In this paper we present an optimal wavelet packet (OWP) method based on Davies-Bouldin criterion for the classification of surface electromyographic signals. To reduce the feature dimensionality of the outputs of the OWP decomposition, the principle components analysis was employed. Then we chose a neural network classifier to discriminate four types of prosthesis movements. The proposed method achieved a mean classification accuracy of 93.75%, which outperformed the method using the energy of wavelet packet coefficients (with mean classification accuracy 86.25%) and the fuzzy wavelet packet method (87.5%).

No abstract

In this paper, an efficient method based on the discrete harmonic wavelet packet transform (DHWPT) is presented to classify surface electromyographic (SEMG) signals. After the relative energy of SEMG signals in each frequency band had been extracted by the DHWPT, a genetic algorithm was utilized to select appropriate features in order to reduce the feature dimensionality. Then, the selected features were used as the input vectors to a neural network classifier to discriminate four types of prosthesis movements. Compared with other classification methods, the proposed method provided high classification accuracy in experimental research. In addition, this method could also save a lot of computational time because the DHWPT has a fast algorithm based on the fast Fourier transform for numerical implementation.

2D perovskite (PEA)2(Cs)n−1PbnI3n+1 (PEA: phenylethylammonium) exhibits more strengthened phase stability than its 3D components under ambient conditions and hence gained great attention in recent years. However, uncontrollable crystallization kinetics in (PEA)2(Cs)n−1PbnI3n+1 leads to difficulty in controlling film morphology and phase‐orientation regulation, resulting in poor power conversion efficiency (PCE). Herein, by incorporating precursor additive N‐methyl‐2‐pyrrolidone iodide (NMPI), the crystallization rate during the deposition of (PEA)2(Cs)n−1PbnI3n+1 film is efficiently regulated. As a result, the 2D or quasi‐2D perovskite solar cell (PSC) delivers record PCEs in all reported 2D or quasi‐2D CsPbX3 families, for instance, the quasi‐2D (n = 20) CsPbI3 PSC exhibits a record PCE of 14.59%, showing significantly enhanced stability. Detailed characterization reveals that the NMPI forms hydrogen bonds with dimethylammonium iodide (DMAI) in the precursor to control crystallization rate for a smooth morphology with small fluctuation, which leads to improved carrier lifetime and reduced trap‐density. More importantly, femtosecond transient absorption (fs‐TA) measurements confirm an improved phase purity and the suppressed nonradiative recombination in quasi‐2D perovskite film. It is believed that this simple additive strategy paves a new route for solving phase transition and crystallization kinetic problems in 2D and quasi‐2D CsPbX3.

No abstract