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TANGLi-qiang ZHENGGui CAIYan-hong 《船舶与海洋工程学报》2004,3(2):73-78
A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (σε) ∝r^-1/(n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain. 相似文献
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This paper presents an investigation of the temporal evolution of commuting mode choice preference structures. It contributes to two specific modelling issues: latent modal captivity and working with multiple repeated crossectional datasets. In this paper latent modal captivity refers to captive reliance on a specific mode rather than all feasible modes. Three household travel survey datasets collected in the Greater Toronto and Hamilton Area (GTHA) over a ten-year time period are used for empirical modelling. Datasets collected in different years are pooled and separate year-specific scale parameters and coefficients of key variables are estimated for different years. The empirical model clearly explains that there have been significant changes in latent modal captivity and the mode choice preference structures for commuting in the GTHA. Changes have occurred in the unexplained component of latent captivities, in transportation cost perceptions, and in the scales of commuting mode choice preferences. The empirical model also demonstrates that pooling multiple repeated cross-sectional datasets is an efficient way of capturing behavioural changes over time. Application of the proposed mode choice model for practical policy analysis and forecasting will ensure accurate forecasting and an enhanced understanding of policy impacts. 相似文献
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以连云港某专用线装卸车站为例,阐述了铁路专用线装卸方式与车站布置之间的相互关系,对各种装卸机械作业条件下的运输组织和车站布置进行了分析,得出合理的配置组合,为专用线装卸车站的布置提供参考. 相似文献
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在山区和多丘陵地区多采用挖方土石混合料填筑路基,并且形成高路堤。因此在路基的自重荷载和行车荷载共同作用下,经常出现路基的整体下沉或部分下沉,特别是一些填挖接头和桥台处,路基不均匀沉降特别突出。经过大量的实际调查以及实验,归纳起来填方路基的不均匀沉降主要有四种基本模式:路基填方压实度不足;地基中存在软弱土层;路基刚度差异过大;填充物成分不均匀。 相似文献
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由于对科研项目实施方式的了解不够深入、重视短期经济利益等原因,部分工程企业,尤其中小型企业围绕工程开展科研项目的意愿比较低.通过简要分析目前依托工程开展科研攻关的主要实施方式,并结合工程案例讨论与分析包括经费筹集、分配、支付与过程管理等在内的经费管理方式,以期提高相关企业参与工程科研攻关的积极性. 相似文献
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段厚省 《上海交通大学学报(哲学社会科学版)》2011,19(5)
当下我国有关民事诉讼构造的研究,从路径上看大致可归入理性主义和经验主义两种思维模式下。但是这两种思维模式曾经遭遇的论证困境,前者如所谓明希豪森困境,后者如休谟问题,并未得到解决。此种困境,也体现在我国有关民事诉讼构造问题的研究中。为解决或者说避开上述困境,可以考虑借鉴哈贝马斯在其交往行为理论基础上提出的法律商谈理论的论证路径,也就是以参与者的共同理性选择,作为建构正当程序的终极依据。 相似文献
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A direct discrete mode choice model is introduced using relative attributes of competing modes as well as socioeconomic characteristics of travelers. The model is calibrated and validated for two available historic databases in the Dallas–Fort Worth region. The validation is conducted against the outputs of a current nested logit model used by the regional planning organization as well as the observed values based on transit ridership surveys for a newly inaugurated commuter rail service. The calibrated model is applied after the introduction of this new transit mode. The results show that the estimated mode shares by the proposed model have a statistically better consistency with the observed values than the estimates of the conventional nested logit model. Unlike the logit model, the structure of the direct model based on relative attributes also has the advantage of not needing recalibration each time a new travel mode is introduced. The model is found to be easier to calibrate and produces more accurate results than the nested logit model, commonly used by many metropolitan planning organizations. 相似文献