Corrective pattern-matching simulation with controlled local-mean histogram   总被引：1，自引：1，他引：0  

Corentin Faucher  Antoine Saucier  Denis Marcotte 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(8):2027-2050

This paper presents a new stochastic simulation method that improves on our unilateral patchwork simulation method (Faucher et al., Stoch Environ Res Risk Assess, 27:253–273, 2012) by eliminating anisotropy biases. As in our unilateral method, images are built by assembling patterns together while controlling the local-mean histogram. The patterns, which are square image-pieces, are picked in a reference image. The reference image is used as a data bank holding the statistical informations about the random field to simulate. In contrast with the unilateral method, the path followed by our new simulation is random and guided by local errors. The new method, called corrective pattern-matching simulation, proceeds iteratively by making local corrections to the simulated image. For several types of images, it is shown that our simulations respect conditioning data and reproduce faithfully the reference image visual appearance. It is shown that the control of the local-mean histogram allows to control one-point statistics and multi-point statistics.  相似文献   

FEM × DEM modelling of cohesive granular materials: Numerical homogenisation and multi-scale simulations   总被引：2，自引：0，他引：2  

Trung Kien Nguyen  Gaël Combe  Denis Caillerie  Jacques Desrues 《Acta Geophysica》2014,62(5):1109-1126

The article presents a multi-scale modelling approach of cohesive granular materials, its numerical implementation and its results. At microscopic level, Discrete Element Method (DEM) is used to model dense grains packing. At the macroscopic level, the numerical solution is obtained by a Finite Element Method (FEM). In order to bridge the micro- and macro-scales, the concept of Representative Elementary Volume (REV) is applied, in which the average REV stress and the consistent tangent operators are obtained in each macroscopic integration point as the results of DEM’s simulation. In this way, the numerical constitutive law is determined through the detailed modelling of the microstructure, taking into account the nature of granular materials. We first elaborate the principle of the computation homogenisation (FEM × DEM), then demonstrate the features of our multiscale computation in terms of a biaxial compression test. Macroscopic strain location is observed and discussed.  相似文献   

An investigation of the SO₂ content of the venusian mesosphere using SPICAV-UV in nadir mode     

Emmanuel Marcq  Denis Belyaev  Anna Fedorova  Ann Carine Vandaele 《Icarus》2011,211(1):58-69

Using the SPICAV-UV spectrometer aboard Venus Express in nadir mode, we were able to derive spectral radiance factors in the middle atmosphere of Venus in the 170-320 nm range at a spectral resolution of R ? 200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model of the upper atmosphere of Venus, we could derive column abundance above the visible cloud top for SO₂ using its spectral absorption bands near 280 and 220 nm. SO₂ column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO₂ column densities at low latitudes (up to 50°N) were found between 5 and 50 μm-atm, whereas in the northern polar region SO₂ content was usually below 5 μm-atm. The observed latitudinal variations follow closely the cloud top altitude derived by SPICAV-IR and are thought to be of dynamical origin. Also, a sudden increase of SO₂ column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO₂ into the upper atmosphere.  相似文献   

Erosive flood events on the surface of Mars: Application to Mangala and Athabasca Valles     

Alistair Simon Bargery  Lionel Wilson 《Icarus》2011,212(2):520-540

We address key factors involved in determining water flow conditions in outflow channels on Mars, including the temperature of the sub-surface water being released and the environmental conditions of low temperature, low atmospheric pressure, and low acceleration due to gravity. We suggest how some of the assumptions made in previous work may be improved. Our model considers the thermodynamic effects of simultaneous evaporation and freezing of water, and fluid dynamical processes including changes in flow rheology caused by assimilation of cold rock and ice eroded at the channel bed, and ice crystal growth due to water freezing. We model how far initially turbulent water could flow in a channel before it erodes and entrains enough material to become laminar, and subsequently ceases to erode the bed. An ice raft will begin to form on the flood while transition occurs between turbulent and laminar flow. Estimates are given for water transit times, ～17–19 h, initial water depths, 50–62 m, and average flow speeds, 5–12 m s^?1, in the Mangala and Athabasca Valles. We show that these two outflow channels, and by implication others like them, could plausibly have been formed in single water release events. Resulting mean erosion rates are approximately 0.7 mm s^?1, a factor of three greater than previous estimates based on combinations of estimates of flood duration and required water volumes. This is explained by the consideration of the effects of eroded ice and the physics of thermal erosion in the present study.  相似文献   

Seston transport and deposition in Pelorus sound,south Island,New Zealand   总被引：2，自引：2，他引：0  

Lionel Carter 《新西兰海洋与淡水研究杂志》2013,47(2):263-282

Transport of seston (suspended sediment) in Pelorus Sound is controlled by tides and freshwater inflow. During high freshwater inflow, a moderately stratified estuarine circulation may be superimposed on the tidal circulation, but the latter dominates and transports seston seawards and landwards with the ebb and flood phases respectively. With extreme freshwater inflow, the estuarine circulation gains impetus and most seston is rapidly transported seaward in the low saline surface layer.

Irrespective of circulation there is a persistent trend in seston concentrations. Highest values occur at the sound's head because of the influence of nearby Pelorus and Kaituna Rivers and because of resuspension of bottom sediment by strong tidal currents. Seston concentrations wane along the sound until near the entrance, where values increase as a result of greater production of biogenic seston and because additional seston is brought in from Cook Strait with the flood tide. This trend parallels variability in the thicknesses of muddy bottom sediments. Muds are thick at the head where an extensive delta extends from the river mouths; muds gradually thin seaward and then thicken markedly in the vicinity of the sound entrance.

Seston weight and composition patterns and 3.5 kHz seismic profiles indicate Pelorus Sound acts as a double‐ended sediment trap. The upper reaches receive and retain river‐derived seston, whereas the sound entrance traps seston derived from Cook Strait. This situation appears to hold for both high and extremely high influxes of sediment.  相似文献   

Contamination of port zone sediments by metals from Large Marine Ecosystems of Brazil     

Buruaem LM  Hortellani MA  Sarkis JE  Costa-Lotufo LV  Abessa DM 《Marine pollution bulletin》2012,64(3):479-488

Sediment contamination by metals poses risks to coastal ecosystems and is considered to be problematic to dredging operations. In Brazil, there are differences in sedimentology along the Large Marine Ecosystems in relation to the metal distributions. We aimed to assess the extent of Al, Fe, Hg, Cd, Cr, Cu, Ni, Pb and Zn contamination in sediments from port zones in northeast (Mucuripe and Pecém) and southeast (Santos) Brazil through geochemical analyses and sediment quality ratings. The metal concentrations found in these port zones were higher than those observed in the continental shelf or the background values in both regions. In the northeast, metals were associated with carbonate, while in Santos, they were associated with mud. Geochemical analyses showed enrichments in Hg, Cd, Cu, Ni and Zn, and a simple application of international sediment quality guidelines failed to predict their impacts, whereas the use of site-specific values that were derived by geochemical and ecotoxicological approaches seemed to be more appropriate in the management of the dredged sediments.  相似文献   

The Influence of Topology on Hydraulic Conductivity in a Sand-and-Gravel Aquifer     

Roger H. Morin  Denis R. LeBlanc  Brent M. Troutman 《Ground water》2010,48(2):181-190

A field experiment consisting of geophysical logging and tracer testing was conducted in a single well that penetrated a sand-and-gravel aquifer at the U.S. Geological Survey Toxic Substances Hydrology research site on Cape Cod, Massachusetts. Geophysical logs and flowmeter/pumping measurements were obtained to estimate vertical profiles of porosity ϕ, hydraulic conductivity K, temperature, and bulk electrical conductivity under background, freshwater conditions. Saline-tracer fluid was then injected into the well for 2 h and its radial migration into the surrounding deposits was monitored by recording an electromagnetic-induction log every 10 min. The field data are analyzed and interpreted primarily through the use of Archie's (1942) law to investigate the role of topological factors such as pore geometry and connectivity, and grain size and packing configuration in regulating fluid flow through these coarse-grained materials. The logs reveal no significant correlation between K and ϕ, and imply that groundwater models that link these two properties may not be useful at this site. Rather, it is the distribution and connectivity of the fluid phase as defined by formation factor F, cementation index m, and tortuosity α that primarily control the hydraulic conductivity. Results show that F correlates well with K, thereby indicating that induction logs provide qualitative information on the distribution of hydraulic conductivity. A comparison of α, which incorporates porosity data, with K produces only a slightly better correlation and further emphasizes the weak influence of the bulk value of ϕ on K.  相似文献   

Simulation of the subsurface mobility of carbon nanoparticles at the field scale     

Erin Cullen  Denis M. O’Carroll  Ernest K. Yanful  Brent Sleep 《Advances in water resources》2010

The production and use of nanomaterials will inevitably lead to their disposal in the natural environment. To assess the risk that these materials pose to human and ecosystem health an understanding of their mobility and ultimate fate is essential. To date, however, relatively little research has been conducted on the fate of nanoparticles in subsurface systems. In this study the subsurface mobility of two carbon nanoparticles: nano-fullerenes (nC₆₀) and multi-walled carbon nanotubes (MWCNTs) is assessed. A two-dimensional finite element model was used to simulate the movement of these nanoparticles under a range of hydrologic and geological conditions, including a heterogeneous permeability field. The numerical model is based on colloid filtration theory (CFT) with a maximum retention capacity term. For the conditions evaluated the carbon nanotubes are much more mobile than nC₆₀ due to the smaller collector efficiency associated with carbon nanotubes. However, the mobility of nC₆₀ increased significantly when a maximum retention capacity term was included in the model. Model results also demonstrate that, for the systems examined, nanoparticles were predicted to be less mobile in heterogeneous systems compared to the homogeneous systems with the same average hydraulic properties.  相似文献   

Morphology,structure and kinematics of a rainfall controlled slow‐moving Andean landslide,Peru          下载免费PDF全文

Swann Zerathe  Pascal Lacroix  Denis Jongmans  Jersy Marino  Edu Taipe  Marc Wathelet  Walter Pari  Lionel Fidel Smoll  Edmundo Norabuena  Bertrand Guillier  Lucile Tatard 《地球表面变化过程与地形》2016,41(11):1477-1493

The large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm³ landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

The Ereendavaa Range (north-eastern Mongolia): an additional argument for Mesozoic extension throughout eastern Asia   总被引：3，自引：0，他引：3  

Yannick Daoudene  Denis Gapais  Patrick Ledru  Alain Cocherie  Sébastien Hocquet  Tatiana V. Donskaya 《International Journal of Earth Sciences》2009,98(6):1381-1393

Mesozoic rift basins locally bounding metamorphic core complexes have been recognized in Transbaikalia and northern China. Numerous basement outcrops located between these two regions, in eastern Mongolia, are considered as pre-Palaeozoic in age. One of these, the Ereendavaa Range, appears as a gneissic core marked by amphibolite-facies metamorphic conditions. The range is overlain to the NW by the unmetamorphosed Mesozoic Onon Basin. Below the basin, the upper part of the range consists of a gently NW-dipping shear zone associated with top-to-the-NW motion. The structural pattern is consistent with syn-extensional exhumation of the range. Preliminary geochronological data indicate that the shear zone is late Jurassic to early Cretaceous in age, coeval with the Onon Basin. These new data from eastern Mongolia constitute a link between Transbaikalia and northern China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region.  相似文献