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排序方式: 共有98条查询结果,搜索用时 15 毫秒
91.
随着世界贸易的快速发展,海运业对环境的污染日益显著,国际海事组织(IMO)海上环境保护委员会提出船舶能效设计指数(EEDI)用来衡量船舶设计能效水平.本文对27 000 dwt多用途船其EEDI指数进行分析研究,该船的EEDI计算过程和计算结果已经得到法国BV船级社的认可,相关研究结论可供船舶设计人员参考. 相似文献
92.
The aim of this study is to evaluate the efficiency of public transport operations undertaken in Swedish counties by the Public Transport Authorities (PTA), taking into account the substantial differences in operating conditions between counties. The analysis will be performed using Stochastic Frontier Analysis (SFA) with annual data from 1986 to 2009 for 26 Swedish counties. The analysis shows how the efficiency of the individual counties has changed over time. The results are used to provide a ranking (in terms of efficiency) of the Swedish public transport authorities that can provide a basis for benchmarking. It is concluded that the efficiency of the public transport providers in all counties fell during the observed time period. Defining cost efficiency as the ratio of minimum cost to observed cost, the overall (average) cost efficiency for the industry fell from 85.7% in the eighties to 60.4% for the period from 2000 to 2009. Possible explanations for the development include increased emphasis on route density as well as higher environmental and safety requirements. 相似文献
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94.
为了在新开发公务船中进行型线优化设计,对两条实船的四种型线裸体船模试验结果进行了分析对比,证实对于方形系数在0.50以下的船型,当Fn为0.40附近时,设球鼻艏增加了有效马力;但在Fn处于0.32~0.35区间时,由于形成有利干扰兴波阻力下降,设倒水滴形球鼻艏能减少有效马力约3%~6%. 相似文献
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96.
条码技术为生产制造执行系统(MES)提供了最佳数据采集手段。生产现场作业员使用条码阅读器或带有条码扫描功能的手持数据终端,进行现场数据采集,替代人工完成大量工作,使之能准确、及时地采集到过程信息,帮助企业极大地提高生产作业效率和管理水平。 相似文献
97.
Alessandro Perugia Jean-François Cordeau 《Transportation Research Part B: Methodological》2011,45(10):1710-1726
This paper presents a model and an algorithm for the design of a home-to-work bus service in a metropolitan area. This type of service must display an equilibrium between conflicting criteria such as efficiency, effectiveness, and equity. To this end, we introduce a multi-objective model in which, among other aspects, equity is considered by time windows on the arrival time of a bus at a stop. Time windows can have other uses such as, for example, guaranteeing synchronization of the service with other transportation modes. This is one of the guiding principles of the proposed model which is based on concepts that simultaneously tackle several issues at once. Along this line, we propose a cluster routing approach to model both bus stop location and routing in urban road networks where turn restrictions exist. The resulting multi-objective location-routing model is solved by a tabu search algorithm. As an application, we analyze a home-to-work bus service for a large research center located in Rome, Italy. This case study provides a benchmark for the algorithmic results, and shows the practical relevance of the proposed methodology. 相似文献
98.
Rico Merkert David A. Hensher 《Transportation Research Part A: Policy and Practice》2011,45(7):686-695
As a result of the liberalisation of airline markets; the strong growth of low cost carriers; the high volatility in fuel prices; and the recent global financial crisis, the cost pressure that airlines face is very substantial. In order to survive in these very competitive environments, information on what factors impact on costs and efficiency of airlines is crucial in guiding strategic change. To evaluate key determinants of 58 passenger airlines’ efficiency, this paper applies a two-stage Data Envelopment Analysis (DEA) approach, with partially bootstrapped random effects Tobit regressions in the second stage. Our results suggest that the effects of route optimisation, in the sense of average stage length of the fleet, are limited to airline technical efficiency. We show that airline size and key fleet mix characteristics, such as aircraft size and number of different aircraft families in the fleet, are more relevant to successful cost management of airlines since they have significant impacts on all three types of airline efficiency: technical, allocative and, ultimately, cost efficiency. Our results also show that despite the fuel saving benefits of younger aircraft, the age of an airline’s fleet has no significant impact on its technical efficiency, but does have a positive impact on its allocative and cost efficiency. 相似文献