Table of contents

15 October 2001, Volume 10 Issue 10 Previous issue    Next issue

GENERAL

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THE PHYSICAL MECHANISM OF COLLISION BETWEEN SOLITONS Zhang Zhuo (张卓), Tang Yi (唐翌), Yan Xiao-hong (颜晓红) Chinese Physics, 2001, 10 (10):  889-892.  DOI: 10.1088/1009-1963/10/10/301 Abstract ( 999 )   PDF (188KB) ( 451 )   An easy and general way to access more complex soliton phenomena is introduced in this paper. The collision process between two solitons of the KdV equation is investigated in great detail with this novel approach, which is different from the sophisticated method of inverse scattering transformation. A more physical and transparent picture describing the collision of solitons is presented.

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ABUNDANT EXACT SOLUTION STRUCTURES OF THE NIZHNIK--NOVIKOV--VESELOV EQUATION Zhang Jie-fang (张解放) Chinese Physics, 2001, 10 (10):  893-896.  DOI: 10.1088/1009-1963/10/10/302 Abstract ( 1143 )   PDF (187KB) ( 739 )   Using the extended homogeneous balance method, we have obtained abundant exact solution structures of a (2+1)-dimensional integrable model, the Nizhnik--Novikov--Veselov equation. By means of leading order terms analysis, the nonlinear transformations of the Nizhnik--Novikov--Veselov equation are given first, and then some special types of single solitary wave solution and multisoliton-like solutions are constructed.

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CONDITIONAL SIMILARITY REDUCTION APPROACH: JIMBO--MIWA EQUATION Lou Sen-yue (楼森岳), Tang Xiao-yan (唐晓艳) Chinese Physics, 2001, 10 (10):  897-901.  DOI: 10.1088/1009-1963/10/10/303 Abstract ( 1172 )   PDF (215KB) ( 819 )   The direct method developed by Clarkson and Kruskal (1989 J. Math. Phys. 30 2201) for finding the symmetry reductions of a nonlinear system is extended to find the conditional similarity solutions. Using the method of the Jimbo－Miwa (JM) equation, we find that three well-known (2+1)-dimensional models－the asymmetric Nizhnik--Novikov--Veselov equation, the breaking soliton equation and the Kadomtsev-Petviashvili equation－can all be obtained as the conditional similarity reductions of the JM equation.

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THE DOUBLE COUPLING OF THE ASHTEKAR GRAVITATIONAL FIELD TO THE DIRAC SPINORAL FIELDS Wu Ya-bo (吴亚波), Gui Yuan-xing (桂元星) Chinese Physics, 2001, 10 (10):  902-906.  DOI: 10.1088/1009-1963/10/10/304 Abstract ( 950 )   PDF (212KB) ( 477 )   By introducing the double spacetime manifold, the double gamma matrices and Dirac spinors, the action of the Dirac spinoral fields is doubled. Furthermore, the double coupling of the Dirac fields to the Ashtekar gravitational fields is studied.

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FREQUENCY CATASTROPHE AND CO-EXISTING ATTRACTORS IN A CELL Ca2+ NONLINEAR OSCILLATION MODEL WITH TIME DELAY Ying Yang-jun (应阳君), Huang Zu-qia (黄祖洽) Chinese Physics, 2001, 10 (10):  907-913.  DOI: 10.1088/1009-1963/10/10/305 Abstract ( 2038 )   PDF (276KB) ( 390 )   Frequency catastrophe is found in a cell Ca2+ nonlinear oscillation model with time delay. The relation of the frequency transition to the time delay is studied by numerical simulations and theoretical analysis. There is a range of parameters in which two kinds of attractors with great frequency differences co-exist in the system. Along with parameter changes, a critical phenomenon occurs and the oscillation frequency changes greatly. This mechanism helps us to deepen the understanding of the complex dynamics of delay systems, and might be of some meaning in cell signalling.

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THE DYNAMIC FRICTION TERM IN THE SPRING-BLOCK MODELS FOR EARTHQUAKES: A CONSTRAINT FROM SEISMIC MOMENT AND ENERGY CATALOGUE Wu Zhong-liang (吴忠良) Chinese Physics, 2001, 10 (10):  914-917.  DOI: 10.1088/1009-1963/10/10/306 Abstract ( 900 )   PDF (196KB) ( 403 )   In the spring-block models of earthquakes, one of the key factors is the dynamic friction term which determines the complexity of the faulting process. Generally, two kinds of friction, namely velocity-dependent friction and slip-dependent friction, are used in the modelling. But until now there has still been a lack of information on which kind of friction term is more suitable for modelling the phenomenology of earthquakes. Based on the numerical studies of Shaw (1998 Bull. Seismol. Soc. Am. 88 1457), we have examined the ratio of the broadband radiated energy and the scalar seismic moment of shallow earthquakes worldwide from 1987 to 1998. The result shows that for earthquakes with strike-slip mechanisms, velocity-dependent friction seems to be predominant, while for thrust and normal events, slip-dependent friction seems predominant. This suggests that in the spring-block models for earthquakes, the type of focal mechanism has to be accounted for, and different types of earthquakes require different dynamic friction terms in the corresponding spring-block model.

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NOISE AND SENSITIVITY IN POLYSILICON PIEZORESISTIVE CANTILEVERS Yu Xiao-mei (于晓梅), Jiang Xing-liu (江兴流), J. Thaysen, O. Hansen, A. Boisen Chinese Physics, 2001, 10 (10):  918-923.  DOI: 10.1088/1009-1963/10/10/307 Abstract ( 1041 )   PDF (293KB) ( 828 )   Piezoresistive cantilevers with dimensions of 200×50×1.8μm3 have been fabricated from polycrystalline silicon using reactive ion etching (RIE) and back etching processes. Full Wheatstone bridges have been designed symmetrically on-chip, with two resistors placed on the cantilevers and two resistors on the substrate. The differential measurements of the two cantilevers can reduce the thermal shift of the signal in the system and the external noise in the laboratory. The characteristics of the fabricated cantilevers have been analysed by measuring the noise and the sensitivity. The measured noise spectra show that the 1/f noise is the dominant noise source at low frequencies. With the linear relation between 1/f noise and bias voltages, the Hooge factor ($\alpha$) was calculated to be 0.0067. The 1/f noise was explained in terms of a lattice scattering model, which occurs in the depletion region of the grains. The displacement sensitivity of the cantilevers  $(\frac{\Delta R}{R}z^{-1})$ was calculated to be 1×10-6nm-1 by measuring the resistance change and the vertical deflection of the cantilever. The gauge factor of the piezoresistive cantilever was calculated to be 19. At a 3 V bias voltage and 1000 Hz measurement bandwidth, 1 nm of minimum detectable deflection has been obtained.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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TRIGONOMETRIC $SU(N)$ GAUDIN MODEL Cao Jun-peng (曹俊鹏), Hou Bo-yu (侯伯宇), Yue Rui-hong (岳瑞宏) Chinese Physics, 2001, 10 (10):  924-928.  DOI: 10.1088/1009-1963/10/10/308 Abstract ( 1025 )   PDF (232KB) ( 380 )   In this paper, we obtain the eigenstates and the eigenvalues of the Hamiltonians of the trigonometric $SU(N)$ Gaudin model based on the quasi-classical limit of the trigonometric $SU(N)$ chain with the periodic boundary condition. By using the quantum inverse scattering method, we also obtain the eigenvalues of the generating function of the trigonometric $SU(N)$ Gaudin model.

ATOMIC AND MOLECULAR PHYSICS

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STARK STRUCTURE OF THE RYDBERG STATES OF ALKALINE-EARTH ATOMS Zhi Miao-chan (郅妙婵), Dai Chang-jian (戴长建), Li Shi-ben (李士本) Chinese Physics, 2001, 10 (10):  929-934.  DOI: 10.1088/1009-1963/10/10/309 Abstract ( 1398 )   PDF (300KB) ( 1029 )   The Stark effects of the Rydberg states in the alkaline-earth atoms are studied theoretically. Using a method similar to the treatment of alkali atoms, the properties of the Stark states of Mg, Ca, Sr and Ba atoms in the regions far away from the perturbers are investigated. The Stark maps for Mg (n=16, M=0), Ca (n=10, M=0), Sr (n=12, M=0) and Ba (n=13, |M|=0,1) are presented. Topics such as the general methods of calculation, the treatment of fine structure, and the structure of level anti-crossings are discussed. The comparison between the theoretical and experimental Stark maps is satisfactory.

CLASSICAL AREAS OF PHENOMENOLOGY

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THE EXACT SOLUTION OF A TWO-LEVEL ATOM MOVING IN A QUANTIZED TRAVELLING LIGHT FIELD AND A GRAVITATIONAL FIELD Zou Xu-bo (邹旭波), Xu Jing-bo (许晶波), Gao Xiao-chun (高孝纯), Fu Jian (符建) Chinese Physics, 2001, 10 (10):  935-940.  DOI: 10.1088/1009-1963/10/10/310 Abstract ( 1081 )   PDF (249KB) ( 552 )   We adopt a dynamical algebraic approach to study the system of a two-level atom moving in a quantized travelling light field and a gravitational field with a multiphoton interaction. The exact solution of the system is obtained and used to discuss the influence of the gravitational field on the collapses and revivals of atomic population, sub-Poissonian statistics.

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SPECTRUM OF A FEW-CYCLE LASER PULSE PROPAGATING IN A TWO-LEVEL ATOM MEDIUM Xiao Jian (肖健), Wang Zhong-yang (王中阳), Xu Zhi-zhan (徐至展) Chinese Physics, 2001, 10 (10):  941-945.  DOI: 10.1088/1009-1963/10/10/311 Abstract ( 1150 )   PDF (224KB) ( 520 )   The spectrum evolution of a few-cycle optical pulse in a resonant two-level atom medium is studied theoretically by using the full Maxwell--Bloch equations. On the propagating pulse, significantly much faster oscillation components separated with the main pulse appear due to strong self-phase modulation and pulse reshaping. In this case, ideal self-induced transparency cannot occur for a 2$\pi$ pulse. The spectrum of the 4$\pi$ pulse shows an evident oscillatory feature because of the continuum interference of the separate pulses. For larger pulse areas, continuum generation from near ultraviolet to infrared occurs.

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TEMPORAL CHARACTERIZATION OF LASER PULSES FROM JIGUANG-I LASER FACILITY WITH A COMPACT DUAL FUNCTION AUTOCORRELATOR Xia Jiang-fan (夏江帆), Wei Zhi-yi (魏志义), Qiu Yang (邱阳), Lü Tie-zheng (吕铁铮), Teng Hao (腾浩), Wang Zhao-hua (王兆华), Zhang Jie (张杰) Chinese Physics, 2001, 10 (10):  946-950.  DOI: 10.1088/1009-1963/10/10/312 Abstract ( 1071 )   PDF (219KB) ( 790 )   An optical pulse autocorrelator for rapid and slow scanning is described in this paper. Using an audio loudspeaker on one arm, an interferometric rapid-scanning signal of the output from a high-repetition laser oscillator is obtained. However, by adjusting the positions of the mirrors and using a step-motor on another arm, the intensity autocorrelation function of the output from a low-repetition laser amplifier can be easily measured. Using all-reflecting optics and an adequate nonlinear crystal, the whole instrument is very compact and has been used to measure sub-20 fs light pulses in both configurations with excellent agreement. In the slow-scanning configuration, a pulse train as long as 500ps has been determined. Using this autocorrelator, the home-made JIGUANG-I CPA laser facility was characterized for its pulse duration evolution.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (I) Dong Shun-le (董顺乐), Wang Yan (王燕), Li Qi (李琪) Chinese Physics, 2001, 10 (10):  951-957.  DOI: 10.1088/1009-1963/10/10/313 Abstract ( 1197 )   PDF (273KB) ( 427 )   Lattice dynamical calculations of ice VIII have been carried out by using a slightly modified set of force constants obtained recently for ice Ih (Li J C and Ross D K 1993 Nature 365 327). A weak interaction was introduced between the two interpenetrated sublattices in the ice VIII structure. The calculated results for H2O and D2O ice VIII are in reasonable agreement with the measured inelastic neutron scattering spectra. The eigenvectors of phonon modes in the range of translational and librational bands have been studied in order to understand the properties of the vibrational modes. It is found that the third peak at 26.7meV in the translation results from weak hydrogen bond interactions, and the first peak (14.7meV) is much higher than it is in ice Ih (～7.1meV), which is partially due to the interactions between the two sublattices.

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NEUTRON SCATTERING AND LATTICE DYNAMICAL STUDIES OF THE HIGH-PRESSURE PHASE ICE (II) Dong Shun-le (董顺乐), Wang Yan (王燕) Chinese Physics, 2001, 10 (10):  958-965.  DOI: 10.1088/1009-1963/10/10/314 Abstract ( 1272 )   PDF (290KB) ( 459 )   Lattice dynamical calculations have been carried out for ice II based on the force field constructed for ice Ih. In order to fully understand ice II inelastic neutron scattering spectra, the decomposed phonon density of states was shown mode by mode. Calculated results have shown that the hydrogen bond force constant between the six-molecule rings is significantly weaker, 75eV/nm2, compared with the force constant, 220eV/nm2, within the rings. Inelastic neutron scattering spectra of clathrate hydrate H2O+He are almost the same as ice II. This means that the absorption of He atoms cannot affect the bond strengths of the ice II host lattice. Based on the force field model for ice II, the van der Waals interactions between water molecules and helium atoms are considered. The results obtained are consistent with experimental data. Lattice dynamical calculations have been carried out for ice II using seven rigid pairwise potentials. It was found that MCY makes the stretching and bending interactions in ice II too weak and makes the O-O bond length too long (～5%), thus its lattice densities are obviously lower than other potential lattices or experimental values.

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INCREASING THE PHOTOLUMINESCENCE INTENSITY OF Ge ISLANDS BY CHEMICAL ETCHING Gao Fei (高斐), Huang Chang-jun (黄昌俊), Huang Da-ding (黄大定), Li Jian-ping (李建平), Kong Mei-ying (孔梅影), Zeng Yi-ping (曾一平), Li Jin-min (李晋闽), Lin Lan-ying (林兰英) Chinese Physics, 2001, 10 (10):  966-969.  DOI: 10.1088/1009-1963/10/10/315 Abstract ( 1116 )   PDF (391KB) ( 509 )   Self-assembled Ge islands were grown on Si(100) substrate by Si2H6-Ge molecular beam epitaxy. After being subjected to chemical etching, it is found that the photoluminescence from the etched Ge islands became more intense and shifted to the higher-energy side compared to that of the as-deposited Ge islands. This behaviour was explained by the effect of chemical etching on the morphology of the Ge islands. Our results demonstrate that chemical etching can be a way to change the luminescence property of the as-deposited islands.

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

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LARGE MAGNETIC ENTROPY CHANGE NEAR CHARGE-ORDERED TRANSITION TEMPERATURE IN PEROVSKITE-TYPE MANGANITE Chen Peng (陈鹏), Du You-wei (都有为) Chinese Physics, 2001, 10 (10):  970-973.  DOI: 10.1088/1009-1963/10/10/316 Abstract ( 969 )   PDF (202KB) ( 474 )   The magnetocaloric effect in polycrystalline of Pr1-xSrxMnO3 (x=0.33, 0.43, 0.50) has been investigated. A large magnetic entropy change (7.1J/kgK) was discovered in Pr0.5Sr0.5MnO3 under a low magnetic field of 1T at charge-ordered state transition temperature (161K). The physical mechanism is related to a drastic magnetization change at a temperature where the field-induced magnetic, electron and structural phase transitions occur (from the antiferromagnetic charge-ordered state to the ferromagnetic charge-disordered state).

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A STUDY OF FINE PRECIPITATES IN ALLOYS BY POSITRON ANNIHILATION Wang Jing-cheng (王景成), You Fu-qiang (尤富强), Yin Jun-lin (殷俊林), Gao Guo-hua (高国华), Liang Ling (梁玲), Duan Yong (段勇) Chinese Physics, 2001, 10 (10):  974-978.  DOI: 10.1088/1009-1963/10/10/317 Abstract ( 1360 )   PDF (223KB) ( 485 )   Measurements were performed using the positron annihilation technique associated with physical metallurgical techniques for several engineering alloys containing fine precipitates. It is shown that positron annihilation is an effective method to detect fine precipitates, providing a sound basis for a further intense research of these.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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NON-THERMAL RADIATION FROM A NON-KERR－NEWMAN BLACK HOLE Xie Shi-chong (谢实崇), Yang Xue-te (杨雪特), Yang Shu-zheng (杨树政), Lin Li-bin (林理彬) Chinese Physics, 2001, 10 (10):  979-982.  DOI: 10.1088/1009-1963/10/10/318 Abstract ( 1090 )   PDF (148KB) ( 516 )   In the spacetime of a charged spinning black hole, the distribution of particle energy levels has been studied. Near the event horizon of such a black hole a crossing of the particle energy levels exists, which leads to the occurrence of non-thermal radiation of the black hole. This quantum effect is non-thermal and also different from those of the Kerr and Kerr－Newman black holes.