Vol. 59, No. 3 (2010)
2010-02-05
GENERAL
2010, 59 (3): 1403-1408.
doi: 10.7498/aps.59.1403
Abstract +
The approximate solution for a class of nonlinear disturbed dispersive equation is considered using a simple and valid technique. We first introduce the solitary wave solution of the corresponding typical differential equation, and then the approximate solution of the singular solitary wave for an original nonlinear disturbed dispersive equation is obtained using the homotopic mapping method.
2010, 59 (3): 1409-1415.
doi: 10.7498/aps.59.1409
Abstract +
The （G′/G）-expansion method is extended to construct non-traveling wave solutions and explore the fractal structure for high dimensional nonlinear physical equation. As an example, a series of non-traveling solutions is obtained for the （2+1）-dimensional dispersive long wave system with variable coefficient. Furthermore, by setting properly the arbitrary functions in the solutions, a class of novel fractal structures, namely, the cross-like fractal structures are firstly observed.
2010, 59 (3): 1416-1422.
doi: 10.7498/aps.59.1416
Abstract +
This paper proposes a new algorithm for computing two-dimensional （un）stable manifolds in time continuous systems. With this algorithm, one can not only get a picture of a manifold efficiently, but also has many information of its every point, which are very useful for investigating the global dynamics of a system geometrically, such as features of stability region, evolution of the system flow and so on. The algorithm is mainly by finding many well distributed trajectories by solving initial value problems. An example on Lorenz system suggests this algorithm is very convenient. In addition, we study the chaotic dynamic of a three-dimensional neural network by detecting a heteroclinic orbit.
2010, 59 (3): 1423-1427.
doi: 10.7498/aps.59.1423
Abstract +
In this paper, a new kind of inverse problems of Noether’s theory for Hamiltonian systems is studied. The general solution and the specific solutions of constructing the Hamiltonians and the symmetries from known first integrals by using Noether’s theory are obtained. Two corollaries according to which the conserved quantities can be deduced directly from the Hamiltonians are presented. Two examples are given to illustrate the application of the results.
2010, 59 (3): 1428-1436.
doi: 10.7498/aps.59.1428
Abstract +
In this paper, the dynamic modeling theory of a spatial flexible beam, which undergoes large overall motion and nonlinear deformation, is investigated. As we know, in spacecraft and space station, there are a lot of flexible appendices so the dynamic modeling of a flexible beam is essential. Yet the existing models, in our opinion, lack several important coupling terms. This paper supplies these important coupling terms. Based on the new approach of deformation of fully geometrically nonlinear beam model developed，the finite element method is used for the system discretization and the coupling dynamic equations of flexible beam are obtained by Lagrange’s equations. The complete expression of stiffness matrix and all coupling terms are included in the dynamic equations. The second order coupling terms between rigid large overall motion, arc length stretch, lateral flexible deformation kinematics and torsional deformation terms are included in the present exact coupling model to expand the theory of one-order coupling model. The dynamic modeling method in this paper is of theoretical significance and has reference value for the rigid-flexible coupling system dynamic investigation .
2010, 59 (3): 1437-1448.
doi: 10.7498/aps.59.1437
Abstract +
In this paper, the Green function method is used to obtain the exact solution of Couette flow. By defining the Couette flow energy, the relative energy and the energy increase ratio, we discuss the relations between the structure of initial field and the evolution of Couette flow energy, the relations between the time corresponding to Couette flow energy attaining to its maximum and the structure of initial field together with the structure of initial field which can optimal excitated Couette flow energy increasing within a finite time interval. We further investigate the relations between the perturbed initial field and the evolution of Couette flow energy. The conclusions of this paper are supplementary to Farrell’s conclusions.
2010, 59 (3): 1449-1455.
doi: 10.7498/aps.59.1449
Abstract +
One-dimensional quantum tunneling dynamics between two-component Bose-Einstein condensates confined in a double-well magnetic trap is investigated. One-dimensional Gross-Pitaevskii equations for two-component Bose-Einstein condensates are derived from the three-dimensional ones. We derive Feynman equations from one-dimensional Gross-Pitaevskii equations. To study tunneling dynamics we solve Feynman equations in terms of a completely numerical procedure. In contrast to single-component condensates between two-component condensates, we find that this system can take on abundant tunneling results, the full tunneling dynamical behavior is summarized in phase portrait with constant energy lines. It is found that this system can achieve self-trapping when increase interatomic interactions exceed a critical value. We give the analytical critical expressions of interatomic interactions from the system Hamiltonian.
2010, 59 (3): 1456-1461.
doi: 10.7498/aps.59.1456
Abstract +
Dealing with the motion of single pendulum, classical mechanics shows, by the effective center of mass method, that the pendulum ball performs periodical spatial movement. However, using the same method, quantum mechanics presents a totally different answer: the pendulum ball moves randomly in space without a definite period. We provide the criteria conditions for the two different predictions, and propose the experimental conditions for the ball to obey quantum mechanics. Our results show that it is quite easy with current experimental apparatus to observe the spatial quantum transition of a macroscopic objects of the micrometer-seale.
2010, 59 (3): 1462-1467.
doi: 10.7498/aps.59.1462
Abstract +
The entanglement character between a two-level atom and a two-mode field as well as two-level atoms in the non-degenerate two photons Tavis-Cummings model in the resonance and non-resonance cases have been investigated, and the analytical expression about entanglement is obtained. Based on two kinds of initial states, the effects of field frequency, atomic frequency and dipole-dipole coupling between atoms on the entanglement are shown in detail. The cases of resonance and non-resonance are compared.
2010, 59 (3): 1468-1472.
doi: 10.7498/aps.59.1468
Abstract +
Spin model plays an important role in the realization of quantum information processing. Quantum entanglement can be constructed, also （swap）n quantum logic gate is available if anisotropy is ignored, when Heisenberg interaction between spins is used; thus a complete quantum computing gate will be realized by combining single-qubit rotation gate. To study the influence of anisotropy on logic gate has high academic value since anisotropy is inevitable in any solid material. In this paper, swap operation in a two-qubit anisotropy XYZ model in the presence of an inhomogeneous magnetic field is discussed. The swap errors caused by the anisotropy parameter ν of the exchange interaction between spins and the inhomogeneous field δ are evaluated. We can see clearly when the swap operation can be approximately used as an ideal swap gate.
2010, 59 (3): 1473-1480.
doi: 10.7498/aps.59.1473
Abstract +
Security of continuous-variable quantum key distribution with four-state protocol based on discrete modulation of noisy coherent states is analyzed. Combing discrete modulation and reverse reconciliation, this protocol can be used for long distance cryptography. There is a small difference between the state Alice sends in the discrete modulation protocol and the Gaussian modulation protocol, and it can be treated as excess noise and loss in the channel. As Alice cannot do a precise modulation, she will induce noise to the coherent state. We look this noise as the source noise and derive a lower bound to the secure key rate assuming the eavesdropper cannot benefit from the noise in the source. For avoiding the fast and random phase locking between the signal and local oscillator in experiment, we also analyze the security of four-state protocol using no-switching scheme.
2010, 59 (3): 1481-1486.
doi: 10.7498/aps.59.1481
Abstract +
By the thin film model and the local thermal equilibrium assumption, the instantaneous radiation power and instantaneous radiation energy flux near the event horizon of the dynamic spherically symmetric black hole have been studied. When the cut-off distance η takes a fixed value, the following results can be obtained. For Vaidya black hole, its instantaneous radiation energy flux of the scalar field near the event horizon is related to both the black hole mass and the change rate of the event horizon. But its instantaneous radiation power is only related to the change rate of the horizon. For Vaidya-Bonner black hole, the instantaneous radiation power and instantaneous radiation energy flux are all related to the mass, the charge of the black hole and the change rate of the event horizon. These results show that the gravitational field, electromagnetic field and the change of the horizon will all affect the thermal radiation of the black hole.
2010, 59 (3): 1487-1493.
doi: 10.7498/aps.59.1487
Abstract +
By using the analog variable of the holonomy variable of loop quantum gravity and the corresponding quantization method, the gravity field near the center of the Schwarichild-de Sitter black hole is processed though quantization. The spectrums of 1/r and the curvature invariant are computed near the black hole center and the result that the both spectrums is bounded from above are obtained. Following the above quantization method and by computing the quantum Hamiltonian constraint equation of the gravity field near the classical singularity r=0, the evolution formula of the black hole wave function is obtained and the result that the wave function can evolve though the classical singularity is obtained.
2010, 59 (3): 1494-1498.
doi: 10.7498/aps.59.1494
Abstract +
The stochastic resonance in an overdamped harmonic oscillator driven by cross-correlation Gaussian white noises in which one of the noises is modulated by a periodic signal is studied. By means of the Fourier transform of the stationary correlation function, an exact expression of the signal-to-noise ratio for the overdamped harmonic oscillator stochastic model is derived. Results reveal that there are two types of stochastic resonance in an overdamped harmonic oscillator stochastic model. One type of stochastic resonance is that a resonance peak exists in the curves of signal-to-noise ratio versus the multiplicative noise intensity Q. Another type of stochastic resonance is that a resonance peak exists in the curves of signal-to-noise ratio versus the oscillator frequency ω. By changing the value of signal frequency Ω, the signal-to-noise ratio versus Q curve can exhibit three different forms: the form with a signal peak, the form with a peak following a valley, and the monotonic form.
2010, 59 (3): 1499-1506.
doi: 10.7498/aps.59.1499
Abstract +
The dynamics of one-dimensional random quantum Ising model with both nearest-neighbor and next-nearest-neighbor （NNN） interactions is investigated in the high temperature limit by the method of recurrence relations. Spin autocorrelations and the corresponding spectral densities of the system are calculated. Supposing that the exchange couplings （or the transverse fields） satisfy the double-Gaussian distribution, the effects of this distribution on the dynamics of the system is studied. The results show that the dynamics of the system undergoes a crossover from a collective-mode behavior to a central-peak one when the standard deviations σJ（or σB）of the random variables are small and there is no crossover when σJ（or σB）are large. Meanwhile, the effects of NNN interactions on the dynamics of the system are studied. It is found that the central-peak behavior becomes more obvious and the collective-mode behavior becomes weaker as Ki increase, especially when Ki>Ji/2（Ji and Ki are exchange couplings of the NN and NNN interactions, respectively）. However, the effects are small when the NNN interactions are weak （KiJi/2）.
2010, 59 (3): 1507-1523.
doi: 10.7498/aps.59.1507
Abstract +
With the development of information technology and network, multimedia protection has become a major concern, in which images are the important research objects. Especially, the image degradation is one of basic fields. This paper introduces a three-dimensional Z-matrix map which can be used for encryption, and shows its satisfactory property. Then, two color image degradation algorithms based on different templates for selective encryption are proposed. Finally, the performance and security of them are analyzed. Simulation results indicate the reliability of these schemes.
2010, 59 (3): 1524-1531.
doi: 10.7498/aps.59.1524
Abstract +
A new circuit unit for the analysis and synthesis of the chaotic behaviors in the new fractional-order system is proposed in this paper. Based on the approximation theory of fractional-order operator, an electronic circuit is designed to demonstrate the dynamic behaviors of the fractional-order Liu system with α=09 An effective controller is designed based on a theory of stability identification based on Lyapunov equation. The results between simulation and experiment are in good agreement, thereby proving the existence of chaos in the fractional-order new system and the effectiveness of our proposed control method.
2010, 59 (3): 1532-1539.
doi: 10.7498/aps.59.1532
Abstract +
The generalized synchronization （GS） of two different unidirectional coupled Lorenz systems is studied. According to the method of auxiliary-system, by using the theories of stability and the boundary of the responsed system, a sufficient criterion is rigorously proven. Furthermore, based on the modified system approach, GS is classified into three types, the first type,the second type and the third type of GS when the modified system has an asymptotically stable equilibrium of zero solution, asymptotically stable equilibrium of non-zero solution, asymptotically stable limit cycles, respectively. Moreover, using the Routh-Hurwitz theorem to analyze the stability of equilibrium of the modified system, the existence of the first type and the second type of GS are strictly theoretically proved. Numerical simulations show the effectiveness of the method.
2010, 59 (3): 1540-1548.
doi: 10.7498/aps.59.1540
Abstract +
Based on third-order spiral chaotic Colpitts oscillator model, by introducing two piecewise-linear triangular function, a novel four-dimensional multi-scroll hyperchaotic system is constructed, which can generate （2M+1）×（2N+1）, （2M+1） and （2N+1）-scroll chaotic and hyperchaotic attractors. By using phase portrait, Poincaré mapping, Lyapunov exponent spectrum and bifurcation diagram, the dynamical behaviors of the proposed multi-scroll hyperchaotic system are analyzed. These results indicate that Hopf bifurcation point of multi-scroll hyperchaotic system is only related with the control parameter, but its scroll number and ranges of the control parameter for chaotic and hyperchaotic states increase along with the number of turning points. Furthermore, an analog circuit was designed to realize the four-dimensional multi-scroll hyperchaotic system. The results of experimental output and numerical simulation are basically the same.
2010, 59 (3): 1549-1553.
doi: 10.7498/aps.59.1549
Abstract +
Chaos synchronization in fractional-order unified chaotic system is disscussed in this paper. Based on the stability theory of fractional-order system, the control law is presented to achieve chaos synchronization. The advantage of the proposed controllers is that they are linear and have lower dimensions than that of the states. With this technique it is very easy to find the suitable feedback constant. Simulation results for fractional-order Lorenz, Lü and Chen chaotic systems are provided to illustrate the effectiveness of the proposed scheme.
2010, 59 (3): 1554-1561.
doi: 10.7498/aps.59.1554
Abstract +
Optimization of self-adaptive synchronization is investigated to estimate a group of five unknown parameters in one certain chaotic neuron model, which is described by the Hindmarsh-Rose. Two controllable gain coefficients are introduced into the Lyapunov function, which is necessary to get the form of parameter observers and controllers for parameter estimation and synchronization, to adjust the transient period for complete synchronization and parameter identification. It is found that the identified results for the minimal parameter （three orders of magnitude less than the maximal parameter） oscillate with time （the estimated results for this parameter is not exact） while the four remaining parameters are estimated very well when one controller and five parameter observers are used to work on the driven system （response system）. To the best of our knowledge, it could result from the great difference of five target parameters （values）. As a result, this problem could be solved when two controllers and five parameter observers are used to change the driven system and all the unknown parameters are identified with high precision. Furthermore, longer transient period for parameter estimation and complete synchronization is required when too strong gain coefficients are used, whils parameters can not be estimated exactly if too weak gain coefficients are used. Therefore, appropriate gain coefficients are critical to achieve the shortest transient period for parameter identification and complete synchronization of chaotic systems, and the optimization of gain coefficients depends on the model being studied. Furthermore, it is confirmed by our numerical results that this scheme is effective and reliable to estimate the parameters even if some parameters jump suddenly.
2010, 59 (3): 1562-1567.
doi: 10.7498/aps.59.1562
Abstract +
The synchronization problem of two time-varying delayed chaotic systems with unknown parameters is studied. A novel fuzzy adaptive H∞ control method is proposed to realize the synchronization of two time-varying delayed chaotic systems based on Lyapunov functional theory and linear matrix inequality techniques. The sufficient criterion for the stability of the synchronization error system is presented. Finally, an illustrative example is provided to demonstrate the effectiveness of the proposed method.
2010, 59 (3): 1568-1575.
doi: 10.7498/aps.59.1568
Abstract +
The scattering inside the computer box is studied. Some results are found through scattering matrix elements. The ensemble-averaged scattering matrix can be obtained by the measured radiation scattering. With the increase of cavity loss, scattering fluctuations are reduced, and insertion phase shift distribution is becoming more and more uniform. Based on the Dyson’s circular ensemble, the scattering behavior within computer box is found to be chaotic. According to RMT, normalized impedance matrix within the microwave chaotic cavity is universal in their statistical description, depending only upon the value of a single dimensionless cavity loss-parameter.
2010, 59 (3): 1576-1582.
doi: 10.7498/aps.59.1576
Abstract +
The choice of delay time and embedding dimension have no correlation in the process of phase-space reconstruction. Based on this principle, a new idea for determining the embedding dimension is proposed. It uses CAO theory after determining the delay time by the mutual information function. Numerical simulations show that the method is applicable for determining the appropriate delay time and the best embedding dimension. The method can recover the original phase space from the time series effectively, and can be used as an effective method to identify the chaotic signal.
2010, 59 (3): 1583-1592.
doi: 10.7498/aps.59.1583
Abstract +
Based on the stability theory of fractional order linear systems, the dynamic behavior of the fractional order Newton-Leipnik system with double attractor is studied. Our research shows that the fractional order Newton-Leipnik system involves reverse Hopf bifurcation course, i.e., with the decrease of fractional order, the fractional order Newton-Leipnik system shows mutation from double attractor to single attractor, the dynamic behavior experiences chaos, transient period and converges to one stable equilibrium.
2010, 59 (3): 1593-1599.
doi: 10.7498/aps.59.1593
Abstract +
Suppression of spiral waves and spatiotemporal chaos are considered based on the LuoRud91model. We apply local feedback to suppress spiral wave and spatiotemporal chaos. Two control strategies are proposed, namely the static and the moving control methods. It is found that when related parameters are properly chosen spiral wave can be suppressed by static controller, whereas spatiotemporal chaos cannot be suppressed effectively. However, spiral wave and spatiotemporal chaos can be suppressed effectively by moving controller. The corresponding control speed depends on the traveling speed of controller. Spiral wave and spatiotemporal chaos can be suppressed in a short time when the control parameters are suitably chosen.
2010, 59 (3): 1600-1607.
doi: 10.7498/aps.59.1600
Abstract +
Complex network theory is used to characterize the temporal and phase space features of a time series when it is transferred into a network. In this paper, we study the motif ranks of complex networks induced from different categories of time series with periodic bifurcations and chaos, which are generated with two algorithms: the Visiblity Graph （VG） algorithm and the Phase-space Reconstruction （PR） algorithm. The advantages of both algorithms are analyzed.
2010, 59 (3): 1608-1614.
doi: 10.7498/aps.59.1608
Abstract +
In the last few years, the complex network has received considerable attention. It is proven that the small-word effect and scale-free property exist in various real-life networks. In this paper, based on the deterministic fractal—the Sierpinski gasket, two deterministic complex network evolving models, S-DSWN and S-DSFN, are proposed by iterative approach. S-DSWN can generate small-world network, while S-DSFN can generate scale-free networks. The iterative algorithms to generate the models are also designed. Then, some relevant characteristics of the networks, such as degree distribution, clustering coefficient, and diameter, are computed or predicted analytically, which match well with the characterizations of various real-life networks. Finally, an integrated model is introduced to unify S-DSWN and S-DSFN into the same framework, which makes it convenient to study the complexity of the real networked systems within the framework of complex network theory. Moreover, we have proven that these network models are maximal planar graphs.
2010, 59 (3): 1615-1619.
doi: 10.7498/aps.59.1615
Abstract +
According to the theory of passivity, the force control on the robot system is studied from a relatively new perspective. In general, a strictly passive dynamic system has a good dynamic characteristics and robustness. Therefore, a passive approach to force control is presented in the force controller design. In view of the uncertainty and environmental impacts in robot modeling, the paper adds a compensation term to compensate for model uncertainty in force control loop. The simulation results show that this control program enhances the dynamic performance and robustness of the system.
2010, 59 (3): 1620-1624.
doi: 10.7498/aps.59.1620
Abstract +
Radiation detector of high performance was fabricated using free-standing thick CVD diamond films. The CVD diamond detector has “cross-finger” coplanar electrodes. The electrical contact between electrodes and diamond films is ohmic. The effective area is 3×3 mm2. When working under electric field strength of 30 kV/cm, the dark current of the detector is only about 01 nA, the rise time of the signal is about 590 ps, its sensitivity is about 110 mA/W. Besides, the detector has fairly good linearity on dose rate.
2010, 59 (3): 1625-1631.
doi: 10.7498/aps.59.1625
Abstract +
The principles of the new static polarization wind imaging interferometer and the light beam splitting of the four-sided pyramid prism were briefly introduced. Both the light ray’s transmitting direction and the transmitted point coordinates in the section of the prism were deduced by the ray tracing method. When the parallel ray had passed through the four-sided pyramid prism, the relation between the incidence angle and the deviation angle was calculated, the relation between the incidence angle and the transmissivity was also calculated. All the above relations were simulated by the computer. According to the parameters of the static polarization wind imaging interferometer, both the angle between the side and the base and the length of the base were determined. This research was very important to the design and manufacture of the static polarization wind imaging interferometer.
2010, 59 (3): 1632-1637.
doi: 10.7498/aps.59.1632
Abstract +
The optical properties of the ion-implanted and annealed silicon wafer in visible spectral range are close to the single crystalline silicon due to the annealing-induced recrystallization, resulting in the unavailability of normal visible spectroscopic ellipsometry （SE） measurements. In this study, the SE measurements are performed in infrared range （2—20 μm） to characterize the implanted and annealed wafers. An optical model based on the classical Drude free-carrier absorption equation is developed, with which the impurity concentration profile, resistivity, mobility of the carriers, and the dispersion relations of the implanted layer are determined. The relationships between these parameters and the implantation dose are also analyzed. The results suggest that the infrared SE is an effective method to characterize the annealed silicon wafers. Longer wavelength should be used to distinguish lower impurity concentration.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2010, 59 (3): 1638-1642.
doi: 10.7498/aps.59.1638
Abstract +
The novel technical scheme of oval supercavity is presented. The light intensity in focus of oval supercavity are computed. By using the Compton scattering theory, the high brightness laser synchrotron source based on the technique of oval supercavity, including photon yield and radiant power, are calculated and discussed. The results show that when the reflectivity of oval supercavity mirror is equal to 99.99%, the light intensity in focus of oval supercavity is about 5000 times higher than that of the incident intensity （I0）. the γ-ray with energy up to 10975 MeV are expected to be produced by Compton vertical scattering of laser photons on the 3.5 GeV electron bunches, the photon yield and the radiant power of Compton vertical scattering between electron bunches and laser beam in focus of oval supercavity is about 25×107 times higher than that of Compton vertical scattering between electron bunches and single laser beam.
NUCLEAR PHYSICS
2010, 59 (3): 1643-1650.
doi: 10.7498/aps.59.1643
Abstract +
This paper presents the formation of the magnetic insulation and the basic principles of its computer simulation. This paper uses the non-uniform grid model successfully to fulfill the requiremet of three-dimensional simulation modeling of the double post-hole convolute whose structures are complex. By using the metallic struts to realize the load modeling of the computer implementation, we explored the feasibility of applying the MPI parallel algorith in the simulation. Finally the simulation results are checked by using the double post-hole convolute of vacuum section of the Z accelerator as an example.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (3): 1651-1657.
doi: 10.7498/aps.59.1651
Abstract +
The method B3LYP of the density functional theory （DFT） at 6-311++G（d, p） level has been used to obtain equilibrium structure of the ground state of CaS molecule, optimized parameters, dipole moment, charge distribution, HOMO energy level, LUMO energy level, energy gaps, infrared spectrum and harmonic frequency under different external electric fields ranging from -0.03 a.u. to 0.045 a.u. The results shows that with increasing the external electric field, the molecular geometry becomes strongly dependent on the field strength and behaves asymmetrically to the direction of the applied electric field. At the same time, the bond length and dipole moment μ of the ground state are changed from decreasing to increasing. At F=0.02 a.u., the minimum of bond length and dipole moment are 0.2289 nm and 1.5969 D. HOMO energy level and LUMO energy level are changed from increasing to decreasing. A decrease of the total energy gaps are found in the process of increasing the external electric field, which tells that the molecule is excited easily under a specific electric field. Excitation energies and oscillator strengths are affected by the external electric field. These results are useful for the study on the electroluminescence of CaS molecule.
2010, 59 (3): 1658-1664.
doi: 10.7498/aps.59.1658
Abstract +
Employing hybrid HF/DFT functional in conjunction with the relativistic effective core potential for Pu atoms and all-electron basis set 6-311g（d） for O atoms, the equilibrium geometrical structures of PuO, PuO2 and Pu2O3 molecules are obtained in the geometry optimization. The infrared and Raman spectra are also calculated. The bond lengths and harmonic vibration frequencies of ground states of PuO and PuO2 molecules are all in agreement with available experimental data. In geometry optimization of Pu2O3 molecule, we have tested more than twenty initial structures with different spin multiplicities （1, 3, 5, 7, 9, 11 and 13）. A C2v geometry corresponding to electronic state of 11B2 is considered as the ground state of Pu2O3 molecule. The harmonic frequency, IR intensity, Raman scatting activity and depolarization ratio of Pu2O3 molecule are obtained for the first time in theory. The vibrational modes corresponding to the maximum peaks are assigned for PuO2 and Pu2O3 molecules. In all studied molecules, the charge transfers from Pu to O atoms are found from natural bonding orbital analysis （NBO）. Relative to PuO and PuO2 molecules corresponding to Pu-O single- bond, the interactions between Pu and O in Pu2O3 are much weaker. The spin magnetic moments of studied molecules stem mainly from the 5f atomic orbitals of Pu atoms, but for O atoms the antiparallel spins from 2p atomic orbital are exhibited.
2010, 59 (3): 1665-1670.
doi: 10.7498/aps.59.1665
Abstract +
The influence of laser beam on the transmittance properties of anomalous dispersion photonic crystals （PCs） is investigated. Our calculations show that the pass band of anomalous dispersion PCs is tunable when altering the electron population in the atomic ground state of the anomalous dispersion material by the optical pumping method. With circularly polarized pump light, a huge Faraday rotation can be achieved under weak light intensity. Tunable pass band of anomalous dispersion PCs may lead to important technological applications in the optically controlled optical switch.
2010, 59 (3): 1671-1676.
doi: 10.7498/aps.59.1671
Abstract +
We investigate the interaction between a two-level atomic system and a phase controllable light field. The quantum diffraction of the population probability for the excited state is described analytically. The physical sense of the wave function evolution is analyzed in detail. The polarization of the atoms is shown with the help of Cornu spiral of the wave function and the temporal evolution of the real and imaginary part for the wave function. It is shown that the polarization of the atoms and the temporal evolution of the wave function as well as the propagation of light can be controlled by manipulating the phase of the light field.
2010, 59 (3): 1677-1680.
doi: 10.7498/aps.59.1677
Abstract +
Using N+2 as the molecular probe, we investigate the ionization behavior of the nitrogen molecule buffered in different rare gases （helium and neon） by optical heterodyne velocity modulation spectroscopy. The spectral intensity of an individual rovibronic line of N+2 is proportional to the product of the velocity modulation index and the concentration of N+2. Therefore, the relative ionization depth can be deduced via measuring the spectral intensity in different buffer gases.
2010, 59 (3): 1681-1688.
doi: 10.7498/aps.59.1681
Abstract +
The interface electronic structure, molecular orientation and surface morphology of the organic semiconductor 3,4,9,10-perylene tetracarboxylic dianhydride （PTCDA） grown on Au （111） surface have been studied by means of X-ray photoelectron spectroscopy （XPS）, synchrotron radiation ultraviolet photoelectron spectroscopy （SRUPS）, near edge X-ray absorption fine structure spectroscopy （NEXAFS） and atomic force microscopy （AFM）. It can be seen from the SRUPS results that the Shockley-type Au （111） surface state near the Fermi level extinguishes immediately after sub-monolayer of PTCDA is deposited onto the Au surface without the emergence of interface hybrid state. This indicates that a charge transfer process takes place at the interface between PTCDA molecule and Au（111）, but does not lead to strong chemical reaction. Angle dependent NEXAFS and SRUPS show that the PTCDA overlayers are ordered and the molecules lie flatly on the Au（111） surface. According to the AFM images and the evolution of Au 4f7/2 and C 1s integral intensities with increasing film thickness, the typical Stranski- Krastanov growth mode is proposed for PTCDA deposition on Au（111） surface, that is, layer by layer growth followed by island growth mode. The Dewetting transition occurs between the 2D and 3D growth modes.
2010, 59 (3): 1689-1694.
doi: 10.7498/aps.59.1689
Abstract +
In this paper, the close-coupling method and the Tang-Toennies potential are applied to the collisions of 3He,4He,9He and 10He with H2 systems when the incident energy is 07 eV. The vibrational and rotational excitation cross sections are calculated. By analyzing the partial wave cross sections, the changing tendencies of the partial wave cross sections with the quantum number and reduced mass in the isotopic substitution systems are obtained.
2010, 59 (3): 1695-1701.
doi: 10.7498/aps.59.1695
Abstract +
A new Monte-Carlo （M-C） curve fitting algorithm which is more stable than other iterative fitting algorithms is presented, and it is used to improve the unsatisfactory fitting results of the data of electron momentum spectroscopy（EMS） experiment due to the serious overlap of adjacent peaks of orbital energy resulting from the poor energy resolution. The VB program of this method has been compiled. The results of EMS data of CF2Br2 using the M-C program is compared with the one using PeakFit software, which is based on Levenberg-Marquardt algorithm, and shows much better effect. Furthermore, the ordering of the four outer valence orbitals（4b2, 2a2, 4b1 and 6a1） has been assigned, which suports the conclusion of the Hartree-Fock and OVGF calculation and revises the assignment using PES.
2010, 59 (3): 1702-1706.
doi: 10.7498/aps.59.1702
Abstract +
The triple differential cross section for Ar（3p6） in the special geometry of coplanar large energy loss and close to minimum momentum transfer has been calculated with the modified distorted wave Born approximation （DWBA）. The polarization interaction between the electron and the target, especially in the near-target region, and the post-collision interactions are included in the calculation. The theoretical results with modified DWBA are compared with the recent experimental data, the standard DWBA and DWBA-G. It is shown that the polarization are very important in the calculation of TDCS in coplanar asymmetric （e,2e） reaction.
2010, 59 (3): 1707-1711.
doi: 10.7498/aps.59.1707
Abstract +
Generalized gradient approximation of density functional theory is used to study the geometric and electronic properties of the endohedral fullerene N2@C60. It is found that the two nitrogen atoms, in the form of N2 molecule, is located at the center of C60. The bonding analysis, energy levels, density of states, and charge analysis show that the effect brought by the N2 molecule on the electronic property of C60 is rather small.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (3): 1712-1720.
doi: 10.7498/aps.59.1712
Abstract +
Using theoretical analysis and numerical calculation, it has been demonstrated that the closed periodic cusped magnetic （PCM） field can effectively confine the sheet electron beam in two transverse directions simultaneously to realize the stable long distance transport, where the beam cross-section has an attainable shape of the state of the art. Moreover, the method for matching the transverse magnetic focusing force and the inner space charge force in the wide dimension of the sheet beam is given, which can be used to determine the longitudinal periodic length and the cross section shape of the closed PCM structure. The calculation has also shown that the optimum focusing can be acquired through adjusting the width of the closed PCM structure independently. And besides, it has been proven that the offset PCM structure is not a good choice for sheet beams’ confinement. The work presented in the paper indicates that the closed PCM structure is very promising, and it’s helpful for guiding the practical engineering design.
2010, 59 (3): 1721-1725.
doi: 10.7498/aps.59.1721
Abstract +
A high current density cylindrical electron optics system is designed for extended interaction oscillator, including the design of electron gun and focusing magnetic field. To obtain good beam properties, a theory of ideal circular beam focusing is used in design. The focusing magnetic field is calculated by balancing the radial forces. CST PARTICLE STUDIO simulation under space-charge-limited emission model shows good beam qualities with a parallel beam flow throughout the gun and interaction sections. The simulation result is in good agreement with design theory, the beam mean current density attains 244 A/cm2, fill factor 767%, beam transmission 100%.
2010, 59 (3): 1726-1733.
doi: 10.7498/aps.59.1726
Abstract +
The magnetic field excited by the offset-pole periodic cusped permanent magnet （OPPCPM） used for focusing the sheet electron beam has been approximately expressed in two different forms for the convenience of future numerical calculation and theoretical analysis, respectively. Firstly, the surface-current-sheet model has been used to approximate the OPPCPM, and an accurate expression has been obtained using Biot-Savart law. This expression would rather be applied to numerical calculation than theoretical analysis because of the complication. The optimization of entrance taper of the OPPCPM has been performed as an example of application of the expression, implying the high efficiency of the calculation brought by the expression. Secondly, to obtain simple expression of the magnetic field for the convenience of future theoretical analysis, the OPPCPM field has been divided into two parts: the periodic cusped magnetic （PCM） field component and the side-focusing magnetic field component. The expressions of the PCM field component have been obtained using the method of undetermined coefficient, while the expressions of the other one have been obtained using two-magnetic-charge-sheet model. The results are useful to study the transportation of the sheet electron beam in the offset-pole PCM field.
2010, 59 (3): 1734-1739.
doi: 10.7498/aps.59.1734
Abstract +
Since the traditional anti-statistical algorithms in the inversion of refractivity from radar clutter （RFC） need too much calculation, a new physical algorithm （variation adjoint combined with the regularization method） is proposed instead. In the variation adjoint method, the tangent model, adjoint equations and accompanying boundary conditions, the solving expression of adjoint equations, and the mathematical functional expression of the gradient were derived respectively, and the problem of how to coordinate functional gradient of the complex equations is solved. In the regularization method, to take into account the characteristics of radar electromagnetic wave propagation, we choose a suitable regularization term to solve the inversion of the ill-posed problems. Finally, the implementation of the iterative inversion algorithm was derived.
2010, 59 (3): 1740-1748.
doi: 10.7498/aps.59.1740
Abstract +
The generation and interference of vortex beam have been investigated both theoretically and experimentally in this paper. The interference pattern of fractional and integral vortex beams with vortex beams with spherical wave and plane wave have been studied numerically, and the corresponding experimental results are presented. The experimental results and numerical results are practically consistent. It is found that the interference pattern varies with the topological charge of vortex beams. This phenomenon can be used to detect the topological charge of fractional vortex beam.
2010, 59 (3): 1749-1755.
doi: 10.7498/aps.59.1749
Abstract +
Based on the basic theory of electromagnetic scattering and radiation transmission, the scattering phase functions of various kinds of atmospheric aerosol with special distributions in typical UV band are presented. A direct sample method has been used to simulate the discrete polydisperse Mie phase functions of haze aerosol. Comparisons are made between the Henyey-Greenstein phase function, the modified Henyey-Greenstein phase function, the direct sample phase function presented in this paper and the polydisperse Mie phase function. The influence of different scattering phase function simulation methods on radiative transfer properties has been studied by using the Monte Carlo method. Numerical results showed that the rigorous simulation of scattering phase function is of importance in radiative transfer problems.
2010, 59 (3): 1756-1761.
doi: 10.7498/aps.59.1756
Abstract +
By use of the Jones vector we deduced the Jones matrix of actual polarizer and light transmission expression, as well as the light attenuation coefficient （LAC） of two polarizers. According to computation, certain error exists when using Malus-Law to calculate polarizer’s light attenuation ratio at high attenuation level. So the deduced LAC expression can be considered as a correction to Malus-Law. We get the maximum light attenuation ratio 2ε2 of two polarizers and light transmission expression about θ2 of three polarizers. Both the expression and experimental data indicate that the maximum light attenuation ratio can reach 2ε4 when［θ1,θ2］=［90°,135°］or［90°,315°］.
2010, 59 (3): 1762-1768.
doi: 10.7498/aps.59.1762
Abstract +
A method of constructing optical Hash function based on nonlinear cascaded Fourier transform is proposed. The proposed method consists of two single one-way encryption processes. In the first process, the digital information is divided to several data blocks with 512-bit each. The data blocks are encoded to 8 by 8 sub-images with 256 gray scales, creating information planes. Then take a nonlinear cascaded Fourier transform of sub-image to generate a data matrix through an optical/digital hybrid system. By extending the data matrix we get four information planes. Again, taking nonlinear cascaded Fourier transform to built information planes, we get a Hash value 64-bit long （hash1）. In the second process, we shift cydically every numerical value of the original information planes by 4-bit, constructing auxiliary information planes. Thereafter we take the same operations as we have done in the first process to the Hash value （hash2）. Once hash1 and hash2 obtained, they are combined to form a final Hash value 128-bit long （hash）. Furthermore, the avalanche effect coefficient （AEC） was also proposed to evaluate the performance of the optical Hash function. Theoretical analysis and simulation results are presented to show the effectiveness of optical Hash function constructed by our approach and the constructed optical Hash function has good performance of avalanche effect and collision resistance.
2010, 59 (3): 1769-1774.
doi: 10.7498/aps.59.1769
Abstract +
The experiment of multiple optical orthogonal codes （MOOC） sequences-based optical labels receiving is reported for the first time. In this work, 2 groups of MOOC with code length 19 and code weight 3 are used to identify optical labels. This paper firstly presents the scheme and principle of optical packets switching networks based on MOOC sequences-based optical labels. Since optical labels contain the optical packet switching and routing information, optical label processing is crucial to achieve successfully packets switching. Therefore, the importance of MOOC-based optical labels processing with multiple inconsecutive, random and burst characteristics in optical packets switching network is pointed out. Considering the MOOC-based optical labels, we design a circuit consisting of widened net and multi-level concatenated amplifiers to receive multiple single-optical-label pulse with a period of 2 ns and low power. The experimental results show that the designed scheme is feasible.
2010, 59 (3): 1775-1779.
doi: 10.7498/aps.59.1775
Abstract +
Using the quantum phase space technique and the information-theory like the Wehrl entropy, the Husimi function and the Wehrl entropy of the quantum pure states and the corresponding mixed states in thermo field dynamics are studied. It is found that the Husimi function and the Wehrl entropy of the thermal coherent state agree with that of the corresponding mixed states. And the Wehrl entropy of thermal coherent state is not related with the displacement factor. Therefore for a quantum system, the quantum fluctuations of the observable quantities and corresponding uncertainty relation are also not related with the displacement factor in the thermal coherent state.
2010, 59 (3): 1780-1785.
doi: 10.7498/aps.59.1780
Abstract +
The time evolution properties of the field quantum entropy in the system of a trapped ion interacting resonantly with a standing-wave laser field is studied by utilizing the Von Neumann reduced quantum entropy theory, and our attention focuses on the discussion of the influence of the Lamb-Dick parameter, the position of the ion in the standing-wave laser field and the initial state of the trapped ion on the evolution properties of the field quantum entropy. The results obtained from the numerical calculation indicate that: the value of the Lamb-Dick parameter effect the oscillation frequency and amplitude of the quantum entanglement between the trapped ion and the standing-wave laser field, the larger the Lamb-Dick parameter is, the weaker the average entanglement level between the ion and the field will be. When moving the tapped ion from the node of the standing-wave laser to the loop, the vibration frequency of the quantum entanglement between the field and the ion becomes slow gradually, and the entanglement degree gets weaker and weaker. With the decrease of the probability of the trapped ion being in the excited state, the quantum entanglement between the trapped ion and the stanging-wave laser field shows the tendency of increase first and then decrease. These properties have certain reference value for the preparation of entangled states and for the quantum communications with the thapped ion, and so on.
2010, 59 (3): 1786-1790.
doi: 10.7498/aps.59.1786
Abstract +
The cavity field spectra of two modes field both in the binomial state interacting with a two-level atom in an ideal cavity is investigated. The results for the weak initial fields are calculated. The influence of the quantum interference on the cavity field spectra is discussed. It’s shown that the quantum interference term performs periodical damped oscillation with the changing of the difference of the two field frequencies. The periodicity is about 016 g（g is the coupling coefficient between the atom and the fields）. When the difference of the two field frequencies is larger than 16 g, the quantum interference term can be ignored. Otherwise, the quantum interference term is related to photon number of initial field. The quantum interference term strengthens gradually with the photon number increasing, but weakens abruptly when the maximal photon number becomes greater than 4 The quantum interference phenomenon almost vanishes when the photon number is greater than 6.
2010, 59 (3): 1791-1796.
doi: 10.7498/aps.59.1791
Abstract +
We studied the properties of the X- and Y- polarized photon emission from the single quantum dot system driven by external cw laser using the generating function approach developed recently. The results demonstrate that the X- and Y- polarized photon show sine or cosine behavior with the field direction in the weak field region. They show, however, stronger nonlinear behavior in the strong field region.
2010, 59 (3): 1797-1801.
doi: 10.7498/aps.59.1797
Abstract +
The solvent-dependent and frequency-dependent nonlinear optical （NLO） properties of one-dimensional charge transfer （1DCT） molecule, p-nitroaniline （pNA） and two-dimensional charge transfer （2DCT） molecule, 1,3-diamino-4,6- dinitrobenzen （DADB） have been studied by using the density functional theory （DFT） and time-dependent coupled perturbed Hartree-Fork （TDHF） method, respectively. The reasons of the influence of the solvent polarity and incident light frequency on the NLO properties for 1DCT and 2DCT molecules were also discussed. Theoretical results demonstrate that the first hyperpolarizability β and ultraviolet spectra strongly depend on the dielectric constant ε of solvent, but solvent polarity has little effect on the anisotropy ratio η and depolarization ratio D due to the linear relationship between ︱βxxy︱ and ︱βyyy︱ with the increase of the solvent dielectric constant ε. In addition, the incident frequency has a great influence on β,η and D . It is found that the solvent effect and the frequency dispersion effect should be considered in calculations for obtaining accurate results.
2010, 59 (3): 1802-1808.
doi: 10.7498/aps.59.1802
Abstract +
The radiation properties of a whispering-gallery-mode （WGM） fibre laser based on skew beam pumping have been studied. It is found from experiment that when pumped by skew light along the fibre’s axis, both transverse electric wave （TE） and transverse magnetic wave （TM） exist in WGM lasing emission simultaneitly. With the increase of refractive index of cladding dye solution, the wavelength spacing between TE and TM waves of which the radial mode number and angular mode number are the same value decreases, and the central lasing wavelength of WGM bluely shifts to short wavelength direction. Based on radiation theory of WGM fibre laser and a model of four-energy levels of dye laser, the obtained experimental results are well explained.
2010, 59 (3): 1809-1815.
doi: 10.7498/aps.59.1809
Abstract +
The solvent-dependent and frequency-dependent nonlinear optical （NLO） properties of one-dimensional charge transfer （1DCT） molecule, p-nitroaniline （pNA） and two-dimensional charge transfer （2DCT） molecule, 1,3-diamino-4,6- dinitrobenzen （DADB） have been studied by using the density functional theory （DFT） and time-dependent coupled perturbed Hartree-Fork （TDHF） method, respectively. The reasons of the influence of the solvent polarity and incident light frequency on the NLO properties for 1DCT and 2DCT molecules were also discussed. Theoretical results demonstrate that the first hyperpolarizability β and ultraviolet spectra strongly depend on the dielectric constant ε of solvent, but solvent polarity has little effect on the anisotropy ratio η and depolarization ratio D due to the linear relationship between ︱βxxy︱ and ︱βyyy︱ with the increase of the solvent dielectric constant ε. In addition, the incident frequency has a great influence on β,η and D . It is found that the solvent effect and the frequency dispersion effect should be considered in calculations for obtaining accurate results.
2010, 59 (3): 1816-1822.
doi: 10.7498/aps.59.1816
Abstract +
In this paper, on the basis of Talbot effect and using numerical simulation, we analyzed the two-dimensional amplitude and fixed- phase-difference arrays and found that these arrays can easily be affected by temperature, and the intensity distribution at z position behind them can’t be tuned. To solve the problem, an external electric field is used to tune the phase-difference of the phase array. We derived a theoretical model which realizes uniform distribution of light intensity via the application of an external electric field to tune the phase-difference, and the model agreed with Paturzo’s experimental results. The result make a good foundation for the research of new kinds of arrays.
2010, 59 (3): 1823-1830.
doi: 10.7498/aps.59.1823
Abstract +
We numerically investigate the deflection characteristics of incoherent coupled bright and dark photovoltaic spatial soliton pairs in a photovoltaic photorefractive crystal with diffusion effect. The numerical results show that, owing to the incoherent interaction, a bright soliton and a dark soliton in the crystal trap each other and the centers of the two solitons move along the same trajectory. It is found that, the deflection of the bright soliton can be controlled by adjusting the input background intensity of the dark soliton when the input peak intensity of the bright soliton is fixed; and the deflection of the bright soliton is suppressed when the input background intensity of the dark soliton is at a special value, while the bright soliton undergoes a deflection when the input background intensity of the dark soliton deviates from this special value. Also, the deflection of the dark soliton can be controlled by adjusting the input peak intensity of the bright soliton when the input background intensity of the dark soliton is fixed.
2010, 59 (3): 1831-1838.
doi: 10.7498/aps.59.1831
Abstract +
A holographic polymer dispersed liquid crystal （H-PDLC） switchable lens is reported. The diffraction efficiency was analyzed at different phase separation coefficients within the visible band （400—800 nm） with the coupled wave theory for a phase-type H-PDLC switchable lens. In our experiments, the maximum efficency of 70% was achieved. The H-PDLC switchable lens shows excellent imaging performance and fast response.It is potentially useful in many applications, such as optical communications, optical imaging,e.g.,in digital cameras.
2010, 59 (3): 1839-1846.
doi: 10.7498/aps.59.1839
Abstract +
By the solvent vaporization convection self-assembly method, silica colloidal crystal template was prepared. At 200℃, using GeH4 as the precursor gas, plasma enhanced chemical vapour deposition method was then used to fill the high refractive index material germanium, and germanium inverse opal photonic crystal was obtained. At the temperature lower than the temperature of thermal decomposition, GeH4 filling of germanium is realized. The morphology, composition, and optical property of the resulting samples were characterized by scanning electron microscopy, X-ray diffraction and Fourier transform microscopic IR spectroscopy. Results show that of germanium is amorphous, it is transformed into polycrystalline state by annealing. The germanium is homogeneously distributed inside the voids of silica template. The reflective spectrum of the sample has remarkable optical reflective peaks and shows the photonic band gap effects. The center wavelength of the photonic band gap lies in 1650nm and 2640nm. There is good agreement between the measured spectra and the calculated band structure. Germanium was also deposited on the SU-8 film, this shows that the SU-8 photoresist can with stand the deposition temperature. Low temperature deposition method decreases the deposition temperature. So this method can use macromolecule materials as templates. Thus the three-dimensional photonic crystal with more kinds of structure can be obtained by single-inversion procedure.
2010, 59 (3): 1847-1850.
doi: 10.7498/aps.59.1847
Abstract +
Left-handed metamaterials were fabricated and tested. As the first step in the test, the transmission spectra of electric resonator array and magnetic resonator array were measured, from which their respective negative parameter regions can be determined. Then, the transmission spectra of the left-handed metamaterial composed of electric and magnetic resonators were obtained. From the measured scattering parameters, effective permittivity and permeability can be retrieved. The experiment results show that there is a pass-band in the overlapping region where there is a respective stop-band for both the electric and magnetic arrays. In this pass-band, both the effective permittivity and permeability are negative, which verifies the validity of left-handed metamaterials composed of electric and magnetic resonators.
2010, 59 (3): 1851-1856.
doi: 10.7498/aps.59.1851
Abstract +
Based on electric resonance principle and image theory, a new type of periodical grounded edge-coupled split ring resonator （SRR） structure is designed in this paper. Then the proposed metamaterial structure is used to suppress the mutual coupling between elements in microstrip array. Compared with the traditional structures for suppressing mutual coupling, the proposed metamaterial structure has not only small size （to be specific, a small thickness of 0005 operation wavelength）, but also the ability to suppress the mutual coupling with excellent performance （-168 dB）. The obtained results indicate that the metamaterial has an enormous potential in designing compact and high-performance microstrip arrays.
2010, 59 (3): 1857-1862.
doi: 10.7498/aps.59.1857
Abstract +
Sinusoidal phase modulated pulse could provide broad bandwidth and high modulation frequency for spectral dispersion method in high power laser driver system. Phase modulation could be converted to intensity modulation due to dispersion during the pulse propagation in the fiber,and the intensity modulation enhances the nonlinear effect in the large-mode-area double-clad fiber amplifier and make the spectral controlling more difficult. 2 GHz and 1425 GHz phase modulation pulses propagated in fibers with different lengths were measured, and based on the dispersion model in the fiber, theoretical analysis shows good similarity between simulation and experimental results for the 2 GHz phase modulation pulse.
2010, 59 (3): 1863-1869.
doi: 10.7498/aps.59.1863
Abstract +
A dissipative-soliton mode locked laser based on Yb-doped single polarization large-mode-area photonic crystal fiber is demonstrated. The dissipative soliton dynamics is explored by numerical simulation. Compared with all normal dispersion fiber lasers, there are more pulse shaping mechanisms in a dissipative-soliton fiber laser, including the nonlinear absorption of SESAM, spectrum filtering of the chirped pulse and gain dispersion, which results in robust and stable operation. Among them, spectrum filtering plays a dominant role in mode-locking, it shapes pulse both in frequency domain and time domain and keeps the pulse duration below 1 ps in the cavity. For the first time, sub-1 ps pulse is directly generated in a dispersion compensation free cavity. The fiber laser directly generates 777 fs pulse at 1 W average power at a repetition rate of 514 MHz, corresponding to a single pulse energy of 20 nJ.
2010, 59 (3): 1870-1876.
doi: 10.7498/aps.59.1870
Abstract +
Basing on dry contact model of soft spheres the segregation processes of spherical and non-spherical particles were simulated using threes-dimensional discrete element methods（DEM）. Particle segregation mechanism was analyzed in view of force, torque and energy conversion between particles. Influence of segregation speed affected by particle size ratio was also discussed. The result shows that large particles are more active than small ones in segregation process, and non-spherical particles have higher energy, which makes up the influence of particle shape to segregation process to some extent, are more active than spherical particles. Average normal force, tangential force between large particles, their torque and kinetic energy are all greater than those of small particles. Particle segregation speed increases significantly with the increasing of size ratio. When the size ratio is greater than the critical value 3, the amplitude of increase in segregation speed will be slowed down.
2010, 59 (3): 1877-1883.
doi: 10.7498/aps.59.1877
Abstract +
Based on the study of isothermal inert particle sedimentation, the Arbitrary Lagrangian-Eulerian technique was used to solve the problem of sedimentation of two solid particles with thermal convection, including the energy equation. The results show that because of the dynamic wake caused by thermal convection, the trajectory of particles are distinct from each other when settling in isothermal, cool and hot fluid; there is vortex shedding in hot fluid, while in cool fluid a strong upward thermal plume forms.
2010, 59 (3): 1884-1889.
doi: 10.7498/aps.59.1884
Abstract +
The arbitrary Lagrangian-Eulerian technique was used in the direct numerical simulation of the sedimentation of particle with thermal convection between parallel walls. The fluid motion is computed from the Navier-Stokes equation and energy equation using the finite-element method. The particle was tracked according to the equations of motion of a rigid body under the action of gravity and hydrodynamic forces arising from the motion of the fluid, the model was used without former experience or presumption. The results shows that the particle experiences different regimes of motion: steady motion with and without overshoot and weak, strong and irregular oscillations. The thermal convection changes the sedimentation velocity and the oscillation amplitude of the particle，and the impact of particle by the thermal convection was decreased with solid-liquid density ratio increasing.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (3): 1890-1894.
doi: 10.7498/aps.59.1890
Abstract +
A surface-wave driven plasma antenna has been built. An exponential model of the surface current distribution has been proposed to calculate the radiation pattern of the plasma antenna. The results show that the plasma density decreases exponentially with the axial length. The magnitude of the imaginary part of the surface wave vector shows similar exponentially decaying profile with the plasma density under normal conditions, while the real part of the wave vector remains almost constant. The surface current distribution shows a traveling wave mode with exponentially decaying magnitude. The calculated radiation pattern of a typical “8” figure fits the experimental values well using the proposed surface current distribution model. The radiation pattern is broadened when the input RF power decreases.
2010, 59 (3): 1895-1901.
doi: 10.7498/aps.59.1895
Abstract +
A numerical solution for the self-consistent differential equations describing the laminar-flow equilibrium in magnetically focused relativistic electron beams is given and proved to be available by comparison with analytical results of solid electron beam in the case of pθ=0 （magnetically shielded sources）. With the numerical method, the space-charge limited current and the externally applied magnetic field of both solid and annular electron beam in three cases of pθ=0,pθ=const and pθ∝r2 （magnetically immerged sources） are presented and compared. It is shown that the conditions at the source with respect to the canonical angular momentum pθ have little effect on the space-charge limited current and the externally applied magnetic field, but more intense annular electron beam generated by the source with pθ=const. can be transported in the same drift tube under lower guided magnetic field than solid ones.
2010, 59 (3): 1902-1906.
doi: 10.7498/aps.59.1902
Abstract +
The Bohm criterion for a collisinal plasma sheath in an oblique magnetic field is investigated with a two-fluid model. It is shown that the upper and lower limits for the sheath criterion exist. And the range of the ion Mach number depends on the magnetic field and the incidence status of the ions.
2010, 59 (3): 1907-1912.
doi: 10.7498/aps.59.1907
Abstract +
The mechanism of modulation and rf extraction of an S-band on an injection locked, long pulse, relativistic extended interaction cavity oscillator （REICO） is studied in this paper by experiment, theory, and simulation. The origin of pulse shortening and mode competition of the REICO driven by the long pulse intense relativistic electron beams （IREBs） is explored. The modified structure of REICO with coupler is proposed for the first time, which suppresses the pulse shortening and mode competition remarkably. The pulse width of the modulated IREB is increased from 60 ns to 140 ns, and the magnitude of the modulated IREB is increased from 2 kA to 5 kA. The microwave radiation power and efficiency are promoted obviously after adjusting the parameters of the IREB and the leading magnetic field. Using a 580 kV, 48 kA, 210 ns electron beam with 11 T leading magnetic field, more than 400MW radiated power was extracted in 160 ns FWHM pulses at 289 GHz. The power efficiency is 27%, and the energy efficiency is 23%. The radiated power is 400 MW and the FWHM pulse is 184 ns when pulse repetition frequency of IREBs is 20 Hz. The experimental results are well consistent with the simulations. The injection locked REICO generates high power microwave of power 400 MW with pulse width 100 ns.
2010, 59 (3): 1913-1916.
doi: 10.7498/aps.59.1913
Abstract +
Measurement of radiation field near a implosion pellet M band X-ray is a important area in ICF research. On the SG Ⅱ laser facility, M band X-ray from Au plasma was measured in half-hohlraum radiation from the end. The experimental set-up and typical result were given. And weve also used the view-factor program to simulate this experiment. The results indicate that angular distribution of M band X-ray from the end of half-hohlraum doesnt assume linear relationship with the cosine of eradiating angle. The results are useful for the research of implosion experiment and target design.
2010, 59 (3): 1917-1922.
doi: 10.7498/aps.59.1917
Abstract +
The evolution of filaments structure with the applied voltage and gas pressure in dielectric barrier discharge in argon/air mixture is studied, which is also analyzed in the aspect of two-dimensional phase transition. With the increase of the applied voltage, the filaments structure undergoes stages of sparse random filaments-dense random filaments-hexagon structure-hexagonal superlattice structure-chaos, which can be considered as a phase transition from gas-liquid-simple solid-superlattice solid-liquid. The changes of the lattice constant and the distance between two neighboring lattice points are investigated in the process of formation of the hexagonal superlattice structure in the phase transition. In addition, the formation of the large spots and the Penta-Hepta defects in the hexagonal superlattice structure are also studied.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (3): 1923-1927.
doi: 10.7498/aps.59.1923
Abstract +
The temperature distribution in the cell of single crystal diamond grown by the temperature gradient method has been studied, which is based on the finite element method. Our results shwo that the temperature distribution in the synthetic process of single crystal diamond is not uniform. The highest temperature in the cell is located at the outside of single carbon solvent, and the lowest temperature in the cell is located near the diamond seed. The heat transfer and the mass transport have a same direction （from outside of carbon source to diamond seed）. The temperature gradient in the axial direction is higher than that in the radial direction, which explains why the size of synthetic single crystal diamond in the axial direction is larger than that in the radial direction. The model will be useful for the design of single crystal diamond grown by the temperature gradient method. Furthermore, this work will be hopeful to improve the cubic anvil type high pressure techniques for the synthesis of high quality diamond crystals.
EDITOR'S SUGGESTION
2010, 59 (3): 1928-1937.
doi: 10.7498/aps.59.1928
Abstract +
The detailed core structures of misfit dislocations in the AlSb/GaAs（001） heterostructure system were studied by 200 kV LaB6 filament high-resolution electron microscope. In combination with image deconvolution, the［110］ images were transformed into the projected structure maps, and the image resolution was enhanced up to the information limit of the microscope. To distinguish Al and Sb atoms in the AlSb film, the image contrast change with the sample thickness was analyzed for the perfect region in deconvoluted image, and the positions of Al and Sb atoms in the dumbbells were determined based on the image contrast theory of the pseudo-weak-phase object approximation. Then the structure models of two types of misfit dislocations were constructed. As the simulated images are in good agreement with the experimental images, the AlAs type interface and the core structures of obtained Lomer and 60° misfit dislocations were determined.
EDITOR'S SUGGESTION
2010, 59 (3): 1938-1945.
doi: 10.7498/aps.59.1938
Abstract +
The rapid expansion of the photovoltaic （PV） all market requires an abundant supply of silicon feedstock. A creative and simple three-layer method and apparatus have been developed for electrorefining of silicon for solar cell application. The anode is solidified from a hypereutectic solution of copper and metallurgical grade silicon. At the temperature of operation （950℃）, elements which have an electronegativity greater than that of silicon （e.g., Cu, B, P, etc.） will remain at the anode and then the Cu-Si phase can be used under certain conditions as a filter for purifying silicon with an electrorefining process. Two typical morphologies of deposit are found as coherent layer and osteoporosis layer, and deposited silicon particles with different grain size are found embedded in electrolyte. Furthermore, with increasing operation time and current density, re-combination of silicon particles is revealed which yields a larger-sized silicon ball of 1—2 cm in size. The analysis of the anode feed and refined silicon shows a remarkable reduction of B and P concentration, from 127 to 22 ppmw and 986 to 41 ppmw, respectively.
2010, 59 (3): 1946-1951.
doi: 10.7498/aps.59.1946
Abstract +
Microwave absorbing coating samples were fabricated with carbon nanotube （CNT） and nanoscaled tetrapod-shaped ZnO （NT-ZnO） as the absorbents and epoxy resin as the binder. The influence of the content of CNT and NT-ZnO in the absorbing coatings on microwave absorbing property was investigated. After 3-layer coating, when the content of CNT reached 12%, NT-ZnO reached 8% and the coating thickness was 15 mm, the results showed that the minimum reflection was -2307 dB. The frequency width reached 5 GHz below -10 dB and the area density was 2 kg/m2 The microwave absorbing performance has obviously improved compared with that of the pure carbon nanotube and nano tetrapleg ZnO coating. Finally, the absorbing mechanism was discussed.
2010, 59 (3): 1952-1957.
doi: 10.7498/aps.59.1952
Abstract +
We have used molecular dynamics method with quantum corrected Sutton-Chen type many-body potentials to study the structure and thermal stability of［110］ Au nanowires, and investigate its melting mechanism and shape evolution by introducing the Lindemann index and the minimum radius. The results show that the transformation from fcc to hcp structure occurs in local regions of nanowire before premelting. The melting starts from surface and evolves into interior region, resulting in the overall melting of the nanowire. Subsequently, the neck occurs and induces the final breaking of nanowire into a spherical cluster.
2010, 59 (3): 1958-1963.
doi: 10.7498/aps.59.1958
Abstract +
The effects of the pulse voltage amplitude （U） and duty cycle （d） on the growth characteristics, microstructure, phase component and corrosion resistance of the coating formed by microarc oxidation （MAO） on commercially pure titanium substrates in colloid have been systematically studied. The results show that, with the increase of U or d, the coating thickness increases almost linearly, the pore size and the roughness of the surface increases gradually, while the pore density decreases. The coatings almost entirely consist of dense layer, and they are completely composed of rutile TiO2 except the one formed at the duty cycle of 10% （U=450 V）, which contains a small amount of anatase TiO2 The corrosion resistance test in sulfuric acid solution （30%） shows that the corrosion resistance of the samples is closely related to U and d, with the increase of U or d, the corrosion resistance of the samples increases gradually.
2010, 59 (3): 1964-1969.
doi: 10.7498/aps.59.1964
Abstract +
In accordance with the character of diffusing Ga and Al in SiO2/Si system and in the use of magnetic-control device for controlling accurately the doping quantity of Ga, the double-impurity doping of both Ga and Al is completed consecutively in the same high-temperature diffusion furnace. It is shown that the doping is with good uniformity，repeatability and continuity．A uniform distribution of impurity concentration can be achieved．Since the covalent radiuses of the atoms，Ga and Al，are close to that of Si，and the temperature is slowly dropped after the high temperature, the defects of the lattice is obviously reduced．The lifetime of minority carrier is significantly increases and the voltage drop is reduced．In this paper, the mechanism of enhancing the performances of thyristors by Ga-A1 doping is investigated．Our result shows that the double-impurity doping technique is conducive to raising the level of breakdown voltage and surge capacity，and improving the characteristics of current，triggering and dynamics significantly．The double-impurity doping technique is better than other known techniques of doping．
2010, 59 (3): 1970-1976.
doi: 10.7498/aps.59.1970
Abstract +
Total ionizing dose （TID） effects of the deep submicron MOSFET （metal oxide semiconductor field effect transistor） with delta doping profiles and uniform doping profiles in the channel region are analyzed in this paper. The influence of both doping profiles on the leakage current and threshold voltage is investigated. The results show that, the leakage current of MOSFET with delta doping profile is 2—3 orders lower than that with the uniform doping profile when the radiation dose is lower than 500 krad. Yet when the radiation dose is higher than 500 krad, the delta doping profile dose not show significant improvement compared with uniform doping profile as the trapped holes in the MOSFET saturate. But the threshold voltage shift is about 40 mV less than that with the uniform doping profile. Therefore, the TID effects of the deep submicron MOSFET can be improved by adopting the delta doping profile. The optimization of the delta-doping profile to further improve the TID effects is also given in this paper, which provides the guideline for the radiation hardened design.
2010, 59 (3): 1977-1984.
doi: 10.7498/aps.59.1977
Abstract +
The parabolic compound X-ray refractive lenses are a kind of novel optical components, especially suitable for hard X-rays. Due to their parabolic profiles they are free of spherical aberration and are proper devices for sub-micrometer focusing and imaging. The focusing performance of the parabolic compound X-ray refractive lenses is studied theoretically and experimentally in this paper. Firstly, the derivation of the exact focal length formula using matrix optics method and a criterion of the thin lens approximation are described. And the intensity distribution near focus, limiting focal spot size, effective aperture and transmittance are deduced based on the diffraction theory. Several parabolic compound X-ray refractive lenses with PMMA material were fabricated by means of deep X-ray lithography. Then the X-ray microbeam experimental system was built on the 4W1A beamline of Beijing Synchrotron Radiation Facility （BSRF） based on the parabolic compound X-ray refractive lenses we fabricated. The focusing performances of three PMMA parabolic compound X-ray refractive lenses were measured and analyzed under 8 keV monochromatic X-rays. According to the experimental results, it is concluded that the PMMA parabolic compound X-ray refractive lenses promises good hard X-ray focusing performance.
2010, 59 (3): 1985-1990.
doi: 10.7498/aps.59.1985
Abstract +
A new model is presented to predict the radiation response for complementary metal oxide semiconductor（CMOS）devices at low dose rate in space environment. In comparison with the linear system response theory model, the prediction results for CMOS devices at low dose rate radiation by using the new model are more close to actually experiment data, and the experimental results for different dose rate of radiation verify the accuracy of the model. Finally, the radiation effects on sensitive parameters of CMOS devices at low dose rate in space environment are predicted by making use of the new model.
2010, 59 (3): 1991-1996.
doi: 10.7498/aps.59.1991
Abstract +
The crystal structure and the locations of the hydrogen of lithium imide （Li2NH） are studied by first-principle plane wave pseudopotential method based on the density function theory（DFT）. Three models are used to investigating the effects of the Li, N and nearest-neighbor N—H bonds to N—H bond orientation, respectively. The calculated results show that Li2NH crystal can be described by a layered tetragonal crystal （P42） structure. Four N—H bonds of each conventional cell align in two layers. The two imide groups in the same layer prefer to be antiparallel and the imide groups in the nearest-neighbor layers tend to be vertical. The density of states （DOS） and the electron local function （ELF） analysis show strong ionic interaction between the Li and N—H dimmer, while the bonding between the N and H has covalent character. Our P42 structure of Li2NH crystal yields a hydrogen storage Li2NH2+H2/LiNH2+LiH reaction enthalpy of 69.6 kJ/mol H2 at T=0 K, in good agreement with experimental reports of 66 kJ/mol H2 for this reaction.
2010, 59 (3): 1997-2003.
doi: 10.7498/aps.59.1997
Abstract +
Optimization of interconnect power and repeater area is an important issue in the design of nanometer CMOS ICs. Based on RLC delay model, the paper proposes a new optimal model to minimize power and area overhead with constraints of target delay and target bandwidth. The proposed model is verified at 90 nm, 65 nm and 45 nm CMOS technology. Experimental result shows that the proposed model can save an average power consumption of 46% and 61% and can save an average area of 65% and 83% at the expense of 1/3 and 1/2 bandwidth, respectively. The proposed optimal model can be used in computer-aided design for nanometer CMOS system-on-chip.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (3): 2004-2009.
doi: 10.7498/aps.59.2004
Abstract +
We employ ab initio plane-wave pseudopotential density functional theory to calculate the coordinates， equilibrium lattice parameters，bulk modulus，shear modulus and elastic constant of PtN2，and those calculated results agree well with the other experimental data and the published theoretical data. The curve of volume dependence of energy indicates the energy of STAAstructure is lower than that of pyrite structure. According to our result and the experimental criterion raised by Pugh, we come to the conclusion that the PtN2 is a very hard and fragile material. But when the pressure increases, the PtN2 becomes malleable gradually. It is revealed that the pyrite structure of the PtN2 is a semiconductor and the STAA structure of the PtN2 is a conductor by analyzing their density of states and band structure.
2010, 59 (3): 2010-2015.
doi: 10.7498/aps.59.2010
Abstract +
Using first-principles density functional theory and non-equilibrium Green’s function method, we investigated the electronic transport properties of C20F20 molecule. The calculation shows that the zero bias equilibrium conductance of C20F20 molecule is 0.385 G0. The I-V curve presents good linear characteristic. Under finite bias voltage the molecule displays stable conductance characteristic, and could be made as one steadying resistance molecular device.
2010, 59 (3): 2016-2021.
doi: 10.7498/aps.59.2016
Abstract +
Electronic structure, densities of states and optical properties of orthorhombic OsSi2 was calculated by the first-principle density function theory pseudopotential method. The calculated results show that OsSi2 is an indirect semiconductor with the band gap of 0.813 eV, the valence bands of OsSi2 are mainly composed of Os 5d and Si 3p, the conduction bands are mainly composed of Si 3p, 3s as well as Os 5d . The stastic dielectric function ε1（0） is 15.43, the reflectivity n0 is 3.93. Furthermore, the dielectric functions, refractivity index, reflectivity, absorption, conductivity and loss function of OsSi2 are analyzed in terms of the calculated band structure and densities of states. The results offer theoretical data for the design and application of OsSi2.
2010, 59 (3): 2022-2026.
doi: 10.7498/aps.59.2022
Abstract +
The electronic structure of Ti alloys has been calculated by the recursion method. Alloying elements Ni, Co, Pt, Ru and Ir were confirmed to segregate on the surface of Ti alloys. Ni and Co atoms form atomic clusters, while Pt, Ru and Ir atoms form the ordered phase with Ti atoms. The microcells are formed between the area with alloying atomic clusters and the region without alloying elements. Ti is dissolved preferentially in the corrosive media, and the enrichment layer on the surface of Ti alloys is formed by the remaining insoluble grain of the alloying elements. The enrichment layer of alloying atoms serves as the electrocatalytic surface, which facilitates the passivation of Ti alloys and improves the corrosion resistance. The co-added alloy elements, such as Ru-Ni, Ru-Ir, Ru-Mo and Ru-W, have the same effect as adding the noble metals （such as Pt）.
First-principles study on the band structure and optical properties of strained Ru2Si3 semiconductor
2010, 59 (3): 2027-2032.
doi: 10.7498/aps.59.2027
Abstract +
We calculated the band structure, density of states and optical properties of semiconductor material Ru2Si3 epitaxial-grown on Ru2Si3 （100）//Si（001） with Ru2Si3［010］//Si［110］ by using the pseudo-potential plane wave method based on first principles methods. As shown by the calculated results, orthorhombic Ru2Si3 is not only a direct semiconductor with the band gap of 0773 eV, but also in stable condition when the lattice parameter a is 1093 nm.The valence bands of Ru2Si3 are mainly composed of Ru 4d and the conduction bands are mainly composed of Ru 3d and Si 3p. Its static dielectric function ε1（0） is 1891, the refractive index n0 is 4349
2010, 59 (3): 2033-2037.
doi: 10.7498/aps.59.2033
Abstract +
A exact diagonalization solution method for solving the one-dimensional Holstein model of DNA is discussed in this paper. We compared the results of this paper with the former results of coherent state variational method （CVM） to check the reliability and accuracy of CVM. It is clearly seen that the ground state energy calculated by exact diagonalization solution method is considerably smaller than that of the CVM and can reach the saturation with smaller site number. With the strict method we can not only obtain the ground state energy, but also the spectra of all excited states. Therefore there is a significant improvement in the studying of Holstein model than the former CVM .
2010, 59 (3): 2038-2044.
doi: 10.7498/aps.59.2038
Abstract +
ZnO/MgO multi-quantum wells with modulation structure are grown on oxidated Al2O3 （0001） substrates using radio-frequency reactive magnetron sputtering method. X-ray reflectivity and X-ray diffraction measurement，electronic probe，atom force microscopy，transmission spectrum and PL spectrum are used to characterize the samples. The XRD scan and phi-scan results show the films are highly （001） textured and have epitaxial relationship with the substrates. The width of quantum well is determined to be between 838 nm and 2178 nm by XRR and EPMA. The AFM results show that the RMS roughness of the MQWs increases from 64 nm to 212 nm with the decrease of period of modulation. Low temperature PL spectrum shows the peak can be assigned to the radiative recombination of bound excitons，and the activation energy is estimated to be about 30 meV. The emission due to spatially separated carriers caused by quantum-confined Stark effect is also found in the spectrum of sample with smaller well width.
2010, 59 (3): 2045-2050.
doi: 10.7498/aps.59.2045
Abstract +
Chalcohalide glasses 20GeSe2-（80-x）Sb2Se3-xCsCl（x＝2，4，8，10 mol%）were synthesized by the conventional melt-quenching method. The optical transmission spectra were measured from the visible to the far-infrared range. The effect of CsCl content on the short-edged wavelength was investigated. Moreover，the differential thermal analysis curves of a typical 20GeSe2-76Sb2Se3-4CsCl glass were measured under different heating rates，and its crystallization kinetics was analyzed under the non-isothermal condition. The results show that，the introduction of CsCl into the glass lowers the non-bonding energy level，which leads to the increase of the electronic bandgap Eg，and blue-shift of the short edged wavelength. Compared with the conventional Johnson-Mehl-Avrami model，the autocatalytic model gives a better description of the kinetic process for the glass sample.
2010, 59 (3): 2051-2056.
doi: 10.7498/aps.59.2051
Abstract +
First-principles plane wave pseudopotential method based on the density functional theory is used to study the structural stability and electronic properties of ZnO atomic chains. The results show that ZnO molecules can form atomic chains with linear，ladder and double ladder one-dimensional stable structures whereas the zigzag chain is unstable. Our calculations also show that the stable chains exhibit indirect band gap characteristics while the unstable zigzag chain exhibits that of metal-like band gap.
2010, 59 (3): 2057-2063.
doi: 10.7498/aps.59.2057
Abstract +
Growth of Pt nanocrystals has been investigated by means of electron beam evaporation of Pt layer and post rapid thermal annealing. The results indicate that the density of nanocrystals increases first with the annealing temperature and the annealing time，followed by a slight decrease. Uniformly distributed nanocystals with a density of 30×1011 cm-2 can be obtained in the case of the annealing at 800℃ for 20 s. Further，memory effect of Al2O3/Pt nanocrystals/HfO2-based MOS capacitors has been characterized，indicating a capacitance-voltage （C-V） hysteresis window as large as 201 V in the sweep voltage range of -3—+8 V. In terms of the same programming time，the flat band voltage shift of the memory capacitor starts to increase remarkably when the programming voltage is increased to 9 V. This is related to a decrease in the energy barrier across the tunneling layer for electrons，i.e.，the tunnel mechanism of electrons is changed from direct tunneling to Fowler-Nordheim tunneling. Moreover，the memory capacitor also exhibits a capability of continuous electron trapping with prolonging of the programming duration.
2010, 59 (3): 2064-2067.
doi: 10.7498/aps.59.2064
Abstract +
There is great interest in using the strained Si CMOS technology lately for carrier mobility enhancement. Intrinsic carrier concentration is the important physical parameter for the characterization of strained Si materials and the determination of the electrical properties of strained Si-based devices. Starting from analyzing the band structure of strained Si/（001）Si1-xGex，the model of its intrinsic carrier concentration related to Ge fraction （x） at 300 K was established with the frame of K.P theory，which provides valuable reference to the understanding on the strained Si-based device physics and its design.
2010, 59 (3): 2068-2072.
doi: 10.7498/aps.59.2068
Abstract +
In order to investigate the influence of anneal treatment on the Co-based melt extraction wires, the soft magnetic properties and giant magnet-impedance （GMI） effect of the annealed Co75Fe40Si8B12Nb1 wire are investigated. Samples are prepared using melt extraction technology in vacuum and annealed at 450℃ without magnetic field or with miagntic field either longitudinal or transverse to the axis of wire of strength from 500 Oe to 4000 Oe，respectively. The magnetic softness and GMI response are measured using HP4192 Impedance Analyzer and Lakeshore7407 VSM. Test results show that the circular anisotropy and GMI response are reduced after longitudinal field anneal treatment. GMI profiles are single-peaked and the maximum impedance ratio ΔZ/Z is 131% and field sensitivity is 7%/Oe. The circular permeability and GMI response are improved after transverse field anneal treatments because of the increased circular anisotropy. At higher frequencies，the GMI profiles change from single-peaked to two-peaked after being annealed in strong transverse field. The circular permeability is increased and GMI effect gets stronger with the increase of current frequency and anneal field. The largest impedance ratio of 190% with a field sensitivity of 26%/Oe is obtained for the Co-based transverse field annealed wires at 10 MHz. The correlations between the circular permeability，the GMI effect and the current frequency are discussed in the light of a skin effect model.
2010, 59 (3): 2073-2077.
doi: 10.7498/aps.59.2073
Abstract +
The polycrystal samples of Ho2-xTbxTi2O7（x=0，05，1，15，2） were prepared by solid reaction method. The result of X-ray diffraction （XRD） and dc susceptibility measurement from 2 K to 300 K both indicate that as the content of Tb3+，i.e. x，increases，the system crosses over from Ho2Ti2O7spin ice to Tb2Ti2O7 spin liquid，the lattice constant of cubic pyrochlore increases，while the Curie constant and effective magnetic moment decrease. Especially，the Curie-Weiss temperature decreases from positive to negative with the decrease of x，implying the transition from ferromagnetic Ho2Ti2O7 to anti-ferromagnetic Tb2Ti2O7. The detailed analysis shows that as x in Ho2-xTbxTi2O7 increases，the intensity of long-range dipolar interaction Dnn decreases. Being ferromagnetic or anti-ferromagnetic，and the change in intensity of long-range dipolar interaction, may be the two crucial factors influencing on the system to form spin ice state or cooperative paramagnetic state，i.e. the spin liquid state.
2010, 59 (3): 2078-2084.
doi: 10.7498/aps.59.2078
Abstract +
The BiFeO3 nano-powder has been synthesized by sol-gel method. The structure and morphology of BiFeO3 nano-powder have been characterized by X-ray diffraction （XRD），scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM）. The results showed that the samples sintered at 700℃ for 2 h or 25 h is in the formed of pure BiFeO3 with the grain size about 30 nm，and the structure is hexagonal of R3-m［166］ space group with lattice constants a=b=05580 nm，c=06939 nm，and the spacing of （101） and （110） are about 0396 nm and 0273 nm，respectively. The room temperature magnetic properties of samples have been measured on vibrating sample magnetometer （VSM）. It was showed that the BiFeO3 nano-powder gives a complete hysteresis loop，which means that BiFeO3 nano-powder possesses weakly ferromagnetic at room temperature，its coercive force （Hc） could reach to over 700 Oe，and the magnetic mechanism comes from the double exchange of Fe3+-O-Fe2+. Moreover，with the increase of the sintering time，the grain size is influenced；the saturation magnetization （Ms） has a small change，however，the coercive force （Hc） of the BiFeO3 nano-powder decreased obviously.
2010, 59 (3): 2085-2089.
doi: 10.7498/aps.59.2085
Abstract +
Co89Cu11 nanowire arrays with particular bunchy shape have been fabricated in anodic aluminum oxide templates by electrodeposition. The analysis of structure indicates that the bunchy shape of the nanowire actually is a very high concentration of stacking faults parallel to the wire. Then we give explanation to the structure according to the growth mechanism. Relatively high squareness parallel to the nanowire arrays of about 096 at room temperature were achieved owing to the larger shape anisotropy than the nanowire arrays with general structure. The results of magnetic measurement and calculation demonstrate that the symmetric fanning mechanism of sphere-chains model can be employed to explain the magnetization reversal process which rest with the structure of the Co89Cu11 nanowire arrays.
2010, 59 (3): 2090-2096.
doi: 10.7498/aps.59.2090
Abstract +
The magnetization reversal processes of cobalt nanowires under different constant external magnetic fields have been studied by using the finite element micromagnetism simulation approach. The results show that magnetic domains with opposite magnetizations will be formed at one end of nanowires with a diameter of 10 nm after a nucleation time. The domain wall is classified as a transverse wall，which can be driven to move with a constant velocity by a constant external applied field from one end to the other. The velocity of domain wall is linearly dependent on the magnitude of external applied magnetic field. When H is 1000 kA/m，it is found that two head-to-head domains are found at both ends of nanowires. The calculation results show that the domain wall moves a constant distance during a period in which the direction of any magnetic moment rotates a cycle，which is independent of the magnitude of applied magnetic field.
2010, 59 (3): 2097-2103.
doi: 10.7498/aps.59.2097
Abstract +
An absolute measuring principle and method of bidirectional reflection distribution function （BRDF） is presented. A spectral radiation meter with 3 nm spectral resolution and a three-dimensional rotating system with 001° accuracy are utilized to establish the automatic measuring platform. The spectral BRDF of typical space target’s surface materials （yellow and silver tinfoil） is measured in the range of 400—2500 nm. Measured results show that the scattering angle，which corresponds to the maximum value of BRDF curve，is generally in the specular reflection direction；the other BRDF values change slowly as scattering angle varies，declining from middle to both sides and approximately following the cosine distribution. A BRDF error analysis method is introduced by using the RMS error calculation，which provides a new way for the BRDF measurement system evaluation. The measurement error is 495%. With five-parameter model of BRDF and the simulated annealing （SA） algorithm，the optimum parameters of the model at each wavelength in the measured spectrum are retrieved at intervals of 1 nm. A comparison of the data calculated by the parametric model with the data measured originally verifies the feasibility and reliability of the modeling. The measuring and modeling results can provide reference data for space target detection and identification.
2010, 59 (3): 2104-2108.
doi: 10.7498/aps.59.2104
Abstract +
Optical transmission of quartz glass is measured during loading and unloading process，and the stress was kept below their Hugoniot elastic limit. The results show that the quartz glass maintains good transparency for more than 15 μs under loading processes of 18 GPa，then it starts to lose its transparency about 07 μs after unloading，with 30% decrease of transmittance. This phenomenon，which reflects the growth and evolution of failure induced by unloading process in quartz glass，has been explained reasonably by the growth of spherical particles and the scattering model. The results are different from the explanation of liquid-solid phase transition given in literature［J. Chem. Phys. 2004，121 9050］. This paper is significant for studying the transparency of other transparent material.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
EDITOR'S SUGGESTION
2010, 59 (3): 2109-2113.
doi: 10.7498/aps.59.2109
Abstract +
Nano-sized Sn-Ti alloy anode material prepared by magnetic sputtering was characterized with X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The charge/discharge and cyclic voltammograms of the films electrodes were tested by the high precision battery testing system. The results indicated that the Sn/Ti compound films and Ti/Sn compound films have large difference in performance. Sn/Ti compound films have excellent cycling stability and tolerably high reversible capacity. Its initial discharge specific capacity and charge specific capacity are 9275 mAh/g and 6954 mAh/g, respectively，and the initial capacity fade is 25%. After 30 cycles，specific discharge capacity of 4152 mAh/g was retained and the coulombic efficiency was the same as the value before 30 cycles. This is ascribed to the isolation effect of inactive element Ti between active element Sn and the electrolyte.
2010, 59 (3): 2114-2119.
doi: 10.7498/aps.59.2114
Abstract +
The elevated temperature creep behavior of in situ 20vol%TiCP/LD7Al matrix composite and LD7Al alloy was investigated under the condition of constant compressive stress at 523 K，573 K and 623 K，respectively. The stress exponents of the composite material and the matrix aluminium alloy were obtained by fitting the creep rate and the applied stress in log-log plot，respectively. By introducing an effective stress （σ-σ0） to the power equation and extroplating the linearly-regressed experemental data to zero creep rate，the threshold stresses were obtained. The results showed that both the stress exponents and the threshold stresses of the composite were higher than those of LD7Al，indicating that the presence of TiC particles significantly improved the elevated temperature creep property of LD7Al. By introducing a threshold stress，the high-temperature creep behavior of the composite can be explained by the cooperative effect of the dislocation-climbing and the particle hindrance to the matrix deformation.
2010, 59 (3): 2120-2125.
doi: 10.7498/aps.59.2120
Abstract +
The recently developed method to detect the stress-cracking and crack healing of glasses in real-time （called the RMS-CH in short，Wu et al.，Appl. Phys. Lett. 92，011918-1（2008）） is applied to the detections of crystals. The experimental results of dimethyl phthalate crystal indicate that，under the condition of constant heating rate：1） the crack-healing rate shows a sharp peak as a function of temperature，the peak temperature can be taken as the characteristic temperature Tcch of the crack-healing ，and Tcch=206 K；2） the peak is not symmetric，and the low temperature side is wider than the high temperature side，which means that the crack-healing has started at lower temperatures and the amount of healing below Tcch is more than that above Tcch. This behavior is similar to that in glasses，but Tcch is higher than that of glassy state. Moreover，Tcch is much lower than the melting point of the crystal，which indicates that the crack-healing mechanism is quite different from that of recrystallization. We would like to point out that two dynamical loss peaks related to the crack-healing process are observed for the first time，which will be helpful to the understanding of the mechanisms. The above results also show the feasibility and validity of the RMS-CH method to investigate the stress-cracking and crack-healing in crystals as in glasses.
2010, 59 (3): 2126-2130.
doi: 10.7498/aps.59.2126
Abstract +
In this article，we investigate the effect of cathode work function，exciton generation rate and temperature as well as carriers and field distribution in the organic layer on the open-circuit voltage （Voc） of single layer organic solar cell with Schottky contact by using numerical method. It is demonstrated that the decrease of cathode work function （Wc） contribute to the increase of open-circuit voltage until Wc is close to the LOMO level of the organic material. The open-circuit voltage reaches a saturation value，when Wc is smaller then |EL|，and this open-circuit saturation voltage increases with the enhancement of exciton generation rate. For a given anode and cathode work function，the open-circuit voltage increases with exicton generation rate. When the exciton generation rate reaches a certain value，Voc goes to saturation instead of further increase，and the saturation value equals to the built-in voltage. Additionally，the saturated Voc decreases with the increase of temperature，and the decrease rate reduces with the increase of the exciton generation rate.
2010, 59 (3): 2131-2136.
doi: 10.7498/aps.59.2131
Abstract +
Hole mobility of poly［2-methoxy-5-（2′-ethylhexyloxy）-1，4- phenylenevinylene］ （MEH-PPV） film fabricated by spin-casting and drop-casting has been measured by time-of-flight （TOF） technique. The non-dispersive hole transport current waveform is obtained. The results exhibit that the hole mobility of MEH-PPV prepared by drop-casting is higher than that of the film prepared by spin-casting. The solar cells based on MEH-PPV and fullerene derivative blend films prepared by spin-casting and drop-casting，respectively，were fabricated. The power-conversion efficiency （PCE） of the drop-casting device has a great improvement of over 35%，compared with that of spin-casting one. The improvement is attributed to the stronger absorption and better balance of electron and hole transport in MEH-PPV polymer films.
2010, 59 (3): 2137-2146.
doi: 10.7498/aps.59.2137
Abstract +
An energy harvester is presented to scavenge energy from ambient vibrations using magnetostrictive/piezoelectric laminated magnetoelectric （ME） transducer. A cantilever beam is employed as the vibration sensitive element of the harvester，and a magnetic circuit made up of four NdFeB magnets is placed on the free end of the beam. Since the magnetic circuit produces a concentrated flux gradient in the air gap，the ME transducer can induce large magnetic field variations in the low level vibration，thus high output power can be obtained. Based on the equivalent magnetic charge theory，the magnetic field distribution of the air gap and the magnetic force of the magnetic circuit are analyzed，and the nonlinear vibration performance of the harvester is studied using the Lindstedt-Poincaré method. The mechano-magneto-electric performance of the harvester at resonance is analyzed by combining the vibration equation of the harvester with the magnetoelectric characteristics of the ME transducer. The experimental results verified the analytical results，and a prototype produces a power of 1124 μW for an acceleration of 05g at its resonant frequency of 33 Hz.
2010, 59 (3): 2147-2155.
doi: 10.7498/aps.59.2147
Abstract +
Through the research on the fractional-order FitzHugh-Nagumo model neuron，it is found that the Hopf bifurcation point of the fractional-order model，where the state of the model neuron changes from quiescence to periodic spiking，is different from that of the corresponding integer-order model when the externally applied current is considered as the bifurcation parameter. We further demonstrate that the range of the strength of the externally applied current in the fractional-order model neuron，which can make the model neuron exhibit periodic spiking，is smaller than that in the corresponding integer-order model neuron. However，the firing frequency of the fractional-order model neuron is higher than that of the integer-order counterpart. Meanwhile，we show that the synchronization rate of two electrically coupled fractional-order FitzHugh-Nagumo model neurons is greater than that of the integer-order counterpart. The Adomian decomposition method is employed to calculate fractional-order differential equations numerically because of its rapid convergence and high accuracy.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (3): 2156-2162.
doi: 10.7498/aps.59.2156
Abstract +
Based on the normalized raindrops size distribution，dielectric model of raindrop and Mie scattering theory，the scattering characteristic of raindrop cluster in the microwave and millimeter domain are calculated，the effect of raindrop size distribution，rain-rate，incidence wave frequency and temperature on the microwave transmission are discussed. The results show that the scattering capabilities of raindrop clusters decrease in the order of JD，MP，Gamma and JD. The effect of rain-rate on microwave transmission is the strongest，the incidence wave frequency takes second place，and the temperature is the weakest. These results will be helpful to the evaluation of the effect of precipitation on microwave transmission and the improvement of the precipitation detection precision of millimeter radar and precipitation-measuring radar，etc.
2010, 59 (3): 2163-2168.
doi: 10.7498/aps.59.2163
Abstract +
The relative total electron content （TEC） is obtained through the combination of COSMIC radio occultation ionospheric measurements L1 and L2 phase. The TEC data are then calibrated by non-occultation observation data on the auxiliary side to remove portion of TEC above the LEO orbit altitude. The electron density profile can be retrieved from TEC by Abel integral transformation，with a spherically symmetric assumption of electron density and an approximation of signal straight-line propagation. The computation standard deviation of F2-layer critical frequency f0F2 is about 059 MHz，and the standard deviation of F2-layer peak altitude hmF2 is about 3308 km，as through comparing 4903 COSMIC ionospheric occultation profiles with those from ionosonde stations，of which the longtitude deviations are less than 10°，the latitude deviations are less than 2°.
2010, 59 (3): 2169-2172.
doi: 10.7498/aps.59.2169
Abstract +
The active region of GaAs/AlGaAs bound-to-continuum terahertz quantum-cascade laser （THz QCL） is grown by gas-source molecular beam epitaxy. The device fabrication process of semi-insulating surface-plasmon THz QCL is studied in detail. The electrical and optical characteristics of the fabricated THz QCL device are measured using a far-infrared Fourier transform infrared spectrometer with a deuterated triglycerine sulfate far-infrared detector. At 10 K，the measured lasing frequency is 32 THz and the threshold current density is 275 A/cm2.
