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81.
Florent Dominé Emmanuel Thibert Eric Silvente Michel Legrand Jean-Luc Jaffrezo 《Journal of Atmospheric Chemistry》1995,21(2):165-186
Laboratory and field measurements have been performed in order to improve our understanding of the HCl air-snow transfer function. The solubility and diffusion of HCl in laboratory grown single crystals of ice have been measured as a function of HCl partial pressure,P
HCl, between –8 and –25 °C. Measurements ofP
HCl and of the mole fraction of HCl in snow,X'HCl, have been measured at Summit, Greenland. Comparison of the field and laboratory measurements show that theX'HCl values are well below equilibrium values. The major processes involved in the formation of snow crystals and in their evolution after deposition are discussed in order to attempt to understand theX'HCl values and their variations. The discussion is focussed on a few well identified snow layers. It is concluded that sublimation and recrystallization of snow probably play a major role in the evolution ofX'HCl, but that our understanding of the HCl transfer function is very incomplete. Laboratory and field measurements are suggested to improve this situation. 相似文献
82.
Marine circulation above the northern Brazilian continental shelf is subject to energetic forcing factors of various origins: high water buoyancy fluxes induced by the Amazon River freshwater discharge, a strong coastal current associated with a mesoscale current (North Brazil Current (NBC)), a forcing by semidiurnal tide and by Northeast or Southeast trade winds according to the season. Using a three-dimensional (3-D) hydrodynamic numerical model (MOBEEHDYCS), and realistic bathymetry and coastline of the northern Brazilian shelf, this paper aims at studying the influence of some specific physical processes on the morphology of the Amazon plume. The very large volume discharge (180 000 m3/s on average) and the weak effect of Coriolis force are additional characteristics of the studied system, which induce a particular dynamics. The various forcing factors are successively introduced into the model in order to simulate and to determine their respective influences upon the plume extent and the hydrodynamics at the shelf scale. Simulation reveal that the coastal current is at the origin of the permanent northwestward Amazon plume extension while wind effect can either reinforce or moderate this situation. The tide intervenes also to modify the position of the salinity front: a horizontal migration of salinity front is observed under its action. 相似文献
83.
84.
85.
Jean-Luc Got Vadim Monteiller Jean Virieux Stéphane Operto 《Geophysical Prospecting》2008,56(4):477-491
Double-difference tomographic methods use directly accurate time delays computed between similar signals. Such methods are designed to image very heterogeneous media, such as volcanoes or fault zones. In seismological applications, similar signals are recorded at a given station from earthquakes sharing similar and close-by sources. In seismic exploration experiments, similar signals are often recorded at neighbouring receivers. After a brief presentation of the tomographic algorithm used, a seismological application is summarized. The potential and limits of double-difference tomographic methods are explored using various numerical experiments. They show that two effects are competing in double-difference tomography: (i) the degradation of the stability of the inversion due to the geometrical proximity of the rays used in the differentiation and (ii) the decrease in modelling error, which allows improving the stability of the inversion and using smaller quantities of a priori information when data are sufficiently accurate. The best resolution is obtained for an optimal value of the inter-source or inter-receiver distance. For optimal values of these distances and a priori information, tomography using traveltime differences provides significantly better resolved results than using traveltimes. 相似文献
86.
Evolution of the Upper Rhone River discharge and suspended sediment load during the last 80 years and some implications for Lake Geneva 总被引:1,自引:0,他引:1
87.
One of the main limitations to the sensitivity of observations carried out withthe ISOCAM infrared camera comes from the responsivity variations and glitchescaused by impacts of charged particles. After more than 28 months of successfuloperations, the predicted glitch rate has been re-evaluated and compared toin-flight measurements. Glitch properties have been studied in orderto improve the removal algorithms, and thus the ultimate sensitivity of ISOCAM.All informations about the glitch phenomenon are very useful in order toprepare next space experiments. 相似文献
88.
Vincent Bouchot Patrick Ledru Catherine Lerouge Jean-Luc Lescuyer Jean-Pierre Milesi 《Ore Geology Reviews》2005,27(1-4):169
The French Massif Central constitutes an exceptional study area due to the diversity of its metallic deposits, its internal position in the Variscan belt, and the abundance of available geological, geophysical and metallogenic data obtained within the GeoFrance 3D programme. The deposits, formed towards the end of the orogenic evolution, represent the economic products of two distinct mineralizing systems, a Au ± Sb hydrothermal system and a W ± Sn and rare-metals magmatic–hydrothermal system, which were simultaneously active during a short time span between ca. 310 and 300 Ma.Two types of gold deposit can be distinguished on the basis of their depth of emplacement: “deep-seated” gold deposits developed under lithostatic to hydrostatic pressure during rapid exhumation, and “shallow” gold deposits emplaced under hydrostatic pressure with no significant uplift.Deposits of W ± Sn and rare-metals were emplaced in the upper crust during final crystallization of specialized magmas after their rapid ascent, perhaps enhanced by simultaneous regional uplift. The gold-bearing systems are associated with a complex network of re-activated crustal-scale faults initially active during the period between 335 and 315 Ma. Normal motion along the faults, coeval with 335 to 315 Ma granite–migmatite domes, played a major role in the 3D distribution of the hydrothermal plumbing system. Gold and related metals were carried within huge hydrothermal cells, which reached ca. 100 km by 10 km in area, and 30 km in depth. In contrast, granites rich in magmatophile elements (W, Sn, rare-metals) generated smaller hydrothermal cells (10 km by 10 km in area, and < 6 km deep). Extraction of metals, by both deep-seated fluids and specialized magmas, occurred during granulitization of the lower crust at 300 ± 15 Ma. In the French Massif Central, the genesis of the two late Carboniferous mineralizing systems coincided with the end of syn-collisional extension and ended just before post-collisional extension. 相似文献
89.
We provide a generalized discussion of tidal evolution to arbitrary order in the expansion of the gravitational potential
between two spherical bodies of any mass ratio. To accurately reproduce the tidal evolution of a system at separations less
than 5 times the radius of the larger primary component, the tidal potential due to the presence of a smaller secondary component
is expanded in terms of Legendre polynomials to arbitrary order rather than truncated at leading order as is typically done
in studies of well-separated system like the Earth and Moon. The equations of tidal evolution including tidal torques, the
changes in spin rates of the components, and the change in semimajor axis (orbital separation) are then derived for binary
asteroid systems with circular and equatorial mutual orbits. Accounting for higher-order terms in the tidal potential serves
to speed up the tidal evolution of the system leading to underestimates in the time rates of change of the spin rates, semimajor
axis, and mean motion in the mutual orbit if such corrections are ignored. Special attention is given to the effect of close
orbits on the calculation of material properties of the components, in terms of the rigidity and tidal dissipation function,
based on the tidal evolution of the system. It is found that accurate determinations of the physical parameters of the system,
e.g., densities, sizes, and current separation, are typically more important than accounting for higher-order terms in the
potential when calculating material properties. In the scope of the long-term tidal evolution of the semimajor axis and the
component spin rates, correcting for close orbits is a small effect, but for an instantaneous rate of change in spin rate,
semimajor axis, or mean motion, the close-orbit correction can be on the order of tens of percent. This work has possible
implications for the determination of the Roche limit and for spin-state alteration during close flybys. 相似文献
90.
S. Pires J.-L. Starck A. Amara R. Teyssier A. Réfrégier J. Fadili 《Monthly notices of the Royal Astronomical Society》2009,395(3):1265-1279
With increasingly large data sets, weak lensing measurements are able to measure cosmological parameters with ever-greater precision. However, this increased accuracy also places greater demands on the statistical tools used to extract the available information. To date, the majority of lensing analyses use the two-point statistics of the cosmic shear field. These can be either studied directly using the two-point correlation function or in Fourier space, using the power spectrum. But analysing weak lensing data inevitably involves the masking out of regions, for example to remove bright stars from the field. Masking out the stars is common practice but the gaps in the data need proper handling. In this paper, we show how an inpainting technique allows us to properly fill in these gaps with only N log N operations, leading to a new image from which we can compute straightforwardly and with a very good accuracy both the power spectrum and the bispectrum. We then propose a new method to compute the bispectrum with a polar fft algorithm, which has the main advantage of avoiding any interpolation in the Fourier domain. Finally, we propose a new method for dark matter mass map reconstruction from shear observations, which integrates this new inpainting concept. A range of examples based on 3D N -body simulations illustrates the results. 相似文献