1,721,112 research outputs found
Black hole shadows and invariant phase space structures
No full textUtilizing concepts from dynamical systems theory, we demonstrate how the existence of light rings, or fixed points, in a spacetime will give rise to families of periodic orbits and invariant manifolds in phase space. It is shown that these structures can define the shape of the black hole shadow as well as a number of salient features of the spacetime lensing. We illustrate this through the analysis of lensing by a hairy black hole.</p
Gauduchon-Tod structures, Sim holonomy and de Sitter supergravity
No full textSolutions of five-dimensional De Sitter supergravity admitting Killing spinors are considered, using spinorial geometry techniques. It is shown that the null solutions are defined in terms of a one parameter family of 3-dimensional constrained Einstein-Weyl spaces called Gauduchon-Tod structures. They admit a geodesic, expansion-free, twist-free and shear-free null vector field and therefore are a particular type of Kundt geometry. When the Gauduchon-Tod structure reduces to the 3-sphere, the null vector becomes recurrent, and therefore the holonomy is contained in Sim(3), the maximal proper subgroup of the Lorentz group SO(4,1). For these geometries, all scalar invariants built from the curvature are constant. Explicit examples are discussed. © SISSA 2009.Brannlund J, 2008, CLASSICAL QUANT GRAV, V25, DOI 10.1088-0264-9381-25-19-195007; Cacciatori SL, 2007, J HIGH ENERGY PHYS; Calderbank DMJ, 2001, DIFFER GEOM APPL, V14, P199, DOI 10.1016-S0926-2245(01)00037-7; Cardoso V, 2004, PHYS REV D, V70, DOI 10.1103-PhysRevD.70.024002; Cohen AG, 2006, PHYS REV LETT, V97, DOI 10.1103-PhysRevLett.97.021601; Coley A, 2009, CLASSICAL QUANT GRAV, V26, DOI 10.1088-0264-9381-26-10-105016; Coley A, 2009, CLASSICAL QUANT GRAV, V26, DOI 10.1088-0264-9381-26-12-125011; Coley AA, 2008, CLASSICAL QUANT GRAV, V25, DOI 10.1088-0264-9381-25-14-145017; Dunajski M, 2001, DIFFER GEOM APPL, V14, P39, DOI 10.1016-S0926-2245(00)00037-1; Gauduchon P, 1998, J GEOM PHYS, V25, P291, DOI 10.1016-S0393-0440(97)00032-6; GAUDUCHON P, 1984, MATH ANN, V267, P495, DOI 10.1007-BF01455968; Gauntlett JP, 2003, CLASSICAL QUANT GRAV, V20, P4587, DOI 10.1088-0264-9381-20-21-005; Gauntlett JP, 2003, PHYS REV D, V68, DOI 10.1103-PhysRevD.68.105009; Gauntlett JP, 2004, PHYS REV D, V70, DOI 10.1103-PhysRevD.70.089901; Gibbons GW, 2007, PHYS REV D, V76, DOI 10.1103-PhysRevD.76.081701; Gibbons GW, 2008, CLASSICAL QUANT GRAV, V25, DOI 10.1088-0264-9381-25-12-125015; Gillard J, 2005, CLASSICAL QUANT GRAV, V22, P1033, DOI 10.1088-0264-9381-22-6-009; Gran U, 2007, J HIGH ENERGY PHYS; Gran U, 2008, J HIGH ENERGY PHYS; Gran U, 2005, CLASSICAL QUANT GRAV, V22, P2453, DOI 10.1088-0264-9381-22-12-010; Gran U, 2007, J HIGH ENERGY PHYS; Gran U, 2007, J HIGH ENERGY PHYS; Grover J, 2009, AIP CONF PROC, V1122, P129, DOI 10.1063-1.3141231; Grover J, 2008, J HIGH ENERGY PHYS; Grover J, 2009, NUCL PHYS B, V809, P406, DOI 10.1016-j.nuclphysb.2008.08.024; GUTOWSKI JB, ARXIV09030179; JONES PE, 1985, CLASSICAL QUANT GRAV, V2, P565, DOI 10.1088-0264-9381-2-4-021; KUNDT W, 1961, Z PHYS, V163, P77, DOI 10.1007-BF01328918; LUKIERSKI J, 1985, PHYS LETT B, V151, P382, DOI 10.1016-0370-2693(85)91659-4; Meessen P, 2009, J HIGH ENERGY PHYS, DOI 10.1088-1126-6708-2009-05-042; Nariai H., 1950, Science Reports of the Tohoku University, First Series, V34; Nariai H., 1951, Science Reports of the Tohoku University, First Series, V35; PILCH K, 1985, COMMUN MATH PHYS, V98, P105, DOI 10.1007-BF01211046; Podolsky J, 2009, CLASSICAL QUANT GRAV, V26, DOI 10.1088-0264-9381-26-10-105008; Skenderis K, 2006, PHYS REV LETT, V96, DOI 10.1103-PhysRevLett.96.191301; STEPHANI H, 2003, EXACT SOLUTIONS EINS, pCH31; TOD KP, 1992, J LOND MATH SOC, V45, P34114151
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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