1,721,038 research outputs found
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
Impact Structures: How post-impact thermal conditions influence magnetic behavior
Get PDFLarge scale meteorite impact events are some of the most catastrophic and instantaneous geological processes in nature. These events release high amounts of energy, and generate pressures which will vaporize, melt and metamorphose the target rock. Large impact events create impact structures with very characteristic features, one of which being intense magnetic anomalies. These anomalies are caused by a contrast of the total magnetization in the shocked target, newly formed impactites (that is, rocks formed by, or related to the impact event) and the regional background magnetization. The total magnetization (Mtot) is the sum of natural remanent magnetization (NRM) and induced magnetization (κ*B, κ is magnetic susceptibility and B is Earth’s magnetic field). Shock deformation causes a sharp loss of up to 90% of NRM and κ in the magnetite-bearing target. The demagnetization of magnetite is caused by the shock-induced physical deformation, such as brittle grain fracturing and fragmentation, and ductile crystal lattice defects. Physical defects also enhance magnetic domain wall-pinning, which decreases the apparent domain state of magnetite, from originally multi-domain (MD) towards pseudo-single domain (PSD), or even single domain (SD) states. The change in apparent domain state is concomitant with an increase in magnetic coercivity, and further decreases κ. However, a recent study found that post-shock thermal annealing of shocked magnetite causes a “healing” of some of the reversible ductile lattice defects, which reduces domain wall-pinning and allows for the restoration and recovery of some magnetic properties, including an increase of κ.
Natural post-impact magnetic recovery through temperature has not been studied to date, and is particularly relevant for large impact craters such as the Chicxulub (Mexico). In this study we compared the large Chicxulub (diameter ca. 200 km) with the smaller Nördlinger Ries structure (Germany, diameter ca. 25 km). In both impact structures, high temperature impactites (>900°C) and post-impact hydrothermalism may lead to optimal conditions for natural annealing to take place. The effect that this phenomenon has on the characteristic magnetic signature of the craters remains unclear until now.
To address this knowledge gap, magnetite samples from the Chicxulub and Nördlinger Ries craters were investigated through rock-magnetic, petrographic and mineral chemical methods. Two generations of magnetite common to both craters were observed: (1) a pure, stoichiometric shocked magnetite with large (~100 μm) grains in the basement; and (2) a newly formed, generally low-cation substituted (Ti-) magnetite, with smaller (~10-50 μm) grains and no visible shock deformation, in the impactites.
Naturally shocked MD magnetite was found to show an apparent domain state decrease towards PSD, similar to magnetite shocked experimentally in laboratory conditions. Temperatures above 540°C create an irreversible increase in κ, and restore some apparent MD state contributions. The threshold for annealing and magnetic recovery is estimated to be ~540°C. If the magnetite is oxidized and hematite is present in the sample, it transforms back to magnetite if experimentally heated above 560°C in an argon atmosphere. The transformation creates very small magnetite grains with mottled textures and SD to superparamagnetic (SP) domain states, in a process that masks annealing if both occur concomitantly. This is an underappreciated phenomenon, that may lead to NRM remagnetization and overprint in nature, under certain conditions.
In Chicxulub, the shocked magnetite of the uplifted basement shows shock-reduced NRM and κ values, leading to a low total magnetization in the peak-ring. We attribute the negative anomaly in the peak-ring to this lack of magnetization. The hydrothermal system did not significantly overprint the magnetic signal, and its temperatures (~450°C) were not high enough to anneal the magnetite naturally, and thus it did not affect significantly the magnetic anomaly in the peak-ring. Natural annealing takes place in contact with the impact melt, where basement magnetite shows increased κ, and a transformation of pre-impact oxidation-derived hematite into newly formed SD-SP magnetite. The impact melt shows strong NRM and κ values, but in the peak-ring it constitutes only a thin layer, which also does not significantly contribute to the anomaly.
In Nördlinger Ries, the basement magnetite is similarly demagnetized, and natural annealing occurs locally due to the prevalence of melt bearing suevite dykes in the basement, with high emplacement temperatures (>900°C). The hydrothermal system in Nördlinger Ries had shorter duration and lower temperatures than in Chicxulub (max. 300°C), and also does not significantly affect the magnetic anomalies of the crater. The impact melt shows weak magnetization, with κ values comparable to the shocked and demagnetized basement. On the other hand, impact breccia (suevite) in Nördlinger Ries show high κ and strong reverse polarity magnetization, which contributes to the negative magnetic anomalies
Biogenic and hydrogenous magnetic mineral formation in upward oxygenated sediments of the East Pacific Rise
No full textThe Clarion-Clipperton Zone is a deep-sea area in the eastern Pacific Ocean. Due to low sedimentation rates, the sediment cover in this region is thin and discontinuous. This allows low-temperature hydrothermal activity in the underlying crustal rocks, bringing oxygen and other solutes into the sediments from below. Therefore, the geochemical zonation in the deeper sediments is reversed. The sediment composition, mineral diagenesis and (bio)geochemical processes in this environment have not yet been studied in detail. This work, based on a combination of sediment-magnetic methods and geochemical analyses, investigates the mineralogy and the processes in these hydrothermally influenced sediments. The influx of oxygen from below supports the preservation of magnetic minerals in the sediments and enables reliable magnetic dating over several million years. Hydrothermal oxygen and chemoremanent overprinting have no significant effects. However, it was discovered that microaerophilic magnetotactic bacteria can live deep inside the hydrothermally oxygenated sediments, where no such bacteria have been expected in the past. The secondary biogenic magnetite produced by these bacteria accumulates locally and results in magnetic anomalies and overprinting. This discovery has far-reaching consequences for hydrothermally active deep-sea regions and, in particular, for ridge flank systems
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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