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91.
Klein HP Horowitz NH Levin GV Oyama VI Lederberg J Rich A Hubbard JS Hobby GL Straat PA Berdahl BJ Carle GC Brown FS Johnson RD 《Science (New York, N.Y.)》1976,194(4260):99-105
Three different types of biological experiments on samples of martian surface material ("soil") were conducted inside the Viking lander. In the carbon assimilation or pyrolytic release experiment, (14)CO(2) and (14)CO were exposed to soil in the presence of light. A small amount of gas was found to be converted into organic material. Heat treatment of a duplicate sample prevented such conversion. In the gas exchange experiment, soil was first humidified (exposed to water vapor) for 6 sols and then wet with a complex aqueous solution of metabolites. The gas above the soil was monitored by gas chromatography. A substantial amount of O(2) was detected in the first chromatogram taken 2.8 hours after humidification. Subsequent analyses revealed that significant increases in CO(2) and only small changes in N(2) had also occurred. In the labeled release experiment, soil was moistened with a solution containing several (14)C-labeled organic compounds. A substantial evolution of radioactive gas was registered but did not occur with a duplicate heat-treated sample. Alternative chemical and biological interpretations are possible for these preliminary data. The experiments are still in process, and these results so far do not allow a decision regarding the existence of life on the plonet Mars. 相似文献
92.
Grundy WM Buratti BJ Cheng AF Emery JP Lunsford A McKinnon WB Moore JM Newman SF Olkin CB Reuter DC Schenk PM Spencer JR Stern SA Throop HB Weaver HA;New Horizons Team 《Science (New York, N.Y.)》2007,318(5848):234-237
The New Horizons spacecraft observed Jupiter's icy satellites Europa and Ganymede during its flyby in February and March 2007 at visible and infrared wavelengths. Infrared spectral images map H2O ice absorption and hydrated contaminants, bolstering the case for an exogenous source of Europa's "non-ice" surface material and filling large gaps in compositional maps of Ganymede's Jupiter-facing hemisphere. Visual wavelength images of Europa extend knowledge of its global pattern of arcuate troughs and show that its surface scatters light more isotropically than other icy satellites. 相似文献
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Control of nitrogen export from watersheds by headwater streams 总被引:9,自引:0,他引:9
Peterson BJ Wollheim WM Mulholland PJ Webster JR Meyer JL Tank JL Marti E Bowden WB Valett HM Hershey AE McDowell WH Dodds WK Hamilton SK Gregory S Morrall DD 《Science (New York, N.Y.)》2001,292(5514):86-90
A comparative (15)N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds. 相似文献
97.
Flasar FM Achterberg RK Conrath BJ Pearl JC Bjoraker GL Jennings DE Romani PN Simon-Miller AA Kunde VG Nixon CA Bézard B Orton GS Spilker LJ Spencer JR Irwin PG Teanby NA Owen TC Brasunas J Segura ME Carlson RC Mamoutkine A Gierasch PJ Schinder PJ Showalter MR Ferrari C Barucci A Courtin R Coustenis A Fouchet T Gautier D Lellouch E Marten A Prangé R Strobel DF Calcutt SB Read PL Taylor FW Bowles N Samuelson RE Abbas MM Raulin F Ade P Edgington S Pilorz S Wallis B Wishnow EH 《Science (New York, N.Y.)》2005,307(5713):1247-1251
Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites. 相似文献
98.
Sutton T Baumann U Hayes J Collins NC Shi BJ Schnurbusch T Hay A Mayo G Pallotta M Tester M Langridge P 《Science (New York, N.Y.)》2007,318(5855):1446-1449
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100.
Nichols ML Allen BJ Rogers SD Ghilardi JR Honore P Luger NM Finke MP Li J Lappi DA Simone DA Mantyh PW 《Science (New York, N.Y.)》1999,286(5444):1558-1561
Substance P receptor (SPR)-expressing spinal neurons were ablated with the selective cytotoxin substance P-saporin. Loss of these neurons resulted in a reduction of thermal hyperalgesia and mechanical allodynia associated with persistent neuropathic and inflammatory pain states. This loss appeared to be permanent. Responses to mildly painful stimuli and morphine analgesia were unaffected by this treatment. These results identify a target for treating persistent pain and suggest that the small population of SPR-expressing neurons in the dorsal horn of the spinal cord plays a pivotal role in the generation and maintenance of chronic neuropathic and inflammatory pain. 相似文献