船用大型锅炉的水位研究及仿真

结合欧堡公司MISSION~(TM) D型船用锅炉,通过对影响水位的主要因素的分析,建立控制模型来实现对其仿真并达到预定的控制效果。     

CO2 emissions: Are land-use changes enough for California to reduce VMT? Specification of a two-part model with instrumental variables

With vehicle miles of travel increasing at a faster pace than population, one strategy being actively pursued by both state and local governments is compact development. California recently passed legislation that aggressively promotes sustainability by endorsing and rewarding compact development. Likewise, the California Air Resources Board has set a statewide reduction target of 5MMT of greenhouse gas reductions from land use, based largely on achieving compact development patterns. In this paper, we use a multivariate two-part model with instrumental variables, which corrects for residential location self-selection bias. We use a much larger and more geographically representative travel survey on household travel patterns and socio-economic characteristics than represented in previous California studies; this allows us to robustly consider other influences on travel. Our results indicate that, all else equal, a 10% in residential density would reduce VMT by 1.9%. This elasticity is larger than the reported in previous econometric studies for the US, and specifically for California. However, as we show, the magnitude of this impact is still low considering reasonable ranges for policies aimed to increase residential density.     

船体梁抗弯能力的计算

在船舶纵弯曲强度的可靠性分析中,需要计算船体梁的抗弯能力,本文提供一种实用计算方法。在此方法中取材料厚度(或剖面积)和屈服限、弹性模量等均为随机变量,利用随机函数的线性化原理,求得船体断面几何要素以及抗弯能力的统计特征值。文中还介绍了国产船用钢材的厚度和屈服极限的变异系数,并利用组合梁模型试验资料对采用梁模型带来的计算误差及其修正办法作了讨论。该计算方法采用了造船人员熟悉的常规强度计算中的格式,便于在船舶设计中应用。     

A stochastic quarter-car model for dynamic analysis of vehicles with uncertain parameters

A quarter-car model is used to investigate the vibration response of cars with uncertainty under random road input excitations in this paper. The sprung mass, unsprung mass, suspension damping, suspension stiffness, and tyre stiffness are considered as random variables. The road irregularity is considered a Gaussian random process and modelled by means of a simple exponential power spectral density. The power spectral density, mean value, standard deviation, and variation coefficient of the vehicle's natural frequencies and mode shapes are obtained by using the Monte Carlo simulation method. The computational expressions for the numerical characteristics of the mean square value of the vehicle's random response in the frequency domain are developed by means of the random variable's functional moment method. The influences of the randomness of the vehicle's parameters on the vehicle's dynamic response are investigated in detail using a practical example, and some useful conclusions are obtained.     

债务经济的稳定性分析

从我国国债规模日趋扩大的现状出发，分析了债务经济稳定性的实质，并从国债依存度、国民经济负债率、个人负债率等几个指标进一步研究了国债市场的应债能力、承受空间及其它稳定性问题。     

预测通道客运分担率的MNL模型特性变量选取

基于非集计离散选择模型理论,结合通道内各种运输方式特性,给出了在运用MNL模型预测通道客运分担率时特性变量的选取原则。分析了影响旅客出行方式选择的出行时间、安全性、舒适性、方便性、费用等因素间的关系以及各因素作为特性变量的适应性,认为在运用MNL模型预测通道客运分担率时应选取出行时间、费用收入比和发车频率作为特性变量,并给出了各特性变量的取值标定方法。结合旅客出行特征调查数据,进行了实证分析和各个特性变量灵敏度分析,得出制定客运专线运营策略时应主要考虑出行时间、费用和出行者收入变化影响的结论。     

城市交通出行行为中的潜变量研究综述

潜变量是提高交通出行行为预测精度的有效方法,潜变量的提出为出行行为 研究提供了新视角.为解决目前出行行为中缺少潜变量概念认知及潜变量应用的问题,本 文从社会心理学入手,分析已有出行行为建模方法的特点,提出潜变量研究的必要性,对 出行行为中潜变量内涵、应用领域、模型构建进行系统梳理,明确潜变量研究的三个核心 问题是识别、有效性验证及计算.评述与研究涵盖潜变量的出行行为整合模型的机遇、难 点和挑战.并揭示潜变量测度方法与SP/RP 调查的关联性,综述潜变量模型检验判定标 准,最后总结出行行为潜变量研究的发展趋势及发展方向.     

结构可靠度的改进虚拟变量算法

针对当结构功能函数的构成为相关任意分布随机变量以及结构功能函数非线性程度产高时，虚拟变量法不适用的问题，提出了计算结构可靠指标的改进的虚拟变量算法，算例结果表明该方法可有效克服一般虚拟变量算法的不足，适用于结构功能函数非线性程度较高且其构成为相关任意分布随机变量的情况。     

The impact of urban form on automobile travel: disentangling causation from correlation

A longstanding question within the field of transportation demand management is the strength of the relationship between urban form and mobility behavior. Although several studies have identified a strong correlation between these variables, there is as yet scant evidence to support policy interventions that target land use as a means of influencing travel. To the contrary, some of the more recent research has cast skepticism on the proposition that the relationship is causative, recognizing the possibility that households endogenously self-select themselves into communities that support their preferences for particular transportation modes. Focusing on individual automobile travel, the present study seeks to contribute to this line of inquiry by estimating econometric models on a panel of travel-diary data collected in Germany between 1996 and 2003. Specifically, we employ the two-part model (2PM)—a procedure involving probit and OLS estimators—to assess the determinants of the discrete decision to use the car and the continuous decision of distance traveled. Beyond modeling variables that capture the urban form features that are commonly suggested to influence mobility behavior, including mixed use and public transit, this study employs instrumental variables to control for potential endogeneity emerging from the simultaneity of residential and mode choices. Unlike much of the work to date, our results suggest that urban form has a causative impact on car use, a finding that is robust to alternative econometric specifications.