1,720,957 research outputs found
Fidelity and Reversibility in the Three Body Problem
No full textWe use the Reversibility Error Method and the Fidelity to analyze the global effects of a small
perturbation in a non-integrable system. Both methods have already been proposed and used
in the literature but the aim of this paper is to compare them in a physically significant example
adding some considerations on the equivalence, observed in this case, between round-off and random
perturbations.
As a paradigmatic example we adopt the restricted planar circular three body problem. The
cumulative effect of random perturbations or round-off leads to a divergence of the perturbed
orbit from the reference one. Rather than computing the distance of the perturbed orbit from
the reference one, after a given number n of iterations, a procedure we name the Forward Error
Method (FEM), we measure the distance of the reversed orbit (n periods forward and backward)
from the initial point. This approach, that we name Reversibility Error Method (REM), does
not require the computation of the unperturbed map. The loss of memory of the perturbed map
is quantified by the Fidelity decay rate whose computation requires a statistical average over an
invariant region. Two distinct definitions of Fidelity are given. The asymptotic equivalence of
REM and FEM is analytically proved for linear symplectic maps with random perturbations. For
a given map, the REM plot provides a picture of the dynamic stability regions in the phase space,
very easy to obtain for any kind of perturbation and very simple to implement numerically. The
REM and FEM for linear symplectic maps are proved to be asymptotically equivalent. The global
error growth follows a power law in the regions of integrable (or quasi integrable) motion and an
exponential law in the regions of chaotic motion. We prove that the power law exponent is 3/2 for a
generic anisochronous system, but drops down to 1/2 if the system is isochronous. Correspondingly
the Fidelity F(t) exhibits an exponential decay and −ln F(t) grows just as the square of the FEM
or REM error. The Reversibility Error and Fidelity can be used for a quantitative analysis of
dynamical systems and are suited to investigate the transition regions from chaotic to regular
motion even for Hamiltonian systems with many degrees of freedom such as the N-body problem
Errors, correlations and fidelity for noisy Hamilton flows. Theory and numerical examples
No full textWe analyse the asymptotic growth of the error for Hamiltonian flows due to small random perturbations. We compare the forward error with the reversibility error, showing their equivalence for linear flows on a compact phase space. The forward error, given by the root mean square deviation σ(t) of the noisy flow, grows according to a power law if the system is integrable and according to an exponential law if it is chaotic. The autocorrelation and the fidelity, defined as the correlation of the perturbed flow with respect to the unperturbed one, exhibit an exponential decay as exp (-2π2σ2(t)). Some numerical examples such as the anharmonic oscillator and the Hénon Heiles model confirm these results. We finally consider the effect of the observational noise on an integrable system, and show that the decay of correlations can only be observed after a sequence of measurements and that the multiplicative noise is more effective if the delay between two measurements is large
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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