1,721,161 research outputs found
Fabrication and Characterization of a Wavenumber-Spiral Frequency-Steerable Acoustic Transducer for Source Localization in Plate Structures
No full textThis paper reports on the fabrication and the experimental
characterization of a wavenumber frequency-steerable
acoustic transducer (WS-FSAT). Here, the transducer is employed for the localization of broadband acoustic events corresponding to the propagation of guided elastic waves in an isotropic plate. The WS-FSAT records the plate response and defines the source location through a time-frequency analysis of the received signal. This is achieved by exploiting the frequency selective response of the transducer which directly maps the dominant component of the received signal to the direction of arrival of the incoming wave. This feature is the result of the spatial filtering effect produced by the characteristic shape of the sensing surface, which is designed in the wavenumber domain. Experiments are performed on a prototype fabricated on a polyvinylidene fluoride substrate mounted on an aluminum test plate. Tests are conducted for various source locations, and with multiple sources activated simultaneously. The results highlight the robustness of the proposed device, its good sensitivity and angular resolution, as well as the low complexity of hardware
and signal processing. This paper suggests the WS-FSAT as an attractive solution for the detection of broadband acoustic events, such as impacts on structural substrates, and its potential use as part of active structural health monitoring systems based on pitch-catch or pulse-echo operations
Erratum: Double-channel, frequency-steered acoustic transducer with 2-D imaging capabilities [Jul 11 1430-1441]
No full textA modal approach for dynamic response monitoring from experimental data
No full textThe objective of this paper is the definition and verification of an iterative procedure for the detailed monitoring of the dynamic response of a structural system based on the experimental modal model of the system on ground and a limited number of measurements in the operativing condition. The application of this approach only needs the modal characterization of the structure, achievable with a preliminary modal survey with an arbitrary large amount of experimental points, and it allows the monitoring of the structure during operativing conditions by reconstructing the overall response from the measurements of few sensors. The method is formulated starting from a linear model, but it can be applied to weakly non-linear system, because of the iterative nature of the algorithm. It does not require the definition of a numerical model but an experimental representation in the modal coordinates. The proposed method is presented as well as its implementation and several numerical test cases in order to validate its formulation. Experimental analyses are performed on an uniform beam and on an helicopter component with promising results. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved
Quantized Electric Multipole Moments in Insulators
No full textPresented at the Workshop on Topological Protection in Messy Matter on May 15, 2018 at 10:00 a.m.-10:40 a.m. in the Marcus Nanotechnology Building, Rooms 1116-1118, Georgia Tech.Chairs: Massimo Ruzzene and Vincenzo VitelliTaylor Hughes is with the University of Illinois at Urbana-Champaign.Runtime: 39:24 minute
An improved beamforming technique for increased imaging resolution in GW-based SHM
No full textStructural Health Monitoring (SHM) of 2D areas can be performed bycombining time waveforms acquired by an array of Guided Wave (GW) transducersthrough phased addition algorithms. However, spatial resolution in defectlocalization is often limited by both dispersion in wave mode propagation andimaging noise associated to conventional delay-and-sum (DAS) beamforming.Starting from a statistical interpretation of DAS, this paper combines arecently proposed time-frequency procedure based on the Warped FrequencyTransform (WFT) and convex optimization with an adaptive thresholding techniqueto process multi-mode and dispersive Lamb waves. The proposed signal processingis applied to time waveforms recorded at an array of scan points after waveguideexcitation. The results show high-resolution source and scatterer imaging, thusconsiderably improving localization accuracy by imaging noise removal
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
- …
