Polynomial approximation of Poincaré maps for hamiltonian systems     

Claude Froeschlé  Elena Lega 《Earth, Moon, and Planets》1996,72(1-3):51-56

Different methods are proposed and tested for transforming a nonlinear differential system, and more particularly a hamiltonian one, into a map without having to integrate the whole orbit as in the well known Poincaré map technique. We construct piecewise polynomial maps by coarse-graining the phase surface of section into parallelograms using values of the Poincaré maps at the vertices to define a polynomial approximation within each cell. The numerical experiments are in good agreement with the standard map taken as a model problem. The agreement is better when the number of vertices and the order of the polynomial fit increase. The synthetic mapping obtained is not symplectic even if at vertices there is an exact interpolation. We introduce a second new method based on a global fitting . The polynomials are obtained using at once all the vertices and fitting by least square polynomes but in such a way that the symplectic character is not lost.  相似文献   

M.I.T. studies of transient X-ray phenomena     

Claude R. Canizares 《Astrophysics and Space Science》1976,42(1):111-122

A variety of transient X-ray phenomena have been studied by the M.I.T. X-ray Astronomy Group. Data from the OSO-7 satellite reveal both long and short time-scale transients. Extensive observations have been made of the Lupus X-ray Nova (3U1543-47) and of GX339-4 (MX1658-48) which may represent a very different type of transient source A unique, intense X-ray flare lasting ten minutes was also recorded, and the X-ray emission from the active galaxy Cen A was found to vary significantly over a period of several days. In a recent ballon flight the Crab, pulsar, NP0532, was observed to exhibit a transient pulsed component distinct from the usual main pulse and interpulse. A sounding-rocket experiment detected an ultrasoft transient X-ray source tentatively associated with SS Cygni, and preliminary results from SAS-3 show a very hard spectrum for the new source A0535+26. On the other hand, extensive OSO-7 null observations of both Type I and II supernovae and of the flaring radio star Algol make it unlikely that these types of objects are potent transient X-ray emitters.Supported in part by the National Aeronautics and Space Administration under contracts NGL 22-009-015, NSR 22-009-654 and grant NGL 22-099-730 and by the National Science Foundation under grant GP-31378.Paper presented, at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

On the thermal structure of the southern Tibetan crust     

Claude Jaupart  Jean Francheteau  Xian-Jie Shen 《Geophysical Journal International》1985,81(1):131-155

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An Application of Multivariate Simulation in the Cement Industry     

Denis Marcotte  Keyvan Naraghi  Claude Bellehumeur  Erwan Gloaguen 《Mathematical Geology》2005,37(5):493-512

The profitability of a cement plant depends largely on its capacity to produce homogeneous cement with chemical composition close to specified targets for the cement type produced. One crucial step is the mixing of limestone with other raw materials in proportions calculated to meet these targets. Major design and operation decisions depend on the efficiency of this homogenizing step. The adequate modeling of the mixing process requires simulation of representative cross-correlated time series of chemical compositions of the raw materials involved. The chemical composition signals are obtained by multivariate geostatistical simulation using an LU (Cholesky) decomposition of the covariance matrix. Modifications to the usual LU method are presented. First, the effect on the raw covariance matrix of the closure property of chemical analysis is imposed. Second, the problem of memory space limitations in the LU method is tackled by using overlapping sliding neighbourhoods. The simulation algorithm is applied to the Joppa cement plant owned by Lafarge North America. The simulated raw material input streams are fed into the quality mix control (QMC), a proprietary software that models and controls the mixing operation to produce an output stream with cement characteristics as close as possible to desired targets. Two signal series are studied, one autocorrelated with a moderate temporal range and one with no autocorrelation. The QMC produces C₃S output signals having comparable short scale periodic variograms except that the variance of the uncorrelated signal is four times greater than those of the autocorrelated signal and the real Joppa data. The raw material feeder variograms have the same sill for both the white noise and the autocorrelated signals. However, the autocorrelated signal feeder variogram presents lower short term dispersion variance, a characteristic feature of Joppa operations. Our results show the importance of simulating the right temporal structure of the raw materials to realistically forecast the behavior of the output signals. We also discuss some practical implications of these findings for the design and operation of a cement plant.  相似文献   

Early diagenesis impact on precise U-series dating of deep-sea corals: Example of a 100-200-year old Lophelia pertusa sample from the northeast Atlantic     

Edwige Pons-Branchu  Claude Hillaire-Marcel  Pierre Deschamps  Bassam Ghaleb  Daniel J. Sinclair 《Geochimica et cosmochimica acta》2005,69(20):4865-4879

Deep-sea coral has proved useful for paleoceanographic reconstructions and for documenting ¹⁴C-ages of water masses using ²³⁰Th-ages. However, for precise and accurate U-series dating, further information on coral-age structure, growth rate and diagenetic evolution is still needed. To document such processes, we used U-Th-²²⁶Ra systematics in a 40 cm diameter, Lophelia pertusa specimen collected in 1912 from the Eastern Atlantic (Sea of the Hebrides). External parts of the specimen are thought to have been alive when collected whereas more internal parts were likely dead. The “live-collected” and “dead” parts of the skeleton were sampled and analyzed for their ²³⁰Th, ²³²Th, ²³⁴U, ²³⁸U, ²²⁶Ra and Ba contents by thermal ionization and multicollector inductively coupled plasma mass spectrometry. ²³⁰Th/²³⁴U ratios in the most recent parts yielded ages of 86 ± 6 a and 92 ± 9 a, in agreement with the date of recovery. The older parts yielded ²³⁰Th ages ranging from 169 ± 15 to 211 ± 10 a (n = 5), but had a 31% higher U content than more recent parts of the skeleton. This raises concerns about the possibility of secondary diagenetic U uptake, although an environmentally controlled U/Ca shift between coral growth stages cannot be ruled out. ²²⁶Ra/Ba measurements were made, and model- ²²⁶Ra/Ba ages averaging 250 ± 12 yr were calculated for the older part, assuming a constant initial ²²⁶Ra/Ba ratio in bottom waters. These ages are slightly older than ²³⁰Th-ages, suggesting either that ²²⁶Ra/Ba ratios of ambient-seawater changed over time or that a diagenetic phenomenon have affected the U-series system, or both. Scanning electron microscope observations revealed bioerosion and secondary biomineralization in the older part of the coral skeleton, supporting the hypothesis that diagenetic processes may have influenced the ages obtained by the U-series toolbox. Modeled U-series ages for such an open system are discussed. However, a comparison between ¹⁴C- and ²³⁰Th-ages performed on both pristine and bioeroded parts of the coral gives coherent values (ca 450 a) for the preindustrial ¹⁴C-reservoir age of North Atlantic waters. It remains to be determined, however, whether diagenesis occurs rapidly over a short period of time, or whether it continues for longer periods. In the latter case, diagenetic processes would hamper paleoceanographic interpretations as well as the precise calculation of ¹⁴C ages of deep-water masses, based on comparative U/Th- and ¹⁴C-chronologies.  相似文献   

Coupled modeling of thermics and hydrogeology with the Cast3M code: application to the Rainbow hydrothermal field (Mid-Atlantic Ridge, 36°14′N)     

Florian Perez  Claude Mügler  Philippe Jean-Baptiste  Jean Luc Charlou 《Computational Geosciences》2013,17(2):217-237

We present a new numerical tool developed in the Cast3M software framework to model hydrothermal circulation. Thermodynamic properties of one-phase pure water are calculated from the International Association for the Properties of Water and Steam formulation. This new numerical tool is validated on several test cases of convection in closed-top and open-top boxes. Simulations of hydrothermal circulation in a homogeneous-permeability porous medium also give results in good agreement with already published simulations. This new numerical tool is used to construct a geometric and physical conceptual model of the Rainbow vent site at 36°14^′N on the Mid-Atlantic Ridge. Several configurations are discussed, showing that high temperatures and high mass fluxes measured at the Rainbow site cannot be modeled with hydrothermal circulation in a homogeneous-permeability porous medium. These high values require the presence of a fault or a preferential pathway right below the venting site. We propose and discuss a two-dimensional single-pass model that allows us to simulate both high temperatures and high mass fluxes. This modeling of the hydrothermal circulation at the Rainbow site constitutes the first but necessary step to understand the origin of high concentrations of hydrogen issued from this ultramafic-hosted vent field.  相似文献   

Modelling and in-situ measurements of intense currents during a winter storm in the Gulf of Aigues-Mortes (NW Mediterranean Sea)     

Héloïse Michaud  Yann Leredde  Claude Estournel  Éric Berthebaud  Patrick Marsaleix 《Comptes Rendus Geoscience》2013,345(9-10):361-372

While oceanic circulation in the Gulf of Lion (GoL) has often been studied in calm weather or with northerly winds (Tramontane or Mistral) through observations and numerical circulation models, few studies have focused on southeasterly storm events. Yet, correct representation of the circulation during storms is crucial if the suspension of sediments is to be correctly modelled throughout the Gulf. The purpose of this paper is to describe the hydrodynamics in the Gulf of Aigues-Mortes (NW of the GoL) during the storm of 18 February 2007 by using a set of data from an ADCP station placed at a depth of 65 m on the sea bed off the coast at Sète, supplemented by the ocean circulation model SYMPHONIE. This storm was characterized by a moderate south-easterly wind (15 m . s^?1) and waves of up to 5 m of significant height at its apex. At the ADCP, strong currents of up to 0.8 m . s^?1 near the surface and 0.5 m . s^?1 near the bottom were recorded, parallel to the coast, flowing towards the south-west. The simulated currents were widely underestimated, even taking the effect of waves into account in the model. It was suspected that the representation of the wind in the atmospheric model was an underestimation. A new simulation was therefore run with an arbitrarily chosen stronger wind and its results were in much better agreement with the measurements. A simplified theoretical analysis successfully isolated the wind-induced processes, responsible for the strong currents measured during the apex and the strong vertical shear that occurred at the beginning of the storm. These processes were: 1/ the barotropic geostrophic current induced by a wind parallel to the coast and 2/ the Ekman spiral. The duration of the storm (about 36 h at the apex) explains the continuous increase of the current as predicted by the theory. The frictionally induced Ekman transport explains the current shear in the surface layer in the rising stage of the storm, and the addition of high waves and strong wind at the apex is more in favour of strong vertical mixing in the surface layer.  相似文献   

The particular “rammed earth” of the Saadian sugar refinery of Chichaoua (XVIth century,Morocco): mineralogical,chemical and mechanical characteristics     

Naoual Gamrani  Khalid R’kha Chaham  Mouncif Ibnoussina  Fabio Fratini  Luisa Rovero  Ugo Tonietti  Mohammed Mansori  Lehcen Daoudi  Claude Favotto  Nasrrddine Youbi 《Environmental Earth Sciences》2012,66(1):129-140

This work focuses on the building material used in the Saadian sugar refinery of Chichaoua (about 70 km southwest of Marrakesh). The study involved a classification of different types of rammed earth, followed by their mineralogical characterization based on optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). These studies are complemented by chemical investigations, X-ray fluorescence, and thermal analysis (DTA and TGA). The results demonstrate the use of two types of earth for the realisation of rammed earth, the first one non-plastic, -grained with added lime, the other one of low plasticity, and fine grained without addition of lime. Mechanical tests on site and in laboratory how at the first type of material exhibits great strength, exceeding the values known for rammed earth.  相似文献