Transport in a 2-D saturated porous medium: A new method for particle tracking   总被引：2，自引：0，他引：2  

Frédérick Delay  Hélène Housset-Resche  Gilles Porel  Ghislain de Marsily 《Mathematical Geology》1996,28(1):45-71

A new method for solving the transport equation based on the management of a large numbe of particles in a discretized 2-D domain is presented. The method uses numerical variables to represent the number of particles in a given mesh and is more complex than the 1-D problem. The first part of the paper focuses on the specific management of particles in a 2-D problem. The method also would be valid for three dimensions as long as the medium can be modeled similar to a layered system. As the particles are no longer tracked individually, the algorithm is fast and does not depend on the number of particles present. The numerical tests show that the method is nearly numerical dispersion free and permits accurate calculations even for simulations of low-concentration transport. Because each mesh is considered as a closed system between two successive time steps, it is easy to add adsorption phenomenon without any problem of numerical stability. The model is tested under conditions that are extremely demanding for its operating mode and gives a good fit to analytical solutions. The conditions in which it can be used to best advantage are discussed.  相似文献   

New challenges for north sea research -20 years after FLEX ’76     

Jürgen Sündermann 《Ocean Dynamics》1997,49(2-3):107-108

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Measurement and research method of metallogenic depths of Jiaojia orefield and Linglong orefield Shandong Province, China   总被引：1，自引：0，他引：1  

Guxian Lü 《中国科学D辑(英文版)》1997,40(5):449-455

Taking the contribution of the tectonic force to the total hydrostatic pressure into account, the author puts forward a new method on the calculation of the depth of petrogenesis and metallogenesis which is summarized as follows: first the tectonic added hydrostatic pressured P_s is subtracted from the total hydrostatic pressure P, then using their difference P_r, according to the general method the depth of petrogenesis and metallogenesis can be determined in consideration of lateral constraint. By the new method the following data on the depths of the metallogenesis are obtained: 2 243.6 m (No. I and No. II veins with metallogenic epoch of 105 Ma) and 1 632. 38 m (No. III vein with 105 Ma) for Jiaojia orefield, and 3 454.97 m (NE-trending zone with 213.2 Ma), 1 902.79 III (ENE-trending zone with 100.28 Ma), 1 090.97 m (NE-trending zone with 80.67 Ma) and 720.55 m (NNE-trending zone with 71.86 Ma) for Linglong orefield. Project supported by the Foundation of the State Planning Commission, China and the Foundation of the State Science and Technology Commission, China.  相似文献   

Hypolimnetic density currents traced by sulphur hexafluoride (SF6)     

Jürg W. Schlatter  Alfred Wüest  Dieter M. Imboden 《Aquatic Sciences - Research Across Boundaries》1997,59(3):225-242

The artificial tracer sulphur hexafluoride (SF₆) has been used to study the density-driven deep water exchange between two sill-separated basins of Lake Lucerne, Gersauersee and Urnersee. The sources of the density gradients between the two basins are (1) salinity differences between the major inlets due to the different geology of their drainage areas, and (2) temperature differences due to spatial variation of wind forcing. Wind speeds are generally larger in Urnersee, especially in spring during the so-called Föhn events, when winds blow from the south. In contrast, Gersauersee is protected form these winds. In spring 1989, a total of 630 g of SF₆ was released at 80 to 120 m depth in the small Treib Basin located between Urnersee and Gersauersee. During about 100 days the distribution of SF₆ in the lake was determined by gaschromatography. Two models are used to quantify the exchange flow, (1) a one-box mass balance model for SF₆ in the deep part of Treib Basin, and (2) a one-dimensional diffusion/advection model describing the temporal and vertical temperature variation in Urnersee. According to the first model, the flow into the deep hypolimnion of Urnersee, decreases from 21·10⁶ m³·d^?1 at the end of March to about 8·10⁶ m³·d^?1 in late April. The second model yields similar flow rates. The decrease of the flow rate during spring, confirmed by both approaches, is consistent (1) with the decreasing strength of the density gradient above the sill during spring and early summer, and (2) with hydrographic information collected in Lake Lucerne during other years.  相似文献   

ASPI experiment: measurements of fields and waves on board the INTERBALL-1 spacecraft     

S. Klimov  S. Romanov  E. Amata  J. Blecki  J. Büchner  J. Juchniewicz  J. Rustenbach  P. Triska  L. J. C. Woolliscroft  S. Savin  Yu. Afanas’yev  U. de Angelis  U. Auster  G. Bellucci  A. Best  F. Farnik  V. Formisano  P. Gough  R. Grard  V. Grushin  G. Haerendel  V. Ivchenko  V. Korepanov  H. Lehmann  B. Nikutowski  M. Nozdrachev  S. Orsini  M. Parrot  A. Petrukovich  J. L. Rauch  K. Sauer  A. Skalsky  J. Slominski  J. G. Trotignon  J. Vojta  R. Wronowski 《Annales Geophysicae》1997,15(5):514-527

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and searchcoil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.  相似文献   

A systematic algorithm for obtaining SODAR wind profiles     

S. G. Bradley  S. v. Hünerbein 《Meteorology and Atmospheric Physics》2004,85(1-3):77-84

Summary Current methods of obtaining wind profiles from SODARs generally employ ad hoc strategies for Doppler spectrum peak selection, profile smoothing, and consistency checks. This paper addresses the problem of systematically obtaining vertical profiles of wind vectors from a SODAR. A new approach is to regard every spectrum frequency as a possible estimator of the radial wind component, but to weight these Doppler estimates according to the spectral power at each frequency. This allows the peak detection, smoothing, and assimilation of a priori information to be combined into a constrained linear inversion methodology. The inversion process also allows an estimation of signal-to-noise ratio, degrees of freedom, and information content versus height. Examples are given of profiles obtained using this new inverse method. The relationship to the physical limitations of the SODAR instrument and the atmosphere is discussed.  相似文献   

Composition of Kerogen in Kupferschiefer from Southwest Poland     

孙玉壮 《中国地球化学学报》2004,23(2):101-111

Thirty-seven Kupferschiefer samples from southwestern Poland were analyzed by microscopy, Rock-Eval approach and instrumental neutron activation analysis to understand the geochemical and morphological characteristics of kerogen present in the samples. The analytical results indicate that there are two different types of kerogens. One type was only subjected to thermal alteration processes, and the other was further oxidized after deposition of the sediment.In the oxidized samples migrabitumen was transformed into pyrobitumen. Rock-Eval analyses show a significant decrease in HI values in the oxidized samples and an increase in OI values in relation to the samples that were not influenced by oxidation. Variations in S2 versus Corg contents indicate a change in kerogen from Type II to Type III with progressing oxidation. The presence of pyrobitumen and the depletion of hydrogen in the altered kerogen allow one to conclude that the kerogen was used as hydrogen donor for thermochemical sulfate reduction(TSR).  相似文献   

Simulation of oasis breeze circulation in the arid region of the Northwestern China   总被引：2，自引：0，他引：2  

U Shihua  AN Xingqin  CHEN Yüchun 《中国科学D辑(英文版)》2004,47(Z1)

In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V = 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary,the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis.Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00.  相似文献   

Revising macroseismic data in Switzerland: The December 20, 1720 earthquake in the region of Lake Constance     

Monika Gisler  Donat Fäh  Reto Schibler 《Journal of Seismology》2004,8(2):179-192

Upgrading the Earthquake Catalog of Switzerland (ECOS) included revising the earthquake of 1720. This change has major importance for history and seismology.Although that quake has been the subject of several publications, none was based on critical methods. This re-evaluation of the event is built upon a new and more reliable database established after investigating archives and libraries. Using data from such historical sources, we assigned new site intensities, adopting the criteria established by the European macroseismic scale EMS 98 (Grünthal, 1998).We discovered that the event had been assigned an overestimated intensity, due to interpretation errors in former earthquake catalogs and compilations. We recommend reducing the intensity from I₀= VIII to I₀= VI (EMS 98). The moment magnitude is given as M_W= 4.6. Since the event had been considered the largest for its respective area, downgrading it now will influence the seismic hazard assessment for this region.  相似文献   

Ambiguous Moment Tensors and Radiation Patterns in Anisotropic Media with Applications to the Modeling of Earthquake Mechanisms in W-Bohemia   总被引：3，自引：0，他引：3  

Rössler  D.  Rümpker  G.  Krüger  F. 《Studia Geophysica et Geodaetica》2004,48(1):233-250

Anisotropic material properties are usually neglected during inversions for source parameters of earthquakes. In general anisotropic media, however, moment tensors for pure-shear sources can exhibit significant non-double-couple components. Such effects may be erroneously interpreted as an indication for volumetric changes at the source. Here we investigate effects of anisotropy on seismic moment tensors and radiation patterns for pure-shear and tensile-type sources. Anisotropy can significantly influence the interpretation of the source mechanisms. For example, the orientation of the slip within the fault plane may affect the total seismic moment. Also, moment tensors due to pure-shear and tensile faulting can have similar characteristics depending on the orientation of the elastic tensor. Furthermore, the tensile nature of an earthquake can be obscured by near-source anisotropic properties. As an application, we consider effects of inhomogeneous anisotropic properties on the seismic moment tensor and the radiation patterns of a selected type of micro-earthquakes observed in W-Bohemia. The combined effects of near-source and along-path anisotropy cause characteristic amplitude distortions of the P, S1 and S2 waves. However, the modeling suggests that neither homogeneous nor inhomogeneous anisotropic properties alone can explain the observed large non-double-couple components.The results also indicate that a correct analysis of the source mechanism, in principle, is achievable by application of anisotropic moment tensor inversion.  相似文献