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Vol. 58, No. 11 (2009)

2009-06-05
GENERAL
Infinitely many symmetries and symmetry reduction of (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff equation
Zhang Huan-Ping, Chen Yong, Li Biao
2009, 58 (11): 7393-7396. doi: 10.7498/aps.58.7393
Abstract +
Integrability condition of (2+1)-dimensional generalized Calogero-Bogoyavlenskii-Schiff equation are obtained by Painléve-test. Based on this condition and Painléve-test, the bilinear form of GCBS equation is found. Towards this bilinear form infinitely many formal series symmetries are found by the formal series symmetry method, the obtained symmetries are used to get the symmetry reductions of GCBS equation.
Variational iteration method for solving a class of strongly nonlinear evolution equations
Mo Jia-Qi, Zhang Wei-Jiang, Chen Xian-Feng
2009, 58 (11): 7397-7401. doi: 10.7498/aps.58.7397
Abstract +
A class of strongly nonlinear evolution equations are studied. Using the variational iteration method, the corresponding varationa is first constructed,then the suitable initial approximation is selected; and then, by using the iteration method, the approximate solution of arbitrary degree of accuracy for the solitary wave is obtained.
New application of (G′/G)-expansion method to high-dimensional nonlinear physical equations
Ma Yu-Lan, Li Bang-Qing, Sun Jian-Zhi
2009, 58 (11): 7402-7409. doi: 10.7498/aps.58.7402
Abstract +
The (G′/G)-expansion method is firstly extended to construct exact non-traveling wave general solutions of high-dimensional nonlinear equations, explore special soliton-structure excitation and evolution, and investigate the chaotic patterns and evolution of these solutions. Taking as an example, new non-traveling solutions are calculated for (3+1)-dimensional nonlinear Burgers system by using the (G′/G)-expansion method. By setting properly the arbitrary function in the solutions, special soliton-structure excitation and evolution are observed, and the chaotic patterns and evolution are studied for the solutions.
Study of the partition functions of SiO2 molecules
Wan Hui-Jun, Xie An-Dong, Wu Dong-Lan, Cheng Xin-Lu, Yang Xiang-Dong
2009, 58 (11): 7410-7413. doi: 10.7498/aps.58.7410
Abstract +
The total internal partition functions are calculated for 16O28Si16O at temperatures from 20—6000 K. In deducing the rotational partition sums Qrot, the centrifugal distortion corrections are taken into account. The method used for calculating the vibrational partition sums Qvib is the harmonic oscillator approximation. The temperature range is divided into five regions and the calculated total internal partition functions are fitted to a fourth-order polynomial in T, and the coefficients are evaluated in the five temperature regions. This permits rapid and accurate calculation of the total internal partition functions in the temperature range from 20—6000 K.
Analysis on theory of selective model
Wei Wei-Feng
2009, 58 (11): 7414-7420. doi: 10.7498/aps.58.7414
Abstract +
Selective model provided a way to explain the generation of index law and power law on the basis of preferential probability analysis. A transformation formula between the selective scope rule and selective distribution was deduced through the research on preferential trials. It was named as preferential transformation, which offered a mean to study the rule of monotone distributions. A corresponding continuous transformation can be deduced by the preferential transformation for analyzing probability density function. Compared with the discrete distribution, we defined a comparison function for continuous distribution, and pointed out the relationship between the discrete distribution and continuous distribution. Through selective model, we simulated and analyzed the power law phenomena. Selective theory was important to the research on huge complex system and social behavior. It could also expand the foundation of statistical physics and probability theory.
Noether symmetry and Mei symmetry of discrete holonomic system in phase space
Wang Peng, Lu Kai, Fang Jian-Hui, Zhang Ming-Jiang
2009, 58 (11): 7421-7425. doi: 10.7498/aps.58.7421
Abstract +
The Noether symmetry, the Mei symmetry and the conserved quantities of discrete holonomic system in phase space are studied in this paper. Using the difference discrete variational approach, the difference discrete variational principle of discrete holonomic system in phase space is derived. The discrete canonical equations and energy evolution equation are established. The criterion of Noether symmetry and Mei symmetry of the system are given. The discrete Noether and Mei conserved quantities and the conditions for their existence are obtained. An example is discussed to show the applications of the results.
Mei symmetries and the Noether conserved quantities of super-thin elastic rod
Cui Jian-Xin, Gao Hai-Bo, Hong Wen-Xue
2009, 58 (11): 7426-7430. doi: 10.7498/aps.58.7426
Abstract +
Based on Kirchhoff’s analogue,generalized Hamilton canonical equations for the dynamics of super-thin elastic rod are analyzed. The Mei symmetry transformations and the theorem are introduced.And the condition and theorem of Noether conserved quantity are deduced directly by Mei symmetry for the super-thin elastic rod system. An example is given to illustrate the application of the result.
Effects of gauge transformations on symmetries of Birkhoffian system
Ding Guang-Tao
2009, 58 (11): 7431-7435. doi: 10.7498/aps.58.7431
Abstract +
The effects of gauge transformation on Noether symmetry, Lie symmetry and Mei symmetry of a Birkhoff system are studied. Under certain conditions, the system can keep its Noether symmetry and conserved quantity. The Lie symmetry and Hojman conserved quantity of the system will still remain unchanged. The Mei symmetry and a new-type conserved quantity of the system may very, and the conditions under which the Mei symmetry and the new-type conserved quantity will remain are obtained. An example is given to illustrate the application of the results.
Birkhoff symmetries and conserved quantities of generalized Birkhoffian systems
Zhang Yi
2009, 58 (11): 7436-7439. doi: 10.7498/aps.58.7436
Abstract +
The problem of Birkhoff symmetry for generalized Birkhoffian systems is studied, and the corresponding conserved quantities are given. A theorem known for nonsingular equivalent Lagrangians is generalized to the generalized Birkhoffian systems. We prove that under certain conditions the matrix Λ, which is related with the generalized Birkhoffian equations obtained from two groups of dynamical functions B,Rμ,Λμ and B,Rμ,Λμ, has the property that the traces of all its integer powers are the conserved quantities of the system. An example is given to illustrate the application of the results.
A new type of Mei adiabatic invariant induced by perturbation to Mei symmetry for nonholonomic mechanical systems
Ding Ning, Fang Jian-Hui
2009, 58 (11): 7440-7446. doi: 10.7498/aps.58.7440
Abstract +
A novel type of Mei adiabatic invariant induced by perturbation to Mei symmetry for nonholonomic mechanical system is reported. The form of criteria and restriction equations for Mei symmetry after being disturbed are given. The new form and conditions of the Mei adiabatic invariant are obtained.
Lagrange symmetries and conserved quantities for nonholonomic systems of non-Chetaev’s type
Ge Wei-Kuan, Zhang Yi
2009, 58 (11): 7447-7451. doi: 10.7498/aps.58.7447
Abstract +
This paper focuses on Lagrange symmetries and conserved quantities for nonconservative mechanical systems with nonholonomic constraints of non-Chetaev's type. The definition and criterion of Lagrange symmetry of the systems are given. The conditions under which a Lagrange symmetry can lead to a new conserved quantity(first integral)are obtained and the form of the new conserved quantity(first integral)is presented. Two examples are given to illustrate the application of the results.
A simple method for solving nonlinear wave equations for their peaked soliton solutions and its application
Liu Yu
2009, 58 (11): 7452-7457. doi: 10.7498/aps.58.7452
Abstract +
According to the characteristics of peaked soliton solution, the undetermined coefficient method for solving nonlinear wave equations for their peaked soliton solutions is submitted and by means of the method several kinds of peaked soliton solutions are obtained for five nonlinear wave equations: the Camassa-Holm, fifth -order KdV-like, generalized Ostrovsky, combined KdV-mKdV and Klein-Gordon equations. The solutions given in literature about Camassa-Holm equation become the special cases of the solutions in this paper. The graphs of some solutions are given through numerical simulation. The special conditions under which the wave equation will have peaked soliton solution is briefly described. The method used in this paper can also be used for solving many other nonlinear equations.
The spatio-temporal stochastic resonance of calcium in coupled hepatocytes systems affected by subthreshold stimuli and noise
Lu Qi-Shao, Lü Shu-Juan, Wang Bao-Hua
2009, 58 (11): 7458-7465. doi: 10.7498/aps.58.7458
Abstract +
The influence of subthreshold periodic stimuli on temporal-spatial resonance of [Ca2+] in a stochastic coupled hepatocytes system is studied. When the frequency of stimuli is close to that of the determinate coupled system before the Hopf bifurcation, the eruption rate of [Ca2+] is enhanced greatly in the stochastic system. By computing the autocorrelation function of the eruption rate, it is found that the temporal resonance of [Ca2+] becomes more ordered by the subthreshold stimuli. Furthermore, for a given coupling strength between cells, there is an optimal noise level to make the [Ca2+] resonance reach maximum, and the optimal noise level also increases with the coupling strength increasing. Though the action of subthreshold stimuli promotes the temporal resonance of the system, it strengthens the sensibility to noise and then depresses the spatial ordered calcium waves induced by medium-strength noise only, as shown by the analysis by the spatial Fourier transform and its structure function.
Near classical states of oscillator in square potential well with infinitely high walls
Li Xing-Hua, Yang Ya-Tian, Xu Gong-Ou
2009, 58 (11): 7466-7472. doi: 10.7498/aps.58.7466
Abstract +
We define such quantum state as near classical state (NCS), in which the mean values of coordinates equal to the classical solution in macroscopic scale. We obtained the NCS for oscillator in square potential well with infinitely high walls as example.
Dispersion relation and Landau damping of linear waves in quantum plasma
Ji Pei-Yong, Lu Nan, Zhu Jun
2009, 58 (11): 7473-7478. doi: 10.7498/aps.58.7473
Abstract +
The dispersion relation and Landau damping of electron plasma waves in the quantum plasma are derived by kinetic theory. Starting from the quantum hydrodynamic equation of electron and photon kinetic equation, photon Landau damping is discussed. Research indicates that quantum effects enlarge the frequency of electron plasma waves and do not change the dispersion of electromagnetic waves. It is also found that electron and photon Landau damping rates are both reduced by quantum effects, so the exchange of energy between particles and waves is retarded.
Pairwise entanglement in three-qubit Heisenberg model with Dzyaloshinskii-Moriya interaction
Wang Yan-Hui, Xia Yun-Jie
2009, 58 (11): 7479-7485. doi: 10.7498/aps.58.7479
Abstract +
In this paper, we study the improvement and manipulation of pairwise thermal entanglement in one-dimentional three-qubit Heisenberg model, where Dzyaloshinskii-Moriya (DM) interaction is considered and concurrence is calculated to research this entanglements property. The results show that for XXX model, DM interaction can induce entanglement in the antiferromagnetic and ferromagnetic spin chains although the required critical values are different for these cases. For XXZ model, by introducing DM interaction D, antiferromagnetic spin chain has entanglement which is absent when D=0, and in addition, for antiferromagnetic and ferromagnetic cases, DM interaction D and the anisotropy parameter Δ have different effects on entanglement. As a result, the entanglement can be controlled and enhanced by choosing appropriate DM interaction and anisotropy parameter. Furthermore, we find that at the same temperature, no matter for antiferromagnetic or ferromagnetic spin chains, the critical DM interaction inducing entanglement should be greater in a three-qubit XXZ model than that in a two-qubit XXZ model.
Thermal particles model and radiation power of static spherically symmetric black holes
Meng Qing-Miao, Jiang Ji-Jian, Wang Shuai
2009, 58 (11): 7486-7490. doi: 10.7498/aps.58.7486
Abstract +
Using the thermal particles model of the static spherically symmetric black holes, the thermal radiation laws of the black hole are studied. When η takes the value of inherent thickness, the following results can be obtained. For all Schwarzschild black holes, the radiation power are the same, and the radiation energy flux on the event horizon is inversely proportional to the square of the black hole mass. While the radiation energy flux received by the observer far away from the black hole is inversely proportional to the square of the distance between the observer and the black hole. For Reissner-Nordstrm black holes, the radiation energy flux and the radiation power on the event horizon are not only related to the black hole mass, but also the charge of black holes. For fixed values of η, m and Q, the radiation energy flux received by the observer is also inversely proportional to the square of the distance between the observer and the black hole. For extreme Reissner-Nordstrm black holes, the radiation energy flux and the radiation power are all equal to zero.
Charged particle tunneling in a static dilaton black hole
Zhang Chang-Ping, Wang Zhong-Lin, Liu Cheng-Zhou
2009, 58 (11): 7491-7496. doi: 10.7498/aps.58.7491
Abstract +
In the Parikh and Wilczek’s tunneling framework,Hawking radiation of charged particle in the Gibbons-Maeda dilaton black hole is investigated. When a particle with electromagnetic charge tunnels across the event horizon,energy conservation and electromagnetic charge conservation of the spacetimes are emphasized and the back-reaction effects of the charged particle are considered.The present results show that the tunneling probability is related to the difference of the Benkenstin-Hawking entropy of the black hole.This implies that black hole radiation is consistent with information conservation and the underlying unitary theory.
Effect of the position of accident on traffic waves
Zhao Shou-Gen
2009, 58 (11): 7497-7501. doi: 10.7498/aps.58.7497
Abstract +
In this paper, we adopted the traffic flow model with the consideration of the accident probability, which is recently developed by Tang et al. (Tang T Q, Huang H J, Xu G 2008 Physica A 387 6845), to study the effect that the accident position has on shock and rarefaction wave. The simulation results show that our model can perfectly reproduce the effects that the accidental position produces on the two traffic waves and the effects are completely related to the accident position.
The high temperature weak degeneration effect of charged particle system in two external field
Sun Yan-Qing, Huang Chao-Jun, Long Shu-Ming, Liu Ya-Feng, Yin Ji-Wu
2009, 58 (11): 7502-7506. doi: 10.7498/aps.58.7502
Abstract +
In light of the semiclassical statistical theory and method proposed by Thomas-Fermi, this paper conducts a research of the thermodynamic properties of charged particle system restricted by the homogeneous electric and the resonance field. Based on the derivation of the quantum state density of the charged particle system under the condition of high temperature and weak degeneration, the analytic formula of its chemical potential, internal energy and heat capacity is calculated, follow by a detailed analysis of the influence of the two fields on the chemical potential, internal energy and heat capacity. It is finally concluded that the two external fields exert a high temperature and weak degeneration effect on the charged particle system.
Langevin model of the flow control in the internet and its phase transition analysis
Fan Hua, Li Li, Yuan Jian, Shan Xiu-Ming
2009, 58 (11): 7507-7513. doi: 10.7498/aps.58.7507
Abstract +
One of the big challenges in the field of Internet research is to elucidate the relationship between micro-algorithms of the flow control protocols and macro-properties of the Internet with a proper model. In this paper, we build up a Langevin equation under the transmission control protocol using deductive method. Then we analyze the effectiveness of the active queue management based on the Langevin model. We have proved that there is a phase transition sequence from smooth state to congestion state then to paralysis state in all such kind of algorithms. We also provide explicit formulas of the critical points in terms of the system parameters. Although the model used in this paper focuses on a specific algorithm, we believe this method has a great potential in analyzing and understanding various network congestion control algorithms.
An extension system with constant Lyapunov exponent spectrum and its evolvement
Li Chun-Biao, Wang Han-Kang
2009, 58 (11): 7514-7524. doi: 10.7498/aps.58.7514
Abstract +
By introducing linear terms and constant terms in dynamic equations, the extension system with constant Lyapunov exponent spectrum is proposed based on the improved constant-Lyapunov-exponent-spectrum system. Firstly, the dynamical behaviour of the extension system is investigated and expounded by simulation of Lyapunov exponent spectrum, bifurcation diagram and numerical analysis on amplitude evolvement of state variables. Secondly, a class of subsystems with the same properties but different phase trajectories is obtained through different combinations of linear terms from the extension system. The dynamical characteristics including equilibrium, eigenvalue and Lyapunov exponents are analyzed in detail simultaneously. Finally, it is pointed out that the chaotic system will have a tremendous application prospect in chaotic radar, secure communications and other information processing systems.
A piecewise-linear Sprott system and its chaos mechanism
Chen Jian-Jun, Yu Si-Min
2009, 58 (11): 7525-7531. doi: 10.7498/aps.58.7525
Abstract +
In this paper, a piecewise-linear Sprott system is proposed and its chaos mechanism is analyzed. According to the Shilnikov theorem, on the condition that the basic characteristics of heteroclinic orbit, Shilnikov inequality and eigenvalue equation are satisfied, by finding a heteroclinic orbit formed by three geometric invariant sets, namely the unstable manifold, heteroclinic point, and stable manifold, a set of real parameters in accordance with the condition of existence of heteroclnic orbit are obtained for this chaotic system. Thus, the existence of heteroclnic orbit has been proved. Finally, according to this set of real parameters, the circuit design and experimental verification has been carried out.
A new method of adaptive tracking control for chaotic system
Li Hua-Qing, Chen Qiu-Hua, Luo Xiao-Hua
2009, 58 (11): 7532-7538. doi: 10.7498/aps.58.7532
Abstract +
In this paper, a new strategy of adaptive tracking control of chaotic system is proposed.By designing the compensatory controller in advance, this method transforms the tracking control problem of reference signals which are tracked by chaotic system states variables into the adaptive synchronization problem of identical-structured chaotic system variables. Tracking controller is equal to the sum of compensatory controller and adaptive controller.Truth of tracking controller designed by proposed strategy is proved theorically based on Lyapunov stability theory.Finally, taking hyperchaotic Chen system as controlled object, tracking controllers are designed in this way to track fixed points, sine signals, cosine signals, identical-structured chaotic system state variables and different-structured chaotic system state variables. The response time is very short, showing the effectiveness of the strategy.
The synchronization of spatiotemporal chaos of all-to-all network using nonlinear coupling
Lü Ling, Jing Xiao-Dan
2009, 58 (11): 7539-7543. doi: 10.7498/aps.58.7539
Abstract +
N Fitzhugh-Nagumo models are used as network nodes, and synchronization of spatiotemporal chaos is studied using a all-to-all network constructed through a nonlinear coupling. The general principle of selecting coupling functions between nodes of the complex network is introduced. The theoretical analysis of the conditions for synchronization is made and the range of the feedback gain is obtained based on Lyapunov stability theory. The simulation is made to test the synchronization effect of the spatiotemporal chaos of the all-to-all network whose nodes are Fitzhugh-Nagumo models. The results show that the synchronization is fast and efficient, and the size of the network size has no sensitive effect on the stability of the network synchronization.
The perimeter measure analysis of chaotic attractor morphology of inclined oil-water two phase flow patterns
Zong Yan-Bo, Jin Ning-De, Wang Zhen-Ya, Wang Zhen-Hua
2009, 58 (11): 7544-7551. doi: 10.7498/aps.58.7544
Abstract +
In two-dimensional phase space, the attractor morphology parameters of perimeter measures, such as area, lengths of long axis and short axis, are defined, and the variations of these parameters with the delay time are investigated. It was found that the growth rates of the above parameters do not change notably in the first zone during the attractor unfolding process, which is suitable for attractor morphology characterization. The classification effectiveness of this method is verified by applying it to simulating signals, such as sine signal, white noise, mixed signals and Lorenz signals. By the experiment of inclined oil-water two phase flow, the conductance signals were acquired from the vertical multi-electrode array sensor, and the water dominated inclined oil-water flow patterns are analyzed by using the attractor morphology parameters and we found that the growth rate of area is an invariant quantity of attractor morphology, which can give a good classification of dispersion of oil in water-pseudoslugs flow and dispersion of oil in water-countercurrent flow.
Sliding mode variable-structure control of chaos in direct-driven permanent magnet synchronous generators for wind turbines
Yang Guo-Liang, Li Hui-Guang
2009, 58 (11): 7552-7557. doi: 10.7498/aps.58.7552
Abstract +
The directly driven wind turbine with permanent magnet synchronous generator (D-PMSG) is investigated. Its mathematical model is deduced and chaotic behaviors is demonstrated while its parameters have a certain range of values or under certain working conditions. A sliding mode variable structure method for controlling chaos in D-PMSG is presented, and realized through controlling pitch angle β. In view of the non-linear property and parameter changing characteristic, etc. for wind turbine, and based on the mechanism of the wind turbine, this paper obtained the wind turbines linear model at a certain condition point under some assumptions, and then proposed the sliding model control strategy by taking full use of the SMCs non-sensitivity merit towards the model error and the parameter change as well as exterior disturbance. the simulation result indicates that the proposed control plan is effective, the control property of response is obtained quickly and the system also has good robustness, and is suitable for uncertain parameter in the system. Research results may have value for D-PMSG chaos control.
Resonance response of a single-degree-of-freedom nonlinear dry system to a randomly disordered periodic excitation
Rong Hai-Wu, Wang Xiang-Dong, Xu Wei, Fang Tong
2009, 58 (11): 7558-7564. doi: 10.7498/aps.58.7558
Abstract +
The resonance response of a single-degree-of-freedom nonlinear dry oscillator of Coulomb type to narrow-band random parameter excitation is investigated. The analysis is based on the Krylov-Bogoliubov averaging method. The averaged equations are solved exactly and the algebraic equation of the amplitude of the response is obtained in the case without random disorder. Linearization method and moment method are used to obtain the mean square response amplitude for the case with random disorder. The effects of damping, nonlinear intensity, detuning, bandwidth, dry intensity, and magnitudes of random excitations are analyzed. The theoretical analyses are verified by numerical results. Theoretical analyses and numerical simulations show that the peak amplitudes may be strongly reduced and the bifurcation of the system will be delayed when intensity of the nonlinearity increases. The peak amplitudes will also be reduced and the bifurcation of the system will be delayed when damping and dry intensity of the system increases.
Output feedback adaptive maneuvering for multi-input multi-output uncertain nonlinear systems
Zang Qiang, Zhou Ying
2009, 58 (11): 7565-7572. doi: 10.7498/aps.58.7565
Abstract +
The output maneuvering problem generally consists of geometric task and dynamic task. In this paper, the adaptive maneuvering control based on output feedback is studied for multi-input multi-output nonlinear system with parametric uncertainty. The virtual estimation of the controlled system states is achieved by introducing filters and observer. Based on the backstepping approach in vector form, an output feedback adaptive maneuvering control scheme is proposed and three kinds of adaptive laws governing the path variable are presented. The geometric and the dynamic tasks are solved, meanwhile the global stability of the closed loop systems is guaranteed through the control scheme. The simulation results show the effectiveness of the proposed scheme.
Reflection of plane wave in oscillatory media
Lü Yao-Ping, Gu Guo-Feng, Lu Hua-Chun, Dai Yu, Tang Guo-Ning
2009, 58 (11): 7573-7578. doi: 10.7498/aps.58.7573
Abstract +
The reflection of plane waves in oscillatory media described by complex Ginzburg-Landau equation has been researched. The reflection condition and the angle formed by the boundary line between incident and reflected waves and the boundary line separating two regions of different kinetics are theoretically given. Two kinds of reflections have been found. One is a back refraction-induced reflection. The corresponding angle is theoretically obtained. The other is a pure reflection, which is independent of refraction. The theoretical results are supported by numerical results. The theoretical and numerical results show that the reflection takes place only if the angle of incidence is larger than a critical value. The angle of reflection is equal to the critical angle of incidence, and it increases as the frequency of the incident wave increases for the pure reflection.
Fractal characterization for subharmonic motion of completely inelastic bouncing ball
Jiang Ze-Hui, Zhao Hai-Fa, Zheng Rui-Hua
2009, 58 (11): 7579-7583. doi: 10.7498/aps.58.7579
Abstract +
The motion of a completely inelastic ball dropped vertically on the vibrating table will undergo a series of subharmonic bifurcations, controlled solely by the normalized vibration acceleration. It has been shown that the bifurcation diagram for the ball’s motion consists of almost equally spaced dense regions, in which the bifurcation behavior is sensitively dependent on the control parameter. The dense regions have complex interior geometrical structures. Here they are treated as fractal entities, and the fractal dimension for each of them is calculated. It is shown that the magnitude of the fractal dimension gradually increases, approaching a constant around 1.785.
Investigation on traffic bottleneck induce by bus stopping with a two-lane cellular automaton model
Li Qing-Ding, Dong Li-Yun, Dai Shi-Qiang
2009, 58 (11): 7584-7590. doi: 10.7498/aps.58.7584
Abstract +
In this paper, the influence of typical bus stops on traffic flow is investigated with the cellular automaton traffic model. For on-line and off-line bus stops, a two-lane cellular automaton model is proposed to simulate the traffic bottleneck induced by bus stopping under the open boundary condition. The phase diagram in the phase plane of injection probability and bus fraction is provided and two phases, i.e., the free flow phase and congested flow phase, are distinguished. The distributions of the mean density and velocity near the bus stop in different traffic phases are given and the comparison of dynamical characteristics of traffic flows is made for different types of bus stops. It is found that using the off-line bus stop can significantly improve the traffic flow in its neighboring region, compared with the on-line bus stop in the case of small fraction of buses.
A cellular automaton model of traffic considering the dynamic evolution of velocity randomization probability
Tang Tie-Qiao, Ding Jian-Xun, Huang Hai-Jun
2009, 58 (11): 7591-7595. doi: 10.7498/aps.58.7591
Abstract +
Few cellular automaton models of traffic have taken the relationship between the randomization probability of velocity and the specific value of current velocity into account. On the basis of Nagel-Schreckenberg model, this paper presents a modified cellular automaton model in which the randomization probability evolves with the driver’s remembering to historic experience and with the traffic condition around. Numerical simulation results show that the proposed model can reveal the influence of driver’s remembering on the traffic and generate higher average velocity and flux.
Multi-vapor embryos nucleation process and spinodal temperature analysis of expandable superheated water system
Li Si-Jie, Bai Bo-Feng
2009, 58 (11): 7596-7602. doi: 10.7498/aps.58.7596
Abstract +
This study uses molecular dynamics simulation to analyze the homogeneous nucleation process in superheated water. The temperature and pressure of the system are controlled with Langevin dynamics method while the system volume is variable. In this way, the expanding process of the liquid system into vapor system is studied phenomenologically. In metastable liquid system with higher superheating degree, there can be seen large quantities of regions with no liquid moleculer inside: i.e., the vapor embryos. These vapor embryos are unstable in nature and are deforming with time. By analyzing the attraction and repulsion between molecules, we find the mechanisms that govern the merging, formation and dying out of vapor embryos. Vapor embryo violates some predictions of classical bubble dynamics theory, it indicates that formation of vapor embryo may have a more microcopic nature than the formation of bubble. We compared systems under different temperatures to study the effects of superheating degree. The spinodal temperature of water at atmospheric pressure determined under our simulation condition is about 535 K, within the scope of available experimental results.
Study of multilevel pulse train control technique for switching converters
Qin Ming, Xu Jian-Ping
2009, 58 (11): 7603-7612. doi: 10.7498/aps.58.7603
Abstract +
A new control technique, multilevel pulse train (MPT), for switching converters is proposed in this paper. By using MPT control, according to different operation states, multilevel pulses are combined to generate a multilevel pulse train for the control of switching converters. MPT control technique is easy to realize, with great robust ness and good transient performance. The principle and implementation of the control technique are introduced, and the operation, characteristics and small-signal model of MPT controlled buck converter are also studied. The analysis, simulation and experimental results show that MPT control technique has much faster transient response than traditional PWM control technique and much lower output voltage ripple than the pulse train control technique.
Propagation of femtosecond laser pulses through metal-coated tapered fibre probe
Teng Shu-Yun, Cheng Chuan-Fu, Liu Gui-Yuan, Song Hong-Sheng, Liu Man
2009, 58 (11): 7613-7620. doi: 10.7498/aps.58.7613
Abstract +
Using the three-dimensional finite difference time domain (3D-FDTD) method, we calculate light field in metal-coated optical fiber probes with different taper angles and different lengths under illumination of femtosecond laser pulses. The transmission of temporal fields of the laser pulses propagating in the probes and the properties of their frequency spectrum and phases are studied. The influences of the taper angle and the length of the probe on these properties are analyzed. The calculation results show that the structure of probe leads to the broadening, amplitude oscillation and the spectrum splitting of the laser pulses. With the analysis of the spectrum and the phase variation, we give a preliminary explanation to the phenomena of the pulse broadening and the periodic variation of the pulse amplitude with time.
ATOMIC AND MOLECULAR PHYSICS
Calculation of fine-structure intervals of nd series high Rydberg states of Na
Ma Yi-Pei, He Li-Ming, Zhang Meng, Zhu Yun-Xia
2009, 58 (11): 7621-7626. doi: 10.7498/aps.58.7621
Abstract +
A new numerical calculation method has been used to solve the relativistic Hartree-Fock (RHF) equation of atomic system. The retardation term in Breit interaction was given in a explicit and succinct formulation. The established theoretical method and computational program have been used to study the fine structure of nd(n=17—31) series of sodium. We obtained the fine structures by using RHF method in a self- consistent procedure for the first time, rather than perturbation method often used by other authors. The results show that the exchange interaction between the core and valence electrons in the frame of relativity is the main reason of abnormal fine structure. By combining the effect of Breit interaction, it is shown that a relativistic calculation reproduces the inverted fine structure of sodium exactly and our work is far better than other theoretical results.
Calculation of positron lifetime of single crystals of elements of the periodic table with the theory of local density approximation
Chen Xiang-Lei, Kong Wei, Du Huai-Jiang, Ye Bang-Jiao
2009, 58 (11): 7627-7632. doi: 10.7498/aps.58.7627
Abstract +
On the basis of local density approximation, superposed-neutral-atom model and the finite-difference method (SNA-FD) are used to calculate the positron bulk lifetime and positron monovacancy lifetime in crystals of elements of the periodic table. The distribution of positron wavefunction and positron annihilation rate are analyzed. The calculated results of positron bulk lifetime in elementary substance agree well with the experiment results in literatures, which shows that the method of SNA-FD is an effective method in the study of positron annihilation in elementary substance.
Role of potential function in high order harmonic generation of model hydrogen atoms in intense laser field
Li Peng-Cheng, Zhou Xiao-Xin, Li Hui-Shan
2009, 58 (11): 7633-7639. doi: 10.7498/aps.58.7633
Abstract +
By constructing one-dimensional model potential function with variable parameters, we investigate the high order harmonic generation (HHG) of one-dimensional model hydrogen atoms and real hydrogen atom with same ground state energy in 1 cycle and 16 cycles of intense laser fields. Our results show that in the over-barrier ionization region, the intensities of HHG for one-dimensional model atoms with different potential parameters are closely related with the depth of the potential well, but independent of the Coulomb singularity of the potential.
Terahertz and Raman spectra of L-threonine
Wang Wei-Ning
2009, 58 (11): 7640-7645. doi: 10.7498/aps.58.7640
Abstract +
The THz absorption within the range of 0.2—2.8 THz(6.7—93.2 cm-1)and Raman scattering spectra within the range of 10—4000 cm-1 of polycrystalline L-threonine have been examined with terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy. Infrared spectrum between 400 and 4000 cm-1 were also recorded. We assigned the polar and the non-polar vibrational modes of the polycrystalline molecule in the range of both 6.7—93.2 cm-1 and 400—4000 cm-1 based on the theory of space group and the comparison of Raman and absorption spectra. Normal frequency vibrational modes were calculated for the single crystal form using the B3LYP method of density functional theory (DFT) and 6-311+G** basis set. All the experimental THz absorption peaks and low frequency Raman scattering peaks of polycrystalline L-threonine were assigned.
Elastic collision between S and D atoms at low temperatures and accurate analytic interaction potential and molecular constants of the SD(X2Π) radical
Shi De-Heng, Sun Jin-Feng, Liu Yu-Fang, Zhu Zun-Lüe, Zhang Jin-Ping
2009, 58 (11): 7646-7653. doi: 10.7498/aps.58.7646
Abstract +
The equilibrium internuclear separations, harmonic frequencies and interaction potentials have been calculated by employing the CCSD(T) theory in combination with the series of the correlation- consistent basis sets, cc-pVnZ and aug-cc-pVnZ (n=2, 3, 4, 5), of Dunning and co-workers. The potential energy curves are all fitted to the Murrell-Sorbie functions, which are used to determine the spectroscopic parameters. At the CCSD(T)/aug-cc-pV5Z level of theory, the values of D0, De, Re, ωe, αe, B0 are 3.65730 eV, 3.77669 eV, 0.13424 cm-1, 1938.372 cm-1, 0.09919 cm-1, 4.88585 cm-1 and 4.8872 cm-1, respectively, which conform almost perfectly with the available measurements. With the analytic interaction potential obtained at the CCSD(T)/aug-cc-pV5Z level of theory, a total of 23 vibrational states has been predicted for the first time when the rotational quantum number J is set to equal zero (J=0) by solving the radial Schrdinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced from the SD(X2Π) potential when J=0 The total and various partial-wave cross sections are calculated for the elastic collisions between the ground-state S and D atoms at energies from 1.0×10-11 to 1.0×10-4 a.u. when the two atoms approach each other along the SD(X2Π) interaction potential. No shape resonances can be found in the total elastic cross sections. The results show that the shape of the total elastic cross sections is mainly dominated by the s-partial wave at very low temperatures. Because of the weakness of the shape resonances coming from various partial waves, they are all covered up by the strong total elastic cross sections.
CLASSICAL AREA OF PHENOMENOLOGY
Experimental studies on the statistical functions of speckle fields based on the extraction of the complex amplitudes by use of interference beam
Zhang Ning-Yu, Cheng Chuan-Fu, Teng Shu-Yun, Song Hong-Sheng, Liu Gui-Yuan, Liu Man
2009, 58 (11): 7654-7661. doi: 10.7498/aps.58.7654
Abstract +
Using the interference patterns of speckle fields and the reference beam, we extract digitally the complex amplitudes, phases and intensities of speckles fields and then study experimentally their properties. The influences of noise on the measurement of statistical functions, especially on that of the probability density function, appearing in the conventional method is satisfactorily eliminated. The experimental studies of the statistical properties of the complex amplitude and the phases of the speckle fields were also performed. By the practical measurement of speckle fields scattered at different angles, we find that the speckles are laterally broadened gradually with increase of the scattering angle, and their average widths become anisotropic. Such anisotropy brings about no change in the probability density function of the speckle fields, which remain circularly Gaussian as in the case of the traditional small angle scattering.
Ultra-fast pulsed digital holographic diagnosis of ejected material in femtosecond laser ablation of aluminum
Hu Hao-Feng, Wang Xiao-Lei, Li Zhi-Lei, Zhang Nan, Zhai Hong-Chen
2009, 58 (11): 7662-7667. doi: 10.7498/aps.58.7662
Abstract +
The dynamic process of material ejection and plasma evolution in single 50 fs laser pulse ablation of aluminum target is investigated using pulsed digital micro-holography, and highly temporally and spatially resolved dynamic digital holograms are obtained. The secondary material ejection induced by the thermoelastic wave is observed in the holograms, and at the same time, we firstly report the phenomenon of anomalous fringe shift at large time delays that results from the effect of the ejected material towards the probe beam of 400 nm wavelength. Through digital reconstruction, the two-dimensional phase shift distribution of the probe beam is obtained. By employing inverse Abel transform, we also obtained the dynamic process of spatial and temporal evolution of refractive index and free electron density distribution of the plasma. The structure and composition of the ejected material is analyzed according to its optical properties which are obtained through experiment and calculation.
A theoretical scheme for zero-knowledge proof quantum identity authentication
Wang Yu-Wu, Zhan You-Bang
2009, 58 (11): 7668-7671. doi: 10.7498/aps.58.7668
Abstract +
A theoretical scheme for zero-knowledge proof quantum identity authentication is proposed by the absolutely impartial third party CA, which has been realized based on remote state preparation and assisted cloning controlled means. In the process of identification, only CA knows the information of quantum identity card and the first party Alice and the second party Bob can accomplish the quantum identity authentication without knowing it. We discuss the probability of accomplishing this job. The security of this scheme is unconditional and it is guaranteed by quantum mechanism.
Research on CRIT property in ring-in-ring structure resonator
Wang Nan, Zhang Yun-Dong, Wang Jin-Fang, Tian He, Wang Hao, Zhang Xue-Nan, Zhang Jing, Yuan Ping
2009, 58 (11): 7672-7679. doi: 10.7498/aps.58.7672
Abstract +
Considering the insertion loss of coupler, we theoretically analyzed the CRIT effect of the ring-in-ring structure resonator. In the process of the theoretical analysis, the transmission coefficient and effective phase shift were deduced using iterative approach, and then the dispersion was obtained, including the effect of the insertion loss. The analysis shows the effective phase shift, group velocity and bandwidth of the whole system can be controlled by the insertion loss, the multiples between the lengths of rings and the number of rings. The control of dispersion in ring-in-ring structure is important for applications of this structure in rotating sensor, optical delay line, optical buffer and filtering.
Coherence length tunable semiconductor laser
Kong Ling-Qin, Fan Lin-Lin, Wang An-Bang, Wang Yun-Cai
2009, 58 (11): 7680-7685. doi: 10.7498/aps.58.7680
Abstract +
We report a technique for continuous tuning the coherence length of semiconductor laser. The coherence length of the semiconductor laser is controlled by using optical feedback scheme. The results show that the coherence length of semiconductor laser can be shortened from several meters of the original solitary laser to 100 μm by the implementation of optical feedback. Experimental results indicate that the coherence length of the laser depends strongly on the feedback strength, but is insensitive to the bias current. The results of numerical simulations using rate equation of semiconductor laser are fully consistent with our experimental results.
LD pumped Nd:YAG ceramic/KTP green laser
Liu Hong, Wang Zheng-Ping, Zhang Huai-Jin, Wang Ji-Yang, Yu Hao-Hai, Lü Yao-Hui, Sang Yuan-Hua, Xu Xin-Guang, Lan Rui-Jun, Ren Quan
2009, 58 (11): 7686-7689. doi: 10.7498/aps.58.7686
Abstract +
A CW green laser was reported with ceramic Nd:YAG as gain material and KTP crystal as frequency doubler. When the pump power was 21.6 W, the 1064 nm fundamental output was 11.3 W, corresponding to an optical conversion efficiency of 52.3%. When a type-II cut KTP crystal was inserted in the straight cavity as a frequency doubler, the maximum 532 nm green output was 1.86 W, and the optical conversion efficiency was 7%. The one-dimensional intensity distribution of the green facula was of Gaussian type, and the M2 factor was measured to be 1.7 when the output power was 1 W.
Generation of 100-J sub-picosecond laser pulse in high energy Nd:glass chirped pulse amplification system
Xie Xu-Dong, Zhu Qi-Hua, Zeng Xiao-Ming, Wang Xiao, Huang Xiao-Jun, Zuo Yan-Lei, Zhang Ying, Zhou Kai-Nan, Huang Zheng
2009, 58 (11): 7690-7694. doi: 10.7498/aps.58.7690
Abstract +
Generation of high energy sub-picosecond laser pulse was demonstrated in the Nd:glass chirped pulse amplification system. Seeded with pulse originating from OPA front end, the laser system output chirped pulse with maximum energy up to 168 J, and the spectral width was 5.5 nm (FWHM), centering at 1054 nm. Systematic investigation showed the spectral width of pulses was about 4—6 nm with energy higher than 100 J, which supports high energy laser pulse with pulse duration less than 300 fs. The final pulse was compressed to as short as 710 fs by a mosaic grating compressor.
Research on tunable erbium-doped ring fiber laser based on a high-birefringence Sagnac loop: theory and experiment
Wang Jing, Zheng Kai, Li Jian, Liu Li-Song, Chen Gen-Xiang, Jian Shui-Sheng
2009, 58 (11): 7695-7701. doi: 10.7498/aps.58.7695
Abstract +
A simple erbium-doped ring fiber laser based on a high-birefringence Sagnac loop filter is proposed. The Sagnac is composed of a polarization controller (PC) and a polarization-maintaining fiber (PMF). The effect of PC and PMF on tunable laser is analyzed in theory. In experiment, the single, double and multiple wavelength lasers are obtained by adjusting the PC. The interval of wavelength varies with the length of PMF. The experimental results are in good agreement with the theorefical analysis. In experiment the stable laser output with 20% slope efficiency, 0.016 nm 3 dB line-width, 0.097 nm 30 dB line-width and 40 dB SMSR was obtained.
Focusing property of two-dimensional photonic crystals with ring-shaped air holes
Kong Ling-Kai, Zheng Zhi-Qiang, Feng Zhuo-Hong, Jiang Cui-Hua, Li Xiao-Yan, Ming Hai
2009, 58 (11): 7702-7707. doi: 10.7498/aps.58.7702
Abstract +
Imaging properties of two-dimensional photonic crystal slab lens consisting of a triangular lattice of ring-shaped air holes in a high-refraction-index dielectric medium have been studied. The results calculated by the plane wave expansion method (PWE) and the finite-difference time-domain method (FDTD) show that the effective index n=-1 can be realized in this structure. A perfect image can be obtained by increasing the inner radius of ring-shaped holes from 0 to 0.13a with the outer radius 0.4a at the normalized frequency 0.3(a/λ). Based on the result of normalized frequency with effective refraction index -1 versus inner radius of ring-shaped holes we theoretically analyzed the effects of structure parameters to equifrequency contours of respective normalized frequency and imaging properties.
Coupling characteristics of dual-core high birefringence photonic crystal fibers
Fu Bo, Li Shu-Guang, Yao Yan-Yan, Zhang Lei, Zhang Mei-Yan, Liu Si-Ying
2009, 58 (11): 7708-7715. doi: 10.7498/aps.58.7708
Abstract +
A kind of dual-core high birefringence photonic crystal fibers (DHB-PCFs) has been proposed in this paper. The birefringence, coupling length and dispersion characteristics of DHB-PCFs have been studied by multipole method using mode coupling theory. It is found that the birefringence of DHB-PCF with pitch 1.2 μm and air-hole diameter 1.0 μm is 1.24×10-2 in optical communication band of 1.55 μm wavelength. Correspondingly, dual-core coupling lengths are 21.6 μm and 24.3 μm for x-polarized mode and y-polarized mode, respectively. The DHB-PCF with high degree of polarization and very short coupling length is useful for manufacturing minitype photonic apparatus.
Quantitative analysis on median-time-to-fail of copper interconnect with lose object defects
Zhou Wen, Liu Hong-Xia
2009, 58 (11): 7716-7721. doi: 10.7498/aps.58.7716
Abstract +
In the paper, influence of lose object defects on electromigration median-time-to-failure (MTF) for six-layer copper interconnect is investigated. The temperature model with defects for each interconnection layer and MTF model for defects in different interconnection layers are presented respectively. So, the defect influence on electromigration MTF of copper interconnect can be calculated quantitatively, and the method to increase MTF is also presented. The bigger the ratio of interconnect width to the effective interconnect width at the defects, the shorter the MTF, and higher temperature at defects can also shorten the MTF. When the parameters of interconnect wire vary greatly between different layers, the MTF is affected by the ratios and the temperature, and decreases rapidly. Based on the physical model, the temperature and the MTF of copper interconnect can be calculated accurately, which can guide IC design and manufacture effectively.
Femtosecond pump-probe technique assisted by surface plasmon resonance
Long Yong-Bing, Zhang Jian, Wang Guo-Ping
2009, 58 (11): 7722-7726. doi: 10.7498/aps.58.7722
Abstract +
Femtosecond pump-probe technique assisted by surface plasmon resonance (SPR) is investigated numerically in this paper. Our calculations show that the signal ratio ΔR/R is increased by 2—3 orders of magnitude higher than the standard pump-probe technique, where ΔR and R are the intensity change and total intensity of the probe beam, respectively. It should also be pointed out that ΔR/R is sensitive to the incident angle of the pump beam and the thickness of the metal film. In particular for the metal-absorbing material system, ΔR induced by the hot electrons in the metal is only 2 percent of that induced by excited absorbing material, so ΔR/R is mainly related to the dynamics of the absorbing material. This technique will be interesting in investigating the ultrafast surface dynamics of thin films.
An Yb-doped large-mode-area photonic crystal fiber mode-locking laser with free output coupler
Zhang Chi, Hu Ming-Lie, Song You-Jian, Zhang Xin, Chai Lu, Wang Qing-Yue
2009, 58 (11): 7727-7734. doi: 10.7498/aps.58.7727
Abstract +
The theoretical and experimental study of an Yb-doped double clad large mode area photonic crystal fiber laser is reported. This fiber laser system uses one facet of the fiber directly as a cavity mirror, which is fine-polished to 0° angle after collapsing. Lasing is obtained with the feedback of this facet, and mode-locking is achieved by using a semiconductor saturable absorber as another cavity mirror and adding a grating-pair as the spectral filter. By adjusting the filtering conditions, continuous tuning from wide filtering condition to narrow filtering condition is achieved. Under the wide filtering condition, the system generates femtosecond pulses, the highest average power of which is 2.2 W, corresponding to 29.3 nJ pulse energy and 367 fs pulse duration; under the narrow filtering condition, it generates picosecond pulses, the highest average power of which is 4 W, corresponding to 53.3 nJ pulse energy and 1.14 ps pulse duration. In numerical simulation, the evolution and cavity-position-related characteristics of pulses are studied by using split-step Fourier method.
Transmission property of elastic wave through one-dimensional compound materials
Cao Yong-Jun, Yang Xu, Jiang Zi-Lei
2009, 58 (11): 7735-7740. doi: 10.7498/aps.58.7735
Abstract +
The models of elastic waves in one-dimensional compound materials, including one-dimensional periodical phononic crystals, abnormal Fibonacci qusi-periodical phononic crystals, generalized Fibonacci qusi-periodical phononic crystals and absolutely disordered compound materials, are proposed in this paper. The transmission coefficients of elastic waves through the above systems are numerically calculated using the mode matched theory method. The results shows that larger band gap can be obtained, and much more localized modes are present in the band gap of a given quasi-periodical structure phononic crystals than in the periodical phononic crystals. The effect of quasi-periodical structure is the same as that of the prcsence of defects in periodical phononic crystals. The study of the localized states of elastic waves/acoustic waves in compound materials is useful to the fabrications of the elastic/acoustic wave filters or wave-guides.
An extraction method of seabed reflection loss based on towed tilted line array
Li Xue-Gang, Yang Kun-De, Zhang Tong-Wei, Qiu Hai-Bin
2009, 58 (11): 7741-7749. doi: 10.7498/aps.58.7741
Abstract +
Seabed acoustic parameters are very important to underwater acoustic field prediction in shallow water. The existing inversion methods generally uses a vertical line array to receive the signal and its platform is stationary, which can not be operated for a large area with high resolution. The methods for extracting seabed reflection losses based on three kinds of line arrays were studied. A fast inversion scheme for the seabed acoustic parameters was presented, which uses a towed tilted line array and three acoustic sources to cover a large scope of grazing angles. The error analysis was made for this method. The simulation results show that different arrays require different experimental configurations to cover the same scope of grazing angles. The vertical line array must operate with several acoustic sources and require a stationary platform of the array. The towed horizontal line array needs only one acoustic source but requires a large-aperture line array. The towed tilted line array combines the merits of the vertical line array and the horizontal line array, which can inverse the seabed acoustic parameters in a moving and high resolution way and requires only a line array of smaller aperture.
Discrete element method simulation on the force chains in the two-dimensional granular system under gravity
Mu Qing-Song, Miao Tian-De, Yi Chen-Hong
2009, 58 (11): 7750-7755. doi: 10.7498/aps.58.7750
Abstract +
The discrete element method is used to research the distribution of forces within the two-dimensional granular system under gravity. The force chains among the particles are generated according to the magnitudes of the forces. Then the simulation results are compared with the well-known q-model,α-model and experimental results obtained through the photoelastic test under the same conditions. According to the computational solution, we conclude that the simulation results are similar to the experimental results are some what different from the two probability models. In addition, we also obtained that the probability distribution of the force is very uneven. The probability of the large force decays exponentially and the distribution of the force chains takes on a fractal character.
Effect of exit Reynolds number on self-preservation of a plane jet
Deo Ravinesh C, Nathan Graham J, Feng Bao-Ping, Mi Jian-Chun
2009, 58 (11): 7756-7764. doi: 10.7498/aps.58.7756
Abstract +
We investigated in experiment the effect of exit Reynolds number on self-preservation of a turbulent plane jet. Centerline velocity statistics were measured in plane jets issuing from the same nozzle but, respectively, with seven Reynolds numbers varying between Re = 4,582 and Re = 57,735, where Re ≡ Uj h/ν(Uj being the momentum-averaged exit mean velocity, h the slot height and ν the kinematic viscosity). All measurements were conducted using single hot-wire anemometry and over an axial distance (x) of 40 h. These measurements revealed a significant Re-dependence of either the mean or turbulent flow field. As Re increases, the pace of the jet development decreases and, as a result, both the mean and turbulent properties reach their self-preserving states over a longer downstream distance (x). The centerline integral scale L for all jets grows linearly with x and the growth rate decreases as Re is increased. It is also found that the local Reynolds number ReL scales with x as ReL∝x1/2. The study suggests that differences of the self-preserving states observed may be related to the differences in the underlying turbulence structures in the near field of the seven jets.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
A study of RHEED pattern from the epitaxial growth of Si-Ge crystal
Zhang Chong, Ye Hui, Zhang Lei, Huang-Fu You-Rui, Liu Xu
2009, 58 (11): 7765-7772. doi: 10.7498/aps.58.7765
Abstract +
The patterns of Reflection high energy electron diffraction (RHEED) from the epitaxial growth of Si-Ge crystal are interpreted basing on the kinetical diffraction theory of crystal. The transmission pattern is studied and interpreted, which relates to the rough surface after crystal growth. The RHEED patterns of polycrystalline rings and twin crystal and their evolvements are analyzed with respec to the epitaxial growth conditions.
Effect of the transverse electric field on the pitch and reflective characteristics of the planar texture cholesteric liquid crystals
Deng Luo-Gen, Zhao Zhao-Li
2009, 58 (11): 7773-7780. doi: 10.7498/aps.58.7773
Abstract +
The reflective spectrums of the cholesteric liquid crystals under the condition of normal incident light are computed by using Jones matrix method. A theoretical model for discussing the influence of the transverse electric field on the twist angle and the pitch of the planar texture cholesteric liquid crystals under the in-plane switching mode is established. Based on the model, the relation between the electric field and the reflective peak for the cholesteric liquid crystals, and the relation between the electric field and the reflective spectral width for the cholesteric liquid crystals are calculated. The effects of the transverse electric field on the pitch and the reflective characteristics of the planar texture cholesteric liquid crystals are studied under different anchoring conditions. The results show that, under the in-plane switching mode, the color of the light reflected from the cholesteric liquid crystals can be changed by the applied transverse electric field, which supplies a theoretical support for the planar texture cholesteric LC color display based on the electrically-controlled pitch.
Formation and thermal stability of compound stucture of carbon nanotube and silicon nanowire
Zhang Kai-Wang, Meng Li-Jun, Xiao Hua-Ping, Tang Chao, Zhong Jian-Xin
2009, 58 (11): 7781-7786. doi: 10.7498/aps.58.7781
Abstract +
We have studied the formation process of carbon nanotube-silicon nanowire compound structures by using empirical molecular dynamics method and their thermal stability by empolying Lindemann index. Our results show that, in some cases, liquid Si encapsulated in C(13,0) and C(14,0) carbon nanotubes can crystallize into nanowires composed of linked Si16 and Si20 fullence cages, respectively. The Si nanowire inside the carbon nanotube has higher melting temperature then the Si nanowire in free space. By calculating interaction potential energy between SiNW clusters and carbon nanotubes with different diameters, we have found that the radial stress on Si20NW induced by the carbon nanotube can increase melting temperature of Si20NW. For Si20NW under free boundary condition, this radial stress can be released by the deformation of Si20NW which results in decrease of the melting temperature of Si20NW cluster.
Phonon spectra and specific heat calculation of single wall carbon nanotube
Wu Yan-Zhao, Xie Ning, Liu Jian-Jing, Jiao Yong-Fang
2009, 58 (11): 7787-7791. doi: 10.7498/aps.58.7787
Abstract +
In this paper, the phonon spectra of infinite length single-wall carbon nanotubes are calculated based on the force constant model. The dependence of specific heat on the tube diameter and temperature is discussed. It is found that the specific heat will increase with increasing temperature and In this paper, the phonon spectra of infinite length single-wall carbon nanotubes are calculated based on the force constant model. The dependence of specific heat on the tube diameter and temperature is discussed. It is found that the specific heat will increase with increasing temperature and diameter and approaches to a constant value. Also, the vibrational spectra of the finite length (5,5) carbon nanotube are calculated. The relationships between the vibrational frequency and length are presented for some particularly modes.diameter and approaches to a constant value. Also, the vibrational spectra of the finite length (5,5) carbon
Variable charge molecular dynamics simulations of the intergranular films in SiC
Ma Ying, Chen Shang-Da, Xie Guo-Feng
2009, 58 (11): 7792-7796. doi: 10.7498/aps.58.7792
Abstract +
Variable charge molecular dynamics simulations of SiC intergranular glassy films have been performed based on the iterative fluctuation charge model. The atomistic structures of different configurations of the intergranular films are simulated. Charge transfer between the films and their neighboring crystals is observed and the equilibrium film thickness is found to be dependent on the charge transfer. Our results provide a direct proof for the existence of space charges and show that electrostatic interaction contributes to the equilibrium thickness of the intergranular films.
Two-bubble interaction under the sound field
Zhang Peng-Li, Lin Shu-Yu
2009, 58 (11): 7797-7801. doi: 10.7498/aps.58.7797
Abstract +
The paper established the motion equation of two-bubble walls under the sound field, and obtained the resonant frequency, vibration radius and radiation pressure of the double-bubble cavitation. From the frequency equation, radius of vibration and sound pressure equation we can see that the movement of two-bubble is different from a single bubble. Resonance frequency, resonance amplitude and radiation pressure are related to the distance between the bubble. By carrying out the numerical solution by MATLAB, we found that the resonance frequency and amplitude resonance increased with the distance between the two-bubble.
Phase-field simulation of non-isothermal solidification dendrite growth of binary alloy under the force flow
Cai Qi-Zhou, Chen Li-Liang, Long Wen-Yuan, Lü Dong-Lan, Xia Chun, Pan Mei-Man
2009, 58 (11): 7802-7808. doi: 10.7498/aps.58.7802
Abstract +
Based on the binary phase-field model, the phase-field model coupling with solute field,temperature field and flow field was developed. The mass and momentum conservation equations are solved by using the Simple algorithm, and the thermal governing equation is numerically solved using an alternating implicit finite difference method. The dendrite growth processes during isothermal and non-isothermal solidification of the binary alloy under convection was simulated. The difference in dendrite growth, solute distribute and temperature distribution were investigated. The result of dendrite growth during isothermal and non-isothermal solidification were compared.The effect of latent heat on the dendrite growth under convection was analyzed.
Thermal conductivity of carbon nanotube: From ballistic to diffusive transport
Hou Quan-Wen, Cao Bing-Yang, Guo Zeng-Yuan
2009, 58 (11): 7809-7814. doi: 10.7498/aps.58.7809
Abstract +
Length dependence of the thermal conductivity of (5, 5) carbon nanotube at 300 K and 1000 K is studied by nonequilibrium molecular dynamics simulations. At room temperature the thermal conductivity shows linear length dependence for the tube length less than 40 nm, which shows completely ballistic transport. The calculated ballistic thermal conductance per unit area is 5.88×109 Wm-2K-1. The thermal conductivity increases with the increase of the nanotube length, but the increase rate decreases as the length increases. It shows that the phonon transport is in the ballistic-diffusive regime, and transits from ballistic to diffusive with increase of the tube length. The thermal conduction is close to completely diffusive transport and the ballistic transport can be ignored when the nanotube is longer than 10 μm. In the simulations, the power exponent of the thermal conductivity of carbon nanotube to the tube length decreases by decaying exponential function as the tube length increases. Different from one-dimensional material, in the thermodynamic limit, a completely diffusive transport will dominate the thermal transport in carbon nanotubes, and the thermal conductivity will converge to a finite value.
Growth of graphene structure on 6H-SiC(0001): Molecular dynamics study
Ji Lu, Zhang Kai-Wang, Tang Chao, Meng Li-Jun, Sun Li-Zhong, Zhong Jian-Xin
2009, 58 (11): 7815-7820. doi: 10.7498/aps.58.7815
Abstract +
The growth process of graphene structure on 6H-SiC(0001) surface has been studied using the classical molecular dynamics (MD) simulation and the simulated annealing technique. We show that carbon atoms of the 6H-SiC(0001) subsurface after sublimation of Si atoms can be self-organized to form local monolayer graphene structures. This process is similar to the formation of graphene on the 6H-SiC(0001) surface, depending strongly on annealing temperature and coverage of carbon atoms on the SiC(0001)surface. The local graphene structures can be formed on 6H-SiC(0001)as the annealing temperature is around 1400 K. This transformation temperature is in good agreement with experimental observations (1080 ℃), but is lower than that of growing graphene on SiC(0001) surface (T≈1450 K). In addition, not only single layer but also bilayer graphene structure can be formed, associated with the increase of the coverage of carbon atoms on SiC(0001)surface.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First-principles study on 3C-SiC(001)-(2×1)surface atomic structure and electronic structure
Liu Fu, Zhou Ji-Cheng, Tan Xiao-Chao
2009, 58 (11): 7821-7825. doi: 10.7498/aps.58.7821
Abstract +
We calculate the atomic and electronic structure of 3C- SiC(001)-(2×1) using density functional calculations within the generalized gradient approximation. The calculated results show that the atomic structure of 3C-SiC(001)-(2×1) surface can be described by dissymmetrical Si dimmer model. The bond length of Si dimmer of 3C-SiC(001)-(2×1) surface is 0.232 nm. The calculated results of electronic structure show that a prominent density of states exists at the Fermi level, so the 3C-SiC(001)-(2×1) surface has the characteristics of metal. There are four surface state bands in the gap, one of which is located near the Fermi level, another at 5 eV above Fermi level, and the others in the valence bands below Fermi level.
Electronic structure and bonding mechanism of La-Ir-Si: A first-principles study
Liu Jun-Min, Sun Li-Zhong, Chen Yuan-Ping, Zhang Kai-Wang, Zhong Jian-Xin, Yuan Hui-Qiu
2009, 58 (11): 7826-7832. doi: 10.7498/aps.58.7826
Abstract +
Using first-principles method, we studied the electronic structure and the bonding mechanism of La-Ir-Si materials. The results of the band structure and the density of the states indicated that the superconducting property of the La-Ir-Si system is determined by the p-d coupling strength between the transition element Ir-d and Si-p states of the material. In order to quantitatively describe the p-d coupling strength, we calculated the charge transfer during the bond process of the materials using the atom-in-molecule method. The results revealed that the superconducting transition temperature TC is linerly proportional to the atomic basin charges of Ir.
Study on the thermal stability of carbon nanotubes by simulation
Zhu Ya-Bo, Bao Zhen, Yang Yu-Jie, Cai Cun-Jin
2009, 58 (11): 7833-7837. doi: 10.7498/aps.58.7833
Abstract +
Tight-binding molecular dynamics was used to simulate the thermal behavior of carbon nanotubes (CNTs) in this paper. A few kinds of single wall CNTs (SWCNTs) and double wall CNTs (DWCNTs) were studied during the simulation experiment at temperatures of 300—4000 K and the pressure of 1 atm. The results showed that the chiral SWCNTs have higher thermally stability than the armchair and zigzag type, and that the bigger the nanotube diameter is, the more stable the nanotube stucture is for those with the same chiral angles. The DWCNTs with at least one chiral structured wall are more stable than the others, but that with two zigzag walls were damaged badly, which also gives support to the study about SWCNT thermo-stability. One factor to describe CNTs in connection with their thermo-stability was proposed, and some data were theoretically analyzed based on carbon bond structures.
Long-range Finnis-Sinclair potential for molecular dynamics simulation of α-Al2O3
Hu Zhi-Gang, Liu Yi-Hu, Wu Yong-Quan, Shen Tong, Wang Zhao-Ke
2009, 58 (11): 7838-7844. doi: 10.7498/aps.58.7838
Abstract +
The molecular dynamics (MD) simulation of metal-metal oxide interface requires a uniform potential to simultaneously describe metal and metal oxide. Accordingly, we obtained a set of long-range Finnis-Sinclair (F-S) potential parameters of α-Al2O3. All of the parameters were fitted to the targets, i.e. the experimental lattice energy, lattice constants, and elastic constants of α-Al2O3. Meanwhile, we compared our results with those reported by EAM, Glue and modified Matsui (m-Matsui) potentials and found that our rcsults are equivalent or better. After that, MD simulation of α-Al2O3 at 300 K with our long-range F-S potential was performed and the pair correlation functions, coordination numbers were calculated. The good agreement between calculation results and experiments validated the feasibility of this set of F-S potential parameters to the description of α-Al2O3 system.
An effective method for suppressing the mode competition in a rectangular cavity loaded with photonic crystals
Liu Yang, Gong Hua-Rong, Wei Yan-Yu, Gong Yu-Bin, Wang Wen-Xiang, Liao Fu-Jiang
2009, 58 (11): 7845-7851. doi: 10.7498/aps.58.7845
Abstract +
In this paper, the photonic crystal loaded rectangular resonant cavity is studied. Because the conventional way cannat ensure single-mode operation in the cavity when operated with higher-order modes, characteristic impedance method and perturbation method are employed to change the structure of the conventional photonic crystals cavity. The improved cavity that can work with a single higher-order mode is realized. On this basis, the conventional photonic crystal shielded cavity, which can work with a mode of TM530, is reformed by the new method. The new structures are analyzed by using analytical methods and HFSS. The physical reasons of these methods solving the problem of mode competition are also analyzed. The investigation reveals that the method can effectively suppress mode competition and realize single-modc operation in the cavity when operated with higher-order modes.

EDITOR'S SUGGESTION

First-principles study on field emission properties of carbon nanocone
Zhang Jiao-Qiang, Wang Liu-Ding, Chen Guo-Dong, Yang Min, Wang Yi-Jun, An Bo
2009, 58 (11): 7852-7856. doi: 10.7498/aps.58.7852
Abstract +
The first-principles calculation was performed to study the electron field emission properties of carbon nanocones (CNC) with different cone angles and geometrical structures. The results show that with the increase of the applied electric field (Eadd), the electronic structure of CNC changes significantly, the density of states (DOS) shifts towards to low energy position. Especially, DOS at Ef increases and the pseudogap decreases respectively, and a majority of electrons congregate at the close end. The investigation of DOS, HOMO/LUMO and Mulliken population analysis indicates that CNC3 and CNC4 are very suited for electron field emission.
Martensitic transformation and magnetocaloric effect in Ni-Co-Mn-Sn Heusler alloy
Zhang Hao-Lei, Li Zhe, Qiao Yan-Fei, Cao Shi-Xun, Zhang Jin-Cang, Jing Chao
2009, 58 (11): 7857-7863. doi: 10.7498/aps.58.7857
Abstract +
The crystal structure and phase transition in Ni50-xCoxMn38Sn12(x=1, 2, 4, 6, 8) Heusle alloys were investigated by means of structure analysis and magnetism measurements. The results show that the doping of the Co atom affects neither the original structure of Ni-Mn-Sn Heusler alloys, nor the ferromagnetic interaction strengthens in the austenitic state. Furthermore, based on Maxwell equation, the magnetic entropy change (ΔSM) of three samples (x=2, 4, 6) has been calculated. A large magnetic entropy change of 37.09 J/kg K at about 320 K for a magnetic field change of 50 kOe is obtained in Ni48Co2Mn38Sn12 alloy.
Effect of hydrogenation on the luminescence evolution of GaN under low energy electron beam irradiation
Dierre Benjamin, Sekiguchi Takashi, Wang Yan, Shen Bo, Xu Fu-Jun
2009, 58 (11): 7864-7868. doi: 10.7498/aps.58.7864
Abstract +
Luminescence evolution of GaN irradiated by low energy electron beam before and after hydrogenation has been investigated by means of cathodoluminescence (CL), in connection with the diffusion properties of hydrogen in GaN. It is found that under low energy electron beam irradiation, the band to band emission of GaN shows a decrease before hydrogenation, while it shows an initial increase and a subsequent decrease after hydrogenation, and the decrease after hydrogenation is relatively weak. Moreover, there is no luminescence recovery in 20 hours after the first irradiation after hydrogenation. The experimental results indicate a luminescence enhancement effect of hydrogen by passivating certain defects in GaN. However, such effect must be realized by overcoming high migration barrier in GaN. In the experiments, low energy electron beam supports enough energy to hydrogen to diffuse and passivate defects in GaN. These results show strongly the importance of diffusion of hydrogen in the passivation process in semiconductors.
Microparticles manipulation based on dielectrophoresis in microsystem
Ren Yu-Kun, Ao Hong-Rui, Gu Jian-Zhong, Jiang Hong-Yuan, Antonio Ramos
2009, 58 (11): 7869-7877. doi: 10.7498/aps.58.7869
Abstract +
Dielectrophoresis (DEP) has a high potential in the manipulation of low concentration microparticles in microsystem, which is an urgent project. The complex DEP expression was induced based on the basic DEP theory. The main factor of the conventional DEP force and the traveling wave DEP force was analyzed and 2D analytical model with star electrodes as well as parallel electrodes were founded in order to act as the manipulation construction of them. Boundary conditions were set and the real part and imaginary part were coupled to compute the DEP force. The DEP distribution of the two electrodes was simulated numerically in order to obtain the parameters for the experiment. Based on the conventional DEP force, the star electrodes were used to collect microparticles and based on the travelling wave DEP force, the parallel electrodes were used for microparticles lift and directional driving, respectively. Comparing the experimental results with theoretical and simulation analysis, they had a good agreement. The results show that DEP force can be used to manipulate microparticles effectively in microsystem.
Properties of electric transport in crystallized silicon films under different annealing temperatures
Song Chao, Chen Gu-Ran, Xu Jun, Wang Tao, Sun Hong-Cheng, Liu Yu, Li Wei, Chen Kun-Ji
2009, 58 (11): 7878-7883. doi: 10.7498/aps.58.7878
Abstract +
Hydrogenated amorphous Si thin films were prepared by plasma-enhanced chemical vapor deposition. As-deposited samples were annealed at different temperatures to obtain nano-crystalline Si. During the transition process from amorphous to nano-crystalline structure, Raman scattering spectroscopy was used to characterize the changes of microstructures. The temperature-dependent conductivity was measured in order to understand the electric transport processes in the films. It was found that the crystallization occurs at around 700 °C. The crystal volume fraction (Xc) increases with the increase of annealing temperature, and in the case of the Si film annealed at 1000 ℃, the Xc is beyond 90%. The carrier transport characteristics in the films annealed at the different temperatures are different from the as-deposited film. For the sample annealed at 700 ℃, the carrier transport is strongly influenced by the defect states resulting from the effusion of hydrogen, and it is controlled by the hopping conduction of the localized states in the difference measurement temperature regions causing the dual activation energies. For the highly crystallized Si film annealed at 1000 °C, the transport process is strongly influenced by the transport of the extended states in the crystalline silicon, while in the high temperature region, the quantum tunneling process plays an important role in the carrier transport property.
Determination of electron diffusion length in HgCdTe photodiodes using laser beam induced current
Yin Fei, Hu Wei-Da, Quan Zhi-Jue, Zhang Bo, Hu Xiao-Ning, Li Zhi-Feng, Chen Xiao-Shuang, Lu Wei
2009, 58 (11): 7884-7890. doi: 10.7498/aps.58.7884
Abstract +
The standard diffusion length (Lp) test procedure is apt to damage the p-n junction, so we often use characteristic decay length (L) obtained by laser beam induced current (LBIC) instead of Lp. Two dimensional modeling is used to get the relations of L and Lp. Calculated L/Lp ratio is about 1.1, and it is not affected by doping concentration, Shockley-Read-Hall (SRH) lifetime and mobility. For HgCdTe photodiodes, we get characteristic decay length from the LBIC experiment, and get the true diffusion length by division by the ratio 1.1.
Effects of absorption layer parameters and hetero-interface charge on photoresponse of 12.5 μm long-wavelength HgCdTe photodiode
Hu Wei-Da, Yin Fei, Ye Zhen-Hua, Quan Zhi-Jue, Hu Xiao-Ning, Li Zhi-Feng, Chen Xiao-Shuang, Lu Wei
2009, 58 (11): 7891-7896. doi: 10.7498/aps.58.7891
Abstract +
The effects of absorption layer parameters and hetero-interface charge on photoresponse of long-wavelength HgCdTe photodiode have been studied. The correlations between thickness of absorption layer and absorption length and diffusion length are investigated. An empirical formula is proposed to estimate the optimal thickness of absorption layer. Our theoretical investigations indicate that, when the wavelength of incident light is longer than the cut-off wavelength, the photoresponse monotonically increases with the increase of absorption layer thickness, and saturates subsequently. The wavelength of the maximal photoresponse increases with the increase of absorption layer thickness, and tends to shift toward long wavelength region. The optimal absorption layer thickness increases with increasing minority carrier life time and wavelength of incident light. It is found that the positive interface charge can induce a p-n junction at the substrate interface and significantly reduce the photoresponse. By using the metal-oxide-semiconductor diode model, possible physics mechanisms are investigated, and an approach is proposed to reduce the effects of hetero-interface charge on the photoresponse.
The theory of physical doping in organic semiconductor
Meng Wei-Min, Wang Run-Sheng, Ma Chao-Zhu, Li Rong-Hua, Xie Hong-Wei, Wang Ying, Zhao Ming, Yuan Jian-Ting, Peng Ying-Quan
2009, 58 (11): 7897-7903. doi: 10.7498/aps.58.7897
Abstract +
A theory for carrier concentration in physically doped organic semiconductors has been presented based on Gaussian energy distribution of the lowest unoccupied molecular orbitals (LUMOs) and the highest occupied molecular orbitals (HOMOs) as well as the Fermi - Dirac distribution of carriers in allowed quantum states. The dependence of carrier concentration on doping concentration, ambient temperature and energy gap of organic semiconductors were numerically investigated. It is shown that carrier concentration will increase with the ambient temperature in doped or undoped organic semiconductors, and the carrier concentration decreases exponentially with the reciprocal of temperature. For intrinsic organic semiconductor, carrier concentration will decrease exponentially with the energy gap (the difference between the average energy levels of HOMO and LUMO )and increase exponentially with the square of the width of Gaussian distribution. We then discussed the effect of doping concentration on carrier concentration for different HOMO and LUMO positions of the dopant relative to that of the host.
The nonlinear sensing property and electric mechanism of carbon humidity-sensitive membranes
Chen Huan, Peng Zhen-Kang, Fu Gang
2009, 58 (11): 7904-7908. doi: 10.7498/aps.58.7904
Abstract +
The nonlinear sensing property and electric mechanism of carbon humidity-sensitive membranes under investigation were manufactured by using hydroxyethyl cellulose (HEC), carbon black (CB) and humidizer sorbitol. Microstructures examined by scanning electronic microscopy (SEM) show that, an effective carbon black electric network in humidity-sensing membrane would make the membrane’s resistance to have strong nonlinear property near 80%RH; so that the amount of 2wt% carbon black is in the proximity of the electric percolation threshold. The voltage-current characteristic suggested that the nonlinear sensing property and electric mechanism of the carbon humidity membranes are closely related. Particularly, impedance spectroscopy of sample at 92%RH was made up by two semi-circular arcs and a straight tail near 45° angle. The membrane′s equivalent circuit was three RC circuits in series that corresponds to the contributions of the carbon bulk resistance, CB-grain-boundary resistance and electrode contact resistance, respectively.
Spin-polarized transport in quantum waveguide systems with attached stubs
Li Xiao-Mao, Chen Yu-Guang, Xiao Xian-Bo
2009, 58 (11): 7909-7913. doi: 10.7498/aps.58.7909
Abstract +
We theoretically studied the spin-polarized electron transport properties of quantum waveguide systems with attached stubs in the presence of Rashba spin-orbit coupling (SOC) by the lattice Green function approach. It is shown that the structure-induced Fano resonance and SOC-induced Fano resonance exist in the charge conductance in consequence of the bound states interfering with the conductance states. At the same time, the Fano resonance and antiresonance structures are also found in the spin polarization. In addition, due to the effect of quantum interference and backscattering caused by abrupt change of quantum wire width, a series of resonant peaks and dips appear in the charge conductance and spin conductance. However, all these effects are suppressed and quantization plateau is recovered in the charge conductance and spin conductance when applying a magnetic field to the system. The underlying physics is that the effect of the magnetic field is equivalent to the enhancement of the lateral confining potential, which reduces the intersubband mixing.
Up-conversion luminescence of CdTe and CdTe/CdS quantum dots excited by femtosecond laser of low intensity
Yang Yan-Qiang, Song Wei-Si, Su Wen-Hui, An Li-Min, Zeng Qing-Hui, Chao Ke-Fu, Kong Xiang-Gui
2009, 58 (11): 7914-7920. doi: 10.7498/aps.58.7914
Abstract +
We studied the steady-state and time-resolved luminescence properties of CdTe and CdTe/CdS core/shell quantum dots by one-and two-photon excitation with a femtosecond laser of low intensity. The 800 nm excitation causes a blue shift of the emission peak compared with 400 nm laser excitation. Near-quadratic laser power dependence of the up-conversion intensity and biexponential decay kinetics are observed. It is found that upconversion luminescence is composed of a photoinduced trapping and a band edge excitonic state. The blue shift of the emission peak is caused by the relative change in luminescence intensity between excitonic and trapping states. Two-step two-photon absorption involving the surface as intermediate states has been proposed for the mechanism of up-conversion luminescence of CdTe/CdS quantum dots.
Interface treatment of amorphous silicon thin film solar cells on flexible substrate
Wang Lin-Shen, Zhao Jing-Fang, Sui Yan-Ping, Zhang De-Xian, Cai Hong-Kun, Tao Ke
2009, 58 (11): 7921-7925. doi: 10.7498/aps.58.7921
Abstract +
The experiment and AMPS modeling have been used to analyze the characteristics of a-Si solar cells on flexible substrate with different buffer layers at the i/p interface. Combining with technology parameters, this paper uses different band gap and the defect density of states of the interface layer to simulate the characteristics of solar cells. The modeling results show that the solar cells are deteriorated by the interface layer with a big band gap and large defect density of states. By optimizing treatment of i/p interface, the amorphous silicon solar cell on polyimide substrate has been achieved with an efficiency of 7.09%.
Tunneling coefficient and persistent current in triple-arm quantum ring with double δ barrier
Du Jian, Wang Su-Xin, Yang Shu-Min
2009, 58 (11): 7926-7933. doi: 10.7498/aps.58.7926
Abstract +
In this paper tunneling coefficient and persistent current in triple-arm quantum ring with double δ barrier is investigated. The results show that the tunneling coefficient and persistent current show oscillating behavior with the length of the semiconductor quantum ring increasing. The tunneling coefficient and persistent current depend not only on spin orientation of tunneling electrons but also on the ferromagnetic magnetization direction. When the size of the quantum ring is fixed, the tunneling coefficient and persistent current will generate isochronal oscillation with the increasing of the AB magnetic flux. Furthermore, δ barrier and Rashba spin-orbit interaction have different effect on the properties of the tunneling coefficient and persistent current.
Separating of dislocation ring at finite temperature
Xu Ai-Guo, Lu Guo, Zhang Guang-Cai, Fang Bu-Qing
2009, 58 (11): 7934-7946. doi: 10.7498/aps.58.7934
Abstract +
We constructed a partial dislocation ring with Burgers vector b=[112]/6 in the glide plane (111) of copper crystal, and studied its self-contraction process in the temperature range, from 0 to 350 K by using molecular dynamics simulations. The results reveal that, at zero temperature the dislocation ring cannot pass the Peierls-Nabarro potential barrier, so its migrating velocity is zero; below 50 K, the screw part and the edge part of the dislocation have nearly the same migrating velocity. With the increasing of temperature, the edge dislocation migrates more quickly than the screw dislocation. At a higher temperature, the dislocation core becomes wider, consequently, it may contain more complex internal structures and becomes easier for separating. At the same time, local stress gradient within the mixed dislocation zone becomes steeper and results in the generation of four partial dislocation rings. The four new dislocation rings first grow with time under the influence of original dislocation ring. When the original ring finally disappears, the newly created rings begin to shrink and finally disappear. This is a new dislocation source, different from the Frank-Read,L or double cross-slip type.
Band structure of strained Si1-xGex
Song Jian-Jun, Zhang He-Ming, Hu Hui-Yong, Xuan Rong-Xi, Dai Xian-Ying
2009, 58 (11): 7947-7951. doi: 10.7498/aps.58.7947
Abstract +
There has been a lot of interest in the Si based strained technology lately, especially the modification of band structures which provides a theoretical basis for the design of the high-speed and high-performance devices and circuits. The band structure models of strained Si1-xGex on (001),(101),(111) relaxed Si are set up using K.P perturbation method coupled with deformation potential theory. Ge fraction (x) dependence of the conduction band (CB) and the valence band (VB) edge levels, CB and VB splitting energy and the indirect bandgap were obtained. The quantitative data from the models can supply valuable references to the design of devices.
Influence of penetrating V-pits on leakage current of GaN based p-i-n UV detector
Zhang Shuang, Zhao De-Gang, Liu Zong-Shun, Zhu Jian-Jun, Zhang Shu-Ming, Wang Yu-Tian, Duan Li-Hong, Liu Wen-Bao, Jiang De-Sheng, Yang Hui
2009, 58 (11): 7952-7957. doi: 10.7498/aps.58.7952
Abstract +
The leakage mechanism of GaN-based p-i-n (p-AlGaN/i-GaN/n-GaN) UV detector has been investigated. With the same dislocation density, devices made from material with higher density of V-pits on surface produce larger leakage current. SEM images show that some V-pits penetrate into i-GaN layer, sometimes even the n-GaN layer. If p-ohmic contact metal (Ni/Au) deposits in the V-pits, Schottky contact would be formed at the interface of metal and i-GaN, or form ohmic contact at the interface of metal and n-GaN. The existence of parallel Schottky junction and ohmic contact resistance enhances the leakage current greatly.
The in situ two-temperature process of preparation of CeO2 films on sapphire substrates and technical improvements of fabrication of Tl-2212 films
Huang Guo-Hua, Wang Xiang-Hong, Xie Qing-Lian, Wang Zheng, You Feng, Ji Lu, Zhao Xin-Jie, Fang Lan, Yan Shao-Lin
2009, 58 (11): 7958-7965. doi: 10.7498/aps.58.7958
Abstract +
The preparation of CeO2 buffer layers on r-cut sapphire substrates by in situ two-temperature process and Tl-2212 superconducting films has been studied. The results of XPS and AFM show that this simple process of growing buffer layer produces CeO2 film with smooth surface, which can hold back the diffusion of Al from sapphire into Tl-2212 film. The 530 nm thick Tl-2212 films grown on the CeO2 buffer layers subsequently possess excellent electrical property. The films have a high transition temperature (Tc =108.2 K), a high critical current density (Jc=6.58 MA/cm2at 77 K and zero applied magnetic field) and a low surface resistance (Rs=185 μΩ at 10 GHz and 77 K), and their superconductivity can be improved significantly.

EDITOR'S SUGGESTION

Properties of MgB2 films fabricated under different conditions by ex-situ annealing of Mg/B multilayer precursor
Liu Liang, Ma Xiao-Bai, Nie Rui-Juan, Wang Fu-Ren, Yao Dan
2009, 58 (11): 7966-7971. doi: 10.7498/aps.58.7966
Abstract +
The effects of annealing temperature, annealing time and film thickness on the properties of MgB2 thin films prepared by ex-situ annealing of Mg/B multilayer have been studied. The films with the thickness of 250 nm annealed at temperatures as low as 400 ℃ exhibited a superconducting transition. The optimal annealing condition of 250 nm thick MgB2 films regarding to the transition temperature, Tc, was 750 ℃ for 20—30 min. Tc became lower as the film thickness decreased and the Tc of thinner MgB2 films was influenced more greatly by the annealing temperature. With reducing the thickness of each single layer, we were able to fabricate the 20 nm thick MgB2 superconducting film with a Tonsetc of 31K.
Effect of interface on microstructure and soft magnetic properties of Fe65Co35 thin films
Kamzin A. S., Li Yan-Bo, Liu Xi, Li Zheng-Hua, Fu Yu, Wei Fu-Lin, Yang Zheng
2009, 58 (11): 7972-7976. doi: 10.7498/aps.58.7972
Abstract +
Bilayer films with Fe65Co35 main layer/underlayer structure were successfully prepared by magnetron sputtering on different underlayers (Co93Fe7 and Fe). X-ray diffraction (XRD) analysis and magnetic measurements show that Fe65Co35 thin films deposited on different underlayers have different textures. Moreover, the soft magnetic properties of Fe65Co35 thin films with (200) texture are better than that of Fe65Co35 thin films with (110) texture. Investigation of several typical samples by conversion electron Mssbauer spectrum (CEMS) reveals that the vector of magnetization of Fe65Co35 thin films have a little deviation from the film plane, and the deviation from the film plane of Fe65Co35 thin films with (110) texture are bigger than that of Fe65Co35 thin films with (200) texture. Further study exhibits that this phenomenon is caused by the interface anisotropy induced by magnetoelastic anisotropy at the interface between Fe65Co35 thin film and underlayer.
Effect of Pt spacers on the interface of Co/FeMn
Fu Yan-Qiang, Liu Yang, Jin Chuan, Yu Guang-Hua
2009, 58 (11): 7977-7982. doi: 10.7498/aps.58.7977
Abstract +
Co/FeMn/Co multilayers were prepared by magnetron sputtering. The change of magnetic moments by insertion of Pt spacer at the Co (bottom)/FeMn interface and FeMn/Co (top) interface has been investigated. According to the hysteresis loops measured by alternating gradient magnetometer (AGM), the saturation magnetization (Ms) of multilayers is changed by the Pt spacer at the Co (bottom)/FeMn interface, and there is an asymptotic approach of Ms to the theoretical value of Ms of the cobalt bulk of 1440 kA/m as the thickness of Co layer (tCo) is increased. This behavior is due to the production of net magnetic moments at the Co (bottom)/FeMn interface, which are decreased by Pt spacer at the Co (bottom)/FeMn interface. However, a significant difference between the Co (bottom)/FeMn interface and the FeMn/Co (top) interface is observed, as little influence of the Pt spacer on magnetic moments is shown when inserted at the FeMn/Co (top) interface.
Magnetism of aluminum atomic chains
Lin Qiu-Bao, Wen Yu-Hua, Zhu Zi-Zhong, Li Ai-Yu
2009, 58 (11): 7983-7987. doi: 10.7498/aps.58.7983
Abstract +
By using the first-principles method based on the density functional theory, the magnetism of Al monoatomic chains have been studied. The present calculations show that both the linear and zigzag Al chains can exhibit ferromagnetism. However, the magnetism appears only when the Al chains are elongated. The underlying mechanism has been understood based on the atomic orbital interaction picture, taking into consideration the electronic density of states in combination with the Stoner criteria.
Effects of applied magnetic field on microstructure and magnetic properties of template-based Co nanowire arrays
Liu Wen-Bang, Meng Wei-Min, Lou Yuan-Fu, Liu Xi, Zhang Lu-Ran, Zheng Xin-Qi, Wei Fu-Lin
2009, 58 (11): 7988-7992. doi: 10.7498/aps.58.7988
Abstract +
Arrays of Co nanowires were fabricated by ac electrochemical deposition of metal into high order anodic alumina templates prepared through two-step oxidation method. The effects of applied magnetic field and the pH value of the electrolyte on growth of nanowires were investigated. Arrays of Co nanowires of hcp structure were deposited in the electrolyte whose pH values are 6.0 and 6.5 without magnetic field, then 0.3 T magnetic field was applied along the long axis of nanowires. The experimental results show that external magnetic field and adjustment of pH value of the electrolyte impel the easy magnetization axis of the hcp Co grain to grow along length direction of nanowires. The Co nanowire arrays show higher perpendicular anisotropy, larger coercivity and high M/Ms because the superposition of the crystal anisotropy of hcp Co grains and shape anisotropy of nanowire along length direction.
Magnetic properties of ultrathin (4?)Fe film studied by polarized neutron reflectometry
Li Tian-Fu, Chen Dong-Feng, Wang Hong-Li, Sun Kai, Liu Yun-Tao
2009, 58 (11): 7993-7997. doi: 10.7498/aps.58.7993
Abstract +
Ultrathin Fe film 200  V/4  Fe/900  V/MgO(100) has been prepared by molecular beam epitaxy (MBE). The structure parameters, such as the surface and interface roughness and the thickness of each layer, were obtained by X-ray and neutron reflectivity measurement. The magnetic properties of the thin Fe layer were investigated by polarized neutron reflectometry at different temperature. The result shows that the magnetic moment of an Fe atom is about 1.0±0.1 μB at room temperature and increases to 1.5±0.1 μB at 10 K. The Curie temperature of the thin Fe film is estimated to be 310±30K.
Current-induced magnetization switching in spin valves
Bao Jin, Xu Xiao-Guang, Jiang Yong
2009, 58 (11): 7998-8001. doi: 10.7498/aps.58.7998
Abstract +
Recently, current-induced magnetization switching (CIMS) behavior in current-perpendicular-to-plane (CPP) exchange-biased spin valve (ESPV) nanopillars has been attracting great attention. In this paper, we experimentally study the CIMS in a special antisymmetric ESPV structure. With the increase of the external magnetic field, the device shows a transition from inverted CIMS to normal CIMS, which is possibly due to the different magnetic configuration in the antisymmetric ESPV.
First-principles calculation of microwave dielectric properties of Al-doping ZnO powders
Huang Yun-Xia, Cao Quan-Xi, Li Zhi-Min, Li Gui-Fang, Wang Yu-Peng, Wei Yun-Ge
2009, 58 (11): 8002-8007. doi: 10.7498/aps.58.8002
Abstract +
The band structure and dielectric properties of the pure ZnO and the Al-doped ZnO were studied by using a first-principle ultrasoft pseudopotential approach of the plane wave based on the density functional theory. The pure ZnO and the Al-doped ZnO powders were prepared via the solid state reaction at 600°C with holding time of 1.5 h. The prepared powders were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The dielectric parameters were determined by the vector network analyzer in the frequency range of 8.2—12.4 GHz. Results show that the volume of super-cell has no obvious change and the Fermi energy level is introduced into conduction band through introducing Al ions. XRD patterns indicate that all the samples have pure wurtzite structure of ZnO. It is found that Al ions form the substitutional impurity in ZnO crystal according to the result of XPS. The experimental results show that both the real part ε′ and imaginary part ε″ of permittivity of the samples are increased by Al doping, in agreement with the result of calculation.
Thickness dependence of microstructure for La0.9Sr0.1MnO3/Si films determined by micro-Raman spectroscopy
Liu Xue-Qin, Han Guo-Jian, Huang Chun-Kui, Lan Wei
2009, 58 (11): 8008-8013. doi: 10.7498/aps.58.8008
Abstract +
La0.9Sr0.1MnO3 films on Si (100) substrate of different thickness were prepared by sol-gel routine, and the microstructure of LSMO/Si was studied by XRD and confocal micro Raman spectroscopy. Both XRD and Raman results show different structures in LSMO films of different thickness. There are two strong peaks around 490 cm-1and 600 cm-1 that is characteristic of Jahn-Teller distortion in spectra and characteristic peak of rhombohedral structure of the film with thickness of 90 nm, which show the coexistence of two phases. Lattice constants of LSMO film vary with film thickness. Lattice constants vary as film thickness increases, which is because the tilting angle of MnO6 octahedron and the bond length of Mn-O increase as film thickness increases. Raman spectra of 532 nm-laser and 325 nm-laser show, that there are two phases existing in LSMO/Si film, namely the phase in LSMO/Si interface, and the rhombohedral phase in the surface.
High performance white organic light-emitting devices based on a novel red fluorescent dye 3-(dicyanomethylene)-5, 5-dimethyl-1-(4-dimethylamino-styryl) cyclohexene
Wen Wen, Li Lu, Yu Jun-Sheng, Jiang Ya-Dong, Wang Bo
2009, 58 (11): 8014-8020. doi: 10.7498/aps.58.8014
Abstract +
White organic light-emitting devices based on a red fluorescent dye 3-(dicyanomethylene)-5, 5-dimethyl-1-(4-dimethylamino-styryl) cyclohexene(DCDDC) were fabricated and investigated. Two kinds of devices were processed using ultrathin technology and doping technology. The structures of the devices were as followed: 1) indium-tin oxide (ITO)/N, N′-diphenyl-N, N′-bis(1-naphthyl-pheny1)-1, 1′-biphenyl-4, 4′-diamine (NPB)/4, 4′-bis(2, 2′-diphenylvinyl)-1, 1′-diphenyl (DPVBi)/tris(8-quinolinolato) aluminum (Alq3)/DCDDC/Alq3/Mg:Ag; 2) ITO/NPB /Alq3:DCDDC/NPB/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP)/Mg:Ag. The luminescence and efficiency characteristics of these two devices were measured and compared. The results showed that both devices A and B exhibited white light consisting of RGB three primary colors. Moreover, device A had a turn on voltage of 4 V, a maximum power efficiency of 2.4 lm/W at 5.5 V and a maximum luminance of 16690 cd/m2 at 185 V. Also, pure white emission with Commissions Internationale De L’Eclairage (CIE) coordinates near (0.330. 0.300) having a slight variation of (-0.020, +0.002) in a wide range of voltages was observed. In contrast, devices B showed a turn on voltage of 5 V, a maximum power efficiency of 1.4 lm/W at 5.5 V and a maximum luminance of 12580 cd/m2 at 17 V. The CIE coordinates had a red shift as the voltage increased and then kept near the optimum white point of (0.33, 0.33) over 9 V. It was found that the difference in characteristics of these two devices was dependent on the variation of charge recombination zone. To be specific, it was due to the direct charge trapping effect of DCDDC ultrathin layer and the properties of incomplete energy transfer in Alq3:DCDDC doping system.
Simulation of light coupling enhancement and localization of transmission field via subwavelength metallic gratings
Gan Qiao-Qiang, Bai Wen-Li, Guo Bao-Shan, Cai Li-Kang, Song Guo-Feng
2009, 58 (11): 8021-8026. doi: 10.7498/aps.58.8021
Abstract +
Surface plasmons(SPs) generated in nano metallic gratings on medium layer can greatly enhance the transmission field through the metallic gratings. The enhancement effect is achieved from λ=500 nm to near-infrared domain. The enhancement rate is about 110% at the wavelength of about 610 nm and about 180% at λ=700 nm and 740 nm where most kinds of thin film solar cells have a high spectral response. These structures should provide a promising way to increase the coupling efficiency of thin film solar cells and optical detectors of different wavelength response.
Optical constants of sol-gel derived TiO2 films characterized by spectroscopic ellipsometry
Wang Xiao-Dong, Shen Jun, Wang Sheng-Zhao, Zhang Zhi-Hua
2009, 58 (11): 8027-8032. doi: 10.7498/aps.58.8027
Abstract +
Nanostructured titanium oxide films were deposited on silicon substrate via sol-gel dip coating method with tetrabutyl titanate as precursor. With reflective spectroscopic ellipsometry, the ellipsometric parameters Ψ and Δ of TiO2 films were measured. Then, with the Cauchy model, the ellipsometric data were fitted, and both the thickness and the optical constants at 380—800 nm wavelength of the films were obtained. A comparison was made between the reflectance of the films derived with the spectrophotometer and the simulated results. Meanwhile, the thickness of the films was calculated by interference method. Moreover, with the atomic force microscopy the surface microstructures of the films annealed at different temperatures were observed, and the relationship between the surface microstructures and optical constants of films was further discussed. The results showed that Cauchy model works well in describing the dispersion relationship of the TiO2 films, and the variation rules of optical constants (the refractive index, the extinction coefficient) with wavelength were obtained. The optical constants of the films were related with the microstructure. Those simulated reflectance spectrum accorded well with the measured result. And with a deviation of only 25%, the calculated value of the thickness was in accordance with which was obtained by spectroscopic ellipsometry.
Study on the compound film of diamond for absorbing radiation
Jiang Zhi-Gang, Liang Zhong-Zhu, Liang Jing-Qiu, Wang Wei-Biao, Fang Wei, Zheng Na
2009, 58 (11): 8033-8038. doi: 10.7498/aps.58.8033
Abstract +
The solar radiation has significant impact on the earth climate and environment, so it’s important to detect it. High thermal conductivity and high absorptivity material for absorbing radiation is highly needed to improve the performance of the radiation detector. The compound diamond films were deposited using microwave plasma chemical vapor deposition (MW-PCVD) and hot cathode direct current plasma chemical vapor deposition (DC-PCVD) methods. The absorptivity of the compound diamond film is 99%—99.2%. With the increase of the thickness of black diamond layer, the thermal conductivity of the compound diamond film decreases a little, but the thermal conductivity is always larger than 16 W/K·cm when the thickness of black diamond layer is less than 15 μm and so it is still a high thermal conductivity material. The black diamond layer deposited on high purity diamond film by hot cathode DC-PCVD method has apparent wide Raman peaks at 1500—1600 cm-1and 1350 cm-1 which correspond to non-diamond carbon phase. With the increase of methane, this non-diamond carbon phase also increases. As the non-diamond carbon phase, like graphite, increases, the transmissivity of the compound diamond films decreases. The black diamond layer deposited on the high purity diamond acts as the heat sink and has high surface adhesion property, and high thermal conductivity.
Optical absorbance of diamond doped with nitrogen and the nitrogen concentration analysis
Jia Xiao-Peng, Liang Zhong-Zhu, Liang Jing-Qiu, Li Gui-Ju, Zheng Na
2009, 58 (11): 8039-8043. doi: 10.7498/aps.58.8039
Abstract +
The combination of outstanding properties, such as high thermal conductivity, high refractive index, extreme hardness, radiation resisting, and high insulation, makes diamond an ideal material for optical application under extreme requirements. The relationship between the optical absorbance of diamond doped with nitrogen and the nitrogen concentration were studied. The calculation method of nitrogen concentration used in this study was a modification of the typical calculation method. The high nitrogen concentration diamond was synthesized in Fe80Ni20-carbon and sodium azide system. The absorbant intensity of diamond increases in 800—1400 cm-1 range. The nitrogen concentration in diamond increases with the increasing contents of NaN3. The color of diamond changes with the increase of NaN3 content, in the order of green, dark green and black. The diamond synthesized with addition of NaN3 contains nitrogen exceeding 1450 ppm which is much higher than the normal diamond. The optical transmission of diamond decreases with the increase of nitrogen concentration. The diamond with nitrogen doping can be used as optical material with better absorbance and many physical characters at some wavenumber.
Tailoring the morphology and wettability of ZnO one-dimensional nanostructures
Cai Wei, Wu Xiang, Qu Feng-Yu
2009, 58 (11): 8044-8049. doi: 10.7498/aps.58.8044
Abstract +
Diverse one-dimensional (1D) nanostructures of ZnO, such as tower-like, conical, mushroom-like and ring-like, have been synthesized through vapor phase deposition method using metals and semiconductors as the substrates. SEM and TEM are used to characterize the morphologies and microstructures of as-synthesized products. Results indicate that the substrates have important effect on the morphology and structure of as-synthesized products.The growth mechanism of as-grown tower-like nanostructure is explained and the corresponding wettability is studied.
Optical and scintillation properties of Ce:YAG crystal and transparent ceramics
Bi Qun-Yu, Shi Yun, Li Hong-Jun, Su Liang-Bi, Liu Qian, Pan Yu-Bai, Xu Jun, Yang Xin-Bo
2009, 58 (11): 8050-8054. doi: 10.7498/aps.58.8050
Abstract +
In this work, Ce:YAG crystal and transparent ceramics were prepared by the temperature gradient technique (TGT) and sintering in vacuum, respectively. The optical and scintillation properties of the as-prepared Ce:YAG crystal and ceramics were investigated and compared. Both crystal and ceramics show typical Ce3+ absorption bands at 230,340 and 460 nm and a 540 nm emission peak. However, the color center absorption bands at 296 and 370 nm with an emission peak at 398 nm were also observed in the TGT crystal. X-ray fluorescence spectra of crystal and ceramics show an emission peak at 520 nm, but another emission peak at 300 nm was found in the crystal which can be attributed to the YAl antisite defects. An average light output of 16800 and 9800 photons/MeV and a single exponential decay with the decay time constants of 61.9 and 62.97 ns were found in the as-prepared Ce:YAG crystal and ceramics. Compared with Ce:YAG ceramics, Ce:YAG crystal shows a higher light yield and faster response.
Numerical simulation of three-dimensional dendritic growth using phase-field method
Feng Li, Wang Zhi-Ping, Xiao Rong-Zhen, Zhu Chang-Sheng
2009, 58 (11): 8055-8061. doi: 10.7498/aps.58.8055
Abstract +
Quantitative numerical simulation of three-dimensional dendritic growth in pure undercooled melt is carried out based on phase-field model of thin-interface limit and incorporating interfacial energy anisotropy which is solved by an accelerated algorithm of the dynamic computing regions, the dendritic growth is faithfully described. The dendritic tip is analyzed by cutaway view, indicating that the anisotropy of main branches’ section is not more obvious than that of main branches. The dendritic tip growth speed, tip radius, tip Peclet number as well as classic stability parameter σ* are simulated, compared with reported values under same condition,and they agree well with each other. Dendritic growth law that is in accordance with crystalline theroy is achieved, and it is proved that it is feasible and effective to simulate three-dimensional dendritic growth using phase-field method.
The waveguide effect of hard X-ray photon sieves
Xie Chang-Qing, Zhu Xiao-Li, Jia Jia
2009, 58 (11): 8062-8066. doi: 10.7498/aps.58.8062
Abstract +
In this work,the waveguide effect inside the high high-aspect-ratio metal structure of hard X-ray photon sieves is studied based on fast fourier transform beam propagation method (FFT-BPM). After the physical boundary condition immediately downstream of hard X-ray photon sieves is determined by FFT-BPM, the angular spectrum method is used to calculate the point spread function,and the absorber thickness impact on the focusing performance is analyzed. The results show that the waveguide effect can suppress the emergence of the high order diffraction of hard X-ray photon sieves to some extent,thus improve its focusing performance.Under the same feature size conditions, the spatial resolution of hard X-ray photon sieves is better than that of Fresnel zone plates,with the drawback of lower diffraction efficiency.With the absorber thickness increasing, both the focusing performance and diffraction efficiency of photon sieves will improve, but the difficulty of the corresponding nanofabrication process will also increase.
The effect of concentrated light intensity on output performance of solar cell arrays
Li Ming, Lin Wen-Xian, Wei Sheng-Xian, Xu Yong-Feng, Wang Liu-Ling, Zhang Xing-Hua, Xiang Ming, Wang Yun-Feng
2009, 58 (11): 8067-8076. doi: 10.7498/aps.58.8067
Abstract +
Detailed analysis on the output characteristic and power influence factors of crystal silicon solar cell arrays and GaAs cell arrays have been done based on trough concentrating photovoltaic/thermal system. The results show that under concentrated light intensity, the output performance of GaAs cell array is better than crystal silicon solar cell arrays. Band-gap of solar cell arrays narrows and short circuit current increases very much in concentrated light intensity, which are good for output power. But open circuit voltage of cells drops a little for high recombination rate in depletion region produced by high light intensity, which has a restrictive effect to output power. At the same time the series resistance of cell arrays increases and working temperature of cell arrays rises which are brought about by high concentrated light intensity. In high concentrated light intensity, series resistance of cell arrays hugely affect the output power. When series resistance increases from 0 Ω to 1 Ω, the out put power of four cell arrays respectively drop by 6778%, 7493%, 7730% and 5801%.
First-principles study on the influence of component element substitution on the dehydrogenation ability of LiNH2 hydrogen storage materials
Zhang Hui, Qi Ke-Zhen, Zhang Guo-Ying, Wu Di, Zhu Sheng-Long
2009, 58 (11): 8077-8082. doi: 10.7498/aps.58.8077
Abstract +
The influence mechanism of element substitution on the dehydrogenation ability of LiNH2 was investigated by plane wave pseudo-potential method based on density functional theory. The binding energy, density of states (DOS) and overlap population were obtained by structure calculation, the stability of LiNH2 structure and the binding nature between atoms were analyzed. Results showed that the bond strength between N and H is reduced when the Li atoms of LiNH2 are partially replaced by the Ca, Na, or Al atoms. The best effect is get by Al, Mg co-doping. The N atoms of Li(Mg)NH2 are partially replaced by the B, C, or P atoms, the effect of C is best. It is predicted that a hydrogen storage material with lower desorption temperature can be obtained by Mg, Al, C substitution to Li, N of LiNH2.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Modified effective medium modeling and seismic wave field in un-cemented marine sediments with hydrates
Deng Ju-Zhi, Fang Gen-Xian, Li Hong-Xing, Tao Chun-Hui, Zhou Jian-Ping, Deng Xian-Ming
2009, 58 (11): 8083-8093. doi: 10.7498/aps.58.8083
Abstract +
Elastic-wave velocity estimation in marine sediments with hydrates is an important part of hydrate seismic survey method and engineering. Suspending model and grain contact model are two main hydrate microscopic patterns for the non-cemented sediments with hydrates. Through numerical analysis, we discovered the velocity of compression wave and transverse wave and the Poisson's ratio forecasted by suspending model and grain contact model have bugs in physical understanding. Considering the hydrate microscopic model as the suspending model or grain contact model singly is unreasonable. We point out that the hydrate microscopic model is related with the hydrate saturation and established a modified effective medium modeling of non-cemented sediments with hydrates using the Lagrange interpolation method. This model considers the effect of hydrate saturation on the hydrate microscopic model, and the numerical analysis indicated that the new model is more reasonable. We made numerical simulation of seismic wave field based on the modified effective medium model and studied the characteristics and mechanism of BSR and blanking zone, and then expounded some phenomena observed practically based on the possiblly existing models.
Diagnosis of vertical helicity, divergence flux and their extensions in heavy-rainfall events
Ran Ling-Kun, Chu Yan-Li
2009, 58 (11): 8094-8106. doi: 10.7498/aps.58.8094
Abstract +
On the basis of vertical helicity, we define three parameters, namely, the divergence flux, moisture vertical helicity and moisture divergence flux. The parameters are calculated with NCEP/NCAR real analysis data in the two heavy-rainfall events occurring in China. The result shows that the parameters are closely related to the precipitation systems since they are capable of describing the typical vertical structure of dynamical and moisture fields. The anomalies of the parameters vertically integrated well correspond with the observed 6h-accumulated surface rainfall. This suggests that the parameters are capable of predicting and indicating the development and propagation of precipitation systems. The calculation with the 6-hour forecasting data of NCEP-GFS shows that the parameters have the ability of predicting precipitation and the moisture divergence flux is significantly beller than the other parameters in predicting precipitation.
Spatial-temporal characteristics of record-breaking temperature events over China in recent 46 years
Hu Jing-Guo, Xiong Kai-Guo, Wang Qi-Guang, Feng Guo-Lin
2009, 58 (11): 8107-8115. doi: 10.7498/aps.58.8107
Abstract +
Based on the theory of probability distribution of record-breaking events and daily high/low observational temperature data in China form 1960 to 2005, the spatial-temporal characteristics of record-breaking temperature are investigated. We found that the annual mean frequency of record-breaking high temperature is about 2.5 times greater than normal in 1976—2005, while for record-breaking low temperature is 4.5 times less. Record-breaking high temperature is obviously more than normal in Northwest, North China, Northeast and Tibet, while the record-breaking low temperature is obviously less than normal there. As to the relative trend of record-breaking temperature events, the record-breaking high temperature somewhat increases in most parts of China, but the record-breaking low temperature become less and less all over China. For the development trend of strength, the record-breaking high temperature events, have somet enhancement in high latitude areas of China, but the record-breaking low temperature events have no change or only eventually become weakening in this area and also in XinJiang and Tibet. It should to be payed attention that the strength of record-breaking low temperature events becomes obviously enhanced in south China. In studying the relationship of annual frequency of record-breaking high/low temperature events and pacific warm pool index, we found that there are significant correlations between them for most parts of China.
Analysis of the variability periodicities of quasar 3C345
Dong Fu-Tong, Zhang Xiong
2009, 58 (11): 8116-8122. doi: 10.7498/aps.58.8116
Abstract +
This paper has collected all available optical B magnitudes of quasar 3C345 of more than 100 years, and acquired it's long-term light curve. We make a muti-time scale analysis to it's B band data with the wavelet analysis method, and get the wavelet transform coefficient plots to demonstrate the explosion process of the optical B band of 3C345. From the analysis, we have found that threr exist approximate periods of 450 d, 780 d, 1830 d and 3540 d. The inverse wavelet transform shows the light curve variability of 3C345 on different time scales, so we can predict it's possible explosion time is the year of 2010.