菲涅耳全息投影中零级光的消除

采用菲涅耳相位全息图进行全息投影显示时,再 现像的视觉效果受到空间光调制器(SLM)像素结构引起 零级光的影响。为消除零级光的影响,本文基于原有的菲涅耳全息投影系统,在SLM后面引 入成像透镜, 并在透镜的后焦面设置高通滤波器以滤除零级光。为抵消成像透镜引起 的相位变化,通过引入发散球面, 实现调节全息再现像成像位置的目的。实验结果表明,在 不改变菲涅耳相位全息图重构距离的情况下,可以有效消除零级光对全息再现像的影响。     

预放大离轴菲涅耳数字全息显微技术

预放大离轴全息方法引入了高数值孔径显微物镜,放大了物体的精细结构,使得全息图的信息量更容易与CCD的抽样能力相匹配,与同轴全息显微技术相比,只需拍摄一张全息图,操作简单,具有良好的应用价值.依据全息理论和菲涅耳衍射理论,推导出预放大离轴菲涅耳全息显微系统中CCD记录面的二维光波信息.设计了采用平面光波作为参考光的透射式数字全息显微系统,并对系统分辨率进行了分析.利用该系统对新鲜的洋葱细胞样本和百合的茎细胞样本进行了实验研究,得到了其高分辨率的再现像.     

光学显微三维测量解耦合准则

光学显微三维测量耦合效应是指沟槽或台阶样品高度测量准确性受横向周期影响产生原理误差的现象。采用卷积不相关原则和有限能量损失原则,分别建立了薄样品和深沟槽样品光学显微三维测量的解耦合模型,揭示了被测样品特征参数与光学仪器表征能力之间的关联关系。与现有W/3准则相比,光学显微三维测量解耦合准则能够客观反映光学仪器表征能力受样品结构差异变化的影响,指示高度测量解耦合评定的示值区域,预见高度测量原理误差产生,为沟槽或台阶样品三维结构表征提供了一种新的计量评定准则。     

Robust locality preserving projection based on maximum correntropy criterion

Conventional local preserving projection (LPP) is sensitive to outliers because its objective function is based on the L2-norm distance criterion and suffers from the small sample size (SSS) problem. To improve the robustness of LPP against outliers, LPP-L1 uses L1-norm distance metric. However, LPP-L1 does not work ideally when there are larger outliers. We propose a more robust version of LPP, called LPP-MCC, which formulates the objective problem based on maximum correntropy criterion (MCC). The objective problem is efficiently solved via a half-quadratic optimization procedure and the complicated non-linear optimization procedure can thereby be reduced to a simple quadratic optimization at each iteration. Moreover, LPP-MCC avoids the SSS problem because the generalized eigenvalues computation is not involved in the optimization procedure. The experimental results on both synthetic and real-world databases demonstrate that the proposed method can outperform LPP and LPP-L1 when there are large outliers in the training data.     

Micro-CT of Pseudocneorhinus bifasciatus by projection X-ray microscopy

The projection X-ray microscope utilises a very small X-ray source emitted from a thin (0.1-3 microm) target metal film excited by the focused electron beam of a scanning electron microscope. When an object is placed just below the target metal film, the diverging X-rays enlarge the shadow of the object. Because no X-ray optics such as a zone-plate is used, the focal depth is, in principle, infinitely large. We exploited this to apply projection X-ray microscopy to three-dimensional (3-D) structure analysis by means of cone-beam computed tomography. The projection images of a small arthropod (Pseudocneorhinus bifasciatus, 5 mm in length), was recorded at 3 degrees increments over the whole range (360 degrees) of a stepping-motor-controlled sample rotator. A 3-D image was reconstructed from corn-beam projections using a filtered back-projection algorithm. The reconstructed 3-D image showed in detail the internal structure of an opaque object.     

Fresnel lenses in optical waveguides

Fresnel lenses in optical waveguides have been designed, analyzed, and experimentally fabricated and evaluated in BaO waveguides. Diffraction limited spot size, 18 dB of the signal-to-noise ratio, angular field of view of 15°, and 23 percent diffraction efficiency have been observed experimentally. Limitations of and methods for improving its performanee are discussed.     

基于分明矩阵的序贯属性约简算法

根据决策表信息系统的分明矩阵及序贯思想,提出了序贯属性约简算法,该算法首先构造递增序列的分明函数,然后利用逐次增加的属性核对分明函数进行分支运算,并建立属性约简树,从而求出所有约简.该算法避免了大量的逻辑运算,实现了高维数据的高效属性约简.理论分析和实验结果表明该算法具有更高的运行效率.     

一种改进的基于差别矩阵的属性约简算法

为解决决策表属性约简完备算法约简质量低的问题，在基于差别矩阵的属性约简完备算法的基础上，引入信息论中信息熵和互信息增益的定义，给出一种启发式属性约简完备方法，通过实例说明启发式信息可以提高完备算法的约简质量，比较不同启发信息对完备算法的约筒质量和约简效率。试验结果表明，采用基于信息论定义的两种启发信息的完备算法约筒效率基本一致，该算法较非启发式完备算法有更好的约简质量。     

菲涅耳衍射系统的分数级传递函数

基于分数傅里叶变换与菲涅耳衍射的等效性和线性系统理论,给出了菲涅耳衍射系统在分数傅里叶变换下光学传递函数的数学表达式,分析了其基本特征,阐述了其物理意义,证明了常规傅里叶变换下的光学传递函数为分数传递函数的特例,对光学分数傅里叶变换在光学测量、信息处理和像质评价等的应用具有实用价值。计算机模拟文验验证了结论的正确与可行。     

混合数据的邻域区分度增量式属性约简算法

增量式属性约简是一种针对动态环境下的数据挖掘方法.目前已经提出的增量式属性约简算法仅适用于符号型的信息系统,而很少有对混合信息系统进行相关的研究,这促使在混合信息系统下构建相关的增量式属性约简算法.区分度是用于设计属性约简的一种重要方法,本文将传统的区分度在混合信息系统下进行推广,提出邻域区分度的概念,然后分别研究了邻域区分度在混合信息系统下对象增加和对象减少时的增量式学习,最后根据这种增量式学习分别提出了对应的增量式属性约简算法.UCI数据集上的相关实验结果表明,所提出的增量式属性约简比非增量式属性约简能够更快速的更新约简结果.     

关于波带板的焦移

实验测定了波带板的焦移,接近与广义程函数理论。     

A cylindrical Fresnel zone antenna

A cylindrical Fresnel zone antenna as a candidate for a base station in wireless indoor LAN systems is described. An arbitrary angle-tilted fan beam in azimuth can be achieved by moving the position of the strip dipole feed at the cylinder center. A simple theory based on the diffraction integral is developed which predicts the antenna radiation characteristics. The antenna fabrication and measurement are carried out at 9 GHz with good agreement between calculated and measured results     

Offset Fresnel zone plate antennas

The theory of offset Fresnel zone plate antennas is presented. Explicit formulae for the design of the zone boundaries for the offset Fresnel zone plate are given. Theorectical equations and numerical results for the far-field analysis are presented. It is found that when the offset angle increases, the zone boundaries become more elliptic and the plate becomes more asymmetric in the E-plane. With the number of full wave zones and the plate width in the W-plane fixed, the plate width in the E-plane increases with the offset angle, which keeps the projected aperture area constant. Within a limited range of offset angles, the offset configuration can be employed without degrading the radiation performance much. For large offset angles, however, the asymmetry of the configuration may lead to increased sidelobes and decreased antenna directivity. An experiment with one particular phase reversal zone plate antenna with 30° offset angle shows good agreement between the measured antenna pattern and the theoretical prediction.     

Fresnel studies of reflected beams

It is shown that standard numerical methods based on the Fresnel equation accurately model the reflection of a collimated TE-polarized Gaussian beam from a planar dielectric interface when the beam is incident on the interface at arbitrary nonnormal angles     

Fresnel zones for ground-based antennas

The ordinary Fresnel zone concept is modified to include the influence of finite ground conductivity. This is important for ground-based antennas because the influence on the radiation pattern of irregularities near the antenna is determined by the amplitude and phase of the groundwave. A new definition of Fresnel zones which takes into account the phase shift of groundwave propagation is given and it is shown that these new zones are zones of greatest influence, at least when discontinuities of the electrical parameters of the ground are considered. Numerical results for the first Fresnel zone are given, and it is shown that the zone is much smaller for a finite conductivity than for an infinity conductivity, especially for small angles of elevation.     

菲涅尔加密点阵全息图

本文根据二元振幅衍射图的衍射原理提出了现点阵全息图的菲涅尔加密的方法,并在此基础上提出了相应的再现系统。理论和实验均证明这一方法是可行的。     

一个新的差别矩阵及其求核方法

首先利用反例指出HU的利用差别距阵来求粗糙集中的核的方法是错误的,然后给出一个新的差别距阵的定义和求核方法,并证明了方法的正确性.     

菲涅耳数字全息在图像加密中的应用

基于小波变换和光学菲涅尔变换原理,提出一种新的数字水印算法。首先,原始的水印图像经过离散菲涅尔变换转化成数字全息图,并对数字全息图进行灰度变换;再对宿主图像进行一层小波分解;最后将变换后的数字全息图嵌入到宿主图像较大的小波系数中。实验结果表明,该水印算法具有较强的鲁棒性,能抵抗较大的剪切、有损压缩和滤波等攻击。     

光生等离子体菲涅尔波带板天线

本文描述一种光生等离子体菲涅尔波带板天线的设计方法.利用中心波长为808 nm的近红外激光器阵列通过光学掩膜(菲涅尔波带板的照相底片)照射高电阻率的硅片,使硅片呈现出菲涅尔波带板的衍射特性,实现对入射毫米波的聚焦.给出了这种天线在94GHz处的实验验证,并得到了4dB的天线增益效果.