Triton's Geyser-Like Plumes: Discovery and Basic Characterization     

Soderblom LA  Kieffer SW  Becker TL  Brown RH  Cook AF  Hansen CJ  Johnson TV  Kirk RL  Shoemaker EM 《Science (New York, N.Y.)》1990,250(4979):410-415

At least four active geyser-like eruptions were discovered in Voyager 2 images of Triton, Neptune's large satellite. The two best documented eruptions occur as columns of dark material rising to an altitude of about 8 kilometers where dark clouds of material are left suspended to drift downwind over 100 kilometers. The radii of the rising columns appear to be in the range of several tens of meters to a kilometer. One model for the mechanism to drive the plumes involves heating of nitrogen ice in a subsurface greenhouse environment; nitrogen gas pressurized by the solar heating explosively vents to the surface carrying clouds of ice and dark partides into the atmosphere. A temperature increase of less than 4 kelvins above the ambient surface value of 38 +/- 3 kelvins is more than adequate to drive the plumes to an 8-kilometer altitude. The mass flux in the trailing clouds is estimated to consist of up to 10 kilograms of fine dark particles per second or twice as much nitrogen ice and perhaps several hundred or more kilograms of nitrogen gas per second. Each eruption may last a year or more, during which on the order of a tenth of a cubic kilometer of ice is sublimed.  相似文献   

Scent organ development in creatonotos moths: regulation by pyrrolizidine alkaloids     

Schneider D  Boppré M  Zweig J  Horsley SB  Bell TW  Meinwald J  Hansen K  Diehl EW 《Science (New York, N.Y.)》1982,215(4537):1264-1265

7-Hydroxy-6,7-dihydro-5H-pyrolizine-1-carboxaldehyde is the major volatile component of the scent organs in males of two species of Creatonotos (Lepidoptera, Arctiidae). The biosynthesis of this presumed pheromone depends on the presence of pyrrolizidine alkaloids in plants that are ingested by the larvae. In addition, these secondary plant substances control the morphogenesis of the scent organs. This morphogenetic effect of an alkaloid has not been observed previously.  相似文献   

Probing the Local Effects of Magnetic Impurities on Superconductivity     

A Yazdani  BA Jones  CP Lutz  MF Crommie  DM Eigler 《Science (New York, N.Y.)》1997,275(5307):1767-1770

The local effects of isolated magnetic adatoms on the electronic properties of the surface of a superconductor were studied with a low-temperature scanning tunneling microscope. Tunneling spectra obtained near magnetic adsorbates reveal the presence of excitations within the superconductor's energy gap that can be detected over a few atomic diameters around the impurity at the surface. These excitations are locally asymmetric with respect to tunneling of electrons and holes. A model calculation based on the Bogoliubov-de Gennes equations can be used to understand the details of the local tunneling spectra.  相似文献   

A 50,000-year record of climate oscillations from Florida and its temporal correlation with the heinrich events     

Grimm EC  Jacobson GL  Watts WA  Hansen BC  Maasch KA 《Science (New York, N.Y.)》1993,261(5118):198-200

Oscillations of Pinus (pine) pollen in a 50,000-year sequence from Lake Tulane, Florida, indicate that there were major vegetation shifts during the last glacial cycle. Episodes of abundant Pinus populations indicate a climate that was more wet than intervening phases dominated by Quercus (oak) and Ambrosia-type (ragweed and marsh-elder). The Pinus episodes seem to be temporally correlated with the North Atlantic Heinrich events, which were massive, periodic advances of ice streams from the eastern margin of the Laurentide Ice Sheet. Possible links between the Tulane Pinus and Heinrich events include hemispheric cooling, the influences of Mississippi meltwater on sea-surface temperatures in the Gulf of Mexico, and the effects of North Atlantic thermohaline circulation on currents in the Gulf.  相似文献   

Carcinoembryonic antigen present in human colonic neoplasms serially propagated in hamsters   总被引：2，自引：0，他引：2  

D M Goldenberg  H J Hansen 《Science (New York, N.Y.)》1972,175(26):1117-1118

Carcinoembryonic antigen, as measured by radioimmunoassay, is present in two different human colonic tumors that have been serially transplanted and maintained in the cheek pouches of unconditioned, adult golden hamsters. This finding shows that a human tumor-associated antigen can be produced in an animal host.  相似文献   

RELATION OF DUAL PHENOMENON IN PENICILLIUM NOTATUM TO PENICILLIN PRODUCTION     

Hansen HN  Snyder WC 《Science (New York, N.Y.)》1944,99(2570):264-265

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Diverse plant and animal genetic records from Holocene and Pleistocene sediments   总被引：1，自引：0，他引：1  

Willerslev E  Hansen AJ  Binladen J  Brand TB  Gilbert MT  Shapiro B  Bunce M  Wiuf C  Gilichinsky DA  Cooper A 《Science (New York, N.Y.)》2003,300(5620):791-795

Genetic analyses of permafrost and temperate sediments reveal that plant and animal DNA may be preserved for long periods, even in the absence of obvious macrofossils. In Siberia, five permafrost cores ranging from 400,000 to 10,000 years old contained at least 19 different plant taxa, including the oldest authenticated ancient DNA sequences known, and megafaunal sequences including mammoth, bison, and horse. The genetic data record a number of dramatic changes in the taxonomic diversity and composition of Beringian vegetation and fauna. Temperate cave sediments in New Zealand also yielded DNA sequences of extinct biota, including two species of ratite moa, and 29 plant taxa characteristic of the prehuman environment. Therefore, many sedimentary deposits may contain unique, and widespread, genetic records of paleoenvironments.  相似文献   

Establishment and Identification of Cytoplasmic Male Sterility in Brassica napus by Intergeneric Somatic Hybridization   总被引：2，自引：0，他引：2  

Hu Qiong  LI Yun-chang  MEI De-sheng  FANG Xiao-ping  Lise N Hansen  Sven B Andersen 《中国农业科学(英文版)》2003,2(12)

Exploitation of novel cytoplasmic male sterility(CMS)is a main approach for widening the cytoplasmic genetic background of hybrid oilseed rape and avoiding epidemic risk in oilseed rape production.In this study,symmetric somatic hybrids between Brassicanapus var.Zhongshuang4 and Sinapis arvensis(Yeyou18)were produced by protoplast fusion.Two of the six established hybrids were male sterile showing trace or no pollen release upon flowering with non-or slightly extended stamens.Using Zhongshuang4 as a recurrent parent to pollinate the male sterile plants,the ratio of male sterile plants increased with the number of backcrosses.As early as in BC3 generation,most of the sterile families had nearly 100%sterile plants.Up to BC4 generation,the male sterility became stable and no fertility segregation was observed.All F1 progenies from tested crosses using restorer and maintainer lines of Polima CMS were 100%sterile,indicating that the established CMS by somatic hybridization is different from Polima CMS.The origin of the cytoplasm and potential use of this hovel CMS in oilseed rape breeding were discussed.Key wotds:Oilseed rape,Protoplast fusion,Cytoplasmic male sterility,Sinapis arvensis  相似文献   

THE ROCKEFELLER FOUNDATION     

Christensen BE  Hansen E  Cheldelin VH  Stark JB 《Science (New York, N.Y.)》1939,89(2310):319-321

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Carbon-14 Tetrachloride Produced by Neutron Irradiation of Aniline-and Pyridine-CCl4 Solutions     

Hein RE  Setser DW  Terhaar CJ  Chang SC  McFarland RH  Hansen MF 《Science (New York, N.Y.)》1957,125(3240):195-196

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