1,721,254 research outputs found
Harmonic analysis of nonlinear structures by means of Generalized Frequency Response Functions coupled with NARX models
No full textThe harmonic analysis of non-linear structures can be equivalently carried out with many different approaches, such as generalised frequency response functions (GFRF) or, more commonly, direct integration methods, Integration techniques provide only approximate results, since the integration procedure is usually carried out for few iteration steps. On the other hand, computational questions and accuracy problems may also arise with GFRFs for different reasons: for example, jump phenomena cannot be detected by means of GFRFs. In practice, for all these reasons, particular care is required in the usage and interpretation of these tools. In this paper, a comparison of the two methodologies is drawn by means of a simple example, and the advantages and drawbacks of GFRF-based harmonic analysis methodology are discussed in extent. In particular, it is shown how GFRFs can be effectively used to derive parametric approaches for harmonic analysis, which represents a substantial advantage over direct integration methods and allows for the development of modular algorithms. In fact, a simple and modular procedure which couples these tools with NARX/NARMAX modelling is proposed. The methodology is tested on a laboratory-scale model of a dam buttress
Seismic behaviour of buttress dams: nonlinear modeling of a damaged buttress based on ARX/NARX models
No full textThe paper reports a full model identification study carried out on a scale model of a dam buttress subjected to seismic-like excitations generated by means of a shake table. The use of linear and non-linear models is discussed, since the buttress has an artificial crack and is subjected to high-intensity inputs. In particular, a suitable class of polynomial NARX models is considered, which captures most of the system dynamics. Several questions related to the NARX identification methodology are addressed in the paper; use of non-linear models greatly increases model accuracy and reliability, but many specific operational problems arise in practice. In particular, the validity of classical model selection approaches is questionable; satisfactory non-linear models are obtained in this case with many fewer parameters than suggested by conventional performance indices. Also, it is difficult to guarantee a satisfactory model performance in simulation and, sometimes, even stability is hard to obtain. With reference to specific identified models a further analysis step is carried out, which shows the evolution of the dynamic characteristics of the model in the various phases of the earthquake-like excitation. Also, the role of the particular non-linearities included in the model is discussed
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
Memoryless Solution to the Optimal Control Problem for Linear Systems with Delayed Input
No full textP. Palumbo (ed.) A Place in the Sun: Africa in Italian Colonial Culture from Post-Unification to the Present. Berkeley, CA: University of California Press, 2003.
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