排序方式： 共有85条查询结果，搜索用时 203 毫秒
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Ludovic Van Waerbeke Takashi Hamana † Román Scoccimarro Stephane Colombi Francis Bernardeau 《Monthly notices of the Royal Astronomical Society》2001,322(4):918-926
As pointed out in previous studies, the measurement of the skewness of the convergence field κ will be useful in breaking the degeneracy among the cosmological parameters constrained from weak lensing observations. The combination of shot noise and finite survey volume implies that such a measurement is likely to be performed in a range of intermediate scales (0.5 to 20 arcmin) where neither perturbation theory nor the hierarchical ansatz applies. Here we explore the behaviour of the skewness of κ at these intermediate scales, based on results for the non-linear evolution of the mass bispectrum. We combined different ray-tracing simulations to test our predictions, and we find that our calculations describe accurately the transition from the weakly non-linear to the strongly non-linear regime. We show that the single lens-plane approximation remains accurate even in the non-linear regime, and we explicitly calculate the corrections to this approximation. We also discuss the prospects of measuring the skewness in upcoming weak lensing surveys. 相似文献
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Toni Schulz Pavel P. Povinec Ludovic Ferrire A. J. Timothy Jull Andrej Kov
ik Ivan Sýkora Jonas Tusch Carsten Münker Dan Topa Christian Koeberl 《Meteoritics & planetary science》2020,55(2):294-311
The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high‐field strength and highly siderophile element (HSE) data, Sr‐Nd‐Hf‐W‐Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high‐field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars’ tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (187Os/188Os = 0.1289 ± 15 and an ε182W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu‐Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm‐Nd and Lu‐Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre‐atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic‐ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general. 相似文献
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Matthew S. HUBER Ludovic FERRIÈRE Anna LOSIAK Christian KOEBERL 《Meteoritics & planetary science》2011,46(9):1418-1424
Abstract– Planar deformation features (PDFs) in quartz, one of the most commonly used diagnostic indicators of shock metamorphism, are planes of amorphous material that follow crystallographic orientations, and can thus be distinguished from non‐shock‐induced fractures in quartz. The process of indexing data for PDFs from universal‐stage measurements has traditionally been performed using a manual graphical method, a time‐consuming process in which errors can easily be introduced. A mathematical method and computer algorithm, which we call the Automated Numerical Index Executor (ANIE) program for indexing PDFs, was produced, and is presented here. The ANIE program is more accurate and faster than the manual graphical determination of Miller–Bravais indices, as it allows control of the exact error used in the calculation and removal of human error from the process. 相似文献
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Jaffrennou C Giamarchi P Cabon JY Stephan L Burel-Deschamps L Bautin F Thomas A Dumont J Le Floch S 《Marine pollution bulletin》2007,54(12):1932-1939
Coal is currently becoming an increasingly interesting fossil energy resource and that is the reason why its maritime transport, and hence the risk of collier accidents, increase. In this work, the environmental impact of an accidental coal immersion at sea is studied: the physicochemical effects are estimated using innovative experimental setups – a laboratory seawater canal called “polludrome” is used to evaluate the behaviour of coal particles submitted to a seawater flow, and a specifically designed tub is used to study the physicochemical consequences induced when coal is introduced into continuously renewed seawater. When coal is introduced into seawater, the most easily visible consequences are physical: fine coal particles reduce the daylight penetration up to 100% and move along with the flow, and coal chunks accumulate on the floor. Chemical effects are also measured: humic matters are dissolved from coal into seawater (up to 2 mg L−1), but no release of polycyclic aromatic hydrocarbons is evidenced. Some inorganic compounds are dissolved, among which manganese, whose concentrations can reach 1 μg L−1. Fortunately, the results show that the environmental impact of this type of accident would remain limited. 相似文献
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Sergey N. Vecherin Vladimir E. Ostashev Christopher W. Fairall D. Keith Wilson Ludovic Bariteau 《Boundary-Layer Meteorology》2013,149(2):165-178
The spatial resolution of a sonic anemometer is limited by the distance between its transducers, and for studies of small-scale turbulence and theories of turbulence, it is desirable to increase this spatial resolution. We here consider resolution improvements obtainable by treating the sonic anemometer as a small tomography array, with application of appropriate inverse algorithms for the reconstruction of temperature and velocity. A particular modification of the sonic anemometer is considered when the number of its transducers is doubled and the time-dependent stochastic inversion algorithm is used for reconstruction. Numerical simulations of the sonic anemometer and its suggested modification are implemented with the temperature and velocity fields modelled as discrete eddies moving through the sonic’s volume. The tomographic approach is shown to provide better reconstructions of the temperature and velocity fields, with spatial resolution increased by as much as a factor of ten. The spatial resolution depends on the inverse algorithm and also improves by increasing the number of transducers. 相似文献
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Ludovic Puig Kate Isaak Martin Linder Isabel Escudero Pierre-Elie Crouzet Roger Walker Matthias Ehle Jutta Hübner Rainer Timm Bram de Vogeleer Pierre Drossart Paul Hartogh Christophe Lovis Giusi Micela Marc Ollivier Ignasi Ribas Ignas Snellen Bruce Swinyard Giovanna Tinetti Paul Eccleston 《Experimental Astronomy》2015,40(2-3):393-425
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Jérôme Gattacceca Roger H. Hewins Jean‐Pierre Lorand Pierre Rochette France Lagroix Cécile Cournède Minoru Uehara Sylvain Pont Violaine Sautter Rosa. B. Scorzelli Chrystel Hombourger Pablo Munayco Brigitte Zanda Hasnaa Chennaoui Ludovic Ferrière 《Meteoritics & planetary science》2013,48(10):1919-1936
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Ludovic Ravanel Philip Deline Christophe Lambiel Christian Vincent 《Geografiska Annaler: Series A, Physical Geography》2013,95(1):51-66
Rockfalls are dominant in the rock slopes and rock ridge morphodynamics in high mountain areas and endanger people who pass along or stay there, as well as infrastructure that host them (cable cars, refuges). Risks are probably greater now because of fast permafrost degradation and regression of surface ice, two consequences of the atmospheric warming of the last decades. These two commonly associated factors are involved in the instability of rock slopes by modifying the mechanical behaviour of often ice‐filled rock fractures and the mechanical constraints in the rock masses. This paper examines over 15 years the instability of the lower Arête des Cosmiques on the French side of the Mont Blanc massif. Its vulnerability is due to the presence of a high‐capacity refuge on its top (3613 m a.s.l.). In 1998, a part of the refuge was left without support when a collapse of 600 m3 occurred immediately below it. Since this date, reinforcement work has been carried out in this area, but the whole ridge has been affected by around 15 relatively shallow rockfalls. Through a multidisciplinary approach, this article assesses the role of the cryospheric factors in the triggering of these rockfalls. 相似文献
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The influence of ground ice distribution on geomorphic dynamics since the Little Ice Age in proglacial areas of two cirque glacier systems 
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下载免费PDF全文 Jean‐Baptiste Bosson Philip Deline Xavier Bodin Philippe Schoeneich Ludovic Baron Marie Gardent Christophe Lambiel 《地球表面变化过程与地形》2015,40(5):666-680
Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris‐covered glacier, ice‐rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debris‐covered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献