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41.
Amir Babak Aazami Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2006,372(4):1692-1698
Gravitational lensing of a background source by a foreground galaxy lens occasionally produces four images of the source. The cusp and the fold relations impose conditions on the ratios of magnifications of these four-image lenses. In this theoretical investigation, we explore the sensitivity of these relations to the presence of substructure in the lens. Starting with a smooth lens potential, we add varying amounts of substructure, while keeping the source position fixed, and find that the fold relation is a more robust indicator of substructure than the cusp relation for the images. This robustness is independent of the detailed spatial distribution of the substructure, as well as of the ellipticity of the lensing potential and the presence of external shear. 相似文献
42.
43.
Acta Geochimica - The Varzaghan district at the northwestern margin of the Urumieh–Dokhtar magmatic arc, is considered a promising area for the exploration of porphyry Cu deposits in Iran. In... 相似文献
44.
Siahsarani Amir Karami Khaniki Ali Aliakbari Bidokhti Abbas-Ali Azadi Majid 《Ocean Science Journal》2021,56(3):225-240
Ocean Science Journal - A storm surge is a complex phenomenon in which current, tide, and waves interact with each other. Even if the wind is the main force of driving the surge, waves and tide are... 相似文献
45.
In the Makran subduction zone, earthquake focal mechanisms and geodetic data indicate that the deforming prism currently experiences N–S compression. However, palaeostress inversions performed on normal faults observed along the coast reveal local stress components consistent with N‐S extension. Previously proposed mechanisms such as gravitational collapse are not favoured by N–S compression and surface uplift. We propose that the observed kinematics result from transient stress reversals following large earthquakes. During the interseismic period (now), the region experiences N–S compression. However, following a large reverse rupture on the subduction interface, stresses in the inner wedge relax, enabling a brief period of extensional faulting before a compressive stress state is re‐established. This mechanism, also observed in other subduction zones, requires low overall stresses in the upper plate and that the margin ruptures in large megathrust earthquakes that result in nearly complete stress drops. 相似文献
46.
Improving urban cellular automata performance by integrating global and geographically weighted logistic regression models 总被引:1,自引:0,他引:1
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In many of the conventional cellular automata (CA) models, particularly Urban‐CA which are used for urban growth, the spatial heterogeneities and local differences of the land use conversion processes are ignored. Global logistic regression (LR) is a popular model employed to define the transition rules of Urban‐CA. By considering the local characteristics, Geographically Weighted Logistic Regression (GWLR) provides interesting capabilities for urban growth modelling. In this research, in addition to using GWLR in the definition of transition rules, the advantages of integrating GWLR and LR for urban growth simulation were evaluated; these have not been considered in previous studies. Local and global probabilities obtained from the calibration of GWLR and LR were combined to define the transition rules of an Urban‐CA. Urban growth was simulated in the Islamshahr sub‐region located southwest of Tehran, Iran for the two periods 1992‐1996 and 1996‐2002, and data from these periods were used for training and testing the prediction abilities, respectively. In the first period, GWLR showed good performance and a significant contribution to the enhancement of the simulation performance, but in the second period, the effectiveness of LR on the prediction accuracy increased. Due to their complementary roles, the integration of the GWLR and LR models resulted in improved simulation performance in both periods. 相似文献
47.
We evaluate the accuracy of the speed-up provided in several wind-loading standards by comparison with wind-tunnel measurements and numerical predictions, which are carried out at a nominal scale of 1:500 and full-scale, respectively. Airflow over two- and three-dimensional bell-shaped hills is numerically modelled using the Reynolds-averaged Navier–Stokes method with a pressure-driven atmospheric boundary layer and three different turbulence models. Investigated in detail are the effects of grid size on the speed-up and flow separation, as well as the resulting uncertainties in the numerical simulations. Good agreement is obtained between the numerical prediction of speed-up, as well as the wake region size and location, with that according to large-eddy simulations and the wind-tunnel results. The numerical results demonstrate the ability to predict the airflow over a hill with good accuracy with considerably less computational time than for large-eddy simulation. Numerical simulations for a three-dimensional hill show that the speed-up and the wake region decrease significantly when compared with the flow over two-dimensional hills due to the secondary flow around three-dimensional hills. Different hill slopes and shapes are simulated numerically to investigate the effect of hill profile on the speed-up. In comparison with more peaked hill crests, flat-topped hills have a lower speed-up at the crest up to heights of about half the hill height, for which none of the standards gives entirely satisfactory values of speed-up. Overall, the latest versions of the National Building Code of Canada and the Australian and New Zealand Standard give the best predictions of wind speed over isolated hills. 相似文献
48.
Mohammad Parsa Abbas Maghsoudi Emmanuel John M. Carranza Mahyar Yousefi 《Natural Resources Research》2017,26(4):443-455
In this study, stream sediment geochemical data have been subjected to robust principal components analysis (RPCA) and singularity mapping (SM) to enhance and map significant multivariate geochemical anomalies (i.e., mineralization-related) in Ahar area, NW Iran. The RPCA was applied to (a) account for the compositional nature of stream sediment geochemical data using suitable log-ratio transformation, (b) modulate the effect of outliers in component estimation and (c) derive a multivariate geochemical footprint of mineralization. The SM was applied to extract anomalous patterns of the multivariate geochemical footprint of mineralization. The exploration targets were then delineated using Student’s t-statistics analysis. The correlations of mapped exploration targets with the known mineral occurrences and mineralization-related patterns were further evaluated using normalized density index and overall accuracy analyses. 相似文献
49.
Special Economic Zones (SEZs) are important vectors of neoliberal globalization in India. Despite facing widespread resistance against the proposed land acquisition for these zones, they are still being promoted across the country. We argue that the wealth redistribution to the country's elites and the fractured resistance movements enable neoliberalism and its practices to grow in the countryside. Using a private sector SEZ in Gurgaon as a case study, this article explores how special economic zoning, as a neoliberal policy, has been implicated in the spatialized production of poverty. We also show that the main actors who promote neoliberalism in India (the state and the large‐scale urban private sector) have found a seemingly unlikely ally in rural India in the form of farmers with large landholdings, rural elites who are willing to let go of their land under certain conditions. The data for the article was collected in India in 2009–10. 相似文献
50.
Earth fissures have developed at Wadi Al-Yutamah, western Saudi Arabia. The fissues are associated with land subsidence which is considered to be due to both rapid draw down of the ground-water level and hydrocompaction of the wadi soil after flooding. This phenomenon is relatively recent in the area.The wadi soil was investigated and classified in the field, and disturbed and undisturbed samples were collected for laboratory testing and analysis. The engineering properties of the wadi soils were determined, including in situ field density, specific gravity, liquid limit, plastic limit, plasticity index, shrinkage limit, and consolidation characteristics such as total settlement and coefficient of subsidence (collapse).Four types of silty soil of different colours were identified, in addition to yellowish-brown sand (representing the dunes) which accumulated on the surface of the study area. The silty soils include yellowish-brown silty sand, yellowish-gray silt, pale brown silt and yellowish-brown clayey silt. The results of X-ray diffraction analysis indicated that the clay is mainly kaolinite and illite with minor smectite. The dominant soil type in the study area is silt of low plasticity, high void ratio and low density which decreased with depth. This soil was classified as loess-like materials.The studied soils are of a collapsing type, and settlement is greatly increased by excessive wetting under constant pressure. The calculated coefficients of subsidence (collapse) of the soils at different depths generally increased with decreasing soil density and ranged between 3·1% and 10·8%. The wadi soils are considered to pose a moderate problem when wetted. 相似文献