WILBUR CLITONT KNIGHT     

Nelson A 《Science (New York, N.Y.)》1903,18(456):406-409

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The silica balance in the world ocean: a reestimate   总被引：8，自引：0，他引：8  

Tréguer P  Nelson DM  Van Bennekom AJ  Demaster DJ  Leynaert A  Quéguiner B 《Science (New York, N.Y.)》1995,268(5209):375-379

The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teramole = 10(12) moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years.  相似文献   

Intercalation of sea urchin proteins in calcite: study of a crystalline composite material     

Berman A  Addadi L  Kvick A  Leiserowitz L  Nelson M  Weiner S 《Science (New York, N.Y.)》1990,250(4981):664-667

Sea urchin skeletal elements are composed of single crystals of calcite. Unlike their synthetic counterparts, these crystals do not have well-developed cleavage and are consequently much more resistant to fracture. This phenomenon is due in part to the presence of acidic glycoproteins occluded within the crystals. By means of x-ray diffraction with synchrotron radiation, it is shown that the presence of the protein in synthetic calcite only slightly decreases the coherence length but significantly increases the angular spread of perfect domains of the crystals. In biogenic calcite, the coherence length is 1/3 to 1/4 as much as that in synthetic calcite and the angular spread is 20 to 50 times as wide. It is proposed that the presence of macromolecules concentrated at mosaic boundaries that are oblique to deavage planes is responsible for the change in fracture properties. These results may be important in the material sciences, because of the unusual nature of this material, namely, a composite based on the controlled intercalation of macromolecules inside single-crystal lattices.  相似文献   

Liver Tumors in Rats Fed Thiourea or Thioacetamide     

Fitzhugh OG  Nelson AA 《Science (New York, N.Y.)》1948,108(2814):626-628

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Revisiting the taxonomic impediment     

de Carvalho MR  Bockmann FA  Amorim DS  de Vivo M  de Toledo-Piza M  Menezes NA  de Figueiredo JL  Castro RM  Gill AC  McEachran JD  Compagno LJ  Schelly RC  Britz R  Lundberg JG  Vari RP  Nelson G 《Science (New York, N.Y.)》2005,307(5708):353

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Spatial Variability of Turbulent Mixing in the Abyssal Ocean   总被引：3，自引：0，他引：3  

KL Polzin  JM Toole  JR Ledwell  RW Schmitt 《Science (New York, N.Y.)》1997,276(5309):93-96

Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.  相似文献   

Fuel savings by lowering thermostats     

Reed JW  Ferrar TA  Nelson JP 《Science (New York, N.Y.)》1975,189(4207):1015

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Australia: education and science are looking up "down under"     

Nelson B 《Science (New York, N.Y.)》1968,160(3824):170-173

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Mazama ash in the northeastern pacific     

Nelson CH  Kulm LD  Carlson PR  Duncan JR 《Science (New York, N.Y.)》1968,161(3836):47-49

Volcanic glass in marine sediments off Oregon and Washington correlates with continental deposits of Mount Mazama ash by stratigraphic position, refractive index, and radiocarbon dating. Ash deposited in the abyssal regions by turbidity currents is used for tracing of the dispersal routes of postglacial sediments and for evaluation of marine sedimentary processes.  相似文献   

Pteridinium and the precambrian-cambrian boundary     

Ford TD  Cloud PE  Nelson CA 《Science (New York, N.Y.)》1967,157(3791):957-958

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