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41.
低质量指纹图像的特征提取和变形指纹的匹配是当前指纹识别研究中的两个主要问题。很多算法在特征提取时不区分高、低质量区域,结果在高质量区域耗费了过多的运算时间和计算资源。本文提出了一种基于图像质量分区的指纹特征提取方法,先用一种简单的图像区域质量计算方法评价各区域的图像质量,然后对高质量区域直接从灰度图像跟踪纹线、提取节点,对低质量区域执行传统的方向计算、增强、二值化和细化后提取特征。实验结果表明,该方法不仅提高了特征提取的速度,在准确性上也有所提高。 相似文献
42.
Traditionally, for the flat-end tool, due to the intertwined dependence relationship between its axis and reference point, most 5-axis tool-path generation algorithms take a decoupled two-stage strategy: first, the so-called cutter contact (CC) curves are placed on the part surface; then, for each CC curve, tool orientations are decided that will accommodate local and/or global constraints such as minimum local gouging and global collision avoidance. For the former stage, usually simplistic “offset” methods are adopted to determine the cutter contact curves, such as the iso-parametric or iso-plane method; whereas for the latter, a common practice is to assign fixed tilt and yaw angle to the tool axis regardless the local curvature information and, in the case of considering global interference, the tool orientation is decided solely based on avoiding global collision but ignoring important local machining efficiency issues. This independence between the placement of CC curves and the determination of tool orientations, as well as the rigid way in which the tilt and yaw angle get assigned, incurs many undesired problems, such as the abrupt change of tool orientations, the reduced efficiency in machining, the reduced finishing surface quality, the unnecessary dynamic loading on the machine, etc. In this paper, we present a 5-axis tool-path generation algorithm that aims at alleviating these problems and thus improving the machining efficiency and accuracy. In our algorithm, the CC curves are contour lines on the part surface that satisfy the iso-conic property — the surface normal vectors on each CC curve fall on a right small circle on the Gaussian sphere, and the tool orientations associated to a CC curve are determined by the principle of minimum tilt (also sometimes called lead) angle that seeks fastest cutting rate without local gouging. Together with an elaborate scheme for determining the step-over distance between adjacent CC curves that seeks maximum material removal, the presented algorithm offers some plausible advantages over most existing 5-axis tool-path generation algorithms, particularly in terms of reducing the angular velocity and acceleration of the rotary axes of the machine. The simulation experiments of the proposed algorithm and their comparison with a leading commercial CAM software toolbox are also provided that demonstrate the claimed advantages. 相似文献
43.
Part orientation is one of the important factors in manufacturing with three dimensional printing (3DP) of rapid prototyping system. The minimum building time, being achieved by the part’s minimum building height and minimum width in 3DP’s y direction, is set as the objective of optimizing the part orientation. Genetic algorithm is adopted to find the minimum building height of parts and then ergodic searching is used to get the minimum width of part in y direction. A corresponding program for optimizing pa... 相似文献
44.
According to the classic harmonic approach, an orientation density function (odf)f is expanded into its corresponding Fourier orthogonal series with respect to generalized spherical harmonics, and a pole density function (pdf)
into its corresponding Fourier orthogonal series with respect to spherical harmonics. While pdfs are even (antipodally symmetric) functions, odfs are generally not. Therefore, the part
of the odf which cannot be determined from normal diffraction pdfs can be mathematically represented as the odd portion of its series expansion. If the odff is given, the even part
can be mathematically represented explicitly in terms off itself. Thus, it is possible to render maps ofharmonic orientation ghosts, and to evaluatevariants of mathematical standard odfs resulting in identical pdfs independent of pdf data. However, if only normal diffraction pdfs are known, the data-dependentvariation width of feasible odfs remained unaccessible, and within the harmonic approach a measure of confidence in a solution of the pdf-to-odf inversion problem does not exist.According to any discrete approach, an odff defined on some setG of orientations is expanded into its corresponding Fourier orthogonal series with respect to indicator functions of the elements of a partition ofG, and a pdf
defined on the upper (lower) unit hemisphereS
+
3
3 into its corresponding Fourier orthogonal series with respect to indicator functions of the elements of a partition ofS
+
3
. The ambiguity of the pdf-to-odf inversion problem is discussed in terms of column-rank deficiency of the augmented projection matrix. The implication of the harmonic approach to split an odf into auniquely determined and anundetermined part does no longer seem to be reasonable. However, it is possible to numerically determine data-dependent confidence intervals for the Fourier coefficients with respect to the indicator functions which can be immediately interpreted as mean orientation densities within the elements of the partition ofG. Doing so for all Fourier coefficients in the finite series expansion, i.e. for all elements of the partition of the setG, eventually results in the data-dependent variation width of odfs feasible with respect to given pdf data, and to the partitions ofG andS
+
3
.Thus it is confirmed that the appearance of orientation ghosts, in particular correlations oftrue andghost orientation components, depends on the representation of an odf. It may be questioned whether in practical applications the implicit assumption of the harmonic method that the even part
can be determined uniquely and free of error is generally a reasonable initial condition to develop ghost correction procedures. 相似文献
45.
Taiju Takahashi Yukihiro Kudoh Yuichi Saito Yoshihiro Aoyagi 《Journal of the Society for Information Display》2023,31(3):101-111
Recently, there has been considerable research on optical devices, such as liquid crystal (LC) lenses and special optical plates, using LCs. In such devices, relatively small LC cells are frequently used, or unique LC orientations are required. As an LC orientation process, we focused on the LC director's orientation induced by the magnetic force line distribution of a small neodymium magnet. We propose a simple method for obtaining radial orientation, which is rather difficult to obtain using the ordinary rubbing method. The initial orientation in the LC cell is a vertical orientation cell with almost zero azimuth anchoring. With the proposed method, the reorientation process is performed with an assisting electric field and a small permanent magnet, unlike the conventional magnetic field orientation process that requires a large electromagnet. Furthermore, a polymer stabilization treatment is used to fix the obtained radial orientation pattern in the LC cell. After the treatment, the applying voltage can control the tilt angle of the director in weak polymer treatment, and a completely fixed orientation pattern can be obtained that in strong. 相似文献
46.
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48.
Nucleation Crystallography of Ni Grains on CrFeNb Inoculants Investigated by Edge‐to‐Edge Matching Model in an IN718 Superalloy 下载免费PDF全文
Wenchao Yang Pengfei Qu Lin Liu Ziqi Jie Taiwen Huang Feng Wang Jun Zhang 《Advanced Engineering Materials》2018,20(2)
49.
基于情感词典扩展技术的网络舆情倾向性分析 总被引:7,自引:0,他引:7
随着Web2.0时代的到来,网络已逐渐成为反映社会舆情的重要载体之一,网络舆情发现及网民的观点和倾向性挖掘也成为新的研究热点,但是目前尚无有效反应网民对热点事件或话题总体态度的舆情分析系统.本文针对网民关于话题评论简单、数目众多的特点,应用HowNet和NTUSD两种资源对现有情感词典进行扩展,建立了一个新的、具有倾向程度的情感词典.基于扩展的情感词典,开发了一个半自动化网络舆情分析系统.该系统能够为用户提供更加细致、准确的评论倾向性分析结果. 相似文献
50.
当前,随着环境问题的日益突出,要求加强对环境的保护、修复和美化已成为人们实践活动中的一个关键内容,而与解决环境问题紧密相关的环境艺术设计更是责任重大,尤其是在资源型城市(如矿山、油田、旅游区等),要尝试探索如何充分理解自然生态系统运行规律和自然美学价值,宏观地赋予环境艺术设计新的内涵和价值,在功能、形式、生态、经济和人文诸多因素中谋求环境与人的平衡。 相似文献