1,721,024 research outputs found
Nonlinear oscillations, transition to chaos and escape in the Duffing system with non-classical damping
Full text linkThe nonlinear dynamics of a single-degree-of-freedom oscillator with an external excitation and complex non-viscous damping is examined. The complex nature of the damper introduces a hidden variable to the set of equations of motion. We examine nonlinear oscillations, bifurcations and the escape from the potential well in that system. The shape of the resonance curve is obtained by the multiple time scales method and it is confirmed numerically. By treating the excitation and damping effects as perturbations we found the heteroclinic orbits connecting the saddle points of the Hamiltonian and estimate the range of system parameters leading to a chaotic behaviour by means of the Melnikov method. This result is also confirmed by numerical simulations. The mechanism of escape from the potential well is analyzed by means of behaviour charts and basins of attraction
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
A comparison of different approaches to detect the transitions from regular to chaotic motions in SMA oscillator
No full textIt is well known that dynamical systems that include devices based on shape memory alloys (SMA) can exhibit a wide spectrum of responses: periodic, quasi-periodic and chaotic motions. In view of the different types of possible applications, it is important to recognize the qualitative features of the system vibrations. To this end, various methods have been proposed in the literature and evaluated in different conditions. In this work, a comparison between some of the available methods is proposed, focusing attention on their ability to detect the regular–chaotic and chaotic–regular transitions. The specific system under consideration is a thermomechanical SMA oscillator with superelastic behavior subject to harmonic excitation. The diagnostic methods compared are 0–1 test, maximum Lyapunov exponent and the recurrence indicators. The obtained results show that each method used is suitable for distinguishing between the regular and non-regular response of the SMA oscillator, so one of them can be chosen, taking into account, for example, the length and a sampling of the collected data
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
Estimation of a noise level using coarse-grained entropy of experimental time series of internal pressure in a combustion engine
No full textWe report our results on non-periodic experimental time series of pressure in a single cylinder spark ignition engine.
The experiments were performed for different levels of loading. We estimate the noise level in internal pressure calculating
the coarse-grained entropy from variations of maximal pressures in successive cycles. The results show that the
dynamics of the combustion is a non-linear multidimensional process mediated by noise. Our results show that so
defined level of noise in internal pressure is not monotonous function of loading
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
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