Table of contents

15 July 2000, Volume 9 Issue 7 Previous issue    Next issue

GENERAL

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TIME-DEPENDENT LANDAU SYSTEM AND NON-ADIABATIC BERRY PHASE IN TWO DIMENSIONS Jing Hui (景辉), Wu Jian-sheng (吴健生) Chinese Physics, 2000, 9 (7):  481-484.  DOI: 10.1088/1009-1963/9/7/001 Abstract ( 1060 )   PDF (178KB) ( 483 )   By applying the time-independent unitary transformation, the time-dependent Landau system is transformed into a product of a time-independent Landau system's Hamiltonian and a factor only depending on time, which can be solved exactly. Both the invariant operator and the eigenstate are obtained. In the periodical time-dependent case, the non-adiabatic Berry's phase is also presented.

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THE GROWTH RATE AND STATISTICAL FLUCTUATION OF BOSE-EINSTEIN CONDENSATE FORMATION Yan Ke-zhu (闫珂柱), Tan Wei-han (谭维翰) Chinese Physics, 2000, 9 (7):  485-489.  DOI: 10.1088/1009-1963/9/7/002 Abstract ( 1442 )   PDF (116KB) ( 492 )   Using the generating function method to solve the master equation of Bose-Einstein condensate and to evaluate the growth rate, statistical fluctuation of condensate atoms, we find out that there is a plateau in the growth rate curve and a super-Poisson distribution observed.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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THE NONLINEAR QCD DYNAMICAL EQUATIONS WITH HIGHER ORDER EFFECTIVE COUPLING He Bo (何波), Zhu Wu-ming (朱吾明) Chinese Physics, 2000, 9 (7):  490-493.  DOI: 10.1088/1009-1963/9/7/003 Abstract ( 1119 )   PDF (94KB) ( 373 )   Through studying the nonlinear QCD dynamical equations with higher order effective coupling, we find that shadowing effect is substantially weaker than that neglecting higher order effective coupling. This conclusion is very important for explaining the data from DESY ep collider HERA.

NUCLEAR PHYSICS

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STUDY OF THE NUCLEAR PHENOMENA IN THE LOW ENERGY (60-360 keV) PROTON BEAM IMPLANTATION ON METALS Wang Tie-shan (王铁山), Zhu Yong-tai (诸永泰), Wang Zhi-guo (王志国), Li Song-lin (李松林), Wang Shu-jin (王树金), Jin Gen-ming (靳根明) Chinese Physics, 2000, 9 (7):  494-499.  DOI: 10.1088/1009-1963/9/7/004 Abstract ( 1176 )   PDF (1892KB) ( 505 )   A series of studies on the nuclear interaction and its effects in solids during proton implantation were performed in the energy region between 60 and 360keV. Some charged particle products were observed in the implantation experiments on metal samples such as deuterated titanium, titanium alloy, titanium foil on molybdenum substrate, molybdenum and stainless steel, etc.. The energies of the charged particle products are about 3.9, 5.6 and 8.4MeV, respectively. These particles were identified as alpha particles with both detector telescope and absorption measurements. These three kinds of alpha products were found from different proton sub-barrier reactions. The exciting curve of this reaction increases exponentially with the growth of proton energy in the energy region from 90 to 330keV. The radiation damages induced by the nuclear products in the sample have been studied with scanning electron microscopy technique. The possible surface damages induced by them were observed evidently. The origin of the nuclear reactions and their effect on implantation are discussed.

ATOMIC AND MOLECULAR PHYSICS

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STUDY OF BRANCHING RATIONS OF 3p3/2nd (J=1,3) AUTOIONIZING SERIES OF NEUTRAL MAGNESIUM Li Cong-qi (李从奇), Dai Chang-jian (戴长健), Lü Jun (吕俊) Chinese Physics, 2000, 9 (7):  500-503.  DOI: 10.1088/1009-1963/9/7/005 Abstract ( 1343 )   PDF (136KB) ( 503 )   With the K matrix and multichannel quantum defect theory, we have studied the branching ratios of 3p3/2nd (J=1,3) autoionizing series of Mg above the 3p1/2 ion limit. The calculations are compared with the previous experimental spectra, and the unmeasured branching ratios are presented. The conclusion is that 3p3/2nd state prepared by the three-step excitation can form population inversion between the 3p1/2 and 3s1/2 ionic states.

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MODEL STRETCHING ENERGY LEVELS FOR SF6 MOLECULE Zhu Jun (朱俊), Cheng Yan (程艳), Chen Xiang-rong (陈向荣), Gou Qing-quan (芶清泉) Chinese Physics, 2000, 9 (7):  504-507.  DOI: 10.1088/1009-1963/9/7/006 Abstract ( 1305 )   PDF (98KB) ( 479 )   A four-parameter nonlinear model is introduced to the description of the X-Y stretching modes of XY6 octahedral molecules in the electronic ground state. We here only apply it to the calculations of S-F stretches of SF6 molecule. The model calculations appear to describe the observed data well, and predict some new vibrational bands at accurate energies not yet observed.

CLASSICAL AREAS OF PHENOMENOLOGY

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ON THE BREAKDOWN OF A LONG STREAK IN A TRANSITIONAL BOUNDARY LAYER Lee Cun-biao (李存标), Fu Song (符松) Chinese Physics, 2000, 9 (7):  508-514.  DOI: 10.1088/1009-1963/9/7/007 Abstract ( 1287 )   PDF (5207KB) ( 522 )   Transition in regular K-regime of boundary layer is studied. The features of the long streak that is considered as a form of soliton/like coherent structure (CS-soliton) are investigated briefly. The experiment shows that the breakdown of long streak is generated by chain of ring-like vortices.

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LATTICE BOLTZMANN METHOD SIMULATION ON THE FLOW OF TWO IMMISCIBLE FLUIDS IN COMPLEX GEOMETRY Fang Hai-ping (方海平), Wan Rong-zheng (万荣正), Fan Le-wen (范乐文) Chinese Physics, 2000, 9 (7):  515-518.  DOI: 10.1088/1009-1963/9/7/008 Abstract ( 1398 )   PDF (124KB) ( 507 )   The multicomponent nonideal gas lattice Boltzmann model by Shan and Chen (S-C) can be used to simulate the immiscible fluid flow. In this paper, we show that the relaxation constant $\tau$ ≤ 1 is a necessary condition for the immiscible fluid flow in the S-C model. In a system with very complex boundary geometry, for 0.8≤ $\tau$ ≤1, the S-C model describes the immiscible flow quite well, and $\tau$ =1 is the best.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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EFFECT OF EXCITATION-AUTOIONIZATION IN NON-LOCAL THERMODYNAMIC EQUILIBRIUM PLASMAS Wu Ze-qing (吴泽清), Zhang Ben-ai (张本爱), Qiu Yu-bo (邱玉波) Chinese Physics, 2000, 9 (7):  519-522.  DOI: 10.1088/1009-1963/9/7/009 Abstract ( 1273 )   PDF (115KB) ( 545 )   Based on the detailed configuration accounting model, the authros have developed a method to calculate the rate of excitation-autoionization (EA) in the average atom model and used it in the rate equations. The numerical results show that EA effect is signifficant in high temperature low density plasma and can cause an additional ionization up to 15% of an ionization stage.

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CRITICAL MAGNETIC SHEAR FOR THE TOKAMAK IDEAL INTERNAL KINK MODE IN THE ION KINETIC REGIME Shi Bing-ren (石秉仁), Long Yong-xing (龙永兴), Sui Guo-fang (隋国芳), Li Ji-quan (李继全) Chinese Physics, 2000, 9 (7):  523-527.  DOI: 10.1088/1009-1963/9/7/010 Abstract ( 1249 )   PDF (147KB) ( 460 )   It is shown that for the ideal internal kink mode of tokamak plasma, there exists a critical magnetic shear s0c for its excitation when the finite ion Larmor radius effect is considered in the mode singular layer. This can be related to the sudden onset of the sawtooth and also to the stabilization of the sawtooth by the trapped hot ions observed experimentally. The alpha particle effect on this mode is revisited and some new results are reported.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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MICROSTRUCTURE AT THE INTERFACE OF TITANIUM CARBIDE AND NICKEL ALUMINIDES Shen Dian-hong (沈电洪), Wu Xing-fang (吴杏芳), Lu Hua (陆华), N. Froumin, M. Polak Chinese Physics, 2000, 9 (7):  528-531.  DOI: 10.1088/1009-1963/9/7/011 Abstract ( 1364 )   PDF (3483KB) ( 575 )   Microstructure at the interface of titanium carbide and nickel aluminides in the samples obtained by infiltration of molten Ni3Al alloy has studied by a scanning electron microscopy (SEM) and an analytical transmission electron microscopy (ATEM) with an energy dispersive spectrometer (EDS). It is found that the morphology at the interfaces between hard phase skeleton of TiC0.7 and metallic phases depends on the ratio of Ti/C in carbide. Some periodic zigzag fringes are observed at a smooth interface between metallic phase and carbides in the sample of Ni3Al/TiC0.7. The results of analysis using EDS show that Ti in TiC0.7 carbide is easier than that in TiC0.7 to dissolve into the molten alloy during solid-liquid reaction. The formation of this periodic zigzag fringe,which may be a growth zone of a new Ti-Ni-Al phase,in the interface of TiC0.7/Ni3Al would occur during the initial stage of solidification.

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RAPID DENDRITIC GROWTH INVESTIGATED WITH ARTIFICIAL NEURAL NETWORK METHOD Wang Nan (王楠), Zhang Jun (张骏), Wei Bing-bo (魏炳波), Dai Guan-zhong (戴冠中) Chinese Physics, 2000, 9 (7):  532-536.  DOI: 10.1088/1009-1963/9/7/012 Abstract ( 1328 )   PDF (147KB) ( 508 )   Rapid dendritic growth of $\gamma$-(Ni, Fe) phase, $\beta$-CoSb intermetallic compound and $\alpha$-Fe phase was realized by undercooling Ni-10%Fe single phase alloy, Co-60.5%Sb intermetallic alloy and Fe-40%Sn hypomonotectic alloy to a substantial extent. Their experimentally measured dendrite growth velocities were 79.5m/s, 12m/s and 0.705m/s, corresponding to undercooling levels of 303K(0.18TL), 168K(0.11 TL) and 219K(0.15 TL) respectively. Since the usual dendrite growth theory deviates significantly from reality at great undercoolings, an artificial neural network incorporated with stochastic fuzzy control was developed to explore rapid dendrite growth kinetics. It leads to the reasonable prediction that dendritic growth always exhibits a maximum velocity at a certain undercooling, beyond which dendrite growth slows down as undercooling increases still further. In the case of Fe-Sn monotectic alloys, $\alpha$-Fe dendrite growth velocity was found to depend mainly on undercooling rather than alloy composition.

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

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FABRICATION AND CHARACTERIZATION OF THE SIZE-CONTROLLED AND PATTERNED nc-Si DOTS Li Jian (李健), Wang Li (王立), Huang Xin-fan (黄信凡), Jiang Ming (蒋明), Li Wei (李伟), Wang Zhao-ye (王朝晔), Xu Jun (徐骏), Liu Zhi-guo (刘治国), Chen Kun-ji (陈坤基) Chinese Physics, 2000, 9 (7):  537-540.  DOI: 10.1088/1009-1963/9/7/013 Abstract ( 1261 )   PDF (1488KB) ( 665 )   A new method of phase-modulated excimer laser crystallization is adopted to fabricate the patterned nanometer-sized crystalline silicon (nc-Si) dots within the sandwiched structure (a-SiNx:H/a-Si:H/a-SiNx:H) films. The results of transmission electron microscopy, electron diffraction and Raman scattering show the ultra-thin and single-layer nc-Si films were patterned in the lateral direction and the size of crystallites is controlled by the thickness of as-deposited a-Si film in the longitudinal direction. The effects of the laser energy density on the structures of the samples and the crystallization mechanism are discussed.

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MAGNETIC VISCOSITY OF NANOCOMPOSITE Sm-Fe-Cu-Zr-Ga-C RIBBONS Zhang Shao-ying (张绍英), Zhang Hong-wei (张宏伟), Zhao Peng (赵鹏), Shen Bao-gen (沈保根), F. R. de Boer, K. H. J. Buschow Chinese Physics, 2000, 9 (7):  541-544.  DOI: 10.1088/1009-1963/9/7/014 Abstract ( 1296 )   PDF (136KB) ( 521 )   The magnetic viscosity was investigated at temperatures between 100 and 293 K for the nanocomposite Sm2Fe18.25Zr0.25Cu0.5Ga2C2 ribbons prepared by melt-spinning and subsequent annealing. It was found that the maximum S and $\chi$irr, located near coercivity, increase with increasing temperature. The viscosity parameter Sv was found to be strongly dependent on the applied fields at lower fields than the coercivities. The relation between Sv and coercivity was analyzed. The coercivity mechanism is mainly controlled by domain-wall pinning. The activation volume associated with magnetization reversal, which can be calculated from Sv, is much smaller than the grain volume.

CROSS DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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CRYSTALLINE CARBON NITRIDE THIN FILMS DEPOSITED BY MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION Zhang Yong-ping (张永平), Gu You-song (顾有松), Chang Xiang-rong (常香荣), Tian Zhong-zhuo (田中卓), Shi Dong-xia (时东霞), Zhang Xiu-fang (张秀芳), Yuan Lei (袁磊) Chinese Physics, 2000, 9 (7):  545-549.  DOI: 10.1088/1009-1963/9/7/015 Abstract ( 937 )   PDF (1097KB) ( 762 )   The crystalline carbon nitride thin films have been prepared on Si (100) substrates using microwave plasma chemical vapor deposition technique. The experimental X-ray diffraction pattern of the films prepared contain all the strong peaks of $\alpha$-C3N4 and $\beta$-C3N4, but most of the peaks are overlapped.The films are composed of $\alpha$-C3N4 and $\beta$-C3N4. The N/C atomic ratio is close to the stoichiometric value 1.33. X-ray photoelectron spectroscopic analysis indicated that the binding energies of C 1s and N 1s are 286.43eV and 399.08 eV respectively. The shifts are attributed to the polarization of C-N bond. Both observed Raman and Fourier transform infrared spectra were compared with the theoretical calculations. The results support the existence of C-N covalent bond in $\alpha$- and $\beta$-C3N4 mixture.

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

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GREAT MAGNETIC ENTROPY CHANGE IN La(Fe, M)13 (M=Si, Al) WITH Co DOPING Hu Feng-xia (胡凤霞), Shen Bao-gen (沈保根), Sun Ji-rong (孙继荣), Zhang Xi-xiang (张西祥) Chinese Physics, 2000, 9 (7):  550-553.  DOI: 10.1088/1009-1963/9/7/016 Abstract ( 2459 )   PDF (172KB) ( 1059 )   Very large magnetic entropy change $\Delta$SM, which originates from a fully reversible second-order transition at Curie temperature TC, has been discovered in compounds La(Fe, Si)13, La(Fe, Al)13 and those with Co doping. The maximum change $\Delta$SM $\approx$ 19 J·kg-1·K-1, achieved in LaFe11.4Si1.6 at 209K upon a 5T magnetic field change, exceedsthat of Gd by more than a factor of 2. The TC of the Co-doped compounds shifts to higher temperatures. $\Delta$SM still has a considerable large magnitude near room temperature. The phenomena of very large $\Delta$SM, convenience of adjustment of TC, and also thesuperiority of low cost, strongly suggest that the compounds La(Fe,M)13(M=Si, Al) with Co doping are suitable candidates for magnetic refrigerants at high temperatures.