This article proposes a simple post hoc segmentation approach to revisit Household Travel Survey data and sketch archetypal mobility figures (clusters) that relate to people's daily mobility experiences. Describing the mobility behaviors of the different clusters and the distribution of the population between clusters is a powerful means to draw the mobility landscape of a metropolitan area and make comparisons over time and across places. Furthermore, clusters can be used to contextualize mobility behaviors in a variety of social inquiries and can be complementary to traditional quantitative mobility indicators or qualitative investigations. 相似文献
The capability of RADARSAT synthetic aperture radar (SAR) for the purpose of snow-line/accumulation area mapping for a temperate alpine glacier is examined. In agreement with other orbital C-band SAR studies, RADARSAT can discriminate between firn and bare ice facies. Limited observations are reported with respect to the electromagnetic variability of the ice facies in the ablation area, but they are inconclusive. Operational considerations are discussed with respect to reconciling the uncertainties of late-summer weather and their possible impact on the dielectric and scattering properties of the glacier surface. Vagaries associated with other glacier settings, mass balance states and their associated facies configurations are discussed including the difficulty of using the transient snow-line to define the equilibrium line and the lower extent of the accumulation area for glaciers where superimposed ice may form. The radar remote-sensing reconnaissance of equilibrium line altitude (ELA) and accumulation area ratio (AAR) for estimating glacier mass balance requires serious consideration in those instances where traditional ground measurements used in the direct glaciological method are absent. However, with respect to the ELA, such estimates can vary depending on the accuracy of the reference digital elevation information. Moreover, for many glacier configurations, where mass balance variations due to altitude are influenced or in some cases completely masked by local balance variations, defining the ELA may be an irreconcilable problem. Using the AAR may be more robust in this regard. It is further determined that the total error inherent in the reconnaissance method would have serious implications for the confident estimation of mass balance normals and climate-related trends if the method were to be utilized over the longer term. 相似文献
To test the potential of heat flux prospecting in active volcanic areas using shallow temperature data taken along vertical
profiles, we carried out two thermal profile surveys, one not far from Yasur cone on Tanna Island, and another inside the
caldera of Ambrym (New Hebrides arc, southwestern Pacific). The basic steady heat flux of internal volcanic origin was determined,
taking into account both conductive and convective heat transfers. At both locations there exists, over small distances, significant
differences in the heat flux. These differences correspond to shallow sources of heat. The use of a network of vertical profiles
allowed: (a) heat flux mapping; (b) location of shallow volcanic heat sources; and (c) observation of the detailed structure
of the heat release at quiescent but active volcanoes.
Received: 18 July 1997 / Accepted: 13 May 1998 相似文献
In the analysis of geographical spillovers, a commonly accepted hypothesis is that the different actors of innovation need to be physically closed to one another because the transfer of tacit knowledge implies frequent face-to-face relations. This hypothesis is put under closer examination in this paper. The first section analyses the need for economic agents to be closely located to develop research and innovative activities, starting with the analysis of their need for co-ordination and using some case studies. Based on the example of three French regions, the second section examines the importance given by the local development policies to geographical proximity in order to support the rapid development of local networks favouring innovation. In both sections, nonlocal relations appear as a key factor to develop innovation. As a conclusion, nonlocal relations should be encouraged by local development policies in the same way as local relations. 相似文献
Hydrologic model development and calibration have continued in most cases to focus only on accurately reproducing streamflows. However, complex models, for example, the so‐called physically based models, possess large degrees of freedom that, if not constrained properly, may lead to poor model performance when used for prediction. We argue that constraining a model to represent streamflow, which is an integrated resultant of many factors across the watershed, is necessary but by no means sufficient to develop a high‐fidelity model. To address this problem, we develop a framework to utilize the Gravity Recovery and Climate Experiment's (GRACE) total water storage anomaly data as a supplement to streamflows for model calibration, in a multiobjective setting. The VARS method (Variogram Analysis of Response Surfaces) for global sensitivity analysis is used to understand the model behaviour with respect to streamflow and GRACE data, and the BORG multiobjective optimization method is applied for model calibration. Two subbasins of the Saskatchewan River Basin in Western Canada are used as a case study. Results show that the developed framework is superior to the conventional approach of calibration only to streamflows, even when multiple streamflow‐based error functions are simultaneously minimized. It is shown that a range of (possibly false) system trajectories in state variable space can lead to similar (acceptable) model responses. This observation has significant implications for land‐surface and hydrologic model development and, if not addressed properly, may undermine the credibility of the model in prediction. The framework effectively constrains the model behaviour (by constraining posterior parameter space) and results in more credible representation of hydrology across the watershed. 相似文献
Most groundwater models simulate stream‐aquifer interactions with a head‐dependent flux boundary condition based on a river conductance (CRIV). CRIV is usually calibrated with other parameters by history matching. However, the inverse problem of groundwater models is often ill‐posed and individual model parameters are likely to be poorly constrained. Ill‐posedness can be addressed by Tikhonov regularization with prior knowledge on parameter values. The difficulty with a lumped parameter like CRIV, which cannot be measured in the field, is to find suitable initial and regularization values. Several formulations have been proposed for the estimation of CRIV from physical parameters. However, these methods are either too simple to provide a reliable estimate of CRIV, or too complex to be easily implemented by groundwater modelers. This paper addresses the issue with a flexible and operational tool based on a 2D numerical model in a local vertical cross section, where the river conductance is computed from selected geometric and hydrodynamic parameters. Contrary to other approaches, the grid size of the regional model and the anisotropy of the aquifer hydraulic conductivity are also taken into account. A global sensitivity analysis indicates the strong sensitivity of CRIV to these parameters. This enhancement for the prior estimation of CRIV is a step forward for the calibration and uncertainty analysis of surface‐subsurface models. It is especially useful for modeling objectives that require CRIV to be well known such as conjunctive surface water‐groundwater use. 相似文献
Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon. Here, we present new field data, petrography, and first comprehensible whole-rock geochemistry data and discuss the protolith and tectonic significance of these serpentinites in the region. The studied rock samples are characterized by pseudomorphic textures, including mesh microstructure formed by serpentine intergrowths with cores of olivine, bastites after pyroxene. Antigorite constitutes almost the whole bulk of the rocks and is associated (to the less amount) with tremolite, talc, spinel, and magnetite. Whole-rock chemistry of the Eseka serpentinites led to the distinction of two types. Type 1 has high MgO (> 40 wt%) content and high Mg# values (88.80) whereas Type 2 serpentinite samples display relatively low MgO concentration and Mg# values (< 40 and 82.88 wt%, respectively). Both types have low Al/Si and high Mg/Si ratios than the primitive mantle, reflecting a refractory abyssal mantle peridotite protolith. Partial melting modeling indicates that these rocks were derived from melting of spinel peridotite before serpentinization. Bulk rock high-Ti content is similar to the values of subducted serpentinites (> 50 ppm). This similarity, associated with the high Cr contents, spinel-peridotite protolith compositions and Mg/Si and Al/Si ratios imply that the studied serpentinites were formed in a subduction-related environment. The U-shaped chondrite normalized-REE patterns of serpentinized peridotites, coupled with similar enrichments in LREE and HFSE, suggest the refertilized nature due to melt/rock interaction prior to serpentinization. Based on the results, we suggest that the Eseka serpentinized peridotites are mantle residues that suffered a high degree of partial melting in a subduction-related environment, especially in Supra Subduction Zone setting. These new findings suggest that the Nyong series in Cameroon represents an uncontested Paleoproterozoic suture zone between the Congo craton and the São Francisco craton in Brazil.
The physical partitioning of Hg into different grain size fractions of till is predominantly controlled by the primary bedrock mineralogy, the distance of glacial transport, and the relative stability of cinnabar (HgS) in the soil weathering environment. At sites located short distances down-ice from bedrock cinnabar mineralization, the highest Hg concentrations in unoxidized till were measured in the sand- and granule-sized fractions reflecting the abundance of cinnabar in those size ranges. Similar partitioning was measured in oxidized till as cinnabar was found to be relatively resistant to postglacial weathering. Discrete clay-sized cinnabar grains obtained from the unoxidized till were viewed under the scanning electron microscope and suggest that the terminal grade of cinnabar is in the clay-sized range. In till collected from areas barren of cinnabar mineralization, the highest Hg levels were found in the clay-sized fraction which is attributed to the high adsorption of Hg by clay minerals. 相似文献