1,721,013 research outputs found
Seeking dark matter with γ -ray attenuation
No full textThe flux of high-energy astrophysical gamma rays is attenuated by the production of electron-positron pairs from scattering off of extragalactic background light (EBL). We use the most up-to-date information on galaxy populations to compute their contributions to the pair-production optical depth. We find that the optical depth inferred from gamma-ray measurements exceeds that expected from galaxies at the similar to 2 sigma level. If the excess is modeled as a frequency-independent re-scaling of the standard contribution to the EBL from galaxies, then an excess (an overall 14-30% increase of the EBL) is favored over the null hypothesis of no excess at the 2.7 sigma level. If the frequency dependence of the excess is instead modeled as a two-photon decay of a dark-matter axion, then the excess is favored over the null hypothesis at the 2.1 sigma confidence level. While we find no evidence for a dark-matter signal, the analysis sets the strongest current bounds on the photon-axion coupling over the 8-25 eV mass range. This work highlights the sensitivity of gamma-ray optical depth measurements to ALPs, which is expected to improve with new observatories and better EBL determinations from future observations
Exploring the role of the halo-mass function for inferring astrophysical parameters during reionization
Get PDFDetecting the 21-cm signal at z ≳ 6 will reveal insights into the properties of the first galaxies responsible for driving reionization. To extract this information, we perform parameter inference with three-dimensional simulations of the 21-cm signal embedded within a Bayesian inference pipeline. Presently, when performing inference, we must choose which sources of uncertainty to sample and which to hold fixed. Since the astrophysics of galaxies is much more uncertain than that of the underlying halo-mass function (HMF), we typically parametrize and model the former while fixing the latter. However, doing so may bias our inference of the galaxy properties. In this work, we explore the consequences of assuming an incorrect HMF and quantify the relative biases on our inferred astrophysical model parameters when considering the wrong HMF. We then relax this assumption by constructing a generalized five parameter HMF model and simultaneously recover it with our underlying astrophysical model. For this, we use 21CMFAST and perform simulation-based inference using marginal neural ratio estimation to learn the likelihood-to-evidence ratio with SWYFT. Using a mock 1000-h observation of the 21-cm power spectrum from the forthcoming Square Kilometre Array, conservatively assuming foreground wedge avoidance, we find that assuming the incorrect HMF can bias the recovered astrophysical parameters by up to ∼ 3–4σ even when including independent information from observed luminosity functions. Using our generalized HMF model, although we recover our astrophysical parameters with a factor of ∼ 2–4 larger marginalized uncertainties, the constraints are unbiased, agnostic to the underlying HMF and therefore more conservative
A galaxy-free phenomenological model for the 21-cm power spectrum during reionization
Get PDFUpper limits from the current generation of interferometers targeting the
21-cm signal from high redshifts have recently begun to rule out physically
realistic, though still extreme, models of the Epoch of Reionization (EoR).
While inferring the detailed properties of the first galaxies is one of the
most important motivations for measuring the high- 21-cm signal, they can
also provide useful constraints on the properties of the intergalactic medium
(IGM). Motivated by this, we build a simple, phenomenological model for the
21-cm power spectrum that works directly in terms of IGM properties, which
bypasses the computationally expensive 3-D semi-numerical modeling generally
employed in inference pipelines and avoids explicit assumptions about galaxy
properties. The key simplifying assumptions are that (i) the ionization field
is binary, and composed of spherical bubbles with an abundance described well
by a parametric bubble size distribution, and (ii) that the spin temperature of
the ``bulk'' IGM outside bubbles is uniform. Despite the simplicity of the
model, the mean ionized fraction and spin temperature of the IGM recovered from
mock 21-cm power spectra generated with \textsc{21cmfast} are generally in good
agreement with the true input values. This suggests that it is possible to
obtain comparable constraints on the IGM using models with very different
assumptions, parameters, and priors. Our approach will thus be complementary to
semi-numerical models as upper limits continue to improve in the coming years.Comment: 23 pages, 14 figures, accepted for publication in MNRAS, code
publicly available at https://github.com/mirochaj/micro21c
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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