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Electronic structure and magnetism of Fe-doped SiC nanotubes

science china(Physics,Mechanics & Astronomy) 2010年第9期53卷 1582-1589页

作者： ZHANG WeiHu1,2,3,ZHANG FuChun3,ZHANG ZhiYong4,LU ShuYuan5 & YANG YanNing3 1 xi’an Institute of Optics and Precision Mechanics,Chinese Academy of sciences,xi’an 710068,china 2 Graduate university of Chinese Academy of sciences,Beijing 100049,china 3 College of Physics and Electronic information,Yan’an university,Yan’an 716000,china 4 information science and technology institution,northwest university,xi’an 71012.,china 5 Department of Telecommunications,xi’an Institute of Posts and Telecommunications,xi’an 71012.,china 1. xi’an Institute of Optics and Precision Mechanics Chinese Academy of Sciences Xi’an 710068 China2. Graduate University of Chinese Academy of Sciences Beijing 100049 China3. College of Physics and Electronic Information Yan’an University Yan’an 716000 China4. Information Science and Technology Institution Northwest University Xi’an 710127 China5. Department of Telecommunications Xi’an Institute of Posts and Telecommunications Xi’an 710121 China

The electronic structure and magnetic properties of Fe-doped SiC nanotubes are investigated by using the first-principles method based on density functional theory(DFT) in the local spin density approximation(LSDA).The calculation results indicate that the SiC nanotube of Fe substitution for C exhibits antiferromagnetism while ferromagnetism features prominently when Fe substitutes *** is a kind of half-metal magnetic *** formation energy calculation results show that the formation energy of ferromagnetic structure is 3.2 eV lower than that of antiferromagnetic *** atoms are more likely to replace Si ***-orbit coupling induces electron spin polarization in the ground ***,the doping Fe atoms make relaxation towards the outside of the tube to some extent and larger geometric distortion occurs when Fe substitutes C,but the whole geometric structure of SiC nanotubes is not damaged due to the *** is revealed in the calculation of energy band structure and density of states that more dispersed distribution of energy levels is produced near the Fermi *** Fe substitution for Si,obviously there are spin-split and intense p-d hybrid effects by Si 3p electron spins and Fe 3d electron spins localized at the exchanging interactions between magnetic transitional metal(TM) *** electronic density results indicate that system magnetic moments are mainly generated by the unpaired 3d electrons of Fe *** these results show that the transition metal doping SiC nanotube could be a potential route to fabricating the promising magnetic materials.

关键词： SiC nanotube the first-principles doped magnetic properties

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L1/2 regularization

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science china(information sciences) 2010年第6期53卷 1159-1169页

作者： XU ZongBen 1 , ZHANG Hai 1,2 , WANG Yao 1 , CHANG xiangYu 1 & LIANG Yong 3 1 Institute of information and System science, xi'an Jiaotong university, xi'an 710049, china 2 Department of Mathematics, northwest university, xi'an 710069, china 3 university of science and technology, Macau 999078, china 1. Institute of information and System science Xi’an Jiaotong University Xi’an 710049 China2. Department of Mathematics Northwest University Xi’an 710069 China3. University of Science and Technology Macau 999078 China

In this paper we propose an L1 /2 regularizer which has a nonconvex *** L 1/2 regularizer is shown to have many promising properties such as unbiasedness, sparsity and oracle properties.A reweighed iterative algorithm is proposed so that the solution of the L 1/2 regularizer can be solved through transforming it into the solution of a series of L 1 *** solution of the L 1/2 regularizer is more sparse than that of the L 1 regularizer, while solving the L 1/2 regularizer is much simpler than solving the L 0 *** experiments show that the L 1/2 regularizer is very useful and efficient, and can be taken as a representative of the Lp(0 < p < 1) regularizer.

关键词： machine learning variable selection regularizer compressed sensing

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The essential ability of sparse reconstruction of different compressive sensing strategies

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science china(information sciences) 2012年第11期55卷 2582-2589页

作者： ZHANG Hai1,2,LIANG Yong3,GOU HaiLiang1 & XU ZongBen1 1 Institute for information and System science,xi'an Jiaotong university,xi'an 710049,china 2Department of Mathematics,northwest university,xi'an 710069,china 3university of science and technology,Macau 999078,china 1. Institute for information and System science Xi’an Jiaotong University Xi’an 710049 China2. Department of Mathematics Northwest University Xi’an 710069 China3. University of Science and Technology Macau 999078 China

We show the essential ability of sparse signal reconstruction of different compressive sensing strategies,which include the L1 regularization,the L0 regularization(thresholding iteration algorithm and OMP algorithm),the Lq(0 2 regularization can be taken as a representative of the Lq(0 2 2 regularization always yields the sparsest solutions and when 0 2 the performance of the regularizations takes no significant *** results of this paper provide experimental evidence for our previous work.

关键词： compressive sensing regularization sparsity L1/2 regularization

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Refractive index changes induced by sheet beams with various intensity distributions in LiNbO_(3):Fe crystal

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science china(Physics,Mechanics & Astronomy) 2005年第4期48卷 399-412页

作者： ZHANG Peng1, ZHAO Jianlin1, XU Honglai1, SUN Yidong2, YANG Dexing1 & WANG Meirong1 1. Institute of Optical information science and technology, School of science, northwestern Polytechnical university, xi’an 710072, china 2. School of science, xi’an Jiaotong university, xi’an 710049, china 1. Institute of Optical information science and Technology School of Science Northwestern Polytechnical University 710072 Xi’an China 2. School of science Xi’an Jiaotong University 710049 Xi’an China

According to the Kukhtarev equations and a simplified model based on the photovoltaic charge carriers transport mechanism, the distributions of the index changes (DICs) in LiNbO3:Fe crystals induced by sheet beams with various intensity profiles are theoretically analyzed. The numerically simulated results coincide with the analytic expressions deduced from the simplified model. The DICs in a LiNbO3:Fe crystal induced by sheet beams with rectangular, Gaussian and square law profiles are measured by using the interferometric method. By employing the analytic expressions, the experimental data points are well fitted. By utilizing the angular spectrum theory and the ray equation, the uniformities of the intensity profiles of the writing beams along the propagation directions and the influences of the self-defocusing effect of the crystal are numerically simulated, respectively. The results show that the experimental results are reliable. The numerically simulated method and the analytic expressions can be both employed to predict the DICs induced by sheet beams with various light intensity profiles. Furthermore, utilizing writing beams with proper intensity profiles, any desired index distributions could be obtained.

关键词： LiNbO3:Fe crystal, light intensity profile, distribution of refractive index changes, sheet beam.

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Hydrothermal Synthesis Ultralong Single-crystal Sb_2S_3 Nanowires

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Journal of Wuhan university of technology(Materials science) 2010年第3期25卷 411-414页

作者：刘运 School of Electric and information Engineering Shaanxi University of Science and Technology

This paper describes an ethylene glycol（EG）-assisted approach to the ultralong Sb2S3 nanowires,formed by a simple hydrothermal reaction between SbCl3 and Na2S in the presence of distilled *** electron microscopy and scanning electron microscopy studies indicate that these Sb2S3 nanowires possess a diameter around 200 nm and length up to 100 μ ***-resolution transmission electron microscopy and selected area electron diffraction studies reveal that each Sb2S3 nanowire is a single-crystal along the [001] *** possible formation mechanism of the nanowires was *** effects of volume ratio of ethylene glycol/water on the morphology of Sb2S3 nanowires were also *** reflectance spectrum result shows that the final products have an apparent blue shift by quantum size effect.

关键词： nanostructures chemical synthesis electron microscopy electron diffraction

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Design and analysis of a wideband photonic crystal waveguide with low group-velocity and low dispersion

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science china(Physics,Mechanics & Astronomy) 2010年第3期53卷 481-485页

作者： Lü ShuYuan, ZHAO JianLin & ZHANG Dong Institute of Optical information science and technology, Shanxi Key Laboratory of Optical information technology, School of science, northwestern Polytechnical university, xi’an 710072, china 1. Institute of Optical information science and technology Shanxi Key Laboratory of Optical Information Technology School of Science Northwestern Polytechnical University Xi’an 710072 China

The slow light propagation in a line waveguide in the two-dimensional triangular photonic crystal has been numerically studied, based on which a wideband photonic crystal waveguide with low group-velocity and low dispersion is proposed. The numerical simulation analysis shows that it is possible to maximize the group index and minimize the group-velocity dispersion in wide bandwidth by increasing the radius of the basic air hole and changing the position of the first two rows of air holes in photonic crystal waveguides. Such a photonic crystal waveguide exhibits low group velocity and low group-velocity dispersion over a broad wavelength range. A larger group index-bandwidth product is achieved in this type of waveguide structure. The numerically computed results present the normalized bandwidth as 0.32%, 0.48% and 0.642% corresponding to the group index of 85, 58 and 45, respectively.

关键词： photonic crystal waveguide slow light group-velocity group-velocity dispersion group index

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A mathematical model for concept granular computing systems

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science china(information sciences) 2010年第7期53卷 1397-1408页

作者： QIU GuoFang1, MA JianMin2, YANG HongZhi3 & ZHANG Wenxiu3 1School of Management, xi’an university of Architecture & technology, xi’an 710055, china 2Faculty of science, Chang’an university, xi’an 710064, china 3Faculty of science, xi’an Jiaotong university, xi’an 710049, china 1. School of Management Xi’an University of Architecture & Technology Xi’an 710055 China2. Faculty of Science Chang’an University Xi’an 710064 China3. Faculty of Science Xi’an Jiaotong University Xi’an 710049 China

Extent-intent and intent-extent operators are introduced between two complete lattices in this paper and a mathematical model for concept granular computing system is established. We proved that the set of all concepts in this system is a lattice with the greatest element and the least element. This framework includes formal concept lattices from formal contexts, L fuzzy concept lattices from L fuzzy formal contexts and three kinds of variable threshold concept lattices, i.e. the extension and the intension of a concept are a crisp set and a crisp set, a crisp set and a fuzzy set, a fuzzy set and a crisp set, respectively. Finally, some iterative algorithms for constructing concepts are proposed and they are proved to be optimal concepts under some conditions in this system.

关键词： granular computing formal concept analysis concept lattice mathematical model

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A centrality measure based on spectral optimization of modularity density

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science china(information sciences) 2010年第9期53卷 1727-1737页

作者： FU LiDong1,2*,GAO Lin1 & MA xiaoKe1 1School of Computer science and Engineering,xidian university,xi'an 710071,china 2College of Computer,xi'an university of science and technology,xi'an 710054,china 1. School of Computer science and Engineering Xidian University Xi’an 710071 China2. College of Computer Xi’an University of Science and Technology Xi’an 710054 China

Centrality analysis has been shown to be a valuable method for the structural analysis of complex *** is used to identify key elements within networks and to rank network elements such that experiments can be tailored to interesting *** this paper,we show that the optimization process of modularity density can be written in terms of the eigenspectrum of kernel *** on the eigenvectors belonging to the largest eigenvalue of kernel matrix,we present a new centrality measure that characterizes the contribution of each node to its assigned community in a network,called modularity density *** measure is illustrated and compared with the standard centrality measures by using respectively an artificial example and a classic network data *** statistical distribution of modularity density centrality is investigated by considering large computer generated graphs and two large networks from the real *** results show the significance of the proposed approach.

关键词： centrality modularity density centrality kernel matrix eigenspectrum

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Lattice-based artificial endocrine system model and its application in robotic swarms

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science china(information sciences) 2011年第4期54卷 795-811页

作者： XU QingZheng 1,2 & WANG Lei 1 1 School of Computer science and Engineering,xi’an university of technology,xi’an 710048,china 2 xi’an Communication Institute,xi’an 710106,china 1. School of Computer science and Engineering Xi’an University of Technology Xi’an 710048 China2. Xi’an Communication Institute Xi’an 710106 China

To solve the problem of controlling robot swarms in a distributed manner,we propose a novel latticebased artificial endocrine system (LAES) model,inspired by modern endocrinology *** on a latticed environment,relying on cell intelligentization,connected by cumulative hormones,and directed by target cells,the LAES model can finally adapt to the continuous volatility of the external environment and maintain the relevant stability of the internal dynamics of the system,thus exhibiting the self-organizing and self-repairing features of the biological endocrine *** show that the LAES model enables a robotic swarm to search an unfamiliar space and seize multiple targets automatically without using unique global identifiers or a centralized control strategy for the individual *** demonstrates that the model can reliably be used to simulate large scale swarm behavior through wireless communication.

关键词： artificial endocrine system robotic swarms endocrine cell hormone self organization self repair searching and seizing

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A STUDY OF OSCILLATING FLOWS OVER PROPAGATING RIPPLES:PART Ⅱ. VORTICITY DYNAMICS

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Journal of Hydrodynamics 2000年第1期12卷 8-15页

作者： Lu xi yun Department of Modern Mechanics, university of science and technology of china, Hefei 230026, P.R.china Univ of science and technology of China Hefei China

Vortex shedding for an oscillating flow over ripples is numerically investigated by solving 2 D time dependent incompressible Navier Stokes equations in curvilinear coordinates. The dynamics of vortex structures generated by flow separation is studied in order to understand some phenomena which take place near the bottom and in particular to get insight into the mechanism through which sediment grains are lifted up and maintained in suspension. Based on our calculated results, some important phenomena, such as vortex shedding, vortices pairing, vortices coalescence, vortex interaction with the free shear layer and so on, can be found. The behaviors of energy dissipation in the flow field and of shear stress along the ripple surface are also discussed for studying the dynamics of sediment grains in suspension and to obtain new information on the suspended load over the ripples.

关键词： oscillating flow ripple vorticity dynamics separation flow

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