1,720,960 research outputs found
A hybrid model to evaluate subsurface chemical weathering and fracture karstification in quartz sandstone
No full textA hybrid numerical, finite differences and semi-analytical/empirical model has been developed to evaluate the
spatial and time scale of chemical weathering along a fracture in quartz sandstones. The model is based on the
diffusion transport occurring from the bedrock mass toward the fracture walls driven by the SiO2 concentration
gradient between water in the bedrock pores (high silica content) and water flowing in the fracture (low silica
content). Because of molecular diffusion, intergranular water becomes undersaturated with respect to silica. This
promotes dissolution of quartz at grain boundaries and results in a porosity profile decreasing from the fracture
walls toward the rock interior. Bedrock individual grains are released and gradually removed by the water
flowing into the fracture when a critical value of porosity is reached (Grain Release Threshold, GRT): this process
drastically increases the fracture enlargement rate.
The model outcomes establish a minimum time of 90 ka to reach the GRT. This time is independent of length,
aperture and dip of the fracture, but is controlled by parameters such as the initial fracture aperture, water
temperature, quartz grain size, and initial bedrock porosity. It is attested that the water flowing in the fracture
remains undersaturated with respect to silica over very long timescales (in the order of 105 years) and over very
long flow paths. In turn, this suggests that the extremely slow reaction between quartz and water is the keyfactor
for the formation of subterranean karst-like features in quartz sandstone, otherwise silica saturation would
be reached after short distances and deep weathering in this lithology would be prevented.
Finally, the model outcomes were compared to field data from the Gran Sabana caves (Venezuela) and other
quartz sandstone weathering landforms elsewhere, showing that dissolution/diffusion in the rock matrix is a
reliable mechanism for the formation of these peculiar karst-like features
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Discovering Small Target Sets in Social Networks: A Fast and Effective Algorithm
Full text linkGiven a network represented by a graph (Formula presented.), we consider a dynamical process of influence diffusion in G that evolves as follows: Initially only the nodes of a given (Formula presented.) are influenced; subsequently, at each round, the set of influenced nodes is augmented by all the nodes in the network that have a sufficiently large number of already influenced neighbors. The question is to determine a small subset of nodes S (a target set) that can influence the whole network. This is a widely studied problem that abstracts many phenomena in the social, economic, biological, and physical sciences. It is known that the above optimization problem is hard to approximate within a factor of (Formula presented.), for any (Formula presented.). In this paper, we present a fast and surprisingly simple algorithm that exhibits the following features: (1) when applied to trees, cycles, or complete graphs, it always produces an optimal solution (i.e, a minimum size target set); (2) when applied to arbitrary networks, it always produces a solution of cardinality which improves on previously known upper bounds; (3) when applied to real-life networks, it always produces solutions that substantially outperform the ones obtained by previously published algorithms (for which no proof of optimality or performance guarantee is known in any class of graphs)
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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