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81.
82.
83.
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
84.
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
85.
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
86.
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
87.
Marina Brozovic Lance A.M. Benner Steven J. Ostro Jon D. Giorgini Jean-Luc Margot Randy Rose 《Icarus》2010,208(1):207-220
Arecibo (2380 MHz, 12.6 cm) and Goldstone (8560 MHz, 3.5 cm) delay-Doppler radar images obtained in July and August of 2000 reveal that 4486 Mithra is an irregular, significantly bifurcated object, with a central valley ∼380 m deep and a long axis potentially exceeding 2 km. With its bimodal appearance, Mithra is a strong candidate for a contact binary asteroid. Sequences of Goldstone images spanning up to 3 h per day show very little rotation and establish that Mithra is an unusually slow rotator. We used Goldstone and Arecibo data to estimate Mithra’s 3D shape and spin state. We obtain prograde (λ = 337°, β = 19°) and retrograde (λ = 154°, β = −19°) models that give comparable fits, have very similar shapes roughly resembling an hourglass, and have a rotation period of 67.5 ± 6.0 h. The dimensions of these two models are very similar; for the prograde solution the maximum dimensions are X = 2.35 ± 0.15 km, Y = 1.65 ± 0.10 km, Z = 1.44 ± 0.10 km. Dynamical analysis of our models suggests that in the past, Mithra most likely went through a period of even slower rotation with its obliquity close to 90°. The spin rate is predicted to be increasing due to thermal torque (YORP), while the obliquity, which is currently +68° and +106° for the prograde and retrograde models, respectively, is predicted to move away from 90°. 相似文献
88.
Emilie Pourtier Jean-Luc Devidal François Gibert 《Geochimica et cosmochimica acta》2010,74(6):1872-66
The solubility of synthetic NdPO4 monazite end-member was experimentally determined from 300 up to 800 °C, at 2000 bars in pure water, and in aqueous chloride or phosphate solutions. Both the classical weight-loss method and a new method based on isotope dilution coupled with thermal ionization mass spectrometer were used. In the range of temperature studied monazite showed a prograde solubility from 10−5.4 m at 300 °C up to 10−2.57 m at 800 °C. Experiments in H2O-H3PO4-NaCl-HCl solutions suggested Nd(OH)30 was the major species that was formed at high temperature and pressure. The equilibrium constants (log K) for the reaction:
89.
Eric Lantz Jean-Luc Blanchet Luca Furfaro Fabrice Devaux 《Monthly notices of the Royal Astronomical Society》2008,386(4):2262-2270
A multi-imaging strategy is proposed and experimentally tested to improve the accuracy of photon counting with an electron multiplying CCD (EMCCD), by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on one pixel. This strategy is based on Bayesian estimation on each image, with a priori information given by the sum of the images. The method works even for images with large dynamic range, with more improvement in the low light level areas. In these areas, two thirds of the variance added by the EMCCD in a conventional imaging mode are removed, making the physical photon noise predominant in the detected image. 相似文献
90.
Michael W. Busch Jon D. Giorgini Lance A.M. Benner Randy Rose Petr Pravec Michael J. Ireland Stephen B. Broschart Michael C. Nolan Jean-Luc Margot 《Icarus》2007,190(2):608-621
Near-Earth Asteroid (29075) 1950 DA may closely encounter Earth in 2880. The probability of Earth impact may be as high as 1/300, but the outcome of the encounter depends critically on the physical properties of the asteroid [Giorgini et al., 2002. Science 196, 132-136]. We have used Arecibo and Goldstone radar data and optical lightcurves to estimate the shape, spin state, and surface structure of 1950 DA. The data allow two distinct models. One rotates prograde and is roughly spheroidal with mean diameter 1.16±0.12 km. The other rotates retrograde and is oblate and about 30% larger. Both models suggest a nickel-iron or enstatite chondritic composition. Ground-based observations should be able to determine which model is correct within the next several decades. 相似文献