1,720,959 research outputs found
Reconstruction of the sound radiation field from plate flexural vibration measurements taken with multiple cameras
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Reconstruction of cylinder flexural vibration and sound radiation fields from multi-view single-camera measurements
No full textThis paper presents experimental results on the reconstruction from video measurements taken with a single camera of the flexural vibration and sound radiation fields of a baffled cylinder. The study is focused on the vibration and sound radiation generated by a time-harmonic radial force acting on the cylinder at selected resonance frequencies. The measurement setup is composed by a single high-resolution and high-speed camera, which, however, has been set to acquire multi-views of the radiating cylinder in order to implement a frequency-domain triangulation to derive the cylinder flexural vibration field. The cylinder sound radiation field was then reconstructed with a closed form integral expression derived from the Kirchhoff-Helmholtz integral equation. More precisely, the integral expression was approximated into a summation over a grid of elements the cylinder surface had been divided into. The study shows that the proposed measurement approach accurately estimates the flexural vibration and the sound radiation fields of the cylinder at selected resonance frequencies
Reconstruction of the sound radiation field from flexural vibration measurements with multiple cameras
No full textThis paper presents the background theory and the experimental implementation of a new approach for the reconstruction of the sound radiation field produced by the flexural vibration of a distributed structure using video image acquisitions. The study is focused on tonal flexural vibration and sound radiation at the first five resonance frequencies of a baffled flat rectangular plate model-structure. The plate is divided into a regular mesh of rectangular elements whose centres are marked with small bullets. The transverse vibrations at the grid of target points are estimated via triangulation from the images acquired with six cameras unevenly spread along half of a circle located, with a small offset, parallel to the surface of the plate. The sound radiation field in free space is then reconstructed from the Rayleigh integral, which is approximated into a finite sum over the mesh of elements. Both the flexural vibration field and the sound radiation field derived from the cameras video acquisitions are contrasted with measurements taken respectively with a laser vibrometer and an array of microphones
3D sound radiation reconstruction from camera measurements
Full text linkIn general, the measurement of the sound radiation field by machinery and partitions requires time-consuming tests, which should be carried out in specially dedicated anechoic/reverberant facilities with calibrated sensors and complex acquisition and post processing equipment. This article introduces a two-step method for the identification from optical measurements of the free-field sound radiation generated by flexural vibrations of closed shells. In the first step, the flexural vibration of the shell is reconstructed with a frequency domain triangulation technique based on short multi-view video acquisitions made with a single high-resolution, high-speed camera. In the second step, the free-field sound radiation is derived from a discretized boundary integral formulation. The study is focused on the identification of the sound radiation from the flexural vibration of a baffled cylinder model structure. The vibration and sound fields reconstructed from the camera measurements are validated against direct measurements taken with a laser scanner vibrometer and a microphone array, respectively. Overall, this research demonstrates that optical methods based on camera measurements can be suitably employed to produce fast and accurate full-field measurements of sound radiation of closed shells (without the need for a dedicated measurement environment, e.g. reverberant, anechoic chambers)
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
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