Vol. 64, No. 4 (2015)

A parameter optimization nonlinear adaptive denoising algorithm for chaotic signals
Wang Meng-Jiao, Wu Zhong-Tang, Feng Jiu-Chao
2015, 64 (4): 040503. doi: 10.7498/aps.64.040503
Abstract +
In the parameter optimization issue of nonlinear adaptive denoising algorithm for chaotic signals, the window length is affected by different factors. In this paper, a criterion is proposed for selecting the optimal window length. According to the difference in autocorrelation function between chaotic signal and noise, first, the different window sizes are used for denoising noisy chaotic signals. Then, the residual autocorrelation degree (RAD) of each window length is computed. Finally, the optimal window length is obtained by shrinking the window length corresponding to the minimum RAD. Simulation results show that this criterion can automatically optimize the window length efficiently under different conditions, which improves the adaptivity of the denoising algorithm of chaotic signals.
Design of an adaptive sliding mode controller for synchronization of fractional-order chaotic systems
Pan Guang, Wei Jing
2015, 64 (4): 040505. doi: 10.7498/aps.64.040505
Abstract +
In this paper, the synchronization of fractional-order chaotic systems is investigated. Based on sliding mode control and adaptive control theory, a fractional order integral sliding surface with strong robustness is designed, and an adaptive sliding controller is proposed for synchronizing the fractional-order chaotic systems with retaining the nonlinear part. Numerical simulations on synchronizing the Chen chaotic systems, the Liu chaotic systems, and Arneodo chaotic systems are carried out separately. The simulation results show the validity and feasibility of the adaptive sliding controller.
Hybrid algorithm for weak signal detection in chaotic sea clutter
Xing Hong-Yan, Zhang Qiang, Xu Wei
2015, 64 (4): 040506. doi: 10.7498/aps.64.040506
Abstract +
According to the empirical mode decomposition (EMD) theory, a prediction method of support vector machine (SVM) is proposed based on particle swarm optimization. The ensemble EMD method is used to decompose the signal into some intrinsic mode function components which are taken as the input of the SVM to predict the data. All the predicted values are combined, and the weak signals submerged in chaos background, including the transient signal and periodic signal, are detected from the prediction error. Lorenz attractor and the data from the McMaster IPIX radar sea clutter database are used in the simulation. The results show that the proposed method can effectively detect the weak target from chaotic signal. When the signal-to-noise ratio is 102.8225 dB in the chaotic noise background, by using the new method the root mean square error can be reduced by five orders of magnitude, reaching 0.00000033092, while the conventional SVM can reach only 0.049 under the condition of -54.60 dB and the weak target detected in sea clutter has the harmonic characteristics, which shows the prediction model has a lower threshold and error.
Analysis on the slow-scale bifurcation behaviors of one-cycle-controlled three-level Boost power factor correction converter
Liu Hong-Chen, Guan En-Hui, Wang Yun, Zhao Dan, Zhou Qi-Kun, Xu Yong-Xiang
2015, 64 (4): 040502. doi: 10.7498/aps.64.040502
Abstract +
In this paper, the slow-scale bifurcation phenomenon of the one-cycle-controlled three-level Boost power factor correction (PFC) converter is studied in depth, aiming at analyzing the influence of main circuit parameters on the stability of the system based on Floquet multiplier method. Firstly, the working principle of the circuit is analyzed, and a simplified model is derived according to the power balance principle. The periodic solutions are investigated using the harmonic balance method, and its stability is studied by the Floquet theory. By calculating the Floquet multiplier, the influence of the voltage compensator resistor Rvf on the slow-scale behavior of the system is analyzed. The simulation result verifies the correctness of the simplified model and theoratical analysis. Finally, the stability boundary composed of filter capacitor C and load resistor R as well as feedback resistor Rvf and capacitor Cvf is calculated and simulated under certain conditions. The circuit simulation result is consistent with the theoretical calculation. The results show that the correct choice of circuit parameters of three-level Boost PFC converter is very important for achieving its stable operation and improving the power factor.
Analysis of chaos in permanent magnet synchronous generator and optimal output feedback H∞ control
Yang Yi-Fei, Luo Min-Zhou, Xing Shao-Bang, Han Xiao-Xin, Zhu Huang-Qiu
2015, 64 (4): 040504. doi: 10.7498/aps.64.040504
Abstract +
The permanent magnet synchronous generator (PMSG) is investigated and its mathematical model is established in two-phase synchronous rotating coordinates. Aiming at the fact that PMSG may present chaotic behaviors at certain values of parameters and under certain working conditions, the output feedback control gain matrix with the minimum performance index is obtained by solving the Riccatic equation and fed back to the system in order to improve the system performance with considering the disturbance. Results show that the optimal output feedback H∞ control based on Riccatic equation can respond to PMSG very quickly and accurately in the chaotic state when disturbance occurs.
Investigation of thermodynamic properties of weakly interacting Fermi gas in weakly magnetic field by using the N-E-V distribution and pseudopotential method
Li He-Ling, Wang Juan-Juan, Yang Bin, Shen Hong-Jun
2015, 64 (4): 040501. doi: 10.7498/aps.64.040501
Abstract +
Based on the fact that most of low temperature experiments of quantum systems are explored in an external field on condition that the particle numbers, volumes and energies of systems may be changed, the thermodynamic properties of weakly interacting Fermi systems in weak magnetic field are studied by using the statistical distribution of the completely open system with variable particle number, volume, and energy (N-E-V distribution). Firstly, the analytical expressions of internal energy and heat capacity, which are in the Fermi integral form, are obtained in the general case, and the analytical expressions and numerical results of energy and heat capacity are given under the extreme condition of supper-low temperature. The calculation results by the N-E-V distribution (with particle number density being variable) are compared with those by a pseudopotential method (with particle number density being unchanged). It can be found that the deviations of the internal energy and heat capacity calculated by the two different methods are very small, and the N-E-V distribution method can partially compensate for the error caused by the pseudo potential method. The most interesting point of the results obtained by the N-E-V distribution method is that there is a phase transition temperature in the weakly interacting Fermi system in weak magnetic field under the low temperature condition. The phase transition temperature is just in the range where occur the Fermi systems, Bose-Einstein condensation (BEC), Bardeen-Cooper-Schrieffer (BCS) phase transition, and BEC-BCS crossover, and does not vary with strength nor characteristic (attraction or repulsion) of the weak interaction, but it decreases with the strengthening of the external magnetic. When there is no external magnetic, the phase transition temperature is highest (more than 0.184 times Fermi temperature).
Quantum channel establishing rate model of quantum communication network based on entangled states
Chen Peng, Cai You-Xun, Cai Xiao-Fei, Shi Li-Hui, Yu Xu-Tao
2015, 64 (4): 040301. doi: 10.7498/aps.64.040301
Abstract +
Targeting the quantum communication network based on entangled states, a network model is proposed. According to the model, the quantum channel establishing rate of basic links is then analyzed. For different quantum channel establishment methods, the quantum channel establishing rates of long relay links are also analyzed. Then the quantum channel establishing rates corresponding to the point-by-point method and segmentation method are calculated. Finally, the quantum channel establishing rate between two arbitrary points in a large-scale quantum entanglement communication network is analyzed based on the percolation model. The quantum channel establishing rate in a quantum communication network of n nodes is Ω (1/n).
Optical bistability and optical storage based on injection locked Fabry-Perot semiconductor laser
Huang Biao, Yu Jin-Long, Wang Wen-Rui, Wang Ju, Xue Ji-Qiang, Yu Yang, Jia Shi, Yang En-Ze
2015, 64 (4): 044204. doi: 10.7498/aps.64.044204
Abstract +
All-optical bistability based on injection locked Fabry-Perot semiconductor laser (FP-LD) and its application in all-optical storage are studied in this paper. Injection locking of FP-LD is experimentally studied in this paper. The output power characteristic of injection locked FP-LD is analyzed experimentally, showing that threshold width of hysteresis loop and the extinction-ratio are influenced by the difference in the injection optical-wavelength detuning. Furthermore, 2.5 GHz optical storage with 10 Gb/s input signal is realized by reasonably setting the control signal power. The feasibility of implementing high-speed all-optical storage is verified by using the injection locked FP-LD, which shows great applicability to the field of high speed optical fiber communication.
New differential-mode-source cable bundle crosstalk model based on multiconductor transmission lines theory
Sun Ya-Xiu, Zhuo Qing-Kun, Jiang Qing-Hui, Li Qian
2015, 64 (4): 044102. doi: 10.7498/aps.64.044102
Abstract +
The traditional cable bundle crosstalk model is established based on an intra-system common mode source, without considering the crosstalk of cable bundles stimulated by a differential-mode source between different systems. To solve the physical problem of crosstalk between independent circuit cable bundles which is stimulated by a differential-mode source, in this article we propose a new differential-mode source cable bundle crosstalk calculation method based on the multiconductor transmission line theory. According to the mechanism of the differential-mode-stimulated transmission line coupling, using this method we obtain a new three-conductor transmission line parasitic parameter circuit model and mathematic matrix model through using the transmission line propagating transverse electro magnetic mode. We deduce the parasitic parameter calculation formula by an image method and Neumann formula, and then obtain the new cable bundle crosstalk chain parameter array equations in frequency domain. By using the top and end boundary conditions of the new differential-mode cable bundle crosstalk model, we finally work out the crosstalk voltage in frequency domain. In this article, we take the crosstalk between differential-mode parallel double culprit cables and the victim cable from other independent circuit for example. By simulating the crosstalk voltage of victim cable in different position arrangements, we obtain the crosstalk physical law between cable bundles under the differential-mode source condition, that is, the crosstalk of the victim cable located between differential-mode circuits is much larger than that situated outside the differential-mode circuit. We can also verify that this model can be used to calculate the crosstalk caused by differential-mode source at different frequencies. In this article, we analytically calculate the crosstalk problems caused by differential-mode source cable bundles for the first time, which provides theoretical basis for solving some practical electromagnetic compatibility problems such as the bundling of a large quantity of wires and the predicting of cable bundle crosstalk. Therefore it perfects the application of multiconductor transmission line model to cable bundle crosstalk problem, and has strong guiding significance.
Image smoothing model based on the combination of the gradient and curvature
Zhou Xian-Chun, Wang Mei-Ling, Shi Lan-Fang, Zhou Lin-Feng, Wu Qin
2015, 64 (4): 044201. doi: 10.7498/aps.64.044201
Abstract +
In image processing, in order to keep the detailed information about image edge, we propose a curvature smoothing model based on the nature of diffusion coefficient and curvature. Considering the fact that the curvature will change significantly when the image is affected by noise pollution, in this article we will continue to take the level set curvature as a detection factor and substitute it into the model, then we present a new model which combines gradient and curvature. Analysis and simulation indicate that the new model can keep more image information than the Perona-Malik model, and it can strengthen the sharp edge of the image efficiently, and well keep the straight lines of image, and edges, corners, slopes and small-scale features of curve at the same time, so this model is an ideal model.
Experimental study of multiple optical parametric oscillator based on MgO:APLN and its evolution analysis of back conversion
Yu Yong-Ji, Chen Xin-Yu, Wang Chao, Wu Chun-Ting, Dong Yuan, Li Shu-Tao, Jin Guang-Yong
2015, 64 (4): 044203. doi: 10.7498/aps.64.044203
Abstract +
In this paper, a multiple optical parametric oscillator based on MgO:APLN is reported. The polarization structure of MgO:APLN and output coupler transmittance are optimized, with a high repetition rate of 200 kHz and 1064 nm laser pumping. The 1.57 μm and 3.84 μm cross period parameters light output can be achieved by a single poled crystal for the first time. The maximum average output powers of 2.4 W at 1.57 μm and 1.31 W at 3.84 μm are obtained, corresponding to optical-optical conversion efficiency of 11.54% and 6.25%, respectively. For the phenomenon of energy back conversion appearing in the multiple optical parametric oscillation process, the numerical evolution of multi-wave coupling process through the coupled wave equations is investigated, and the concept of “back conversion in energy transmission area” is induced, and indicates that the existence of back conversion in energy transmission area causes the weak gain parameters of optical parametric oscillator to be enhanced twice. The theoretical analyses are basically in agreement with the experimental results.
A method of retrieving the constitutive parameter matrix of magnetoelectric coupling metamaterial
Xu Xin-He, Liu Ying, Gan Yue-Hong, Liu Wen-Miao
2015, 64 (4): 044101. doi: 10.7498/aps.64.044101
Abstract +
The constitutive parameters of single negative (only electric permittivity or only permeability less than zero) metamaterials and wires-split ring resonator metamaterials can usually be retrieved by the S parameter method. Due to the cross polarization phenomenon in magnetoelectric coupling metamaterial, only two constitutive parameters of permittivity and permeability cannot accurately describe the electromagnetic characteristics of the magnetoelectric coupling metamaterial. The traditional S parameter retrieval method starts with the assumption that the metamaterial has only two constitutive parameters of permittivity and permeability, so the method to retrieve the constitutive parameters of magnetoelectric coupling metamaterials is obviously restricted. In this paper, the electric component and magnetic component in a magnetoelectric coupling metamaterial cell are treated as being equivalent to the surface current and surface magnetic flow, respectively. By deriving the relationship of the average electric flux density and the average magnetic flux density to the external electromagnetic field, we obtain a constitutive parameters matrix (2×2) of the magnetoelectric coupling metamaterial, and find analytical formulas for the relationship between these four constitutive parameters of the magnetoelectric coupling metamaterial and the parameters such as the permittivity of the electric component, permeability of magnetic element, spatial dispersion, and coupling coefficient, and then deduce the refractive index formula. We use the refractive index formula to nonlinearly fit retrieval refractive index curves, and find very good agreement between the refractive index values theoretically predicted by analytical formulas and those obtained from numerical retrievals based on full-wave simulations, thereby verifying the proposed constitutive matrix analytic formula and the refractive index expression. According to the fitting results, we obtain the frequency response curves of the four electromagnetic parameters in constitutive matrix. The proposed method of retrieving the constitutive matrix parameters will provide an important theoretical reference for the researchers engaged in analyzing and studying the coupling phenomenon between electric component and magnetic component in a magnetoelectric metamaterial cell.
Self-excited oscillation mechanism of a standing-wave thermoacoustic system
Wang Tuo, Wu Feng, Li Duan-Yong, Chen Hao, Lin Jie
2015, 64 (4): 044301. doi: 10.7498/aps.64.044301
Abstract +
The onset process of a thermoacoustic prime mover is a process generating and maintaining self-excited oscillation. It is helpful to have a better understanding of thermoacoustic effect by investigating the mechanism of thermoacoustic self-excited oscillation. The network model of a representative standing-wave thermoacoustic prime mover is established on the basis of thermoacoustic network theory. Comparing thermoacoustic network to electric network, the apparent power flux which inputs the thermoacoustic network is calculated by using the Hermitian form. In the network, the apparent power flux balance means establishing the self-excited oscillation. Based on the above, the threshold temperature and operation frequency of a thermoacoustic prime mover are calculated on condition that the imaginary part of angular frequency is equal to zero. The calculation results are in good agreement with the experimental results. For the coupling relationship of the main pressure with the threshold temperature and operation frequency, the calculation results are roughly close to the experimental results. The obtained results are helpful for the further studying of the thermoacoustic effect and the optimal designing of a thermoacoustic system.
Single mode optoelectronic oscillator assisted by active ring resonance cavity filtering
Li Hong-Xia, Jiang Yang, Bai Guang-Fu, Shan Yuan-Yuan, Liang Jian-Hui, Ma Chuang, Jia Zhen-Rong, Zi Yue-Jiao
2015, 64 (4): 044202. doi: 10.7498/aps.64.044202
Abstract +
In this paper, a single mode optoelectronic oscillator assisted by active ring resonance cavity filtering is presented and verified. Using the high Q optical comb frequency response to select the oscillation mode of an optoelectronic oscillator, the system can effectively suppress the side-mode and generate single mode signal. Theoretically, the optoelectronic oscillator oscillation mode and the frequency response of the active cavity are analyzed. The simulation results show that the active ring resonance cavity filtering is of benefit to the side-mode suppression and single mode output in an optoelectronic oscillator system. By comparing with experimental result, the theoretical prediction is verified. The output of a 20 GHz single-mode signal with a side-mode suppression ratio of 58.83 dB and a phase noise of -97 dBc/Hz at 10 kHz from carrier is also obtained. This scheme has the advantages of the existing optoelectronic oscillator side-mode suppression methods. In addition, it has more convenient manipulation, and good flexibility and tunability.
A new scheme of measuring Sagnac effect based on microwave resonant
Wu Qiong, Yu Jin-Long, Wang Ju, Wang Wen-Rui, Jia Shi, Huang Gang-Bin, Hei Ke-Fei, Li Li-Juan
2015, 64 (4): 044205. doi: 10.7498/aps.64.044205
Abstract +
The main principle of the existing optical gyroscope is based on the Sagnac effect. How to improve the measurement accuracy of the Sagnac effect is an important research topic of improving the gyro accuracy. The traditional optical gyro uses the short wavelength characteristic of light to improve the detection accuracy. But when considering the fact that the detection accuracy of the microwave phase/frequency is much higher than that of light wave phase/frequency, if the microwave can be used to detect the Sagnac effect, the detection accuracy higher than optical gyro accuracy can be obtained, which makes it possible to achieve high-accuracy microwave gyro. The Sagnac effect is detected by using the optoelectronic oscillator based light-carrying microwave structure. Experimental results prove the feasibility of detecting Sagnac effect by using microwave, which lays the foundation for realizing the high-precision microwave resonant gyroscope in the future.
Dynamic effective mass and power dissipation of the granular material under vertical vibration
Yu Tian, Zhang Guo-Hua, Sun Qi-Cheng, Zhao Xue-Dan, Ma Wen-Bo
2015, 64 (4): 044501. doi: 10.7498/aps.64.044501
Abstract +
The dependences of the dynamic effective mass() and power dissipation p() of tungsten particles system on frequency are studied under vertical vibration excitation. It is found that there appears a sharp resonance peak in each of spectra of the real part M1 (), the imaginary part M2 () of the effective mass, and the power dissipation for a given vibrating strength. With the increase of the pressure acting on the top surface of the particle, each peak frequency of the M1 (), M2 () and power dissipation moves to higher frequency, and the peak height also increases accordingly. Further study finds that the resonance frequency fg of the real part of the effective mass satisfies piecewise power-law with the change of pressure P acting on the top surface. At low P value, the power exponent is 0.3, and at high P value the power exponent decreases to 1/6. The reciprocal of quality factor of the granular system, 1/Q, decreases exponentially with the change of pressure P.
Information spreading in correlated microblog reposting network based on directed percolation theory
Wang Xiao-Juan, Song Mei, Guo Shi-Ze, Yang Zi-Long
2015, 64 (4): 044502. doi: 10.7498/aps.64.044502
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Due to the properties of rapidity, explosive, timeliness and complicated behavior for user, the research on information spreading progress and influence factors for microblog becomes a hot area of network public opinion. In this paper, firstly we use the contracting mapping principle to discuss the convergence conditions of the iterative algorithm. The numerical solution of the percolation threshold and the size of the largest out-component are proposed. Then the influence of assortativity is analyzed based on the generation model with varying parameter. The feasibility of the proposed algorithm is verified by collecting microblog reposting data. Experimental results demonstrate that four correlation characteristics are shown to have assortativity and disassortativity, but the results of message spreading are closer to that of the assortative network which is related to in-in and in-out degree correlation. It can be verified that the four types of correlation characteristics of a large part of nodes show their consistency for assortativity, through deleting a few nodes as well as extracting link scale for four degree correlations.
Dynamical model of Cosserat elastic rod based on Gauss principle
Liu Yan-Zhu, Xue Yun
2015, 64 (4): 044601. doi: 10.7498/aps.64.044601
Abstract +
Based on the generalized principles of dynamics, the feature of Gauss principle of least constraint is that the motion law can be directly obtained by using the variation method of seeking the minimal value of the constraint function without establishing any dynamic differential equations. According to the Kirchhoff's dynamic analogy, the configuration of an elastic rod can be described by the rotation of rigid cross section of the rod along the centerline. Since the local small change of the attitude of cross section can be accumulated infinitely along the arc-coordinate, the Kirchhoff's model is suited to describe the super-large deformation of elastic rod. Therefore the analytical mechanics of elastic rod with arc-coordinate s and time t as double arguments has been developed. The Cosserat model of elastic rod takes into consideration the factors neglected by the Kirchhoff model, such as the shear deformation of cross section, the tensile deformation of centerline, and distributed load, so it is more suitable to modeling a real elastic rod. In this paper, the model of the Cosserat rod is established based on the Gauss principle, and the constraint function of the rod is derived in the general form. The plane motion of the rod is discussed as a special case. As regards the special problem that different parts of the rod in space are unable to self-invade each other, a constraint condition is derived to restrict the possible configurations in variation calculation so as to avoid the invading possibility.
Numerical validation study of high power microwave soil breakdown
Tang Tao
2015, 64 (4): 045203. doi: 10.7498/aps.64.045203
Abstract +
The nonlinear changes of soil resistivity will be caused when the high power microwave (HPM) propagates in soil, and these changes in turn counteract the propagation process so that the energy transmission efficiency of the HPM is reduced. By analyzing the dynamic ionization process of soil, a HPM soil propagation model is constructed by combining the Maxwell equations. The model is numerically validated by using a finite difference time domain method. The numerical results show the physical processes of the HPM propagation and attenuation in soil and the nonlinear change process of soil resistivity. These numerical results are verified by a theoretical analysis.
Simulation of X-ray spectrum of Ar tracer in indirectly driven implosion
Qiao Xiu-Mei, Zheng Wu-Di, Gao Yao-Ming
2015, 64 (4): 045201. doi: 10.7498/aps.64.045201
Abstract +
As the X-ray spectrum of tracer in inertial confinement fusion implosion target is usually used to infer electron temperature, density, and the mixture of fuel and shell, it is necessary to study the relation between the characteristics of X-ray emission spectrum and the implosion process, which is helpful for inferring the implosion status. Under the condition of SGIII prototype, approximately 0.5% atomic percent of Ar atoms are doped in an indirectly driven implosion target, X-ray spectrum of Ar is numerically simulated. In this article, the influences of line re-absorption effect, tracer concentration, and profile of fuel plasma state on the emission spectrum are studied. The relation between the temporal evolution of the emission spectrum and the implosion process is also investigated. It is found that as the tracer concentration increases up to ~1%, the X-ray intensity is enhanced, but the influence of line re-absorption becomes severe. Temporal evolution shows that the peak time of Ar X-ray intensity is almost the same as that of neutron production (the former delays about 15 ps, which usually cannot be resolved). As is well known, the strong line emission occurs in the plasma with high temperature, high electron density, and proper ionization. The detailed analysis shows that at the peak emission time, as the core Ar plasma is over ionized, the main X-ray line emission region is located near the boundary region of the fuel, and this thin shell, whose thickness is about 4 μm and whose volume accounts for 56% of the total fuel plasma volume, emits the X-ray whose intensity is about 72% of the total line intensity. Therefore, the space-averaged plasma temperature and density, which are obtained by fitting the emission spectrum, mainly reflect the plasma state in this region.
Experimental study of shock waves induced by a nanosecond pulsed laser in copper target
Wang Ji-Xun, Gao Xun, Song Chao, Lin Jing-Quan
2015, 64 (4): 045204. doi: 10.7498/aps.64.045204
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In this paper, the shock waves induced by a nanosecond pulsed laser in copper target are studied and the relative pressures of shock waves are measured by using the piezoelectric polyvinylidene fluoride piezoelectric sensors. The evolutions of the relative pressures of shock waves with laser pulse energy and target thickness are discussed. Experimental results show that the pressure of shock wave is 2.1 MPa when the nanosecond pulsed laser with an energy of 500 mJ irradiates on a 2 mm thick copper target. When the laser energy increases from 200 to 500 mJ, the pressures of shock wave can increase 162% and 231%, with the target thickness values being 2 and 4 mm respectively. But when the thickness of the copper target increases from 2 to 6 mm, the pressures of shock waves with laser pulse energies of 400 and 500 mJ are reduced by 32% and 49%, respectively.
Optical properties of direct current glow discharge plasmas at high pressures
Wang Jian-Long, Ding Fang, Zhu Xiao-Dong
2015, 64 (4): 045206. doi: 10.7498/aps.64.045206
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In this work, the parallel bright and dark plasma striations are observed in direct correct glow discharge plasmas at high pressures (>100 Torr, 1 Torr=1.33322×102 Pa), and the effect of working gas on the plasma optical property is studied by combining the measurements of optical emission spectra. With the increase of the methane concentration, the length of striations decreases and the corresponding electron excitation temperature reduces. As the concentration of methane increases, the species with the low ionization energy increases, and the average ionization energy of the species decreases. In this case, the electron accelerated in a smaller distance can obtain enough energy to excite the gas species and produce visible light emission, and thus the length of plasma striations becomes shorter. With the introduction of argon, the plasma striations appear clearly. The length of striations increases with the increase of argon content, which is also correlated with the higher ionization energy of argon, while the corresponding electron excitation temperature rises. The length of plasma striations shows a response to the electron temperature as working gas changes.
Critical value of volume ignition and condition of nonequilibriem burning of DT in inertial confinement fusion
Zhao Ying-Kui, Ouyang Bei-Yao, Wen Wu, Wang Min
2015, 64 (4): 045205. doi: 10.7498/aps.64.045205
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In the local thermodynamic equilibrium approximation, we study the problems on low-temperature volume ignition of DT fuel. The temperature and compression threshold of volume ignition are given by solving the ion, electric and radiation energy equation. The ignitions points are affected by the albedo, DT mass, abundance ratio, etc. At the point of ignition, the temperature reduces with the increase of areal density. The trends of variations in radiation and electron temperature become closer to each other. The most important fact is that the subsequent development of the system can be given by analyzing the stationary solution based on the linear stability method. In other words, we can estimate whether the system can enter into a deep-burning state by using this method.
Spectroscopic study on the laser-induced breakdown flame plasma
Liu Yu-Feng, Zhang Lian-Shui, He Wan-Lin, Huang Yu, Du Yan-Jun, Lan Li-Juan, Ding Yan-Jun, Peng Zhi-Min
2015, 64 (4): 045202. doi: 10.7498/aps.64.045202
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The emission spectra from a flame-breakdown atmospheric pressure plasma generated by a nanosecond pulsed 1064 nm beam of Nd:YAG laser are investigated by using a PI-MAX-II intensified charge coupled device. The emission lines of the main elements, such as carbon, hydrogen, oxygen and nitrogen are identified according to the national institute of standards and technology database of atomic emission. It is found that the relative intensities of the atomic emission lines are different from each other under different combustion conditions by making a comparative analysis of the spectra of laser induced breakdown air plasma, alcohol burner flame plasma, and alcohol blast burner flame plasma. The obtained results in this work provide an experimental basis for applying the laser-induced breakdown technology to the combustion diagnostics, and have an important reference and significance for analyzing the characteristics of hydrocarbon fuel combusting in air.
First-principles study of N/Cu co-doped anatase TiO2
Yang Jun, Miao Ren-De, Zhang Xi
2015, 64 (4): 047101. doi: 10.7498/aps.64.047101
Abstract +
Using the first-principles plane-wave ultra-soft pseudo-potential method based on the density functional theory, the structures, electronic-structures and optical properties of pure anatase TiO2, N (Cu) doped TiO2, and N/Cu co-doped TiO2 crystal are studied by the local-spin density approximation plus Hubbard U method. It is shown that the lattice constants become larger because of the lattice distortion caused by doping. Impurity levels in the band gap of TiO2 are introduced by N and Cu doping, and the forbidden band width is correspondingly changed. For N doped TiO2, the reduction of the band gap is weak, while the N/Cu co-doped TiO2 band gap decreases remarkably. It leads to a red shift of visible absorption spectrum and enhances optical catalysis. The effect is useful for the practical application of photo-catalytic.


First-principles study of electronic properties of MoSi2 thin films
Peng Qiong, He Chao-Yu, Li Jin, Zhong Jian-Xin
2015, 64 (4): 047102. doi: 10.7498/aps.64.047102
Abstract +
Electronic properties of tetragonal MoSi2 thin films are studied by the first-principles method. The results show that the MoSi2 film is always metallic, and its density of states and electronic structure are gradually close to their bulk counterpart as the film thickness increases. We further show that the three-atomic-layer film with the lowest energy is magnetic and has a magnetic moment of 0.33 B for its unit cell, and the film becomes non-magnetic when its thickness is more than three atomic layers. Moreover, we investigate the electronic properties of the three-atomic-layer MoSi2 films under unilateral and bilateral hydrogenation and find that the film with unilateral hydrogenation is magnetic and has a magnetic moment of 0.26 B, while the film with bilateral hydrogenation is non-magnetic. The spin polarizations for the films without hydrogenation and unilateral hydrogenation are 30% and 33%, respectively. These results suggest that three-atomic-layer MoSi2 film is metallic or magnetic when it is under suspension or grown on substrate, indicating its potential applications in nanoscale electronic and spintronic devices.
Near infrared broadband from Er-Tm codoped zinc oxide and temperature-dependent properties
Chen Dan-Dan, Xu Fei, Cao Ru-Nan, Jiang Zui-Min, Ma Zhong-Quan, Yang Jie, Du Hui-Wei, Hong Feng
2015, 64 (4): 047104. doi: 10.7498/aps.64.047104
Abstract +
Er-Tm codoped ZnO thin film is synthesized by co-sputtering from separated Er, Tm, and ZnO targets. A flat and broad emission band is achieved in a range of 1400-2100 nm by optimizing annealing temperature, and the observed 1460, 1540, 1640 and 1740 nm emission bands are attributed to the transitions of Tm3+: 3H4 →3F4, Er3+ 4I13/2 →4I15/2, Tm3+ 1G4 → 3F2 and Tm3+ 3F4 → 3H6 transitions, respectively, which cover S, C, L, U bands. The intensity ratios of 1640 to 1535 nm and 1740 to 1535 nm below 1000 ℃ are nearly constant, while the ratios increase sharply above 1000 ℃. The temperature dependence of photoluminescence (PL) spectrum is studied under 10-300 K. With increasing the operation temperature, the bandwidth of broadband is nearly invariable (340-360 nm), and the Tm3+ PL emission intensities of 1640 nm and 1740 nm from Er-Tm co-doped ZnO thin film decrease by a factor of 1.5 and 2, respectively. Moreover, the 1535 nm emission intensity is increased by a factor of 1.2. This phenomenon is attributed to the complicated energy transfer (ET) processes involving both Er3+ and Tm3+ and the increase of phonon-assisted ET rate with temperature as well. And the cross relaxation between Tm3+ ions does not occur.
Thermomagnetic power generation of Mn1.2Fe0.8P1-xSix compounds in strong field of permanent magnet
Liu Zhong-Shen, Tegus O, Ou Zhi-Qiang, Fan Wen-Di, Song Zhi-Qiang, Ha Si Chao Lu, Wei Wei, Han Rui
2015, 64 (4): 047103. doi: 10.7498/aps.64.047103
Abstract +
In this paper, we study the thermomagnetic power generation performances of compound series Mn1.2Fe0.8P1-xSix in a strong magnetic field of permanent magnet. The compounds are synthesized by using the high-energy ball milling and solid state reaction method. The crystalline structures, magnetic properties, and the thermomagnetic power generation performances of the compound series Mn1.2Fe0.8P1-xSix are measured. The results show that Mn1.2Fe0.8P0.37Si0.63 and Mn1.2Fe0.8P0.35Si0.65 are the compounds of a first-order phase transition and the soft ferromagnetic materials, and they are of Fe2 P-type hexagonal structure, Curie temperatures of these compounds are 334 K and 348 K in the industrial waste heat temperature zone. According to this feature that temperature variation of the first-order phase transition material leads to a large change of magnetization at the Curie temperature, we design a demonstration device for thermomagnetic generator, and measure the relationships of induction current generated in ferromagnet phase transition with the coil turn number, mass and surface area of thermomagnetic generator material, and the gradient of surface temperature for compounds Mn1.2Fe0.8P0.37Si0.63 and Mn1.2Fe0.8P0.35Si0.65. The results show that the Mn1.2Fe0.8P1-xSix compound series possess the high performances of thermomagnetic power generation, and they are expected to be candidates of magnetic materials for thermomagnetic power generation.
Room-temperature thermoelectric properties of GaN thin films grown by metal organic chemical vapor deposition
Wang Bao-Zhu, Zhang Xiu-Qing, Zhang Ao-Di, Zhou Xiao-Ran, Bahadir Kucukgok, Na Lu, Xiao Hong-Ling, Wang Xiao-Liang, Ian T. Ferguson
2015, 64 (4): 047202. doi: 10.7498/aps.64.047202
Abstract +
The GaN thin films with different doping concentrations are grown by metal organic chemical vapor deposition. Carrier concentrations, mobilities and Seebeck coefficients of the GaN thin films are measured by Hall and Seebeck system at room temperature. The power factor and the thermoelectric figure of merit are calculated by experimental and theoretical data. The mobility and Seebeck coefficient of GaN thin film decrease with the increase of carrier concentration. The conductivity of GaN thin film increases with the increase of carrier concentration. The Seebeck coefficient of GaN thin film varies from 100 to 500 μV/K, depending on carrier concentration. The highest power factor is 4.72×10-4 W/mK2 when the carrier concentration is 1.60×1018 cm-3. The thermal conductivity of GaN thin film decreases with the increase of carrier concentration due to the increase of phonon scattering. The largest thermoelectric figure of merit of the GaN thin film at room temperature is 0.0025 when the carrier concentration is 1.60×1018 cm-3.
Mutual compensation property of electrooptic and magnetooptic effects and its application to sensor
Li Chang-Sheng
2015, 64 (4): 047801. doi: 10.7498/aps.64.047801
Abstract +
Mutual compensation property between electrooptic and magnetooptic modulations in a crystal with electrooptic and magnetooptic effects and its application to magnetooptic sensor are investigated theoretically and experimentally. Under the condition of light intensity modulation, electrooptic and magnetooptic modulation effects can compensate for each other, so that the transmitted light intensity through the crystal can be kept at a certain fixed value. Based on this mutual compensation property, a novel optical current (or magnetic field) sensor is proposed and demonstrated experimentally by use of a single bismuth germanate (Bi4Ge3O12, BGO) crystal. The optical sensing unit is composed mainly of two polarizers and a block of BGO crystal with the shape of parallelogram. The BGO crystal itself can produce an optical phase bias of π/2, and it can be used as both a current sensing element and an electrooptic compensator. The change of magnetooptic rotation angle through the crystal can be compensated in real time by the change of electrooptic phase retardation caused by the applied voltage, thus the closed-loop optical measurement of current (or magnetic field) can be achieved. The 50 Hz ac current within 5 A is measured experimentally. The required compensating ac voltage is about 21.2 V/A in root-mean-square value. Experimental data show a good linear relationship between measured current and compensating voltage, and the nonlinear error is less than 1.7%.
Thermoelectric properties of the Bi2Te3 nanocrystalline bulk alloy pressed by the high-pressure sintering
Wu Fang, Wang Wei
2015, 64 (4): 047201. doi: 10.7498/aps.64.047201
Abstract +
Bi2Te3 nanowires and nanoparticles are synthesized by hydrothermal method, and the nanopowders are pressed into bulk pellets by high-pressure sintering or vacuum hot-pressed. The scanning electron microscope (SEM) results and thermal properties of such bulk samples are compared. The SEM result shows that the grain size of the high-pressure sintering sample is much smaller than that of the hot-pressed sample. The thermal properties show that the electrical resistivity, Seebeck coefficient, and thermal conductivity of the high-pressure sintering sample are all better than those of the hot-pressed sample. The ZT value of the high-pressure sintering sample prepared by nanowires reaches 0.5 at room temperature, which is much higher than that of the hot-pressed sample. Therefore the high-pressure sintering provides an effective method to press nanopowders to bulk.


Atomic configurations of dislocation cores in a small-angle grain boundary of 3C-SiC film
Cui Yan-Xiang, Wang Yu-Mei, Li Fang-Hua
2015, 64 (4): 046801. doi: 10.7498/aps.64.046801
Abstract +
[110] images are taken for 3C-SiC/(001)Si hetero epitaxial films containing small-angle grain boundaries by using a 200 kV LaB6 filament high-resolution transmission electron microscope. Deconvolution processing is performed to transform the experimental images which do not represent intuitively the projected crystal structure into structure images. First, Si and C atomic columns with a distance of 0.109 nm are resolved in a perfect structure image region, and then recognized from each other by analyzing the image contrast change with sample thickness based on the pseudo-weak phase object approximation. Subsequently, two complex dislocation cores located in the vicinity of small-angle grain boundaries are obtained at an atomic level, and the atomic structure models are constructed and confirmed by matching the experimental images with the simulated ones. Hence, the atomic configurations of dislocation cores are derived from only a single experimental image with the average structure of perfect crystal known in advance. The formation of small-angle grain boundaries in 3C-SiC/Si with the occurence of complex dislocations in their vicinity is discussed.
A molecular dynamics study of temperature and depth effect on helium bubble released from Ti surface
Liang Li, Tan Xiao-Hua, Xiang Wei, Wang Yuan, Cheng Yan-Lin, Ma Ming-Wang
2015, 64 (4): 046103. doi: 10.7498/aps.64.046103
Abstract +
Using molecular dynamics simulation, the effects of temperature and depth of helium bubble on volume, pressure and releasing process of helium bubble in metal Ti are investigated. First, through studying the states of helium bubble at different depths at room temperature, the variation regularities of volume, pressure and releasing process of helium bubble with its depth are acquired. The results show that with depth augmenting, the pressure of helium bubble increases gradually, while the volume decreases, but these two parameters are kept at some level when the depth is greater than 2.6 nm. Then, the evolutions of model system with helium bubble at various temperatures are simulated. The critical temperatures of helium bubble released from Ti surface at different depths are greatly different. On the whole, the critical temperature is in direct proportion to depth. But the releasing rates at different temperatures are almost unanimous. Finally, the mechanism of helium bubble released from Ti surface is explained on the basis of statistics and analyses of pressure of helium bubble and tensile strength of the metal thin film above the bubble. It is found that helium bubble would tear the Ti film above it when the pressure in helium bubble is greater than the strength of Ti film, and then helium atoms will be released from the metal.
Electronic properties of doped hexagonal graphene
Tian Wen, Yuan Peng-Fei, Yu Zhuo-Liang, Tao Bin-Kai, Hou Sen-Yao, Ye Cong, Zhang Zhen-Hua
2015, 64 (4): 046102. doi: 10.7498/aps.64.046102
Abstract +
Zigzag- and armchair-edged hexagonal graphenes are sandwiched between two Au electrodes to construct molecular nanodevices, and the effects of the orderly and locally doped with B, N, and BN for such graphene nanoflakes are considered, respectively. Based on the first-principles method, the electronic transport properties of these devices are investigated systematically. Our calculated results show that the using of B and BN to dope armchair-edged hexagonal graphenes can modulate the electronic transport properties significantly. Intrinsic and doped zigzag-hexagonal graphenes presents a semiconductoring behavior, and when it is doped with N and BN, there appears a negative differential resistance (NDR) phenomenon, especially for N-doping, and a very obvious NDR can be observed in zigzag-edged hexagonal grapheme: this might be important for developing molecular switches. The underlying causes for these findings are clearly elucidated by the transmission features and the doping-induced changes in electronic properties of a hexagonal graphene.
Effect of intense laser irradiation on the structural stability of 3C-SiC
Deng Fa-Ming, Gao Tao, Shen Yan-Hong, Gong Yan-Rong
2015, 64 (4): 046301. doi: 10.7498/aps.64.046301
Abstract +
Using the linear response method based on the density functional perturbation theory, we simulate the effect of intense laser irradiation on the zinc-blende structural stability of silicon carbide crystal. By calculating the phonon dispersion curves for the 3C-SiC crystal of the zinc-blende structure at different electronic temperatures, we find that the transverse acoustic phonon frequencies of 3C-SiC become imaginary as the electron temperature increases. The critical electronic temperature is 3.395 eV. This means that the lattices of 3C-SiC become unstable under the intense laser irradiation. These results are very similar to the previous results for the diamond structure(C and Si) and the zinc-blende structure (GaAs and InSb). In an electron temperature range of 0-4.50 eV, the LO-TO splitting at Γ gradually increases with the increase of electronic temperature. When the electron temperature is beyond 4.50 eV, the splitting decreases. The results indicate that only under the intense enough laser irradiation, the ionic strength can be weakened by the electronic excitation.
Dynamic stability of Zr under high pressure and high temperature
Hu Cui-E, Zeng Zhao-Yi, Cai Ling-Cang
2015, 64 (4): 046401. doi: 10.7498/aps.64.046401
Abstract +
The phase transitions and structure stabilities of materials have always attracted much attention of the experimental and theoretical investigators. When calculating the phonon dispersion of the cubic structure of the transition metal Zr (β -Zr), the traditional methods always give the negative phonon frequencies. So the quasi-harmonic approximation cannot solve this kind of problem. We obtain the phonon dispersion of β -Zr at high pressure and high temperature by using the newly developed self-consistent ab initio lattice dynamics method, which can well consider the phonon-phonon interactions. And then the stable region of β -Zr in the high pressure and high temperature phase diagram is predicted. The full phase diagram of Zr is also predicted. We also obtain the high temperature equation of state (EOS) and thermal expansion of β -Zr, which can help to construct the EOS data base of Zr.
The effect of temperature on the mechanical properties of the diamond coating at the film-substrate interface
Jian Xiao-Gang, Zhang Yun-Hua
2015, 64 (4): 046701. doi: 10.7498/aps.64.046701
Abstract +
The model of the diamond coating at the film-substrate interface is established by using the molecular dynamic method. The interaction between the atoms in this model is described by the Morse potential function and Tersoff potential function. Based on the above, we carry out the molecular dynamic simulation of the mechanical properties of the model in a temperature range from 0 to 800 K. The simulation results show that the tensile strength of diamond coating at the film-substrate interface presents a downward trend as the temperature rises from 0 to 800 K: the downward trend is evident when the temperature is in a range of 0-300 K, and the downward trend is smooth when the temperature is in a range of 300-800 K. Meanwhile, the variation of system energy with temperature presents a downward trend similar to the variation trend of the tensile strength.
Fluorescence resonance energy transfer between CdTe quantum dots and copper phthalocyanine
He Zhi-Cong, Li Fang, Li Mu-Ye, Wei Lai
2015, 64 (4): 046802. doi: 10.7498/aps.64.046802
Abstract +
The fluorescence resonance energy transfer in CdTe quantum dots (QDs)-copper phthalocyanine (CuPc) is investigated by ultrafast time-resolved spectroscopy technique equipped with femtosecond laser (780 nm, 76 MHz, 130 fs). The results show that the fluorescence lifetime of CdTe QDs decreases with the increase of CuPc concentration, and the energy transfer efficiency is found to increase with the increase of CuPc concentration. Moreover, the influence of the laser excitation power on the energy transfer efficiency is also studied. It is found that transfer efficiency decreases as excitation laser power increases, the physical mechanism is the thermal activation in the high power and the excited state transitions of high order induced by two-photon. The energy transfer efficiency can reach 43.8%, when the laser power is 200 mW, via two-photon excitation. This study indicates that the CdTe QDs-CuPc composite system has high potential as the third generation of photosensitizers.
Nanopore change law and mechanism of polyacrylonitrile based carbon fiber precursor in spinning process
Tang Hai-Tong, Ao Yu-Hui, Wang Cong, Zhao Rui-Xue, Gao Zhong-Min, Meng Fan-Ling
2015, 64 (4): 046101. doi: 10.7498/aps.64.046101
Abstract +
In this paper, we quantitatively characterize the morphological structure parameters including the nanopore size, shape, volume fraction, absolute number of nanopores and total prosity of polyacrylonitrile based carbon fiber precursor. Meanwhile, the change law and reason in the process of washing, drawing in washing, heat-densification, drawing in high pressure steam and hoting-stabilization are investigated. Results show that spinning drawing and high-temperature heat treatment make the prosity of fibers decline gradually in the process of fabrication. The result of micropore volume fraction Vi shows that at the beginning of the spinning and drawing in washing process the Vi of smaller nanopore which is less than 10 nm3 and the Vi of greater nanopore which is larger than 103 nm3 are 0.217 and 0.369, respectively, while these values sharply turn to 0.948 and 0.015 after the late spinning process of hoting-stabilization. The reason for this is not the increase of content of smaller nanopore content in the drawing process in high pressure steam and hoting-stabilization, but the sharp decrease of the greater nanopore content. The result about nanopore shape shows that the spinning multiple drawing in the process increases the axial (long-axis-to-short-axis) ratio of nanopores, while heat treatment over the glass transition temperature reduces the axial ratio of nanopore, and this shrinkage is more significant for smaller nanopores.
Performance evaluation of the simulated daily average temperature series in four seasons in China by Beijing Climate Center climate system model
Zhao Shan-Shan, He Wen-Ping
2015, 64 (4): 049201. doi: 10.7498/aps.64.049201
Abstract +
In the present paper, the detrended fluctuation analysis (DFA) method is first used to analyze the daily average temperature records in four seasons in China, and the results show that the seasonal temperature records exhibit long-range correlation in China, especially in Xinjiang and Xizang in western China. Based on the long-range correlation in observational temperature records, we use DFA to evaluate the performances of the simulated daily average temperature series in four seasons in China by Beijing Climate Center climate system model (BCC_CSM) (1.1 m), and find that the BCC_CSM (1.1 m) can reflect the long-range correlations in different seasons. In general, the simulated results are best in spring except for the bad performance in Jiangnan. In summer, the simulation performance is poor in middle-east China and most areas in Tibet, especially in the southern North China, western Huanghai, Jiangnan and South China. The long-rang correlation of the simulated data for autumn is stronger in Northeast China, southeast North China, while weaker in the most of Northwest China. In winter, except for the eastern seaboard, the simulated long-range correlations of daily temperature are weaker than that of observational records in most China. And the simulated performance is poor in Northwest China, Southwest China, northern South China, southern Jiangnan and northern Northeast China, especially in the western Tibet.
Improvement and adaptability evaluation of standardized precipitation evapotranspiration index
Zhao Jing, Yan Deng-Hua, Yang Zhi-Yong, Hu Yong, Weng Bai-Sha, Gong Bo-Ya
2015, 64 (4): 049202. doi: 10.7498/aps.64.049202
Abstract +
In view of the question about larger estimate error in arid areas by using the Thornthwaite method of estimating potential evaporation in the process of calculating standardized precipitation evapotranspiration index, we use the FAO Penman-Monteith method instead of Thornthwaite method to improve the method of calculating the standardized precipitation evapotranspiration index. Based on the 1961-2013 daily meteorological data offered by 541 stations of Meteorology Bureau, the distribution of test and standardized rainfall index, Palmer drought severity index and soil moisture are used to analyze the consistency with standardized rainfall evaporation index when used to evaluate drought in the applicability of area and season. Result shows that the improvement on the method of evaporation capacity calculation can significantly expand the application of standardized precipitation evapotranspiration index in area and season, making standardized precipitation evapotranspiration index applied to national drought assessment well, making up the shortcomings in the applicability of standardized precipitation evapotranspiration index in winter at a short time scale level in arid region. In addition, both yearly time scale and monthly time scale of drought assessment ability about modified standardized precipitation evapotranspiration index are improved, meeting the demand for drought assessment in our country, which is given priority to seasonal drought.
Stable components in extended-range forecasting during the continuous high temperature event in August 2013 over the mid-eastern China
Zeng Yu-Xing, Ye Tian-Shu, Wang Kuo, Shen Qian
2015, 64 (4): 049203. doi: 10.7498/aps.64.049203
Abstract +
Based on the continuous high temperature process over the mid-eastern China in August 2013, using the NCEP/NCAR (United States National Centers for Environmental Prediction/National Center for Atmospheric Research) daily average of 500 hPa height field, the wind field reanalysis data, and the NOAA (National Oceanic and Atmospheric Administration) reconstruction sea surface temperature (SST) data, through the selection method similar to the early adoption of SST forcing, band-pass filtering and empirical orthogonal function decomposition method to extract the 10-30 days of stable components, and through a stable component of diagnostic analysis, we investigate the mechanisms for sustaining and reducing high temperature process. Results show that by selecting and using the case that is the most similar to a pre-SST forcing 30-year climatology instead of the normal 30-year climatology (1981-2010), the steady-state component extracted climate proportion is reduced, and the proportion of anomalously stable components is significantly enhanced and the described influence strength and stability are improved significantly, which can more clearly show the extended maintenance mechanism of weather processes. It suggests that early consideration SST forcing in the extraction component is very necessary. Meanwhile, the analysis of extension of stable components shows that the process of maintaining and reducing high temperature is mainly caused by the combined effect of the Arctic Oscillation, continental high latitudes zonal circulation situation in Asia and the western Pacific subtropical high intensity and location.
Characterizations of clusters generated by pure xenon and hydrogen xenon gas mixture at room temperature
Zhao Jia-Rui, Li Yi-Fei, Ma Jing-Long, Wang Jin-Guang, Huang Kai, Han Yu-Jing, Ma Yong, Yan Wen-Chao, Li Da-Zhang, Yuan Da-Wei, Li Yu-Tong, Zhang Jie, Chen Li-Ming
2015, 64 (4): 042101. doi: 10.7498/aps.64.042101
Abstract +
Rayleigh scattering method can be used to investigate the cluster size and the cluster formation process, and its advantages are that it is easy to perform and non-disruptive. In this paper, by measuring the Rayleigh scattering intensities of clusters generated respectively in pure xenon gas and hydrogen-xenon gas mixture, the relationships of Rayleigh scattering intensity to time, backing pressure, and mixture ratio are studied, and according to these relationships, the average sizes of clusters under different conditions are estimated. Through the scaling law of the Rayleigh scattering intensity obtained in hydrogen-xenon gas mixture with respect to upstream gas pressure, i.e., I= (1.5 10-5)P6.47, the hydrogen of mixed gas is found to be conducible to the generating of xenon clusters. The advantages of hydrogen-xenon gas mixture for generating clusters are analyzed theoretically from the perspective of thermodynamics and intermolecular forces, and a new phenomenon, i.e., the hydrogen xenon gas mixture is not easy to liquefy, is found. This finding provides a new way to generate larger size clusters. Our results are expected to provide guidelines for the future experimental researches of the X-ray generated by xenon clusters and of the neutron generated by the deuterium-xenon mixture gas.
Angular resolution of a neutron scatter imaging system
Zhang Mei, Zhang Xian-Peng, Li Kui-Nian, Sheng Liang, Yuan Yuan, Song Chao-Hui, Li Yang
2015, 64 (4): 042801. doi: 10.7498/aps.64.042801
Abstract +
Using a combination of imaging and spectroscopic capabilities, neutron scatter imaging is a novel method of detecting neutrons in an energy range from 1 to 20 MeV. The technique can be applied to measurements in a variety of areas, including solar and atmospheric physics, radiation therapy, and nuclear materials monitoring. Angular resolution is an important parameter for a neutron scatter imaging system. There are some factors causing the uncertainty in the reconstructed image due to the imperfection of the detector system and natures of neutron scattering. These factors mainly are the uncertainties of the position and the energy. In this paper, the contributions of these factors to the angular resolution are discussed. The results show that the angular resolution varies with scatter angle; the position uncertainty not only directly affects the angular resolution, but also indirectly contributes to the angular uncertainty by influencing energy uncertainty; when the detector dimension is less than 5 cm, the energy uncertainty becomes a dominating factor for angular resolution. The prototype is designed based on the above analysis results. The angular resolution of the designed prototype is tested on Cf252 source. The experimental results are basically consistent with the simulation results.
Computational study of structures and electronic properties of SimGen (m+n=9) clusters
Wu Li-Jun, Sui Qiang-Tao, Zhang Duo, Zhang Lin, Qi Yang
2015, 64 (4): 042102. doi: 10.7498/aps.64.042102
Abstract +
The researches of the structural and electronic properties of silicon and germanium clusters are of great significance for developing novel microelectronic materials. This paper aims to study the geometric structures and electronic properties of SimGen (m+n=9) clusters by combining genetic algorithm and density functional tight binding method. The study shows that there are two low energy stable atomic stacking configurations for SimGen(m+n = 9) clusters: one is a pentagon double cone stacking two small adjacent pyramids, the other is a tetrahedron close packing with a Ge atom on a bridge. Both stacking configurations are changed greatly with gradually increasing the Ge atom number in the cluster. The shape of the lowest-energy configuration changes from the pentagon double cone stacking two adjacent pyramids on the same side into the pentagon double cone stacking two adjacent pyramids on both sides of the up and down. With this change, the electron distribution and the gap of the highest occupied molecular orbital and the lowest unoccupied molecular orbital gap are obviously dependent on the difference in components of Ge and Si elements contained.


Photon and photoelectron emission of the atom under the action of high-frequency laser pulse
Cui Xin, Li Su-Yu, Guo Fu-Ming, Tian Yuan-Ye, Chen Ji-Gen, Zeng Si-Liang, Yang Yu-Jun
2015, 64 (4): 043201. doi: 10.7498/aps.64.043201
Abstract +
By numerically solving the time-dependent Schrdinger equation, we investigate the ionization probability, photoelectron spectrum, and harmonic emission spectrum of the atom under the action of high-frequency laser pulses. It is found that with the increase of incident laser pulse intensity, the ionization probability of the atom first increases to a maximum value gradually and then decreases, and in this process, both the photoelectron spectrum and high-order harmonic generation spectrum change from a single-peak structure to a multi-peak one. Through the time-frequency analysis of the harmonic emission spectrum, we also find that the harmonic emission is suppressed around the pulse peak, and it occurs at the rising edge and the falling edge, which interfere with each other, thus forming the multi-peak structure. Utilizing the laws of the changes of photoelectron and harmonic spectra with incident laser pulse intensity, we can diagnose the laser intensity at which the atomic ionization suppression occurs.
Ground state properties and excitation properties of ZnSe under different external electric fields
Li Shi-Xiong, Wu Yong-Gang, Linghu Rong-Feng, Sun Guang-Yu, Zhang Zheng-Ping, Qin Shui-Jie
2015, 64 (4): 043101. doi: 10.7498/aps.64.043101
Abstract +
The Hartree-Fork (HF) method with LANL2DZ basis set is used to investigate the equilibrium structures, atomic charge distributions, the highest occupied molecular orbital (HOMO) energy levels, the lowest unoccupied molecular orbital (LUMO) energy levels, energy gaps, dipole moments, harmonic frequencies and infrared intensities of ZnSe under different external electric fields ranging from -0.025 to 0.040 a.u. The excitation energies, transition wavelengths and oscillator strengths under the same external electric fields are calculated by the time-dependent-HF method. The results show that the bond length and electric dipole moment are proved to be first decreasing, and then increasing with the variation of the external field; the total energy is found to decrease linearly with the variation of external field; but the HOMO energy and energy gap are proved to increase with the variation of external field. The harmonic frequency and LUMO energy are found to first increase, and then decrease, but the infrared intensities are proved to first decrease, and then increase. The external electric field has significant effect on the excitation properties of ZnSe molecule. The excited energies from ground state to the first nine excited states are found to increase, and the transition wavelengths are decreasing with the variation of the external field. Meanwhile, the strongest excited state becomes very weak, and the weak excited state becomes strongest by the external field. The excitation properties of ZnSe material can be changed with external electric field.
Elastic collisions between excited-state Li and ground-state Ar atoms at low temperature and analytic potentic energy function and molecular constants of the LiAr (A2Π) radical
Han Ya-Nan, Jiang Gang, Fan Quan-Ping, Gao Yu-Feng, Du Ji-Guang
2015, 64 (4): 043401. doi: 10.7498/aps.64.043401
Abstract +
The potential energy curve (PEC) for the first excited state (A2Π) of LiAr is calculated using the multireference configuration interaction method in combination with the basis set, ang-cc-PCVQZ. The Davidson correlation (+Q) and the scalar relativistic effect (+DK) are taken into account in the calculations. And PEC is fitted to analytical Hartree-Fock-dispersion potential function, thereby determining the spectroscopic parameters. These obtained parameters are in excellent agreement with the available experimental and theoretical values. By solving the radial Schrödinger equation of nuclear motion, the vibration levels, rotary inertia and six centrifugal distortion constants (Dv, Hv, Lv, Mv, Nv, Ov) are obtained for the first time. The elastic collisions between the excited-state Li and the ground-state Ar atoms are investigated at low and ultralow temperatures when the two atoms approach to each other along the LiAr (A2Π ) interaction potential. The total and various partial-wave cross sections are calculated at energies from 1.0×10-12 to 1.0×10-3 eV by numerical calculation. The effect of each partial-wave cross section on the total elastic cross section is discussed carefully. The results show that the total elastic cross section is very large and almost constant at ultralow temperatures, and its shape is mainly dominated by the s-partial wave. But with the increase of collision energy, contribution of s-partial wave to the total cross section decreases and the contribution of higher-order partial wave to scattering cross section increases gradually.
Investigation of quantum discord for two-spin system
Wang Dan-Qin, He Chuang-Chuang
2015, 64 (4): 043403. doi: 10.7498/aps.64.043403
Abstract +
By adopting the concept of the geometric measure of quantum discord, we explore the property of quantum correlation in the two-spin Heisenberg model, gain the analytic expression of quantum discord in the general case, and discuss the influences of the coupling constant, temperature, the intensity of the external magnetic field on magnitude of the quantum correlation. The corresponding scheme of tuning quantum correlation is also given in this paper. In addition, we find that quantum discord has a sudden transition in the lower temperature. Results show that adjusting systematic parameters, which are temperature, coupling strength, magnetic field intensity, etc, is an effective way to control the value of quantum correlation in the double spin Heisenberg model system. This provides a certain reference and significant guidance for the precise control of quantum discord and realizing the teleportation of quantum state and the design of quantum logic gates.
Influence of isotopic effect on the stereodynamics of reaction H+NH→N+H2
Wang Ming-Xin, Wang Mei-Shan, Yang Chuan-Lu, Liu Jia, Ma Xiao-Guang, Wang Li-Zhi
2015, 64 (4): 043402. doi: 10.7498/aps.64.043402
Abstract +
The stereodynamics of the H+NH reaction and its isotopic variants are investigated by the quasi-classical trajectory method at the collision energies of 8 kcal/mol and 16 kcal/mol based on the ground state potential energy surface of NH2 reported by Zhai and Han [Zhai H S, Han K L 2011 J. Chem. Phys. 135 104314]. Vector correlations of k- j' and k- k'- j', such as angular distributions of P(θr), P(φr), P(θr, φr) and the distributions of the polarization-dependent differential cross-sections are discussed in detail. The results indicate that for the two collision energies, the isotopic effect on sterodynamic property of H+NH reaction is apparent which could be attributed to the difference in mass factor in isotopy-susbstituting reaction.
Organic memristive devices based on DNA embedded in silver nanoparticles layer
Wang Yuan, Dong Rui-Xin, Yan Xun-Ling
2015, 64 (4): 048402. doi: 10.7498/aps.64.048402
Abstract +
Two-terminal electrical bistable device is fabricated with structure “Al/deoxyribonucleic acid-cetyltrimethylam- monium bromide/silver nanoparticles/deoxyribonucleic acid-cetyltrimethylammonium bromide/indium tin oxide”, and I-V curves are measured. The results show that the conductivity and the memristive characteristics are significantly improved by the embedding Ag nanoparticles layer. The optimal particle diameters are in a range of 15 - 20 nm, and the maximum on/off current ratio can reach 103. It is also found that I-V characteristic of the device depends on the sweeping voltage amplitude VA. As VA increases, switching voltages (VSET, VRESET) and the on/off current ratio ION/IOFF increase. Furthermore, the transition between high-and low-resistance-state depends on the direction of the applied electric field, which shows that the device possesses polarity.
The model of interdependent network based on positive/negativecorrelation of the degree and its robustness study
Chen Shi-Ming, Lü Hui, Xu Qing-Gang, Xu Yun-Fei, Lai Qiang
2015, 64 (4): 048902. doi: 10.7498/aps.64.048902
Abstract +
The model of interdependent network based on positive/negative correlation of the degree is constructed by the typical Barabási-Albert network in this paper. Dependency modality and dependency degree are considered in the model. Two parameters F and K are defined, which represent the proportion of dependency node and the redundancy of dependency, respectively. We study the influences of different values of F and K on the robustness of interdependent network in cascading failures under degree-based attacks and random attacks and also compare the results with those from the random interdependent network model. The simulation results show that the robustness of both random independency and interdependent network based on positive/negative correlation of the degree decreases as F increases and increases as K increases; in the model of full interdependence (F = 1), the robustness of interdependent network based on positive correlation of the degree is optimal under random attacks; the interdependent network based on negative correlation of the degree shows stronger robustness in the model of partial interdependence (F= 0.2, 0.5, 0.8). While the interdependent network based on positive correlation of the degree shows poorer robustness with any value of F under degree-based attacks.
Chaos control and anti-control in Boost converter based on altering correlation
Zhang Fang-Ying, Hu Wei, Chen Xin-Bing, Chen Hong, Tang Xiong-Min
2015, 64 (4): 048401. doi: 10.7498/aps.64.048401
Abstract +
Chaos control and anti-control are one pair of inverse problems. In this paper, the correlation of system state variables is investigated, and the method of realizing the chaos control and anti-control of system under the condition of variation of correlation coefficients of current controlled continuous current mode Boost converter is analyzed. The above these lay the theoretical foundation for practical applications. Discrete-time model of system is established. The mechanisms of chaos control and anti-control in Boost converter are theoretically explained by monodromy matrix theory. The research results indicate that only when the correlation coefficient of system is changed, the Boost converter can be controlled from any state to period 1, 2, 4 orbits or chaotic state, which means that the output of the system can realize chaos control and anti-control. Simulation results verify the analysis results.
Load-induced cascading failure in interdependent network
Peng Xing-Zhao, Yao Hong, Du Jun, Wang Zhe, Ding Chao
2015, 64 (4): 048901. doi: 10.7498/aps.64.048901
Abstract +
The study of load-induced cascading failures in interdependent networks is of great realistic significance, which can provide valuable reference for designing high robust interdependent network or improving their robustness. In this paper, we establish a cascading model for a double layer interdependent network, and study the effects of the contributions of inter-degree and intra-degree to the loads, the coupling, and the intra-node linking similarity on the cascading failure in the interdependent network. Our studies show that when the contributions of inter-degree and intra-degree to the loads attain some values, the interdependent network reaches the highest robustness against cascading failures. As a notable feature for the interdependent network that is different from an isolated network, the coupling must have a significant influence on cascading failure in the interdependent network. In order to reach higher robustness, we suggest that the disassortative coupling be used and the inter-degree be made as homogeneous as possible under condition that a larger average inter-degree is adopted. In addition, we find that it is contrary to the case of neglecting loads that when the Pearson correlation coefficient for measuring the intra-layer degree-degree relation is larger, the interdependent network is more robust against cascading failures.
Experimental study on multicolor two-photon excited fluorescence microscopy
Qiu Jun-Peng, Liang Run-Fu, Peng Xiao, Li Ya-Hui, Liu Li-Xin, Yin Jun, Qu Jun-Le, Niu Han-Ben
2015, 64 (4): 048701. doi: 10.7498/aps.64.048701
Abstract +
Two-photon excited fluorescence (TPEF) microscopy is a nonlinear optical microscopy technique. The advantages of TPEF microscopy include high temporal and spatial resolutions, high signal-to-noise ratio and inherent three-dimensional sectioning. In traditional TPEF microscopy, a wavelength tunable ultrashort pulsed laser is used as an excitation source. In practical applications, sample usually contains various fluorophores or unknown components. Therefore the excitation wavelength of the ultrafast laser has to be tuned to achieve optimal excitation efficiencies of various fluorophores. In order to acquire the fluorescent signals of different fluorophores simultaneously, we develop a multicolor TPEF microscope system based on a supercontinuum laser source. In experiments, TPEF images of Lily rhizome sample slide stained by two fluorescent dyes with different excitation and emission wavelengths are obtained without tuning the wavelength. Experimental results show that the high-contrast TPEF images of the sample with various fluorophores can be obtained simultaneously by using the multicolor TPEF microscope compared with by using traditional TPEF microscopy. The system is simple in structure, easy in operation, and can provide rich information about the sample, which allows it to be widely used in life and material sciences.