Table of contents

15 May 2000, Volume 9 Issue 5 Previous issue    Next issue

GENERAL

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INFLUENCE OF SEED CRYSTAL DIMENSION ON CRYSTAL GROWTH FROM SOLUTION UNDER MICROGRAVITY Zhu Zhen-he (朱振和), Ge Pei-wen (葛培文), Xu Zheng-yi (许政一) Chinese Physics, 2000, 9 (5):  321-324.  DOI: 10.1088/1009-1963/9/5/001 Abstract ( 1169 )   PDF (123KB) ( 415 )   The influence of the dimension of seed crystal on the characteristics of crystal growth from solution under microgravity is studied. The dimensionless average velocity of fluid Vav, the dimensionless maximum velocity of fluid Vmax, the temperature distribution index $S_{\theta}$, the concentration distribution index $S_{\phi}$ and the dimensionless average growth rate of crystal $\overline{V}_{\rm cg}$ are calculated by only taking into account the variation of the solution density caused by the temperature change, that caused by the concentration change being neglected. In certain regions of the parameter (Ra, Pr, Sc and $\mu$) space, some scaling laws are generated: the scales of $S_{\phi}$ and $\overline{V}_{\rm cg}$ are given by power functions of $\mu$ with negative exponents. It is shown that the characteristics of crystal growth for small seed crystal are different from those for large seed crystal.

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EXACT SOLUTION FOR SUPER-JAYNES-CUMMINGS MODEL Lu Huai-xin (逯怀新), Wang Xiao-qing (王晓芹), Zhang Yong-de (张永德) Chinese Physics, 2000, 9 (5):  325-328.  DOI: 10.1088/1009-1963/9/5/002 Abstract ( 1014 )   PDF (175KB) ( 730 )   Based on the linear quantum transformation theory, we further propose a supersymmetric unitary transformation, whose operator can be constructed by the supersymmetric generators of Lie superalgebra. Therefore, by making use of the supersymmetric unitary transformation, we can obtain the eigenspectrum, the eigenstates and the super-partition function for the Super-Jaynes-Cummings model when the coupling constants are Grrassmann valued.

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ROTATING RINDLER SPACE TIME WITH CONSTANT ANGULAR VELOCITY Wang Yong-cheng (王永成) Chinese Physics, 2000, 9 (5):  329-332.  DOI: 10.1088/1009-1963/9/5/003 Abstract ( 1094 )   PDF (93KB) ( 405 )   A new space time metric is derived from Kerr metric if its mass and location approach to infinite in an appropriate way. The new space-time is an infinitesimal neighborhood nearby one of the two horizon poles of an infinite Kerr black hole. In other words, it is the second order infinitesimal neighborhood nearby one of the two horizon poles of a Kerr black hole. It is flat and has event horizon and infinite red shift surface. We prove that it is a rotating Rindler space time with constant angular velocity.

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A METHOD OF CONTROLLING SPATIOTEMPORAL CHAOS IN COUPLED MAP LATTICES Luo Xiao-shu (罗晓曙), Fang Jin-qing (方锦清) Chinese Physics, 2000, 9 (5):  333-336.  DOI: 10.1088/1009-1963/9/5/004 Abstract ( 1426 )   PDF (218KB) ( 501 )   We propose a method that allows one to control spatiotemporal chaos by applying pulses proportional to the system variables and compressing the phase space of strange attractor in nonlinear system. The method is illustrated by the coupled map lattices at different strengths of coupling. Various numerical results are given. The advantage of this method is that it does not need to know any previous knowledge of the system dynamics.

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GENERAL SYNCHRONIZATION OF CHAOS IN A SYSTEM OF TWO NON-IDENTICAL LASERS Zhu Shi-qun (朱士群), Lü Xiang (吕翔), Chen Xian-feng (陈险峰), K. S. Thornburg, Jr., G. D. VanWiggeren, R. Roy Chinese Physics, 2000, 9 (5):  337-341.  DOI: 10.1088/1009-1963/9/5/005 Abstract ( 1205 )   PDF (294KB) ( 514 )   General synchronization of the chaotic intensity fluctuations of two spatially coupled Nd:YAG lasers with pump modulation is investigated theoretically when the losses of the two lasers are different. It is shown that the chaotic synchronization still exists for medium coupling even though the two lasers are different. For strong coupling the system shows periodic motion of laser intensities. While for weak coupling, the two lasers oscillate independently. It is obvious that the increase of difference between the two lasers reduces the degree of chaotic synchronization.

ATOMIC AND MOLECULAR PHYSICS

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PYRAMIDAL-HOLLOW-BEAM DIPOLE TRAP FOR ALKALI ATOMS Yin Jian-ping (印建平), Gao Wei-jian (高伟建), Wang Yu-zhu (王育竹), Zhu Yi-fu (朱一夫), Wang Yi-qiu (王义遒) Chinese Physics, 2000, 9 (5):  342-350.  DOI: 10.1088/1009-1963/9/5/006 Abstract ( 1127 )   PDF (350KB) ( 408 )   We propose a dark gravito-optical dipole trap, for alkali atoms, consisting of a blue-detuned, pyramidal-hollow laser beam propagating upward and the gravity field. When cold atoms from a magneto-optical trap are loaded into the pyramidal-hollow beam and bounce inside the pyramidal-hollow beam, they experience efficient Sisyphus cooling and geometric cooling induced by the pyramidal-hollow beam and the weak repumping beam propagating downward. Our study shows that an ultracold and dense atomic sample with an equilibrium 3D momentum of ～3 $\hbar$ $k$ and an atomic density above the point of Bose-Einstein condensation may be obtained in this pure optical trap.

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ENERGETIC ABOVE-THRESHOLD IONIZATION SPECTRA OF H-ATOM IN INTENSE LASER FIELDS Chen Bao-zhen (陈宝振) Chinese Physics, 2000, 9 (5):  351-352.  DOI: 10.1088/1009-1963/9/5/007 Abstract ( 1032 )   PDF (75KB) ( 384 )   The above-threshold ionization (ATI) spectra of H-atom in intense laser fields (laser intensity I is up to 1018W/cm2) are calculated. It is found that the kinetic energy of the ejected electron at the location of the peak of the ATI spectra is about equal to the corresponding ponderomotive potential of the applied laser fields. This result is consistent with that obtained by Wilks et al. and fits the experimental results of the super thermal electron. A possible new mechanism of the super thermal electron generation is proposed.

CLASSICAL AREAS OF PHENOMENOLOGY

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FLAKE STRUCTURE IN THE SPECKLE FIELD PRODUCED BY A FEW SCATTERERS Liu De-li (刘德丽), Qi Dong-ping (亓东平), Teng Shu-yun (滕树云), Cheng Chuan-fu (程传福) Chinese Physics, 2000, 9 (5):  353-358.  DOI: 10.1088/1009-1963/9/5/008 Abstract ( 1081 )   PDF (412KB) ( 414 )   This paper reports a new phenomenon, namely, flake structure in the speckle field produced by a few scatterers. This structure appears in the off-axis region and its size is much larger than that of the normal speckles. The one-dimensional simulations show that as the roughness of the random surface sample increases or its lateral correlation length decreases, the flakes go farther away from the axis, their relative intensities increase, their sizes become bigger and the fluctuations in them decrease. A sub-scatterer model that we call isoclinic element is proposed to explain the formation and properties of flakes. Experimental evidence shows the existence of the flake structure.

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DIFFUSION PARAMETERS DEPENDENT OSCILLATION CHARACTERISTICS IN Ti-DIFFUSED Nd:LiNbO3 CHANNEL WAVEGUIDE LASER Zhang De-long (张德龙), Chen Cai-he (陈才和), Ding Gui-lan (丁桂兰) Chinese Physics, 2000, 9 (5):  359-367.  DOI: 10.1088/1009-1963/9/5/009 Abstract ( 1036 )   PDF (273KB) ( 518 )   The TM mode size, effective refractive index, effective pump area and coupling efficiency between pump and laser modes as function of Ti-stripe initial width W, diffusion temperature T and Ti-stripe initial thickness H in c-cut Ti-diffused Nd:LiNbO3 waveguide laser have been theoretically investigated using variational method. The main features of the mode sizes in terms of these diffusion parameters were collected and compared with the published experimental results, a qualitative agreement has been obtained. The effective pump area, being proportional to threshold pump power, reveals weak dependences on both W and H in the considered respective ranges 4-16 μm and 40-160 nm, and a strong dependence on T (950-1100℃); while the coupling efficiency relative to slope efficiency hardly changes (with values 0.82-0.85) with these parameters.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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SIMULATION OF MULTIPLE FRACTAL AND COMPACT GROWTH OF ULTRA-THIN FILMS ON HEXAGONAL SUBSTRATE Wang Dai-mu (王戴木), Wu Zi-qin (吴自勤) Chinese Physics, 2000, 9 (5):  368-374.  DOI: 10.1088/1009-1963/9/5/010 Abstract ( 1041 )   PDF (421KB) ( 432 )   The multiple cluster growth of ultra-thin films with different deposition rate and different substrate temperature has been studied by kinetic Monte-Carlo simulation. With increasing diffusion rate along cluster edges (corresponding to an increasing substrate temperature), pattern structures change smoothly from fractal islands, compact islands with random shapes, to regular islands, and the average branch width of clusters increases continuously up to some constant value in the compact island limit. The formation of the multiple fractal and compact clusters can be described quantitatively by multifractal. The results of multifractal analysis show that with pattern change from fractal to compact islands, the Hausdorff dimension D0, the information dimension D1, and the correlation dimension D2 decrease, while the width and height of the multifractal spectra increase.

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

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THE RAMAN SCATTERING OF CARBON NANOTUBES PRODUCED IN DIFFERENT INERT GASES AND THEIR PRESSURES BY ARC DISCHARGE Zhang Hai-yan (张海燕), Chen Jian (陈建), Liu Song-hao (刘颂豪), Chen Di-hu (陈第虎), Wu Chun-yan (伍春燕), He Yan-yang (何艳阳), Liang Li-zheng (梁礼正), Peng Shao-qi (彭少麒) Chinese Physics, 2000, 9 (5):  375-378.  DOI: 10.1088/1009-1963/9/5/011 Abstract ( 1157 )   PDF (804KB) ( 692 )   First- and second-order Raman spectra of carbon nanotubes produced in helium and argon atmospheres at a pressure ranging from 11 to 92 kPa by arc discharge have been measured and compared with each other. The position and bandwidth of the spectral lines depend on the kind of inert gases and their pressure. The Raman spectra of the nanotubes produced in argon gas atmosphere are much more similar to that of polycrystalline graphite than those of the nanotubes produced in helium gas atmosphere. The position and bandwidth of nanotube Raman peaks change with gas pressure in arc discharge because different diameter distribution of nanotubes is produced at different inert gas pressure. The Raman spectra of nanotubes produced at high pressure is much more like that of graphite than those produced in lower pressure

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INDIRECT UP-CONVERSION SENSITIZATION LUMINESCENCE OF Tm(0.1) Yb(10.9): OXYFLUORIDE VITROCERAMICS INDUCED BY 800nm DIODE LASER Chen Xiao-bo (陈晓波), Deng Zhi-wei (邓志威), N. Sawanoborib, Chao Meng (超孟), Zhang Guang-yin (张光寅), Li Mei-xian (李美仙) Chinese Physics, 2000, 9 (5):  379-383.  DOI: 10.1088/1009-1963/9/5/012 Abstract ( 1006 )   PDF (156KB) ( 375 )   This paper reports researches about the indirect up-conversion sensitization luminescence of Tm(0.1)Yb(10.9): oxyfluoride vitroceramics(TmYb:FOV) induced by 800nm diode laser. From the initial comparison research of indirect up-conversion sensitization luminescence between TmYb:FOV and Tm(0.1)Yb(10.9): oxyfluoride glass (TmYb:FOG), it is found that the up-conversion luminescence intensity of TmYb:FOV is much higher than that of TmYb:FOG. It is shown that this is an effective method to e5nhance up-conversion efficiency. It is found also that the fluorescence branch ratio and the meticulous structures are different between vitroceramics and glass. This disparity comes from cluster effect resulting from micro crystallization of the material.

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PHOTOLUMINESCENCE STUDY OF InAs/GaAs SELF-ORGANIZED QUANTUM DOTS WITH BIMODAL SIZE DISTRIBUTION Guo Zhong-sheng (郭忠圣), Wang Hai-long (王海龙), Ning Dong (宁东), Feng Song-lin (封松林) Chinese Physics, 2000, 9 (5):  384-388.  DOI: 10.1088/1009-1963/9/5/013 Abstract ( 1079 )   PDF (252KB) ( 433 )   We have investigated the temperature dependence of the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy image for uncapped sample. The power-dependent PL study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. Due to lacking of the couple between quantum dots, an unusual temperature dependence of the linewidth and peak energy of the dot ensemble photoluminescence has not been observed. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 μm at room temperature.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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STATISTICAL-MECHANICAL ENTROPY OF THE GENERAL STATIC BLACK HOLE DUE TO ELECTROMAGNETIC FIELD Jing Ji-liang (荆继良), Yan Mu-lin (闫沐霖) Chinese Physics, 2000, 9 (5):  389-393.  DOI: 10.1088/1009-1963/9/5/014 Abstract ( 982 )   PDF (226KB) ( 723 )   Statistical-mechanical entropy arising from the electromagnetic field in the general four-dimensional static black hole spacetime is investigated by means of the "brick wall" model. An expression for the entropy is obtained and some examples are considered. The results show that the entropy arising from the electromagnetic field is exactly twice the one for a massless scalar field.