Vol. 48, No. 5 (1999)
STOCHASTICITY OF THE EFFECTIVE SUBSPACE TAKEN UP BY A COHERENT STATE IN QUANTUM SYSTEM CORRESPONDING TO CLASSICAL CHAOTIC ONE
1999, 48 (5): 769-774. doi: 10.7498/aps.48.769
It is well known that all torus are destroyed in the Poincare' section with a certain energy E0 when a classical system is in completely chaotic state. But in its quantum counterpart, the features of the subspace taken up by a coherent state with central energy E0=E0 is not yet clear. In the present paper, taking nuclear Lipkin model as an example, we study the properties of such a subspace taken up by the coherent state of SU(3) group. An effective subspace is obtained by using a new renormalization approach. Our results show that in such an effective subspace the distribution of the nearest level spacings, the elements of effective Hamiltonian matrix, and the one-to-one correspondent map from the subspace of an integrable system to that of nonintegrable one are all consistent with predictions of random matrix theory.
1999, 48 (5): 775-786. doi: 10.7498/aps.48.775
In this paper we investigate the quantum jump in a multi-level atom and construct a formal solution to the optical Block equation describing the interaction system of the multi-level atom with incident resonant laser. It is proved that pure state analysis theory is no longer applicable to a multi-level atom system, so a mixed one is developed, concluding that the resetting density of a multi-level atom should be described by mixed state analysis theory. We also discuss the continuous quantum measurement along with quantum jumping in a multi-level atom.
1999, 48 (5): 787-794. doi: 10.7498/aps.48.787
In describing various modes of chaotic oscillators, generalized winding numbers are defined in tangent space corresponding to Lyapunov exponents of the chaotic attractor. Bifurcation behaviors from synchronous chaos of coupled Duffing oscillators are investigated using these concepts. The results show that a kind of Hopf bifurcation can take place from the synchronous chaotic state. Analysis of power spectrum indicates that the characteristic frequency created by the Hopf bifurcation is equal to the generalized winding number of the critical transverse modes just before the bifurcation.
1999, 48 (5): 795-801. doi: 10.7498/aps.48.795
A new dynamical system under external sinusoidal modulation based on acousto-optic bistable it-erative model is consturcted and investigated numerically. The results show that the state of the system takes on hysterical chaos and several kinds of evolution pattern under the modulation of the sinusoidal signal. As the amplitude of the modulation increases, the number of some evolution patterns in a modulation period will increase, the iterations needed for the first period window of the system will decrease, and the sketch amplitude of the modulated system will increase. In addition, the modulation frequency has no effect on the dynamical characteristics, only changing the number of the evolution pattern.
1999, 48 (5): 802-807. doi: 10.7498/aps.48.802
The problem of controlling conservative chaotic systems is investigated in this paper. Based on time delay feedback (TDF), a novel control method named auxiliary reference feedback (ARF) is presented. Different from TDF method, the basis to choose controlling parameters has been given. Only by appropriately adjusting feedback parameters and reference term, any periodical orbit can be reached by ARF. Numerical simulation results show that, ARF method is effective to control both dissipative and conservative systems. Moreover, we find that periodic windows controlled by ARF are stable in the presence of weak external noise.
1999, 48 (5): 808-815. doi: 10.7498/aps.48.808
In this paper, the fundamental diagram of the average traffic flow speed in the asymptotic steady state as a function of vehicle density for deterministic Nagel-Schreckenberg(NS) traffic flow cellular automaton model of high speed car without stochastic delay has been studied. It is proved that due to self organization of traffic flow, the fundamental diagram in steady state of deterministic NS model is exactly the same as the of deterministic Fukui-Ishibashi(FI) traffic flow model. The result shows if the abrupt acceleration scenario(where the speed of a car may be accelerated to the velocity limit M or the maximum velocity permitted by the spacing ahead in only one time step) is changed to the gradual acceleration scenario (where the speed of a car can increase one unit at most in one time step), the traffic flow behavior in asymptotic steady state will not be changed by self organization car interactions).
ATOMIC AND MOLECULAR PHYSICS
A STUDY OF OPTICAL OSCILLATOR STRENGTHS IN THE VALENCE AND CONTINUUM REGIONS (11.0—19.0 eV) OF MOLECULAR HYDROGEN
1999, 48 (5): 816-824. doi: 10.7498/aps.48.816
By considering channel characters and thermal distribution of the totational levels, experimen-tally determined absolute photoabsorption spectrum of molecular hydrogen have been analysed: these vibronic oscillator strengths in the region of 11.0—15.0 eV are determined, the total photodisso-ciation of B′1Σ+u is also obtained. Meanwhile, the photoabsorption spectrum in the valence and continuum regions (11.0—19.0 eV) of molecular hydrogen has been calculated based on multi-scattering self-consistent field. The theoretical calculations are in good agreement with experimental results.
1999, 48 (5): 825-833. doi: 10.7498/aps.48.825
The nonsequential ionization of one-dimensional helium atom under an intense ultrashort laser pulse is investigated with a classical ensemble theory. Through the dynamic simulation of the average Coulomb potential and the average distance between electron and nucleus, we found that high intensity and long wavelength favour the occurrence of nonsequential ionization for a given duration of pulse.
1999, 48 (5): 834-839. doi: 10.7498/aps.48.834
We analyzed the features and the line profile of velocity-modulation laser spectroscopy theoreti-cally, and reported the observed spectra of N+2 and CO+ molecular ions in the visible region.
1999, 48 (5): 840-849. doi: 10.7498/aps.48.840
In this paper, five groups of stronger hyperfine transitions of iodine molecule (127I2) are reported, which are to our knowledge first observed by us. Frequency separations and relative intensities of each transition are calculated. The calculated results and the observed values match very well. With the calculated results, we assigned the vib-rotational bands of each transition. Because the intensities of the newly observed transitions are hundreds of times stronger than transition R(127)11-5, which is applied to frequency-stabilized He-Ne laser, we use them as reference lines of iodine frequency stabilized tunable diode laser and get an output laser 3mW. This kind of frequency-stabilized diode laser may become a new kind of frequency standard.
CLASSICAL AREA OF PHENOMENOLOGY
1999, 48 (5): 850-861. doi: 10.7498/aps.48.850
After the discussion of the numerical simulation method based on the FDTD method and the PML technique, the motions of the charges and the electrical field lines were first employed to describe the radiation procedures of the pulse electromagnetic waves. Then the causes of how the charges are accelerated and how the motion status of the charges are maintained were further studied from the angle of interaction of charge and field. After these analyses, it was pointed out that the pulse radiation is due to the suddenly occurred time-varying electrical field (displacement current) in the open space. This view was further evidenced by two examples: one is the partly resistance loaded antenna, the other is the partly curved antenna. The radiation procedures of the pulse electromagnetic waves of many different situations were simulated throughout this paper with the contours and waveforms of electric field given. These figures are very helpful to the understanding of the radiation mechanism of the pulse electromagnetic waves.
1999, 48 (5): 862-875. doi: 10.7498/aps.48.862
The rotational angular momentum orientation of acetylene in vibrationally excited discrete rotational state (X1Σ+g，ν″2＝1，J″) has been selectively prepared by circularly polarized laser stimulated Raman pumping. From the induced fluorescence by a circularly polarized UV laser, A1Au(ν′3＝1)←X1Σ+g(ν″2＝1), the orientation of C2H2(X1Σ＋g，ν″2＝1，J″＝4，7，8，…，13）is measured for the first time. The decay rate constants and transfer of the orientation from the initial excited level to neighboring rotational states have been extracted.
1999, 48 (5): 876-881. doi: 10.7498/aps.48.876
By means of the technique of rational harmonic mode-locking(RHML), we succeeded in obtaining the optical pulses at repetition rate (fp) being integer multiples of the RF drive frequency(fm≈1.4 GHz) with detuning ratio of﹥10-6. The generation of maximum frequency was about 6 GHz and the stable rational harmonic mode-locking occurs only at fp=2fm. According to the result of our experiments, we put forth a possible mechanism of using RHML to generate high bit-zate pulses and point out the cause of the occurrence of instability in higher PHML. Furthermore, we demonstrate an effective method to elliminate the amplitude fluctuations of output pulse train.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
1999, 48 (5): 882-886. doi: 10.7498/aps.48.882
Completeness relation of the squared Jost functions to the NLS+ equation is proven by generalized Marchenko equation derived in this note. Hence the direct perturbation theory for dark multi-solitons is performed.
An exact direct perturbation theory of the KdV equation with corrections is developed for multi-soliton case. After showing that the derivatives of the squared Jost functions with respect to x are the eigenfunctions of the linearized operator, suitable definitions of the adjoint functions and the inner product are introduced. Orthogonality relations are derved and the expansion of the unity in terms of the squared Jost functions is implied. The completeness relation of the squared Jost functions is shown by the generalized Marchenko equation. The final result indicates that in the expression of the completeness relation, the integral path is along the real axis from －∞ to ∞ but runs over near the origin, which is contrary to the Cauchy principal value appearing in previous works. This leads to the disappear once of the shelf behind the soliton due to perturbations, which was considered as a characterized effect in the previous theories.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (5): 898-903. doi: 10.7498/aps.48.898
Two types of structure of lead tungstate scintillating crystals grown from high-temperature melt of the mixed powders of PbO and WO3 have been reported in the literatures. One is of space group C64h-I41/a,i.e. the scheelite structure, and the other D4-P4/nnc. It is not easy to determine its exact structure by the X-ray powder diffraction technique. On the bases of measuring its Raman spectra under different geometrical configurations and analyzing its vibration modes in the two different structures by the group theory the scheelite structure of the crystals grown from a stoichiometric melt was determined in the present paper.
1999, 48 (5): 904-912. doi: 10.7498/aps.48.904
We prepared alternating CNx/TiN composite films using a dc magnetron sputtering system in which a closed unbalanced magnetic field was adopted and a negatively biased grating was placed in front of each substrate. The composition of the thin film was analyzed by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and transmission electron diffraction (TED) revealed that the CNx films deposited at grating voltages lower than 400V are amorphous. β-C3N4 and subic-C3N4(c-C3N4) were formed at higher voltages. A high grating voltage is indispensable for synthesis of c-C3N4. The lattice constants of C3N4 evaluated from the experimental data agree well with reported theoretical values.
1999, 48 (5): 913-916. doi: 10.7498/aps.48.913
Branch structure of carbon nanotubes was found in the specimen prepared by pyrolysis of hydrocarbon in two different ways. Morphological and structural aspects of these as-grown tubes were investigated by TEM. The topographic defects related to the branches were discussed and can be considered as a modification for the graphine network.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Currently, the extended Hubbard model, which is a good approximation only for narrow-band system, suggests that the width of polaron in polymer is heavily reduced by the electron-electron interaction. However, the polymers possess wide band, so the off-diagonal correlation cannot be neglected. We considered the effects of full electron-electron correlation on the width and the creation energy of polaron in polymer. In the case of strong screening, our results are greatly different from those of Hubbard model. This suggests that in polymer, the Hubbard model should be gone beyond.
IMPURITIES AND INTERFACE SCATTERING EFFECT ON THE DIFFERENTIAL CONDUCTANCE NORMAL METAL-d-WAVE SUPERCONDUCTOR JUNCTIONS
1999, 48 (5): 926-935. doi: 10.7498/aps.48.926
Taking into account the impurities and rough interface scattering, using Bogoliubov-de Gennes (BdG) equations and Bolonedr-Tinkham-Klapwijk (BTK) model, we calculate the differential conductance of normal metal-d-wave superconductor. It is found that the tunneling spectum depends strongly on both the incident angle electrons and the crystalline axis orientation of superconductor, and exhibits the zero-bias conductance peak under suitable arrangements. Morevover, the zero-bias conductance dip can be splitted into two small conductance dips by the impurities scattering, the tunnel conductance peak at the energy gap and the zero-bias conductance are suppressed and smoothed by the interface roughnes. Our result can explain many experimental measurements on the tunneling spectum of high-Tc superconductors.
1999, 48 (5): 936-941. doi: 10.7498/aps.48.936
The properties of multiayer Fe/[NiFe/Cu]30 wire arrays were investigated by ferromagnetic resonance (FMR) technique. The arrays with wire density of 250 line/mm and 500 line/mm were fabricated utilizing laser hologram lithography and ion beam etching. In the wire array samples, optical peak occurs at higher field than the acoustic peaks and the exchange coupling between the NiFe layers is therefore antiferromagnetic. The optical peak along the easy axis lies closer to its acoustic counterpart than that along the hard axis. For wire arrays the paramagnetic resonance of the Cu layers is much stronger than the continuous film. This shows the degradation of the layer structure after the array fabrication.
1999, 48 (5): 942-947. doi: 10.7498/aps.48.942
Ferroeletromagnetic Pb(Fe1/2Nb1/2)O3(PFN) ceramics has been investigated systematically. Differential Scanning Calorimetric (DSC) analysis revealed that para-ferroelectric transition at about 380K and para-antiferromagnetic transition at about 145K were first order and weak first order or second order transition, respectively. Electronic Paramagnetic Resonance (EPR) indicated that above Néel temperature the resonance shows paramagnetic characters and under Néel temperature it shows antimagnetic characters. The spontaneous polarization and coercive field of PFN at room temperature are 11.5μC/cm2 and 3.04kV/cm, respectively. Dielectric measurement showed that the para-ferroelectric transition is diffusive character and the diffuse exponent is 1.62. Selected area electron diffraction pattern of PFN showed that the occupations of Fe3+ and Nb5+ ions in B site are disordered, leading to the diffuse characters of the para-ferroelectric transition.
1999, 48 (5): 948-954. doi: 10.7498/aps.48.948
In this paper we study the indirect upconversion-sensitization luminescence of Tm(0.1)Yb(10.9)：oxyfluoride glass induced by 800nm diode laser. Through the comparison between Tm(0.1)Yb(10.9)：oxyfluoride and Tm(0.1)Yb(3)：ZBLAN glasses we found that the upconversion luminescence intensity of Tm(0.1)Yb(10.9)：oxyfluoride glass was greatly enhanced and exceeded the level of Tm(0.1)Yb(3)：ZBLAN glass under the condition of indirect upconversion-sensitization. The results illustrated that under this kind of upconversion mechanism, it is possible to find some kind of material which has higher rare earth doped concentration and cut-off phonon energy, thus showing much higher upconversion efficiency than ZBLAN. This work and the results obtained will be helpful to promote the upconversion research to practical application. To our best knowledge, there have not been similar works published domestically and a broad.
THE STUDY OF EPITAXIAL GROWTH ZnO THIN FILM ON A (0112) SAPPHIRE SUBSTRATE USING ECR PLASMA SPUTTERING METHOD
1999, 48 (5): 955-960. doi: 10.7498/aps.48.955
Epitaxial growth of ZnO film on sapphire substrate has important applications in surface acoustic wave and acousto-optical transducers. An epitaxial ZnO film has been grown on a (0112) sapphire substrate using ECR plasma sputtering method at a substrate temperature of 380℃. The film is colourless, transparent and surface smooth. In order to explore the relationship between the deposition parameter and crystal structure of ZnO film, it have been studied that epitaxied growth of ZnO film in different substrate temperatures and deposition rates by XRD method.
1999, 48 (5): 961-965. doi: 10.7498/aps.48.961
In this paper we investigate the phase coherence of hyper-Raman lines in strongly driven two-level systems, and find that when the coherent superposition of excited and ground states is preparated, the high-order harmonics will disappear and the remainder of hyper-Raman lines in the emitted specturm are highly correlated. If the corresponding amplitude and phase of the hyper-Raman lines are selected, a train of subfemtosecond pulses will be generated.
1999, 48 (5): 966-972. doi: 10.7498/aps.48.966
Quantum tunneling effect at excited states in antiferromagnetic particles is studied with the help of the periodic instanton mdthod. The transition amplitude, energy shift and prefactor of WKB exponential are given for various low-lying excited states. The tunneling rate at definite temperature is obtained by statistical average and the theoretical dependence of the tunneling rate on temperature is in agreement with the experimental results.
1999, 48 (5): 973-976. doi: 10.7498/aps.48.973
The magnetic properties of the radula of chiton acanthochton rubrolinestus lischke, and the structure of magnetic particles contained in such radula have been studied. The morphology, orientation and magnetic anisotropy of these magnetic particles in chiton are discussed.