Mantle phase changes and deep-earthquake faulting in subducting lithosphere   总被引：2，自引：0，他引：2  

Kirby SH  Durham WB  Stern LA 《Science (New York, N.Y.)》1991,252(5003):216-225

Inclined zones of earthquakes are the primary expression of lithosphere subduction. A distinct deep population of subduction-zone earthquakes occurs at depths of 350 to 690 kilometers. At those depths ordinary brittle fracture and frictional sliding, the faulting processes of shallow earthquakes, are not expected. A fresh understanding of these deep earthquakes comes from developments in several areas of experimental and theoretical geophysics, including the discovery and characterization of transformational faulting, a shear instability connected with localized phase transformations under nonhydrostatic stress. These developments support the hypothesis that deep earthquakes represent transformational faulting in a wedge of olivine-rich peridotite that is likely to persist metastably in coldest plate interiors to depths as great as 690 km. Predictions based on this deep structure of mantle phase changes are consistent with the global depth distribution of deep earthquakes, the maximum depths of earthquakes in individual subductions zones, and key source characteristics of deep events.  相似文献   

Io volcanism seen by new horizons: a major eruption of the Tvashtar volcano     

Spencer JR  Stern SA  Cheng AF  Weaver HA  Reuter DC  Retherford K  Lunsford A  Moore JM  Abramov O  Lopes RM  Perry JE  Kamp L  Showalter M  Jessup KL  Marchis F  Schenk PM  Dumas C 《Science (New York, N.Y.)》2007,318(5848):240-243

Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition.  相似文献   

1 alpha, 25-Dihydroxyvitamin D3 nuclear receptors in pituitary     

H A Gelbard  P H Stern  D C U'Prichard 《Science (New York, N.Y.)》1980,209(4462):1247-1249

Specific binding of 1 alpha,25-dihydroxyvitamin D(3) was found in nuclear and cytosol fractions of the bovine pituitary. For nuclear binding. the dissociation constant was 0.1 namomole per liter, and maximum binding was 104 femtomoles per milligram of protein. In competition studies, 25-hydroxyvitamin D(3) was 300 times weaker than 1 alpha,25-dihydroxyvitamin D(3). The existence of high-affinity sites supports a physiologic role for 1 alpha,25-dihydroxyvitamin D(3) in the pituitary.  相似文献   

The Origin of the Great Bend of the Nile from SIR-C/X-SAR Imagery     

RJ Stern  MG Abdelsalam 《Science (New York, N.Y.)》1996,274(5293):1696-1698

The course of the Nile in northern Sudan follows a contorted path through Precambrian bedrock. Radar imagery shows that basement structures control the river's course in this region. Northward-flowing segments follow Precambrian fabrics, whereas east-west segments follow faults of much younger age. These faults may reflect recent uplift of the Nubian Swell and deflection of the river to the southwest to form the great bend of the Nile.  相似文献   

The struggle to govern the commons   总被引：8，自引：0，他引：8  

Dietz T  Ostrom E  Stern PC 《Science (New York, N.Y.)》2003,302(5652):1907-1912

Human institutions--ways of organizing activities--affect the resilience of the environment. Locally evolved institutional arrangements governed by stable communities and buffered from outside forces have sustained resources successfully for centuries, although they often fail when rapid change occurs. Ideal conditions for governance are increasingly rare. Critical problems, such as transboundary pollution, tropical deforestation, and climate change, are at larger scales and involve nonlocal influences. Promising strategies for addressing these problems include dialogue among interested parties, officials, and scientists; complex, redundant, and layered institutions; a mix of institutional types; and designs that facilitate experimentation, learning, and change.  相似文献   

Divalent cations directly affect the conductance of excised patches of rod photoreceptor membrane   总被引：2，自引：0，他引：2  

J H Stern  H Knutsson  P R MacLeish 《Science (New York, N.Y.)》1987,236(4809):1674-1678

Phototransduction in rod cells is likely to involve an intracellular messenger system that links the absorption of light by rhodopsin to a change in membrane conductance. The direct effect of guanosine 3',5'-monophosphate (cGMP) on excised patches of rod outer segment membrane strongly supports a role for cGMP as an intracellular messenger in phototransduction. It is reported here that magnesium and calcium directly affect the conductance of excised patches of rod membrane in the absence of cGMP and that magnesium, applied to intact rod cells, blocks a component of the cellular light response. The divalent cation-suppressed conductance in excised patches showed outward rectification and cation-selective permeability resembling those of the light-suppressed conductance measured from the intact rod cell. The divalent cation-suppressed conductance was partly blocked by a concentration of the pharmacological agent L-cis-diltiazem that blocked all of the cGMP-activated conductance. Divalent cations may act, together with cGMP, as an intracellular messenger system that mediates the light response of the rod photoreceptor cell.  相似文献   

Uranium enrichment     

Stern SA 《Science (New York, N.Y.)》1975,189(4199):251

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The spectrum of comet austin from 910 to 1180 a     

Green JC  Cash W  Cook TA  Stern SA 《Science (New York, N.Y.)》1991,251(4992):408-410

A spectrum of comet Austin (1988 c(1)) has been obtained from 910 to 1180 A. Three bright emission lines were detected, including a forbidden oxygen line (1128 A), which are attributable to radiative pumping of neutral oxygen by solar Lyman beta. The relative strengths of the observed features should prove to be a useful diagnostic of the physical conditions and radiation fields in cometary comae. In addition, the absence of strong spectral features from highly volatile species such as He, Ar, or N(2) can be used to place constraints on the thermal environment under which the comet was formed and has been processed.  相似文献   

Polar lightning and decadal-scale cloud variability on Jupiter     

Baines KH  Simon-Miller AA  Orton GS  Weaver HA  Lunsford A  Momary TW  Spencer J  Cheng AF  Reuter DC  Jennings DE  Gladstone GR  Moore J  Stern SA  Young LA  Throop H  Yanamandra-Fisher P  Fisher BM  Hora J  Ressler ME 《Science (New York, N.Y.)》2007,318(5848):226-229

Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter.  相似文献   

Influence of antibody treatment of Campylobacter jejuni on the dose required to colonize chicks   总被引：1，自引：0，他引：1  

N J Stern  R J Meinersmann  H W Dickerson 《Avian diseases》1990,34(3):595-601

This study was designed to clarify the role of antibodies in controlling chicken colonization by Campylobacter jejuni. Cecal colonization by C. jejuni was compared after the organism was exposed either to phosphate-buffered saline, normal rabbit serum, rabbit hyperimmune anti-C. jejuni serum, or anti-C. jejuni antibodies extracted from chicken bile. Antibodies from chicken bile were extracted by affinity absorption against outer-membrane proteins from the challenge organism. Sera were heated 1 hour at 56 C to destroy complement activity. Bacterial inoculum levels were enumerated after 1 hour exposure at 4 C to the various treatments. The heated sera and the bile antibodies were not bactericidal, and bacterial agglutination was not evident. Serial dilutions of the antibody-treated C. jejuni were given by gavage into 1-day-old chicks. Six days later, the ceca were removed from the chicks, and samples were cultured on Campylobacter-charcoal differential agar. The colonization dose-50% was increased by twofold to 160-fold when the organism was preincubated with hyperimmune antiserum or the bile antibodies as compared with preincubation with phosphate-buffered saline. We conclude that antibodies inhibit chicken cecal colonization by C. jejuni.  相似文献