Near-Earth asteroid surface roughness depends on compositional class   总被引：1，自引：0，他引：1  

Lance A.M. Benner  Steven J. Ostro  Michael C. Nolan  Jon D. Giorgini  Jean-Luc Margot  Michael W. Busch 《Icarus》2008,198(2):294-304

Radar observations of 214 near-Earth asteroids (NEAs) reveal a very strong correlation of circular polarization ratio with visible-infrared taxonomic class, establishing distinct differences in the centimeter-to-several-decimeter structural complexity of objects in different spectral classes. The correlation may be due to the intrinsic mechanical properties of different mineralogical assemblages but also may reflect very different formation ages and collisional histories. The highest ratios are measured for groups associated with achondritic igneous rocky meteorites: the E class, whose parent body may be 3103 Eger, and the V class, derived from the mainbelt asteroid (and Dawn mission target) 4 Vesta.  相似文献   

On the use of long-term observation of water level and temperature along the shore for a better understanding of the dynamics: example of Toulon area,France     

Rey  Vincent  Dufresne  Christiane  Fuda  Jean-Luc  Mallarino  Didier  Missamou  Tathy  Paugam  Caroline  Rougier  Gilles  Taupier-Letage  Isabelle 《Ocean Dynamics》2020,70(7):913-933

Ocean Dynamics - A dense network of instruments has been deployed within harbors along the Mediterranean coast, in the Toulon Metropole area, between the Hyères islands and the Sanary Bay in...  相似文献   

A Bayesian method for missing rainfall estimation using a conceptual rainfall–runoff model     

Siao Sun  Günther Leonhardt  Santiago Sandoval  Jean-Luc Bertrand-Krajewski  Wolfgang Rauch 《水文科学杂志》2017,62(15):2456-2468

The estimation of missing rainfall data is an important problem for data analysis and modelling studies in hydrology. This paper develops a Bayesian method to address missing rainfall estimation from runoff measurements based on a pre-calibrated conceptual rainfall–runoff model. The Bayesian method assigns posterior probability of rainfall estimates proportional to the likelihood function of measured runoff flows and prior rainfall information, which is presented by uniform distributions in the absence of rainfall data. The likelihood function of measured runoff can be determined via the test of different residual error models in the calibration phase. The application of this method to a French urban catchment indicates that the proposed Bayesian method is able to assess missing rainfall and its uncertainty based only on runoff measurements, which provides an alternative to the reverse model for missing rainfall estimates.  相似文献   

Locating a point on a spherical surface relative to a spherical polygon of arbitrary shape     

Michael Bevis  Jean-Luc Chatelain 《Mathematical Geology》1989,21(8):811-828

An algorithm for determining if any given point,P, on the surface of a sphere is located inside, outside, or along the border of an arbitrary spherical polygon,S, is described. The polygon is described by specifying coordinates of its vertices, and coordinates of some pointX which is known to lie withinS. The algorithm is based on the principle that an arc joiningX andP will cross the border ofS an odd number of times ifP lies outsideS, and an even number of times ifP lies withinS. The algorithm has been implemented as a set of FORTRAN subroutines, and a listing is provided. The algorithm and subroutine package can be used with spherical polygons containing holes, or with composited spherical polygons.  相似文献   

The last 750 ka in loess–palaeosol sequences from northern France: environmental background and dating of the western European Palaeolithic     

Pierre Antoine  Sylvie Coutard  Jean-Jacques Bahain  Jean-Luc Locht  David Hérisson  Emilie Goval 《第四纪科学杂志》2021,36(8):1293-1310

This study presents an overview of Middle Pleistocene loess–palaeosol sequences (LPS) in northern France and discusses the palaeoclimatic significance of the pedosedimentary record in the context of western European LPS and of global climatic cycles for the last 750 ka. In this area, the oldest loess deposits (early Middle Pleistocene) are preserved in sedimentary traps (leeward scarps of fluvial terraces and dissolution sinkholes). They result from local deflation processes reworking Pleistocene sandy fluvial deposits or relicts of Tertiary sands. A large extension of typical calcareous loess over the landscape, the Loess Revolution, is then observed during MIS 6, with heavy mineral assemblages testifying to long-distance transport from the polar desert area of the dried eastern Channel. A correlation scheme is proposed between the global records of northern France in continental environments and both global palaeoclimatic records and other main western European LPS. After 30 years of research, northern France LPS stand as a fundamental archive of the impact of interglacial–glacial climatic cycles as well as millennial events. Finally, these works provide a robust chronoclimatic framework for the study of the western European Late Acheulean and Middle Palaeolithic and for the relative dating of the various fluvial terraces that they fossilise.  相似文献   

(Pre-) historic changes in natural and anthropogenic heavy metals deposition inferred from two contrasting Swiss Alpine lakes     

Florian Thevenon  Stéphane Guédron  Massimo Chiaradia  Jean-Luc Loizeau  John Poté 《Quaternary Science Reviews》2011,30(1-2):224-233

Continuous high-resolution sedimentary record of heavy metals (chromium (Cr), copper (Cu), lead (Pb), zinc (Zn), manganese (Mn), and mercury (Hg)), from lakes Lucerne and Meidsee (Switzerland), provides pollutant deposition history from two contrasting Alpine environments over the last millennia. The distribution of conservative elements (thorium (Th), scandium (Sc) and titanium (Ti)) shows that in absence of human disturbances, the trace element input is primarily controlled by weathering processes (i.e., runoff and erosion). Nonetheless, the enrichment factor (EF) of Pb and Hg (that are measured by independent methods), and the Pb isotopic composition of sediments from the remote lake Meidsee (which are proportionally more enriched in anthropogenic heavy metals), likely detect early mining activities during the Bronze Age. Meanwhile, the deposition of trace elements remains close to the range of natural variations until the strong impact of Roman activities on atmospheric metal emissions. Both sites display simultaneous increases in anthropogenic trace metal deposition during the Greek and Roman Empires (ca 300 BC to AD 400), the Late Middle Ages (ca AD 1400), and the Early Modern Europe (after ca AD 1600). However, the greatest increases in anthropogenic metal pollution are evidenced after the industrial revolution of ca AD 1850, at low and high altitudes. During the twentieth century, industrial releases multiplied by ca 10 times heavy metal fluxes to hydrological systems located on both sides of the Alps. During the last decades, the recent growing contribution of low radiogenic Pb further highlights the contribution of industrial sources with respect to wood and coal burning emissions.  相似文献   

Characterisation of rapid infiltration flows and vulnerability in a karst aquifer using a decomposed fluorescence signal of dissolved organic matter     

Marine Quiers  Christelle Batiot-Guilhe  Cristina C. Bicalho  Yves Perrette  Jean-Luc Seidel  Sandra Van Exter 《Environmental Earth Sciences》2014,71(2):553-561

The fluorescent properties of dissolved organic matter (DOM) have been used as natural tracers in various water systems. However, only few studies have focused on groundwater systems, specifically, on karst systems. The aim of this study was to develop the use of the DOM fluorescence signal as a natural tracer, considering the multiple compartments of a karst system. This method was applied to the Lez hydrosystem, which supplies the city of Montpellier with drinking water. The hydrodynamics and hydrochemistry of the spring were monitored beginning March 2006. The DOM fluorescence was measured by the excitation–emission matrix spectroscopy technique. The analysis of the total fluorescence signal confirms the efficiency of this tool to trace rapid infiltration flows. Moreover, the decomposition of the signal into different fluorophores complements the information provided by the total signal. Indeed, the fluorescence emitted by the humic compounds seems to be the ideal tool for identifying rapid infiltration flows. Nevertheless, the fluorescence of protein-like compounds is better correlated with the inflow of faecal bacteria at the outlet. This decomposition of the fluorescence signal is an interesting way to provide information on both the rapid infiltration flow as well as the vulnerability of the karst aquifers.  相似文献   

Radar and infrared observations of binary near-Earth Asteroid 2002 CE26     

Michael K. Shepard  Jean-Luc Margot  Michael C. Nolan  Benjamin Estes  Eric L. Volquardsen  Lance A.M. Benner  Steven J. Ostro 《Icarus》2006,184(1):198-210

We observed near-Earth Asteroid (NEA) 2002 CE26 in August and September 2004 using the Arecibo S-band (2380-MHz, 12.6-cm) radar and NASA's Infrared Telescope Facility (IRTF). Shape models obtained based on inversion of our delay-Doppler images show the asteroid to be 3.5±0.4 km in diameter and spheroidal; our corresponding nominal estimates of its visual and radar albedos are 0.07 and 0.24, respectively. Our IRTF spectrum shows the asteroid to be C-class with no evidence of hydration. Thermal models from the IRTF data provide a size and visual albedo consistent with the radar-derived estimate. We estimate the spin-pole to be within a few tens of degrees of λ=317°, β=−20°. Our radar observations reveal a secondary approximately 0.3 km in diameter, giving this binary one of the largest size differentials of any known NEA. The secondary is in a near-circular orbit with period 15.6±0.1 h and a semi-major axis of 4.7±0.2 km. Estimates of the binary orbital pole and secondary rotation rate are consistent with the secondary being in a spin-locked equatorial orbit. The orbit corresponds to a primary mass of M=1.95±0.25×¹⁰¹³ kg, leading to a primary bulk density of , one of the lowest values yet measured for a main-belt or near-Earth asteroid.  相似文献   

Evolution of Mercury's obliquity     

Marie Yseboodt  Jean-Luc Margot 《Icarus》2006,181(2):327-337

Mercury has a near-zero obliquity, i.e. its spin axis is nearly perpendicular to its orbital plane. The value of the obliquity must be known precisely in order to constrain the size of the planet's core within the framework suggested by Peale [Peale, S.J., 1976. Nature 262, 765-766]. Rambaux and Bois [Rambaux, N., Bois, E., 2004. Astron. Astrophys. 413, 381-393] have suggested that Mercury's obliquity varies on thousand-year timescales due to planetary perturbations, potentially ruining the feasibility of Peale's experiment. We use a Hamiltonian approach (free of energy dissipation) to study the spin-orbit evolution of Mercury subject to secular planetary perturbations. We can reproduce an obliquity evolution similar to that of Rambaux and Bois [Rambaux, N., Bois, E., 2004. Astron. Astrophys. 413, 381-393] if we integrate the system with a set of initial conditions that differs from the Cassini state. However the thousand-year oscillations in the obliquity disappear if we use initial conditions corresponding to the equilibrium position of the Cassini state. This result indicates that planetary perturbations do not force short-period, large amplitude oscillations in the obliquity of Mercury. In the absence of excitation processes on short timescales, Mercury's obliquity will remain quasi-constant, suggesting that one of the important conditions for the success of Peale's experiment is realized. We show that interpretation of data obtained in support of this experiment will require a precise knowledge of the spin-orbit configuration, and we provide estimates for two of the critical parameters, the instantaneous Laplace plane orientation and the orbital precession rate from numerical fits to ephemeris data. Finally we provide geometrical relationships and a scheme for identifying the correct initial conditions required in numerical integrations involving a Cassini state configuration subject to planetary perturbations.  相似文献   

A microphysically-based approach to modeling emissivity and albedo of the martian seasonal caps     

Janusz Eluszkiewicz  Jean-Luc Moncet  Gary B. Hansen 《Icarus》2005,174(2):524-534

A new model of albedo and emissivity of the martian seasonal caps represented as porous CO₂ slabs containing spherical voids and dust particles is described. In the model, a radiative transfer model is coupled with a microphysical model in order to link changes in albedo and emissivity to changes in porosity caused by ice metamorphism. The coupled model is capable of reproducing temporal changes in the spectra of the caps taken by the Thermal Emission Spectrometer onboard the Mars Global Surveyor and it can be used as the forward model in the retrievals of the caps' physical properties (porosity, dust abundance, void and dust grain size) from the spectra. Preliminary results from such inversion studies are presented.  相似文献