1,721,008 research outputs found
ECG P-Wave Smoothing and Denoising by Quadratic Variation Reduction
No full textAtrial fibrillation is the most common persistent cardiac arrhythmia and it is characterized by a disorganized atrial electrical activity. Its occurrence can be detected, and even predicted, through P-waves time-domain and morphological analysis in ECG tracings. Given the low signal-to-noise ratio associated to P-waves, such anal- ysis are possible if noise and artifacts are effectively filtered out from P-waves. In this paper a novel smoothing and denoising algorithm for P-waves is proposed. The algorithm is solution to a convex optimization problem. Smoothing and denoising are achieved reducing the quadratic variation of the measured P-waves. Simulation results confirm the effectiveness of the approach and show that the proposed algorithm is remarkably good at smoothing and denoising P-waves. The achieved SNR gain exceeds 15 dB for input SNR below 6 dB. Moreover the proposed algorithm has a computational complexity that is linear in the size of the vector to be processed. This property makes it suitable also for real-time applications
Pupil edge detection and morphological identification from blurred noisy images
No full textThe fluctuations of the human pupil in presence of light stimulation have been long investigated in several clinical applications, both in natural and artificial conditions. The pupil dynamics offer useful information in order to make non-invasive diagnoses of neurological diseases. Typically the pupil is shot by a CCD camera, which is the core of the measurement apparatus, called pupillometer, and the resulting image is analysed. In this paper we present the application of a multiscale approach to edge detection to identify the morphological parameters of the pupil edge. First, we determine the degradation parameters of the measured image, which is assumed to be blurred by a Gaussian kernel and corrupted by an additive white noise; then we apply the edge detection procedure and the optimal fitting, showing the main results; a first dynamical analysis is also presente
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
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
Heart rate variability analysis during bicycle ergometer exercise
No full textDuring exercise the concomitant increase of arterial pressure and heart rate indicates that arterial baroreflex control of the heart period is modified. It has been shown that during dynamic exercise heart rate increases are due to both a parasympathetic withdrawal and an augmented sympathetic activity. Aim of this study is to investigate the role of the pedaling action on heart rate variability signals. Six healthy subjects underwent a 4-phases exercise, consisting of active and passive cycling, and active and passing muscle contraction, at fixed frequencies. ECG (I lead) and pedaling frequency signals (when present) were acquired by using a commercial acquisition board. Heart rate variability signal has been analyzed by performing the spectral analysis of RR interval series (resampled at 4 Hz). We found that during a bycicle ergometer exercise at 100 W there is a spectral component at the pedaling frequency in the HRV spectrum only if it is present in the spectrum of the body movement series. Also, stimulation of the mechano and/or chemosensitive receptors of the gastrocnemious muscle elicited in our experiment was not sufficient to activate the cardiovascular control regions
On the resolution of ECG acquisition systems for the reliable analysis of the P-wave
No full textThe analysis of the P-wave on surface ECG is widely used to assess the risk of atrial arrhythmias. In order to provide reliable results, the automatic analysis of the P-wave must be precise and reliable and must take into account technical aspects, one of those being the resolution of the acquisition system. The aim of this note is to investigate the effects of the amplitude resolution of ECG acquisition systems on the P-wave analysis. Starting from ECG recorded by an acquisition system with a less significant bit (LSB) of 31 nV (24 bit on an input range of 524 mVpp), we reproduced an ECG signal as acquired by systems with lower resolution (16, 15, 14, 13 and 12 bit). We found that, when the LSB is of the order of 128 μV (12 bit), a single P-wave is not recognizable on ECG. However, when averaging is applied, a P-wave template can be extracted, apparently suitable for the P-wave analysis. Results obtained in terms of P-wave duration and morphology revealed that the analysis of ECG at lowest resolutions (from 12 to 14 bit, LSB higher than 30 μV) could lead to misleading results. However, the resolution used nowadays in modern electrocardiographs (15 and 16 bit, LSB <10 μV) is sufficient for the reliable analysis of the P-wave
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