中国物理B

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MEASURE OF CHAOTIC ORBITS FOR STANDARD MAP

陈式刚, 王友琴

1993 (7): 481-489. doi: 10.1088/1004-423X/2/7/001

摘要 ( 1415 )

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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→∞, 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 D_b = 2-β. The behaviour of m₀(k) and D_b(k) is studied numerically.

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INVESTIGATION ON THE MULTIDIMENSIONAL NUCLEAR FISSION DYNAMICS

包景东, 卓益忠, 吴锡真

1993 (7): 490-499. doi: 10.1088/1004-423X/2/7/002

摘要 ( 1013 )

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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,α} parametrization. The realistic Langevin calculations of two-dimensional transient rate are compared with the one-dimensional case and generalized Kramers rate formula.

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MULTIPLE-SCATTERING THEORETICAL CALCULATIONS AND ANALYSIS FOR THE ELECTRONIC STRUCTRURES OF RYDBERG STATES IN A SODIUM MOLECULE

潘永乐, 范戆, 李家明

1993 (7): 500-507. doi: 10.1088/1004-423X/2/7/003

摘要 ( 1122 )

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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 μ and the electronic-vibrational interaction (i.e. dμ/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

梅刚华, 黄贵龙, 王嘉珉, 杨德林, 张原, 朱熙文

1993 (7): 508-515. doi: 10.1088/1004-423X/2/7/004

摘要 ( 1039 )

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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.

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NEUTRAL HYDROGEN DENSITY MEASUREMENT IN TMSPP

姚鑫兹, T.F.YANG, F.R.CHANG-DIAZ

1993 (7): 516-522. doi: 10.1088/1004-423X/2/7/005

摘要 ( 952 )

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Resonance fluorescence of neutral hydrogen illuminated by H_α (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_α 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.

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THERMODYNAMIC ANALYSIS AND FORMATION ENTHALPY CALCULATION OF OXYGEN VACANCY DEFECT IN DOPED LITHIUM NIOBATE CRYSTALS

强亮生, 张洪喜, 徐崇泉, 徐玉恒

1993 (7): 523-527. doi: 10.1088/1004-423X/2/7/006

摘要 ( 1117 )

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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.

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BOND STRUCTURE AND ELECTRON STATES OF CHARGED C₆₀

傅柔励, 叶红娟, 傅荣堂, 陈樟, 孙鑫

1993 (7): 528-536. doi: 10.1088/1004-423X/2/7/007

摘要 ( 1186 )

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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 I_h to D_5d. 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 R₂Fe₁₄BN_x

张晓东, 潘琪, 董生智, 葛森林, 杨应昌, 杨继廉, 张百生, 丁永凡, 叶春堂

1993 (7): 537-543. doi: 10.1088/1004-423X/2/7/008

摘要 ( 1406 )

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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 R₂Fe₁₄BN_x, 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

何元金, 吴文, 段晓东

1993 (7): 544-549. doi: 10.1088/1004-423X/2/7/009

摘要 ( 1310 )

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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.

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