On the relation between excess hydraulic head and flow in a conduit imbedded within a porous matrix     

David E. Loper  Ibrahim A. Eltayeb 《地球物理与天体物理流体动力学》2013,107(3):281-297

This article provides a partial answer to the question “What is the relation between excess hydraulic head and volume flux of water in a conduit within a porous matrix?”, focusing on the case that the forcing is steady. The conduit is modelled as a horizontal circular cylinder, imbedded within a porous matrix of rectangular cross section, having constant head prescribed on the sidewalls and being confined top and bottom. Laminar flow in the matrix is assumed to obey Darcy's law, while turbulent flow in the conduit is quantified using the Darcy–Weisbach equation. Analysis of the latter equation shows that the length scale of variations in the direction of the conduit is large compared with the scale of lateral and vertical variations. This permits separation of the full three-dimensional non-linear problem into a two-dimensional linear problem for head within the matrix and a one-dimensional non-linear problem for head within the conduit. Analytic solutions are obtained for the distribution of head in the matrix and in a conduit of either infinite or finite length. In both cases, the volume flux of water is proportional to the excess head to the 2/3 power, the conduit radius to the 5/3 power, the matrix permeability to the 1/3 power and gravity to the 1/3 power. The scale of variation of head along the conduit is proportional to the excess head to the ?1/3 power, the conduit radius to the 5/3 power, the matrix permeability to the ?2/3 power and gravity to the 1/3 power.  相似文献   

PATTERNS OF SPATIAL DISPERSION IN METROPOLITAN COMMUTING     

《Urban geography》2013,34(3):232-253

The simultaneous impact of residential and employment decentralization in the form of multinucleations on patterns of commuting concentration and dispersion is examined for the Washington metropolitan area with 1980 data. Because of the area's generally white-collar labor force, the impact of segregated occupational groups is minimized and it is possible to examine strictly the spatial dimensions of commuting dispersion. Commuting becomes increasingly more dispersed from the center of the area to about 12 miles outward. Beyond that point, the patterns of commuting become considerably more complex, responding to a wide range of sizes of employment in a widely dispersed pattern of nucleations. In some sectors, commuting dispersion remains somewhat constant. In one sector, commuting patterns revert to some level of concentration, possibly responding to a somewhat unique situation of employment concentration along a corridor. These findings contribute to the recognition that tomorrow's transit structure cannot rely on its traditional form, but must become more selective.  相似文献   

The Urban Geography of Subsidiary Headquarters in North America: Explorations by sector and Foreign Linkage     

《Urban geography》2013,34(5):595-622

The complexity of the firm is a hallmark of the current economy. Corporate subsidiaries and their headquarters are a key expression of the development of businesses today. The analysis presented here extends on previous subsidiary research by analyzing the evolving headquarters location of foreign and domestic subsidiaries in the United States and Canada from 1996 to 2004. This study finds that certain U.S. and Canadian sectors are home to disproportionate numbers of subsidiaries. It also shows that different sectors in each country have seen major changes in their subsidiary communities, that foreign and domestic subsidiaries in the United States and Canada exhibit distinctive geographies, and that parent corporations from various countries follow distinctive strategies in locating their U.S. and Canadian subsidiary headquarters. The study argues that this line of research is one component in the strengthening of theory related to the location of elite corporate activities.  相似文献   

Wholeness as a hierarchical graph to capture the nature of space     

Bin Jiang 《International journal of geographical information science》2013,27(9):1632-1648

According to Christopher Alexander’s theory of centers, a whole comprises numerous, recursively defined centers for things or spaces surrounding us. Wholeness is a type of global structure or life-giving order emerging from the whole as a field of the centers. The wholeness is an essential part of any complex system and exists, to some degree or other, in spaces. This paper defines wholeness as a hierarchical graph, in which individual centers are represented as the nodes and their relationships as the directed links. The hierarchical graph gets its name from the inherent scaling hierarchy revealed by the head/tail breaks, which is a classification scheme and visualization tool for data with a heavy-tailed distribution. We suggest that (1) the degrees of wholeness for individual centers should be measured by PageRank (PR) scores based on the notion that high-degree-of-life centers are those to which many high-degree-of-life centers point, and (2) that the hierarchical levels, or the ht-index of the PR scores induced by the head/tail breaks, can characterize the degree of wholeness for the whole: the higher the ht-index, the more life or wholeness in the whole. Three case studies applied to the Alhambra building complex and the street networks of Manhattan and Sweden illustrate that the defined wholeness captures fairly well human intuitions on the degree of life for the geographic spaces. We further suggest that the mathematical model of wholeness be an important model of geographic representation, because it is topological oriented, which enables us to see the underlying scaling structure. The model can guide geodesign, which should be considered as the wholeness-extending transformations that are essentially like the unfolding processes of seeds or embryos, for creating built and natural environments of beauty or with a high degree of wholeness.  相似文献   

CTA在头颈部创伤性异物中的诊断价值     

王强  洪居陆 《CT理论与应用研究》2013,(3):479-484

目的:探讨CTA在头颈部创伤性异物中的诊断价值。材料和方法:搜集创伤性异物行头颈部CTA检查病例5例,均有完整的手术资料,分析其诊断价值。结果:5例CTA清晰显示异物位置及血管关系,无血管损伤。1例术前发现异物周围软组织肿胀伴出血,其余4例软组织散在积气。术中异物取出顺利,均无大出血,3例局部少许渗血。异物均为金属,2例斑片状,1例新月形,1例铁丝状,1例刀状。结论:CTA在头颈部创伤性异物中的诊断价值明确,能提供异物与血管关系及血管损伤信息,指导临床手术。  相似文献   

一种单缸双作用往复泵泵头的设计          下载免费PDF全文

朱科 《探矿工程》2013,40(1):41-44

对一种全新结构的双作用往复泵泵头结构及原理进行分析,提出了其应用方法。  相似文献   

Analytical solutions for the steady-state seepage field in a finite seabed with a lined tunnel     

Hong-wei Ying  Xiao-nan Gong  Xiao Wang 《Marine Georesources & Geotechnology》2013,31(8):972-978

Abstract

Analytical solutions for the steady-state seepage field in a finite seabed under homogeneous and isotropic conditions with a drained circular lined tunnel are developed. A numerical model is established using the COMSOL Multiphysics software to verify the solutions presented in this study, and strong agreement is found. A parameter analysis considering the seabed thickness, coefficient of permeability, tunnel burial depth and lining thickness is presented. The results indicate that the error induced by ignoring the thickness of the seabed cannot be neglected when the tunnel is close to the bottom of the seabed.  相似文献   

垃圾土渗透性和持水性的试验研究   总被引：5，自引：2，他引：3  

张文杰  陈云敏  邱战洪 《岩土力学》2009,30(11):3313-3317

通过室内常水头试验测定了垃圾土的饱和渗透系数,通过室内压力板仪试验测得垃圾土的土-水特征曲线。基于土-水特征曲线预测了垃圾土的非饱和渗透系数,并通过室内入渗试验进行了初步验证。常水头试验得到深层、中层和浅层垃圾土的饱和渗透系数分别为3.56×10-4、3.50×10-3、4.81×10-2 cm/s。土-水特征曲线试验表明,垃圾土饱和含水率和残余含水率较高,进气值很小,土-水特征曲线在低基质吸力时存在陡降段,其中浅层垃圾土的陡于深层垃圾。验证试验表明,预测得到的非饱和渗透系数与实测结果接近,基于土-水特征曲线预测垃圾土非饱和渗透系数的方法基本可行。  相似文献   

中国东部中生代软流圈上涌与构造 岩浆 矿集区          下载免费PDF全文

邢集善杨巍然  邢作云刘建华 邵建设 《地学前缘》2009,16(4):225-239

在深入研究华南地震层析成像的基础上,按照大地构造环境和软流圈上涌形状和热度,将中国东部(大陆)中生代上地幔中岩石圈 软流圈构造划分为3类:(1)陆台区(华北块和扬子块),软流圈沿古裂陷上涌,其柱头上方形成幔壳混熔花岗质岩及相应Au、Cu、Mo、Pb Zn等矿集区,并于软流圈与岩石圈厚区之陡接触带形成中基性杂岩及相应Fe矿集区;(2)褶皱带中心区(南岭及其延伸带),软流圈在适当深度、热量充足、较大范围内“平卧”,因热传导而致使地壳内物质部分重熔,形成壳源型花岗质岩及相应的W、Sn、稀有元素矿集区;(3)褶皱带边缘区(大兴安岭南部及华南南缘),在软流圈上涌柱上方形成幔源或幔壳混熔的花岗质岩,相应为Cu、Au、Pb Zn、Mo、Ag矿集区。总之,软流圈上涌是中生代构造、岩浆、矿集区形成之根源。  相似文献   

断层带震相及其应用研究现状与展望     

郑建常 《中国地震》2014,30(1):1-12

利用断层带特有震相通过观测模拟可以得到断层带介质的性质。本文回顾了地震学领域中断层带震相研究的发展历程,对断层带首波、断层带围陷波的国内外研究现状进行了综述,并结合国际上有关断层带震相研究的最新进展,对基于地震波形研究断层性质的前景进行了展望。  相似文献