Application of polyurethane geocomposites to help maintain track geometry for high-speed ballasted railway tracks

There are many issues surrounding the performance of critical assets on high-speed ballasted railway lines. At assets like switch & crossings and bridge transitions high track forces can be produced resulting in higher ballast settlements and hence track misalignments. The latter result in higher track forces and hence more settlement, leading to the need for increased track maintenance to ensure comfort and safety. Current technologies for solving issues like ballast movement under high-speed loading regimes are limited. However, a technique that has been well used across the UK and now increasingly overseas to stabilise and reinforce ballasted railway tracks is the application of in-situ polyurethane polymers, termed XiTRACK. This paper discusses how this technique can be used to solve these types of long-standing issues and presents actual polymer application profiles at two typical critical sites, namely a junction and a transition onto concrete slab-track.     

Characteristics of interior noise of a Chinese high-speed train under a variety of conditions

This paper presents an investigation into the characteristics of interior noise of a Chinese high-speed train under several typical conditions. Interior noises within Vehicle TC01, which can be used as a head car or an end car, and Vehicle TP03, the third car counting from TC01, are measured for the train running at speeds from 260 km/h to 385 km/h, along two types of track including a slab track and a ballast track and either on the ground surface or in a tunnel. Data analyses are performed for sound pressure overall levels, frequency, area contributions, and possible generation mechanisms, showing how they are affected by train speed, running direction, track type, and tunnel. The results show that, whether TC01 is used as head car or end car, the interior noise characteristics in the VIP cabin are mostly related to aerodynamic noise. Differences in interior noise between tracks become smaller as the train speed increases. The effect of a tunnel on the interior noise is more important for the middle coach than that for the head coach. This study can provide a basis for noise control of high-speed trains.     

Dynamic track-soil interaction——calculations and measurements of slab and ballast tracks

The dynamic behaviour of slab and ballast tracks was investigated using measurements and calculations. Hammer impacts and train passages were analysed and measurements were made using geophones(velocity transducers) which had been time-integrated to displacements. The calculations were carried out in the frequency-wavenumber domain for multi-beamon-continuous soil models. The characteristics of the different tracks and track elements were established in theory and by experiment. The frequency-dependent compliances(displacement transfer functions) showed clear rail-on-railpad resonances or highly damped track-soil resonances. Compared to the rail and sleeper, the track slab had much lower amplitudes. The slab track usually had the highest rail amplitudes due to soft railpads. Train passage yielded track displacements which were a superposition of the axle loads from the two neighbouring axles of a bogie and from the two bogies of two neighbouring carriages. This global behaviour was characteristic of the track slab of the slab track, whereas the rails of the slab and the ballast tracks behaved more locally with only one bogie of influence. The measurements agreed very well with the theory of continuous soil in the case of the six measured slab tracks and acceptably well for the six measured ballast tracks. The measurements allowed us to find appropriate model parameters and to check the models. For example, the Winkler model of the soil was found to be less appropriate because it reacted more locally.     

一种高速列车-轨道三维空间耦合动力学模型

研究目的：基于车辆-轨道耦合动力学理论分析方法,建立一种高速列车-轨道三维耦合动力学模型,并明确列车-轨道耦合模型与单节车辆-轨道耦合模型在高速列车-车九道耦合动力学性能分析中的差异。创新要点：建立一种高速列车-轨道三维耦合动力学模型,模型中考虑列车的纵向动力学行为以及车间连接装置对列车中不同车辆动态响应的影响,并基本明确完善的列车-轨道耦合模型在高速列车-轨道耦合动力学性能分析中的重要性。重要结论：单节车辆-轨道耦合模型会过高地估计高速列车在运营过程中的振动响应和动力学性能指标,而完善的列车-轨道耦合动力学模型的计算结果则更加接近实际情况。     

Influence of substrate surface morphology on wetting behavior of tracks during selective laser melting of aluminum-based alloys

AlSi12 samples were prepared by selective laser melting (SLM) under different processing conditions in order to obtain different top surface morphologies, where single tracks were produced using a fixed processing parameter to reveal the mechanism of the single track on different morphologies. The results show that the morphologies of single tracks changed with roughness of the top surface (Top R_a) of SLM parts, reflected in the variation of wetting angles on the surface processed previously as well as in dimensions of height, width, and depth at the cross-section of each single track. These changes were mainly caused by different wettability and flow behavior of the molten metal under various solidification environments of the single track during SLM. A poor solidification environment in which numerous balls existed limited an effective wetting behavior of molten metal on a previously processed surface of a SLM sample because of an increasing solid-liquid contact area, thus causing dramatical instability of the melt pool and attendant inferior processability of the single track. Meanwhile, under the action of surface tension, the molten metal had a high tendency to transfer into a pore near the single track to form an extending track or flow toward an upper region of melt to form a balling track, hence showing various morphologies of single tracks. This study proposes a theory of the solidification mechanism of single track on the non-ideal surface to provide a better understanding of the SLM processing of Al-Si alloy.     

Theoretical investigation into the effect of rail vibration dampers on the dynamical behaviour of a high-speed railway track

Installation of rail vibration dampers (rail dampers for short) onto rails between sleepers is one of the measures to control rail noise generation and roughness growth. Amid the rapid expansion of high-speed and underground railway networks in China, many suppliers are actively marketing and promoting their products, often giving confusing information. In this paper, a parametric study is used to investigate the effect of rail dampers on the dynamical behavior of a Chinese high-speed railway track. The Fourier transform-based method developed for analyzing dynamics of a railway track as an infinitely long periodic structure, with or without rail dampers, is applied in the investigation. It is hoped that results in this paper can help develop the understanding of the working mechanism of rail dampers, and provide useful information for product design and application.     

高寒地区隧道的冻害机理综述

简述衬砌混凝土的冰冻破坏、局部存水冻胀破坏、冻胀性围岩冻胀破坏以及既有裂缝裂隙水的冻胀破坏等因素对高寒地区隧道的冻害机理。     

高寒地区隧道的冻害机理综述

简述衬砌混凝土的冰冻破坏、局部存水冻胀破坏、冻胀性围岩冻胀破坏以及既有裂缝裂隙水的冻胀破坏等因素对高寒地区隧道的冻害机理。     

CRTSⅡ型轨道板施工质量控制

中国铁路无砟轨道具有轨道稳定性好、平顺性好、刚度均匀性好、结构耐久性强、维修工作量显著减少、旅客列车的安全性和舒适性显著提高等优点。CRTSⅡ型无砟轨道板作为无砟轨道系统的重要组成部分,具有结构稳定,利于工厂化生产,利于提高施工效率等特点。主要阐述轨道板制作过程的质量控制,分别从原材料、钢筋制作安装、模具安装、混凝土作业、轨道板存放、轨道板打磨六个方面具体说明。同时对常见质量问题进行原因分析,提出预防及解决办法。通过有助于高速铁路建设各方工程管理技术人员对CRTSⅡ型无砟轨道板制作进行有效控制,确保高速铁路工程建设质量。     

Track recommendation bias: Gender,migration background and SES bias over a 20‐year period in the Dutch context

Bias in track recommendations is an important mechanism, which causes education inequity in a tracked educational system (streaming). If teacher biases in track recommendations change over time, inequity in society and in the education system may also change. We investigated changes in track recommendation bias over time for gender, immigration status and socioeconomic status (SES), based on a longitudinal empirical study of nine cohorts of Dutch students in their final year (grade 6) of primary education in the period 1995–2014. An overview of educational and societal trends was provided, alongside the empirical analysis, to explain the findings in variation over time in track recommendation bias. Results indicate that the level of track recommendations provided to the students gradually increased over time. For a similar performance, a higher track recommendation was awarded in 2014 compared to 1995. This development coincided with an increase in parental education level, the valuing of education and the introduction of lower‐status pre‐vocational education tracks. Track recommendation bias favouring students with a migrant background and female students decreased, which coincided with growing cultural intolerance and attention to the ‘boy problem’. Bias in track recommendations related to SES appeared stable, with only small deviations from year to year. The results of this study indicate that track recommendation bias and teacher considerations are dependent on time and context.     

Investigation of differential movement at railroad bridge approaches through geotechnical instrumentation

Railway transitions experience differential movements due to differences in track system stiffness, track damping characteristics, foundation type, ballast settlement from fouling and/or degradation, as well as fill and subgrade settlement. This differential movement is especially problematic for high speed rail infrastructure as the ??bump?? at the transition is accentuated at high speeds. Identification of different factors contributing towards this differential movement, as well as development of design and maintenance strategies to mitigate the problem is imperative for the safe and economical operation of both freight and passenger rail networks. This paper presents the research framework and initial instrumentation details from an ongoing research effort at the University of Illinois at Urbana-Champaign. Three bridge approaches experiencing recurrent geometry problems were instrumented using multidepth deflectometers (MDDs) and strain gages to identify different factors contributing to the development of differential movements.     

低合金高速钢的分类及合金化原理

文章综合了国内外大量文献资料,对低合金高速钢进行了分类,分析了低合金高速中合金元素的作用,并较详细地阐述了低合金高速钢的合金化原理。     

浅析合唱曲目的选择

选择合适的合唱曲目对合唱团来说十分关键。人们常说,良好的开始是成功的一半。合唱成功的良好开端很大程度取决于是否选择了好的并且合适的曲目。因此,选择好合唱曲目是很讲究艺术的,不论是音乐会性质、比赛性质、庆典性质或者纪念性演出性质的合唱曲目。本文主要从曲目的题材内容、曲目是否悦耳以及曲目的难易程度三方面来阐述。     

Does being assigned to a low school track negatively affect psychological adjustment? A longitudinal study in the first year of secondary school

Previous research suggests that the 1st year in secondary school for some students goes hand in hand with an increase in adjustment difficulties. One factor that might influence this process on an individual, compositional, and institutional level is the academic track a student attends. It was hypothesized that being assigned to a low-qualifying track predicts a stronger increase in adjustment problems than being assigned to higher tracks. A sample of 734 seventh-grade students from Switzerland attending 1 of 3 regular academic tracks or special educational classes participated. Pupils reported anonymously on their antisocial behavior, anger control problems, self-worth, and emotional distress. Multilevel analyses were performed, predicting end of seventh-grade adjustment by track controlling for initial adjustment and background variables. Students enrolled in the low-qualifying regular track increased significantly more than students from other tracks regarding their problems with global adjustment, antisocial behavior, and emotional distress.     

多雷达综合:航迹合成(英文)

目前多雷达跟踪空中交通管制系统的雷达数据处理有两种方法,其中之一是航迹合成法。本文讨论把来自不同雷达站的同一目标的当地航迹合成唯一的一条系统航迹的方法和主要问题,并具体讨论了其中座标变换的问题,分析了由于变换公式的近似引起的实际变换误差。     

Bottom of the class? The leaving certificate applied programme and track placement in the Republic of Ireland

Across many countries, young people are differentiated into academic and vocational tracks, a pattern that is closely related to their social class background. The Irish secondary system has been largely undifferentiated, but the introduction of a pre-vocational programme, the Leaving Certificate Applied (LCA), has brought an element of tracking into upper secondary education. This article explores whether allocation into the LCA track reflects processes similar to those highlighted in international research. It goes further than these studies by explicitly recognising the role of school organisation in influencing student's learning careers and educational decisions. The purpose of this paper is to estimate the determinants of track placement in the Republic of Ireland. Using in-depth qualitative case study interviews with students from Irish post-primary schools, this paper examines the factors influencing students' decisions to enter the LCA programme. This paper explores the extent to which individual agency and school-level factors influence track choice by focusing on the learning careers of individual students within specific school contexts.     

绝对和相对小车结合法在长轨精调技术中的应用研究

高铁无砟轨道在长轨铺设完后需要对线路进行全面静态调整,将轨道几何尺寸调整到允许误差范围内,使线路轨道平顺性充分满足高铁联调联试前提要求.由于过程中消除轨道病害时间短、任务重,快速查找病害位置和消除方法便成为关键.位于高寒、高海拔、风沙环境下的兰新铁路LXS-2标段及时研究并采用绝对和相对小车结合法轨道调整技术,不仅提高...     

Tracking and Mixed‐ability Grouping in Secondary School Mathematics Classrooms: A case study1

This article reports the findings of a retrospective study of ‘tracked’ grouping in a mathematics department in a co‐educational comprehensive school in Greater London. Tracking consisted here of just two tracks, a ‘fast track’ for the top 25‐30% of a cohort, and a ‘mixed track’ for the remainder. The article outlines the reasons for introducing tracking and explores its effects through interviews with teachers and data on the progress of students from age 14 to age 16. The teachers reported that tracking impacted differently on different students, and this is borne out by the quantitative data. It was not possible to provide for ‘setting’ across all the mathematics classrooms in the focal cohort, and therefore one mixed‐ability class was created. The use of analysis of covariance (ANCOVA) models shows that fast‐track students were not significantly advantaged by their placement in these tracks, but the progress of students in the mixed‐ability group showed a significant interaction between progress and prior attainment, with placement in the mixed‐ability group conferring a significant advantage on lower attaining students, while the disadvantage to higher attaining students was much smaller.     

Longitudinal resistance performance of granular ballast beds under cyclic symmetric displacement loading

The longitudinal resistance performance of a granular ballast bed under cyclic symmetric displacement loading was studied based on a full-scale test model of ballast track structures. The change law of the longitudinal resistance characteristics of the ballast bed under variable displacement amplitudes was analyzed. The results show that: the resistance-displacement curves of a granular ballast bed are a set of closed hysteretic curves, indicating obvious energy consumption; a granular ballast bed softens gradually during the cyclic process with constant displacement amplitude, and the residual deformation rate increases nonlinearly with increasing cycle number; the peak value of the longitudinal resistance of lines decreases with increasing cycle number; the cyclic softening of a granular ballast bed is dependent on the displacement amplitude–the higher the displacement, the more severe the cyclic softening will become; after cyclic displacement loading is applied several times, the longitudinal resistance of the bed will degenerate obviously, and the higher the displacement amplitude, the higher the longitudinal resistance attenuation rate of the ballast bed will become.     

Tracking and the effects of school‐related attitudes on the language achievement of boys and girls

In this study we examined whether the underachievement of boys in language at the end of secondary education is related to school‐related attitudes. Data were drawn from the LOSO project, a longitudinal research project in secondary education. The results showed that there were gender differences in language achievement in favour of girls in the lower tracks, but not in the highest track. The underachievement of boys was associated with boys’ less positive relationships with teachers, less positive well‐being at school and less positive attitude towards schoolwork. Furthermore, the results showed that—in the lower tracks—boys who were the least attentive in the classroom, the least interested in learning tasks and the least motivated towards learning tasks achieved better than expected. Post‐hoc analyses revealed that these are the more intelligent boys. Possible explanations of the demotivation of the more intelligent boys in the lower tracks are discussed.