Vol. 48, No. 8 (1999)
1999-04-20
GENERAL
1999, 48 (8): 1389-1393.
doi: 10.7498/aps.48.1389
Abstract +
In this paper, simultaneously considering the variation of classical mass and the relativistic effect of mass variation with velocity, a relativistic four-covariant equation of variable mass body is built. And the physical meaning of this equation is demonstrated. Ackeret formula is derived from the equation.
1999, 48 (8): 1394-1398.
doi: 10.7498/aps.48.1394
Abstract +
Explicit expressions of n B?cklund-Darboux (BD) transformations and corresponding symmetries for generalized KdV (GKdV) equation, were constructed by using factorization of Gelfand-Dickey operator. This extends Lou's recent result about the BD transformations and non-local symmetries for KdV, Kadomtsev-Petviashvilli equations. As a by-product, we also derive a representation of Wronskian determinant for the GKdV solution.
1999, 48 (8): 1399-1404.
doi: 10.7498/aps.48.1399
Abstract +
Coupled squeezed states for the Landau system (planar charged particle moving in a uniform magnetic field) are built. These coupled squeezed states and decoupled squeezed Landau states give some information about the circular motion of charged particles respectively.
1999, 48 (8): 1405-1411.
doi: 10.7498/aps.48.1405
Abstract +
After analyzing the course of forming‘garbage blocks’, we proposed an alternative for preparing the pseudo-pure states. It can be used to reduce or even to remove the‘garbage blocks’.
1999, 48 (8): 1412-1419.
doi: 10.7498/aps.48.1412
Abstract +
The multiple cluster growth with fractal or compact morphology in ultra-thin films has been simulated with various permitted diffustion steps. It is shown that the fractal dimension increases with increasing cluster size in the fractal growth. The nucleation rate decreases with increasing diffusion steps and drops rapidly with increasing deposition time. The cluster size S can be described by a power law as S-(t-t0)κ, where (t-t0) is the growth time. The growth index κ is slightly smaller than 1 given by the classical nucleation and growth theory, due to the branching effect between clusters. A nonlinear phenomenon (i.e., the larger the cluster size, the larger the growth index κ) has been obtained.
NUCLEAR PHYSICS
1999, 48 (8): 1420-1425.
doi: 10.7498/aps.48.1420
Abstract +
The projected shell model is applied to the nuclei 186Pb, 188Pb and 190Pb. The low-lying prolate bands of them are calculated and the results are compared with experimental data, the low-lying bandheads of these three nuclei are predicted, the reliability of this prediction is validated when we apply this model to the nucleus 186Hg and it gives a satisfactory agreement with the experimental data.
ATOMIC AND MOLECULAR PHYSICS
1999, 48 (8): 1426-1432.
doi: 10.7498/aps.48.1426
Abstract +
Charge transfer processes for double-electron colliding systems H++He and He2++He have been studied by using the asymptotic two-state atomic expansion method developed recently. Our results for the cross sections of electron capture are in good agreement with those given by the boundary-corrected first-order Born (B1B) approximation and experimental data in high-intermediate energies, and in the low-intermediate energies the present results are better than those obtained by the B1B approximation. Finally, we point out that the reason that capture cross sections predicted by first-order perturbation theory are in poor agreement with experimental data.
CLASSICAL AREA OF PHENOMENOLOGY
1999, 48 (8): 1433-1438.
doi: 10.7498/aps.48.1433
Abstract +
We study the statistical properties in the superpositions of SU(1,1) coherent states ｜ζ，k〉and ｜ζ，k〉. The even SU(1,1) coherent state (｜ζ，1/4〉) and odd SU(1,1) coherent state (｜ζ，3/4〉) correspond to squeezed vacuum state and squeezed one photon number state, respectively. It is shown that the superposed states can exhibit much stronger squeezing and antibunching for the suitable phase of ζ and the relative phase in superposition. We also propose a method of generating such superposed states.
1999, 48 (8): 1439-1445.
doi: 10.7498/aps.48.1439
Abstract +
The effects of photon antibunching in the interaction system of a two-level Rydberg atom with a single-mode thermal field via two-photon processes are studied, by considering the second-order correction of atomic scattering. The influences of the nonlinear correction term, the two photon frequency detuning and the thermal noise on the photon antibunching are discussed.
1999, 48 (8): 1446-1451.
doi: 10.7498/aps.48.1446
Abstract +
The propagation characteristics of flattened Gaussian beams (FGBs) and super-Gaussian beams (SGBs) have been studied and compared with each other. Numerical illustrative examples have been given. The main result obtained in this paper is that the FGB and SGB with the same M2 factor and beam width demonstrate the very similar propagation and transformation characteristics, including the intensity distribution and diffraction effect due to the aperture, while they propagate through an optical system.
1999, 48 (8): 1452-1458.
doi: 10.7498/aps.48.1452
Abstract +
We have studied theoretically a beat effect in a four-level system due to fifth-order optical polarization, and considered the cases that the pump beams have either narrowband or broadband linewidth. We have found that the accuracy for the energy-level splitting meaurement is determined by the homogeneous linewidths of the optical transitions. That is to say, this technique can achieve Doppler-free precision in the measurement of the eaergy level splitting between two excited states which are dipolar forbidden from the ground state.
1999, 48 (8): 1459-1469.
doi: 10.7498/aps.48.1459
Abstract +
We have studied the spontaneous emission from a three-level atom with an external-driving field in a photonic crystal. As a result of quantum interference and photon localization, the population in the two upper levels displays quasi-oscillatory or oscillatory behavior. This depends on the initial atomic state and the relative positions of the two upper levels from the forbidden gap. The intensity and the phase of the external field can affect spontaneous emission from the atom. The properties are different from a three-level atom either in vacuum or in a photonic crystal without an external driving field.
1999, 48 (8): 1470-1476.
doi: 10.7498/aps.48.1470
Abstract +
We present a Lattice Boltzmann model to simulate compressible flows by introducing an attractive potential based on the simple selectable sound speed model. The corresponding macro-dynamical equation from Chapman-Enskog expansion shows that this model has the advantage to soften sound speed effectively and then the Mach number is raised greatly(up to more than 3). Simulations of March cone and the comparison between theoretical expectations and simulations demonstrate that the scheme is effective in simulation of compressible flows with high Mach numbers, which would open many new applications.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (8): 1477-1483.
doi: 10.7498/aps.48.1477
Abstract +
The highest occupied molecular orbitle(HOMO) and lowest unoccupied molecular orbitle(LUMO) charge density distributions of adsorbed C60 with different orientations are calculated by using discreted variational-local density functional (DV-LDF) method. The theoretical simulations of scanning tunneling microscope (STM) images are based on Tersoff-Hamann theory. The results show that the charge density distribution parttens have their own‘fingerprint’. The LUMO charge distributions are more reliable than HOMO distributions when using them to simulate STM images. The molecular orientations can be easily determined by comparing with observed STM images in experiments and theoretical calculations in the literatures. Morevoer, according to the STM images obtained from our experiments, a new adsorbed orientation of C60 on Si(111)-7×7 surface has been found. Namely, C60 can adsorb with its 5—6 bond facing towards the substrate surface. At the same time, experimentalist can get some useful imformation from the results of this paper, and the orientations of the other molecules can also be determined by using the method.
1999, 48 (8): 1484-1490.
doi: 10.7498/aps.48.1484
Abstract +
The features of the electroluminescence spectra in amorphous silicon p-i-n diodes were ecxellently explained by dispersive-transport-controlled recombination. The misunderstanding to the efficiency and peak position of the electroluminescence for many yera was thereby clarified by the theory. The experimental methods of local states in the intrinsic layer of a-Si-H solar cells studied by the electro-luminescence were described in detail. The studied results showed that the defect energy distribution exhibited a single narrow peak when the samples were prepared by diluted silane using hydrogen, while the defect energy distribution was wider with double peaks in the samples deposited by pure silane.
1999, 48 (8): 1491-1495.
doi: 10.7498/aps.48.1491
Abstract +
Radiation-induced segregation of Ni element in Fe-1 wt%Ni alloy was investigated by ion accelerator and high voltage electron microscope. The results show that the complexes of Ni, vacancy and hydrogen diffuse towards voids due to the inverse Kirkendall effect. Ni atoms would precipitate along {110} planes near voids. Streak diffraction pattern from the coherent precipitates of Ni can be observed.
1999, 48 (8): 1496-1502.
doi: 10.7498/aps.48.1496
Abstract +
Transmitting energy spectra of 500keV—1MeV He+ ions penetrating 50—90μm thick seed coat of maize, fruit peel of grape and of tomato are measured. The results indicate that these thick biological targets, as seen by penetrating ions, are inhomogencous and there are open“channel like” paths along which the incident ions can transmit the targets easily. While most of the incident ions are stopped in the targets, some of the transmitting ions only lose a small fraction of their initial incident energy. The transmitting energy spectra show a pure electronic stopping feature. Transmission electron microscopic taken from these samples with thickness of 30μm indicate that 150keV electron beam can penetrate the thick samples to give very good images with clear contrast. The electronic structures of β-1,4-glucosan molecular chains, which is deemed as the important constituent of the cell walls of seed coats and peels of fruits, are calcuated to show the possible channeling directions existing in biological samples.
1999, 48 (8): 1503-1508.
doi: 10.7498/aps.48.1503
Abstract +
The low-frequency internal friction in Cr75Fe16Mn9 alloy has been measured in temperature range of 100—600K and at frequencies lower that 10Hz. It is found that an internal fraction peak at 450K and corresponding jump of modules exist in the paramagnetic phase. This indicates there is a disorder-order transition on coupling states between individual spins for the Cr and Fe components. There is a broad internal friction peak in the temperature range from 200 to 300K, which consists of a peak at 280K and the extended broad peak at 220—270K. We suggest that this effect is the reflection of the spin density wave antiferromagnetic transition and the coexistence of different magnetic phases in the alloy. Our results reflect the fact that internal friction method would be a sensitive and effective probe for investigating the change of microstructure including electric structure.
1999, 48 (8): 1509-1513.
doi: 10.7498/aps.48.1509
Abstract +
In nucleation process of thin film growth, stable clusters will gradually cover substrate surface. The growth will occur in the covered parts of substrate, and the nucleation will proceed in the uncovered parts. In this paper, we investigate the influence of coverage on nucleation and growth of thin films and give a series of revised formulae for the widely used theory of thin film growth. We get that the nucleation rate is proportional to the square of uncovered area. It looks rough that the nucleation rate is considered to be a constant in thin film theories.
1999, 48 (8): 1514-1517.
doi: 10.7498/aps.48.1514
Abstract +
The nucleation thermodynamics of dot structure in the groove structure of substrate surface by vapor deposition has been studied. A growth model of dot structure by controlling the nucleation taking place in the designed microscopic structure was suggested. The Gibbs free energy of the critical nuclei formation in the groove structure was calculated, and found that the groove structure can effectively promote the nucleation. Finally, considering the groove structure trapping effect, we deduced that the growth rate of the stable atomic cluster in the groove structure is larger than that of the atomic cluster on a flat surface.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1999, 48 (8): 1518-1522.
doi: 10.7498/aps.48.1518
Abstract +
The conducting mechanism of the cathode material La1-xSrxMnO3 was investigated from is structural characteristics. The conducting mechanism which was confirmed by the correlation of conductivity and temperature is the small polaron hopping process at temperatures below 1000℃.
1999, 48 (8): 1523-1528.
doi: 10.7498/aps.48.1523
Abstract +
The growth process of large fractal aggregates formed by diffusion and rotation of silver clusters on sillicone oil surfaces in investigated. Our results indicate that the silver clusters rotate randomly on the liquid substrates and the mean square angle displacement 2> and time difference Δt satisfy the generalized Einstein relation 2>=4DθΔt. The random rotation coefficient Dθ scales with the cluster size S as Dθ∝S－γθ, where γθ＝2.4±0.3. The dependence of the fractal dimension of the aggregates on the deposition rate and aggregate time is also presented.
1999, 48 (8): 1529-1534.
doi: 10.7498/aps.48.1529
Abstract +
The measurement of dielectric susceptibility under various frequencies for Pb(Zr0.52Ti0.48)O3 (PZT) ceramics shows that there exists a dielectric loss peak below and close to phase transition temperature, which is relaxational characteristic but disagrees with Arrhenius relation. The peak arise from the interaction between domain walls, lattice and pinning defects. In this paper the behavior of the dielectric loss peak of PZT under various frequencies is simulated by using the dynamic equation of viscous motion of domain walls and by considering the Curie temperature dispersion in ceramics as well. The agreement between the simulatied result and experimental data is quite satisfactory. And from the parameters of simulation the viscous coefficient of the motion of domain walls and the recovering force constant of pinning defects are calculated.
1999, 48 (8): 1535-1540.
doi: 10.7498/aps.48.1535
Abstract +
Based on our interchain coupled theoretical model for quasi-one-dimensional organic ferromagnet, we took into account the nearest and the next nearest hopping interactions between neighboring chains, to study the charge density wave and the spin density wave along the main chain. The calculated results showed that the interchain coupling results in the transfers of charge density and spin density between the main chain and the side radicals of the two coupled chains.
STRUCTURAL AND OPTICAL PROPERTIES OF SELF-ASSEMBLED InAs QUANTUM DOTS GROWN ON GaAs(311) A SUBSTRATE
1999, 48 (8): 1541-1546.
doi: 10.7498/aps.48.1541
Abstract +
We report the structural and optical characteristics of InAs quantum dots (QDs) grown on GaAs (311)A substrates. Atomic force microscopic result shows that QDs on (311)A surface exhibit a nonconventional, faceted, arrowhead-like shapes aligned in the [233] direction. The photolumi-nescence (PL) intensity, peak position and the full width at half maxinum (FWHM) are all colsely related to the measurement temperature. The fast redshift of PL energy and monotonous decrease of linewidth with increasing temperature were observed and explained by carriers being thermally activated to the barrier produced by the wetting layer and then being retrapped and recombined in energetically lower-lying QDs states. This model explains our results well.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1999, 48 (8): 1547-1551.
doi: 10.7498/aps.48.1547
Abstract +
By allowing the segregation coefficient and interface temperature to depend on interface speed in a thermodynamically-consistent way, the non-equilibrium effects are incorporated into a linear stability analysis of planar front. The absolute stability limit of the cellular mode is modified. A new oscillatory instability is found, which leads to the formation of solute bands in the solid, and its absolute-stability limit is determined by solute trapping and kinetics. The results of this theory are in agreement with observations.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
1999, 48 (8): 1556-1557.
doi: 10.7498/aps.48.1556
Abstract +
The evolution characters of angular velocity Ωh of central black holes of accretion disks (including thin and thick disks) are investigated by considering both accretion and the Blandford-Znajek (BZ) process. It is shown that the rate of change of Ωh with respect to time truns from the positive value to the negative, as the dimensionless angular momentum a* evolves to a critical value. Evolving in a non-monotonous way, Ωh increases at first, and then decreases in a prograde accretion process. Therefore there exists a maximum of Ωh. It is pointed out that dimensionless angular momentum a* is more appropriate to describe the spinning state of a central black hole of an accretion disk than angular momentum J and angular velocity Ωh.
1999, 48 (8): 1558-1564.
doi: 10.7498/aps.48.1558
Abstract +
After considering thermal character of the inner horizon of Kerr black hole, we give a new form of the Bekenstein-Smarr formula and re-define black hole entropy. The balck hole entropy re-defined must go to zero as the temperature of black the approaches absolute zero. The entropy satisfies the Nernst theorem, so it can be regarded as the Planck absolute entropy of black hole.
