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2008年, 第17卷, 第5期　刊出日期：2008-05-20 上一期    下一期

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A hybrid scheme for computing incompressible two-phase flows 周 军, 蔡 力, 周凤岐 2008 (5):  1535-1544.  doi: 10.1088/1674-1056/17/5/001 摘要 ( 1359 )   PDF(1992KB) ( 775 )   We propose a hybrid scheme for computations of incompressible two-phase flows. The incompressible constraint has been replaced by a pressure Poisson-like equation and then the pressure is updated by the modified marker and cell method. Meanwhile, the moment equations in the incompressible Navier--Stokes equations are solved by our semi-discrete Hermite central-upwind scheme, and the interface between the two fluids is considered to be continuous and is described implicitly as the 0.5 level set of a smooth function being a smeared out Heaviside function. It is here named the hybrid scheme. Some numerical experiments are successfully carried out, which verify the desired efficiency and accuracy of our hybrid scheme. 相关文章 | 计量指标

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Unified symmetry of mechano-electrical systems with nonholonomic constraints 李元成, 夏丽莉, 刘 冰, 焦志勇, 王小明 2008 (5):  1545-1549.  doi: 10.1088/1674-1056/17/5/002 摘要 ( 1325 )   PDF(149KB) ( 665 )   The unified symmetry of mechano-electrical systems with nonholonomic constraints are studied in this paper, the definition and the criterion of unified symmetry of mechano-electrical systems with nonholonomic constraints are derived from the Lagrange--Maxwell equations. The Noether conserved quantity, Hojman conserved quantity and Mei conserved quantity are then deduced from the unified symmetry. An example is given to illustrate the application of the results. 相关文章 | 计量指标

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Perturbation to Mei symmetry and adiabatic invariants for Hamilton systems 丁 宁, 方建会 2008 (5):  1550-1553.  doi: 10.1088/1674-1056/17/5/003 摘要 ( 1698 )   PDF(130KB) ( 555 )   Based on the concept of adiabatic invariant, this paper studies the perturbation to Mei symmetry and adiabatic invariants for Hamilton systems. The exact invariants of Mei symmetry for the system without perturbation are given. The perturbation to Mei symmetry is discussed and the adiabatic invariants induced from the perturbation to Mei symmetry of the system are obtained. 相关文章 | 计量指标

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Noether symmetry and Lie symmetry of discrete holonomic systems with dependent coordinates 施沈阳, 黄晓虹 2008 (5):  1554-1559.  doi: 10.1088/1674-1056/17/5/004 摘要 ( 1357 )   PDF(148KB) ( 582 )   The Noether symmetry, the Lie symmetry and the conserved quantity of discrete holonomic systems with dependent coordinates are investigated in this paper. The Noether symmetry provides a discrete Noether identity and a conserved quantity of the system. The invariance of discrete motion equations under infinitesimal transformation groups is defined as the Lie symmetry, and the condition of obtaining the Noether conserved quantity from the Lie symmetry is also presented. An example is discussed to show the applications of the results. 相关文章 | 计量指标

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Mei symmetry and Mei conserved quantity of nonholonomic systems with unilateral Chetaev type in Nielsen style 贾利群, 解加芳, 罗绍凯 2008 (5):  1560-1564.  doi: 10.1088/1674-1056/17/5/005 摘要 ( 1428 )   PDF(151KB) ( 857 )   This paper studies the Mei symmetry and Mei conserved quantity for nonholonomic systems of unilateral Chetaev type in Nielsen style. The differential equations of motion of the system above are established. The definition and the criteria of Mei symmetry, loosely Mei symmetry, strictly Mei symmetry for the system are given in this paper. The existence condition and the expression of Mei conserved quantity are deduced directly by using Mei symmetry. An example is given to illustrate the application of the results. 相关文章 | 计量指标

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Young's modulus surface and Poisson's ratio curve for tetragonal crystals 张建民, 张 研, 徐可为, Ji Vincent 2008 (5):  1565-1573.  doi: 10.1088/1674-1056/17/5/006 摘要 ( 1499 )   PDF(1188KB) ( 752 )   This paper gives the general expressions for the compliance s' ijkl , Young's modulus E(hkl) and Poisson's ratio \upsilon (hkl,θ ) along arbitrary loading direction [hkl] for tetragonal crystals. The representation surface for which the length of the radius vector in the [hkl] direction equals E(hkl) and representation curve for which the length of the radius vector with angle θ deviated from the reference directions [00\overline 1 ], [100], [00\overline 1 ], [10\overline 1 ] and [11\overline 2 ] equals \upsilon (100,θ ), \upsilon (001,θ ), \upsilon (110,θ ), \upsilon (101,θ ) and \upsilon (111,θ ) respectively, are constructed for nine tetragonal crystals (ammonium dihydrogen arsenate, ammonium dihydrogen phosphate, barium titanate, indium, nickel sulfate, potassium dihydrogen arsenate, potassium dihydrogen phosphate, tin and zircon). The characteristics of them are analysed in detail. 相关文章 | 计量指标

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The multicomponent (2+1)-dimensional Glachette--Johnson (GJ) equation hierarchy and its super-integrable coupling system 于发军, 张鸿庆 2008 (5):  1574-1580.  doi: 10.1088/1674-1056/17/5/007 摘要 ( 1314 )   PDF(167KB) ( 550 )   This paper presents a set of multicomponent matrix Lie algebra, which is used to construct a new loop algebra \tilde{A}M. By using the Tu scheme, a Liouville integrable multicomponent equation hierarchy is generated, which possesses the Hamiltonian structure. As its reduction cases, the multicomponent (2+1)-dimensional Glachette--Johnson (GJ) hierarchy is given. Finally, the super-integrable coupling system of multicomponent (2+1)-dimensional GJ hierarchy is established through enlarging the spectral problem. 相关文章 | 计量指标

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A simple approach to solving double sinh--Gordon equation 谢元喜, 苏卡林, 朱曙华 2008 (5):  1581-1586.  doi: 10.1088/1674-1056/17/5/008 摘要 ( 1443 )   PDF(135KB) ( 554 )   By introducing an auxiliary ordinary differential equation and solving it by the method of variable separation, abundant types of explicit and exact solutions for the double sinh--Gordon equation are derived in a simple manner. 相关文章 | 计量指标

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Quantum teleportation of an arbitrary superposition of atomic states 陈 琼, 方细明 2008 (5):  1587-1592.  doi: 10.1088/1674-1056/17/5/009 摘要 ( 1582 )   PDF(169KB) ( 624 )   This paper proposes a scheme to teleport an arbitrary multi-particle two-level atomic state between two parties or an arbitrary zero- and one-photon entangled state of multi-mode between two high-$Q$ cavities in cavity QED. This scheme is based on the resonant interaction between atom and cavity and does not involve Bell-state measurement. It investigates the fidelity of this scheme and find out the case of this unity fidelity of this teleportation. Considering the practical case of the cavity decay, this paper finds that the condition of the unity fidelity is also valid and obtains the effect of the decay of the cavity on the successful probability of the teleportation. 相关文章 | 计量指标

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One step to generate quantum controlled phase-shift gate using a trapped ion 张世军, 马 驰, 张文海, 叶 柳 2008 (5):  1593-1596.  doi: 10.1088/1674-1056/17/5/010 摘要 ( 1346 )   PDF(166KB) ( 452 )   This paper presents a very simple scheme for generating quantum controlled phase-shift gate with only one step by using the two vibrational modes of a trapped ion as the two qubits. The scheme couples two vibration degrees of freedom coupled with a suitable chosen laser excitation via the ionic states. 相关文章 | 计量指标

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Scheme for implementing quantum dense coding with W-class state in cavity QED 何 娟, 叶 柳, 倪致祥 2008 (5):  1597-1600.  doi: 10.1088/1674-1056/17/5/011 摘要 ( 1305 )   PDF(148KB) ( 713 )   An experimentally feasible protocol for realizing dense coding by using a class of W-state in cavity quantum electrodynamics (QED) is proposed in this paper. The prominent advantage of our scheme is that the successful probability of the dense coding with a W-class state can reach 1. In addition, the scheme can be implemented by the present cavity QED techniques. 相关文章 | 计量指标

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Squeezing via coupling of Bose--Einstein condensates in a double-well potential with a cavity light field 周 鲁, 孔令波, 詹明生 2008 (5):  1601-1606.  doi: 10.1088/1674-1056/17/5/012 摘要 ( 1380 )   PDF(229KB) ( 719 )   Squeezing via the interaction between the cavity light field and the Bose--Einstein Condensate (BEC) in a double-well potential is considered within the context of the two-mode approximation. For the cavity light field initially in a coherent state, it is shown that by choosing appropriate parameters, quadrature squeezing of the cavity light field can be achieved and it exhibits periodic oscillation. We also study the case in which BEC is tuned to resonance by periodically modulating the trapping potential, and the quadrature squeezing of the cavity field exhibits periodic collapse and revival effect. Both analytic and numerical calculations are performed, and they are found to be in good agreement with each other. The result shows that the quantum statistical properties of the cavity light field can be manipulated by its coupling with the condensates in the double-well potential. On the other hand, dynamical properties of the condensates in the double-well potential will be reflected by the quadrature squeezing of the light field. 相关文章 | 计量指标

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Remote atom entanglement in a fibre-connected three-atom system 郭彦青, 陈 菁, 宋鹤山 2008 (5):  1607-1613.  doi: 10.1088/1674-1056/17/5/013 摘要 ( 1402 )   PDF(564KB) ( 476 )   An Ising-type atom--atom interaction is obtained in a fibre-connected three-atom system. The interaction is effective when Δ≈γ0>> g. The preparations of remote two-atom and three-atom entanglements governed by this interaction are discussed in a specific parameter region. The overall two-atom entanglement is very small because of the existence of the third atom. However, the three-atom entanglement can reach a maximum very close to $1$. 相关文章 | 计量指标

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A scheme for approximate conditional teleportation of entangled two-mode cavity state without Bell state measurement 钟志荣 2008 (5):  1614-1617.  doi: 10.1088/1674-1056/17/5/014 摘要 ( 1451 )   PDF(183KB) ( 482 )   An alternative scheme to approximately conditionally teleport entangled two-mode cavity state without Bell state measurement in cavity QED is proposed. The scheme is based on the resonant interaction of a ladder-type three-level atom with two bimodal cavities. The entangled cavity state is reconstructed with only one atom interacting with the two cavities successively. 相关文章 | 计量指标

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Generation of cluster-type entangled squeezed vacuum states 文晶姬, 邵晓强, 金星日, 张 寿, Yeon Kyu-Hwang 2008 (5):  1618-1622.  doi: 10.1088/1674-1056/17/5/015 摘要 ( 1483 )   PDF(247KB) ( 576 )   We present a scheme to prepare cluster-type entangled squeezed vacuum states (CTESVS) by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field. After the realization of simple atomic measurements, the generation of CTESVS in four separate cavities is accomplished within the cavity decay time. In the case of large atom--cavity detuning, the scheme is immune to the effect of atomic spontaneous emission. 相关文章 | 计量指标

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Quantum phase transition and von Neumann entropy of quasiperiodic Hubbard chains 朱 璇, 童培庆 2008 (5):  1623-1628.  doi: 10.1088/1674-1056/17/5/016 摘要 ( 1361 )   PDF(897KB) ( 599 )   The half-filled Hubbard chains with the Fibonacci and Harper modulating site potentials are studied in a self-consistent mean-field approximation. A new order parameter is introduced to describe a charge density order. We also calculate the von Neumann entropy of the ground state. The results show that the von Neumann entropy can identify a CDW/SDW (charge density wave/spin density wave) transition for quasiperiodic models. 相关文章 | 计量指标

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Hawking radiation from gravity's rainbow via gravitational anomaly 曾晓雄, 杨树政, 陈德友 2008 (5):  1629-1632.  doi: 10.1088/1674-1056/17/5/017 摘要 ( 1421 )   PDF(155KB) ( 731 )   Based on the anomaly cancellation method, initiated by Robinson and Wilczek, we investigates Hawking radiation from the modified Schwarzschild black hole from gravity's rainbow from the anomaly point of view. Unlike the general Schwarzschild space--time, the metric of this black hole depends on the energies of probes. The obtained result shows to restore the underlying general covariance at the quantum level in the effective field, the covariant compensating flux of energy--momentum tensor, which is related to the energies of the probes, should precisely equal to that of a (1 + 1) -dimensional blackbody at the Hawking temperature. 相关文章 | 计量指标

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Real scalar field scattering with polynomial approximation around Schwarzschild--de Sitter black-hole 刘墨林, 刘宏亚, 张敬飞, 于 飞 2008 (5):  1633-1639.  doi: 10.1088/1674-1056/17/5/018 摘要 ( 1378 )   PDF(726KB) ( 476 )   As one of the fitting methods, the polynomial approximation is effective to process sophisticated problem. In this paper, we employ this approach to handle the scattering of scalar field around the Schwarzschild--de Sitter black-hole. The complicated relationship between tortoise coordinate and radial coordinate is replaced by the approximate polynomial. The Schr?dinger-like equation, the real boundary conditions and the polynomial approximation construct a full Sturm--Liouville type problem. Then this boundary value problem can be solved numerically for two limiting cases: the first one is the Nariai black-hole whose horizons are close to each other, the second one is the black-hole with the horizons widely separated. Compared with previous results (Brevik and Tian), the field near the event horizon and cosmological horizon can have a better description. 相关文章 | 计量指标

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Quantum optical ABCD theorem in two-mode case 范洪义, 胡利云 2008 (5):  1640-1644.  doi: 10.1088/1674-1056/17/5/019 摘要 ( 1391 )   PDF(151KB) ( 781 )   By introducing the entangled Fresnel operator (EFO) this paper demonstrates that there exists ABCD theorem for two-mode entangled case in quantum optics. The canonical operator method as mapping of ray-transfer ABCD matrix is explicitly shown by EFO's normally ordered expansion through the coherent state representation and the technique of integration within an ordered product of operators. 相关文章 | 计量指标

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Design and analysis of doped left-handed materials 张洪欣, 包永芳, 吕英华, 陈天明, 王海侠 2008 (5):  1645-1651.  doi: 10.1088/1674-1056/17/5/020 摘要 ( 1263 )   PDF(1693KB) ( 702 )   We devise three sorts of doped left-handed materials (DLHMs) by introducing inductors and capacitors into the traditional left-handed material (LHM) as heterogeneous elements. Some new properties are presented through finite-difference time-domain (FDTD) simulations. On the one hand, the resonance in the traditional LHM is weakened and the original pass band is narrowed by introducing inductors. On the other hand, the original pass band of the LHM can be shifted and a new pass band can be generated by introducing capacitors. When capacitors and inductors are introduced simultaneously, the resonance of traditional LHM is somewhat weakened and the number of original pass bands as well as its bandwidth can be changed. 相关文章 | 计量指标

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Synchronization of different chaotic systems via active radial basis functions sliding mode controller 郭会军, 尹有为, 王华民 2008 (5):  1652-1663.  doi: 10.1088/1674-1056/17/5/021 摘要 ( 1621 )   PDF(280KB) ( 700 )   This paper presents a new method to synchronize different chaotic systems with disturbances via an active radial basis function (RBF) sliding controller. This method incorporates the advantages of active control, neural network and sliding mode control. The main part of the controller is given based on the output of the RBF neural networks and the weights of these single layer networks are tuned on-line based on the sliding mode reaching law. Only several radial basis functions are required for this controller which takes the sliding mode variable as the only input. The proposed controller can make the synchronization error converge to zero quickly and can overcome external disturbances. Analysis of the stability for the controller is carried out based on the Lyapunov stability theorem. Finally, five examples are given to illustrate the robustness and effectiveness of the proposed synchronization control strategy. 相关文章 | 计量指标

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Circuit realization of the fractional-order unified chaotic system 陈向荣, 刘崇新, 王发强 2008 (5):  1664-1669.  doi: 10.1088/1674-1056/17/5/022 摘要 ( 1664 )   PDF(2010KB) ( 1038 )   This paper studies the chaotic behaviours of the fractional-order unified chaotic system. Based on the approximation method in frequency domain, it proposes an electronic circuit model of tree shape to realize the fractional-order operator. According to the tree shape model, an electronic circuit is designed to realize the 2.7-order unified chaotic system. Numerical simulations and circuit experiments have verified the existence of chaos in the fraction-order unified system. 相关文章 | 计量指标

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New results on global exponential stability of competitive neural networks with different time scales and time-varying delays 崔宝同, 陈 君, 楼旭阳 2008 (5):  1670-1677.  doi: 10.1088/1674-1056/17/5/023 摘要 ( 1413 )   PDF(200KB) ( 612 )   This paper studies the global exponential stability of competitive neural networks with different time scales and time-varying delays. By using the method of the proper Lyapunov functions and inequality technique, some sufficient conditions are presented for global exponential stability of delay competitive neural networks with different time scales. These conditions obtained have important leading significance in the designs and applications of global exponential stability for competitive neural networks. Finally, an example with its simulation is provided to demonstrate the usefulness of the proposed criteria. 相关文章 | 计量指标

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Impulsive control of permanent magnet synchronous motors with parameters uncertainties 李 东, 王时龙, 张小洪, 杨 丹, 王 慧 2008 (5):  1678-1684.  doi: 10.1088/1674-1056/17/5/024 摘要 ( 1366 )   PDF(273KB) ( 721 )   The permanent magnet synchronous motors (PMSMs) may have chaotic behaviours for the uncertain values of parameters or under certain working conditions, which threatens the secure and stable operation of motor-driven. It is important to study methods of controlling or suppressing chaos in PMSMs. In this paper, robust stabilities of PMSM with parameter uncertainties are investigated. After the uncertain matrices which represent the variable system parameters are formulated through matrix analysis, a novel asymptotical stability criterion is established. Some illustrated examples are also given to show the effectiveness of the obtained results. 相关文章 | 计量指标

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Hash function based on the generalized Henon map 郑 凡, 田小建, 李雪妍, 吴 斌 2008 (5):  1685-1690.  doi: 10.1088/1674-1056/17/5/025 摘要 ( 1300 )   PDF(229KB) ( 524 )   A new Hash function based on the generalized Henon map is proposed. We have obtained a binary sequence with excellent pseudo-random characteristics through improving the sequence generated by the generalized Henon map, and use it to construct Hash function. First we divide the message into groups, and then carry out the Xor operation between the ASCII value of each group and the binary sequence, the result can be used as the initial values of the next loop. Repeat the procedure until all the groups have been processed, and the final binary sequence is the Hash value. In the scheme, the initial values of the generalized Henon map are used as the secret key and the messages are mapped to Hash values with a designated length. Simulation results show that the proposed scheme has strong diffusion and confusion capability, good collision resistance, large key space, extreme sensitivity to message and secret key，and it is easy to be realized and extended. 相关文章 | 计量指标

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Bifurcation analysis and control of periodic solutions changing into invariant tori in Langford system 刘素华, 唐驾时, 秦金旗, 尹小波 2008 (5):  1691-1697.  doi: 10.1088/1674-1056/17/5/026 摘要 ( 1459 )   PDF(273KB) ( 853 )   Bifurcation characteristics of the Langford system in a general form are systematically analysed, and nonlinear controls of periodic solutions changing into invariant tori in this system are achieved. Analytical relationship between control gain and bifurcation parameter is obtained. Bifurcation diagrams are drawn, showing the results of control for secondary Hopf bifurcation and sequences of bifurcations route to chaos. Numerical simulations of quasi-periodic tori validate analytic predictions. 相关文章 | 计量指标

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Dynamical evolution processes of traffic flow and travel cost in urban transportation networks 郭仁拥, 黄海军 2008 (5):  1698-1702.  doi: 10.1088/1674-1056/17/5/027 摘要 ( 1437 )   PDF(204KB) ( 583 )   Considering such a fact that travellers dynamically adjust their routes and the resultant link traffic flows in a network evolve over time, this paper proposes a dynamical evolutionary model of the traffic assignment problem with endogenous origin--destination (OD) demands. The model's stability is analysed and the resultant user equilibrium (UE) state is shown to be stable under certain conditions. Numerical results in a grid network indicate that the model can generate convergent flow patterns and finally terminates at the UE state. Impacts by the parameters associated with OD demand function and link cost function are also investigated. 相关文章 | 计量指标

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Cascades with coupled map lattices in preferential attachment community networks 崔 迪, 高自友, 赵小梅 2008 (5):  1703-1708.  doi: 10.1088/1674-1056/17/5/028 摘要 ( 1370 )   PDF(235KB) ( 642 )   In this paper, cascading failure is studied by coupled map lattice (CML) methods in preferential attachment community networks. It is found that external perturbation R is increasing with modularity $Q$ growing by simulation. In particular, the large modularity $Q$ can hold off the cascading failure dynamic process in community networks. Furthermore, different attack strategies also greatly affect the cascading failure dynamic process. It is particularly significant to control cascading failure process in real community networks. 相关文章 | 计量指标

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A dynamic macromodel for distributed parameter magnetic microactuators 方玉明, 黄庆安, 李伟华 2008 (5):  1709-1715.  doi: 10.1088/1674-1056/17/5/029 摘要 ( 1330 )   PDF(346KB) ( 721 )   This paper presents a reduced-order model to describe the mechanical behaviour of microbeam-based magnetic devices. The integration for magnetic force is calculated by dividing the microbeam into several segments, and the nonlinear equation set has been developed based on the magnetic circuit principle. In comparison with previous models, the present macromodel accounts for both the micro-magnetic-core reluctance and the coupling between the beam deflection and magnetic force. This macromodel is validated by comparing with the experimental results available in some papers and finite-element solutions. 相关文章 | 计量指标

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The He--McKellar--Wilkens effect for spin-1 particles on non-commutative space 李 康, 沙依甫加马力.达吾来提, 王剑华 2008 (5):  1716-1719.  doi: 10.1088/1674-1056/17/5/030 摘要 ( 1300 )   PDF(170KB) ( 707 )   By using star product method, the He--McKellar--Wilkens (HMW) effect for spin-one neutral particle on non-commutative (NC) space is studied. After solving the Kemmer-like equations on NC space, we obtain the topological HMW phase on NC space where the additional terms related to the space--space non-commutativity are given explicitly. 相关文章 | 计量指标

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Boundedness and convergence of perturbed corrections for helium-like ions in ground states 赵云辉, 海文华, 赵乘麟, 罗小兵 2008 (5):  1720-1728.  doi: 10.1088/1674-1056/17/5/031 摘要 ( 1422 )   PDF(225KB) ( 527 )   Applying the improved Rayleigh--Schr?dinger perturbation theory based on an integral equation to helium-like ions in ground states and treating electron correlations as perturbations, we obtain the second-order corrections to wavefunctions consisting of a few terms and the third-order corrections to energicity. It is demonstrated that the corrected wavefunctions are bounded and quadratically integrable, and the corresponding perturbation series is convergent. The results clear off the previous distrust for the convergence in the quantum perturbation theory and show a reciprocal development on the quantum perturbation problem of the ground state helium-like systems. 相关文章 | 计量指标

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Improvements on the third generation of electron momentum spectrometer 宁传刚, 张书锋, 邓景康, 刘 昆, 黄艳茹, 罗志弘 2008 (5):  1729-1737.  doi: 10.1088/1674-1056/17/5/032 摘要 ( 1265 )   PDF(1440KB) ( 469 )   The significant modifications to our recently constructed electron momentum spectrometer have been implemented. Compared with our previous report, the energy and the angle resolutions are significantly improved and reach ΔE=0.45eV, Δθ=±0.53o and Δπ=±0.84o, respectively. Moreover, the details of data reduction and the relation between azimuthal angle range and the sensitivity are discussed. 相关文章 | 计量指标

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Analytical potential energy function for the electronic states 2П1/2 and 2П3/2 of O2x(x=+1, --1) 吕 兵, 令狐荣锋, 周 勋, 杨向东, 朱正和, 程新路 2008 (5):  1738-1742.  doi: 10.1088/1674-1056/17/5/033 摘要 ( 1243 )   PDF(215KB) ( 567 )   The splitting of potential energy levels for ground state X2$\Pi$g of O2x(x=+1, -1) under spin--orbit coupling (SOC) has been calculated by using the spin--orbit (SO) multi-configuration quasi-degenerate perturbation theory (SO-MCQDPT). Their Murrell--Sorbie (M--S) potential functions are gained, and then the spectroscopic constants for electronic states 2$\Pi$1/2 and 2$\Pi$3/2 are derived from the M--S function. The vertical excitation energies for O2x(x=+1, -1) are $\nu$ [O2+1 (2$\Pi$3/2 → X2$\Pi$1/2)]=195.652cm-1, and $\nu$ [O2-1(2$\Pi$1/2 → X2$\Pi$3/2 )]=182.568cm-1, respectively. All the spectroscopic data for electronic states 2$\Pi$1/2 and 2$\Pi$3/2 are given for the first time. 相关文章 | 计量指标

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Composite optical vortices in noncollinear Laguerre--Gaussian beams and their propagation in free space 程 科, 刘普生, 吕百达 2008 (5):  1743-1751.  doi: 10.1088/1674-1056/17/5/034 摘要 ( 1506 )   PDF(343KB) ( 579 )   Taking two Laguerre--Gaussian beams with topological charge l=±1 as an example, this paper studies the composite optical vortices formed by two noncollinear Laguerre--Gaussian beams with different phases, amplitudes, waist widths, off-axis distances, and their propagation in free space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β, amplitude ratio η, waist width ratio \textitζ, or off-axis distance ratio μ. The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams. The motion, creation and annihilation of composite vortices take place in the free-space propagation, and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane. 相关文章 | 计量指标

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Spatial correlation properties and phase singularity annihilation of Gaussian Schell-model beams in the focal region 刘普生, 潘留占, 吕百达 2008 (5):  1752-1757.  doi: 10.1088/1674-1056/17/5/035 摘要 ( 1518 )   PDF(290KB) ( 449 )   By using the generalized Debye diffraction integral, this paper studies the spatial correlation properties and phase singularity annihilation of apertured Gaussian Schell-model (GSM) beams in the focal region. It is shown that the width of the spectral degree of coherence can be larger, less than or equal to the corresponding width of spectral density, which depends not only on the scalar coherence length of the beams, but also on the truncation parameter. With a gradual increase of the truncation parameter, a pair of phase singularities of the spectral degree of coherence in the focal plane approaches each other, resulting in subwavelength structures. Finally, the annihilation of pairs of phase singularities takes place at a certain value of the truncation parameter. With increasing scalar coherence length, the annihilation occurs at the larger truncation parameter. However, the creation process of phase singularities outside the focal plane is not found for GSM beams. 相关文章 | 计量指标

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Non-geometrical effects on Gaussian beams transmitting through a thin dielectric slab 李春芳, 张 妍, 陈 玺, 朱绮彪 2008 (5):  1758-1768.  doi: 10.1088/1674-1056/17/5/036 摘要 ( 1202 )   PDF(488KB) ( 496 )   It is shown that a Gaussian light beam transmitting through a planar thin dielectric slab in the air undergoes four different effects, i.e. lateral Goos--Hänchen-like (GHL) displacement, angular deflection, width modification and longitudinal focal shift as compared with the results predicted by geometrical optics. According to the Taylor expansion of the exponent of transmission coefficient when expressed as an exponential form, the lateral GHL displacement and the angular deflection are the first-order effects and can be negative or positive. The width modification and the longitudinal focal shift are the second-order effects and can also be positive or negative. Owing to the waist-width dependent term, the non-geometrical effects of transmitted beam are not identical with the non-specular effects of reflected beam. The conditions for the validity of those effects are suggested and numerical simulations are also given. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Study on holographic grating diffraction for Laguerre--Gaussian beam generation 刘义东, 高春清, 高明伟 2008 (5):  1769-1776.  doi: 10.1088/1674-1056/17/5/037 摘要 ( 1658 )   PDF(1406KB) ( 735 )   Laguerre--Gaussian beams, as a special model with spiral phase structure, have been intensively investigated. Holographic grating method is a convenient method of generating Laguerre--Gaussian beams and measuring their orbital angular momenta. But due to some inevitable adverse factors such as lateral displacement, angular deflection and elliptical incident profile of incident beam, the practical effectiveness should be reevaluated. This paper is devoted to the study on the influences of the abovementioned three adverse factors on the holographic grating method. The characteristics of the mode decomposition of diffractive order and the relative powers of the orbital angular momentum eigen-states are also given. 相关文章 | 计量指标

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Amplitude-squared squeezing of superposition of coherent states Muhammad Ashfaq Ahmad, 任 珉, 马爱群, 刘树田 2008 (5):  1777-1783.  doi: 10.1088/1674-1056/17/5/038 摘要 ( 1591 )   PDF(883KB) ( 553 )   This paper discusses the amplitude-squared squeezing for the superposition of two coherent states with their phase differences being separately π/2, 3π/2, and π, as well as for the superposition state of two pseudoclassical states. According to the analysis, it is found that the superposition state of two coherent states with their phase differences π/2 and 3π/2, and the superposition state of two pseudoclassical states both do exhibit the amplitude-squared squeezing. Also, some specific states are found to exhibit even stronger squeezing effects when relative phase of the superposition is equal to the average photon number. Amplitude-squared squeezing is dependent on the difference in phase between two coherent states. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Coherence-enhanced entanglement between two atoms at high temperature 胡要花, 方卯发, 姜春蕾, 曾 可 2008 (5):  1784-1790.  doi: 10.1088/1674-1056/17/5/039 摘要 ( 1675 )   PDF(489KB) ( 615 )   This paper studies the entanglement properties in a system of two dipole--dipole coupled two-level atoms resonantly interacting with a single-mode thermal field. The results show that, when the temperature of the cavity is high enough (corresponding to the large value of the mean photon number), the entanglement is greatly enhanced due to the initial atomic coherence. These results are helpful for controlling the atomic entanglement by changing the initial parameters of the system. 相关文章 | 计量指标

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Wigner function for the generalized excited pair coherent state 孟祥国, 王继锁, 梁宝龙, 李洪奇 2008 (5):  1791-1797.  doi: 10.1088/1674-1056/17/5/040 摘要 ( 1326 )   PDF(1006KB) ( 588 )   This paper introduces the generalized excited pair coherent state (GEPCS). Using the entangled state $|\eta\rangle$ representation of Wigner operator, it obtains the Wigner function for the GEPCS. In the $\rho$--$\gamma$ phase space, the variations of the Wigner function distributions with the parameters $q$, $\alpha$, $k$ and $l$ are discussed. The tomogram of the GEPCS is calculated with the help of the Radon transform between the Wigner operator and the projection operator of the entangled state $|\eta_1, \eta_2, \tau_1, \tau_2\rangle$. The entangled states $|\eta\ragnle$  and $|\eta_1, \eta_2, \tau_1, \tau_2$ provide two good representative space for studying the Wigner functions and tomograms of various two-mode correlated quantum states. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Two narrow bandwidth photons interfering in an electromagnetically induced transparency (EIT) system 王福源, 史保森, 陆小松, 郭光灿 2008 (5):  1798-1803.  doi: 10.1088/1674-1056/17/5/041 摘要 ( 1632 )   PDF(1075KB) ( 611 )   In this paper, we have analysed in detail the quantum interference of the degenerate narrowband two-photon state by using a Mach--Zehnder interferometer, in which an electromagnetically induced transparency (EIT) medium is placed in one of two interfering beams. Our results clearly show that it is possible to coherently keep the quantum state at a single photon level in the EIT process, especially when the transparent window of the EIT medium is much larger than the bandwidth of the single photon. This shows that the EIT medium is possibly a kind of memory or repeater for the narrowband photons in the areas of quantum communication and quantum computer. This kind of experiment is feasible within the current technology. 相关文章 | 计量指标

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Investigation of an X-band magnetically insulated transmission line oscillator 樊玉伟, 钟辉煌, 李志强, 舒 挺, 杨汉武, 杨建华, 王 勇, 罗 玲, 赵延宋 2008 (5):  1804-1808.  doi: 10.1088/1674-1056/17/5/042 摘要 ( 1315 )   PDF(2049KB) ( 803 )   An X-band magnetically insulated transmission line oscillator (MILO) is designed and investigated numerically and experimentally for the first time. The X-band MILO is optimized in detail with KARAT code. In simulation, the X-band MILO, driven by a 720kV, 53kA electron beam, comes to a nonlinear steady state in 4.0ns. High-power microwaves (HPM) of TEM mode is generated with an average power of 4.1GW, a frequency of 9.3GHz, and power conversion efficiency of 10.8% in durations of 0--40ns. The device is fabricated according to the simulation results. In experiments, when the voltage is 400kV and the current is 50kA, the radiated microwave power reaches about 110MW and the dominating frequency is 9.7GHz. Because the surfaces of the cathode end and the beam dump are destroyed, the diode voltage cannot increase continuously. However, when the diode voltage is 400kV, the average power output is obtained to be 700MW in simulation. The impedance of the device is clearly smaller than the simulation prediction. Moreover, the duration of the microwave pulse is obviously shorter than that of the current pulse. The experimental results are greatly different from the simulation predictions. The preliminary analyses show that the generations of the anode plasma, the cathode flare and the anode flare are the essential cause for the remarkable deviation of the experimental results from the simulation predictions. 相关文章 | 计量指标

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Numerical simulation of end-pumped CW Nd3+:GdVO4 laser at 1063nm 祖宁宁, 孙桂娟, 戴振文 2008 (5):  1809-1816.  doi: 10.1088/1674-1056/17/5/043 摘要 ( 1437 )   PDF(267KB) ( 502 )   A theoretical model to simulate an end-pumped CW Nd3+:GdVO4 laser at 1063nm is presented. Its essence is to use the propagation equations to demonstrate the spatial evolutions of the pump and the laser powers in the cavity, hence it is applicable to both low and high gain lasers. The simulation results obtained by this model are in good agreement with the experimental observations reported in the literature for a Ti:sapphire-pumped Nd3+:GdVO4 laser. Moreover, some parameters, such as the reflectivity of output coupler, the spot size of laser beam and the crystal length, are discussed with a view to optimizing the laser performance. 相关文章 | 计量指标

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Stimulated photoluminescence emission and trap states in Si/SiO2 interface formed by irradiation of laser 黄伟其, 许 丽, 王海旭, 金 峰, 吴克跃, 刘世荣, 秦朝建, 秦水介 2008 (5):  1817-1820.  doi: 10.1088/1674-1056/17/5/044 摘要 ( 1167 )   PDF(523KB) ( 661 )   Stimulated photoluminescence (PL) emission has been observed from an oxide structure of silicon when optically excited by a radiation of 514nm laser. Sharp twin peaks at 694 and 692nm are dominated by stimulated emission, which can be demonstrated by its threshold behaviour and linear transition of emission intensity as a function of pump power. The oxide structure is formed by laser irradiation on silicon and its annealing treatment. A model for explaining the stimulated emission is proposed, in which the trap states of the interface between an oxide of silicon and porous nanocrystal play an important role. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Theoretical study on phase conjugation in weakly injected vertical-cavity surface-emitting lasers 张伟利, 潘 炜, 罗 斌, 李孝峰, 邹喜华, 王梦遥 2008 (5):  1821-1825.  doi: 10.1088/1674-1056/17/5/045 摘要 ( 1338 )   PDF(433KB) ( 658 )   This paper gives a detailed theoretical investigation on phase conjugation induced by nearly degenerate four-wave mixing in single mode vertical-cavity surface-emitting lasers (VCSELs) with weak optical injection. Considering VCSELs that can work in linearly polarized or elliptically polarized states, it derives the theoretical expression of the conjugated field by small signal analysis based on the vectoral rate equations---the spin-flip model. For linearly polarized state, VCSELs show similar conjugate spectra to edge-emitting semiconductor lasers. For the elliptically polarized state, dichroism and birefringence parameters as well as the spin-flip rate can change the conjugate spectra. Especially, when frequency detuning of the probe and pump waves is between the positive and negative relaxation oscillation frequency, changes are evident. For specific values of parameters, conjugate efficiency between 20\,dB to 40dB are obtained. 相关文章 | 计量指标

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Self-compression of femtosecond pulses in argon with a power close to the self-focusing threshold 陈晓伟, 曾志男, 戴 君, 李小芳, 李儒新, 徐至展 2008 (5):  1826-1832.  doi: 10.1088/1674-1056/17/5/046 摘要 ( 1274 )   PDF(221KB) ( 504 )   Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionization (MPI) or space--time focusing and self-steepening effects can induce pulse shortening, but they predominate at different beam intensities during the propagation. The latter effects play a key role in the final pulse self-compression. By choosing an appropriate focusing parameter, action distance of the space--time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration as short as two optical cycles. It is also found that, for our calculation cases in which an input pulse power is close to the self-focusing threshold, either group velocity dispersion (GVD) or multiphoton absorption (MPA) has a negligible influence on pulse characteristics in the propagation process. 相关文章 | 计量指标

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Light propagation characteristics in quantum well structures of photonic crystals 刘 靖, 孙军强, 黄重庆, 陈 敏, 黄德修 2008 (5):  1833-1839.  doi: 10.1088/1674-1056/17/5/047 摘要 ( 1261 )   PDF(2961KB) ( 557 )   Two-dimensional (2D) closed-cavity single quantum well (SQW) and multiple quantum well (MQW) structures are proposed based on the traditional 2D open-cavity SQW structures of photonic crystals. The numerical calculation results show that the proposed structures can greatly improve the optical characteristics compared with the traditional structures. It is found that the barrier thickness has a great impact on the optical characteristics of the closed-cavity MQW structures: when the barrier thickness is narrower, each resonant peak which appears in the SQW would split, the number of split times is just equal to the number of wells, and each well in the MQW structures is a travelling-wave-well, similar to the well in the open-cavity SQW structures; when the barrier thickness is wider, there is no effect of spectral splitting, and each well in the MQW structures is a standing-wave-well, just like the well in the closed-cavity SQW. The physical origin of different field distributions and the effect of the spectral splitting are provided. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Design of phase plates for shaping partially coherent beams by simulated annealing 李建龙, 吕百达 2008 (5):  1840-1844.  doi: 10.1088/1674-1056/17/5/048 摘要 ( 1379 )   PDF(506KB) ( 522 )   Taking the Gaussian Schell-model beam as a typical example of partially coherent beams, this paper applies the simulated annealing (SA) algorithm to the design of phase plates for shaping partially coherent beams. A flow diagram is presented to illustrate the procedure of phase optimization by the SA algorithm. Numerical examples demonstrate the advantages of the SA algorithm in shaping partially coherent beams. An uniform flat-topped beam profile with maximum reconstruction error RE<1.74% is achieved. A further extension of the approach is discussed. 相关文章 | 计量指标

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The effect of configuration complex on dielectronic recombination process in highly ionized plasmas 焦荣珍, 冯晨旭 2008 (5):  1845-1847.  doi: 10.1088/1674-1056/17/5/049 摘要 ( 1278 )   PDF(137KB) ( 469 )   This paper analyses the effect of configuration complex on dielectronic recombination (DR) process in highly ionized plasmas (Xe26+, Dy38+, W46+) by using the multiconfiguration relativistic Hartree--Fock method. Resonant and nonresonant radiative stabilizing transitions and decays to autoionizing levels followed by radiative cascades are included. Collisional transitions following electron capture are neglected. The remarkable difference between the isoelectronic trend of the rate coefficients for DR through 3d9414l' and through 3d94l 5l' is emphasized. The trend of DR through 3d94l4l' shows irregularities at relatively low temperature due to the progressive closing of DR channels as atomic number Z increases. 相关文章 | 计量指标

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges 吴 静, 张鹏云, 孙继忠, 张 健, 丁振峰, 王德真 2008 (5):  1848-1853.  doi: 10.1088/1674-1056/17/5/050 摘要 ( 1262 )   PDF(722KB) ( 705 )   Measurements of dust plasma parameters were carried out in the discharges of (SiH4/C2H4/Ar) mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the variations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids. 相关文章 | 计量指标

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Resonant detection of terahertz radiation utilizing plasma waves in high-electron-mobility transistors 马明瑞, 陈钰玲, 王立敏, 王 长 2008 (5):  1854-1857.  doi: 10.1088/1674-1056/17/5/051 摘要 ( 1230 )   PDF(300KB) ( 633 )   This paper theoretically studies the high-electron-mobility transistor (HEMT) driven by the terahertz radiation. It calculates the gate-to-source/drain admittance and the detection responsivity of the HEMT as a function of the signal frequency. It finds that the peaks of the admittances and the responsivity show redshift, and the heights of the peaks decrease with increasing the lengths of the source-to-gate and gate-to-drain spacing. Such phenomena may be useful in designing different HEMTs by utilizing the effects associated with the plasma oscillations excitation. 相关文章 | 计量指标

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Structural and magnetic properties of Co1-xZnxFe2O4 nanoparticles 王 丽, 李发伸 2008 (5):  1858-1862.  doi: 10.1088/1674-1056/17/5/052 摘要 ( 1522 )   PDF(226KB) ( 972 )   Co1-xZnxFe2O4 nanoparticles, prepared by the polyvinyl alcohol sol--gel method, have been investigated by x-ray diffraction and M?ssbauer spectroscopy. These results are compared with those for the bulk material. The lattice parameters of CoZn ferrite nanoparticles are larger than those of the bulk material. Thermal scanning of M?ssbauer measurement shows that the transition temperatures for nanoparticles are higher than those of the bulk material except for the sample CoFe2O4. 相关文章 | 计量指标

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Cellular automaton model considering headway-distance effect 胡守信, 高 坤, 汪秉宏, 陆玉凤 2008 (5):  1863-1868.  doi: 10.1088/1674-1056/17/5/053 摘要 ( 1356 )   PDF(7384KB) ( 594 )   This paper presents a cellular automaton model for single-lane traffic flow. On the basis of the Nagel--Schreckenberg (NS) model, it further considers the effect of headway-distance between two successive cars on the randomization of the latter one. In numerical simulations, this model shows the following characteristics. (1) With a simple structure, this model succeeds in reproducing the hysteresis effect, which is absent in the NS model. (2) Compared with the slow-to-start models, this model exhibits a local fundamental diagram which is more consistent to empirical observations. (3) This model has much higher efficiency in dissolving congestions compared with the so-called NS model with velocity-dependent randomization (VDR model). (4) This model is more robust when facing traffic obstructions. It can resist much longer shock times and has much shorter relaxation times on the other hand. To summarize, compared with the existing models, this model is quite simple in structure, but has good characteristics. 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Quantum mechanical effects on heat generation in nano-scale MOSFETs 吉 敏, 赵 凯, 杜 刚, 康晋锋, 韩汝琦, 刘晓彦 2008 (5):  1869-1873.  doi: 10.1088/1674-1056/17/5/054 摘要 ( 1243 )   PDF(2091KB) ( 513 )   The Monte Carlo simulation is performed to investigate the quantum mechanical (QM) effects on heat generation in nano-scale metal oxide semiconductor field effect transistors (MOSFETs) by solving the quantum Boltzmann equation. The influence of QM effects both in real space and $K$ space on the heat generation is investigated. 相关文章 | 计量指标

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Electronic structures and magnetoelectric properties of tetragonal BaFeO3: an ab initio density functional theory study 冯宏剑, 刘发民 2008 (5):  1874-1880.  doi: 10.1088/1674-1056/17/5/055 摘要 ( 1338 )   PDF(393KB) ( 1032 )   First-principles calculations have been performed to investigate the ground state electronic properties of BaFeO3 (BFO). Local spin density approximation (LSDA) plus U (LSDA+U) treatment modified the metallic behaviour to insulated one with a band gap of 4.12eV. The spontaneous polarization was found to be 89.3\muC/cm2 with Berry phase scheme in terms of the modern theory of polarization. Fe-3d eg were split into two singlet states (dz2 and d x2-y2}), and Fe-3d t2g were split into one doublet states(dxz and dyz) and one singlet states(dxy) after Fe and O displaced along the c axis. Meanwhile the occupation numbers of dz2, dyz, dxz and OT pz (on the top of Fe) were increased at the expense of those in xy plane. Our results showed that it was the sensitivity of hybridization to ferroelectric distortions, not just the total change of hybridization, that produced the possibility of ferroelectricity. Moreover, the increasing occupation numbers of OT pz and Fe dz2 favoured the 180o coupling between Fe-3d eg and Fe-3d t2g, leading to ferromagnetic ordering, which has been confirmed by the increase of magnetic moment by 0.13μB per formula unit in the polarized direction. Hence, the magnetization can be altered by the reversal of external electric field. 相关文章 | 计量指标

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Structural and electronic properties of carbon nanotubes under hydrostatic pressures 张 影, 曹觉先, 杨 薇 2008 (5):  1881-1886.  doi: 10.1088/1674-1056/17/5/056 摘要 ( 1405 )   PDF(2141KB) ( 786 )   We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations. It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases. The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase. The band structure calculations show that band gap of (10, 0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa), band gap of (10, 0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover, the calculated charge density shows that a large pressure can induce an {sp}2-to-{sp}3 bonding transition, which is confirmed by recent experiments on deformed carbon nanotubes. 相关文章 | 计量指标

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Characteristics of pentacene organic thin film transistor with top gate and bottom contact 袁广才, 徐 征, 赵谡玲, 张福俊, 姜薇薇, 宋丹丹, 朱海娜, 李少彦, 黄金英, 黄 豪, 徐叙瑢 2008 (5):  1887-1892.  doi: 10.1088/1674-1056/17/5/057 摘要 ( 1450 )   PDF(269KB) ( 962 )   High performance pentacene organic thin film transistors (OTFT) were designed and fabricated using SiO2 deposited by electron beam evaporation as gate dielectric material. Pentacene thin films were prepared on glass substrate with S--D electrode pattern made from ITO by means of thermal evaporation through self-organized process. The threshold voltage VTH was --2.75± 0.1V in 0---50V range, and that subthreshold slopes were 0.42± 0.05V/dec. The field-effect mobility (μEF) of OTFT device increased with the increase of VDS, but the μEF of OTFT device increased and then decreased with increased VGS when VDS was kept constant. When VDS was --50V, on/off current ratio was 0.48× 105 and subthreshold slope was 0.44V/dec. The μEF was 1.10cm2/(V.s), threshold voltage was --2.71V for the OTFT device. 相关文章 | 计量指标

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Zeeman effects on Josephson current in d-wave superconductor/d-wave superconductor junctions 廖艳华, 董正超, 尹在峰, 付 浩 2008 (5):  1893-1901.  doi: 10.1088/1674-1056/17/5/058 摘要 ( 1377 )   PDF(527KB) ( 602 )   This paper solves a self-consistent equation for the d-wave superconducting gap and the effective exchange field in the mean-field approximation, and studies the Zeeman effects on the d-wave superconducting gap and thermodynamic potential. The Josephson currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S junctions are calculated as a function of the temperature, exchange field, and insulating barrier strength under a Zeeman magnetic field on the two d-wave Ss. It is found that the Josephson critical currents in d-wave S/d-wave S junction to a great extent depend on the relative orientation of the effective exchange field of the two S electrodes, and the crystal orientation of the d-wave S. The exchange field under certain conditions can enhance the Josephson critical current in a d-wave S/I/d-wave S junction. 相关文章 | 计量指标

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Magnetization reversal of Fe ultrathin film on Cu(100) 何 为, 詹清峰, 王得勇, 陈立军, 成昭华 2008 (5):  1902-1906.  doi: 10.1088/1674-1056/17/5/059 摘要 ( 1303 )   PDF(580KB) ( 437 )   The magnetization reversal of Fe/Cu(100) ultrathin films grown at room temperature is investigated by using an in situ magneto-optical Kerr effect polarimeter with a magnet that can rotate in a plane of incidence. There occur spin reorientation transitions from out-of-plane to in-plane magnetizations in 8 and 12 monolayers (ML) thick iron films. The coercive fields are observed to be proportional to the reciprocal of the cosine with respect to the easy axis, suggesting that the domain-wall displacement plays a main role in the magnetization reversal process. 相关文章 | 计量指标

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Luminescence characteristics of Eu3+ activated borate phosphor for white light emitting diode 李盼来, 杨志平, 王志军, 郭庆林 2008 (5):  1907-1910.  doi: 10.1088/1674-1056/17/5/060 摘要 ( 1338 )   PDF(386KB) ( 2028 )   In this paper, the Sr3Y2 (BO3)4:Eu3+ phosphor was synthesized by high temperature solid-state reaction method and the luminescence characteristics were investigated. The emission spectrum exhibits one strong red emission at 613nm corresponding to the electric dipole 5D0--7F2 transition of Eu3+ under 365nm excitation, this is because Eu3+ substituted for Y3+ occupied the non-centrosymmetric position in the crystal structure of Sr3Y2 (BO3)4. The excitation spectrum indicates that the phosphor can be effectively excited by ultraviolet (254nm, 365nm and 400nm) and blue (470nm) light. The effect of Eu3+ concentration on the red emission of Sr3Y2 (BO3)4:Eu3+ was measured, the result shows that the emission intensities increase with increasing Eu3+ concentration, then decrease. The Commission Internationale del'Eclairage chromaticity (x, y) of Sr3Y2(BO3)4:Eu3+ phosphor is (0.640,0.355) at 15 mol% Eu3+. 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Organic light emitting diodes using magnesium doped organic acceptor as electron injection layer and silver as cathode 曹国华, 秦大山, 关 敏, 曹峻松, 曾一平, 李晋闽 2008 (5):  1911-1915.  doi: 10.1088/1674-1056/17/5/061 摘要 ( 1305 )   PDF(478KB) ( 806 )   Organic light emitting diodes employing magnesium doped electron acceptor 3, 4, 9, 10 perylenetetracarboxylic dianhydride (Mg:PTCDA) as electron injection layer and silver as cathode were demonstrated. As compared to Mg:Ag cathode, the combination of the Mg:PTCDA layer and silver provided enhanced electron injection into tris (8-quinolinolato) aluminium. The device with 1:2 Mg:PTCDA and Ag showed an increase of about 12% in the maximum current efficiency, mainly due to the improved hole-electron balance, and an increase of about 28% in the maximum power efficiency, as compared to the control device using Mg:Ag cathode. The properties of Mg:PTCDA composites were studied as well. 相关文章 | 计量指标

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Periodic thermodynamics of laser-driven molecular motor 李 丹, 郑文伟, 王志松 2008 (5):  1916-1924.  doi: 10.1088/1674-1056/17/5/062 摘要 ( 874 )   PDF(218KB) ( 558 )   Operation of a laser-driven nano-motor inevitably generates a non-trivial amount of heat, which can possibly lead to instability or even hinder the motor's continual running. This work quantitatively examines the overheating problem for a recently proposed laser-operated molecular locomotive. We present a single-molecule cooling theory, in which molecular details of the locomotive system are explicitly treated. This theory is able to quantitatively predict cooling efficiency for various candidates of molecular systems for the locomotive, and also suggests concrete strategies for improving the locomotive's cooling. It is found that water environment is able to cool the hot locomotive down to room temperature within 100 picoseconds after photon absorption. This cooling time is a few orders of magnitude shorter than the typical time for laser operation, effectively preventing any overheating for the nano-locomotive. However, when the cooling is less effective in non-aqueous environment, residual heat may build up. A continuous running of the motor will then lead to a periodic thermodynamics, which is a common character of many laser-operated nano-devices. 相关文章 | 计量指标

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Elimination of spiral waves and spatiotemporal chaos by the pulse with a specific spatiotemporal configuration 袁国勇, 杨世平, 王光瑞, 陈式刚 2008 (5):  1925-1934.  doi: 10.1088/1674-1056/17/5/063 摘要 ( 1495 )   PDF(7310KB) ( 568 )   Spiral waves and spatiotemporal chaos are sometimes harmful and should be controlled. In this paper spiral waves and spatiotemporal chaos are successfully eliminated by the pulse with a very specific spatiotemporal configuration. The excited position D of spiral waves or spatiotemporal chaos is first recorded at an arbitrary time (t0). When the system at the domain D enters a recovering state, the external pulse is injected into the domain. If the intensity and the working time of the pulse are appropriate, spiral waves and spatiotemporal chaos can finally be eliminated because counter-directional waves can be generated by the pulse. There are two advantages in the method. One is that the tip can be quickly eliminated together with the body of spiral wave, and the other is that the injected pulse may be weak and the duration can be very short so that the original system is nearly not affected, which is important for practical applications. 相关文章 | 计量指标

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Interdecadal variability of the tropospheric biennial oscillation in the western North Pacific 郑 彬, 林爱兰, 谷德军, 李春晖 2008 (5):  1935-1938.  doi: 10.1088/1674-1056/17/5/064 摘要 ( 1255 )   PDF(451KB) ( 599 )   The observed tropospheric biennial oscillation (TBO) in the western North Pacific (WNP) monsoon region has an interdecadal variability with a period of 40--50 yr. That suggests a weaker effect of the TBO on the East Asia followed by a stronger one. A simple analytic model was designed to investigate the mechanism of the interdecadal variability of the TBO. The results indicated that a local TBO air--sea system not only supports the TBO variability in the WNP monsoon region but also produces an interdecadal variability of the TBO. 相关文章 | 计量指标