Vol. 56, No. 10 (2007)
2007-05-20
GENERAL
2007, 56 (10): 5565-5568.
doi: 10.7498/aps.56.5565
Abstract +
A time delay equation for sea-air oscillator model is studied. We aim at the cre ateion of an approximate method for solving sea-air oscillator model of nonlinea r equation, employing the theory of homotopic mapping, with due colisideration o f the approximate solution of the corresponding problem. This is an approximate analytical method, which can be further used for analyzing other behaviors of th e sea surface temperature anomaly of the atmosphere-ocean oscillator model.
2007, 56 (10): 5569-5574.
doi: 10.7498/aps.56.5569
Abstract +
In this paper, the finite point method is used to obtain the solution of a one-d imensional inverse heat conduction problem with a source parameter, and the corr esponding discrete equations are obtained. Compared with the numerical methods b ased on mesh, the finite point method only needs the scattered nodes instead of meshing the domain of the problem. The finite point method is a meshless method in which the moving least-square approximation is used to form the meshless appr oximation functions. And the collocation method is used to discretize the govern ing partial differential equations. The finite point method has the advantages o f simpler numerical procedures, lower computation cost and arbitrary nodes. The result of a numerical example is presented to show the method is effective.
Mei symmetry and Mei conserved quantity of nonholonomic systems of non-Chetaev’s type in event space
2007, 56 (10): 5575-5579.
doi: 10.7498/aps.56.5575
Abstract +
This paper studies the Mei symmetry and Mei conserved quantity of non-Chetaev's type in the event space. The differential equations of motion of non-holonomic s ystems of non-Chetaev's type in event spaces are established. The definition and the criteria of Mei symmetry are given. The condition and the form of Mei conse rved quantity are deduced directly from the Mei symmetry. An example is given to illustrate the application of the results.
2007, 56 (10): 5580-5584.
doi: 10.7498/aps.56.5580
Abstract +
The perturbation of Lie symmetries and new non-Noether adiabatic invariants for the Lagrangian system are studied. The exact invariants of Lutzky type arising f rom the Lie symmetries of Lagrangian system without perturbation are given. Base d on the definition of high-order adiabatic invariants of a mechanical system, the perturbation of Lie symmetries for Lagrangian system under the action of smal l disturbances is investigated, and a type of Lutzky adiabatic invariants of the system are obtained. An example is given to illustrate the application of the m ethod and results.
2007, 56 (10): 5585-5590.
doi: 10.7498/aps.56.5585
Abstract +
Based on the new expansion of the first kind of elliptic function, a method for constructing Jacobi elliptic function solutions to nonlinear wave equations is p roposed. The method is applied to the coupled KdV-mKdV equation and some new Jacobi elliptic function solutions to the equation are obtained. Some specific kind s of solutions and their relevant figures are also presented.
2007, 56 (10): 5591-5596.
doi: 10.7498/aps.56.5591
Abstract +
A scheme combining three processes of quantum teleportation, optimal universal quantum flipping and optimal universal quantum cloning for universal teleflipping and telecloning of arbitrary qubit is proposed. When a particular four-particle entangled state shared by the sender and three spatially separated receivers is used as quantum information channel, after the sender's Bell measurement, class ical communication and each receiver's local unitary operation, one receiver can get one orthogonal complementing state of the original unknown state with the o ptimal fidelity of 2/3, the other two receivers can respectively get one copy of the original unknown state with the optimal fidelity of 5/6. This scheme implem ents the universal quantum teleflipping and telecloning simultaneously with corr esponding optimal fidelity by using the reduced entanglement. The key to realizi ng this scheme is the construction of the particular four-particle entangled sta te shared by the sender and three receivers used as quantum information channel. The entanglement structure of the special four-particle entangled state is anal yzed.
2007, 56 (10): 5597-5601.
doi: 10.7498/aps.56.5597
Abstract +
The time-dependent invariant of a quantum frequency conversion system in an optical cavity is found from the simple observation that the dynamical evolution of a sum-frequency generation process preserves the total number of the idler photons and the signal photons involved in the process. By using this invariant and the Lewis-Riesenfeld quantum invariant approach, the Schrdinger equation for the coupled system of the two quantized modes of the electromagnetic field is solved under detuned condition. The explicitly analytical formulae of the quantum states and the evolution operators of the system are obtained. It should be useful for further studies on the various quantum properties of the quantum system.
2007, 56 (10): 5602-5606.
doi: 10.7498/aps.56.5602
Abstract +
Using the idea of code concatenation in classical coding theory, we make the suggestion of constructing general concatenated quantum codes by choosing certain quantum codes as outer code and inner code. Then by concatenating quantum RS outer codes with a set of special quantum inner codes, one can construct a family of concatenated quantum codes, which is asymptotically good. In the field of quantum error-correcting codes, this is the first time that a family of asymptotically good quantum code is constructed using bad classical codes.
2007, 56 (10): 5607-5612.
doi: 10.7498/aps.56.5607
Abstract +
For a Bose-condensed gas in a combined potential consisting of an axially-symmetric harmonic magnetic trap and one-dimensional (1D) optical lattices, the motional interference side peaks along the axis direction are formed after the combined potential is switched off. Based on this physical system, we make a new experimental suggestion which can be realized with current experimental technique to investigate the side peak superposition and discuss the second interference and amplification effect of a Bose condensate. In the region where the side peaks undergo constructive interference, the density of condensed atomic cloud will be amplified effectively.
2007, 56 (10): 5613-5617.
doi: 10.7498/aps.56.5613
Abstract +
Based on the method of transformation, this paper studies the Fokker-Planck equation of a stochastic system with double singularities driven by aussian colored noise. According to the definition of Shannon's information entropy and the Schwartz inequality principle, the explicit time dependence of the upper bound of the rate of entropy change is obtained for the first time. The relationship between the properties of double singularities, noise correlation time and dissipative parameter and their effect on the upper bound of the rate of entropy change are discussed.
2007, 56 (10): 5618-5622.
doi: 10.7498/aps.56.5618
Abstract +
In this paper,the phenomenon of stochastic resonance in an asymmetric bistable system with time-delayed feedback and correlated noises is investigated . The explicit expression for signal-to-noise ratio is obtained under the condition of small time delay approximation and adiabatic approximation. The effects of the delay time,the noises correlation and the static asymmetry to the signal-to-noise ratio are discussed.
2007, 56 (10): 5623-5628.
doi: 10.7498/aps.56.5623
Abstract +
The phenomenon of stochastic resonance (SR) in an asymmetric bistable system driven by correlated multiplicative and additive noise and two periodic fields is investigated. Analytic expressions of the signal-to-noise ratio (SNR) for fundamental and higher harmonics are derived using the two-state theory. The SR appears in both fundamental and higher harmonics. Moreover, the suppression exists for higher harmonics. The effects of static asymmetry and the noise intensity and the strength of coupling between noises on the SNR are studied.
2007, 56 (10): 5629-5634.
doi: 10.7498/aps.56.5629
Abstract +
In the chaos range of Lorenz equation, there is interaction between the smaller and larger scales. On the one hand, the Rayleigh number r determines the convective and turbulent flows in the air. On the other hand, the convective and turbulent flows have a feedback to the larger scale condition. The result of interaction between the scales leads to the decrease of the value of r, until the steady state of Lorenz equations is established. During the feedback process, the variation in vertical thermal flux xy and vertical temperature gradient z are the main causes that decide the change of number r. Moreover the end result of feedback displays a abrupt change.
2007, 56 (10): 5635-5639.
doi: 10.7498/aps.56.5635
Abstract +
Basing on the batch arrival concept in the queue theory, this paper proposes a Poisson network model with node batch arrival. The Nodes arrive the system as a Poisson process with rate λ. In the first model, the batch is a power function of the batch number with exponent θ(0≤θ<+∞). Using Poisson process theory and continuum approach, we found that the stationary mean degree distribution of this model is a power-law distribution, and its power-law exponent is between 1 and 3. In the second model, the batch is a log function of the batch number and we obtained that the power-law exponent of stationary mean degree distribution is 3 when the batch rises more slowly. So our model is not only the extension of the BA model, but also a theoretical foundation of many real networks of which the power-law exponent is between 1 and 2.
2007, 56 (10): 5640-5647.
doi: 10.7498/aps.56.5640
Abstract +
Using add-order method to translate the problem of generalized synchronization of different orders of chaotic systems into the synchronization of systems of identical order. Based on Lyapunov stability theory and adaptive control method, we give the expression of adaptive controller and the updating rule of parameters, then achieve generalized synchronization of different order of chaotic systems with unknown parameters and enable the estimation of the parameters of the drive and the response systems. This method has been applied to solve the generalized synchronization problem of hyperchaotic Lü system, Lorenz system, generalized Lorenz system, and Liu system with unknown parameters. It is proved theoretically that this method is feasible. Numerical simulations show the effectiveness of the adaptive control technique.
2007, 56 (10): 5648-5654.
doi: 10.7498/aps.56.5648
Abstract +
To realize the control of chaos in the voltage-mode BUCK converter, the output time-delayed feedback control (TDFC) is introduced into its control prototype. Based on the quantified analyses in the frequency domain, harmonic balance method is used to ascertain the regulating range of feedback control gain and delay time. Meanwhile the TDFC is equivalent to a kind of simple passive feedback control when the delay time is much smaller than the switch period. And the simulation results of these two methods are considered the same. In the end the experimental circuit of the voltage-mode BUCK converter with passive feedback control is set up. By this means the chaos state of BUCK converter can be quickly controlled into period state and the ripple of voltage and current will be decreased.
2007, 56 (10): 5655-5660.
doi: 10.7498/aps.56.5655
Abstract +
In this paper we discuss the new chaotic system proposed by Huang Wei. We give the sufficient conditions for the stabilization and synchronization of this new chaotic system via impulsive control. For these sufficient conditions that B is not necessarily symmetric. Thus, our results can be used for a wider class of nonlinear systems. Simulation results are provided to show the effectiveness of the proposed method.
2007, 56 (10): 5661-5664.
doi: 10.7498/aps.56.5661
Abstract +
The tracking control of chaotic Chen system is realized using a nonlinear single-input controller. According to the structure characteristic of the Chen system, proper feedback form is selected and an adaptive single-input controller is designed, which makes the Chen system track a certain variable of the Rossler system with unknown parameters. The Lyapunov direct method is applied to prove that the error signal asymptotically approaches zero. Numerical simulations show that the proposed control method is feasible, and the identification of unknown parameters can be realized.
2007, 56 (10): 5665-5673.
doi: 10.7498/aps.56.5665
Abstract +
In this paper, the stochastic chaos of the stochastic Bonhoeffer-Van der Pol system with bounded random parameter and its control by noise are investigated. The stochastic Bonhoeffer-Van der Pol system is first transformed into an equivalent deterministic system using the Chebyshev polynomial approximation, so that the problem of controlling stochastic chaos is reduced to the problem of controlling deterministic chaos in the equivalent system. Thus, the top Lyapunov exponent of the equivalent system can be used to examine the chaotic behavior and its control of the responses. The numerical simulations show that the chaos behavior in the stochastic Bonhoeffer-Van der Pol system is by and large similar to that in the equivalent deterministic Bonhoeffer-Van der Pol system. The chaos behavior can be controlled to the periodic states by noise, but under the effect of the random parameter and its intensity, it has cortain specific features.
2007, 56 (10): 5674-5678.
doi: 10.7498/aps.56.5674
Abstract +
Based on the Nagel-Schreckenberg traffic flow model，the traffic flow models for electronic and manual toll collection systems are established. The fundamental diagrams of traffic flow are obtained under different parameters via computer simulation. Moreover, the characteristics of electronic and manual toll collection mixed system are analyzed and discussed.
2007, 56 (10): 5679-5683.
doi: 10.7498/aps.56.5679
Abstract +
Stochastic resonance is a common natural phenomenon in nonlinear systems. By studying the relations between the out put signal-to-noise ratio (SNR) of the biologic neural network with small-world character and the rewiring probability p which reflects the effect of small-world,the coupling strength c, amplitude A of input signal, we revealed some regularities of the second super-harmonic stochastic resonance in the biologic neural network, and found that the out put SNR doesn't monotonicly increase as the forcing amplitude A increases, but there exists an optimal value AO for the Hodgkin-Huxley (HH) neural network with small-world character. The out put SNR reaches its maximum when A is equal to AO.
2007, 56 (10): 5684-5690.
doi: 10.7498/aps.56.5684
Abstract +
In this paper we report on the Ti:sapphire mode-locked femtosecond laser based optical frequency comb apparatus and developed by NIM its application in optical frequency measurement of the I2 stabilized 532nm Nd∶YAG laser installed in NIM. The measurement result of 127I2 R(56)32-10 hyperfine transition is 563260223512991±20 (Hz), with a relative frequency uncertainty of 3.6×10-14. To our knowledge，this result is the first optical frequency measurement in China which is referenced directly to the Cs microwave frequency standard.
2007, 56 (10): 5691-5697.
doi: 10.7498/aps.56.5691
Abstract +
A novel microstructure for in-situ measuring residual stress in micromechanical thin films by the method of critical buckling observation was proposed and two different samples were fabricated using surface micromachining technique. The experimental apparatus was built for in-situ observation of critical buckling patterns of these microstructures during sacrificial layer etching. Then, the states of residual stresses can be distinguished directly by the buckling patterns and the magnitudes can be estimated with finite element method (FEM) when the values of critical etching length have been measured. Before the measurement, effects of various parameters on the critical buckling stress were investigated in detail with FEM in advance. After that, measurements of residual stresses using the new microstructures were carried out and the results were in good agreement with that obtained from micro rotating structures. It is consequently revealed that measurement of residual stresses by this new microstructure has evident advantages over the conventional buckling observation methods. Both compressive and tensile residual stresses in wide ranges of amplitude can be measured, just using a single appropriately designed microstructure. Therefore, the usefulness of layout space can be greatly improved.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (10): 5698-5703.
doi: 10.7498/aps.56.5698
Abstract +
The paper present a simplified new model for computing state equation and ionization degree of inert plasma, which is based on the Thomas-Feimi(TF)statistical model. We fitted the numerical results of the ionization potential calculated by TF statistical model and obtained the analytic function for computing the ionization potential. Then in the local thermal equilibrium (LTE) case we assume the density of plasma n(Z*) is a continuous function of Z*, and based on Saha equation with Debye-Hückel correction we established a simplified model of state equation of inert plasma. Using this simplified model we calculated the average degree of ionization and the state equation for Helium, Neon and Argon Plasma. The results from this simplified model are basically in agreement with both theory and experimental data. This simplified model can be used to calculate the state equation of plasma mixtures and is expected to have a wider applieation in the field of strongly ionized plasma.
2007, 56 (10): 5704-5708.
doi: 10.7498/aps.56.5704
Abstract +
Based on the obtained equilibrium structure for the ground state of SiO molecular, the ground states of SiO molecule under electric fields ranging from -0.03 to 0.03a.u. are optimized using the density functional theory DFT/B3P86 at 6-311++g(d, p)level. The effects of electric fields on the bond length, system energy, charge distribution, energy levels, HOMO-LUMO gaps and the infrared spectrum for the ground states of SiO molecule have been studied. The results show that the molecular geometry is strongly dependent on the field strength and behaves asymmetrically to the directions of the applied electric field. At the same time, the energy gaps between the HOMO and LUMO become closer as the applied electric field along the molecular axis O-Si increases, which shows that the molecule is apt to be excited under specific electric field.
2007, 56 (10): 5709-5714.
doi: 10.7498/aps.56.5709
Abstract +
The radiative opacities of iron and bromine plasmas have been calculated using an average atom (AA) model with modification of the transition energy. The line positions obtained after the modification have better agreement with the results of the detailed term accounting model. However,discrepencies still exist for some strong transition peaks. To eliminate the discrepencies the charge state distribution should be included. The mean opacity of iron was calculated. We found that the transition energy shift has obvious effect on the mean opacity of iron plasma at relatively lower densities.
2007, 56 (10): 5715-5722.
doi: 10.7498/aps.56.5715
Abstract +
On the basis of full relativistic theory, transition probabilities of 2p4f—2p3d for NⅡ have been calculated using multi-configuration Dirac-Fock method. The results are well consistent with experimental value. In the present work, the influence of relativistic effects, electron correlation, relaxation effects, Breit interaction and quantum electrodynamic effects on fine structure and transition probabilities are investigated in detail. The results show that the relativistic effects, electron correlation and relaxation effects are important to the calculations of energy structure and transition probabilities.
2007, 56 (10): 5723-5726.
doi: 10.7498/aps.56.5723
Abstract +
By using QCISD(T)/aug-cc-pvtz method, the equilibrium geometry of LiO2 molecule has been calculated. The possible electronic state and the reasonable dissociation limit of the ground state of LiO2 molecule is determined based on atomic and molecular reaction statics. The analytic potential energy function of LiO2(C2V，X2A2) molecule was derived by many-body expansion theory.
2007, 56 (10): 5727-5733.
doi: 10.7498/aps.56.5727
Abstract +
In this paper, we investigate the quantum dynamics of the Λ configuration atom-molecular three-level system analytically and numerically. Then the production rate of molecule is consequently studied. Our results show that the production rate depends on the initial condition. Under ideal condition, one can have complete transformation with the equivalent Rabi frequency when the initial state is the atomic state, while for the dark state, the production rate is constant. The detuning of the coupling optical field usually decreases the production rate, but increases it for the dark state.
2007, 56 (10): 5734-5738.
doi: 10.7498/aps.56.5734
Abstract +
The electron emission yield of the interaction of highly charged argon ions with silicon surface is reported. The experiment was done at the Atomic Physics Research Platform on the Electron Cyclotron Resonance (ECR) Ion Source of the National Laboratory HIRFL (Heavy Ion Research Facility in Lanzhou). In the experiment, the potential energy and kinetic energy was selected by varying the projectile charge states and extracting voltage, thus the contributions of the projectile potential energy deposition and electronic energy loss in the solid are extensively investigated. The results show that, the two main factors leading to surface electron emission,namely the potential energy deposition and the electronic energy loss, are both approximately proportional to the electron emission yield per ion.
2007, 56 (10): 5739-5745.
doi: 10.7498/aps.56.5739
Abstract +
An analytic expression of the potential energy surface (PES) of the ground state of the Ne-HBr complex has been obtained by utilizing nonlinear least square method to fit the intermolecular interaction energies, which have been calculated at the coupled cluster singles and doubles including the connected triple excitation level and with the augmented correlation consistent polarized quadruple zeta basis set (CCSD (T)/aug-cc-pVQZ). On the basis of the above result, the partial cross sections (PCS) at the energies of 40, 60, 80 and 100meV for collisions between Ne atoms and HBr molecules have been calculated by using the quantum close-coupling method. Then the influence of the long-range attractive and the short-range anisotropic interaction of the CCSD (T) potential energy surface on the inelastic PCS has been discussed in detail. The results show: (1) The transitions of j=0 →j′=1, 2 contribute to the total inelastic PCS predominantly. The long-range attractive well of the PES results in the tail maximum of the inelastic PCS at the position of the higher J, which mainly comes from the transition of j=0 →j′=1. While the short-range repulsion results in the main peak at the position of the lower J, which mainly comes from the transition of j=0 →j′=2. The balance between the short-range repulsive and long-range attractive interaction results in a pronounced minimum in the inelastic PCS. (2) There is the same collision parameter corresponding to the maximums and minimums of the inelastic PCS at different incident energies although the corresponding quantum number J of total angular momentum is different. The collision parameter samples the same part of the PES.
2007, 56 (10): 5746-5753.
doi: 10.7498/aps.56.5746
Abstract +
The geometries，total energies，and frequencies of ZrnFe(n=2—13)clusters have been systematically investigated by using density functional theory with the generalized gradient approximation, and the equilibrium geometries at different spin multiplicities as well as the ground-state structures have been determined. The calculated results of the averaged binding energy, the second-order difference of cluster energies as well as the HOMO-LUMO gap of the ZrnFe(n=2—13) clusters indicate that the relative stabilities of Zr5Fe, Zr7Fe and Zr12Fe are stronger than that of other sized clusters. The true ground state for Zr12Fe cluster has icosahedral structure with Ih symmetry, and moreover, the stability of Zr12Fe is strongest among all the investigated clusters. In addition, not only the relative stabilities of Zr5Fe, Zr7Fe and Zr12Fe clusters are stronger than other sized clusters, but also they are all magnetic clusters (however, the magnetic moment of Zrn clusters is quenched for n≥5), thus it can be seen thant we can acquire magnetic clusters with higher stabilities by choosing appropriate doping atom. Mulliken population analysis shows that there is a weak charge transfer from Zr atoms to Fe atom except for Zr12Fe cluster, in which a small amount of charge transfers from Fe atom to Zr atoms.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (10): 5754-5757.
doi: 10.7498/aps.56.5754
Abstract +
Based on the static electric-field simulation, the structures of 20 GW diode and its insulator, as well as the position and shape of guide magnetic-field are designed and optimized. Then the experiments on the repetition rate of intense current electron-beam diode are carried out on 20 GW pulsed power source, it can deliver intense electron-beam pulses of 1MV/20 kA with pulse width 45 ns and repetition rate 100Hz.
2007, 56 (10): 5758-5765.
doi: 10.7498/aps.56.5758
Abstract +
A general study of the Seidel aberration of the lens systems made of left-handed media is presented according to the primary aberration theory. The Seidel aberration of the planar interface between air and left-handed medium was analyzed showing that its surface shape are more abundant when it is free from spherical aberration and it could be applied to real imaging systems. Based on the Seidel sum formulae of thin lens, three types of left-handed media thin lenses free from partial Seidel aberrations are designed with specific parameters. Finally, the Seidel aberration-free lens systems based on the use of left-handed media are presented. It is pointed out that left-handed media can be used to simplify the structure of lens system for the same or superior imaging performance.
2007, 56 (10): 5766-5771.
doi: 10.7498/aps.56.5766
Abstract +
A method for polynomial fitting of Wassermann-Wolf surfaces and the results are presented. Conformal optics by which the missile dome is shaped to aerodynamic requirements generally introduces various kinds of aberrations as targe as tens to hundreds of wave lengths across the field of regard. Through polynomial fitting of Wassermann-Wolf surfaces and using Zernike polynomials instead of traditional merit function, the conformal optical system is implemented and an example is demonstrated. The results show that MTF of the optical system approaches to the diffraction limit across the field of view.
2007, 56 (10): 5772-5777.
doi: 10.7498/aps.56.5772
Abstract +
By using the rigorous Fourier's modal theory and recursion algorithm of the reflection-transmission coefficient matrix(RTCM), the propagation of Hermite-Gaussian beams of different orders through gratings with sinusiodal and rectangular reliefs whose characteristic size is comparable with the wavelength, are studied and compared in detail. It is shown that the field distribution of incident beam and the structure of grating relief affect intensity distributions within the gratings. Better beam smoothing is achieved by using the rectangular-reliefed grating than using the sinusoidal-reliefed grating.
2007, 56 (10): 5778-5783.
doi: 10.7498/aps.56.5778
Abstract +
Based on the angular spectrum representation and strict modal theory, the propagation of linearly polarized Gaussian beams through a bar relief diffraction grating whose characteristic size is comparable with the wavelength, and the influence of errors of grating structure parameters on the maximum intensity in the relief layer are studied. It is shown that the propagation behavior of beams in each layer is different. The intensity in the relief part is higher than that in the unfilled part. The influence of errors of the grating period on the maximum intensity in the relief layer is dominant. By using the simulated anneal algorithm, system parameters are optimized to control the output beam intensity profile.
2007, 56 (10): 5784-5789.
doi: 10.7498/aps.56.5784
Abstract +
By using Fourier optics, a model based on the far field about the Gauss pulse is set up，by which the effect of seams on the far field can be studied. Numerical simulation shows that pulse-width narrowing will appear in the case of single seam and the Fourier-translation-limited pulse-width of the input pulse will determine whether the pulse width in the far field becomes narrow or broad. In addition, the irradiance in the focus decreases and two sub-peaks appear beside the central peak, and their intensties increase with the widening of seams.
2007, 56 (10): 5790-5795.
doi: 10.7498/aps.56.5790
Abstract +
A single photon detector operating in the Geiger mode is cooled to a moderate temperature by using Peltier cooling, and a gate pulse is coupled to the avalanche diode through capacitance. It uses a moderate delay and sampling gate modulation to prevent the positive and the negative transient pulses from influencing the detection of true photon avalanches, a dead time modulation feedback control circuit to suppress the afterpulsing, and an optimized circuit to reduce the dark counts. The performance test shows that at the optimum operation point the quantum efficiency is about 18%, the dark count rate is less than 4×10-6 ns-1 and the noise-equivalent power is 2.4×10-19 W/Hz1/2.
2007, 56 (10): 5796-5801.
doi: 10.7498/aps.56.5796
Abstract +
We propose a new quantum key distribution scheme based on random phase coding. In this scheme, the sender and the receiver can share the secret information without basis reconciliation,and besides, this scheme is more efficient. As the phase of the qubit is coded randomly, this protocol is robust even when the source is not a prefect single photon. We show theoretically that it has higher security against the attacks, such as the photon-number-splitting, the impersonation attack, and the Trojan attack, etc., than the previous QKD scheme.
2007, 56 (10): 5802-5807.
doi: 10.7498/aps.56.5802
Abstract +
By solving the density matrix equation of three-level molecular system, the pulsed laser pumped D2O gas terahertz laser was theoretically studied, the expression of terahertz signal gain coefficient(Gs)and the pumping signal absorption coefficient (Gp) were obtained, the output power density of terahertz laser was calculated numerically by iteration method. The calculation shows that the spectral characteristics of terahertz laser was in full accordance with the stimulated Raman emission. The signal frequency detuning obviously affects the amplification process, and there exists splitting in the curve because of the dipole of D2O gas molecule being disturbed by the field of pumping pulse. The theoretical spectrum is in good agreement with reported experimental results.
2007, 56 (10): 5808-5812.
doi: 10.7498/aps.56.5808
Abstract +
Under consideration of the basic factors such as the level hyperfine structure and isotope split etc., the spectral structures of spontaneous emission of copper atom 578/511nm lines are calculated. A sealed operation CuBr laser with periodical refreshment of the buffer gas are designed and constructed. The 578/511nm spectral structures, produced by CuBr laser at lower Ne buffer gas pressure were measured under different working temperatures and exciting voltages. The spectral structure of spontaneous emission of copper atom 578/511nm lines have multi-peaks similar to their laser spectral structure, but the 578nm laser line isstrongly dependent on the working temperature and the exciting voltage. Some possible reasons are suggested to qualitatively explain the experimental results.
2007, 56 (10): 5813-5817.
doi: 10.7498/aps.56.5813
Abstract +
According to Holstein's theory about radiation trapping effect, the influence of gas temperature and ground-state population density on the effective lifetime of the resonance level is discussed. The results show that the ground-state population density is the dominating factor in the radiation trapping effect. The threshold parameters of radiatoin trapping have been calculated for seven resonance metastable transition laser lines in Ca+, Sr+, Ba+ and Hg+ in different ionization ratios. The threshold temperature of radiation trapping was found to be consistent with the initial lasing temperature for the ionization ratio of 5%, which matches the ionization ratio of 3% to 5% observed in experiment. This consistency reveals that the threshold condition of radiation trapping effect is an important factor for population inversion in lastrs based on the ionic resonance to metastable transition.
2007, 56 (10): 5818-5820.
doi: 10.7498/aps.56.5818
Abstract +
For the laser diode pumped Cr,Nd∶YAG passively Q-switched Nd:YVO4 laser, in order to improve the stability of the Q-switched pulses, a long cavity is adopted, and the gain medium is located at the middle of the cavity. In the experiments, stable pulses are obtained. At the maximum incident pump power of 17.5W, the repetition rate increases to 71.3 kHz and the pulse width (FWHM) is narrowed to 0.4μs. The pulse-to-pulse amplitude fluctuation is less than ±10%. The inter-pulse timing jitter of the Q-switched pulse train is found to be less than ±3.5%.
2007, 56 (10): 5821-5826.
doi: 10.7498/aps.56.5821
Abstract +
The morphology and mechanism of lithium niobate (LiNbO3) crystal ablated by a femtosecond laser pulse have been studied. The ablated spots and surface diffraction grating have been examined by means of scanning electron microscopy (SEM) and atom force microscopy (AFM). Sub-diffraction limit spots in LiNbO3 crystal ablated by femtosecond laser have been obtained. The diameters of ablation spots are 400nm and 800nm when 170nJ single pulse and 100nJ 17 pulses are used, respectively. There are ripples with about 200nm periodic on the bottom surfaces of the spots at low laser energy. The result shows that the sub-diffraction limit structures may be formed by the multi-photon excitation, and the femtosecond laser ablation is an innovative tool for manufacturing LiNbO3-based optical devices.
2007, 56 (10): 5827-5830.
doi: 10.7498/aps.56.5827
Abstract +
Surface plasmon modulated nano-aperture vertical-cavity surface-emitting lasers were fabricated from common 850nm VCSELs. When the diameter of the aperture was 200nm, and the period of grating was 400nm, the maximum far-field output power reached 0.3mW at a driving current of 15mA. The fabrication process was described and the beaming properties were studied via experimentally and theoretically.
2007, 56 (10): 5831-5834.
doi: 10.7498/aps.56.5831
Abstract +
According to optical waveguide theory, the far-field profile of laser diode arrays is derived. Basing on the distribution, an off-axis external cavity is designed. By employing the external cavity, at the operating current of 17A, the BPP of output laser is reduced from 1100mm·mrad to 128mm·mrad and the beam quality has about 8.5-fold improvement. The output power is 75% of the radiated power in free-running state without external cavity.
2007, 56 (10): 5835-5842.
doi: 10.7498/aps.56.5835
Abstract +
Using the method based on the technique of symmetry reduction, we find the general analytical parabolic asymptotic self-similar solutions for the varying coefficient of Ginzburg-Landau equation that take consideration of the influence of the doped fiber retarding time. The parabolic asymptotic amplitude function, change of strict linear phase chirp and the effective temporal pulse width of self-similar pulse with gain dispersion are given for the dispersion decreasing fibers with longitudinal exponential distribution and hyperbolic distribution. And these theoretical results have been confirmed by numerical simulation in this paper.
2007, 56 (10): 5843-5848.
doi: 10.7498/aps.56.5843
Abstract +
Based on double harmonic oscillator (DHO) approximation, the static vibrational first hyperpolarizabilities,and the IR and Raman spectra of 4-N-methylstilbazonium salt derivatives are calculated using coupled perturbed Hartree-Fock (CPHF) approach. Two vibrational normal modes which dominate the contribution to the vibrational first hyperpolarizabilities are obtained. It is found that the static vibrational first hyperpolarizabilities of title molecules are large and show a good linear relationship with their electronic counterparts. For the first time we give an approach of estimating the vibrational first hyperpolarizabilities using a few normal modes identified from IR and Raman spectral peaks, which the name as the few mode approach. The results indicate that this approach is practical in the estimation of the vibrational first hyperpolarizability.
2007, 56 (10): 5849-5854.
doi: 10.7498/aps.56.5849
Abstract +
On the basis of computing models of stimulated Brillouin scattering (SBS), the optical limiting response characteristics in SBS process are investigated theorctieally. Dependence of limiting parameter ——residual energy on pump parameters (input power density, pulse duration), medium parameters (gain, phonon life time) and configuration parameters (focusing length, cell length) are analyzed. Response characteristics of SBS limiting are given by studying the variation of delay time, residual peak power and residual energy. Ideal response system can be obtained by choosing a medium with larger gain and shorter phonon life time. But the vesidual energy could not be got rid of by choosing SBS medium parameters only. In experiment, we obtained flat-roofed optical limiting pulse shapes in SBS process using dye absorption.
2007, 56 (10): 5855-5861.
doi: 10.7498/aps.56.5855
Abstract +
In high-power lasers, nonlinear hot image is likely to damage expensive optics. The location and intensity of hot image of plane light wave has widely been studied. However, in the operating lasers, the light beam possesses a limited spatial width. Based on the aberrationless model of self-focusing, the location and intensity of hot image of Guassian optical beams is investigated. It is shown that the location and intensity of hot image greatly differ from those of plane light wave when the Guassian beam has a small beam waist, while they approximately equal those of plane light wave for a very big beam waist.
2007, 56 (10): 5862-5871.
doi: 10.7498/aps.56.5862
Abstract +
The solitary evolution and deflection of matching Gauss beam have been investigated in biased dissipative photovoltaic-photorefractive crystals. For a given dissipative system that supports a determinate dissipative screening-photovoltaic soliton (DHSP), one call find a corresponding Gauss beam which matches with the system parameters, which will evolve into a steady-state spatial soliton and propagate steadily in the given dissipative crystal. At the same time, we have investigated the impact of diffusion on the propagation (or solitary evolution) of the matching Gauss beam in the dissipative system. It is indicated that the diffusion effect can cause deflection of the matching Gauss beam during the transmission, and the deflection process is extremely similar to that of the corresponding DHSP soiliton. By comparing the two deflection results, we found that for the matching Gauss beam, the numerical result of deflection is close to the analytical result of the bright DHSP soliton. In a word, the solitary evolution and propagation (including the deflection) of the matching Gauss beam is quite close to those of the DHSP in the dissipative system.So the matching Gauss beam can be used as the incident beam to replace the bright DHSP beam, which is more convenient in theory and experiment.
2007, 56 (10): 5872-5877.
doi: 10.7498/aps.56.5872
Abstract +
In this paper, we investigate the mechanism of tunable parametric superfluorescence(PS) based on the second harmonic generation and parametric processes taking place in the same nonlinear crystal(BBO). The tunable spectra of PS has been generated between 480 nm and 530 nm, which is pumped by the second-harmonic from the high-power Ti:sapphire laser system at 1 kHz repetition rate. We present the generation mechanism of PS theoretically and simulate the process of PS ring using the amplification transfer function. The experiment and the theory show that PS will appear when the phase matching angle for second-harmonic generation is close to the optimal pump angle for optical parametric generation, and then the tunable spectra of PS are generated by slightly adjusting the crystal angle. The result provides a theoretical basis for controlling the generation of PS and quantum entanglement states, which is of great significance for the development of quantum imaging, quantum communications and other applieations.
2007, 56 (10): 5878-5882.
doi: 10.7498/aps.56.5878
Abstract +
We theoretically studied the band gap structure of one-dimensional photonic crystals constituted by alternate layers of left-handed and right-handed materials, and found that the band gap structure is different from the usual photonic crystals. With an appropriate choice of the parameters, we show that it is possible to realize an absolute band gap for either TE or TM polarization of the electromagnetic waves, which can not be found in normal photonic crystals. The wave function of electric field in the pass band is strongly localized compared with the normal photonic crystals. And we give an example in which we substitute the left-handed materials with dispersion materials, and get different energy bands in different areas.
2007, 56 (10): 5883-5889.
doi: 10.7498/aps.56.5883
Abstract +
We introduce a structure made of periodic arrays of H-shaped metallic pattern that offers a potentially simple approach in building left-handed metamaterials with simultaneous negative permittivity and permeability. We have investigated experimentally the transmittance in the rectangle waveguide and found unambiguously a passband that can be tuned easily at microwave frequencies by changing the parameter t. Using phase shift experiment, prism refraction experiment and S-parameter retrieval method, we have confirmed that the H-shaped metamaterials have negative refractive indices, negative permittivity and negative permeability at the passband frequencies. Compared with the conventional left-handed metamaterials consisting of arrays of wires and split ring resonators, H-shaped left-handed metamaterials show not only magnetic resonance but also electric resonance, so they will be a good candidate in the microwave applications due to their simple structure and easy preparation.
2007, 56 (10): 5890-5894.
doi: 10.7498/aps.56.5890
Abstract +
The GRIN-rod lenses are made by two steps ion-exchanging, and the refractive index distribution of the sample is measured by the YaMing interferometer. The results show large differences in the refractive index of the samples. The reason for the increase of the refractive index difference by two-step ion-exchanging is discussed. The results of this research may help to produce GRIN materials.
2007, 56 (10): 5895-5902.
doi: 10.7498/aps.56.5895
Abstract +
Based on the photoisomerization and photoinduced birefringence in azo-containing polymers, a theoretical model for all-optical logic gates is developed and a novel scheme of all-optical logic gates using pump-probe technique is presented theoretically and realized experimentally. The all-optical logic AND, OR, XOR and XNOR gate operations have been demonstrated experimentally based on the modulation of intensity or polarization of the pump beam and signal. The experimental results show a good performance, which are in agreement with the theoretical prediction.
2007, 56 (10): 5903-5908.
doi: 10.7498/aps.56.5903
Abstract +
A novel distributed optical fiber vibration sensing system is proposed and demonstrated, using a ring structure-based Mach-Zehnder interferometer (MZI). The direct current light-based real-time and dynamic locating technique is exploited. By introducing the ring structure into the interferometer, the linear interferometer is changed into ring type, resulting in two counter-propagating light waves, thus one MZI equally operates as two. When a vibration acts on the sensing fiber, the counter-propagating signals produce identical phase-changes simultaneously, which propagate along different paths to optical receivers. With the help of digital processing technologies to analyze the received signals, the characteristic parameters of vibration, including the spatial position, frequency and amplitude can be achieved in real time. A spatial resolution better than 40m is successfully verified in a 1.01 km prototype system of single vibration. Furthermore, the feasibility of detecting and locating multiple vibrations is theoretically analyzed and simulated.
2007, 56 (10): 5909-5914.
doi: 10.7498/aps.56.5909
Abstract +
Conical transducer offers both good lateral resolution and large depth of detecting region for ultrasonic imaging. In this paper, the superposition of Gaussian beams is utilized to simulate the source distribution of the conical focused transducer. On the basis of the KZK equation, we obtain the analytical solution of the nonlinear sound field from the conical focused source. A conical focused PVDF transducer has been fabricated in our Lab and the sound field distributions of the fundamental and second harmonic components were experimentally measured. The measured results are in reasonably good agreement with the theoretical predictions.
2007, 56 (10): 5915-5921.
doi: 10.7498/aps.56.5915
Abstract +
Pattern time delay shift coding scheme uses the time delay shift values of the Pattern to code the information whose anti-ISI (intersymbol interference) ability is related to the kind and duration of the Pattern. Spread spectrum communications is competent for long-range underwater acoustic communications for its spread spectrum gain, but the low communications rate seriously restricts its application. The proposed new scheme is adapted to the underwater acoustic environment, which integrates the spread spectrum with Pattern time delay shift coding and works at M-ary mode spread spectrum and several communications channels. The scheme could achieve good performance of the spread spectrum and also improve the data transfer rate. The results of lake trial show that the M-ary chaotic spread spectrum Pattern time delay shift coding scheme is robust and feasible.
2007, 56 (10): 5922-5925.
doi: 10.7498/aps.56.5922
Abstract +
The relationship between the granular flow rate Q on a two-dimensional conveyor belt and the opening-angle θ at choke point together with the velocity of the conveyor belt and the exit-size has been studied in the experiment. The result shows that the granular flow rate Q is influenced chiefly by the following factors: the exit width R, the speed of the conveyor belt and the opening-angle θ at choke point. The rate of flow Q increases linearly with the speed v and the exit width R, and the rate of flow Q decreases linearly with cosθ when the opening-angle θ is larger than 15° for the dilute granular flow.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2007, 56 (10): 5926-5930.
doi: 10.7498/aps.56.5926
Abstract +
As a prospective target material, micro-droplet is of great interest. In this paper, the characteristics of the 20μm-diameter singledroplets are measured by means of shadowgraphs. The detailed process of the droplet formation is observed. Meanwhile, the droplet parameter, backing pressure, modulation amplitude and frequency are optimized to attain the conditions to realize droplets with uniform spatial distribution.
2007, 56 (10): 5931-5936.
doi: 10.7498/aps.56.5931
Abstract +
The collision of the two shockwaves induced by laser confined ablation is investigated by time-resolved shadowgraph. Through the observation of the temporal and spacial evolution of the two shockwaves, it is found that the shockwaves do not interact with each other but interact with the plasma induce by ablation in the collision.
2007, 56 (10): 5937-5944.
doi: 10.7498/aps.56.5937
Abstract +
Based on the theory of wave propagation and scattering in random medium, the analysis method of the pulse propagating in the plasma medium is presented. Under the condition of strong fluctuations, we have deduced the two-frequency second moment and fourth moment equations, and calculated the two-frequency intensity correlation function and scintillation index in terms of the different electron density spectra. The statistical parameters of the self-correlation function, the correlation bandwidth and time are obtained, in order to provide a basis for studing the characteristic of the pulse propagation in plasma medium.
2007, 56 (10): 5945-5951.
doi: 10.7498/aps.56.5945
Abstract +
The impulses of vaporized target material with solid target are measured by using the intense pulse of Q-Nd:YAG laser irradiating the solid target in quasi-vacuum. Analyzing the interaction mechanism of laser with target and vaporized target material, numerical calculation of impulse acting on the target with different laser intensity is performed with fluid dynamics theory and three-dimensional difference scheme. The comparison and analysis are performed between numerical and experimental results. The experimental results are given a reasonable explanation further. It is shown from the consistency between numerical results and experimental results that the numerical calculation model used in this paper can represent the mechanical response of the target to the laser.
2007, 56 (10): 5952-5957.
doi: 10.7498/aps.56.5952
Abstract +
Traditional enthalpy probe system use the Mass Flux Controller (MFC) to measure the flux rate of sample gas. However, this method much depend on the composition of plasma working gas under the condition of steady state of sample gas inside the probe, so it takes much more time to measure the enthalpy of a point. In order to overcome the disadvantage of traditional probe, the rapid enthalpy probe system we devised measure the molar weight of sample gas by using a known volume gas container instead of MFC, making it possible to measure the enthalpy of one point in several seconds. The accuracy of result acquired by our rapid enthalpy probe system is verified through our four different experiments.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2007, 56 (10): 5958-5964.
doi: 10.7498/aps.56.5958
Abstract +
A non-template CVD method was used to synthesize well-aligned carbon nanotube (ACNT) arrays. Ferrocene was used as a catalyst, xylene as the carbon source. This process carried out in a single-furnace system. The products were characterized by Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM), Energy Dispersive Spectrometry(EDS) and Raman Spectroscopy. The effects of process parameters on ACNT arrays growth were also investigated. The results show that well-aligned carbon nanotubes can be easily grown on polished silicon substrate at 800℃ with catalyst concentration of 0.02mg/L. Under the above conditions the rate of growth of ACNT arrays can reach 25μm/min.
2007, 56 (10): 5965-5968.
doi: 10.7498/aps.56.5965
Abstract +
One-dimensional strain impact experiments were performed for the high purity aluminum (HPA) (99.999%). The spall characteristics of HPA in dynamic tensile fracture have been discussed according to the quantitative metallographic analysis of the shock recover of samples. By defining the product of the tensile stress and the time as a parameter called tensile impulse (I), the statistic resultsindicate that an obvious critical behavior for the damage evolution appears with the increasing of I. When the I is low, the damage grows slowly with alinear increment. Once the I reaches a critical value, the damage grows rapidly and an exponential increase is observed. Our preliminary results indicate that the critical value of I for HPA is about 0.34 GPa·μs and the corresponding critical damage is about 0.12.
2007, 56 (10): 5969-5973.
doi: 10.7498/aps.56.5969
Abstract +
The Einstein model to consider thermal effect in universal equations of state is modified, and an approach to solve parameters at absolute zero temperature from experimental data at a reference temperature is proposed and applied to the Baonza equation. The thermal Baonza equation is applied to study thermo-physical properties of α, β and γ-Si3N4. Through analyzing experimental data in literature, the input data-set for the three phases are determined. The results calculated from the thermal Baonza equation is in agreement with available experimental data.
2007, 56 (10): 5974-5978.
doi: 10.7498/aps.56.5974
Abstract +
The ZnO films were prepared on Si substrates by RF magnetron sputtering and doped with N by ion-implantation. The samples were then annealed at different temperatures, and showed p-type conduction. The properties were examined by scanning electron microscopy(SEM), X-ray diffraction (XRD), and Hall measurement. The results show that the ZnO films have good surface morphology and are highly c-axis oriented. Hall measurement showed that the resistivity and hole concentration were 41.5Ω·cm and 1.68×1016cm-3， respectively. This paper focuses on the discussion and analysis of the influence of the temperature and time of annealing on the p-type transition of the ZnO films.
2007, 56 (10): 5979-5985.
doi: 10.7498/aps.56.5979
Abstract +
ZnO thin films were electrodeposited on glasses coated with a transparent-conductive film (InSnO) with different deposition currents. We have studied the dependence of microstructure, morphology and photoluminescence (PL) on the deposition current by X-ray diffraction, scanning electron microscopy and PL measurement at room temperature. We found that all the films show highly c-axis textured structure and the surface morphology is strongly current-dependent. The transmission spectra show that the films have a transmittance higher than 80% in the visible range. The films have an increase in thickness with the deposition current. The PL spectra exhibit two emission bands, an ultraviolet (UV) one from the exciton transition and a visible light one that might emerge from the defects in the films. The UV emission band has an obvious blueshift, which is found to be due to in doping during the deposition. With the increase of deposition current, the UV emission decreases while the visible light emission goes up.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2007, 56 (10): 5986-5989.
doi: 10.7498/aps.56.5986
Abstract +
We investigated structural instability and polarization of BaTiO3/SrTiO3 superlattice under stress by using first-principles calculation. Our results show that stress induces lattice distortion and charge transfer between Ti atom and O atom. With stress increasing，atomic displacement in BaTiO3/SrTiO3 superlattice grows gradually，resulting in the enhancement of polarization. Furthermore，polarization of superlattice BaTiO3/SrTiO3 can be controlled by changing the stress.
2007, 56 (10): 5990-5995.
doi: 10.7498/aps.56.5990
Abstract +
In this article，optical and electronic properties of CIS are studied from DFT calculations. For the exchange-correction energy，we employ GGA in the form of RPBE. The interactions between valence electrons and ionic core are represented by the ultrasoft pseudo potential. By analyzing the results，a mixed bonding state is found to exist in CIS，which is a strong ionic bond with a much weaker covalent bond. The interactions between Cu and Se are much stronger than that between In and Se. It was clarified that CuInSe2 has a direct band gap. We also calculate various optical properties of this material，such as reflection index，refraction index，adsorption spectrum and dielectric constant. For the adsorption spectrum，there are six peaks：3.1，7.6，10.0，16.1，19.0eV，21.0eV and the strongest adsorption peak is located in ultraviolet region.
2007, 56 (10): 5996-6002.
doi: 10.7498/aps.56.5996
Abstract +
The electronic structures and optical properties, the atomic population, bond lengths, band structures and density of states (DOS) of undoped and doped rare earth elements (Y, La) in γ-Si3N4 have been calculated by means of plane wave pseudo-potential method (PWP) with generalized gradient approximation (GGA). The gap after doping will decrease and enables the formation of new semiconductor，which affords to help finding new semiconductor. We researched optical properties after doping of rare earth elements (Y, La), and found that the static dielectric constant of doped γ-Si3N4 is much higher than that of the undoped material，which may serve as new dielectric and refractive material，and may have special applications in certain optical devices.
Effects of optimized contact scheme on the performance of high-power GaN-based light-emitting diodes
2007, 56 (10): 6003-6007.
doi: 10.7498/aps.56.6003
Abstract +
Due to the lateral current transport in the mesa-structure GaN based LEDs，the resistance of the n-type material of the GaN and lower confinement layer is not negligible for large area and high applied current density applieations，which causes the current spreading nonuniformly along the lateral direction. With an optimized contact scheme to reduce the length for the lateral current transport，two different kinds of contact schemes of high-power GaN-based flip-chip LEDs (FCLEDs) are fabricated. It is shown that the forward voltage of this FCLED with interdigitated contact scheme is 3.35V at forward current 350mA，and exceeds that of FCLEDs with optimized ring-shaped interdigitated contact scheme by 0.15V. Although the light emitting area of FCLEDs with optimized ring-shaped interdigitated contact scheme is slightly smaller than that of FCLEDs with interdigitated contact scheme，it is found that the light output from the former is larger than that from the later at higher injection currents. Furthermore，the light output from the FCLEDs with optimized ring-shaped interdigitated contact scheme saturates slowly at higher injection currents as compared to the FCLEDs with interdigitated contact scheme，indicating that the saturation behavior of the FCLEDs with interdigitated contact scheme is more pronounced. It is confirmed that an optimized contact scheme，which leads to the more uniform current spreading，can decrease joule heat generated and considerably improve the electrical and optical characteristics of the FCLEDs.
2007, 56 (10): 6008-6012.
doi: 10.7498/aps.56.6008
Abstract +
In order to understand the different effects of Ca and Mg doping on the electronic transport properties of LiCoO2，which is the primary cathode material in Li-ion secondary batteries，the electronic structures of the relevant systems are studied with the ab initio method based on the density-functional theory. It is found that both Ca and Mg partial substitution for Co in LiCoO2 crystal will give rise to partially occupied acceptor band near the Fermi level，but these bands are substantially localized. Moreover，Ca-doped system has a clear energy gap between the acceptor band and the valence band，whereas for the Mg-doped system there isn't such a gap. It's believed that the existence of this gap is the main factor resulting in the non-significant increase of the electronic conductivity in the Ca-doped LiCoO2. In addition，the remarkable distinction in the ionic radii of Ca2+ and Mg2+ can also induce noticeably different effects on the electronic conductivities.
2007, 56 (10): 6013-6018.
doi: 10.7498/aps.56.6013
Abstract +
Variable temperature Hall effect measurement was performed on the AlGaN/AlN/GaN structure with AlN interlayer grown on sapphire by metalorganic chemical vapor deposition. It was measured that the mobility and density of the two dimensionalelectron gas at the interface of AlN/GaN were 1.4×104cm2·V-1·s-1 and 9.3×1012cm-2 at 2K，respectively. Low temperature variable magnetic field measurement manifested that only a single type of carriers contributed to the conductivity in this structure. Quantum Hall effect was observed in field as low as 3T at 2K. The calculated quantum scattering time of 0.23ps is longer than that of AlGaN/GaN structure. This improvement is attributed to the AlN interlayer which effectively reduces the scattering. In addition，further analysis revealed that the small-angle scattering was important in this structure.
2007, 56 (10): 6019-6022.
doi: 10.7498/aps.56.6019
Abstract +
The exact solution of time evolution operator was obtained by applying the gauge transform of algebra dynamic. Such an operator describes the quantum state of time dependence of mesoscopic LC circuit containing voltage source. The zero-state response in mesoscopic LC circuit was researched, and the charge and current zero-state response of the import signal were also acquired. The result showed that the system of mesoscopic LC circuit has linear time invariant feature, and the response in mesoscopic LC circuit is the same as in the macroscopic LC circuit.
2007, 56 (10): 6023-6027.
doi: 10.7498/aps.56.6023
Abstract +
Tantalum thin films with thicknesses varying from 15 to 250nm were grown on silicon substrates by magnetron sputtering. Surface morphology of the films was investigated by atomic force microscopy. Then the film surface dynamic evolution was analyzed within the framework of dynamic scaling theory. The results show that the growth exponent β is about 0.17 for the films thinner than 50nm and 0.45 for thicker films. With the increase of film thickness，the roughness exponent α increases from 0.24 to 0.69 and remains constant for the films thicker than 50nm. The dynamic surface evolution reveals the growth transition from island coalescence to bulk film growth. Surface islands prefer lateral growth to vertical growth during island coalescence.
2007, 56 (10): 6028-6032.
doi: 10.7498/aps.56.6028
Abstract +
Polycrystalline lead iodide (PbI2) thin films have been prepared on glass substrates by vacuum evaporation. The influences of evaporating rate，the distance between the resources and the substrates，the thickness of the films and the temperature of the substrate on the structure of the film were studied. The structures of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results shows that the films were (001) preferentially grown，when the substrate was at room temperature. At higher substrate temperature，the films were mostly (003) preferentially grown and the size of the grains were larger. The internal stress became smaller when the substrate temperature became higher.
2007, 56 (10): 6033-6037.
doi: 10.7498/aps.56.6033
Abstract +
Using Bogoliubov-de Gennes equations，we study the quasiparticle transport in quantum-wire/insulator/p wave superconductor junction (q/I/p). In the framework of the Blonder-Tinkham-Klapwijk model，we calculate the tunneling conductance in q/I/p as a function of the bias voltage at zero temperature and finite temperature. Differently from the case in quantum-wire/insulator/d wave superconductor junctions，there are zero-bias conductance peaks in the single-mode case. With the barrier strength becoming strong，the zero-bias conductance is gradually enhanced.
2007, 56 (10): 6038-6044.
doi: 10.7498/aps.56.6038
Abstract +
The scattering matrix approach is applied to study tunneling spectra in normal metal/normal metal/superconductor double junctions. The abnormal minigap in tunneling conductance is attributed to the phase coherence of electrons and Andreev-reflected holes in the middle metallic film. We consider a combination of the coherent tunneling with the sequential tunneling and the calculated results provide a reasonable explanation for the abnormal minigap observed in recent experiments.
2007, 56 (10): 6045-6049.
doi: 10.7498/aps.56.6045
Abstract +
Orthorhombic LiMnO2 (o-LiMnO2) are synthesized by hydrothermal technique. Two samples were obtained which crystallize in orthorhombic structure with space group Pmnm. From rietveld refinements，the samples exhibit respectively a spot of cationic disorder on the lithium and manganese sites 4% and 8%，which，however，has no great influence on the magnetism. We have investigated the static and dynamical response of clusters in o-LiMnO2 oxide，and a sequenceof transformations of magnetic states，i.e. antiferromagnetic to ferromagnetic state at T≤TC≈118K and ferromagnetic to canted spin glass state at T≤Tf≈50K are observed.
2007, 56 (10): 6050-6055.
doi: 10.7498/aps.56.6050
Abstract +
NiFe2O4 nanoparticle series samples in the grain size range of 8—47nm were successfully synthesized by low-temperature solid-state reaction. The X-ray diffractometer (XRD)，HRPT neutron powder diffractometer，vibrating sample magnetometer (VSM) and superconducting quantum interference devices (SQUID) were used to characterize the structure，magnetic properties and surface anisotropy of nanoparticles. Data of XRD and neutron diffraction showed that the lattice constants of NiFe2O4 nanoparticles were lager than that of the bulk counterpart. Oxygen parameters suggested that lattice distortion were decreased with reduced particle sizes. In comparison with the bulk material，smaller magnetization，larger coercive force and anisotropy energy density for nanoparticles were observed. The critical sizes for transition from multidomain to single domain and for superparamagnetic transition were estimated to be 40nm and 16nm，respectively.
2007, 56 (10): 6056-6060.
doi: 10.7498/aps.56.6056
Abstract +
Fe-doped BaTiO3 has been synthesized with sol-gel technique. The doped perovskite was found to have tetragonal structure. The transformation point of ferroelectric to paraelectric and the latent heat of the transformation were observed to be a little less than those for pure BaTiO3. Layered composites Tb1-xDyxFe2-y/Fe∶BaTiO3 have been fabricated. Their mgnetoelectric (ME) effect has been investigated. The transverse ME voltage coefficient for the bilayer Tb1-xDyxFe2-y-Fe∶BaTiO3 and the trilayer Tb1-xDyxFe2-y-Fe∶BaTiO3-Tb1-xDyxFe2-y can reach 6.225 adn 26.25mV·(A·m-1)-1·cm-1，respectively，under a bias magnetic field of 2.8×104A/m at room temperature，which are about 50% larger than those for the bilayer and trilayer composed of pure BaTiO3.
2007, 56 (10): 6061-6067.
doi: 10.7498/aps.56.6061
Abstract +
In this work, influence of the formation of macroscopic dipoles with space charges enclosed in a void (electric domain) and their polarization enhancement on the charging current characteristic and the conductivity of cellular polypropylene (PP) film were studied by the corona charging with a grid in combination with the reverse-polarity corona charging compensation method. By measuring the isothermal surface potential decay and analyses of open-circuit and short-circuit thermally stimulated discharging current spectra, the charge stability and charge dynamics of PP ferroelectrets in relation to the formation and density variety of macroscopy dipoles were also discussed. The experimental results indicate that the decrease of charge stability of cellular PP film with high polarization should be attributed to the increase of the conductivity induced by the self-field of macroscopic dipoles. For cellular electret film with weak polarization, macroscopic dipoles formed by space charges should only be trapped at two sharp ends of lens-like void and, therefore, detrapped charges will transport along the side surfaces at both ends of the void. When the sample has high polarization, the trapped charges are distributed in the whole surface layer of the void. Most of the detrapped charges excited by the electret field drift through the solid dielectric layer between adjacent voids, which leads to their decay.
2007, 56 (10): 6068-6074.
doi: 10.7498/aps.56.6068
Abstract +
Multiferroic BiFeOδ ceramics of various oxygen contents (δ) were prepared by solid state reaction. Frequency dependence of dielectric properties of BiFeOδ samples at room temperature was measured in the frequency range from 40Hz to 1MHz with a HP4294A precision impedance analyzer. For all the samples, the dielectric constant and loss decrease with measurement frequency. The effect of introducing oxygen vacancy or excess oxygen is to reduce the dielectric constant of BiFeO3. The dielectric loss in BiFeOδ increases with oxygen content. The large change (10%—35%) in the dielectric properties of BiFeO3 samples with various oxygen content(δ) may be understood in terms of the space charge limited conduction associated with crystal defects. The effects of oxygen content on the crystal structure of BiFeO3 ceramics were also investigated using positron annihilation technique (PAT). It has been found that the mean positron lifetime in BiFeOδ is strongly dependent on the oxygen content. Introducing oxygen vacancy leads to an increase in positron lifetime and a decrease in local electron density of BiFeO3 ceramics.
Analysis of self-collimation and subwavelength imaging in one-dimensional metal-dielectric structure
2007, 56 (10): 6075-6079.
doi: 10.7498/aps.56.6075
Abstract +
The dispersion curve of one-dimensional metal-dielectric structure is calculated, and the finite-difference time-domain (FDTD) method is used to simulate the self-collimation in one-dimensional metal-dielectric structure, to which a Gaussian beam is incident at different angles. The influence of the dissipation of the metal layer on self-collimation is discussed. Subwavelength imaing with the one-dimensional metal-dielectric structure is also analyzed. The resolution of λ/8 is achieved for single point source when the thickness of 1DMD is equal to λ/2. The resolution will gradually degrade as the source moves beyond the near-field domain. Imaging with double slits source is also demonstrated, and a resolution of λ/3 is achieved.
2007, 56 (10): 6080-6083.
doi: 10.7498/aps.56.6080
Abstract +
Photoresponse characteristics of Pr0.7Ca0.3MnO3 thin films were investigated under different applied voltages and excitation light energy densities at room temperature.The transient resistance change of 92.3% and response time of～36ns were observed under the excitation with a 532 nm laser pulse of 7ns duration at a light energy density of 275.16mJ/cm2.Both the resistance change and response time showed nonlinear behavior as a function of the light energy density, and the resistance and the response time were reduced when the intensity increased. However, the applied voltage had almost no effect on the photoresponse at room temperature. The phenomena are explained in terms of the photoinduced nonequilibrium insulator-to-metal transition in the film, which may have potential applications in optoelectronic devices.
2007, 56 (10): 6084-6089.
doi: 10.7498/aps.56.6084
Abstract +
The Bi4-xNdxTi3O12(x=0.00,0.30,0.45,0.75,0.85,1.00,1.50) ferroelectric thin films were prepared on the Pt/Ti/SiO2/Si(100) substrates using sol-gel method. The effect of neodynium doping on the microstructures and ferroelectric properties of films were studied. The experimental results show that Nd3+ only substitutes Bi3+ in the pseudo-perovskite block when Nd content x is lower than 0.45. When Nd content x is about 0.45, the film has the largest remnant polarization (2Pr) of 32.7μC·cm-2 at an applied field of about 270kV·cm-1. At x>0.45, part of Nd ions are incorporated into the (Bi2O2)2+block, which would change the microstructure of (Bi2O2)2+ block and weaken its functions as the insulating layer and the space charge storage, resulting in the decrease of the 2Pr. When x=1.50, the dopout would destroy the structure of (Bi2O2)2+ block, which leads to ferroelectric-paraelectric phase transition of the film.
2007, 56 (10): 6090-6097.
doi: 10.7498/aps.56.6090
Abstract +
Er3+: GdVO4 is a new laser material which is suitable for high-power laser systems. In this paper we firstly measured the absorption spectrums of Er3+ in the sample Er3+: GdVO4, then the intensity parameters were calculated using Judd-Ofelt theory. After that we calculated some predicted spectroscopic parameters, such as the spontaneous radiative transition rate, branching ratio and integrated emission cross section, which were then compared with the data of other common materials. It was found that there are many transitions with large oscillator strength and large integrated emission cross section, especially 2H11/2→4I15/2, 4S3/2→4I15/2, 4F9/2→4I15/2 and 4I13/2→4I15/2, which are useful in solid-state laser and communications fields. Finally, we discuss the splitting of the energy levels of Er3+ in the crystal GdVO4 through the group theory, and also analyze the intermix of Jz in Starks levels.
2007, 56 (10): 6098-6103.
doi: 10.7498/aps.56.6098
Abstract +
Regularly arrayed nanocomposite system of zinc oxide/silicon nanoporous pillar array (ZnO/Si-NPA) was prepared by chemical vapor deposition utilizing Si-NPA as substrate, and the corresponding structure and photoluminescence properties were characterized. Our experimental results disclosed that all the pillars of ZnO/Si-NPA have a core-shell structure. Different from the red and blue emission from Si-NPA, two strong and wide emission bands were observed in the ultraviolet and blue-green ranges. These emission bands are attributed to the band-edge exciton transition of ZnO crystallites and two kinds of deep-level transitions originating from its intrinsic defects.
2007, 56 (10): 6104-6108.
doi: 10.7498/aps.56.6104
Abstract +
Single-layer polymer light-emitting diodes with high work function gold cathode were fabricated using a series of novel conjugated polyelectrolytes and their neutral precursors: aminoalkyl-substituted polyfluorenes with different 4,7-di-2-thienyl-2,1,3-benzothiadiazole contents. At the current density of 38.7mA/cm2, the external efficiency reaches 0.42% with the Commission Internationale de I'Eclairage coordinates x=0.67 and y=0.33 for PFN-DBT10. It has been shown that these polymers also can be used as electron injection layer in double-layer devices with high work function gold cathode, which favors the manufacture of solution processing multilayer devices. Based on single-layer and double-layer device structures, it was found that the improvement of device performance is attributed to the interface effect between gold cathode and polyelectrolytes layer.
2007, 56 (10): 6109-6113.
doi: 10.7498/aps.56.6109
Abstract +
The photocurrent curves of reflection-mode GaAs photocathodes as a function of time, when were illuminated by white light with an intensity of 0, 33 and 100lx, respectively, were measured using a multi-information measurement system. The calculated lifetimes of cathodes are 320, 160 and 75min, respectively, showing that the stability of cathodes degraded with the increase of light intensity. The lifetime of cathode, illuminated by white light with an intensity of 100lx, while no photocurrent was being drawn during the illumination, was 100min. Through comparison, we found that the influence of illumination on cathodes stability is greater than that of photocurrent. The quantum-yield curves of cathodes as a functions of time, when illuminated by white light with an intensity of 33lx, were measured also. The measured results show that the shape of the yield curves changes with increasing illumination time due to the faster quantum-yield degradation rate of low energy photons. Based on the revised quantum-efficiency equations for the reflection-mode cathodes, the variation of yield curves are analyzed to be due to the intervalley diffusion of photoelectrons and the evolution of the surface potential barrier profile of the photocathodes during degradation process.
2007, 56 (10): 6114-6117.
doi: 10.7498/aps.56.6114
Abstract +
The temperature dependence of field emission from multiwalled carbon nanotubes deposited on a W tip was studied. It is found that the emission current increases with increase of temperature, while the stability of the emission current did not change. The field emission characteristic deviates from classic Fowler-Nordheim theory. This may result from a dispersion in the field enhancement factor of the carbon nanotubes.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2007, 56 (10): 6118-6123.
doi: 10.7498/aps.56.6118
Abstract +
The electrical resistivity, microhardness, tensile strength and elongation of rapidly solidified Cu-xwt.%Sn (x=7, 13.5, 20) hypoperitectic alloys are investigated, and the relationships between cooling rate and properties of the alloys are further analyzed theoretically. It is found that, under rapid solidification, the microstructure is refined and the amount of grain boundary increases, and the scattering of free electrons is thus intensified, resulting in the rise of alloy resistivity. Provided that the value of grain boundary reflection coefficient r is about 0.992, the electrical resistivity of the alloys can be theoretically analyzed by the M-S model. With the increase of cooling rate, the microhardness and tensile strength of alloy foils increase linearly, but the elongation decreases within the range of 1.0%—4.6%.
2007, 56 (10): 6124-6131.
doi: 10.7498/aps.56.6124
Abstract +
Liquid foam is a dense packing of gas bubbles in a small amount of surfactant liquid, which has well-organized structure and behaves as typical soft condensed matter. Forced drainage is the flow of constantly input liquid through the network of interstitial channels between bubbles in foams under actions of gravity and capillarity, which is one of major mechanisms causing liquid foam evolution. Firstly in this paper, we improved the newly proposed method introduced by Hutzler et al. (2005) by considering the light transmission ratio to eliminate the incident light intensity discrepancy along the one dimensional foam formed within a slender Hele-Shaw silicon rectangular tube. After the film rupture and the bubble coarsening were carefully slowed down, forced foam drainages in one dimension were studied by using the improved light scattering technique. We found that the characteristic quantities, such as the drainage wave front velocity and liquid fraction evolution, are consistent with traditional foam drainage results based on Poiseuille-type flow assumption in Plateau borders. And the light transmission ratio is found not to be the reciprocal of the liquid fraction as similar with the transmission probability in diffuse-transmission spectroscopy technique, but prevails the relationship T=0.293+1.038e-29.39(0.01<0.13). We then deduced the viscous energy of foams based on Kelvin cell structure during forced drainage process and calculated the surface energy of foam using the software of Surface Evolver. The evolution of the two kinds of energy at local area of foam was predicted based on the quasi-static assumption of Kelvin cell structure evolution along with liquid fraction variation. The study of foam drainage from a view of energy will be useful in the further study on foam drainage and foam stability control in various applications.
2007, 56 (10): 6132-6136.
doi: 10.7498/aps.56.6132
Abstract +
A new method for retrieving aerosol size distribution from measurement of aerosol optical depth is reported. Depending on the rigorous Mie scattering theory and the measured optical depth, dispersing the aerosol size distribution, by using linear-regression method, the aerosol size distribution can be calculated directly. And also the suitable wavelength band to retrieve the aerosol size distribution is obtained by analyzing the multi-collinearity.
2007, 56 (10): 6137-6142.
doi: 10.7498/aps.56.6137
Abstract +
Through building several multi-symmetric initial shapes in Surface Evolver software, after refining them and doing a long time of evolvement step by step, we obtained some new budding vesicles with small energy whose coefficients are consistent with the theoretical values. Through changing the coefficient and scanning the direction of different shapes, we found a discontinuous phase transition and a reversible continuous phase transition and two new stable shapes. Furthermore, we obtained two kinds of starfish shaped abruption processes which have been supported by experiment.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (10): 6143-6149.
doi: 10.7498/aps.56.6143
Abstract +
In order to describe the reservoirs more accurately, the characteristics of the earth medium must be considered comprehensively, such as the anisotropy, viscoelasticity and pore, etc. Consequently, an anisotropic viscoelastic porous medium model is presented in this paper, and the elastic wave equation in this medium has been derived. The seismic wavefield numerical modeling was simulated by using the pseudo-spectral method. Synthetic seismograms are used to show the characteristics of the seismic wave in complex medium. The research work is useful to understanding seismic wave propagation in earth medium.
2007, 56 (10): 6150-6156.
doi: 10.7498/aps.56.6150
Abstract +
The climate system is a chaotic, hierarchical open nonlinear system. The system of higher level dominates the behavior of the lower one and determines the basic configuration of climate change. Generally, what the observational data record is the output of lower layer system which necessarily contains the information of interaction between different levels. How to extract information of higher level system from observational data has been a hotspot in the research of nonlinear spatio-temporal distribution theory and methods of observational data processing. A unified form ulation of the climate system has not yet been established. For the convenience of study, in this paper we use a two-level model comprising the Logistic model and Lorenz model, and analyze the output of lower level system through power spectrum and wavelet analysis under different control parameter and obtain the scaling rules for extracting information of the higher level system.
2007, 56 (10): 6157-6163.
doi: 10.7498/aps.56.6157
Abstract +
Pulsars rotate extremely stably, they can be used as time standard. However, pulsar time defined by single pulsar is influenced by several noise resources. To weaken these influences to get a more stable time scale, one can take ensemble analysis to obtain the ensemble pulsar time. Since different pulsars have different rotation frequency, and the noise source have different influence on different frequency of each pulsar，we can apply wavelet analysis to integrate the pulsar time, and this algorithm can take consideration of the long-term and short-term stability of pulsar time. On the other hand, the pulsar timing residuals are caused by reference atomic clock and pulsar itself, so we can apply Wiener filtration analysis to distinguish the two parts, and then calculate the ensemble pulsar time with the residuals after removing the error of reference atomic clock. Based on both of the two algorithms, a new algorithm of Wiener filtration in wavelet domain has been presented, which combines the merits of wavelet analysis and Wiener filtration and can remove the noise influence to pulsar time more effectively. Experimental results prove that Wiener filtration in wavelet domain can reduce noise influence of pulsar timing residuals effectively.
2007, 56 (10): 6164-6168.
doi: 10.7498/aps.56.6164
Abstract +
Taking into consideration the self-gravitational interaction and energy conservation, Hawking radiation from Reissner-Nordstrom black hole is re-investigated using the Damour-Ruffini method. It is found that the radiation is not exactly thermal, and the non-thermal Hawking radiation can carry information from the black hole. This can be used to explain the black hole information paradox, and the process satisfies the unitary thoery. A new method to calculate the corrected non-thermal Hawking radiation is given, which is more general. It can be used to study not only both the scalar field and Dirac field, but also massive and massless particle radiations.
