检索结果-南通市图书馆

Two possible mechanisms for vortex self-organization

在线全文

学校读者我要写书评

暂无评论

Science china Earth Sciences 2006年第2期49卷 202-211页

作者： LUO Zhexian2. ZHOU Xiuji1 & GAO Shouting3 1. Chinese Academy of Meteorological Sciences, beijing 100081, china 2. {2. of Space Information Science, Nanjing University of Information Science and technology, Nanjing 2.0044, china 3. institute of Atmospheric Physics, Chinese Academy of Sciences, beijing 10002., china 2. department of Environmental Science Nanjing University of Information Science and Technology Nanjing 210044 China 1. Chinese Academy of Meteorological Sciences Beijing 100081 China 3. institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029 China

The vortex self-organization is investigated in this paper by four groups of numerical experiments within the framework of quasi-geostrophic model, and based on the experimental results two types of possible mechanisms for vortex self-organization are suggested. The meso-scale to-pography may enable separated vortices to merge into a larger scale vortex; and the interaction of meso-γ and meso-β scale systems may make separated vortices to self organize a typhoon-like vor-tex circulation.

关键词： vortex, self-organization, meso-scale topography, interaction of different scales.

Fabrication of Biomimetic Water Strider Legs Covered with Setae

在线全文

学校读者我要写书评

暂无评论

Journal of Bionic engineering 2009年第1期6卷 1-6页

作者： Zhi-guo Zhou, Zhi-wen Liudepartment of Electronic engineering,{2., beijing 100081, P. R. china [a]department of Electronic engineering Beijing Institute of Technology Beijing 100081 P. R. China

Water striders have remarkable water-repellent legs that enable them to stand effortlessly and move quickly on *** physics indicates this feature is due to a surface-tension effect caused by the special hierarchical structure of the legs,which are covered with a large number of inclined setae with fine nanogrooves inducing water *** inspires us to fabricate special water-repellent structure on functional surfaces through the cooperation between the surface treatment and the surface micro-and nanostructures,which may bring great advantages in a wide variety of *** this paper we present a procedure for fabricating biomimetic water strider legs covered with setae using Polycarbonate Track-Etched(PCTE)membranes as *** choosing appropriate membrane lengths,diameters,pitches and densities of the setae,the biomimetic legs can be fabricated conveniently and at a low *** we investigated the relationship between stiffness of the molding materials,high aspect ratio and density,which affect the fidelity of fabrication and self adhesion,to optimize the stability of *** knowledge we gained from this study will offer important insights into the biomimetic design and fabrication of water strider setae.

关键词： water strider biomimetic setae PCTE membrane Polydimethylsiloxane (PDMS) nanoparticle adhesion

Parallel Computing of Ocean General Circulation Model

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2001年第Z1期6卷 568-573页

作者： Zhang Li lun 1, Song Jun qiang 1, Li Xiao mei 2.1. School of computer Science, National University of Defense technology, Changsha 410073,{2. 2. department of computer, institute of Command technology, beijing 100081,{2. School of computer Science National University of Defense Technology Changsha 410073 P.R. China

This paper discusses the parallel computing of the third generation Ocean General Circulation Model (OGCM) from the State Key Laboratory of Numerical Modeling for Atmospheric Science and Geophysical Fluid Dynamics(LASG),institute of Atmosphere Physics(IAP). Meanwhile, several optimization strategies for parallel computing of OGCM (POGCM) on Scalable Shared Memory Multiprocessor (S2.P) are presented. Using Message Passing Interface (MPI), we obtain super linear speedup on SGI Origin 2.00 for parallel OGCM(POGCM) after optimization.

关键词： parallel computing OGCM optimization strategy S2.P

On the stability of diffusion processes with state-dependent switching

在线全文

学校读者我要写书评

暂无评论

Science china Mathematics 2006年第9期49卷 1258-1274页

作者： XI Fubao & ZHAO Liqin department of Mathematics, beijing institute of technology,{2., china School of Mathematical Sciences, beijing Normal University, beijing 100875, china department of Mathematics Beijing Institute of Technology Beijing 100081 China School of Mathematical Sciences Beijing Normal University Beijing 100875 China

In this paper we consider the stability for diffusion processes with state-dependent switching. We first prove their Feller continuity by the coupling methods. Furthermore, we also prove their strong Feller continuity and their exponential ergodicity under some reasonable conditions. Finally, we append a very brief discussion about the regularity of these processes.

关键词： Feller continuity, coupling, strong Feller continuity, exponential ergodicity,state-dependent switching.

Effect of Activator and Curing Mode on Fly Ash-based Geopolymers

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of technology(Materials Science) 2009年第5期24卷 711-715页

作者：侯云芬 institute of Civil engineering and Traffic Beijing Institute of Civil Engineering and Architecture department of Material China University of Mining and Technology

The influences of concentration and modulus of sodium silicate solution and curing mode on the phase composition, microstructure and strength development in the geopolymers prepared using Class F fly ash were investigated. X-ray diffraction （XRD）, Fourier transform infrared spec-troscopy （FTIR） and MAS NMR were utilized. Results show that the compressive strength increases as sodium silicate solution modulus increases, but when modulus exceeds 1.4, the compressive strength decreases, and it decreases markedly while the modulus is greater than 2.0. The compressive strength was improved by the increase of sodium silicate solution concentration. When the concentration is 32., the compressive strength reaches the maximum, then it reduces as concentration increasing. Elevated temperature can increase the strength of samples that synthesized from sodium silicate solution with 32. concentration and modulus 1.2. Compared to the strength of the sample cured at 50 ℃, the strength of the samples cured at 65 ℃ and 80 ℃ are higher at 1 d and 3 d, but the same at 7 d. At high temperature, prolonged curing time will decrease the strength. Long precuring at room temperature before application of heat is beneficial for strength development, and there is about 50% increase in strength of the samples cured at 1 d precuring and 2.d elevated temperature as compared to the strengths of the samples cured for 3 d at elevated temperatures or cured for 2. d at room temperature. The main product of reaction in the geopolymeric material is amorphous alkali aluminosilicate gel.

关键词： geopolymers fly ash activator elevated temperature

Formation control for networked spacecraft in deep space:with or without communication delays and with switching topology

在线全文

学校读者我要写书评

暂无评论

Science china(Information Sciences) 2011年第3期54卷 469-481页

作者： WANG Nan 1,2. ZHANG TianWu 2.& XU JieQiong 1 1 School of Aeronautic Science and engineering, beijing University of Aeronautics and Astronautics, beijing 100191, china 2.department of computer Science and engineering, Henan institute of engineering, Zhengzhou 451191, china 1. School of Aeronautic Science and engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China2. Department of Computer Science and Engineering Henan Institute of Engineering Zhengzhou 451191 China

In this paper, several formation controllers are developed with constant and variable connected communication topology for six-degree-of-freedom (6-DOF) networked spacecraft flying in deep space with constant and time-varying communication delays considered. In the control algorithm, any explicit leader does not exist in the formation team and it is required that each spacecraft communicate only with its neighbors and therefore the required communication loads of the whole formation is greatly reduced. The proposed control strategies allow that each spacecraft can track its desired position and attitude and simultaneously the whole group moves to the desired formation and obtain its desired relative attitudes with its neighbors. Simulation results demonstrate the effectiveness of the proposed controllers.

关键词： deep space graph theory formation control communication topology delays

Detection and parameter estimation of multicomponent LFM signal based on the fractional Fourier transform

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science in china(Series F) 2004年第2期47卷 184-198页

作者： QI Lin1, 2. TAO Ran1, ZHOU Siyong1 & WANG Yue1 1. department of Electronic engineering,{2., beijing 100081, china 2. School of Information engineering, Zhengzhou University, Zhengzhou 450052. china Correspondence should be addressed to QI Lin (email: qilin@***) 1. department of Electronic engineering Beijing Institute of Technology 100081 Beijing China 2. School of Information engineering Zhengzhou University 450052 Zhengzhou China

This paper presents a new method for the detection and parameter estimation of multicomponent LFM signals based on the fractional Fourier transform. For the optimization in the fractional Fourier domain, an algorithm based on Quasi-Newton method is proposed which consists of two steps of searching, leading to a reduction in computation without loss of accuracy. And for multicomponent signals, we further propose a signal separation technique in the fractional Fourier domain which can effectively suppress the interferences on the detection of the weak components brought by the stronger components. The statistical analysis of the estimate errors is also performed which perfects the method theoretically, and finally, simulation results are provided to show the validity of our method.

关键词： LFM signal parameter estimation fractional Fourier transform.

Preparation of graphitic carbon nitride by electrodeposition

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2003年第16期48卷 1737-1740页

作者： LI Chao1,2. CAO Chuanbao1 & ZHU Hesun1 1. Research Center of Materials Science, beijing institute of technology, beijing 100081,{2. 2. department of Chemical engineering, Zhengzhou institute of Light Industry, Zhengzhou 450002.china Correspondence should be addressed to Cao Chuanbao Research Center of Materials Science Beijing Institute of Technology Beijing 100081 China department of Chemical engineering Zhengzhou Institute of Light Industry Zhengzhou 450002 China

The CNx thin film was deposited on Si(100) substrate from a saturated acetone solution of cyanuric tri-chloride and melamine (cyanuric trichloride/melamine=1︰1.5) at room temperature. X-ray diffraction (XRD) results showed that the diffraction peaks in the pattern coincided well with those of graphite-like carbon nitride calculated in the literature. The lattice constants (a=4.79 ? c=6.90 ) for g-C3N4 matched with those of ab initio calculations (a=4.74 ? c=6.72.? quite well. X-ray photoelectron spectroscopy (XPS) measurements indicated that the elements in the de-posited films were mostly of C and N (N/C=0.75), and N (400.00 eV) bonded with C (2.7.72.eV) in the form of six-member C3N3 ring. The peaks at 800 cm-1, 1310 cm-1 and 1610 cm-1 in the Fourier transform infrared (FTIR) spec-trum indicated that triazine ring existed in the product. These results demonstrated that crystalline g-C3N4 was ob-tained in the CNx film.

关键词：沉淀薄膜饱和丙酮溶液三聚氰胺 X射线衍射石墨碳氮化合物晶格恒量光电子光谱测量法傅立叶变换红外光谱三嗪

Lie symmetries of mechanical systems with unilateral holonomic constraints

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2000年第15期45卷 1354-1358页

作者： ZHANG Yi & MEI Fengxiang1. department of Basic Courses, Suzhou institute of Urban Construction & Environmental Protection, Suzhou 2.5011,{2. 2. department of Applied Mechanics, beijing institute of technology, beijing 10008I,{2. department of Basic Courses Suzhou Institute of Urban Construction & Environmental Protection Suzhou China department of Applied Mechanics Beijing Institute of Technology Beijing China

In the recent twenty years, the study on the Lie symmetries and conserved quantities of constrained mechanical systems has been making great progress[1-5]. Up to now, however, all the studies are limited to the mechanical systems with ideal bilateral constraints. This note further studies the Lie symmetries of mechanical systems with unilateral holonomic constraints, and two problems of Lie symmetries for the systems are put forward and solved, i.e. finding the conserved quantity from a Lie symmetric transformation of the system and finding the corresponding Liesymmetry from an integral of the systemi ? 梛 ? Jsymmetry from an integral of the system.

关键词： analytical mechanics unilateral constraint holonomic system Lie symmetry conserved quantity.