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2008年, 第17卷, 第7期　刊出日期：2008-07-09 上一期    下一期

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An estimation formula for the average path length of scale-free networks 李旲, 曹宏铎, 山秀明, 任勇 2008 (7):  2327-2332.  doi: 10.1088/1674-1056/17/7/001 摘要 ( 1718 )   PDF(216KB) ( 920 )   A universal estimation formula for the average path length of scale free networks is given in this paper. Different from other estimation formulas, most of which use the size of network, $N$, as the only parameter, two parameters including $N$ and a second parameter $\alpha $ are included in our formula. The parameter $\alpha $ is the power-law exponent, which represents the local connectivity property of a network. Because of this, the formula captures an important property that the local connectivity property at a microscopic level can determine the global connectivity of the whole network. The use of this new parameter distinguishes this approach from the other estimation formulas, and makes it a universal estimation formula, which can be applied to all types of scale-free networks. The conclusion is made that the small world feature is a derivative feature of a scale free network. If a network follows the power-law degree distribution, it must be a small world network. The power-law degree distribution property, while making the network economical, preserves the efficiency through this small world property when the network is scaled up. In other words, a real scale-free network is scaled at a relatively small cost and a relatively high efficiency, and that is the desirable result of self-organization optimization. 相关文章 | 计量指标

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Periodic-soliton solutions of the (2+1)-dimensional Kadomtsev--Petviashvili equation 扎其劳, 李志斌 2008 (7):  2333-2338.  doi: 10.1088/1674-1056/17/7/002 摘要 ( 1697 )   PDF(2721KB) ( 1041 )   $2N$ line-soliton solutions of the (2+1)-dimensional Kadomtsev--Petviashvili equation can be presented by resorting to the Hirota bilinear method. By extending the real parameters into complex parameters, this paper obtains $N$ periodic-soliton solutions of the (2+1)-dimensional Kadomtsev--Petviashvili equation from the $2N$ line-soliton solutions. 相关文章 | 计量指标

GENERAL

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Thermal entanglement and teleportation of a thermally mixed entangled state of a Heisenberg chain through a Werner state 黄利元, 方卯发 2008 (7):  2339-2345.  doi: 10.1088/1674-1056/17/7/003 摘要 ( 1589 )   PDF(1722KB) ( 714 )   The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg $XXX$ chain under the Dzyaloshinski--Moriya (DM) anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of the noisy quantum channel are studied in detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol. 相关文章 | 计量指标

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Scheme for implementing perfect remote state preparation with W-class state in cavity QED 王学文, 彭朝晖 2008 (7):  2346-2351.  doi: 10.1088/1674-1056/17/7/004 摘要 ( 1611 )   PDF(165KB) ( 742 )   remote state preparation, $W$-class state, cavity QED 相关文章 | 计量指标

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Efficient quantum secure communication with a publicly known key 李春燕, 李熙涵, 邓富国, 周宏余 2008 (7):  2352-2355.  doi: 10.1088/1674-1056/17/7/005 摘要 ( 1591 )   PDF(154KB) ( 657 )   This paper presents a simple way for an eavesdropper to eavesdrop freely the secret message in the experimental realization of quantum communication protocol proposed by Beige et al (2002 Acta Phys. Pol. A 101 357). Moreover, it introduces an efficient quantum secure communication protocol based on a publicly known key with decoy photons and two biased bases by modifying the original protocol. The total efficiency of this new protocol is double that of the original one. With a low noise quantum channel, this protocol can be used for transmitting a secret message. At present, this protocol is good for generating a private key efficiently. 相关文章 | 计量指标

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Orbital effect in the stationary axisymmetric field 龚添喜, 王永久 2008 (7):  2356-2360.  doi: 10.1088/1674-1056/17/7/006 摘要 ( 1601 )   PDF(149KB) ( 536 )   This paper uses an elegant mathematical method to calculate the orbital effects in the axisymmetric field created by the spinning mass with electric charge and a large number of magnetic monopoles. In comparison with that in the Reissner--Nordstr\"om (R--N) field, the correction terms caused by the spinning mass decrease the advanced effect as the revolution direction of the test particle coincides with that of the Kerr field, however, the correction terms caused by the spinning charged mass increase the advance effect as the revolution direction of the test particle coincides with that of the Kerr--Newman--Kasnya (KNK) field. Generalizing the effect in the axisymmetric field, it obtains interesting results by discussing the parameters of the celestial body, these parameters provide a feasible experimental verification of the general relativity. 相关文章 | 计量指标

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Structure properties and Noether symmetries for super-long elastic slender rod 傅景礼, 赵维加, 翁玉权 2008 (7):  2361-2365.  doi: 10.1088/1674-1056/17/7/007 摘要 ( 1339 )   PDF(520KB) ( 539 )   DNA is a nucleic acid molecule with double-helical structures that are special symmetrical structures attracting great attention of numerous researchers. The super-long elastic slender rod, an important structural model of DNA and other long-train molecules, is a useful tool in analysing the symmetrical properties and the stabilities of DNA. This paper studies the structural properties of a super-long elastic slender rod as a structural model of DNA by using Kirchhoff's analogue technique and presents the Noether symmetries of the model by using the method of infinitesimal transformation. Based on Kirchhoff's analogue it analyses the generalized Hamilton canonical equations. The infinitesimal transformations with respect to the radial coordinate, the generalized coordinates, and the quasi-momenta of the model are introduced. The Noether symmetries and conserved quantities of the model are obtained. 相关文章 | 计量指标

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New insights into traffic dynamics: a weighted probabilistic cellular automaton model 李兴莉, 邝华, 宋涛, 戴世强, 李志鹏 2008 (7):  2366-2372.  doi: 10.1088/1674-1056/17/7/008 摘要 ( 1659 )   PDF(2173KB) ( 606 )   From the macroscopic viewpoint for describing the acceleration behaviour of drivers, a weighted probabilistic cellular automaton model (the WP model, for short) is proposed by introducing a kind of random acceleration probabilistic distribution function. The fundamental diagrams, the spatiotemporal patterns, are analysed in detail. It is shown that the presented model leads to the results consistent with the empirical data rather well, nonlinear flow--density relationship existing in lower density regions, and a new kind of traffic phenomenon called neo-synchronized flow. Furthermore, we give the criterion for distinguishing the high-speed and low-speed neo-synchronized flows and clarify the mechanism of this kind of traffic phenomenon. In addition, the result that the time evolution of distribution of headways is displayed as a normal distribution further validates the reasonability of the neo-synchronized flow. These findings suggest that the diversity and the randomicity of drivers and vehicles have indeed a remarkable effect on traffic dynamics. 相关文章 | 计量指标

GENERAL

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Extraction of periodic signals in chaotic secure communication using Duffing oscillators 王云才, 赵清春, 王安帮 2008 (7):  2373-2376.  doi: 10.1088/1674-1056/17/7/009 摘要 ( 1540 )   PDF(921KB) ( 630 )   This paper presents a novel approach to extract the periodic signals masked by a chaotic carrier. It verifies that the driven Duffing oscillator is immune to the chaotic carrier and sensitive to certain periodic signals. A preliminary detection scenario illustrates that the frequency and amplitude of the hidden sine wave signal can be extracted from the chaotic carrier by numerical simulation. The obtained results indicate that the hidden messages in chaotic secure communication can be eavesdropped utilizing Duffing oscillators. 相关文章 | 计量指标

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Impulsive control of nonlinear systems with time-varying delays 于永斌, 鲍景富, 张洪斌, 钟其水, 廖晓峰, 虞厥邦 2008 (7):  2377-2387.  doi: 10.1088/1674-1056/17/7/010 摘要 ( 1530 )   PDF(328KB) ( 716 )   A whole impulsive control scheme of nonlinear systems with time-varying delays, which is an extension for impulsive control of nonlinear systems without time delay, is presented in this paper. Utilizing the Lyapunov functions and the impulsive-type comparison principles, we establish a series of different conditions under which impulsively controlled nonlinear systems with time-varying delays are asymptotically stable. Then we estimate upper bounds of impulse interval and time-varying delays for asymptotically stable control. Finally a numerical example is given to illustrate the effectiveness of the method. 相关文章 | 计量指标

GENERAL

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One-way hash function based on hyper-chaotic cellular neural network 杨群亭, 高铁杠 2008 (7):  2388-2393.  doi: 10.1088/1674-1056/17/7/011 摘要 ( 1534 )   PDF(973KB) ( 769 )   The design of an efficient one-way hash function with good performance is a hot spot in modern cryptography researches. In this paper, a hash function construction method based on cell neural network with hyper-chaos characteristics is proposed. First, the chaos sequence is gotten by iterating cellular neural network with Runge--Kutta algorithm, and then the chaos sequence is iterated with the message. The hash code is obtained through the corresponding transform of the latter chaos sequence. Simulation and analysis demonstrate that the new method has the merit of convenience, high sensitivity to initial values, good hash performance, especially the strong stability. 相关文章 | 计量指标

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Fast-scale border collision bifurcation in SEPIC power factor pre-regulators 刘芳 2008 (7):  2394-2404.  doi: 10.1088/1674-1056/17/7/012 摘要 ( 1628 )   PDF(5785KB) ( 901 )   In this paper we report a kind of fast-scale instability occurring in the single-ended primary inductance converter (SEPIC) power factor pre-regulator, which is designed to operate in discontinuous conduction mode. Main results are given by exact cycle-by-cycle computer simulations as well as theoretical analysis. It is found that the instability phenomenon manifests itself as a fast-scale bifurcation at the switching period, which implies the occurrence of border collision bifurcation, or is related to the transition of the regular operating mode of the SEPIC. According to the theoretical analysis and simulation results, the effects of parameters on system stability, and the locations of the bifurcation points are confirmed. Moreover, the effects of such an instability on power factor and switching stress are also discussed. Finally, the occurrence of the asymmetric bifurcation locations is investigated. The results show that this work provides a convenient means of predicting stability boundaries which can facilitate the selection of the practical parameters. 相关文章 | 计量指标

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Controlling bifurcations and chaos in discrete small-world networks 刘峰, 关治洪, 王华 2008 (7):  2405-2411.  doi: 10.1088/1674-1056/17/7/013 摘要 ( 1645 )   PDF(261KB) ( 832 )   We propose an impulsive hybrid control method to control the period-doubling bifurcations and stabilize unstable periodic orbits embedded in a chaotic attractor of a small-world network. Simulation results show that the bifurcations can be delayed or completely eliminated. A periodic orbit of the system can be controlled to any desired periodic orbit by using this method. 相关文章 | 计量指标

GENERAL

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Adaptive control and synchronization of an uncertain new hyperchaotic Lorenz system 蔡国梁, 郑松, 田立新 2008 (7):  2412-2419.  doi: 10.1088/1674-1056/17/7/014 摘要 ( 1648 )   PDF(254KB) ( 783 )   This paper is involved with the adaptive control and synchronization problems for an uncertain new hyperchaotic Lorenz system. Based on the Lyapunov stability theory, the adaptive control law is derived such that the trajectory of hyperchaotic Lorenz system with unknown parameters can be globally stabilized to an unstable equilibrium point of the uncontrolled system. Furthermore, an adaptive control approach is presented to the synchronizations between two identical hyperchaotic systems, particularly between two different uncertain hyperchaotic systems. Numerical simulations show the effectiveness of the presented method. 相关文章 | 计量指标

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Local bifurcation analysis of a four-dimensional hyperchaotic system 吴文娟, 陈增强, 袁著祉 2008 (7):  2420-2432.  doi: 10.1088/1674-1056/17/7/015 摘要 ( 1726 )   PDF(754KB) ( 975 )   Local bifurcation phenomena in a four-dimensional continuous hyperchaotic system, which has rich and complex dynamical behaviours, are analysed. The local bifurcations of the system are investigated by utilizing the bifurcation theory and the centre manifold theorem, and thus the conditions of the existence of pitchfork bifurcation and Hopf bifurcation are derived in detail. Numerical simulations are presented to verify the theoretical analysis, and they show some interesting dynamics, including stable periodic orbits emerging from the new fixed points generated by pitchfork bifurcation, coexistence of a stable limit cycle and a chaotic attractor, as well as chaos within quite a wide parameter region. 相关文章 | 计量指标

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Control of beam halo-chaos by Gauss function in the triangle periodic-focusing channel 余海军, 白龙, 翁甲强, 罗晓曙, 方锦清 2008 (7):  2433-2437.  doi: 10.1088/1674-1056/17/7/016 摘要 ( 1519 )   PDF(1034KB) ( 525 )   This paper studies the Kapchinsky--Vladimirsky (K--V) beam through a triangle periodic-focusing magnetic field by using the particle-core model. The beam halo-chaos is found, and an idea of Gauss function controller is proposed based on the strategy of controlling the halo-chaos. It performs multiparticle simulation to control the halo by using the Gauss function control method. The numerical results show that the halo-chaos and its regeneration can be eliminated effectively, and that the radial particle density is uniform at the centre of the beam as long as the control method and appropriate parameter are chosen. 相关文章 | 计量指标

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Evolution of spiral wave and pattern formation in a vortical polarized electric field 马军, 易鸣, 李炳伟, 李延龙 2008 (7):  2438-2445.  doi: 10.1088/1674-1056/17/7/017 摘要 ( 1588 )   PDF(4835KB) ( 581 )   In this paper, the evolution of the pattern transition induced by the vortical electric field (VEF) is investigated. Firstly, a scheme is suggested to generate the VEF by changing the spatial magnetic field. Secondly, the VEF is imposed on the whole medium, and the evolutions of the spiral wave and the spatiotemporal chaos are investigated by using the numerical simulation. The result confirms that the drift and the breakup of the spiral wave and the new net-like pattern are observed when different polarized fields are imposed on the whole medium respectively. Finally, the pattern transition induced by the polarized field is discussed theoretically. 相关文章 | 计量指标

GENERAL

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Dynamical behaviour of a controlled vibro-impact system 王亮, 徐伟, 李颖 2008 (7):  2446-2450.  doi: 10.1088/1674-1056/17/7/018 摘要 ( 1739 )   PDF(254KB) ( 547 )   In this paper, we give a controlled two-degree-of-freedom (TDOF) vibro-impact system based on the damping control law, and then investigate the dynamical behaviour of this system. According to numerical simulation, we find that this control scheme can suppress chaos to periodic orbit successfully. Furthermore, the feasibility and the robustness of the controller are confirmed, separately. We also find that this scheme cannot only suppress chaos, but also generate chaos in this system. 相关文章 | 计量指标

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Spectral anomalies of diffracted pulsed Hermite--Gaussian beams in dispersive media 赵志国, 潘留占, 吕百达 2008 (7):  2451-2457.  doi: 10.1088/1674-1056/17/7/019 摘要 ( 1772 )   PDF(384KB) ( 449 )   This paper derives and uses the recurrence expressions for the power spectra of diffracted pulsed Hermite--Gaussian (HG) beams in dispersive media to study the spectral anomalies of pulsed HG beams in the far field. Numerical results are given to illustrate the dependence of spectral switches on the pulse parameters, truncation parameter and dispersive property of the medium. The potential application of spectral anomalies of ultrashort pulsed beams in information encoding and transmission is discussed. 相关文章 | 计量指标

NUCLEAR PHYSICS

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Transverse momentum and transverse mass distributions of charged hadrons produced in Au--Au collisions at high energies 刘福虎 2008 (7):  2458-2465.  doi: 10.1088/1674-1056/17/7/020 摘要 ( 1441 )   PDF(353KB) ( 494 )   The transverse momentum distribution and the transverse mass distribution of charged hadrons produced in nucleus--nucleus collisions at high energies are described by using a two-cylinder model. The results calculated by the model are compared and found to be in agreement with the experimental data of the STAR and E895 Collaborations, measured in Au--Au collisions at the relativistic heavy ion collider (RHIC) and alternating-gradient synchrotron (AGS) energies, respectively. In the energy range concerned, the excitation degree of emission source close to the central axis of cylinders increases obviously with the collision centrality and incident energy increasing, but it does not show any obvious change with the increase of the (pseudo)rapidity in central collisions. The excitation degree of emission source close to the side-surface of cylinders does not show any obvious change with the collision centrality, the (pseudo)rapidity, and the incident energy increasing. 相关文章 | 计量指标

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Radiation forces on a three-level atom in the high-order Bessel beams 王正岭, 印建平 2008 (7):  2466-2477.  doi: 10.1088/1674-1056/17/7/021 摘要 ( 1548 )   PDF(317KB) ( 690 )   The general expressions of the average dissipative and dipole forces acting on a $\Lambda $-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic density matrix elements, and the general properties of the average dissipative and dipole forces on a three-level atom in the linearly-polarized high-order Bessel beams (HBBs) are analysed. We find a resonant property (with two resonant peaks) of the dissipative force and a non-resonant property (with two pairs of non-resonant peaks) of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Meanwhile we find a saturation effect of the average dissipative force in the HBB, which comes from the saturation of the upper-level population. Our study shows that the general expressions of the average dissipative and dipole forces on the three-level atom will be simplified to those of the two-level atom under the approximation of large detuning. Finally, we study the axial and azimuthal Doppler cooling of atoms in 1D optical molasses composed of two counter-propagating HBBs and discuss the azimuthal influence of the HBB on the Doppler cooling limit. We also find that the Doppler limit of atoms in the molasses HBB is slightly below the conventional Doppler limit of ${\hbar \Ga} /({2k_{\rm B}})$ due to the orbital angular momentum $l\hbar $ of the HBB. 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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First-principles study of structures and electronic properties of cadmium sulfide clusters 楚合营, 刘朝霞, 邱国莉, 孔德国, 武四新, 李蕴才, 杜祖亮 2008 (7):  2478-2483.  doi: 10.1088/1674-1056/17/7/022 摘要 ( 1600 )   PDF(1286KB) ( 1286 )   The lowest-energy structures and the electronic properties of Cd$_{n}$S$_{n}$ ($n=1-8$) clusters have been studied by using density-functional theory simulating package DMol$^{3}$ in the generalized gradient approximation (GGA). The ring-like structures are the lowest-energy configurations for $n=2, 3$ and the three-dimensional spheroid configurations for $n=4-8$. The three-dimensional structures may be considered as being built from the Cd$_{2}$S$_{2}$ and Cd$_{3}$S$_{3}$ rings. Compared to the previous reports, we have found the more stable structures for Cd$_{n}$S$_{n}$($n=7,8$). Calculations show that the magic numbers of Cd$_{n}$S$_{n}$ ($n=1-8$) clusters are $n=3$ and 6. As cluster size increases, the properties of Cd$_{n}$S$_{n}$ clusters tend to bulk-like ones in binding energy per CdS unit and Mulliken atomic charge, obtained by comparing with the calculated results of the wurtzite and zinc blende CdS for the same simulating parameters. 相关文章 | 计量指标

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Theoretical research on the performance of a practical helix travelling wave tube 段兆云, 宫玉彬, 魏彦玉, 王文祥 2008 (7):  2484-2490.  doi: 10.1088/1674-1056/17/7/023 摘要 ( 1457 )   PDF(209KB) ( 575 )   On the basis of a rigorous field theory, two different physical models of attenuator and sever have been proposed. One is named High attenuation (HATT) model in which both attenuator and sever are considered as a unified attenuator, but the sever is regarded as an area of very high loss; the other is called Sever and attenuator (SATT) model in which the sever is modelled as a drift area in which the electric and magnetic fields both vanish. A complex function is derived and potential sinking effect is also considered. Thus, a set of more practical self-consistent equations of nonlinear beam--wave interaction is formulated. Simulations are carried out under the conditions of the two different physical models, and the simulation results are compared with the experimental data. The results show that in the case of single signal drive, the unknown second harmonic should be included for predicting the saturated output power. It is also evident that the SATT model and the HATT model predict the same physical nature, whereas the results predicted by the HATT model are much closer to the experimental data than those obtained from the SATT model. Therefore, these results provide a strong theoretical basis for designing broadband and high gain helix travelling wave tubes. 相关文章 | 计量指标

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Investigation on electromagnetic scattering from rough soil surface of layered medium using the small perturbation method 任新成, 郭立新 2008 (7):  2491-2498.  doi: 10.1088/1674-1056/17/7/024 摘要 ( 1568 )   PDF(629KB) ( 646 )   Electromagnetic scattering from a rough surface of layered medium is investigated, and the formulae of the scattering coefficients for different polarizations are derived using the small perturbation method. A rough surface with exponential correlation function is presented for describing a rough soil surface of layered medium, the formula of its scattering coefficient is derived by considering the spectrum of the rough surface with exponential correlation function; the curves of the bistatic scattering coefficient of HH polarization with variation of the scattering angle are obtained by numerical calculation. The influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the roughness surface parameters and the frequency of the incident wave on the bistatic scattering coefficient is discussed. Numerical results show that the influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the rms and the correlation length of the rough surface, and the frequency of the incident wave on the bistatic scattering coefficient is very complex. 相关文章 | 计量指标

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The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling 方亮, 杜惊雷, 郭小伟, 王景全, 张志友, 罗先刚, 杜春雷 2008 (7):  2499-2503.  doi: 10.1088/1674-1056/17/7/025 摘要 ( 1726 )   PDF(1184KB) ( 679 )   The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons (SPPs) was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference time-domain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments. 相关文章 | 计量指标

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Refraction of extraordinary rays and ordinary rays in the Savart polariscope 吴俊芳, 张淳民, 张英堂, 刘汉臣, 翟学军 2008 (7):  2504-2508.  doi: 10.1088/1674-1056/17/7/026 摘要 ( 1678 )   PDF(144KB) ( 660 )   The refraction of rays in the Savart polariscope is different from the isotropic medium. We have analysed and discussed the refraction of rays in the Savart polariscope on the basis of the Snell law. The refraction formulae of the extraordinary rays and ordinary rays were derived. Results obtained may provide theoretical and practical guide lines for studying, developing and engineering of polarization interference imaging spectrometer. 相关文章 | 计量指标

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The number of least degrees of freedom required for a polarization controller to transform any state of polarization to any other output covering the entire Poincaré sphere 张晓光, 郑远 2008 (7):  2509-2513.  doi: 10.1088/1674-1056/17/7/027 摘要 ( 1423 )   PDF(463KB) ( 641 )   Using two typical types of polarization controller, this paper analyses theoretically and experimentally the fact that it is necessary to adjust at least three instead of two waveplates in order to transform any state of polarization to any other output covering the entire Poincar\'{e} sphere. The experimental results are exactly in accordance with the theory discussed in this paper. It has corrected the conventional and inaccurate point of view that two waveplates of a polarization controller are adequate to complete the transformation of state of polarization. 相关文章 | 计量指标

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Distillation of bi-partite entanglement from W state with cavity QED 邓黎, 陈爱喜, 陈德海, 黄克林 2008 (7):  2514-2516.  doi: 10.1088/1674-1056/17/7/028 摘要 ( 1513 )   PDF(135KB) ( 650 )   Following the theoretical protocol described by Fortescue and Lo [Fortescue B and Lo H K 2007 {\it Phys. Rev. Lett.} {\bf 98} 260501], we present a scheme in which one can distill maximally entangled bi-partite states from a tri-partite $W$ state with cavity QED. Our scheme enables the concrete physical system to realize its protocol. In our scheme, the rate distillation also asymptotically approaches one. Based on the present cavity QED techniques, we discuss the experimental feasibility. 相关文章 | 计量指标

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Numerical study of the Ne-like Cr x-ray laser at 28.6nm 赵静, 董全力, 王首钧, 张蕾, 张杰 2008 (7):  2517-2521.  doi: 10.1088/1674-1056/17/7/029 摘要 ( 1555 )   PDF(173KB) ( 601 )   We investigate the Ne-like Cr x-ray laser at $28.6\,\mathrm{nm}$ by using a modified 1D lagrangian hydrodynamic code MED103 coupled with an atomic physics data package and a 2D ray tracing code as a post-processor. The laser pumping configuration includes two prepulses and one main pulse. The first prepulse normally irradiates the target, while the second prepulse and the main pulse irradiate the target at grazing-incident angles. We predict that saturation can be achieved for the Ne-like Cr x-ray lasers with a total pumping energy of $125\,\mathrm{mJ}$. Good beam qualities with no deflecting angle and a small divergence angle of $5\,\mathrm{mrad}$ are observed. 相关文章 | 计量指标

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Population transfer by femtosecond laser pulses in a ladder-type atomic system 樊锡君, 李爱云, 仝殿民, 刘呈普 2008 (7):  2522-2526.  doi: 10.1088/1674-1056/17/7/030 摘要 ( 1461 )   PDF(1356KB) ( 638 )   The population transfer in a ladder-type atomic system driven by linearly polarized sech-shape femtosecond laser pulses is investigated by numerically solving Schr\"{o}dinger equation without including the rotating wave approximation (RWA). It is shown that population transfer is mainly determined by the Rabi frequency (strength) of the driving laser field and the chirp rate, and that the ratio of the dipole moments and the pulse width also have a prominent effect on the population transfer. By choosing appropriate values of the above parameters, complete population transfer can be realized. 相关文章 | 计量指标

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Rotating soliton clusters in nonlocal nonlinear media 王玉青, 郭旗 2008 (7):  2527-2534.  doi: 10.1088/1674-1056/17/7/031 摘要 ( 1526 )   PDF(1107KB) ( 681 )   From the study of the dynamics for the ring-like soliton clusters, we find that there exists a critical value of the ring radius, $d_{\rm cr}$, for the stationary rotation of the clusters with respect to the beam centre even in the presence of the relatively strong noise, and that the soliton clusters will not rotate but only undergo periodic collisions in the form of simple harmonic oscillator if the ring radius is large enough. We also show that the direction of the rotation can be opposite to the direction of phase gradient when the relative phase difference is within the domain $0<|\theta|<\pi$, while along the direction of phase gradient when the relative phase difference is within the domain $\pi<|\theta|<2\pi$. 相关文章 | 计量指标

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Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds 向红, 田志远, 王树峰, 王振伟, 李智, 杨宏, 姚建年, 龚旗煌 2008 (7):  2535-2538.  doi: 10.1088/1674-1056/17/7/032 摘要 ( 1545 )   PDF(317KB) ( 719 )   This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830\,nm wavelength with pulse duration of 120\,fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability, $\gamma$, of Compound 1 is of $1.0\times 10^{ - 31}$\,esu. Due to the charge transfer, the $\gamma$ of Compound 2 with electron donor and acceptor group is $4.9\times10^{ - 31}$\,esu, which is a four-time enhancement in comparison with Compound 1. The absorption spectra show that the electron push--pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity. 相关文章 | 计量指标

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Temporal development of open-circuit bright photovoltaic solitons 张磊, 卢克清, 张美志, 刘雪明, 张彦鹏 2008 (7):  2539-2543.  doi: 10.1088/1674-1056/17/7/033 摘要 ( 1563 )   PDF(1164KB) ( 665 )   This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton peak intensity and the dark irradiance, is small, the quasi-steady-state soliton width decreases monotonically with the increase of $\tau $, where $\tau $ is the parameter correlated with the time, that when the intensity ratio of the soliton is big, the quasi-steady-state soliton width decreases with the increase of $\tau $ and then increases with $\tau $, and that the formation time of the steady-state solitons is not correlated with the intensity ratio of the soliton. It finds that the local nonlinear effect increases with the photovoltaic field, which behaves as that the width of soliton beams is small and the self-focusing quasi-period is short. On the other hand, we also discuss that both the time and the temperature have an effect on the beam bending. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Effective permittivity and permeability of one-dimensional dielectric photonic crystal within a band gap 郭继勇, 陈鸿, 李宏强, 张冶文 2008 (7):  2544-2552.  doi: 10.1088/1674-1056/17/7/034 摘要 ( 1667 )   PDF(1697KB) ( 864 )   We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as $\varepsilon$-negative materials (ENMs) with $\varepsilon <0$ and $\mu >0$, or $\mu$-negative materials (MNMs) with $\varepsilon >0$ and $\mu <0$. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material (ENM or MNM) under some restrictions. 相关文章 | 计量指标

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Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler 任刚, 郑婉华, 王科, 杜晓宇, 邢名欣, 陈良惠 2008 (7):  2553-2556.  doi: 10.1088/1674-1056/17/7/035 摘要 ( 1628 )   PDF(317KB) ( 530 )   In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric (TE) guided mode and transverse-magnetic (TM) guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguides is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.5$\mu$m. A finite-difference time-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20\,dB. 相关文章 | 计量指标

CLASSICAL AREAS OF PHENOMENOLOGY

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Design of novel three port optical gates scheme for the integration of large optical cavity electroabsorption modulators and evanescently-coupled photodiodes 廖栽宜, 杨华, 王圩 2008 (7):  2557-2561.  doi: 10.1088/1674-1056/17/7/036 摘要 ( 1523 )   PDF(760KB) ( 534 )   This paper presents a novel scheme to monolithically integrate an evanescently-coupled uni-travelling carrier photodiode with a planar short multimode waveguide structure and a large optical cavity electroabsorption modulator based on a multimode waveguide structure. By simulation, both electroabsorption modulator and photodiode show excellent optical performances. The device can be fabricated with conventional photolithography, reactive ion etching, and chemical wet etching. 相关文章 | 计量指标

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Design, fabrication and characterization of a high-performance microring resonator in silicon-on-insulator 黄庆忠, 余金中, 陈少武, 徐学俊, 韩伟华, 樊中朝 2008 (7):  2562-2566.  doi: 10.1088/1674-1056/17/7/037 摘要 ( 1653 )   PDF(2514KB) ( 750 )   A high-performance microring resonator in a silicon-on-insulator rib waveguide is realized by using the electron beam lithography followed by inductively coupled plasma etching. The design and the experimental realization of this device are presented in detail. In addition to improving relevant processes to minimize propagation loss, the coupling efficiency between the ring and the bus is carefully chosen to approach a critical coupling for high performance operating. We have measured a quality factor of 21,200 and an extinction ratio of 12.5dB at a resonant wavelength of 1549.32nm. Meanwhile, a low propagation loss of 0.89dB/mm in a curved waveguide with a bending radius of 40$\mu $m is demonstrated as well. 相关文章 | 计量指标

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A visible-near infrared tunable waveguide based on plasmonic gold nanoshell 张海汐, 古英, 龚旗煌 2008 (7):  2567-2573.  doi: 10.1088/1674-1056/17/7/038 摘要 ( 1725 )   PDF(1407KB) ( 893 )   A tunable plasmonic waveguide via gold nanoshells immerged in a silica base is proposed and simulated by using the finite difference time-domain (FDTD) method. For waveguides based on near-field coupling, transmission frequencies can be tuned in a wide region from 660 to 900\,nm in wavelength by varying shell thicknesses. After exploring the steady distributions of electric fields in these waveguides, we find that their decay lengths are about 5.948--12.83\,dB/1000\,nm, which is superior to the decay length (8.947\,dB/1000\,nm) of a gold nanosphere plasmonic waveguide. These excellent tunability and transmittability are mainly due to the unique hollow structure. These gold nanoshell waveguides should be fabricated in laboratory. 相关文章 | 计量指标

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Growth and collapse of laser-induced bubbles in glycerol--water mixtures 刘秀梅, 贺杰, 陆建, 倪晓武 2008 (7):  2574-2579.  doi: 10.1088/1674-1056/17/7/039 摘要 ( 1777 )   PDF(608KB) ( 852 )   Comprehensive numerical and experimental analyses of the effect of viscosity on cavitation oscillations are performed. This numerical approach is based on the Rayleigh--Plesset equation. The model predictions are compared with experimental results obtained by using a fibre-optic diagnostic technique based on optical beam deflection (OBD). The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. It is observed that the increasing of viscosity decreases the maximum bubble radii but increases the minimum bubble radii and the oscillation time. These experimental results are consistent with numerical results. 相关文章 | 计量指标

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The pressure field in the liquid column in the tube-arrest method 应崇福, 李超, 徐德龙, 邓京军 2008 (7):  2580-2593.  doi: 10.1088/1674-1056/17/7/040 摘要 ( 1445 )   PDF(1830KB) ( 677 )   We have been using the method of tube-arrest as a means of producing transient single cavitation bubble. In the present paper we seek to comprehend the mechanism of production and inquire into the structure of the {\em ab initio} pressure field in the arrested liquid column. The generated pressure wave is shown by combining the theoretical analysis with the experimental observation to be a slightly varied version of water hammer. With relatively clean liquid, the magnitude of the tension peak generating the TSB is likely to reach of several millions Pa. It is also shown that the so generated cavitation bubble originating from the gas-containing bulk liquid is in `violent' motion. 相关文章 | 计量指标

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Single-and-double electron loss of O2+ in collisions with argon and helium 刘玉文, 陈熙萌, 鲁彦霞, 丁宝卫, 付宏斌, 高志民, 崔莹, 邵剑雄, 孙光智, 陈林, 尹永智 2008 (7):  2590-2593.  doi: 10.1088/1674-1056/17/7/041 摘要 ( 1543 )   PDF(311KB) ( 493 )   This paper reports that the ratios of double to single electron loss cross-section (R) of O2+ in collision with Ar and He at the velocity of 1--4\nu0 (\nu0 is the Bohr velocity) have been obtained by the coincidence technique. The trend of R-V in the experiment indicates that the effective charge varies with injected velocity. The effective charge can be obtained by the n-body classical trajectory Monte Carlo method, which is interpreted by the molecular Coulomb over barrier model. 相关文章 | 计量指标

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The instability of dust acoustic waves in inhomogeneous dusty plasmas with non-adiabatic dust charge fluctuation 张丽萍, 薛具奎 2008 (7):  2594-2599.  doi: 10.1088/1674-1056/17/7/042 摘要 ( 1634 )   PDF(564KB) ( 648 )   This paper investigates the propagation of linear dust acoustic waves in inhomogeneous dusty plasmas due to spatial gradients of dust charge, plasma densities. A linear dispersion relation is obtained with the non-adiabatic dust charge fluctuation and the non-thermally distributed ions. The numerical results show that the inhomogeneity, non-thermal ions and non-adiabatic dust charge fluctuation have strong influence on the frequency and the damping rate of waves. 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Solitons and defects in nematic liquid crystals under a simple shear flow and in a static external magnetic field 罗开富, 蒋秀丽, 杨玉良 2008 (7):  2600-2609.  doi: 10.1088/1674-1056/17/7/043 摘要 ( 1369 )   PDF(505KB) ( 716 )   Under a simple shear flow and in a static external magnetic field, the production of defects in the director-aligning regime of nematic liquid crystals has been investigated in terms of the Leslie--Ericksen theory. The equation of motion of the nematic director, which conforms to the driven over-damped sine-Gordon equation, has a soliton solution of the amplitude $\pi$. We show that the stationary state with the director uniformly oriented at a Leslie angle is only a metastable state and the potential, which governs the motion of the director, has a number of stable stationary states. For a strong magnetic field, the higher energy barrier between the stable and unstable states leads the director to be locked along the magnetic field direction. However, at the appropriate shear rate and magnetic field the defects, which appear as a stable solitary solution, can be nucleated from a uniformly aligned nematic liquid crystal. We have calculated the stationary travelling velocity of the solitary waves and the distance between a pair of defects. 相关文章 | 计量指标

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Exact analytic solutions for an elliptic hole with asymmetric collinear cracks in a one-dimensional hexagonal quasi-crystal 郭俊宏, 刘官厅 2008 (7):  2610-2620.  doi: 10.1088/1674-1056/17/7/044 摘要 ( 1399 )   PDF(371KB) ( 722 )   Using the complex variable function method and the technique of conformal mapping, the anti-plane shear problem of an elliptic hole with asymmetric collinear cracks in a one-dimensional hexagonal quasi-crystal is solved, and the exact analytic solutions of the stress intensity factors (SIFs) for mode III problem are obtained. Under the limiting conditions, the present results reduce to the Griffith crack and many new results obtained as well, such as the circular hole with asymmetric collinear cracks, the elliptic hole with a straight crack, the mode T crack, the cross crack and so on. As far as the phonon field is concerned, these results, which play an important role in many practical and theoretical applications, are shown to be in good agreement with the classical results. 相关文章 | 计量指标

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The elastic properties and energy characteristics of Au nanowires: an atomistic simulation study 刘珊珊, 文玉华, 朱梓忠 2008 (7):  2621-2626.  doi: 10.1088/1674-1056/17/7/045 摘要 ( 1584 )   PDF(689KB) ( 704 )   This paper have performed molecular static calculations with the quantum corrected Sutten--Chen type many body potential to study size effects on the elastic modulus of Au nanowires with [100], [110] and [111] crystallographic directions, and to explore the preferential growth orientation of Au nanowires. The main focus of this work is the size effects on their surface characteristics. Using the common neighbour analysis, this paper deduces that surface region approximately consists of two layer atoms. Further, it extracts the elastic modulus of surface, and calculate surface energy of nanowire. The results show that for all three directions the Young's modulus of nanowire increases as the diameter increases. Similar trend has been observed for the Young's modulus of surface. However, the atomic average potential energy of nanowire shows an opposite change. Both the potential and surface energy of [110] nanowire are the lowest among all three orientational nanowires, which helps to explain why Au nanowires possess a [110] preferred orientation during the experimental growth proceeds. 相关文章 | 计量指标

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Power dissipation characteristics of great power and super high speed semiconductor switch 梁琳, 余岳辉, 彭亚斌 2008 (7):  2627-2632.  doi: 10.1088/1674-1056/17/7/046 摘要 ( 1445 )   PDF(223KB) ( 542 )   The power dissipation characteristics of pulsed power switch reversely switched dynistors (RSDs) are investigated in this paper. According to the expressions of voltage on RSD, derived from the plasma bipolar drift model and the RLC circuit equations of RSD main loop, the simulation waveforms of current and voltage on RSD are acquired through iterative calculation by using the fourth order Runge--Kutta method, then the curve of transient power on RSD versus time is obtained. The result shows that the total dissipation on RSD is trivial compared with the pulse discharge energy and the commutation dissipation can be nearly ignored compared with the quasi-static dissipation. These characteristics can make the repetitive frequency of RSD increase largely. The experimental results prove the validity of simulation calculations. The influence factors on power dissipation are discussed. The power dissipation increases with the increase of the peak current and the n-base width and with the decrease of n-base doping concentration. In order to keep a low power dissipation, it is suggested that the n-base width should be smaller than 320$\mu $m when doping concentration is 1.0$\times $10$^{14}$cm$^{ - 3}$ while the doping concentration should be higher than 5.8$\times $10$^{13}$cm$^{ - 3}$ when n-base width is 270$\mu $m. 相关文章 | 计量指标

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Molecular dynamics simulation of surface melting behaviours of the V(110) plane 阳喜元, 胡望宇, 袁晓俭, 蔡新华 2008 (7):  2633-2638.  doi: 10.1088/1674-1056/17/7/047 摘要 ( 1537 )   PDF(288KB) ( 693 )   The modified analytic embedded-atom method and molecular dynamics simulations are applied to the investigation of the surface premelting and melting behaviours of the V(110) plane by calculating the interlayer relaxation, the layer structure factor and atomic snapshots in this paper. The results obtained indicate that the premelting phenomenon occurs on the V(110) surface at about 1800K and then a liquid-like layer, which approximately keeps the same thickness up to 2020K, emerges on it. We discover that the temperature 2020K the V(110) surface starts to melt and is in a completely disordered state at the temperature of 2140K under the melting point for the bulk vanadium. 相关文章 | 计量指标

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Electronic structure and thermodynamic properties of LiBC under high pressure 艾琼, 付志坚, 程艳, 陈向荣 2008 (7):  2639-2645.  doi: 10.1088/1674-1056/17/7/048 摘要 ( 1439 )   PDF(258KB) ( 874 )   This paper investigates the electronic structure and thermodynamic properties of LiBC in the hexagonal structure by using the generalized gradient approximation (GGA) and local density approximation correction scheme in the frame of density functional theory. The geometric structure of LiBC under zero pressure, and the dependences of the normalized lattice parameters $a/a_{0}$ and $c/c_{0}$, the ratio $c/a$, the normalized primitive volume $V/V_{0}$ on pressure are given. The thermodynamic quantity (including the heat capacity $C_{V}$, Debye temperature $\Th _{\rm D}$, thermal expansion $\alpha $ and Gr\"{u}neisen parameter \textit{$\gamma $}) dependences on temperature and pressure are obtained through the GGA method and the quasi-harmonic Debye model. The band structures and density of state of LiBC under different pressures have also been analysed. 相关文章 | 计量指标

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High density gas state at water/graphite interface studied by molecular dynamics simulation 王春雷, 李朝霞, 李敬源, 修鹏, 胡钧, 方海平 2008 (7):  2646-2654.  doi: 10.1088/1674-1056/17/7/049 摘要 ( 1852 )   PDF(3706KB) ( 1430 )   In this paper molecular dynamics simulations are performed to study the accumulation behaviour of N$_{2}$ and H$_{2}$ at water/graphite interface under ambient temperature and pressure. It finds that both N$_{2}$ and H$_{2}$ molecules can accumulate at the interface and form one of two states according to the ratio of gas molecules number to square of graphite surface from our simulation results: gas films (pancake-like) for a larger ratio and nanobubbles for a smaller ratio. In addition, we discuss the stabilities of nanobubbles at different environment temperatures. Surprisingly, it is found that the density of both kinds of gas states can be greatly increased, even comparable with that of the liquid N$_{2}$ and liquid H$_{2}$. The present results are expected to be helpful for the understanding of the stable existence of gas film (pancake-like) and nanobubbles. 相关文章 | 计量指标

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Effect of the stoichiometry on the electronic structure of the Ni(111)/ɑ-Al2O3(0001) interface: a first-principles investigation 施思齐, 田中真悟, 香山正憲 2008 (7):  2655-2661.  doi: 10.1088/1674-1056/17/7/050 摘要 ( 1327 )   PDF(265KB) ( 733 )   In this paper first-principles calculations of Ni(111)/$\alpha $-Al$_{2}$O$_{3}$(0001) interfaces have been performed, and are compared with the preceding results of the Cu (111)/$\alpha $-Al$_{2}$O$_{3}$(0001) interface [2004 {\em Phil. Mag. Lett.} \textbf{84} 425]. The Al-terminated and O-terminated interfaces have quite different adhesion mechanisms, which are similar to the Cu(111)/$\alpha $-Al$_{2}$O$_{3}$(0001) interface. For the O-terminated interface, the adhesion is caused by the strong O-2p/Ni-3d orbital hybridization and ionic interactions. On the other hand, the adhesion nature of the Al-terminated interface is the image-like electrostatic and Ni--Al hybridization interactions, the latter is substantial and cannot be neglected. Charge transfer occurs from Al$_{2}$O$_{3}$ to Ni, which is opposite to that in the O-terminated interface. The charge transfer direction for the Al-terminated and O-terminated Ni(111)/$\alpha$-Al$_{2}$O$_{3}$(0001) interfaces is similar to that in the corresponding Cu(111)/$\alpha$-Al$_{2}$O$_{3}$(0001) interface, but there exist the larger charge transfer quantity and consequent stronger adhesion nature, respectively. 相关文章 | 计量指标

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Electron resonance-transmission through a driven quantum well with spin--orbit coupling 张存喜, 王瑞, 聂一行, 梁九卿 2008 (7):  2662-2669.  doi: 10.1088/1674-1056/17/7/051 摘要 ( 1820 )   PDF(265KB) ( 655 )   We have studied the spin-dependent electron transmission through a quantum well driven by both dipole-type and homogeneous oscillating fields. The numerical evaluations show that Dresselhaus spin--orbit coupling induces the splitting of asymmetric Fano-type resonance peaks in the conductivity, in which the dipole modulation and the homogeneous modulation are\ equivalent. Therefore, we predict that the dipole-type oscillation, which is more practical in the experimental setup, can be used to realize the tunable spin filters by adjusting the field oscillation-frequency and the amplitude as well. 相关文章 | 计量指标

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Field-assisted electron transport through a symmetric double-well structure with spin--orbit coupling and the Fano-resonance induced spin filtering 张存喜, 聂一行, 梁九卿 2008 (7):  2670-2677.  doi: 10.1088/1674-1056/17/7/052 摘要 ( 1484 )   PDF(269KB) ( 664 )   We have investigated theoretically the field-driven electron-transport through a double-quantum-well semiconductor-heterostructure with spin--orbit coupling. The numerical results demonstrate that the transmission spectra are divided into two sets due to the bound-state level-splitting and each set contains two asymmetric resonance peaks which may be selectively suppressed by changing the difference in phase between two driving fields. When the phase difference changes from $0$ to $\pi$, the dip of asymmetric resonance shifts from one side of resonance peak to the other side and the asymmetric Fano resonance degenerates into the symmetric Breit--Wigner resonance at a critical value of phase difference. Within a given range of incident electron energy, the spin polarization of transmission current is completely governed by the phase difference which may be used to realize the tunable spin filtering. 相关文章 | 计量指标

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Carriers recombination processes in charge trapping memory cell by simulation 宋云成, 刘晓彦, 杜刚, 康晋锋, 韩汝琦 2008 (7):  2678-2682.  doi: 10.1088/1674-1056/17/7/053 摘要 ( 1845 )   PDF(463KB) ( 504 )   We have evaluated the effects of recombination processes in a charge storage layer, either between trapped electrons and trapped holes or between trapped carriers and free carriers, on charge trapping memory cell's performances by numerical simulation. Recombination is an indispensable mechanism in charge trapping memory. It helps charge convert process between negative and positive charges in the charge storage layer during charge trapping memory programming/erasing operation. It can affect the speed of programming and erasing operations. 相关文章 | 计量指标

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Effect of fabrication conditions on the properties of indium tin oxide powders 谢卫 2008 (7):  2683-2688.  doi: 10.1088/1674-1056/17/7/054 摘要 ( 1564 )   PDF(197KB) ( 765 )   This paper reports that indium tin oxide (ITO) crystalline powders are prepared by coprecipitation method. Fabrication conditions mainly as sintering temperature and Sn doping content are correlated with the phase, microstructure, infrared emissivity $\varepsilon $ and powder resistivity of indium tin oxides by means of x-ray diffraction, Fourier transform infrared, and transmission electron microscope. The optimum sintering temperature of 1350${^\circ}$C and Sn doping content 6$\sim $8wt{\%} are determined. The application of ITO in the military camouflage field is proposed. 相关文章 | 计量指标

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

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The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures 张金风, 毛维, 张进城, 郝跃 2008 (7):  2689-2695.  doi: 10.1088/1674-1056/17/7/055 摘要 ( 1759 )   PDF(743KB) ( 1295 )   To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scattering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer. 相关文章 | 计量指标

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Reliability analysis of GaN-based light emitting diodes for solid state illumination 杨凌, 马晓华, 冯倩, 郝跃 2008 (7):  2696-2700.  doi: 10.1088/1674-1056/17/7/056 摘要 ( 1549 )   PDF(3423KB) ( 912 )   In this paper, we have discussed the effect of electrical stress on GaN light emitting diode (LED). With the lapse of time, the LED with an applied large current stress can reduce its current more than without such a stress under a large forward-voltage drop. Its scanning electron microscopy (SEM) image shows that there exist several pits on the surface of the p-metal. With an electrical stress applied, the number of pits greatly increases. We also find that the degradation of GaN LED is related to the oxidized Ni/Au ohmic contact to p-GaN. The electrical activation of H-passivated Mg acceptors is described in detail. Annealing is performed in ambient air for 10 min and the differential resistances at a forward-voltage drop of 5\,V are taken to evaluate the activation of the Mg acceptors. These results suggest some mechanisms of degradation responsible for these phenomena, which are described in the paper. 相关文章 | 计量指标

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A note on localized transition in the spin-boson model by variational calculation 陈芝得, 侯志兰 2008 (7):  2701-2706.  doi: 10.1088/1674-1056/17/7/057 摘要 ( 1409 )   PDF(190KB) ( 528 )   We present mathematical analyses of the evolution of solutions of the self-consistent equation derived from variational calculations based on the displaced-oscillator-state and the displaced-squeezed-state in spin-boson model at a zero temperature and a finite temperature. It is shown that, for a given spectral function defined as $J(\omega)=\pi\sum_k c_k^2=\ddfrac{\pi}{2}\alpha \omega^{ s}\omega_{\rm c}^{ 1-s}$, there exists a universal $s_{\rm c}$ for both kinds of variational schemes, the localized transition happens only for $s\le s_{\rm c}$, moreover, the localized transition is discontinuous for $s 相关文章 | 计量指标

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Rectifying effect of heterojunctions between metals and doped conducting polymer nanostructure pellets 龙云泽, 尹志华, 惠雯, 陈兆甲, 万梅香 2008 (7):  2707-2711.  doi: 10.1088/1674-1056/17/7/058 摘要 ( 1484 )   PDF(1696KB) ( 927 )   This paper reports that the Schottky junctions between low work function metals (e.g. Al and In) and doped semiconducting polymer pellets (e.g. polyaniline (PANI) microsphere pellet and polypyrrole (PPy) nanotube pellet) have been prepared and studied. Since Ag is a high work function metal which can make an ohmic contact with polymer, silver paste was used to fabricate the electrodes. The Al/PANI/Ag heterojunction shows an obvious rectifying effect as shown in $I-V$ characteristic curves (rectifying ratio $\gamma = 5$ at $\pm $6\,V bias at room temperature). As compared to the Al/PANI/Ag, the heterojunction between In and PANI (In/PANI/Ag) exhibits a lower rectifying ratio $\gamma = 1.6$ at $\pm $2\,V bias at room temperature. In addition, rectifying effect was also observed in the heterojunctions Al/PPy/Ag ($\gamma = 3.2$ at $\pm $1.6\,V bias) and In/PPy/Ag ($\gamma = 1.2$ at $\pm $3.0\,V bias). The results were discussed in terms of thermoionic emission theory. 相关文章 | 计量指标

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The effects of interstitial oxygen on superconducting electronic phases in strontium and oxygen co-doped La1.937Sr0.063CuO4+δ 申彩霞, 慎晓丽, 陆伟, 董晓莉, 李正才, 熊季午, 周放 2008 (7):  2712-2716.  doi: 10.1088/1674-1056/17/7/059 摘要 ( 1326 )   PDF(726KB) ( 493 )   Strontium and oxygen co-doped La$_{1.937}$Sr$_{0.063}$CuO$_{4 + \delta }$ superconductor with $T_{\rm c}\approx 40$\,K, which is obtained by oxidizing strontium-doped starting ceramic sample La$_{1.937}$Sr$_{0.063}$CuO$_{4}$ in NaClO solution, is annealed under different conditions to allow interstitial oxygen to redistribute. The evolution of the intrinsic superconducting property with the oxygen redistribution is studied in detail by magnetic measurements in various fields. It is found that there occurs the electronic phase separation from the single superconducting phase with $T_{\rm c} \approx40$\,K into two coexisting superconducting states with values of $T_{\rm c}$: 15 and 40\,K or of 15 and 35\,K in this system, depending on annealing condition. Our results indicate that the 15, 35 and 40\,K superconducting phases associated with the excess oxygen redistribution are all thermodynamically meta-stable intrinsic states in this Sr/O co-doped cuprate. 相关文章 | 计量指标

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Spontaneous magnetization and resistivity jumps in bilayered manganite (La0.8Eu0.2)4/3Sr5/3Mn2O7 single crystals 赵建军, 鲁毅, 浩斯巴雅尔, 邢茹, 杨仁福, 李庆安, 孙阳, 成昭华 2008 (7):  2717-2720.  doi: 10.1088/1674-1056/17/7/060 摘要 ( 1486 )   PDF(181KB) ( 502 )   Owing to the inhomogeneous state resulting from the doping of a small number of Eu ions into La$_{4 / 3}$Sr$_{5 / 3}$Mn$_{2}$O$_{7}$, from the resulting single crystal (La$_{0.8}$Eu$_{0.2})_{4 / 3}$Sr$_{5 / 3}$Mn$_{2}$O$_{7}$ we have observed the magnetization jump, the resistivity jump, as well as the relaxation phenomena. For (La$_{0.8}$Eu$_{0.2})_{4 / 3}$Sr$_{5 / 3}$Mn$_{2}$O$_{7}$, it has a very delicate ground state due to the interplays among spin, charge, orbital, lattice degrees of freedom. Consequently, the magnetization state is sensitive to temperature, magnetic field, as well as time. Meanwhile, the evolution of the magnetization with time shows a spontaneous jump when both the temperature and the magnetic field are constant. Similar step-like behaviours are also observed in resistivity. All these results suggest that Eu doping can greatly modulate the physical properties of La$_{4 / 3}$Sr$_{5 / 3}$Mn$_{2}$O$_{7}$ and cause such interesting behaviours. 相关文章 | 计量指标

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Electron spin resonance study of the Ba-doping manganite Nd0.5Sr0.5MnO3 赵建军, 邢茹, 鲁毅, 浩斯巴雅尔, 赵明宇, 金香, 郑琳, 宁伟, 孙阳, 成昭华 2008 (7):  2721-2724.  doi: 10.1088/1674-1056/17/7/061 摘要 ( 1695 )   PDF(457KB) ( 504 )   We have performed magnetization measurements and electron spin resonance (ESR) on polycrystalline manganites of Nd$_{0.5}$Sr$_{0.5 - x}$Ba$_{x}$MnO$_{3}$ ($x = 0.1$). Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260\,K ($\sim T_{\rm C})$ and 185\,K ($\sim T_{\rm N})$, the system coexists of the paramagnetic phase and the ferromagnetic (FM) phase. Between 185\,K and 140\,K, the system coexists of the FM phase and the antiferromagnetic (AFM) phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd$_{0.5}$Sr$_{0.4}$Ba$_{0.1}$MnO$_{3}$ by partially substituting the larger Ba$^{2 + }$ ions for the smaller Sr$^{2 + }$ ions. 相关文章 | 计量指标

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The performance enhancement in organic light-emitting diode using a semicrystalline composite for hole injection 曹峻松, 关敏, 曹国华, 曾一平, 李晋闽, 秦大山 2008 (7):  2725-2729.  doi: 10.1088/1674-1056/17/7/062 摘要 ( 1545 )   PDF(725KB) ( 620 )   A semicrystalline composite, 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) doped N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (NPB), has been fabricated and characterized. An organic light-emitting diode using such a composite in hole injection exhibits the improved performance as compared with the reference device using neat NPB in hole injection. For example, at a luminance of 2000 cd/m$^{2}$, the former device gives a current efficiency of 2.0cd/A, higher than 1.6cd/A obtained from the latter device. Furthermore, the semicrystalline composite has been shown thermally to be more stable than the neat NPB thin film, which is useful for making organic light emitting diodes with a prolonged lifetime. 相关文章 | 计量指标

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

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A CMOS-compatible silicon substrate optimization technique and its application in radio frequency crosstalk isolation 李琛, 廖怀林, 黄如, 王阳元 2008 (7):  2730-2738.  doi: 10.1088/1674-1056/17/7/063 摘要 ( 1490 )   PDF(14383KB) ( 432 )   In this paper, a complementary metal--oxide semiconductor (CMOS)-compatible silicon substrate optimization technique is proposed to achieve effective isolation. The selective growth of porous silicon is used to effectively suppress the substrate crosstalk. The isolation structures are fabricated in standard CMOS process and then this post-CMOS substrate optimization technique is carried out to greatly improve the performances of crosstalk isolation. Three-dimensional electro-magnetic simulation is implemented to verify the obvious effect of our substrate optimization technique. The morphologies and growth condition of porous silicon fabricated have been investigated in detail. Furthermore, a thick selectively grown porous silicon (SGPS) trench for crosstalk isolation has been formed and about 20dB improvement in substrate isolation is achieved. These results demonstrate that our post-CMOS SGPS technique is very promising for RF IC applications. 相关文章 | 计量指标

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Enhancement of water permeation across nanochannels by partial charges mimicked from biological channels 弓晓晶, 方海平 2008 (7):  2739-2744.  doi: 10.1088/1674-1056/17/7/064 摘要 ( 1208 )   PDF(1526KB) ( 546 )   In biological water channel aquaporins (AQPs), it is believed that the bipolar orientation of the single-file water molecules inside the channel blocks proton permeation but not water transport. In this paper，the water permeation and particularly the water-selective behaviour across a single-walled carbon nanotube (SWNT) with two partial charges adjacent to the wall of the SWNT are studied by molecular dynamics simulations, in which the distance between the two partial charges is varied from 0.14\,nm to 0.5\,nm and the charges each have a quantity of 0.5\,$e$. The two partial charges are used to mimic the charge distribution of the conserved non-pseudoautosomal (NPA) (asparagine/proline/alanine) regions in AQPs. Compared with across the nanochannel in a system with one +1\,$e$ charge, the water permeation across the nanochannel is greatly enhanced in a system with two +0.5\,$e$ charges when charges are close to the nanotube, i.e. the two partial charges permit more rapid water diffusion and maintain better bipolar order along the water file when the distance between the two charges and the wall of SWNT is smaller than about 0.05\,nm. The bipolar orientation of the single-file water molecules is crucial for the exclusion of proton transfer. These findings may serve as guidelines for the future nanodevices by using charges to transport water and have biological implications because membrane water channels share a similar single-file water chain and positive charged region at centre and provide an insight into why two residues are necessitated in the central region of water channel protein. 相关文章 | 计量指标

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Analysis of precipitation characteristics of South and North China based on the power-law tail exponents 封国林, 龚志强, 支蓉, 章大全 2008 (7):  2745-2752.  doi: 10.1088/1674-1056/17/7/065 摘要 ( 1746 )   PDF(295KB) ( 684 )   Precipitation sequence is a typical nonlinear and chaotic observational series, and studies on precipitation forecasts are restricted to the use of traditional linear statistical methods, especially when analysing the regional characteristics of precipitation. In the context of 20 stations' daily precipitation series (from 1956 to 2000) in South China (SC) and North China (NC), we divide each precipitation series into many self-stationary segments by using the heuristic segmentation algorithm (briefly BG algorithm). For each station's precipitation series, we calculate the exponent of power-law tail (EPT) of the cumulative probability distribution of segments with a length larger than $l$ for precipitation and temperature series. Our results show that the power-law decay of the cumulative probability distribution of stationary segments might be a common attribution for precipitation and other nonstationary time series; the EPT somewhat indicates the precipitation duration and its spatial distribution that might be different from area to area. The EPT in NC is larger than in SC; Meanwhile, EPT might be another effective way to study the abrupt changes in nonlinear and nonstationary time series. 相关文章 | 计量指标