Table of contents

15 September 2000, Volume 9 Issue 9 Previous issue    Next issue

GENERAL

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SELF-ORGANIZED CRITICALITY IN ONE-DIMENSIONAL PACKET FLOW MODEL Yuan Jian (袁坚), Ren Yong (任勇), Shan Xiu-ming (山秀明) Chinese Physics, 2000, 9 (9):  641-648.  DOI: 10.1088/1009-1963/9/9/001 Abstract ( 1589 )   PDF (241KB) ( 460 )   Packet flow affects the behavior of Internet routers, which in return regulates the flow. Even a non-correlated uniform packet flow from a terminal will be modulated to show correlated fluctuations by going through the network nodes. In this paper, we study a simple model in an abstract level to describe intuitively the self-organized criticality in packet level, the emergence of collective behavior of packets, which causes the long-range dependence of congestion in computer networks. We find that the character of the jam lifetime is consistent with the measurement results, the packet delivery time appears the feature of 1/f noise, and the intervals between the packet arrivals are power-law distributed.

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PHASE TRANSITION PROPERTIES OF A TWO-COMPONENT FINITE MAGNETIC SUPERLATTICE Wang Xiao-guang (王晓光), Liu Ning-ning (刘宁宁), Pan Shao-hua (潘少华), Yang Guo-zhen (杨国桢) Chinese Physics, 2000, 9 (9):  649-651.  DOI: 10.1088/1009-1963/9/9/002 Abstract ( 1565 )   PDF (179KB) ( 504 )   We study an (l,n) finite superlattice, which consists of two alternative magnetic materials(components) of l and n atomic layers, respectively. Based on the Ising model, we examine the phase transition properties of the magnetic superlattice. By transfer matrix method we derive the equation for Curie temperature of the superlattice. Numerical results are obtained for the dependence of Curie temperature on the thickness and exchange constants of the superlattice.

ATOMIC AND MOLECULAR PHYSICS

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GLOBAL ANALYSIS OF SPECTRA OF THE PO2 RADICAL IN THE GAS PHASE Liu Yu-yan (刘煜炎), Liu Xiao-yong (刘效庸), Liu Hong-ping (刘红平), Guo Yuan-qing (郭远清), Huang Guang-ming (黄光明), Lin Jie-li (林洁丽), Gao Hui (高晖), Duan Chuan-xi (段传喜) Chinese Physics, 2000, 9 (9):  652-655.  DOI: 10.1088/1009-1963/9/9/003 Abstract ( 1215 )   PDF (206KB) ( 462 )   A global analysis of all available and identified spectra of the PO2 radical has been performed. In this analysis, the infrared spectra of the $\nu$3 band, the microwave and far infrared laser magnetic resonance transitions in the ground state are fitted simultaneously to the effective Hamiltonian for asymmetric top molecules. Since the analysis absorbs reliable experimental data extensively, it bears the most precise and most complete set of molecular constants for PO2. These molecular constants can be used to reproduce the spectra of PO2 accurately. Attention is also paid to the similarity and difference between PO2 and NO2.

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ELECTRONIC STRUCTURE OF CLUSTER-ASSEMBLED Al12C (Si) SOLID Quan Hong-jun (全宏俊), Gong Xin-gao (龚新高) Chinese Physics, 2000, 9 (9):  656-660.  DOI: 10.1088/1009-1963/9/9/004 Abstract ( 1156 )   PDF (222KB) ( 531 )   The electronic structures of the cluster-assembled solid Al12C(Si) are studied by the ab initio method. We find that Al12C(Si) can solidify into a van der Waals solid. The electronic band structures show very weak dispersion. The main features in the electronic structure of cluster are retained in the solid, and an energy gap up to about 1.5 eV is observed for Al12C and Al12Si solids.

CLASSICAL AREAS OF PHENOMENOLOGY

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MULTIMODE THEORY OF WHISPERING-GALLERY-MODE MICROSPHERE LASER Chai Jin-hua (柴金华), Lu Yi-qun (路轶群), Leung Pui-tang (梁培) Chinese Physics, 2000, 9 (9):  661-666.  DOI: 10.1088/1009-1963/9/9/005 Abstract ( 1098 )   PDF (237KB) ( 571 )   A multimode theory of whispering-gallery-mode microsphere laser is developed based on the linear and nonlinear semiclassical theory of the microsphere laser. The average photon-number of each lasing mode and the pumping level requirement for multimode coexistence are derived. The comparison between the theory and experimental results shows that the theory can be used to treat the practical problems on microsphere laser.

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STABILITY OF BRIGHT SCREENING-PHOTOVOLTAIC SPATIAL SOLITONS Liu Jing-song (刘劲松), Zhang Du-ying (张都应), Liang Chang-hong (梁昌洪) Chinese Physics, 2000, 9 (9):  667-671.  DOI: 10.1088/1009-1963/9/9/006 Abstract ( 1222 )   PDF (214KB) ( 577 )   We present a theoretical analysis of the stability of screening-photovoltaic (SP) spatial solitons in biased photovoltaic-photorefractive materials in the case of neglecting the loss of the material and the effect of diffusion. When an incident optical beam is a SP soliton, this beam propagates along a linear path with its shape kept unchanged. When the maximum amplitude, width and functional form of an incident optical beam are slightly different from those of a SP soliton, the beam reshapes itself and tries to evolve into a solitary wave after a short distance. That is, these SP solitons are stable against small perturbations. However, optical beams that significantly differ from SP soliton solutions tend to experience larger cycles of compression and expansion, and their maximum amplitudes oscillate with propagation distances. The larger the perturbations, the stronger the oscillation.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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EFFECT OF SMALL CLUSTER DIFFUSION DURING TWO-DIMENSIONAL THIN FILM GROWTH ON METAL SURFACE Wu Feng-min (吴锋民), Li Qiao-wen (李巧文), Wu Zi-qin (吴自勤) Chinese Physics, 2000, 9 (9):  672-675.  DOI: 10.1088/1009-1963/9/9/007 Abstract ( 1326 )   PDF (183KB) ( 587 )   The diffusion of small clusters such as dimers and trimers on metal surface and the growth of two-dimensional thin films are studied by Monte Carlo simulation, using realistic growth model and physical parameters. It is found that small cluster diffusion plays an important role in the process of thin film growth at not very low temperature. It affects not only the island density and the size of islands but also the critical value of saturation occurring during growth of thin films. The effect of small cluster diffusion depends on both the size of critical nucleus and the growth temperature. The simulation results also show that the larger the cluster allowed to diffuse, the easier the saturation that takes place, giving rise to the lower critical coverage of saturation occurring. It is suggested that the effect of small cluster diffusion should be included in establishing the growth models of thin films.

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

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ELECTRICAL PROPERTIES, EQUATIONS OF STATE AND PHASE TRANSITION IN SOLID C60 AT HIGH PRESSURE Bao Zhong-xing (鲍忠兴), V. H. Schmidt , N. S. Dalal , C. S. Tu , N. J. Pinto, Liu Cui-xia(柳翠霞), Li Yu-liang(李玉良), Zhu Dao-ben(朱道本) Chinese Physics, 2000, 9 (9):  676-679.  DOI: 10.1088/1009-1963/9/9/008 Abstract ( 1414 )   PDF (197KB) ( 471 )   Electrical properties and equations of state in solid C60 at room temperature and high pressure have been studied in a diamond anvil cell using capacitance and resistance measurements and a piston-cylinder type device using P-V measurements, respectively. Experimental results by capacitance and P-V measurements indicate that solid C60 also undergoes a phase transition at room temperature and a lower pressure, about 2GPa. The phase transition may be from a face-centered-cubic to a simple-cubic structure.

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THE SIGN REVERSAL AND SCALING RELATIONS OF HALL ANOMALY IN THE MIXED STATE TYPE-II SUPERCONDUCTORS Wei Yeu Chen, Ming Ju Chou, Huang Zhong Bing(黄忠兵) Chinese Physics, 2000, 9 (9):  680-684.  DOI: 10.1088/1009-1963/9/9/009 Abstract ( 1409 )   PDF (205KB) ( 570 )   We present a new model for the anomalous Hall effect in the mixed state of type-II superconductors. In this model we consider the thermally activated motion of the many body correlating vortex lattice system. The sign change of the Hall resistivity is the result of the competition between the motion of effective antivortices and the motion of the pinned vortex lattice together with the interstitial vortices. Within this model many essential experimental results for the complicated Hall effect can be explained.

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STRUCTURE AND M?SSBAUER STUDY OF NANOCRYSTALLINE Ni-Zn FERRITE Wang Li (王丽), Li Fa-shen (李发伸), Zhou Qing-guo (周庆国) Chinese Physics, 2000, 9 (9):  685-688.  DOI: 10.1088/1009-1963/9/9/010 Abstract ( 1501 )   PDF (204KB) ( 697 )   Ni1-xZnxFe2O4 (0.0≤x≤1.0) nanoparticles have been prepared by the polyvinyl alcohol (PVA) sol-gel method. The lattice parameter of Ni-Zn ferrite nanoparticles is larger than that of the bulk material. The variation of saturation magnetization (Ms) as a function of x has been studied. The M$\ddot{\rm o}$ssbauer spectra of the samples at room temperature showed the presence of ultrafine particles, exhibiting superparamagnetic relaxation. At higher annealing temperature, the portion of the ferromagnetic ultrafine particles increased.

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ANISOTROPY OF OPTICAL ABSORPTION INTENSITY IN Tm3+ DOPED YVO4 CRYSTALS Lin Xiu-hua (林秀华), Jiang Bing-xi (江炳熙) Chinese Physics, 2000, 9 (9):  689-694.  DOI: 10.1088/1009-1963/9/9/011 Abstract ( 1121 )   PDF (225KB) ( 526 )   Seven absorption group-bands (1D2, 1G4, 3F2, 3F3, 3H4, 3H5, 3F4) of Tm3+ in YVO4 single crystals have been observed in the orientation absorption spectra recorded in the spectral range from 200 to 4000 nm at 300K. The integrated absorption cross section for each group-band was accurately evaluated. On the assumption that the anisotropy of this uni-axial crystal is small, the Judd-Ofelt theory was extended for the calculation of 4f-4f transition intensities of Tm3+ in YVO4. Two sets of phenomenological intensity parameters were derived from a least-squares-fit procedure. For c-axis cut sample we have $\varOmega$2=10.18 (10-20cm2), $\varOmega$4=1.96 (10-20cm2), $\varOmega$6=0.75 (10-20cm2).For a-axis cut sample we have $\varOmega$2=8.20 (10-20cm2), $\varOmega$4=2.47 (10-20cm2), $\varOmega$6=0.91 (10-20cm2). The anisotropy of the optical absorption intensities of Tm3+:YVO4 was theoretically analyzed in detail.