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921.
The authors identify and describe the following global forces of nature driving the Earth’s climate: (1) solar radiation as a dominant external energy supplier to the Earth, (2) outgassing as a major supplier of gases to the World Ocean and the atmosphere, and, possibly, (3) microbial activities generating and consuming atmospheric gases at the interface of lithosphere and atmosphere. The writers provide quantitative estimates of the scope and extent of their corresponding effects on the Earth’s climate. Quantitative comparison of the scope and extent of the forces of nature and anthropogenic influences on the Earth’s climate is especially important at the time of broad-scale public debates on current global warming. The writers show that the human-induced climatic changes are negligible. 相似文献
922.
3D behaviour of contamination in landfill sites using 2D resistivity/IP imaging: case studies in Portugal 总被引:2,自引:0,他引:2
Aiming at defining a valid spatial contamination model, resistivity and induced polarization (IP) measurements were used to
investigate contamination plumes in the vicinity of two municipal landfills (Ovar and ílhavo). Previous geophysical surveys
and underground water samples confirmed the contamination. However 2D resistivity/IP surveys enabled in obtaining a more accurate
spatial model. The Ovar survey consisted of two profiles with nine Wenner soundings each; the ílhavo survey was carried out
along two individual lines using a Wenner standard pseudo-section. In both situations, negative IP values were found associated
with positive IP values, which can be explained mainly by 2D or 3D geometric effects caused by the presence of the conductive
plumes. The data were modelled using a 2D inversion program (RES2DINV) and the resulting resistivity and chargeability distributions
were displayed as pseudo-sections. The resistivity and chargeability pseudo-sections define the contamination plumes and the
sedimentary structure. These case studies illustrate the advantages of 2D resistivity/IP surveys for the mapping of shape
and dimension of contamination associated with landfills. 相似文献
923.
924.
The integrated radio luminosities of 311 long-period (P > 0.1 s) and 27 short-period (P < 0.1 s) pulsars have been calculated using a new compilation of radio spectra. The luminosities are in the range 1027 ? 1030 erg/s for 88% of the long-period pulsars and 1028 ? 1031 erg/s for 88% of the short-period pulsars. We find a high correlation between the luminosity L and the estimate L 1 = S 400 d 2 from the catalog of Taylor et al. The factor η for the transformation of the rotational energy of the neutron star into radio emission increases-decreases with increasing period for long-period and short-period pulsars. The mean value of η is ?3.73 for the long-period and ?4.85 for short-period pulsars. No dependence was found between L and the pulsar’s kinematic age t k = |z|/〈v z〉, where |z| and 〈v z〉 = 300 km/s are the pulsars’ height above the plane of the Galaxy and mean velocity. A dependence of L on the rate of rotational energy losses ? was found for both groups of pulsars. It is shown that L ∝ ? 1/3 for the entire sample. The pulsar luminosity function is constructed, and the total number and birth rate of pulsars in the Galaxy are calculated. 相似文献
925.
926.
Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system 总被引:1,自引:0,他引:1
O. M. Rosen L. K. Levskii D. Z. Zhuravlev A. Ya. Rotman Z. V. Spetsius A. F. Makeev N. N. Zinchuk A. V. Manakov V. P. Serenko 《Stratigraphy and Geological Correlation》2006,14(6):581-601
Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced. 相似文献
927.
S-S. Xu A. F. Nieto-Samaniego S. A. Alaniz-Álvarez L. G. Velasquillo-Martínez 《International Journal of Earth Sciences》2006,95(5):841-853
The power-law exponent (n) in the equation: D=cL
n
, with D = maximum displacement and L = fault length, would be affected by deviations of fault trace length. (1) Assuming n=1, numerical simulations on the effect of sampling and linkage on fault length and length–displacement relationship are done in this paper. The results show that: (a) uniform relative deviations, which means all faults within a dataset have the same relative deviation, do not affect the value of n; (b) deviations of the fault length due to unresolved fault tip decrease the values of n and the deviations of n increase with the increasing length deviations; (c) fault linkage and observed dimensions either increase or decrease the value of n depending on the distribution of deviations within a dataset; (d) mixed deviations of the fault lengths are either negative or positive and cause the values of n to either decrease or increase; (e) a dataset combined from two or more datasets with different values of c and orders of magnitude also cause the values of n to deviate. (2) Data including 19 datasets and spanning more than eight orders of fault length magnitudes (10−2–105 m) collected from the published literature indicate that the values of n range from 0.55 to 1.5, the average value being 1.0813, and the peak value of n
d (double regression) is 1.0–1.1. Based on above results from the simulations and published data, we propose that the relationship between the maximum displacement and fault length in a single tectonic environment with uniform mechanical properties is linear, and the value of n deviated from 1 is mainly caused by the sampling and linkage effects. 相似文献
928.
Cyclicity in the Main and Upper Zones of the Bushveld Complex, South Africa: Crystallization from a Zoned Magma Sheet 总被引:9,自引:0,他引:9
The major element composition of plagioclase, pyroxene, olivine,and magnetite, and whole-rock 87Sr/86Sr data are presented forthe uppermost 2·1 km of the layered mafic rocks (upperMain Zone and Upper Zone) at Bierkraal in the western BushveldComplex. Initial 87Sr/86Sr ratios are near-constant (0·7073± 0·0001) for 24 samples and imply crystallizationfrom a homogeneous magma sheet without major magma rechargeor assimilation. The 2125 m thick section investigated in drillcore comprises 26 magnetitite and six nelsonite (magnetiteilmeniteapatite)layers and changes up-section from gabbronorite (An72 plagioclase;Mg# 74 clinopyroxene) to magnetiteilmeniteapatitefayaliteferrodiorite (An43; Mg# 5 clinopyroxene; Fo1 olivine). The overallfractionation trend is, however, interrupted by reversals characterizedby higher An% of plagioclase, higher Mg# of pyroxene and olivine,and higher V2O5 of magnetite. In the upper half of the successionthere is also the intermittent presence of cumulus olivine andapatite. These reversals in normal fractionation trends definethe bases of at least nine major cycles. We have calculateda plausible composition for the magma from which this entiresuccession formed. Forward fractional crystallization modelingof this composition predicts an initial increase in total iron,near-constant SiO2 and an increasing density of the residualmagma before magnetite crystallizes. After magnetite beginsto crystallize the residual magma shows a near-constant totaliron, an increase in SiO2 and decrease in density. We explainthe observed cyclicity by bottom crystallization. Initiallymagma stratification developed during crystallization of thebasal gabbronorites. Once magnetite began to crystallize, periodicdensity inversion led to mixing with the overlying magma layer,producing mineralogical breaks between fractionation cycles.The magnetitite and nelsonite layers mainly occur within fractionationcycles, not at their bases. In at least two cases, crystallizationof thick magnetitite layers may have lowered the density ofthe basal layer of melt dramatically, and triggered the proposeddensity inversion, resulting in close, but not perfect, coincidenceof mineralogical breaks and packages of magnetitite layers. KEY WORDS: layered intrusion; mineral chemistry; isotopes; magma; convection; differentiation 相似文献
929.
B. Tapley J. Ries S. Bettadpur D. Chambers M. Cheng F. Condi B. Gunter Z. Kang P. Nagel R. Pastor T. Pekker S. Poole F. Wang 《Journal of Geodesy》2005,79(8):467-478
A new generation of Earth gravity field models called GGM02 are derived using approximately 14 months of data spanning from
April 2002 to December 2003 from the Gravity Recovery And Climate Experiment (GRACE). Relative to the preceding generation,
GGM01, there have been improvements to the data products, the gravity estimation methods and the background models. Based
on the calibrated covariances, GGM02 (both the GRACE-only model GGM02S and the combination model GGM02C) represents an improvement
greater than a factor of two over the previous GGM01 models. Error estimates indicate a cumulative error less than 1 cm geoid
height to spherical harmonic degree 70, which can be said to have met the GRACE minimum mission goals.
Electronic Supplementary Material Supplementary material is available in the online version of this article at 相似文献
930.
Pieraccini M. Fratini M. Parrini F. Pinelli G. Atzeni C. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(1):28-30
The authors propose the use of a high-speed interferometric radar for remotely measuring both transient displacements and steady-state vibrations of architectural heritage structures in order to test their stability conditions. Demonstrative results of application of the technique to a prominent cultural heritage artwork, the tower of Giotto in Florence, Italy, are reported. 相似文献