1,721,100 research outputs found
Prediction of ultrasonic guided waves excitability to support the non-invasive assessment of human long bones
No full textThe characterization of bones via axial ultrasonic transmission techniques can be fully exploited only once the complexities of guided wave propagation are unveiled. Generally, plate/cylindrical waveguide models, where the soft tissues and their damping role are generally neglected, are used to identify the propagating waves in the bone. Here, a numerical strategy for a more rigorous simulation of guided wave propagation in elongated bones is proposed. First, from a computed tomography image of a human leg a three-dimensional finite element (FE) mesh of the problem is built by converting voxels into elements. At this level, the mechanical properties of bones and soft tissues can be obtained converting the Hounsfield units. If necessary, the FE mesh can be enhanced by smoothing the outer surfaces of the bone and/or skin. Next, time-transient three-dimensional explicit FE simulations are performed to simulate the propagation of stress waves along the bone with and without the soft tissues. The propagative energy is revealed by processing the bone time-responses with a 2D-FFT transform suitable for guided waves extraction. Finally, a representative bi-dimensional cross-section of the bone only is used to set the guided wave equation by means of a Semi-Analytical Finite Element (SAFE) formulation. Via SAFE, the dispersion curves are obtained and compared with the 2D-FFT energy map. The proposed strategy can support the research on non-invasive techniques based on stress waves for the assessment of long bones
Error estimation by compatibility in patches for plate structures
No full textError estimation is a key tool in modern finite element technology in order to verify and validate the finite element simulations, as well as to improve results and control the error, when combined with adaptivity. An efficient and practical way to derive a posteriori error estimators is offered by recovery procedures. The error, generally in stress based norms, is estimated by comparing the original finite element solution with the recovered one. The major steps forward in using recovery procedures were taken with the Superconvergent Patch Recovery (SPR) developed by Zienkiewicz and Zhu [1] and the Recovery by Equilibrium in Patches (REP) developed by Boroomand and Zienkiewicz [2]. Both these procedures have been successfully applied to plate problems in [3]. Recently, a new superconvergent procedure called Recovery by Compatibility in
Patches (RCP) has been proposed by one of the authors [4] and shown to provide an excellent basis for error estimation in 2D problems [5].
Thin structures like plates and shells constitute an important class among finite element analyses because of their large application fields. With this in mind, the aim of the present paper is to develop an extension of the RCP-based error estimation to Reissner-Mindlin plates finite element analysis. The basic idea of this procedure is the same as the RCP in its original version, that is to recover stress resultants by enforcing compatibility over patches of elements.
Displacements computed by the finite element analysis are prescribed on the boundary of the patch, and improved stress resultants are computed by minimizing the complementary energy of
such a sub-model. The resulting procedure is simple, efficient, numerically stable and does not need any knowledge of superconvergent points. Some numerical examples involving thin and thick plates under different loading and support conditions are given.
References
[1] Zienkiewicz OC, Zhu JZ, The superconvergent patch recovery and a posteriori error estimates. Part I: The recovery technique, International Journal for Numerical Methods in Engineering, 33, 1992, 1331–1364.
[2] Boroomand B, Zienkiewicz OC, An improved REP recovery and the effectivity robustness test, International Journal for Numerical Methods in Engineering, 40, 1997, 3247–3277.
[3] Boroomand B, Ghaffarian M, Zienkiewicz OC, On application of two superconvergent recovery procedures to plate problems, International Journal for Numerical Methods in Engineering, 61, 2004, 1644–1673.
[4] Ubertini F, Patch recovery based on complementary energy, International Journal for Numerical Methods in Engineering, 59, 2004, 1501–1538.
[5] Benedetti A, de Miranda S, Ubertini F., A posteriori error estimation based on the superconvergent Recovery by Compatibility in Patches, International Journal for Numerical Methods in Engineering, in press
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
Seismic Vulnerability Assessment of a Historical Church: Limit Analysis and Nonlinear Finite Element Analysis
Full text linkThe seismic vulnerability of a historical Basilica church located in Italy is studied by means of limit analysis and nonlinear finite element (FE) analysis. Attention is posed to the failure mechanisms involving the façade of the church and its interaction with the lateral walls. In particular, the limit analysis and the nonlinear FE analysis provide an estimate of the load collapse multiplier of the failure mechanisms. Results obtained from both approaches are in agreement and can support the selection of possible retrofitting measures to decrease the vulnerability of the church under seismic loads
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
First-aid and provisional devices in historical structures with collapse risk after seismic shock
No full textRealization of first-aid devices for the safety of heavily damaged structures of the Cultural Heritage assets is one of the main problems in the post-earthquake emergency phase. However, the adopted solutions, characterized by the utmost urgency, often appear uneven, ineffective and expensive. Six years after the earthquake in Emilia Romagna Region, which damaged numerous historical buildings, above all churches, it seems worthwhile to reflect on the management of the post-earthquake emergency and reconstruction interventions. As a matter of fact, in 2012, many Public Institutions were unprepared to deal with such an event: the lack of an appropriate knowledge about how to intervene in such conditions has led to solutions that are unnecessarily expensive, technically ineffective and, sometimes, even harmful for the building itself. Frequently, the strengthening devices had to be entirely redesigned during the subsequent phase of definitive intervention, entailing additional costs for the removal of those realized in the emergency phase. The cases in which the provisional devices have been designed in preparation for the final strengthening, sometimes even becoming definitive themselves, are rare. Therefore, this experience has raised some reflections concerning the functionality of the temporary safety measures. It has been noticed that an appropriate design of the provisional devices is fundamental in order to avoid interventions that could compromise the value of the architectural asset, to allow the knowledge of the structure for designing the definitive strengthening and to consider the permanent implications of such safety measures. This note presents some case-studies related to strengthening actions following the 2012 earthquake in Emilia, aiming to identify possible solutions for implementing the first-aid interventions in an integrated way with the subsequent strengthening phase in order to significantly reduce economic, material and time costs
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