1,720,962 research outputs found
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
A simple stochastic model of point source solute transport in rivers based on gauging station data with implications for sampling requirements
No full textA simple point-source water quality model was constructed to explore hypothetical scenarios of linear alkylbenzene sulphonate (LAS) load variability, chemical degradation kinetics, river discharge and river velocities within the context of planned water quality monitoring in the river Lambro, northern Italy. LAS is an anionic surfactant and a commonly used ingredient of household detergents. Input loads were derived from flow and concentration measurements at sewage treatment works (STW). River travel times are approximated using hydraulic geometry concepts based on existing records of stage, discharge and velocity measurements. The model proved to be especially useful in predicting the impact of overflows from an undersized STW near the top of the catchment on diurnal variations in water quality downstream. Probability density functions (pdf's) of LAS concentrations for a number of points on the river were approximated by running the model stochastically (using a Monte Carlo procedure) over independent frequency distributions of discharge, temperature and input load. The predicted concentration pdf's were then used to estimate the number of random grab and 24h composite samples, which would be required in order to estimate mean concentrations with confidence. This is especially important in situations where the analysis is expensive and the sample budget is limited. The model results showed that grab sampling was not a viable strategy in the Lambro largely due to the very strong diurnal variability in concentrations induced by the STW overflow. This conclusion was corroborated by field data. Copyright (C) 1999 Elsevier Science Ltd
Root strength and density decay after felling in a Silver Fir-Norway spruce stand in the Italian Alps
No full textAims: Forests induce a mechanical reinforcement of soil, generally quantified in terms of additional root cohesion (cr), which decreases due to root decay after felling. The aim of this work is providing new field data on soil reinforcement by roots after trees cutting. Methods: The present work investigated cr decay in a mixed Silver Fir-Norway Spruce (Abies alba Mill. Picea abies (L.) Karst.) stand in the Italian Alps over a period of 3 years after felling by monitoring the two cr driving variables: root tensile resistance and root density. Results: Results showed that a significant difference in root resistance occurred only 3 years after felling, whereas the decrease in the number of roots was significant in the second year. The degradation process was more rapid in shallower layers and for thinner roots, as a consequence of the pattern of biological activity rate. The reduction of cr after felling was, for a reference profile depth of 70 cm, 55 % in the first 2 years and another 16 % in the third year. Conclusions: The findings of this study, providing new data on the decrease of cr after felling, can be introduced into geotechnical models allowing a better estimation of the stability of forest 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
Analisi della stabilità temporale dell'umidità del suolo in un piccolo bacino dolomitico
No full text(volume curato da G. Bischetti
Vegetation analysis and estimation of forest reconstitution time in protected areas of Val Camonica (Southern Alps) where a commercial mixture of seeds was sown. eco.mont (Journal on Protected Mountain Areas Research)|eco.mont Vol. 9 No. 1 9 1|
No full textThis study examined the vegetation composition of five sites of the Southern Alps (Val Camonica, Italy) where a commercial seed mixture had been used to restore vegetation at the end of soil stabilization works. The five sites are located in two protected areas of the Alps (the Parco dell’Adamello and the Riserva Naturale delle Valli di Sant’Antonio), and represent a chronosequence of year of sowing. We used a set of floristic-vegetational indices (index of maturity, indices of the life forms, and Landolt ecological indices) to analyse the characteristics of the vegetation of the five sites and to find a model that would allow an estimation of forest reconstitution time. From data analysis we found that, in areas which have had more recovery time, the sown heliophilous species and the ruderal herbaceous species decrease, while shrubs, trees and typical species of mature forests increase. The values of the index of maturity also increase according to time elapsed after sowing; the relationship that, in the present case, links the index of maturity to time was expressed formulaically. This model provided an estimation of the time required for the reconstitution of the forest community which, in this case, was about twenty years. This research, prompted by a request from the managing institutions of the two protected areas for a botanical investigation into the outcome of using the seed mixture, provided information that will enable them to assess whether to use the mixture in future environmental restoration work in the same areas
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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