SCIPION, a new flexible ionospheric sounder in Senegal     

Y. M. Le Roux  J. Ménard  J. P. Jolivet  P. J. Davy 《Annales Geophysicae》1998,16(6):738-742

SCIPION is a new state of the art digital sounder that has been developed by France Telecom-CNET for ionospheric monitoring and research. Extensive data processing using DSP technology has resulted in a low power, low cost and full featured system for both vertical and oblique soundings. A SCIPION system is in the process of being installed in Dakar, Senegal, to study HF propagation in the sub-equatorial ionosphere. However, preliminary results have still been obtained during experiments wit a prototype system. In this paper, the system is described and some illustrative examples of its capabilities are shown.  相似文献   

Rainfall-frequency curves with a recent urban dense rainfall measurement network     

Christian Roux  Michel Desbordes 《Atmospheric Research》1996,42(1-4)

Urban areas are becoming better equipped with dense rainfall measurement networks and there is a growing demand for local specific rainfall-frequency curves. However, the time series from such networks are generally short, often less than 20 yr, and spatially correlated (1 station per 5 or 10 km²) even at small time steps, usually less than 1 h. It is therefore necessary to use a method which takes the available information as much as possible into account in order to minimize the confidence intervals of the estimates. The French Department of Seine-Saint-Denis, covering an area of 236 km² in the eastern part of the Paris area, manages a 17-year-old rainfall data-base which contains about 250 station-years of checked data. These data are considered within a discussion of the issues of homogeneity of correlated time-series on an urban area, and the amount of information such a network includes at small time steps. Local rainfall frequency curves are developed with a regional approach and put into a non-dimensional form. They are compared with those obtained from a long-term series (more than 30 yr) available in Paris and with the curves obtained by the station-year method on 21 independent stations in the north of France.  相似文献   

Petrogenesis of picrite and associated basalts from the southern Mid-Atlantic Ridge     

Leon A. van Heerden  Anton P. le Roex 《Contributions to Mineralogy and Petrology》1988,100(1):47-60

Basalts dredged from the south wall of a fracture zone transecting the southern Mid-Atlantic Ridge (SMAR) at 54° S are unusual in that they include a suite of highly olivine phyric basalts, sampled along with more normal sparsely plagioclase phyric basalts, and a highly plagioclase phyric basalt. Four basalt types (olivine phyric, sparsely plagioclase phyric, evolved sparsely plagioclase phyric and highly plagioclase phyric) are readily distinguished on the basis of petrography, mineralogy and bulk composition. They range from primitive to evolved, with the olivine phyric basalts having elevated MgO (up to 15.5%) and the plagioclase phyric basalt having elevated Al₂O₃ (19.3%) and CaO (13.1%) contents. Compositional variations are extremely consistant, with the olivine phyric basalts and the sparsely plagioclase phyric basalts defining coherent linear trends. On the basis of the ratios and covariation of the incompatible trace elements Zr, Nb, Y and Ba, distinct parental magmas for each basalt type are required. An investigation of Fe-Mg and Mg-Ni distribution coefficients between olivine and magma indicates that olivines from the olivine phyric basalts are on average too forsteritic and too Ni poor to have crystallized in a magma corresponding to the host bulk rock composition. This implies that these basalts are enriched in xenocrystic olivine. Olivines from the other basalt types are mostly of equilibrium composition, although there are some exceptions. Petrogenetic models for the formation of the different basalt types are quantitatively evaluated in terms of fractional crystallization/crystal accumulation processes. These indicate that (1) the olivine phyric basalts are the products of olivine and minor Cr-spinel accumulation and do not represent analogues of primary magma, or a liquid fractionation trend; (2) that the sparsely plagioclase phyric basalts were formed by polybaric fractional crystallization of olivine, plagioclase and clinopyroxene; and (3) that the evolved sparsely plagioclase phyric basalts are not readily related to one another. The single highly plagioclase phyric basalt is unrelated to the other basalt types and is cumulus enriched in plagioclase.The different basalt types are unrelated to one another and document the presence of at least four distinct magma types erupted in close proximity at this ridge/transform intersection on the southern end of the Mid-Atlantic Ridge.  相似文献   

Optimization with the Gradual Deformation Method   总被引：1，自引：0，他引：1  

Mickaële Le Ravalec-Dupin  Benoît Ntinger 《Mathematical Geology》2002,34(2):125-142

Building reservoir models consistent with production data and prior geological knowledge is usually carried out through the minimization of an objective function. Such optimization problems are nonlinear and may be difficult to solve because they tend to be ill-posed and to involve many parameters. The gradual deformation technique was introduced recently to simplify these problems. Its main feature is the preservation of the spatial structure: perturbed realizations exhibit the same spatial variability as the starting ones. It is shown that optimizations based on gradual deformation converge exponentially to the global minimum, at least for linear problems. In addition, it appears that combining the gradual deformation parameterization with optimizations may remove step by step the structure preservation capability of the gradual deformation method. This bias is negligible when deformation is restricted to a few realization chains, but grows increasingly when the chain number tends to infinity. As in practice, optimization of reservoir models is limited to a small number of iterations with respect to the number of gridblocks, the spatial variability is preserved. Last, the optimization processes are implemented on the basis of the Levenberg–Marquardt method. Although the objective functions, written in terms of Gaussian white noises, are reduced to the data mismatch term, the conditional realization space can be properly sampled.  相似文献   

Water organisation at the solid–aqueous solution interfaceOrganisation de l'eau à l'interface solide–solution aqueuse     

Laurent J. Michot  Frédéric Villiéras  Michèle François  Isabelle Bihannic  Manuel Pelletier  Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):611-631

The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631.  相似文献   

Heat capacity and entropy of rutile (TiO<Subscript>2</Subscript>) and nepheline (NaAlSiO<Subscript>4</Subscript>)     

D. de Ligny  P. Richet  E. F. Westrum Jr  J. Roux 《Physics and Chemistry of Minerals》2002,29(4):267-272

 From heat capacities measured adiabatically at low temperatures, the standard entropies at 298.15 K of synthetic rutile (TiO₂) and nepheline (NaAlSiO₄) have been determined to be 50.0 ± 0.1 and 122.8 ± 0.3 J mol⁻¹ K, respectively. These values agree with previous measurements and in particular confirm the higher entropy of nepheline with respect to that of the less dense NaAlSiO₄ polymorph carnegieite. Received: 23 July 2001 / Accepted: 12 October 2001  相似文献   

Flexibility, technology, and the daily life practices of distance students living beyond the digital mainstream     

Ståle Angen Rye 《Geoforum》2007,38(5):1028-1039

In this paper it is argued that even though communication technologies release distance students considerably from their dependency on a campus, students are still very much connected to places in their daily lives. These connections are constituted through the “placing” of technology, the students’ relations to people in their daily lives and the students’ relations to the education institution. Communication technology not only releases students from the spatial dimensions; it also attaches them to specific places. It is argued that the use of technology in distance education can reduce the students’ flexibility even if they do not have to attend campus regularly. The empirical analysis presented in this paper is based on a case study of a Master’s degree programme in Public Management offered by Open University Indonesia (Universitas Terbuka).  相似文献   

Late Holocene Mediterranean coastal change along the Tiber Delta and Roman occupation of the Laurentine shore, central Italy     

Helen M. Rendell  Amanda J. Claridge  Michle L. Clarke 《Quaternary Geochronology》2007,2(1-4):83-88

A line of Roman villas once dominated the Mediterranean coastline to the south of the Tiber river mouth near Ostia in central Italy. The Roman remains, which were constructed within a series of dune ridges, now lie up to 900 m from the current shoreline as a result of the continued evolution of the Tiber delta in response to postglacial sea level rise, sediment inputs from the Tiber river catchment and tectonic uplift. Infrared stimulated luminescence (IRSL) ages of potassium-rich feldspars extracted from dune sands are in good agreement with the independent age control provided by the Roman structures and allow us to hypothesise an increase in aggradation rates of five times since the end of the period of Roman occupation compared with the earlier Holocene.  相似文献   

Acoustic–gravity waves during solar eclipses: Detection and characterization using wavelet transforms     

P. &#x;auli  S.G. Roux  P. Abry  J. Bo&#x;ka 《Journal of Atmospheric and Solar》2007,69(17-18):2465

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Analysis of karst hydrodynamics through comparison of dissolved and suspended solids' transport     

Danièle Valdes  Jean-Paul Dupont  Nicolas Massei  Benoît Laignel  Joël Rodet 《Comptes Rendus Geoscience》2005,337(15):1365-1374

In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of $T\text{–}C$ curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005).  相似文献