Feature extraction using orthogonal discriminant local tangent space alignment

A novel algorithm called orthogonal discriminant local tangent space alignment (O-DLTSA) is proposed for supervised feature extraction. Derived from local tangent space alignment (LTSA), O-DLTSA not only inherits the advantages of LTSA which uses local tangent space as a representation of the local geometry so as to preserve the local structure, but also makes full use of class information and orthogonal subspace to improve discriminant power. The experimental results of applying O-DLTSA to standard face databases demonstrate the effectiveness of the proposed method.     

基于改进RX算法的高光谱异常检测

针对RX算法中局部背景协方差矩阵估计的局限性,提出一种改进的RX (I-RX)异常检测算法。基于奇异值分解(SVD),将高光谱图像投影到背景的正交子空间上,获得仅包含噪声和异常的残留图像。在此基础上,通过计算各样本的空间秩深度将残留图像划分为噪声背景和潜在异常两个样本集,利用噪声背景集估计整幅图像的背景协方差矩阵,并将潜在异常集作为测试样本进行异常检测。对模拟数据和真实高光谱数据进行了实验仿真,ROC曲线表明,在相同的虚警概率下,I-RX算法的检测概率相较于RX平均提高了2倍左右。     

A New Discriminant Principal Component Analysis Method with Partial Supervision

Principal component analysis (PCA) is one of the most widely used unsupervised dimensionality reduction methods in pattern recognition. It preserves the global covariance structure of data when labels of data are not available. However, in many practical applications, besides the large amount of unlabeled data, it is also possible to obtain partial supervision such as a few labeled data and pairwise constraints, which contain much more valuable information for discrimination than unlabeled data. Unfortunately, PCA cannot utilize that useful discriminant information effectively. On the other hand, traditional supervised dimensionality reduction methods such as linear discriminant analysis perform on only labeled data. When labeled data are insufficient, their performances will deteriorate. In this paper, we propose a novel discriminant PCA (DPCA) model to boost the discriminant power of PCA when both unlabeled and labeled data as well as pairwise constraints are available. The derived DPCA algorithm is efficient and has a closed form solution. Experimental results on several UCI and face data sets show that DPCA is superior to several established dimensionality reduction methods.     

不同泵浦波长光纤激光器模式不稳定效应对比

一般认为,光纤激光器模式不稳定效应主要来自于泵浦源量子亏损和增益光纤泵浦吸收所产生的热效应。理论分析了光纤中的热源,发现诱发模式不稳定的热效应主要来源于泵浦吸收、其次是量子亏损;利用课题组开发的仿真软件SeeFiberLaser对该结论进行仿真。仿真结果表明:泵浦吸收系数越低,光纤中的最高温度和温度梯度越低,越有利于抑制热致折射率光栅的形成,提高模式不稳定阈值。搭建了纤芯/包层直径为30/400 μm的前向泵浦掺镱光纤激光振荡器,对比研究了中心波长为976 nm 、915 nm和940 nm的泵浦源泵浦时激光器的模式不稳定阈值特性。结果表明,分别采用中心波长为976 nm 、915 nm和940 nm 的半导体激光器作为泵浦源时,激光器模式不稳定阈值分别为279 W、502 W和697 W,光光转化效率分别为67.7%、61%和63%。由此可以发现,泵浦吸收系数对模式不稳定阈值的影响大于量子亏损对模式不稳定阈值的影响,通过改变泵浦波长降低泵浦吸收系数可以有效提升模式不稳定阈值。优化泵浦波长,兼顾量子效率和泵浦吸收系数,是光纤激光器实现高光束质量高模式不稳定阈值的重要技术路线之一。     

环境辐射对热像仪测温的影响

不同于传统的离散光谱测温,热像仪测温的实质是一种在一定波段范围内的基于探测器光谱响应的连续光谱测温。除了目标的发射率会影响热像仪所测温度与真实温度的关系外,反射的环境辐射也是热像仪测温结果的重要影响因素。目前的热像仪测温精度研究在对目标反射环境辐射的处理中,大都把环境辐射看做是均匀入射的或者是把目标看做了镜面反射体,这样做虽然可以大大简化模型,但是却远远不符合实际情况。针对这一现状,利用辐射度学原理和热像仪探测器的光谱响应特性,建立了在环境辐射非均匀入射条件下的热像仪对漫射目标的测温模型,结果表明:环境辐射对热像仪测温的影响,除了与目标的反射率和环境辐射源的温度有关外,还与环境辐射源对目标所张的投影立体角有关。根据所得模型,分析了热像仪测温的影响因素,重点对几种典型环境辐射条件下对热像仪测温的影响进行了定量计算和分析,并进行了实验验证。相关结果一方面可以为热像仪测温设计提供参考,另一方面可以为复杂环境条件下热像仪测温与真实温度的误差估算提供理论依据。     

多枚红外诱饵弹运动轨迹仿真

对于载机连续发射多枚红外诱饵弹的运动轨迹进行了仿真。首先考虑无动力燃烧型诱饵弹在发射后因为燃烧而导致质量损失的因素,建立了诱饵弹运动轨迹递归迭代计算模型,然后运用此模型计算了不同条件下的多枚诱饵弹发射后的运动轨迹,最后利用可视化技术对载机平台发射多枚诱饵弹的场景进行了可视化仿真。     

差分吸收相干激光雷达中偏振分集技术研究

为减小差分吸收相干激光雷达(DIAL)中偏振衰落对 回波信号功率反演精度影响,研究了偏振分集技术(PDT)在相干DIAL中 的作用,构建了利用STM32控制的双光束切换DIAL实验装置。依托构 建的装置,利用平衡探 测,分别采用PDT和一般外差探测完成多组次实验,应用单频检测方法得到20m光程下吸收 气体不同浓度下相干中频信号的振 幅值,并由此求解出on光和off光回波信号功率。对回波信号功率值差分信息与由HITRAN得 到的参考差分信息比较 发现:应用PDT能使探测分辨率提高4倍,对应到2km距离内,可以探测到3.5×10－6ppm的CO₂浓度变化,满足了 气候研究所需的优于1％的精度要求,验证了PDT消除偏振衰落以及提高相干DIAL分辨精度的 作用。     

多波段兼容伪装方法的分析研究

多波段兼容伪装是未来伪装技术发展的方向,但每增加一个伪装波段,都对兼容伪装的实现带来了很大难度。介绍单波段伪装的作用机理及相关要求,并分析多波段伪装的几种常用方法。设计了两种新型的光子晶体薄膜伪装结构。     

Density mapping of hardened cement paste using ptychographic X-ray computed tomography

Ptychographic X-ray computed tomography (PXCT) allows for a non-destructive, three-dimensional mapping of the electron density. Its quantitativeness combined with a resolution in the 100 nm range makes it a suitable tool for the assessment of densities of the individual phases in complex materials, such as hardened cement pastes. Here we present results of an experiment performed on a cylindrical sample of epoxy-impregnated hardened cement paste of about 30 μm in diameter. Two-dimensional cross sections of the three-dimensional electron density map show a microstructure that bears distinct similarity to that observed by back-scattered scanning electron microscopy. Domains of various residues of cement grains, calcium hydroxide, calcium carbonate, epoxy-resin impregnated calcium silicate hydrates, epoxy-resin impregnated porosity, and unimpregnated porosity are revealed and are manifested as distinguishable peaks in the histogram of the three-dimensional electron density map. On assumptions of (i) a priori knowledge of the chemical composition and (ii) the purity of the analysed regions, the mass densities of the above mentioned individual material phases are estimated. The potential of PXCT for the science of cement and concrete is discussed.     

基于Bi_2Te_3合金材料的热发电模块研究

为了提高Bi2Te3热电材料的性能,采用Bi2Te3纳米粉体前驱物快速熔炼烧结法,制备了在室温条件下具有温度敏感性的Bi2Te3合金材料,在425K时此材料的热电优值达到0.548。在此基础上,研制了热电模块,并对其性能进行了测试。结果表明,以该Bi2Te3合金材料制备的热发电模块具有良好的伏安特性和稳定的内阻,当热冷端温度分别为140和60℃时,模块的最大输出功率可达到0.39W,显现出潜在的应用前景。