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11.
Jane Bemigisha John Carranza rew K. Skidmore Mike McCall Chiara Polce Herbert H.T. Prins 《Transactions in GIS》2009,13(3):273-293
In a project to classify livestock grazing intensity using participatory geographic information systems (PGIS), we encountered the problem of how to synthesize PGIS-based maps of livestock grazing intensity that were prepared separately by local experts. We investigated the utility of evidential belief functions (EBFs) and Dempster's rule of combination to represent classification uncertainty and integrate the PGIS-based grazing intensity maps. These maps were used as individual sets of evidence in the application of EBFs to evaluate the proposition that " This area or pixel belongs to the high, medium, or low grazing intensity class because the local expert(s) says (say) so ". The class-area-weighted averages of EBFs based on each of the PGIS-based maps show that the lowest degree of classification uncertainty is associated with maps in which "vegetation species" was used as the mapping criterion. This criterion, together with local landscape attributes of livestock use may be considered as an appropriate standard measure for grazing intensity. The maps of integrated EBFs of grazing intensity show that classification uncertainty is high when the local experts apply at least two mapping criteria together. This study demonstrates the usefulness of EBFs to represent classification uncertainty and the possibility to use the EBF values in identifying and using criteria for PGIS-based mapping of livestock grazing intensity. 相似文献
12.
Estimating seismic demands on structures, to predict their performance level with confidence, requires explicit consideration
of the structural inelastic behaviour: to this end, the use of nonlinear static procedures is inevitably going to be favoured
over complex nonlinear time-history methods.
The currently available assessment procedures have been tested predominantly against building frames. A newly derived assessment
procedure is proposed within the scope of bridge applications, based on an innovative displacement-based adaptive pushover
technique. The procedure, which can be incorporated into a performance-based engineering philosophy, is applicable to MDOF
continuous span bridges with flexible or rigid superstructures, and for varying degrees of abutment restraint.
As a first application to determine the viability of the proposed procedure, a parametric study is conducted on a ensemble
of bridges subjected to earthquake motion. It is shown that, compared to the seismic demand estimated by means of the more
accurate nonlinear dynamic analysis tool, the novel static assessment method can lead to the attainment of satisfactory predictions,
both in terms of displacement as well as moment demand on members. 相似文献
13.
Synthetic orthopyroxenes free of trivalent cations Mg x Fe 2-x Si2O6 (x=0; 1; 1.6) were investigated using both Mössbauer spectroscopy (MS) and single-crystal X-ray diffraction (XRD) in order to compare the results obtained on the same samples by the two techniques. The Mg-Fe distribution over M1 and M2 octahedral sites was determined on compounds with x = 1 and x=1.6, unheated and annealed at 650, 850 and 1040° C for 29 to 42 hours to obtain different degrees of order. The data obtained by the two techniques are in very good agreement, thus suggesting, for these compositions, the absence of systematic errors. The investigation of a synthetic compound with x=0 (ferrosilite) confirmed that the accuracy of both methods is very good. The observed small discrepancies between the results are not significant if compared with the relevant standard deviations which, for both methods, were derived by leastsquares calculations. The best fit is obtained for Fe(M1)/ Fe(tot) parameters that, in both methods, are directly calculated without using data from chemical analysis. For the unheated samples the values by MS and XRD are respectively: 0.185(9) and 0.180(4) for x = 1.6; 0.282(8) and 0.285(2) for x=1; 0.503(7) and 0.502(1) for x=0. For all the investigated samples the correlation between the geometrical distortion parameters, calculated by X-ray refinement, and the quadrupole splitting values, measured by Mössbauer spectroscopy, agrees with the theoretical model of Ingalls (1964). 相似文献
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Assessment of the role of facies heterogeneity at the fine scale by numerical transport experiments and connectivity indicators 总被引:2,自引:1,他引:1
The heterogeneity of facies at the scale of individual lithological levels controls, at a macroscopic scale, water flow and contaminant transport in porous sediments. In particular the presence of organized features such as permeable connected levels, has a significant effect on travel times and dispersion. Here, the effects of facies heterogeneity on flow and transport are studied for three blocks, whose volume is of the order of a cubic meter, dug from alluvial sediments from the Ticino valley (Italy). Using the results of numerical tracer experiments on these domains, the longitudinal dispersion coefficient is computed with an Eulerian approach based on the fit of the breakthrough curves with the analytical solution of the convective-dispersive transport equation. Moreover, the dispersion tensor is computed with a Lagrangian approach from the second order moments of particle distributions. Three types of connectivity indicators are tested: (1) connectivity function; (2) flow, transport and statistical connectivity; (3) original (intrinsic, normal and total) indicators of facies connectivity. The connectivity function provides the most complete information. Some of the transport and statistical connectivity indicators are correlated with dispersivity. The simultaneous analysis of the three indicators of facies connectivity emphasizes the fundamental geometrical features that control transport. 相似文献
16.
Raphaël di Chiara Roupert Gerhard Schäfer Philippe Ackerer Michel Quintard Guy Chavent 《Comptes Rendus Geoscience》2010,342(11):855-863
Multiphase flow modelling is a major issue in the assessment of groundwater pollution. Three-phase flows are commonly governed by mathematical models that associate a pressure equation with two saturation equations. These equations involve a number of secondary variables that reflect the fluid behaviour in a porous medium. To improve the computational efficiency of multiphase flow simulators, several simplified reformulations of three-phase flow equations have been proposed. However, they require the construction of new secondary variables adapted to the reformulated flow equations. In this article, two different approaches are compared to quantify these variables. A numerical example is given for a typical fine sand. 相似文献
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Lorenzo Tomassini Olivier Geoffroy Jean-Louis Dufresne Abderrahmane Idelkadi Chiara Cagnazzo Karoline Block Thorsten Mauritsen Marco Giorgetta Johannes Quaas 《Climate Dynamics》2013,41(11-12):3103-3126
An overview of radiative climate feedbacks and ocean heat uptake efficiency diagnosed from idealized transient climate change experiments of 14 CMIP5 models is presented. Feedbacks explain about two times more variance in transient climate response across the models than ocean heat uptake efficiency. Cloud feedbacks can clearly be identified as the main source of inter-model spread. Models with strong longwave feedbacks in the tropics feature substantial increases in cloud ice around the tropopause suggestive of changes in cloud-top heights. The lifting of the tropical tropopause goes together with a general weakening of the tropical circulation. Distinctive inter-model differences in cloud shortwave feedbacks occur in the subtropics including the equatorward flanks of the storm-tracks. Related cloud fraction changes are not confined to low clouds but comprise middle level clouds as well. A reduction in relative humidity through the lower and mid troposphere can be identified as being the main associated large-scale feature. Experiments with prescribed sea surface temperatures are analyzed in order to investigate whether the diagnosed feedbacks from the transient climate simulations contain a tropospheric adjustment component that is not conveyed through the surface temperature response. The strengths of the climate feedbacks computed from atmosphere-only experiments with prescribed increases in sea surface temperatures, but fixed CO2 concentrations, are close to the ones derived from the transient experiment. Only the cloud shortwave feedback exhibits discernible differences which, however, can not unequivocally be attributed to tropospheric adjustment to CO2. Although for some models a tropospheric adjustment component is present in the global mean shortwave cloud feedback, an analysis of spatial patterns does not lend support to the view that cloud feedbacks are dominated by their tropospheric adjustment part. Nevertheless, there is positive correlation between the strength of tropospheric adjustment processes and cloud feedbacks across different climate models. 相似文献
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