Vol. 50, No. 10 (2001)
The stability of a kind of cosmological models is given. The variations of the cosmological model for parameters λ and k were discussed respectively. Near λ=0, the cosmological model is unstable with the change of λ, and near λ=β=0, the cosmological model is unstable with the change of k. So when we consider the stable cosmological model, we must consider the no-zero cosmological constant.
With the phase-plane analysis method, we obtain the general relativity motion equation in the gravitational field of the extreme charged black hole, and we plot the picture of the orbital phase-plane-and analyze the orbital stability.
2001, 50 (10): 1837-1841. doi: 10.7498/aps.50.1837
Noether’s theory of Birkhoff systems with unilateral constraints by introducing the quasi-symmetry of infinitesimal transformations of the transformation group Gr is presented and an example is given to illustrate the application of the result.
2001, 50 (10): 1842-1845. doi: 10.7498/aps.50.1842
The deformation theory for the solutions of BBM equation and generalized B-BBM equation and homogenous balance methods(HBM) for B-BBM equation are studied. The authors propose a new class of deformation formula which can produce the exact explicit solutions of generalized B-BBM equation by deforming the known solution of BBM equation. This paper concludes with an elementary example. As a byproduct, another class of deformation relation(called hybrid) is obtained.
2001, 50 (10): 1846-1850. doi: 10.7498/aps.50.1846
A method is presented here to direct the chaotic motion towards desired low-period motion by using notch filter output feedback control in lots of chaotic systems. The mathematic and physical mechanism of this method is also discussed based on Melnikov Method which is perturbation criteria for chaos. The control results of some typical chaotic systems are given, which has been shown that the method of controlling chaos can be easily and practically realized in physical systems. The method, furthermore, can be applied to achieve control for hyper-chaotic systems.
The hyperchaotic synchronization was achieved in LC oscillator via the mutual coupling method. The method to confirm coupling coefficient was given, the largest Lyapunov exponent spectra were calculated, and the connection between the coupling parameter and the synchronization time is discussed and given. Synchronization will be lost in the case of mismatched parameters.
2001, 50 (10): 1856-1861. doi: 10.7498/aps.50.1856
An encryption approach to digital communication by using spatiotemporal chaos synchronization is proposed. Two one-way coupled map lattice (OCOML) systems driven by a chaotic signal are synchronized. The chaotic outputs of the OCOML systems serve as the encryption and decryption keys and the main secret key is a set of coupling parameters of the OCOML. The advantages of the cryptosystem are its high communication efficiency, higher level of security and easy implementation by software. An example of duplex real-time voice communication between two computer users is described.
2001, 50 (10): 1862-1870. doi: 10.7498/aps.50.1862
An essential condition for controlling dissipative systems has been obtained via an analysis of the dynamical character of open-loop periods pulses, at the same time, we extend the applied range of the periods pulses. After a close-loop pertubation is added, a method for controlling global chaotic in two-dimensional Hamiltonian systems is proposed in a model of the standard map. The method is robust under the presence of weak external noise.
DEFINING THE CONTROLLING CONDITIONS OF LOW-DIMENSIONAL CHAOTIC SYSTEMS CONTROLLED BY TIME DELAYED FEEDBACK
2001, 50 (10): 1871-1876. doi: 10.7498/aps.50.1871
Based on the occurrence conditions of Hopf bifurcation of a delay system and corresponding handling methods, we have proposed an analytic method for achieving the controlling conditions when a low-dimensional chaotic system is controlled by applying time-delayed feedback on a control variable. Using an analytic method, we can obtain the functional relation of various parameters at the critical points. This method has been applied to some examples and the results show that it is an important means to control chaotic systems.
2001, 50 (10): 1877-1883. doi: 10.7498/aps.50.1877
We present the electronic structures and the basic properties of the first transition metal phthalocyanines (Pc) as well as their simulated STM images obtained by using the first-principles method. The simulated STM images show submolecular structures and reproduce the main features of the experimental images.The results show that the valence configuration of the metal ion has a strong influence on the STM images.At small tip bias voltage, unlike ScPc,NiPc and CuPc,wherein the central metal ions appear as a hole in the molecular images, the metal ion in other M Pcs STM images are the highlighted bumps. Moreover, we have studied the dependentce of the STM images of ScPc and NiPc molecules on the bias voltage, and predicted that the central metal ions in ScPc and NiPc images appear as bumps when the tip bias voltage is larger than -0.8V and 0.7V, respectively. The simulated STM images are interpreted as that the ScPc,NiPc and CuPc molecules have no significant dz2 character near the Fermi level, while the TiPc, VPc,CrPc,MnPc,FePc and CoPc systems have.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2001, 50 (10): 1884-1887. doi: 10.7498/aps.50.1884
The existence of the interaction between the neutron spin and the gravitation in the experiment of neutron-gravitation interferometry,in addition to the Aharonov-Carmi effect (gravitational A-B effect),is proposed in the paper.The authors obtain the exact solutions to the time-dependent Schrdinger equation describing this interaction by making use of the invariant-related unitary transformation formulation.
2001, 50 (10): 1888-1895. doi: 10.7498/aps.50.1888
Using a temperature, density, isospin and momentum dependent equation of state of nuclear matter obtained within the framework of Extended Skryme Hartree Fock theory, we study the chemical and mechanical instabilities of nuclear matter at different temperatures, density and relative neutron excess,and compare them with the results of the simplified three-parameter potentials, namely soft and hard potentials in which the symmetry energy part is added by hand. It is found that the asymmetric nuclear matter has remarkable chemical instability in the mechanically stable region. The relationship between the mechanical and chemical instabilities is different from the result of soft and hard potentials, which is shown to result from the difference of the density dependence form of single particle potentials. We also provide the chemical and mechanical spinodal regions in pressure density plane, and their isospin dependence is discussed. In particular, the behaviours of chemical instability around the critical temperature and the possible consequences in heavy ion collisions at intermediate energy are investigated.
ATOMIC AND MOLECULAR PHYSICS
2001, 50 (10): 1896-1901. doi: 10.7498/aps.50.1896
Density functional (B3LYP) method with Relativistic Effective Core Potential (RECP) have been used to optimize the structures and to calculate the potential energy function both for the ground and excited states of UH and UH2 molecules. Results show that the ground state of UH and UH2 molecules are X4Π and X3A2, which belongs to C2v symmetry, and the disassociation energies are 2.886 eV and 5.249ev respectively, and the spectral data of UH and UH2 have also been derived both for the ground and excited state. The potential energy functions of UH and UH2 have been derived based on normal equation fitting method and the many-body expansion theory. The information is useful to mechanism analysis of the aging effect of the hydrogen storage material.
CONTRIBUTION OF THE BOUND STATES AND CONTINUUM STATES OF AN ATOM IN INTENSE LASER FIELDS TO HIGH HARMONIC GENERATION
2001, 50 (10): 1902-1906. doi: 10.7498/aps.50.1902
Solving the time-dependent Schrodinger equation for a one-dimensional atom in an intense laser field based on the basis function expansion and a linear-least-squares fitting method, we examine the influence of the bound states,-continuum states and the interference between them of the model atom on the high harmonic generation. It is found that the main contributions to the low-energy harmonic generations come from the bound-bound interaction, while the high-energy harmonic generations are from the bound-continuum interaction. Beyond the cut-off, the interference of the bound-bound and bound-continuum interactions leads to the disappearance of the harmonic generation.
GEOMETRICAL AND ELECTRONIC STRUCTURES OF VANADIUM CLUSTERS, AND THEIR EVOLUTION FROM MOLECULAR TO BULK PHASE
2001, 50 (10): 1907-1913. doi: 10.7498/aps.50.1907
We have optimized the geometrical structures of the vanadium clusters Vn and discussed their evolution with cluster sizes in the average nearest-neighbor distances, coordination numbers, binding energies, ionization potential, electron affinities, density of states, valence band width, and magnetic moments using the density functional theory.We found that the clusters from V2 to V9 have distinctly molecular behaviour with dramatic size variations; V13, V15, and V19 are the transition regions from the molecular features to the bulk structures, and V27 and V51 possess almost the bulk properties.
CLASSICAL AREA OF PHENOMENOLOGY
2001, 50 (10): 1914-1919. doi: 10.7498/aps.50.1914
In this paper,the temporal auto-correlation properties of diffusing light in ultrasound-modulated random media were studied.The mathematical expression of auto-correlation function of diffusion light in an infinite medium modulated by ultrasound was obtained.The influences of ultrasound and scattering parameters on modulation parameter,modulation amplitude and its decaying were discussed.The feasibility of imaging an object hidden in random media with an auto-correlation function was also studied by use of Monte Carlo simulations.The ultrasound-modulated auto-correlation functions of normal and diseased tissues are different,which can be used to diagnosis diseased tissue hidden in normal tissue.
INFLUENCE OF A VIRTUAL PHOTON FIELD ON THE STATISTIC PROPERTIES OF PHOTONS IN A SYSTEM OF TWO-MODE SQUEEZED VACCUM FIELD INTERACTING WITH ATOMS
2001, 50 (10): 1920-1924. doi: 10.7498/aps.50.1920
The statistic properties of photons in a system of two-mode squeezed vacuum field interacting with a two-level atom are studied without the rotating-wave approximation by means of quantum theory, and the influence of the virtual-photon process on the statistic properties of photons is discussed emphatically. The results obtained using a numerical method indicate that the influence of the virtual-photon process on the statistic properties of photons qives rise to quantum chaos, that is related to the initial state parameters of the system.
2001, 50 (10): 1925-1929. doi: 10.7498/aps.50.1925
In this paper, we establish the general quantum theory of the micromazer with Kerr medium. When a two-Level atom enters into the Kerr medium cavity field of a coherent state via z motion, we analyze and calculate the atomic emission probability of different regimes (thermal-atom and ultracold-atom regimes).The influence of coupling constant χ,detuning Δ and the atomic injection rate r on the atomic emission probability is discussed emphatically.
GENERATION OF 4.5MW FEMTOSECOND PULSE WITH A COMPACT ALL SOLID-STATE CAVITY-DUMPED Ti:SAPPHIRE LASER
2001, 50 (10): 1930-1934. doi: 10.7498/aps.50.1930
A cavity-dumped Kerr-lens Mode-Locked (KLM) Ti:S laser is demonstrated with an all solid-state continuous-wave 532nm laser as the pump resource. Stable mode-locked laser pulse with a peak power of 4.5MW was obtained under 5.4W pump power. The pulse duration width is shorter than 18fs and the repetition rates can be tuned as low as 20kHz. To our knowledge, this is the lowest repetition rate and the most compact size from the solid-state cavity-dumped femtosecond laser.
2001, 50 (10): 1935-1938. doi: 10.7498/aps.50.1935
Based on the misaligned diffraction integral formula for misaligned optical systems, the diffraction for misaligned Lohmann's fractional Fourier transformation system and quasi-asymmetrically inhomogeneous medium are analysed, respectively. It is found that there exist similar expressions of misaligned diffraction integral formula and they are essentially equivalent. And also, a new concept of misaligned fractional Fourier transform is put forward.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2001, 50 (10): 1939-1945. doi: 10.7498/aps.50.1939
On the basis of numerical solution of Maxwell equations and fluid motion equations in 1-dimension, it is obtained that the travelling wave-solution of the longitudinal motion equation of electrons in the plasmas with ultra-intense laser pulse. The influence of electro-static field in the plasmas on the longtudinal motion is also analyzed.
2001, 50 (10): 1946-1949. doi: 10.7498/aps.50.1946
In the self-generated magnetic field produced by ultra-intense laser-plasma interaction or background magnetic field, even relativistic harmonics is excited by the ultra-intense laser propagating in underdense plasma which is magnetized by the self-generated magnetic field or backgroud magnetic field. In this paper, the second harmonics and its parameters are investigated.
2001, 50 (10): 1950-1955. doi: 10.7498/aps.50.1950
According to energy balance consideration, the ablation ratio formula of target irradiated by pulsed laser is derived, and the spatial-characteristic equations of plasma generated by pulsed laser are obtained by using fluid dynamic theory. Combining the ablation ratio formula with the spatial-characteristic equations of plasma, the effects of different laser power density and wavelength on the deposition characteristics of Kta0.65Nb0.35O3(KTN) thin film are studied on the basis of our experiments. And many valuable results are obtained which have been discussed in detail. The calculated results are in agreement with experiments on the whole.
ELECTROSTATIC FLUCTUATIONS AND TURBULENT TRANSPORT STUDIES IN THE HT-7 SUPERCONDUCTING TOKAMAK EDGE PLASMAS
2001, 50 (10): 1956-1963. doi: 10.7498/aps.50.1956
Electrostatic fluctuations and turbulence-induced particle flux have been investigated in the plasma boundary region of the HT-7 superconducting tokamak. There is a poloidal velocity shear layer driven by Er×BT located in the vicinity of the limiter radius, which has a suppression effect on the fluctuations and results in reductions in the normalized fluctuation level, coherence between the two plasma parameter fluctuations of φp, Te and ne. The radial decorrelation effect of the poloidal velocity shear causes a decrease in the turbulent flux. The time evolution of the turbulent flux shows bursts in turbulent transport. The frequency range where the turbulent flux, which comes in bursts, is dominant has been identified. It is in this frequency range that the spectral region with power decay close to 1/f of the power spectrum of the floating voltage fluctuation has been found. This result could be a signature of the turbulent transport close to instability threholds.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2001, 50 (10): 1964-1969. doi: 10.7498/aps.50.1964
The adsorption behaviours of glycine on Cu(111) have been investigated under ultra-high vacuum conditions at room temperature using scanning tunneling microscopy(STM). At lower coverage, it has been found that glycine can form only a two-dimensional gas phase on the Cu(111) surface. When the coverage is high enough, glycine will form a two-dimensional solid phase, i.e., the (4×8) superstructure. Two possible models have been proposed for the (4×8) superstructure. The models can explain STM images well. In addition, in a coverage range between those of the gas and solid phases, two intermediate phases are formed depending on different conditions of deposition and annealing. One is a stripe structure; the other is a hexagonal structure. To understand these intermediate phases further investigations are needed.
2001, 50 (10): 1970-1978. doi: 10.7498/aps.50.1970
The kinetics of ordering in a (001) deposition monolayer in fcc alloy system is investigated by means of the micromaster equation method in the pair approximation. The time evolutions of the long-range order (LRO) and short-range order (SRO) parameters are calculated. There are transient ordered states during the relaxation from the disordered state to the equilibrium state. The transient ordered states have various features are due to different characteristic times for the atomic migration, the different first- and second-nearest- neighbors interactions, the different influence of short-range correlation and long-range correlation on relaxation.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2001, 50 (10): 1979-1983. doi: 10.7498/aps.50.1979
Starting from general transmission line equation with an electron beam, a self-consistent nonlinear simulation on third-harmonic complex cavity gyrotron with gradual transition is presented, in which some practical factors are taken into account. The interaction between the electron beam and- H511-H521 RF field for third-harmonic gyrotron is simulated. The influences of the thickness and the velocity spread and the velocity ratio of the electron beam and the fluctuation of the magnetic field on the multi-modes interaction with an electron beam are analyzed.
2001, 50 (10): 1984-1990. doi: 10.7498/aps.50.1984
We show that there exist double-charge solitons in a one-dimensional mesoscopic-junction array-in which-there are two excess electrons respectively on two different islands. The prominent feature of a double-charge soliton is its potential peak splitting into double peaks. The two peak values are not equal generally. The dependences of the peak potentials and threshold voltage of a double-charge soliton on the structure parameters of the tunnel junction array are also discussed. We also propose an equivalent single-charge soliton-description for a double-charge soliton.
A wedge-shaped aluminum thin film system, deposited on glass surfaces by a vapor deposition method, has been fabricated. By using the expansive and movable behaviours of silicone oil drops, the Al films are quenched gradually by the silicone oil during the deposition process. An anomalous wedge-shaped structure with a slope of 10-6—10-7 spontaneously forms. The I-V characteristic of the system has been studied and its rough effect cannot be interpreted as RRN model of the normal rough thin films.
2001, 50 (10): 1996-2000. doi: 10.7498/aps.50.1996
We have investigated the dynamics of a Josphson junction circuit, which consists of a dc biased Josephson junction coupled to a resonant tank. Numerical simulations indicate that period-3 and chaotic states coexist when this system is driven by a proper external dc current. The detailed structures of the attractors and the basins of attraction are given to specify the features of these states. This provides one with valuable information to avoid chaos in Josephson junction devices.
EXPERIMENTAL STUDY OF LOCAL FLUX CREEP ON A CYLINDRICAL MELTING-TEXTURED GROWN YBa2Cu3O7-δ SAMPLE AT APPLIED FIELDS
2001, 50 (10): 2001-2007. doi: 10.7498/aps.50.2001
Using semiconductor Hall probes,we studied the local flux creep on a cylindrical melting-textured grown YBa2Cu3O7-δ sample at liquid nitrogen temperature and low applied field.The measurements on the top surface of the sample show that the local flux creep fits well the logarithmic time dependence in both the field-on and field-off cases.The obtained activation energy U0 in the field-on case is greater than the field-off one.The local magnetization was almost changing with the applied field synchronously in the measurement of magnetic hysteresis loops.The field was almost identical at a fixed local point under various sweep ratios of the applied field.The results imply that besides the side surface the applied field penetrates into the upper and lower surfaces to a certain extent too.The disparity in U0 results from the difference of the angle between the flux line and the ab plane.This study also shows that the measurement of flux creep at the low field has a potential to become a simple and effective method to investigate the pinning property in large size samples.
INFLUENCE OF NONSTOICHIOMETRY AND DOPING ON ELECTRICAL PROPERTIES OF (Na1/2Bi1/2)0.92Ba0.08TiO3 CERAMICS
2001, 50 (10): 2012-2016. doi: 10.7498/aps.50.2012
Influence of nonstoichiometry and doping on piezoelectric properties and depolarization temperature of lead-free piezoelectric ceramics (Na1/2Bi1/2)0.92Ba0.08TiO3 was studied. Nonstoichiometry of A-site can improve their piezoelectric properties. Doping in B-site has great influence on electric properties, which is similar to the corresponding rules of Pb(Ti,Zr)O3-based ceramics. Variation of coupling effect of A-site cation on BO6 octahedra as results of nonstoichiometry, and the doping in NBBT ceramics leads to variations of the depolarization temperature. The higher the depolarization temperature of Na1/2Bi1/2 TiO3-BaTiO3 ceramics studied,the lower the piezoelectric constant.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
OPTICAL PROPERTIES OF AMORPHOUS FLUORINATED CARBON FILMS PREPARED BY ELECTRON CYCLOTRON RESONANCE PLASMA
2001, 50 (10): 2017-2022. doi: 10.7498/aps.50.2017
The optical property of amorphous fluorinated carbon (α-C∶F) films are investigated, which are prepared by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) using trifluromethane (CHF3) and benzene (C6H6) as source gases. The optical energy gap Eg of the α-C∶F films deposited at 140—700W powers and CHF3∶C6H6=1∶1—10∶1 are between 1.76 and 2.85eV. The amount of fluorine in the films has an effect on optical absorption and energy gap. The absorption edge increases as the amount of fluorine is raised. The optical energy gap Eg is mainly determined by CF bond in the films, which results in the change of the density of states in band tail of the valence band.
2001, 50 (10): 2023-2027. doi: 10.7498/aps.50.2023
The BC2N thin films in stalklike growth have been deposited by hot filament assisted and rf plasma chemical vapor deposition (CVD). It was shown that the composition of the thin films mainly consists of BC2N, in which B, C and N were combined in atomic bonds. And the surface of the film took the shape of stalks, they were in regular arrangemeut with a uniform orientation observed with scanning electron microscopy.-In addition, we found this kind of growth had intimate relation with the deposition parameters. Finally, we analyzed the growth machanism of the stalklike BC2N.
2001, 50 (10): 2028-2031. doi: 10.7498/aps.50.2028
The effect of pulsed current on the microstructures and distribution of alloying elements of LY12 Al alloy during solidification process was studied. The experimental result showed that the microstructures of a LY12 Al alloy was evidently changed by pulsed current treatment, the eutectic structure which aggregated at grain boundary and dendrite net, was greatly reduced. The net became discontinuous, the dispersive and approximately spherical eutectic particles were formed inside the grains and near the boundary. The pulsed current can effectively reduce the segregation of Cu and Mg in the alloy, especially for Cu, and can remarkably improve the negative segregation phenomena of Cu in Al alloy, make Cu element more uniformly distributed in the whole sample.
STUDIES ON THE PROPERTIES OF ELECTRONIC ENERGY SPECTRA FOR TWO DIMENSIONAL FIBONACCI-CLASS QUASICRYSTALS WITH ONE KIND OF ATOMS
2001, 50 (10): 2032-2037. doi: 10.7498/aps.50.2032
In the framework of the single-electron tight-binding nearest interaction on-site model, we have studied the splitting rules of electronic energy spectra for two-dimensional Fibonacci-class quasicrystals FC(n) with one kind of atoms by means of the decomposition-decimation method based on the renormalization-group technique and have also calculated the electronic energy spectra numberically. It was found that there are-only three kinds of clusters,n×n, n×(n+1), and (n+1)×(n+1) for all of the two-dimensional quasilattices FC(n) and the electronic energy bands split as Ym-n-l . The general formula of the energy level numbers was obtained. We discovered that there was a kind of so called Fibonacci class number sets for the parameters used to describe the energy level number and got the first 11 determined integers of the sets. The experienced formula have been sought out. The analytic results are confirmed by numerical simulations.
2001, 50 (10): 2038-2043. doi: 10.7498/aps.50.2038
We report a correlated discharging process in current transport through metal-semiconductor-metal structures containing InAs self-assembled quantum dots.Due to the charged and discharged states of quantum dots,two different current states with a round hysteresis loop are usually observed in our structure.The transitions between the two current states are controlled by the applied voltages.Besides the normal charging and discharging processes,a correlated discharging is observed at 77K.Interactions that relate to the electrons in the quantum dots in the system are considered.The correlated discharging process is attributed to the interaction between electrons in the quantum dots and the conducting two-dimensional electron gas beneath the dot layer.Based on our analysis a simple picture of the relaxation process is given.
2001, 50 (10): 2044-2048. doi: 10.7498/aps.50.2044
The temperature dependences of resistivity and Hall coefficient of MgB2 and Mg0.93Li0.07B2 were measured, and the temperature dependence of cot-ΘH was calculated. The result of resistivity indicates that MgB2 and Mg0.93Li0.07B2 nearly have the same transition temperature. The-possible effect on transition temperature has been discussed. The measurement of Hall coefficient suggests the type of charge carriers is hole, and the Hall coefficient of Mg0.93Li0.07B2 becomes a little smaller compared with that of MgB2 which is attributed to Li doping . Both the decrease with increasing temperature-and-the temperature dependence of cotangent of Hall angle are proportional to the square of temperature.