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Bifurcations of Limit Circles and Center Conditions for a Class of Non-analytic Cubic Z_2 Polynomial Differential Systems

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Acta Mathematica Sinica,English Series 2012年第11期28卷 2275-2288页

作者： feng LI Yi Rong LIU Yin lai JIN School of Science Linyi University School of Mathematical Science and Computing Technology Central South University

In this paper, bifurcations of limit cycles at three fine focuses for a class of Z2-equivariant non-analytic cubic planar differential systems axe studied. By a transformation, we first transform non- analytic systems into analytic systems. Then sufficient and necessary conditions for critical points of the systems being centers are obtained. The fact that there exist 12 small amplitude limit cycles created from the critical points is also proved. Henceforth we give a lower bound of cyclicity of Z2-equivaxiant non-analytic cubic differential systems.

关键词： Non-analytic center-focus problem Lyapunov constant limit cycles bifurcation

Theoretical calculation and experimental study on the interaction mechanism between TKX-50 and AP

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Defence Technology（防务技术） 2020年第4期16卷 825-833页

作者： jun Tao Xiao-feng Wang Kun Zhang Xue-song feng The Second Department Xi'an Modern Chemistry Research InstituteXi'an 710065China

The combination of 5,5'-bistetrazole-1,1'-diolate(TKX-50) and ammonium perchlorate(AP) can make greater use of the chemical energy of TKX-50 based energetic *** research on the interaction mechanism between TKX-50 and AP is very important for designing TKX-50-AP compounds and judging the formation feasibility of composite particles,which can lay a theoretical foundation for the preparation of TKX-50-AP mixed crystals and the application of TKX-50 in propellant,propellant and ***,in order to research the interaction mechanism between TKX-50 and AP,density-functional theory calculation was applied to optimize three configurations of TKX-50-AP *** geometry structure,electrostatic potential and binding energy of the compounds were predicted,and the electronic density topological analysis was also carried *** TKX-50-AP mixed crystals structures were constructed,and the radial distribution function of H-O and H-N in mixed crystals was ***,solvent/non-solvent method was applied to prepare TKX-50-AP composites,and the infrared spectro scopy and the non-isothermal decomposition perfo rmance of the composites were *** show that the superposition of positive charges in TKX-50 molecule and negative charges in AP makes the electrostatic potential distributions of TKX-50-AP compounds different from that of TKX-50 and *** interaction energies of TKX-50-AP 1,TKX-50-AP 2 and TKX-50-AP 3 are 39.743 kJ/mol,61.206 kJ/mol and 27.702 kJ/mol,*** interaction between TKX-50 molecules and AP molecules in TKX-50-AP mixed crystals both depends on hydrogen bonds and van der Waals force,and the number and strength of hydrogen bonds are significantly greater than that of van der Waals *** composition of AP and TKX-50 makes the absorption peak of the five-membered rings and NH_3 OH^+ of TKX-50 shift to low wavenumber in the infrared *** general,TKX-50 interacts with AP via hydrogen bonds and va

关键词： 5,5'-bistetrazole-1,1'-diolate Ammonium perchlorate Density-functional theory Molecular dynamics Hydrogen bond

First-Principles Study on Electronic and Optical Properties of Graphene-Like Boron Phosphide Sheets

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Chinese Journal of Chemical Physics 2015年第5期28卷 -页

作者： Shao-feng Wang Xiao-jun Wu CAS Key Laboratory of Materials for Energy Conversion and Department of Materials Science and Engineering University of Science and Technology of China Hefei 230026 China CAS Key Laboratory of Materials for Energy Conversion and Department of Materials Science and Engineering University of Science and Technology of China Hefei 230026 ChinaSynergetic Innovation Center of Quantum Information & Quantum Physics University of Science and Technology of China Hefei 230026 ChinaSchool of Chemistry and Materials Science and Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China Hefei 230026 China

Two-dimensional semiconducting materials with moderate band gap and high carrier mobility have a wide range of applications for electronics and optoelectronics in nanoscale. On the basis of first-principles calculations, we perform a comprehensive study on the electronics and optical properties of graphene-like boron phosphide (BP) sheets. The global structure search and first-principles based molecular dynamic simulation indicate that two-dimensional BP sheet has a graphene-like global minimum structure with high stability. BP monolayer is semiconductor with a direct band gap of 1.37 eV, which reduces with the number of layers. Moreover, the band gaps of BP sheets are insensitive to the applied uniaxial strain. The calculated mobility of electrons in BP monolayer is as high as 106 cm2/(V·s). Lastly, the MoS2/BP van der Waals heterobilayers are investigated for photovoltaic applications, and their power conversion efficiencies are estimated to be in the range of 17.7%–19.7%. This study implies the potential applications of graphene-like BP sheets for electronic and optoelectronic devices in nanoscale.

关键词： Density functional theory BP sheet Electronic structure Optical properties

Stability and Robust Stability of Switched Positive Linear Systems With All Modes Unstable

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IEEE/CAA Journal of Automatica Sinica 2019年第1期6卷 167-176页

作者： Shaoxia feng Juan Wang jun Zhao Shanxi Institute of Mechanical and Electrical Engineering the College of Information Scienceand Engineering Northeastern University the Faculty of Information and Control Engineering Shenyang Jianzhu University the State Key Laboratory of Synthetical Automationfor Process Industries (Northeastern University) the Collegeof Information Science and Engineering Northeastern University

This paper is concerned with the stability and robust stability of switched positive linear systems(SPLSs) whose subsystems are all unstable. By means of the mode-dependent dwell time approach and a class of discretized co-positive Lyapunov functions, some stability conditions of switched positive linear systems with all modes unstable are derived in both the continuous-time and the discrete-time cases, respectively. The copositive Lyapunov functions constructed in this paper are timevarying during the dwell time and time-invariant afterwards. In addition, the above approach is extended to the switched interval positive systems. A numerical example is proposed to illustrate our approach.

关键词： Discretized co-positive Lyapunov functions mode-dependent dwell time robust stability switched positive linear systems (SPLSs) unstable subsystem

QoS multicast routing scheme using QGA in IP/DWDM networks

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The Journal of China Universities of Posts and Telecommunications 2008年第4期15卷 95-100页

作者： XING Huan-lai BAI Lin JI Yue-feng Key Laboratory of Optical Communications and Lightwave Techno ogies Beijing University of Posts and Telecommunications Beijing 100876 China

This article studies multi-constraints least-cost multicast routing problem in internet protocol over dense wavelength division multiplexing （IP/DWDM） networks. To address this problem, an individual-difference-based quantum genetic algorithm （IDQGA） is proposed. This algorithm considers individual differences among chromosomes by introducing an adaptive rotation angle step determination scheme and a grouping-based quantum mutation operation. Simulations are conducted over network topologies. The results indicate that compared with other heuristic algorithms, IDQGA has better optimal performance on solving quality of service （QoS） multicast routing problem in IP/DWDM networks and is characterized by strong robustness, high success ratio and excellent capability on global searching.

关键词： IP-over-DWDM multicast QoS quantum genetic algorithm

Indexing the bit-code and distance for fast KNN search in high-dimensional spaces

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第6期8卷 857-863页

作者： LIANG jun-jie feng Yu-cai College of Computer Science ＆ Technology Huazhong University of Science and Technology Wuhan 430074 China Faculty of Mathematics ＆ Computer Science Hubei University Wuhan 430062 China

Various index structures have recently been proposed to facilitate high-dimensional KNN queries, among which the techniques of approximate vector presentation and one-dimensional (1D) transformation can break the curse of dimensionality. Based on the two techniques above, a novel high-dimensional index is proposed, called Bit-code and Distance based index (BD). BD is based on a special partitioning strategy which is optimized for high-dimensional data. By the definitions of bit code and transformation function, a high-dimensional vector can be first approximately represented and then transformed into a 1D vector, the key managed by a B+-tree. A new KNN search algorithm is also proposed that exploits the bit code and distance to prune the search space more effectively. Results of extensive experiments using both synthetic and real data demonstrated that BD out- performs the existing index structures for KNN search in high-dimensional spaces.

关键词： High-dimensional spaces KNN search Bit-code and distance based index (BD) Approximate vector

A survey on orbital dynamics and navigation of asteroid missions

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Acta Mechanica Sinica 2014年第3期30卷 282-293页

作者： He-Xi Baoyin jun-feng Li School of Aerospace Tsinghua University

Asteroid exploration is currently one of the most concerned topics among international space agencies. Or- bital dynamics and navigation are obviously crucial for asteroid exploration. This paper aims to give a brief review on the dynamics, control and navigation of asteroid reconnaissance orbits, including the heliocentric transfer orbit and near as- teroid orbit. The developments in optimization techniques of the transfer segment are discussed in detail. We surveyed global researches in this field and made comments on several important progresses. The final section proposed a prospec- tive of future studies with emphasis on the key techniques of these issues in the asteroid exploration missions.

关键词： Asteroid Orbital dynamics Navigation Control Guidance

TIDAL CONSTITUENTS IN THE BOHAI AND YELLOW SEAS FROM AN ADJOINT NUMERICAL MODEL WITH TOPEX/POSEIDON DATA

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Journal of Hydrodynamics 2005年第3期17卷 275-282页

作者： QIUZhong-feng HEYi-jun LVXian-qing InstituteofOceanology ChineseAcademyofSciencesQingdao266071China／／GraduateSchooloftheChineseAcademyofSciencesBeijing100039China InstituteofOceanology ChineseAcademyofSciencesQingdao266071China LaboratoryofPhysicalOceanography OceanUniversityofChinaOingdao266003China

Eleven tidal constituents K_1, O_1, P_1, Q_1, M_2, S_2, N_2, K_2, M_4, MS_4 and M_6, which are extracted from 10 years TOPEX/Poseidon altimetry data along track points in the Bohai and Yellow Seas, are assimilated synchronously into a two-dimension non-linear tidal model with adjoint method. And the bias between calculations and observations are provided. The deviations of M_2 are 7.1×10~ -2 m in amplitude and 4.7° in phase-lag. Those of O_1 are 2.8×10~ -2 m and 5.4° accordingly. Compared with other models, our discrepancy is less. It is shown that the precision of the model is more accurate. The co-tidal charts of the eleven constituents are also drawn. The general patterns are in good agreement with those literatures cited.

关键词： adjoint assimilation TOPEX/Poseidon tidal constitutes

Recent advances in solid-state NMR of zeolite catalysts

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National Science Review 2022年第9期9卷 79-101页

作者： Weiyu Wang jun Xu feng Deng National Center for Magnetic Resonance in Wuhan State Key Laboratory of Magnetic Resonance and Atomic and Molecular PhysicsWuhan Institute of Physics and MathematicsInnovation Academy for Precision Measurement Science and TechnologyChinese Academy of Sciences University of Chinese Academy of Sciences

Zeolites are important inorganic crystalline microporous materials with a broad range of applications in the areas of catalysis, ion exchange, and adsorption/separations. Solid-state nuclear magnetic resonance(NMR) spectroscopy has proven to be a powerful tool in the study of zeolites and relevant catalytic reactions because of its advantage in providing atomic-level insights into molecular structure and dynamic behavior. In this review, we provide a brief discussion on the recent progress in exploring framework structures, catalytically active sites and intermolecular interactions in zeolites and metal-containing ones by using various solid-state NMR methods. Advances in the mechanistic understanding of zeolite-catalysed reactions including methanol and ethanol conversions are presented as selected examples. Finally, we discuss the prospect of the solid-state NMR technique for its application in zeolites.

关键词： solid-state NMR zeolites characterization active sites reaction mechanism