1,720,959 research outputs found
Accurate Heartbeat Detection on Ballistocardiogram Accelerometric Traces
Full text linkThis paper presents an automated procedure for acquisition and analysis of BallistoCardioGraphy (BCG) traces. A tri-axial accelerometer and a microcontroller unit are used to record heart-induced recoil forces generated from a lying subject. The problem of BCG J-peak annotation is split into two sub-tasks: candidates extraction, based on a detection signal, and actual annotation, guided by subject-specific search windows. Such procedure is derived from an automatic calibration, which is carried out with no need of concurrent ElectroCardioGram (ECG) or user intervention. The algorithm also implements post-annotation checks for refinement of annotation, which effectively reduces the number of missed J-peaks. The impact of each algorithm phase is analyzed, assessing statistical significance of each step; finally, performance is optimized in a data-driven fashion. Results show that the proposed methodology is able to achieve high sensitivity and precision (the median score is 98.9% and 98.1%, respectively) in J-peak detection. The quality of J-peaks timing annotation is further demonstrated by a very low discrepancy between BCG and ECG HR estimates. Over all population, the standard deviation of such error was found to be approximately 6.56 ms, whereas the Mean Absolute Error just 4.7 ms (i.e. ≈1.18;Ts, where Ts = 4 ms is the sampling period). Such scores, indeed, improve over recent related literature
Fully Automated Annotation of Seismocardiogram for Noninvasive Vital Sign Measurements
Full text linkThis paper presents a fully automated procedure for acquiring and analyzing seismocardiographic (SCG) traces from an Inertial Measurement Unit (IMU) placed over a subject’s sternum. An automated calibration procedure allows for straightforward adaption to different subjects. Calibration is performed once per subject, exploiting ECG (electrocardiogram) markers; relevant patterns and parameters are automatically extracted and used for successive SCG processing, which does not require concurrent ECG information any longer. Annotation of SCG traces is performed in two steps: in the first one, a suitably engineered signal is derived from SCG and used as coarse heartbeat detector; then, annotation can be performed by comparing the prototype extracted at calibration time with segments of SCG data, near to the detected beats. The proposed methodology is validated by direct comparison with ECG, adopted as gold-standard. In particular, three main metrics are taken into account: sensitivity (i.e. percentage of correctly identified heartbeats, compared to ECG), precision (i.e. impact of false positives on truly detected beats) and R2 (i.e. linearity between beat-to-beat measurements as computed by ECG and SCG). Results show satisfactory performance, more than adequate to continuous, long-term monitoring: overall, approximately 90% of heartbeats are correctly detected, on average, with minimal false positives (≈1%). Linearity between ECG and SCG-computed beat-to-beat intervals is extremely high (R2 > 0.95, on average), indicating good agreement between the two measurement methods. These results suggest SCG can be used as a reliable, contactless measure of heart-related parameters
High-Accuracy, Unsupervised Annotation of Seismocardiogram Traces for Heart Rate Monitoring
Full text linkThis article presents an unsupervised, automated procedure for the analysis of SeismoCardioGram (SCG) signals. SCG is a measure of chest vibrations, induced by the mechanical activity of the heart, that allows to extract relevant parameters, including Heart Rate (HR) and HR Variability (HRV). An initial self-calibration is performed, solely based on SCG traces, yielding a suitable heartbeat template (personalized for each subject). Then, beat detection and timing annotation are performed in two steps: at first, candidate beats are identified and validated, by means of suitably defined detection signals; then, precise timing annotation is achieved by best aligning such candidate beats to the previously extracted template. The algorithm has been validated on two separate datasets, featuring different acquisition setups: the first one is the publicly available CEBS database, reporting SCG signals from subjects lying in supine position, whereas the second one was acquired using a custom setup, involving sitting subjects. Results show good sensitivity and precision scores (98.5%, 98.6% for the CEBS database, and 99.1%, 97.9% for the Custom one, respectively). Also, comparison with ECG gold-standard is given, showing good agreement between beat-to-beat intervals computed from SCG and the ECG gold-standard: on average, R2 scores of 99.3% and 98.4% are achieved on CEBS and Custom datasets, respectively. Furthermore, a low RMS Error is achieved on the CEBS and Custom dataset, amounting to 4.6 ms and 6.2 ms, respectively (i.e. 2.3 Ts and 3.1 Ts, where Ts is the sampling period): such results well compare to related literature. Validation on two different datasets indicates the robustness of the proposed methodology
An accurate and stable bed-based ballistocardiogram measurement and analysis system
No full textAn experimental BallistoCardioGram (BCG) measurement and analysis system is presented, featuring accelerometers placed between the mattress and bed slats. The system can sample BCG waveforms at 500 Hz and can perform unsupervised BCG heartbeat detection and heartbeat interval measurements. The approach is validated on an experimental dataset consisting in 14 subjects recorded while lying in three different positions: supine, left side and right side. The overall performance is good, comparing to other works in literature. In fact, the average sensitivity and precision across subjects and positions is 98.2% and 98.0%, respectively; similarly, an R2 score of 98.2% was achieved between BCG and reference ECG measurements, while Mean Absolute Error and Root Mean Squared Error are as low as 3.9 ms and 5.6 ms. The presented methodology is shown to be resilient to different sleeping positions, as confirmed by Kruskal-Wallis statistical tests (p≈0.91 for sensitivity, p≈0.73 for precision, p≈0.81 for R2, p≈0.26 for MAE, p≈0.20 for RMSE). Moreover, results are in line and comparable to those already achieved on a different measurement scenario featuring a different bed structure. This further proves the stability of the presented BCG measurement and analysis system
Accurate annotation of SeismoCardioGram exploiting multi-dimensional accelerometry
No full textThis paper presents a methodology to assess heartrelated parameters (such as heart rate and heart rate variability) from SeismoCardioGram (SCG) signals acquired with an Inertial Measurement Unit (IMU). Specific SCG landmarks are detected and identified, including Aortic valve Opening (AO) and Isovolumetric Moment (IM) phases. In order to improve detection accuracy and robustness, information from all 3 accelerometer's axes are combined. Preliminary results are promising, highlighting good overall linearity (r 2 > 0.965) with respect to reference ECG-based (ElectroCardioGram) measurements. By considering all 3 accelerometer axes, performance improves over single-axis approaches. Results suggest the feasibility of accurate, continuous measurements of heart rate and its variability (in restconditions) in AAL scenarios, where such information may effectively complement physical activity and activity intensity data
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
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