1,721,011 research outputs found
Improved modelling of the magnetic resonance signal in the presence of shallow aquifers
No full textInternational audienceThis paper aims to investigate the magnetic resonance signal generated by shallow aquifers and its influence on the interpretation of magnetic resonance sounding (MRS) data. To improve the accuracy of MRS modelling in the presence of shallow aquifers, an enhanced mathematical model, which takes into account the higher harmonics of the transmitted pulse and a non-zero frequency offset between the Larmor frequency and the pulse frequency, is used. It is shown that in the presence of shallow aquifers, the magnetic resonance signal is complex even when the subsurface has a low electrical conductivity. At large pulse moments, water in shallow aquifers may generate a signal comparable in amplitude to a signal generated by water in deeper aquifers. Two types of error related to a shallow aquifer may occur. For a one-aquifer system, interpretation using the simplified model may reveal an artefact that appears to be a deeper aquifer, although in reality it is non-existent (a phantom aquifer). For a multi-aquifer system, the signal from a shallow aquifer may offset the signal from a deeper aquifer, thus reducing the depth of investigation in comparison with a simple one-aquifer formation (offset of a deep aquifer). It is shown numerically that the depth resolution of the MRS method could be significantly improved by considering not only the amplitude but also the phase of the MRS signal. However, taking into account the non-linearity of the spin system for a large flip angle, the mathematical model for the inversion of complex signals needs to be further improved or at least checked for consistency before inversion. For verification of the numerical results, a re-interpretation of MRS field data reported in the literature is presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
MRS measurements and inversion in presence of EM noise
Get PDFInternational audienceThe Magnetic Resonance Sounding method (MRS) is based on the resonance behavior of proton magnetic moments in the geomagnetic field. As the signal generated by the protons is very small, the method is sensitive to electromagnetic noise and this is one of the major limitations for practical application. The frequency of the magnetic resonance signal is directly proportional to the magnitude of the geomagnetic field, and varies between 800 Hz and 2800 Hz around the globe. Whilst natural noise within this frequency range is generally not very large (excepting magnetic storms or other temporary disturbances), the level of cultural noise (electrical power-lines, generators, etc.) may be very high. Both the depth of investigation and resolution of the MRS method depend on signal to noise ratio. If measured data are corrupted by noise, it will have an effect on the accuracy and reliability of MRS results. Consequently, the MRS signal has to be measured with an acceptable signal to noise ratio. For improving the signal to noise ratio different filtering techniques could be applied. Selection of the filtering scheme depends on the noise origin. In any case, application of the stacking is necessary. A large number of repetitive measurements are often required for stacking and consequently one sounding may take from one to twelve hours. In this paper, efficiency of different filtering techniques, inversion strategy and influence of non-filtering noise on MRS results are discussed
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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