对迭代位移叠加像复原方法的改进

迭代位移叠加法(ISA)是一种天文高分辨空域统计重建方法,对双星等多点源天文目标的空域统计重建试验表明,多点源目标的重建效果优于经典的重谱法,计算速度也比重谱法快.该方法不能直接应用于太阳或卫星等天文和空间扩展目标的高分辨重建中.因此对迭代位移叠加法进行修正后进行了不同光子水平下的人造卫星的高分辨重建的数值仿真试验.对暗弱扩展目标的仿真重建试验表明,修正的迭代位移叠加法具有明显的抑制光子噪声的效果,具有比重谱法等频域重建方法更好的重建效果.     

抚顺页岩油的高分辨核磁共振研究

用高分辨液体核磁共振氢谱、碳谱、二维碳氢相关谱和DEPT谱(无畸变极化转移增强法)对我国抚顺页岩油的不同组分进行了详细研究,得出了一些结构信息和变化规律。     

一种适用于非周期结构高分辨象模拟计算的新方法

通常的FFT多片层法(FFTMS)动力学衍射计算中,由于采用了边界采样点周期性延伸的假设,从而导致非周期结构高分辨象模拟的严重失真。在仔细研究这种误差成因的基础上,本文提出了一种适用于非周期结构的高分辨象模拟计算新方法,它基于实空间多片层(RSMS)象模拟计算方法,但在势投影及传播因数计算中充分考虑了非周期结构的特点,从而得到与实验符合较好的结果。 关键词：     

基于Nuttall窗三谱线插值的激光多普勒信号处理方法研究

快速傅里叶变换(FFT)是主要的激光多普勒测速系统信号处理方法,由于受到频谱泄露和栅栏效应的影响,其处理精度并不理想。基于Nuttall窗三谱线插值法的激光多普勒信号处理方法就是一种好的处理方法,它可以有效地抑制频谱泄漏和栅栏效应,改善信号分析精度,提高速度测量精度。由于Nuttall四项余弦窗的能量集中在主瓣,旁瓣非常小,因此加Nuttall四项余弦窗的FFT三谱线插值算法能够极大地减小频谱泄漏的影响,谱间干扰也很小,能很好地减小频谱泄漏和栅栏效应。     

噪声过程的计算机模拟

本文介绍一种在通用数字计算机上产生同时具有规定的振幅概率分布和功率谱的伪随机序列的方法,即FFT-CT方法。先用FFT方法得到有完全合乎要求的谱特性的伪随机序列作为参考序列,然后用相关传递法(CT法)使具有给定振幅分布的基础序列具有与参考序列相同的谱特性。本文分析了FFT-CT方法的性能与序列样点数的关系,还给出了几个模拟有一定振幅分布和谱特性的噪声过程的实例。     

水声学中的信号处理

综述了水声学及水声信号处理的历史发展概况及它们在军事及民用方面的重要作用，介绍了与水声信号处理有关的换能器、布阵理论、波束成形理论、卡尔曼滤波、自适应滤波、目标识别、专家系统等课题，同时介绍水声信号处理中的一些现代技术，如FFT，Zoom FFT,LOFAR,DEMON及高分辨力谱分析的基本知识。     

FFT-BP神经网络模型对车载γ能谱辐射剂量率的预测分析

为了实现车载γ谱仪巡测系统对辐射剂量率的准确测定，提出基于快速傅里叶变换(FFT)本底扣除法的改进型BP神经网络模型(FFT-BP神经网络模型)。实验采用γ射线能谱分析法，对不同间距处的137Cs放射源进行车载γ能谱测试，将得到的谱数据通过快速傅里叶变换(FFT)扣除本底，获得新的谱线数据。应用FFT-BP神经网络模型对未知剂量的车载γ谱线作辐射剂量率的定量预测，将预测结果同3个函数模型的拟合结果比较，验证FFT-BP神经网络模型的预测效果。结果表明，FFT扣除法能较好的削弱散射本底对γ谱线的影响，能有效的降低谱线本底。通过新谱线获得的特征峰面积和净谱线面积与辐射剂量率的相关系数均为0.99(p<0.05)，相关性显著。模型拟合分析过程中，FFT-BP神经网络模型表现出较强的学习泛化能力，预测较理想，相对误差和累计误差分别低于0.6%和9%，效果明显优于数学模型和γ能谱全能峰法，可显著降低γ能谱分析辐射剂量率的误差，且能有效提升工作效率。因此，FFT-BP神经网络模型适用于γ能谱辐射剂量的预测分析，为车载γ谱仪巡测系统测量辐射剂量提供了一种新型有效的分析方法。     

快速傅里叶变换湍流相位屏高频误差的补偿方法

基于快速傅里叶变换(FFT)的湍流相位屏模拟方法存在低空间频率及高空间频率湍流分量采样不足的问题。提出了一种相位屏高频误差补偿方法。在这种补偿方法中,通过数值积分计算出未采样部分高频功率谱对应的二维相位自相关矩阵,然后该自相关矩阵经过FFT得到各功率谱采样点需补偿的功率谱值。仿真结果表明,该方法可以很好地补偿高频误差,模拟的相位结构函数误差约为0.1%。     

固态富马酸单乙酯在变温1H MAS与CRAMPS研究

富马酸单乙酯(FAME)的单脉冲¹H MAS谱由-高分辨成分与-宽线谱成分组成.高分辨成分可由Hahn回波脉冲序列单独获得.文中通过变温¹H MAS与CRAMPS实验对两组分的性质进行了系统的研究.发现当温度趋于样品的熔点时,其¹H CRAMPS谱可观察到化学位移明显区别的两套谱,它们分别对应于¹H MAS谱的高分辨与宽线组分.实验表明:高分辨成分来自FAME样品的-塑性相,而宽线组分来自通常的刚性相.文中所给出的实验事实充分说明¹H MAS与CRAMPS技术是研究有机塑性固体的强有力的工具.     

高分辨电子显微象实空间象模拟方法的改进

在深入研究高分辨实空间象模拟方法的基础上,本文导出了一个通用的收敛判据。这个判据确定了实空间象模拟计算中,在x-y平面上的取样间距δ和在电子束入射方向上片层厚度δ的依赖关系,从而有效地克服了实空间法中存在的发散问题。此外,还给出了精确计算传播因子的新公式,并在动力学衍射计算中获得了和传统的FFT多片层法符合很好的结果。 关键词：     

Retrieval of frequencies,amplitudes, damping factors,and phases from time-domain signals using a linear least-squares procedure

A new method for quantitative analysis of time-domain signals is reported. It amounts to fitting a function consisting of exponentially damped sinusoids with arbitrary phases to the data. By invoking the principle of linear prediction (LP) the fitting can be carried out by a linear least-squares (LS) procedure, and therefore needs no starting values The LS procedure is based on singular value decomposition (SVD), which enables one to distinguish between signal and noise. The method, denoted by LPSVD, yields a list comprising the frequency, damping factor, amplitude, and phase of each retrieved sinusoid. In addition, LPSVD is insensitive to truncation at the beginning and/or the end of the signal, and in fact is capable to accurately reconstruct the missing part. Preprocessing of the data is not necessary. Finally, the method achieves higher resolution than fast Fourier transformation.     

Full Automation of Quantitation of in Vivo NMR by LPSVD(CR) and EPLPSVD

A full automatic and reliable method for NMR quantification is proposed. It is based on the linear prediction singular-value decomposition with continuous regularization [LPSVD(CR)] and on the enhancement procedure (EP) followed by LPSVD (EPLPSVD). Advantages of both methods have been considered. LPSVD(CR) has been used to find a good estimate for the number of spectral components. A significance test allows refining this number, which is then used in the EPLPSVD method. A Monte Carlo study has proved that EPLPSVD is a maximum-likelihood estimator. This new algorithm leads to reliable estimates for the spectral parameters even for signals with a low signal-to-noise ratio. No a priori knowledge is needed.     

Fractional Fourier Transformation for Quantum Mechanical Wave Functions Studied by Virtue of IWOP Technique

Starting from the optical fractional Fourier transform (FFT) and using the technique of integration withinan ordered product of operators we establish a formalism of FFT for quantum mechanical wave functions. In doing so, theessence of FFT can be seen more clearly, and the FFT of some wave functions can be derived more directly and concisely.We also point out that different FFT integral kernels correspond to different quantum mechanical representations. Theyare generalized FFT. The relationship between the FFT and the rotated Wigner operator is studied by virtue of theWeyl ordered form of the Wigner operator.     

The Use of Continuous Regularization in the Automated Analysis of MRS Time-Domain Data

In this paper, it is shown how the advantages of continuous regularization (CR) can be exploited to achieve an improved, fully automated LPSVD analysis of MRS time-domain data. The main advantage of CR is its ability to determine the number of spectral components even at low signal-to-noise ratios, which suggested its use forin vivospectroscopy. Estimation of the spectral parameters is possible. Two alternatives of automated data-analysis schemes are thoroughly investigated by means of Monte Carlo studies. The results suggest the combination of CR for model-order estimation with other methods for more-accurate parameter estimation. Several possible combinations, including those with an improved enhancement procedure and a total-least-squares method for quantitation, are discussed. Recommendations are given for spectral analysis, and a new data-analysis protocol which performs significantly better than previously used protocols of the same type is proposed.     

荧光寿命的快速傅里叶变换拟合方法

介绍了一种利用快速傅里叶变换算法对稀土掺杂物质的荧光寿命进行数据拟合的方法。稀土掺杂物质可用来制备多种光学传感器,用于温度、pH值等多种参量测量领域。本方法利用快速傅里叶变换(FFT)结果作为基础,从非零项的相位角的正切值得出被测的荧光寿命,具有速度快、误差小、不受本底干扰等一系列优点。以掺铒光纤为例,通过数字仿真将本方法与其它几种传统的拟合方法进行了比较。快速傅里叶变换方法的测量偏差不到Prony方法的50％,为对数似合(log-fit)方法测量偏差的1／6。另外,快速傅里叶变换方法由于不受本底噪声影响,可以不必在信号处理时去掉本底噪声,因而可以明显缩短测量时间。     

Measurement of curvature distribution using digital speckle three-shearing aperture interferometry

Digital speckle three-shearing-aperture interferometry used for the measurement of curvature distribution fields of a deformation object is proposed for the first time. In this method, pure curvature distribution fringes without containing slope distribution fringes can be obtained by using digital speckle three-shearing-aperture interferometry. Two specklegrams, one before and the other after object deformation, are recorded by a CCD camera and stored in a computer. A 2-D fast Fourier transform (FFT) and a 2-D inverse FFT (IFFT) are performed on the two specklegrams. The subtraction of the transformed specklegrams will produce curvature distribution fringes, and the speckle noises in curvature distribution fringes can be removed after these fringes pass through low-pass filtering. Results from theory and experiments are in good agreement.     

光纤应变监测系统的数据处理方法研究

光纤应变监测系统的数据不可避免的存在噪声,导致系统的虚假预警。为了有效的消除数据噪声,提高数据准确性,减小系统的预警误报,提出了一种新的数据处理方法。首先对应变数据进行小波多层滤波处理,然后用FFT低通滤波获得信号的轮廓,再用小波滤波后的信号减去FFT低通滤波后的信号,得到消除温度影响后的应变变化信号。结果表明：该方法能够有效减小温度与噪声的影响,提高光纤应变监测系统的准确率。     

基于液晶空间光调制器的全息显示

在传统的纯相位全息显示系统中, 一般基于快速傅里叶变换(FFT)算法来计算相位全息图, 在FFT的计算中需要遵循Nyquist采样定理, 因此, 重建图像的尺寸往往受限于空间光调制器的固定采样率. 这个限制可以通过卷积算法或者两步菲涅耳衍射算法来解决, 但是需要使用多个FFT的计算, 导致计算量增大. 鉴于此, 提出了一种基于透镜的纯相位全息图计算方法. 在全息图的计算中, 通过透镜的成像原理建立一个采样率可变的虚拟全息面, 通过调节相应的距离参数使得在全息图的计算中可以任意调节原始图像的采样率, 摆脱了传统方法中液晶空间光调制器带宽积对重建图像尺寸的限制, 并且这种算法只需使用一次FFT就能达到变采样率的衍射计算, 大幅提高了全息图的计算速度. 数值模拟及光学实验结果证明了此方法可以在全息显示光学系统中清晰地重建不同尺寸的图像. 同时该系统可以有效地消除由空间光调制器的像素化结构带来的零级衍射.     

A sapphire fibre thermal probe based on fast Fourier transform and phase-lock loop

A sapphire fibre thermal probe with Cr³⁺ ion-doped end is developed by using the laser heated pedestal growth method. The fluorescence thermal probe offers advantages of compact structure, high performance and ability to withstand high temperature in a detection range from room temperature to 450℃. Based on the fast Fourier transform (FFT), the fluorescence lifetime is obtained from the tangent function of phase angle of the non-zeroth terms in the FFT result. This method has advantages such as quick calculation, high accuracy and immunity to the background noise. This FFT method is compared with other traditional fitting methods, indicating that the standard deviation of the FFT method is about half of that of the Prony method and about 1/6 of that of the log-fit method. And the FFT method is immune to the background noise involved in a signal. So, the FFT method is an excellent way of processing signals. In addition, a phase-lock amplifier can effectively suppress the noise.     

复化辛普森法和傅里叶法在衍射计算上的比较

通过快速傅里叶变换(FFT)法和复化辛普森法对衍射的数值进行计算,可以看出快速傅里叶变换法是一种积分变换法,而复化辛普森法则是迭代相加的方法.通过计算得出了FFT法的计算速度高于复化辛普森法,计算精度则远低于复化辛普森法;复化辛普森法适合近距离菲涅尔衍射和近场衍射,而FFT法不适合.