语音信号去噪的最优方案选取

针对噪声的引人对语音信号的保真有很大的影响,本文主要采用matlab中小波工具中的一些小波变换去噪函数对语音信号进行去噪仿真研究,其中的阈值去噪的方法是一种实现简单、效果较好的小波去噪方法。且与一般的傅里叶变换去噪进行对比,显示了小波去噪的优良特性。     

差分吸收光谱测量臭氧浓度信号去噪的实验研究

对差分吸收光谱测量臭氧浓度信号去噪进行了实验研究。首先利用常用的小波变换、Savitzky-Golay滤波和傅里叶变换滤波这3种方法对臭氧的吸收光谱分别进行去噪处理,得到各自去噪后的吸收光谱,发现小波变换与Savitzky-Golay滤波可以很好地拟合特征吸收,傅里叶变换滤波稍差;然后,利用信噪比与均方根误差对所得光谱进行分析评价。实验结果表明:Savitzky-Golay滤波对信号去噪的效果最好,可优先应用于臭氧的光谱计量分析。     

基于分数阶聚能带分析的微弱故障特征提取研究

提出了一种分数阶聚能带时频累加谱方法,快速实现长数据的时频分析,突出目标分量,用于提取变速器急加速过程微弱故障特征。根据变速器输入轴转速信号及传动比确定分数阶傅里叶变换（Fractional Fourier Transform, FRFT）最佳阶次,对变速器急加速过程振动信号进行最佳阶次FRFT,根据FRFT模值谱确定聚能带,计算分数阶聚能带时频累加谱,通过对比多组正常和故障数据的分数阶聚能带时频累加谱结果和阶比谱结果,验证该方法的有效性。试验结果表明：根据转速信号能快速、准确确定FRFT最佳阶次;选取聚能带内的FRFT结果进行时频分析,计算量小,分辨率高,分数阶聚能带时频累加谱具有聚焦和局部放大的特点, 能很好地突出目标分量,抑噪噪声,是提取变速器急加速过程信号微弱故障特征的有效方法。     

基于全相位FFT的油套环空中声速计算方法

油套环空中会产生各种噪声,使测得的接箍反射信号非常复杂,环隙中真实的声速则很难计算准确,可通过对原始接箍数据进行傅里叶变换的方法对声速进行估计,但是存在不可忽视的误差。全相位傅里叶变换是傅里叶变换的一种改进方法,能够获得更加准确的频率谱与相位谱。文章采用全相位快速傅里叶变换（all-phase Fast Fourier Transform,apFFT）得到原始接箍信号的频谱,然后通过该频谱进一步计算环隙声速,可得到更加准确的声速估计。通过对不同信噪比下的模拟接箍信号采用快速傅里叶变换（Fast Fourier Transform,FFT）和全相位快速傅里叶变换（apFFT）得到其频谱,可以验证apFFT具有很强的抑制频谱泄漏的能力,且抗噪性能比FFT更好。根据FFT谱和apFFT谱分别计算出声速并对比其精度,可以验证通过apFFT谱计算出的声速稳定性更好、精度更高。然后采用上述两种方法对不同深度井的实测接箍数据进行频谱分析与对比,验证了apFFT较之于FFT对谱峰位置的辨识能力更强,根据谱峰位置计算声速的准确性也将更高。     

一种新的声发射信号消噪及故障诊断方法

在旋转机械故障诊断中,声发射信号极易受到噪声的干扰。针对经验模态分解(EMD)易产生模态混叠现象,提出了一种基于经验小波变换(Empirical Wavelet Transform,EWT)的消噪和旋转机械声发射碰摩故障诊断的方法。利用了EMD和小波变换的优点,通过对傅里叶频谱进行自适应划分,并构建小波滤波器组来提取声发射信号所包含的不同固有模态分量,可有效消除模态混叠现象,同时对分量进行Hilbert变换从而实现声发射信号的消噪和故障诊断。采用该方法对仿真信号进行加噪声和消噪处理,在同信号源下,对比基于d B4全阈值消噪、d B4默认软阈值消噪、d B4对高频系数处理消噪和EMD消噪效果。并将该方法应用到实际的声发射碰摩信号中。仿真和实验分析结果表明:EWT方法可以有效地分解出信号的固有模态,分解出的模态少,并且不存在难以解释的虚假模态,消噪效果优于其他方法,并且在声发射故障诊断中也有较大的优势。     

基于多分辨分析的时频分析

短时傅里叶变换由于采用固定宽度的时域窗，在缓变与瞬变信号共存的宽频带信号分析中，其时间与频率分辨力矛盾突出。采用Mallat算法的小波变换能够将信号正交分解成多尺度的信号分量，然而所提供的时频信息不很直观，难以识别其时频谱。通过对短时傅里叶变换和小波变换在时频分析中的优缺点分析，发现两者具有互补性。因此本文提出基于多分辨分析的短时傅里叶变换（取名为WAVSTFT），即采用Mallat算法将信号分解成多个尺度信号分量，再对各分量分别做与其尺度相适应的短时傅里叶变换，最后把得到的各时频谱在同一个不相平面上叠加，从而得到信号的总体时频构造。经理论分析与实例验证，该方法有效可行，为工程测试中的时频分析提供了一种有效的手段。     

基于FRFT的改进多尺度线调频基稀疏信号分解方法

针对全局搜索基函数计算量大的问题,提出了基于分数阶傅里叶变换(Fractional Fourier Transform,FR-FT)确定基函数的改进多尺度线调频基稀疏信号分解方法。通过解析信号的FRFT消除实信号FRFT结果中的对称项,两级搜索FRFT幅度谱确定信号的最佳基函数,检验该方法的计算效率和抗噪性能,并采用该方法分解频率呈曲线变化的多分量非平稳信号。试验结果表明:对解析信号进行FRFT能有效消除实信号FRFT结果中的对称项;基于FRFT确定基函数速度快、精度高、抗噪能力强,与频偏大小、频率变化快慢无关,不需先验知识,有效克服了全局搜索方法计算量过大的问题;基于FRFT的改进多尺度线调频基稀疏信号分解方法能快速、准确地分解频率呈曲线变化的多分量信号,适合于旋转机械瞬变工况下非平稳信号的瞬时频率估计与目标分量隔离分析。     

基于傅里叶分解-小波包分析的爆破信号去噪方法

针对由于爆破现场施工环境复杂,爆破振动信号包含大量高频噪声的问题,提出一种基于傅里叶分解(FDM)联合小波包阈值方法的降噪方法.首先,基于傅里叶分解理论将爆破振动信号分解为若干傅里叶固有频带函数(FIBFs);然后,分别计算分解所得模态分量与原始信号的相关系数,使用相关系数法筛选出优势分量,将筛选所得优势模态分量进行重构;最后,利用小波包阈值方法对重构所得信号进一步降噪,得到最终纯净的爆破振动信号.结果表明:引入的新方法兼具傅里叶分解及小波包分析的优点,与现有常用方法相比,傅里叶分解-小波包分析联合降噪方法信噪比(10.3940)最高,均方根差(0.0889)最小,所得时程曲线更为平滑,去噪效果更好,为类似爆破振动信号去噪提供新的途径.     

基于S变换谱阈值去噪的冲击特征提取方法

提纯旋转机械设备故障振动信号中的冲击特征,可以有效地实现相关故障的诊断。利用S变换适合于处理冲击特征信号的特点,提出基于S变换谱阈值去噪的冲击特征提取方法。先将信号进行S变换,得到其时频谱。考虑到此S变换谱为一复数矩阵,故而根据谱系数的模值大小进行阈值去噪。去噪过程中分别采用了基本的硬阈值函数和软阈值函数。对于最优阈值的估计,以所提出的改进风险函数为评价标准,利用步长迭代算法在零到系数最大模值的区间内获取。最后将去噪后的时频谱进行S逆变换,重构得到时域冲击特征。仿真信号与滚动轴承故障振动信号的处理结果表明,利用所获取的最优阈值,S变换谱阈值去噪方法能够从噪声混合信号中提取出冲击特征,从而实现相关故障的诊断。     

基于EEMD-Fast ICA-STFT的车用起动电机噪声源识别

提出基于集成经验模态分解(EEMD)、快速独立分量分析(Fast ICA)和短时傅里叶变换(STFT)的噪声源识别方法,对起动电机噪声信号进行声源识别研究。首先采用集成经验模态分解法将单一通道的电机噪声信号分解为一系列本征模态分量,随后用Fast ICA算法提取独立成分,最后利用短时傅里叶变换良好的时频分析特性,对Fast ICA分离结果进行时频分析,结合时频分析结果和电机噪声的先验知识,确定了各独立分量与电机不同噪声源的对应关系。     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Study on Bond Ability of Arc-Spraying Coatings with Different Surface Pretreatment on Cast-Iron

Arc spraying coatings are widely used in various applications, but uncommon in cast iron substrate. Different surface pretreatment technology is tested on substrates of gray cast iron. Surface roughness and residual stress were measured by TR200 and X-ray diffraction analyzer. Influence of different surface pretreatment methods ( dry blasting and fusebond) on roughness and residual stress was analyzed. The arc-sprayed coatings of wire 3Cr13 (φ2mm) on gray cast iron substrate is studied. The microstructure and interface of bonding layer were observed by SEM. The bond strength was taken by tensile test. Results show that bond strength with grit blasting is higher than fuse-bond; it is feasible to make wire 3Cr13 coating with arc spraying on cast iron substrate roughened by grit blasting.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.     

Evaluation of fatigue life of steel using steel grain size

The insightful discussion of the relationship between the construction of metallographic and fatigue life and proposition of mathematical relationships describing this relationship was conducted in the paper. This paper presents a method for estimating the fatigue life, based on the construction of the microstructural material taking into account the grain size and the participation of ferrite and pearlite phase.