Influence of hydraulic conductivity on communities of microorganisms and invertebrates in porous media: a case study in drinking water slow sand filters   总被引：3，自引：0，他引：3  

Laurie Mauclaire  Andreas Schürmann  Florian Mermillod-Blondin 《Aquatic Sciences - Research Across Boundaries》2006,68(1):100-108

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Mineralogical alteration and associated permeability changes induced by a high-pH plume: Modeling of a granite core infiltration experiment     

Josep M. Soler  Urs K. Mäder 《Applied Geochemistry》2007

Within the framework of the HPF project (Hyperalkaline Plume in Fractured Rock) at the Grimsel Test Site (Switzerland), a small scale core infiltration experiment was performed at the University of Bern. A high-pH solution was continuously injected, under a constant pressure gradient, into a cylindrical core of granite containing a fracture. This high-pH solution was a synthetic version of solutions characteristic of early stages in the degradation of cement. The interaction between the rock and the solutions was reflected by significant changes in the composition of the injected solution and a decrease in the permeability of the rock. Changes in the mineralogy and porosity of the fault gouge filling the fracture were only minor. One-dimensional reactive transport modeling, using a modified version of the GIMRT code, was used to interpret the results of the experiment. Dispersive and advective solute transport, mineral reaction kinetics and a coupling between porosity and permeability changes were taken into account. In order to obtain a reasonable agreement between models and experimental results, reactive surface areas of the order of 10⁵ m²/m³ rock had to be used. These values are much smaller than the values measured for the fault gouge filling the fracture, which are in the order of 10⁶–10⁷ m²/m³ rock. However, the results could be improved by adding a small fraction of fine grained mineral, which could explain the high initial peaks in Al and Si concentration. With the inclusion of this fine grained fraction, the initial surface areas in the model were within the range of the measured specific surface areas of the fault gouge. The fact that the decrease in permeability was significant despite the minor changes in mineralogy, suggests that permeability may be controlled by changes in the structure of the rock (pore geometries) rather than by only the bulk volumetric (porosity) changes.  相似文献   

Affine distortion of small GPS networks with large height differences     

Steffen Schön 《GPS Solutions》2007,11(2):107-117

GPS is a promising tool for real-time monitoring of deformations of slopes or large structures. However, remaining systematic effects in GPS phase observations after double differencing and application of a priori models affect the resulting coordinates. They complicate the proper separation of the actual deformations from pseudo-deformations induced by the systematic effects. This paper shows that for small monitoring networks (baseline lengths <5 km) only affine distortions of the network geometry are generated by the remaining distance dependent systematic effects, e.g. unmodelled tropospheric and ionospheric propagation effects, or satellite orbit errors. Hence, a generic correction model is given by a three-dimensional affine transformation involving a maximum of 12 transformation parameters. For the determination of these parameters, four high quality GPS stations are necessary which are not affected by the actual deformations to be monitored. Based on the analysis of network geometries of synthetic GPS networks with large height differences and considering the physics of the GPS observations it is shown, however, that less than 12 parameters are sufficient for the computation of the corrections. The proposed 8 parameter model was applied to the GPS monitoring network of the Gradenbach landslide. For this small network with large height differences, it was shown that the distortions can be reduced by about 75%.  相似文献   

Solar activity,volcanic dust and temperature: Statistical relationships since 1160 A. D.     

Dr. C. D. Schönwiese 《Meteorology and Atmospheric Physics》1981,30(1-2):1-22

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Bemerkungen zur numerischen Bandpaßfilterung von Zeitreihen unter besonderer Berücksichtigung meteorologischer Daten     

Oberreg.-Rat Dipl.-Met. Dr. Christian-Dietrich Schönwiese 《Meteorology and Atmospheric Physics》1975,24(3):311-320

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U-Pb and Rb-Sr dating of a polymetamorphic nappe terrain: The Caledonian Jotun nappe,southern Norway     

Urs Schärer 《Earth and Planetary Science Letters》1980,49(2):205-218

The Caledonian Jotun nappe in the Tyin area of southern Norway has been investigated using U-Pb analysis of zircon and sphene and Rb-Sr measurements of minerals and whole rocks, with special reference to the reaction of the isotope systems to various kinds of metamorphic event. The nappe consists of Precambrian basement rocks and their cover, inversely thrust over the Baltic shield and its parautochthonous, presumably lower Paleozoic sediments during the Caledonian orogeny. While the nappe basement retained its pre-Caledonian structures, the nappe cover was penetratively deformed and metamorphosed to lower greenschist facies conditions.U-Pb analyses of zircon and sphene ofnappe basement rocks point to the crystallization of a syenitic to monzonitic magma at 1694± 20m.y., the intrusion of gabbros into the syenites and monzonites at 1252_?25⁺²⁸ m.y., and the metamorphism (upper greenschist-lower amphibolite facies) and deformation (gneissification and mylonitization) of the whole complex at 909± 16m.y. Although this latest event caused strong lead loss in all zircon populations, it had no influence on the Rb-Sr system on a whole rock scale. The Caledonian movements did not disturb the U-Pb system of zircon and sphene but strongly influenced the Rb-Sr system in certain minerals and zircon and/or its inclusions (K-feldspar and brown biotite partially, green biotite completely reset).In contrast to the nappe basement, zircons from thecover rocks show pronounced lead loss during the Caledonian metamorphism/deformation — U-Pb analysis give discordia lower intercept ages of 415± 21 m.y. and 395± 6m.y. Again, however, the Rb-Sr whole-rock system has not been reset in Caledonian time. Minerals from the same rocks which provided the zircons give Rb-Sr isochron ages of 390± 11m.y. and 386 ± 20 m.y.Comparison of U-Pb and Rb-Sr results from the nappe basement demonstrates that only the analysis of U-Pb systematics in zircon and especially sphene resolved the 900-m.y. event. Rb-Sr mineral data alone yield ambiguous results.The results from the nappe cover confirm that U-Pb analyses from penetratively deformed sediments are very useful in dating a metamorphic/tectonic event in lower greenschist facies conditions.From the measured cell dimensions of the zircon populations it is concluded that lead can be completely retained in zircon during recrystallization.  相似文献   

Das Präkambrium der Arabischen Wüste Ägyptens     

H. M. E. Schürmann 《International Journal of Earth Sciences》1956,45(2):179-193

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Microanalysis of nitrogen isotope abundances: association of nitrogen with noble gas carriers in Allende     

Urs Frick  R.O. Pepin 《Earth and Planetary Science Letters》1981

Current research efforts to explore and account for the distribution of nitrogen isotope abundances in the ancient and present-day solar wind and in meteorites often require measurement of nitrogen abundances and isotopic compositions in very small samples of rare extraterrestrial materials. Isotopic analysis of ～ 1 μg of N₂ is possible with modern techniques of dynamic mass spectrometry, but even this high sensitivity is a limiting factor for certain critical samples. We have utilized a statistically operated mass spectrometer coupled to an ultrahigh vacuum gas extraction and processing system to lower this limit by approximately four orders of magnitude. Quantities of N₂ ranging from ～ 100 ng to < 100 pg are measurable with permil to percent precision in isotope ratios. Nitrogen and all noble gases evolved during stepwise combustion of fine-grained matrix material separated from the Allende meteorite have been meausred simultaneously in a pilot experiment using this technique. Isotopically heavy H-Xe (CCF-Xe) and isotopically light N are co-sited in a carbonaceous carrier phase, supporting a nucleosynthetic origin for¹⁵N-depleted nitrogen in Allende. The great isotopic uniformity of trapped Ar in all carrier phases indicates that simple, physical mass fractionation in gravitational escape of volatiles from the primitive nebula cannot have played a significant role in generating the nitrogen compositions observed in solar system matter.  相似文献   

Determination of vertical temperature profiles for the atmospheric boundary layer by ground-based microwave radiometry     

Bernd Schönwald 《Boundary-Layer Meteorology》1978,15(4):453-464

A useful method for remote sensing of vertical temperature profiles in the atmospheric boundary layer is described. From angular measurements of brightness temperature at 58 GHz, profiles have been inferred up to an altitude of 700 m. Calculations were done with an iterative inversion procedure (Smith et al., 1972) using Twomey-type smoothing (Twomey, 1963). It is shown how an initial-guess profile can be directly derived from the radiation measurements using, a nomogram.  相似文献   

A fast convolution approach to the transformation of surface gravity waves: Linear waves in 1DH     

Hemming A. Schäffer 《Coastal Engineering》2009,56(5-6):517-533

The transformation of irrotational surface gravity waves in an inviscid fluid can be studied by time stepping the kinematic and dynamic surface boundary conditions. This requires a closure providing the normal surface particle velocity in terms of the surface velocity potential or its tangential derivative. A convolution integral giving this closure as an explicit expression is derived for linear 1D waves over a mildly sloping bottom. The model has exact linear dispersion and shoaling properties. A discrete numerical model is developed for a spatially staggered uniform grid. The model involves a spatial derivative which is discretized by an arbitrary-order finite-difference scheme. Error control is attained by solving the discrete dispersion relation a priori and model results make a perfect match to this prediction. A procedure is developed by which the computational effort is minimized for a specific physical problem while adapting the numerical parameters under the constraint of a predefined tolerance of damping and dispersion error. Two computational examples show that accurate irregular-wave transformation on the kilometre scale can be computed in seconds. Thus, the method makes up a highly efficient basis for a forthcoming extension that includes nonlinearity at arbitrary order. The relation to Boussinesq equations, mild-slope wave equations, boundary integral equations and spectral methods is briefly discussed.  相似文献