具有惯性表面的两层流体的柯西-泊松问题(英文)

This paper is concerned with the generation of waves due to initial disturbances at the upper surface of a two-layer fluid, as the upper layer is covered by an inertial surface and the lower layer extends infinitely downwards. The inertial surface is composed of thin but uniform distribution of non-interacting material. In the mathematical analysis, the Fourier and Laplace transform techniques have been utilized to obtain the depressions of the inertial surface and the interface in the form of infinite integrals. For initial disturbances concentrated at a point, the inertial surface depression and the interface depression are evaluated asymptotically for large time and distance by using the method of stationary phase. They are also depicted graphically for two types of initial disturbances and appropriate conclusions are made.     

Regulation,trust and contractual incentives around transport contracts – Is there anything bus operators can learn from public air service contracts?

This paper compares recent experiences in contract negotiation and subsequent commitment in public air services with the bus industry. The heart of the paper is a survey of European and Australian regional airlines, which we mirror with revealed experiences of bus operators. We aim to identify a number of elements in the contracting regimes that have exposed ambiguity and significant gaps in what the principal (e.g., transport department) expected, and what the agent (airline or bus operator) believed they were obliged to deliver. Ultimately airline and bus services are similar in that public authorities procure transport services that are desirable for the society but would be unprofitable without government involvement. In both sectors (theoretically fairly similar) public transport contracts are used, and those usually include obligations and performance measurements. In terms of similarities, one of the surveyed contract details that had a perceived high clarity in both industries was “payment procedures” and amongst those with rather poor clarity was also in both industries “incentives to improve performance and grow patronage”. We also show differences between regional air services and bus operations with regard to performance measurement and pre-specified obligations. Because of the strong safety culture around air services we find that regulation and trusting partnerships are even more important to aviation than to the bus sector. Because of the high level of trust but also because of simpler and more complete contracts in aviation, there is much less (re-)negotiation going on compared to the bus operations.     

Towards a simplified performance-linked value for money model as a reference point for bus contract payments

The burgeoning commitment to contracting the delivery of bus services through competitive tendering or negotiated performance-based contracts has been accompanied by as many contract payments schemes as there are contracts. We are now well placed to design a simplified performance-linked payment (SPLP) model that can be used as a reference point to ensure value for money, given the accumulation of experiences throughout the world which have revealed substantive common elements in contracts. Whether the payment to the operator is framed as a payment per passenger or as a payment per service kilometre, the SPLP identifies efficient subsidy outcomes that are linked to a proxy indicator of net social benefit per dollar of subsidy. We illustrate how the SPLP model can be applied to obtain the gross (subsidy) cost per passenger (or per passenger km) from measures of gross cost efficiency and network effectiveness. This model can then be used as part of a benchmarking activity to identify reference value of money prospects in respect of passengers per $ subsidy outlay by adjusting for influences not under the control of the service provider. A single framework to identify contract payments to operators, and to assess (i.e., benchmark) operator performance on critical KPIs, is provided by internalising critical key performance indicators (KPIs) in the design of the SPLP. The proposed SPLP model is sufficiently general to be independent of the procurement method (competitive tendered or negotiated, for example) and of the treatment of revenue allocation (net or gross based contracts), with the additional advantage of being able to assess value for money for government.     

The Myth of Travel Time Saving

Abstract

The idea that the main benefit of improvements to transport infrastructure is the saving of travel time has been central to transport economic analysis. There is, however, little empirical evidence to support this proposition. Indeed, in the long run average travel time is conserved, implying that travellers take the benefit of improvements in the form of additional access to more distant destinations made possible by higher speeds. Such a perspective, based on considerations of the value of access, has implications for economic appraisal, modelling and policy.     

Choosing Public Transport—Incorporating Richer Behavioural Elements in Modal Choice Models

The development of behaviourally richer representations of the role of well-established and increasingly important influences on modal choice, such as trip time reliability and accounting for risk attitude and process rules, has moved forward at a fast pace in the context of automobile travel. In the public transport setting, such contributions have, with rare exception, not been considered. In this paper, we discuss and empirically illustrate the merits of advanced modelling developments aimed at improving our understanding of public transport choice, namely the inclusion of reliability in extended expected utility theoretic forms, to recognize risk attitude and perceptual conditioning, the consideration of passenger crowding and its inclusion in linear additive models, and the role of multiple heuristics in representing attribute processing as a way of conditioning modal choice. We illustrate the mechanics of introducing these behaviourally appealing extensions using a modal choice data set collected in Sydney.     

Role of the Railways in the Future of Air Transport

Abstract

The role of the railways in the air transport industry is usually limited to provision of access to airports. However, the development of high-speed rail networks and the congestion and environmental problems faced by the air transport industry suggest the railways could have a greater role in working with the airlines to provide an integrated transport service for medium-distance journeys (up to 800 km). Many air journeys involve two flights and a transfer at a hub airport. The alternative being investigated here would replace air journeys by a rail journey and a flight, and a transfer between them at the hub airport. Such integration could offer a positive alternative to aircraft on some routes and lead to railway journeys to airports becoming part of air transport services, and not only to provide access to them. Integration could therefore provide a better use of available air capacity rather than duplicating some high-speed rail routes and services.     

Accommodating risk in the valuation of expected travel time savings

Valuation of travel time savings is a critical measure in transport infrastructure appraisal, traffic modelling and network performance. It has been recognised for some time that the travel times associated with repeated trips are subject to variation, and hence there is risk embedded in the treatment of expected travel time. In the context of the expected utility framework, we use a nonlinear probability weighting function to accommodate choice made under risk. Although the empirical findings suggest small differences between the value of expected travel time savings (VETTS) in the presence and absence of risk, the mean estimate does make a noticeable difference to time benefits when applied to real projects. By incorporating nonlinear probability weighting, our model reveals that the probabilities associated with specific travel times that are shown to respondents in the choice experiment are transformed, resulting in overweighting of outcomes with low probabilities and underweighting of outcomes with high probabilities. Copyright © 2011 John Wiley & Sons, Ltd.     

Urea-SCR system optimization with various combinations of mixer types and decomposition pipe lengths

The demand for NO_x after-treatment system has increased dramatically due to the stricter NO_x emission regulations for diesel vehicles. The urea-SCR system is one of the NO_x after-treatment methods found to be quite effective to meet the regulation requirement enforced by various authorities including the Euro-6. In order to develop an effective urea-SCR system, it is critical to establish an even distribution of reductant over the catalyst surface since this favorable distribution can increase reduction reaction and in turn, improve NO_x conversion efficiencies. In the current study, a number of design variations of the urea-SCR system which included two mixer types and three decomposition pipe lengths, were evaluated systematically using CFD analysis and experimental measurements. The purpose of the CFD analysis was to estimate the distribution of reductant within the urea-SCR system with a specific configuration and the purpose of the engine emission test was to measure the amount of NO_x reduction, respectively. The results from the systematic analysis revealed the relation between the reductant distribution over the SCR and the performance of the NO_x reduction.