1,720,975 research outputs found
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
Effects of lithospheric strength on convection in the Earth's mantle
Full text linkThesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2000.Includes bibliographical references (p. 235-244).Convection in Earth's mantle is driven largely by horizontal density gradients that form when cold, dense, mantle lithosphere descends into the mantle interior, either through subduction for plate-scale flow, or as localized convective instability beneath lithospheric plates. The deformation associated with these processes is resisted by the extreme temperature-dependence of the lithosphere's strength. Ways in which lithosphere deformation affects convection in the mantle are examined here, by comparing both theory and the results of numerical experiments. Convective instability at the base of a cold thermal boundary layer with temperature and strain-rate-dependent viscosity is investigated by defining a quantity, termed here the "available buoyancy," that takes into account the tradeoff between cold temperatures both promoting and resisting convective instability. This quantity can be used to determine approximately whether, and how fast, convective instability grows. Horizontal shortening is also included, which tends to increase gravitational instability, allowing up to 60% of the mantle lithosphere to be convectively removed. The subsequent influx of hot, buoyant, asthenosphere could cause rapid surface uplift. For plate-scale flow, subduction zone deformation may resist convection. This possibility is studied here using a regional finite element model of subduction. This model shows that for sufficiently strong lithosphere, convection is resisted more by the bending deformation of a subducting plate than by shearing of the underlying mantle. Such behavior can be explained by a variation of boundary layer theory that includes an analytic expression for the energy required to bend a viscous plate. For the mantle, the bending resistance should control plate velocities if the effective lithosphere viscosity is greater than about 1023 Pa s. This produces a reasonable distribution of plate velocities for Earth and may reconcile models for its thermal evolution with surface heat flow observations. These results are verified using a new method for implementing subduction that parameterizes plate bending within a small region of a mantle-scale convection model. This model also shows that small-scale convection, by removing the basal part of the oceanic lithosphere, can decrease the bending resistance and thus may be an essential aspect of plate tectonics on Earth.by Clinton Phillips Conrad.Ph.D
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
Assessing Models for Pacific Absolute Plate and Plume Motions
No full textAbsolute plate motion (APM) models derived from hot spot trails must satisfy trail geometries, ages, and paleolatitudes, which requires modeling explicit plume motions. Models lacking plume motions or derived independently from seamounts must also fit these data, provided the implicit plume motions are geodynamically reasonable. We evaluate eight Pacific APM models; three have explicitly modeled plume motions. Seven derive from seamount age progressions; one is a geodynamic model driven by slab pull and ridge push. Using the long‐lived Hawaii‐Emperor and Louisville chains, we derive implicit motions of Hawaii and Louisville plumes for models lacking explicit estimates and compare them with observed paleolatitudes. Inferred plume motions are plausible given rheological constraints on mantle flow, but rates vary considerably and not all models fit the data well. One potential endmember model predicts no APM direction change at 50 Ma, which best explains trails and paleolatitudes, minimizes predicted rotation of Pacific‐Farallon ridge and assumes no true polar motion, yet its implicit plume drift is inconsistent with global circulation models. Alternatively, a global moving hot spot model yields acceptable fits to geometry and ages, implies a major APM change at 50 Ma, but requires significant true polar wander to explain observed paleolatitudes. The inherent inconsistency between age progressions and paleolatitudes may be reconciled by true polar wander, yet questions remain about the accuracy of age progressions for older sections of the Emperor and Louisville chains, the independent geologic evidence for an APM change at 50 Ma, and the uniqueness and relevance of true polar wander estimates
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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