1,720,967 research outputs found
Astrophysical jets from boosted compact objects
Get PDFWe perform full 3D numerical simulations of compact objects, such as black holes or neutron stars, boosted through an ambient forcefree plasma that posses a uniform magnetization. We study jet formation and energy extraction from the resulting stationary late time solutions. The implementation of appropriate boundary conditions has allowed us to explore a wide range of boost velocities, finding the jet power scales as γv2 (being γ the Lorentz factor). We also explore other parameters of the problem like the orientation of the motion respect to the asymptotic magnetic field or the inclusion of black hole spin. Additionally, by comparing a black hole with a perfectly conducting sphere in flat spacetime, we manage to disentangle curvature effects from those produced by the perfect conducting surface. It is shown that when the stellar compactness is increased these two effects act in combination, further enhancing the luminosity produced by the neutron star.Fil: Cayuso, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Perimeter Institute for Theoretical Physics; CanadáFil: Carrasco, Federico León. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Universidad de las Islas Baleares; España. Institut d’Estudis Espacials de Catalunya; EspañaFil: Sbarato, Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Reula, Oscar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin
Formación de Jets por agujeros negros viajando a altas velocidades en un campo magnético
Get PDFTesis (Lic. en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2018.En este trabajo se continuó el estudio numérico de formación de jets por agujeros negros viajandoa altas velocidades con respecto a un campo magnético uniforme comenzado en [1]. El esquema numérico implementado es el utilizado en [2] el cual presenta un esquema numérico 3D para la evolución de las ecuaciones de la electrodinámica force-freealrededor de un agujero negro de Kerr.Tratamos en este trabajo tres situaciones físicas distintas: i) Un agujero negro de Schwarzschild viajando con velocidades ortogonales al campo magnético asintóticamente uniforme. ii) Un agujero negro de Schwarzschild viajando con velocidades no ortogonales al campo magnético asintóticamente uniforme. iii) Un agujero negro de Kerr en la situación de i) donde el eje de rotación del agujero negro puede estar, o no, alineado con el campo magnético asintóticamente uniforme.This work continues the numerical study of jet formation as result of black holes traveling with fast velocities with respect to a uniform magnetic eld, study that was started in [1]. The numerical scheme implemented is the one used in [2], which presents a novel 3D numerical implementation of the force-free electrodynamics evolution around a Kerr black hole. We study three different physical situations: i) A Schwarzschild black hole traveling with velocities that are orthogonal to the asymptotically uniform magnetic eld. ii) A Schwarzschild black hole traveling with velocities that are not orthogonal to the asymptotically uniform magnetic eld. iii) A Kerr black hole in the i) scenario, where the axis of rotation of the black can be aligned, or not, to the asymptotically uniform magnetic eld
Gravitational collapse in Quadratic Gravity
Get PDFThis study explores the gravitational collapse of a massless scalar field
within Quadratic Gravity treated as a dimension-four operator Effective Field
Theory extension to General Relativity. The additional degrees of freedom
associated with the higher derivatives in this theory are removed by an Order
Reduction approach, where the truncated expansion nature of the theory is
exploited. Through simulations, we find scenarios where solutions remain within
the bounds of the Effective Field Theory while displaying significant
deviations from General Relativity in the dynamics of curvature invariants
during the collapse. Limitations of the approach taken, the Effective Field
Theory approximation, and the appearance of instabilities are also discussed
Black hole dynamics in Effective Field Theory extensions to General Relativity
Get PDFThis thesis aims to develop and implement mathematical and numerical techniques to enable the study of deviations from General Relativity (GR) in the nonlinear regime. The focus is on studying the nonlinear dynamics of higher derivative Effective Field Theory (EFT) extensions to GR and employing innovative methods to address the associated mathematical and practical challenges. To this end, we utilize two crucial techniques: the Fixing the Equations method, which controls spurious high frequencies, and the Order reduction approach to address challenges related to higher than second order time derivatives
and ghosts.
The research starts with a detailed study of black hole dynamics in a higher derivative extension of General Relativity described by a dimension-eight operator EFT. A fully nonlinear/non-perturbative treatment is presented for constructing initial data and studying its dynamical behavior in spherical symmetry when coupled to a massless scalar field.
Subsequently, we extend the previous work to explore the evolution of black holes merging in quasi-circular orbits within the same higher-derivative EFT extension. This scenario poses more demanding challenges; a toy model and the single-boosted black hole scenario are considered to build up to the binary merger case. The effects of modifications
on the dynamics and gravitational wave emission in the binary merger scenario are studied.
The research work culminates with a study of gravitational collapse in Quadratic Gravity, the leading order correction to GR from an EFT perspective in the presence of matter fields. An Order Reduction approach is used to eliminate additional degrees of freedom associated with higher order time derivatives. We study the collapse of a massless scalar field into a black hole in spherical symmetry. We explore the stability of our simulations, whether the solutions remain within the bounds of EFT, and their deviations from General Relativity during the collapse
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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