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Vol. 58, No. 2 (2009)

2009-01-20
GENERAL
Approximate analytic solution to a class of generalized Canard systems
Mo Jia-Qi
2009, 58 (2): 695-698. doi: 10.7498/aps.58.695
Abstract +
Using the variational iteration theory, we obtain the approximations to the solution of the generalized Canard systems. Firstly, a set of functional is introduced. Then the iteration expressions of solving the original equation are constructed. Finally, the analytic expressions of the Canard solution are obtained.
Time-integral theorems for generalized Birkhoff system
Mei Feng-Xiang, Ge Wei-Kuan
2009, 58 (2): 699-702. doi: 10.7498/aps.58.699
Abstract +
The purpose of this paper is to study the time-integral theorems for a generalized Birkhoff system. A time-integral identity of the system is presented. A power-like equation,a Virial-like theorem,an integral variational principle and a differential variational principle for the system are deduced by using the time-integral identity.
Existence of oscillatory travelling wave solution of flood wave with viscosity
Wu Hai-Yan, Zhang Li-Feng, Zhang Liang, Wang Ji-Peng
2009, 58 (2): 703-711. doi: 10.7498/aps.58.703
Abstract +
Using the shooting technique, we investigate the existence of oscillatory travelling wave solution of viscous flood wave in a wide rectangular channel with constant inclination. We prove the existence and uniqueness of an oscillatory travelling wave solution when the parameters of the viscous coefficient, frictional coefficient, inclination and altitudinal ratio satisfy certain conditions. Owing to the difficulty of analytical calculation, Matlab is used to compute the value of altitudinal ratio, and the structure of oscillatory travelling wave solution is also discussed.
Quesne-like ring-shaped spherical harmonic oscillator potential and pseudospin symmetry
Zhang Min-Cang
2009, 58 (2): 712-716. doi: 10.7498/aps.58.712
Abstract +
A Quesne-like ring-shaped spherical harmonic oscillator potential is put foword and studied for spin 1/2 particles based on the Dirac equation, the Dirac Hamiltonian contains a scalar and a vector Quesne-like ring-shaped harmonic oscillator potentials. Setting Σ=S(r)+V(r)=0,we obtain the bound state solutions and eigenenergies with the two-component approach. The result shows the pseudospin symmetry exists in the Quesne-like ring-shaped harmonic oscillator potential. The general properties of both the ring-shaped spherical harmonic oscillator potential and the ring-shaped non-spherical harmonic oscillator potential are discussed.
A single photon source based on entangled photon pairs
Wang Su-Mei, Ma Hai-Qiang, Wu Ling-An
2009, 58 (2): 717-721. doi: 10.7498/aps.58.717
Abstract +
A single-photon source scheme based on entangled photon pairs from parametric down conversion is proposed, by means of which the single-photon quality is greatly improved, i.e. the multi-photon-pulse probability is reduced 100 times compared with that of an ordinary attenuated weak light source. The optical set-up and data acquisition are explained in detail. Experimental results show the good potential of this system for practical applications.
Quantum properties of the entangled coherent light field under the anti-Jaynes-Cummings model
Zhang Ying-Jie, Xia Yun-Jie, Ren Ting-Qi, Du Xiu-Mei, Liu Yu-Ling
2009, 58 (2): 722-728. doi: 10.7498/aps.58.722
Abstract +
A two-level atom drvien by a strong classical field interacts with a single-mode light field, and the interaction between the atom and the light field can turn into an effective anti-Jaynes-Cummings model under the conditions of strong driving and large detuning. In this paper, we mainly study the two-mode entangled coherent light field in this model, in which one mode of the entangled coherent light field interacts with a two-level atom driven by a strong classical field. During the evolution of the total system, we make a selective measurement on the atom. Through tuning the evolution time and the parameter of the coherent field, we can easily control the quantum statistical properties of the other mode of the entangled light fields and generate the expected non-classical light field in a longer interaction time and a wider region of coherent parameter.

EDITOR'S SUGGESTION

Nonlinear Landau-Zener tunneling in two-dimensional photonic lattices
Wang Sha, Yang Zhi-An
2009, 58 (2): 729-733. doi: 10.7498/aps.58.729
Abstract +
Nonlinear Landau-Zener tunneling in two-dimensional photonic lattices of Kerr nonlinearity media is investigated. We first derive the nonlinear three-level Landau-Zener model in photonic lattices for the case of hexagonal symmetry, and then simplify this model to a nonlinear two-level Landau-Zener model under a certain initial condition. For the three-level tunneling model, we calculate the tunneling probability numerically and study its changing rules under the specific initial condition.
Multi-order corrections of variational-integral perturbation for heavy quarkonium
Hai Wen-Hua, Zhu Qian-Quan, Zhao Yun-Hui
2009, 58 (2): 734-739. doi: 10.7498/aps.58.734
Abstract +
We employ the improved variational-perturbation method based on integral equation (variational-integral perturbation method) to solve the heavy quarkonium in the 2S state. Setting the mother Hamiltonian including variational parameter as the zero-order Hamiltonian and choosing the exact solution of the mother Hamiltonian system as the trial wave function, we obtain the multi-order corrected wave functions consisting of a few terms and calculate the multi-order energy corrections. The corrected wave functions are quadratically integrable and the energy corrections are in good agreement with the exact data. The boundedness and convergence of the perturbation series solution are also verified. The results show that the variational-integral perturbation method can not only raise precision of the result but also keep convergence of the wave function.
Statistical entropy of Gibbons-Maeda black hole computed by generalized uncertainty principle
He Feng, Zhao Fan
2009, 58 (2): 740-743. doi: 10.7498/aps.58.740
Abstract +
Statistical entropy of scalar field outside Gibbons-Maeda black hole is computed by the equation of state density corrected by the generalized uncertainty principle and by WKB approximation method. The result shows that the black hole entropy is proportional to its horizon area, which is the same as that given by Brick-Wall method. The difference from the Brick-Wall method is that the present result is convergent without any cutoff.
Fermions tunneling of the Vaidya-Bonner black hole
Lin Kai, Yang Shu-Zheng
2009, 58 (2): 744-748. doi: 10.7498/aps.58.744
Abstract +
The Hawking radiation of the Vaidya-Bonner black hole is studied by the theory of fermions tunnelling. By applying the following coordinate transformation and assuming proper γμ matrixes, we study the tunneling characteristics of the fermions with 1/2 spin from the Vaidya-Bonner black hole.
Phase synchronization of coupling systems
Liu Yong
2009, 58 (2): 749-755. doi: 10.7498/aps.58.749
Abstract +
The influence of the linear and nonlinear coupling parameters on the phase synchronization of chaos between two sub-systems with primary resonance is investigated by introducing the conception of the phase for a chaotic motion. The evolution process from non-synchronized state to imperfect phase synchronization and further to perfect phase synchronization between two sub-systems with approximate primary resonance is discussed. Further investigation reveals that the transition between different phase states are related to the critical change of the Lyapunov exponents. The results show that phase synchronization between two sub-systems is enhanced with the increase of the linear coupling strength and decayed with the increase of nonlinear coupling strength.
Predication of multivariable chaotic time series based on maximal Lyapunov exponent
Zhang Yong, Guan Wei
2009, 58 (2): 756-763. doi: 10.7498/aps.58.756
Abstract +
A method for prediction of multivariable chaotic time series through selecting many neighboring reconstructed vectors is proposed with reference to the method for prediction of single-variable chaotic time series based on maximal Lyapunov exponent. The new method is used to forecast the chaotic time series of two Rssler equations coupled system, Rssler equation and Hyper Rssler equations coupled system for onestep and multistep. Results show that the algorithm can forecast multivariable chaotic time series precisely and has strong anti-chirp ability. The relation between the result and the number of neighbor points is discussed.
An attractor with invariable Lyapunov exponent spectrum and its Jerk circuit implementation
Wang De-Chun, Li Chun-Biao
2009, 58 (2): 764-770. doi: 10.7498/aps.58.764
Abstract +
A novel three-dimensional chaotic attractor derived from Colpitts equation is proposed in this paper. When the given parameter varies in a broad range, the amplitude of the singals of the first two dimensions changes linearitly while the third one keeps its amplitude in the same range. At the same time, the Lyapunov exponent spectrum keeps invariable. This chaotic system is developed by substituting the absolute term for the exponent term in normalized Colpitts equation. Lyapunov exponent, Poincaré mapping, phase portrait and spectrum are given to verify that the attractors are chaotic. In addition, some basic dynamical characteristics of the new system are investigated briefly. Based on Lyapunov exponent spectrum analysis, it is demonstrated that the new system can go into periodic and chaotic behaviors. At last, the Jerk function of the new system is put forward and its circuit implementation is designed. The feature that the chaotic characteristic of this system has nothing to do with the given parameter while the amplitude of some state variables can be changed linearly makes it reasonable to predict that the chaotic system will have tremendous potential applications in chaotic radar, secure communications and other information processing systems.
Building and analysis of properties of a class of correlative and switchable hyperchaotic system
Jiang Chang-Sheng, Liu Yang-Zheng
2009, 58 (2): 771-778. doi: 10.7498/aps.58.771
Abstract +
A class of four-dimensional correlative and switchable hyperchaotic systems are built by adding an additional state, the nonlinear functions and anti-control into the three-dimensional chaotic system. Some of their basic properties are studied, such as the feature of equilibrium, the phase portraits of hyperchaotic attractor, Lyapunov exponent and the evolution of the dynamical action. The practical circuit is designed to realise these systems.
Linear and nonlinear generalized synchronization of a class of chaotic systems by using a single driving variable
Li Nong, Liu Yu-Ping, Gan Yi, Li Jian-Fen
2009, 58 (2): 779-784. doi: 10.7498/aps.58.779
Abstract +
By designing a suitable response system to a class of chaotic systems, we realise the linear and nonlinear generalized synchronizations for these chaotic systems by only transmitting a single variable. The method of obtaining the response system from chaotic system is proposed. Since chaos synchronization can be achieved by transmitting the single variable from driving system to response system, this method is more practical. Theoretical deduction and computer simulation show the effectiveness of the proposed method.
A new three-dimensional chaotic system and its circuit simulation
Tang Liang-Rui, Li Jing, Fan Bing, Zhai Ming-Yue
2009, 58 (2): 785-793. doi: 10.7498/aps.58.785
Abstract +
A new three-dimensional chaotic system is reported in this paper, which is different from the Lorenz and Chen systems. This new system contains five system parameters and two quadratic cross-product terms. The basic dynamic properties of the new system are investigated via theoretical analysis, numerical simulation, Lyapunov exponent spectrum, bifurcation diagrams, Lyapunov dimension and Poincare diagrams. The different dynamic behaviors of the new system are analyzed when each system parameter is changed. Finally, the chaotic circuit is designed and realized by the Multisim software. It confirms that the chaotic system can be achieved.
Detection of ship targets on the sea surface based on Lyapunov exponents of image block
Shi Ai-Guo, Li Tian-Wei, He Si-Hua, Yang Shao-Qing
2009, 58 (2): 794-801. doi: 10.7498/aps.58.794
Abstract +
The change of background's chaos feature when there are moving targets was analysed, and a new algorithm based on Lyapunov exponents of image block for moving targets detection on the sea surface, which is used for ship targets detection on the sea surface, was proposed. The new method defines the term of image gray level distance, extends the calculation method of Lyapunov exponents from single dimension signal to image signal based on the improved Wolf method, uses the change of the largest gray level distance Lyapunov exponents to detect ship targetssubmerged in chaos background. Experimental results show that the sea surface background has chaos feature. The proposed algorithm can detect ship targets effectively and can get better result than statistical analysis.
Adaptive synchronization and anti-synchronization of two different chaotic systems
Cai Na, Jing Yuan-Wei, Zhang Si-Ying
2009, 58 (2): 802-813. doi: 10.7498/aps.58.802
Abstract +
Chaos synchronization and anti-synchronization of two chaotic systems with different structures are investigated. When the parameters are known in advance, the synchronization and anti-synchronization are realized by the active control. The method of designing controllers with active control is generalized. When the parameters are completely unknown, the adaptive controllers and the adaptive laws of parameters are given based on the Lyapunov stability theory and adaptive control method, which realizes adaptive synchronization and anti- synchronization of two different chaotic systems, and identifies the unknown parameters. The drive system and response system are interchanged during the controller designing. The relationship of the controllers and the adaptive laws before and after the interchangement are investigated. The numerical simulation results verify the effectiveness of the proposed scheme.
Anti-synchronization of nonlinear-coupled spatiotemporal chaotic systems
Lü Ling, Xia Xiao-Lan
2009, 58 (2): 814-818. doi: 10.7498/aps.58.814
Abstract +
The anti-synchronization of two nonlinear-coupled spatiotemporal chaotic systems is discussed. A special nonlinear-coupled term is constructed through suitably separating the spatiotemporal chaotic systems to linear and nonlinear terms, and anti-synchronization of two two-dimensional coupled map lattices is realized. The nonlinear-coupled method is further generalized to anti-synchronize the complex networks composed of two-dimensional coupled map lattices. The artificial simulation results show that this method is still effective.
Projective synchronization of Chua chaotic system based on fuzzy observer
Meng Juan, Wang Xing-Yuan
2009, 58 (2): 819-823. doi: 10.7498/aps.58.819
Abstract +
The generalized projective synchronization of Chua chaotic system is investigated. A new fuzzy observer is designed based on the Takagi-Sugeno (T-S) fuzzy model. According to the Lyapunov stability theory, it is verified that the proposed scheme is feasible and globally stable. Numerical simulations further demonstrate that the projective synchronization of Chua circuit can be achieved by using the proposed scheme. The designed procedure is simple, and the method can be adapted to other chaotic systems.
Response to bounded noise excitation of stochastic Mathieu-Duffing system with time delay state feedback
Rong Hai-Wu, Xing Zhen-Ci, Xu Wei, Wang Bao-Yan
2009, 58 (2): 824-829. doi: 10.7498/aps.58.824
Abstract +
We investigate the principal parametric resonance of Mathieu-Duffing Equation under a narrow-band random excitation with time delay feedback. The method of multiple scales is used to determine the equations of modulation of amplitude and phase. The bifurcation of the system is discussed. We find that the bifurcation can be influenced by the detuning parameter, time delay, and the intensity of the non-linear term, and an appropriate choice of these parameters can change the response of bifurcation. In addition the stability of nontrivial solution is studied. The nontrivial solution of necessary and sufficient condition for stability is obtained. Moreover, we find that when the bandwidth of the random excitation is smaller, the multi-solution phenomenon still exists, and bifurcation and jumping phenomenon will occur. Theoretical analysis is verified by numerical results.
One-dimensional cellular automaton model of traffic flow considering drivers’ features
Peng Li-Juan, Kang Rui
2009, 58 (2): 830-835. doi: 10.7498/aps.58.830
Abstract +
Based on the WWH model and SDNaSch model for one-dimensional cellular automaton traffic flow, a Driver-SDNaSch model considering the drivers′ features is established. In this model, drivers are classified into such three types as aggressive, cautious and neutral, and their states are updated following their respective evolution rules, which are made according to the different driving features of these three types. In addition, the safe deceleration probability is introduced when considering the condition of having a stationary vehicle ahead. By using the computer numerical simulation of the Driver-SDNaSch model, the velocity-density and flow-density diagrams of the mixed traffic flow, whose features are also analysed and discussed, with the three types of drivers in different proportions, are presented. The Driver-SDNaSch model, compared with the NaSch model and SDNaSch model, is believed to further reduce the traffic jams so as to increase the traffic capacity.
A lane-changing model considering the maneuver process and its applications
Yang Xiao-Bao
2009, 58 (2): 836-842. doi: 10.7498/aps.58.836
Abstract +
An improved lane-changing model based on the Nagatani's method is proposed. The threshold of the safety headway in lane-changing process is calibrated. Both the lane-changing process and the impact of the lane-changing vehicle on the adjacent vehicles are incorporated into the proposed model. Therefore, simulated results using the proposed model agree with the surveyed results. The marginal decrease of lane capacity with the number of lanes is analysed and validated upon the proposed lane-changing model. We find that the vehicle velocity decreases and the lane changing probability increases with the increasing number of lanes under the congested condition of highways in cities.
An improved method for implementation of wavelet transform utilizing switched-current filters
Zhao Wen-Shan, He Yi-Gang
2009, 58 (2): 843-851. doi: 10.7498/aps.58.843
Abstract +
A new scheme of implementing wavelet transform using switched-current filters is proposed in this paper. Based on approximation theory of network function, the basic wavelet function is synthesized with the sum of rational fraction obtained by a systematic algorithm. And then the basic wavelet function filter is implemented by a parallel structure of switched-current circuits. Herein, the first derivative of Gaussian function is selected as an example with the construction procedure of approximation network and structure of switched-current filters elaborated. The filter network employs six biquadratic switched-current filters in a parallel connection, in which the S2I memory cell is used as the core of the filter. Theoretical analysis and simulation result show that the proposed scheme is superior to the original method in approximation precision, system stability and circuit performance.
Performance analysis of the substrate-free focal plane array in infrared imaging
Cheng Teng, Zhang Qing-Chuan, Wu Xiao-Ping, Shi Hai-Tao, Gao Jie, Chen Da-Peng
2009, 58 (2): 852-859. doi: 10.7498/aps.58.852
Abstract +
Based on the proposed optical readout uncooled infrared (IR) imaging system,several batches of the substrate-free focal plane array (FPA) with different pitches have been successively fabricated,and by using these fabricated FPAs,the thermal images were obtained at room temperature. However,the theoretical analysis indicates that the deviation between the theoretical model assuming constant temperature of the supporting frames of the FPAs and the experimental results gradually increases with the decreasing pitch size of from 200μm to 60μm. Based on the finite element method,the thermal characteristic of those FPAs was simulated and the reason for the deviation is found to be that the temperature-constant assumption is not quite appropriate for the substrate-free FPA,and the absorption of the thermal radiation will obviously result in the temperature rise of the supporting frame,which would increase the temperature of the adjacent pixels. The imaging performance of the substrate-free FPA is also analyzed. Compared with the substrate FPA with the same pitch, the thermal detection sensitivity of the substrate-free FPA with 60μm pitch increases by about one order of magnitude.
NUCLEAR PHYSICS
Degradation model of the optical properties of the thermal control coatings
Shen Zi-Cai, Feng Wei-Quan, Ding Yi-Gang, Liu Yu-Ming, Zheng Hui-Qi, Zhao Xue, Zhao Chun-Qing, Kong Wei-Jin
2009, 58 (2): 860-864. doi: 10.7498/aps.58.860
Abstract +
On the basis of experimental results,the degradation model of the optical properties of thermal control coatings due to space environment interaction are proposed. The optical properties of thermal control coatings prepared by complex refractive index materials are analyzed by using the concept of graded index,and the expressions of the changed optical properties of the coatings are given. Applications of the degradation model are also discussed.
Stability of traditional neutron magic numbers
Lu Ding-Hui, Ding Bin-Gang, Zhang Da-Li
2009, 58 (2): 865-870. doi: 10.7498/aps.58.865
Abstract +
By systematically analyzing the single particle level and the occupation probability near the Fermi surface,and the rule of nuclear particle number deviations with proton numbers for N=8,20,28,50,82,126 neutron chains within the relativistic mean-field model with BCS theory,we have discussed the stability of the shell structure for the traditional neutron magic in the whole range of nuclear spectrum from neutron line to proton line,and predicted that traditional neutron magic number effect shall possibly disappear only in light neutron-rich nuclei. Our results are also compared with the results of other recent reports.
Influence of incidence channel condition on isospin fractionation ratio based on the revised isospin-dependent quantum molecular dynamics
Guo Wen-Jun, Sun Chang-An, Liu Jian-Ye
2009, 58 (2): 871-875. doi: 10.7498/aps.58.871
Abstract +
Isospin degree of freedom is introduced in Skyrme potential and momentum dependent interaction to obtain the revised isospin dependent quantum molecular dynamics. The isospin effect of isospin fractionation ratio is studied for different beam energies and different colliding systems based on the revised isospin dependent quantum molecular dynamics. It is found that the isospin effect of isospin fractionation ratios is important for different incident channel conditions,for example,the isospin fractionation ratios for different incident channel conditions are reduced after the isospin degree of freedom in Skyrme potential and momentum dependent interaction are included. However, the isospin fractionation ratio is also sensitive to symmetry potential. In this case it is also a good probe for extracting information on the symmetry potential in heavy ion collisions.
Surface dry treatment of RF superconducting cavity by sputtering
Zhu Feng, Jiao Fei, Quan Sheng-Wen, Hao Jian-Kui, Zhao Kui
2009, 58 (2): 876-881. doi: 10.7498/aps.58.876
Abstract +
We have developed a new technique of surface treatment of RF superconducting cavity by sputtering under ultra high vacuum. In this paper,impacts of sputtering treatment on the surface properties of niobium sample and niobium cavity are analysed in detail. Compared with the traditional “wet" cavity treatment (buffered chemical polishing and electro-polishing),this dry treatment is simple,easy to control,less costly and without pollution. It is a potential superconducting cavity surface treatment method and can improve the performance of the cavity.
Lead-tin-fluorophosphates scintillating glass doped with stilbene 420 excited by gamma ray
Kang Ke-Jun, Xia Liang-Bin, He Xiao-Ling, Gu Mu, Ouyang Xiao-Ping, Wang Qun-Shu
2009, 58 (2): 882-886. doi: 10.7498/aps.58.882
Abstract +
Lead tin fluorophosphates (PTFP) glass doped with organic dye stilbene 420 is prepared. The melting temperature of the doped glass is below 250℃,and the characteristic temperature is about 75℃. The luminescence excited by 60Co 1.25MeV gamma ray is measured,and is compared with organic scintillator ST401 with the same thickness. The scintillation of doped PTFP glass is from 1 to 2 percent that of ST401.
ATOMIC AND MOLECULAR PHYSICS
Theoretical study of the adsorption of water molecule on (TiO2)n(n=3—6) clusters
Chen Hong-Shan, Meng Fan-Shun, Li Xiang-Fu, Zhang Su-Ling
2009, 58 (2): 887-892. doi: 10.7498/aps.58.887
Abstract +
Possible adsorption structures of H2O on (TiO2)n(n=3—6) clusters were studied by using genetic algorithm combined with empirical potential function. The structures were further optimized using DFT method B3LYP/6-31G**. The results show that H2O molecule is adsorbed on TiO2 clusters through the attachment of oxygen atom to the titanium atom with lower coordination number. Molecular orbitals show that the bond between water and cluster is formed mainly by the 3s3p orbitals of titanium,the orbitals of H2O keep the basic features unchanged but are more delocalized after adsorption. Combined with population analysis and calculation of vibration frequencies,the results show that the O—H bond becomes weaker after H2O is adsorbed on TiO2 clusters.
CLASSICAL AREA OF PHENOMENOLOGY
Effect of high static magnetic field and AC current on solidification of Zn-30wt%Bi monotectic alloy
Wang Jiang, Zhong Yun-Bo, Ren Wei-Li, Lei Zuo-Sheng, Ren Zhong-Ming, Xu Kuang-Di
2009, 58 (2): 893-900. doi: 10.7498/aps.58.893
Abstract +
Effect of high static magnetic field (HSMF) coupled with AC current of different intensities and frequencies on solidification morphology of Zn-30wt%Bi monotectic alloy was studied. The gravity segregation of Zn-30wt%Bi monotectic alloy could not be suppressed thoroughly only by superimposing AC current or 10T HSMF separately at the cooling rate of 25℃/min. When the 10T HSMF and 50Hz AC current were superimposed simultaneously,the induced alternate Lorentz force could reduce the gravity segregation remarkably. More homogeneous solidification morphology could be obtained when increasing the AC current density,magnetic flux density or current frequency separately. However,each of the above-mentioned three parameters has its own optimum value on deviating from which the homogeneous distribution morphology could not be obtained. The mechanism on the coupled fields affecting the gravity segregation of Zn-30wt%Bi monotectic was discussed based on the magneto-hydrodynamic theory. The results reveal that it is possible to manufacture homogeneous monotectic alloy under normal gravity surroundings and at a low cooling rate by superimposing coupled fields in the solidification process.
Floquet mode analysis on the resonance behavior of metamaterials
Yang Rui, Xie Yong-Jun, Li Xiao-Feng, Jiang Jun, Wang Yuan-Yuan, Wang Rui
2009, 58 (2): 901-907. doi: 10.7498/aps.58.901
Abstract +
The field distribution over a split ring resonator is expanded into Floquet modes,revealing the fact that the evanescent floquet modes actually lead to the metamaterial resonance behavior. Transmission through metamaterials is examined for arbitrary incident wave. It is shown that the resonance happens in the transmitted modes with the same polarization as that of the wave incident in the main plane. The electric and the magnetic resonances vary with the incidence angle. For the wave from other incident planes,the TE- and TM- Floquet modes will share the resonance.
The high-frequency method for scattering from the wedges of complex conductive targets in half space
Li Xiao-Feng, Xie Yong-Jun, Fan Jun, Wang Yuan-Yuan
2009, 58 (2): 908-913. doi: 10.7498/aps.58.908
Abstract +
The high-frequency method for solving the scattering from the wedges of conductive targets with electrically large size in half space is presented in this paper. To take into account of the influence of environment,the half-space equivalent edge current method is deduced by introducing the half-space Greens function into the equivalent edge current method. Combined with the graphical-electromagnetic computing method,the shadow regions are eliminated quickly and the edge pixel parameters are obtained by reading the edge pixels. Meanwhile,we also make use of the half-space physical optical method to treat the complex targets,and then the radar cross section of the complex targets can be exactly calculated in half space. The numerical results show that this method is efficient and accurate.
Theoretical analysis of second-harmonic conversion efficiency in negative-index materials
Zhou Cheng, Wang Pei-Ji, Zhang Zhong, Li Ping, Gao Yan-Xia
2009, 58 (2): 914-918. doi: 10.7498/aps.58.914
Abstract +
For negative-index materials(NIM) of second-harmonic wave(SHW) and positive-index materials of fundamental frequency wave(FFW),the equations of the coupled wave was deduced,taking account of absorption coefficient,walk-off effect,phase mismatching capacity and the approximation of slow-varying amplitudes of the plane wave. On the basis of the equations,a formulation of SHW conversion efficiency was obtained in condition of small signal approximation for FFW. Through numerical simulation, the effects of phase mismatching capacity,walk-off angle and absorption coefficient of SHW on the conversion efficiency of SHW were scrutinized respectively. The maximum conversion efficiency of SHW was realized via increasing the length of NIM,that is,there exists an optimum length of NIM; however, the conversion efficiency of SHW shows an evidencet periodic evolution and the maximum conversion efficiency always diminishes. The conversion efficiency decreases with the increases of the phase mismatching capacity and the absorption coefficient. The influence of walk-off effect is not evident so that it may be neglected with respect to the conversion efficiency of SHW. This study provides a basis for investigating nonlinear theory of negative-index materials.
Terahertz antenna based on the carbon nano-tube in the nano-scopic domain
Wu Qun, Wang Yue, He Xun-Jun, Yin Jing-Hua, Shi Wei
2009, 58 (2): 919-924. doi: 10.7498/aps.58.919
Abstract +
A novel nano-antenna for the generation and applications of terahertz wave and the Pocklingtons integral equation are proposed based on the carbon nanotube structure. The radiation characteristics of carbon nanotube antenna in terahertz range have been investigated by numerical simulation and theoretical computation. Both the numerical and analytical results demonstrate that the antenna with half wave length of 60μm takes on the dual frequency properties at the center frequencies of 2.5THz and 7.6THz,with the corresponding -10dB return loss (S11) bandwidths of 8.4% and 2.7%,respectively. Compared with the gain of 0.598dB of a single dipole antenna the maximum gain of a typical 10×10 carbon nanotube antenna array is 10.30dB. The results could be useful for the design of carbon nanotube antenna arrays for generating terahertz wave.
Influence of reflection of the output port on beam-wave interaction in gyrotron traveling wave amplifier
Luo Ji-Run, Sun Hai-Yan, Jiao Chong-Qing
2009, 58 (2): 925-929. doi: 10.7498/aps.58.925
Abstract +
Based on the nonlinear self-consistent theory of gyrotron traveling wave amplifier (gyro-TWA),the influence of the reflection from the tapering output port on the beam-wave interaction in the gyro-TWA is studied. The simulation results show that the amplitude and phase of the reflection coefficient resulting from the variation of the tapering angle at the output port and the beam-wave interaction length have great effect on the beam-wave interaction for a Ka band TE01 gyro-TWA. Reasonably selecting the tapering angle at the output port may increase the beam-interaction frequency bandwidth with a relatively short beam-wave interaction length while keeping the saturated output power of the gyro-TWA at almost the same level.
Theoretial analysis on extending the field-of-view of the imaging spectrometer based on combined Wollaston prisms
Wu Hai-Ying, Zhang Chun-Min, Zhao Bao-Chang
2009, 58 (2): 930-935. doi: 10.7498/aps.58.930
Abstract +
The principle of beam splitting of spectrometer based on the combination of two Wollaston prisms and a half-wave plate is presented. The propagation track of light wave in the combination is analysed by wave normal-tracing method at random incidence angle and the formulas of the path difference between the e and o wave normal are deduced. Computer simulations are carried out to explain why the combination can increase the field of view of spectrometer. The results will provide a very important theoretical basis for the study of polarization interference imaging spectrum technology and the development of static large field of view polarization interference imaging spectrometer developed by us.
Photoluminescence and magnetic properties of cobalt doped SnO2 nano-powder
Liu Chun-Ming, Fang Li-Mei, Zu Xiao-Tao
2009, 58 (2): 936-940. doi: 10.7498/aps.58.936
Abstract +
The influence of cobalt dopant on the photoluminescence and magnetic properties of SnO2 nano-powder is studied in detail. The cobalt dopant has little influence on the photoluminescence peaks' positions. However,the intensity ratio of ultra-violet to blue emission band is reduced with the increase of cobalt doping. The ferromagnetism is absolutely absent when the cobalt dopant level reaches 0.02. The magnetic interaction mechanism is discussed. Due to the non-uniform distribution of doping,and the coupling between the polarized spin on defects and the dopants,the anti-ferromagnetic interaction destroys the ferromagnetism.
Q-switched pulse polarization-maintaining Nd3+-doped fiber laser
Yao Jian-Quan, Wei Zhen, Ren Guang-Jun
2009, 58 (2): 941-945. doi: 10.7498/aps.58.941
Abstract +
The Nd3+-doped pulse polarization-maintaining fiber laser pumped by 808nm semiconductor laser is investigated experimentally and theoretically. The wave form of output pulse was detected by a TDS5104 oscillograph,and the spectrogram of the output pulse was obtained by using a spectrum analysis apparatus. Originally,the single pulse energy of 2.3mJ with average power of 2.55W was generated at the repetition rate of 1kHz. By changing the resonance cavity and making other modificantions of the laser, we obtained the highest single pulse energy of 3.3mJ with peak power of 17.9kW at the repetition rate of 1kHz,and the pulse width was 184ns and the average power of the output pulse was 3.5W.
Properties of Cassegrain optical antenna with inclined optical axis
Xu Quan, Xie Kang, Ran Ying-Hua, Yang Hua-Jun, Huang Jin
2009, 58 (2): 946-951. doi: 10.7498/aps.58.946
Abstract +
A Cassegrain optical antenna with parabolic structure is designed. By detailed analysis of Cassegrain optical antenna in partial axis situation,the expression of the area of the receiving spot and the power decline curve are obtained for different deflection angles. The relations between the received antenna gain and the wavelength and deflection angles are discussed in partial axis situation,the curves of gain for partial axis and axis alignment are simulated. The simulation result indicates that the gain of the maximal partial axis decreases by 6.564dB compared with that of axis alignment. Experiments of the optical spot test and the antenna coupling efficiency test are carried out separately for axis alignment and certain partial axis situations. The results show that the antenna coupling efficiency under partial axis situation is 26.97% lower than that of axis alignment. This study will provide a theoretical foundation for the control system to realise perfect alignment of optical axis in inter-satellite optical communications.
Computer generated holography based on Fourier transform using conjugate symmetric extension
Yu Ying-Jie, Huang Su-Juan, Wang Shuo-Zhong
2009, 58 (2): 952-958. doi: 10.7498/aps.58.952
Abstract +
A new computer generated holography (CGH) algorithm based on Fourier transform is proposed. The complex amplitude of the light wave to be recorded is extended to produce a conjugate symmetric function. The function is then Fourier transformed to generate a real valued distribution containing both the amplitude information and the phase information of the light wave. The obtained real distribution is coded to give a gray-scale hologram,which can be used to reconstruct the original light wave. Unlike the existing CGH algorithms based on interference of object and reference light waves,the proposed method does not require simulatingthe interference to produce the hologram. The algorithm is highly efficient,and can produce good results both in digital and electroholographic reconstruction. Theoretical and experimental results are presented to verify the validity of the method.
Enhanced external quantum efficiency of light emitting diodes by fabricating two-dimensional photonic crystal sapphire substrate with holographic technique
Lin Han, Liu Shou, Zhang Xiang-Su, Liu Bao-Lin, Ren Xue-Chang
2009, 58 (2): 959-963. doi: 10.7498/aps.58.959
Abstract +
Investigation in fabricating two-dimensional (2D) photonic crystal (PC) on sapphire substrates for enhancing external efficiency of GaN based light emitting diodes (LEDs) is presented. 2D-PC was fabricated on a sapphire substrate using holographic lithography and inductively coupled plasma (ICP) dry etching. LEDs with 2μm thick n-GaN layer,four pairs of InGaN/GaN quantum well structures and 200nm thick p-GaN layer were grown on the patterned sapphire substrate (PSS) by metal organic chemical vapor deposition (MOCVD). The PC fabricated on PSS has 2D hexagonal lattice pattern,with 3.8μm lattice constant and 800nm depth. LED output measurement shows 100% increase in the average luminous intensity of PSS-LEDs compared with that of conventioanl LEDs. The measured X-ray rocking curves of (0002) diffraction for GaN layers grown on patterned and non-patterned sapphire substrates indicate that the quality of GaN crystal grown on PSS is not improved,which implies that the large enhancement of external quantum efficiency of PSS-LED is not caused by the increase in internal efficiency but possibly by the increase in extraction efficiency,which results from the scattering of the PSS.
Theoretical and experimental investigation of optical bistability in end-pumped Tm,Ho:YLF lasers
Zhang Xin-Lu, Li Li, Jiang Bo, Wang Yue-Zhu, Ju You-Lun
2009, 58 (2): 964-969. doi: 10.7498/aps.58.964
Abstract +
We demonstrate the strong optical bistability of a 2μm continuous wave Tm,Ho:YLF laser end pumped by a 792nm fiber-coupled laser diode. The quasi-three-level rate equation theoretical model is given under consideration of the energy transfer upconversion and ground state reabsorption effects. The bistable output of Tm,Ho:YLF laser is predicted theoretically by solving the coupled rate equations and the mechanism of the bistability output is analyzed. The bistable output is also studied experimentally. When the laser crystal is at 253K,the width of the bistable region is 1.6W and the jump power at the tujump point is 82.5mW. The theoretical results are in agreement with the experimental results,showing that the theoretical model is reasonable.
A high power quasi-continuous-wave yellow laser based on intracavity sum-frequency generation
Bo Yong, Gao Hong-Wei, Peng Qin-Jun, Cui Da-Fu, Xu Zu-Yan, Lu Yuan-Fu, Xie Shi-Yong, Cui Qian-Jin, Zong Nan
2009, 58 (2): 970-974. doi: 10.7498/aps.58.970
Abstract +
This paper reports a high-power all-solid-state yellow laser based on intracavity KTP crystal sum-frequency generation. In order to achieve high output power,three key techniques are used:Firstly,the system is designed to operate in a pulsed mode to increase the beam quality and optical-to-optical conversion efficiency under the same pump level. Secondly,thermal near-unstable resonator design and two-rod birefringence compensation is used to acquire large fundamental mode size in Nd:YAG rod. Thirdly,by optimizing an L-shaped co-folding-arm plane-concave symmetrical cavity,the two fundamentals have a high spatial overlap in the sum-frequency crystal and satisfy the power ratio requirement. As a result of the applications of these techniques,a quasi-continuous-wave yellow laser with output power of 7.6W and repitition frequency of 1.1kHz is obtained. To the best of our knowledge,this is the highest yellow laser output power produced by an intracavity sum-frequency Nd:YAG laser.
A novel method for simulating source-field distribution of diode laser
Xiong Ling-Ling, Li Jian-Long, Lü Bai-Da
2009, 58 (2): 975-979. doi: 10.7498/aps.58.975
Abstract +
Based on the non-paraxial diffraction theory and experimental results of the far-field distributions of diode lasers and by means of the amplitude-phase retrieval algorithm,a novel method for simulating source-field distribution of the diode laser is proposed. The simulation procedure is described and illustrated by the example of a double-heterostructure diode. It is shown that this method is precise enough so long as acurate experimental data are available,and would find some practical applications.
Nonlinear processes in strong ultrashort pulse pumped semiconductor optical amplifier
Liu Mao-Tong, Yang Ai-Ying, Sun Yu-Nan
2009, 58 (2): 980-988. doi: 10.7498/aps.58.980
Abstract +
A theoretical model of semiconductor optical amplifier (SOA) is presented with carrier density pulsation (CDP),free-carrier absorption (FCA),stimulated emission (SE),two-photon absorption (TPA),spectral hole burning (SHB) and ultrafast nonlinear refraction (UNR) taken into account. The model is proved by comparing with the reported experimental results. The prevailing SOA model is revised. The influences of FCA and TPA processes on ultrashort strong optical pulses are analysed. When the strong optical pulse with several-picosecond pulsewidth is injected into the SOA operating under the transparency current,the intensity characteristics of the optical pulse are mainly influenced by TPA and FCA. As a result of taking the FCA effect into account,the intensity transmission characteristics of 200fs optical pulses obtained by the new model basically agree with the experimental results. It broadens the applicability of the model.
Chaotic parallel synchronization of optoelectronic feedback semiconductor lasers
Wu Zheng-Mao, Fan Li, Xia Guang-Qiong
2009, 58 (2): 989-994. doi: 10.7498/aps.58.989
Abstract +
A chaotic parallel synchronization model of optoelectronic feedback semiconductor lasers is proposed. The complete synchronization and generalized synchronization are studied,while the effect of intrinsic parameter mismatch on the difference in the synchronization performances between the drive laser and receive laser or between the parallel receive lasers is emphatically discussed. The results show that zero-time-lag complete synchronization between the drive laser and parallel receive laser can be realised under parameter match. For generalized synchronization,if one of the intrinsic parameters of the receive laser is changed,the cross correlation between the parallel receive lasers is larger than thatbetween the drive laser and the receive laser over a wide parameter mismatch range.
Competition between the excited-state refraction and excited-state absorption induced transient thermal refraction of metallic porphyrin compound
Chen Yu-Ming, Wang Yu-Xiao, Zhang Xue-Ru, Song Ying-Lin, Yang Jun-Yi, Jiang Li, Li Yu-Liang
2009, 58 (2): 995-1001. doi: 10.7498/aps.58.995
Abstract +
The competition between the excited-state absorption induced transient thermal refraction and the excited-state refraction of a novel metallic porphyrin compound Zn-porphyrin was studied by the excited-state absorption induced transient thermal refraction theory combined with the excited-state refraction theory. The transformation between self-focusing and self-defocusing of the sample for different pulse widths was observed. The sample exhibited self-focusing effect attributed mainly to excited-state refraction for 4 ns laser pulse, while in the self-defocusing effect for 8 ns laser pulse the excited-state absorption induced transient thermal refraction dominates the excited-state refraction.
Ultrafast optical Kerr effect in amorphous chalcogenide films
Qian Shi-Xiong, Liu Qi-Ming, He Xuan, Gan Fu-Xi
2009, 58 (2): 1002-1006. doi: 10.7498/aps.58.1002
Abstract +
Amorphous chalcogenide As2S3, As2Se3, GeS2, GeSe2, Ge20As25S55, Ge20As25Se55, Ge10As40S20Se30 films were studied by femtosecond OHD-OKE. Ict was indicated that the third-order nonlinear susceptibility χ(3) was as large as 10-12 esu, and they also exhibited a very fast response time shorter than 200 fs. Their nonlinear refractive indices and absorption were also calculated from the above results. The ultrafast response and large third-order nonlinearity in amorphous chalcogenide films are attributed to the ultrafast distortion of the electron cloud of atoms.
Dynamics of acrylamide-based photopolymer holographic gratings
Chen Ke, Cheng Jian-Qun, Xiao Yong, Tang Dao-Guang, Huang Ming-Ju
2009, 58 (2): 1007-1013. doi: 10.7498/aps.58.1007
Abstract +
The theoretical photochemical and photopolymerization diffusion model and the dynamic parameters of the photopolymer are studied. A new holographic photopolymer which is composed of acrylamide as monomer, ployvinylalcohol as binder, triethanolamine as initiator sensitized by erythrosine B is prepared. By means of fitting the experimental data of transmittance and diffraction efficiency as a function of time, the influence of the molar-absorption coefficient ε, the quantum yield Φ and the photobleaching coefficient k in photochemical dynamics for different concentrations of erythrosine B, and polymerization rate k0, diffusion time constant τD and the maximal refractive index modulation Δn in photopolymerization diffusion dynamics for different exposure intensity, are presented.
A new way of uniform splitting of the optical power by directional coupling between the photonic crystal waveguides
Zhu Gui-Xin, Yu Tian-Bao, Chen Shu-Wen, Shi Zhe, Hu Shu-Juan, Lai Zhen-Quan, Liao Qing-Hua, Huang Yong-Zhen
2009, 58 (2): 1014-1019. doi: 10.7498/aps.58.1014
Abstract +
Directional coupler can be constructed by putting multiple photonic crystal waveguides together. The propagation of the optical field entering this system symmetrically was analysed numerically according to self-imaging principle. On the basis of this structure, ultracompact multiway beam splitter was designed and the ones with three and four output channels were discussed in details as examples. By simply tuning the effective refractive index of two dielectric rods in the coupler symmetrically to induce the redistribution of the power of the optical field, uniform or free splitting can be achieved. Compared with the reported results, this way is simpler, more feasible and more efficient and has extensive practical value in future photonic integrated circuits.
Enhancing the emission efficiency in photonic crystal waveguide with coupled waveguide arrays
Wang Qiong, Cui Yi-Ping, Yan Chang-Chun, Zhang Ling-Ling, Zhang Jia-Yu
2009, 58 (2): 1020-1024. doi: 10.7498/aps.58.1020
Abstract +
We propose a system of enhanced emission efficiency by employing coupled waveguide arrays to a single-mode photonic crystal waveguide. The FDTD simulation results show that, when the coupled waveguide arrays are placed properly at the exit plane of the single-mode photonic crystal waveguide, the output light can be split into many light beams, and the interference of these light beams can produce a focusing emission beam, which greatly enhances the emission efficiency. In addition, when the row number of the waveguide arrays is larger than a certain value (2N=8), the state of the emission is nearly steady and the most compact structure can be obtained. This type of photonic crystal has potential applications in near-field optics or integrated optics.
The light intensity-dependent superprism phenomenon in nonlinear photonic crystals
Chen Xiao-Jun, Wu Li-Jun, Hu Wei, Lan Sheng
2009, 58 (2): 1025-1030. doi: 10.7498/aps.58.1025
Abstract +
We investigate the light intensity-dependent superprism phenomenon in the two-dimensional Kerr nonlinear photonic crystal (PhC) by nonlinear finite-difference time-domain (FDTD) technique. Results show that when the intensity of the self-pumping beam is increased from 70 to 300 W/μm, the refraction angle of the beam can be tuned about 10 degree. Furthermore, when the input power is high enough, the wave vector can be rotated by the local refractive index interfaces induced by the pumping power. By monitoring the transmission efficiency at different depths in PhCs, the propagating beam is found to undergo several states which correspond to different power loss mechanisms.
A left-handed metamaterial composed of structures with both magnetic resonance and electric resonance
Yang Yi-Ming, Wang Jia-Fu, Qu Shao-Bo, Xu Zhuo
2009, 58 (2): 1031-1035. doi: 10.7498/aps.58.1031
Abstract +
To realise simultaneously negative permittivity and negative permeability in one structure,there must exist both electric resonance and magnetic resonance in the same band for the structure. Based on this principle, we fabricated a structure and investigated its “double-negative” characteristics by means of numerical simulation and experimental test. Compared with other left-handed metamaterials, this structure exhibits simultaneously negative permittivity and negative permeability and its equivalent circuit is much simpler. Moreover, it has much broader left-handed pass-band in which both the permittivity and the permeability are negative. The structures were fabricated by using screen-printing technology, which is much easier and economical.
Q value analysis of a first-order IIR microwave photonic filter based on SOA
Zhang Xin-Liang, Xu En-Ming, Huang De-Xiu, Zhou Li-Na
2009, 58 (2): 1036-1041. doi: 10.7498/aps.58.1036
Abstract +
The Q value of a first-order infinite impulse response (IIR) microwave photonic filter based on a semiconductor optical amplifier (SOA) in a loop is investigated theoretically and experimentally. The maximum Q value measured is around 200 by setting a narrow bandwidth optical filter in the active loop and changing the input optical power of the loop and the pump current of the SOA. Analysis shows that increasing the signal to noise ratio and the gain of the signal light through the loop contributes to achieving higher Q value. The influences of the input optical power, the pump current of the SOA and the bandwidth of the optical filter in the loop on the Q value are calculated, based on the amplified spontaneous emission (ASE) noise of the SOA being investigated. Experimental results are in good agreement with the calculated results.
A full electromagnetic analysis of a filter substrate lens for spatiotemporal terahertz pulse shaping
Zhu Yan-Wu, Shi Shun-Xiang, Liu Ji-Fang, Sun Yan-Ling
2009, 58 (2): 1042-1045. doi: 10.7498/aps.58.1042
Abstract +
A novel filter substrate lens for THz pulse is presented, which could efficiently couple the THz radiation in a desired frequency range into free space. The band-pass and band-stop filter lens is designed and studied by difference time method. The results show that the design is well supported by the theoretical analyses.
Analysis of non-degenerate four-wave-mixing crosstalk in DWDM system
Du Jian-Xin
2009, 58 (2): 1046-1052. doi: 10.7498/aps.58.1046
Abstract +
Four-wave mixing (FWM) tone degrades system performance in dense wavelength-division-multiplexed (DWDM) optical transmission. A method of evaluating the efficiency of non-degenerate FWM tone for return-to-zero modulation scheme is developed without ignoring group-velocity walk-off of random bit sequence between channels. A theoretical model evaluating the standard deviation of FWM tone is then given. Some calculation examples show that, when the duty cycle and channel separation become small, the initial relative time delay of random bit sequences in different channels and fiber dispersion are more important to the FWM noise. Choosing optimal values of them is important to make the system to have low dispersion and small FWM crosstalk.
A method of color image single-channel encryption
Li Zhi-Lei, Wang Xiao-Lei, Zhai Hong-Chen, Wang Ming-Wei, Gao Li-Juan, Yang Xiao-Ping
2009, 58 (2): 1053-1056. doi: 10.7498/aps.58.1053
Abstract +
A new method for color image single-channel encryption is proposed. According to tricolor grating theory, a color image is encoded into a gray scale image, and then the gray scale image is encrypted by double-phase encoding. Thus by combining multi-channel with single-channel, only one laser is needed for encryption. With this method, both single-channel encryption and high security are ensured, and the system is simpler and more practical. Computer simulation proves the validity of the proposed method.
Multi-scale simulation of the deformation in nano-indentation under different crystal orientations
Wang Hua-Tao, Qin Zhao-Dong, Ni Yu-Shan, Zhang Wen
2009, 58 (2): 1057-1063. doi: 10.7498/aps.58.1057
Abstract +
The nano-indentation process of an fcc Al film under three different crystal orientations (x[1 1 1],y[1 1 0],z[1 1 2]; x[1 1 2],y[1 1 1],z[1 1 0] and x[1 1 0],y[0 0 1],z[1 1 0]) are studied using the quasi-continuum method. The load-displacement responses of the film under different crystal orientations are presented respectively. The local atomics in the regions where sharp deformation occurred are plotted to analyse their mechanisms on atomic scale. The results show that the micro-mechanisms of the deformation in the film are different for different crystal orientations. Under the orientation of x[1 1 1], y[1 1 0], z[1 1 2], in which the indentation direction is parallel to the close-arranged plane, the deformation in the film is mainly dominated by the dislocation nucleation caused by the slip of the plane, and the hardness and the out-of-plane displacement of the crystal are large. Under the x[1 1 2],y[1 1 1],z[1 1 0] orientation, in which the indentation direction is perpendicular to the close-arranged plane, the deformation in the film is mainly dominated by the deformation twinning, and both the hardness and the out-of-plane displacement of the crystal are the largest. Under the x[1 1 0], y[0 0 1], z[1 1 0] orientation, in which the indentation direction is at some degrees inclined to the close-arranged plane, the deformation in the film starts from a small dislocation line nucleating on a slip plane at the beginning of the loading and then deformation twinning is formed with the increasing loading, and the hardness and the out-of-plane displacement of the crystal are the smallest.
Effect of loading-wave-front width on micro-jet from aluminum surface
Wang Pei, Shao Jian-Li, Qin Cheng-Sen
2009, 58 (2): 1064-1070. doi: 10.7498/aps.58.1064
Abstract +
With smoothed particle hydrodynamics, we calculate the formation of micro-jet from the groove of metal surface, and reveal the dependence on the width of loading wave front. The calculated results show that, with the decreasing loading speed,both the mass and the front velocity of ejection decrease, and the mass fraction with low velocity increases. We draw the conclusion that the formation of micro-jet is a result of the particles near the groove acquiring axial velocity and impacting at the axis, and the efflux derives from a layer near the groove. The thin layer becomes smaller when widening the wave front, which is because some particles can no longer satisfy the lock condition of jet strength with the decreasing impact velocity and the increasing impact angle, and then can jet no more.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Defect mode properties of magnetized plasma photonic crystals
Zhang Hai-Feng, Ma Li, Liu Shao-Bin
2009, 58 (2): 1071-1076. doi: 10.7498/aps.58.1071
Abstract +
The piecewise linear current density recursive convolution (PLCDRC) finite-difference time-domain (FDTD) method for magnetized plasmas is applied to study the characteristic of one_dimensional magnetized plasma photonic crystals with a defect layer. In frequency domain, the transmission ratio of electromagnetic Gaussian pulses is computed, and the effects of periodic constant, parameters of plasma and parameters of defect layer such as dielectric length and position on defect mode properties of magnetized photonic crystals are analysed. The results show that the frequency of defect mode cannot be tuned by changing the parameters of position and periodic constant, changing the length of the defect layer can increase the number of defect mode, and the frequency and peak of defect mode can be changed by different parameters of plasma.
Numerical calculation of the electron-phonon coupling relaxation time in pulse laser ablation
Hu De-Zhi
2009, 58 (2): 1077-1082. doi: 10.7498/aps.58.1077
Abstract +
The key to improving the quality of thin film prepared by pulse laser deposition, is to properly control the electron-phonon coupling relaxation time which determines the pulse duration and the laser fluence. Taking the aluminum targets as an example, we obtain the evolution temperature of electron subsystem and ionsubsystem by solving the standard two temperature equation using the finite-difference time-domain (FDTD) method. Then, we obtain the electron-phonon coupling relaxation time, which can distinguish between the thermal ablation and the non-equilibrium ablation to ensure that we can control the process of pulse laser ablation well. In addition, we find out how does the electron-phonon coupling relaxation time change with the pulse duration and the laser fluence.
Effects of various inductances on the dynamic models of the Z-pinch implosion of nested wire arrays
Ding Ning, Zhang Yang, Liu Quan, Xiao De-Long, Shu Xiao-Jian, Ning Cheng
2009, 58 (2): 1083-1090. doi: 10.7498/aps.58.1083
Abstract +
Z-pinch experiments have demonstrated that the soft X-ray power increases 40% with a nested-wire array compared with that with a single-layered wire array. However, the development of the technique of obtaining higher X-ray power using nested wire array configurations has been largely empirical. This has, in part, been due to the absence of adequate theoretical models to describe the mechanism of interaction of the two arrays. As is well known, 2D MHD modeling of nested wire array implosions is difficult, and is very inconvenient to optimize the design of nested-wire arrays. In this paper, the Z-pinch implosion dynamics of nested wire array has been described by its equivalent electric circuit and by solving the corresponding circuit equation. The currents flowing through the outer and inner arrays in the initial stage of implosion depend on the array dimensions, especially on the array inductances. The analysis indicates that the arrays inductance variation can result in four dynamic models of the Z-pinch implosion of nested wire arrays, which is the same as that predicted by previous works. Fast and inexpensive 0D modeling can predict the implosion time and the rate of thermalization of the kinetic energy of the nested-wire array at Qingguang-1 facility, and estimate the implosion model that the inner array wires remain discrete until the outer array material has passed through their gaps. The full current is then transferred rapidly to what was initially the inner, imploding it rapidly onto the outer array material on the axis. Some suggestions are put forward which may be helpful in the nested-wire array design for Z-pinch experiments.
Semi-analytical dual edge element method and its application to waveguide discontinuities
Chen Jie-Fu, Zhu Bao, Zhong Wan-Xie
2009, 58 (2): 1091-1099. doi: 10.7498/aps.58.1091
Abstract +
A semi-analytical dual edge element is proposed to solve the waveguide discontinuities. The governing equations for electromagnetic waveguide are converted to the Hamiltonian system, and the corresponding variational principle based on the dual variables is given. For waveguide sections which are homogeneous along the longitudinal direction, the dual edge element is employed to discretize the cross section, and a precise integration method based on the Riccati equations is used for the longitudinal integration to generate the export stiffness matrices. The whole waveguide discontinuity problems can be solved by combining the export stiffness matrices of homogeneous waveguide sections with the system matrices by conventional three-dimentional finite element method for inhomogneous waveguide sections. Numerical examples demonstrate the high accuracy and efficiency of this method for solving waveguide discontinuity problems.
Observation of macroscopic postsolitons in ultrashort ultraintense laser-plasma interaction
Wang Yu-Xiao, Gu Yu-Qiu, Liu Hong-Jie, Wu Yu-Chi, Wen Xian-Lun, Jiao Chun-Ye, Teng Jian, He Ying-Ling, Zhu Bin, Wang Lei, Wang Jian
2009, 58 (2): 1100-1104. doi: 10.7498/aps.58.1100
Abstract +
Experiments were performed using ultrashort (30fs) ultraintense (up to 1018 W/cm2) laser pulse focused into underdense deuterium plasmas (ne<1020/cm3). Macroscopic bubblelike structures were observed using monochromatic plasma irradiance imaging method. These structures are interpreted as the overdense shells of postsolitons generated in the plasma by the laser pulse, which is found to have important influence on the formation of plasma channel.
Relativistic Cherenkov source with modified photonic band-gap cells
Gao Xi, Yang Zi-Qiang, Hou Jun, Qi Li-Mei, Lan Feng, Shi Zong-Jun, Liang Zheng, Li Da-Zhi
2009, 58 (2): 1105-1109. doi: 10.7498/aps.58.1105
Abstract +
A relativistic Cherenkov source with slow wave system consisting of modified photonic band-gap cells is proposed and investigated. The high frequency structure simulator and three-dimensional particle-in-cell simulation code are used to study the dispersion characteristic of TM01-like mode and the interaction between electromagnetic wave and electron beam. The results show that, in the slow wave system with modified photonic band-gap cells, the TM01-like mode has much better azimuthal symmetry, the non-axisymmetry mode can be efficiently suppressed and the operation efficiency can be enhanced greatly.
Study of central plasma structure using soft X-ray signals
Ma Tian-Peng, Hu Li-Qun, Chen Kai-Yun
2009, 58 (2): 1110-1114. doi: 10.7498/aps.58.1110
Abstract +
A method for studying the central plasma structure using soft X-ray signals in the HT-7 tokamak is reported. Through analysing a typical discharge with MHD instability, the position and rotation direction of magnetic island are obtained from the soft X-ray signals. The magnetic island position and rotation direction are validated from the contour map of soft X-ray emissivity and the m=2 mode rotation direction observed on the Mirnov signals.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Growth kinetics and growth process control of nanocrystalline TiO2 anatase
Hu Lin-Hua, Dai Jun, Liu Wei-Qing, Wang Kong-Jia, Dai Song-Yuan
2009, 58 (2): 1115-1119. doi: 10.7498/aps.58.1115
Abstract +
Structural transformation of nanocrystalline titania prepared by sol-gel process with hydrolysis precursor titanium isopropoxide was investigated. The growth kinetics of TiO2 anatase was also studied. It is found that under acid conditions, the activation energies for the growth of anatase below and above 250℃ are (15.8±4.5) kJ/mol and (80.2±1.0) kJ/mol, respectively, which is due to the structural transformation from anatase to rutile resulting from the increasing temperature during the autoclave heating process. Under base conditions, the activation energy of anatase growth is (3.5±0.4) kJ/mol. The growth of anatase under acid conditions is slower than that under base conditions without phase transformation. That is, the growth of anatase becomes significant at higher temperature under acid conditions, whereas under base conditions, the crystallite growth is obviously accelerated by the longer autoclaving time. The above research results will contribute to realize the control of TiO2 nanoparticle size and will also provide us the theoretical and experimental bases for the mass production of TiO2nanoparticles in the future.
Synthesis of large-area, vertically aligned α-Fe2O3 nanowire and nanobelt arrays
Hai Kuo, Tang Dong-Sheng, Yuan Hua-Jun, Peng Yue-Hua, Luo Zhi-Hua, Liu Hong-Xia, Chen Ya-Qi, Yu Fang, Yang Yi
2009, 58 (2): 1120-1125. doi: 10.7498/aps.58.1120
Abstract +
Large-area (10 mm×10mm), vertically aligned α-Fe2O3 one-dimensional nanostructure (nanobelts and nanowires with controllable diameters) arrays are successfully synthesized by thermally oxidizing iron foil directly, which grow in the [110] direction of the hexagonal crystal. The morphology and microstructure of the synthesized arrays depend strongly on the growth conditions such as the oxygen pressure, temperature and reaction time. We found that the growth of α-Fe2O3 one-dimensional nanostructures follows a top-growth mechanism, in which the ratio of iron and oxygen atoms near the point of growth plays a key role.
Comparative theoretical study of hydrogen storage in single-walled boron-nitride and carbon nanotubes
Sun Wei-Guo, Liu Xiu-Ying, Wang Chao-Yang, Tang Yong-Jian, Wu Wei-Dong, Zhang Hou-Qiong, Liu Miao, Yuan Lei, Xu Jia-Jing
2009, 58 (2): 1126-1131. doi: 10.7498/aps.58.1126
Abstract +
Using the grand canonical Monte Carlo simulations (GCMC), the physisorption storage of hydrogen in single-walled boron-nitride nanotubes (SWBNNTs) and single-walled carbon nanotubes (SWCNTs) is studied. The influences of nanotube diameter, temperature and chirality on physisorptions in SWBNNTs and SWCNTs are mainly investigated comparatively. The results show that, the physisorption properties of SWBNNTS are superior to those of SWCNTS at lower temperatures; however, with the increasing of temperature, the differences between them become smaller. The physisorption amounts of SWBNNTs are comparable with those of SWCNTs at ambient temperature, which are only slightly larger than SWCNTs under higher pressures; a reasonable theoretical explanation is also given. In addition, with respect to the influences of temperature, tube diameter and chirality on physisorptions of hydrogen storage, the SWBNNTs have the same trend as the SWCNTs.
A cellular automaton model for dendrite solidification of pure substance
Shan Bo-Wei, Lin Xin, Wei Lei, Huang Wei-Dong
2009, 58 (2): 1132-1138. doi: 10.7498/aps.58.1132
Abstract +
A cellular automaton (CA) model was developed to describe microstructural evolution of pure substance. A self-consistent interface energy conservation was used to determine the growth velocity of solid-liquid interface instead of the KGT model as is commonly used in previous CA models. The mesh and time dependency of the morphological evolution was also investigated, and the stability of the model was validated. The free dentritic growth of pure succinonitrile in the undercooled melt was simulated by the present model. The results were compared with Glicksman's isothermal dendtitic growth experiment and LMK marginal stability theory. The model reproduced qualitatively most of the dendritic features observed experimentally. The results were in good agreement with theoretical and experimental results.
Thermal dynamics properties of bcc Mo nanofilm from MD simulation
Jia Ming, Lai Yan-Qing, Tian Zhong-Liang, Liu Ye-Xiang
2009, 58 (2): 1139-1148. doi: 10.7498/aps.58.1139
Abstract +
Using molecular dynamics simulation with the modified analytic embedded-atom method (MAEAM), we calculated Gibbs free energy and surface free energy of bcc Mo with high melting temperature Tf, and further obtained the Gibbs free energy of its nanofilms. Based on the Gibbs free energy of nanofilms, we investigated the heat capacity of molybdenum nanofilms at constant pressure or at constant volume. The analysis reveals that the molar heat capacity of bulk sample is lower than that of the nanofilms, and the difference increases with the decrease of the film thickness. It is also observed that such size effect of Mo nanofilm is not really significant until the thickness is less than about 15—20nm. It is the surface atoms that determine the size effect on the thermodynamic properties of nanofilms. The difference between CV and CP of nanofilms is firstly analysed quantitatively and the calculated result for CV/CP varies linearly with T/Tf and relates directly to film thickness.
Influence of helium on volume change and stability of titanium structure: An atomistic simulation
Chen Min, Wang Jun, Hou Qing
2009, 58 (2): 1149-1153. doi: 10.7498/aps.58.1149
Abstract +
Molecular dynamics was employed to study the effects of the size of helium cluster and the helium content on the elastic properties and the volume change of the material under different pressures. We tried to analyse the cause that induced volume change of titanium and the instability of the system. With the increasing of helium content, the cohesive energy reduces, the external volume of the material expands, and the materials becomes unstable. When the size of He cluster is small, with the helium bubble growing, the cohesive energy rises, a volume contraction of the material occurs, and the system tends to keep stable. When the number of helium atoms in helium bubble is over 74, it is difficult for the helium bubble to grow.
Plastic deformation of helium bubble and void in aluminum under shock loading
Chen Xiang-Rong, Deng Xiao-Liang, Song Zhen-Fei, Wang Hai-Yan, Zhu Wen-Jun
2009, 58 (2): 1154-1160. doi: 10.7498/aps.58.1154
Abstract +
The characteristic of microscopic plasticity associated with collapse of helium bubble and void in single-crystal aluminum under the same shock loading strength has been investigated by molecular dynamics (MD) simulations. The results show that both the helium bubble and the void collapse through the emission of shear dislocation loops, while prismatic dislocation loops are never observed in the simulations. The preferential dislocation nucleation sites are similar for the helium bubbles and the voids, but the number of dislocations emitted from the helium bubble outnumbers that from the voids, and the dislocation loops emitted from the helium bubbles move faster than that from the voids. Meanwhile, it is more difficult to emit dislocation loops from the leading side (the side which the shock hits first) of both the helium bubbles and the voids than from the trailing side. By analysing the resolved shear stress along the slip plane, we found that the internal pressure of the helium bubbles increase the resolved shear stress and make the dislocation emission from the helium bubbles much easier than from the voids. The curvature change from the leading side to the trailing side produced by the shock modifies the critical shear stress for dislocation nucleation, which explains the difference in the plasticity between the leading side and the tailing side of both the helium bubbles and the voids. The result will contribute to a better understanding of the microscopic mechanism through which irradiation damages affect the dynamic properties of metals.
Influence of 60Co γ-ray irradiation on AlGaN/GaN high electron mobility transistors
Gu Wen-Ping, Zhang Jin-Cheng, Wang Chong, Feng Qian, Ma Xiao-Hua, Hao Yue
2009, 58 (2): 1161-1165. doi: 10.7498/aps.58.1161
Abstract +
AlGaN/GaN high electron mobility transistors (HEMT) unpassivated with different gate lengths are irradiated with 60Co γ-rays to doses up to 1 Mrad(Si). The bigger the doses are and the smaller the gate lengthis, the greater the changes in drain current and transconductanceare. While the gate leakage current is significantly increased after irradiation, the threshold voltage is relatively unaffected. By analysing the series resistance of channel and the threshold voltage, we find that irradiation induced electronegative surface state charges is one of the important reasons of radiation damage.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Electronic structure and optical properties of ZnO doped with Fe and Ni
Hu Zhi-Gang, Duan Man-Yi, Chen Qing-Yun, Dong Cheng-Jun, Linghu Rong-Feng, Zhou Xun, Xu Ming
2009, 58 (2): 1166-1172. doi: 10.7498/aps.58.1166
Abstract +
The band structure, density of states, optical absorption properties and dielectric function of ZnO doped with Fe or Ni and co-doped with Fe and Ni have been investigated by using density functional theory. The calculated results show that the density of states near Fermi level is derived from Fe 3d and Ni 3d states. A new peak appears at 0.46eV in the imaginary part of dielectric function of doped ZnO. Moreover, the optical absorption spectrum shows an obvious red shift, and a strong peak is observed at 1.3eV after doping. The above results were qualitatively discussed in combination with the experimental and calculated results reported in the literature.
First-principles study on the electronic structures of the ladder compound NaV2O4F
Hu Fang, Ming Xing, Chen Gang, Wang Chun-Zhong, Wei Ying-Jin, Huang Zu-Fei, Fan Hou-Gang
2009, 58 (2): 1173-1178. doi: 10.7498/aps.58.1173
Abstract +
The electronic structures of ladder structural compound NaV2O4F are studied by first-principles calculations with pseudo-potential plane-wave method and spin-polarized generalized gradient approximation (GGA) based on density functional theory (DFT). Four possible spin-ordered states are simulated and the calculated results reveal that the magnetic ground state of NaV2O4F is the antiferromagnetic (AFM) state with AFM interactions both inside the rungs and along the ladder legs. The insulating behavior is successfully simulated with a band gap of about 1.0eV. According to crystal-field theory, the dxy orbitals of V atoms located in the VO4F pyramids have the lowest energy and are split from other d orbitals. The covalent interaction on the rungs becomes weak with the presence of F-ions. Using the calculated total energies for the various spin-ordered states of NaV2O4F, the spin exchange coupling constants are fit out with Noodleman's broken symmetry method. The calculated results indicate that there are ferromagnetic(FM) interactions between the ladders with competitive strength to that on the rungs and thereby NaV2O4F may not be a spin-ladder material.
First-principles study of hydrogen atom in interstitial sites of NiAl and Cr
Shang Jia-Xiang, Yu Tan-Bo
2009, 58 (2): 1179-1184. doi: 10.7498/aps.58.1179
Abstract +
The site occupancy of hydrogen atom in B2-NiAl and Cr alloys and its effect on NiAl and Cr were studied by the first-principle plane-wave pseudopotential method. For NiAl system the impurity formation energies of hydrogen are -2.365 and -2.022eV in the Al-rich octahedral site and Ni-rich octahedral site, respectively, while it is unstable in a tetrahedral site. For Cr system, the impurity formation energies of hydrogen are -2.344 and -2.605eV in the octahedral site and tetrahedral site, respectively. The most stable site of hydrogen is the Al-rich octahedral site in NiAl and the tetrahedral site in Cr. It is most probable that hydrogen mainly occupies the interstitial site in NiAl/Cr alloy. By analysis of the atomic structure, electron population, valence electron density and the density of states, the effects of hydrogen atom on atomic structure and electronic structure of NiAl and Cr alloys are discussed.
Effect of wire width on strain distribution and bandgap in quantum-wire nanostructures based on continuum elasticity theory
Yao Wen-Jie, Yu Zhong-Yuan, Liu Yu-Min, Lu Peng-Fei
2009, 58 (2): 1185-1189. doi: 10.7498/aps.58.1185
Abstract +
The strain distributions of quantum-wire structures are discussed by two methods, namely the continuum elasticity theory treated as a finite difference problem and the Green-function. Analytical expressions are derived for the strain fields with Green-function, which is simple for the regular shaped quantum-wire. The strain fields for arbitrary-shaped quantum-wire can be calculated by continuum elasticity theory and the influences of elastic constants are considered for different materials, although the results are less accurate. The effect of quantum-wire width on strain distribution and bandgap is analysed for InGaAs/GaAs quantum-wire nanostructures. The absolute magnitude of the strain in the bulk of the wire is attenuated significantly along the width direction. At the wire center, the strain-modified direct bandgap increases with the decrease in wire width.
First-principles study of electron field emission from the carbon nanotube with nitrogen doping and H2O adsorption
Chen Guo-Dong, Wang Liu-Ding, An Bo, Yang Min, Cao De-Cai, Liu Guang-Qing
2009, 58 (2): 1190-1194. doi: 10.7498/aps.58.1190
Abstract +
The electron field emission performance of CNT doped with one nitrogen atom in different atomic layers and adsorbed with H2O molecules of different numbers was investigated through the first-principles calculations. The results show that the structure of the systems investigated is stable. The margin of the density of states (DOS) shifting towards low energy position increases with the applied electric field and the number of water molecules, and the HOMO/LUMO gap decreases with these parameters. The analysis of adsorption energy, DOS/LDOS, HOMO/LUMO and their gap indicates that N3CNT+βH2O system is more propitious to the electron′s field emission than other systems.
Ferromagnetic quantum phase transition in Co(S1-xSex)2 system
Yang Jin-Hu, Wang Hang-Dong, Du Jian-Hua, Zhang Zhu-Jun, Fang Ming-Hu
2009, 58 (2): 1195-1199. doi: 10.7498/aps.58.1195
Abstract +
In Co(S1-xSex)2 system, a transition from ferromagnetic to paramagnetic state occurs near x = 0.11. In order to research the physical properties of the samples near this transition, polycrystalline samples of Co(S1-xSex)2 (0.0≤x≤0.16) were prepared. And their structure and resistivity were measured. It is found that the ferromagnetic transition temperature TC is suppressed by Se doping in the relation TC~(1-x)1/2. And the ferromagnetic phase transition goes from the second to the first order. The temperature dependence of resistivity, ρ(T), shows a Fermi-liquid behavior, ρ(T)=ρ0+AT2, in Co(S1-xSex)2 (xρ(T) occurs in the samples near a critical concentration x=0.11. It is suggested that the phase transition near x=0.11 is a quantum phase transition, and the quantum critical spin fluctuation at zero temperature results in non-Fermi liquid behavior.
Distribution of partial electric field and CO molecules adsorbed on the surface of nanostructured nanoellipsoids
Huang Xiao-Jing, You Rong-Yi
2009, 58 (2): 1200-1204. doi: 10.7498/aps.58.1200
Abstract +
The abnormal infrared effect(AIRE) will happen when CO molecules are adsorbed on the nanostructured transition-metal surface, which can be explained by the partial agglomeration of the adsorbate and the increase of interaction energy due to the effect of external electric field. Based on our previous studies,in this paper, the calculation results are given with respect to the nanoellipsoid growing out from the metal substrate. Based on the surface structure model that the metal nanoellipsoids are arranged symmetrically on a metal substrate in the uniform electric field, the partial electric fields near the nanoellipsoid surfaces are calculated by using the classical electromagnetic theory. On the basis of the calculation results, the CO molecules being modeled as equivalent dipoles, and considering the three kinds of interactions between dipoles and partial electric field, dipole and dipole, as well as dipoles and substrate, we give the spatial configuration of CO molecules adsorbed on the nanoellipsoid surfaces by using Monte-Carlo numerical simulation.
Phenomenon of deep charging in polymer under electron beam irradiation
Zhang Zhen-Long, Han Jian-Wei, Huang Jian-Guo, Quan Rong-Hui, Yan Xiao-Juan
2009, 58 (2): 1205-1211. doi: 10.7498/aps.58.1205
Abstract +
Deep charging and discharging effect is one of the key factors threatening the satellites safety in space environment. We develop a new model and simulate the surface potential evolution, internal charge distribution and electrical field distribution in the polymer charged by electron beam of different intensities. The results are compared with experimental results, which show that the polymer′s surface potential increases with electron beam intensity and its resistance, and the time to reach charging equilibrium is determined mainly by the polymer′s resistance.
Effect of rough interface on the thermoelectric figure of merit of the Bi2Te3/PbTe superlattice
Mu Wu-Di, Cheng Hai-Feng, Chen Zhao-Hui, Tang Geng-Ping, Wu Zhi-Qiao
2009, 58 (2): 1212-1218. doi: 10.7498/aps.58.1212
Abstract +
Electron transport is analysed in Bi2Te3 quantum well of Bi2Te3/PbTe superlattice. The hybrid quantum-classical size effect model, considering the Boltsmann transport equation and classical size effect, is introduced to analyse the effect of rough interface on the electron transport and scattering and the thermoelectric figure of merit of Bi2Te3/PbTe superlattice. The PbTe barrier thickness is kept constant to avoid the influence of the variation in tunnel effect on attenuation of the carrier concentration in Bi2Te3 quantum well of Bi2Te3/PbTe superlattice. The result shows that roughness has strong influence on the thermoelectric figure of merit of Bi2Te3/PbTe superlattice. The Bi2Te3/PbTe thermoelectric figure of merit decreases with the decreasing of the portion (p) of mirror reflection in the hybrid effects. And when p is 0.3, the figure of merit is close to the experiment value.
A high-voltage and high-current photoconductive semiconductor switch and its breakdown characteristics
Shi Wei, Tian Li-Qiang, Wang Xin-Mei, Xu Ming, Ma De-Ming, Zhou Liang-Ji, Liu Hong-Wei, Xie Wei-Ping
2009, 58 (2): 1219-1223. doi: 10.7498/aps.58.1219
Abstract +
Semi-insulating GaAs photoconductive semiconductor switch (PCSS) with withstand voltage of 32 kV and peak current of 3.7 kA has been developed. The breakdown mechanism of the PCSS is analyzed. It is shown that the breakdown of PCSS fabricated from indirect band-gap semiconductors is determined mainly by limited conduction of trap filling, but for PCSS's fabricated from materials that exhibit the transferred-electron effect, such as GaAs, breakdown of the PCSS is caused mainly by the negative-resistance-induced electric field enhancement at the anode boundary. Based on the Gunn effect electronics, the breakdown voltage of the semi-insulating GaAs PCSS is calculated, and the calculated results agree with the experimental results.
Improved performance of white polymer light emitting diodes
Zou Jian-Hua, Tao Hong, Wu Hong-Bin, Peng Jun-Biao
2009, 58 (2): 1224-1228. doi: 10.7498/aps.58.1224
Abstract +
White polymer light-emitting diodes (WPLEDs) with bilayer structure were fabricated by spin coating method using polymers of different solubilities. The device structure used here is ITO/PEDOT(50nm)/PVK∶PFO-BT∶PFO-DBT(40nm)/PFO(40nm)/Ba(4nm)/Al(120nm),at the weight ratio of 100∶4∶3 (PVK∶PFO-BT∶PFO-DBT). White fluorescent light emission with CIE coordinates of (0.33, 0.34) is achieved, and the maximal luminance efficiency of 2.4 cd/A and the maximal luminance of 3215 cd/m2 are obtained. By attaching a layer of water-soluble electronic transporting material of PFN to the cathode, the maximal luminance efficiencies increase up to 5.28 cd/A with CIE coordinates kept at (0.34, 0.36), and the device stabitity is also improved.
Vacancy induced spin state transition in La0.7Sr0.3-x□xCoO3 (0≤x≤0.2) cobaltites
Xie Qi-Yun, Wu Xiao-Shan
2009, 58 (2): 1229-1236. doi: 10.7498/aps.58.1229
Abstract +
Effects of vacancy doping in polycrystalline La0.7Sr0.3-xxCoO3 (0≤x≤0.2) cobaltites on their crystal structure, magnetic and transport properties have been systematically investigated. With increasing Sr deficiency, the antiferromagnetic superexchange is promoted at the expense of double exchange between ferromagnetic clusters, with cluster-glass state being prevailing, which is due to the gradual decrease of A site ionic radius as well as more intrinsic disorder. As x is increased beyond 0.1, it is found that the Co—O bond length shrinks remarkably. This tends to enlarge the crystal-field splitting energy and most Co3+ ions are inclined to prefer low spin states. The ground state shows superparamagnetic-like features, thus giving rise to metal-insulator transition.
Room-temperature ferromagnetism in Co-doped ZnO fabricated by coprecipitation method
Lu Zhong-Lin, Xie Kai-Xuan, Mo Zhong-Rong, Zou Wen-Qin, Wang Shen, Yue Feng-Juan, Wu Di, Zhang Feng-Ming, Du You-Wei, Yan Guo-Qing
2009, 58 (2): 1237-1241. doi: 10.7498/aps.58.1237
Abstract +
Nanocrystalline Zn1-xCoxO samples were prepared by coprecipitation and annealing at 300 ℃ for 3 h in 5vol.%H2/Ar flow. Scanning electron microprobe measurements indicate that the samples with nominal Co contents of 0.05, 0.10, and 0.15 have the actual Co contents of 0.054, 0.100, and 0.159 respectively. X-ray diffraction patterns show that the major phase of the samples is of wurtzite structure, while the minor phase of CoO is observed in samples with Co contents of x=0.100 and 0.159. X-ray photoelectron spectroscopy shows that Co has three states: Co incorporated into ZnO matrix, CoO and metallic Co. It was found through magnetic measurements, that room-temperature ferromagnetism exists in all the samples and it comes from both the weak ferromagnetism of Zn-doped CoO1-δ and the magnetism of metallic Co clusters.
Influence of in-plane fields on the three kinds of hard domains
Sun Hui-Yuan, Hu Yun-Zhi
2009, 58 (2): 1242-1245. doi: 10.7498/aps.58.1242
Abstract +
The influence of in-plane field on three kinds of hard domains was studied experimentally by means of direct current bias fields reconstruction. The experiment verifies that VBLs in those three kinds of hard domains collapse gradually under the in-plane field. And the conclusion we obtained that these hard domains have the same range of the critical in-plane field [H1ip,H2ip] corrects the previous view that (H1ip)IIDH1ip)IDH1ip)OHB. By revealing that the breakdown of VBLs affected by in-plane field is independent of the rigidity of the hard domains, this paper provides an important clue for interpreting the mechanism of the VBLs' vanishing and a new scheme for exactly measuring the critical in-plane field under which VBLs begin to disappear.
Effect of annealing pressure on the structure and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films
Li Jian-Jun, Yu Jun, Li Jia, Yang Wei-Ming, Wu Yun-Yi, Wang Yun-Bo
2009, 58 (2): 1246-1251. doi: 10.7498/aps.58.1246
Abstract +
The effect of annealing pressure on the structure and ferroelectric properties was investigated for Bi3.25La0.75Ti3O12(BLT) thin film prepared on Pt/TiO2/SiO2/p-Si(100) substrate by sol-gel method. The amorphous film samples were annealed at 750 ℃ for 30 min under oxygen pressures varying from 10-4 to 3 atm. Then the structure, crystallization degree, and morphology were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscope (FSEM) to clarify the effect of annealing pressure on the structure of the film. The XRD and Raman spectroscopy results showed a clear decreasing of the crystallization degree of the film annealed under oxygen pressures of 10-4 and 3 atm. FSEM results showed different growth orientations of grains under different oxygen pressures. The structure of the BLT film was revealed to affect their ferroelectric properties. The largest remanent polarization of 17.8 μC/cm2 with the coercive field of 73.6 kV/cm and good fatigue property were obtained for the film annealed under oxygen pressure of 0.1 atm.
Ultraviolet resonant Raman scattering in InGaN films
Wang Rui-Min, Chen Guang-De
2009, 58 (2): 1252-1256. doi: 10.7498/aps.58.1252
Abstract +
Ultraviolet Raman scattering spectra of InxGa1-xN films with different In compositions were investigated using 325nm laser line. For photon energy above the energy gap, strong enhanced 2A1(LO)phonon scattering lines were observed. Four 2LO peaks shift from twice the energy of the first-order LO peak, to the high energy end and the shifts increase with In contents in the samples. It is attributed to the multiple resonance resulting from intraband-Frhlich interaction. The composition dependence of LO phonon mode frequency and line shape was analysed. The phase separation was observed in Raman spectra and compared with the data of X-ray diffraction. Furthermore, the E2 phonon combination mode of InxGa1-xN was observed at about 1310cm-1.
Luminescence characteristics of LiBaBO3:Eu2+ phosphor for white LED
Wang Zhi-Jun, Li Pan-Lai, Wang Ying, Yang Zhi-Ping, Guo Qing-Lin
2009, 58 (2): 1257-1260. doi: 10.7498/aps.58.1257
Abstract +
The LiBaBO3:Eu2+ green phosphor was synthesized by high temperature solid-state method. With the Eu2+ doping of 1mol%, the emission and excitation spectra of LiBaBO3:Eu2+ phosphor were measured. The emission spectrum shows two peaks at 482 and 507nm, which are in good agreement with the theoretical values. The excitation spectrum for 482nm emission has two excitation peaks at 287 and 365nm, and for 507nm excitation emission at 365 and 405nm. The effect of Eu2+ concentration on the emission spectrum of LiBaBO3:Eu2+ phosphor was investigated. The results show that red shift takes place in the blue and green emission spectra with increasing Eu2+ concentration, and the blue emission disappears at 3 mol% Eu2+. However, the green emission always exists. The dependence of luminescent intensity of LiBaBO3:Eu2+ phosphor on the Eu2+ concentration was studied, and the results show that the luminescent intensity firstly increases with the increasing Eu2+ concentration, then decreases, and reaches the maximal value at 3 mol% Eu2+. According to the Dexter theory, the concentration quenching mechanism is the d-d interaction.
Energy transfer via cooperative upconversion between Er3+ ions in a tellurite glass
Dai Shi-Xun, Zhou Ling, Xu Tie-Feng, Nie Qiu-Hua, Huang Shang-Lian, Zhou Ya-Xun
2009, 58 (2): 1261-1268. doi: 10.7498/aps.58.1261
Abstract +
Erbium-doped tellurite-based glasses with compositions of TeO2-ZnO-Na2O(TZN)and TeO2-ZnO-La2O3(TZL)are prepared, and fluorescence properties of Er3+:4I13/2→4I15/2 transition have been investigated as a function of erbium-doping concentration. It is found that fluorescence intensity decreases evidently with increasing erbium-doping concentration under higher doping, and it is mainly a result of concentration quenching effect in which energy migration takes place due to energy transfer via cooperative upconversion between Er3+ ions when the procedure of removing OH-1 by bubbling oxygen is adopted in melting glass. By fitting the rate equations of population to the normalised fluorescence decay curves, the coefficients of cooperative upconversion are obtained, and the values for the 4I13/2 are estimated to be CTZN=3.27×10-18cm3/s and CTZL=3.01×10-18cm3/s, respectively. Also, the critical concentration and the critical interaction distance are calculated, and the values for the TZN and TZL glasses are QTZN=11.2×1020 cm-3 and QTZL=11.8×1020cm-3, RTZN=0.597nm and RTZL=0.587nm, respectively. Compared with some other glasses reported, the tellurite glass prepared by us has a better rare-earth Er3+ ion solubility and a lower rate of energy transfer via cooperative upconversion, and may serve as good glass host for broadband fiber amplifiers.
Effects of magnetic field on current in polymer photovoltaic cell
Lei Yan-Lian, Liu Rong, Zhang Yong, Tan Xing-Wen, Xiong Zu-Hong
2009, 58 (2): 1269-1275. doi: 10.7498/aps.58.1269
Abstract +
Polymer photovoltaic cells were fabricated with the basic device structure of ITO/PEDOT: PSS/P3HT: PCBM/Ca/Al. The magnetic-field-dependent current under illumination and in darkness in these devices were measured respectively under different bias. It was found that the light current was enhanced by the magnetic field whereas the dark current was suppressed. Based on the formation mechanism of the light current and the dark current in polymer solar cell, the observed magnetic field effects were explained. The results show that the magnetic field can effectively change the relative ratio between the singlet and the triplet polaron pairs, resulting in an increase in the density of the free carriers. The concentration augmentation of photo-generated free carriers is responsible for the increase of the photocurrent. On the other hand, the interaction between the free carriers and triplet excitons leads to the decrease of the dark current. Around the open circuit voltage, the magnetic field dependent photocurrent and dark current acting together causes the magnetic field effect of light current.
Optical limiting performance of multi-walled carbon nanotubes
Yuan Yan-Hong, Miao Run-Cai
2009, 58 (2): 1276-1279. doi: 10.7498/aps.58.1276
Abstract +
The multiwalled carbon nanotubes (MWNTs) were synthesised by chemical vapor deposition and then dissolved in toluene solution. It is discovered experimentally that MWNTs have obvious optical amplitude limiting when the transmittance is measured by means of ps laser pulses with wavelength of 1064nm. In the case of low incident intensity, the transmittance varies linearly with incidenct intensity. However, the transmittance increases slowly under the condition of high incidenct light intensity and at last becomes saturated. Transmission is near 100% for weak incidenct light. But it is 30% when incidence intensity is 8GW/cm2. The calculated results based on three-photon-absorption theory agree well with the experimental results and it is inferred that the optical limiting of MWNTs results from its three-photon-absorption. The absorption coefficient γ is 1.36×10-20cm3/W2 and its corresponding absorption section σ′3 is 2.8×10-77cm6·s2.
Lifetime of a new type of reservoir oxide cathode
Wang Xiao-Xia, Liao Xian-Heng, Luo Ji-Run, Zhao Qing-Lan, Zhang Xiao-Wei
2009, 58 (2): 1280-1286. doi: 10.7498/aps.58.1280
Abstract +
The lifetime of a new type of reservoir oxide cathode and a conventional oxide cathode was experimentally studied. Concentrations of Ba in different coating depths of the cathodes were analysed by XPS during the lifetime testing process. The mechanism of the reservoir oxide cathode lifetime was discussed according to the analysis results, the cathode structures and the characteristics of the reservoir emission materials. The results show that the lifetime of the reservoir oxide cathode is about seven times that of the conventional oxide cathode. Ba concentration keeps steady in the depth of cathode coating, which plays an important role in the long lifetime of the reservoir oxide cathode.
Characterization of homoepitaxial and heteroepitaxial diamond films grown by chemical vapor deposition
Li Rong-Bin
2009, 58 (2): 1287-1292. doi: 10.7498/aps.58.1287
Abstract +
Sulphur-doped and boron-sulphur co-doped diamond thin films were prepared by using chemical vapour deposition on p-type Si (100) and HTHP-diamond (100) substrates. The structures and properties of CVD diamond films were investigated with atom force microscope (AFM), Raman spectrum, sanning tunneling microscopy (STM) and current imaging tunneling current spectroscopy (CITS). Comparing the structures and properties of the doped diamond films grown on Si and HTHP diamond substrates, we find that the films deposited on Si substrates are composed of spherical grains with size of one hundred nanometer, the doped diamond films on Si substrates consist of large grains with a high fraction of grain boundaries due to the successive secondary nucleation,and the roughness of the films is estimated to be around 18.5nm. The doped diamond films on HTHP diamond substrates are composed of nanometer crystal grains with the sizes of 10—50nm and the film surface is flat with the roughness estimated to be around 1.8nm. Raman and resistivity measurements reveal that the films deposited on HTHP diamond substrates have much higher quality, fewer defects and lower stress, and higher conductivity than the films grown on Si substrates. Current imaging tunnelling current spectroscopy (CITS) images indicate that some grain boundaries and crystalline facets near the grain boundaries are he high electron emission regions. However, the grain boundaries and crystalline facets of the doped diamond films on HTHP diamond substrates have uniform electron emission currents, which indicates that the doped atoms are uniformly distributed in that films. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate the n-type conduction.
Influence of boron on the properties of intrinsic microcrystalline silicon thin films
Sun Fu-He, Zhang Xiao-Dan, Wang Guang-Hong, Xu Sheng-Zhi, Yue Qiang, Wei Chang-Chun, Sun Jian, Geng Xin-Hua, Xiong Shao-Zhen, Zhao Ying
2009, 58 (2): 1293-1297. doi: 10.7498/aps.58.1293
Abstract +
A series of microcrystalline silicon thin films were fabricated by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) in a single-chamber under different boron-contamination conditions. The influence of boron on the properties of intrinsic microcrystalline silicon thin film was studied. The results show that the dark conductivity decreases with the increase of boron contamination and the photosensitivity shows the opposite change. The activation energy varies due to different degrees of boron contamination on these thin films. The boron contamination decreases the crystalline volume fraction and weakens the (220) prefered orientation intensity. However, the effect of contamination is less serious to the material, prepared at relatively high power and high hydrogen dilution, which has higher crystalline volume fraction and stronger (220) preferred orientation.
Fabrication of Yb3+,Er3+:YAG transparent ceramics and study of its 1.5 μm fluorescence spectrum
Jiang Ben-Xue, Li Jiang, Shi Yun, Liu Wen-Bin, Pan Yu-Bai, Huang Li-Ping, Guo Jing-Kun, Huang Tong-De, Wu Yu-Song
2009, 58 (2): 1298-1304. doi: 10.7498/aps.58.1298
Abstract +
5at%Yb3+,2at%Er3+:YAG transparent ceramics possessing a high transmittance was sintered at 1760℃ for 30 h by solid-state method and vacuum sintering technique. The sample exhibited pore-free structure and had no secondary phase in the grain boundary and in the grain, as observed in the SEM photograph. The sample's absorption and fluorescent spectra show that the Yb3+ ions have a high absorption coefficient at 940nm. The decay life-time at the 1030nm wavelength is only 0.274 ms and the initial intensity has an ascending tendency in the fluorescent life-time curve at the wavelength range of 1.5 μm, both of which demonstrate the existence of energy transfer from Er3+ ions to Yb3+ ions. The life-time and stimulated emission cross section of electronic transition between some levels were calculated with the intensity parameter Ωλ of Er3+ acquired from Judd-ofelt theory. The experimental results of the spectrum parameters (the emission cross section and fluorescent life-time)of Er3+ ions in the wavelength range of 1.5μm are the same as the results of the Judd-Ofelt theory. The transition between 4I13/2 and 4I15/2 simultaneously has a large stimulated emission cross section, fluorescence ratio and upper level life-time relative to the other energy level transitions of the sample, which makes the laser output of Er,Yb:YAG transparent ceramics in the wavelength range of 1.5 μm, the eye-safe wavelength range, possible.
Revealing the transport mechanisms of silicon oxidation by H218O/H216O isotopic labeling
Gong Jia, Jiang Yi-Ming, Zhong Cheng, Deng Bo, Liu Ping, Li Jin
2009, 58 (2): 1305-1309. doi: 10.7498/aps.58.1305
Abstract +
A new method was proposed to investigate the transport mechanism of silicon oxidation at 1100 ℃ using H216O/H218O isotopic labeling. The formation and structure of silicon oxide film was analysed. The distribution of 16O and 18O in the oxide film was analysed by means of secondary ion mass spectroscopy (SIMS). The results demonstrate that the oxide film is non-crystalline during the oxidation of silicon in the water vapor and the transport mechanism is substitutional diffusion mechanism.
Mn/PbTe(111) interface behavior studied by photoemission
Wu Hai-Fei, Zhang Han-Jie, Liao Qing, Lu Yun-Hao, Si Jian-Xiao, Li Hai-Yang, Bao Shi-Ning, Wu Hui-Zhen, He Pi-Mo
2009, 58 (2): 1310-1315. doi: 10.7498/aps.58.1310
Abstract +
We performed X-ray photoemission spectroscopy (XPS) investigation on the interface behavior at the Mn/PbTe(111) interface. The measurement shows the drastic changes at atomic level and the Mn/PbTe(111) interface formation. Upon Mn deposition, a new peak component associated with metallic Pb appears in the Pb core-level at low binding energies, and a new peak component related to MnTe compound appears in the Te core-level at high binding energies. These new features become more and more obvious in XPS spectra with increasing Mn thickness, and at the Mn thickness higher than 7 ML (beyond the escape depths of Pb and Te), the substrate features disappear. Upon further deposition of Mn, the intensity of the metallic Pb core level keeps constant, while the intensity of Te 3d core level of MnTe compound decreases with increasing Mn thickness, and finally the Te 3d core level disappears at Mn thickness of about 102 ML. Based on these results, we can conclude that, upon Mn depostion, both Te and Pb segregate to the surface region, the segregated Pb as metallic Pb floats on the top of Mn overlayer, and the segregated Te is bound in the Mn overlayer as MnTe.
Effects of secondary neutrons on fast-neutron image quality in thick scintillator
Zhang Fa-Qiang, Yang Jian-Lun, Li Zheng-Hong, Ye Fan, Xu Rong-Kun
2009, 58 (2): 1316-1320. doi: 10.7498/aps.58.1316
Abstract +
The effects of secondary neutrons on the image quality is simulated using FNRSC (fast neutron radiography simulation code) for a series of scintillator thickness values ranging from 5 mm to 300 mm. The calculated results show that with an incident neutron energy of 14 MeV, the effects of secondary neutrons on the image quality strongly depends on the thickness d of the scintillator for d smaller than 50 mm. When d is higher than 50 mm, this effect is almost saturated. By comparing the image contrast calculated by MCNP (Monte Carlo neutron and photo transport code) with that by FNRSC, we find that the main reasons for the discrepancy is that, the distribution of secondary neutrons strongly depends on that of incident neutrons in the scintillator; contributions of secondany neutrons resulting from energy deposit and fluorescence photons to fast neutron images are different. The results also indicate that a drop occurs in the contrast of neutron images when the elastic scattering cross section between incident neutrons and carbon nucleus is larger.
Effect of F?rster-type bimolecular annihilation on fluorescence decay of porphyrin side-chain polymer
Chen Zhi-Feng, Wang Hui, Zhang Yan-Wei, Zhang Wei, Ji Liang-Nian, Li Ai-Zhen, Yu Han-Cheng, Huang Jin-Wang
2009, 58 (2): 1321-1325. doi: 10.7498/aps.58.1321
Abstract +
Transient fluorescence dynamics of a new kind of porphyrin side-chain polymer film [poly[porphyrin acrylate-styrene] (P[(por)A-S]) at high excitation density has been measured by using time-resolved fluorescence spectroscopy. The fluorescence decay becomes more rapid with the increase of the interchain polymer concentration. The origin of the concentration quenching has been analysed according to the Frster-type bimolecular annihilation theory. The theoretical analyses are in good agreement with the experimental results. Rosults show that, in the case of high excitation density, the Frster-type bimolecular annihilation is the main reason of the fast initial luminescence decay and the low luminescence efficiency of the porphyrin side-chain polymers.
Computational study of heterogeneous absorption spectra under femtosecond laser pulse
Wang Lu-Xia, Fan Fei
2009, 58 (2): 1326-1331. doi: 10.7498/aps.58.1326
Abstract +
Ultrafast heterogeneous electron transfer, including direct transition from the surface attached molecule into the semiconductor band states, is introduced with the focus on a system of perylene on TiO2. The contribution of intramolecule transition and direct electron transition to the absorption spectra are analysed theoretically. By comparing with the intramolecule transition contributions, the ultrafast direct transition contributions to the absorption spectra with different physical parameters are analysed.
Laser pulse control of bridge state electron transfer in heterogeneous structures
Zhao Hong-Min, Wang Lu-Xia
2009, 58 (2): 1332-1337. doi: 10.7498/aps.58.1332
Abstract +
Combined with one-dimensional reduced vibrational model and optimal control theory, the heterogeneous electron transfer in bridge mediated systems is theoretically studied. Laser pulse control of heterogeneous system with single bridge and double parallel bridges are simulated, the the dynamic process and the optimal pulse are analysed. The influence of bridge molecules on the ultrafast electron transfer path is also discussed.
Effect of TiO2 particle size on the properties of electron transport and back-reaction in dye-sensitized solar cells
Liang Lin-Yun, Dai Song-Yuan, Hu Lin-Hua, Dai Jun, Liu Wei-Qing
2009, 58 (2): 1338-1343. doi: 10.7498/aps.58.1338
Abstract +
The mechanisms of electron transport and back-reaction kinetics in dye-sensitized solar cell (DSC) were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The DSCS with three different sizes of TiO2 particles were measured by IMPS/IMVS. The results indicate that the effective diffusion coefficient (Dn) increases along with the increase of particle size, while the electron lifetime (τn) and the electron transit time (τd) decrease with the increase of particle size under different induced-light intensities. The increase of Dn is attributive to the decrease of the film surface area. The decrease of τn is interpreted according to the frequency of electron trapping and de-trapping in defects. The decrease of trap concentration in TiO2 films leads to the decrease of τd.
An optical emission spectroscopy study on the high rate growth of microcrystalline silicon films
Han Xiao-Yan, Geng Xin-Hua, Hou Guo-Fu, Zhang Xiao-Dan, Li Gui-Jun, Yuan Yu-Jie, Wei Chang-Chun, Sun Jian, Zhang De-Kun, Zhao Ying
2009, 58 (2): 1344-1347. doi: 10.7498/aps.58.1344
Abstract +
The growth process of microcrystalline silicon thin films deposited at high growth rate was monitored online by optical emission spectroscopy. The properties of the material were studied by Raman and FTIR spectroscopy. The results indicated that the I[SiH*]/I[Hβ*] ratio decreased during the process, particularly at low total gas flows, which was consistent with the Raman results. The I[Hβ*]/I[Hα*]ratio detected after the plasma glowed for 5 minutes showed that the electronic temperature first decreased then increased with the increasing Ftotal. The FTIR spectra showed that the microstructure defect fraction R first decreased then increased with increasing Ftotal. This means that the electronic temperature in hydrogen plasma plays an important role in determining the properties of the microcrystalline silicon thin films.
Nonlinear nature of spectral components in heart rate variability
Poon Chi-Sang, Li Cheng, Fang Yong, Sun Jin-Tao, Ding Guang-Hong, Wu Guo-Qiang, Tang Da-Kan
2009, 58 (2): 1348-1352. doi: 10.7498/aps.58.1348
Abstract +
We proposed a new hybrid method combining the band-phase-randomized surrogate data with noise titration to discern the influence of spectral components on heartbeat chaos. The results demonstrate that the chaotic strength of phase-randomized surrogate data in the high frequency band (HF) of heart rate variability (HRV) is reduced significantly, which indicates that the frequency components of spectral analysis involve intrinsic chaotic information. The hybrid method proposed in this study is effective to distinguish the different contributions of spectral components to chaotic strength of the test data. This method is applicable not only to HRV but also to other deterministic signals.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
A false limit in atmospheric radiative transfer and the physics behind it
Duan Min-Zheng, Guo Xia
2009, 58 (2): 1353-1357. doi: 10.7498/aps.58.1353
Abstract +
When both the solar and view zenith direction approach horizontal, the reflected radiance at the top of the atmosphere, derived from the plain-parallel atmospheric radiative transfer equation, is different and it depends on the path how the incidence and reflected directions tend to be horizontal. This phenomenon under extreme condition is called limit discontinuity in mathematics. However, the discontinuity of the limits is contradictory to the physical nature of atmospheric radiative transfer and it is obtained by neglecting an implicit physics principles, the Snell's law. The Snell's law must be used in the radiative transfer algorithm for radiance under this extreme condition to avoid obtaining wrong results.
Cognitive radio spectrum assignment based on quantum genetic algorithm
Zhao Zhi-Jin, Peng Zhen, Xu Shi-Yu, Zheng Shi-Lian, Lou Cai-Yi, Yang Xiao-Niu
2009, 58 (2): 1358-1363. doi: 10.7498/aps.58.1358
Abstract +
Cognitive radio spectrum assignment based on quantum genetic algorithm is proposed, and simulations are conducted to compare the proposed method with color sensitive graph coloring algorithm. Results show that the proposed method greatly outperforms the color sensitive graph coloring algorithm as it better optimizes network utilization. The proposed method can find the optimal solutions after only several generations, while the relative differences between solutions obtained by color sensitive graph coloring algorithm and the optimal solutions are quite large.
REVIEW OF FRONTIER AREA
Recent progress in cubic boron nitride film synthesis
Yang Hang-Sheng, Nie An-Min, Zhang Jian-Ying
2009, 58 (2): 1364-1370. doi: 10.7498/aps.58.1364
Abstract +
Cubic boron nitride (cBN) thin films, as artificially prepared materials, have excellent mechanical, thermal, electronic and optical properties, thus have potentially significant technological applications in cutting tools, high-temperature electronic devices, and protective coatings for optical elements. Cubic BN films have attracted worldwide attention since the early 1980s; however, a numbers of difficulties hindered their applications. In this paper, recent important achievements in cBN film preparation are reviewed, and perspectives for future study of cubic boron nitride film are presented.