Seismic slip and down-dip strain rates in wadati-benioff zones     

Bevis M 《Science (New York, N.Y.)》1988,240(4857):1317-1319

The rate of accumulation of seismic moment in Wadati-Benioff zones is used to estimate strain rates in subducting slabs that are sinking through the asthenosphere. Between depths of 75 and 175 kilometers a typical down-dip strain rate is about 10(-15) per second, which implies that slabs in this depth range typically accumulate strain of order 10(-1). This result is in accord with geometrical arguments that subducted slabs must experience large membrane strains to deform to their observed shapes. Mantle seismicity (repeated catastrophic shear failure) is apparently a primary mechanism by which large membrane strains accumulate in the cold cores of subducting slabs. Slabs are penetratively deformed, and they have low flexural rigidity compared to oceanic plates at the earth's surface.  相似文献   

NASA Delays Space Telescope     

Waldrop MM 《Science (New York, N.Y.)》1988,241(4871):1281

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Taking Back the Night: The bad news is that the astronomical environment is steadily being degraded; the good news is that the astronomers have allies     

Waldrop MM 《Science (New York, N.Y.)》1988,241(4871):1288-1289

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The meadowcroft rockshelter     

Adovasio JM  Carlisle RC 《Science (New York, N.Y.)》1988,239(4841):713-714

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Anglo-French nuclear missile under study     

Dickson D 《Science (New York, N.Y.)》1988,239(4841):720-721

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Europeans decide on a trip to saturn     

Dickson D 《Science (New York, N.Y.)》1988,242(4884):1375-1376

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Dynamic properties of molecularly thin liquid films     

Israelachvili JN  McGuiggan PM  Homola AM 《Science (New York, N.Y.)》1988,240(4849):189-191

An experimental technique is described for simultaneously measuring the static and dynamic interactions of very thin liquid films between two surfaces as they are moved normally or laterally relative to each other. Film thickness can be measured and controlled to 1 angstrom. Initial results are presented of the transition in the physical properties of liquid films only one molecular layer thick to thicker films whose properties are practically indistinguishable from the bulk. In particular, the results show that two molecularly smooth surfaces, when close together in simple liquids, slide (shear) past each other while separated by a discrete number of molecular layers, and that the frictional force is "quantized" with the number of layers.  相似文献   

Mayor Seeks to Polish the "S" in Unesco: The U.N. agency's new director-general, Federico Mayor, says he wants to sharpen the focus of its science programs on two areas: "frontiers of science" and environmental problems     

Dickson D 《Science (New York, N.Y.)》1988,240(4849):137-138

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NTIS: Up for Grabs Again?     

Crawford M 《Science (New York, N.Y.)》1988,239(4845):1236-1237

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Comparative water relations of three successional hardwood species in central Wisconsin     

Abrams MD 《Tree physiology》1988,4(3):263-273

Water relations of co-occurring understory saplings of Quercus ellipsoidalis E.J. Hill, an early successional, xeric species, Populus tremuloides Michx., an early successional, mesic species, and Acer rubrum L., a late successional species that occurs on both wet and dry sites, were evaluated on four dates during the 1986 growing season. The understory was characterized by high soil water content, low irradiance and low vapor pressure deficit throughout the growing season. Stomatal conductance and calculated transpiration flux were lowest for A. rubrum and highest for P. tremuloides and Q. ellipsoidalis. Except early in the growing season, leaf water potentials were lower in P. tremuloides than in the other species. Populus tremuloides had the highest bulk modulus of elasticity, Q. ellipsoidalis the lowest. Over the growing season, Populus tremuloides and Q. ellipsoidalis, but not A. rubrum, exhibited a decrease in osmotic potential at both full and zero turgor. Of the three species, Populus tremuloides exhibited the sharpest decrease in leaf water potential and turgor pressure with decreasing relative water content.  相似文献