Table of contents

20 February 2006, Volume 15 Issue 2 Previous issue    Next issue

GENERAL

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Non-Noether symmetries and Lutzky conservative quantities of nonholonomic nonconservative dynamical systems Zheng Shi-Wang (郑世旺), Tang Yi-Fa (唐贻发), Fu Jing-Li (傅景礼) Chinese Physics, 2006, 15 (2):  243-248.  DOI: 10.1088/1009-1963/15/2/001 Abstract ( 1678 )   PDF (222KB) ( 670 )   Non-Noether symmetries and conservative quantities of nonholonomic nonconservative dynamical systems are investigated in this paper. Based on the relationships among motion, nonconservative forces, nonholonomic constrained forces and Lagrangian, non-Noether symmetries and Lutzky conservative quantities are presented for nonholonomic nonconservative dynamical systems. The relation between non-Noether symmetry and Noether symmetry is discussed and it is further shown that non-Noether conservative quantities can be obtained by a complete set of Noether invariants. Finally,an example is given to illustrate these results.

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Variational principle and dynamical equations of discrete nonconservative holonomic systems Liu Rong-Wan (刘荣万), Zhang Hong-Bin (张宏彬), Chen Li-Qun (陈立群) Chinese Physics, 2006, 15 (2):  249-252.  DOI: 10.1088/1009-1963/15/2/002 Abstract ( 1567 )   PDF (197KB) ( 710 )   By analogue with the methods and processes in continuous mechanics, a Lagrangian formulation and a Hamiltonian formulation of discrete mechanics are obtained. The dynamical equations including Euler--Lagrange equations and Hamilton's canonical equations of the discrete nonconservative holonomic systems are derived on a discrete variational principle. Some illustrative examples are also given.

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The 3D solitons and vortices in 3D discrete monatomic lattices with cubic and quartic nonlinearity Xu Quan (徐权), Tian Qiang (田强) Chinese Physics, 2006, 15 (2):  253-265.  DOI: 10.1088/1009-1963/15/2/003 Abstract ( 1378 )   PDF (388KB) ( 618 )   By virtue of the method of multiple-scale and the quasi-discreteness approach, we have discussed the nonlinear vibration equation of a 3D discrete monatomic lattice with its nearest-neighbours interaction. The 3D simple cubic lattices have the same localized modes as a 1D discrete monatomic chain with cubic and quartic nonlinearity. The nonlinear vibration in the 3D simple cubic lattice has 3D distorted solitons and 3D envelop solitons in the direction of $k_{x}=k_{y}=k_{z}=k$ and $k=\pm \pi$/6$a_{0}$ in the Brillouin zone, as well as has 3D vortices in the direction of $k_{x}=k_{y}=k_{z}=k$ and $k=\pm \pi$/$a_{0}$ in the Brillouin zone.

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Flexural vibration band gaps in thin plates with two-dimensional binary locally resonant structures Yu Dian-Long (郁殿龙), Wang Gang (王刚), Liu Yao-Zong (刘耀宗), Wen Ji-Hong (温激鸿), Qiu Jing (邱静) Chinese Physics, 2006, 15 (2):  266-271.  DOI: 10.1088/1009-1963/15/2/004 Abstract ( 1380 )   PDF (273KB) ( 847 )   The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases. The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.

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Effect of disturbance in perfect state transfer Liu Dan (刘丹), Zhang Jing-Fu (张竞夫) Chinese Physics, 2006, 15 (2):  272-275.  DOI: 10.1088/1009-1963/15/2/005 Abstract ( 1112 )   PDF (211KB) ( 474 )   The influence of the disturbance caused by the imperfection of the engineering coupling constants in the perfect state transfer is calculated. The results show that the fidelity for the perfect state transfer is seriously affected by the errors occurring near the input and output spins. Such results are helpful for the realization of the perfect state transfer in the case where there exist errors in experiments.

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Linear optics implementation for quantum game under quantum noise Cao Shuai (曹帅), Fang Mao-Fa (方卯发) Chinese Physics, 2006, 15 (2):  276-280.  DOI: 10.1088/1009-1963/15/2/006 Abstract ( 1194 )   PDF (228KB) ( 537 )   It has recently been shown that linear optics alone would suffice to implement efficient quantum computation. Quantum computation circuits using coherent states as the logical qubits can be constructed from very simple linear networks, conditional measurements and coherent superposition resource states. We present the quantum game under quantum noise and a proposal for implementing the noisy quantum game using only linear optics.

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The scattering fields for a spherical target irradiated by a plane electromagnetic wave in an arbitrary direction Li Ying-Le (李应乐), Huang Ji-Ying (黄际英) Chinese Physics, 2006, 15 (2):  281-285.  DOI: 10.1088/1009-1963/15/2/007 Abstract ( 1581 )   PDF (202KB) ( 581 )   The relation between corresponding trigonometric functions in two rotating coordinate systems is presented. The transformation formula for a vector in the two rotating spherical coordinate systems is obtained. The scattering fields for a spherical target irradiated by a plane electromagnetic wave in an arbitrary direction are derived. These fields in a particular case retrogress to those available in the literature. The obtained results have great potential in practical applications.

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Quantum logic gates operation using SQUID qubits in bimodal cavity Song Ke-Hui (宋克慧) Chinese Physics, 2006, 15 (2):  286-291.  DOI: 10.1088/1009-1963/15/2/008 Abstract ( 1277 )   PDF (248KB) ( 738 )   We present a scheme to realize the basic two-qubit logic gates such as the quantum phase gate and SWAP gate using a detuned microwave cavity interacting with three-level superconducting-quantum-interference-device (SQUID) qubit(s), by placing SQUID(s) in a two-mode microwave cavity and using adiabatic passage methods. In this scheme, the two logical states of the qubit are represented by the two lowest levels of the SQUID, and the cavity fields are treated as quantized. Compared with the previous method, the complex procedures of adjusting the level spacing of the SQUID and applying the resonant microwave pulse to the SQUID to create transformation are not required. Based on superconducting device with relatively long decoherence time and simplified operation procedure, the gates operate at a high speed, which is important in view of decoherence.

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Tunnelling effect from a Vaidya--de Sitter black hole Ren Jun (任军), Zhao Zheng (赵峥) Chinese Physics, 2006, 15 (2):  292-295.  DOI: 10.1088/1009-1963/15/2/009 Abstract ( 1321 )   PDF (217KB) ( 522 )   In this paper, we extend Parikh' recent work to the Vaidya--de Sitter black hole which is non-stationary. We view Hawking radiation as a tunnelling process across the event horizon and calculate the tunnelling probability when the particle crosses the event horizon. From the tunnelling probability we also find a leading correction to the semiclassical emission rate.

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The propagation of solitary waves in clouds of Bose--Einstein condensed atoms Ao Sheng-Mei (敖胜美), Yan Jia-Ren (颜家壬) Chinese Physics, 2006, 15 (2):  296-300.  DOI: 10.1088/1009-1963/15/2/010 Abstract ( 1403 )   PDF (215KB) ( 464 )   The Gross--Pitaevskii equation which describes the motion of a Bose--Einstein condensed (BEC) atom in an elongated trap is solved analytically, and a solitary-wave solution is obtained in the low-density case without neglecting the effect of the interatomic interaction on the transverse function. It is shown that this effect leads to the velocity of the solitary wave slowing down and the profile of the solitary wave widening.

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Chaotic dynamics of the fractional-order Ikeda delay system and its synchronization Lu Jun-Guo (卢俊国) Chinese Physics, 2006, 15 (2):  301-305.  DOI: 10.1088/1009-1963/15/2/011 Abstract ( 1641 )   PDF (357KB) ( 942 )   In this paper we numerically investigate the chaotic behaviours of the fractional-order Ikeda delay system. The results show that chaos exists in the fractional-order Ikeda delay system with order less than 1. The lowest order for chaos to be able to appear in this system is found to be 0.1. Master--slave synchronization of chaotic fractional-order Ikeda delay systems with linear coupling is also studied.

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A simple asymptotic trajectory control of full states of a unified chaotic system Yu Dong-Chuan (禹东川), Wu Ai-Guo (吴爱国), Wang Dong-Qing (王冬青) Chinese Physics, 2006, 15 (2):  306-309.  DOI: 10.1088/1009-1963/15/2/012 Abstract ( 1291 )   PDF (194KB) ( 603 )   A simple full-state asymptotic trajectory control (FSATC) scheme is proposed to asymptotically drive full states of a unified chaotic system (UCS) to arbitrary desired trajectories. The FSATC uses only information, i.e. one state of the UCS. A sinusoidal wave and two chaotic variables are taken as illustrative tracking trajectories to verify that using the proposed FSATC can make full UCS states track desired trajectories with high tracking accuracy in a finite time.

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An NLMS algorithm with optimized preparatory step-size parameters for SQUID-based MCG data processing Li Zhuo (李倬), Chen Geng-Hua (陈庚华), Zhang Li-Hua (张利华), Yang Qian-Sheng (杨乾声), Feng Ji (冯稷) Chinese Physics, 2006, 15 (2):  310-314.  DOI: 10.1088/1009-1963/15/2/013 Abstract ( 1180 )   PDF (246KB) ( 421 )   We present a new least-mean-square algorithm of adaptive filtering to improve the signal to noise ratio for magnetocardiography data collected with high-temperature SQUID-based magnetometers. By frequently adjusting the adaptive parameter $\alpha $ to systematic optimum values in the course of the programmed procedure, the convergence is accelerated with a highest speed and the minimum steady-state error is obtained simultaneously. This algorithm may be applied to eliminate other non-steady relevant noises as well.

NUCLEAR PHYSICS

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A method to measure the nonlinear force caused emittance growth in a RF photoinjector Li Zheng-Hong (李正红), Yang Zhen-Ping (杨振萍) Chinese Physics, 2006, 15 (2):  315-318.  DOI: 10.1088/1009-1963/15/2/014 Abstract ( 1176 )   PDF (213KB) ( 502 )   Based on the multi-slit method, a new method is introduced to measure the non linear force caused emittance growth in a RF photoinjector. It is possible to reconstruct the phase space of a beam under some conditions by the multi-slit method. Based on the reconstructed phase space, besides the emittance, the emittance growth from the distortion of the phase space can also be measured. The emittance growth results from the effects of nonlinear force acting on electron, which is very important for the high quality beam in a RF photoinjector.

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Physical design and cooling test of C-band standing wave accelerating tube Bai Wei (柏伟), Xu Zhou (许州), Jin Xiao (金晓), Li Ming (黎明) Chinese Physics, 2006, 15 (2):  319-323.  DOI: 10.1088/1009-1963/15/2/015 Abstract ( 1136 )   PDF (318KB) ( 701 )   The physical design and cooling test of a C-band 2MeV standing wave (SW) accelerating tube are described in this paper. The designed accelerating structure consists of 3-cell buncher and 4-cell accelerating section with a total length of about 163mm，excited with 1MW magnetron. Dynamic simulation presents that about 150mA beam pulse current and 30% capture efficiency can be achieved. By means of nonlinear Gauss fit on electron transverse distribution, the diameter of beam spot FWHM (full width at half maximum of density distribution) is about 0.55mm. Cooling test results of the accelerating tube show that frequencies of cavities are tuned to 5527MHz and the field distribution of bunching section is about 3:9:10.

ATOMIC AND MOLECULAR PHYSICS

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Spin polarization effect for molecule Ta2 Xie An-Dong (谢安东) Chinese Physics, 2006, 15 (2):  324-328.  DOI: 10.1088/1009-1963/15/2/016 Abstract ( 1237 )   PDF (229KB) ( 554 )   Density functional theory (DFT) (B3p86) has been used to optimize the structure of the molecule Ta$_2 $. The result shows that the ground state of molecule Ta$_2 $ is a 7-multiple state and its electronic configuration is $^{7}\Sigma _{u}^{ + }$, which shows the spin polarization effect for molecule Ta$_2 $ of transition metal elements for the first time. Meanwhile, spin pollution has not been found because the wavefunction of the ground state does not mix with those of higher states. So, the fact that the ground state of molecule Ta$_2 $ is a 7-multiple state indicates a spin polarization effect of molecule Ta$_2 $ of the transition metal elements, i.e. there exist 6 parallel spin electrons and the non-conjugated electrons are greatest in number. These electrons occupy different space orbitals so that the energy of molecule Ta$_2 $ is minimized. It can be concluded that the effect of parallel spin of the molecule Ta$_2$ is larger than the effect of the conjugated molecule, which is obviously related to the effect of d-electron delocalization. In addition, the Murrell--Sorbie potential functions with parameters for the ground state $^{7}\Sigma _{u}^{ + }$ and other states of the molecule Ta$_2$ are derived. The dissociation energy $D_{\rm e}$, equilibrium bond length $R_{\rm e}$ and vibration frequency $\omega_{\rm e}$ for the ground state of molecule Ta$_2$ are 4.5513eV, 0.2433 nm and 173.06\,cm$^{-1}$, respectively. Its force constants $f_2$, $f_3$ and $f_4$ are 1.5965$\times $10$^{2}$aJ$\cdot$nm$^{-2}$, --6.4722$\times $10$^{3}$aJ$\cdot$nm$^{-3}$ and 29.4851$\times $10$^{4}$aJ$\cdot$nm$^{-4}$, respectively. Other spectroscopic data $\omega_{\rm e}$ $\chi_{\rm e}$, $B_{\rm e}$ and $\alpha_{\rm e}$ for the ground state of Ta$_2 $ are 0.2078 cm$^{-1}$, 0.0315 cm$^{-1}$ and 0.7858$\times $ 10$^{-4}$ cm$^{-1}$, respectively.

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The evaluation of bond dissociation energies for NO2 scission in nitro compounds using density functional and complete basis set methods Shao Ju-Xiang (邵菊香), Cheng Xin-Lu (程新路), Yang Xiang-Dong (杨向东), He Bi (何碧) Chinese Physics, 2006, 15 (2):  329-333.  DOI: 10.1088/1009-1963/15/2/017 Abstract ( 1383 )   PDF (205KB) ( 891 )   By using the density functional theory (B3LYP) and four highly accurate complete basis set (CBS-Q, CBS-QB3, CBS-Lq, and CBS-4M) ab initio methods, the $X$(C, N, O)--NO$_{2}$ bond dissociation energies (BDEs) for CH$_{3}$NO$_{2}$, C$_{2}$H$_{3}$NO$_{2}$, C$_{2}$H$_{5}$NO$_{2}$, HONO$_{2}$, CH$_{3}$ONO$_{2}$, C$_{2}$H$_{5}$ONO$_{2}$, NH$_{2}$NO$_{2}$ (CH$_{3})_{2}$NNO$_{2}$ are computed. By comparing the computed BDEs and experimental results, it is found that the B3LYP method is unable to predict satisfactorily the results of bond dissociation energy (BDE); however, all four CBS models are generally able to give reliable predication of the $X$(C, N, O)--NO$_{2}$ BDEs for these nitro compounds. Moreover, the CBS-4M calculation is the least computationally demanding among the four CBS methods considered. Therefore, we recommend CBS-4M method as a reliable method of computing the BDEs for this nitro compound system.

CLASSICAL AREAS OF PHENOMENOLOGY

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Partially coherent nonparaxial modified Bessel--Gauss beams Gao Zeng-Hui (高曾辉), Lü Bai-Da (吕百达) Chinese Physics, 2006, 15 (2):  334-339.  DOI: 10.1088/1009-1963/15/2/018 Abstract ( 1155 )   PDF (237KB) ( 488 )   The concept of partially coherent nonparaxial modified Bessel--Gauss (MBG) beams is proposed. Based on the generalized Rayleigh-Sommerfeld diffraction integral, the analytical propagation equations of nonparaxial MBG beams in free space are derived and analysed, and some special cases are discussed. In particular, under the paraxial approximation our results reduce to the corresponding paraxial ones. Numerical calculation examples are given to illustrate the dependence of intensity and spectral degree of coherence on the beam order $m$, $\xi $ and $f$ parameters, and to compare the difference between the paraxial and nonparaxial results.

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Strong optical feedback in birefringent dual frequency laser Mao Wei (毛威), Zhang Shu-Lian (张书练) Chinese Physics, 2006, 15 (2):  340-346.  DOI: 10.1088/1009-1963/15/2/019 Abstract ( 1080 )   PDF (300KB) ( 533 )   Strong optical feedback in a birefringent dual frequency He--Ne laser with a high reflectivity feedback mirror has been investigated for the first time. The output characteristics of two orthogonally polarized modes are demonstrated in two different optical feedback cases: one is for both modes being fed back and the other is for only one of the modes being fed back. Strong mode competition can be observed between the two modes with strong optical feedback. And when one mode's intensity is near its maximum, the other mode is nearly extinguished. When both modes are fed back into the laser cavity, the mode competition is stronger than when only one mode is fed back. The difference in initial intensity between the two orthogonally polarized modes plays an important role in the mode competition, which has been experimentally and theoretically demonstrated.

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Image recovery from double amplitudes in fractional Fourier domain Liao Tian-He (廖天河), Gao Qiong (高穹) Chinese Physics, 2006, 15 (2):  347-352.  DOI: 10.1088/1009-1963/15/2/020 Abstract ( 1283 )   PDF (372KB) ( 729 )   The classical Gerchberg--Saxton algorithm is introduced into the image recovery in fractional Fourier domain after adaptation. When this algorithm is applied directly, its performance is good for smoothed image, but bad for unsmoothed image. Based on the diversity of fractional Fourier transform on its orders, this paper suggests a novel iterative algorithm, which extracts the information of the original image from amplitudes of its fractional Fourier transform at two orders. This new algorithm consists of two independent Gerchberg--Saxton procedures and an averaging operation in each circle. Numerical simulations are carried out to show its validity for both smoothed and unsmoothed images with most pairs of orders in the interval [0, 1].

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Three-body entanglement induced by spontaneous emission in a three two-level atoms system Liao Xiang-Ping (廖湘萍), Fang Mao-Fa (方卯发), Zheng Xiao-Juan (郑小娟), Cai Jian-Wu (蔡建武) Chinese Physics, 2006, 15 (2):  353-364.  DOI: 10.1088/1009-1963/15/2/021 Abstract ( 1365 )   PDF (285KB) ( 541 )   We study three-body entanglement induced by spontaneous emission in a three two-level atoms system by using the entanglement tensor approach. The results show that the amount of entanglement is strongly dependent on the initial state of the system and the species of atoms. The three-body entanglement is the result of the coherent superposition of the two-body entanglements. The larger the two-body entanglement is, the stronger the three-body entanglement is. On the other hand, if there exists a great difference in three two-body entanglement measures, the three-body entanglement is very weak. We also find that the maximum of the two-body entanglement obtained with nonidentical atoms is greater than that obtained with identical atoms via adjusting the difference in atomic frequency.

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Experimental investigation of slow light propagation in degenerate two-level system Wang Li-Rong (汪丽蓉), Zhao Yan-Ting (赵延霆), Ma Jie (马杰), Zhao Jian-Ming (赵建明), Xiao Lian-Tuan (肖连团), Jia Suo-Tang (贾锁堂) Chinese Physics, 2006, 15 (2):  365-370.  DOI: 10.1088/1009-1963/15/2/022 Abstract ( 1357 )   PDF (253KB) ( 576 )   Slowing a light pulse in a degenerate two-level system is observed with a double-frequency sweeping technique. The effects of coupling beam intensity, cell temperature and frequency detunings of the coupling and probe beams in resonance, on the slowing of light propagation in such a system are investigated. It is found that group velocities depend strongly on polarization combinations. A group velocity $v_{\rm g}$=6760m/s of light pulses in caesium vapour is obtained under the optimal parameters.

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A secure identification system using coherent states He Guang-Qiang (何广强), Zeng Gui-Hua (曾贵华) Chinese Physics, 2006, 15 (2):  371-374.  DOI: 10.1088/1009-1963/15/2/023 Abstract ( 1112 )   PDF (236KB) ( 454 )   A quantum identification system based on the transformation of polarization of a mesoscopic coherent state is proposed. Physically, an initial polarization state which carries the identity information is transformed into an arbitrary elliptical polarization state. To verify the identity of a communicator, a reverse procedure is performed by the receiver. For simply describing the transformation procedure, the analytical methods of Poincaré sphere and quaternion are adopted. Since quantum noise provides such a measurement uncertainty for the eavesdropping that the identity information cannot be retrieved from the elliptical polarization state, the proposed scheme is secure.

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Theory of two-photon micromaser: competition among different transition processes Sun Wei-Hui (孙为辉), Du Si-De (杜四德), Chen Xiao-Shuang (陈效双) Chinese Physics, 2006, 15 (2):  375-382.  DOI: 10.1088/1009-1963/15/2/024 Abstract ( 1106 )   PDF (309KB) ( 433 )   We have investigated the steady-state cavity-field properties of a single-mode two-photon micromaser when the atoms in a cascade three-level configuration are initially prepared in a mixture of the upper and intermediate states. The mean photon number, trapping state and sub-Poissonian effect are discussed with upper (intermediate)-state population changing from 1(0) to 0(1). These properties are very different from those in a pure two- or one-photon transition process, due to the competition among different transition processes. In particular, the trapping states of nonzero photons are discovered in this system under some conditions, which is contrary to the previous findings.

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Trichromatic phase manipulation of the response of a two-level medium to an arbitrarily intense probe field Guo Hong-Ju (郭洪菊), Hu Xiang-Ming (胡响明), Li Jing-Yan (李景艳), Li Xiao-Xia (李晓霞), Shi Wen-Xing (石文星), Xu Qing (徐清) Chinese Physics, 2006, 15 (2):  383-388.  DOI: 10.1088/1009-1963/15/2/025 Abstract ( 1185 )   PDF (250KB) ( 630 )   The phase dependence and independence of the response of a trichromatically driven two-level medium to an arbitrarily intense probe field have been studied. The sum of the relative phases of the sideband components of the trichromatic field compared to the central component plays a crucial role in the response of the medium. For a weak probe field, as the sum of the relative phases changes from $0$ to $\pi $, multiple switching can be achieved, in which switching from normal to anomalous dispersion occurs in multiple separate frequency regimes. The remarkable dependence on the sum phase is also shown for a strong probe field. On the other hand, when the sum of the two relative phases is fixed, the changes in the respective phases have no influence on the response of the medium.

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Self-assembled germanium nano-structures by laser-assisted oxidation Huang Wei-Qi (黄伟其), Liu Shi-Rong (刘世荣) Chinese Physics, 2006, 15 (2):  389-393.  DOI: 10.1088/1009-1963/15/2/026 Abstract ( 1021 )   PDF (244KB) ( 535 )   The investigation on the oxidation behaviour of Si$_{1-x}$Ge$_{x}$ alloys ($x$=0.05, 0.15, and 0.25) is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8--2.8nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by the low-temperature laser-assisted dry oxidation of Si$_{1 - x}$Ge$_{x}$ substrate. A new scanning method on the decline cross-section of the multiple-layer sample is adopted to measure the layer thickness and the composition. Some new peaks in photoluminescence (PL) spectra are discovered, which could be related to the nano-cap and the nano-particles of germanium. A suitable model and several new calculating formulae with the unrestricted Hartree--Fock--Roothaan (UHFR) method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.

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Evolution and stability of spatial solitons in a photorefractive two-wave mixing system Liu Jin-Song (刘劲松), Zhang Hui-Lan (张慧蓝), Zhang Guang-Yong (张光勇), Wang Cheng (王程) Chinese Physics, 2006, 15 (2):  394-402.  DOI: 10.1088/1009-1963/15/2/027 Abstract ( 1354 )   PDF (461KB) ( 598 )   The dynamical evolution and stability of bright dissipative holographic solitons in biased photorefractive materials in which the self-trapping beam obtains a gain from the pump beam via two-wave mixing has been investigated numerically. Results show that these solitons are stable relative to small perturbations. Adjusting some system parameters, such as the bias field and the angle between beams, can easily control the generation of such solitons. Potential applications in optical switches or repeaters are discussed.

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Waveguides induced by grey screening solitons Lu Ke-Qing (卢克清), Zhao Wei (赵卫), Yang Yan-Long (杨延龙), Zhang Mei-Zhi (张美志), Li Jin-Ping (李金萍), Liu Hong-Jun (刘红军), Zhang Yan-Peng (张彦鹏) Chinese Physics, 2006, 15 (2):  403-406.  DOI: 10.1088/1009-1963/15/2/028 Abstract ( 1081 )   PDF (228KB) ( 664 )   We investigate the properties of waveguides induced by one-dimensional grey screening solitons in biased photorefractive crystals. The results show that waveguides induced by grey screening solitons are always of single mode for all intensity ratios, i.e. the ratios between the peak intensity of the soliton and the dark irradiance. Our analysis indicates that the energy confined near the centre of the grey soliton and the propagation constant of the guided mode of the waveguide induced by the grey screening soliton increase monotonically with intensity ratio increasing. On the other hand, when the soliton greyness increases, the energy confined near the centre of the grey soliton and the propagation constant of the guided mode of the waveguide induced by the grey screening soliton decrease monotonically. Relevant examples are provided where photorefractive crystal is of the strontium barium niobate type.

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Formation mechanism of the low-frequency locally resonant band gap in the two-dimensional ternary phononic crystals Wang Gang (王刚), Liu Yao-Zong (刘耀宗), Wen Ji-Hong (温激鸿), Yu Dian-Long (郁殿龙) Chinese Physics, 2006, 15 (2):  407-411.  DOI: 10.1088/1009-1963/15/2/029 Abstract ( 1260 )   PDF (233KB) ( 320 )   The low-frequency band gap and the corresponding vibration modes in two-dimensional ternary locally resonant phononic crystals are restudied successfully with the lumped-mass method. Compared with the work of C. Goffaux and J. Sánchez-Dehesa (Phys. Rev. B 67 14 4301(2003)), it is shown that there exists an error of about 50% in their calculated results of the band structure, and one band is missing in their results. Moreover, the in-plane modes shown in their paper are improper, which results in the wrong conclusion on the mechanism of the ternary locally resonant phononic crystals. Based on the lumped-mass method and better description of the vibration modes according to the band gaps, the locally resonant mechanism in forming the subfrequency gaps is thoroughly analysed. The rule used to judge whether a resonant mode in the phononic crystals can result in a corresponding subfrequency gap is also verified in this ternary case.

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Propagation of acoustic wave in viscoelastic medium permeated with air bubbles Liang Bin (梁彬), Zhu Zhe-Min (朱哲民), Cheng Jian-Chun (程建春) Chinese Physics, 2006, 15 (2):  412-421.  DOI: 10.1088/1009-1963/15/2/030 Abstract ( 1157 )   PDF (324KB) ( 629 )   Based on the modification of the radial pulsation equation of an individual bubble, an effective medium method (EMM) is presented for studying propagation of linear and nonlinear longitudinal acoustic waves in viscoelastic medium permeated with air bubbles. A classical theory developed previously by Gaunaurd (Gaunaurd GC and überall H, J. Acoust. Soc. Am., 1978; 63: 1699--1711) is employed to verify the EMM under linear approximation by comparing the dynamic (i.e. frequency-dependent) effective parameters, and an excellent agreement is obtained. The propagation of longitudinal waves is hereby studied in detail. The results illustrate that the nonlinear pulsation of bubbles serves as the source of second harmonic wave and the sound energy has the tendency to be transferred to second harmonic wave. Therefore the sound attenuation and acoustic nonlinearity of the viscoelastic matrix are remarkably enhanced due to the system's resonance induced by the existence of bubbles.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Electron field emission from single-walled carbon nanotube nonwoven Song Li (宋礼), Liu Shuang (刘双), Zhang Geng-Min (张耿民), Liu Li-Feng (刘利峰), Ma Wen-Jun (马文君), Liu Dong-Fang (刘东方), Zhao Xiao-Wei (赵小伟), Luo Shu-Dong (罗述东), Zhang Zeng-Xing (张增星), Xiang Yan-Juan (向彦娟), Shen Jun (沈俊), Zhou Jian-Jun (周建军), Wang Gang (王刚), Zhou Wei-Ya (周维亚) Chinese Physics, 2006, 15 (2):  422-427.  DOI: 10.1088/1009-1963/15/2/031 Abstract ( 1317 )   PDF (430KB) ( 403 )   Field emission from single-walled carbon nanotube (SWNT) nonwoven has been investigated under high vacuum with different vacuum gaps. A low turn-on electric field of 1.05\,V/$\mu $m is required to reach an emission current density of 10 $\mu $A/cm$^{2}$. An emission current density of 10 mA/cm$^{2}$ is obtained at an operating electric field of 1.88\,V/$\mu $m. No current saturation is found even at an emission current of 5\,mA. With the vacuum gap increasing from 1 to 10 mm, the turn-on field decreases monotonically from 1.21 to 0.68\,V/$\mu $m, while the field amplification is augmented. The good field-emission behaviour is ascribed to the combined effects of the intrinsic field emission of SWNT and the waved topography of the nonwoven.

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Molecular dynamics study of the ternary compound Li3AlB2O6 Zhang Hong (张红), Wu Hai-Ying (吴海英), Chen Yu-Yu (陈钰钰), Cheng Xin-Lu (程新路) Chinese Physics, 2006, 15 (2):  428-431.  DOI: 10.1088/1009-1963/15/2/032 Abstract ( 1388 )   PDF (201KB) ( 476 )   A new compound with the same chemical composition as Li$_{3}$AlB$_{2}$O$_{6}$ but with a different x-ray powder diffraction pattern as reported before was synthesized and studied experimentally by M. He, Chen X L et al (J. Solid State Chem. 163, 369 (2002)), but there lacks first principles study on the structure of it. Using conjugant gradient (CG) molecule dynamics (MD) simulation with a full relaxation of the atomic positions and of the shape and size of the cell, the structure of Li$_{3}$AlB$_{2}$O$_{6}$ is studied from first principles. For the density functional, the local density approximation (LDA) and the generalized gradient approximation (GGA) forms are used respectively. Both the LDA and GGA results support the experimental structure of M. He et al. The result of MD simulation using GGA agrees with the experimental result much better. The energy bands are also studied, the band gap given by LDA and GGA are 5.65 eV, 5.34eV, respectively.

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X-ray diffraction study of effect of deposition conditions on $\alpha-\beta$ phase transition and stress evolution in sputter-deposited W coatings Wang Cong (王聪), Pascal Brault, Alain Pineau, Pascale Plantin, Anne-Lise Thomann Chinese Physics, 2006, 15 (2):  432-436.  DOI: 10.1088/1009-1963/15/2/033 Abstract ( 1118 )   PDF (411KB) ( 555 )   Pure W and W--Cu--W trilayer coatings were deposited on an Fe substrate by d.c. magnetron sputtering. The $\alpha -\beta$ phase evolution, intragranular stress evolution in sputter-deposited W layer were investigated by x-ray diffraction. They are directly related to the film microstructure, density and adhesion. Therefore, control of the film stress and phase component transition is essential for its applications. The phase component transition from $\beta$-W to $\alpha $-W and intragranular stress evolution from tensile to compressive strongly depend on the deposition parameters and can be induced by lowering Ar pressure and rising target power. The compressively stressed films with $\alpha $-W phase have a dense microstructure and high adhesion to Fe substrate.

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

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Adaptive split-step Fourier method for simulating ultrashort laser pulse propagation in photonic crystal fibres Li Shu-Guang (李曙光), Xing Guang-Long (邢光龙), Zhou Gui-Yao (周桂耀), Han Ying (韩颖), Hou Lan-Tian (侯蓝田), Hu Ming-Lie (胡明列), Li Yan-Feng (栗岩锋), Wang Qing-Yue (王清月) Chinese Physics, 2006, 15 (2):  437-443.  DOI: 10.1088/1009-1963/15/2/034 Abstract ( 1399 )   PDF (306KB) ( 1070 )   In this paper, the generalized nonlinear Schr?dinger equation (GNLSE) is solved by an adaptive split-step Fourier method (ASSFM). It is found that ASSFM must be used to solve GNLSE to ensure precision when the soliton self-frequency shift is remarkable and the photonic crystal fibre (PCF) parameters vary with the frequency considerably. The precision of numerical simulation by using ASSFM is higher than that by using split-step Fourier method in the process of laser pulse propagation in PCFs due to the fact that the variation of fibre parameters with the peak frequency in the pulse spectrum can be taken into account fully.

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Deposition and characterization of YBCO/CeO2/YSZ/CeO2 multilayers on biaxially textured Ni substrates "Wang Shu-Fang (王淑芳), Zhao Song-Qing (赵嵩卿), Liu Zhen (刘震), Zhou Yue-Liang (周岳亮), Chen Zheng-Hao (陈正豪), Lü Hui-Bin (吕惠宾), Jin Kui-Juan (金奎娟), Cheng Bo-Lin (程波林), Yang Guo-Zhen (杨国桢) Chinese Physics, 2006, 15 (2):  444-448.  DOI: 10.1088/1009-1963/15/2/035 Abstract ( 1470 )   CeO$_{2}$/YSZ/CeO$_{2}$ buffer layers were deposited on biaxially textured Ni substrates by pulsed laser deposition. The influence of the processing parameters on the texture development of the seed layer CeO$_{2}$ was investigated. Epitaxial films of YBCO were then grown in situ on the CeO$_{2}$/YSZ (yttria-stabilized ZrO$_{2}$)/CeO$_{2}$-buffered Ni substrates. The resulting YBCO conductors exhibited self-field critical current density $J_{\rm c}$ of more than 1 MA/cm$^{2}$ at 77K and superconducting transition temperature $T_{\rm c}$ of about 91K.

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Influence of magnetic field sweep rate on the hysteresis loops of Ni0.8Fe0.2/Fe0.5Mn0.5 exchange bias bilayer He Ke (何珂) Chinese Physics, 2006, 15 (2):  449-453.  DOI: 10.1088/1009-1963/15/2/036 Abstract ( 1276 )   PDF (235KB) ( 632 )   The influence of the magnetic field sweep rate on the hysteresis loops of exchange bias Ni$_{0.8}$Fe$_{0.2}$/Fe$_{0.5}$Mn$_{0.5}$ bilayers has been investigated with a vibrating sample magnetometer. It was found that the sweep rate of 13.6 kA/4$\pi $ms is high enough to bring about obvious changes in the hysteresis loops of the exchange bias bilayer. High sweep rate in the magnetization reversal stage enlarges the coercivity of the sample, while high sweep rate in the saturation state reduces the coercivity. The above phenomena were attributed to magnetic viscosity in the ferromagnetic layer enhanced by the interface exchange interaction and domain magnetization reversals assisted by thermal fluctuation in the antiferromagnetic layer respectively.

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Experimental study of noncontact ultrasonic motor with non-symmetrical electrode Yang Bin (杨斌), Liu Jing-Quan (刘景全), Chen Di (陈迪), Zhou Wei-Min (周伟民), Cai Bing-Chu (蔡炳初) Chinese Physics, 2006, 15 (2):  454-459.  DOI: 10.1088/1009-1963/15/2/037 Abstract ( 1085 )   PDF (298KB) ( 405 )   We have proposed a novel noncontact ultrasonic motor based on non-symmetrical electrode driving. The configuration of this electrode and the fabrication process of rotors are presented. Its vibration characteristics are computed and analysed by using the finite element method and studied experimentally. Good agreement between them is obtained. Moreover, it is also shown that this noncontact ultrasonic motor is operated in antisymmetric radial vibration mode of $B_{21}$ mode. The maximum revolution speed for three-blade and six-blade rotors are 5100 and 3700 r/min at an input voltage of 20V, respectively. Also, the noncontact high-speed revolution of the rotors can be realized by the parts of I, III of the electrode or II, IV of the electrode. The levitation distance between the stator and rotor is about 140$\mu $m according to the theoretical calculation and the experimental measurement.

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The influence of electronic transport across interface junction between Si substrate and the root of ZnO micro-prism on field emission performance Xuan Kai (宣凯), Yan Xiao-Hong (颜晓红), Ding Shu-Long (丁书龙), Yang Yu-Rong (杨玉荣), Xiao Yang (肖杨), Guo Zhao-Hui (郭朝辉) Chinese Physics, 2006, 15 (2):  460-465.  DOI: 10.1088/1009-1963/15/2/038 Abstract ( 1341 )   PDF (634KB) ( 217 )   ZnO micro-prisms are prepared on the p-type and n-type Si substrates, separately. The $I$--$V$ curves analysed by AFM show that the interface junctions between the ZnO micro-prisms and the p-type substrate and between the ZnO micro-prisms and the n-type Si substrate exhibit p--n junction behaviour and ohmic contact behaviour, respectively. The formation of the p--n heterojunction and ohmic contact is ascribed to the intrinsic n-type conduction of ZnO material. Better field emission performance (lower onset voltage and larger emission current) is observed from an individual ZnO micro-prism grown on the n-type Si substrate. It is suggested that the n-Si/n-ZnO interfacial ohmic contact benefits the electron emission; while the p-Si/n-ZnO interface heterojunction deteriorates the electron emission.