1,721,005 research outputs found
On black hole temperature in Horndeski gravity
Get PDFIt has been observed that for black holes in certain family of Horndeski gravity theories Wald's entropy formula does not lead to the correct first law for black hole thermodynamics. For this family of Horndeski theories speeds of propagation of gravitons and photons are in general different and gravitons move on an effective metric different than the one seen by photons. We show that the temperature of the black hole should be modified from surface gravity over 2π to include effects of this effective metric. The modified temperature, with the entropy unambiguously computed by the solution phase space method, yields the correct first law. Our results have far reaching implications for the Hawking radiation and species problem, going beyond the Horndeski theories
On Larger Values in the CMB Dipole Direction
Get PDFOn the assumption that quasars (QSO) and gamma-ray bursts (GRB) represent
\textit{standardisable candles}, we provide evidence that the Hubble constant
adopts larger values in hemispheres aligned with the CMB dipole
direction. If substantiated, this trend signals a departure from FLRW
cosmology. In particular, QSOs show a definite trend, whereas our findings in
GRBs are consistent with an isotropic Universe, but we show in a sample of GRBs
calibrated with Type Ia supernovae (SN) that this conclusion may change as one
focuses on GRBs more closely (mis)aligned with the CMB dipole direction. The
statistical significance in QSOs alone is and when combined
with similar trends in strong lensing, Type Ia SN and calibrated GRBs, this
increases to . Our findings are consistent with reported
discrepancies in the cosmic dipole and anisotropies in galaxy cluster scaling
relations. The reported variations in across the sky suggest that Hubble
tension may be a symptom of a deeper cosmological malaise.Comment: v1 align with the CMB dipole at
sites.google.com/apctp.org/cosmoprinciple; v2 simulations and references
added, presentation improved; v3 the anisotropic Universe marches on at PR
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
Quasar standardization: Overcoming Selection Biases and Redshift Evolution
Get PDFQuasars (QSOs) are extremely luminous active galatic nuclei currently
observed up to redshift . As such, they have the potential to be the
next rung of the cosmic distance ladder beyond SNe Ia, if they can reliably be
used as cosmological probes. The main issue in adopting QSOs as standard
candles (similarly to Gamma-Ray Bursts) is the large intrinsic scatter in the
relations between their observed properties. This could be overcome by finding
correlations among their observables that are intrinsic to the physics of QSOs
and not artifacts of selection biases and/or redshift evolution. The
reliability of these correlations should be verified through well-established
statistical tests. The correlation between the ultraviolet (UV) and X-ray
fluxes developed by Risaliti \& Lusso is one of the most promising relations.
We apply a statistical method to correct this relation for redshift evolution
and selection biases. \textbf{Remarkably, we recover the the same parameters of
the slope and the normalization as Risaliti \& Lusso. Our results establish the
reliability of this relation, which is intrinsic to the QSO properties and not
merely an effect of selection biases or redshift evolution. Hence,} the
possibility to standardize QSOs as cosmological candles, thereby extending the
Hubble diagram up to .Comment: 11 pages, 5 figures, 1 Table. The paper is now accepted in Ap
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
- …
