Table of contents

22 January 2004, Volume 13 Issue 1 Previous issue    Next issue

GENERAL

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Backlünd transformation and multiple soliton solutions for the (3+1)-dimensional Nizhnik－Novikov－Veselov equation Bai Cheng-Lin (白成林) Chinese Physics, 2004, 13 (1):  1-4.  DOI: 10.1088/1009-1963/13/1/001 Abstract ( 1291 )   PDF (139KB) ( 606 )   We develop an approach to construct multiple soliton solutions of the (3+1)-dimensional nonlinear evolution equation. We take the (3+1)-dimensional Nizhnik－Novikov－Veselov (NNV) equation as an example. Using the extended homogeneous balance method, one can find a Backlünd transformation to decompose the (3+1)-dimensional NNV into a set of partial differential equations. Starting from these partial differential equations, some multiple soliton solutions for the (3+1)-dimensional NNV equation are obtained by introducing a class of formal solutions.

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Extended Jacobi elliptic function method and its applications to (2+1)﹣dimensional dispersive long-wave equation Chen Yong (陈勇), Li Biao(李彪), and Zhang Hong-Qing Chinese Physics, 2004, 13 (1):  5-10.  DOI: 10.1088/1009-1963/13/1/002 Abstract ( 1401 )   PDF (173KB) ( 527 )   An extended Jacobi elliptic function method is proposed for constructing the exact double periodic solutions of nonlinear partial differential equations (PDEs) in a unified way. It is shown that these solutions exactly degenerate to the many types of soliton solutions in a limited condition. The Wu－Zhang equation (which describes the (2+1)﹣dimensional dispersive long wave) is investigated by this means and more formal double periodic solutions are obtained.

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The experiment on the saturation polarization of Rb vapour Huang Xiang-You (黄湘友), You Pei-Lin (游佩林), Du Wei-Min (杜为民) Chinese Physics, 2004, 13 (1):  11-13.  DOI: 10.1088/1009-1963/13/1/003 Abstract ( 1433 )   PDF (158KB) ( 449 )   A cylindrical capacitor containing rubidium vapour is made. The capacitance of it at different voltages is measured under a certain Rb vapour pressure. The experimental C－V curve shows that the saturation polarization of Rb vapour is easily observed. The experiment further supports the idea that the Rb atom has a large permanent electric dipole moment.

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Implementation of non-local multiple qubits controlled-not operation via partially entangled channels Chen Li-Bing (陈立冰), Lu Hong (路洪) Chinese Physics, 2004, 13 (1):  14-18.  DOI: 10.1088/1009-1963/13/1/004 Abstract ( 1238 )   PDF (162KB) ( 403 )   We propose two different schemes for probabilistic implementing a non-local multiple qubits controlled-not operation via partially entangled quantum channels. The overall physical resources required for accomplishing these schemes are different, and the successful implementation probabilities are also different.

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Research on high-Tc SQUID based non-destructive evaluation Wang Hui-Wu (王会武), Kong Xiang-Yan (孔祥燕), Ren Yu-Feng (任育峰), Yu Hong-Wei (于洪伟), Ding Hong-Sheng (丁红胜), Zhao Shi-Ping (赵士平), Chen Geng-Hua (陈赓华), Zhou Yue-Liang (周岳亮), Zhang Li-Hua (张利华), He Yu-Sheng (何豫生), Yang Qian-Sheng (杨乾声) Chinese Physics, 2004, 13 (1):  19-23.  DOI: 10.1088/1009-1963/13/1/005 Abstract ( 1255 )   PDF (1447KB) ( 426 )   A non-destructive evaluation system based on high-Tc dc-SQUID (superconducting quantum interference device) incorporating a gradient field excitation has been built. By using this system a 1mm-diameter hole at a depth of 2mm inside an aluminium plate at room temperature can be easily detected and imaged in an unshielded environment. The relation between the spatial resolution, or the smallest detectable flaw size, and experimental parameters is briefly analysed in terms of a simple metal ring model. The result shows that the spatial resolution depends strongly on the sensor-sample separation as well as on some other parameters, such as signal-to-noise ratio of excitation, excitation frequency and material conductivity.

ATOMIC AND MOLECULAR PHYSICS

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Kinetic energy release of diatomic and linear triatomic molecules in intense femtosecond laser fields Chen Jian-Xin (陈建新), Ma Ri (马日), Ren Hai-Zhen (任海振), Li Xia (李霞), Wu Cheng-Yin (吴成印), Yang Hong (杨宏), Gong Qi-Huang (龚旗煌) Chinese Physics, 2004, 13 (1):  24-29.  DOI: 10.1088/1009-1963/13/1/006 Abstract ( 1296 )   PDF (261KB) ( 482 )   The kinetic energy release of fragment ions produced by the interaction of femtosecond laser pulse radiation with diatomic and linear triatomic molecules N$_2$, CO, CO$_2$ and CS$_2$ is investigated. In the case of linear polarization, angles at which the kinetic energy release of ions has the maximum value are different from the alignment of molecules though the kinetic energy release of fragment atomic ions depends on the angle between the laser polarization vector and the detection axis of the time-of-flight. For the diatomic molecules, the critical internuclear distance in multielectron dissociative ionization with a circularly polarized light is larger than that with a linearly polarized light. For linear triatomic molecules, our data indicate that a concerted Coulomb explosion process is a universal phenomenon in the interaction of molecules with intense laser fields, even in the circularly polarized regime. During two C－O (or C－S) bonds breaking simultaneously, the C ion obtained larger energy in circular polarization than that in the linear polarization. Different variations of kinetic energy release between the diatomic and the linear triatomic molecules are discussed.

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The closed-orbit and the photoabsorption spectra of lithium atom in varying magnetic fields Wang De-Hua (王德华), Ding Shi-Liang (丁世良) Chinese Physics, 2004, 13 (1):  30-35.  DOI: 10.1088/1009-1963/13/1/007 Abstract ( 1286 )   PDF (282KB) ( 410 )   Using a simple analytic formula from closed orbit theory, we have calculated the photoabsorption spectra of Li atom in different magnetic fields. Closed orbits in the corresponding classical system have also been obtained for B=5.96T. We demonstrate schematically that the closed orbits disappear gradually with the decrease of the magnitude of the magnetic field. This gives us a good method to control the closed orbits in the corresponding system by changing the magnetic field, and thus changing the peaks in the photoabaorption spectra. By comparing the photoabsorption spectra of Li atom with those of hydrogen case, we find the core-scattered effects play an important role in multi-electron Rydberg atoms.

CLASSICAL AREAS OF PHENOMENOLOGY

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Dependence of electromagnetically induced transparency on temperature Xiao Feng (肖峰), Guo Rui-Min (郭瑞民), Li Lu-Ming (李路明), Yang Dong-Hai (杨东海), Chen Xu-Zong (陈徐宗) Chinese Physics, 2004, 13 (1):  36-39.  DOI: 10.1088/1009-1963/13/1/008 Abstract ( 1205 )   PDF (172KB) ( 531 )   We performed an experimental study on the dependence of the linewidth of electromagetically induced transparency (EIT) on the temperature of medium in a $\Lambda$-type configuration using caesium vapour. We found that the transparent window is narrowed in the EIT whose two ground levels are composed of two hyperfine levels, and broadened in the case when the two ground levels are degenerated Zeeman sublevels, as the temperature of vapour cell is increased. The explanation for the phenomena is given qualitatively.

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A unified incompressible lattice BGK model and its application to three-dimensional lid-driven cavity flow He Nan-Zhong (何南忠), Wang Neng-Chao (王能超), Shi Bao-Chang (施保昌), Guo Zhao-Li (郭照立) Chinese Physics, 2004, 13 (1):  40-46.  DOI: 10.1088/1009-1963/13/1/009 Abstract ( 1158 )   PDF (1028KB) ( 618 )   A unified lattice Bhatnagar－Gross－Krook (ILBGK) model iDdQq for the incompressible Navier－Stokes equation is presented. To test its efficiency, the lid-driven cavity flow in three-dimensional space for Reynolds number Re=3200 and span aspect ratio SAR=1, 2 and 3 is simulated in detail on a 48×48×(48×SAR) uniform lattice using the model. The test results agree well with those in previous experiments and numerical works and show the efficiency and strong numerical stability of the proposed ILBGK model.

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Lattice Boltzmann method for three-dimensional moving particles in a Newtonian fluid Fang Hai-Ping (方海平), Chen Shi-Yi Chinese Physics, 2004, 13 (1):  47-53.  DOI: 10.1088/1009-1963/13/1/010 Abstract ( 1386 )   PDF (263KB) ( 571 )   A lattice Boltzmann method is developed to simulate three-dimensional solid particle motions in fluids. In the present model, a uniform grid is used and the exact spatial location of the physical boundary of the suspended particles is determined using an interpolation scheme. The numerical accuracy and efficiency of the proposed lattice Boltzmann method is demonstrated by simulating the sedimentation of a single sphere in a square cylinder. Highly accurate simulation results can be achieved with few meshes, compared with the previous lattice Boltzmann methods. The present method is expected to find applications on the flow systems with moving boundaries, such as the blood flow in distensible vessels, the particle－flow interaction and the solidification of alloys.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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The dispersive properties of a dielectric-rod loaded waveguide immersed in a magnetized annular plasma Li Wei (李伟), Gong Ma-Li (巩马理), Wei Yan-Yu (魏彦玉), Xie Hong-Quan (谢鸿全) Chinese Physics, 2004, 13 (1):  54-59.  DOI: 10.1088/1009-1963/13/1/011 Abstract ( 1132 )   PDF (206KB) ( 558 )   Propagation properties of electromagnetic waves in a dielectric-rod waveguide immersed in a magnetized annular plasma are presented in this paper. The dispersion relations are derived and calculated. The results show that the dielectric-rod loading can make the structure less dispersive and the transmission frequency-band broadened.

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The KP and ZK equations for electrostatic waves with grain charge fluctuation Xue Ju-Kui (薛具奎), Lang He (郎和) Chinese Physics, 2004, 13 (1):  60-64.  DOI: 10.1088/1009-1963/13/1/012 Abstract ( 1285 )   PDF (172KB) ( 488 )   The propagation of three-dimensional nonlinear dust-acoustic and dust-Coulomb waves in unmagnetized/magnetized dusty plasmas consisting of electrons, ions, and charged dust particles is investigated. The grain charge fluctuation effect is also incorporated through the current balance equation. By using the perturbation method, a Kadomtsev－Petviashvili equation and a Zakharov－Kuznetsov equation governing the nonlinear waves in the unmagnetized and magnetized systems are obtained respectively. It has been shown that with the combined effects of grain charge fluctuation, the transverse perturbation, and the external magnetic field would modify the wave structures. Waves in those systems are unstable to the high-order long-wave perturbations.

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Influence of ion species ratio on grid-enhanced plasma source ion implantation Wang Jiu-Li (王久丽), Zhang Gu-Ling (张谷令), Liu Yuan-Fu (刘元富), Wang You-Nian (王友年), Liu Chi-Zi (刘赤子), Yang Si-Ze (杨思泽) Chinese Physics, 2004, 13 (1):  65-70.  DOI: 10.1088/1009-1963/13/1/013 Abstract ( 1184 )   PDF (312KB) ( 535 )   Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique to modify the inner-surface properties of a cylindrical bore. In this paper, a two-ion fluid model describing nitrogen molecular ions N$_2^+$ and atomic ions N$^+$ is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process, which is an extension of our previous calculations in which only N$_2^+$ was considered. Calculations are concentrated on the results of ion dose and impact energy on the target for different ion species ratios in the core plasma. The calculated results show that more atomic ions N$^+$ in the core plasma can raise the ion impact energy and reduce the ion dose on the target.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Optical vibration modes and electron－phonon interaction in ternary mixed crystals of polar semiconductors Liang Xi-Xia (梁希侠), Ban Shi-Liang (班士良) Chinese Physics, 2004, 13 (1):  71-81.  DOI: 10.1088/1009-1963/13/1/014 Abstract ( 1315 )   PDF (326KB) ( 594 )   Optical vibrations of the lattice and the electron－phonon interaction in polar ternary mixed crystals are studied in the framework of the continuum model of Born and Huang and the random-element-isodisplacement model. A normal-coordinate system to describe the optical vibration in ternary mixed crystals is correctly adopted to derive a new Fr?hlich-like Hamiltonian for the electron－phonon interaction including the unit-cell volume variation influence. The numerical results for the phonon modes, the electron－phonon coupling constants and the polaronic energies for several typical materials are obtained. It is verified that the nonlinearity of the electron－phonon coupling effects with the composition is essential and the unit-cell volume effects cannot be neglected for most ternary mixed crystals.

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Effect of nonstoichiometry on Raman scattering of VO2 films Yuan Hong-Tao (袁宏韬), Feng Ke-Cheng (冯克成), Wang Xue-Jin (王学进), Li Chao (李超), He Chen-Juan (何琛娟), Nie Yu-Xin (聂玉昕) Chinese Physics, 2004, 13 (1):  82-84.  DOI: 10.1088/1009-1963/13/1/015 Abstract ( 1449 )   PDF (162KB) ( 703 )   We report on Raman scattering of VO$_2$ films prepared by radio frequency magnetron sputtering under different conditions. Our investigations revealed that the dominated Raman peaks shift towards high frequency for both V-rich and O-rich VO$_2$ films, compared with the stoichiometry VO$_2$ films. The experimental evidence is presented and the cause for nonstoichiometry dependence of Raman spectra of VO$_2$ films is discussed.

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Chemisorption of Au on Si(001) surface Wei Shu-Yi (危书义), Wang Jian-Guang (汪建广), Ma Li (马丽) Chinese Physics, 2004, 13 (1):  85-89.  DOI: 10.1088/1009-1963/13/1/016 Abstract ( 1442 )   PDF (194KB) ( 516 )   The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B$_1$ site(bridge site), resulting in a Au－Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.

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

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Effect of preparation procedure on the magnetic and transport properties of double perovskite Sr2FeMoO6 Wang Jin-Hui (王锦辉), Yu Zhi (余智), Liu Gong-Qiang (刘公强), Du You-Wei (都有为) Chinese Physics, 2004, 13 (1):  90-94.  DOI: 10.1088/1009-1963/13/1/017 Abstract ( 1244 )   PDF (210KB) ( 379 )   Ordered and disordered double perovskite Sr$_2$FeMoO$_6$ ceramics have been investigated by powder x-ray diffraction, magnetic and transport measurements, as well as M?ssbauer spectroscopy. The heavily disordered sample can be acquired by annealing the ordered samples in argon. The annealing procedure affects not only the nature of grain boundaries but also the grain itself. The evidence of M?ssbauer spectra performed at 77 and 300 K indicates that there exist small oxygen deficient clusters of SrFeO$_{3-y}$ in the disordered sample. The paramagnetic Fe$^{4+}$ and Fe$^{3+}$ ions in the compound subsist down to 77 K and the ratio of Fe$^{4+}$/Fe$^{3+}$ increases with decreasing temperature.

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Transmission of electron through an Aharonov－Bohm interferometer with a quantum dot in Coulomb blockade regime Sun Ke-Wei (孙科伟), Xiong Shi-Jie (熊诗杰) Chinese Physics, 2004, 13 (1):  95-99.  DOI: 10.1088/1009-1963/13/1/018 Abstract ( 1362 )   PDF (200KB) ( 520 )   We calculate conductance of an Aharonov－Bohm (AB) interferometer for which a single-level quantum dot in the Coulomb blockade regime is embedded in one of its arms. Using the Schr?dinger equations and taking into account the Coulomb interaction on the dot, we calculate conductance G as a function of flux $\phi$ threaded through the ring and as a function of gate voltage V applied to the dot. It is found that the AB oscillations of $G(\phi)$ depend on the particle occupation on the dot, controlled by V. If the system is closed, there is no loss of particles, $G(\phi)$ is periodic and $G(\phi)=G(-\phi)$, satisfying the Onsager relation. In this case $G(\phi)$ can reach its maximum value, $2e^2/h$, at the resonance. When the system is open, one has $G(\phi)≠G(-\phi)$, $G(\phi)$ yields a phase shift which depends on the loss rate of electrons in this open system.

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Development of 1.3GHz high-T-c rf SQUID Liu Xin-Yuan (刘新元), Xie Fei-Xiang (谢飞翔), Meng Shu-Chao (孟树超), Dai Yuan-Dong (戴远东), Li Zhuang-Zhi (李壮志), Ma Ping (马平), Yang Tao (杨涛), Nie Rui-Juan (聂瑞娟), Wang Fu-Ren (王福仁), Chinese Physics, 2004, 13 (1):  100-104.  DOI: 10.1088/1009-1963/13/1/019 Abstract ( 1069 )   PDF (218KB) ( 499 )   A new high-Tc (HTc) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HTc coplanar superconducting resonator and a large-area HTc superconducting film concentrator. We have achieved in the 1.3GHz HTc rf SQUID system a minimal flux noise of $2.5×10^{-5}\varPhi_0/\sqrt{\rm Hz}$ and a magnetic field sensitivity of 38fT/$\sqrt{\rm Hz}$ in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm2 substrate is 1.35mm2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HTc rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.

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Monte Carlo simulation of magnetic nanostructured thin films Guan Zhi-Qiang (关治强), Yutaka Abe, Jiang Dong-Hua (姜冬华), Lin Hai (林海), Yoshitake Yamazaki, Wu Chen-Xu (吴晨旭) Chinese Physics, 2004, 13 (1):  105-110.  DOI: 10.1088/1009-1963/13/1/020 Abstract ( 1197 )   PDF (647KB) ( 523 )   Using Monte Carlo simulation, we have compared the magnetic properties between nanostructured thin films and two-dimensional crystalline solids. The dependence of nanostructured properties on the interaction between particles that constitute the nanostructured thin films is also studied. The result shows that the parameters in the interaction potential have an important effect on the properties of nanostructured thin films at the transition temperatures.

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Transient saturation absorption spectroscopy excited near the band gap at high excitation carrier density in GaAs Wu Song-Jiang (吴松江), Wang Dan-Ling (王丹翎), Jiang Hong-Bing (蒋红兵), Yang Hong (杨宏), Gong Qi-Huang (龚旗煌), Ji Ya-Lin (季亚林), Lu Wei (陆卫) Chinese Physics, 2004, 13 (1):  111-114.  DOI: 10.1088/1009-1963/13/1/021 Abstract ( 1258 )   PDF (218KB) ( 424 )   Transient saturation absorption spectroscopy in GaAs thin films was investigated using femtosecond pump and supercontinuum probe technique at excitation densities higher than $1\times10^{19}$cm$^{-3}$. The Coulomb enhancement factor of the electron－hole plasma results in a spectrum hole at the pump wavelength. Two distinct transmission peaks at two sides of the pump wavelength are observed, arising from the bleaching of transitions from the heavy- and light-hole bands to the conduction band. The dynamic process of the transient saturation absorption is fitted using a bi-exponential function. The fast decay process is dominated by the carrier-phonon scattering and the slow process may be attributed to the electron－hole recombination.

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Comprehensive research about the cooperative up-conversion luminescence of the ytterbium-doped oxyfluoride vitroceramics Chen Xiao-Bo (陈晓波), Song Zeng-Fu (宋增福) Chinese Physics, 2004, 13 (1):  115-124.  DOI: 10.1088/1009-1963/13/1/022 Abstract ( 1332 )   PDF (313KB) ( 428 )   The cooperative up-conversion blue luminescence of Yb$^{3+}$ ion-doped oxyfluoride vitroceramic material (Yb:FOV) and the influence of co-doped Ho$^{3+}$ ion, when excited by a 960 nm diode-laser, are studied in this paper. A strong blue 479.1 nm up-conversion luminescence of the Yb:FOV material is discovered. It is found that the 479.1 nm luminescence results from the cooperative up-conversion of the coupled states of the Yb$^{3+}$－Yb$^{3+}$ clusters formed by two adjacent Yb$^{3+}$ ions. The measured cooperative up-conversion luminescence main peak 479.1 nm of this paper is different from the characteristic fluorescence main peak of the Tb$^{3+}$ ion positioned at about 495－504 nm wave-range. Our result coincides with all the published correct papers, whose cooperative up-conversion luminescence main peaks of the direct Yb$^{3+}$－Yb$^{3+}$ clusters are all positioned at about 476－480 nm wave-range. All of these indicate that the large cooperative up-conversion blue luminescence of the direct Yb$^{3+}$－Yb$^{3+}$ clusters discovered in this paper is stable. It further proves that the cooperative up-conversion green luminescence may result from the Yb$^{3+}$-Tb$^{3+}$ cooperative effect. In particular, the original work of this paper improves considerably on the traditional concept by the experimental facts that the blue 479.1 nm cooperative up-conversion luminescence strength of Yb(5):FOV is 230 times greater than that of fluoride glass Yb(3):ZBLAN. This is a great development to meet the practical requirements for blue up-conversion luminescence strength. This result indicates that the large cooperative up-conversion blue luminescence could be achieved excellently by using a suitable material, such as oxyfluoride vitroceramic, which provides a better chance to form better Yb$^{3+}$－Yb$^{3+}$ clusters and has less relaxation to keep the more efficient up-conversion luminescence. It is also found that impurities seriously reduce the cooperative up-conversion luminescence intensity due to the cross-relaxation from the Yb$^{3+}$－Yb$^{3+}$ clusters, which means that the cooperative up-conversion blue luminescence could be further improved by pure Yb$^{3+}$ ion-doped materials that have as few impurities as possible to reduce the cross-relaxation. The large cooperative up-conversion blue luminescence of Yb(5):FOV also comes from its higher concentration (5 mol%) of activator Yb$^{3+}$ ion which acts well because the cooperative up-conversion blue luminescence intensity varies linearly against the square of the concentration of Yb$^{3+}$ ions in the range of 0.5－5 mol%. In summary, the great improvement of our work on cooperative up-conversion blue luminescence results from the comprehensive enhancement of the factors of better-coupled chance of the Yb$^{3+}$－Yb$^{3+}$ clusters, less cross-relaxation, better concentration contribution of Yb$^{3+}$ activator, non-saturation, and better up-conversion luminescence efficiency.