阈值分割法在直升机驾驶舱模拟器中的应用研究

通过对直升机起降特点及视角转换的分析研究,建立模拟起降模型。以VC++为工具,采用双缓冲技术及光栅处理技术,解决了驾驶舱图片透明化过程中存在的闪烁问题。在完成驾驶舱透明化处理的基础上通过采用阈值分割方法_[1],实现了驾驶舱与跑道在同一窗体不同区域中的显示,通过组件调用的方式完成驾驶舱按键对飞机起降的控制,并结合多线程技术完成了直升机模拟起降的仿真测试。该方法能直观清楚的反映直升机起降过程中驾驶舱内部及外部跑道的情况,对直升机起飞降落故障研究有一定的参考价值。     

基于灰色预测的直升机齿轮箱状态预测方法

作为直升机上重要的关键部件,直升机齿轮箱能够将动力转换为动力输出形式,从而满足不同形式下动力的需要。针对直升机齿轮箱状态无法准确预测的技术难题,本文将灰色系统理论中的灰色预测方法运用到直升机齿轮箱中,有效解决了齿轮箱使用状态难以准确预测的技术难题。首先对采集到的直升机齿轮箱的不同的振动信号进行特征提取,然后采用信息融合技术,将不同振动信号的特征值进行融合,最后运用灰色预测方法对直升机齿轮箱的使用状态进行预测。文中对所提出的方法进行了试验验证,结果表明,所提出的基于灰色预测的直升机齿轮箱状态预测方法能够实现对直升机齿轮箱的状态准确预测的效能,并对其他航空设备以及机械设备的状态预测具有一定的借鉴意义。     

主成分分析在舰船辐射噪声分类识别中的应用

主成分分析(PCA)是经典的多元统计分析方法,在处理多变量综合问题方面有比较突出的优势。本文主要探讨了主成分分析在舰船辐射噪声信号分类识别中的应用。在经典功率谱的基础上尝试将PCA技术运用在两种不同的方法中,对两种舰船辐射噪声进行了特征提取和分类识别,得到了较好的效果。     

改进的基于二维主分量分析的掌纹识别

主分量分析(PCA)是一种在众多生物特征识别中获得成功应用的特征提取技术,是一种基于二阶统计的在最小均方误差意义上的最优维数据压缩技术,它所提取的各特征分量之间是互不相关的。传统的PCA变换是对图像向量的分析,但向量维数一般都很高。二维主分量分析方法是最近兴起的针对图像矩阵的主分量分析方法,与一维主分量分析相比能更精确的计算原始数据的协方差矩阵。将其应用于掌纹识别,并在主分量的选取上加以改进,选取了更适合于分类的主分量。实验结果表明,该方法不仅有更高的识别率,而且维数更低。     

基于子空间分析的人脸识别方法研究

人脸识别技术是模式识别和机器视觉领域的一个重要研究方向,在众多人脸识别的算法中,基于子空间分析的特征提取方法以其稳定可靠的识别效果成为了人脸识别中特征提取的主流方法之一。本文对目前应用较多的子空间分析方法进行了研究,具体介绍了线性子空间分析方法：主成分分析（PCA）、线性鉴别分析（LDA）、独立主成分分析（ICA）、快速主成分分析（FastICA）等及非线性子空间分析方法：基于核的PCA （KPCA）等的基本思想及其在人脸识别中的研究进展,包括一些新的研究成果。此外,还应用orl及Yale B人脸库对几个基础的子空间方法进行了验证实验。实验结果表明,在几个子空间分析方法中,FastICA算法取得了最高的识别率。最后结合实验结果对各算法的优缺点进行了分析总结。     

基于OTDR和光功率测试的光纤故障监测应用方法

为了降低光纤光缆故障率和缩短光缆网络故障诊断时间,提出了一种基于光功率测试和光时域反射仪的光纤故障监测方法;利用光功率测试技术对光缆性能进行实时监控并预警光缆故障;分析光纤功率衰减的原因,计算得到光缆修理增加的长度,设计了修正故障地点的算法;当光缆网络发生故障时,利用光时域反射仪测试故障位置,并利用误差检测算法对电缆衰减进行分析排除,对故障地点进行故障位置修正以便快速抢修;结果表明,该方法可以降低光缆网络故障率,在故障定位中可以提高光缆故障定位的精度,计算的故障位置与实际故障位置的误差不超过10 m,可以进行实时快速的维修,对于运营时间较长的光缆网络的效果更明显,具有较好的应用价值。     

基于小波分析的最优故障特征提取研究

针对因模拟电路的故障模型复杂、有容差、非线性等导致的模拟电路故障特征提取难度大、严重依赖于专家的经验的现状,对基于小波分析的模拟电路最优故障特征提取技术进行了研究。以四运放电路为实验基础,采用Morlet和Haar两种小波基分别从不同的维度上做数据预处理,能量化、归一化后组成故障特征,而后通过克隆选择算法的诊断结果分析对比特征提取的效果。实验结果为通过两种小波基提取的故障特征在不同的情况下达到最高故障诊断率均接近89%,表明基于两种小波基的故障特征提取技术都是优秀可用的,以及单点采样数据的有效性;同时实验结果还反映了模拟电路故障特征的详细程度与诊断正确率成正比例关系。这对实际复杂模拟电路的故障特征提取具有指导性的意义。     

基于光学传输矩阵的太赫兹时域光谱分析

提出了基于光学传输矩阵的提取太赫兹时域光谱光学参数的理论方法。相比于传统的提取主脉冲方法,该方法在未来可以推广用以分析主脉冲与次脉冲无法分辨的太赫兹时域光谱。利用该方法得到了蓝宝石(α-Al2O3)样品在0.3~1.0太赫兹频段的复折射率。通过与利用提取主脉冲方法得到的复折射率的结果比较,验证了基于光学传输矩阵的理论分析方法的可靠性和精确性。所提出的方法为今后主次脉冲无法分辨的太赫兹时域光谱的准确分析提供了坚实的理论基础。     

基于信息融合的模拟电路故障的特征提取与融合方法

在模拟电路故障诊断中,故障特征的提取是一个非常重要的环节,其提取结果的好坏将直接影响最终的诊断正确率。对现有文献研究发现,每种特征提取方法单独使用时都有一定的局限性,为了能够更加充分的提取模拟电路故障特征,提出了小波包分析与主元分析并行应用的方法,并将两种方法提取的特征向量依据不同规则进行了三种类型的融合,方便对比实验。为获取最优小波特征,提出了特征偏离度,并以此为标准选择最优小波基。最后,通过设计一种改进的神经网络分类器模型,将融合后的三种特征向量送入其中进行仿真验证,得出最终诊断结果。结果表明,该方法能够有效克服单一特征提取方法提取不充分的缺点,提高故障诊断的正确率,并且融合因子 适中时诊断正确率最高。     

JEMS-FDTD软件在电磁脉冲区域传播数值模拟中的应用

电磁脉冲区域传播数值模拟是电磁环境效应分析的重要环节, 面临空间尺度巨大、多辐射源、复杂地貌等技术挑战。本文介绍了三维时域全波电磁模拟并行软件JEMS-FDTD的研制进展。在大规模并行计算FDTD方法的基础上结合自适应网格技术, 研制了一种适应于大区域电磁脉冲传播的高效时域全波计算方法。并基于该技术实现了千km2级城市电磁脉冲区域传播的数值模拟, 获取了全空间的时域电磁场信息, 验证了软件在电磁脉冲区域传播仿真应用中的可行性。     

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.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.