Vol. 41, No. 9 (1992)
1992, 41 (9): 1389-1395. doi: 10.7498/aps.41.1389
The higher dimensional exterior solutions of Einstein equations with cosmological constant for a charged radiating sphere is obtained. And the different expressions of the electromagnetic energy-momentum tensor in higher dimensional space-time are also investegated.
1992, 41 (9): 1396-1405. doi: 10.7498/aps.41.1396
The time-dependent problem of Fokker-Planck equation of the nonlinear systems without detailed balance is solved in the weak noise limit by using the Ω-expansion of the Green function. We further reveal the possibility of the dimension reduction and some scaling relations in the relaxation of the system from the unstable state to the stable state.
CLUSTER SIZE DISTRIBUTION IN THE n-POLYMER COAGULATION PROCESSES AND THE JOINT COAGULATION PROCESSES
1992, 41 (9): 1406-1417. doi: 10.7498/aps.41.1406
We have considered coagulation processes containing n-polymer interactions by means of a generalized Smoluchovski's equation, which is solved as a monodisperseinitial-value problem to the kernel: K(i1,i2,…,in)=A sumfrom i=1 to n i1+B, K(i1,i2,…,in)=A sumfrom i=1 to n i1. According to the connection between model K(i1,i2,…,in)=A sumfrom i=1 to n i1+B and K(i1,i2,…,in)= S(i1)S(i2)…S(in)(S=Ak+B),we obtain the pre-gel solution of the latter model. We also study a kind of joint coagulation process containing two-polymer and three-polymer collisions with the kernel K2(i, j)=i+j and K3(i,j,k) = i+j+k and get the explicit expression of Cm(t). Finally, we discuss the long-term behavior of Cm(t), Which can be extented to the general case.
ATOMIC AND MOLECULAR PHYSICS
INVESTIGATION ON VARIETIES OF EFFECTS AND VARIAT-ION OF ENERGY AS SIZE AND SHAPE OF THE NONLOCAL HOLE VARIES WITH ELECTRIC DENSITY
1992, 41 (9): 1418-1423. doi: 10.7498/aps.41.1418
The electron self-interaction present in local-density theory can be removed by assuming a nonlocal hole in the electron density to generate the exchange-correlation energy. The potential derived from this energy has two contributions: the electrostatic potential from the hole and terms which describe the variation of the energy as the size and shape of the hole varies with density. All previous authors have included the first contribution, but the treatment of the second ranges from neglect to including them exactly. This work examines the effect of including these terms exactly, approximating them locally or neglecting them completely. Complete neglect yields severely distorted wave functions. This work shows how these terms may be generally estimated locally, which is much simpler than treating them exactly.
In the processes of electron elastic scartering from spinless atoms, the incident electrons are treated as moving relativistically in an effective central potential V(r). The potential is calculated by relativistic self-consistent-field method with Slater local exchange approximations (i.e. Dirac-Slater SCF). Elastic scattering amplitudes are calculated by relativistic partial-wave expansion method. Then we calculated the differential cross section for electron elastic scattering from Xe atom and the spin polarization parameters. Detail comparisons of the theoretical and complete experimental results show the validity of the theoretical method adopted.
CLASSICAL AREA OF PHENOMENOLOGY
We propose a scheme of building a free-electron laser in the soft X-ray region pumped by the soliton laser. Making use of soliton laser wave evolution shape and single-pass small signal analysis, we find that this laser has two special advantages over the previous electromagnetic wave undulator free-electron lasers namely, (1) a very small "mass-shift effect" because of the special characteristics of soliton lasers, (2) an additional "frequency tuning effect" based on the conventional free-electron laser's tuning ability. We also obtain the small signal gain and carry out some discussion.
1992, 41 (9): 1436-1439. doi: 10.7498/aps.41.1436
The anionic group theory for nonlinear optical crystal has been applied to calculate SHG coefficients of Na2SbF5 crystal. The calculated dm is 4.48×10-10 esu, which agrees well with the experimental value. The theoretical results indicated an important fact that the major part of SHG coefficient is determined by the lone pair orbital of anionic group (SbF5)2-. Moreover, through analyzing the location of lone pair energy level, the reason why Na2SbF5 crystal has so small second-order susceptibility has been explained.
1992, 41 (9): 1440-1447. doi: 10.7498/aps.41.1440
Two wave coupling experiments of doped KNSBN single crystals have been performed. The gain coefficient of two wave coupling Γ as a function of the crossing angle of the beam 2θ, and Γ as a function of the intensity of light / in various samples were measured. The effective photo-refractive charge density, the effective electro-optic coefficient and the hole-electron competition factor have been determined by model fitting. The analytical expression of the intensity-dependent gain coefficient is deduced. We use this expression to analyse the experiment data of Γ-I. Our result shows that high values of Γ(>15 cm-1) exist in some kinds of doped KNSBN crystals.
EQUILIBRIUM AND NONEQUILIBRIUM CORRELATIONS FUNCTIONS OF A FLUID SOLVED BY CELLULAR AUTOMATA APPROACH SIMULATIONS
1992, 41 (9): 1448-1451. doi: 10.7498/aps.41.1448
The spatial correlation functions in a fluid subjected to an external temperature gradient have been computed by using cellular automata simulations of a simple lattice-gas model with temperature. We obtain numerical results and show a quite good qualitative agreement with the predictions of the fluctuating hydrodynamics.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1992, 41 (9): 1452-1457. doi: 10.7498/aps.41.1452
The vanadium-nitrogen-vacancy complexes appearing in the dilute Fe-V alloys doped with nitrogen have been studied using positron annihilation technique. The positron lifetime and formation enthalpy of the complex were estimated. The results provide an experimental evidence to explain the enhanced diffusion of vanadium in dilute Fe-V-N alloys.
1992, 41 (9): 1458-1462. doi: 10.7498/aps.41.1458
The discrete variational method, cluster model and a fully-three dimensional numerical relaxation technique are used to study the atomic configuration, positron annihilation characteristics and electronic structure of the V-N-vacancy complex in the dilute Fe-V-N alloy. Optimum location of nitrogen and vanadium in the V-N-vacancy complex is determined, according to the result of the positron annihilation lifetime experiment and minimizing the total energy. The bond characteristics and charge transfer in the V-N-vacancy complex are analyzed.
1992, 41 (9): 1463-1473. doi: 10.7498/aps.41.1463
According to the recent studies on interfaces in crystals, it is evident that most grain boundaries and phase boundaries have two dimensional periodic structures. Starting from this fact, using the representation of Fourier series expansion, in the case of given interface structure, i.e., in mathematical sense, formerly given the boundary condition, the elastic fields near the phase boundary between two anisotropic phases are found. As an example, we compute numerically the field of a twist grain boundary in Ni. The method and equations presented in this paper are generally applicable for studying various types of grain boundaries and phase boundaries, providing an effective and concise method for treating this kind of problem.
1992, 41 (9): 1474-1481. doi: 10.7498/aps.41.1474
Zn-Al diffution couples were formed by ion implantation. The diffusion model of impurity atoms in single-phase region was suggested for the case that the implanted concentration was less than its solid solubility in host. Zn diffusion profiles calculated from this model with numerical method were in good agreement with the results of experiment. By the enhanced diffusion effect accompanied with ion implantation, the diffusion coefficients of Zn in polycrystalline Al between 260-380℃ were obtained, which were difficult to determine using conventional deposition method.
1992, 41 (9): 1482-1486. doi: 10.7498/aps.41.1482
In this paper, the formation enthalpies of the final phases presented in annealed contacts composed of transition metals (Pd, Pt, Ni, Ir, Rh, Co, Ti, Cr, V, Zr) and GaAs are calculated by using Miedema's semi-empirical model. Furthermore, the free energies of reaction both for the formations of the final phases and for the decompositions of the final phases containing As are calculated. These calculated results are compared with the experimental values. We reach the conclusion that for most of the above systems, the free energies of reaction can be adopted to assess the formation temperatures and the stabilities for the final phases.
1992, 41 (9): 1487-1492. doi: 10.7498/aps.41.1487
The XPS(X-ray photoelectron spectroscope) measurements of the 80K phase Bi-Sr-Ca-Cu-Li-O ceramics were carried out on surfaces obtained by polishing in ultrahigh vacuum. The results show that the chemical bond natures of Bi and Sr almost did not change, but the binding energies of Ca, Cu and O shifted apparently toward higher energy when Li doped in the Bi-Sr-Ca-Cu-O system. The XPS spectrum of O Is has only singe peak (528.8eV) from clean surfaces polished in vacuum and consists of the OH (531eV) and OL (528.8eV) components from conventionally polished surfaces.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1992, 41 (9): 1493-1498. doi: 10.7498/aps.41.1493
Resonant tunneling in rectangular multi-barrier structures are studied theoretically. Analytical expressions of the transmission coefficient and the resonance condition are strictly derived. It is found that the resonance energies are different from the eigenvalues in the quantum well due to coupling between wells in the multi-barrier structures. The resonance condition corresponds to the energy range of the physically possible wave functions in the Kronig-Penney model. It is confirmed that the transmission spectrum is a Lorentzian nearby energies of resonance. We believe that the expression are useful for evaluating the energy variations of transmission coefficient and estimating the resonance energy, and also useful in fabrication of resonant tunneling devices.
1992, 41 (9): 1499-1503. doi: 10.7498/aps.41.1499
The ground state energy of a coupled system of a quantum tunneling state with phonons is investegated by a variational approach. We find that the ground state of the system may be described by two variation states-displaced state and displaced-squeezed state, and the transition of the stable ground state from displaced state to displaced-squeezed state will occur as coupling strength increases. The phase diagram of the transition is also given.
1992, 41 (9): 1504-1509. doi: 10.7498/aps.41.1504
The X-ray powder diffraction, properties of normal state and superconducting state (especially carrier concentration) measurements were carried out for the high quality and single phase polycrystal Bi2Sr2CaCu2O8+δ samples annealed in low vacuum or H2 atmosphere at various temperatures. The results reveal that the oxygen atoms escape for Bi2Sr2CaCu2O8+δ samples annealed in H2 atmosphere is devided into two steps. First, the extra oxygen atoms residing between the Bi-O layers escape, and the carrier concentration of samples decreases, the superconducting transition temperature Tc of samples is modulated. Second, the oxygen atoms in the CuO2 planes are removed, and the oxygen vacancies, which induce the short range 2D-AFM order of Cu2+ to decrease, emerge in the CuO2 planes, We suggest that the variation of Tc led by hydrogen absorption in the Bi2Sr2CaCu2O8+δ superconductor might be mainly brought on by the oxygen content variation in the course of absorbing hydrogen, rather than by the electron dopping effect of hydrogen atoms.
1992, 41 (9): 1510-1516. doi: 10.7498/aps.41.1510
The relation of crystal structure, oxygen content, normal state resistivity with. temperature and superconducting critical temperature of Y1-xCaxBa2Cu3-xMxO7-δ(M = Fe, Ni) systems have been studied. In comparison with YBa2Cu3-xMxO7-δ (M = Fe,Ni) systems, it is found that the superconducting Tc of Y1-xCaxBa2Cu3-xFexO7-δ system is remarkably higher than that of YBa2Cu3-xFexO7-δ system with the same x value. On the contrary, the Tc of Y1-xCaxBa2Cu3-xNixO7-δ system is lower than that of YBa2Cu3-xNixO7-δ system. These results show that the variation of the carrier concentration (nH) due to Ca and Fe substitutions has been compensated and the sharp decreases of nH and Tc are prevented when Ca and Fe simultaneously substitute for Y and Cu(I). But in the case of Ca and Ni simultaneous substitutions, the compensation of the carrier concentration is not important and the correlation of Ca and Ni substitutional effects is weak. We suggest that the carrier concentration is an essential factor to determine Tc when the element substitution occurs out of the CuO planes, such as in Y1-xCaxBa2Cu3-xFexO7-δ system, but the pair-breaking effect is more important when Ni2+ ions substitute mainly into Cu(II) sites in Y1-xCaxBa2Cu3-xNixO7-δ system and Tc is directly suppressed by the pair-breaking effect.
A SUPERCELL LDA-LMTO-ASA CALCULATION OF COMPOSI-TION DEPENDENCE OF HOPFIELD CONSTANT AND Tc IN Ba1-xKxBiO3
1992, 41 (9): 1517-1522. doi: 10.7498/aps.41.1517
The electronic structure of (Ba1-xKx)BiO3 has been calculated by using a supercell LDA-LMTO-ASA method at some compositions. The calculation was performed by doubling unit-cell for x=0.25, 0.5 and 1.0 and by quadruple unit-cell for x = 0.25 and 0.75. The band parameters, total density of states TDOS (EF), partial DOS PDOS (EF) and self-consistent potential Vt(r), obtained from LMTO calculation were combined with the experimental Debye temperature ΘD From this, the Hopfield constant ηt, electron-phonon coupling constant λ and superconducting transition temperature Tc and its x-dependence were evaluated by the McMillan theory and Gaspari-Gyorffy approximation. It was found that the λ≈1 and the maximum Tc≈ 10K which is a slowly varying function of composition x. Our results exhibit a significant difference between the traditional theory and experiment and imply a mechanism which would be related to the composition dependent structure transformation besides the BCS methanism.
A SUPERCELL CALCULATION OF ELECTRONIC STRUCTURE IN SUPERCONDUCTOR Ba1-xKxBiO3 (x=0.25, 0.5 and 0.75)
1992, 41 (9): 1523-1530. doi: 10.7498/aps.41.1523
Electronic structure for ordered Ba1-xKx)BiO3 alloys has been calculated with a supercell LMTO method. The results indicate that the band parameters obtained from this approach are more accurate than that from rigid-band approximation. The composition dependence of the band parameters at Fermi surface is given. The hybrid feature of the valence orbitals between the inequivalent oxygen and metal atoms is discussed.
1992, 41 (9): 1531-1536. doi: 10.7498/aps.41.1531
The crystal structure, superconducting and magnetic properties of Pr0.2Yb0.8-xLaxBa2Cu3O7-δ have been investigated. The res ults show that with the concentration of Pr being constant, the critical transition temperature Tc of this syster decreases with the increasing of La concetration and Tc is quenched at x = 0.6. The coefficient of electron specific heat and the density of states N(0) inferred from magnetic measurements also decrease with x. The relation between the effective radii of rare earth elements and hybridization is discussed in brief.
1992, 41 (9): 1537-1541. doi: 10.7498/aps.41.1537
In this paper, we report the investigation of nickel ultrafine particles (UFP) with surface oxide through the measurement of macro-magnetic properties. Besides the strong effective ani-stropy on the surface or/and the interface, we find that the nickel UFP, shows extra magnetization, which is contributed by the surface or/and the interface.
1992, 41 (9): 1542-1546. doi: 10.7498/aps.41.1542
The influence of halogen family elements on the SERS signal was studied. The relation-shap between the SERS intensity and the concentration of halide and reversal phenomena of intensity of Raman peaks were discovered. Finally, some explanations were givea.
MONTE-CARLO STUDIES OF RADIATION DAMAGE CAU-SED BY FUSION a-PARTICLES IN THE FIRST WALL(Ⅲ)——DEPTH DISTRIBUTION OF DISPLACED ATOMS IN SOLIDS
1992, 41 (9): 1547-1553. doi: 10.7498/aps.41.1547
By means of the Monte-Carlo method based on the binary collision approximation, we investigate the depth distribution of displaced atoms in solids induced by fusion α-particles. The relations between the distribution of displaced atoms and the energy deposition profiles in solids are studied. The dependence of the incident energy and angle of a-particles, as well as the component of the target element on the depth distribution of displaced atoms are presented. It is shown that the displacement damage has close relation with the deposition energy caused by ion-bombardment. Also, the displacement damage created by fusion α-particles is stainless steel (Fe0.73Cr0.18Ni0.09) is less than that in SiC.
The angular distributions of sputtered Al and Sn atoms ejected from the Al-Sn multi phase alloy bombarded by 30keV Ar+ ion have been measured with collector technique and RBS analysis. The sputtered surface has been observed with scanning electron microscopy (SEM), and its compositions have been analyzed both in sputtered and unsputtered areas with electron x-ray probe microanalyser (EPMA). The results show that the angular distribution of sputtered Al atoms is nearly cosine, and that of Sn is over-cosine. To explain the experimental results we propose a reasonablt sputtering yield equation, Y(θ) = ∑Yi(θ) each , Yi(θ) stands for the sputtering yield of the area in which its surface topography and compositions is different from other areas.