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KEYHOLE IMAGE PROCESSING OF VARIABLE POLARITY PLASMA ARC WELDING BASED ON WAVELET TRANSFORM

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Chinese Journal of Mechanical Engineering 2001年第1期14卷 62-66+73页

作者： Liu Zhonghua Wang Qilong Zhu Jiaqi Welding department, Harbin institute of technology 哈尔滨工业大学黑龙江哈尔滨

In order to realize the feedback control for variable polarity plasma arc welding (VPPAW) formation in the welding process, the geometrical sizes of the keyhole image must be extracted. With the properties of multiscale edge through the wavelet theory, the edge points were detected by getting the maximum modules of the gradient vector in the dircetion towards which the gradient vector points in the image plane. At coarse scales, the local maxima of modules have different positions and only detected the sharp edge. At fine scale, there are many maxima created by the image noise. The best scale where the edges are well discriminated from noises is discussed by the multiscale transform. At last, a new method of peak analysis for threshold selection is provided. It is based on the wavelet transform which provides a multiscale analysis of the information of the histogram. Many experiments show these ways are effective for the keyhole image to get the geometry parameters of the keyhole in the real time VPPAW image processing.

关键词： PAW Variable polarity Keyhole Image

Chaotic attitude and reorientation maneuver for completely liquid-filled spacecraft with flexible appendage

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Acta Mechanica Sinica 2009年第2期25卷 271-277页

作者： B. Yue department of Mechanics, School of Science,Beijing institute of technology, 100081 Beijing, China department of Mechanics School of Science Beijing Institute of Technology 100081 Beijing China

The present paper investigates the chaotic attitude dynamics and reorientation maneuver for completely viscous liquid-filled spacecraft with flexible appendage. All of the equations of motion are derived by using Lagrangian mechanics and then transformed into a form consisting of an unperturbed part plus perturbed terms so that the system＇s nonlinear characteristics can be exploited in phase space. Emphases are laid on the chaotic attitude dynamics produced from certain sets of physical parameter values of the spacecraft when energy dissipation acts to derive the body from minor to major axis spin. Numerical solutions of these equations show that the attitude dynamics of liquid-filled flexible spacecraft possesses characteristics common to random, non- periodic solutions and chaos, and it is demonstrated that the desired reorientation maneuver is guaranteed by using a pair of thruster impulses. The control strategy for reorientation maneuver is designed and the numerical simulation results are presented for both the uncontrolled and controlled spins transition.

关键词： Nonlinear attitude dynamics Attitude reorientation maneuver Control strategyLiquid-filled spacecraft

EXPONENTIAL STABILITY OF A REPARABLE MULTI-STATE DEVICE

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Journal of Systems Science & Complexity 2007年第3期20卷 437-443页

作者： Weiwei HU Houbao XU Jingyuan YU Guangtian ZHU Beijing institute of information and Control Beijing 100037 China. department of mathematics Beijing Institute of Technology Beijing 100081 China. Academy of mathematics and Systems Science Chinese Academy of Sciences Beijing 100080 China.

The exponential stability of a multi-state device is discussed in this paper. We present that the Co-semigroup generated by the system operator is quasi-compact and irreducible. It is known that 0 is a simple eigenvalue of the system operator. In combination with this, we obtain that the time-dependent solution exponentially converges to the steady-state solution, which is the positive eigenfuction corresponding to the simple eigenvalue O.

关键词： C0-semigroup exponential stability irreducibility quasi-compact.

Moving Symplectic Curves in Kahler-Einstein Surfaces

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Acta Mathematica Sinica,English Series 2000年第4期16卷 5+542-548页

作者： Jingyi Chen Gang Tian department of mathematics. The University of British Columbia. Vancouver. B. C. V6T1Z2 Canada department of mathematics. Massachusetts institute of technology. Cambridge. MA 02139 U.S.A. department of mathematics The University of British Columbia Vancouver B. C. V6T 1Z2 Canada department of mathematics Massachusetts Institute of Technology Cambridge MA 02139 U.S.A.

We derive a parabolic equation for the Kahler angle of a real surface evolving under the mean curvature How in a Khler-Einstein surface and show that symplectic curve remains symplectic with the How.

关键词： Mean curvature flow Kahler angle Symplectic curve

NEW DESIGN AND ANALYSIS OF FINITE DIFFERENCE DOMAIN DECOMPOSITION ALGORITHM FOR THE TWO-DIMENSIONAL HEAT EQUATION

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Journal of Systems Science & Complexity 2010年第2期23卷 403-412页

作者： Zhengsu WAN Baolin ZHANG Guangnan CHENG department of mathematics Itunan Institute of Science and Technology Yueyang 414006 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China.

It is presented in this paper that the new design and its analysis of finite difference domain decomposition algorithms for the two-dimensional heat equation, and the numerical results have shown the stability and accuracy of the algorithms, where SauFyev asymmetric schemes have been used at the interface points. The Algorithm II in this paper has further extended those developed by Dawson and the others, Zhang and Shen.

关键词： Domain decomposition finite difference Saul'yev schemes two-dimensional heat equation

Gradient Estimates for the Heat Kernels in Higher Dimensional Heisenberg Groups

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Chinese Annals of mathematics,Series B 2010年第3期31卷 305-314页

作者： Bin QIAN department of mathematics and Statistics, Changshu institute of technology, Changshu 215500, Jiangsu, China Institut de Math′ematiques de Toulouse, Universit′e de Toulouse, CNRS 5219, France. department of mathematics and Statistics Changshu Institute of Technology Changshu 215500 Jiangsu China Institut de Mathématiques de Toulouse Université de Toulouse CNRS 5219 France

The author obtains sharp gradient estimates for the heat kernels in two kinds of higher dimensional Heisenberg groups -- the non-isotropic Heisenberg group and the Heisenberg type group Hn,m. The method used here relies on the positive property of the Bakry-Emery curvature F2 on the radial functions and some associated semigroup technics.

关键词： Gradient estimates Г2 curvature Heat kernels Sublaplace Heisenberg group

Gerbes and twisted orbifold quantum cohomology

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Science China mathematics 2008年第6期51卷 995-1016页

作者： PAN JianZhong~1 RUAN YongBin~(2,3) YIN XiaoQin~(1,3+) 1 institute of mathematics,Academy of mathematics and Systems Science,Chinese Academy of Sciences,Beijing 100080,China 2 department of mathematics,University of Wisconsin-Madison,WI 53706,USA 3 department of mathematics,The Hong Kong University of Science and technology,Hong Kong,China institute of mathematics Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing 100080 China department of mathematics University of Wisconsin-Madison WI 53706 Madison USA department of mathematics The Hong Kong University of Science and Technology Hong Kong China

In this paper,we construct an orbifold quantum cohomology twisted by a flat gerbe. Then we compute these invariants in the case of a smooth manifold and a discrete torsion on a global quotient orbifold.

关键词： gerbe orbifold quantum cohomology 53D45

On the coupled NBEM and FEM for a class of nonlinear exterior Dirichlet problem in R^(2*)

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Science China mathematics 2004年第z1期47卷 181-189页

作者： WU Zhengpeng, KANG Tong & YU Dehaoinstitute of Computational mathematics and Scientific/Engineering Computing, Academy of mathematics and System Sciences, Chinese Academy of Sciences, Beijing 100080, China department of Applied mathematics, Beijing Broadcasting institute, Beijing 100024, China Combinatorial and Computational mathematics Center, Pohang University of Science and technology, Phoang 790-784, Republic of Korea Chinese Acad Sci Acad Math & Syst Sci Inst Computat Math & Sci Engn Comp Beijing 100080 Peoples R China Beijing Broadcasting Inst Dept Appl Math Beijing 100024 Peoples R China Pohang Univ Sci & Technol Combinatorial & Computat Math Ctr Phoang 790784 South Korea

In this paper, based on the natural boundary reduction advanced by Feng and Yu, we couple the finite elementapproach with the natural boundary element method to study theweak solvability and Galerkin approximation of a class ofnonlinear exterior boundary value problems. The analysis is mainlybased on the variational formulation with *** provethe error estimate of the finite element solution and obtain theasymptotic rate of convergence. Finally, we also give anumerical example.

关键词： natural boundary integral method, finite element method, coupling method, error estimate.

THE　OPTIMAL　CONTROL　OF　AGE－DEPENDENT　POPULATION　DYNAMICS　BASED　ON　PARITY　PROGRESSION

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Systems Science and Mathematical Sciences 1996年第4期9卷 333-344页

作者： GUO Baozhu(department of Applied mathematics, Beijing institute of technology, Beijing 100081, China)WU Guofu(institute of Applied mathematics, Academia Sinica, Beijing 100080, China) department of Applied mathematics Beijing Institute of Technology Beijing 100081 China op.uky.edu

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关键词： Optimal birth number control age-structured population parity ratio progression model maximum principle.