一种多通道纳秒分幅相机

相机采用棱镜分光,薄片管增强象,电选通分幅。由四个薄片管组成四个通道,每一个通道代表一个单幅相机,分幅时序由专门电控电路进行控制,接触相机记录图象,最短曝光时间3ns,动态空间分辩率5～81lp/mm,最高分幅速率2×10⁸幅/秒,动态范围50°,在爆炸、激光、放电,光谱学等方面有广泛的应用。     

The signature operator at 2

It is well known that the signature operator on a manifold defines a K-homology class which is an orientation after inverting 2. Here we address the following puzzle: What is this class localized at 2, and what special properties does it have? Our answers include the following:

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the K-homology class Δ_M of the signature operator is a bordism invariant;

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the reduction mod 8 of the K-homology class of the signature operator is an oriented homotopy invariant;

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the reduction mod 16 of the K-homology class of the signature operator is not an oriented homotopy invariant.

     

Correcting non-linear lens distortion in cameras without using a model

Camera lens distortion calibration is the first step in resolving any metric application with a camera. To date, lens distortion was corrected using some existing lens distortion non-metric or self-calibration methods. Using a lens distortion model means defining a global rule to correct the entire image. This global rule does not take into account particular lens distortion effects not represented by the model. Moreover, to calibrate the model, only some features of the scene such as straight lines, circles or vanishing points are used. Since only the feature of the scene used to calibrate the model is guaranteed by the distortion rectification, it is certain that the model will not be precise. The result is an approximation of the real image distortion.To improve the lens distortion rectification, a method without using a model is proposed. Using a set of control points distributed across the entire image, they are corrected to assure all the restrictions of the scene. With both sets of points, the points detected in the image and the undistorted ones, image local transformations are defined considering only nearby control points. Rather than calibrating a global model, local functions are characterized. The distortion correction is defined by a rectification surface composed of local surface patches each influenced by nearby control points. This method is more sensitive to local deformations and allows the image to be corrected in accordance with its distortion.     

Focal shift of hollow Gaussian beams through a thin lens

In this paper, the focal shift of hollow Gaussian beams (HGBs) passing through a thin lens is investigated in detail. An analytic expression of the location of the axial maximum intensity for the HGBs is derived. It is found that, both the relative focal shift and the relative location of the axial maximal intensity of the HGBs is strongly affected by the ratio α (where α=s/f, here s is the axial distance from the input plane to the lens plane and f is the focus length of the lens), and it is also greatly affected by the changes of both the effective Fresnel number N_w and the order n of HGBs.     

高清晰低畸变细径化电子内镜物镜设计

设计了一款用于医疗方面的视场为74°的电子内镜物镜.电子内镜外径为8 mm从而实现无麻醉,内镜前端可弯曲来实现无盲区检测.物镜有效焦距为4 mm,后工作距为4.8 mm.系统的畸变最大值少于4%,场曲最大值为0.27 mm.为了提高成像质量,将非球面引入此五片镜系统.所设计的光学系统尤其适用于0.25英寸CCD像传感器,且显示模式为SVGA.     

56mm焦距重心定位用光学系统

文章中介绍的光学系统是一个56mm焦距,相对孔径为1/1.3,视场角为11.3°,后截距>10mm,光谱范围为046～0.75μm的六块无胶合透镜组成的镜头.该光学系统只有两种低吸收、物理、化学性能良好的普通光学玻璃材料(Bak6和ZF2)组成,因此可以有高的透过车;全视场范围内各色光重心偏之差小于±1.2μm,象面上80%能量集中在24μm～54μm之间.与一般光学系统相比,它具有各色光重心偏差值小、和轴上、轴外能量分布比较一致的特点.     

光学优化设计中一阶和二阶偏导数的解析求法

以复合函数的微分法则为基础,提出了光学设计中目标函数对结构参数一阶和二阶偏导数解析求导的方法,给出了相应的推导过程和计算实例。     

A stereoscopic digital speckle photography system for 3-D displacement field measurements

Stereoscopic digital speckle photography offers a technique to measure object shapes and 3-D displacement fields in experimental mechanics. The system measures the displacement of a random white light speckle pattern, which somehow is present on the object surface, using digital correlation. This paper describes a general physical model for stereo imaging systems. A camera calibration algorithm, which takes the distortion in the lenses into account, is also presented and evaluated by real experiments. Standard deviations of small deformations as low as 1% of the pixel size for in-plane deformations and 6% of the pixel size for the out-of-plane component are reported. Using the calibration algorithm described, the main source of errors is random errors originating from the correlation algorithm.     

Interferometric focal length measurement of power-distributed lenses

An interferometric method for measuring the focal length of power-distributed lenses is described. The test lens is illuminated by a regular pitch interferometric pattern produced by a reflective diffraction grating interferometer. In order to measure the focal length, a CCD camera digitizes the image of the pattern magnified by the lens, and fast Fourier transformed to reconstruct the phase modulo 2π along each row. The change in spatial frequency is determined by unwrapping the phase along each row of the digitized imaged pattern. The technique is used for measuring the focal length distribution inside the progression corridor of both positive and negative progressive lenses.     

Relating geologic units and mobility system kinematics contributing to Curiosity wheel damage at Gale Crater,Mars

Curiosity landed on plains to the north of Mount Sharp in August 2012. By June 2016 the rover had traversed 12.9 km to the southwest, encountering extensive strata that were deposited in a fluvial-deltaic-lacustrine system. Initial drives across sharp sandstone outcrops initiated an unacceptably high rate of punctures and cracks in the thin aluminum wheel skin structures. Initial damage was found to be related to the drive control mode of the six wheel drive actuators and the kinematics of the rocker-bogie suspension. Wheels leading a suspension pivot were forced onto sharp, immobile surfaces by the other wheels as they maintained their commanded angular velocities. Wheel damage mechanisms such as geometry-induced stress concentration cracking and low-cycle fatigue were then exacerbated. A geomorphic map was generated to assist in planning traverses that would minimize further wheel damage. A steady increase in punctures and cracks between landing and June 2016 was due in part because of drives across the sharp sandstone outcrops that could not be avoided. Wheel lifetime estimates show that with careful path planning the wheels will be operational for an additional ten kilometers or more, allowing the rover to reach key strata exposed on the slopes of Mount Sharp.