Vol. 58, No. 1 (2009)
2009, 58 (1): 363-372. doi: 10.7498/aps.58.363
The structure of the collisionless electrostatic shockwave (CES) and the process of the ion acceleration by shock wave are investigated with a series of two dimensional particle-in-cell (PIC) simulations. It is found that only ions satisfying some criteria can be accelerated due to the bipolar electric field in the shock wave front. A comparative investigation of the ion acceleration process by shock wave and solitary wave has been made. Only ions located in the sheath can be accelerated by the solitary wave. We also compare the shock wave for different laser intensities and different plasma densities. The ion energy spectrum of the shock wave has a platform. It can be used to ignite as the ignition material.
Thermal dynamic analysis of picosecond and nanosecond single pulse laser flash-heating of Al/NC nanoenergetic composites
2009, 58 (1): 655-661. doi: 10.7498/aps.58.655
Thermal dynamic process of single pulse laser-induced reaction is theoretically analyzed for a novel system of composite energetic materials containing nanometallic particles. The instantaneous power density of laser energy absorbed by nanometallic particles dispersed in a matrix is exactly deduced. The process of absorbing pulse laser energy for nanometallic aluminum particles embedded in nitrocellulose (Al/NC) thin film and the heat propagation process of hot spot accompanying exothermic chemical reaction are simulated numerically based on thermal decomposition mechanism. The reaction diameters are calculated for different concentrations of Al/NC thin films flashed by 100ps, 10ns and 25ns single pulse laser with the reaction threshold intensities having been obtained from experiment, respectively. Calculation results are compared with the experiment data, which shows that the thermal decomposition mechanism generally corresponds to the reaction processes of 10ns and 25ns pulse laser but does not correspond to that of the 100ps pulse laser.
2009, 58 (1): 1-8. doi: 10.7498/aps.58.1.1
The characteristics of the population distribution of China is analyzed based on the method of statistical physics. The results show that in the last 20 years, the total population of China increases roughly exponentially with time and the growth rate is found to be slowing down. The population distribution in provinces, cities or counties follows approximately the same rule: the population distribution changes slowly for small k, while it changes rapidly for large k and the distribution obeys the Zipf's law. This shows that the population distribution of China has self-similarity. A solvable model of migration-driven aggregate growth based on scale-free network is also proposed to simulate the population size distribution of China. It is found that the theoretical results are in good agreement with the realistic data.
2009, 58 (1): 9-15. doi: 10.7498/aps.58.9
Image thresholding segmentation method based on two-dimensional minimum Tsallis-cross entropy is proposed by utilizing the non-extensive property of Tsallis entropy in the paper. Firstly, the two-dimensional Tsallis-cross entropy is given, then the particle swarm optimization is used to search the best two-dimensional threshold vector by minimizing the two-dimensional Tsallis-cross entropy. The proposed method not only considers the spatial information of pixels, but also the interaction between the object and the background. Its segmentation performance is superior to thresholding methods using Shannon entropy and minimum one-dimensional Tsallis-cross entropy. Experimental results show that the proposed method can give good segmentation results with less computation time.
Lie symmetry and conserved quantity of Appell equation for a Chetaev’s type constrained mechanical system
2009, 58 (1): 16-21. doi: 10.7498/aps.58.16
Lie symmetry of Appell equation and conserved quantity deduced directly by Lie symmetry for a Chetaev's type constrained mechanical system are investigated. The relations between Lagrange function and A function are analyzed. A general approach of studying conserved quantity deduced by Lie symmetry of Appell equation for a Chetaev's type constrained mechanical system is discussed. The definition and the criterion of Lie symmetry of Appell equations under the infinitesimal transformations of groups are given. The structural equation of Lie symmetry and the expression of conserved quantity deduced directly by Lie symmetry are obtained. An example is given to illustrate the application of the results.
2009, 58 (1): 22-27. doi: 10.7498/aps.58.22
Conformal invariance and conserved quantities of Mei symmetry for general holonomic systems are studied thoroughly. By introducing a single-parameter infinitesimal transformation group and its infinitesimal transformation vector of generators, definitions of the conformal invariance of Mei symmetry for the system are provided. Conditions that the conformal invariance should satisfy are derived using the Euler operator, and their determining equations are then presented. Moreover, the relationship between conformal invariance and the three symmetries, i.e., Noether symmetry, Lie symmetry and Mei symmetry, are discussed. The system’s corresponding conserved quantities are obtained, according to the structure equation satisfied by the gauge function. Finally, an example is provided to illustrate how the given result can be applied.
Non-Noether conserved quantities for nonholonomic controllable mechanical systems with relativistic rotational variable mass
2009, 58 (1): 28-33. doi: 10.7498/aps.58.28
The non-Noether conserved quantities (the Hojman conserved quantity) for nonholonomic controllable mechanical systems with relativistic rotational variable mass are discussed. The differential equations of motion of the systems are established. The definition and criterion of the Mei symmetries and the Lie symmetries of the system are discussed respectively. The necessary and sufficient condition under which the Mei symmetry is Lie symmetry is presented. The condition under which a non-Noether conserved quantity can be induced by the Mei symmetries and the form of the conserved quantity are obtained. An example is presented to illustrate the application of the result.
2009, 58 (1): 34-39. doi: 10.7498/aps.58.34
The analytical formulation of dynamics of a super-thin elastic rod was studied on the basis of Gauss variation. The definition of virtual displacement in the generalized acceleration space with respect to the arc-coordinate and the time were given with expression of Gauss variation，respectively. The nonholonomic constraint equations of the virtual displacements expressed by Gauss variation were given. The Gauss’s principle of the dynamics of a super-thin elastic rod was established, from which the Kirchhoff equation, the Lagrange equation, the Nielsen equation and the Appell equation of the rod can be derived. The Lagrange equation with indeterminate multipliers was obtained for the case when the rod is subjected to the nonholonomic constraints. The Gauss's principle of least compulsion of a super-thin elastic rod was proved and the compulsion function has a minimum for the actual motion and its physical meaning was indicated.
The transformation between the third-order Eulerian and Lagrangian solutions for irrotational progressive gravity waves
2009, 58 (1): 40-49. doi: 10.7498/aps.58.40.1
This study reports the transformation between the third-order Eulerian and Lagrangian solutions for the progressive water gravity waves propagating on water of uniform depth. Regarding to the motion of a marked fluid particle, the instantaneous velocity, mass conservation and free surface must be the same for solufions of either Eulerian or Lagrangian method. Using a successive Taylor series expansion to the path and the period of particle motion, the given conventional Eulerian solutions can be transformed into the completely unknown Lagrangian solutions and the reversible process is also identified. In the asymptotic solution, the explicit parametric equation of water particles can be obtained. In particular, the Lagrangian mean level and the Lagrangian wave frequency which differ from those in the Eulerian approach are found as part of the solutions. It shows that the present technique provides a modified method to obtain the third-order Lagrangian solution from the known Eulerian solutions.
2009, 58 (1): 50-54. doi: 10.7498/aps.58.50
In this paper we have investigated the entanglement evolutions between a two-level atom and a single-mode field as well as two two-level atoms in different W-like initial states in T-C model. It is shown that the evolutions of the formation entanglement between them are periodical, and the periods of the entanglement evolutions are different according to the difference of the initial states.The so-called sudden death of entanglement occures between two atoms as the initial states is some W-like initial state.
Energy level-splitting of ground state in spinor Bose-Einstein condensate with large number of atoms
2009, 58 (1): 55-60. doi: 10.7498/aps.58.55
We study the mode deviation effect of a spin-1 Bose-Einstein condensate with large number of atoms in optical trap beyond the single-mode approximation. Based on the effective Hamiltonian with nondegenerate level of the collective spin states, we get the mode deviation factor and explicitly calculate the level splitting energy as function of the atom number N.
2009, 58 (1): 61-65. doi: 10.7498/aps.58.61
A generalized non-harmonic oscillator potential for spin 1/2 particles is studied. The Dirac Hamiltonian contains a scalar and a vector non-harmonic oscillator potentials. Setting either or both combinations Σ(r)=S(r)+V(r) and Δ(r)=V(r)-S(r) to zero, analytical solutions for bound states of the corresponding Dirac equation are found. The eigenenergies and wave functions are presented, showing the pseudospin symmetry exists exactly.The relations between radial nodes of upper and lower components of the Dirac spinor are obtained.
Effects of the thickness of spacing layer and capping layer on the strain distribution and wavelength emission of InAs/GaAs quantum dot
2009, 58 (1): 66-72. doi: 10.7498/aps.58.66
A systematic investigation is given about the influence of thickness of the spacing layer on the strain distribution during the capping stage of the quantum dot. The calculated results show that the mismatch between the lattice constant of the spacing layer along the growth direction and that of the quantum dot is very important for the the strain distribution. The height of the quantum dot is compressed during the capping stage, which is qualitatively interpreted form the strain distributions. When the thickness of the spacing layer equals the quantum dot, the influence of thickness of the capping layer on strain distribution is also discussed. Based on the deformation potential theory, the dependence of the emission wavelength on the thickness of the capping layer is investigated. The calculated results agree well with the experiment results. We conclude that, during the capping stage of the quantum dot, the strain is very critical for both the shape of the quantum dot and the optical characteristics; extension of the emission wavelength via quantum dot strain engineering is an effective means.
2009, 58 (1): 73-77. doi: 10.7498/aps.58.73
Quantum cryptography protocols have the feature of unconditional security, which is ensured by attack-detection. A new method is introduced to improve the precision of the estimation of the error rate in the information bits. With the new technique, more information about the error bits can be obtained, then the value of error rate of the information bits can be obtained by classical signal estimation. This method can improve the precision of attack-detection within a single running of all quantum cryptography protocols.
2009, 58 (1): 78-82. doi: 10.7498/aps.58.78
Using entropy density near event horizon of the non-stationary Dilaton-Maxwell black hole, the instantaneous emission flux is calculated, and we come to a conclusion that the instantaneous emission flux of blank hole in any direction at any time is always proportionate to the quartic power of temperature of the event horizon of black hole in that direction. It is found that the coefficient of generalized Stefan-Boltzmann is no longer a constant, but a dynamic proportional coefficient related to the rate of change of event horizon, the structure of space-time near event horizon and the radiation absorption coefficient of black hole. It shows that an inner relation between the gravitational field around black hole and its thermal radiation must exist.
2009, 58 (1): 83-89. doi: 10.7498/aps.58.83
In the real world, condensation based on preferential aggregate mechanism, such as migration-driven aggregate growth system and packets routing in complex networks, is an important phenomenon. The research studies the ZRP condensation based on preferential aggregate mechanism in sale-free networks, in order to understand how the weighted transport with preferential hopping rates influences real systems. Instead of the approach of grand canonical ensemble which is generally used in a zero range process, an alternate approach of the mean field equations is used to study the dynamics of ZRP. The research finds that there are three phases when preferential aggregate index is greater than zero: namely the complete condensation, partial condensation, and well-proportioned condensation. But the ZRP system has only two phases when the preferential aggregate index is smaller than zero:the partial condensation and well-proportioned condensation. On the other hand, the mean particle distribution in the stationary state depends on the jumping rate, link weight, and preferential aggregate indexes. Monte Carlo simulation also validates the analytical results.
2009, 58 (1): 90-96. doi: 10.7498/aps.58.90
A scalar model of force network ensemble is proposed to investigate the force distribution in static granular system. The Laplace transform method is found as an effective method to solve the integral issue of probability density under complex constraints. On the condition that the system has few layers, the analytical expression for the limit distribution is accounted for which is the product of the polynomial function and the exponential function. When the force is near the average force, the distribution has its maximum value, when it's above the average force, the distribution decreases exponentially.
2009, 58 (1): 97-101. doi: 10.7498/aps.58.97
We introduced two correlated Gaussian multiplicative white noises into the Logistic growth model for an anti-tumor system subject to immune surveillance. Considering various active thresholds to initiate the immunity of the anti-tumor system, we made numerical simulations to investigate how the intensity λ of two correlated white noises influences the immune effect of an anti-tumor system. Our numerical results reveal that the correlation intensity λ has an optimal value, at which the anti-tumor system will achieve functionally the best immunity.
Effect of the time period modulation of color noise correlation intensity on the stochastic resonance of the single-mode laser
2009, 58 (1): 102-106. doi: 10.7498/aps.58.102
Stochastic resonance is studied in single-mode laser driven by colored noise with time period modulation of the noise correlation intensity. By means of the linear approximation method, we calculate the power spectrum and signal-to-noise ratio of the laser intensity. Effects of the noise intensity D and Q, the time period modulation frequency Ωλ, the noise self-correlation-time τ1 and τ2, and the noise correlation intensity λ on the signal-to-noise ratio R are discussed. The results reveal that the evolution of the signal-to-noise ratio with the noise intensity shows the single-peak resonance, the evolution of the signal-to-noise ratio with the time period modulation frequency shows periodic resonance and the evolution of the signal-to-noise ratio with the noise self-correlation-time shows monotonie increase.
Mamdani-Larsen fuzzy system based on expectation maximization algorithm and its applications to time series prediction
2009, 58 (1): 107-112. doi: 10.7498/aps.58.107
This work explores how Epanechnikov mixture model can be translated to Mamdani-Larsen fuzzy model. The mathematical equivalence between the conditional mean of an Epanechnikov mixture model and the defuzzified output of a Mamdani-Larsen fuzzy model is proved. The result provides a new perspective of studying the Mamdani-Larsen fuzzy model by interpreting a fuzzy system from a probabilistic viewpoint. Instead of estimating the parameters of the fuzzy rules directly, the parameters of an Epanechnikov mixture model can be firstly estimated using any popular density estimation algorithm, such as expectation maximization. Mamdani-Larsen fuzzy model trained in the new way has higher accuracy and stronger anti-noise capability. After comparing the simulation results with the ones obtained from other fuzzy system modeling tools, it can be claimed that the results are successful.
Chaotic digital communication system based on field programmable gate array technology—Design and implementation
2009, 58 (1): 113-119. doi: 10.7498/aps.58.113
A novel universal approach for design and implementation of chaotic digital communication system based on IEEE-754 standard and field programmable gate array technology (FPGA) is proposed, combing chaos encryption with traditional cipher realization. By using the Euler algorithm and appropriate discrete processing, the continuous chaotic system is converted to a discrete chaotic system. Using FPGA hardware design system, digital chaotic sequence is generated as the key. Scrambling and expansion encryption algorithm is realized and analyzed. Driven and response of secure communication system is designed by constructing a loop including the signal and achieving chaotic synchronization between sender and receiver. Taking grid Chua chaotic system as an example, the secure communication system using FPGA hardware platform is implemented. The technical development process, algorithm flow chart, hardware design and realization result are also given.
Generation of grid multi-scroll Chua’s chaotic attractors with combination of hysteresis and step series
2009, 58 (1): 120-130. doi: 10.7498/aps.58.120
In this paper, a new approach to generating two types of grid multi-scroll chaotic attractors from canonical Chua’s circuit is reported. Different from the techniques reported in current literature for generating multi-scroll chaotic attractors by constructing only the same type of non-linear function, the present approach constructs both hysteresis series and step series in the same Chua's circuit, and extends the saddle-focus equilibrium points with index-2 in phase space by combining both series in different ways, which makes it possible to create two kinds of grid multi-scroll chaotic attractors. The effectiveness of this method has been verified by theoretical analysis, numerical simulation and circuit implementation.
2009, 58 (1): 131-138. doi: 10.7498/aps.58.131
A lag synchronization controller is designed to realize synchronization between spatiotemporal chaos systems. The structure of the lag synchronization controller and the error equations of state variables are determined based on Lyapunov stability theory. Autocatalytic reaction-diffusion chaotic system is taken as an example to verify the effectiveness of the controller. The parameter identifier is further designed to provide effective identification of the parameters in the uncertain autocatalytic reaction-diffusion chaotic system. The method is proved to have better performance in anti-jamming by studying the synchronizing effect under bounded noise.
2009, 58 (1): 139-142. doi: 10.7498/aps.58.139
Using delayed state-feedback controller and analytic technique, the synchronization control of discrete-time neural network with delay is investigated. Sufficient conditions guaranteeing the synchronized behavior are obtained without assuming the boundedness and differentiability of activation functions. Numerical simulations show the effectiveness of the control scheme.
2009, 58 (1): 143-149. doi: 10.7498/aps.58.143
Spatiotemporal chaos control in a one-dimensional nonlinear drift-wave equation is considered. We propose a method of coupled feedback to suppress the spatiotemporal chaos of the drift-wave,based on the flocking algorithms. By using real agents and virtual agents as our target, we show numerically that the spatiotemporal chaos can be controlled to a regular state if appropriate control strength is chosen. The physical mechanism is analyzed based on the correlation coefficient
Multi-fractal identification of the fluctuation of silicon content in blast furnace hot metal based on multi-resolution analysis
2009, 58 (1): 150-157. doi: 10.7498/aps.58.150
With data of silicon content in hot metal collected respectively from No. 6 blast furnace of Baotou Steel, No. 7 blast furnace of Handan Steel and No.1 blast furnace of Laiwu Steel as sample spaces, quantitative analysis was employed to identify the multi-fractal characteristics of silicon content series. The long term trend of silicon content series was removed by performing multi-resolution analysis and the multi-fractal characteristics of the remaining part was analyzed. Comprehensive and quantitative details of the partial fluctuant singularity and fluctuant singularity at different levels are displayed through computation of generalized Hurst index, scaling function and multi-fractal spectrum. Simulation results proved that the fluctuation of silicon content series from 3 different blast furnaces showed significant multi-fractal characteristics, which is far from sufficient to be described by a single Hurst index or box dimension.
2009, 58 (1): 158-164. doi: 10.7498/aps.58.158
This paper deals with L2—L∞ control for leader-following coordination of second-order multi-agent systems with external disturbance and time-delay on fixed topology. In practical applications, the peak value of the controlled output is often required to be within a certain range and the ranges of the position and the velocity are different, so we introduce the weighted coefficients for the controlled outputs of the position and the velocity separately. Then, we obtain a multi-agent system of the model.Based on the Lyapunov-Krasovskii theory, both networks with and without time-delay are analyzed for leader-following corrdination of the position vector and the velocity vector with the desired L2—L∞ performance. Furthermore, sufficient conditions in terms of bilinear matrix inequality are given to guarantee the consensus problems for the multi-agent systems with and without time-delay sparately. Finally,numerical simulations are provided to show the effectiveness of our strategies.
2009, 58 (1): 165-173. doi: 10.7498/aps.58.165
Er3+ doped Y2O3 nano-crystals with different size are prepared using combustion method. Size effect on luminescence properties of Er3+ doped Y2O3 nano crystals are investigated. No shift of the absorption peak in the photo-acoustic spectra is observed with the decrease of the Y2O3particle size, indicating that the size induced energy shifts of the rare-earth levels are negligible. However, the emission spectra under 488nm excitation indicate that the ratio of the intensity of 4S3/2→4I15/2 transition to that of 2H11/2→4I15/2 decreases with the decrease of the particle size. It is believed that the rate of hypersensitive transition of 2H11/2→4I15/2 increases with the decrease of the particle size more quickly than that of transition of 4S3/2→4I15/2. The time dependence of the 554nm luminescence decay excited by 518nm reveals that the rate of up-converted energy transfer occurring between two Er3+ ions in 4S3/2 state increases with the decrease of the particle size.
2009, 58 (1): 174-177. doi: 10.7498/aps.58.174
The single-scattering-foil method is the basic of passive proton beam spreading system. In this paper, the angular distribution and energy distribution of proton beam on passing through a single scattering foil are calculated using Monte-Carlo multi-particle transport code Fluka2006.3b.2., including the effect of proton energy, scattering material and target thickness on scattering angle. The result shows that thin-high-atomic-number material can be used as the scattering material.
ATOMIC AND MOLECULAR PHYSICS
2009, 58 (1): 178-184. doi: 10.7498/aps.58.178
Quadratic configuration interaction calculation (QCISD) and B3LYP methods have been used to optimize the possible ground-state structures of H2, BeH and BeH2 molecules. The results show that their ground electronic states are H2(1Σg), BeH(2Σ) and BeH2(1Σg); the stable structure of BeH2molecule is of D∞h symmetry. The Murrell-Sorbie potential energy function with 8 parameters of BeH and H2 molecule has been derived from the least square method, according to which spectral data and force constants are deduced. The analytical potential energy function of BeH2 is derived from the many-body expansion theory. Since BeH2(D∞h) formed from H+BeH has a deep potential trap, the complex com pound molecule of H-Be-H is easily formed. The reaction of Be+H2→HBeH with ΔH=-1.4654eV is an exothermic reaction.
2009, 58 (1): 185-192. doi: 10.7498/aps.58.185
Quadratic configuration interaction method including single and double substitutions has been used to optimize the possible structures of BeH2 and H2S molecules with the 6-311++g(3df,3pd) basis set. The results show that the ground state of BeH2 molecule is of D∞h symmetry and is in the X1Σ+g state, the ground state of H2S molecule is of C2v symmetry and in the X1A1 state. The equilibrium geometry, dissociation energy, harmonic frequencies and force constants have been calculated. The potential energy functions of BeH2 and H2S have been derived by using the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules.
2009, 58 (1): 193-200. doi: 10.7498/aps.58.193.1
The electronic properties of multiferroic BiFeO3 with paraelectric paramagnetic phase at high-temperature and ferroelectric antiferromagnetic phase are calculated using density functional theory with spin-polarized generalized-gradient approximation (GGS) and plane wave pseudopotentials. study of Born effective charges shows that the greatest contributor to the ferroelectric distortion is Bi atoms' displacement. We obtained very large theoretical electric polarization, which agrees very well with the results of thin-film test. The calculation shows that BiFeO3 ground state has G type anti-ferromagnetic order and the theoretical magnetic moments of Fe ion accord with experimental values. After ferroelectric phase transformation, the chemical bond changes much due to Bi-6s and Bi-6p state charge transfer, and the effect of Bi-6s electrons becomes more pronounced. Partial density of states calculation indicates that the energy split between bonding orbit of Bi-6p state and anti-bonding orbit is bigger than that between other electronic states, by which covalent bond between Bi-6p state and O-2p state is strengthened, which is the origin of off-center displacement. Thus the discussion about the BiMnO3 is testified. Bi-6s state is polarized due to the static electric repulsion, but does not take part in the hybridization of Bi-6p and O-2p electrons. The charge transfer originates from its weak covalent interaction with the O-2s, 2p orbits, by which the Bi-6s state electronic polarization is reinforced. This kind of covalent interaction helps the relative replacement of Bi-O, which is the reason for the strong systemic electric polarization.
2009, 58 (1): 201-208. doi: 10.7498/aps.58.201
Using the QCISD/6-311++G(3df,3pd) and B3P86/6-311++G(3d2f) respectively, the possible ground-state structures of SiH2 and SiF2 molecules have been optimized. The results show that the ground state of SiH2 molecule is of C2v symmetry and in the 1A1 state, whose angle, equilibrium nuclear distance and dissociation energy are 92.5025°, 0.15149nm and 3.7098eV, respectively, The results also show that the ground state of SiF2 molecule is of C2v symmetry in the 1A1 state, whose angle, equilibrium nuclear distance and dissociation energy are 100.7079°, 0.16014nm and 14.1391eV, respectively, and their harmonic frequencies and force constants have been calculated. The present paper correctly determines the dissociation limits based on group theory and atomic and molecular reactive statics (AMRS). Analytical potential energy functions for the ground states X1A1 of SiX2(X=H，F) have been derived using many-body expansion method. The structure and energy of SiX2(X=H，F) can correctly reappear on the potential surface. Molecular reaction kinetics of SiH+H and SiF+F based on the potential energy functions is discussed briefly.
2009, 58 (1): 209-214. doi: 10.7498/aps.58.209
Isolated-core excitation and autoionization detection method are combined to measure even-parity high-lying excited states of Sm atom. The experimental results are classified and discussed in detail in the light of different autoionization channels. With the information of energy levels and their relative intensities converging to different thresholds, the Rydberg states are identified from the valence states in the same region. In addition, with the effective technique to recognise different types of high-lying states, the spectroscopic properties of Rydberg states and valence states in the region between 41800 cm-1 and 43800 cm-1 are discussed and analyzed in detail.
2009, 58 (1): 215-222. doi: 10.7498/aps.58.215
Resonant ionization spectra of Sm atom are studied with a two-step photoexcitation and photoionization method. Two different excitation paths are carried out as the following: In the path 1, the first laser whose wavelength is fixed at 478.44nm excites the Sm atom from the 4f66s2［7F1］ state to the 4f66s6p［7D1］ state，and then the second laser whose wavelength λ2 is scanned from 480nm to 530nm excites it further to the high-lying state with even parity. In the path 2, the first laser whose wavelength is fixed at 574.81nm excites the Sm atom from the 4f66s2［7F2］ state to the 4f66s6p［5G3］ state，and then the second laser whose wavelength λ2 is scanned from 460nm to 470.5nm excites it further to the high-lying state with even parity. These Sm atoms in the high-lying state are probed by photoionization via the third laser. All together 26 and 76 states of Sm atom in the 39465—39932 cm-1 and the 40000—42010 cm-1 energy region, respectively, have been detected below the first ionization limit. The energy levels and relative strengths of these states have been determined. Among them, 51 states are newly discovered, while the rest agree well with the values published in literature. In addition, efforts are also made to determine their spectral designation.
2009, 58 (1): 223-228. doi: 10.7498/aps.58.223
The line intensities of 0300 a—0000 s transition of the symmetric-top NH3 molecule at high temperature were obtained by directly calculating the partition functions while regarding the rotationless transition dipole moment squared as a constant. The calculated values of the total internal partition sums (TIPS) are consistent with the data of HITRAN database within 0.19% at 296 K. The calculated line intensities data at 2000 K and 3000 K are also in excellent agreement with the data in HITRAN database with discrepancies less than -0.65% and -1.77%, which strongly supports the calculations of partition function and line intensity at high temperature. Then we extended the calculation to higher temperature. The line intensities and simulated spectra of 3ν2 band of the symmetric-top NH3 molecule at 4000 K and 5000 K were reported. The results are of significance for the study of the high-temperature molecular spectra in experiment and in theory.
2009, 58 (1): 229-233. doi: 10.7498/aps.58.229
Differential cross sections (DCSs) for collisions in 3He-HBr, 4He-HBr, 6He-HBr and 7He-HBr are calculated by the close-coupling approach from the anisotropic intermolecular potential of the He-HBr system established by the author. The calculations are performed separately at the collision energies of 40 and 75 meV. The influence of the incident isotope He atoms on DCSs is discussed in detail. The results show that the angular distribution of the total DCSs at zero degree increases and the position of oscillation minimum of the same order gradually shifts towards small scattering angle along with the increase of the incident isotope He atom mass at identical collision energy. And crossing angle between the elastic and total inelastic DCSs gradually decreases and the total inelastic DCS gradually increases. The rainbow phenomenon becomes more evident the lower the collision energy and the larger mass of the incident He isotope atom.
CLASSICAL AREA OF PHENOMENOLOGY
2009, 58 (1): 234-237. doi: 10.7498/aps.58.234
According to the electron-cloud-conductor model, there should exist interaction of electromagnetic induction between light and electron when they meet, and this interaction may result in the energy exchange between them. Energy exchange between light and free electron in vacuum is analyzed with the model, and the result consists with that of the existing theory. The model can also be used to explain the experimental result of ionization rate of N2 molecules by short laser pulses and the behavior of ionization of molecules by X-ray. It is concluded that one of the root causes for energy exchange between light and an electron is electromagnetic induction between them.
2009, 58 (1): 238-242. doi: 10.7498/aps.58.238
Based on the dispersion equation of electromagnetic mode and the nolinear theory of gyrotron traveling wave amplifier (gyro-TWA), the influence of the thickness of the lossy layer on beam-wave interaction in the gyro-TWA is studied. The simulation results show that large attenuation for competing mode TE21 can be realized while that of operating mode is small by appropriately choosing the thickness and conductivity of the lossy layer. The bandwidth decreases with the increase of the thickness, but the output power of the middle of the bandwidth increases and becomes more smooth. This is useful for improving the stability of gyro-TWA.
2009, 58 (1): 243-249. doi: 10.7498/aps.58.243
A modified diffusion approximation is investigated. In this theoretical model, diffusion coefficient D of the standard diffusion approximation is substituted by diffusion coefficient Dasym of P3 approximation. Analytic solution RHybrid(ρ) of this hybrid diffusion for reflectance in single source approximation and steady-state case with extrapolated boundary is obtained; influences of the transport albedo a′ on the standard diffusion approximation RDA(ρ) and the hybrid diffusion approximation RHybrid(ρ) are compared; recovering of optical parameters from diffuse reflectance RHybrid(ρ) is demonstrated, and the errors and application ranges are studied. The results show that this hybrid diffusion approximation RHybrid(ρ) can be used in strong absorption media and at short source-detector separation.
2009, 58 (1): 250-257. doi: 10.7498/aps.58.250
By using the interference law for partially coherent light, the interference in a four-pinhole interferometer with square symmetry illuminated by partially coherent light is studied. It is found that the complete destructive interference in the four-pinhole interferometer may appear, and there may exist phase singularities of intensity and spectral degree of coherence. A comparison with the interference of two and three partially coherent point sources is made and the results can be physically interpreted in such a way, that in spite of the partial coherence of four point sources, the sum of the fields emerging from two point sources may be fully correlated with the sum of the fields emerging from the other two point sources.
2009, 58 (1): 258-263. doi: 10.7498/aps.58.258
In this paper, the transverse optical trapping of absorbing double-layer spherical particle is studied based on geometrical optics model. A model for double-layer spherical particle with optical absorption is presented. The transverse optical trapping force of a double-layer dielectric spherical particle with linear absorption in the outer layer illuminated by a focused Gaussian beam of TEM00 mode is simulated numerically. Our results show that the characteristicsof optical trapping, including the stable trapped positions, the peak intensityand the stiffness of stable trapping, greatly depend on by the absorption coefficient of the double-layer spherical particle. Besides, the ratio of the inner radius to the outer radius of the particle also has modulating influence on the properties of transverse trapping. It is possible to trap transversely the double-layer spherical particle with absorption on the axis of the incident Gaussian beam and on a circle centered at the optical axis for different axial offsets of sphere center from the beam waist as well.
Resolution restoration algorithm based on maximum a posteriori from Poisson-Markov distribution and blind multichannel deconvolution
2009, 58 (1): 264-271. doi: 10.7498/aps.58.264
Single input multichannel output (SIMO) imaging system which enhances the spatial resolution by resampling the same scene increasingly has large applications, and the corresponding image restoration algorithm for uncontrollable SIMO has became the subject of current research. By the assumptions of Poisson, Markov stochastic field and regulation of improved multichannel constraint, the multichannel blind image reconstruction is proposed based on maximum a posteriori rules. The algorithm doesn't need to know the prior knowledge such as character, type and distribution of the degraded point spread function (PSF) in each channel. The pixels and PSF are projected into the amplitude restrained set and energy invariable set, respectively, and their estimates converge to the global optimum solutions by the alterative iteration, and finally, the super-resolution image is restored. Algorithm simulations and the real micro-shift, micro-defocus experiments indicate that it has good restoration effect and stability at different signal noise ratios and for different PSF supports.
2009, 58 (1): 272-277. doi: 10.7498/aps.58.272.1
The system of a single-mode field interacting with a -type three-level atom in a harmonic trap is investigated. The linear entropy of the field, the atomic internal states and the atomic mass center motion are explored. It is shown that the atomic mass center motion not only can affect the linear entropy of the field and the atomic internal states, but also effectively changes their relationship.
2009, 58 (1): 278-284. doi: 10.7498/aps.58.278.1
We conducted an investigation into the polarized absorption and emission spectra, the absorption for unpolarized pump light, and the continuous-wave (cw) laser properties of the Yb:KLu(WO4)2 crystal. The low symmetry of the crystal leads to strong anisotropy in the crystal spectroscopy; the strongest absorption and emission occur in the polarization direction parallel to the Nm principal axis. The Ng-cut crystal has highest absorption efficiency for unpolarized pump light and largest potential for generating laser output power. With 11 W of cw output power produced by using a 2 mm thick crystal, the optical-to-optical conversion and slope efficiencies amount to 68% and 80%, respectively, with respect to the absorbed pump power.
2009, 58 (1): 285-289. doi: 10.7498/aps.58.285.1
The properties of the Anti-Reflection coated (AR-coated) GaAs diode lasers are investigated systematically in Littrow configuration. The tuning range of about 30 GHz is obtained without any mode-hops by the current compensation technique. Using a heterodyne detection technique, the linewidth of the AR-coated ECDL is measured, which is about 120 kHz. We also investigate the intensity noise of the AR-coated ECDL as a function of the current and the wavelength. The relations between the intensity noise of the ECDL and the driving current and wavelength are obtained and analyzed. This laser system can be used in many areas, such as atomic physics, laser spectroscopy and quantum optics, etc.
2009, 58 (1): 290-297. doi: 10.7498/aps.58.290
We present a theoretical treatment for the repeatedly dressed FWM processes in N5B five-level atomic system. Based on our previous work, the evolution of Autler-Townes splitting in a multi-dressed FWM spectrum is expounded using the characteristic method of Independence effect. Under condition that the coupling and probe fields which induced the FWM are strong, we further demonstrate the suppression and enhancement of FWM signal intensity. The results indicate that one cpupling field can dresse the atom twice and produce the donbly dressed state and triply dressed states. Many applications of multi-dressed FWM spectrum can benefit from the investigation on the atomic energy level and the nonlinear processes of mutiwave mixing(MWM).
Anisotropic diffraction pattern formation from a nematic liquid crystals film induced by low-power linearly polarized beam
2009, 58 (1): 298-303. doi: 10.7498/aps.58.298.1
Anisotropic diffraction patterns were observed on far-field screen induced by a weak (0.16 W/cm2) linearly polarized collimated beam passing through a homeotropic C60-doped nematic liquid crystal (5CB) cell. Based on orientational photorefractive effect, two-wave coupling experiment was carried out to induce liquid crystal molecule re-orientation. The form of space-charge field with the Gaussian distribution induced by the Gaussian beam incident on the sample is investigated. The outline of far-field diffraction pattern is concentric ring, and shows symmetrical gaps in the direction perpendicular to the direction of polarization of light. In addition, diffraction pattern changes when the polarization of the incident light is changed, effective nonlinear index coefficient is n20.3 cm2/W. The results showed that our theoretical analyzsis was consistent with the observed experimental phenomena.
Study on the choosing of new SBS medium perfluoro-compound for phase conjugation mirror and optical limiter
2009, 58 (1): 304-308. doi: 10.7498/aps.58.304
In this paper, new stimulated Brillouin scattering (SBS) medium of perfluoro-compound with low absorption and high power-load are reported. The choosing of medium for conjugation mirror (PCM) and optical limiting are discussed respectively, and validated in the Nd: YAG Q-switched laser system. The results indicate that medium with small molecular weight, low kinematic viscosity and large gain coefficient should be chosen for SBS PCM; however, medium with large molecular weight, great kinematic viscosity and small gain coefficient is needed in the optical limiting. The discovery of the new medius diversifies the SBS media and the medium choosing rules provide a guide to the application the new medium.
2009, 58 (1): 309-314. doi: 10.7498/aps.58.309
A ZnO film with two-dimensional periodic structure was grown on Si substrate by radio-frequency plasma-assisted molecular beam epitaxy. The influence of wet-chemical etching on Si (100) and Si (111) substrates patterned with dot arrays was investigated for achieving a ZnO film with good periodic structure. X-ray diffraction and scanning electron microscopy mesurements demonstrate better crystalline quality and surface morphology of ZnO film grown on Si (111) than that on Si (100). The results suggest that the growth method is feasible for the fabrication of ZnO film with good periodic structure.
Analysis for phase shifts transformation of chirped pulse from frequency-domain to time-domain based on Fourier transform
2009, 58 (1): 315-320. doi: 10.7498/aps.58.315
Based on spectral interferometry and Fourier transformation, the method that spectral phase shifts of chirped pulse are transformed to transient temporal phase shifts is investigated theoretically. The error transferring formula of phase shifts from Fourier-domain to time-domain is derived, and the temporal resolution of temporal phase shifts restricted by the spectral bandwidth of reference pulse is given. The transformation process of phase shifts is simulated. The results show that phase shifts obtained is characteristic of temporal change, and the spectral phase shifts error is transferred to time-domain with reduced magnitude, and it is in agreement with calculated result by the error transferring formula.
2009, 58 (1): 321-327. doi: 10.7498/aps.58.321
An approximate analytical expression of the stress birefringence for Panda polarization-maintaining fiber (Panda-PMF) was deduced by using elasticity theory and complex function method. Based on this expression, the birefringence properties of this fiber were analyzed numerically by using the finite-element method. The results show that the birefringence expressed by core average stress mode is more accurate than that expressed by the core center stress mode and the error of the former is less than 0.18% compared with that of the analytic method. Further more, the birefringence degradation of the Panda-PMF induced by stress area mismatch was analyzed and proved by the related experiment.
2009, 58 (1): 328-332. doi: 10.7498/aps.58.328
Transfer function of single-stage acousto-optic tunable filter (AOTF) has sidelobes higher than -9 dB, and this large sidelobes level limits AOTF application. In this paper, the sidelobes of two single-stage AOTF's, which are polarization-dependent collinear and polarization-independent quasi-collinear respectively, are investigated, and the transfer function of double-stage filter is obtained. The calculations on single- and double-stage AOTF's have shown that the double-stage device can provide significant improvement in sidelobe suppression. In experiment, two single-stage AOTF's are cascaded, and filtering property of this double-stage device is measured. The experimental results show that the sidelobes of this cascaded AOTF is suppressed to -19dB，and the 3-dB bandwidth is narrowed to some outent.
2009, 58 (1): 333-340. doi: 10.7498/aps.58.333
Helmholtz equation least square method (HELS) is based on the assumption that the acoustic field can be approximated by the superposition of a series of spherical waves. According to the principle of least square error between the reconstruction and measurement, the expansion number of the spherical wave equation and the related coefficients can be determined by the least-square method. The HELS method is applied in the practice due to its efficient computing and less measurements comparing with other acoustical holography algorithms. HELS and other near-field acoustic holography methods are all based on the stationary acoustic field. As a special example of the non-stationary acoustic field, the cyclostationary acoustic field is usually analyzed by dealing with signals in a single channel and its nth order statistics are often utilized to detect mechanical faults. In the present paper, HELS method is modified to analyze the cyclostationary acoustic field with the variance of cyclic spectrum density. The reconstruction in the appropriate cyclic frequency will supply visible acoustic field information, especially that hidden under the cyclostationary condition. A numerical simulation is done to verify the validity of the modified HELS, in which the effects of the ways of measurement are discussed. At last, a spherical sound box driven by cyclostationary signal is set in a semi-anechoic chamber and the acoustic field is reconstructed by modified HELS method.
2009, 58 (1): 341-346. doi: 10.7498/aps.58.341
Granular gas is a far from equilibrium discrete system. Due to intrinsic energy dissipation, the system will cool down when there is no energy input. In this paper we report our experimental study on this cooling process in a quasi 2-D granular gas system under gravity. By using fast video photography, particles excited by air flow from the bottom of the container were traced during cooling. The cooling process contains two regimes: One of them is when inelastic collisions of particles in the gas phase is dominant. In this regime condensation at the bottom will occur at a rate determined by three factors, namely the constant piling rate α, granular temperature T and vertical mass velocity vg. The second regime is near the end of the cooling, the energy dissipation is mainly contributed from the surface area of the condensation region. This time the piling rate and the dissipation rate both show exponential dependence.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2009, 58 (1): 347-353. doi: 10.7498/aps.58.347
Electron plasma waves driven by high-power laser pulses are described as an effective geometric background by means of optical metrics. The motion equations of probe photons and Hamilton expression for photons under the background of electron plasma waves are derived via Maxwell equations in the curved spacetime. The contribution of electron plasma wave to photons Berry phase is obtained and the corresponding modification to photons Berry phase in vacuum spacetime is estimated under the conditions of the present experimental facility.
Zonal flow dynamics in background of ion-temperature-gradient mode turbulence based on minimal freedom model
2009, 58 (1): 354-362. doi: 10.7498/aps.58.354
In the ITG (ion-temperature-gradient) mode turbulence background, the dynamics of zonal flow generation is studied based on the minimal freedom model. We study the dynamical instability and present detailed numerical results. The energy cascade process in the ITG mode turbulence and the relationship between Reynolds stress and zonal flow are also discussed. The mechanism of turbulence suppression by zonal flow is clearly explored and displayed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2009, 58 (1): 373-377. doi: 10.7498/aps.58.373
The High temperature Raman spectra of LBO crystal and melt were studied. The rule of structure change of BGO crystal with increasing temperature was analyzed. The results show that the peaks of spectra move to the lower wavelength and broaden in different degrees. The intensities of spectra peaks decrease，too. In addition，the phase transformation of LBO crystal was studied by using high temperature Raman spectra as well. There is an apparent phase transformation of LBO at 1100K.
2009, 58 (1): 378-383. doi: 10.7498/aps.58.378
In this article，hole-doped nonstoichiometric manganites La0.67Sr0.33-x□xMnO3 (x=0，0.05，0.1，0.15，0.2，0.25，0.3，0.33) with A-site vacancy were synthesized using the solid-state reaction technique and the effect of A-site vacancy on structure and transport properties were studied. Results from Rietveld refinement of powder X-ray diffraction patterns showed that all samples were single phase with space group R3c and there were no structural phase transition for vacancy content x ranging from 0 to 0.33. The lattice parameters and volume of unit cell vary distinctly with x. These variations maybe result from the uncertain occupation ratio of vacancies at A-sites and Mn-sites. The bond angle of Mn—O—Mn decreases with increasing x，which indicates the presence of further distortion of MnO6 octahedron. Electrical measurements of La0.67Sr0.33-x□xMnO3 showed that the samples exhibited a metallic-insulator phase transition for xTMI towards higher temperature. In the range of 0.25≤x≤0.33，the samples exhibit insulating behavior without metallic-insulator transition，and also the effect of the magnetic field is to lower the resistivity.
2009, 58 (1): 384-389. doi: 10.7498/aps.58.384
The specific heat of liquid Ni60Cu20Fe20 ternary alloy was measured by electromagnetic levitation drop calorimetry in the temperature range from 1436 to 2008K. The maximum undercooling achieved in experiment is 232K (0.14TL). The specific heat was determined as 33.27J·mol-1·K-1 which varied slightly with temperature. Furthermore，the temperature dependence of the specific heat of normal and undercooled liquid Ni60Cu20Fe20 alloy was calculated by molecular dynamics method with embedded-atom potential (EAM) and quantum Sutton-Chen many-body potential (QSC). The calculated results indicate that the specific heat increases slowly with the decrease of temperature. By comparing these theoretical calculations with experiments，we found that the QSC model is more reasonable for predicting the specific heat of liquid Ni60Cu20Fe20 alloy than the EAM model.
2009, 58 (1): 390-398. doi: 10.7498/aps.58.390
A simple derivation of phase-field model for pure materials based on entropy functional is provided and then solved by adaptive finite element method (AFEM) to simulate the free dendritic growth from undercooled nickel melt. To investigate the evolutions of the dendrite and reproduce the real physical process，the modeling is performed in a larger domain and thinner interface with the highly computationally efficient and accurate AFEM. The simulated results show that the secondary arms grow in an unsymmetrical mode and their development is controlled by the thermal diffusion and affected by noises which are arbitrarily introduced in the phase-field governing equation. As the latent heat released during the migration of solid-liquid interface is accumulated sufficiently，it prompted initiation of other secondary arms at the same side of the primary arm. As the computation proceeds，the secondary arms become coarsened apparently through four different modes.
2009, 58 (1): 399-403. doi: 10.7498/aps.58.399
Spinel specimens deposited with a thin heavy metal (Cu，Au) film were implanted with inert-gas-ions and annealed in vacuum subsequently. The surface-plasmon-resonance-absorbance peak corresponding to metallic nanoparticles in the dielectric matrix was observed in the ultraviolet-visible absorbance spectra，indicating metallic nanoparticles were formed in the spinel specimens. The influence of the thickness of the metallic film deposited on the spinel specimen surface on the nanoparticle formation is evident besides the effect of annealing temperature.
2009, 58 (1): 404-410. doi: 10.7498/aps.58.404
The experiment of GaAs/Ge solar cells co-irradiated by proton and electron was done in space environment simulation equipment. The materials of GaAs/Ge solar cell are irradiated by proton beam with fixed energy of 100keV and dose from 1×109 to 3×1012cm-2. The I-V characteristic，spectral response and photoluminescence (PL) spectra were measured before and after irradiation in order to study the cells performance degradation induced by irradiation. The result indicated that the parameters such as short circuit current (Isc)，open circuit voltage (Voc)，maximum output power (Pmax) and fill factor (FF) all suffer degradation at different degrees as the irradiation fluence increases. The results show that proton irradiation induces a great damage in optical characteristics of the solar cell，resulting from the large quantity of irradiation defects that would destroy crystal lattice integrity and reduce the diffusion distance of minority carrier，and thus increase the surface recombination velocity. The damage extent of GaAs/Ge solar cell increases with proton dose in the ranges under investigation.
2009, 58 (1): 411-416. doi: 10.7498/aps.58.411
The possible discrete breathers are obtained numerically in the system of one-dimensional mixed Klein-Gordon/Fermi-Pasta-Ulam chain on the basis of simplified motion equations by using extended rotating plane wave approximation. Furthermore，the effect of each nonlinear parameter on the static，first-order harmonic and second-order harmonic components of the discrete breathers is investigated.
Universal scaling relations of the Hall resistivity and Hall angle near the vortex glass transition and the unified Hall resistivity equation
2009, 58 (1): 417-420. doi: 10.7498/aps.58.417
Universal scaling relations of the pinning effect on the Hall resistivity ρxy and Hall angle θH were shown. Considering the extended power law form of ρxx and the microscopic analysis of σxy，we derive unified ρxy equations for superconductors with and without double sign reversal.
2009, 58 (1): 421-426. doi: 10.7498/aps.58.421
We built the quasicrystal structures which are five-fold，eight-fold，ten-fold and twelve-fold rotational symmetric artificially，and measured their drag-reduction in the mixed solution of water and glycerin by viscometer. We found the twelvefold symmetric structure has a drag-reduction of 15%—9% when shear rate is 200—2000s-1. The drag-reduction can be much greater when the structure is compounded with rough surface consisting of micro/nano-structures.
Experimental investigation on formation of Al-Si clusters and nanocrystals in the segregation of ion-implanted Al on Si(100)
2009, 58 (1): 427-431. doi: 10.7498/aps.58.427
By high-temperature annealing of Si(100) samples containing ion-implanted Al atoms，thermodynamic behaviors of the segregated Al atoms on the surfaces have been investigated. Experiments of annealing the samples at 900℃ show that Al and Si atoms conbine to form Al-Si clusters with size of 2—3nm，while segregated Al atoms form epitaxial Al film and islands on Si(100) surfaces. Further annealing at 1200℃ indicates that rapid cooling of samples leads to formation of cubic Al4Si grains of 20—30nm size. The Al-Si clusters seem to be independent of the substrate structure and tend to come together，which are probably the precursor of the Al-Si alloy formed in the process of the high-temperature annealing and rapid cooling.
Influence of deposition parameter on chemical structure and moisture resistant properties for SiNx films deposited by DC pulse magnetron sputtering
2009, 58 (1): 432-437. doi: 10.7498/aps.58.432
Hydrogen-free SiNx films were deposited by direct current pulse magnetron sputtering at room temperature. We have studied the influence of N2 flow rate and Si target sputtering power on the structural characteristics and properties of deposited films by using Fourier-transform infrared spectroscopy，auto water vapor permeability tester，ultraviolet-visible spectrophotometer，stylus profilometer，and contact angle measurement. The results indicate that the content of Si—O bonding in SiNx films increaseds and moisture resistant property of SiNx films decreases with increasing N2 flow rate or decreasing Si target sputtering power. The films deposited at 300W of Si sputtering power and 6sccm of N2 flow rate show excellent water vapor permeability (0.764) with transmittance higher than 97.5% in visible range.
2009, 58 (1): 438-443. doi: 10.7498/aps.58.438
In this paper，large area CdS thin film was prepared by chemical bath deposition (CBD). The structure and morphology and optical characteristics of the thin film were investigated with XRD，optical transmittance spectra analyzer and AFM. The experimental results indicate that the properties of the thin film were homogeneous. The CdTe solar cells with different thickness of window layer by using the prepared CdS thin film were fabricated. It was found that the short circuit current density，Jsc，of the CdTe solar cells increases with the reduction of the thickness of CdS window layer and the device performance is improved. The module of CdTe solar cells with substrate size 30cm×40cm and total area of 993.6cm2 was fabricated. The results showed that the electrical behaviors of the 27 interconnected unitc were homogeneous too. The efficiency of greater than 8% for the module of CdTe solar cells with area of 993.6 cm2 was obtained.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The mechanism of the influence of Bi(or Sb) and rare earth on high temperature performance of AZ91 magnesium alloy
2009, 58 (1): 444-449. doi: 10.7498/aps.58.444
The atomic structure models of α matrix and the symmetric ［0001］ tilt boundary in AZ91 magnesium alloy were set up by using the concept of coincidence-site lattice (CSL). The total structure energy of α matrix and the grain boundary (GB)，the environment sensitive embedding energies (EESE) of alloy elements and the interaction energies between the atom clusters were calculated by using recursion method. Calculation results show that the cluster formed by Al and RE in bulk AZ1 Magnesium alloy is rather stable，but the cluster of Al，Bi(or Sb) and RE atom is unstable. When Bi(or Sb) and RE atoms coexist in AZ91 magnesium alloy，Bi or Sb will combine with RE to form dispersed particles which are mainly RE2Bi (or RE2Sb ) and RE-Sb(or RE-Bi) distributed at the grain boundary，and Al11RE3 will form in the bulk in AZ91 magnesium alloy. The consumption of Al in magnesium alloy inhibits the formation of the discontinuous precipitate phase Mg17Al12. The melting points of compounds formed by RE and Al (or Bi，Sb) are high，thus the high temperature performance of AZ91 magnesium alloy would be obviously improved.
2009, 58 (1): 450-458. doi: 10.7498/aps.58.450
Calculations of electronic structures and optical properties of Mg (or Si) and Mn co-doped GaN were carried out by means of first-principle plane-wave pesudopotential (PWP) based on density functional theory. The spin polarized impurity bands of deep energy levels were found for both systems. They are half metallic and suitable for spin injectors. Compared with GaN：Mn，GaN：Mn-Mg exhibits a significant increase in TC，while the 1.3eV absorption peak in GaN：Mn disappears due to addition of Mg. In addition，a strong absorption peak due to 4T1(F)→4T2(F) transition of Mn4+ were observed near 1.1eV. Nevertheless，GaN：Mn-Si failed to show increase of TC，and the absorption peak was not observed at the low energy side.
2009, 58 (1): 459-464. doi: 10.7498/aps.58.459
The ground and the excited states for the nondegenerate polymer such as cis-PA have been studied using the Kronig-Penney model with unequal potential barriers in the real space. The electronic states，the electron density distributions，and the lattice distortions in the system with different states are obtained. By comparing with those obtained in the Su-Schrieffer-Heeger (SSH) model，we find that our results of electron state densities and electron density distribution are more precise.
Effect of different effective mass and electric field on the electronic structure in GaN/AlxGa1-xN spherical quantum dot
2009, 58 (1): 465-470. doi: 10.7498/aps.58.465
In this paper，we have calculated the impurity electronic states and the binding energy with the variation of the quantum dot radius and Al content in GaN/AlxGa1-xN spherical quantum dot (QD) using the plane wave method. The modification of the energy states is discussed when the difference in effective electron mass in GaN and AlxGa1-xN is taken into account. The results show that the difference in effective mass can not be neglected when Al content is large. In addition，with the consideration of the difference in effective mass，we investigate the binding energy as function of quantum dot radius, impurity position and external electric field. The results are meaningful and can be widely applied in the design of optoelectronic devices.
2009, 58 (1): 471-476. doi: 10.7498/aps.58.471
Optical properties and surface structures of InAs/GaAs serf-assembled QDs grown on 2ML GaSb and x-ML GaAs combined strain-buffer layer are investigated systematically by photoluminescence (PL) and atomic force microscopy (AFM). The QD density varies from 1.2×10cm-2 to 8.0×10cm-2 due to the influence of the lattice mismatch. The combined layer favors the increasing of In incorporated into dots and the average height-to-width ratio，which resulted in the red-shift of the emission peaks.For the sample of 5ML GaAs thin film the ground state transition is shifted to nearly 1300nm at room temperature.
Ultrafast rising of output electric impulse of lock-on model of semi-insulated GaAs photoconductive switches
2009, 58 (1): 477-481. doi: 10.7498/aps.58.477
In the lock-on model of semi-insulating GaAs photoconductive switches，the output current pulse has ultra-fast rise character，the rise time can be even less than that of the laser pulse. Fluid model is used to simulate the transport of photo-induced carrier. The results show that photo-activated charge domain formed in the transport process of carriers is the main cause of ultra-fast rise time. Further studies on the establishment of photo-activated charge domain and the absorption process show：1. The photo-activated charge domains during the establishment enhance the electron density gradient. 2. When the photo-activated charge domains are absorbed by the anode，rapid decline of bias electric voltage will accelerate the rise rate of output current pulse. Due to the two processes, the output current pulse in the lock-on model shows ultra-fast rise character.
Trap capture properties of space charge and void breakdown charge in a cellular polypropylene electret film
2009, 58 (1): 482-487. doi: 10.7498/aps.58.482
The following aspects have been indicated by systematic studies on the cellular polypropylene (PP) electret film. Trap capture properties of space charges changed with their injected amount or surface potential of the sample. The space charges were captured largely in the deep traps of the sample surface and the second-deep traps of the near-surface region at small amount of charge injection. They would fill these traps in the surface layer (surface and near-surface region) and the shallow traps in bulk at the same time in the case of greater amount of charge injection. The charge detrapping temperatures of the three kinds of trap centers are about 160℃，138℃ and 92℃，respectively. The charges formed due to void breakdown (called the void breakdown charges) were captured not only in the surface layers of voids which have similar traps as the surface layer of the sample，but also there were numerous void breakdown charges which penetrated the void surface layer，entered into the bulk，and were captured by the shallow bulk traps.
2009, 58 (1): 488-493. doi: 10.7498/aps.58.488
The current induced magnetic switching (CIMS) effect could occur without the magnetic field in nano-scale pseudo-spin valves that have the potential perspective for application in nonvolatile magnetic random access memory. In this paper, spin transport process in the pseudo-spin valve nanopillars has been investigated with macroscopic double conducting channel diffusion model. Dynamic equation of the magnetization of free layer is established with the consideration of the influence of transverse component of the magnetization vector of free layer. And the boundary conditions of the spin current continuity and chemical-potential-split equality are employed. The critical current in CIMS effect is calculated. The influences of the conductance mismatch of ferromagnetic and nonmagnetic layers and longitudinal applied field on the critical current is interpreted.
2009, 58 (1): 494-497. doi: 10.7498/aps.58.494
Threshold voltage of SiC Schottky barrier source/drain MOSFET (SBSD MOSFETs) is different from the threshold voltage of traditional MOSFETs. Based on a comprehensive analysis of the operational mechanism，the threshold voltage of SBSD MOSFET is extracted and analyzed with 2-D simulator ISE. The threshold voltage of the device is defined as the gate voltage at which carriers from the source contact enter the channel by field emission while the channel is strongly inverted.
2009, 58 (1): 498-504. doi: 10.7498/aps.58.498
Zn0.95Co0.05O and Zn0.94Co0.05Al0.01O films were prepared by inductively coupled plasma enhanced physical vapor deposition with magnetic confinement system under different oxygen partial pressure. The local structure and charge transfer properties were investigated by X-ray absorption fine structure and resonant inelastic scattering spectroscopy at O-K, Co-K and Co-L edges. The Co K-edge and L-edge X-ray absorption fine structure revealed that Co2+ ions substituted for tetrahedrally coordinated Zn2+ ions without changing the wurtzite structure. The main defects were oxygen vacancies when the films were deposited under very low oxygen partial pressure. The resonant inelastic scattering spectroscopy indicated that the charge transfer between Co-3d and the electrons in Zn0.94Co0.05Al0.01O films was much stronger than that in Zn0.95Co0.05O. The oxygen partial pressure had an important effect in the charge transfer of Co-doped ZnO films.
2009, 58 (1): 505-510. doi: 10.7498/aps.58.505
Frequency selective surface (FSS) composed of a novel element is presented in this paper. The novel element is designed by adding L-shaped slots to the cross aperture at its four ends. By disconnecting the novel element，a corresponding disconnected element FSS is designed. Based on the spectral-domain approach，two FSS structures with the novel element are calculated and analyzed theoretically. The influence on the center frequency for changing angles of TE incidence，polarization of large angle incident waves and the pass band width in the operating frequency band are researched. With filming technology and lithography，two FSS samples are made. The tests are made in the microwave darkroom. The measured curve shows good agreement with the calculated curve. It is shown that the resonant frequency of both FSS structures are angle independent for TE incident waves or polarization independent for large angle incidence. Meanwhile，our disconnected element FSS structure has wider pass band with little change of the resonance frequency.
2009, 58 (1): 511-517. doi: 10.7498/aps.58.511
After subjecting to different high-field stress and gate stress，a recoverable degradation has been found，consisting of the decrease of saturation drain current IDsat and maximal transconductance gm，and the positive shift of threshold voltage VTH. AlGaN/GaN HEMTs were degradated more with the high-field strss voltage and the stress time increasing. Relatively，under gate pulse stress and on-state gate stress，the degradation was more obvious than under off-state gate stress. By analyzing the shift of primary parameters，we found that the hot carriers generated by impact ionization and trapped by traps in AlGaN barrier layer，and the emission of electrons from gate electrode filling in surface states at high gate-to-drian electric fileds, were the primary reasons causing device degradation after different stress. Off-state stress，on-state stress and pulse-state stress measurements reveal that the passivation treatment just changes short-time current collapse into long-time degradation，which dose not solve the reliability problem of AlGaN/GaN.
2009, 58 (1): 518-522. doi: 10.7498/aps.58.518
The charge-carrier mobility of the blend films consisting of organic small molecule and quantum dots (QDs)，Alq3 and CdSeS，are studied by time-of-flight (TOF) technique. The dependence of charge-carrier mobility in the blend films on electric filed and QD concentration is measured. The results show that the positional disorder in the blend films are increased with the increase of QD concentration. Moreover，the charge transport mechanisms between Alq3 and QDs and the number of electron hoppings between QDs will lead to the change of the charge-carrier mobility.
2009, 58 (1): 523-528. doi: 10.7498/aps.58.523
In this paper defect structure was investigated by dielectric response of pure ZnO ceramics，binary and multi-element ZnO-Bi2O3 based varistor ceramics with the help of broad band dielectric spectroscopy. It is found that no loss peak appears at room temperature in pure ZnO ceramics，while there is one and two loss peaks in the binary and multi-element ZnO-Bi2O3 based varistor ceramics，respectively. According to relaxation polarization theory and electronic relaxation theory，it is obtained that electronic relaxation process is equivalent to relaxation polarization in dielectric spectroscopy and the characteristic peak near 105Hz at room temperature arises from relaxation process of electrons trapped by oxygen vacancies and zinc interstitials. Based on the difference in the dependence of the two loss peaks on the temperature and the atmosphere of heat treatment，aging mechanism is explained as the desorption of oxygen.
2009, 58 (1): 529-535. doi: 10.7498/aps.58.529
Semi-super junction (S-SJ) is developed on the basis of the super junction (SJ) structure by adding BAL (bottom assist layer) in the base region. One should only adjust the depth and the doping concentration of the BAL in the S-SJ structure to obtain higher working voltages. At the same on resistance, the aspect ratio of p-column in the S-SJ structure is less than that in the super junction structure, which means simpler process of epitaxial growth and ion implantation, which is very effective in reducing the process difficulty and the manufacture cost. Because the band gap of SiGe material can be adjusted by changing the Gefraction and the epilayers strain, the carrier mobility is increased with the increasing Ge content, the manufacture process is compatible with Si process, and great importance has been gradually attached to the SiGe material. To meet the requirements of low forward conducting voltage drop, high breakdown voltage, minimum reverse leakage current, and fast and soft reverse recovery process for power diodes in high frequency power electronics circuits, a S-SJ SiGe diode with remarkable improvement in all these characteristics of present power diode is proposed by combining both merits of S-SJ structure and SiGe material in this paper.
2009, 58 (1): 536-540. doi: 10.7498/aps.58.536
A metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT) with atomic layer deposition (ALD) of 10nm Al2O3 gate dielectric is manufactured. The superiorities in saturation current and leakage current of the novel MOS-HEMT device are verified by comparison of the MOS-HEMT with traditional MES-HEMT devices at room temperature. The statistical analysis of the features of temperature variation of the device characteristics in the 30—180℃ range, which shows the distinction in degration degree by temperature on the two kinds of devices, is also illustrated. The conclusion that the device saturation current and the transconductance degradations are mainly caused by transport characteristic degradation is reached at. Thus, the conclusion can be drawn that all statistical and analytical results witness the significant role played by the reduced surface states in the surface of the AlGaN in optimizing the characteristics of the device.
2009, 58 (1): 541-545. doi: 10.7498/aps.58.541
The magnetic properties of inverse-spinel LiNiVO4 have been investigated. It is found that there is a strong spin-orbit coupling effect in the system via fitting the paramagnetic data at high-temperature portion. A short-range antiferromagnetic ordering shows at low temperature with Neel temperature 35 K，which results from the restriction of the geometrical frustration due to the random distribution of Li+/Ni2+ ions.
Magnetoelectric response of magnetostrictive/piezoelectric composite on a trapezoidal elastic substrate
2009, 58 (1): 546-553. doi: 10.7498/aps.58.546
A magnetostrictive /elastic substrate /piezoelectric composite has been developed where the elastic substrate takes the form of trapezium to amplify the strain. By using the equivalent circuit, the magnetoelectric response of the composite in the longitudinal vibration has been analyzed. The magnetoelectric response of a Terfenol-D/trapezoidal Be-bronze/PZT-5H composite is calculated and is compared with the experiment. It is indicated that the theoretical response shows a similar variation tendency as the experimental in spite of the difference in resonant frequencies and the values of the magnetoelectric voltage coefficients, which is the result of neglecting the glue behavior. At the same time, the composite on a trapezoidal substrate and the composite on a rectangular substrate are compared, which indicates that the former has higher magnetoelectric voltage coefficient. The length ratio of the trapezoidal elastic substrate and the thickness ratio of the composite are further analyzed. It is found that the composite will have maximum magnetoelectric voltage coefficient when: (1) the ratio of the length of wide section to the total length of a trapezoidal elastic substrate is 0.45; (2) the thickness of a trapezoidal elastic substrate is one fourth that of Terfenol-D layer.
2009, 58 (1): 554-558. doi: 10.7498/aps.58.554
Periodically poled LiNbO3 was prepared by applying external field. Through a comparison study on switching currents of different sized PPLN, a new method of determining the nucleation time and the velocity of domain tip propagation toward the opposite face of the crystal was proposed. According to this method, a conclusion could be drawn that the nucleation time is 80ns and the tip velocity of switching domain is 0.1667m/s, when the external field is 25.1kV/mm, 50ms square wave pulse.
Reflectivity of semi-infinite one-dimensional photonic crystal composed of alternate layers of ordinary material and negative refraction material
2009, 58 (1): 559-564. doi: 10.7498/aps.58.559
The reflection on the semi-infinite periodic one-dimensional photonic crystal composed of alternate layers of ordinary material and negative refraction material is investigated. We find that the reflectivity is exactly equal to 1 in the forbidden frequency gap, and in the pass band, it averages out the rapid fluctuation of reflection of the finite structure. When the optical thickness of both ordinary material and negative refraction material are in opposite sign, there will be a zero-n band gap. We analytically prove that the zero-n band gap is insensitive to incident angle and polarization. It is also anticipated that the zero-n band gap is invariant with the scaling of lattice constant.
Effect of hydrogen dilution on crystalline properties of nano-crystalline silicon thin films in fast growth
2009, 58 (1): 565-569. doi: 10.7498/aps.58.565
Nano-crystalline silicon films were prepared from SiH4 diluted with hydrogen by plasma enhanced chemical vapor deposition at a pressure of 230 Pa. The effect of hydrogen dilution on their growth rate and crystalline properties were investigated. The experimental results indicate that the crystalline fraction and grain size increase with increasing hydrogen dilution ratio, and when the hydrogen dilution ratio increases to 99%, the crystalline fraction reaches 70%. The deposition rate decreases with increasing hydrogen dilution ratio, when the hydrogen dilution ratio decreases from 99% to 95%, the deposition rate of thin film increases from 0.3nm/s to 0.8nm/s.
2009, 58 (1): 570-574. doi: 10.7498/aps.58.570
The high temperature Raman spectra of KTN crystal and melt were studied. The structures of KTN crystal and melt were analyzed. The rule of structure change of KTN crystal with increasing temperature was analyzed. The results show that the peaks of spectra move to the lower wavelength and broaden by different degrees. The intensities of spectra peaks decrease, too. Raman peaks at 538, 585, 835, 868 and 875cm-1 were analyzed in detail. Phase transition from tetragonal to cubic was observed and explained. In high temperalure KTN melt, the ［Ta/NbO6］ octahedron entities disappeared. Meanwhile, there were many Ta/Nb O double bonds in the ［Ta/NbO3］- entities. It showed that there were ［Ta/NbO3］- growth unities in KTN melts.
2009, 58 (1): 575-579. doi: 10.7498/aps.58.575
This paper investigates the effect of vacuum thermal treatment on current-voltage (I-V) and capacitance-voltage (C-V) characteristics, hydrophobic properties and microstructure of CH4 doped SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane (D5) electron cyclotron resonance plasma. The results show that the desorption of thermally unstable CHx groups during the heat treatment can lead to the decrease of leakage current, the variation of SiCOH/Si interface state and the decrease of surface roughness. However, the desorption of CHx groups also leads to the deterioration of hydrophobic property.
RE-TM antiferromagnetic coupling and laser induced ultrafast magnetization reversal dynamics in GdFeCo magneto-optical films
2009, 58 (1): 580-584. doi: 10.7498/aps.58.580
The RE-TM antiferromagnetic coupling behavior and magnetization reversal dynamics in passing through the fermimagnetic compensation temperature (Tm) due to laser heating of GeFeCo films are investigated using femtosecond time-resolved pump-probe Kerr spectroscopy. Owing to sample temperature passing through Tm and hence the exchange of net magnetic moment carriers, an abnormal hysteresis loop is observed. The saturation magnetization difference between magnetization states above and below coercive field is found under a same direction of magnetic field, which reveals the incomplete rigid coupling between RE and TM sub-lattices in GdFeCo. A complete ultrafast magnetization reversal and recovery dynamic process is experimentally observed at the saturation magnetic bias on the sample with Al heat sink layer. Besides, by comparing magnetization reversal at saturation magnetic bias with magnetization recovery at remanence, it was found that the magnetic field applied externally does not affect the rate of domain nucleation and growth, but only their magnetization direction.
2009, 58 (1): 585-589. doi: 10.7498/aps.58.585
Nanorod GdPO4:Eu3+ phosphor was prepared by solovothermal reaction and the phosphorus source and the pH value of the solution were important to the final product. Photoluminescence properties of nanorod GdPO4:Eu3+ phosphor was compared with bulk GdPO4:Eu3+ phosphor. The luminescence colour purity of nanorod GdPO4:Eu3+ phosphor was better than that of the bulk GdPO4:Eu3+ phosphor under 147nm excitation. The host absorption band and Eu-O charge transfer band of nanorod GdPO4:Eu3+ phosphor were blue shifted compared with the bulk GdPO4:Eu3+ phosphor.
2009, 58 (1): 590-595. doi: 10.7498/aps.58.590
InGaN/GaN quantum wells have been grown by metal-organic chemical vapor deposition. InGaN/GaN quantum well with n-type InGaN/GaN thin layer or InGaN/GaN superlattice layer were studied. By introducing n-type InGaN/GaN thin layer or InGaN/GaN superlattice layer, the strain in quantum well active area was released, the surface morphology was improved and the density of V-type defect was redued. It was also found that the multiple quantum well photoluminescence intensity and the radiation efficiency of light emitting diodes were both higher than that of the structure without InGaN/GaN superlattice layer.
2009, 58 (1): 596-601. doi: 10.7498/aps.58.596
Polarized blue electroluminescence has been achieved from the oriented poly (9, 9-dioctylfluorene) (PFO) film on a rubbed hole injection layer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) at the CIE coordinates of (0.20, 0.21). Polarized absorption and photoluminescence spectra reveal that the dichroism of the PFO film is influenced by the rubbing strength of the alignment layer, the annealing temperature, and annealing time, among which the annealing temperature is the most significant factor. An electroluminescence polarization ratio of about 3 is achieved when the rubbing depth is 50μm, the annealing temperature is 200℃ and the annealing time is 30 min.
2009, 58 (1): 602-606. doi: 10.7498/aps.58.602
Based on the U-tube, one new type of sonoluminescence apparatus —the conical bubble sonoluminescence straight tube has been set up. Using the apparatus, the ultrabright cavitation luminescence was obtained and the spectra were measured. Results show that the spectra consist in a broad background ranging from the ultraviolet region to the visible region, on which five clear sequences of Swan bands and three sequences of B2Σ+→X2Σ+ transition of CN are superimposed. A band assigned to the A2Δ→X2Π transition of CH has also been measured. Specially, the vibrational structures of Swan bands could be resolved clearly. In addition, the achieved molecular vibrational temperature is estimated to be about 5100±200 K. Finally, the chemical reactions in the sonoluminescence are discussed, which shows the excitence of chemiluminescence in sonoluminescence from organic solution.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2009, 58 (1): 607-611. doi: 10.7498/aps.58.607
Single-phase CuO thin films have been obtained on Si(100) and quartz substrates using pulsed laser deposition technique. The structure, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The SEM image demonstrates that the grain size is about 45nm. The third-order optical nonlinearities in CuO films were investigated by Z-scan method using a femtosecond laser (800nm, 50fs). The results show that CuO films have ultrafast nonlinear optical response and large optical nonlinearity with the real and imaginary parts of third-order nonlinear susceptibility, χ(3), being -7.88×10-11 esu and -2.13×10-11 esu, respectively, indicating CuO thin films are potential materials for applications in nonlinear optical devices.
The effects of melt spinning process on microstructure and thermoelectric properties of Zn-doped type-I clathrates
2009, 58 (1): 612-618. doi: 10.7498/aps.58.612
The single-phase Zn-doped type-I Ba8Ga12Zn2Ge32 clathrates have been prepared by a novel melt spinning (MS) technique combined with spark plasma sintering (SPS) method, and the effects of melt spinning process on their microstructure and thermoelectric transport properties have been investigated. The results show that the free surface of ribbon obtained by MS consists of cubic grains with the size of 0.3—1.0μm, and after SPS a highly dense bulk material with lots of fine-layered structure has been obtained. Compared with the bulk Ba8Ga12Zn2Ge32 material prepared by melting method combined with SPS (MM+SPS sample), the bulk Ba8Ga12Zn2Ge32 material obtained by melting method combined with MS and SPS (MM+MS+SPS sample) has higher carrier concentration and lower carrier mobility at room temperature. Furthermore, the MS process leads to a slight decrease of electrical conductivity, somewhat increase of Seebeck coefficient, as a well as a remarkable decrease of lattice thermal conductivity for bulk Ba8Ga12Zn2Ge32 clathrates in the testing temperature range of 300—900K. At 900K, the latticethermal conductivities of MM+SPS sample and MM+MS+SPS sample are 1.06 and 0.42W/mK respectively. As a result, the maximum dimensionless figure of merit ZT of 0.90 is obtained at 900K for the MM+MS+SPS sample. Compared with that of MM+SPS sample, it increases by 75% at the same temperature.
2009, 58 (1): 619-630. doi: 10.7498/aps.58.619
Based on elastic dumbbell model of polymer melt and tensor description of fiber orientation, a mathematic multi-scale model with a general equation for the non-equilibrium reversible-irreversible coupling (GENERIC) of polymeric melt with fiber suspensions is presented by the coupling of reversible and irreversible thermodynamics. And the model provides a general framework with homogeneous GENERIC structure for the multi-scale governing equations. Through analyzing the components of GENERIC structure, stress contributions from information on different scales can be achieved.
Microscopic phase field simulation for the evolution of antisite defect of L12 structure and D022 structure in Ni75Al5.3V19.7 alloy
2009, 58 (1): 631-637. doi: 10.7498/aps.58.631
The antisite defect for L12-structure Ni3Al and D022-structure Ni3V of Ni75Al5.3V19.7 alloy is studied by microscopic phase field method in this paper. The results show that the concentration of antisite defects AlNi，VNi and NiAl for L12 structure，VNi, AlNi,Niv and AlV for D022 structure all decrease with precipitate process and reach to equilibrium values at the early stage of precipitation respectively. With the elapse of time, the two structures grow up while the concentrations of antisite defects always keep unchanged. The concentrations of equilibrium state antisite defects AlNi and VNi for L12 structure α site, VNi and AlNi for D022 structure α site are of the 10-2 order, and antisite defect NiAl for L12 structure β site, NiV for D022 structure β site are of 10-1 order, the two defects being the main antisite defects for the L12 and D022 structures. The addition element has a great site-preference for a certain ordered phase, V atom prefers to occupy L12 structure β site while Al atom prefers to occupy D022 structure α site.
2009, 58 (1): 638-643. doi: 10.7498/aps.58.638
The resistivity-temperature curve of 7050 aluminium alloy prepared by different casting methods (DC and LFEC) has been measured with D.C. four-probe method. By analysing the curve, it was found that a change occurred to the slope at 250℃ when the samples were heated, and the resistivity of LFEC sample changed with temperature more quickly than that of DC. Both the solidus and liquidus temperatures of LFEC samples were higher than those of DC samples during the process of temperature rise from room temperature to 900℃. However, the resistivity of DC samples increased remarkably when the temperature was kept at 900℃ and before it was decreased to 600℃. With the help of microstructure observation, the characteristics and phenomenon of the resistivity evolution with temperature were studied.
2009, 58 (1): 644-649. doi: 10.7498/aps.58.644
The microstructural characteristics of rapid solidified Cu-Pb hypermonotectic alloys were investigated by melt-spun method, the electrical resistivity and mechanical properties of the alloys were characterized, and the relationships between cooling rate and microstructural morphology as well as the properties of the alloys were analyzed theoretically. Results show that, under rapid solidification, (Cu) and (Pb) phases grow in the form of dendrite, which is characterized by uniform and fine equiaxied grain. With the rise of cooling rate, the equiaxied grain is refined remarkably, the amount of grain boundaries increase, the scattering of free electrons is intensified, leading to the increases of electrical resistivity. Meanwhile, the tensile strength of alloy foils increases linearly, but the elongation of alloys decreases.
2009, 58 (1): 650-654. doi: 10.7498/aps.58.650
The KKSO multi-phase field model is employed to simulate the lamellar-rod transition with different pulling velocities and different solute diffuse coefficients in liquid. The simulation results show that the eutectic keeps lamellar growth after lamellar merging at small pulling velocity. With an increase of the pulling velocity, the lamellar eutectic transits to rod-like eutectic after lamellar merging. And the further increase of the pulling velocity will make the lamellar grow steadily with its initial lamellar spacing. It's also found that the simulations of different solute diffusion coefficients in liquid are similar to those of different velocities and the transition from lamellar eutectic to rod-like takes place only in a certain range of each parameter. All of the simulated results are in agreement with the experiments qualitatively.
2009, 58 (1): 662-668. doi: 10.7498/aps.58.662
The soot in the atmosphere exhibits irregular fractal agglomerate structure. In this study, the reconstruction of agglomerate structure is observed for soot generated by spark discharge in both propene ozonolysis and photooxidation systems. This process makes the agglomerate soot more compact, and is possibly caused by the peroxy radicals and hydroxyl radicals generated from propene oxidation. The result furthers our understanding of the atmospheric aging process of soot agglomerate. Since the reconstruction directly changes the size distribution of soot, it may induce important changes to the soot's physical and chemical properties in the atmosphere.
2009, 58 (1): 669-673. doi: 10.7498/aps.58.669
The solar cells based on the blend of MEH-PPV(poly(2-methoxy-5-(2′-ethylhexoxy)- 1,4-phenylene vinylene) as donor and TiO2 nanorods as acceptor were fabricated. We analyzed the cause of performance change of the device in detail by the ultraviolet-visible absorption spectroscopy(UV-vis), photoluminescence spectroscopy(PL), the current density-voltage(J-V) curve. When TiO2 nanorods are dispersed in a polymer matrix, the performance of the device is greatly enhanced. The highest efficiency is achieved for the 1∶3 (MEH-PPV: TiO2 nanorods) weight ratio composition. We get an open circuit voltage of 0.7V, short circuit current density of 0.41 mA/cm2 and fill factor of 31.8% under air-mass 1.5 solar simulator illumination, yielding a 0.091% power conversion efficiency (PCE)，which is a nearly 60 times enhancement over the PCE of the device based on the MEH-PPV as active layer. The device PCE is further increased twofold by refluxing in phenthiol.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Evolution of average intensity distribution and angular spread of partially coherent Hermite-sinh-Gaussian beams propagating through turbulent atmosphere
2009, 58 (1): 674-683. doi: 10.7498/aps.58.674
The analytical expressions for the average intensity and angular spread of partially coherent Hermite-sinh-Gaussian (H-ShG) beams propagating through turbulent atmosphere are derived and used to study the evolution of average intensity distribution and angular spread of partially coherent H-ShG beams in turbulence. It is shown that an increase of the refraction index structure constant C2n and a decrease of the spatial correlation length σ0 accelerate the evolution process. The relative angular spread is introduced to quantitatively describe the resistance of a beam to turbulence. The smaller the spatial correlation length σ0, the waist width w0, the Sh-part parameter Ω0, and the larger the beam orders m, n, the less the angular spread of partially coherent H-ShG beams is affected by turbulence.
2009, 58 (1): 684-689. doi: 10.7498/aps.58.684
Based on Geant4 particle transfer simulation, the internal current density, dose rate and charge deposition profiles of Teflon are acquired, and then the electric field under high energy and low density e-beam radiation is calculated with radiation-induced conductivity model of charging dynamics, which includes the continuity equation, Poisson equation and deep trap equation. According to Geant4 package, the charging model of dielectric is simplified as a compound structure consisting of shielding aluminum and multiple-layer plates radiated by 1.0MeV energy and 0.1 pA/cm2 flux density surface source. With statistical method, the distributions of internal current density, dose rate and charge deposition are obtained and normalized with the above flux density. Substituting these results into RIC model, the distributions of electric field in Teflon are calculated under various grounding conditions. It shows that the charge density, electric field and potential for the back side grounding are higher than these for the front side grounding, which tends to induce internal discharging. The electric field calculated for the critical internal discharging conditions in space is also consistent with the threshold field of dielectric Teflon(1e7V/m).
2009, 58 (1): 690-694. doi: 10.7498/aps.58.690
In this paper, we tried to find the relation between the deflection angle of light in the geometrical optic approximation of electromagnetic wave and wave vector according to the quantum theory of light, the energy conservation principle, and the weak equivalence principle. Using the electromagnetic wave equation in gravitational field, we give a general method of calculating the deflection of light by gravitational field under the condition of weak field approximation. Finally, the deflection angles in Schwarzchild metric and Kerr-Newman metric are calculated.