1,721,007 research outputs found
A scenario for a baryonic dark halo
No full textThe recent observations of microlensing events in the LMC by the MACHO and EROS collaborations suggest that an important fraction of the galactic halo is in the form of Massive Halo Objects (MHO) of about 0.1Msun_. Here, we argue that the galactic halo is mainly baryonic and that besides MHO also H_2_ molecular clouds may significantly contribute to it. We propose a scenario in which dark clusters of MHO and/or H_2_ molecular clouds form in the halo at galactocentric distances larger than ~10-20kpc, since there we expect less collisions among proto globular cluster clouds and a smaller UV radiation flux. Cosmic ray protons may induce a significant γ-ray flux in H_2_ molecular clouds. Our calculation gives an upper bound to this flux which is below present detectability
Is the Galactic halo baryonic?
No full textRecent observations of microlensing events in the Large Magellanic Cloud suggest that a sizeable fraction of the Galactic halo is in the form of massive astrophysical compact halo objects (MACHOs) with mass less than about 0.1 Msun. Here, the authors argue that molecular clouds (mainly of H2) located in the Galactic halo can contribute substantially to its total mass. They outline a scenario in which dark clusters of MACHOs and molecular clouds naturally form in the halo at large galactocentric distances. Possible ways of detecting MACHOs via infrared emission and molecular clouds via the induced γ-ray flux are discussed. Molecular clouds located in the dark halo of M31 could be discovered through cosmic background radiation anisotropies or emission lines in the microwave band
Gamma rays from a baryonic dark halo
No full textA recent re-analysis of EGRET data by Dixon et al [1] has led to the discovery of a statistically significant diffuse gamma-ray emission from the galactic halo. We show that this emission can naturally be accounted for within a previously-proposed model for baryonic dark matter, according to which dark clusters of brown dwarfs and cold self-gravitating H-2 clouds populate the outer galactic halo and can show up in microlensing observations. Basically, cosmic-ray protons in the galactic halo scatter on the clouds clumped into dark clusters, giving rise to the observed gamma-ray flux. We derive maps for the corresponding intensity distribution, which turn out to be in remarkably good agreement with those obtained by Dixon et al [1]. We also address future prospects to test our predictions
MACHOs as Brown Dwarfs
No full textRecent observations of microlensing events in the LMC suggest that a sizable fraction of the galactic halo is in the form of MACHOs. We describe a scenario in which dark clusters of MACHOs and cold molecular clouds naturally form at galactocentric distances larger than 10-20 kpc
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
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