Magnetic susceptibility and viscosity of soils in a weak time varying field     

Michel Dabas  Alain Jolivet  Alain Tabbagh 《Geophysical Journal International》1992,108(1):101-109

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Factors influencing the abundance of deep pelagic bioluminescent zooplankton in the Mediterranean Sea     

Jessica Craig  Alan J. Jamieson  Rory Hutson  Alain F. Zuur  Imants G. Priede 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(11):1474-1484

Measurements of the density of deep pelagic bioluminescent zooplankton (BL) were made with the Intensified Silicon Intensifier Target (ISIT) profiler in the Ligurian, Tyrrhenian, Adriatic, Ionian Seas and the Strait of Sicily from ～300 m to near seafloor. Mean BL densities ranged from 2.61 m^?3 at 500–1000 m depth in the Adriatic Sea to 0.01 m^?3 at 4000–5000 m depth in the E Ionian Sea. We investigated drivers of spatial variation of deep pelagic BL density. Linear regression was applied between surface chlorophyll a (Chl a) concentration and underlying BL density. Chl a values were determined from satellite derived 100 km radius composites (six 10-day means per ISIT deployment, over preceding 60 days). At 500–1000 m depth we found a significant positive relationship between mean BL density and mean Chl a in the period prior to 0–10 days (at 1% level) and prior to 10–40 days (at 5% level). Beyond 40 days no relationship between BL density and Chl a was found at this depth. At depths 1000–1500 m BL density values were low and no significant relationship with Chl a was detected. Generalised additive modelling (GAM) was used to assess the influence of benthic hotspots (seamount; cold water coral mound; mud volcano) on overlying BL density. A reduction in BL density was found downstream of the Palinuro seamount from 300 to 600 m. No effect on BL density in the overlying water column was detected from the presence of cold water corals. Higher BL densities were detected over the W Madonna dello Ionio mud volcano than at other sites sampled in the NW Ionian Sea. We find surface Chl a to be a good predictor of BL density in the mesopelagic zone; below this depth we hypothesise that processes affecting the efficiency of particle export to deep water may exert greater influence on BL density.  相似文献   

The evolution of clusters in the CLEF cosmological simulation: X-ray structural and scaling properties     

Scott T. Kay  Antonio C. da Silva  Nabila Aghanim  Alain Blanchard  rew R. Liddle  Jean-Loup Puget  Rachida Sadat  Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2007,377(1):317-334

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Archaeological reconstruction of medieval lead production: Implications for ancient metal provenance studies and paleopollution tracing by Pb isotopes     

Sandrine Baron  Ccile Le-Carlier  Jean Carignan  Alain Ploquin 《Applied Geochemistry》2009,24(11):2093-2101

The identification of metal provenance is often based on chemical and Pb isotope analyses of materials from the operating chain, mainly ores and metallic artefacts. Such analyses, however, have their limits. Some studies are unable to trace metallic artefacts or ingots to their ore sources, even in well-constrained archaeological contexts. Possible reasons for this difficulty are to be found among a variety of limiting factors: (i) problems of ore signatures, (ii) mixing of different ores (alloys), (iii) the use of additives during the metallurgical process, (iv) metal recycling and (v) possible Pb isotopic fractionation during metal production. This paper focuses on the issue of Pb isotope fractionation during smelting to address the issue of metal provenance. Through an experimental reconstruction of argentiferous Pb production in the medieval period, an attempt was made to better understand and interpret the Pb isotopic composition of ore smelting products. It is shown that the measured differences (outside the total external uncertainties of 0.005 (2*sd) for ²⁰⁶Pb/²⁰⁴Pb ratios) in Pb signatures measured between ores, slag and smoke are not due to Pb mass fractionation processes, but to (1) ore heterogeneity (Δ²⁰⁶Pb/²⁰⁴Pb_slag-ores = 0.066) and (2) the use of additives during the metallurgical process (Δ²⁰⁶Pb/²⁰⁴Pb_slag-ores = 0.083). Even if these differences are due to causes (1) and/or (2), smoke from the ore reduction appears to reflect the ore mining area without a significant disturbance of its Pb signature for all the isotopic ratios (Δ²⁰⁶Pb/²⁰⁴Pb_smokes-ores = 0.026). Thus, because the isotopic heterogeneity of the mining district and additives is averaged in slags, slag appears as the most relevant product to identify ancient metal provenance. Whereas aiming at identifying a given mine seems beyond the possibilities provided by the method, searching for the mining district through analysis of the smelting workshop materials should provide a more appropriate approach in cases where no archaeological evidence of ancient mining is available. Furthermore, smoke Pb isotopic composition does not seem to be significantly affected by the metallurgical process. Paleopollution recorded in peat deposits could help to detect ancient mining production and workshops. Integrated collaboration between mining archaeologists and geochemists appears crucial to achieve this goal.  相似文献   

Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock     

Alain Millard  Jobst Maßmann  Amel Rejeb  Shin Uehara 《Environmental Geology》2009,57(6):1325-1335

The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase, followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model, the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the numerous seasonal variations cycles and the resulting shrinkage.  相似文献   

Groundwater flow modelling in the central zone of Hanoi, Vietnam   总被引：3，自引：2，他引：1  

Simon Jusseret  Vu Thanh Tam  Alain Dassargues 《Hydrogeology Journal》2009,17(4):915-934

On the basis of a review of the Quaternary sedimentary architecture in the area of Hanoi city (Vietnam), a numerical, deterministic and three-dimensional groundwater flow model has been built for a simulation between 1995 and 2004. The sedimentary architecture has been constructed on the basis of the data from 32 drillings covering the entire Quaternary sequence (but with little sedimentological detail), as well as hydrographical and hydrogeological data. Both steady- and transient-state conditions were tested. Results calculated by the model seem to indicate that the conceptual hypotheses adopted are reasonable for the modelled domain and period. The simulation allows for calculation of the regional groundwater flow trends. It is also used for assessing the relative importance of the various recharge sources of the shallow aquifer system in Hanoi, and for estimating the interactions between groundwater and the Red River.  相似文献   

Application of multiple-point geostatistics on modelling groundwater flow and transport in a cross-bedded aquifer (Belgium)   总被引：3，自引：1，他引：2  

Marijke Huysmans  Alain Dassargues 《Hydrogeology Journal》2009,17(8):1901-1911

Sedimentological processes often result in complex three-dimensional subsurface heterogeneity of hydrogeological parameter values. Variogram-based stochastic approaches are often not able to describe heterogeneity in such complex geological environments. This work shows how multiple-point geostatistics can be applied in a realistic hydrogeological application to determine the impact of complex geological heterogeneity on groundwater flow and transport. The approach is applied to a real aquifer in Belgium that exhibits a complex sedimentary heterogeneity and anisotropy. A training image is constructed based on geological and hydrogeological field data. Multiple-point statistics are borrowed from this training image to simulate hydrofacies occurrence, while intrafacies permeability variability is simulated using conventional variogram-based geostatistical methods. The simulated hydraulic conductivity realizations are used as input to a groundwater flow and transport model to investigate the effect of small-scale sedimentary heterogeneity on contaminant plume migration. Results show that small-scale sedimentary heterogeneity has a significant effect on contaminant transport in the studied aquifer. The uncertainty on the spatial facies distribution and intrafacies hydraulic conductivity distribution results in a significant uncertainty on the calculated concentration distribution. Comparison with standard variogram-based techniques shows that multiple-point geostatistics allow better reproduction of irregularly shaped low-permeability clay drapes that influence solute transport.  相似文献   

A multifractal formalism for vector-valued random fields based on wavelet analysis: application to turbulent velocity and vorticity 3D numerical data     

Pierre Kestener  Alain Arneodo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(3):421-435

Extreme atmospheric events are intimately related to the statistics of atmospheric turbulent velocities. These, in turn, exhibit multifractal scaling, which is determining the nature of the asymptotic behavior of velocities, and whose parameter evaluation is therefore of great interest currently. We combine singular value decomposition techniques and wavelet transform analysis to generalize the multifractal formalism to vector-valued random fields. The so-called Tensorial Wavelet Transform Modulus Maxima (TWTMM) method is calibrated on synthetic self-similar 2D vector-valued multifractal measures and monofractal 3D vector-valued fractional Brownian fields. We report the results of some application of the TWTMM method to turbulent velocity and vorticity fields generated by direct numerical simulations of the incompressible Navier–Stokes equations. This study reveals the existence of an intimate relationship between the singularity spectra of these two vector fields which are found significantly more intermittent than previously estimated from longitudinal and transverse velocity increment statistics.

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Alain ArneodoEmail:

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Forecasting the energy produced by a windmill on a yearly basis     

Alain Bensoussan  Pierre Rapha?l Bertrand  Alexandre Brouste 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(8):1109-1122

The objective of this article is to study as extensively as possible the uncertainties affecting the annual energy produced by a windmill. In the literature, the general approach is to estimate the mean annual energy from a transformation of a Weibull distribution law. Then the issue is reduced to estimating the coefficients of this distribution. This is obtained by classical statistical methods. Therefore, the uncertainties are mostly limited to those resulting from the statistical procedures. But in fact, the real uncertainty of the random variable which represents the annual energy cannot been reduced to the uncertainty on its mean and to the uncertainties induced from the estimation procedure. We propose here a model, which takes advantage of the fact that the annual energy production is the sum of many random variables representing the 10?min energy production during the year. Under some assumptions, we make use of the central limit theorem and show that an intrinsic uncertainties of wind power, usually not considered, carries an important risk. We also explain an observation coming from practice that the forecasted annual production is always overestimated, which creates a risk of reducing the profitability of the operation.  相似文献   

Nutrient fluxes between water column and sediments: Potential influence of the pearl oyster culture   总被引：1，自引：0，他引：1  

Gaertner-Mazouni N  Lacoste E  Bodoy A  Peacock L  Rodier M  Langlade MJ  Orempuller J  Charpy L 《Marine pollution bulletin》2012,65(10-12):500-505

This study quantifies benthic nutrient fluxes and sedimentation rates in the Ahe Atoll lagoon (French Polynesia), in two stations located under pearl oyster frames, and two control stations away from the pearl culture facility. Dissolved inorganic nitrogen fluxes ranged between 2 and 35μmolNm(-2)h(-1) and Soluble Reactive Phosphorus varied between -3 and 8.2μmolPm(-2)h(-1). Particulate sedimentation rates beneath the oysters were approximately five times higher than in the control zone and the percentage of small particles (?63μm) were about the twice. In contrast, sediment composition was similar under and outside the direct influence of oyster frames. In this ecosystem, where primary production is dependent on the available nitrogen, our study revealed that, while highly variable, benthic fluxes could sometimes contribute up to 28% of the nitrogen demand for primary production.  相似文献