CCD像元尺寸对傅里叶变换法相位测量精度的影响

针对傅里叶变换分析法中的离散过程理论分析存在的不足,对CCD采样过程中影响相位测量精度的主要因素进行了详细分析和仿真研究。讨论了CCD像元尺寸在采样过程中对傅里叶变换频谱的影响,理论分析了傅里叶变换法中CCD像元的尺寸、随机噪声和量化误差对相位测量精度的影响。计算机仿真和实验结果均表明,用傅里叶变换分析法对具有不同密度的干涉图进行分析时,CCD像元尺寸对采样后输出的光强信号的调制度、信噪比和频谱展宽均有影响,像元尺寸越大,采样后条纹信号的调制度和信噪比越低,其频谱展宽越大,经相位解算后得到的相位测量误差越大。以相位测量误差的RMS值大于0.05λ作为判断基准,信号的信噪比约为20,为扩展傅里叶变换分析法的动态测量范围提供了理论基础。

某卧式单缸柴油机气缸系统的运动仿真分析

以某农机卧式单缸柴油机气缸曲轴系统模型为例进行运动分析,在耐久性模块下完成仿真后,采用后处理模块进行数据的后处理。从应力云图中找到气缸系统的最大应力,从应变云图中找到系统的最大应变。结合FFT曲线图及3DFFT曲线图进行分析,发现样机模型中曲轴的谱密度幅值的峰值分别发生在55、128和200 Hz处,连杆谱密度幅值的最大峰值发生在175 Hz处,较小峰值发生在50、90和125 Hz处。研究结果可为模型系统性能的研究提供一定的依据。

类星体长周期光变分析方法的研究

给出了4种分析类星体长周期光变的方法,用一个模拟的周期信号y=sinθ检验这4种分析方法,结果表明:(1)天体光变采样的数据点个数相对少到一定值时,Jurkevich方法、时间补偿离散傅里叶变换分析方法(DCDFT)、离散相关分析方法(DCF)和功率谱密度分析方法(PSD)的分析结果不一样,获取最短的连续数据点后,Jurkevich方法分析结果在4种方法中可能最为精确可靠,且计算方法简捷实用;(2)获得了Jurkevich分析方法的最佳参数,当m=9时分析结果最佳;(3)用m=9时的Jurkevich方法分析了类星体3C 279及3C 454.3的光变周期,得出3C 279的可能光变周期为(2.81±0.54)年,3C 454.3的可能光变周期为457 d。

差分二次平均修正的频域相位补偿线谱检测方法

针对常规平均功率谱方法幅度平方后相位信息丢失造成检测性能损失问题,通过对观测数据分段进行快速傅里叶变换后的统计特性进行分析,提出了高斯噪声背景下检测未知线谱的频域相位补偿方法。采用蒙特卡洛法估计相位补偿因子,先进行差分法去除零星野值,然后使用二次平均(TPM)去除连续野值,最后使用估计的相位补偿因子均值构造广义似然比检验统计量实现检测。从理论上对比了广义平均周期图(AVGPR)法、广义功率谱(GPR)法及文中方法的检测性能。仿真结果表明,文中方法充分利用信号的相位信息,参数估计简单,相位补偿因子估计准确,在一定虚警概率下较AVGPR法的检测性能提高了接近5 dB左右。

基于Simulink的变流技术仿真实验研究

针对变流技术中典型的几种电路如整流、斩波、ZVS-PWM变换电路、三电平SPWM逆变电路以及斩控单相调压电路利用Simulink建立了系统模型,对电路仿真输出进行了分析与研究,将部分电路在仿真的基础上进行了FFT分析,进一步增加了电力电子变流技术实验内容、深度与广度,扩宽了实验者的思路。与传统电力电子变流技术实验相比,通过对这几个难度递增的基本电路进行实验仿真分析,使实验者从验证性实验转变为设计性、研究性及综合性实验,极大的调动了实验人员的主观能动性,为变流技术实验研究提供了有益的帮助。

木质复合材料无损检测中振动信号的处理方法

探讨了木质复合材料无损检测中常用的处理振动信号的三种方法 :时域波形参数分析方法、傅里叶变换分析方法、小波分析方法的特点。从理论上分析了这三种方法在处理振动信号时的优缺点 ,提出了进行木质复合材料的振动无损检测时 ,不同的检测目的选择相应的振动信号处理方法。

基于Zoom-FFT频谱细化的水声目标螺旋桨轴数提取技术

基于对水声目标调制谱结构特征的分析,在传统包络信号探测(DEMON)谱分析方法基础上,采用细化-快速傅里叶变换(Zoom-FFT)算法,提高轴频位置带宽内的频率分辨率,实现频谱细化处理,从而提取到水声目标螺旋桨轴数。利用实测信号数据及仿真试验数据进行了分析验证。试验结果表明,该算法对于水声目标螺旋桨轴数的识别准确率可达80%以上,具有工程实用价值。

基于Retinex与STFT的非接触指纹图像增强

针对数字相机拍摄的指纹图像存在脊线和谷线对比度低、抖动模糊等问题,提出一种基于Retinex理论和短时傅里叶变换(STFT)分析的非接触指纹图像增强算法。依据Retinex理论,利用图像各个像素的相对明暗关系消除光照非均衡性影响,提高脊线和谷线的对比度,实现非接触指纹图像的初次增强。采用STFT分析的方法获取指纹图像的方向图、频率图等纹理信息,并据此构建角度滤波器和半径滤波器,对初次增强结果进行频域滤波处理,进一步增强图像对比度,同时有效抑制噪声的干扰。实验结果表明,该算法对非接触指纹图像的增强效果较好,可以有效提高指纹脊线和谷线对比度,较好地保持指纹脊线的连续性,而且平均处理速度比同态滤波和Garbor滤波相结合的方法也略有提高。

差分吸收光谱FFT+FT频谱细化方法研究

利用差分吸收光谱法(DOAS)可以实现污染气体的在线监测。为了提高监测精度,通常利用傅里叶变换滤波法(FFT)处理差分吸收光谱数据,但是因其频率分辨率的限制,影响其幅值精度,导致气体浓度的测量误差较大。提出了一种将FFT和FT相结合的差分光谱数据处理方法(FFT+FT),首先对差分吸收光谱数据做FFT变换,得到其全景谱,再对峰值点附近的频谱用改进的连续FT进行细化,提高特征吸收频段的分辨率,对幅值误差进行补偿,从而提高气体浓度在线监测的精度。实验配制了不同浓度的SO_(2)和NO_(2)气体,当细化倍数为15时,SO_(2)和NO_(2)气体的最大测量误差不超过3.68%和3.17%,相对于FFT法,平均误差分别降低了1.82%和1.45%;相对于传统的多项式拟合法,平均误差分别降低了14.9%和1.80%;对恒定浓度的SO_(2)和NO_(2)气体分别进行了多次测量,验证了FFT+FT方法的稳定性。分析了细化倍数对测量精度的影响,当细化倍数小于15时,浓度测量误差随着细化倍数的增加而降低;当细化倍数从15增加到20时,误差反而逐渐变大,在大于20以后,误差出现波动,且都大于细化倍数为15时的测量误差。由于细化倍数太大,使谱线过于密集,找到频谱序列最大值的概率降低了,因此在有噪声的情况下采用该法进行频谱校正时,会出现细化倍数加大而测量精度反而降低的现象。确定了最优细化倍数,在确保测量精度前提下,使频谱细化的计算量最小,满足DOAS法实时在线监测气体浓度的要求。

FTIR Spectroscopic Study of Broad Bean Diseased Leaves

[Objective] The aim was to indentify diseased leaves of broad bean by vibra- tional spectroscopy. [Method] In this paper, broad bean rust, fusarium rhizome rot, broad bean zonate spot, yellow leaf curl virus and normal leaves were studied using Fourier transform infrared spectroscopy combined with chemometrics. [Result] The spectra of the samples were similar, only with minor differences in absorption inten- sity of several peaks. Second derivative analyses show that the significant difference of all samples was in the range of 1 200-700 cm2. The data in the range of 1 200- 700 cm＇ were selected to evaluate correlation coefficients, hierarchical cluster analy- sis （HCA） and principal component analysis （PCA）. Results showed that the correla- tion coefficients are larger than 0.928 not only between the healthy leaves, but also between the same diseased leaves. The values between healthy and diseased leaves, and among diseased leaves, are all declined. HCA and PCA yielded about 73.3% and 82.2% accuracy, respectively. [Conclusion] This study demonstrated that FTIR techniques might be used to detect crop diseases.

Study on FTIR Spectra of Corn Germs and Endosperms of Three Different Colors Combining with Cluster Analysis

[Objective] This research aimed to study the FTIR spectra of corn germs and endosperms so as to provide a scientific way for identifying corn of different types. [Method] The corn germs and endosperms of three types were studied by using Fourier transform infrared spectroscopy（FTIR） technology, combined with cluster analysis. [Result] The overall characteristics of original FTIR spectra were basically similar within the range of 700-1 800 cm^-1. The FTIR spectra were mainly composed by the absorption peaks of polysaccharides, proteins and lipids. Within the wavelength range of 700-1 800 cm^-1, there were only tiny differences in original FTIR spectra among the corn germs and endosperms of three different types. The spectra were then processed by using first derivative and second derivative. The second derivative spectra were used for hierarchical cluster analysis（HCA）. The results showed that with the wavelength range of 700-1 800 cm^-1, the second derivative spectra of the 52 samples could be better clustered according to the tree types and corn germ and corn endosperm. The clustering correct rate reached 96.1%.[Conclusion] FTIR technology, combined with cluster analysis, can be used to identify different types of corn germs and endosperms, and it is characterized by convenience and rapidness.

Geochemistry of Kasnau-Matasukh lignites, Nagaur Basin, Rajasthan （India）

The distribution and verticals variation of geochemical components in the Kasnau-Matasukh lignites of Nagaur Basin, Rajasthan, were investigated using microscopy, proximate and ultimate analyses, Rock-Eval Pyrolysis, X-ray diffraction and Fourier Transform Infrared analyses, and major/minor/trace element determination. The relationship of elements with ash content and with macerals have also been discussed. These lignites are stratified, black, dominantly composed of huminite group macerals with subordinated amounts of liptinite and inertinite groups. They are classified as type-III kerogen and are mainly gas prone in nature. The concentration （in vol%） of mineral matter is seen to increase towards upper part of seam and so is the concentration （in wt%） of the volatile matter, elemental carbon and sulphur. The common minerals present in these lignitesare mixed clay layer, chlorite, and quartz as identified by X-ray diffraction study. Compared with world average in brown coal, the bulk concentration of Cu is anomalously high in most of the samples while Cd is 2-3 times high and Zn is high in one band. Based on interrelationship, different pyrite forms are noticed to have different preferential enrichment of various elements. The concentration of disseminated pyrite is more than the other pyrite forms and is followed by discrete pyrite grains and massive pyrite.

Multiparty Quantum Secret Sharing Using Quantum Fourier Transform

A （n, n）-threshold scheme of multiparty quantum secret sharing of classical or quantum message is proposed based on the discrete quantum Fourier transform. In our proposed scheme, the secret message, which is encoded by using the forward quantum Fourier transform and decoded by using the reverse, is split and shared in such a way that it can be reconstructed among them only if all the participants work in concert. Fhrthermore, we also discuss how this protocol must be carefully designed for correcting errors and checking eavesdropping or a dishonest participant. Security analysis shows that our scheme is secure. Also, this scheme has an advantage that it is completely compatible with quantum computation and easier to realize in the distributed quantum secure computation.

Feasibility studies on cleaning of high sulfur coals by using ionic liquids

Coal has been used as an energy resource around the world, primarily for the generation of electricity. The cleaning of coal by removing its unwanted sulfur and mineral matter components is utmost essential before their gainful utilizations. The ionic liquids （ILs） are considered as non-toxic solvents for using in different industrial processes. The effect of two ILs namely, 1-n-butyl, 3-methylimidazolium tetrafluoro borate （ILl） and 1-n-butyl, 3-methylimidazolium chloride （IL2） in oxidative de-sulfurization and de-ashing of two industrially important high sulfur coal samples from Meghalaya （India） is discussed in this paper. The maximum removal of total sulfur, pyritic sulfur, sulfate sulfur and organic sulfur are observed to be 37.36 %, 62.50 %, 83.33 % and 31.63 % respectively during this oxidative process. The quantitative diffuse reflectance Fourier transform-infrared spectroscopy analysis supports the formation of sulfoxides （S--O） and sulfones （-SO2） and their subsequent removal during the oxidation of the coals in presence of ILs. The X-ray fluorescence combined with near edge X-ray absorption fine structure and scanning electron microscopic studies reveal the removal of mineral matters （ash yields） from the coal samples. The thermogravimetric analysis of the raw and clean coals indicates their high combustion efficiencies and suitability for using in thermal plants. The method is partially green and the ILs could be recovered and reused in the process.

TG–FTIR analysis of pyrolusite reduction by major biomass components

Pyrolusite reduction processes by three major biomass components cellulose,hemicelluloses and lignin,represented by CP,HP and LP,respectively,were investigated by thermogravimetric analyzer coupled with Fourier transform infrared spectrometry(TG-FTIR).The Sestak-Berggren(SB) equation was used to evaluate the kinetics of reduction processes.TG analysis reveals that the main reduction processes occur at 250-410 ℃,220-390 ℃,and 190-410 ℃ for CP,HP,and LP,respectively.FT-IR and XRD results indicate that various reducing volatiles(e.g.aldehydes,furans,ketones and alcohols) are produced from the pyrolysis with the three major components,which directly reduce MnO_2 in ore to MnO.The processes are described by the SB equation with three parameters(m,n,p).Their non-zero values suggest that pyrolusite reduction is controlled by the diffusion of reducing gaseous products through an ash/inert layer associated with minerals.The apparent activation energies for pyrolusite reduction by CP,HP and LP are 40.48,25.70 and 40.10 kJ·mol^(-1),respectively.

Evolvement behavior of microstructure and H_2O adsorption of lignite pyrolysis

The effect of pyrolysis on the microstructure and moisture adsorption of lignite was investigated with low field nuclear magnetic resonance spectroscopy. Changes in oxygen-containing groups were analyzed by Fourier transform infrared spectroscopy （FTIR）, and H20 adsorption mechanism on the surface of lignite pyrolysis was inferred. Two major changes in the pore structure of lignite char were observed as temperature increased in 105-200 ℃ and 500-700 ℃. Pyrolysis temperature is a significant factor in removing carboxyl and phenolic hydroxyl from lignite. Variation of ether bond content can be divided into three stages; the content initially increased, then decreased, and finally increased. The equilibrium adsorption ratio, content of oxygen-containing groups, and variation of pore volume below 700° were closely correlated with each other. The amount of adsorbed water on char pyrolyzed at 700 ℃ increased. Moreover, the adsorption capacity of the lignite decreased, and the adsorption state changed.

Adsorption of cadmium ions from aqueous solutions by activated carbon with oxygen-containing functional groups

The adsorption of aqueous cadmium ions(Cd(Ⅱ)) have been investigated for modified activated carbon(AC-T)with oxygen-containing functional groups.The oxygen-containing groups of AC-T play an important role in Cd(Ⅱ) ion adsorption onto AC-T.The modified activated carbon is characterized by scanning electron microscopy,Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS).The results of batch experiments indicate that the maximal adsorption could be achieved over the broad pH range of 4.5 to 6.5.Adsorption isotherms and kinetic study suggest that the sorption of Cd(Ⅱ) onto AC-T produces monolayer coverage and that adsorption is controlled by chemical adsorption.And the adsorbent has a good reusability.According to the FT-IR and XPS analyses,electrostatic attraction and cation exchange between Cd(Ⅱ) and oxygen-containing functional groups on AC-T are dominant mechanisms for Cd(Ⅱ) adsorption.

Synthesis and properties of UV curable polyurethane acrylates based on two different hydroxyethyl acrylates

Two kinds of UV curable polyurethane acrylate oligomers （PUPA and PUCA） were synthesized via the addition reaction between isophorone diisocyanate （IPDI） and polyethylene glycol monoacrylate （PEA6） or polycaprolactone modified hydroxyethyl acrylate （PCLA2）. The structures of PUPA and PUCA were characterized by Fourier transform infrared spectroscopy （FT-IR）, IH nuclear magnetic resonance （^H NMR）, gel permeation chromatography （GPC） and differential scanning calorimeter （DSC）, and the thermal stability and dynamic mechanical thermal properties of their cured films were measured by thermogravimetric analysis （TGA） and dynamic mechanical analysis （DMA）, respectively. The viscosity of the oligomers and mechanical properties of the cured films were also studied. The results show that both oligomers have narrow molecular weight distribution. The viscosity of PUPA is 2.310 Pa.s at 25 ℃, while that of PUCA is： up to 3.980 Pa-s. The UV cured PUPA and PUCA films have homogeneous phase structure, and the PUCA film shows higher glass transition temperature and storage modulus. Furthermore, the PUCA film possesses better mechanical properties than PUPA, while the latter shows better alkali resistance.

Fourier-shape-based reconstruction of rock joint profile with realistic unevenness and waviness features

Rock joint shape characteristics,waviness and unevenness play essential but distinct roles in shear mechanism of rock joints.This study presents a novel method to generate virtual rock joint profiles with realistic waviness and unevenness features.Firstly,joint profiles are obtained by 3D laser scanning device.Secondly,quantification of waviness and unevenness is conducted by traditional method,including digital filtering technique and roughness parameter RL.Thirdly,the discrete Fourier transform(DFT)method is employed to analyze the joint outlines.Two representative Fourier shape descriptors(D3,D8)for characterization of waviness and unevenness are suggested.Then,the inverse discrete Fourier transform(IDFT)is adopted to reconstruct the joint profiles with random values of phase angles but prescribed amplitudes controlled by D3 and D8.The traditional method is then applied to the reconstructed joint profiles to examine statistically the relationships between D3 and D8 and parameters RL of waviness and unevenness,respectively.The results show that larger D8 tends to result in larger waviness while higher D3 tends to increase unevenness.Reference charts for estimation of waviness and unevenness with different pairs of D3 and D8 are also provided to facilitate implementation of random joint reconstruction.

CS_2 extraction and FTIR & GC/MS analysis of a Chinese brown coal

The abundance of low-rank coals in China, such as bituminous and brown coals, makes studies of their composition and structure of great significance to both coal chemistry research and for efficient utilization of the coal. We describe how a Chinese brown coal was ultrasonically extracted with carbon disulfide （CS2） and the raw and extracted coals were characterized by Fourier Transform Infrared Spectroscopy （FTIR）. The corresponding extract was analyzed with a coupled gas chromatograph mass spectrometer （GC/MS）. The FTIR analysis shows a great abundance of amidocyanogen, carbonyl, aromatic and hetero aromatic rings and single carbon-beteroatom bonds. This suggests the possible occurrence of compounds like alcohols, phenols, amines, esters, carboxylic acids, ethers, aromatics or heteroaromatics. The GC/MS analysis of the CS2 extract detected 62 compounds, among which the non-polar ones were of lower abundance while the polar ones were in higher abundance and were structurally diverse. This demonstrates the compositional and structural complexity of Shengli coal.