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排序方式: 共有475条查询结果,搜索用时 31 毫秒
161.
162.
Jason W. Barnes Jacob Bow Jacob Schwartz Robert H. Brown Jason M. Soderblom Alexander G. Hayes Graham Vixie Stéphane Le Mouélic Sebastien Rodriguez Christophe Sotin Ralf Jaumann Katrin Stephan Laurence A. Soderblom Roger N. Clark Bonnie J. Buratti Kevin H. Baines Philip D. Nicholson 《Icarus》2011,216(1):136-140
We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan’s north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water. 相似文献
163.
Sanaz Vahidinia Jeffrey N. Cuzzi Matt Hedman Bruce Draine Roger N. Clark Ted Roush Gianrico Filacchione Philip D. Nicholson Robert H. Brown Bonnie Buratti Christophe Sotin 《Icarus》2011,215(2):682-694
We present models of the near-infrared (1-5 μm) spectra of Saturn’s F ring obtained by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) at ultra-high phase angles (177.4-178.5°). Modeling this spectrum constrains the size distribution, composition, and structure of F ring particles in the 0.1-100 μm size range. These spectra are very different from those obtained at lower phase angles; they lack the familiar 1.5 and 2 μm absorption bands, and the expected 3 μm water ice primary absorption appears as an unusually narrow dip at 2.87 μm. We have modeled these data using multiple approaches. First, we use a simple Mie scattering model to constrain the size distribution and composition of the particles. The Mie model allows us to understand the overall shapes of the spectra in terms of dominance by diffraction at these ultra-high phase angles, and also to demonstrate that the 2.87 μm dip is associated with the Christiansen frequency of water ice (where the real refractive index passes unity). Second, we use a combination of Mie scattering with Effective Medium Theory to probe the effect of porous (but structureless) particles on the overall shape of the spectrum and depth of the 2.87 μm band. Such simple models are not able to capture the shape of this absorption feature well. Finally, we model each particle as an aggregate of discrete monomers, using the Discrete Dipole Approximation (DDA) model, and find a better fit for the depth of the 2.87 μm feature. The DDA models imply a slightly different overall size distribution. We present a simple heuristic model which explains the differences between the Mie and DDA model results. We conclude that the F ring contains aggregate particles with a size distribution that is distinctly narrower than a typical power law, and that the particles are predominantly crystalline water ice. 相似文献
164.
Anthony Boccaletti Jean Schneider Wes Traub Pierre-Olivier Lagage Daphne Stam Raffaele Gratton John Trauger Kerri Cahoy Frans Snik Pierre Baudoz Raphael Galicher Jean-Michel Reess Dimitri Mawet Jean-Charles Augereau Jenny Patience Marc Kuchner Mark Wyatt Eric Pantin Anne-Lise Maire Christophe Vérinaud Samuel Ronayette Didier Dubreuil Michiel Min Michiel Rodenhuis Dino Mesa Russ Belikov Olivier Guyon Motohide Tamura Naoshi Murakami Ingrid Mary Beerer 《Experimental Astronomy》2012,34(2):355-384
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450?C900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5?C10?AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (??2 Earth radii, ??10 M??) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System. 相似文献
165.
B. Christophe L. J. Spilker J. D. Anderson N. André S. W. Asmar J. Aurnou D. Banfield A. Barucci O. Bertolami R. Bingham P. Brown B. Cecconi J. -M. Courty H. Dittus L. N. Fletcher B. Foulon F. Francisco P. J. S. Gil K. H. Glassmeier W. Grundy C. Hansen J. Helbert R. Helled H. Hussmann B. Lamine C. L?mmerzahl L. Lamy R. Lehoucq B. Lenoir A. Levy G. Orton J. Páramos J. Poncy F. Postberg S. V. Progrebenko K. R. Reh S. Reynaud C. Robert E. Samain J. Saur K. M. Sayanagi N. Schmitz H. Selig F. Sohl T. R. Spilker R. Srama K. Stephan P. Touboul P. Wolf 《Experimental Astronomy》2012,34(2):203-242
166.
Günter Blöschl Marc F.P.
Bierkens Antonio Chambel Christophe
Cudennec Georgia Destouni Aldo Fiori 《水文科学杂志》2013,58(10):1141-1158
ABSTRACTThis paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come. 相似文献
167.
Three-dimensional poromechanical back analysis of the pulse test accounting for transverse isotropy 总被引:3,自引:2,他引:1
The pulse test is usually considered as an efficient test for measuring the permeability of weakly permeable porous media. It is generally interpreted by comparison of experimental and theoretical curves obtained by a simplified 1D analytical solution. In a previous work, we proposed an improvement for test interpretation, through fully coupled numerical modeling in 2D axisymmetric configurations. The numerical modeling took into account the poromechanical coupling and exhibited 2D effects that cannot be assessed with classical interpretation. The modeling was coupled with an inverse method permitting the assessment of intrinsic permeability, mechanical parameters such as Young??s modulus, and poromechanical coupling parameters such as Biot coefficient. The interpretation of the tests on argillites showed anisotropy of the material and revealed the fundamental importance of this anisotropy for further works. The present paper aims at taking into account the transverse isotropy of the rock samples in the poromechanical back analysis of the test. A transverse isotropic poroelastic constitutive law has been developed and implemented in Code_Aster (Edf), and 3D modeling is required to account for all possible orientations of the samples. The poromechanical modeling is still coupled with an inverse method, also implemented in the finite element code. The method was applied to laboratory tests on Meuse/Haute-Marne argillites, on cylindrical samples with axis either parallel or perpendicular to the isotropy planes, and the results were compared with isotropic interpretation. The 3D transverse isotropic modeling provides more consistent values of the parameters than the 2D modeling, particularly for the mechanical parameters. 相似文献
168.
Abstract The Mamora area (Morocco) is located in the northern part of the Meseta and the southern part of Rharb. The recent formations (Mesozoic to Quaternary) lie unconformably on a Paleozoic basement. This study based on hydrogeological, sedimentological, drilling data and seismic reflection profiles interpretation, proposes new interpretations of geodynamical evolution of this area particularly in terms of tectonic patterns. The most ancient formations recognized in this region are Paleozoic schists and quartzites in the Tifíete sector. They represent the basement of the basin on which Triassic conglomerates and red mudstones associated with basalts lie unconformably. Jurassic and Cretaceous sediments are limestones and marls. The Mio-pliocene formations are open marine blue marls. Plio-quaternary sediments are limestones and sands containing gravel and pebbles. Miocene to Pliocene blue marls facies corresponds to deep marine marls (bathyal as indicated by planctonic foraminifers) with an attributed age from upper Miocene [9] to middle Pliocene [7]. A facies distribution map of the top of the blue marls has been realized where four main facies—conglomerate, shelly sandstone, limestone and marls—indicate a major regression in the Mamora basin. The datation of the formations was mostly realized by Wernli [22, 23, 24, 25], and Cirac [10], In the Mamora area, Hercynian faults show two main structural directions, N020°E-N040°E (Agadir-Rabat), N120°E (Rabat- Tiflète) [5], and a new major Hercynian fault (K2S). The seismic profiles have been studied between Sidi Slimane and Sidi Yahia area, to illustrate the structure of the Mamora, and to replace it, in the geodynamical evolution. The seismic reflection lines and drilling data show that the eastern Mamora was subdivided into two sectors: i) the southern sector is affected by Hercynian faults which create horsts and grabens in the Paleozoic. Mio-Pliocene formations infill these depressions and are covered by Quaternary sediments; ii) the northern sector is constituted by various formations: 1. Paleozoic formation as basement covered by autochthonous Mesozoic to Miocene, 2. Prerifain nappes (marls and evaporites), 3. Mio-Plio-Pleistocene formations as subautochthonous to autochthonous. These two sectors are separated by a major fault (K2S). On the other hand, in the occidental Mamora, the facies distribution and the Plio-Pleistocene thickening seem to be induced by faults with a NE-SW and NW-SE trends which affect the Paleozoic basement. Then, between the Meseta domain and the septentrional Rharb basin, two major Hercynian initially dextral shear zones, Rabat- Tiflete and K2S, have been recognised. During the Atlantic Ocean opening, they are probably senestral shear zones. At the same time the subsidence in Rharb basin is active, major action of these faults is normal. Therefore, Mamora represents a real hinge between stable Meseta and unstable septentrional Rharb basin. © 2001 Éditions scientifiques et médicales Elsevier SAS 相似文献
169.
170.
Christophe Proisy Nicolas Gratiot Edward J. Anthony Antoine Gardel François Fromard Patrick Heuret 《Continental Shelf Research》2009
Mud bank colonization by mangroves on the Amazon-influenced coast of French Guiana was studied using light detection and ranging (lidar) data which provide unique information on canopy geometry an sub-canopy topography. The role of topography was assessed through analysis of vegetation characteristics derived from these data. Measurements and analyses of mangrove expansion rates over space and time led to the identification of two distinct colonization processes. The first involves regular step-by-step mangrove expansion to the northwest of the experimental site. The second is qualified as ‘opportunistic’ since it involves a clear relationship between specific ecological characteristics of pioneer Avicennia and mud cracks affecting the mud bank surface and for which probabilities of occurrence were computed from terrain elevations. It is argued from an original analysis of the latter relationship that mud cracks cannot be solely viewed as water stress features that reflect desiccation potentially harmful to plant growth. Indeed, our results tend to demonstrate that they significantly enhance the propensity for mangroves to anchor and take root, thus leading to the colonization of tens of hectares in a few days. The limits and potential of lidar data are discussed with reference to the study of muddy coasts. Finally, the findings of the study are reconsidered within the context of a better understanding of both topography and vegetation characteristics on mangrove-fringed muddy coasts. 相似文献