1,720,958 research outputs found
Superluminous supernovae in large astronomical surveys
No full textThis thesis focuses on the photometric classification and the properties of superluminous supernovae (SLSN), as observed in large astronomical surveys. When working with large samples of transients and a limited spectroscopic follow-up campaign, photometric classifications are the only tool available to select objects which can subsequently be used to study their statistical properties including the rate and its evolution. I begin by introducing the surveys which produce the transients archive used in this work. I discuss the effect of their properties and design on the work performed in this thesis. I also introduce the sources of auxiliary data, including the spectroscopic followup facilities as well as summarise the Dark Energy Survey (DES) spectroscopic sample of SLSNe. Next, I develop a number of models and techniques used to simulate both core-collapse supernovae (CCSN) and SLSNe. I use the spin-down of a magnetar model in conjunction with spectroscopic UV absorption templates to build SLAP, a tool for simulating SLSN at any redshift, in any arbitrary photometric system. Similarly, I develop CoCo which can be used to simulate and generate the templates for CCSNe. I then use the tools developed in this thesis to build a definition of SLSNe in terms of the spin-down of a magnetar model and apply it to a sample of transients detected by the Supernova Legacy Survey (SNLS), uncovering one previously unclassified SLSN. I use this and two previously spectroscopically confirmed objects to calculate the rate of SLSNe at z∼ 1 with the help of a Monte Carlo simulation of the survey. I find the rate to be 91+76 −36 SNe Yr−1 Gpc−3, equivalent to 2.2+1.8 −0.9 × 10−4 the rate of CCSN at the same redshift. Finally, I use the models of CCSN and SLSNe developed in this work as well as the simulations of SN Ia and AGN to build a large artificial training sample of DES-like transients to be used in the photometric selection of SLSNe. Based on this, I build a two-stage machine learning photometric classification tool. In the first step I separate SN from other contaminating transients with an accuracy of 99.8%. Then, I separate the sample of SNe into its individual subclasses, achieving an overall accuracy of 97.85%. Using complementary selection techniques, I identify 26 new SLSNe candidates in DES
A statistical approach to identify superluminous supernovae and probe their diversity
Full text linkWe investigate the identification of hydrogen-poor superluminous supernovae (SLSNe I) using a photometric analysis, without including an arbitrary magnitude threshold. We assemble a homogeneous sample of previously classified SLSNe I from the literature, and fit their light curves using Gaussian processes. From the fits, we identify four photometric parameters that have a high statistical significance when correlated, and combine them in a parameter space that conveys information on their luminosity and color evolution. This parameter space presents a new definition for SLSNe I, which can be used to analyse existing and future transient datasets. We find that 90% of previously classified SLSNe I meet our new definition. We also examine the evidence for two subclasses of SLSNe I, combining their photometric evolution with spectroscopic information, namely the photospheric velocity and its gradient. A cluster analysis reveals the presence of two distinct groups. ‘Fast’ SLSNe show fast light curves and color evolution, large velocities, and a large velocity gradient. ‘Slow’ SLSNe show slow light curve and color evolution, small expansion velocities, and an almost non-existent velocity gradient. Finally, we discuss the impact of our analyses in the understanding of the powering engine of SLSNe, and their implementation as cosmological probes in current and future surveys
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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