Asymptotic edge-and-vertex diffraction theory

Uniformly asymptotic formulae for edge-and-vertex diffraction in the time-domain, involving elementary functions of time, traveltimes and GTD amplitudes, are derived. Explicit expressions for diffraction at a pyramid and a triangle are constructed. They can be applied to the numerical calculation of a field reflected and diffracted at 3-D objects with sharp edges and to reflection from triangulated surfaces. the computational cost is very low.     

Towards a theory of targeting

A representative economic model is used to analyze local policies to reestablish full employment. It addresses three types of barriers: 1. Rigid wages, 2. Occupational (or industrial) immobility, and 3. Geographic immobility. These factors are considered in the framework of three types of policies: 1. Laissez-faire, 2. Narrowly targeted employment incentives, and 3. Broadly targeted incentives. The paper concludes that the usefulness of the abstract model will depends upon the ability of local development officials to combine the implications of the model with information about the local economic development narrative. In turn, the narrative depends upon an in-depth local knowledge of history, institutions, practices and personalities.     

Towards a theory of the discordant border

Borders are often portrayed in stark terms, perhaps as national‐scale threats, or as sites of suffering, or conversely as hosts to socio‐cultural symbiosis. Yet borders are many things all at once. In this paper, we use the comparative context of the US–Mexico border and the Mexico‐Guatemala border to critique what we call the ‘border as hegemony’, a borderscape constructed through obstructions, punitive policing and reinforcing the limits of state control. Instead, we propose a model of the ‘border as discord’. In our heuristic framework, diverse mobilities are embraced, interests of borderlanders are acknowledged and prioritized, and borders are interpreted not as a security threat but as a resource for change.     

Indicator favorability theory for mineral potential mapping

Favorability methods produce a unique measure for mineral potential mapping and quantitative estimation of mineral resources. Indicator favorability theory is developed in this study to account for spatial (auto and cross) correlations of regionalized geological, geochemical, and geophysical fields based on the indicator concept. Target and explanatory indicators are introduced to describe, respectively, direct and indirect evidence of the mineralization of interest. Mineralization is represented by a combination () of a set of target indicators. Indicator favorability theory estimates a regionalized favorability function in two stages: (1) estimate a linear combination of target indicators by maximizing var() and (2) estimate favorability functionF by minimizing estimation variance var[F–]. The model is established on the basis of a conceptual model of target. The favorability estimates can be justified by correlation analysis and cross validation in control areas. The indicator favorability theory is demonstrated on a case study for gold-silver mineral potential mapping based on geophysical, structural, and geochemical fields.     

Long-period corrections to body waves: theory

Summary. The usual asymptotic methods used to correct the high-frequency solutions of the wave equation are unsatisfactory as they do not give the low-frequency, partial reflections expected from a region of high velocity gradient. A new iterative solution is obtained which uses the first term of the Langer asymptotic expansion as the zeroth iterate. This satisfactorily gives the partial reflections from a region of high velocity gradient, even when they are generated near the turning point of the ray. Although the results are somewhat complicated in the frequency domain, in the time domain all types of wave interaction are described by six universal time functions. For any problem, these functions are scaled in time according to the depth of the interaction, and in strength according to the magnitude of the coupling parameter. Numerical results and approximations are given for these functions. Coupling parameters are investigated for acoustic and elastic waves in a plane model, and acoustic and elastic-gravitational waves in a spherical model. The same universal time functions allow the excitation of elastic waves to be studied when the source is in a region of high velocity gradient or is near the wave's turning point. Results are given for a moment tensor, point source in plane and spherical models.     

基于Lancaster特性理论的旅游目的地选择模式——理论分析与江西省旅游客流的实证研究

针对传统旅游需求研究中对消费者与产品的属性和旅游流的时空特性的忽视,本文基于Lancaster的消费特性理论和旅游目的地映象理论,提出了旅游流的目的地选择的概念模式和分析模型,进一步拓展了Lancaster的消费特性理论在旅游中的应用,并以江西省国内入游旅游流为例进行了实证研究。     

The new basic theory on Quaternary environmental research

On the basis of extensive survey to the Quaternary paleosols, soils and weathering layers in the vast northern China and the Loess Plateau, we found some unusually special phenomena of chemical components such as unsuccessive illuvium, twin illuviums, unusually thick illuvium and multi-illuviums etc. According to the analysis on the content of CaCO3 and the data of penetrating experiment, a new theory of illuvial depth or removal depth of CaCO3 in weathering and leaching belt was constructed, which indicates that the time of CaCO3 removing to the illuvial depth is very short, and the effect of time factor on illuvial depth can be ignored. The theory can be taken as a credible foundation for studying many geological and geographical problems in weathering and leaching belt. When the illuvial depth of CaCO3 is bigger than the thickness of developing belt of soil or paleosol, it can be determined that the paleosol has turned into weathering crust. When the illuvial depth of CaCO3 is bigger than the thickness of paleosol, paleosol is leaching moderately acid soil. When two, three layers or unusually thick CaCO3 illuviums exist in the same weathering section or at the bottom of the same paleosol, there were two or more periods forming paleosol and corresponding climatic stages at that time. On the basis of the equation of relationship between mean annual rainfall (y) and illuvial depth of CaCO3 (x) (y = 305.5x + 168.5) determined in the paper, mean annual precipitation during the development of paleosol can be calculated.