利用坐标变换分析塔差对编码器测角精度测试的影响

为了实现编码器测角精度的高精度测量,介绍了应用多面棱体和自准直仪组合测量编码器测角精度的原理和方法,建立了多面棱体坐标系和自准直仪测量坐标系,利用坐标变换的方法推导了塔差对测角精度测试结果影响的精确模型。结果表明,编码器转轴的倾斜角度和倾斜方向会影响编码器测角精度的测量结果。测量误差随编码器的倾斜角度的增大而增大,且近似成平方关系。测量误差随随编码器的倾斜方向改变,倾斜方向角为0°或180°时,测量误差最小;倾斜方向角为90°或270°时,测量误差最大。当倾斜角度为5′时,引入的测量误差为0.11″~0.48″,这对于Ⅰ~Ⅲ级编码器的测试是不能忽略的。根据被测编码器的精度等级将塔差控制在恰当的范围内,给出了不同精度等级编码器测试时塔差的控制要求。     

精密光学棱体加工

<正> 随着现代科学技术的发展,光学棱体的应用范围越来越广。例如:固体超声延迟线的十四面体;高速摄影中作为高速曝光器件的十六面体;计量工作中作为角度传递基准的二十四、三十六面体……;以及彩色电视、激光雷达中的专用精密光学棱体等等。下面我们对光学棱体的加工作一探讨。     

晶粒棱长、尺寸与拓扑学特征之间关系的Monte Carlo仿真研究

采用Potts模型Monte Carlo方法研究了晶粒棱长、尺寸与拓扑学特征之间的统计关系.结果表明,晶粒棱长与晶粒面数之间呈线性统计关系,并且平均N面体晶粒模型和Poisson-Voronoi组织均支持该结论.不同时刻的晶粒长大仿真数据表明,在准稳态晶粒长大阶段晶粒棱长的分布具有自相似性.个体晶粒的平均棱长随晶粒面数（或晶粒尺寸）的增加而逐渐增大,这说明一些理论模型中采用的“不同面数的晶粒平均棱长均相等”的假设具有局限性.仿真数据和纯铁实验数据均表明,晶粒尺寸与晶粒面数之间的统计关系表现为一条单调递增的凸曲线. 关键词： 晶粒棱长 晶粒尺寸 拓扑学 Monte Carlo仿真     

具有倾斜校正作用的激光扫描光学系统设计

阐述了用于激光印字机、具有倾斜校正作用的镯面ｆ－θ物镜的激光扫描系统的设计，有效地消除了偏转反射面的倾斜引起的扫描线错位。提出了确定系统主要参数的原则，分析了准直物镜、柱面镜、ｆ－θ物镜、多面棱体转镜等部件的设计问题     

水中悬浮颗粒的三维体散射函数测量

提出了一种水中悬浮颗粒的三维体散射函数测量方法,采用抛物面镜结合传感器探测方式,同时获取了半球空间内多个散射面所对应的体散射函数。搭建了三维体散射函数测量装置,采用粒径为57~954nm的标准聚苯乙烯颗粒作为样本,获得了方位角0°~180°对应的多个散射面内的水中颗粒体散射函数,测量的散射角范围为18°~160°。实验结果与计算结果吻合,验证了利用该装置对水体中粒径小于1μm的悬浮颗粒的体散射函数进行测量的可行性。     

多光谱多点标定的CCD二维温度场重建方法的研究

以多光谱技术作为基础,针对CCD二维温度场测量的特点,提出了彩色CCD二维温度场多光谱真温在线多点标定系统。通过对多光谱辐射测温理论和CCD的测量模型的分析,推导出气体燃烧时的真温与CCD亮度之间的近似关系。使用多光谱多点测温技术计算出多点的发射率和真温并使用这些真温值完成CCD面阵上与之对应点的真温标定。将该真温标定系统应用于CO₂激光焊接火焰的二维温度场测量过程中,不但得到了波长与光谱发射率之间的变化规律同时也得到了CO₂激光焊接火焰的二维真温分布图。研究提出的多光谱标定技术具有实时性、灵活性的特点, 是一种可行的CCD在线真温多点标定与测量的方法。     

多个CCD交汇测量系统的理论研究

本文介绍了采用多个线阵ＣＣＤ 组成交汇测量系统的基本原理,导出了测量坐标的计算公式,并利用有关的误差理论对该方法的测量精度进行了详细分析。研究结果表明,多个ＣＣＤ 交汇测量系统能够得到较高的目标捕获几率,同时还能有效地提高坐标测量精度。对大靶面、高速小目标物体的精密测量具有重要意义     

瞬时多光谱辐射测温方法

采用光学多道分析仪测量了溴钨灯和氙闪光灯的辐射光谱,给出了一种辐射测温的数据处理方法,即在Planck灰体模型假定的基础上,进一步考虑发射率ε与波长的多项式依赖关系以及辐射本底对实验结果的影响,建立相应的多光谱测温数据处理方法,并用溴钨灯和氙闪光灯的实测光谱对其进行了验证.结果表明:对于连续光谱且发射率逼近黑体,可以假定发射率为常量,按Planck灰体模型处理;对于非连续光谱,当电流密度不高时,发射率与波长依赖关系较强,可以根据发射率与依赖波长的多项式关系并结合0＜ε＜1限定按Planck灰体模型处理.     

基于多面体重叠网格的多体分离计算分析

分离问题在航空航天领域频繁出现,对各类运载火箭、飞行器等完成任务使命至关重要,并事关主体/分离体的安全。基于带边界层加密的多面体网格、重叠网格和刚体六自由度运动方程,利用CFD数值模拟方法,对某标模外形开展了多体分离数值模拟,研究了不同初始弹射力对多体分离安全性的影响,从纵向和横航向两方面分析了标模的分离特性及与弹射力的关系,对工程研究有一定的参考作用。     

多段电容式锅炉液位测量系统设计

由于传统的锅炉汽包水位测量多采用差压式水位计、云母水位计等方法,测量过程中存在汽水分界面不明显,需要温度、压力补偿及投入麻烦等缺陷,为解决上述问题,提出了一种基于电容数字转换技术专用芯片Pcap01的智能多段式液位测量系统,并且应用HART通讯单元访问传感器的测量过程参数、设备组态、校准等信息。对多段电容式液位测量系统的总体方案、传感器设计、电容测量电路、HART通讯电路的设计进行了详细论述,同时设计了HART通讯软件和液位测量采集软件。对所设计的多段电容式锅炉液位测量系统经过试验表明,该液位计精度高、操作简单方便,解决了传统液位测量的缺陷,可以满足实际现场要求。     

Spectrum of a particle on a polyhedron enclosing a synthetic magnetic monopole

We consider a single particle hopping on a tight binding lattice formed by the vertices of a regular polyhedron and discuss the effect of a magnetic monopole enclosed in the polyhedron. The presence of the monopole induces phases on the hopping terms, given by Peierls substitution. By requiring the flux through each face of a regular polyhedron to be the same, Dirac’s quantization condition is obtained in this discrete setting. For each regular polyhedron, we calculate the energy spectrum for an arbitrary value of the flux through a Dirac string coming in from one of the faces. We find that the energy levels are degenerate only when the flux through the Dirac string corresponds to a quantized monopole. We show that the degeneracies in the presence of the monopole can be classified using the double group of the symmetry of the polyhedron and label all energy levels with corresponding irreducible representations.     

Isotropic filtering using polyhedral phase cycles: application to singlet state NMR

A technique is described for filtering out the components of an NMR signal that have passed through an isotropic spin order term. The method involves a coordinated cycle of three radiofrequency phase angles, where two of the phases correspond to the polar angles describing the vertices of a regular polyhedron, and the third angle is stepped around a circle. The most economical isotropic filtering scheme involves a 12-step phase cycle based on tetrahedral symmetry. The method is used to filter out NMR signals that have passed through singlet populations in a solution NMR experiment.     

Construction of the Dirichlet–Voronoi translation-compatible polyhedrons based on the Zelling parameters

A method of constructing the Dirichlet–Voronoi translation-compatible polyhedrons for sublattices of complex crystal compounds is presented. With the use of the Zelling parameters, this problem is reduced to a linear programming problem which can be solved on a personal computer for a finite ratio of translation-compatible polyhedron volumes. Particular solutions are derived for cubic and tetragonal systems with different orientations of the Bravais frame and polyhedron types.     

Dynamics of entanglement of bosonic modes on symmetric graphs

We investigate the dynamics of an initially disentangled Gaussian state on a general finite symmetric graph. As concrete examples we obtain properties of this dynamics on mean field graphs (also called fully connected or complete graphs) of arbitrary sizes. In the same way that chains can be used for transmitting entanglement by their natural dynamics, these graphs can be used to store entanglement. We also consider two kinds of regular polyhedron which show interesting features of entanglement sharing.     

Refinement of hydrogen positions in Phase II of β-LiNH4SO4

The atomic positions and thermal parameters of the crystal structure for phase II of β-LiNH₄SO₄ are determined from single crystal neutron diffraction data at room temperature to refine N-H bond lengths for ammonium ions. The neutron data are collected using an E5 diffractometer in BENSC (HMI, Berlin, Germany). Atomic positions and thermal parameters are determined by the least-squares method up to R = 0.072 and wR = 0.057. It is shown that an ammonium ion polyhedron is the regular tetrahedron. The text was submitted by the authors in English.     

Molecular dynamics simulation of polyhedron analysis of Cu–Ag alloy under rapid quenching conditions

In this study, the formation mechanism of polyhedron clusters in Cu₅₀Ag₅₀ binary alloy system consisting of 50 000 atoms has been investigated by using molecular dynamics simulations based on embedded atom method (EAM) during the rapid cooling processes. The cluster-type index method (CTIM) has been used to describe the evaluation properties of clusters and the structural development has been investigated by using radial distribution function (RDF). The simulation results show that the amorphous phase is formed by the main bonded pairs of 1551, 1541 and 1431 in the system, and ideal icosahedral (icos) cluster (12 0 12 0) and other basic polyhedron clusters, such as defective icos, Frank–Kasper, Bernal polyhedron, play a critical role under the rapid cooling conditions. The results of our simulations that have been disclosed show that high cooling rate favors the icos and defective icos clusters for model alloy system.     

Classifying novel phases of spinor atoms

We consider many-body states of bosonic spinor atoms which, at the mean-field level, can be characterized by a single-particle wave function for the Bose-Einstein condensation and Mott insulating states. We describe and apply a classification scheme that makes explicit the spin symmetries of such states and enables one to naturally analyze their collective modes and topological excitations. Quite generally, the method allows classification of a spin F system as a polyhedron with 2F vertices. We apply the method to the many-body states of bosons with spins two and three. For spin-two atoms we find the ferromagnetic state, a continuum of nematic states, and a state having the symmetry of the point group of the regular tetrahedron. For spin-three atoms we obtain similar ferromagnetic and nematic phases as well as states having symmetries of various types of polyhedra with six vertices.     

Atomic-core dynamics and the electronic structure of some endo-and exohedral complexes of fullerenes with light elements

The atomic and electronic structure of some endo-, exo-, and endo-exohedral complexes of the fullerene C₆₀ with various guest atoms and molecules (He_n, H₂, and Li₂) are investigated using semiempirical and nonempirical quantum-chemical methods. The atomic core dynamics is studied by the method of molecular dynamics. It is shown that guest atoms and molecules in fullerene polyhedra acquire an orbital angular momentum due to the correlated motion of nuclei above the low-energy barriers of the potential surface within the carbon polyhedron even at low temperatures (from 4 to 78 K). The emergence of orbital angular momenta of nuclei of guest atoms and molecules is attributed to a change in the contribution of the orbital angular momentum of electrons to the potential surface of the complexes. The motion of Li ions in a polyhedron leads to blurring of the top of the valence band and to the emergence of a charge polarization wave in the carbon polyhedron.     

Visualization of conduction channels and the dynamics of ion transport in superionic conductors

A method for visualizing conduction channels is proposed. This method is based on graphical analysis of conduction channel fragments which belong to a Voronoi-Dirichlet elementary polyhedron and lie outside the rigid sphere centered at a fixed-sublattice ion that is located at the geometric center of the elementary polyhedron under consideration. Taking into account the weak nonrigidity of spheres and root-mean-square displacements of ions in the fixed sublattice makes it possible to construct a channel as the surface of the mobile ion density. The most probable regions of mobile ion motion are quantum-mechanically interpreted as channel walls, which is confirmed by constructing the equipotential surfaces of interionic potential for α-AgI. It is found that the Andersson mathematical dynamics and the dynamics of ion transport in AgI lead to the same pattern of the motion. The symmetry rules are used for predicting the directions of motion along the allowed vibrational coordinates of tetrahedral and octahedral α-CuI fragments.     

Electron-phonon interactions in bct white tin

The electron-phonon interactions are evaluated exactly over the actual shape of the atomic polyhedron as well as the lattice polyhedron of diatomic white tin by making use of simple coordinate axes transformations and crystal symmetry. It is shown that the expressions for the interference factor,S(q, t) of the atomic polyhedron are complex while those for the lattice polyhedron are real and the reciprocal lattice vectors derived from the former do not correspond to those derived either from the latter or from x-ray structure factors. By comparing these expressions with each other as well as with those obtained by approximating these polyhedra by an ellipsoid of equivalent volume, apparent differences between the interference factors of atomic and lattice polyhedra, consequent ambiguity regarding the shape and size of the first Brillouin zone of white tin, validity of the Wigner-Seitz approximation for a diatomic lattice and the manner in which the electron-phonon interactions contribute to acoustical and optical modes of vibration are discussed.