Pliocene paleoclimate and East antarctic ice-sheet history from surficial ash deposits   总被引：1，自引：0，他引：1  

Marchant DR  Swisher CC  Lux DR  West DP  Denton GH 《Science (New York, N.Y.)》1993,260(5108):667-670

The preservation, age, and stratigraphic relation of an in situ ashfall layer with an underlying desert pavement in Arena Valley, southern Victoria Land, indicate that a cold-desert climate has persisted in Arena Valley during the past 4.3 million years. These data indicate that the present East Antarctic Ice Sheet has endured for this time and that average temperatures during the Pliocene in Arena Valley were no greater than 3 degrees C above present values. One implication is that the collapse of the East Antarctic Ice Sheet due to greenhouse warming is unlikely, even if global atmospheric temperatures rise to levels last experienced during mid-Pliocene times.  相似文献   

REPORTS     

West CJ  Hull C 《Science (New York, N.Y.)》1933,78(2020):240-241

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HST and VLT investigations of the fragments of comet C/1999 S4 (LINEAR)     

Weaver HA  Sekanina Z  Toth I  Delahodde CE  Hainaut OR  Lamy PL  Bauer JM  A'Hearn MF  Arpigny C  Combi MR  Davies JK  Feldman PD  Festou MC  Hook R  Jorda L  Keesey MS  Lisse CM  Marsden BG  Meech KJ  Tozzi GP  West R 《Science (New York, N.Y.)》2001,292(5520):1329-1333

At least 16 fragments were detected in images of comet C/1999 S4 (LINEAR) taken on 5 August 2000 with the Hubble Space Telescope (HST) and on 6 August with the Very Large Telescope (VLT). Photometric analysis of the fragments indicates that the largest ones have effective spherical diameters of about 100 meters, which implies that the total mass in the observed fragments was about 2 x 10(9) kilograms. The comet's dust tail, which was the most prominent optical feature in August, was produced during a major fragmentation event, whose activity peaked on UT 22.8 +/- 0.2 July 2000. The mass of small particles (diameters less than about 230 micrometers) in the tail was about 4 x 10(8) kilograms, which is comparable to the mass contained in a large fragment and to the total mass lost from water sublimation after 21 July 2000 (about 3 x 10(8) kilograms). HST spectroscopic observations during 5 and 6 July 2000 demonstrate that the nucleus contained little carbon monoxide ice (ratio of carbon monoxide to water is less than or equal to 0.4%), which suggests that this volatile species did not play a role in the fragmentation of C/1999 S4 (LINEAR).  相似文献   

Foundress associations in polistine wasps: dominance hierarchies and the evolution of social behavior   总被引：3，自引：0，他引：3  

M J West 《Science (New York, N.Y.)》1967,157(796):1584-1585

Interactions among female paper wasps of newly founded colonies suggest that dominance relations assign social (reproductive) roles to siblings in a way advantageous to both dominants and subordinates. In various social animals dominance relations may have been an important prerequisite for the evolution of a division of labor between reproductive and nonreproductive (or less reproductive) adults.  相似文献   

Permethylpolysilanes: Silicon Analogs of Hydrocarbons: Cyclic polysilanes resemble aromatic hydrocarbons in electronic and chemical properties     

West R  Carberry E 《Science (New York, N.Y.)》1975,189(4198):179-186

Studies of the spectra of cyclopolysilanes have led to several significant conclusions. These molecules possess both easily ionized Si-Si bonding electrons and low energy delocalized antibonding orbitals, and can therefore serve either as electron donors or acceptors. This model explains the similarity in properties between cyclopolysilanes and aromatic hydrocarbons. Further investigations of cyclopolysilanes seem likely to provide the key to understanding of controversial questions of bonding in metalloid compounds even as studies of their carbon analogs, the cyclic and cage hydrocarbons, have been crucial to present knowledge of organic stereochemistry and reaction mechanisms. The reactions of cyclopolysilanes are not only interesting in themselves, but have opened the way to the synthesis of complex polysilanes and thus to whole new areas of study. Improved methods of synthesis and isolation are needed, but the number and kinds of compounds that can be prepared seem almost limitless. Perhaps a polymetal chemistry comparable in breadth and variety to carbon chemistry is now developing.  相似文献   

Letters to the editor     

West R 《Science (New York, N.Y.)》1966,151(3709):402-404

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IX. RESEARCH INFORMATION SERVICE     

West CJ 《Science (New York, N.Y.)》1933,78(2019):203-206

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Insulators and boundaries: versatile regulatory elements in the eukaryotic genome     

Bell AC  West AG  Felsenfeld G 《Science (New York, N.Y.)》2001,291(5503):447-450

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Human embryonic stem cells     

Wilmut I  West MD  Lanza RP  Gearhart JD  Smith A  Colman A  Trounson AO  Campbell KH 《Science (New York, N.Y.)》2005,310(5756):1903

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Cell survival promoted by the Ras-MAPK signaling pathway by transcription-dependent and -independent mechanisms     

Bonni A  Brunet A  West AE  Datta SR  Takasu MA  Greenberg ME 《Science (New York, N.Y.)》1999,286(5443):1358-1362

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