检索结果-南通市图书馆

Preconditioned pseudo-compressibility methods for incompressible Navier-Stokes equations

中国科学：物理学、力学、天文学英文版 2010年第11期53卷 2090-2102页

作者： QIAN ZhanSen ,ZHANG JingBai & LI ChunXuan School of Aeronautics Science and Engineering,beihang university,beijing 100191,China 1. School of Aeronautics Science and Engineering Beihang University Beijing 100191 China

This paper investigates the pseudo-compressibility method for the incompressible Navier-Stokes equations and the preconditioning technique for accelerating the time marching for stiff hyperbolic equations,and derives and presents the eigenvalues and eigenvectors of the Jacobian matrix of the preconditioned pseudo-compressible Navier-Stokes equations in generally cur-vilinear *** on the finite difference discretization the cored for efficiently solving incompressible flows numerically is *** reliability of the procedures is demonstrated by the application to the inviscid flow past a circular cylinder,the laminar flow over a flat plate,and steady low Reynolds number viscous incompressible flows past a circular *** is found that the solutions to the present algorithm are in good agreement with the exact solutions or experimental *** effects of the pseudo-compressibility factor and the parameter brought by preconditioning in convergence characteristics of the solution are investigated *** results show that the upwind Roe’s scheme is superior to the second order central scheme,that the convergence rate of the pseudo-compressibility method can be effectively improved by preconditioning and that the self-adaptive pseudo-compressibility factor can modify the numerical convergence rate significantly compared to the constant form,without doing artificial tuning depending on the specific flow *** validation is also performed by numerical simulations of unsteady low Reynolds number viscous incompressible flows past a circular *** results are also found in good agreement with the existing numerical results or experimental data.

关键词： pseudo-compressibility method preconditioning upwind scheme incompressible flow Navier-Stokes equations

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Relationship between surface subsidence factor and mining depth of strip pillar mining

引用

中国有色金属学会会刊：英文版 2011年第S3期21卷 594-598页

作者： GUO Wen-bing1, 2. HOU Quan-lin 1, ZOU You-feng2.1. college of Earth Science, Graduate university of Chinese Academy of Sciences, {2. 100049, China 2. School of Energy Science and Engineering, Henan Polytechnic university, Jiaozuo 454000, China Chinese Acad Sci Coll Earth Sci Grad Univ Beijing 100049 Peoples R China Henan Polytech Univ Sch Energy Sci & Engn Jiaozuo 454000 Peoples R China

Strip pillar mining is one of the most important technical measures to control mining subsidence in China. Mining depth is one of the most important factors that can affect the mining subsidence in strip pillar mining. Six numerical simulation models were set up to simulate the surface subsidence of strip pillar mining in different mining depths. The mining depth in these six models ranges from 300 to 800 m. The simulated results were compared and analyzed. The formula was established based on the simulated results. It demonstrated that the subsidence of strip pillar mining method is related to mining depth. While the other conditions are the same, the subsidence of strip pillar mining increases with the increase of mining depth by logarithmic relationship.

关键词： subsidence factor strip pillar mining mining depth numerical simulation

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A heuristic path-estimating algorithm for large-scale real-time traffic information calculating

引用

Science China(Technological Sciences) 2008年第S1期51卷 165-174页

作者： L WeiFeng1,ZHU TongYu1,WU DongDong2.DAI Hong3 & HUANG Jian1 1 State Key Laboratory for Software Development Environment,beihang university,beijing 100083,China 2.beijing Transportation Information Center,beijing 100055,China 3 college of Arts & Science,beijing Union university,beijing 100083,China 1. State Key Laboratory for Software Development Environment Beihang University Beijing 100083 China 2. beijing Transportation Information Center Beijing 100055 China 3. college of Arts & Science Beijing Union University Beijing 100083 China

As the original Global Position System (GPS) data in Floating Car Data have the accuracy problem,this paper proposes a heuristic path-estimating algorithm for large-scale real-time traffic information calculating. It uses the heuristic search method,imports the restriction with geometric operation,and makes comparison between the vectors composed of the vehicular GPS points and the special road network model to search the set of vehicular traveling route candidates. Finally,it chooses the most optimal one according to weight. Experimental results indicate that the algorithm has considerable efficiency in accuracy (over 92.7%) and com-putational speed (max 8000 GPS records per second) when handling the GPS tracking data whose sampling rate is larger than 1 min even under complex road network conditions.

关键词： path-estimating floating car data (FCD) road network vector GPS

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A computational trust model for access control in P2.

引用

Science China(Information Sciences) 2010年第5期53卷 896-910页

作者： LANG Bo State Key Laboratory of Software Development Environment, beihang university, beijing 100191, China 1. State Key Laboratory of Software Development Environment Beihang University Beijing 100191 China

Trust brings a new method for building scalable and fine-grained access control mechanism in P2. systems. The quantificational expression of trust and the calculation of trust in a trust network are the basis of trust degree based access control. In this paper, the properties of trust is analyzed by referring to the fruits from social science; the semantics of trust in the context of access control is described, and a trust degree based access control model named TDBAC is introduced. Basing on the properties and semantics of trust, a computational trust model which includes a multilevel comprehensive evaluation method for expressing direct trust and calculators for computing recommended trust is put forward. To compute trust in a trust network, an algorithm that transforms a trust network to a computable expression is given. The algorithm simplifies the computation process and is also flexible.

关键词： trust management access control trust degree based access control computational trust model trust graph expression

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Existence of the solutions and the attractors for the large-scale atmospheric equations

引用

Science China Earth Sciences 2006年第6期49卷 650-660页

作者： HUANG Haiyang1 & GUO Boling2.1. Department of Mathematics, beijing Normal university, beijing 100875, China 2. Institute of Applied Physics and Computational Mathematics, beijing 100080, China 1. Department of Mathematics Beijing Normal University Beijing 100875 China 2. Institute of Applied Physics and Computational Mathematics Beijing 100080 China

In this paper, firstly, the proper function space is chosen, and the proper expression of the operators is introduced such that the complex large-scale atmospheric motion equations can be described by a simple and abstract equation, by which the definition of the weak solution of the atmospheric equations is made. Secondly, the existence of the weak solution for the atmospheric equations and the steady state equations is proved by using the Galerkin method. The existence of the non-empty global attractors for the atmospheric equations in the sense of the Chepyzhov-Vishik’s definition is obtained by constructing a trajectory attractor set of the atmospheric motion equations. The result obtained here is the foundation for studying the topological structure and the dynamical behavior of the atmosphere attractors. Moreover, the methods used here are also valid for studying the other atmospheric motion models.

关键词： atmosphere equations, weak solution, trajectory attractor, global attractor, equilibrium.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Suppressing azimuth ambiguity in spaceborne SAR images based on compressed sensing

引用

Science China(Information Sciences) 2012年第8期55卷 1830-1837页

作者： YU Ze&LIU Min School of Electronics and Information Engineering,beihang university,beijing 100191,China 1. School of Electronics and Information Engineering Beihang University Beijing 100191 China

In spaceborne synthetic aperture radar,undersampling at the rate of the pulse repetition frequency causes azimuth ambiguity,which induces ghost into the *** paper introduces compressed sensing for azimuth ambiguity suppression and presents two novel methods from the perspectives of system design and image formation,known as azimuth random sampling and ambiguity separation,*** first method makes the imaging results for the ambiguity zones as disperse as possible while ensuring that the imaging results for the main scene are affected as little as *** second method separates the ambiguity signals from the echoes and achieves imaging results without the ambiguity *** results show that the two methods can reduce the ambiguity levels by about 16 dB and 99.37%,respectively.

关键词： synthetic aperture radar compressed sensing azimuth ambiguity orthogonal matching pursuit

来源：

同方期刊数据库评论

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

The study of two-color excitation upconversion of Pr(0.5)Yb(3):ZBLAN

引用

Science China(Physics,Mechanics & Astronomy) 2006年第2期49卷 169-177页

作者： CHEN Xiaobo1 & SONG Zengfu2.1. Applied Optics beijing Area Major Laboratory, Analysis and testing center, beijing Normal {2., beijing 100875, China 2. Peking {2., Physics School, beijing 100871, China Applied Optics beijing Area Major Laboratory Analysis testing center Beijing Normal University Beijing 100875 China Physics School Peking University Beijing 100871 China

The excited state absorption upconversion of Pr(0.5)Yb(3):ZBLAN glass material, under two-color excitation of the 960 nm semiconductor laser and the Xe lamp light simultaneously, is reported in this article. It was found that the upconversion emission spectra of 480.1, 519.0, 601.9 and 631.8 nm coincide with the common emission spectra. Meanwhile, the upconversion-excitation spectrum has three obvious peaks under two-color excitation, and they respectively correspond to the 856.0 nm upconversion ex-citation transition [1G4(Pr3+)→1I6(Pr3+) and 1G4(Pr3+)→3P1(Pr3+)], the 789.0 nm upconver-sion excitation transition 1G4(Pr3+)→3P2.Pr3+), and the 803.7 nm upconversion excitation transition 3H6(Pr3+)→1D2.Pr3+). The upconversion excitation transition 1G4(Pr3+)→1I6(Pr3+) is strong because its oscillator strength f = 2..040×10?6 is large, which results in a large peak appearing in the upconversion excitation spectrum. That is just the new interesting two-color excitation upconversion luminescence phenomenon of Pr(0.5)Yb(3):ZBLAN induced by one laser and one continuous normal light simultaneously.

关键词： upconversion volumetric three-dimensional display two-color excitation.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Explanation of the mechanism of carcinogenesis and syntheses of anticancer agents with high selectivity

引用

Science China Chemistry 2006年第1期49卷 44-62页

作者： DAI Qianhuan1,2.1. Center of Chemistry and Bioengineering of Cancer Research, beijing Polytechnic university (Now known as beijing Univer-sity of Technology), beijing 10002., China 2. Center of Environmental Sciences, Peking university, beijing 100871, China 1. Center of Chemistry and Bioengineering of Cancer Research Beijing Polytechnic University Beijing 100022 China 2. Center of Environmental Sciences Peking University Beijing 100871 China

In 1979, the mechanism of chemical carcinogenesis, a challenging anddifficult scientific problem pending for a number of years, was explained by Dai Qianhuan. Themechanism named di-region theory predicted that a carcinogen always metabolizes to form a specialbi-functional alky-lating agent. This agent induces cross-linkages between the complementary basepairs in DMA and switches on initial mutageneses in genomes including point and frameshiftmutations. This, in turn, induces further deep mutageneses including the production of variouschimeric chromosomes, deletions and other aberrations found in genomes. In the end this initiatescarcinogenesis of the whole cell through the reverse transcription mechanism after a lengthyincubation period. Recently, this laboratory has verified that physical carcinogenesis, includingthe oncogenesis induced by radiation and asbestos as well as the carcinogenesis induced byendogenous factors such as estrogen or diethyl-stilbestrol switch on carcinogenesis by inducing theformation of cross-linkages between the complementary base pairs in DNA. Di-region theory has nowbeen supported by many experimental observations such as mutational spectra of various *** potential for carcinogenesis, teratogenesis, sterility and mutagenesis lumped together asgenetic toxicity appears to originate almost uniformly from the cross-linking between complementarybases, i.e. malignant cross-linking, which is in accordance with di-region theory. Other forms ofcross-linking between non-complementary bases, benign cross-linkings, show bi-functional alkylationanticancer activity but lack genetic toxicity. The predictable design and synthesis of a highselectivity anticancer agent with high efficacy and low genetic toxicity, a goal long pursued incancer chemotherapy, have been realized for the first time in this laboratory by inhibitingmalignant and heightening benign cross-linking using the principles of di-region theory. A series ofpatented new anticanc

关键词： mechanism of carcinogenesis, di-region theory, minoplatin, selectivity of anticancer agent, cross-linking between DNA bases, anticancer platinum complexes, predictive design of anticancer agent, second generation anticancer agent.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

The toxicity of Cu^(2.) to Microcystis aeruginosa using dielectric spectroscopy

引用

Science China Chemistry 2010年第3期53卷 631-636页

作者： YU YanLi1,BAI Wei1,ZHAO KongShuang1& ZHOU YunLong2.1college of Chemistry,beijing Normal {2.,beijing 100875,China 2.0} of Life Science,beijing Normal {2.,beijing 100875,China 1. college of Chemistry Beijing Normal University Beijing 100875 China2. College of Life Science Beijing Normal University Beijing 100875 China

Dielectric spectroscopy(DS) was utilized to investigate the toxicity of the Cu2. solution to Microcystis *** was found that 0.04 mM Cu2. had no effect on dielectric increment,whereas the Cu2. concentrations above 0.1 mM decreased the value of Δε/Δε *** toxic effect of Cu2. on *** cells was time-dependent and *** was a threshold concentration between 0.04 mM and 0.1 mM,which affected the cell membrane,suggesting that Cu2. at the concentrations higher than 0.1 mM caused serious plasmalemma damage to *** *** addition of 1 mM Ca2. or Mg2. did not protect *** cells from 1 mM Cu2. *** study demonstrates that DS monitors cell biomass facilitating observation of the toxic effects of metal ions.

关键词： Microcystis aeruginosa dielectric spectroscopy dielectric increment cupric ion toxicity

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Effect and mechanism of stresses on rock permeability at different scales

引用

Science China Earth Sciences 2006年第7期49卷 714-723页

作者： YIN Shangxian1 & WANG Shangxu2.1. Safety Engineering college, North China Institute of Science and Technology, Yanjiao, beijing 101601, China 2. Key Laboratory of Geophysics Exploration, China {2. of Petroleum, beijing 100083, China 1. Safety Engineering college North China Institute of Science and Technology Yanjiao Beijing 101601 China 2. Key Laboratory of Geophysics Exploration China University of Petroleum Beijing 100083 China

The effect of geo-stress fields on macroscopic hydro-geological conditions or micro-cosmic permeability of water-bearing media should follow some laws or principles. Cases study and tests show that: (1) At macro-geologic large scale, deformed and crashed rocks which were induced by geo-stress fields changing provided space for groundwater storage and flow. Groundwater adjusts water-bearing space and dilatants fractures by flowing and press transferring. Coupling of liquid and solid can be implemented for rocks and groundwater. Although tectonic fields witness several times of change and build-up in geological time, stress fields forming regional tectonic framework are coherent with seepage fields, orientation of the maximum horizontal stress demonstrates main seepage direc-tions. (2. At macro-geologic middle scale, zones of stresses changing sharply, quite low stresses, stress or shear concentration can be used to show locations and types of main fractures, zones of geo-stresses changing equably can be acted as normal base media zones of tri-porosity media. (3) At micro-geologic small scale, tri-porosity media include fractured rocks, porous rocks and capillary rocks. Investigations indicate that porosity or permeability is functions of effective stresses, and po-rosity or permeability changing rules of porous rocks with variation of effective stresses can be de-scribed as the index model, the model of power exponent functions is suitable for those of fractured rocks, the model of the second power parabola for capillary rocks. The porosity and permeability loss in fractured rocks, which are greater than that in porous rocks, are shown by calculation of effective compressive coefficient and closing pressure in cracks. The calculations can also explain the mecha-nism why porosity changes are always larger than permeability changes. It is proved by the thick wall cylinder theory that the second power parabola relation between porosity or permeability loss and effective

关键词： geo-stress fields, seepage fields, tri-porosity media, effective stresses, permeability, porosity,scale.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：