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931.
932.
933.
934.
The error of closure in the 2000 census, or the difference between estimated and enumerated populations, poses special problems for public agencies that rely on census data. Nationally and at the state level, populations were only slightly underestimated, but underestimations were high in rapidly growing counties in the South and intermontaine West, as well as in New York City. Race‐specific estimates proved far less reliable, with severe overestimates and underestimates of all racial groups in various counties nationwide. We offer explanations for the estimation error and discuss its impact on cancer rates and trends and its implications for cancer surveillance research. 相似文献
935.
The Influence of Strong-Motion Duration on the Seismic Response of Masonry Structures 总被引:2,自引:3,他引:2
Julian J. Bommer Guido Magenes Jonathan Hancock Paola Penazzo 《Bulletin of Earthquake Engineering》2004,2(1):1-26
The influence of strong-motion duration on the response of saturated soils is clearly recognised and accounted for in the
assessment of liquefaction potential. The degree to which duration of shaking influences damage to structures, however, remains
a topic of debate, with resolution of the issue complicated by the variety of definitions of duration and the variety of structural
behaviours, as well as the difficulty of decoupling the specific effect of duration from other features of the ground motion.
A suite of seven structural models with strength and stiffness degrading characteristics, designed to reflect the seismic
behaviour of masonry structures commonly encountered in many parts of Europe, are analysed using a suite of almost 500 strong-motion
accelerograms. Correlations are explored between the damage, measured in terms of the strength degradation, and a range of
strong-motion parameters, demonstrating that Arias intensity and spectral acceleration at the fundamental initial period of
the structure are both reasonably good damage indicators for such structures. A significantly improved correlation is obtained
by using the elastic spectral accelerations averaged over a period range from the initial period of the structure to a value
approximately three times greater, reflecting the stiffness degradation as the shaking progresses. The scatter in the correlation
is shown to be partially explained by differences in duration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
936.
Relative oxidation states of magmas inferred from Ce(IV)/Ce(III) in zircon: application to porphyry copper deposits of northern Chile 总被引:15,自引:2,他引:15
Julian R. Ballard Michael J. Palin Ian H. Campbell 《Contributions to Mineralogy and Petrology》2002,144(3):347-364
Major- and trace-element compositions of zircons and whole rocks from 14 barren and seven ore-bearing calc-alkaline intrusions from the Chuquicamata-El Abra porphyry copper belt of northern Chile have been measured in situ by excimer laser ablation (ELA) ICP-MS. These data permit the Ce(IV)/Ce(III) ratio within zircon to be calculated using a lattice-strain model for mineral-melt partitioning of Ce(IV) and Ce(III). Zircon Ce(IV)/Ce(III) and EuN/EuN* ratios, and by inference magmatic oxidation states, generally increase from older, mafic to younger, felsic units. Within this sequence, porphyry copper mineralization is directly associated only with intrusions with zircon Ce(IV)/Ce(III)>300 and EuN/EuN*>0.4. Such trends can be understood in terms of interdependent relations between oxygen fugacity, sulfur speciation and solubility, and chalcophile element partitioning in silicate magmas. Because zircon occurs in most calc-alkaline intrusions and is resistant to subsolidus alteration, zircon Ce(IV)/Ce(III) ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic-hydrothermal Cu-Au mineralization. The approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks. 相似文献
937.
Francis J. Merceret 《Boundary-Layer Meteorology》1977,11(1):121-123
Small-scale turbulence measurements above the top of the boundary layer in Hurricane Eloise (1975) showed an anomalous peak in the power spectrum of horizontal velocity fluctuation at a scale of 20 cm. Double diffusive convection is suggested as the most reasonable explanation for the presence of the peak. 相似文献
938.
Claude J. Allègre Michel Treuil Jean-François Minster Bernard Minster Francis Albarède 《Contributions to Mineralogy and Petrology》1977,60(1):57-75
This paper describes an extended application of the Rayleigh distillation law to trace element behavior in a fractional crystallization sequence. Using a trace element with a very low bulk partition coefficient as a reference (as suggested by Anderson and Greenland, 1969, and extended by Treuil and Varet, 1973), we can derive bulk partition coefficients for other elements and, in turn, the mineralogical composition of the cumulates. Trace elements with large D, such as Ni and Cr, further constrain the system, and we can deduce the initial composition of the magma. An example of this technique is shown for Terceira Island in the Azores.Contribution IPGNS no 229Now at Dept. of Geological Sciences, California Institute of Technology, Pasadena, California, USA 相似文献
939.
940.
Annie Michard-Vitrac Francis Albarede Christian Dupuis Hugh P. Taylor Jr 《Contributions to Mineralogy and Petrology》1980,72(1):57-72
The Maladeta plutonic complex formed during the latest stages of the Variscan orogeny. It was emplaced into the Paleozoic sedimentary sequence of the Pyrenees. The eastern part, investigated in the present study, consists of an early intrusion of cumulate gabbronorites followed in order of emplacement by the main biotite-hornblende granodiorite, which was itself intruded by two small stocks of two-mica cordierite granite. An 87Rb-87Sr isochron dates the granodiorite at 277±7 m.y. with an initial (87Sr/86Sr)o ratio of 0.7117±3. Gabbroic rocks have lower strontium initial ratios, down to 0.7092, while those of granite range from that of the granodiorite up to about 0.715. The three rock types have distinctive 18O values: 8.7 to 9.6 for the gabbronorites, 9.4 to 10.4 for the granodiorites and 10.3 to 11.8 for the granites. Lead isotopic compositions of rocks and feldspars are all radiogenic. Feldspars give consistent Pb model ages around 280 m.y., with and values of about 9.7 and 4.05, respectively. No pristine, mantle-derived magma was found among the investigated samples and the rocks cannot be related to one another by any simple mechanism of fractional crystallization. Some type of mixing process involving two end members seems to be required: a high-18O, high-87Sr material that is clearly of crustal origin, and a lower-18O, lower-87Sr end member derived from the mantle. Examination of various mixing models does not support magma mixing nor assimilation of crustal rocks by a mafic magma. The most acceptable model involves melting at different levels of a vertically-zoned source in the continental crust; this source was formed by mixing between mantle-derived magmas and crustal metasediments. This material was apparently thickened, tectonically downwarped and partially melted. None of the Maladeta magma-types appear to have been derived at a consuming plate boundary.Contribution Number 3280, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA 相似文献