电控高压共轨喷油系统结构参数对轨内压力波动仿真分析

采用GT软件建立电控高压共轨燃油喷射系统模型,并利用构建的仿真模型研究高压油泵的进油阀组件、排油阀组件以及活塞凸轮组件,其三个主要部分的结构参数变化对共轨管中压力波动的影响。通过研究可知高压泵在实际工作时所承受的压力波与活塞的状态有直接关系,且活塞状态包括其质量、长度、直径、容积等。为了更好地研究进排油阀对压力波动之间的关系,选用8组参数进行实验研究并验证进排油阀体直径、质量、弹簧预紧力、弹簧刚度的变化与压力波动之间的相互影响作用,进而通过对比选取最佳阀体。通过仿真分析可知,共轨喷油系统压力波动程度会受到系统结构参数的影响,并可以为系统的优化设计提供参考依据。     

钢纤维混凝土桥面铺装层的细观应力破坏分析

基于复合材料力学和线弹性断裂力学,简化了桥面铺装层及桥面板体系的力学模型,建立了修正的剪滞控制方程组.将模型裂缝区及远场的应力、位移条件合理转换为所建立计算模式的求解边界条件,进而得到了桥面铺装层和桥面板各子层的位移分布函数.运用能量法则,考虑温度效应对桥面铺装层的影响,得到了桥面铺装层破坏应力的解析解.运用该计算模式对某桥桥面铺装层的破坏进行了仿真分析,证实了该方法的适用性.     

水泥混凝土路面板底脱空的原因及防治措施

根据水泥混凝土路面破坏情况的调查,分析了混凝土路面产生板底脱空现象的原因及其防治措施,对预防早期破坏,延长水泥混凝土路面的使用寿命具有指导意义.     

考虑反射强度的全自动运行列车障碍物检测算法研究

针对轨道交通全自动运行列车轨行区障碍物检测问题,提出了一种基于激光雷达的且考虑激光反射强度的障碍物检测算法.该算法使用欧式聚类法对点云进行聚类,并结合了自适应的反射强度阈值处理以及体素滤波器、聚类半径差异化等方法,提升算法的障碍物检测速度与精度.实验表明该算法具有良好的检测性能.     

基于多指标的钢轨打磨目标廓形设计

提出了一种基于多维度指标综合最优的钢轨打磨目标廓形设计方法,该方法通过对车辆稳定性、曲线导向性、轮轨接触特性曲线平滑性和轮轨接触点均布性等4个指标进行综合考虑,基于轮轨接触特性的逆向求解方法,实现轮轨接触特性曲线的自动优化和钢轨打磨目标廓形的计算机智能化设计.太原铁路局北同蒲线打磨应用结果表明,打磨后钢轨光带位置和实测...     

稀浆封层路面层间黏结性能试验研究

为了对稀浆封层层间黏结性能进行评价,自行设计了以改进的剪切仪为基础的试验方法,能较好地模拟路面真实受力情况.试验结果说明,随着温度的升高,稀浆封层与沥青碎石下面层之间黏结强度在减小;不同的路面层间处理措施对黏结强度均有明显的影响;采用较大公称粒径的沥青混合料,或者对路面做凿毛处理均可以有效提高层间黏结强度.     

Long Memory of Financial Time Series and Hidden Markov Models with Time‐Varying Parameters

Hidden Markov models are often used to model daily returns and to infer the hidden state of financial markets. Previous studies have found that the estimated models change over time, but the implications of the time‐varying behavior have not been thoroughly examined. This paper presents an adaptive estimation approach that allows for the parameters of the estimated models to be time varying. It is shown that a two‐state Gaussian hidden Markov model with time‐varying parameters is able to reproduce the long memory of squared daily returns that was previously believed to be the most difficult fact to reproduce with a hidden Markov model. Capturing the time‐varying behavior of the parameters also leads to improved one‐step density forecasts. Finally, it is shown that the forecasting performance of the estimated models can be further improved using local smoothing to forecast the parameter variations. Copyright © 2016 John Wiley & Sons, Ltd.     

基于模糊综合理论的铁路建设项目综合后评价研究

进入21世纪以来,铁路作为人类社会赖以生存的基础设施,一直在国家固定资产投资中占据着主导地位,因此,如何提高铁路建设项目的质量就显得尤为关键。本文提出铁路建设项目综合后评价的概念,并将铁路建设项目综合后评价的内容概括为工程管理水平、投融资管理水平和财务效益水平三个部分。在此基础上,建立了基于模糊综合理论的铁路建设项目综合后评价的模糊综合评价模型,并通过实例验证了该模型的实用性。     

Do Long‐Run Theory Restrictions Help in Forecasting?

Do long‐run equilibrium relations suggested by economic theory help to improve the forecasting performance of a cointegrated vector error correction model (VECM)? In this paper we try to answer this question in the context of a two‐country model developed for the Canadian and US economies. We compare the forecasting performance of the exactly identified cointegrated VECMs to the performance of the over‐identified VECMs with the long‐run theory restrictions imposed. We allow for model uncertainty and conduct this comparison for every possible combination of the cointegration ranks of the Canadian and US models. We show that the over‐identified structural cointegrated models generally outperform the exactly identified models in forecasting Canadian macroeconomic variables. We also show that the pooled forecasts generated from the over‐identified models beat most of the individual exactly identified and over‐identified models as well as the VARs in levels and in differences. Copyright © 2011 John Wiley & Sons, Ltd.     

Price–Dividend Ratios and Stock Price Predictability

A long‐standing puzzle to financial economists is the difficulty of outperforming the benchmark random walk model in out‐of‐sample contests. Using data from the USA over the period of 1872–2007, this paper re‐examines the out‐of‐sample predictability of real stock prices based on price–dividend (PD) ratios. The current research focuses on the significance of the time‐varying mean and nonlinear dynamics of PD ratios in the empirical analysis. Empirical results support the proposed nonlinear model of the PD ratio and the stationarity of the trend‐adjusted PD ratio. Furthermore, this paper rejects the non‐predictability hypothesis of stock prices statistically based on in‐ and out‐of‐sample tests and economically based on the criteria of expected real return per unit of risk. Copyright © 2011 John Wiley & Sons, Ltd.