1,721,006 research outputs found
On the Importance of Considering Realistic Orography Into the Evaluation of Lightning Electromagnetic Fields in Mixed Path
No full textA lightning event striking the sea could induce several damages to the near infrastructures located on the coast. The possible damages are connected to the induced voltages caused by the electromagnetic fields generated by the lightning discharge. In order to compute them, several simplified approaches have been developed, using ideal models for the surrounding geometry and for the electrical parameters of the soil. This works provides the evaluation of the lightning electromagnetic fields generated by a lightning event striking on the sea taking into account the possible elevation of the terrain with respect to the sea level and the inclination of the seabed. The analysis has been carried out taking into account several distances between the coast and the striking location as well as different observation points, in order to evaluate the induced effects on a structure located close to the sea-land interface as well as in a more distant location. The analysis, implemented with the aid of the finite element method, leads to important conclusions on the components of the electric and magnetic field that are more affected by the realistic characteristics of the surrounding orography
Where does a glacier end? Integrated geophysical, geomorphological and photogrammetric measurements to image geometry and ice facies distribution
No full textIn this study we integrated different techniques, spanning from Ground Penetrating Radar to geomorphological and photogrammetric data, to characterize the glacial and proglacial environments of the Sforzellina Glacier (Central Alps, Italy). Direct data highlighted the presence of debris-covered ice and even of dead ice patches in front of the actual glacier terminus. Such an information was further proved by geophysical data. We try to correlate the dead ice patches occurrence with several parameters such as debris cover thickness, ground tem-perature, solar radiation, elevation, velocity of glacier retreat, and dip of the topographic surface without finding relevant correlations, except for the local bedrock morphology. In fact, the latter factor seems to be crucial to make the favourable conditions to dead ice patches formation and preservation with time.Since ice is not always outcropping, while dead ice patches never outcrop because they are hidden by continuous debris cover, classical glaciological monitoring techniques are not always successfully applicable.On the basis of the obtained results, we argue that estimates of glacier extension just related to surficial in-formation, like in the case of exclusive use of remote sensing data and outcropping ice monitoring, can produce relevant underestimations. The presence of hidden ice patches, even not strictly part of the glacier body, is further important to quantify the total water equivalent, as well as to make affordable forecasts of the future glaciers evolution
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
Lightning Location and Peak Current Estimation From Lightning-Induced Voltages on Transmission Lines With a Machine Learning Approach
Full text linkIn this article, a machine-learning-based model for the regression of cloud-to-ground lightning location and peak current from time-domain waveforms of lightning-induced voltage measurements on overhead transmission lines is presented. A principal component analysis (PCA) procedure is applied for extracting significant features and decreasing the dimension of the input vector. Then, a shallow neural network is trained with the results of the PCA. The obtained results show that the proposed approach can be the base for a tool able to regress lighting location with an accuracy comparable to or even better than traditional methods [i.e., lightning location system (LLS)] and provide a peak current estimate more accurate than LLS and more actual and widespread than direct tower measurements (which are limited to a reduced number of recorded events in some specific regions). Such a tool would also have significant advantages in terms of costs, since it would not require a dedicated instrumentation
Relating transmission line overvoltages and lightning location: a machine learning–based procedure
No full textPurposeThis study aims to investigate the use of machine learning-based algorithms in the field of lightning stroke localization. This work is an important step ahead with respect to the research recently started by the authors, i.e. the possibility of locating a lightning discharge from the voltage induced on overhead transmission lines; more in detail it seeks new insights into the inclusion of both first and subsequent return strokes of negative cloud-to-ground flashes.Design/methodology/approachThis study uses a quantitative approach, using supervised learning techniques for a regression problem (data preprocessing, model selection, training, testing, validation or algorithm optimization). Data are collected from a dedicated lightning-induced overvoltage simulator and analyzed using a specific machine learning-based procedure developed and programmed by the authors.FindingsThe results reveal significant improvements in localization accuracy for both first and subsequent strokes, with respect previous works, indicating that the novel approach is promising for future investigation with more complex power system configurations and the use of experimental data. These findings provide evidence that dedicated models for each type of stroke yield better performance, offering significant implications for the integration of machine learning-based lightning location systems into the existing power infrastructure.Originality/valueThe proposed method is, to the best of the authors' knowledge, entirely new and constitute an innovation with respect to the present literature, both of the same authors and of other research groups. In particular, a new preprocessing procedure of the voltage data is proposed, and the performances of different neural networks are evaluated, both for the first and the subsequent stroke. The application to both first and subsequent stroke is an innovation itself because it has not been proposed before
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
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