1,720,958 research outputs found
Quantum black holes in bootstrapped Newtonian gravity
Get PDFWe analyze the classical configurations of a bootstrapped Newtonian potential generated by homogeneous spherically symmetric sources in terms of a quantum coherent state. We first compute how the mass and mean wavelength of these solutions scale in terms of the number of quanta in the coherent state. We then note that the classical relation between the ADM mass and the proper mass of the source naturally gives rise to a generalized uncertainty principle (GUP) for the size of the gravitational radius in the quantum theory. Consistency of the mass and wavelength scalings with this GUP requires the compactness remains at most of order one even for black holes, and the corpuscular predictions are thus recovered, with the quantized horizon area expressed in terms of the number of quanta in the coherent state. Our findings could be useful for analyzing the classicalization of gravity in the presence of matter and the avoidance of singularities in the gravitational collapse of compact sources
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
Analytical Studies of Black Hole Systems
Get PDFThis work includes a series of analytical projects aimed at providing accurate initial data parameters for full Numerical Relativity evolutions of binary black holes (BBH), allow the evolution of multiple black hole systems, and the interpretation and modeling of high- energy collision of black holes. We first describe how to obtain accurate initial data for the evolution of BBH by extending the determination of quasi-circular orbital parameters described in [1] to 3.5PN, and by incorporating the small mass ratio limit by explicitly including the Schwarzschild and Kerr limits [2]. We then focus on eccentric binary black hole systems, developing a new estimation method for their eccentricity based on post-Newtonian (PN) theory, introducing the fractional parameter f to quantify the change of tangential momenta relative to the corresponding quasi-circular one at the initial turning points of the orbit. In the third project, we study initial data for triple black hole systems in a hierarchical system of three black holes, as one of the main candidates to explain non negligible residual eccentricity in late stages of the inspiral. Specifically, we extend the method described in [3, 4] to second order to solve the Hamiltonian constraint equation of the transverse and conformally flat initial data problem in General Relativity. This method is then applied to compute approximate initial data for the evolution of triple black hole systems [5]. Lastly, in the fourth project [6], we employ the Zero Frequency Limit (ZFL) expansion to semi-analytically model the energy and angular momentum radiated during the merger of high-energy-collisions of binary black boles as a function of their impact parameter and initial relativistic momenta. We thus stress the relevance of combining analytic with full numerical methods to study the dynamics of black holes in astrophysical scenarios and beyond
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
Corpuscolar description of bootstrapped Newtonian gravity
Get PDFOne of the main features of General Relativity is that, under very general assumptions
and for sufficiently dense objects, it always leads to the creation of space-time singularities
that are quite difficult to handle both from an intuitive and a mathematical point of view.
Moreover, these singularities are in contrast with the Heisenberg uncertainty principle
since they would form a region of space with infinite density of energy. In the last
years, Dvali and Gomez suggested a novel approach to black holes' physics, according to
which the gravitational field can be described as a collection of soft gravitons. In this
picture some phenomena that are very well known in the geometrical picture of gravity
are explained in terms of Quantum Mechanical effects related to gravitons. The aim of
this work is to provide a self consistent quantum corpuscolar description of gravitational
interactions with a classical background given by the bootstrapped Newtonian gravity,
where no space-time singularities arise, and compare the results with the assumptions
made by Dvali and Gomez about the properties of gravitons
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
Diffusione di onde elettromagnetiche
Get PDFIn questa tesi, viene considerato il problema della diffusione
della radiazione eletromagnetica da parte della materia nell’ambito della elettrodinamica
classica. La radiazione diffusa verrà studiata nel regime di campo lontano
sotto l’ipotesi che i processi di diffusione siano totalmente elastici
e che gli eventi di diffusione multipla siano trascurabili.
Ci si soffermerà in particolare su come determinare la sezione di diffusione differenziale e totale trattando in maniera più dettagliata il caso in cui la radiazione incidente è non polarizzata ed interagisce con un grande numero di centri diffusori di dimensioni molto più piccole della sua lunghezza d’onda. Come applicazione verrà
esaminata la diffusione della luce solare dalla atmosfera
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