Vol. 45, No. 7 (1996)
1996, 45 (7): 1073-1080. doi: 10.7498/aps.45.1073
Using everyone of the realization of the centerless Virasoro type symmetry algebra, [σ(f1(t)),σ(f2(t))] =σ(f1f2-f2f1), we can get various higher dimensional models. By means of a concrete realization, many (3+1)-dimensional equations which possess Kac-Moody-Virasoro type infinite di-mensional symmetry algebra are obtained.
1996, 45 (7): 1081-1086. doi: 10.7498/aps.45.1081
When Lax pairs have property of anti-Hermitian evolution, the 2×2 matrix form Riemann problem with zeros is solved explicitly. And the multi-soliton solutions of the NLS equation and the sG equation are also found explicitly.
STABILITY OF SOLITARY WAVE FOR THE KdV TYPE EQUATIONAND TRAVELLING WAVE FOR THE KdV-BURGERS TYPE EQUATION
1996, 45 (7): 1087-1090. doi: 10.7498/aps.45.1087
In this paper, it is shown that solitary wave for the KdV type equation and travelling wave for the KdV-Burgers type equation are unstable in the Liapunov sense . Some incorrect conclusions in literatures are corrected.
We examine plane symmetric solutions to the Einstein equations under the assumption of func-tional separability of the metric coefficients. Under the further assumption that the energy-momen-tum tensor is of the form Ttt=Txx=Tyy=-σ(t,z), three new solutions are found, the global prop-erties of the spacetimes, such as their symmetries and singularities are investigated.
1996, 45 (7): 1100-1106. doi: 10.7498/aps.45.1100
A new method of the nonlinear delayed feedback on a Poincare section is used to stabilize the unstable periodic orbits (UPO) embedded in a chaotic attractor. As examples we studied the casee of Henon map and two-photon laser system with an injected signal. The advantages of this method are that it does not need to know the linear properties and the periodicity about a UPO or the one of the UPO extracted from the chaotic attractor, and the convergence to UPO does not depend on time of appling delayed feedback control action.
ATOMIC AND MOLECULAR PHYSICS
1996, 45 (7): 1107-1112. doi: 10.7498/aps.45.1107
Basing on the three Euler angles, the rotation operator approach is efficient to describe spin dy-namics of arbitrary shaped selective pulse. In this paper, a quaternion is employed so that the product of rotations is well performed. Hence a simple method is given for the calculation of the Euler angles for shaped pulses.
1996, 45 (7): 1113-1121. doi: 10.7498/aps.45.1113
The depositing process of (Cu)13 cluster, on Cu(001) surface with icosahedral structure and en-ergy ranging from 5 to 20 eV per atom, is investigated by molecular-dynamics simulations. A many-body hybrid potential, which is a combination of the tight-binding with Moliere potential, is used. The dynamic behavior of deposition is studied by taking the "snapshots" of cluster-substrate interac-tion. It is found that the cluster atoms rearrange and form epitaxial layers on the surface without cre-ating point defects after full relaxation at low energy. A clear trend of deeper penetration of the clus-ter atoms into the substrate with increasing energy is observed. A cluster with energy 20 eV per atom completely embeds itself inside the substrate while creating radiation damage. Energy analyses show that the cluster atoms activate the substrate atoms in impact regjon through collective collisions in a very short time (some tenth picoseconds), and provide energies for the migration and reconstruction of atoms.
CLASSICAL AREA OF PHENOMENOLOGY
The interaction between solitons of the nonlinear Schr?dinger equation is derived by the least action principle approach as a function of the soliton' s separation △ and their initial relative phase δ. The equation shows that two solitons with δπ/2 repel, and there is almost no interaction when δ=π/2, and that the interaction decreases exponential-ly as △ raises. The results obtained is well consistent with that of the experiment quantitatively.
1996, 45 (7): 1130-1137. doi: 10.7498/aps.45.1130
In this paper, a new type of linearly polarized wiggler, its the magnetic field amplitude and peri-od of which can be varied conveniently, has been investigated in detail. The wiggler consists of many loops which separately arrange on the wiggler framework. Varying the radius and period, we can ob-tain the field profile as was expected. The theory about the magnetic field profile in the wiggler has been derived and results of computer simulation show that it can produce any magnetic field profile that we desire by following methods:a)variation of loop radius only;b)variation of the wiggler period only;c) variation of the both.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1996, 45 (7): 1138-1145. doi: 10.7498/aps.45.1138
In this paper , we have analysed the physical procedures of RF discharges with negative bias , using the hydrodynamics method, and have calculated the spatiotemporal distributions of charged par-ticals and the electric field. The contributions of each terms in momentum-balance equation of ions are also discussed under different approximations.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1996, 45 (7): 1146-1152. doi: 10.7498/aps.45.1146
In this paper, by using a linear combination of atomic orbitals approach with the density func-tional formalism, the stuctures and the magnetic properties of FenB clusters (n=1-6) have been studied in detail. It is found that the B atom is favored to locate at the surface not the center of the cluster, and the tetrahedron for Fe4B and the triangular prism for Fe6B clusters are not the most stable structures. When one atom in Fen+1 cluster is replaced by a B atom forming FenB cluster, the binding energy increases, while the moment of Fe atom decreases. The variation of average moment with the atomic percentage of B atom is nonlinear in FenB cluster, differing from the behavior of bulk amorphous Fe-B alloys. It is indicated that the environmemt and doping play an important role on the stability and magnetic properties of cluster.
1996, 45 (7): 1153-1159. doi: 10.7498/aps.45.1153
The Raman spectra of KTP single crystal that is an excellent material applicable to the nonlinear optical devices have been obtained. And its features are discussed in some detail in terms of group the-ory, lattice dynamics and ligand field theory.
1996, 45 (7): 1160-1167. doi: 10.7498/aps.45.1160
In this paper, it is reported that the nickel ions (140 keV, 5×1015-2×1017ions/cm2) were implanted at room temperature into the specimens of yttria which were partially stabilized by zirconi-a. The annealing processes were decided . By making use of electric measurement, Rutherford back scattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, we have studied the effects of implantation and annealing on the electrical properties of the surface and the structure of implanted layer of polycrystalline ZrO2.
1996, 45 (7): 1168-1177. doi: 10.7498/aps.45.1168
With cell model, the orientional order parameter, the positional order parameter and the orien-tion and position coupling order parameter are defined on cell center. By choice of interaction potential of biaxial molecules with a permanent electric dipole moment transverse to the molecular long axis, the free energy of the system is obtained . A differential equation of the director is derived by calculating the variation with respect to free energy, and the director tilt and helical change about the normal of molecular layer are obtained. The approximate formulas of tilt angle and pitch for three classic SmC* Liquid crystals of DOBAMBC, etc., are presented. The calculated results agree satis-factorily with the experimental ones.
1996, 45 (7): 1178-1184. doi: 10.7498/aps.45.1178
The composition depth profiles of the Mn thin films grown on GaAs(00l) surface using MBE technique are studied with X-ray photoelectron spectroscopy(XPS) . The experimental results show that the fcc-Mn/GaAs(001) system grown on a 400 K substrate has a sandwich structure with a Mn-Ga-As buffer layer located between the fcc-Mn layer and the GaAs substrate; the α-Mn/GaAs (001) system grown on a 300 K substrate also has a similar buffer layer which is much thinner than that of the fcc-Mn/GaAs(001) system;and the system grown on a 450 K substrate is a Mn-Ga-As alloy beyond the GaAs substrate and it has no Mn-dominated area. It is concluded that to keep the substrate at a proper temperature(400 K) during growth to obtain a suitable thickness of buffer layer is an essential requirement to grow fcc-Mn on GaAs(00l) surface.
1996, 45 (7): 1185-1190. doi: 10.7498/aps.45.1185
We have used scanning tunneling microscopy working at 4.2 K to study the transition metal dichalcogenide 1T-TaSe2. The charge density wave (CDW) superstructure (131/2α0×131/2α0) and atomic modulation are well resolved, as well as the associated CDW energy gap. In particular we used high purity iron as tip material and demonstrated clearly the existence of single electron tunnel-ing (so-called Coulomb blocade) effects, further experiments with stainless steel tips also confirmed this observation. It is pointed out that during STM/STS studies tips covered with oxides are very likely to display Coulomb blocade effects due to their small capacitance. Therefore, extra cautious are needed when analyzing spectroscopic features in the area that could be affected by Coulomb blocade effects. At the mean time, high quality scanning images can still be regularly obtained through reso-nant tunneling process.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1996, 45 (7): 1191-1196. doi: 10.7498/aps.45.1191
In virtue of stochastic autocorrelation function description of the impurity scattering potential in non-dissoluble magnetic-nonmagnetic granular films, we find a relationship between the resistivity of system and the size of gruanules. Furthermore, by introducing a phenomenological factor to account for the increase of correlation length caused by the external magnetic field, we get an analytical ex-pression for the giant magnetoresistance coffiecient. The calculations show that our theory agrees qualitatively with the experimental results.
1996, 45 (7): 1197-1204. doi: 10.7498/aps.45.1197
Some scaling behaviors of a fractal resistor network are studied based on a hierarchical model with an exponentially wide distribution obeying g=g0eWx. We analyse the effects of the disorder width W on the overall resistance and the moments of distributions, and corresponding universal curves are found. We regard the problem as a crossover behavior between the competing effects of the size of the network and the width of the distribution of conductances. Our results are in good agreement with the numerical simulation reported by Tong on Sierpinski honeycomb network.
1996, 45 (7): 1205-1211. doi: 10.7498/aps.45.1205
A moderately strong electron-phonon interaction is supposed to be the causes of paring. On the basis of (1) the observation that the local electron-phonon interaction is rather strong in experiment and (2) the quasi-two-dimensional feature of CuO2 plane in ceramic oxides, a two-dimensional bisoli-ton model is established. The soliton solution with topological stability is given. It is shown that the bisoliton moves always with a velocity less than that of sound and it is varied along different direc-tions, they do not emit phonons, i.e., they do not transform their kinetic energy into a thermal one. The absence of an isotopic effect is explained because the critical temperature is independent of the mass of crystal lattice cell.
1996, 45 (7): 1212-1219. doi: 10.7498/aps.45.1212
The suppressive effect of the nonmagnetic doping on the high- Tc superconductivity has been studied based on the BCS-van Hove mechanism. Taking into account the bilayer coupling and three-dimensionality effects, we generalize the van Hove scenario into the multiband BCS model and calcu-late the relation between the transition temperature and the chemical potential. The results obtained are in good agreement with the experiments.
1996, 45 (7): 1220-1224. doi: 10.7498/aps.45.1220
The dielectric permittivity of La-doped BaTiO3 ceramics exhibits reverse U-shape variation with increasing La-content in the range of 0.4 at% La, and with increasing frequency f it decreases quickly for f≤1000 Hz and changes very slowly for f>1000 Hz. These variations of dielectric property result from variation of defects due to doping La as follows: isolated Ba-vacancy ( V″Ba)→ associated defect (LaBa·V″Ba)→(LaBa·V″Ba·LaBa).
1996, 45 (7): 1225-1231. doi: 10.7498/aps.45.1225
The first and second order differential dielectric spectra have been first presented to seperate various polarizations of material conveniently and definitelly in the time domain measurement. The polarization response function introduced traditionaly as the form of exp(-(t/τ)α) can be deter-mined by the differential spectral curve. The experiments show that there are two typical differential spectral curves corresponding to τ=1 and τ-1/2. The number of the polarization mechanisms, the individual mechanism contribution to the total polarization and its response time τ can be derived from the number, the height and the location of peaks of the differential spectral curves. The seper-ability of the differential spectral curves indicates that there is no reason for the conventional assump-tion that τ has some distribution function while a is a constant. The measurements on paraffin sam-ple demonstrate the slow polarization informations about the motions of the localized segment and the whole of a molecular chain in the process of the paraffin melting. The experiments also give the re-sult that the response time τ increases exponentially with temperature which is in contradistinction from the temperature dependence of relaxation time followed from frequency domain measurement.
1996, 45 (7): 1232-1238. doi: 10.7498/aps.45.1232
Porous silicon is treated in NH3 gas by rapid thermal annealing. FTIR spectra indicate that the surface of the sample is covered with Si(NH)2 and Si3N4 species. ESR signal shows that the sample has rather low density of dangling bonds. The photoluminescence intensity of the treated sample de-creases slightly compared to the sample without the treatment and is very stable while storing in at-mosphere. These results show that nitride can be an excellent passivation film on porous silicon and may be important to the practical applications.
1996, 45 (7): 1239-1243. doi: 10.7498/aps.45.1239
In this paper the microemulsion preparation, the morphology and structural characteristics of toil nanoparticles are reported in detail. The quantum confinement effect upon the strong polarizable nanoparticle are described with interfacial polarization, and their linear and nonlinear optical absorp-tion responses are explained with self trapped exciton model.
1996, 45 (7): 1244-1248. doi: 10.7498/aps.45.1244
The photoemission spectra with a sychrotron radiation of (3×1) Na adsorbed orderly and disor-derly on Si(lll)-7×7 surface are analyzed and compared with the spectra of clean Si(lll)-7×7 surface. Na atoms are not simply adsorbed on the adatoms or rest atoms. The formation of the Schot-tky barrier is decided by the interaction between Na and Si atoms and seem to bear no relation to the surface structure. The Schottky barrier height(SBH) from experimental data is agreement with the value estimated by MIGS theory.