1,721,046 research outputs found
Interaction of guided electromagnetic waves with defects emerging in metallic plates
No full textUltra-wideband guided electromagnetic waves have been recently adopted to detect damage in structures. Transmission and reflection coefficients are indeed sensitive to any defect within the waveguide and can potentially warn the presence of hidden failures. Within this context, the paper shows a detection and localization approach for a structural health monitoring system based on elctromagnetic sensors permanently integrated with the structure to be monitored. A metallic plate is equipped with a dielectric waveguide patch attached to the structure's surface and a multi-input multi-output approach is adopted to interrogate the host component characterized by a reversible defect in different position. The findings show the sensitivity of transmission and reflection loss to the defect presence in between 3-20 GHz. Furthermore, an optimal frequency band beyond 12-15 GHz can be generally found. Based on wave spectrum changes, damage indicators result reliable means of detection. On top of that, they can be further elaborated to reconstruct and localize the defect. Both the amplitude and the phase of the signals are worth being investigated as detection and localization features
Elliptical monopole antenna design for the early breast cancer imaging at high frequencies
No full textThis paper presents a design of an ultra-wideband, slotted, elliptical monopole antenna for breast cancer imaging. The antenna has a compact size of 9 mm × 7 mm to cover the frequency range from 16 to 24 GHz. Its operation is optimized to direct contact with the patient breast's skin without any coupling medium. On top of that, the antenna also features as an electrode for the electrical impedance tomography (EIT) applications. Experimental results on a female volunteer's breast verify the excellent microwave performance of the antenna. In addition, the results also indicate the reliability of the breast tissues models, which were used in the simulation. Finally, a simple EIT measurement setup also demonstrates the multi- functional detection capabilities from the antenna element
ASSESSMENT OF DAMAGE IN METALLIC PLATES BY ULTRA-WIDEBAND GUIDED ELECTROMAGNETIC WAVES
No full textGuided electromagnetic wave propagation using ultrawideband signals is a barely new approach for damage detection. However, still many challenges are present, including the way to deal with the GHz domain signals and the physics behind the interaction phenomena enabled by any type of flaw. The present work proposes a feasibility analysis for a structural health monitoring system employing permanently integrated microwave sensors. This setup allows to interrogate the structure continuously using multiple transmitters and multiple receivers when the electromagnetic waveguide is established. To this end, a metallic plate is equipped with a dielectric waveguide patch attached to the structures' surface. To validate the detectability of damage, a reversible defect is modeled through removable bolts accessible from the other surface of the plate. The experiments are carried out considering different bottom holes at different spatial locations of the plate. In addition, concurrent measurements are adopted to characterize the noise level within the signal. The characteristic changes of electromagnetic wave signals are caught using a damage index approach returning whether the defect can be detected sensitively or not. Different coupling conditions are used to let the guided electromagnetic waves propagate and interact with underlaying structure. The results show that this approach can be adopted for damage detection with a reasonable signal to noise ratio, especially when the waveguide is well coupled. In addition, both transmission and reflection loss can be monitored reliably
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
Ultra-wideband microwave leakage monitoring for stringer debonding detection in carbon composite fuselage structures
No full textUltra-wideband guided electromagnetic waves have been proposed recently for non-destructive testing and structural health monitoring applications. However, many possibilities are still unexplored given by the multitude of possible microwave waveguides. The present work introduces the concept of microwave leakage monitoring to detect stringer debondings in hollow carbon composite structures. The principle is to monitor the wave propagation characteristics within the cavity formed by the stringer and the airframe skin using transmission measurements. Changes in the transmission path, e.g. occurring from microwave leakage in the debonded region, can be assessed through a damage indicator approach.
To proof this concept, an experimental campaign was carried out according to the building block approach typically used in aeronautics. First, a small-scale specimen with a debonded stringer was investigated in the laboratory. Then, a large-scale fuselage structure was used for technology demonstration enabling stringer debonding with increasing severity through static and fatigue loading. The paper shows that the microwave characteristics in the waveguide (stringer tunnel) is affected by the debonding conditions according to its severity and depth. This allows designing a structural health monitoring system based on guided electromagnetic waves trapped in the tunnel
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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