A Comparison of Various Computer Simulation Models for Predicting the Directional Responses of Articulated Vehicles

This paper presents the results of a comparative study of the predictions, made using computer simulation models of different levels of complexity, of the directional responses of commercial articulated vehicles in steady-state and lane-change maneuvers. The differences in the predictions obtained using various models are examined and are compared with available experimental data. The objective of this study is to compare the capabilities and limitations of various simulation models for predicting the directional behavior of articulated vehicles.     

Privatization of urban transit: The Los Angeles jitney experience

This paper reports on a recent attempt to provide private transit in the form of jitney service in downtown Los Angeles. It describes the process undertaken to initiate jitney service and the resultant organization's structure and operation. A survey of jitney passengers provided information on the users and their tripmaking characteristics. A group of loyal jitney riders emerged who patronized the service because of its lower travel times and more personalized atmosphere. This group formed the core of frequent users. The Los Angeles experience is analyzed in terms of the economic feasibility of jitney service and the impact on the financial status of public transit. The public transit agency experienced a slight negative financial impact as a result of the jitney service. Ridership during peak hours declined somewhat but the jitney service was not frequent enough to carry sufficient passengers to allow the transit agency to cut costly peak hour service. This analysis shows that the jitney service ultimately was not an economically successful operation. The factors which would have increased the likelihood of success were increased frequency of service and higher fares, which would have been sustainable if not for unexpected developments in public transit financing. A labor pool willing to work for low wages, high transit use in the central city, relatively high transit fares and the availability of inexpensive vehicles appear to be prerequisites to a successful urban jitney operation.     

Management of coastal eutrophication: Integration of field data, ecosystem-scale simulations and screening models

A hybrid approach for eutrophication assessment in estuarine and coastal ecosystems is presented. The ASSETS screening model (http://www.eutro.org) classifies eutrophication status into five classes: High (better), Good, Moderate, Poor and Bad (worse). This model was applied to a dataset from a shallow coastal barrier island system in southwest Europe (Ria Formosa), with a resulting score of Good. A detailed dynamic model was developed for this ecosystem, and the outputs were used to drive the screening model. Four scenarios were run on the research model: pristine, standard (simulates present loading), half and double the current nutrient loading. The Ria Formosa has a short water residence time and eutrophication symptoms are not apparent in the water column. However, benthic symptoms are expressed as excessive macroalgal growth and strong dissolved oxygen fluctuations in the tide pools. The standard simulation results showed an ASSETS grade identical to the field data application. The application of the screening model to the other scenario outputs showed the responsiveness of ASSETS to changes in pressure, state and response, scoring a grade of High under pristine conditions, Good for half the standard scenario and Moderate for double the present loadings. The use of this hybrid approach allows managers to test the outcome of measures against a set of well-defined metrics for the evaluation of state. It additionally provides a way of testing and improving the pressure component of ASSETS. Sensitivity analysis revealed that sub-sampling the output of the research model at a monthly scale, typical for the acquisition of field data, may significantly affect the outcome of the screening model, by overlooking extreme events such as occasional night-time anoxia in tide pools.     

A game-theoretic analysis of competition among container port hubs: the case of Busan and Shanghai 1

Countries throughout the world, and especially within Asia, are investing heavily in container port infrastructure in the hopes of capturing a larger share of global shipping activity for their economies. Many existing ports are emphasizing developing the capacity to serve as a hub port, building deepwater berths with large terminals to facilitate transfer of containers from feeder ships to mother ships for intercontinental transport. We develop a game-theoretic best response framework for understanding how competitor ports will respond to development at a focus port, and whether the focus port will be able to capture or defend market share by building additional capacity. We apply this model to investment and competition currently occurring between the ports of Busan and Shanghai.     

盾构隧道管片结构纵向错台研究

盾构隧道通缝拼装管片结构的错台一直是困扰盾构隧道施工的技术问题，且由错台引起的管片开裂、拼装困难和防水隐患等问题对施工和运营的影响日益凸显，并直接影响到工程质量。以上海轨道交通二号线西延伸段盾构隧道工程为背景，采用现场监测和数值计算方法对盾构推进过程中管片错台进行分析，获得了管片结构错台发生及发展的变化规律。进一步探讨了盾构千斤顶的顶力对错台大小及发展规律的影响，为盾构施工中减小错台，提高施工精度和质量，以及盾构隧道设计施工提供依据。     

Analysis of the capabilities of a two-stage turbocharging system to fulfil the US2007 anti-pollution directive for heavy duty diesel engines

This article presents a two-stage turbocharged heavy-duty diesel (HDD) engine designed to fulfil the US2007 anti-pollution directive. This directive imposes very restrictive limits on the NOx and particle emissions of HDD engines. In this work, the possibility of combining particle traps in the exhaust line to reduce soot emissions with very high EGR rates to reduce NOx emissions is considered. This new generation engine implements two-stage turbocharging in order to improve the bsfc when the engine is working on steady conditions as well as to optimize the engine transient response. After carrying out the tests, the results were analyzed and the engine settings were adjusted to maximise its behaviour and minimise pollutant emissions. NOx and soot emission peaks were also analyzed at engine transient conditions in order to keep them under certain levels, and thus maintain the overall pollutant emissions to a level that is as low as possible. In summary, a double-stage turbocharging configuration can greatly improve engine driveability (between 23% and 36% depending on engine speed), while reducing NOx emissions during transient evolution without increasing opacity peaks beyond the stated limits.     

Méthode de validation formelle d’un poste d’aiguillage informatique

In this article, we discuss on how to solve the following problems: the checks and tests before putting the safety facilities into service, and the results of these tests which are essential, time consuming and may show great variations among each other. Economic constraints and the increasing complexity associated with the development of computerized tools tend to limit the capacity of the classic approval process. In practice, a reduction of the test cover rate is observed. The method presented in this article makes it possible to formally validate the new computerized mechanisms of the existing French interlocking systems with real-time functional interpreted Petri nets. The aim of our project was to provide SNCF with an operating method for the formal validation of interlocking systems. A formal proof method by assertion, applicable to our interlocking system, which covers equally the specification and its real software implementation, is presented in this article. With the proposed method and its associated tools, we completely verify that the system follows all safety procedures at all times and does not show superfluous conditions. This replaces all plateform tests checks. It is included in the existing testing procedures. The advantages of using this method are the following: a significant reduction of testing time and of the related costs, an increase of the test coverage rate (determinisitic safety vs. probabilistic safety), and an answer to the new demand of railway infrastructure maintenance engineering to modify and validate computerized interlocking systems. The mastery of formal methods by infrastructure engineers is surely a key to prove that additional safety is not expensive.     

Hydrographic conditions affecting two fishing grounds of Mallorca island (Western Mediterranean): during the IDEA Project (2003–2004)

This paper describes the hydrographic conditions observed during six surveys carried out during 2003 and 2004, in the framework of the “IDEA Project” (acronym for “Influence of oceanographic structure and dynamics on demersal populations in waters of the Balearic Islands”). The surveys were developed on the shelf and slope of Mallorca Island, in particular in two fishing grounds at the north and south of the Mallorca channel. Periodic movements of the fishing fleet between these two areas have been regularly reported, suggesting a seasonal variability of the resources which could be in turn associated with the hydrodynamic variability. With this motivation, water masses affecting these grounds have been identified and their seasonal variability has been studied. Different oceanographic and environmental conditions have been found between the two fishing grounds. These differences are related to the presence of mesoscale structures, associated with the Western Mediterranean Intermediate Water (WIW) at the north of the Ibiza channel and big gyres detached from the Algerian Current. The former has been shown to have influence on the regional oceanic circulation and the latter could affect the progress of fresh Atlantic Water (AW) towards the channels and make possible the presence of high salinity values at intermediate waters at the south of Mallorca Island. Historical data from other oceanographic cruises carried out in the region are finally used to discuss the interannual variability of these mesoscale structures.     

转K1型转向架组装工艺

介绍了转K1型转向架的结构特点和关键技术参数,着重分析了侧架导框的加工、侧架与支撑座板的组焊和转向架的组装工艺等。