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91.
The diffusion equation governs thermal conduction and groundwater flow phenomena. In this paper, we study the two‐dimensional radial propagation of a sinusoidal perturbation radiating from a cylindrical source within an infinite slab of homogeneous material. The solution of this problem has several applications. For instance, it can be used to determine the hydraulic diffusivity of the subsurface based on measurements of the hydraulic head around a vertical well during its development. For thermal problems, it can be used to determine the thermal diffusivity based on measurements of the temperature distribution around a cylindrical heat source generating a sinusoidal power per unit length. In this paper, we present a comprehensive analytical solution of this problem and we compare these solutions with numerical solutions. Two approximate analytical solutions, which can be relevant in practice, are also presented. Finally, we give an upper bound for the survival time of the transient part of the solution and we provide an estimate of the radius of influence of the sinusoidal solicitation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
92.
Markus Fuchs Sebastian Kreutzer Denis‐Didier Rousseau Pierre Antoine Christine Hatté France Lagroix Olivier Moine Caroline Gauthier Jiri Svoboda Lenka Lisá 《Boreas: An International Journal of Quaternary Research》2013,42(3):664-677
The Dolní Věstonice loess section in the Czech Republic is well known for its high‐resolution loess–palaeosol sequence of the last interglacial–glacial climatic cycle (Upper Pleistocene). The loess section is situated in a climatic transition zone between oceanic and continental climates and is therefore of great value in reconstructing past regional climate conditions and their interaction with climate systems, in particular that of the North Atlantic. Based on a combination of optically stimulated luminescence (OSL) ages, stratigraphic field observations and magnetic susceptibility measurements, a chrono‐climatic interpretation of the Dolní Věstonice loess section is presented. To establish a reliable Upper Pleistocene chronology, a quartz OSL approach was applied for equivalent dose (De) determination. Monomineralic quartz extracts of three distinct grain sizes, fine (4–11 μm), middle (38–63 μm) and coarse (90–200 μm), were used and compared. Within error limits, the calculated OSL ages are the same for the different grain sizes, and the OSL ages are in stratigraphic order. The established OSL chronology is in agreement with a Weichselian litho‐ and pedostratigraphy. The Dolní Věstonice loess section is characterized by four pedosedimentary subsequences. At the base of the profile, subsequence I is characterized by a distinct Early Glacial soil complex, OSL‐dated to c. 110 to 70 ka, representing one of the most complete records of environmental change in the European loess belt. Subsequence II is allocated to the Lower Pleniglacial and is characterized by laminated sandy loess. Middle Pleniglacial subsequence III is represented by a brown soil complex, and is followed by the uppermost subsequence IV, characterized by a thick body of laminated sandy loess, indicating strong wind activity and a high sedimentation rate of more than ~1 mm a?1 during the Upper Pleniglacial. According to the OSL chronology, as well as to the sedimentological and palaeopedological investigations, it is likely that the sequence at Dolní Věstonice has recorded most of the climatic events expressed in the NGRIP δ18O reference record between 110 and 70 ka. 相似文献
93.
Antoine de Haller Alexandre Tarantola Martin Mazurek Jorge Spangenberg 《Swiss Journal of Geoscience》2011,104(3):493-506
Abundant veins filled by calcite, celestite and pyrite were found in the core of a 719 m deep borehole drilled in Oftringen
near Olten, located in the north-western Molasse basin, close to the thrust of the Folded Jura. Host rocks are calcareous
marl, argillaceous limestone and limestone of the Dogger and Malm. The δ18O values of vein calcite are lower than in host rock carbonate and, together with microthermometric data from fluid inclusions
in vein calcite, indicate precipitation from a seawater-dominated fluid at average temperatures of 56–68°C. Such temperatures
were reached at the time of maximum burial of the sedimentary pile in the late Miocene. The depth profile of δ13C and 87Sr/86Sr values and Sr content of both whole-rock carbonate and vein calcite show marked trends towards negative δ13C, high 87Sr/86Sr, and low Sr content in the uppermost 50–150 m of the Jurassic profile (upper Oxfordian). The 87Sr/86Sr of vein minerals is generally higher than that of host rock carbonate, up to very high values corresponding to Burdigalian
seawater (Upper Marine Molasse, Miocene), which represents the last marine incursion in the region. No evidence for internally
derived radiogenic Sr (clay minerals) has been found and so an external source is required. S and O isotope composition of
vein celestite and pyrite can be explained by bacterial reduction of Miocene seawater sulphate. The available data set suggests
the vein mineralization precipitated from descending Burdigalian seawater and not from a fluid originating in the underlying
Triassic evaporites. 相似文献
94.
Shavkat Rakhmatullaev Antoine Marache Frédéric Huneau Philippe Le Coustumer Masharif Bakiev Mikael Motelica-Heino 《Environmental Earth Sciences》2011,63(3):447-460
The paper presents the results of a new geostatistical approach to generate bathymetric surface models from point measurement
converted into continuous contour surfaces of reservoir bottoms in Uzbekistan. Sedimentation of reservoirs raises engineering,
environmental and economical issues for the communities around the world in areas affected by a strong water deficit. Because
of Uzbekistan’s arid climatic conditions, and uneven spatial and temporal water resources distribution, responsive and innovative
water availability assessment surveys of all major water reservoirs are required. Bathymetric surveying is a traditional method
that is carried out for the estimation of reservoir volumes and surface areas of the corresponding reservoir stages in order
to assess the water availability. Volume and surface area differences derived from multiple surveys of a reservoir provide
storage loss estimates over time due to sedimentation. However, two main factors, such as intensive field data measurement
and post data-processing, often limit the frequency of these surveys. Alternatively, innovative depth measurement technologies
coupled with contouring and surface mapping programs provide automated reservoir volume and surface area calculations. This
significantly reduces time, workload and financial burdens for reservoir sedimentation projects. This research proposes the
use of geostatistical approach to assess the reservoir sedimentation in the Akdarya reservoir of Uzbekistan. The geostatistical
approach includes (semi-) variogram analysis and interpolation (kriging and simulations—turning bands) techniques predicting
values at unsampled locations for generating digital bathymetric surface models of reservoir bottom conditions in order to
calculate the volume and surface area at a given water elevation. The simulation enables to have range of reservoir volumes
and surface areas with the same probability, in comparison to the kriging and traditional methods. This gives a real estimation
of the resource availability for water operators to manage natural resources and hydraulic infrastructure in a sustainable
manner. 相似文献
95.
Analysis and Estimation of Multi-unit Deposits: Application to a Porphyry Copper Deposit 总被引:1,自引:1,他引:0
Serge Antoine Séguret 《Mathematical Geosciences》2013,45(8):927-947
This work concerns mineral deposits consisting of geological bodies whose metal grades have different characteristics in terms of distribution and variogram, which means that estimating grades by ordinary kriging may produce unrealistic spatial continuity. This paper proposes a method based on the indicators of the geological objects (hereafter called units) and their product with the metal grade. This is illustrated by an application to a porphyry copper deposit. The aim of this paper is essentially to promote the use of variogram ratios to analyze and characterize deposits. 相似文献
96.
Closed‐form solutions are proposed for natural seepage in semiconfined (leaky) aquifers such as those existing below the massive Champlain Sea clay layers in the Saint‐Lawrence River Valley. The solutions are for an ideal horizontal leaky aquifer below an ideal aquitard that may have either a constant thickness and a constant hydraulic head at its surface, or a variable thickness and a variable hydraulic head at its surface. A few simplifying assumptions were needed to obtain the closed‐form solutions. These have been verified using a finite element method, which did not make any of the assumptions but gave an excellent agreement for hydraulic heads and groundwater velocities. For example, the difference between the two solutions was smaller than 1 mm for variations in the 5 to 8 m range for the hydraulic head in the semiconfined aquifer. Note that fitting the hydraulic head data of monitoring wells to the theoretical solutions gives only the ratio of the aquifer and aquitard hydraulic conductivities, a clear case of multiple solutions for an inverse problem. Consequently, field permeability tests in the aquitard and the aquifer, and pumping tests in the aquifer, are still needed to determine the hydraulic conductivity values. 相似文献
97.
Julie Dabkowski Nicole Limondin‐Lozouet Pierre Antoine Julian Andrews Alina Marca‐Bell Vincent Robert 《第四纪科学杂志》2012,27(8):790-799
Marine Isotope Stage (MIS) 11 palaeoclimate has so far been documented in marine and ice sheet isotopic records. However, excepting some lacustrine pollen records, very little is known about palaeoclimatic conditions in continental areas. This study uses geochemical records in calcareous tufa deposits from rivers as a basis for reconstructing temperate palaeoclimatic conditions. Tufa deposits are now proven to record high‐quality palaeoclimatic information in recent to Holocene deposits. Work on older interglacial tufas is just starting and in this paper we present the first comprehensive results from a MIS 11 tufa. The tufa comes from the Seine Valley (La Celle, northern France). Geochemical data in the tufa calcite are interpreted to record primarily air temperature (δ18O) and humidity (δ13C and Mg/Ca and Sr/Ca). The combined data identify a warm and wet climatic optimum followed by two temperature decreases associated with oscillations in humidity. These marked climatic variations recorded through the La Celle profile are strongly coherent with the palaeoenvironmental reconstructions from malacological data. The abrupt climatic and environmental events recorded could be related to short‐term degradation of vegetation cover in Europe, which is itself controlled by global palaeoclimatic events. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
98.
With the pyramid transform, 2D dip spectra can be characterized by 1D prediction‐error filters (pefs) and 3D dip spectra by 2D pefs. These filters, contrary to pefs estimated in the frequency‐space domain (ω, x) , are frequency independent. Therefore, one pef can be used to interpolate all frequencies. Similarly, one pef can be computed from all frequencies, thus yielding robust estimation of the filter in the presence of noise. This transform takes data from the frequency‐space domain (ω, x) to data in a frequency‐velocity domain (ω, u=ω·x) using a simple mapping procedure that leaves locations in the pyramid domain empty. Missing data in (ω, x) ‐space create even more empty bins in (ω, u) ‐space. We propose a multi‐stage least‐squares approach where both unknown pefs and missing data are estimated. This approach is tested on synthetic and field data examples where aliasing and irregular spacing are present. 相似文献
99.
SECCHI-EUVI telescopes provide the first EUV images enabling a 3D reconstruction of solar coronal structures. We present a
stereoscopic reconstruction method based on the Velociraptor algorithm, a multiscale optical-flow method that estimates displacement maps in sequences of EUV images. Following earlier
calibration on sequences of SOHO-EIT data, we apply the algorithm to retrieve depth information from the two STEREO viewpoints
using the SECCHI-EUVI telescope. We first establish a simple reconstruction formula that gives the radial distance to the
centre of the Sun of a point identified both in EUVI-A and EUVI-B from the separation angle and the displacement map. We select
pairs of images taken in the 30.4 nm passband of EUVI-A and EUVI-B, and apply a rigid transform from the EUVI-B image in order
to set both images in the same frame of reference. The optical flow computation provides displacement maps from which we reconstruct
a dense map of depths using the stereoscopic reconstruction formula. Finally, we discuss the estimation of the height of an
erupting filament. 相似文献
100.
Adriana Sima Denis-Didier Rousseau Masa Kageyama Gilles Ramstein Michael Schulz Yves Balkanski Pierre Antoine Franois Dulac Christine Hatt 《Quaternary Science Reviews》2009,28(25-26):2851-2866
Western European loess sequences of the last glaciation (100,000–15,000 years BP) exhibit strong, cyclic variations of the sedimentation rate, which are coeval to the Greenland stadial/interstadial cycles and the Heinrich events. These North-Atlantic rapid climate changes appear, thus, as a potential cause for the sedimentation variations, via changes in dust intensity cycle. Here we make a first step in testing this hypothesis, by modelling the impact of the North-Atlantic abrupt climate variations on dust emission. Our dust emission calculations use meteorological fields generated by the LMDZ atmospheric general circulation model at a resolution down to 60 km over Western Europe. Three numerical experiments are run, representing a Greenland stadial, an interstadial and a Heinrich event. Orbital parameters and ice-sheet configuration correspond to conditions from Marine Isotope Stage 3 (60,000–25,000 years BP), a period characterized by strong millennial-scale climate variability. The only differences we impose in the boundary conditions regard the North-Atlantic surface temperature and sea-ice cover in the latitudinal band 30°–63°N. The changes in wind, precipitation, soil moisture and snow cover from one simulated state to another result in small differences in dust emission intensity. In contrast, when the inhibition of the aeolian erosion by vegetation is taken into account, the dust fluxes for the cold climate states (Greenland stadial and Heinrich event) become generally more than twice higher than those for the relatively warmer Greenland interstadial, in agreement with the loess data. These results support the hypothesis that the North-Atlantic millennial-scale variability is imprinted in Western European loess profiles, and point to vegetation changes as the main factor responsible for millennial-scale sedimentation variations. An analysis for the English Channel and southern North Sea areas, major potential dust sources, shows that the seasonality of dust emission is not controlled by the wind speed, as in modern large deserts, but by the surface conditions. Consequently, the dusty season lasts from late winter to early summer, with maximum activity in April–May, and is shifted towards summer when the climate is colder. 相似文献