1,721,087 research outputs found
The influence of hoeing and earthing-up in conjunction with chemical weed-killers on sunflower yield
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Detection of discontinuities in vibration signals from mechanical systems
No full textthis paper an approach to the detection of discontinuities in signals from mechanical systems based on the use of wavelet transform is presented. Morlet wavelets have been used, by defining an automated procedure to detect phase and amplitude changes of the transform which can be related to variations of the statistical structure of the signals. The results obtained by processing synthetic signals which simulated possible fault conditions, and some first results with real signals are reported. It emerged that the method is capable of detecting the presence of typical discontinuities, and that is susceptible of an automated application
Automatic detection of surface EMG activation timing using a wavelet transform based method
No full textThe problem of the identification of the muscle contraction timing by using surface electromyographic signal is addressed. The timing detection of the muscular activation in dynamic conditions has a real clinical diagnostic impact. Widely used single threshold methods still rely on the experience of the operator in manually setting that threshold. A new approach to detect the muscular activation intervals, that is based on discontinuities detection in the wavelet domain, is proposed. Accuracy and precision of the algorithm were assessed by using a set of simulated signals obtaining values lower than 11.0 and 8.7 ms for biases and standard deviations of the estimation, respectively. Moreover an experimental application of the algorithm was carried out recruiting a population of 10 able-bodied subjects and processing the myoelectric signals recorded from the lower limb during an isokinetic exercise. The algorithm was able to reveal correctly the timing of muscular activation with performance comparable to the state-of-the-art methods. The detection algorithm is automatic and user-independent, it manages the detection of both onset and offset activation, it can be fruitfully applied even in presence of noise and, therefore, it can be used also by unskilled operators. (C) 2010 Elsevier Ltd. All rights reserved
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