1,721,169 research outputs found
Employment of a Healthgrid for evaluation and development of polysomnographic biosignal processing methods
No full textLongterm biosignal recordings, such as overnight sleep recordings (so-called polysomnographies, PSG), often vary in signal quality and signal shape. Movement artifacts occur frequently. This may impede successful application of automated processing algorithms designed for well-defined short-term recordings. To test existing algorithms on suitability for PSG analysis, and develop robust analysis tools, an environment that offers efficient application of biosignal methods on comprehensive and representative reference data is required. In this article, a Grid based biosignal processing platform is presented, that provides a large set of clinical PSG reference data collected within the SIESTA project. To date, different processing and evaluation methods with focus on polysomnographic electrocardiogram (PSG-ECG) based analysis are implemented. First results for heart rate analysis of PSG-ECG are given, including the introduction of a performance quality measure for non-annotated PSG-ECG. Different publicly available heart beat detection algorithms have been tested. As an example, the wqrs algorithm, provided by the PhysioNet shows a sensitivity of over 99% and a positive predictive value of over 94% on the PhysioNet's PSG reference data. Processed on the SIESTA data, it only detects around 60% of the heart beats, resulting in a low average performance quality of 0.28. Evaluation of further algorithms has led to the development of an improved, robust algorithm with a high average performance quality of 0.98
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
Sleep Apnea Screening by Autoregressive Modelsfrom a Single ECG Lead
No full textThis paper presents a method for obstructive sleep
apnea (OSA) screening based on the electrocardiogram (ECG)
recording during sleep. OSA is a common sleep disorder produced
by repetitive occlusions in the upper airways and this phenomenon
can usually be observed also in other peripheral systems such as the
cardiovascular system. Then the extraction ofECGcharacteristics,
such as the RR intervals and the area of the QRS complex, is useful
to evaluate the sleep apnea in noninvasive way. In the presented
analysis, 50 recordings coming from the apnea Physionet database
were used; data were split into two sets, the training and the testing
set, each of which was composed of 25 recordings. A bivariate timevarying
autoregressive model (TVAM) was used to evaluate beatby-
beat power spectral densities for both the RR intervals and the
QRS complex areas. Temporal and spectral features were changed
on a minute-by-minute basis since apnea annotations where given
with this resolution. The training set consisted of 4950 apneic and
7127 nonapneic minutes while the testing set had 4428 apneic and
7927 nonapneic minutes. The K-nearest neighbor (KNN) and neural
networks (NN) supervised learning classifiers were employed
to classify apnea and non apnea minutes. A sequential forward
selection was used to select the best feature subset in a wrapper
setting.With ten features the KNN algorithm reached an accuracy
of 88%, sensitivity equal to 85%, and specificity up to 90%, while
NN reached accuracy equal to 88%, sensitivity equal to 89% and
specificity equal to 86%. In addition to the minute-by-minute classification,
the results showed that the two classifiers are able to
separate entirely (100%) the normal recordings from the apneic
recordings. Finally, an additional database with eight recordings
annotated as normal or apneic was used to test again the classifiers.
Also in this new dataset, the results showed a complete separation
between apneic and normal recordings.time-varying autoregressive model,
Electrocardiogram,
heart rate variability,
neural network,
pattern classificatio
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