1,720,975 research outputs found
Cardiac cells stimulated with an axial current-like waveform reproduce electrophysiological properties of tissue fibers
Full text linkBackground and objective: In silico electrophysiological models are generally validated by comparing simulated results with experimental data. When dealing with single-cell and tissue scales simultaneously, as occurs frequently during model development and calibration, the effects of inter-cellular coupling should be considered to ensure the trustworthiness of model predictions. The hypothesis of this paper is that the cell-tissue mismatch can be reduced by incorporating the effects of conduction into the single-cell stimulation current. Methods: Five different stimulation waveforms were applied to the human ventricular O'Hara-Rudy cell model. The waveforms included the commonly used monophasic and biphasic (symmetric and asymmetric) pulses, a triangular waveform and a newly proposed asymmetric waveform (stimulation A) that resembles the transmembrane current associated with AP conduction in tissue. A comparison between single-cell and fiber simulated results was established by computing the relative difference between the values of AP-derived properties at different scales, and by evaluating the differences in the contributions of ionic conductances to each evaluated property. As a proof of the benefit, we investigated multi-scale differences in the simulation of the effects induced by dofetilide, a selective IKr blocker with high torsadogenic risk, on ventricular repolarization at different pacing rates. Results: Out of the five tested stimulation waveforms, stimulation A produced the closest correspondence between cell and tissue simulations in terms of AP properties at steady-state and under dynamic pacing and of ionic contributors to those AP properties. Also, stimulation A reproduced the effects of dofetilide better than the other alternative waveforms, mirroring the ’beat-skipping’ behavior observed at fast pacing rates in experiments with human tissue. Conclusions: The proposed stimulation current waveform accounts for inter-cellular coupling effects by mimicking cell excitation during AP conduction. The proposed waveform improves the correspondence between simulation scales, which could improve the trustworthiness of single-cell simulations without adding computational cost. © 202
Limitations in electrophysiological model development and validation caused by differences between simulations and experimental protocols
Full text linkModels of ion channel dynamics are usually built by fitting isolated cell experimental values of individual parameters while neglecting the interaction between them. Another shortcoming regards the estimation of ionic current conductances, which is often based on quantification of Action Potential (AP)-derived markers. Although this procedure reduces the uncertainty in the calculation of conductances, many studies evaluate electrophysiological AP-derived markers from single cell simulations, whereas experimental measurements are obtained from tissue preparations. In this work, we explore the limitations of these approaches to estimate ion channel dynamics and maximum current conductances and how they could be overcome by using multiscale simulations of experimental protocols. Four human ventricular cell models, namely ten Tusscher and Panfilov (2006), Grandi et al. (2010), O'Hara et al. (2011), and Carro et al. (2011), were used. Two problems involving scales from ion channels to tissue were investigated: 1) characterization of L-type calcium voltage-dependent inactivation ICa,L; 2) identification of major ionic conductance contributors to steady-state AP markers, including APD90, APD75, APD50, APD25, Triangulation and maximal and minimal values of V and dV/dt during the AP (Vmax, Vmin, dV/dtmax, dV/dtmin). Our results show that: 1) ICa,Linactivation characteristics differed significantly when calculated from model equations and from simulations reproducing the experimental protocols. 2) Large differences were found in the ionic currents contributors to APD25, Triangulation, Vmax, dV/dtmaxand dV/dtminbetween single cells and 1D-tissue. When proposing any new model formulation, or evaluating an existing model, consistency between simulated and experimental data should be verified considering all involved effects and scales
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
T-wave alternans and autonomic nervous system activity during orthostatic stress after 5 days of head-down bed-rest
Full text linkDispelling 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
Sistema de Identidad Soberana basada en Blockchain sobre Dispositivos Móviles
Full text linkThe growth of the internet use has caused the realization of its users regarding their personal data and how it has exponentially been exposed to other third party sites, such is the example of social networks or the creation of accounts of any kind.
The increasing importance of the privacy of our data has been accompanied by a new concept, called self-sovereign identity. This concept is based on the fact that no one has control of our data except us and that we are responsible of the transfer of this data, which should not be stored by a third party. The birth of Blockchain technology has made it possible to create protected identities in the blockchain network itself and with a mobile phone, an element that everybody has access nowadays, is able to transfer this data under our authorization.
This project is aimed at analyzing the tools for the development of applications based on self-sovereign identity, thanks to the use of a blockchain network, and to evaluate the quality of said development tools. As a secondary objective, a pilot has been carried out to demonstrate whether it is possible to create applications that can support self-sovereign identity. This has forced to split the project into two different phases: A research phase and a development phase.
The results of this study let us to observe the current state of Blockchain technology and the pilot generated, which has allowed the analysis of blockchain tools. The information obtained has made it possible to evaluate the viability of applications based on self-sovereign identity today, in addition to setting a path for the future of these.Con el crecimiento del uso de internet el usuario ha podido ver como sus datos personales se han ido exponiendo cada vez más a múltiples terceros, tanto con las redes sociales como con la creación de una cuenta de cualquier tipo.
El incremento de la importancia que se da a la privacidad de nuestros datos ha venido acompañado de un concepto nuevo llamado identidad soberana autogestionada. Este concepto se basa en que nadie tiene el control de nuestros datos excepto nosotros y en la que nosotros somos responsables de ceder estos datos, los cuales no deberían ser almacenados por un tercero. Con el nacimiento de la tecnología Blockchain ha sido posible la creación de identidades protegidas en la propia red blockchain y con un móvil, elemento que todos tenemos en la actualidad, poder ceder estos datos bajo nuestra autorización.
El presente proyecto tiene como objetivo principal analizar las herramientas para la realización de aplicaciones basadas en identidad soberana autogestionada gracias al uso de una red blockchain y evaluar la madurez de estas mismas. Como objetivo secundario, se ha realizado un piloto que permita demostrar si es posible crear aplicaciones que soporten la identidad soberana autogestionada. Esto ha separado el proyecto en una fase de investigación y en otra de desarrollo.
Los resultados permiten ver el estado actual de la tecnología Blockchain y el piloto generado, que ha permitido analizar las herramientas blockchain. Esta información obtenida ha permitido evaluar la viabilidad de las aplicaciones basadas en identidad soberana autogestionada en la actualidad, además de generar una visión de futuro de estas
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