Table of contents

15 April 2001, Volume 10 Issue 4 Previous issue    Next issue

GENERAL

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BIRKHOFF'S EQUATIONS AND GEOMETRICAL THEORY OF ROTATIONAL RELATIVISTIC SYSTEM Luo Shao-kai (罗绍凯), Chen Xiang-wei (陈向炜), Fu Jing-li (傅景礼) Chinese Physics, 2001, 10 (4):  271-276.  DOI: 10.1088/1009-1963/10/4/301 Abstract ( 1266 )   PDF (247KB) ( 487 )   The Birkhoffian and Birkhoff's functions of a rotational relativistic system are constructed, the Pfaff action of rotational relativistic system is defined, the Pfaff-Birkhoff principle of a rotational relativistic system is given, and the Pfaff-Birkhoff-D'Alembert principles and Birkhoff's equations of rotational relativistic system are constructed. The geometrical description of a rotational relativistic system is studied, and the exact properties of Birkhoff's equations and their forms on $\vec{R}\times T*M$ for a rotational relativistic system are obtained. The global analysis of Birkhoff's equations for a rotational relativistic system is studied, the global properties of autonomous, semi-autonomous and non-autonomous rotational relativistic Birkhoff's equations, and the geometrical properties of energy change for rotational relativistic Birkhoff's equations are given.

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A GENERATION OF EXACTLY SOLVABLE ANHARMONIC SYMMETRIC OSCILLATORS Liu Ke-jia (刘克家) Chinese Physics, 2001, 10 (4):  277-281.  DOI: 10.1088/1009-1963/10/4/302 Abstract ( 1257 )   PDF (167KB) ( 392 )   Using the ideas of supersymmetric quantum mechanics, we exactly solve a continuous family of anharmonic potentials, which are the supersymmetric partners of the linear harmonic oscillators. The family includes a series of potentials in which the excited-state energy is the same as that of the harmonic oscillators, but the ground-state energy can be any value lower than the excited states. The shape of the potential is variable, which includes the double-well and triple-well potentials. All the potentials obtained in this paper are free of singularities, and the supersymmetry of the solutions is unbroken.

NUCLEAR PHYSICS

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THE NUCLEAR STRUCTURE AND BACKBENDING PHENOMENON FOR 114-130Xe ISOTOPES Shi Zhu-yi (石筑一), Liu Yong (刘庸), Sang Jian-ping (桑建平) Chinese Physics, 2001, 10 (4):  282-285.  DOI: 10.1088/1009-1963/10/4/303 Abstract ( 1124 )   PDF (265KB) ( 423 )   In view of interacting boson fermion formalism, a microscopic sdIBM-2 +2q.p. model is used to describe the ground-state band, $\beta$-band, $\gamma$-band and two-quasi-particle band for 114-130Xe isotopes. The theoretical investigations indicate that the backbending is caused by crossing of the two-quasi-proton band and the ground-state band. This result seems to provide a possible way for understanding the backbending phenomenon of 114-130Xe isotopes.

ATOMIC AND MOLECULAR PHYSICS

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CALCULATIONS OF STRETCHING VIBRATIONAL ENERGY LEVELS OF THE CH3I MOLECULE BY A NONLINEAR MODEL Zhu Jun (朱俊), Gou Qing-quan (芶清泉) Chinese Physics, 2001, 10 (4):  286-289.  DOI: 10.1088/1009-1963/10/4/304 Abstract ( 1537 )   PDF (192KB) ( 554 )   A nonlinear model, i.e. the quantized discrete self-trapping equation, is applied to calculate the highly excited CH stretching vibrational energy levels of the CH3I molecule in the liquid phase at the electronic ground state up to n=8. The obtained results agree well with the experimental data and with those obtained from local mode model calculations. We note that the dominant feature of the methyl CH stretching vibrational energy levels of the CH3I molecule is a pattern of local mode pairs. When n≥7, all the vibrational energy of the CH3 group can nearly be localized on a single CH bond.

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EXCHANGE AND FINAL CHANNEL SCREENING EFFECTS IN (e, 2e) PROCESSES Chen Zhang-jin (陈长进), Xu Ke-zun (徐克尊) Chinese Physics, 2001, 10 (4):  290-294.  DOI: 10.1088/1009-1963/10/4/305 Abstract ( 1142 )   PDF (208KB) ( 418 )   The DS3C model has been improved by taking into account the final channel screening effects. The triple differential cross sections for electron impact ionization of helium at an incident energy of 40 eV are considered. The results of the present DS3C model are compared with the absolute measurements and those of other theoretical models. It has also been shown in which situation the exchange effects are crucial.

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FRACTAL PATTERN GROWTH OF METAL ATOM CLUSTERS IN ION IMPLANTED POLYMERS Zhang Tong-he (张通和), Wu Yu-guang (吴瑜光), Sang Hai-bo (桑海波), Li Yong-liang (李永良), Zhou Gu (周固) Chinese Physics, 2001, 10 (4):  295-299.  DOI: 10.1088/1009-1963/10/4/306 Abstract ( 1402 )   PDF (815KB) ( 437 )   The fractal and multi-fractal patterns of metal atoms are observed in the surface layer and cross section of a metal ion implanted polymer using TEM and SEM for the first time. The surface structure in the metal ion implanted polyethylene terephthalane (PET) is the random fractal. Certain average quantities of the random geometric patterns contain self-similarity. Some growth origins appeared in the fractal pattern which has a dimension of 1.67. The network structure of the fractal patterns is formed in cross section, having a fractal dimension of 1.87. So it can be seen that the fractal pattern is three-dimensional space fractal. We also find the collision cascade fractal in the cross section of implanted nylon, which is similar to the collision cascade pattern in transverse view calculated by the TRIM computer program. Finally, the mechanism for the formation and growth of the fractal patterns during ion implantation is discussed.

CLASSICAL AREAS OF PHENOMENOLOGY

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ABSORPTION PROPERTIES OF A DRIVEN FOUR-LEVEL DOPPLER-BROADENED SYSTEM Yuan Shi (袁石), Wu Jin-hui (吴金辉), Gao Jin-Yue (高锦岳) Chinese Physics, 2001, 10 (4):  300-306.  DOI: 10.1088/1009-1963/10/4/307 Abstract ( 1193 )   PDF (216KB) ( 489 )   This paper deals with the absorption spectra of a weak probe in a four-level Doppler-broadened system driven by three coherent fields. The main aim is to extend earlier studies of the spontaneous emission spectrum and to present a comprehensive survey of the spectral features of this system. In addition to a derivation of exact formulae for the spectra, we give an explanation with the help of an appropriate set of dressed atomic states. We also get a deeper insight into the physical origin of gain in view of the existence of a population inversion between the levels of the lasing transition. Finally, we explore the effect of Doppler broadening on the absorption profile of the weak probe.

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STEADY SOLUTIONS OF THE OPTICAL SOLITON EQUATION WITH A NONLINEAR RESPONSE DELAY TERM Lin Chang (林长), Zhang Xiu-Lian (张秀莲) Chinese Physics, 2001, 10 (4):  307-309.  DOI: 10.1088/1009-1963/10/4/308 Abstract ( 1112 )   PDF (175KB) ( 498 )   The exact solution of the optical soliton equation with a nonlinear response delay term has been obtained by using the method of separating variables. The new type of optical solitary wave solution, which is quite different from the bright and dark soliton solutions, has been found for a special case.

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INCOHERENTLY COUPLED SCREENING--PHOTOVOLTAIC SOLITON FAMILIES IN BIASED PHOTOVOLTAIC PHOTOREFRACTIVE CRYSTALS Hou Chun-feng (侯春风), Li Bin (李斌), Sun Xiu-dong (孙秀冬), Jiang Yong-yuan (姜永远), Xu Ke-bin (许克彬) Chinese Physics, 2001, 10 (4):  310-313.  DOI: 10.1088/1009-1963/10/4/309 Abstract ( 1312 )   PDF (179KB) ( 599 )   It is shown that the existence of incoherently coupled screening-photovoltaic soliton families is possible in biased photovoltaic photorefractive crystals under steady-state conditions. These screening-photovoltaic soliton families can be established provided the multiple incident beams have the same polarization and wavelength, and are mutually incoherent. Such soliton families reduce to screening-photovoltaic soliton pairs when they contain only two components. Relevant examples are presented where the photovoltaic photorefractive crystal is of the lithium niobate type.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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PHOTON ACCELERATION DRIVEN BY AN INTENSE LASER PULSE Ji Pei-yong (季沛勇), Bao Jia-shan (鲍家善) Chinese Physics, 2001, 10 (4):  314-319.  DOI: 10.1088/1009-1963/10/4/310 Abstract ( 1039 )   PDF (244KB) ( 923 )   Interaction of a laser field with a plasma wave is studied by metric optics. Analysis shows that the frequency upshifting of the laser pulse results from the plasma density gradient. A laser beam can be thought of as a packet of photons moving in a plasma and thus the laser frequency upshifting is equivalent to photon acceleration. Examination of the three-dimensional motion equations shows that a laser beam diffraction occurs in the presence of a radial variation of the plasma density. It is argued that the focusing mechanism originating from the plasma wave can curb laser diffraction so that photons may be trapped in the plasma wave and accelerated continuously.

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THE INFLUENCE OF ELECTRON OSCILLATION ON PLASMA TRANSPORT THROUGH A MAGNETIC DUCT Zhang Tao (张涛), T. K. Kwok (郭达勤), P. K. Chu (朱剑豪), I. G. Brown Chinese Physics, 2001, 10 (4):  320-323.  DOI: 10.1088/1009-1963/10/4/311 Abstract ( 1031 )   PDF (182KB) ( 390 )   A magnetic duct is inserted between the cathodic arc plasma source and the chamber to eliminate the macroparticles. In this paper, the plasma output of the magnetic duct is determined as a function of the magnetic field and the bias voltage under the Bilek biasing mode and entire duct biasing mode. The computer simulation and the experimental result indicate that the $\vec{E}\times\vec{B}$ drift results in an extra diffusion flux under the Bilek biasing mode. The test verifying the electron oscillation was conducted in the magnetic duct biased in the Bilek mode. The electron behaviour under Bilek biasing mode is different from that under entire duct biasing mode. The Bilek biasing mode has a lower plasma output than the entire duct biasing mode.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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ANALYSIS OF THE X-RAY PHOTOELECTRON SPECTRA OF a-SiOCF FILMS PREPARED BY PLASMA-ENHANCED CHEMICAL VAPOUR DEPOSITION Ding Shi-jin (丁士进), Wang Peng-fei (王鹏飞), Zhang Wei (张卫), Wang Ji-tao (王季陶), Wei William Lee Chinese Physics, 2001, 10 (4):  324-328.  DOI: 10.1088/1009-1963/10/4/312 Abstract ( 1142 )   PDF (217KB) ( 493 )   The preparation of a-SiOCF films from Si(OC2H5)4, C4F8 and/or Ar using the plasma-enhanced chemical vapour deposition method is reported. The chemical bonding structures of the films are analysed by x-ray photoelectron spectroscopy (XPS). In the case of the films deposited from the mixture with and without Ar, the configurations of F-Si-O-Si, Si-OH, Si-O-Si, C-CF and C-F are contained. However, there is also the C-C configuration in the film prepared from the mixture with Ar. Moreover, it is found that the photoelectron peaks of Si 2p, O 1s and F 1s for the film deposited from the feeding gas with Ar show the same shift of about 1eV toward high binding energy in comparison with those for the film prepared from the feeding gas without Ar. No evidence reveals the presence of an Si-C bond in the films.

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ADATOM, VACANCY AND SPUTTERING YIELDS OF ENERGETIC Pt ATOMS IMPACTING ON Pt(100) BY MOLECULAR DYNAMICS SIMULATION Ye Zi-yan (叶子燕), Zhang Qing-yu (张庆瑜) Chinese Physics, 2001, 10 (4):  329-334.  DOI: 10.1088/1009-1963/10/4/313 Abstract ( 1054 )   PDF (286KB) ( 506 )   We have studied the influence of incident atoms with low energy on the Pt(100) surface by molecular dynamics simulation. The interaction potential obtained by the embedded atom method (EAM) was used in the simulation. The incident energy changes from 0.1eV to 200eV, and the target temperature ranges from 100 to 500 K. The target scales are 6×6×4 and 8×8×4 fcc cells for lower and higher incident energies, respectively. The adatom, sputtering, vacancy and backscattering yields are calculated. It was found that there is a sputtering threshold for the incident energy. When the incident energy is higher than the sputtering threshold, the sputtering yield increases with the increase of incident energy, and the sputtering shows a symmetrical pattern. We found that the adatom and vacancy yields increase as the incident energy increases. The vacancy yields are much higher than those obtained by Monte Carlo simulation. The dependence of the adatom and sputtering yields on the incident energy and the relative atomistic mechanisms are discussed.

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

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STRUCTURE AND SUPERCONDUCTIVITY OF Mg(B1-xCx)2 COMPOUNDS Zhang Shao-ying (张绍英), Zhang Jian (张健), Zhao Tong-yun (赵同云), Rong Chuan-bing (荣传兵), Shen Bao-gen (沈保根), Cheng Zhao-hua (成昭华) Chinese Physics, 2001, 10 (4):  335-337.  DOI: 10.1088/1009-1963/10/4/314 Abstract ( 1031 )   PDF (154KB) ( 504 )   In this paper, we report on the structural properties and superconductivity of Mg(B1-xCx)2 compounds. Powder X-ray diffraction results indicate that the samples crystallize in a hexagonal AlB2-type structure. Due to the chemical activity of Mg powders, a small amount of MgO impurity phase is detected by X-ray diffraction. The lattice parameters decrease slightly with the increasing carbon content. Magnetization measurements indicate that the non-stoichiometry of MgB2 has no influence on the superconducting transition temperature and the transition temperature width. The addition of carbon results in a decrease of Tc and an increase of the superconducting transition width, implying the loss of superconductivity.

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HIGH-PRESSURE SYNTHESIS OF MgB2 SUPER-CONDUCTOR WITH Tc ABOVE 39 K Li Shao-chun (李绍春), Zhu Jia-lin (朱嘉林), Yu Ri-cheng (禹日成), Li Feng-ying (李凤英), Liu Zhen-xing (刘振兴), Jin Chang-qing (靳常青) Chinese Physics, 2001, 10 (4):  338-339.  DOI: 10.1088/1009-1963/10/4/315 Abstract ( 1144 )   PDF (259KB) ( 472 )   We report on the high-pressure synthesis and superconductivity of MgB2 intermetallic compounds. The compounds have been obtained through high-pressure sintering of the mixtures of magnesium and boron fine powders under 5.0 GPa and at ～1000℃ for 30 min. Magnetic measurements using a SQUID magnetometer show the sharp bulk superconducting transition above 39 K; the four-probe dc resistivity measurements indicate the highly-conductive normal state and sharp superconducting transition. The results highlight that high-pressure synthesis would be a promising way to promote the studies of this new kind of intermetallic superconductors.

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WEAK QUANTUM FLUX CREEP AND STRONG PINNING IN THE NEW SUPERCONDUCTOR MgB2 Hot! Zhao Zhi-wen (赵志文), Wen Hai-hu (闻海虎), Li Shi-liang (李世亮), Ni Yong-ming (倪泳明), Ren Zhi-an (任治安), Che Guang-can (车广灿), Yang Hai-peng (杨海朋), Liu Zhi-yong (刘志勇), Zhao Zhong-xian (赵忠贤) Chinese Physics, 2001, 10 (4):  340-342.  DOI: 10.1088/1009-1963/10/4/316 Abstract ( 1263 )   PDF (173KB) ( 572 )   The newly discovered superconductor MgB2 has a transition temperature Tc of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB2 and compare it with other superconductors. We have measured the magnetization relaxation of MgB2 sintered at high temperature and high pressure. It is found that the quantum tunnelling and the thermally activated flux creep are very weak, implying a strong pinning in this material.

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STRUCTURE ANALYSIS OF NEW SUPERCONDUCTOR MgB2 He Lun-hua (何伦华), Hu Gui-qing (胡桂清), Zhang Pan-lin (张泮霖), Yan Qi-wei (严启伟) Chinese Physics, 2001, 10 (4):  343-344.  DOI: 10.1088/1009-1963/10/4/317 Abstract ( 1037 )   PDF (143KB) ( 1020 )   The superconductivity of a sintered pellet of the newly discovered MgB2 superconductor has been studied with magnetic measurements and its crystal structure was analysed using the Rietveld method of powder X-ray patterns. It has hexagonal symmetry (S.G. P6/mmm) with unit cell lattice parameters a=0.308136(14)nm and c=0.351782(17)nm.

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STRUCTURE, MAGNETIC PROPERTIES AND GIANT MAGNETORESISTANCE OF YMn6Sn6-xGax (x=0-0.6) COMPOUNDS Zhang Shao-ying (张绍英), Zhao Peng (赵鹏), Li Run-wei (李润伟), Sun Ji-rong (孙继荣), Cheng Zhao-hua (成昭华), Zhang Hong-wei (张宏伟), Shen Bao-gen (沈保根) Chinese Physics, 2001, 10 (4):  345-348.  DOI: 10.1088/1009-1963/10/4/318 Abstract ( 1127 )   PDF (189KB) ( 570 )   Structure, magnetic and transport properties of YMn6Sn6-xGax (0≤x≤0.6) compounds with a HfFe6Ge6-type structure were investigated. It was found that the Ga substitution leads to a contraction of the unit-cell volume. A transition from an antiferromagnetic to a ferromagnetic (or ferrimagnetic) state can be observed for samples (0.1≤x≤0.2) with increasing temperature. The antiferro-ferromagnetic transition for samples with x≤0.2 can also be induced by an external field. The required field is very low, and decreases with increasing Ga concentration. More Ga concentration (x≥0.3) leads to the samples being ferromagnetic in the whole temperature range below the Curie temperature. The Ga substitution weakens the interlayer magnetic coupling between the Mn spins. Corresponding to the metamagnetic transition, a magnetoresistance as large as 32% under a field of 5 T was observed at 5 K for the sample with x=0.2.