城市灰尘的元素地球化学特征

根据湖州市吴兴区采样数据,分析了城市灰尘元素中亲铁元素、亲铜元素、亲石元素和常量元素的含量和累积状况,并探讨这些元素与土壤背景的关系.结果表明,湖州市城市灰尘四类元素含量差异较大,但与土壤背景变化趋势基本一致;同种元素在不同功能区的富集等级基本相同,但同类元素间存在明显的累积差异;各功能区灰尘元素与土壤背景的关联度都较...     

Development of a Method for Determination of Volatile Organic Compounds (C6-C9) by Thermal Desorption-Gas Chromatography. Application to Urban and Rural Atmospheres.

ABSTRACT

An analytical method for the determination of 15 Volatile Organic Compounds (VOC): benzene, n-heptane, toluene, n-octane, chlorobenzene, ethylbenzene, m-xylene, o-xylene, p-xylene, isopropylbenzene, n-propylbenzene, n-decane, 1,4-dichlorobenzene, 1,3-dichlorobenzene and 1,2-dichlorobenzene, by thermal desorption coupled with gas chromatography (GC) was proposed. The flame ionisation detector (FID) and mass spectrometry (MS) detector were used. The variables that have an influence on the desorption process (time, inert gas flow and temperature) were studied, obtaining detection limit ranges from 15 to 120 pg (GC-FID), 3.8 to 32 pg (GC-MS, SIM mode) and 15 to 300 pg (GC-MS, SCAN mode). In order to detect possible VOC urban sources, samples were taken from 6 points in A Coruña (N.W. Spain) to analyse. Sampling time and flow rate were 30 minutes and 50 mL/min respectively. VOC profile and their total concentrations can be considered as typical of an urban area. Other samples were also obtained from a nearly rural zone to determine the influence of these VOC sources.     

Analysis of Heavy Metals in Scalp Hair Samples of Hypertensive Patients by Conventional and Microwave Digestion Methods

The abnormal metabolism of metal ions plays an important role in health and disease conditions, and studies about them have been attracting significant interest. The aim of our study was to assess the heavy metals (cadmium, copper, iron, nickel, chromium, lead, and zinc) in scalp hair samples of 200 hypertensive (HT) patients of an urban population together with 215 non‐hypertensive male subjects in the age group of 30–60 years. Hair samples were digested with conventional wet ashing and microwave digestion. Analyses of both digests were done by flame and graphite furnace atomic absorption spectrometry. The validity of methodology was checked by use of the certified reference material (CRM 397) hair, provided the Community Bureau of Reference, Commission of the European Communities. According to a statistical evaluation of the results, the microwave digestion method was a valid alternative to the conventional acid digestion method, p value >0.05, but it gave a faster digestion. The overall metal recoveries were 96–98% of those obtained with microwave digestion. Among the toxic elements determined, levels of nickel, cadmium, copper, chromium, and lead in scalp hair samples of hypertensive patients were significantly higher compared normal male subjects, whereas the essential elements such as iron and zinc were found to be low compared age‐matched non‐hypertensive subjects.     

基于社团结构的城市地铁网络模型研究

本文运用复杂网络理论, 对我国北京、上海、广州和深圳等城市的地铁网络进行了实证研究. 分别研究了地铁网络的度分布、聚类系数和平均路径长度. 研究表明, 该网络具有高的聚类系数和短的平均路径长度, 显示小世界网络的特征, 其度分布并不严格服从幂律分布或指数分布, 而是呈多段的分布, 显示层次网络的特征. 此外, 它还具有重叠的社团结构特征. 基于实证研究的结果, 提出一种基于社团结构的交通网络模型, 并对该模型进行了模拟分析, 模拟结果表明, 该模型的模拟结果与实证研究结果相符. 此外, 该模型还能解释其他类型的复杂网络(如城市公共汽车交通网络)的网络特性. 关键词： 复杂网络 地铁网络 小世界 社团     

Including Preference and Social Distance Dynamics in Multi-Factor Theories of Segregation

All agree that many factors contribute to ethnic segregation, but controversy continues regarding the relevance of particular factors. In my paper I acknowledge the importance of discrimination, but I direct attention to the role of ethnic preferences and social distance dynamics. I do so because many dismiss the relevance of these factors for contemporary segregation without engaging formal theories and analytic models which suggest that dynamics associated with in-group attraction and out-group avoidance may take on increasing importance as past forms of discrimination slowly fade. Agent-based modeling shows promise for exploring the issue of whether prejudice against out-groups and affinity toward in-groups can build and sustain segregation in the absence of discrimination. Research drawing on this approach is at an early stage of development but is significant for highlighting two things. One is that the implications of preferences for segregation are strongly conditioned by the ethnic demography of the city. Another, closely tied to the first, is that different views about the implications of preferences for segregation often hinge on inconsistencies in how notions of integration and segregation are applied in discussions of individual location choices, the ethnic mix of single neighborhoods, and the ethnic distributions for all neighborhoods in a city. Critiques of agent-based models of Schelling-style preference effects will carry more force when they outline models indicating how location decisions guided by preferences documented in surveys can produce or sustain integration.     

基于结构洞理论的城市复杂项目群组织优化研究

研究目的:从城市复杂项目群组织的复杂性着手,针对目前项目群组织管理和控制在实际应用中出现的问题,研究一种优化项目群组织的有效方法.研究过程:基于结构洞理论模型,通过分析城市复杂项目群组织结构的网络特性,找到项目群组织中各个关系人之间的结构洞,以此作为研究的对象来建立组织的优化模型,在确立目标函数的情况下,通过结构约束算法求取网络规模的密度约束,并通过最小二乘法进行有效的修正.研究结论:通过模型的构建,可以得出结构洞理论是研究城市复杂项目群组织关系的有效理论方法,为其组织优化提供了交互视角,有利于组织中关系人目标的实现.     

基于复杂网络理论的北京公交网络拓扑性质分析

为分析公交复杂网络的拓扑性质, 本文以北京市为例, 选取截止到2010年7月的北京全市(14区、2县)的1165条公交线路和9618个公交站点为样本数据, 运用复杂网络理论构建起基于邻接站点的有向加权复杂网络模型. 该方法以公交站点作为节点, 相邻站点之间的公交线路作为边, 使得网络既具有复杂网络的拓扑性质同时节点(站点)又具有明确的地理坐标. 对网络中节点度、点强度、强度分布、平均最短路径、聚类系数等性质的分析显示, 公交复杂网络的度和点强度分布极为不均, 网络中前5%和前10%节点的累计强度分布分别达到22.43%和43.02%; 点强度与排列序数、累积强度分布都服从幂律分布, 具有无标度和小世界的网络特点, 少数关键节点在网络中发挥着重要的连接作用. 为分析复杂网络中的关键节点, 本文通过承载压力分析和基于"掠夺" 的区域中心节点提取两种方法, 得到了公交复杂网络中两类不同表现的关键节点. 这些规律也为优化城市公交网络及交通规划发展提供了新的参考建议.     

公交服务治理模式的效益比较研究

公交服务的市场化改革需要选择合理的治理模式以应对产生的种种问题,各模式间的效益比较就成为选择的关键因素。在理论比较PPP模式和网络治理模式的基础上,本文以PPP模式为参照对象,假定公交服务参与主体平等的合作,从各主体的控制权分配、努力水平和产出效率构建公交服务总效益模型,并进行了模型的理论分析和数据模拟,结果表明:总效益与各方主体的努力水平、控制权和产出效率紧密相关,仅当政府和社会群体间的边际成本替代率在合理范围内时,网络治理模式的总效益大于PPP模式,当超出合理范围时会使前者小于后者。     

Variable density bore interaction with block obstacles

A horizontally variable density flow model is used to simulate hydraulic bore interactions with idealised urban obstacles. The 2D non-linear shallow water equations are solved using a second-order Monotonic Upstream-centered Schemes for Conservation Laws-Hancock Godunov-type HLLC approximate Riemann scheme. Validation test results are reported for wave propagation over a hump, a constant-density circular dam break and two 1D dam breaks involving different spatial distributions of solute concentration. Detailed parameter studies are then considered for hydraulic bore interactions with single and multiple-square obstacles under subcritical, critical and supercritical flow conditions. In all cases, reflected and diffracted wave patterns are generated immediately after the bore impacts the obstacle(s). Later, the incident bore reconstitutes itself downstream of the obstacle(s). Variable density flows are also considered, with the upstream volumetric concentrations set to values corresponding to water–sediment mixture densities of 1165 and 1495 kg/m³. It is found that the upstream Froude number, gap spacing between obstacles and upstream to downstream density difference influence the strength of the bore–structure interaction, run-up at the front face of the obstacle(s), and subsequent wave–wave interactions.     

城市土壤对铅和锌的吸附热力学特征

采用批量法对温州景山森林公园5种不同城市土壤对Pb和Zn的吸附热力学行为进行了研究。结果表明,吸附等温线符合Freundlich等温式和Temkin等温式,相关系数都在0．85以上,5种土壤对Ph的吸附强度由高到低的次序为C,E,B,A,D,对Zn的吸附强度由高到低的次序为C,E,D,B,A。