267,906 research outputs found
Automated Classification Model With OTSU and CNN Method for Premature Ventricular Contraction Detection
Premature ventricular contraction (PVC) is one of the most common arrhythmias which can cause palpitation, cardiac arrest, and other symptoms affecting the work and rest activities of a patient. However, patients hardly decipher their own feelings to determine the severity of the disease thus, requiring a professional medical diagnosis. This study proposes a novel method based on image processing and convolutional neural network (CNN) to extract electrocardiography (ECG) curves from scanned ECG images derived from clinical ECG reports, and segment and classify heartbeats in the absence of a digital ECG data. The ECG curve is extracted using a comprehensive algorithm that combines the OTSU algorithm with erosion and dilation. This algorithm can efficiently and accurately separate the ECG curve from the ECG background grid. The performance of the classification model was evaluated and optimized using hundreds of clinical ECG data collected from Fujian Provincial Hospital. Additionally, thousands of clinical ECG reports were scanned to digital images as the test set to confirm the accuracy of the algorithm for practical application. Results showed that the average sensitivity, specificity, positive predictive value, and accuracy of the proposed model on the MIT-BIH dataset were 95.47%, 97.72%, 98.75%, and 98.25%, respectively. The classification average sensitivity, specificity, positive predictive value, and accuracy based on clinical scanned ECG images can reach to 97.24%, 81.6%, 83.8%, and 89.33%, respectively, and the clinical feasibility is high. Overall, the proposed method can extract ECG curves from scanned ECG images efficiently and accurately. Furthermore, it performs well on heartbeat classification of normal (N) and ventricular premature heartbeat
Stress-strain synchronization for high strain rate tests on brittle composites
Nowadays, many researchers develop rate-dependent composite material models for application in dynamic simulations. Ideally, full stress-strain curves at a wide range of strain rates are available for identification of the different parameters of these models. Dynamic tensile tests are needed to produce the experimental input data. However, especially for brittle materials, the data acquisition during these tests becomes critical. The effect of synchronization on the test results is investigated by conducting a series of dynamic tensile tests on three different brittle continuous-fibre composite laminates. It is demonstrated that synchronization errors of the order of 1 microsecond already have a significant effect on the test outcome at high rates. With the aid of a finite-element model, the limiting factors on the maximum attainable strain rate are quantified
Threshold-free Evaluation of Medical Tests for Classification and Prediction: Average Precision versus Area Under the ROC Curve
When evaluating medical tests or biomarkers for disease classification, the
area under the receiver-operating characteristic (ROC) curve is a widely used
performance metric that does not require us to commit to a specific decision
threshold. For the same type of evaluations, a different metric known as the
average precision (AP) is used much more widely in the information retrieval
literature. We study both metrics in some depths in order to elucidate their
difference and relationship. More specifically, we explain mathematically why
the AP may be more appropriate if the earlier part of the ROC curve is of
interest. We also address practical matters, deriving an expression for the
asymptotic variance of the AP, as well as providing real-world examples
concerning the evaluation of protein biomarkers for prostate cancer and the
assessment of digital versus film mammography for breast cancer screening.Comment: The first two authors contributed equally to this paper, and should
be regarded as co-first author
Speeding up Simplification of Polygonal Curves using Nested Approximations
We develop a multiresolution approach to the problem of polygonal curve
approximation. We show theoretically and experimentally that, if the
simplification algorithm A used between any two successive levels of resolution
satisfies some conditions, the multiresolution algorithm MR will have a
complexity lower than the complexity of A. In particular, we show that if A has
a O(N2/K) complexity (the complexity of a reduced search dynamic solution
approach), where N and K are respectively the initial and the final number of
segments, the complexity of MR is in O(N).We experimentally compare the
outcomes of MR with those of the optimal "full search" dynamic programming
solution and of classical merge and split approaches. The experimental
evaluations confirm the theoretical derivations and show that the proposed
approach evaluated on 2D coastal maps either shows a lower complexity or
provides polygonal approximations closer to the initial curves.Comment: 12 pages + figure
Rayleigh Wave Calibration of Acoustic Emission Sensors and Ultrasonic Transducers.
Acoustic emission (AE) sensors and ultrasonic transducers were characterized for the detection of Rayleigh waves (RW). Small aperture reference sensors were characterized first using the fracture of glass capillary tubes in combination with a theoretical displacement calculation, which utilized finite element method (FEM) and was verified by laser interferometer. For the calibration of 18 commercial sensors and two piezoceramic disks, a 90° angle beam transducer was used to generate RW pulses on an aluminum transfer block. By a substitution method, RW receiving sensitivity of a sensor under test was determined over the range of frequency from 22 kHz to 2 MHz. Results were compared to the sensitivities to normally incident waves (NW) and to other guided waves (GW). It was found that (1) NW sensitivities are always higher than RW sensitivities, (2) differences between NW and RW receiving sensitivities are dependent on frequency and sensor size, (3) most sensors show comparable RW and GW receiving sensitivities, especially those of commonly used AE sensors, and (4) the receiving sensitivities of small aperture (1 mm diameter) sensors behave differently from larger sensors
(DH) Noise and Signal scaling factors in Digital Holography in week illumination: relationship with Shot Noise
We have performed off axis heterodyne holography with very weak illumination
by recording holograms of the object with and without object illumination in
the same acquisition run. We have experimentally studied, how the reconstructed
image signal (with illumination) and noise background (without) scale with the
holographic acquisition and reconstruction parameters that are the number of
frames, and the number of pixels of the reconstruction spatial filter. The
first parameter is related to the frequency bandwidth of detection in time, the
second one to the bandwidth in space. The signal to background ratio varies
roughly like the inverse of the bandwidth in time and space. We have also
compared the noise background with the theoretical shot noise background
calculated by Monte Carlo simulation. The experimental and Monte Carlo noise
background agree very well together
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