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Vol. 57, No. 8 (2008)

2008-04-20

INVITED REVIEW

Integral invariants of a generalized Birkhoff system
Mei Feng-Xiang, Cai Jian-Le
2008, 57 (8): 4657-4659. doi: 10.7498/aps.57.4657
Abstract +
Integral invariants of a generalized Birkhoff system are studied in this paper. The condition under which the integral invariants exist in the system is given. A linear integral invariant, a universal integral invariant and an absolute integral invariant of second order of the system are obtained under the given condition. An example is given to illustrate the application of the result.

INVITED REVIEW

Switch effect of Bose-Einstein condensates in a triple-well potential
Yang Shi-Ping, Wang Hai-Lei
2008, 57 (8): 4700-4705. doi: 10.7498/aps.57.4700
Abstract +
We propose a scheme utilizing mean-field approach to exhibits the switching effect in a symmetrical Bose-Einstein condensate triple-well potential. Our study shows that tunneling from the left well to the right well of a large number of atoms can be controlled by a small amount of atoms in the middle well. We also discuss the role played by the relative phase and the relation between the zero-point and the critical value of working range. The potential applications of our model are pointed out.
GENERAL
Generalized variational iteration solving method for gain gluence of a laser pulse amplifier
Mo Jia-Qi, Zhang Wei-Jiang, Chen Xian-Feng, Lin Wan-Tao
2008, 57 (8): 4641-4645. doi: 10.7498/aps.57.4641
Abstract +
The model for gain fluence of a laser pulse amplifier is studied. Firstly, using the generalized variational iteration method, the Lagrange multipicator is determined. Then the iteration expansions are constructed. Thus approximate solutions for the corresponding model are obtained.
Approximate solution for a class of solitons of the Landau-Ginzburg-Higgs perturbed equation
Mo Jia-Qi, Chen Li-Hua
2008, 57 (8): 4646-4648. doi: 10.7498/aps.57.4646
Abstract +
The corresponding solution for a class of Landau-Ginzburg-Higgs equation is considered using the analytic method. From the generalized variational iteration theory, the solution of corresponding equation is obtained. And then the approximate soliton solution of the solution for the equation is obtained.
An inverse problem of dynamics of a generalized Birkhoff system
Mei Feng-Xiang, Xie Jia-Fang, Gang Tie-Qiang
2008, 57 (8): 4649-4651. doi: 10.7498/aps.57.4649
Abstract +
For the generalized Birkhoff system dynamics, the authors present a kind of inverse problem. The generalized Birkhoff system equations are established by using given integral manifolds. The solution of the problem, in general, is not unique. In order to obtain a determining solution, some additional conditions are required. An example is given to illustrate the application of the result.
Non-Noether conserved quantity for relativistic nonholonomic controllable mechanical system with variable mass
Xia Li-Li, Li Yuan-Cheng
2008, 57 (8): 4652-4656. doi: 10.7498/aps.57.4652
Abstract +
The non-Noether conserved quantity for relativistic nonholonomic controllable mechanical system with variable mass is discussed under special infinitesimal transformations in which the time is not a variable. The differential equations of motion of the system are established. The definition and criterion of the form invariance of the system under special infinitesimal transformations are discussed. The necessary and sufficient conditions under which the form invariance is a Lie symmetry is presented. The conditions under which a non-Noether conserved quantity can be induced by the form invariance and the form of the conserved quantity are obtained. An example is presented to illustrate the application of the result.
Phase separation in a three-dimensional granular gas system
Liu Rui, Li Yin-Chang, Hou Mei-Ying
2008, 57 (8): 4660-4666. doi: 10.7498/aps.57.4660
Abstract +
Granular systems, without any energy injection, tend to be clustered or condensed due to inelasticity of the particle collisions. Even in a driven granular gas, this notable phenomenon would be present locally and lead to a spatial inhomogeneity, just like the forming of liquid droplets in gases. The present work, by extending an existing two-dimensional theory, offers a three-dimensional model for such a phase-separation phenomenon in a driven granular gas under zero gravity. According to the model, exact conditions for phase separation are obtained through numerical calculations. Event-driven molecular dynamics simulations confirm the theoretical results, and show new morphologies of phase separation in three-dimensional granular gases.
Force distribution in static granular matter in two dimensions
Sun Qi-Cheng, Wang Guang-Qian
2008, 57 (8): 4667-4674. doi: 10.7498/aps.57.4667
Abstract +
Granular matter is a large assemblage of individual solids, which is fundamentally different from any other type of matters, such as solid and liquid. The intrinsic nature of granular matter is of multi-scale, inclusive of microscale of particle size, mesoscale of force chain and macroscale of the bulk of granular matter. The mesoscale of force chain bridges single particle and granular matter, and leads to unique properties and behaviours of granular matters, and thus acts as the key issue in the study of granular matter. In this work, we firstly propose a multiscale methodology for granular matter dynamics, and point out that the characteristics of force chain is the key to the granular dynamics. We then propose a discrete element model based on rigorous Hertzian contact law and Mindlin-Deresiewicz contact theory for normal and tangential contact forces, respectively. The static packing of 12000 sand grains under the action of gravity in two dimensions is simultaed, and the force chain pattern and stress distribution are obtained. The force distribution, force chain length distribution and the angle distribution are calculated and analyzed. Friction coefficient of particle is found to be a very sensitive factor affecting properties of granular matter, and thus its influence on the above parameters is studied as well.
Stability and approximate solution of a relative-rotation nonlinear dynamical system under harmonic excitation
Shi Pei-Ming, Liu Bin, Liu Shuang
2008, 57 (8): 4675-4684. doi: 10.7498/aps.57.4675
Abstract +
The dynamical equation of a relative-rotation nonlinear dynamical system with nonlinear elastic force and common friction and harmonic excitation is deduced. The singularity stability of the autonomous system is studied by constructing the Lyapunov function. The approximate solution of unautonomous equation with different resonance response under harmonic excitation is obtained by the method of multiple scales, and the stability of main resonance stable state of motion is studied.
Coherent population trapping in a specific model
Bi Dong-Yan
2008, 57 (8): 4685-4688. doi: 10.7498/aps.57.4685
Abstract +
Coherent population trapping is shown to occur in a driven symmetric double-well potential. In the model of the ammonia molecule, for a molecule initially prepared in its lower doublet, under certain circumstances, the upper level remains unpopulated, this occurs in spite of the fact that the laser field is resonant with the |2〉→|3〉 trasition. This is a coherent population trapping phenomenon which cannot be accounted for with the convential models.
Quantum secret sharing with bidirectional authentication
Du Jian-Zhong, Sun Ying, Qin Su-Juan, Wen Qiao-Yan, Zhu Fu-Chen
2008, 57 (8): 4689-4694. doi: 10.7498/aps.57.4689
Abstract +
A quantum secret sharing scheme with two-way authentication was proposed and discussed. Based on two-particle quantum entanglement, the scheme is implemented using the Hash function and the quantum local operations. The authentication keys and the secret order of transmitted particles ensure the security of the scheme. One Bell state can be used to share two classical bits on average if the particles for authentication and eavesdropping detection are not concernred.
Encoding and decoding of quantum convolutional codes
Xing Li-Juan, Li Zhuo, Bai Bao-Ming, Wang Xin-Mei
2008, 57 (8): 4695-4699. doi: 10.7498/aps.57.4695
Abstract +
The research on quantum convolutional codes is aimed at protecting a flow of information over long distance communications. The polynomial representation of a quantum state is defined. Based on the Calderbank-Shor-Steane(CSS)-type construction of quantum codes, a new method for encoding and decoding of CSS-type quantum convolutional codes is presented and corresponding networks are described. The basis state of the code is transformed into the product of an information polynomial by the generator polynomial. Then networks can be realized by operations of polynomial multiplication. Finally, inspired by classical convolutional decoding idea, a quantum Viterbi algorithm with linear complexity is put forward.
Stochastic resonance of frequency modulated signals in a linear model of single-mode laser
Cao Li, Jin Guo-Xiang, Zhang Liang-Ying
2008, 57 (8): 4706-4711. doi: 10.7498/aps.57.4706
Abstract +
By adding frequency modulated signal to the equation of the laser intensity of the gain-noise model of the single-mode lasers, we use the linear approximation method to calculate the power spectrum and signal-to-noise ratio (SNR) of the laser intensity, which is driven by two white noises correlated in the form of δ function. The result shows that the SNR shows typical stochastic resonance with the change of intensities of the pump noise and quantum noise. As the amplitude of a modulated signal has an effect on the SNR, it shows suppression, monotonic increase, resonance, suppression and resonance and so on, with the varing of the frequencies of the carrier signal and modulated signal.
Chaotic synchronization of network of Chen’s chaotic attractors using nonlinear coupling function
Yu Hong-Jie, Zheng Ning
2008, 57 (8): 4712-4720. doi: 10.7498/aps.57.4712
Abstract +
This article offers a method to realize the synchronization of non-symmetrically nonlinear-coupled chaotic systems, studies the chaotic synchronization of Chen's chaotic attractors, and analyzes the influence of chaotic synchronization by numerical simulation under different coupling strengths and different initial conditions. We also extend the synchronization method of non-symmetrically nonlinear-coupled systems to the study of large network linked by numerous Chen's attractor system units by all-to-all-coupling and star coupling. We deduced the equation of errors which ensures the stability of synchronous state, studied the influence of different coupling strengths on synchronization stability and determined the range of coupling strengths which ensures the synchronization. By numerical simulation we proved that if we choose nonlinear functions as coupling functions, it effectively realizes the synchronization of all-to-all-coupling network and large network linked from star sub-networks. We can foresee that the non-symmetrically nonlinear-coupled synchronization method could be widely used in network synchronization.
Adaptive slide mode control for a class of chaotic systems with perturbations
Li Xiu-Chun, Xu Wei, Xiao Yu-Zhu
2008, 57 (8): 4721-4728. doi: 10.7498/aps.57.4721
Abstract +
Based on the adaptive slide mode control method, we investigated the robust synchronization for a class of chaotic systems with random perturbations. This approach can be applied to may chaotic systems; and the upper bound of random perturbations is not necessarily known in advance and it is estimated through an adaptive control process. Finally, two-scroll chaotic system, Lorenz system and hyperchaotic Rssler system are taken as examples to illustrate the effectiveness of the proposed method.
Anti-synchronizing different chaotic systems using active sliding mode control
Liu Fu-Cai, Song Jia-Qiu
2008, 57 (8): 4729-4737. doi: 10.7498/aps.57.4729
Abstract +
An active sliding mode control is designed to anti-synchronize different chaotic systems. The closed loop error dynamics depends on the linear part of the response systems and parameters of the controller. Therefore, the anti-synchronization rate can be adjusted through these parameters. Analysis of the stability for the proposed method is done based on the Lyapunov stability theorem. Finally, numerical results are presented for the Lorenz, Chen and Lü systems. This method may realize the anti-synchronization quickly, and the robust stability is good.
Design and implementation of chaotic generators based on IEEE-754 standard and field programmable gate array technology
Zhou Wu-Jie, Yu Si-Min
2008, 57 (8): 4738-4747. doi: 10.7498/aps.57.4738
Abstract +
A new approach for the design and hardware implementation of field programmable gate array (FPGA) general chaotic and hyperchaotic signal generators based on IEEE-754 standard is proposed. Firstly, using Euler algorithm and appropriate discrete processing, the continuous chaotic systems can be converted to discrete chaotic systems, which is appropriate for realization by digital signal processor. Secondly, according to IEEE-754 standard and module-based design idea, five basic floating-point operational modules, namely the multiplication operation module, addition operation module, symbolic function operation module, positive and negative absolute operation module, and initial and iteration value selection module, are constructed by using Verilog-HDL. Based on this method, different types of chaotic and hyperchaotic signals via FPGA are generated. Finally, using configurable voice device, chaotic signals are output through the stereo left and right channels and attractors can be observed by the oscillograph. The characteristic of this method is its universality. Furthermore, the floating-point algorithm and working principle are analyzed. The algorithm flow chart, technical development process, hardware design and realization result are given.
Synchronization and control of autocatalytic chemical reaction in continuous stirring tank reactor
Li Yong, Zhang Xiao-Fang, Bi Qin-Sheng
2008, 57 (8): 4748-4755. doi: 10.7498/aps.57.4748
Abstract +
The synchronization problem for a chemical reaction system composed of two continuous stirring tank reactorv is explored. Based on Lyapunov stability theory, a new method is proposed to design the controlling function. The range of the coupling strength to realize the synchronization between the two chemical systems is investigated both for the case with static velocity and with periodically disturbed velocity of the input material. Numerical simulations are then performed to demonstrate the effectiveness of the proposed scheme, which show that the method is suitable for both the autonomous system and the non-autonomous system with periodic perturbation.
Modelling of chaotic systems using wavelet kernel partial least squares regression method
Li Jun, Dong Hai-Ying
2008, 57 (8): 4756-4765. doi: 10.7498/aps.57.4756
Abstract +
Based on the powerful nonlinear mapping ability of kernel learning, and in combination with the partial least square (PLS) algorithm for linear regression, a wavelet kernel partial least square (WKPLS) regression method is proposed. By the method, the input-output data are firstly mapped to a nonlinear higher dimensional feature space, a linear PLS regression model is then constructed by the classic kernel transformation trick used in support vector machines. The PLS approach utilizes the covariance between input and output variables to extract latent features, and the wavelet kernel which is an admissible support vector kernel function is characterized by its local analysis and approximate orthogonality. Hence, the proposed WKPLS method combining PLS approach with wavelet kernel function shows excellent learning performance for modeling nonlinear dynamic systems. The WKPLS is then applied to modelling of several chaotic dynamical systems and compared with the kernel partial least squares(KPLS) method using Gaussian kernel function. Simulation results confirm that the WKPLS identifier is fast and can accurately approximate unknown chaotic dynamical system, and its approximation accuracy is higher than the KPLS under the same conditions.
Generalized synchronization of spatiotemporal chaos systems by phase compression
Lü Ling, Jing Xiao-Dan
2008, 57 (8): 4766-4770. doi: 10.7498/aps.57.4766
Abstract +
A phase compression scheme is proposed to achieve generalized synchronization for spatiotemporal chaos systems. The method is shown to be effective and practical by applying it to the numerical simulation of the Fitzhugh-Nagumo system, a kind of spatiotemporal chaos of reaction diffusion system. The effect of synchronization on the system is studied under bounded noise and the results show that the synchronization method has strong capability in anti-jamming. Generalized synchronization of two arbitrary spatiotemporal chaos systems can be realized by the method, which shows its universality in applications. The structure of the synchronous controller is simple and easy to use.
Stability and Hopf bifurcation of the simplified Lang-Kobayashi equation
Wang Zuo-Lei
2008, 57 (8): 4771-4776. doi: 10.7498/aps.57.4771
Abstract +
Stability and Hopf bifurcation of the simplified Lang-Kobayashi equation is considered. The critical time delay associated with Hopf bifurcation of the zero equilibrium is determined by applying the bifurcation theorem. A formula for determining the direction of the Hopf bifurcation and the stability of bifurcating periodic solutions is given by using the normal form method and center manifold theorem. Finally, numerical simulations are performed to verify the analytical prediction.
Multi-value cellular automata model for mixed non-motorized traffic flow
Li Xin-Gang, Gao Zi-You, Zhao Xiao-Mei, Jia Bin
2008, 57 (8): 4777-4785. doi: 10.7498/aps.57.4777
Abstract +
In this paper, a multi-valued cellular automata model for mixed non-motorized traffic flow is proposed and the simulation results are studied. The mixed non-motorized traffic flow is mainly composed of bicycles and tricycles in Chinese towns. According to the fact that bicycles and tricycles have different sizes, a bicycle is assumed to occupy one unit cell space and a tricycle two units of cell space. The simulation results show that: In the system with slow bicycles and tricycles, the ratio and the first moving probability of tricycles do not affect the flux, however, the first moving probability of tricycles will impact on the average velocity of bicycles and tricycles. In the system with fast bicycles and tricycles, the multiple state effect appears both in free flow and congested flow regions under the deterministic case, and it disappears when the fast bicycles has the randomization effect.
A cellular automaton model for studying the on-ramp control of highway
Tang Tie-Qiao, Huang Hai-Jun, Mei Chao-Qun
2008, 57 (8): 4786-4793. doi: 10.7498/aps.57.4786
Abstract +
In this paper, a cellular automaton model for studying the on-ramp traffic control problem of highway is proposed. The number of vehicles contained in a highway segment adjacent to the ramp merging region is used to control the on-ramp signal light. Simulation results show that the on-ramp control can improve the highway traffic, particularly when the ramp traffic is heavy. It is found that the location of detected highway segment, the length of ramp merging region and the control parameter governing the light change affect the highway and ramp traffic simultaneously. These three parameters should be coordinately designed for the improvement of both highway and ramp traffic. In general, the detected highway segment should be located at the upstream of the ramp merging region and cover it in the proper direction.
Two-sex epidemic spreading on bipartite scale-free networks
Yang Xiao-Fan, Zhong Jiang, Wen Luo-Sheng
2008, 57 (8): 4794-4799. doi: 10.7498/aps.57.4794
Abstract +
Applying the SIS (susceptible-infected-susceptible) model, we study the epidemic spreading on the web of human sexual contacts. When only heterosexual contacts are considered, the web is a bipartite scale-free network. By using the rate equation approach, we analyze the relation between epidemic threshold and infection rates of female-to-male and male-to-female. We find that the ratio of infected female density to infected male density is determined by the topology of the network and the proportion between infection rates of females and males. This demonstrates the importance of the topology of network. Finally, we present numerical simulation results that support the analytic results.
Optimizing the synchronizability of generalized deactivation networks
Liu Shu-E, Tian Liang, Shi Da-Ning, Dai Cun-Li
2008, 57 (8): 4800-4804. doi: 10.7498/aps.57.4800
Abstract +
We research the synchronizability of the generalized deactivation networks without changing its degree distribution. The synchronizability measured by the eigenratio R can be effectively optimized by adjusting the only parameter, the number of active nodes M. The eigenratio R is shown very sensitive to the M, and larger M will lead to better synchronizability. Furthermore, we find that, in a wide interval, the eigenratio R obeys a approximate power-law in the form of R~M-2.0. By introducing a perturbation, the synchronizability of network can be effectively optimized.
A network model with exponential cut-off degree distribution and local-cluster property
Yuan Shao-Qian, Zhao Hai, Li Chao, Zhang Xin
2008, 57 (8): 4805-4811. doi: 10.7498/aps.57.4805
Abstract +
According to the character of local evolving mechanism in real network, we propose a new local-clustered network evolving model (LC model). Theoretical analysis and numerical simulations show that the LC model obeys a power-law degree distribution with an exponential cut-off, and its cluster coefficient is much bigger than the local-world model (LW model) proposed by Li and Chen and is more, close to real network. We simulate the performance of LC model against random errors and malice attacks, and discover that LC model is more fragile under attacks because of its large cluster coefficient.
Fast reconstruction of two-dimensional temperature distribution in participating medium
Liu Dong, Wang Fei, Huang Qun-Xing, Yan Jian-Hua, Chi Yong, Cen Ke-Fa
2008, 57 (8): 4812-4816. doi: 10.7498/aps.57.4812
Abstract +
An original model was presented for fast reconstruction of two-dimensional temperature distribution in participating medium using radiative information captured by charge-coupled device cameras. Compared with present models for temperature reconstruction, the model developed here is based on backward Monte Carlo method and reconstruction speed is faster, it is more efficient and can describe the scattering medium better. An exact two-dimensional temperature was assumed to be the reconstruction object and results show that even if there are measurement errors, the reconstructed temperature distribution can reproduce the original temperature distribution.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Accurately calculate cross section of the n+n→2π0 reaction in the n-n renormalization chain diagram
Pan Yu, Wang Kai-Jun, Fang Zhen-Yun, Wang Xian-You, Peng Qing-Jun
2008, 57 (8): 4817-4825. doi: 10.7498/aps.57.4817
Abstract +
Adopting Lorentz-invariant coupling model of neutron n-antineutron n and neutral meson strong interaction, we made physical analysis and accurate calculation of the n-n renormalization chain diagram propagator, and obtained the theoretical results. Furthermore, in applying it to the physical process analysis and cross-section evaluation in the reaction n+n→2π0, its differential cross-section is obtained. Through the comparison between this calculation and those scenarios, namely the n-n tree diagram and renormalization chain diagram propagator contribution, some important information about radiative correction was obtained. This study would offer certain academic references to the further research on Lorentz-invariant coupling model and the nuclear physics about cross section problem of particles in nucleon antinucleon and neutral meson strong interaction in terms of theoretical calculations. In addition, it will also provide something valuable on relevant physical processes, and on the renormalization calculation orderly with different approaches in perturbation theory of quantum field theory.
NUCLEAR PHYSICS
Theoretical investigation of β- decays in neutron-rich nitrogen isotope
Zhang Yu-Mei, Xu Fu-Rong
2008, 57 (8): 4826-4832. doi: 10.7498/aps.57.4826
Abstract +
We have studied the low-lying level schemes of 18,19,20,21O and the β--decay branching ratios of nitrogen isotope. The shell-model calculations have been carried out in the psd shell space. The results are compared with the recent experimental data with reasonable agreement. Our calculations also predict the β--decay property of 21N and the structure of 21O.
ATOMIC AND MOLECULAR PHYSICS
Analytical potential energy function for tritium water molecule T2O(X1A1)
Xie An-Dong, Zhang Li, Zhu Zheng-He, Ruan Wen, Luo Wen-Lang
2008, 57 (8): 4833-4839. doi: 10.7498/aps.57.4833
Abstract +
The greatest difficulty in deriving the analytical potential energy function of T2O(X1A1) lies in its identity with that of H2O(X1A1) under the Born-Oppenheimer approximation. However, molecular potential energy function is actually a function of internal coordinates, such as bond length and bond angle which correlate with vibration energy, hence with vibration frequency, force constants and isotopic mass. Based on these relations, by using nuclear vibration, rotation, and translation energies to correct electronic energies, the force constants of T2O(X1A1) can be obtained, which represent the difference in masses of isotopes H and T. The calculations are reasonably consistent with reference values. After determining the dissociation limits and dissociation energy and all parameters of two-body terms of T2O(X1A1), the analytical potential energy function has finally been derived by using many-body expansion theory with due consideration of the isotopic effect. The potential energy contours correctly show the equilibrium structure of T2O(X1A1) and the characteristics of the reactions T+OT→T2O and O+T2→T2O. The results lay a sound basis for further researches on reactive collisions.
The design of quadrapole-Ioffe configuration trap for quantum degenerate Fermi-Bose mixtures
Wang Peng-Jun, Chen Hai-Xia, Xiong De-Zhi, Yu Xu-Dong, Gao Feng, Zhang Jing
2008, 57 (8): 4840-4845. doi: 10.7498/aps.57.4840
Abstract +
The quadrapole-Ioffe configuration (QUIC) trap consists of two identical quadrupole coils and one Ioffe coil, which has been applied widely to trap neutral atoms for evaporation cooling. We have designed two different structures of the QUIC trap. By the numerical calculation and experimental test, we obtained the optimized structure. In the QUIC trap, the magnetically trapped rubidium-87 atoms are cooled evaporatively to below the phase transition of Bose-Einstein condensation, at the same time, the potassium-40 atoms are cooled sympathetically to the Fermi degeneracy.
Measurement of single-electron transfer cross sections in collision of C3+ with neon at intermediate velocity
Liu Hui-Ping, Chen Xi-Meng, Liu Zhao-Yuan, Gao Zhi-Min, Liu Yu-Wen, Du Juan, Zhang Hong-Qiang, Sun Guang-Zhi, Wang Jun, Xi Fa-Yuan, Wang Yuan
2008, 57 (8): 4846-4850. doi: 10.7498/aps.57.4846
Abstract +
Absolute cross sections for single-electron transfer of neon induced by C3+ at intermediate velocity (2.2v0—4.2v0) were measured and calculated using n-body classical trajectory Monte Carlo (nCTMC) method. Good overall agreement between experimental and nCTMC results is found. Screening effect, changes of the ionization potential and the effective charge are taken into account in interpreting the qualitative differences between theoretical and experimental results. In addition, the mechanism of transfer ionization is discussed briefly.
Density functional theory study of the structure and electronic properties of MgnOn(n=2—8) clusters
Luo You-Hua, Ge Gui-Xian
2008, 57 (8): 4851-4856. doi: 10.7498/aps.57.4851
Abstract +
Geometric structures of MgnOn(n=2—8) clusters are optimized by using the generalized gradient approximation density functional theory. Energy, vibrational frequency and electronic properties have been calculated. The geometries of the global minima of MgnOn(n=2, 3) are ring-like. The three-dimensional structures of MgnOn(n≥4) may be built from Mg2O2 and Mg3O3 rings. The stability of clusters gained from obtuse O—Mg—O angles and much charge transfer. The transferred charge increases between Mg and O atoms with cluster size increasing, showing a tendency towards bulk charges. Mg3O3 and Mg6O6 clusters are shown to be more stable than neighboring ones by the investigations on vertical ionization potential, electron affinities and the energy gaps between the highest occupied and lowest unoccupied molecular orbitals.
Density functional theory study of the stability, electronic and magnetic properties of Scn, Yn and Lan (n=2—10) clusters
Guo Yun-Dong, Wang Hong-Yan, Li Xi-Bo, Luo Jiang-Shan, Wu Wei-Dong, Tang Yong-Jian
2008, 57 (8): 4857-4865. doi: 10.7498/aps.57.4857
Abstract +
Several functionals combined with different basis sets have been examined for the Sc2, Y2 and La2 dimer by using density functional theory. Compared with previous theoretical and experimental data of dimers, the BP86/CEP121G level for Scn and Yn clusters, the PBE1PBE/LANL2DZ level for Lan (n=2—10) clusters were selected to investigate the geometry, stability, electronic and magnetic properties of these clusters. The relative stability of these clusters of the same group have the same results, which can be explained by the model with geometry of dense packing. The highest occupied molecular orbital—lowest unoccupied molecular orbital gap of Lan clusters are bigger than those of Scn and Yn clusters, and a relative bigger energy gap are found for the magic clusters with n=4, 7 and 9. The vertical ionization energy VIP and electron affinity were calculated, and the VIP is in good agreement with experiments for yttrium clusters. The static polarizabilities can characterize the stability of these clusters. Big and anomalous magnetic moments are discovered and are in agreement with the experiments for Scn, Yn and Lan clusters, but they decrease with the increasing of cluster size and have local oscillatory character.
Density functional theory study of [Mg(NH2)2]n(n=1—5) clusters
Kang Long, Luo Yong-Chun, Zhang Cai-Rong, Ma Jun, Chen Yu-Hong
2008, 57 (8): 4866-4874. doi: 10.7498/aps.57.4866
Abstract +
Possible geometrical structures and relative stabilities of [Mg(NH2)2]n(n=1—5) clusters are studied by using the hybrid density functional theory (B3LYP) with 6-31G* basis sets. For the most stable isomers, the electronic structure, vibrational properties, bond properties and ionization potentials are analyzed. The calculated results show the following tendencies: the Mg and N atom are bonded with each other to form catenulate structures. The bond lengths for [Mg(NH2)2]n (n=1—5) clusters are about 0.190—0.234nm for Mg—N, and 0.101—0.103 nm for the N—H bonds, the bond angles of H—N—H are about 100.2°—107.5°. The population analysis suggests that the natural charge of N atoms are about -1.551e—-1.651e, that of Mg atoms are about 1.585e—1.615e, that of H atoms are about 0.369e—0.403e, and that of—NH2 are about -0.784e—-0.845e, and the bonds between Mg and —NH2 have strong ionicity. The comparative study of structures and spectra of clusters and crystal show that —NH2 keeps the integrity in the crystal and in clusters.
CLASSICAL AREA OF PHENOMENOLOGY
High frequency characteristics of a magnetically insulated transmission line oscillator oscillating in HEM11 mode
Deng Jing-Kang, Wang Dong, Chen Dai-Bing, Fan Zhi-Kai
2008, 57 (8): 4875-4882. doi: 10.7498/aps.57.4875
Abstract +
Coaxial disk-loaded waveguide has been widely used in magnetically insulated transmission line oscillators (MILO). Although TM00 mode is assumed to be its main mode, the asymmetric mode might be excited by slight asymmetry of the structure, asymmetric emission of the beam, or both. So the research on asymmetric mode in coaxial disk-loaded waveguide is necessary. The general eigen equation with both symmetric and asymmetric modes in coaxial disk-loaded slow-wave structures is theoretically analyzed. Then, a HEM11 mode working MILO is designed and a tentative experiment is carried out to test its performance. Employing an electron beam of about 480 kV and 39 kA, HEM11 mode working MILO generates a high power microwave output of about 1.2 GW with 40 ns pulse duration at 1.98GHz. The power conversion efficiency is about 6.5% and the generated microwave mode is TE11 in the coaxial output region.
Investigation on the electromagnetic characteristics of lossy metamaterial covered dielectric cylinder
Wu Jian, Wang Hai-Long, Wu Qun, Meng Fan-Yi, Li Le-Wei
2008, 57 (8): 4883-4890. doi: 10.7498/aps.57.4883
Abstract +
The electromagnetic characteristics of the model with an electric line source radiating in the direction parallel to a lossy metamaterial covered infinitely long dielectric circular cylinder have been investigated. Firstly, the electromagnetic model is presented and the exact solution is derived. Secondly, this exact solution is employed in numerical calculations. The patterns of the near field under different electromagnetic parameters are obtained. The characteristics of the far field properties are also studied through the directivity and the normalized radiation resistance. Due to the effect of the negative refraction and the loss of the lossy metamaterial, in comparing the lossless metamaterial layer and the lossy conventional material layer, very different electromagnetic characteristics on the near and the far field of the lossy metamaterial covered dielectric cylinder are revealed.
Study on the near field modulation and laser induced damage of beam sampling grating
Wen Sheng-Lin, Yao Xin, Gao Fu-Hua, Li Jian-Feng, Zhang Yi-Xiao, Guo Yong-Kang
2008, 57 (8): 4891-4897. doi: 10.7498/aps.57.4891
Abstract +
The beam sampling grating (BSG) is one kind of important diffractive optical elements which is used in sampling and diagnosis. In terminal optical system of the inertial confinement fusion (ICF) system, the modulation produced by strong laser in the near field, may cause laser induced damage to the BSG. It makes the element work abnormally. In order to provide the theoretical basis for protecting this kind of optical element from laser induced damage under the strong laser condition, this paper uses the Fourier modal theory to carry on the numerical simulation of the interior modulation for BSG in near field. The results indicate that the interior modulation of BSG is weak, but the optical field distribution is still not even, thus in these areas the damage probability is higher than in other positions. Moreover, through the fabrication error analysis of BSG, the relationship between modulation in near field and fabrication error was obtained. The computed results indicate that the depth error and the duty cycle error of grooves affect the modulation of the light beam in near field, but the influence of groove depth error is larger than the duty cycle error. However, if the groove depth error does not exceed a definite value, its modulation also remains on a lower level. Therefore the BSG can still work in the ICF driver normally.
Multilayer dielectric thin film reflector for spectrum reshaping of chirped pulse laser in Nd:glass chirped pulse amplification system
Dai Ya-Ping, Wang Tao, Zhang Bin, Li Ming, Huang Wei, Fan Zheng-Xiu
2008, 57 (8): 4898-4903. doi: 10.7498/aps.57.4898
Abstract +
In order to compensate for the gain narrowing and gain saturation effects, and also to improve the signal to noise ratio of the output high-power laser pulse, lots of attention have been paid to the spatial distribution, the temporal profile, as well as the spectrum reshaping in the design of kilo-joule peta-watt chirped pulse amplification (CPA) systems. In this paper, a new method for the spectrum reshaping is proposed, which utilizes a multilayer dielectric thin film reflector with specific construction to realize the spectrum reshaping of the chirped pulse laser in large energy and high power Nd:glass CPA system. The results show that the reflectivity distribution of the multilayer dielectric film reflector can be controlled effectively only if the parameters of the thin film reflector are chosen appropriately. The spectrum modulation radio can be varied over 60% under the condition that the phase of the reflecting light remains nearly constant. The thin film reflector designed for spectrum reshaping of the Nd:glass CPA system with the central wavelength of 1053nm exhibits a bandwidth of reflect light of 196nm, the chromatic resolving capability of about 0.1nm and the phase aberration in the range of the tens of nanometer of up to 12mrad, which can meet the requirement of the “Senguang-Ⅱ” kilo-joule peta-watt reconstruction project.
Diffraction property of multi-layer dielectric gratings studied by rigorous coupled-wave analysis
Kong Wei-Jin, Yun Mao-Jin, Sun Xin, Liu Jun-Hai, Fan Zheng-Xiu, Shao Jian-Da
2008, 57 (8): 4904-4910. doi: 10.7498/aps.57.4904
Abstract +
The rigorous coupled-wave analysis technique for describing the diffraction of multi-layer diffraction grating (MDG) is put forward. Formulations for a stable and efficient numerical implementation of diffraction efficiency are presented for MDG for TE polarization and Littrow angle. With the merit function of the -1 order diffraction efficiency higher than 96%, the parameters of MDG are optimized for HfO2 and SiO2 top layers, respectively. Numerical calculation indicates that a larger grating parameter range can be obtained with HfO2 rather than the SiO2 on the top. The manufacture tolerance and the effective incident angle for the optimized structure of MDG are discussed in the end.
Composite coherence vortices in the superimposed field of partially coherent vortex beams and their propagation dynamics
Cheng Ke, Yan Hong-Wei, Lü Bai-Da
2008, 57 (8): 4911-4920. doi: 10.7498/aps.57.4911
Abstract +
The composite coherence vortices formed by superimposing two parallel, off-axis partially coherent flattened vortex beams are studied in detail. It is shown that the number and position of composite coherence vortices depend on the beam order, relative off-axis distance and coherence parameter, as well as on the free-space relative propagation distance. The “hidden" composite coherence vortex in the partial coherence regime corresponds to its counterpart——the composite optical vortex in the full coherence regime. In the coherent limit the composite coherence vortex evolves into the composite optical vortex.
Electromagnetically induced absorption and electromagnetically induced transparency in an optical-radio two-photon coupling configuration
Zhang Lian-Shui, Li Xiao-Li, Wang Jian, Yang Li-Jun, Feng Xiao-Min, Li Xiao-Wei, Fu Guang-Sheng
2008, 57 (8): 4921-4926. doi: 10.7498/aps.57.4921
Abstract +
Electromagnetically induced transparency (EIT) resonance is obtained in a well-studied lambda three level system where an optical coupling field and a probing field interact with two optical transitions. However, both electromagnetically induced absorption (EIA) and EIT can be obtained in a modified quasi-lambda four level system consisting of an optical-radio two-photon coupling field and a probing field. By solving the density matrix equation of motion, a physical account of EIA and EIT is given in terms of a dressed state picture. It can be seen that the optical coupling field in this quasi-lambda four level system has a crucial effect on the forming of EIA and EIT. An EIA is observed under a resonant optical coupling and it evolves into an EIT when there is a detuning. Furthermore, the width of EIA or EIT increases as the optical coupling Rabi frequency increases.
The comparison of steady-state gain of V-type and Λ-type atomic systems of lasing without inversion
Liu Jian-Cheng, Chang Zeng-Guang, Yan Ke-Zhu
2008, 57 (8): 4927-4932. doi: 10.7498/aps.57.4927
Abstract +
In this paper we study the dependence of steady-state gain of a closed V-type atomic system and a closed Λ-type atomic system of lasing without inversion on the detuning of the coherence lasers under the condition that the corresponding parameters of the two atomic systems are equal. By the way of numerical simulation and comparison, we find that the curves of probe-laser gain of the two atomic systems versus the detuning of probe-laser have similar shapes but their values are different, which are related to the characteristics of atomic coherence and population distribution of the two atomic systems directly. In addition, we find that the driving laser deturning and the additional atomic coherence caused by spontaneously generated coherence can exert a great influence upon the probe-laser gain.
Experimental schemes for developing fiber-based source of entangled photon pairs
Yang Lei, Li Xiao-Ying, Wang Bao-Shan
2008, 57 (8): 4933-4940. doi: 10.7498/aps.57.4933
Abstract +
Based on the theory of third-order nonlinear Kerr effect in optical fiber, we experimentally demonstrate the generation of photon pairs by exploiting spontaneous four-wave mixing. The photon pairs are produced by pumping a fiber Sagnac loop and a piece of straight fiber with a pulsed laser, respectively. By comparing the experimental results, we analyze how to optimize the experimental parameters to obtain entangled photon pairs with high purity. Our results are useful for developing the all-fiber source of photon pairs and single photon source, which are well suited for quantum communication.
Quantum key distribution based on time coding and phase coding
Zhang Jing, Wang Fa-Qiang, Zhao Feng, Lu Yi-Qun, Liu Song-Hao
2008, 57 (8): 4941-4946. doi: 10.7498/aps.57.4941
Abstract +
A new quantum key distribution scheme is proposed to realize both phase coding and time coding based on two unbalanced Mach-Zehnder interferometers. The pulses which are discarded in the phase coding scheme can be coded in time coding, so the useful bit rate in the present scheme can be doubled. At the same time, the phase coding keys and the time coding keys are obtained. We can use one group of keys to communicate and the other one to guard against eavesdropping, or combine both of them to form new keys. This scheme has favorable application prospect.
Influence of negative refractive index materials on repulsive Casimir forces
Liu Shu-Tian, Zeng Ran, Yang Ya-Ping
2008, 57 (8): 4947-4952. doi: 10.7498/aps.57.4947
Abstract +
The influence of negative refractive index materials on repulsive Casimir forces is studied. The repulsive Casimir interaction is determined by the electric and magnetic properties of the material slabs and the intermediate medium. Through theoretical analysis and numerical calculation, the condition for obtaining repulsive forces is presented. For the negative refractive index materials described by dispersive permittivity and permeability of Drude-Lorentz type, repulsive Casimir force can be realized by tuning the characteristic frequencies.
A difference method to solve the laser kinetic model involving temporal-special evolution
Chen Gang, Zhuang De-Wen, Zhang Hang, Xu Jun, Cheng Cheng
2008, 57 (8): 4953-4959. doi: 10.7498/aps.57.4953
Abstract +
Based on the rate equation theory and numerical difference method, a kinetic model was developed to describe the temporal-special distribution of the particles and photon densities in a laser tube. This method improves the normal rate equation and can be used to study the laser evolution and the energy distribution.
One-dimensional periodic nanocrystalline silicon arrays made by pulsed laser interference crystallization
Yasuyuki Miyamoto, Shunri Oda, Yao Yao, Fang Zhong-Hui, Zhou Jiang, Li Wei, Ma Zhong-Yuan, Xu Jun, Huang Xin-Fan, Chen Kun-Ji
2008, 57 (8): 4960-4965. doi: 10.7498/aps.57.4960
Abstract +
One-dimensional periodic nanocrystalline silicon (nc-Si) arrays were fabricated by laser interference crystallization combined with one-dimensional phase shifting grating mask (PSGM). The laser energy density irradiated on the surface of samples with different thicknesses of a-Si:H can be modulated by the PSGM with periodicity of 400 nm. Raman spectra confirmed the crystallization of the irradiated stripe-patterned area of the samples. The transmission electron microscopic and atomic force microscopic images demonstrate that the periodicity of one-dimensional nc-Si arrays is the same as that of the PSGM. And by controlling the laser energy density, a stripe width of 30 nm in each period was obtained as the thickness of a-Si:H decreased from 10 to 4 nm. The high resolution transmission electron microscope images show the clear crystalline lattice of nc-Si within the stripe patterns.
Experimental and theoretical study on designing of cooling device for the kilowatt-level double cladding fiber laser
Lou Qi-Hong, Zhou Jun, Qi Yun-Feng, Dong Jing-Xing, Wei Yun-Rong, Zhu Hong-Tao
2008, 57 (8): 4966-4971. doi: 10.7498/aps.57.4966
Abstract +
Though the double cladding fiber (DCF) laser’s ability of heat dissipation is better than the traditional solid-state laser’s, the heat generation in double-cladding fiber laser is the bottleneck in the development of high power lasers. The distribution of heat deposition in the practical 400 W DCF laser is quantitatively analyzed for the first time. Based on the heat dissipation model developed in this work, in order to ensure the safe and stable operation of the kilowatt-level DCF laser, the convective coefficient near the pumping ends should be greater than 2.8×10-2W·cm-2K-1. The cooling device for high power DCF laser’s pumping ends was designed and successfully used in a laser system, and the output power of 1kW was obtained.
Investigation on a TEM00-mode dynamic stable resonator with two Nd:YAG rods
Liu Chong, Ge Jian-Hong, Xiang Zhen, Chen Jun
2008, 57 (8): 4972-4977. doi: 10.7498/aps.57.4972
Abstract +
In order to achieve high power, high brightness lasers, a TEM00-mode dynamic stable resonator with two Nd:YAG rods is constructed. The thermal induced birefringence is compensated by two identically pumped rods. The laser output 61W is achieved in cw mode under lamp pumped regime. The influence of the cavity parameters on the laser output properties is investigated using the equivalent thermal lens method. It turns out that the distance of the output coupler and the high reflectivity mirror from the laser rods play different roles on the laser properties.
High order dispersion effect of Ginzburg-Landau equation and its self-similar analytical solutions
Xu Wen-Cheng, Liu Wei-Ci, Li Shu-Xian, Liu Song-Hao, Feng Jie
2008, 57 (8): 4978-4983. doi: 10.7498/aps.57.4978
Abstract +
Using the methods based on the technique of self-similar analyzing, we find the parabolic asymptotic self-similar analytical solutions with third-order dispersion effect of constant coefficient Ginzburg-Landau equation which considers both the influence of high order dispersion and gain dispersion on the evolution of self-similar pulse. The self-similar amplitude function, phase function, strict linear chirp function and effective temporal pulse width are given in the paper. The results show that self-similar pulses still have linear chirp and remarkable third-order dispersion effect. And these theoretical results are consistent with numerical simulations.
Study of imaging system based on the tunable terahertz wave source with quasi-Gaussian beam output
Zhang Xian-Bin, Shi Wei
2008, 57 (8): 4984-4990. doi: 10.7498/aps.57.4984
Abstract +
A terahertz wave imaging system based on the tunable terahertz source with the quasi-Gaussian beam output is reported. In this imaging system, terahertz wave beam is easy to be focused and transmitted owing its spatial distribution with the excellent beam quality factor of M2x=1.15 and M2z=1.25. The experimental results show the spatial resolving power of this imaging system is close to the typical terahertz wavelength of 250μm. In the output range of 1.0—2.5THz, the signal to noise ratio (SNR) is higher than 1000dB, and the SNR is above 6000dB at 1.8THz. Based on this system, the terahertz imaging experiments for the several samples were performed, and clear pictures were obtained.
Brillouin-enhanced nondegenerate four-wave mixing
Sun Jiang, Liu Xia, Niu Jin-Yan, Mi Xin, Jiang Qian, Wu Ling-An, Fu Pan-Ming
2008, 57 (8): 4991-4994. doi: 10.7498/aps.57.4991
Abstract +
We have observed Brillouin-enhanced nondegenerate four-wave mixing (NFWM) induced by an acoustic wave and Rayleigh-type NFWM induced by molecular reorientation in CS2. It was found that the acoustic wave and the molecular reorientation grating are not mutually independent. The existence of the acoustic wave destroys the phase coherence between the polarizations of the Rayleigh-type NFWM and the Brillouin-enhanced NFWM.
All optical wavelength conversion and optimum longitudinal mode selection using an injection-locked Fabry-Perot laser diode
An Yi, Wang Yun-Cai, Zhang Ming-Jiang, Niu Sheng-Xiao, Wang An-Bang
2008, 57 (8): 4995-5000. doi: 10.7498/aps.57.4995
Abstract +
Based on the cross-gain modulation effect in Fabry-Perot laser diode (FP-LD), the 2.7GHz optical pulsed signal at 1552.30nm is converted to a continuous-wave light at 1548.22nm in experiment. The variation of wavelength conversion efficiency with injection optical power and wavelength are examined in detail. Our research results indicate that there always exists a fixed longitudinal mode for a given FP-LD under certain working conditions to maximize the extinction ratio of conversion signal and conversion efficiency when the longitudinal mode is locked by the probe light. Our theoretical analysis accords with the experiment results. Moreover, there always exist an optimum signal power and a detuning range between the probe light and the longitudinal mode to improve the conversion signal further under the same longitudinal mode locked by the probe light. The optimum longitudinal mode can be determined by the FP-LD characteristics and its working conditions.
Optical beams in nonlocal nonlinear media: A variational solution of the Laguerre-Gauss form
Dai Ji-Hui, Guo Qi
2008, 57 (8): 5001-5006. doi: 10.7498/aps.57.5001
Abstract +
The 1+2D nonlocal nonlinear Schrdinger equation can be transformed to the variational approach in a cylindrical coordinate system, and is applied to a model describing the propagation of optical beam in strongly nonlocal nonlinear media. By solving variational problems with expanding media response functions and assuming reasonable ansatz, the solution of the Laguerre-Gauss form is obtained. The Laguerre-Gaussian beams will form solitons or be reduced to Gaussian beams under certain conditions.
Growth and spectral properties of Tm:Y2SiO5 single crystal
Xu Xiao-Dong, Zhao Zhi-Wei, Xu Wen-Wei, Wu Feng, Xu Jun, Wang Xiao-Dan
2008, 57 (8): 5007-5014. doi: 10.7498/aps.57.5007
Abstract +
High-quality Tm:Y2SiO5 (Tm:YSO) single crystal was grown by the Czochralski method. The lattice parameter and separation coefficient of the crystal were measured. The three polarization axis: 〈010〉, D1 and D2 of this monoclinic single crystal were determined by Laue method. Absorption spectra, fluorescence spectra and fluorescent lifetime of this single crystal were measured along the three polarization axes. Its absorption line width and absorption cross section were also calculated. A stronger absorption peak at 790nm and a fluorescence peak with enhanced emission at 2μm were observed along the D1 polarization axis compared with other two axes. Besides, this crystal exhibits bigger absorption cross section and longer fluorescence lifetime along D1 polarization axis. Therefore, Tm:YSO single crystal is suitable for AlGaAs diode-pumped laser and it possesses great potentiality in the application of 2μm solid-state laser.
The design of left-handed metamaterials composed of magnetic resonators and electric resonators
Wang Jia-Fu, Zhang Jie-Qiu, Yang Yi-Ying, Ma Hua, Qu Shao-Bo, Xu Zhuo
2008, 57 (8): 5015-5019. doi: 10.7498/aps.57.5015
Abstract +
In designing left-handed metamaterials composed of magnetic resonators and electric resonators, two design principles, that is, the single-loop mirror-symmetry design principle and double-loop (quadruple-loop) mirror-symmetry design principle, were respectively proposed for the design of magnetic resonators and electric resonators. Based on the two principles, new structures with simultaneously negative permeability and permittivity were designed. By means of simulation experiments, the double-negative property of the proposed structure as well as the two design principles was verified. The two design principles and structures proposed in this paper are of great practical values in designing new types of left-handed metamaterials.
Characteristics of multistage quartz optical filter based on the optical rotatory dispersion effect
Zhang Shan, Wu Fu-Quan, Wu Wen-Di
2008, 57 (8): 5020-5026. doi: 10.7498/aps.57.5020
Abstract +
Based on optical rotatory dispersion effect, the principle of the multistage quartz crystal filter was theoretically analyzed by using Muller matrix and Stokes parameter. The wavelength of the main peak and full width at half maximum (FWHM) of peaks of the multistage optical filter were deduced. The characteristics of the single and multistage quartz crystal optical filters were systematically investigated by the spectrometer, and the experimental results verified the theoretical analysis. The results proved that, compared with the single quartz crystal optical filter, the FWHM can be effectively compressed by multistage quartz crystal optical filter, and the compression ability increases with the increase of the stage number.
Studies on nanosecond laser induced damage to fused fibers
Zhao Xing-Hai, Gao Yang, Xu Mei-Jian, Duan Wen-Tao, Yu Hai-Wu
2008, 57 (8): 5027-5034. doi: 10.7498/aps.57.5027
Abstract +
The properties of high_peak pulsed laser induced damage to fibers have been investigated by damage experiments. It was found that all of damaged parts are located on fiber endings, and the damage topography fall into three classes: the pit damage, fusion damage and sputtering damage. The experimental setup of laser induced damage to fibers, fiber damage judgment criterions and data processing methods were developed and validated. The zero probability damage threshold was calculated by linear fitting to be 3.85GW/cm2. The processes of laser induced damage to fibers were summarized and the fiber end face damage mechanism was studied. The experimental results indicated that the main factor that makes the fiber end faces susceptible to laser induce damage is the existence of surface imperfections. The nanosecond laser induce damage to fiber end faces are detected experimentally; the central areas of input end faces are damaged probably because the input laser beam is Gaussian. So the use of uniform beam for injecting the fiber is favorable to the laser-induced damage resistance.
Study on the suppression of the stimulated Brillouin scattering in high-power single-frequency multicore fiber amplifier
Wang Chun-Can, Zhang Fan, Tong Zhi, Ning Ti-Gang, Jian Shui-Sheng
2008, 57 (8): 5035-5044. doi: 10.7498/aps.57.5035
Abstract +
The set of differential equations for an multicore fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradient caused by heat generation, is presented. The thermal conduction equations are solved by finite element method. The influence of pump schemes, pump power, convective coefficient, initial power of Stokes, density of the rare earth dopant and fiber length on suppression of the stimulated Brillouin scattering is studied. The results show that the backward pump scheme has advantage over the forward pump scheme in suppression of stimulated Brillouin scattering. Increasing density of the rare earth dopant can lead to higher slope efficiency and shorter optimal fiber length, which can further suppress stimulated Brillouin scattering. The stimulated Brillouin scattering gain and maximum operating temperature are compared between single core fiber amplifier and 19-core fiber amplifier with the same optimal fiber length. Compared with the single core fiber amplifier, the 19-core fiber amplifier has lower maximum operating temperature, which provides more space for further increase in output power.
A mode-locked Yb3+-doped double-clad large-mode-area fiber laser
Li Jin-Yan, Chen Wei, Song You-Jian, Hu Ming-Lie, Liu Qing-Wen, Chai Lu, Wang Qing-Yue
2008, 57 (8): 5045-5048. doi: 10.7498/aps.57.5045
Abstract +
A compact and highly stable high pulse energy passively mode-locked fiber laser is presented. A segment of Yb3+-doped double-clad large-mode-area fiber with extremely low nonlinearity is developed as the active medium. The self-starting mode-locked operation is achieved by the cooperation of nonlinear polarization evolution and semiconductor saturable-absorber mirror. The fiber laser generates laser pulses with the average power of 160mW at the repetition rate of 55.9MHz (corresponding to pulse energy of 3nJ), and the pulse duration is 10.6ps.
An ultrasonic measurement model to predict the response from flat bottom hole for dual crystal contact probe
Zhao Xin-Yu, Gang Tie, Zhang Bi-Xing
2008, 57 (8): 5049-5055. doi: 10.7498/aps.57.5049
Abstract +
Dual crystal contact probes play an important role in many practical ultrasonic inspections, so it is essential to develop an ultrasonic measurement model in order to get a thorough understanding of the characteristics of this kind of transducers. By combining the multi-Gaussian beam model and the Kirchhoff approximation scattering model, a complete ultrasonic measurement model is provided to predict testing signals of a flat bottom hole for a dual crystal focused direct contact probe. By comparing with experimental results, the accuracy of predicted signals using this model has been verified.
Torsional buckling of a double-walled carbon nanotube under the action of coupled thermo-mechanical load
Yao Xiao-Hu, Han Qiang
2008, 57 (8): 5056-5062. doi: 10.7498/aps.57.5056
Abstract +
Taking into account the effects of surrounding elastic medium and van der Waals forces between the inner and outer nanotubes and using the shell theory in continuum mechanics, the governing equation of carbon nanotube under the action of coupled thermo-mechanical load is established. Based on the model, an explicit formula for the critical load is derived in terms of the buckling modes of the shell and the parameters that indicate the effects of temperature change, surrounding elastic medium and the van der Waals force. Numerical simulation results show that at low and room temperature the critical load for infinitesimal buckling of a double-walled carbon nanotube increases as the value of temperature change increases, while at high temperature the critical load for infinitesimal buckling of a double-walled carbon nanotube decrease as the value of temperature change increases.
Simulation research on the law of flow of liquid metal in micro-channels
Ren Ming-Xing, Li Bang-Sheng, Yang Chuang, Fu Heng-Zhi
2008, 57 (8): 5063-5071. doi: 10.7498/aps.57.5063
Abstract +
We modified the traditional Navier-Stokes equation, and used the Fluent software to simulate the microscopic law of flow of Zn-Al alloy melt in the micro-channel. The simulation results show that when the diameter of the channel is 0.5mm, the liquid metal in the micro-channel is in a critical state. Relative thickness of boundary-velocity layer increases with the decrease of diameter of the channel, and micro-channel flow shows obvious convex-front effect, which has not been observed in the macroflow. The convex-front effect weakens when the inlet pressure increases. Between the flow front and upstream region, there exist negative pressure gradient zones, which become more outstanding in finer channels.
Parameter identification of gas bubble model in pressure pulsations using genetic algorithms
Jiang Dan, Li Song-Jing, Bao Gang
2008, 57 (8): 5072-5080. doi: 10.7498/aps.57.5072
Abstract +
Pressure changes in the flowing fluid result in the growth and collapse of gas bubbles and cavitation, which affects the fluid flowing and pressure. In order to predict gas bubble and cavitation volume change during the pressure pulsations in fluid control system and their effects on the pulsations, a mathematical model of gas bubble and cavitation is studied based on gas bubble resolving and releasing physical processes. The method using genetic algorithms (GAs) in parameter identification for the gas bubble model is presented, including the parameters of initial gas bubble volume, gas resolving time constant and releasing time constant. An example of pressure transients accompanying gas bubble and cavitation inside the hydraulic pipeline is simulated and tested. According to the simulation and experimental results, the feasibility of parameter identification for gas bubble model using GAs is verified.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Numerical simulation of particle species behavior in atmosphere plasmas with different ionization degree
Pang Xue-Xia, Deng Ze-Chao, Dong Li-Fang
2008, 57 (8): 5081-5088. doi: 10.7498/aps.57.5081
Abstract +
A zero-dimensional model is used for studying the behavior of main particle species in atmosphere plasmas with different ionization degrees. The electron lifetimes are obtained for different initial density in an afterglow plasma, and the temporal evolutions of the main charged and neutral species are presented. The results show that the electron number density decays fast, and the lifetimes decrease with ionization degree increasing. Some important neutral species such as O, N, O3 and NO are also analyzed with ionization degree increasing.
Study on the defect mode properties of unmagnetized plasma photonic crystals
Zhang Hai-Feng, Ma Li, Liu Shao-Bin
2008, 57 (8): 5089-5094. doi: 10.7498/aps.57.5089
Abstract +
The piecewise linear current density recursive convolution in finite-difference time-domain method is used to study the characteristics of one-dimensional unmagnetized plasma photonic crystals with a defect layer. In the frequency domain, the transmission ratios of electromagnetic Gaussian pulses are computed and we analyzed the effect on defect mode properties of unmagnetized photonic crystals produced by its periodic constant, parameters of plasma and parameters of the defect layer, such as its dielectric coefficient, length and position. The results show that different defect modes can be realized by changing the parameters.
Numerical simulation on the energy deposition of double-layer target irradiated by intense pulsed ion beam
Gong Ye, Zhang Jian-Hong, Wang Xiao-Dong, Liu Jin-Yuan, Liu Yue, Wang Xiao-Gang, Ma Teng-Cai, Wu Di
2008, 57 (8): 5095-5099. doi: 10.7498/aps.57.5095
Abstract +
Gaussian distribution models of voltage wave form of magnetically insulated diode (MID) of TEMPⅡ accelerator and intense pulsed ion beam (IPIB) density near the MID focus region have been built according to the results of experiments. Interaction of IPIB with a double-layer aluminum target coated by a thin film of gold has been studied using Monte Carlo method. The spatial and temporal evolution of deposited energy is obtained, the states of deposited energy for the different gold thickness are discussed, and the enhanced adhesion at interfaces by IPIB is investigated.
Experimental study on extreme ultraviolet light generation from high power laser-irradiated tin slab
Cai Yi, Wang Wen-Tao, Yang Ming, Liu Jian-Sheng, Lu Pei-Xiang, Li Ru-Xin, Xu Zhi-Zhan
2008, 57 (8): 5100-5104. doi: 10.7498/aps.57.5100
Abstract +
An experimental system has been set up for producing extreme ultraviolet light with high conversion efficiency by employing high power YAG laser irradiated tin slab. The dependence of extreme ultraviolet light intensity and conversion efficiency on the pump energy were studied, and the saturation effect of conversion efficiency was observed. The highest conversion efficiency of 1.6% in producing 13.5nm extreme ultraviolet light with 0.27nm bandwidth was achieved at pump energy of 250mJ, which corresponds to an intensity of 1.8×1011W/cm2.
Study of space voltage distribution between large-area parallel-plate electrodes for very high frequency plasma enhanced chemical vapor deposition
Ge Hong, Zhang Xiao-Dan, Yue Qiang, Zhao Ying, Zhao Jing
2008, 57 (8): 5105-5110. doi: 10.7498/aps.57.5105
Abstract +
The two-dimensional quasi-planar circuit model is used to study the space voltage distribution between large-area parallel-plate electrodes of very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) reactor. The results show that the voltage standing wave effects become the important factor affecting non-uniform voltage distribution when the electrode dimensions and excitation frequency are increased. For a large-area parallel-plate electrode with 1.2m by 0.8 m lateral dimension, driven respectively at frequencies of 40.68 and 60MHz, the space voltage non-uniformity about ±2.5% and ±5.5% are obtained by optimization of the number and position of the power feeding points. These results provide important theoretical guidance for large-area parallel-plate electrodes used for VHF-PECVD.
Sheath structure of a magnetized plasma
Zou Xiu, Liu Hui-Ping, Gu Xiu-E
2008, 57 (8): 5111-5116. doi: 10.7498/aps.57.5111
Abstract +
The structure of plasma sheath in an oblique magnetic field is numerically investigated by using fluid dynamics method. The simulation results reveal that the magnetic field has significant effects on the plasma sheath. Especially, the ion density distribution near the sheath edge changes obviously. Two cases of ion incidence are considered here. The action states of ions are more complicated when the ions enter the sheath with an oblique incidence angle. Under suitable conditions, Lorentz force induces fluctuations in the ion density. Ions could gather in some regions.
Experimental study of optical radiation of hot electrons transport in targets at the rear-side radiation
Chen Tao, Zhang Ting, Zhang Jian-Wei, Wang Guang-Chang, Zheng Zhi-Jian, Gu Yu-Qiu, Wen Xian-Lun
2008, 57 (8): 5117-5122. doi: 10.7498/aps.57.5117
Abstract +
This paper reports the image pattern of spatial distribution and spectrum of optical radiation measured in the normal direction from the rear side of the target employing optical CCD camera and optical multi-channel analysor on the 100 TW femtosecond laser facility. The image pattern of spatial distribution has a ring-shape, the region of optical radiation has larger radiation angle and optical intensity distribution, and the radiation is comprised of many components. The spectrum of optical radiation shows a sharp peak near 800nm, which is attributed to the laser fundamental (ω0), and is ascribed to the coherent transition radiation (CTR) generated by microbunches of hot electron beams generated in transport. With the increase of the laser energy, the peak of the CTR moves further to the long wavelength side, the red shift is caused by the expansion of the critical density surface. The acceleration of hot electron comes mainly from resonance absorption.
Langmuir probe measurement and theoretical studies on inductively coupled plasma in Ar-N2 discharge
Gao Fei, Mao Ming, Ding Zhen-Feng, Wang You-Nian
2008, 57 (8): 5123-5129. doi: 10.7498/aps.57.5123
Abstract +
In this article we use the Langmuir probe and kinetic model to study the electron energy distribution function (EEDF), the electron temperature, and the electronic density in the radio-frequency inductively coupled plasma of Ar-N2 discharge. It has been found that, with the increase of the N2 flow, the EEDF varies from the bi-temperature distribution to the tri-temperature distribution; the electron temperature drops monotonically at low pressures (pp>1.3 Pa). In addition, due to the recombination of electrons and nitrogen molecular ions, the electron density drops substantially at high pressures when a small amount of N2 is added to the gas mixture. Although the theoretically obtained electron temperature is high than the experimentally measured one, the theoretical model presents good predictions of the influences of N2 ratio in Ar-N2 mixture on the electron temperature and EEDF.
Investigation on surface damage phenomena induced by flashover across semiconductor
Zhao Wen-Bin, Zhang Guan-Jun, Yan Zhang
2008, 57 (8): 5130-5137. doi: 10.7498/aps.57.5130
Abstract +
The flashover across semiconducting materials disables many high power semiconductor devices from their further application under high electric field. Up to now, the physical mechanism of the flashover was still not understood clearly. Surface flashover experiments of silicon and gallium arsenide were performed under pulsed high voltage. The filament current channels on their surface were observed in the infrared photographs, and the infrared radiation bright spot was found in the central region between the electrodes. On the surface of different samples undergone flashover events for several times, the filament damage phenomena were observed, and for the n100 silicon sample, some circular pits were found around the filament channel, with a conical jut in the center of each pit. According to the damage phenomena at the edge of electrodes, the thermal injection and relaxation characteristics of majority carriers were discussed. An injection model induced by minority carriers was proposed, which emphasizes the surface field enhancement by non-equilibrium carrier channel, which possibly leads to the ionization of the ambient gas above the filament channel. The model was consistent with the observed experimental results.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Study on the optical absorption of gold nanoshells by Mie theory
Wu Da-Jian, Liu Xiao-Jun
2008, 57 (8): 5138-5142. doi: 10.7498/aps.57.5138
Abstract +
The variations of optical absorption of gold nanoshells with the shell thickness, size of the core, and core dielectric constant have been investigated by means of Mie theory. It was found that with the increase in the thickness of the shell, the strength of absorption peak increases first and then decreases. We also observed that with increasing core size the maximum optical absorption of the particles decreases. Furthermore, the increase of the core dielectric constant reduces the strength of absorption peak and the hollow gold nanoshells have the maximum optical absorption. We ascribe the change of the absorption peaks to the plasmon hybridization and the competition between the variations of conduction and oscillation electrons.
Lattice dynamics of single wall BC3 nanotubes
Wang Hui, Feng Min, Cao Xue-Wei, Wang Yu-Fang, Jin Qing-Hua, Ding Da-Tong, Lan Guo-Xiang
2008, 57 (8): 5143-5150. doi: 10.7498/aps.57.5143
Abstract +
The structures of single wall BC3 nanotubes are described in the present paper. The symmetry and lattice dynamics of single wall BC3 nanotubes are analyzed in detail. Based on the force constant model we calculate the phonon dispersion relations of single wall BC3 nanotubes with different diameters and chiralities. For Raman and infrared active modes, the diameter-dependence of vibrational frequency has been established. It can be inferred that the Raman and infrared spectra of BC3 nanotubes would be more complex than those of single carbon nanotubes.
Epitaxial growth and mechanical properties of AlN/Si3N4 nanostructured multilayers
Yu Li-Hua, Dong Song-Tao, Dong Shi-Run, Xu Jun-Hua
2008, 57 (8): 5151-5158. doi: 10.7498/aps.57.5151
Abstract +
Monolithic AlN,Si3N4 films and AlN/Si3N4 multilayers with different modulation periods were prepared by reactively magnetic sputtering. The films were characterized by X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation. The results showed that the crystal structure of Si3N4 layers in the multilayers and the hardness of AlN/Si3N4 multilayers depend on the thickness of Si3N4 layer. When the thickness of AlN is 4.0nm and that of Si3N4 layer is 0.4nm, Si3N4 layers grew epitaxially with AlN and form strong columnar crystals which extend over several modulation periods. A large degree of hardness enhancement of the multilayer was produced. The microstructure of Si3N4 changes from crystalline to amorphous as Si3N4 thickness increases, leading to blocking of the epitaxial growth and the superhardness effect disappears. The critical thickness of Si3N4 layers, which marks the change from crystalline to amorphous, has been calculated through thermodynamic and elastic considerations. The hardening mechanisms of AlN/Si3N4 multilayers are discussed.
Coalescence of helium clusters in titanium crystals: Molecular dynamics simulation
Xie Zhao, Hou Qing, Wang Jun, Sun Tie-Ying, Long Xing-Gui, Luo Shun-Zhong
2008, 57 (8): 5159-5164. doi: 10.7498/aps.57.5159
Abstract +
In this paper, the helium behavior in titanium crystals has been simulated by molecular dynamics method. The coalescence of helium clusters has been investigated in great detail in a range from 300 to 800K. It was found that increasing temperature contributes to the coalescence of helium clusters. However, the helium cluster resulting from coalescence assumes its three-dimensional configuration in this temperature range for the time scale of simulation. The simulation results also indicate that, at room temperature, the attractive force between helium clusters plays a key role in helium cluster coalescence.
A study of damage evolution during annealing of helium-implanted magnesium-aluminate spinel
Zhang Chong-Hong, Yang Yi-Tao, Zhou Li-Hong, Li Bing-Sheng
2008, 57 (8): 5165-5169. doi: 10.7498/aps.57.5165
Abstract +
Evolution of damage in single-crystalline magnesium-aluminate spinel implanted with helium ions was studied using Rutherford backscattering technique in channeling geometry combined with surface investigation by atomic force microscopy. It was found that the damage induced by helium-ion implantation in the crystal showed significantly different annealing behavior depending on the implantation fluence. The difference in annealing behavior is ascribed to the strong dose dependence of clustering/resolution of helium atoms.
Influences of substrate temperature on crystalline characteristics and mechanical properties of SiNx films deposited by microwave electron cyclotron resonance magnetron sputtering
Ding Wan-Yu, Xu Jun, Lu Wen-Qi, Deng Xin-Lu, Dong Chuang
2008, 57 (8): 5170-5175. doi: 10.7498/aps.57.5170
Abstract +
Hydrogen-free SiNx films were deposited at substrate temperature ranging from room temperature to 700℃ by microwave electron cyclotron resonance plasma enhanced unbalanced magnetron sputtering system. We have studied the influence of substrate temperature on the structural characteristics of deposited films including growth rate, microstructure, grain size, and hardness by using transmission electron microscopy, Fourier-transform infrared spectroscopy, and nano-indentation. The results indicate that the films deposited at room temperature are amorphous, and α-Si3N4 grains with random epitaxial sizes appear when substrate temperature is higher than 300℃. The α-Si3N4 grain size increases with substrate temperature up to 620℃, and then decreases at 700℃. At 700℃, the grains have uniform epitaxial sizes, and value of the film hardness reaches the maximum (36.7GPa).
Substrate temperature and B-doping effects on microstructure and electronic properties of p-type hydrogenated microcrystalline silicon films
Yang Shi-E, Wen Li-Wei, Chen Yong-Sheng, Wang Chang-Zhou, Gu Jin-Hua, Gao Xiao-Yong, Lu Jing-Xiao
2008, 57 (8): 5176-5181. doi: 10.7498/aps.57.5176
Abstract +
P-type hydrogenated microcrystalline silicon thin films have been prepared by radio-frequency plasma-enhanced chemical vapor deposition with B2H6 as a doping gas. The effects of substrate temperature and the doping ratio on the microstructure and dark conductivity of the p-type hydrogenated microcrystalline silicon films have been investigated. The results show that the films deposited at higher substrate temperature are amorphous even if the doping ratio is very low. The crystalline volume fraction of films monotonically decreases and the dark conductivity initially increases slowly and then decreases rapidly with substrate temperature increasing, which is very similar to the effects of the doping ratio. Finally the growth mechanism of p-type hydrogenated microcrystalline silicon thin films has been discussed in particular.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The reaction sequence of lithiation in Mg2Ge and the changes of its electronic structure
Liu Hui-Ying, Yang Yong, Zhu Zi-Zhong
2008, 57 (8): 5182-5190. doi: 10.7498/aps.57.5182
Abstract +
Mg2Ge is a promising new anode material for lithium ion batteries. The ab initio pseudopotential method with the plane wave expansion of the crystal wave function was employed to study the lithiation properties of anode material Mg2Ge. The reaction sequence of lithiation in Mg2Ge have been calculated. It was found that Li ions firstly occupy the interstitial sites until the interstitial sites are full, and then substitute the Mg sites until half of the Mg sites are replaced to form the phase of Li2MgGe. The calculation results also show that the crystal volume firstly expands and then shrinks as the number of Li ions increases. The changes of crystal volume are very big during the whole process which is the cause of bad cycle performance of the material. The electronic structures are also analyzed, which indicates that the host material changes from semiconducting to metallic then to semiconducting with the increase of Li intercalations.
Influence of layers’ mutual effect and radius on electronic energy of spherical nanometric system
Zheng Rui-Lun, Wu Qiang
2008, 57 (8): 5191-5197. doi: 10.7498/aps.57.5191
Abstract +
On the basis of interaction between layers, the physical model of the bilayer spherical namometric system have been worked out. With the Green function method and Fourier transform, the electronic potential energy has been figured out for the system. In the example of HgS/CdS spherical nanometric system, the effect of system size and the layers' mutual effect has been discussed in terms of the electronic potential energy. The results show that: the layers' mutual effect could make the average height of the electronic potential barrier of the spherical namometric system lower; the more the layers' mutual effect is, the lower the height of the electronic potential barrier is, and the greater the undulation of the electronic potential energy curve is. For the same layers' mutual effect, electronic ground state energy and revised energy by layers' mutual effect will be reduced with the increase of particle radius; but for the same size, the revised energy by layers' mutual effect will increase with the increase of the layers' mutual effect.
Thermoelectric properties of transverse transport in nanowire array structures
Zhang Yi-Qun, Shi Yi, Pu Lin, Zhang Rong, Zheng You-Dou
2008, 57 (8): 5198-5204. doi: 10.7498/aps.57.5198
Abstract +
The electronic structures of nanowire-composite arrays are calculated theoretically in the framework of effective-mass envelope function theory,and various coefficients about electronic transport are obtained. At the same time,a closed-form expression based on boundary scattering theory for lattice thermal conductivity is presented. Then the thermoelectric properties of Si nanowire/Ge host material are investigated as function of the Fermi energy,wire diameter and separation between nanowire sidewalls. The results show that the ZT value of nanowire-composite can be significantly increased by carefully adjusting the correlative parameters of the structure.
Radiation degradation model of metal-oxide-semiconductor field effect transistor based on pre-irradiation 1/f noise
Peng Shao-Quan, Du Lei, He Liang, Chen Wei-Hua, Zhuang Yi-Qi, Bao Jun-Lin
2008, 57 (8): 5205-5211. doi: 10.7498/aps.57.5205
Abstract +
Based on metal-oxide-semiconductor field effect transistor (MOSFET) noise theory of carrier number fluctuation and mobility fluctuation, a quantitative mathematic model between pre-irradiation 1/f noise parameters and post-irradiation threshold voltage drift due to oxide traps and interface traps is established. It agrees well with the experimental results. This model shows that 1/f noise in MOSFET is priginates from the random trapping/detrapping processes between oxide traps and the channel, which causes fluctuations in both the number and the mobility of channel carriers. So pre-irradiation 1/f noise magnitude is directly proportional to post-irradiation oxide-trap charge. The results not only explain the correlation between MOSFET pre-irradiation 1/f noise power spectral density and radiation degradation in theory, but also provide the theory for forecasting MOSFET radiation-resistant capability.
Ag doped p-type ZnO films and its optical and electrical properties
Wang Jing-Wei, Bian Ji-Ming, Sun Jing-Chang, Liang Hong-Wei, Zhao Jian-Ze, Du Guo-Tong
2008, 57 (8): 5212-5216. doi: 10.7498/aps.57.5212
Abstract +
Ag doped ZnO films (ZnO:Ag) were deposited on quartz glass substrates by ultrasonic spray pyrolysis technology. Zn(CH3COO)2 and Ag(NO3)3 aqueous solution were used as the sources of Zn and Ag, respectively. The effect of substrate temperature on structural, electrical and optical properties of ZnO:Ag films were studied using X-ray diffraction, Hall effect measurement, photoluminescence spectra, and transmittance spectra measurement. All the measurements were performed at room temperature. It is found that the electrical and optical properties of the obtained ZnO:Ag thin films change dramatically due to Ag doping. The Ag doped p-type ZnO films with hole carrier concentration of 5.295×1015cm-3 and Hall mobility of 6.61cm2·V-1s-1 at room temperature have been successfully obtained at optimal conditions. In photoluminescence measurements, a strong ultraviolet emission centered at 379nm and a relatively weak green emission band were observed, and in transmittance measurements, a high transmittance of~70% in the visible region and a sharp absorption edge at 375nm were observed for all samples.
Dynamical study on charge injection and transport in a metal/poly(p-phenylene vinylene)/metal structure
Li Dong-Mei, Li Hai-Hong, Li Yuan, Xie Shi-Jie, Liu De-Sheng
2008, 57 (8): 5217-5225. doi: 10.7498/aps.57.5217
Abstract +
On the basis of the tight-binding Su-Schrieffer-Heeger model, the dynamical process of charge injection from metal electrode to a polymer in a metal/poly(p-phenylene vinylene) (PPV)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PPV. The formation of the wave packet sensitively depends on the applied voltage, the electric field, and the contact between PPV and the metal electrode. In the absence of external fields, the charge can be injected into PPV chain and form wave packet under the critical bias voltage. With the increase of the electric field, the charge carriers can be ejected from PPV to the right metal electrode. But when the electric field becomes high enough, the wave packet can not be formed because it moves too fast in PPV. It is also shown that the number of ejected charges is not an integral multiple of the elementary charge e.
Effect of substrate constraint on stress-induced cracking of sputtered tungsten thin film
Sun Hao-Liang, Song Zhong-Xiao, Xu Ke-Wei
2008, 57 (8): 5226-5231. doi: 10.7498/aps.57.5226
Abstract +
A comparative investigation was performed on the stress-induced surface cracking of tungsten films sputter deposited on polyimide (PI) and Si substrates. Microscopic observations suggest that with the same film thickness, two different types of cracking behaviors were observed. Wedge-shaped cracks are formed on the surface of film deposited on the Si substrate. However, the cracks of film deposited on the polyimide consist of aligned grains. The localized plastic deformation in the nanocrystalline W film on polyimide is mediated by the alignment of grains, which results from the grain rotation along the in-plane and out-of-plane directions. However, on the Si substrates the wedge-shaped cracks originate from the in-plane rotation of grains. The analysis implies that the different deformation behaviors are associated with the evolution of stress in the film and the substrate constraint.
Positive magnetoresistance in In0.53Ga0.47As/In0.52Al0.48As quantum well
Li Dong-Lin, Gao Hong-Ling, Zeng Yi-Ping, Shang Li-Yan, Lin Tie, Guo Shao-Ling, Yu Guo-Lin, Chu Jun-Hao, Zhou Wen-Zheng
2008, 57 (8): 5232-5236. doi: 10.7498/aps.57.5232
Abstract +
Magnetotransport measurements have been carried out on In0.53Ga0.47As/In0.52Al0.48As quantum wells in a temperature range between 1.5 and 77K. We have observed a large positive magnetoresistance in the low magnetic field range, but saturating in high magnetic fields. The magnetoresistance results from two occupied subbands in the two-dimensional electron gas. With the intersubband scattering considered, we obtained the subband mobility by analyzing the positive magnetoresistance. It is found that the second subband mobility is larger than that of the first due to the existence of the intersubband scattering.
Influence of annealing oxygen pressure on the laser-induced thermoelectric voltage effect in YBa2Cu3O7-x thin films
Jiang Zui-Min, Xiong Fei, Zhang Hui, Li Hong-Shan, Zhang Peng-Xiang
2008, 57 (8): 5237-5243. doi: 10.7498/aps.57.5237
Abstract +
The laser-induced thermoelectric voltage (LITV) signals were measured in the YBa2Cu3O7-x (YBCO) films annealed under different oxygen pressure. It was found that the detected LITV signals were enhanced 2—4 times with the increasing of annealing oxygen pressure. The effect can be explained by the dependence of thermoelectric anisotropy on the oxygen content in YBCO. When the films were illuminated by continuous lasers in the wavelength range of 473—808nm, the measured signals in the films annealed under 5000Pa oxygen pressure were larger than those in other films. Meanwhile, pulse ultraviolet laser illumination produced the largest signal in the films annealed under oxygen pressure of 105Pa. The response time of LITV signals was observed to become shorter with the increasing of annealing oxygen pressure, which was shown to have resulted from the increasing of thermal conductivity theoretically. The films annealed under 5000Pa oxygen pressure had the fastest response to the pulsed ultraviolet laser. The response time was 70ns and the rise time of 29ns was comparable to the duration of the applied laser pulse (about 28ns).
Effects of external magnetic field on the effective g factor of (Ga,Mn)As
Zhou Rong, Sun Bao-Quan, Ruan Xue-Zhong, Gan Hua-Dong, Ji Yang, Wang Wei-Zhu, Zhao Jian-Hua
2008, 57 (8): 5244-5248. doi: 10.7498/aps.57.5244
Abstract +
With the help of time resolved magneto-optic Kerr rotation measurements, the optically induced spin precession in heavily doped diluted magnetic semiconductor Ga0.937Mn0.063As was observed. It was found that the effective g factor increases with increasing magnetic field, which is attributed to the magnetic-field-induced increase of the density of the non-localized holes. Those free holes will couple with the localized magnetic ions by p-d interactions, leading to the formation of spontaneous magnetization in Ga0.937Mn0.063As, which in turn to the enhancement of the effective g factor.
Influence of annealing on the properties of Mn and N co-doped Zn0.88Mn0.12O:N films
Qiu Dong-Jiang, Wang Jun, Jia Yin, Ding Kou-Bao, Shi Hong-Jun
2008, 57 (8): 5249-5255. doi: 10.7498/aps.57.5249
Abstract +
Mn and N codoped ZnO (or Zn1-xMnxO:N) films were grown on Si(001) and quartz substrates via reactive electron beam evaporation in the NH3 atmosphere. The growth temperature was 300℃. The as-grown Zn0.88Mn0.12O:N film was cut into two pieces and one of them was then annealed in O2 atmosphere at 400℃ for 30 min. X-ray diffraction measurements reveal that Zn0.88Mn0.12O or Zn0.88Mn0.12O:N films have the single-phase wurtzite structure. The (002) diffraction peak of Zn0.88Mn0.12O:N film is located at a smaller angle and has a wider line width compared with that of Zn0.88Mn0.12O film. Hall measurement shows that the as-grown Zn0.88Mn0.12O:N film is the n-type and changes to p-type after annealing. DC magnetization analysis shows that the as-grown Zn0.88Mn0.12O:N films are ferromagnetic at room temperature (RT) but the ferromagnetism (FM) is weak and unstable. However, the FM of Zn0.88Mn0.12O:N film at RT is remarkably enhanced and its stability efficiently improved by annealing in O2 atmospher. The origin of FM of Zn0.88Mn0.12O:N film at RT, as well as the mechanisms of its FM enhancement and stability improvement by annealing are discussed.
The formation of vertical Bloch line in the garnet bubble films subjected to pulsed bias field
Hu Yun-Zhi, Sun Hui-Yuan
2008, 57 (8): 5256-5260. doi: 10.7498/aps.57.5256
Abstract +
We studied experimentally the dynamic characteristics of hard domains produced in the garnet bubble films at different pulse widths. The results show that the dumbbell domains contracted from multi-branched domains at zero static bias field rotate clockwise, independent of the pulse width of the pulsed bias field in which the multi-branched domains were produced. In the direct current fixed bias fields, soft domain segments harden and become dumbbell domains. How the dumbbell domains rotate is dependent on the pulse widths of the hardening pulsed bias field applied in the experiment. The results show that all the dumbbell domains rotate anticlockwise when the pulse width is narrow, and they rotate clockwise and anticlockwise simultaneously and then they all rotate clockwise as the width of hardening pulse becomes wider and wider. It reveals that the direct current bias field and pulsed bias field have great influence on the types of vertical Bloch line in the garnet bubble films.
Study on equivalent electromagnetic parameters and absorbing properties of honeycomb-structured absorbing materials
He Yan-Fei, Gong Rong-Zhou, Wang Xian, Zhao Qiang
2008, 57 (8): 5261-5266. doi: 10.7498/aps.57.5261
Abstract +
Based on strong interference theory and the assumption of long wave band,formulae for computing the equivalent electromagnetic parameters of honeycomb-structured absorbing materials are presented. It is pointed out that the equivalent permeability and permittivity of honeycomb-structured absorbing materials are smaller than those of the absorbing layer, but the equivalent permittivity is reduced more significantly, so the equivalent permeability is more close to the equivalent permittivity. This is helpful for the design of impedance matching of absorbing materials. It is indicated by reflectivity results that the absorbing layer should have an optimum thickness to make the reflectivity minimal for honeycomb-structured absorbing materials with different height of honeycombs. These results are useful for design of honeycomb-structured absorbing materials.
Raman scattering study of the spin ladder compound Sr14(Cu1-yFey)24O41
Hu Ni, Xiong Rui, Wei Wei, Wang Zi-Yu, Wang Li-Li, Yu Zu-Xing, Tang Wu-Feng, Shi Jing
2008, 57 (8): 5267-5271. doi: 10.7498/aps.57.5267
Abstract +
Serials of spin ladder compound Sr14(Cu1-yFey)24O41 with different doping level have been prepared by conventional solid state reaction method. The polarized Raman spectroscopy shows the existence of (4Ag+4B1g+3B2g+B3g) modes, and the peak at 1170 cm-1 for all the samples are associated with the longitudinal phonon mode which reveals the information of the ladder. Furthermore, we have compared the result of the Raman spectroscopy with the conduction behavior.
Spectral characteristics and crystal field parameters of the Cr3+ doped Cd3Al2Ge3O12
Yuan Xiao-Bo, Yuan Jian-Hui, Yang Chang-Hu, Zhang Zhen-Hua
2008, 57 (8): 5272-5276. doi: 10.7498/aps.57.5272
Abstract +
Polycrystalline Cd3Al2Ge3O12:Cr3+ was synthesized by high temperature solid-state method. Its crystal structure was analyzed by X-ray diffraction. Based on its absorption spectrum at room temperature and the emission spectra at room temperature and 77K, the spectral properties were investigated and the crystal field parameter was calculated. The results show that under the excitation of 450nm light, the emission spectrum of Cd3Al2Ge3O12:Cr3+ at room temperature mainly consists of three broad bands with a weak R line. The three broad bands correspond to 4T1→4A2, 2T2→4T2, and 4T2→4A2 transitions of Cr3+, respectively. The broad band emissions weaken and the R line becomes stronger and sharper at low temperature. The calculated results showed the crystal field strength Dq/B=2.32, Stokes displacement ΔES=1919cm-1 and Huang-Rhys factor S=5.58, which indicates that Cr3+ in Cd3Al2Ge3O12 garnet are located in a weak crystal field strength and the coupling between the electrons and the phonons is strong, The distance ΔE between 4T2 zero phonon energy level and 2E energy level is only 326.5cm-1, which is beneficial to the output of Cr3+ tunable laser.
Low energy oscillatory phenomena in photoreflectance and photo-modulation reflectance spectra of GaMnAs films grown by low temperature molecular-beam epitaxy
Wang Jian-Nong, Luo Xiang-Dong, Ji Chang-Jian, Wang Yu-Qi
2008, 57 (8): 5277-5283. doi: 10.7498/aps.57.5277
Abstract +
GaMnAs grown by low temperature molecular beam epitaxy have been investigated by Fourier transform infrared and photo-modulation reflectance (PR) measurements. Besides the band gap of Ga(Mn)As,Franz-Keldysh oscillations and spin-orbit coupling energy, low energy oscillations, lower than the GaAs band gap, were well observed in the PR spectra of GaMnAs. And these oscillations were also observed clearly in reflectance spectra of GaMnAs. By fitting the oscillations of the reflectance spectra, it was attributed to the variable refractive indexes induced by the high hole density in GaMnAs, which was caused by Mn doping in GaAs. At the same time, the PR spectra of high-resistance GaMnAs at low temperature were also studied.
Influence of low rate p/i interface layer on the performance of high growth rate microcrystalline silicon solar cells
Han Xiao-Yan, Hou Guo-Fu, Li Gui-Jun, Zhang Xiao-Dan, Yuan Yu-Jie, Zhang De-Kun, Chen Xin-Liang, Wei Chang-Chun, Sun Jian, Geng Xin-Hua
2008, 57 (8): 5284-5289. doi: 10.7498/aps.57.5284
Abstract +
In the process of the high growth rate μc-Si:H film deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD), the high energy ion impinging on the growing surface could deteriorate the device performance. Incorporation of a low growth rate intrinsic μc-Si:H p/i buffer layer was advanced in this paper. The results show that the introduced low growth rate buffer layer could improve the characteristics of p/i interface and the vertical uniformity of the intrinsic layer. It was found that the defects in intrinsic layer first decreased and then increased with increasing thickness of the buffer layer. These results led to an optimal thickness for the buffer layers. The efficiency of solar cells was increased about 1% when the thickness was optimized. As a result, the efficiency of 8.11% has been achieved at an i-layer deposition rate of 8.5nm/s.
Investigation on the effect of lamellar thickness on three-dimensional lamellar eutectic growth by multi-phase field model
Yang Yu-Juan, Wang Jin-Cheng, Zhang Yu-Xiang, Zhu Yao-Chan, Yang Gen-Cang
2008, 57 (8): 5290-5295. doi: 10.7498/aps.57.5290
Abstract +
Using the multi-phase field model proposed by Kim, Kim, Suzuki and Ode (KKSO), numerical studies have been carried out to investigate the effect of lamellar thickness on the lamellar eutectic growth in three dimensions. Simulation results showed that the lamellar thickness has significant effects on the eutectic morphology evolution with a given lamellar spacing. When the lamellar thickness is comparatively small, the eutectic lamellar growth is similarly to the two-dimensional case. Increasing the lamellar thickness, the effect of lamellar thickness becomes stronger, as a result, the lamellar structure distorts vertically, and oscillations on both the direction of the width and the direction of the thickness occur alternatively after a further increase of the lamellar thickness. When the lamellar thickness is bigger than the lamellar width, a stronger oscillation in the thickness direction than that in the width direction occurs, and eventually the oscillation in the width direction is suppressed but only an approximate 1λ oscillation in the thickness direction can be found. Moreover, simulation results also showed that the change of undercooling is consistent with the morphology transition.
Effect of exciton rotational relaxation on luminescence decay of low-doped porphyrin side-chain polymers
Chen Zhi-Feng, Wang Hui, Zhang Wei, Shen Han, Lai Tian-Shu, Ji Liang-Nian, Yu Han-Cheng, Huang Jin-Wang
2008, 57 (8): 5296-5301. doi: 10.7498/aps.57.5296
Abstract +
Effect of rotational motion of porphyrin molecules on the luminescence dynamic of low-doped porphyrin side-chain polymers has been studied by using the theory of exciton rotational diffusion. It is shown that the rotational motion of porphyrin molecules is an important way that induces the nonradiative relaxation of excitons. The more easily porphyrins rotate, the more rapidly energy decays, therefore, the faster the luminescence decay process. In the case of low doping concentration of porphyrins and long interchain distance, the rotational motion of porphyrin molecules is the main reason of fast luminescence decay and low luminescence efficiency. The transient luminescence relaxation processes of two kinds of polymers were fitted with the theoretical expression, the theoretical analysis are in good agreement with the experimental results.
Effects of organic adsorbent on the photoluminescence of porous silicon microcavities
Liu Guang-You, Tan Xing-Wen, Wang Zhen, Yao Jin-Cai, Xiong Zu-Hong
2008, 57 (8): 5302-5309. doi: 10.7498/aps.57.5302
Abstract +
The effects of organic absorbent on the refractive index and photoluminescence of porous silicon microcavities were theoretically investigated by using the Bruggeman effective medium approximation. Experimentally, porous silicon microcavities were fabricated by computer controlled electrochemical etching, and then interacted with the molecules of oil vapor from a rotary pump. We found that the narrow photoluminescence spectra of porous silicon microcavities were sensitive to the adsorption and de-adsorption of the oil vapor molecules, which leads to a 71nm red-shift and the intensity variation in photoluminescence spectrum. The experimental results are qualitatively consistent with the theoretical estimate.
Study on the flatband potential of nanoporous TiO2 film electrode
Dai Jun, Hu Lin-Hua, Liu Wei-Qing, Dai Song-Yuan
2008, 57 (8): 5310-5315. doi: 10.7498/aps.57.5310
Abstract +
The flatband potential of nanoporous TiO2 film electrodes has been studied by spectroelectrochemical method. The effect of film thickness and TiCl4 treatment on the flatband potential of nanoporous TiO2 electrodes and the photovoltaic performance of dye-sensitized solar cells were determined. The results showed that with the increasing of film thickness, the flatband potential shifts in the positive direction, and the open circuit voltage of corresponding solar cells decreases. In addition, after TiCl4 treatment, the flatband potential and the open circuit voltage of corresponding solar cells were not obviously changed. All this suggests that the flatband potential of nanoporous TiO2 electrode can reflect the changing trend of open circuit voltage of solar cells well.
Effects of interfacial couplings on charge transport properties of DNA molecule
Meng Xian-Lan, Qu Zhen, Kang Da-Wei, Xie Shi-Jie, Liu De-Sheng, Gao Xu-Tuan
2008, 57 (8): 5316-5322. doi: 10.7498/aps.57.5316
Abstract +
Using the three-dimensional tight-binding model and the matrix transfer method, effects of interfacial couplings on the charge transport properties of DNA molecule have been studied. The results indicate that when the interfacial couplings are ideal, both transmission coefficient and localization length of electrons are larger, the molecule shows higher conductivity, while the case is the contrary when the interfacial couplings are unideal. When the molecule and the metallic electrodes couple ideally, through voltage-current characteristic, it is found that the onset voltage of poly(dG)-poly(dC) DNA is lower than that for the poly(dA)-poly(dT) counterpart, and the current of the former is larger than that of the latter under the same bias voltage, so the conductivity of poly(dG)-poly(dC) DNA is higher than that of the poly(dA)-poly(dT) counterpart.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Multi-angular polarized characteristics of cirrus clouds
Gu Xing-Fa, Chen Liang-Fu, Yu Tao, Tian Guo-Liang, Cheng Tian-Hai
2008, 57 (8): 5323-5332. doi: 10.7498/aps.57.5323
Abstract +
Cirrus is mainly composed of non-spherical ice crystals in various shapes and plays an important roles in Earth's radiation budget and global climate change. Knowledge of cirrus properties is crucial for studying the radiation budget and climate change. Thus studies of the optical, microphysical, and physical properties of cirrus have become the popular issue. The optical properties of cirrus at 0.865μm are studied. And the reflectance and polarized reflectance are evaluated with the adding-doubling method by solving the vector radiative transfer model, and the sensitivity of reflectance and polarized reflectance to cirrus optical parameters and surface albedo are evaluated. The results indicate that the polarized reflectance over a large range of scattering angles can show the information of cirrus properties. Based on the studies of the sensitivity, the basic theory of using the remote sensing data of multi-angular polarized measurements to retrieve the properties of cirrus is proposed.
Determining the threshold of extreme events with detrended fluctuation analysis
Yang Ping, Hou Wei, Feng Guo-Lin
2008, 57 (8): 5333-5342. doi: 10.7498/aps.57.5333
Abstract +
When the dynamic system is in the extreme states, or it is affected by an intensive disturbance, we will get an extreme event. The detrended fluctuation analysis (DFA) measures the long-term correlation of a system, so the extreme events has no effect on systems long-term correlation. Based on this idea, we determined the threshold of extreme events with detrended fluctuation analysis and the results testify its effectiveness. By this method, we analyzed the exreme events in Beijing for the temperature and rain. The results show that before the metaphase of the 1970s, the frequency and inensity of the extreme temperature events is mitigatory, and from 1970s to 1990s, there were very few extreme events. But from the metaphase of the 1990s to now, the extreme temperature events are frequent. The extreme low temperature event has a downtrend from the 1950s to now and never happened after 1978s. The frequency and intensity of extreme precipitations are periodic. The frequency and intensity were high in the metaphase of 1950s and 1960s, and were low in the remaining period. The transition occurred in the 1970s.
The research on long range correlation of Lorenz system
Zhi Rong, Zhang Zeng-Ping, Wang Qi-Guang
2008, 57 (8): 5343-5350. doi: 10.7498/aps.57.5343
Abstract +
This paper takes the typical chaotic system, the Lorenz system, as the subject. We use the detrended fluctuation analysis method to study the systems long-range correlation for different initial values and parameters. It turns out that the systems long range correlation is related with its initial values phase space position. When the initial value is close to the unstable equilibrium points, the systems long rang correlation is strengthened, the scaling exponents α are bigger, and the predictability of the system is better. When the system is in complete chaotic state, its long range correlation becomes weak with the parameters increasing, and the scaling exponents α are decrease, the predictability of the system becomes weaker. This reveals the relationship between the systems long range correlation and its predictability. We disturbed the system equation with random noise and found that the systems long range correlation decreases with the increase of random noise intensity. This result further signifies out that the Lorenz system's long range correlation is a physical parameter that may serves as an effective predictability criterion.
Analysis of dynamical statistical characteristics of temperature correlation networks of 1—30d scales
Zhi Rong, Zhou Lei, Gong Zhi-Qiang, Feng Guo-Lin
2008, 57 (8): 5351-5360. doi: 10.7498/aps.57.5351
Abstract +
Based on reanalysis data of National Center of Environment Prediction of America, temperature correlation networks of different time scales are constructed and their dynamical statistical properties are also analyzed. Results show that temperature correlation networks of 1 and 30d belong to small world and semi-globally coupled network, respectively. The time scale condition is 11—12d for networks to shift from one type to the other. For 1 d scale, the total number of links at each geographic location is semi-symmetrical between north and south hemisphere, the equatorial nodes have a larger number of connections in three regions: the equatorial Indian ocean, equatorial east Pacific ocean and equatorialeast Atlantic ocean. Sub-system networks of both mid-latitude and low-latitude belong to the small world network, while the accumulative degree distribution of low-latitude follows the exponentical and Gaussian distributions and that of mid-latitude follows the semi-Gaussian distribution. The range of correlation condition value for temperature network belonging to small world network is 0.2—0.9. Meanwhile for the 30 d scale, ocean nodes show a larger number of connections than the land nodes. The ocean and the land sub-system networks belong to the semi-globally coupled and the small world networks, respectively. The range of correlation condition value for temperature network belonging to semi-globally coupled network is 0—0.6.