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Numerical study of point spread function of a fast neutron radiography system based on scintillating-fiber array

Science China(Physics,Mechanics & Astronomy) 2007年第6期50卷 698-706页

作者： ZHANG FaQiang1,LI ZhengHong1,YANG JianLun1,YE Fan1,2,WANG Zhen1,2,XIA GuangXin1,YING ChunTong2 & LIU GuangJun2 1 Institute of Nuclear Physics and Chemistry,Mianyang 621900,China 2 Department of Engineering Physics,Tsinghua University,Beijing 100084,China Institute of Nuclear Physics and Chemistry Mianyang China Department of Engineering Physics Tsinghua University Beijing China

For a scintillating-fiber array fast-neutron radiography system,a point-spread-function computing model was introduced,and the simulation code was developed. The results of calculation show that fast-neutron radiographs vary with the size of fast neutron sources,the size of fiber cross-section and the imaging geometry. The results suggest that the following qualifications are helpful for a good point spread function: The cross-section of scintillating fibers not greater than 200 μm×200 μm,the size of neutron source as small as a few millimeters,the distance between the source and the scintillating fiber array greater than 1 m,and inspected samples placed as close as possible to the array. The results give suggestions not only to experiment considerations but also to the estimation of spatial resolution for a specific system.

关键词： fast neutron radiography, scintillating-fiber array, point spread function, Monte Carlo simulation For a scintillating-fiber array fast-neutron radiography system, a point-spread- function computing model was introduced, and the simulation code was developed. The results of calculation show that fast-neutron radiographs vary with the size of fast neutron sources, the size of fiber cross-section and the imaging geometry. The results suggest that the following qualifications are helpful for a good point spread function: The cross-section of scintillating fibers not greater than 200μm×200μm, the size of neutron source as small as a few millimeters, the distance between the source and the scintillating fiber array greater than 1 m, and inspected samples placed as close as possible to the array. The results give suggestions not only to experiment considerations but also to the estimation of spatial resolution for a specific system.……

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Average number of iterations of some polynomial interior-point——Algorithms for linear programming

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Science China Mathematics 2000年第8期43卷 829-835页

作者：黄思明 Institute of Policy and Management Chinese Academy of Sciences Beijing 100080 China

We study the behavior of some polynomial interior-point algorithms for solving random linear programming (LP) problems. We show that the average number of iterations of these algorithms, coupled with a finite termination technique, is bounded above by O( n1.5). The random LP problem is Todd’s probabilistic model with the standard Gauss distribution.

关键词： linear programming interior point algorithms probabilistic LP models average number of itera-tions.

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A ROBUST INTERIOR point METHOD FOR COMPUTING THE ANALYTIC CENTER OF AN ILL-CONDITIONED POLYTOPE WITH ERRORS

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Journal of Computational Mathematics 2019年第6期37卷 843-865页

作者： Zhouhong Wang Yuhong Dai Fengmin Xu School of Science Beijing Jiaotong UniversityBeijing 100044China LESC ICMSECAcademy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190and School of Mathematical SciencesUniversity of Chinese Academy of Sciencest Beijing 100049China School of Economics and Finance Xi'an Jiaotong UniversityXi'an 710061China

In this paper we propose an efficient and robust method for computing the analytic center of the polyhedral set P={x€R^n|Ax=b,x>0},where the matrix A€ Rm×n is ill-conditioned,and there are errors in A and b.Besides overcoming the difficulties caused by ill-cond计ioning of the matrix A and errors in A and b,our method can also detect the infeasibility and the unboundedness of the polyhedral set P automatically during the compu tation.Det ailed mat hematical analyses for our method are presen ted and the worst case complexity of the algorithm is also given.Finally some numerical results are presented to show the robustness and effectiveness of the new method.

关键词： Analytic center Ill-conditioning Unboundedness Primal-dual interior point algorithm Convergence Polynomial complexity

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Single-point and Filtered Relative Position Estimation for Visual Docking

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Computer Modeling in Engineering & Sciences 2016年第2期111卷 147-169页

作者： Dylan Conway Daniele Mortari Aerospace Engineering Texas A&M UniversityCollege Station77843

This paper presents a new method to estimate position from line-ofsight measurements to known targets when attitude is known.The algorithm has two stages.The first produces a closed-form unbiased estimate for position that does not account for the measurement error covariance.The second stage is iterative and produces an estimate of position that explicitly accounts for the measurement error covariance and the coupling between measurement error and sensor-to-target distance.The algorithm gives an accurate estimate of both position and the corresponding position error covariance and has a low computational cost.The computational complexity is O(n)for n point-targets and only a 3×3 linear system must be solved.The algorithm is demonstrated for single-point position estimation to verify the accuracy of the resulting position and covariance.Significant improvements over current methods are shown through statistical tests.The algorithm is then demonstrated in the context of sequential filtering for space vehicle docking.

关键词： Visual point algorithm

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The Brouwer fixed point theorem and tetragon with all vertexes in a surface

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Science China Mathematics 1999年第1期42卷 18-25页

作者：麦结华 Institute of Mathematics Shantou University Shantou China

Let D be a disc with radius r in the Euclidean plane R2, and let F be a Lipschitz continuous real valued function on D. Suppose A1A2A3A4 is an isosceles trapezoid with lengths of edges not greater than r, and ∠A1A2A3=α≤π/2. By means of the Brouwer fixed point theorem, it is proved that if F has a Lipschitz constant λ≤min{1, tgα}, then there exist four coplanar points in the surface M = {（x, y, F（x, y））∈R3: （x, y）∈D}which span a tetragon congruent to A1A2A3A4. In addition, some further problems are discussed.

关键词： surface Lipschitz constant continuous functional homotopy mapping degree Brouwer fixed point theorem.

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A novel method to avoid turning point singularities for the semi-regular hexagons Gough-Stewart parallel manipulator

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Science China(Technological Sciences) 2008年第7期51卷 897-910页

作者： WANG YuXin LI YuTong PAN ShuangXia College of Mechanical Engineering&Energy Zhejiang UniversityHangzhou 310027China

This paper presents a novel disturbance function method to avoid turning point singularities for the semi-regular hexagons 6-SPS Gough-Stewart manipulator. Through analysis of the configuration bifurcation characteristics of the manipulator at the type-II singular points, it is found that the type-II singularities under signal input parameter belong to turning point bifurcation. The configuration patterns for the manipulator to pass through the turning points are divided into three types: persistent, non-persistent and path configuration. Utilizing the universal unfolding approach, the configuration bifurcation characteristics under the perturbation pa- rameters applied to the extendable legs are analyzed. The investigation reveals that all configuration branches converged in the same singular point in the unperturbed system will be separated in the disturbed system. Based on this discovery, a novel method for the parallel manipulator to pass through the singular points with the desired configuration is presented. Then the disturbance functions for the manipulator to pass through the turning points with the persistent configuration and the non-persistent configuration are constructed. The method presented in this paper can be applied to avoiding the singularities in such cases where the path and orientation of the manipulator are strictly programmed.

关键词： parallel manipulator turning point singularity disturbance function

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Third-order point contact approach for five-axis sculptured surface machining using non-ball-end tools (Ⅰ): Third-order approximation of tool envelope surface

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Science China(Technological Sciences) 2010年第8期53卷 1904-1912页

作者： ZHU LiMin1, DING Han2 & XIONG YouLun2 1 State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China 2 State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong University Shanghai China State Key Laboratory of Digital Manufacturing Equipment and Technology Huazhong University of Science and Technology Wuhan China

In this paper, the geometric properties of a pair of line contact surfaces are investigated. Then, based on the observation that the cutter envelope surface contacts with the cutter surface and design surface along the characteristic curve and cutter contact (CC) path, respectively, a mathematical model describing the third-order approximation of the cutter envelope surface according to just one given cutter location (CL) is developed. It is shown that at the CC point both the normal curvature of the normal section of the cutter envelope surface and its derivative with respect to the arc length of the normal section can be determined by those of the cutter surface and design surface. This model characterizes the intrinsic relationship among the cutter surface, cutter envelope surface and design surface in the neighborhood of the CC point, and yields the mathematical foundation for optimally approximating the cutter envelope surface to the design surface by adjusting the cutter location.

关键词： five-axis NC machining rotary cutter cutter envelope surface normal curvature third-order point contact

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On Generalized Algebraic Cone Metric Spaces and Fixed point Theorems

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Chinese Annals of Mathematics,Series B 2019年第3期40卷 429-438页

作者： Qing MENG School of Mathematical Sciences Qufu Normal University

In this paper, the author first introduces the concept of generalized algebraic cone metric spaces and some elementary results concerning generalized algebraic cone metric spaces. Next, by using these results, some new fixed point theorems on generalized(complete) algebraic cone metric spaces are proved and an example is given. As a consequence, the main results generalize the corresponding results in complete algebraic cone metric spaces and generalized complete metric spaces.

关键词： Generalized algebraic cone metric space Canonical decomposition Fixed point

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A forcing relation of braids from Nielsen fixed point theory

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Science China Mathematics 2019年第9期62卷 1799-1806页

作者： Jiaoyun Wang Xuezhi Zhao School of Science Tianjin Chengjian UniversityTianjin300384China Department of Mathematics Capital Normal UniversityBeijing100048China

In this paper, we focus our attention on the connections between the braid group and Nielsen fixed point theory. A new forcing relation between braids is introduced, and we show that it can be fulfilled by using Niels... 详细信息

关键词： braid group fixed point disk fundamental group

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Simulation of Dynamic 3D Crack Propagation within the Material point Method

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Computer Modeling in Engineering & Sciences 2017年第4期113卷 389-410页

作者： Y.J.Guo J.A.Nairn Univ.of Utah Salt Lake CityUT 84112USA2119 Hillside Oak LnHoustonTX 77062USA Wood Science&Engineering Oregon State UniversityCorvallisOR 97330USA

This paper presents the principles and algorithms for simulation of dynamic crack propagation in elastic bodies by the material point method(MPM),from relatively simple two-dimensional cases to full three-dimensional,mixed-mode crack propagation.The paper is intended to give a summary of the latest achievements on simulation of three-dimensional dynamic crack propagation,which is essentially an unexplored area.Application of the methodology presented in this paper to several dynamic crack propagation problems has shown that the MPM is a reliable and powerful approach for simulating three-dimensional,mixed-mode crack propagation.

关键词： Material point method (MPM) dynamic fracture crack propagation threedimensional cracks mixed-mode

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