Determination of Total Sugar in Tobacco by Near-Infrared Spectroscopy and Wavelet Transformation-Based Calibration

Based on wavelet transformation (WT) and mutual information (MI), a simple and effective procedure is proposed for multivariate calibration of near-infrared spectroscopy. In such a procedure, the original spectra of the training set are first transformed into a set of wavelet representations by wavelet prism transform. Then, the MI value between each wavelet coefficient variable and the dependent variable is calculated, resulting in a MI spectrum; by retaining a subset set of coefficients with higher MI, an update training set consisting of wavelet coefficients is obtained and reconstructed/converted back to the original domain. Based on this, a partial least square (PLS) model can be constructed and optimized. The optimal wavelet and decomposition level are determined by experiment. A NIR quantitative problem involving the determination of total sugar in tobacco is used to demonstrate the overall performance of the proposed procedure, named RPLS, meaning PLS in reconstructed original domain coupled with MI-induced variable selection in wavelet domain (RPLS). Three kinds of procedures, that is, conventional full-spectrum PLS in original domain (FPLS), PLS in original domain coupled with MI-induced variable selection (OPLS), and direct PLS in MI-based wavelet coefficients (WPLS), are used as reference. The result confirms that it can build more accurate and robust calibration models without increasing the complexity.     

感应耦合等离子体刻蚀在聚合物光波导制作中的应用

提出了利用感应耦合等离子体(ICP)刻蚀技术提高聚合物光波导器件性能的方法,介绍了ICP刻蚀技术的原理和优点。选取聚甲基丙烯酸甲酯-甲基丙烯酸环氧丙酯(P(MMA-GMA))作为波导材料,采用氧气作为刻蚀气体,研究了ICP参数变化对刻蚀效果的影响。介绍了倒脊形光波导的制备过程,采用改变单一工艺参数的方法,分析了刻蚀效果随时间、功率、压强、气体流量等参数的变化,对参数优化后刻蚀得到的凹槽和平板结构进行了表征。实验结果表明:在天线射频功率为300 W,偏置射频功率为30 W,气体压强为0.5 Pa,氧气流速为50 cm³/min的条件下,可获得侧壁陡直、底面平整的P(MMA-GMA)凹槽结构。     

近红外光谱小波分析在土壤参数预测中的应用

从田间采集了150个田间土壤样本,在分析了所有样本的土壤参数统计特征之后,对原始近红外光谱数据进行了聚类分析,分别得到了50个土壤全氮和50个土壤有机质的等价样本及其对应光谱。对样本光谱曲线进行8层Biorthogonal小波包分解,分解得到的最低低频[80]结点对应着土壤水分以及土壤质地的光谱变化趋势,最高高频[8 255]结点对应着土壤粒度、光谱仪精度等引起的高频震荡。对以上两个结点进行重构并从样本光谱曲线中剔除以上影响成分,得到了对应的土壤参数特征光谱。基于特征光谱建立了土壤参数偏最小二乘回归模型：全氮偏最小二乘预测模型的预测系数r_c达到了0.960,验证系数r_v达到了0.920;有机质偏最小二乘预测模型的预测系数r_c达到0.922,验证系数r_v达到0.883。模型精度明显提高,满足实际生产的需要。     

基于小波变换的木材近红外光谱去噪研究

木材近红外光谱常常被一系列噪声所污染,影响光谱分析结果。为了提高近红外光谱分析精度,需要对光谱数据进行预处理。光谱导数可以消除光谱背景干扰和基线漂移等因素影响,提高光谱分辨率,但导数光谱在增强信号的同时,也使信号噪声得到增强。应用小波变换对杉木木材近红外一阶导数光谱进行去噪研究,分别采用9点平滑法、25点平滑法、非线性小波硬阈值和软阈值法、9点平滑+小波变换法和25点平滑+小波变换法对光谱数据进行去噪研究。结果显示, 小波变换能够有效去除导数光谱中的噪声信号,保留光谱中的有效信息,提高光谱信噪比,提高光谱的分析能力,在木材近红外光谱分析中具有很好的应用前景。     

Detection of rolling bearing defects using discrete wavelet analysis

In the detection of bearing faults the so much desired objective remains the extraction of the defect vibratory signature from the measured signal in which immerses the random noise and other components of the machine. In this article a denoising method of the measured signals is presented. Based on the optimization of wavelet multiresolution analysis, it uses the kurtosis as an optimization and evaluation criterion, several parameters were then selected. The experimental results show the validity of this method within the detection of several defects simulated on ball bearings. The various configurations, in which the signals were measured, allow leading to optimum conditions of its application. The application of WMRA on filtered signals allows better results than its application on wide bands signals or a simple band pass filtering.     

Identification of time-varying hysteretic structures using wavelet multiresolution analysis

In this paper, a wavelet multiresolution technique is proposed to identify time-varying properties of hysteretic structures. It is well known that arbitrary transient functions can be effectively and accurately approximated using wavelet multiresolution expansions due to wavelet's good time-frequency localization property. By decomposing the time-varying parameters with wavelet multiresolution expansion, a time-varying parametric identification problem can be transformed into a time-invariant non-parametric one. The identification in the time-invariant wavelet multiresolution domain can be achieved by choosing a wavelet basis function and performing a suitable parameter estimation technique. Since wavelet representation of arbitrary signal uses only a small number of terms, the orthogonal forward regression algorithm can be adopted for significant term selection and parameter estimation. Single and multiple degrees of freedom Bouc-Wen hysteretic structures with gradual and abrupt varying properties are used to illustrate the proposed approach. Results show that the wavelet multiresolution technique can identify and track the time-varying hysteretic parameters quite accurately. The effect of measurement noise is also studied. It is found that the presence of noise would affect more on the damping ratios and the Bouc-Wen parameters but less on the equivalent stiffness coefficients.     

基于小波变换的MHD信号的提取

混有干扰的Mirnov信号是一类非平稳,和Fourier变换的方法进行MHD信号的提取不能取得满意的效果,因而提出采用小波变换的方法对Mirnov信号进行处理。理论分析与实验结果表明,利用小波变换的时频分析特怀对Mirrnov信号进行滤波处理,可以有效地去除干扰,提取出有用的MHD信号。     

基于一类新的半离散的小波变换的信号重构公式

在基小波ψ(t)为带限的条件下,基于半离散的小波变换(Wψf)(na,a)(n∈Z,a∈R)信号f(t)的重构公式被给出.     

小波变换-偏最小二乘算法及其在复方甲硝唑注射液分析中的应用

提出了结合小波变换的偏最小二乘法（ＷＰＬＳ）,即先对光谱信号进行小波变换,去除噪声,再用偏最小二乘法对多组分同时测定。将该法用于模拟体系及复方甲硝唑注射液体系,结果表明,该法优于偏最小二乘法。