Vol. 46, No. 7 (1997)
1997-04-05
GENERAL
1997, 46 (7): 1249-1253.
doi: 10.7498/aps.46.1249
Abstract +
Using a non-local symmetry of the Kaup-Kupershmidt (KK) equation, we find a new exact solution in two different ways. Firstly, using the standard prolongation approach, we obtain the finite Lie B?cklund transformation and the single soliton solution of the KK equation. Secondly,combining some local symmetries and the nonlocal symmetry, we get the group invariant solution and obtain the new soliton solution of the KK equation.
1997, 46 (7): 1254-1258.
doi: 10.7498/aps.46.1254
Abstract +
Some solitary wave solutions for a class of nonlinear wave equations utt－a1uxx＋a2ut＋a3u+a4u3=0 are obtained by homogeneous balance method and Wu-eliminition method. Many well-known equations in physics such as φ4 equation, Klein-Gordon equation, Duffing equation and telegraph equation are special cases of the wave equation presented in this paper.
1997, 46 (7): 1259-1266.
doi: 10.7498/aps.46.1259
Abstract +
The Hermitian cosine and sine operators for two particular models of two-mode space are obtained. As they commute, the common eigenstates are constructed. The properties of the operators and eigenvectors are discussed. The expectation values of these operators under the P-B phase representation are also studied.
1997, 46 (7): 1267-1272.
doi: 10.7498/aps.46.1267
Abstract +
It is shown that the raising and lowering operators derived from the factorization of the radial Schrdinger equation for the two-dimensional hydrogen atom and the isotropic oscillator are equivalent to the Runge-Lenz vector. This implies that the factorizability of the radial Schr?dinger equation is intimately connected with the closeness of classical orbits and the dynamical symmetry.
1997, 46 (7): 1273-1281.
doi: 10.7498/aps.46.1273
Abstract +
By discussing on the dynamical equations of sorts of particles in the non-stationary Rindler and the Vaidya space-time,it is shown that after introducing new coordinates into a time-dependent metric,the method to define the tortoise coordinate transformation in a stationary space-time can be generalized to a non-stationary case.The character of the obtained tortoise transformation is that the temperature function is obviously dependent on time.It is also shown that the Hawking processes are independent of the source terms in the dynamical equations.Particularly,we find a picture where particle-scattering must be twice in the Hawking radiation described by the general time t such as in the non-stationary Rindler case.
1997, 46 (7): 1282-1289.
doi: 10.7498/aps.46.1282
Abstract +
In this Paper, we investigate a nonlinear system composed of an effective two-level atom or ion interacting with two quantized cavity fields.We propose a fairly universal intensity-dependent Raman model to describe the atomic or ionic transitions involving 2k photons.Using the standard and unified method we have put forward, we obtain the analytical expressions of the model′s energy eigenvalues and eigenvectors, evolution operator,photon number operators for the two quantized modes,as well as the atomic inversion operator.
1997, 46 (7): 1290-1299.
doi: 10.7498/aps.46.1290
Abstract +
For state space reconstruction of the chaotic signals overwhelmed in the noise,based on dynamical systems theory and current methods of reconstruction, we propose a new reconstruction method by using the subset of principal components with the largest variance. We also discuss the reconstruction window. The new approach is verified by analyzing the singular spectra and the phase portraits of the Lorenz′s signal superposed with white noise.
1997, 46 (7): 1300-1306.
doi: 10.7498/aps.46.1300
Abstract +
Generally,dynamical analysis is just for the time series on the whole of value field.The time series on a value subfield is a subseries of the one on the whole of value field,and appears to be sampled nonuniformly in time.In this paper,by using the method of fuzzy delay coordinate reconstruction,we study the correlation dimensions,the largest Lyapunov exponents and the prediction of the time series on the value subfield of Kent-map. It is shown that the subseries behaves like some other chaotic time series,and the smaller the value subfield is, the larger the correlation dimensions and the largest the Lyapunov exponents are,and thus the poorer the characterization of prediction is.
1997, 46 (7): 1307-1311.
doi: 10.7498/aps.46.1307
Abstract +
Employing a kind of piece-wise linear map with a hole,we show that “hole-induced crisis” is a result of the emergence of a “strange repeller due to discontinuity”. The strange repeller forces the iteration orbit to escape from the original chaotic attractor.Thus the attactor suddenly expands.We have proved that the lifetime of iterations in original attractor is inversely proportional to the escaping ratio,which enables us to obtain the dependence of the mean lifetime on the control parameter analytically.
NUCLEAR PHYSICS
1997, 46 (7): 1312-1318.
doi: 10.7498/aps.46.1312
Abstract +
Fragment-fragment correlation functions have been measured for 40Ar+159Tb collisions at E/A=30MeV.Emission time of intermediate mass fragments has been extracted from correlation functions using the three-body trajectory model.The average emission time varies with the energy of fragments.It decreases from about 500fm/c for low energy fragments to about 100fm/c for energetic fragments.The emission time also decreases with increasing beam energy,which implies the emission mechanism of fragments translates from sequential binary decay to multifragmentation disassembly.The transitional beam energies are about 35—45MeV/nucleon for 40Ar+159Tb collisions.
ATOMIC AND MOLECULAR PHYSICS
1997, 46 (7): 1319-1325.
doi: 10.7498/aps.46.1319
Abstract +
This paper presents the molecular dynamics simulations of atomic structures of nanocrystals (1—3nm).The X-ray diffraction patterns and the radial distribution functions corresponding to the above nanocrystalline structures were also computed.The results show that the interfacial component exhibits short-range order,and the distortion in crystalline component increases with the decrease of grain size.
1997, 46 (7): 1326-1331.
doi: 10.7498/aps.46.1326
Abstract +
This paper provides a molecular dynamics simulation for atomic structure of nanocrystals (1—3nm).Lattice parameter.grain size and lattice distortion were computed by X-ray diffraction simulation.The results show that the basic structure of the grain and grain boundaries are the same in both nanocrystal and coarse grain materials.The decrease of grain size and the increase of volume fraction of grain boundaries lead to different properties of nanocrystals.
CLASSICAL AREA OF PHENOMENOLOGY
1997, 46 (7): 1332-1337.
doi: 10.7498/aps.46.1332
Abstract +
We show that in macroscopic derivation of nonlocal material relation for a moving fluid,the involved local rest frame should be rotated with the fluid together.To determine the- relationship between the local rest and laboratory frames,outside the velocity,there will appear- three space angles in the set of state variables for the fluid.They satisfy three general equations.Although this work is given for a simple model of relaxation time,the provided approaches- are general,and applicable for obtaining more complicated material relations with dispersion and nonlinearity,which are invariant under the Lorentz transformation.
1997, 46 (7): 1338-1343.
doi: 10.7498/aps.46.1338
Abstract +
In the approximation of pertubation,the thermal wave imaging was proved to be linear shift invariant under some conditions.Based on this fact ,the signal formation mechanism of such a system was interpreted when used in nondestructive evaluation of opaque materials.
1997, 46 (7): 1344-1348.
doi: 10.7498/aps.46.1344
Abstract +
In this paper we show that nondegenerate Λ three-level medium without external coherent driving can produce a large index of refraction at a point of vanishing absorption via the atomic coherence which is induced by the probe field itself.
1997, 46 (7): 1349-1353.
doi: 10.7498/aps.46.1349
Abstract +
In this paper,a quasi-Dirac equation is founded in Compton regime for free electron laser.The equation is solved by using an approximation method and the formula of the current density obtained corresponds to the new wave function. Our result shows that the spin influences the distributions of the wave function and the current density.
1997, 46 (7): 1354-1359.
doi: 10.7498/aps.46.1354
Abstract +
This paper discusses a kind of Cantor fractal film set including absorbing materials. The reflectivity of the film set is calculated and the characteristics of the reflection spectrum is discussed. Unlike the situation where absorbing materials do not exist,there is no self similarity in the whole reflection spectrum. However,under certain conditions the part of the spectrum beyond a certain frequency is approximately self similar.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1997, 46 (7): 1360-1368.
doi: 10.7498/aps.46.1360
Abstract +
The Hα line shape has been fitted with Gaussian function. Hα intensities emitted by the hydrogen atoms,which are reflected by the limiter,and produced from hydrogen molecular dissociation and charge-exchange,were obtained. We have also obtained their incident velocity and ion temperature from Doppler broadening and Doppler shift. This paper discussed the hydrogen atom transport with a simplified model gave the profile of hydrogen atom density and emission coefficient,and analyzed the influence of incident velocity on particle confinement time. Hydrogen atom energy spectra have been also derived from the Hα line shape,It shows that the main molecular processes at the edge of the plasma are hydrogen molecular dissociative excitation and ionic dissociation.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1997, 46 (7): 1369-1374.
doi: 10.7498/aps.46.1369
Abstract +
Amorphous specimens of Fe78Si9B13 have been treated by ultrashort pulse current. It was obtained that the α-Fe(Si) single-phase structure precipitated from the amorphous matrix of Fe78Si9B13 by adjusting the parameters of pulse current. It can be considered that the single-phase crystallization results from the periodic repulsion between the moving electrons and the vacancy-like structural defects in the amorphous parts.That is,the repulsive effect causes the metalloid atoms B to precipitate from the amorphous structural units and Fe(Si) atoms segregate in some localized region. So the basic metal phase is forced to nucleate at a lower temperature. However the directional migration of vacancy-like defects will be accompanied by diffusion of atoms B. Obviously,the segregation of atoms B and the precipitation of Fe-B compound will be checked by both factors the mentioned above.
1997, 46 (7): 1375-1379.
doi: 10.7498/aps.46.1375
Abstract +
The (111) textured C60 films have been fabricated on the fluorophlogopite crystal by hot wall method. X-ray diffraction patterns and Raman spectrum of C60 films indicate that the C60 film is in fcc structure,and tends to have a (111) texture. The surface structure and the crystal morphology of C60 films are measured by scanning electron microscopy and atomic force microscopy. At 77K and 300K,photoluminescence spectra of the textured C60 films are measured. And radiative mechanisms are discussed.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1997, 46 (7): 1380-1387.
doi: 10.7498/aps.46.1380
Abstract +
The electronic spectra for the Vicsek fractal at any stage have been discussed using the tight-binding method with the nearest-neighbor interaction approximation. The calculated results have shown the relationship between the persistent modes from one stage to the next. The particularity of the spectra for the fifth stage of Vicsek fractal obtained by numerical calculation was analyzed.
1997, 46 (7): 1388-1394.
doi: 10.7498/aps.46.1388
Abstract +
The Gaussian wave functional method is applied to investigate the effects of the scattering of a local impurity to the one dimensional conduction electrons,whose low energy behavior can be described by the Luttinger model. Our results show that both the single particle scattering and pair particle scattering are important in this case. The competition between these two scattering mechanisms gives rise to the renormalized masses for both charge and spin density waves. The vanishing of these masses depicts the phase boundaries in the parameter space,different dynamical behaviors are thus determined.
1997, 46 (7): 1395-1399.
doi: 10.7498/aps.46.1395
Abstract +
The low temperature photovoltaic (PV) spectroscopy was used to study the optical transitions between subbands of strained In0.18Ga0.82As/GaAs quantum well,experimental results are well consistent with that of theoritical calculation. The dependence of PV peak transition energy on temperature has been analysed and the strain factor and conduction band offset Qc for quantum well have been found to be almost independent of temperature.The full width at half maxium (HWHM) of transition peaks as a function of temperature has been studied. From a good fit,we discuss the influences of the exciton phonon coupling,alloy disorder and interface roughness on the line shape.
1997, 46 (7): 1400-1405.
doi: 10.7498/aps.46.1400
Abstract +
We have developed a new method of passivating the surfaces of mercury cadmium telluride (MCT) by growing anodic oxidation films in a pulse mode. A novel equipment of pulse anodic oxidation was designed and developed successfully. The interface obtained by this method was superior to that grown by the traditional constant current. The influence of pulse oxidation on MCT surface was investigated by means of SEM, AES and photoconductivity decay. The optimum pulse oxidation condition to reduce the surface recombination velocities has been investigated. The mechanism of the growth of pulse oxidation film is analyzed and discussed.
1997, 46 (7): 1406-1414.
doi: 10.7498/aps.46.1406
Abstract +
Using a three dimensional-quasi-one dimensional-three dimensional model to depict the point contact between a scanning tunneling microscope tip and a metal crystal, by indenting the tip into a metal surface and then withdrawing we have studied the electron transport properties of the microstructure. By means of the single electron approximation and the transfer matrix method, we solve the Schr?dinger equation for this three dimensional system, and calculate the variation regularity of its conductance by quantum mechanics method. The variation of the conductance with constricting and stretching of the constriction is studied, and the quantization of the conductance in units of 2e2/h and 2×2e2/h are obtained.
1997, 46 (7): 1415-1419.
doi: 10.7498/aps.46.1415
Abstract +
The electrical resistivity ( ρ ) and magnetoresistance of polycrystalline pellets of La1-xCaxMnO3 were measured in the 10—300K range in magnetic fields up to 1.8T. It was found that when x increases, both the peak of the electrical resistivity and the peak of magnetoresistance occurs at lower temperatures.The authors suggested that the change of x results in the change of proportion of Mn4+ ions.Variation of the proportion of Mn4+ ions leads to the change of magnetic structure of La1-xCaxMnO3.Zener's model of double exchange coupling can be used to explain the experimental results.
1997, 46 (7): 1420-1426.
doi: 10.7498/aps.46.1420
Abstract +
Co-Zr/Pd multilayers were prepared by a radio frequency sputtering method.The thickness of the Co-Zr magnetic layers was fixed at 1.8nm,and the thickness of Pd layers was changed from 0.5 to 6nm.The oscillation of saturation magnetization with a period of about 1nm was obtained as the thickness of Pd layers increased.This can be attributed to the oscillation of the polarization of Pd layers.X-ray diffraction showed that magnetic alloy Co-Zr layers were in a crystalline state when the Pd layers were thicker than 1.3nm though a thick Co-Zr single layer was in an amorphous state.The superlattice peaks in the high angle X-ray diffraction patterns showed that there existed a coherent growth between the Co-Zr layers and Pd layers when the Pd layers were thicker than 1.3nm.Moreover,as the thickness of the Pd layers increased,periodically oscillatory phenomena were found both in the crystalline grain size perpendicular to the film plane and in the interplanar distance of the fcc(111) plane.These phenomena may be related to the oscillatory interlayer coupling between Co-Zr magnetic layers through Pd layers.
1997, 46 (7): 1427-1436.
doi: 10.7498/aps.46.1427
Abstract +
Based on the electrostatic crystal field model of Faucher et al., in which the induced electric dipoles of ligands are obtained from a set of self consistent combined equations and the contributions from farther ligands are considered,the crystal field energy parameters of nano crystal X1-Y2SiO5: Eu3+ are calculated by using related data of its crystal structure and physical properties.Moreover,we successfully extend the above model to calculate the transition intensities,thus giving a theoretical luminescence spectroscopy,which approximately agree with the experimental one.Additionally,the useful wavefunctions of crystal field states are obtained in this calculation process thereby.
1997, 46 (7): 1437-1443.
doi: 10.7498/aps.46.1437
Abstract +
This paper introduces the preparation of fullerence doped silica aerogels by “chemically doped” and sol gel process.The infrared spectra and time of flight mass spectra show that C60 were successfully incorporated into the silica aerogel and the structures were retained in the fabrication process.Photoluminescence spectra shows that fullerence doped silica aerogels exhibit broad visible light under Ar+ laser(488nm).The photoluminescence is blue shifted compared with pure C60.In this paper, we give an explanation to this blue shift.
1997, 46 (7): 1444-1448.
doi: 10.7498/aps.46.1444
Abstract +
One new diamond form,the amorphous diamond (a-D) film,is prepared by filtered arc deposition.The field emission properties and mechanism of a-D film are presented,to our knowledge,for the first time.The field emission current of more than 20μA is detected below a field intensity of 20V/μm. This result is even superior to all previously reported results.The Fowler-Nordheim field- emission behavior has been observed in a-D films.The a-D films have a low work function and negative- electron affinity.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1997, 46 (7): 1449-1456.
doi: 10.7498/aps.46.1449
Abstract +
High quality SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si substrates were obtained using pulsed laser deposition combined with annealing at 700℃ in oxygen. The high diffraction peak of(008) and (115) was characterized by X-ray diffractometer.Good ferroelectric properties were obtained from the thin films;the remnant polarization and coercive field were about 10μC/cm2 and 57kV/cm, respectively. No fatigue was observed at up to 1010 switching cycles.Leakage current and the dc breakdown field measurement were about 4×10-8A/cm2 at 5V and 250kV/cm,respectively.
