A simulation‐based reliability assessment approach for congested transit network

This paper is an attempt to develop a generic simulation‐based approach to assess transit service reliability, taking into account interaction between network performance and passengers' route choice behaviour. Three types of reliability, say, system wide travel time reliability, schedule reliability and direct boarding waiting‐time reliability are defined from perspectives of the community or transit administration, the operator and passengers. A Monte Carlo simulation approach with a stochastic user equilibrium transit assignment model embedded is proposed to quantify these three reliability measures of transit service. A simple transit network with a bus rapid transit (BRT) corridor is analysed as a case study where the impacts of BRT components on transit service reliability are evaluated preliminarily.     

Is DOC the main source of organic matter remineralization in the ocean water column?

Recent interpretations of carbon flux data and deep-sea processes have led to a reconsideration of the role of dissolved organic carbon (DOC) in supporting water column remineralization and other mid-water biogeochemical transformations (Suzuki et al., 1985; Cho and Azam, 1988; Karl et al., 1988; Christensen et al., 1989; Naqvi and Shailaja, 1993). To date, there have been no direct comparisons of particulate carbon flux data with water column metabolic rates. Here, for the first time, particulate carbon flux and respiratory electron transport activity (from which metabolic CO₂ production is derived), have been monitored simultaneously for one year in the same area of the northwestern Mediterranean Sea. In the aphotic layer (200–1000 m), particulate organic carbon (POC) can support only 20% of the overall organic matter remineralization. Remineralization rates are consistent with recent calculations of DOC exported from the euphotic layer in this area, confirming the vital importance of DOC in maintaining deep-water metabolism. This finding would apply to other regions of mesotrophic and oligotrophic production and thus affect our understanding of carbon recycling in the water column, new production and O₂ utilization.     

Ecology of bottom ice algae: II. Dynamics, distributions and productivity

Spring blooms of bottom ice algae are a common feature of landfast congelation ice in polar regions. Because ice algae are usually associated with a substrate, their population dynamics can be followed with considerable confidence. Although ice algal dynamics are closely related to irradiance, their dynamics and distributions are influenced by other abiotic and biotic factors. Ice algal abundance varies horizontally over all scales examined. Factors such as grazing and nutrient availability may contribute to local and geographic differences. Loss terms for most sea ice assemblages are largely unquantified. Ice algal biomass is most concentrated near the ice-water interface in spring.Environmental factors affecting ice algal abundance and productivity are considered here, emphasizing recent results from several well-studied sites. Biomass accumulation, growth rates and productivity have been documented for spring blooms of bottom interstitial and sub-ice assemblages. On an areal basis biomass accumulation in bottom ice assemblages can be comparable with planktonic systems. At low ambient temperatures and irradiances average specific growth rates (≤ 0.25 d⁻¹) and production rates (≤ 1.0 mg C mg Chl⁻¹ h⁻¹) for ice algae are low. Current methods of measuring productivity are compared. Results are consistently low but variable with little systematic difference among them. At present, apparent differences in productivity between bottom ice assemblages in the Arctic and Antarctic, or among different antarctic assemblages, are so confounded by methodological and other sources of variability that no firm differences can be detected.     

关于河船冒雾航行的对策

船舶航行的安全问题一直是船舶驾驶员最关心的问题,它直接关系到国家的财产和人们的生命安全.船舶在内河航道行驶,由于受到雾、水深、航道窄、船舶密度大等因素的影响,发生船舶搁浅、碰撞等事故屡见不鲜.本文作者就内河船舶在有雾的情况下,驾驶员冒雾航行的原因及对策进行了分析和探讨.     

回风站进站信号显示升级的问题

2004年5月21日19点57分，朔黄线回风站上行Ⅱ道正线接车，上行进站信号机显示却由黄灯变为绿灯，接近区段向机车发送绿码，列车机外停车后引导接车。信号值班人员在控制台确认故障现象后，马上到信号机械室进行故障查找，发现SⅡ LXJF在错误吸起状态，致使上行进站信号机显示升级。     

Uncertainty in predictions of oil spill trajectories in a coastal zone

A method is introduced to determine the uncertainties in the predictions of oil spill trajectories using a classic oil spill model. The method considers the output of the oil spill model as a function of random variables, which are the input parameters, and calculates the standard deviation of the output results which provides a measure of the uncertainty of the model as a result of the uncertainties of the input parameters.In addition to a single trajectory that is calculated by the oil spill model using the mean values of the parameters, a band of trajectories can be defined when various simulations are done taking into account the uncertainties of the input parameters. This band of trajectories defines envelopes of the trajectories that are likely to be followed by the spill given the uncertainties of the input.The method was applied to an oil spill that occurred in 1989 near Sines in the southwestern coast of Portugal. This model represented well the distinction between a wind driven part that remained offshore, and a tide driven part that went ashore. For both parts, the method defined two trajectory envelopes, one calculated exclusively with the wind fields, and the other using wind and tidal currents. In both cases reasonable approximation to the observed results was obtained.The envelope of likely trajectories that is obtained with the uncertainty modelling proved to give a better interpretation of the trajectories that were simulated by the oil spill model.     

NJ2型内燃机车简介

介绍了从美国GE公司进口的NJ2型交流传动内燃机车的特点和所采用的先进技术。主要包括,先进的车载微机控制系统、强化程度较高和控制良好的电子喷射柴油机、新式的电子空气制动系统、单轴交流电传动装置,和一些功能很强的辅助设备等。     

科隆-莱茵/美因高速铁路新线试运行 --另一角度论系统工程的挑战与成就

只有采用新一代列车才能实现科隆-莱茵/美因新建高速铁路线上科隆至法兰克福两大都市间运行时间缩短1/2的商业目标.而要实现这一商业目标,并且要与环境协调,唯一途径是选择紧靠既有"A3"高速公路的线路.由此提出的列车、轨道、指挥与控制系统工程项目,以及投入运用与审批程序,均对新线的开发与整个系统工程的完成构成了一大挑战.