共查询到20条相似文献，搜索用时 171 毫秒
1.
M. E. Everett 《Geophysical Journal International》1997,130(1):193-200
A new spherical mesh generator is described. It represents an efficient, deterministic packing of tetrahedra into a solid sphere, a spherical shell, or both. The mesh can be used for finite-element solutions to a wide variety of global numerical modelling problems in the geosciences. The nodes within the mesh are distributed uniformly, and long, thin tetrahedra are avoided. The method proposed here offers several advantages over 3-D Delaunay algorithms for finite-element mesh generation. For the related problem of trivariate scattered data interpolation, which is not considered here, the 3-D Delaunay algorithms are the method of choice. 相似文献
2.
Imag(in)ing 'homeless places': using auto-photography to (re)examine the geographies of homelessness 总被引：1，自引：0，他引：1
Despite its growing popularity as a method across the social sciences, the methodological literature on auto-photography is remarkably sparse. In an effort to begin redressing this gap, this paper provides an account of the ways in which auto-photography was used to complement other research methods in a (re)examination of the geographies of homelessness. It describes how auto-photography illuminated 'hidden' spaces that do not typically feature in public (or academic) imaginations of homelessness, and provided more nuanced understandings of the use, meanings and dynamics associated with other, apparently already 'known' spaces. It concludes that whilst auto-photography presents a number of logistical and ethical challenges – particularly when used with such a vulnerable group – it is nevertheless a powerful heuristic tool. 相似文献
3.
大气降尘收集方法及相关问题研究 总被引：23，自引：5，他引：23
降尘监测是探索大气降尘对环境的影响和生态效应评估不可缺少的手段之一。根据集尘容器内同定降尘介质的不同，目前常用的收集方法分为干法、湿法和玻璃球法3种。在实际监测中，每种方法都有不同的研究者采用，3种方法的收集效率也有一定的差别。研究表明，干法的集尘效率为湿法的73％和玻璃球法的95％；玻璃球法的集尘效率为湿法的77％。3种方法的集尘量之间具有良好的线性关系，可以依此进行数据的转换。不同的收集容器会对集尘效率产生影响，其测量精度也不相同。另外，这3种收集方法不能很好地区别干沉降和湿沉降过程，应该加以改进。因此，采用统一的标准开展大气降尘的合作研究很有必要。 相似文献
4.
Robust smooth magneto tell uric transfer functions 总被引：3，自引：0，他引：3
Jimmy C. Larsen Randall L. Mackie Adele Manzella Adolfo Fiordelisi Shirley Rieven 《Geophysical Journal International》1996,124(3):801-819
5.
Terry A. Slocum 《The Professional geographer》1990,42(1):84-94
Ninety mainstream quantitative methods used in 14 major geographical journals are analyzed for four selected years: 1956, 1966, 1976, and 1986. Mainstream methods are used in 53% of all articles in 1986, as opposed to 3% in 1956. Both the intensity and variety of methods used also increased, particularly in physical and techniques articles compared to human articles. Major methods that dominate the entire period include bivariate correlation and regression, multiple regression, factor analyses, and chi-square. The use of nonparametric methods is increasing, although their frequency of occurrence is still low. Spatial autocorrelation and advanced multiple regression appear to be strong newcomers to the discipline. 相似文献
6.
A theoretical approach to the propagation of interacting cracks 总被引：2，自引：0，他引：2
We propose a scheme to compute interaction effects between two randomly oriented cracks under compressive stresses and we discuss the role crack interactions play in the crack coalescence process. Stress intensity factors are computed by using an iterative technique based on the method of successive approximations. Once crack propagation occurs, curved wing cracks grow from the initial crack tips. The stress intensity factors at the wing crack tips are calculated as the sum of two terms: a component for a single wing crack subjected to both the applied stresses and the interaction effect, and a component due to the sliding of the initial crack. We have applied our procedure to various crack geometries. Our results show that interaction effects act on the crack propagation path. For cracks under tension, our approach correctly predicts the curving, hook-shaped paths of interacting cracks that have been observed in various materials. For en echelon compressive cracks, interaction effects depend on the geometry of stepping. For right-stepping cracks, no mode I crack coalescence occurs. A mixedmode propagation criterion may be introduced to check whether coalescing secondary shear fractures initiate. For left-stepping cracks, depending on whether or not there is overlapping, crack coalescence is achieved by tension wing cracks at the inner crack tips. Without overlapping, the growing wing cracks delimit a region where a tensile secondary fracture may develop and lead to coalescence. These results are consistent with previous work and show that our procedure may be now extended to a population of cracks. 相似文献
7.
Reflection coefficients for weak anisotropic media 总被引：1，自引：0，他引：1
Matthias Zillmer Dirk Gajewski Boris M. Kashtan 《Geophysical Journal International》1997,129(2):389-398
The interaction of plane elastic waves with a plane boundary between two anisotropic elastic half-spaces is investigated. The anisotropy dealt with in this study is of a general type. Explicit expressions for energy-related reflection and transmission coefficients are derived. They represent an approximation which is valid for a small deviation of the elastic parameters from isotropy.
Classical perturbation theory is applied on a 6times6 non-symmetric real eigenvalue problem to calculate first-order corrections for the polarization and stress of the plane waves. The explicit solution of the isotropic problem is used as a reference case. Degenerate perturbation theory is used to consider the splitting of the isotropic S -wave into two anisotropic qS-waves. The boundary conditions for two half-spaces in welded contact lead to a 6times6 system of linear equations. A correction to the isotropic solution is calculated by linearization. The resultant coefficients are functions of horizontal slowness, Lamé parameters and densities of the reference media, and of the perturbation of the elasticity tensors from isotropy. 相似文献
Classical perturbation theory is applied on a 6times6 non-symmetric real eigenvalue problem to calculate first-order corrections for the polarization and stress of the plane waves. The explicit solution of the isotropic problem is used as a reference case. Degenerate perturbation theory is used to consider the splitting of the isotropic S -wave into two anisotropic qS-waves. The boundary conditions for two half-spaces in welded contact lead to a 6times6 system of linear equations. A correction to the isotropic solution is calculated by linearization. The resultant coefficients are functions of horizontal slowness, Lamé parameters and densities of the reference media, and of the perturbation of the elasticity tensors from isotropy. 相似文献
8.
《The Professional geographer》2013,65(1):68-76
Fertility research in population geography is rooted in a spatial demography tradition which places emphasis on the use of quantitative methodologies to analyse, model and project fertility. As data sources have become more sophisticated and abundant some have questioned whether research within the discipline is now too data-oriented resulting in a reluctance to embrace new methods and concepts. Alternative conceptualisations of fertility and reproduction are outlined which represent a shift away from general explanation to more differentiated understandings of reproductive behaviour and favour the use of qualitative methodologies in combination or in a multi-level framework. The paper illustrates, with reference to a research project in the Kalahari of Botswana, the potential for methodological pluralism in the study of fertility. 相似文献
9.
Deborah Sporton 《The Professional geographer》1999,51(1):68-76
Fertility research in population geography is rooted in a spatial demography tradition which places emphasis on the use of quantitative methodologies to analyse, model and project fertility. As data sources have become more sophisticated and abundant some have questioned whether research within the discipline is now too data-oriented resulting in a reluctance to embrace new methods and concepts. Alternative conceptualisations of fertility and reproduction are outlined which represent a shift away from general explanation to more differentiated understandings of reproductive behaviour and favour the use of qualitative methodologies in combination or in a multi-level framework. The paper illustrates, with reference to a research project in the Kalahari of Botswana, the potential for methodological pluralism in the study of fertility. 相似文献
10.
We investigate the reconstruction of a conductive target using crosswell time-domain electromagnetic tomography in the diffusive limit. The work is a natural extension of our ongoing research in the modification of time-domain methods for the rugged marine mid-ocean-ridge environment, an environment characterized by extreme topography and pronounced variations in crustal conductivity on all scales. We have proved both in theory and in practice that 'traveltime', the time taken for an electromagnetic signal to be identified at a receiver following a change of current in the transmitter, is an excellent, robust estimator of average conductivity on a path between transmitter and receiver. A simple estimate of the traveltime for a parallel electric dipole-dipole system is the time at which the derivative of the electric field with respect to logarithmic time at the receiver reaches its maximum. We have derived the fundamental relationship between the traveltime and the conductivity of the medium for a uniform whole-space. We have applied the concept of the traveltime inversion to the related crosswell problem and demonstrated reconstructions of finite targets based on tomographic analyses. Results show that the crosswell time-domain electromagnetic tomography can supply useful information, such as the location and shape of a conductive target. 相似文献
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12.
以2003年5月29日福州市LandsmETM＋影像为数据源,对2种地表温度空间降尺度算法——EM算法和HUTS算法进行实验、比较与分析,EM算法是利用高空间分辨率的地表比辐射率对低空间分辨率的亮度温度影像进行调节,从而达到提高热红外影像空间分辨率的目的;HUTS算法则是引入了归一化差异植被指数NDVI和地表反照率d,通过在低空间分辨率拟合二者与地表温度LST之间的关系,然后根据其尺度不变性,将该关系应用到高空间分辨率的影像上,从而达到提高热红外影像空间分辨率的目的．研究结果表明：1）2种算法所得结果影像都能在有效提高空间分辨率的同时较好地保持了原始地表温度影像的空间分布特征,达到了较好的降尺度效果;2）以RMSE为定量评价指标,HUTS算法要略优于EM算法,其中,EM算法的RMSE为1．2494,而HUTS算法仅为0．9869． 相似文献
13.
Shoji Sekiguchi 《Geophysical Journal International》2006,166(3):1105-1124
A new traveltime tomographic method was developed with hierarchical shape functions of the finite element method as slowness or velocity interpolation functions. The degree of the approximation of velocity modelling is adjusted by selecting a set of hierarchical shape functions in each element. The ray density parameter of each element controls the selection to make the approximation fine or coarse in the high- or low-ray-density area. The proposed method is applied to both synthetic traveltime data and actual data. The AIC is used to determine the number of model parameters. The result of the synthetic data shows that low-resolution model parameters can be eliminated by the ray density parameter. The result of the actual data shows that the velocity pattern is approximately the same in the fine approximation area and that the velocity fluctuation is suppressed in the coarse approximation area, compared with that obtained from a full set of hierarchical shape functions. The number of model parameters is drastically reduced. The resolution can be estimated by the checkerboard restoration test. The result of the real data set was compared with that of the linear velocity grid model. 相似文献
14.
Sara L. McLafferty 《The Professional geographer》1995,47(4):436-442
Despite their limitations, quantitative methods have an important role in feminist geographic research. As discussed in this essay, quantitative methods can contribute by describing and analyzing the broad contours of difference, by providing a basis for informed policy making and progressive political change, by identifying people and places for in-depth study, and by situating qualitative research in a broader context. At the same time, feminist insights can enhance quantitative analysis. Collaboration between quantitative and qualitative researchers is essential. 相似文献
15.
Matthias Zillmer Dirk Gajewski & Boris M. Kashtan 《Geophysical Journal International》1998,132(1):159-166
In this article the interaction of plane waves with a weak-contrast interface between two weakly anisotropic half-spaces is investigated. The anisotropy dealt with is of a general type. The stress–displacement vectors of the plane waves are calculated by perturbation theory. By assuming that the jump in elastic parameters and density across the interface is small, one can derive a simple expression for the R qPqP coefficient. In cases in which the wave motion is restricted to a symmetry plane of an anisotropic medium, simple expressions for the R qSVqSV and R SHSH coefficients are also derived. 相似文献
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17.
We describe finite-difference approximations to the equations of 2-D electromagnetic induction that permit discrete boundaries to have arbitrary geometrical relationships to the nodes. This allows finite-difference modelling with the flexibility normally ascribed to finite-element modelling. Accuracy is demonstrated by comparison with finite-element computations. We also show that related approximations lead to substantially improved accuracy in regions of steep, but not discontinuous, conductivity gradient. 相似文献
18.
《The Professional geographer》2013,65(4):436-444
Chemical weathering is commonly assumed to be negligible in the denudation of alpine landscapes. Spot samples of dissolved ions from alpine streams on the Blanca Massif had minimum average concentrations in 1978 of 35.53 ppm (range: 14.9–75.6 ppm) and in 1979, 20.23 ppm (range: 7.35–35.0 ppm). Correlations between the variation in the concentration of dissolved ions (silica, pH, and minimum ion concentration) and the elevations and drainage-basin areas of sample sites were significant at the 0.05 level. 相似文献
19.
Niki A. Rust Amber Abrams Daniel W. S. Challender Guillaume Chapron Arash Ghoddousi Jenny A. Glikman 《社会与自然资源》2017,30(10):1304-1310
Qualitative methods are important to gain a deep understanding of complex problems and poorly researched areas. They can be particularly useful to help explain underlying conservation problems. However, the significance in choosing and justifying appropriate methodological frameworks in conservation studies should be given more attention to ensure data are collected and analysed appropriately. We explain when, why, and how qualitative methods should be used and explain sampling strategies in qualitative studies. To improve familiarity with qualitative methods among natural scientists, we recommend expanding training in social sciences and increasing collaboration with social scientists. Given the scale of human impacts on the environment, this type of nuanced analytical skill is critical for progressing biodiversity conservation efforts. 相似文献
20.
人类时空间行为数据观测体系架构及其关键问题 总被引：2，自引：0，他引：2
大数据的行为研究具有丰富的数据源,但在数据的尺度、信度、精度、粒度和研究边界等方面仍存在诸多问题,且涉及隐私、可预测性等广泛争议。依据"信息获取方式确定—信息获取手段整合—信息类型划分—信息解析与要素提取—行为属性与要素集成"的思路,构建了整合高精度、全要素和多视角的行为数据观测体系架构。梳理与论述了行为研究中行为变化的尺度依赖特征,个体行为与群体行为数据的区分与综合,行为数据需求与个体隐私边界界定及行为数据的解析、匹配与整合等关键问题。尝试从科学问题的边界界定与数据需求、多源数据采集与整合方法、多要素行为数据解析与集成方法及应用驱动的行为数据应用模式与途径等方面,对行为数据的综合采集与集成处理进行界定。 相似文献