The Most-Cited 1985 Physical-Sciences Articles: Some Knots in Superstrings Untied and Quasicrystals Not So Quasi Anymore

Current Cammsnts” EUGENE GARFIELD INSTITUTE FOR SCIENTIFIC lNFORMAT(ON@ 3501 MARKET ST, PHILADELPHIA, PA 19104 The Most-Cited 1985 Physical-Sciences Articles: some Knots in Superstrings Untied and Quasicrystals Not So Quasi Anymore

Number 45 November 9, 1987

Every year since 1979 we have examined It is important to remind readers, as we the papers in the life and physical sciences do in each of these essays, that the studies that were published two years earlier and do not necessarily identifi the most impor- identified the papers most cited during that tanr papers published in the target year. two-year span. The majority of papers pub- Many significant papers may start out slowly lished each year will be cited just a few but eventually achieve Cit@’on Classic@ sta- times—and many never at all. But a rela- tus. Nevertheless, we are convinced that tively small group of papers have an imme- most of these early bloomers will go on to diate, high impact on the research commu- even greater heights. nity. This usually indicates an exciting, new development, the emergence of a new re- Superstrings search area, or a controversial topic. In this essay, we discuss the list of 1985 Table 1 lists the research fronts that have physical-sciences articles that were most at least two of the 1985 most-cited physi- cited in 1985 and 1986—the “hottest” pa- cal-sciences papers as core documents. In pxs published in the physical sciences in both the 1983 and 1984 lists of most-cited 1985. It should be noted that although the physical-sciences papers, a considerable term “physical sciences” is not limited to number of research fronts concerned hlgh- physics, we have chosen to discuss the most- energy physics and materials science.z.s cited 1985 papers for chemistry in a sepa- Both of these areas are still prominent in this rate, future essay, Thus, articles from such year’s study. But immediately apparent upon top chemistry journals as the Journal of fhe examining the titles in Table 1 is the virtual American Chemical Society are not includ- absence of high-energy experimental physics ed in the list. This essay foeuses on physics; and the preponderance of fronts concerned for the modem distinction between the two with high-energy theories of strings and su- interrelated disciplines, see our three-part perstrings. Since research fronts generally essay on chemical-physics and physi- indicate the cutting edge of research in a cal-chemistry journals. 1 given area, they represent a verification of The 104 papers in the Bibliography re- the importance and currency of the papers ceived an average of 54 citations each—9 in this study, in 1985 and 45 in 1986. The 13 least-cited Superstring theory is an attempt to recon- papers received 32 citations-the threshold :ile Einstein’s geometric description of grav- for inclusion. The most-cited paper pub- ity with quantum theory, in which the force lished in 1985 was cited in over 300 articles >f gravity is mediated by particles known and in 1987 has already received 159 cita- Mgravitons (the existence of which is con- tions through August (see the graph in jectured rather than proven). q String Figure 1 for a bimonthly record of how the theorists propose conceiving of elementary 1987 citations have accumulated). particles not as spatial points but as one-di-

328 mensiotud extended objects, or ‘‘strings.”5 pen accidentally, and several other indica- String theory is usually expressed as tors signal that sometling important is go- ‘‘superstringtheory.” Superstrings usual- ing on in this field. For example, 4 of the ly incorporate the constraint of supersym- 10 research fronts in Table 1 concern vari- metry, which relates bosons (particles with ous aspects of string theory-including the quantum spins that can be expressed in two largest fronts, ‘‘Supersymmetry, com- whole integers) to fermions (particles with pactification, supergravity, low-energy su- quantum spins that are expressed in half in- perstring models, and related superstring tegers).6 They also usually incorporate theory” (#86-0706), which has 736 citing more than the four dimensions of length, documents, and ‘‘Twodimensional confor- width, depth, and time; the “extra” dimen- mal invariance and related superstring sions are “rolled up” into inconceivably theory” (#86-0702), which has 487. small spaces.T (p. 150-61) Another sign of the heightened interest in Superstrings can manifest themselves as string theory is that all 5 of the most-cited subatomic particles: the different vibrations papers in the study are core to front of the strings and whether they are “open” #86-0706; it has a total of 38 papers in (like a curve) or “closed” (like a loop) ac- its core— 14 of which appear in the count for the differences between parti- Bibliography. cles.6 They currently comprise the only It should be noted, however, that there are theories mathematically capable of uniting several other large research fronts devoted the force of gravity with electroweak theory to other topics. For example, ‘‘Diflis- (which combines electromagnetism with the sion-limited aggregates and fractal growth” weak force, responsible for the transmuta- (#86-1385) has 486 citing documents; 3 of tion of subatomic particles) and quantum its 55 core papers appear in the Bibliogra- chromodynamics (the description of the phy, including articles by E. Ben-Jacob, strong force that binds quarks permanently University of Michigan, Ann Arbor, and together inside nuclear particles) in a quan- colleagues; Johann Nittmann, Dowell tum model that describes all four forces as Schlumberger Research and Development facets of a single, fundamental phenome- Center, St. Etieme, France, and colleagues; non. g and b-mid A. Turkevich and Harvey Scher, String and superstring theories have been CoWorate Research Center, Standard Oil around for severrd years but, according to Company, Cleveland, Ohio. These papers Jeffrey A. Harvey, Princeton University, concern the dynamics of the interactions be- New Jersey, they had gone into “a sort of tween materials of different densities, such hibernation.”9 The emergence of super- as the flow of a fluid through a denser fluid string theory in this year’s study represents medium. an important new development in the field. Another large research front in Table 1 An indication is the very prominence of the is “Anderson localization, quantum oscilla- term “superstring.” In our study of the 1983 tions, and electron-electron interaction in papers most cited in 1983 and 1984,2 not disordered systems” (#86-0097). This front a single research front or paper contained has 475 papers published on this topic. the words’ ‘string” or’ ‘superstring” in its There are 5 of its 37 core papers in the Bib- title. However, by the following year, in our liography, The core papers were written by study of the 1984 papers most cited in 1984 M. Biittiker, IBM Thomas J. Watson Re- and 1985,s ‘‘superstrings” appeared in the search Center, Yorktown Heights, New title of one research front and in the titles York, and colleagues; Patrick A. Lee, Mas- of two papers. This year, “string” or’ ‘su- sachusetts Institute of Technology, Cam- perstrings” appear in 24 article titles. bridge, and T.V. Ramakrishnan, Banaras This terminology shift can be seen in a mi- Hindu University, Varanasi, India; Lee and crohistory of the field, shown in Figure 2. A. Douglas Stone, IBM Thomas J. Watson Such a shift in terminology does not hap- Research Center (the latter of whom also

329 Table 1: The 1985 and 1986 SCF /SSCF research fronts that include 1985 mea!-cited physical-sciences pspers as core dncumenta. The 1985 research fronts contain at least two papers from tie Bibliography; 1986 research fronts contain at least three. A= number of papers in the Bibliography included in the core of each research fremt. B= total numkr of core dncuments. C =toral number of citing dncuments for the ymr dc.signsted by the prefix in the research-front number.

Name AB c

85-0507 IcosahedmJ order and symmetry properties of quasicrystafs and crystak, 2 22 164 85-1259 Levitation, confinement, and cnnhng of atoms, aerosnls, and particles by laser 2 27 196 radiation pressure 85-2347 Compacrification, supersymmetty, and anomalies in the supemtrin8 theory of 2 10 183 supergravity 864X97 Anderson localization, quantum oscillations, and electron-electron interaction in 5 37 475 disordered systems 86-0523 Structure and stability of icosahedml A1-Mn alloys, Penrose dhrrgs, and other 12 44 345 quasicrystals 86-0527 Ukmahort opticaf pulses and mcde-lncking of various lasers 3 53 325 86-0702 Twodimensionaf confomrat invariance and related superstring themy 5 35 487 86-0706 Supersymmet~, compacdfication, supergmvity, low-energy superstring models, and 14 38 736 related superstring theory 86-1385 Diffision-hmhed aggregates and fmctaf growth 3 55 486 86-1690 Covariant and gauge-inv~iant string field theories 4 20 202 was the sole author of another core paper); Figure 1: The 1987 citations to the paper by Gross D J in l%ys. Rev. La 54:502-5, 1985, at bimonthly and R.A. Webb and colleagues, all of the intervals.” IBM Thomas J. Watson Research Center. These articles concern the properties and 44 conditions that affect electrical conductance in various materials. Nevertheless, this year’s study is dominated by papers concerning string theory. And perhaps the most dramatic indication that something important has occurred in the superstring field is that the five top-cited papers are all related and that three have received an unprecedented number of citations for a tw~year study in the physical sciences. The most-cited paper on this year’s list received 304 citations. But more typical of past studies were the 170 citations collected in two years by the paper announcing the Jan- Mar- May- July- discovery of the W+ and W- particles. 10 Feb April June 1Aug These particles mediate the weak force, and zerland, and Simon van der Meer, also of their discovery constituted experimental CERN, won the prize in 1984 for design- proof of the electroweak theory. Incidental- ing CERN’s Proton-Antiproton Super- ly, Sheldon Glashow, Harvard University, collider and confirming the theory. iz Cambridge, Massachusetts; Steven Wein- The superstring field had been plagued by berg, University of Texas, Austin; and Ab- ;ompeting theories, all of which had math- dus Salam, Imperial College of Science and ematical diftictdties and none of which Technology, University of London, UK, ;eemed more plausible than any of the and the International Centre for Theoretical xl-sers.But as so often happens in science, Physics, Trieste, Italy, shared the 1979 No- me discovery set the stage for the advances bel Prize in physics for developing the the- hat followed. In a breakthrough paper en- OV. ]] Carlo Rubbia of Harvard and tie itled ‘‘Irtfltity cancellations in S0(32) SU- multinational European Organization for xzmtringtheory, ” Michael B. Green, Queen Nuclear Research (CERN), Geneva, Swit- Wwy College, University of London, and

330 symmetry, ‘‘ “suc&zravity.” and “Yang~MiUs theories” to “sucersrrings.” Numbers at the bnttom of each bnx refer to ~e num--rer-ofcikf/citing pap&s for each research fr&rt. -

82.08SS 85-1184 84-0712 YangMills snd Supersyrnmetric _ %W!&?m- _ Urrlftedtheorias of supergravftyand Il%W’””d thaories with 9U- supsymmetry pergravityeffects 85-0698 18/115 52i516 571597 Supargravltyand supasymmetrlc R:’*c%%- 84-11s9 88-070E Vector bosons — Supersymmetry, and production of 2W254 compactificatlon, supergravity, 12+s. k%$;~rgy energ supwstdng mndes,Y and re- 85-2S47 colllders Iated suparstring COmpacttfkation, — thecuy 2/30 supersymmetry W-f%> and anomrdies k P!!!z2J John H. Schwarz, California Institute of This problem was solved, however, less Technology, Pasadena, demonstrated that a than a month later (in February 1985), when particular variant of superstring theory was this study’s most-cited paper, a letter on free of mathematical anomalies, thus ‘‘Heterotic string, ” was published. It was strengthening the theQry’s claim to validi- coauthored by David J. Gross, Harvey, Emil ty. Martinet, and Ryan Rohm, Joseph Henry As noted by Fmnk E. Close, formerly the Laboratories, Princeton—a group also senior principal scientist, Rutherford Apple- known as the Princeton string quartet. 14 ton Laboratory, Oxfordshire, UK, and The theory is called <‘heterotic” because Queen Mary College, now (thanks to the it borrows “desirable features from the brain drain) of the Oak Ridge National Green-Schwarz theory to make a vigorous Laboratory, Temessee, this marks “the fsrst hybrid”4 with another type of string time.. that a unique mathematical structure theory, known as bosonic string.g Heterotic had been imposed on the theories, as if the string shows that it is possible to construct universe itself actually required this struc- a model from Green and Schwarz’s descrip- ture and no other.’ ‘dGreen and Schwarz’s tion that not only disposes of anomalies description also “required a detailed in- naturally but also may account for the terdependency of @ravityand the other three observed physical phenomem of the real timdamental forces of nature], making universe-although, as pointed out by Heinz unification of the forces both a profound and R. PageIs, adjunct professor of physics, The necessary ingredient in superstring Rockefeller University, New York, and ex- theory.”4 Their paper, published in Janu- ecutive director, New York Academy of ary 1985, received 28 citations in that year Sciences, “it is difficult to connect these and 87 in 1986 for a total of 115. Schwarz, string theories with observations. ~owever, by the way, was named to a fellowship by although] string theories have made no ex- the John D. and Catherine T. MacArthur perimental predictions, their structure is Foundation in 1986 and will receive leading physicists into new areas of $280,000 over the next five years. 13 mathematics.’ ‘bGross and colleagues con- However, the superstring theory for clude that heterotic string theory “is perhaps which Green and Schwarz provided such the most promising candidate for a unified compelling mathematical evidence did not field theory. ” fully describe the reality of electric charges In addition to being core papers for re- and other attributes of subatomic Particles.q search front #86-0706, the paper by the

331 Table 2: Tbe number of aurbors per pa~r for the 1985 essarily result if heterotic string theory is in- physicakiences articles most cited in the SCF, deed vahd and perform calculations that sup- 1985-1986. prt the theory. Their paper, published in Number of Number August 1985, collected only 11 citations that Authors of year but 258 in 1986. Witten was the sole per Paper Papers author of the other top-cited paper, entitled 29 1 “Symmetry breadcingpatterns in superstrirtg 19 1 models, ” that hmher explores the implica- 16 1 tions of heterotic string. It was also pub- 14 1 13 2 lished in August 1985. It was cited only 3 11 1 times that year but received 110 more in 8 1 1986. 7 3 6 4 It is worth noting that Witten has consis- 5 7 tently been among the most prolific authors 4 20 in our physical-sciences studies over the last 3 19 few years. Along with Martinet, one of the 2 25 1 18 authors in the Princeton quartet, Witten has more papers in this year’s Bibliogra- Princeton group and the one by Green and phy—four—than any other author. This is Schwarz are also core to the 1985 front on the same number of papers he had in the ‘‘Compactification, supersymmetry, and Bibliography of last year’s essay;s he also anomalies in the superstnng theory of su- had four papers in the Bibliography of the pergravity” (#85-2347), which has eight study of the 1983 articles most cited in 1983 other core papers, Gross and colleagues also and 1984.z Witten received a MacArthur published an article in Nuclear Physics B, fellowship in 1982.13 entitled ‘‘Heterotic string theory,” in which they give a fuller treatment of the theory Dearth of High-Energy Experimental outlined in their letter to Physical Review Physics AfYeetaStudy Statistia firfers; published in July 1985, it was cited only 7 times that year but 192 times in 1986. The virtual absence of high-energy exper- Gross, incidentally, was also the 1986 re- imental physics papers from this year’s list cipient of a five-year MacArthur Founda- had several effects on the statistics we usu- tion fellowship of $285,(KM.IS ally report in these studies. For instance, The features of the heterotic string theory since such papers generally have a large are so fertile and promising that they have number of authors (three of those by opened up many new avenues of research. CERN’S UA1 Collaboration that appeared Some of this work was done in the other two in last year’s study had over 130 authors top-cited papers in the Bibliography, which each), the average number of authors per build on the work by Green and Schwarz paper in the study of the 1983 papersz was and the Princeton quartet. over 11 and for the essay on the 1984 pa- One is entitled “Vacuum configurations perss was almost 9. In this year’s study, for superstrings” and was written by Philip however, the average dropped to just under Candelas, Center for Theoretical Physics, four (see the graph in Figure 3 for a year- University of Texas, and the Institute for by-yearcomparison of the total number of Theoretical Physics, University of Califor- ~uthor bylines from 1983-1985). There are nia, Santa Barbara; Gary T. Horowitz, Uni- 367 unique authors in this year’s study– versity of California, Santa Barbara; An- = Table 2 for a compiete breakdown of the drew Strorninger, institute for Advanced number of authors per paper. Study, Princeton; and Edward Witten, Jo- In addition, in last year’s study,s the seph Henry Laboratories. The authors con- most-cited paper was produced by the UA 1 sider some of the implications that must nec- collaboration at the multinational CERN fa-

332 Figure 3: Year-by-year comparison of the total numb was a key factor influencing the number of of author bylines for the most-cited physical-scienc papers these countries placed on our list. papers from 1983 to 1985. The same two journals that have domirtat- - ilru ed our physical-sciences studies for many years once again published a majority of the papers in this year’s study (Table 4 lists the journals and gives a breakdown of the number of papers each placed in the study). Physical Review Letters published 38 out of 104 papers (36.5 percent), and Physics M- ters B published 18(17.3 percent) for a total of 53.9 percent of rdl the articles in the study.

Quasicrystals Another exciting, emerging area of interest reflected in this year’s study concerns quasicrystals, a new phase of solid matter never seen before. 15At least a dozen arti- 1s%3 l&34 1685 cles and two research fronts concern the Year of Publication structure and properties of quasicrystals, One front is entitled’ ‘Icosahedral order and cility, which topped the ligt of institution, symmetry properties of quasicrystals and affiliations appearing in both the 1983 am crystals” (#85-0507) and has 22 core pa- 1984 Bibliographies.2,s This year, bowel pers; the other is named “Structure and sta- er, the many campuses of the University i bility of icosahedral A1-Mnalloys, Penrose California were first, with 18 paper: tilings, and other quasicrystals” (44M-0523), AT&T’s Bell Laboratories in Murray Hil with 44 core papers (12 of which appear in Holmdel, and Crawford Hill, New Jersq this study). was next with 13 papers. CERN, which ha Icosahedral structures and coordination in 15 paperg in last year’s study, has 7 in th liquids and glasses have long been dis- one. Table 3 lists the national affiliations t cussed. lfI Crystallographer Alan L. the institutions listed by authors in the Bil Mackay, Birkbeck College, University of liography. London, has compiled a 695-item The table shows some other interestim bibliography of this literature. IT Icosahe- features of the national affiliations in th dral alloys were discovered in 1984 by D. year’s study. For example, Ihdia, which w~ Shechtman and I. Blech, Department of absent from our reports from the previot Materials Engineering, Israel Institute of six years, appears in thk year’s Bibliogri Technology, Haifa; D. Gratias, Center for phy with one papeq the same is true of Ne the Study of Chemical Metallurgy, CNRS, Zealand. Also noteworthy is the number f Vitry, France; and J. W, Cahn, Center for countries that appeared in the 1984 stnd~ Materials Science, National Bureau of Stan- but have dropped out of this year’s essa~ dards, Gaithersburg, Maryland, and were the People’s Republic of China, Finku.u reported in a paperlg that appeared in last Greece, Spain, Sweden, and Venezueli year’s physical-sciences hh parade.J They Since many of the authors from these COLU are unique for several reasons. tries in the 1984 stxdys participated in tl A crystal is a solid in which the atoms or large, international collaborations in higl molecules are arranged in a regularly repeat- energy experimental physics, the disappea ing pattern. 19To be more precise, accord- ante of such paps from this year’s repo ing to Mackay, atoms or molecules in a

333 crystal “are repeated by translations in three Table 3: National locatiomsof the institutional affiiatiom non-coplanar directions that generate a listed by autfwrain tfreBibliography, according to totaf ap~ances [column A). B= number of papers three-dimensional lattice. Each lattice point coauthored with researchers affiliated wtth institutions has identical surroundings, and the crystal in other countries. C = mtional locations of insmutions is assumed to have so many repetitions that Ilsted by coauthors.

the presence of a surface makes no ap- Country A B c preciable difference. A lattice can helong to only 1 of 14 different types with various us 78 16 Canada, France, FRG, symmetries; none of these lattices has sym- India, Israel, New Zealand, Switzerland, metries other than two-, three-, four-, and UK six-fold axes. Accordingly, none but these Switzerland 10 1 France, FRG, Italy, US symmetry axes appear in diffraction patterns France 86 The Netherlands, Switzerland, UK, US from crystals. ” lb FRG 73 Switzerland, US One way in which crystals maybe grown UK 14 France, US in the laboratory is through the solidifica- Canada 31 us Japan o tion of a molten metal.20 In metals, crys- Israel 2 us talline structure is typically based on cubic Italy 2 Swnzerland (four-sided) or, at most, hexagonal (six- USSR 0 Denmark 0 sided) symmetry.z 1But Shechtman and col- India 1 us leagues discovered that, when very rapidly The Nerberlands 1 France cooled, certain alloys of aluminum with spe- New Zealand 1 us cific percentages of manganese, iron, or chromium form crystals with diffraction ef- University of Oxford, UK, who in 1974pro- fects that have the till symmetry pattern of posed what he termed a “randomly period- an icosahedronlf%hat is, they have a ic” arrangement of geometrically shaped three-dimensional symmetry that includes tiles.zd Another well-known version of six five-fold symmetry axes.zz Shechtman Penrose’s tiling pattern appeared in an arti- and B1echhave also coauthored a paper that cle by science writer Martin Gardner in appears in this year’s Bibliography. 1977.2S For a true crystal, this icosahedral ar- Mackay states that, in three dimensions, rangement is not merely unusual; it is im- the Penrose tiling is an arrangement of two possible. 18,22Mackay and other crystallog- kinds of rhomohedra-a cube elongated raphers have pointed out that a tendency for along its body diagonally and the same cube atoms to arrange themselves icosahedrally compressed along its diagonal axis. lb during the formation of certain crystals is “Penrose described definite rules for the familiar. However, it is common knowledge construction of a tiling [pattern] of infksite among crystallographers that as the crystal :xtent that was not periodic,” Mackay said. grows, the 20-sided arrangement is aban- “It was regular, having rules, but was not doned.zz a crystal lattice, not having translational Mathematicians and others have neverthe- symmetry. ” 1b Indeed, according to Stein- less been attracted to the problem of calcu- hardt, the arrangement of tiles that Penrose lating the structure of a “forbidden,” ico- ievised is quasipenodic, not “randomly sahedral ‘‘quasicrystal.’ ’22 Among those wiodic” as he described it.zg who did so, Dov Levine and Paul J. Stein- Thus, according to Mackay, this Penrose hardt, University of Pemsylvania, Philadel- iling arrangement has the same diffraction phia, proposed the leading model to explain ~attem as the icosahedral symmetry ob- icosahedral alloys. They also coined the ;erved by Shechtrnan and his colleagues for term ‘‘quasicrystal” and were the first to heir alloy. lb It also proved useful to Levine suggest the model and compute its diffrac- md Steinhardt in performing the theoretical tion pattem.zg This model is based on con- work necessary to properly identify the structions of mathematician Roger Penrose, pasiperiodic translational order that could

334 Table 4: The21 jownsts thatpublishedthepaperslisted in the Levine-Steinhardt paper,zb was coauthored Bibliography.Thenumberrin parenthcsssarethe 198Sinrpsct factorsfor rhejournats.(The 1985 impactfactorequafsthe by P,A. Krdugin, A.Yu. Kitaev, and L.S. numbarof 1985citatioasre@ivrdby the 1983-1984articles Levitov, L.D. Landau Institute of Theoret- in a ioumaldividedby thenumberof articlespublishedby ths jou&l duringthat&re period.)Datawere tsken t%xathe ical Physics, Academy of Sciences of the JCJP. The figuresattherightindkaterhenumberof papers USSR, Moscow; it also appears in this from eachjouraalthatappearsin the list. year’s Bibliography. Numb Even in the paper in which they an- of nounced the discovery of an icosahedral Jourrsat Papers crystal, Shechtmrm and colleagues argued phyS. Rev. btt. (6.91) 313 that crystals “cannot and do not exhibit the Phys. f-at. B (3.92) 18 icosahedral point-group symmetry. ” 1g Phys. Rev. B–Condensed Matter (3.58) 9 f+lc[, Phys, B (5. 18) 6 They immediately investigated the possibili- Astrophys. J. (3.51) 4 ty that the diffraction pattern was due to Phys. Rev. D–Part. Fields (2.65) 4 twinning, a phenomenon in which wveral J. Chem. Phys. (3.10) 3 Nature (12.86) 3 different crystals grow together but appear Phys. Rep, -Rev. Sect. Phys. Len. 3 to be a single crystaL22 (6.24) In fact, just such an explanation for the Rev. Mod, Phys, (20.74) 3 Appl. Phys. L&t.( 3.59) 2 occurrence of qtrasicrystals was proposed by J. Appl. Phys. (1.92) 2 Nobel laureate Linus Pauling, Linus Paul- J. Phys. .%c. Jpn. (1.63) 1 ing Institute of Science and Medicine, Palo 1 J. Vat. Sci. Technol. A(2.49) Alto, California, whose paper appears in the Met. Trsns. A—Phys. Met Mater. Sc. 1 (1.27) Bibliography. However, ti.u-therstudy with Nucl. Phys, A(2.49) 1 electron microscopes showed that this was Optics Letters (2.57) 1 not the case—that, although quasicrystals Phil. Msrg. B(2.94) I *Pisma Zh. Eksp. Teor. Fiz. (1.51) 1 could not be true crystals (hence the name), Phys. Rev. A–Gen. Phys. (2.35) 1 they nevertheless exhibited a highly orga- Annu. Rev. Astron. Astr. (9.84) 1 Nzed structure and each one grew outward *translated in JETP Lctt.-Engl. Tr. from a single center, like an ordinary crys- (1.51) tal.zz Quasicrystals, in fact, have a regular, crystalline formation along some axes of ro- be extended to explain icosahedral and other tation but lack the periodic arrangement of symmetries.zs (In case you wondered, the atoms that tme crystals have in all direc- original 1974 Penrose paper has been cited tions. only about 80 times since its publication.) Mhough Levine and Steinhardt published Astrophysics their paper detailing thk diffraction pattern Several interesting papers in astrophysics at about the same time that Shechtman and appear on this year’s list. Two concern the colleagues announced their discovery, the celestial objeet known as Cygnus X-3, an two knew nothing of the work of the object in the Cygnus constellation that is an Shechtman group .26 Nevertheless the intense, periodic source of X rays. Cygnus Levine-Steinhardt diffraction pattern was X-3 is thought to be a binary system in virtually identical to that of the “crystal” which one partner is a massive neutron star that Shechtman’s group had grown.zz (a star composed of degenerate matter in Levine and Steinlmrdt’s paperzb was in the which the electrons have been crushed grav- Bibliography of last year’s study,s and the itationally into the nuclei) and the other is two were among a group of six authors who a relatively normal companion. 27The sys- wrote a paper appearing in this year’s tem generates a shower of X rays so ener- Bibliography. A similar mathematical getic that they are more properly known as discussion of the properties of icosahedral gamma rays; indeed, Cygnus X-3 is the symmetry, but one that took note of both the most powerful known source of such radia- Shechtman discovery lg and the 1984 tion in the galaxy.

335 However, even more energetic radiation verse, theoracians have made various sug- may be pouring out of the Cygnus X-3 sys- gestions concerning gas and dust. But for tem, and in huge quantities. M.L. Marshak a number of reasons, astronomers have mkxl and colleagues, University of Mimesota, out the possibilities that the matter might be Mimeapolis, and the Argonne National composed of such ordinary forms of mat- Laboratory, Illinois, reported that high-en- ter. In fact, the idea that cold dark matter ergy particles, the nature of which is might be made of enormous quantities of ex- unknown but which seem to be responsible otic quantum particles-such as neutrinos, for the production of muons at the surface gravitinos, photinos, or axions—has been of the earth, are being generated by Cyg- gaining acceptance in remnt years, and the nus X-3. A group from various locations calculations presented by Marc Davis, In- throughout Italy and Switzerland, headed by stitute for Theoretical Physics, and col- G. Battistoni, National Laboratory, National leagues support this conclusion. Institute of Nuclear Physics, Frascati, Ita- ly, independently confirmed the Marshak The Earth’s Atmosphere group’s observations. If the Marshak One of the controversial topics that ap- group’s evidence (that Cygnus X-3 is emit- peared in the study of the 1984 papersq dis- ting radiation of a type not producd in the cussed the effects of massive injections of solar system) is established conclusively, it smoke into the atmosphere after a global may have profound implications for theo- thermonuclear war.zg Another paper that reticians striving toward a grand unified concerns a controversy over the effects hu- theory. man activity may have on the atmosphere Another paper in astrophysics concerns also appears in this year’s list—observations cold dark matter, which is thought to make of the ozone layer over Antarctica by J. C. up the bulk of matter in the universe. Cold Farman, B.G. Gardiner, and J.D. Shankht, dark matter is material that has mass but that British Antarctic Survey, Natural Environ- is invisible at virtually all wavelengths of the ment Research Council, Cambridge, UK. spectrum, One of the main reasons that the- Ozone, a relatively rare form of oxygen oreticians have been led to postulate the ex- (03 instead of 02), is a natural component istence of such peculiar matter is that “the of the upper atmosphere and helps protect gravitational dynamics of galaxies and life on the earth’s surface by absorbing the clusters of galaxies seem to be inconsistent sun’s ultraviolet radiation. 30 unless there is additional mass present However, ozone is broken down by nat- beyond that seen, ” according to Harvey. 9 ural chemicals (such as volcanic chlorine) He notes that support is lent to this idea by and pollutants (such as the chlorofluorocar- the inflationary model of the universe.zj bons found in refrigerants and aerosol pro- This model predicts that the universe has a pellants). In recent years, concern has grown certain total mass density-a value that that the vital ozone layer is being depleted would require a great deal more mass than or even destroyed by such chemicals. A pro- has yet been observed. Indeed, the mass of ~onged reduction in atmospheric ozone all the obse~able stars is not enough to would permit more and more ultraviolet ra- generate the gravitational force necessary to diation to reach the earth and might result hold grdaxies in their observed shapes; in an increase in the incidence of certain similarly, the gravity created by the mass forms of cancer and conditions caused by of galaxies themselves is not great enough ~enetic damage. The mechanics of ozone to result in the observed distribution of Formationand circulation in the atmosphere galaxies in large ‘‘chssters” and’ ‘superchrs- we poorly understood, making interpreta- ters” throughout the universe.zg tion of the British Antarctic Survey team’s To account for the “missing mass, ” as :esults problematic; but the team’s data do well as the observed structure of galaxies ;how a sharp drop fi-om October 1980 and their distribution throughout the uni- hrough March 1984—’‘a feature entirely

336 lacking in the 1957-1973 data set, ” accord- for even indirect experimental confirmation ing to the authors. We plan to dkcuss earth’s of the tenets of superstring theory, but the ozone layer and its possible depletion in a study of quasicrystals may have immediate future essay. implications in the field of materials technology. As usual, only time will tell which Pn36pecta for Future Studies of these fields will continue at a high rate In speculating about what highly cited pa- of activity over the next few years and which pers may grow out of those appearing in this will be subsumed by new, as-yet-un- essay, we must take into account that some dreamed-of fields. fields will probably be able to take advan- ***** tage of the advances in this year’s group of hot papers more quicldy than others. For ex- My thanks to Stephen A. Bortduce and ample, we may have to await the comple- Eric lhurschwell for their help in the prep- tion of the Superconducting Super Collider aration of this essay. o,Me71s1

REFERENCES 1. Gstrfleld E. Journal citation studies. 46. PhysicaJ chemistry and chemical physics journals. Parts I-3, Current Crrrrfents(1):3-10, 6 January 1986; (2):3-10, 13 January 1986; (3):3-12, 20 January 1986. 2. ------The 1983 articles most cited in 1983 and 1984.2, Physical sciences, Essays of an infarmztion scientist: ghom+ridng and other essays. Phdadelphla: 1S1 Press, 1986. Vol. 8. p. 480-%. 3. ------The most-cited 1984 physical-sciences articles-high-energy physics dominates. Current Conterrrs(473:3-17, 24 November 1986. 4. Close F E. Superstrirrgs. (Calhoun D, cd,) 1988 yearbook of science and the future, Chicago, JL: Encyclopedia Britannica, 1987. p, 44-57. 5, Trigg G L, Brown S, TerwiUfger R & Wells G, Personal communication. 15 September 1987. 6. Pstgels H R. PersonaJ cmrrrrmnicstion. 29 September 1987, 7. Davka P. Super@ce. New York: Simon & Schuster, 19S4. 255 p. 8. Wehrherg S. Particies, fields, and now strings. (de Boer J, Dal E & Ulfbeck O, eds.) lle lesson of quarsoorr lAeary. New York Elsevier Science, 19S6. p. 227-39. 9. Hrrcvey J A. Personal conrnnmication. 7 October 1987. 10. Arniaarr G et af. (UAl CoUaharattarr). ExperirrrentaJahaerwation of isolated large transverse energy electrons with asacciatcd missing energy at W= 540 GeV. Phys. Left. B 122:103-16, 1983. 11. Garfteld E. Are the 1979 prizewinners of Nabel clam? Essays af an information scientist. Philadelphia: 1S1 press, 1981. Vol. 4. p. 609-17. 12. ------The 1984 Nobel Prize in physics gues to Carlo Rubbh and Simon van der Meer; R. Bruce Merrifield is awarded the cfwnistry prize. J6id., 1986. Vol. 8. p. 432-43. 13. Cowen R. Taking a measure of MacArthur Prize. THE SCIENTIST 13 July 1987. p. 4; 28. 14. Garfield E. The crime of pun-ishment. Current Conrerus (27):3-7, 6 Jrdy 1987. 15. Fraaier K. The year in science: sn overview. (Calhmrn D, ed. ) 1984 yearfwok of science and the future. Chicago, IL: Encyclopedia Britannica, 1987. p. 303-11. 16. Mackay A L. Personai cormmrnicarion. 14 September 1987. 17. ------A bibliography of quasicrystals. Int. J. Rapid .%lid$?caticm 2(4): S1-41, 1987. 18. Shechtman D, Bleeh I, Gratirw D & Calm J W. Metallic phaae with long-range orientational order and no translational symmetry. Phys. Rev. f-a. 53:1951-3, 1984. 19. Hobbs H H. Crystal, (Parker S P, cd.) McGraw-Hill enc@@dia of physics. New York: McGraw-Hill, 1983. p. 192. 20. Fowler W B. Crystal defects. (Parker S P, cd.) McGraw-ffi/l encyclopedia of physics. New York: McGraw-Hiil, 1983, p. 195-200. 21. Dekeyaer W C. Crystal structure. (Parker S P, cd.) McGraw-Hi/l errcycbpedia of physics. New York McGrrrw-Hill, 1983. p, 205-12. 22. Schwam.acfdld B M. Forbidden fivefold symmehy mrryindicate quasicrystal phase. Phys. T&y 38(2): 17-9, 1985. 23. Steinhrsrdt P J. Personal communication. 14 September 1987. 24. Penrose R. The role of aessherics in pure and applied mathematicrd research. Bull. he?. Math. ~pp[. 10266-7), 1974. 25. Gardner M. Mathematical games. Sci. Amer. 236:110-21, 1977. 26, Levine D & Steirrhacdt P J. Quaaicrystals: a new class of ordered structures. Phys. Rev, Lat. 53:2477-80, 1984. 27. Maddox J. What happens on Cygnus X-3? Akzure 322:591, 1986. 28. Pagela H R. Perfecf symrrrerry.New York: Bantam, 1986. p. 122-5. 29. Covey C, Schneider S H & ThompaanS L. Global atmospheric effects of massive smoke injections from nuclear war: results from general circulation mndel simulations. Nature 308:21-5, 1984. 30. Kerr R A. Has stratospheric ozone started to disappear? Science 237(481 1):131-2, 1987.

337 Most-Cited 1985 Physical-Sciences Articles

BiiJfiographw The 1985 physicat-sciemcs articles most cited m tfw SCF, 1985-1986. A&lea are listed in alphabetic order by first author. Numbers fofiowing the bibliographic entry indicate the 1985 and 1986 SCIL$SCW rescarch- fmnt specialties for which these are core papers. A= number of 1985 citations. B =number of 1986 citations. C =total number of 1985-1986 citations.

ABC

74047 Ahfrichs R, Wharf P & Etsrhstrdt C. The coupled pair functional (CPF). A size consistent modification of the CI(SD) baaed on an energy functional. J. Chem. Phys. 82:890-8, 1985. 86-0333 10 22 32 Bachelet G B & Cbriatenaen N E. Relativistic and core-relaxation effwrs on the energy bands of gallium arsenide and germanium. Pfsys, Rev. B–Condensed Matfer 31:879-87, 1985. 28 66 94 Bak P, Phenomenological theory of icosahedraf incommensurate (’ ‘quasipsricaiic”) order in Mn-A1 alloys. Phys. Rev. Mr. 54:1517-9, 1985.85-0507, 86-0523 2 32 34 Bafarrtefdn A B, Buttcher C, Strayer M R & Lee S J. Production of new particles in heavy-ion collisions, Phys. Rev. La. 55:461-1, 1985.86-1214 14 % 110 Barrcel P A, Heiney P A, Stephena P W, GobJnrrsrsA I & Horn P M. Structure of rapidly quenched A1-Mn. Phys. Rev. l-a. 54:2422-5, 1985, 85-0507, 86-0523 7 29 36 Bando M, Kugo M, Ueham S, Yamawakf K & Yemagida T. Is the Q meson a dynamical gauge boamr of hidden local symmetry? Phys. RCV. Lat. 54:1215-8, 1985.86-0249 16 16 32 Barger V, Hagiwara K, Keung W-Y & Wuodaisk J. Testing supersymmetry interpretations of anomalous missing-% events observed at the CERN PP colfider. Phys. REW.D—Par?. Fields 31:528-38, 1985, 16 24 40 Batey J, Wright S L & DiMaria D J. Energy band-gap diaeontinuities in GaAs: (Al,Ga)As heterojunctions. J. AppL Phys. 57:484-7, 1985.86-0923 7 29 36 Battiatord G, Bellutti E, Bloke C, Bnlogsm G, Campana P, Caatagnofi C, Caateffirm A, ChiareUa V, Ciocio A, Cmedy D, D’Ettorre-PfazaofiB, FiorirdE, GakottiP, Iaruccl E, Liguorf C, MarrsmcctriG, Murtaa G, Negri P, Nkoletti G, Pfccfsi P, Price M, PuUia A, Ragazzi S, Rollier M, Saavedra O, .%tta L, Serri P, Versretto S & Zmsotti L. Obsewation of a time modulated muon flux in the dkction of Cygnus X-3. Phys. Lzrr. B 155:465-7, 1985.86-1054 0 41 41 Benderaky L. Quasic~stat with one-dimensional translational symmetry and a tenfold rotation axis. Phys. Rev. L@. 55:1461-3, 1985. 86-0523 3 30 33 Ben-Jacob E, Gudhey R, Gnldenfeld N D, Koplfk J, LArre H, Mueller T & Sander L M. Experimental demonstration of the role of aniaotropy in interracial pattern formation. Phys. Rev. Lzrf. 55:1315-8, 1985.86-1385 7 32 39 Berzsteia R H, Bock G J, Carlarrrith D, Cotspaf D, Cremin J W, GoUfn G D, Kefirsg W, NiaMkawa K, Nnrton H W M, Wimsteks B, Peyaud B, Turlay R & Zylheratejn A. Measurement of c’/c in the neutral kaon system. Phys. Rev. hr. 54:16314, 1985. 86-0318 15 34 49 Bhatt R N & Yosmg A P. Search for a transition in the three-dimensional *J lsing spin- glass. Phys. Rev. L.ett. 54;924-7, 1985.86-0032 6 30 36 Black J K, B1att S R, Campbetl M K, Kssaha H, Mamselli M, Schmidt M P, Sclswarz C B, Adair R K, Larsen R C, Leipuner L B & Mnrae W M. Measurement of the CP- nonconservation parameter //6. Phys. Rev. Lest. 54:1628-30, 1985. 86-0318 5 34 39 Bluumfield L A, Freeman R R & Brown W L. Photofragmentation of mass-resolved Si+2.,2 clusters. Phys. Rev. La. 54:2246-9, 1985.86-2748 6 36 42 Brrmdenherger R H. Quantum field theory methuds and inflationary universe mndek. Rev. Mod. Phys. 57:1-60.86-0054 2 56 58 Breit J D, Ovrut B A & Segre G C. E6 symmetry breaking in the superstring theory. F’hys. Len. B 158:33-9, 1985.86-0706 10 22 32 Broido D A & Sham L J. Effective masses of holes at GaAs-AIGaAs heterojunctions. Phys. Rev. B—Condensed hfarter 31:888-92, 1985, 85-2598, 86-3290 83240 Buttiker M, hrsry Y, Larrdmser R & Pinhaa S. Generalized many-chamel conductance formuia with application to small rings. Phys. Rev. B–Coadensed Matwr 31:6207-15, 1985. 86-0is97 0 55 55 Calfan C G, Friedasr D, Martinet E J & Perry M J. Strings in background fields. Nucf. Phys. B 262:593-609, 1985.86-0702 11 258 269 Candelaa P, Horowitz G T, Strominger A & Wkten E. Vacuum configurations for supcrstrings. NUCLPhys. B 258:46-74, 1985. 86-07C6 6 39 45 Cecotti S, Derendfnger J-P, Ferrara S, Girardeflo L & Roncadelti M. properties of Ee breaking and superstring theory Phys. I.efI. B 156:318-26, 1985. g6-0706

338 ABC Bibliographic Data

13 22 35 Close F E, Jaffe R L, Roberts R G & ROSSG G. Chsnge of confinement scale in nuclei: predictions for structure hmctions confront elcctroproduction data. Phys. Rev. D—Parr. Fidd.r 3I:1OO4-I3, 1985.86-0107 0 32 32 Cohen E, Elm J, Enqvist K & Nanopmh D V. Experkncntsl predictions from the supcr$tring. Phys. Lat. B 165:76-82, 1985. 86-0706 2 31 33 Cohen E, Elf&sJ, Enqvtst K & Nartopouhrs D V. Scales in superstrin8 models. Phys. Mr. B 161:85-90, 1985. 5 45 50 Cowan T, Bm!ke H, Begenrmm M, Bethge K, Bokemeyer H, Fofger H, Greenberg J S, Grekt H, Grupps A, Kfdo Y, Kiuver M, Schwafrn D, Schweppe J, StieldnsK E, Trrmtrnwrrt N & Vincent P, Arrmmdous positron peaks ffom supercritica.1collision systems. Phys. Rev. L@. 54:176 I-4, 1985. 86-[214 6 26 32 Dai H L, Korpa C L, Kinsey J L & Neld R W. Roration-inductd vibrational rnixin8 in ,@,41 formaldehyde: non-negligible dynamical conwquences of rorstion. J. Chem. Phys, 82:1688-701, 1985.86-4218 12 47 59 Davis M, Efstathiou G, Frenk C S & white S D M. The evolution of lerge-wsie structure in a universe dominated by cold dark mstter. Artrophys. f. 292:371-94, 1985, 86-0054 18 18 36 Dawsori S, Ek?hten E & Qrrigg C, Search for suparsymmetric particle-s in badron-hedron coifisions. Phys. Rev, D-Parr. Fields 31:1581-637, 1985, 7 27 34 Derendhcger J P, Ibauez L E & NOles H P. On Orelow energy d=4, N= 1 super8rsvity theory extracted from the d= 10, N= 1 superstrin8. Phys. La. B 155:65-70, 1985. 10 56 66 Dine M, Rohm R, Seiberg N & Witten E. Gluimr condensation in supcrstring mrxiels. Phys. fin. B 15655-60, 1985.86-0706 1 61 62 Dine M, Kaplunovsky V, Mmrgrmo M, Nappi C & Seiberg N. Superstrin8 model building. Nucl. Phys. B 259:549-71, 1985, 86-0706 9 83 92 Duneau M & Katz A. Qrmsiperiodic patterns, P/rys. Rev. lat. 54:2688-91, 1985.86-0523 1 37 38 Eckrnmm J-P & Ruelle D. Ergodc theory of chaos and strange attractors. Rev. Mod. Phys. 57:617-56, 1985. 3 62 65 Elaer V. Indexing problems in quasicrystai diffraction. Phys. Rev. B 32:4892-8, 1985. 86-0523 0 47 47 Efeer V & Herdey C L. Crystal and quasicrystsl strucmres in A1-Mn-Si alloys. Phys. Rev. .%-n. 55:2883-6, 1985.86-0523 9 26 35 Ertmer W, Biatt R, Hall J L & Zhu M. Laser manipulation of atomic beam vehxities: demonstration of stoppsd atoms and velocity reverssl. Phys. Rev. Z.eW.54996-9, 1985. 85-1259, 86-1250 0 54 54 Farrumr J C, Gardiner B G & Shmridfn J D. Large losses of total ozone in Antarctica reveal seasonal CIOt/NOX interaction. Nature 315:207-10, 1985. 86-1604 14 31 45 Ftsber D S. Siidkrg chargedensity waves as a dynamic critical phenomenon. Phys. Rev. B—Corrderwed Matter 31:1396-427. 19g5. 86-1744 23840 Fradkin E S & Tseytfin A A. Effective field theory from quantized strings. Phys. Lett. B 158:316-22, 1985.86-0702 21 42 63 Fremrd P G O. Supcrstrings from 26 dmensions. Phys. ht. B 15I:387-90, 1985.86-0706 10 42 52 Frfedarr D, Qiu Z & Sherrker S. Suparconforrnsl invariance in two dimensions and the tricriticat Ising model. Phys, Lztt. B 151:37-43, 1985.86-0702 0 38 38 Frietfan D, Shenker S & Martinet E. Covariant qurmtization of superstrings. Phys. hft. B lt43:55-61 , 1985.86-1690 12 32 44 Glrvfn S M, MacDormfd A H & PhWsmmr P M. Collective-excitation gap in the fractional quantum Hall effect. Phys. Rev. b% 54:581-3, 1985.86-0922 5 28 33 Goddard P & Ofive D. Kac-Mnudy sigebras, conforrnal symmetry and criticsl exponents. iiUC[. Phys. B 257:226-52, 1985.864702 2 35 37 Godfrey S & Isgrrr N. Mesons in a relativir.ed quark model with chromnrfynamics. Phys. Rev. D—Part. Fields 32:189-231.1985. 3 35 38 Gott J R. Gravitational Iensing effscta of vacuum strings: exact solutions. Astmphys. J. 288:422-7, 1985.86-1182 28 87 115 Green M B & Schwora J H. hrfinhy cancellations in S0(32) superatring theory. Phys. La B 151:21-5, 1985. 8S-2347, 86-0706 7 192 199 Gross D J, Harvey J A, Martinet E & Rohm R. Heterotic string theory. Nucf. Phy$. B 256:253-84, 1985.86-0706 65 239 304 Gross D J, Harvey J A, Mrrrtinee E & Rofrrn R. Heterotic string. Phys. Rev. Lx. 54:502-5, 1985.85-2347, 86-0706 7 47 54 Grrmer G & Zetti A. Charge density wave conduction a novel collective transport phenomenon in soiids. Phys. Rep. –Rev. Sect. Phys L-m. 119:1 i7-232, 1985.86- i744 2 52 54 Guyat P & AudIer M. A quasicrystsl structure model for A1-Mn. Phil. Msg. B 52: L15-9, 1985.86-0523 32 66 98 Haber H E & Kone G L. The search for supersyrnmetry: probing physics beyond the starr- dsrd model. Phys. Rep. –Rev. Sect. Phys Letr. 1i7:75-263, 1985.86-0706

339 ABC Biblingrapbic Data

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