, thus erasing past discrepancies. (See, for example Aubert et al. Phys. Rev. Lett. 89,201802, 2002 and Abe et al., Phys. Rev. Lett. 8989898989, 071801, 2002.)

THE g-2 EXPERIMENT THE g-2 EXPERIMENT THE g-2 EXPERIMENT THE g-2 EXPERIMENT THE g-2 EXPERIMENT at Brookhaven seeks to observe a departure of the muon’smagnetic moment (related to the muon’s spin by the g parameter) from 2, the value it wouldhave in the absence of interactions between the muon and virtual particles in the universalvacuum, including possible exotica outside the standard model such as the supersymmetricentities. Although the prospective SUSY particles are rare and unstable their virtual existencein the vacuum would modify observable quantities such as the muon magnetic moment.Thus a measurement of the magnetic moment, made by watching muons decay even as theywobble about in a strong magnetic field, would give indirect evidence for the extra particles.Moderate evidence in this direction was previously reported by the g-2 team. The newresults, reported also in Amsterdam, follow suit but with twice the precision of the lastreport. (Bennett et al., Phys. Rev. Lett. 8989898989, 101804, 2002.)

A PYROELECTRIC ACCELERAA PYROELECTRIC ACCELERAA PYROELECTRIC ACCELERAA PYROELECTRIC ACCELERAA PYROELECTRIC ACCELERATORTORTORTORTOR. A pyroelectric crystal has a permanent electricdipole moment, masked by adsorbed ions on the crystal’s faces until there is a change intemperature, which creates strong electric fields at those surfaces. Now, James Brownridgeof SUNY Binghamton and Stephen Shafroth of the University of North Carolina, Chapel Hill,have used those electric fields to create stable, self-focused electron beams with energies ashigh as 170 keV. The beams were apparent in a dilute gas atmosphere, and emanated fromthe so-called -z face of crystalline LiNbO

3 after heating the +z face. The energy conversion

was not especially efficient—watts of heating energy produced only microwatts of outputelectron beam energy—but that might not be important. Brownridge says that such a focusedelectron beam could be used in a portable, economical x-ray fluorescence device for theelemental analysis of complex materials like tree leaves, rocks, air filters, or blood samples.(J. D. Brownridge, S. M. Shafroth, Appl. Phys. Lett. 7979797979, 3364, 2001.)

A LIQUID-GAS PHASE TRANSITION FOR NUCLEIA LIQUID-GAS PHASE TRANSITION FOR NUCLEIA LIQUID-GAS PHASE TRANSITION FOR NUCLEIA LIQUID-GAS PHASE TRANSITION FOR NUCLEIA LIQUID-GAS PHASE TRANSITION FOR NUCLEI. In school, most physicists learnedthe liquid-drop model of the nucleus. In recent years, several groups have addressed thenext question: Is there also an equilibrium nuclear “vapor” such that changing a parameterakin to pressure ortemperature can send thenucleus back and forthbetween the two states ofmatter? Now, two groups haveanalyzed data from theIndiana Silicon Sphere (ISiS)experiment at BrookhavenNational Laboratory, in whichpions and protons wereslammed into gold nuclei toinduce so-called nuclearmultifragmentation. A groupfrom Michigan StateUniversity found strongcircumstantial evidence for aliquid-gas phase transition, while a group from Lawrence Berkeley National Laboratory wasable to fully map out a liquid-vapor coexistence line, with a critical point, in the nuclearphase diagram. That a finite system like a nucleus, with only about 200 particles, not onlyshows a robust phase transition but also has discoverable quantities like vapor pressure,evaporation enthalpy, and surface energy is “very exciting,” according to Luciano Moretto,the leader of the Berkeley group. (T. Lefort, L. Beaulieu et al., Phys. Rev. C 6464646464, 064603-4,2001; M. K. Berkenbusch et al., Phys. Rev. Lett. 8888888888, 022701, 2002; J. B. Elliott et al. Phys. Rev.Lett. 8888888888, 042701, 2002.)

A TA TA TA TA TABLETOP NEUTRON SOURCEABLETOP NEUTRON SOURCEABLETOP NEUTRON SOURCEABLETOP NEUTRON SOURCEABLETOP NEUTRON SOURCE is being used to calibrate a dark-matter detector.Expected to be the dominant type of matter in the universe, dark matter interacts only veryweakly with normal matter. Like a neutrino detector, a dark-matter detector will succeedonly if it has enough target atoms with enough mass, operates over an adequately longperiod, and has sufficient background suppression. In one prototype detector using bothliquid and gaseous xenon, an incoming weakly interacting massive particle (WIMP) wouldstrike a Xe nucleus and produce both scintillation light and free electrons from ionized Xeatoms, a process strikingly similar to elastic neutron-Xe interactions. Therefore, to calibratethe detector, physicists at Imperial College, London, aimed neutrons into the Xe bath using

an inexpensive and compact plasma focus discharge device as a neutron source. Deuteriumfusion reactions in a pinched plasma produced helium-3 nuclei plus forward-directed 2.45-MeV neutrons. The tabletop neutron source (a pulsed device that delivers about 20 millionneutrons per shot) might also be handy for the detection of nitrogen-based explosives or inthe transmutation of nuclear waste. (F. N. Beg et al., Appl. Phys. Lett. 8080808080, 3009, 2002.)

MICROSAMICROSAMICROSAMICROSAMICROSATELLITE PLASMA PROPULSIONTELLITE PLASMA PROPULSIONTELLITE PLASMA PROPULSIONTELLITE PLASMA PROPULSIONTELLITE PLASMA PROPULSION. Thanks to new MEMSmicroelectromechanical systems) technology, the development of low-mass spacecraft—less than 20 kg—has gone well, with one notable exception: suitably miniaturized thrusters,the minirockets that steerthe craft and make otherflightpath adjustments. JohnFoster, a researcher atNASA’s Glenn ResearchCenter in Cleveland, Ohio,has now built a tinypropulsion system thatdevelops thrust from apressurized gas of xenonthat is ionized by energeticelectrons as it escapesthrough 0.18-mmapertures. Foster boiled theelectrons off a filament andused a cusp in a magneticfield to focus them onto theapertures. The resulting ionswere then accelerated to the50-200 eV range to generate thrust. Only about 50 mm across, the device is extremely fuel-efficient: 88% of the fuel is successfully turned into ions. The new compact plasma acceleratorcould also be used for modifying surface chemistry and making thin films. (J. E. Foster, Rev.Sci. Instrum. 7373737373, 2020, 2002.)

LASER-DRIVEN JETS OF CARBON AND FLUORINELASER-DRIVEN JETS OF CARBON AND FLUORINELASER-DRIVEN JETS OF CARBON AND FLUORINELASER-DRIVEN JETS OF CARBON AND FLUORINELASER-DRIVEN JETS OF CARBON AND FLUORINE have been produced at the rearof thin foil targets. Using the powerful laser at the Laboratoire pour l’Utilisation des LasersIntenses (LULI) in Palaiseau, France, a multinational group of physicists aimed 300-fs pulsesat 50-mm-thick metal foil targets coated on the rear side with a thin layer of either carbon orcalcium fluoride. First, the physicists heated the target to remove contaminants. The laserthen generated, at the front of the target, relativistic electrons that penetrated the foil andshot out the back side. Those freed electrons set up a strong space-charge field that ionizedatoms near the foil’s back surface and then accelerated those ions outward. The researcherssucceeded in accelerating fluorine and carbon ions, both having several different chargestates, to energies that exceeded 5 MeV per nucleon and within a distance of only about 10mm. Furthermore, the jets were bright (1012 particles per burst) and well collimated, possiblymaking them useful for future work in particle physics or fusion. According to team memberManuel Hegelich, an outgoing beam of fluorine ions could be used to heat a 100-mm-sizedsecondary target to a temperature of 200-300 eV (equivalent to 100,000 K) in merepicoseconds. During that tick of time, the crystal of atoms in the target would be heatedisochorically (the lattice would not have time to expand), and thus approximate the conditioninside stars. Previously, several groups have similarly accelerated protons. (M. Hegelich et al.,Phys. Rev. Lett. 8989898989, 085002, 2002.)

THE FRAGMENTTHE FRAGMENTTHE FRAGMENTTHE FRAGMENTTHE FRAGMENTAAAAATION OF POSITRONIUMTION OF POSITRONIUMTION OF POSITRONIUMTION OF POSITRONIUMTION OF POSITRONIUM owing to collisions with helium atoms hasbeen experimentally investigated. The lightest “atom” made of an electron and a positivelycharged mate is not hydrogen but positronium, a bound electron-positron pair. Ps lives foronly about 140 nanoseconds before its constituents annihilate each other, but that can belong enough to do an experiment. In recent years, physicists have been able to generate Psbeams and measure total cross sections for Ps scattering from various targets. Now, a teamof physicists at University College London has conducted an experiment in which Ps scattersinelastically off helium atoms and splits apart. The separated electrons and positrons continueto be highly correlated, and the measured cross section is in good agreement with a coupled-state calculation. A longitudinal-energy peak suggests that some of the resulting electronsare lost to the continuum. (S. Armitage et al., Phys. Rev. Lett. 8989898989, 173402, 2002.)

Test firing of a compact plasma accelerator device (CourtesyNASA Glenn Research Center)

OTHER PHYSICS HIGHLIGHTS

THE 2002 NOBEL PRIZE FOR PHYSICSTHE 2002 NOBEL PRIZE FOR PHYSICSTHE 2002 NOBEL PRIZE FOR PHYSICSTHE 2002 NOBEL PRIZE FOR PHYSICSTHE 2002 NOBEL PRIZE FOR PHYSICS recognizes work that led to the establishmentof two new branches of astrophysics, those involving x rays and neutrinos. The award will bepresented to Raymond Davis (University of Pennsylvania and Brookhaven Natl. Lab),Masatoshi Koshiba (University of Tokyo), and Riccardo Giacconi (Associated UniversitiesInc.). In the 1960s Davis was the first to detect neutrinos coming from the sun. The numberof nu’s recorded fell short of predictions made by John Bahcall (Institute for AdvancedStudy) and thus was born the “solar neutrino problem.” Later detector experiments, such asKamiokande, SAGE and Gallex, also failed to observe the expected number of neutrinosfrom the sun. The best explanation for the shortfall was that electron neutrinos made in thesolar core, as products of nuclear fusion reactions, might be transforming while in flighttoward Earth into other types of neutrino such as muon neutrinos, which could not berecorded in terrestrial detectors.

This hypothesis was put to the test in the Kamiokande detector, which had earlier soughtto find evidence for proton decay. Koshiba and his collaborators enlarged the Kamiokandedetector and finally affirmed (by observing asymmetries in cosmic-ray-engendered nu’scoming through the Earth to the detector or directly into the detector from Earth’s atmosphere)that nu’s were indeed transforming, or “oscillating.” Still more proof for the oscillationprinciple arrived in 2002 when the Sudbury Neutrino Observatory (SNO), capable of directlydetecting all three types of neutrino, reported that all solar nu’s (albeit not the same mix aswas produced in the sun) were accounted for.

As for x-ray astrophysics, Giacconi was the first to employ an x-ray telescope in space(1962) and observe specific x-ray sources outside our solar system. There followed decadesof new orbiting x-ray telescopes (e.g., ASCA, RXTE, ROSAT, Einstein, Yokhoh, Chandra) andnotable x-ray discoveries, such as the detection of an x-ray background, resolving thatbackground mostly into point sources, and the detection of x rays from a variety of sources,such as comets, black holes, quasars, and neutron stars.

A TINY MICROPHONE DIAPHRAGMA TINY MICROPHONE DIAPHRAGMA TINY MICROPHONE DIAPHRAGMA TINY MICROPHONE DIAPHRAGMA TINY MICROPHONE DIAPHRAGM based on fly ears has been built. Ronald Miles(SUNY Binghamton) and his colleagues based their diaphragm on Ormia ochracea, a smallparasitic fly that uses sound to track down its cricket host even in complete darkness. The flycan detect changes as small as two degrees in a sound’s direction. Such directional sensitivity—

Phase diagrams for two analogous systems: (left) the nucle-ons in a krypton nucleus and (right) Krypton atoms in a gas(Courtesy LBNL).

8

Physics News in 2002

cooling again. Curiously, the DO events typically were1500 years apart, but sometimes skipped a beat andoccurred after 3000 or 4500 years. The researchersused a global climate model with added environmental“white noise” in the form of random changes in theamount of precipitation and melted ice and snowentering the Nordic seas. Through the SR mechanism,that random influx of fresh water could amplify a weakunderlying 1500-year signal of unknown (but perhapssolar) origin. The scientists found that North Atlanticocean currents, on crossing a salinity threshold, couldhave flipped between two different states, one in whichwarm Gulf Stream waters reached only to midlatitudesand another in which warm waters penetrated muchfarther north. The SR-based model reproduces keyfeatures of the DO events and North Atlantic oceancirculation during the last Ice Age. If confirmed, thismechanism may help to explain why the Ice Age climatewas so much less stable than that of the past 10,000years, in which human civilization has thrived. (A.Ganopolski, S. Rahmstorf, Phys. Rev. Lett. 8888888888, 038501,2002.)

A NEW KIND OF OCEAN WA NEW KIND OF OCEAN WA NEW KIND OF OCEAN WA NEW KIND OF OCEAN WA NEW KIND OF OCEAN WAAAAAVE HAS BEEN DETECTED.VE HAS BEEN DETECTED.VE HAS BEEN DETECTED.VE HAS BEEN DETECTED.VE HAS BEEN DETECTED. The Hawaii-2 Observatory,which sits on the sea floor between Hawaii and California, observes waves of many varieties.Some are acoustic waves that alternately expand and compress water as they propagatethrough the ocean at the speed of sound in water. Others are Rayleigh waves that aretriggered by earthquakes and propagate as horizontal and vertical motions of Earth’s crust,including the sea floor. Researchers have now detected a “coupled” acoustic and Rayleighwave that swaps energy across the interface at the ocean’s floor. Propagating at the soundvelocity of water, the wave both induces motion of the seafloor sediments and createsregions of expansion and compression in the water. The new wave requires that the Rayleighwavelength be shorter than the water’s depth and that the shear velocity at the interface notexceed the water’s sound velocity. The researchers speculate that similar modes might occurat the air-soil interface. (R. Butler, C. Lomnitz, Geophys. Res. Lett. 2929292929, 57, 2002.)

THE QUANTUM ORIGIN OF OXYGEN STORAGE IN CERIUM OXIDETHE QUANTUM ORIGIN OF OXYGEN STORAGE IN CERIUM OXIDETHE QUANTUM ORIGIN OF OXYGEN STORAGE IN CERIUM OXIDETHE QUANTUM ORIGIN OF OXYGEN STORAGE IN CERIUM OXIDETHE QUANTUM ORIGIN OF OXYGEN STORAGE IN CERIUM OXIDE has beenelucidated. Many environmentally friendly technologies, such as catalytic converters andsolid-oxide fuel cells, exploit an amazing property of solid CeO

2, also known as ceria. Under

oxygen-poor conditions, ceria can release oxygen, transforming itself into Ce2O

3. The Ce

2O

3,

in turn, easily takes up oxygen under oxygen-rich conditions and changes back to ceria.Now, physicists from several universities in Sweden offer a detailed quantum-mechanicaldescription of how these reactions occur. The researchers showed that the pivotal transitionfrom CeO

2 to Ce

2O

3 results from the formation of an oxygen vacancy, in which the oxygen

leaves behind two electrons that become localized on two nearby cerium ions. The chargeon that pair of ions then changes from +4 to +3, and a series of reduced compounds form,ending with Ce

2O

3. The ability of solid cerium oxide to store, transport, and release oxygen

is therefore an industrially important example of the quantum process of electron localization.(N. V. Skorodumova et al., Phys. Rev. Lett. 8989898989, 166601, 2002.)

as good as humans’—isunexpected, since the fly’s ears arejust a few hundred microns apart.Mammals’ ears, in contrast, arewell separated from one another,so that differences in soundsignals at the ears providelocalization cues (see PhysicsToday, November 1999, page 24).The fly’s hearing organs are a pairof mechanically coupledmembranes: Sound wavesincident on one membrane candeflect the other. With thiscoupling, the fly can obtain boththe average pressure of anincoming sound and its pressuregradient, which together providelocalization information. The Binghamton researchers’ 2-mm2 prototype microphonediaphragm, shown above, closely reproduced the fly ears’ characteristics. This unconventionalapproach to localizing sound may lead to new applications, such as a compact hearing aidthat responds only to sound in front of the wearer. The work was presented at a December2001 Acoustical Society of America meeting in Ft. Lauderdale, Florida.

ELEMENT 118 RETRACTIONELEMENT 118 RETRACTIONELEMENT 118 RETRACTIONELEMENT 118 RETRACTIONELEMENT 118 RETRACTION. In 1999, physicists at Lawrence Berkeley National Labreported observing three events amid high energy collisions in which it appeared that anucleus corresponding to element 118 had been produced; in each case the nucleus hadquickly decayed into daughter nuclei. Two years later these same researchers came to believethat their analysis of the events, and therefore their claim for discovery of the element, wasdoubtful. (Ninov et al., Phys. Rev. Lett. 8989898989, 039901(E), 2002.)

BELL LABS/LUCENT RESEARCHER DID FBELL LABS/LUCENT RESEARCHER DID FBELL LABS/LUCENT RESEARCHER DID FBELL LABS/LUCENT RESEARCHER DID FBELL LABS/LUCENT RESEARCHER DID FABRICAABRICAABRICAABRICAABRICATE DATE DATE DATE DATE DATTTTTAAAAA. The committee ofindependent scientists investigating charges of misconduct in the way certain Lucentexperiments were performed or reported in scientific journals finally issued its report. Thecommittee asserts that “The evidence that manipulation and misrepresentation of dataoccurred is compelling.” They conclude that Hendrik Schon, but not the coauthors on hismany articles, falsified and fabricated data. (http://www.lucent.com/news_events/pdf/researchreview.pdf )

DID ENVIRONMENTDID ENVIRONMENTDID ENVIRONMENTDID ENVIRONMENTDID ENVIRONMENTAL “NOISE” TRIGGER A CLIMAAL “NOISE” TRIGGER A CLIMAAL “NOISE” TRIGGER A CLIMAAL “NOISE” TRIGGER A CLIMAAL “NOISE” TRIGGER A CLIMATIC ROLLER COASTERTIC ROLLER COASTERTIC ROLLER COASTERTIC ROLLER COASTERTIC ROLLER COASTERDURING THE LAST ICE AGE?DURING THE LAST ICE AGE?DURING THE LAST ICE AGE?DURING THE LAST ICE AGE?DURING THE LAST ICE AGE? Under certain conditions, noise can paradoxically increasea weak signal’s delectability and influence. This phenomenon, called stochastic resonance(SR), has been observed in settings as diverse as chaotic lasers and human reflex systems (seePhysics Today, March 1996, page 39). Andrey Ganopolski and Stefan Rahmstorf of the PotsdamInstitute for Climate Impact Research in Germany have shown that SR may have played a rolein triggering 20 or so abrupt and dramatic warming events-called Dansgaard-Oeschger(DO) events-during the last Ice Age, which lasted from about 120,000 to 10,000 yearsbefore the present. Each DO event started with a roughly 10-year warming of about 10degrees Celsius over the North Atlantic, and each lasted for up to a few centuries before

JANUARJANUARJANUARJANUARJANUARYYYYY::::: OSTP Director John Marburgerpredicts that war on terrorism will not divertthe conduct of science in the U.S. At a Januaryastronomical society meeting, Marburger saysBush Administration “values discovery-oriented science.” DOE Secretary SpencerAbraham expresses willingness to reconsiderU.S. participation in the ITER fusion project.A DOE high energy physics panel identifiesproposed $5 - $7 billion linear particleaccelerator as centerpiece of twenty-year roadmap for field.

FEBRUARFEBRUARFEBRUARFEBRUARFEBRUARYYYYY::::: Bush Administration sendsFY 2003 request to Congress with 8%increase for federal R&D, primarily for DODand NIH. House Science Committeeminority staff comments that overall civilianR&D portfolio request is “business-as-usual.” Marburger states “life sciences maystill be underfunded relative to the physicalsciences.” Science Committee ChairmanSherwood Boehlert (R-NY) later tellsMarburger that if not for defense andnational security needs, “this committeecollectively would be madder than hell, toput it bluntly.” Incoming Director of theDOE Office of Science, Ray Orbach, has aneasy Senate nomination hearing.

MARCH:MARCH:MARCH:MARCH:MARCH: Appropriators roundlycriticize Administration plans to cut USGS.New NASA Administrator, Sean O‘Keefe, isquestioned closely at congressional hearingabout ultimate size of space station. Firstmeeting of President’s Council of Advisorson Science and Technology (PCAST) is held.Friendly and low-key appropriationshearings held on FY 2003 DOE sciencerequest. Science Committee hearing setsstage for higher NSF authorization. Moveto disband DOD’s JASON advisory paneldraws concern. Science Committee hearingon proposed cuts to ATP reveals

congressional support for program.

APRIL:APRIL:APRIL:APRIL:APRIL: Administration publishes new ITARregulations on university-based space research.Science Committee states concern about balancein federal R&D portfolio. Orbach speaks of30-40% budget growth over next five years asappropriate for his office. Proposedunderground physics laboratory at SouthDakota’s Homestake Mine draws attention.House appropriators express strong support forNSF funding. O‘Keefe outlines his vision forNASA. Marburger describes “balance” as amisleading and dangerous term when lookingat science funding. Space station configurationis subject of congressional hearing andindependent advisory committee report.Proposed Administration ATP reformscharacterized as controversial. Congressionalmove to approve use of the Yucca Mountainnuclear waste repository.

MAMAMAMAMAYYYYY::::: O‘Keefe tells appropriators that it ishis “fondest hope” that a larger space stationis ultimately built. Senate appropriators speakout against Administration’s proposed NSFbudget. Senate hearing on Yucca Mountainplan reveals range of opinion. House andSenate authorizers recommend 1.4% to 2.8%increase in total defense R&D.

JUNE: JUNE: JUNE: JUNE: JUNE: By overwhelming recorded vote,House passes legislation to authorize eventualdoubling of NSF budget. Looking ahead,White House issues memorandum guiding FY2004 R&D priorities. Secretary of State ColinPowell highlights role of science in foreignpolicy. Administration report acknowledgeshuman role in global warming. Presidentsends homeland security legislation toCongress containing prominent S&T role.House appropriators approve almost 15%increase in FY 2003 defense S&T funding.OSTP report finds neutron scattering demand

exceeds supply. Senate authorizers holdhearing on NSF, with no mention of billmirroring House bill.

JULJULJULJULJULYYYYY::::: Science Committee drafts S&Tcomponents of homeland security bill.Appropriators recommend increased USGSbudget, rejecting proposed Administrationcuts. Senate roll call vote clears anotherhurdle for the Yucca Mountain repository.Advisory group offers recommendations onDOE lab security. Senate appropriators votefor 9.2% increase in defense S&T. Twohearings on climate change reveal muchcontroversy, with one senator callingAdministration approach “baloney.” Senateappropriators approve big increase for NIBIBat NIH, an almost 12% increase for NSF, and2% increase for NASA. Appropriators’recommendations for DOE physics programsrange from cuts to 7.5% increase.

AUGUSTAUGUSTAUGUSTAUGUSTAUGUST::::: Senate appropriators rejectproposed Administration cuts in ATP. Teacherquality grant funding receives 8.8 % increasein Senate bill, but specific funding forEducation Department science and mathteaching remains low. Bill introduced inSenate to double authorization for NSF.

SEPTEMBER:SEPTEMBER:SEPTEMBER:SEPTEMBER:SEPTEMBER: PCAST prepares draftletter to President Bush urging significantincreases in federal research funding forphysical sciences and some engineeringfields. A DOE fusion advisory panel releasesconsensus strategy document identifyingITER participation as important step. ASenate committee proposes consolidationof NSF and Department of Education mathand science partnership programs. ASenate nano-technology bill is introduced.House appropriators approve DOE bill withzero to 7.5% increases for various physicsprograms.

OCTOBER:OCTOBER:OCTOBER:OCTOBER:OCTOBER: PCAST meets, with no publicdiscussion of draft letter to President Bush.Appropriators clear FY 2003 DOD bill with16.2% increase for defense S&T programs.DOD S&T advisory board recommends thatAdministration allocate 3% of entiredefense budget for S&T. Houseappropriators recommend almost 13%increase for NSF in FY 2003. House Sciencecommittee hearing on balancing homelandsecurity with research and education. Houseappropriators recommend 2.7% increasefor NASA, with this and Senate billcontaining 11.3% to 15.9% increases foragency’s S&T budget. Congress deadlockson appropriations bills, and recesses aftervoting to keep spending at FY 2002 levelsuntil January. National Academies’presidents issue statement on science andsecurity.

NOVEMBER:NOVEMBER:NOVEMBER:NOVEMBER:NOVEMBER: Orbach appears beforevarious DOE science advisory panels, layingout ambitious schedules and offering strongsupport. Congress passes bill authorizingdoubling of NSF budget.

DECEMBER:DECEMBER:DECEMBER:DECEMBER:DECEMBER: President Bush signsHomeland Security Act containing S&Tprovisions; Lawrence Livermore NationalLaboratory most immediately affected. Aforum in Washington addresses science andengineering workforce issues. A fusionadvisory panel approves plan to put fusion-generated electricity on the grid in about35 years. Administration seeks commentson a new climate change plan. NationalScience Board releases a preliminaryinfrastructure report. President Bush signsNSF authorization bill. Months-long FY2003 budget stalemate continues.Richard M. JonesThe American Institute of Physics

A microphone diaphragm based on fly ears (Courtesy RonaldMiles et al.)

Depiction of two glacial climatestates: a stable “cold” mode (bot-tom) and an unstable “warm” mode(top).

Highlights of Science PHighlights of Science PHighlights of Science PHighlights of Science PHighlights of Science Policy and Budgolicy and Budgolicy and Budgolicy and Budgolicy and Budgeeeeet Det Det Det Det Devvvvvelopments in 2002elopments in 2002elopments in 2002elopments in 2002elopments in 2002

9

10 February 2003 NEWS

Proteins are the smallest objectsin biology with a specific function,and as such are building blocks—much like atoms in chemistry andquarks in high energy physics.Proteins have enough stability tomaintain their 3D structure, whileretaining the flexibility to performsimple tasks. Knowledge of the 3Dstructure of proteins is necessary tounderstand their biological func-tions, and also for applications likedrug design.

Some HistorySome HistorySome HistorySome HistorySome HistoryIt is difficult to pinpoint exactly

when modern quantitative molecu-lar biophysics started, but 50 yearsago on 28 February 1953 is a natu-ral entry point, when James Watsonand Francis Crick completed theirfamous molecular model of thedouble helix structure of DNA, basedon the x-ray diffraction work ofRosalind Franklin and MauriceWilkins. In their paper in Nature,their understated remark “It has notescaped our notice that the specific pair-ing we have postulated immediatelysuggests a possible copying mechanismfor the genetic material,” opened upthe modern era in biochemistry.

The discovery of the structure ofDNA is perhaps the most importantscientific event of the second half ofthe 20th century. This structure in-troduced the idea of complementarity,in which knowing one strand deter-mines what the opposite strandshould be, with the base pairs A, Tand G, C always occurring together.This pairing provides the basis forgenetics and reproduction. This is allnow taken for granted, but weshould not forget that just monthsbefore the Watson and Crick paper,Linus Pauling had published a threehelix model for DNA.

While DNA provides the geneticcode, these are only the encodedinstructions which must be decodedand implemented to be useful.

In the last 50 years, molecular biol-ogy has gradually become morequantitative. With the recent near-completion of the human, mouse andother genomes, the genetic code is nowavailable as the base pairs of DNA. It isthis sequence (ATGCAATCGA… ),about 3 billion altogether, that containsall the information needed for life. DNAis largely inert— it is the computer code,but of much more interest is what hap-pens when the program is run.

About 2% of the genetic materialis genes, which are specific

Protein Folding, HIV and Drug Designby Michael Thorpe

sequences of bases that encodeinstructions on how to string aminoacids together to make the polypep-tide chains that will then fold to form3D proteins. At each site of DNA,there is a choice of one of the basesA, T, G, or C. Hence to encode forthe 20 amino acids, it takes three ad-jacent sites of DNA, called a codon,which leads to 64 choices. This re-dundancy has bothered people, andmany elegant encoding schemeswere proposed. The truth turned outto be somewhat prosaic, with be-tween 1 and 6 codons mapping ontoeach amino acid, in a many to onemapping.

To physicists who are inclined tothink that nature always goes forelegance, the translation schemefrom DNA, via RNA transcription,to amino acid sequence can be adisappointment. However, realizingthat the complex systems of biol-ogy have evolved continuouslythrough a series of very small evo-lutionary steps, we may regardbiology being locally optimized. Itis a design that works.

When the polypeptide chain foldsinto a 3D structure, it becomes afunctioning protein. We are now see-ing molecular biology beingunderstood from the ground up —starting with the smallest molecularbuilding blocks from the base pairsof DNA that encode for the aminoacid sequences of proteins, to the3D structure of proteins, to com-plexes containing proteins, DNA andRNA, and up to self-contained bio-logical entities like viruses and cells.

ProteinsProteinsProteinsProteinsProteinsThe forefront of molecular bio-

physics has now moved to proteins.Each one has a simple task, out ofwhich something as complex as amouse or you and I is constructed.Indeed, both have very similar setsof proteins, totaling around 30,000,with about 95% being the same orvery similar. This has come as a con-siderable shock to some humans,but mice have remained quiet aboutit. The linear sequence of aminoacids, as shown in Figure 1, folds asit comes off the ribosome, which isthe molecular machine where theamino acids are assembled into apolypeptide chain in the right se-quence, according to the geneticcode. The DNA sequence for the firstfive amino acids of the protein HIVprotease is CCT CAA ATC ACT CTT,which encodes for the amino acids

proline, glutamine, isoleucine, threo-nine and leucine.

Proteins arise from exponentiallyunlikely sequences of amino acidsas determined by evolution. Theunfolded polypeptide chain is arather uninteresting 1D random coilthat has no useful function until itfolds into a compact 3D protein asshown in Figure 2. How a proteinfolds in times that range from a mi-crosecond to a few seconds remainsthe subject of much study, as the pro-

tein does not have enough time tosample all possible conformations.Thus some kind of sequential orhierarchical process must occur,where perhaps secondary structureslike the alpha helices and beta sheetsform first, and then they in turn cometogether to form a rather compact3D structure. It is important thatproteins are three-dimensional, bothfor functionality, and as the smallestcomponent that defines us as threedimensional objects.

Proteins are compact macromol-ecules that exist and function in anaqueous environment. Protein func-

tions are very varied, such as dock-ing against another protein, RNA orDNA, forming a channel for ions topass through, or the proteins calledproteases which can chop apolypeptide chain into segments ofthe right length.

FlexibilityFlexibilityFlexibilityFlexibilityFlexibilityThe balance between stability

and function can be studied byusing constraint theory. The con-straints associated with the unfoldedpolypeptide chain are the covalentbond lengths and angles, and thelocking of the dihedral angle associ-ated with rotation around thepeptide bond. The additional con-straints that are responsible for the3D protein structure are hydropho-bic interactions and the hydrogenbonds that act to cross-link differ-ent pieces of the polypeptide chain.

Although constraint theory onlyinvolves topology, it is necessary toknow the 3D protein structure fromx-ray diffraction experiments inorder to assign hydrophobic and hy-drogen bond constraints. In 1970,the Dutch mathematician GerardLaman worked out a completetheory of constraints for 2D systems.This allows the rigid regions and theflexible joints between them to beidentified. Some parts of the rigidregions may be over-constrained andcontain redundant bonds and theseare also identified.

In 1985, the mathematiciansTlong-Seng Tay and WalterWhiteley extended this work withthe Molecular Framework conjec-ture, which applies to the subsetof all 3D networks such as thosefound in macromolecules withcovalent bonding, and so can beapplied to proteins. It is now pos-sible to determine the rigid regionsin a 3D protein and the flexiblejoints between them, as shown inFigure 2. Such knowledge is impor-tant in understanding the stabilityand function of the protein. Thelower panel in Figure 2 shows thesame protein with a small ligandattached, which inhibits the func-tion of the protein associated withthe opening and closing of the twoflaps at the top. These now becomepart of the rigid core with the ligandpresent. This is the basis of mostdrug design—shutting down theactivity of one protein, while avoid-ing the toxicity that would result ifother proteins were affected.

When proteins unfold due to

environmental changes in thelocal pH etc., or in the lab byincreasing the temperature, func-tionality is lost. While the detailedpathways associated with thisunraveling differ for different pro-teins, the whole process can becharacterized by an overall loss ofrigidity. As non-covalent bond con-straints are broken, the rigid coregets slightly smaller, and then frac-tures into smaller rigid pieces verymuch like a weak first order phasetransition. There is a correspond-ing increase in the number ofindependent motions associatedwith internal degrees of freedomthat are now possible. Within theconstraint approach, thesemotions have no restoring forceassociated with them, but in real-ity are low frequency or floppymodes. This viewpoint emphasizesthe similarities among all proteins,and identifies the mean coordina-tion as the reaction coordinate forprotein unfolding and folding. Themean coordination is the averagenumber of constraints per atomtaken over the whole protein.

Drug DesignDrug DesignDrug DesignDrug DesignDrug DesignRigid region decompositions,

shown in Figure 2, are a useful aid inunderstanding protein function, andalso in applications such as thesearch for drug candidates in thepharmaceutical industry. Drugs aresmall molecules with typicallybetween 10 and 100 atoms, whichattach themselves to a protein andinhibit its function. A good attach-ment requires a good steric fit aswell as favorable van der Waals con-tacts. The computer screening oflarge databases of molecules tosearch for drug candidates is becom-ing more sophisticated usingsoftware such as SLIDE. Of coursethis is only the first step in the drugdiscovery process. The lower panelin Figure 2 shows how an inhibitorattaches itself to the protein HIV pro-tease. The flaps at the top can nolonger open and close, rendering theprotein dysfunctional, which in thiscase is of course very beneficial, andhas given the best success so far inthe worldwide fight against AIDS.

Michael Thorpe is currentlyUniversity Distinguished Professorof Physics at Michigan State University.From the middle of the year he will beProfessor of Physics, Chemistry and Bio-chemistry at Arizona State University.He is a Fellow of the APS.

Figure 2. The protein HIV proteaseis a dimer that consists of 2 polypep-tide chains, each containing 99amino acids, and is an importantpart of the HIV virus.

AWARDS from page 1

under age 30, for his or her out-standing scientific contribution tothe knowledge of physics.” To beeligible, a candidate must turn 30no earlier than April 1, 2003.

Another prize open to all fieldsis the Julius Edgar Lilienfeld PrizeJulius Edgar Lilienfeld PrizeJulius Edgar Lilienfeld PrizeJulius Edgar Lilienfeld PrizeJulius Edgar Lilienfeld Prize,which carries a stipend of $10,000and which “shall be awarded foroutstanding contributions to phys-ics by a single individual who alsohas exceptional skills in lecturing todiverse audiences.” Last year a spe-cial canvassing committee solicited

nominations for the Lilienfeld Prizewith considerable success, but addi-tional nominations are being soughtthis year as well to keep the poolstrong and up-to-date.

The descriptively named Prize toPrize toPrize toPrize toPrize toa Faculty Member for Research ina Faculty Member for Research ina Faculty Member for Research ina Faculty Member for Research ina Faculty Member for Research inan Undergraduate Institution an Undergraduate Institution an Undergraduate Institution an Undergraduate Institution an Undergraduate Institution needslittle further explanation. It is givenfor research in any field of physicsperformed at a non-PhD granting in-stitution, and typically rewards aprogram of research that involvesnot only the faculty member but un-dergraduates as well. Both the faculty

member and his or her institutionreceive stipends of $5000.

The LeRoy Apker ALeRoy Apker ALeRoy Apker ALeRoy Apker ALeRoy Apker Awarwarwarwarwarddddd wasestablished in 1978 and is given foroutstanding research by an under-graduate. Typically two awards aregiven each year in parallel compe-titions, one for research done at aPhD-granting institution, and onefor research at a college or univer-sity that does not grant the PhDdegree in physics. From the poolof nominees, six finalists are cho-sen, three in each category. Thefinalists each receive $2000 and

their institutions $1000. The tworecipients each receive $5000, andtheir respective institutions alsoare awarded $5000 to be used tosupport undergraduate research.

Other APS awards open to re-search in any field of physics includethe EdwarEdwarEdwarEdwarEdward A. Bouchet Ad A. Bouchet Ad A. Bouchet Ad A. Bouchet Ad A. Bouchet Awarwarwarwarwarddddd whichis given to recognize “a distinguishedminority physicist who has made sig-nificant contributions to physicsresearch” and is sponsored by a grantfrom the Research Corporation; andthe Maria GoepperMaria GoepperMaria GoepperMaria GoepperMaria Goeppert-Mayer At-Mayer At-Mayer At-Mayer At-Mayer Awarwarwarwarwarddddd,which is given “to recognize and

enhance outstanding achievement bya woman physicist in the early yearsof her career” and is supported bythe GE Fund. Both these awardsinclude a program in which therecipient travels to a number of insti-tutions to present lectures on researchand also to serve as a role model forthe students who may be consider-ing physics as a career.

Information on all these prizesand awards, including eligibilityrequirements, deadlines, and nomi-nation procedures, may be found onthe web site at wwwwwwwwwwwwwww.aps.or.aps.or.aps.or.aps.or.aps.org/prawg/prawg/prawg/prawg/praw.....

Figure 1. The first 5 amino acids ofthe polypeptide chain of the proteinHIV protease that result from theinstructions in the DNA codons givenin the text. Here the green spheresare C atoms, blue are N, red are Oand grey is H.

February 2003 11NEWS

LETTERSBohr Misunderstood Heisenberg’s Motivation

As an APS member I alwaysread with interest the informationcontained in APS NEWS. TheAugust/September issue came tomy attention only now after my re-turn from extended trips. Havingworked under Werner Heisenbergfrom 1950 to 1970, and havingbeen told by him, in 1969, at myrequest, about his visit to Bohr in1941, I read with particular inter-est the article by Frederick Seitz“Letters Reveal New Insights Intothe Bohr-Heisenberg Meeting”.

This article shows a goodunderstanding of Heisenberg’s per-sonality and of the situation in whichhe found himself in Nazi Germany.However, Seitz misses the main mo-tivation of Heisenberg’s visit toCopenhagen in 1941. Heisenberghad been drafted by Army Ord-nance, at the beginning of the war in1939, to work on the feasibility ofan atomic bomb. By 1941 he hadcome to the conclusion that the pro-duction of such weapons would bepossible in the long run but techni-cally so difficult, by isotopeseparation as well as by the produc-tion of what is now called plutonium,that it would take many years, at leastin Germany under war conditions,to make just one bomb.

Atomic weapons might decidethe war only if the war dragged onlong enough. Couldn’t the smallinternational community ofnuclear scientists, in the meantime,come to an agreement not to build

such bombs? What would Bohr,the father figure of that commu-nity, think about this idea? C.F. vonWeizsaecker suggested thatHeisenberg ask Bohr. A conferenceon astrophysics was arranged atthe German Cultural Institute setup in Copenhagen for propagandapurposes by the Cultural Divisionof the German Foreign Ministry, ofwhich Weizsaecker’s father was thetop civil servant. Bohr boycottedthat Institute but for Heisenberg,lecturing at its conferencetogether with several well-knownGerman astrophysicists, it was theonly possibility to get permissionfor a visit to occupied Denmark,and to see Bohr.

Heisenberg paid several visits toBohr and to Bohr’s institute on thatoccasion. At one of them,Heisenberg began to tell Bohr aboutthe technical feasibility of nuclearbombs, in very involved languageso that Bohr would understand butnot any potential Gestapo eaves-dropper. But Bohr did not want tolisten when this subject came up.He was upset and excited. He mis-understood Heisenberg’s indirecthints as meaning that Heisenbergwas trying to build the bombwhereas Heisenberg had onlymeant to say that he understood theproblem after two years of study-ing, and that the construction, verydifficult and at present not feasibleanyway, could still be avoided.Moreover, Bohr resented

Heisenberg’s suggestion that Bohrgive up his boycott of the GermanCultural Institute although, as Bohr’sunsent letters now show, Bohr real-ized that Heisenberg was motivatedby his concern for Bohr’s futuresafety and well-being. In Septemberof 1941 it looked as if Germanymight win the war.

In any case, Bohr’s anger cannothave been very deep. Two days afterhis ill-fated discussion with Bohr onthe bomb, Heisenberg paid anothervisit to Bohr at Bohr’s home. On thatoccasion they avoided politics, theydiscussed physics, Heisenbergplayed the piano, and Bohr read astory to him. As Heisenberg wroteto his wife while still in Copenhagen,it was a harmonious meeting just asin the old days. Heisenberg postedthis letter after his return to Germanyto avoid censorship. It was foundonly recently by the Heisenberg fam-ily among private papers and is partlypublished by H. Rechenberg in theforthcoming proceedings of theHeisenberg Centennial of theSaxonian Academy of Sciences.

Regarding the remark by Fermi’sstudent quoted by Seitz at the endof his article: It seems thatHeisenberg never looked as if he hadever done “anything important.” Hewas said to look like a farm boy atthe time he discovered the uncer-tainty principle. When I first metHeisenberg in 1949 I thought thathe looked like a successful, good-natured, reasonably athletic,down-to-earth owner of a medium-sized business, not at all like a deepthinker oblivious of his surround-ings. His high spirits revealedthemselves in discussions only.Klaus GottsteinMunich, Germany

The article by Ken Krane (APSNews, Back Page, November, 2002)is an enlightening and welcomereport on attempts by a task forceto identify success factors that at-tract students to enroll in physicscurricula. I find the report to beconsistent with the increasing ef-fort to populate the humanresources physical sciences pool,not only to provide professionalsin physics but also to augment thecapability of professionals wherethe knowledge of physics contin-ues to play such an indispensablerole in recent developments ofother fields. In fact, the value ofthese developments prompts me towonder if in due course “physics”will go the way of “natural philoso-phy” as known in earlier times.While this thought might bear con-sideration in the design of futurecurricula, it should not detract fromthe course reported by Krane.

The article alludes to the diffi-culty of attracting women andminority students into the physicscurricula. Among the factors thatthe task force is cited to have singledout as one measure of a “thrivingundergraduate physics program,” isthe presence of a “significant rep-resentation of women andminorities.” The article also indi-cates the task force will focus onthis topic in a meeting held thismonth.

Whatever may be the outcomeof said meeting, I wish to cite myexperience related thereto, par-t icularly since I was askedrecently to offer my view on thereason “students of color” haveless preference for pursuing stud-ies in physics as compared toother sciences. One of my imme-

diate suggestions was that thepractical value of other sciencesis ever more evident in use ofhousehold goods, e.g., use of dis-infectants (chemistry andmedicine), cultivating plants, es-pecially use of herbs (biology),etc. In this case, familiaritybreeds attraction. I also recalledan earlier posed personal viewthat the unfavorable socioeco-nomic conditions experienced bystudents of color detract frompursuit those careers thatrequire relatively long term studywhen choosing to remain a con-tributing family breadwinner isof higher priority.

The desired response to theabove cited first view seems clear.In this connection, perhaps animportant opportunity wasmissed in not communicating ef-fectively the role of physics in theevolution of our space program.Rightly so, the role of engineer-ing in this national effort wasproperly communicated with duerecognition that an entire federalagency was dedicated to it. As forthe socioeconomic factor, it alsoseems clear that where theproper economic assistance isavailable for a particular courseof study, students of color willgravitate toward it. The best evi-dence offered for this view is thesupport that the National Insti-tutes of Health (NIH) has devotedto attracting students of colorsince 1974—nearly 30 years ofsustained interest—when thefirst effort began. My visits tocolleges and universities to en-courage students to pursuecareers in the physical sciencesillustrates that the principal com-petition for drawing students ofcolor into these areas comesfrom the NIH-supported bio-medical programs that offerstudents viable and long termsupport for their education. Asurvey of the results achieved bythese commendable NIH pro-grams should bear out this point.

The one program in the physi-cal sciences that has shownunquestionable success in my viewis the one initiated by Bell Labs andco-designed by the Society’s Com-mittee of Minorities, of which I amone of five founders. I would beremiss if I did not acknowledge theindispensable role that Bell Labsemployee, Joseph Burton (thenAPS Treasurer and since deceased)played in facilitating this interac-tion. The Bell Labs program wasdesigned to take undergraduatephysics students of color and pro-vide them the long term supportthrough the doctorate degree.Thus, I offer that the obstacle toattracting students of color intophysics is basically one of econom-ics. In addition, any efforts by theSociety to make better known thevalue of physics to parents, guard-ians and younger students undertheir charge, would lend strongcollateral incentive for attractingstudents to the physical sciences.J. V. MartinezBethesda, MD

Economic Assistance Key for Students of Color

John Marburger deserves greatpraise for his Back Page article, “Tellthe truth about particle physics.”(APS News, December 2002). It isthe most articulate and coherentpresentation of the justification forBig Physics—in fact, for physicsprojects on any scale—that I haveread, as well as being a realisticdescription of the funding environ-ment in which big science projectsmust live (or die). I believe that weare fortunate indeed to have some-one of his capabilities in a key policyposition.

The only observation that Iwould add to his discussion is thatbig science projects have no nec-essary schedule for their initiation,except perhaps in times of greatcrisis. This suggests to me that thereare other options for funding suchprojects besides the traditionalmassive commitment by Congress,an approach that suffers from thepolitical instabilities thatMarburger notes.

One alternative might be forCongress to enact, and NSF tomanage, small set-asides for eachdiscipline each year that couldaccumulate untouched until a fundreaches the size needed to carryout a big project on which, e.g., theparticle physics community couldagree. While such a fund could bevulnerable to increasing politicalpressures within a given disciplineas the fund grew, it would be largelyisolated from external factors.

I imagine that there are many morepractical ways in which individual bigscience projects could escape the fate

of the SSC, but I suspect that anysuccessful general strategy will hingeon the fact that doing worthwhilescience, big or small, is essentially atimeless endeavor.William F. HallThousand Oaks, California

Create a Physics Piggy Bank

I enjoyed reading about the2002 Ig Nobel Prizes in theDecember APS News. I was, how-ever, a little surprised to see amongthe listed winning topics “Estima-tion of the Total Surface Area InIndian Elephants.” It might soundlike a frivolous, pedantic topic, butknowing the surface area of an ani-mal is not quite as trivial as onemight suppose. The total surfacearea determines an animal’s rateof heat loss and their basal meta-bolic rate (BMR). In veterinarymedicine, drug dosage (i.e., # ofmgs) is based on estimates of totalsurface area, not on kilograms ofbody mass, because it is the BMRwhich determines how fast thedrug will be metabolized. This isstill partially true in human medi-cine and dates back to the early20th century, when a husband andwife physiology team (du Bois anddu Bois) actually pasted pieces ofpaper on to human subjects in or-der to determine their totalsurface area and to develop asemi-empirical formula that wouldestimate it using body length, whichis easily measured.Michael D. DelanoBrooklyn, New York

Elephant’s AreaImportant

There are fundamental scien-tific questions that intrigueprominent scientists that ought notbe characterized as pseudoscienceand thus be prevented from beingdiscussed in science classes.Lawrence M. Krauss [APS News,August/September 2002] dis-misses such questions when hedisparages intelligent design andcasts it together with young earthcreationism, UFO sightings, etc.

I should like to recommend thebook “Cosmos, Bios, Theos: Scien-

Book Gives Perspective on Science and Religiontists Reflect on Science, God, andthe Origins of the Universe, Life,and Homo sapiens,” edited by H.Margenau and R. A. Varghese. Thisanthology presents the perspectiveon the relationship between thescientific enterprise and the reli-gious view of reality. Contributorsinclude over twenty Nobel Prizewinners and distinguished scien-tists from different disciplines.Moorad AlexanianWilmington, North Carolina

Some Recent Focus Stories:

Deconstructing BirdsongA mathematical model of a few neurons in the birdbrain reproduces a surprising range of real sparrowtunes.

Spooky at Any SpeedMoving at close to the speed of light may createentanglement in particles that seemingly had nonewhile at rest.

http://focus.aps.orghttp://focus.aps.orghttp://focus.aps.orghttp://focus.aps.orghttp://focus.aps.org

Down-to-earth accounts of hot research from thePhysical Review journals—ideal for college physics majors andresearchers interested in work outside their specialty. Write tojoin-focus@lists.apsmsgs.orgjoin-focus@lists.apsmsgs.orgjoin-focus@lists.apsmsgs.orgjoin-focus@lists.apsmsgs.orgjoin-focus@lists.apsmsgs.org to get weekly e-mail updates.

J.R. Sauer

J. Devaud/NIST

12 February 2003 NEWS

APS News welcomes and encourages letters and submissions from its members responding to these and other issues. Responses may be sent to: letters@aps.org.

THE BACK PAGE

It’s 2002 and there are still phys-ics departments with no womenfaculty, and many more with nominorities. The trends are generallyin the right direction, but change ispainfully slow, in marked contrastto progress in the equally demand-ing disciplines of biology, chemistry,engineering, mathematics, andmedicine. So why has physicsproved so resistant to change?

When I (gently) ask my col-leagues around the country whythey hire mostly or only men, theysay there simply are no womenavailable to hire. But the top 10physics departments graduated138 women with PhDs in physicsin the five-year period 1988-1992(10.7% of total PhDs). Twenty tothirty of the top physicists pro-duced each year are women. In2000, 13% of physics PhDs wentto women. Women are indeedavailable.

Recruitment is often targeted,however, perhaps more so in themore elite universities. They wantthe best, and they don’t expectthem to float up through the appli-cations process. Thus, hiringwomen requires (a) valuing theirtalents, and (b) thinking of themwhen a job (or talk or prize) is athand. This does not appear to hap-pen automatically. So where are wefalling down? My physics col-leagues are good people. They donot discriminate, they would notdeny opportunity to women be-cause they are women. So where isthe problem? Let me try to answerthis question with three stories.

1. The powerful act powerless—the system worked for them, and theyexpect it to work for everyone. At theMarch 2002 APS meeting in India-napolis, the chair of a large physicsdepartment at a major Midwesternuniversity pointed out what he seesas the problem. “At the beginningof my introductory physics class,”he explains, “I ask which studentsare planning to major in physics,and the women do not raise theirhands!” His department is respon-sible for graduating many physicsmajors and PhDs, yet he is con-vinced that women simply don’t likephysics and there is nothing he cando to change their minds. He andhis colleagues feel powerless toaffect gender imbalance. Anotherphysicist nods his head in agree-ment, convinced that women aresimply more interested in otherfields, like biology and chemistry.

But the young students in thephysics chair’s class are new to thediscipline. Perhaps they have neverhad a physics class before, or per-haps their high school class did notcatch their imagination. Is it nec-essary that they know they lovephysics before they’ve studied it?Is early certainty of one’s vocationa sign of one’s talent for it? Shouldphysicists come only from theranks of those who enjoy what mayhave been a boring, rote-like class

Speeding up the Long Slow Path to Changeby Meg Urry

with little connection to modernphysics research? Shouldn’t phys-ics professors take as theirresponsibility the mission of show-ing students how very interestingand rewarding physics can be?

But most professors teach phys-ics the way they were taught. Thisis where the problem starts to be-come clear. The students in classtoday are not junior versions oftheir professors. Their paths in lifehave been different, their interestsmay be different, their approachesto science may be different. Yet westill define the best students as be-ing those who are just like us. Thissolipsistic approach stems from therelative homogeneity of our phys-ics faculty, and it reinforces thathomogeneity. Yet diversity histori-cally has led to intellectualbreakthroughs; the greatest newideas are born in the roiling watersat the confluence of different riv-ers of thought. A narrow set ofviews and styles in physics will ben-efit no one—not women andminorities, and most importantly,not the science.

(2) “You’re not a member of myclub.” A young woman physicist,an assistant professor at a small butexcellent four-year college— ener-getic, smart, talented, attractive,and with a friendly personality—goes to the 2002 APS March meet-ing in Indianapolis to give a talk.She wanders through the conven-tion center and separatelyencounters three women physi-cists. They all smile and offer tohelp her, as she is obviously justarriving. But they don’t have theprogram and the registration deskhas closed for the night. She walksover to a group of young menabout her age, who are sitting andtalking nearby. She stands politelywaiting for them to acknowledgeher. But apparently what they arediscussing is so earthshaking thatthey fail to notice her presence.Finally, she butts in and asks if any-one has the program for the nextday. “Certainly not,” answers thefirst man, annoyed at the interrup-tion. “Why would I carry thataround? It’s heavy.” The secondchimes in and lets her know howstupid her question is and how herpresence is interrupting their im-portant discussion. She turns away,uncomfortable and upset, and thenext day is still fretting about thisepisode.

This story demonstrates thatsome young male physicists can beboors, perhaps, but more that it isall too easy for women physiciststo feel ill at ease and out of place.There are few role models for mostof us. There are few women fac-ulty and few fellow female students.Women physicists have no clearpath in front of them, no clear con-nection between where they are(pursuing physics) and where theywant to be: advancing in the pro-fession.

It is no wonderthat women physi-cists tend to havegreater self-doubtthan men. In astudy at MIT,graduate studentsin male-domi-nated science andtechnology fieldswere asked to ratetheir own abilities,and their profes-sors were asked torate them as well.The actual distri-butions of abilityfor men and women did not differ,according to the professors, butthe self-evaluations did. On aver-age, the women rated themselvesbelow average and the men ratedthemselves above average.

In physics departments aroundthe country, women are feeling illat ease, out of place, not at home.Often it’s as simple as statementsabout what makes a good scien-

tist, or what some famous scientistwas like. Think of our heroes: readFeynman’s autobiography and tellme what you thought. Maybe youliked him, maybe you hated him,maybe you envied him —but prob-ably you didn’t feel asuncomfortable as his women read-ers did. Several wives gounmentioned or at leastundescribed, and women in gen-eral appeared to play a remarkablysmall role in his life—except for theones he was trying to date.

3) Sociology holds some of the an-swers, if physicists would only listen.Studies have shown that refereesjudge gender of author, not qualityof work. In 1983, Paludi and Bauerpublished a revealing study aboutthe influence of gender on percep-tion of excellence. Three-hundred-sixty referees, half menand half women, were each sent amathematics paper to rate, with theauthor’s name given variously asJohn T. McKay, Joan T. McKay, or J.T. McKay. The reviewers found thatthe man’s paper was considerablybetter than the woman’s. The neu-tral, initials-only designation wasalso rated rather lower than theman’s paper, apparently becausemany referees believed the initialsto represent a woman. Both menand women found the paper writ-ten by the woman to be markedlyless good than the man’s paper. Soit isn’t just men undervaluingwomen’s work, it is all of us.

Gender-based bias can also befound in the literary/artistic world.The Modern Language Associationreferees abstracts submitted for itsannual meeting before accepting

them. In1974, theMLA began“blind” refer-eeing, inwhich ther e f e r e e swere nolonger toldthe authors’ident i t i e s .Prior to this,women hadgiven veryfew papersat MLA meet-ings. Within

a few years of the change, womenwere giving papers in roughly thesame percentage as in the submit-ted abstracts. A similar shift to blindauditions for the world’s great or-chestras has greatly increased thenumber of female musicians ac-cepted.

A few years ago Nature pub-lished several articles about genderbias in applications for research

Meg UrryMeg UrryMeg UrryMeg UrryMeg Urry

“We are almost all prejudiced in the sense thatwe have absorbed the gender and racestereotypes that prevail in our society.”

support from the Swedish MedicalResearch Council. Two researchersobtained the applications and thegrades and comments. They foundthat women had to have publishedmuch more, and had to have beenrated much more highly, in orderto have an equivalent chance at thefellowship. In quantitative terms, awoman had to be more than twiceas good as a man to rank equallyon the final list.

These results agree well withlongitudinal studies of women andmen PhD scientists, closelymatched in ability and field, whichfound strong evidence of lesseradvancement for even very tal-ented women. Even taking intoaccount variables like family statusand productivity, the overwhelm-ing predictor of success wasgender. Women were paid less,were less likely to be hired into fac-ulty positions, took longer to gettenure, and fewer got tenure thanthe men.

Your female colleagues are sub-jects of sociological experimentsevery day, when they are inter-rupted and their speech occupiesa smaller fraction of the discussion,when their idea is dismissed or over-looked but lauded if a man suggestsit a few minutes later, when stu-dents are skeptical of theirexpertise but unhesitatinglyassume male professors are fullycompetent. The popular image ofsuccess, of competence, of science,is male. We are almost all preju-diced in the sense that we haveabsorbed the gender and race ste-reotypes that prevail in our society.The best any of us can do is to rec-ognize it and correct for it, long

enough to change the face of sci-ence, and thus to render obsoletethe present stereotypes.

So what is the strategy for mov-ing forward? Clearly, we need toraise awareness about the extrabarriers for women. These socio-logical barriers affect many otherarenas besides physics, but phys-ics is still lower in the percentageof women and slower/harder tochange. My own speculation isthat physics is more hierarchical,more elitist, than other profes-sions, and thus women’s feelingsof inadequacy are exaggerated.The effect on women is thereforeharsher in physics. It’s an hypoth-esis that bears testing, if we canfind an objective way to assess elit-ism.

Meanwhile, there are a fewcommon sense recommendations.First, let us not assume others arelike us. Interest in physics comesat different stages and manifestsin different ways. Female talent isout there—let’s look for it and nur-ture it. If girls and women comeforward less readily, let’s not inter-pret that as disinterest orreluctance or lack of skill. Second,we must compensate for the lackof role models, offer better sup-port, and teach parents, teachers,guidance counselors to encourageinterest from girl proto-scientists.Third, women who have persistedpast the barriers may well feel iso-lated, invisible, and marginalized.No women or men should imag-ine the playing field ever reallylevels out. We hope it will some-day, but there is no evidence thatit has done so yet.

I believe there is good reasonfor optimism. The percentage ofphysics PhDs going to women isincreasing, albeit slowly. Some se-nior male colleagues are taking thischallenge as their own, and havehelped effect change. The numberof women hired as junior facultymay be even be roughly the samepercentage of assistant professorsas of postdocs. Finally, the dearthof women in physics is receivingserious, concentrated attention, asin the national Commission on theAdvancement of Women andMinorities in Science, Engineer-ing, and Technology Developmentreport (See www.nsf.gov/od/cawmset/start.htm) and the Interna-tional Conference on Women inPhysics (See www.if.ufrgs.br/~barbosa/conference.html). But wecannot wait complacently forphysics to enter the modern erain gender equality. It is too diffi-cult a problem and only persistentpressure will make the big beastmove.

Meg Urry is a professor ofphysics at Yale University. Thisarticle was adapted from a longerarticle that appeared in the fall 2002issue of The Gazette, the newslet-ter of the APS Committee on theStatus of Women in Physics.