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951.
952.
M. Stepanova T. Vucina-Parga E. Antonova I. Ovchinnikov Y. Yermolaev 《Journal of Atmospheric and Solar》2005,67(17-18):1815
Fluctuations of the plasma bulk velocity across the plasma sheet are studied using single-point measurements from the Corall instrument on board the Interball/Tail satellite. Several hour-long intervals of continuous data corresponding to quiet geomagnetic conditions and different phases of isolated substorms are analyzed. The plasma sheet flow appears to be strongly turbulent, i.e. dominated by fluctuations that are unpredictable. Corresponding eddy diffusion coefficients were obtained as a function of the autocorrelation time and rms velocity of the fluctuations. It was found that the amplitude of the turbulence and the values of eddy-diffusion coefficients increase significantly during substorm growth and expansion phases and they decrease to their initial level during the recovery phase. We also studied a relationship between the eddy-diffusion coefficients and the absolute value of the geomagnetic field, also measured by the Interball/Tail satellite. It was found that this relationship varies depending on the phase of substorm, indicating possible change in the turbulence regimen with substorm phase. 相似文献
953.
Curie-point depth from spectral analysis of magnetic data in central-southern Europe 总被引:3,自引:0,他引:3
The basal depth of the outer layer with internal magnetic sources was calculated from magnetic data available within a roughly 500 km wide and 1200 km long area, running from central Germany to southern Italy. The dataset, deriving from different aeromagnetic surveys, is reduced to the reference altitude of 3000 m a.s.l. and a reference year of 1980.0. The adopted method, which transforms the spatial data into the frequency domain, provides a relationship between the two-dimensional spectrum of the magnetic anomalies and the top and centroid depths of the magnetic sources. The magnetic layer bottom depth (MLBD) thus obtained is 29-33 km deep in the stable areas (central Europe Variscan units, Corsica-Sardinia Variscan block) and corresponds to the Moho, having an average temperature of 560 °C. From the Alps to the Apennines, MLBD ranges between 22 and 28 km and is clearly shallower than the Moho. In these units, the wide variation of MLBD appears to be compatible with the presence of shallow magnetised bodies, consisting of lower crustal rocks (Ivrea-Verbano zone), ophiolitic units (Penninic zone and Voltri Massif) and intrasedimentary basic volcanic bodies (Po Basin). An average value of 25 km can be attributed to MLBD, which corresponds to a temperature of 550 °C. In the peri-Tyrrhenian zone and the Ligurian Sea, MLBD is below the Moho, which ranges from 17 to 20 km depth, and it has a temperature matching approximately to the Curie temperature of magnetite (580 °C). 相似文献
954.
955.
W. WU S. S. Y. WANG 《国际泥沙研究》2005,20(3):233-243
1INTRODUCTION A headcut is a vertical or near-vertical drop or discontinuity on the channel bed of a stream,rill or gully,at which a free overfall flow often occurs,as shown in Fig.1.A headcut is usually eroded by the action of hydraulic stress,basal sapping,weathering,or the combination of these processes.Headcut erosion can accelerate soil loss,increase sediment yields in streams,damage earthen spillways,and disturb bank stability.Therefore,the prediction of headcut migration is a very … 相似文献
956.
Y. Viswanadham 《Boundary-Layer Meteorology》1979,17(4):537-544
Values of Richardson number (Ri) and the wind profile curvature () in the atmospheric surface layer are evaluated from experimental data. The relationship between Ri and shows some scatter, but gives agreement with the theoretical relation derived by Businger et al. (1971). 相似文献
957.
Rory O. R. Y. Thompson 《Dynamics of Atmospheres and Oceans》1979,4(1):45-55
Pollard et al. (1973) proposed a closure hypothesis for the entrainment process in the stress-mixed layer of a stratified fluid. Some laboratory experiments suitable for testing the hypothesis were carried out by Kantha et al. (1977) and by Kato and Phillips (1969). In the early period of each experiment, before side-wall friction becomes important, these experiments support the closure hypothesis, with a critical Froude number close to 1, perhaps F = 1.2 ± 0.2. 相似文献
958.
Y S O’Reilly 《中国科学D辑(英文版)》2006,49(9):926-937
The partial melting and metasomatism are two most important geological processes of changing chemical compositions of mantle. Extracting partial melt from primitive mantle leads residual mantle to deplete in- compatible elements, whereas the metasomatism … 相似文献
959.
Organic carbon and nitrogen stable isotopes in the intertidal sediments from the Yangtze Estuary, China 总被引:2,自引:0,他引:2
The natural isotopic compositions and C/N elemental ratios of sedimentary organic matter were determined in the intertidal flat of the Yangtze Estuary. The results showed that the ratios of carbon and nitrogen stable isotopes were respectively −29.8‰ to − 26.0‰ and 1.6‰–5.5‰ in the flood season (July), while they were −27.3‰ to − 25.6‰ and 1.7‰–7.8‰ in the dry season (February), respectively. The δ13C signatures were remarkably higher in July than in February, and gradually increased from the freshwater areas to the brackish areas. In contrast, there were relatively complex seasonal and spatial changes in stable nitrogen isotopes. It was also reflected that δ15N and C/N compositions had been obviously modified by organic matter diagenesis and biological processing, and could not be used to trace the sources of organic matter at the study area. In addition, it was considered that the mixing inputs of terrigenous and marine materials generally dominated sedimentary organic matter in the intertidal flat. The contribution of terrigenous inputs to sedimentary organic matter was roughly estimated according to the mixing balance model of stable carbon isotopes. 相似文献
960.
Upscaling is a major issue regarding mechanical and transport properties of rocks. This paper examines three issues relative
to upscaling. The first one is a brief overview of Effective Medium Theory (EMT), which is a key tool to predict average rock
properties at a macroscopic scale in the case of a statistically homogeneous medium. EMT is of particular interest in the
calculation of elastic properties. As discussed in this paper, EMT can thus provide a possible way to perform upscaling, although
it is by no means the only one, and in particular it is irrelevant if the medium does not adhere to statistical homogeneity.
This last circumstance is examined in part two of the paper. We focus on the example of constructing a hydrocarbon reservoir
model. Such a construction is a required step in the process of making reasonable predictions for oil production. Taking into
account rock permeability, lithological units and various structural discontinuities at different scales is part of this construction.
The result is that stochastic reservoir models are built that rely on various numerical upscaling methods. These methods are
reviewed. They provide techniques which make it possible to deal with upscaling on a general basis. Finally, a last case in
which upscaling is trivial is considered in the third part of the paper. This is the fractal case. Fractal models have become
popular precisely because they are free of the assumption of statistical homogeneity and yet do not involve numerical methods.
It is suggested that using a physical criterion as a means to discriminate whether fractality is a dream or reality would
be more satisfactory than relying on a limited data set alone. 相似文献