1,721,027 research outputs found
Thermodynamics of scalar-tensor gravity
No full textISSN:1550-7998ISSN:0556-2821ISSN:1550-2368ISSN:0556-2821ISSN:1550-236
Past-directed scalar field gradients and scalar-tensor thermodynamics
Full text linkWe refine and slightly enlarge the recently proposed first-orderthermodynamics of scalar-tensor gravity to include gravitational scalar fieldswith timelike and past-directed gradients. The implications and subtletiesarising in this situation are discussed and an exact cosmological solution ofscalar-tensor theory in first-order thermodynamics is revisited in light ofthese results.<br
Fluid nature constrains Horndeski gravity
Full text linkThe elusive physical nature of Horndeski gravity is elucidated in a new
approach depicting this class of theories as a dissipative effective fluid.
Requiring the constitutive equations of the latter to be those of a Newtonian
fluid restricts the theory to only two disconnected subclasses of "viable"
Horndeski gravity. Therefore, a stress-energy tensor of Horndeski effective
fluid, linear in the first derivatives of the fluid's 4-velocity, is a
sufficient condition for gravitational waves to propagate at light speed. All
other Horndeski theories correspond to exotic non-Newtonian effective fluids.Comment: 28 pages, 2 tables. Matches published version in General Relativity
and Gravitatio
Scalar field as a perfect fluid: thermodynamics of minimally coupled scalars and Einstein frame scalar-tensor gravity
Full text linkWe revisit the analogy between a minimally coupled scalar field in generalrelativity and a perfect fluid, correcting previous identifications ofeffective temperature and chemical potential. This provides a usefulcomplementary picture for the first-order thermodynamics of scalar-tensorgravity, paving the way for the Einstein frame formulation (which eludedprevious attempts) and raises interesting questions to further develop theanalogy.<br
Exercises in environmental physics
No full textFirst exercise book dedicated to environmental physicsFor use in various courses in environmental sciences
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
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