Blind source separation of spatio-temporal mixed signals using time-frequency analysis

The cocktail party problem deals with the specialized human listening ability to focus one's listening attention on a single talker among a cacophony of conversations and background noise. The blind source separation problem corresponds to a way to enable computers to solve the cocktail party problem in a satisfactory manner. The simplest version of spatio-temporal mixture problem, which is a type of blind source separation problems, is solved using time-frequency analysis. The analytic wavelet transform is used to represent time-frequency information and a numerical simulation is given.     

Numerical simulation of flow over urban-like topographies and evaluation of turbulence temporal attributes

We have used large-eddy simulation with an immersed boundary method to study turbulent flows over distributions of uniform height, staggered cubes. The computational domains were designed such that both the roughness sublayer and a region of the inertial layer are resolved. With this, we record vertical profiles of time series of fluctuating streamwise and vertical velocity at different locations throughout the domain. Contour images of these fluctuating quantities shown relative to elevation and time are studied; contour images of Reynolds shear stresses owing to ‘sweeps’ and ‘ejections’ are also studied. These images show that periods of momentum excess (deficit) in the inertial-layer precede excitation (subdual) of cube-scale coherent vortices in the roughness sublayer. We compute this time lag (termed advective lag) and demonstrate that it scales linearly with wall-normal elevation. The advective lag is attributed to coherent, low- and high-momentum regions in the aloft inertial layer. Vortex identification is used to illustrate the presence of hairpin packets encapsulating low-momentum regions. Based on this, the reported inclination angle associated with hairpin packets is used to guide the development of a model for prediction of advective lag with height. The model captures the advective lag profiles reasonably well. In the interest of generality, additional cases of flow over homogeneous roughness (aerodynamic drag imposed with the equilibrium logarithmic law) are considered. We again observe that advective lag scales linearly with wall-normal elevation. Advective lag predictions from the aforementioned model agree well with results for these cases.     

基于亮度对比度传递的红外与可见光图像融合方法研究

基于亮度一对比度传递技术提出了一种红外和彩色可见光图像的融合方法,该算法通过对红外图像和可见光图像在HIS空间进行二次融合,保留了可见光图像的颜色特性,并获得一幅具有良好亮度和对比度效果的融合图像。实验结果表明该方法融合噪声小、细节缺失少、融合速度快。     

啁啾脉冲频域干涉仪相位重建方法的理论研究

理论研究了啁啾脉冲频域干涉仪的时域相移重建技术,对于接近实际的频谱干涉条纹,分别采用傅里叶变换和小波变换的方法完成了时域相位扰动信号的重建。傅里叶变换方法产生的重建误差受到滤波参数的影响,相对而言,小波变换方式解谱过程中,不需要进行特意的滤波操作,从而避免了重建结果存在误差不确定性的问题。     

Strichartz Estimates for Wave Equations with Coefficients of Sobolev Regularity

Wave packet techniques provide an effective method for proving Strichartz estimates on solutions to wave equations whose coefficients are not smooth. We use such methods to show that the existing results for C ^{1, 1} and C ^{1, α} coefficients can be improved when the coefficients of the wave operator lie in a Sobolev space of sufficiently high order.     

一个小波函数指数参数变化的分岔现象

研究一个高斯小波函数产生的混沌分岔现象.随着小波函数中指数参数的增加，它的分岔图出现了倍周期分岔，然后出现混沌，经过一段混沌区域后又出现2的幂周期.在整个过程中，正分岔与逆分岔完整地结合在一起.改变小波函数的系数出现一些明显的奇数周期，如3周期、5周期等.绘制Lyapunov指数曲线及映射折射过程，对混沌现象进行研究.将小波函数展开成近似的多项式函数，对近似多项式函数的分岔图进行了分析. 关键词： 混沌 分岔 小波函数     

Wavelet method applied to specific adhesion of elastic solids via molecular bonds

We propose a wavelet method to analyze the stochastic-elastic problem of specific adhesion between two elastic solids via ligand-receptor bond clusters, which is governed by a nonlinear integro-differential equation with a singular Cauchy kernel to describe the mean-field coupling between deformation of elastic materials and stochastic behavior of the molecular bonds. To solve this problem, Galerkin method based on a wavelet approximation scheme is adopted, and special treatment which transforms the singular Cauchy kernel into a smooth one has been proposed to avoid the cumbersome calculation of singular integrals. Numerical results demonstrate that the method is fully capable of solving the specific adhesion problems with complex nonlinear and singular equations. Based on the proposed method, investigations are performed to reveal the relation between steady-state pulling force and mean surface separation under different stress concentration indexes, which is crucial for assembling the overall constitutive relations for multicellular tumor spheroids and polymer-matrix microcomposites.     

Treatment of MZI sensor signal with an improved wavelet neighboring coefficients

In order to gain the wavelength drift of Mach–Zehnder interferometer (MZI) sensor system, achieve the measurement of ambient environment parameters precisely, so, need to treatment optical fiber sensing signal with noise. Firstly, introduce the method of neighborhood wavelet coefficient by analyzing the drawback of traditional wavelet de-noising methods. Secondly, an improved threshold is putted forward based on neighboring coefficients in this paper which is to overcome the shortcomings of traditional wavelet methods. Finally, the threshold function proposed by this paper deal with MZI sensing noisy signal together with improved threshold. The simulation result shows that the new method can get the better signal-to-noise ratios (SNR) and root of mean square error (MSE) simultaneously and gain the reconstruction signal of the higher correlation coefficient (CC). Compared with the soft and hard threshold method, its SNR increases by 2–4 db, and compared with NeighCoeff, its SNR improves by 1.2 db. The peak error is 1.6 pm. So, the system can meet the requirement of improving sensor detection precision.