俄罗斯铁道车辆制冷设备的

目前对压缩式制冷设备使用的破坏臭氧层的R12类制冷剂已限期停止使用.R12的代用品都有一定的缺陷.本文介绍一种比较理想的新型制冷剂,既避免了代用品的缺陷,又具有省电的功能,现已成功地应用于铁路机械冷藏车和客车空调上.     

Tackling traffic congestion in Accra,Ghana: A road user's perspective

A fast emerging component of the urban transportation problem in cities of the Third World is the problem of traffic congestion. Rapid increases in car ownership coupled with poor land use planning, inadequate road space, lack of regulated parking systems, uneducated use of the road by pedestrians, and bad driving behavior of motorists have all combined to produce congestions comparable to those experienced in cities in the advanced parts of the world. Traffic management measures have been tried in some of the major cities such as road expansion and redistribution of land uses in city centers, but most have produced minimal results. It is recommended in this paper that city authorities adopt an integrated approach to congestion with emphasis on influencing the behavior of the road users.     

A computer model for finding the time-dependent minimum path in a transit system with fixed schedules

This paper describes the development of a computer model and algorithms for finding the time-dependent minimum path between two stations in a multi-route, multi-mode transit system running to fixed schedules. Selection of the minimum path can be based either on journey time or on weighted time. A worked example using a simple transit network is given to illustrate how the model works. The model has several applications in transport planning: it can be used for generating route schedule information to guide transit users, for assisting in route schedule coordination, and for analyzing transit system accessibility.     

A model for the evaluation of some shipping company decisions

This paper describes a model which may be used in the evaluation of the relative effectiveness of policies used in the areas of ship chartering and the switching of combined carriers between the dry-cargo market and the tanker market. The policies for chartering and market switiching are expressed in the form of 'desired proportions' of the fleet operating in a particular charter-mode or a particular market. Graphical illustration of this form of expression of policies can be easily understood, so that alternative policies can be designed with relative case. The effectiveness of a particular from of policy under various freight market conditions can be determined from the model, the use of which is illustrated by its application to the deployment of the fleet of an hypothetical shipping company. It is assumed that the feedback connection between the company's actions and the market-place is negligible.     

An analysis of seasonality of non-OPEC supply

The purpose of this study is first to find out whether quarterly averages of non-OPEC (Organization of the Petroleum Exporting Countries) supply follow a seasonal pattern. If that is mathematically established, then, second, it is attempted to estimate the best seasonal factors to decompose the forecast yearly average into quarterly averages. A set of historical data consisting of quarterly supply averages of individual countries, regional subtotals and the aggregate non-OPEC supply for the period 1973-2002 forms the basis of the analysis. The study applies Fourier analysis to quarterly supply series to test for seasonality, and provides estimates of seasonal factors for the years 2000-2002 by applying the so-called X-11 decomposition method to the historical annual averages. The accuracy of the results of the application of X-11 is then tested. It is demonstrated that the combination of the Fourier and X-11 methods provides mostly acceptable and in some cases, such as that of China, impressively accurate forecast quarterly supply averages.     

低同步串级调速系统转差功率反馈方式的研究

绕线式异步电机转差功率反馈到电网进行调速的方法已在许多工业部门得到广泛应用,但由于调速过程中转子电势将低于电网电压,因而这种调速方式需要在电网与逆变器之间接入一个升压变压器。本文提出了一种省去升压变压器和直接将转差功率反馈到定子绕组的新的串级调速方法。文中对定子绕组反馈点的选择、等效电路数模及主要参数作了分析,并在一台改制的绕线式异步电机上作了试验,结果表明这种调速方法除经济简便外,仍具有优良的调速性能。     

What are we going to do about public transportation?

Traffic congestion in the world's metropolitan areas is going from bad to worse. Urban/suburban transportation has become like the weather; people talk a lot about it but shrug it away as something they can't do much about. This is a world-wide phenomenon, as motor vehicle use grows, and as urban sprawl continues.     

A note on using Davidson's function in equilibrium assignment

This paper describes the use of the Davidson congestion function in modelling network flows using equilibrium assignment. A modification to the function is given, which defines the function over all flows values, and consequently removes computational difficulties noted in earlier studies. The modification requires the inclusion of an additional model parameter, and the selection of a suitable value for this parameter is studied for two sets of data. The modified Davidson function is also compared to two alternative functions; a step-wise linear function and a quartic polynomial function, which have both been proposed as congestion functions. Comparisons are made between observed link volumes and the assigned volumes from these models. It is concluded that the modified Davidson function is useful for inclusion in an equilibrium assignment model, given its ability to reflect differences in network link type (e.g. capacity and speed) and environment through its parameters, the conceptual advantage of the function through its derivation from queueing theory, and the previous discovery of reliable methods for estimating its parameters. A value of about 0.8–0.9 is suggested for the parameter (μ, 0 < μ < 1) introduced in the modification.