Mercury exosphere: II. The sodium/potassium ratio     

Francois Leblanc  Alain Doressoundiram 《Icarus》2011,211(1):10-20

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A two level scaling-up method for multiphase flow in porous media; numerical validation and comparison with other methods     

Alain Bourgeat  Mladen Jurak 《Computational Geosciences》2010,14(1):1-14

We present a robust and accurate strategy for upscaling two-phase flow in heterogeneous porous media composed of different rock-types. The method is tested by means of numerical simulations and compared with other upscaling methods.  相似文献   

Long-term Field Observations on Seasonality in Chlorophyll-<Emphasis Type="Italic">a</Emphasis> Concentrations in a Shallow Coastal Marine Ecosystem,the Wadden Sea     

Catharina Johanna Maria Philippart  Jolanda Martine van Iperen  Gerhard Cornelis Cadée  Alain François Zuur 《Estuaries and Coasts》2010,33(2):286-294

Analyses of long-term field observations (1974–2007) on chlorophyll-a concentrations in the western Wadden Sea showed no long-term trends in the timing of the wax and wane of phytoplankton spring blooms. There is weak evidence, however, that the height of the autumn bloom has decreased since the early 1990s. This fading of the autumn bloom may have had consequences for the carbon transfer to higher trophic levels, currently hampering primary consumer species that mostly rely on food supply during late summer. Current and other findings suggest a shortening of the growing season due to the fading of the autumn bloom in the Wadden Sea and a lengthening of the growing season due to an advancement of the spring bloom in the North Sea. These regionally different changes in seasonality may have contributed to the coinciding decrease in bivalve filtering capacity in the western Wadden Sea and the large-scale offshore shift of juvenile plaice from the Wadden Sea to the adjacent North Sea.  相似文献   

Erratum à l’article « Relevés de température au marégraphe de Marseille » [C. R. Geoscience 342 (1) (2010) 75–78]     

Alain Coulomb 《Comptes Rendus Geoscience》2010,342(9):754

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Phase-sensitive Holography of Solar Activity     

Braun  D.C.  Lindsey  C. 《Solar physics》2000,192(1-2):307-319

Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. We have now applied techniques in phase-sensitive seismic holography to data from the Solar Oscillations Investigation – Michelson Doppler Imager (SOI-MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft to obtain high resolution phase-correlation maps of a large, complex active region and the `acoustic moat' which surrounds it. We report the following new results: First, the reduced sound travel-time perturbations in sunspots, acoustic moats, and isolated plages increase approximately in proportion to the logarithm of the surface magnetic flux density, for flux densities above 10 G. This is consistent with an interpretation of the travel-time anomalies, observed with holographic and other local-helioseismic procedures, as caused by acoustic Wilson-like depressions in photospheres of magnetic regions. Second, we find that, compared with isolated plages, the acoustic moats have an additional sound travel-time reduction on the order of 3–5 s which may be explained by a thermal excess due to the blockage of convective transport by the sunspot photosphere. Third, the combined effect of the Wilson depression in plages, acoustic moats, and sunspots may explain the observed variation of global p-mode frequencies with the solar cycle. Fourth, we find that active regions, including sunspots, acoustic moats, and plages, significantly reflect p modes above the acoustic cut-off frequency, where the surface of the quiet Sun acts as a nearly perfect absorber of incident acoustic radiation.  相似文献   

Helioseismic Holography of Active-Region Subphotospheres – (Invited Review)     

Braun  D.C.  Lindsey  C. 《Solar physics》2000,192(1-2):285-305

The development of solar acoustic holography has opened a major new diagnostic avenue in local helioseismology. It has revealed `acoustic moats' surrounding sunspots, `acoustic glories' surrounding complex active regions, and `acoustic condensations' suggesting the existence of significant seismic anomalies up to 20 Mm beneath active-region photospheres. Phase-sensitive seismic holography is now yielding high-resolution maps of sound travel-time anomalies caused by magnetic forces in the immediate subphotosphere, apparent thermal enhancements in acoustic moats, and Doppler signatures of subsurface flows. It has given us the first seismic images of a solar flare, and has uncovered a remarkable anomaly in the statistical distribution of seismic emission from acoustic glories. Seismic holography will probably give us the means for early detection of large active regions on the far-surface of the Sun, and possibly of deep subsurface activity as well. This powerful diagnostic now promises a new insight into the hydromechanical and thermal environments of the solar interior in the local perspective.  相似文献   

Extension et sédimentation au paléozoïque terminal et au Mésozoïque dans le bassin de Majunga (Nord-Ouest de Madagascar)     

Yolande Razafindrazaka  Thogne Randriamananjara  Alain Piqu  Catherine Thouin  Edgard Laville  Jacques Malod  Jean-Pierre Rhault 《Journal of African Earth Sciences》1999,28(4):949-959

The Majunga Basin is located in the northwestern part of Madagascar with a N45–60°E trending axis. It was filled by almost exclusively continental Karoo Supergroup sediments, which are Permian to Early Jurassic in age, and by younger sequences, mainly marine, that were deposited from the Middle Jurassic to the present.The Karoo Basin geometry is deduced from the analysis of seismic sections. A central northeast trending horst is flanked by two sub-basins. Deposition of the Karoo sequences was controlled by these northeast trending faults. On the contrary, the Middle Jurassic to present sequences witness only a slight tilting of the basement towards the northwest.The development of the Majunga Basin includes, therefore, two successive stages. In the synrift episode, from Permian to Early Jurassic times, the sedimentation was syntectonic, controlled by synsedimentary faulting and the creation of a horst and graben extensive pattern. The postrift episode started during the Middle Jurassic.These two stages of the Majunga Basin development correspond to the geodynamic evolution recorded elsewhere in this part of the Gondwana.  相似文献   

Linking uplift,erosion, and sedimentation using landscape evolution models: Madagascar since the Late Cretaceous     

Ruohong Jiao  Jean Braun  Antoine Delaunay  Cécile Robin  François Guillocheau 《地球表面变化过程与地形》2023,48(1):215-229

We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.  相似文献   

VLBI measurements of the parallax and proper motion of U Herculis     

Huib Jan van Langevelde  Philip J. Diamond  Wouter Vlemmings  Alain Baudry  Harm J. Habing  Richard T. Schilizzi 《New Astronomy Reviews》1999,43(8-10)

The OH 1667 maser in the circumstellar shell around the Mira variable U Her has been observed with the VLBA at 6 epochs, spread over 4 years. By using straightforward phase referencing techniques the stellar proper motion can be measured. Preliminary analysis indicates that the parallactic motion is also detected. An important question is whether the maser spots can be assumed to be fixed with respect to the star. The observations show both evidence supporting and contradicting the idea that one maser spot is the amplified stellar image.  相似文献   

Dynamics of dissolved major (Na,K, Ca,Mg, and Si) and trace (Al,Fe, Mn,Zn, Cu,and Cr) elements along the lower Orinoco River          下载免费PDF全文

Abrahan Mora  Jürgen Mahlknecht  Juan Carlos Baquero  Alain Laraque  Juan A. Alfonso  Daniel Pisapia  Laura Balza 《水文研究》2017,31(3):597-611

This study addresses the changes in dissolved major and trace element concentrations along the Orinoco River, including the mixing zone between the Orinoco and Apure Rivers. Water samples from the Apure and Orinoco Rivers were collected monthly in four sectors over a period of 15 months. Auxiliary parameters (pH, dissolved oxygen, conductivity, and temperature), total suspended sediments, dissolved organic carbon (DOC), and major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) element concentrations were measured in all sectors. The relative contribution of both rivers after the Apure–Orinoco confluence was determined using Ca as a tracer. Moreover, a mixing model was developed to determine whether dissolved species exhibit a conservative behavior during mixing. The results indicate that DOC is removed from waters during the Apure–Orinoco mixing, probably due to absorption of DOC on mineral phases supplied by the Apure River. Dissolved Na, Ca, and Mg behave conservatively during the mixing processes, and their concentrations are controlled by a dilution process. The anomaly in the temporal pattern of K in the Orinoco is caused by the input of biogenic K originating from the Apure River during the high‐water stage. The loss of dissolved Si during the low‐water stage can be explained by the uptake of Si by diatoms. Dissolved Mn, Zn, Al, and Fe showed a non‐conservative behavior during the Apure–Orinoco mixing. The removal of Mn and Zn from the dissolved phase can be explained by the formation of Mn‐oxyhydroxides and the scavenging of Zn onto Mn oxides. Dissolved Fe is controlled by redox processes, although the removals of Fe and Al due to the preferential adsorption of large organometallic complexes by mineral surfaces after the Apure–Orinoco confluence can affect the mobility of both elements during transport. The conservative behavior shown by Cu and Cr can be related to the tendency of both elements to be complexed with small organic colloids, which are not preferentially adsorbed by clays.  相似文献