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排序方式: 共有226条查询结果,搜索用时 15 毫秒
102.
Smith BA Soderblom L Batson R Bridges P Inge J Masursky H Shoemaker E Beebe R Boyce J Briggs G Bunker A Collins SA Hansen CJ Johnson TV Mitchell JL Terrile RJ Cook AF Cuzzi J Pollack JB Danielson GE Ingersoll AP Davies ME Hunt GE Morrison D Owen T Sagan C Veverka J Strom R Suomi VE 《Science (New York, N.Y.)》1982,215(4532):504-537
Voyager 2 photography has complemented that of Voyager I in revealing many additional characteristics of Saturn and its satellites and rings. Saturn's atmosphere contains persistent oval cloud features reminiscent of features on Jupiter. Smaller irregular features track out a pattern of zonal winds that is symmetric about Saturn's equator and appears to extend to great depth. Winds are predominantly eastward and reach 500 meters per second at the equator. Titan has several haze layers with significantly varying optical properties and a northern polar "collar" that is dark at short wavelengths. Several satellites have been photographed at substantially improved resolution. Enceladus' surface ranges from old, densely cratered terrain to relatively young, uncratered plains crossed by grooves and faults. Tethys has a crater 400 kilometers in diameter whose floor has domed to match Tethys' surface curvature and a deep trench that extends at least 270 degrees around Tethys' circumference. Hyperion is cratered and irregular in shape. Iapetus' bright, trailing hemisphere includes several dark-floored craters, and Phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours. Within Saturn's rings, the "birth" of a spoke has been observed, and surprising azimuthal and time variability is found in the ringlet structure of the outer B ring. These observations lead to speculations about Saturn's internal structure and about the collisional and thermal history of the rings and satellites. 相似文献
103.
Smith BA Soderblom LA Johnson TV Ingersoll AP Collins SA Shoemaker EM Hunt GE Masursky H Carr MH Davies ME Cook AF Boyce J Danielson GE Owen T Sagan C Beebe RF Veverka J Strom RG McCauley JF Morrison D Briggs GA Suomi VE 《Science (New York, N.Y.)》1979,204(4396):951-972
The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites. On Jupiter itself, atmospheric motions-the interaction of cloud systems-display complex vorticity. On its dark side, lightning and auroras are observed. A ring was discovered surrounding Jupiter. The satellite surfaces display dramatic differences including extensive active volcanismn on Io, complex tectonism on Ganymnede and possibly Europa, and flattened remnants of enormous impact features on Callisto. 相似文献
104.
105.
Smith BA Soderblom LA Banfield D Barnet C Basilevsky AT Beebe RF Bollinger K Boyce JM Brahic A Briggs GA Brown RH Chyba C Collins SA Colvin T Cook AF Crisp D Croft SK Cruikshank D Cuzzi JN Danielson GE Davies ME De Jong E Dones L Godfrey D Goguen J Grenier I Haemmerle VR Hammel H Hansen CJ Helfenstein CP Howell C Hunt GE Ingersoll AP Johnson TV Kargel J Kirk R Kuehn DI Limaye S Masursky H McEwen A Morrison D Owen T Owen W Pollack JB Porco CC Rages K Rogers P Rudy D Sagan C Schwartz J 《Science (New York, N.Y.)》1989,246(4936):1422-1449
Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptune's atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptune's zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen. 相似文献
106.
107.
Conformations of signal peptides induced by lipids suggest initial steps in protein export 总被引:21,自引:0,他引:21
Despite the requirement for a functional signal sequence in protein export, little is known of the conformational properties and membrane interactions of these highly hydrophobic amino terminal extensions on nearly all exported proteins. The Escherichia coli lambda phage receptor signal sequence was studied in phospholipid monolayers by circular dichroism and Fourier transform infrared spectroscopy; the signal peptide was shown to prefer an alpha-helical conformation when inserted into the lipid phase. However, interaction with the lipid surface without insertion induced the signal sequence, which is unstructured in bulk aqueous solution, to adopt a beta structure. These observations are combined in a model for the initial steps in signal sequence-membrane interaction in vivo. 相似文献
108.
Güdel M Briggs KR Montmerle T Audard M Rebull L Skinner SL 《Science (New York, N.Y.)》2008,319(5861):309-312
Most stars form as members of large associations within dense, very cold (10 to 100 kelvin) molecular clouds. The nearby giant molecular cloud in Orion hosts several thousand stars of ages less than a few million years, many of which are located in or around the famous Orion Nebula, a prominent gas structure illuminated and ionized by a small group of massive stars (the Trapezium). We present x-ray observations obtained with the X-ray Multi-Mirror satellite XMM-Newton, revealing that a hot plasma with a temperature of 1.7 to 2.1 million kelvin pervades the southwest extension of the nebula. The plasma flows into the adjacent interstellar medium. This x-ray outflow phenomenon must be widespread throughout our Galaxy. 相似文献
109.
110.
V M Briggs 《Science (New York, N.Y.)》1987,238(4824):176-180
In sharp contrast with the experiences of all other industrialized nations, the size of the labor force of the United States is growing rapidly while, simultaneously, its age, gender, and ethnic composition are changing markedly. Consequently, human resource issues present an unprecedented challenge in the nation's quest to achieve a fully employed and equitable society. New public policies that focus on labor market adjustment policies will be required if these developments are to be a boon rather than a bane to the emerging postindustrial economy. 相似文献