1,721,309 research outputs found
Real-time Train Scheduling: reactive and proactive algorithms for safe and reliable railway networks
Full text linkTrain scheduling is a critical activity in rail traffic management, both off-line (timetabling) and on-line/in real-time (dispatching). This research aims at the design and development of advanced optimization models and methods for the real-time re-scheduling. The study covers two overlapping areas: managing the train service plans in an increasingly dynamic management scenario; and ensuring the safety and reliability of the railway system in case of major disruptions.
Although the real-time re-scheduling problem is relatively easy to depict, due to the interdependent nature of trains moving along the networks lines, a huge challenge looms in the search for an optimal schedule. A great variety of approaches have been proposed over the years, but here we are interested in those based on Mixed Integer Linear Programming, which are the most widely adopted in the literature. The main issue that such approaches must face is how to represent the fact that two trains cannot occupy simultaneously the same track (or other pairs of incompatible railway resources). Typically, Time-Indexed (TI) formulations for scheduling problems are stronger than other classical formulations, like big-M models. Moreover, they can be easily adapted to cope with complicating constraints and non-linear objectives. Unfortunately, their size grows usually very large with the size of the scheduling instance. As a consequence, TI formulations are not suitable for attacking real-life instances, especially when fast, on-line responses are required. Further, the approximation introduced by time discretization often leads to solutions which cannot be realized in practice.
The Dynamic Discretization Discovery (DDD), introduced by Boland for the continuous-time service network design problem, is a novel technique to keep at bay the growth of TI formulations (and thus their response times) and, at the same time, ensure the necessary modelling precision. Exploiting and extending the DDD paradigm, we develop a primal-dual exact approach to train dispatching. The result is a restricted TI formulation and a procedure with running times comparable with the best alternatives presented in the literature on our real-life instances of train dispatching. Furthermore, the method implemented does not suffer by the approximation error introduced by a standard time discretization. In our comparisons the big-M approach maintains the lead on average, but the distance is getting smaller. Even though the method developed in this research is at its early stage, it is very promising not only in a railway context but, more generally, for the broader field of job-shop scheduling. In addition, it offers many hints and opportunities for enhancements that will be investigated in future works.
On the other hand, when major disruptions occur in a rail network a simple rescheduling is not sufficient to re-ensure the viability of the network. Indeed, parts of the network may become unavailable for inbound trains, and decisions must be taken to mitigate the impact on the overall traffic. Arguably the most critical point is to avoid creating deadlocks, a situation that arises when a group of trains is positioned in such a way that none can move due to other trains in the group blocking their path. The infrastructure manager and train operating companies in these cases may be forced to stop trains until the normal status is recovered. A crucial aspect is thus to identify, for each train, a location where the train can hold during the disruption, avoiding to disconnect the network and allowing for a quick recovering of the original plan, at restart. A good location for holding a train is called a safe place and it additionally serves the purpose of preventing trains to drive past the last location where they can be safely parked, which could otherwise lead to further blockages and deadlocks. We outline some necessary and sufficient conditions to achieve the desired safe places properties. We then translate such conditions into constraints for a binary formulation of the problem, which we named Safe Place Assignment Problem (SPAP).
The SPAP finds an application in the current usage of Advanced Traffic Management Systems (ATMSs). This digital train management solutions are called to solve instances of a hard optimization problem in very limited computational time and they may fail to return a plan for different reasons. Finding a solution to the SPAP in these cases adds an additional level of safety, as dispatchers are provided with the last safe location for a train to drive within the plan's horizon.
Computational results on a set of instances provided by a Class I U.S. railroad company show how the approach can be used effectively in the real-life setting that motivates the study, by returning optimal assignments in fractions of second.
Both research outputs are very innovative and off the beaten track. The achievements regards both the theoretical and methodological point of view and present in addition a practical relevance
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
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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