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The spectral sensitivity at the opponent stage of the visual system is traditionally measured by a hue-cancellation procedure. Comparison with a direct hue-matching method shows that cancellation overestimates short-wavelength sensitivity by as much as a factor of 30. The observation implies that different mechanisms control the perception of short-wavelength and long-wavelength redness. 相似文献
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A new bisxanthone, named jacarelhyperols D (1), was isolated from the whole plant of Hypericum japonicum. Its chemical structure was elucidated as 6-[1',5',6'-trihydroxy-2'-(alpha-hydroxy-alpha-methyl)ethyl-3',4'-dihydrofuran (2',3',3',4') xanthone-3'-oxyl]-1,3,5-trihydroxy-xanthone on the basis of spectroscopic analysis. 相似文献
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Keller LP Bajt S Baratta GA Borg J Bradley JP Brownlee DE Busemann H Brucato JR Burchell M Colangeli L d'Hendecourt L Djouadi Z Ferrini G Flynn G Franchi IA Fries M Grady MM Graham GA Grossemy F Kearsley A Matrajt G Nakamura-Messenger K Mennella V Nittler L Palumbo ME Stadermann FJ Tsou P Rotundi A Sandford SA Snead C Steele A Wooden D Zolensky M 《Science (New York, N.Y.)》2006,314(5806):1728-1731
Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust. 相似文献
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Hörz F Bastien R Borg J Bradley JP Bridges JC Brownlee DE Burchell MJ Chi M Cintala MJ Dai ZR Djouadi Z Dominguez G Economou TE Fairey SA Floss C Franchi IA Graham GA Green SF Heck P Hoppe P Huth J Ishii H Kearsley AT Kissel J Leitner J Leroux H Marhas K Messenger K Schwandt CS See TH Snead C Stadermann FJ Stephan T Stroud R Teslich N Trigo-Rodríguez JM Tuzzolino AJ Troadec D Tsou P Warren J Westphal A Wozniakiewicz P Wright I Zinner E 《Science (New York, N.Y.)》2006,314(5806):1716-1719
Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth. The morphologies of these surprisingly diverse features were created by particles varying from dense mineral grains to loosely bound, polymineralic aggregates ranging from tens of nanometers to hundreds of micrometers in size. The cumulative size distribution of Wild 2 dust is shallower than that of comet Halley, yet steeper than that of comet Grigg-Skjellerup. 相似文献
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Brownlee D Tsou P Aléon J Alexander CM Araki T Bajt S Baratta GA Bastien R Bland P Bleuet P Borg J Bradley JP Brearley A Brenker F Brennan S Bridges JC Browning ND Brucato JR Bullock E Burchell MJ Busemann H Butterworth A Chaussidon M Cheuvront A Chi M Cintala MJ Clark BC Clemett SJ Cody G Colangeli L Cooper G Cordier P Daghlian C Dai Z D'Hendecourt L Djouadi Z Dominguez G Duxbury T Dworkin JP Ebel DS Economou TE Fakra S Fairey SA Fallon S Ferrini G Ferroir T Fleckenstein H Floss C Flynn G 《Science (New York, N.Y.)》2006,314(5806):1711-1716
The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales. 相似文献
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农药混剂的选择毒性研究 总被引:1,自引:0,他引:1
稻瘟净或异稻瘟净与乐果或马拉松混用,对抗性黑尾叶蝉有明显的增效作用,对小白鼠急性口服毒性也有所增加。小白鼠口服稻瘟净或异稻瘟净后,鼠肝中水解乐果和N—甲基正己酰胺的羧酰胺酶活力明显下降;水解醋酸α-萘酯的羧酸酯酶活力也被抑制。羊肝微粒体的羧酰胺酶在体外分别被稻瘟净、异稻瘟净、磷酸三苯酯、磷酸三甲苯酯、苯硫磷、氧乐果和西维因强烈抑制,它们的I_(50)值为1.3×10~(-8)—4.0×10~(-5)克分子浓度。稻瘟净、异稻瘟净、磷酸三苯酯和西维因分别是羊肝羧酰胺酶和羧酸酯酶的竞争性抑制剂,它们的K_i值在4.8×10~(-8)—1.0×10~(-7)克分子浓度之间。这些结果表明稻瘟净、异稻瘟净等增加乐果和马拉松对哺乳动物的毒性的机制,可能主要是由于它们抑制了哺乳动物体内正常解毒乐果和马拉松的水解酶。文中讨论了这些农药混剂的选择毒性问题。 相似文献
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Zolensky ME Zega TJ Yano H Wirick S Westphal AJ Weisberg MK Weber I Warren JL Velbel MA Tsuchiyama A Tsou P Toppani A Tomioka N Tomeoka K Teslich N Taheri M Susini J Stroud R Stephan T Stadermann FJ Snead CJ Simon SB Simionovici A See TH Robert F Rietmeijer FJ Rao W Perronnet MC Papanastassiou DA Okudaira K Ohsumi K Ohnishi I Nakamura-Messenger K Nakamura T Mostefaoui S Mikouchi T Meibom A Matrajt G Marcus MA Leroux H Lemelle L Le L Lanzirotti A Langenhorst F Krot AN Keller LP Kearsley AT 《Science (New York, N.Y.)》2006,314(5806):1735-1739
The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk. 相似文献