1,720,955 research outputs found
Wiggly tails: A gravitational wave signature of massive fields around black holes
No full textMassive fields can exist in long-lived configurations around black holes. We examine how the gravitational wave signal of a perturbed black hole is affected by such "dirtiness" within linear theory. As a concrete example, we consider the gravitational radiation emitted by the infall of a massive scalar field into a Schwarzschild black hole. Whereas part of the scalar field is absorbed/scattered by the black hole and triggers gravitational wave emission, another part lingers in long-lived quasibound states. Solving numerically the Teukolsky master equation for gravitational perturbations coupled to the massive Klein-Gordon equation, we find a characteristic gravitational wave signal, composed by a quasinormal ringing followed by a late time tail. In contrast to "clean" black holes, however, the late time tail contains small amplitude wiggles with the frequency of the dominating quasibound state. Additionally, an observer dependent beating pattern may also be seen. These features were already observed in fully nonlinear studies; our analysis shows they are present at linear level, and, since it reduces to a 1+1 dimensional numerical problem, allows for cleaner numerical data. Moreover, we discuss the power law of the tail and that it only becomes universal sufficiently far away from the dirty black hole. The wiggly tails, by constrast, are a generic feature that may be used as a smoking gun for the presence of massive fields around black holes, either as a linear cloud or as fully nonlinear hair. � 2014 American Physical Society
HKT geometry and de Sitter supergravity
No full textSolutions of five-dimensional minimal de Sitter supergravity admitting Killing spinors are considered. It is shown that the timelike solutions are determined in terms of a four-dimensional hyper-Kähler torsion (HKT) manifold. If the HKT manifold is conformally hyper-Kähler the most general solution can be obtained from a sub-class of supersymmetric solutions of minimal N = 2 ungauged supergravity, by means of a simple transformation. Examples include a multi-BMPV de Sitter solution, describing multiple rotating black holes co-moving with the expansion of the universe. If the HKT manifold is not conformally hyper-Kähler, examples admitting a tri-holomorphic Killing vector field are constructed in terms of certain solutions of three-dimensional Einstein-Weyl geometry. © 2008 Elsevier B.V. All rights reserved.ALVAREZGAUME L, 1981, COMMUN MATH PHYS, V80, P443, DOI 10.1007-BF01208280; Behrndt K, 2004, CLASSICAL QUANT GRAV, V21, P4107, DOI 10.1088-0264-9381-21-17-006; Behrndt K, 2003, CLASSICAL QUANT GRAV, V20, P4177, DOI 10.1088-0264-9381-20-19-304; Bergshoeff Eric A, 2007, JHEP-Journal of High Energy Physics, DOI 10.1088-1126-6708-2007-07-067; BRAATEN E, 1985, NUCL PHYS B, V260, P630, DOI 10.1016-0550-3213(85)90053-7; Breckenridge JC, 1997, PHYS LETT B, V391, P93, DOI 10.1016-S0370-2693(96)01460-8; Cacciatori S.L., 2007, JHEP, V0707, P046; CALLAN CG, 1991, NUCL PHYS B, V359, P611, DOI 10.1016-0550-3213(91)90074-8; CANDELAS P, 1985, NUCL PHYS B, V258, P46, DOI 10.1016-0550-3213(85)90602-9; Chave T, 1996, PHYS LETT B, V383, P262, DOI 10.1016-0370-2693(96)00760-5; Chen W, 2006, NUCL PHYS B, V732, P118, DOI 10.1016-j.nuclphysb.2005.10.018; CURTRIGHT TL, 1984, PHYS REV LETT, V53, P1799, DOI 10.1103-PhysRevLett.53.1799; DELDUC F, 1993, CLASSICAL QUANT GRAV, V10, P1201, DOI 10.1088-0264-9381-10-7-003; Elvang H, 2004, PHYS REV LETT, V93, DOI 10.1103-PhysRevLett.93.211302; FIGUERAS P, 2006, JHEP, V611, P36; Gauduchon P, 1998, J GEOM PHYS, V25, P291, DOI 10.1016-S0393-0440(97)00032-6; 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, 1999, CLASSICAL QUANT GRAV, V16, P1, DOI 10.1088-0264-9381-16-1-001; Gauntlett JP, 2004, PHYS REV D, V70, DOI 10.1103-PhysRevD.70.089901; Gibbons GW, 1997, NUCL PHYS B, V508, P623, DOI 10.1016-S0550-3213(97)00599-3; GIBBONS GW, 1978, PHYS LETT B, V78, P430, DOI 10.1016-0370-2693(78)90478-1; Gibbons GW, 2005, PHYS REV LETT, V94, DOI 10.1103-PhysRevLett.94.131602; Gillard J, 2005, CLASSICAL QUANT GRAV, V22, P1033, DOI 10.1088-0264-9381-22-6-009; GRAN U, 2007, JHEP, V702, P43; Gran U, 2005, CLASSICAL QUANT GRAV, V22, P2453, DOI 10.1088-0264-9381-22-12-010; GRAN U, 2007, JHEP, V702, P44; Gran U., 2007, JHEP, V0708, P074; GRAN U, ARXIV08021799; GROVER J, ARXIV08020231; Gutowski J, 2000, PHYS LETT B, V472, P45, DOI 10.1016-S0370-2693(99)01412-4; Herdeiro CAR, 2003, NUCL PHYS B, V665, P189, DOI 10.1016-S0550-3213(03)00484-X; HOWE PS, 1987, NUCL PHYS B, V289, P264, DOI 10.1016-0550-3213(87)90380-4; HOWE PS, 1988, CLASSICAL QUANT GRAV, V5, P1647, DOI 10.1088-0264-9381-5-12-014; HULL CM, 1986, LECT NONLINEAR SIGMA; HULL CM, 1998, JHEP, V9807, P21; KASTOR D, 1993, PHYS REV D, V47, P5370, DOI 10.1103-PhysRevD.47.5370; KLEMM D, 2001, JHEP, V102, P31; Liu JT, 2001, PHYS LETT B, V498, P123, DOI 10.1016-S0370-2693(00)01350-2; LIU JT, 2004, JHEP, V401, P7; LUKIERSKI J, 1985, PHYS LETT B, V151, P382, DOI 10.1016-0370-2693(85)91659-4; PAPADOPOULOS G, 1995, PHYS LETT B, V356, P249, DOI 10.1016-0370-2693(95)00756-B; PILCH K, 1985, COMMUN MATH PHYS, V98, P105, DOI 10.1007-BF01211046; SKENDERIS K, ARXIV07043918; Skenderis K, 2006, PHYS REV LETT, V96, DOI 10.1103-PhysRevLett.96.191301; Vaula S, 2007, PHYS LETT B, V653, P95, DOI 10.1016-j.physletb.2007.07.048; WITTEN E, 1984, COMMUN MATH PHYS, V92, P455, DOI 10.1007-BF01215276; ZUMINO B, 1979, PHYS LETT B, V87, P203, DOI 10.1016-0370-2693(79)90964-X24202
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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