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The Scientist has asked a group of experts to comment periodically upon recent articles that they have found noteworthy. Their selections, presented herein every issue, are neither endorsements of content nor the result of systematic searching. Rather, the list represents personal choices of articles the columnists believe the scientific community as a whole may also find interesting. Reprints of any articles cited here may be ordered through The Genuine Article, 3501 Market St., Philadelphia, Pa. 19104, or by telephoning (215) 386-4399. Author: PETER D. MOORE Department of Biology King's College London, U.K. Recent studies on the rates of the spread of trees following the last glaciation show that some heavy-seeded species, such as oaks and beeches, spread as fast as light-seeded trees. Carriage of fruits by small mammals, such as squirrels, cannot account for the rates of about 300 meters per annum that are often recorded. Transport by blue jays, however, could provide a mechanism to explain such rapid tree invasion. W.C. Johnson, T. Webb III, "The role of blue jays (Cyanocitta cristata L.) in the postglacial dispersal of fagaceous trees in eastern North America," Journal of Biogeography, 16, 561-71, November 1989. (Virginia Polytechnic Institute and State University, Blacksburg; Brown University, Providence, R.I.) A study of the coral reefs off Barbados has permitted the reconstruction of sea levels since the last glacial maximum, when the sea in that area was more than 120 meters lower than at present. The data support the hypothesis that deglaciation was fastest between 13,000 to 11,000 and 10,000 to 8,000 years ago. R.G. Fairbanks, "A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation," Nature, 342, 637-42, 7 December 1989. (Lamont-Doherty Geological Observatory of Columbia University, Palisades, N.Y.) Harvesting animals from an ecosystem can be compatible with conservation practices if the population dynamics of the species is adequately understood. In fluctuating environments, however, it may prove difficult to develop acceptable models. The magpie goose in tropical Australia, for example, is hunted, but its population is strongly affected by variable patterns of rainfall. Harvesting policy needs to account for the resulting population instability, which could involve reducing the crop by about 25%. P. Bayliss, "Population dynamics of magpie geese in relation to rainfall and density: implications for harvest models in a fluctuating environment," Journal of Applied Ecology, 26, 913-24, December 1989. (Conservation Commission of the Northern Territory, Palmerston, Australia) The effects of tropical forest fragmentation on its vast insect fauna are, as yet, not known. In a pioneer study of beetles, which took place in the clearing of a previously uncut Brazilian forest, it was found that there is very little movement between isolated forest patches. Species richness is lower, populations are sparser, and body size is lower with fragmentation. Low dung beetle frequency could account for poor dung decomposition in small forest stands. B.C. Klein, "Effects of forest fragmentation on dung and carrion beetle communities in central Amazonia," Ecology, 70, 1715-25, December 1989. (University of Florida, Gainesville) Author: THEODORE DAVIDSON Institute of Materials Science University of Connecticut Storrs "Ionenes" are polymers bearing ionic charge on their backbone chain. A recent paper describes their unique combination of optical properties: The refractive index is in the range of inorganic glasses, and the dispersion can be varied by altering chain structure and counterions. When processed from a solution or a melt, ionenes produce glassy films with excellent optical transmission in the visible and near-ultraviolet regions. H.-U. Simmrock, A. Mathy, L. Dominguez, W.H. Meyer, G. Wegner, "Polymers with a high refractive index and low optical dispersion," Angewandte Chemie International Edition in English, 26, 1122-3, August 1989. (Max Planck Institute for Polymer Research, Mainz, W.Ger.) Metal lines of submicron width have been deposited electrochemically on polymer films and substrates, using a variant of the scanning tunneling microscope. The use of an ionically conducting polymer as the solid electrolyte improves resolution and avoids electrodeposition on the tip. Gold, silver, copper, and palladium have been deposited atop the polymer. Alternatively, conductive substrates coated with polyelectrolyte can serve as sites for deposition or etching. O.E. Hüsser, D.H. Craston, A.J. Bard, "Scanning electrochemical microscopy," Journal of the Electrochemical Society, 136, 3222-9, November 1989. (University of Texas, Austin) Another milestone study in the National Research Council's continuing appraisal of scientific progress and opportunities details research hotspots, compares international efforts, and surveys manpower and education. National Research Council (U.S.) Committee on Materials Science and Engineering, "Materials Science and Engineering for the 1990s: maintaining competitiveness in the age of materials," National Academy Press, 1989. (Washington, D.C.) In his Institute of Metals Lecture, William D. Nix describes several nontraditional techniques for mechanical measurements on thin films. Submicron indentation tests measure hardness, elastic modulus, and time-dependent deformation properties. Laser scanning reveals biaxial stresses and shows that both elastic and plastic properties can be measured on microfabricated cantilever beams. Applications discussed include microelectronic and magnetic thin films. W.D. Nix, "Mechanical properties of thin films," Metallurgical Transactions A, 20A, 2217-45, November 1989. (Stanford University, Calif.) In experiments using careful reactor design, the bimolecular hydrogen abstraction reaction is made to dominate over monomolecular methane decomposition. The result is fewer impurities in the polycrystalline diamond film and more regular facet development. H. Alkyo, K.-I. Kondo, "Diamond synthesis suppressing the thermal decomposition of methane in a hot-filament CVD," Japanese Journal of Applied Physics, 26, L1631-3, September 1989. (Tokyo Institute of Technology) High resolution (1.6Angstrom) transmission electron micrographs show the lattice and defect structure in thin film high-Tc superconductors. Flux pinning, crucial for thin films to carry large critical currents, seems to depend on structural defects in the lattice. A large assortment and density of defects is found in thin films, owing to nonequilibrium deposition conditions. Observation of these new stacking sequences points out the utility of laser deposition processes "to produce new metastable structures with novel properties." R. Ramesh, D.M. Hwang, T. Venkatesan, T.S. Ravi, et al., "Direct observation of structural defects in laser-deposited superconducting Y-Ba-Cu-O thin films," Science, 247, 57-59, 5 January 1990. (Bellcore, Redbank, N.J., Rutgers University, Piscataway, N.J.; et al.) Author: BRUCE G. BUCHANAN Department of Computer Science University of Pittsburgh Pittsburgh, Pa. Constraints are ubiquitous in problem solving, but there are no computational algorithms both powerful enough and general enough to solve all constraint satisfaction problems. Three authors present a family of algorithms and focus on one: an incremental constraint propagation procedure. B.N. Freeman-Benson, J. Maloney, A. Borning, "An incremental constraint solver," Communications of the ACM, 33, 54-63, January 1990. (University of Washington, Seattle) A major problem in using networked computers effectively has been the absence of so-called seamless file systems, in which data can be retrieved from heterogeneous databases as if they were a single, centralized database. An architecture for a distributed database system, named DATAPLEX, addresses this problem. C.-W. Chung, "DATAPLEX: an access to heterogeneous distributed databases," Communications of the ACM, 33, 70-80, January 1990. (General Motors Research Labs, Warren, Mich.) Security of computer systems is a well-publicized problem. Part of the quandary is conceptual: We don't know how to define security in a formal way. Another aspect is technical: Given that formal model of security, we need theorems that guarantee the behavior of implementations of the model. J. McLean, "The specification and modeling of computer security," IEEE Computer, 23, 9-16, January 1990. (Naval Research Laboratory, Washington, D.C.) Legal questions surrounding software protection have always been murky. One such question is analyzed, regarding the reconstruction of a program based on observing its behavior. Partly owing to the fact that reverse engineering is so widespread and widely viewed as speeding the development of improved products, it is argued that laws against reverse engineering would be counterproductive. P. Samuelson, "Reverse-engineering someone s software: Is it legal?" IEEE Software, 7, 90-6, January 1990. (University of Pittsburgh, Pa.) The process of writing software is itself only modestly understood; understanding the process of managing software projects is far behind. F.P. Brooks (The Mythical Man-Month, Reading, Mass., Addison-Wesley, 1978) highlighted the fallacy that assumed one could halve the production time by doubling the manpower. The relationships among scheduled time, actual time, staffing, and costs of large software projects are observed. T.K. Abdel-Hamid, "Investigating the cost/schedule trade-off in software development," IEEE Software, 7, 97-105, January 1990. (Naval Postgraduate School, Monterey, Calif.) Author: RON MAGOLDA Medical Products Department E.I. Du Pont de Nemours & Co. Wilmington, Del. Expansion of the genetic alphabet has been achieved for the first time (from four to six letters) by incorporating a new base pair into duplex DNA and RNA, while meeting design, synthesis, and incorporation requirements. The application of this new technology opens new opportunities for molecular biology. J.A. Piccirilli, T. Krauch, S.E. Moroney, S.A. Benner, "Enzymatic incorporation of a new base pair into DNA and RNA extends the genetic alphabet," Nature, 343, 33-7, 4 January 1990. (Laboratory for Organic Chemistry, Zurich) A new synthetic method generates acyl- and aroyllithium via a lithium-tellurium exchange with tellurolesters. T. Hiiro, Y. Morita, T. Inoue, N. Kambe, et al., "A new access to acyl- and aroyllithiums via lithium-tellurium exchange," Journal of the American Chemical Society, 112, 455-7, 3 January 1990. (Osaka University, Japan) Trialkylsilyl enol ethers are common intermediates in organic synthesis. The utility of this intermediate has been extended. P. Magnus, B. Mugrage, "New trialkylsilyl enol ether chemistry. Regiospecific and stereospecific sequential electrophilic addition," Journal of the American Chemical Society, 112, 462-4, 3 January 1990. (University of Texas, Austin) The natural product norsecurinine has been prepared in an optically active form by using an intramolecular Diels-Alder reaction with the appropriately substituted acetylemic oxazole. P.A. Jacobi, C.A. Blum, R.W. DeSimone, U.E.S. Udodong, "Total synthesis of (+)- and (-)-norsecurinine," Tetrahedron Letters, 30 (51), 7173-6, 1989. (Wesleyan University, Middletown, Conn.) Using ultraviolet radiation, cross links between RNA and RNA enzymes were generated to identify pivotal contact points in reaching an understanding of enzyme mechanisms. C. Guerrier-Takada, N. Lumelsky, S. Altman, "Specific interactions in RNA enzyme-substrate complexes," Science, 246, 1578-85, 22 December 1989. (Yale University, New Haven, Conn.) A major approach in cancer chemotherapy research is the design and synthesis of agents that recognize DNA duplexes in a sequence-specific fashion. The intact DNA duplex, along with two compounds bound to DNA duplexes, is analyzed using X-ray diffraction and nuclear magnetic resonance spectroscopy. Y.-C. Liaw, Y.-G. Gao, H. Robinson, G.A. van der Marel, et al., "Antitumor drug nogalamycin binds DNA in both grooves simultaneously: molecular structure of nogalamycin-DNA complex," Biochemistry, 28, 9913-18, 26 December 1989. (University of Illinois, Urbana-Champaign; Leiden State University, The Netherlands)

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