Study of the Anisotropic Properties of Argillite Under Moisture and Mechanical Loads     

Diansen Yang  Serge Chanchole  Pierre Valli  Liufeng Chen 《Rock Mechanics and Rock Engineering》2013,46(2):247-257

Due to various factors, such as sedimentation, layered morphology of clay minerals, in situ stress, etc., argillite rocks often exhibit anisotropic behavior. In order to study the anisotropic properties of the Callovo-Oxfordian (COx) argillite of the Meuse–Haute-Marne site in France considered as a possible host rock for high-level radioactive nuclear waste repository, a series of tests including uniaxial compression and dehydration and hydration at different constant applied stress levels are carried out. In this study, a specific setup combining moisture and mechanical loading with optical observation is used and it allows to continuously capture surface images from which the full-field strains are determined by using Digital Image Correlation techniques. The results show evidence of the mechanical and hydric anisotropy of the material. The anisotropy parameters are identified, assuming the studied argillite as transversely isotropic. The shrinkage and swelling depend on the applied stress and the angle with respect to the vertical direction of the mechanical load and the stratification plane, and this dependence is quantified. The non-linearity and the hysteresis observed during dehydration and hydration cycles are discussed.  相似文献   

Gradual diversions of the Rio Pastaza in the Ecuadorian piedmont of the Andes from 1906 to 2008: role of tectonics, alluvial fan aggradation, and ENSO events     

Carolina Bernal  Frédéric Christophoul  Jean-Claude Soula  José Darrozes  Luc Bourrel  Alain Laraque  José Burgos  Séverine Bès de Berc  Patrice Baby 《International Journal of Earth Sciences》2012,101(7):1913-1928

The successive courses of the Rio Pastaza in the upper Amazonian Puyo plateau (Ecuador) during the past century have been followed using historical maps, aerial photographs, satellite imagery, topographic and river long profiles, and field studies. The abrupt change in direction of the Rio Pastaza from transverse to longitudinal was a result of two avulsions occurred between 1906 and 1976 at the braided-meandering transition of the former alluvial plain. These avulsions are related to aggradation at the toe of a braided piedmont fan prograding on to a hinterland-dipping topographic slope formed by ongoing tectonic backtilting. The main avulsion proceeded by annexation of a south-dipping depression created in front of the cordillera by backtilting of the plateau. A partial and gradual avulsion having occurred upstream of the former site between 1976 and 2008 is marked by the progressive predominance of a newly formed inner branch. Tectonic backtilting enhanced aggradation upstream of the initial site while it offered the newly avulsed channel a still more favorable way along the cordillera by creating a westward lateral slope. The correlation between ENSO events and the occurrence of the 1976–2008 avulsions strongly suggests that the triggers of the avulsions were the floods caused by the high water and sediment discharges associated with ENSO (La Ni?a) events contrasting with the regular monthly discharge and the lack of actual ‘normal’ floods during the inter-ENSO periods.  相似文献   

Maximum-likelihood method for estimating the mass and period distributions of extrasolar planets     

Serge Tabachnik  Scott Tremaine 《Monthly notices of the Royal Astronomical Society》2002,335(1):151-158

We investigate the distribution of mass M and orbital period P of extrasolar planets, taking account of selection effects caused by the limited velocity precision and duration of existing surveys. We fit the data on 72 planets to a power-law distribution of the form  d n = CM ^−α P ^−β(d M / M )(d P / P )  , and find  α= 0.11 ± 0.10  ,  β=−0.27 ± 0.06  for   M ≲ 10 M _J  , where   M _J  is the mass of Jupiter. The correlation coefficient between these two exponents is −0.31, indicating that uncertainties in the two distributions are coupled. We estimate that 4 per cent of solar-type stars have companions in the range  1 M _J < M < 10 M _J  ,  2_d < P < 10 yr  .  相似文献   

Ecological primordialism: the human–environment nexus in Soqotra     

Serge D. Elie 《GeoJournal》2018,83(5):897-913

This article depicts the initial human–environmental relations that prevailed during the pre-modern period of Soqotra’s history prior to its incorporation into a state-led modernization process and its subsequent enclosure within a United Nations-designed conservation zoning plan and ecotourism economy. The term ecological primordialism is coined to highlight the primacy of the environment as the enabling and constraining context for the constitution of the Soqotran community. It entails a symbiotic relationship between an ecosystem and a human social system, which structured the contingent relations between the raw materials for livelihood making and community formation: people, resources and space. The article elucidates how Soqotrans managed this mostly constraining human–environment nexus through a series of adaptive practices: their taxonomic appropriation and practical domestication of the island’s environmental resources; their transformation of the landscape into a domain of livelihood; their organization of dispersed settlements into a socio-political unit; their demarcation of the island into geographical zones of cultural differentiation; and their establishment of mutual aid institutions that simultaneously regulated resource use while integrating all islanders into relations of social kinship. The article concludes with a cautionary tale about the use of anachronistic human–environment relations as the basis of conservation policy.  相似文献   

Shifting zonal patterns of the southern boreal forest in eastern Canada associated with changing fire regime during the Holocene     

Guillaume de Lafontaine  Serge Payette 《Quaternary Science Reviews》2011,30(7-8):867-875

This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n = 7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n = 6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000 cal. yr B.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000 cal. yr B.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal. yr B.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available.  相似文献   

A conceptual framework for the integral management of marine protected areas     

Celia Ojeda-Martínez  Francisca Giménez Casalduero  Just T. Bayle-Sempere  Carmen Barbera Cebrián  Carlos Valle  Jose Luis Sanchez-Lizaso  Aitor Forcada  Pablo Sanchez-Jerez  Pablo Martín-Sosa  Jesús M. Falcón  Fuensanta Salas  Mariagrazia Graziano  Renato Chemello  Ben Stobart  Pedro Cartagena  Angel Pérez-Ruzafa  Fréderic Vandeperre  Elisabeth Rochel  Serge Planes  Alberto Brito 《Ocean & Coastal Management》2009,52(2):89-101

A general conceptual framework for the management of marine protected areas (MPAs) was developed. The driver-pressure-state-impacts-response (DPSIR) framework was used to determine the elements affecting MPAs. The developed evaluation framework helped to select an appropriate suite of indicators to support an ecosystem approach, an assessment of the MPAs functioning and policy decisions. Gaps derived from the management and policy responses in the MPAs were also outlined. It was concluded that the DPSIR framework can help to simplify the complexity of MPA management. This document is a tool for policy makers, scientists and general public on the relevance of indicators to monitor changes and MPAs management.  相似文献   

Comparison of numerical methods for simulating strongly nonlinear and heterogeneous reactive transport problems—the MoMaS benchmark case     

Jérôme Carrayrou  Joachim Hoffmann  Peter Knabner  Serge Kräutle  Caroline de Dieuleveult  Jocelyne Erhel  Jan Van der Lee  V. Lagneau  K. Ulrich Mayer  Kerry T. B. MacQuarrie 《Computational Geosciences》2010,14(3):483-502

Although multicomponent reactive transport modeling is gaining wider application in various geoscience fields, it continues to present significant mathematical and computational challenges. There is a need to solve and compare the solutions to complex benchmark problems, using a variety of codes, because such intercomparisons can reveal promising numerical solution approaches and increase confidence in the application of reactive transport codes. In this contribution, the results and performance of five current reactive transport codes are compared for the 1D and 2D subproblems of the so-called easy test case of the MoMaS benchmark (Carrayrou et al., Comput Geosci, 2009, this issue). This benchmark presents a simple fictitious reactive transport problem that highlights the main numerical difficulties encountered in real reactive transport problems. As a group, the codes include iterative and noniterative operator splitting and global implicit solution approaches. The 1D easy advective and 1D easy diffusive scenarios were solved using all codes, and, in general, there was a good agreement, with solution discrepancies limited to regions with rapid concentration changes. Computational demands were typically consistent with what was expected for the various solution approaches. The differences between solutions given by the three codes solving the 2D problem are more important. The very high computing effort required by the 2D problem illustrates the importance of parallel computations. The most important outcome of the benchmark exercise is that all codes are able to generate comparable results for problems of significant complexity and computational difficulty.  相似文献   

Weather regimes over Senegal during the summer monsoon season using self-organizing maps and hierarchical ascendant classification. Part II: interannual time scale     

A. K. Guèye  Serge Janicot  A. Niang  S. Sawadogo  Benjamin Sultan  A. Diongue-Niang  S. Thiria 《Climate Dynamics》2012,39(9-10):2251-2272

The aim of this work is to define over the period 1979–2002 the main synoptic weather regimes relevant for understanding the daily variability of rainfall during the summer monsoon season over Senegal. “Interannual” synoptic weather regimes are defined by removing the influence of the mean 1979–2002 seasonal cycle. This is different from Part I where the seasonal evolution of each year was removed, then removing also the contribution of interannual variability. As in Part I, the self-organizing maps approach, a clustering methodology based on non-linear artificial neural network, is combined with a hierarchical ascendant classification to compute these regimes. Nine weather regimes are identified using the mean sea level pressure and 850?hPa wind field as variables. The composite circulation patterns of all these nine weather regimes are very consistent with the associated anomaly patterns of precipitable water, mid-troposphere vertical velocity and rainfall. They are also consistent with the distribution of rainfall extremes. These regimes have been then gathered into different groups. A first group of four regimes is included in an inner circuit and is characterized by a modulation of the semi-permanent trough located along the western coast of West Africa and an opposite modulation on the east. This circuit is important because it associates the two wettest and highly persistent weather regimes over Senegal with the driest and the most persistent one. One derivation of this circuit is highlighted, including the two driest regimes and the most persistent one, what can provide important dry sequences occurrence. An exit of this circuit is characterised by a filling of the Saharan heat low. An entry into the main circuit includes a southward location of the Saharan heat low followed by its deepening. The last weather regime is isolated from the other ones and it has no significant impact on Senegal. It is present in June and September, and missing in July and August, meaning that this is a weather regime more specific of the intermediate seasons than the summer. It is included in a large-scale pattern covering the northern latitudes of Europe. The correspondence between these “interannual” synoptic weather regimes and the “pure” synoptic regimes defined in Part I has been established. By selecting a high statistical significance level for these correspondences, each of five out of nine “interannual” weather regimes has a close correspondence with one “pure” synoptic weather regime, one out of them have links with two “pure” regimes, and the last three regimes have no significant correspondence in terms of “pure” regimes. However when considering more moderate links, two out of these three regimes show a connection with a “pure” regime, and the last one remains isolated. The ensemble of the weather regimes occurrences can explain a significant part of interannual variability of summer rainfall amount over Senegal, especially linked to the driest and the wettest weather regimes occurrences. It is also shown that Senegal rainfall state is very sensitive to a small displacement or deformation of the weather regime patterns.  相似文献   

A method for regional climate change detection using smooth temporal patterns     

Aurélien Ribes  Jean-Marc Azaïs  Serge Planton 《Climate Dynamics》2010,35(2-3):391-406

This paper introduces an original method for climate change detection, called temporal optimal detection method. The method consists in searching for a smooth temporal pattern in the observations. This pattern can be either the response of the climate system to a specific forcing or to a combination of forcings. Many characteristics of this new method are different from those of the classical “optimal fingerprint” method. It allows to infer the spatial distribution of the detected signal, without providing any spatial guess pattern. The spatial properties of the internal climate variability doesn’t need to be estimated either. The estimation of such quantities being very challenging at regional scale, the proposed method is particularly well-suited for such scale. The efficiency of the method is illustrated by applying it on real homogenized datasets of temperatures and precipitation over France. A multimodel detection is performed in both cases, using an ensemble of atmosphere-ocean general circulation models for estimating the temporal patterns. Regarding temperatures, new results are highlighted, especially by showing that a change is detected even after removing the uniform part of the warming. The sensitivity of the method is discussed in this case, relatively to the computation of the temporal patterns and to the choice of the model. The method also allows to detect a climate change signal in precipitation. This change impacts the spatial distribution of the precipitation more than the mean over the domain. The ability of the method to provide an estimate of the spatial distribution of the change following the prescribed temporal patterns is also illustrated.  相似文献   

Theoretical and numerical studies of the Vishniac instability in supernova remnants     

Cécile Cavet  Hung Chinh Nguyen  Claire Michaut  Emeric Falize  Serge Bouquet  Laurent Di Menza 《Astrophysics and Space Science》2009,322(1-4):91-95

Vishniac instability has been theoretically studied in supernova remnants where it is supposed to explain the fragmentation of the interstellar medium. However its role is not fully demonstrated in these astrophysical objects. Conditions and assumptions required for the instability growth are explained in detail in the present paper. In addition the HYDRO-MUSCL hydrodynamic code has been used to simulate this instability in order to compare the numerical growth rate with the Vishniac analytical solution.  相似文献