Vol. 56, No. 12 (2007)
Special soliton structures and the phenomena of fission and annihilation of solitons for the (2+1)-dimensional Broer-Kaup system with variable coefficients
2007, 56 (12): 6777-6783. doi: 10.7498/aps.56.6777
By an improved mapping approach, a series of excitations of the (2+1)-dimensional Broer-Kaup system with variable coefficients is derived. Based on the derived solitary wave excitation, we obtain some special soliton structures and study the phenomena of fission and annihilation of solitons.
New mapping solutions and localized structures for the (2+1)-dimensional asymmetric Nizhnik-Novikov-Veselov system
2007, 56 (12): 6784-6790. doi: 10.7498/aps.56.6784
The mapping approach is a kind of classic, efficient and well-developed method to solve nonlinear evolution equations. Its remarkable characteristic is that we can have infinitely different ansatzs and thus end up with the abundance of solutions. By an improved mapping approach and a variable separation method, a series of excitations of the (2+1)-dimensional asymmetric Nizhnik-Novikov-Veselov system is derived. Based on the derived solitary wave excitation, we obtain some special localized structures such as peakon solitons and fractal solitons, then we discuss the phenomenon of “chase and collision”.
Solving solitary wave solutions of higher dimensional nonlinear evolution equations with the homotopy analysis method
2007, 56 (12): 6791-6796. doi: 10.7498/aps.56.6791
We obtained a class of approximate solitary wave solutions for the (2+1)-dimensional modified Kadomtsev-Petviashvili equation by using the homotopy analysis method (HAM). The solutions obtained agree very well with the exact solutions. The results indicate that the HAM is still valid for solving solitary wave solutions of a class of higher dimensional evolution equations.
2007, 56 (12): 6797-6802. doi: 10.7498/aps.56.6797
A scheme for 1→2 universal telecloning of an arbitrary two-particle entangled state using a single, particular four-particle entangled state as quantum information channel is proposed. The spatially separated two receivers respectively receive one copy of the original unknown state with the fidelity of 5/6 which isindependent of the original state and is greater than the one in the currently existing schemes.Our scheme has been generalized to the case of 1→N(N>2) universal telecloning of an arbitrary two-particle entangled state. Using this scheme, the spatially separated N receivers respectively obtain one copy with the fidelity of (2N+1)/(3N) which is independent of the original state. Furthermore, we also proposed a scheme using the same four-particle entangled state as quantum information channel with the assistance of multi-target-qubit Control-Not gate and additional qubits, for 1→2 universal telecloning of an arbitrary n-particle(n≥3) Greenberger-Horne-Zeilinger (GHZ) state. This scheme is also generalized into the situation of 1→N(N>2) telecloning of an arbitrary n-particle GHZ state. Compared with previous proposals, our schemes require a reduced amount of entangled states as quantum channels to accomplish the task of universal telecloning of entangled state with better fidelity.
2007, 56 (12): 6803-6808. doi: 10.7498/aps.56.6803
Weak signal detection under the condition of adiabatic elimination in large parameters has been solved by step-changed stochastic resonance algorithm. Adaptive stochastic resonance based on approximate entropy measurement is proposed, and it can give the best result of the step-changed stochastic resonance adaptively. Because the approximate entropy of the periodic signal does not suffer from the change of its amplitude and phase, a periodic signal of frequency f0 with given signal-to-noise ratio which is to be detected can be made under the same condition as the raw data, and its approximate entropy is calculated as the criterion. By adjusting the structural parameters and calculation step automatically, a series output of the bistable system can be got, and an approximate entropy distance matrix can be constructed. After getting the minimum value of the matrix, the best parameters of the nonlinear dynamical system can be obtained.
2007, 56 (12): 6809-6814. doi: 10.7498/aps.56.6809
According to the Takens theorem, we reconstruct the chaotic time series to multivariate data and use the multivariate local polynomial estimator to predict the chaotic time series. This kernel estimator has the advantages of both the local model and the global model. The simulation shows that the estimator can predict the chaotic time series accurately.
2007, 56 (12): 6815-6819. doi: 10.7498/aps.56.6815
In this paper, we study the projective synchronization in two coupled fractional order chaotic Chen systems. An approximate integer order system model for the fractional order Chen system is constructed. A wellknown state error feedback control method is utilized to control the scaling factor to a desired value. Mathematical analysis proofs the feasibility and the numerical simulation shows the effectiveness of the proposed method.
2007, 56 (12): 6820-6827. doi: 10.7498/aps.56.6820
A clustering-based selective support vector machine ensemble forecasting model is presented. For improving the generalization ability of support vector machine ensemble, a hybrid clustering algorithm which combines the SOM and K-means algorithm is used to select the most accurate individual support vector machine from every cluster for ensembling, which ensures accuracy of individual support vector machines and improves the diversity of the individual support vector machines. This method can improve support vector machine ensemble generalization ability effectively with low cost. To illustrate the performance of the proposed forecasting model, simulations on chaotic time series prediction of the Mackey-Glass time series and the time series generated by the Lorenz systems are performed. The results show that the chaotic time series are accurately predicted, which demonstrates the effectiveness of this method.
2007, 56 (12): 6828-6835. doi: 10.7498/aps.56.6828
The synchronization of two symmetrical and nonsymmetrical nonlinear-coupled chaotic systems is discussed. A special nonlinear-coupling term is constructed by suitable separation between linear and nonlinear terms of the chaotic system, and the phenomenon of stable chaotic synchronization can be found in a certain region of the coupling strength. We used this method in hyperchaotic synchronization of Rssler system. The method can also be generalized to a form for hyperchaotic synchronization of networks linked by star coupling connection. By varying parameters in a region, we observed its effects on the stability of chaotic synchronization. Numerical calculation showned that the method is effective for hyperchaotic synchronization of Rssler system.
2007, 56 (12): 6836-6842. doi: 10.7498/aps.56.6836
To recover the initial signals from coupled map lattices (CML) is of great importance in signal processing. But like all chaotic systems, CML is highly sensitive to noise. It is hard for CML to recover the initial signals that have been corrupted by noise. A multi-CML system, which couples many one-dimensional CMLs paratactically together, is proposed in this paper. Through the coupled one-dimensional CML, the chaotic trajectories, which tend to be exponentially separated in noisy environment, become closer, so the noise influence is restrained. The numerical results verified the robustness and noise-restraining property of the multi-CML system. Given the proper selection of coupling parameters, even in the environment that initial signals are noise-corrupted, compared with single one-dimensional CML, the multi-CML system not only can recover the statistical property of initial conditions well, but also performs well in recovery of single initial signal with a high correlation.
2007, 56 (12): 6843-6850. doi: 10.7498/aps.56.6843
This paper studies the realization of anti-synchronization of hyperchaotic Chen system by three methods, i.e., the active control method, global control method and variable replacement method. The methods are proved valid by Lyapunov stability theory and numerical calculation of the largest Lyapunov exponent. The variable replacement method is more practical because it can anti-synchronize drive system and response system by transmitting one single signal. Numerical simulations show the effectiveness of the three methods.
2007, 56 (12): 6851-6856. doi: 10.7498/aps.56.6851
Based on Lyapunov stability theory, a tracking control scheme for single Lorenz system is used to the tracking control of Lorenz systems in unidirectional coupling network. A controller put on one node of this network suffices to realized tracking of some output signals of this network to approach to any desired orbit. Computer simulation shows that tracking controls can be realized even for different chaotic systems as long as the unidirectional coupling strength is large enough.
2007, 56 (12): 6857-6864. doi: 10.7498/aps.56.6857
In consideration of interfering Gauss noise, the results of encoding and decoding are simulated and analyzed for the Lorenz chaotic system and Liu chaotic system. It was shown that the capacity of Liu chaotic system resisting noise is better than that of Lorenz chaotic system, and the capacity of the continuous signal resisting noise is superior to that of the discrete signal resisting noise during the encoding and decoding processes.
2007, 56 (12): 6865-6873. doi: 10.7498/aps.56.6865
In this paper a novel four-dimensional autonomous hyperchaotic system is presented. Some basic dynamical properties are investigated. The fractional order oscillator circuit of this novel hyperchaotic system realized is simulated using EWB.
Study of gear-alternating control regulation in the interfluent location of on-ramps with cellular automaton model
2007, 56 (12): 6874-6880. doi: 10.7498/aps.56.6874
The gear-alternating control regulation was first actualized at the interfluent location of on-ramps in Shanghai elevated roads, which was theoretically studied in this paper. Different traffic flow models were established for the cases with and without the alternate controlling regulation based on the Fukui-Ishibashi cellular automaton traffic model. With the models, the traffic behavior at the interfluent location of on-ramp was investigated and some results were obtained. When there are many inflowing vehicles on the elevated road and ramp, the traffic situation on the elevated road with the controlling regulation is much better than that without it; when there are less inflowing vehicles, the elevated road situation on the whole remains the same in the two cases.
2007, 56 (12): 6881-6885. doi: 10.7498/aps.56.6881
Based on the diffusion-limited aggregation model, the kinetic aggregation process of magnetic particle with power-law coupling interaction is investigated by Monte Carlo method in this paper. The evolution of the average coupling energy Ec of clusters with particle number N for different values of exponent α during the growth process is studied in detail. The simulation shows that, for α≥5, Ec(N) almost does not vary with N; for α＝2, Ec(N) decreases slowly and then approaches a steady value as N further increases. For smaller values of α, however, Ec(N) varies linearly with N. The influence of the coupling parameter on the average coupling energy Ec for different values of α is also studied.
2007, 56 (12): 6886-6893. doi: 10.7498/aps.56.6886
Modularity is one on the important parameters to evaluate the community structure of network. The community structure of small-world networks (Watts-Strogatz model) and scale-free networks (Barabàsi-Albert model) were explored in the framework of the modularity using numerical simulations. We found that, firstly, the community structure in Watts' small-world networks is clear, while in Barabàsi's scale-free networks it is unclear; secondly, community structure is affected by the density of the network, namely, the sparser the network connections, the clearer is the community structure; thirdly, modularity in Watts' small-world networks is a dynamic variable which changes as a nonmonotonic function of the probability of rewiring connections. Hence, community structure should be one of the complex network properties. The real social networks may exhibit clear community structure, small-world phenomena and scale-free properties simultaneously. None of the current network models, such as the random network, Watts-Strogatz model, or Barabsi-Albert model, fits these social networks very well. A new social network structure is pending construction.
A newly micro-X-ray fluorescence spectrometer and applications for non-destructive analysis of archaeological objects
2007, 56 (12): 6894-6898. doi: 10.7498/aps.56.6894
The structure，performance and characteristics and the applications in archaeology of a new micro-X-ray fluorescence system based on rotating anode X-ray generator and polycapillary X-ray optics has been introducted in this paper. The polycapillary X-ray optics used here can focus the primary X-ray beam down to some tens of micro meters in diameters that enables non-destructive local analysis of sub-mm samples with minor/trace level sensitivity. In order to prove the potentials of this instrument used in archaeology， a piece of Chinese ancient blue and white porcelain produced in Ming Dynasty was analyzed. The results showed that intensities of MnKα，CoKα lines varied in accordance with the thickness of blue glaze. Correlation analysis indicated that the Mn and Co have good linear correlations. So，the concentrations or ratio of Mn and Co were crucial to determine the provenance of a Chinese ancient blue and white porcelain or to descriminate the true one from a fake.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2007, 56 (12): 6899-6904. doi: 10.7498/aps.56.6899
Using three-dimentional model，the hybrid particle in cell method is used to simulate the inflation of magnetic field by injecting plasma into dipole magnetic field. Two different types of magnetic field expansions are considered：the high density plasma is injected into a dipole magnetic field with or without a background magnetic field. It is found that the existence of background magnetic field not only changes the particle distribution，but also significantly changes the extent of magnetic field inflation. The effects of plasma injection velocity on the magnetic field inflation are also studied. It is shown that the higher the injection velocity， the larger is the size of the inflated magnetic bubble. For the lower injection velocity，the gyroradius of the injected particle is small compared with the dipole field scale length， so that the particles are trapped in the dipole field and the effect on dipole magnetic field can be ignored.
The disappearance of conventional magic numbers and the appearance of new numbers near drip-line region studied using relativistic mean-field plus BCS model
2007, 56 (12): 6905-6910. doi: 10.7498/aps.56.6905
A theoretical method which is applied to examine the shell effects is presented. Namely， by calculating the particle number fluctuation in the framework of the relativistic mean-field model including BCS method，we find that the size of the particle number fluctuation is related to the nuclear shell structure. Based on this method， the disappearance of conventional magic numbers and the presence of new magic numbers near drip-line region are studied.
2007, 56 (12): 6911-6917. doi: 10.7498/aps.56.6911
A dual temperature thermonuclear burn model is presented， based on which the variation of the particle temperature， effective radiation temperature and the particle number density has been calculated for burn processes under various initial D-T density conditions. In comparison with the approximation that alpha particles deposit their energy instantaneously， the alpha particle slowing down effect during ignition has been studied. It was found that the peak of particle temperature delays and was about 13keV lower than that in the instantaneous case when the alpha particle slowing down effect was considered. Calculation also showed that in the case of lower initial temperature and density， the alpha particle slowing down effect is more remarkable.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (12): 6918-6923. doi: 10.7498/aps.56.6918
We have developed and carried out a detailed characterization of a cryogenically cooled (80K) high-pressure (50×105Pa) solenoid driven pulsed valve that has been used to produce dense jets of deuterium atomic clusters for interaction studies with high intensity laser. Rayleigh scattering was employed to investigate the scaling law between cluster size and upstream gas pressure，which was shown to be of the form Nc∝P2.890. Cluster size gets to its peak Nc≈2630 at 80K，48×105Pa. We also studied the cluster formation process，portrayed a characteristic curve which revealed cluster size temporal evolution. Our results are important for analyzing the cluster interaction with intense laser， and are expected to provide guidelines to choose proper fire time.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (12): 6924-6930. doi: 10.7498/aps.56.6924
The mathematic model of strut was established on the model of Yee grid in three-dimensional space and on the model of leapfrog in time-domain. The formula of strut current and inductance per unit length in three-dimensional Cartesian coordinates were deduced. The realization of struts in different orientations and different coordinate systems in two-dimensional and three-dimensional space was discussed. At the same time the iterative process under main finite-differential time-domain iteration of strut was given. Finally， magnetically insulated transmission line oscillator was used as an example to validate the simulation for output power and particle movement.
The gain computation for the traveling wave tube with dielectric-loaded rectangular waveguide grating
2007, 56 (12): 6931-6936. doi: 10.7498/aps.56.6931
The dielectric-loaded rectangular waveguide grating traveling wave tube (TWT) is a new kind of high power millimeter wave device. The “hot" dispersion equation of this circuit loaded with an electron beam is presented in this paper， and the “Newton downhill" method is used to solve the transcendental equation. The investigations of the effect of dielectric-layer dimensions and electron beam parameters on the small signal gain are carried out. The calculation results indicated that dielectric-loading can widen the bandwidth of the rectangular waveguide grating TWT and decrease the gain. In order to make up the gain-decrement，the groove-depth can be slightly increased，or the current of the electron beam enhanced within certain limits. The presented analysis will be a guide to the design of this kind of TWTs.
A recursive convolution-finite-difference time-domain implementation of electromagnetic scattering by magnetized ferrite medium
2007, 56 (12): 6937-6944. doi: 10.7498/aps.56.6937
The permeability of magnetized ferrite medium in the frequency domain is transformed to the time domain， and the complex magnetic susceptibility dyadic matrix and the complex magnetic strength vector in time domain are introduced. A recursive convolution-finite-difference time-domain (RC-FDTD) method of electromagnetic scattering by magnetized ferrite medium is analysed in detail based on the convolution principle. To exemplify the availability of the algorithm， the backscattering radar scattering section of a magnetized ferrite sphere is computed， and the numerical results are the same as the reference values， which shows that the RC-FDTD method is correct and efficient.
Near field modulation and laser induced damage of color separation gratings and combined color separation gratings-beam sampling gratings optical elements for use in inertial confinement fusion system
2007, 56 (12): 6945-6953. doi: 10.7498/aps.56.6945
Aiming at restricting the number and the thickness of elements used in the inertial confinement fusion (ICF) system and utilize the characteristic of easy integration of diffractive optical element (DOE)，we can integrate different DOEs in one optical element for the system optimization in the final optics assembly. In order to lay a theoretical foundation for normal running of combined elements used in the ICF system under strong laser irradiation， this paper uses Fourier modal method to simulate the modulation characteristics of single color separation gratings (CSG) and the color separation gratings-beam sampling gratings (CSG-BSG) combined optical elements in the near field， respectively. We found that the maximal modulation of every layer of CSG-BSG combined optical element was 10% to 47% smaller than that of single CSG. However， the probability of laser induced risk for CSG-BSG combined optical element is also in the interface of every layer as in single CSG. In addition，through comparison of the simulated distribution of optical amplitude in the area from exit surface to 1μm for CSG and CSG-BSG elements with the cross section distribution of optical amplitude after transmitting 0.001 and 0.800μm for the two optical elements， it was shown that CSG-BSG combined optical element can realize both harmonic separation and beam sampling， but hardly change the exit optical field distribution. So CSG-BSG combined optical element can meet the requirement for the ICF driver.
Simulation of effect of non-uniform input image on characteristics of output image of optical novelty filter based bacteriorhodopsin film
2007, 56 (12): 6954-6960. doi: 10.7498/aps.56.6954
Effect of the non-uniform input image on the characteristics of output image for the optical novelty filter based bacteriorhodopsin film was investigated. In contrast to the input image with uniform light distribution， when the incident intensity of the blue and yellow beam changes as the sine function， the light distribution of the output image changes non-monotonically and there are two peaks with weak intensity value between them. The lifetime τ of M state and the velocity of the object also affect the light distribution on the output image. The longer the lifetime τ of M state， the smaller the transmitted intensity of the blue light， and the reduction in intensity decreases with increasing lifetime τ， approaching a value practically equal to zero when τ is longer than 50s. Under the same incident intensity， the intensity of the blue beam at the corresponding position of the output image increases with the increase of velocity of the input image.
2007, 56 (12): 6961-6969. doi: 10.7498/aps.56.6961
Interaction of multi-level atoms with multi-mode fields is studied. Under rotation wave approximation， one can reveal the evolution laws of an N-level atom interacting with (N-1) mode cavity fields， and obtain the analytic solution of the corresponding Schrdinger equation in the interaction picture. Furthermore，the evolution expression of a three-level atom interacting with two mode fields and a four-level atom interacting with three mode fields， respectively， are given in detail. When the initial states of atoms are ground states， the probability amplitude of ground states will have the same evolution expression for both three-level atoms and four-level atoms.
2007, 56 (12): 6970-6975. doi: 10.7498/aps.56.6970
We apply nondegenerate four-wave mixing processes to the generation of stable continuous variable entangled light and study the time evolution of continuous variable entangled light. We analytically get the characteristic function of the two-mode field and find that the system is an optical parametric amplifier. We also show that the two-mode cavity field exhibits stable continuous variable entanglement under certain conditions. The degree of entanglement depends upon the two-photon intensity I2，the cooperativity parameter C and the side-mode detuning Δ′.
A kinetics model for alternate oscillation of self-terminating and recombination lasers in strontium ions
2007, 56 (12): 6976-6981. doi: 10.7498/aps.56.6976
A self-consistent model has been developed to simulate the kinetics of alternate oscillation of self-terminating and recombination lasers in univalent ions of strontium excited by high-repetition-rate pulsed discharge. Photoelectric pulse waveforms predicted by the model are in good agreement with the experimental measurement. Temporal behaviors of long-life particles， the upper and the lower level poplulations and the electron temperature in He-Sr discharge plasma are given by the model. The emission process of the two laser alternate oscillation， the characteristic of the laser pulse width and the population inversion mechanics are also analyzed. It is presumed whether the electron temperature can rise up quickly in the early discharge and fall down rapidly during the discharge afterglow is the key to realize the alternate oscillation of self-terminating and recombination lasers in univalent ions of strontium in experiment.
2007, 56 (12): 6982-6988. doi: 10.7498/aps.56.6982
The periodic oscillations and clock division in semiconductor laser with external optical injection have been studied theoretically and experimentally. The resuts indicate that double period oscillation due to semiconductor laser with extenal optical injection can lead to clock division of the injected optical pulses We have simulated the time series and power spectrum of output light from semionductor laser by the coupled rate-equation method， and studied a series of periodic oscillations in laser cavity. When the slave laser was drived into the dynamical period_two state with propriety injection optical power， and modulation frequency of injected optical pulses is twice the oscillation frequency， the clock division of injected optical pulses occurs. Moreover， in experiment，we have demonstrated that the output pulses appear at a repetition rate of 3.16GHz when optical pulses with 6.32GHz repetition rate are injected into the Fabry-Perot laser diode. The experimental result is well consistent with theoretical analysis.
2007, 56 (12): 6989-6993. doi: 10.7498/aps.56.6989
Three autonomous equations for pulse parameters were deduced by substituting quasi-soliton solution to the master equation of regenerative mode locking lasers. The steady-state solutions without and with chirp were derived and their stability was analyzed by the method of linear stability analysis. The results show that the evolution of the steady-state output parameters of the system varies with the values of modulation parameters， group velocity dispersion and self phase modulation. Thus the steady-state output can be controlled by adjusting the modulation parameters in the system.
2007, 56 (12): 6994-6998. doi: 10.7498/aps.56.6994
The stimulated Raman scattering mode competition in hexamethylene(C6H12) pumped by different wavelength is observed. The high-gain Raman mode is determined by the pump wavelength. The Raman mode ω2(2852—3038cm-1) is generated when pumped by short wavelength(404, 532nm)laser, while the Raman mode ω1(802 cm-1) is generated when pumped by the long wavelength (808nm)laser. Similar phenomenon is generally observed in Raman experiments. The mechanism of the phenomenon and its possible application are discussed.
2007, 56 (12): 6999-7008. doi: 10.7498/aps.56.6999
Two-dimensional multicolored transverse arrays were demonstrated experimentally for the first time in a quadratic nonlinear medium. Cascaded noncollinear quadratic processes took place between input pulses and quadratic spatial solitons formed by spatial breakup of one of the pump beams with small ellipticity. Two-dimensional multicolored transverse arrays as well as transient grating were formed by cascaded noncollinear quadratic processes. Synchronously seeded supercontinuum pulses were diffracted and amplified, resulting in two-dimensional multicolored up-conversion parametric amplification. These two kinds of two-dimensional patterns were readily suppressed by seeding with weak second harmonic pulses in one of the pump pulses.
2007, 56 (12): 7009-7014. doi: 10.7498/aps.56.7009
In the absorption spectrum of the medium a burning hole appeared by coherent population oscillation, and the linewidth of this feature was approximately the inverse of the ground state population recovery time. Based on the theoretical analysis of gain the effect of absorption was different for different pump power. In a medium with absorption the oscillation leads to the pulse experiencing absorption saturation and propagation delay; in a medium with gain this effect induces the pulse experiencing gain saturation and propagation advance. Making use of coherent population oscillation we controlled the group velocity of light propagation in erbium-doped optical fiber. In experiment, the slowest group velocity was 2.857×103m/s, and the corrresponding group index was 10.5×104. According to coherent population oscillation and gain, we obtained the analytic expression of the group delay from rate equation and its simulation results were quantitatively coincident with our experimental data. The methods of controlling group velocity were comprehensively analyzed through the analytic model.
2007, 56 (12): 7015-7022. doi: 10.7498/aps.56.7015
A theoretical analysis of the magneto-photorefractive effect for different holographic recording configurations in LiNbO3:Fe is presented. All of the magneto-photovoltaic tensor elements are tabulated. And the equations of the bulk photovoltaic and the magneto-photovoltaic current for four different holographic recording configurations are given. Our results show that the diffraction efficiency of holographic grating depends on the applied magnetic field for each configuration, since the magneto-photorefractive effect induces a change in the electric current. For different configurations, the influence of the nonlinear effect in LiNbO3:Fe induced by the magnetic field is different. A method for measuring certain tensor elements is discussed.
2007, 56 (12): 7023-7028. doi: 10.7498/aps.56.7023
Nd-doped and Nd-Al-codoped high silica glasses were obtained by sintering porous glass impregnated with Nd3+ and Al3+ ions. The absorption, fluorescence spectra and fluorescence lifetime of Nd-doped and Nd-Al-codoped high silica glasses were measured. The intensity parameters Ωt (t=2, 4, 6), fluorescence lifetime, radiative quantum efficiency and stimulated emission cross section were calculated by Judd-Ofelt theory. The effect of aluminum codoping on the fluorescence and structural properties of Nd-doped silica glass has been discussed. By comparing the spectroscopic properties with other Nd-doped oxide glasses and commercial silicate glasses, this Nd-doped high silica glass is likely to be a promising laser material for use in high power and high repetition rate lasers.
Optimal design based on a two-dimensional photonic crystal of hexagonal lattice with a large complete band gap
2007, 56 (12): 7029-7033. doi: 10.7498/aps.56.7029
Using the plane wave expansion method, a kind of two-dimensional photonic crystal with a hexagonal lattice of GaAs columns in air is optimized by connecting the dielectric rods with veins of proper width. The optimal parameters are calculated in order to obtain the largest complete band gap. The width of the complete band gap is insensitive to the radius of dielectric columns, so this kind of two-dimensional photonic crystal is of great practicability.
Encoder and decoder of fiber Bragg gratings in optical code division multiple access system based on reconstruction-equivalent-chirp
2007, 56 (12): 7034-7038. doi: 10.7498/aps.56.7034
Fiber Bragg grating (FBG) encoder-decoder is considered as one of the most competent coding components in optical code division multiple access (OCDMA) systems, and high-performance low-cost encoder_decoder is required for its wide application. With the same performance, the reconstruction-equivalent-chirp (REC) technique reduces the complexity of fabrication setup, in which only micron or sub-micron precision control is required in the fabricating process, instead of the nanometer precision of conventional super-structured FBGs (SSFBGs). In this paper, the principle of REC-based encoder_decoders is discussed, and 511 chip 6.4×109/s encoder-decoders are fabricated. In order to quantitatively evaluate these encoder-decoders, the autocorrelation intensity peak to the maximum wing level ratio and the autocorrelation intensity peak to the maximum cross correlation level ratio are measured in OCDMA system. The experiment results show that these ratios achieved are above 8dB, which demonstrates the feasibility of the proposed encoder_decoders in practical OCDMA system application.
2007, 56 (12): 7039-7045. doi: 10.7498/aps.56.7039
Based on the general model of two parallel long-period grating coupler, the device stability was investigated by studying the grating longitudinal offset. Influences of modulation depth, surrounding refractive index and fiber cladding thickness were analyzed and the conditions for achieving 100% add_drop filtering was obtained. The measured experimental results demonstrated that efficient add_drop channel filter could be achieved even if the claddings were not reduced, which provided a method to simplify device fabrication in the further.
2007, 56 (12): 7046-7050. doi: 10.7498/aps.56.7046
Coherent beam combination of fiber laser array is an important technology in realizing high power fiber laser systems. Mutual injection locking of two fiber lasers was achieved by a fiber coupling apparatus. Through experiments, we conclude that in the free running state the beam profile is the simple intensity superposition as expected of two incoherent beams, but in the mutual injection locking, interference fringes with high contrast ratio was obtained, showing good mutual coherence between two laser beams. Through the interference fringes, we concluded that the two lasers are always in the out-of-phase mode, as predicted by theory.
Theoretical and experimental study of enhanced subharmonic emission from microbubbles with chirp excitation
2007, 56 (12): 7051-7057. doi: 10.7498/aps.56.7051
Subharmonic contrast imaging provides improved ultrasound imaging quality by taking advantage of increased contrast to tissue ratio. This article presents a novl approach to enhance the subharmonic emission from microbubbles by using a chip excitation technique. The chirp excitation pressure threshold and the sound pessure dependence of subharmonic are theoretically evaluated based on the Churc's model. Measurements validate that the optimized bandwidth and time duration of the chirp excitation can improve subharmonic amplitude and reduce side-lobe level. Both theoretical and experimental results demonstrate that the chirp excitation can improve the amplitude up to 22dB over the pulse excitation at the subharmonic frequency when comparing the coded excitation with traditional pulse excitation.
Numerical simulation of laser-generated ultrasonic waves in steel with gradient changes of near-surface elastic property
2007, 56 (12): 7058-7063. doi: 10.7498/aps.56.7058
Laser-generated ultrasonic wave is effective for evaluating near-surface elastic property. Taking account of the gradient changes of the near-surface elastic property caused by surface heat treatment or laser shock peening, a finite element method is developed to simulate the laser thermo-elastic generation and the propagation of acoustic waves in the system of multiple gradient layers of the substrate. The number of discretized layers has an effect on the generalized wave modes. Two systems with the surface layer softened and the surface layer hardened substrates are respectively considered. And the two-dimensional fast Fourier transform method has been used to obtained the phase velocity dispersion of different modes. The conclusion could be useful to the further study of the near-surface elastic property.
2007, 56 (12): 7064-7069. doi: 10.7498/aps.56.7064
Chinese is a tonal language， and the tone information is very important for the recognition of Chinese speech.Conventional methods generally focus on the normal tone in reading speech，rather than on the complicated spontaneous speech specifically. The real-context model is proposed as a new concept to be used in the tone unit selection. Then a method based on hierarchical clustering is performed to generate a more refined tone model. Experimental results have proved the effectiveness of the methods.
Characteristics of wave propagating through carbon nanotubes investigated on the basis of micropolar elasticity
2007, 56 (12): 7070-7077. doi: 10.7498/aps.56.7070
Relationship of stress and strain for a carbon nanotube was obtained on the basis of micropolar elasticity. The principle of Hamilton was utilized to derive the dynamic differential equation. Dispersion relationship (the relationship between frequency and wavenumber) of wave propagating through a carbon nanotube was obtained from the dynamic differential equation. In addition, group velocities and characteristic wave surfaces were also investigated. The obtained results are discussed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2007, 56 (12): 7078-7083. doi: 10.7498/aps.56.7078
The current density， field intensity and charge distribution in transient dielectric barrier discharge have been investigated. The energy transfer during the discharge has also been analyzed. The results showed that both the energy from the applied high-voltage source and the energy increment of the electric field were related with the density of wall charge. However, the work done by the discharge current in the gas region is independent of the density of wall charge and the kind of current waveform.
2007, 56 (12): 7084-7089. doi: 10.7498/aps.56.7084
Stimulated Raman scattering (SRS), which is the basic problem in laser plasma interactions, was studied by a Vlasov-Maxwell code developed by us. It was found that, there is a close relation between the occurrence of SRS and the electron velocity distribution. When a vortex is formed in the phase space of electron velocity distribution, the amplitude of back SRS increases, and when the distribution function is flattened in the phase velocity of plasma waves, the SRS ceases. In our simulation, we clearly observed the pictures of the burst of SRS, the formation and vanishing of the vortex in the phase space of electron distribution function and electron trapping, etc.
2007, 56 (12): 7090-7099. doi: 10.7498/aps.56.7090
A fluid sheath model of a cylindrical concave electrode and the distribution of the dust particles in the sheath have been stimulated. Factors, such as the number and the size of the dust particles, and the size of the electrode, which affect the distribution of the dust particles are considered. The result shows that the sheath is thin if the density of the plasma is high; otherwise, the sheath is thick. And structure of one level is formed if the number of the dust is small, while multilevel structure is formed if the number of the dust is large. With various sizes of the electrode, the dust shows complex and interesting structures.
2007, 56 (12): 7100-7105. doi: 10.7498/aps.56.7100
We adopted plasma fluid theory to analyze the harmonic generation of high power microwave in plasma filled waveguide, and the analytical theory is presented. The numerical calculation and analysis of second-order harmonic were also done in this paper. The theoretical and numerical analysis showed that high power microwave can generate harmonics in the plasma filled waveguide, and wave of both TE0n mode and TM0n mode can excite harmonics as TM mode.
Splitting of ultrashort laser pulses propagating in plasmas and the generation of soliton-like structures
2007, 56 (12): 7106-7113. doi: 10.7498/aps.56.7106
Using the one-dimensional particle-in-cell simulation, we studied the splitting of ultrashort laser pulses propagating in plasmas and the generation of soliton-like structures, and compared the effect on these phenomenon by changing the duration and intensity of initial laser pulse. It was shown the solitons moving with high group velocities can be formed by the ultrashort laser pulse with in a few cycles of duration. When the pulse duration and intensity of initial laser pulses increase, the group velocities of solitons decrease with greater frequency down-shifts. The decay of high-order solitons are generated by self-steepening and self-frequency shift, so the initial laser pulse splits into several daughter_pulses, and two solitons with different group velocities can be formed and propagate in the plasma. The number of daughter-pulses observed in simulations has been predicted by the theoretical calculation of soliton-orders.
The conditions of generating a single plasma channel in air are studied by using picosecond and femtosecond laser pulse. A stable and single plasma channel can be generated by a picosecond laser pulse with energy of 8—12mJ and focusing length of 15cm. The self-generated light emission is observed to be confined in the plasma channel and propagates in the channel. When using short focal length lenses it is easy to generate a single plasma channel in air with femtosecond laser with energy less than 10mJ.
2007, 56 (12): 7120-7126. doi: 10.7498/aps.56.7120
The microwave test method of space reflective wave was applied to study the attenuation characteristics of differently polarized wave scattered by microwave argon plasma jet in vacuum and its influencing factors. Experimental results show that in the 4—8GHz frequency area of testing wave, the plasma absorbs vertically and horizontally polarized wave obviously. The mass flow rate and power of generator and the background pressure affect the attenuation of vertically polarized wave. But the power of generator and degree of vacuum almost do not affect the horizontally polarized wave attenuation.
Monte Carlo simulation of Kα source produced by ultrashort and ultrahigh laser interaction with Cu target
2007, 56 (12): 7127-7131. doi: 10.7498/aps.56.7127
When the superthermal electrons produced by ultrashort and ultrahigh laser interacion with solid target tranport in the target, the Kα X-rays will irradiate from the target. According to classical scaling law, superthermal electrons' temprature in the normal direction can be got. Using Monte Carlo method, the tranportation of electrons in the solid target is researched. We simulate the Kα yield and spatial distribution for different target thickness, also simulate the Kα conversion efficiency versus temprature. Simulation result accords with experimental results. We conclude that, at a given temprature, the Kα yield will reach saturation and the spatial distribution will become more nonisotropic when the target thickness increases. There exists an optimial temprature for Kα X-rays conversion efficiency.
Study of the harmonics of coherent transition radiation emitted by hot electrons generated in ultra-intense laser plasma interaction due to different heating mechanism
2007, 56 (12): 7132-7137. doi: 10.7498/aps.56.7132
Coherent transition radiation (CTR) emitted by hot electrons generated in ultra-intense laser plasma interaction presents spikes at the harmonics of the laser frequency. If the hot electrons are generated in different heating mechanisms, CTR can have different ratios of the intensities of harmonics of the laser frequency (e.g., 2ω0 to ω0), from which we can infer the dominant heating process. For example, forward hot electrons are generated once in a laser circle when resonant absorption or vacuum heating takes effect, while CTR will present spikes at nω0; energetic electrons can be accelerated twice in a laser circle when j×B heating dominates, while CTR will give more prominence to 2nω0 than (2n-1)ω0. The latter will have higher ratio of theintensities of harmonic of 2ω0 to ω0 than the former. We deduced an equation of the relation between the ratio of the intensity of harmonic of 2ω0 to ω0 and the ratio of the number of electrons produced by different heating mechanism, by which we can study the main heating mechanism in ultra-intense laser plasma interactions. The ratio of the intensity of harmonics also depends on the temperature of the hot electrons, as well as the thickness of the target.
2007, 56 (12): 7138-7146. doi: 10.7498/aps.56.7138
Utilizing the method of longitudinal field and the dielectric tensor of the magnetized plasma, the accurate expressions for the field in the plasma drifting channel were derived. Under given boundary conditions and using the moments method, the dispersion relations were obtained. The dispersion characteristics in low-density and high-density loaded plasmas were studied. The plasma space-charge wave and the formation of the hybrid modes were discussed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2007, 56 (12): 7147-7152. doi: 10.7498/aps.56.7147
Subsolidus phase relations in the ternary system Y2O3-Eu2O3-SnO2 have been investigated by means of X-ray powder diffraction. The samples are prepared by solid-state chemical reaction. The (Y1-xEux)2Sn2O7 and (Y1-xEux)2O3 binary systems form complete solid solutions with pyrochlore-type and cubic structures, respectively. The characteristic photoluminescence peaks observed from (Y1-xEux)2Sn2O７ and (Y1-xEux)2O3 compounds correspond to Eu3+ intra-4fn shell transitions. The difference between the emission and excitation spectra of (Y1-xEux)2Sn2O7 and (Y1-xEux)2O3 can be explained by considering the surroundings of crystallographic site occupied by Eu3+. Y2O3-Eu2O3-SnO2 ternary s
2007, 56 (12): 7153-7157. doi: 10.7498/aps.56.7153
Based on the grating diffraction theory, the duty cycle and refractive index change of the periodically poled microstructure (PPMS) crystal are studied theoretically by light diffraction efficiency. The duty cycle and refractive index change of PPMS LiNbO3∶MgO and PPMS LiNbO3 were investigated using a laser of wavelength 532nm and maximal power 80mW, respectively. The refractive index change of PPMS LiNbO3∶MgO is larger than that of PPMS LiNbO3.
2007, 56 (12): 7158-7164. doi: 10.7498/aps.56.7158
The Co nano-films of different thickness (1—100nm) were successfully deposited on the monocrystalline silicon surface. Atomic force microscope， X-ray photoelectron spectrum (XPS) and X-ray diffraction analyses have been applied to study the surface topography and quality of Co nano-films of different thickness (1—100nm). We found that the deposited grain morphology transformed from acerose cellula by two-dimensional growth to globular aggregates of grains with film thickness increasing when the films thickness was 1—10nm. When film thickness was 3nm, the film had maximal roughness, which then decreased with the film thickness increasing. Atomic concentration and chemical states of cobalt were investigated by XPS scanning. The analysis results show that the chemical states of cobalt in the surface of nano-films are Co, CoO and Co2O3.
2007, 56 (12): 7165-7169. doi: 10.7498/aps.56.7165
Using the chemical vapor deposition method, a structure of carbon cones was vertically grown on graphite substrate, where a carbon nanotube was synthesized as the core of the carbon cone and protruded out at the carbon cone's tip. This structure can serve as a field emission device or a probe of scanning probe microscope. With the help of the electron microscope, the optimum growth conditions were determined, and the growth mechanism was discussed.
2007, 56 (12): 7170-7175. doi: 10.7498/aps.56.7170
Electric and magnetic properties of TiNi alloy have been investigated near the temperatures of martensite-austenite phase transition. The paramagnetism resulted from conduction electrons and the ferromagnetism resulted from a few located electrons have been analyzed from M-H curves. There is an abrupt drop of magnetization at about 180K in cooling M-T curve, and there is an abrupt rise at about 230K in heating curve. The temperature dependence of resistivity shows similar behavior to the M-T curve, i.e. the resistivity ρ-T of the samples also experiences abrupt change at similar temperatures. Furthermore, the temperature dependence of specific heat capacity for the sample displays an obvious peak during heating process. All the results show that the temperatures of martensite and austenite phase transition are about 180 and 230K respectively. On the other hand, the M-T curves show that the magnetization of martensite phase is smaller than that of austenitic phase at the same temperature. Moreover, when the strain is no more than 6%, the mechanical strain weakens the magnetism of TiNi alloy samples, while it does not change the temperature of martensite-austenite phase transition.
2007, 56 (12): 7176-7182. doi: 10.7498/aps.56.7176
In order to describe the change of noise signal in Al thin-film during electromigration process and its invalidation mechnism, correlation dimension was used in the electromigration noise signal analysis. Through calculating correlation dimension of electromigration noise signals attained by our experiment, the result showed that the main component of noise signal changed from stochastic to determinate during electromigration process, indicating that the noise changed from stochastic signal to chaotic dynamic signal. Dispersion theory was used to explain the above phenomenon. During vacancy dispersion, the main cause of noise is the stochastic dispersion of vacancies; during the process of vacancies accumulation to void nucleation, the main cause of noise is the change from stochastic dispersion to ballistic chaotic cavity transport. Compared with traditional parameters, the result showed that correlation dimension could be used to predict the invalidation of electromigration damage.
The effect of pressure on growth rate and quality of diamond films prepared by microwave plasma chemical vapor deposition
2007, 56 (12): 7183-7187. doi: 10.7498/aps.56.7183
The effect of total pressure on growth rate and quality of diamond films prepared by microwave plasma chemical vapor deposition was investigated. The results show that when the total pressure changed from 1.03×104 to 1.68×104Pa the growth rate increased from 3 to 16μm/h. For the diamond films prepared at high deposition pressure, scanning electron microscope images show clearly the crystals and the Raman spectra have sharp peaks at 1332 cm-1, which shows good quality of diamond films. However, the voltage-current relation shows the electrical quality of diamond films decreased since the defect density of surface may increase at high deposition pressures.
2007, 56 (12): 7188-7194. doi: 10.7498/aps.56.7188
Fe/Si multi-layer films were fabricated on Si(100) substrates utilizing the radio frequency magnetron sputtering system. Si/β-FeSi2 structure was found in the films after the deposition. A series of characterization methods were employed, including transmission electron microscopy and high-resolution transmission electron microscopy, to explore the dependence of the microstructure of β-FeSi2 film on the preparation parameters. It was found that β-FeSi2 particles were formed after the deposition without annealing, whose size was less than 20nm and the band-gap was 0.94eV. After annealing at 850℃, particles grew larger， however, the stability of thin films was still good.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2007, 56 (12): 7195-7200. doi: 10.7498/aps.56.7195
The electronic structures of F-doped SnO2 are calculated by first principles based on density function theory. The cell structures of F-doped SnO2 are optimized and the result shows that the cell parameters remain unchanged after doping. It is found that there are two nonequivalent oxygen sites in the unit cell where one of corresponding oxygen atom will be preferentially replaced by F atoms. Then, the band structures, density of states, partial density of states of undoped and doped SnO2 are calculated using plane wave ultra-soft pseudo-potential method. The influence of F-doping on the electronic structure and properties of SnO2 crystal and the optical absorbtion edge are analyzed. Moreover, the effect of different doping concentration on the electronic structure has been further analyzed.
First principles investigation of structural stability and electronic and optical properties of LiF and NaF under high pressure
2007, 56 (12): 7201-7206. doi: 10.7498/aps.56.7201
First principles calculation of LiF and NaF (NaCl phase and CsCl phase) underhigh pressure was carried out with the full potential linearized augmented plane wave plus local orbital method. It was shown that NaCl-type LiF transforms to a CsCl-type phase at about 450 GPa. Calculations of the electronic properties of LiF at high pressure compared with the energy band structural information indicate that a non-structureal transition occurs at about 53GPa, in which the direct band structure transforms to an in-direct band structure. We also calculated the complex electronic dielectric function and the static dielectric constants of LiF as functions of pressure. The results obtained for LiF are also compared with siilar data of NaF system.
2007, 56 (12): 7207-7212. doi: 10.7498/aps.56.7207
The effect of noise to the dynamical localization is discussed, and it is found that although the localization although this condition becomes strict, the resistance of the system to noise is not changed, which means we can obtain satisfactory localization effect in a long quantum dot array in practice. The height of localization peak of long-term averaged occupation probability has close relation with the resistance of the system to noise, which provides a method to improve the localization effect in practice.
Effects of emitting and hole transporting layers on the performance of white organic light-emitting divice
2007, 56 (12): 7213-7218. doi: 10.7498/aps.56.7213
By using Zn(BTZ)2, an efficient material to transport electrons, as blue emitting layer, a white organic light-emitting device with the structure of indium tin oxide (ITO)/N,N′-diphenyl-N, N′-bis(3-methylphenyl)-1,1-biphenyl-4,4′-diamine) (TPD): N,N′-bis-(1-naphenyl)-N,N′-biphenyl -1,1′-biphenyl-4-4′-diamine (NPB)(1:5%)(30nm) /NPB(10nm)/ bis［2-(2-hydroxyphenyl) benzothiazolate］zinc (Zn(BTZ)2)(30nm)/ bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum (BAlq)∶ 5,6,11,12-tetraphenyl-naphthacene (rubrene) (30nm)/tris(8-hydroxyquinoline)(Alq)(15nm)/Mg∶Ag has been successively made after trying several kinds of hole transporting layers and different thicknesses of emitting layers. The device can efficiently control the injecting and distributes of carriers (electrons and holes). When the voltages changes from 8 to 13V, the Commission Internationale de l′Eclairage coordinates change from (0.32，0.40) to (0.30，0.38) within the white-light region. The maximum external efficiency of this device is 0.85%, and when the driving voltage is 15V, it shows the maximum brightness of 11240cd/m2. By chosing proper hole transporting layers and the best thicknesses of emitting layers, the device achieves a balance between the hole and electron injection, which is presumed to be responsible for the improved performances of the device.
2007, 56 (12): 7219-7223. doi: 10.7498/aps.56.7219
The half-shell gold particle film was fabricated by nanolithography and self-assembly monolayer technique. The structures and the unique optical properties of the films were studied by scanning electron microscope and spectrometer. It was found that the localized surface plasmon resonance effect was determined by particle size and the inter-particle distance. The peak extinction wavelength is sensitive to the surrounding dielectric constant. The experimental results showed that the structure uniformity is the key to obtain stable optical properties.
2007, 56 (12): 7224-7229. doi: 10.7498/aps.56.7224
We propose a general canonical transformation for mesoscopic capacity-coupled dissipative RLC circuit and prove its feasibility and correctness. Using this transformation, the quantization of a double-loop capacity-coupled dissipation circuit is studied, and the diagonalized Hamiltonian of the system has an additional nonlinear term which has not been reported in literature. This general canonical transformation may have physical significance for the study of quantum fluctuation and quantum noise in the multiple-loop coupled dissipative circuits.
Langevin dynamics simulation of complex of semiflexible polyelectrolyte chain with oppositely charged particles
2007, 56 (12): 7230-7235. doi: 10.7498/aps.56.7230
The complex of semiflexible polyelectrolyte chain with oppositely charged particles and its stretching properties were studied with Langevin dynamics simulation. Attention is focused on the effect of particle charge and salt concentration. When there is no external force, the complex exhibits a beads-on-a-string configuration at low salt concentration and an aggregate configuration at high salt concentration. When external force is applied at the two ends of the chain, the particles unwrap from the chain in two steps with the increasing force.
2007, 56 (12): 7236-7241. doi: 10.7498/aps.56.7236
A high-power low-loss fast and soft recovery p+(SiGeC)-n--n+ heterojunction diode is presented to meet the need of higher frequency in power electron circuits. Compared with conventional Si p-i-n diodes, the forward voltage drop of p+ (SiGeC)-n--n+ diodes is reduced by 20% when the operating current density does not exceed 1000 A/cm2, which effectively reduces the operating loss. The reverse recovery characteristics of the novel SiGeC diodes are much improved. The reverse recovery time is more than half shorter, the peak reverse current is 25% lower and the softness factor is increased 1.3 times. Furthermore, the leakage current and reverse block voltage are almost unchanged. Ge and C content is the important parameters to affect the characteristics of p+ (SiGeC)-n--n+, which offers more freedom to device design.
2007, 56 (12): 7242-7247. doi: 10.7498/aps.56.7242
A novel gate-coupled electrostatic discharge (ESD) protection structure, called bonding-pad capacitance gate-coupled device, is designed. The new structure solves the problem of the traditional gcMOS device not being able to give correct transient response to some specific ESD events. The device layout area is also reduced. The measured results show that the novel structure has a 26%—41% layout area reduction and a high ESD robustnesss greater than 8 kV in a standard 0.5 μm single poly triple metal complementary metal-oxide-semiconductor process.
The surface mapping and crystal orientation of body-centered cubic thin metal tungsten films of different thickness
2007, 56 (12): 7248-7254. doi: 10.7498/aps.56.7248
Body-centered cubic (BCC) W films of different thickness were deposited on Si(100) substrate by magnetron sputtering and then annealed in vacuum at 400 ℃ for an hour. An investigation of the crystalline orientation and surface morphology evolution of the annealed W thin films suggests that the change of film texture coefficient T110 depends on the competition between the strain and surface energy. The surface structure evolution of annealed W thin films of different thickness reflects the competition between the strain energy and the surface energy. In addition, the correlation between the texture coefficient T110 and the surface structure anisotropy of the thin films is established by an approach of integrating the discrete wavelet transform and fractal geometry concepts.
The effect of temperature of substrate and oxygen partial pressure on V2O5 films fabricated by magnetron sputtering
2007, 56 (12): 7255-7261. doi: 10.7498/aps.56.7255
The properties of vanadium pentoxide (V2O5) films deposited by reactive DC sputtering from vanadium target were investigated. In particular, the chemical state of elements and microstructure of films were analyzed by X-ray photoelectron spectroscopy, X-ray diffraction and field-emission scanning electron microscopy. The percentage of oxygen in the sputtering chamber affects the chemical state of vanadium in the film. Higher oxygen partial pressure makes to vanadium to be oxidized from V4+ to V5+， and the grain size increased with grain a shape of needles, but the content of oxygen with high binding energy decreases. Higher temperature of substrates causes the grains to grow from needles to large flakes lying parallel to the substrate, and vanadium is oxidized to the stable high binding energy states.
2007, 56 (12): 7262-7265. doi: 10.7498/aps.56.7262
Using the full-potential linear-muffin-tin-orbital programs and the linear-response linear-muffin-tin-orbital programs，we calculated the electronic band structure, phonon spectrum and electron-phonon coupling strength in MgB2 film, and studied the effect of tension of MgB2 film on its superconductivity. It is shown that the softening of E2g phonon frequency, enchancement of the electron-phonon coupling and the phonon logarithm average frequency with contraction of the lattice constant along c-axis and elongation along a-axis resulted in the increase of superconducting transition temperature Tc. Our results are in good agreement with corresponding experiment.
Composition dependence of L10 ordering of FePt (001) thin films on MgO underlayer grown at room temperature
2007, 56 (12): 7266-7273. doi: 10.7498/aps.56.7266
We investigated the effect of extensive compositional change on the structure and magnetic properties of the post-annealed FexPt100-x (48≤x≤68) thin films with and without MgO underlayer deposited at room temperature. It was found that, during annealing, the FePt films on MgO underlayer with Fe-rich composition around 59at% exhibit much faster ordering than those with other compositions although the single layer FePt films were found to have the optimum composition for the chemical ordering of only slightly Fe-rich composition of 52at% of Fe. The film of MgO(10 nm)/Fe59Pt41(8 nm) after annealing at 600℃ for 30 min showed perpendicular magnetization with coercivity about 800 kA/m and the squareness was close to 1 due to the formation of (001) oriented ordering phase. The results of FePt thin films on MgO underlayer deposited at room temperature present a striking contrast with those of FePt grown on heated MgO single crystal substrate, where the optimum composition for the ordering was around 62at% of Pt. An interpretation on the observed experimental phenomena is given in this paper.
Analyzing the magnetization reversal mechanism of magnetic nanowire using the chain of truncated ellipsoid model
2007, 56 (12): 7274-7279. doi: 10.7498/aps.56.7274
A chain of truncated ellipsoid model is proposed to study the magnetization reversal mechanism of the magnetic nanowire in accordance with the real topological structure. Based on this model, the expressions of critical field for the irreversible reversal magnetization and the coercive force are derived for both the parallel rotation and symmetric fanning mechanisms. The influences of the contactangle of the ellipsoids, the uniaxial magnetocrystalline anisotropy, the angle between the applied magnetic field and the axis of the chain, the number of ellipsoids and the shape factor of single ellipsoid on the critical field and the coercive force are discussed. The results based on the model indicate that the magnetization reversal process of the Ni nanowire may have the symmetric fanning mechanism.
2007, 56 (12): 7280-7285. doi: 10.7498/aps.56.7280
Transmission of multiple heterostructures consisting of two kinds of single_negative materials are studied by transfer matrix method. The results show that the tunneling modes emerge on every interface of dual_periodical dielectric heterostructures when the heterostructure has zero effective refractive index, owing to the resonant coupling of the evanescent_wave_based interface modes. The zero effective refractive index tunneling mode is independent of the incident angle, polarization, period and scale length and have zero phase delay, which can be utilized to design zero_phase_shift omni_directional multiple_channeled filters. However, the tunneling modes situated on both sides of the center shift away from the center with decrease of incident angle, period and scale length.
2007, 56 (12): 7286-7294. doi: 10.7498/aps.56.7286
Er/Yb co-doped borate-silicate glass with 0.5mol% Er2O3 were fabricated by solid reaction. The concentration of Yb2O3 was in the range of 0.0mol% to 5.5mol%. The spectra of absorption, photoluminescence (PL) and up-conversion luminescence were analyzed. A critical value is found in the dependence of PL and absorption on the concentration of Yb2O3. When the concentration of Yb2O3 is greater than the critical value, the area of the absorption cross-section of Er3+ ions near 1535 nm has a linear increase with the increase of Yb2O3 concentration. Yb3+ co-doping makes the PL intensity to enhance and the PL spectra of Er3+ ions to broaden considerably. Quantitative analysis indicates that the inverse transfer energy from the acceptor to the donor does increase with the increase of Yb2O3 concentration. However, it could not be the dominaing factor causing the saturation of PL intensity. We ascribe the saturation of PL intensity to be due to the decrease of PL quantum efficiency and the saturation of excited states in the system caused by the increase of sensitizers. The sensitization of Yb3+ ions also results in the increase of Yb3+-2F5/2 and Er3+-4I11/2 populations, which promotes the cooperative up-conversion between Er3+ and Yb3+ ions.
2007, 56 (12): 7295-7299. doi: 10.7498/aps.56.7295
InGaN/GaN multiple quantum wells have been grown by metal-organic chemical vapor deposition. InGaN/GaN mulitiple quantum well with and without indium doped GaN barriers were study. The results show the sample with In-doped GaN barrier had a poor interface, but the photoluminescence spectrum showed clearly increased peak intensity and integral intensity, enhanced IBL/IYL ratio and reduced surface roughness. Electroluminescence of light emitting diodes with In-doped GaN barrier had better relative intensity and wavelength uniformity. We presume that the introduction of indium is the dominant factor leading to the decrease of the lattice mismatch strain between well and barrier, decrease of piezoelectricity and improvement in radiative recombination efficiency.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2007, 56 (12): 7300-7308. doi: 10.7498/aps.56.7300
Uniform and transparent titanium dioxide films were successfully deposited on glass by pulsed bias arc ion plating. Phase structure, surface morphology, microstructure, optical property and hardness of the films deposited at different biases were measured with X-ray diffractometer, atomic force microscope, scanning electron microscope, ultraviolet-visible spectrophotometer and nanoindenter. The results show that the deposited films are amorphous, and the pulsed negative bias plays a key role on the film properties. With the increase of the bias, the film thickness, hardness and elastic modulus change in a similar manner. They all first rise, and then decline. The film thickness reaches a peak in the range from -100 to -200 V, and the latter two parameters reach peak values when the bias ranges from -250 to -350 V. The film deposited at -300 V has atomic smooth surface, Rrms=0.113 nm, and highest refractive index of n550=2.51, which is greater than or equal to the maximum value ever reported. At this bias, the film has the best general properties. The mechanism of how the bias affects film properties is also discussed.
2007, 56 (12): 7309-7314. doi: 10.7498/aps.56.7309
The single-phase p-type Ag0.5(Pb8-xSnx)In0.5Te10 compounds were prepared by melt reaction and spark plasma sintering (SPS). Influences of Sn substitution for Pb on the carrier transport property and thermoelectric properties of the Ag0.5(Pb8-xSnx)In0.5Te10 (x=2, 2.5, 3, 3.5, 4) were investigated. Results indicate that: the carrier concentration and electrical conductivity increase with the increase of Sn substitution fraction x, the carrier mobility remains stable with the increase of x, the Seebeck coefficient and lattice thermal conductivity decrease with the increasing of x. Thermal conductivity decreases further after spark plasma sintering. The dimensionless figure of merit ZT of Ag0.5(Pb5Sn3)In0.5Te10(after SPS) reached a high maximum value of 1.05 at 700K.
2007, 56 (12): 7315-7319. doi: 10.7498/aps.56.7315
SrBi2Ta2O9/Bi4Ti3O12 multiple thin films were prepared on p-Si substrates by sol-gel method. The effect of ratio of SrBi2Ta2O9:Bi4Ti3O12 and annealing temperature on growth behavior, ferroelectric characteristics of SrBi2Ta2O9/Bi4Ti3O12 multiple thin films were investigated. Bi4Ti3O12 films on p-Si exhibit preferred c-axis-orientation growth, which favored the grow the high quality SrBi2Ta2O9/Bi4Ti3O12 multiple thin films. The remanent polarization Pr and the coercive field Ec of SrBi2Ta2O9/Bi4Ti3O12 multiple films both chage with the thickness ratio of SrBi2Ta2O9:Bi4Ti3O12 and annealing temperature. An appropriate ratio of multilayer thin films consisting of 1 layer of SrBi2Ta2O9 and 3 layers of Bi4Ti3O12 annealed at 650—700 ℃ gave the best ferroelectric properties with Pr of 8.1 μC/cm2 and Ec of 130 kV/cm, which is comparable to that of pure Bi4Ti3O12 films, and was fatigue-free up to 1011 switching cycles.
Experimental study of wear resistance of nickel based WC composite coating prepared by flame spraying and remelting
2007, 56 (12): 7320-7329. doi: 10.7498/aps.56.7320
Nickel based WC composite coating was prepared by the method of flame spraying and remelting, and its wear resistance was researched. The surface morphology of the coating after wear test was observed with scanning electric microscope, and the effects of WC volume fraction, the homogeneity of grain distribution, and the size of the packed powder grain on the wear were analyzed. The results showed that the hardness and wear resistance of the coating improve with WC volume fraction increasing, but the coating density lowers when WC volume fraction is too high, and the hardness and wear resistance decrease as a reaults. The distribution of WC grain with the blending method of polyethylene glycol (PEG) 400+ PEG2000+ethanol is most even, which decreases the degree of wear. Wear resistance of coating containing the same volume fraction of sub-micron WC powders is better than that of WC powders of micron size.
2007, 56 (12): 7330-7338. doi: 10.7498/aps.56.7330
Electroencephalogram data is used to extract functional networks connecting correlated human brain sites. Analysis of the resulting network shows statistical characteristic of complex network: the clustering coefficient is orders of magnitude larger than those of equivalent random networks, which is typical of small-world network and the distribution of degree is close to the scale-free network. All these properties reflect important functional information about brain states. To the alcoholic, the characteristic index of their brain is obviously different from the control group. Brain neural network information entropy and brain neural network normal information entropy are also defined to measure the complex network characteristic. A criterion in diagnosis and therapy of clinical encephalopathy is given. Calculation results illustrate that the brain neural network information entropy of alcoholic is quite distinct from the control.
2007, 56 (12): 7339-7345. doi: 10.7498/aps.56.7339
Animals such as dolphin and bat feature powerful biological sonar structure. The research on the mechanism and principle of signal processing performed by neural system will provide a novel viewpoint for signal processing. In this paper, a biological neural loop is established to handle Doppler signal based on neural coding theory of ordered space. From simulation, the system loop achieves fast operation and high resolution. Furthermore, Doppler signals of continuously-changing frequency can be properly coped with as well. The network structure for handling Doppler signals may take many forms. However, the structure proposed in the paper is possibly the simplest one, for it comprises only one or two neuron(s), ensuring rapid processing and high resolution.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (12): 7346-7354. doi: 10.7498/aps.56.7346
Based on the theory of the ring current formed primarily through injection driven by strong convective electric fields, E×B drift and subsequent trapping of particles from the plasma sheet into the inner magnetosphere, and considering the ring current ion loss by charge exchange and ion precipitation, a model of ring current ion distribution during main phase of storm is improved and tested in this paper. We simulated the properties of ring current ions in magnetosphere during different levels of storm main phase, and investigated the response of the partial ring current to convective electric field. The simulation was satisfactory. The results showed that partial ring currents dominate the ring current during main phase with a set of asymmetries between dawn to dusk and dayside to nightside, ions precipitation and the anisotropic distribution of pitch angles. The convective electric fields are positively correlated to the ion flux intensity and the ion distribution ranges. The simulations accord well with the observations and are reasonable.
2007, 56 (12): 7355-7358. doi: 10.7498/aps.56.7355
By applying the radiation spectrum obtained from tunnel effect, we obtain the normal canonical entropy of black hole by discussing the entropy of non-rotation black hole. The entropy satisfies the Bekenstein-Hawking area law, and contains the terms of correction whose main terms are proportional to the logarithm of the area, and the rest of the correction terms are related to the thermal capacity of black hole. With the help of the obtained normal canonical entropy, we studied the phase transition and showed that when the thermal capacity is emanative, there are no plural numbers at this point in the normal canonical entropy, which shows that the phase transition is of the second order.