欧洲的高速运输--列车方案的比较

近年来城市和干线的铁路运输得到复兴.在旅客运输中,高速列车为解决道路堵塞和空域拥挤,以及提高环保意识发挥了积极作用.在高速路网紧密相连的欧洲,这种高速列车具有特殊的运输政治意义,轨道高速运输(HGV)在国际上也显得越来越重要.文章对欧洲几种高速列车方案,即动力集中和动力分散动车组、单个车辆方案和铰接式列车、双层列车和加宽车辆列车以及ICE 3和磁悬浮列车进行了比较.     

A variational formulation of kinematic waves: Solution methods

This paper presents improved solution methods for kinematic wave traffic problems with concave flow-density relations. As explained in part I of this work, the solution of a kinematic wave problem is a set of continuum least-cost paths in space-time. The least cost to reach a point is the vehicle number. The idea here consists in overlaying a dense but discrete network with appropriate costs in the solution region and then using a shortest-path algorithm to estimate vehicle numbers. With properly designed networks, this procedure is more accurate than existing methods and can be applied to more complicated problems. In many important cases its results are exact.     

准连续电流型变压变流器及其新型ZVS结构

提出了一种优化变压器,它可将输入电压用整数因数2、3、4进行乘、除,具有很高的性能.逐步介绍了准连续电流型变压变流器,最后介绍了全双向零电压开关(ZVS)变流器.理论研究表明,只要降低变压器磁化电感的值便可实现ZVS工作.ZVS工作条件产生了有利的变流器控制方法,并提出了一种离散变频控制方法.变压器中允许有三角形电流使ZVS具有较高的电流有效值.对电流的估算进行了理论研究.实验结果显示其效率高于97.5%,并证实了理论研究的精确性.     

Numerical Model of a Tilting Body Railway Vehicle Compared With Rig and on Track Tests

The aim of the paper is to describe and verify a numerical model for the simulation of the dynamic behaviour of a tilting body railway vehicle, with particular attention to the curve negotiation conditions. In the model the dynamics of the tilting active control devices are reproduced, combining the numerical mechanical model of the vehicle with the control software used on the real vehicle. In order to validate the numerical simulation model, numerical results and experimental ones, from both a test rig and out-door tests, were compared.     

Combined effect of boost pressure and injection timing on the performance and combustion of CNG in a DI spark ignition engine

There is an increasing interest in supercharging spark ignition engines operating on CNG (compressed natural gas) mainly due to its superior knock resisting properties. However, there is a penalty in volumetric efficiency when directly injecting the gaseous fuel at early and partial injection timings. The present work reports the combined effects of a small boost pressure and injection timing on performance and combustion of CNG fueled DI (direct injection) engine. The experimental tests were carried out on a 4-stroke DI spark ignition engine with a compression ratio of 14. Early injection timing, when inlet valves are still open (at 300°BTDC), and partial injection timing, in which part of the injection occurs after the inlet valves are closed (at 180°BTDC), were varied at each operating speed with variation of the boost pressure from 2.5 to 10 kPa. A narrow angle injector (NAI) was used to increase the mixing rate at engine speeds between 2000 and 5000 rpm. Similar experiments were conducted on a naturally aspirated engine and the results were then compared with that of the boosting system to examine the combined effects of boost pressure and injection timing. It was observed that boost pressure above 7.5 kPa resulted in an improvement of performance and combustion of CNG DI engine at all operating speeds. This was manifested in the faster heat release rates and mass fraction burned that in turn improved combustion efficiency of the boosting system. An increased in cylinder pressure and temperature was also observed with boost pressure compared to naturally aspirated engine. Moreover, the combustion duration was reduced due to concentration of the heat release near to the top dead center as the result of the boost pressure. Supercharging was also found to reduce the penalty of volumetric efficiency at both the simulated port and partial injection timings.     

An analytical approximation for the macroscopic fundamental diagram of urban traffic

This paper shows that a macroscopic fundamental diagram (MFD) relating average flow and average density must exist on any street with blocks of diverse widths and lengths, but no turns, even if all or some of the intersections are controlled by arbitrarily timed traffic signals. The timing patterns are assumed to be fixed in time. Exact analytical expressions in terms of a shortest path recipe are given, both, for the street’s capacity and its MFD. Approximate formulas that require little data are also given.For networks, the paper derives an upper bound for average flow conditional on average density, and then suggests conditions under which the bound should be tight; i.e., under which the bound is an approximate MFD. The MFD’s produced with this method for the central business districts of San Francisco (California) and Yokohama (Japan) are compared with those obtained experimentally in earlier publications.     

An intersection control strategy for a short‐headway P.R.T. network

Much PRT development and research is currently being undertaken assuming quasi‐synchronous longitudinal control of guideway vehicles. This method of control has the characteristic that intersection performance has a substantial influence on the efficiency of trip demand processing. An algorithm for the control of a PRT intersection is discussed here, which would appear to have significant advantages over all other known existing stratagems. The stratagem is not only efficient but its flexibility facilitates tailoring to diverse local conditions; furthermore, the algorithm does not require intractable computations or excessive computer memory requirements. The algorithm is described and simulation results are presented. A comparative study is also made between this algorithm and its fore‐runner.     

Public law litigation and marine affairs: The boldt decision

Abstract

The management and conservation of the marine environment and its natural resources are increasingly understood to be issues of public policy with consequences for society at large. On a variety of dramatic occasions over the last decades, the federal judiciary has departed from its traditionally passive role in the shaping of social policy. This paper examines a critical marine controversy, the Boldt Decision (U.S. v. Washington 1974), to illustrate and evaluate nontraditional judicial behavior. The first two sections introduce Indian‐United States treaties concerning Pacific Northwest salmon resources, and the unfolding of the Boldt Decision. A third section argues that a “public law”; model of litigation fits the legal events of the Boldt Decision. A fourth section addresses the competence of the Boldt court as it is manifest in judicial organization, analysis, and implementation. A final section comments on the potential for public law litigation elsewhere in the governing of marine affairs.     

Interurban road network planning model with accessibility and robustness objectives

Abstract

Road network planning (or design) problems consist of determining the best investment decisions to be made with regard to the improvement of a road network. In this paper, we propose an optimization model for long-term interurban road network planning where accessibility and robustness objectives are simultaneously taken into account. Three network robustness measures were defined to assess different robustness concerns: network spare capacity; city evacuation capacity; and network vulnerability. The results that may be obtained from the application of the model are illustrated for three random networks. Special attention is given to the implications of adopting each one of the robustness measures upon the optimum solution provided by the model.     

Book reviews

R. S. Farrow, with J. M. Broadus, T. A. Grigalunas, P. Hoagland III, and J. J. Opaluch. 1990. Managing the Outer Continental Shelf Lands: Oceans of Controversy. New York: Taylor & Francis New York, 168 pp., paper.

Richard A. Kenchington. 1990. Managing Marine Environments. New York: Taylor & Francis, 248 pp.