闪电瞬态电场信号波形去噪方法

 通过对传统数字滤波和Birge-Massart小波阈值法的比较，对闪电瞬态电场信号进行了去噪研究。构建了双指数衰减脉冲信号并在其上叠加了高斯白噪声信号来仿真闪电瞬态电场实测波形，通过计算去噪前后信号的均方误差和幅值误差，比较了加权平滑滤波、FIR数字低通滤波器和小波阈值法的去噪效果，从处理仿真波形和实测波形结果可以发现，小波阈值去噪方法明显优于另外两种传统滤波方法。通过比较仿真信号由不同小波分解层数去噪结果的均方误差和幅值误差，确定在对闪电电场实测信号的去噪过程中，小波系数分解层数应选5~7。     

Instantaneous intensity analysis of impulsive sound by the wavelet transform

The method for measuring instantaneous intensity by using the wavelet transform is proposed. We also conducted an analysis of the experimental data by using the hammering noise and confirmed the applicability of this calculation method.     

Improved acoustic signals discrimination using fractional Fourier transform based phase-space representations

In this communication we propose performing two-dimensional correlation operation between phase-space representations based on the fractional Fourier transform, instead of correlating the signals themselves. A numerical examples clearly indicates superior discrimination performance.     

瞬态信号的小波变换波达方向估计

针对瞬态信号方位估计问题,提出了基于连续小波变换的多重信号分类测向算法(CWT_MUSIC)。首先由信号特征确定小波尺度参数,构造Morlet小波,对信号进行小波变换,利用获得的小波变换系数建立多分辨时频阵列信号模型,并据此模型设计基于子空间的MUSIC算法以实现瞬态信号的波达方向估计;然后对该算法的多分辨与误差性能进行分析,最后仿真实验和实际爆炸试验验证了所提出的CWT_MUSIC算法能有效地提高空间谱的分辨率和DOA估计性能。     

炮体表面瞬态温度分布的散斑干涉测试研究

为了可以实现对炮体表面瞬态温度分布变化的实时监测,同时克服传统瞬态高温测试仪器单点探测以及热惯性大等局限性,设计了基于散斑干涉与光谱频域分析相结合的瞬态温度分布测试系统。系统采用散斑干涉技术将炮体瞬态温度变化引发的微小形变转换成散斑干涉条纹,再由傅氏变换完成干涉条纹形变到光谱分布的函数转换,从而通过光谱分布函数反演任意采样时刻上的温度分布。实验采用ZX-FB1型光纤测温仪测试单点位置上瞬态温度作为标准值,再由555 nm激光器与面阵CCD采集散斑干涉条纹,分别使用图像识别法与傅氏变换法完成干涉条纹与瞬态温度的算法匹配,从而反演瞬态温度。实验结果显示,两种方法均能实现瞬态温度检测,但基于傅氏变换频谱分析的散斑干涉法精度更高,并且可以有效地克服由表面瑕疵、漆面磨损等问题造成的粗大误差。     

抵消Wigner-Ville分布交叉项的窄带运动声源无源测速

利用声波的多普勒频移可以对窄带运动声源进行单传感器无源测速,其性能很大程度上取决于能否精确地估计出声波的瞬时频率.Wigner-Ville分布虽然时频分辨率高,但存在交叉项干扰,很少被直接用于瞬时频率估计。对此,提出了抵消Wigner-Ville分布交叉项的单传感器窄带声源无源测速方法。利用交叉项与声源速度的关系构造一个抵消项,引入到Wigner-Ville分布中,通过对声源速度估计值进行迭代更新,使抵消项与交叉项相位相反,从而约掉交叉项。经实测噪声数据验证,对一辆以6.07 m/s匀速运动的卡车(信噪比约为29 dB)测速误差为0.1 m/s,运行时间为4.6 s,对一架以28.90 m/s匀速运动的直升机(信噪比约为16 dB)测速误差为0.46 m/s,运行时间为1.2 s,均优于匹配Wigner变换和多普勒线性调频小波变换测速方法.     

Infrared Absorption Intensity Analysis as a New Tool for Investigation of Salt Effect on Proteins

通过观测红外光谱的强度变化研究了在不同温度下盐离子对谷氨酸和三种水溶性蛋白质(细胞色素C、DsbC和DsbC-G49R)的影响. 证实了Onsager反应场理论. 区分并且定义了随温度变化的蛋白质盐效应盐溶过程和解离过程. 同时利用Van't Hoff关系式对实验结果进行线性拟合,获得了蛋白质及其二级结构在上述两个过程中的热力学常数.     

Generalization of the Poincare sphere to process 2D displacement signals

Traditionally the multiple phase method has been considered as an essential tool for phase information recovery. The in-quadrature phase method that theoretically is an alternative pathway to achieve the same goal failed in actual applications. The authors in a previous paper dealing with 1D signals have shown that properly implemented the in-quadrature method yields phase values with the same accuracy than the multiple phase method. The present paper extends the methodology developed in 1D to 2D. This extension is not a straight forward process and requires the introduction of a number of additional concepts and developments. The concept of monogenic function provides the necessary tools required for the extension process. The monogenic function has a graphic representation through the Poincare sphere familiar in the field of Photoelasticity and through the developments introduced in this paper connected to the analysis of displacement fringe patterns. The paper is illustrated with examples of application that show that multiple phases method and the in-quadrature are two aspects of the same basic theoretical model.     

General transient solutions for the four-coupled Bloch-type equations for a two-level system

When the collisional dynamics of two states under consideration for a radiative transition is different, the polarization and population relaxations in gas phase at low pressure are governed by four-, instead of three-, coupled Bloch-type equations. The general transient solutions of these four-coupled equations are solved by using the Laplace transformation technique. It has been found that an additional exponential term appears because of the effect. This is also responsible for the non-exponential character in the decay signal of a transient microwave pulse experiment, besides other factors reported earlier.     

轴锥镜光强分布的角谱衍射数值分析法

针对理论上推导轴锥镜的衍射光场分布解析式较为困难,且用菲涅耳衍射理论分析时存在近轴近似及不能适用于近场衍射光场分析的问题,采用了严格遵从标量衍射亥姆霍兹方程的角谱衍射波前重建方法,对轴锥镜在单色和准单色高斯光波照射下的横向和轴向衍射光强分布特性,以及在单色均匀平面光波照射下的轴向衍射光强分布进行了数值计算和分析。结果表明,轴锥镜后单色光衍射光强分布在几何光束重叠的菱形区域内为近似无衍射贝塞尔光强分布,轴上光强沿光轴方向呈振荡变化,轴上光强分布规律与入射光波的垂轴横向光强分布有关;入射光的准单色性使得贝塞尔衍射条纹对比度略下降、轴上光强沿光轴方向振荡程度减小,但分布规律与单色光一致。     

针对磁共振射频脉冲的时频域分析方法比较研究

射频脉冲可实现样本自旋体系的精确操控,进而产生预期的核磁共振(NMR)信号,在NMR信号产生过程中扮演重要角色.该文分别采用短时傅里叶变换(STFT)、连续小波变换(CWT)和维格纳-威利分布(WVD)几种时频域分析方法对射频脉冲(优化形状脉冲)进行特性分析和比较.结果表明,三种方法各自具有优缺点,结合各自优势对射频脉冲进行各种方法分析,可以更好地理解复杂脉冲的幅度、相位特性在时频域的分布情况.该文的研究方法将为直观理解复杂射频脉冲对自旋体系的作用机制提供参考.     

Eigenvalue spectrum analysis for temporal signals of Kerr optical frequency combs based on nonlinear Fourier transform

Based on the nonlinear Schr?dinger equation(NLSE) with damping, detuning, and driving terms describing the evolution of signals in a Kerr microresonator, we apply periodic nonlinear Fourier transform(NFT) to the study of signals during the generation of the Kerr optical frequency combs(OFCs). We find that the signals in different states, including the Turing pattern, the chaos, the single soliton state, and the multi-solitons state, can be distinguished according to different distributions of the eigenvalue spectrum. Specially, the eigenvalue spectrum of the single soliton pulse is composed of a pair of conjugate symmetric discrete eigenvalues and the quasi-continuous eigenvalue spectrum with eye-like structure.Moreover, we have successfully demonstrated that the number of discrete eigenvalue pairs in the eigenvalue spectrum corresponds to the number of solitons formed in a round-trip time inside the Kerr microresonator. This work shows that some characteristics of the time-domain signal can be well reflected in the nonlinear domain.     

Improved optical performance of the Radon-Wigner display for one-dimensional signals

An improved optical implementation of the Radon-Wigner display for one-dimensional signals based on fractional Fourier transform is proposed. All of the fractional Fourier transform orders with the correct magnification can be achieved simultaneously by the suggested new setup with high precision, which consists of only two optical elements, a cemented linear varifocal lenses and a curvy image plane. This setup can offer practical applications for analyzing and processing of stationary or non-stationary signals.     

木塑复合材料缺陷及损伤的声发射信号特征分析及神经网络模式识别

针对木塑复合材料五种典型的缺陷及损伤机制，选择合适的木塑试样，应用三点弯曲的加载方法采集声发射信号。对主损伤区附近的声发射事件，应用小波变换提取特征参数，确定五类主要损伤机制所对应的声发射信号特征。采用B—P型反向传播神经网络构成的智能化模式分类器，对此五类声发射信号进行识别，获得了满意的效果。     

Multichannel sampling theorem for bandpass signals in the linear canonical transform domain

The linear canonical transform (LCT) describes the effect of first-order quadratic phase optical system on a wave field. The classical multichannel sampling theorem for common bandlimited signals has been extended differently to bandlimited signals associated with LCT. However, a practical issue associated with the reconstruction of the original bandpass signal from multichannel samples in LCT domain still remains unresolved. The purpose of this paper is to introduce a practical multichannel sampling theorem for bandpass signals in LCT domain. The sampling expansion which is constructed by the ordinary convolution in the time domain can reduce the effect of spectral leakage and is easy to implement. The classical multichannel sampling theorem and the well-known sampling theorems for the LCT are shown to be special cases of it. Some potential applications of the multichannel sampling are also presented to show the advantage of the theory.     

一阶光学系统分数傅里叶变换的相空间分析

在维格纳相空间中,通过将一阶光学系统的传输矩阵分解为坐标旋转、比例缩放和啁啾矩阵的组合,得到了一阶光学系统在空域的分数傅里叶表示.结果表明:任意一阶光学系统均可表示为经过比例缩放和二次相位调制的分数傅里叶变换.通过将输入输出光场在相空间中作π/2角旋转,得到了一阶光学系统在频域的传输矩阵和衍射积分公式,进而得到了一阶光学系统在频域的分数傅里叶表示.比较空域和频域一阶光学系统的相空间变换矩阵,说明2个系统本质上属同一变换在不同基坐标下的表示,并推导出了光学系统在空域和频域具有相同分数傅里叶变换的条件.     

Analysis of the characteristics of time-resolved signals for transient radiative transfer in scattering participating media

Transient radiative transfer (TRT) in one-dimensional (1-D) homogeneous and inhomogeneous media with ultra-short pulse laser irradiated is investigated by means of the finite volume method (FVM) in the present research. Comparing with the steady radiative transfer (SRT), the extra time-resolved information can be obtained in TRT. Meanwhile, the propagation speed of short-pulse laser and the geometric thickness of the media should be considered in the simulation of TRT problem besides the optical thickness. A new nondimensional number ζ=ct_p/L is presented. For the homogeneous media, the temporal signals would overlap one another with different combinations of the pulse duration and the thickness of the media with the same ζ. Furthermore, in two-layer media, the influence of the scattering albedo, optical thickness and the geometric thickness of the participating media on ‘dual-peak’ are studied thoroughly. The improved expression of the ‘local minimum’ in the ‘dual-peak’ and the interface location of the multi-layer media are provided.     

PC based instrument for impedance analysis, cyclic voltammetry and transient analysis

A low cost PC based instrument for low frequency impedance measurements and analysis has been designed, fabricated and tested. A software program has been implemented to generate the equivalent circuit from the impedance measurements. The same set-up can also be used for time domain techniques like cyclic voltammetry and transient studies.     

非均匀光栅的振幅分布和光强特性分析

从光栅自身的空间结构出发,用菲涅尔衍射公式推导了非均匀光栅的振幅分布公式(θi)和光强特性公式I(θi),用Maple程序给出了算例之不规则光栅衍射光强I(θi)随sinθi变化曲线,得到了非均匀光栅的衍射特性。一维透射平面光栅的振幅分布(θ)和光强分布I(θ)不仅与非均匀光栅的平均光栅常量有关,还与每个单元单缝的缝宽a有关。这一特性,补充完善了平面光栅衍射性质,同时,也为通过调整光栅空间结构,设计、研制、测试非线性光栅提供了理论依据。     

超洛伦兹-高斯光束SLG11模的分数傅里叶变换特性

 引入了一簇互相正交的超洛伦兹-高斯光束以描述半导体激光器所产生的大角度高阶模远场分布。将分数傅里叶变换应用于超洛伦兹-高斯光束SLG­₁₁模的传输特性的研究中。利用傅里叶变换的卷积原理,导出了SLG₁₁模经分数傅里叶变换系统后场分布的解析表达式。根据所得到的公式进行了数值计算,系统分析了分数傅里叶变换阶数和光束各参数对SLG₁₁模在分数傅里叶变换面上光强分布的影响。结果显示：SLG₁₁模在分数傅里叶变换面上的归一化强度分布随分数傅里叶变换的阶数呈周期性变化,周期为2;随着光束参数的增大,SLG₁₁模在分数傅里叶变换面上的光斑尺寸增大。