Table of contents

20 July 1993, Volume 2 Issue 7 Previous issue    Next issue

GENERAL

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MEASURE OF CHAOTIC ORBITS FOR STANDARD MAP CHEN SHI-GANG (陈式刚), WANG YOU-QIN (王友琴) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  481-489.  DOI: 10.1088/1004-423X/2/7/001 Abstract ( 1520 )   PDF (253KB) ( 414 )   In this paper, the measure m0 of the chaotic orbits in phase space for standard map is studied. As the nonlinearity parameter k→0, the contribution to chaotic measure m0(k) is mainly from the stochastic layers near separatrices of resonance regions. As k→$\infty$, the contribution to non-chaotic measure (1 - m0(k)) is mainly from the accelerator modes. The behaviour of m0(k) in these regions is studied analytically and numerically. For medial k value, the chaotic orbit forms a fat fractal, its boundary is a typical fractal with dimension Db = 2-$\beta$. The behaviour of m0(k) and Db(k) is studied numerically.

NUCLEAR PHYSICS

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INVESTIGATION ON THE MULTIDIMENSIONAL NUCLEAR FISSION DYNAMICS BAO JING-DONG (包景东), ZHUO YI-ZHONG (卓益忠), WU XI-ZHEN (吴锡真) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  490-499.  DOI: 10.1088/1004-423X/2/7/002 Abstract ( 1125 )   PDF (208KB) ( 434 )   The expression of multidimensional fission rate with quantum effect at finite temperature has been obtained by menus of the approach of path integral expressed as Fourier series. The covariant form of the fission diffusion equations and the quantities related to it under general coordinate transformations in phase space are studied. The differences between two or three-dimensional and one-dimensional cases are analyzed carefully by using the {c, h, $\alpha$} parametrization. The realistic Langevin calculations of two-dimensional transient rate are compared with the one-dimensional case and generalized Kramers rate formula.

ATOMIC AND MOLECULAR PHYSICS

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MULTIPLE-SCATTERING THEORETICAL CALCULATIONS AND ANALYSIS FOR THE ELECTRONIC STRUCTRURES OF RYDBERG STATES IN A SODIUM MOLECULE PAN YONG-LE (潘永乐), FAN ZHUANG (范戆), LI JIA-MING (李家明) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  500-507.  DOI: 10.1088/1004-423X/2/7/003 Abstract ( 1254 )   PDF (310KB) ( 664 )   Based on the independent-particle-approximation and the multiple-scattering self-consistent-field theory, we have systematically calculated the electronic struc-tures of sodium molecular Rydberg series, analysed the quantum defect $\mu$ and the electronic-vibrational interaction (i.e. d$\mu$ /dR). The influences of double excitation configuration on the Rydberg series have been discussed. The electronic structures of Rydberg states and related dynamic behavior in a sodium molecule have been eluci-dated. Our theoretical results are in fair agreement with the available experimental measurements.

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PRODUCTION OF POLARIZED 7Li ATOMIC BEAM IN STRONG MAGNETIC FIELD BY OPTICAL PUMPING MEI GANG-HUA (梅刚华), HUANG GUI-LONG (黄贵龙), WANG JIA-MIN (王嘉珉), YANG DE-LIN (杨德林), ZHANG YUAN (张原), ZHU XI-WEN (朱熙文) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  508-515.  DOI: 10.1088/1004-423X/2/7/004 Abstract ( 1124 )   PDF (219KB) ( 360 )   The production of a polarized 7Li atomic beam in a strong magnetic field was experimentally studied by laser optical pumping of a single ground hyperfine F level. It was shown that nearly complete negative and partial positive polarizations of 7Li atoms could be realized under appropriate conditions by this pumping scheme, which was in agreement with the rate equation calculations. Based on the analyses of transition probabilities, the maximum polarizations for various transitions and light polarizations were given.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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NEUTRAL HYDROGEN DENSITY MEASUREMENT IN TMSPP YAO XIN-ZI (姚鑫兹), T.F.YANG, F.R.CHANG-DIAZ Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  516-522.  DOI: 10.1088/1004-423X/2/7/005 Abstract ( 1031 )   PDF (183KB) ( 444 )   Resonance fluorescence of neutral hydrogen illuminated by H$\alpha$ (656.3 nm) radiation provides a technique for spatially and temporally resolved density measurements of neutral hydrogen in high temperature plasma. Experiments have been performed in the exhaust of a tandem mirror space propulsion device. The laser fluorescence signal from plasma has been separated successfully by eliminating the H$\alpha$ radiation from plasma and laser stray light using differential method of two optical paths. The resolution of signal is greatly enhanced. The radial distribution of hydrogen decreases from edge toward the center.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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THERMODYNAMIC ANALYSIS AND FORMATION ENTHALPY CALCULATION OF OXYGEN VACANCY DEFECT IN DOPED LITHIUM NIOBATE CRYSTALS QIANG LIANG-SHENG (强亮生), ZHANG HONG-XI (张洪喜), XU CHONG-QUAN (徐崇泉), XU YU-HENG (徐玉恒) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  523-527.  DOI: 10.1088/1004-423X/2/7/006 Abstract ( 1202 )   PDF (140KB) ( 404 )   Based on the thermodynamic analysis of oxygen vacancy defects in lithium niobate (LiNbO3 (LN)) and the data of thermogravimetric experiment, the formation enthalpies of congruent and several rare-earth (RE) doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping with valence-changeable RE ions. The experimental results were discussed and a new reduction process for photorefractive LN crystals at a relatively low temperature was proposed, and the reduction-treated crystals showed good effect in practical use.

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

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BOND STRUCTURE AND ELECTRON STATES OF CHARGED C60 FU ROU-LI (傅柔励), YE HONG-JUAN (叶红娟), FU RONG-TANG (傅荣堂), GHEN ZEANG (陈樟), SUN XIN (孙鑫) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  528-536.  DOI: 10.1088/1004-423X/2/7/007 Abstract ( 1309 )   PDF (304KB) ( 367 )   In the alkali-metal doped C60, the charge transfer induces the distortion of the bond structure and forms the self-trapping electronic bound states. Our theory manifests: 1, the charge transfer reduces the symmetry of C60 from Ih to D5d. 2, Both the bond distortion and the self-trapping states possess layer structures and are localized in the equatorial area. 3, The carbon atoms in charged C60 are divided into eight layers with an inversion center, then there exist four nonequivalent groups of carbon atoms. It makes the NMR line split into a fine structure with strength ratio 1:1:2:2. 4, The charged C60 has two self-trapping bound states, one is 0.06eV above HOMO with odd parity and the other is 0.05 eV below LUMO with even parity.

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CRYSTALLOGRAPHIC STRUCTURE AND INTRINSIC MAGENTIC PROPERTIES OF R2Fe14BNx ZHANG XIAO-DONG (张晓东), PAN QI (潘琪), DONG SHENG-ZHI (董生智), GE SEN-LIN (葛森林), YANG YING-CHANG (杨应昌), YANG JI-LIAN (杨继廉), ZHANG BAI-SHENG (张百生), DING YONG-FAN (丁永凡), YE CHUN-TANG (叶春堂) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  537-543.  DOI: 10.1088/1004-423X/2/7/008 Abstract ( 1501 )   PDF (204KB) ( 464 )   We found that the nitrogen atoms can enter into the R2Fe14B structure by a proper heat treatment in nitrogen atmosphere. The crystallographic structure and magnetic properties of R2Fe14BNx, R =Nd and Y, have been investigated by using X-ray and neutron diffraction techniques as well as magnetic measurements. The neutron diffrac-tion data show that the nitrogen atoms occupy the 4f interstices. The interstitial nitrogen atoms were found to have an effect of enhancing Curie temerature, whereas, decreasing saturation magnetization and magneto-crystalline anisotropy. The rela-tionship of the crystal structure and the intrinsic magnetic properties of this crystal is discussed.

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POSITRONIUM EMISSION FROM SURFACE OF Si SUBSTRATES PASSIVATED BY HF ETCHING HE YUAN-JIN (何元金), WU WEN (吴文), DUAN XIAO-DONG (段晓东) Acta Physica Sinica (Overseas Edition), 1993, 2 (7):  544-549.  DOI: 10.1088/1004-423X/2/7/009 Abstract ( 1394 )   PDF (204KB) ( 366 )   In order to develop a low-temperature heat-treatment technique for the prepa-ration of Si substrates to be used in-situ in molecular beam epitaxy (MBE), surface defects of the HF etched and passivated substrates were investegated with a slow positron beam analysis, the analysis system was equipped on-line with the molecu-lar beam epitaxy device. The fraction of positronium (Ps) emission from Si surface at different temperatures was estimated by a "peak-method", after comparing with the reflection high energy electron diffraction patterns, it was concluded that for a HF treated specimen a clean and stable passivated surface suitable to MBE can be obtained by an in-situ low-temperature (about 550℃) treatment. However, the pa-rameters of HF treatment (etching time, HF concentration, etc.) should be precisely adjusted in order to avoid the production of excessive damages on Si surfaces.