Exposure to PM2.5 Related to Road Traffic: Comparison between Crossroads and Outside of Crossroads at Cotonou, Benin

Background: Several studies have analysed the pollution issues owing to road traffic in Cotonou, Benin. Concentration levels of particles are higher on high traffic than a low traffic. The exposure of human populations to air pollution is more intense on the roads. In Benin, the density of traffic on the crossroads is indeed more important. Are traffic locations such as crossroads, areas where the level of exposure PM2.5 is increased? Methods: This study was conducted along the 5 km high-traffic road in the city of Cotonou. It is a high traffic lane with two crossroads. Sampling and measurements were carried out in dry sea-son (January and February) and rainy season (June and July). For each season the measurements were made over two months from 7 am to 9 pm. PM2.5 measurements were made at different locations at crossroads and also along the track. To compare concentrations of PM2.5 at crossroads and outside of roundabout, we used the Generalized Linear Mixed Model. Results: In the rainy season the PM2.5 hourly concentrations ranged between 400 μg/m3 and 500 μg/m3 while in the dry season 100 μg/m3 and 300 μg/m3. In the rainy season, the average of PM2.5 concentration was 463.25 ± 66.21 μg/m3 at crossroads and 264.75 ± 50.97 μg/m3 outside of crossroads. In the dry season, the average of PM2.5 concentration was 232.75 ± 97.29 μg/m3 at crossroads and 123.31 ± 63.79 μg/m3 outside of crossroads. Both in dry and rainy seasons, PM2.5 concentration level peaks are observed from 7 am to 9 am and from 7 pm to 9 pm. The Generalized Linear Mixed Model showed that there is high significant difference between concentrations of PM2.5 at crossroads compared to outside of crossroads. Occupation of the roadside (in particular crossroads) for various economic activities is common practice in Cotonou thus health risk for people working around crossroads increases. Conclusion: Locations such as crossroads are areas where the level of exposure PM2.5 is highest on road traffics.

Effects of Fiber Volume Fraction on Damping Properties of Three-Dimensional and Five-Directional Braided Composites

The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental modal analysis method. Meanwhile,carbon fiber plain woven laminated / epoxy resin composites with different fiber volume fraction were concerned for comparison. The experimental result of braided specimens shows that the first three orders of natural frequency increase and the first three orders of the damping ratios of specimens decrease, when the fiber volume fraction increases. Furthermore,larger fiber volume fraction will be valuable for the better anti-exiting property of braided composites,and get an opposite effect on dissipation of vibration energy. The fiber volume fraction is an important factor for vibration performance design of braided composites. The comparison between the braided specimens and laminated specimens reveals that 3D braided composites have a wider range of damping properties than laminated composites with the same fiber volume fractions.

Effective Thermal Conductivity for 3D Five-Directional Braided Composites Based on Microstructural Analysis

A method for predicting effective thermal conductivities(ETCs) of three-dimensional five-directional(3D5D) braided composites is presented. The effective thermal conductivity prediction method contains a digital image processing technology. Multiple scanning electron microscopy(SEM)images of composites are analyzed to obtain actual microstructural features. These actual microstructural features of 3D5D braided composites are introduced into representative volume element(RVE) modeling. Apart from applying actual microstructural features,compression effects between yarns are considered in the modeling of RVE,making the RVE more realistic. Therefore,the ETC prediction method establishes a representative unit cell model that better reflects the true microstructural characteristics of the 3D5D braided composites. The ETCs are predicted with the finite element method. Then thermal conductivity measurements are carried out for a 3D5D braided composite sample.By comparing the predicted ETC with the measured thermal conductivity, the whole process of the ETC prediction method is proved to be effective and accurate,where a relative error of only 2.9 % is obtained.Furthermore,the effects of microstructural features are investigated,indicating that increasing interior braiding angles and fiber fill factor can lead to higher transverse ETCs. Longitudinal ETCs decrease with increasing interior braiding angles,but increase with increasing fiber fill factor. Finally,the influence of variations of microstructure parameters observed in digital image processing are investigated. To explore the influence of variations in microstructural features on variations in predicted ETCs,the actual probability distributions of microstructural features obtained from the 3D5D braided composite sample are introduced into the ETC investigation. The results show that,compared with the interior braiding angle,variations in the fiber fill factor exhibit more significant effects on variations in ETCs.

Fracture Mechanism of 3D, Five-directional Braided (SiO_2)_f /SiO_2 Composites Prepared by Silicasol-infiltration-sintering Method

Three-dimensional （3D） five-directional braided （SiO2）/SiO2 composites were prepared by silicasol-infiltration-sintering （SIS） method. The flexural properties and microstructures were studied. The flexural strength and flexural elastic modulus were found to be 73 MPa and 12 GPa, respectively. The results of stress vs deflection curve and SEM examinations revealed that the fracture mechanism of 3D, five-directional braided （SiO2）/SiO2 composite was a mixture mode of ductile and brittle. The ductile mode was attributed to the weak bonding strength of fiber/matrix at low temperature. The brittle fracture might be caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.

At a New Crossroads

In 1997, international arms control and disarmament comes once again to anew crossroads. A consensus has as yet to be built concerning the next step. Forthe US-led Western nations, the focus continues to be prevention against the pro-liferation of Weapons of Mass Destruction (WMD), missiles and high-tech conven-tional weapons and accelerated development and deployment of anti-missile sys-

双十字路口交通灯控制Stateflow和App Designer仿真

为培养学生能够独立从事自动化相关领域的工程设计、应用研究,解决自动化领域复杂工程实施过程中遇到的关键技术问题,以双十字路口交通灯为研究对象,为计算机辅助建模与仿真类课程设计了一个综合性教学案例。教学案例主要内容为双十字路口Simulink/Stateflow建模与基于Matlab App Designer的交通灯控制可视化仿真。通过此教学案例的实施,明显提高了学生对Matlab的综合应用和工程设计能力,并为后续课程“单片机原理及应用”和“电气控制和PLC”作铺垫。

黑岱沟露天矿运输道路交叉路口优化研究

为了降低当黑岱沟露天矿山交叉路口处车辆碾压、碰撞风险,分析了黑岱沟露天煤矿作业现场运输道路设置和挡墙修筑现状,对坑下道路分布、挡墙高度对小型车辆影响、矿用卡车盲区大等典型问题进行分析研究。通过设计交叉路口优化改进技术路线和研究方案,针对性地调用现场不同小型车辆实地测试最佳驾驶视野,并对所得出实验数据进行归纳分析。结果表明:现场交叉路口10 m处挡墙修筑最佳高度1.2~1.3 m,可减少挡墙高度对小型车辆驾驶视野影响;在双向道路中间设置足够长度的标准化分道挡墙,可规范生产现场车辆行车秩序;制定相应安全监管措施,在交叉路口处设置指示、警示标志和超速监测系统,可加强对现场车辆行驶速度约束力和人员警惕意识;同时,优化运输车本安型防撞预警系统,提升对自动刹车装置状态监测判别度和自动刹车精准度,可从本质上提升车辆故障安全功能和失误安全功能,极大地避免了交叉路口处车辆碰撞事故发生。

基于车流量检测的西门子1200与触摸屏的交通灯控制系统

为了提高十字路口交通效率,提出了基于车流量检测的西门子1200与触摸屏的交通灯控制系统。依托西门子PLC程序和环形线圈检测器检测到的十字路口车流量,对交通灯绿灯时长进行合理调整,缓解高峰期车辆拥堵情况。并且通过制作触摸屏界面,使监控人员能及时了解十字路口交通灯情况,为交通管理提供便利。

基于EZStrobe的道路交叉口仿真模型及通行效率分析

在物料运输量大、强度高且空间资源有限的土木水利工程中,道路交叉口作为承接工程物料运输的基础与核心要素,对物料的运输效率及安全影响重大.为模拟复杂道路交叉口的通行状态,提升交叉口的运输安全与效率,本文构建了一种通用且直观的道路交叉口仿真模型,并通过工程实例进行了模型验证.首先,在分析交叉口通行状况的基础上,构建交叉口通行时间计算模型;其次,模拟真实施工现场,在有无信号灯的情况下分别构建了基于EZStrobe的交叉口仿真模型,仿真计算并输出道路交叉口物料运输效率与成本;最后,以水利工程双向四路交叉口为例,通过改变车流量及信号灯的设置,对不同交通运输方案进行仿真计算并将结果进行对比分析.结果表明,模型仿真结果符合道路交叉口的存在降低了运输效率的现象以及提高了运输成本的客观问题,验证了模型的可行性;此外设置合理的交通信号灯时长以及车流量有利于提高交叉口通行效率,表明本文建立的仿真模型可以有效评价运输效率并估算运输费用,为道路交通运输系统中的交叉口组织选择提供了一定参考.

针对东大路升级改造的方案研究

该文主要通过对东大路的老路面、既有桥梁、人行道、交叉路口等一系列现场调查,本着优化交通组织,提高通行效率,提升道路安全性、行车舒适性的设计目的和改造原则,针对东大路老路现状提出行车道沥青路面病害处理、人行道及非机动车道路面调整、道路美化升级、交通设施完善、十字交叉路口渠化方案调整等一系列的升级改造方案。这一方案使东大路焕然一新,成为南京市江北国家新区的南大门。

考虑因素属性及层级关系的十字路口汽车事故致因分析

为了从层次划分的角度分析十字路口汽车交通事故发生的深层原因,引入解释结构模型和交叉影响矩阵相乘法模型并加以改进,利用国家车辆事故深度调查体系中4个省份共290起十字路口汽车交通事故数据,建立事故致因体系。通过构建改进灰色关联度矩阵与解释结构模型并进行混合建模,揭示各因素间的层级作用关系。同时,采用交叉影响矩阵相乘法构建驱动力依赖性坐标图以进一步分析各致因因素间的相互作用关系。结果显示:十字路口汽车交通事故致因可划分为6级3阶的递阶结构,其中道路状况和交通管理因素是最根本因素,道路设施因素是最关键的间接因素,人的影响是最直接因素。这表明优先解决不良道路状况和其他驱动力因素会明显减少汽车事故发生,提高道路交通安全水平。

基于BP神经网络的路口短时交通流量预测方法

交叉路口是一个城市交通的重要组成部分,其各方向的交通流量预测更是该城市智能交通系统中的重中之重,本文提出一种基于BP神经网络预测路口短时交通流量的方法,该方法将路口其他非预测方向和交通信号配时方案对流量预测的影响因素考虑在内。

城市十字交叉口汽车尾气污染扩散模式

从交通流特性和街道交叉角度等方面概括了十字交叉口处影响汽车尾气污染排放扩散的一些特征,然后建立了一个十字交叉口汽车尾气污染扩散模式。该模式在普通的道路线源污染扩散模式基础上加入了考虑汽车排队等待以及拐弯变速的计算因子,是对前人模式的一种改进。

铁路道口无人监控的WSN应用研究

为减少铁路道口行车事故,基于对火车行进中振动信号的检测,研究了无线传感器网络新技术在道口无人监控系统中的应用。提出了分簇的多跳汇聚树路由算法,用以减少参与网络运行的结点个数,节约全网能量;使用了振动信号数据融合机制,实现数据处理精度的提高。在IRIS结点和MTS400CB传感器板上进行系统设计,利用MIB520网关实现了无线网和有线网之间的桥接。仿真结果表明该系统合理,减少了结点能耗,能够延长系统寿命。

城市交通干线智能线控系统研究

根据城市交通的特点,提出采用多十字路口统一线控的方法,在基于PC-PLC网络下对干线交通信号进行智能协调控制,有助于主干路方向车流的流动,可有效地减少停车次数和等待时间,提高干线的交通车流量。以实际的城市交通道路为对象进行的计算机仿真结果表明,城市交通干线智能控制方法在提高干线通行能力方面优于单点控制,可为解决城市交通问题提供一种新的途径。

平面交叉路口交通信号控制策略研究

在分析当前平面交叉口交通信号控制技术的基础上,重点研究交通信号控制配时策略,结合现代智能交通的需求,提出一种平面交叉路口的通用模型及描述各种实际路口的通用方法,根据路口的各车流向的期望车流量的实时预测结果实时生成最优配时的自适应算法。算法实时改变相位车流向组成,系统适应能力有较大的提高。

十字路口交通信号相位个数的优化设计

为了解决交通拥挤，减少人们在交通路口等待时间，主要是通过提高交通信号灯的循环效率即找到交通信号灯的最优相位个数来实现的。通过引入图论中“圆染色”的概念，将城市路口交通信号灯最优相位个数归结为其交通流模型图的圆色数。在这篇文章中，根据十字路口交通流状况，给出了8种交通流模型图和它们圆色数，也即为对应交通信号灯的最优相位个数。

典型十字路口指路标志信息布局试验研究

针对大多数驾驶员在十字路口认知指路标志时,不能对版面信息进行有效加工处理,无法正确理解标志版面信息的含义。一些城市在指路标志版面信息布局设计时,对我国《道路交通标志和标线:交通标志部分》(GB5768.2-2009)的相关规定进行了调整,在版面信息布局时,采取了将同向信息中远地点置于上方的做法;通过利用问卷调查的方法,验证了该做法的合理性,结果表明对国标进行调整后的版面信息布局设计更符合大多数人的认知规律。本研究对于其他路口(T字路口、环形路口、立交路口等)的指路标志信息布局同样具有参考意义。

服役桥梁混凝土耐久性试验研究

服役一定年限后,由于结构自然老化、不良环境影响、车辆荷载增加以及养护维修欠缺,钢筋混凝土桥梁往往出现一定程度的病害,如混凝土腐蚀、钢筋锈蚀、梁体开裂,甚至保护层剥落等劣化现象。这势必导致桥梁结构的承载能力和耐久性降低、使用功能减退。通过检测鉴定,对服役桥梁的工作现状作出合理的评价具有重要的工程指导意义。通过现场和实验室试验,对已服役15年的青岛市振华路立交桥主梁混凝土的碳化及氯离子渗透情况进行了定量研究,分析了钢筋锈蚀的可能性,并依此对该桥的混凝土耐久性现状进行了评价,对已面临混凝土碳化威胁的桥梁耐久性提升提出了合理的建议。