Articles Alert

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. Department of Biology King's College London, U.K. The sex of a turtle, as in the case of several reptiles, depends on the temperature at which it was incubated when still in the egg. At Cape Canaveral, Fla., hatchling loggerhead turtles were found to be 93% female, owing to the high temperatures in the turtle nest. Is it possible that this sexual imbalance will become even more pronounced with global warming? N. Mrosovsky, J. Provancha, "Sex ratio of loggerhead sea turtles hatching on a Florida beach," Canadian Journal of Zoology, 67, 2533-9, October 1989. (University of Toronto; Kennedy Space Center, Fla.) Palaeobotanists continue to argue about what factors have made the seed (and therefore the seed plant) such a successful organ. It is wrapped up in integuments, but so are the megaspores of some pteridophytes. The full benefit may lie in the continued differentiation of megaspore (seed) and microspore (pollen grain) leading to the plant's ability to provide more adequate food resources for the developing embryo. D. Haig, M. Westoby, "Selective forces in the emergence of the seed habit," Biological Journal of the Linnean Society of London, 38, 215-38, November 1989. (Macquarie University, New South Wales, Australia) In this green-veined white butterfly, the virgin females are extremely attractive to males and are constantly harassed by them, but once mated (usually in the morning) they cease to be appealing, possibly because they emit repellent pheromones. They are then able to lay their eggs in peace. But the repulsion gradually wears off, and mated females usually undergo a second mating, probably to discourage general male attention and, thus, disturbance to their egg-laying activities. They remate only in the afternoon, however, a time when egg-laying is seldom contemplated anyway, so time is available. J. Forsberg, C. Wiklund, "Mating in the afternoon: time-saving in courtship and remating by females of a polyandrous butterfly Pieris napi L.," Behavioural Ecology and Sociobiology, 25, 349-56, November 1989. (University of Stockholm) Aquatic plants may have to cope with a daytime scarcity of inorganic carbon for use in photosynthesis, and some have been found to use a biochemical process for carbon assimilation similar to Crassulacean Acid Metabolism. This system has been found in some brown algae (Pelvetia, Fucus, and Ascophyllum). L. Axelsson, S. Carlberg, H. Ryberg, "Adaptations by macroalgae to low carbon availability. II. Ultrastructural specializations, related to the function of a phosynthetic buffer system in the Fucaceae," Plant Cell and Environment, 12, 771-8, November 1989. (Kristineberg Marine Biological Station, Fiskeb„ckskil, Sweden; et al.) A genotype of Norway spruce from calcareous soils in Germany was found to be particularly sensitive to aluminum when compared with a genotype from acid soils. The calcicole ecotype was unable to exclude aluminum or to maintain normal calcium and magnesium relations. But when a mycorrizal fungus was present, the effects of aluminum toxicity were reduced. Such infections could be related to acid rain tolerance. D.A. Wilkins, M.J. Hodson, "The effects of aluminum and Paxillus involutus Fr. on the growth of Norway spruce [Picae abies (L.) Karst.]," The New Phytologist, 113, 225-32, October 1989. (University of Birmingham, England) Medical Products Department E.I. Du Pont de Nemours & Co. Wilmington, Del. Asymmetric alkylation methodologies continue to offer new powerful tools for organic synthesis. A new and efficient alternative is presented for the preparation of chiral á, á disubstituted carboxylic acids. J.-M. Fang, C.-J. Chang, "Asymmetric alkylation of a chiral à-amino alkenenitrile," Journal of the Chemical Society-Chemical Communications, 22, 1787-8, 15 November 1989. (National Taiwan University, Taipei) Two communications report a general approach to the phorbol ester family of natural products along with the first total synthesis of phorbol. These natural products are potent tumor promoters and are used extensively to assist the understanding of human carcinogenesis. P.A. Wender, H.Y. Lee, R.S. Wilhelm, P.D. Williams, "Studies on tumor promoters. 7. The synthesis of a potentially general precursor of the tiglianes, daphnanes, and ingenanes," Journal of the American Chemical Society, 111, 8954-7, 22 November 1989. (Stanford University, Calif.) P.A. Wender, H. Kogen, H.Y. Lee, J.D. Munger, Jr., et al., "Studies on tumor promoters. 8. The synthesis of phorbol," Journal of the American Chemical Society, 111, 8957-8, 22 November 1989. (Stanford University, Calif.) Two new biologically interesting natural products have been identified. W.A. Ayer, L.M. Browne, H. Orszanska, Z. Valenta, J.-S. Liu, "Alkaloids of Lycopodium selago. On the identity of selagine with huperzine A and the structure of a related alkaloid," Canadian Journal of Chemistry, 67, 1538-40, October 1989. (University of Alberta, Edmonton, et al.) Y. Kashman, S. Hirsh, O.J. McConnell, I. Ohtani, et al., "Ptilomycalin A. A novel polycyclic guanidine alkaloid of marine origin," Journal of the American Chemical Society, 111, 8925-6, 22 November 1989. (Tel Aviv University, Israel; et al.) The identification and understanding of microbial degradation of man-made compounds is of significant scientific, industrial, and ecological interest. The properties of an enzyme that has "evolved" to degrade nylon by-products as the sole carbon and nitrogen source are reported. S. Negoro, T. Mitamura, K. Oka, K. Kanagawa, H. Okada, "Determination of the active-site serine of 6-aminohexanoate-dimer hydrolase," European Journal of Biochemistry, 185, 521-4, 20 November 1989. (Osaka University, Japan) A description of a novel bacteriophage lambda vector system, which has been used to generate a library of antibody Fab fragments, has been presented. This method offers genetic capability, which has the potential of superseding present-day hybridoma technology. W.D. Huse, L. Sastry, S.A. Iverson, A.S. Kanag, et al., "Generation of a large combinatorial library of the immunoglobulin repertoire in phage lambda," Science, 246, 1275-81, 8 December 1989. (Research Institute of Scripps Clinic, La Jolla, Calif.; et al.) Recent protein crystal structures offer a significant insight into the understanding of the origin of the genetic code and the interaction of an inhibitor with the HIV proteinase. The potential impact is quite far-reaching in molecular biology and the development of AIDS therapeutics. M.A. Rould, J.J. Perona, D. S”ll, T.A. Steitz, "Structure of E. coli glutaminyl-tRNA synthetase complexed with tRNAGln and ATP at 2.8 Å resolution," Science, 246, 1135-42, 1 December 1989. (Yale University, New Haven, Conn.) M. Miller, J. Schneider, B.K. Sathyanarayana, M.V. Toth, et al., "Structure of complex of synthetic HIV-1 protease with a substrate-based inhibitor at 2.3 Angstrom resolution," Science, 246, 1149-52, 1 December 1989. (NCI-Frederick Cancer Research Facility, Md.; et al.) Department of Computer Science University of Pittsburgh Pittsburgh, Pa. Analogical reasoning has many facets, but because it has not been well understood, it has been left out of the tool kit of reasoning programs. This paper explores the computations as parts of a model under which an analogy is used to solve a new problem by mapping internal structures of a base description to a target description. B. Falkenhainer, K.D. Forbus, D. Getner, "The structure mapping engine: algorithm and examples," Journal of Artificial Intelligence, 41, 1-64, November 1989. (University of Illinois, Urbana) Programs that learn from examples often need to find all specializations of a concept definition that exclude a counter example (negative instance). Brute force search can be used, but a new algorithm described here speeds the computation by two orders of magnitude. The key is a bit vector representation of examples and concept definitions. K. VanLehn, "Efficient specializations of relational concepts," Journal of Machine Learning, 4, 99-106, October 1989. (Carnegie Mellon University, Pittsburgh) As computers become simpler and more widely available, more attention must be paid to end users. Several classes of end users are defined and organized in a unifying framework, the "user cube." W.W. Cotterman, K. Kumar, "User cube: a taxonomy of end users," Communications of the ACM, 32, 1313-20, November 1989. (Georgia State University, Atlanta) Spatial information in maps is important in many problem-solving activities. In the work reported here, a prototype computer system scans simplified maps, recognizes patterns, and answers questions about the roads and cities on the map. R. Kasturi, R. Fernandez, M.L. Amlani, W. Feng, "Map data processing in geographic information systems," Computer, 22, 10-21, December 1989. (Pennsylvania State University, University Park) Behavioral models of how human partners respond in human-machine systems are important in designing such systems. A proposed analytic model would explain and predict responses of operators of teleoperated vehicles who would base decisions on the views provided from the vehicle. D.D. Sworder, K.S. Haaland, "A hypothesis evaluation model for human operators," IEEE Transactions on Systems, Man, and Cybernetics, 19, 1091-1100, September/October 1989. (University of California, San Diego) Most computer scientists think of programs in syntactic terms, with semantics assigned to the syntax. This paper suggests that software design start with denotations, which describe the essential parts of a system, and that the syntax be derived from them later. A. Blikle, "Denotational engineering," Science of Computer Programming, 12, 207-53, September 1989. (Polish Academy of Sciences, Warsaw) IBM Research Division Thomas J. Watson Research Center Yorktown Heights, N.Y. Not just pretty pictures! Scanning tunneling microscopy (STM) of DNA yields valuable structural information. The possibility of sequencing nucleic acids by direct STM imaging is projected in a recent report. D.D. Dunlap, C. Bustamante, "Images of single-stranded nucleic acids by scanning tunnelling microscopy," Nature, 342, 204-6, 9 November 1989. (University of New Mexico, Albuquerque) The fractional quantum Hall effect in a two-dimensional electron gas has yielded some of the most challenging and exciting physics in the last few years. A recent paper reports observations of the same effect in one-dimensional electron gas with provocative implications. G. Timp, R. Behringer, J.E. Cunningham, R.E. Howard, "Fractional quantum Hall effect in one dimension," Physical Review Letters, 63, 2268-71, 13 November 1989. (AT&T Bell Laboratories, Holmdel, N.J.) High carrier mobilities are highly desirable in electronic devices, but high hole mobilities are hard to come by. A recent paper reports high hole mobilities in technologically important Si/SiGe/Si heterostructures grown by ultrahigh vacuum/chemical vapor deposition (UHV/CVD). P.J. Wang, B.S. Meyerson, F.F. Fang, J. Nocera, B. Parker, "High hole mobility in Si/Si1-xGex/Si p-type modulation-doped double heterostructures," Applied Physics Letters, 55, 2333-5, 27 November 1989. (IBM Watson Research Center, Yorktown Heights, N.Y.) At the same time, researchers are intensely investigating the structure of Si-Ge interfaces and superlattices. Two very recent examples have been published. E. Müller, H.-U. Nissen, M. Ospelt, H. von K„nel, "Chemical ordering and boundary structure in strained-layer Si-Ge superlattices," Physical Review Letters, 63, 1819-22, 23 October 1989. (Eidgen”ssiche Technische Hochschule, Zürich) R. Hull, J.C. Bean, "Thermal stability of Si/GexSi1-x/Si heterostructures," Applied Physics Letters, 55, 1900-2, 30 October 1989. (AT&T Bell Laboratories, Murray Hill, N.J.) Constraints dictated by thermodynamics often frustrate attempts to grow desirable structures. A new paper shows that manipulation of surface energetics makes it possible to beat thermodynamic odds. M. Copel, M.C. Reuter, E. Kaxiras, R.M. Tromp, "Surfactants in epitaxial growth," Physical Review Letters, 63, 632-35, 7 August 1989. (IBM Research Division, T.J. Watson Research Center, Yorktown Heights, N.Y.)

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