Biologically induced differences in erodibility and aggregation of subtidal and intertidal sediments: a possible cause for seasonal changes in sediment deposition

This study was carried out to describe the difference in erodibility and aggregation in a tidal basin including both subtidal and intertidal study sites and to use these results to explain the shifting erosion/deposition cycles at the sites. Erosion thresholds, erosion rates and settling velocities of the eroded material were measured at a mudflat transect and at sediment cores taken from a nearby tidal channel during surveys made in May 2000 and March 2002. Surface samples were analysed for grain-size, chl. a content, faecal pellet content, dry bulk density and organic content. Additionally, surface samples were taken at eight occasions in the period January 2002 to May 2003 from shallow tidal channels in the area. These samples were analysed for mud content and showed that major shifts in sediment distribution occurred in the period. The erodibility of the mudflat was generally high due to pelletization by the mudsnail Hydrobia ulvae but close to the salt marsh much lower erodibility was found, probably due to stabilisation by microphytobenthos. In contrast, the erodibility of the channel bed seemed to be very little influenced by biological activity and the relatively low erodibility found here was caused by physical characteristics of the sediment. The sediment eroded from the mudflat was generally strongly pelletized and showed high settling velocities whereas less aggregation and lower settling velocities were found for the channel bed sediments. Temporal variations of the mudflat stability and hydrodynamics resulted in temporal variations of deposition and erosion and the changing stability at the mudflat is likely to be one of the main reasons for a general transport of fine-grained sediment from the mudflat to the channel in the cold seasons and vice versa during the rest of the year.     

关于纯电动面包物流车漏雨问题的分析与研究

文章针对纯电动面包物流车淋雨密封存在的一些漏雨问题,阐述了现状及典型淋雨漏水点,并分析了其漏水原因及进行了优化改善,进一步提高了其一次性淋雨通过率,明显提升了纯电动面包物流车的淋雨密封品质。     

现场总线在地铁列车清洗机上的应用

Profibus- DP(现场总线)用于现场设备的高速数据传输.中央处理器通过高速串行总线同分散的现场设备进行通信,分散的DP从站通过总线连接到可编程程序控制器上.Profibus- DP提供强有力的组态和诊断功能,是一种低成本、灵活的信号传输解决方案,可替代麻烦的并行线路.列车清洗机是地铁列车表面自动清洗的设备.阐述...     

城市公交线路模态工况构建方法研究

采用GPS设备对西安城市公交典型线路的运行工况进行实测,分别运用瞬态转模态方法和多目标优化法构建出城市客车模态工况。以8个特征参数相对误差为标准,对两种方法的精度进行了对比研究。研究表明,两种方法均能有效地完成工况构建,其中多目标优化法精度最高,瞬态转模态方法简单快捷,从而为工况构建方法的选取提供了思路和数据验证。     

半刚性基层材料动态模量研究

文章针对我国常用的水泥稳定碎石和二灰稳定碎石两种半刚性材料,通过大量的室内试验研究,建立了两种材料动态模量与无侧限抗压强度和静态模量的关系,为没有条件进行动态模量试验的单位进行路面结构设计提供建议。     

地铁垂直交叉隧道工程施工

研究目的:随着越来越多的城市都将地下交通网线作为解决交通拥挤的最为有效手段,地铁隧道线路垂直交叉施工情况日益增多,这给地铁隧道施工带来更多的风险和挑战。本文就垂直交叉施工中的重难点及施工中应采取的措施进行研究,以供地铁隧道施工参考。研究结论:交叉隧道施工中,超前预报、爆破控制、监控量测等施工手段是极为有效的方法,三者缺一不可、相辅相成,其中爆破控制是关键,超前预报与监控量测是重点。只有通过超前预报提前了解掌子面内部实际地质情况,并根据监控量测数据及时掌握地面沉降变化情况,才能够制定出最为合理有效的爆破控制参数,排除潜在风险,保证交叉隧道顺利施工。     

地下车站的混凝土开裂数值分析及抗裂试验研究

针对上海地区富水软土地层中地下车站渗漏水问题,在混凝土开裂原理分析的基础上,建立了地铁车站混凝土结构的有限元损伤模型,揭示了水土荷载作用下混凝土裂缝起裂特点、分布及其发展规律.采用光栅光纤监测技术开展了混凝土温度-应变现场实验,得到了在施工全过程中混凝土结构的温度及应变变化规律,分析了温度、养护时间、抗裂剂等因素对混凝土开裂的影响.研究表明:根据形态特点,裂缝可分为贯通裂缝和非贯通裂缝,其中贯通裂缝可引起车站结构渗漏水.由于约束作用,贯通裂缝主要发生在侧墙靠近中板和底板的位置.添加抗裂剂、延长养护时间可有效提高混凝土抗裂性能和防水抗渗性能.     

下穿铁路地道基坑降水分析

该文以下穿某铁路的地道工程为例,运用基坑降水引起铁路路基沉降的计算模型,根据不同降水方案对地面的沉降量进行计算、分析,阐述了降水相关技术要求,预防铁路路基不均匀沉降的措施,从而提高设计的经济效益和社会效益。     

浅谈公交车辆前桥工字梁承孔维修工艺

本文介绍了车辆前桥工字梁承孔在行驶当中踩刹车时突然断裂的机械事故的原因，阐述了公交车辆前桥工字梁承孔的重要性，论证了对公交车辆前桥工字梁承孔维修的必要性和重要性，得出了相关的方法和建议。     

地铁车站票务运作的策略

伴随着社会经济的持续快速发展,地铁交通已经成为城市居民出行的首要选择,城市地铁的建设里程不断延长,城市地铁的运力不断增强,这些都在很大程度上促进了城市经济的持续快速发展。在实践中,地铁运力的增加,势必会对车站票务运作产生直接的影响。为更好的优化车站票务的运作效率,有必要采用高效且科学的策略,切实提升票务运作的整体成效与质量。