New media, the new economy and new spaces   总被引：8，自引：0，他引：8  

Andy C. Pratt 《Geoforum》2000,31(4)

This paper counters proponents of the ‘weightless economy’ who have suggested the ‘death of distance’ in relation to economic and social activities that use the worldwide web (WWW). An analysis of new media developers in New York’s ‘Silicon Alley’ demonstrates that place and distance are still important. The most important aspect of this co-location is the possibility of social interaction. This paper points to the value of analysis of the material practice of the social (and the economic and cultural). The notion of ‘untraded dependencies’ is developed through looking at its manifestation and constitution in the specificity of space, time and economic activity.  相似文献   

Unsteady source flow in weakly heterogeneous porous media     

Peter Indelman 《Computational Geosciences》2000,4(4):351-381

Average nonuniform flows in heterogeneous formations are modeled with the aid of the nonlocal effective Darcy's law. The mean head for flow toward source of instantaneous discharge in a heterogeneous medium of given statistics represents the fundamental solution of the average flow equation and is called the Mean Green Function (MGF). The general representation of the MGF is obtained for weakly heterogeneous formations as a functional of the logconductivity correlation function. For Gaussian logconductivity correlation, the MGF is derived in terms of one quadrature in time t and it is analyzed for isotropic media of any dimensionality d and for 3D axisymmetric formations. The MGF is further applied to determining the mean head distribution for flow driven by a continuous source of constant discharge. The large time asymptotic of the mean head is analyzed in details.  相似文献   

Uniqueness conditions in a hyperbolic model for oil recovery by steamdrive     

J. Bruining  C.J. van Duijn 《Computational Geosciences》2000,4(1):65-98

In this paper we study a one-dimensional model for oil recovery by steamdrive. This model consists of two parts: a (global) interface model and a (local) steam condensation/capillary diffusion model. In the interface model a steam condensation front (SCF) is present as an internal boundary between the hot steam zone (containing water, oil and steam) and the cold liquid zone (containing only water and oil). Disregarding capillary pressure away from the SCF, a 2× 2 hyperbolic system arises for the water and steam saturation. This system cannot be solved uniquely without additional conditions at the SCF. To find such conditions we blow up the SCF and consider a parabolic transition model, including capillary diffusion. We study in detail the existence conditions for traveling wave solutions. These conditions provide the missing matching conditions at the SCF in the hyperbolic limit. We show that different transition models yield different matching conditions, and thus different solutions of the interface model. We also give a relatively straightforward approximation and investigate its validity for certain ranges of model parameters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

社会资本与地方经济发展 :以广东新会为例     

孟晓晨  赵星烁  买买提江 《地理研究》2007,26(2):355-362

海外关系网络是一种特殊的社会资本,对地方经济的发展可以起到一定的促进作用。本文从社会网络作为资源配置渠道的角度,以广东新会为例,通过实地调研、数据统计及问卷分析,探讨了海外关系网络对地方经济发展的作用。研究发现,通过海外关系网络进入侨乡的资金主要有侨汇、捐赠和投资三种形式,三者都直接或间接地作用于新会地方经济发展的各个方面,对新会地方发展起到了重要的作用。然而,随着经济的发展和市场的建立,社会网络的作用正在减弱,说明社会资本只能在特定的时期和特定的历史条件下起作用。侨乡经济要取得持续发展,就必须加强市场的建设。  相似文献   

TTI介质弹性波频率-空间域有限差分数值模拟   总被引：3，自引：0，他引：3  

吴国忱  罗彩明  梁楷 《吉林大学学报(地球科学版)》2007,37(5):1023-1033

由周期性薄互层引起的VTI介质是研究比较广泛的一类各向异性介质。当VTI介质对称轴偏离垂向,本构坐标系与观测坐标系不重合时,会形成观测坐标系下的TTI介质。引入25点优化差分算子,推导出二维TTI介质频率域弹性波动方程;为压制边界反射,采用完全匹配层法吸收边界条件,并计算出优化差分系数;最后采用集中力源,模拟了弹性波在TTI介质中的传播过程。从波场快照和地面共炮记录可以看出,笔者采用的数值模拟算法能有效压制数值频散。TTI介质中的波场传播比较复杂,纵波传播相对稳定,横波波前的三分叉现象比较明显,并存在振幅奇异性。当VTI介质的对称轴偏转后,还会增加地面地震记录的复杂性。  相似文献   

Health Seeking Behavior: Q‐Structures of Rural and Urban Women in India with Sexually Transmitted Diseases and Reproductive Tract Infections     

Suprabha Tripathi 《The Professional geographer》2000,52(2):218-232

I use a gender framework to examine why women need to utilize social networks to discover and resolve problems related to reproductive tract infections (RTI) and sexually transmitted diseases (STDs). In India, women's health is linked with social status and perception of their health needs. This paper provides insight on how social networks are gender‐, location‐, and context‐specific and how they are linked to STD issues. This paper examines why social networks are integral to women. The health‐seeking behavior of rural and urban casual sex workers is examined via Q‐analysis, a language of mapping relationships. Results from Q‐analysis reveal women's use of four systems—kinship, belief, traditional medical, and western medical services. Finally, I conclude with important implications for research on gender relations and social networks.  相似文献   

Joint inversion of receiver function and surface wave dispersion observations   总被引：16，自引：0，他引：16  

J. Julià  C. J. Ammon  R. B. Herrmann  A. M. Correig 《Geophysical Journal International》2000,143(1):99-112

We implement a method to invert jointly teleseismic P wave receiver functions and surface wave group and phase velocities for a mutually consistent estimate of earth structure. Receiver functions are primarily sensitive to shear wave velocity contrasts and vertical traveltimes, and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages. Their combination may bridge resolution gaps associated with each individual data set. We formulate a linearized shear velocity inversion that is solved using a damped leastsquares scheme that incorporates a priori smoothness constraints for velocities in adjacent layers. The data sets are equalized for the number of data points and physical units in the inversion process. The combination of information produces a relatively simple model with a minimal number of sharp velocity contrasts. We illustrate the approach using noisefree and realistic noise simulations and conclude with an inversion of observations from the Saudi Arabian Shield. Inversion results for station SODA, located in the Arabian Shield, include a crust with a sharp gradient near the surface (shear velocity changing from 1.8 to 3.5 km s¹ in 3 km) underlain by a 5kmthick layer with a shear velocity of 3.5 km s¹ and a 27kmthick layer with a shear velocity of 3.8 km s¹, and an upper mantle with an average shear velocity of 4.7 km s¹. The crustmantle transition has a significant gradient, with velocity values varying from 3.8 to 4.7 km s¹ between 35 and 40 km depth. Our results are compatible with independent inversions for crustal structure using refraction data.  相似文献   

ScSp observed on North Island, New Zealand: implications for subducting plate structure     

Michael Bourne  Graham Stuart 《Geophysical Journal International》2000,142(3):925-932

Seismic phase conversions provide important constraints on the layered nature of subduction zone structures. Recordings from digital stations in North Island, New Zealand, have been examined for converted ScS ‐to‐ p ( ScSp ) arrivals from deep (>150 km) Tonga–Kermadec earthquakes to image layering in the underlying Hikurangi subduction zone. Consistent P ‐wave energy prior to ScS has been identified from stations in eastern and southern North Island, where the subducted plate interface is at a depth of between 15 and 30 km. Two ScS precursors are observed. Ray tracing indicates that the initial precursor ( ScSp ₁) corresponds to conversion from the base of an 11–14 km thick subducting Pacific crust. The second precursor is interpreted as a conversion from the top of the subducting plate. The amplitude ratio, ScSp ₁: ScS , increases from 0.10 to 0.19 from northern to southern North Island. This is within the range expected from a simple first‐order velocity discontinuity at an oceanic Moho. A 1–2 km thick layer of low‐velocity sediment at the top of the subducting plate is required to explain the remaining ScSp waveform. Our results imply that the abnormally thick Hikurangi–Chatham Plateau has been subducting beneath New Zealand for at least 2.9 Myr, thus explaining the high uplift rates observed across eastern North Island.  相似文献   

Seismic wave propagation in cracked porous media   总被引：6，自引：0，他引：6  

Tim Pointer  Enru Liu  & John A. Hudson 《Geophysical Journal International》2000,142(1):199-231

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三维地震勘探技术预测瓦斯的可行性研究     

杨双安  宁书年  张会星  储文胜 《煤田地质与勘探》2006,34(3):72-74

常规地震勘探方法都是基于单相介质中的弹性波动方程,忽略了流体对地震波传播规律的影响。本文基于双相介质理论,探讨了游离态的瓦斯在煤田地震资料上的地震波场特征,旨在有效地判断瓦斯的富集区域,防治煤与瓦斯突出给矿井生产带来的灾难。   相似文献