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Study on the unified algorithm for three-dimensional complex problems covering various flow regimes using Boltzmann model equation

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Science china(Physics,mechanics & Astronomy) 2009年第1期52卷 124-138页

作者： LI ZhiHui1,2.& ZHANG HanXin1 1 National Laboratory for Computational Fluid Dynamics, beijing 100083, china 2.1} Aerodynamics Research and Development center, Hypervelocity Aerodynamics institute, Mianyang 62.000, china 1. National Laboratory for Computational Fluid Dynamics Beijing 100083 China 2. china Aerodynamics Research and Development center Hypervelocity Aerodynamics Institute Mianyang 621000 China

The Boltzmann simplified velocity distribution function equation describing the gas transfer phenomena from various flow regimes will be explored and solved numerically in this study. The discrete velocity ordinate method of the gas kinetic theory is studied and applied to simulate the complex multi-scale flows. Based on the uncoupling technique on molecular movement and colliding in the DSMC method, the gas-kinetic finite difference scheme is constructed to directly solve the discrete velocity distribution functions by extending and applying the unsteady time-splitting method from computational fluid dynamics. The Gauss-type discrete velocity numerical quadrature technique for different Mach number flows is developed to evaluate the macroscopic flow parameters in the physical space. As a result, the gas-kinetic numerical algorithm is established to study the three-dimensional complex flows from rarefied transition to continuum regimes. The parallel strategy adapted to the gas-kinetic numerical algorithm is investigated by analyzing the inner parallel degree of the algorithm, and then the HPF parallel processing program is developed. To test the reliability of the present gas-kinetic numerical method, the three-dimensional complex flows around sphere and spacecraft shape with various Knudsen numbers are simulated by HPF parallel computing. The computational results are found in high resolution of the flow fields and good agreement with the theoretical and experimental data. The computing practice has confirmed that the present gas-kinetic algorithm probably provides a promising approach to resolve the hypersonic aerothermodynamic problems with the complete spectrum of flow regimes from the gas-kinetic point of view of solving the Boltzmann model equation.

关键词： Boltzmann model equation kinetic theory velocity distribution function discrete velocity ordinate technique hypersonic flow parallel computing numerical methods

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Experimental realization of quantum cryptography communication in free space

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Science china(Physics,mechanics & Astronomy) 2005年第2期48卷 237-246页

作者： WANG Chuan1, ZHANG Jingfu1, WANG Pingxiao1, DENG Fuguo1, AI Qing1 & LONG Guilu1,2.1. Department of Physics, Key Laboratory for Quantum Information and Measurements, Tsinghua Univer- sity, beijing 100084, china 2. {2. for Atomic and Molecular NanoSciences, Tsinghua University, beijing 100084, china Department of Physics Key Laboratory for Quantum Information and Measurements Tsinghua University Beijing 100084 China Atomic and Molecular NanoSciences Tsinghua University Beijing 100084 China

Utilizing linear optical devices, the principle of B92.quantum key distribution (QKD) protocol is demonstrated in free space with a distance of transmission of 2.2.meters. The faint laser pulses with 650 nm wavelength are used as the single photon sources. The experimental results show that the eavesdropping behavior in the signal transmission can be detected. We also discuss the problems and solutions in using the quantum cryptography communication practically. It is pointed out that one of the approaches to increasing the distance of the quantum communication is to overcome the attenuation of the single photon in transmission. This could not be solved by the use of single photon source, and new quantum communication protocols are needed to solve these problems.

关键词： quantum key distribution, free space, linear optics, faint pulses.

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Closed form solutions for free vibrations of rectangular Mindlin plates

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Acta Mechanica Sinica 2009年第5期25卷 689-698页

作者： Yufeng Xing Bo Liu The Solid mechanics Research center, Beihang University,100191 {2., china The Solid mechanics Research center Beihang University 100191 Beijing China

A new two-eigenfunctions theory, using the amplitude deflection and the generalized curvature as two fundamental eigenfunctions, is proposed for the free vibration solutions of a rectangular Mindlin plate. The three classical eigenvalue differential equations of a Mindlin plate are reformulated to arrive at two new eigenvalue differential equations for the proposed theory. The closed form eigensolutions, which are solved from the two differential equations by means of the method of separation of variables are identical with those via Kirchhoff plate theory for thin plate, and can be employed to predict frequencies for any combinations of simply supported and clamped edge conditions. The free edges can also be dealt with if the other pair of opposite edges are simply supported. Some of the solutions were not available before. The frequency parameters agree closely with the available ones through pb-2.Rayleigh-Ritz method for different aspect ratios and relative thickness of plate.

关键词： Mindlin plate Free vibration Closed form solution Separation of variable

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An eigenelement method and two homogenization conditions

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Acta Mechanica Sinica 2009年第3期25卷 345-351页

作者： Yufeng Xing Xingming Wang The Solid mechanics Research center, Beihang University, 100083 {2., china The Solid mechanics Research center Beihang University 100083 Beijing China

Under inspiration from the structure-preserving property of symplectic difference schemes for Hamiltonian systems, two homogenization conditions for a representative unit cell of the periodical composites are proposed, one condition is the equivalence of strain energy, and the other is the deformation similarity. Based on these two homogenization conditions, an eigenelement method is presented, which is characteristic of structure-preserving property. It follows from the frequency comparisons that the eigenelement method is more accurate than the stiffness average method and the compliance average method.

关键词： Composites Homogenization ,The equivalence of strain energy Deformation similarityEigenelement method

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The size effect on transport properties of colossal magnetoresistance materials La_(0.67)Ca_(0.33)MnO_3

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Science china(Physics,mechanics & Astronomy) 2008年第3期51卷 251-257页

作者： LI PeiGang1,2.LEI Ming1,2.GUO YanFeng2.GUO Xi2.CHEN LeiMing2. TANG WeiHua1,2.SONG PengYun3 & CHEN JinPing3 1 Department of Physics,center for Optoelectronics Materials and Devices,Zhejiang Sci-Tech University,Hangzhou 310018,china 2.National Laboratory for Condensed Matter Physics,{2. of Physics,Chinese Academy of Sciences,beijing 100080,china 3 Department of Physics,Peking University,beijing 100875,china 1. Department of Physics Center for Optoelectronics Materials and Devices Zhejiang Sci-Tech University Hangzhou 310018 China 2. National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 3. Department of Physics Peking University Beijing 100875 China

High quality La0.67Ca0.33MnO3 (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO3(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2.and 1.5 μm,the insulator-to-metal transition temperature (TP) keeps un-changed compared with the film. For the micro-bridges with width of 1 μm,the TP shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm,the insulator-to-metal transition disappears. The magnetoresistance be-havior of these micro-bridges was studied,and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced.

关键词： colossal magnetoresistance pulsed electron deposition electron beam lithography electrical transport properties

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New numerical algorithms in SUPER CE/SE and their applications in explosion mechanics

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Science china(Physics,mechanics & Astronomy) 2010年第9期53卷 237-243页

作者： WANG Gang1,2.WANG JingTao1 & LIU KaiXin1,3 1 LTCS and College of Engineering,Peking University,beijing 100871,china 2.LHD,{2. of mechanics,Chinese Academy of Sciences,beijing 100190,china 3 center for Applied Physics and Technology,Peking University,beijing 100871,china 1. LTCS and College of Engineering Peking University Beijing 100871 China2. LHD Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China3. Center for Applied Physics and Technology Peking University Beijing 100871 China

The new numerical algorithms in SUPER/CESE and their applications in explosion mechanics are studied. The researched al-gorithms and models include an improved CE/SE (space-time Conservation Element and Solution Element) method,a local hybrid particle level set method,three chemical reaction models and a two-fluid model. Problems of shock wave reflection over wedges,explosive welding,cellular structure of gaseous detonations and two-phase detonations in the gas-droplet system are simulated by using the above-mentioned algorithms and models. The numerical results reveal that the adopted algorithms have many advantages such as high numerical accuracy,wide application field and good compatibility. The numerical algo-rithms presented in this paper may be applied to the numerical research of explosion mechanics.

关键词： new algorithm SUPER CE/SE numerical simulation explosion mechanics

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New evidence for lack of CMB power on large scales

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Science china(Physics,mechanics & Astronomy) 2010年第3期53卷 567-570页

作者： LIU Hao1 & LI TiPei1,2.3 1 Key Laboratory of Particle Astrophysics, institute of High Energy Physics, Chinese Academy of Sciences, beijing 100049,{2. 2.Department of Physics & center for Astrophysics, Tsinghua University, beijing 100084,{2. 3 Department of Engineering Physics & center for Astrophysics, Tsinghua University, beijing 100084,{2. 1. Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China2. Department of Physics & Center for Astrophysics Tsinghua University Beijing 100084 China3. Department of Engineering Physics & Center for Astrophysics Tsinghua University Beijing 100084 China

A digitalized temperature map is recovered from the first light sky survey image published by the Planck team, from which an angular power spectrum of the cosmic microwave background (CMB) is derived. The amplitudes of the low multipoles (low-l) measured from the preliminary Planck power spectrum are significantly lower than those reported by the WMAP team. Possible systematical effects are far from enough to explain the observed low-l differences.

关键词： cosmology cosmic microwave background data analysis

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Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback

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Science china(Technological Sciences) 2010年第3期53卷 595-607页

作者： ZHANG Li1,WANG HuaiLei1 & HU HaiYan1,2.1 MOE Key Lab of mechanics and Control of Aerospace Structures,Nanjing University of Aeronautics and Astronautics,Nanjing 2.0016,china 2.School of Aerospace Engineering,{2. institute of Technology,{2. 100081,china 1. MOE Key Lab of mechanics and Control of Aerospace Structures Nanjing University of Aeronautics and Astronautics Nanjing 210016 China2. School of Aerospace Engineering Beijing Institute of Technology Beijing 100081 China

This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state *** on a detailed analysis of the stability switches of the trivial equilibrium of the system,the stability charts are given in a parameter space consisting of the time delay and the feedback *** center manifold reduc-tion and the normal form method are used to study Hopf bifurcations with respect to the time *** gain an insight into the persistence of a Hopf bifurcation as the time delay varies farther away from its critical value,the method of multiple scales is used to obtain the global view of Hopf bifurcations with respect to the time *** the analytical results of Hopf bifurca-tions and global view of those bifurcations are validated via a collocation scheme implemented on *** most important discovery in this paper is the well-structured global view of Hopf bifurcations for the system of concern,showing the generality of the persistence of Hopf bifurcations.

关键词： Hopf bifurcation global view center manifold reduction method of multiple scales collocation scheme

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Systematic study of survival probability of excited superheavy nuclei

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Science china(Physics,mechanics & Astronomy) 2011年第S1期54卷 109-113页

作者： XIA ChengJun1, SUN BaoXi1, ZHAO EnGuang2.3 & ZHOU ShanGui2.3 1College of Applied Sciences, beijing University of Technology, beijing 10012.,{2. 2.3} of Theoretical Physics, Chinese Academy of Sciences, beijing 100190,{2. 3center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000,{2. Chinese Acad Sci Inst Theoret Phys Beijing 100190 Peoples R China beijing Univ Technol Coll Appl Sci Beijing 100124 Peoples R China Ctr Theoret Nucl Phys Natl Lab Heavy Ion Accelerator Lanzhou 730000 Peoples R China

The stability of excited superheavy nuclei (SHN) with 100 Z 134 against neutron emission and fission is investigated by using a statistical model. In particular, a systematic study of the survival probability against fission in the 1n-channel of these SHN is made. The present calculations consistently take the neutron separation energies and shell correction energies from the calculated results of the finite range droplet model which predicts an island of stability of SHN around Z = 115 and N = 179. It turns out that this island of stability persists for excited SHN in the sense that the calculated survival probabilities in the 1n-channel of excited SHN at the optimal excitation energy are maximized around Z = 115 and N = 179. This indicates that the survival probability in the 1n-channel is mainly determined by the nuclear shell effects.

关键词： survival probability superheavy elements island of stability neutron emission fission

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Half-lives and fine structure for the α decay of deformed even-even nuclei

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Science china(Physics,mechanics & Astronomy) 2011年第S1期54卷 24-31页

作者： NI DongDong1,2.& REN ZhongZhou1,2.3 1Department of Physics, Nanjing University, Nanjing 2.0093, china 2.avli institute for Theoretical Physics china, beijing 100190, china 3center of Theoretical Nuclear Physics, National Laboratory of Heavy-Ion Accelerator, Lanzhou 730000, china Nanjing Univ Dept Phys Nanjing 210093 Jiangsu Peoples R China Kavli Inst Theoret Phys china Beijing 100190 Peoples R China Ctr Theoret Nucl Phys Natl Lab Heavy Ion Accelerator Lanzhou 730000 Peoples R China

The α-decay properties of well-deformed even-even nuclei are systematically calculated within the multichannel cluster model (MCCM). Instead of working in the WKB framework, the quasibound solution to the coupled Schro¨dinger equation is presented with outgoing wave boundary conditions, and the coupling potential is taken into full account in terms of the general quantum theories. The calculated α-decay half-lives are found to agree well with the experimental data with a mean factor of less than 2. The fine structure observed in α decay is also well reproduced by the four-channel microscopic calculation. Very strikingly, the MCCM can give relatively precise descriptions of the branching ratio to excited 4+ states, which is often overestimated in the usual WKB calculations. We expect it to be a significant development of theoretical models toward quantitative descriptions of α transitions to high-spin daughter states.

关键词： α decay half-lives cluster model coupled channel approach

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