Vol. 42, No. 6 (1993)
1993, 42 (6): 867-873. doi: 10.7498/aps.42.867
In this paper, three kinds of q -deformations of three-dimensional isotropic oscillator are discussed in detail, the Hamiltonians of which have S3, SUq(2) , and Uq(3) symmetries, repectively. Especially, in the third case a specific realization of Uq(3)?SOq′ (3) is given. Relation between the q -deformed oscillator and the classical one is also discussed.
SIMULATION OF TEMPERATURE DISTRIBUTION IN REST FLOW AND COUETTE FLOW BY USING 12 BIT LATTICE GAS AUTOMATON MODEL
1993, 42 (6): 874-879. doi: 10.7498/aps.42.874
To understand thermal properties in lattice gas automata, a twelve bit multispeed model on hexagonal lattice is used to simulate rest flow and Couette flow. Simulating results are compared with theoretical results and some useful conclusion are drawn.
1993, 42 (6): 880-885. doi: 10.7498/aps.42.880
In this paper, the renormalisation group approach is used to treat the problem of percolation on a two-dimensional square lattice with ‘glost' field and next-nearst-neighbour interactions. The critical probability Pc and the critical exponents α,β,γ,ν,δ,η are obtained.
ATOMIC AND MOLECULAR PHYSICS
1993, 42 (6): 886-892. doi: 10.7498/aps.42.886
In this paper, the effect of the spatial inhomogeneity of the laser field and the size of detector acceptance angle or aperture on strong-field autoionization photoelectron spectra is investigated. It is shown that the photoelectron spectra are drastically affected by the above factors , for small detector acceptance angle or aperture size, peak switching appears in the photoelectron spectra, but for large detector acceptance angle or aperture size, peak switching is destroyed completely.
1993, 42 (6): 893-904. doi: 10.7498/aps.42.893
A new formalism for describing the evolution of density operators was proposed. It can evaluate the evolution of density operators of strongly and weakly coupled spin systems in a u-nified way, and describe the experiments involving weak RF pluse. Some problems were explicitly treated including spin tickling, isotropic mixing in systems of two coupled nuclei (I= 1/2), dipolar evolution and strongly coupled AB and ABX spin systems.
DIFFERENTIAL CROSS SECTION CALCULATIONS OF THE e-H ELASTIC SCATTERING BASED ON A MULTIPLE-SCATTERING EXPANSION METHOD
1993, 42 (6): 905-910. doi: 10.7498/aps.42.905
New calculations are conducted for the differential cross sections of e-H elastic scattering in the energy range of 100-200 eV based on a multiple-scattering expansion method. Discussion of the present results is given and comparison is made with experimental data.
CALCULATIONS OF POSITRON SCATTERING BY ATOMIC HYDROGEN BASED ON A MULTIPLE-SCATTERING EXPANSION METHOD
1993, 42 (6): 911-917. doi: 10.7498/aps.42.911
Calculations are conducted for the differential cross sections of elastic scattering of atomic hydrogen by positron in the energy range of 50-300 eV based on a multiple-scattering expansion method. Discussion of the present results is given and comparison is made with other current theoretical calculations.
CLASSICAL AREA OF PHENOMENOLOGY
Based on the definition of Pegg-Barnett phase state, the phase probability distribution functions of various light fields, such as Fock state, coherent state, squeezed state, pair coherent state, entangled state, and so forth and the time evolution of that of some single-mode light fields through the propagation in medium are analytically calculated, while the corresponding computational simulations are presented.
1993, 42 (6): 925-929. doi: 10.7498/aps.42.925
The spontaneous-emission line shape of two atoms interacting with a vacuum field in an ideal cavity with different couplings is investigated. In general, the "vaccum-field Rabi splitting" will show a 12-peaked structure. The 2-peaked structure for one atom and 6-peaked structure for two identical atoms may be obtained as two examples.
1993, 42 (6): 930-934. doi: 10.7498/aps.42.930
We have experimentally studied the instabilities of a homogeneously broadened single-longitudinal mode CO2 laser with transverse magnetic field. Self-pulsing and chaos have been observed by varying the magnetic field. The strange attractor of the laser system has also been obtained. A discussion is made on the mechanism of the phenomena observed.
1993, 42 (6): 935-939. doi: 10.7498/aps.42.935
In this paper, the flat type of CFEL partialy loading dielectric with wiggler is studied using two dimensional kinetic coupling mode theory of three waves. It is shown that the system for arbitary thickness of dielectric can generate short wavelength coherent radiation by using low energy electron beam. Suitably choosing the system parameters, the growth rate of the kind of CFEL may be much higher than general FEL and CFEL. It is also shown that the main mode of super radiation in the system is LSE mode.
1993, 42 (6): 940-948. doi: 10.7498/aps.42.940
The results of experimental and theoretical study on population inversion in the He-like Al ions are presented for the pumping laser intensity range of ～2×1014W|cm2. The effects of different target structure (foil, plane and half-cylinder) on the 2p-3d population inversion of the He-like Al ions (45nm) in a spot focused laser plasma have been studied experimentally. The plasma parameters such as electron temperature, electron density and the ratio of H-like ion density to He-like ion density, are diagnosed by spectroscopic methods. Results are compared with C-R model calculations.
SPECIAL SOLUTION OF SECOND HARMONIC WAVE EQUATION IN NONLINEAR ACOUSTICS AND APPLICATIONS TO BOUNDARY-VALUE PROBLEM
1993, 42 (6): 949-953. doi: 10.7498/aps.42.949
Based on the perturbation theory, an investigation on reflection and refraction of nonlinear wave on a boundary in fluids or solids was carried out a familiar result was obtained that the second harmonic wave always satisfies an inhomogeneous wave equation. In order to find its special solution, the method of separated variables as well as Lagrange's method of variation parameters were invoked , and a trouble to the boundary-value problem of nonlinear acoustics will consequently result in that a separation constant is to be determined. In this paper , the constant was determined and the special solution was given uniquely. It is shown that a paradox will occur unless we select a special solution from the following two solutions, which are accumulation along the direction either parallel to or perpendicular to the boundary plane. Whether one can be selected depends on the boundary situation. By using the theory, the reflection and the refraction on a plane boundary were analysed. Furthermore, it is pointed out that this theory can deal with all of the boundary-value problems in nonlinear acoustics.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1993, 42 (6): 954-962. doi: 10.7498/aps.42.954
An investigation on the lattice deformation of porous silicon layer was completed by means of symmetric and asymmetric X-ray double crystal diffraction. The structure change of porous layer is larger for the sample under lower current density during the anodization in hydrofluoric acid. Both the orientation offset and the lattice expansion in the direction normal as well as parallel to the surface of the matrixes have been measured. The crystal lattice of porous layer formed on the (111) silicon surface is proposed to be triangular distorted, and it gradually matches the lattice of substrate silicon after a time in the atmosphere.
1993, 42 (6): 963-968. doi: 10.7498/aps.42.963
The Raman scattering by LO phonon-plasmon coupled (LOPC) mode in heavily carbon doped p-type GaAs grown by MOMBE has been studied. It was shown by the lineshape analysis based on a theoretical model for the Raman scattering rate that the p-type GaAs has only one LOPC structure in contrast to the two modes in n-type doping case. The influence of heavily doping on the Raman spectroscopy was also discussed based on the experimental results. The linewidth broadening and the red shift of the LOPC mode scattering peak at the ul-trahigh doping level are induced by the crystalline disorder and effects of lattice deformation.
EFFECT OF STRUCTURE ON IONIC CONDUCTIVITY IN THE NANOCRYSTALLINE MATERIALS CaF2 AND Ca0.75La0.25F2.25
1993, 42 (6): 969-977. doi: 10.7498/aps.42.969
Two kinds of nanocrystalline materials CaF2(grain fineness D =16nm) and Ca0.75La0.25F2.25(D = 11nm) possessing clean interfaces were prepared with the method of inert gas evaporation and pressed under ultra high vacuum, Their complex impedance spectra were meas-sured in detail in the temperature range of 31℃ to 530℃. The results show that (1) In the range of 300℃ to 530℃, both of the two kinds of nanocrystalline ionic solids obey the Arrhe-nius equation well; (2) Ionic conductivity of nano-CaF2 is about one order of magnitude higher than that of polycrystalline CaF2, two order of magnitude higher than that of monocrystalline CaF2, activation energy for ionic conduction, E=1.14eV; (3) Ionic conductivity of nano-Ca0.75La0.25F2.25 is 1(300℃)-0.6(525℃) order of magnitude higher than that of nano-CaF2, activation energy E is 1.00eV, somewhat lower than that of nano-CaF2, (4) When the temperature rises from 250℃ to 525℃ , the resistance of grains drops about one order of magnitude, but the resistance of interfaces descends monotonously over four order of magnetude. It is demostrated that migration of F- depends on diffusion among grains at temperature lower than 400℃, and also upon diffusion among interfaces at temperature higher than 450℃. To decrease grain fineness of materials to nanometer-size as well as to mingle fluoride with higher valence can increase the ionic conductivity obviously.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1993, 42 (6): 978-986. doi: 10.7498/aps.42.978
The mechanism of Tc suppression induced by Zn substitution for Cu in YBa2Cu3O7-y system has been studied with respect to its electronic transport properties in normal state, superconducting critical temperature, crystal structure, oxygen stoichiometry and so forth. The results show that Zn ion acts as impurity scattering centre, leading to the increase in the resistivity as well as to the anomalous changes of the resistance-temperature relation. In addition , Zn substitution for Cu reduces the carrier concentration due to the reduction of the number of Cu other than the oxidation state in CuO planes, which precludes the band-filling and carrier-over-saturation models for explaining the mechanism of Tc suppression. Semi-quantitative results reveal that each Zn ion present a scattering cross section with a radius larger than the average Cu-O bond length of the CuO planes. This means that a non-superconducting core may appear around each Zn ion. As a result, the superconducting path in CuO plane will be destroyed gradually.as a percolation process. The percolation threshold observed experimentally is consistent with the theoretical calculation. We believe that the emergence of the normal core together with the consequent percolation is the reason why Tc is suppressed so rapidly by Zn substitution for Cu.
MONTE CARLO STUDY OF THE PHASE DIAGRAM OF ISING FERROMAGNET WITH MIXED SPINS OF S=l/2 AND S=l WITH A CRYSTAL FIELD INTERACTION ON THE HONEYCOMB LATTICE
1993, 42 (6): 987-991. doi: 10.7498/aps.42.987
The single-spin-flip Metropolis-Monte-Carlo algorithm is applied to the study of phase diagram of Ising ferromagnet with mixed spins of S = l/2 and S = 1 with a crystal field interaction on the honeycomb lattice. The phase diagram we obtained is very close to the exact solutions and better than the results of effective field theory with correlations. All these make us arrixe the conclusion that the Metropolis Monte Carlo algorithm can also be used to study the mixed-spin model.
1993, 42 (6): 992-998. doi: 10.7498/aps.42.992
Based on our previous work, introducing an extended Goldbart ansatz, all eigenvalues of the Hessian matrix in our three-dimensional spin glass model are obtained. It is found that the vanishing smallest eigenvalue λ3 has two solutions, which correspond to the Gabay-Toulouse (GT) upper and Almeida-Thouless (AT) lower critical lines respectively. Finally, the relation between our theory and other method is discussed.
1993, 42 (6): 999-1005. doi: 10.7498/aps.42.999
We have prepared (Er1-xSmx)2Fe17Cy(x≤0.8,1.5≤y≤2.5) Compounds with a rhombo-hedral Th2Zn17- type structure by melt-spinning . These carbides are found to be stable at high temperature. The (Er1-xSmx)2Fe17Cy carbides with y = 2. 5 have unit cell volumes about 6.3% larger and Curie tewperatures about 330-360K higher than those of the 2:17 parent compounds. Room-temperature saturation magnetizations increase with increasing C content. It is found that the carbides containing Sm exhibit easy c-axis anisotropy at room temperature. The anisotropy field of (Er0.2Sm0.82Fe17C1.5 at room temperature is 8T.
1993, 42 (6): 1006-1011. doi: 10.7498/aps.42.1006
The ferromagnetic resonance spectra of FeCrZr amorphous alloys have been studied, and compared with that of FeCrB. It is found that there is a greater change in the resonance spectra of Fe-base amorphous alloys when the material is doped with Zr instead of B. The experimental results are analysed.
1993, 42 (6): 1012-1019. doi: 10.7498/aps.42.1012
In order to discribe piezoelectric strain optical modulator (PESOM), we analyzed LiNbO3 crystal resonator excited by distributed piezoelectric source in detial in this paper. The quantitative results of structure of strain field are obtained in one-dimension approximation for PESOM.
1993, 42 (6): 1020-1026. doi: 10.7498/aps.42.1020
Axis-cut LiNbO3 crystal piezoelectric strain optical modulators (PESOM)and its properties when they used as laser mode lockers are analysed in detail. We have proved that x-cut plate is the best form used for laser mode locker. And y-cut or z-cut plate will result in loss modulation and frequency modulation at the same time, so in principle they are not suitable for using as laser mode locker operating at steady state.
1993, 42 (6): 1027-1034. doi: 10.7498/aps.42.1027
In this work we investigate damages on graphite surface gercerated by bombardment with 530 KeV Au+ or 4.5 MeV Au++ at a dose of 1×1012 cm-2. The most significant damages are hillocks with a diameter around 1. 8 nm, as seen from our STM images. Very often they are surrounded by variable 31/2×31/2R30° superstructures of graphite, which die away within a distance of 1 to 3 nm. The density of the hillocks is in good agreement with the ion dose, indicating that they were induced by individual incident gold ions. Besides, in the STM images of higher magnifications there exist many smaller hillocks, which might be caused by the secondary ions or atoms.