Experimental analysis of compaction of concrete and mortar     

Nicolas Burlion  Gilles Pijaudier‐Cabot  Noël Dahan 《国际地质力学数值与分析法杂志》2001,25(15):1467-1486

Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 mm can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto‐plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

An event-by-event assessment of tropical intraseasonal perturbations for general circulation models     

Jean Philippe Duvel  Hugo Bellenger  Gilles Bellon  Marine Remaud 《Climate Dynamics》2013,40(3-4):857-873

We detect and characterize each large-scale intraseasonal perturbation in observations (1979–2009) and in coupled general circulation models of Institut Pierre Simon Laplace (IPSL) and of Centre National de Recherches Météorologiques (CNRM). These ensembles of intraseasonal perturbations are used to assess the skill of the two models in an event-by-event approach. This assessment addresses: (1) the planetary-scale (i.e. the whole Indo-Pacific area) extent of wind and rainfall perturbations and the reproducibility of the perturbation patterns for a given season; (2) the size and amplitude of rainfall and wind anomalies at basin-scale (i.e. for a particular phase of the perturbation) and; (3) the evolution of the vertical structure of the perturbations (U, T and RH) for selected events. The planetary-scale extent of rainfall perturbations is generally too small for both models. This extent is also small for the wind perturbation in the IPSL model, but is correct, or even too large in boreal winter, for the CNRM model. The reproducibility of the planetary-scale patterns is exaggerated for wind perturbations in the CNRM model and is very poor for all parameters in the IPSL model. Over the Indian Ocean during boreal winter, rainfall and wind anomalies at basin-scale are too large for the CNRM model and too small for the IPSL model. The CNRM model gives a realistic baroclinic perturbations structure for wind, moisture and temperature, but with too large amplitude due in part to a zonally extended rainfall anomaly over the eastern Indian Ocean and the Maritime Continent. The IPSL model gives a realistic response for low-level wind only. Temperature and moisture perturbations are barotropic with a wrong warm anomaly at rainfall maximum and there is no gradual increase in low-level moisture prior to this rainfall maximum. These results suggest that this version of the IPSL model is unable to initiate the coupling between the convection and the dynamic necessary to develop the perturbation. It is difficult to say if this is due to, or is at the origin of the lack of basin-scale organization of the convection. We discuss the likely role of the convective schemes in the differences found between these two versions of the CNRM and IPSL models.  相似文献   

A micro-Raman survey of 10 IDPs and 6 carbonaceous chondrites     

Eric Quirico  Janet Borg  Pierre-Ivan Raynal  Gilles Montagnac  Louis d&#x;Hendecourt 《Planetary and Space Science》2005,53(14-15):1443-1448

This paper presents a micro-Raman survey of a set of 10 IDPs and 6 pristine carbonaceous chondrites. The higher sensitivity of the present micro-spectrometers allowed to record a dozen of spectra for each objects, whereas only one was available in previous studies. First, as in previous studies, the first-order carbon bands G and D were the only detected features, superimposed onto a fluorescence background of variable intensity, and the spectral characteristics of these bands point to a very disordered polyaromatic organic matter (OM). Nevertheless, these new data reveal that in IDPs, unlike chondrites, the presence of the Raman bands is not systematic, evidencing a much higher heterogeneity in the spatial distribution or the chemical composition of OM. Second, as a consequence, a single spectrum is not representative of a whole IDP, and the classification previously proposed by Wopenka [ 1988. Raman observations on individual interplanetary dust particules. Earth and Planet. Sci. Lett. 88, 221—231.] is no longer tenable. At last, this study shows that the fluorescence signal induced by the laser irradiation mostly originates from OM.  相似文献   

Outstanding Issues for Post-Main Sequence Evolution:     

Gilles Fontaine  Pierre Brassard  Stéphane Charpinet 《Astrophysics and Space Science》2003,284(1):257-268

We review the question of the empirical and theoretical instabilityregions in the HR diagram for evolved, compact stars. These include thethree families of pulsating white dwarfs (g-mode pulsators excitedthrough mechanisms associated with partial ionization and convection inthe stellar envelope), the pulsating subdwarf B stars (p-mode variablesexcited through a classic kappa mechanism associated with the radiativelevitation of iron in the stellar envelope), and the `Betsy stars',the brand new class of long-period, g-mode pulsators of the subdwarf Btype discovered recently.  相似文献   

Dispersion Coefficients for Gaussian Puff Models     

Xiaoying Cao  Gilles Roy  William J. Hurley  William S. Andrews 《Boundary-Layer Meteorology》2011,139(3):487-500

The Gaussian distribution is a good approximation for transient (instantaneously released) puff concentration distributions within a short period of time after release. Artificial neural network (ANN) models for puff dispersion coefficients were developed, based on observations from field experiments covering a wide range of meteorological conditions (in March, May, August and November). Their average predictions were in very good agreement with measurements, having high correlation coefficients (r > 0.99). A non-linear multi-variable regression model for dispersion coefficients was also developed, under the assumption that puff dispersion coefficients increase with time, and follow power laws. Both ANN-based and multi-regression non-linear models were able to use easily measured atmospheric parameters directly, without the necessity of predefining the Pasquill stability category. Predictions of ANN-based and multi-regression-based Gaussian puff models were compared with those of Gaussian puff models using Slade’s dispersion coefficients and COMBIC, a sophisticated model based on Gaussian distributions. Predictions from our two new models showed better agreement with concentration measurements than the other Gaussian puff models, by having a much higher fraction within a factor of two of measured values, and lower normalized mean square errors.  相似文献   

Analysis of the tropical climate variability in a two-column framework     

Gilles Bellon  Guillaume Gastineau  Aur��lien Ribes  Herv�� Le Treut 《Climate Dynamics》2011,37(1-2):73-81

This work examines the relevance of a classical two-column modeling framework of the tropical climate in terms of observed natural variability. A method is developed to analyze the observed tropical climate in a simple framework that features a moist, ascending column and a dry, subsiding one. This method is used to analyze the natural variability of the tropical climate in the ERA40 reanalysis and in ISCCP satellite data. It appears that the seasonal cycle of the tropic-wide sea surface temperature (SST) is almost linearly linked to the seasonal cycle of the relative area of the moist regions, as predicted by the sensitivity of the two-column models. A more detailed analysis shows that this link is the product of a complex interaction and adjustments between the moist and dry regions. The seasonal cycle of low-cloud cover in the dry regions also appears to interact with the SST seasonal cycle: the low-cloud cover influences the tropic-wide SST via its direct radiative forcing on the local SST and it appears to be controlled by the SST difference between moist and dry regions. By contrast, the SST interannual variability appears to be driven by the El Ni?o Southern Oscillation (ENSO), with no significant impact from the changes in the relative area of the moist regions or in the low-cloud cover in the dry regions independently of the ENSO. ENSO-related changes in the area of moist regions and low-cloud cover constitute negative feedbacks on the ENSO-related SST variability.  相似文献   

Preserved‐amplitude angle domain migration by shot‐receiver wavefield continuation     

Frédéric Joncour  Gilles Lambaré  Julie Svay‐Lucas 《Geophysical Prospecting》2011,59(2):256-268

We present preserved‐amplitude downward continuation migration formulas in the aperture angle domain. Our approach is based on shot‐receiver wavefield continuation. Since source and receiver points are close to the image point, a local homogeneous reference velocity can be approximated after redatuming. We analyse this approach in the framework of linearized inversion of Kirchhoff and Born approximations. From our analysis, preserved‐amplitude Kirchhoff and Born inverse formulas can be derived for the 2D case. They involve slant stacks of filtered subsurface offset domain common image gathers followed by the application of the appropriate weighting factors. For the numerical implementation of these formulas, we develop an algorithm based on the true amplitude version of the one‐way paraxial approximation. Finally, we demonstrate the relevance of our approach with a set of applications on synthetic datasets and compare our results with those obtained on the Marmousi model by multi‐arrival ray‐based preserved‐amplitude migration. While results are similar, we observe that our results are less affected by artefacts.  相似文献   

Influence of the organic matter composition on benthic oxygen demand in the Rhône River prodelta (NW Mediterranean Sea)     

Lucie Pastor  Bruno Deflandre  Eric ViollierCécile Cathalot  Edouard MetzgerChristophe Rabouille  Karine Escoubeyrou  Emily LloretAudrey M. Pruski  Gilles Vétion  Martin Desmalades  Roselyne BuscailAntoine Grémare 《Continental Shelf Research》2011,31(9):1008-1019

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Geomorphologic approach for modelling the surface features of arid environments in a model of dust emissions: application to the Sahara desert     

Yann Callot  Béatrice Marticorena  Gilles Bergametti 《Geodinamica Acta》2013,26(5):245-270

Abstract

Mineral dust emissions from arid regions are influenced by the surface features encountered in the source regions. These surface features control both the erosion threshold and the intensity of the dust flux. Recently, a soil-derived dust emission scheme has been designed in order to provide an explicit representation of the mineral dust accounting for the influence of the surface features on the dust emissions. This physical scheme has been validated with micro-scale field measurements. Its large scale application has required the development of additional relations to estimate the input parameters from more accessible data: the mean height and the covering rate of the roughness elements and the min-eralogical soil type. The determination of these surface data has been based on a geomorphologic approach which describes the surface features of arid areas in a 1 × l° grid. Inside each square degree, up to five different areas characterised by different surface features have been distinguished. However, these areas have not been located inside the square degree. Each area can be constituted by several combined surface features, including roughness, vegetation, granulometry. Five main types of landscapes and eight main types of surface features have been distinguished. This approach is based on the combination of various data, mainly topographical, geological maps and climatological analysis. In addition to the problem of scale transfer, the main constraints to obtain a quantitative assessment are the confidence level of the existing data and the number of parameters to document. On the opposite, with this method, the fine scale required by the dust modelling can be separated from the scale accessible by the mapping approach, of the order of the square degree. This method can also be easily improved by aggregating new data and can be extended to other deserts. An example of application is given for the north-west of the Algerian Sahara where the method has been elaborated. The data provided by the modelling of the surface have been used to simulate dust emissions for 1990, 1991 and 1992 over the central and western Sahara. Over these three years, the mean annual dust emission is about 760 Mt-year^?1 Although a significant interannual variability exists (mainly due to changes in the wind pattern), the most intensive emissions remain quite constant in terms of location. The percentage of agreement with satellite observations higher than 0.7 is 74 %, but only 32 % when using a model having a single threshold function for dust emission (i.e. the same surface feature for the whole Sahara) (cf. later Marticorena et al., 1997). © 2000 Éditions scientifiques et médicales Elsevier SAS  相似文献   

Floor-age constraining of a tectonic paroxysm of the Pyrenean orogen. Late Middle Eocene mammal age of a faulted karstic filling of the Quercy phosphorites,south-western France     

Jean Guy Astruc  Gilles Escarguel  Bernard Maranda  Régine Simon-Coinçon 《Geodinamica Acta》2013,26(5):271-280

Abstract

Breaking effects of a Pyrenean compressive tectonic phase are recognised in northern Pyrenean foreland, such as in the Quercy Jurassic limestone platform. The age of this phase still remains poorly constrained. In the so-called Quercy phosphorites area, within the Prajoux—Mémerlin paleokarst system near the city of Cajarc, a clay filling shows a strike slip fault effect, close to N-S direction. According to an analysis of the mammal fauna and inferred chronology of the polyphased paleokarst infilling, the age of the faulted clay is late Middle Eocene, with a mammal age estimate of 41.5 Ma. This provides reliable precise floor-age constraining for the involved sismo-tectonic paroxysm, seemingly related to the Pyrenean tectonic compressive phase. © 2000 Editions scientifiques et médicales Elsevier SAS  相似文献