1,721,086 research outputs found
A novel measure of atrial fibrillation organization based on symbolic analysis
Full text linkMeasures of electrical activity organization in atrial electrogram (AEG) are used to guide the ablation treatment in subjects with atrial fibrillation (AF). We proposed an improved morphological index for measuring the degree of organization in AEGs. As for other indexes, the metric provides an estimate of the probability of founding couples of similar waves and it increases with a higher AF organization. However, it also considers the order of arrival of the wavefronts on a set of bipolar electrodes (BE). Doing so, the index is inherently influenced by the direction of propagation of the wavefronts. To quantify organization, the AEGs were encoded with sequences of words of six symbols: three describing the order of arrival of the wavefronts on the BEs, while the others depending on the shape of each wave. The organization degree (OD) of each AEG was finally obtained as a function of the entropy of the sequence of words. The method was tested on 10 subjects before and after infusion of isoproterenol (ISO). During sinus rhythm, the effects of ISO did not significantly altered the organization of the atria (on average OD= 0.75 before and 0.74 after). Instead, in atrial fibrillation, ISO significantly reduced the level of organization (OD= 0.35 before vs 0.32 after, p < 0.05, paired t-test). The results were coherent with the pharmacological effects expected from the drug
Some theoretical results on the observability of repolarization heterogeneity on surface ECG
No full textAssessing repolarization heterogeneity (RH) from surface ECG recording is an open issue in modern electrocardiography, despite the fact that several indexes measured on the T-wave have been proposed and tested. To understand how RH occurring at myocite level is reflected on T-wave shapes, in this paper we propose a mathematical framework that combines a simple statistical model of cardiac repolarization times with the dominant T-wave formalism. Within this framework we compare different T-wave features such as T-wave amplitude, T-wave amplitude variability or QT intervals and we describe mathematically how they are linked to the spatial and temporal components of repolarization heterogeneity
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
On the reliability of frequency components in systolic arterial pressare in patients with atrial fibrillation
No full textAtrial fibrillation (AF) is characterized by desynchronization of atrial electrical activity causing a consequent irregular ventricular response. In AF, the beat-to-beat variation of blood pressure is increased because of variations in filling time and contractility. However, only a few studies have analyzed short-term blood pressure variations in AF, and we have recently observed a harmonic low-frequency (LF) component in systolic arterial pressure (SAP) during AF. Aim of the present study is to propose a method to verify the reliability of the spectral component found in SAP series, based on the position of the poles of the autoregressive spectral decomposition in the z-plane. In particular, 1,000 random permutations of the series allowed the definition of an area in the z-plane where poles from random process are likely to occur. Poles lying outside this area are considered as reliable oscillations. We tested the method on 53 recordings obtained at rest from patients with persistent AF. LF component was found in, respectively, 51 and 43 recordings in SAP and RR series. High-frequency (HF) component was found in all the recordings for both SAP and RR series. Using the proposed test, the percentage of reliable components in LF and HF bands was 80 and 38 in SAP series, and 20 and 18 in RR series. We concluded that, at variance with RR ones, SAP LF components are likely to represent true physiological oscillation
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
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
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