Vol. 57, No. 3 (2008)

Approimate solution for three dimentional equatorial sea-air oscillator model
Mo Jia-Qi, Lin Wan-Tao
2008, 57 (3): 1291-1294. doi: 10.7498/aps.57.1291
Abstract +
An equation for the equatoral Kelvin wave is considered. By using the variational iteration method, the approximate solution is studied. The variational iteration method is an analytic method, the obtained solution can be analytic operation sequentially.
The auxiliary equation for constructing the exact solutions of the variable coefficient combined KdV equation with forcible term
Taogetusang, Sirendaoerji
2008, 57 (3): 1295-1300. doi: 10.7498/aps.57.1295
Abstract +
Based on the auxiliary equation method, a method of auxiliary equation of elliptic function combined with function transformation is proposed. The method is applied to constructed the Jacobi-like elliptic function exact solutions, degenerated solitary-like solutions and triangle-like function wave solutions of variable coefficient combined KdV equation with forcible term with the help of symbolic computation system Mathematica.
On d-δ commutation relation of constrained differential systems
Guo Yong-Xin, Zhao Zhe, Liu Shi-Xing, Liu Chang
2008, 57 (3): 1301-1306. doi: 10.7498/aps.57.1301
Abstract +
An important problem of calculus of variations used in constrained differential systems, i.e., the commutation relation of differential operator and variational oprerator, is investigated by means of Frobenius theorem of integrability. Based on analyzing the d-δ commutation relation for the linear stationay differential constrained systems and affine differential constrained systems, the relationship between noncommutator of differentiation and variation and nonholonomicity of the differential constraints is briefly proved by means of Frobenius integrability theory. The commutation relation for non-linear differential constrained systems is also discussed in the paper. Finally, three examples are given to verify the results.
The study of symmetries and conserved quantities for one-dimensional damped-amplified harmonic oscillators
Lou Zhi-Mei
2008, 57 (3): 1307-1310. doi: 10.7498/aps.57.1307
Abstract +
In this paper, a constant of motion of one-dimensional damped-amplified harmonic oscillators is derived from Newton's equations, and the Lagrangian and the Hamiltonian of system are expressed in term of the constant of motion. According to the expression of the Hamiltonian, we make an ansatz for the conserved quantity and then three conserved quantities are obtained by using the definition of Poisson bracket. The Noether symmetry and Lie symmetry of the infinitesimal transformations of the three conserved quantities are studied and the essence of symmetries and conserved quantities are also explained in this paper.
A special nonholonomic mechanical system calculated by symplectic method
Liu Shi-Xing, Guo Yong-Xin, Liu Chang
2008, 57 (3): 1311-1315. doi: 10.7498/aps.57.1311
Abstract +
This paper studies numerically a special nonholonomic mechanical system. A better algorithm of structure-preserving is adopted to calculate numerically and compare it to the classical R-K method. By comparing the results of two methods, the advantage of symplectic method used on this special nonholonomic mechanical system is presented.
Time-dependent perturbation theory of KdV soliton
Pan Liu-Xian, Yu Hui-You, Yan Jia-Ren
2008, 57 (3): 1316-1320. doi: 10.7498/aps.57.1316
Abstract +
The effects of the periodical time-dependent perturbation on a KdV (Korteweg de Vries) soliton are studied. Expanding the perturbation term into a Fourier series, we find that the time-independent term will lead to the secular terms. In this paper, the soliton parameters (height, width and velocity) are derived by eliminating the secular terms, and the corrections on a soliton caused by perturbation are obtained with the help of other terms in Fourier series in the first-order approximation.
Chaotic motion of some relative rotation nonlinear dynamic system
Shi Pei-Ming, Liu Bin, Hou Dong-Xiao
2008, 57 (3): 1321-1328. doi: 10.7498/aps.57.1321
Abstract +
The chaotic motion of a relative rotation nonlinear dynamic system possessing both homoclinic and heteroclinic orbits is investigated. Firstly, the dynamics equation of relative rotation nonlinear dynamics system with nonlinear stiffness and nonlinear damping and forcing excitation is deduced. Secondly, a global bifurcation of the system and a probable route leading to chaos have been discussed by using Melnikov method, and the necessary condition of chaotic motion of system is presented. The chaotic motion of system is complemented by top Lyapunov exponents maps, bifurcation maps, Poincare maps and phase plane plots.
Stability of equilibrium state of a kind of nonlinear relative rotation dynamic system and associated harmonic approximate solution
Meng Zong, Liu Bin
2008, 57 (3): 1329-1334. doi: 10.7498/aps.57.1329
Abstract +
The nonlinear dynamic equation with two masses in relative rotation is established, which contains a kind of generalized nonlinear elastic force. Using variable gradient method, the Lyapunov function is gotten, and the stability of the relative rotation nonlinear autonomous system is studied. The approximate solution of the associated harmonic response of the relative rotation nonlinear non-autonomous system under two forcing excitations of different frequencies is obtained by the method of perturbation.
Geometrical explanation and application of some algebraic direct methods
Zhang Shan-Qing
2008, 57 (3): 1335-1338. doi: 10.7498/aps.57.1335
Abstract +
Based on the polygons of the differential equation, geometrical explanation for some algebraic direct methods is given, and its generalization of differential system is presented. Finally, the validity of this explanation is illustrated with variant Boussinesq system.
Teleportation of on N-particle GHZ state via one three-particle W state
Zha Xin-Wei, Zhang Chun-Min
2008, 57 (3): 1339-1342. doi: 10.7498/aps.57.1339
Abstract +
Recently Yang Hon-qin et al proposed a scheme for teleporting a three-particle GHZ state from a sender to either of two receivers with two three-particle W state quantum channel. In this paper, the theoretical analysis is given and the new scheme for teleporting an N- particle GHZ state using only one three-particle W state quantum channel is proposed.
Bright soliton solution in 1D Tonks-Girardeau gas
Liu Hong, Wei Jia-Yu, Lou Sen-Yue, He Xian-Tu
2008, 57 (3): 1343-1346. doi: 10.7498/aps.57.1343
Abstract +
Base on spherical symmetric trap treatment, we analyze how to change a generalized Gross-Pitaevskii equation to a quintic nonlinear Schrdinger equation. Analysing the nonlinear Schrdinger equation, we find a typical bright soliton solution in Tonks-Girardeau gas region. This will help experimental observations.
Recurrence spectra and closed orbits of He+2 in parallel electric and magnetic fields
Wang Xiao-Yan, Wang Peng-Cheng, Feng Sheng_Ping, Xie Jin_Dong
2008, 57 (3): 1347-1351. doi: 10.7498/aps.57.1347
Abstract +
By the semi-classical closed orbit theory and region-splitting consistent iteration method, we calculated the recurrence spectra and closed orbits of He+2 in parallel electric and magnetic fields. Using the new potential with electronic exchange interaction, complex channel quantum defects and molecular closed orbits theory, we discussed the influence of molecular core to the recurrence spectra and closed orbits.
Performance of various quantum-key-distribution systems using 1.55 μm up-conversion single-photon detector
Jiao Rong-Zhen, Feng Chen-Xu, Ma Hai-Qiang
2008, 57 (3): 1352-1355. doi: 10.7498/aps.57.1352
Abstract +
The performance of various quantum-key-distribution (QKD) systems is analyzed using 1.55 μm up-conversion single-photon detector. The dependence of quantum efficiency and dark count rate change on the pump power was also discussed. The comparison is based on the secure communication rate as a function of distance for three QKD protocols: the Bennett-Brassard 1984, the Bennett-Brassard-Mermin 1992, and the coherent differential-phase-shift keying protocols. We show that the up-conversion detector allows for higher communication rate and longer communication distance than the commonly used InGaAs/InP APD for all three QKD protocols, and the properties of quantum key distribution system can be greatly improved by this detector.


The design of entangled source for free space quantum communications
Wang Shao-Kai, Ren Ji-Gang, Jin Xian-Min, Yang Bin, Yang Dong, Peng Cheng-Zhi, Jiang Shuo, Wang Xiang-Bin
2008, 57 (3): 1356-1359. doi: 10.7498/aps.57.1356
Abstract +
We design and build an entanglement source suitable for free space quantum communications experiment. The coincidence counting rate after single mode fiber is 20000 cps. The entanglement visibility is more than 95% in horizontal vertical base and more than 90% in diagonal base. The Bell inequality was broken by more than 100 standard deviations in local experiment. The entanglement source satisfies the requirements for 20 km free space quantum communications experiment.
Exact solution of SU(2)-invariant Thirring model with non-diagonal open boundaries
Tang Mei-Juan, Wang Yan-Shen
2008, 57 (3): 1360-1364. doi: 10.7498/aps.57.1360
Abstract +
The SU(2)-invariant Thirring model with non-diagonal open boundaries in one spatial and one time dimensions is studied in the framework of quantum inverse scattering method. With the help of guage transformation independent of spectral parameter in the auxiliary space, suitable Fock vacuum state is constructed. The eigenvalues and its Bethe Ansatz equations of the transfer matrix are obtained by mean of Bethe Ansatz, and finally the boundary freedom degrees of the system are discussed.
Study on the traffic behavior of on-ramp system with two-lane main road under signal controlling
Teng Ya-Fan, Gao Zi-You, Jia Bin, Li Feng
2008, 57 (3): 1365-1374. doi: 10.7498/aps.57.1365
Abstract +
In this paper we investigate the two-lane main road on-ramp system with signal-controlling using the cellular automata traffic flow model. The traffic signal is setup at the merging part between the main road and the on-ramp so that it can control the vehicles of both roads. We simulate the effect of traffic signal on vehicle flows of main road and on-ramp, and the traffic capacity and average velocity at the merging part are discussed. Through the analysis of the phase diagram, it can be found that the on-ramp system with two-lane main road can embody more complicated and realistic traffic flow characteristics than the on-ramp system with single-lane main road. Compared with the model introduced by Jiang Rui [Jiang R 2003 J. Phys. A 36 11713], the simulation results indicate that the state of traffic flow is improved obviously and the capacity of the on ramp system has increased.
Transient properties of a tumor cell growth system driven by color Gaussian noises: Mean first-passage time
Wang Can-Jun, Wei Qun, Zheng Bao-Bing, Mei Dong-Cheng
2008, 57 (3): 1375-1380. doi: 10.7498/aps.57.1375
Abstract +
The transient properties (mean first passage time T)of the tumor cell growth system driven by color Gaussian noise are investigated. The approximate Fokker-Planck Equation is obtained based on the Novikov theorem and the Fox approach and the explicit expression of the mean first passage time is derived. The numerical computation results show that T behaves with different characters in the cases of 0λλλλT exhibits complex behavior, namely T has one maximum with the multiplicative noise intensity D and its self-correlation time τ1 increasing.
Influence of user requirement behaviors on internet collective dynamics
Ma Wei-Dong, Wang Lei, Li You-Ping, Shui Hong-Shou, Zhou Ming-Tian
2008, 57 (3): 1381-1388. doi: 10.7498/aps.57.1381
Abstract +
The complex network dynamics of the Internet is mainly influenced by user requirement behaviors, and can be statistic in time series. A large number of complex networks, both natural and artificial, share the presence of highly heterogeneous, scale-free degree distributions and small-world phenomena. This paper analyzed the empirical collective behavior of user requirements in a region, and discovered that the frequency and the in-degree distributions of bipartite networks constructed by user visiting web sites follows the power-law, and the exponent is between 1.7 and 1.8. A novel two-tier model, the virtual resource networks (VRN) and physics topology networks (PTN), is proposed to study the influences on the Internet collective behaviors. The mapping process mechanisens of VRN to PTN simulates how the dynamic behaviors of resource network influence the internet physics topology networks. The power-law characteristics of VRN can bring forth the result that the phase transition critical point moves left and network performance is more incapable. The distributed mapping process of VRN to PTN was constructed for the small subset with the high degree nodes, then the phase transition critical point of PTN moves right and the network performance is improved obviously.
Chaotic point process description of converter discrete subsystem and EMI suppression
Yang Ru, Zhang Bo, Qiu Dong-Yuan
2008, 57 (3): 1389-1397. doi: 10.7498/aps.57.1389
Abstract +
The converter is described as a continuous-discrete system based on hybrid system theory. According to the theory of chaotic PWM, chaotic point process model of converter is established. Chaotic PWM control is done with piece-wise chaotic maps. The characteristic function and distribution of chaotic PWM are obtained, the spectrum of chaotic PWM and periodic PWM are obtained too. Experimental results verify that the peak spectrum of chaotic converter can be suppressed with stable output, and EMI is improved distinctly.
An encryption approach to chaos synchronization communications by using CPRNG
Li Wei, Hao Jian-Hong, Qi Bing
2008, 57 (3): 1398-1403. doi: 10.7498/aps.57.1398
Abstract +
A data encryption approach to chaos synchronization communications by using a novel chaos-based pseudo-random number generator (CPRNG) is proposed. Chaotic sequence generated by the drive system is turned into encryption keys in CPRNG and the data can be alternately encrypted according to byte by using the keys. The advantages of the cryptosystem are its higher level of security and synchronization, and it is easily implemented by software.
Parameter identification based on linear feedback control for uncertain chaotic system
Li Nong, Li Jian-Fen, Liu Yu-Ping, Ma Jian
2008, 57 (3): 1404-1408. doi: 10.7498/aps.57.1404
Abstract +
An adaptive control method is proposed for the synchronization of chaos systems with uncertain parameters. Based on the Lyapunov stability theory, an adaptive control law of parameters is derived to make the states of the drive system and the response system asymptotically synchronized, by which the uncertain parameters of response system are identified. To demonstrate the effectiveness of the proposed scheme, numerical simulations results are given for the Lorenz system and Chua’s circuit.
A method for generating chaotic spread-spectrum sequences and their optimized selection algorithm
Yu Zhen-Biao, Feng Jiu-Chao
2008, 57 (3): 1409-1415. doi: 10.7498/aps.57.1409
Abstract +
A method for generating chaotic spread-spectrum sequences based on the combined chaotic map is proposed. An optimized selection algorithm based on the property requirement of spread-spectrum sequences and the performance index of multiple access interference is also presented. Simulation is performed for the optimized chaotic sequence, and an optimized logistic sequence is applied to a direct sequence spread-spectrum CDMA system under different channel conditions. The results show that the chaotic spread-spectrum sequences generated by the proposed method have similar performance as the logistic spread-spectrum sequences and have better security.
Study on the fractional-order Liu chaotic system with circuit experiment and its control
Chen Xiang-Rong, Liu Chong-Xin, Wang Fa-Qiang, Li Yong-Xun
2008, 57 (3): 1416-1422. doi: 10.7498/aps.57.1416
Abstract +
In this paper, applying frequency domain techniques based on Bode diagram, fractional-order Liu chaotic system is studied. An electronic circuit unit of tree shape is designed to realize the fractional-order chaotic Liu system. Circuit experiment of 2.7-order Liu system, as well as simulation results of fractional-order Liu chaotic system with α=0.8—0.1 in step size of 0.1, verify the circuit unit's effectiveness, and prove that chaos actually exists in the fractional-order Liu chaotic system with order as low as 0.3. A simple, but effective linear feedback controller is designed to realize the chaotic control of fractional-order Liu chaotic system.
The neighbor point selection method for local prediction based on information criterion
Meng Qing-Fang, Peng Yu-Hua, Qu Huai-Jing, Han Min
2008, 57 (3): 1423-1430. doi: 10.7498/aps.57.1423
Abstract +
The number of nearest neighbor points is an important parameter for the local prediction method, which has an important impact on the prediction accuracy and computation complexity of the local model. Based on the information criterion, the neighbor point selection method for the local prediction method is proposed in this paper. We illustrate this method by analyzing chaotic time series from Lorenz model and the experimental laser data- Santa Fe Data A. Simulation results show that using the proposed method to select neighbor points, the one-step and multi-step prediction accuracy of the local prediction method is good, and the computation complexity is reduced.
Adaptive control of uncertain chaotic systems with time delays using dynamic structure neural network
Zhang Min, Hu Shou-Song
2008, 57 (3): 1431-1438. doi: 10.7498/aps.57.1431
Abstract +
A kind of control methods is surveyed to deal with a class of nonlinear systems with uncertain time delay. By combining the Lyapunov-Krasovskii function and Lyapunov function, the time-delay compensator with adjustable parameters is presented to make the control input independent of the multiple time delays. At the same time, the dynamic structure adaptive neural network is introduced to eliminate the uncertainties in the chaotic system, which approximates the function with better relationship between the calculation rate and structure complexity by increasing hidden units when the tracking error is beyond the allowable bound. The demonstration with a given Duffing chaotic system shows the presented control method is effective.
A new hyperchaotic Lü system and its circuit realization
Liu Yang-Zheng
2008, 57 (3): 1439-1443. doi: 10.7498/aps.57.1439
Abstract +
The four-dimensional hyperchaos system is built by adding an additional state to the three-order Lü system. Some of its basic dynamical properties are studied briefly, such as the feature of equilibrium, the hyperchaos attractor, Lyapunov exponent and fractal dimension. An electronic circuit is designed to realize the four-dimensional hyperchaos system. Moreover, a novel analogue circuit is realized for the verification of various attractors.
Stability analysis of complex networks with multi-links
Gao Yang, Li Li-Xiang, Peng Hai-Peng, Yang Yi-Xian, Zhang Xiao-Hong
2008, 57 (3): 1444-1452. doi: 10.7498/aps.57.1444
Abstract +
In this paper,a new idea about network split is presented according to the different nature of the network links. Time-delay has been introduced into networks to effect the split and on that a model of complex dynamical networks with multi-links has been constructed. Based on Lyapunov theory,the stability analysis of networks with multi-links is also studied. The sufficient conditions of the stability of networks with time-delay and without time-delay are respectively presented. The validility of the results are proved by numerical simulation of this paper.
Nonlinear observer based full-state projective synchronization for a class of fractional-order chaotic system
Chen Xiang-Rong, Liu Chong-Xin, Li Yong-Xun
2008, 57 (3): 1453-1457. doi: 10.7498/aps.57.1453
Abstract +
In this paper, based on the stability theory of the fractional-order system, an idea of using state observer to realize the full-state projective synchronization of fractional-order chaotic system is proposed. The designed observer can achieve full-state projective synchronization in a class of nonlinear fractional-order systems without the limitation of partial-linearity, extend the scope of application of projective synchronization, and does not require the calculation of the conditional Lyapunov exponents. In addition, this synchronization method is simple and theoretically rigorous, capable to achieve a full-state synchronization of arbitrary scaling factor. Finally, the method has been applied to realize the full-state projective synchronization of fractional-order Rssle system, and the simulation results verified the effectiveness of the method.
Adaptive dual-model control and synchronization of generalized Hénon chaotic systems
Liu Fu-Cai, Liang Xiao-Ming, Song Jia-Qiu
2008, 57 (3): 1458-1464. doi: 10.7498/aps.57.1458
Abstract +
A kind of adaptive dual-model control and synchronization algorithm for generalized Hénon chaotic system was proposed. Chaos attractor of generalized Hénon map is much more complicated than that of Hénon chaotic systems. It is more difficult to control and synchronize. The generalized Hénon chaotic systems under consideration makes the communications system more secure. This algorithm adopts adaptive dual-model control, which realizes the tracking control and synchronization of generalized Hénon chaotic systems, and meanwhile advances the ability of restraining the parameter perturbation and stochastic disturbance. The robustness performance of controlled system is improved. Theoretical analysis and simulation results proved the effectiveness of this method.
Robust synchronization of a class of chaotic systems based on integral observer method
Li Xiu-Chun, Xu Wei, Xiao Yu-Zhu
2008, 57 (3): 1465-1470. doi: 10.7498/aps.57.1465
Abstract +
Using the integral-observer approach, chaos synchronization is achieved for a class of chaotic systems when both the parameters and the output of the system are perturbed. Based on Lyapunov stability theory and LMI technique, we give the sufficient criterion, which can make the drive system and the response system globally exponentially synchronized. In the end, we take MLC chaotic system as an example to verify the effectiveness of the proposed method.
A test method for weak nonlinearity in time series
Jiang Ke-Yu, Cai Zhi-Ming, Lu Zhen-Bo
2008, 57 (3): 1471-1476. doi: 10.7498/aps.57.1471
Abstract +
Nonlinearity is necessary for time series to be treated as chaotic time series. A new test statistic for nonlinearity, which is based on the ratio of the multistep normalized prediction error with respect to linear AR models and nonlinear AR models, is used to detect the weak nonlinear components contained in time series by the surrogate data method. Taking example for Lorenz time series, the effect of related parameters for test statistic estimation is analyzed. By the nonlinearity tests for chaotic time series, the proposed test statistic δNAR has better discrimination power for weak nonlinearity than the test statistic δAIC based on AIC rules and the zeroth order nonlinear prediction error δZP, which shows that the proposed test statistic has strong adaptive abilities for time series. And, for different time series, the parameters with best nonlinearity discrimination performance are kept constant. The stabilization of parameters facilitates the nonlinearity test for other time series.
Breaking a chaotic direct sequence spreading spectrum secure communication system
Hu Jin-Feng, Guo Jing-Bo
2008, 57 (3): 1477-1484. doi: 10.7498/aps.57.1477
Abstract +
In this paper, a novel method is proposed for the breaking of chaotic direct sequence spread spectrum (CD3S) secure communication system. Chaotic fitting is defined based on the concept of generalized synchronization, then the method based on unscented Kalman filter and chaotic fitting is presented based on the principle of CD3S and the characteristic that the information symbol varies slowly. Furthermore, addressing to the tracking error induced by the processing noise and chaotic fitting error, a modified unscented Kalman filter based on tracking-error-controlled factor is suggested. The CD3S is unmasked according to the error-amplitude of the tracking-error. We can extract the binary message signal from the CD3S signal without knowing either the structure or the parameters of the chaotic transmitter. Simulation results verify the method.
Projective synchronization of the fractional order unified system
Wang Xing-Yuan, He Yi-Jie
2008, 57 (3): 1485-1492. doi: 10.7498/aps.57.1485
Abstract +
This paper calculates the largest Lyapunov exponent and correction dimension of the fractional order unified system when changing the system parameter, and studies the dynamical behavior of this system. Based on the stability criterion of linear systems, a new approach for constructing projective synchronization of fractional order unified system is proposed. Numerical simulations of fractional order Chen system, fractional order Lü system and fractional order Lorenz-like system are provided to demonstrate the effectiveness of the proposed scheme.
Analysis and circuit implementation of a new four-dimensional non-autonomous hyper-chaotic system
Cang Shi-Jian, Chen Zeng-Qiang, Yuan Zhu-Zhi
2008, 57 (3): 1493-1501. doi: 10.7498/aps.57.1493
Abstract +
A new four-dimensional non-autonomous hyper-chaotic system is presented by adding input signal to a hyper-chaotic system based on Lorenz system. The resulting hyper-chaotic system may have any dynamic beharior among the periodic orbits, two-tori, chaos and hyper-chaos by controlling the frequency of input signal, while the periodic orbits are more prominent. The phenomenon in well demonstrated by numerical simulations and bifurcation analysis. Finally, an analog electronic circuit is designed to implement the new system,and the experimental results of the non-autonomous hyper-chaotic circuit well agreed with the simulation results.
Improving chaotic carrier fundamental frequency in VCSELs with optical feedback by strong light injection
Liu Sheng-Fang, Xia Guang-Qiong, Wu Jia-Gui, Li Lin-Fu, Wu Zheng-Mao
2008, 57 (3): 1502-1505. doi: 10.7498/aps.57.1502
Abstract +
In this paper, the influence of the external light injection on the chaotic carrier fundamental frequency of vertical-cavity surface-emitting lasers (VCSELs) with optical feedback have been investigated. The results show that, for the fixed frequency offset between the master laser diode and the slave VCSEL, the chaotic carrier fundamental frequency will generally increase with the increase of injection intensity; the chaotic carrier fundamental frequency can be improved significantly by adjusting frequency offset and injection intensity. For the normalized injection intensity K of 330 and frequency offset 42 GHz, chaotic output with 47.3GHz fundamental frequency can be obtained.
Bifurcations of safe basins and chaos in Flickering oscillator under multi-frequency harmonic and bounded noise excitation
Rong Hai_Wu, Wang Xiang-Dong, Xu Wei, Fang Tong
2008, 57 (3): 1506-1513. doi: 10.7498/aps.57.1506
Abstract +
The erosion of the safe basins and related chaotic motions of a Flickering oscillator under multi-frequency external periodic forces and bounded random noise are studied. By the Melnikov method, the system's Melnikov integral is computed and the parametric threshold for the onset of chaos is obtained. The Melnikov's global perturbation technique is therefore generalized to higher dimensional systems. Using the Monte-Carlo and Runge-Kutta method, the erosion of safe basins is also discussed. As an alternative definition, stochastic bifurcation may be defined as a sudden change in the character of stochastic safe basins when the bifurcation parameter of the system passes through a critical value. This definition applies equally well either to randomly perturbed motions or to purely deterministic motions. It is found that increasing the number of forcing frequencies or increasing the random noise may destroy the integrity of the safe basins, bring forward the occurrence of the stochastic bifurcation and make the threshold for onset of chaos vary in a larger extent,which hence makes the system less safe and chaotic motions easier to occur.
Mass exponent spectrum analysis of human ECG signals based on multiple scale factors
Yang Xiao-Dong, Ning Xin-Bao, He Ai-Jun, Du Si_Dan
2008, 57 (3): 1514-1521. doi: 10.7498/aps.57.1514
Abstract +
Life is one of the most complex nonlinear systems and heart is the core of this lifecycle system. The complexity of electrocardiogram (ECG) signals may reflect the physiologic function and health status of the heart. In this paper, we introduced two novel parameters of the multifractal mass exponent spectrum curvature and area. The evaluation of Cantor set validated that the two indicators are entirely effective in exploring the complexity of chaotic time series. Using the multiscale analysis method, we studied the mass exponent spectra of ECG signals taken from the cohorts of healthy, ischemia and myocardial infarction (MI) sufferer under different sampling frequencies and data lengths. Then we compared these new indicators with other nonlinear parameters and also expected to acquire some valuable nonlinear eigenvalues to distinguish the healthy from the heart diseased through those individual discrepancies. The classification indexes and ANOVA testing results both indicated that our method could achieve better results. These conclusions may be of much value in early diagnoses and clinical applications.
Studied on low-frequency oscillation in the Boost converter with one cycle control
Wang Fa-Qiang, Zhang Hao, Ma Xi-Kui
2008, 57 (3): 1522-1528. doi: 10.7498/aps.57.1522
Abstract +
On the assumption that the frequencies of the inductor current and output voltage are much lower than the switching frequency of the converter, the critical condition between the discontinuous conduction mode (DCM) and the continuous conduction mode (CCM) is given, and the transfer function of the closed loop output to the reference voltage under DCM and CCM are derived respectively. The analytical results show that the DC-DC Boost converter can be stable in the state of period 1 in DCM, but it can not be stable in CCM, i.e., the low-frequency oscillation will occur. Further, the frequency of the low-frequency oscillation is calculated by using zero-pole analysis method, and the oscillation amplitude of the output voltage is calculated in terms of the topology of the circuit. Finally, the theoretical results are verified by numerical simulations and circuit experiments.
Adaptive synchronization research on the uncertain complex networks with time-delay
Luo Qun, Wu Wei, Li Li-Xiang, Yang Yi-Xian, Peng Hai-Peng
2008, 57 (3): 1529-1534. doi: 10.7498/aps.57.1529
Abstract +
The synchronization problem of uncertain dynamical network model with time-delay nodes has been researched, where the network structure is known or totally unknown. Based on Lyapunov stability theorem, the synchronization controller of complex networks and the adaptive controller of synchronization of complex networks are designed respectively under the circumstances of known parameters and unknown parameters. The sufficient condition of network synchronization is given to guarantee that the dynamical network asymptotically synchronizes at the individual node state in arbitrary specified network. Finally, numerical simulations are provided to verify the effectiveness of the developed methods.
Quark phase transition in supernova and the effect of quark mass on the process
Lai Xiang-Jun, Luo Zhi-Quan, Liu Jing-Jing, Liu Hong-Lin
2008, 57 (3): 1535-1541. doi: 10.7498/aps.57.1535
Abstract +
Based on constituent quark mass and current quark mass model, the phase transition of two-flavor quark matter to more stable three-flavor quark matter in the core of supernova is studied. It is shown that the timescale of the process is shorter than 10-8 seconds for both cases, and the smaller the quark mass (current quark mass), the quicker the process; and the equilibrium parameters, except the temperature, such as s-quark abundance, neutrino abundance and total neutrino energy in supernova core, have a slight increase compared to the former result after the conversion according to constituent quark mass model. But the values of those parameters (including temperature) increase significantly based on current quark mass model. The current quark mass will be more favorable for the success of the delayed neutrino-heating mechanism for the explosion.
Thickness and optical constant determination of hydrogenated amorphous silicon thin film from transmittance spectra of ellipsometer
Liao Nai-Man, Li Wei, Jiang Ya-Dong, Kuang Yue-Jun, Qi Kang-Cheng, Li Shi-Bin, Wu Zhi-Ming
2008, 57 (3): 1542-1547. doi: 10.7498/aps.57.1542
Abstract +
To cope with the problem that the thickness and optical constants of thin film can not be measured accurately when deposited on a transparent substrate due to the incoherent reflected-light from the back-side of the substrate, a method is presented to determine the thickness and optical constants of hydrogenated amorphous silicon (a-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from the transmittance spectra of ellipsometer only. The influence of the substrate temperature (Ts) and the gas temperature (Tg) before glow discharge on the thickness and optical constants of a-Si:H thin films is analysed. The results show that the thickness of a-Si:H thin films determined by transmittance spectra agrees well with that measured by scanning electron microscopy (SEM). The optical constants of the films deduced from the transmittance spectra accord with the results obtained by other researchers. This method can be applied in deposition of amorphous or polycrystal thin films on transparent substrates.
Vector polarization mode switch mechanism of the vertical-cavity surface-emitting laser with anisotropic optical feedback injection
Zhong Dong-Zhou, Cao Wen-Hua, Wu Zheng-Mao, Xia Guang-Qiong
2008, 57 (3): 1548-1556. doi: 10.7498/aps.57.1548
Abstract +
Vector polarization mode switch mechanism of the vertical-cavity surface-emitting laser with anisotropic optical injection is numerically investigated. The results are as follows:First, when the injection current is near the threshold current, the polarization state of the VCSEL output is determined by the power of each polarization mode of the optical feedback injection,which is controlled by the external parameter of the VCSEL and the polarizer. Second, the polarization state of the VCSEL output induced by anisotropic optical feedback injection under the controll of polarizer changes periodically. Third, the x^-polarization mode competes drastically with the y^_polarization mode when the power of the x^-polarization of the feedback injection is equivalent to that of the y^_polarization, which induces slight external disturbance of the laser to break the balance of two competing polarization modes. So, on this condition, the polarization state is sensitive to the external parameter change. At last,the y^_polarization mode obtains enough big gain when the injection current is much higher above the threshold current. At this time, the output of the VCSEL is in steady y^_polarization mode. In other words, the polarization state of the VCSEL output is now independent of other parameters.
Systematic investigation of shape-coexistence in Se,Kr,Sr and Zr isotopes with relativistic mean field theory
Sheng Zong-Qiang, Guo Jian-You
2008, 57 (3): 1557-1563. doi: 10.7498/aps.57.1557
Abstract +
The even-even nuclei of Se, Kr, Sr and Zr isotopes are investigated systemically by the constrained relativistic mean field theory with the interactions NL3. The calculated binding energies of ground state for Se, Kr, Sr and Zr isotopes are described fairly well as compared with experiments. By examining the potential energy surfaces obtained by this microscopic approach, it can be found that the shape-coexistence phenomenon is very common in this region. The possible nuclei with shape-coexistence are pointed out systemically and the energy differences between the two minima in the potential energy surfaces for those nuclei are presented as well. In addition, by examining the potential energy surfaces and the microscopic neutron single particle spectra, N=70 are suggested to be a possible neutron magic number in this region.
Evolution from vibration to rotation of 102Ru nucleus discussed within microscopic theory
Shi Zhu-Yi, Zhang Chun-Mei, Tong Hong, Zhao Xing-Zhi, Ni Shao-Yong
2008, 57 (3): 1564-1568. doi: 10.7498/aps.57.1564
Abstract +
Based on the microscopic sdIBM-2 approach and the single-particle energies from experiment, with the use of the most general Hamiltonian, the vibrational band and rotational band of 102Ru nucleus as well as its evolutional process are reproduced very well by two parameters of nucleon-nucleon effective interactions, respectively. Microscopic and phenomenological study identifies that: 1) the coexisting region of two excitation models are located in the interval between the state 8+1 and state 12+1 (which is an interval with Ex=2.50—4.00 MeV), the 8+1 state is a state predominant in the vibrational model, the 12+1 state is one predominant in the rotational model, while the state 10+1 is neutral relative to two models; 2) the 12+1 state is a medial state decoupled from the 14+1 state to the 10+1 state as well released photons; 3) the yrast states from the ground-state up to the 20+1 state are collective states, hereafter the first breaking up and aligning state may be a neutron two-particle-state in the intruder orbits h11/2; 4) this structure evolution is not very furious, but achieved softly by the boson structure constant changing unobviously in the coexisting region.
The driving potential and cross sections for synthesizing super heavy nuclei with hot fusion
Huang Ming-Hui, Gan Zai-Guo, Fan Hong-Mei, Su Peng-Yuan, Ma Long, Zhou Xiao-Hong, Li Jun-Qing
2008, 57 (3): 1569-1575. doi: 10.7498/aps.57.1569
Abstract +
The dinuclear model of the formation mechanism of a superheavy compound nucleus assumes that when all nucleons of the projectile have been transferred in to the target nucleus the compound nucleus is formed. The nucleon transfer is determined by the driving potential. For some reaction channels, the relation between nucleon transfer and the evolution path of the neutron/proton ratio is rather complicated. In principle, both the dynamical equation and the driving potential should be a two-dimensional explicit function of the neutron and proton. For the sake of simplicity we calculated the driving potential by choosing the path of the nucleon transfer which is related to the nutron/proton ratio, and the calculated evaporation residue cross-sections to synthesize the superheavy nuclei are much closer to the experimental data.
Theory and method of X_ray grating phase contrast imaging
Chen Bo, Zhu Pei_Ping, Liu Yi-Jin, Wang Jun-Yue, Yuan Qing_Xi, Huang Wan_Xia, Ming Hai, Wu Zi-Yu
2008, 57 (3): 1576-1581. doi: 10.7498/aps.57.1576
Abstract +
In this work,we make a theoretical analysis of X_ray grating phase contrast imaging (XGPCI) and give an equation to show the relationship between the transmittance and the relative shift of the two gratings,which was named as the shift curve.According to this equation,we develop a new method to retrieve phase information from the experimental data in theory.Finally,we analyze the influence of the experimental setup to the resolution of the image.
The structure and potential energy function of AlOH(CS,X1A′)
Yang Ze-Jin, Gao Qing-He, Guo Yun-Dong, Cheng Xin-Lu, Zhu Zheng-He, Yang Xiang-Dong
2008, 57 (3): 1582-1586. doi: 10.7498/aps.57.1582
Abstract +
By using MP4/6-311G(3df,3pd) method, the equilibrium geometry of AlOH molecule has been calculated .The possible electronic state and the reasonable dissociation limit for the ground state of AlOH (CS,X1A′) molecule is determined based on atomic and molecular reaction statics. The analytic potential energy function of AlOH molecule was derived by many-body expansion theory.
The structure and potential energy function of SiOH and HSiO
Yang Ze-Jin, Gao Qing-He, Guo Yun-Dong, Cheng Xin-Lu, Zhu Zheng-He, Yang Xiang-Dong
2008, 57 (3): 1587-1591. doi: 10.7498/aps.57.1587
Abstract +
By using B3P86/6-311++G** method, the equilibrium geometry of SiOH/HSiO (CS,X2A′)molecule has been calculated .The possible electronic state and the reasonable dissociation limit for the ground state of SiOH molecule is determined based on atomic and molecular reaction statics. The analytic potential energy function of SiOH molecule was derived by many-body expansion theory.
Density functional theory studies on spectral properties of H3PAuPh and (H3PAu)2(1,4-C6H4)2
Jiao Yu-Qiu, Zhao Kun, Lu Gui-Wu
2008, 57 (3): 1592-1598. doi: 10.7498/aps.57.1592
Abstract +
The structures of the H3PAuPh and (H3PAu)2(1,4-C6H4)2 are optimized using the density functional theory for the ground states. The lowest-energy absorption spectra are calculated by the time-dependent density functional theory,and it is found that the 257.5nm line arises from 1A'→1A' transition for H3PAuPh and the 307.6nm line arises from 1A→1A transition for (H3PAu)2(1,4-C6H4)2. The lowest-energy absorption spectra of the Au complexes have the nature of pπ(aromatic_nucleus)→pπ*(aromatic_nucleus)C(2p)→Au(6p) charge transfer which is accompanied by Au(5d)→Au(6p) transition character. The (H3PAu)2(1,4-C6H4)2 is approximately made up of double H3PAuPh. So the molecular orbitals of (H3PAu)2(1,4-C6H4)2 can be regarded as the compounding of the molecular orbitals of H3PAuPh. The compounding of the molecular orbitals with the reciprocities of pπ* or pπ makes the lowest-energy absorption energy of (H3PAu)2(1,4-C6H4)2 lower than that of H3PAuPh.
Studies on the high-lying vibrational energies and molecular dissociation energies for some electronic states of K2 molecule
Liu Yan, Ren Wei-Yi, Wang A-Shu, Liu Song-Hong
2008, 57 (3): 1599-1607. doi: 10.7498/aps.57.1599
Abstract +
In view of the importance of the full vibrational spectrum and the molecular dissociation energies of K2 molecule to many studies and applications, this paper uses the SUN and REN's algebraic method (AM) which is based on perturbation theory and the algebraic energy method (AEM) based on the AM to study the vibrational spectroscopic constants, and the full vibrational spectra (Eυ) including the excited high-lying vibrational energies of electronic states X1Σ+g,a3Σ+u,0-g,B1Πu and 33Πg of K2 molecule, and obtain the accurate theoretical values of dissociation energies(De) of these states. The full vibrational spectra, especially the high-lying vibrational energies and dissociation energies, are difficult to determine experimentally, so this study can provides physical data for scientific research.
Regular and chaotic motions of a single Paul-trapped ion interacting with double-δ-kicked pulses
Chen Wen-Qin, Hai Wen-Hua, Song Jian-Wen
2008, 57 (3): 1608-1615. doi: 10.7498/aps.57.1608
Abstract +
We investigate the regular and chaotic motions of a single Paul-trapped ion under the pseudopotential approximation, which interacts with a double-δ-kicked periodic potential. We apply the method of integral-equation to construct the exact solution of the classical equation and use the numerical technique to plot the orbits in phase space and the time evolutions of average energies. Combining the analytical results with the numerical ones, we arrived at two interesting conclusions: Firstly, there are regular stable motions of the double δ-kicked system,at variance with the resonance case of the corresponding single δ-Kicked system. Secondly, when the time interval between the double δ pulses becomes shorter, the regular motion of the system becomes chaotic, and the speed of classical diffusion of the average energy is related to the degree of chaos. It is shown that the resonance may lead to loss of stability and the instability can be controlled by adjusting the laser wave vector.
The influence of molecular ground state wave function on high-order harmonic generation from N2 molecules in intense laser fields
Guo Zhong-Hua, Zhou Xiao-Xin
2008, 57 (3): 1616-1621. doi: 10.7498/aps.57.1616
Abstract +
Vector polarization mode switch mechanism of the vertical-cavity surface-emitting laser with anisotropic optical injection is numerically investigated. The results are as follows:First, when the injection current is near the threshold current, the polariz
Electric quadrupole transitions of K-like ions (Z=22—42)
Yang Fu-Li, Yi You-Gen
2008, 57 (3): 1622-1625. doi: 10.7498/aps.57.1622
Abstract +
A fully relativistic multiconfiguration Dirac-Fock method with Breit and QED corrections is used to calculate the 4s 2S─3d 2D(Z=22—42)transition energy level separations, transition probabilities and oscillator strengths for the K-like ions. In the calculation, we have considered the significant Breit and QED corrections. The results are in good agreements with recent experimental data and other theoretical values. The results show that the electric quadrupole transition probabilities are in correspondence with these of E1 transitions and can not be ignored in the laser plasma of high temperature in ICF and MCF Fusion.
Control of vibrational excitation for the linear triatomic molecule by the Lie-algebra approach
Feng Hai-Ran, Ding Shi-Liang
2008, 57 (3): 1626-1631. doi: 10.7498/aps.57.1626
Abstract +
In this paper the control of vibrational excitation for the linear triatomic molecule has been studied. Selective vibrational excitation has been achieved successfully. Multiphoton excitation and the influence of the laser pulse shape on control have also been discussed.
A modification method of additivity rule for total cross section calculations of electron scattering from molecules considering the geometric shielding effect
Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lüe, Liu Yu-Fang
2008, 57 (3): 1632-1639. doi: 10.7498/aps.57.1632
Abstract +
Taking into consideration the changes of the geometric shielding effect in a molecule as the incident electron energy varies, a modification method of additivity rule model for total cross section calculations of electron scattering from molecules at intermediate and high energies, is presented. Employing the modified additivity rule model, the total cross sections for electron scattering from NO, N2O, NO2 and C2H6 are calculated over a wide energy range from 50 to 5000 eV by using the experimental results of electron scattering from atoms C, N, H and O. The calculated values of total cross sections are compared with those obtained by measurements and other theories wherever available, and good agreement is attained over a wide energy range. It is shown that the total cross sections obtained by the modified additivity rule model are much closer to the measurements than the unmodified one and other theories. And it is also shown that the modification of complex optical potential must be related with energy of incident electrons so that the potential for total cross section calculations of electron scattering from free atoms is made suitable for the total cross section calculations of electron scattering from the ones in the molecule.
A theoretical study on non_first_order effects of BBK model in the (e,2e) process for hydrogen
Yang Huan, Gao Kuang, Wu Xing-Ju, Zhang Sui-Meng
2008, 57 (3): 1640-1647. doi: 10.7498/aps.57.1640
Abstract +
The triple differential cross sections for electron impact ionization of hydrogen at incident energies of 54.4, 150 and 250eV in the coplanar asymmetric geometry are calculated by use of BBK model and modified BBK model. The present results are compared with the results of first order approximation and experimental measurements. The non-first-order effects of modified BBK model are analysed and discussed. It is found that screening of three bodies in the final state conveys rich information of the non-first-order effects.


Density functional theory study of structures and electronic properties of XMgn (X=B, Al, n=1—12) clusters
Tian Fu-Yang, Wang Yuan-Xu, Jing Qun, Tian Kai, Luo You-Hua
2008, 57 (3): 1648-1655. doi: 10.7498/aps.57.1648
Abstract +
Geometry optimization and electronic properties of BMgn, AlMgn(n=1—12) clusters have been studied based on density functional theory (DFT). With the increase of the number of Mg atoms, the boron atom gradually comes into the interior of the Mgn cluster. However, the growth patterns of AlMgn clusters are similar to that of magnesium clusters. Doping of a B or Al atom makes the average binding energy higher and the stability enhanced. The atomic configuration plays a dominant role in the stability of B, Al atom doped magnesium clusters. The induction of B, Al atoms makes the NBO charge population of host magnesium clusters obviously altered. The peak of the average NBO charges population of 3p orbital of Mg atoms in AlMgn clusters is in agreement with the stability of AlMgn (n=1—12) clusters.
Propagation of linearly polarized Gaussian beam through the compound modulated diffraction grating
Li Jian-Long, Lü Bai-Da
2008, 57 (3): 1656-1661. doi: 10.7498/aps.57.1656
Abstract +
A new type of diffraction grating called the compound modulated diffraction grating is proposed, which incorporates both surface relief and periodic refractive index modulation. Based on the angular spectrum representation and strict modal theory, the propagation of linearly polarized Gaussian beam through the compound-modulated diffraction grating whose characteristic size is comparable with the wavelength is studied. It is shown that the propagation of beam in each layer is different and the intensity fluctuation frequency in the compound-modulated grating is smaller than that in the conventional relief grating at the same transmission depth. Using the compound modulated grating model, the influence of surface fluctuation of the sub-wavelength_volume phase holographic grating and waist width of the incident beam on the diffraction efficiency is analyzed.
The law of the bubble motion near the wall
Zhang A-Man, Yao Xiong-Liang
2008, 57 (3): 1662-1671. doi: 10.7498/aps.57.1662
Abstract +
Based on the assumption of potential flow, the coupled numerical model of the bubble and the wall is created and it is calculated with boundary integral method and a three-dimensional computing program is developed. The calculated result agrees with the experimental result well. Starting with the basic phenomenon of the interaction between the bubble and the wall, the dynamics of the bubble near a rigid wall is studied systematically with the program developed in this paper, including both cases of the parallel wall and the oblique wall. The relation between Bjerknes effect of the wall and the characteristic parameters is studied and the calculated results of various cases are compared and discussed with the Blake criterion based on the Kelvin-impulse theory. The analysis shows that the jet direction and the pressure on the rigid wall have close relationship with the bubble's characteristic parameters. Besides, the application range of Blake criterion is given. This paper aims to provide reference for the relevant researches on the dynamics of bubble near the wall.
The dynamics of bubbles
Zhang A-Man, Yao Xiong_Liang, Li Jia
2008, 57 (3): 1672-1682. doi: 10.7498/aps.57.1672
Abstract +
The fluid is assumed to be inviscid and incompressible and the flow irrotational. The three_dimensional numerical model is established to simulate the interaction of multiple bubbles and the fast Fourier transform on multipoles (FFTM) method is combined with the higher order boundary method (BEM) to study the physics of multiple bubble dynamics. FFTM method is employed to speedup the solution of the boundary integral equation while achieving the same order of accuracy, enabling to simulate the dynamics of multiple bubbles in a reasonable time. Elastic mesh technique (EMT), which is a new mesh regulation technique, is applied to maintain the regularity of the triangular element mesh used to discretize the dynamic boundary surface during the evolution of bubbles. All these measures make the present approach viable and robust, which is validated by computations of several bubble dynamics problems. Numerical analysi was carried out for the interaction of multiple bubbles and the bubble dynamics. Some physical behaviors of the multiple bubbles are presented in this work. The factors affecting the expansion, collapse, moving of multiple bubbles and the jet formation are also discussed.
Propagation dynamics of off-axis phase singularities
Liu Pu-Sheng, Cheng Ke, Lü Bai-Da
2008, 57 (3): 1683-1688. doi: 10.7498/aps.57.1683
Abstract +
An analytical expression for the half-plane diffraction of off-axis phase singularity beams based on Gaussian intensity profile is derived, which enables us to study the propagation dynamics of off-axis phase singularities in detail. It is shown that the half-plane screen diffraction, off-axis displacement and propagation distance affect the propagation behavior and spatial distribution of phase singularities. By varying the off-axis displacement and propagation distance, the creation, shift and annihilation of phase singularities in the diffraction field may appear.
Transfer of quantum information via the two-photon process
Yang Xiong, Tong Zhao-Yang, Kuang Le-Man
2008, 57 (3): 1689-1692. doi: 10.7498/aps.57.1689
Abstract +
A scheme is presented for transferring quantum information based on interaction between Jaynes-Cummings model with large detuning and two two-level atoms. It can be shown that quantum information can be transferred from one atom to the other atom, or from the cavity mode to the two atoms by manipulating the interactions between cavity field and two atoms, and the information contained in the transferring atom or cavity mode is completely erased.
The interactions of a two-level atom with a coherent field of time-varying frequency: the two-photon transition
Li Zheng-Hong, Yu Ming-Zhang, Yang Ya-Ping
2008, 57 (3): 1693-1698. doi: 10.7498/aps.57.1693
Abstract +
The two-photon transition for a two-level atom interacting with a single-mold electromagnetic field has been investigated. The initial coherent states with time-varying frequency are considered. The effects of the frequency modulation in sinusoidal form on the atomic population inversion and the squeezing properties of the atom and field are studied. The frequency change can lead the collapse-revival period of population inversion to increase, the maximum value of the revival to decrease, and the squeezing effects of the field and atom are weakened.
Optical bistability performance of laser-diode end-pumped Tm, Ho: YLF laser
Zhang Xin-Lu, Wang Yue-Zhu, Li Li, Ju You-Lun
2008, 57 (3): 1699-1703. doi: 10.7498/aps.57.1699
Abstract +
The bistable output of a 792 nm laser-diode end pumped continuous wave Tm, Ho: YLF laser is reported for the first time. When the temperature of the Tm, Ho: YLF crystal is 283 K, the width of bistable section is 100 mW, and the jump power at the turning point is 15 mW. The influence of crystal temperature on the bistable performance of 2 μm laser is studied in the experiment. The width of bistable section was reduced from 100 mW to 60 mW and the jump power at the turning point reduced from 15mW to 6 mW respectively, when the temperature of laser crystal is increased from 283 K to 298 K. The bistable output in the continuous wave Tm, Ho: YLF laser comes from the co-effect of the energy transfer upconversion, excited state absoption and lower level reabsorption of 2 μm laser light.
Influence of spherical aberration of the thermal lens on the mode profile of a large-volume TEM00-mode resonator
Liu Chong, Ge Jian-Hong, Xiang Zhen, Chen Jun
2008, 57 (3): 1704-1708. doi: 10.7498/aps.57.1704
Abstract +
The spherical aberration of the thermal lens of the active media is obvious when the solid state lasers are strongly pumped. It can change the mode profile, the single-pass loss, the output power and so on, especially in a large-volume TEM00-mode resonator. The self-consistent mode is calculated using Fox-Li diffraction iterative algorithm. There are side lobes with the fundamental mode when the spherical aberration is introduced, hence the beam quality is degraded. The calculation results agree well with the experimental results. The beam filling factor plays an important role in the design of a laser system. The optimized value of the beam filling factor should be determined experimentally according to the spherical aberration.
A method to measure the Brillouin linewidth of SBS medium using mixture media
Hasi Wu-Li-Ji, Liu Shu-Jie, Lü Zhi-Wei, Yin Guo-He, Teng Yun-Peng, He Wei-Ming, Zhao Xiao-Yan
2008, 57 (3): 1709-1713. doi: 10.7498/aps.57.1709
Abstract +
In order to measure the Brillouin linewidth of SBS medium, a method using mixture media in two-cell stimulated Brillouin scattering (SBS) system is proposed, which uses the medium to be measured as amplifier medium and the mixture media as generator medium. The profile of gain coefficient versus the difference of Brillouin frequency shift is fitted with Lorentzian curve. The width at half-maximum of this curve is the Brillouin linewidth. In the experiment, using Nd:YAG Q-switched laser system and CCl4/C6H6 mixture, we measured the Brillouin linewidth of SBS media tetrachloroethylene (C2Cl4), hexachlorobutadiene (C4Cl6), acetone (C3H6O) and n-hexane (C6H14). The results show that the measured values are close to those calculated or published by other authors.
Stimulated Raman scattering of YbVO4 crystal
Hu Da-Wei, Wang Zheng-Ping, Zhang Huai-Jin, Xu Xin-Guang, Wang Ji-Yang, Shao Zong-Shu
2008, 57 (3): 1714-1718. doi: 10.7498/aps.57.1714
Abstract +
With an ultra-cavity single-pass configuration, the stimulated Raman scattering (SRS) of a new crystal YbVO4 was investigated. When the pump source was a 532 nm pico-seconds laser, as many as three Stokes lines (558.47, 587.92 and 620.67 nm) and one anti-Stokes line (507.58 nm) were observed. The steady-state Raman gain coefficient for the first Stokes line was measured to be 17.8±0.2 cm/GW, and the total conversion efficiency reached 37%. For the first time, the SRS of YbVO4 crystal for 355 nm pump laser was realized. The first Stokes line (366.11 nm) was observed, and according to the pumping thresholds, the steady-state Raman gain coefficient was determined to be 29.0±0.3 cm/GW.
Experimental and theoretical investigation of fused silica rod-fiber phase conjugator
Wang Sha, Chen Jun, Tong Li-Xin, Gao Qing-Song, Liu Chong, Tang Chun
2008, 57 (3): 1719-1724. doi: 10.7498/aps.57.1719
Abstract +
A novel combined phase conjugator consisting of a fused silica rod and silica fiber is used in the high repetition laser system to improve the light quality. It has the advantages of higher stimulated Brillouin scattering reflectivity, higher stimulated Brillouin scattering damage threshold and lower stimulated Brillouin scattering threshold. In experiment, under the repetition rate of 100 Hz, maximum 42.05% stimulated Brillouin scattering reflectivity is obtained. According to the coupling wave equations and the boundary conditions of the experiment, the numerical value calculated from this model is in accordance with the experiment result. And the way to improve the working state of this combined phase conjugator is brought forward by our modeling.
Investigation on frequency-detuning induced optical chaos synchronization switching
Qiu Xin, Xia Guang-Qiong, Wu Jia-Gui, Wu Zheng-Mao
2008, 57 (3): 1725-1729. doi: 10.7498/aps.57.1725
Abstract +
A theoretical model characterizing a reported experiment on optical chaos synchronization switching is presented. Based on the model, the characteristics of optical chaos synchronization switching have been numerically simulated for different feedback strength and injection strength. The results show that: for a fixed feedback strength, both on-off switching ratio and width of the chaos switching will vary with the change of injection strength. When the injection strength equals to the feedback strength, the on-off switching ratio will reach a maximum. Furthermore, when the feedback strength and the injection strength are increased synchronously, both the on-off switching ratio and the width of the chaos switching will increase monotonicly.
Design and optimization of photonic crystal coupling layer for bi-color quantum well infrared photodetectors
Wang Ke, Zheng Wan-Hua, Ren Gang, Du Xiao-Yu, Xing Ming-Xin, Chen Liang-Hui
2008, 57 (3): 1730-1736. doi: 10.7498/aps.57.1730
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Finite difference time domain (FDTD) method is used for the simulation and analysis of electromagnetic field in the top coupling layer of GaAs/AlGaAs quantum well infrared photodetector (QWIP). Simulation results demonstrated the coupling efficiencies and distributions of electromagnetic (EM) field in a variety of 2D photonic crystal coupling layer structures. A photonic crystal structure for bi-color-QWIP is demonstrated with high coupling efficiency for two wavelengths.
Polarization beam splitter for self-collimated beams in photonic crystals
Shen Xiao-Peng, Han Kui, Li Hai-Peng, Shen Yi-Feng, Wang Zi-Yu
2008, 57 (3): 1737-1741. doi: 10.7498/aps.57.1737
Abstract +
We present the design and simulation of an ultra-compact high-efficiency polarization beam splitter (PBS) based on self-collimation effect and photonic crystal band gap in two dimensional photonic crystals. The splitting properties of the PBS have been numerically studied using the finite difference time domain (FDTD) method. It was shown that a 90° separating angle and efficiency of greater than 85% for TE- and TM- modes over a wide frequency range 0.268—0.278(c/a) can be obtained. The size of PBS is only 9 μm×9 μm at optical communication wavelength λ=1.55 μm. These features of the proposed PBS make it a promising candidate in optical communications application.
Self-starting mode-locked Cr4+:YAG laser with Gires-Tournois interferometer mirror for dispersion compensation
Zhou Bin-Bin, Zhang Wei, Zhan Min-Jie, Wei Zhi-Yi
2008, 57 (3): 1742-1745. doi: 10.7498/aps.57.1742
Abstract +
A self-starting mode-locked Cr4+:YAG laser is reported, which incorporates a broadband SESAM and uses a piece of GTI mirror to compensate the intra-cavity group-delay dispersion. 65-fs pulses are generated at an average power of 95 mW with a 45 nm spectral bandwidth centered at 1508 nm under the pump power of 9 W.
The elastic wave propagation in two-dimensional phononic crystal at low frequencies and the anisotropy of effective velocity
Cai Li, Han Xiao-Yun, Wen Xi-Sen
2008, 57 (3): 1746-1752. doi: 10.7498/aps.57.1746
Abstract +
The propagation of elastic waves in two-dimensional phononic crystal is investigated theoretically in the long-wavelength limit by the MST method. Exact analytical formulas for effective velocities of elastic waves are derived according to the behavior of the Mie scattering solution and the lattice sum in the long-wavelength limit. It has been found that the coupling effect between the two second-order components of the cylindrical scattered wave changes with the propagation orientation. Therefore whether the effective velocities of the propagating modes are anisotropic depends on whether the second-order components of the Mie scattering are indispensable.
Study on point-to-point mobile underwater acoustic communication
Yin Jing-Wei, Hui Jun-Ying, Guo Long-Xiang
2008, 57 (3): 1753-1758. doi: 10.7498/aps.57.1753
Abstract +
Point-to-point mobile underwater acoustic (UWA) communication is one of the key technologies for UWA networks which consists of mobile and stationary nodes. The mobile communication UWA channels are analyzed, whose eigen rays have different Doppler shifts which enhances the complexity of intersymbol interference (ISI) caused by the multipath channel, that goes against the UWA communication. The channel equalization using single sensor passive phase conjugation mirror (PPCM) is proposed to compensate for the Doppler shift in real time and to focus the multipath signals. The application of single sensor PPC to communication system based on Pattern time delay shift coding scheme is carried out in lake trials. The results of lake trials validated the capability of PPCM mitigating ISI and the robustness of the communication system.
Effect of a Planckian radiation field on population of bound-electrons
Wang Wei, Zhang Jie, Zhao Gang
2008, 57 (3): 1759-1764. doi: 10.7498/aps.57.1759
Abstract +
The basic atomic physical processes of laser beams interacting with a solid target is checked and the effects of a Planckian radiation field on the population of bound electrons are studied. The results illustrate that the radiation field, if it has a truly Planckian distribution, will influence on the physical processes in plasmas. For instance, it can ensure the distribution of the population on the different ionization stages under the LTE conditions even when the plasmas density is low enough that the collision rates do not dominate over radiative rates.
Investigation on an S-band relativistic klystron oscillator
Huang Hua, Gan Yan-Qing, Lei Lu-Rong, Jin Xiao, Ju Bing-Quan, Xiang Fei, Feng Di-Chao, Liu Zhong
2008, 57 (3): 1765-1770. doi: 10.7498/aps.57.1765
Abstract +
The physics of modulation and rf extraction of an S-band relativistic klystron oscillator is studied in this paper via experiment, theory, and simulation. It is found that the intense relativistic electron beams (IREBs) can be intensely current-modulated when the IREBs drift through three pillboxes with high coupling. After bunching in the downstream the modulated IREBs can excite high-power microwave in the triaxial cavity. These properties, which have short oscillating time, compact geometry and high beam-wave conversion efficiency, were encouraging. Using a 1 MV, 13 kA, 40 ns electron beam and a 0.9 kGs leading magnetic field, 3.5 GW radiated power was extracted in 20 ns FWHM pulses at 2.86 GHz. The efficiency was 27%, and the instantaneous bandwidth was 2%. The radiated power was 3.4 GW when the repetition rate IREBs was 20 Hz. The experimental results agree well with the simulations.
Integrated all fiber optical pulse generation system for laser fusion driver
Lin Hong-Huan, Wang Jian-Jun, Sui Zhan, Li Ming-Zhong, Chen Guang-Hui, Ding Lei, Tang Jun, Deng Qing-Hua, Luo Yi-Ming, Dong Yi-Fang, Li Feng
2008, 57 (3): 1771-1777. doi: 10.7498/aps.57.1771
Abstract +
We demonstrate an integrated all fiber optical pulse generation system for laser fusion driver. CW laser signal generated from a single longitudinal fiber oscillator was modulated by phase modulator and amplitude modulator to form an optical pulse with shaped waveform and bandwidth of 0.1 nm. The pulse was amplified and split by fiber multiplexer to four pulses. Time delay of each pulse was controlled by synchronization unit and power of each pulse was adjusted by programmable variable optical attenuator. The four pulses were amplified and then transmitted through a 150 m fiber to the pre-amplify system. The fiber system can generate almost arbitrarily shaped optical pulse with duration of 0.2—20 ns, bandwidth of 0.1 nm and power of several nJ. As the front-end of the SG-Ⅲ prototype facility, it has successfully lunched about 2.6 million shots of pulses. The fiber system is compact and highly stable and reliable.
Short-pulsed explosive field emission and plasma expansion of carbon nanotube cathodes
Liao Qing-Liang, Zhang Yue, Huang Yun-Hua, Qi Jun-Jie, Gao Zhan-Jun, Xia Lian-Sheng, Zhang Huang
2008, 57 (3): 1778-1783. doi: 10.7498/aps.57.1778
Abstract +
A large area cold cathode based on carbon nanotube films has been successfully fabricated. Investigation of the explosive field emission properties of the carbon nanotube cathode in a double-pulse mode was carried out and a high emission current density of 245 A/cm2 was obtained. The turn-on time of the CNT cathode is about 40 ns. The time- and space-resolution of the electron beam emitted from the cathode was investigated. The formation of the cathode plasma layer was proved and the plasma expanded at a velocity of ~8.17 cm/μs toward the anode. The plasma has big influences on the intensity and distribution of electron beams. The formation of cathode plasma had no preferential position and the local enhancement of electron beams was random. This carbon nanotube cathode appears to be suitable for high-power microwave device applications.
Improving parallel electrode method by sputtering atoms' angle distribution rule
Xie Guo-Feng
2008, 57 (3): 1784-1787. doi: 10.7498/aps.57.1784
Abstract +
In atomic vapor laser isotope separation (AVLIS) engineering, the parallel electrode method has the advantage of simple structure, but when the extraction voltage is high, the sputtering loss is very large and the collection ratio is very low. This paper calculates the angular distribution of sputtering atoms by Trim code. The results show that the angular distribution follows the cosine rule. The collection method is modified according to the rule, which makes the collection ratio very high.
Diagnostic study on the electron density distribution of microwave plasma jet in local vacuum environment
Yang Juan, Xu Ying-Qiao, Zhu Liang-Ming
2008, 57 (3): 1788-1791. doi: 10.7498/aps.57.1788
Abstract +
In order to diagnose the electron density of microwave plasma jet confined by solid boundary walls, the emission/Langmuir probe was applied to measure the plasma space potential and current and voltage property when the probe is charged by heating and scanning power supply separately. According to the plasma space potential, saturated current on the current-voltage characteristics of plasma can be distinguished, which can be used to estimate the number density of electrons in the plasma. The results show that the magnitude of electron density ranges from 8.8×1014 to 7.53×1016/m3, the electron density on the centerline of jet decreases linearly off the nozzle exit plane, but it has approximately parabolic distribution along the plasma jet direction when leaving the centerline. Increasing mass flow rate at constant power and increasing power at constant mass flow rate will increase electron density.
Utilization of convex crystal spectrograph to obtain monochromatic X-ray images of Z-pinch plasmas
Ye Fan, Xue Fei-Biao, Guo Cun, Li Zheng-Hong, Yang Jian-Lun, Xu Rong-Kun, Zhang Fa-Qiang, Jin Yong-Jie
2008, 57 (3): 1792-1795. doi: 10.7498/aps.57.1792
Abstract +
The spectral resolution, spatial resolution of monochromatic X-ray images of a spectrograph based on convex crystal were discussed by ray tracing calculations taking into consideration the effect of rocking curve of the crystal. A mica convex crystal spectrograph was designed and then tested successfully on “QiangGuang-1" pulsed power facility. Time integrated monochromatic X-ray images of Al Z-pinch plasmas showed the X-ray line emissions of K-shell came from the core region of a diameter of about 2.3 mm.
Characterization of ZrN films deposited by ICP enhanced RF magnetron sputtering
Liu Feng, Meng Yue-Dong, Ren Zhao-Xing, Shu Xing-Sheng
2008, 57 (3): 1796-1801. doi: 10.7498/aps.57.1796
Abstract +
ZrN films have been prepared by inductively coupled plasma (ICP)-enhanced RF magnetron sputtering. The effects of substrate temperature and ICP power on the microstructure and properties of ZrN films have been investigated systemically. The ZrN films show (111) preferred orientation with the substrate temperature below 300℃. ZrN(200) is observed at 450℃ regardless of ICP power, and the texture coefficient of (111) decreases. Columnar structure, which is observed in the films deposited by conventional magnetron sputtering, disappears in the film synthesized at ICP power of 200 W and substrate temperature of 300℃. With the increase of substrate temperature, N/Zr ratio and the resistivity of films decrease. The films deposited with ICP power on show denser structure, higher hardness and lower stress than those by conventional magnetron sputtering.
Influence of dielectric parameters on temporal behavior of dielectric barrier discharge
Dong Li-Fang, Wang Hong-Fang, Liu Wei-Li, He Ya-Feng, Liu Fu-Cheng, Liu Shu-Hua
2008, 57 (3): 1802-1806. doi: 10.7498/aps.57.1802
Abstract +
The Influences of different temperature and materials of dielectrics on temporal behavior of dielectric barrier discharge in argon at atmospheric pressure are studied by using a device with asymmetric dielectric parameters. It is found that the temporal waveform of discharge current in each half cycle is almost the same at lower applied voltage, whereas the number of discharge current pulses is different in half cycles of different polarity at higher applied voltage. The analysis shows that both temperature and material of dielectrics affect the accumulation of wall charges, resulting in the change of temporal behavior of discharge.
Ionization of background gas by an intense relativistic electron beam
Song Fa-Lun, Zhang Yong-Hui, Xiang Fei, Chang An-Bi
2008, 57 (3): 1807-1812. doi: 10.7498/aps.57.1807
Abstract +
In the paper, the interaction of an intense relativistic electron beam with the background gas in the high power microwave diode is studied. According to the experimental data, the plasma density generated by impact ionization have been calculated using the numerical methode and particle-in-cell code. The results show that the values of the plasma density produced by impact ionization obtained by the two calculating methods agree well. The ionized plasma densities are 4-12×109cm-3 at the pressures of 0.01 Pa—0.05 Pa. Even considering the two- and three-body recombination effects, the values of the plasma densities produced by impact ionization obtained by the numerical methode and particle-in-cell code still agree well. In addition, the results of PIC simulation show that there is a hump in the plasma density curve with the increasing of pressure. Different from the simple numerical calculation, in calculating the plasma densities, the experimental data are used. The results obtained by the two calculation methodes using the experimental data will be very useful for high power microwave diode and microwave devices.
Prediction of the crystallization temperature and crystallization driving force for Mg-Ni-Nd amorphous alloys
Wu Dong-Chang, Huang Lin-Jun, Liang Gong-Ying
2008, 57 (3): 1813-1817. doi: 10.7498/aps.57.1813
Abstract +
A method for predicting the crystallization temperature and crystallization driving force of ternary amorphous alloys was provided. This method is an extension of the smallest-vacancy model suggested by Buschow for evaluating crystallization temperatures. The crystallization enthalpy and crystallization driving force are evaluated by using Miedema's semi-empirical model and the crystallization temperature is predicted. Calculation of the crystallization temperatures and enthalpy for (Mg70.6Ni29.4)1-xNdx(x=5,10,15) amorphous alloys are performed by using this method. The calculated results accord well with experimental data and the relative error is less than 8% and 7% for crystallization temperature and crystallization enthalpy, respectively. It is found that with the increasing of crystallization driving force the retention rates of discharge capacity of Mg-Ni-Nd amorphous alloys decreases. For the (Mg70.6Ni29.4)1-xNdx(x=1—20) amorphous alloys, the lowest crystallization driving force appears when the Nd content reaches 6.3%. That means (Mg70.6Ni29.4)93.7Nd6.3 amorphous alloy could have better retention rate of discharge capacity.
Synthesis and welding of H-doped and N-doped carbon nanowires
Wang Zhen-Xia, Pan Qiang-Yan, Yong Zheng-Zhong, Hu Jian-Gang, Zhu Zhi-Yuan
2008, 57 (3): 1818-1822. doi: 10.7498/aps.57.1818
Abstract +
A efficient and novel experimental method for synthesis and welding of amorphous carbon nanowires (ACNWs) by using double ion irradiations and heat-treatment is described. Experimental samples were characterized using high resolution transmission electron microscopy (HR-TEM). The results demonstrate that the proper combination of double ion irradiations and heat-treatment may make the multiwalled carbon nanotubes (MWCNTs) to become amorphous carbon nanowiro, thus enabling the welding of crossed ACNWs. In addition, the atomic evolution in carbon structural phase transformation is briefly discussed in connection with the current prevailing ideas.
Study on the structural and energetic properties of two-dimensional ground state of Ag+ ion-vacancy in fast ionic conductor AgxTiS2
Song Qing-Gong, Jiang En-Yong
2008, 57 (3): 1823-1828. doi: 10.7498/aps.57.1823
Abstract +
Three-dimensional cell models are constructed for fast ionic conductor AgxTiS2 according to the two-dimensional ordered structure of Ag+ ion-vacancy. Geometry optimization and total energy computation are performed for ordered AgxTiS2(x=0,1/4,1/3,1/2,2/3,3/4,1)series using plane-wave pseudo-potential method based on local density approximation to density-functional theory, and the results are compared with the LixTiS2 series. The increments of lattice parameters Δa0 and Δc0 increase monotonically with increasing ion concentration, which well accords with experimental results. The total energies of AgxTiS2 and LixTiS2 system decrease linearly with increasing ion concentration, and the former decreases more rapidly. The negative formation energies of AgxTiS2(x=1/4, 1/3, 1/2, 2/3, 3/4)system indicate their ground state property, among which the formation energy of Ag1/3TiS2 system with 3{1/2}a0×3{1/2}a0 superstructure is the lowest. The formation energy of ordered AgxTiS2(x=1/4, 1/3, 1/2, 2/3, 3/4)system is lower than that of LixTiS2 system, implying higher temperature of order-disorder transition and higher activation energy of ionic diffusion. Reasonable explanation for related experimental results are presented according to these computational results.
The influence of proton irradiation on the microstructure of pure Al films
Fan Xian-Hong, Chen Bo, Guan Qing-Feng
2008, 57 (3): 1829-1833. doi: 10.7498/aps.57.1829
Abstract +
In this work, we investigated the microstructures of pure aluminum films irradiated with 160 keV proton by varying the irradiation dose. The vacancy clusters induced by proton irradiation in Al films are characterized by TEM, and the density and size distribution are determined. In the irradiation dose range of our studies, the density and size of vacancy clusters and the dislocation density increase with increasing irradiation dose. Our experimental results show that the dislocation density and size of vacancy clusters increase as the irradiation dose increases from 1×1011 to 4×1011/mm2. When the irradiation dose is as high as 6×1011/mm2, the number density of dislocation loops decreases, while the size of dislocation loop increases obviously. The vacancies tend to form larger clusters, accompanied by the formation of banded structures in the irradiated sample at higher irradiation doses. We found that there were small crystal orientation differences among the boundaries of banded structure. This banded structure is closely related to the degradation of mechanical and physical performance of irradiated material.
The nonlinear elastic behavior of crystalline solids: An atomistic simulation study
Wen Yu-Hua, Zhang Yang, Zhu Zi-Zhong
2008, 57 (3): 1834-1839. doi: 10.7498/aps.57.1834
Abstract +
In this paper, we employ molecular static approach with quantum corrected Sutten-Chen many-body potential to study the elastic responses of nickel monocrystal subjected to uniaxial tensile and compressive loading, and consider three different loadings, i.e., the [001], [011] and [111] loding. The simulated results show that strong nonlinear effects are found in the elastic behavior of monocrystal under the [011] loading, while the lateral deformations are essentially isotropic under [100] and [111] loadings. The further discussions are focused on the dependence of the Young's moduli and Poisson's ratios on the applied strain, and a brief comparison with first-principles calculations is also presnted.
Influence of fused interface on the optical and thermal characteristics of vertical cavity lasers
He Guo-Rong, Zheng Wan-Hua, Qu Hong-Wei, Yang Guo-Hua, Wang Qing, Cao Yu-Lian, Chen Liang-Hui
2008, 57 (3): 1840-1845. doi: 10.7498/aps.57.1840
Abstract +
From the effective absorption coefficient of bonded interface and the relationship of interface to reflectivity at cavity mode for double bonded vertical cavity laser, it can be seen that bonded interfaces should be positioned at the null of standing wave distribution, and the thickness of interface should be less than 20 nm. Using the finite elements method, the temperature contour map of laser can be calculated. Results showed that the influence of thin interface to thermal characteristics of VCSELs is slight, while thick interface will lead to temperature increase of active region. SEM images demonstrate that hydrophobic bonding is suitable for the fabrication of the device, while hydrophilic bonding interface is unfavorable to optical and thermal properties of devices with interface thickness larger than 40 nm.
The influence of impurities on segregation of the (110) surface of O/RhxPt1-x alloy system
Zhang Hui, Zhang Guo-Ying, He Jun-Qi, Wang Dan, Yang Shuang
2008, 57 (3): 1846-1850. doi: 10.7498/aps.57.1846
Abstract +
The atomic cluster models of (110) surface of RhxPt1-x disordered binary alloy were constructed under the condition that there is interaction between adsorption and segregation. The coverage of O is 0.5. Also,the models that may have an impact on the alloy debased with Cu,Ni and W were set up by computer respectively. It followed that impurities replaced every Rh which should be the nearest neighbor of O. The environment sensitive inlaid energy (EESE) and the electronic structure of the alloy surface doped with Cu,Ni and W was calculated by recursion method. The results of EESE show that, the influence of Ni,Cu and W on Rh-Pt alloy are all to reverse the segregation of the alloy surface. Furthermore,Ni is the most effective imupurity,and then Cu and W. Doped with impurities Cu,Ni and W,the covalent interaction between Rh and O is reduced,which reverses the surface segregation,so Pt segregates on the surface.
Growth and electrical conductivity of Gd2O3 doped CeO2 ion conductor electrolyte film on sapphire substrate
Jiang Xue-Ning, Wang Hao, Ma Xiao-Ye, Meng Xian_Qin, Zhang Qing-Yu
2008, 57 (3): 1851-1856. doi: 10.7498/aps.57.1851
Abstract +
Nanocrystalline Gd2O3 doped CeO2 (abbreviated as GDC) ion conductor electrolyte thin films synthesized by reactive magnetron sputtering on (0001) sapphire substrates have been characterized by X-ray diffraction (XRD),atomic force microscopy (AFM) and AC impedance analysis. The results show that,the f.c.c structured GDC films have strong (111) textures at all the substrate temperatures of our investigation while the surface morphology varied with the temperature. Small, round growth islands transform to large prismatic islands at temperatures from room temperature to 300℃, and the reverse process occurr at temperatures from 400℃ to 700℃. This morphology change characterizing different nucleation mechanisms at the beginning of film growth is probably due to transformation of the surface structure of the (0001) sapphire at different temperatures. The AC impedance complex plane plot of the GDC film is mainly determined by grain boundary resistances. The conductivity activation energy (1.2—1.5eV) calculated by the Arrhenius plot is close to the reported value for the grain boundary conductivity and decreases with rising substrate temperature (Ea300Ea400Ea600). Difference in activation energy and grain size for GDC films causes unequal increasing rates of electrical conductivity at higher temperatures.
The theoretical model of broad band dye laser and experimental validation
Wang Mo-Ge, Lu Qi-Sheng, Xu Xiao-Jun, Guo Shao-Feng
2008, 57 (3): 1857-1861. doi: 10.7498/aps.57.1857
Abstract +
The spectral competition in pulsed dye laser is modified by semiclassical dye laser theory,showing good agreement with experimental results.Under the circumstance of interrelated competition of double-wave,the tuned spectrum is expanded by 25%.The spectrum is gradually compressed with the increasc of the coupler loss under the condition of broad spectrum width.
First-principles research on the effect of high oxygen vacancy concentration in anatase TiO2 on Mott phase transition, absorption spectrum Einstein shift and life_time of electrons
Hou Qing-Yu, Zhang Yue, Zhang Tao
2008, 57 (3): 1862-1866. doi: 10.7498/aps.57.1862
Abstract +
Based on the study of density function using first-principles theory,by studying the concentration of oxygen vacancies,the DOS and the absorption spectrum of anatase,we discovered that the high concentration of oxygen vacancies has great influence on the forbidden band gap,absorption spectrum Einstein shift and life_time of electrons,and explained the reason why the concentration of oxygen vacancy makes the forbidden band gap to narrow. At the same time,the anatase semiconductor has Mott transition when there is a high concentration of oxygen vacancies. The conclusion that suitably controlling the concentration of oxygen vacancy leads to Einstein shift is deduced by comparing the Einstein shift experiment of oxygen vacancies in anatase with that in the plasma. It offered credible data for preparation visible light activator suitably by controlling the concentration of oxygen vacancies in anatase.
The effect of the substituted transitional atom M on the magnetism of the intermetallic compounds YFe11M
Huang Zheng, Chen Bo, Ma Huan-Feng, Zhang Xiu-Lan, Gao Guo-Qiang, Qiang Wei-Rong, Sun Guang-Ai
2008, 57 (3): 1867-1871. doi: 10.7498/aps.57.1867
Abstract +
Based on the density functional theory (DFT),using full-potential linearized augmented plane wave and improved local orbital (APW+lo),the structure and magnetism of the magnetic materials YFe11M (M=Ti,Si etc.) are analyzed and calculated. The possible positions of the substitutional atom M are analyzed. The effect of the substituted atom M on the magnetism of the intermetallic compounds YFe11M is discussed.
Study of conductive property for a N-VDMOS interface trap under X-ray radiation
Sun Guang-Ai, Hu Gang-Yi, Yang Mo-Hua, Xu Shi-Liu, Zhang Zheng-Fan, Liu Yu-Kui, He Kai-Quan, Zhong Yi
2008, 57 (3): 1872-1877. doi: 10.7498/aps.57.1872
Abstract +
An N-channel VDMOS I-V curve is measured after X-ray radiation under condition of different power dissipation. It is found that the property of new interface traps induced by X-ray radiation of self-annealing VDMOS sample does not conform to existing theory reasonably well. Based on measured data,we advance the viewpoint that the interface trap has current conductive property besides being charged up, and the conduction is assumed to be the generation or recombination current caused by new interface traps, which can not be simply identified quantitatively from the I-V curve.
Single electron pumping at higher frequency in a novel semiconductor-based quantum dot device
Li Ling, Kaestner B, Blumenthal M D, Giblin S, Janssen T J B M, Pepper M, Anderson D, Jones G, Ritchie D A, Gao Jie
2008, 57 (3): 1878-1885. doi: 10.7498/aps.57.1878
Abstract +
The π-shift sinusoidal signals with different amplitudes applied directly to the two metallic finger gates on a shallow etched GaAs/AlGaAs quantum wire,tune unequally the two barriers of a static quantum dot induced by applying negative dc voltages on these two finger gates. Single electrons are transported through a periodically formed quantum dot without source-drain bias. Since single electron pumping in the novel semiconductor-based quantum dot device does not rely on Coulomb blockade of tunnelling,the device can not be limited to much lower frequency by the fixed tunneling time constant. Current plateaus due to single electron transport can be observed at 1.7K with frequencies up to 3GHz and a current level of 0.5nA. This novel device represents another possible path in the realization of a high current high accuracy quantum standard for electrical current,and also provides another means for high specd high accuracy transport of single electrons.
Study of AlGaN/GaN MOSHEMT device with Al2O3 insulating film
Feng Qian, Hao Yue, Yue Yuan-Zheng
2008, 57 (3): 1886-1890. doi: 10.7498/aps.57.1886
Abstract +
On the basis of AlGaN/GaN HEMT,the AlGaN/GaN MOSHEMT device was fabricated with Al2O3 insulating film for the first time, which was deposited by ALD.The X-ray photoelectron spectroscopy measurements showed successful deposition of Al2O3 layer on the AlGaN/GaN film. The results of Schottky capacitance,I-V characteristics and DC transfer characteristics measurement showed that the interface state density between the AlGaN film and the Al2O3 insulating film was fairly low and the MOSHEMT device showed successful gate control of drain current up to VGS=+3V and achieved drain saturation current of 800mA/mm,which was much larger than that of the HEMT device. Furthermore,the gate leakage current of MOSHEMT is two orders lower in the reverse bias condition as compared with the Schottky gate structure,which increased the device breakdown voltage,while the leakage current was governed by the Fowler-Nordheim tunneling mechanism.
A new analytical model of breakdown voltage for the SD LDMOS
Li Qi, Zhang Bo, Li Zhao-Ji
2008, 57 (3): 1891-1896. doi: 10.7498/aps.57.1891
Abstract +
In this paper,a novel analytical model for breakdown voltage of SD LDMOS is developed. Based on the 2-D Poisson's solution,the model gives the analytical solutions of the surface potential and electrical field distributions as functions of the structure parameters and drain bias;and the dependence of breakdown voltage on structure parameters is calculated. An effective way to attain the optimum high-voltage devices is also proposed. All analytical results were verified by simulation results obtained by MEDICI and previous experimental data,showing the validity of the present model. As a result of the modulation of the drift region and subtrate' field,the on-resistance is decreased and new electrical field peak are produced inside the drift region which improves the surface electrical field distribution and increases the breakdown voltage. The SD structure led to a significant improvement of breakdown voltage of about 26% and a reduction of on-resistance of about 33% compared to the conventional structure.
Retarded modes of lateral ferromagnetic/ferromagnetic superlattice
Liu Yan-Fen, Liu Jing-Hui, Jia Cheng
2008, 57 (3): 1897-1901. doi: 10.7498/aps.57.1897
Abstract +
In this paper,we calculated the retarded modes of semi-infinite lateral ferromagnetic/ ferromagnetic superlattice with the effective-medium theory. We took the Co/Ni system surface modes and bulk modes as the examples for the superlattice and found some interesting properties different from that of the lateral ferromagnetic/nonmagnetic superlattice. Lateral magnetic/magnetic superlattice have some complex retarded modes which are very common in the systems. Changing the ratio of the thicknesses of the ferromagnetic layers, the two branches of surface mode frequency and bulk mode frequency band can be adjusted consequently. This tailoring effect is related to the two ferromagnetic layers' saturation magnetization values, and it is quite pronounced when the two saturation magnetization values are quite different from each other. If the difference between the tow values is large,the tailoring effect of f1 is more obvious. When the saturation magnetization value of the second ferromangtic medium approaches to zero,this system will become the magnetic/nonmagnetic superlattice. If in Maxwell equation ε=0,the retarded modes will transit to the ferromangtic/ferromangnetic superlattice magnetostatic modes.
Piezoelectric properties and charge transport for fluorocarbon polymers with cellular structure
Zhang Xiao-Qing, Huang Jin-Feng, Wang Fei-Peng, Xia Zhong-Fu
2008, 57 (3): 1902-1907. doi: 10.7498/aps.57.1902
Abstract +
A new method for prepering piezoelectric polymer with cellular structure (piezoelectret) is introduced. Their piezoelectric activity and thermal stability are investigated for the fluorocarbon piezoelectret films produced in this method. The quasistatic piezoelectric d33 coefficients up to 2200pC/N are obtained for the fluorocarbon piezoelectret films; d33 coefficients are relatively independent on the applied pressure in the range of 20kPa; comparing to polypropylene piezoelectret film the new fluorocarbon films show not only higher values of d33,but also much better thermal stability; Furthermore,the thermal stability of the fluorocarbon piezoelectret film can be further improved by the process of pre-ageing. The enhanced thermal stability of d33 for such fluorocarbon films is due to the good thermal stability of charges in fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE),and the dimension stability of such cellular structure. The charge recombination is mainly through the drifting of the detraped charges along the inside surfaces of the cavities when the films are thermally stimulated.
Optical properties of InGaAs/GaAs quantum chains
Wang Bao-Rui, Sun Zheng, Xu Zhong-Ying, Sun Bao-Quan, Ji Yang, Z. M. Wang, G. J. Salamo
2008, 57 (3): 1908-1912. doi: 10.7498/aps.57.1908
Abstract +
We have investigated the steady-state and transient optical properties of InGaAs/GaAs quantum chains and found that the photoluminescence (PL) decay time exhibits a strong photon energy dependence. It increases with the decrease of the emission energy. It is also found that the PL decay time increases with the excitation power. When the excitation power is large enough the PL decay time tends to be saturated. All these experimental results show that there is a strong carrier coupling along the chain direction in the quantum dot chain structure. The polarization PL measurements further confirm the carrier transfer process along the chain direction.
A novel white organic electroluminescent device with both phosphorescent and fluorescent dopants
Zhang Li-Juan, Hua Yu-Lin, Wu Xiao-Ming, Zhang Guo-Hui, Wang Yu, Yin Shou-Gen
2008, 57 (3): 1913-1917. doi: 10.7498/aps.57.1913
Abstract +
A double-layer white organic electroluminescent device was fabricated by using hole transporting material NPB doped with phosphoresecent dye Ir(piq)2(acac) as red emitting layer and CBP doped with fluorescent dye TBPe as blue emitting layer. The configuration of this device was ITO/NPB/NPB:Ir(piq)2(acac)/CBP/CBP:TBPe/BCP/Alq3/Mg:Ag/Ag in which Alq3,NPB(undoped),CBP(undoped) and BCP films functioned as electron transporting layer,hole transporting layer and exciton blocking layer,respectively. White emission was be successfully achieved from the device with good EL performance by adjusting the thicknessess of light-emitting layers and the proportion of the dopants (TBPe,Ir(piq)2(acac)). With a low turn-on voltage of 4.8V,it shows a maximum luminance of 7500cd/m2 and external quantum efficiency of 1.24% at the driving voltage of 9V. Pure white light with Commission Internationale de l'Eclairage (CIE) coordinates of(0.33 0.30)was obtained at an applied voltage of 15V.
Optoelectronic properties of the red light-emission chelating electrophosphorescent polymers
Zhen Hong-Yu, Luo Chan, Zhu De-Xi, Ye Hui, Wang Jun-Pei
2008, 57 (3): 1918-1923. doi: 10.7498/aps.57.1918
Abstract +
Photo luminesence, electrochemical and electroluminescent properties of the chelating electrophosphorescent polymers with red light-emission were investigated in this paper. The device performances of the polymers were improved by optimizing the structure. Mixing PBD in emission layer was found to decrease the luminous efficiency,but the device performances were enhanced by inserting PVK layer because of the energy transfer from PVK to the chelating polymer. The best performance was achieved in device ITO/PEDOT/PVK/ PFBtpIrm5/Ba/Al with the maximal external quantum efficiency of 4.25 at the CIE coordinates of (0.69,0.29).
Preparation and emission properties of a sub-micrometer carbonate emission material
Wang Xiao-Xia, Liao Xian-Heng, Luo Ji-Run, Zhao Qing-Lan
2008, 57 (3): 1924-1929. doi: 10.7498/aps.57.1924
Abstract +
Oxide cathodes have widely been used as electron emission source in vacuum electronic devices. Emission of an oxide cathode is dependent upon the ratio of the different ingredients of three kinds of alkaline earth carbonates on the cathodesurface and its microcopic shape. The synthesizing method plays a key role on the shape and ingredient of the carbonates. A new synthesis method,gas-liquid method,has been used to prepare the carbonates in this paper. The grains of the carbonates have filamental shape with sub-micrometer diameter. The testing results show that the cathode prepared with this sub-micrometer carbonate has large emission current density and long lifetime. The surface state and structure of the cathode are also analyzed with SEM in order to understand the mechanism of the enhanced emission current.
Peierls phase transition and field emission of carbon nanotubes in a magnetic field
Sun Hai-Jun, Liang Shi-Dong
2008, 57 (3): 1930-1934. doi: 10.7498/aps.57.1930
Abstract +
Using the tight-binding approach with the WKB method,we study the Peierls phase transition of the single-wall carbon nanotube and the field emission in a magnetic field along the tube axis. We find that the Peierls phase transition may occur above room temperature,which induces an energy gap near the Fermi level,leading to the metal-semiconducting phase transition of the carbon nanotubes. The Peierls distortion of the carbon nanotubes suppresses the field emission current. The Peierls distortion may be modified by the magnetic field applied along the tube axis. The energy band structure of the carbon nanotubes depends on the competition between the Peierls distortion and the magnetic field effect,which affects the field emission current of the carbon nanotubes.
Study on the mechanical properties of diamond like carbon films with Si doping
Zhao Dong-Cai, Ren Ni, Ma Zhan-Ji, Qiu Jia-Wen, Xiao Geng-Jie, Wu Sheng-Hu
2008, 57 (3): 1935-1940. doi: 10.7498/aps.57.1935
Abstract +
A series of samples with different Si concentration were prepared by adjusting the numbers of Si-doped graphite targets and pure graphite targets. It was found that the stress in the thin films decreased from 4.5GPa to 3.1GPa when the Si concentration reached 6.7at.%,but the hardness kept constant at about 3600Hv,almost the same as of un-doped thin films,and the friction coefficient of thin films kept constant at about 0.15. As the Si concentration in the thin film kept on increasing,the concentration of C-Si bond will increase,leading to the decrease of hardness and stress and the increase of friction coefficient.
The study of ultraviolet properties of resistant-boat evaporated LaF3 films
Shang Shu-Zhen, Shao Jian-Da, Fan Zheng-Xiu, Zhao Zhu-Xin
2008, 57 (3): 1941-1945. doi: 10.7498/aps.57.1941
Abstract +
The effects of depositing temperature on structure and optical properties of resistant-boat evaporated LaF3 single layers were investigated. The films were produced at different temperatures from 200℃ to 350℃ by increasing step of 50℃. The optical loss, optical constants, optical band gap and cut-off wavelength were deduced on the basis of the transmittance and reflectance curves. Profile and surface roughness measurement instrument was used to determine the rms surface roughness. Microstructure of the samples was characterized by X-ray diffraction (XRD). It was found that the total optical loss,the grain size and the rms surface roughness increased with the increasing of the depositing temperature at the short wavelength period. And the increasing total optical loss with depositing temperature was attributed to the absorption because the scattering occupied the very low percent in the whole loss. The samples deposited at higher temperature had the higher refractive index and extinction coefficient and lower optical band gap. The cut-off wavelength shifted to the long wavelength as the depositing temperature increased.
Low-loss 193nm anti_reflection coatings
Shang Shu-Zhen, Shao Jian-Da, Fan Zheng-Xiu
2008, 57 (3): 1946-1950. doi: 10.7498/aps.57.1946
Abstract +
The optical constants suitable for designing and depositing 193nm AR coatings were calculated, and 193nm AR coatings were designed, produced and characterized on the basis of the calculated results. It was found that the extinction loss of the substrate material had such an important effect that when it was beyond a certain level the designed transmittance could not reach the ideal value. The designed and manufactured results of the single_surface AR coatings revealed that scattering loss began to play the key role when the absorbance loss decreased to a certain extent. High performance 193nm AR coatings with residual reflectance lower than 0.2% have been prepared by the resistant boat evaporation method.
Fabrication and optical properties of 2D ordered arrays of CdS nanocrystals by nanosphere lithography
Sun Ping, Xu Ling, Zhao Wei-Ming, Li Wei, Xu Jun, Ma Zhong-Yuan, Wu Liang-Cai, Huang Xin-Fan, Chen Kun-Ji
2008, 57 (3): 1951-1955. doi: 10.7498/aps.57.1951
Abstract +
We realized the fabrication of 2D ordered arrays of CdS nanocrystals by nanosphere lithography by use of a monolayer of self-assembled polystyrene spheres 220nm in diameter as a mask. We used scanning electron microscope (SEM) to characterize the structure of samples. The results indicate that the 2D arrays of CdS nanocrystals produced by nanosphere lithography have highly ordered structure which has the same period of the original PS mask. According to the transmission spectrum,it is estimated that the forbidden band width of the CdS nanocrystals is around 2.60eV,which shows a size-dependence of the CdS nanocrystals. This structure has the promising application in the light filter and single-photon emitter.
Research on the electron transport and back-reaction kinetics in TiO2 films applied in dye-sensitized solar cells
Liang Lin-Yun, Dai Song-Yuan, Fang Xia-Qin, Hu Lin-Hua
2008, 57 (3): 1956-1962. doi: 10.7498/aps.57.1956
Abstract +
The mechanics of electron transport and properties of back-reaction kinetics were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The theoretical expression fitting the experimental data of five different porous TiO2 films applied in DSC and the values of absorption coefficient (α),the diffusion coefficient (Dn),electron lifetime (τn),the electron transit time (τd) and IPCE can be obtained. The results showed that the electrons transit faster in the thinner films,while the electron concentration increase in the thicker films. The influence of film thickness on the electron generation,transport and recombination processes was investigated in the microscopic level in this paper.
A study of applicability of light emitting diodes in differential optical absorption spectroscopy measurements
Li Su-Wen, Xie Pin-Hua, Liu Wen-Qing, Si Fu-Qi, Li Ang, Peng Fu-Min
2008, 57 (3): 1963-1967. doi: 10.7498/aps.57.1963
Abstract +
The applicability and application of modern light emitting diodes (LEDs) as active source in differential optical absorption spectroscopy (DOAS) was discussed in this paper. The radiative properties of LEDs and spectral shape,spectral range,spectral stability were analyzed. When temperature was not constant,the Fabry Perot etalon structures of LEDs would interfered with the DOAS evaluation. If they were treated as a kind of ‘component' of atmosphere and retrieved with other atmospheric components together,their effect on the measurements could be restricted to a minimum. The experimental results showed that LEDs can be used successfully as light sources in active DOAS to measure NO2 in the atmosphere. The correlation of the NO2 concentration measured by the LEDs-DOAS and the xenon arc light DOAS was 0.99. The detection limits of 1.1×10-9 were obtained for the path length of a 0.7km in the atmosphere.
Observation of the lightning_induced voltage in the horizontal conductor and its simulation
Yang Jing, Qie Xiu-Shu, Wang Jian-Guo, Zhao Yang, Zhang Qi-Lin, Yuan Tie, Zhou Yun-Jun, Feng Gui-Li
2008, 57 (3): 1968-1975. doi: 10.7498/aps.57.1968
Abstract +
Characteristics of induced voltage in a horizontal conductor due to a natural lightning with 9 dart leader/return stroke sequence were analyzed. Effect of various parameters on the induced voltage was examined by numerical simulation. The induced voltage varied from a minimum of 4.6 kV to a maximum of 18.6 kV with a geometric mean of 11.2 kV. The geometric mean of the half-peak width and the down time of the induced voltage was 0.87 and 2.9 μs, respectively. The simulated results showed that the induced voltage on both ends of the horizontal conductor would increase with increasing return stroke velocity and also increase with increasing height of the horizontal conductor. The voltage would also increase with increasing of the matched grounding impedances on both ends of the horizontal conductor but the relationship was nonlinear. The induced voltage at the higher impedance end was much larger than that at the lower impedance one provided that the impedances at both ends were not matched, which indicates that good grounding can decrease effectively the induced voltage along the conductor.
The research of detecting abrupt climate change with approximate entropy
Wang Qi-Guang, Zhang Zeng-Ping
2008, 57 (3): 1976-1983. doi: 10.7498/aps.57.1976
Abstract +
The approximate entropy method is applied to an ideal time series. It is indicated that the method is capable of distinguishing between different structural dynamics and detecting structural dynamics mutation. And then,this method is applied to the observation data of the daily temperature and precipitation of the 740 sites between 1960 and 2000. The results showed that,the approximate entropy distribution of the temperature and precipitation has a characteristic of obvious district distribution,and displays the territorial difference of dynamic structures of climate system. Abrupt climate changes have been detected by the approximate entropy of the annual precipitation and temperature between 1970s and 1980s. The characteristics of the in homogeneity of temporal and spatial distribution of abrupt climate changes and the complexity of climate systems have been demonstrated.
The new method of modeling horizontal error functions in variational assimilation with orthogonal wavelet
Cao Xiao-Qun, Huang Si-Xun, Du Hua-Dong
2008, 57 (3): 1984-1989. doi: 10.7498/aps.57.1984
Abstract +
Background error covariance is an important part of variational data assimilation system,which is used to spread the observation information to other grid points and vertical levels of the model. In order to model the inhomogeneity and anisotropy in horizontal error functions of raw background error covariance,a new method is proposed to model horizontal error functions based on orthogonal wavelet transforms. The results of experiments show that the new method successfully modeled the heterogeneity and anisotropy included in the local correlation functions and depicted the structure and feature of raw covariance correctly.