Suitability of a lumped rainfall–runoff model for flashy tropical watersheds in New Caledonia     

Térence Desclaux  Hugues Lemonnier  Pierre Genthon  Benoit Soulard  Romain Le Gendre 《水文科学杂志》2013,58(11):1689-1706

ABSTRACT

The GR4H lumped hourly rainfall–runoff model was assessed for its integration in a ridge-to-reef modelling framework. Particular attention was paid to rainfall representation, robustness of parameter estimates and ability to reproduce the main runoff features. The study was conducted in four tropical mountainous watersheds in New Caledonia, which are exposed to intense rainfall events, large annual climatic variations triggered by El Niño oscillation, and wildfires. The inverse distance and elevation weighting algorithm outperformed other classical rainfall interpolation methods under data-limited conditions. The time span of data needed for robust calibration was site specific and varied from 6–7 years to 10 years, which may be linked to El Niño events and to wildfires. With sufficient data, simulation quality was equivalent during the calibration and validation periods. The GR4H model was generally able to simulate both flash floods and large annual variations. The model was more reliable when simulating wet years and watersheds not subject to land-cover changes.  相似文献   

Effects of material variability on the ductility of composite beams and overstrength coefficients     

Srour Nofal  Hugues Somja  Mohammed Hjiaj  Quang Huy Nguyen 《地震工程与结构动力学》2013,42(7):953-972

The aim of this paper is to investigate the plastic rotation capacity of composite beams as well as the overstrength factors for composite joints considering the actual European steel production. It relies on the statistical data of the mechanical properties of steel profiles and reinforcement bars produced in several European steel mills that have been collected during the European research project OPUS. Several steel and composite structures have been designed following the EN 1998 rules, and the effect of the statistical distribution of the steel properties on the design has been analyzed. In such structures, the first attainment of the rotation capacity is expected to happen in the hogging region. The plastic rotation capacity was evaluated using the so‐called standard beam concept. The moment–rotation curve was constructed by joining together the pre‐buckling branch, determined using a fiber model, and the post‐buckling part derived by considering the local plastic failure mechanism as suggested by Gioncu. A program in MATLAB (MATLAB version 7.10.0. Natick, Massachusetts: The MathWorks Inc., 2010) was developed to establish such curve for arbitrary composite beams. The predictions of the model compare favorably against the experimental results. On the basis of the probabilistic model for the mechanical properties of steel, we derive the statistical distribution of the maximum rotation defined at the intersection of the pre‐buckling and post‐buckling curves. Next, we estimate the so‐called overstrength factors. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Fine‐grained material of 81P/Wild 2 in interaction with the Stardust aerogel     

Hugues LEROUX 《Meteoritics & planetary science》2012,47(4):613-622

Abstract– The deceleration tracks in the Stardust aerogel display a wide range of morphologies, which reveal a large diversity of incoming particles from comet 81P/Wild 2. If the large and dense mineral grains survived the extreme conditions of hypervelocity capture, this was not the case for the fine‐grained material that is found strongly damaged within the aerogel. Due to their low mechanical strength, these assemblages were disaggregated, dispersed, and flash melted in the aerogel in walls of bulbous deceleration tracks. Their petrologic and mineralogical properties are found significantly modified by the flash heating of the capture. Originating from a quenched melt mixture of comet material and aerogel, the representative microstructure consists of silica‐rich glassy clumps containing Fe‐Ni‐S inclusions, vesicles and “dust‐rich” patches, the latter being remnants of individual silicate components of the impacting aggregate. The average composition of these melted particle fragments is close to the chondritic CI composition. They might originate from ultrafine‐grained primitive components comparable to those found in chondritic porous IDPs. Capture effects in aerogel and associated sample biases are discussed in terms of size, chemical and mineralogical properties of the grains. These properties are essential for the grain survival in the extremely hot environment of hypervelocity impact capture in aerogel, and thus for inferring the correct properties of Wild 2 material.  相似文献   

A TEM study of exsolution in Ca-rich pyroxenes from the Paris and Renazzo chondrites: Determination of type I chondrule cooling rates          下载免费PDF全文

Priscille Cuvillier  Noël Chaumard  Hugues Leroux  Brigitte Zanda  Roger H. Hewins  Damien Jacob  Bertrand Devouard 《Meteoritics & planetary science》2018,53(3):482-492

We conducted a transmission electron microscope study of the exsolution microstructures of Ca-rich pyroxenes in type I chondrules from the Paris CM and Renazzo CR carbonaceous chondrites in order to provide better constraints on the cooling history of type I chondrules. Our study shows a high variability of composition in the augite grains at a submicrometer scale, reflecting nonequilibrium crystallization. The microstructure is closely related to the local composition and is thus variable inside augite grains. For compositions inside the pyroxene miscibility gap, with a wollastonite (Wo) content typically below 40 mole%, the augite grains contain abundant exsolution lamellae on (001). For grain areas with composition close to Wo₄₀, a modulated texture on (100) and (001) is the dominant microstructure, while areas with compositions higher than Wo₄₀ do not show any exsolution microstructure development. To estimate the cooling rate, we used the spacing of the exsolution lamellae on (001), for which the growth is diffusion controlled and thus sensitive to the cooling rate. Despite the relatively homogeneous microstructures of augite grains with Wo < 35 mole%, our study of four chondrules suggests a range of cooling rates from ~10 to ~1000 °C h⁻¹, within the temperature interval 1200–1350 °C. These cooling rates are comparable to those of type II chondrules, i.e., 1–1000 °C h⁻¹. We conclude that the formation of type I and II chondrules in the proto-solar nebula was the result of a common mechanism.  相似文献   

Pyroxenes microstructure in comet 81P/Wild 2 terminal Stardust particles     

Damien Jacob  Julien Stodolna  Hugues Leroux  Falko Langenhorst  F. Houdellier 《Meteoritics & planetary science》2009,44(10):1475-1488

Abstract— We report the examination by transmission electron microscopy (TEM) of four Stardust terminal particles extracted from two neighboring tracks (32 an 69). The particles are made of well‐preserved crystalline grains dominated by low‐Ca pyroxene ranging from nearly pure enstatite to pigeonite. Some olivine grains are also found, in chemical equilibrium with the surrounding pyroxenes. Various microstructures are observed, as a function of the composition of the grains. They include (100)‐twinned pigeonite, clino/ortho domains in enstatite and exsolution in a Ca‐rich grain. The microstructures are mostly consistent with a formation by cooling from high‐temperature phases, which could be associated to igneous processes. Some dislocations in glide configuration are also present, probably attesting for small intensity shocks. Possible effects of the rapid heating/cooling stage and thermal shock associated to the collect are discussed. It appears that most of the microstructural features reported here are plausibly pristine.  相似文献   

Causes and impacts of changes in the Arctic freshwater budget during the twentieth and twenty-first centuries in an AOGCM   总被引：2，自引：1，他引：1  

Olivier Arzel  Thierry Fichefet  Hugues Goosse  Jean-Louis Dufresne 《Climate Dynamics》2008,30(1):37-58

The fourth version of the atmosphere-ocean general circulation (AOGCM) model developed at the Institut Pierre-Simon Laplace (IPSL-CM4) is used to investigate the mechanisms influencing the Arctic freshwater balance in response to anthropogenic greenhouse gas forcing. The freshwater influence on the interannual variability of deep winter oceanic convection in the Nordic Seas is also studied on the basis of correlation and regression analyses of detrended variables. The model shows that the Fram Strait outflow, which is an important source of freshwater for the northern North Atlantic, experiences a rapid and strong transition from a weak state toward a relatively strong state during 1990–2010. The authors propose that this climate shift is triggered by the retreat of sea ice in the Barents Sea during the late twentieth century. This sea ice reduction initiates a positive feedback in the atmosphere-sea ice-ocean system that alters both the atmospheric and oceanic circulations in the Greenland-Iceland-Norwegian (GIN)-Barents Seas sector. Around year 2080, the model predicts a second transition threshold beyond which the Fram Strait outflow is restored toward its original weak value. The long-term freshening of the GIN Seas is invoked to explain this rapid transition. It is further found that the mechanism of interannual changes in deep mixing differ fundamentally between the twentieth and twenty-first centuries. This difference is caused by the dominant influence of freshwater over the twenty-first century. In the GIN Seas, the interannual changes in the liquid freshwater export out of the Arctic Ocean through Fram Strait combined with the interannual changes in the liquid freshwater import from the North Atlantic are shown to have a major influence in driving the interannual variability of the deep convection during the twenty-first century. South of Iceland, the other region of deep water renewal in the model, changes in freshwater import from the North Atlantic constitute the dominant forcing of deep convection on interannual time scales over the twenty-first century.  相似文献   

The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly”     

Hugues Goosse  Elisabeth Crespin  Svetlana Dubinkina  Marie-France Loutre  Michael E. Mann  Hans Renssen  Yoann Sallaz-Damaz  Drew Shindell 《Climate Dynamics》2012,39(12):2847-2866

Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.  相似文献   

Oxidation state of iron and extensive redistribution of sulfur in thermally modified Stardust particles     

Hugues Leroux  Mathieu Roskosz  Damien Jacob 《Geochimica et cosmochimica acta》2009,73(3):767-3513

Two representative thermally modified Stardust samples were investigated by analytical transmission electron microscopy in order to decipher their iron oxidation state after the strong thermal episode due to the capture in aerogel. Their dominant microstructure consists of evenly distributed rounded Fe-Ni-S nano-droplets within a silica-rich glassy matrix. The mineralogy and associated redox state of iron is assessed using a Fe-Mg-S ternary diagram on which ferromagnesian silicates, sulfides and metal can be represented and potentially compared with any other extraterrestrial material. In this diagram, all the data (bulk and local analysis of silicates, sulfide + metal) scatter along a mixing line between the Mg corner and the average composition of the iron-sulfide. There is an obvious genetic relationship between the different phases observed in such samples, further supported by the very low concentration of iron in the glassy matrix. Silicate glasses contain a significant concentration of dissolved sulfur probably present as MgS complexes. This chemical signature is typical of highly reduced environments. These secondary microstructures were established during the high temperature stage of the capture. A significant part of the Fe-droplets formed in situ by reduction at high temperature of ferromagnesian silicates (olivine and pyroxenes) during the impact. At this stage, the indigenous sulfides destabilized and sulfur readily volatilized as S₂, diffused into molten materials and condensed later onto the Fe-precipitates that formed in the silicate melt. This scenario is supported by the structure of Fe-Ni-S beads with a metal core and a sulfide rim. It will be difficult to derive reliable information on the redox state of 81P/Wild 2 particles based on bulk analyses of whole tracks because particles found along the walls of tracks suffered strong reduction reactions, contrary to terminal particles that may have preserved their pristine redox state. The capture effect must be taken into account for comparison of Wild 2 particles with other chondritic material.  相似文献   

A transmission electron microscopy (TEM) investigation of opaque phases in shocked chondrites     

Pascal Joreau  Hugues Leroux  Jean-Claude Doukhan 《Meteoritics & planetary science》1996,31(2):305-312

Abstract— Shock defects in the most common silicate minerals of chondrites (olivine, pyroxenes and feldspars) have been investigated in detail, but there have been almost no studies of the shock defects in other components, like metal and sulfide. This probably stems from the fact that these latter phases are opaque in the optical microscope. The same reason explains why veins and melt pockets, which are constituted of microcrystalline or glassy phases (i.e., isotropic) are also poorly documented. We have investigated such phases by analytical transmission electron microscopy (ATEM) in two shocked chondrites, Tenham (L6) and Gaines County (H5). We have characterized shock defects in troilite very similar to those occurring in silicates (i.e., a mosaic texture and sets of straight and very narrow, ?10 nm, lamellae of amorphized FeS). There are many small regions in shocked chondrites that are composed of very fine grained (?1 μm) mixtures of metal and sulfide or of various silicates. They must result from local melting followed by a rapid cooling that prevented grain growth. We have determined the chemical compositions and the volume proportions of the tiny grains in these veins and melt pockets, which has allowed their temperature and pressure (T, P) history to be partially deciphered. Finally, we have observed a dense network of very narrow fractures (down to 10 nm) in the olivine and enstatite grains. These fractures are systematically filled with an amorphous (or cryptocrystalline) material that stems from the melt pockets and was injected when the fractures were opened by the rarefaction wave. This material was then quenched at the contact with the colder crystalline rims.  相似文献   

Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in situ reduction     

Hugues Leroux  Guy Libourel  Laurence Lemelle  Fran&#x;ois Guyot 《Meteoritics & planetary science》2003,38(1):81-94

Abstract— An analytical transmission electron microscopy (ATEM) study was undertaken in order to better understand the formation conditions of dusty olivines (i.e., olivines containing abundant tiny inclusions of Fe‐Ni metal) in primitive meteorites. Dusty olivines from type I chondrules in the Bishunpur chondrite (LL3.1) and from synthetic samples obtained by reduction of San Carlos olivines were examined. In both natural and experimental samples, micron size metal blebs observed in the dusty region often show preferential alignments along crystallographic directions of the olivine grains, have low Ni contents (typically <2 wt%), and are frequently surrounded by a silica‐rich glass layer. These features suggest that dusty olivines are formed by a sub‐solidus reduction of initially fayalitic olivines according to the following reaction: Some volatilization of SiO_gas may account for the apparent excess of metal relative to silica‐rich glass observed in both experimental and natural samples. Comparison with experimentally produced dusty olivines suggests that time scales of the order of minutes usually inferred for chondrule formation are also adequate for the formation of dusty olivines. These observations are in agreement with the hypothesis that at least part of the metal phase in chondrites originated from reduction during chondrule formation.  相似文献