Vol. 48, No. 6 (1999)
We explore the time evolution of BEC condensates under different condition by solving the time-dependent nonlinear Schr?dinger equation (NLSE) that describes an inhomogeneous, weakly interacting Bose-Einstein condensate at zero temperature. We present numerical results of interference of two condensates which have different number of atoms in them and examine the evolution of a Bose-Einstein condensate which has split into two parts.
1999, 48 (6): 983-986. doi: 10.7498/aps.48.983
By use of algebraic method, the exact solution of the time-dependent Dirac equation was obtained, and the exchange symmetry in the solution was discussed.
TWO NEW CLASSES OF CONDITIONALLY EXACTLY SOLVABLE POTENTIAL AND THEIR NONLINEAR SPECTRUM-GENERATING ALGEBRAS
1999, 48 (6): 987-991. doi: 10.7498/aps.48.987
Using ideas of supersymmetric quantum mechanics, two new classes of conditionally exactly solvable potentials are constructed from the displaced harmonic oscillator potential. The supersymmetry as well as the space symmetry is broken in one class of them. Furthermore we construct the nonlinear spectrum-generating algebras for them.
1999, 48 (6): 992-994. doi: 10.7498/aps.48.992
The conformal flat space-time solutions in electromagnetic and scalar theory are shown, and the indefiniteness of the plane-symmetric solutions and the method for defining a noncontinuous field by the intersection of multi-solutions are demonstrated.
1999, 48 (6): 995-1002. doi: 10.7498/aps.48.995
The BEC in finite-number trapped atoms is investigated in this paper. The results show that the transition temperature is decreased by the finite-number effect, and the interactions between the atoms change the transition temperature, too. The specific heat below the transition point is no longer proportional to T3/2. In addition to the above effects, the distribution of the trapped atoms depend on its number. The repulsive interaction between the atoms also dilute the density of the atoms.
1999, 48 (6): 1003-1010. doi: 10.7498/aps.48.1003
We discussed the kinetics of n-polymer aggregation processes with source-reinforced, The asymptotic expression of Cm(t) is obtained by the steady-state solution of generalized Smolu-chovski's equation with source. Universal power law distributions of cluster size are obtained in gelling systems.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
INVARIANT-RELATED UNITARY TRANSFORMATION METHOD AND EXACT SOLUTIONS FOR THE QUANTUM DIRAC FIELD IN A TIME-DEPENDENT SPATIALLY HOMOGENEOUS ELECTRIC FIELD
1999, 48 (6): 1011-1022. doi: 10.7498/aps.48.1011
On the basis of the generalized invariant formulation, the invariant-related unitary transformation method is used to study the evolution of the quantum Dirac field in a time-dependent spatially homogeneous electric field. We solve the functional Schr?dinger equation for the Dirac field and obtain the exact solutions and corresponding total phase. The total phase includes both the dynamical phase and geometric phase (Aharonov-Anandan phase).
ATOMIC AND MOLECULAR PHYSICS
1999, 48 (6): 1023-1029. doi: 10.7498/aps.48.1023
High-order harmonic spectra are obtained by numerically solving the one-dimension time-dependent Schr?dinger equation with single-active-electron approximation. The influence of the initial phase of the excitation field on the single-atom high harmonic generation is analysized through Gabor analysis of the acceleration of the atomic dipole. The influence of the initial phase on the process of the high harmonic generation stronger for the shorter-duration pulses than for the longer case. A pulse train or a single pulse of subfemtosecond level could be obtained by high harmonic generation through the adjustment of the phase of the excitation laser field.
CLASSICAL AREA OF PHENOMENOLOGY
1999, 48 (6): 1030-1036. doi: 10.7498/aps.48.1030
Sn-Bi nanometer powders were produced by an electrohydrodynamic technique. The microstructural feature of Sn-Bi nanometer powders was investigated by means of XRD, TEM and HREM. The results show that Sn-Bi nanometer powders produced are composed of tetragonal β-Sn monophase supersaturated solid solution and rhombohedral Bi monophase supersaturated solid solution. Most of the Sn-Bi nanometer powders are single crytals, only a few Sn-Bi nanometer powders are twin crystals. The particles of﹤10nm in diameter are perfect single crystals. There exist dislocations in the particles larger than 10nm in diameter. The formation mechanism of microstructure for Sn-Bi nanometer powders is analyzed.
1999, 48 (6): 1037-1043. doi: 10.7498/aps.48.1037
When a cluster of particles is immersed in a uniform electric field, the particles are coupled to-gether due to the mutual interaction among them. This interaction causes the dipole moment of the cluster to be dependent upon the spatial arrangement and relative permittivity of the particles and up-on the cluster size. In this work, we attempt to estimate the dipole moment of finite cubic arrays of particles, in terms of that of particle chains which has been known. We assume that a chain may be replaced by a single equivalent sphere with the same dipole moment. With replacing the chain by equivalent sphere, a cluster is simplified to a planar array, and this planar array is simplified to a chain, then the dipole moment is obtained. Numerical calculations are performed. It is found that our results are acceptable.
THE GENERAL SOLUTION FOR THE PROBLEM OF A PLANE ELECTROMAGNETIC WAVE REFLECTED AND TRANSMITTED FROM THE INTERFACE BETWEEN A STATIONARY DIELECTRIC MEDIUM AND A DIELECTRIC MEDIUM MOVING IN AN ARBITRARY DIRECTION
1999, 48 (6): 1044-1051. doi: 10.7498/aps.48.1044
The problem of reflection and transmission of an electromagnetic plane wave incident from a dielectric medium, reflected and transmitted by another dielectric medium which moving in an arbitrary direction is analyzed in detail. The field vectors of the reflected and transmitted waves, and the reflection and transmission coefficients as well as the energy relations are deduced for the reflected, transmitted and incident waves. In particular, the properties of the force exerted on the moving medium by a plane wave are discussed in comparison with the case in which the incident space is free space and some new phenomenon are suggested for notice.
1999, 48 (6): 1052-1059. doi: 10.7498/aps.48.1052
A nonconductive isotropic chiral medium is described by using classical electromagnetic theroy. The phenomenon of nonlinear optical activity of a linearly polarized aignal light under the action of a circularly polarized pump light is investigated. The expressions of nonlinear optical rotational angle are given. The calculated results using the expressions are in accordance to the experimental results.
ULTRA-SHORT PULSE PROPAGATING IN FIBONACCI QUASI-PERIODIC OPTICAL SUPER-LATTICE INFLUENCED BY GVD AND SPM
1999, 48 (6): 1060-1065. doi: 10.7498/aps.48.1060
In this paper, from the structure feature of the Fibonacci super-lattice, based on the principles of self phase modulation (SPM) and group velocity dispersion (GVD), we make use of the split step FFT method, conduct an investigation in SPM and the effects of higher order GVD to spectral devel-opment and temporal shaping of ultra-short pulses propagating in the Fibonacci super-lattice. It is shown, when the ultra-short pulses propagating in the Fibonacci super-lattice, because of SPM and GVD, the evolution of the pulse shape and development of the spectra are asymmetric. With increasing length of the super-lattice, the pulse will split into two separate sub-pulses, and the pulse spectra may also split.
THE INTERACTION CHARACTERISTICS BETWEEN SPACE CHARGE AND DIPOLE IN THE HOST-GUEST NLO POLYMER ELECTRET DR1/PMMA FILMS
1999, 48 (6): 1066-1071. doi: 10.7498/aps.48.1066
In this papet the interaction characteristics between space charge and dipole in the host-guest nonlinear optical polymer electret DR1/PMMA films are studied by means of the open-circuit thermal stimulate discharge(TSD) technique and measurements of the isothermal surface potential decay and the electro-optical effect. The results indicate that there are two kinds of charges：space and dipole in the poled material, the energy level for most of the space charge trapped by the traps of sample is higher than the bound level of dipole charge originating from the dipole alignment after suitable heat than the bound level of dipole charge originating from the dipole alignment after suitable heat treatment, and there is a strong interaction between space charge and dipole. The decay of space charge will cause the change of charge distribution in the materials, which subsequently leads to relaxation of the dipoles. The stability of space charge trapped in the material significantly affects the life of dipole alignment for the material.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
The growth process of microsize charged grains is investigated. Two growth mechanisms of collecting ion flow and coagulation are considered, in which the latter dominates and forms a monodisperse distribution of grain size. A simplified physical model has been suggested on the basis of energy equipartition theorem and a dynamic equation for the distribution function of grain size has been deduced. The preliminary computational results are in agreement with the above consideration on the growth mechanisms.
1999, 48 (6): 1078-1085. doi: 10.7498/aps.48.1078
The interaction between particle and temperature fields of AC plasma arc is studied. Attention is given to the interaction and its effects on temperature fields and particle's thermal history. The effect of convection is also discussed. It is demonstrated that such interaction is improtant and the particle can increase the stability of arc column and the convection decrease it.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (6): 1086-1094. doi: 10.7498/aps.48.1086
The roles of STM tungsten tip and external static electric field in single corner silicon adatom extracting from Si(111)-7×7 surface are studied using discrete variational-local density functional (DV-LDF) method with cluster models. The binding energy and the different charge density distri-bution of the system are calculated under various conditions. The results show that, the activation barrier decreasing is a chemical effect due to the procimity of the eletrodes. The effect of external electric field depends on its polarity. A monotonous decrease in the activation barrier is seen for positive bias case, while a small increasing is seen for negative bias case. The single corner silicon adatom cannot transfer from the sample surface if only considering the role of the static interaction among the tip, external electric field and sample surface. The mechanisms of atomic manipulation on semiconductor surfaces are discussed.
1999, 48 (6): 1095-1102. doi: 10.7498/aps.48.1095
We present the structure features of diamond-like films, discuss the relation between the coefficients in the preparation of diamond-like films and analyse how these coefficients affect the structure and property of the films in detail.
1999, 48 (6): 1103-1106. doi: 10.7498/aps.48.1103
We have investigated the structure of the crystal LiNbO3: MgO at both low temperature and room temperature. The results showed that the crystal structure had changed little after doping of Mg2+. At room temperature the lattice showed distorted a little, which caused the appearance of overlaping of some individual scattering peaks. As the temperature decreased, the overlaping reduced gradually.
GAMMA IRRADIATION ON ROOM TEMPERATURE SHOPR-WAVELENGTH HgCdTe PHOTOVOLTAIC DEVICE STUDIED BY ADMITTANCE SPECTROSCOPY
1999, 48 (6): 1107-1112. doi: 10.7498/aps.48.1107
Admittance Spectroscopy (AS) measurements have been performed on n+-on-p Hg1-xCdxTe(x=0.6) photodiodes. Before gamma-irradiation, a deep level located 0.15 eV above the valence band is observed, its trap density Nt=4.8×1015cm-3 with the capture cross section of approximately 2.2×10-17cm2, which is probablely induced by a compound defect correlated with Hg vacancy. After 104 Gy gamma-irradiation, a new trap center located 0.19 eV above the valence band is found, and the pre-irradiation trap level 0.15 eV above the valence band is no longer seen. The trap densities for these two levels are almost the same. This defect level change ultimately makes the device performance deteriorated.
1999, 48 (6): 1113-1117. doi: 10.7498/aps.48.1113
Changes of surface electronic states of InP under 1 keV X-ray irradiation is studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet ray energy spectroscopy (UPS). Our results show that the soft X-ray irradiation has little effect on In atoms but much on P atoms. We analysed the mechanism of irradiation and explained the major effect.
1999, 48 (6): 1126-1131. doi: 10.7498/aps.48.1126
In this article Au was deposited on PVF(Polyviny formal) film which was kept at 253 K to grow Au submonolayer film. It is found that there are special areas whose morphology differs from other's experiment in which metal was deposited on single crystal. In these areas especially big clusters were found and they were surrounded by empty bands. Our deduction that this is caused by variation of local coefficient is proved by a modified DDA(Deposition-Diffusion-Aggregation) model which includes edge diffusion. We also argue that the relationship between cluster diffusion coefficient DS, and particles numbers S which the cluster contains should be exponential for Au cluster on PVF film instead of power-dependent in original DDA model.
1999, 48 (6): 1132-1137. doi: 10.7498/aps.48.1132
The electrical property of 1—4 stages of intercalation compounds of CuCl2, which were synthesized with 2—3μｍ graphite powder, was measured by the four-probe method. Their conductivity was 1.5—2.2 times as that of their host material, graphite. The higher the stage, the higher the conductivity. The microanalysis of chemical compounds by the X-ray energy spectrum scanning analysis of TEM testified that the atom ratio of chlorine and cupric was non-stoichoimetric. The vacancy of the chlorine anion the GICs increased the concentration of the carrier particle. They link up in c-axis, and enlarged the activity space of the carrier particle. The exchange of the electrovalence of the cupric ion has been testified by XPS-ESCA. Graphite and chloride in the stage structure, seem to be the conductor and insulator, which form the “sandwich” structure. This special structure produced a weak chemical bond belt and provided the carrier space in the perpendicular direction to the c-axis. These factors in and vertical to the direction of c-axis together increased the electrical properties.
DYNAMIC INTERACTING FORCE AND EVOLUTION OF COULOMB EXPLOSION PATTERNS FOR SWIFT H+2 PENETRATING THROUGH SOLIDS
1999, 48 (6): 011118. doi: 10.7498/aps.48.11118
We simulate the Coulomb explosion patterns for swift H+2 ions penetrating through solids by solving the equations of motion. The forces acting on individual fragments are given by the stopping force and the dynamic interacting force. With the plasmon-pole approximation dielectric function, the linear-response dielectric theory is used to determine the dynamic interacting force. The initial directions of the molecular axis with respect to the beam direction are assumed to be random. It is found that due to the dynamic-interaction effects, the molecular axes tend to align to the beam direction and the energy losses of the trailing ions are larger than that of the leading ions.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
EXCITON STATES AND LUMINESCENT PROPERTIES IN ONE-DIMENSIONAL SEMICONDUCTOR POLYMER AND THE EFFECT OF LATTICE DISTORTION
1999, 48 (6): 1138-1146. doi: 10.7498/aps.48.1138
We use Lanczos exact diagonalization method to analyze the energy and the wave functions of exciton states in one-dimensional semiconductor polymer with electron-electron interactions. On the basis of this we further calculate the effect of the local lattice distortion on the exciton states and luminescent properties and find that the efficiency of luminescence is proportional to the strength of local lattice distortion under special electron-electron interaction parameters.
1999, 48 (6): 1147-1151. doi: 10.7498/aps.48.1147
The thermal conductivity and the electrical conductivity of Cr75FexMn25-x(x=16,18) alloys have been measured over the temperatures range from 77K to 300K. The change of slope on thermal conductivity-temperature curve and the maximum on electrical conductivity-temperature curve have been found near the transition temperature of spin density wave type antiferromagnetism, which is related to the opening of the energy gap. Both alloys exhibit a rise in the phonon thermal eonductivity with decreasing temperature as being characteristic of umklapp processes.
1999, 48 (6): 1152-1162. doi: 10.7498/aps.48.1152
The characteristic of microwave radiation (λ＝8mm) response of YBCO granular films was reported. Experimental results show that the response behavior can be described with nonequilibrium response effect, instead of thermal effect model. Near below the transition temperature T∞, nonequilibrium microwave response signal decays gradually and disappears with the sample resistance becoming zero. It was also found that the response signal is very sensitive to a weak magnetic field. The sample I-V curve was studied carefully, and the Kosterlitz-Thouless transition model can be used to describe the two-dimensional transport characteristic of the YBCO granular films. Based on the analysis and experimental results, we believe that the mechanism of nonequilibrium microwave response may be related with the breaking of the votex-antivotex pair in high Tc superconductor.
1999, 48 (6): 1163-1169. doi: 10.7498/aps.48.1163
Spin density wave in organic ferromagnets with open ends was studied and the results were compared with that in a closed organic ferromagnet ring. It was found that an end-open chain structure is unfavorable for the formation of the ferromagnetic ground. The competition of electron-electron interactions and the π-electron-radical spin couplings and their different effect on the SDW in the main chain were discussed.
1999, 48 (6): 1170-1174. doi: 10.7498/aps.48.1170
Using XRD and TEM techniques, the modification mechanism of Fe3O4-SrFe12O19 particles has been studied. We have also studied the growth mechanism of spinel phase coating overlayer, and demonstrated that there exists a strong exchange coupling between coating overleyer and core particles due to the complexation of Fe2+ ions in suspension and Fe3+ ions extracted from the core particles. After modification, crystal structure and magnetic properties of SiFe12O19 particles were modified.
1999, 48 (6): 1175-1178. doi: 10.7498/aps.48.1175
The self diffusion coefficients D of lithium ions in PAN-EC/PC-LiClO4 gel polymer electrolytes with different compositions and at different temperatures have been directly measured by field gradient NMR spin echo technique. The results indicated that self diffusion coefficients D of lithium ions were dependent on the mass ratio x% of lithium salt, and had a maxiumum at x=10 in the range of x=5 to 20. It was suggested that this was probably involved with transport mechanisms of the hopping of lithium ions, and with two kinds of interactions: the interaction between Li+ ions and plasticizer EC, and the interaction between Li+ ions and network polymer PAN.
1999, 48 (6): 1179-1184. doi: 10.7498/aps.48.1179
The optical anisotropy of organic molecular films induced by molecular reorientation was investi-gated by using the perturbation method.We presented theoretical formulae about the dependence of second harmonic generation (SHG) intensity on the polarization of fundamental beam.SHG beam and the dipping direc tion.The experimental studies and discussion were given under some special conditions.The expermental results agreed well with the theoretical calculation.