Vol. 49, No. 5 (2000)
2000-03-05
GENERAL
2000, 49 (5): 819-824.
doi: 10.7498/aps.49.819
Abstract +
The mathematical formulas of the conservation law in the double-wave quantnm theory are studied.As an example,the constants of motion and their classical limits of a 3-dimensional isotropic harmonic oscillator are discussed.The results indicate that the conservation law of the double-wave quantnm theory is applicable to single particle systems,and the conservation law of the usual quantnm theory is applicable only to statistical ensembles.
2000, 49 (5): 825-829.
doi: 10.7498/aps.49.825
Abstract +
Entangled state and entanglement have important action in quantum computation and quantum communication.In this paper,we consider the quantum pure state,show its properties when time reversal transformation is used,and study the representation of corresponding density matrix in Hilbert-Schmidt space.Finally we give a geometrical interpretation for entanglement.
2000, 49 (5): 830-832.
doi: 10.7498/aps.49.830
Abstract +
We study the synchronization of the drive system and response system which are described by the same chaotic maps but have different parameters.We propose a parametric adaptive control algorithm and show that when the maps are logistic ones,we can draw a sufficient condition for the synchronization,and that when they are general maps,we can draw a necessary condition for the synchronization.This paper also studies the synchronization of two chaotic systems which are subjected to common noise.
2000, 49 (5): 833-837.
doi: 10.7498/aps.49.833
Abstract +
Some basic problems of Lyapunov Characteristic Exponents (LCE) are discussed, including the computational method and the fact that the Lyapunov exponent of any limit set other than an equilibrium point must be zero, namely one of the Lyapunov exponents should vanishes. The conclusion is deduced that the dimension of a hyper-chaotic attractor must be great than 3. The LCEs of several important models are studied, more reasonable results are yielded. An efficient method for calculating the conditional LCEs is suggested. By studying the conditional LCEs of the hyper-chaotic system, we conclude that it cannot be synchronized with only one driving variable. The infection of random initial values in Wolf's program of LCEs computation is pointed out.
2000, 49 (5): 838-843.
doi: 10.7498/aps.49.838
Abstract +
Based on the nonlinear control system theory and Lyapunov technique,we have designed a nonlinear feedback controller for controlling the scalar output signal of a smooth (hyper) chaotic system to synchronize with any continuous time scalar (hyper) chaotic signal under some assumptions.The result,which is global,is rigorously proved by means of Lyapunov theroy.An application to the synchronization of two (hyper) chaotic systems is presented.
2000, 49 (5): 844-848.
doi: 10.7498/aps.49.844
Abstract +
A new kind of stochastic web due to discontinuity was found in classical 1-dimensional kicked billiards model (1D-KBM),which is a discontinuous Hamiltonian system.Its classical diffusion characteristics have been discussed in our previous article.The quantum diffusion characteristics of 1D-KBM was studied,the interesting thing is that it was found to be related with the classical diffusion characteristics,and some more special characteristics for the quantum case were also pointed out,especially those present different properties forα[0,π/2) and α[-π/2,0).
2000, 49 (5): 849-853.
doi: 10.7498/aps.49.849
Abstract +
In this paper,a method of chaos control based on the linear and nonlinear transformation of system variables is proposed.The Henon map and Lorenz system are taken as two typical examples to demonstrate the effectiveness of this method.The results show that the UPOs embedded in the chaotic system can be stably controlled by changing the linear transformation matrix of system variables.We can obtain lots of new stable dynamical behavior when this method is extended to nonlinear transformation.At the same time,we discuss the physical mechanism of this chaos control method from point of view of the information entropy.
2000, 49 (5): 854-862.
doi: 10.7498/aps.49.854
Abstract +
The surface topographies of Si-substrate and ZnO films as-deposited and annealed were measured by atomic force microscope (AFM).Five methods (variance from average height,absolute deviation from average height,height based on the minimum height of the rough surface,height based on a depth from the surface,height based on the bottom of the film) for determining height distribution probability are used to calculate the multifractal spectra of AFM images.It is found that the former three methods could not satisfy the scaling law well when the smaller probability subsets provide the main contribution to the partition function.On the other hand,the latter two methods can satisfy the scaling law close to 3 orders of magnitude and can be used to compare roughness between different rough surface quantitatively.
2000, 49 (5): 863-867.
doi: 10.7498/aps.49.863
Abstract +
Using a ray-tracing code,the imaging process of non-point light sources through a concave grating has been studied.It is demonstrated that under specially designed conditions,a plane spectrum can be formed for non-point light sources.The positions for the plane spectrum have been derived for the sources at different distance from the grating.A criterion has been defined under which the effects of variation of the source-size on the focal plane can be neglected.
NUCLEAR PHYSICS
2000, 49 (5): 868-874.
doi: 10.7498/aps.49.868
Abstract +
On the basis of the energy spectra, the angular and Z distributions of the fragments emitted at forward and intermediate angle region in 25MeV/u 40Ar+115In reaction, the evolution of emission mechanisms of fragments with the emission angles of the fragments in the laboratory system and the charge numbers of the fragments is discussed. The model of modified quantum molecular dynamics(MQMD) is employed to investigate the angular and Z distributions of the fragments. The theoretical calculations are in good agreement with the experimental data in general. But in the forward angles the yield of the fragments is underestimated by MQMD model while in the case of the intermediate angle region, the calculated result is higher than the experimental data for the fragments whose charge numbers are in the vicinity of the projectile. The angular and charge distributions of the fragments are also compared with the statistical model of GEMINI. It is found that a small proportion of the statistical evaporation component exists in the forward angle region while in the intermediate angle region, this statistical evaporation component shows a little increase. With the decrease of the fragment charge number, the non-equilibrium intermediate-velocity component goes up step by step and plays a leading role while the equilibrium evaporation one diminishes gradually.
ATOMIC AND MOLECULAR PHYSICS
2000, 49 (5): 875-879.
doi: 10.7498/aps.49.875
Abstract +
In this paper the quantum dynamics of the trapped atom which acts with a standing light field and a travelling light field is investigated. Evolution of the quantum mean energy of the ion with time displays the characteristic of collapse-revival which implies that the vibration states of the system have squeezing effect. The larger the nonlinearity of the system, the higher the frequency of collapse-revival of the system, and the smaller the quantum mean energy of the ion. The higher the intensity of the travelling light field, the higher the degree of squeezing of the vibration states of the system can be observed.
CLASSICAL AREA OF PHENOMENOLOGY
2000, 49 (5): 880-886.
doi: 10.7498/aps.49.880
Abstract +
Considering the three transport mechanisms of diffusion, drift and the photovoltaic effect, we set up a set of coupling differential equations that describe the dynamics of the two-color holographic storage in doubly doped LiNbO3:Fe:Mn in the case of small signal and modulation, and solve the equations to explain the time dynamic development process of holographic storage by using the numerical calculation method. On the basis of these results, we analyze the effect of oxidation-reduction on the process of holographic storage, the non-volatile holographic storage is realized only if the sum Na of number density of the acceptors (Fe3+ and Mn3+) is larger than the number density of iron ions N2. Diffraction efficiency of fixed grating increases with oxidation, photorefractive sensitivity decreases with oxidation, higher diffraction efficiency is at the cost of lower photorefractive sensitivity. When the concentration of doped iron is constant, the higher the concentration of doped manganese, the larger the effective dynamic range of state of oxidation-reduction is, in which holograph can be saved permanently.
2000, 49 (5): 887-892.
doi: 10.7498/aps.49.887
Abstract +
A general expression of emission spectrum for a two-level atom interacting with gray-body radiation field is given in this paper. We investigate how the photon-number distribution of the incident field, the absorptivity of the cavity and the temperature of the system affect the time-dependent physical spectrum.
2000, 49 (5): 893-897.
doi: 10.7498/aps.49.893
Abstract +
In this paper a simple pendulum equation with damping term is found for a free-electron laser. The equation is solved by using iteration in small signal regime and the formula of the gain function obtained corresponds to the iteration solution. Particularly, the simplified formulae are also derived of the gain function in both weak damping and overdamping regimes in free-electron lasers, and the origin and the physical meaning of the damping term in the simple pendulum equation are discussed in detail.
2000, 49 (5): 898-903.
doi: 10.7498/aps.49.898
Abstract +
The main structures and features of stationary and rotational transverse patterns in the cylindrically symmetric lasers have been discussed in the good cavity limit. The numerical analogue shows that the intensities and the frequencies of the modes which form the patterns obey the cooperative frequency shift law.
2000, 49 (5): 904-910.
doi: 10.7498/aps.49.904
Abstract +
The polyetherketone (PEK-c) guest-host system thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. Their second-order nonlinear optical (NLO) coefficients χ33(2) were measured by using Maker fringe method for the polymer films doped with different weight percents of DCNP. Experimental results indicate that the second-order NLO properties of the poled polymer films could decrease with the chromophore loading increasing when the chromophore loading reaches a fairly high level. In this paper, the relationship between the macroscopic second-order NLO coefficient and the chromophore number density was modified under considering the role of the electrostatic interactions of chromophores in the polymer film. According to the modified relationship, the macroscopic second-order NLO coefficient is no longer in direct proportion with the chromophore number density in the polymer film. The effect of the electrostatic interactions of chromophores on second-order NLO properties was discussed. The attenuation of the macroscopic second-order NLO activity can be demonstrated by the role of the chromophore electrostatic interactions at high loading of chromophore in the polymer systems.
2000, 49 (5): 911-914.
doi: 10.7498/aps.49.911
Abstract +
From thermodynamic relations, the initial values of the quark-gloun plasma from relativistic nucleus-nucleus collisions are obtained. From these initial values we have studied the dilepton production on the basis of the (3+1) dimensional relativistic hydrodynamic model established by the present authors, and found that with increasing incident energy a characteristic plateau indicating the formation of quark-gluon plasma appears in the total yield, which may be tested in future experiments in CERN and Brookhaven.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2000, 49 (5): 915-921.
doi: 10.7498/aps.49.915
Abstract +
The generation and transportation of suprathermal electrons are important to both traditional ICF scheme and “Fast Ignition” scheme. This paper discusses the effects of electronion collision on the generation and transportation of the suprathermal electrons by parametric instability. It indicates that the weak electron-ion term in the PIC simulation results in the enhancement of the collisional absorption and increase of the hot electron temperature and reduction in the maximum electrostatic field amplitude while wave breaking. Therefore the energy and distribution of the supratermal electrons are changed. They are distributed more close to the phase velocity of the electrostatic wave than the case without electron-ion collision term. The electron-ion collision enhances the self-consistent field and impedes the suprathermal electron transportation. These factors also reduce the supratermal electron energy. In addition, we discuss the effect of initial condition on PIC simulation to ensure that the results are correct.
2000, 49 (5): 922-925.
doi: 10.7498/aps.49.922
Abstract +
Langmuir probe is an important tool to diagnose the plasma in radio frequency (rf) glow discharge. A new method has been used to obtain the electron energy distribution function in plasma by the numerical differentiation of the I-V probe characteristic.This method is based on Fourier transform and could overcome the defects of other methods. In this way, the second derivative signal of Langmuir probe I-V characteristic is obtained automatically and accurately. The mean electron energy and electron concentrations in rf glow discharge plasma in silane were obtained by Langmuir probe.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2000, 49 (5): 926-930.
doi: 10.7498/aps.49.926
Abstract +
On the basis of lattice wave theory, the several side-band profiles of X-Ray diffraction of spinodal decomposition for Cu-4wt%Ti alloy are simulated by computer through supposing the rectangular distribution of solute atoms in the alloy, and the profiles are extremely similar to experimental results. Moreover, in the light of the principle of superposition, the composition of the above-mentioned profiles which are perpendicular to each other in two directions is carried out and the simulated diffraction patterns obtained are extremely good consistent with TEM diffraction pattern.
2000, 49 (5): 931-935.
doi: 10.7498/aps.49.931
Abstract +
With elastic constants as functions of the order parameters, we have obtained a Landau's elastic free energy expression for biaxial nematic liquid crystals similar to that used by Govers. The relationship between this Govers form and the Saupe form for biaxial nematics is obtained. It shows that simple distortion, splay, twist or bend, may lead to a first order phase transition from isotropic phase to biaxial nematic phase. However, in the case of cholesteric liquid crystal, there exists a critical chirality, above which, instead of first order, the phase transition becomes second order.
2000, 49 (5): 936-938.
doi: 10.7498/aps.49.936
Abstract +
Using a Frhlich Hamiltonian for the electron-lattice interaction, an expression for the Peierls phase transition temperature (Tp) of armchair carbon nanotube (ABT(n)) has been derived.As an illustration, the formula is used to estimate Tp of ABT(8) and ABT(10). The results indicate that Tp of ABT(n) will decrease with increasing of their diameters,and they are stable against the Peierls distortion and preserve metallic property at and far bellow room temperature.
2000, 49 (5): 939-942.
doi: 10.7498/aps.49.939
Abstract +
Synthesized C20 at the target surface of ultra high molecular weight polyethylene during Ar+ ion irradiation at room temperature was studied by high resolution transmission electron microscopy/electron diffraction, time of flight mass spectroscopy,IR and Raman Spectroscopy.We believe that radiation-induced crystallites consist of caged C20.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2000, 49 (5): 943-948.
doi: 10.7498/aps.49.943
Abstract +
In this article we present a first-principles calculation on the electronic structures and magnetism of Gd pnictides. Calculations are based on the local (spin-) density approximation of the density functional theory (DFT).The calculation method we used in this study is the linear muffin-tin orbitals in the atomic-sphere approximation (LMTO-ASA). Our result shows that in the non-spin polarized case the calculated band structures of Gd-V(V=N,P and As) exhibit characteristics of semimetals. After performing a wide band self-energy corrections, only the band structure of GdN is found to be a semiconductor with a narrow band gap (～019eV). Within the local-spin density approximations,the majority and minor spin bands of GdN display different features, i.e., the spin up band is semimetallic and the spin down band is semiconductor-like with a narrow gap (Eg≈036eV). All systems studied except GdN were found to be semimetallic with a hole section of the Fermi surface near Γ and an electron section near X.
2000, 49 (5): 949-953.
doi: 10.7498/aps.49.949
Abstract +
The ridge-loaded helical traveling wave tube (TWT) is a new kind of high power millimeter wave device. The “hot” dispersion equation of this circuit loaded with an electronic beam is presented in this paper, and the Downhill method is used to solve the transcendental equation. The physical dimensions of a 474GHz ridge-loaded helical groove slow wave structure (SWS) with a 20kV electron beam are given and the investigations of the effect of the ridge dimensions and electron beam parameters on the small signal gain are carried out. It is indicated from the calculation results that this type of structure is suitable for use as s SWS of high power, high gain but narrow passband millimeter TWT, of which the 3dB gain bandwidth is 34%. In order to increase the bandwidth, the reduction of the ridge gap or the increase of the electron beam current in an allowable range may be useful. The presented analysis will be a guide to the design of this kind of traveling wave tube.
2000, 49 (5): 954-958.
doi: 10.7498/aps.49.954
Abstract +
Electron-phonon interactions in ZnS are studied. Based on these results, high field transport processes at different temperatures are investigated by means of Monte Carlo method. The transient acceleration time of electrons do not vary with temperature. As the temperature increases, the kinetic energy distribution shifts to lower energy side and the average kinetic energy drops. The intervalley distribution of electrons shifts to lower valley as the temperature increases. The drift velocity of electrons decreases with increasing temperature. The detailed changes of these parameters with temperature are also given in this article.
2000, 49 (5): 959-964.
doi: 10.7498/aps.49.959
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We have simultaneously determined the densities and mobilities of light and heavy holes at various temperatures (12K to 300K) in two molecular beam epitaxy-grown p-type Hg1-xCdxTe (x=0.224) samples from variable magnetic-field Hall measurement by using a hybrid approach consisting of mobility spectrum analysis followed by a multi-carrier fitting procedure.In addition, we directly observe the contribution of the light hole to the conductivity tensor component. The experimental values obtained in this work should be useful in modeling of HgCdTe infrared detectors.
2000, 49 (5): 965-968.
doi: 10.7498/aps.49.965
Abstract +
A method of quantizing an active RLC circuit is developed, and the quantum fluctuations of the charge and current in the mesoscopic RLC circuit in the squeezed vacuum state, especially the influences of the resistance and the squeezing parameters on the quantum fluctuations are investigated.
2000, 49 (5): 969-973.
doi: 10.7498/aps.49.969
Abstract +
The effect of level statistics on critical level spacings c> of odd/even electrons are calculated by using the mean field self-consistency equation in three different Gauss ensembles (Gauss Orthogonal Ensemble, Gauss Unitary Ensemble, and Gauss Symplectic Ensemble) according to Random Matrix Theory. We obtain the ratios of critical level spacings of even electrons to those of odd electrons in different spin-orbit coupling and magnetic fields quantitatively， and the relations of Δ((0) and average level spacings o> in the odd case.
2000, 49 (5): 974-982.
doi: 10.7498/aps.49.974
Abstract +
Interference method is introduced to study the Fowler-Nordheim tunneling current oscillations. An accurate and simple formula for measuring the oxide thickness and the electron effective mass in the conduction band of the oxide is given.A comparison between the results calculated directly from the Schrdinger equation and those from the interference method for the triangular barrier case shows that the interference method suits very well for studying Fowler-Nordheim tunneling current oscillations.The interference method reveals the wave nature of the electron tunneling in the barrier.An important feature of this method is that it may be applicable to various shapes of potential barriers and wells. We also analyze the experimental results and give the physical meanings of them.
2000, 49 (5): 983-988.
doi: 10.7498/aps.49.983
Abstract +
Phosphor-doped nc-Si:H(nc-Si:H(P)) films were obtained by plasma enhanced chemical vapor deposition.The structural characteristics of nc-Si:H(P) films were investigated by means of scanning tunneling microscopy、Raman scattering,Fourier transform,infrared absorption spectroscopy, electron spin resonance and resonant nuclear reaction techniques.The measurements showed that the nc-Si:H(P) films have two-phase structure and the grains were embedded in the amorphous matrix.It was found that the grain size of the nc-Si:H(P) films was about 25—45nm,whichwas smaller than that of nc-Si:H films (about 3—6nm).It was also found that the optical absorption coefficient was quite high and the optical gap Eoptg was in a range of 173—178eV，which was almost the same as that of nc-Si:H films.The conductivity of nc-Si:H(P) films was in the range of 10-1—101Ω-1·cm-1,two magnitudes higher than that of nc-Si:H films and the maximum room-temperature conductivity reached to 505Ω-1·cm-1.The activation energy of conductivity of the nc-Si:H(P) films was in the range of 001—003eV，lower than that of nc-Si:H film.
2000, 49 (5): 989-996.
doi: 10.7498/aps.49.989
Abstract +
On the basis of the two-dimensional (2D) characteristics of the superconducting transportation as well as Josephson weak link behaviors in granular YBCO films,a 2D Josephson junction array is proposed as a model system for this film.Using this simplified model,we have discussed the decoupling procedure of vortex-antivortex pairs by bias current,and analytically developed temperature distribution of free vortices n(T,I) below TKT.As compared with experimental results,we find that the temperature dependency of n(T,I) is similar to the behaviors of microwave response of granular YBCO films near K-T transition temperature.This similarity implies,to a certain extent,some intrinsic relationship between vortex-antivortex decoupling and non-equilibrium radiation response dissipation in the high-Tc superconducting granular films.
2000, 49 (5): 997-1001.
doi: 10.7498/aps.49.997
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We present the detailed studies of the exchange bias effect,the coercivity and the enhanced coercivity of exchange bias bilayer Fe/MnPd,both experimentally and theoretically.We have,so far as we know for the first time,demonstrated that the existence of large higher order anisotropies due to exchange coupling between different Fe and MnPd layers can account for the large increase of coercivity in Fe/MnPd system.The linear dependence of coercivity on inverse Fe thickness can be well explained by a phenomenological model by introducing higher order anisotropy term into the total free energy of the system.
2000, 49 (5): 1002-1005.
doi: 10.7498/aps.49.1002
Abstract +
The development of a new-type photocathode for laser-driven high-brightness e-beam injector was reported.By the use of Cs+ ion implantation,a Mg-Cs alloy photocathode on Mg substrate was made.Some parameters of the ion implantation,the sputtering process,the photoemission and its mechanism were studied.Compared with the pure Mg photocathode,an order of magnitude improvement in the quantum efficiency from this photocathode has been obtained,meanwhile,we have also obtained a single-photon electron emission under the driving of 532nm green laser,the latter is a new development for the first time so far as we know in the world.Our experimental results provided a new way for the technology of high current,ultra short pulse e-beam.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2000, 49 (5): 1006-1009.
doi: 10.7498/aps.49.1006
Abstract +
Quality Ba0.8Sr0.2TiO3 (BST) thin films with a remnant polarization of about 3.5μC/cm2,and a coercive field of about 53kV/cm have been successfully prepared by a sol-gel processing using a 0.05mol/L precursor solution.X-ray diffraction and field emission scanning electron microscope investigations show that the BST films exhibit a tetragonal structure (c/a=1.009) and consist dominantly of large columnar grains of about 150nm in diameter.The observed good ferroelectricity and insulating property render the sol-gel derived BST thin films promising for uncooled infrared detector and thermal imaging applications.
2000, 49 (5): 1010-1013.
doi: 10.7498/aps.49.1010
Abstract +
It was studied by us that new technologies using strong pulsed magnetic field and electric current were applied to refine metal's solidified structure.These technologies improved remarkably the solidified structure of LY12 aluminum alloy and made the solidified grains more equiaxed and apparently finer compared with that of the normal sample,which is of more dendrite grains.The stronger the strength of the pulsed electromagnetic field,the better the improvement effect was.The refinement mechanisms of the new technologies were analyzed theoretically.New phenomena and problems occurred in our experiments were also pointed out in this paper.
2000, 49 (5): 1014-1018.
doi: 10.7498/aps.49.1014
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The growth kinetics of the oxide film and oxidation mechanism on tin films prepared by the electron-beam evaporation in the temperature range of 250—400℃ by an isothermal process were investigated. Based on an X-ray diffraction, auger electron spectrum, scanning electron microscope and alpha-step instrument, the evolution of the structure, composition, morphology and thickness of the oxide on tin films has been studied. In the studied temperature region, the growth of the oxide film was found to obey a parabolic growth-rate law with an activation energy of about 0.34eV, and is controlled by the oxygen diffusion from the loose oxide. It is concluded that the growth of the oxide begins from the formation of a SnO phase，with the increase of the oxidation time, the SnO phase decomposes and a Sn3O4 phase forms due to the SnO thermal and chemical unstability, and the deeper oxidation transfers the Sn3O4 phase to a SnO2 phase.
LETTERS
2000, 49 (5): 1019-1022.
doi: 10.7498/aps.49.1019
Abstract +
Amorphous Si/SiO2 superlattices have been deposited on glass substrates using two-target alternation magnetron sputtering technique. The samples are characterized using transmission electron microscope and low-angle X-ray reflectance techniques. The results indicate that most of the regions in Si layers consist of amorphous phase in the superlattices, while the regular structure appears in some local regions rarely. The thicknesses of Si layers are in a range from 18 to 3.2nm and the thickness of SiO2 layer is 4.0nm in all cases. The samples are systematically studied using absorption, photoluminescence (PL) and Raman spectroscopy techniques. The absorption edge positions and PL peaks shift towards shorter wavelengths while Raman spectra show broader peaks with decreasing Si layer thickness. The results are mainly attributed to the quantum confinement effects.
