智能优化算法应用于近红外光谱波长选择的比较研究

近红外光谱(NIRS)是一种间接分析技术,其应用需建立相应的校正模型。为了提高模型的解释能力、预测准确度和建模效率,需要对NIRS进行波长选择,优选最小化冗余信息。智能优化算法是以生物的行为方式或物质的运动形态为背景,经过数学抽象建立算法模型,通过迭代计算来求解组合最优化问题,其核心策略是以某种目标函数为标准,基于多元校正建模并以逐步逼近的方法筛选出有效的波长点。选用蚁群优化(ACO)、遗传优化(GA)、粒子群优化(PSO)、随机青蛙(RF)和模拟退火(SA)5种智能优化算法对烟叶总氮和烟碱近红外光谱数据进行特征波长选择,结合偏最小二乘(PLS)算法,构建了多个烟叶总氮和烟碱的校正模型,结果显示：所选用两个数据集的总氮最优模型分别为PSO-PLS和GA-PLS模型,烟碱最优模型分别为GA-PLS和SA-PLS模型,五种智能优化算法所建模型预测性能并非全部优于全谱PLS模型,但是通过智能优化算法进行波长选择后建立的PLS模型大大简化,模型的预测精度、可解释性和稳定性均有所提高。同时也对优选波长进行了解释和分析,烟叶总氮特征波长优选组合为4 587~4 878和6 700~7 200 cm-1;烟叶烟碱特征波长优选组合为4 500~4 700和5 800~6 000 cm-1,优选出来的特征波长具有实际物理意义。     

波长漂移对近红外光谱PLSR分析模型的影响

在近红外光谱分析过程中,单台仪器在不同时间的波长变化及多台仪器间的波长一致与否会对化学计量学定标模型的校正及传递效果产生影响,上述问题可以统一为波长漂移对定标模型的影响.以分析小麦粉中粗蛋白含量为例,首先结合不同谱区光谱数据,利用偏最小二乘回归(PLSR)方法建立了两个定标模型.再由计算机生成不同类型、不同幅度的波长漂...     

粒子群优化算法在光纤光栅传感器波长解调中的应用

为了提高光纤光栅(FBG)解调系统的波长解调精度,采用粒子群优化(PSO)算法结合参考光纤光栅(FBG),对常用波长解调器Fabry-Perot型光纤滤波器(FPF)的透射光谱中心波长与控制电压之间存在的非线性和回滞特性进行了研究,并提出一种实时建立FPF透射光中心波长与其控制电压之间关系模型的方法。该方法利用粒子群优化算法收敛快、易实现的特点,保证了FPF模型建立的准确性和实时性。实验结果证明,利用所建模型可有效提高FBG传感系统的波长测量准确度,测量误差不超过25 pm。系统结构简单,对提高FBG传感系统的测量准确度具有重要意义。     

PCA-SVR联用算法在近红外光谱分析烟草成分中的应用

由50份烟草样品的近红外漫反射光谱组成的光谱矩阵经过主成分分析降维,采用基于支持向量机回归(SVR)算法,以常规化学分析方法测定的总糖、还原糖、总氮、烟碱的含量为参考值,建立了烟草中主要成分近红外光谱定量分析定标模型,并采用留一法交叉验证(LOOCV)对模型进行验证。以内部交叉验证预测的RMSE值为判据,从核函数类型、惩罚因子C和不敏感函数ε取值等方面对定标模型进行优化,获得不同成分定标模型的优化参数。烟草总糖、还原糖、总氮、烟碱优化定标模型的RMSE值分别为1.581,1.412,0.117和0.313。同时建立了烟草以上成分的偏最小二乘回归(PLS)、多元线性回归(MLR)以及误差反向传播人工神经网络(BP-ANN)定标模型,通过内部交叉验证的RMSE值与SVR定标模型进行比较,结果表明SVR模型具有更好的预测效果。     

玉米秸秆纤维素和半纤维素NIRS特征波长优选

预处理是提高玉米秸秆生物转化利用效率的有效途径。玉米秸秆经生物炼制转化为生物燃料时,转化率与其原料内的纤维素和半纤维素含量直接相关。为了实现对预处理后玉米秸秆的生物炼制过程的有效调控,提出使用近红外光谱(NIRS)对玉米秸秆的纤维素和半纤维素含量进行快速检测,解决传统化学方法测试速度慢、成本高的问题。为了提高NIRS检测的效率和精度,将遗传算法与模拟退火算法相结合构建遗传模拟退火算法(GSA)用于预处理后玉米秸秆纤维素和半纤维素含量NIRS特征波长优选。GSA算法以NIRS波长点数为码长进行二进制编码,以偏最小二乘法(PLS)回归模型的交叉验证均方根误差为目标函数,结合温度参数设计适应度函数,基于Metropolis判别准则实现扰动解的选择复制,能够在避免早熟的同时有效提高进化后期的搜索效率。采用碱预处理、生物预处理及其相结合的方法对采集的玉米秸秆进行预处理后制备样品120个,并测定其纤维素和半纤维素含量及NIRS。使用7点Savitzky-Golay平滑结合多元散射校正和标准正则变换对光谱进行预处理后,利用Kennard-Stone法按3∶1比例划分校正集和验证集。然后,使用GSA算法对NIRS全谱进行特征波长优选(记为Full-GSA)、对协同区间偏最小二乘法(SiPLS)优选后谱区进行特征波长优选(记为SiPLS-GSA)、对反向区间偏最小二乘法(BiPLS)优选后谱区进行特征波长优选(记为BiPLS-GSA),并使用PLS回归模型和验证集对特征波长优选结果进行评测。Full-GSA以全谱1 557个波长点为基因,执行16次算法,优选出118个纤维素特征波长点和164个半纤维素特征波长点。SiPLS-GSA经SiPLS优选的纤维素和半纤维素谱区波长点数分别为388个和160个,再经GSA进一步优选后得到157个纤维素特征波长点和148个半纤维素特征波长点。BiPLS-GSA经BiPLS优选的纤维素和半纤维素谱区波长点数分别为358个和180个,再经GSA进一步优选后得到130个纤维素特征波长点和153个半纤维素特征波长点。结果表明,通过波长优选,不仅参与建模的波长点数量显著减少,而且回归模型的性能显著优于全谱建模。其中,采用Full-GSA优选的纤维素特征光谱回归性能最佳,采用SiPLS-GSA优选的半纤维素特征光谱回归性能最佳。回归模型验证集的平均相对误差(MRE)分别为1.752 4%和2.020 8%,较全谱建模分别降低了13.636 6%和25.368 4%。基于结合温度参数设计适应度函数的策略构建的GSA具有良好的全局搜索性能,适用于玉米秸秆纤维素和半纤维素含量NIRS特征波长优选。GSA以全谱每个波长点为染色体基因的编码方案适用于NIRS全谱的特征波长优选。GSA同样适用于SiPLS和BiPLS优选后谱区的特征波长优选,能够有效实现优选后谱区的波长点优选。     

利用法布里-珀罗标准具提高天文高分辨光谱仪的波长定标精度

用于天文高分辨光谱波长定标的法布里-珀罗标准具(FPE)具有宽波长覆盖与密集透过峰序列的光谱,有望实现比传统定标源更高的波长定标精度。然而FPE透过峰波长是未知的,这为定标带来了挑战。本研究在不借助额外精密测量设备(如傅里叶变换光谱仪)情况下,使用天文高分辨光谱仪常规定标源钍氩灯(ThAr)为FPE提供波长信息,再利用FPE密集的透过峰序列以及电介质反射膜穿透深度与波长关系的平滑性质,修正波长信息中的误差,得到FPE透过峰精确的波长并完成波长定标。在兴隆2.16 m望远镜高分辨光纤光谱仪上的定标测试显示,FPE的波长定标精度达到0.053 pm,相比单独使用ThAr的波长定标精度(0.290 pm)有显著的提高。     

超光谱大气CO_2监测仪光谱定标误差修正

超光谱大气CO_2探测需对遥感器进行精确表征及定标,其中光谱定标工作最为基础。针对传统实验室定标方法获取的波长定标系数不确定度高等特点,开展基于气体吸收法原理的光谱定标误差修正研究,该方法与仪器使用状态一致,提高了定标系数实用性。首先利用辐射传输进行了理论光谱及误差因素模拟计算,并基于大气环境模拟定标仓开展了大气XO_2吸收光谱测量实验,最后采用LM算法进行光谱误差修正迭代优化。光谱定标误差修正结果表明:光谱偏差均值由修正前的0.03 cm~(-1)下降到修正后0.008 cm~(-1),且系统性与突变性误差得以剔除,大大提高了地面光谱定标精度,为后续温室气体反演奠定了基础。     

基于光谱技术的Bipls算法结合CARS算法的苹果可溶性固形物含量检测

可溶性固形物含量是判断苹果内部品质的重要参考属性之一。利用高光谱技术获取苹果感兴趣区域的反射光谱,以S-G平滑(Savitzky-Golay smoothing)和直接正交信号校正(Direct orthogonal signal correction, DOSC)算法对光谱数据进行梯度预处理后,用后向区间偏最小二乘法(Bipls)优选出3,5,6,7,8,9,13,14,15,16,17,18,19,20,21,23等16个子区间,共计177个波长。结合竞争自适应重加权采样算法(CARS)再作进一步筛选,提取出449.6,512.9,544.8,547.2,594.3,596.8,928.2 nm等7个特征波长,利用偏最小二乘算法(PLS)建立基于特征波长的可溶性固形物含量检测模型,所得模型评价为R_c=0.906 2,RMSEC为0.482 2,R_p=0.871 6,RMSEP为0.614 0。该算法模型预测性能同Bipls和Bipls-SPA模型相比更为优异,证明了Bipls结合CARS算法在提高苹果可溶性固体物含量检测精度方面的有效性。     

超结构换热器网络综合优化的遗传/模拟退火算法-Ⅱ.遗传/模拟退火算法及应用

本文提出了用于换热器网络综合的改进的遗传/模拟退火算法.最优综合的模型基于本文第一部分所提出的通用解方法.所采用的遗传算法结合了模拟退火算法和爬山优化算法,同时引进精英策略和结构变异策略以增强算法的搜索能力.采用本文提出的算法对文献提出的算例进行了计算并得到了更好的结果.     

EMD和SPA算法在光谱法检测面粉过氧化苯甲酰添加量中的应用

将经验模态分解(EMD)和连续投影算法(SPA)结合用于面粉过氧化苯甲酰(BPO)添加量的近红外光谱检测分析中。在波长898～1 725 nm范围内采集添加了BPO的面粉样本光谱,先通过EMD分解法对其进行噪声预处理,然后利用SPA算法提取光谱特征波长。EMD处理后的光谱建模精度比原始光谱建模精度大大提高,通过SPA算法从512个波长中提取了7个特征波长,基于特征波长建立的模型,与EMD处理后全波长建模结果相比,建模波长个数大幅缩减,但是模型精度与全谱建模相当,结果表明：EMD和SPA结合可有效用于面粉BPO检测的光谱去噪和特征波长提取,该结果为开发便携式面粉BPO检测仪提供了参考和依据。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.