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Metropolitan land-use patterns by economic function: a spatial analysis of firm headquarters and branch office locations in Australian cities 总被引：1，自引：0，他引：1
This paper develops a comparative means by which to understand metropolitan spatial structure through the dynamics of economic activities. Clustering and suburbanization have been key processes within the contemporary urban landscape, but few scholarly accounts have systematically merged the two to explain the geographies of economic activity. Using firm location as a variable to discern sector- and industry-based locational requirements, we explore land-use and economic activity in Australia’s five largest metropolitan areas. Drawing upon the respective headquarters and branch office locations of a set of publically traded firms, we seek to establish general spatial patterns across Australian cities using two proxy measures for clustering and suburbanization, being well-established drivers of firm locational choice. Despite the complexity that post-industrial and suburbanizing processes add to metropolitan land-use patterns, we contend that certain patterns exist that can be generalized from one context to another across urban space, and that certain emerging trends such as the development of CBD-fringe precincts merit greater attention. 相似文献
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The structure of macroporous or aggregated soils and fractured rocks is generally so complex that it is impractical to measure the geometry at the microscale (i.e., the size and the shape of soil aggregates or rock matrix blocks, and the myriad of fissures or fractures), and use such data in geometry-dependent macroscale flow and transport models. This paper analyzes a first-order type dual-porosity model which contains a geometry-dependent coefficient, β, in the mass transfer term to macroscopically represent the size and shape of soil or rock matrix blocks. As a reference, one- and two-dimensional geometry-based diffusion models were used to simulate mass transport into and out of porous blocks of defined shapes. Estimates for β were obtained analytically for four different matrix block geometries. Values for β were also calculated by directly matching analytical solutions of the diffusion models for a number of selected matrix block geometries to results obtained with the first-order model assuming standard boundary conditions. Direct matching improved previous results for cylindrical macropore geometries, especially when relatively small ratios between the outer soil mantle and the radius of the inner cylinder were used. Results of our analysis show that β is closely related to the ratio of the effective surface area available for mass transfer, and the soil matrix volume normalized by the effective characteristic length of the matrix system. Using values of β obtained by direct matching, an empirical function is derived to estimate macroscopic geometry coefficients from medium properties which in principle are measurable. The method permits independent estimates of β, thus allowing the dual-porosity approach eventually to be applied to media with complex and mixed types of structural geometry. 相似文献
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Accurate estimates of groundwater recharge are essential for effective management of groundwater, especially when supplies are limited such as in many arid and semiarid areas. In the Hebei Plain, China, water shortage is increasingly restricting socioeconomic development, especially for agriculture, which heavily relies on groundwater. Human activities have greatly changed groundwater recharge there during the past several decades. To obtain better estimates of recharge in the plain, five representative sites were selected to investigate the effects of irrigation and water table depth on groundwater recharge. At each site, a one‐dimensional unsaturated flow model (Hydrus‐1D) was calibrated using field data of climate, soil moisture, and groundwater levels. A sensitivity analysis of evapotranspirative fluxes and various soil hydraulic parameters confirmed that fine‐textured surface soils generally generate less recharge. Model calculations showed that recharge on average is about 175 mm/year in the piedmont plain to the west, and 133 mm/year in both the central alluvial and lacustrine plains and the coastal plain to the east. Temporal and spatial variations in the recharge processes were significant in response to rainfall and irrigation. Peak time‐lags between infiltration (rainfall plus irrigation) and recharge were 18 to 35 days in the piedmont plain and 3 to 5 days in the central alluvial and lacustrine plains, but only 1 or 2 days in the coastal plain. This implies that different time‐lags corresponding to different water table depths must be considered when estimating or modeling groundwater recharge. 相似文献
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Dadda Abdelali Geindreau Christian Emeriault Fabrice Rolland du Roscoat Sabine Esnault Filet Annette Garandet Aurélie 《Acta Geotechnica》2019,14(3):597-613
The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space (localized at the contact between grains, over the grain surfaces) and the contact properties: coordination number, contact surface area, contacts orientation and types of contact. In the present work, all these micromechanical properties are computed, for the first time, from 3D images obtained by X-ray tomography of intact biocemented sand samples. The evolution of all these properties with respect to the volume fraction of calcite is analyzed and compared between each other (from untreated sand to highly cemented sand). Whatever the volume fraction of calcite, it is shown that the precipitation of the calcite is localized at the contacts between grains. These results are confirmed by comparing our numerical results with analytical estimates assuming that the granular medium is made of periodic simple cubic arrangements of grains and by considering two extreme cases of precipitation: (1) The calcite is localized at the contact, and (2) the grains are covered by a uniform layer of calcite. In overall, the obtained results show that a small percentage of calcite is sufficient to get a large amount of cohesive contacts.
相似文献6.
Abdelali Dadda Christian Geindreau Fabrice Emeriault Sabine Rolland du Roscoat Aurélie Garandet Leslie Sapin Annette Esnault Filet 《Acta Geotechnica》2017,12(5):955-970
An experimental study has been performed to investigate the effect of the biocalcification process on the microstructural and the physical properties of biocemented Fontainebleau sand samples. The microstructural properties (porosity, volume fraction of calcite, total specific surface area, specific surface area of calcite, etc.) and the physical properties (permeability, effective diffusion) of the biocemented samples were computed for the first time from 3D images with a high-resolution images obtained by X-ray synchrotron microtomography. The evolution of all these properties with respect to the volume fraction of calcite is analysed and compared with success to experimental data, when it is possible. In general, our results point out that all the properties are strongly affected by the biocalcification process. Finally, all these numerical results from 3D images and experimental data were compared to numerical values or analytical estimates computed on idealized microstructures constituted of periodic overlapping and random non-overlapping arrangements of coated spheres. These comparisons show that these simple microstructures are sufficient to capture and to predict the main evolution of both microstructural and physical properties of biocemented sands for the whole range of volume fraction of calcite investigated. 相似文献
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Groundwater Modeling with Nonlinear Uncertainty Analyses to Enhance Remediation Design Confidence 
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下载免费PDF全文 Soil and groundwater contamination are often managed by establishing on‐site cleanup targets within the context of risk assessment or risk management measures. Decision‐makers rely on modeling tools to provide insight; however, it is recognized that all models are subject to uncertainty. This case study compares suggested remediation requirements using a site‐specific numerical model and a standardized analytical tool to evaluate risk to a downgradient wetland receptor posed by on‐site chloride impacts. The base case model, calibrated to observed non‐pumping and pumping conditions, predicts a peak concentration well above regulatory criteria. Remediation scenarios are iteratively evaluated to determine a remediation design that adheres to practical site constraints, while minimizing the potential for risk to the downgradient receptor. A nonlinear uncertainty analysis is applied to each remediation scenario to stochastically evaluate the risk and find a solution that meets the site‐owner risk tolerance, which in this case required a risk‐averse solution. This approach, which couples nonlinear uncertainty analysis with a site‐specific numerical model provides an enhanced level of knowledge to foster informed decision‐making (i.e., risk‐of‐success) and also increases stakeholder confidence in the remediation design. 相似文献
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Brazilian legislation defines coastal zone as a national patrimony – the geographic space of interaction of air, sea and land formed by the counties directly influenced, but not necessarily by those located in the coastline; also included are those distant until 50 km from the coastline, holding activities of great impact for the coastal zone or its ecosystems. The definition includes also the territorial sea of 12 nautical miles. Coastal management is conducted by a national plan legally enforced, complemented by states and counties plans, and a coastal ecologic-economic zoning limited to small portions of the coastal zone. A resolution of the “Environmental National Council” defines as “permanent preservation areas”, of very restricted use, coastal ecosystems as mangroves, sand dunes, and reproduction sites of wild fauna. One could expect that the Brazilian coast should be more protected and properly managed than other countries where a national management plan is lacking (Argentina) or where the guidelines exist but are not yet legally enforced (South Africa). Notwithstanding, we note today in Brazil an intensification of conflicts opposing small-scale vs. industrial fishermen; shrimp farming vs. mangrove crab harvesting; resorts installation vs. native communities; oil and gas activities vs. NGOs; and conflicts on environmental permit between federal and state governmental agencies. This paper evaluates the possible reasons for the failure of the complex legal suite available in Brazil and suggests that participatory management and concerted actions with relevant stakeholders are the key elements for the successful cases. 相似文献
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Rolf Kilian Christoph Schneider Johannes Koch Martinus Fesq-Martin Harald Biester Gino Casassa Marcelo Arvalo Gert Wendt Oscar Baeza Jan Behrmann 《Global and Planetary Change》2007,59(1-4):49
Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on 14C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field. 相似文献
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Abdelali Dadda Christian Geindreau Fabrice Emeriault Annette Esnault Filet Aurélie Garandet 《国际地质力学数值与分析法杂志》2019,43(2):568-577
The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space, coordination number, contact surface area, and types of contact. In the present work, some of these microscopic properties are computed, from 3D images obtained by X-ray tomography of biocemented sand. These properties are then used as an input in current analytical models to estimate the elastic properties (Young and shear moduli) and the strength properties (Coulomb cohesion). For the elastic properties, the analytical estimates (contact cement theory model) are compared with classical bounds, self-consistent estimate and numerical results obtained by direct computation (FEM computation) on the same 3D images. Concerning the cohesion, an analytical model initially developed to estimate the cohesion due to suction in unsaturated soils is modified to evaluate the macroscopic cohesion of biocemented sands. Such analytical model is calibrated on experimental data obtained from triaxial tests performed on the same biocemented sand. In overall, the presented results point out the important role of some microstructural parameters, notably those related to the contact, on such effective parameters. 相似文献