Airline competition and market frequency: A comparison of the s-curve and schedule delay models

We compare two common ways of incorporating service frequency into models of airline competition. One is based on the so called s-curve, in which, all else equal, market shares are determined by frequency shares. The other is based on schedule delay—the time difference between when travelers wish to travel and when flights are available. We develop competition models that differ only with regard to which of the above approaches is used to capture the effect of frequency. The demand side of both models is an approximation of a nested logit model which yields endogenous travel demand by including not traveling in the choice set. We find symmetric competitive equilibrium for both models analytically, and compare their predictions concerning market frequency with empirical evidence. In contrast to the s-curve model, the schedule delay model depicts a more plausible relationship between market share and frequency share and accurately predicts observed patterns of supply side behavior. Moreover, the predictions from both models are largely the same if we employ numerical versions of the model that capture real-world aspects of competition. We also find that, for either model, the relationship between airline frequency and market traffic is the same whether frequency is determined by competitive equilibrium, social optimality, or social optimality with a break-even constraint.     

综合管廊抗震分析研究进展综述

针对目前城市综合管廊建设方兴未艾、抗震防灾需求日益凸显的现状，总结评述目前综合管廊抗震分析的研究进展。首先，归纳总结综合管廊结构的震害特点和关键影响因素，并在此基础上对国内外综合管廊抗震研究的发展历程和重要突破进行综述；然后，重点从影响综合管廊地震响应机制的关键要素出发，即从输入地震动特征、工程场地特性、管廊结构形式与构造特点3个方面对综合管廊抗震研究现状以及存在的不足之处进行综述；最后，对综合管廊减隔震研究现状进行讨论。研究表明： 1)输入地震动特征会对综合管廊地震响应产生显著影响，对于浅埋结构还应关注地表Rayleigh波的作用； 2)工程场地特性研究聚焦在饱和液化地层、断层破碎带等不利场地条件对综合管廊结构地震响应的影响机制方面； 3)新型管廊结构形式和节点构造层出不穷，但目前的研究工作主要关注管廊结构自身的地震响应特征。建议后续研究重视综合管廊功能性对抗震安全性的需求，进一步加强“结构-功能”一体化抗震性能设计方法与指标体系的研究工作。     

高性能船性能综合评估方法研究

为了在高性能船推广应用时按任务需求选择综合性能最优的船型,开展了高性能船性能综合评估方法研究。基于层次分析法和多属性效用理论,首先按照指标体系的构建原则选定高性能船性能评价的指标,构建指标体系层次结构,然后建立高性能船性能综合评估方法,并对一船型平台选型实例进行计算分析。研究表明,所建立的性能综合评估方法可以为高性能船应用中的选型决策提供技术支撑。     

海底管线隧道运营检测体系的建立与应用实践

文章分析了建立海底管线隧道运营检测体系的必要性,提出建立运营检测体系须考虑海底隧道的结构安全、水文地质环境特点、运营条件和使用工况以及管线要求等因素,认为检测体系应分成日常检查、定期检测、特别检测和专项检测4类,并给出了检测频率、检测内容、检测方法、技术状况评定标准和各分项指标的权重。最后以深圳前湾隧道为例,采用上述检测体系对隧道进行了定期检测,并摘录了部分检测结果。结论表明,文中给出的检测内容和评定标准能够客观反映海底管线隧道的安全性能及工况状态,采用文中提出的检测方法可准确获得上述指标,从而为隧道病害整治提供科学的决策依据和技术支撑。     

与地铁结合的地下盾构综合管廊设计方法研究

为解决在已建成的城市中心区采用大规模明挖工法建设地下综合管廊的可实施性差的问题,提出了与地铁结合,同步规划、同步设计和同步实施,采用盾构工法建设地下综合管廊的设计理念和实践案例。对盾构综合管廊的主要组成及各组成部分的功能,盾构综合管廊与地铁的结合形式,防火分区长度划分原则和出地面口部（逃生口和吊装口）间距要求,大型供水管线入廊的安装、运营维护和防爆管措施,隧道内部结构体系的型式,盾构综合管廊管线灵活出线的解决方式等关键技术问题,予以分析和阐述,并付诸实践,系统性地解决了中心城区地下综合管廊的应用问题。     

Transition choice probabilities and welfare analysis in random utility models with imperfect before–after correlation

Welfare in random utility models is used to be analysed on the basis of only the expectation of the compensating variation. De Palma and Kilani (De Palma, A., Kilani, K., 2011. Transition choice probabilities and welfare analysis in additive random utility models. Economic Theory 46(3), 427–454) have developed a framework for conditional welfare analysis which provides analytic expressions of transition choice probabilities and associated welfare measures. The contribution is of practical relevance in transportation because it allows to compute shares of shifters and non-shifters and attribute benefits to them in a rigorous way. In De Palma and Kilani (2011) the usual assumption of unchanged random terms before and after is made.The paper generalises the framework for conditional welfare analysis to cases of imperfect before–after association of the random terms. The joint before–after distribution of the random terms is introduced with postulated properties in terms of marginal distributions and covariance matrix. Analytic expressions, based on the probability density function and the cumulative distribution function of the joint before–after distribution, and simulation procedures for computation of the transition choice probabilities and the conditional expectations of the compensating variation are provided. Results are specialised for multinomial logit and probit. In the case without income effects, it is proved that the unconditional expectation of the compensating variation depends only on the marginal distributions.The theory is illustrated by a numerical example which refers to a multinomial logit applied to the choice of the transport mode with two specifications, one without and one with income effects. Results show that transition probabilities and conditional welfare measures are affected significantly by the assumption on the before–after correlation. The variability in the transition probabilities across transitions tends to decrease as the before–after correlation decreases. In the extreme case of independent random terms, the conditional expectations of the compensating variation tend to be close to the unconditional expectation.     

基于仿真分析的预制拼装综合管廊抗燃爆研究

综合管廊凭借其自身优点正广泛应用于城市建设中,采用Ansys/Ls-dyna基于仿真分析综合管廊发生燃气爆炸具有十分重要的实际意义。以预制拼装综合管廊为研究对象,采用流固耦合的计算方法,建立预制拼装综合管廊、可燃爆气体和空气等三部分的有限元仿真模型。通过分析预制拼装综合管廊内混凝土的应力时程曲线、主要节点位移时程曲线及预应力钢筋的轴向应力时程曲线,分析预制拼装综合管廊在燃气爆炸作用下的抗燃爆性能,提出抗燃爆防护及设计意见。     

成都陆肖 TOD 市政管线迁改及微型管廊方案

TOD地下空间开发所涉及的市政用地面积比常规地下空间大，市政管线迁改需从区域的角度统筹考虑，兼顾工期、经济性、管线运维可靠性。陆肖TOD为成都首个TOD综合开发示范项目，对区域所涉及的市政管线进行迁改设计，并探索规划“一横一纵”微型管廊。