具有选择与遗忘机制的极端学习机在时间序列预测中的应用

针对训练样本贯序输入时的极端学习机 (ELM)训练问题,提出一种具有选择与遗忘机制的极端学习机 (SF-ELM),并研究了其在混沌时间序列预测中的应用. SF-ELM以逐次增加新训练样本的方式实现在线训练,通过引入遗忘因子以减弱旧训练样本的影响,同时以泛化能力为判断依据,对其输出权值进行选择性递推更新. 混沌时间序列在线预测实例表明,SF-ELM是一种有效的ELM在线训练模式. 相比于在线贯序极端学习机,SF-ELM具有更快的在线训练速度和更高的在线预测精度,因此更适于混沌时间序列在线预测. 关键词： 混沌时间序列 时间序列预测 神经网络 极端学习机     

错位光纤干涉激光谱结合BP神经网络的温度传感研究

在分析不同温度时单模错位光纤干涉光谱对应波长的条件下,搭建三层BP神经网络模型对温度传感进行研究,解决了常规光纤测温系统复杂和精度不高的问题。对建立的网络模型参数进行探讨,将采集的激光波长与对应的温度数据,经BP神经网络训练,对比得到最佳网络结构,达到在训练完成的网络输入层输入激光波长值时,便可在输出层得到对应的温度预测值。结果证明,实验输出的预测温度值与实际温度值之间表现出明显的相关性,即预测值能够逼近实测值。温度校正和预测相关系数分别达到0.999 61和0.979 27,校正标准误差与预测标准误差分别为0.017 5和0.144 0,得到预测集的平均相对误差为0.17%,剩余预测误差RPD可达到5.258 3,RPD大于3.0,说明定标效果良好,所建模型可用于实际的检测。另外,将该算法用于了带校正的双耦合结构单模错位光纤测温系统中,结果表明BP神经网络方法能够较好的处理错位光纤测温系统中激光光谱数据和温度之间的非线性关系,预测温度值与实测温度值之间的相关度为0.996 58,得到预测温度值与实际温度值之间平均相对误差为0.63%,从而提高了光纤测温传感器的精度和稳定性,同时也验证了该算法在光纤传感上的可行性,也为错位光纤的压力、曲率等其他物理量传感的精确测量提供了新思路。     

基于光谱技术的双孢蘑菇新鲜度量化检测技术研究

双孢蘑菇质地柔嫩、营养丰富,具有很好的降血压、降血脂、消炎护肝等多种保健价值,其新鲜度是反映内外部品质的重要指标之一。目前双孢蘑菇新鲜度鉴别大多依据其外观品质变化（褐变）,缺乏精准的量化评价指标与方法,因此提出了以贮藏天数为新鲜度检测的量化指标,并利用近红外光谱技术对双孢蘑菇新鲜度进行检测分析。依据存储天数不同,将双孢蘑菇样本分为1~5组,每组40个样本,依次采集每组双孢蘑菇的近红外光谱数据。针对采集的原始光谱数据,首先选用卷积平滑滤波（SG）与多元散射校正（MSC）消除原始光谱噪声、基线平移以及光散射的影响,并选取399.81~999.81 nm的光谱波段作为数据处理范围;然后分别使用主成分分析（PCA）和连续投影算法（SPA）进行光谱降维和特征波长选择,继而建立极限学习机（ELM）分类模型;同时考虑到ELM模型中初始值对分类准确率影响较大,分别选用粒子群优化算法（PSO）、海鸥优化算法（SOA）对ELM中初始权值及阈值进行寻优,形成PSO-ELM,SOA-ELM优化组合分类模型;最后分别将全光谱、提取主成分以及所选的特征波长｛556.87,445.51,481.15,885.10,802.25,720.90,861.34,909.79,924.44,873.17 nm｝输入到分类模型中,建立不同输入、不同分类模型的双孢菇新鲜度检测模型。最终试验结果表明,当ELM为分类模型,以全光谱、主成分以及特征波长为输入时的预测精度分别为75%,95%,88%;以SPA优选特征波长作为输入的PSO-ELM、SOA-ELM分类模型训练集精度为96.25%,93.25%,预测集精度为92.5%,94%。可知,SPA波长选择算法可以有效降低光谱信息中存在的冗余信息,加快建模效率,同时海鸥优化算法能较好的优化ELM分类模型的初始参数,分类精度较ELM模型提高了6.8%,同时不产生过拟合现象。因此,利用光谱特征可以快速、准确无损的识别双孢蘑菇的新鲜度,研究结果为便携式双孢蘑菇新鲜度快速无损检测设备的开发提供了理论依据。     

SiPLS-CARS与GA-ELM对哈密瓜冠层叶片含水率的反演估测

传统的叶片含水率检测方法效率低、操作繁琐且是有损的检测,不利于大田哈密瓜叶片含水率的快速获取。为实现对大田哈密瓜生长期进行更精细的田间灌水管理,利用光谱技术分别获取了哈密瓜植株在成长期（M₁）、开花期（M₂）、结果期（M₃）、成熟期（M₄）四个时期内的冠层叶片样本,采用烘干法测得叶片样本的含水率。为提高预测模型的精度和稳定性,首先开展并讨论极限学习机（ELM）模型中的核函数与隐含层神经元个数的选择对ELM模型精度的影响。随后分别利用联合子区间偏最小二乘法（SiPLS）及其与竞争性自适应重加权采样法（CARS）、遗传算法（GA）、连续投影算法（SPA）的组合算法对全波段光谱数据中与叶片含水率相关性高的特征波长进行筛选提取。再分别使用GA与粒子群算法（PSO ）对已经确定最佳核函数与隐含层神经元个数的ELM模型中的输入层与隐含层间的连接权值（W）和隐含层神经元阈值（B）进行优化选择,获取最优且稳定的W与B值,进一步提高模型的稳定性和预测精度。最后将四种特征波长提取算法优选出的特征波长分别进行ELM,GA-ELM,PSO-ELM建模分析,以校正集和预测集的相关系数R_c与R_p为模型评价指标,经过对比分析优选出能准确预测哈密瓜冠层叶片含水率的反演估测模型。采用SiPLS及其与CARS,GA和SPA的组合算法提取特征波长,筛选出的变量数分别为273,20,32和6,占全光谱变量的15.6%,1.2%,1.9%和0.03%。进一步将筛选出的特征波长作为自变量,叶片的含水率作为因变量,建立了ELM的预测模型,最佳预测精度R_p值为0.845 0,预测精度不是很理想。故引入GA与PSO对ELM中随机产生的W与B值进行优化选择。最终,经过研究发现,利用GA优化后的ELM模型结合SiPLS-CARS筛选出的特征波长建立的哈密瓜冠层叶片含水率预测精度最优,故反演叶片含水率的最优建模方式为SiPLS-CARS-GA-ELM,R_c值为0.928 9,R_p值为0.903 2,所建模型精度较高,可为大田哈密瓜冠层叶片的含水率进行快速检测,为田间灌溉管理提供科学依据。     

基于光谱和改进极限学习机的土壤含盐量分析

研究盐碱地的性质、组成,对于生态环境具有重要意义。传统的含盐量测定方法大多基于化学分析,因其成本高、效率低的缺点使得应用于大面积土地的可行性很低。极限学习机（ELM）作为一种基于前馈神经网络构建的机器学习系统,在许多研究中作为一种光谱处理方法被成功运用。为了改进传统的盐碱地含盐量检测方法,采用光谱学结合改进的极限学习机（ELM）模型的方法对盐碱地进行研究。根据镇赉县采集得到的62个土壤表层样本得到对应的光谱反射率和含盐量数据,提出了基于随机值改进粒子群优化算法（RVIPSO-MELM）优化的多层极限学习机模型。首先使用主成分分析提取光谱数据特征,并使用ELM算法对光谱数据建立分类模型,引入改进的粒子群优化算法以提高精度和速度。该模型结合了具有随机值的多层ELM（RV-MELM）和改进PSO算法的多层ELM（IPSO-MELM）二者的优点,在运用启发式算法搜索最优值的同时还具有随机性,提高了模型优化速度,同时以提高模型性能为目的对隐含层之间参数进行优化和选择。并且该模型可以推广到多层,对隐含层之间的参数的两种选择方法,根据经验公式计算和使用改进的启发式算法搜索,进行了提高模型性能和优化时间的讨论,实践结果表明,选择第一层参数使用改进粒子群优化算法,确定随后的隐含层之间参数选择,使用经验公式进行计算得到一种更具现实意义的方法模型。模型在进行启发式搜索最优值之前,利用蒙特卡罗方法确定一个较好的初值,使得模型能保持较高准确率的条件下,优化速度进一步提高。相比于传统方法,这种光谱分析结合ELM的模型节省时间和经济成本,有一定推广意义。     

灰色极限学习机在滚动轴承故障预测中的应用

针对较强噪声环境下的滚动轴承故障预测问题,为提高轴承故障预测的精度,提出并研究了一种新的滚动轴承预测技术。采用将灰色模型和极限学习机（ELM）相结合的方法,针对轴承运行状态值的非线性特点,先将样本数据进行灰色处理,解决数据的随机性和波动性问题,然后代入学习速度快,泛化精度高的ELM神经网络进行训练。在训练完毕后,对未来的轴承运行状态数据进行分析,将其与轴承设备的理论诊断标准相比较以达到故障预测的目的。     

自然循环流动不稳定性的多目标优化极限学习机预测方法

极限学习机是近年来提出的一种前向单隐层神经网络训练算法,具有训练速度快、不会陷入局部最优等优点,但其性能会受到随机选取的输入权值和阈值的影响.针对这一问题,提出一种基于多目标优化的改进极限学习机,将训练误差和输出层权值的均方最小化同时作为优化目标,采用带精英策略的快速非支配排序遗传算法对极限学习机的输入层到隐层的权值和阈值进行优化.将该算法应用于摇摆工况下自然循环系统不规则复合型流量脉动的多步滚动预测,分析了训练误差和输出层权值对不同步长预测效果的影响.仿真结果表明,优化极限学习机预测误差可以用较小的网络规模获得很好的泛化能力.为流动不稳定性的实时预测提供了一种准确度较高的途径,其预测结果可以作为核动力系统操作员的参考.     

改进的QGA-ELM算法水稻叶面积指数反演模型

为了通过植被指数（VI）准确、可靠的获取不同施肥梯度、不同品种的水稻叶面积指数（LAI）,提出了一种基于改进的QGA-ELM算法应用于水稻LAI反演。首先通过8折交叉验证确定极限学习机(ELM)最佳的隐含层神经元个数与隐含层激活函数类型,再通过引入组合动态旋转角策略、单点混沌交叉操作、混沌变异操作、确定性选择策略、量子灾变操作对量子遗传算法（QGA）进行改进,最后使用改进后的QGA算法优化ELM神经网络输入层到隐含层的连接权值和隐含层的阈值。为了验证该模型普适性和有效性,依次建立多元线性回归、BP、ELM、QGA-ELM、改进的QGA-ELM算法5种模型,并在不同数据集上进行反演效果比较,结果表明：（1）对比QGA-ELM算法和改进的QGA-ELM算法进化过程,改进的算法能有效提升模型寻优能力,避免算法早熟,且能寻得更优结果。（2）对比五种算法在不同数据集上的反演效果,验证了NDVI,RVI与LAI之间主要为非线性关系,且ELM神经网络模型反演效果要优于BP神经网络模型和多元线性回归模型。（3）对比五种算法在不同数据集上的反演效果,改进的QGA-ELM算法绝大部分情况下拥有最高的反演精度和最低的误差,改进后的算法反演精度得到了明显提升,泛化性能也得到了增强。（4）改进的QGA-ELM算法在各种施肥梯度上均具有最高反演精度和最低误差,且精度较高,能为不同生长状况水稻LAI反演提供依据。（5）五种模型对庆和香LAI反演精度均要高于龙稻18,而改进的QGA-ELM算法在不同水稻品种上依然具有较高的反演精度,且在不同水稻品种上反演精度相差极小,远低于其他四种模型,能很好适应不同水稻品种LAI反演要求,极大提升模型的稳定性性,为不同水稻品种反演提供参考意义。     

基于D-ELM的矿井气体FTIR光谱定量分析

为了对D-ELM的矿井气体定量分析效果进行比较和分析,建立了3种矿井气体定量分析模型,分别是SVM模型、极限学习机（ELM）模型和动态极限学习机（D-ELM）模型。由于每个模型每次预测结果在一定范围内变化,所以取每个模型运行10次预测结果平均均方根误差（ARMSE）、平均相关系数（AR）、平均模型运行时间（AT）来评价各模型对气体定量分析的性能。PSO-SVM模型的结果为:[0.054 2,0.998,200.38 ];ELM模型的结果为:[1.042 1,0.989 4,0.26];D ELM模型结果为:[0.043 8,1,2.01]。综合预测精度和预测速度表明,D ELM模型要优于另外2种模型。     

基于近红外光谱和ELM算法的菱镁矿石品级分类研究

由工业发展需求,针对菱镁矿石矿物含量不同以及分布不均匀而难以判定其品级的情况,提出一种由近红外光谱技术结合ELM的菱镁矿石品级分类模型。该模型可以实现菱镁矿石品级的快速分类。近红外光谱利用菱镁矿中不同种类含H基团对近红外光谱有不同吸收的特性,用来测定菱镁矿石的成分及其含量,其操作简便、不破坏样品、速度快、准确高效。以辽宁省营口市大石桥的菱镁矿石30组为研究对象,采集菱镁矿石的近红外光谱数据样本30×973。采用主成分分析(PCA)对其进行降维处理,以主元贡献率大于99.99%而得到10维的特征变量值。建立了ELM算法定量分析数学模型,取20组样本为训练样本(包括6组特级,14组非特),其余10组作为测试样本(其中4组特级,6组非特),ELM算法模型的隐含层节点数选取20。为了进一步提高分类效果,提出两种ELM算法模型的改进：采用循环模式对传统ELM的输入权值和阈值进行寻优的精选ELM和在精选ELM基础上进行集成的集成-精选ELM。并与用人工方法、化学方法和BP神经网络模型方法对菱镁矿石样品品级分类作对比。结果表明：近红外光谱和ELM菱镁矿石品级分类模型不论在时间上还是成本上,都具有明显的优势,且其准确率能够达到90%以上,为菱镁矿石品级分类提供了一条新的途径。     

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.     

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.     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

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.