Table of contents

20 November 1996, Volume 5 Issue 11 Previous issue    Next issue

GENERAL

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THE FRACTAL BEHAVIOUR OF CRACK PROPAGATION IN BRITTLE MATERIALS DING HONG-ZHI (丁洪志), ZHAO RU-BAO (赵如宝), XING XIU-SAN (邢修三) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  801-808.  DOI: 10.1088/1004-423X/5/11/001 Abstract ( 1256 )   PDF (216KB) ( 423 )   In this paper we try to show how a reasonable equation for crack propagation in brittle materials naturally leads to self-affine or statistically self-similar failure structures. We argue that the fractal behaviours of crack propagation in brittle mate-rials are in essence determined by the scale-invariance of the Fokker-Planck equation. This approach provides a good illustration for understanding the microscopic origin of fractal behaviour in real materials.

ATOMIC AND MOLECULAR PHYSICS

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STRUCTURES IN THE SPECTRUM OF MULTIPHOTON DETACHMENT RATES OF NEGATIVE IONS ZHU QI-REN (朱颀人), WANG BING-BING (王兵兵), PAN SHOU-FU (潘守甫) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  809-816.  DOI: 10.1088/1004-423X/5/11/002 Abstract ( 1066 )   PDF (227KB) ( 362 )   With the help of a model calculation, the following features in the multiphoton detachment rate spectrum of negative ions are shown: (1) the global behavior of the rate, as a function of the photon frequency, does follow the so-called ‘step-like' pattern; (2) a Wigner-type cusp occurs at every threshold open for the lower photon number channel; (3) a clear dip appears at a certain frequency point slightly lower than each threshold frequency. All these features are interpreted as the general characteristics of multiphoton detachments on the R-matrix-Floquet analysis. Comparisons are made with the previous results. To the best of our knowledge, the third feature may be for the first time explained in this paper, though it is not first found by us.

CLASSICAL AREAS OF PHENOMENOLOGY

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VECTOR COUPLED-WAVE THEORY OF DIFFRACTIVE OPTICS IN THE RESONANCE DOMAIN ZHANG GUO-PING (张国平), YE JIA-XIONG (叶嘉雄), LI ZAI-GUANG (李再光) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  817-823.  DOI: 10.1088/1004-423X/5/11/003 Abstract ( 1013 )   PDF (172KB) ( 427 )   In this paper, based on Maxwell's equations and boundary continuity condi-tions of electromagnetic fields, we derive rigorous vector coupled-wave equations of two-dimensional diffractive patterns for an arbitrary polarization in the resonance domain, and describe the solution to these equations. We verify this theory with a practical example, and show the effectiveness of this method for the resonance-domain diffractive optics.

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THEORETICAL STUDY ON TRANSMISSION OF RAPIDLY PHASE-MODULATED SIGNAL IN PHOTOREFRACTIVE TWO-WAVE MIXING LI YAN (李焱), SUN XIU-DONG (孙秀冬), JIANG YONG-YUAN (姜永远), ZHOU ZHONG-XIANG (周忠祥), XU KE-BIN (许克彬) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  824-832.  DOI: 10.1088/1004-423X/5/11/004 Abstract ( 1085 )   PDF (218KB) ( 329 )   The transmission of rapidly phase modulated signal beams in photorefractive two-wave mixing is studied theoretically. The analytical expressions of output intensities are given both in diffusion regime and in drift regime.

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TEMPORAL CHARACTERISTICS OF DECAY OF LIGHT-INDUCED ABSORPTION IN PHOTOREFRACTIVE BaTiO3 CRYSTALS ZHANG JIA-SEN (张家森), DOU SHUO-XING (窦硕星), GAO HONG (高宏), WU XING (吴星), YE PEI-XIAN (叶佩弦) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  833-839.  DOI: 10.1088/1004-423X/5/11/005 Abstract ( 1045 )   PDF (171KB) ( 402 )   We report the observations of the decay processes of light-induced absorption in one undoped and two Ce-doped BaTiO3 crystals. Two decay times were found, they had not a strong dependence on intensity in our experiment. We present a model with two different shallow trap centers to explain the experimental results. The theoretical and experimental resales agree well with each other. The light-induced absorption coefficients and decay times corresponding to the two shallow levels are also given.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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THEORETICAL STRENGTH AND PHASE STABILITY OF Cu AND Ni UNDER [100] UNIAXIAL LOADING CAI JUN (蔡军), YE YI-YING (叶亦英) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  840-848.  DOI: 10.1088/1004-423X/5/11/006 Abstract ( 1095 )   PDF (305KB) ( 494 )   Based on Born's criteria we studied phase stability and theoretical strength of fcc crystals of copper and nickel under [100] uniaxial loading. The calculation was carried out using a simple and completely analytical embedded atom method(EAM) potential proposed by the present authors. For Cu, the calculated value of its theoretical strength (0.33×1011 dyn·cm-2) agrees well with the experimental value (0.30×1011 dyn·cm-2), while the calculated strain (9.76%) is somewhat larger than the experimental one (2.8%). For Ni, its theoretical strength and strain predicted using the EAM potential are found smaller than those predicted using a pair potential. It is worthy to note that unlike previous calculations, in which pair potentials were used and three unstressed fcc, bcc, and fct structures included (for Ni only fcc state is found stable, while for Cu both fcc and bcc states are predicted stable), in present calculations using EAM potential the [100] primary loading path passes through only two zeroes (a stable unstressed fcc structure and an unstable stress-free bcc structure) either for Cu or for Ni.

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

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THE EFFECT OF DIRECT f-f HOPPING ON THE HYBRIDIZATION GAP INSULATING BEHAVIOR OF THE PERIODIC ANDERSON LATTICE HU LIANG-BIN (胡梁宾), YANG FU-MIN (杨富民), SUN JIN-ZUO (孙金祚), LIN ZONG-HAN (林宗涵) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  849-856.  DOI: 10.1088/1004-423X/5/11/007 Abstract ( 1090 )   PDF (219KB) ( 313 )   By using the well known slave-boson technique and within the framework of mean field approximation, we study the effect of the direct f-f hopping on the low-temperature hybridization gap insulating behavior of the periodic Anderson lattice. The results show that the direct f-f hopping will decrease the hybridization gap or lead it to vanish. In the latter case, the lattice will exhibit no hybridization gap insulating behavior even if the lower renormalized band is fully occupied.

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THERMODYNAMIC STUDY ON THE Sm-Ba-Cu-O SYSTEM XING XIAN-RAN (邢献然), QIAO ZHI-YU (乔芝郁), WEI SHOU-KUN (魏寿昆), CHEN XIAO-LONG (陈小龙), LIANG JING-KUI (梁敬魁), RAO GUANG-HUI (饶光辉) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  857-862.  DOI: 10.1088/1004-423X/5/11/008 Abstract ( 1287 )   PDF (134KB) ( 312 )   The assembly for EMF measurement with CaF2 single crystal or MgO partially stabilized zirconia as solid state electrolyte has been constructed. From the EMF data, the standard Gibbs energies, standard enthalpies of formation and standard entropies of sir complex oxides in the Sm-Ba-Cu-O system were calculated. The decomposition pressures of these complex oxides were derived.

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GIANT MAGNETORESISTANCE OF MAGNETIC SUPERLATTICES: QUANTUM SIZE EFFECT ZHANG LING-YUN (张凌云), SUN HONG (孙虹), LI BO-ZANG (李伯臧), PU FU-CHO (蒲富恪) Acta Physica Sinica (Overseas Edition), 1996, 5 (11):  863-838.  DOI: 10.1088/1004-423X/5/11/009 Abstract ( 1131 )   PDF (162KB) ( 318 )   In this paper the quantum size effect in giant magnetoresistance of magnetic superlattices is studied. The electrons are considered to be confined in a set of quantum wells, which are different for the ferromagnetic and antiferromagnetic ordering in magnetic superlattices. The oscillation of giant magnetoresistance with increasing thickness of the nonmagnetic spacer layer is explained. It is shown that the influence of quantum size effects on the giant magnetoresistance of magnetic superlattices is considerable.