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EXACT NONREFLECTING BOUNDARY CONDITIONS FOR AN ACOUSTIC PROBLEM IN THREE DIMENSIONS

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Journal of Computational Mathematics 2003年第1期21卷 15-24页

作者： Houde Han Chunxiong Zheng (department of Mathematical sciences,{2., beijing 100084, china) department of Mathematical sciences Tsinghua University 北京 100084

In this paper, nonreflecting artificial boundary conditions are considered for an acoustic problem in three dimensions. With the technique of Fourier decomposition under the orthogonal basis of spherical harmonics, three kinds of equivalent exact artificial boundary conditions are obtained on a spherical artificial boundary. A numerical test is presented to show the performance of the method.

关键词： Exterior problem Nonreflecting artificial boundary condition Acoustic equa-tion Three-dimensions.

Γ-CONVERGENCE OF INTEGRAL FUNCTIONALS DEPENDING ON VECTOR-VALUED FUNCTIONS OVER PARABOLIC DOMAINS

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Chinese Annals of Mathematics,Series B 2000年第2期21卷 249-258页

作者： JIAN HUAIYU(department of Mathematical sciences,{2., beijing 100084, china.) department of Mathematical sciences Tsinghua University Beijing 100084 China

This paper studies Γ-convergence for a sequence of parabolic functionals, where the integrand f is nonconvex, and periodic on the first variable. The author obtains the representation formula of the Γ-limit. The results in this paper support a conclusion which relates Γ-convergence of parabolic functionals to the associated gradiend flows and confirms one of De Giorgi’s conjectures partially.

关键词： Γ-convergence Parabolic-minima Nonconvex functionals Parabolic equations

Generalized gradient projection neural networks for nonsmooth optimization problems

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science china(Information sciences) 2010年第5期53卷 990-1005页

作者： LI GuoCheng 1 , SONG ShiJi 2.? & WU Cheng 2.1 department of Mathematics, beijing Information {2. and Technology university, beijing 100192. china 2.department of Automation, tsinghua university, beijing 100084, china department of Mathematics Beijing Information Science and Technology University Beijing China department of Automation Tsinghua University Beijing China

Generalized gradient projection neural network models are proposed to solve nonsmooth convex and nonconvex nonlinear programming problems over a closed convex subset of R n . By using Clarke’s generalized gradient, the neural network modeled by a differential inclusion is developed, and its dynamical behavior and optimization capabilities both for convex and nonconvex problems are rigorously analyzed in the framework of nonsmooth analysis and the differential inclusion theory. First for nonconvex optimization problems, the quasi convergence results similar to those achieved by previous work are proved. For convex optimization problems, the global convergence results are proved, i.e. any trajectory of the neural network converges to an asymptotically stable equilibrium point, which is an optimal solution of the primal problem whenever it exists. This result remains valid even if the initial condition is chosen outside the feasible set. In addition, an asymptotic control result involving a Tykhonov like regularization shows that any trajectory of the revised neural network can be forced to converge toward a particular optimal solution of the primal problem. Finally, two simulation optimization algorithms for solving the optimization and control problems are designed respectively, and three typical simulation experiments are illustrated to present the accuracy and efficiency of theoretical convergence results of this paper.

关键词： nonsmooth optimization problem generalized gradient projection networks differential inclu sions convergence

THE GLOBAL ARTIFICIAL BOUNDARY CONDITIONS FOR NUMERICAL SIMULATIONS OF THE 3D FLOW AROUND A SUBMERGED BODY

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Journal of Computational Mathematics 2003年第4期21卷 435-450页

作者： Hou-de Han Xin Wen (department of Mathematical sciences,{2., beijing 100084, china) department of Mathematical sciences Tsinghua University 北京 100084

We consider the numerical approximations of the three-dimensional steady potential flow around a body moving in a liquid of finite constant depth at constant speed and distance below a free surface in a channel. One vertical side is introduced as the upstream artificial boundary and two vertical sides are introduced as the downstream artificial boundaries. On the artificial boundaries, a sequence of high-order global artificial boundary conditions are given. Then the original problem is reduced to a problem defined on a finite computational domain, which is equivalent to a variational problem. After solving the variational problem by the finite element method, we obtain the numerical approximation of the original problem. The numerical examples show that the artificial boundary conditions given in this paper are very effective.

关键词： Ship wave Potential flow Global artificial boundary condition Finite element method.

Theoretical research progress in new-generation Internet architecture

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science in china(Series F) 2008年第11期51卷 1634-1660页

作者： WU JianPing1,2.3,LIU Ying2.3 & WU Qian2.3 1 department of Computer science,{2. university,beijing 100084,china 2.Network Research Center,{2. university,beijing 100084,china 3 {2. National Laboratory for Information science and Technology(TNList) ,beijing 100084,china department of Computer science Tsinghua University Beijing China Network Research Center Tsinghua University Beijing China tsinghua National Laboratory for Information science and Technology (TNList) Beijing China

Internet has become the most important information infrastructure supporting modern socio-economic development, social progress and technological Innovation. Invented 30 years ago, today Internet is facing increasingly severe technical challenges. This paper introduces the progress of the major international newgeneration Internet research plans; analyzes its basic characteristics and the principal contradictions during the development; detsiledly introduces the research carried out by 973 Project ＂Research of Future Internet Architecture＂ on the key scientific issues of new-generation Internet architecture and its latest research results; and looks to the future of the research-focus faced with the new situations of the basic research of new-generation Internet architecture as well as the new demands of innovative applications on Internet architecture.

关键词： new-generation Internet network architecture multi-dimension scalability

Effects of Si Content and the Addition Amount of Al-3B Master Alloy on the Solidification Structures of Hypoeutectic Al-Si Alloys

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Rare Metals 2001年第3期20卷 168-173页

作者： Donghui Wang,Jianguo Li, Yankang Zheng, Bingzhe Bai department of Materials science and Engineering,{2., beijing 100084, china 清华大学北京 100084

Effects of Si content and the addition amount of Al-3B master alloy on the solidification structures of hypoeutectic Al-Si alloys were studied. The addition amounts of the master alloy were 0.2., 0.4%, 0.7% and 1% (mass fraction, so as the follows), respectively. The Si content of Al-Si binary alloys investigated varied from 1% to 11%. The observation of macrostructures of non-refined samples showed that 3% Si constitutes a transition point at which the minimum grain size can be obtained. It was also found that Al-3B master alloy can shift the transition point towards a higher Si value when its addition amount increases, making this point appear at 4%, 5% and 6% Si as its addition amount increases up to 0.4%, 0.7% and 1%, respectively.

关键词： Al-3B master alloy hypoeutectic Al-Si alloy grain refinement

HIGH TEMPERATURE OXIDATION AND STRUCTURE OF SCALE AND WHISKERS FOR Fe-Ni-Cr SEALING ALLOYS

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Acta Metallurgica Sinica(English Letters) 1993年第8期6卷 147-150页

作者： DONG Zhili MA Jusheng TANG Xiangyun YOU Liang tsinghua university,beijing,{2. lecturer department of Materials science and Engineering,tsinghua university,beijing 100084,{2. tsinghua Univ Beijing China

The oxidation rate,the growth,morphology and structure of oxide scale and whiskers for Fe-Ni-Cr sealing alloys in H_2.H_2. atmosphere at high temperatures have been studied. The growth rate of scale is controlled by *... 详细信息

关键词： oxidation oxide scale oxide whisker Fe-Ni-Cr sealing alloy

Extremal eigenvalues of measure differential equations with fixed variation

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science china Mathematics 2010年第10期53卷 2573-2588页

作者： ZHANG MeiRong 1,2.1 department of Mathematical sciences,{2. university,beijing 100084,china 2.Zhou Pei-Yuan Center for Applied Mathematics,{2. university,beijing 100084,china department of Mathematical sciences Tsinghua University Beijing China Zhou Pei-Yuan Center for Applied Mathematics Tsinghua University Beijing China

In this paper we will study eigenvalues of measure differential equations which are motivated by physical problems when physical quantities are not absolutely *** taking Neumann eigenvalues of measure differential equations as an example,we will show how the extremal problems can be completely solved by exploiting the continuity results of eigenvalues in weak* topology of measures and the Lagrange multiplier rule for nonsmooth *** results can give another explanation for extremal eigenvalues of SturmLiouville operators with integrable potentials.

关键词： measure differential equation eigenvalue extremal value weak* topology Frechét derivative sub-differential

To enhance the reproduction of Phanerochaete chrysosporium by adding natural lixiviums in liquid medium

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Journal of Environmental sciences 2003年第6期15卷 808-814页

作者： LIN Gang, WEN Xiang-hua, QIAN Yi (department of Environmental science and Engineering,{2., beijing 100084, china. department of Environmental science and Engineering Tsinghua University 北京 100084

Great promotion to the reproduction of white rot fungus Phanerochaete chrysosporium by adding natural lixiviums such as from wood, maize core and potato in liquid medium was found in this research. Incubated in the liquid medium contained 10 mg/L glucose as carbon source with natural lixiviums for three days, the production of mycelium pellet reaches more than 80 g/L, which is 5 times more than that of without natural lixiviums. Incubated in the liquid medium contained 5 mg/L glucose as carbon source with natural lixiviums for three days, the production of mycelium pellet can reach 69.5 g/L, while the production in the medium without natural lixiviums is very low. When the liquid medium contained 1—2. g/L glucose as carbon source, the production of mycelium pellet in 3 d can only reach 12.5 g/L to 14.5 g/L. The fungus in the medium with potato lixiviums are easily contaminated by other microorganisms and in the medium with maize core lixiviums are easily bulking, while in the medium with wood lixiviums are neither easily contaminated nor bulking. Medium with wood lixiviums can produce more pellet than other medium, endure contamination and keep better sedimentation capacity. So that, wood lixivium is better additive to the culture of white rot fungi in liquid medium. Addition of the mixture of wood, maize core and potato lixiviums is of advantage to the production of mycelium pellet. The difference of the production in the medium with different amount of wood lixiviums showed little in the first 3 d, while it expanded after 3 d. Wood lixiviums stimulate the growth of P. chrysosporium instead of supply organics which fungi need.

关键词： white rot fungi medium additive