1,720,957 research outputs found
Crack detection of immersed metallic structure in water with surface oscillation using scanning laser pulse
No full textThere are some difficulties of non-destructive test and evaluation for immersed or submerged structures such as nuclear reactor pipe line, submarine or huge ship. This paper proposes the method of damage detection of immersed metallic structure which has crack on weld zone and placed in the water with slight and random surface oscillation using ultrasonic wave propagation imaging (UWPI) system with piezoelectric transducer. A T-shape metallic structure with artificial surface crack on weld zone, which with size 2 mm by 0.3 mm and the depth 2 mm, used as the specimen. A 532 nm Q-switched continuous wave laser is used for scanning an area of 20 mm by 40 mm. A piezoelectric sensor with magnetic sensor head, which is attachable to metallic structure is used as a contact ultrasonic sensor. The tests are performed in three cases: a specimen without water, a specimen immersed in water and a specimen immersed in water with random surface oscillation. Ultrasonic wave propagation image algorithm and adjacent wave subtraction (AWS) algorithm are used for visualizing wave propagation and detecting the crack. For the case where the specimen is immersed in the water, the signal amplitude is increased compared with the specimen without water case. In AWS algorithm results of the immersed case, scattering waves which are generated by cracks were observed. In random surface oscillation case, the excitation laser beam is refracted randomly by Snell’s law resulting in the diluted wave propagation images. However, improvements in signal-to-noise ratio using repeat scan technology enable to the detection of the crack and estimation of the crack size. This paper examines the damage detection using ultrasonic wave propagation caused by laser excitation from outside of the water even when the water surface oscillation exists and implies the possibility of application of ultrasonic propagation imaging system to submerged structures
Damage detection of composite structures using a stabilized extrinsic Fabry-Perot interferometric sensor system
No full textIn the case of an extrinsic Fabry-Perot interferometric sensor, a phase compensating technique is particularly necessary in applying the sensor to detecting an acoustic emission signal because of a fade-out problem. The technique makes it possible to maintain the phase at the quadrature point. In this paper, we developed the phase-stabilization control sensor system, which is composed of a broadband light source, a fiber Fabry-Perot (FP) tunable filter and a control-circuit board. We verified the performance of the developed stabilization sensor system through two preliminary tests. One was a test on the stabilization of the phase and the other was a pencil-break test. Finally, the acoustic emissions of fracture signals generated by a tensile test of a cross-ply composite specimen were successfully detected with the help of the phase-stabilization control system, which solved the fade-out problem
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
In-flight health monitoring of a subscale wing using a fiber Bragg grating sensor system
No full textIn this paper, fiber Bragg gratings (FBGs) were applied to measure dynamic strains inside a subscale wing under real-time wind tunnel testing. Two re-coated FBGs were embedded in the wing skin. The FBG sensor system includes a wavelength swept fiber laser with a wavelength indicator and fast signal processing modules. The agreement among the three kinds of sensor inside the subscale wing (FBG, electric strain gauge and PZT sensor) was confirmed in the bench test. The optical fiber strain sensors had an excellent resolution (<5 muepsilon) in the time domain and could detect a frequency response up to 100 Hz. Through the wind tunnel test of the subscale smart wing, the flutter was experimentally detected using FBG sensors and their usefulness as an in-flight health monitoring system was demonstrated.
Damage detection of composite structures using a stabilized extrinsic fabry-perot interferometric sensor system
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