1,720,959 research outputs found
A Benders decomposition algorithm for demand-driven metro scheduling
Full text linkMetro timetables are usually planned with a top-down approach. After dividing the day into different periods, the trains are scheduled between the terminals of the line with a fixed frequency per period. In this paper we adopt an alternative paradigm where trains are scheduled individually. The schedule is developed so as to best match the passenger demand, and trains may short-turn at intermediate stations, thus reversing their direction before reaching the line terminal. This type of approach is particularly suited for automated metro lines, since it has a limited impact on personnel management. Considering the objective of minimizing the passenger waiting times on a two-directional metro corridor, we make two operating assumptions when designing the train schedule. Specifically, we assume the presence of a root station, which cannot be skipped by short-turning, and we assume that idling is only allowed immediately after a short-turn, and for a maximum amount of time. We present a path-based formulation for the problem and develop an efficient exact algorithm for it using a Benders-based branch-and-cut algorithm. We evaluate the proposed formulation and algorithm on a number of test instances. Through our computational experiments, we demonstrate the effectiveness of the developed formulation and algorithm
Demand-Driven Timetabling for a Metro Corridor Using a Short-Turning Acceleration Strategy
Full text linkThe efficient management of metro lines is a major concern for public transport operators. Traditionally, metro lines are operated through regular timetables, that is, timetables where trains have a constant headway between all stations. In this paper, we propose a demand-driven metro timetabling strategy and elaborate exact solution methods for the case of a two-directional metro corridor. In doing so, we avoid imposing any predetermined structure to the timetable, and instead control the trains individually to best match passenger demand. We consider that trains may short turn, that is, trains that are not required to serve the line from terminal to terminal, but instead may reverse direction before reaching the terminal. We present a mixed integer linear programming formulation for the demand-driven timetabling problem of a two-directional metro corridor with short turning. Furthermore, we develop an efficient exact algorithm using cut generation for an alternative formulation with an exponential number of constraints, and derive two classes of valid inequalities. We evaluate the proposed formulation and algorithm considering seven possible cut generation strategies on a number of test instances from artificially generated lines and on two test beds derived from real-world lines. Through the computational experiments, we demonstrate the effectiveness of the developed algorithm and the added value of the proposed strategy in terms of passengers' waiting time
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
Scheduling a pick and place packaging line
Full text linkIn this paper, we introduce the Pick and Place Packaging Problem (P4), for optimally scheduling a packaging system with one input conveyor (pick) and one output conveyor (place). We give a formal definition of the underlying dynamic optimization problem. We describe two properties that hold for its solutions and present an efficient row generation approach exploiting these properties. Starting from a basic version of the problem, we introduce two variants where we account for the possibility of holding the grip of items and variable conveyor speed. We extend the proposed exact solution method to these two cases. Then, we present an efficient Iterated Local Search heuristic for the problem and its variants. Numerical results show the effectiveness of our approach
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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