Vanishing point detection using cascaded 1D Hough Transform from single images

Vanishing point detection algorithms based on 2D histogramming techniques have been employed in a variety of computer vision systems. Previous algorithms achieved some good results but still failed to maintain a balanced performance in both accuracy and time. Recent research (Li et al., 2010) shows that, vanishing point detection could be converted to a 1D histogram search problem, which largely accelerates the procedure. In this paper, we further improve this idea and propose a complete scheme for vanishing point detection from images of the so called “Manhattan world”. We test our algorithm and some commonly used vanishing point detection methods on public database YorkUrbanDB and our own implemented database PKUCampusDB. Our algorithm shows significant performance improvements.     

地图投影的拓扑学原理

根据拓扑映射的定义,指出了“刺孔球面”（S2-｛z｝）与二维平面R2的同胚性质。从有限闭区间及其彼此等势的拓扑学原理,推出f（A）为非空集。f（A）的边界是二维平面上的约当闭曲线,约当闭曲线的任意性,使得f（A）可以在拓扑变换下变形为任意的形状,构造多种多样的投影网格。以若干实例说明了拓扑映射ff1、f2的实现方法。     

Rank-1 constraint for camera calibration based on spheres

With the rank-1 constraint, a method for camera intrinsic parameters calculation based on spheres is proposed. The geometric interpretation of the rank-1 constraint is explored from the relation of the image of the absolute conic and the sphere image. Three algebraic equations are derived from the rank-1 constraint. The relation of the sphere images and the camera intrinsic parameters is clearly interpreted in vision geometry. Finally, a nonlinear optimized method is used with the three constraint equations for improving the accuracy. Experimental results show that our method is robust. Compared with the traditional method, it can improve the accuracy of the results of the intrinsic parameters.     

3D numerical simulation of the behaviour of a spherical particle suspended in a Newtonian fluid and submitted to a simple shear

The 3D flow around a rigid spherical particle suspended in a Newtonian fluid and submitted to simple shear is numerically studied using Rem3D^® finite element code. The sphere motion is imposed by a sticking contact between the sphere and the fluid. The effect of the particle size as compared with the finite dimension of the shear cell was investigated. The direct calculations show that 3D modelling is necessary to correctly predict the sphere behaviour. The proximity of the particle and the cell walls strongly affects the flow velocities, the sphere motion (increase of the rotation period of the sphere) and the stress field (change of orientation angle and increase of maximal local stresses).     

Fabrication of nanoscaled silica layer on the surfaces of submicron SiO2-Ag core-shell spheres

A two-step silica deposition process, including prefunctionalization with poly(vinylpyrrolidone) and the following silica deposition, has been used to fabricate silica layer on the surface of nanoscaled silver shell. The influencing parameters of silica coating process were optimized to prevent the precoated silver nanoparticles from desquamating from silica spheres, finally to obtain mono-dispersed silica spheres with silver and silica multilayer films. The resulted silica layer was dense and uniform, its thickness was controllable in the range of 20–50 nm. Such coated silica layer can provide improved thermal stability of the SiO₂-Ag core-shell structural spheres.     

N元光纤光栅传感器阵列解调信号的最低可见度分析

研究了非平衡光纤Mach-Zehnder干涉仪解调N元光纤光栅传感器阵列时的偏振衰落问题．运用邦加球和光纤偏振光传输理论，利用简化模型，通过详细的理论分析，得到优化控制下阵列传感信号最低可见度的下限表达式，并通过计算机仿真，验证了结果的正确性，并详细分析了仿真实验的结果．     

中间主应力对球形孔扩张的影响

基于Mohr—Coulomb理论推导的球形孔扩张问题的弹塑性解没有考虑中间主应力的影响。因而与实际结果有误差。为此，本文利用双剪强度理论建立了球形孔扩张问题时的弹塑性解。通过算例表明：基于双剪强度理论所求的球形孔扩张的塑性区半径小于M—C准则。据此可充分发挥材料自身的承载能力，减少支护，对实际工程具有重要的理论和实际意义。     

水平气力输送系统中颗粒波状流的模拟

对用于两相流计算的硬球模型进行简化，模拟了水平气力输送系统中颗粒波的动态流型。模型中，气体状态由两相耦合的Navier—Stokes方程描述，颗粒运动通过单颗粒的运动轨迹描述。并且，颗粒的碰撞运动由冲量守恒原理控制，颗粒的悬浮运动由力平衡方程决定，相间耦合作用依据牛顿第三定律处理。模拟结果从介观层次呈现了水平气力输送系统中与实验特征吻合的颗粒波状流，说明了颗粒波的传播速度取决于气体速度，它并不敏感地依赖于系统中的存料量及物料密度。     

离焦和球差效应对高分辨率电镜性能参数的影响

从离焦效应和球差效应出发，分析了它们对高分辨率电子显微镜分辨率和通带宽度的影响。得出了最佳欠焦量下分辨率与球差系数和电子波长的关系．在最佳欠焦条件下，分辩率与球差系数的-1/4次方成正比，与电子波长的-3/4次方成正比，通带宽度随欠焦量绝对值的增大而减小．     

钒球的中子倍增率与活化反应率

以一直径138cm的聚乙烯球作为中子慢化剂与全吸收探测器，采用全吸收法测量了钒球的14MeV中子的泄漏倍增率。用1支与H对热中子具有相同1／V吸收规律的^6Li玻璃探测器的测量子全吸收体的径向中子计数率分布。实验得到了钒球中心D－T中子时的Al、Fe、In和V一组阈探测器的绝对活化反应率的分布。用MCNP／4A程序、ENDF／B－Ⅵ和FENDL－2核数据进行了模拟计算。与实验结果相比较可知：用ENDF／B－Ⅵ库数据的计算结果与实验结果符合良好，而用FENDL－2库数据的计算结果比实验结果约高4％。