1,720,989 research outputs found
Valutazione del contributo degli apparati radicali nell’analisi di stabilità ei movimenti franosi superficiali
No full textA 3-D probabilistic stability model incorporating the variability of root reinforcement
Full text linkA comparison between different methods for determining grain distribution in coarse channel beds
No full textThe determination of grain size distribution in alluvial channels plays a crucial role in understanding fluvial dynamics and processes (e.g., hydraulic resistance, sediment transport and erosion, and habitat suitability). However, to determine an accurate distribution, tremendous field efforts are often required. Traditionally, the grain size distribution of channel beds have been obtained by manually counting a set of randomly selected stones (the “pebble count”). Based on this elementary principle, many authors have proposed different adaptations to overcome weaknesses and problems with the original method; with the development of digital technology, photographic methods have been developed in order to significantly reduce the time spent in the field. Two of these “image-assisted” methods include Automated Grain Sizing, AGS, and Manual Photo Sieving, MPS. In this study, AGS and MPS were applied under ideal laboratory conditions, to be used as reference, and in two field conditions with different degrees of difficulty in terms of visual determination of the grain size distribution; these included an artificial unlined channel and two natural mountainous streams. The results were compared with those obtained with the pebble-count method. In general, strong agreement between the methods was found when they were applied under favorable conditions (”the laboratory”), and the differences between the image-assisted and pebble count methods were similar to those found in previous studies. Despite being more time consuming, MPS was deemed preferable to AGS when conditions are not optimal; in these cases, the time spent on image elaboration significantly increased in the AGS method (approximately three-fold), but the estimation error of the median grain size decreased by approximately 37%. The use of image-assisted analysis has proven to be robust for characterizing sediment in watercourse beds and reducing fieldwork time, but because field conditions can significantly affect the accuracy of results, the method choice must be carefully considered
Variability in the tensile resistance of roots in Alpine forest tree species
No full textThe quantification of the tensile resistance of roots and its variability is relevant to several fields of application, including slope stability, soil bioengineering techniques, and stream restoration. Data on root tensile resistance in combination with root density allow for the estimation of additional root cohesion, a parameter that is essential to account for the presence of vegetation on hillslopes and embankments.
In this study, root resistance was investigated to expand our knowledge of the values typical of the Alpine environment and to assess the variability among species and within a given species. Seven tree species that are common in the Alpine environment (spruce fir, European larch, European beech, sweet chestnut, maple, ash and hornbeam) were sampled in various sites of Lombardia (northern Italy), and their force-diameter relationships were calculated and statistically compared.
The values obtained fall within the same range as results from previous studies and confirm the power law relationships between root diameter and both breaking force and breaking stress, as commonly adopted.
As a result of genetic factors, there is a statistically significant difference in resistance among the species studied, with a clear ranking order. The European beech is approximately two times more resistant than are ash, larch, sweet chestnut and spruce (the mean corrected breaking forces are 84 N and 47-40 N, respectively); the values for maple (65 N) and hornbeam (56 N) are intermediate.
By comparing the force-diameter relationships obtained for a given species at different sampling sites, statistically significant differences have been observed in some cases but not in all, as a result of environmental constraints. A multiple regression analysis between force values and the main environmental factors was not able to explain such variability (except in a very partial way for site elevation), besides the effect of root diameter.
By introducing the Forest District (which represents areas of fairly homogeneous growing conditions) as a criterion of discrimination, an explanation of within-species variability was obtained in most cases. Although the present data do not permit definitive conclusions, such an approach is viewed as promising for describing plant reinforcement variability, and Forest District appears to be a landscape criterion useful for assessing the stability of forested hillslopes
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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