Flow pattern and sediment transport in a braided river: The “torrent de St Pierre” (French Alps)     

P. Meunier  F. Mtivier  E. Lajeunesse  A.S. Mriaux  Joël Faure 《Journal of Hydrology》2006,330(3-4):496-505

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Investigation of hydrochemical characteristics of groundwater from the Cretaceous-Eocene limestone aquifer in southern Ghana and southern Togo using hierarchical cluster analysis   总被引：4，自引：1，他引：4  

Tina Helstrup  Niels Oluf Jørgensen  Bruce Banoeng-Yakubo 《Hydrogeology Journal》2007,15(5):977-989

The most relevant controls on the water quality within the Cretaceous-Eocene limestone aquifer of the Keta Basin, Ghana, and the coastal sedimentary basin of Togo were assessed using Q-mode hierarchical cluster analysis (HCA) and mass-balance modelling. The pattern recognition technique of HCA was employed for partitioning hydrochemical data from a total of 65 surface and borehole samples from the study area into water groups. A spatial plot of the water groups consisting of samples from the limestone aquifer shows that the vast majority of samples belonging to the same group are located in close proximity to one another, suggesting the same processes and/or flow paths in the limestone aquifer system. Geochemical reaction models of selected water groups were constructed using PHREEQC-2. The hydrochemical compositions of the water groups and the mass-balance calculations indicate that the dominant processes and reactions responsible for the hydrochemical evolution in the system are: (1) carbonate equilibria, (2) silicate weathering reactions, (3) limited mixing with saline water, and (4) ion exchange. The combined use of HCA and mass-balance modelling has shown to be a useful approach in interpreting groundwater hydrochemistry in an area where large uncertainties exist in the understanding of the groundwater flow system.  相似文献   

Magmatic history of granite-derived mylonites from the southern Desná Unit (Silesicum, Czech Republic)     

P. Hanžl  V. Janoušek  V. Žáček  D. Wilimský  J. Aichler  V. Erban  M. Pudilová  M. Chlupáčová  K. Buriánková  P. Mixa  V. Pecina 《Mineralogy and Petrology》2007,89(1-2):45-75

Summary In the southern part of the Hruby Jeseník Mts. (Silesicum, Bohemian Massif) granitic orthogneisses and quartz-feldspars mylonites occur that were variously deformed, metamorphosed and imbricated with the overlaying Devonian volcano-sedimentary complex during the Variscan orogeny. Based on combined mapping, petrologic and geochemical studies, three main rock groups are distinguished. The fairly primitive nature of the tonalite suite is shown by low ⁸⁷Sr/⁸⁶Sr₅₅₀ ratios (0.7034–0.7038) and positive ε _Nd ⁵⁵⁰ values (+3.8 and +3.1). Isotopic composition of the metagranite suite is similar (ε _Nd ⁵⁵⁰ = +1.9 to +2.9). Both suites probably belong to a single Cadomian calc-alkaline tonalite–granite association, which can be correlated with acid-intermediate plutonic rocks of the eastern Brunovistulicum (Slavkov Terrane). All these units are interpreted as representing dismembered fragments of the same continental margin magmatic arc system. The leucogranite suite is most likely early Variscan in age. The initial Nd isotopic composition (ε _Nd ³³⁰ = +0.8 and +2.3) is consistent with its formation by a Variscan remelting of the metaigneous Cadomian crust represented by the rocks of the tonalite–granite association. The within-plate granite affinity of the leucogranite suite is most likely related to the break-up of the Brunovistulicum during the Variscan orogeny.  相似文献   

The importance of alternative conceptual models for simulation of concentrations in a multi-aquifer system     

Lars Troldborg  Jens Christian Refsgaard  Karsten Høgh Jensen  Peter Engesgaard 《Hydrogeology Journal》2007,15(5):843-860

Four different conceptual models based on alternative geological interpretations were formulated for a shallow 600 km² aquifer system in Denmark comprising Quaternary deposits. Each of the four models was calibrated against groundwater heads and discharge measurements through inverse modeling. Subsequently, the transport capabilities of the four models were compared to 32 concentration measurements of environmental tracers (tritium ³H, helium-3 ³He, chlorofluorocarbons CFC11, CFC12 and CFC113). The flow simulations showed only minor differences in spatial head distribution associated with alternative conceptualizations despite the complexity of the aquifer system and the significant differences in geological interpretations. The models, however, showed major differences in predictions of the age of the groundwater and environmental tracer concentrations, differences that are seen as an effect of model structure uncertainty, because no additional calibrations to these data were performed. A single conceptualization may be adequate in characterizing the natural behavior of a field system after calibration, because the calibration procedure is able to compensate for errors in the data or in the conceptual model through biased parameter values. However, once extrapolation beyond the calibration base is attempted, different conceptual model formulations result in significantly different results. Consequently, it is crucial to take model conceptual uncertainty into account when making predictions beyond the calibration base.  相似文献   

How chalcophile is rhenium? An experimental study of the solubility of Re in sulphide mattes     

Raúl O.C. Fonseca  Guilherme Mallmann  Hugh St.C.O''Neill  Ian H. Campbell 《Earth and Planetary Science Letters》2007,260(3-4):537-548

Although the Re/Os isotopic system has proved to be a valuable aid in understanding the evolution of the Earth's mantle, interpretation of the data is currently hindered by limited knowledge of the high-temperature geochemical behaviour of Re. In particular, the extent to which Re in the mantle is hosted by sulphide or silicate phases is poorly known. We report the results of an experimental study of the solubility of Re in sulphide melts (called here “mattes”) coexisting with a Re-rich Re–Fe alloy in the system Fe–Re–S–O over a range of fO₂, fS₂ and temperatures, which allow extrapolation to conditions pertinent to the Earth's mantle. The solubility of Re in mattes increases with increasing fS₂, with Re dissolving as Re⁴⁺ at high fS₂ and Re⁰ at low fS₂. The effect of fO₂ is negligible except at high fO₂ where O in the matte becomes important. At constant fS₂, an increase in temperature leads to an increase in the solubility of Re⁰ in the matte, but a decrease in the solubility of Re⁴⁺. These results, coupled with data for the Re solubility in silicate melts taken from the literature, allow the calculation of Re matte/silicate–melt partition coefficients (D_Re^matte/sil) for a range of conditions. The calculated D_Re^matte/sil show a large dependence on fO₂, and a lesser dependency on fS₂, with Re behaving as a chalcophile element for relatively reduced MORB-type mantle and as a lithophile element for the oxidised sources of island-arc basalts. The sensitivity of Re to fS₂ and fO₂ reconciles the apparent discrepancies between previous estimates of this parameter, which can vary by more than five orders of magnitude within the range of fS₂ and fO₂ covered by terrestrial basaltic magmas.  相似文献   

Probabilistic Visibility Forecasting Using Neural Networks   总被引：1，自引：0，他引：1  

John Bjørnar Bremnes  Silas Chr. Michaelides 《Pure and Applied Geophysics》2007,164(6-7):1365-1381

Statistical methods are widely applied in visibility forecasting. In this article, further improvements are explored by extending the standard probabilistic neural network approach. The first approach is to use several models to obtain an averaged output, instead of just selecting the overall best one, while the second approach is to use deterministic neural networks to make input variables for the probabilistic neural network. These approaches are extensively tested at two sites and seen to improve upon the standard approach, although the improvements for one of the sites were not found to be of statistical significance.  相似文献   

Effect of bed topography on soil aggregates transport by rill flow     

Rafael Giménez  Joël Léonard  Yves Duval  Guy Richard  Gerard Govers 《地球表面变化过程与地形》2007,32(4):602-611

After its formation, a rill may remain in the field for months, often receiving lower flow rates than the formative discharge. The objective of this work was to evaluate the rill flow transport capacity of soil aggregates at discharges unable to erode the rill, and to analyse the influence of the rill macro‐roughness on this transport process. A non‐erodible rill was built in which roughness was reproduced in detail. In order to assess only the rill macro‐roughness, a flat channel with a similar micro‐roughness to that in the rill replica was built. Rill and channel experiments were carried out at a slope of 8 and at six discharges (8·3 × 10^?5 to 5·2 × 10^?4 m³ s^?1) in the rill, and eight discharges (1·6 × 10^?5 to 5·2 × 10^?4 m³ s^?1) in the channel. Non‐erodible aggregates of three sizes (1–2, 3–5 and 5–10 mm) were released at the inlet of the rill/channel. The number of aggregates received at the outlet was registered. The number and position of the remaining aggregates along the rill/channel were also determined. The rill flow was a major sediment transport mechanism only during the formation of the rill, as during that period the power of the flow was great enough to overcome the influence of the macro‐roughness of the rill bed. At lower discharges the transport capacity in the previously formed rill was significantly less than that in the flat channel under similar slope and discharge. This was determined to be due to local slowing of flow velocities at the exit of rill pools. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Importance of borehole deviation surveys for monitoring of hydraulic fracturing treatments     

Petr Bulant  Leo Eisner  Ivan P&#;en&#;ík  Joël Le Calvez 《Geophysical Prospecting》2007,55(6):891-899

During seismic monitoring of hydraulic fracturing treatment, it is very common to ignore the deviations of the monitoring or treatment wells from their assumed positions. For example, a well is assumed to be perfectly vertical, but in fact, it deviates from verticality. This can lead to significant errors in the observed azimuth and other parameters of the monitored fracture‐system geometry derived from microseismic event locations. For common hydraulic fracturing geometries, a 2° deviation uncertainty on the positions of the monitoring or treatment well survey can cause a more than 20° uncertainty of the inverted fracture azimuths. Furthermore, if the positions of both the injection point and the receiver array are not known accurately and the velocity model is adjusted to locate perforations on the assumed positions, several‐millisecond discrepancies between measured and modeled SH‐P traveltime differences may appear along the receiver array. These traveltime discrepancies may then be misinterpreted as an effect of anisotropy, and the use of such anisotropic model may lead to the mislocation of the detected fracture system. The uncertainty of the relative positions between the monitoring and treatment wells can have a cumulative, nonlinear effect on inverted fracture parameters. We show that incorporation of borehole deviation surveys allows reasonably accurate positioning of the microseismic events. In this study, we concentrate on the effects of horizontal uncertainties of receiver and perforation positions. Understanding them is sufficient for treatment of vertical wells, and also necessary for horizontal wells.  相似文献   

POLAR 5—an electron accelerator experiment within an aurora. 2. Scattering of an artificially produced electron beam in the atmosphere     

B.N. Maehlum  B. Grandal  T.A. Jacobsen  J. Trøim 《Planetary and Space Science》1980,28(3):279-289

The interaction between an artificially produced narrow beam of electrons and the upper atmosphere has been studied by the POLAR 5 electron accelerator “mother”-“daughter” rocket. It is shown how the beam develops a “halo” of scattered electrons and how the low energy electron population in this “halo” is produced partly during the ionization process (at low altitudes), partly by a “wave-plasma” interaction which accelerates the ionospheric background electrons.  相似文献   

ISOCAM Long Wave Detector Glitches: Data and Ray-Tracing Simulations     

Petteri Nieminen  John Sørensen 《Experimental Astronomy》2000,10(2-3):381-391

The affected pixel number distribution of the ISOCAM Long-Wave (LW) detector in cosmic ray-induced glitchesis calculated. The methods employed are Monte Carlo ray-tracing techniques and the taxi metric, which allows direct calculation of the affected pixels based on the knowledge of entry and exit points of the ray. The simulation results are compared with long-term experimental data. Based on the simulations combined with the CREME96 cosmic ray model for solar quiet period, it is estimated that the detector is on average traversed by 0.3 cosmic ray protons per second. For the experimental data, a corresponding minimum bound of 0.14 cosmic ray protons per second is obtained. Deviations in the simulated and measured pixel number distributions are discussed.  相似文献