1,720,955 research outputs found
Modelling the non-linear viscoelastic behaviour of brain tissue in torsion
Full text linkBrain tissue accommodates non-linear deformations and exhibits time-dependent mechanical behaviour. The latter is one of the most pronounced features of brain tissue, manifesting itself primarily through viscoelastic effects such as stress relaxation. To investigate its viscoelastic behaviour, we performed ramp-and-hold relaxation tests in torsion on freshly slaughtered cylindrical ovine brain samples (25 mm diameter and ∼10 mm height). The tests were conducted using a commercial rheometer at varying twist rates of {40, 240, 400} rad m−1 s−1, with the twist remaining fixed at ∼88 rad m−1, which generated two independent datasets for torque and normal force. The complete set of viscoelastic material parameters was estimated via a simultaneous fit to the analytical expressions for the torque and normal force predicted by the modified quasi-linear viscoelastic model. The model's predictions were further validated through finite element simulations in FEniCS. Our results show that the modified quasi-linear viscoelastic model—recently reappraised and largely unexploited—accurately fits the experimental data. Moreover, the estimated material parameters are in line with those obtained in previous studies on brain samples under torsion. These material parameters could enhance our understanding of slow-progressing pathologies such as tumour growth or neurodegeneration and inform the development of improved in silico models for brain surgery planning and training. Our novel testing protocol also offers an efficient, robust and reliable method for determining the viscoelastic properties of brain tissue under much more rapid loading conditions, which are of crucial importance for modelling traumatic brain injury.This publication has emanated from research jointly funded by Taighde Éireann – Research Ireland under grant number GOIPG/2024/3552 (Griffen Small), and by the College of Science and Engineering at the University of Galway under the Millennium Fund scheme for the project “Modelling Brain Mechanics” (Valentina Balbi). Francesca Ballatore acknowledges support from the PNRR M4C2 through the project “Made in Italy Circolare e Sostenibile (MICS)”, CUP: E13C22001900001. The authors are grateful to the anonymous reviewers for their constructive criticisms, helpful suggestions and insights.peer-reviewe
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
Modelling the time-dependent behaviour of brain tissue in torsion
No full textAs is the case for most biological soft tissues, brain tissue displays highly complex mechanical behaviour: it can accommodate finite deformations and its response to applied forces is markedly non-linear; it is incompressible and biphasic, consisting of a porous permeable solid matrix saturated with an interstitial fluid; it is structurally anisotropic and it exhibits isotropic, time-dependent mechanical behaviour. The latter is one of the most pronounced features of brain tissue, manifesting itself primarily through two distinct but coupled phenomena: poroelasticity and viscoelasticity. The viscoelastic response is associated with the deformation of the solid skeleton, whereas the movement of interstitial fluid through the solid skeleton gives rise to a poroelastic response. Since its coupled poro-viscoelastic behaviour remains only partially understood, brain tissue is typically modelled either as a biphasic poroelastic material or as a monophasic viscoelastic material. The main goal of this work is to use each of these approaches in turn to investigate how poroelastic and viscoelastic effects influence the mechanical behaviour of brain tissue under torsional loading, which is one of the most robust and reliable protocols for determining its material parameters.
Using a biphasic poroelastic model developed within the general framework of mixture theory, we show for the first time computationally that poroelastic effects can significantly influence the torsional response of brain tissue, depending on the loading conditions and the choice of poroelastic material parameters. The sensitivity to these parameters is particularly relevant given the wide range of values reported in the literature. This highlights the need for robust and reliable testing protocols capable of providing a comprehensive and systematic characterisation of the porous behaviour of brain tissue, which is currently lacking in the literature.
Treating brain tissue as a monophasic viscoelastic material, we combine computational and experimental methods to devise the first protocol for determining the viscoelastic material parameters in torsion. From the computational perspective, we develop a monophasic viscoelastic model based on the recently reappraised but largely unexploited modified quasi-linear viscoelastic model. Using a commercial rheometer, we perform ramp-and-hold relaxation tests in torsion on cylindrical brain samples prepared from freshly slaughtered ovine brains, which generates two independent datasets for the torque and normal force. We then use our proposed viscoelastic model to derive analytical expressions for the torque and normal force required to maintain the cylindrical samples in a state of torsion, which allow us to identify the complete set of viscoelastic material parameters through a simultaneous fit to the two datasets. Beyond advancing brain tissue's mechanical characterisation and validating the efficacy of the MQLV model, our results have broader implications. When coupled with bespoke finite element models, the estimated viscoelastic material parameters could enhance our understanding of slow progressing pathologies, such as tumour growth or neurodegeneration, and inform the development of improved in silico models for brain surgery planning and training. Our novel testing protocol also offers an efficient, robust and reliable method for determining the viscoelastic properties of brain tissue under much more rapid loading conditions, which are of crucial importance for modelling traumatic brain injury.Research Ireland (grant number GOIPG/2024/3552), University of Galwa
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
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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