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Piezoelectric shunting arrays are employed to control the elastic wave propagation in L-shape beams. Unlike straight beams where longitudinal and flexural waves usually propagate independently, these waves are coupled in an L-shape beam. Based on transfer matrix method and Bloch theorem, dispersion curves and vibration transmissibility are evaluated and analyzed. A locally resonant gap is produced on the flexural and longitudinal waves, respectively, whose locations are nonoverlapped if the shunt damping is void. However, the longitudinal wave band gap can be completely overlaid by the flexural one when a proper shunting resistance is involved. With the decreasing of shunting inductance, the locations of longitudinal and flexural wave gaps both go up to higher frequencies which agree with the variation of resonant frequencies, but they are less affected by shunting resistance. As the resistance increases, the width of the band gaps grows, whereas the attainable maximum attenuation within the band gaps shows a significant decrease. Also, finite element simulations are performed to validate the numerical predictions, which demonstrate that the resulting transmissibility of displacements agree well with the band gaps. [ABSTRACT FROM AUTHOR]

Abstract: Periodic arrays of shunted piezoelectric patches are employed to control the wave propagation in a thin plate. The performance is characterized through the application of finite element method and Bloch theorem. This article proposes an effective approach to gain the dispersion properties of the periodically shunted plate in any directions from the solutions of transcendental eigenvalue problems. The results show that resistive shunts can tune the location and attenuation constants of the Bragg gap, while the internal resonances of resonant shunting system split the dispersion curves and form a locally resonant band gap. Moreover, the Bragg gap is directional, whose width varies enormously with directions. However, the locally resonant gap almost keeps the same in different directions, i.e., the gap is complete. Also, the influences of different shunting parameters to the band gaps are investigated in detail. [Copyright &y& Elsevier]

In this study, the dispersion relationships and characteristics of directional periodic structure waveguides with Sierpinski carpet unit cells were investigated. Finite element method was used to analyze the Sierpinski-carpet periodic structures with square Pb cylinders inserted in the rubber background. The dispersion curves of unit cells with different stages were investigated first, then group velocities of periodic structures at given frequencies were calculated and used to analyze the directional waveguide characteristics in the Sierpinski-carpet periodic structures. The dynamic responses of finite periodic structures were investigated to observe the directional features, and the results were used to support the fact that Sierpinski carpet unit cells with different stages can control the propagation behavior of elastic waves in specific ways; the dispersion curves grew compressed as the stage increased. Multiple band characteristics were observed in the case of the second-stage fractal configuration. The directional propagation characteristics in Sierpinski carpet periodic structures can be utilized to further extend the range of vibration reduction zones. The results of this study have significant potential in terms of the application of Sierpinski-carpet periodic structures for vibration isolation. [ABSTRACT FROM AUTHOR]

Allied to the extensive use of online shopping, product recommendation on websites is vitally important for E-commerce. Consequently, collaborative filtering and content-based filtering have been widely used in recommendation systems on E-commerce websites. However, these filtering methods have many problems, such as cold start, prejudiced ratings and inaccurate suggestions. To generate valid and accurate suggestions, researchers have proposed integrating semantic features of the data in an ontology into the recommendation process. However, most existing studies only include the type and features of a product without considering the relational characteristics thereof. Given that the relational characteristics can provide much useful information during the recommendation process, we have designed an easily realizable recommendation system framework based on relational data by integrating the relational data in the domain ontology and applying a genetic algorithm to process the recommendation. Experimental results show that there are obvious improvements in the methods for dealing with sparsity and cold start problems as well as the accuracy and timeliness of recommendations. [ABSTRACT FROM AUTHOR]

PM2.5 pollution in China is getting worse. The relationship between PM2.5 concentration and weather elements exhibits complex non-linear feature. Therefore, it is very important to study the sophisticated mathematical and nonlinear method about the relationship between PM2.5 concentration and weather elements. Coupling detrended fluctuation analysis (CDFA) method can reveal the multifractal properties of more than two series. The coupled correlations between PM2.5 concentration and weather elements in Hangzhou and Guangzhou are explored by CDFA. We find that coupled correlations are not only multifractal but also anti-persistent. Compared with Guangzhou, Hangzhou has stronger correlations. Both long-range correlation and fat-tailed distribution can cause the coupled multifractality. and the long-range correlation has a greater influence on the coupled multifractality. In addition, the coupling sensitivity degree (CSD(Y)) is used to study which weather element plays a key role in the change of PM2.5 concentration. • The coupling correlations between PM2.5 concentration and weather elements are discussed by CDFA and CSD. • The coupling correlations between PM2.5 concentration and weather elements are multifractal and anti-persistent. • The coupling multifractality is caused not only by long-range correlation but also by fat-tailed distribution. • The coupling sensitivity degree (CSD(Y)) is used to explore which weather element plays a key role (more sensitive) in the change of PM2.5 concentration. [ABSTRACT FROM AUTHOR]

The daily average PM2.5 concentrations of Mong Kok (MK), Tsuen Wan (TW) and Tap Mun (TM) in Hong Kong were obtained from Hong Kong Environmental Protection Department and were analyzed. Without any spatial differentiation, PM2.5 concentrations all were higher in winter and lower in summer. In order to more accurately explore the multifractal characteristic of PM2.5 time series, the empirical mode decomposition (EMD) based multifractal detrended fluctuation analysis (MF-DFA) method is used in this paper. The results show that the PM2.5 time series for MK, TW and TM are all anti-persistence, that is, whenever the PM2.5 concentrations has been up (down), it is more likely that it will be down (up) in the close future. The multifractality is caused not only by long-range correlation but also by fat-tailed distribution. Moreover, the roadside site MK displays the highest degree of multifractality, followed by the urban (TW) and the rural (TM) one. The proposed method can more accurately analyze the multifractal characteristic of PM2.5 time series, which provides a solid foundation for further PM2.5 pollution research. • The multifractal scaling properties of PM2.5 time series are discussed by EMD-based MFDFA. • Time series of PM2.5 concentrations for MK, TW and TM are all multifractal and anti-persistence. • The multifractality is caused not only by long-range correlation but also by fat-tailed distribution. • The roadside site (MK) possesses the highest degree of multifractality, followed by the urban (TW) and the rural one (TM). [ABSTRACT FROM AUTHOR]