1,721,001 research outputs found
Detection and Orbital Architecture Characterization of Planetary Systems Around Cool Stars
No full textM dwarfs have proven to be fascinating targets for exoplanetary search, from the growing evidence from transit (e.g., Kepler) and radial-velocity (e.g, HARPS, HARPS-N) surveys, even if several complex obstacles hamper the analysis and detection of planetary systems around them. For these reasons, it is pivotal to intensify the efforts towards the detection and characterization of extrasolar planets around M dwarfs, since new discoveries will help bring the statistical support still needed for the study of peculiar classes of planets, while the precise orbital characterization of both known and new systems will tighten the constraints on formation and migration processes.
The many open issues on M dwarfs host and their planetary systems, and the development of new methodologies to investigate them, are the foundation of the motivation for my PhD work.
In my thesis I first present the topic of M dwarfs exoplanetary systems, both from the observational and statistical point of view. I then report my work on performance analysis of three periodogram tools, the Generalised Lomb-Scargle Periodogram (GLS), its modified version based on Bayesian statistics (BGLS), and the multi-frequency periodogram scheme called FREquency DEComposer (FREDEC), motivated by the ubiquitousness of multiple systems with low-mass components. The results illustrated reinforce the need for the strengthening and further developing of the most aggressive and effective ab initio strategies for the robust identification of low-amplitude planetary signals in RV data sets. I describe the high-performance algorithms for single and multiple Keplerian signals modeling used by the research group I am part of, and their applications both on blindly analyzed simulated RV measurements including realistic stellar and planetary signals, and on high- precision HARPS archive data of an M dwarf star with a multiplanet system of Super Earths.
I then report the first results I obtained from the analysis of RV data collected as part of the HADES (HArps-n red Dwarf Exoplanet Survey) project, that is the detection of a long-period low-mass planet orbiting the M1 dwarf GJ15A, one of the nearest stars to the Sun, which was already known to host a short-period Super Earth. Since the host star is part of a binary system with the M dwarf GJ15B, I derived an improved orbital solution for GJ15B and studied a suite of numerical simulations of the long-term evolution of the planetary system under eccentric Lidov-Kozai oscillations, which proved that this dynamical interaction can easily enhance the eccentricity of the outer planet, up to and even above the observed value. Finally, I describe the strategy and preliminary results of the ongoing Bayesian analysis of the full HADES survey, aiming to compute the occurrence rates of planets around small mass stars and the global detectability of the survey
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
Searching for planetary signals in Doppler time series: a performance evaluation of tools for periodogram analysis
Full text linkWe carry out a comparative analysis of the performance of three algorithms widely used to identify significant periodicities in radial-velocity (RV) data sets: the generalized Lomb-Scargle (GLS) periodogram, its modified version based on Bayesian statistics (BGLS) and the multifrequency periodogram scheme called FREquency DEComposer (FREDEC). We apply the algorithms to a suite of numerical simulations of (single and multiple) low-amplitude Keplerian RV signals induced by low-mass companions around M-dwarf primaries. The global performance of the three period search approaches is quite similar in the limit of an idealized, best-case scenario (single planets, circular orbits, white noise). However, GLS, BGLS and FREDEC are not equivalent when it comes to the correct identification of more complex signals (including correlated noise of stellar origin, eccentric orbits, multiple planets), with variable degrees of efficiency loss as a function of system parameters and degradation in completeness and reliability levels. The largest discrepancy is recorded in the number of false detections: the standard approach of residual analyses adopted for GLS and BGLS translates in large fractions of false alarms (∼30 per cent) in the case of multiple systems, as opposed to ∼10 per cent for the FREDEC approach of simultaneous multifrequency search. Our results reinforce the need for the strengthening and further development of the most aggressive and effective ab initio strategies for the robust identification of low-amplitude planetary signals in RV data sets, particularly now that RV surveys are beginning to achieve sensitivity to potentially habitable Earth-mass planets around late-type stars
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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