Vol. 47, No. 3 (1998)
1998, 47 (3): 353-362. doi: 10.7498/aps.47.353
The homogeneous balance method is very effective for finding exact solutions of nonlinear soliton equations.But only soliton-type solutions can be obtained.In this paper we improve some key steps in this method,then by using modified homogeneous balance method we are able to obtain some new families of exact solutions to nonliear soliton equations.Solitary wave solutions are merely a special case of one famility.
THE FOAM-LIKE STRUCTURE OF SPACE-TIME AND THE CANCELLATION OF THE DIVERGENCE OF QUANTUM ELECTRODYNAMICS
1998, 47 (3): 363-367. doi: 10.7498/aps.47.363
The new vertexes created from the space-time foam-like structure in quantum electrodynamics (QED) will cancel the three primitive divergences of lowest order in QED exactly.
1998, 47 (3): 368-381. doi: 10.7498/aps.47.368
N-atom single-mode radiation field interaction system is regarded as an interacting quasi-boson-photon system and is treated as a grand canonical ensemble.The explicit expression for the thermodynamical potential of the system is obtained using cluster expansion method.Some thermodynamic quantities are derived in terms of the general thermodynamic formulas.The numerical calculation and diagrams exhibit the thermodynamic behavior of the system.The singularities appearing in the critical line and other places furnish evidences of existence of the second kind of phase transformation in this collective system.
THE STOCHASTIC RESONANCE AND CHAOS IN THE EVOLUTION OF THE CONSEQUENT ROCK BLOCK SLOPE (INCLINED AND VERTICAL)
1998, 47 (3): 382-390. doi: 10.7498/aps.47.382
The paper studies the evolution of the consequent rock block slope (inclined and vertical).We find that there exist stochastic resonance and chaos in the process of evolution.When stochastic resonance happens,any weaker stochastic factors can cause large deformation and crook for the slope.The stochastic chaos is induced by the periodical change of the environment,so the forecast of landslide is more difficult to make.
1998, 47 (3): 391-396. doi: 10.7498/aps.47.391
We study the problem of controlling chaotic behavior of a two-parameter laser system.We give different equations for controlling chaos with different parameters and compare their effects.Numerical results show that chaotic states of laser output can be controlled to 1P,2P,…2nP,P standing for period.We find that each equation obeys a definite rule.Finally,we analyze and discuss some related problems.
This paper investigates the methods for controlling chaos in the Lorenz system with nonlinear control theory. Applying a bang-bang control, we are able to transform the chaotic motion of the Lorenz system to stable motion which may contain apparent short-(or intermediate-) term chaotic motion. In particular, using the control method, we can eliminate the effect of initial conditions on the indeterminateness of the motion and drive the chaotic system to a specified equilibrium state.
ATOMIC AND MOLECULAR PHYSICS
1998, 47 (3): 403-410. doi: 10.7498/aps.47.403
The energies , fine structures and lifetimes of the 2s2s2p2P0 and 2s2p2p2D triply excited states of the Li isoelectronic sequence are calculated using multichannel saddle-point and saddle-point complex-rotation methods. A restricted variational method is used to extrapolate a better nonrelativistic energy. The relativistic corrections are calculated with first-order perturbation theory. The shifts and widths are studied with one open channel at a time as well as fully coupled open channels. The radiative transition rates and the fine-structure splittings for the 2P0 and 2D states are also calculated. These results are compared with the existing theoretical and experimental data in the literature.
A THEORETICAL STUDY ON ABSOLUTE TRIPLE DIFFERENTIAL CROSS SECTIONS FOR NEAR-THRESHOLD He+(e,2e) REACTIONS
1998, 47 (3): 411-418. doi: 10.7498/aps.47.411
A correlated three-body continuum wave function proposed by Brauner et al. has recently been modified further to allow for the three-body effects by introducing Sommerfeld parameters (Berakdar and Briggs),it is used to calculate the triple differential cross sections for electron impact ionization of He+ in coplanar equal-energy sharing and symmetric geometry. The initial channel wave function involves a Coulomb wave function due to the long range Coulomb attraction between the incident electron and the screened ionic nucleus. Since the present work deals with symmetric collisions, the electron exchang effect between the two continuum electrons has been taken into account properly. It is shown that the initial channel Coulomb field play a major role in determining the triple differential cross sections at near-threshold incident energy and small impact parameter values.
A STUDY OF OPTICAL OSCILLATOR STRENGTHS AND DIFFERENTIAL CROSS SECTIONS IN THE DISCRETE REGION OF CARBON MONOXIDE
1998, 47 (3): 419-427. doi: 10.7498/aps.47.419
The absolute optical oscillator strength density spectrum of carbon monoxide has been measured at an impact energy of 1.5keV and a mean scattering angle of 0° in an energy region of 7—21eV with typical FWHM 60meV. The absolute optical oscillator strengths corresponding to vibrational levels of A1Π,B1Σ+，C1Σ+ and E1Π are determined and compared with previous experimental and theoretical results. The reason why discrepancies exist among experimental results obtained by various methods has been explained and the limitation of dipole (e,e) method in determining optical oscillator strengths has been discussed.
CLASSICAL AREA OF PHENOMENOLOGY
1998, 47 (3): 428-431. doi: 10.7498/aps.47.428
An experimental setup is designed to stimulate thermal dark spatial optical solitons under even boundary condition, and the experiment in chlorophyll acetone is introduced in the paper. Finally, the quantum effect of dark spatial optical solitons is discussed.
1998, 47 (3): 432-437. doi: 10.7498/aps.47.432
We have demonstrated that circular and ring waveguides can be written and stored in photovoltaic and self-defocusing photorefractive medium (LiNbO3∶Fe crystals). The interractions between the ring waveguides have been observed. The methods writing these types of waveguides have important potential applications.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1998, 47 (3): 438-444. doi: 10.7498/aps.47.438
Based on the analysis of the X-ray diffraction data of liquid Al and Sn, temperature-induced structural transformations are found for liquid Al in the range of 1050—1250℃ and for liquid Sn near 800 and 1200℃. The nearest neighbor distance r1 of Al and Sn decreases with the increase of temperature. The structure of liquid Sn is similar to α-Sn on the short-range order length scale. The physical meaning of the correlation radius rc is discussed.
1998, 47 (3): 445-453. doi: 10.7498/aps.47.445
The electronic structure of tungsten tip of (111) surface under external electric fields is studies by using discrete variational-local density functional method. The tunneling orbitals(TOs) and the charge distributions of the tip are calculated and analysed in detail under different conditions. The results show that the components of TOs are sensitive to the polarity, amplitude of the external electric field and the distances between tip and sample. It is found that although 5dz2 has some contribution to TOs, it is not dominant, which differs from the previous theoretical calculations. The dominating contributions are from 5dxz and 5dyz orbitals under positive bias voltages. However, under negative bias voltages, TOs are made of many orbitals including 6s orbital. Our results can explain the phenomenon in STM experiments that the resolution of STM images will be changed using the same tip when the polarity of the electric field is reversed, and can also predict that if one uses tungsten tip of (111) surface, the inverted STM images should be observed.
1998, 47 (3): 454-460. doi: 10.7498/aps.47.454
VO2 thermochromic thin films have been deposited by using the magnetron sputtering method. Both macro, micro and electronic structures of the films have been characterized by X-ray diffraction,X-ray photoelectron spectroscopy and atomic force microscopy. The results show that the films have high purity, monophase and excellent polycrystallinity, which are coincident with the optical and electrical properties.
1998, 47 (3): 461-466. doi: 10.7498/aps.47.461
By using in-situ reflection high energy electron diffraction, the epitaxial growth of Co films on GaAs(001) surface is studied. When the growth temperature was 150℃, the growth process of Co films can be divided into three stages. The crystal structure of the first 3nm of the Co film is body-center-cubic(bcc) metastable phase. Then the next 4nm film is a complicated polycrystalline phase. After the thickness exceeds 7nm, the Co film is a single-crystalline hexagonal-close-packed(hcp) stable phase. This new result clears up the controversy in former experiments about the structure of the Co epilayer, and establishes, for the first time to our knowledge, a clear physical picture of the epitaxial growth of Co films on GaAs(001).
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1998, 47 (3): 467-471. doi: 10.7498/aps.47.467
The results of first-principles virtual-crystal calculations for the GaxAlyIn1-x-yN disordered alloys are presented. Electronic structures and energy gaps of the alloy with zinc blende and wurtzite structures have been studied as a function of composition (x,y) for the whole range (x,y=0 to 1). The energy gap of the alloy Eg(x,y) with a wurtzite structure has been found.
1998, 47 (3): 472-477. doi: 10.7498/aps.47.472
The Hamiltonian matrices formulae of 5D state for 3d4/3d6 ions in cubic symmetry are derived using a two spin-orbit (SO) coupling parameter model. The Hamiltonian matrices are 25×25(5D) dimensions. On the basis of the formulae, the fine-structure splittings of the ground state in cubic ZnSe∶Fe2+ crystal are calculated. The Zeeman splitting,the Raman shift and the magnetization in magnetic fields up to 30T along the ［100］ and ［111］ directions are investigated, respectively. The present results are in excellent agreement with the experimental ones.
1998, 47 (3): 478-484. doi: 10.7498/aps.47.478
By using the method of few-body physics, we study the relations between the energy of ground states and angular momentum of the four-electron systems in two-dimensional quantum dots in magnetic fields. The influences of the magnetic field and confined potential on ground states of the four-electron systems have been numerically calculated. The numerical results show that the quantum mechanical symmetry is the origin of magic numbers.
1998, 47 (3): 485-493. doi: 10.7498/aps.47.485
Theoretical and experimental results of intense beam confinement by conducting meshes in a relativistic klystron amplifier (RKA) are presented.Electron motions in a steady intense electron beam confined by conducting meshes are analyzed with an approximate space charge field distribution. And the conditions for steady beam transportation are discussed.Experimental results of a long distance (60cm) transportation of an intense beam (400kV,2.5kA) generated by a linear induction accelerator are presented.Experimental results of modulated beam transportation confined by the mesh array are presented also.The results show that the focusing ability of the conducting meshes is not very sensitive to the beam energy.And the meshes can be used effectively in a RKA to replace the magnetic field system.
RESONANT SUBBAND-LANDAU-LEVEL COUPLING FOR HIGH-LYING SUBBANDS OF TWO-DIMENSIONAL ELECTRON GASES IN GaAs/AlGaAs HETEROJUNCTION
1998, 47 (3): 494-501. doi: 10.7498/aps.47.494
The resonant subband-Landau-level coupling(RSLC) between the N=1 Landau level of the lowest subband and the N＝0 Landau level of the subbands with quantum index up to i＝5 of two-dimensional electron gases in GaAs/AlGaAs heterojunction was observed under relatively low magnetic field.Several intersubband energies were accurately determined. The experimental results were in good agreement with the self-consistent calculations including the depolarization shift and exciton-like effect corrections.The quantum index dependence of the level splitting due to the RSLC was discussed.
1998, 47 (3): 502-507. doi: 10.7498/aps.47.502
Using a Ge-SiO2 (GSO) composite target with the Ge wafer in the target having percentage areas of 0%,5% and 10%,three types of nanometer Ge particles embedded Si oxide films were deposited on p-type Si substrates by the rf magnetron sputtering technique. These samples were annealed in a N2 atmosphere at 300,600,800 or 900℃ for 30min.From Raman scattering spectra,we obtained the sizes of nanometer Ge particles which increase with increasing percentage area of the Ge wafer in the sputtering target.From the fitting of Raman scattering spectra,average diameters of nanometer Ge particles in the GSO(5%) sample increase from 5.4 to 9.5nm with annealing temperature increasing from 600 to 900℃. The peak with energy around 2.1eV exists in the photoluminescence spectra of all the different sizes of nanometer Ge particles embedded silicon oxide samples.The photoluminescence spectrum of the silicon oxide film prepared using a pure SiO2 target has other two peaks with light emission energies around 1.9 and 2.3eV respectively. The experimental facts are inconsistent with the predication of the quantum confinement model,but can be explained by the quantum confinement/luminescence center model.
1998, 47 (3): 508-513. doi: 10.7498/aps.47.508
Magnetic properties of Fe/SnO2 amorphous multilayers prepared by rf sputtering are investigated. With the thickness ds of SnO2 layers fixed (5.0nm),the saturation magnetization Ms of the samples decreases with decreasing dm. This is due to the contributions from the dead-layer effect and the dimensional effect. On the other hand, when the dm of the samples is very thin, quasi-two-dimensional magnetic behavior is found. The Curie temperature TC decreases with decreasing dm, and coercivity Hc has a peak as dm varies. With the thickness of Fe fixed at 2nm, Ms increases with decreasing ds.
1998, 47 (3): 514-519. doi: 10.7498/aps.47.514
The nucleation and initial growth of diamond on Si(100) by biased hot filament chemical vapor deposition have been studied by scanning electron microscopy,Raman spectra,infrared absorption spectra and X-ray photoelectron spectra.After bias pretreated for 15min at -300V and 100mA,the nucleation density was found to be over 1010cm-2 on mirror-polished Si and was inhomogeneous,which can be divided into three regions on Si surface:A,cones at the edges;B,nanocrystalline diamond at the transition region between the edge and the centre;and C,SiC layers at the centre.The films with defects,textured films,and big discrete grains of diamond were formed at A,B,C regions respectively after 4h growth without bias.The nucleation enhancement by substrate negative bias is believed to be a combination effect of the ion bombardment and emission electron.The non-uniformity of ion distribution led to an uneven nucleation on the Si substrate surface.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1998, 47 (3): 520-528. doi: 10.7498/aps.47.520
The deformation and energy absorbing characteristics and mechanisms of foamed aluminum with two different matrixes were investigated through examination of the compressive stress-strain behaviors. It was found that,like other porous solid materials, the stress-strain curve of foamed Al shows distinguished three regions, that is linear elasticity, plastic collapse or brittle crushing and densification. The energy absorbing capacity increases with increasing relative density, and brittle foam exhibits higher capacity than plastic one with the similar yield strength. Foamed Al reaches its peak value of energy absorbing efficiency at relatively lower strain, about 0.15—0.25. With increasing density, the peak values tend to decrease.