中国物理B

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Mirror nodes in growing random networks

戴硕, 郭云均

2004 (4): 423-427. doi: 10.1088/1009-1963/13/4/001

摘要 ( 981 )

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In this article, we consider mirror nodes, which are widely used to reduce local burden, and present two models that are practical for the Internet and probably some other networks. One model introduces an upper limit to the number of links that a node can have, beyond which the node will share the total links with a newly introduced one. Similarly, in the second model, if the number of links exceeds a limit, a new node will be introduced. Unlike the first model, the new node shares with the old one the chance of receiving new links but not the existing links. These models are analytically treated, and from the degree distribution, we can see that the number of nodes with medium links (half the upper limit) increases at the expense of the loss of highly connected nodes. By reducing the burden, this may improve the robustness of the networks.

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A new method to avoid PPP in data evaluation

陈振鹏, 孙业英

2004 (4): 428-433. doi: 10.1088/1009-1963/13/4/002

摘要 ( 1016 )

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The Peelle Pertinent Puzzle (PPP) has been studied systematically. The results obtained by using several proposed methods to deal with a sample of {}^6Li(n, t) are compared with each other. The cause of PPP occurrence has been found. A new method to avoid PPP is introduced, whose main idea is ‘to selectively make suitable correction for systematic error according to the relative extent of discrepancy'. The method is able to produce the best result and should be used to avoid the PPP at first.

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Numerical analysis of fluid flow through a cylinder array using a lattice Boltzmann model

董平, 冯士德, 赵颖

2004 (4): 434-440. doi: 10.1088/1009-1963/13/4/003

摘要 ( 1355 )

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In this paper we present a detailed computational study of an incompressible Newtonian fluid flow across a periodic array of two-dimensional cylinders which is a simplest non-trivial representation of a porous media. A two-dimensional Lattice Boltzmann Method is used to solve the governing Navier－Stokes equation taking into account of viscous dissipation effects and influence of nonlinear fluid drag. Both the flow fields and the Darcy－Forchheimer drag coefficient as a function of the solid volume fraction are calculated for a wide range of flow Reynolds numbers. The predictions were compared with the results from conventional numerical and empirical models for verification. Apart from confirming that inertial effects can cause a significant deviation from Darcy's law for large velocities the results also show that the characteristics of the vorticity field vary considerably as the Reynolds number increases, which will have major implications to the transport of passive particulate substances within the pores and their removal rate.

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A certain critical two-soliton solution of the nonlinear Schr?dinger equation

颜家壬, 潘留仙, 卢竞

2004 (4): 441-444. doi: 10.1088/1009-1963/13/4/004

摘要 ( 1248 )

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An exact two-soliton solution of the nonlinear Schr?dinger equation is derived by using the Hirota direct approach. This solution describes such a critical process that two still solitons separated infinitely approach and then pass through each other and keep straight on infinitely.

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The supersymmetric WKB approximation of ring-shaped oscillator potential in r and θ dimensions with spherical polar coordinates

陈刚, 陈子栋

2004 (4): 445-447. doi: 10.1088/1009-1963/13/4/005

摘要 ( 1256 )

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According to calculation of the energy spectrum of ring-shape oscillator potential by using the supersymmetric WKB approximation, it is shown that the energy spectrum of some noncentral separable potentials can be exactly obtained in r and $\theta$ dimensions by above method.

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Frequency sensitivity of sub-excitable systems coupled with different topology

李思昊, 王宏利, 欧阳颀

2004 (4): 448-453. doi: 10.1088/1009-1963/13/4/006

摘要 ( 1693 )

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We have investigated numerically the behaviours of identical FitzHugh－Nagumo systems, which are coupled into topologies of regular one-dimensional lattice, small-world network and scale-free network, and driven by white noise and an external signal. We found that when a number of uniform systems are coupled into a network, the system's signal-to-noise ratio remains at a high level in a wider frequency range than in the case of a single oscillator. Different architectures manifest different impact, with the scale-free network being the most remarkable. Results presented here suggest a possible approach to improve the sensitivity of a system to external signals and are helpful for designing communication equipments.

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Chaotic time series prediction using least squares support vector machines

叶美盈, 汪晓东

2004 (4): 454-458. doi: 10.1088/1009-1963/13/4/007

摘要 ( 1510 )

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We propose a new technique of using the least squares support vector machines (LS-SVMs) for making one-step and multi-step prediction of chaotic time series. The LS-SVM achieves higher generalization performance than traditional neural networks and provides an accurate chaotic time series prediction. Unlike neural networks' training that requires nonlinear optimization with the danger of getting stuck into local minima, training LS-SVM is equivalent to solving a set of linear equations. Thus it has fast convergence. The simulation results show that LS-SVM has much better potential in the field of chaotic time series prediction.

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Adaptive regulation of uncertain chaos with dynamic neural networks

谭文, 王耀南, 曾照福, 黄丹, 周少武

2004 (4): 459-463. doi: 10.1088/1009-1963/13/4/008

摘要 ( 1119 )

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A novel adaptive control for uncertain nonlinear chaotic system is presented. A dynamical neural networks is used to perform ‘black box' identification. Based on the identifier, the state feedback control is employed to drive the unknown chaotic system toward the desired target. Simulations show the derived control via the neuro-identifier turns out to be very effective.

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Semiclassical calculation of the recurrence spectra of He Rydberg atom in perpendicular electric and magnetic fields

王德华, 林圣路

2004 (4): 464-468. doi: 10.1088/1009-1963/13/4/009

摘要 ( 1152 )

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Closed orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. By developing the closed orbit theory from two degrees of freedom to three non-separable degrees of freedom, we calculated the recurrence spectra of He Rydberg atom in perpendicular electric and magnetic fields. The closed orbits in the corresponding classical system have also been obtained. Fourier transformed spectra of He atoms have allowed direct comparison between the resonance peaks and the scaled action values of closed orbits, whereas the nonhydrogenic resonance can be explained in terms of the new orbits created by the core scattering. The semiclassical result is in good agreement with the quantum spectra, which suggests that our method is correct.

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Non-factorizable contributions in D⁰→π⁺π^- decay

吴向尧, 尹新国, 郭义庆

2004 (4): 469-472. doi: 10.1088/1009-1963/13/4/010

摘要 ( 1059 )

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We have analyzed the D⁰→$\pi^+\pi^-$ decay with α_s corrections in quantum chromodynamic (QCD) factorization and with the soft-gluon corrections in the light cone QCD sum rules. The soft-gluon effects are firstly calculated in the decay channel. The results show that once the factorization contributions, the α_s corrections, and the soft-gluon effects are all considered, we can satisfactorily explain the experimental data in the decay channel.

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Luminescence of Ba_0.85MgAl₁₀O_16.94:Eu²⁺_0.09 with different fluxes

邓朝勇, 何大伟, 庄卫东, 王永生, 康凯, 黄小卫

2004 (4): 473-480. doi: 10.1088/1009-1963/13/4/011

摘要 ( 959 )

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BaMgAl_{10}O_{17}:Eu^{2+}, known as BAM, is a very important blue-emitting phosphor used in plasma display panels (PDP) and three band fluorescent lamps. In this paper, the Ba_{0.85}MgAl_{10}O_{16.94} :Eu^{2+}_{0.09} phosphors with different fluxes (BaF_2, MgF_2, AlF_3, BaCl_2, MgCl_2, AlCl_3, H_3BO_3) were prepared by high temperature solid-state reaction method and the influence of different fluxes on the luminescence of Ba_{0.85}MgAl_{10}O_{16.94}:Eu^{2+}_{0.09} phosphor was studied under 254nm excitation and vacuum ultraviolet (VUV) excitation. It was found that fluorides have better flux effects than chlorides and H_3BO_3. The mechanism of particle growth in the presence of flux in the process of phosphor preparation is discussed in detail. Particle size distribution and the crystal structure of the phosphors are also analysed.

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Momentum correlation of the final-state wavefunction for (e, 3e) collisions on helium

张穗萌

2004 (4): 481-488. doi: 10.1088/1009-1963/13/4/012

摘要 ( 1232 )

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Based on our earlier paper, the momentum correlation of the four bodies in the final state is further considered for (e, 3e) processes on helium. A fivefold differential cross section (FDCS) for electron-impact double ionization of helium is calculated by use of the modified model for high incident energy (1－5.6keV). It has been found that the present results give a better description for the experimental data, as compared with the results of our earlier paper.

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Theoretical study on structures of Ga₃N, GaN₃, Ga₃N₂ and Ga₂N₃ clusters

宋斌, 凌俐, 曹培林

2004 (4): 489-496. doi: 10.1088/1009-1963/13/4/013

摘要 ( 1434 )

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The structures of Ga_3N, GaN_3, Ga_3N_2 and Ga_2N_3 clusters are studied using the full-potential linear-muffin-tin-orbital molecular dynamics (FP-LMTO MD) method. Four structures for Ga_3 N, five structures for GaN_3, nine structures for Ga_3N_2 and nine structures for Ga_2N_3 have been obtained. The most stable structures of these clusters are planar ones. A strong dominance of the N－-N bond over the Ga－-N and Ga－-Ga bonds appears to control the structural skeletons, supporting the previous result obtained by Kandalam and co-workers. The most stable structures of these small GaN clusters displayed semiconductor-like properties through the calculation of the HOMO－LUMO gaps.

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Controlling dipole squeezing of two atoms inside a cavity via manipulating an atom outside the cavity

刘堂昆, 王继锁, 冯健, 詹明生

2004 (4): 497-500. doi: 10.1088/1009-1963/13/4/014

摘要 ( 1102 )

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Considering that three two-level atoms are initially in the GHZ single state and two of the atoms are simultaneously put into a cavity initially in the coherent state, we investigate the dipole squeezing properties of the two atoms inside the cavity under the condition of resonant interaction. It is shown that dipole squeezing properties of the two atoms inside the cavity are strongly affected by rotation manipulating of the atom outside the cavity.

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Mathematical modelling of gain-switched RF-excited CO₂ waveguide laser

巴德, 田兆硕, 王骐

2004 (4): 501-504. doi: 10.1088/1009-1963/13/4/015

摘要 ( 1370 )

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The detailed mathematical models for the evolution of light pulses in RF-excited CO_2 waveguide lasers are derived. Explicit expressions for the pulse characteristics in RF-excited CO_2 waveguide lasers are obtained. The effects of losses and unsaturated gain on output power are calculated.

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Experimental investigation of the impact on nearby solid boundary during laser-generated bubble collapse

陈笑, 徐荣青, 沈中华, 陆建, 倪晓武

2004 (4): 505-509. doi: 10.1088/1009-1963/13/4/016

摘要 ( 1176 )

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Cavitation damage has been considered as being responsible for many effects in hydraulic machinery and biological medicine. In order to better understand the cavity interaction with nearby solid surfaces, the impact loading induced by the high-speed liquid-jet and subsequent jet flow during the final stage of the bubble collapse in a static fluid is investigated by focusing a Q-switched pulsed laser into water. By means of a new method based on a fibre-coupling optical beam deflection technique, a detailed experimental study has been made to clarify the relationship of the impact pressure against a solid boundary as a function of the dimensionless γ that is generally used to describe the bubble dynamics with its definition γ= s/R_{max}(R_{max} being the maximum bubble radius and s denoting the distance of the cavity inception from the boundary). The experimental results are shown that for γ in the range of about 0.67 to 0.95 with a pulsed laser energy 230mJ, the transient pressure applied on the solid surface is maximum; while for γ>1 or γ<0.67, it is gradually decreased. By combination of our experimental results with the other work that detected the acoustic emission during the bubble collapse at different γ, it is concluded that in this range of 0.67－0.95, the destructive effect due to a liquid-jet and the following jet flow impact actually outweighs the well-known effect of shock wave emission and plays a vital role during the cavitation bubble collapse.

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Finite-size effect and Kondo screening effect in an A-B ring with a quantum dot

吴绍全, 王顺金, 孙威立, 余万伦

2004 (4): 510-515. doi: 10.1088/1009-1963/13/4/017

摘要 ( 1152 )

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The properties of the ground state of a closed dot－ring system with a magnetic flux in the Kondo regime are studied theoretically by means of a one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. It is shown that at T=0, a suppressed Kondo effect exists in this system even when the mean level spacing of electrons in the ring is larger than the bulk Kondo temperature. The physical quantities depend sensitively on both the parity of the system and the size of the ring; the rich physical behaviour can be attributed to the coexistence of both the finite-size effect and the Kondo screening effect. It is also possible to detect the Kondo screening cloud by measuring the persistent current or the zero field impurity susceptibility χ_{imp} directly in future experiments.

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Effect of phonon scattering mechanisms on the lattice thermal conductivity of skutterudite-related compound

杨磊, 吴建生, 张澜庭

2004 (4): 516-521. doi: 10.1088/1009-1963/13/4/018

摘要 ( 1259 )

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We have prepared the skutterudite-related compounds FeCo_3Sb_{12} and La_{0.75}Fe_3CoSb_{12} with different average grain sizes (about 0.8 and 3.9μm) by hot pressing. Samples were characterized by XRD, EPMA and SEM. The lattice thermal conductivity was investigated in the temperature range from room temperature to 200℃. Based on the Debye model, we analyse the change in lattice thermal conductivity due to various phonon scattering mechanisms by examining the relationship between the weighted phonon relaxation time τ(ω/ω_D)^2 and the reduced phonon frequency ω/ω_D. The effect of grain boundary scattering to phonon is negligible within the range of grain sizes considered in this study. The large reduction in lattice thermal conductivity of FeCo_3Sb_{12} compound contributes to the electron－phonon scattering. As for La_{0.75}Fe_3CoSb_{12} compound, the atoms of La filled into the large voids in the structure of the skutterudite produce more significant electron－phonon scattering as well as more substitute of Fe at Co site at the same time. Moreover, the point-defect scattering appears due to the difference between the atoms of La and the void. In addition, the scattering by the rattling of the rare-earth atoms in the void is another major contribution to the reduced lattice thermal conductivity. Introducing the coupling of the electron－phonon scattering with the point-defect scattering and the scattering by the rattling of the rare-earth atom is an effective method to reduce the lattice thermal conductivity of the skutterudite-related compounds by substitution of Fe for Co and the atoms of La filled in the large voids in the skutterudite structure.

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Nonlinear current－voltage characteristics of sintered tungsten－vanadium oxide

刘祖黎, 杨林峰, 王豫, 姚凯伦, 王传聪

2004 (4): 522-528. doi: 10.1088/1009-1963/13/4/019

摘要 ( 1046 )

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We have studied the densification behaviour, microstructure and electrical properties of WO_3 ceramics with V_2O_5 as the additive ranging from 0.5 to 15mol%. Scanning electron microscopic photos indicated that the grain size of WO_3－V_2O_5 specimens is smaller than that of pure WO_3. The addition of V_2O_5 to WO_3 showed a tendency to enhance the densification rate and to restrict the grain growth. Electrical properties of all specimens were measured for different electrodes at different temperatures. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I－V behaviour. The nonlinear coefficient was obtained at the current density J=0.01, 0.1 and 1mA/cm^2 for a series of WO_3－V_2O_5 samples. The V0.5mol% specimen showed an abnormal phenomenon that the nonlinear characteristics appeared at 350℃ and disappeared at lower and higher temperatures. This implies that it could be applied as a high-temperature varistor. The double Schottky barrier model was adopted to explain the phenomena for the WO_3-V_2O_5 varistors.

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Fiske steps in surface intrinsic Josephson junctions of Bi₂Sr₂CaCu₂O_8+δ single crystals

朱晓波, 魏延锋, 赵士平, 陈赓华, 杨乾声

2004 (4): 529-531. doi: 10.1088/1009-1963/13/4/020

摘要 ( 1263 )

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Current－voltage characteristics of the surface intrinsic Josephson junctions under a magnetic field parallel to CuO_2 planes have been studied experimentally. Fiske steps in such a junction have been observed. The Swihart velocity for the junction is found to be 7.2×10^5m/s, which corresponds to the velocity mode of a single junction.

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Investigation of spontaneous magnetization of coupled 2×2 superconducting π ring array

李壮志, 王福仁, 杨涛, 刘新元, 马平, 谢飞翔, 聂瑞娟, 戴远东

2004 (4): 532-537. doi: 10.1088/1009-1963/13/4/021

摘要 ( 1225 )

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We present the theoretical investigation of spontaneous magnetization of a coupled 2×2 πring array. It is indicated by free energy calculation that the system has the lowest energy when the four π rings have the full antiparallel configuration. Furthermore, the numerical evaluation results show that the system which favours full antiparallel spontaneous magnetization is a quantum effect deriving from the phase cohering of the superconducting quantum wavefunctions in the four superconducting rings through the shared Josephson junctions.

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Mode-locking behaviour: ac response of a driven disordered vortex lattice

汪友梅, 曹义刚, 焦正宽

2004 (4): 538-541. doi: 10.1088/1009-1963/13/4/022

摘要 ( 1182 )

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Using random pinning force simulations, we study numerically the alternating current (ac) response of the driven disordered vortex lattice. In the presence of a superimposed ac force, mode-locking steps are observed in the velocity－direct current (dc) force characteristics at high dc forces, where a smectic order occurs. The step width shows damped oscillations with the strength of interaction between vortices, in good agreement with recent experiments.

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Giant magnetoresistance in Y_0.9La_0.1Mn₆Sn₆ compound

姚金雷, 汪汝武, 杨德仁, 严密, 张立刚

2004 (4): 542-545. doi: 10.1088/1009-1963/13/4/023

摘要 ( 1146 )

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Magnetic transitions and magnetoresistance effect of the HfFe_6Ge_6-type Y_{0.9}La_{0.1}Mn_6Sn_6 compound have been investigated in the temperature range of 5－380K. The sample displays antiferromagnetic behaviour in the whole temperature range below Néel temperature T_N=309K. The metamagnetic transition from antiferromagnetism to ferromagnetism can be induced by an applied field. The metamagnetic transition field decreases monotonically from 2T at 5K to 0.4T at 300K. The giant magnetoresistance effect is observed with the metamagnetic behaviour, such as -10.4% at 245K under a field of 5T.

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Effects of Fe－Fe bond length change in NaZn₁₃-type intermetallic compounds on magnetic properties and magnetic entropy change

王光军, 胡凤霞, 王芳, 沈保根

2004 (4): 546-551. doi: 10.1088/1009-1963/13/4/024

摘要 ( 1216 )

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In this paper the effects of Fe－Fe bond length change on magnetic properties and magnetic entropy change have been investigated on LaFe_{12.4-x}Si_xCo_{0.6} and LaFe_{12.3-x}Al_xCo_{0.7} intermetallic compounds. According to the analyses of Fe－Fe bond length change, the variation of Curie temperature and the unusual magnetic phase transition which results in the large magnetic entropy change were explained. The effects of the substitution of Co and Si for Fe on magnetic entropy change and field-induced itinerant-electron metamagnetic transition in LaFe_{12.4-x}Si_xCo_{0.6} compounds were also studied and the considerable magnetic entropy change has been achieved.

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Magnetization and demagnetization behaviours of melt-spun Pr₁₂Fe₈₂B₆ and Pr₈Fe₈₇B₅ ribbons

杜晓波, 张宏伟, 荣传兵, 张健, 张绍英, 沈保根, 闫羽, 金汉民

2004 (4): 552-555. doi: 10.1088/1009-1963/13/4/025

摘要 ( 1330 )

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Nanocrystalline Pr_{12}Fe_{82}B_6 and nanocomposite Pr_8Fe_{87}B_5 ribbons have been prepared using a melt spinning technique. Recoil loops have been measured at 20, 200 and 300K. Demagnetization curves are analysed by dividing it into reversible and irreversible portions. High recoil loop susceptibility at low applied field and large reversible change in the demagnetization curve have been found in Pr_8Fe_{87}B_5 ribbons, showing that the reversible behaviours in nanocomposite permanent magnets originate primarily from the magnetically soft phase. The hysteresis in recoil loops found in Pr_8Fe_{87}B_5 ribbons originates from the soft phase α-Fe that suffers a stress.

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Spin flop in one-dimensional Heisenberg antiferromagnet KCuF₃

史庆藩, 李良生, 王琪

2004 (4): 556-560. doi: 10.1088/1009-1963/13/4/026

摘要 ( 1218 )

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Following Yamada and Kato [J. Phys. Soc. Japan 63 (1994) 289], we have calculated the frequency－field diagram of antiferromagnetic resonance of KCuF_3 using an eight-sublattice model and mean field approximation. A spin flop is found to take place from the [110]_p to a direction perpendicular to [110]_p in the c-plane at H\simeq 42172A/m, which is in good agreement with the data obtained by measuring magnetic susceptibility.

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Characterizations of Tb:Zn₂SiO₄ films on silicon wafer prepared by sol-gel dip-coating and solid-phase reaction

季振国, 赵士超, 向因, 宋永梁, 叶志镇

2004 (4): 561-563. doi: 10.1088/1009-1963/13/4/027

摘要 ( 1135 )

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Terbium-doped Zn_2SiO_4 films were successfully prepared on Si wafers by a simple sol-gel dip-coating and solid-phase reaction method of ZnO and SiO_2. X-ray diffraction (XRD) and UV－Vis absorption results revealed that films processed below 850℃ were ZnO in wurzite structure, and films processed above 850℃ were Zn_2SiO_4 in wellimite structure. Photoluminescence measurements of the Tb-doped Zn_2SiO_4 films showed two strong emission bands at 490 and 545nm. The photoluminescence lifetime was 4.6ms.

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Production of large size single transient cavitation bubbles with tube arrest method

陈岐岱, 王龙

2004 (4): 564-570. doi: 10.1088/1009-1963/13/4/028

摘要 ( 1136 )

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Large size single transient cavitation bubbles of maximum diameter up to 3 cm with sonoluminescence have been generated in water by the ‘tube arrest' method. A simplified one-dimensional model of bubble growing and water column motion is proposed. The results of numerical simulation are compared with the experimental data of the bubble size and oscillation period as the key parameters.

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