1,720,968 research outputs found
Parity violation in gravitational waves and observational bounds from third-generation detectors
Get PDFIn this paper, we analyze parity-violating effects in the propagation of
gravitational waves (GWs). For this purpose, we adopt a newly proposed
parametrized post-Einstenian (PPE) formalism, which encodes modified gravity
corrections to the phase and amplitude of GW waveforms. In particular, we focus
our study on three well-known examples of parity-violating theories, namely
Chern-Simons, Symmetric Teleparallel and Hor\v ava-Lishitz gravity. For each
model, we identify the PPE parameters emerging from the inclusion of
parity-violating terms in the gravitational Lagrangian. Thus, we use the
simulated sensitivities of third-generation GW interferometers, such as the
Einstein Telescope and Cosmic Explorer, to obtain numerical bounds on the PPE
coefficients and the physical parameters of binary systems. In so doing, we
find that deviations from General Relativity cannot be excluded within given
confidence limits. Moreover, our results show an improvement of one order of
magnitude in the relative accuracy of the GW parameters compared to the values
inferred from the LIGO-Virgo-KAGRA network. In this respect, the present work
demonstrates the power of next-generation GW detectors to probe fundamental
physics with unprecedented precision.Comment: 19 pages, 8 figures. Accepted for publication in Phys. Rev.
Role of spatial curvature in the primordial gravitational wave power spectrum
No full textThis paper investigates the effects of nonvanishing spatial curvature on the propagation of primordial gravitational waves produced during inflation. In particular, we consider tensor perturbations over a homogeneous and isotropic background and describe the propagation of gravitational waves in the de Sitter phase with spatially curved geometries. We thus derive the expression of the primordial power spectrum at the horizon crossing in the case of open and closed universes. Then, we analyze how tensor modes propagate in the postinflationary era, showing the evolution of transfer functions in the radiation and matter epochs, as well as the matching conditions in the intermediate regime. To account for the intrinsic nature of different relativistic species, we also explore the corrections to the standard behavior of the radiation energy density. For this purpose, we introduce the effective number of degrees of freedom of relativistic particles contributing to the primordial energy and entropy densities. Under the subhorizon approximation, we obtain the spectral energy density of relic gravitational waves in terms of the curvature density parameter. Finally, we discuss the capability of present and future experiments to detect the primordial gravitational wave signal at different frequency regimes
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
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
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