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.     

Wheel/Rail Contact: Geometrical Study*

Before trying to ascertain the precise nature of the Wheel-Rail contact (internal stresses and strains, wear and friction, security against a derailment, dynamic behaviour of the vehicle, etc.) the geometrical problem must necessarily be solved. That is, for each position of the wheelset (this is defined by 6 parameters, of which only 4 are independent) the two dependent parameters and the coordinates of the points of contact of each wheel, and rail must be obtained. A new method is proposed of obtaining the spatial position of a wheelset with reference to the rails, from the most general point of view.     

Some evidence of transit demand elasticities

This paper draws together empirical evidence from a variety of sources about the magnitudes of transit price elasticities and cross-elasticities. A number of different practical measures of demand elasticity are first defined and some expectations about magnitude are discussed. Evidence is then collated from the analysis of transit operating statistics, from experience in demonstration projects and from attempts to develop cross-sectional models of demand and modal choice.In general, all of the limited evidence available suggests that transit demand is inelastic with respect to money price. Typically, ridership is significantly more sensitive to changes in the level of service (particularly door-to-door journey time) than to changes in fare, although service elasticities also are usually numerically less than unity.In broad terms, short-run direct fare elasticities are characteristically observed to lie within the range of -0.1 to –0.7. A more precise value in a particular instance will depend on a variety of factors in ways which largely support a priori notions. Thus in very large cities, central city areas, at peak hours, and in other circumstances where the prices of alternative modes are high, transit fare elasticities are usually numerically at the lower end of the range.Estimates of cross-elasticities (representing the volumes of transit traffic diverted to other modes by transit price increases) are much harder to come by, and in fact only a few very uncertain estimates are presented here.This paper is a condensation of an Urban Institute Working Paper of the same title (WP 708-52, November 1971). Opinions expressed are those of the author and do not necessarily represent the views of The Urban Institute or its sponsors.     

Control Behaviour of Motorcycle Riders

The control behaviour of motorcycle riders is studied by means of a simulation model for the ridermotorcycle system, which stresses the control actions of the riders. The rider model describes the major steering torque control as well as the rider's own body control actions. This simulation model is applied to a single lane change maneuver and the results of this simulation are compared with the experiments in order to examine its validity.     

The economic use of subsidies for urban mass transportation

The energy crisis and various urban problems stemming from auto congestion, pollution, and the cost of providing public highways have created enormous interest in revitalizing our urban mass transit systems. Currently much is being said and written regarding the efficacy of granting federal, state and/or local operating subsidies. In this article, the author reviews the transit industry's peak capacity problem, and questions the economic wisdom of providing operating subsidies, as some are now being provided, and how most will probably be administered in the near future. An alternative plan suggests the manner in which subsidies can eventually help the transit industry. The article concludes with an analysis of what research efforts are needed in many urban transit systems and how subsidies can be used to support such research.     

Shipping control and the changing use of marine space

In this paper Professor Couper discusses the divisions of marine space as set out in the Revised Single Negotiating Text of UNCLOS III in relation to maritime accidents. This is followed by a contribution by Mr Burger on statistical material related to the incidence of marine accidents in North-West European waters. The third section of the paper by Captain S. Abdelgalil, is devoted to a technical discussion on traffic lanes in confined waters.