1,720,990 research outputs found
Metric concepts and implications in describing compositional changes for world river's water chemistry
No full textThe paper is designed to give the reader an outline that is useful for understanding the importance of distance, as a metric concept, and its implications when compositional (geochemical) data are managed from a statistical point of view in a given sample space. Application examples are shown by considering the construction of confidence regions and mixing models. The analyzed data are related to the chemistry of the most important rivers of the world as referring to the GEMS/WATER Global Register of River Inputs when each sample (river) is represented as a composition. A compositional vector of d parts, x = [x(1),x(2),...,x(d)], is defined as a vector in which the only relevant information is contained in the ratios between its components. All the components of the vector are assumed positive and are called parts (variables), while the whole compositional vector, with the sum of the parts equal to a constant, represents the composition. In this case data are not represented by variables free to vary from 00 to +infinity within a Euclidean space but occupy a restricted part of it called the simplex. The d-part simplex. S(d), is a subset of a d-dimensional real space. In this context the metric of the R space, with the definition of basic algebraic operations and of inner product, norm and distance, thus giving an Euclidean vector space structure, cannot be applied since the scale is relative and not absolute. (C) 2011 Elsevier Ltd. All rights reserved
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
3-BODY POTENTIAL EFFECTS IN THE STRUCTURE OF FLUID KRYPTON
No full textThe low-density expansion and a new integral equation have been used to calculate the pair correlation function and several related quantities for krypton, using realistic pair potentials and several models for the three-body potentials: the Axilrod-Teller-Muto model, the multipolar model up to the triple quadrupole term and the Loubeyre model. The results are compared with experimental data in some detail. The models describe the three-body effects in correlation functions in a qualitative sense, but quantitative differences are observed, suggesting that shorter-ranged effects must also be included
Long-range pair potential from the low density S(k) of 4He around 6 K
No full textThe static structure factor S(k) of gaseous 4He at various densities along the T=6.13 K isotherm has been determined with the G4.1 diffractometer at LLB (Saclay, F). Thanks to the explored k-values (1<k/nm^-1<34), the long range behaviour of the interatomic interaction potential U(r^N) can be conveniently investigated. The resulting structure factors S(k) are presented and compared with previous determinations obtained at almost the same thermodynamic conditions using the D4B and D11 diffractometers at ILL (Grenoble, F). By means of a well known low-k expansion of the Fourier transform of the direct correlation function c(k), the London dispersion coefficient C6 of the r^-6 tail in U(r^N) has been experimentally evaluated for the first time and compared with the values present in literature
Three-body effects in simple insulating liquids: a small angle neutron scattering study in Kr
No full textSANS/VSANS investigation of porosity microstructure in rocks from a natural CO2 reservoir
No full textCarbon capture and storage (CCS) is considered a valid option to reduce the CO2 concentration in atmosphere. The gas is collected from industrial plants, then injected and stored underground in geological reservoir. A very wide range of information about chemical-physical characteristics of the sequestration site is therefore needed and, among them, data on porosity microstructure are crucial. Part of the processes which affect micro-porosity and act during and after the rocks formation can be reconstructed by studying the micro-porosity features. We have therefore performed a couple of SANS and VSANS experiments on rocks coming from a CO2 reservoir (which represents a natural analogue of a CCS site) in order to define the role and the possible effects of CO2 alteration in determining the micro-porosity and to check the sealing potential of rocks overlying the reservoir, which act as a barrier with respect to CO2-rich gas. The collected data are expected to be beneficial for developing theoretical model about the effects of CO2 sequestration in deep geological reservoirs
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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