基于光场相机的深度面光场计算重构

光场相机与传统相机不同,通过在主镜组和传感器间特定位置设置微透镜阵列,实现在采集物方光强的同时记录光线方向。为了重构物方光场,研究了基于光场相机的深度面计算重构算法,对该算法所采用的焦点堆栈、投影切片定理进行研究。首先,对四维光场定义及光场相机工作原理进行分析;建立了相机内部深度面重构模型,分析了投影切片定理在深度面获取的应用,并推导出不同深度面图像表达式;根据得到不同深度位置图像,研究了计算重构算法,搭建了含有微透镜阵列的微型单相机光场采集系统,采集原始光场,利用本文方法实现了物方光场的逆向重构。实验结果表明:利用本文重构算法,光场相机采集的物方光场可通过滤波计算方法逆向重构,通过重构光场数据可获得物方场景深度信息。本文深度面获取算法较其他算法节省30%以上的时间,各深度面图像峰值信噪比在25~30dB之间,实现了高精度、稳定可靠的计算光场重构。     

The resolution of photoelectron microscopes with UV, X-ray, and synchrotron excitation sources

The resolution of emission electron microscopes is calculated by determining the intensity distribution in the image. The object is a small disc of uniform brightness centered on the axis. A finite object, as distinct form a point source, provides a non-zero current in the image without the requirement of infinite object brightness and the consequent infinities in the geometrical intensity distribution. The minimum object size, which in turn affects the resolution of the microscope, depends on the minimum current or contrast required in the image. In photoelectron microscopes with UV illumination just above the threshold for emission the predominant aberrations are the chromatic and spherical aberrations of the accelerating field and the spherical aberration of the objective lens. For higher energies, e.g. in the soft X-ray range, the chromatic aberration of the objective lens must also be taken into account, as the aberration coefficients of the accelerating field are greatly reduced. The intensity distributions in the image are calculated first for single energies. The intensity distribution for a beam with a range of energies is obtained by adding a series of single-energy distribution curves weighted according to the energy distribution function. In the presence of spherical aberration the position of the image formed by the electrons depends on the angle of emission. In image planes between the paraxial and marginal planes the combination of spherical aberration and defocus causes the the image spot to have a retrograde type of behavior as the angle of emission increases. The image spot initially moves away from the axis in the azimuth of emission and then returns to the axis and moves away in the opposite azimuth. As a result the intensity in the central portion of the image plane is enhanced. The single-energy intensity distribution curves calculated as a function of depth in the image reveal the existence of a compact, high-intensity image peak in an image plane located between the paraxial and marginal planes. This peak occurs in the plane in which the image spot has a maximum retrograde displacement equal to its radius. The present analysis shows that the resolution in the high-intensity plane is better than in the plane of least confusion, and the effects of aberrations in these two planes are quite different.(ABSTRACT TRUNCATED AT 400 WORDS)     

'Five-parameter' analysis of grain boundary networks by electron backscatter diffraction

This paper describes state‐of‐the‐art analysis of grain boundary populations by EBSD, with particular emphasis on advanced, nonstandard analysis. Data processing based both on misorientation alone and customised additions which include the boundary planes are reviewed. Although commercial EBSD packages offer comprehensive data processing options for interfaces, it is clear that there is a wealth of more in‐depth data that can be gleaned from further analysis. In particular, determination of all five degrees of freedom of the boundary population provides an exciting opportunity to study grain boundaries by EBSD in a depth that was hitherto impossible. In this presentation we show ‘five‐parameter’ data from 50 000 boundary segments in grain boundary engineered brass. This is the first time that the distribution of boundary planes has been revealed in a grain boundary engineered material.     

平行平板平行度的检测

通过非接触式的光学检测方法对两平面间的平行度进行检测。若两平面平行,则两光斑完全重叠在一起;若两光斑没有完全重叠,说明两平面间有倾角。针对两光斑没有重叠的情况,通过理论分析两光斑圆心之间的距离与倾角之间的关系及两光斑间的相对位置与倾角的方向间的关系,然后图像处理实验图得出两光斑间的圆心距,即可确定两端面间倾角的大小及方向,通过圆心测距法求得的倾角误差小于2′。     

Crack detection in beams using experimental modal data and finite element model

In this paper, an analytical, as well as experimental approach to the crack detection in cantilever beams by vibration analysis is established. An experimental setup is designed in which a cracked cantilever beam is excited by a hammer and the response is obtained using an accelerometer attached to the beam. To avoid non-linearity, it is assumed that the crack is always open. To identify the crack, contours of the normalized frequency in terms of the normalized crack depth and location are plotted. The intersection of contours with the constant modal natural frequency planes is used to relate the crack location and depth. A minimization approach is employed for identifying the cracked element within the cantilever beam. The proposed method is based on measured frequencies and mode shapes of the beam.     

基于深度图像的不规则零件检索技术研究

提出了一种基于深度图像的三维零件模型的检索技术，通过比较模型在三个方向上的投影图像来进行零件本身的相似距离计算。该检索算法首先对零件模型进行方位规范化，然后将其投影到三个正交平面上，对投影图像利用不变矩和极半径傅里叶变换分别提取图像特征，其联合特征向量可以很好地进行图像比较，最后加权三个图像之间的相似距离得到三维模型的相似距离。该算法充分利用了机械零件自身的特点，有较好的检索性能。     

KDP晶体三倍频晶面微观力学行为及加工性能

为了揭示磷酸二氢钾(KDP)晶体三倍频晶面微观弹塑性力学行为及加工性能,开展了纳米压痕研究。建立了KDP晶体三倍频晶面各向异性力学模型,基于光滑粒子流体动力学(SPH)方法对纳米压痕进行了数值仿真并完成了纳米压痕测试实验。实验结果表明:实验与仿真计算的载荷-压入深度关系曲线的相关系数为0.996 328,吻合度较高,验证了力学模型的正确性,得出KDP晶体三倍频晶面的屈服强度为240MPa。数值仿真结果显示:由于材料的各向异性,工件内部应力呈不规则圆弧状分布;载荷大小与等效应力影响深度呈近似线性递增关系;材料表面等效塑性应变分布形状与压头投影面几何形状相类似,存在复映效果。当载荷小于2mN时,各压头的残余应力深度差异性较小(小于0.2μm);随着载荷逐渐增大,这种差异不断扩大。得到的结果为实现KDP晶体三倍频晶面的高效低损伤加工提供了理论支撑。     

Relation between correction masses and bearing forces in a rigid rotor

Bearing forces on a rigid rotor are mainly characterized by unbalance distribution. The forces can be divided into two arbitrary planes along a rotor shaft since any unbalance in the rigid rotor is able to be expressed on two planes. The correction mass quantities on two arbitrary planes are analytically found in terms of the bearing force measurements from the basic concept of three-dimensional rigid body dynamics. The quantities are expressed in terms of the geometry of rotor — the distance between two bearings and the positions of two planes from the bearings — and the bearing forces: amplitudes of the alternating component of forces and angular positions of their peak values. The validity of the proposed method is proved using a simulation example.     

Global spatial sampling with isotropic virtual planes: estimators of length density and total length in thick, arbitrarily orientated sections

Existing design-based direct length estimators require random rotation around at least one axis of the tissue specimen prior to sectioning to ensure isotropy of test probes. In some tissue it is, however, difficult or even impossible to define the region of interest, unless the tissue is sectioned in a specific, nonrandom orientation. Spatial uniform sampling with isotropic virtual planes circumvents the use of physically isotropic or vertical sections. The structure that is contained in a thick physical section is investigated with software-randomized isotropic virtual planes in volume probes in systematically sampled microscope fields using computer-assisted stereological analysis. A fixed volume of 3D space in each uniformly sampled field is probed with systematic random, isotropic virtual planes by a line that moves across the computer screen showing live video images of the microscope field when the test volume is scanned with a focal plane. The intersections between the linear structure and the virtual probes are counted with columns of two dimensional disectors.
Global spatial sampling with sets of isotropic uniform random virtual planes provides a basis for length density estimates from a set of parallel physical sections of any orientation preferred by the investigator, i.e. the simplest sampling scheme in stereology. Additional virtues include optimal conditions for reducing the estimator variance, the possibility to estimate total length directly using a fractionator design and the potential to estimate efficiently the distribution of directions from a set of parallel physical sections with arbitrary orientation.
Other implementations of the basic idea, systematic uniform sampling using probes that have total 3D × 4π freedom inside the section, and therefore independent of the position and the orientation of the physical section, are briefly discussed.     

Preliminary confocal scanning laser microscopy study of fluid inclusions in quartz

The initial results of the first dedicated confocal scanning laser microscopy (CSLM) study of fluid inclusions in quartz are presented. CSLM imaging of a large inclusion shows the quartz crystal to contain numerous small (< 1 μm), highly reflective inclusions arranged along planes in at least two directions that are not readily visible in transmitted light. The technique allows measurements to be made of the angular intersection and orientation of the planes in both two and three dimensions. Results suggest that larger inclusions (> 10 μm) occur where two planes of small inclusions intersect, and that the shape of the large inclusions is controlled by the angular relationship between intersecting planes.     

PX650型平旋盘专用铣床的设计

钢锭模底平面是方环形的几何平面,用一般切削机床加工效率低,质量稳定性差。PX650型平旋盘专用铣床是专门为加工这类环形几何端面而设计的。其主轴转速为45r/min,一次切削最大深度为10mm,进给量为0.354mm/r。该铣床结构简单、加工质量稳定,效率高。     

Three-dimensional microscopic biopsy of in vivo human skin: a new technique based on a flexible confocal microscope

A new noninvasive microscopic technique of three-dimensional optical biopsy from in vivo human skin based on real-time confocal microscopy and computer reconstruction is demonstrated. A tandem scanning confocal microscope is a prototype of a mobile, flexible design for the in-depth microscopic exploration of the skin on the human body. The various skin layers were observed in real-time, at the subcellular level down to a depth of 200 μm with a vertical resolution of 2 μm. Rapid video recording of the Z-series through the ventral aspect of the forearm avoided shifts caused by subject movement and blood flow pulsations. Two video frames were averaged, and the average was digitized, providing a stack of 64 optical sections in 1-μm vertical steps. Three-dimensional reconstructions of in vivo human skin were obtained with sets of orthogonal slices, and slices at arbitrary planes through a volume containing the stack of slices. This method clearly shows the spatial relationships between the different cell layers. The use of orthogonal cutting planes is preferred because of its analogy with classical vertical sections of histopathology. Linear structures (surface lines) within the stratum corneum are described and their global orientations were determined by the use of Fourier transform analysis. En face optical sections constitute unusual views of this tissue, since typical pathohistological studies are based on sagittal (vertical) slices. The noninvasive optical microscopic technique provides a three-dimensional optical biopsy of in vivo human skin.     

A new step towards the lattice reconstruction in 3DAP

The spatial resolution of images produced by 3DAP is known not to be limited by the detector performance but by the physics of field ionisation and field evaporation. This resolution can be expressed by two parameters: the depth resolution and the lateral resolution, which have been shown to achieve, respectively, 0.06 and 0.2nm in an ideal case of a pure metal. By using this model and these values, the resolution along any crystallographic direction can be predicted. In addition, it is possible to predict the suitable sites of analysis where a given type of atomic planes can be resolved. Furthermore, it is shown that three types of planes with non-coplanar directions can be imaged in 3D reconstructed volumes. Thus, the reconstruction of the original tungsten lattice can be achieved with the use of Fourier Transform image analysis techniques. It is shown that the reliability of the method can be achieve the value of 90%.     

一种新的无损测定金属表层应力随层深分布方法的探讨

本文提出了一种无损测定金属表层应力随层深分布的试验方法,此法主要在不同波长的X－射线辐照下选用一系列不同的衍射晶面来进行测定。从而获得不同有效穿透深度内的平均残余应力值,由于X-射线强度随层深增加是按指数e{sup}(-ux)衰减的,因此用X－射线测得的应力值是一个加权平均值,由它再来计算试样不同层深的实际应力值,并绘出金属部件随层深分布的应力曲线。在普通的衍射仪上,此法最大探测深度为40～50u,它取决于被选用的靶和衍射晶面,所以对研究各种经过表面处理和磨削后的金属部件的表面质量仍然是有效的。曾对经过磨削的炭钢试样,WC刀具,氮化处理的试样等进行了一系列的测定,并绘制了相应的应力分布曲线。本试验必须在附有试样侧倾装置的衍射仪上进行。     

Observations of thermoelastic instability in mechanical face seals

Sliding contact between the primary and mating rings of a mechanical seal will result in the generation of frictional heat. In some cases this resulting frictional heat will lead to a condition of thermoelastic instability of the sealing planes. Various field and laboratory cases are reviewed with respect to the development of surface disturbances at the seal interface. The effect of interface cooling on the sealing planes is also shown.     

星轮轴的有限元分析

星轮轴是蜗杆压缩机的主要部件之一,利用有限元方法分析其特性。首先对其进行静力学分析,仿真结果表明星轮轴满足强度和刚度要求;利用有限元法进行残余应力和弯曲应力分析,得到了最大法向应力分布规律和沿指定平面的SWT等效应力分布规律;最后对星轮轴进行了模态分析,得到了其前六阶固有频率和振型。     

Anisotropy of machined surfaces involved in the ultra-precision turning of single-crystal silicon—a simulation and experimental study

A new method was proposed for simulating the anisotropic surface quality of machined single-crystal silicon. This represents the first time that not only the mechanical properties of silicon, but also the crystal orientation, which is closely linked to the turning process, have been given consideration. In this paper, the crystallographic relationship between machined crystal planes and slip planes involved in ultra-precision turning was analyzed. The elasticity, plasticity, and brittleness properties of silicon in different crystal orientations were calculated. Based on the brittle–ductile transition mechanism of ultra-precision turning of single-crystal silicon, the orientation dependence of the surface quality of (111), (110), and (100) crystal planes were investigated via computer simulation. According to the simulation results, the surface quality of all machined planes showed an obvious crystallographic orientation dependence while the (111) crystal plane displayed better machinability than the other planes. The anisotropic surface properties of the (111) plane resulted from the continuous change of the cutting direction, which causes a change of actual angle between the slip/cleavage plane and machined plane. Anisotropic surface properties of planes (100) and (110) result from anisotropy of mechanical properties and the continuous changes of the cutting direction, causing the actual angle between slip/cleavage plane and machined plane to change simultaneously. A series of cutting experiments were carried out on the (111) and (100) crystal planes to verify the simulation results. The experimental results showed that cutting force fluctuation features and surface roughness are consistent with the anisotropy characteristics of the machined surface as revealed in simulation studies.     

Subsurface Damage in Scratch Testing of Potassium Dihydrogen Phosphate Crystal

Potassium dihydrogen phosphate (KDP) is an important electro-optic crystal, often used for frequency conversion and Pockels cells in large aperture laser systems. To investigate the influence of anisotropy to the depth of subsurface damage and the profiles of cracks in subsurface of KDP crystal, an experimental study was made to obtain the form of subsurface damage produced by scratches on KDP crystal in [100], [120] and [110] crystal directions on (001) crystal plane. The results indicated that there were great differences between depth and crack shape in different directions. For many slip planes in KDP, the plastic deformation and cracks generated under pressure in the subsurfacewerecomplex. Fluctuations of subsurface damage depth at transition point were attributed to the deformation of the surface which consumed more energy when the surface deformation changed from the mixed region of brittle and plastic to the complete brittle region along the scratch. Also, the process of subsurface damage from shallow to deep, from dislocation to big crack in KDP crystal with the increase of radial force and etch pit on different crystal plane were obtained. Because crystallographic orientation and processing orientation was different, etching pits on (100) crystal plane were quadrilateral while on (110) plane and (120) plane were trapezoidal and triangular, respectively.     

Instantaneous Point, Line, and Plane Motions Using a Clifford Algebra

The motions of points, lines, and planes, embedded in a rigid body are expressed in a unified algebraic framework using a Clifford algebra. A Clifford algebra based displacement operator is addressed and its higher derivatives from which the coordinate-independent characteristic numbers with simple geometric meaning are defined. Because of the coordinate independent feature, no tedious coordinate transformation typically found in the conventional instantaneous invariants methods is needed.     

Progress in quantitative X-ray microanalysis of frozen-hydrated bulk biological samples

The analysis of bulk frozen-hydrated biological samples has developed now to a level where practical application of the technique is possible. Provided the sample is carefully coated with a conductive metal, the development of a space charge capable of causing a significant distortion of the electron diffusion volume does not seem to occur, and analytical resolution can be conveniently held to approximately 2 μm (both depth and lateral resolution). Two valid quantitative methods are available, and two methods of determining dry weight fractions are also available. An area where further research could lead to improvement in analysis of frozen-hydrated bulk samples is in the investigation of fracturing methods. If fracture planes that were flat and reproducible could be easily obtained, some of the difficulties of analysing frozen-hydrated bulk samples would be considerably reduced.