Table of contents

01 February 2007, Volume 16 Issue 1 Previous issue    Next issue

RAPID COMMUNICATION

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Effective-mass theory for coupled quantum dots grown on (11N)-oriented substrates Li Shu-Shen(李树深) and Xia Jian-Bai(夏建白） Chinese Physics, 2007, 16 (1):  1-5.  DOI: 10.1088/1009-1963/16/1/001 Abstract ( 2055 )   PDF (132KB) ( 1453 )   The electronic structures of coupled quantum dots grown on (11N)-oriented substrates are studied in the framework of effective-mass envelope-function theory. The results show that the all-hole subbands have the smallest widths and the optical properties are best for the (113), (114), and (115) growth directions. Our theoretical results agree with the available experimental data. Our calculated results are useful for the application of coupled quantum dots in photoelectric devices.

GENERAL

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Complexiton solutions of the (2+1)-dimensional dispersive long wave equation Chen Yong(陈勇) and Fan En-Gui(范恩贵) Chinese Physics, 2007, 16 (1):  6-15.  DOI: 10.1088/1009-1963/16/1/002 Abstract ( 1674 )   PDF (127KB) ( 789 )   In this pager a pure algebraic method implemented in a computer algebraic system, named multiple Riccati equations rational expansion method, is presented to construct a novel class of complexiton solutions to integrable equations and nonintegrable equations. By solving the (2+1)-dimensional dispersive long wave equation, it obtains many new types of complexiton solutions such as various combination of trigonometric periodic and hyperbolic function solutions, various combination of trigonometric periodic and rational function solutions, various combination of hyperbolic and rational function solutions, etc.

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Density matrix for an electron confined in quantum dots under uniform magnetic field and static electrical field Pang Qian-Jun(庞乾骏) Chinese Physics, 2007, 16 (1):  16-22.  DOI: 10.1088/1009-1963/16/1/003 Abstract ( 1690 )   PDF (125KB) ( 588 )   Using unitary transformations, this paper obtains the eigenvalues and the common eigenvector of Hamiltonian and a new-defined generalized angular momentum (Lz) for an electron confined in quantum dots under a uniform magnetic field (UMF) and a static electric field (SEF). It finds that the eigenvalue of Lz  just stands for the expectation value of a usual angular momentum lz in the eigen-state. It first obtains the matrix density for this system via directly calculating a transfer matrix element of operator $\exp( -\beta H$) in some representations with the technique of integral within an ordered products (IWOP) of operators, rather than via solving a Bloch equation. Because the quadratic homogeneity of potential energy is broken due to the existence of SEF, the virial theorem in statistical physics is not satisfactory for this system, which is confirmed through the calculation of thermal averages of physical quantities.

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Establishing path integral in the entangled state representation for Hamiltonians in quantum optics Wang Ji-Suo(王继锁), Meng Xiang-Guo(孟祥国), Feng Jian(冯健), and Gao Yun-Feng(高云峰) Chinese Physics, 2007, 16 (1):  23-31.  DOI: 10.1088/1009-1963/16/1/004 Abstract ( 1682 )   PDF (127KB) ( 539 )   Based on two mutually conjugate entangled state representations, we establish the path integral formalism for some Hamiltonians of quantum optics in entangled state representations. The Wigner operator in the entangled state representation is presented. Its advantages are explained.

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Parallel numerical simulations for quantized vortices in Bose--Einstein condensates Huang Zhao-Hui(黄朝晖) and Wang De-Sheng(王德生) Chinese Physics, 2007, 16 (1):  32-37.  DOI: 10.1088/1009-1963/16/1/005 Abstract ( 1613 )   PDF (975KB) ( 573 )   We employ the parallel computing technology to study numerically the three-dimensional structure of quantized vortices of Bose--Einstein condensates. For anisotropic cases, the bending process of vortices is described in detail by the decrease of Gross--Pitaevskii energy. A completely straight vortex and the steady and symmetrical multiple-vortex configurations are obtained. We analyse the effect of initial conditions and angular velocity on the number and shape of vortices.

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Quantum dense coding using a peculiar tripartite entangled state Cheng Wei-Wen(程维文), Huang Yan-Xia(黄燕霞), Liu Tang-Kun(刘堂昆), and Li Hong(李宏) Chinese Physics, 2007, 16 (1):  38-41.  DOI: 10.1088/1009-1963/16/1/006 Abstract ( 1688 )   PDF (99KB) ( 651 )   Following a recent proposal ( Phys. Lett. A 346 (2005) 330) about quantum dense coding using a tripartite entangled GHZ state and W state, this paper proposes an experimentally feasible scheme for dense coding in cavity QED by using another peculiar tripartite entangled state. In the scheme the atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field, the successful probability of dense coding scheme with this peculiar tripartite entangled state equals 1.

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Time dependence of entropy flux and entropy production for a dynamical system driven by noises with coloured cross-correlation Xie Wen-Xian(谢文贤), Xu Wei(徐伟), and Cai Li(蔡力) Chinese Physics, 2007, 16 (1):  42-46.  DOI: 10.1088/1009-1963/16/1/007 Abstract ( 1562 )   PDF (143KB) ( 613 )   This paper shows the Fokker--Planck equation of a dynamical system driven by coloured cross-correlated white noises in the absence and presence of a small external force. Based on the Fokker--Planck equation and the definition of Shannon's information entropy, the time dependence of entropy flux and entropy production can be calculated. The present results can be used to explain the extremal behaviour of time dependence of entropy flux and entropy production in view of the dissipative parameter $\gamma$ of the system, coloured cross-correlation time $\tau$ and coloured cross-correlation strength $\lambda$.

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Strength dynamics of weighted evolving networks Wu Jian-Jun(吴建军), Gao Zi-You(高自友), and Sun Hui-Jun(孙会君) Chinese Physics, 2007, 16 (1):  47-50.  DOI: 10.1088/1009-1963/16/1/008 Abstract ( 1831 )   PDF (263KB) ( 577 )   In this paper, a simple model for the strength dynamics of weighted evolving networks is proposed to characterize the weighted networks. By considering the congestion effects, this approach can yield power law strength distribution appeared on the many real weighted networks, such as traffic networks, internet networks. Besides, the relationship between strength and degree is given. Numerical simulations indicate that the strength distribution is strongly related to the strength dynamics decline. The model also provides us with a better description of the real weighted networks.

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Passive magnetic shielded spin polarized electron source with optical electron polarimeter Ding Hai-Bing(丁海兵), Pang Wen-Ning(庞文宁), Liu Yi-Bao(刘义保), and Shang Ren-Cheng(尚仁成) Chinese Physics, 2007, 16 (1):  51-57.  DOI: 10.1088/1009-1963/16/1/009 Abstract ( 1443 )   PDF (464KB) ( 519 )   A new GaAs(100) spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel--iron--molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5×10-7 T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95cm distance through an 1mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8$\pm$3.5% measured with a He optical polarimeter.

NUCLEAR PHYSICS

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Study on `soft' and `hard' interactions in $\bar{\rm p}$p (pp) collisions using HIJING and PYTHIA Zhang Yi-Fei(张一飞), Huang Sheng-Li(黄胜利), Zhang Zi-Ping(张子平), and Wu Jian(伍健) Chinese Physics, 2007, 16 (1):  58-61.  DOI: 10.1088/1009-1963/16/1/010 Abstract ( 1551 )   PDF (135KB) ( 524 )   This paper presents a study on `hard' and `soft' interactions in $\bar{\text{p}}$p (pp) collisions using a phenomenological model of HIJING, the jet-cone reconstruction method is employed to select the `hard' and `soft' event sub-samples from minimum bias events. It is found that the HIJING model can reproduce the energy scaling behaviour of mean transverse momentum ($\langle$ pT$\rangle$) distributions of charged hadrons versus multiplicity (Nch) in `soft' events. From the PYTHIA simulation comparing with the HIJING model, the enhancement of the kaon and proton yields from `hard' interactions comparing with `soft' interactions is observed to be due to the mini-jets effect. These mechanisms responsible for the increase of charged hadron's $\langle$ pT$\rangle$ are different in `soft' and `hard' interactions.

ATOMIC AND MOLECULAR PHYSICS

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Electronic structure of ScN and YN:density-functional theory LDA and GW approximation calculations LüTie-Yu(吕铁羽) and Huang Mei-Chun(黄美纯) Chinese Physics, 2007, 16 (1):  62-66.  DOI: 10.1088/1009-1963/16/1/011 Abstract ( 1473 )   PDF (139KB) ( 699 )   The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of 0.142eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544\,eV respectively, as revealed by calculations performed using GW approximation.

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Lifetime of resonant state in a spherical quantum dot Li Chun-Lei(李春雷) and Xiao Jing-Lin(肖景林) Chinese Physics, 2007, 16 (1):  67-71.  DOI: 10.1088/1009-1963/16/1/012 Abstract ( 1560 )   PDF (133KB) ( 629 )   This paper calculates the lifetime of resonant state and transmission probability of a single electron tunnelling in a spherical quantum dot (SQD) structure by using the transfer matrix technique. In the SQD, the electron is confined both transversally and longitudinally, the motion in the transverse and longitudinal directions is separated by using the adiabatic approximation theory. Meanwhile, the energy levels of the former are considered as the effective confining potential. The numerical calculations are carried out for the SQD consisting of GaAs/InAs material. The obtained results show that the bigger radius of the quantum dot not only leads significantly to the shifts of resonant peaks toward the low-energy region, but also causes the lengthening of the lifetime of resonant state. The lifetime of resonant state can be calculated from the uncertainty principle between the energy half width and lifetime.

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Elastic cross sections for electron--carbon scattering Liu Jun-Bo(刘俊伯), Wang Yang(王旸), and Zhou Ya-Jun(周雅君) Chinese Physics, 2007, 16 (1):  72-76.  DOI: 10.1088/1009-1963/16/1/013 Abstract ( 1738 )   PDF (123KB) ( 547 )   We used the close-coupling optical (CCO) approach to investigate the open-shell carbon atom. The elastic cross sections have been presented at the energies below 90eV, and the present CCO results have been compared with other theoretical results. We found that polarization and the continuum states have significant contributions to the elastic cross sections. The present calculations show that the CCO method is capable of calculating electron scattering from open-shell atoms.

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Local structure changes of Cu55 cluster during heating Zhang Lin(张林), Zhang Cai-Bei(张彩碚), and Qi Yang(祁阳) Chinese Physics, 2007, 16 (1):  77-82.  DOI: 10.1088/1009-1963/16/1/014 Abstract ( 1879 )   PDF (655KB) ( 712 )   The structural relaxation of a cluster containing 55 atoms at elevated temperatures is simulated by molecular dynamics. The interatomic interactions are given by using the embedded atom method (EAM) potential. By decomposing the peaks of the radial distribution functions (RDFs) according to the pair analysis technique, the local structural patterns are identified for this cluster. During increasing temperature, structural changes of different shells determined by atom density profiles result in an abrupt increase in internal energy. The simulations show how local structural changes can strongly cause internal energy to change accordingly.

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High-order harmonic generation and multi-photon ionization of Na2 in laser fields Zhang Yan-Ping(张艳萍), Zhang Feng-Shou(张丰收), Meng Ke-Lai(蒙克来), and Xiao Guo-Qing(肖国青) Chinese Physics, 2007, 16 (1):  83-87.  DOI: 10.1088/1009-1963/16/1/015 Abstract ( 1687 )   PDF (615KB) ( 585 )   In this paper high-order harmonic generation (HHG) spectra and the ionization probabilities of various charge states of small cluster Na2 in the multiphoton regimes are calculated by using time-dependent local density approximation (TDLDA) for one-colour (1064 nm) and two-colour (1064 nm and 532 nm) ultrashort (25 fs) laser pulses. HHG spectra of Na2 have not the large extent of plateaus due to pronounced collective effects of electron dynamics. In addition, the two-colour laser field can result in the breaking of the symmetry and generation of the even order harmonic such as the second order harmonic. The results of ionization probabilities show that a two-colour laser field can increase the ionization probability of higher charge state.

CLASSICAL AREAS OF PHENOMENOLOGY

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Influence of spatiotemporal coupling on the capture-and-acceleration-scenario vacuum electron acceleration by ultrashort pulsed laser beam Lu Da-Quan(陆大全), Qian Lie-Jia(钱列加), Li Yong-Zhong(李永忠), and Fan Dian-Yuan(范滇元) Chinese Physics, 2007, 16 (1):  88-94.  DOI: 10.1088/1009-1963/16/1/016 Abstract ( 1535 )   PDF (191KB) ( 420 )   This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario (CAS) vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration TFWHM <5 T0, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.

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The influence of nickel dopant on the microstructure and optical properties of SnO2 nano-powders Liu Chun-Ming(刘春明), Fang Li-Mei(方丽梅), Zu Xiao-Tao(祖小涛), and Zhou Wei-Lie(周伟列) Chinese Physics, 2007, 16 (1):  95-99.  DOI: 10.1088/1009-1963/16/1/017 Abstract ( 1644 )   PDF (342KB) ( 978 )   The microstructure and optical properties of Ni-doped SnO2 nano-powders are studied in detail. By Ni-doping, not only the grain size reduces, but also the grain shape changes from nano-rods to spherical particles. The crystallization becomes better with annealing temperature increasing. The band gap energy decreases as nickel doping level increases. The sp--d hybridization and alloying effect due to amorphous SnO2-x phase should be responsible for the band gap narrowing effect. Nickel dopant does not change the photoluminescence (PL) peak positions.

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Diffraction of an ultrashort pulsed beam with arbitrary polarization state from a volume holographic grating in LiNbO3 crystals Wang Chun-Hua(王春花), Liu Li-Ren(刘立人), Yan Ai-Min(闫爱民), Zhou Yu(周煜), Liu De-An(刘德安), and Hu Zhi-Juan(胡志娟) Chinese Physics, 2007, 16 (1):  100-105.  DOI: 10.1088/1009-1963/16/1/018 Abstract ( 1587 )   PDF (190KB) ( 522 )   Based on a modified coupled wave theory of Kogelnik, we have studied the diffraction of an ultrashort pulsed beam with an arbitrary polarization state from a volume holographic grating in photorefractive LiNbO3 crystals. The results indicate that the diffracted intensity distributions in the spectral and temporal domains and the diffraction efficiency of the grating are both changed by the polarization state and spectral bandwidth of the input pulsed beam. A method is given of choosing the grating parameters and input conditions to obtain a large variation range of the spectral bandwidth of the diffracted pulsed beam with an appropriate diffraction efficiency. Our study presents a possibility of using a volume holographic grating recorded in anisotropic materials to shape a broadband ultrashort pulsed beam by modulating its polarization state.

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Nonclassical properties in the resonant interaction of a three level Λ-type atom with two-mode field in coherent state Wu Huai-Zhi(吴怀志) and Su Wan-Jun(苏万钧) Chinese Physics, 2007, 16 (1):  106-110.  DOI: 10.1088/1009-1963/16/1/019 Abstract ( 1274 )   PDF (210KB) ( 627 )   In this paper, we study the nonclassical properties of the electromagnetic field resulting from the interaction of a three-level Λ-type atom with a two-mode field initially in the coherent state, such as squeezing properties and sub-Poisson statistics. We show that the squeezing can be enhanced by selective atomic measurement.

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Entropy as a measure of the noise extent in a two-level quantum feedback controlled system Wang Tao-Bo(王涛波), Fang Mao-Fa(方卯发), and Hu Yao-Hua(胡要花) Chinese Physics, 2007, 16 (1):  111-117.  DOI: 10.1088/1009-1963/16/1/020 Abstract ( 1690 )   PDF (427KB) ( 525 )   By introducing the von Neumann entropy as a measure of the extent of noise, this paper discusses the entropy evolution in a two-level quantum feedback controlled system. The results show that the feedback control can induce the reduction of the degree of noise, and different control schemes exhibit different noise controlling ability, the extent of the reduction also related with the position of the target state on the Bloch sphere. It is shown that the evolution of entropy can provide a real time noise observation and a systematic guideline to make reasonable choice of control strategy.

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Teleportation of an n-bit one-photon and vacuum entangled GHZ cavity-field state Lai Zhen-Jiang(赖振讲), Fan Feng-Guo(范凤国), Zhu Gang-Yi(朱刚毅), and Bai Jin-Tao(白晋涛) Chinese Physics, 2007, 16 (1):  118-122.  DOI: 10.1088/1009-1963/16/1/021 Abstract ( 1721 )   PDF (108KB) ( 514 )   A scheme for teleporting an arbitrary n-bit one-photon and vacuum entangled Greenberger--Horne--Zeilinger (GHZ) state is proposed. In this scheme, the maximum entanglement GHZ state is used as a quantum channel. We find a method of distinguishing four Bell states just by detecting the atomic states three times, which is irrelevant to the qubit number of the state to be teleported.

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Stochastic resonance in a gain--noise model of a single-mode laser driven by pump noise and quantum noise with cross-correlation between real and imaginary parts under direct signal modulation Chen Li-Mei(陈黎梅), Cao Li(曹力), and Wu Da-Jin(吴大进) Chinese Physics, 2007, 16 (1):  123-129.  DOI: 10.1088/1009-1963/16/1/022 Abstract ( 1667 )   PDF (192KB) ( 528 )   Stochastic resonance (SR) is studied in a gain--noise model of a single-mode laser driven by a coloured pump noise and a quantum noise with cross-correlation between real and imaginary parts under a direct signal modulation. By using a linear approximation method, we find that the SR appears during the variation of signal-to-noise ratio (SNR) separately with the pump noise self-correlation time $\tau$, the noise correlation coefficient between the real part and the imaginary part of the quantum noise $\lambda$q , the attenuation coefficient $\gamma$  and the deterministic steady-state intensity $I_0$ . In addition, it is found that the SR can be characterized not only by the dependence of SNR on the noise variables of $\tau$ and $\lambda$q, but also by the dependence of SNR on the laser system variables of $\gamma$  and I0. Thus our investigation extends the characteristic quantity of SR proposed before.

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Stimulated emission and multi-peaked absorption in a four level N-type atom Wang Kai(王凯), Gu Ying (古英), and Gong Qi-Huang(龚旗煌) Chinese Physics, 2007, 16 (1):  130-136.  DOI: 10.1088/1009-1963/16/1/023 Abstract ( 1766 )   PDF (178KB) ( 582 )   Absorption and refraction of the inner transition F2$\leftrightarrow$ F3 of the closed four level N-type atom have been investigated under a weak field. The outer transitions F1 $\leftrightarrow$ F3 and F2 $\leftrightarrow$ F4 are resonantly interacted with drive field with frequency $\omega$c and Rabi frequency $\varOmega$c, and saturation field with $\omega$s and $\varOmega$s, respectively. For the suitable Rabi frequencies $\varOmega$c and $\varOmega$s, we obtain the Mollow absorption spectrum of probe field. The reason is that the drive field excites the atom to the upper level F3 and simultaneously the saturation field takes the atom out of the lower level F2, leading to the stimulated emission. Meanwhile, due to the dynamic energy splitting induced by the drive and saturation fields, the two- and four-peaked absorption spectra are observed. At the zero off-resonance detuning of probe field, we also find the transfer of dispersion from negative to positive with an increment of $\varOmega$s. Finally, the refractive index enhancement is predicted for a wide spectral region.

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Focusing properties of Gaussian Schell-model beams by an astigmatic aperture lens Pan Liu-Zhan(潘留占) and Ding Chao-Liang(丁超亮) Chinese Physics, 2007, 16 (1):  137-142.  DOI: 10.1088/1009-1963/16/1/024 Abstract ( 1565 )   PDF (165KB) ( 661 )   This paper studies the focusing properties of Gaussian Schell-model (GSM) beams by an astigmatic aperture lens. It is shown that the axial irradiance distribution, the maximum axial irradiance and its position of focused GSM beams by an astigmatic aperture lens depend upon the astigmatism of the lens, the coherence of partially coherent light, the truncation parameter of the aperture and Fresnel number. The numerical calculation results are given to illustrate how these parameters affect the focusing property.

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Vectorial Hermite--Laguerre--Gaussian beams beyond the paraxial approximation Wang Bei-Zhan(王备战), Zhao Zhi-Guo(赵志国), Lü Bai-Da(吕百达), and Duan Kai-Liang(段开椋) Chinese Physics, 2007, 16 (1):  143-147.  DOI: 10.1088/1009-1963/16/1/025 Abstract ( 2060 )   PDF (249KB) ( 548 )   Starting from the vectorial Rayleigh--Sommerfeld integrals, the free-space propagation expressions for vectorial Hermite--Laguerre--Gaussian (HLG) beams beyond the paraxial approximation are derived. The far-field expressions and the scalar paraxial results are given as special cases of our general expressions. The intensity distributions of vectorial nonparaxial HLG beams are studied and illustrated with numerical examples.

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Interactions of adjacent pulsating, erupting and creeping solitons Song Li-Jun(宋丽军), Li Lu(李录), and Zhou Guo-Sheng(周国生) Chinese Physics, 2007, 16 (1):  148-153.  DOI: 10.1088/1009-1963/16/1/026 Abstract ( 1637 )   PDF (1155KB) ( 542 )   This paper investigates the adjacent interactions of three novel solitons for the quintic complex Ginzburg--Landau equation, which are plain pulsating, erupting and creeping solitons. It is found that different performances are presented for different solitons due to isolated regions of the parameter space where they exist. For example, plain pulsating and erupting solitons exhibit mutual annihilation during collisions with the decrease of total energy, but for creeping soliton, the two adjacent pulses present soliton fusion without any loss of energy. Otherwise, the method for restraining the interactions is also found and it can suppress interactions between these two adjacent pulses effectively.

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A method to measure the Brillouin frequency shift of the medium through Brillouin amplification ratio Hasi Wu-Li-Ji(哈斯乌力吉), Lü Zhi-Wei(吕志伟), Li Qiang(李强), and He Wei-Ming(何伟明) Chinese Physics, 2007, 16 (1):  154-158.  DOI: 10.1088/1009-1963/16/1/027 Abstract ( 1573 )   PDF (128KB) ( 517 )   In order to measure the Brillouin frequency shift (BFS) of the medium, this paper proposes a method using mixtures in a two-cell stimulated Brillouin scattering system, which uses a medium to be measured as amplifier medium and a mixture medium as generator medium. The seed light from the generator gains effective amplification in the amplifier and the amplification ratio changes with the mixing fraction. Only when the BFS of the mixture medium is equal to that of the medium in the amplifier does the seed light obtain the maximum amplification ratio. The method has the advantage of independence of the wavelength of the incident light.

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Grey spatial solitons due to two-photon photorefractive effect Zhang Yu(张宇), Hou Chun-Feng(侯春风), and Sun Xiu-Dong(孙秀冬) Chinese Physics, 2007, 16 (1):  159-164.  DOI: 10.1088/1009-1963/16/1/028 Abstract ( 1468 )   PDF (128KB) ( 769 )   This paper predicts that grey spatial solitons can exist in two-photon photorefractive materials. In steady state and under appropriate external bias conditions, it obtains the grey spatial soliton solutions of the optical wave evolution equation. The intensity profile, phase distribution，and transverse velocity of these grey solitons are discussed.

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Quasistable bright dissipative holographic solitons in photorefractive two-wave mixing system Liu Jin-Song(刘劲松) Chinese Physics, 2007, 16 (1):  165-172.  DOI: 10.1088/1009-1963/16/1/029 Abstract ( 1526 )   PDF (709KB) ( 548 )   The dynamical evolution of both signal and pump beams are traced by numerically solving the coupled-wave equation for a photorefractive two-wave mixing system. The direct simulations show that, when the intensity ratio of the pump beam to the signal beam is large enough, the pump beam presents a common decaying behaviour without modulational instability (MI), while the signal beam can evolve into a quasistable spatial soliton within a regime in which the pump beam is depleted slightly. The larger the ratio is, the longer the regime is. Such quasistable solitons can overcome the initial perturbations and numerical noises in the course of propagation, perform several cycles of slow oscillation in intensity and width, and persist over tens of diffraction lengths. From physical viewpoints, these solitons actually exist as completely rigorous physical objects. If the ratio is quite small, the pump beam is apt to show MI, during which the signal beam experiences strong expansion and shrinking in width and a drastic oscillation in intensity, or completely breaks up. The simulations using actual experimental parameters demonstrate that the observation of an effectively stable soliton is quite possible in the proposed system.

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Frequency bands of negative refraction in finite one-dimensional photonic crystals Chen Yuan-Yuan(陈园园), Huang Zhao-Ming(黄肇明), Shi Jie-Long(施解龙), Li Chun-Fang(李春芳), and Wang Qi(王奇) Chinese Physics, 2007, 16 (1):  173-178.  DOI: 10.1088/1009-1963/16/1/030 Abstract ( 1619 )   PDF (214KB) ( 665 )   We have discussed theoretically the negative refraction in finite one-dimensional (1D) photonic crystals (PCs) composed of alternative layers with high index contrast. The frequency bands of negative refraction are obtained with the help of the photonic band structure, the group velocity and the power transmittance, which are all obtained in analytical expression. There shows negative transverse position shift at the endface when negative refraction occurs, which is analysed in detail.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Non-steady interaction of plasma with aircraft in its near wake region Hu Tao-Ping(胡涛平) and Luo Qing(罗青) Chinese Physics, 2007, 16 (1):  179-185.  DOI: 10.1088/1009-1963/16/1/031 Abstract ( 1517 )   PDF (196KB) ( 462 )   Non-steady interactions between plasmas and aircraft in its near wake region are investigated in detail. Under the non-static limit, a set of equations that describe these interactions are obtained. The results of the numerical simulation show that the cavitons of transverse plasmas are excited and density cavitons appear when the envelope of plasma becomes sufficiently intensive. This is very important for detecting the moving body that has a `stealth' characteristic.

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Role of on-board discharge in shock wave drag reduction and plasma cloaking Qiu Xiao-Ming(邱孝明), Tang De-Li (唐德礼), Sun Ai-Ping(孙爱萍), Liu Wan-Dong(刘万东), and Zeng Xue-Jun (曾学军) Chinese Physics, 2007, 16 (1):  186-192.  DOI: 10.1088/1009-1963/16/1/032 Abstract ( 1752 )   PDF (169KB) ( 628 )   In the present paper, a physical model is proposed for reducing the problem of the drag reduction of an attached bow shock around the nose of a high-speed vehicle with on-board discharge, to the problem of a balance between the magnetic pressure and gas pressure of plane shock of a partially ionized gas consisting of the environmental gas around the nose of the vehicle and the on-board discharge-produced plasma. The relation between the shock strength and the discharge-induced magnetic pressure is studied by means of a set of one-fluid, hydromagnetic equations reformed for the present purpose, where the discharge-induced magnetic field consists of the electron current (produced by the discharge)-induced magnetic field and the partially ionized gas flow-induced one. A formula for the relation between the above parameters is derived. It shows that the discharge-induced magnetic pressure can minimize the shock strength, successfully explaining the two recent experimental observations on attached bow shock mitigation and elimination in a supersonic flow during on-board discharge [Phys. Plasmas 9 (2002) 721 and Phys. Plasmas 7 (2000) 1345]. In addition, the formula implies that the shock elimination leaves room for a layer of higher-density plasma rampart moving around the nose of the vehicle, being favourable to the plasma radar cloaking of the vehicle. The reason for it is expounded.

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Characteristic parameters of diffusive supersonic radiation transport in low density materials Jiang Shao-En(江少恩), Yang Jia-Min(杨家敏), Zheng Zhi-Jian(郑志坚), and Ding Yong-Kun(丁永坤) Chinese Physics, 2007, 16 (1):  193-199.  DOI: 10.1088/1009-1963/16/1/033 Abstract ( 1450 )   PDF (142KB) ( 560 )   Diffusive heat waves play an important role in radiation hydrodynamics. In low density material, it may be possible that the radiative energy flux dominates the material energy flux and thus energy flow can be determined. In this paper by means of a simple algebraic method, the expressions characterizing the condition of diffusion approximation and supersonic transport of heat wave are found. In this case, the ratio of the radiative energy flux to the material energy flux is directly proportional to the product of Mach number M multiplied by optical depth $\tau$. And it may also be expressed by radiation temperature heating material. The material density and length may be determined in order to achieve above-mentioned conditions when the driven temperature and duration are given.

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The first results of divertor discharge and supersonic molecular beam injection on the HL-2A tokamak Yao Liang-Hua(姚良骅), Yuan Bau-Shan(袁保山), Feng Bei-Bin(冯北滨), Chen Cheng-Yuan(陈程远), Hong Wen-Yu(洪文玉), and Li Ying-Liang(李英量) Chinese Physics, 2007, 16 (1):  200-206.  DOI: 10.1088/1009-1963/16/1/034 Abstract ( 1599 )   PDF (482KB) ( 551 )   HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed divertor were simulated by the current filament code and they were in agreement with the diagnostic results in the divertor. Supersonic molecular beam injection (SMBI) system was first installed and tested on the HL-2A tokamak in 2004. In the present experiment low pressure SMBI fuelling on the HL-2A closed divertor was carried out. The experimental results indicate that the divertor was operated in the `linear regime' and during the period of SMB pulse injection into the HL-2A plasma the power density convected at the target plate surfaces was 0.4 times of that before or after the beam injection. It is a useful fuelling method for decreasing the heat load on the neutralizer plates of the divertor.

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A new method of asymmetric Abel inversion for magnetic equilibrium configuration state in tokamaks Tian Chong-Li(田崇利), Zhou Yan(周艳), Shi Zhong-Bing(石中兵), and Li Ying-Liang(李英量) Chinese Physics, 2007, 16 (1):  207-209.  DOI: 10.1088/1009-1963/16/1/035 Abstract ( 1717 )   PDF (105KB) ( 459 )   It is difficult to obtain the asymmetrical factor along the observation direction parallel to the plasma mid-plane when the detected radiation is also in the mid-plane. This paper considers the magnetic surfaces and Grad--Shafranov shift, and develops a new method for inverse asymmetric electron density information, during magnetic equilibrium configuration in a tokamak.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Computer simulation of symmetrical tilt grain boundaries in noble metals with MAEAM Zhang Jian-Min(张建民), Huang Yu-Hong(黄育红), Xu Ke-Wei(徐可为), and Ji Vincent Chinese Physics, 2007, 16 (1):  210-216.  DOI: 10.1088/1009-1963/16/1/036 Abstract ( 1590 )   PDF (202KB) ( 587 )   This paper reports that an atomic scale study of [$\bar{1}$10] symmetrical tilt grain boundary (STGB) has been made with modified analytical embedded atom method (MAEAM) for 44 planes in three noble metals Au, Ag and Cu. For each metal, the energies of two crystals ideally joined together are unrealistically high due to very short distance between atoms near the grain boundary (GB) plane. A relative slide between grains in the GB plane results in a significant decrease in GB energy and a minimum value is obtained at specific translation distance. The minimum energy of Cu is much higher than that of Ag and Au, while the minimum energy of Ag is slightly higher than that of Au. For all the three metals, the three lowest energies correspond to identical (111),  (113) and (331) boundary successively for two translations considered; from minimization of GB energy, these boundaries should be preferable in [$\bar{1}$10] STGB for noble metals. This is consistent with the experimental results. In addition, the minimum energy increases with increasing reciprocal planar coincidence density $\varSigma$, but decreases with increasing relative interplanar distance $d/a$.

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Elastic and thermodynamic properties of c-BN from first-principles calculations Hao Yan-Jun(郝彦军), Cheng Yan(程艳), Wang Yan-Ju(王艳菊), and Chen Xiang-Rong(陈向荣) Chinese Physics, 2007, 16 (1):  217-222.  DOI: 10.1088/1009-1963/16/1/037 Abstract ( 1488 )   PDF (166KB) ( 935 )   The elastic constants and thermodynamic properties of c-BN are calculated using the first-principles plane wave method with the relativistic analytic pseudopotential of the Hartwigen, Goedecker and Hutter (HGH) type in the frame of local density approximation and using the quasi-harmonic Debye model, separately. Moreover, the dependences of the normalized volume V/V0 on pressure P, as well as the bulk modulus B, the thermal expansion $\alpha$, and the heat capacity CV on pressure P and temperature T are also successfully obtained.

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Evolution of soliton-like train in Klein--Gordon lattice system Xia Qing-Lin(夏庆林), Yi Jian-Hong(易健宏), Peng Yuan-Dong(彭元东), Ye Tu-Ming(叶途明), Li Li-Ya(李丽娅), and Wang Hong-Zhong(王红忠) Chinese Physics, 2007, 16 (1):  223-227.  DOI: 10.1088/1009-1963/16/1/038 Abstract ( 1373 )   PDF (197KB) ( 488 )   This paper studies the evolution of wave in the system of a pure anharmonic lattice with a double well on-site potential by numerical calculation. It finds that an initial distribution of static or moving wave can evolve into two travelling soliton-like trains with contrary directions and a region of oscillation in this lattice system. It presents that some cases with cosine-square-shape and Gaussian-shape initial distribution of static or moving wave will produce ordered soliton-like train. Careful numerical observation shows that the centre oscillation region in this system may act as a resource of generating soliton-like train.

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Discrete gap breathers in a diatomic K2--K3--K4 chain with cubic nonlinearity Tian Qiang(田强) and Li Mi-Shan(李宓善) Chinese Physics, 2007, 16 (1):  228-235.  DOI: 10.1088/1009-1963/16/1/039 Abstract ( 1186 )   PDF (257KB) ( 529 )   The discrete gap breathers (DGBs) in a one-dimensional diatomic chain with K2--K3--K4 potential are analysed. Using the local anharmonicity approximation, the analytical investigation has been implemented. The dependence of the central amplitude of the discrete gap breathers on the breather frequency and the localization parameter are calculated. With increasing breather frequency, the DGB amplitudes decrease. As a function of the localization parameter, the central amplitude exhibits bistability, corresponding to the two branches of the curve $\omega = \omega (\zeta)$. With a nonzero cubic term, the HS mode of DGB profiles becomes weaker. With increasing $K_{3}$, the HS mode of DGB profiles becomes weaker and a bit narrower. For the LS mode, with increasing K3, the central particle amplitude becomes larger, and the DGB profile becomes much sharper. But, as k3 increases further, the central particle amplitude of the LS mode becomes smaller.

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

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An improved formula for the surface resistance of normal metals at millimetre wavelengths Zhang Xiao-Xia(张晓霞), Pan Wei(潘炜), and Liu Yong-Zhi(刘永智) Chinese Physics, 2007, 16 (1):  236-239.  DOI: 10.1088/1009-1963/16/1/040 Abstract ( 1336 )   PDF (105KB) ( 529 )   A number of researchers have reported discrepancies between surface resistance (SR) measurements and classical theoretical predictions in normal metals for millimetre wavelengths (MW). In this paper, a rigorous model is developed for analysing SR of normal metals. This model is based on quantum mechanical analysis of the spatial dispersion within the metal. We use the model to predict SR and eliminate the discrepancies between SR measurements and classical theoretical predictions in normal metals for MW. Moreover, we have compared the results of this model with that of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency- but also wave-vector-dependent for MW. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals for MW.

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Schottky barrier MOSFET structure with silicide source/drain on buried metal Li Ding-Yu(李定宇), Sun Lei(孙雷), Zhang Sheng-Dong (张盛东), Wang Yi(王漪), Liu Xiao-Yan(刘晓彦), and Han Ru-Qi(韩汝琦) Chinese Physics, 2007, 16 (1):  240-244.  DOI: 10.1088/1009-1963/16/1/041 Abstract ( 2031 )   PDF (387KB) ( 662 )   In this paper, we propose a novel Schottky barrier MOSFET structure, in which the silicide source/drain is designed on the buried metal (SSDOM). The source/drain region consists of two layers of silicide materials. Two Schottky barriers are formed between the silicide layers and the silicon channel. In the device design, the top barrier is lower and the bottom is higher. The lower top contact barrier is to provide higher on-state current, and the higher bottom contact barrier to reduce the off-state current. To achieve this, ErSi is proposed for the top silicide and CoSi2 for the bottom in the n-channel case. The 50 nm n-channel SSDOM is thus simulated to analyse the performance of the SSDOM device. In the simulations, the top contact barrier is 0.2e V (for ErSi) and the bottom barrier is 0.6eV (for CoSi2. Compared with the corresponding conventional Schottky barrier MOSFET structures (CSB), the high on-state current of the SSDOM is maintained, and the off-state current is efficiently reduced. Thus, the high drive ability (1.2mA/μm at Vds=1V, Vgs=2V) and the high Ion/Imin ratio (106) are both achieved by applying the SSDOM structure.

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Fabrication and characteristics of high-K HfO2 gate dielectrics on n-germanium Han De-Dong(韩德栋), Kang Jin-Feng(康晋锋), Liu Xiao-Yan(刘晓彦), Sun Lei(孙雷), Luo Hao(罗浩), and Han Ru-Qi(韩汝琦) Chinese Physics, 2007, 16 (1):  245-248.  DOI: 10.1088/1009-1963/16/1/042 Abstract ( 1553 )   PDF (126KB) ( 615 )   This paper reports that the high-K HfO2 gate dielectrics are fabricated on n-germanium substrates by sputtering Hf on Ge and following by a furnace annealing. The impacts of sputtering ambient, annealing ambient and annealing temperature on the electrical properties of high-K HfO2 gate dielectrics on germanium substrates are investigated. Experimental results indicate that high-K HfO2 gate dielectrics on germanium substrates with good electrical characteristics are obtained, the electrical properties of high-K HfO2 gate dielectrics is strongly correlated with sputtering ambient, annealing ambient and annealing temperature.

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Controlling optical responses through local dielectric resonance in nanometre metallic clusters Chen Liang-Liang(陈亮亮), Gu Ying(古英), Wang Li-Jin(王立金), and Gong Qi-Huang(龚旗煌) Chinese Physics, 2007, 16 (1):  249-257.  DOI: 10.1088/1009-1963/16/1/043 Abstract ( 1543 )   PDF (570KB) ( 490 )   Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances $\varepsilon$1 and $\varepsilon$2. Through varying the difference admittance ratio $\eta [ = (\varepsilon _2 - \varepsilon_0 ) / (\varepsilon _1 - \varepsilon _0 )]$, we find that their optical responses are determined by the local resonance. There is a blueshift of absorption peaks with the increase of $\eta$. Simultaneously, it is known that the absorption peaks will be redshifted by enlarging the cluster size. By adjusting the nano-metallic cluster geometry, size and admittances, we can control the positions and intensities of absorption peaks effectively. We have also deduced the effective linear optical responses of three-component composites $\varepsilon _{\rm e} = \varepsilon _0\bigl(1 + \sum_{n = 1}^{n_{\rm s} } [({{\gamma _{n_1 } + \eta \gamma_{n_2 } })/({\varepsilon _0 (s - s_{n} )})]} \bigr)$, and the sum rule of cross sections: $\sum_{n = 1}^{n_{\rm s} } {(\gamma _{n_1 } +\eta \gamma _{n_2 } ) = N_{h_1 } + N_{h_2 } } $, where $N_{h_1}$ and $N_{h_2}$ are the numbers of $\varepsilon _1 $ and $\varepsilon _2$ bonds along the electric field, respectively. These results may be beneficial to the study of surface plasmon resonances on a nanometre scale.

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Electric and magnetic behaviour in double doped La$_{2/3+4x/3}$Sr$_{1/3-4x/3}$Mn$_{1-x}$Mg$_{x}$O$_{3}$ Qu Zhe(屈哲), Pi Li(皮雳), Fan Ji-Yu(樊济宇), Tan Shun(谭舜), Zhang Bei (张贝), Zhang Meng(张锰), and Zhang Yu-Heng (张裕恒) Chinese Physics, 2007, 16 (1):  258-265.  DOI: 10.1088/1009-1963/16/1/044 Abstract ( 1543 )   PDF (485KB) ( 562 )   The double-doped La$_{2/3+4x/3}$Sr$_{1/3-4x/3}$Mn$_{1-x}$Mg$_{x}$O$_{3}$ samples with fixed Mn3+/Mn4+ ratio equal to 2/1 are investigated by means of magnetism and transport measurements. Phase separation is observed at temperature higher than Tconset for x=0.10 and 0.15. For x=0.10, rather strong phase separation induces drastic magnetic random potential and results in the localization of carriers. Thus, the variable-range hopping process dominates. For other samples, there is no or only weak phase separation above Tconset. Thus, thermal activation mechanism is responsible for the high temperature transport behaviour. For x=0.20 and 0.25, unexpected AFM behaviour is observed at low temperature. All these results are well understood by considering the special role of the ``double-doping".

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Edge method for measuring source spot-size and its principle Shi Jiang-Jun(施将君), Liu Jun(刘军), Liu Jin(刘进), and Li Bi-Yong(李必勇) Chinese Physics, 2007, 16 (1):  266-271.  DOI: 10.1088/1009-1963/16/1/045 Abstract ( 1072 )   PDF (439KB) ( 389 )   The edge method is used to measure the source spot-size. In this paper, the measuring principle and applying range are discussed. It is shown that the method can directly be used to measure the spot-size of either light source, or low-energy x-ray source, or x-ray source with an energy higher than 250 keV.

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Extended Holstein polaron model for charge transfer in dry DNA Liu Tao(刘涛), Wang Yi(王忆), and Wang Ke-Lin(汪克林) Chinese Physics, 2007, 16 (1):  272-276.  DOI: 10.1088/1009-1963/16/1/046 Abstract ( 1261 )   PDF (151KB) ( 461 )   The variational method is applied to the study of charge transfer in dry DNA by using an extended Holstein small polaron model in two cases: the site-dependent finite-chain discrete case and the site-independent continuous one. The treatments in the two cases are proven to be consistent in theory and calculation. Discrete and continuous treatments of Holstein model both can yield a nonlinear equation to describe the charge migration in an actual long-range DNA chain. Our theoretical results of binding energy Eb, probability amplitude of charge carrier $\phi$ and the relation between energy and charge--lattice coupling strength are in accordance with the available experimental results and recent theoretical calculations.