African shippers' organizations: the Ghanaian experience

This paper looks at how the Shippers‘ Council could operate to make shipping cost-effective and to play its role as a servant of trade—a servant of the shippers. It looks at the key problems that confront the shipper requiring intervention by a Shippers‘ Council and surveys how the organization of the Shippers’ Council effectively handles problems. The final sections draw conclusions which could contribute to increasing the efficiency of Shippers' Councils, as well as improving the understanding of the Councils as managers of the demand side of shipping.     

The measure of all things: reflections on changing conceptions of the individual in travel demand modeling

Transportation demand modeling has evolved in scope, theory, and practice in the many decades since the US Bureau of Public Roads pioneered home interview transportation studies in metropolitan households in the early 1940s. The major currents of these developments are discussed in the present paper through consideration of the changing role of the individual—as a source of data, as a unit of analysis, and as the intended beneficiary. In addition to reviewing this history we raise, but are unable to resolve, a growing current concern, namely how the public interest can be best served when the transportation data of greatest value is collected by private entities.     

The crisis for transportation planning modelling

The paper considers the performance of land‐use transportation study techniques over the past ten years. Although primarily viewed from a U.K. perspective the paper reviews matters of principle which are of international relevance. The changing context and tasks for modelling are reviewed and the current role and applications of such models considered. The capability of established models to meet these changing requirements is examined. Attention is drawn to model specification and the ability of models both to represent new policies and to predict traveller responses to them. Also relevant is the ‘behavioural’ theme and the way in which survey technique conditions the data obtained.

Particular emphasis is placed on the accuracy of modelling, both in the representation of base year travel patterns and in the forecast mode. The inherent uncertainty concerning input data is discussed and the frequent failures to establish model validity are noted.

Three crises for U.K. transportation planning practice are identified: the ageing of data bases, the accuracy and validity of models and the current changes to the institutional context of transport planning in the U.K. Some potential remedies for the first two difficulties are proposed. It is concluded that only the last ‘crisis’ represents a real threat to the application of rational methods in transportation planning.     

Linking mercury exposure to habitat and feeding behaviour in Beaufort Sea beluga whales

Mercury (Hg) levels in the Beaufort Sea beluga population have been increasing since the 1990's. Ultimately, it is the Hg content of prey that determines beluga Hg levels. However, the Beaufort Sea beluga diet is not understood, and little is known about the diet Hg sources in their summer habitat. During the summer, they segregate into social groups based on habitat use leading to the hypothesis that they may feed in different food webs explaining Hg dietary sources. Methyl mercury (MeHg) and total mercury (THg) levels were measured in the estuarine-shelf, Amundsen Gulf and epibenthic food webs in the western Canadian Arctic collected during the Canadian Arctic Shelf Exchange Study (CASES) to assess their dietary Hg contribution. To our knowledge, this is the first study to report MeHg levels in estuarine fish and epibenthic invertebrates from the Arctic Ocean. Although the Mackenzie River is a large source of Hg, the estuarine-shelf prey items had the lowest MeHg levels, ranging from 0.1 to 0.27 μg/g dry weight (dw) in arctic cisco (Coregonus autumnalis) and saffron cod (Eleginus gracilis) respectively. Highest MeHg levels occurred in fourhorn sculpin (Myoxocephalus quadricornis) (0.5 μg/g dw) from the epibenthic food web. Beluga hypothesized to feed in the epibenthic and Amundsen Gulf food webs had the highest Hg levels matching with high Hg levels in associated food webs, and estuarine-shelf belugas had the lowest Hg levels (2.6 μg/g dw), corresponding with the low food web Hg levels, supporting the variation in dietary Hg uptake. The trophic level transfer of Hg was similar among the food webs, highlighting the importance of Hg sources at the bottom of the food web as well as food web length. We propose that future biomagnification studies incorporate predator behaviour with food web structure to assist in the evaluation of dietary Hg sources.     

The competitiveness of short sea shipping in multimodal logistics supply chains: service attributes

In Europe, ports are confronted with a closer integration in the maritime and shipping industries. The co-operation agreements can take several forms such as alliances and mergers among shipping lines, conferences, involvement of shipping companies in terminal management, and extending interests in inland transport of shipping companies. In this paper we give a brief overview of these different types of agreement and we examine the consequences of this evolution of the market structures in which ports and shipping companies have to operate. More specifically, attention goes to the competitive position of the port in this new environment. It is clear that the role of the port and the port authorities has to be redefined to guarantee that it remains a fully fledged player in this fast evolving integrated market.     

Priority Berthing For Congested Ports: rationale and a model

Adverse effects on a national economy of port congestion are identified. The rationale underlying a system of priority berthing for awaiting vessels is described and contrasted with the operational system of first‐come, first‐served. A system of priority berthing is capable of minimizing the generalized social cost of congestion and this is structured mathematically as a multi‐attribute, decision‐making problem. A worked example is outlined and a computer program described.     

Book reviews

Road haulage licensing and EC Transport Policy. By K. J. Button. (Aldershot: Gower Publishing Co., 1984.) [Pp.127.] £14.50.

Bicycles and Public Transportation: New Links to Suburban Transit Markets. By Michael A. Replogle. (Bicycle Federation, Washington DC, 1983.) [Pp. 171.] US$15.95.

Urban Transport in ASEAN. By V. Setty Pendakur. (Institute of Southeast Asian Studies — Research Notes and Discussions Papers Series No. 43, 1984.) [Pp. 65] $4.50 ISBN 9971–902–67–2.

The World Railway System. By Bernard de Fontgalland (Cambridge Univerisity Press, 1984.) [Pp. 209.] £16.00.     

机车的直接传动

长期以来,设计人员希望能简化电力机车动车的传动装置,尤其是希望去掉传动齿轮.为此对直接传动作了许多研究试验.牵引电动机去掉传动齿轮,必须按传动比发挥相应大的转矩.转矩大小对电机的体积有着决定性的影响.所以不是所有类型的电机都适用于直接传动.文章在永磁同步电机的基础上研究了全弹性悬挂和非弹性悬挂的机车直接传动.     

Influence of injection parameters on the transition from PCCI combustion to diffusion combustion in a small-bore HSDI diesel engine

In this paper, the influence of injection parameters on the transition from Premixed Charge Combustion Ignition (PCCI) combustion to conventional diesel combustion was investigated in an optically accessible High-Speed Direct-Injection (HSDI) diesel engine using multiple injection strategies. The heat release characteristics were analyzed using incylinder pressure for different operating conditions. The whole cycle combustion process was visualized with a high-speed video camera by simultaneously capturing the natural flame luminosity from both the bottom of the optical piston and the side window, showing the three dimensional combustion structure within the combustion chamber. Eight operating conditions were selected to address the influences of injection pressure, injection timing, and fuel quantity of the first injection on the development of second injection combustion. For some cases with early first injection timing and a small fuel quantity, no liquid fuel is found when luminous flame points appear, which shows that premixed combustion occurs for these cases. However, with the increase of first injection fuel quantity and retardation of the first injection timing, the combustion mode transitions from PCCI combustion to diffusion flame combustion, with liquid fuel being injected into the hot flame. The observed combustion phenomena are mainly determined by the ambient temperature and pressure at the start of the second injection event. The start-of-injection ambient conditions are greatly influenced by the first injection timing, fuel quantity, and injection pressure. Small fuel quantity and early injection timing of the first injection event and high injection pressure are preferable for low sooting combustion.     

Analysis of a Passive Sequential Hydraulic Damper for Vehicle Suspension

Vibration isolation characteristics of a sequential hydraulic damper, employing external pressure relief valves, are investigated via analytical means. The sequential hydraulic damper is modelled as a nonlinear dynamical system incorporating nonlinearities due to orifice flows, gas spring and pressure relief mechanisms. The damping characteristics of the sequential hydraulic damper, are compared to those of a constant orifice and a semi-active sequential damper, and discussed in view of their vibration isolation performance. It is established that the performance characteristics of the sequential hydraulic damper are similar to that of a semi-active sequential damper. A tuning methodology to achieve appropriate control of the resonant peak and effective vibration isolation is proposed. The shock and vibration isolation performance of the vehicle model employing a sequential damper are evaluated and compared to those of the vehicle model employing a constant orifice hydraulic damper. It is concluded that the vehicle ride performance can be improved considerably using an adequately tuned sequential damper.