europhysicsnews · europhysicsnews v o l u m e 3 7 ¥ n u m b e r 4 i n s t i t u t i o n a l s u b...

europhysicsnewsV

olu

me 37

•nu

mb

er 4

Institutional subscription price:99 euros per year

37/42006

The tenth article of Ettore MajoranaVita brevis of antibubbles

The chemical physics of the photostability of lifeSeismic waves in the ionosphere

Nanostructures and nanowires by field emission

European Physical Society

Article available at http://www.europhysicsnews.org

http://www.europhysicsnews.org

number 4 • volume 37 • 1

contents

europhysicsnews

europhysicsnews2006 • Volume 37 • number 4

Report on

EPS council 2006

Seismic waves

in the ionosphere

Vita brevis

of antibubbles

m PAGE 06

m PAGE 11

m PAGE 24

cover picture: stone-printed fish eating another one . © CosmoCaixa museum, Barcelona. (see p. 31)

EDITORIAL03 The European Institute of Technology

O. Poulsen

HIGHLIGHTS04 Some light on electric arcs

Wetting or not wetting?05 More on helium molecules

The space elevator not yet for tomorrow

NEWS06 Report on EPS Council 2006 07 The 2006 Sackler prize08 Irish science takes centre stage09 Letters10 World conference on physics and sustainable development

FEATURES11 Seismic waves in the ionosphere

P. Lognonné, R. Garcia, F. Crespon, G. Occhipinti, A. Kherani and J. Artru-Lambin

15 The tenth article of Ettore MajoranaR.N. Mantegna

17 Physics in daily life: cycling really fastL.J.F. (Jo) Hermans

18 Quicksand!A. Khaldoun, G. Wegdam, E. Eiser and D. Bonn

20 The chemical physics of the photostability of lifeA.L. Sobolewski and W. Domcke

24 Vita brevis of antibubblesS. Dorbolo, N. Vandewalle, E. Reyssat and D. Quéré

26 Physical properties of nanostructures and nanowires by field emissionS.T. Purcell, P. Vincent and C. Journet

MUSEUM REVIEW29 CosmoCaixa, Barcelona

BOOK REVIEW30 Europe’s quest for the universe31 Worlds of flow

europhysicsnews2006 • Volume 37 • number 4

europhysicsnews is the magazine of the Europeanphysics community. It is owned by the EuropeanPhysical Society and produced in cooperation withEDP Sciences. The staff of EDP Sciences are involvedin the production of the magazine and are notresponsible for editorial content. Most contributorsto europhysicsnews are volunteers and their work isgreatly appreciated by the Editor and the EditorialAdvisory Board. europhysicsnews is also availableonline at: www.europhysicsnews.comGeneral instructions to authors can be found at :www.eps.org/publications.html

Editor: Claude Sébenneemail: [email protected]

Science Editor: George Morrisonemail: [email protected]

Executive Editor: David Leeemail: [email protected]

Graphic designer: Xavier de Araujoemail: [email protected]

Director of Publication: Jean-Marc Quilbé

Editorial Advisory BoardChairman: George MorrisonMembers: Alexis Baratoff, Giorgio Benedek, Marc Besançon, Carlos Fiolhais, Bill Gelletly, Frank Israel, Thomas Jung, Karl-Heinz Meiwes-Broer, Jens Olaf Pepke Pedersen, Jerzy Prochorow, Jean-Marc Quilbé, Christophe Rossel, Claude Sébenne, Wolfram von Oertzen

©European Physical Society and EDP Sciences

EDP SciencesManaging Director: Jean-Marc QuilbéProduction: Agnès HenriAdvertising: Isaline Boulven

Address: EDP Sciences17 avenue du Hoggar, BP 112, PA de Courtabœuf,F-91944 Les Ulis Cedex A • Francetel: +33 169 18 75 75 / fax: +33 169 28 84 91web: www.edpsciences.org

EPS Secretariataddress: EPS • 6 rue des Frères LumièreBP 2136 • F-68060 Mulhouse Cedex • Francetel/fax: +33 389 329 440/449 • web: www.eps.org

The Secretariat is open 08.00–17.00 CETexcept weekends and French public holidays.

SubscriptionsIndividual Ordinary Members of the European PhysicalSociety receive europhysicsnews free of charge. Members of EPS National Member Societies receiveeurophysicsnews through their society, except membersof the Institute of Physics in the United Kingdom andthe German Physical Society who receive a bimonthlybulletin. The following are subscription prices availablethrough EDP Sciences. Institutions 99 euros (VAT included, European Unioncountries); 99 euros (the rest of the world). Individuals 58 euros (VAT included, European Unioncountries); 58 euros (the rest of the world).

Contact: [email protected] or visit www.epdsciences.com

ISSN 0531-7479ISSN 1432-1092 (electronic edition)Printer Printer Rotofrance • Lognes, FranceDépôt légal: Juillet 2006


editorial

The European Institute of Technology- a further step towards European excellence?

Two major challenges are facing European attempts to build a stronger knowledgebased economy and thus better ensure a continued European competitive edge aswell as Europe being one of the strong nodes in the global value networks. The first andmost important policy issue is the creation of a European research area (ERA), thesecond the coordinated effort of European countries to reform their tertiary educa-tional systems, this latter reform process being better known as the Bologna process.

Both these policy processes are important and of crucial importance in ensuringcontinued European pre-eminence in the sciences. Innovation studies point to scienceand technology being important drivers of economic growth.With this said everythinglooks fine and then why not create a European Institute of Technology (EIT)? Evenmore so because EIT is the next logical step in a development we have witnessed overthe last 20 years through a successive range of EU Framework programs (FP). The firstFramework programs were weekly coordinated projects with participating scientistfrom EU-member countries. The last FP’s have seen coordinated actions under theheading of centres of excellence. These centres not only involve research teams butthey also strongly engage institutions. Institutions themselves have seen this develop-ment and have formed clusters of universities in order better to face this continuingpressure to coordinate.

The EIT is the latest offspring in this development. EU programs have until nowbeen based on national resource centres and universities to implement the thematicpriorities in the FPs. The EIT is the exact opposite. Now the very best of the Europeanknowledge centres shall form knowledge communities (KC’s) and not any longer coor-dinate their actions themselves but rather form integrated partnerships in order toachieve strategic goals identified by the Governing Board of the EIT.

In other words, the EIP will be a new legal superstructure of unknown dimensions.Focus shall be on top-down identification of technological and commercial themes oflong term benefit to European competitiveness. Key words are innovation in the heartof the knowledge triangle, an entrepreneurial mindset and knowledge transfers intostart-up activities. The commercial counterpart is the Airbus consortium so successfulin making up competition in what was once an American monopoly.

The European Physical Society (EPS) can support the core objectives behind the EITinitiative,i.e.devoting more resources to scientific excellence,particularly technological inno-vation and enhancing international and interdisciplinary collaboration.Excellence in scienceis a prerequisite for further economic progress and the physics community fully endorsesmore focus on the creation of better research infrastructures to achieve such worthy goals.Nonetheless, much more discussion is necessary on many essential elements of the EIT,including its structure and funding.

The EPS represents 100,000 physicists working in 39 countries in Europe. Many ofthese physicists are working hard in support of the ERA and to fulfill the ambitions ofthe EU. However, many of these physicists conduct their research in outdatedresearch facilities, while at the same time new superstructures emerge outside theirreach unless they leave their institutions and their countries.

Why is this observation important? Simply because these 100,000 physicists, togetherwith their fellow scientists and engineers form the backbone of the knowledge commu-nities through education of the next generation of scientists! This is the reason why theEIT can not be an isolated institution.A precondition for a strong EIT is an even strongerhigher educational system in Europe.Accordingly the Bologna process, which, in mostcountries, is introduced without any investment capital to mediate the transformationprocess, must be given more attention and supported, be it through national meansand/or by redirecting substantial parts of EU infrastructure funds into this build-up ofthe educational system.

The EPS has studied the recruitment of students to physics and OECD and otherbodies are conducting similar studies on a regular basis within all of the sciences. Theyall point to one imminent threat: young students don’t follow our recommendations togo into science. It is my conviction that this is not because of lack of interest, but ratherdue to our inability to provide them with a modernised educational system.

EIT does not address this diverse problem in a serious way. In any construction itis always wise to repair and strengthen the foundation before starting to build theupper floors. This also holds true for this case.

Ove Poulsen, EPS President

Some light on electric arcsThe electric arc was discovered only shortly after the first electric power sources becameavailable in the early 19th century. Today, electric arcs are used for various purposes inscience, industry and everyday life (e.g. as light sources, circuit breakers, etc.) However, thephysical phenomena are still not fully understood. Crucial for both an understanding of theunderlying physics and the improvement of commercial applications are the transitionlayers between the electrodes and the arc plasma. For fundamental research, we have devel-oped a prototype free-burning arc discharge serving as a model for high intensity discharge(HID) lamps. These lamps are used in many ways including video beamers, cinemaprojectors and automotive headlights.

The discharge is operated in argon under atmospheric pressure and uses cathodes witha diameter of 0.6mm. Besides a corresponding high spatial resolution to overcome the largegradients in temperature and particle density, one needs to be aware of the deviationsfrom the state of local thermodynamic equilibrium (LTE) in the near-cathode region. Inthis paper we present spatially resolved spectroscopic measurements of the electrondensity, the electron temperature and (for the first time) of non-LTE parameters as the gastemperature. The evaluation of the data obtained by (passive) quantitative plasmaspectroscopy and (active) power-interruption experiments is based on a plasma model forpartial thermodynamic equilibrium (pLTE). n

G. Kühn and M. Kock, J. Phys. D: Appl. Phys. 39, 1 (2006), “A spatially resolved relaxation method for pLTE plasma diagnostics in free-burning arcs”.

Wetting or not wetting?The importance of surfaces in condensedmatter physics was acknowledged recur-ringly throughout the last century, duringwhich a plethora of problems were tackledand, some of them, solved. One of the mostobstinate problems in the list is related tothe surface properties of the Ising model, inparticular the nature of its wetting transi-tion. Quite generally, this phase transitionoccurs when one of two coexisting phases(think liquid and vapour) is energeticallypreferred by the confining walls of thesystem. Far from being a technical detail,the wetting transition has deep implicationssince it is intrinsically linked to the vanish-ing of the contact angle formed by thedrop of one of the phases (liquid, say). Thehard question is "Does the wetting transi-tion occur continuously or abruptly?", orin jargon, "What is the order of the wettingtransition for the three dimensional Isingmodel?". This problem is particularlyappealing since the dimension d=3 is themarginal case separating the mean-fieldregime (d>3) from the fluctuation domi-nated regime (d<3), and the influence offluctuations is not an easy matter to assess.

An exact solution of the 3D Ising modelis, of course, prohibitively difficult and the-orists have resorted to coarse-graineddescriptions based on “interfacial models”characterised by a surface tension and aneffective potential W. The predictions ofthis coarse-grained treatment are, however,completely at odds with simulation studiesof the Ising model.

In the present paper, we derive a coarse-grained description which appears toconsistently resolve this, and other contro-versies. In this theory, the potential W hasan elegant diagrammatic representation

which accounts for missing physics in theoriginal interfacial description and allowsone to “see” the shape of a free-energy.

The model also opens the door to moresystematic studies of wetting at micro-patterned and sculpted substrates, relevantto nano-fluidics, which were not possible inprevious descriptions. n

A.O. Parry, C. Rascón, N.R. Bernardino &J.M. Romero-Enrique, J. Phys.: Condensed Matter 18, 6433 (2006),“Derivation of a non-local interfacialHamiltonian for short-ranged wetting 1:Double-parabola approximation”.

4 • volume 37 • number 4 europhysicsnews

Highlights from european journals

. The hot core region of the arc discharge. The cathode consists of thoriated tungsten and is0.6mm in diameter. The blue plasma region in front of it features peak electron temperaturesabove 20000K.

hig

hlig

hts

More on helium moleculesAdvances in techniques for cooling andtrapping atoms have led to many new pos-sibilities.Among these is that of performingprecise spectroscopy of the diatomic mole-cules formed when two cold atoms absorba photon. While most cold-atom work hasinvolved the alkalis, some groups havecooled and trapped metastable Helium.These atoms have a lifetime of about 8000s and so, for most purposes, are stable.Because of their high excitation energy (20eV), Baldwin has described these atoms asnano-grenades and single-atom detectionis possible. Bose-Einstein condensateswere prepared in 2001 from metastableHelium. Using the availability of such coldatoms Leonard et al. excited them to weak-ly bound, ultra-long-range, molecules withclassical internuclear separations up to1150 bohr [Walhout et al. Europhysics News36, 86 (2005)].

Helium has a stable isotope, 3He, which isrelatively inexpensive, and has also been

cooled to mK temperatures. It offers theadditional interest of being a fermion andits nuclear magnetic moment gives rise tohyperfine structure. In contrast to the alka-lis, this structure is comparable to the finestructure arising from the electron magnet-ic moment. The theoretical description ofthese molecules is relatively simple as pri-marily the properties of atomic Heliumonly are needed and several groups haveobtained theoretical results for the bindingenergies in 4He in excellent agreementwith the observations. Our paper hasnow explored theoretically whethercold metastable 3He atoms can alsoform ultra-long range molecules. Thetheory neglects some terms whichhave been shown to be small for 4He.The figure displays one of the adiabat-ic potentials that should supportbound vibrational levels and four suchlevels are marked. As with 4He, we seethat ultra-long-range molecules mayexist so it is to be hoped that this work

will encourage a search for these exoticbosonic molecules with fermionic con-stituents. n

A.S. Dickinson, Eur. Phys. J. D 37, 435 (2006), “Ultra-long-range states in excited 3He2”.

The space elevator not yet for tomorrowA space elevator has been proposed for car-rying payloads into space, which consists ofa very long (~150 000 km) cable attached tothe Earth’s surface. The centrifugal forceexceeds the gravity of the cable, which staysfixed geosynchronously. Once sent farenough, climbers would be accelerated bythe Earth’s rotational energy. The cablerequires a material with very high strengthand low density. The maximum stress is 63GPa and tensile tests of carbon nanotuberopes give an ideal strength of about 100GPa.

Nicola M Pugno of Politecnico di Torinoshows that, unfortunately, even a fewvacancies in a single nanotube play a dra-matic role. In such a huge cable we expectpre-existing defects for statistical reasonsand as a consequence of damage nucle-ation.After reviewing the mechanics of thecable, Pugno considers the effect of damageon the strength, using different determinis-tic and statistical models.All these methodssuggest that the mega-cable strength isreduced by at least ~70% with respect tothe theoretical nanotube strength, puttingin doubt the feasibility of the space elevator.Experiments and atomistic simulationsbased on molecular- or quantum-mechanicson carbon nanotubes confirm this argu-ment. Size-effects deduced by in-silicon

experiments of carbon nanotube-basedropes confirm this strength reduction, inagreement with the first observations onthe strength of meter-long nanotube-basedropes by Zhang et al.

Thus, the feasibility of the space elevatoris placed in doubt.A detailed analysis of therole of defects in the cable seems to be cru-cial: in addition to strength and density, thefracture toughness has to be taken intoaccount. The QFM criteria introduced byPugno could help in solving, if a solutionexists, the problem of a correct nano-struc-tured megacable design, whereas classicalatomistic simulations or experimental

analyses remain unrealizable due to thetremendous size of the megacable. n

Nicola M Pugno, J. Phys: Condensed Matter, Special Issue“Nanoscience and Nano-technology”(July 2006), “On the strength of thecarbon nanotube-based space elevatorcable: from nano- to mega-mechanics”.

europhysicsnews number 4 • volume 37 • 5

highlights

. Strength of defective SWCNT versus holesize (QFM dashed line, rhombs atomisticsimulations), or versus crack length (QFMcontinuous line, points atomisticsimulations).

. The twelfth 0- potential of 3He2 moleculesand the energies of the rotationlessvibrational levels supported.

The EPS Council meeting in 2006 washeld in Mulhouse on 24-25 March

2006. This was the first Council meeting tobe held in the new EPS building on thecampus of the Université de Haute-Alsace.Just as the morning session on 24 Marchended, a violent explosion occurred in theEcole Nationale de Chimie, also located oncampus approximately 100 meters from theEPS offices, killing one person and wound-ing 11 others. Although the cause of theaccident is still undetermined, the mostlikely explanation is the explosion of anethylene container. The campus was evac-uated, and quick thinking by the Mulhousestaff allowed the Council meeting to con-tinue at the Hotel du Parc in downtownMulhouse.

Ove Poulsen, the EPS President empha-sised that the EPS needs to be involved inpolicy decisions regarding physics educa-tion. Physics and the natural sciences playa decisive role in the development andstabilisation of democracy by providinginsight on important issues such as energy,environment and security. However, thereare serious problems in recruiting youngpeople to follow careers in natural sciences,as pointed out in the EPS MAPS study,ROSE, and in the OECD Meeting organ-ised in November 2005. The EPS hasdrafted a position paper on Education(EPN 37-1) which outlines our role andactions in this area. Regional meetings willbe planned throughout 2006 and 2007 toaddress issues such as:• The quality of physics teaching;• Exchange of best practice innovative and

efficient teaching methods;• Enhancing contacts between university

researchers and physics teachers; and • Mainstreaming in physics education.

The EPS is also concerned with the state ofpublishing in Europe. Currently, many pub-lications, particularly from the US are moreimportant for the career development and

visibility of scientists than those in Europe.Amore balanced publishing market would bebeneficial to all scientists and recognise theimportance of research in Europe. The EPSwill be working with publishers in Europe tostudy the feasibility of a European publish-ing platform that will provide authors,readers, subscribers, and publishers withtools that will highlight the quality of Euro-pean journals.A position paper on this topicis currently under preparation.

Conferences organised by the EPS Divi-sions and Groups are one of our majorcontributions to promoting scientific excel-lence. To increase the visibility of physicsto the community, and decision makers,EPS conference policy is also changing.O. Scholten, the incoming chairman of theAction Committee on Conferences hasannounced a change in the focus and work-ing methods of this committee.Among thepriorities are more funds for conferencegrants for young people, more open andstable administrative procedures, andincreasing the number of conferencesorganised by the EPS Secretariat.

Elections to the Executive Committeewere held. The outgoing members (M.Allegrini, G. Delgado Barrio, M.C.E. Huber,P.Hoyer,H.Kelder,P.H.Melville,Z.Rudzikas)were warmly thanked for their contribu-tions to the EPS. Elected to the ExecutiveCommittee for a two year term were: J.Beeby(Treasurer), A. di Virgilio, B. Feuerbacher(Secretary of the Executive Committee),K. Hämäläinen, M. Kolwas, A.M. Levy,F. Masnou-Seeuws, V. Urumov, and R.Velasco. F.Wagner was elected as President-Elect, and will become President in 2007.O. Poulsen was confirmed as president forthe second year of his two year term.

In keeping with the successful format ofthe 2005 Council meeting, 2 special ses-sions were also organised in 2006. Thesesessions allow a more detailed discussion ofimportant policy issues, and allow EPSCouncil delegates to participate directlyand immediately in the formulation of EPSstrategy.

The first was an in depth discussion ofEPS conference policy. Conferences organ-ised by EPS Divisions and Groups are giventhe label “Europhysics Conferences”. Theseform a series of conferences dating back to1968 and are recognised as some of bestphysics meetings in Europe. Other highlevel conferences in Europe can apply forthe label of “EPS Sponsored Conference”,which increases the visibility of the EPSand allows them to apply for EPS grants.

The EPS Secretariat offers a full rangeof services exclusively for EurophysicsConferences. Since the creation of theConference Services Department in 2000,the EPS has successfully organised a varietyof events, from small workshops with 60participants, to large conferences with over1400 participants. Electronic paper submis-sion and scoring, registration and paymentand conference publications are all part ofthe services offered. The services can beadapted to the individual needs of the Divi-sions and Groups. One example of thesuccess of the EPS Conference Servicesdepartment is CLEO/Europe – EQECwhich is jointly owned by the EPS, theOSA, and the IEEE/LEOS. The EPS hasassumed a lead role in the organisation ofthis conference since 2003. Another areawhere the EPS may be able to play a role isin the conferences organised by the Atom-ic and Molecular Physics Division. This isa lively field, and many good conferencesare organised, such as EGAS, ECAMPIG,HCI, etc. It may be possible to form a part-nership (as with CLEO/Europe-EQEC) tobring together these conferences, andensure a more transparent and coherentstructure and increase attendance. TheEPS will be actively soliciting Divisions andgroups to use EPS Conference Services in2006.

The EPS Sponsored Conference label isdesigned to increase EPS visibility, and helpphysicists choose among the conferencesorganised in Europe. The difficulty is con-vincing the conference organisers to applyfor the label. By streamlining the applica-tion procedures, and involving morephysicists in the review process, it wouldbe possible to promote the EPS SponsoredConference label. As these conferences canapply for EPS conference grants, it wouldalso be necessary to look at the fundsdevoted to these purposes, and the admin-istrative procedures.

Mainstreaming in Physics Educationwas also developed as a theme for input byCouncil. Presentations were made by C.Fox Maule, G. Gehring, and C. Thibault. Itis widely recognised that physics faces asevere recruiting challenge. One possiblesolution is to develop educational frameswhere physics is made more attractive togroups in the population that are under-represented, specifically women.At present,physics is a white male mono-culture.Although physics research is objective, andphysicists try to be neutral, there is still anunderlying cultural bias. Greater diversity


Report on EPS Council 2006

new

s a

nd v

iew

s

. Damage to the Ecole Nationale de Chimie.

in the population can improve sciencebecause more ideas, viewpoints and inter-ests are represented.

Gender balance is one specific aspect ofmainstreaming. G. Gehring identified someof the factors that discourage women fromfollowing careers in science. These barriersinclude peer pressure, unimaginative teach-ing, and the negative image of the careersthemselves. C. Thibault reported that inFrance, global figures for female represen-tation in research did not at first glanceseem to be troublesome.For example,38.5%of all entry level university professors inscience are women. But a more detailedanalysis shows that women represent only16% of higher level university professors inscience. Other examples of gender biaspresented by C. Fox Maule include poorerreviews for articles written, and less fund-ing for research projects. Moreover, womenare promoted more slowly.Various respons-es are being studied to improve genderequality, which include active involvementby women scientists in the promotion ofscience to young people and informationcampaigns that highlight the role of womenin science. It is also necessary to increase thenumber of women on editorial boards, andon project review committees. More studiesare not needed. The EPS should encourageuniversities and research institutes to setgoals with regard to the recruitment ofwomen students and faculty with clearlydefined targets. An EU code of conduct hasbeen drafted, and the EPS could subscribe,and promote this to its members. A websiteon best practice for gender equality could beset up and maintained by the EPS. The EPScould establish prizes for excellent workdone by women scientists. Finally, the EPScould establish guidelines for conferenceorganisers specifically addressing genderequality issues. n

m F. Wagner, EPS President elect.

. The Mainstreaming Session L-R: C. Thibault, C. Fox Maule, G. Gehring.


news and views

The 2006 Sackler prize in theoretical orexperimental nuclear/hadron Physics

The Raymond and Beverly SacklerPrizes in the Physical Sciences are

awarded each year, under the supervisionof the Tel Aviv University, in the disciplinesof either Physics or Chemistry. The SacklerPrize supports dedication to science, origi-nality and excellence, and it is intended foryoung scientists who have made interna-

tionally outstanding and fundamental con-tributions in their fields. The laureates ofthe 2006 prizes are:• Prof. Thomas Glasmacher, NSCL, Michi-gan State University, for the development ofnew sensitive methods of studying nuclearstructure, utilizing Coulomb excitationwith fast beams of rare isotopes.

• Prof. Yuri Kovchegov, Ohio State Univer-sity, for a number of groundbreakingcontributions to theoretical understandingof Quantum Chromo-dynamics (QCD) atvery high energies and gluon densities.

The prizes were remitted at the annual ses-sion of the Tel Aviv University (TAU) Board ofGovernors meeting on 21 May 2006. n

The Irish Science on Stage delegationwas awarded an EIROforum Science

Teaching Award for their outstanding pre-sentation of “Teaching Science as a Process”at the European Science Teaching Festivalin CERN, Geneva, which was held on21–25 November 2005. The EFDA awardwas given to the Irish team in recognitionof “teaching excellence, inspiration andmotivation of young people in a contribu-tion to the Science on Stage festival”.

Science on Stage is organized by theseven intergovernmental European researchorganizations within the EIROforum part-nership (a collaboration between CERN,ESA, ESO, EMBL, ESRF, ILL and EFDA).The festival is an integral part of theEIROforum European Science Teachers’Initiative (ESTI), supported by the Euro-pean Commission in the context of thenew NUCLEUS project for science educa-tion. The festival aims to strengthen theawareness and interest of young people inscience and technology, and to foster arenewal of science teaching in Europe, byencouraging the exchange of new conceptsand best practices among teachers from allover the continent. The festival developedfrom the highly successful Europe-widePhysics On Stage programme. (POS)

The Irish team of nine delegates was ledby Dr Eilish McLoughlin from the physicsdepartment at Dublin City University andincluded two teacher network coordinatorsfrom the Institute of Physics in Ireland – PaulNugent from Dublin and Siobhan Crowefrom Wicklow. Also participating were thevice-chairman of Irish Science Teachers’Association, Seamus O’Donghaile fromRoscommon; Alison Graham from Dublin;Sean Fogarty from Wexford; Rachel Linney

from Kildare; Damienne Letmon fromDublin; and from the Department of Educa-tion, second level support service physicscoordinator, Kerry based, Tim Regan.

These enthusiastic science teachers wereselected as national delegates for theirexcellence in teaching and motivatingyoung people in science. The “TeachingScience as a Process” was initiated by teammember Alison Graham. The UK Scienceon Stage team included the third Irish Insti-tute teacher network coordinator, VidaGiven, who is based in Northern Ireland.

Science on Stage was the final event of atwo-year-long programme of events in 29participating countries and brought togeth-er around 500 science educators. Each dayof the festival had its specific topic, aroundwhich presentations, demonstrations andworkshops were themed. The topics wereEinstein Day; Sustainability Day (e.g. envi-ronment, climatology, oceanography,energy); Space and Astronomy Day; LifeSciences Day (e.g. health, biotechnology,genetics); and Science and Technology inSociety Day. “At the festival, teachers havethe chance to view things from a newperspective, to be entertained and enchant-ed by science,” said Rolf Landua, head ofeducation at CERN and chairman of theevent.“As well as taking to the stage, they setup stalls in fair-like surroundings to sharetheir most successful teaching tricks.”

EIROforum, the Irish government agency,Discover Science and Engineering, the Insti-tute of Physics in Ireland and the IrishDepartment of Education and Sciencethrough the Second Level Support Serviceprovided the support for the Irish Science onStage delegation.A series of workshops basedon demonstrations from Science on Stage will

be presented across Ireland over the comingyear and the team plans to publish a compila-tion of the best of the demonstrations andteaching ideas from the festival,which will bedistributed to all Irish science teachers.

This follows on from the success of thethree editions of the Physics on Stage pro-gramme 2000–2003. Indeed in 2003,Ireland also took a prize at the 3rd POSconference in Noorwijk, the Netherlands.Tim Roe, a retired physics lecturer from theGalway-Mayo Institute of Technology,brought a model which splendidly demon-strated the Coriolis effect, winning theaward for ‘most original demonstration of ascientific principle.’ The best of the demon-strations from Physics on Stage 3 wererecently published by the Irish NationalSteering Committee. Speaking at thelaunch of the booklet in Dublin in Decem-ber 2005, Minister for Education andScience, Mary Hanafin said, ‘the bookletemphasises the use of simple equipment todemonstrate the most fundament physicalconcepts in a way that fascinates everyone,regardless of their background in science.What struck me also was the way in whichscience can be investigated and demon-strated with everyday objects and materials– it really brings home the fact that scienceis all around us and that so many aspectsof our lives depend upon it’.

More information and downloads canbe found on the Irish Science on Stage web-site at http://ireland.iop.org/sos/ and via thelinks provided there. n


Irish science takes centre stageEilish McLoughlin and Sheila Gilheany,(IOP in Ireland) Dublin City University • Ireland

b The Irish Science on Stage delegation (leftto right): Sean Fogarty, Seamus O’Donghaile,Siobhan Crowe, Rachel Linney, EilishMcLoughlin, Alison Graham, DamienneLetmon, Paul Nugent and Tim Regan.

m Mary Hanafin is pictured here withstudents Graham Kelly and Leah McConnelldemonstrating “The flame tube”at thelaunch of the Physics on Stage 3 booklet.

new

s a

nd v

iew

s


news and views

About W. R. HamiltonMarc Dixmier, Dublin • Ireland

I wish to comment upon Luke Drury’s inter-esting overview of Hamilton’s scientific works,published in Europhysics News 37/1, 8 (2006).

Among his many contributions to Mathe-matics, Hamilton also delved into another sortof non-commutative algebra, that of squarematrices, to which he contributed the theoremof Cayley-Hamilton: “any square matrix satis-fies its own characteristic equation.”

Hamilton’s contributions to Optics, Mechanicsand Algebra were actually connected in a muchdeeper way than he could have foreseen: the least-action principles of optics and mechanics ledLouis de Broglie, in 1923-1924, to postulate theexistence of matter waves.The non-commutationof operators forms the mathematical basis of thequantum uncertainty principle, put forward byWerner Heisenberg in 1925.These two approach-es later merged into modern quantum mechanics.

Although Hamilton did coin the expressions“scalar product” and “vector product”, he is notthe founder of modern vector calculus; thatbelongs to the American Josiah Willard Gibbs(1839-1903) whose methods supersededHamilton’s. I often think that this is unfortunatesince Hamilton’s quaternions provide a logicalexplanation for the breaking of time reversalsymmetry and of mirror symmetry (i.e. parity)in some physical systems.

Since I now live in Ireland it is a pleasure forme to add my own contribution to the cult ofWilliam Rowan Hamilton. n

Remark on the Earth dipole moment decay Emmanuel Dormy, CNRS/ENS/IPGP • France

In Europhysics News (Vol. 37/2),“The origin of the Earth’s magnetic field”, I pre-sent a figure showing the rapid decay of the Earth’s dipole moment. This graphlargely relies on the GUFM field model, which is based on historical measurementof field intensity and direction over the 1600-1990 period. This plot is often usedto support the possibility of an approaching polarity reversal. In fact, as Dr. FrankLowes kindly pointed to me, no direct intensity measurements were available priorto C.F. Gauss’s invention of a method for determining intensity in 1832. As aresult, while directional observations over the period 1600-1832 can constrain fieldmorphology, the intensity is left unknown. Following Barraclough (1974), theGUFM model was therefore scaled in time assuming a linear decrease of the axialdipole strength. It results that there is absolutely no evidence in the GUFM modelfor, or against, a decrease in the dipole moment prior to 1832. The decrease in dipolemoment, as shown in figure 1 of the article, is only supported by observations after1832 (see figure, with histor-ical measurements afterFraser-Smith, 1987). Thisfact only appears to weakenthe clues for an approachingreversal. For completeness,we should however note thatindirect intensity measure-ments from archaeologicalsources appear to confirmfield decay over the last 3000years. n

References [1] D.R. Barraclough,“Spherical Harmonic Analyses of the Geomagnetic Field for Eight

Epochs between 1600 and 1910”, Geophys. J. R. Astr. Soc., 36, 497-513 (1970).

[2] A.C. Fraser-Smith,“Centered and Eccentric Geomagnetic Dipoles and Their Poles,16001985, Reviews of Geophysics, 25, 1-16 (1987).

Letters

The European Home of Photonic Research and Technology!

CLEO®/Europe-IQEC is the largest, most comprehensiveand prestigious gathering of optics and photonicsresearchers and engineers in Europe in 2007. This high-ly respected peer-reviewed conference is complementedby LASER. World of Photonics 2007, the world's largestexhibition of laser and optical technology, making it aunique opportunity for learning, networking and doingbusiness. Munich provides a dynamic but hospitablebackdrop for work, for catching up with old friends andfor making new ones. Join us in developing the heart ofEuropean photonics.

CLEO®/EUROPE—IQEC 2007 European Conference on Lasers and Electro-OpticsInternational Quantum Electronics Conference

17 – 22 June 2007 • Munich ICM,International Congress Centre, Munich, Germany

Abstract & Summary deadline:15 January 2007

Submit your paper online: starting 16 October 2006

The conference is organised by the EPS

For further information, please register online.

> more on: www.cleoeurope.org

It is now some months since the WorldConference on Physics for Sustainable

Development was held in Durban, SouthAfrica in October/November last year.Organized by the International Union ofPure and Applied Physics (IUPAP) andUNESCO, with the South African Instituteof Physics taking responsibility for localissues, this was unlike any conference heldpreviously. More than 300 physicists fromover 70 developing and developed countiescame together, not to present and discussphysics, but to decide on a programme ofactions to be undertaken using physics tohelp developing countries. EPS was wellrepresented. The conference had four mainthemes: physics education, physics andeconomic development, energy and envi-ronment, physics and health. Much of thetime was spent in subgroups within thesemain themes, each working up a project,before coming together again in plenarysession to endorse the final projects.

The projects on physics educationinvolve: establishing a website and educationresource centres in Asia, Africa and LatinAmerica; developing supplementaryinstructional materials for secondary physicscourses on how physics can contribute tosustainable development; developing model

workshops for teacher trainers in Asia,Africa and Latin America; providing supportto mobile science practitioners.

The economic development projects arethe establishment of a training programmeon economic development for physicists indeveloping countries, and the developmentof two web-based networks for developingcountries – one on physics and agriculture andone on nanoscience and nanotechnology.

The projects on energy and the environ-ment concern the enhancement of theefficiency and the reduction of pollution intransportation, promotion of the use andapplication of solar energy and the devel-opment of a model for an inexpensivebiomass plant.

Physics and health concentrated on theshortage of medical physicists in developingcountries covering physics and engineeringresources for healthcare and development,curriculum and programme validation forphysicists in medicine, development ofregional training centres for the physics ofradiation therapy, development of a web-based training tool for radiation therapyphysics.

The effort is now in taking these projectsforward and making them work. Not allthese projects will succeed, but the hope is

that those that do will make a difference fordeveloping countries. EPS is focusing itsattention on the training programme oneconomic development. It is working withthe Institute of Physics (IOP), IUPAP andthe Abdus Salam International Centre forTheoretical Physics (ICTP) to set up a pilotworkshop at the end of November/ start ofDecember this year. This will be run atICTP, which regularly organizes courses forpeople from developing countries, hasmany contacts with physicists in develop-ing countries and has the facilities forhosting such a workshop. IOP has assem-bled a team of volunteer lecturers and isputting the final programme together inconsultation with the other partiesinvolved. The emphasis is on commerciali-sation of intellectual property, not just onhow to patent and license it but also onidentifying if and where there is a marketneed. The course will be illustrated by anumber of case studies. n


World conference on physics and sustainable development

Peter Melville, Society Secretary of EPS 2004 - March 2006 • Associate Secretary General, IUPAP • International Director, Institute of Physics

. South African Science and TechnologyMinister Mosibudi Mangena addresses theopening session of the World Conference onPhysics and Sustainable development inDurban

new

s a

nd v

iew

s

40years after the beginning of Earth observation fromspace, the monitoring of Earth’s seismic activity and

the recording of the seismic waves generated by quakes isexclusively done by global and regional seismic networks.Contrary to geomagnetism or gravimetry, seismology doesnot yet benefit from data acquired from space, and has todeal with a non-homogeneous coverage of seismic stations.In particular, the oceans, which cover more than 70% of theEarth surface, are almost devoid of measurements.

Seismic data are indeed based on the detection of very lowground displacements: even at the most noisy frequency, 0.15Hz,associated with a global seismic noise generated by the oceanicwaves, the amplitude of the ground displacement noise is in therange of 0.1-10 micrometers and good signal to noise seismicwaves have amplitudes of a hundred to a thousand times higher...Such amplitudes are far below the resolution of any space altime-try methods, especially due to the Earth’s atmosphere and itsinteraction with the radio waves or with visible light. Remotedetection of the seismic signals from space seems hopeless...

However, the atmosphere is also affected by waves, and turns outto offer a possible solution to the problem. After an earthquake,seismic waves generate vertical and horizontal motion of the sur-face of the Earth. In some case, tsunami or oceanic gravity wavesare also generated and produce surface oscillations. By continuityof vertical displacement at the surface, the atmosphere is thenforced to move with the same vertical velocity as the ground surface.The perturbation propagates upward as an atmospheric wave andproduces pressure and temperature variations, and oscillations ofthe atmospheric layers. Can these atmospheric waves be detectedremotely? Let us look at the amplitudes...

The seismic waves with the largest ground amplitude are thesurface waves and especially the Rayleigh waves. They propagatealong the Earth’s surface, in the crust or upper mantle, with veloci-ties ranging from 3 to 4 km/s. For large and superficial quakes, theirdisplacement amplitude, even at an epicentral distance of 10000km, can reach several mm or even cm, as was observed after thelarge Sumatra earthquake of December, 26, 2004. The propagationspeed of the wave front being much larger than the sound speedin the atmosphere, the generated air waves propagate almost verti-cally from the surface location of the Rayleigh wave front. Withtheir long periods (T > 10-20 s), the infrasonic atmospheric wavesare not attenuated by the atmospheric viscosity: they propagatewith a constant kinetic energy and therefore, their amplitude growsexponentially as the inverse of the square root of density. As shownby Fig. 1, the density decays by 10 orders of magnitude between theground and 200 km of altitude and amplification of 105 can there-fore be encountered by air waves during their upward propagation.But the neutral atmosphere is not the only one to oscillate.A trans-fer is made by collision processes to the ionospheric ions andassociated electrons, which oscillate almost in phase. Finally forquakes of magnitude 7 or more, the ionosphere electrons areoscillating with velocities of a few tens of m/s and are displaced bya few hundred of meters. These forced ionospheric waves, withhorizontal speed imposed by the true solid earth surface waves, arethe target for remote sensing observation of the surface waves.

The first observation of ionospheric surface waves wereobtained after a very large Alaskan quake in 1964.At that time, theionosphere was monitored for the purpose of nuclear explosiondetection, and both the theories and the instruments necessary forthe interpretation of the atmospheric gravity waves generated by

megatonic atmospheric explosions[1] had been developed, especially atthe Seismological Laboratory of theCalifornia Institute of Technology.The pressure fluctuations generatedby quakes are much smaller thanthose generated by typical gravitywaves. The seismic source is indeedlocated in the solid earth and thecoupling between the solid part andthe atmosphere transfers only 10-4 to10-5 of the energy [2]. Resonancesare however found first near 3.7mHz, where spheroidal modes haveup to 0.05 % of their energy in theatmosphere and also near 4.4 mHz.These two maximums result from awavelength matching of the Rayleigh


features

Seismic waves in the ionospherePhilippe Lognonné 1, Raphael Garcia 1, François Crespon 1, Giovanni Occhipinti 1, Alam Kherani 1 and Juliette Artru-Lambin 2,1 Institut de Physique du Globe de Paris, Saint Maur des Fossés • France2 Centre National d’Etudes Spatiales, Toulouse • France

b Fig. 1: Density and sound speedprofile with altitude in the Earthatmosphere. The ionosphere isdeveloping above 120 km of altitudeand a maximum of ionization isreached at 350-400 km of altitude.

waves with the mesospheric wave guide [2] and can lead to typicalbi-chromatic seismic signals after volcanic atmospheric explo-sions [3].

Even for a magnitude 8 quake, the pressure fluctuations reachonly a few microbars at the surface and must be recorded withcomplex measurements systems. The Earth atmosphere is howev-er acting as a natural amplifier and leads to large signals at 150 kmor more of altitude in the ionosphere, for quakes of magnitude 7 orlarger. The ionospheric oscillations can be remotely sounded by aDoppler sounder [4]. The principle of the Doppler sounder is tosend an electromagnetic wave in the range of 1 to 15 MHz. Theemitted wave reaching the plasma modifies its propagation as theelectron density increases and will be fully reflected at a given alti-tude, where the plasma frequency (a function of local electrondensity) matches the radio wave frequency. If the reflecting layer isoscillating vertically, a Doppler effect is indeed observable in the

reflected signal. The ground-based Doppler sounding can there-fore follow the oscillations ionospheric layers up to 350 km ofaltitude, where the maximum of ionization is reached. Moderninstruments can detect vertical velocities of a few 10 of cm/s,enabling therefore the detection of all quakes with magnitudegreater than 7 (Fig. 2).

If these techniques are paving the way of a seismic remote sens-ing of the signals, they however remain single point measurementsand do not allow the wavefield to be imaged. A second step wastherefore necessary toward such 2D or 3D mapping of the seismicwaves in the atmosphere. Our team, with the French SME Novel-tis, has used for this goal the dense GPS networks, located eitherin California, Japan or Europe. With about 1200 receivers theJapan network is the densest and as each receiver can see from 6to 10 satellites, this network provides about 10000 ionosphericsounding each second. These data allow, by tomographic tech-niques, the airwaves in 2D and 3D to be captured, through theirperturbations of the electronic content of the ionosphere [5].Typically, these perturbations reach a few percent of the electrondensity for quakes with magnitude larger than 8 (Fig. 3). The ver-tical and horizontal propagation of the wave front can then bestudied. By using the Southern California GPS network, thesurface waves of the November, 3, 2002 (M=8.2) quake were clear-ly detected between an altitude of 200 and 400 km (see the moviesof the ionospheric perturbations and more information on theSpectre project [6]). Estimates of the horizontal group velocity hasbeen obtained and successfully compared with the velocity from3D models of the Earth lateral variations [7]: we can even imagineusing these techniques for measuring the seismic velocities of theEarth upper mantle and crust, especially in locations where seis-mometers cannot be easily deployed (Fig. 4). Although on Earththis technique would never provide the same quality of seismicdata as a seismic network, it can be the unique way to obtainseismic data on planets too hostile for the deployment of longlived seismic stations. Venus is the best example [8]. In addition,the coupling strength is proportional to the acoustic impedance ofthe atmosphere, equal to rc where r is the density and c theacoustic speed. As the atmospheric density at the surface ofVenus is about 60 kg/m3 and the acoustic velocity is slightlyhigher (410 m/s) than on Earth, this leads to an acoustic imped-ance about 60 times greater than on Earth, where the atmosphericdensity is 1.2 kg/m3. Moreover, at 50 km of altitude, where theVenus pressure is comparable to Earth ground pressure, thedecrease by almost 2 orders of magnitude of the density leadsalready to an amplification of 10 of the waves. Consequently,Venus quakes will generate atmospheric infrasonic waves withamplitudes 600 larger than on the Earth surface. This profitableeffect gives a unique opportunity for a future Venus quakes detec-tion by a satellite sounding the Venus ionosphere.

Let’s however go back to Earth...Tsunamis can also be detected with such a remote sensingapproach. Tsunamis are surface gravity waves that propagate forgreat distances in the oceans, usually triggered by earthquakes orlandslides. In the open ocean, their long wavelengths (typically200 km), long periods (20 minutes) and small amplitudes (a fewto 50 cm for the gigantic event of December, 26) make their detec-tions very challenging with the GPS buoy systems or ocean bottompressure sensors. Recently, satellite altimetry has proved to be capa-ble of measuring the sea surface variation in the case of largetsunamis [9] including for the recent Sumatra, December 26 tsuna-mi [10], but these techniques do not allow a real time imaging ofthe oceanic wave.


fea

ture

s

m Fig. 2: These signals correspond to the ionospheric verticalvelocity. They are recorded by the Doppler sounder of CEA, at 143and 169 km of altitude, by using the reflection of two radio waves at3.849 and 4.624 MHz respectively. Data were recorded after a Mw=8quake in the South Indian Ocean, on June 18, 2000. The bottomtrace corresponds to the data recorded by a seismometer. For alldata, synthetics are computed by using a spherically symmetricEarth model, for both the solid Earth or its atmosphere. Most of thedifferences at the ground are associated with the 3D structure of theEarth, which is not taken into account in the synthetics. Differencesin the amplitude of the ionospheric waves are probably due to anon-correct viscosity profile in the atmosphere, such data beingbadly known at high altitude. Data from CEA-DASE are reprintedfrom [4].

As for surface waves, early theoretical works in the 1970s pre-dicted that atmospheric gravity waves are generated in the wake ofa tsunami [11]. If one hour is, for the gravity wave, the time to reachthe ionosphere (versus ~10 minutes for seismic-acoustic waves),after this delay the ionospheric perturbation follows the tsunamifront and, as for the seismic waves, the atmospheric oscillationsare amplified with altitude. It should be noted moreover that, due

to their much shorter wavelength and period, the surface noise ofocean swell does not produce significant upward propagatingwaves in the atmosphere: the atmosphere acts as a filter, enhanc-ing the long wavelength tsunami perturbation over other sources.

The first observation had however to wait almost 30 years. It wasperformed after the Peru, June 32, 2001 tsunami [12]. The tsuna-mi arrival was observed on Japanese tide gauges between 20 and 22


features

b Fig. 3: TEC time series from satellite 26, plottedas a function of time and distance to theepicenter. The TEC data were obtained from thedifference of the two GPS carriers propagationtimes and then band-pass filtered between 150 sand 350 s, with a central period of 225 s. Eachtrace corresponds to the TEC obtained with agiven GPS station at the sub-ionospheric point.The satellite elevation is about 60-65 degrees atthe time of signal observation. The positions ofthe sub-ionospheric points are obtained from re-processed satellite coordinates with a 30 sresampling. The black dashed line represents atypical Rayleigh wave on the ground, with amean velocity of 3.5 km/s. Differences in arrivaltime might be related to lateral variation. On thetop left: Piercing points for ionosphericmeasurements from all receivers in California(SCIGN + BARD + IGS) and all satellites. The redstar shows the epicenter location for the Denaliearthquake and the red points are the position ofthe sub-ionospheric points.

m Fig. 4: Map of the ionospheric perturbations over Japan after the Tokacho-Oki earthquake of September 25, 2003, occurring at 19h50. Thetime interval between each map is 30 s. A spectacular ionospheric perturbation is observed near the source, corresponding mainly to acousticwaves generated by the quake and appears approximately 10 minutes after. At larger distances, we also observe Rayleigh waves along the coastof the Japan Sea. The amplitudes observed are comparable to those of the Denali event and are typically 0.1 TECU peak-to-peak.

hours after the earthquake, with wave amplitudes between 10 and40 cm (open ocean amplitude were estimated to be of 1-2 cm) anddominant periods of 20 to 30 minutes. Shortly after, a large ionos-pheric perturbation was detected through a specific processing ofdata from the continuous GPS network in Japan (GEONET). Fig.5 shows the signal observed at approximately 6:30 pm. Each dotrepresents the Total Electron Content (TEC) calculated from onesatellite-receiver ray, corrected for ray zenithal angle and high-pass filtered to remove diurnal variation. The locations of thepoints correspond to the intersections of the rays with the F2 peakin the ionosphere, named “piercing points”. The arrival time,orientation, wavelength, velocity of the wave packet observed areconsistent with what is expected for a tsunami-induced perturba-tion. The gigantic and dramatic Sumatra tsunami of December, 26,2004 (M=9, 00:58 UTC) confirmed the possibilities of observingtsunami ionospheric signals, and signals were detected on the TotalElectronic Content (TEC) measurement on-board theTOPEX/Poseidon and JASON satellites, and on the GPS stations inIndonesia and in the India Ocean [13]. The modeling of theionospheric signal was performed, and both the waveform andthe amplitude observed by Jason and Topex has been reproduced[14]. These results confirm the interest of a real-time monitoring ofthe ionosphere, which could be carried out either with activemicrowave radar or by optical systems detecting the airglow asso-ciated with the ion recombination in the ionosphere.

In conclusion, advances in the monitoring of small-scaleperturbations of the ionosphere have allowed the detection ofatmospheric Rayleigh waves as well as tsunami-induced gravitywaves with both ground systems based on GPS, and ionosphericsounding performed by TOPEX and JASON and Dopplersounders. These new data open exciting prospects in seismologysuch as the remote sensing of the Rayleigh seismic wave fronts,especially over the ocean, where the deployment of dense seismicnetworks is the most challenging. These prospects are also veryexciting for tsunamis because they are extremely difficult toobserve in the open ocean, but their associated gravity waves havea clear impact on the ionosphere and can be detected by remotesensing systems. The monitoring of the ionosphere by jointground/space techniques, such as continuous GPS networks, over-

the-horizon radar or even by a future dedicated space system,might improve our understanding of tsunami propagation in theopen ocean and possibly the efficiency of the future tsunami warn-ing systems. n

References[1] D.G. Harkrider, J. Geophys. Res., 69, 5295, 1964.

[2] P. Lognonné, C. Clévédé and H. Kanamori, Geophys. J. Int., 135, 388,1998.

[3] H. Kanamori, and J. Mori, Geophys. Res. Lett., 19, 721, 1992.

[4] J. Artru, T. Farges, P. Lognonné, Geophys. J. Int., 158, 1067, 2004.

[5] R. Garcia, F. Crespon,V. Ducic, P. Lognonné, Geophys. J. Int, 163, 1049,2005.

[6] More information on the Spectre project can be found athttp://www.noveltis.fr/spectre. A movie showing the 3D propaga-tion of the wave can be downloaded at:http://ganymede.ipgp.jussieu.fr/~garcia/Denali.Vcut.Az2.movie.mpg.gz

[7] V. Ducic, J. Artru and P. Lognonné, Geophys. Res. Lett., 30, 1951, 2003

[8] R. Garcia, P. Lognonné and X. Bonnin, Geophys. Res. Lett., 32, L16205,2005,

[9] E.A. Okal, , Piatanesi, A. and P. Heinrich, J. Geophys. Res., 104, 599,1999.

[10] Y. Tony Song, C. Ji, L.L. Fu,V. Zlotnicki, C. K. Shum,Y.Yi and V. Hjor-leifsdottir, Geophys. Res. Lett, 32, 2005

[11] W.R. Peltier and C.O. Hines, J. Geophys. Res., 81, 1995, 1976.

[12] J. Artru,V. Ducic, H. Kanamori, P. Lognonné and M. Murakami ,Geophy. J. Int., 160, 840, 2005.

[13] P. Lognonné , P.J. Artru, R. Garcia, F. Crespon, V. Ducic, E. Jeansou,G. Occhipinti, J. Helbert, G. Moreaux, P.E. Godet, Planet. Space. Sci-ence, in press, 2006

[14] G. Occhipinti, P. Lognonné, E. Kherani, H. Hébert, Geophys. Res. Lett,submitted, 2006.


fea

ture

s

b Fig. 5: Observedsignal for the June23, 2001 tsunami(initiated offshorePeru): TEC variationsplotted at theionospheric piercingpoints. A wave-likedisturbance ispropagatingtowards the coast ofHonshu. Thisperturbationpresents theexpectedcharacteristics of atsunami-inducedgravity wave, andarrivesapproximately at thesame time as thetsunami wave itself.

This year is the centenary of the birth of Ettore Majorana, one ofthe major Italian physicists of all times. The centenary has trig-

gered a series of initiatives. Among them there is the InternationalConference on “Ettore Majorana’s legacy and the Physics of theXXI century” organized by the Dipartimento di Fisica e Astrono-mia of University of Catania, Italy that will be held in Catania onOctober 5-6.Another initiative of the Società Italiana di Fisica con-cerns the publication of a volume including all Majorana’s articlesboth in the original language (in most cases Italian) and in English.The volume will also contain a brief descriptive note on each of thearticles. Lastly, the International School on Complexity of the“Ettore Majorana Foundation and Centre for Scientific Culture” ofErice, Italy co-directed by A. Zichichi, G. Benedek, M. Gell-Mann,L. Pietronero and C. Tsallis, has scheduled a Course on September17-23 entitled “Statistical Laws in Physics and Economics” directlyinspired by one of Majorana’s articles, specifically his 10th article.This article is probably the least known among his articles.

In this note we briefly sketch a few biographical details aboutEttore Majorana and introduce and discuss the main points ofMajorana’s 10th article. The biographical notes are mainly based oninformation that can be found in [1,2]. The aim of this note is toinvite the readership of Europhysics News to consider the mainmessage of Majorana’s last contribution with its focus on the valueof statistical laws in physics and social sciences [3].

Ettore Majorana was born in Catania, Italy on August 5th 1906 ina well known and influential family of that city. His father wasFabio Massimo Majorana, an engineer that was appointed to beGeneral Inspector of the Italian Ministry of Communication inRome in 1928. Fabio Massimo Majorana was the younger brotherof Quirino Majorana a renowned professor of experimentalphysics at Bologna University and a member of the prestigiousAccademia dei Lincei. Fabio Massimo Majorana married DorinaCorso and they had two daughters and three sons, specifically,Rosina, Salvatore, Luciano, Ettore and Maria.

The family moved to Rome in 1921.Ettore Majorana studied at thesecondary schools “Istituto Massimo” and “Liceo Statale TorquatoTasso”where he obtained his diploma.He then enrolled at theSchool of Engineering of Rome University (at that timeonly “La Sapienza”University existed).At the School ofEngineering he started to interact with Emilio Segré.In 1926 Emilio Segré moved from the School ofEngineering to the Institute of Physics whereEnrico Fermi (at that time 26 years old) wasnominated to the position of full professor ofTheoretical Physics. The same path was fol-lowed by other successful Italian physicistssuch as, for example, Edoardo Amaldi. In thenew environment of physics, Emilio Segréwas often talking about the exceptional qual-ities of Ettore Majorana and meanwhile heattempted to convince Ettore to join thegroup of physicists led by Enrico Fermi. Thepassage of Ettore Majorana from the School ofEngineering to the Institute of Physics did hap-pen at the beginning of 1928. At that time theinvolvement of Ettore Majorana as a student andthen as a professional physicist started.

Ettore Majorana was one of the greatest theoretical physicists ofthe heroic period of the development of quantum mechanics andnuclear physics in the first half of the last century. Ettore Majoranagraduated in physics in 1929 under the supervision of E. Fermi.During the years from 1929 to 1933 he devoted all his energy totheoretical physics and produced most of his work in this field. In1933 he visited Lipsia, where he positively interact with W. Heisen-berg, and briefly Copenhagen where he met Niels Bohr. After hisreturn to Rome during the fall of 1933 his involvement in theoret-ical physics research declined until 1937 when he again showed anactive interest in theoretical physics by taking part in a nationalexamination to obtain a position of professor of theoretical physicsat Palermo University. The Committee composed of E. Fermi,O. Lazzarino, E. Persico, G. Polvani and A. Carelli, unanimouslyconsidered his work to be outstanding and above comparison withthe work of the other candidates and therefore proposed that theMinister of Education should nominate E. Majorana as a fullprofessor for “chiara fama”, namely outside the examination proce-dure. He therefore became professor of theoretical physics atNaples University where he taught a quantum mechanics courseduring the academic year 1937-38.

Ettore Majorana mysteriously disappeared in March 1938during a trip on the ship connecting Palermo to Naples. His bodywas never found although the search for Majorana both bygovernment officials and members of the Majorana family contin-ued for a long time. Enrico Fermi had a very high estimation ofhim. In the letter he wrote in 1938 to the Italian prime Minister ofthat time, Benito Mussolini, asking the government to intensify thesupport of Ettore’s research, Fermi stated “I have no hesitation tostate to You, and I am not saying this as an hyperbolic statement,that of all Italian and foreign scholars that I have had the opportu-nity to meet, Majorana is among all of them the one that has moststruck me for his deep sharpness” [2].

Majorana was not a prolific author. He just published 9 articlesbefore his disappearance and a 10th article, whose manuscript was

found by Majorana’s brother among his files, was publishedin 1942 after his disappearance in the international

Italian journal Scientia, through the interest of hisfriend Giovanni Gentile Jr.. Nine of these arti-

cles were written in Italian and one inGerman. Italian is not a widespread lan-

guage and this limitation has preventedMajorana’s work becoming known andcorrectly evaluated by a vast commu-nity of scientists. I have translated the10th article of Majorana “The value ofstatistical laws in physics and socialsciences” to provide to a broad audi-ence of physicists the possibility ofdirect access to the article.The transla-tion was recently published inQuantitative Finance 5, 133-140 (2005).


features

The tenth article of Ettore MajoranaRosario Nunzio Mantegna,Dipartimento di Fisica e Tecnologie Relative, Università di Palermo, Viale delle Scienze, Edificio 18, I-90128 Palermo • Italy

b Fig. 1: Photo of Ettore Majorana fromthe University ID dated November 3rd

1923.

The article is a rather special article in several respects. In theoriginal presentation for Scientia, Giovanni Gentile Jr. wrote thatthe article was originally written for a sociology journal. Thisarticle was therefore intended to present the point of view of aphysicist about the value of statistical laws in physics and socialsciences to scholars of a broad spectrum of different disciplinessuch as sociology and economics. In his article, Majorana consid-ers quantum mechanics as a fundamental and successful theoryable to describe the basic processes involving single particles andatoms. He explicitly considers the theory as a statistical theorybecause the theory is not able to describe the time evolution of asingle particle or atom in a precise environment at a determinis-tic level. As an example of the lack of determinism in the timeevolution of a single system he discusses the case of the decay ofa radioactive atom. This lack of determinism at the level of anelementary physical system motivated him to suggest a formalanalogy between statistical laws observed in physics and the socialsciences. In his article, he concludes that there is an “essential anal-ogy between physics and the social sciences, between which anidentity of value and method has turned out”. These words seemto pioneer the view that an investigation of complex systems(indeed this term is literally present in the article) of economic orsocial origin might be conducted on the same epistemologicalbasis as the modeling of physical systems.

His conclusion was considered as rather peculiar and wasaccepted as a general belief by only a minority of physicists forseveral years. For example in the book “La vita e l’opera di EttoreMajorana” [1], Edoardo Amaldi just wrote a single sentence onthis article in a biographical and scientific note of 49 pages. Eventoday, Majorana’s point of view might indeed still be rather unpop-ular among mainstream physicists, in spite of more than 70 yearsof quantum mechanics and after some major breakthrough in thefields of critical phenomena and chaos theory.

There is a pioneering nature of this article both from theperspective of physics and economics. From the physics point ofview, Majorana took a clear position about the key aspect thatquantum mechanics forces scientists to use a statistical descrip-tion down to events involving single entities. From the point ofview of economics and social sciences, there is an emphasis on theobservation that statistical laws have to be used in economic andsocial modeling. It should be noted this position was not that of the

majority of scholars working in the thirties ofthe last century in both the disciplines

considered. In fact, during the thir-ties of the last century the

interaction between social sci-ences and natural scientists

was de velop ed underthe paradigm of celestialmechanics (the onlye x c e p t i o n t o t h i sapproach was the onepursued by Louis Bache-lier that at that time hadno impact on the acade-my [4]). This interactiongoes back to the deve-l opm e nt of ge n e r a l

equilibrium theory pursued

by Walras, Pareto, Schlesinger and Wald. The emphasis of Majo-rana on the intrinsic statistical nature of most of the underlyingprocesses describing natural phenomena suggests that statisticallaws should be incorporated into a modeling approach to socialphenomena. This approach has eventually found its best achieve-ment in finance with the Black and Scholes modeling of optionpricing [5].

The topic considered by Majorana in his article is timely todayfor a series of reasons. First, it should be noted that a cross-disciplinary consensus about the epistemological value of statisticallaws in different disciplines is not easily found today. The majorparadigm of the validity of a scientific theory is still based on thefalsification procedure of a law. It is undisputable that this approachhas been devised having in mind the most characteristic laws inphysical sciences, i.e. deterministic laws or laws having a determin-istic part (as is the case for quantum mechanics when the timeevolution of the wave function is considered or for random walktheory when one considers the statistical description of an ensem-ble of walks). During the past years it has been progressivelyrealized that such an approach might not be the most appropriateto other disciplines such as, for example, biology. For this importantand successful discipline, the nature of the laws (or sometimestheories) is often intrinsically related to the prevalence of indeter-minacy owing to the high frequency of stochastic processesunavoidably involved and moreover a double causality (one relat-ed to the external conditions and forces and one governed by theamount of information inherited at the biological level under con-sideration) is present in most cases [6]. Similar observations aremost probably also valid for social sciences.

Physics might certainly benefit from a deeper understanding ofthe role, necessity and peculiarity of statistical laws in physics.Some of the statistical laws are eventually reinterpreted in terms ofmore fundamental and deterministic laws. However there are caseswhen a reduction seems to be impossible. One of these cases isindeed quantum mechanics and other more recent examples con-cern the topics of chaos and critical phenomena theory. Bysomewhat inverting the perspective of the relations betweenphysics, biology and the social sciences, it might be worth dis-cussing the possibility that physicists should also start to consideras proper to their discipline the investigation of systems where thebasic elements composing the system are in possession of a certainlevel of internal information and are characterized by a certainability to react to external stimuli by properly processing the avail-able external information with inherited or adaptive rules.Investigations of this kind have been performed with tools ofstatistical physics properly adapted or extended. For example, oneof these models is the minority game [7, 8] recently investigatedwithin the new research field of econophysics [9].

In summary, the 10th article of Majorana raised the necessity offocusing the attention of several disciplines on the value andnature of statistical laws. From physics, to biology and to socialsciences, all the scientific disciplines present statistical laws andscholars of these disciplines need to reflect about their role with-in each discipline. Majorana noticed that quantum mechanicsmade clear that a scientific description without statistical laws isimpossible. Today there is still a need to assess the status of statis-tical laws and to consider the validation procedures that are mostappropriate to these sorts of laws.Validation procedures probablyneed to be different from those originally devised having in minddeterministic laws.

I hope the occasion of the centenary of the birth of Ettore Majo-rana will be useful to remember and to reconsider not only hisexceptional achievements in theoretical physics but also his fresh

europhysicsnews

b Fig. 2: Ettore Majorana atNaples in 1938.

16 • volume 37 • number 4

fea

ture

s

and original views on the essential aspects, importance and role ofstatistical laws in physics and in other disciplines such as thesocial sciences. n

About the authorRosario Nunzio Mantegna is a professor of Applied Physics andchairman of the PhD school in Applied Physics of Palermo Uni-versity. Mantegna’s research is focused on the application ofmethods of statistical physics to physical, biological and economiccomplex systems. He is currently coordinating the research groupObservatory of Complex Systems of Dipartimento di Fisica e Tec-nologie Relative of Palermo University (http://lagash.dft.unipa.it).Mantegna is managing editor of the International Journal of The-oretical & Applied Finance and member of the editorial board ofQuantitative Finance. He has co-authored with H.E. Stanley thebook An Introduction to Econophysics, CUP, Cambridge 2000.

References[1] Edoardo Amaldi, La vita e l’opera di Ettore Majorana, Accademia

Nazionale dei Lincei (Roma, 1966).

[2] Erasmo Recami, Il Caso Majorana, Di Renzo Editore (Roma, 2002)

[3] Ettore Majorana, Il valore delle leggi statistiche nella fisica e nellescienze sociali, Scientia, Quarta serie, Febbraio-Marzo 1942 pp. 58.English translation in Ettore Majorana, The value of statistical lawsin physics and social sciences, Quantitative Finance 5, 133 (2005).

[4] Louis Bachelier, Théorie de la spéculation, Ph.D. thesis in mathematics,Annales Scientifiques de l’Ecole Normale Supèrieure, III-17, 21(1900).

[5] F. Black and M. Scholes, The Pricing of Options and Corporate Liabil-ities, J. Polit. Econ., 81, 637 (1973).

[6] Ernst Mayr, The autonomy of biology: The position of biology amongthe sciences, The Quarterly Review of Biology, 71, 97 (1996).

[7] Damien Challet, Matteo Marsili,Yi-Cheng Zhang, Minority Games :Interacting Agents in Financial Markets, Oxford University Press(2005).

[8] A.C.C. Coolen, The Mathematical Theory of Minority Games : Statisti-cal Mechanics of Interacting Agents, Oxford University Press (2005).

[9] J. Doyne Farmer, Martin Shubik, and Eric Smith, Is Economics theNext Physical Science?, Physics Today 58, 37 (2005).

europhysicsnews

features

We remember that the cyclist on a horizontal road has to beattwo forces. One is the rolling resistance, proportional to the

total weight (Crmg). The other one is air drag, proportional to thefrontal area, the air density and the velocity squared (CD.A. 1/2rv2).The two are equal at roughly 15 km/h for a normal bicycle. In viewof the v2 dependence, drag is by far dominant at record-breakingspeeds: If you want to go fast, get rid of the drag.

One way to minimize drag is to use super-streamlined, recum-bent bikes: HPV’s, for Human Powered Vehicles. Their mainadvantage is a reduction of the drag coefficient CD to 0,1 which isan order of magnitude smaller than the value for a normal bike.As a result, speeds above 90 km/h have been a piece of cake forexperienced riders ever since the 1980s. Indeed, in the U.S. duringthe nationwide speed limit of 55 mph (88 km/h), several ridersearned an honorary speeding ticket from the California HighwayPatrol. More recently, in 1998, the landmark of 130 km/h was firstreached by the Canadian Sam Whittingham.

For the real speed devil that’s not good enough.Why not abolishdrag altogether, by riding behind a fast car having a large verticalboard at its rear end (a technique also called Motor Pacing)? Thisis precisely what Dutchman Fred Rompelberg from Maastricht didin 1995, on the Bonneville Salt Flats in Utah, USA. He set offbehind a powerful car on a special-design bicycle (but not anHPV) and reached a breathtaking 268 km/h. Sure enough, thatmade him the fastest man-on-a-bike ever.

Now let us take this a bit further, by also reducing therolling resistance. Let us do a though-experiment andcalculate how fast we could ride on the moon.Reasonable input data would be a peak powerof 750 watt for the rider (which is what atrained cyclist briefly reaches on earth), amass m = 100 kg (including the space

suit), Cr = 0.0045 (a typical value for bicycles) and g = 1.62 m/s2.Since the rolling resistance is the only force to be overcome, all wehave to do is solve the equation Crmgv = 750 W.The resulting speed v turns out to be some 3700 km/h. That is real-ly fast: over Mach 3 in terms of the terrestrial speed of sound atambient temperature. But for lack of an atmosphere, we do nothave to worry about sonic booms on the moon.

Much faster than that, however, may become a problem: 3700km/h, that is about half theescape velocity… n

Physics in daily life: cycling really fastL.J.F. (Jo) Hermans, Leiden University • The Netherlands


It is a classical scene from western movies. The bad guy ends upin a pool of quicksand, and sinks away in it until only his hat

remains, floating on the quicksand. Or, at the very last moment,his head barely sticking out of the quicksand, he is saved by the leadcharacter, who pulls him out of the quicksand with his horse.Hollywood produced dozens of movies in which people drown inquicksand; the most classic one is probably The Hound of theBaskervilles. In the movie a young lady (and later on almostSherlock Holmes himself, also) disappears into ‘wet’ quicksand.

Our recent experiments at the University of Amsterdam showthat when investigated by physicists, the Hollywoodian quicksandmyths are mostly pure figments of imagination. The first importantquestion is what quicksand really is. Geophysicists do not have aclear answer to this question. In most geophysics textbooks,“quick-sand” is the generic name for sand that has been fluidized byupwelling water, i.e., with an underground water source. If the

underground water flows sufficiently rapidly to the surface, theflow destroys the packing of the sand grains, and what remains isliquid: water with the sand particles suspended in it. This canhave dramatic consequences in areas that are earthquake pronesuch as in Japan: after earthquakes often water wells up, and if thesand is fluidized by this, whole buildings can topple over. This how-ever has nothing to do with the quicksand in which the poor ladyof “Hound of the Baskervilles” drowned, or with quicksand thatwe know from muddy areas, for instance in the bay of the Mont StMichel in France.

When on holidays in Iran, one of us (DB) encountered a hugequicksand area near a salt lake between Tehran and Qom. Thisquicksand area is very ill-reputed in Iran (local shepherds insistthat whole camels were swallowed up by the quicksand) and hasthe big advantage that nobody has interfered with it, as is the casefor instance in certain areas of the Mont St Michel bay. The analy-sis of the soil samples brought back from Iran showed that besidessand and water, the quicksand contained considerable amounts ofclay (5-10%) and salt. The detailed analysis of the flow propertiesof the quicksand then allowed us to explain the myths that havesurrounded quicksand for centuries.

The first myth says that when one ends up in quicksand, oneshouldn’t move, because it makes you sink in deeper. The secondmyth says that once you are trapped in quicksand, that it is impos-sible to get out. The third myth is that you can drown in it. Theconclusion of our research is that the first two myths are true.The third, on the other hand, is not: it is impossible to drown inquicksand.

The quantitative analysis of the mixture of salt water, sand andclay shows that there is remarkably little sand in the quicksand,only about 40% in volume. This makes the sand structure veryfragile: for comparison, for a pile of oranges on the market, thefruits take up approximately two-thirds of the space. If there werea way to remove almost half of the oranges without making the pilecollapse, the packing would look like that of the sand in quicksand.This fragile packing is stabilized by the presence of the clay; theclay we found in the quicksand forms a colloidal gel with the con-sistency of thick yogurt, preventing the sand grains from falling.The clay itself is, on the other hand, not solid enough to supportyour weight: if you are standing on quicksand, more than 90% ofyour weight is carried by the sand. All this could be verified by

Quicksand!A. Khaldoun, G. Wegdam, E. Eiser and D. Bonn,Van der Waals-Zeeman Institute, University of Amsterdam • The Netherlands • Email: [email protected]

m Fig. 1: Liquefaction of quicksand under stress: viscositymeasurements show that there can be almost a factor of 1 milliondifference between quicksand in its normal ‘solid’ state, andquicksand that has been liquefied because it was disturbed toomuch (a too large stress was applied to the system).


fea

ture

s

preparing a “laboratory quicksand”: a mixture of bentonite (aswelling clay) sand and salt water that perfectly reproduces the flowproperties of our natural quicksand.

Once you stand on quicksand, it is not a very good idea to move.Your movement will liquefy the clay (much like yogurt, whenstirred), and that allows the sand structure to collapse. In the exper-iments, this corresponds to a sudden viscosity decrease of a factor1 million: the difference between sinking away with a few mil-limetres every hour, and sinking with a meter per second. Thus, assoon as you move, you will sink away rapidly. This has dramaticconsequences: after the clay has liquefied and you have sunk away,the sand will settle to the bottom and water will float on top of it.This turns out to be where the salt is important: for a sufficientamount of salt, the clay will not only liquefy, but destabilizescompletely. This is a generic feature of swelling clays: for too highsalt, clay particles that were electrostatically stabilized in suspen-sion stick together (flocculate) because of their mutual attractiondue to van der Waals forces. The aggregated particles then sink tothe bottom, too. The results of this is the formation of a very dense-ly packed sand layer around your feet. The density is 80 volume%:there are smaller oranges or tangerines between the oranges, sincethis is a higher volume fraction than a random close packing ofspheres of the same size. The only way you can unstick your footis then to introduce water into this densely packed sand. However,the sand is so fine, with a typical grain size of 60 µm, that thisturns out to be very, very difficult. For the typical poresize of theIranian quicksand, pulling up a model ‘foot’ of 10 cm x 10 cmrequires a force of some 10 4 N. This force is comparable to thatnecessary for lifting up a car! So we are forced to conclude that thesecond myth: once you get stuck, it is impossible to get out, is alsotrue. The classical Hollywood-scene of the hero being pulled out ofthe quicksand by his horse, on the other hand, is very wrong: thehorse is likely to pull our hero into two pieces.

The third myth is that one can drown in quicksand. There ishowever hope for people that get stuck. A simple experiment infact shows that it is close to impossible for people or animals(including camels) to drown. The bottom line is that the density ofquicksand is roughly twice that of water, and that the buoyancyforce will simply make you float. The figure shows a ‘cartoon’version of the experiment. Taz, the little figurine standing on thequicksand, has been carefully engineered to have exactly a densi-ty of 1 g /cm3, the density of men and mammals. To mimicsomeone moving in quicksand, we vibrate the whole containerwith Taz on it with a mechanical shaker. We observe that indeed,he sinks away, and more quickly so if we shake harder. Still, how-ever hard we try, we never succeed in drowning Taz completely:Archimedes was right, and Hollywood wrong. Formulating, for

the quicksand, the equivalent of Archimedes’ buoyancy forcecalculation is however a very difficult problem: a part of theweight of the sand grains is carried by other grains, and thisweight does not contribute to the buoyancy force. The conclusionmust therefore be that one will sink away somewhere betweenhalfway (because the quicksand has twice the density of water)and completely (if only the water counts). The experimentalreality is somewhere in between, as Taz clearly shows: it is impos-sible to drown.

This of course poses the question where this third myth finds itsorigin. We suspect that this has everything to do with the placeswhere quicksand is usually found, namely at the estuaries ofrivers. This is a direct consequence of its composition: the riverstransport clay, and where the clay meets the salty seawater, all theingredients are present to make quicksand. The problem one mayencounter then is the high tide coming in when one is stuck inquicksand: in this situation drowning is unfortunately very wellpossible. n

About the AuthorsAsmae Khaldoun got a PhD in science at the Universite Abdel-malek Essaadi in Tetouan (Marocco) on the physico-chemicalproperties of clay soils. Currently she is working at the Van derWaals-Zeeman Institute of the University of Amsterdam on quick-sand and quickclay.Erika Eiser received her M.Sc. degree in 1992 from the Universityof Konstanz, Germany and her PhD degree in 1997 from the Weiz-man Institute, Israel, working in polymer physics at surfaces. Sheextended her expertise to x-ray scattering and rheology in self-assembled soft materials. Since 2000 E.Eiser is assistant professor inthe chemistry department of the University of Amsterdam, TheNetherlands.Gerard Wegdam is professor in Soft Condensed Matter at the Uni-versity of Amsterdam. Recently the focus of his research is ongranular matter, glass formation and phase transitions in colloidalsystems.Daniel Bonn is a CNRS researcher at the Laboratoire de PhysiqueStatistique at the Ecole Normale Supérieure in Paris, where he leadsthe 'complex fluids' group and a part-time professor at the van derWaals-Zeeman Institute of the University of Amsterdam. His cur-rent research interests are liquid surfaces, rheology, hydrodynamics,fracture and complex fluids.

m Fig. 2: Sinking experiment: the figurine has been carefully tailoredto have exactly the density of a human being. He sinks away, butdoesn’t drown in the quicksand.


features

20 • volume 37 • number 4

fea

ture

s

Life appears as incredibly complex when it is investigated withatomic resolution.However,the vast majority of biological matter

consists of rather few building blocks, which are comparatively sim-ple organic molecules. The building blocks of life are, first of all, thefour nuclei acid bases adenine, cytosine, guanine and thymine (seeScheme I), which encode the genetic information of all living crea-tures in DNA (deoxyribonucleic acid). The exceedingly multifariousworld of proteins is built from only 20 amino acids (a few of themare shown in Scheme II). Another widespread molecular motif arecarbohydrates (e.g.,sugars).Sugar molecules are part of the backboneof DNA and of structure-forming biopolymers such as cellulose.

Organic molecules are not stable under persistent irradiation withultraviolet (UV) light. UV photons can break covalent bonds andthus can induce a great variety of chemical transformations (iso-merizations or fragmentations). In view of this, it is amazing that lifecan thrive under full exposition to sunlight. Moreover, biogenesistook place long before the formation of the stratospheric ozone layer(which today filters out the most dangerous UV components of sun-light) and thus under conditions of extremely intenseshort-wavelength UV radiation. As pointed out by Sagan, this musthave resulted in an extreme selection pressure for UV protection [1].These considerations suggest that photostability may have been thedecisive selection criterion which has determined the moleculararchitecture of life at the beginning of the biological evolution.

In this article, we discuss recent theoretical and experimentalresults which support the hypothesis that the fundamental build-ing blocks as well as the supramolecular structures of life areoptimized with respect to photostability.

PhotostabilityThe concept of photostability and the physical mechanisms pro-viding photostability can best be explained by referring to so-calledphotostabilizers [2], which are in widespread technical use for theprotection of organic polymers. Photostabilizers are organic com-pounds (usually intramolecularly hydrogen-bonded aromaticmolecules) which absorb UV photons with a large cross sectionand convert the photon energy into heat, without undergoingdestructive photochemical reactions. The best photostabilizerscan neutralize nearly a million of photons before being destroyedby a photochemical reaction. The essential mechanism is ultrafastradiationless decay of the photoexcited singlet state to the elec-tronic ground state. This process is called internal conversion. It

converts the potentially dangerous energy of the UV photon intovibrational energy (heat) which is subsequently dissipated into theenvironment. As we shall discuss below, the DNA bases and espe-cially the supramolecular structures of DNA and proteins availthemselves of very efficient excited-state deactivation mechanismswhich are similar to those of commercial photostabilizers.

Potential-energy surfaces, conical intersections and radiationless decayTo explain the physical mechanisms of photostability, it is necessaryto introduce two fundamental theoretical concepts. The first con-cept is the Born-Oppenheimer (BO) potential-energy surface. As iswell known, the BO approximation is based on the large mass differ-ence between electrons and nuclei, resulting in a separation of timescales. It is usually a good approximation to assume that the fastelectrons follow instantaneously the much slower motion of thenuclei. In this BO adiabatic approximation,the nuclear motion is thustied to a particular eigenvalue of the electronic Schrödinger equation,the so-called BO potential-energy surface.The second concept is theconical intersection of BO potential-energy surfaces,dating back to afundamental paper by von Neumann und Wigner [3]. Von Neu-mann and Wigner realized that in a polyatomic molecule, otherthan in diatomic molecules, BO energy surfaces generically areallowed to have exact crossings. These crossings are called conicalintersections, since the energy surfaces have the shape of a doublecone in a suitable two-dimensional subspace of the nuclear coordi-nates.At these conical intersections, the BO adiabatic approximationis strictly invalid, since the nonadiabatic couplings, which usually are

The chemical physics of the photostability of lifeAndrzej L. Sobolewski 1 and Wolfgang Domcke 2

1 Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw • Poland • Email: [email protected] Department of Chemistry, Technical University of Munich, D-85747 Garching • Germany

adenine thymine guanine cytosine

m Scheme I . Scheme II

glycine alanine glutamine

m Fig. 1: Schematic view ofthe radiative excitation of a

chromophore and itsdeactivation via a conical

intersection of the S1 and S0

energy surfaces. The dots andarrows are intended to give a

qualitative visualization of themotion of the optically prepared

wave packet.

europhysicsnews


features

minimum of the lowest excited singlet state (1nπ*, where n denotesa nonbonding molecular orbital) of adenine. It can be reached in anearly barrierless manner from the first 1ππ* state, which is the lowestUV absorbing state of adenine.Similar results have been obtained forcytosine, guanine and thymine. Taken together, these computationalresults confirm the existence of very efficient channels of radiation-less deactivation in the DNA bases. The DNA bases thus appear tobe optimized with respect to photostability. This property canexplain the selection of just these four species at the beginning ofthe biological evolution. They may have played the role of integrat-ed sunscreens in the earliest biopolymers (presumably RNA).

Photostability of DNA base pairsIt is a most remarkable feature of life that only two base pairs (ade-nine-thymine (AT) and guanine-cytosine (GC)) encode all thegenetic information. Recently, is has become possible to obtain theelectronic and vibrational spectra of these hydrogen-bonded base

neglected, become infinite. The molecule thus can switch extremelyefficiently from the energy surface of the excited state to the energysurface of the electronic ground state at such conical intersections.Extensive research in computational chemistry during the last decadehas revealed that (i) conical intersections are indeed ubiquitous inpolyatomic molecules [4, 5] and (ii) internal conversion at conicalintersections is essentially instantaneous, that is, it occurs within afraction of the relevant vibrational periods [6, 7]. Conical intersec-tions thus are the key mechanistic elements for photostability,provided they are accessible in a barrierless manner on the excited-state potential-energy surface. A schematic view of the radiativeexcitation process and the rapid radiationless deactivation process viaa conical intersection is shown in Fig. 1.While the excitation processis “vertical”, that is, occurs at the ground-state equilibrium geometryof the molecule, the deactivation process involves a photochemicalreaction which is aborted at the conical intersection.

It is clear from this brief outline that a reliable first-principlescharacterization of the electronic potential-energy surfaces isessential for the theoretical understanding of photostability. Wecannot cover here the rather involved technical aspects of thesecalculations. Detailed information about the electronic-structuremethods can be found in the quoted literature.

Photostability of isolated DNA basesPhotostability of the molecular encoding of genetic informationclearly is of utmost importance for the existence of life. Althoughthe DNA bases absorb strongly in the 200 – 300 nm range, thequantum yields of their photoproducts are very low. The kinetics ofthe radiationless decay of individual DNA bases has been investi-gated in the gas phase as well as in solution, see [8] for a recentreview. The measured lifetimes indeed are very short, of the orderof a few hundred femtoseconds in solution [8].

It has recently been shown by several research groups that themethods of ab initio quantum chemistry can contribute significant-ly to the identification of the excited-state deactivation mechanismsof isolated DNA bases (see [9] and references therein). Two typesof photochemical reaction paths, which lead to low-lying conicalintersections of excited-state and ground-state energy surfaces,havebeen identified: (i) the torsion of certain C-N bonds of the six-membered rings, and (ii) the abstraction of hydrogen atoms fromazine or amino groups. Fig. 2 shows, as an example, the energy pro-files of the electronic ground state (S0) and the three lowest excitedstates of adenine as a function of the reaction coordinate (primari-ly torsion of the C2N3 bond of the six-membered ring of adenine)leading to the lowest-energy conical intersection.

The curve crossings, which are accentuated by colored circles inFig. 2, become conical intersections when the remaining nucleardegrees of freedom are taken into account. It is seen that the stabi-lization of the second excited singlet state of ππ* character (π/π* areoccupied/unoccupied molecular orbitals with a node in the molec-ular plane) leads to a conical intersection of this state with theelectronic ground state. This intersection is lower in energy than the

m Fig. 2: Potential-energy profiles of the ground state (S0) and thelowest excited singlet states (1nπ*, 1ππ*) of adenine along thereaction path leading from the ground-state equilibrium geometry(left) to the S1-S0 conical intersection (right).

b Fig. 3: Equilibriumstructures of theguanine-cytosine (a) andadenine-thymine (b)Watson-Crick base pairs.Colour code: yellow:carbon; blue: nitrogen;red: oxygen; grey:hydrogen.

(a) (b)


fea

ture

s

pairs in isolation by laser evaporation and subsequent cooling in asupersonic jet. The isolated AT and GC base pairs can exist in a vari-ety of structures (so-called conformers) which differ in thehydrogen-bonding geometry.With sophisticated double-resonancelaser techniques and first-principles calculations of the vibrationalspectra, it has been possible to assign the observed spectra to specificconformers [10]. The so-called Watson-Crick conformers of AT andGC, that are the only ones relevant for biology, are displayed in Fig. 3.It is seen that GC (AT) are connected by three (two) hydrogen bonds(dotted lines). For the GC base pair, the spectra of three conformershave been detected [10, 11]. Remarkably, the resonantly enhancedmulti-photon ionization spectrum of the Watson-Crick conformer ofGC is extremely weak and broad, in sharp contrast to the strong andsharp signals of the two other conformers [11].An excited-state life-time of a few femtoseconds has been estimated from the spectra ofthe Watson-Crick conformer of GC. The UV spectrum of the Wat-son-Crick conformer of AT has not yet been observed.

Calculations of the potential-energy functions of GC and AThave led to the discovery of a new mechanism of excited-statedeactivation which is specific for hydrogen-bonded aromatic sys-tems [12]. The calculations have revealed that electron-drivenproton-transfer processes between the bases play an important rolein the photophysics of these systems. The key player in this mech-anism is a “dark” charge-transfer (CT) state which connects theoptically accessible locally-excited state with the electronic groundstate via two conical intersections along the proton-transfer coor-dinate. The exceptionally short lifetime of the UV-absorbing statesof the Watson-Crick conformer of the GC base pair is explained bya barrierless access to the reactive charge-transfer state, see Fig. 4a,which provides the mechanism for fast return of the photoexcitedsystem to the electronic ground state. In the two other conformersof GC, the photochemically reactive charge-transfer state is locat-ed higher in energy, resulting in a barrier along the proton-transferreaction path and thus a considerably longer excited-state lifetime[12]. The same qualitative features are predicted by the calculationsfor the AT base pair: only in the Watson-Crick conformer the local-ly-excited state is crossed near its minimum by the reactivecharge-transfer state, see Fig. 4b [12]. These results suggest thatthe biologically relevant Watson-Crick structures of GC and AT aredistinguished by uniquely efficient excited-state deactivationmechanisms which maximize their photostability.

Additional evidence for enhanced excited-state deactivation viathe electron-driven proton-transfer mechanism has also beenfound for a biomimetic model of the Watson-Crick base pairs, the2-aminopyridine dimer. Femtosecond time-resolved pump-probemeasurements have revealed that the excited-state lifetime is short-ened by a factor of twenty in the hydrogen-bonded dimer [13].Calculations have predicted the existence of a reactive charge-transfer state in the dimer, which connects the locally-excited statewith the electronic ground state via two conical intersections [13].

Photostability of proteinsThe so-called secondary structure of folded native proteins is deter-mined to a large extent by hydrogen bonds between NH and COgroups of the backbone.Well-known structural motifs in proteins areα-helices and β-sheets. At present, ab initio electronic-structurecalculations of excited electronic states are possible only for relative-ly small oligomers of amino acids, which are called peptides.

The molecular structure of a small peptide, the glycine trimer,is shown as inset in Fig. 5. The dangling bonds of the backbonehave been capped by methyl groups. This structure is a model of aso-called β-turn of the peptide backbone which is stabilized by aC=O…H-N hydrogen bond (dotted line).

m Fig. 4: Potential-energies of the ground state (S0), the lowestlocally-excited states (1nπ*(LE), 1ππ*(LE)) and the lowest charge-transfer state (1ππ*(CT)) as functions of the proton-transfercoordinate in the GC (a) and AT (b) Watson-Crick base pairs. Theexcited-state energies have been calculated at the minimum-energygeometries of the respective states, while this designated as S0

(CT )

has been determined at the minimum-energy geometries of thecharge-transfer state

m Fig. 5: Potential-energies of the locally-excited state (blue), thecharge-transfer state (red) and the electronic ground state (black) asfunctions of the proton-transfer coordinate in the glycine trimer. The1nπ*(LE) and 1ππ*(CT) energies have been determined at theminimum-energy geometries of the respective states. The ground-state energies designated as S0 have been calculated at theminimum-energy geometries of the S0 state, while those designatedas S0

CT have been determined at the minimum-energy geometries ofthe charge-transfer state.


features

An analysis of the excited electronic states of this model pep-tide reveals that these can be classified, in a qualitative sense, aslocally-excited and charge-transfer states [14]. The lowest locally-excited state involves excitation of an electron from the highestoccupied molecular orbital to the lowest unoccupied molecularorbital, which are both localized on the lower branch of the back-bone. The lowest charge-transfer state, on the other hand, involvesexcitation from an occupied molecular orbital on the lower branchto an unoccupied orbital on the upper brach of the backbone.Similar to what has been found for the DNA base pairs, the protonof the NH group wants to follow the electron, leading to a pro-nounced stabilization of the energy of the charge-transfer state byproton transfer. As shown in Fig. 5, the energy surface of thecharge-transfer state (red) crosses the energy surfaces of both thelocally-excited state (blue) as well as the ground state (black).Againthe energy surface of the locally-excited state, which is generated bythe absorption of a UV photon, is connected via two conical inter-sections with the energy surface of the ground state. These conicalintersections provide the mechanism for the ultrafast deactivationof the excited state.

ConclusionsHydrogen bonds are ubiquitous in biological matter. Their univer-sal role in structure formation, molecular recognition andcatalysis is well known [15]. Life on earth thus depends essentiallyon the functionality of hydrogen bonds.

Herein, we have provided evidence that the photoinduced excit-ed-state chemistry of hydrogen bonds may be as essential for theexistence of life as the ground-state chemistry. As has been dis-cussed above for the examples of DNA base pairs and modelpeptides, the photochemistry of hydrogen bonds provides amechanism for the deactivation of the potentially reactive excitedstates which is of unrivalled efficiency.

The overall radiationless deactivation process may be visual-ized as an electron-driven proton-transfer mechanism asschematically indicated in Fig. 6. Once the charge-transfer state ispopulated, the proton moves from the donor atom towards theacceptor atom, following the electron; after the back-transfer of theelectron at the conical intersection of the charge-transfer state withthe S0 state, the proton is driven back to the original location. Thisway, the energy of the UV photon is converted into vibrationalenergy of the hydrogen bond, which subsequently is dissipated toother intramolecular as well as intermolecular vibrational degreesof freedom. The unusually large electronic energy gradients andthe small mass of the proton ensure the exceptionally fast rate ofthis process. The photoexcited biomolecule thus returns to theclosed-shell electronic ground state before deleterious photochem-ical reactions can take place. n

About the AuthorsAndrzej L. Sobolewski studied physics at the University of Warsawand received his PhD in the Institute of Physics of the Polish Acad-emy of Sciences in 1981. Since 1989 he has been Professor of

Physics at this Institute. His research interests are concerned withdifferent aspects of the theory of molecular photophysics.Wolfgang Domcke studied physics and received his PhD at theTechnical University of Munich in 1975. He has been Professor ofTheoretical Chemistry at the Universities of Heidelberg, Düssel-dorf and, since 1999, at the Technical University of Munich. Hisresearch interests comprise molecular electronic-structure theoryas well as theoretical aspects of chemical reaction dynamics andmolecular spectroscopy.

References[1] C. Sagan, J. theor. Biol. 39, 195 (1973).

[2] J.-E. A. Otterstedt, J. Chem. Phys. 58, 5716 (1973).

[3] J. von Neumann and E. Wigner, Physik. Z. 30, 467 (1929).

[4] D. R.Yarkony, Rev. Mod. Phys. 68, 985 (1996).

[5] M. A. Robb, F. Bernardi and M. Olivucci, Pure and Appl. Chem. 67, 783(1995).

[6] W. Domcke and G. Stock, Adv. Chem. Phys. 100, 1 (1997).

[7] W. Domcke, D.R.Yarkony and H. Köppel (Eds.), Conical Intersections:Electronic Structure, Dynamics and Spectroscopy,World Scientific,Singapore, 2004.

[8] C.E. Crespo-Hernandez, B. Cohen, P.M. Hare and B. Kohler, Chem.Rev. 104, 1977 (2004).

[9] S. Perun, A. L. Sobolewski and W. Domcke, J. Am. Chem. Soc. 127,6257 (2005); see also A.L. Sobolewski, C. Woywod and W. Domcke,J. Chem. Phys. 98, 5627 (1993).

[10] E. Nir, C. Janzen, P. Imhof, K. Kleinermanns and M.S. de Vries, Phys.Chem. Chem. Phys. 4, 732 (2002); C.Plützer, I. Hünig, K. Kleiner-manns, E. Nir and M.S. de Vries, ChemPhysChem 4, 838 (2003).

[11] A. Abo-Rizig, L. Grace, E. Nir, M. Kabelac, P. Hobza and M.S. deVries, Proc. Natl. Acad. Sci. USA 102, 20 (2005).

[12] A.L. Sobolewski and W. Domcke, Proc. Natl. Acad. Sci. USA 102,17903 (2005); S. Perun, A.L. Sobolewski and W. Domcke, J. Phys.Chem. A, in press.

[13] T. Schultz, E. Somoylova, W. Radloff, I.V. Hertel, A.L. Sobolewski andW. Domcke, Science 306, 1765 (2004).

[14] A.L. Sobolewski and W. Domcke, ChemPhysChem. 7, 561 (2006).

[15] P. Schuster, G. Zundel and C. Sandorfy, The Hydrogen Bond - RecentDevelopments in Theory and Experiments. II. Structure and Spec-troscopy, North Holland, Amsterdam, 1976.

c Fig. 6: Schematic view of ultrafast excited-state deactivation viathe electron-driven proton-transfer process: the locally excited (LE)electronic state is deactivated via two sequential electron-transfer(ET) processes at conical intersections of the locally-excited state(blue) and the electronic ground state (black) with a charge-transferstate (red). After each electron transfer, the proton follows theelectron, thus accepting the energy deposited by the UV photon inthe molecular system.

Starting here in the Latin world, a bubble is originally a bulla,that is, a ball; a metallic ball, first, attached to a seal, and by

continuity the papal decree stamped with this seal; or a bulla,blown by children from a soapy water, or observed inside asparkling liquid. Nowadays, bolla designates in Italian both thebubble inside a liquid and the papal seal – in French, we similarlyhave bulle for both meanings, as in Spanish with bula (wherebubbles in liquids are however most often qualified by the moremodern burbuja). Hence a bubble is first defined by its shape, thatis, the pure sphere that we all observed for small gas cavities inChampagne, or for larger spherical bubbles blown by children, thepretext for admirable paintings by Chardin or Manet. Here wedescribe the negative of this object: as an antibolla in Italian (orantibulle in French [1], and antibula in Spanish) designated thebolla of an antipope (when they existed), an antibubble will be thecontrary of a soap bubble, namely, a thin shell of air surroundingwater, and immersed in water [2]. We first discuss the way to gen-erate such objects; then, we comment on their (brief) life and theirdeath, comparing them with those of soap bubbles.

Antibubble generators The simplest method to obtain an antibubble consists of pouringsoapy water inside a bath of the same nature (Fig. 1). The bath isfirst filled, in such a way that the surface is clean, without anybubble. Then, a drop of the same liquid is deposited at this surface.Owing to the presence of surfactants, it floats a few seconds beforemerging [3]. This situation can be made much longer by makingthe bath vibrate, as recently shown by Couder et al. [4]. But evenwithout this trick, the floating drop can be gently fed so that itbecomes centimetric. Pushing this globule below the surface witha jet can produce an antibubble. An even simpler way consists ofmaking the jet directly impact the bath, with a velocity large

enough to make it penetrate the bath coated with a film of air. TheRayleigh-Plateau instability (which transforms a jet coming out ofa faucet into drops) may destabilize this jet, which generates awhole flottilla of antibubbles (Fig. 1).

The presence of a shell of air will make the antibubble rise,pushed by buoyancy forces. The velocity of rise allows us to deter-mine the typical thickness of the shell, which is found to be of theorder of 5 microns, a value comparable to the thickness of a soapbubble [5]. In order to avoid this rise (which is fatal for our globule,as it reaches the upper surface of the bath), the impinging liquidcan be salted, and the antibubble formed in a bath containing(heavy) glycerol at the bottom: then, the antibubble will first sink,and then stop at the place which matches its density. There it canbe peacefully observed.

Such an antibubble will be centimetric. It is shining due to a totalreflection of the light on the film of air (Fig. 2a). The shape is spher-ical (which minimizes the surface area of the interfaces), but an airbubble of the same volume as the air shell would of course have amuch smaller surface area: as for a soap bubble, our object will thusbe only metastable or unstable.You can also observe a slight bumpat the top: air tends to rise and to accumulate at this pole. Interfer-ence fringes indicate variations of the film thickness. All theseobservations show that the film of air gets thinner at the bottom,which is confirmed by the motion of the fringes, and by the factthat the antibubble generally starts bursting close to the South pole.

DrainageThe lifetime of an antibubble is generally several minutes [5].Indeed, it does not suffer the main cause of aging for a classicalsoap bubble, namely, evaporation, but like it, it is subjected todrainage. Air slowly rises along the shell (or in other words, theinner globule slowly sinks in the film of air on which it sits). Thekinetics of drainage should be dictated by a balance between vis-cous friction (in the film) and buoyancy. Denoting as ρ the waterdensity, g the gravity acceleration, η the air viscosity and ε the filmthickness, this balance can be written dimensionally: ηV/ε2 ~ ρg,where V is the mean velocity of the rising air. This velocity is all thesmaller since the film is thin, owing to the boundary condition atthe air/water interface, which should nearly stop the flow at thisinterface (the water viscosity being about 100 times larger thanthe air viscosity): the thinner the film, the larger the proportion ofgas governed by this boundary condition, and thus the slower themotion. This kinetics (often called a Reynolds kinetics) was alsoobserved by Couder, who studied the thinning of an air film placedbetween a bath of viscous oil and a large oil drop deposited on thisbath [4]. If an antibubble bursts when it reaches a thickness εo, thekinetics of thinning will be dominated by the approach to εo. Sincethe flow takes place on the scale R of the globule, we deduce thatthe drainage time should scale as τ ~ R/V(εo) ~ ηR/ρgεo

2.The question is thus to determine εo. For “classical” bubbles, and

if the surfactants are charged, the final film thickness results from a


Vita brevis of antibubblesStéphane Dorbolo 1, Nicolas Vandewalle 1, Etienne Reyssat 2 and David Quéré 2,1 GRASP, Université de Liège • Belgium2 PMMH, UMR 7636 du CNRS, ESPCI, Paris • France

b Fig. 1: Submarine photo showing the generation of antibubblesfrom an impacting jet. The black contour, around each globule,betrays the existence of a film of air.

fea

ture

s

balance between van der Waals forces (which tend to thin the film)and a repulsion of electrostatic origin: the counter-ions comingfrom the surfactant heads occupy a certain zone, which (entropi-cally) resists squeezing. These (meta)stable films of typicalthickness a few tens of nanometers are the so-called black films(observed by Newton, Hooke and Jean Perrin). For antibubbles, thesituation should be quite different (Figure 2b): van der Waals forcesthin the film without anything to stop the thinning process. Hencethe thickness εo should be given by the range of these forces, that is,about 100 nanometers. This gives for the lifetime τ about one hour,at most.

The antibubbles are generally observe to live shorter (less than10 minutes). This quicker aging might be related to the formationof radial channels: instead of having a homogeneous flow of airalong the shell, air seems to be transported from the film to thechannels (thus, over a short distance, which is the inter-channeldistance); then, it quickly rises along the channels (as water doesin gutters, or in Plateau boarders, that is, the channels separatingadjacent films in a foam). The distance L between these channelsis millimetric, which makes τ ~ L/V(εo) about ten times smallerthan when assuming a homogeneous flow, in agreement with theobservations (lifetime of a few minutes instead of one hour).

Death of the antibubbleThe bursting of an antibubble can be captured using a high speedcamera. Figure 3 shows such an event. As mentioned earlier, theexplosion often starts at the South pole where the film is thinner.However, the most remarkable point is the fact that the air filmdisaggregates at several places at the same time. This mode ofexplosion resembles the so-called spinodal dewetting of nanomet-ric liquid films [6]: without any stabilizing forces for the film, holesresult from the amplification of thermal fluctuations, owing to vander Waals forces. Several holes are thus likely to open simultane-ously, with a spatial distribution that integrates the (destabilizing)action of van der Waals forces, and the (stabilizing) effect of surfacetension, which opposes surface fluctuations.

The mode of rupture observed in Figure 3 thus confirms thatthe film thinned down to the van der Waals thickness. In contrastwith bubbles, nothing then stabilizes the globule. You will noticein the same Figure a bulge at the North pole, resulting from thedrainage of air, which accumulated at this place.

ConclusionIn contrast to soap bubbles, antibubbles are globules which areintrinsically unstable, without the electrostatic interaction makingpossible the existence of metastable black films: there is no blackantibubble. Their lifetime thus simply results from the slow rise of

air within the shell. The thinning takes place until the film thick-ness becomes of the order of the range of van der Waals forces,around 100 nm. Then, van der Waals forces (which make theouter water attract the inner water) squeeze the shell, provokingits explosion.

The slowness of the drainage (several minutes) makes theantibubble an interesting object for the encapsulation of chemicalsor colloidal materials, which can thus be transported without mix-ing nor coalescence in microfluidic devices. The content can berecovered by activating the film bursting, owing to a pulse of pres-sure, or by any means favouring the film rupture. The dynamics ofthe rupture would itself deserve a study; unlike bubbles, for whichthe kinetics of the explosion is dictated by the film properties (den-sity or viscosity), the bursting speed should be limited by theproperties of the surrounding liquid (the film of air having a neg-ligible density and viscosity). Note finally that a special case ofantibubble is the one where the film consists of oil [7], making thisfilm much more viscous. In addition, the density contrast betweenthe two fluids is smaller in this case, making this variety of antibub-ble much more resistant to aging.

References[1] E. Littré, Dictionnaire de la langue Française, Hachette (1873).

[2] W. Hughes and A.R. Hughes, Nature 129, 59 (1932) ; C.L. Stong,Scientific American 230, 116 (1974).

[3] Y. Amarouchène, G. Cristobal and H. Kellay, Physical Review Letters87, 206104 (2001).

[4] Y. Couder, E. Fort, C.H. Gautier and A. Boudaoud, Physical ReviewLetters 94, 177801 (2005).

[5] S. Dorbolo, E. Reyssat, N.Vandewalleand D. Quéré, Europhysics Letters 69, 966(2005).

[6] G. Reiter, Science 282, 888 (1998).

[7] K.P. Galvin, S.J. Pratten, G.M. Evansand S. Biggs, Langmuir 22, 52 (2006).


features

b Fig. 2: (a) Photo of an antibubbleclose to the surface of the bath. (b)Transverse cut of the air film: thesurface is coated by surfactantmolecules, whose hydrophobic tailsface each other.

b Fig. 3:Disintegration ofthe film of airsurrounding acentimetricantibubble: thefilm explodes atseveral places atthe same time.

(a) (b)


fea

ture

s

Question : what physical object is currently being investigatedfor its new possibilities in electronic components (FETs,

wiring, memories, optoelectronics, lasers...), nanometric scale sen-sors (gas and fluid flow, temperature…), mechanical reinforcement(composites, textiles…), energy storage (hydrogen, rechargeablebatteries…), near field probes (SNOM, AFM, STM …), electro-mechanical systems (oscillators, motors…), electron sources (flatscreens, xray generators, rf amplifiers…), etc. and etc.? If youanswered carbon nanotubes [1] or nanowires [2] or to be moregeneral (N&Ns), pass to the front of the line. One should add thatnanotubes have become an excellent testing ground for comparingfine experimental measurements to fundamental moleculardynamics and ab initio band-structure studies. This is because ofthe existence of interesting new phenomena at the nanometerscale, the number of atoms in the real system is tractable by avail-able computing power and techniques have been developed tofabricate, manipulate and measure them individually. N&Ns enjoya huge advantage over their cluster sisters in that they can be morereadily connected to leads for thermal and electrical transportphenomena. The result of all this is that a wide cross–section ofphysicists, chemists and biologists has now devoted research pro-gramme to carbon nanotubes (CNTs), and with increasing vigourto nanowires.

This is a field where the links between basic science andapplications are extremely strong and it is simply inconceivable torealise working devices without delving deeply into fundamentalstudies of these systems. Concretizing the possibilities willdepend on understanding and mastering their specific geomet-

rical structure and physical properties such as electrical resistivi-ty, thermal conductivity, optical adsorption and emission,stiffness, surface reactivity, etc. for each application. Currently,independent, specific and often quite elaborate experiments areset up to study each of these properties separately while in factthey are actually strongly correlated, particularly through theimportant and pervasive role of defects. An important advancewould be the development of measurement methods of the dif-ferent properties on the same individual N&N, in the sameexperimental setup that would also allow control of tempera-ture, manipulation of defects, controlled adsorption andoverlayer deposition, etc.After this long introduction, the point ofthis article is that good old “field emission” (FE) [3], which is itselfone of the leading applications areas for nanotubes, can satisfythis demand because it can give simultaneous access to manyN&N properties.

To understand how, consider the classic field emission experi-ment for an N&N in Fig. 1. A large voltage VS is applied betweenthe support on which the N&N cathode is attached and ananode/screen. They can be readily attached to support tips by avariety of methods including gluing, capillarity, rubbing anddirect growth and they need contact at only one end. The supporttips themselves are mounted on tungsten heating loops that allowhigh temperature heat cleaning. The experiments are generallycarried out in ultra high vacuum (UHV - 10-10 Torr) to minimiseadsorption. When a high enough voltage is applied, a current isemitted from the N&N apex where a high electric field F is creat-ed because of the large aspect ratio (length(l)/apex radius(r)).

From simple electrosta-tics F ≅const x (l/r)VS.This field emission cur-rent is due to electronstunnelling through thesurface barrier. Theagreement between itspredicted and measuredcurrent/voltage behav-iour was one of the firstproofs of quantum the-ory back in the late1920’s.

The emitted elec-trons are accelerated bythe electric field againstthe screen/anode giving

Measuring the physical properties of nanostructures and nanowires by field emission

S.T. Purcell*, P. Vincent and C. Journet,Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Lyon 1, CNRS, UMR 5586, Domaine Scientifique de la Doua, F-69622 Villeurbanne cedex • France*[email protected]

b Fig. 1: Schematic ofthe field emissionexperiment used tomeasure the physicalproperties of carbonnanotubes or nanowires.


features

a sort of magnified image of the nanotube apex. This is called FEmicroscopy. Also the electrons can be projected into an energyanalyzer giving rise to FE electron spectroscopy. These are tradi-tionally used to study a tip apex surface – crystal structure,surface diffusion, work function, field enhancement factor anddensity of states near the Fermi energy. Such studies permit thedevelopment of FE cathodes. However, in principle the spectracan be fitted to give the voltage level at the end of the nanotubeEFA (Fermi level) and temperature TA at the tip apex which maybe different that those of the support because of a voltage dropIR and Joule heating along the N&N length [4, 5]. The positionsof the spectra give directly R = (EFS - EFA)/I. The high energyside of the spectra is given by the Fermi function and hence isfitted to give TA.

The physical properties of most tip materials usually come intoplay only when an emitter is pushed to high currents where it suf-fers abrupt breakdown due to runaway phenomena linked toresistive heating and surface diffusion. EFA and TA are not differentfrom the support EFS and TS because the voltage drop IR is toosmall to be detected (<µvolt) and if the tip temperature starts torise the emitter proceeds immediately to breakdown through a cat-astrophic runaway.

The crucial difference for carbon nanotubes and the semi-con-ducting nanowires that we are also measuring is that they remainstable even when the current induces high temperatures. This isbecause of their excellent crystal stability and because the resistiv-ity varies less or even decreases with temperature, in turnrestraining runaway heating effects. Consequently large values ofTA and IR are readily created and measured. Temperatures of up to2000 K [4] (see Fig. 2) and IR = 1.5 Volts have been measured inexperiment for a CNT (Fig. 3).We have more recently measured upto 120 Volt for a SiC nanowire. The high temperatures in CNTsare accompanied by light emission visible by eye due to blackbody radiation whose wavelength dependence was also measuredby optical spectroscopy [5, 6] (see Fig. 4). (For the inverse configu-ration we have recently installed an optical bench for lightabsorption where the field emitted current will vary and henceprobe the optical absorption.)

To extract the physical parameters from the measurements, sim-ulations of the one dimensional heat transport problem have beencarried out to fit the experimental curves which use as inputs theresistivity ρ(T), the thermal conductivity κ(T) and in principle theoptical emissivity e(T) [6]. The main elements of the problem aredepicted in Fig. 1 where Joule heating, thermal transport to thesupport and radiation cooling are taken into account. In Fig. 3 weinclude the rough first results for ρ(T) and κ(T) for our originalmeasurements for CNTs [4, 7], assuming e(T)=1 which is a rea-sonable value for carbon. Better values must await more extensivemeasurements and an absolute calibration of the optical system.However it is the first time that the two parameters could be esti-mated for one nanotube. This can permit a correlation of the meanfree paths of phonons and electrons that depend on structuralquality of the nanotube.

Another property accessible in this same configuration is themechanical stiffness or Young’s Modulus E(T). This is found bysimply applying a sinusoidal voltage to the support or the anodeas depicted in Fig. 1 to excite the natural frequencies of the sameN&N [8]. When correct frequencies are found the N&N vibratesand the emission pattern is enlarged and the current varies. Thefrequencies of these resonances give an excellent measure of theN&N stiffness. Actually many series of higher frequency reso-nances are found by this method (see Fig. 5 for a CNT) and theindividual peaks are characterized by jumps and hysteresis. This isbecause of the non-linear driving of the nanotube in this arrange-ment. An added bonus in this experiment was that we found thatthe electric fields pull so strongly on the CNT that it allows a tun-ing of the resonance frequencies by up to a factor of ten times. Suchelectrical surface force tuning is a direct consequence of first-yearphysics principles and to the authors’ knowledge had not beendemonstrated before. It is unique to N&Ns because it scales with1/r and is almost negligible for wires thicker than about a micron.It is not difficult to imagine that this tuning and the currentvariation during resonance are useful tools in future nano-electro-mechanical systems (NEMS) and in fact have already been put touse in several nano-oscillator devices [9, 10].

Now that one can quantify these various properties, it is inter-esting to study how they vary when an N&N undergoesmodifications. In Fig. 1, we point out that many treatments in the

m Fig. 2: Temperature at the nanotube apex against field emissioncurrent. The high temperatures are induced by Joule heating.

m Fig. 3: Measured total resistance of the nanotube R(TA) againstapex temperature and the simulated thermal conductivity κ(T)against absolute temperature T, necessary for fitting theexperimental curves in Fig. 2 and Fig. 3. ρ(T) is also found in thesimulations and is very close to (πr2/l).R(TA).


fea

ture

s

UHV environment used for FE make it possible to modify theseproperties. One simple example is the variation of the frequenciesof resonance as the nanotube adsorbs gas after a flash heating. Wefound that even for a large multiwall CNT, the variation of reso-nances could detect the adsorption of a hundredth of a monolayerof adsorbates.A second example is that we have recently found thatSiC nanowires cleaned to high temperatures in UHV can have Qfactors as high as 40,000. These two examples emphasize the obvi-ous but often ignored fact that surfaces play a large role in thebehaviour of N&Ns. The UHV environment of FE is ideal forstudying this.

Before concluding, it must be admitted that this methodologyhas certain limitations. The apex must be cleaned to high temper-ature when one wants to avoid measuring adsorption effects andthis often causes the loss of glued samples. Getting down to below20 K is rare in FE studies where many interesting transport phe-nomenon could be explored. Because of the finite size of thespectra, it is difficult to measure voltage drops of less than about 20

meV and hence electrical resistances <20 kOhms. Separate electronmicroscopy is still necessary to understand the structure of theN&N. Experiments specific to each physical parameter probablygive more reliable and precise results. However, the conclusion ofthis article is that the FE has two important advantages. Firstly, it ispossible to have access to σ, κ, e and E for a single nanotube, orother nanowires, in a single experimental setup under the bestUHV conditions and secondly to follow their evolution during anystage of a certain class of controlled modifications. These advan-tages should make it possible to better understand how the physicalparameters are connected in an efficient manner and how theydepend on the structural quality of the N&Ns. This should aid incontrolling their values and to find new phenomena for futureapplications. n

About the AuthorsStephen Purcell, Scientist french CNRS since 1982. Rank –“Directeur de Recherches”. Team leader « Physics of Nanostruc-tures and Field Emission». Member Scientific Council -International GDR Nanotubes. Postdoc, Philips Research, 1989-91.Ph.D. Canada 1989, Ultrathin Magnetic films.Pascal Vincent, Assist Prof U. Lyon1 since Sep. 2003. PostdocThales Research, 2002-3. Doctorate U. Lyon1, 2002. Field emissionnanotubes.Catherine Journet, Assist Prof U. Lyon1 since Sep. 1999. PostdocStuttgart, 1999. Doctorate U. Montpellier, 1998. Growth and Char-acterisation of nanotubes.Current main interests of the team: Nanotubes, nanowires, elec-tron and ion field emission.

References[1] R. Saito, G. Dresselhaus, M.S. Dresselhaus, Physical Properties of Car-

bon Nanotubes, Imperial College Press, London (1998).

[2] Yi Cui, C.M. Lieber, Science 291, 851 (2001).

[3] R. Gomer, Field emission and field ionisation, Harvard UniversityPress, Cambridge (1961).

[4] S.T. Purcell, P.Vincent, C. Journet,Vu Thien Binh, Phys. Rev. Lett. 88,105502 (2002).

[5] S.T. Purcell, P.Vincent, M. Rodriguez, C. Journet, S.Vignoli, D. Guillot and A. Ayari, Chemical VapourDeposition, (in Press).

[6] M. Sveningsson, M. Jonsson, O.A. Nerushev, F.Rohmund, E.E.B. Campbell, Appl. Phys. Lett., 81, 1095(2002).

[7] P.Vincent, S.T. Purcell, C. Journet,Vu Thien Binh,Phys. Rev. B 66, 075406 (2002).

[8] S.T. Purcell, P Vincent, C Journet,Vu Thien Binh,Phys. Rev. Lett. 89, 276103, (2002).

[9] V. Sazonova,Y.Yaish, H. Ustunel, D. Roundy, T. A.Arias, and P.L. McEuen, Nature (London) 431, 284(2004).

[10] D.V. Scheible, C. Weiss, J.P. Kotthaus, R.H. Blick,Phys. Rev. Lett. 93, 186801 (2004).

m Fig. 4: Optical spectrum of a carbon nanotube that heats duringfield emission.

b Fig. 5: Scan of mechanical resonances of ananotube in the field emission configuration. Thecurves are found by measuring the emitted fieldemission current which varies when the nanotubecomes into resonance. The resonances continue toat least to 20 MHz.


museum review

You may have chosen to visit the Cata-lan capital for Gaudi’s architectural

projects and his Sacrada Familia,or for live-ly tours along Las Ramblas. But, if you havenot yet done it, you should include on yourlist a visit to the new science center onTibidabo hill. I knew the previous small sci-ence museum of La Caixa (the bank, whichalso finances the new museum) headed byJorge Wagensberg , a very stimulating sci-entist at the University of Barcelona. Since1991, Jorge has worked on a very ambi-tious project: the new science Museum,CosmoCaixa of la Fundacion “la Caixa”.Built on a spectacular setting of 4 hectaresabove the city of Barcelona, it opened in thefall of 2004 and has welcomed already in itsfirst year over 2 million visitors. The archi-tectural project is beautiful and well fittedto its mission. For example, a gigantic trop-ical tree forms the axis of the inner staircaseextending over 5 stories and looks like atypical Gaudi architectural feature. Variousmeeting rooms are designed to promoteinteractivity. A large part of the exhibits ispresented in a very large open space limit-ed at its back by a gigantic vertical glass wallthrough which you can see a real tropicalsite from above the water as well as under it,with its animal and vegetal manifestations.

The museum includes naturally the typ-ical elements of a science museum withpermanent interactive exhibits as well astemporary ones such as the display onEinstein in 1905. But its originality lies inits declared goal to restore each element asa central feature surrounded by its occur-rence in nature or science (e.g., a periodictiling can be found on a desktop by packinga two dimensional array of inflatablespheres, on the surface of a Benard convec-tion experiment, on a shell of a tortoise, oras a decorative feature in Moorish art or inEscher’s works). The physical aspect andfunction of the given object is then outlined

with its cultural and symbolic meaning.This implies a multicultural approach andJorge Wagensberg likes to describe his pro-ject as a ‘total museum’ going beyond theclassical manual interactivity (often called‘hands on’), to the awakening of curiosity(‘minds on’), and emotion (‘heart on’). Inthis respect, the CosmoCaixa can bethought as a kind of Art museum.

Indeed the presentation of large geologicalplates on a wall is not so different, in its emo-tional value, from an abstract modernpainting. In addition, simple experiments areproposed to explain the processes involved ingeology such as faulting, layering of rocks,etc.. The museum content is so rich andoriginal that I can only mention two exam-ples that I discovered with great pleasure.

The first one is a full exhibition of arche-typal forms such as spheres, spirals,catenoids, angles…, which explains withnice examples taken from the living andnon-living world the specificity and charac-teristics of these forms (e.g.,minimal surfacefor a sphere). Their symbolic and culturalaspects are emphasized and experimentsproposed to demonstrate how to make suchforms (e.g. in soap bubble experiments).

The second example is taphonomy, thescience aiming at reconstructing a past his-tory from its prints on stones.A large roomis devoted to this original topic and shows

how progress in scientific research can beachieved with taphonomy. The visitor canadmire how an ammonite engraved its pathon a rock or how fishes in the process of eat-ing each other left prints of their entangledbackbone (cover picture). Why so? We arealso invited to try to reconstruct the deadlyadventure of a colony of ants suddenly cov-ered by a large drop of amber, which fellfrom a tree some hundreds of years ago – areminder of Pompei in miniature! Thisparticular amber sample has been studiedover more than 10 years by scientists andamateurs at different centres.Detailed mod-els are presented in various publicationswith a clear interdisciplinary approach. Thephysicists in particular have had their wordto say: the photo-elastic study explains howthe drop of amber solidifies; the mechanicsdescribe how the ants’ antennas bent alongthe local flow of the solidifying paste.

The educational and scientific conceptof the CosmoCaixa Museum* is truly orig-inal. Hopefully I have convinced you that itis worth a visit. It fits very well my ownperception of what I would wish to find insuch a place: not so much a load of teach-ing documents and explanations, whichcan be found usually in books or on theweb, but more a way to sharpen theappetite and curiosity for Science and itsapplications. This museum is also a uniqueopportunity to give Science its due placewithin our culture and everyday life. n

Etienne Guyon, Ecole Supérieure de Physique et ChimieIndustrielle de Paris • France

* On 13 May 2006, CosmoCaixa received in Lis-bon, for both its architecture and its content,the accolade of ‘European Museum of the Year’awarded since 1977 by the European MuseumForum of the Council of Europe.

CosmoCaixa, the new and original science museum in Barcelona

. Photo-elastic effect at touching interfaces (before: a; after: b)

(a) (b)


bo

ok

revi

ew

community. It is inspiring to see how suchsuccess was achieved, and how the manypolitical, financial and technical impedi-ments that always turn up when grandprojects are realised, were overcome.

Two of the chapters in Europe’s Quest forthe Universe are of a more sociologicalcontent: one on publications and the otheron researchers and funding of Europeanastronomy. It is shown how the astro-nomers in the various European countriespublish their results, and how this com-pares with other parts of the world. Onealso finds a thoughtful discussion of thereliability and significance of citationindices and impact factors, i.e., the quanti-tative indicators that are often used tojudge the scientific performance of candi-dates for positions and promotions.Among the many data on funding, there isa comparison of spending for spaceresearch between Europe and the US, withthe conclusion that “… even with [forEurope] optimistic estimates, the differ-ence between the US and Europe is a factorof five.” Less depressing and shockingcomparisons show the spending per astro-nomer and the cost per page published inthe refereed astronomical literature acrossEurope.

Woltjer has confidence in Europe andbelieves in the potential of Europeanresearchers. He concludes his book by ask-ing: “… is it too much to dream of the day,when pan-European scientific organisa-tions foster research on the continent,create a scientific center for peacefulresearch second to none and collaborate ona basis of equality with others who havethe same aim?”

Europe’s Quest for the Universe should berequired reading for people involved inEuropean science policy – and perhaps forscience journalists as well. At the sametime, the book is suitable for all astro-nomers, amateur and professional. Theformer will appreciate the clear explana-tion of technical and scientific aspects andthe latter will enjoy learning the insidestory of developments, of which they mayhave had superficial knowledge only. Andit wouldn’t do any harm if administratorswere to carefully study the presentationand lucid discussion of the situation inpublishing and funding. n

Martin Huber, Lab. for Astrophysics, Paul ScherrerInstitut, Villigen • Switzerland

Here is a highly readable account of theimpressive development that has

taken place in European astronomy overthe past decades. Following the affirmationthat “The progress of science depends onthe technological development of itsinstrumentation”, the main part of thebook traces the origins and the develop-ment of the large European facilities on theground and in space that are nowadaysavailable to astronomers and astrophysi-cists. The history of instrumentation isinterwoven with the story of advances inour knowledge of the Universe and thephysical principles, on which today’sobserving tools are based, are introducedwhere appropriate. Everything is explainedin an admirably clear language.

The author reports in detail on the VeryLarge Telescope (VLT), which has beenconstructed, and is now operated by theEuropean Southern Observatory (ESO).This European facility, located at thesuperb, extremely dry site of Cerro Paranalin Chile, is the largest telescope currentlyexisting. Given its site, the VLT and its focalplane instruments have an excellent per-formance not only at ultraviolet and visiblewavelengths, but also in the infrared range.It may be said that the VLT has broughtEurope to the forefront of contemporaryoptical astronomy. As Head of ESO from1975 to 1987,Woltjer directed the elabora-tion of the VLT concept – four 8-mtelescopes that can be optically linked tomake them work as an interferometer. Hefurther initiated the required technologicaldevelopments, and found the ideal site forthis magnificent astronomical resource.Unanimous approval for the VLT wasgiven in 1987 by the eight member states(CH, B, D, DK, F, I, NL and S) that adheredto ESO at the time.After leading the imple-mentation of the VLT from its start to hissuccessors, Woltjer guided, in the early1990s, as chair of the Survey Committee,the planning exercise that led to the long-range scientific programme, ‘Horizons2000’, of the European Space Agency(ESA).

Europe’s Quest for the Universe offers tothe reader an authentic, yet objective report– with all the necessary background – onhow Europe’s large facilities for bothground-based and space astronomy wereconceived, evaluated and selected, on howtheir design was then optimised andbrought into operation,and how these facil-ities are now used by the wide scientific

Lodewijk Woltjer,EDP Sciences ©2006, 322 pages, 35 €,ISBN 2-86883-813-8

Europe’s quest for the universe — ESO and the VLT, ESA and other projects


book review

Olivier Darrigol is a physicist turnedinto a recognized historian of sci-

ences, whose recent works concern theMechanics of continuous media. His bookis quite remarkable. It puts together at itsbest level the evolution of a very activedomain since the 18th century and thescientific description of resolved problemsin fluid mechanics. It uses a modern pre-sentation, for example in the notationsand in referring to recent advances, whileremaining faithful to the approaches ofthe original documents. The subjectsunder scrutiny have known only a limiteddevelopment during the 20th century,which has been marked by the large scien-tific expansion following the works ofMaxwell, Einstein, and others. One maynote that the advances brought about byMaxwell and Kelvin, among others, restedon mechanical approaches. Nevertheless,some of the subjects which are re-discov-ered today stayed asleep for a long time, orat least remained ignored by a majority ofphysicists. Who would have cared in thesixties about the hydrodynamical solitonor about the Kelvin angle of a wake? Atthe same time, who was familiar with thework of Helmholtz on vorticity when sim-ilar problems were properly treated in solidstate physics? I have been introduced tothese subjects through the Josephson effectand the vortices in superfluids!

One example: a surprising effect, shownin the figure, led a young engineer, JohnScott Russell, around 1830, to the discoveryof the solitary wave. At the time, it wasknown that a boat hauled by horses along anarrow canal highly perturbed the surface,forming, behind the stern, energy-con-suming waves, that were also aggressive tothe banks (a). A ship-owner had noticed,upon observing a hauling horse to bolt,that above a given speed (6 to 8 km/h), theresistance to the advancement of the boatdecreased sharply and the rear waves dis-appeared; at this point the boat moved as

transported by a single wave (b). In orderto understand what was going on, Russelldid a set of systematic experiments and theGods were with him: upon a sudden stopof a boat moving in such a “high speed”regime, he observed the formation of alarge amplitude wave propagating alongthe canal without deformation (non-lineareffects compensate the dispersion). Ridinga horse, Russell was able to follow thewave for a mile. He could launch newexperiments to relate size and speed of thewave; such solitary waves exist in variousdomains, including light in optical fibres.

The chapter devoted to such surfacewave phenomena is particularly interest-ing. It starts from fundamental calculationsof French mathematicians such as Laplace,Poisson and Cauchy, then develops,beyond Russell’s experiments (and Bazinin France), into the precise description ofthe theoretical analysis made independent-ly by Boussinesq (20 years before KortewegDeVries) and Rayleigh, then Stokes andThomson: a beautiful association of Physicsand classical Mathematics!

The book is up to date in severaldomains such as non-linear waves, thefluid gliding along a wall, the rotatingflows, the fluid instabilities, etc. It is a greatreference book, which invites us to make adate with Hydrodynamics. n

Etienne Guyon, Ecole Supérieure de Physique et ChimieIndustrielle de Paris • France

Olivier Darrigol,Oxford University Press, 2005,300 pages, 35£

Worlds of flow; a history of Hydrodynamics from the Bernoullis to Prandtl

europhysicsnews · europhysicsnews v o l u m e 3 7 ¥ n u m b e r 4 i n s t i t u t i o n a l s u b...

Documents