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排序方式: 共有1243条查询结果,搜索用时 450 毫秒
991.
胡文华 《华东交通大学学报》2007,24(4):67-70
介绍了一类由开关放大电路与线性放大电路复合而成的电压跟随器型电源,分析其构成原理,拓扑结构.理论分析、仿真和实验结果表明它具有高效与优波兼顾的特性,以及适应多类负载(含非线性负载)和抗负载扰动的能力. 相似文献
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根据某电动汽车的计算参数,文章在理论研究的基础上,对驱动电机、动力电池、传动系统和轮胎进行了参数匹配。基于AVL Cruise建立了整车性能仿真模型,继而对该款电动汽车整车进行了动力性和经济性模拟仿真分析。通过仿真验证了该款汽车动力性指标和经济性指标均符合要求,且验证了其动力系统理论匹配和经济性分析方法的合理性。 相似文献
995.
预制拼装技术是水务结构施工工艺的重要发展趋势,接缝处理是当前预制拼装技术的关键技术难点。超高性能混凝土(UHPC)具有强度高、韧性大、耐久性好等技术优势,成为解决预制拼装结构接缝连接的有效途径。考虑到该技术在水务工程领域应用相对较少,根据实际工程开展了相关的研究。首先,针对UHPC湿接缝在排水结构的适用性问题、临时支撑的快速周转、高温与低温施工等难点进行了分析研究,通过全尺寸UHPC浇筑工艺试验,对施工参数进行了探索,并提出了高温与低温条件下浇筑策略。研究保证了UHPC湿接缝浇筑施工的顺利进行,有效提高了预制拼装施工效率,提升了湿接缝浇筑质量。 相似文献
996.
In this paper, we use continuous urban structure instead of zonal model, try to calculate unbiased excess commuting with joint distribution of homes and workplaces developed by Vaughan (1974), and describe the relationship between urban structure and commuting distance explicitly and theoretically for generalized home-workplace assignment pattern. We simplify the quadrivariate distribution model to a model with three important parameters: the spread of homes, the spread of workplaces, and the spatial correlation of homes and workplaces. Then we show that excess commuting and capacity utilization are expressed by the imbalance and the spatial correlation of jobs-housing structure in a theoretical context, moreover it explicitly evaluates targeting US and Japanese/Korean cities. 相似文献
997.
Matthew G. Karlaftis Dimitrios Tsamboulas 《Transportation Research Part A: Policy and Practice》2012,46(2):392-402
The need to measure transit system performance along with its various dimensions such as efficiency and effectiveness has led to the development of a wide array of approaches and vast literature. However, depending upon the specific approach used to examine performance, different conclusions are oftentimes reached. Using data from 15 European transit systems for a ten year time period (1990-2000), this paper discusses three important transit performance questions; (i) Do different efficiency assessment methodologies produce similar results? (ii) How are the two basic dimensions of transit performance, namely efficiency and effectiveness, related? and (iii) Are findings regarding organizational regimes (public operations, contracting and so on) sensitive to the methodological specifications employed? Results clearly indicate that efficiency scores and associated recommendations are sensitive to the models used, while efficiency and effectiveness are - albeit weakly - negatively related; these two findings can have far reaching policy implications. 相似文献
998.
Christophe Rizet Michael BrowneEric Cornelis Jacques Leonardi 《Transportation Research Part D: Transport and Environment》2012,17(4):293-300
This article compares the energy consumption and CO2 emissions of supply chains in Belgium, France and UK looking in particular at, jeans, yogurts, apples, tomatoes and furniture. We use a generic methodology that allows comparability across the supply chain of products, supply chains, and countries. Our benchmarking show relatively high emissions for maritime transport and the consumer leg, while logistics activities such as storage and road freight exhibit relatively low emissions. The influences of distance, retail type, area density and consumer behaviour are also examined. 相似文献
999.
There is a drive towards delivering and operating public infrastructure through public–private partnership (PPP) rather than traditional public procurement. The assessment of the value for money achieved by the two alternative approaches rests in the cost of financing and their efficiency in delivery and operation. This paper focuses on the cost of financing, in particular the cost associated with transferring risk from the public to private sphere. If capital markets were efficient and complete, the cost of public (government) and private financing should be the same, with the relative delivery and operational efficiency remaining as the primary determinant of value-for-money. Evidence suggests, however, that the risk transfer to a PPP entails an inefficient risk pricing premium which goes beyond the direct cost of financing. We argue that a high price for PPPs results from large risk transfers, risk treatment within the private sector, and uncertainty around the past and future performance of public–private consortia. The corollary is that the efficiency gains from a PPP must be much higher than commonly expected to deliver a greater value for the money than under a traditional approach. 相似文献
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