Vol. 43, No. 7 (1994)
Using the Miura and Cole-Hopf transformations, we prove that ten sets of time independent symmetries of the Kaup-Kupershmidt equation constitute a non-Abelian Lie algebra. Ten hierarchies of equations corresponding to these ten sets of symme-tries possess a common strong symmetry. The time independent symmetries of ten hierarchies of integrable models and the Lie algebras constituted by these symmetries are also given.
1994, 43 (7): 1050-1055. doi: 10.7498/aps.43.1050
We established a formal series symmetry theory for a type of generalized 2+1 dimensional bilinear equation in two different ways. Starting from a known time in-dependent symmetry or an arbitrary function of 1-D space, we can get a formal series symmetry with an arbitrary function of time t. For the 2+1 dimensional bilinear Sawada-Kotera equation, there exist six truncated symmetries. These truncated symmetries constitute an infinite dimensional Lie algebra. Some significant subalge-bras such as the Virasoro algebras are also given.
ATOMIC AND MOLECULAR PHYSICS
1994, 43 (7): 1056-1065. doi: 10.7498/aps.43.1056
In this article, the B spline technique is employed to calculate the energy values of a number of low-lying states of hydrogen atom in the presence of a homogeneous magnetic field of arbitrary strength (０＜Ｂ≤４．７×１０8T) our results fill the gaps in the results of the works by Rosner et al. and Ivanov, and agree well with those obtained by other theoretical calculations. B spline functions are proved to be powerful in treating the excited, as well as ground states of hydrogen in magnetic field.
The XUV spectra emitted from line focused laser-produced Ge plasma were observed. A 1-m grazing-incidence spectrograph viewed the plasma in the axial direction. The spectra due to transitions in GeXX-GeXXVI were identified. The wavelengths and intensities were obtained. Calculations on spontaneous decay rates and oscillator strengths of the spectra were performed.
1994, 43 (7): 1072-1076. doi: 10.7498/aps.43.1072
According to our measurement, the coefficient of microwave power shift in the 87Rb frequency standard is always positive. The previous explanation about microwave power shift can not explain this phenomenon. The theory presented in the present paper, starting from the view of AC Zeeman effect caused by microwave field, can explain it.
DEVICE FOR MEASURING THE TOTAL CROSS-SECTION (TCS) OF ELECTRON SCATTERING AND THE EXPERIMENTAL ELECTRON-MOLECULAR NITROGEN TCS AT INTERMEDIATE ENERGY
1994, 43 (7): 1077-1082. doi: 10.7498/aps.43.1077
This paper presents a device designed for the absolute measurement of total electron-atom and electron-molecule cross section at intermediate energy. The experimental total cross sections for electron scattering from nitrogen molecular in the energy range 500-2600eV are also given.
THE THEORETIC CALCULATION OF ENERGY DIFFERENTIAL AND INTEGRAL CROSS SECTIONS FOR ELECTRON-HYDROGEN COLLISION
1994, 43 (7): 1083-1089. doi: 10.7498/aps.43.1083
A distorted wave born exchange (DWBE) approximation is used to calculate the cross section of electron impact ionization for atomic hydrogen. Both the energy differential cross sections and the integral cross sections from calculation are compared with the latest experimental data. The comparison shows good agreement between theoretical and experimental results. The small difference between these results is also discussed.
CLASSICAL AREA OF PHENOMENOLOGY
1994, 43 (7): 1090-1095. doi: 10.7498/aps.43.1090
In this paper, it is revealed that, degenerate two-photon lasers can show both lasing without inversion and without lasing, for two proper atom-field coupling coefficients, under the condition of equal atomic decay rates, not too large single-photon detunings, and not too saturation.
1994, 43 (7): 1096-1104. doi: 10.7498/aps.43.1096
A canonical formulation is given of the motion of the equilibrium electrons in a reversed-guide-field free-electron laser. It is found that the helical orbits of electrons are always stable. By generating Poincare surface-of-section maps, the influences of the self-fields on the phase orbits of electrons are investigated. The results show that although the current of the electron beam is high up to 6000A, the phase orbits do not become chaotic for MIT's experimental parameters. Compared with the case of a conventional positive-guidefield, our results indicate that using a reversed guide field can apparently prevent the quality of the electron beam from degeneracy.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1994, 43 (7): 1105-1110. doi: 10.7498/aps.43.1105
The errors may be introduced in the process of measurement and evaluation for preparing radial distribution function (RDF), They will cause the error distortion that RDF can be partly upset. RDF method is based on structual isotropy of amor-phous materials, however, a structural anisotropy, i.e orientation, hes been found in amorphous polymeric, inorganic and metallic materials. The orientation will greatly affect RDF, and will lead to a new distortion that RDF may be wholly upset. Obvirously, if it is not given due regard, a misinterpretation on RDF can occur. The feature of the so-called orientation distortion is discussed in the present paper.
1994, 43 (7): 1111-1117. doi: 10.7498/aps.43.1111
Using the empirical tight-binding method, the bond lengths and lattice constants in the GexSi1-x alloys are calculated through minimizing the total energy in zincb-lend-like crystal models, with which the GexSi1-x alloys are simulated. With the tight-binding method the electronic band structures are calculated for the models before and after the atoms relax and the calculated results are compared with that obtained in virtual crystal approximation. The calculated results are as follows: The bond lengths in the GexSi1-x alloys generally do not depend up on the alloy compo-sition and nearly equal to the bond lengths in the Ge and Si crystals respectively. This result is consistent with the experiments quite well. The relaxation of atoms has little effects on the electronic band structures for the alloys. However, the chemical composition disorder plays the most important role in determining them.
1994, 43 (7): 1118-1122. doi: 10.7498/aps.43.1118
In this paper the MBE nucleation mode on vicinal GaAs(001)surface is simu-lated by Monte Carlo method. The results show that on A-surface the 2-dimension nucleation mode is dominant at 800-1000K. On B-surface the 2-dimension nucleation mode is dominant at low temperatures, but at high temperatures the step flow mode is dominant. And at both high and low temperature, there is a saturation phenomenon.
The ion beam producing ionization of N= has been successfully utilized as the N source for nitride growth. Cubic GaN thin films are thus grown on GaAs(100) substrates. The width of the (200) X-ray diffraction peak of the epilayer is 23′ only, and the high-resolution electron energy loss spectroscopy measurements show that the optical surface phonon of cubic GaN appears at the loss energy of 82 meV.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1994, 43 (7): 1129-1136. doi: 10.7498/aps.43.1129
The interfacial defects at the p-Si MBE layer/p-Si substrate interface have been observed and analysed. By solving Poisson equation, we can obtain the energy band diagram for this kind of structure with Shottky barrier at the surface and high dencity defects at the interface. The electron concentration at the defect level varying with external voltage can also be got by the calculation. Using deep level transient spectrascopy (DLTS) measurement to detect the interfacial defects, we found that the DLTS spectra for the emission and capture of electrons by the defect level can be got simultaneously at one temperature scan and the difference from conventional DLTS method is also discussed. The experimental results show that the energy level of the interface defects is located at Ec-0.30eV.
1994, 43 (7): 1137-1143. doi: 10.7498/aps.43.1137
The effect of rapid thermal annealing on the electrical properties of heavily boron doped Si epilayer grown by molecular beam epitaxy and coevaporation of B２Ｏ3 is studied. It is found that an increment of carrier concentration by a factor of 4 and an improvement of the Hall mobility equivalent to that of bulk Si at the same doping concentration are achieved by annealing at 1100℃ for 10s. The rapid thermal annealing process does not affect the steep distribution of carrier concentration at the epilayer/substrate interface which differs about 6 order of magnitude across the interface with the leading edge slope of 25-30nm /decade.
1994, 43 (7): 1144-1151. doi: 10.7498/aps.43.1144
The surface morphology and V-I characteristics of the Ag thin films deposited on the fractal substrates of α－Ａｌ２Ｏ3 ceramics by rf magnetron sputtering have been investigated. The fractal surface morphology, poor crystallinity and abnormal nonli-near do V-I behavior of the thin films have been observed. The crystallinity of the films deposited on the fractal substrates is improved by increasing the substrate temperature and the thickness of the thin film. The nonlinear V-I characteristics are influenced by the thickness of the thin films, substrate temperature and measu-ring environment.
1994, 43 (7): 1152-1158. doi: 10.7498/aps.43.1152
Based on the singly occupied a-picture and the mechanism of charge fluctuation, the effective Hamiltonian of two-band Hubbard model is derived by using the degeneracy perturbation theory for the non-cuprate comoound Ｂａ1-xＫxＢｉＯ3. By considering the next neighbour pairing of two opposite spin holes in coordinate space, the Green's function equation of motion and superconductivity equation are obtained. Furthermore, how the superexchange interaction and the hopping energy affect the next neighbour pairing has been explained reasonably, and the superconductivity window is due to the Cooper pairing in coordinate space.
1994, 43 (7): 1159-1165. doi: 10.7498/aps.43.1159
It is different from the case of conventional superconductors that the alkali-metal-doped fullerenes have wide-frequency-range phonon spectra whose high-and low-frequency phonon modes are, respectively, comparable to the Fermi energy EF and the zero-temperature gap △0. This property will lead to a modification to the theory of conventional strong coupling superconductivity. In this paper, by solving the Eliash-berg equations, the expressions of Tc and △0 are obtained. The results show that both the intermolecular low-frequency modes and the intramolecular highfrequency modes participate the electron-phonon interactions; Tc mainly arise from the high-frequency modes while △0's enhancement mainly arise from the low-frequency modes. So, the experimental results can be explained, especially, the large ratio of ２△0／ｋBＴc.
1994, 43 (7): 1166-1171. doi: 10.7498/aps.43.1166
The dependence of resistance on temperature was measured for a Tl (2223) Ag-sheathed tape with high Ｊc(Ｊc＝１．５×１０４Ａ·ｃｍ-2，７７Ｋ，０Ｔ) in an applied magnetic field range from 0 to 0.8T. The experimental results were explained in terms of the thermally activated flux creep model. The relationship between activation energy U0 and the applied magnetic field H oriented parallel to and perpendicular to the ab plane is respectively Ｕ0∥＝０．２１ H-0.3(eV) and Ｕ0⊥＝０．１5 H-0.4(eV). The unit of H is in 0.1T. The dissipation independent of a macroscopic Lorentz force for H and measuring current I lying in the same ab plane and H parallel to I was discussed.
1994, 43 (7): 1172-1176. doi: 10.7498/aps.43.1172
Using the integral equation method, we have got the analytic expressions of the internal energy and specific heat for the one-dimensional Ising model with nearest-neighbour antiferromagnetic repulsion Js and infinitely long-range exponential (Kae-Helfand-type) ferromagnetic attraction J1 acting only on even-numbered neighbours. Under the conditions of J1=1 and Js being 0.05, 0.1 and 0.3 respectively, we have drawn the curves of the internal energy and specific heat varying with temperature in zero external magnetic field, and pointed out its critical phase transition point. Under the conditions of J1=1,Js=0.1, we have drawn the curves of influence of the external magnetic field upon the internal energy and specific heat. Because there exist double solutions for the system under low temperatures, zero or weak external magnetic field and weaker antiferromagnetic interactions, it is inferred that there should exist another quasi-stable state of the model under the given conditions.
1994, 43 (7): 1177-1184. doi: 10.7498/aps.43.1177
A systematic study on the structural and magnetic properties of the Rfe10.5V1.5Nx series, where R=Y, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er, has been carried out by X-ray diffraction and magnetic measurements. Rfe10.5V1.5Nx compounds show a higher Curie temperature and a larger saturation magnetization due to the lower content of V compared with Rfe10V2Nx In NdRfe10.5V1.5Nx the c-axis is the easy axis from 0 K to Tc, the anisotropy field is up to 185 kOe at 1.5 k and 102 kOe at room temperature with a combination of a high Curie temperature of 784 K and a large room temperature saturation magnetization of 139.1 emu/g, the intrinsic magnetic properties are favourable for permanent magnet applications.
1994, 43 (7): 1185-1191. doi: 10.7498/aps.43.1185
There are unidirectional anisotropy in 81 NiFe/Cr multilayers prepared by electronic beam evaporated, The samples exhibit asymmetrical hysteresis loop. which eguivalent to the existence of an exchange bias of the order of 1 Oe. Two branches of magnetoresistance loop measured with increasing and decreasing magnetic field respectively are different especially in transvers field condition. The maximum value of transvers magnetoresistance of some samples reaches 0.78% and with maximum anisotropy magnetoresistance （Ｒｍａｘ－Ｒｍｉｎ）／Ｒ of 4.72%.That value is more larger than the value 3%[１］ of 82 NiFe alloy with high quality. We consider that the ma-gnetoresistance effect of these multilayer not only caused by spin-orbit coupling ma-chanism but also under the influence of spin dependent scattering of conduction electron machanism.
1994, 43 (7): 1192-1202. doi: 10.7498/aps.43.1192
The polarizing optical behaviors and the stress-optical behaviors of optically heterogeneous fiber reinforced composites were studied. It was discovered that the light intensity vs azimuth curves (I-θ curves) consist of no more than three main variables, the zero, 2nd, and 4th variable, and can be represented in terms of these three variables with 5ma11 error. The more important point of this paper is the correlation of the 4th variable of I∥-θ curves(// here stands for the testing condition of the plane polariscopes with dark field) with stress. It was discovered that the value of the 4th modulus changes sinusoidally with the change in principal stress difference, (σ1-σ2∥), and the initial phase angle of the 4th variable coincides with the principal birefringent direction. Based on these experimental results, an equivalent birefringence theory was proposed as a substitution for conventional birefringence in the heterogeneous field.
1994, 43 (7): 1203-1207. doi: 10.7498/aps.43.1203
The light-emission of the porous silicon is an indirect recombination process of the excited electron through the surface states. During spontaneous oxidation new surface states are formed which make the photoluminescence spectra shift.
1994, 43 (7): 1208-1216. doi: 10.7498/aps.43.1208
In this paper, the mean grain diameters of nanomaterial Fe2O3 are determined by X-ray diffraction. The measurements of positron lifetime have been performed. The annealing temperature dependence of D and the short lifetime component τ1, intermediate lifetime component τ2 and their intensity ratio Ｉ2／Ｉ1 as function of D are given. The interface construction of nanomaterial Fe2O3 as well as the corresponding relationship between mean positron lifetime τ and S-parameter of Doppler broadening spectrum are discussed.