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261.
S. G. Sturmey 《Maritime Policy and Management》1991,18(4):263-282
The object of my book British Shipping and World Competitionwas to answer the question: 'Why has the tonnage of ships registered in the United Kingdom declined from over 45% of the world total in 1900 to about 16% of that total in 1960?'. There was never any normative element to this question, a point which has been much misunderstood. In answering the question, two different methodologies were used. Chapters II through VIII are industrial economic history, whereas Chapters IX through XIV are applied economics. When the two groups are thought of as siblings, not as Siamese twins, it can be seen that the first group has worn rather well, but that the applied economics chapters have a distinctly dated air. Most of this article is concerned with the applied economics chapters, where I try to examine what is said in the book in the light of my subsequent experience and thinking. There is one absolutely gross error in the material. Unfortunately, this is implicitly reflected in the Code of Conduct and in the EC Maritime Regulations. The original answer to the question has been rephrased in the article; I hope this will put to rest the idea that the question was normative in intent. The rephrasing does not alter the answer: the decline which needed to be accounted for can be explained solely in terms of internal constraints. The remainder was a 'natural' result of changing international patterns in resource allocation. 相似文献
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263.
Paul S. FANCHER 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1985,14(4):201-227
This review of the state of the art emphasizes recent results that have been obtained in extending conventionalanalysis techniques to the treatment of “Highway Trains”, that is, to heavy trucks that have multiple articulation points and employ suspensions with multiple axles. Equations of motion applicable to the equilibrium turning performances of articulated vehicles are examined with respect to using analysis techniques involving steering gains, understeer gradients, effective wheel-bases, handling diagrams, and critical speeds. These examinations provide the basis for in sights into simplified approaches for understanding the steady turning mechanics of articulated, multi-axle vehicles riding on pneumatic tires. 相似文献
264.
S. Farrell 《Maritime Policy and Management》1986,13(4):277-290
In the long debate about the UNCTAD Code, many opinions have been put forward about the consequences of cargo reservation. Some have been based on theory, whilist others have transposed behaviour patterns from other industries or other periods of time. Several countries, however, have been operating cargo reservation laws for sufficiently long to enable some initial observations to be made. This article outlines recent experience in Brazil. 相似文献
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266.
The structure and dynamics of the benthic invertebrate megafauna of the Southeastern Brazilian shelf were studied over a 2-year period. Two regions presenting different oceanographic conditions, Ubatuba-SP and Cabo Frio-RJ were compared in terms of biomass, density of organisms and species richness. Two to three 30-min tows were undertaken at each of the stations, located at 40 and 100 m isobath, in a normal transect offshore of both regions. Faunal distributional patterns correlated with water mass dynamics, depth and sediment parameters. In the Cabo Frio region, subjected to a Ekman-driven seasonal coastal upwelling, the impact of the South Atlantic Central Water (SACW) on the inner shelf leads to a change in the benthic communities, with a high dominance of top carnivores such as the crab Portunus spinicarpus and the sea-star Astropecten brasiliensis, which accounted for the larger part of the total biomass. Distinct species associations were found in each of the two regions and the total biomass at Cabo Frio inner shelf was almost twice that of Ubatuba during the 2002 summer, when a marked upwelling was verified. The relationship between megabenthic biomass and input of organic matter to the sea floor during upwelling events is discussed. 相似文献
267.
It has been proposed that grade A should be replaced with a tougher steel for ship construction. This recommendation is not supported by casualty statistics. Brittle fractures have decreased from once every 10 ship years at the time of the Liberty ships, to once every 100 ship years in the 1950s, and now stand at around once every 10,000 ship years. The authors have developed a probabilistic fracture mechanics approach indexed to the Charpy 27 Joule temperature, T27J. This is used here to analyse the Liberty ship failures. Comparison with a databank of T27J values for grade A steel spanning 1920 to 1995 suggests that the Liberty ship steel was unusually brittle. The probability analysis shows good agreement between predicted and observed fracture casualty rates for the Liberty ships and helps explain why brittle fractures are now uncommon in grade A steel ships. 相似文献
268.
Grade information may be needed for route surveys and is important when fuel consumption is studied. An instrumented car was used to measure acceleration along the road surface by double differentiating accumulated pulses generated off the drive train. A second acceleration measure included the component due to gravity relative to the car body. The difference between these acceleration measures contains grade information but it also influenced by suspension dynamics and pitch of the car body. The effect of suspension dynamics was removed by filtering which limited the minimum wavelength to 160 m. The effect of pitch was removed by a correction based on acceleration, jerk and the square of vehicle speed. The correction was computed from data collected on a level airfield runaway. The method is verified for a high capacity arterial road. Grade is measured to within 0.001 rad (95% confidence limits). Elevation derived from the grade data was consistent with road construction drawings to the same limits. 相似文献
269.
The paper reviews the current situation on-board microprocessor applications. It first describes the aspects of vehicle technology and performance that are the focus for on-board computing equipment, from engine management systems through to fully intergrated driver decision support. In the second section a wider perspective is taken by examining the interaction of the vehicle and its environment. The third and final section of the paper considers elements of communication which permit extensive transmission of vehicle and journey data for public and private use. The conclusion identifies factors which will influence the speed with which further applications will be adopted. 相似文献
270.
何春 《变流技术与电力牵引》2006,(1):12-17
所有由接地的电网系统供电并向可变输出系统供电的开关变流器拓扑结构,都会在负载装置上产生共模电压.系统地分析了用在交流传动装置上的各种变流器拓扑结构的共模电压,包括两点式电压源逆变器(VSI)、电流源逆变器(CSI)以及多点式逆变器.还分析了每种拓扑结构中使用的有源前端整流器.分析了共模电压的来源,并比较了由不同变流器拓扑结构产生的共模电压幅值.讨论了共模电压和降低共模电压技术的实际意义,并提供仿真和试验结果加以证明. 相似文献