Vol. 60, No. 7 (2011)
2011-04-05
GENERAL
2011, 60 (7): 070201.
doi: 10.7498/aps.60.070201
Abstract +
The Noether-Lie symmetry and conserved quantities of the Rosenberg problem are studied. From the study of the Rosenberg problem,the Noether symmetry and the Lie symmetry for the equation are obtained, thereby the conserved quantities are deduced. Then the definition and the criterion for Noether-Lie symmetry of the Rosenberg problem are derived. Finally,the Noether conserved quantity and the Hojman conserved quantity are deduced from the Noether-Lie symmetry.
EDITOR'S SUGGESTION
2011, 60 (7): 070202.
doi: 10.7498/aps.60.070202
Abstract +
The paper deals with the stability and the bifurcation of a class of inertial neural networks. Based on sensitivity theory, we determine the suitable bifurcation parameter. Using Routh-Hurwitz criterion and bifurcation theory, we give some new criteria for stability,Hopf bifurcation and steady state bifurcation. Numerieal simulations are given to validate the theoretieal analysis showing that the delayed feedback controller can control the occurrence of bifurcation effectively and the amplitude of the bifurcated limit cycle as well.
2011, 60 (7): 070203.
doi: 10.7498/aps.60.070203
Abstract +
In order to obtain infinite sequence exact solutions to the sine-Gordon-type equations, the auxiliary equations of triangular function type and hyperbolic function type, Bäcklund transformation and nonlinear superposition formula of the solutions are presented. And the method is used to construct new infinite sequence exact solutions to the sine-Gordon equation, mKdV-sine-Gordon equation, (n+1)- dimensional double sine-Gordon equation and the sinh-Gordon equation with the help of symbolic computation system Mathematica, which include infinite sequence triangular function solutions, the infinite sequence hyperbolic function solutions, infinite sequence Jacobi elliptic function solutions and infinite sequence computation solutions.
2011, 60 (7): 070204.
doi: 10.7498/aps.60.070204
Abstract +
To construct infinite sequence peak solitary wave solutions to nonlinear evolution equations, Bäcklund transformation of Riccati equation and nonlinear superposition formula of the solutions are introduced, then Degasperis-Procesi equation is taken as an example and infinite sequence peak solitary wave solutions and periodic solutions of the equation are obtained with the help of symbolic computation system Mathematica.
2011, 60 (7): 070205.
doi: 10.7498/aps.60.070205
Abstract +
In this paper, we prove the existence of the global attractor for strongly damped nonlinear thermoelastic coupled rod equation with the initial boundary value, and make the dimension estimate of the global attractor, according to the operator semigroups theory.
2011, 60 (7): 070206.
doi: 10.7498/aps.60.070206
Abstract +
Based on both the error estimates of moving least-square approximation in the Sobolev space Wk,p(Ω) and the continuity and coercion of the bi-linearity in the weak form of the elasticity, the error analysis of element-free Galerkin method for elasticity is discussed in this paper, the relationship between the error and the radius of the weight function is given, and the theorem of the error estimate presented. The error estimate proves to be of optimal order when nodes and shape functions satisfy some conditions. From the error analysis, it is shown that the error bound of the elasticity is directly related to the radius of the weight function. And a numerical example is given to verify the correctness of the given results.
2011, 60 (7): 070301.
doi: 10.7498/aps.60.070301
Abstract +
Secure multi-party ranking problem is used to rank n private integers without leaking further information. It is an extended problem of secure two-party comparing problem. A secure multi-party quantum ranking protocol in semi-honest model is presented based on the a quantum implicit module n+1 addition. The security for multi-parties of the protocol is analyzed.
2011, 60 (7): 070501.
doi: 10.7498/aps.60.070501
Abstract +
A linear delayed position feedback is introduced into a Helmholtz oscillator system, and its effects on controlling the erosion of safe basins are investigated. The condition of fractal erosion of the basin boundary of the delayed feedback controlled system is acquired, there by the threshold of the excitation of the fractal erosion is obtained. Then considering time delay as a variable parameter and employing the 4th-order Runge-Kutta method and the point-to-point mapping method, evolutions of safe basins with time delay are presented. It is found that the increasing of time delay can enhance the threshold of the fractal erosion and reduce the erosion of safe basin effectively under a weak feedback gain. All the results imply that delayed position feedback can be used as a good strategy to control the erosion of safe basins.
2011, 60 (7): 070502.
doi: 10.7498/aps.60.070502
Abstract +
Symbolic dynamics, which partitions the infinite number of finite length trajectories into a finite number of trajectory sets, allows a simplified and "coarse-grained" description of the dynamics of a system with a limited number of symbols. In this paper, we further develop the symbolic vector dynamical estimation method in coupled map lattice (CML). We take the CML of Logistic map as an example, to show that the control parameters affect the dynamical characters of symbolic vector sequence. We study the ergodic property of CML by using the inverse function of CML. We give the symbolic vector dynamical description of the initial values, the forbidden words and the control parameters for studying pattern formation in CML. We also give a coupling coefficient estimation approach based on the ergodic property.
2011, 60 (7): 070503.
doi: 10.7498/aps.60.070503
Abstract +
In this paper, we present an attack on a cryptosystem designed by using a spatiotemporal chaotic system. We show that the decryption system proposed in (Phys. Rev. E 66, 065202 (2002)) degenerates to the one-dimensional map under the constant input, and it is insensitive to the slight perturbations to input in specially selected intervals. Consequently, the attacker can use a very simple optimization algorithm to obtain the proper input value within only hundreds of iterations. Furthermore, we prove that there exits a linear dependency between the secret key and the obtained input value, so that the attacker can break this spatiotemporal chaos-based secure communication scheme easily. Both theoretical and experimental results show that the lack of security discourages the use of these cryptosystems for practical application.
2011, 60 (7): 070504.
doi: 10.7498/aps.60.070504
Abstract +
Blind demodulation (breaking) of chaotic direct sequence spread spectrum (CD3S) signals is a challenging and leading issue under multipath fading channel in the field of chaotic communication. Until now, there are neither equalization methods to remove the impact of the channel, nor the immediate breaking methods. Based on the existing study, the breakability of CD3S signals is analyzed under multipath fading channel by using unscented Kalman filter (UKF) chaotic fitting in this paper. Beginning with the state space equation for the CD3S signals in UKF chaotic fitting, the channel influence on the tracking error is analyzed in the process of UKF chaotic fitting, then the range of the message state estimation is derived, and finally a sufficient condition theorem is proposed for the CD3S signals to be broken. Simulation results show that CD3S signals can be broken successfully under the proposed condition with excellent performance of bit error rate (BER), no matter whether the channel characteristic is either time-invariant or time-variant.
2011, 60 (7): 070505.
doi: 10.7498/aps.60.070505
Abstract +
To reduce effectively channel noise, parameter mismatch, and inter-user interference, a dual unscented Kalman filter (DUFK) algorithm with combining blind extraction algorithm and different state space models for chaotic communication systems with multiuser is proposed. The simulation results indicate that the algorithm has a faster convergence speed and can realize effectively multiuser communications in a multi-input multi-output channel.
2011, 60 (7): 070506.
doi: 10.7498/aps.60.070506
Abstract +
Based on fractional calculus and the fact that the capacitor and the inductor are fractional in nature, the fractional mathematical model and the fractional state averaged model of the Boost converter in continuous conduction mode operation are built and analyzed. Also, the condition for the continuous conduction mode operation of the Boost converter is given. Finally, in order to verify the theoretical analysis, the simulation model of the Boost converter in continuous conduction mode operation is established by using the software of Matlab/Simulink.
2011, 60 (7): 070507.
doi: 10.7498/aps.60.070507
Abstract +
The fast-slow dynamics of a nonlinear electrical circuit with multiple switching boundaries is investigated in this paper. For suitable parameters, periodic bursting phenomenon can be observed. The full system can be divided into slow and fast subsystems because of the difference between variational speeds of state variables. According to the slow-fast analysis, the slow variable, which modulates the behavior of the system, can be treated as a quasi-static bifurcation parameter for the fast subsystem to analyze the stabilities of equilibrium points in different areas of vector field. The bifurcation is dependent on the switching boundary in the vector field. In particular, for the two-time scale non-smooth system with fast-slow effect, the bifurcation of fast subsystem is determined by the characteristics of equilibrium points on both sides of the switching boundary. Furthermore, the generalized Jacobian matrix at the non-smooth boundary is introduced to explore the type of non-smooth bifurcation (i.e., multiple crossing bifurcation) in the fast subsystem, which can also be used to explain the mechanism for symmetric bursting phenomenon of the full system.
2011, 60 (7): 070508.
doi: 10.7498/aps.60.070508
Abstract +
According to the stability of fractional order linear systems theory, the system is decomposed into stable linear parts and the corresponding nonlinear parts. The active controller is designed to compensate the nonlinear parts, and the fractional order chaotic system is suppressed to an equilibrium point. In order to improve the compensation ability of active controller, a multiple least square support vector machine (M-LS-SVM) regression model is presented based on feedback. The subtractive clustering is adopted to divide the input space into several sub-spaces, and sub-models are built by a LS-SVM in each sub-space. In order to minimize the severe correlation among sub-models and to improve the accuracy and the robustness of the model, the sub-models are combined by principal component regression (PCR).The experiment result shows that by using the method the compensation accuracy and the system response indices can be improved.
2011, 60 (7): 070509.
doi: 10.7498/aps.60.070509
Abstract +
The doubly fed induction generator (DFIG) is investigated. Its mathematical model under d-q axis is deduced. According to 2MW mainstream DFIG actual parameters the chaotic behaviors are demonstrated to appear in a certain range of parameter values or under certain working conditions. Based on active control method, an active sliding mode controller is designed, which enables chaotic systems to be stablized under arbitrary initial conditions. The stability of the controlling method is analyzed by Lyapunov stability theorem. Finally, numerical results are presented for the DFIG system. This method may realize the chaos synchronization, and both the stability and the robustness are good.
2011, 60 (7): 070510.
doi: 10.7498/aps.60.070510
Abstract +
In this paper, a class of wide range Julia set of parameter identification problem is investigated. Based on the nonlinear feedback controller and the discretized equation theory, the designed generally applicable adaptive synchronization controller and the parameter adaptive law are obtained, and it is proved that the designed controller of generalized Julia set can achieve the synchronization. Moreover, it can identify the unknown parameters of the generalized Julia set. Particularly, the parameter identification of the basic form of Julia set is discussed in the paper.
2011, 60 (7): 070511.
doi: 10.7498/aps.60.070511
Abstract +
In this paper a method is presented to estimate the unknown parameters of chaotic system based on the variational principle, which can be applied to all chaotic systems governed by the following equation:x= F(x,θ). Firstly,the equation of the chaotic system is included into the objective functional. Secondly, the universal formulas of the adjoint equation for chaotic systems and the functional gradient for unknown parameters are derived using the variational principle. Thirdly, the algorithm to estimate unknown parameters of chaotic system is designed according to above formulas. Finally, all unknown parameters of the typical Lorenz chaotic system and the hyperchaotic Chen system are estimated separately. Numerical simulations show that the effectiveness and the feasibility of the proposed method to estimate unknown parameters of chaotic systems.
2011, 60 (7): 070512.
doi: 10.7498/aps.60.070512
Abstract +
We have studied the methodology of estimating the embedding dimension for phase space reconstruction of chaotic time series according to the Takens theorem. We present an approach to the estimation of the embedding dimension based on the prediction of nonlinear performance. That is, we determine the embedding dimension by considering the variation of the performance of prediction model of chaotic time series with embedding dimension. Numerical simulations verify that the method is applicable for determining an appropriate embedding dimension.
2011, 60 (7): 070513.
doi: 10.7498/aps.60.070513
Abstract +
For the chaotic time series single-step and multi-step prediction, Gaussian processes (GPs) method based on composite covariance function is proposed. GP priors over functions are determined mainly by covariance functions, and through learning from training data sets, all hyperparameters that define the covariance function and mean function can be estimated by using matrix operations and optimal algorithms within evidence maximum bayesian framework. As a probabilistic kernel machine, the number of tunable parameters for a GP model is greatly reduced compared with those for neural networks and fuzzy models. GP models with different composite covariance functions are applied to chaotic time series single-step and multi-step ahead prediction and compared with other models such as standard GP model with single covariance function, standard support vector machines, least square support vector machine, radial basis functional (RBF) neural networks, etc. Simulation results reveal that GP method with using different composite covariance functions can be used to accurately predict the chaotic time series and show stable performance with robustness. Hence,it provides an effective approach to studying the properties of complex nonlinear system modeling and control.
2011, 60 (7): 070514.
doi: 10.7498/aps.60.070514
Abstract +
By using multiple-scale method, we study analytically the soliton characteristics of the two-dimensional condensates with two- and three-body interaction. The results show that a ring dark soliton can be found in the condensates when the two-body interaction is repulsive and three-body interaction is attractive. With the strength of the three-body interaction decreasing, the height of the center peak of the ring dark soliton decreases. When the three-body interaction vanishes, the ring dark soliton becomes a perfect dark soliton. If the two- and the three-body interaction are both repulsive,the width and the amplitude of the dark soliton decrease with the strength of the three-body interaction increasing. Especially, if the strength of the three-body interaction is large, which is on the order of that of the two-body interaction, the condensat collapse takes place.
2011, 60 (7): 070701.
doi: 10.7498/aps.60.070701
Abstract +
The calibration-free wavelength modulation absorption spectrum is studied based on the second harmonic (2f) signal to remove the calibration procedure for tunable diode laser absorption gas sensing. The simulated 2f signal is obtain from the analysis of peak and trough from measured 2f signal line shape. The gas concentration is calculated by the linear fitting of measured and simulated 2f signals. The experiment on CO2 detection is carried out at transition of 6336.24cm-1 in a 10 cm absorption cell. The results prove that the calibration-free wavelength modulation absorption spectrum is suited for on-site gas sensing at various conditions. The average absolute error of gas concentration is 0.67% at modulation index ranging from 1.8 to 3.2. With gas concentration and pressure varied, the average absolute errors of gas concentration are measured to be about 0.98% and 0.74%.
2011, 60 (7): 070702.
doi: 10.7498/aps.60.070702
Abstract +
In order to make a good use of Chinese polarized satellite sensor, the directional polarized camera (DPC) has been developed and tested in the flight experiments. DPC camera is designed to observe the polarized and directional reflected radiation of the earth-atmosphere system. Retrieval of physical parameters from DPC data depends on the accuracy of calibration. The polarized camera radiative calibration includes two aspects: intensity and polarization. Based on the predecessors' work, we explore the polarization calibration principles and methods. Using the DPC aerial remote sensing experiment data, we have realized the polarization calibration and analyzed the results. This work may contribute to fundamental basis for the data processing and in-flight calibration of the future Chinese polarized satellite sensor.
2011, 60 (7): 070703.
doi: 10.7498/aps.60.070703
Abstract +
The principle of interference imaging spectrometer is introduced. In this paper, ray tracing method is employed to present the rules of the prism Sagnac and the polariscope Savart in interference imaging spectrometer. The explicit formulae for the optical feux are deduced. The representative solutions such as the optical fluxes of Savart and Sagnac are both analyzed and compared. By performing the computer simulation, some important curves are obtained for the variations of optical flux with incident angle and wavelength. The work in this paper provides a theoretical guidance for the study of polarization interference imaging spectrometer.
2011, 60 (7): 070704.
doi: 10.7498/aps.60.070704
Abstract +
To obtain straight interference fringes over larger field of view and thus acquire high-accuracy interference data, a wide field of view polarization interference imaging spectrometer based on a combined Savart plate is presented. The Savart plate is composed of positive and negative uniaxial crystals. The relationship between the optical path difference and incident angle is given. By numerical modeling and analysis examples with similar spectral resolution and total thickness, The simulation results show that the field of view to obtain straight interference fringes for the combined Savat plate is ten times as large as that for the conventional Savart plate.
NUCLEAR PHYSICS
2011, 60 (7): 072901.
doi: 10.7498/aps.60.072901
Abstract +
According to the experiment, we analyze the propagation process of the electromagnetic wave on the pulse forming line with water-dielectric, which is the long pulse high power microwave-driven source. And then an equivalent method of discharge process is put forward to study the cause of the flattop waveform distortion. We ind the relationship between the variation trend of the output flattop waveform and the voltage waveform on the pulse forming line, which is validated through the Pspice simulation. By adjusting the breakover time of laser triggered switch, we obtain an output pulse with a flattop of 60 ns, FWHM (full width of half maximum) of 150 ns and voltage amplitude of several hundred kV, showing the distinct improvement on the flattop waveform.
2011, 60 (7): 072902.
doi: 10.7498/aps.60.072902
Abstract +
In recent years, separate absorption, charge and multiplication avalanche photodiodes (SACM-APDs), including InP/InGaAs, InAlAs/InGaAs and Si/Ge APD, have drawn a lot of attention in the field of optical communication. In this paper, on the basis of the circuit model, the frequency response is studied systematically for APDs with different thicknesses of epitaxial layers, different multiplication materials and device structures. The effects of the absorption layer thickness, the dimension of the active area and the parasitic parameters on frequency response are addressed to Si/Ge APD. The simulation resuets are in good agreement with the experimental results, which indicates that the circuit model is helpful for the design optimization of APDs.
ATOMIC AND MOLECULAR PHYSICS
2011, 60 (7): 073101.
doi: 10.7498/aps.60.073101
Abstract +
The electron transport properties of the single molecular junctions composed of isomers of 4,4-(ethene-1,2-diyl) dibenzoic acid and two gold electrodes are investigated systematically using elastic scattering Green's function method. The conductance characteristics are quite different for the two isomers which can be used to construct molecular switch. Our study shows that the molecules are chemically adsorbed on the gold surface by the terminal carboxyl group. Each molecular junction has three different stable conductances, which correspond to the different contact structures between the molecules and electrodes. The different conductances result mainly from the variation of the electronic structures, caused by the interaction between the molecules and the electrodes. Our theoretical simulation is consistent with the experimental measurement.
2011, 60 (7): 073102.
doi: 10.7498/aps.60.073102
Abstract +
The five low-lying configurations of CH3C(O)OSSOC(O)CH3 are studied by ab initio calculations by B3LYP, MP3 and MP4 methods with Aug-cc-pVDZ basis set. Their rotational constants and dipole moments of these five configurations are determined. The vertical ionization energies of the configurations, calculated with electron propagator theory in the P3/6-311++G(2d,2p) approximation, are in agreement with the experimental data from photoelectron spectroscopy. The relative energies of the configurations and the comparison between the simulated and the experimental photoelectron spectra demonstrate that there are at least two configurations of CH3C(O)OSSOC(O)CH3 in the gas-phase experiments. The geometrical parameters of five lowest-lying configurations are optimized in the cationic state and compared with those of the neutral configuration. Remarkable structural relaxations after ionization are found, especially for the dihedral angles D(C2O4S5S10) and D(O4S5S10O9).
2011, 60 (7): 073103.
doi: 10.7498/aps.60.073103
Abstract +
Elemental mercury (Hg) adsorptions on small neutral, cationic and anionic gold clusters, Auqn (n=1—6, q=0, +1, -1), are systematically investigated by using the density functional theory(DFT) in the generalized gradient approximation. The result shows that the frontier molecular orbital theory (FMOT) is useful for predicting the favorable binding configurations of Hg adsorbed on neutral and charged Aun clusters. Most of the lowest energy AunHg complexes can be successfully predicted. The size and the charge state of the clusters have strong influence on the adsorption of Hg on gold clusters. The adsorption energy on the neutral clusters reaches a local maximum at n=4, which is about 0.661eV. The adsorption energies for cationic clusters decrease with cluster size increasing, although there is a local peak at n=5. Similarly, for anionic clusters, the adsorption energies decrease with cluster size, except for n=3. The adsorption energies on the cationic clusters are generally stronger than those on the neutral and anionic clusters. For the lowest energy AunHg complexes, an approximate linear correlation between the adsorption energy and the Mulliken charge on adsorbed Hg is found. The more the charges transfer to the cluster, the higher the adsorption energy is.
2011, 60 (7): 073201.
doi: 10.7498/aps.60.073201
Abstract +
The Y2O3:Yb3+,Tm3+ nanomaterials are prepared by a combustion method. The sample is excited by 980 nm, thereby producing a bright blue emission transition peak (476 nm and 487 nm) and a weak red emission peak(about 650 nm) that can be clearly observed. More important two ultraviolet emission peaks 1I6→3H6 (~297 nm) and 1D2→3H6 (~363 nm) are found. In addition, the change of upconversion emission intensity dependent on the Yb3+ concentrations was recorded and the possible eauses are discussed. Finally, the pump energy dependences of the emission intensity are investigated. The results show that blue and red emissions originate from a three-photon process and ultraviolet emission peak (363 nm) takes its source at a four-photon process.
2011, 60 (7): 073202.
doi: 10.7498/aps.60.073202
Abstract +
In this paper, the cold cesium atoms are excited to Rydberg states via two-photon transition and the ion signal of Rydberg atoms is obtained by the selective field-ionization method. The evolution of the 36D and 34S states population is acquired by changing delay time; the corresponding effective lifetimes are obtained by fitting the experimental data, which are in agreement with the existing theoretical results.
2011, 60 (7): 073203.
doi: 10.7498/aps.60.073203
Abstract +
The Hamiltonian operator of a system of V-type three-level atomic Bose-Einstein condensate interacting with two-mode squeezed coherent light field is analyzed in terms of the lattice-liquid model. It is indicated that the contribution of the interaction between atoms to the Hamiltonian in the literature is unreasonable,so the Hamiltonian operator is improved and the squeezing properties of two-mode squeezed field interacting with V-type three-level atoms are studied. The results show that two quadrature comonents of light can be squeezed periodically and that maximum depth of squeezing is closely related to the initial squeezing parameter of light and that the duration is determined by the frequency of two-mode field.
2011, 60 (7): 073401.
doi: 10.7498/aps.60.073401
Abstract +
The dynamics for the collision of BH with He is investigated based on the CCSD(T) potential energy surface. State-to-state differential, partial and integral cross sections are calculated for the first time. The effects of the long-range attractive and the short-range anisotropic interactions on inelastic scattering dynamics are also discussed in detail. As a result, the nearly-linear collision of He atom from H atom side with the BH molecules is the most effective manner for j=0→j'=1.Furthermore, it is of advantage for the Δj=1 transition at lower energy and for the Δj=2 transition at higher energy. The state-to-state integral cross section displays a pronounced oscillatory structure. The long-range partial cross section has only an effect on the integral cross section for j=0→j'=1, and the cross sections for j'≥3 are almost determined by the anisotropic short-rang partial.
2011, 60 (7): 073601.
doi: 10.7498/aps.60.073601
Abstract +
Based on the most stable structures of the magic MgO clusters, the adsorption of H2 onto the rocksalt and hexagonal tube (MgO)9,12 is studied using first principal method. The results show that physical adsorption can be formed on Mg+q or O-q ions at different sites of the clusters. On the top of the Mg+q ions, H2 is adsorbed in the side-on manner and donates electrons to the ions. On the top of the O-q ions, H2 is adsorbed in the end-on manner and the molecule is polarized. The strength of the adsorption depends mainly on the location of the Mg/O ions, and the smaller the coordination number of the ions, the stronger the adsorption of H2 is. For the Mg/O ions with the same coordination number, the adsorption formed onto the Mg+q is stronger. According to the Mg or O ions and their locations, the adsorption energy ranges from 0.03 eV to 0.08 eV.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2011, 60 (7): 074101.
doi: 10.7498/aps.60.074101
Abstract +
The modes in a three-layered structure made of single-negative materials have been investigated. For the propagation mode, the tunneling mode can be formed in the structure. When tunneling mode appears the variations of electric field distribution and the transmission with incident angle are studied. We find that there appear two new localized modes when the thickness of the middle layer changes. The frequency interval of the two localized modes can be increased by decreasing the thickness of the middle layer. For the guided mode, the electromagnetic wave is evanescent in semi-infinite vacuum which is on the both sides of the structure. We have analyzed the existence condition of its electromagnetic mode,that is, the dispersion relation. The result shows that a strong local field appears in the interface of the material.
2011, 60 (7): 074201.
doi: 10.7498/aps.60.074201
Abstract +
By analyzing dielectric cube with high permittivity based on dielectric resonator theory, a new approach to the analyzing of left-handed metamaterials simultaneously with negative permittivity and negative permeability is proposed. The approach indicates that dipoles with Lorentz-type resonance electromagnetic responses can realize negative effective parameters in their negative resonant region. The dipole originates from standing wave in high permittivity dielectric cube. By combining electric dipole with magnetic dipole together, the interaction between two kinds of dipoles will destroy the standing wave and realize a left-handed passband. Numerical simulations indicate that by combining dielectric cubes with same sizes but different permittivities together, the electric resonant frequency and the magnetic resonant frequency can be coincident. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial constructed by this means.
2011, 60 (7): 074202.
doi: 10.7498/aps.60.074202
Abstract +
Based on the equivalent transmission line theory, a three-layer tunable composite absorber with active frequency selective surface (AFSS) is designed. The first layer is an AFSS substrate. The middle layer is an AFSS, which is composed of a frequency selective surface (FSS) and a PIN diode array. The third layer is an insulator. Reflectance measurement shows that the reflection characteristic of the absorber can be dynamically adjusted by adjusting the bias voltage of the PIN diode array. When the bias voltage is 5 V, the best absorption property is observed. Reflection coefficient is below -8 dB and -10 dB at the frequency bands of 5—15 GHz and 5.3—13 GHz, respectively. Replacing PIN diodes with surface mount device (SMD) resistors, the reliability of the above results is further verified.
2011, 60 (7): 074203.
doi: 10.7498/aps.60.074203
Abstract +
The emission property of two-dimensional random laser under femtosecond laser pumping is theoretically investigated by using the time-dependent theory. The effects of peak intensity, duration and shape of a pumping pulse on temporal property of the random laser emission are discussed. Results show that the behavior of random lasing depends strongly on the pumping process, thereby one can control the random laser output waveshape through modifying the pumping parameters. The present work can provide more guidance for the controllability of random laser.
EDITOR'S SUGGESTION
2011, 60 (7): 074204.
doi: 10.7498/aps.60.074204
Abstract +
A modified delta-P1 approximation is studied in this paper. An analytic solution Rδ-P1(ρ) of this model for reflectance in double source approximation is developed by taking the source series expansion terms to the first order. It is shown that when the source in extended to first order, a better description for high absorption and high scattering media will be developed. The new model can give satisfactory results in describing irradiance distribution close to source compared with the RSDA(ρ) of diffusion approximation. Moreover, Rδ-P1(ρ) provides the prediction of the second-order parameter γ, which is significant for developing the inversion algorithm to recover optical parameters from spatially-resolved diffuse reflectance by using smaller source-detector separations.
2011, 60 (7): 074205.
doi: 10.7498/aps.60.074205
Abstract +
Based on the extended Huygens-Fresnel principle, the propagations of a partially coherent vortex beam through atmospheric turbulence along an uplink path and a downlink path are studied, where the Gaussian Schell-model (GSM) vortex beam is taken as a typical example of partially coherent vortex beam. The analytical expressions for the average intensity, rms width and cross-spectral density function of GSM vortex beam propagating through atmospheric turbulence along a slant path are derived and used to study the influence of atmospheric turbulence along an uplink path and a downlink path on GSM vortex beam propagation and on coherence vortex. It is shown that under the same conditions the influence of atmospheric turbulence along a downlink path on GSM vortex beam propagation is smaller than that along a uplink path, and the conservation distance of the topological charge of GSM vortex beam along a downlink path is longer than that along a uplink path. The results are explained in physics.
2011, 60 (7): 074206.
doi: 10.7498/aps.60.074206
Abstract +
In active coherent beam combination (CBC), a single-frequency seed laser is often considered to be indispensable for improving the spatial coherence property and obtaining high brightness in the far field. Nevertheless, the single-frequency radiation restricts the output power of coherently combined fiber amplifiers, owing to low stimulated Brillouin scattering (SBS) threshold. The seed laser oscillating at different frequencies proves to have the potential in mitigating SBS effects in fiber amplifiers, and therefore it is able to increase the emission power of CBC greatly. In this study, the basic mathematical model is founded on the basis of the fundamentals of CBC, and the multi-wavelength two-channel CBC estimation formula is proposed on the calculation of some two-channel examples. The optical path difference is the key factor in multi-wavelength CBC. We propose the concepts of "controllable area" and "uncontrollable area" for the optical path difference. If and only if the optical path difference falls into the controllable area, desirable combination effects can be obtained by the active control. In the case of getting the value of optical path difference randomly, excellent combination effects can still be gained and the probability has a close correlation with the spectrum profile, which is inversely proportional to the number of wavelengths approximatively. The multiple control method is competent for the multi-wavelength CBC. In this method, the optical path difference is adjusted into the controllable area by large optical path controllers and then the phase of each channel is locked by precise optical path controllers.
2011, 60 (7): 074207.
doi: 10.7498/aps.60.074207
Abstract +
Starting from the plane angular spectrum theory, we establish a transmission model of beam refraction at the interface between air and glass. Based on this model, we reveal a transverse angular shift in the optical Magnus effect. For a certain linearly and elliptically polarized light beam, the field centroid of refraction beam exhibits a transverse angular shift. However, the transverse angular shift would vanish when the incident light beam is circularly polarized. At an interface between positive and negative refractive indexes, the transverse angle shift presents a reversed phenomenon which is caused by negative diffraction in the left-handed materials. Ultra-high refractive index can significantly reduce the transverse angular shift. On the contrary, the ultra-low refractive index can significantly enhance the transverse angular shift. These findings provide a new method of how to adjust and enhance the optical Magnus effect.
2011, 60 (7): 074208.
doi: 10.7498/aps.60.074208
Abstract +
According to Whittaker scalar theory, a vector transmission model of circularly polarized beam is established. Based on this model, the anomalous rotating characteristics of circularly polarized beam in left-handed materials are investigated. By analyzing the polarization state and diffraction, the abnormal rotation characteristics of beam centroid are revealed. When the circularly polarized light beam propagates in a left-handed material,the rotation characteristic is reversed and the corresponding rotation angle is equal to the Gouy phase. We find that this abnormal rotating characteristic is caused by the reversed transverse energy flow. These findings provide a better understanding of the transmission characteristics of beam in left-handed materials.
2011, 60 (7): 074209.
doi: 10.7498/aps.60.074209
Abstract +
The analytical expression for the propagation of an optical vortex dipole (OVD) nested in a Gaussian beam diffracted by a half screen is derived and used to study the evolution of the diffracted OVD. It is shown that Compared with the case of the OVD evolution in free space, multi-pairs of the OVD may take place in the diffracted field, and the annihilation fashion depends on the off-axis displacement. A variety of the evolution behaviors of OVDs appear by varying the off-axis parameter, but the topological charge is conserved in the evolution process.
2011, 60 (7): 074210.
doi: 10.7498/aps.60.074210
Abstract +
Based on the resarch of the traditional Fourier transform profilometry, Fourier transform profilometry of tilted measurement system is proposed in this paper. The proposed technology makes the three constraints of the traditional Fourier transform profilometry measurement system less stringent. The optical axis in the CCD imaging system is not necessarily perpendicular (with a certain tilting angle) to the reference plane. The connection line between the centers of the exit pupil of the projecting system and the entrance pupil of the CCD imaging system is not required to be horizontal to the reference plane. The optical axis of the CCD imaging system and that of the projecting system are not coplanar, moreover, the two axises do not intersect at a point in the reference plane. Through the stringent theoretical analysis, the mathematical relationship between phase and height is obtained. Compared with the traditional Fourier transform profilometry, the tilted measurement system is more practical.
2011, 60 (7): 074211.
doi: 10.7498/aps.60.074211
Abstract +
The basic principle of measuring the upper atmosphere using the polarization atmosphere Michelson interferometer (PAMI) is briefly described. The relationships between the intensity and the visibility of the PAMI and the Delayed phase of the wave plate are presented. The visibility and the intensity of the PAMI are dependent on the wavelength of spectral line, showing that the 732nm line is inapplicable for measuring spectral line if the PAMI is designed specifically for the 630 nm line. The research provides a theoretical basis and practical guidance both for the theoretical study of polarization atmosphere Michelson interferometer and for the design and development of the new polarization atmosphere Michelson interferometer.
2011, 60 (7): 074212.
doi: 10.7498/aps.60.074212
Abstract +
Based on the paraxial vectorial theory of the propagation of beam in uniaxially anisotropic medium,the analytical formula for an elliptical Gaussian beam propagating in uniaxial crystal orthogonal to the optical axis is derived. And some numerical simulations were preformed to study the effect of the anisotropy on the polarization property of the diffracted elliptical Gaussian beam in the output plane. The results show that the linear polarization state and the symmetry of beam cannot remain unchanged during propagation due to the anisotropy of crystals.
2011, 60 (7): 074213.
doi: 10.7498/aps.60.074213
Abstract +
From the tuning mechanism of the DFB laser diode, we establish an analytical model for current and temperature tuning characteristics. The parameters of the model are identified by experimental results. The model is used to analyze the four DFB diode lasers, and the transient characteristics of the lasers are obtained. We also obtain the static characteristics of these lasers from Agilent 86142B Spectrometer. The comparison between the two values indicates that the correlation coefficients are both more than 0.9999. At the same time, according to the absorption spectrum of CO2 gas, we also measure the emission wavelength of lasers. Comparing it with the HITRAN spectrum of CO2 absorption lines, the two errors are shown to be within 3pm. The analytical model can accurately predict the transient output wavelength of lasers in tuning, the accuracy can meet the spectrum, optical coherence measurements and other practical requirements.
2011, 60 (7): 074214.
doi: 10.7498/aps.60.074214
Abstract +
Investigated are the effects of the cross-correlation time τ or the self-correlation times τ1 and τ2 on the relaxation time T of an optical bistable system using the Mei's method(Mei D C, Xie C W, Zhang L 2003 Phys. Rev. E 68 051102). It is found that the relaxation time T increases with the increase of the cross-correlation time τ between the two noises or the self-correlation time τ1 of the multiplicative noise, and that a one-peak structure appears on the T－τ2 plot. T increases with the increase of correlation intensity λ but decreases with the increase of multiplicative noise intensity Q.
2011, 60 (7): 074215.
doi: 10.7498/aps.60.074215
Abstract +
Compared with local spatial optical solitons and linearly propagating beams, nonlocal spatial optical solitons each have a large phase shift during their propagation. However no one has paid attention to the intrinsic characteristics since the theoretical proof by Guo. We develop the phenomenological theory of Guo and find that there appears π phase shift with the change of the soliton power or the power of the pump soliton. Based on the conclusion that the modulation of the pump-soliton power on the signal-soliton phase has a high sensitivity, we propose a feasible scheme of realizing the optical switch.
2011, 60 (7): 074216.
doi: 10.7498/aps.60.074216
Abstract +
Asymmetrical collisions among three coherent photovoltaic spatial solitons are investigated by numerical method. The numerical results show that the solitons will split or annihilate depending on the incident angle of signal beams in a certain range. If we only change the initial phase difference among the solitons, the collision behavior of solitons will also change correspondingly, showing an interesting conversion of split between annihilation. Furthermore, the numerical results show that the photovoltaic spatial solitons will maintain conservations of momentum and energy in these collision processes, although the dynamical system of photovoltaic solitons is a non-integrable Hamilton one.
2011, 60 (7): 074217.
doi: 10.7498/aps.60.074217
Abstract +
A hybrid algorithm of time domain integral equation (TDIE) and time domain Kirchhof approximation (TDKA) is proposed to compute the TM transient scattering from a 2-dimensional (2D) perfectly conducting (PEC) target above 2D PEC randomly rough surface. Explicit and implicit procedures of Marching-on-in-time (MOT) are developed, respectively. TDKA is applied to the rough surface while TDIE is applied to the target, and the mixed iteration of TDIE/TDKA is introduced to take into account the interactions between the target and the rough surface. In numerical examples, both bent strip (open structure) and cylinder (closed struc- ture) are considered and numerical results present the target surface current response and the far scattered electric field response, which are compared with those obtained from whole TDIE. Numerical results demonstrate the efficiency and the accuracy of the hybrid algorithm. Still in numerical examples, the influence on the far scattered electric field caused by the target is discussed.
2011, 60 (7): 074218.
doi: 10.7498/aps.60.074218
Abstract +
The feasibility of ferrite magnetism materials applied to THz waveguide devices is investigated. A novel continuously tunable bandpass filter and switch under the control of an external magnetic field in a terahertz wave band are designed. Detailed calculations on the shift and the variation in the position of the bandgap reveal that the filter and the switch achieved by this two-dimensional magnetic photonic crystal waveguide have good performancs.
2011, 60 (7): 074219.
doi: 10.7498/aps.60.074219
Abstract +
A model of two-dimensional photonic band gap structure resonant cavity composed of GaAs pillars with graphite lattice is proposed. The variation of its TEy mode formant wavelength with temperature is calculated by finite difference time domain method. The results show that there is a sectional linear characteristic between the main formant wavelength and temperature for this kind of photonic crystal resonant cavity, and the sensitivity responding to temperature is more than 1.60nm/℃. At the same time, the results show that this kind of resonant cavity possesses an excellent characterisitc of frequency switching. Finally, the cause for its switching characteristic is explained by the calculated results.
2011, 60 (7): 074220.
doi: 10.7498/aps.60.074220
Abstract +
All-optical multicasting is a key technology of future transparent photonic network, and in this paper it is presented and experimentally demonstrated based on four-wave mixing (FWM) with multi-frequency pump in 100 m dispersion flattened highly nonlinear photon crystal fiber (HNL-PCF). A signal together with double orthogonal pumps is input into the PCF, and four idlers at new frequencies can be generated through degenerate multi-frequency pump FWM processes, which carry the same data information as the input signal and then a 4×10 Gbit/s wavelength multicasting has been obtained with a tunable operation wavelength range of 35.2 nm and total channel span of 4.4THz. The optimal conversion efficiency and the optimal Q factor are -22 dB and 5.3, respectively. The system is transparent to both bit rate and modulation format. The advantage of this scheme consists in the ability of bandwidth, and the multicasting channel scalable due to dispersion flattening of PCF is used. Furthermore, it is all optical fiber, compact and robust, which makes it more competitive as well as easily accessible for the uses in practical optical communication systems.
2011, 60 (7): 074221.
doi: 10.7498/aps.60.074221
Abstract +
A new earthquake detection demodulation system for monitoring several points and several parameters at the same time is proposed by using the linear sideband of super-fluorescent fiber source as an edge filter. The sensitivity of whole demodulation system is determined by the detecting sensitivity of source light. Through the optimization of light, the slope of light linear part is improved greatly. According to the rising and the falling of light, the system is divided into two parts each with four channels. Through the stimulation experiments of all the channels, the static wavelength sensitivities of the two parts are 887.5 mV/nm and -971.7 mV/nm, and their stain resolutions reseach 0.95με and 0.86με respectively. This demodulation system has high sensitivity, good stability, quick demodulation speed, etc. It is the most important is that it can realize real-time detection for several points and several parameters at the same time.
2011, 60 (7): 074222.
doi: 10.7498/aps.60.074222
Abstract +
A novel terahertz transmission optical fiber with low absorption loss and high birefringence is proposed. The proposed fiber is composed of alternate teflon and air-hole layers to form a two-fold symmetry configuration. Using the finite element method, the dependences of absorption loss and birefringence on the configuration parameter of the fiber are presented. The numerical results show that the birefringence can reach as large as 0.08. In addition, when the mode absorption loss is less than 20 dB/m,the birefringence can still be larger than 0.02.
2011, 60 (7): 074223.
doi: 10.7498/aps.60.074223
Abstract +
We propose a double-channel narrowband filter based on anomalous large Goos-Hänchen shift reflected from a symmetrical metal-cladding optical waveguide. We demonstrate that two filtering peaks are 859.604nm and 859.688nm respectively. The 3 dB bandwidth is found to be 0.036 nm with an extinction ratio of 15.3dB at a light wavelength of 859.60nm. The filtering peaks can be tuned by choosing an appropriate incident angle and a aperture position.
2011, 60 (7): 074224.
doi: 10.7498/aps.60.074224
Abstract +
In this paper, the optical stopping effect of thin film waveguide with doping As2S8 and As2S8 is studied. Based on this, the mechanisms of formation and transfer of abnormal electron configuration are discussed, and the dynamic models of optical stopping and reversion process are proposed. The numerical analysis results are in good agreement with the experimental data, so the phenomenon in experiment can be predicted by this model, which implies that this model holds the basic features and the essence of the optical stopping effect.
2011, 60 (7): 074225.
doi: 10.7498/aps.60.074225
Abstract +
Resonant tunneling of light through double-well structure is investigated by the R-matrix algorithm. We find that the resonant frequency can be controlled by the coupling strength between the two wells. The transmission probability shows the 2-fold peak-splitting in a symmetric double-well system, and the distortion of the resonance peak-splitting in an asymmetric double-well system. The distortion of the resonance peak-splitting by alternately placing Right-hand and Left-hend materials in the two wells is different from that resulted from the asymmetry of well-width. Moreover the distortion of the resonance peak-splitting is analyzed by means of the one-dimensional photonic QW system. The former can be understood by the destructive interference, which may lead to the complete cancellation of resonant mode, while the latter is due to the relative sifts of eigenmodes in the two wells.
2011, 60 (7): 074301.
doi: 10.7498/aps.60.074301
Abstract +
A stochastic resonance mechanism of improving wideband and low frequency vibration energy harvesting of piezoelectric cantilever beam (PCB) is studied using the system nonlinearity. By adding a pair of rectangular permanent magnets, the structure of standard piezoelectric cantilever beam is improved. Results reveal that the improved PCB may be a bistable system under a nonlinear magnetic force and an appropriate distance between two magnets. Then a stochastic resonance phenomenon will happen by the input of wideband and low frequency stochastic vibrations. Under the condition of stochastic resonance, the electrical output of the improved PCB increases greatly. So the proposed method will be useful for extending the resonant band and improving the electrical output of a standard PCB.
2011, 60 (7): 074302.
doi: 10.7498/aps.60.074302
Abstract +
In order to overcome the deficiency of robustness of low altitude passive acoustic target recognition, the manifold learning is applied to the feature extraction of acoustic targets. Based on the classical algorithm of manifold learning, in the paper we study and discuss the low-dimensional manifold in the frequency-domain of acoustic signals. This method is used to solve the target recognition problem with two data sets to verify its effectiveness, after which the performance is analyzed. The result indicates that the manifold learning can discover the intrinsic feature and increase the accuracy and the robustness of low altitude passive acoustic target recognition system.
2011, 60 (7): 074303.
doi: 10.7498/aps.60.074303
Abstract +
We propose a three-dimensional (3D) microwave-induced thermo-acoustic imaging technique for early-stage breast cancer detection, which offers a high imaging contrast and high spatial resolution. The robust Capon beam-forming (RCB) algorithm, which is a data-adaptive approach, is considered for signal processing and image formation. The finite-difference time-domain (FDTD) method is applied to electromagnetic simulation as well as acoustic simulation. The feasibility of this technique is demonstrated via a numerical example based on a 3D breast model.
2011, 60 (7): 074501.
doi: 10.7498/aps.60.074501
Abstract +
In this paper, the segregation patterns of size-type binary granular systems with different damp coefficients in a rotating horizontal drum are simulated by the discrete element model. The process and the mechanism of segregation are studied, and the effects of damping on segregation model of size-type binary granular system in a rotating horizontal drum are discussed. The simulation results show that the segregation process and the flow pattern of granulae in a flowing layer depend strongly on damping. According to the simulation results we predict that the radial segregation patterns that form in a size-type binary granula system in a thin rotating horizontal drum will be the sun pattern when the damp coefficients is in a middle value range, otherwise, the moon pattern will appear.
2011, 60 (7): 074601.
doi: 10.7498/aps.60.074601
Abstract +
The influences of inertia, elastic-plastic effect and initial void size are studied on the damage evolution in spallation of ductile metals under planar impact loading by using the hollow spheroid model. Numerical analysis indicates that inertia, elastic-plastic effect and initial void size each have a significant influence. Influence of Initial damage or initial void size on spallation damage cannot be neglected. In this paper we attempt to develop a method to analyse initial void size due to its importance on spallation damage.
2011, 60 (7): 074701.
doi: 10.7498/aps.60.074701
Abstract +
Three infinite sequences of analytical solution numbers for partially reflected n-chromatic n-directional short-crested waves by a vertical wall breakwater are found, which are significant for water wave theory and engineering application.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2011, 60 (7): 075201.
doi: 10.7498/aps.60.075201
Abstract +
The broadening mechanisms are investigated for the energy spectrum of ions accelerated by electrostatic shocks in overdense plasmas irradiated by intense ultra-short laser pulses. It is found that the width of the shock-accelerated ion spectrum could be ineluctably broadened by three mechanisms, which are the continuously decreasing speed of the shock front due to the energy dissipation into ions, the collisions between the particles, and the further acceleration by the sheath field at the rear of target where when energetic ions arrive. Other effects, such as effect of driving laser pulse duration, are also studied.
2011, 60 (7): 075202.
doi: 10.7498/aps.60.075202
Abstract +
Based on the symmetry adapted tight-binding model, the electronic energy band structures of single wall carbon nanotubes are calculated by considering the spin-orbit coupling interaction. The energy gaps at the Dirac point for the armchair nanotubes are formed due to the spin-orbit coupling interaction and the curvature effect. For the zigzag and chiral carbon nanotubes,the energy band splittings for the lowest unoccupied states and the highest occupied states are also formed by the spin-orbit coupling interaction. The energy splittings are not only dependedent on the diameter and the chiral angle of the carbon nanotubes, but also a symmetric with respect to the Fermi energy level. According to the chiral index (n, m), different tube behaviors are grouped into three families. The numeral results are in good agreement with the experimental results.
2011, 60 (7): 075203.
doi: 10.7498/aps.60.075203
Abstract +
The interaction between laser and hohlraum can generate a large number of suprathermal electrons which obey the Maxwell distribution. The transport properties of the hot electrons and the suprathermal electrons in the hohlraum are investigated by using the Monte Carlo simulation program. In this paper we give the variations of hard X-ray spectrum with hot electrons and suprathermal electrons temperature and fraction, hohlraum size, and hohlraum thickness, and the determinant of efficiency of hard X-ray is obtained. The combination of Monte Carlo program and hot electrons induced by hard X-ray demonstrates the accuracy of the initial hot electrons.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Physical simulation of homogeneous Zn-Bi monotectic alloy prepared by electric-magnet compound field
2011, 60 (7): 076101.
doi: 10.7498/aps.60.076101
Abstract +
Through physical simulation, we study the influence mechanism of electromagnetic field on the solidification structure of homogeneous Zn-Bi monotectic alloy, the transformation rule of the diameter of molten secondary phase under the compound field, and the process of the shattering of the layered structure into matrix by the Lorentz force. The results show that the diameter of the secondary drop decreases with AC current density and magnetic field increasing. The influence of AC frequency has an optimal value from which the deviation can weaken the suppression of diameter, which accords with the experimental result. The layered metal liquid can be uniformly mixed under the action of electromagnetio field. The above effects can effectively release segregation of the second phase of monotectic alloy. The simulation results show the main factors of preparing the homogeneous monotectic alloy in an electromagnetic field intuitively.
2011, 60 (7): 076102.
doi: 10.7498/aps.60.076102
Abstract +
In this paper, we use the Lennard-Jones atom-atom potential to describe the interaction between C60 molecules in (C60)N clusters. Considering the orientation of each C60 molecule,we have calculated the energies of the closed-shell (C60)N(Ni.e., IH,fcc,hcp,DH and SC. Our results show that the IH structure is the most stable one in a small size (NNN60 )N clusters decrease monotonically for the four typical structures of IH, fcc, hcp and DH,but the average molecular energy changes irregularly for the SC structure which undergoes structural reconstruction,implying that the SC (C60)N clusters are unstable in the size range investigated,and the lowest-energy structures of those (C60)N clusters are still far from their crystal forms.
2011, 60 (7): 076103.
doi: 10.7498/aps.60.076103
Abstract +
Ge is deposited on an ultrathin SiO2 layer obtained chemically at room temperature, followed by annealing process. High density and uniform Ge quantum dots, rather than superdomes in traditional treatment, are obtained. Growth mechanism is suggested to explain the unusual microstructure dependence on annealing temperature. Raman spectrum is used to investigate the strain. Two peaks are found to be around 500 nm and 1350 nm respectively from the photoluminescence characterization.
2011, 60 (7): 076104.
doi: 10.7498/aps.60.076104
Abstract +
GaN-based LED wafers with nano-folding InGaN/GaN multiple quantum wells (MQWs) are grown on n-GaN nanopillar array templates which are fabricated using self assembled Ni nanodots as etching mask. Photoluminescence (PL) spectra of the wafer show uniform light emission wavelength over the whole area of it. No blue shift of the main peak is observed in the electroluminescence (EL) spectra of the LED devices fabricated with the wafer as the injection current increases from 10 mA to 80 mA. This can be ascribed to the reduced quantum confinement Stark effect (QCSE) and the resulting less band gap tilted by strain relaxation in the nano-folded MQWs. The device shows an excellent rectifying behavior with a forward voltage of 4.6 V under 20 mA injection current.
2011, 60 (7): 076201.
doi: 10.7498/aps.60.076201
Abstract +
The elastic constants of α-ScH x (x=0, 1/4, 1/8, 1/32) and α-ScHe x (x=0, 1/4, 1/8, 1/32) are studied by the first-principles method. It is found that the addition of hydrogen to the scandium has an effect greatly different from the addition of helium to this rare-earth metal. The elastic constants of the α-ScH x system almost increase with hydrogen concentration increasing, which is in agreement with the experimental observation. Whereas, in the case of α-ScHe x system, the elastic constants almost decrease with the increase of helium concentration.
2011, 60 (7): 076202.
doi: 10.7498/aps.60.076202
Abstract +
The explosion characteristic of propylene oxide/nano-, micro-alumium component were comparably investigated under the changed induced incident shock waves. The ignition delay times of two explosion systems were determined by the monochromater synchronous test technology. The structure, morphology, surface oxide layer of the products were analyized by scanning electron microscopy(SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the products of nano-Al are the spongy-structure, need-structure and fiber-structure, the morphology of the products of microsize aluminum is mainly in spherical structure. The different phases of alumina(α,β,γ,ε,δ) in compress section , ignition section, combustion section, explosion section, propagation section, and compressed products section was revealed by XRD data. It shows that the reaction in nano-Al reaction system is more violent than that in micro-Al one and the decreasing temperature align the axial cause the different phases of alimina . XPS spectrum show that the oxide layers on the surface of nano-alumina is about 35nm, alumina is almost is 92%; while the oxide layer on the surface of micro-alumina is 30nm, alumina is merely 65%. The experimental results that indicated the existing two different ignition mechanisms and combustion mechanism will be useful to the addition of energy material.
2011, 60 (7): 076501.
doi: 10.7498/aps.60.076501
Abstract +
We investigate the phase transition pressure, elastic and thermodynamic properties of CaPo by the first-principles plane wave pseudo-potential method in the framework of density functional theory. By the isoenthalpy principle, the phase transition pressure from B1 structure to B2 structure is found to be about 22.8GPa. From the high pressure elastic constants obtained, we find that the B1 structure CaPo is unstable when the applied pressure is larger than 20 GPa, which is in good agreement with the results from the isoenthalpy principle. Moreover, the thermodynamic properties of pressure and temperature of B1 structure CaPo(including specific heat capacity, the Debye temperature, thermal expansion and Grüneisen parameter) are also successfully obtained.
2011, 60 (7): 076801.
doi: 10.7498/aps.60.076801
Abstract +
We investigate the rheological properties of silica nanoparticle monolayers at the air-water interface by using two orthogonal Wilhelmy plates in the Langmuir trough and Brewster angle microscopy (BAM). Remarkable anisotropic effect of surface pressure is observed when the layers are fully covered by particles. The pressure anisotropy is the most prominent for the layer of particles with 34%SiOH on their surface. The elastic compression and the shear moduli present the maxima at intermediate hydrophobicity. The dependence of rheological properties on particle hydrophobicity is closely related to the foamability and the stability of the foams made from these particle dispersions. A shape memory effect is observed in the condensed layer of the most hydrophobic particle(20%SiOH), which may result from the irreversible organization of particles and the particle arrangement driven by the inner stress stored in the layer.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2011, 60 (7): 077101.
doi: 10.7498/aps.60.077101
Abstract +
The electronic structures of pure, Zn doped, and Zn, O codoped wurtzite AlN are calculated by using first-principles ultrasoft pseudopotential approach to the plane wave based on the density functional theory, and the crystal structure, the energy bands, the electronic density of states, the differential charge distribution and the charge population. The results show that in the Zn, O codoped method, the introduction of active donator, atom O, causes acceptor energy level to shift toward low energy, thereby forming the energy levels of shallow acceptor. At the same time, the energy band widens and nonlocal characteristics become significant, thereby increasing the doping concentration of Zn atoms and the stability of the system. Zn, O codoping is more conducible to obtaining the p-type AlN.
2011, 60 (7): 077102.
doi: 10.7498/aps.60.077102
Abstract +
The capacitance-voltage characteristics and the variations of threshold voltage of strained Si1-xGe x channel p-MOSFET with Ge fraction are investigated via two-dimansional numerical simulation. The results indicate that with the increase of Ge fraction, the subthreshold current increases remarkably, and that the gate capacitance changes significantly when the device is in inversion, moreover, the Ge fraction dependence of the variation of threshold voltage is linear. Combining the change of the Si1-xGex channel length with the relevant physical model, the mobility of holes in channel is demonstrated to be inversely proportional to the derivative of the total resistances with respect to the channel length in a weak applied field.
2011, 60 (7): 077103.
doi: 10.7498/aps.60.077103
Abstract +
First-principle calculations are carried out to investigate the energies and the electronic structures of Mg2Ni alloy and its high/low temperature hydrides. Results show that strong bonding interaction between Mg and Ni atoms exists in the Mg2Ni alloy. With H inserted, the charge transfer occurs from Mg to Ni-3d, which gives rise to a band gap between Ni-3d and Ni-4p orbitals. The interaction between Mg and Ni in LT/HT-Mg2NiH4 hydrides is weakened due to the covalent bonding between Ni-4s and H-1s. Therefore, it neads more energy to remove H atoms from LT-Mg2NiH4 than from HT-Mg2NiH4, indicating that HT-Mg2NiH4 is more suitable for de-hydrogenation reaction while the LT-Mg2NiH4 is suitable for hydrogenation reaction.
2011, 60 (7): 077104.
doi: 10.7498/aps.60.077104
Abstract +
According to the first principles methods, we theoretically study the mechanical properties of He doped AlΣ3 grain boundary (GB). Our results show that He has the lowest formation energy 2.942 eV in GB and low segregation energy 0.085 eV from bulk to GB. Under the extending tensile, the clean GB has a theoretical strength of 8.95 GPa, and the crack appears first from the GB. While, after the He doping, the tensile strength reduces to 7.14 GPa, and one flat effect is present in the curve of strain-stress. By analyzing the variation of the bond-length and the charge distribution, we believe that He-induced reduction of tensile strength is probably ascribed to the weaker interaction between He and Al atoms as well as the weakening Al-Al bonds, owing to the charge screening by full-shell electron structure of He.
2011, 60 (7): 077105.
doi: 10.7498/aps.60.077105
Abstract +
In this paper, the effect of uniaxial stress along [110] direction on the energy-band structure parameters of (001)-bulk Si is discussed, thereby we investigate the equilibrium carrier concentration and the expressions of effective density of state (DOS) in conduction and valence band, which contain explicit physical significance. The model of intrinsic carrier concentration is proposed by combining the expressions of DOS and bandgap. The pro- posed method in this paper is also applicable to modeling the intrinsic carrier concentration under the action of uniaxial stress along an arbitrary direction, and provides some references for design, mode- ling and simulation of similar uniaxial strained Si devices.
2011, 60 (7): 077106.
doi: 10.7498/aps.60.077106
Abstract +
In this paper, based on the two-dimensional (2D) Possion's equation, an analytical model of threshold voltage, which is applied to a sub-100nm strained-Si/SiGe nMOSFET, is pro- posed. The secondary effects induced by reducing size such as short-channel effects, quantum mechanical effects are also taken into consideration in order to ensure the accuracy of the model. Then the evidence for the validity of our model is derived from the comparison between analytical results and the simulation data from the 2D device simulator ISE. Finally, the influence of conventional arts in sub-100 nm device fabrication on threshold voltage is also discussed. The proposed model can also be easily used for reasonable analysis and design of sub-100nm strained-Si/SiGe nMOSFET.
2011, 60 (7): 077107.
doi: 10.7498/aps.60.077107
Abstract +
The effects of operating temperature and the interfacial thermal resistance on device are researched by using a two-dimensional numerical simulator. A comparison between the simulated results and the experiment data demonstrates that hot electrons make a significant contribution to the negative differential output conductance which will increase with the increase of the work temperature under low drain voltage, and under upper drain voltage, the self-heating effect is an important factor to the current collapse which will become more serious with the work temperature and interfacial thermal resistance inereasing.
2011, 60 (7): 077201.
doi: 10.7498/aps.60.077201
Abstract +
For the Cantor-styled artificial DNA sequence constructed by following the inflation rule A→ABA and B→BBB, using the one-dimensional random walk model and Hurst analysis, we calculate numerically the displacement and its standard deviation, the rescaled range function and the Hurst exponent. The results are compared with those of one-dimensional random binary sequence. We show that Cantor-styled DNA sequence presents correlated behavior, scaling invariability, and self-similarity. In addition, according to the renormalization-group method, we study the charge transfer properties of Cantor-styled DNA sequence, including localization length, charge transmission coefficient and Lyapunov exponent. We find that some resonant peaks can survive in relatively long Cantor-styled DNA sequences, which also implies that there are long-range correlations in Cantor-styled DNA sequences.
2011, 60 (7): 077202.
doi: 10.7498/aps.60.077202
Abstract +
The evolution-operator approach is applied to studying photon-electron pumping effects on a quantum dot connected to two magnetic leads in the presence of both via-dot and over-dot tunneling channels. It is found that a microwave field applied to the quantum dot may give rise to charge and spin pumpings at zero-bias voltage for asymmetric magnetic junctions. More interestingly, a pure spin current can be pumped for symmetric magnetic junctions in the anti-parallel magnetization configuration, providing a new scheme for the design of spin batteries.
2011, 60 (7): 077203.
doi: 10.7498/aps.60.077203
Abstract +
In spintronics, general spin injection is achieved by the superlattice, spin valve, tunnel junction, other typical method of spin injection is to dilute magnetic semiconductor such as: GaMnAs. In this paper, spin Fe particles are injected into the GaAs matrix by using the magnetron sputtering to form the granular film (GaAs)19Fe81, in which saturated Hall resistivity ρxys is shown to be 15 μΩ·cm at room temperature, which is about 2 orders larger than that of pure Fe. So the spin injection is successfully realized.
2011, 60 (7): 077204.
doi: 10.7498/aps.60.077204
Abstract +
A new model pseudopotential is presented following Behari's model and used in the calculation of the electrical resistivity of liquid Pb, with the help of experimental structure factor and hard-sphere structure factor. The results are in good agreement with the experimental data. The validity of the model pseudopotential and errors of calculation are discussed.
2011, 60 (7): 077205.
doi: 10.7498/aps.60.077205
Abstract +
According to the model of ionized impurity scattering, acoustic phonon intravalley scattering and optical phonon intervalley scattering, the dependences of electron mobility of strained Si/(001)Si1-xGex with different germanium constituents on impurity concentration are studied based on Subband occupation by solving Boltzmann equation. The results show that electrons almost totally occupy the Δ2 valley when germanium constituent is up to 0.2, and the mobility with germanium constituent 0.4 is 64% higher than that of the unstrained silicon at low impurity concentration; and vertical channel is not so good for tensile stained Si devices. The model can also be used to calculate the electron mobility of other crystal face with an arbitrarily orientation if the parameters are correctly chosen, so the model offers some useful foundation for strained silicon devices and circuits.
2011, 60 (7): 077206.
doi: 10.7498/aps.60.077206
Abstract +
The solar cells based on different solvent blends of poly(3-hexylthiophene) (P3HT) and -phenyl C61-butyric acid methyl ester (PCBM) as acceptors are fabricated. Annealing treatment effects on the performances of solar cells based on different solvent blend systems are analyzed by UV-vis absorption spectroscopy and photoluminescence (PL) spectroscopy. The results show that high boiling point solvent leads to an enhanced P3HT ordering in the P3HT:PCBM blend system, and causes an increased incident light absorption and PL spectrum, which contributes to the enhancement of device performance. After 130 ℃ thermal annealing, The UV-Vis absorption, PL spectrum and the performance of the device are further enhanced. The performance of the device prepared with low boiling point chloroform solvent increases obviously after thermal annealing. The solar cell prepared with chlorobenzene solvent after 130 ℃ thermal annealing achieves an open circuit voltage(Voc)of 0.57 V, short circuit current density(Isc)of 8.74 mA/cm2, fill factor (FF ) of 59.2% and power conversion efficiency (PCE) of 2.95% under 100 mW/cm2 air-mass 1.5 solar simulator illumination.
2011, 60 (7): 077207.
doi: 10.7498/aps.60.077207
Abstract +
Polymer solar cell with excellent performance is currently composed of the blend bulk-heterojunction formed by conjugated polymer as donor material and fullerene as acceptor material, among which P3HT and PCBM are most widely used. For the photoelectric thin film device, the optical and the electric characteristics of the active layer can affect the device performance directly. The optical constants of the active layer are obtained primarily based on the Forouhi-Bloomer model. According to the Fresnel coefficient matrix, the numbers of photons absorbed by different active layer thick devices are investigated by calculating electromagnetic field distributions inside this structure. To make a specific analysis of the thickness effect on dissociation probability of bound pairs without external excitation, the model of Onsager-Braun is adopted. Theoretical analysis shows that the active layer with a thickness of 100 nm can maximize photon absorption by the device without reducing the dissociation probability of excitons obviously. As a result, an optimal thickness of the active layer is about 100 nm, which is confirmed by the theoretical and the experimental results from the device with the structure of ITO/PEDOT/ P3HT:PC60BM /LiF/Al.
2011, 60 (7): 077208.
doi: 10.7498/aps.60.077208
Abstract +
Charge coupled device (CCD) is a key component in a remote sensing system. In order to obtain high signal-to-noise ratio (SNR) and dynamic range in low illumination and quantization circumstance, first, according to CCD architecture and noise physical characteristics, relationship between analog gain quantization step and CCD SNR is proposed; next, integrating sphere calibration system is established, shot noise, photo response nonuniformity and noise floor model are also built, and the next relationship between analog gain and SNR in low illumination condition is analyzed thoroughly; finally, the practical photographing system is built, and remote images in different gain parameters are acquired. Theoretical analysis, experimental calibration, and practical images all indicate that when analog gain is increased by one to two times, the SNR is improved greatly and dynamic range is acceptable.
2011, 60 (7): 077209.
doi: 10.7498/aps.60.077209
Abstract +
The effects of nitrogen substitutional doping in Stone-Wales (SW) defect on the electronic structure and the optical property of single-walled nanotube are simulated by using the density functional theory based on the first-principles. It is found that the system energy reduces and binding becomes stabler, and the nitrogen in SW produces a semi-full band near the Fermi level in which the electron effective mass varies with the changing of the position of nitrogen. The absorption and the reflectivity weakened obviously and absorption and reflection peak are both redshifted in the lower energy region. There is a distinct peak at the energy less than 11eV.The results are discussed theoretically. The nitrogen doping and SW defect of carbon nanotubes are expected to provide a theoretical basis for the photoelectric material applications.
2011, 60 (7): 077301.
doi: 10.7498/aps.60.077301
Abstract +
The binding energies of the charged excitons(negative X- and positive X+ excitons) are calculated using the finite-difference method within the quasi-one-dimensional effective potential model. The effects due to the magnetic filed and quantum confinements on the binding energy are analyzed, and the following results are obtained:(1) relative electron and hole harmonic oscillator confinement each have a strong effect on the stablity of charged excitons, the binding energy of X+ is not always larger than that of X-, e.g., due to the increase of the hole harmonic oscillator length, leading to the crossing of X+ and X- lines as recently observed experimentally;(2) the magnetic field leads to an increase of the binding energy, and the magnetic field dependence of the binding energy is related to the harmonic oscillator length.
2011, 60 (7): 077302.
doi: 10.7498/aps.60.077302
Abstract +
With the decrease of the feature size of MOS based circuits, the power consumption of micro-processors has dramatically increased during the last decade, which now mainly restricts the development of the micro-processors.Single-electronic transistors (SETs) are considered as the attractive candidates for post-COMS VLSI due to their ultra-small size and low power consumption.Based on Orthodox theory,the model of conductance is investigated in detail.The conductance of SET with single island is in damped oscillation with a period of T(Vds), and it is close to an intrisical value with the increase of |Vds|. This characteristic of Gds is affected by temperature, parameters of junctions, and so on. The results show that the analysis of conductance is very useful for the very large scale integration of SET devices.
2011, 60 (7): 077303.
doi: 10.7498/aps.60.077303
Abstract +
The structural stability and the electronic field emission properties of cone-capped carbon nanotubes have been deeply analyzed by the density functional theory. The results show that their structurs are much more stable than those of carbon nanocones and carbon nanotubes sealed with a C30 hemisphere, and their electronic field emission properties are closely related to the configuration of cone apex and the magnitude of cone angle. Meanwhile, the combination property of cone1@(6,6) with a ridge-shaped tip and 38.9° cone angle is optimal. When it is used as a field emission source the field emission current density and the lifetime of device will be remarkably increased.
2011, 60 (7): 077304.
doi: 10.7498/aps.60.077304
Abstract +
According to the macroscopic-long Ag nanowire bundle which is prepared by the solid-state ionics method, we fabricate a macroscopic-long Ag2S nanowire bundle using a gas-solid reaction. Their morphologies and components are characterized by the SEM, TEM, EDS and XPS. Au paints as electrodes are coated on both ends of a cm-long Ag2S nanowire bundle and then connected to an external circuit. The transport properties of the Ag2S nanowire bundle are studied at different temperatures or under the light irradiation of different wavelengths. Without light irradiation, as temperature T increases from 144 K to 380 K, the dark conductance increases nonlinearly with T. At room temperature, the significant positive photoconductivity induced by the 532 nm or 1064 nm laser is observed. These results demonstrate that Ag2S nanowire is a kind of ideal material for making the nanoscale temperature and photoelectric sensors.
2011, 60 (7): 077305.
doi: 10.7498/aps.60.077305
Abstract +
Injector-like nanostructure samples of ZnO, which are synthesized by hydrothermal method, are experimentally investigated for the field emission (FE) properties, especially the current density varying with the intensity of the applied electric field; and the fascinating two-stage behavior of electric field enhancement factor (β) is observed. The good performance and the two-stage behavior of the β are explained based on the combination of the intensive electric field effect in semiconductor and its influence on the Fermi energy level with the effective series connection circuit of FE detection systems. Finally, the previous analysis conclusion is well experimentally demonstrated by the FE properties and PL spectra of Znic oxide nanostrucutres fabricated by electrochemically deposition and vapor phase transmitting methods, separately.
2011, 60 (7): 077401.
doi: 10.7498/aps.60.077401
Abstract +
By measuring the levitation forces between a single domain GdBCO bulk superconductor and assembled bar magnets(ABM) in different configurations at liquid nitrogen temperature, the effects of ABM configurations on the levitation force of single domain GdBCO bulk superconductor are investigated. The maximum levitation force is obtained at the same vertical gap distance Z=5 mm between the superconductor and the ABM for configurations with different lateral gap distance(D)between the magnets of the ABM. It is found that 1) for the ABM consisting of 3 bar magnet, the levitation force of the GdBCO bulk decreases from 22.8N to 9.7N with the D value increasing from 0 to 30 mm, when the magnetic pole N of the middle magnet is pointed upwards and the directions of magnetic pole N of two side magnets are pointed to the middle magnet in horizontal direction; the levitation force of the GdBCO bulk increases first from 9.2N to 13.9N and then decreases to10.4 N with D value increasing from 0 to 30mm, if the magnetic pole N of the middle magnet is pointed upwards and the directions of magnetic pole N of two side magnets are pointed downwards;2)for the ABM consisting of 2 bar magnets, the levitation force of the GdBCO bulk decreases from 11.2N to 1.2N with D value increasing from 0 to 30mm, when the directions of magnetic pole N of two side magnets are pointed upwards; the levitation force of the GdBCO bulk increases first from 6.0N to 6.8N and then decreases to 2.9N with D value increasing from 0 to 30mm, if the directions of magnetic pole N of two magnets are anti-parallel in horizontal direction; 3)for the ABM consisting of only 1 bar magnets, D≡0, and the levitation force of the GdBCO bulk is about 9.5N. The results indicate that the magnet configuration and its detailed parameters of ABM are very important for improving the levitation force of a superconductor and helpful for designing and application based on the superconducting magnetic levitation system.
2011, 60 (7): 077402.
doi: 10.7498/aps.60.077402
Abstract +
Using the first principles calculations based on density functional theory, we study the electronic band structure, the phonon dispersion, and the phonon density of states of the iron-based superconductor LiFeAs. The obtained ground state of LiFeAs is of the fluctuated antiferromagnetic order and partial structural relaxation. A comparson of phonon densities of states between in the striped antiferromagnetic ordering and in the nonmagnetic state indicates that the anisotropic spin interactions result in phonon softening of Fe and As atomic vibrations, thereby enhancing the electron-phonon coupling. As a result, the spin-phonon interaction plas an important role in the unconventional superconductivity.
2011, 60 (7): 077501.
doi: 10.7498/aps.60.077501
Abstract +
The structure, the martensitic transformation and the magnetic properties of ferromagnetic shape memory alloy Mn2NiGa aged at low temperature are investigated. The lattice distortion and the internal stress are generated in the samples due to the fine precipitation generated during the aging treatment. When the precipitation concentration exceeds the tolerance limit of the parent phase lattice, it causes the martensitic transformation temperature to increase obviously, and thus the parent phase transforms to martensitic phase with a large coercivity up to 900 Oe. Because of the existence of internal stress, the reverse martensitic transformation is shifted toward high temperature up to 485 K. By extrapolating the experimental data, the Curie temperature of martensite is estimated at 530 K. The internal stress disappears and the martensite turns to be of the parent phase due to the coarsening of the precipitation at higher temperature. Two coarsening threshold temperatures are found to be 423 K and 485 K which are the temperature sensitive and the aging time sensitive, respectively.
2011, 60 (7): 077502.
doi: 10.7498/aps.60.077502
Abstract +
Recently, magnonic crystals which are the magnetic counterparts of photonic crystals or phononic crystals are growing into a hot area of research. In this paper, a plane-wave expansion method in the field of magnonic crystals is proposed. By using this method, band structures of two-dimensional magnonic crystals composed of ferromagnetic materials Fe and EuO are calculated. The numerical results show that the spin-wave gaps will be generated under a definite filling fraction ratio, and the effect of exchange field on the band structure is larger than that of other field in the effective field.
2011, 60 (7): 077503.
doi: 10.7498/aps.60.077503
Abstract +
The transmission of electromagnetic wave at oblique incidence through an antiferromagnetic/nonmagnetic multilayer with a Fibonacci quasi-periodic sequence is calculated by using the transfer matrix approach. Numerical simulations show that many transmission peaks appear in the band gap. Also more and more transmission peak appear as the number of layers in the sequence increases. In addition, the dependence of transmission peak on dielectric constant of nonmagnetic layer, incident angle and wave polarization is also discussed.
2011, 60 (7): 077504.
doi: 10.7498/aps.60.077504
Abstract +
β-Mn2V2O7 powder is successefully prepared at 200—220℃ under pH=6—9 by a novel hydrothermal synthesis technology. The phase, the morphology and the microstructure of the prepared sample are investigated by XRD, SEM, EDS, TEM, HRTEM and SAED. The results show that β-Mn2V2O7 powder has a thortveitite structure with monoclinic system. The powder synthesized at 200 ℃ under pH=6—7 has a rod morphology, while that at 200 ℃ under pH=8—9 has coexistent petal and rod morphologies. HRTEM and SAED measurements indicate that β-Mn2V2O7 grows anisotropically and has crystalline integrality. Magnetic properties are measured by superconducting quantum interference device (SQUID) in a temperature range of 2—300 K under a magnetic field of 1T. The magnetic measurement results indicate that β-Mn2V2O7 undergoes a transition from antiferromagnetic to paramagnetic with a Néel temperature of 24 K. Above 100K, the inverse susceptibility is fitted well to the Curie-Weiss law and paramagnetic Weiss temperature θ=-24.6 K, and the Curie constant C=9.846 K emu mol-f.u.-1 can be caculated, which means that there exists an obvious antiferromagnetic interaction in thortveitite-type β-Mn2V2O7, the antiferromagnetic behavior is caused by the superchange of Mn2+-O2--Mn2+.
2011, 60 (7): 077505.
doi: 10.7498/aps.60.077505
Abstract +
The Co and/or Sn doped ZnO thin films are deposited on the glass substrates by the sol-gel method. The effects of Co and/or Sn doping on surface morphologies and mircrostructures of ZnO films are investigated by metallurgical microscope and X-ray diffraction (XRD). The XRD results indicate that all the ZnO samples show preferential orientation along the (002) direction, and that the Sn-doped ZnO thin film exhibits the best c-axis orientation and largest grain size. XPS results reveal that Co and Sn elements exist as Co2+ and Sn4+, indicating that Co and Sn ions have entered into the ZnO crystal lattices successfully. Strong blue double emission and weak green emission are observed in the PL spectra of all the samples. In addition, the ultraviolet peaks appear in the undoped and the Co-doped ZnO thin films. Our results reveal that the Co and/or Sn doping can tune the band gap, meanwhile, such a doping can also affect oxygen dislocation, zinc oxygen and zinc interstial defect concentrations. Finally, the possible luminescence mechanisms of Co and/or Sn doped ZnO films are discussed.
2011, 60 (7): 077701.
doi: 10.7498/aps.60.077701
Abstract +
Six-layer Ba0.6Sr0.4TiO3 (BST) films are prepared by an improved sol-gel method. The effects of various preheating methods on morphology and dielectric properties are studied. XRD results reveal that all BST films preferentially grow along the (110) direction and have cubic perovskite structures, and that preheating can obviously enhance crystallization. XPS results show that the preheating can also decrease surface non-perovskite structure and cause perovskite structure to increase markedly. AFM results display that as the preheating number increases, BST films show significant improvement on morphology with surface roughness reducing. The dielectric property measurement exhibits that tunability is remarkably increased with the increase of preheating number. BST film with all layers preheated shows that its tunability exceeds 55% at 20V bias voltage, while BST film with odd number layers preheated presents a moderate capacitance, lower dielectric loss, approximately 50% tunability at 20V bias voltage and significant increase in figure of merit (FOM) with the bias voltage. The excellent combination of dielectric properties can satisfy the application demand of microwave tunable devices. Also, the relevant mechanism of high tunability is discussed.
2011, 60 (7): 077702.
doi: 10.7498/aps.60.077702
Abstract +
A modified Landau-Devonshire thermodynamic model is presented, with the contributions of substrate stress, domain wall motion and domain structure transition taken into account. The hysteresis loops of PbZr0.4Ti0.6O3(PZT) films, which are deposited on different substrates, containing nano-scale grain is calculated, and the thickness and grain size dependences of coercive field, remnant polarization and relative permittivity are researched. The results demonstrate that the grain size is dependent on coercive field and relative permittivity as shown in paraboliclike curve, that the pressure stress of substrate enhances the coercive field and remnant polarization, but reduces the relative permittivity, and that the coercive field increases slowly first with the thickness of film, then increases sharply between 200 nm and 310 nm of the thickness, and slowly again after 310 nm. This result is due to the thickness dependence of relative permittivity.
2011, 60 (7): 077801.
doi: 10.7498/aps.60.077801
Abstract +
The coherent anti-Stokes Raman scattering (CARS) and coherent Stokes Raman scattering (CSRS) signals of vibration mode at 397cm-1 of CS2 liquid are manipulated by using two chirped circularly polarized femtosecond pulses in non-collinear excitation geometry. Along the phase matching direction intensity distributions, polarizations and wavelengths of CARS and CSRS signals vary regularly as the polarizations of the laser beams are changed. The intensity distributions of CARS and CSRS reflect the scattering cross sections of the stimulated raman scattering of the sample under different circularly polarizations. The polarizations of CARS and CSRS follow the conservation law of the angular momentum of the excitations. The frequency shifts of CARS and CSRS demonstrate the transitions between the rotational energy levels of CS2. The above information is helpful for understanding the mechanism and the behaviors of the CARS and CSRS of CS2 as well as other molecules.
2011, 60 (7): 077802.
doi: 10.7498/aps.60.077802
Abstract +
Since the visible quantum cutting in Eu3+–Gd3+ material was reported, the importance, the application, and the significance of the quantum cutting phenomenon have been widely recognized.The rate equations which describe the luminescence dynamic processes for different concentrations of (ErxLa1-xP5O14) noncrystal are established in this paper. The coefficients exp{hc k/kT} is introduced in to the calculation of anti-Stokes energy transfer rate to distinguish Stokes energy transfer.All dynamic processes have been simulated separately with and without considering this coefficient for the energy transfer rate of Er0.01La0.99P5O14,Er0.1La0.9P5O14 and ErP5O14 noncrystals when their 2H11/2 ,4I9/2 and4I11/2 levels are excited.The results show that it is essential to take the coefficient into calculation particularly for ErP5O14 noncrystal where energy transfer plays a key role.There is no influence though the distance between rare earth ions is larger.And it is found that infrared quantum cutting exsists in ErP5O14 noncrystal excited by visible light. The relative nonradiative relaxation rate, the spontaneous emission rate and the energy transfer rate are calculated particularly , The relative energy transfer dynamics is analyzed.It is found that the {4H11/2→4I9/2,4I15/2→4I13/2} energy transfer with a rate of 239500s-1, is the main reason for 2H11/2 energy level to have the infrared quantum cutting, Which is meaningful for finding high-efficiency solar cell materials.
2011, 60 (7): 077803.
doi: 10.7498/aps.60.077803
Abstract +
In this paper, GaN-based InGaN/GaN MQW power LEDs are fabricated based on the existing technology through a simple processing, and their optical, electrical, and color properties are tested. Results show that the luminous intensity of the chips with omnidirectional reflector(ODR) has an improvement of 244mcd over that with the ordinary chips, and that the ODR LED's luminous flux, the efficiency and the color purity are improved by 6.04%, 5.74%, 78.64% respectively. One of the advantages of the ODR LED is its low color temperature, which is greatly lower than that of the ordinary LED.
2011, 60 (7): 077804.
doi: 10.7498/aps.60.077804
Abstract +
In experiment, Pr3+,Yb3+:ZBLAN glass is chosen as a frequency up-conversion fluorescence material, and detailed reasons for choosing ZBLAN glass as a material are given. In this paper we also analyze the relations between up-conversion fluorescence intensity and pump light intensity and between up-conversion fluorescence intensity and ions doped concentration. Therefore we obtain experimental conditions to realize a clear two-frequency up-conversion 3-D display.
2011, 60 (7): 077805.
doi: 10.7498/aps.60.077805
Abstract +
White organic light-emitting devices (WOLEDs) have a few technical merits for lighting application. Generally, doping-concentration and carriers-transporting effect inherent in traditional WOLEDs, however, complicate the optimization of device efficiency and color-stability characteristics. In this paper, we design and fabricate a novel WOLED concept,in which an alternant yellow and blue lighting stripe structure is used. We analyze the emission characteristic of this alternate stripe WOLED (AS-WOLED) as a function of yellow and blue stripe size and lighting angle. From the comprehensive analysis, trend in the dependence of emission characteristic on device structure is extracted, and accordingly, a general method for optimizing color characteristics of AS-WOLEDs is suggested.
2011, 60 (7): 077806.
doi: 10.7498/aps.60.077806
Abstract +
The bismuth-doped CdWO4 single crystals are prepared by the Bridgman method. The absorption spectra, emission spectra and X-Ray photoelectron spectroscopy (XPS) of various parts of as-grown Bi: CdWO4 crystal are investigated. The absorption edge of CdWO4 crystal is red-shifted from 345nm to 399nm due to the introdution of Bi into crystal. The four emission peaks at 470, 528, and 1078 and a weak peak at 1504 nm are observed under the excitation of light beams at 311, 373, 808, and 980 nm. From the X-Ray photoelectron spectroscopic measurements of the Bi: CdWO4 single crystals, Bi2O3 (Bi3+) and NaBiO3 (Bi5+) samples, we infer that there coexit Bi3+ and Bi5+ in Bi: CdWO4 crystals. The fluorescence emissions of visible bands at 470 and 528 nm result from both WO6-6 in Bi: CdWO4 and Bi3+ ions doped in the lattice, while the fluorescence emission of the near infrared band at 1078 nm is due to the Bi5+ luminescence. The analysis result of XPS is consistent with the change of the fluorescence intensity: along the growing direction the emission intensity at 1078 nm and the content of Bi5+ ion both decrease gradually, while the intensity at 528 nm and the number of Bi3+ both increase gradually.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2011, 60 (7): 078101.
doi: 10.7498/aps.60.078101
Abstract +
In this paper, a new method is proposed to investigate the transport mechanism of copper thin film oxidation in water vapor using H162O/H182O isotopic labeling. Copper thin films are prepared on glass substrates by vacuum deposition. The structure of copper oxide film is analysed by X-ray diffraction (XRD). The distributions of16O and18O in the oxide film are analysed by secondary ion mass spectroscopy (SIMS). The results demonstrate that the transport mechanism of copper film oxidation is short-circuit diffusion mechanism.
2011, 60 (7): 078102.
doi: 10.7498/aps.60.078102
Abstract +
Si0.82Ge0.18/SOI prepared by epitaxial growth of SiGe layer on SOI wafer in the ultra-high vacuum chemical vapor deposition is used to fabricate the SiGe on insulator (SGOI) substrate (0.24≤xGe≤1) by the cyclic oxidation and annealing processes. The structure and the optical properties of the SGOI with various Ge content are studied by employing HRTEM, Raman spectroscopy, and photoluminescence (PL) spectroscopy. The variations of Ge component and strain in the oxidation process are analyzed. High crystal quality Ge on insulator (GeOI), with a thickness of 11 nm, is obtained with a flat Ge/SiO2 interface. The direct band transition photoluminescence of the GeOI is observed at room temperature. The photoluminescence peak from GeOI is located at 1540 nm, and the PL intensity increases linearly with exciting power increasing. It is indicated that the formed GOI material has a high crystallization quality and is suitable for the applications in Ge optoelectronic and microelectronic devices.
2011, 60 (7): 078103.
doi: 10.7498/aps.60.078103
Abstract +
Meander coil is an important kind of coil configuration used in eddy current testing and electromagnetic acoustic testing. Owing to lack of analytical calculation formulas of impedance and magnetic field for meander coil, the analytical modeling is performed and a method of calculating pulsed response is presented. In terms of the general model for eddy current testing and electromagnetic acoustic testing, the calculation of impedance and pulsed magnetic field is transformed into the superposition of impedance and pulsed magnetic field of single rectangular coils. Based on the second order vector potential and the time harmonic magnetic field equations, the scalar potential analytical expressions of the meander coil are derived. Then the analytical expressions of magnetic flux in all solution area and eddy current in the specimen are obtained. By calculating the induction electric potential and the impedance change, the impedance analytical expression of the rectangular meander coil is derived. An FFT-IFFT method is used to calculate the time domain response to pulsed magnetic field. A model with an 8-meander double-layer double-bundle coil above an aluminium plate is used in calculation, and the results are in good agreement with the experimental result and the TSFEM calculation result, which verifies the analytical model and the accuracy of the calculation method. The analytical calculation largely shortens the calculation time compared with that by TSFEM method.
2011, 60 (7): 078501.
doi: 10.7498/aps.60.078501
Abstract +
One method of non-uniform finger spacing is proposed to enhance thermal stability of multiple finger power heterojunction bipolar transistor. Using coupling thermal resistance to characterize the influence of the change of emitter spacing on thermal coupling, the relation between coupling thermal resistance and emitter spacing is obtained. Temperature distribution on the emitter fingers of multi-finger heterojunction bipolar transistor is studied by a numerical electro-thermal model. The results show that the heterojunction bipolar transistor with non-uniform finger spacing has a smaller temperature difference between fingers thant the traditional uniform finger spacing heterojunction bipolar transistor under the same power dissipation. So the method of non-uniform finger spacing is very effective to enhance the thermal stability.
2011, 60 (7): 078502.
doi: 10.7498/aps.60.078502
Abstract +
SiGe heterojunction bipolar transistor (HBT) on thin film SOI has been successfully integrated with SOI CMOS by "folded collector". This paper deals with the collector of "partially depleted transistor" according to the thin film vertical SiGe HBT structure. A simplified circuit model including vertical and horizontal resistors and depletion capacitance is presented for the first time, and the model of the collector for field, voltage, and depletion width is systematically established. The model is analyzed with reasonable parameters. The results indicate that the space charge region consists of intrinsic junction depletion and MOS capacitance depletion, that the width of the space charge region increases with doping concentration of the collector, larger reverse junction voltage, and smaller substrate voltage, and that the region features a vertical expansion followed by a lateral expansion. This space charge region model of collector provides a valuable reference to the SiGe mm-wave BiCMOS circuit design and simulation on thin film SOI.
2011, 60 (7): 078503.
doi: 10.7498/aps.60.078503
Abstract +
Different thick Ni layers are deposited on the GaN-based LED films grown on Si(111) substrates, then LED films are annealed at 400℃—750 ℃ in the atmosphere of N2 ∶O2=4 ∶1. The Pt / p-GaN contact layer is prepared after removing the Ni-capping layer. It is found that annealing temperature and thickness of Ni-capping layer each have an important influence on the p-type contact of GaN-based LED film. The Ni film can significantly reduce the activation temperature of Mg acceptor of the p-type GaN. The characteristic of p-type contact of Ni-capping sample becomes better first then turns worse with annealing temperature and it become better then turns worse and then better with Ni-capping thickness. After optimization, the specific contact resistivity of Pt/p-GaN in the case of no second annealing can reach 6.1×10-5 Ω·cm2, when Ni-capping layer thickness is 1.5 nm and its annealing temperatune is 450 ℃.
2011, 60 (7): 078504.
doi: 10.7498/aps.60.078504
Abstract +
A two-dimensional simulation of electrical and optical characteristics of the dual-wavelength LED with different numbers of quantum wells is conducted with APSYS software. The results show that the increase of the number of quantum wells will cause uneven distribution of hole concentrations. Therefore, the increase in the number of quantum wells cannot effectively enhance carrier recombination rate, internal quantum efficiency and luminous intensity. Furthermore, it will lead to the rising of threshold voltage and affect the energy conversion efficiency.
2011, 60 (7): 078701.
doi: 10.7498/aps.60.078701
Abstract +
Multiscale base-scale entropy is introduced in this paper.We use it to analyze heart rate variability series.The results show that multiscale base-scale entropy can identify patterns generated from healthy and pathologic states, and can distinguish daytime and nighttime heartbeat time series. We also calculate the multiscale base-scale entropy of surrogate signal (phase randomized data), compare it with the entropy of atrial fibrillation signal, and find that the tends of two entropys are similar to each other, which indicates that atrial fibrillation reflects the linear characteristics of physiological signals. Multiscale base-scale entropy method has potential applications to studying a wide variety of other physiologic and physical time series data.
2011, 60 (7): 078801.
doi: 10.7498/aps.60.078801
Abstract +
In the generalized gradient approximation (GGA), energies, electronic structures and magnetic properties have been investigated for a single Ni atomic chain encapsulated in an armchair single-wall (n,n) carbon nanotubes (5≤n≤9) by using the first-principles projector augmented wave (PAW) potential within the density function theory (DFT) framework. The results show that the (5,5) tube is too narrow to wrap a Ni atomic chain, but the (6,6) tube is the smallest one to wrap a Ni atomic chain, especially at its central axis due to the lowest formation energy. The analyses of the spin-polarized band structures, total density of states (DOS), partial density of states (PDOS) and the magnetic moment of Ni@(6,6) and Ni@(7,7) systems show that the 3d states of Ni atom play determinant rales in DOS at the Fermi level, and the broader carbon nanotubes restrict slightly the magnetic moment of Ni atomic chain compared with with the narrower ones.
2011, 60 (7): 078802.
doi: 10.7498/aps.60.078802
Abstract +
Solar cells with structure of ZnPc (20 nm)/C60 (10 nm) are fabricated by thermal evaporation. The photocurrent density (Jph) expressed by effective applied voltage (V0-Va) and light intensity (I) is derived from an analytical method, and it is shown that the results from the model are in good agreement with experimental results. The short-circuit current density (JSC) exhibits a nearly linear dependence on light intensity, which is partially determined by effective applied voltage. Thermal annealing treatment under an optimal condition of 100 ℃ and 20 min, improves JSC by 43.8%, lengthening its attenuation constant from 5.6h to 22.2 h, which is attributed to the improvement on interfacial morphology and the decrease of series resistance due to better contact of the layers.
2011, 60 (7): 078803.
doi: 10.7498/aps.60.078803
Abstract +
In this article, the PEDOT:PSS doped with sorbitol film is fabricated on an ITO substrate by blending-spin coating method and used as a hole-extraction layer for organic solar cell (OSC). The effect of sorbitol concentration on the photovoltaic performance of the device is investigated based on P3HT:PCBM blend. Compared with a pristine device (i.e., without sorbitol), the sorbitol-doped (8wt %) OSC shows that the short-circuit current density, the fill factor and the power conversion efficiency are inereased from 8.82 to 9.03mA/cm2, 0.43 to 0.474 and 2.12% to 2.39 % (i.e., by about 13%), respectively. The canse of the improvement on performance of the device is discussed, showing that the increase in conductivity and transmittance of composite films is due to the improvement on OSC performances achieved through the incorporation of sorbitol into hole-extraction layer of PEDOT:PSS. The former leads to a lower series resistance of the device, while the latter gives rise to the improvement on the photo-induced carriers of the photovoltaics cells.
2011, 60 (7): 078901.
doi: 10.7498/aps.60.078901
Abstract +
In order to investigate the structural stability for zircon in mothball waste form of radionuclide to resist γ-ray irradiation, the zircon crystals, which are collected from Australia, are studied. The crystal grains are irradiated by a60Co γ-ray source with 1728 kGy doses. The chemical compositions of zircons are analyzed by X-ray fluorescence spectrometry (XRF). Moreover, phases, structures and microstructures of the samples before and after γ-ray irradiation are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the new phases are not found in the crystals before and after γ-ray irradiation with 1728 kGy. The crystal cell parameters change by 10-4 before and after irradiation. Moreover, no obvious damage to the structure is found in the zircon irradiated by γ-ray with 1728 kGy dose. So, the zircon possesses a better capability to resist γ-ray irradiation which hardly influence the degree of disorder for zircon.
2011, 60 (7): 078902.
doi: 10.7498/aps.60.078902
Abstract +
It is shown that community structure has great influence on traffic transportation. Networks with pronounced community structure are less efficient in terms of packet delivery. While the shortest path is chosen at random in the shortest path routing strategy, a routing strategy based on community structure is proposed in this paper which can reduce the betweenness centrality of the nodes on the edge of the community by minimizing the number of the communities that the shortest path passes through. Simulations show that the new strategy can enhance the packet delivery capability with the small-world character and that the more accurately the community is identified, the more efficient the new strategy is.
2011, 60 (7): 078903.
doi: 10.7498/aps.60.078903
Abstract +
Internet forum is the place where online mass incidents usually happen, and is very important in information diffusion and opinion spreading. We empirically analyze the interacting behavior of internet forum users, construct the virtual community network based on implicit interaction behavior. Through inspecting the statistical properties, we find that this virtual community network is directional, asymmetric and disassortative scale free network, and it has hierarchy and community structure.Moreover, user page view is positively correlated with his in-degree, so both can describe the influence power and popularity. From quantitative view, the results show that the effects of influential user with 'contribute-driven' property on information spreading can not be ignored; the success of internet forum needs to increase the activity of the most inert users; if user wants to be authoritative in virtual community networks, he needs to propose interesting message or has a personal brand.
REVIEW OF FRONTIER AREA
EDITOR'S SUGGESTION
2011, 60 (7): 078104.
doi: 10.7498/aps.60.078104
Abstract +
Among others, the removal of boron is the key issue to effectively purify metallurgical silicon into solar grade silicon. An innovative slagging process is proposed in this article after reviewing many previous studies. In the process, strong radiation is employed as catalysis to promote the chemical reaction. The authors have for the first time unveiled the secrets including the newly developed high temperature tools, the materials used, the method of mixing materials before purification, the process for separating silicon from residuals after purification, etc.. In the meantime, the authors also propose a postulate to explain the mechanism of the catalysis process. Except the removal of boron, the processes to remove other impurities, such as phosphorous and residual metals using electron beam and magnetic floating directional solidification are also discussed for the completion of a new industrial process to fabricate pure silicon. In the article, the authors also extend their discussion to the possibility of using the proposed non-imaging heliostat in other fields; to the possibility to further manufacture electronic grade silicon using the same process; to the possibility to obtain more experimental evidences for the postulate of strong radiation catalysis and to other subjects related to authors' claimed creations. It is sincerely hoped that the publication of the innovations reported in this article may provide an alternative way in the route map for the use of renewable energy of low cost and low carbon emission.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2011, 60 (7): 079201.
doi: 10.7498/aps.60.079201
Abstract +
Characteristics of six M-components with peak currents of kilo amperes are analyzed by using the data from the artificially triggering lightning experiment in Shandong 2009, including the current at the base of the discharge channel, the surface electric field change at 30 m from the channel, and the high-speed camera records. The M-component is associated with the abrupt enhancement of channel luminosity with a duration of less than 1ms. Both the current and electric field are characteristic of relatively symmetric waveforms with a rise time of several tens of microseconds. The simultaneous records show that the electric field starts to change and reaches its peak earlier than the channel base current. Because of the obvious continuing current flowing in the channel, the conductivity of the discharge channel prior to the M-component is better than that prior to the leader-return strokes. The channel condition before the occurrence of the M-component is crucial to current amplitude and rise time. According to the waveforms of current and electric field recorded simultaneously, it is inferred that the M-component evolves from up to down and the evolvement continues after contacting the ground, and then an upward reflected process is induced. Further analysis shows that the interaction between these two processes is likely to be changed with altitude.
Regularization method of assimilating Doppler radar data and its influence on precipitation forecast
2011, 60 (7): 079202.
doi: 10.7498/aps.60.079202
Abstract +
A new regularization method is proposed to directly assimilate Doppler radar data into mesoscale numerical weather forecast based on the traditional 3DVAR. For seeking the minimum module solution of the Yo=H(X) with bias δ, the regularization method is adopted and leads to a new cost function. A group of experiments were designed to study the case of a locally strong rainstorm occurred in Beijing area on August 14, 2008. The L-curve principle is used to determine the optimal regularization parameter and the result is α=0.1. Numerical results demonstrate that both regularization method and 3DVAR scheme can efficiently assimilate the Doppler radar data, and that the improved initial condition can alleviate the spin-up phenomenon and improve the nowcasting precipitation forecast. However, when an optimal regularization parameter is choser, better improvement, more accurate precipitation forecast and higher TS score are expected.
2011, 60 (7): 079501.
doi: 10.7498/aps.60.079501
Abstract +
The combined chaotic genetic algorithm for cognitive radio resource allocation is proposed, and corresponding combined chaotic sequence generator is designed. Simulations are conducted by using the combined chaotic genetic algorithm, the particle swarm optimization algorithm, the simulated annealing algorithm, and the simple genetic algorithm, thereby analyzing the multi-users, cognitive radio resource allocation. The results show that the combined chaotic genetic algorithm has advantages of fast convergence rate, vast search space and global convergence. The combined chaotic genetic algorithm has better performance than the other three algorithms in terms of cognitive radio resource allocation, there by reducing the bit error rate and the transmission power consumption of the system. Besides, it also has a faster convergence rate.
