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Author: PETER J. SMITH Department of Earth Sciences Open University Milton Keynes, U.K. The Cleopatra structure on Venus, 100 kilometers in diameter, has the morphology of an impact crater but the distinctly different depth-diameter ratio of a volcanic crater. It is not yet possible to decide whether it is a very strange impact crater or a very strange volcanic crater. A.T. Basilevsky, B.A. Ivanov, "Cleopatra crater on Venus: Venera 15/16 data and impact/volcanic origin controversy," Geophysical Research Letters, 17 Based on the mapping of radar images and the analysis of geologic units and topography, the Freyja Montes deformation zone of Venus has been interpreted as a site of large-scale crustal convergence and imbrication (owing to the underthrusting of the North Polar Plains beneath Ishtar Terra) that have resulted in crustal thickening and uplift. Moreover, these processes appear to be continuing today. The implication is that large-scale tectonic activity was, and is, a feature of Venus' crust. J.W. Head, "Formation of mountain belts on Venus: evidence for large-scale convergence, underthrusting, and crustal imbrication in Freyja Montes, Ishtar Terra," Geology, 18, 99-102, February 1990. (Brown University, Providence, R.I.) Buried carbonate reefs are important hydrocarbon reservoirs. But which came first, the hydrocarbons or the reefs? A case has been made for the hydrocarbons. Nonphotosynthetic bacteria and other microorganisms colonize hydrocarbon seepages on the seabed. The skeletal remains of these organisms combine with precipitated minerals to form reefs, which then absorb hydrocarbons. In short, hydrocarbon-bearing reefs are initiated by the very fluids they contain. M. Hovland, "Do carbonate reefs form due to fluid seepage?" Terra Nova, 2, 8-18, 1990. (Statoil, Stavanger, Norway) The ground-surface adjustments that have occurred in the vicinity of Kilauea Volcano, Hawaii, since the magnitude 7.2 earthquake of 1975 moved the frequently active volcano's south flank seaward. These adjustments, however, have been much more widespread than the more familiar movements associated with the inflation and deflation of the summit magma chamber. The implication is that the Kilauea's plumbing system is much deeper (at least 9 kilometers) and more extensive than hitherto supposed. P.T. Delaney, R.S. Fiske, A. Miklius, A.T. Okamura, M.K. Sako, "Deep magma body beneath the summit and rift zones of Kilauea Volcano, Hawaii," Science, 247, 1311-16, 16 March 1990. (U.S. Geological Survey, Hawaii; Smithsonian Institution, Washington, D.C.) The 800-kilometer section of the Mid-Atlantic Ridge between the Atlantis (30øN) and Kane (24øN) transform faults is not continuous. Instead it comprises 16 distinct spreading segments offset by nontransform discontinuities. The spreading segments vary in length from 20 to 85 kilometers (with an average of 53 kilometers); the offsets range from 0 to 30 kilometers. J.-C. Semp‚r‚, G.M. Purdy, H. Schouten, "Segmentation of the Mid-Atlantic Ridge between 24øN and 30ø40' N," Nature, 344, 427-31, 29 March 1990. (University of Washington, Seattle; Woods Hole Oceanographic Institution, Mass.) The 20-year-old hypothesis that geomagnetic reversals are caused by impact events is unlikely to be valid. A detailed re-examination of one of the supposed coincidences of reversal and impact (as represented by microtektite falls) shows that the two events were not actually coincident, and the data supporting a second supposed coincidence are suspect. The one remaining, adequately documented coincidence is not sufficient to establish a general cause-and-effect relationship. D.A. Schneider, D.V. Kent, "Ivory Coast microtektites and geomagnetic reversals," Geophysical Research Letters, 17, 163-6, February 1990. (Columbia University, New York) Author: MARYE ANNE FOX Department of Chemistry University of Texas Austin Electronic topography of surfaces and adsorbed layers can be related to the chemistry that occurs there. Three examples illustrate the relationship between local electronic structure and reactivity: the direct imaging of chemical bonds on Si(100); site selectivity in the reaction of ammonia on Si(111); and the effect of surface electronic structure, surface reconstruction, and doping in the interaction of boron with Si(111). P. Avouris, "Atom-resolved surface chemistry using the scanning tunneling microscope," Journal of Physical Chemistry, 94, 2246-56, 22 March 1990. (IBM Watson Research Center, Yorktown Heights, N.Y.) Monolayers provide a method for describing interfacial behavior. Permeability and defects attached via thiol linkages to gold can be characterized by electron transfer to acceptors in solution and by capacitance measurements. C.E.D. Chidsey, D.N. Loiacono, "Chemical functionality in self-assembled monolayers: structural and electrochemical properties," Langmuir, 6, 682-91, March 1990. (AT&T Bell Laboratories, Murray Hill, N.J.) Supramolecular chemistry requires the availability of hosts with similar chemical structures but different spatial loci for potential guests. The synthesis of two m-terphenyl-based cyclo- phanes is described. T.K. Vinod, H. Hart, "Synthesis of two noninterconvertible conformers of a single host. Self-filled and vaulted cappedo- phanes," Journal of the American Chemical Society, 112, 3250-2, 11 April 1990. (Michigan State University, East Lansing Olefin metathesis remains an important reaction in petroleum processing, and molybdenum, tungsten, and rhenium have long been recognized as the most active metals in this catalytic conversion. A well-behaved rhenium alkylidene complex with proven metathesis activity is described. R. Toreki, R.R. Schrock, "A well-defined rhenium(VII) olefin metathesis catalyst," Journal of the American Chemical Society, 112, 2448-9, 11 April 1990. (Massachusetts Institute of Technology, Cambridge) Acoustic cavitation causes high-energy, localized hot spots with temperatures of 5,000øC, pressures of 500 atmospheres, and lifetimes of a few microseconds. The resulting shock waves induce high-velocity collisions that cause special reactivity. K.S. Suslick, "Sonochemistry," Science, 247, 1439-45, 23 March 1990. (University of Illinois, Urbana) Advances in electrochemical instrumentation, particularly ultramicroelectrodes, make possible the characterization of electrogenerated transients of lifetimes as short as 20 nanoseconds. R.M. Wightman, D.O. Wipf, "High-speed cyclic voltammetry," Accounts of Chemical Research, 23, 64-70, March 1990. (University of North Carolina, Chapel Hill) Author: FRANK A. WILCZEK School of Natural Sciences Institute for Advanced Study Princeton, N.J. Recently, some impressive images have been taken using coherent beams of electrons. Since the electrons respond sensitively to magnetic fields, and their de Broglie waves have wavelengths under the experimenter's control, electron holograms may become a useful and versatile tool in probing the structure of matter on atomic scales. Some pioneering but already impressive demonstrations of this technique are reviewed by its leading practitioner. A. Tonomura, "Electron holography: a new view of the microscopic," Physics Today, 43, 22-9, April 1990. (Hitachi Ltd. and Research Development Corp. of Japan, Saitama) The heavy fermion superconductors were somewhat eclipsed by the discovery of high-temperature copper oxide superconductors. But as they remain poorly understood, attention is being returned to them. It is becoming increasingly clear that their superconductivity is of an "exotic" sort. For example, whereas conventional superconductivity is generally spoiled by magnetic ordering, at least some heavy fermion superconductors seem to thrive on it. R.N. Kleiman, D.J. Bishop, H.R. Ott, Z. Fisk, J.L. Smith, "Observation of magnetic order in the heavy-fermion superconductor UBe13," Physical Review Letters, 64, 1975-8, 16 April 1990. (AT&T Bell Laboratories, Murray Hill, N.J.; Eidgen”ssische Technische Hochschule Zürich-Hong- gerberg, Switzerland; et al.) Theorists have dreamed up some very strange creatures of contorted shapes with names from fantasyland - skyrmions, anyons, spinning vortices with fractional angular momentum. It is remarkable that recently these dreams have turned out to be portents of realities in the description of condensed matter systems. D.-H. Lee, C.L. Kane, "Boson-vortex-skyrmion duality, spin-singlet fractional quantum Hall effect, and spin-1/2 anyon superconductivity," Physical Review Letters, 64, 1313-17, 19 March 1990. (IBM Watson Research Center, Yorktown Heights, N.Y.) Finally, I would like to mention two articles from a publication few physicists seem to know about, but one that I think scientists in general (or even nonscientists with some modest mathematical background) will find consistently rewarding. A.S. Luchins, E.H. Luchins, "The Einstein-Wertheimer correspondence on geometric proofs and mathematical puzzles," Mathematical Intelligencer, 12, 35-43, Spring 1990. (Rensselaer Polytechnic Institute, Troy, N.Y.) M. Senechal, J. Taylor, "Quasicrystals: the view from Les Houches," Mathematical Intelligencer, 12, 54-64, Spring 1990. (Smith College, Northampton, Mass.; Rutgers University, New Brunswick, N.J.) Author: BRUCE G. BUCHANAN Department of Computer Science University of Pittsburgh Pittsburgh, Pa. A distributed computing environment requires different language design choices from a single user-single processor environment. An experiment highlights several of these choices in the context of an implemented version of Smalltalk for many users on many machines. One of the important sets of issues addressed is how to design an inheritance mechanism in a distributed environment, and the implications of that design. J.K. Bennett, "Experience with distributed Smalltalk," Software - Practice and Experience, 20, 157-180, February 1990. (Rice University, Houston) Incomplete information of various kinds has been studied in the context of relational databases because the original model of relational databases is based on definite facts. Two forms of incomplete information are examined, and a data structure is introduced that can handle them in addition to handling definite information. Extensions to the fundamental relational algebra are presented to show the correctness of the extended model. K.-C. Liu, R. Sunderraman, "Indefinite and maybe information in relational databases," ACM Transactions on Database Systems, 15, 1-39, March 1990. (AT&T Bell Laboratories, Naperville, Ill.; Wichita State University, Kans.) There are many algorithms for comparing sequences of characters, as in the alignment problem in molecular biology. An edit distance between two strings is usually computed as a function of the number of fundamental operations of deletion and insertion required to make a match between the strings. The cost function has been extended to a mixture of functions that have different characteristics for different parts of the sequence. D. Eppstein, "Sequence comparison with mixed convex and concave costs," Journal of Algorithms, 11, 85-101, March 1990. (CSL Xerox PARC, Palo Alto, Calif.) Most theoretical work in computer science assumes no roundoff errors in calculations and assumes no buildup of errors over many iterations of a procedure. When algorithms are used in practical applications, however, both assumptions may well be false. This issue is explored in the context of computational geometry, and a partial solution is proposed. D. Dobkin, D. Silver, "Applied computational geometry: towards robust solutions of basic problems," Journal of Computer and System Sciences, 40, 70-87, February 1990. (Princeton University, N.J.; et al.) Production systems, including rule-based expert systems, spend considerable time matching rules against data, and thus are amenable to speed-up through parallelism. The application of data-flow principles to this central problem of symbolic computation are explored. Some modifications to their implementation are required before data-flow models can be mapped from numeric to symbolic computation. J.-L. Gaudiot, A. Sohn, "Data-driven parallel production systems," IEEE Transactions on Software Engineering, 16, 281-93, March 1990. (University of Southern California, Los Angeles)

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