激光堆焊工艺在修造领域的应用现状及发展趋势

本文详细阐述了激光堆焊工艺在工业修造领域的应用现状及发展趋势,介绍了激光束的能源、输送和聚焦系统、堆焊材料及激光设备。重点说明了其在修造领域的应用工艺。     

Use and perceptions of a real time passenger information system

The use of high-technology systems in the transport sector has increased steadily over recent years. This paper outlines the development of vehicle monitoring and control systems and their use in the public transport arena. The paper shows how one such system, that operated by Datatrak Ltd., has been adapted to provide a real time passenger information system for the RiverBus Partnership in London.

1 The RiverBus service described in this article ceased operation in August 1993. The collapse of the RiverBus Partnership followed the financial difficulties surrounding Olympia and York, developers of Canary Wharf in London Docklands.

Passenger use and perception of the system is evaluated, based on surveys of RiverBus users. This provides an evaluation of the system, and highlights the importance of introducing such systems based on user information needs and as part of the total marketing package.     

Uncertain demand,modal competition and optimal price-capacity adjustments in air transportation

A new microeconomic model for the operation of an airline facing modal competition with uncertain total demand is developed to analyze optimal price capacity combinations. The novelty is the treatment of the capacity restriction, which is not viewed as affecting negatively individual preferences (e.g. probability of a full flight), but does influence aggregate utility. A mode choice model is used to represent unrestricted individual preferences assuming full availability (RDER="0">phone callRDER="0"> demand); air capacity is treated as a variable that acts on the actual choice set. Restricted choices and total demand stochasticity are integrated in welfare calculations (users' benefits and profits). Numerical examples are given and results are analyzed in terms of load factors fare levels, and sensitivity to the stochasticity of requests.This research was partially funded by FONDECYT, Chile, Direction Génerale de l'Aviation Civile, France, the Andes Foundation and the Fulbright Commission.     

An Exploration of the Relationship between Timing and Duration of Maintenance Activities

The timing and duration of an activity episode are two important temporal aspects of activity-travel behavior. Understanding the causal relationship between these two variables would be useful in the development of activity-based travel demand modeling systems. This paper investigates the relationship between these two variables by considering two different causal structures – one structure in which time-of-day choice is determined first and influences duration and a second structure in which activity duration is determined first and affects time-of-day choice. These two structures are estimated within a discrete-continuous simultaneous equations framework employing a full-information maximum likelihood methodology that allows error covariance. The estimation is performed separately for commuter and non-commuter samples drawn from a 1996 household travel survey data set from the Tampa Bay area in Florida. The results of the model estimation effort show that the causal structure in which activity duration precedes or affects activity timing (time of day choice) performs better for the non-commuter sample. For the commuter sample, the findings were less conclusive with both causal structures offering equally good statistical measures of fit. In addition, for the commuter sample, all error correlations were found to be zero. These two findings suggest that time of day choice and activity episode duration are only loosely related for the commuter sample, possibly due to the relatively non-discretionary and inflexible work activity and travel.     

Exploring the impact of walk–bike infrastructure,safety perception,and built-environment on active transportation mode choice: a random parameter model using New York City commuter data

This study estimates a random parameter (mixed) logit model for active transportation (walk and bicycle) choices for work trips in the New York City (using 2010–2011 Regional Household Travel Survey Data). We explored the effects of traffic safety, walk–bike network facilities, and land use attributes on walk and bicycle mode choice decision in the New York City for home-to-work commute. Applying the flexible econometric structure of random parameter models, we capture the heterogeneity in the decision making process and simulate scenarios considering improvement in walk–bike infrastructure such as sidewalk width and length of bike lane. Our results indicate that increasing sidewalk width, total length of bike lane, and proportion of protected bike lane will increase the likelihood of more people taking active transportation mode This suggests that the local authorities and planning agencies to invest more on building and maintaining the infrastructure for pedestrians. Further, improvement in traffic safety by reducing traffic crashes involving pedestrians and bicyclists, will increase the likelihood of taking active transportation modes. Our results also show positive correlation between number of non-motorized trips by the other family members and the likelihood to choose active transportation mode. The model would be an essential tool to estimate the impact of improving traffic safety and walk–bike infrastructure which will assist in investment decision making.     

A new approach for improving the performance of freight train timetabling of a single-track railway system

A new approach for improving the performance of freight train timetabling for single-track railways is proposed. Using the idea of a fixed-block signaling system, we develop a matrix representation to express the occupation of inter- and intra-station tracks by trains illustrating the train blocking time diagram in its entirety. Train departure times, dwell times, and unnecessary stopping are adjusted to reduce average train travel time and single train travel time. Conflicts between successive stations and within stations are identified and solved. A fuzzy logic system is further used to adjust the range of train departure times and checks are made to determine whether dwell times and time intervals can be adjusted for passenger and freight trains at congested stations to minimize train waiting times. By combining manual scheduling expertise with the fuzzy inference method, timetable efficiency is significantly improved and becomes more flexible.     

A comparison of modelled and real-life driving profiles for the simulation of railway vehicle operation

A key factor in determining the performance of a railway system is the speed profile of the trains within the network. There can be significant variation in this speed profile for identical trains on identical routes, depending on how the train is driven. A better understanding and control of speed profiles can therefore offer significant potential for improvements in the performance of railway systems. This paper develops a model to allow the variability of real-life driving profiles of railway vehicles to be quantitatively described and predicted, in order to better account for the effects on the speed profile of the train and hence the performance of the railway network as a whole. The model is validated against data from the Tyne and Wear Metro, and replicates the measured data to a good degree of accuracy.     

Adapting without Retreating: Responses to Shoreline Change on an Inlet-Associated Coastal Beach

Coastal barrier systems around the world are experiencing higher rates of flooding and shoreline erosion. Property owners on barriers have made significant financial investments in physical protections that shield their nearby properties from these hazards, constituting a type of adaptation to shoreline change. Factors that contribute to adaptation on Plum Island, a developed beach and dune system on the North Shore of Massachusetts, are investigated here. Plum Island experiences patterns of shoreline change that may be representative of many inlet-associated beaches, encompassing an equivocal and dynamically shifting mix of erosion and accretion. In the face of episodic floods and fleeting erosive events, and driven by a combination of strong northeast storms and cycles of erosion and accretion, the value of the average Plum Island residence increases by 34% for properties on the oceanfront where protection comprises a publicly constructed soft structure. Even in the face of state policies that ostensibly discourage physical protection as a means of adaptation, coastal communities face significant political and financial pressures to maintain existing protective structures or to allow contiguous groups of property owners to build new ones through collective action. These factors mitigate against adapting to shoreline change by retreating from the coast, thereby potentially increasing the adverse effects of coastal hazards.     

Physical environments influencing bicyclists’ perception of comfort on separated and on-street bicycle facilities

This study investigates the impacts of physical environments on bicyclists’ perceptions of comfort on separated and on-street bicycle facilities. Based on a field investigation conducted in Nanjing, China, we find that physical environmental factors significantly influencing bicyclists’ perception of comfort on the two types of facility. Cyclists’ comfort is mainly influenced by the road geometry and surrounding conditions on physically separated paths while they pay attention to the effective riding space and traffic situations on on-street bicycle lanes.