45,985 research outputs found
Giga-Gauss scale quasistatic magnetic field generation in an 'escargot' target
A simple setup for the generation of ultra-intense quasistatic magnetic
fields, based on the generation of electron currents with a predefined geometry
in a curved 'escargot' target, is proposed and analysed. Particle-In-Cell
simulations and qualitative estimates show that giga-Gauss scale magnetic
fields may be achieved with existent laser facilities. The described mechanism
of the strong magnetic field generation may be useful in a wide range of
applications, from laboratory astrophysics to magnetized ICF schemes.Comment: Submitted to PRL. arXiv admin note: text overlap with arXiv:1409.524
Milky Way demographics with the VVV survey. IV. PSF photometry from almost one billion stars in the Galactic bulge and adjacent southern disk
Accepted for publication in a forthcoming issue of Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Context. The inner regions of the Galaxy are severely affected by extinction, which limits our capability to study the stellar populations present there. The Vista Variables in the VĂa LĂĄctea (VVV) ESO Public Survey has observed this zone at near-infrared wavelengths where reddening is highly diminished. Aims. By exploiting the high resolution and wide field-of-view of the VVV images we aim to produce a deep, homogeneous, and highly complete database of sources that cover the innermost regions of our Galaxy. Methods. To better deal with the high crowding in the surveyed areas, we have used point spread function (PSF)-fitting techniques to obtain a new photometry of the VVV images, in the ZY JHK s near-infrared filters available. Results. Our final catalogs contain close to one billion sources, with precise photometry in up to five near-infrared filters, and they are already being used to provide an unprecedented view of the inner Galactic stellar populations. We make these catalogs publicly available to the community. Our catalogs allow us to build the VVV giga-CMD, a series of color-magnitude diagrams of the inner regions of the Milky Way presented as supplementary videos. We provide a qualitative analysis of some representative CMDs of the inner regions of the Galaxy, and briefly mention some of the studies we have developed with this new dataset so far.Peer reviewe
The Use of Abbreviations in English-Medium Astrophysics Research Paper Titles: A Problematic Issue
In this study, we carry out a qualitative and quantitative analysis of abbreviations in 300 randomly collected research paper titles published in the most prestigious European and US-based Astrophysics journals written in English. Our main results show that the process of shortening words and groups of words is one of the most characteristic and recurrent features in Astrophysics research paper titling construction. In spite of the convenience of abbreviations as a mechanism for word-formation, some of them may pose certain difficulties of understanding and/or misinterpretation because of their specificity, ambiguity, or overlapping. To overcome these difficulties, we propose a series of options which with no doubt would lead to a better interaction among the different branches of Astrophysics in particular and of science in general and would definitely improve how research is currently performed and communicated
Clustering with phylogenetic tools in astrophysics
Phylogenetic approaches are finding more and more applications outside the
field of biology. Astrophysics is no exception since an overwhelming amount of
multivariate data has appeared in the last twenty years or so. In particular,
the diversification of galaxies throughout the evolution of the Universe quite
naturally invokes phylogenetic approaches. We have demonstrated that Maximum
Parsimony brings useful astrophysical results, and we now proceed toward the
analyses of large datasets for galaxies. In this talk I present how we solve
the major difficulties for this goal: the choice of the parameters, their
discretization, and the analysis of a high number of objects with an
unsupervised NP-hard classification technique like cladistics. 1. Introduction
How do the galaxy form, and when? How did the galaxy evolve and transform
themselves to create the diversity we observe? What are the progenitors to
present-day galaxies? To answer these big questions, observations throughout
the Universe and the physical modelisation are obvious tools. But between
these, there is a key process, without which it would be impossible to extract
some digestible information from the complexity of these systems. This is
classification. One century ago, galaxies were discovered by Hubble. From
images obtained in the visible range of wavelengths, he synthetised his
observations through the usual process: classification. With only one parameter
(the shape) that is qualitative and determined with the eye, he found four
categories: ellipticals, spirals, barred spirals and irregulars. This is the
famous Hubble classification. He later hypothetized relationships between these
classes, building the Hubble Tuning Fork. The Hubble classification has been
refined, notably by de Vaucouleurs, and is still used as the only global
classification of galaxies. Even though the physical relationships proposed by
Hubble are not retained any more, the Hubble Tuning Fork is nearly always used
to represent the classification of the galaxy diversity under its new name the
Hubble sequence (e.g. Delgado-Serrano, 2012). Its success is impressive and can
be understood by its simplicity, even its beauty, and by the many correlations
found between the morphology of galaxies and their other properties. And one
must admit that there is no alternative up to now, even though both the Hubble
classification and diagram have been recognised to be unsatisfactory. Among the
most obvious flaws of this classification, one must mention its monovariate,
qualitative, subjective and old-fashioned nature, as well as the difficulty to
characterise the morphology of distant galaxies. The first two most significant
multivariate studies were by Watanabe et al. (1985) and Whitmore (1984). Since
the year 2005, the number of studies attempting to go beyond the Hubble
classification has increased largely. Why, despite of this, the Hubble
classification and its sequence are still alive and no alternative have yet
emerged (Sandage, 2005)? My feeling is that the results of the multivariate
analyses are not easily integrated into a one-century old practice of modeling
the observations. In addition, extragalactic objects like galaxies, stellar
clusters or stars do evolve. Astronomy now provides data on very distant
objects, raising the question of the relationships between those and our
present day nearby galaxies. Clearly, this is a phylogenetic problem.
Astrocladistics 1 aims at exploring the use of phylogenetic tools in
astrophysics (Fraix-Burnet et al., 2006a,b). We have proved that Maximum
Parsimony (or cladistics) can be applied in astrophysics and provides a new
exploration tool of the data (Fraix-Burnet et al., 2009, 2012, Cardone \&
Fraix-Burnet, 2013). As far as the classification of galaxies is concerned, a
larger number of objects must now be analysed. In this paper, IComment: Proceedings of the 60th World Statistics Congress of the
International Statistical Institute, ISI2015, Jul 2015, Rio de Janeiro,
Brazi
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