Role of land-surface changes in arctic summer warming   总被引：2，自引：0，他引：2  

Chapin FS  Sturm M  Serreze MC  McFadden JP  Key JR  Lloyd AH  McGuire AD  Rupp TS  Lynch AH  Schimel JP  Beringer J  Chapman WL  Epstein HE  Euskirchen ES  Hinzman LD  Jia G  Ping CL  Tape KD  Thompson CD  Walker DA  Welker JM 《Science (New York, N.Y.)》2005,310(5748):657-660

A major challenge in predicting Earth's future climate state is to understand feedbacks that alter greenhouse-gas forcing. Here we synthesize field data from arctic Alaska, showing that terrestrial changes in summer albedo contribute substantially to recent high-latitude warming trends. Pronounced terrestrial summer warming in arctic Alaska correlates with a lengthening of the snow-free season that has increased atmospheric heating locally by about 3 watts per square meter per decade (similar in magnitude to the regional heating expected over multiple decades from a doubling of atmospheric CO2). The continuation of current trends in shrub and tree expansion could further amplify this atmospheric heating by two to seven times.  相似文献   

Saturn ring particles as dynamic ephemeral bodies     

Davis DR  Weidenschilling SJ  Chapman CR  Greenberg R 《Science (New York, N.Y.)》1984,224(4650):744-747

Although Saturn's rings are within the Roche zone, the accretion of centimeter-sized particles into large aggregates many meters in diameter occurs readily, on a time scale of weeks. These aggregates are disrupted when tidal stresses exceed their very low strengths; thus most of the mass of the ring system is continually processed through a population of large "dynamic ephemeral bodies," which are continually forming and disintegrating. These large aggregates are not at all like the idealized ice spheres often used in modeling Saturn's ring dynamics. Their coefficient of restitution is low, hence they form a monolayer in the ring plane. The optically observable characteristics of the rings are dominated by the swarm of centimeter-sized particles.  相似文献   

Applied physics. Focus on x-ray diffraction     

Chapman HN 《Science (New York, N.Y.)》2008,321(5887):352-353

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Mercury cratering record viewed from MESSENGER's first flyby     

Strom RG  Chapman CR  Merline WJ  Solomon SC  Head JW 《Science (New York, N.Y.)》2008,321(5885):79-81

Morphologies and size-frequency distributions of impact craters on Mercury imaged during MESSENGER's first flyby elucidate the planet's geological history. Plains interior to the Caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages. Smooth plains exterior to Caloris exhibit a crater density approximately 40% less than on interior plains and are thus volcanic and not Caloris impact ejecta. The size distribution of smooth-plains craters matches that of lunar craters postdating the Late Heavy Bombardment, implying that the plains formed no earlier than 3.8 billion years ago (Ga). At diameters less than or equal to 8 to 10 kilometers, secondary impact craters on Mercury are more abundant than primaries; this transition diameter is much larger than that on the Moon or Mars. A low density of craters on the peak-ring basin Raditladi implies that it may be younger than 1 Ga.  相似文献   

THE BRAIN OF THE ORANG     

Chapman HC 《Science (New York, N.Y.)》1880,1(27):326-328

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THE FAUNA OF PORTO RICO     

Chapman FM 《Science (New York, N.Y.)》1899,10(247):419-420

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Serine-7 of the RNA polymerase II CTD is specifically required for snRNA gene expression     

Egloff S  O'Reilly D  Chapman RD  Taylor A  Tanzhaus K  Pitts L  Eick D  Murphy S 《Science (New York, N.Y.)》2007,318(5857):1777-1779

RNA polymerase II (Pol II) transcribes genes that encode proteins and noncoding small nuclear RNAs (snRNAs). The carboxyl-terminal repeat domain (CTD) of the largest subunit of mammalian RNA Pol II, comprising tandem repeats of the heptapeptide consensus Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7, is required for expression of both gene types. We show that mutation of serine-7 to alanine causes a specific defect in snRNA gene expression. We also present evidence that phosphorylation of serine-7 facilitates interaction with the snRNA gene-specific Integrator complex. These findings assign a biological function to this amino acid and highlight a gene type-specific requirement for a residue within the CTD heptapeptide, supporting the existence of a CTD code.  相似文献   

Plasma Corticosteroids: Changes in Concentration after Stimulation of Hippocampus and Amygdala     

Mandell AJ  Chapman LF  Rand RW  Walter RD 《Science (New York, N.Y.)》1963,139(3560):1212

Plasma 17-OH corticosteroid levels were determined before stimulation and at various intervals after stimulation in these limbic sites in patients in whom implanted electrodes had been placed during evaluation for surgical treatment of psychomotor epilepsy. Stimulation of the amygdala was followed by an elevation of plasma 17-hydroxycorticosteroids. Hippocampal stimulation resulted in a decreased corticosteroid level, followed in two instances by a secondary elevation.  相似文献   

Electricity Demand Growth and the Energy Crisis: An analysis of electricity demand growth projections suggests overestimates in the long run     

Chapman D  Mount T  Tyrrell T 《Science (New York, N.Y.)》1972,178(4062):703-708

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Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis     

Han X  Wang CT  Bai J  Chapman ER  Jackson MB 《Science (New York, N.Y.)》2004,304(5668):289-292

The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.  相似文献