1,722,529 research outputs found
Cosmic backgrounds from the radio to the far-infrared: recent results and perspectives from cosmological and astrophysical surveys
No full textBurigana, C., Battistelli, E.S., Bonavera, L., Choudhury, T.R., Lopez-Caniego, M., Skordis, C., Sullivan, R.M., Tanimura, H., Tizchang, S., Tristram, M., Weltman, A
CONSTRAINTS ON THE THERMAL HISTORY OF THE UNIVERSE FROM THE COSMIC MICROWAVE BACKGROUND SPECTRUM
No full textWe have carried out an extensive numerical analysis of distortions of microwave background spectrum that can arise over a broad interval of cosmic times. The range of validity of existing analytic approximation formulae, holding for large and very small values of the Comptonization parameter y, has been assessed and the shape of distortions that can arise for intermediate values of y has been determined. From a comparison with existing spectral data we have derived upper limits to the amount of energy that could have been dissipated at each cosmic time. The effectiveness of future measurements in tightening such constraints is discussed
FORMATION AND EVOLUTION OF EARLY DISTORTIONS OF THE MICROWAVE BACKGROUND SPECTRUM - A NUMERICAL STUDY
No full textWe present the results of an extensive numerical study on the formation and evolution of early distortions of the microwave background spectrum. The thermalization redshift, Z(therm), of arbitrary amounts of energy has been accurately determined. Simple formulae, yielding Z(therm) as a function of the baryon density and of the chemical potential are given. The process of relaxation to a stationary spectrum (Bose-Einstein like) is investigated in detail; several earlier conclusions are revised. An analytic formula which provides a very accurate description of the final stationary spectrum is presented and used to reassess the observational constraints on the chemical potential. We also give simple formulae, yielding, as a function of the baryon density and of the chemical potential, the wavelength at which the maximum distortion occurs and the amplitude of the distortion
ANALYTICAL DESCRIPTION OF SPECTRAL DISTORTIONS OF THE COSMIC MICROWAVE BACKGROUND
No full textWe present analytic approximation formulae describing spectral distortions of the Cosmic Microwave Background (CMB) as a function of three basic parameters: the amount of energy injected in the radiation field, the time at which the heating occurred, and the baryon density Omega(b). These formulae allow easy exploitation of the high accuracy measurements of the CMB spectrum to derive constraints on physical processes that may have occurred in the early universe, dispensing with the need of resorting to heavy numerical calculations
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
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