1,721,122 research outputs found
Spinning compact objects in extreme-mass-ratio inspirals
Full text linkSince the first landmark observation of gravitational waves (GWs) in 2015, GW astronomy has tremendously impacted fundamental physics and astrophysics. A network of four ground-based detectors (the two LIGOs, Virgo and KAGRA) is now in operation, routinely detecting new events. Future space-based obser- vatories, like the Laser Interferometer Space Antenna (LISA), hold the promise to revolutionize GW astronomy by detecting sources non-observable by current detectors, opening avenues for groundbreaking discoveries. Among the prime targets of LISA are extreme mass ratio inspirals (EMRIs), which are binaries consisting of a stellar-mass compact object slowly inspiraling into a supermassive black hole. These systems are unique probes of astrophysics and fundamental physics. Motivated by their potential, here we study in detail the EMRI dynamics in the presence of a spinning small compact object. The tiny mass-ratio in EMRI binaries allows us to treat the smaller companion as a point particle endowed with mass and spin. The latter are free parameters independent of the internal structure of the infalling compact object. The radiation-reaction forces (known as self-force) and equations of motion are typically modeled with perturbative approaches in the mass ratio. At leading order, the dynamics of the particle is governed by the adiabatic emission of energy and angular momentum in gravitational radiation, causing the secular decay of the orbits. All subleading corrections to this general picture are called post-adiabatic terms. The spin of the small compact object starts affecting the GW phase at the first post-adiabatic order (as does the first-order conservative and second-order dissipative self-force). In this thesis, we focus on the measurability of the smaller companion spin by an EMRI detection with LISA. Using the Teukolsky formalism, we derive the GW fluxes and the adiabatic orbital evolution for a spinning particle in the case of circular, equatorial orbits with (anti-)aligned spins. We provide the spin-induced corrections to GW fluxes (numerically and semi-analytically), along with the corresponding post-adiabatic effects on the GW phase, which are novel results for a Kerr background. Based on the phase difference between the gravitational signal from a spinning and a non-spinning particle, we develop a criterion to determine the minimum value of the spin resolvable by LISA. Our analysis points out that precise, model-independent tests on the nature of the small compact object could be achieved by measuring its intrinsic angular momentum. We also suggest that LISA could test the so-called Kerr bound that limits the maximum spin of a rotating black hole, allowing for theory-agnostic constraints.
We then perform an accurate Fisher-matrix study of the EMRI parameters using Teukolsky waveforms to leading order in an adiabatic expansion on a Kerr background. Our parameter estimation takes into account the motion of the LISA constellation, higher harmonics, and includes the leading correction from the smaller companion spin in the post-adiabatic approximation. We particularly focus on the measurability of the small body spin, showing that, for spin-aligned EMRIs on quasi-circular orbits, it cannot be measured with sufficient accuracy. However, due to correlations, its inclusion in the waveform model can deteriorate the accuracy on the measurements of other parameters by orders of magnitude, unless a physically-motivated prior on the small compact object spin is imposed
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
Spatial modeling of functional regions of interest in fMRI group analysis
No full textThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 49-50).An essential step for discovering a common structure in brain activation regions from multi-subject fMRI data is the ability to find spatial correspondences across subjects. This has proven to be a challenging problem due to the lack of a ground truth and variability in anatomical brain structure, functional activation, and spatial locations of functional regions. Standard methods rely on the correspondences given by anatomical registration to a common space, but fail to account for spatial variability of the functional regions relative to anatomy. We develop a clustering method that relies on the alignment of both the anatomical structure and the functional landmarks. The method is shown to improve over standard group analysis techniques that rely on anatomical alignment only. The validation of our method confirms that peaks of activation exhibit consistent spatial structure. Furthermore, our work creates a framework for future testing of different metrics for similarity of brain activation regions across subjects.by Gabriel Andres Tobón.M.Eng
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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