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Author: PETER D. MOORE Department of Biology King's College London, U.K. Analyses of lake sediments in Panama have provided evidence of the earliest recorded human impact on the forest environment of Central America. In layers dating to 11,000 years ago, there is a sudden appearance of carbon, together with phytoliths of weed species, such as Heliconia. These features indicate the onset of disturbed conditions that may well have been caused by human management of the contemporaneous low biomass forest. D.R. Piperno, M.B. Bush, P.A. Colinvaux, "Paleoenvironments and human occupation in late-glacial Panama," Quaternary Research, 33, 108-16, January 1990. (Smithsonian Tropical Research Institute, Balboa, Panama; Ohio State University, Columbus) The anatomy and morphology of fossil plant leaves provide a valuable guide to the climatic conditions under which they grew. Multivariate analysis has now been applied to assemblages of leaf fossils from rocks above and below the Cretaceous/Tertiary boundary. The results suggest that at this horizon there was a fourfold increase in precipitation and a mean annual increase in temperature of about 10°C. J.A. Wolfe, "Palaeobotanical evidence for a marked temperature increase following the Cretaceous/Tertiary boundary," Nature, 343, 153-6, 11 January 1990. (U.S. Geological Survey, Denver) One of the most serious problems facing a plant in aquatic habitats is that of providing an oxygen supply to its roots and removing carbon dioxide produced by root respiration. Diffusion through air ducts alone cannot account for the flow. It is now believed that some plants develop a convective throughflow, which is stimulated by the photosynthetic activity of the plant. J. Armstrong, W. Armstrong, "Light-enhanced convective throughflow increases oxygenation in rhizomes and rhizosphere of Phragmites australis (Cav.) Trin. ex Steud.," New Phytologist, 114, 121-8, January 1990. (University of Hull, England) We usually think of bats as essentially nocturnal animals, but daylight flying is far from uncommon. In a survey of British records, it is found that day flying incidence increases with latitude, suggesting that night foraging is less likely to provide sufficient food in the north. In winter, daylight hunting occurs mainly on warm, sunny days, when insect prey is more likely to be encountered. J.R. Speakman, "The function of daylight flying in British bats," Journal of the Zoological Society of London, 220, 101-13, January 1990. (University of Aberdeen, Scotland) A salt marsh staphylinid beetle, Bledius spectabilis, has been found to protect its young against being parasitized by an ichneumonid wasp, which can account for 15% of juvenile beetle mortality. The female beetle attends its young in burrows, moving them out when threatened by tidal flooding. But the presence of the mother beetle also deters burrow entry by the parasitic wasp; only in one case in 132 observations did the wasp enter a burrow where a female beetle was present. T.D. Wyatt, W.A. Foster, "Parental care in the subsocial intertidal beetle, Bledius spectabilis, in relation to parasitism by the ichneumonid wasp, Barycnemis blediator," Behaviour, 110, 76-92, October 1989. (University of Cambridge, England) Astronomical cycles underlie the sequence of glacial and interglacial episodes, but the link with climate is not a simple one. Ocean circulation patterns may well hold the clue to the problem of what sends the earth into a glacial mode, and salinity changes could be a driving factor in determining the ocean currents. Recent results show that meltwater from the North American ice sheet at the end of the last glacial episode was suddenly diverted out of the Gulf of Mexico and into the North Atlantic, which plunged Europe into a phase of renewed glaciation. This provides support for the ocean circulation model. W.S. Broecker, G.H. Denton, "What drives glacial cycles?" Scientific American, 262, 49-56, January 1990. (Columbia University, New York; University of Maine, Orono) The influence of mammal grazers on the population dynamics and species composition of plant communities are well documented, but the role of invertebrate root grazers in the soil is not yet appreciated. In a long-term study involving the use of soil insecticides, it was found that plant species richness was about 10% higher in treated plots than in controls. Thus, the effect of root herbivory is precisely opposite that of shoot herbivory. V.K. Brown, A.C. Gange, "Herbivory by soil-dwelling insects depresses plant species richness," Functional Ecology, 3, 667-71, November 1989. (Imperial College, London) The retention of infrared radiation by the atmosphere ("the greenhouse effect") can be measured directly by satellite systems. These confirm that ocean warming has a positive feedback effect, since more water evaporates and water vapor itself acts as a greenhouse gas. Satellite imagery will provide a direct means of tracing the development of the greenhouse effect in the future. A. Raval, V. Ramanathan, "Observational determination of the greenhouse effect," Nature, 342, 758-61, 14 December 1989. (University of Chicago) Many mammals in the Peruvian Amazon forest are frugivores, including brocket deer and peccaries. Both consume the tough-coated seeds of various palms, but they deal with them in different ways. The peccaries crack them with their strong jaws, while the brocket deer digest them in their ruminant stomachs. Perhaps this is due to the evolution of the ruminants, whose ancestors were small, forest-dwelling frugivores. R.E. Bodmer, "Frugivory in Amazonian Artiodactyla: evidence for the evolution of the ruminant stomach," Journal of Zoology, London, 219, 457-67, November 1989. (University of Cambridge, England) Aurhor: SOKRATES T. PANTELIDES IBM Research Division Thomas J. Watson Research Center Yorktown Heights, N.Y. High-resolution electron microscopes have become powerful tools with resolutions approaching one angstrom. A recent review details the way in which quantitative information is extracted from micrographs with a dazzling series of examples. A. Ourmazd, D.W. Taylor, M. Bode, Y. Kim, "Quantifying the information content of lattice images," Science, 246, 1571-7, 22 December 1989. (AT&T Bell Laboratories, Holmdel, N.J.) Good news again about SiGe alloys: The misfit dislocation density is reduced by at least a factor of 20 when you grow SiGe selectively in small areas. That is, of course, an optimum situation in microelectronics. D.B. Noble, J.L. Hoyt, C.A. King, J.F. Gibbons, et al., "Reduction in misfit dislocation density by the selective growth of Si1-xGex/Si in small areas," Applied Physics Letters, 56, 51-3, 1 January 1990. (Stanford Electronics Laboratory, Stanford, Calif.; et al.) The famous (or is it notorious?) D center in amorphous Si was long believed to be immobile, but experimental data now confirm a recent theoretical prediction that D centers are mobile. Do they, however, mediate H diffusion? That remains to be seen. W.B. Jackson, C.C. Tsai, R. Thompson, "Diffusion of paramagnetic defects in amorphous silicon," Physical Review Letters, 64, 56-9, 1 January 1990. (Xerox Palo Alto Research Center, Calif.) =07 Metallic behavior in a disordered two-dimensional Fermi system at T0 has been believed to be forbidden. Scaling arguments provide the basis for the contradictory approach that such a behavior is allowed in some instances and that the resistance has a universal value, independent of all microscopic details. M.P.A. Fisher, G. Grinstein, S.M. Girvin, "Presence of quantum diffusion in two dimensions: universal resistance at the superconductor-insulator transition," Physical Review Letters, 64, 587-90, 29 January 1990. (IBM Watson Research Center, Yorktown Heights, N.Y.; Indiana University, Bloomington) The asbestos scare has caused school districts, other public agencies, and homeowners to spend a great deal of money. A detailed scientific report adds a sanity check to that process. B.T. Mossman, J. Bignon, M. Corn, A. Seaton, J.B.L. Gee, "Asbestos: scientific developments and implications for public policy," Science, 247, 294-301, 19 January 1990. (University of Vermont, Burlington; Johns Hopkins University, Baltimore; Unite INSERM de Recherche, Cretail, France; et al.) A special issue containing a collection of 13 papers on metal-oxide-semiconductor structures has just appeared. Some of the latest interesting results are presented. Semiconductor Science and Technology, 4, December 1989. (Institute of Physics Publishing Ltd., Bristol, England) Author: BRUCE G. BUCHANAN Department of Computer Science University of Pittsburgh Pittsburgh, Pa. Integrity constraints for a database express relationships that must be satisfied by the database. They prevent some undesirable relationships but cannot fully guarantee the integrity of the information they deliver in response to queries. A new model for integrity of relational databases is introduced. This model, which is based on validity and completeness constraints, subsumes the old model. A. Motro, "Integrity = validity + completeness," ACM Transactions On Database Systems, 14, 480-502, December 1989. (University of Southern California, Los Angeles) Programmers and maintainers still rely heavily on hard-copy listings of source code, in spite of improved interactive tools. A conceptually simple model for organizing these listings--the printed book paradigm--improves the readability and maintainability of large programs. Empirical results show an improvement of 10% to 20% in programmers' comprehension of listings when the formatting principles are used. P.W. Oman, C.R. Cook, "The book paradigm for improved maintenance," IEEE Software, 7, 39-45, January 1990. (University of Idaho, Moscow; Oregon State University, Corvallis) Retrieving text from large, unformatted text databases can be expensive, and many search strategies have been developed. At one extreme is full text scanning, which eliminates intermediate access structures but is costly in time. At the other extreme, inverted files are used for rapid retrieval at the expense of storage and maintenance costs. A hybrid system is described here with some favorable performance results in different situations. D.L. Lee, F.H. Lochovsky, "HYTREM--a hybrid text-retrieval machine for large databases," IEEE Transactions on Computers, 39, 111-23, January 1990. (Ohio State University, Columbus; University of Toronto) Machines that operate on bit-slices ("bises") of a set of words are distinguished from conventional machines that operate on a whole word at a time. Searching is a common, and often expensive, operation that can benefit from some degree of concurrency. This paper shows the suitability of bis-sequential machines for several kinds of search. T.Y. Feng, "Search algorithms for bis-sequential machines," Journal of Parallel and Distributed Computing, 8, 1-9, January 1990. (Pennsylvania State University, University Park) A fundamental problem in robotics is preventing moving robots from colliding with obstacles in the environment. A useful technique from the literature is to introduce a "visibility graph," which connects vertices of obstacles if and only if their vertices are visible from each other. A new method of reducing the size of the visibility graph is discussed, which avoids including obstacles with vertices that will never lie on the shortest collision-free path. L.-C. Fu, D.-Y. Liu, "An efficient algorithm for finding a collision-free path among polyhedral obstacles," Journal of Robotic Systems, 7, 129-137, February 1990. (National Taiwan University, Taipei) 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, 1975) highlighted the fallacy in assuming one can 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.)

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