1,720,976 research outputs found
Development of intervention programs for inland waterway networks using genetic algorithms
No full textInland waterways often consist of large numbers of man-made objects to ensure navigability. These objects are of many different types, ages and sizes, and deteriorate in uncountable of different ways. In order to ensure that the deterioration of the objects does not result in a loss of navigability, interventions must be executed. This, however, produces costs, in terms of both labour and material costs and costs of loss of service if the waterway is rendered non-navigable during intervention. In this paper, a methodology is presented to determine optimal multiple time period intervention programmes for inland waterways. The optimal intervention programme is the one that has highest net benefit, i.e. overall benefits minus overall costs, where benefits are the reduction in risk of failure. A genetic algorithm is used to overcome the problem of combinatorial explosion when many objects, in many states, over many time periods are to be considered. The exact formulation of the genome, as well as the genetic fitness function, are presented. They are used to determine an optimal intervention programme for a fictive inland waterway network. The results are presented and discussed, and an outlook is provided on further steps to improve this methodology
Investing in water supply resilience considering uncertainty and management flexibility
No full textThis paper demonstrates how to make investment decisions that optimally improve water supply resilience, taking into consideration both future uncertainty and management flexibility. The demonstration is done by evaluating investment strategies for a 38 Ml/d water treatment plant serving an urban area with approximately 75 000 inhabitants, where there is uncertainty with respect to future population growth, industrial production, external demand and the amount of rainfall due to climate change. It is shown that the quantification and comparison of the possible reductions in service and intervention costs over comparably long periods enables the optimal investment decisions-that is, the ones with the optimal trade-offs between stakeholders. Additionally, it can be seen that the used methodology enables the consistent and transparent consideration of (a) the concerns of multiple stakeholders, (b) the future deep uncertainty associated with key concerns and (c) the flexibility of infrastructure managers to make decisions in the future using new information. The methodology also ensures that managers have clear plans of action and considerable insight into the extent of required future financing
Determination of Risk-Reducing Intervention Programs for Railway Lines and the Significance of Simplifications
No full textBecause failures on railway lines have nonzero probabilities of occurrence and can result in significant costs if they occur, railway infrastructure managers are interested in determining intervention programs that best reduce this risk, taking into consideration their budget constraints. In this paper, a base model is proposed to determine optimal risk-reducing intervention programs for railway lines based on the states of its objects and budget availability. The base model is an integer nonlinear model with an objective function that maximizes net benefit without exceeding budget constraints. The net benefit is the difference between the amount of risk reduction and the costs of executing interventions in terms of both direct costs (i.e.,materials and labor forces) and indirect costs (i.e.,the travel time costs). Three variations of the base model, i.e.,the object model, the block model, and the line model, are used to investigate the trade-offs between increasingly simplified models and decreasing ability to determine the optimal intervention program due to decreasing ability to accurately estimate costs and benefits. In the object model, objects are considered in isolation, i.e.,while each object fails and is restored all other objects in the line are fully functional. In the block model, blocks are observed in isolation, i.e.,while each block fails and is restored all objects in the line are fully functional, whereas the multiple objects within a block may fail and be restored simultaneously. In the line model, all objects in the line may fail and be restored simultaneously. Fault tree analysis is used in the block and line models to estimate the costs of the combined failures of multiple objects. The three models are demonstrated by using them to determine the optimal intervention program for a fictive railway line between two stations that consisted of eight track sections, a bridge, two switches, and two signals. The intervention programs determined using the three models in terms of the interventions included and the net benefit obtained are compared. It is shown that all three variations produce useful results but that there are significant differences in the estimation of the net benefits using the three different models, and that these differences lead to different interventions being included in the determined intervention programs, and consequently in the net benefit that will be achieved through their implementation. It was also shown that each improvement in the estimation of accuracy comes with an increase in modeling complexity. (c) 2017 American Society of Civil Engineers
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
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