1,720,957 research outputs found
Railway catenary tension force monitoring via the analysis of wave propagation in cables
Full text linkThe tensioning forces applied to the contact wire in a railway catenary system influence the performance of the line. In this paper, a method to monitor the status of such tensioning forces is proposed based on the dependency that the waves that propagate through a tensioned wire have on the forces that pull the wire itself. A novel analytical formulation for the propagation of waves in a tensioned wire was proposed, and it was used to obtain the vertical acceleration of the wire when an external force acts as a concentrated input. The analysis of the acceleration with a moving standard deviation allowed a method to be defined for the generation of an index that describes the trend of the tensioning forces. The method was then tested on the wire accelerations obtained with laboratory tests and, afterwards, on the accelerations recorded on a contact wire of an electric railway regularly in operation and excited with the same kind of input
Probabilistic considerations on the effect of specimen size on the critical chloride content in reinforced concrete
No full textA probabilistic model was used to predict the critical chloride content (Ccrit) for reinforcement corrosion
as a function of specimen size. The specimen size is likely to be a reason for the large scatter of Ccrit values
as well as for the high threshold levels often observed in laboratory setups. Regarding test methods, it is
discussed that the common combination of small specimens and low numbers of parallel samples results
in poor reproducibility. If experimental data is to be used for service life modelling, the geometrical
dimensions of the specimens on which Ccrit was measured have to be taken into account
A heuristic wear model for the contact strip and contact wire in pantograph – Catenary interaction for railway operations under 15 kV 16.67 Hz AC systems
Full text linkThe sliding contact between the pantograph and catenary allows the correct operation of electric trains. However, this contact induces wear on both the components involved in the process, namely the contact strip on the pantograph and the contact wire on the catenary. The influence of operating parameter values (i.e., the fed current intensity, uplift force and train speed) has recently gained attention, with the aim of creating wear models for both parts involved in the contact. In this study, a procedure assessed in the literature is adapted to operating conditions with AC catenary systems at 15kV/16.67 Hz and Cu-impregnated carbon contact strips. The resulting models are suitable for the wear prediction of both the contact wire and the contact strip
Detecting lateral track irregularities by onboard measurements of lateral acceleration and displacements and Machine Learning algorithms // Rilievo delle irregolarità laterali del binario attraverso misure di accelerazioni laterali e spostamenti da bordo treno e algoritmi di Machine Learning
No full textUnderstanding the development of track defects, which can have a significant impact on the safety of train operations, is one of the most crucial responsibilities for railway engineers. Analysing track geometry (TG) parameters is necessary to establish an efficient track condition monitoring approach. Research has recently focused on monitoring track geometry irregularities using data collected from trains in service. Most of the previous research has focused on vertical irregularity of track, since the lateral irregularity is considerably more challenging because of the complex relative wheel-rail motion. This research work focuses on finding the relationship between the lateral acceleration and lateral irregularities from the Lateral Displacement of the Wheel relative to the Rail (LDWR). A supervised Machine Learning (ML) model is trained and tested with a dataset composed of numerical simulation on a diverse set of operational conditions. Among the tested algorithms, Random Forest regression shows the best result and polynomial regression is on the second place. Sufficient results are achieved which shows that it is possible to detect the lateral irregularities with on board computer vision sensor which can detect the LDWR. Also, a sensitivity analysis is performed which shows that lateral displacement is the most important parameter in determining the lateral irregularity from vehicle monitoring. The result of this work could be a step toward the predictive maintenance as well
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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