Models in geography revisited

Agent based models (ABMs) have many applications, and illustrate a rapidly developing field of enquiry, spanning both the physical-mathematical and human-social sciences. ABMs are seen as most appropriate in situations where decisions or actions are distributed around particular locations, and in which structure is viewed as emergent from the interaction between individuals. ABMs may be used either as representational devices, to reproduce the patterns observed or desired in the system of interest, or as foundational tools contributing to the development of social or economic theory. The role and status of models and modelling is itself an instantiation of a wider debate concerning representation and explanation. Today, a case can be made that the nature of explanation and the use of scientific interpretation reflect much less definite and exclusive positions and permit more diverse approaches than hitherto. The underlying proposition of this commentary is, therefore, that the time is right for a positive application of ABMs within the discipline of geography, and for a rediscovery and reappraisal of the richness and depth of insight in the model-building enterprise more generally. First, the context for ABM development and application is set with reference to the agency-structure debate. Second, some aspects of the heritage of models in geography is presented, based upon reviews of two benchmark publications bearing that title. Next, some of the most significant characteristics, uses, potentials and limitations of ABMs, are reviewed. Finally, some constructive ways forward are suggested, as informed by theory and method from the interpretative social sciences.     

西北旅游落后现状的突破及列车旅游的新思路--兼论"西部之星"旅游列车的产品设计

近几年，西北地区的旅游业虽然取得了很大的成绩，但其发展相对于东部地区却显得落后，其主要原因之一就是西北地区的旅游资源过于分散，景点间距过大，由此导致游览行程过长，游览内容单薄，这在客观上影响了游客的选择。而与此同时，在国外，列车旅游早已作为各国旅游业的重要旅游产品为世人所熟知。文章从分析我国西北旅游业发展的现状入手，针对景点分散这一制约我国西部旅游业发展的客观不利因素，肯定了开发旅游列车产品的思路。作者以西北地区为例，结合目前我国旅游专列发展现状，提出开通“西部之星”旅游列车的构想，并进行了初步的设计。     

在局域网中如何实现共享上网

在局域网中 ,通过代理服务器等一些软件或者 Internet连接共享路由器此类的硬件来实现在只有一条电话线或者是一个 ADSL接入的条件下共享上网     

Agents of Eviction: The Squatter Control and Clearance Division of Hong Kong's Housing Department

More is known about the policies that produce forced evictions and their consequences than about the agencies whose responsibility it is to conduct them. Understanding the nature of forced evictions requires greater comprehension of responsible agencies since the ways in which they implement policies may be a crucial intervening variable influencing the outcomes. In this paper, I use documentary and ethnographic research to describe the Squatter Control and Clearance Division of the Hong Kong Housing Department. Responsible both for evicting squatters and for controlling squatter areas that are permitted to remain for the time being, officers must respond to the conflicts and challenges of their twin, partially conflicting, mandates. Examination of changes in squatter control and clearance practices since 1954 is followed by a brief case study of the most recent squatter clearance that occurred in July 2001.     

Accessibility Measures in Spatial Mismatch Models

Implicit in all spatial mismatch models is the concept of accessibility. However, there is an immense variety of measures utilized in the literature to index the concept, and it is not clear how much of the disparity in findings between studies is attributable to alternative measures. This research note attempts to provide some evidence on the impact of alternative measures of accessibility in employment probability models.     

加入WTO后中国旅行社的生存与发展

中国入世后，旅游市场的进一步开放将有利于引进先进的经营管理经验，进一步发展中国得天独厚的旅游资源和劳动力优势。同时，伴随着服务贸易总协定(CATS)在各成员国的实施与经济全球化，中国旅行社的生存与发展将面临机遇和挑战。中国旅行社应勇敢面对挑战，从以下几个方面提高竞争力：(1)树立战略发展思想；(2)树立战略管理思想；(3)化危机为商机，积极成为网介者；(4)界定企业发展方向，发展产品核心功能；(5)迎合消费者需求与创新需求；(6)组建集团化旅行社；(7)实行跨国际化经营，参加国际竞争；(8)加强对外宣传。     

中国旅游资源开发模式与旅游区域可持续发展理念

从旅游资源开发与区域关系的角度，指出国内旅游资源在开发方面存在着不同的理念与方法论模式，导致不同的区域旅游开发效果；从旅游可持续发展的原则出发，旅游区域开发在理论上应该建立多元趋势分析旅游开发理论体系，在实践上应建立鞠域“大旅游”的结构系统，并提出区域旅游开发的一些理论。     

2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.     

再论各向异性介质转换波地震学,第一部分:理论

我们业已研发了计算各向异性、非均质介质中P- SV转换波(C-波)的转换点和旅行时的新理论。据此 可以利用诸如相似性分析、迪克斯模型建模、克契 霍夫求和等常规方法来完成各向异性的处理和各向 异性处理,并使各向异性的处理成为可能。这里将 我们的新发展分作两部分来介绍。第一部分为理 论,第二部分为对速度分析和参数计算的应用。第 一部分理论包括转换点的计算和动校正的分析。     

Converted-wave seismology in anisotropic media revisited,Part I: Basic theory

We have developed new basic theories for calculating the conversion point and the travel time of the P-SV converted wave (C-wave) in anisotropic, inhomogeneous media. This enables the use of conventional procedures such as semblance analysis, Dix-type model building and Kirchhoff summation, to implement anisotropic processing, and makes anisotropic processing affordable. Here we present these new developments in two parts: basic theory and application to velocity analysis and parameter estimation. This part deals with the basic theory, including both conversion-point calculation and moveout analysis. Existing equations for calculating the PS-wave (C-wave) conversion point in layered media with vertical transverse isotropy (VTI) are strictly limited to offsets about half the reflector depth (an offset-depth ratio, xlz, of 0.5), and those for calculating the C-wave traveltimes are limited to offsets equal to the reflector depth (x/z=l.0). In contrast, the new equations for calculating the conversion-point extend into offsets about three-times the reflector depth (x/z=3.0), those for calculating the C-wave traveltimes extend into offsets twice the reflector depth (x/z=2.0). With the improved accuracy, the equations can help in C-wave data processing and parameter estimation in anisotropic, inhomogeneous media. This work is funded by the Edinburgh Anisotropy Project (EAP) of the British Geological Survey. First author: Xiangyang Li, Mr. Li is currently a professorial research seismologist (Grade 6) and technical director of the Edinburgh Anisotropy Project in the British Geological Survey. He also holds a honorary professorship in multicomponent seismology at the School of Geosciences, University of Edinburgh. He received his BSc(1982) in Geophysics from Changchun Geological Institute, China, an MSc (1984) in applied geophysics from East China Petroleum Institute (now known as the China University of Petroleum), and a PhD (1992) in seismology from the University of Edinburgh. During 1984–1987, he worked as a lecturer with the East China Petroleum Institute. Since 1991, he has been employed by the British Geological Survey. His research interests include seismic anisotropy and multicomponent seismology.