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2009年, 第18卷, 第10期　刊出日期：2009-10-20 上一期    下一期

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Element-free Galerkin (EFG) method for a kind of two-dimensional linear hyperbolic equation 程荣军, 程玉民, 葛红霞 2009 (10):  4059-4064.  doi: 10.1088/1674-1056/18/10/001 摘要 ( 2021 )   PDF(357KB) ( 1108 )   The present paper deals with the numerical solution of a two-dimensional linear hyperbolic equation by using the element-free Galerkin (EFG) method which is based on the moving least-square approximation for the test and trial functions. A variational method is used to obtain the discrete equations, and the essential boundary conditions are enforced by the penalty method. Compared with numerical methods based on mesh, the EFG method for hyperbolic problems needs only the scattered nodes instead of meshing the domain of the problem. It neither requires any element connectivity nor suffers much degradation in accuracy when nodal arrangements are very irregular. The effectiveness of the EFG method for two-dimensional hyperbolic problems is investigated by two numerical examples in this paper. 相关文章 | 计量指标

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An improved boundary element-free method (IBEFM) for two-dimensional potential problems 任红萍, 张武 2009 (10):  4065-4073.  doi: 10.1088/1674-1056/18/10/002 摘要 ( 1806 )   PDF(217KB) ( 1031 )   The interpolating moving least-squares (IMLS) method is discussed first in this paper. And the formulae of the IMLS method obtained by Lancaster are revised. Then on the basis of the boundary element-free method (BEFM), combining the boundary integral equation (BIE) method with the IMLS method, the improved boundary element-free method (IBEFM) for two-dimensional potential problems is presented, and the corresponding formulae of the IBEFM are obtained. In the BEFM, boundary conditions are applied directly, but the shape function in the MLS does not satisfy the property of the Kronecker δ function. This is a problem of the BEFM, and must be solved theoretically. In the IMLS method, when the shape function satisfies the property of the Kronecker δ function, then the boundary conditions, in the meshless method based on the IMLS method, can be applied directly. Then the IBEFM, based on the IMLS method, is a direct meshless boundary integral equation method in which the basic unknown quantity is the real solution of the nodal variables, and the boundary conditions can be applied directly and easily, thus it gives a greater computational precision. Some numerical examples are presented to demonstrate the method. 相关文章 | 计量指标

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Application of higher-order KdV--mKdV model with higher-degree nonlinear terms to gravity waves in atmosphere 李子良 2009 (10):  4074-4082.  doi: 10.1088/1674-1056/18/10/003 摘要 ( 1688 )   PDF(2601KB) ( 734 )   Higher-order Korteweg-de Vries (KdV)-modified KdV (mKdV) equations with a higher-degree of nonlinear terms are derived from a simple incompressible non-hydrostatic Boussinesq equation set in atmosphere and are used to investigate gravity waves in atmosphere. By taking advantage of the auxiliary nonlinear ordinary differential equation, periodic wave and solitary wave solutions of the fifth-order KdV--mKdV models with higher-degree nonlinear terms are obtained under some constraint conditions. The analysis shows that the propagation and the periodic structures of gravity waves depend on the properties of the slope of line of constant phase and atmospheric stability. The Jacobi elliptic function wave and solitary wave solutions with slowly varying amplitude are transformed into triangular waves with the abruptly varying amplitude and breaking gravity waves under the effect of atmospheric instability. 相关文章 | 计量指标

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Simulation of natural convection under high magnetic field by means of the thermal lattice Boltzmann method 钟诚文, 解建飞, 卓从山, 熊生伟, 尹大川 2009 (10):  4083-4093.  doi: 10.1088/1674-1056/18/10/004 摘要 ( 1598 )   PDF(527KB) ( 1012 )   The thermal lattice Boltzmann method (TLBM), which was proposed by J. G. M. Eggels and J. A. Somers previously, has been improved in this paper. The improved method has introduced a new equilibrium solution for the temperature distribution function on the assumption that flow is incompressible, and it can correct the effect of compressibility on the macroscopic temperature computed. Compared to the previous method, where the half-way bounce back boundary condition was used for non-slip velocity and temperature, a non-equilibrium extrapolation scheme has been adopted for both velocity and temperature boundary conditions in this paper. Its second-order accuracy coincides with the ensemble accuracy of lattice Boltzmann method. In order to validate the improved thermal scheme, the natural convection of air in a square cavity is simulated by using this method. The results obtained in the simulation agree very well with the data of other numerical methods and benchmark data. It is indicated that the improved TLBM is also successful for the simulations of non-isothermal flows. Moreover, this thermal scheme can be applied to simulate the natural convection in a non-uniform high magnetic field. The simulation has been completed in a square cavity filled with the aqueous solutions of KCl (11wt%), which is considered as a diamagnetic fluid with electrically low-conducting, with Grashof number Gr=4.64× 10^4 and Prandtl number Pr=7.0. And three cases, with different cavity locations in the magnetic field, have been studied. In the presence of a high magnetic field, the natural convection is quenched by the body forces exerted on the electrically low-conducting fluids, such as the magnetization force and the Lorentz force. From the results obtained, it can be seen that the quenching efficiencies decrease with the variation of location from left, symmetrical line, to the right. These phenomena originate from the different distributions of the magnetic field strengths in the zones of the symmetrical central line of the magnetic fields. The results are also compared with those without a magnetic field. Finally, we can conclude that the improved TLBM will enable effective simulation of the natural convection under a high magnetic field. 相关文章 | 计量指标

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New explicit and exact solutions of the Benney--Kawahara--Lin equation 谢元喜 2009 (10):  4094-4099.  doi: 10.1088/1674-1056/18/10/005 摘要 ( 1767 )   PDF(92KB) ( 641 )   In this paper, we present a combination method of constructing the explicit and exact solutions of nonlinear partial differential equations. And as an illustrative example, we apply the method to the Benney-Kawahara-Lin equation and derive its many explicit and exact solutions which are all new solutions. 相关文章 | 计量指标

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Entanglement dynamics between an isolated atom and a moving atom in the cavity 邓小娟, 方卯发, 康国栋 2009 (10):  4100-4104.  doi: 10.1088/1674-1056/18/10/006 摘要 ( 1899 )   PDF(188KB) ( 663 )   The entanglement dynamics between an isolated atom and a moving atom interacting with a cavity field is investigated. The results show that there appears sudden death of entanglement between the isolated atom and the moving atom and that the time of entanglement sudden death (ESD) is independent of the initial state of the system. It is interesting that the isolated atom can also entangle with a cavity field, though they do not interact with each other originally, which stems from the fact that the entanglement between the isolated atom and the moving atom may turn into the entanglement between the isolated atom and the cavity. 相关文章 | 计量指标

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An efficient deterministic secure quantum communication scheme based on cluster states and identity authentication 刘文杰, 陈汉武, 马廷淮, 李志强, 刘志昊, 胡文博 2009 (10):  4105-4109.  doi: 10.1088/1674-1056/18/10/007 摘要 ( 1556 )   PDF(165KB) ( 966 )   A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit two bits of classical information per cluster state, and its efficiency of the quantum communication is 1/3, which is approximately 1.67 times that of the previous protocol presented by Wang et al [Chin. Phys. Lett. 23 (2006) 2658]. Security analysis shows the present scheme is secure against intercept-resend attack and the impersonator's attack. Furthermore, it is more economic with present-day techniques and easily processed by a one-way quantum computer. 相关文章 | 计量指标

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Effects of periodic modulation on the nonlinear Landau--Zener tunneling 吴利华, 段文山 2009 (10):  4110-4116.  doi: 10.1088/1674-1056/18/10/008 摘要 ( 1781 )   PDF(241KB) ( 882 )   We study the Landau-Zener tunneling of a nonlinear two-level system by applying a periodic modulation on its energy bias. We find that the two levels are splitting at the zero points of the zero order Bessel function for high-frequency modulation. Moreover, we obtain the effective coupling constant between two levels at the zero points of the zero order Bessel function by calculating the final tunneling probability at these points. It seems that the effective coupling constant can be regarded as the approximation of the higher order Bessel function at these points. For the low-frequency modulation, we find that the final tunneling probability is a function of the interaction strength. For the weak inter-level coupling case, we find that the final tunneling probability is more disordered as the interaction strength becomes larger. 相关文章 | 计量指标

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Entanglement evolution and transfer in a double Tavis--Cumming model in cavity QED 徐庆君, 张士英 2009 (10):  4117-4121.  doi: 10.1088/1674-1056/18/10/009 摘要 ( 1757 )   PDF(711KB) ( 613 )   We have studied entanglement evolution and transfer in a double Tavis--Cumming model where two pairs of entangled two-level atoms AB and CD interact with two single-mode cavity fields a and b. We show that the Bell-like initial state of atoms AB can exhibit entanglement sudden death which should be independent of the initial entanglement of atoms CD. Also, we show that the initial entanglement of one atomic pair can be transferred into another pair, as well as the possible subsystems, that become entangled during evolution. 相关文章 | 计量指标

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Critical rotation of an anharmonically trapped Bose--Einstein condensate 马娟, 李志, 薛具奎 2009 (10):  4122-4129.  doi: 10.1088/1674-1056/18/10/010 摘要 ( 1814 )   PDF(812KB) ( 820 )   We consider rotational motion of an interacting atomic Bose-Einstein condensate (BEC) with both two- and three-body interactions in a quadratic-plus-quartic and harmonic-plus-Gaussian trap. By using the variational method, the influence of the three-body interaction and the anharmonicity of the trap on the lowest energy surface mode excitation and the spontaneous shape deformation (responsible for the vortex formation) in a rotating BEC is discussed in detail. It is found that the repulsive three-body interaction helps the formation of the vortex and reduces the lowest energy surface mode frequency and the critical rotational frequency of the system. Moreover, the critical rotational frequency for the vortex formation in the harmonic-plus-Gaussian potential is lower than that in the quadratic-plus-quartic potential. 相关文章 | 计量指标

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The nonlinear Wannier function in square Kr?nig--Penney model 薛锐, 梁兆新, 李卫东 2009 (10):  4130-4135.  doi: 10.1088/1674-1056/18/10/011 摘要 ( 1616 )   PDF(230KB) ( 574 )   The nonlinear Wannier functions in square Krönig-Penney potential are investigated with the help of a set of exact nonlinear Bloch solutions. The nonlinear interaction makes the Wannier functions fall off as non-exponential law with distance and enhances the tunneling coupling between the neighbor sites. 相关文章 | 计量指标

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The influence of strain-reducing layer on strain distribution and ground state energy levels of GaN/AlN quantum dot 刘玉敏, 俞重远, 任晓敏, 徐子欢 2009 (10):  4136-4142.  doi: 10.1088/1674-1056/18/10/012 摘要 ( 1656 )   PDF(896KB) ( 693 )   This article deals with the strain distributions around GaN/AlN quantum dots by using the finite element method. Special attention is paid to the influence of Al0.2Ga0.8N strain-reducing layer on strain distribution and electronic structure. The numerical results show that the horizontal and the vertical strain components are reinforced in the GaN quantum dot due to the presence of the strain-reducing layer, but the hydrostatic strain in the quantum dot is not influenced. According to the deformation potential theory, we study the band edge modifications and the piezoelectric effects. The result demonstrates that with the increase of the strain reducing layer, the transition energy between the ground state electron and the heavy hole increases. This result is consistent with the emission wavelength blue shift phenomenon observed in the experiment and confirms that the wavelength shifts toward the short wavelength range is realizable by adjusting the structure-dependent parameters of GaN/AlN quantum dot. 相关文章 | 计量指标

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Einstein--Podolsky--Rosen entanglement in time-dependent periodic pumping non-degenerate optical parametric amplifier 赵超樱, 谭维翰 2009 (10):  4143-4153.  doi: 10.1088/1674-1056/18/10/013 摘要 ( 1538 )   PDF(281KB) ( 614 )   The solution of the time-dependent periodic pumping non-degenerate optical parametric amplifier (NOPA) is derived when the pump depletion is considered both above and below thresholds. Based on this solution, the quantum fluctuation calculated shows that a high entanglement and a good squeezing degree of the parametric light beams are achieved near and above thresholds. We adopt two kinds of pump fields: (i) a continuously modulated pump with a sinusoidal envelope; (ii) a sequence of laser pulses with Gaussian envelopes. We analyse the time evolution of continuous variable entanglement by analytical and numerical calculations, and show that the periodic driven pumping also improves the degree of entanglement. The squeezing and Einstein-Podolsky-Rosen (EPR) entanglement by using the two pumping driven functions are investigated from below to above the threshold regions, the tendencies are nearly the same, and the Gaussian driven function is superior to that of the sine driven function, when the maximum squeezing and the minimum variance of quantum fluctuation are considered. In the meantime, the generalization of frequency degenerate OPA to frequency non-degenerated OPA problem is investigated. 相关文章 | 计量指标

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Quantum quasi-cyclic low-density parity-check error-correcting codes 李渊, 曾贵华, Moon Ho Lee 2009 (10):  4154-4160.  doi: 10.1088/1674-1056/18/10/014 摘要 ( 1497 )   PDF(139KB) ( 651 )   Due to the fault of the author(s) of the article entitled “Quantum quasi-cyclic low-density parity-check error-correcting codes”, published in Chinese Physics B, 2009, Vol. 18, Issue 10, pp 4154--4160, has been found to partly copy from the article arXiv:quant-ph/0701020v2 on the arXiv preprint. So the above article in Chinese Physics B has been withdrawn from the publication.  [2 February 2010] In this paper, we propose the approach of employing circulant permutation matrices to construct quantum quasi-cyclic (QC) low-density parity-check (LDPC) codes. Using the proposed approach one may construct some new quantum codes with various lengths and rates of no cycles-length 4 in their Tanner graphs. In addition, these constructed codes have the advantages of simple implementation and low-complexity encoding. Finally, the decoding approach for the proposed quantum QC LDPC is investigated. 相关文章 | 计量指标

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Asymptotic quasinormal modes of scalar field in a gravity's rainbow 刘成周, 朱建阳 2009 (10):  4161-4168.  doi: 10.1088/1674-1056/18/10/015 摘要 ( 1649 )   PDF(193KB) ( 560 )   In the framework of the gravity's rainbow, the asymptotic quasinormal modes of the modified Schwarzschild black holes undergoing a scalar perturbation are investigated. By using the monodromy method, we analytically calculated the asymptotic quasinormal frequencies, which depend on not only the mass parameter of the black hole, but also the particle's energy of the perturbation field. Meanwhile, the real parts of the asymptotic quasinormal modes can be expressed as TH\ln 3, which is consistent with Hod's conjecture. In addition, for the quantum corrected black hole, the area spacing is independent of the particle's energy, even though the area itself depends on the particle's energy. And that, by relating the area spectrum to loop quantum gravity, the Barbero-Immirzi parameter is given and it remains the same as from the usual black hole. 相关文章 | 计量指标

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Effect of road structure on the capacity of a signalized road intersection 盘佳秀, 薛郁, 梁玉娟, 唐铁桥 2009 (10):  4169-4176.  doi: 10.1088/1674-1056/18/10/016 摘要 ( 1809 )   PDF(1067KB) ( 1581 )   In this paper, we use the stochastic Nagel--Schreckenberg (NaSch) model to investigate the influence of a special right-turning lane connecting two main roads on the capacity of a signalized road intersection. It is found that the magnitude of right-turning traffic flow and the linking position of the special right-turning lane can greatly influence the capacity of the signalized road intersection. The relation between traffic flow and entering probability for different distances between the entrance (exit) of the special right-turning lane and the road intersection is simulated and analysed. The corresponding spatiotemporal pattern and phase diagram on different sections of the main road are given under the condition of close proximity to the signalized road intersection, stop-and-go traffic occur and obstruct the intersection. On the contrary, unchanged flux is maintained as the distance exceeds a critical values. All the studies indicate that setting a special right-turning lane by choosing a suitable location near a signalized road intersection can relieve the load of current traffic on the main road and maintain traffic flow. 相关文章 | 计量指标

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Modulational instability for a self-attractive two-component Bose--Einstein condensate 栗生长, 段文山 2009 (10):  4177-4181.  doi: 10.1088/1674-1056/18/10/017 摘要 ( 1982 )   PDF(1140KB) ( 1107 )   By means of the multiple-scale expansion method, the coupled nonlinear Schr?dinger equations without an explicit external potential are obtained in two-dimensional geometry for a self-attractive Bose-Einstein condensate composed of different hyperfine states. The modulational instability of two-component condensate is investigated by using a simple technique. Based on the discussion about two typical cases, the explicit expression of the growth rate for a purely growing modulational instability and the optimum stable conditions are given and analysed analytically. The results show that the modulational instability of this two-dimensional system is quite different from that in a one-dimensional system. 相关文章 | 计量指标

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Effects of signal modulation and coloured cross-correlation of coloured noises on the diffusion of a harmonic oscillator 刘立, 张良英, 曹力 2009 (10):  4182-4186.  doi: 10.1088/1674-1056/18/10/018 摘要 ( 1773 )   PDF(222KB) ( 850 )   The diffusion in a harmonic oscillator driven by coloured noises $\xi(t)$ and $\eta(t)$ with coloured cross-correlation in which one of the noises is modulated by a biased periodic signal is investigated. The exact expression of diffusion coefficient d as a function of noise parameter, signal parameter, and oscillator frequency is derived. The findings in this paper are as follows. 1) The curves of d versus noise intensity D and d versus noises cross-correlation time $\tau_3$ exist as two different phases. The transition between the two phases arises from the change of the cross-correlation coefficient $\lambda$  of the two Ornstein--Uhlenbeck (O-U) noises. 2) Changing the value of $\tau_3$, the curves of d versus Q, the intensity of colored noise that is modulated by the signal, can transform from a phase having a minimum to a monotonic phase. 3) Changing the value of signal amplitude A, d versus Q curves can transform from a phase having a minimum to a monotonic phase. The above-mentioned results demonstrate that a like noise-induced transition appears in the model. 相关文章 | 计量指标

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Synchronization transition of limit-cycle system with homogeneous phase shifts 张廷宪, 郑志刚 2009 (10):  4187-4192.  doi: 10.1088/1674-1056/18/10/019 摘要 ( 1802 )   PDF(543KB) ( 667 )   The behaviors of coupled oscillators, each of which has periodic motion with random natural frequency in the absence of coupling, are investigated when phase shifts are considered. In the system of coupled oscillators, phase shifts are the same between different oscillators. Synchronization and synchronization transition are revealed with different phase shifts. Phase shifts play an important role for this kind of system. When the phase shift α<0.5π, the synchronization state can be attained by increasing the coupling, and the system cannot reach the synchronization state while α≥q0.5π. A clear scaling between complete synchronization critical coupling strength K_pc and α-0.5π is found. 相关文章 | 计量指标

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Spin-3/2 Ising model AFM/AFM two-layer lattice with crystal field ErhanAlbayrak, AliYigit 2009 (10):  4193-4207.  doi: 10.1088/1674-1056/18/10/020 摘要 ( 1776 )   PDF(1551KB) ( 876 )   The spin-3/2 Ising model is investigated for the case of antiferromagnetic (AFM/AFM) interactions on the two-layer Bethe lattice by using the exact recursion relations in the pairwise approach for given coordination numbers q=3, 4 and 6 when the layers are under the influences of equal external magnetic and equal crystal fields. The ground state (GS) phase diagrams are obtained on the different planes in detail and then the temperature-dependent phase diagrams of the system are calculated accordingly. It is observed that the system presents both second- and first-order phase transitions for all q, therefore, tricritical points. It is also found that the system exhibits double-critical end points and isolated points. The model also presents two Néel temperatures, TN, and the existence of which leads to the reentrant behaviour. 相关文章 | 计量指标

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A control method for congested traffic in the coupled map car-following model 沈飞英, 葛红霞, 张辉, 余寒梅, 雷丽 2009 (10):  4208-4216.  doi: 10.1088/1674-1056/18/10/021 摘要 ( 1692 )   PDF(369KB) ( 788 )   Based on the pioneer work of Konishi et al, a new control method is presented to suppress the traffic congestion in the coupled map (CM) car-following model under an open boundary. A control signal concluding the velocity differences of the two vehicles in front is put forward. The condition under which the traffic jam can be contained is analyzed. The results are compared with that presented by Konishi et al [Phys. Rev. 1999 E 60 4000--4007]. The simulation results show that the temporal behavior obtained by our method is better than that by the Konishi's et al. method, although both the methods could suppress the traffic jam. The simulation results are consistent with the theoretical analysis. 相关文章 | 计量指标

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Improving consensual performance of multi-agent systems in weighted scale-free networks 祁伟, 许新建, 汪映海 2009 (10):  4217-4221.  doi: 10.1088/1674-1056/18/10/022 摘要 ( 1753 )   PDF(213KB) ( 734 )   This paper studies consensus problems in weighted scale-free networks of asymmetrically coupled dynamical units, where the asymmetry in a given link is determined by the relative degree of the involved nodes. It shows that the asymmetry of interactions has a great effect on the consensus. Especially, when the interactions are dominant from higher- to lower-degree nodes, both the convergence speed and the robustness to communication delay are enhanced. 相关文章 | 计量指标

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Collision avoidance for a mobile robot based on radial basis function hybrid force control technique 温淑焕 2009 (10):  4222-4228.  doi: 10.1088/1674-1056/18/10/023 摘要 ( 1602 )   PDF(230KB) ( 6180 )   Collision avoidance is always difficult in the planning path for a mobile robot. In this paper, the virtual force field between a mobile robot and an obstacle is formed and regulated to maintain a desired distance by hybrid force control algorithm. Since uncertainties from robot dynamics and obstacle degrade the performance of a collision avoidance task, intelligent control is used to compensate for the uncertainties. A radial basis function (RBF) neural network is used to regulate the force field of an accurate distance between a robot and an obstacle in this paper and then simulation studies are conducted to confirm that the proposed algorithm is effective. 相关文章 | 计量指标

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Images of triple gas electron multiplier with pixel-pads 董静, 胡碧涛, 陈元柏, 谢一冈 2009 (10):  4229-4233.  doi: 10.1088/1674-1056/18/10/024 摘要 ( 1744 )   PDF(1801KB) ( 808 )   Testing of a triple gas electron multiplier (GEM) with pixel-pads is described. Images by scanning and suspending radioactive sources were obtained by using 96 channels digital data acquisition (DAQ) system which was composed of 96 8× 8~mm2 pads and associated electronics channels. 相关文章 | 计量指标

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Four-parameter analytical local model potential for atoms 余飞, 孙久勋, 田荣刚, 杨维 2009 (10):  4234-4241.  doi: 10.1088/1674-1056/18/10/025 摘要 ( 1828 )   PDF(221KB) ( 783 )   Analytical local model potential for modeling the interaction in an atom reduces the computational effort in electronic structure calculations significantly. A new four-parameter analytical local model potential is proposed for atoms Li through Lr, and the values of four parameters are shell-independent and obtained by fitting the results of Xa method. At the same time, the energy eigenvalues, the radial wave functions and the total energies of electrons are obtained by solving the radial Schr?dinger equation with a new form of potential function by Numerov's numerical method. The results show that our new form of potential function is suitable for high, medium and low Z atoms. A comparison among the new potential function and other analytical potential functions shows the greater flexibility and greater accuracy of the present new potential function. 相关文章 | 计量指标

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Theoretical analysis of ionic autoionization spectra of lanthanum via an intermediate state [Xe]5d6d 1P1 仲银鹏, 贾凤东, 钟志萍 2009 (10):  4242-4250.  doi: 10.1088/1674-1056/18/10/026 摘要 ( 1894 )   PDF(1273KB) ( 694 )   In the framework of multi-channel quantum defect theory, eigenquantum defects μα and the transformation matrices Uiα of La+ are calculated from first principles by relativistic multi-channel theory, while the dipole matrix elements D_α are obtained by fitting with experimental data. Then the ionic autoionization spectra of lanthanum via the intermediate state [Xe]5d6d 1P1 in the energy region of 90213--91905~cm-1 are obtained. Experimental peaks are classified and assigned by comparing with the corresponding calculated spectra. More specifically, four ionic autoionization Rydberg series converging to La2+ 5d5/22D5/2 and several states converging to higher lying states of La2+ are found and assigned. 相关文章 | 计量指标

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Investigation of odd-parity Rydberg states of Eu I with autoionization detection 肖颖, 戴长建, 秦文杰 2009 (10):  4251-4258.  doi: 10.1088/1674-1056/18/10/027 摘要 ( 1683 )   PDF(259KB) ( 729 )   Isolated-core-excitation (ICE) scheme and autoionization detection are employed to study the bound Rydberg states of europium atom. The high-lying states with odd parity have been measured using the autoionization detection method with three different excitation paths via 4f76s6p[ 8P5/2], 4f76s6p[ 8P7/2] and 4f76s6p[ 8P9/2] intermediate states, respectively. In this paper the spectra of bound Rydberg states of Eu atom are reported, which cover the energy regions from 36000~cm-1 to 38250~cm-1 and from 38900~cm-1 to 39500 cm-1. The study provides the information about level energy, the possible J values and relative line intensity as well as the effective principal quantum number n^* for these states. This work not only confirms the previous results of many states, but also discovers 11 new Rydberg states of Eu atom. 相关文章 | 计量指标

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Bose--Einstein condensation on an atom chip 颜波, 程峰, 柯敏, 李晓林, 唐九耀, 王育竹 2009 (10):  4259-4263.  doi: 10.1088/1674-1056/18/10/028 摘要 ( 1657 )   PDF(1298KB) ( 1243 )   This paper reports an experiment of creating Bose-Einstein condensate (BEC) on an atom chip. The chip-based Z-wire current with a homogeneous bias magnetic field creates a tight magnetic trap, which allows for a fast production of BEC. After a 4.17-s forced radio frequency evaporative cooling, a condensate with about 3000 atoms appears. The transition temperature is about 300~nK. This compact system is quite robust, allowing for versatile extensions and further studying of BEC. 相关文章 | 计量指标

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Quantum stereodynamics study for the reaction F + HD 刘玉芳, 张伟, 施德恒, 孙金锋 2009 (10):  4264-4273.  doi: 10.1088/1674-1056/18/10/029 摘要 ( 1732 )   PDF(1873KB) ( 754 )   This paper studies the quantum stereodynamics of the F + HD(υ = 0, j = 0) → HD + F/HF + D reaction at the collision energies of 0.52 and 0.87~kcal/mol. The quantum scattering calculations, based on Stark-Werner potential energy surfaces, show that the differential cross sections for the HF(υ' = 2) + D and DF(υ' = 3) + H channels are consistent with the recent theoretical results. Furthermore, the product rotational angular momentum orientation and alignment have been determined for some selected rovibrational states of the HF + D and DF + H channels. 相关文章 | 计量指标

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Surface-induced evaporative cooling 柯敏, 颜波, 程锋, 王育竹 2009 (10):  4274-4280.  doi: 10.1088/1674-1056/18/10/030 摘要 ( 1479 )   PDF(865KB) ( 614 )   The effects of surface-induced evaporative cooling on an atom chip are investigated. The evolutions of temperature, number and phase-space density of the atom cloud are measured when the atom cloud is brought close to the surface. Rapid decrease of the temperature and number of the atoms is found when the atom-surface distance is < 100~μm. A gain of about a factor of five on the phase-space density is obtained. It is found that the efficiency of the surface-induced evaporative cooling depends on the atom-surface distance and the shape of the evaporative trap. When the atoms are moved very close to the surface, severe heating is observed, which dominates when the holding time is >8~ms. It is important that the surface-induced evaporative cooling offers novel possibilities for the realization of a continuous condensation, where a spatially varying evaporative cooling is required. 相关文章 | 计量指标

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Magnetically insulated transmission line oscillator oscillated in a modified HEM11 mode 王冬, 陈代兵, 秦奋, 范植开 2009 (10):  4281-4286.  doi: 10.1088/1674-1056/18/10/031 摘要 ( 1960 )   PDF(1501KB) ( 1109 )   This paper puts forward a novel magnetically insulated transmission line oscillator (MILO) for the first time which takes a modified HEM11 mode as its main interaction mode. The excitation of the oscillation mode is made possible by carefully adjusting the arrangements of each resonant cavity in a two-dimensional (2-D) slow wave structure. The high frequency characteristics are analyzed and a PIC simulation is carried out; the detailed results are discussed to get a better understanding of this new MILO. Employing an electron beam of about 441~kV and 39.7~kA, it finds that the modified HEM11 mode MILO generates a high power microwave output of about 1.47~GW at 1.45~GHz. The power conversion efficiency is about 8.4% and the generated microwave is in a TE11-like circularly polarized mode; its polarization direction is decided by the rotation direction of the SWS. 相关文章 | 计量指标

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Investigation of transmission resonances on the one-dimensional metallic cylindrical gratings in THz frequency range 陈华, 孙毅民, 汪力 2009 (10):  4287-4291.  doi: 10.1088/1674-1056/18/10/032 摘要 ( 1702 )   PDF(702KB) ( 786 )   In the experiments of THz wave transmitting through the metallic cylindrical gratings fabricated by sub-wavelength brass wires, this paper reports that the discrepancy in the sharp resonances occurred as the grating perpendicular or parallel to the electric vector are observed. A simulation based on the finite difference time domain (FDTD) indicated that the enhanced transmission through the grating is attributed to the combined effects of surface plasmons and cavity modes in the perpendicular condition, while the cavity modes dominate the resonant transmission under the other conditions. Additional experimental data and calculated results show that ～1 enhanced coupling efficiency can be realized in some THz frequency, which could be applied to the design and improvement of various optoelectronic devices, or detection of biological molecule and powder samples, etc. 相关文章 | 计量指标

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Experimental study on microdeposition of the copper thin film by femtosecond laser-induced forward transfer 杨丽, 王清月 2009 (10):  4292-4297.  doi: 10.1088/1674-1056/18/10/033 摘要 ( 1738 )   PDF(2814KB) ( 701 )   The morphologies of the deposited dots on the 40~nm-thick copper film by the femtosecond laser-induced forward transfer that depend on the irradiated laser fluence have been studied, and the variations of orderliness of the diameter of deposited dots on the quartz substrate and forward ablated dot on the donor substrate with increasing pulse fluence have been obtained experimentally. The experimental results show that a thinner copper film would generate larger-sized ablated dot and deposited dot at the threshold fluence for transfer. By x-ray diffraction measurement, it is demonstrated that the crystal form of the transferred copper films is unaltered and the size of the crystallites is diminished. 相关文章 | 计量指标

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The (1+1)-dimensional spatial solitons in media with weak nonlinear nonlocality 丁娜, 郭旗 2009 (10):  4298-4302.  doi: 10.1088/1674-1056/18/10/034 摘要 ( 1804 )   PDF(170KB) ( 881 )   We study the propagation of (1+1)-dimensional spatial soliton in a nonlocal Kerr-type medium with weak nonlocality. First, we show that an equation for describing the soliton propagation in weak nonlocality is a nonlinear Schr?dinger equation with perturbation terms. Then, an approximate analytical solution of the equation is found by the perturbation method. We also find some interesting properties of the intensity profiles of the soliton. 相关文章 | 计量指标

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Interaction of light filaments in air 奚婷婷, 鲁欣, 郝作强, 马媛媛, 张杰 2009 (10):  4303-4307.  doi: 10.1088/1674-1056/18/10/035 摘要 ( 1853 )   PDF(262KB) ( 720 )   This paper analytically investigates the interaction of light filaments generated by a femtosecond laser beam in air. It obtains the Hamiltonian of a total laser field and interaction force between two filaments with different phase shifts and crossing angles. The property of the interaction force, which leads the attraction or repulsion of filaments, is basically dependent on the phase shift between filaments. The crossing angle between two filaments can only determine the magnitude of the interaction force, but does not change the property of the force. 相关文章 | 计量指标

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Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay 王燕玲, 周绪桂, 吴洪, 丁良恩 2009 (10):  4308-4313.  doi: 10.1088/1674-1056/18/10/036 摘要 ( 2066 )   PDF(708KB) ( 98591 )   This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet (UV) output energy of 0.32~mJ centered at 270~nm with spectral bandwidth of 2~nm when input beam at 800~nm was 70~fs pulse duration and 6~mJ pulse energy which was extracted from Ti:sapphire laser system by a diaphragm, corresponding to an 800-to-270~nm conversion efficiency of 5.3% and a factor-of-1.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18~mJ from a Ti:sapphire laser system was used and optimized, the UV emission could reach 0.83~mJ. 相关文章 | 计量指标

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High efficiency continuous-wave tunable signal output of an intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate 丁欣, 盛泉, 陈娜, 禹宣伊, 王睿, 张衡, 温午麒, 王鹏, 姚建铨 2009 (10):  4314-4318.  doi: 10.1088/1674-1056/18/10/037 摘要 ( 1611 )   PDF(195KB) ( 1253 )   In this paper we report on a continuous-wave (CW) intracavity singly resonant optical parametric oscillator (ICSRO) based on periodically poled LiNbO3 (PPLN) pumped by a diode-end-pumped CW Nd:YVO4 laser. Considering the thermal lens effects and diffraction loss, an optical ballast lens and a near-concentric cavity are adopted for better operation. Through varying the grating period and the temperature, the tunable signal output from 1406~nm to 1513~nm is obtained. At a PPLN grating period of 29~μ m and a temperature of 413~K, a maximum signal output power of 820~mW at 1500~nm is achieved when the 808~nm pump power is 10.9~W, leading to an optical-to-optical conversion efficiency of 7.51%. 相关文章 | 计量指标

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Surface defect gap solitons in one-dimensional dual-frequency lattices 朱伟玲, 罗莉, 何影记, 汪河洲 2009 (10):  4319-4325.  doi: 10.1088/1674-1056/18/10/038 摘要 ( 1733 )   PDF(1409KB) ( 749 )   We study the surface defect gap solitons in an interface between a defect of one-dimensional dual-frequency lattices and the uniform media. Some unique properties are revealed that such lattices can broaden the region of semi-finite gap, and the semi-finite gap exists not only in the positive and zero defects but also in the negative defect; unlike in the regular lattices, the semi-finite gap exists in the positive and zero defects but does not exist in the negative defect. In particular, stable solitons exist almost in the whole semi-finite gap for the positive and zero defects. These properties are different from other lattices with defects. In addition, it is found that the existence of surface dual-frequency lattice solitons does not need a threshold power. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Photochemical kinetics for holographic grating formation in phenanthrenequinone doped poly (methyl methacrylate) photopolymer 王健, 孙秀冬, 骆素华, 姜永远, 孟庆鑫 2009 (10):  4326-4332.  doi: 10.1088/1674-1056/18/10/039 摘要 ( 1773 )   PDF(219KB) ( 616 )   The photochemical kinetics of phenanthrenequinone (PQ) doped poly (methyl methacrylate) photopolymer in holographic recording was studied theoretically and experimentally. The diffusion of PQ molecules during holographic recording was negligible because of its small diffusion coefficient at room temperature. A photochemical reaction kinetics model of PQ/PMMA was established. The analytical expressions for the temporal variations of transmittance and diffraction efficiency were derived. By fitting the experimental curves, some parameters related with the polymer components were obtained by the proposed model, which can be used to analyze the photochemical process and will be helpful to the optimization of material preparation. 相关文章 | 计量指标

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Modification of spontaneous emission rate of micrometer-sized light sources using hollow-core photonic crystal fibers 卢娇华, 蒙自明, 刘海英, 冯天华, 戴峭峰, 吴立军, 郭旗, 胡巍, 兰胜 2009 (10):  4333-4338.  doi: 10.1088/1674-1056/18/10/040 摘要 ( 1675 )   PDF(2884KB) ( 807 )   We investigate numerically and experimentally the modification of the spontaneous emission rate for micrometer-sized light sources embedded in a hollow-core photonic crystal fiber (HCPCF). The diameter of the light source is deliberately chosen such that they could be easily introduced into the central hole of the hollow-core photonic crystal fiber by capillary force. The photoluminescence from the microparticles is measured by using an inverted microscope in combination with a spectrometer. The modification of the spontaneous emission rate is observed in a wavelength region where there is no band gap. The experimental observations are consistent with the simulation results obtained by the plane wave expansion and finite-difference time-domain techniques. 相关文章 | 计量指标

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First-principles calculations for the elastic properties of Ni-base model superalloys: Ni/Ni3Al multilayers 王云江, 王崇愚 2009 (10):  4339-4348.  doi: 10.1088/1674-1056/18/10/041 摘要 ( 1890 )   PDF(927KB) ( 2666 )   A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ'+2γ to 10γ'+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer's thickness. A Ni/Ni3Al multilayer with 10γ'+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young's modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ' phase volume fraction are calculated by varying the proportion of the γ and γ' phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures. 相关文章 | 计量指标

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Force criterion of different electrolytes in microchannel 任玉坤, 闫辉, 姜洪源, 顾建忠, AntonioRamos 2009 (10):  4349-4352.  doi: 10.1088/1674-1056/18/10/042 摘要 ( 1670 )   PDF(348KB) ( 641 )   The control and handling of fluids is central to many applications of the lab-on-chip. This paper analyzes the basic theory of manipulating different electrolytes and finds the two-dimensional model. Coulomb force and dielectric force belonging to the body force of different electrolytes in the microchannel were analyzed. The force criterion at the interface was concluded, and testified by the specific example. Three basic equations were analyzed and applied to simulate the phenomenon. The force criterion was proved to be correct based on the simulation results. 相关文章 | 计量指标

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Lattice Boltzmann simulation of fluid flows in two-dimensional channel with complex geometries 闻炳海, 刘海燕, 张超英, 王强 2009 (10):  4353-4359.  doi: 10.1088/1674-1056/18/10/043 摘要 ( 1672 )   PDF(339KB) ( 991 )   Boundary conditions (BCs) play an essential role in lattice Boltzmann (LB) simulations. This paper investigates several most commonly applied BCs by evaluating the relative L2-norm errors of the LB simulations for two-dimensional (2-D) Poiseuille flow. It is found that the relative L2-norm error resulting from FHML's BC is smaller than that from other BCs as a whole. Then, based on the FHML's BC, it formulates an LB model for simulating fluid flows in 2-D channel with complex geometries. Afterwards, the flows between two inclined plates, in a pulmonary blood vessel and in a blood vessel with local expansion region, are simulated. The numerical results are in good agreement with the analytical predictions and clearly show that the model is effective. It is expected that the model can be extended to simulate some real biologic flows, such as blood flows in arteries, vessels with stenosises, aneurysms and bifurcations, etc. 相关文章 | 计量指标

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Single point velocity distributions in homogeneous isotropic turbulence 燕秀林, 冉政 2009 (10):  4360-4365.  doi: 10.1088/1674-1056/18/10/044 摘要 ( 1652 )   PDF(157KB) ( 655 )   The starting point for this paper lies in the results obtained by Tatsumi (2004) for isotropic turbulence with the self-preserving hypothesis. A careful consideration of the mathematical structure of the one-point velocity distribution function equation obtained by Tatsumi (2004) leads to an exact analysis of all possible cases and to all admissible solutions of the problem. This paper revisits this interesting problem from a new point of view, and obtains a new complete set of solutions. Based on these exact solutions, some physically significant consequences of recent advances in the theory of homogenous statistical solution of the Navier--Stokes equations are presented. The comparison with former theory was also made. The origin of non--Gaussian character could be deduced from the above exact solutions. 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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High-resolution transmission electron microscopy and bulk magnetometry study of LaFe11.5Si1.5 compound 邹君鼎, 李卫, 沈保根 2009 (10):  4366-4369.  doi: 10.1088/1674-1056/18/10/045 摘要 ( 1885 )   PDF(2734KB) ( 645 )   This paper studies the microstructural and magnetic properties of LaFe11.5Si1.5 compound by means of high-resolution transmission electron microscope and bulk magnetometry measurements. The crystalline structure is accompanied with the noncrystalline and nanocrystalline structures. This characteristic is the reflection of the crystalline process held by quenching. The inverse susceptibilities diverge and deviate from Curie--Weiss law under low applied magnetic fields. This paper proposes the possible mechanism between the anomalous susceptibilities and microstructure, and offers a perspective on the magnetic properties of metastable intermetallic compounds. 相关文章 | 计量指标

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Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques 郑鸥, 马家艳, 王建波, 周嘉萍, 金磊, 赵东山, 王仁卉 2009 (10):  4370-4379.  doi: 10.1088/1674-1056/18/10/046 摘要 ( 1565 )   PDF(8871KB) ( 667 )   Knowledge of the microscopic structure, including three-dimensional (3-D) size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship (OR), other ORs such as Pitsch--Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]α 1.0° from [311]γ and (11\bar 20)α 2.0° from (03\bar 3)γ between the magnesium matrix and the precipitate γ -Mg17Al12 are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100--200~nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness. 相关文章 | 计量指标

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Rotational viscosity of a liquid crystal mixture: a fully atomistic molecular dynamics study 张然, 彭增辉, 刘永刚, 郑致刚, 宣丽 2009 (10):  4380-4384.  doi: 10.1088/1674-1056/18/10/047 摘要 ( 2053 )   PDF(1109KB) ( 1675 )   Fully atomistic molecular dynamics (MD) simulations at 293, 303 and 313~K have been performed for the four-component liquid crystal mixture, E7, using the software package Material Studio. Order parameters and orientational time correlation functions (TCFs) were calculated from MD trajectories. The rotational viscosity coefficients (RVCs) of the mixture were calculated using the Nemtsov--Zakharov and Fialkowski methods based on statistical-mechanical approaches. Temperature dependences of RVC and density were discussed in detail. Reasonable agreement between the simulated and experimental values was found. 相关文章 | 计量指标

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Structural phase transition behaviour of Zn4Sb3 and its substitutional compounds (Zn1.98M0.02)4Sb3 (M= Al, Ga and In) at low temperatures 刘峰, 秦晓英, 刘冕 2009 (10):  4386-4392.  doi: 10.1088/1674-1056/18/10/048 摘要 ( 1566 )   PDF(1077KB) ( 828 )   Structural phase transitions of Zn4Sb3 and its substitutional compounds (Zn1.98M0.02)4Sb3 (M= Al, Ga and In) are investigated by electrical transport measurement and differential scanning calorimetry below room temperature. The results indicate that both β → α and α → α' phase transitions of Zn4Sb3 are reversible and exothermic processes, which may be explained as that both the transitions originate from the ordering of the disordered interstitial Zn and vacancies in regular sizes. The derived activation energies of β → α and α → α' phase transition processes for Zn4Sb3 are E1 =3.9~eV and E2=4.1~eV, respectively. Although no remarkable influence on activation energy E2 is observed after Al doping, Al substitution for Zn causes E1 to increase to 4.6~eV, implying its suppression of β ≤ftrightarrow α transition to a great extent. Moreover, it is found that both β ≤ftrightarrow α and α ≤ftrightarrow α ' transitions are completely prohibited by substitution of either In or Ga for Zn in Zn4Sb3. The underlying mechanisms for these phenomena are discussed. 相关文章 | 计量指标

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Discrete gap breathers in a two-dimensional diatomic face-centered square lattice 吕彬彬, 田强 2009 (10):  4393-4406.  doi: 10.1088/1674-1056/18/10/049 摘要 ( 1636 )   PDF(4014KB) ( 675 )   In this paper we study the existence and stability of two-dimensional discrete gap breathers in a two-dimensional diatomic face-centered square lattice consisting of alternating light and heavy atoms, with on-site potential and coupling potential. This study is focused on two-dimensional breathers with their frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of the existence of two-dimensional gap breathers by using a numerical method. Six types of two-dimensional gap breathers are obtained, i.e., symmetric, mirror-symmetric and asymmetric, whether the center of the breather is on a light or a heavy atom. The difference between one-dimensional discrete gap breathers and two-dimensional discrete gap breathers is also discussed. We use Aubry's theory to analyze the stability of discrete gap breathers in the two-dimensional diatomic face-centered square lattice. 相关文章 | 计量指标

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Phase-field simulation of the effect of interaction among ordered domains on interdiffusion in Ni--Al--Cr alloys 张玉祥, 王锦程, 杨玉娟, 杨根仓, 周尧和 2009 (10):  4407-4412.  doi: 10.1088/1674-1056/18/10/050 摘要 ( 1578 )   PDF(2900KB) ( 737 )   The effect of interaction among γ ' ordered domains on the interdiffusion process in γ +γ ' /γ and γ +γ ' /γ +γ ' diffusion couples is investigated by using the phase-field method, in which bulk free energy and mobility are linked with thermodynamic and kinetic databases. Simulated results show that the interaction among γ ' ordered domains has great influence on the microstructure, the interdiffusion velocity and the volume fraction of γ ' phase on both sides of the diffusion couples. 相关文章 | 计量指标

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The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates 吴玉新, 朱建军, 赵德刚, 刘宗顺, 江德生, 张书明, 王玉田, 王辉, 陈贵锋, 杨辉 2009 (10):  4413-4417.  doi: 10.1088/1674-1056/18/10/051 摘要 ( 1721 )   PDF(2560KB) ( 1257 )   High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural properties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated. 相关文章 | 计量指标

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Lattice strain and p-d repulsion affecting electronic structure of wurtzite Zn1-xCdxO alloys 史力斌, 康莉, 金健维, 迟锋 2009 (10):  4418-4424.  doi: 10.1088/1674-1056/18/10/052 摘要 ( 1923 )   PDF(1027KB) ( 907 )   In the paper, density of states, band structure and electron density difference of Zn1-xCdxO are calculated by first principles, here x varies from 0 to 0.75 at intervals of 0.125, and the band gap obtained from band structure changes from 0.968~eV to 0.043~eV. The lattice strain and p-d repulsion theory are used to investigate variation of the band gap, the results obtained show that the variation is mainly due to the lattice tensile strain. The p-d repulsion in Zn1-xCdxO cannot be neglected. In addition, electron density difference can be used to verify the results. 相关文章 | 计量指标

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Temperature-dependent far-infrared properties of Bi12GeO20 single crystal Muhammad Kamran, 戴耀民, 马继云, 李博宏, 何世坤, 张伟君, 郑小睿, 邱祥冈 2009 (10):  4425-4429.  doi: 10.1088/1674-1056/18/10/053 摘要 ( 1644 )   PDF(193KB) ( 721 )   Far-infrared reflectivity spectra of bismuth germanium oxide (Bi12GeO20) single crystals are measured from room temperature down to 10~K. All the reflectivity spectra are fitted to a complex dielectric function ε(ω) in the factorised form. Phonon modes at low frequency are found to develop upon decreasing temperature and gain considerable spectrum weight below 150~K. The temperature-dependent static dielectric constants are obtained from the Lyddane--Sachs--Teller relation based on the obtained oscillator parameters. The dielectric constants are found to increase upon decreasing temperature, which is attributed to the charge transfer among the ions in the unit cell with the temperature varying. 相关文章 | 计量指标

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Magnetization of two-dimensional heavy holes with boundaries in a perpendicular magnetic field 方诚, 王志刚, 李树深, 张平 2009 (10):  4430-4436.  doi: 10.1088/1674-1056/18/10/054 摘要 ( 2078 )   PDF(975KB) ( 664 )   The magnetisation of heavy holes in III--V semiconductor quantum wells with Rashba spin-orbit coupling (SOC) in an external perpendicular magnetic field is studied theoretically. We concentrate on the effects on the magnetisation induced by the system boundary, the Rashba SOC and the temperature. It is found that the sawtooth-like de Haas--van Alphen (dHvA) oscillations of the magnetisation will change dramatically in the presence of such three factors. Especially, the effects of the edge states and Rashba SOC on the magnetisation are more evident when the magnetic field is smaller. The oscillation center will shift when the boundary effect is considered and the Rashba SOC will bring beating patterns to the dHvA oscillations. These effects on the dHvA oscillations are preferably observed at low temperatures. With increasing temperature, the dHvA oscillations turn to be blurred and eventually disappear. 相关文章 | 计量指标

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All-electron study of ultra-incompressible superhard material ReB2: structural and electronic properties 李延龄, 钟国华, 曾雉 2009 (10):  4437-4442.  doi: 10.1088/1674-1056/18/10/055 摘要 ( 1544 )   PDF(1939KB) ( 715 )   This paper investigates the structural and electronic properties of rhenium diboride by first-principles calculation based on density functional theory. The obtained results show that the calculated equilibrium structural parameters of ReB2 are in excellent agreement with experimental values. The calculated bulk modulus is 361~GPa in comparison with that of the experiment. The compressibility of ReB2 is lower than that of well-known OsB2. The anisotropy of the bulk modulus is confirmed by c/a ratio as a function of pressure curve and the bulk modulus along different axes along with the electron density distribution. The high bulk modulus is attributed to the strong covalent bond between Re-d and B-p orbitals and the wider pseudogap near the Fermi level, which could be deduced from both electron charge density distribution and density of states. The band structure and density of states of ReB2 exhibit that this material presents metallic behavior. The good metallicity and ultra-incompressibility of ReB2 might suggest its potential application as pressure-proof conductors. 相关文章 | 计量指标

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First-principles calculations for electronic and optical properties of the zinc-blende structured BeS compound under pressure 杨欢, 常景, 李哲, 陈向荣 2009 (10):  4443-4448.  doi: 10.1088/1674-1056/18/10/056 摘要 ( 1762 )   PDF(859KB) ( 869 )   The electronic and the optical properties of the cubic zinc-blende (ZB) BeS under high pressure have been investigated by using \it ab initio plane-wave pseudopotential density functional theory method in the generalised gradient approximation (GGA) for exchange-correlation interaction. The electronic band structure and the pressure dependence of the total and partial densities of state under pressure are successfully described. Our calculations show that the ZB BeS has large and indirect band gaps associated with (Γ → X) transitions in ambient conditions. The results obtained are consistent with the experimental data available and other calculations. The optical properties, including dielectric function, energy-loss function, complex refractive index, reflection and absorption spectra, are investigated and analysed at different external pressures. The results suggest that the optical absorption appears mostly in the ultra-violet region and the curve of refractive index shift toward high energies (blue shift) with pressure increasing. 相关文章 | 计量指标

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Pressure influence on the Stark effect of impurity states in a strained wurtzite GaN/AlxGa1-xN heterojunction 张敏, 班士良 2009 (10):  4449-4455.  doi: 10.1088/1674-1056/18/10/057 摘要 ( 1843 )   PDF(248KB) ( 1000 )   A variational method is adopted to investigate the properties of shallow impurity states near the interface in a free strained wurtzite GaN/AlxGa1-xN heterojunction under hydrostatic pressure and external electric field by using a simplified coherent potential approximation. Considering the biaxial strain due to lattice mismatch or epitaxial growth and the uniaxial strains effects, we investigated the Stark energy shift led by an external electric field for impurity states as functions of pressure as well as the impurity position, Al component and areal electron density. The numerical result shows that the binding energy near linearly increases with pressure from 0 to 10~GPa. It is also found that the binding energy as a function of the electric field perpendicular to the interface shows an un-linear red shift or a blue shift for different impurity positions. The effect of increasing x on blue shift is more significant than that on the red shift for the impurity in the channel near the interface. The pressure influence on the Stark shift is more obvious with increase of electric field and the distance between an impurity and the interface. The increase of pressure decreases the blue shift but increases the red shift. 相关文章 | 计量指标

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Model and analysis of drain induced barrier lowering effect for 4H--SiC metal semiconductor field effect transistor 曹全君, 张义门, 贾立新 2009 (10):  4456-4459.  doi: 10.1088/1674-1056/18/10/058 摘要 ( 1676 )   PDF(400KB) ( 855 )   Based on an analytical solution of the two-dimensional Poisson equation in the subthreshold region, this paper investigates the behavior of DIBL (drain induced barrier lowering) effect for short channel 4H--SiC metal semiconductor field effect transistors (MESFETs). An accurate analytical model of threshold voltage shift for the asymmetric short channel 4H--SiC MESFET is presented and thus verified. According to the presented model, it analyses the threshold voltage for short channel device on the L/a (channel length/channel depth) ratio, drain applied voltage VDS and channel doping concentration ND, thus providing a good basis for the design and modelling of short channel 4H--SiC MESFETs device. 相关文章 | 计量指标

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Metal/semiconductor hybrids consisting of self-assembled CdS nanoparticles on Cd nanowires 符秀丽, 彭志坚, 唐为华, 郭熹 2009 (10):  4460-4464.  doi: 10.1088/1674-1056/18/10/059 摘要 ( 1784 )   PDF(4677KB) ( 731 )   We report on the synthesis and the characterisation of metal/semiconductor hybrids consisting of self-assembled CdS nanoparticles on Cd nanowires, which are grown by thermal evaporation of the mixture of CdS and Cr. The growth of the hybrids is attributed to the decomposition of CdS at high temperature and the strain relieving that arises mainly from the lattice mismatch between Cd and CdS. Temperature dependence of zero-field resistance of single nanohybrid indicates that the as-produced Cd/CdS nanohybrid undergoes a metal--semiconductor transition as a natural consequence of hybrid from metallic Cd and semiconducting CdS. The metal/semiconductor hybrid property provides a promising basis for the development of novel nanoelectronic devices. 相关文章 | 计量指标

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The modulation of Schottky barrier height of NiSi/n-Si Schottky diodes by silicide as diffusion source technique 安霞, 范春晖, 黄如, 郭岳, 徐聪, 张兴 2009 (10):  4465-4469.  doi: 10.1088/1674-1056/18/10/060 摘要 ( 1815 )   PDF(5296KB) ( 845 )   This paper reports that the Schottky barrier height modulation of NiSi/n-Si is experimentally investigated by adopting a novel silicide-as-diffusion-source technique, which avoids the damage to the NiSi/Si interface induced from the conventional dopant segregation method. In addition, the impact of post-BF2 implantation after silicidation on the surface morphology of Ni silicides is also illustrated. The thermal stability of Ni silicides can be improved by silicide-as-diffusion-source technique. Besides, the electron Schottky barrier height is successfully modulated by 0.11~eV at a boron dose of 1015~cm-2 in comparison with the non-implanted samples. The change of barrier height is not attributed to the phase change of silicide films but due to the boron pile-up at the interface of NiSi and Si substrate which causes the upward bending of conducting band. The results demonstrate the feasibility of novel silicide-as-diffusion-source technique for the fabrication of Schottky source/drain Si MOS devices. 相关文章 | 计量指标

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Formation of the intermediate semiconductor larger for the Ohmic contact to silicon carbide using Germanium implantation 王阳元, 郭辉, 王悦湖, 张玉明, 乔大勇, 张义门 2009 (10):  4470-4473.  doi: 10.1088/1674-1056/18/10/061 摘要 ( 1632 )   PDF(2869KB) ( 810 )   By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P+ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρc as low as 4.23× 10-5~Ωega \cdotcm2 is achieved after annealing in N2 at 800~°C for 3~min, which is much lower than that (>900~°C) in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5~kΩega /\Box. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge+ ion implantations. 相关文章 | 计量指标

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Physical simulations and experimental results of 4H—SiC MESFETs on high purity semi-insulating substrates 陈刚, 柏松, 李哲洋, 吴鹏, 陈征, 韩平 2009 (10):  4474-4478.  doi: 10.1088/1674-1056/18/10/062 摘要 ( 1525 )   PDF(1528KB) ( 719 )   In this paper we report on DC and RF simulations and experimental results of 4H--SiC metal semiconductor field effect transistors (MESFETs) on high purity semi-insulating substrates. DC and small-signal measurements are compared with simulations. We design our device process to fabricate n-channel 4H--SiC MESFETs with 100~μm gate periphery. At 30~V drain voltage, the maximum current density is 440~mA/mm and the maximum transconductance is 33~mS/mm. For the continuous wave (CW) at a frequency of 2~GHz, the maximum output power density is measured to be 6.6~W/mm, with a gain of 12~dB and power-added efficiency of 33.7％. The cut-off frequency (fT) and the maximum frequency (fmax) are 9~GHz and 24.9~GHz respectively. The simulation results of fT and fmax are 11.4~GHz and 38.6~GHz respectively. 相关文章 | 计量指标

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Tunneling conductance in quantum wire/insulator/dx2 -y2 + idxy mixed wave superconductor junctions 魏健文 2009 (10):  4479-4485.  doi: 10.1088/1674-1056/18/10/063 摘要 ( 1726 )   PDF(237KB) ( 759 )   Using the extended Blonder--Tinkham--Klapwijk (BTK) theory, this paper calculates the tunnelling conductance in quantum wire/insulator/dx2 -y2 + idxy mixed wave superconductor ( q / I /dx2 -y2 + idxy) junctions. That is different from the case in d- and p-wave superconductor junctions. When the angle $\alpha$  between a-axis of the dx2 -y2 wave superconductor and the interface normal is $\pi$ /4, there follows a rather distinctive tunnelling conductance. The zero-bias conductance peak (ZBCP) may or may not appear in the tunnelling conductance. Both the interface potential z and the quasi-particle lifetime factor $\varGamma$ are smaller, there is no ZBCP. Otherwise, the ZBCP will appear. The position of bias conductance peak (BCP) depends strongly on the amplitude ratio of two components for dx2 -y2 + idxy mixed wave. The low and narrow ZBCP may coexist with the BCP in the tunnelling conductance. Using those features in the tunnelling conductance of q / I /dx2 - y2 +  idxy junctions, it can distinguish dx2 - y2 +  idxy mixed wave superconductor from d- and p-wave one. 相关文章 | 计量指标

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Matching effect in superconducting NbN thin film with a square lattice of holes Muhammad Kamran, 何世坤, 张伟君, 曹文会, 李博宏, 康琳, 陈健, 吴培亨, 邱祥冈 2009 (10):  4486-4489.  doi: 10.1088/1674-1056/18/10/064 摘要 ( 1684 )   PDF(746KB) ( 811 )   A square hole array is fabricated over a micro-bridge of NbN thin film by electron beam lithography and reactive ion milling. Magneto-resistance is measured across the micro-bridge filled with a hole array near the superconducting transition temperature. It is found that magneto-resistance minima occur when the number of vortices is an integer multiple or a fractional multiple of the number of holes. The temperature and the current dependences of the matching effect are studied. 相关文章 | 计量指标

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Electronic structures and magnetic properties in SmCo7-xMx 王培吉, 考红, 张昌文, 于峰, 周忠祥 2009 (10):  4490-4496.  doi: 10.1088/1674-1056/18/10/065 摘要 ( 1882 )   PDF(226KB) ( 920 )   The electronic structures and magnetic properties of SmCo7-xMx (M=Ti, Si, Zr, Hf, Cu, B, Ag, Ga, Mn) compounds are investigated by using a spin-polarized MS-X.α method. The results show that the long-range ferromagnetic order is determined by a stronger 3d--5d interaction, rather than the traditional RKKY interaction, and the effects of doping element M on 3d--5d coupling are negligible in Sm--Co-based compounds. The nonmagnetic dopant Si atoms have a larger effect on the moments of 2e site although they preferably occupy the Co 3g sites, which results in the stronger uniaxial anisotropy of this compound. Analysis of the formation energies indicates that 5d-element doped compounds are more stable than other dopants, and furthermore, they have a higher Curie temperature above room temperature, which will be in favor of their potential application as high-temperature permanent magnets. 相关文章 | 计量指标

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Effects of anharmonic lattice distortion on orbital and magnetic orderings in KCuF3 刘大勇, 陈东猛, 邹良剑 2009 (10):  4497-4505.  doi: 10.1088/1674-1056/18/10/066 摘要 ( 1900 )   PDF(416KB) ( 612 )   Lattice, magnetic and orbital structures in KCuF3 are self-consistently determined by our cluster self-consistent field approach based on a spin-orbital-lattice Hamiltonian. Two stable structures are obtained and found to be degenerate, which confirms the presence of the coexistent phases observed experimentally. We clearly show that due to the inherent frustration, the ground state of the system only with the superexchange interaction is degenerate; while the Jahn--Teller distortion, especially the anharmonic effect, stabilizes the orbital ordered phase at about 23\% in the x2--y2 orbit and at 77\% in the 3z2--r2 orbit. Meanwhile the magnetic moment of Cu is considerably reduced to 0.56μB, and magnetic coupling strengths are highly anisotropic, Jz/Jxy \approx 18. These results are in good agreement with the experiments, implying that the anharmonic Jahn--Teller effect plays an essential role in stabilising the orbital ordered ground state of KCuF3. 相关文章 | 计量指标

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Hydrogen absorption of LaFe11.5Si1.5 compound under low hydrogen gas pressure 傅斌, 龙毅, 史普辑, 马涛, 鲍博, 闫阿儒, 陈仁杰 2009 (10):  4506-4510.  doi: 10.1088/1674-1056/18/10/067 摘要 ( 1541 )   PDF(283KB) ( 683 )   Hydrogen absorptions of LaFe11.5Si1.5 compound in 1-atm hydrogen gas at different temperatures are investigated. The hydrogen content in the hydrogenated sample does not increase with the increase of temperature of hydrogen absorption but changes complicatedly. The characteristic of first-order transition in LaFe11.5Si1.5 compound is weakened after hydrogen absorption. It leads the peaks of magnetic entropy to become wider and the hysteresis loss to reduce significantly, but relative cooling power (RCP) is not changed considerably. 相关文章 | 计量指标

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Great enhancement in remnant polarization of SrBi4Ti4O15 thin films by A-site doping of Fe3+ ions 孙家宝, 孙慧, 王伟, 蔡华, 陈小兵 2009 (10):  4511-4514.  doi: 10.1088/1674-1056/18/10/068 摘要 ( 1792 )   PDF(2276KB) ( 705 )   SrBi4-xFexTi4O15 (SBFT-x) thin films (x =0.00, 0.05, 0.08, 0.15) have been synthesized on Pt/Ti/SiO2/Si (100) substrates by sol-gel method. This paper finds that Fe-doping does not change the crystal structure of SrBi4Ti4O15 (SBTi). The coercive filed (Ec) and remnant polarisation (Pr) increase at first, then decrease with the increase of Fe doping content. At a maximum applied field of 229~kV/cm, the 2Pr reaches a maximum value of 91.1~μ C/cm2 at x = 0.05 and the corresponding Ec is 72~kV/cm. The 2Pr increases by about 260% and the Ec decreases by about 6%, respectively. Obviously, the ferroelectric property of SrBi4Ti4O15 is greatly enhanced by Fe doping. The fatigue-endurance characteristic of the SBFT-0.05 is not improved. After 1.1×10^9 read/write cycles at a frequency of 50~kHz, the nonvolatile polarisations (Pnv= P*- PΛ) decreased about 48% of its initial value. 相关文章 | 计量指标

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Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy 施宇蕾, 周庆莉, 张存林 2009 (10):  4515-4520.  doi: 10.1088/1674-1056/18/10/069 摘要 ( 1718 )   PDF(259KB) ( 661 )   This paper investigates the ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs in detail by using a terahertz pump-emission technique. Based on theoretical modelling, it finds that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed after the excitation of pump pulse and we attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperature-dependent measurements are also performed to verify this trapping model. 相关文章 | 计量指标

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Ultraviolet laser-induced voltages in LaSrAlO4 single crystal 吕志清, 赵昆, 赵卉, 赵嵩卿, 周庆莉 2009 (10):  4521-4523.  doi: 10.1088/1674-1056/18/10/070 摘要 ( 1680 )   PDF(170KB) ( 634 )   Laser-induced ultrafast photovoltaic effect is observed in LaSrAlO4 single crystal at ambient temperature without any applied bias. An open-circuit photovoltage is obtained when the wafer is irradiated by a 248-nm-KrF laser pulse of 20~ns duration. The response time and full width at half maximum of the photovoltage pulse are 6~ns and 19~ns, respectively, indicating that LaSrAlO4 single crystal has potential application in ultraviolet detector. 相关文章 | 计量指标

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Synthesis and characterization of Sr3Al2O6:Eu2+, Dy3+ phosphors prepared by sol--gel--combustion processing 黄平, 崔彩娥, 王森 2009 (10):  4524-4531.  doi: 10.1088/1674-1056/18/10/071 摘要 ( 1675 )   PDF(1484KB) ( 2137 )   A type of red luminescent Sr3Al2O+:Eu2+, Dy3+ phosphor powder is synthesised by sol--gel--combustion processing, with metal nitrates used as the source of metal ions and citric acid as a chelating agent of metal ions. By tracing the formation process of the sol--gel, it is found that it is necessary to reduce the amount of NO3- by dropping ethanol into the solution for forming a stable and homogeneous sol--gel. Thermogravimetric and Differential Scanning Calorimeter Analysis, x-ray diffractionmeter, scanning electron microscopy and photoluminescence spectroscopy are used to investigate the luminescent properties of the as-synthesised Sr3Al2O6:Eu2+, Dy3+. The results reveal that the Sr3Al2O6 crystallises completely when the combustion ash is sintered at 1250~℃. The excitation and the emission spectra indicate that the excitation broadband lies mainly in a visible range and the phosphors emit a strong light at 618~nm under the excitation of 472~nm. The afterglow of (Sr0.097Eu0.03Dy0.03)3Al2O6 phosphors sintered at 1250~℃ lasts for over 1000 s when the excited source is cut off. 相关文章 | 计量指标

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A novel Dy3+-doped GdPO4 white-light phosphors under vacuum ultraviolet excitation for Hg-free lamps application 韩国才, 王育华, 吴春芳, 张加驰 2009 (10):  4532-4535.  doi: 10.1088/1674-1056/18/10/072 摘要 ( 1433 )   PDF(621KB) ( 1004 )   Novel Dy3+-doped GdPO4 white light phosphors with monoclinic system were successfully synthesised by hydrothermal method at 240~\du. This paper investigates the luminescence properties of white-light Gd1-xPO4,:xDy3+ under vacuum ultraviolet (VUV) excitation. The strong absorption at around 147~nm in excitation spectrum energy can be transferred to the energy levels of Dy3+ ion from the host absorption. Additionally, this white light phosphors are activated by a single Dy3+ion and with a lower preparation temperature, which tend to decrease the consumption of rare earth resource and energy. Therefore, the luminescence of Gd1-xPO4:xDy3+ under VUV excitation is effective, and proves to be promising in application to mercury-free lamp. 相关文章 | 计量指标

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Effects of doping concentration on properties of Mn-doped ZnO thin films 高立, 张建民 2009 (10):  4536-4540.  doi: 10.1088/1674-1056/18/10/073 摘要 ( 1907 )   PDF(406KB) ( 1228 )   This paper reports that the radio frequency magnetron sputtering is used to fabricate ZnO and Mn-doped ZnO thin films on glass substrates at 500~°C. The Mn-doped ZnO thin films present wurtzite structure of ZnO and have a smoother surface, better conductivity but no ferromagnetism. The x-ray photoelectron spectroscopy results show that the binding energy of Mn_2p3 / 2 increases with increasing Mn content slightly, and the state of Mn in the Mn-doped ZnO thin films is divalent. The chemisorbed oxygen in the Mn-doped ZnO thin films increases with increasing Mn doping concentration. The photoluminescence spectra of ZnO and Mn-doped ZnO thin films have a similar ultraviolet emission. The yellow green emissions of 4~wt.% and 10~wt.% Mn-doped thin films are quenched, whereas the yellow green emission occurs because of abundant oxygen vacancies in the Mn-doped ZnO thin films after 20~wt.% Mn doping. Compared with pure ZnO thin film, the bandgap of the Mn-doped ZnO thin films increases with increasing Mn content. 相关文章 | 计量指标

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Distribution of carriers in gradient-doping transmission-mode GaAs photocathodes grown by molecular beam epitaxy 张益军, 常本康, 杨智, 牛军, 邹继军 2009 (10):  4541-4546.  doi: 10.1088/1674-1056/18/10/074 摘要 ( 1782 )   PDF(193KB) ( 978 )   The gradient-doping structure is first applied to prepare the transmission-mode GaAs photocathode and the integral sensitivity of the sealed image tube achieves 1420~μ A/lm. This paper studies the inner carrier concentration distribution of the gradient-doping transmission-mode GaAs photocathode after molecular beam epitaxy (MBE) growth using the electrochemical capacitance-voltage profiling. The results show that an ideal gradient-doping structure can be obtained by using MBE growth. The total band-bending energy in the gradient-doping GaAs active-layer with doping concentration ranging from 1× 10^19~cm-3 to 1×10^18~cm-3 is calculated to be 46.3 meV, which helps to improve the photoexcited electrons movement toward surface for the thin epilayer. In addition, by analysis of the band offsets, it is found that the worse carrier concentration discrepancy between GaAs and GaAlAs causes a lower back interface electron potential barrier which decreases the amount of high-energy photoelectrons and affects the short-wave response. 相关文章 | 计量指标

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Enhanced field emission characteristics of thin-Au-coated nano-sheet carbon films 顾广瑞, 伊藤利道 2009 (10):  4547-4551.  doi: 10.1088/1674-1056/18/10/075 摘要 ( 1828 )   PDF(4366KB) ( 670 )   This paper reports that the nano-sheet carbon films (NSCFs) were fabricated on Si wafer chips with hydrogen--methane gas mixture by means of quartz-tube-type microwave plasma chemical vapour deposition (MWPCVD). In order to further improve the field emission (FE) characteristics, a 5-nm Au film was prepared on the samples by using electron beam evaporation. The FE properties were obviously improved due to depositing Au thin film on NSCFs. The FE current density at a macroscopic electric field, E, of 9~V/μ m was increased from 12.4~mA/cm2 to 27.2~mA/cm2 and the threshold field was decreased from 2.6~V/μ m to 2.0~V/μ m for Au-coated carbon films. A modified F-N model considering statistic effects of FE tip structures in the low E region and a space-charge-limited-current effect in the high E region were applied successfully to explain the FE data of the Au-coated NSCF. 相关文章 | 计量指标

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Effect of polyacrylamide on morphology and electromagnetic properties of chrysanthemum-like ZnO particles 闫军锋, 张志勇, 游天桂, 赵武, 贠江妮, 张富春, 张晓丹 2009 (10):  4552-4557.  doi: 10.1088/1674-1056/18/10/076 摘要 ( 1521 )   PDF(4443KB) ( 768 )   Through hydrothermal process, the chrysanthemum-like ZnO particles are prepared with zinc acetate dihydrate (Zn(CH3COO)2\cdot 2H2O) and sodium hydroxide (NaOH) used as main resources under the different concentrations of surfactant polyacrylamide (PAM). The microstructure, morphology and the electromagnetic properties of the as-prepared products are characterized by high-resolution transmission electron microscopy (HRTEM), field emission environment scanning electron microscope (FEESEM) and microwave vector network analyzer, respectively. The experimental results indicate that the as-prepared products are ZnO single crystalline with hexagona wurtzite structure, that the values of slenderness ratio L_d are different in different PAM concentrations, and that the good magnetic loss property is found in the ZnO products, and the average magnetic loss tangent tanδu increases with PAM concentration increasing, while the dielectric loss tangent tanδ e decreases. 相关文章 | 计量指标

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Research on the boron contamination at the p/i interface of microcrystalline silicon solar cells deposited in a single PECVD chamber 孙福和, 魏长春, 孙建, 张德坤, 耿新华, 熊绍珍, 赵颖 2009 (10):  4558-4563.  doi: 10.1088/1674-1056/18/10/077 摘要 ( 1353 )   PDF(200KB) ( 730 )   This paper studies boron contamination at the interface between the p and i layers of μ c-Si:H solar cells deposited in a single-chamber PECVD system. The boron depth profile in the i layer was measured by Secondary Ion Mass Spectroscopy. It is found that the mixed-phase μ c-Si:H materials with 40% crystalline volume fraction is easy to be affected by the residual boron in the reactor. The experimental results showed that a 500-nm thick μ c-Si:H covering layer or a 30-seconds of hydrogen plasma treatment can effectively reduce the boron contamination at the p/i interface. However, from viewpoint of cost reduction, the hydrogen plasma treatment is desirable for solar cell manufacture because the substrate is not moved during the hydrogen plasma treatment. 相关文章 | 计量指标

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Electrochemical properties of SnO2 nanorods as anode materials in lithium-ion battery 施松林, 刘永刚, 张敬源, 王太宏 2009 (10):  4564-4570.  doi: 10.1088/1674-1056/18/10/078 摘要 ( 1620 )   PDF(3866KB) ( 944 )   Well-dispersed SnO2 nanorods with diameter of 4--15~nm and length of 100--200~nm are synthesised through a hydrothermal route and their potential as anode materials in lithium-ion batteries is investigated. The observed initial discharge capacity is as high as 1778~mA\cdoth/g, much higher than the theoretical value of the bulk SnO2 (1494~mA.h/g). During the following 15 cycles, the reversible capacity decreases from 929 to 576~mA.h/g with a fading rate of 3.5% per cycle. The fading mechanism is discussed. Serious capacity fading can be avoided by reducing the cycling voltages from 0.05--3.0 to 0.4--1.2~V. At the end, SnO2 nanorods with much smaller size are synthesized and their performance as anode materials is studied. The size effect on the electrochemical properties is briefly discussed. 相关文章 | 计量指标

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Chaos game representation walk model for the protein sequences 高洁, 蒋丽丽, 徐振源 2009 (10):  4571-4579.  doi: 10.1088/1674-1056/18/10/079 摘要 ( 1804 )   PDF(230KB) ( 734 )   A new chaos game representation of protein sequences based on the detailed hydrophobic--hydrophilic (HP) model has been proposed by Yu et al (Physica A 337 (2004) 171). A CGR-walk model is proposed based on the new CGR coordinates for the protein sequences from complete genomes in the present paper. The new CGR coordinates based on the detailed HP model are converted into a time series, and a long-memory ARFIMA(p, d, q) model is introduced into the protein sequence analysis. This model is applied to simulating real CGR-walk sequence data of twelve protein sequences. Remarkably long-range correlations are uncovered in the data and the results obtained from these models are reasonably consistent with those available from the ARFIMA(p, d, q) model. 相关文章 | 计量指标

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Statistical interior properties of globular proteins 姜舟婷, 章林溪, 孙婷婷, 吴太权 2009 (10):  4580-4590.  doi: 10.1088/1674-1056/18/10/080 摘要 ( 1300 )   PDF(955KB) ( 676 )   The character of forming long-range contacts affects the three-dimensional structure of globular proteins deeply. As the different ability to form long-range contacts between 20 types of amino acids and 4 categories of globular proteins, the statistical properties are thoroughly discussed in this paper. Two parameters NC and ND are defined to confine the valid residues in detail. The relationship between hydrophobicity scales and valid residue percentage of each amino acid is given in the present work and the linear functions are shown in our statistical results. It is concluded that the hydrophobicity scale defined by chemical derivatives of the amino acids and nonpolar phase of large unilamellar vesicle membranes is the most effective technique to characterise the hydrophobic behavior of amino acid residues. Meanwhile, residue percentage Pi and sequential residue length Li of a certain protein i are calculated under different conditions. The statistical results show that the average value of Pi as well as Li of all-α proteins has a minimum among these 4 classes of globular proteins, indicating that all-α proteins are hardly capable of forming long-range contacts one by one along their linear amino acid sequences. All-β proteins have a higher tendency to construct long-range contacts along their primary sequences related to the secondary configurations, i.e. parallel and anti-parallel configurations of β sheets. The investigation of the interior properties of globular proteins give us the connection between the three-dimensional structure and its primary sequence data or secondary configurations, and help us to understand the structure of protein and its folding process well. 相关文章 | 计量指标

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Surface diffusion of Si, Ge and C adatoms on Si (001) substrate studied by the molecular dynamics simulation 陈智辉, 俞重远, 芦鹏飞, 刘玉敏 2009 (10):  4591-4597.  doi: 10.1088/1674-1056/18/10/081 摘要 ( 1466 )   PDF(1099KB) ( 701 )   Depositions of Si, Ge and C atoms onto a preliminary Si (001) substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900~K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases. 相关文章 | 计量指标

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Order parameters and synchronization of FitzHugh—Nagumo small-world networks 李延龙, 马军, 张巍, 刘延君 2009 (10):  4598-4602.  doi: 10.1088/1674-1056/18/10/082 摘要 ( 1561 )   PDF(227KB) ( 607 )   This paper numerically investigates the order parameter and synchronisation in the small world connected FitzHugh--Nagumo excitable systems. The simulations show that the order parameter continuously decreases with increasing d, the quality of the synchronisation worsens for large noise intensity. As the coupling intensity goes up, the quality of the synchronisation worsens, and it finds that the larger rewiring probability becomes the larger order parameter. It obtains the complete phase diagram for a wide range of values of noise intensity d and control parameter g. 相关文章 | 计量指标