1,720,965 research outputs found
Polarisation of high energy gamma-rays after scattering
No full textThe polarisation of sunlight after scattering off the atmosphere was first described by Chandrasekhar using a geometrical description of Rayleigh interactions. Kosowsky later extended Chandrasekhar's formalism by using Quantum Field Theory (QFT) to describe the polarisation of the Cosmological Microwave Background radiation. Here we focus on a case that is rarely discussed in the literature, namely the polarisation of high energy radiation after scattering off particles. After demonstrating why the geometrical and low energy QFT approaches fail in this case, we establish the transport formalism that allows to describe the change of polarisation of high energy photons when they propagate through space or the atmosphere. We primarily focus on Compton interactions but our approach is general enough to describe e.g. the scattering of high energy photons off new particles or through new interactions. Finally we determine the conditions for a circularly polarised γ-ray signal to keep the same level of circular polarisation as it propagates through its environment
Constraining dark matter interactions mediated by a light scalar with white dwarfs
Get PDFObservations of white dwarfs in dark matter-rich environments can provide
strong limits on the strength of dark matter interactions. Here we apply the
recently improved formalism of the dark matter capture rate in white dwarfs to
a general model in which dark matter interacts with the white dwarf ion
components via a light scalar mediator. We compute the dark matter capture rate
in the optically thin limit in a cold white dwarf from the globular cluster
Messier. We then estimate the threshold cross-section, which significantly
varies as a function of the light scalar mediator mass in the range of
0.05\, m_\chim_\chi. We
also show that the bounds obtained from the dark matter capture in a white
dwarf from the globular cluster Messier 4 are complementary to direct detection
experiments and particularly strong in the sub-GeV regime.Comment: 6 pages, 2 figure
Probing BSM Physics with CP-violation, Neutrinos and White Dwarfs
Get PDFWhile the Standard Model remains the best theory to describe elementary particles and their interactions, there are still some unresolved issues that cannot be addressed within its current framework. Right handed neutrinos are introduced to the Standard Model to explain the observed active neutrino masses. If CP is violated during their radiative decays an asymmetry between two circularly–polarised photons can be generated. The CP asymmetry is somehow connected to circular polarisation. Therefore, observations of such polarised signal potentially lead to a measurement of the CP violation in the process. Here, we provide the connection between these two asymmetries for both, Dirac and Majorana neutrinos. We then apply this formalism to a minimal seesaw model and give the CP asymmetry in terms of a series of Jarlskog-like parameter. We also provide the formalism to study the changes in the polarisation of photons at any energy, since the intensity of such circularly polarised signal could change as it propagates through the Universe.
Finally, we pay attention to the dark matter paradigm. We discuss the capture of dark matter in compact stellar objects as complementary to direct detection searches.
We particularly work with white dwarfs (WD) since due to their abundance and high temperatures they one of the best observed compact objects proposed as cosmic laboratories for studying physical processes happening at very extreme conditions that cannot be achieved at terrestrial laboratories. Using an observed WD from the Messier 4 globular cluster, we set constraints on the DM interactions
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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