1,721,162 research outputs found
Energy deposition by weakly interacting massive particles: a comprehensive study
Full text linkWe present results obtained with the updated version of our code MEDEA2, which includes
all physical processes necessary to study the energy deposition in the surrounding environment
from primary photons and fast leptons produced by dark matter (DM) particle decay/
annihilation. Such interactions now include also Compton scattering of primary photons
off electrons and pair creation of photons on atoms. Our ultimate aim is a thorough study
of the impact of DM annihilations on the thermal and ionization history of the high-redshift
intergalactic medium (IGM) during the dark ages. In addition, a precise determination of the
effects of DM decays/annihilations can help constrain its nature. We present the results for
some selected DM candidates: (i) a 10-GeV bino-like neutralino; (ii) a heavy DM candidate of
rest mass 1 TeV that pair annihilates into muons; and (iii) a 200-GeV wino-like neutralino with
a pair annihilation into W+W− pairs. An interface to DARKSUSY allows us to use the computed
annihilation spectra in input for our code and follow the complete secondary cascade. The
fractional energy depositions into the IGM depend strongly on the DM particle rest mass:
whereas for the 10-GeV particle the absorbed energy fraction, in the redshift range 10 < z < 1000, is ∼ 50 per cent, higher mass candidates deposit their energy less efficiently (∼1–10 per
cent), making their impact on the high-z IGM considerably weaker. Noticeably, our approach
allows us to consistently follow the low-energy deposition of the cascade products, which
can be of interest for a broad range of applications. Finally, we provide both tabulated results
and analytical fits that can be readily implemented in theoretical studies of the effects and
detectability of the most popular DM candidates
Supernova dust formation and the grain growth in the early universe: The critical metallicity for low-mass star formation
Full text linkWe thank Simone Bianchi for his kind contribution. GC is supported by Research Fellowships of the Japan Society for the Promotion of Science (JSPS) for Young Scientists. This work is supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan and in part by Grant-in-Aid for Scientific Research from the JSPS Promotion of Science (22684004, 23224004, 23540324, 25287040, 25287050, and 26400223). A part of calculations is performed with COMA at Center for Computational Sciences in University of Tsukuba. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement n. 306476. ML acknowledges the following funding sources: PRIN INAF 2009 ‘Supernova Variety and Nucleosynthesis Yields’, and PRIN MIUR 2010–2011, project ‘The Chemical and dynamical Evolution of the Milky Way and Local Group Galaxies’, prot. 2010LY5N2T.We investigate the condition for the formation of low-mass second-generation stars in the early Universe. It has been proposed that gas cooling by dust thermal emission can trigger fragmentation of a low-metallicity star-forming gas cloud. In order to determine the critical condition in which dust cooling induces the formation of low-mass stars, we follow the thermal evolution of a collapsing cloud by a one-zone semi-analytic collapse model. Earlier studies assume the dust amount in the local Universe, where all refractory elements are depleted on to grains, and/or assume the constant dust amount during gas collapse. In this paper, we employ the models of dust formation and destruction in early supernovae to derive the realistic dust compositions and size distributions for multiple species as the initial conditions of our collapse calculations. We also follow accretion of heavy elements in the gas phase on to dust grains, i.e. grain growth, during gas contraction. We find that grain growth well alters the fragmentation property of the clouds. The critical conditions can be written by the gas metallicity Zcr and the initial depletion efficiency fdep,0 of gas-phase metal on to grains, or dust-to-metal mass ratio, as (Zcr/10-5.5 Z☉) = (fdep,0/0.18)-0.44 with small scatters in the range of Zcr = [0.06-3.2] × 10-5 Z☉. We also show that the initial dust composition and size distribution are important to determine Zcr
Matter power spectrum in hidden neutrino interacting dark matter models: a closer look at the collision term
No full textDark Matter (DM) models providing possible alternative solutions to the smallscale crisis of the standard cosmology are nowadays of growing interest. We consider DM interacting with light hidden fermions via well-motivated fundamental operators showing the resultant, matter power spectrum is suppressed on subgalactic scales within a plausible parameter region. Our basic description of the evolution of cosmological perturbations relies on a fully consistent first principles derivation of a perturbed Fokker-Planck type equation, generalizing existing literature. The cosmological perturbation of the Fokker-Planck equation is presented for the first time in two different gauges, where the results transform into each other according to the rules of gauge transformation. Furthermore, our focus lies on a, derivation of a broadly applicable and easily computable collision term showing important phenomenological differences to other existing approximations. As one of the Main results and concerning the small-scale crisis, we show the equal importance of vector and scalar boson mediated interactions between the DM and the light fermions
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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