基于经验模态分解去噪的粗晶材料超声检测

粗晶材料超声检测中,结构噪声严重降低了检测信号的信噪比,缺陷反射难以识别.为了增强检测信号信噪比,提高粗晶材料超声检测的可靠性,采用经验模态分解(EMD)技术对检测信号进行去噪处理,通过3次样条插值形成波形包络,并利用信号的特征时间尺度将非线性、非平稳检测信号自适应的分解成多个本征模态函数(IMF)之和,从而获得信号高阶成份和趋势.利用EMD的这种特性对低信噪比模拟信号进行处理,并将处理结果与小波去噪结果进行对比,信噪比获得更大提高.通过对粗晶材料实测信号进行去噪实验,结果表明EMD去噪具有更强的自适应能力,且需知的原信号先验信息更少.     

基于倒频谱的轴承材料接触疲劳失效诊断

采用轴承接触疲劳试验机,设计了基于Lab VIEW的轴承材料接触疲劳失效诊断的软件系统,利用轴承振动信号的均方根值及温度信号来判定轴承材料的疲劳磨损程度,并通过对振动信号进行倒频谱分析来判定轴承材料的疲劳磨损区域,结果表明:振动信号均方根值结合倒频谱分析能够实现对轴承材料的接触疲劳失效诊断.     

一种改进的局部倒频谱分析方法

针对倒频谱分析难以实现从低信噪比信号中检测故障的问题,在对局部倒频谱分析的基础上,提出了一种改进的局部倒频谱分析方法,并给出了改进局部倒频谱分析的原理和算法。该方法通过在时域引入相关消噪处理,降低时域原始信号中的非周期性分量的干扰,在频域引入相关消噪处理,降低频谱上非周期性谱峰影响,实现了频谱上周期性故障特征向零频率附近的聚集。改进的局部倒频谱分析方法解决了局部倒频谱方法存在的计算频带难以选择的问题,同时消除了对故障频域内周期性特征局部化分布的限制,扩展了应用范围。将该方法用于仿真信号以及故障齿轮实验测试信号的分析,结果表明,与传统倒频谱和局部倒频谱方法相比,提出的改进局部倒频谱分析方法具有强的抗噪能力,实验中较传统倒频谱和局部倒频谱方法分别多提供了8.05bit和1.11bit的诊断信息。该方法可用于实现从低信噪比信号中检测故障。     

基于倒频谱的无噪声运动模糊图像快速复原算法

针对当前运动模糊图像复原算法主要集中在非实时性研究,着重考虑算法的执行质量而不考虑算法执行效率的问题,提出了基于倒频谱的无噪声图像的快速复原算法.该算法对无噪声模糊图像进行倒频谱处理,从倒频谱图中直接得到图像的模糊方向和模糊距离.对于尺寸较大的图像,在执行倒频谱算法前先使用双线性插值算法实现图像压缩,再进行倒频谱操作.通过比较各种复原算法的执行效率及效果,采用维纳滤波对图像进行复原.通过对多幅模糊图像进行仿真复原试验,在获得了良好的复原效果的同时也取得了较高的执行效率.     

倒频谱分析在齿轮故障诊断中的应用

齿轮传动的动态性能和许多因素有关,情况是非常复杂的.本文分析了齿轮传动的频率特性和它所产生的频率和幅值调制信号.利用倒频谱技术可以区分齿轮箱中不同转速的齿轮所产生的振动信号;同时倒频谱不会受信号传递通道和相位所影响.因此倒频谱是分析齿轮缺陷的有效工具.本文并介绍了作者研制的倒频谱分析软件.     

多噪声环境的麦克风小阵语音增强

针对在非平稳和多种噪声并存的语音增强算法抑制噪声能力有限的问题,提出基于最小跟踪噪声功率谱估计的相干滤波与广义旁瓣抵消的麦克风小阵语音增强算法。该方法先利用最小跟踪噪声功率谱估计的相干滤波抑制弱相关噪声,再结合广义旁瓣抵消与端点检测抑制强相关噪声。实验结果表明,方法更加有效地抑制噪声的影响;并提高了语音的可懂度。     

认知无线电中一种非高斯背景下的协同频谱感知方案

在认知无线电系统中,由于需要对一定频谱范围内的认知用户进行频谱检测,而传统经典的检测方法无法满足复杂多变的检测环境,基于此,文章研究了在实际情况中更为普遍的非高斯噪声情况下认知用户的频谱检测问题.由于传统的广义似然比检测计算量较大而且实际工程中较难实现,文章采用广义似然比的一种近似形式即Rao检测.通过采用矩估计方法对系统模型的混合系数等进行参数估计,并在拟合非高斯噪声的背景下应用于认知用户的频谱检测,推导出非高斯噪声中Rao检测的检测统计量和检测性能公式,分析比较了非高斯噪声中Rao检测与高斯Rao检测的性能.仿真结果表明,在虚警概率一定的情况下,基于Rao检测的频谱检测方法能有效地提高认知无线电网络中非高斯噪声背景下认知用户的检测性能.     

应用频谱分析仪测量相位噪声

介绍了利用频谱分析仪直接测量相位噪声的方法。根据相位噪声的定义,给出了频谱分析仪相关测量参数的换算关系,进而得到对测量值的计算方法。并讨论了如何对频谱分析仪输出结果进行误差修正。     

基于小波分析的磨音信号处理

针对傅里叶变换不具有局部分析能力的缺陷,将小波分析的方法引入到磨音处理中,利用小波分析的多分辨率特性,有效地滤除随机噪声的干扰,然后设计一个高通FIR滤波器滤去与磨音频谱无关的低频噪声。将磨音频谱做归一化处理并与基准磨音频谱做差,从而判断磨机的负荷状态。仿真结果表明该方案能够滤除无关噪声,并正确判断出磨机的负荷状态。     

基于改进时延估计的声源定位算法

针对强噪声和强混响条件下, 室内声源定位算法收敛速度慢和定位精度低等问题, 提出一种基于改进时延估计的声源定位方法. 该方法建立在单源多元混响模型下, 首先用四元十字型麦克风阵列估计时延; 然后在广义互相关时延估计算法的基础上, 引入二次相关法以削弱噪声干扰, 同时采用LMS(最小均方)自适应滤波算法弥补广义互相关方法的不足, 提高混响环境下的时延估计精度; 最后, 通过远场近似几何方法定位声源. 实验结果表明, 与相位变换加权广义互相关函数(GCC-PHAT)算法相比, 该方法具有较好的抗噪能力与抗混响能力, 能获得更准确的定位结果.     

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。     

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     

Journal of Donghua University ( English Edition) Contents of Volume 31

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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has