Tracking sediment provenance and erosional evolution of the western Greater Caucasus          下载免费PDF全文

Giovanni Vezzoli  Eduardo Garzanti  Stephen J. Vincent  Sergio Andò  Andrew Carter  Alberto Resentini 《地球表面变化过程与地形》2014,39(8):1101-1114

This article investigates landscape characteristics and sediment composition in the western Greater Caucasus by using multiple methods at different timescales. Our ultimate goal is to compare short‐term versus long‐term trends in erosional processes and to reconstruct spatio‐temporal changes in sediment fluxes as controlled by partitioning of crustal shortening and rock uplift in the orogenic belt. Areas of active recent uplift are assessed by quantitative geomorphological techniques [digital elevation model (DEM) analysis of stream profiles and their deviation from equilibrium] and compared with regions of rapid exhumation over longer time intervals as previously determined by fission‐track and cosmogenic‐nuclide analyses. Complementary information from petrographic and heavy‐mineral analyses of modern sands and ancient sandstones is used to evaluate erosion integrated throughout the history of the orogen. River catchments displaying the highest relief, as shown by channel‐steepness indices, correspond with the areas of most rapid exhumation as outlined by thermochronological data. The region of high stream gradients is spatially associated with the highest topography around Mount Elbrus, where sedimentary cover strata have long been completely eroded and river sediments display the highest metamorphic indices and generally high heavy‐mineral concentrations. This study reinforces the suggestion that the bedrock–channel network can reveal much of the evolution of tectonically active landscapes, and implies that the controls on channel gradient ultimately dictate the topography and the relief along the Greater Caucasus. Our integrated datasets, obtained during a decade of continuing research, display a general agreement and regularity of erosion patterns through time, and consistently indicate westward decreasing rates of erosional unroofing from the central part of the range to the Black Sea. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Experimental investigation of microstructural changes in soils eroded by suffusion using X-ray tomography   总被引：1，自引：0，他引：1  

Nguyen  Cong Doan  Benahmed  Nadia  Andò  Edward  Sibille  Luc  Philippe  Pierre 《Acta Geotechnica》2019,14(3):749-765

Internal erosion is a complex phenomenon which represents one of the main risks to the safety of earthen hydraulic structures such as embankment dams, dikes or levees. Its occurrence may cause instability and failure of these structures with consequences that can be dramatic. The specific mode of erosion by suffusion is the one characterized by seepage flow-induced erosion, and the subsequent migration of the finest soil particles through the surrounding soil matrix mostly constituted of large grains. Such a phenomenon can lead to a modification of the initial microstructure and, hence, to a change in the physical, hydraulic and mechanical properties of the soil. A direct comparison of the mechanical behaviour of soil before and after erosion is often used to investigate the impact of internal erosion on soil strength (shear strength at peak and critical state) using triaxial tests. However, the obtained results are somehow contradictory, as for instance in Chang’s study (Chang and Zhang in Geotech Test J 34(6):579–589, 2011), where it is concluded that the drained strength of eroded soil decreases compared to non-eroded soil, while both Xiao and Shwiyhat (Geotech Test J 35(6):890–900, 2012) and Ke and Takahashi (Geotech Test J 37(2):347–364, 2014) have come to the opposite conclusion. A plausible explanation of these contradictions might be attributed to the rather heterogeneous nature of the suffusion process and to the way the coarse and fine grains are rearranged afterwards leading to a heterogeneous soil structure, a point that, for now, is not taken into account, nor even mentioned, in the existing analyses. In the present study, X-ray computed tomography (X-ray CT) is used to follow the microstructure evolution of a granular soil during a suffusion test, and, therefore, to capture the induced microstructural changes. The images obtained from X-ray CT reveal indeed that fine particles erosion is obviously not homogeneous, highlighting the existence of preferential flow paths that lead to a heterogeneous sample in terms of fine particles, void ratio and inter-granular void ratio distribution.

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Types and mechanisms of strombolian explosions: characterization of a gas-dominated explosion at Stromboli   总被引：1，自引：1，他引：0  

L. Leduc  L. Gurioli  A. Harris  L. Colò  E. F. Rose-Koga 《Bulletin of Volcanology》2015,77(1):1-15

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A User-Oriented Methodology for DInSAR Time Series Analysis and Interpretation: Landslides and Subsidence Case Studies     

Davide Notti  Fabiana Calò  Francesca Cigna  Michele Manunta  Gerardo Herrera  Matteo Berti  Claudia Meisina  Deodato Tapete  Francesco Zucca 《Pure and Applied Geophysics》2015,172(11):3081-3105

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The determination of earthquake location and magnitude from macroseismic data in Europe     

A. A. Gomez-Capera  A. Rovida  P. Gasperini  M. Stucchi  D. Viganò 《Bulletin of Earthquake Engineering》2015,13(5):1249-1280

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Assessment of the dynamic response of unreinforced masonry structures using a macroelement modeling approach          下载免费PDF全文

César Chácara  Francesco Cannizzaro  Bartolomeo Pantò  Ivo Caliò  Paulo B. Lourenço 《地震工程与结构动力学》2018,47(12):2426-2446

The seismic performance of unreinforced masonry structures is strongly associated with the interaction between in‐plane and out‐of‐plane mechanisms. The seismic response of these structures has been thoroughly investigated by means of experimental testing, analytical procedures, and computational approaches. Within the framework of the numerical simulations, models based on the finite element method provide a good prediction of the seismic performance of unreinforced masonry structures. However, they usually require a high computational cost and advanced user expertise to define appropriate mechanical properties and to interpret the numerical results. Because of these limitations, simplified models for practical applications have been developed during the last decades. Despite this, a great number of these models focus mostly on the evaluation of the in‐plane response, assuming box (or integral) behavior of the structure. In this paper, a simplified macroelement modeling approach is used to simulate the seismic response of 2 masonry prototypes taking into consideration the combined in‐plane and out‐of‐plane action. The numerical investigations were performed in the static and dynamic fields by using pushover analyses and nonlinear dynamic analyses respectively. The latter is a novel implementation of a model previously developed for static analysis. The results obtained from this study are in good agreement with those provided by a detailed nonlinear continuum FE approach, demonstrating the applicability of this macroelement model with a significant reduction of the computational cost.  相似文献   

Analytical Solutions of Three‐Dimensional Contaminant Transport Models with Exponential Source Decay          下载免费PDF全文

Ombretta Paladino  Arianna Moranda  Marco Massabò  Gary A. Robbins 《Ground water》2018,56(1):96-108

Despite the availability of numerical models, interest in analytical solutions of multidimensional advection‐dispersion systems remains high. Such models are commonly used for performing Tier I risk analysis and are embedded in many regulatory frameworks dealing with groundwater contamination. In this work, we develop a closed‐form solution of the three‐dimensional advection‐dispersion equation with exponential source decay, first‐order reaction, and retardation, and present an approach based on some ease of use diagrams to compare it with the integral open form solution and with earlier versions of the closed‐form solution. The comparison approach focuses on the relative differences associated with source decay and the effect of simulation time. The analysis of concentration contours, longitudinal sections, and transverse sections confirms that the closed‐form solutions studied can be used with acceptable approximation in the central area of a plume bound transversely within the source width, both behind and beyond the advective front and for concentration values up to two orders of magnitude less than the initial source concentration. As the proposed closed‐form model can be evaluated without nested numerical computations and with simple mathematical functions, it can be very useful in risk assessment procedures.  相似文献   

ISOPHOT Observations of the RS CVN -Type Star HR 7428     

M. Rodonò  I. Pagano  G. Cutispoto  G. Marino  S. Messina  G. Leto 《Astrophysics and Space Science》1997,255(1-2):237-238

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Large scale circulation in the convection zone and solar differential rotation     

G. Belvedere  L. Paternò 《Solar physics》1976,47(2):525-539

In this paper we study the dependence on depth and latitude of the solar angular velocity produced by a meridian circulation in the convection zone, assuming that the main mechanism responsible for setting up and driving the circulation is the interaction of rotation with convection. We solve the first order equations (perturbation of the spherically symmetric state) in the Boussinesq approximation and in the steady state for the axissymmetric case. The interaction of convection with rotation is modelled by a convective transport coefficient k _c = k _co + ?k _c2 P ₂(cos θ) where ? is the expansion parameter, P ₂ is the 2nd Legendre polynomial and k _c2 is taken proportional to the local Taylor number and the ratio of the convective to the total fluxes. We obtain the following results for a Rayleigh number 10³ and for a Prandtl number 1:

1. A single cell circulation extending from poles to the equator and with circulation directed toward the equator at the surface. Radial velocities are of the order of 10 cm s^?1 and meridional ones of the order of 150 cm s^?1.
2. A flux difference between pole and equator at the surface of about 5 percent, the poles being hotter.
3. An angular velocity increasing inwards.
4. Angular velocity constant surfaces of spheroidal shape. The model is consistent with the fact that the interaction of convection with rotation sets up a circulation (driven by the temperature gradient) which carries angular momentum toward the equator against the viscous friction. Unfortunately also a large flux variation at the surface is obtained. Nevertheless it seems that the model has the basic requisites for correct dynamo action.

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Numerical modeling and mechanical analysis of an innovative soil anchoring system     

Claudio di Prisco  Federico Pisanò 《Acta Geotechnica》2014,9(6):1013-1028

In this paper, the pull-out performance of an innovative system for soil anchoring is mechanically interpreted on the basis of a preliminary finite element investigation. The system consists of a tie rod equipped with thick steel sockets, extruding into the soil to increase the overall pull-out bearing capacity. The effectiveness of the anchorage is shown to be mainly due to the steel sockets, producing two correlated strength mechanisms: a direct one, associated with the shear/flexural strength of the sockets themselves; and an indirect one, in the form of a remarkable increase in the normal confinement on the tie rod and hence in the mobilizable shear stresses. The numerical results are finally exploited to conceive a simplified mechanical model for the interpretation/prediction of the pull-out anchor performance.  相似文献