一种新的Fabry-Perot干涉条纹处理方法

介绍了一种提取Fabry-Perot(法布里-帕罗)干涉条纹圆心点坐标和条纹半径的新方法。首先对干涉图像依次进行二值化处理,对所得到的条纹强度曲线进行均平滤波和自适应滤波,根据条纹灰度值强度余弦函数分布的特点,对条纹灰度值数据进行最小二乘法拟合,获得条纹强度峰值坐标,通过精确的迭代算法,进而获得Fabry-Perot干涉条纹圆心点的坐标;然后再对干涉条纹进行圆周积分,从而可以确定每级Fabry-Perot干涉条纹的半径长度。该方法可提高计算精度,减小计算误差。     

一种面向土壤重金属含量检测的X射线荧光光谱预处理方法研究

土壤重金属的污染影响着农作物的产量和质量。传统的土壤重金属检测方法步骤繁琐、检测费用高且速度慢。利用X射线荧光光谱(XRF)分析技术检测土壤中重金属含量,具有处理简单、现场、快速、无损等优点。由于土壤背景复杂,包含大量噪声和无关信息,建立XRF校正模型前,对光谱的预处理能有效的去除不相干信息,保留有用信息,对XRF预测模型的精度有重要影响。主要研究光谱预处理方法对重金属含量预测模型精度的影响。首先,采用向前间隔偏最小二乘(FiPLS)作为校正模型,对比了无预处理、去趋势处理(DT)、标准正态变量变换(SNV)、多元散射校正(MSC)、小波去噪(WT)、SNV+DT、卷积平滑(SG)+一阶导数、卷积平滑(SG)+二阶导数等7种不同预处理条件下的土壤重金属模型的检测精度。初步结果表明,多元散射校正预处理方法效果较好,与原始光谱相比,相关系数r从原始的0.988提高到0.990,预测均方根误差RMSEP、相对误差平均从原来的20.809和0.166分别降低到19.051和0.121。其次,在多元散射校正预处理方法的基础上,针对多元散射校正方法以线性表达式描述非线性关系的局限性,提出了局部加权线性回归多元散射校正(LWLRMSC)和偏最小二乘多元散射校正(PLSMSC),并比较了它们的建模效果。LWLRMSC是基于加权思想,在预测一个点的值时,选择适当的核函数和权重分配策略进行预测点的线性回归,来解决简单线性回归的欠拟合状况;PLSMSC是基于PLS建模思想,考虑了自变量和因变量的最大相关性,来减少拟合误差及失真问题。结果表明,PLSMSC具有最佳的预处理效果,五种重金属Cu,Zn,As,Pb,Cr预测值和实际值的R分别为0.989,0.973,0.991,0.989和0.986,RMSEP分别为8.805,58.360,7.671,12.549和20.851,相比于传统的MSC方法不仅在精度方面有大幅度的提升,且具有更好的泛化性能,能消除光谱噪声,提升有效信息贡献度,为土壤重金属含量预测模型选取合适的预处理方法提供了理论支撑。     

一种开放式磁共振成像主磁体的设计方法

本文提出了一种开放式磁共振成像(MRI)超导磁体的设计方法.在对磁体模型进行简化的基础上获得初始的电流分布,然后将线圈截面的优化问题转化成一个非线性最小二乘问题,通过求解最小二乘问题得到实际的线圈截面参数.文章最后给出了一个设计算例.     

一种添加历史数据的近红外光谱特征提取方法研究

针对近红外光谱定性分析中,增加新的品种进行建模时,原有模型识别效果不够稳定的问题,提出一种在建模样本的基础上添加同类物质的历史光谱数据的特征提取方法,首先采集建模样本的近红外光谱数据,然后添加同种物质样本的历史近红外光谱数据,再对所有近红外光谱数据进行预处理,其次对所有样本数据进行偏最小二乘(PLS)特征提取得到偏最小二乘空间,并只将建模样本数据向构建的偏最小二乘空间进行投影,最后将投影后的建模数据进行正交线性判别分析(OLDA)特征提取。以玉米种子近红外光谱为研究对象,分别对建模数据添加历史近红外光谱以及不添加历史近红外光谱两种情况进行特征提取,并通过仿生模式识别(BPR)方法构建模型进行验证,实验结果表明,添加历史近红外光谱构建偏最小二乘空间的特征提取方法相对于不添加历史近红外光谱的方法,首先在增加建模集品种数量时,原有的品种识别率基本不变;其次在相同PLS维数时,所建模型对不同时间采集的测试集识别效果基本一致,证明了该方法可以提高模型稳健性。在实际应用中就可以在品种鉴别软件中将特征提取维数设置为固定值,免除了品种鉴别软件的用户在增加建模集品种时为了保证最优识别效果重新选定最优PLS参数的麻烦。     

一种基于近红外光谱的天然产物抗氧化活性预测评价方法

提出了一种基于近红外(NIR)光谱的黄酮类提取物抗氧化活性计算预测新方法。采用1,1-二苯-2-苦肼基(DPPH)法测定28种黄酮类中药材提取物的抗氧化活性,并在4 000～10 000 cm-1范围扫描样品的红外光谱,采用偏最小二乘(PLS)算法建立了黄酮类组分近红外光谱与抗氧化活性之间的校正模型。建模过程中,以交叉验证相关系数(R2),交叉验证误差均方根(RMSECV)为指标,确定了用于建模的最优近红外波段和光谱预处理方法。校正模型的RSECV为9.50%,R2为 0.901 7,预测误差均方根(RMSEP)为14.8%。该方法快速无损、操作简便,可用于中药及天然产物提取物抗氧化活性的快速评价。     

一种光学仪器镜面面形的处理方法

光学镜面表面变形包含刚体位移和表面畸变,其中表面畸变是影响成像质量的主要因素,因此需去除刚体位移,分析表面畸变。通过坐标变换生成一个新的理论镜面,用该镜面拟合变形镜面,用拟合镜面与变形镜面轴向差值计算出表面畸变的RMS值及PV值。实例计算表明该算法拟合精度较高,适用于抛物面、球面镜在支撑和装夹下的镜面面形精度分析。     

一种提高国产ADC模块采样精度的方法

为解决武器装备自主可控问题,以国产的处理器和多通道模数转换器（ADC）为核心,设计了一种完全国产化的多通道模拟信号采集模块。由于目前国产模拟芯片特别是模数转换器的精度指标较差,造成模拟信号采集模块精度较低,实用性较差。为提高采样精度,首先在采样时采用递推平均滤波方法,抑制采集信号中的周期性干扰,降低采集的随机误差。其次,对预先测量的几组数值进行一元线性回归,据此对采样值进行最小二乘估计,降低采集的固有偏置误差和增益误差。试验结果表明,该多通道模拟信号采集模块可同时采集多路模拟信号,采样精度高,最大采集误差由0.8%降低到0.12%,并且该模块通道间一致性好,可靠性高,国产化率达到100%,在武器装备中有良好的应用前景。     

谐振法测电感的一种实验方法

本文介绍了测量方法,不仅可用于低频下电感的测量,同时也可用于同频率下测电感,并达到消除线路分布的影响、减小测量误差,提高测量准确度的目的。     

无人水面艇模型辨识及其航向非线性控制的研究

为了实现无人艇的自动航向控制,本文采用Z型和回转实验数据,通过递推最小二乘对无人艇的数学模型进行辨识,然后将模型的仿真实验与实船数据进行对比,验证了模型的正确性和合理性.基于Backstepping方法设计非线性航向控制器,借助Lyapunov 函数证明了闭环系统的稳定性.仿真结果表明系统的实际航向能实时的跟踪设定航向,控制器具有良好的动静态特性和鲁棒性.     

一种光电吊舱安装误差的空中标定方法

针对传统光电吊舱安装误差地面标定需要借助专用仪器,反复调整以致操作繁琐的问题,提出了一种空中标定方法。在载机飞行过程中,通过选取视场内已知坐标的合作目标进行跟踪,利用载机位置、载机姿态、光电吊舱的观测指向角度、合作目标的位置等数据,对光电吊舱的安装误差角进行实时拟合解算处理,保证标定精度的同时,可极大节省工作量,提高效率。     

Optimizing mechanical and thermal expansion properties of carbon/carbon composites by controlling textures

The present study explored the effect of medium texture (MT) content on flexural properties and thermal expansion coefficients (CTE_S) of carbon/carbon (C/C) composites with multilayered pyrolytic carbon. The specimen with 39% MT exhibited maximum flexural strength of 221.55 MPa, increasing by 52% compared with pure high texture. While the flexural strength decreased when the MT content exceeded 39%. The excellent strength can be attributed to crack deflection between multilayered texture and the strong interface bonding between fibers and matrix. Moreover, the four specimens expressed a similar trend of CTE_S in the direction of XY and Z. In the direction of XY, the specimen with 39% MT had the lowest CTE_S from 800 °C to 2100 °C. Therefore, the C/C composites with 39% MT have the best mechanical and thermal expansion properties, which means that the properties of C/C composites can be optimized by controlling the texture.     

Development of high bandwidth powered resonance tube actuators with feedback control

A high bandwidth powered resonance tube (PRT) actuator potentially useful for noise and flow control applications was developed. High bandwidth allows use of the same actuator at various locations on an aircraft and over a range of flight speeds. The actuator selected for bandwidth enhancement was the PRT actuator, which is an adaptation of the Hartmann whistle. The device is capable of producing high-frequency and high-amplitude pressure and velocity perturbations for active flow control applications. Our detailed experiments aimed at understanding the PRT phenomenon are complemented by an improved analytical model and direct numerical simulations. We provide a detailed characterization of the unsteady pressures in the nearfield of the actuator using phase averaged pressure measurements. The measurements revealed that propagating fluctuations at 9 kHz were biased towards the upstream direction (relative to the supply jet). A complementary computational study validated by our experiments was useful in simulating the details in the region between the supply jet and the resonance tube where it was difficult to gather experimental data. High bandwidth was obtained by varying the depth of the resonance tube that determines the frequency produced by the device. Our actuator could produce frequencies ranging from 1600 to 15,000 Hz at amplitudes as high as 160 dB near the source. The frequency variation with depth is predicted well by the quarter wavelength formula for deep tubes but the formula becomes increasingly inaccurate as the tube depth is decreased. An improved analytical model was developed, in which the compliance and mass of the fluid in the integration slot is incorporated into the prediction of resonance frequencies of the system. Finally a feedback controller that varied both the resonance tube depth and spacing to converge on a desired frequency was developed and demonstrated. We are optimistic that numerous potential applications exist for such high bandwidth high dynamic range actuators.     

Optical double resonance spectra under finite bandwidth excitations

A formalism based on the theory of multiplicative stochastic processes is presented to treat the effects of finite band- with excitations on the optical double resonance spectra. Numerical results for the fluorescent spectra and the second-order intensity correlation functions are presented and discussed.     

Perturbation expansion of quantum resonance energies

We present new results concerning the theoretical treatment of quantum resonances based on the use of optical potentials and perturbation theory. A new criterion is presented for selecting an optical potential. As a result, a wide class of optical potentials which lead to efficient asymptotic series is available. A numerical illustration for two shape resonances show that accurate resonance energies and lifetimes can be obtained from a very small number of real square-integrable functions.     

Broad bandwidth optical and mechanical rheometry of wormlike micelle solutions

We characterize the linear viscoelastic shear properties of an aqueous wormlike micellar solution using diffusing wave spectroscopy (DWS) based tracer microrheology as well as various mechanical techniques such as rotational rheometry, oscillatory squeeze flow, and torsional resonance oscillation covering the frequency range from 10(-1) to 10(6) rad/s. Since DWS as well as mechanical oscillatory squeeze flow and torsional resonance oscillation cover a sufficiently high frequency range, the persistence length of wormlike micelles could be determined directly from rheological measurements for the first time.     

Influence of chaotic pump radiation with finite bandwidth on the intensity correlation of resonance fluorescence radiation

It is shown that the bandwidth of chaotic pump radiation can strongly influence the behavior of the intensity correlation of resonance fluorescence in contrast to a laser pump. This different behavior arises from the different higher order coherence properties of chaotic and laser light with the same bandwidth.     

Inverse model of the piezoelectric ceramic polarization under wide bandwidth mechanical excitations with fractional derivative consideration

This paper presents an inverse piezoelectric ceramic polarization model, $T(P)$ , working in wide bandwidth under various mechanical excitations. The model was derived from the polarization model under electric field, $P(E)$ , by use of the correlation ( $E =\alpha \cdot T\cdot P$ ) between the external mechanical excitation and piezoelectric ceramic electric field. Using the model, $T(P)$ , a given polarization could be obtained by calculating the mechanical stress waveform applied to the ceramic. The piezoelectric ceramic P188 was investigated in the experiment; measurement bench and procedures have been developed to evaluate the accuracy of the model. By means of modeling dynamic counterpart (a fractional derivative part), large range of frequency ( $10^{-3} \text{ Hz } < f < 10 \text{ Hz }$ ) imposed polarization have been examined and experimental results turned out to be good both with sinusoidal and triangular waveforms. The same fractional derivative operator is universal both in mechanical and electrical excitations.