1,720,969 research outputs found
Separation of Damping and Velocity Strain Dependencies using an Ultrasonic Monochromatic Excitation
Full text linkPrecise knowledge of the dependence of elastic modulus and Q-factor on amplitude of excitation is a prerequisite for the development and validation of models to explain the hysteresis observed in quasi-static experiments for various media, i.e. the different deformations at the same applied stress observed when stress change rate is positive or negative. Separation of different contributions to dynamic nonlinearity (e.g those due to non equilibrium effects, often termed conditioning) and independent estimation of nonlinearities originated by the strain dependence of velocity and damping factor are required, which is often not possible with standard approaches. Here we propose and validate a method which, measuring the response of a sample to a monochromatic excitation at different amplitudes, allows fast, continuous and quasi real-time monitoring of the dependence of the material elastic properties on amplitude: dynamic elastic modulus (related with velocity through density) and Q-factor of the mechanical resonances (related with wave amplitude attenuation parameter
Enhancement of harmonics generation in hysteretic elastic media induced by conditioning
No full textThe physical origin of harmonics generation in non classical (hysteretic) elastic media and the mechanisms of energy transfer among harmonics are still not completely understood. Furthermore the well known conditioning effect observed in such materials is known to have a significant influence on the elastic response of consolidated granular media and damaged composites and metals. Here, we show that the elastic non linearity of samples belonging to these two categories increases after having been excited with a relatively low amplitude stress. The observed behaviours could be described by activation features intrinsically present in phenomenological multistate models proposed in the literature
Conditioning and elastic nonlinearity in concrete: Separation of damping and phase contributions
No full textElastic properties of concrete are affected, already at low strains, by its nonlinear properties, which are very sensitive to the presence of microcracks and hence to progression of damage. Conditioning and memory effects, which are both nonlinear effects are also manifested in intact samples and understanding their role in the definition of the propagation of elastic waves is crucial for the development of techniques aiming to quantify the nonlinear response and extract information about the microstructure of concrete specimens or concrete-based structures. Results are presented here to make evident the possibility to experimentally detecting and comparing the nonlinearity and conditioning induced by elastic modulus and damping nonlinearities in different concrete samples
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
Nonlinear acoustics measurements of intact and damaged samples: Fast and slow dynamics
No full textWhen excited by elastic waves, nonlinear mesoscopic elastic materials (for example, consolidated granular materials) show, at the same time, fast and slow dynamics effects. Here we introduce suitable parameters for quantifying them and for studying their correlations. We found that significant differences between intact and damaged samples can be observed by studying slow dynamics effects. The longitudinal profiles of the surface deformations induced by a sinusoidal excitation of a cracked sample were also investigated during different measurement configurations, showing that a considerable distortion of the original profile is induced by conditioning. These results can be useful for studying the behavior of cracks and defects in the nonclassical nonlinear regime, in view of their modeling at the microstructural level and for applications in innovative nondestructive test and evaluation techniques
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
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