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Boundary element-free method for elastodynamics

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Science China(Physics,Mechanics & Astronomy) 2005年第6期48卷 641-657页

作者： CHENG Yumin1 & PENG Miaojuan2.1. shanghai Institute of Applied Mathematics and Mechanics, shanghai university, shanghai 2.0072. China 2. department of Civil Engineering, shanghai university, shanghai 2.0072. China 1. shanghai Institute of Applied Mathematics and Mechanics Shanghai University 200072 Shanghai China 2. department of Civil Engineering Shanghai University 200072 Shanghai China

The moving least-square approximation is discussed first. Sometimes the method can form an ill-conditioned equation system, and thus the solution cannot be obtained correctly. A Hilbert space is presented on which an orthogonal function system mixed a weight function is defined. Next the improved moving least-square approximation is discussed in detail. The improved method has higher computational efficiency and precision than the old method, and cannot form an ill-conditioned equation system. A boundary element-free method (BEFM) for elastodynamics problems is presented by combining the boundary integral equation method for elastodynamics and the improved moving least-square approximation. The boundary element-free method is a meshless method of boundary integral equation and is a direct numerical method compared with others, in which the basic unknowns are the real solutions of the nodal variables and the boundary conditions can be applied easily. The boundary element-free method has a higher computational efficiency and precision. In addition, the numerical procedure of the boundary element-free method for elastodynamics problems is presented in this paper. Finally, some numerical examples are given.

关键词： moving least-square approximation, improved moving least-square approximation, elastodynamics, boundary integral equation, meshless method, boundary element-free method, Fourier eigen transform.

Population-size-dependent branching processes in Markovian random environments

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Chinese Science Bulletin 1998年第8期43卷 635-638页

作者： WANG Hanxing 1 and DAI Yonglong 2.1. department of Mathematics, shanghai university,{2. 2.1800, China 2. department of Mathematics, Zhongshan university, Guangzhou 5102.5, China department of Mathematics Shanghai University Shanghai China department of Mathematics Zhongshan University Gunngzhou China

A branching model {Z n} n≥0is considered where the offspring distribution of the population’s evolution is not only dependent on the population size, but also controlled by a Markovian environmental process {ξ n} n≥0. For this model, asymptotic behaviour is studied such as limn→∞Z n and limn→∞Z n/m n in the case that the mean m k, θof the offspring distribution converges to m>1 as the population size k grows to ∞. In the case that {ξ n} n≥0is an irreducible positive recurrent Markov chain, certain extinction (i.e. P(Z n=0 for some n)=1) and noncertain extinction (i.e. P(Z n=0 for some n)<1) are studied.

关键词： Markov chains in random environments stochastic population models branching processes.

Research on nonlinear constitutive relationship of permanent deformation in asphalt pavements

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Science China(Physics,Mechanics & Astronomy) 2006年第6期49卷 671-682页

作者： PENG Miaojuan1 & XU Zhihong2.1. department of Civil Engineering,shanghai{2.,shanghai 2.0072.China 2. School of Transportation Engineering,Tongji{2.,shanghai 2.0092.China 1. department of Civil Engineering Shanghai University Shanghai 200072 China 2. School of Transportation Engineering Tongji University Shanghai 200092 China

To predict correctly the rut depths in asphalt pavements,a new nonlinear viscoelastic-elastoplastic constitutive model of permanent deformation in asphalt pave-ments is presented. The model combines a generalized Maxwell model with an elasto-plastic one. Then from the creep theory,the linear and nonlinear constitutive equations of the generalized Maxwell model are obtained. From the nonlinear finite element method for the rutting of the asphalt pavement,the rut depths of 4 asphalt-aggregate mixtures are obtained. And the results are compared with the ones from the finite element method by SHRP and the experiments by SWK/UN. The results in this paper are better than the ones by SHRP,and agree with the ones of the experiment by SWK/UN. This shows that the nonlinear viscoelastic-elastoplastic constitutive model,which is presented in this paper for the rutting of the asphalt pavement,is effective. The properties,such as nonlinear elastic-ity,plasticity,viscoelasticity and nonlinear viscoelasticity,which affect the rutting of an asphalt pavement,can be shown in the model. And the characteristics of the permanent deformation of the asphalt pavement can be presented entirely in the model.

关键词： asphalt pavement,permanent deformation,nonlinear viscoelastic-elastoplastic constitutive relationship,generalized Maxwell model,creep compliance.

A complex variable meshless method for fracture problems

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Science China(Physics,Mechanics & Astronomy) 2006年第1期49卷 46-59页

作者： CHENG Yumin1 & LI Jiuhong2.1. shanghai Institute of Applied Mathematics and Mechanics, shanghai university, shanghai 2.0072. China 2. department of Building Engineering, Xi’an university of Technology, Xi’an 710048, China shanghai Institute of Applied Mathematics Mechanics Shanghai University Shanghai 200072 China department of Building Engineering Xi’an University of Technology Xi’an 710048 China

Based on the moving least-square (MLS) approximation, the complex variable moving least-square approximation (CVMLS) is discussed in this paper. The complex variable moving least-square approximation cannot form ill-conditioned equations, and has greater precision and computational efficiency. Using the analytical solution near the tip of a crack, the trial functions in the complex variable moving least-square approxi- mation are extended, and the corresponding approximation function is obtained. And from the minimum potential energy principle, a complex variable meshless method for fracture problems is presented, and the formulae of the complex variable meshless method are obtained. The complex variable meshless method in this paper has greater precision and computational efficiency than the conventional meshless method. Some examples are given.

关键词： moving least-square approximation, complex variable moving least-square approximation, meshless method, complex variable meshless method, fracture.

Simultaneously inducing synthesis of semiconductor selenium multi-armed nanorods and nanobars through bio-membrane bi-templates

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Science China chemistry 2004年第6期47卷 507-511页

作者： LI Li1, WU Qingsheng1 DING Yaping2.& LI Ping3 1. department of chemistry, Tongji{2., shanghai 2.0092. China 2. department of chemistry, shanghai university, shanghai 2.04.6, China 3. department of Food, Anhui Agricultural{2., Hefei 2.0036, China 1. department of chemistry Tongji University 200092 Shanghai China 2. department of chemistry Shanghai University 200436 Shanghai China 3. department of Food Anhui Agricultural University 230036 Hefei China

Multi-armed nanorods and nanobars of semiconductor selenium were simultane- ously synthesized in the light of biomineralization process through bio-membrane bi-templates of rush at room temperature. The multi-armed nanorods are 60 nm in diameter and 1.5 μm in length; the nanobars are 150 nm in diameter and 1000—1100 nm in length. The XRD pattern indicates that these nanocrystals were crystallized in the hexagonal structure with lattice constants a = 0.437 nm, c = 0.495 nm. The possible formation mechanism was investigated.

关键词： selenium, multi-armed nanorods, nanobars, bio-membrane, bi-templates.

I-V and C-V properties of TiO_2.thin film by pulsed-laser reactive deposition

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Chinese Science Bulletin 1998年第16期43卷 1344-1349页

作者： FU Zhengwen 1, ZHOU Mingfei 1, ZHANG Shengkun 2.CHEN Lianyao 2.and QIN Qizong 1 1. Laser chemistry Institute, Fudan university,{2. 2.0433, China 2. department of Physics, Fudan university,{2. 2.0433, China Laser chemistry Institute Fudan University Shanghai China department of Pnysics Fudan University Shanghai China

TiO-2.thin films have bee deposited on p-Si(111) substrates by pulsed-laser ablation of metallic Ti target in the O-3 ambient. The current-voltage and capacitance-voltage of the Al/TiO-2.Si capacitors are measured. The results show that the dielectric constant of thin film after being annealed at 700℃ is found to be 46, and the border trap density and the interface state density at the TiO-2.p-Si interface are 1.8×10 12.cm -2.and 2.10 12.eV -1·cm -2. respectively. The conduction mechanisms of as-deposited films are also discussed.

关键词： TiO-2 dielectric properties electrical properties pulsed-laser deposition.

Transverse patterns and spatiotemporal instability of a photorefractive oscillator

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Chinese Science Bulletin 1997年第9期42卷 724-729页

作者： ZHUANG Jun and TAN Weihan1. shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, shanghai 2.1800, China 2.{2., shanghai 2.1800, China shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai China shanghai university Shanghai China

IN time realm,instability and chaos phenomena of a nonlinear optical system have been dis-cussed *** recent years,as much interest was attracted to the transverse ef-fects in nonlinear optics,the study was developed t... 详细信息

关键词： photorefractive oscillator spatiotemporal instability transverse patterns.

The adsorption isotherms, IR and ^(2.)Si MAS NMR spectra of modified MCM-41 molecular sieves

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Chinese Science Bulletin 1997年第10期42卷 828-832页

作者： LONG Yingcai, DONG Weiyang, XU Taiming, GAO Xiaoqin, XIE Guangen and SUN Yaojun1. department of chemistry, Fudan{2., shanghai 2.0433, China 2. Centre of Analysis and Measurement, Fudan{2., shanghai 2.0433, China department of chemistry Fudan University Shanghai China Centre of Analysis and Measurement Fudan University Shanghai China

RECENTLY a new family of mesoporous molecular sieves,M41S,was reported by researchers atMobil R&D *** a member of the family,MCM-41,which exhibits a hexagonalarray of uniform channel mesopores,has been *** channel size can be variedfrom approximately 1.5 nm to greater than 10 nm by choosing different surfactants,auxiliarychemicals(1,3,5-trimethylbenzene)in the reactant,and by changing the reaction *** wall thickness of this kind of molecular sieve is in the range of 0.3 to 1.3 nm esti-

关键词： MCM-41 surface modification adsorption isotherm IR 2.Si MAS NMR.

Fredholm operators in Toeplitz algebras associated with discrete abelian groups

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Chinese Science Bulletin 1998年第14期43卷 1175-1179页

作者： XU Qingxiang 1 and CHEN Xiaoman 2.1. department of Mathematics, shanghai Normal{2., shanghai 2.02.4, China 2. Laboratory of Mathematics for Nonlinear Sciences and Institute of Mathematics, Fudan{2., shanghai 2.0433, China department of Mathematics Shanghai Normal University Shanghai China Laboratory of Mathematics for Nonlinear Sciences and Institute of Mathematics Fudan University Shanghai China

The locally finite below sets are introduced and the Fredholm operators in Toeplitz algebras associated with discrete abelian groups are studied.

关键词： discrete abelian group quasi_ordered group Toeplitz operator Fredholm operator.