一种新的超声导波信号小波阈值去噪方法

在断轨检测中,为了获取有效的超声导波信号,必须对超声导波进行相应的去噪工作,而去噪效果的好坏直接影响到测量结果精度和可靠性。为了进一步提高去噪效果,本文针对传统的阈值函数法的不足,进行适当的改进,即提出一种新的小波阈值函数来提高去噪效果。文中简述了该种小波阈值函数的原理及构建,并进行了相关的仿真和分析;将该种方法的去噪效果与传统的软、硬阈值函数法去噪效果进行比较。结果表明,相对软阈值函数法,新阈值函数方法去噪后信号信噪比提高6%~15%,均方误差降低14%左右;相对硬阈值函数法,新阈值函数方法去噪后信号信噪比提高8%~25%,均方误差降低20%左右,并且新阈值函数方法去噪后信号幅值非常接近原始信号幅值,即该种超声导波小波阈值法相对于上述传统阈值函数法去噪效果有明显提升。     

基于小波阈值的图像信号去噪方法研究

主要对基于小波阈值的图像信号去噪方法展开研究。首先阐述小波分析进行信号分解及重构的算法原理,在此基础上总述了小波阈值进行图像信号去噪的算法原理及流程。最后对去噪效果进行了仿真分析,并将信号去噪结果与均值滤波、中值滤波等经典去噪方法进行比较。仿真结果表明,基于小波阈值的图像信号去噪方法能有效去除一维及图像信号中的噪声,输出信号的信噪比性能较传统滤波去噪方法性能更佳。     

基于小波变换的微震阈值去噪方法

矿山微震信号是微震分析以及定位的重要基础,但是微震信号常含有大量随机噪声,这些噪声会严重地影响微震信号的分析与处理.在全局阈值的基础上,对阈值函数进行了改进,提出了一种基于小波变换的迭代阈值方法.采用Symlet8作为小波基函数对微震信号进行5层分解,利用全局阈值与迭代阈值分别对微震信号进行去噪处理,对比去噪后信号的波形、差剖面、频谱、信噪比和均方差.结果表明:迭代阈值去噪后的信噪比更高,均方差更小,去噪后的信号更接近原始信号,可以将有用信号与噪声进行有效地分离.     

基于小波熵的矿用齿轮箱振动信号相关去噪法

 利用真实信号小波系数相邻层间相关性强的特性,将基于小波熵的相关去噪法应用于矿用齿轮箱振动信号的处理,进行有用系数和噪声系数的划分,并对有用的小波系数进行重构,恢复原有真实信号,去噪过程中采用小波熵自适应设定阈值。为比较小波自适应相关去噪和硬阈值与传统相关性去噪的性能,分别对仿真信号和齿轮箱实测振动信号进行去噪处理,通过3种去噪方法的重构波形对比和信噪比与标准差的定量评价,以及实测信号的功率谱分析,表明小波熵相关去噪法有效提高了矿用齿轮箱振动信号的可信度。     

基于小波分析对地面电场信号的去噪及闪电信息提取

基于小波分析方法,通过对7种小波函数在误差控制和阈值方法选取上的对比,参考信噪比及均方误差等计算结果,选取了较为合理的Rigrsure阈值分析方法和sym5小波函数作为地面大气电场信号的去噪处理方法.该方法不仅能够较好地对电场信号波形平滑处理,降低电场波形中噪声信号的叠加度,还可保留闪电引起的电场的快速变化.在此基础上,利用差分计算方法实现了对闪电信号的自动识别,引入了总闪电频数误差及分时段闪电频数与人工分析结果的相关系数等2个参考量来选取差分计算方法中电场差分阈值,通过该方法可以实现闪电频数和极性等有关信息的提取.     

一种基于局部均值分解的小波阈值信号去噪方法

在时频分析中,针对非平稳信号的滤波去噪的问题,鉴于部分传统的去噪方法对于非线性非平稳信号滤波的效果不是很理想。基于Smith提出的局部均值分解法,结合小波阈值,找出了一种自适应时频分析法。通过实例分析,比较小波阈值去噪、基于EMD小波阈值去噪和基于LMD的小波阈值去噪3种算法在进行信号滤波去噪过程中的效果,采用信噪比和均方根误差2种评价因子对该3种算法进行评价,结果表明基于LMD的小波阈值去噪方法能够更好的去除信号噪声,对信号去噪提供了一种新思路。     

基于新的阈值函数的小波阈值去噪方法

在分析了硬阈值、软阈值小波去噪算法存在问题的基础上,构造了一个新的阈值函数,仿真实验结果显示,与硬、软阈值去噪方法相比,基于新的阈值函数的小波阈值方法能够得到较小的均方误差,并提高了重建信号的信噪比,且去噪后的信号与原始信号的近似性也较好.     

基于改进的小波阈值去噪和二级判断模型的说话人识别

针对目前说话人识别系统中噪声使得识别率严重下降的问题,在特征提取前用小波阈值去噪方法对带噪语音进行去噪处理.对于小波阈值函数以及阈值的选取进行研究,提出一种改进的阈值函数,小波阈值中的噪音方差估计采用基于实际噪音方差估计的谱熵法,将改进的小波阈值去噪结合一种二级判断模型提高噪声环境下的说话人识别率.在不同信噪比条件下进行试验,改进的小波阈值去噪法优于传统小波阈值去噪方法,改进后的阈值函数与二级判断模型相结合的识别率比原始语音DTW模型提高了7.9%,比原始语音GMM提高了4.6%,对于短时语音有较好的识别率.     

小波熵阈值的心电信号去噪及R波检测算法

针对心电信号去噪问题,首先利用小波变换分解心电信号,计算小波分解后信号子带区间的小波熵,将小波熵和小波阈值相结合确定各层高频小波系数阈值门限。用阈值门限以及折中指数自适应阈值函数处理带噪的心电信号,并用bior3.7小波对去噪后的心电信号进行R波峰值定位,最后与原信号R波峰值位置对比。用本方法先对MIT/BIH心率失常心电数据库中117号心电信号去噪,之后与无偏风险阈值、固定阈值、启发式阈值和极大极小阈值去噪算法的性能比较。比较结果表明:当输入信噪比为9.724 7 dB时,小波熵阈值去噪法得到信号的输出信噪比为17.294 1 dB,其输入输出信噪比曲线明显高于其他4种传统阈值去噪法的输入输出信噪比曲线,且其R波检测结果更加精确。     

基于小波包熵的船舶轴频电场信号消噪研究

在海洋环境下,为有效地将微弱的轴频电场信号提取出来,本文在对小波包熵理论分析的基础上,提出了基于小波包熵的船舶轴频电场信号消噪方法.首先使用小波包变换对测量信号进行多子带分解,并将各子带分成几个子区间;然后计算各子带不同子区间的小波包熵,利用最大小波包熵自适应地选择各子带的阈值;最后对各子带的小波包系数进行阈值处理,并利用处理后的小波包系数对信号进行重构.通过实测数据和仿真数据对该消噪方法进行验证,结果表明此方法在低信噪比情况下能较好地将微弱的轴频电场信号从环境背景噪声中分离出来.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with