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2012年, 第21卷, 第11期　刊出日期：2012-10-01 上一期    下一期

GENERAL

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Noether–Mei symmetry of discrete mechanico-electrical system 张伟伟, 方建会 2012 (11):  110201-110201.  doi: 10.1088/1674-1056/21/11/110201 摘要 ( 1032 )   PDF(93KB) ( 592 )   Noether-Mei symmetry of discrete mechanico-electrical system on a regular lattice is investigated. Firstly, the Noether symmetry of discrete mechanico-electrical system is reviewed, and the motion equations and energy equations are derived. Secondly, the definition of Noether-Mei symmetry for the system is presented, and the criterion is derived. Thirdly, conserved quantities induced by Noether-Mei symmetry with their existence conditions are obtained. Finally, an example is discussed to illustrate the results. 参考文献 | 相关文章 | 计量指标

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A nonlinear discrete integrable coupling system and its infinite conservation laws 于发军 2012 (11):  110202-110202.  doi: 10.1088/1674-1056/21/11/110202 摘要 ( 1047 )   PDF(93KB) ( 648 )   We construct a nonlinear integrable coupling of discrete soliton hierarchy, and establish the infinite conservation laws (CLs) for the nonlinear integrable coupling of the lattice hierarchy. As an explicit application of the method proposed in the paper, the infinite conservation laws of the nonlinear integrable coupling of the Volterra lattice hierarchy are presented. 参考文献 | 相关文章 | 计量指标

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A new generalized fractional Dirac soliton hierarchy and its fractional Hamiltonian structure 魏含玉, 夏铁成 2012 (11):  110203-110203.  doi: 10.1088/1674-1056/21/11/110203 摘要 ( 1097 )   PDF(102KB) ( 714 )   Based on differential forms and exterior derivatives of fractional orders, Wu first presented the generalized Tu formula to construct the generalized Hamiltonian structure of the fractional soliton equation. We apply the generalized Tu formula to calculate the fractional Dirac soliton equation hierarchy and its Hamiltonian structure. The method can be generalized to the other fractional soliton hierarchy. 参考文献 | 相关文章 | 计量指标

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Exact solutions for nonlinear partial fractional differential equations Khaled A. Gepreel, Saleh Omran 2012 (11):  110204-110204.  doi: 10.1088/1674-1056/21/11/110204 摘要 ( 1401 )   PDF(105KB) ( 2330 )   In this article, we use the fractional complex transformation to convert the nonlinear partial fractional differential equations to the nonlinear ordinary differential equations. We use the improved (G'/G)-expansion function method to calculate the exact solutions for the time and space fractional derivatives Foam Drainage equation and the time and space fractional derivatives nonlinear KdV equation. This method is efficient and powerful in solving wide classes of nonlinear evolution fractional order equations. 参考文献 | 相关文章 | 计量指标

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Linear superposition solutions to nonlinear wave equations 刘煜 2012 (11):  110205-110205.  doi: 10.1088/1674-1056/21/11/110205 摘要 ( 1007 )   PDF(89KB) ( 823 )   The solutions to a linear wave equation can satisfy the principle of superposition, i.e., the linear superposition of two or more known solutions is still a solution of the linear wave equation. We show in this article that many nonlinear wave equations possess exact traveling wave solutions involving hyperbolic, triangle, and exponential functions, and the suitable linear combinations of these known solutions can also constitute linear superposition solutions to some nonlinear wave equations with special structure characteristics. The linear superposition solutions to the generalized KdV equation K(2,2,1), the Oliver water wave equation, and the k(n,n) equation are given. The structure characteristic of the nonlinear wave equations having linear superposition solutions is analyzed, and the reason why the solutions with the forms of hyperbolic, triangle, and exponential functions can form the linear superposition solutions is also discussed. 参考文献 | 相关文章 | 计量指标

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Robust H∞ control for uncertain systems with heterogeneous time-varying delays via static output feedback 王军威, 曾才斌 2012 (11):  110206-110206.  doi: 10.1088/1674-1056/21/11/110206 摘要 ( 995 )   PDF(137KB) ( 712 )   This paper is concerned with the problem of robust H∞ control for a novel class of uncertain linear continuous-time systems with heterogeneous time-varying state/input delays and norm-bounded parameter uncertainties. The objective is to design a static output feedback controller such that the closed-loop system is asymptotically stable while satisfying a prescribed H∞ performance level for all admissible uncertainties. By constructing an appropriate Lyapunov-Krasvskii functional, a delay-dependent stability criterion of the closed-loop system is presented with the help of the Jensen integral inequality. From the derived criterion, the solutions to the problem are formulated in terms of linear matrix inequalities and hence are tractable numerically. A simulation example is given to illustrate the effectiveness of the proposed design method. 参考文献 | 相关文章 | 计量指标

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A scaled boundary node method applied to two-dimensional crack problems 陈莘莘, 李庆华, 刘应华 2012 (11):  110207-110207.  doi: 10.1088/1674-1056/21/11/110207 摘要 ( 1024 )   PDF(159KB) ( 747 )   A boundary-type meshless method called the scaled boundary node method (SBNM) is developed to directly evaluate the mixed mode stress intensity factors (SIFs) without extra post-processing. The SBNM combines the scaled boundary equations with the moving Kriging (MK) interpolation to retain the dimensionality advantage of the former and the meshless attribute of the latter. As a result, the SBNM requires only a set of scattered nodes on the boundary, and the displacement field is approximated by using the MK interpolation technique, which possesses the δ function property. This thus makes the developed method efficient and straightforward in imposing the essential boundary conditions, and no special treatment techniques are required. Besides, the SBNM works by weakening the governing differential equations in the circumferential direction and then solving the weakened equations analytically in the radial direction. Therefore, the SBNM permits an accurate representation of the singularities in the radial direction when the scaling center is located at the crack tip. Numerical examples using the SBNM for computing the SIFs are presented. Good agreements with available results in the literature are obtained. 参考文献 | 相关文章 | 计量指标

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Relativity and impossibility of superluminal motion 张启仁 2012 (11):  110301-110301.  doi: 10.1088/1674-1056/21/11/110301 摘要 ( 983 )   PDF(86KB) ( 585 )   I prove that not only particle motion but also wave propagation cannot be faster than light according to relativity. 参考文献 | 相关文章 | 计量指标

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Effects of external fields on two-dimensional Klein–Gordon particle under pseudo-harmonic oscillator interaction Sameer M. Ikhdair, Majid Hamzavi 2012 (11):  110302-110302.  doi: 10.1088/1674-1056/21/11/110302 摘要 ( 1133 )   PDF(118KB) ( 1041 )   We study the effects of the perpendicular magnetic and Aharonov-Bohm (AB) flux fields on the energy levels of a two-dimensional (2D) Klein-Gordon (KG) particle subjected to equal scalar and vector pseudo-harmonic oscillator (PHO). We calculate the exact energy eigenvalues and normalized wave functions in terms of chemical potential parameter, magnetic field strength, AB flux field, and magnetic quantum number by means of the Nikiforov-Uvarov (NU) method. The non-relativistic limit, PHO, and harmonic oscillator solutions in the existence and absence of external fields are also obtained. 参考文献 | 相关文章 | 计量指标

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New method for calculating the Berry connection in atom–molecule systems 崔傅成, 吴宝俊 2012 (11):  110303-110303.  doi: 10.1088/1674-1056/21/11/110303 摘要 ( 1003 )   PDF(127KB) ( 654 )   In the mean-field theory of atom-molecule systems, where the bosonic atoms combine to form molecules, there is no usual U(1) symmetry, which presents an apparent hurdle for calculating the Berry connection in these systems. We develop a perturbation expansion method of Hannay's angle suitable for calculating the Berry curvature in the atom-molecule systems. With this Berry curvature, the Berry connection can be naturally computed. We use a three-level atom-molecule system to illustrate our results. In particular, with this method, we compute the curvature for Hannay's angle analytically, and compare it to the Berry curvature obtained with the second-quantized model of the same system. An excellent agreement is found, indicating the validity of our method. 参考文献 | 相关文章 | 计量指标

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Comparison and control of the robustness between quantum entanglement and quantum correlation in open quantum system 嵇英华, 胡菊菊, 胡燕 2012 (11):  110304-110304.  doi: 10.1088/1674-1056/21/11/110304 摘要 ( 1105 )   PDF(168KB) ( 771 )   We investigate the influence of environmental decoherence on the dynamics of coupled qubit system and quantum correlation. We analyse the relationship between concurrence and the degree of initial entanglement or the purity of initial quantum state, and also their relationship with quantum discord. The results show that the decrease of the purity of initial quantum state can induce the attenuation of concurrence or quantum discord, but the attenuation of quantum discord is obviously slower than concurrence's, correspondingly the survival time of quantum discord is longer. Further investigation reveals that the robustness of quantum discord and concurrence relies on the entanglement degree of initial quantum state. The higher the degree of entanglement, the more robust the quantum discord is than concurrence. And the reverse is equally true. The birth and death happen to quantum discord periodically and a newborn quantum discord comes into being under a certain condition, so does the concurrence. 参考文献 | 相关文章 | 计量指标

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Entanglement concentration for arbitrary hybrid less-entangled state and W state using quantum dots and microcavity coupled system 曹聪, 王川, 张茹 2012 (11):  110305-110305.  doi: 10.1088/1674-1056/21/11/110305 摘要 ( 1026 )   PDF(370KB) ( 672 )   We propose a practical entanglement concentration protocol (ECP) for a hybrid entangled state using quantum dots and microcavity coupled system. A hybrid less-entangled state can be concentrated to a most-entangled state with a certain probability using only one ancillary single photon. Moreover, using this protocol, we can also concentrate arbitrary three-particle less-entangled W state using two ancillary photons and classical communication. The proposed protocols provide us with a useful method to concentrate less-entangled states, which can be implemented with current technology. 参考文献 | 相关文章 | 计量指标

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Dynamic stability of parametrically-excited linear resonant beams under periodic axial force 李晶, 樊尚春, 李艳, 郭占社 2012 (11):  110401-110401.  doi: 10.1088/1674-1056/21/11/110401 摘要 ( 1097 )   PDF(552KB) ( 1003 )   The parametric dynamic stability of resonant beams with various parameters under periodic axial force is studied. It is assumed that the theoretical formulations are based on Euler-Bernoulli beam theory. The governing equations of motion are derived by using Rayleigh-Ritz method and transformed into Mathieu equations, which is formed to determine the stability criterion and stability regions for parametricallyexcited linear resonant beams. An improved stability criterion is obtained using periodic Lyapunov functions. The boundary points on the stable regions are determined by using small parameter perturbation method. Numerical results and discussion are presented to highlight the effects of beam length, axial force and damped coefficient on the stability criterion and stability regions. While some stability rules are easy to anticipate, we draw some conclusions: with the increase of damped coefficient, stable regions arise; with the decrease of beam length, the conditions of the damped coefficient arise instead. These conclusions can provide a reference for the robust design of the parametricallyexcited linear resonant sensors. 参考文献 | 相关文章 | 计量指标

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Single source emission of proton projectile fragments in nucleus-emulsion interactions 张东海, 李俊生, 李惠玲 2012 (11):  110501-110501.  doi: 10.1088/1674-1056/21/11/110501 摘要 ( 1102 )   PDF(199KB) ( 551 )   The projected angular distribution and transverse momentum distribution of proton projectile fragments produced in 3.7A GeV 16O, 500A MeV 56Fe, and 1.7A GeV 84Kr induced different kinds of emulsion targets (H, CNO, and AgBr) interactions are investigated. It is found that the projected angular distribution and transverse momentum distribution can be well represented by a single Gaussian distribution. Comparison of transverse momentum distribution with the Maxwell-Boltzmann distribution reveals that proton projectile fragments are emitted from a single-temperature emission source. The temperature is different for different colliding systems, and linearly depends on the target size. 参考文献 | 相关文章 | 计量指标

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Effects of error feedback on a nonlinear bistable system with stochastic resonance 李建龙, 周辉 2012 (11):  110502-110502.  doi: 10.1088/1674-1056/21/11/110502 摘要 ( 1046 )   PDF(212KB) ( 584 )   In this paper, we discuss the effects of the error feedback on the output of a nonlinear bistable system with stochastic resonance. The bit error rate is employed to quantify the performance of the system. The theoretical analysis and the numerical simulation are presented. By investigating the performances of the nonlinear systems with different strengths of the error feedback, we argue that the presented system may provide a guidance for practical nonlinear signal processing. 参考文献 | 相关文章 | 计量指标

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Phase diagrams of the spin-2 Ising model in the presence of a quenched diluted crystal field distribution Ali Yigit, Erhan Albayrak 2012 (11):  110503-110503.  doi: 10.1088/1674-1056/21/11/110503 摘要 ( 1019 )   PDF(308KB) ( 626 )   We have investigated the random crystal field effects on the phase diagrams of the spin-2 Blume-Capel model for the honeycomb lattice using the effective-field theory with correlations. To do so, the thermal variations of magnetization are studied via calculating the phase diagrams of the model. We have found that the model displays both second-order and first-order phase transitions in addition to the tricritical and isolated points. Reentrant behavior is also observed for some appropriate values of certain system parameters. Besides the usual ground-state phases of spin-2 model including ±2, ±1, and 0, we have also observed the phases ±3/2 and ±1/2 which are unusual for spin-2 case. 参考文献 | 相关文章 | 计量指标

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Enhancement of density divergence in an insect outbreak model driven by colored noise 肖荣, 王参军, 张林 2012 (11):  110504-110504.  doi: 10.1088/1674-1056/21/11/110504 摘要 ( 1118 )   PDF(245KB) ( 638 )   The steady states and the transient properties of an insect outbreak model driven by Gaussian colored noise are studied in this paper. According to Fokker-Planck equation in the unified colored-noise approximation, we analyse the stationary probability distribution and the mean first-passage time of this model. By numerical analysis, the effects of self-correlation time of insect birth rate and predation rate respectively reveal a manifest population divergence on the insect density. The decrease of the mean first-passage time indicates an enhancement dynamic on the density divergency with colored noise of large self-correlation time based on the insect outbreak model. 参考文献 | 相关文章 | 计量指标

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Chaos suppression of uncertain gyros in a given finite time Mohammad Pourmahmood Aghababa, Hasan Pourmahmood Aghababa 2012 (11):  110505-110505.  doi: 10.1088/1674-1056/21/11/110505 摘要 ( 1146 )   PDF(207KB) ( 726 )   The gyro is one of the most interesting and everlasting nonlinear dynamical systems, which displays very rich and complex dynamics, such as sub-harmonic and chaotic behaviors. We study the chaos suppression of the chaotic gyros in a given finite time. Considering the effects of model uncertainties, external disturbances, and fully unknown parameters, we design a robust adaptive finite-time controller to suppress the chaotic vibration of the uncertain gyro as quickly as possible. Using the finite-time control technique, we given the exact value of the chaos suppression time. A mathematical theorem is presented to prove the finite-time stability of the proposed scheme. The numerical simulation shows the efficiency and usefulness of the proposed finite-time chaos suppression strategy. 参考文献 | 相关文章 | 计量指标

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Cluster projective synchronization of complex networks with nonidentical dynamical nodes 姚洪兴, 王树国 2012 (11):  110506-110506.  doi: 10.1088/1674-1056/21/11/110506 摘要 ( 1213 )   PDF(159KB) ( 692 )   We investigate a new cluster projective synchronization (CPS) scheme in the time-varying delay coupled complex dynamical networks with nonidentical nodes. Based on the community structure of the networks, the controllers are designed differently for the nodes in one community which have direct connections to the nodes in the other communities and the nodes without direct connections to the nodes in the other communities. Some sufficient criteria are derived to ensure the nodes in the same group projective synchronize and there is also projective synchronization between nodes in different groups. Particularly, the weight configuration matrix is not assumed to be symmetric or irreducible. The numerical simulations are performed to verify the effectiveness of the theoretical results. 参考文献 | 相关文章 | 计量指标

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Non-completely elastic interactions in (2+1)-dimensional dispersive long wave equation 陈未路, 张雯婷, 张立溥, 戴朝卿 2012 (11):  110507-110507.  doi: 10.1088/1674-1056/21/11/110507 摘要 ( 997 )   PDF(539KB) ( 618 )   With the help of a modified mapping method, we obtain two kinds of variable separation solutions with two arbitrary functions for the (2+1)-dimensional dispersive long wave equation. When selecting appropriate multi-valued functions in the variable separation solution, we investigate the interactions among special multi-dromions, dromion-like multi-peakons, and dromion-like multi-semifoldons, which all demonstrate non-completely elastic properties. 参考文献 | 相关文章 | 计量指标

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Leader–following consensus criteria for multi-agent systems with time-varying delays and switching interconnection topologies M. J. Park, O. M. Kwon, Ju H. Park, S. M. Lee, E. J. Cha 2012 (11):  110508-110508.  doi: 10.1088/1674-1056/21/11/110508 摘要 ( 1133 )   PDF(1073KB) ( 953 )   We consider multi-agent systems with time-varying delays and switching interconnection topologies. By constructing a suitable Lyapunov-Krasovskii functional and using the reciprocally convex approach, new delay-dependent consensus criteria for the systems are established in terms of linear matrix inequalities (LMIs), which can be easily solved by various effective optimization algorithms. Two numerical examples are given to illustrate the effectiveness of the proposed methods. 参考文献 | 相关文章 | 计量指标

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Ellipsometric configurations using a phase retarder and rotating polarizer and analyzer at any speed ratio Sofyan A. Taya, Taher M. El-Agez, Anas A. Alkanoo 2012 (11):  110701-110701.  doi: 10.1088/1674-1056/21/11/110701 摘要 ( 1069 )   PDF(434KB) ( 747 )   In this paper, we propose an ellipsometer using a phase retarder and rotating polarizer and analyzer at a speed ratio 1:N. Different ellipsometric configurations are presented by assuming N = 1, 2, and 3. Moreover, two values of the offset angle of the retarder are considered for each ellipsometric configuration. The Muller formalism is employed to extract the Stokes parameters, from which the intensity received by the detector is obtained. The optical properties of c-Si are calculated using all configurations. A comparison between different configurations is carried out considering the effect of the noise on the results and the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients. It is found that the alignment of the phase retarder has a crucial impact on the results and the ellipsometric configuration with speed ratio 1:1 is preferred over the other configurations. 参考文献 | 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Investigation of multiphoton and tunneling ionization of atoms in intense laser field 付妍卓, 赵松峰, 周效信 2012 (11):  113101-113101.  doi: 10.1088/1674-1056/21/11/113101 摘要 ( 1221 )   PDF(144KB) ( 1841 )   We study the ionization probabilities of atoms by a short laser pulse with three different theoretical methods, i.e. the numerical solution of time-dependent Schrödinger equation (TDSE), Perelomov-Popov-Terent'ev (PPT) theory and Ammosov-Delone-Krainov (ADK) theory. Our results show that laser intensity dependent ionization probabilities of several atoms (i.e. H, He, and Ne) obtained from the PPT theory accord quite well with the TDSE results both in the multiphoton and tunneling ionization regimes, while the ADK results fit well to the TDSE data only in the tunneling ionization regime. Our calculations also show that laser intensity dependent ionization probabilities of H atom at three different laser wavelengths of 600 nm, 800 nm, and 1200 nm obtained from the PPT theory are also in good agreement with those from the TDSE, while the ADK theory fails to give the wavelength dependence of ionization probability. Only when the laser wavelength is long enough, will the results of ADK be close to those of TDSE. 参考文献 | 相关文章 | 计量指标

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Chen's lattice inversion embedded-atom method for Ni–Al alloy 张川晖, 黄烁, 申江, 陈难先 2012 (11):  113401-113401.  doi: 10.1088/1674-1056/21/11/113401 摘要 ( 1297 )   PDF(133KB) ( 928 )   The structural properties, the enthalpies of formation, and the mechanical properties of some Ni-Al intermetallic compounds (NiAl, Ni3Al, NiAl3, Ni5Al3, Ni3Al4) are studied by using Chen's lattice inversion embedded-atom method (CLI-EAM). Our calculated lattice parameters and cohesive energies of Ni-Al compounds are consistent with the experimental and the other EAM results. The results of enthalpy of formation indicate a strong chemical interaction between Ni and Al in the intermetallic compounds. Through analyzing the alloy elastic constants, we find that all the Ni-Al intermetallic compounds discussed are mechanically stable. The bulk moduli of the compounds increase with the increasing Ni concentration. Our results also suggest that NiAl, Ni3Al, NiAl3, and Ni5Al3 are ductile materials with lower ratios of shear modulus to bulk modulus; while Ni3Al4 is brittle with a higher ratio. 参考文献 | 相关文章 | 计量指标

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Investigation of ultracold atoms and molecules in a dark magneto-optical trap 汪丽蓉, 姬中华, 元晋鹏, 杨艳, 赵延霆, 马杰, 肖连团, 贾锁堂 2012 (11):  113402-113402.  doi: 10.1088/1674-1056/21/11/113402 摘要 ( 1353 )   PDF(185KB) ( 1345 )   In this paper, ultracold atoms and molecules in a dark magneto-optical trap (MOT) are studied via depumping the cesium cold atoms into the dark hyperfine ground state. The collision rate is reduced to 0.45 s-1 and the density of the atoms is increased to 5.6× 1011 cm-3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15. The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately. The experimental results are analyzed by using the perturbative quantum approach. 参考文献 | 相关文章 | 计量指标

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Fully differential cross sections for C6+ single ionization of helium 李霞, 马晓艳, 孙世艳, 贾祥富 2012 (11):  113403-113403.  doi: 10.1088/1674-1056/21/11/113403 摘要 ( 968 )   PDF(425KB) ( 548 )   Three-Coulomb-wave (3C) model is applied to study the single ionization of helium by 2 MeV/amu C6+ impact. Fully differential cross sections (FDCS) are calculated in the scattering plane and the results are compared with experimental data and other theoretical predictions. It is shown that the 3C results of the recoil peak are in very good agreement with experimental observations, and variation of the position of the binary peak with increasing momentum transfer also conforms better to the experimental results. Furthermore, the contributions of different scattering amplitudes are discussed. It turns out that the cross sections are strongly influenced by the interference of these amplitudes. 参考文献 | 相关文章 | 计量指标

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Cluster size and substrate temperature affect thin film formation during copper cluster deposition on Si (001) surface 龚恒风, 吕炜, 王鲁闽, 李公平 2012 (11):  113601-113601.  doi: 10.1088/1674-1056/21/11/113601 摘要 ( 996 )   PDF(895KB) ( 840 )   The soft deposition of Cu clusters on a Si (001) surface was studied by molecular dynamics simulations. The embedded atom method, the Stillinger-Weber and the Lennar-Jones potentials were used to describe the interactions between the cluster atoms, between the substrate atoms, and between the cluster and the substrate atoms, respectively. The Cu13, Cu55, and Cu147 clusters were investigated at different substrate temperatures. We found that the substrate temperature had a significant effect on the Cu147 cluster. For smaller Cu13 and Cu55 clusters, the substrate temperature in the range of study appeared to have little effect on the mean height of mass center. The clusters showed better degrees of epitaxy at 800 K. With the same substrate temperature, the Cu55 cluster demonstrated the highest degree of epitaxy, followed by Cu147 and then Cu13 clusters. In addition, the Cu55 cluster showed the lowest mean height of mass center. These results suggested that the Cu55 cluster is a better choice for the thin-film formation among the clusters considered. Our studies may provide insight into the formation of desired Cu thin films on a Si substrate. 参考文献 | 相关文章 | 计量指标

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Computer simulation study of the cluster destruction of stratospheric ozone by bromine A. E. Galashev, O. R. Rakhmanova 2012 (11):  113602-113602.  doi: 10.1088/1674-1056/21/11/113602 摘要 ( 948 )   PDF(341KB) ( 511 )   The interaction of (Br-)i(H2O)50-i, 0 ≤ i ≤ 6 clusters with oxygen and ozone molecules is investigated by the method of molecular dynamics simulation. The ozone molecules as well as the bromine ions do not leave the cluster during the calculation of 25 ps. The ability of the cluster containing molecular oxygen to absorb the infrared (IR) radiation is reduced in the frequency range of 0 ≤ ω ≤ 3500 cm-1 when the number of the bromine ions in the cluster grows. The intensity of the Raman spectrum is not changed significantly when the Br- ions are added to the ozone-containing system. The power of the emitted IR radiation is increased when the number of the bromine ions grows in the oxygen-containing system. The data obtained in this study on the IR and the Raman spectra of the water clusters that contain ozone, oxygen, and Br- can be used to develop an investigation of the mechanisms of ozone depletion. 参考文献 | 相关文章 | 计量指标

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Direct frequency comb of two-photon transition spectroscopy in a cesium vapor 张一驰, 武寄洲, 李玉清, 金丽, 马杰, 汪丽蓉, 赵延霆, 肖连团, 贾锁堂 2012 (11):  113701-113701.  doi: 10.1088/1674-1056/21/11/113701 摘要 ( 1028 )   PDF(927KB) ( 658 )   A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an originate way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements. 参考文献 | 相关文章 | 计量指标

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Millimeter and sub-millimeter wave frequency selective surface beamsplitter for geostationary orbit microwave radiometer 崔广斌, 赵海博, 张勇芳, 苗俊刚 2012 (11):  114101-114101.  doi: 10.1088/1674-1056/21/11/114101 摘要 ( 1033 )   PDF(231KB) ( 1132 )   We report the design of three frequency selective surface (FSS) filters used on the FengYun-4 (FY-4) microwave satellite, which separate five-frequency bands in the frequency range of 50-429 GHz with the insertion loss less than 0.4 dB, and separation between adjacent channels more than 20 dB for either TE or TM incidence. Firstly, we briefly introduce the disadvantages of two types of FSS filter: waveguide-array FSS and printed FSS, which are commonly employed in the millimeter and sub-millimeter wave band. In order to meet the insertion loss requirement and specified spectral transmission response, we adopt the filter composed of two closely spaced freestanding metal plates, which contains array of resonant ring slot elements. Computer simulation technology (CST) CST is used to optimize structural dimensions of the resonant unit and interlayer separation. Numerical results show that these FSS filters exhibit transmission loss less than 0.4 dB and separation between adjacent channels more than 20 dB. Simulated transmission coefficients are in close agreement with the required specification, and even exceed the performance specifications. 参考文献 | 相关文章 | 计量指标

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Highly efficient Cherenkov radiation generation in the irregular point of hollow-core photonic crystal fiber 申向伟, 苑金辉, 桑新柱, 余重秀, 饶兰, 夏民, 韩颖, 夏长明, 侯蓝田 2012 (11):  114102-114102.  doi: 10.1088/1674-1056/21/11/114102 摘要 ( 1197 )   PDF(403KB) ( 851 )   Highly efficient Cherenkov radiations (CRs) are generated by the soliton self-frequency shift (SSFS) in the irregular point of a hollow-core photonic crystal fiber (HC-PCF) in our laboratory. The impacts of pump power and wavelength on the CR are investigated, and the corresponding nonlinear processes are discussed. When the average power of the 120 fs pump pulse increases from 500 mW to 700 mW, the Raman soliton shifts from 2210 nm to 2360 nm, the output power of the CRs increases by 2.3 times, the maximum output power ratio of the CRs at 539 nm to that of the residual pump is calculated to be 24.32:1, the width of the output optical spectrum at the visible wavelength broadens from 35 nm to 62 nm, and the conversion efficiency η of the CR in the experiment can be above 32%. 参考文献 | 相关文章 | 计量指标

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Laser feedback interferometer with oscillating feedback mirror 汪之国, 王飞, 肖光宗 2012 (11):  114201-114201.  doi: 10.1088/1674-1056/21/11/114201 摘要 ( 1019 )   PDF(192KB) ( 530 )   A method is proposed to solve the problem of direction discrimination for laser feedback interferometer. By vibrating the feedback mirror with a small-amplitude and high-frequency sine wave, laser intensity is modulated accordingly. The modulation amplitude can be extracted with a phase sensitive detector (PSD). When the feedback mirror moves, the PSD output shows a quasi-sine waveform similar to laser intensity interference fringe but with a phase difference of approximate ±π/2. If movement direction of the feedback mirror changes, the phase difference sign reverses. Therefore, the laser feedback interferometer offers a potential application in displacement measurement with a resolution of 1/8 wavelength and in-time direction discrimination. Without using optical components such as polarization beam splitter and wave plate, the interferometer is very simple, easy to align and less costly. 参考文献 | 相关文章 | 计量指标

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Deriving some quantum optical identities using the general ordering theorem Farid Shähandeh, Mohammad Reza Bazrafkan, Elahe Nahvifard 2012 (11):  114202-114202.  doi: 10.1088/1674-1056/21/11/114202 摘要 ( 1172 )   PDF(88KB) ( 462 )   Using the newly introduced general ordering theorem by Shähandeh and Bazrafkan, we derive and generalize some quantum optical identities and give their applications. 参考文献 | 相关文章 | 计量指标

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Tunneling-induced ultraslow bright and dark solitons in quantum wells 樊双莉, 石义萍, 张红军, 孙辉 2012 (11):  114203-114203.  doi: 10.1088/1674-1056/21/11/114203 摘要 ( 1170 )   PDF(464KB) ( 646 )   We show the formation of tunneling-induced ultraslow bright and dark solitons in an asymmetric double-quantum-well structure based on the tunneling induced transparency. In this semiconductor structure, the pump field is replaced by the electron-tunneling coupling, which can be modulated by a static electric field. With appropriate conditions, we demonstrate by modulating the intensity of the static electric field that the interplay between the group velocity dispersion and the self-Kerr nonlinearity results in the generation of dark and bright solitons with ultraslow group velocity. 参考文献 | 相关文章 | 计量指标

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Saturation of biphoton generation near atomic resonance 陈鹏, 钱军, 胡正峰, 王育竹 2012 (11):  114204-114204.  doi: 10.1088/1674-1056/21/11/114204 摘要 ( 1057 )   PDF(175KB) ( 645 )   We have numerically investigated the biphoton generation rate as a function of several parameters in the spontaneous four wave mixing in cold atoms. It has been found that the biphoton generation rate can easily reach saturation with the intensity of the coupling laser increasing. The saturation intensity is mainly dependent on the dephasing rate of the ground states, unrelated to the pumping laser. It implies that though the biphoton waveform can be manipulated by the coupling laser, the generation rate of the biphoton cannot increase markedly after the saturation. The saturation effect also suggests that there is an optimal coupling laser for obtaining the largest biphoton generation rate with the sufficiently long coherence time. 参考文献 | 相关文章 | 计量指标

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Phase-sensitive nonclassical properties of photon-added-then-subtracted coherent squeezed states 刘刚, 吴木生, 胡利云 2012 (11):  114205-114205.  doi: 10.1088/1674-1056/21/11/114205 摘要 ( 1104 )   PDF(1208KB) ( 630 )   We investigate the nonclassical properties of the photon-added-then-subtracted coherent squeezed state (PASCSS) via the sub-Poissonian statistics, the photon-number distribution, and the negativity of the Wigner function. It is found that the PASSCS is a superposition state of D(β) S(ζ) |0>, D(β) S(ζ ) |1>, and D(β)S(ζ) |2>. We find that the Mandel Q parameter, the photon-number distribution, and the negative volume of the Wigner function of the PASCSS are all periodic functions of the compound φ-θ/2 with a period π involved with squeezing and displacement parameters. 参考文献 | 相关文章 | 计量指标

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Continuously tunable sub-half-wavelength localization via coherent control of spontaneous emission 王飞, 龚成, 谭新玉, 石文星 2012 (11):  114206-114206.  doi: 10.1088/1674-1056/21/11/114206 摘要 ( 1017 )   PDF(713KB) ( 512 )   We propose a continuously tunable method of the sub-half-wavelength localization via the coherent control of the spontaneous emission of a four-level Y-type atomic system, which is coupled to three strong coupling fields including a standing-wave field together with a weak probe field. It is shown that the sub-half-wavelength atomic localization is realized for both resonance and off-resonance cases. Furthermore, by varying the probe detuning in succession, the positions of the two localization peaks are tuned continuously within a wide range of probe field frequencies, which provides convenience for the realization of sub-half-wavelength atomic localization experimentally. 参考文献 | 相关文章 | 计量指标

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Absorption and dispersion control in a five-level M-type atomic system 杨红, 严冬, 张梅, 房博, 张岩, 吴金辉 2012 (11):  114207-114207.  doi: 10.1088/1674-1056/21/11/114207 摘要 ( 1047 )   PDF(312KB) ( 695 )   We investigate the steady optical response of a coherently driven five-level M-type atomic system in three different situations. When all three coupling fields have the same zero detuning, we just find one deep transparency window accompanied by a steep normal dispersion in the probe absorption and dispersion spectra. When two coupling fields are detuned from the relevant transitions to the same extent, however, a second deep transparency window may be observed in the presence of a narrow absorption line of linewidth ～ 50 kHz. In this case, two single-photon far-detuned transitions can be replaced by a two-photon resonant transition, so the five-level M system in fact reduces into a four-level quasi-Λ system. Finally, we note that no deep transparency windows and no narrow absorption lines can be found when all three coupling fields have unequal detunings. 参考文献 | 相关文章 | 计量指标

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Giant Kerr nonlinearity induced by interacting quantum coherences from decays and incoherent pumping 白艳锋, 杨文星, 韩定安, 喻小强 2012 (11):  114208-114208.  doi: 10.1088/1674-1056/21/11/114208 摘要 ( 992 )   PDF(162KB) ( 988 )   A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed. Compared with that generated in a general four-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. By using the numerical results, we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping. 参考文献 | 相关文章 | 计量指标

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Generation of an extreme ultraviolet supercontinuum with a multicycle chirped laser and a static electric field 张刚台, 白婷婷, 张美光 2012 (11):  114209-114209.  doi: 10.1088/1674-1056/21/11/114209 摘要 ( 1021 )   PDF(831KB) ( 601 )   We theoretically present a method for generating an ultrabroad extreme ultraviolet (XUV) supercontinuum by using the combination of a multicycle chirped laser and a static electric field. At a low laser intensity, the spectral cutoff is extended to the 495th order harmonic, and the bandwidth of the supercontinuum spectrum is broadened to 535 eV. At a high laser intensity, the harmonic cutoff is enlarged to the 667th order, and the supercontinuum covering a bandwidth of 1035 eV is generated. In these two cases, the long quantum path is removed, and the short quantum path is selected. Especially for the relatively high laser intensity, an isolated 23-attosecond pulse with a bandwidth of about 170.6 eV is directly obtained. Finally, we also analyze the influences of the chirp parameter and the duration of the chirped pulse as well as the static field strength on the supercontinuum. 参考文献 | 相关文章 | 计量指标

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Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system 常增光, 钮月萍, 张敬涛, 龚尚庆 2012 (11):  114210-114210.  doi: 10.1088/1674-1056/21/11/114210 摘要 ( 1025 )   PDF(207KB) ( 637 )   We theoretically investigate the Doppler effect on the optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity. It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behavior or greatly increase the bistable region, which has been known as the positive Doppler effect on the optical bistability. In addition, we find that the positive Doppler effect can change the optical bistability from the hybrid dispersion-gain type to the dispersive type. 参考文献 | 相关文章 | 计量指标

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Measurements of NO2 mixing ratios with topographic target light scattering-differential optical absorption spectroscopy system and comparisons to point monitoring technique 王杨, 李昂, 谢品华, 曾议, 王瑞斌, 陈浩, 裴显, 刘建国, 刘文清 2012 (11):  114211-114211.  doi: 10.1088/1674-1056/21/11/114211 摘要 ( 1140 )   PDF(206KB) ( 602 )   A topographic target light scattering-differential optical absorption spectroscopy (ToTaL-DOAS) system is developed for measuring average concentrations along a known optical path and studying surface-near distributions of atmospheric trace gases. The telescope of the ToTaL-DOAS system points to targets which are located at known distances from the measurement device and illuminated by sunlight. Average concentrations with high spatial resolution can be retrieved by receiving sunlight reflected from the targets. A filed measurement of NO2 concentration is performed with the ToTaL-DOAS system in Shijiazhuang in the autumn of 2011. The measurement data are compared with concentrations measured by the point monitoring technique at the same site. The results show that the ToTaL-DOAS system is sensitive to the variation of NO2 concentrations along the optical path. 参考文献 | 相关文章 | 计量指标

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Controlling the self-collimation characteristics of near-infrared two-dimensional metallic photonic crystal 冯帅, 任承, 王文忠, 王义全 2012 (11):  114212-114212.  doi: 10.1088/1674-1056/21/11/114212 摘要 ( 1077 )   PDF(1858KB) ( 645 )   Self-collimation characteristics of the two-dimensional square-lattice photonic crystal (PC) consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method. The Drude dispersion model is adopted to describe the metal rod, and the self-collimation behaviours of the near-infrared light through the PC are studied. The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods. 参考文献 | 相关文章 | 计量指标

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Temperature dependences of optical properties, chemical composition, structure, and laser damage in Ta2O5 films 许程, 杨帅, 张生辉, 牛继南, 强颖怀, 刘炯天, 李大伟 2012 (11):  114213-114213.  doi: 10.1088/1674-1056/21/11/114213 摘要 ( 1025 )   PDF(11116KB) ( 578 )   Ta2O5 films are prepared by e-beam evaporation with varied deposition temperatures, annealing temperatures, and annealing time. The effects of temperature on the optical properties, chemical composition, structure, and laser-induced damage threshold (LIDT) are systematically investigated. The results show that the increase of deposition temperature decreases the film transmittance slightly, yet annealing below 923 K is beneficial for the transmittance. The XRD analysis reveals that the film is in the amorphous phase when annealed below 873 K and in thehexagonal phase when annealed at 1073 K. While an interesting near-crystalline phase is found when annealed at 923 K. The LIDT increases with the deposition temperature increasing, whereas it increases firstly and then decreases as the annealing temperature increases. In addition, the increase of annealing time from 4 h to 12 h is favorable to improving the LIDT, which is mainly due the improvement of the O/Ta ratio. The highest LIDT film is obtained when annealed at 923 K, owing to the lowest density of defect. 参考文献 | 相关文章 | 计量指标

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Influence of polymer additives on turbulent energy cascading in forced homogeneous isotropic turbulence studied by direct numerical simulations 李凤臣, 蔡伟华, 张红娜, 王悦 2012 (11):  114701-114701.  doi: 10.1088/1674-1056/21/11/114701 摘要 ( 1003 )   PDF(2929KB) ( 732 )   Direct numerical simulations (DNS) were performed for the forced homogeneous isotropic turbulence (FHIT) with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading influenced by the drag-reducing effects. The finite elastic non-linear extensibility-Peterlin model was used as the conformation tensor equation for the viscoelastic polymer solution. Detailed analyses of DNS data were carried out in this paper for the turbulence scaling law and the topological dynamics of FHIT as well as the important turbulent parameters, including turbulent kinetic energy spectra, enstrophy and strain, velocity structure function, small-scale intermittency, etc. A natural and straightforward definition for the drag reduction rate was also proposed for the drag-reducing FHIT based on the decrease degree of the turbulent kinetic energy. It was found that the turbulent energy cascading in the FHIT was greatly modified by the drag-reducing polymer additives. The enstrophy and the strain fields in the FHIT of polymer solution were remarkably weakened as compared with their Newtonian counterparts. The small-scale vortices and the small-scale intermittency were all inhibited by the viscoelastic effects in the FHIT of polymer solution. However, the scaling law in a fashion of extended self-similarity for the FHIT of polymer solution, within the presently simulated range of Weissenberg numbers, had no distinct differences compared with that of the Newtonian fluid case. 参考文献 | 相关文章 | 计量指标

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Impurity-induced local modes in one-dimensional dusty plasma chains 任永超, 王欣上, 王晓钢 2012 (11):  115201-115201.  doi: 10.1088/1674-1056/21/11/115201 摘要 ( 1180 )   PDF(1041KB) ( 581 )   Effects of impurity on eigenmodes in one-dimensional dusty plasma lattices are studied. It is found that local modes can be excited besides lattice waves, due to the existence of an impurity particle. The dispersion relations of the modes are derived accordingly. Properties of the lattice and local modes are also analyzed and discussed, particularly for their symmetric features and conditions of the mode excitation. 参考文献 | 相关文章 | 计量指标

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Dark lump excitations in superfluid Fermi gases 徐艳霞, 段文山 2012 (11):  115202-115202.  doi: 10.1088/1674-1056/21/11/115202 摘要 ( 965 )   PDF(478KB) ( 543 )   We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. Kadomtsev-Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Cooper-Schrieffer (BCS) regime, Bose-Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity. 参考文献 | 相关文章 | 计量指标

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Nano-scale gap filling and mechanism of deposit–etch–deposit process for phase-change material 任万春, 刘波, 宋志棠, 向阳辉, 王宗涛, 张北超, 封松林 2012 (11):  115203-115203.  doi: 10.1088/1674-1056/21/11/115203 摘要 ( 1056 )   PDF(3252KB) ( 1205 )   Ge2Sb2Te5 gap filling is one of the key processes for phase-change random access memory manufacture. Physical vapor deposition is the mainstream method of Ge2Sb2Te5 film deposition due to its advantages of film quality, purity, and accurate composition control. However, conventional physical vapor deposition process cannot meet the gap-filling requirement with device critical dimension scaling down to 90 nm or below. In this study, we find that the deposit-etch-deposit process shows better gap-filling capability and scalability than single-step deposition process, especially at the nano-scale critical dimension. The gap-filling mechanism of the deposit-etch-deposit process was briefly discussed. We also find that re-deposition of phase-change material from via sidewall to via bottom by argon ion bombardment during etch step was a key ingredient for the final good gap filling. We achieve void-free gap filling of phase-change material on the 45-nm via by two-cycle deposit-etch-deposit process. We gain a rather comprehensive insight into the mechanism of deposit-etch-deposit process and propose a potential gap-filling solution for over 45-nm technology nodes for phase-change random access memory. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Preparation and characterization of nontoxic magnetic-luminescent nanoprobe 尹乃强, 刘玲, 雷洁梅, 刘艳松, 公茂刚, 吴以治, 朱立新, 许小亮 2012 (11):  116101-116101.  doi: 10.1088/1674-1056/21/11/116101 摘要 ( 1061 )   PDF(2440KB) ( 1185 )   A novel nontoxic, magnetic, and luminescent nanoprobe is prepared by using complex nanoparticles, which are composed of Fe3O4 nanoparticles and Mn-doped ZnS quantum dots (QDs). The nanocomposite probe can provide visible optical and magnetic resonance images simultaneously. Compared with the previously toxic cadmium and mercury based QDs, the superiority of the Mn-doped ZnS QDs is little virulence. The structure and the properties of the particles are characterized by energy dispersive X-ray analysis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, photoluminescence spectroscopy, and vibrating sample magnetometer. 参考文献 | 相关文章 | 计量指标

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Thermal expansion properties of Lu2-x FexMo3O12 武梅梅, 彭杰, 祖勇, 刘荣灯, 胡中波, 刘蕴韬, 陈东风 2012 (11):  116102-116102.  doi: 10.1088/1674-1056/21/11/116102 摘要 ( 1111 )   PDF(567KB) ( 652 )   Structures and thermal expansion properties of Lu2-xFexMo3O12 have been investigated by X-ray diffraction (XRD). XRD patterns at room temperature indicate that compounds Lu2-xFexMo3O12 with x≤ 1.3 exhibit orthorhombic structure with space group Pnca; compounds with x=1.5 and 1.7 have monoclinic structure with space group P21/a. Studies on thermal expansion properties show that the linear thermal expansion coefficients of orthorhombic phase vary from negative to positive with increasing Fe content. Attempts to make zero thermal expansion materials indicate that zero thermal expansion can be observed in Lu1.3Fe0.7Mo3O12 in the temperature range of 200-400 ℃. 参考文献 | 相关文章 | 计量指标

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Structural and electronic characteristics of pure and doped ZnO varistors A. Sedky, E. El-Suheel 2012 (11):  116103-116103.  doi: 10.1088/1674-1056/21/11/116103 摘要 ( 1210 )   PDF(18007KB) ( 7859 )   We report here structural, surface morphology, mechanical, and current-voltage characteristics of Zn1-xMxO ceramic samples with various x and M (0.00 ≤ x ≤ 0.20, M = Ni, Cu). It is found that the considered dopants do not influence the well-known peaks related to the wurtzite structure of ZnO ceramics, while the shapes and the sizes of grains are clearly affected. The average crystalline diameters deduced from the SEM micrographs are between 2.06 μ and 4.8 μ for all samples. The oxygen element ratio is increased by both dopants. Interestingly, the potential barrier can be formed by adding Cu up to 0.20, while it is completely deformed by 0.025 Ni addition. The breakdown field can be enhanced up to 4138 V/cm by 0.025 Cu addition, followed by a decrease with further increase of Cu up to 0.20. On the other hand, a gradual decrease in Vickers microhardness is reported for both dopants, and the values in the Ni samples are higher compared to those in the Cu samples. The electrical conductivity is generally improved by Ni, while the addition of Cu improves it only in the over doped region ( ≥ 0.10). These results are discussed in terms of the differences of valency and ferromagnetic ordering. 参考文献 | 相关文章 | 计量指标

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Total dose radiation response of modified commercial silicon-on-insulator materials with nitrogen implanted buried oxide 郑中山, 刘忠立, 于芳, 李宁 2012 (11):  116104-116104.  doi: 10.1088/1674-1056/21/11/116104 摘要 ( 1040 )   PDF(628KB) ( 531 )   Nitrogen ions of various doses are implanted into the buried oxide (BOX) of commercial silicon-on-insulator (SOI) materials, and subsequent annealings are carried out at various temperatures. The total dose radiation responses of the nitrogen-implanted SOI wafers are characterized by high frequency capacitance-voltage (C-V) technique after irradiation using a Co-60 source. It is found that there exist relatively complex relationships between the radiation hardness of the nitrogen implanted BOX and the nitrogen implantation dose at different irradiation doses. The experimental results also suggest that a lower dose nitrogen implantation and a higher post-implantation annealing temperature are suitable for improving the radiation hardness of SOI wafer. Based on the measured C-V data, secondary ion mass spectrometry (SIMS), and Fourier transform infrared (FTIR) spectroscopy, the total dose responses of the nitrogen-implanted SOI wafers are discussed. 参考文献 | 相关文章 | 计量指标

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Dynamic characteristics of nanoindentation in Ni: A molecular dynamics simulation study Muhammad Imran, Fayyaz Hussain, Muhammad Rashid, S. A. Ahmad 2012 (11):  116201-116201.  doi: 10.1088/1674-1056/21/11/116201 摘要 ( 997 )   PDF(4289KB) ( 1876 )   In the present work, three-dimensional molecular dynamics simulation is carried out to elucidate the nanoindentation behaviour of single crystal Ni. The substrate indenter system is modeled using hybrid interatomic potentials including manybody potential (embedded atom method) and two-body Morse potential. Spherical indenter is chosen, and the simulation is performed for different loading rates from 10 m/s to 200 m/s. Results show that the maximum indentation load and hardness of the system increase with the increase of velocity. The effect of indenter size on the nanoindentation response is also analysed. It is found that the maximum indentation load is higher for large indenter whereas the hardness is higher for smaller indenter. Dynamic nanoindentation is carried out to investigate the behaviour of Ni substrate to multiple loading-unloading cycles. It is observed from the results that the increase in the number of loading unloading cycles reduces the maximum load and hardness of the Ni substrate. This is attributed to the decrease in recovery force due to defects and dislocations produced after each indentation cycle. 参考文献 | 相关文章 | 计量指标

RAPID COMMUNICATION

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Quantum Monte Carlo study on the phase transition for a generalized two-dimensional staggered dimerized Heisenberg model 郑睿, 刘邦贵 2012 (11):  116401-116401.  doi: 10.1088/1674-1056/21/11/116401 摘要 ( 1122 )   PDF(410KB) ( 818 )   In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models, we study a generalized staggered dimer model named J0-J1-J2 model, which corresponds to the staggered J-J' model on square lattice and honeycomb lattice when J1/J0 equals 1 and 0, respectively. Using quantum Monte Carlo method, we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1 as a function of coupling ratio α=J2/J0. We extract all the critical values of the coupling ratio αc for these models, and we also obtain the critical exponents ν, β/ν, and η using different finite-size scaling ansatz. All these exponents are not in consistent with the three-dimensional Heisenberg universality class, indicating some unconventional quantum ciritcial points in these models. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Ag-doped ZnO nanorods synthesized by two-step method 陈先梅, 冀勇, 郜小勇, 赵显伟 2012 (11):  116801-116801.  doi: 10.1088/1674-1056/21/11/116801 摘要 ( 1191 )   PDF(1455KB) ( 1594 )   Two-step method is adopted to synthesize Ag-doped ZnO nanorods. A ZnO seed layer is first prepared on a glass substrate by thermal decomposition of zinc acetate. Ag-doped ZnO nanorods are then assembled on the ZnO seed layer using the hydrothermal method. The influences of the molar percentage of Ag ions to Zn ions (RAg/Zn) on the structural and optical properties of the ZnO nanorods obtained are carefully studied using X-ray diffractometry, scanning electron microscopy and spectrophotometry. Results indicate that Ag ions enter into the crystal lattice through the substitution of Zn ions. The <002> c-axis-preferred orientation of the ZnO nanorods decreases as RAg/Zn increases. At RAg/Zn > 1.0%, ZnO nanorods lose their c-axis-preferred orientation and generate Ag precipitates from the ZnO crystal lattice. The average transmissivity in the visible region first increases and then decreases as RAg/Zn increases. The absorption edge is first blue shifted and then red shifted. The influence of Ag doping on the average head face, and axial dimensions of the ZnO nanorods may be optimized to improve the average transmissivity at RAg/Zn < 1.0%. 参考文献 | 相关文章 | 计量指标

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

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Density functional calculations on 13-atom Pd12M (M=Sc-Ni) bimetallic clusters 唐春梅, 陈声伟, 朱卫华, 陶成君, 张爱梅, 巩江峰, 邹华, 刘明熠, 朱峰 2012 (11):  117101-117101.  doi: 10.1088/1674-1056/21/11/117101 摘要 ( 1163 )   PDF(3459KB) ( 622 )   The geometric structures, electronic and magnetic properties of the 3d transition metal doped clusters Pd12M (M=Sc-Ni) are studied using the semi-core pseudopots density functional theory. The groundstate geometric structure of the Pd12M cluster is probably of pseudoicosahedron. The Ih-Pd12M cluster has the most thermodynamic stability in five different symmetric isomers The energy gap shows that Pd12M cluster is partly metallic. Both the absolutely predominant metal bond and very weak covalent bond might exist in the Pd12M cluster. The magnetic moment of Pd12M varies from 0 to 5 μB, implying that it has a potential application in new nanomaterials with tunable magnetic properties. 参考文献 | 相关文章 | 计量指标

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Spin-polarized current in double quantum dots 李爱仙, 段素青 2012 (11):  117201-117201.  doi: 10.1088/1674-1056/21/11/117201 摘要 ( 1163 )   PDF(283KB) ( 698 )   We analyze the transport through an asymmetric double quantum dots with an inhomogeneous Zeeman splitting in the presence of crossed dc and ac magnetic fields. A strong spin-polarized current can be obtained by changing the dc magnetic field. It is mainly due to the resonant tunneling. But for the ferromagnetic right electrode, the electron spin resonance also plays an important role in transport. We show that the double quantum dots with three-level mixing under crossed dc and ac magnetic fields can act not only as a bipolar spin filter but also as a spin inverter under suitable conditions. 参考文献 | 相关文章 | 计量指标

RAPID COMMUNICATION

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The robustness of quantum spin Hall effect to the thickness fluctuation in HgTe quantum wells 郭怀明, 张相林, 冯世平 2012 (11):  117301-117301.  doi: 10.1088/1674-1056/21/11/117301 摘要 ( 1094 )   PDF(1211KB) ( 596 )   The quantum spin Hall effect (QSHE) was first realized in HgTe quantum wells (QWs), which remain the only known two-dimensional topological insulator so far. In this paper, we have systematically studied the effect of the thickness fluctuation of HgTe QWs on the QSHE. We start with the case of constant mass with random distributions, and reveal that the disordered system can be well described by a virtual uniform QW with an effective mass when the number of components is small. When the number is infinite and corresponds to the real fluctuation, we find that the QSHE is not only robust, but also can be generated by relatively strong fluctuation. Our results imply that the thickness fluctuation does not cause backscattering, and the QSHE is robust to it. 参考文献 | 相关文章 | 计量指标

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

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Near-field properties of a shell nanocylinder pair with gain materials 王乔, 吴世法, 王晓钢 2012 (11):  117302-117302.  doi: 10.1088/1674-1056/21/11/117302 摘要 ( 926 )   PDF(180KB) ( 515 )   We study the near-field response of a shell nanocylinder pair, with its core filled by gain materials, using a two-dimensional finite-difference time-domain method. It is shown that the gain materials in the core of the cylinder can compensate the intrinsic absorption of the metal shell, leading to local-field enhancement in the gap of the active pair. A linear dependence is found between the field enhancement and the gain coefficient at resonance. The detailed physics is studied by calculating the electrical-field distribution of the shell pair filled with different gain materials. The influence of the gap width and the shell thickness on the interaction of two adjacent active shell cylinders is also investigated. 参考文献 | 相关文章 | 计量指标

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On the surface plasmon wave propagation along single metal wire 钟任斌, 刘维浩, 周俊, 刘盛纲 2012 (11):  117303-117303.  doi: 10.1088/1674-1056/21/11/117303 摘要 ( 1115 )   PDF(5111KB) ( 1197 )   Recently, the single metal wire (SW) becomes attractive for its potential applications in terahertz and higher frequency range. However, as the most simple and typical surface plasmon polariton (SPP) transmission line, its study seems far from enough. Many important transmission behaviours have not been explained satisfactorily from the viewpoint of physics. In this paper, making use of the modified Drude model (MDM) based on the Sommerfeld theory, the transmission behaviours of SPPs along SW are systemically investigated theoretically. Some important physical phenomena such as the mode transformation, the lifetime of radiative mode and the resonance frequency are revealed, and their mechanisms are explored. The results obtained in the paper will facilitate the general understanding of the features and the physical essence of the SPP transmission, not only for SW itself but also for other SPP transmission lines. 参考文献 | 相关文章 | 计量指标

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Improvement of doping efficiency in Mg-Al0.14Ga0.86N/GaN superlattices with AlN interlayer by suppressing donor-like defects 刘宁炀, 刘磊, 王磊, 杨薇, 李丁, 李磊, 曹文彧, 鲁辞莽, 万成昊, 陈伟华, 胡晓东 2012 (11):  117304-117304.  doi: 10.1088/1674-1056/21/11/117304 摘要 ( 1002 )   PDF(215KB) ( 673 )   We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN superlattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1× 1017 to 9.3× 1017 cm-3, when an AlN interlayer is inserted to modulate the strains. Schrödinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrum for SLs with an AlN interlayer. This supports the theoretical calculations and indicates that, the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement. 参考文献 | 相关文章 | 计量指标

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Broadband light-emitting from multilayer-stacked InAs/GaAs quantum dots 刘宁, 金鹏, 王占国 2012 (11):  117305-117305.  doi: 10.1088/1674-1056/21/11/117305 摘要 ( 1211 )   PDF(835KB) ( 861 )   We report the effect of the GaAs spacer layer thickness on the photoluminescence (PL) spectral bandwidth of InAs/GaAs self-assembled quantum dots (QDs). A PL spectral bandwidth of 158 nm is achieved with a five-layer stack of InAs QDs which has a 11-nm thick GaAs spacer layer. We investigate the optical and the structural properties of the multilayer-stacked InAs/GaAs QDs with different GaAs spacer layer thicknesses. The results show that the spacer thickness is a key parameter affecting the multi-stacked InAs/GaAs QDs for wide-spectrum emission. 参考文献 | 相关文章 | 计量指标

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Model of tunneling through periodic array of quantum dots in a magnetic field I. Yu. Popov, S. A. Osipov 2012 (11):  117306-117306.  doi: 10.1088/1674-1056/21/11/117306 摘要 ( 1132 )   PDF(173KB) ( 518 )   Two-dimensional periodic array of quantum dots with two laterally coupled leads in a magnetic field is considered. The model of electron transport through the system based on the theory of self-adjoint extensions of symmetric operators is suggested. We obtain the formula for the transmission coefficient and investigate its dependence on the magnetic field. 参考文献 | 相关文章 | 计量指标

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Enhanced charge carrier injection in heterojunction organic field-effect transistor by inserting an MoO3 buffer layer 于欣格, 于军胜, 黄伟, 曾红娟 2012 (11):  117307-117307.  doi: 10.1088/1674-1056/21/11/117307 摘要 ( 1038 )   PDF(410KB) ( 723 )   Top-contact organic field-effect transistor (OFET) is fabricated by adopting a pentacene/1,1'-bis(di-4-tolylaminophenyl) cyclohexane (TAPC) heterojunction structure and inserting an MoO3 buffer layer between TAPC organic semiconductor layer and source/drain electrode. The performances of the heterojunction OFET, including output current, field-effect mobility, and threshed voltage, are all significantly improved by introducing the MoO3 thin buffer layer. The performance improvement of the modified heterojunction OFET is attributed to a better contact formed at the Au/TAPC interface due to the MoO3 thin buffer layer, thereby leading to a remarkable reduction of the contact resistance at the metal/organic interface. 参考文献 | 相关文章 | 计量指标

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Three-dimensional Monte Carlo simulation of bulk fin field effect transistor 王骏成, 杜刚, 魏康亮, 张兴, 刘晓彦 2012 (11):  117308-117308.  doi: 10.1088/1674-1056/21/11/117308 摘要 ( 1027 )   PDF(290KB) ( 1183 )   In this paper, we investigate the performance of bulk fin field effect transistor (FinFET) through a three-dimensional (3D) full band Monte Carlo simulator with quantum correction. Several scattering mechanisms, such as the acoustic and optical phonon scattering, the ionized impurity scattering, the impact ionization scattering and the surface roughness scattering are considered in our simulator. The effects of the substrate bias and the surface roughness scattering near the Si/SiO2 interface on the performance of bulk FinFET are mainly discussed in our work. Our results show that the on-current of bulk FinFET is sensitive to the surface roughness and that we can reduce the substrate leakage current by modulating the substrate bias voltage. 参考文献 | 相关文章 | 计量指标

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Spin Hall and spin Nernst effects in graphene with intrinsic and Rashba spin-orbit interactions 朱国宝 2012 (11):  117309-117309.  doi: 10.1088/1674-1056/21/11/117309 摘要 ( 1245 )   PDF(225KB) ( 731 )   Spin Hall and spin Nernst effects in graphene are studied based on Green's function formalism. We calculate intrinsic contributions to spin Hall and spin Nernst conductivities in Kane-Mele model with various structures. When both intrinsic and Rashba spin-orbit interactions are present, their interplay leads to some characteristics of the dependence of spin Hall and spin Nernst conductivities on the Fermi level. When Rashba spin-orbit interaction is smaller than intrinsic spin-orbit coupling, a weak kink in the conductance appears. The kink disappears and a divergence appears when the Rashba spin-orbit interaction enhances. When the Rashba spin-orbit interaction approaches and is stronger than intrinsic spin-orbit coupling, the divergence becomes more obvious. 参考文献 | 相关文章 | 计量指标

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Spin-dependent thermoelectric transport through double quantum dots 王强, 解海卿, 焦虎军, 李志坚, 聂一行 2012 (11):  117310-117310.  doi: 10.1088/1674-1056/21/11/117310 摘要 ( 1282 )   PDF(435KB) ( 750 )   We study the thermoelectric transport through a double-quantum-dot system with spin-dependent interdot coupling and ferromagnetic electrodes by means of the non-equilibrium Green's function in the linear response regime. It is found that the thermoelectric coefficients are strongly dependent on the splitting of the interdot coupling, the relative magnetic configurations, and the spin polarization of leads. In particular, the thermoelectric efficiency can reach a considerable value in the parallel configuration when the effective interdot coupling and the tunnel coupling between the quantum dots and the leads for the spin-down electrons are small. Moreover, the thermoelectric efficiency increases with the intradot Coulomb interaction increasing and can reach very high values at appropriate temperatures. In the presence of the magnetic field, the spin accumulation in the leads strongly suppresses the thermoelectric efficiency, and a pure spin thermopower can be obtained. 参考文献 | 相关文章 | 计量指标

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Canted antiferromagnetic and optical properties of nanostructures of Mn2O3 prepared by hydrothermal synthesis Qurat-ul-ain Javed, Wang Feng-Ping, M. Yasir Rafique, Arbab Mohammad toufiq, M. Zubair Iqbal 2012 (11):  117311-117311.  doi: 10.1088/1674-1056/21/11/117311 摘要 ( 1270 )   PDF(3121KB) ( 2450 )   We have reported new magnetic and optical properties of Mn2O3 nanostructures. The nanostructures have been synthesized by hydrothermal method combined with the adjustment of pH values in the reaction system. The particular characteristics of the nanostructures have been analyzed by employing X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), UV-visible spectroscopy, and the vibrating sample magnetometer (VSM). Structural investigation manifests that the synthesized Mn2O3 nanostructures are orthorhombic crystal. Magnetic investigation indicates that the Mn2O3 nanostructures are antiferromagnetic and the antiferromagnetic transition temperature is at TN = 83 K. Furthermore, the Mn2O3 nanostructures possess canted antiferromagnetic order below the Neel temperature due to spin frustration, resulting in hysteresis with large coercivity (1580 Oe) and remanent magnetization (1.52 emu/g). The UV-visible spectrophotometry was used to determine the transmittance behavior of Mn2O3 nanostructures. Direct optical band gap of 1.2 eV was acquired by using Davis-Mott model. The UV-visible spectrum indicates that the absorption is prominent in visible region, and transparency is more than 80% in UV region. 参考文献 | 相关文章 | 计量指标

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A model for the chain-to-plane charge transfer in YBa2Cu3O6+x V. M. Matic, N. Dj. Lazarov, M. Milic 2012 (11):  117401-117401.  doi: 10.1088/1674-1056/21/11/117401 摘要 ( 1239 )   PDF(124KB) ( 559 )   A model for the chain-to-plane charge transfer is proposed to account for the two plateaus, at 60 K and at 90 K, of the Tc(x) characteristics of the YBa2Cu3O6+x high-Tc superconductor. It is assumed that the number of holes transferred from a CuO chain of length l to two nearby CuO2 sheets is proportional to l (that is, to the number of oxygen atoms in the chain), if the chain length is greater than, or equal to, a certain critical chain length, lcr, that is required to trigger the charge transfer process. No holes are assumed to have been transferred from chains of length l<lcr. The calculated Tc(x) dependence is found to be in excellent agreement with the experimentally reported Tc(x). The critical chain length parameter is estimated to be equal to lcr=11 (eleven oxygen atoms in a chain), which is a greater value than that obtained in the previously proposed model for the chain-to-plane charge transfer (lcr=4). The results obtained out of the proposed model are briefly discussed. 参考文献 | 相关文章 | 计量指标

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Charge oscillation and many-body effect in triangular quantum dots 熊永臣, 王为忠 2012 (11):  117501-117501.  doi: 10.1088/1674-1056/21/11/117501 摘要 ( 936 )   PDF(157KB) ( 627 )   We study the charge oscillation in the triangular quantum dots symmetrically coupled to the leads. A strong charge oscillation is observed even for a very small level difference. We attribute this oscillation behavior to the many-body effect in the strongly correlated system instead of the physical scenarios based on the mean-field approach in the previous works for the two-level dot. The level difference induces the difference of the occupations between different dots, while the symmetry of the many-body states favors the homogeneous distribution of the charge density on the three dots. The interplay of these two factors results in the charge oscillation. 参考文献 | 相关文章 | 计量指标

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The effect of Fe doping on structural and magnetic properties of nanocrystallite Co2Cr1-xFexAl Heusler alloys prepared by mechanical alloying M. Hakimi, P. Kameli, H. Salamati 2012 (11):  117502-117502.  doi: 10.1088/1674-1056/21/11/117502 摘要 ( 992 )   PDF(2046KB) ( 690 )   The mechanical alloying has been used to produce nanocrystallite Co2Cr1-xFexAl (x=0, 0.4, 0.6, 1) Heusler alloys. The formation of the L21 phase of Co2Cr1-xFexAl by the mechanical alloying method was investigated, The effect of Fe doping on the structural and the magnetic properties of the samples was also studied. The results were compared with the Slater Pauling prediction. A comparison between these samples and those prepared by arc-melting method in the literature was made. An increase of the coercivity Hc with the increasing Fe doping level was observed. This phenomenon was explained by the increases of lattice strain and magnetic anisotropy with the increasing Fe content. 参考文献 | 相关文章 | 计量指标

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Wet thermal annealing effect on TaN/HfO2/Ge metal–oxide–semiconductor capacitors with and without a GeO2 passivation layer 刘冠洲, 李成, 路长宝, 唐锐钒, 汤梦饶, 吴政, 杨旭, 黄巍, 赖虹凯, 陈松岩 2012 (11):  117701-117701.  doi: 10.1088/1674-1056/21/11/117701 摘要 ( 1113 )   PDF(452KB) ( 1254 )   Wet thermal annealing effects on the properties of TaN/HfO2/Ge metal-oxide-semiconductor (MOS) structures with and without a GeO2 passivation layer are investigated. The physical and the electrical properties are characterized by X-ray photoemission spectroscopy, high-resolution transmission electron microscopy, capacitance-voltage (C-V) and current-voltage characteristics. It is demonstrated that the wet thermal annealing at relatively higher temperature such as 550 ℃ can lead to Ge incorporation in HfO2 and the partial crystallization of HfO2, which should be responsible for the serious degradation of the electrical characteristics of the TaN/HfO2/Ge MOS capacitors. However, the wet thermal annealing at 400 ℃ can decrease the GeOx interlayer thickness at the HfO2/Ge interface, resulting in a significant reduction of the interface states and a smaller effective oxide thickness, along with the introduction of positive charge in the dielectrics due to the hydrolyzable property of GeOx in the wet ambient. The pre-growth of a thin GeO2 passivation layer can effectively suppress the interface states and improve the C-V characteristics for the as-prepared HfO2 gated Ge MOS capacitors, but it also dissembles the benefits of the wet thermal annealing to a certain extent. 参考文献 | 相关文章 | 计量指标

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Metamaterial absorbers realized in X-band rectangular waveguide 黄勇军, 文光俊, 李建, 钟靖平, 王平, 孙元华, O. Gordon, 朱卫仁 2012 (11):  117801-117801.  doi: 10.1088/1674-1056/21/11/117801 摘要 ( 1102 )   PDF(1342KB) ( 1202 )   In this paper, we demonstrate six types of metamaterial absorbers (MMAs) by measuring their absorptivities in an X-band (8-12 GHz) rectangular waveguide. Some of the MMAs have been demonstrated previously by using the free space measurement method, and the others are proposed firstly in this paper. The measured results show that all of the six MMAs exhibit high absorptivities above 98%, which have the similar absorbing characteristics comparing to those measured in the free space. The numerically obtained surface current densities for each MMA show that the absorbing mechanism is the same as that under the free space condition. Such a demonstration method is superior to the conventional free space measurement method due to the small-scale test samples required, the simple measure device, and the low cost. Most importantly, the proposed method opens a way to make the MMAs used in microwave applications such as the matched terminations. 参考文献 | 相关文章 | 计量指标

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New assembly route for three-dimensional metamaterials obtained through effective medium theory 臧元章, 何明霞, 谷建强, 田震, 韩家广 2012 (11):  117802-117802.  doi: 10.1088/1674-1056/21/11/117802 摘要 ( 995 )   PDF(6604KB) ( 645 )   In this study, we illustrate the effective medium theories in the designs of three-dimensional composite metamaterials of both negative permittivity and negative permeability. The proposed metamaterial consists of random coated spheres with sizes smaller compared to the wavelength embedded in a dielectric host. Simple design rules and formulas following the effective medium models are numerically and analytically presented. We demonstrate that the revised Maxwell-Garnett effective medium theory enables us to design three-dimensional composite metamaterials through the assembly of the coated spheres which are random and much smaller than the wavelength of the light. The proposed approach allows for the precise control of the permittivity and the permeability and guides a facile, flexible, and versatile way for the fabrication of composite metamaterials. 参考文献 | 相关文章 | 计量指标

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Application of artificial neural networks to the inversion of positron lifetime spectrum 安然, 张杰, 孔伟, 叶邦角 2012 (11):  117803-117803.  doi: 10.1088/1674-1056/21/11/117803 摘要 ( 1041 )   PDF(815KB) ( 627 )   A new method of processing positron annihilation lifetime spectra is proposed. It is based on an artificial neural network (ANN)-back propagation network (BPN). By using data from simulated positron lifetime spectra which are generated by a simulation program and tested by other analysis programs, the BPN can be trained to extract lifetime and intensity from a positron annihilation lifetime spectrum as an input. In principle, the method has the potential to unfold an unknown number of lifetimes and their intensities from a measured spectrum. So far, only a proof-of-principle type preliminary investigation was made by unfolding three or four discrete lifetimes. The present study aims to design the network. Besides, the performance of this method requires both the accurate design of the BPN structure and a long training time. In addition, the performance of the method in practical applications is dependent on the quality of the simulation model. However, the chances of satisfying the above criteria appear to be high. When appropriately developed, a trained network could be a very efficient alternative to the existing methods, with very short identification time. We have used the artificial neural network codes to analyze the data such as the positron lifetime spectra for single crystal materials and monocrystalline silicon. Some meaningful results are obtained. 参考文献 | 相关文章 | 计量指标

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Low platinum loading PtNPs/graphene composite catalyst with high electrocatalytic activity for dye-sensitized solar cells 李萍剑, 程凯, 陈远富, 王泽高, 郝昕, 刘竞博, 贺加瑞, 张万里 2012 (11):  118101-118101.  doi: 10.1088/1674-1056/21/11/118101 摘要 ( 1054 )   PDF(606KB) ( 1456 )   Platinum nanoparticles (PtNPs)/graphene composite materials are synthesized by a controlled chemical reduction of H2PtCl6 on graphene sheets. The electrocatalytic activity of PtNPs/graphene composite counter electrode for dye-sensitized solar cell (DSSC) is investigated. The results demonstrate that PtNPs/graphene composite has high electrocatalytic activity for dye-sensitized solar cell. The cell employing PtNPs (1.6 wt%)/graphene counter electrode reaches an conversion efficiency (η) of 3.89% upon the excitation of 100 mW/cm2 AM 1.5 white light, which is comparable to that of the cell with Pt-film counter electrode (η =3.76%). It suggests that one can use only 14% Pt content of conventional Pt-film counter electrode to obtain a comparable conversion efficiency. So it is promising to obtain high performance DSSC by using PtNPs/graphene composite with very low Pt content as counter electrode due to its simplicity, low cost, and large scalability. 参考文献 | 相关文章 | 计量指标

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Structures and magnetic properties of Fe and Ni monoatomic chains encapsulated by Au nanotube 韩志东, 李秀燕, 杨致, 刘瑞萍, 刘绍鼎, 张莹 2012 (11):  118102-118102.  doi: 10.1088/1674-1056/21/11/118102 摘要 ( 1126 )   PDF(937KB) ( 756 )   Structures and magnetic properties of transition metal (TM) Fe or Ni monoatomic chains (MACs) encapsulated by Au (5, 5) nanotube (Fe@Au and Ni@Au) are investigated by using density functional theory (DFT). The calculated results show that both Fe@Au and Ni@Au prefer to adopt ferromagnetic (FM) orders as the ground states. Especially, the Fe@Au could keep the magnetic properties of free-standing Fe MAC, indicating that this system may be viewed as a new candidate in electromagnetic devices. 参考文献 | 相关文章 | 计量指标

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Faceting transitions in crystal growth and heteroepitaxial growth in the anisotropic phase-field crystal model 陈成, 陈铮, 张静, 杨涛, 杜秀娟 2012 (11):  118103-118103.  doi: 10.1088/1674-1056/21/11/118103 摘要 ( 1047 )   PDF(2497KB) ( 696 )   We modify the anisotropic phase-field crystal model (APFC), and present a semi-implicit spectral method to numerically solve the dynamic equation of the APFC model. The process results in the acceleration of computations by orders of magnitude relative to the conventional explicit finite-difference scheme, thereby, allowing us to work on a large system and for a long time. The faceting transitions introduced by the increasing anisotropy in crystal growth are then discussed. In particular, we investigate the morphological evolution in heteroepitaxial growth of our model. A new formation mechanism of misfit dislocations caused by vacancy trapping is found. The regular array of misfit dislocations produces a small-angle grain boundary under the right conditions, and it could significantly change the growth orientation of epitaxial layers. 参考文献 | 相关文章 | 计量指标

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Influence of rotational isomerism on two-photon absorption properties of FTC chromophores 韩广超, 赵珂, 刘朋伟, 张立立 2012 (11):  118201-118201.  doi: 10.1088/1674-1056/21/11/118201 摘要 ( 1006 )   PDF(866KB) ( 608 )   The influence of rotational isomerism on the two-photon absorption (TPA) of FTC chromophores has been investigated by using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rotatable single bonds in the molecule are fully optimized, and it is found that their conformational energies are nearly degenerate. Our calculations demonstrate that the rotational isomerism has important effects on the TPA cross sections. For a certain rotamer, the maximum TPA cross section is enhanced significantly. Also, in the longer wavelength region, the rotational isomerism could lead to a large shift of the TPA position. 参考文献 | 相关文章 | 计量指标

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Entropy dominated behaviors of confined polymer-nanoparticle composites 曹学正, Merlitz Holger, Sommer Jens-Uwe, 吴晨旭 2012 (11):  118202-118202.  doi: 10.1088/1674-1056/21/11/118202 摘要 ( 1144 )   PDF(256KB) ( 1351 )   The stretched polymers would lose their possible configurations if they are mixed with nanoparticles or touch on a hard wall, which leads to a strong depletion attraction responsible for the enrichment of nanoparticles near substrates. Moreover, it is found that there exists a sacrifice mechanism in confined pure polymer samples or polymer-nanoparticle mixtures that part of polymers in order to reach a minimum free energy for the total system, are adsorbed on hard walls even by losing their conformation. The understanding based on the current study provides a simple yet effective approach for the design of thin polymer composites. 参考文献 | 相关文章 | 计量指标

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Application of TiO2 with different structures in solar cells 张天慧, 朴玲钰, 赵谡玲, 徐征, 吴谦, 孔超 2012 (11):  118401-118401.  doi: 10.1088/1674-1056/21/11/118401 摘要 ( 1079 )   PDF(2889KB) ( 1243 )   The applications of TiO2-based devices are mainly dependent on their crystalline structure, morphology, size, and exposed facets. Two kinds of TiO2 with different structures, namely TiO2 pompons and TiO2 nanotubes, have been prepared by hydrothermal method. The TiO2 with different structures is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analysis. Solar cells based on poly(3-hexylthiophene) (P3HT) and TiO2 with different structures are fabricated. In the device ITO/TiO2/P3HT/Au, the P3HT is designed to act as the electron donor, and TiO2 pompons and TiO2 nanotubes act as the electron acceptor. The effects of TiO2 structure on the performance of hybrid heterojunction solar cells are investigated. The device with TiO2 pompons has an open circuit voltage (Voc) of 0.51 V, a short circuit current (Jsc) of 0.21 mA/cm2, and a fill factor (FF) of 28.3%. Another device with TiO2 nanotubes has a Voc of 0.5 V, Jsc of 0.27 mA/cm2, and FF of 28.4%. The results indicate that the TiO2 nanotubes with unidimensional structure have better carrier transport and light absorption properties than TiO2 pompons. Consequently, the solar cell based on TiO2 nanotubes has better performance. 参考文献 | 相关文章 | 计量指标

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Deterministic method study of the impact of the Pauli Principle in double-gate MOSFETs 赵凯, Christoph Jungemann, 刘晓彦 2012 (11):  118501-118501.  doi: 10.1088/1674-1056/21/11/118501 摘要 ( 1065 )   PDF(274KB) ( 472 )   The Pauli principle is included in a multisubband deterministic solver for two-dimensional devices without approximations. The nonlinear Boltzmann equations are treated properly without compromising on accuracy, convergence, or CPU time. The simulation results indicate the significant impact of the Pauli principle on the transport properties of the quasi-2D electron gas, especially for the on state. 参考文献 | 相关文章 | 计量指标

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Efficiency enhancement of InGaN based blue light emitting diodes with InGaN/GaN multilayer barriers 童金辉, 李述体, 卢太平, 刘超, 王海龙, 仵乐娟, 赵璧君, 王幸福, 陈鑫 2012 (11):  118502-118502.  doi: 10.1088/1674-1056/21/11/118502 摘要 ( 1011 )   PDF(168KB) ( 1124 )   The advantages of InGaN based light-emitting diodes with InGaN/GaN multilayer barriers are studied. It is found that the structure with InGaN/GaN multilayer barriers shows improved light output power, lower current leakage, and less efficiency droop over its conventional InGaN/GaN counterparts. Based on the numerical simulation and analysis, these improvements on the electrical and the optical characteristics are mainly attributed to the alleviation of the electrostatic field in the quantum wells (QWs) when the InGaN/GaN multilayer barriers are used. 参考文献 | 相关文章 | 计量指标

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Robust stabilization of state delayed discrete-time Takagi–Sugeno fuzzy systems with input saturation via anti-windup fuzzy design 宋晓娜, 付主木, 刘磊坡 2012 (11):  118701-118701.  doi: 10.1088/1674-1056/21/11/118701 摘要 ( 1148 )   PDF(155KB) ( 549 )   We consider the robust stabilization problem for discrete-time Takagi-Sugeno (T-S) fuzzy systems with time-varying delays subjected to the input saturation. We design static and dynamic anti-windup fuzzy controllers to ensure the convergence of all admissible initial states within the domain of attraction. Based on the project lemma and a classical sector condition, the conditions for the existence of solutions to this problem are obtained and expressed in terms of a set of linear matrix inequalities. Finally, a numerical example is provided to illustrate the effectiveness of the proposed design approach. 参考文献 | 相关文章 | 计量指标

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Cone-beam local reconstruction based on Radon inversion transform 汪先超, 闫镔, 李磊, 胡国恩 2012 (11):  118702-118702.  doi: 10.1088/1674-1056/21/11/118702 摘要 ( 1092 )   PDF(4039KB) ( 590 )   The local reconstruction from truncated projection data is one area of interest in image reconstruction for computed tomography (CT), which creates the possibility for dose reduction. In this paper, a filtered-backprojection (FBP) algorithm based on the Radon inversion transform is presented to deal with the three-dimensional (3D) local reconstruction in the circular geometry. The algorithm achieves the data filtering in two steps. The first step is the derivative of projections, which acts locally on the data and can thus be carried out accurately even in the presence of data truncation. The second step is the nonlocal Hilbert filtering. The numerical simulations and the real data reconstructions have been conducted to validate the new reconstruction algorithm. Compared with the approximate truncation resistant algorithm for computed tomography (ATRACT), not only it has a comparable ability to restrain truncation artifacts, but also its reconstruction efficiency is improved. It is about twice as fast as that of the ATRACT. Therefore, this work provides a simple and efficient approach for the approximate reconstruction from truncated projections in the circular cone-beam CT. 参考文献 | 相关文章 | 计量指标

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A new method for information retrieval in two-dimensional grating-based X-ray phase contrast imaging 王志立, 高昆, 陈健, 葛昕, 朱佩平, 田扬超, 吴自玉 2012 (11):  118703-118703.  doi: 10.1088/1674-1056/21/11/118703 摘要 ( 1094 )   PDF(956KB) ( 700 )   Grating-based X-ray phase contrast imaging has been demonstrated to be an extremely powerful phase-sensitive imaging technique. By using two-dimensional (2D) gratings, the observable contrast is extended to two refraction directions. Recently, we have developed a novel reverse-projection (RP) method, which is capable of retrieving the object information efficiently in one-dimensional (1D) grating-based phase contrast imaging. In this contribution, we present its extension to the 2D grating-based X-ray phase contrast imaging, named the two-dimensional reverse-projection (2D-RP) method, for information retrieval. The method takes into account the nonlinear contributions of two refraction directions and allows the retrieval of the absorption, the horizontal and the vertical refraction images. The obtained information can be used for the reconstruction of the three-dimensional phase gradient field, and for an improved phase map retrieval and reconstruction. Numerical experiments are carried out, and the results confirm the validity of the 2D-RP method. 参考文献 | 相关文章 | 计量指标

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Design of an interventional magnetic resonance imaging coil for cerebral surgery 王文韬, 王文韬, 王为民 2012 (11):  118704-118704.  doi: 10.1088/1674-1056/21/11/118704 摘要 ( 1270 )   PDF(2424KB) ( 932 )   In clinical magnetic resonance imaging (MRI), the design of the radiofrequency (RF) coil is very important. For certain applications, the appropriate coil can produce an improved image quality. However, it is difficult to achieve a uniform B1 field and a high signal-to-noise ratio (SNR) simultaneously. In this article, we design an interventional transmitter-and-receiver RF coil for cerebral surgery. This coil adopts a disassembly structure that can be assembled and disassembled repeatedly on the cerebral surgery gantry to reduce the amount of interferences from the MRI during the surgery. The simulation results and the imaging experiments demonstrate that this coil can produce a uniform RF field, a high SNR, and a large imaging range to meet the requirements of the cerebral surgery. 参考文献 | 相关文章 | 计量指标

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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State of charge estimation of Li-ion batteries in electric vehicle based on radial-basis-function neural network 毕军, 邵赛, 关伟, 王璐 2012 (11):  118801-118801.  doi: 10.1088/1674-1056/21/11/118801 摘要 ( 1211 )   PDF(404KB) ( 1198 )   The on-line estimation of the state of charge (SOC) of the batteries is important for reliable running of the pure electric vehicle in practice. Because the nonlinear feature exists in the batteries and the radial-basis-function neural network (RBF NN) has good characteristics to solve the nonlinear problem, a practical method for the SOC estimation of batteries based on the RBF NN with a small number of input variables and a simplified structure is proposed. Firstly, in this paper, the model of on-line SOC estimation with the RBF NN is set. Secondly, four important factors for estimating the SOC are confirmed based on the contribution analysis method, which simplifies the input variables of the RBF NN and enhances the real-time performance of estimation. Finally, the pure electric buses with LiFePO4 Li-ion batteries running during the period of 2010 Shanghai World Expo are considered as the experimental object. The performance of the SOC estimation is validated and evaluated by the battery data from the electric vehicle. 参考文献 | 相关文章 | 计量指标

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Investigation of merging and diverging cars on a multi-lane road using cellular automation model K. Jetto, H. Ez-Zahraouy, A. Benyoussef 2012 (11):  118901-118901.  doi: 10.1088/1674-1056/21/11/118901 摘要 ( 1120 )   PDF(599KB) ( 711 )   In this paper, we have investigated two observed situations in a multi-lane road. The first one concerns a fast merging vehicle. The second situation is related to the case of a fast vehicle leaving the fastest lane back to the slowest one and targeting a specific way out. We are interested in the relaxation time τ, i.e., which is the time that the merging (diverging) vehicle spends before reaching the desired lane. Using analytical treatment and numerical simulations for the NaSch model, we have found two states, namely, the free state in which the merging (diverging) vehicle reaches the desired lane, and the trapped state in which τ diverges. We have established the phase diagrams for several values of the braking probability. In the second situation, we have shown that diverging from the fast lane targeting a specific way out is not a simple task. Even if the diverging vehicle is in the free phase, two different states can be distinguished. One is the critical state, in which the diverging car can probably reach the desired way out. The other is the safe state, in which the diverging car can surely reach the desired way out. In order to be in the safe state, we have found that the driver of the diverging car must know the critical distance (below which the way out will be out of his reach) in each lane. Furthermore, this critical distance depends on the density of cars, and it follows an exponential law. 参考文献 | 相关文章 | 计量指标

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Modeling online social networks based on preferential linking 胡海波, 郭进利, 陈骏 2012 (11):  118902-118902.  doi: 10.1088/1674-1056/21/11/118902 摘要 ( 1348 )   PDF(486KB) ( 665 )   We study the phenomena of preferential linking in a large-scale evolving online social network and find that the linear preference holds for preferential creation, preferential acceptance, and preferential attachment. Based on the linear preference, we propose an analyzable model, which illustrates the mechanism of network growth and reproduces the process of network evolution. Our simulations demonstrate that the degree distribution of the network produced by the model is in good agreement with that of the real network. This work provides a possible bridge between the micro-mechanisms of network growth and the macrostructures of the online social networks. 参考文献 | 相关文章 | 计量指标

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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A decomposition study of moisture transport divergence for inter-decadal change in East Asia summer rainfall during 1958–2001 戴新刚, 汪萍, 张凯静 2012 (11):  119201-119201.  doi: 10.1088/1674-1056/21/11/119201 摘要 ( 939 )   PDF(1718KB) ( 634 )   In this paper, we report on the results of an investigation into inter-decadal changes in moisture transport and divergence in East Asia for the two periods 1980-2001 and 1958-1979. The aim is to explore the mechanism of summer rainfall change in the region after the abrupt change. The relevant changes are calculated using ERA-40 daily reanalysis datasets. The results show that both stationary and transient eddy moisture transports to the Chinese mainland have declined since the abrupt change in atmospheric general circulation in the late 1970s, leading to more rainfalls in South China and less in the North. The anomalous rainfall pattern coincides well with anomalous large-scale moisture divergence in the troposphere, of which stationary-wave or monsoon transport is dominant, in comparison with the contribution of the transient eddies. Furthermore, their divergences are found to be in opposite phases. In addition, meridional divergence is more important than its zonal counterpart, with an opposite phase in East Asia. Abnormal zonal moisture convergences appear in northwestern and northeastern parts of China, and are related to the excess rainfalls in these regions. An increase in transient eddy activity is one of the major mechanisms for excess rainfall in northern Xinjiang. Consequently, the anomalous rainfall pattern in East Asia results from a decline of East Asian monsoon after the abrupt change, while the rainfall increase in northwestern China involves anomalies of both stationary waves and transient eddies on boreal westerly over the mid- and high latitudes. 参考文献 | 相关文章 | 计量指标

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Comparing different light-emitting diodes as light sources for long path differential optical absorption spectroscopy NO2 and SO2 measurements 陈嘉乐, 凌六一, Andreas Hartl, 郑尼娜, Gerrit Kuhlmann, 秦敏, 孙友文, 谢品华, 刘文清, Mark Wenig 2012 (11):  119301-119301.  doi: 10.1088/1674-1056/21/11/119301 摘要 ( 924 )   PDF(802KB) ( 658 )   In this paper, we present the comparison of different light-emitting diodes (LEDs) as the light source for long path differential optical absorption spectroscopy (LP-DOAS) atmospheric trace gas measurements. In our study, we use a fiber optic design, where high power LEDs used as the light source are coupled into the telescope using a Y shape fiber bundle. Two blue and a ultraviolet (UV) LEDs with different emission wavelength ranges are tested for NO2 and SO2 measurements. The detailed description of the instrumental setup, the NO2 and SO2 retrieval procedure, the error analysis, and the preliminary results from the measurements carried out in Science Island, Hefei, Anhui, China are presented. Our first measurement results show that atmospheric NO2 and SO2 have strong temporal variations in that area and that the measurement accuracy is strongly dependent on the visibility conditions. The measured NO2 and SO2 data are compared to the Ozone Monitoring Instrument (OMI) satellite observations. The results show that the OMI NO2 product underestimates the ground level NO2 by 45%, while the OMI SO2 data are highly influenced by clouds and aerosols, which can lead to large biases in the ground level concentrations. During the experiment, the mixing ratios of the atmospheric NO2 and SO2 vary from 8 ppbv to 36 ppbv and from 3 ppbv to 18 ppbv, respectively. 参考文献 | 相关文章 | 计量指标