Rapid growth of magnesium-carbonate weathering products in a stony meteorite from antarctica     

Jull AJ  Cheng S  Gooding JL  Velbel MA 《Science (New York, N.Y.)》1988,242(4877):417-419

Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the Antarctic meteorite LEW 85320(H5 chondrite). Antarctic meteorites have resided on the earth for periods of 10(4) to 10(6) years, but the time needed for weathering products to form has been uncertain. Isotopic measurements of delta(13)C and delta(18)O indicate that the nesquehonite formed at near freezing temperatures by reaction of meteoritic minerals with terrestrial water and carbon dioxide. Results from carbon-14 dating suggest that, although the meteorite has been in Antarctica for at least 3.2 x 10(4) to 3.3 x 10(4) years, the nesquehonite formed after A.D.1950.  相似文献   

Famine Early Warning System Wins Its Spurs: Monitoring program that spotted new crisis in Ethiopia sheds temporary status, but more is being asked of it     

Walsh J 《Science (New York, N.Y.)》1988,239(4837):249-250

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Olmec settlement data from la venta, tabasco, Mexico     

Rust WF  Sharer RJ 《Science (New York, N.Y.)》1988,242(4875):102-104

Research at La Venta, a major Olmec center on a low salt dome 12 kilometers from the Gulf Coast has revealed evidence of initial occupation (about 1750 to 1400 B.C.) along levees of the silted-in Río Barí, north of the site core in a transitional estuarine-riverine environment. Between 1400 and 1150 B.C. settlement expanded to nearby La Venta itself, which between 1150 and 800 B.C. developed into a major temple-town complex. Local development peaked at La Venta and along the river levees between 800 and 500 B.C. In this span La Venta headed a local three-tiered site hierarchy as social distinctions expanded to the peripheral Río Barí sites. New excavations show that growth in population size and density at La Venta preceded the development of sociopolitical complexity. These data contradict the traditional organizational reconstruction of Olmec society, the "vacant ceremonial center" model, and provide qualified support for a model that presents riverine resource concentration as a significant factor in the evolution of Olmec civilization.  相似文献   

Security at weapons labs     

Norman C 《Science (New York, N.Y.)》1988,242(4877):365

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Press asks reprieve for condemned somalis     

Holden C 《Science (New York, N.Y.)》1988,239(4842):857

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Army shifts on dugway lab     

Norman C 《Science (New York, N.Y.)》1988,241(4874):1749

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Variance in academia: the academic profession     

Kerckhoff AC 《Science (New York, N.Y.)》1988,239(4842):922-923

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Species specialization-another perspective          下载免费PDF全文

Anvik JO  Colontino J  Gudmundson J  Hitt ME 《The Canadian veterinary journal. La revue veterinaire canadienne》1988,29(2):111-113

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Releases in israel ofAphelinus perpallidus,a recently introduced parasite of the pecan blackmargined aphid,Monellia caryella     

F Man Sour  M. K. Harris  J. D. Stone  R. Bueno 《Phytoparasitica》1988,16(2):171-174

Six shipments totaling 3452 mummies of the blackmargined aphid,Monellia caryella (Fitch), parasitized withAphelinus perpallidus Gahan, were obtained by air freight during the years 1982-1985 from Texas A&M Research Center, El Paso, Texas. About two-thirds of the mummies did not yield parasites. A colony ofA. perpallidus was established in the laboratory. Under laboratory conditions the percentage of emerged parasites was higher than that in the imported mummies, and the parasite had very limited impact on the aphid population. Field releases of the parasite were made but no establishment ofA. perpallidus was observed through the years.  相似文献   

Additional species of aphidoidea in Israel     

J. Halperin  A. Binazzi  E. Swirski 《Phytoparasitica》1988,16(3):231-237

Data are presented on 25 species of aphids recorded in Israel during the last 25 years. Information is provided on their host plants, localities and dates of collection. The occurrence of 11 of these species has not been reported previously. Three of the species are noxious:Cinara cupressi (Buckton),Monellia caryella (Fitch) andAphis citricola van der Goot (= ?A. spiraecola Patch).  相似文献