Analyzing Changes in Urban Form and Commuting Time*

Urban work trips have changed in important ways during the last decades. In Québec City, a medium‐sized Canadian metropolitan area, commuting distances increased for both male and female workers between 1977 and 1996, while durations increased for male workers and decreased for female workers. This article seeks to identify spatial and social factors responsible for these changes. We develop a disaggregate model of trip duration estimated on the basis of large samples derived from travel surveys comparable through time. Using categorical variables to specify change, we are able to separate change effects from level effects attributable to various dimensions of urban form. Our analysis clearly indicates that, once travel mode and key social factors are controlled for, the shift from a monocentric to a dispersed city form is responsible, in the Québec metropolitan area, for increasing commuting time. This is contrary to findings in larger metropolitan areas, where, it has been argued, the suburbanization of jobs maintains stability in commuting duration.     

联合利用走时与波形反演技术研究地壳三维速度结构(Ⅰ)——理论与方法

论述地震波走时反演技术中的阻尼最小二乘方法。为了提高解的唯一性,我们把人工地震资料的解释结果作为该方法的特定约束条件。同时还论述了波形反演技术中的遗传算法．     

Crank-Nicolson差分格式及其稳定性研究

本文以自己独特的方式,构造了一维和二维抛物型方程的Ｃｒａｎｋ－Ｎｉｃｏｌｓｏｎ差分格式。本文不仅详细地给出了离散误差的表达式,而且论证了它们的稳定性。该差分格式具有精度高,稳定性好,计算量和存储量都比较小的特点,是一个很理想,便于应用的差分格式。     

广东长坑金银矿床成矿机制热力学模拟研究

长坑金银矿床为沉积岩中的微细浸染型金矿与交代型银矿构成的矿床组合,金、银矿化与碳酸盐和碎屑岩围岩的硅化蚀变关系密切并呈分带现象,矿石类型主要为含矿硅化岩。矿化温度主要在300～170 C之间,成矿流体的主要成分为K~-、Na~-、Ca~(2+)、Mg~(2+)、Cl~(-)。金属配合物的分配计算显示,金在成矿热液中主要以疏氢配合物迁移,而银、铁、铅、锌则以氯配合物为主,铁、铅、锌在成矿后期的中性-弱碱性环境下可转变为羟基和硫氢配合物。热液-碳酸盐岩反应模拟证实水-岩相互作用是银矿石形成的有效机制。矿物组合的溶解度分析表明,金、银矿物分别在早期弱酸性和后期中-碱性条件下沉淀富集,这是造成金、银矿体分离和分带的主要或有利因素。     

三灰桩地基处理方法在工程中的应用

在二灰桩的桩体材料中加入适量水泥,形成三灰桩。加入的水泥,通过桩体材料之间,以及这些材料与桩周土发生的一系列物理化学反应,不仅提高了桩体的强度,而且改变了桩间土的力学性质,在桩身周围形成硬土壳,共同形成较高强度的复合地基。经静力触探法检测,三灰桩锥尖阻力平均达11.45MPa(6根桩),而二灰桩平均只有4.8MPa;单桩复合地基载荷试验表明,三灰桩与二灰桩相比,P-S曲线无明显拐点,当S=0.015B时,三灰桩P值为240kPa,二灰桩P值180kPa。故三灰桩可大幅度地提高复合地基承载力。     

Closed‐form solution for seismic response of adjacent buildings with linear quadratic Gaussian controllers

Closed‐form solution for seismic response of adjacent buildings connected by hydraulic actuators with linear quadratic Gaussian (LQG) controllers is presented in this paper. The equations of motion of actively controlled adjacent buildings against earthquake are first established. The complex modal superposition method is then used to determine dynamic characteristics, including modal damping ratio, of actively controlled adjacent buildings. The closed‐form solution for seismic response of the system is finally derived in terms of the complex dynamic characteristics, the pseudo‐excitation method and the residue theorem. By using the closed‐form solution, extensive parametric studies can be carried out for the system of many degrees of freedom. The beneficial parameters of LQG controllers for achieving the maximum response reduction of both buildings using reasonable control forces can be identified. The effectiveness of LQG controllers for this particular application is evaluated in this study. The results show that for the adjacent buildings of different dynamic properties, if the parameters of LQG controllers are selected appropriately, the modal damping ratios of the system can be significantly increased and the seismic responses of both buildings can be considerably reduced. Copyright © 2001 John Wiley & Sons, Ltd.     

形变模型的统计检验

本文首先介绍了广义参数检验法的基本原理及其在形变模型检验方面的应用,其次证明了对形变模型和约束模型平差所得形变参数是一致的,还证明了形变模型的残差二次型等于约束模型残差二次型与原模型残差二次型之差,即V_d~TP_dV_d=。最后,作为算例,对某坝区监测网两期观测进行了原模型、形变模型的平差计算,以及形变模型的统计检验。     

Slope form and basal stream relationships: A case study in the westend basin of the Southern Pennines,England

Relationships between slope form and stream magnitude, drainage area and stream gradient are investigated in a small upland catchment experiencing active stream incision. Profiles selected on a stratified random basis provide data on five slope form variables. The observed relationships suggest a spatial sequence of slope form, associated with a downstream increase in discharge, characterized by decreasing overall slope convexity and increasing mean slope angle and attributed to a reduction in the relative length of the upslope convexity with respect to the essentially stream-controlled main slope.     

新而徽与徽而新的建筑形式探讨——两个不同环境中的游客服务中心设计构思

本文介绍了歙县和黄山的两个旅游服务中心的规划及建筑设计方案,阐述了两种不同的建筑形式,总结了设计中的构思和感想。     

Certified solutions for hydraulic structures using the node‐based smoothed point interpolation method (NS‐PIM)

A meshfree node‐based smoothed point interpolation method (NS‐PIM), which has been recently developed for solid mechanics problems, is applied to obtain certified solutions with bounds for hydraulic structure designs. In this approach, shape functions for displacements are constructed using the point interpolation method (PIM), and the shape functions possess the Kronecker delta property and permit the straightforward enforcement of essential boundary conditions. The generalized smoothed Galerkin weak form is then applied to construct discretized system equations using the node‐based smoothed strains. As a very novel and important property, the approach can obtain the upper bound solution in energy norm for hydraulic structures. A 2D gravity dam problem and a 3D arch dam problem are solved, respectively, using the NS‐PIM and the simulation results of NS‐PIM are found to be the upper bounds. Together with standard fully compatible FEM results as a lower bound, we have successfully determined the solution bounds to certify the accuracy of numerical solutions. This confirms that the NS‐PIM is very useful for producing certified solutions for the analysis of huge hydraulic structures. Copyright © 2009 John Wiley & Sons, Ltd.