1,720,962 research outputs found
The dark side of the Universe
Full text linkThe knowledge of the Universe surrounding us, nevertheless the big steps forward of the last decade, presents a lot of obscure or not well understood parts, that are usually indicated with the adjective dark. These parts touch every component of the Universe: we have well known radiation in form of photons, and its dark counterpart in form of neutrinos, dark matter beside the ordinary (baryonic) matter and also an obscure form of energy whose nature is completely unknown.
In this context the big challenge of the next generation cosmology is to determine the intrinsic properties of these exotic components by working on available observables and by determining new ways to look at our Universe.
Astrophysicists and Cosmologists developed during the years different techniques to observe the sky, some of which focus on the static properties of the Universe (distances and topology, actual composition), while others point towards a description of its dynamics (evolution of the components' perturbations, expansion of the background and so on). As we will see in detail in this thesis, the general relativity that rules the Universe evolution works in such a way to link statical and dynamical behaviour. This feature gives the Cosmologists the possibility to infer dynamical properties starting from simple geometrical measurements, and this, in last analysis, leads to development of new techniques to study directly also the evolutionary part of the Cosmo. We already have some measurements of this kind, but the best is to come with recently developed experiments that started in the last couple of years or that should start soon. This kind of observations will concentrate on precise and complete dynamical data that hopefully will lead us to comprehend also the darkest part of our knowledge: the dark energy.
My Ph.D. work has been principally focused on the study of the properties of the dark sector of the Universe using all probes actually available
Planck constraints on the effective neutrino number and the CMB power spectrum lensing amplitude
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New constraints on the dark energy equation of state
No full textWe combine recent measurements of cosmic microwave background anisotropies, supernovae luminosity distances, and baryonic acoustic oscillations to derive constraints on the dark energy equation of state w in the redshift range 0<z<2 using a principal components approach. We find no significant deviations from the expectations of a cosmological constant. However, combining the data sets, we find a slight indication for w<-1 at low redshift, thus highlighting how these data sets prefer a nonconstant w. Nevertheless, the cosmological constant is still in agreement with these observations, while we find that some classes of alternative models may be in tension with the inferred w(z) behavior. © 2013 American Physical Society
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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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