Table of contents

16 March 2003, Volume 12 Issue 3 Previous issue    Next issue

GENERAL

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New applications of the homogeneous balance principle Zhang Jin-Liang (张金良), Wang Yue-Ming (王跃明), Wang Ming-Liang (王明亮), Fang Zong-De (方宗德) Chinese Physics, 2003, 12 (3):  245-250.  DOI: 10.1088/1009-1963/12/3/301 Abstract ( 1886 )   PDF (209KB) ( 836 )   The homogeneous balance principle has been widely applied to the exploration of nonlinear transformation, exact solutions (especially solitary wave solution), dromion and similarity reduction to the nonlinear partial differential equations in mathematical physics. In this paper, we use the homogeneous balance principle to derive Bäcklund transformations for nonlinear partial differential equations that have more nonlinear terms and more highest-order partial derivative terms. With the aid of the Bäcklund transformations derived here, we could obtain exact solutions to the nonlinear partial differential equations. The Davey－Stewartson equation and the Nizhnik－Novikov－Veselov equation are considered as the examples.

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Quantum logic networks for probabilistic teleportation Liu Jin-Ming (刘金明), Zhang Yong-Sheng (张永生), Guo Guang-Can (郭光灿) Chinese Physics, 2003, 12 (3):  251-258.  DOI: 10.1088/1009-1963/12/3/302 Abstract ( 1276 )   PDF (264KB) ( 546 )   By means of the primitive operations consisting of single-qubit gates, two-qubit controlled-not gates, Von Neuman measurement and classically controlled operations, we construct efficient quantum logic networks for implementing probabilistic teleportation of a single qubit, a two-particle entangled state, and an N-particle entanglement. Based on the quantum networks, we show that after the partially entangled states are concentrated into maximal entanglement, the above three kinds of probabilistic teleportation are the same as the standard teleportation using the corresponding maximally entangled states as the quantum channels.

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Analysis of global exponential stability for a class of bi-directional associative memory networks Wang Hong-Xia (王宏霞), He Chen (何晨) Chinese Physics, 2003, 12 (3):  259-263.  DOI: 10.1088/1009-1963/12/3/303 Abstract ( 1265 )   PDF (216KB) ( 457 )   In real-time applications of bi-directional associative memory (BAM) networks, a global exponentially stable equilibrium is highly desired. The existence, uniqueness and global exponential stability for a class of BAM networks are studied in this paper, the signal function of neurons is assumed to be piece-wise linear from the engineering point of view. A very concise condition for the equilibrium of such a network being globally exponentially stable is derived, which makes the practical design of this kind of networks an easy job.

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Critical slowing down of the Gaussian spin system on diamond-type hierarchical lattices Zhu Jian-Yang (朱建阳), Zhu Han (朱涵) Chinese Physics, 2003, 12 (3):  264-270.  DOI: 10.1088/1009-1963/12/3/304 Abstract ( 1347 )   PDF (260KB) ( 456 )   Based on the single-spin transition critical dynamics, we have investigated the critical slowing down of the Gaussian spin model situated on the fractal family of diamond-type hierarchical lattices. We calculate the dynamical critical exponent z and the correlation-length critical exponent $\nu$ using the dynamical decimation renormalization-group technique. The result, together with some earlier ones, suggests us to conclude that on a wide range of geometries, z$\nu$=1 is the general relationship, while the two exponents depend on the specific structure. However, we have investigated for various lattices in an earlier paper, the system studied in this paper shows highly universal z=1/$\nu$=2 independent of the structure and the dimensionality.

ATOMIC AND MOLECULAR PHYSICS

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Influence of relaxation effects on probabilities of the 2s2p3 5S2－2s22p2 3P1，2 intercombination transitions in NII Yuan Ping (袁萍), Liu Xin-Sheng (刘欣生), Xie Lu-You (颉录有), Zhang Yi-Jun (张义军), Dong Chen-Zhong (董晨钟) Chinese Physics, 2003, 12 (3):  271-274.  DOI: 10.1088/1009-1963/12/3/305 Abstract ( 1600 )   PDF (225KB) ( 412 )   Transition probabilities of the 2s2p3 5S2－2s22p2 3P1,2 intercombination transitions in NII have been calculated by using a large-scale multiconfiguration Dirac－Fock method. In the calculation the most important effects of relativity, correlation, and relaxation are considered. From the calculated transition probabilities, the lifetime of the 2s2p3 5S2 metastable state is derived. The result is in excellent agreement with the latest experimental result. In the meantime the influence of anomalously strong relaxation effects on probabilities of the 2s2p3 5S2－2s22p2 3P1,2 lines in NII have been found.

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Silane photoabsorption spectra near the Si 2p thresholds: the geometry of Si 2p excited SiH4 Zhang Wei-Hua (张卫华), Xu Ru-Qing (许如清), Li Jia-Ming (李家明) Chinese Physics, 2003, 12 (3):  275-286.  DOI: 10.1088/1009-1963/12/3/306 Abstract ( 1617 )   PDF (339KB) ( 1206 )   Based on the multiple-scattering self-consistent-field method, we have studied the photoabsorption spectra near the Si 2p thresholds of silane. According to our calculations, the clear assignments of the inner-shell photoabsorption spectra are provided. In comparison with the high-resolution experimental spectra, the geometric structure of the Si 2p-excited SiH$_{4}^{**}$ is recommended to be of a $C_{2v}$ symmetry. More specifically, the Si 2p-excited SiH$_{4}^{**}$ have two bond lengths of 2.50 a.u. and another two bond lengths of 2.77 a.u., and the corresponding two bond angles are 104.0° and 112.5° respectively.

CLASSICAL AREAS OF PHENOMENOLOGY

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Quantum entanglement in a two-dimensional ion trap Wang Cheng-Zhi (王成志), Fang Mao-Fa (方卯发) Chinese Physics, 2003, 12 (3):  287-293.  DOI: 10.1088/1009-1963/12/3/307 Abstract ( 1335 )   PDF (260KB) ( 499 )   In this paper, we investigate the quantum entanglement in a two-dimensional ion trap system. We discuss the quantum entanglement between the ion and phonons by using reduced entropy, and that between two degrees of freedom of the vibrational motion along x and y directions by using quantum relative entropy. We discuss also the influence of initial state of the system on the quantum entanglement and the relation between two entanglements in the trapped ion system.

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Entropy squeezing for a two-level atom in the Jaynes－Cummings model with an intensity-depend coupling Li Chun-Xian (李春先), Fang Mao-Fa (方卯发) Chinese Physics, 2003, 12 (3):  294-299.  DOI: 10.1088/1009-1963/12/3/308 Abstract ( 1261 )   PDF (255KB) ( 686 )   We study the squeezing for a two-level atom in the Jaynes－Cummings model with intensity-dependent coupling using quantum information entropy, and examine the influences of the initial state of the system on the squeezed component number and direction of the information entropy squeezing. Our results show that, the squeezed component number depends on the atomic initial distribution angle, while the squeezed direction is determined by both the phases of the atom and the field for the information entropy squeezing. Quantum information entropy is shown to be a remarkable precision measure for atomic squeezing.

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Communications using multi-mode laser system based on chaotic synchronization Wu Liang (吴亮), Zhu Shi-Qun (朱士群) Chinese Physics, 2003, 12 (3):  300-304.  DOI: 10.1088/1009-1963/12/3/309 Abstract ( 1414 )   PDF (236KB) ( 551 )   The communication using chaotic synchronization between two multi-mode Nd:YAG lasers has been investigated numerically. The digital communication using multi-mode chaotic lasers is quite different from that using single mode lasers. By introducing a short break between two adjacent bits in the communication scheme, the digital signals can be successfully encoded into the spiky pulses and decoded through the subtraction of receiver output from the transmitted. Even when the two multi-mode lasers are not synchronized perfectly with certain deviations, the encoded digits can still be decoded correctly.

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Investigation on ultrafast third-order optical nonlinearity of metal(dmit)2/(mnt)2 charge transfer complexes Wang Shu-Feng (王树峰), Huang Wen-Tao (黄文涛), Liu Chu-Ling (刘春玲), Yang Hong (杨宏), Gong Qi-Huang (龚旗煌), Takashi Kobayashi, Tsuyoshi Takeyama, Masashi Horikiri, Yasuhiro F. Miura Chinese Physics, 2003, 12 (3):  305-309.  DOI: 10.1088/1009-1963/12/3/310 Abstract ( 1636 )   PDF (232KB) ( 594 )   We have investigated the transient third-order optical nonlinearity of the solutions of Metal(dmit)2/(mnt)2 salts in acetone by employing femtosecond optical Kerr gate measurement at 830 nm wavelength. An order of enhancement on the second-order hyperpolarizability is found for the above salts with central atoms of Cu and Ni. We have suggested an explanation for the enhancement based on the extension of electronic conjugation by the centring Cu or Ni atom.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Solving a superstructure from two-wavelength x-ray powder diffraction data － a simulation Chen Jian-Rong (陈建荣), Gu Yuan-Xin (古元新), Fan Hai-Fu (范海福) Chinese Physics, 2003, 12 (3):  310-314.  DOI: 10.1088/1009-1963/12/3/311 Abstract ( 1029 )   PDF (248KB) ( 404 )   Two different kinds of phase ambiguities are intrinsic in two-wavelength x-ray powder diffraction from acentric crystal structures having pseudo-translation symmetry. In a test calculation we have solved the problem for the first time by two different phasing procedures developed originally in single-crystal structure analysis. They are the direct method of breaking enantiomorphous phase ambiguity in protein crystallography and that of breaking translational phase ambiguity for superstructures. An artificial structure was used in the test, which is based on atomic coordinates of the known structure, SHAS (C$_5$H$_6$O$_5$N$_3$K), with the atom K replaced by Rb. The arrangement of Rb atoms possesses a subperiodicity of $t=(a+b+c)/2$. Two-wavelength synchrotron x-ray powder diffraction data were simulated with $\lambda_1=0.0816$nm and $\lambda_2=0.1319$nm. Overlapped reflections were uniformly decomposed at the beginning and redecomposed afterward when the partial-structure information became available. The enantiomorphous phase ambiguity was resolved only for reflections with $h+k+l$ even. Phases of reflections with $h+k+l$ odd were derived by the direct method of solving superstructures. A fragment was then obtained, which led to the complete structure in five cycles of Fourier iteration.

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Surface behaviour and undercooling in the liquid Ga-Bi binary system detected by optical second harmonic generation Wang Cong (王聪), Wang Tian-Min (王天民) Chinese Physics, 2003, 12 (3):  315-321.  DOI: 10.1088/1009-1963/12/3/312 Abstract ( 1242 )   PDF (237KB) ( 485 )   We employ an optical second harmonic generation(SHG) technique to investigate the surface behaviours at the liquid(solid)/vapour interface of the Ga-Bi binary metallic system. In a heating and cooling cycle between 280℃ and room temperature, there is no change of the SH-intensity in the heating process, whereas there exists an abrupt and abnormal change of the SH-intensity in the cooling process. It is interesting to find that a macroscopic Bi-rich solid layer is floating on the surface of the Ga-rich liquid phase just below the monotectic temperature (222℃±2℃) in the cooling process, in spite of the Bi-rich phase being heavier than the Ga-rich phase. On the other hand, different undercooling behaviours are observed at the surface and in the bulk. The behaviours of surface solidification and surface melting are different from those in the bulk.

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

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Fabrication and characteristics of lateral Ti/4H-SiC Schottky barrier diodes Wang Shou-Guo (王守国), Yang Lin-An (杨林安), Zhang Yi-Men (张义门), Zhang Yu-Ming (张玉明), Zhang Zhi-Yong (张志勇), Yan Jun-Feng (闫军锋) Chinese Physics, 2003, 12 (3):  322-324.  DOI: 10.1088/1009-1963/12/3/313 Abstract ( 1431 )   PDF (205KB) ( 555 )   This paper describes the fabrication and characteristics of the lateral Ti/4H-SiC Schottky barrier diodes (SBDs). SBDs are fabricated by nitrogen ion implantation into p-type 4H-SiC epitaxial layer. The implant depth profile is simulated using the Monte Carlo simulator TRIM. Measurements of the reverse I－V characteristics demonstrate a low reverse current, that is good enough for many SiC-based devices such as SiC metal-semiconductor field-effect transistors, and SiC static induction transistors. The parameters of the diodes are extracted from the forward I－V characteristics. The barrier height $\phi_{\rm b}$ of Ti/4H-SiC is 0.95 eV.

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Annealing characteristics of ultra-thin high-K HfO2 gate dielectrics Han De-Dong (韩德栋), Kang Jin-Feng (康晋锋), Lin Chang-Hai (林长海), Han Ru-Qi (韩汝琦) Chinese Physics, 2003, 12 (3):  325-327.  DOI: 10.1088/1009-1963/12/3/314 Abstract ( 1539 )   PDF (178KB) ( 535 )   Ultra-thin HfO2 gate-dielectric films were fabricated by ion-beam sputtering a sintered HfO2 target and subsequently annealed at different temperatures and atmospheres. We have studied the capacitance-voltage, current-voltage, and breakdown characteristics of the gate dielectrics. The results show that electrical characteristics of HfO2 gate dielectric are related to the annealing temperature. With increase annealing temperature, the largest value of capacitance decreases, the equivalent oxide thickness increases, the leakage current reduces, and the breakdown voltage decreases.

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Magnetic properties and magnetoresistance effect of Y1-xGdxMn6Sn6 (x=0－1) compounds Li Yun-Bao (李云宝), Zhang Shao-Ying (张绍英), Yao Jin-Lei (姚金雷), Zhang Li-Gang (张立刚), Shen Bao-Gen (沈保根) Chinese Physics, 2003, 12 (3):  328-331.  DOI: 10.1088/1009-1963/12/3/315 Abstract ( 1245 )   PDF (219KB) ( 413 )   The magnetic properties and magnetoresistance effect of Y1-xGdxMn6Sn6 (x=0－1) compounds have been investigated by magnetization and resistivity measurements in the applied field range (0－5 T). Compounds with x=0.4－1 display ferrimagnetic behaviours in the whole magnetic ordering temperature range, while compounds with x=0－0.2 display a field-induced metamagnetic transition, and the threshold fields decrease with increasing Gd content. The compounds with x=0.1－0.2 undergo an antiferromagnetic to ferromagnetic transition with increasing temperature. The cell-parameter a and c and cell-volume V of compounds (x=0－1) increase with increasing Gd content. It was found that the saturation magnetization Ms of the compounds (x=0.4－1) decreases, while the ordering points of the compounds (x=0－1)increase with increasing Gd content. A large MR effect was observed in the compound with x=0.2, and the maximum absolute value of MR at 5 K under 3 T is close to 19.3%.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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The ratio RT of the jet to the unbeamed luminosities for superluminal radio sources Fan Jun-Hui (樊军辉), Lin Rui-Guang (林瑞光) Chinese Physics, 2003, 12 (3):  332-335.  DOI: 10.1088/1009-1963/12/3/316 Abstract ( 1132 )   PDF (198KB) ( 422 )   Relativistic beaming model has been successfully used to explain the observational properties in active galactic nuclei. In this model the emissions are composed of two components, i.e. the boosted and the isotropic emissions. But how much is from each part is unknown. It has been assumed that the luminosity in the jet is proportional to the unbeamed in the comoving frame. However, the value of this ratio is not easy to determine. In this paper, we use the beaming model and the radio sources with superluminal motions to estimate the ratio, RT, for each source. We find RT= 0.044±0.02, which is consistent with that found by Orr and Browne.