1,720,974 research outputs found
Analysis of the haemodynamic changes caused by surgical and transcatheter aortic valve replacements by means fluid-structure interaction simulations
Get PDFAortic valve replacements, both surgical and transcatheter, are nowadays widely employed treatments. Although clinically effective, these procedures are correlated with potentially severe clinical complications which can be associated with the non-physiological haemodynamics that they establish. In this work, the fluid dynamics changes produced by surgical and transcatheter aortic valve replacements are analysed and compared with an ideal healthy native valve configuration, employing advanced fluid-structure interaction (FSI) simulations. The aim of the study is to investigate how existing treatments may affect the aortic valve function, and giving indications about how to improve current therapies.
Simulations were performed using the commercial software LS-DYNA, where the FSI strategy is based on the coupling of a Lagrangian approach for the structures and a Eulerian approach for the fluid, whilst the coupling between the two domains is reached through a hybrid arbitrary-Lagrangian-Eulerian algorithm. Idealised geometries are used for the aortic root and leaflets. The aortic wall was modelled as linear elastic material, whilst leaflets were modelled as hyperelastic incompressible, using an Ogden's constitutive model. A combination of physiological flow velocity and pressure differences are applied as boundary conditions to model realistically the whole cardiac cycle.
Results are analysed throughout the cardiac cycle in terms of leaflets kinematics, flow dynamics, pressure and valve performance parameters. Globally, surgical valves presented worse performance than transcatheter counterparts (reduced effective orifice area, increased transvalvular pressure drop and increased opening and closing times). The clinical parameters of transcatheter devices were improved and closer to those of the healthy native valve, although the vortical activity within the Valsalva's sinuses was substantially altered. Here, the presence of the partition obstructed the washing out, resulting in higher degree of blood stasis and potential blood damage.
The implantation of prosthetic devices produces major haemodynamic changes which alters the valve dynamics and leads to diminished performance. Currently, the design of these substitutes is not optimised to mimic realistic native conditions, particularly in terms of valve opening behaviour. Although transcatheter devices provide systolic performance similar to that estimated for the healthy native aortic model, none of the prosthetic solutions appeared to be able to fully restore healthy physiological conditions
Fluid–structure interaction approach with smoothed particle hydrodynamics and particle–spring systems
Get PDFThis paper presents a novel three-dimensional fluid–structure interaction (FSI) approach, where the meshless smoothed particle hydrodynamics (SPH) method is used to simulate the motion of incompressible fluid flows, whilst structures are represented by a simplified approach based on particle–spring systems. The proposed FSI technique allows to use independent spatial–temporal resolutions for the fluid and structural computational domains. The particle–spring elastic constants are calibrated and relationships with the mechanical material properties, Young’s modulus and Poisson’s ratio, are determined. Fluid and structure computational domains are separated by interfaces made of triangular elements whose position is updated during the simulation following the structural deformation. The coupling of the two media at the fluid–structure interfaces is handled by the introduction of solid and fluid boundary particles. This approach, automatically and without introducing further complexity, avoids the penetration of fluid particles into the solid domain. The efficiency and accuracy and the present method are validated with analytical/benchmark solutions from the literature
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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