Table of contents

16 February 2003, Volume 12 Issue 2 Previous issue    Next issue

GENERAL

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New periodic solutions to a generalized Hirota－Satsuma coupled KdV system Yan Qing-You (闫庆友), Zhang Yu-Feng (张玉峰), Wei Xiao-Peng (魏小鹏) Chinese Physics, 2003, 12 (2):  131-135.  DOI: 10.1088/1009-1963/12/2/301 Abstract ( 1026 )   PDF (194KB) ( 751 )   Using expansions in terms of the Jacobi elliptic cosine function and third Jacobi elliptic function, some new periodic solutions to the generalized Hirota－Satsuma coupled KdV system are obtained with the help of the algorithm Mathematica. These periodic solutions are also reduced to the bell-shaped solitary wave solutions and kink-shape solitary solutions. As special cases, we obtain new periodic solution, bell-shaped and kink-shaped solitary solutions to the well-known Hirota－Satsuma equations.

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Bound states of Klein－Gordon equation for ring-shaped harmonic oscillator scalar and vector potentials Qiang Wen-Chao (强稳朝) Chinese Physics, 2003, 12 (2):  136-139.  DOI: 10.1088/1009-1963/12/2/302 Abstract ( 1228 )   PDF (197KB) ( 623 )   Solving Klein－Gordon equation with equal ring-shaped harmonic oscillator scalar and vector potentials, we obtain the exact normalized bound-state wavefunction and energy equation.

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Cyclic integrals and reduction of rotational relativistic Birkhoffian system Luo Shao-Kai (罗绍凯) Chinese Physics, 2003, 12 (2):  140-143.  DOI: 10.1088/1009-1963/12/2/303 Abstract ( 1405 )   PDF (200KB) ( 496 )   The order reduction method of the rotational relativistic Birkhoffian equations is studied. For a rotational relativistic Birkhoffian system, the cyclic integrals can be found by using the perfect differential method. Through these cyclic integrals, the order of the system can be reduced. If the rotational relativistic Birkhoffian system has a cyclic integral, then the Birkhoffian equations can be reduced at least two degrees and the Birkhoffian form can be kept. An example is given to illustrate the application of the results.

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Explicit exact solitary wave solutions for generalized symmetric regularized long-wave equations with high-order nonlinear terms Zhang Wei-Guo (张卫国) Chinese Physics, 2003, 12 (2):  144-148.  DOI: 10.1088/1009-1963/12/2/304 Abstract ( 995 )   PDF (205KB) ( 451 )   In this paper, we have obtained the bell-type and kink-type solitary wave solutions of the generalized symmetric regularized long-wave equations with high-order nonlinear terms by means of proper transformation and undetermined assumption method.

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Controlling hyperchaos in erbium-doped fibre laser Zhang Sheng-Hai (张胜海), Shen Ke (沈柯) Chinese Physics, 2003, 12 (2):  149-153.  DOI: 10.1088/1009-1963/12/2/305 Abstract ( 1198 )   PDF (255KB) ( 603 )   The dual-ring erbium-doped fibre laser shows a hyperchaotic behaviour under some conditions. The hyperchaotic behaviour can be well controlled to enter into periodicity by modulating the pumping in one of the two rings. The period is different for different modulation index at the same modulation frequency, or for different modulation frequency at the same modulation index.

ATOMIC AND MOLECULAR PHYSICS

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Electronic state and potential energy function for UH2+ Wang Hong-Yan (王红艳), Zhu Zheng-He (朱正和), Meng Da-Qiao (蒙大桥), Wang Xiao-Lin (汪小琳) Chinese Physics, 2003, 12 (2):  154-158.  DOI: 10.1088/1009-1963/12/2/306 Abstract ( 1224 )   PDF (232KB) ( 499 )   Our theoretical study on UH2+X4$\Sigma$) using a density functional method shows that its potential energy curve has both minimum and maximum, which is the so-called "energy trapped" molecules. This sort of potential maximum is mainly caused by Coulomb repulsion. We have proposed the perturbation effect of ionic charges to explain the existence of the potential maximum for diatomic ions, and derived an analytic potential energy function has been derived, and the force constants and spectroscopic data are obtained. Finally, the vertical ionization potential for UH2+has been calculated as well.

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Application of the second-order ground-state correlation and random-phase approximation on photoionization cross section of manganese Lu Peng-Fei (芦鹏飞), Liu Jin-Chao (刘锦超), Yang Xiang-Dong (杨向东), Ma Xiao-Guang (马晓光) Chinese Physics, 2003, 12 (2):  159-163.  DOI: 10.1088/1009-1963/12/2/307 Abstract ( 1105 )   PDF (224KB) ( 377 )   Using the many-body perturbation theory, we have calculated the photoionization cross section of 3p and 3d subshells of the neutral manganese, and discussed the second-order ground-state correlation and random-phase approximation correlations in detail. This is the first theoretical calculation for manganese as far as we know. Our calculated results are more consistent with the experimental results than those given by other methods in the literature.

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Time dependent density functional calculation of plasmon response in clusters Wang Feng (王锋), Zhang Feng-Shou (张丰收), Eric Suraud Chinese Physics, 2003, 12 (2):  164-168.  DOI: 10.1088/1009-1963/12/2/308 Abstract ( 1229 )   PDF (244KB) ( 463 )   We have introduced a theoretical scheme for the efficient description of the optical response of a cluster based on the time-dependent density functional theory. The practical implementation is done by means of the fully fledged time-dependent local density approximation scheme, which is solved directly in the time domain without any linearization. As an example we consider the simple Na2 cluster and compute its surface plasmon photoabsorption cross section, which is in good agreement with the experiments.

CLASSICAL AREAS OF PHENOMENOLOGY

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A theoretical study about the chirped pulse amplification laser Lu Xing-Qiang (卢兴强), Fan Dian-Yuan (范滇元) Chinese Physics, 2003, 12 (2):  169-173.  DOI: 10.1088/1009-1963/12/2/309 Abstract ( 1220 )   PDF (220KB) ( 473 )   Starting from the Maxwell's equation, and using the resonant-dipole equation together with the multilevel rate equations which take the effects of energy relaxation into consideration, we have derived a more realistic numerical model of the chirped pulse amplification for an ultra-broad band width laser amplifier. Numerical simulations of this model show that both the intensity profile and the energy fluence of the amplified chirped pulse are closely connected with the two relaxation effects: the relaxation of the thermalization among the components of the laser multiplets and the depletion of the lower laser level. The results are valuable for the design of ultra-broad bandwidth chirped pulse amplification lasers.

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Effect of four-wave mixing on electromagnetically induced transparency in $\Lambda$-type system with a two-photon probe field Zhang Yan-Liang (张衍亮), Jiang Li (江丽), Sun Zhen-Rong (孙真荣), Ding Liang-En (丁良恩), Wang Zu-Geng (王祖赓) Chinese Physics, 2003, 12 (2):  174-177.  DOI: 10.1088/1009-1963/12/2/310 Abstract ( 1358 )   PDF (220KB) ( 458 )   Using density matrix equation, we calculate analytically as well as numerically the effect of the four-wave mixing (FWM) field on electromagnetically induced transparency (EIT) in the rubidium 5S$_{1/2}$-5P$_{3/2}$-5D$_{5/2}$ $\Lambda$-type system with a two-photon probe field. The calculated results are in good agreement with Fulton's experimental results in 1995 Phys. Rev. A 52 2302.

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Controlling the gain shape of Er3+-doped fluorozirconate fibre amplifier by a coherent field Zhang Hui-Fang (张惠芳), Wu Jin-Hui (吴金辉), Gao Jin-Yue (高锦岳) Chinese Physics, 2003, 12 (2):  178-183.  DOI: 10.1088/1009-1963/12/2/311 Abstract ( 1055 )   PDF (236KB) ( 427 )   We proposed a four-level system to explore the quantum interference effects on optical amplification. We found that the gain of the probe, including positions and values of gain peaks, can be adjusted by changing the coherent field and the incoherent pumping. At the same time, we can also modify the absorption profile of electromagnetically induced transparency by the incoherent pump. The results provide a method to flatten the gain of Erbium-doped fibre amplifiers.

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Patterns in passive optical systems with boundary effects Li Chun-Ping (李春萍), Shen Ke (沈柯) Chinese Physics, 2003, 12 (2):  184-188.  DOI: 10.1088/1009-1963/12/2/312 Abstract ( 1020 )   PDF (236KB) ( 388 )   Pattern formation is closely related to system boundary conditions in nonlinear dynamic systems, apart from the system control parameters. To avoid complexity, system boundary conditions are usually considered to be infinite or periodic, and the initial conditions spatially homogeneous. But it is not always the case in real situations, or sometimes periodic boundary conditions are not exact. To show the important and interesting boundary effects in real pattern formation, we suggest a simple universal boundary condition in a typical optical pattern formation system. Numerical simulations of the passive optical system show that pattern characteristics such as distribution symmetry, peak number, structure strength, evolution course and stability are all greatly influenced by the system boundary conditions.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Bursty events and incremental diffusion in a local diffusion and multi-scale convection system Xu Guo-Sheng (徐国盛), Wan Bao-Nian (万宝年), Song Mei (宋梅) Chinese Physics, 2003, 12 (2):  189-197.  DOI: 10.1088/1009-1963/12/2/313 Abstract ( 1141 )   PDF (348KB) ( 420 )   A one-dimensional cellular automaton is defined without the critical gradient rule ($\Delta h>\Delta h_c$) which is essential to the existence of avalanches in self-organized criticality (SOC) models. Instead, only the local diffusion rule is used, however, the characteristics of SOC, such as the bursty behaviour, power-law decay in fluctuation spectra, self-similarity over a broad range of scales and long-time correlations, are still observed in these numerical experiments. This numerical model is established to suggest that the bursty events and the incremental diffusion observed universally in fusion experiments do not necessarily imply the submarginal dynamics.

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The reliability of measurements on electron energy distribution function in silane rf glow discharges Lin Kui-Xun (林揆训), Lin Xuan-Ying (林璇英), Chi Ling-Fei (池凌飞), Yu Chu-Ying (余楚迎), Yao Ruo-He (姚若河), Yu Yun-Peng (余云鹏) Chinese Physics, 2003, 12 (2):  198-203.  DOI: 10.1088/1009-1963/12/2/314 Abstract ( 1416 )   PDF (265KB) ( 501 )   Electron energy distribution function (EEDF) is a key parameter of plasmas, which is directly proportional to the second derivative of the probe I-V characteristics. Because of an amplifying effect of unavoidable noises in the experimental probe I-V curves during the derivation process, the experimental I-V curves should be smoothed before performing the numerical derivation. This paper investigates the effect of adjustable factors used in the smoothing process on the deduced second derivative of the I-V curves, and an optimum group of the adjustable factors is selected to make the rms deviation of the smoothed I-V curves from the measured curves less than 1%. A simple differentiation circuit is designed and used to measure the EEDF parameter straightforwardly. It is the first time, so far as we know, to measure the EEDF parameters simultaneously by means of both numerical and circuit derivative methods under the same discharge conditions and on the same discharge equipment. The deviation between two groups of mean electron energy E and electron density ne obtained by the above different methods is within about 7%. This apparently improves the reliability of the measurements of the EEDF parameters.

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Space-charge limiting current in spherical cathode diodes Liu Guo-Zhi (刘国治), Shao Hao (邵浩) Chinese Physics, 2003, 12 (2):  204-207.  DOI: 10.1088/1009-1963/12/2/315 Abstract ( 1362 )   PDF (319KB) ( 400 )   The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the non-relativistic situation are presented in this paper. The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface. The generated space-charge limiting current is deduced. In the case of a pin-shaped-cathode diode, the space-charge limiting current is also obtained, indicating that the current is independent of the geometric parameters of the diode. Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that, for pin-arrayed cathodes, the distance between pins should be in the range from 1.2D to 1.5D, where D is the distance between the two electrodes.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Positive deviation from Debye's theory in small-angle x-ray scattering Li Zhi-Hong (李志宏), Gong Yan-Jun (巩雁军), Wu Dong (吴东), Sun Yu-Han (孙予罕), Zhao Hui (赵辉), Dong Bao-Zhong (董宝中), Wu Zhong-Hua (吴忠华), Chinese Physics, 2003, 12 (2):  208-210.  DOI: 10.1088/1009-1963/12/2/316 Abstract ( 1487 )   PDF (178KB) ( 488 )   The small-angle x-ray scattering (SAXS) resulting from a non-ideal two-phase system having sharply defined phase boundaries but with micro-fluctuations of electron density within any phase shows a positive deviation from Debye's theory. We have found a simple method suitable for fitting the slit-smeared SAXS data and correcting the positive deviation. The validity of this procedure is tested on porous ZrO2 xerogel prepared using the sol-gel process.

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Influence of isothermal approximation on the phase-field simulation of directional growth in undercooled melt Yu Yan-Mei (于艳梅), Yang Gen-Cang (杨根仓), Zhao Da-Wen (赵达文), Lü Yi-Li (吕衣礼) Chinese Physics, 2003, 12 (2):  211-217.  DOI: 10.1088/1009-1963/12/2/317 Abstract ( 1105 )   PDF (681KB) ( 455 )   By using the phase-field approach, we have simulated the directional growth of alloys in undercooled molten states under the isothermal and nonisothermal conditions. The influences of the isothermal approximation on simulation results are discussed. We found that for undercooling greater than 25K, the isothermal approximation overestimates the interface growth velocity and reduces a critical velocity for an absolute stable planar interface, thus in this simulation, the interface morphology shows the plane-cell-plane transition with increasing initial undercooling of the melt, and the planar interface obtained under a large undercooling is absolutely stable. Whereas in the nonisothermal simulation, only plane-cell transition occurs in the same range of the initial undercoolings of the melt, and the planar interface tends to be destabilized and evolve into cells.

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Atomic hydrogen induced step bunching and fabrication of quantum wire arrays on GaAs (311)A substrate by molecular beam epitaxy Zhou Da-Yong (周大勇), Lan Qing (澜清), Kong Yun-Chuan (孔云川), Miao Zhen-Hua (苗振华), Feng Song-Lin (封松林), Niu Zhi-Chuan (牛智川) Chinese Physics, 2003, 12 (2):  218-221.  DOI: 10.1088/1009-1963/12/2/318 Abstract ( 1135 )   PDF (474KB) ( 460 )   Atomic hydrogen assisted molecular beam epitaxy (MBE) is a novel type of epitaxial growth of nanostructures. The GaAs (311)A surface naturally forms one-dimensional step arrays by step bunching along the direction of 〈-233〉 and the space period is around 40nm. The step arrays extend over several μm without displacement. The InGaAs quantum wire arrays are grown on the step arrays as the basis. Our results may prompt further development of more uniform quantum wire and quantum dot arrays.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Observation of spontaneous polarization of tourmaline Jin Zong-Zhe (金宗哲), Ji Zhi-Jiang (冀志江), Liang Jin-Sheng (梁金生), Wang Jing (王静), Sui Tong-Bo (隋同波) Chinese Physics, 2003, 12 (2):  222-225.  DOI: 10.1088/1009-1963/12/2/319 Abstract ( 1005 )   PDF (383KB) ( 612 )   Since Tetsujiro Kubo indirectly found the spontaneous polarization of tourmaline through absorbing copper ions in copper sulfate aqueous solutions in 1980s, there is no other evidence to demonstrate the existence of the spontaneous polarization in tourmaline. It was found that after a tourmaline particle was bombarded by electron beams, a spot appeared on the surface of the sample, and that one half of the spot was brighter than the other half under scanning electron microscope. After tourmaline was treated for 2 h at 1223K and then bombarded by electron beams, the bombardment spot did not appear because the crystal structure of tourmaline is destroyed. The existence of the bombardment spot accounts for the spontaneous polarization. The shape and brightness of the bombardment spot not only shows the existence of a surface electric field induced by spontaneous polarization, but also the relation with the direction of the crystal plane of tourmaline.

RAPID COMMUNICATION

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Interactions between DNA and histones－ a dynamic process of nucleosome formation Li Wei (李伟), Wang Peng-Ye (王鹏业), Dou Shuo-Xing (窦硕星), Tong Pei-Qing (童培庆) Chinese Physics, 2003, 12 (2):  226-230.  DOI: 10.1088/1009-1963/12/2/320 Abstract ( 1117 )   PDF (256KB) ( 382 )   We have studied the dynamic process of interactions between a DNA chain and a histone octamer by numerical simulations. It is found that DNA indeed may wrap around the histone octamer about two turns as in the actual situations. The simulation shows that the interaction potential between DNA and histone is a key factor for the wrapping of DNA, and the temperature is also an important parameter in the process.