Using the built environment to oversample walk,transit, and bicycle travel

Characteristics of the built environment (BE) have been associated with walk, transit, and bicycle travel. These BE characteristics can be used by transportation researchers to oversample households from areas where walk, transit, or bicycle travel is more likely, resulting in more observations of these uncommon travel behaviors. Little guidance, however, is available on the effectiveness of such built environment oversampling strategies. This article presents measures that can be used to assess the effectiveness of BE oversampling strategies and inform future efforts to oversample households with uncommon travel behaviors. The measures are sensitivity and specificity, positive likelihood ratio (LR+), and positive predictive value (PPV). To illustrate these measures, they were calculated for 10 BE-defined oversampling strata applied post-hoc to a Seattle area household travel survey. Strata with an average block size of <10 acres within a ¼ mile of household residences held the single greatest potential for oversampling households that walk, use transit, and/or bicycle.     

机车车辆用新型空气过滤器概述

对机车车辆用传统空气过滤器存在的问题进行分析,介绍一种适合机车车辆用新型空气过滤器的结构特点、过滤原理、主要性能及试验情况等。     

电动汽车动力电池低温性能研究与应用

电动汽车锂离子动力电池在低温条件下工作时,电池的内阻明显升高、功率和能量急剧下降,导致整车低温下动力性能不足、续驶里程不足、充电受限等问题。通过试验进行了动力电池的低温特性研究,提出了适合整车低温工作的解决方案,通过实车验证,达到了很好的效果。     

Experimental and numerical investigation on the derailment of a railway wheelset with solid axle

This paper presents the results of an experimental and numerical investigation on the derailment of a railway wheelset with solid axle. Tests were carried out under quasi-steady-state conditions, on a full-scale roller rig, and allowed to point out the effect of different parameters like the wheelset's angle of attack and the ratio between the vertical loads acting on the flanging and non-flanging wheels. On the basis of the test results, some existing derailment criteria are analysed in this paper and two new criteria are proposed. A model of wheel–rail contact is proposed for the mathematical modelling of the flange climb process, and numerical vs. experimental comparisons are used to obtain model validation.     

微表处耐磨性能影响因素试验研究

该文介绍了微表处耐磨性能影响因素试验研究。通过侵水1h湿轮磨耗试验,研究添加不同种类及剂量改性剂的乳化沥青、矿料级配、水泥掺加量等因素对微表处耐磨性能的影响。试验结果表明,在相同油石比的试验条件下:使用SBR胶乳改性乳化沥青的微表处耐磨性能优于使用SBS胶乳改性乳化沥青;随着改性剂剂量的增大,微表处耐磨性能逐渐变好,并趋于稳定;矿料中值级配微表处耐磨性能最好,级配上限与级配下限微表处耐磨性能基本相当;水泥掺加量对微表处耐磨性能有提高,也有降低。     

电动助力转向系统阻力模拟器研究及实现

研究电动助力转向系统阻力模拟器的控制方法，探索一种利用单片机控制电动机转矩为试验台提供转向阻力的方法。介绍了阻力模拟器的结构、控制方法、工作原理，研究了电动助力转向系统阻力模拟器的功能及实现方法。     

新拌混凝土气泡参数分析法评估混凝土抗冻性

通过对国内外资料分析,指出了新拌混凝土气泡参数分析法评估混凝土抗冻性技术是快速无损预控混凝土抗冻性的发展方向,对抗冻混凝土施工具有前瞻性的指导意义。     

浅窄航道非线性兴波阻力数值计算

应用Rankine面元法计算船舶在浅窄航道中作匀速直航运动时的非线性兴波阻力．基于势流理论，在船体表面、自由面以及岸壁分布Rankine源来表达流场速度势，利用迭代方法满足非线性自由面边界条件，采用映像法满足水底边界条件，采用网格错位法满足辐射条件．以Wigley数学船型为例进行计算，通过改变航速和航道宽度参数，得到相应的兴波阻力．通过分析不同航速下航道宽度变化对兴波阻力的影响，得到了一些有意义的结论．     

Experimental study on a model azimuthing podded propulsor in ice

The objective of this study was to investigate the performance of a model azimuthing podded propulsor in ice-covered water. Model tests were carried out with two different depths of cut into the ice (15 and 35 mm), two different ice conditions (presawn and pack ice conditions), and four different azimuthing angles. The depth of cut is the maximum penetration depth of the propeller blade into the ice block. The 0.3-m-diameter model propeller was operated in a continuous ice milling condition. Ice loads were measured by several sensors which were installed in various positions on the model. Six one-axis pancake-style load cells on the top of the model measured the global loads and two six-component dynamometers were installed on the shaft to measure the shaft loads. One six-component dynamometer was attached to the one of the propeller blades inside the hub to measure the blade loads. The pod unit and propeller performance in ice are presented. Ice-related loads, which were obtained when the blade was inside the ice block, are introduced and discussed. During the propeller–ice interaction, a blade can experience the path generated by the previous blade, which is called the shadowing effect. The effects of shadowing, depth of cut, azimuthing angle, and advance coefficient on propulsor performance are presented and discussed.     

聚丙烯纤维砼在水利枢纽工程泵站中的应用

针对无锡市仙蠡桥水利枢纽工程主泵房工程所处环境和工作条件特殊,泵站站身外形和结构复杂的情况,选择掺粉煤灰、聚丙烯纤维以及高效减水剂的泵送砼,进行配合比设计,测试主要物理力学性能和采用合理的施工工艺,得到抗裂、抗渗、抗冻和抗冲耐磨性能均较好的砼结构.