1,721,114 research outputs found
Optimisation of train schedules to minimise transit time and maximise reliability
No full textThe overall performance of a train schedule is measured in terms of the mean and variance of train lateness (reliability) as well as the travel time of individual trains. The concept is a critical performance measure for both urban and non-urban rail passenger services, as well\ud
as rail freight transportation. This thesis deals with the scheduling of trains on single track corridors, so as to minimise train trip times and maximise reliability of train arrival times. A method to quantify the amount of risk of delay associated with each train, each track\ud
segment, and the schedule as a whole, is put forward and used as the reliability component of the constrained optimisation model. As well as for schedule optimisation, the risk of delay model can be applied to the prioritisation of investment projects designed to improve timetable reliability. Comparisons can be made between track, terminal and rolling stock projects, in terms of their likely impact on timetable reliability.\ud
The thesis also describes a number of solution techniques for the scheduling problem. New lower bounds for the branch and bound technique are presented which allow solutions for reasonable size train scheduling problems to be determined efficiently. Three solution heuristic techniques are applied to the train scheduling problem, namely: a local\ud
search heuristic with an improved neighbourhood structure; genetic algorithms with an efficient string representation; and tabu search. Comparisons in terms of the number of\ud
calculations and solution quality are made between the heuristic and branch and bound techniques. The branch and bound technique with the best lower bound out performed\ud
genetic algorithms and tabu search for all except the largest size problems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Modelling aspects of rail track maintenance scheduling
No full textThere are significant productivity gains to be realised in track maintenance through capital expenditure in both the maintenance task itself ( e.g. mechanisation), and by moving to higher quality, lower maintenance track. However, there is also a need to ensure that maintenance of existing networks is undertaken according to a plan which maximises overall net benefit to the rail operator. In Australian freight operations, maintenance costs comprise between 25 -35 percent of total train operating costs. Therefore, it is important that the track maintenance planning function is undertaken in an effective and efficient manner. This applies to short-term planning such as daily scheduling of projects; as well as the medium to long-term planning of required maintenance projects.\ud
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Maintenance activities can be conveniently classified into routine, spot and production activities. Routine activities are those which are insensitive to volume of the traffic. They are usually carried out at regular intervals and include the following: vegetation control; repair of fences, gates, signs and posts; herbicide application; and routine inspections. The main purpose of spot maintenance is to maintain track in its existing state. The activities are usually carried out whenever defects are identified by manual or automated inspections. They include the following: spot replacement of minor track components, sleepers and short rail sections; repair of joints and weldings; spot ballast packing; and spot stone blowing. Production maintenance refers to activities which have a significant impact on track condition. They include the following: tamping; stone blowing; ballast regulation, stabilization and cleaning; rail grinding; re-sleepering; and re-railing.\ud
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Track maintenance policies have traditionally been viewed as engineering led decisions. There is a need to focus effort into the development of tools to assist track maintenance planning in the context of maximising the overall net financial benefit to rail users. This overall aim can be achieved by using well established Operations Research techniques, together with engineering judgement.\ud
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The track maintenance scheduling problem, which involves the allocation of maintenance projects to time windows and crews to projects, is formulated here as an integer programming model. The model presented here was applied to a 89 km track corridor on the eastern coast of Australia. A four day planning horizon was used for which the model was used to test proposed changes including re-scheduling trains and changing the number of maintenance crews. Increasing the time window by moving less important trains was shown to reduce potential delays significantly.\ud
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The model is mainly aimed at providing for an 'off-line' planning function. However, the same model could be used by local track managers and train planners in real-time so that adjustments could be made to a planned schedule of projects in the light of unplanned train services or train cancellations. Such a system would need to be integrated into a train dispatching real-time database
Modelling reliability of train arrival times
No full textThis paper deals with the scheduling of trains so as to minimise train trip times, whilst\ud
maximising reliability of arrival times. The amount of risk of delay associated with a schedule is used as the reliability component of a constrained schedule optimisation model. The paper outlines the model developed to quantify the risk of delays to individual trains, as well as to specific track segments and to the schedule as a whole. The risk model, which deals with single track operations, can be used to estimate the likely impact on reliability of arrival times of changes in train frequencies and operating practices; track and station infrastructure investment strategies; and train technology upgrading.\ud
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An application of the model to the optimisation of schedules on a track corridor is described. The results obtained using the model are compared with the schedules used by train operations planning staff, in terms of overall delay and timetable reliability. The results highlight the significance of including a measure of timetable reliability, such as risk of delays, in the objective function for scheduling optimisation
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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