Vol. 61, No. 6 (2012)
2012, 61 (6): 060201. doi: 10.7498/aps.61.060201
To construct a number of new infinite sequence exact solutions of nonlinear evolution equations and to study the two characteristics of constructivity and mechanicalness of the first kind of elliptic equation, new types of solutions and the corresponding Bcklund transformation of the equation are presented. Then the second kind of KdV equation with variable coefficients is chosen as a practical example and three kinds of new infinite sequence exact solutions are obtained with the help of symbolic computation system Mathematica, where are included the smooth soliton-like solutions, the infinite sequence peak soliton solutions, and the infinite sequence compact soliton solutions. The method can be used to search for new infinite sequence exact solutions of other nonlinear evolution equations with variable coefficients.
2012, 61 (6): 060301. doi: 10.7498/aps.61.060301
Using the numerical method, we study the collapse and the recovery of atom, the anti-bunching and the amplitude-squared squeezing of two-level atoms interacting with nonlinear coherent field. The variations of the quantum properties with the parameter of light field, the initial state of the atom and the Lamb-Dicke parameter of the nonlinear coherent state are discussed.
2012, 61 (6): 060302. doi: 10.7498/aps.61.060302
To enhance the optimization ability of quantum potential well-based particle swarm optimization algorithm, the improved quantum potential well-based particle swarm optimization algorithms are proposed by analyzing the design process of current quantum potential well-based particle swarm optimization algorithms. Firstly, three improved quantum particle swarm optimization algorithms are proposed based on delta potential well, harmonic oscillator and square potential well, respectively, and then a statistic mean-based control parameter design method is presented for the proposed models. Secondly, to highlight the guiding role of the global optimal particle in designing potential well centers, two strategies are presented based on a weighted average of all self-optimal particles and dynamic random variables. The experimental results show that the performances of three improved algorithms are relatively close, the model based delta potential well are slightly better than the other two kinds of model, and the performances of three improved algorithms are superior to that of the original algorithm.
2012, 61 (6): 060303. doi: 10.7498/aps.61.060303
By considering the contribution of the higher order term representing the lowest approximation of beyond mean field correction and taking Roser-Zener tunneling as the underling process, we study the nonlinear Rosen-Zener transition of Fermi superfluid gas in a two-level system. We find that the nonlinearity can affect the quantun trasition in the fast scan limit and the adiabatic limit. We also derive the analytical expression for the of rectangular oscillation period dependent on nonlinear parameter. This provides a theoretical basis for a deeper understanding of the basis properties of Fermi gases.
Inplane oscillation analysis of the highline system with 1:2 internal resonance and dominate resonance
2012, 61 (6): 060501. doi: 10.7498/aps.61.060501
A three-degree-of-freedom nonlinear dynamic model of piecewise highline system during underway replenishment is investigated when the lumped mass swings in which the influences of piecewise characteristic of highline cable's static profile due to cargo deadweight, the incline angle and the horizontal motion of the sending end are considered. Considering 1:2 internal resonance and primary resonance, ordinary differential equations are gained by decoupling the inertial terms. Perturbation analysis and numerical analysis are carried out by adopting the multiple-scale method, which will be the theoretical basis of the further research of nonlinear dynamics.
2012, 61 (6): 060502. doi: 10.7498/aps.61.060502
Generalized information domain is the space of all digital information that can be expressed by binary code. In this paper, a random number generator based on discrete trajectory transform in generalized information domain is proposed. The generator exploits generalized information domain as the space of entropy source, and uses the digital information selected by the user as the output of entropy source, and then utilizes the discrete trajectory transform method to generate random number based on the reconstruction of the output of entropy source. The proposed generator shows good characteristics of balance, period and anti-collision, and it demonstrates satisfactory randomness through the National Institute of Standards and Technology test. This generator can be utilized to generate high secure random number quickly and conveniently.
Noise-level estimation of noisy chaotic time series based on the invariant of the largest Lyapunov exponent
2012, 61 (6): 060503. doi: 10.7498/aps.61.060503
A novel method of estimating the noise level from a noisy chaotic time series based on the invariant of the largest Lyapunov exponent is presented in this paper. The influence of noise on the distance between two points in an embedding phase space is considered, and then based on the invariant of the largest Lyapunov exponent in a different dimensional embedding phase space, the algorithm is proposed to estimate the noise level. Simulation results show that the estimated values of noise level agree well with the true values when the noise level is less than 10%. And this method is not sensitive to the distribution of noise. Therefore, the method is useful for estimating the noise level of noisy chaotic time series.
2012, 61 (6): 060504. doi: 10.7498/aps.61.060504
The complicated dynamical evolution of a generalized BVP circuit system with piecewise linear characteristics is explored. The phase space is divided into different types of regions by the nonsmooth boundaries. In each region, the stabilities of the equilibrium points are investigated, from which the critical conditions related to simple bifurcations as well as Hopf bifurcations are obtained. By employing the analysis of the distribution of the eigenvalues of the generalized Jacobian matrix, the bifurcation behaviors related to the nonsmooth boundaries are explored in detail. It is pointed out that when pure imaginary eigenvalues associated with the generalized Jacobian matrix appear, the Hopf bifurcation may take place, leading the system to change from periodic motion into the quasi-periodic oscillation, while when zero eigenvalue occurs, it may lead the system to oscillate between different equilibrium points. Combined with the numerical simulations, two typical oscillation behaviors of the system verify the theoretical results.
Projective synchronization of a five-term hyperbolic-type chaotic system with fully uncertain parameters
2012, 61 (6): 060505. doi: 10.7498/aps.61.060505
A new simple hyperbolic-type three-dimensional autonomous chaotic system is proposed. It is of interest that the chaotic system has only five terms which mainly rely on a nonlinear quadratic hyperbolic sine term and a quadratic cross-product term. Compared with other three-dimensional chaotic systems, the new system has not only less terms, but also a wider range of chaos when the parameter varies. Basic dynamical properties of the system are studied by numerical and theoretical analysis. Moreover the projective synchronization of the five-term hyperbolic-type chaotic system with fully uncertain parameters is also investigated in this paper. Based on Lyapunov stability theory and Barbalat's lemma, a new adaptive controller with parameter update law is designed to projectivly synchronize two chaotic systems asymptotically and globally, including two identical exponential-type chaotic systems and two non-identical chaotic systems. Numerical simulations show the effectiveness and the feasibility of the developed methods.
Hamiltonian model-based H control of chaos in permanent magnet synchronous generators for wind power systems
2012, 61 (6): 060506. doi: 10.7498/aps.61.060506
Aiming at chaos in the wind turbine systems, the H control strategy is presented based on the Hamiltonian model, which makes systems disengage chaos and operate stably. Firstly, the permanent magnet synchronous generator of wind power system is transformed into a model which is similar to a Lorenz-like classical mathematic model through a series of transforms, and demonstrates existing chaos phenomena when its parameter values are in a certain range. Then, the Hamiltonian model of chaos system is established by taking full advantage of the physics structure of wind power system without the compensation of workless forces. Moreover, an H controller is investigated under the external disturbance. This controller is not only simple but also can reflect the interior structure and dynamic characteristics of system. The proposed strategy proves to be valid by simulations.
Network synchronization of spatiotemporal chaos and parameter identification in complex Ginzburg-Landau equation
2012, 61 (6): 060507. doi: 10.7498/aps.61.060507
The synchronization and the parameter identification of a complex network are studied, in which nodes are uncertain spatiotemporal chaos systems. The recognition laws of parameters are designed, and the unknown parameters in spatiotemporal chaos systems at the nodes of the complex network are identified. An appropriate Lyapunov function is constructed, and the conditions of realizing global synchronization of the network are discussed and confirmed based on the stability theory. The uncertain complex Ginzburg-Landau equation having spatiotemporal chaos behavior is taken as nodes in the complex network, and simulation results of spatiotemporal chaos synchronization and parameter identification show the effectiveness of the method.
2012, 61 (6): 060508. doi: 10.7498/aps.61.060508
Based on Lyapunov stability theory, optimal control principle and step design methodology, nonlinear feedback controller and optimal controller are designed, in which the nonlinear feedback controller makes the trajectory error between two neuron systems tend to zero, and the optimal controller makes the spent energy meet minimum, which is spent in the process of synchronizing. In this paper, the uncertain cable model is taken as an example to illustrate the full-order optimal synchronization of two neurons. The uncertain cable model and the uncertain Hindmarsh-Rose (HR) model are taken to illustrate the reduced-order optimal synchronization of two neurons. In addition, the unknown parameters are identified successfully. Numerical Simulation results show the effectiveness of the strategy further.
2012, 61 (6): 060509. doi: 10.7498/aps.61.060509
Based on the physical processes of dielectric barrier discharge (DBD) and quasi-direct-current (quasi-DC) discharge, the plasma aerodynamic actuation mechanism is analyzed, then the numerical model of plasma aerodynamic actuation is founded, finally the DBD and the quasi-DC discharge plasma flow control processes are simulated in the cases of low velocity and high velocity. The results show that the aerodynamic actuation mechanism of DBD plasma is that the discharge changes three kinds of forces in continuum fluent medium, these being shear stress caused by Newton friction, body force caused by electro hydrodynamic and impulsive active force caused by pressure change, and the main aerodynamic actuation mechanism of DBD plasma is body force caused by electro hydrodynamic. The effect of body force is stronger in near space than in the sea level, plasma induced flow velocity increases in near space. The main aerodynamic actuation mechanism of quasi-DC discharge plasma in supersonic air flow is the thermal mechanism of heat plasma, the exploding wires diathermanous model found in this paper is good for the simulation of the process of surface quasi-DC discharge plasma incident shock. The effect of quasi-DC discharge plasma on the supersonic flow field is conform with the effect of protuberance with a bevel to the supersonic flow field, so it can be used to control the shock wave in supersonic aircraft.
2012, 61 (6): 060701. doi: 10.7498/aps.61.060701
Driver's drowsiness is one of the major causes of road accidents. The monitoring of a given driver's eye state by the use of a camera is considered to be a promising way to detect driver's drowsiness due to its accuracy and non-intrusiveness. However, eye location remains a challenging vision problem because of the constantly changing of illumination and driver's pose. Active shape model (ASM) is introduced in this paper to align the face. Though the ASM is a powerful statistical tool, it can suffer from changes in illumination and posture. Three contributions are involved in this paper. First, in order to maximize the tolerance of the ASM algorithm to illumination changes, we propose a robust ASM method with a novel local texture model learned from the self-quotient image instead of the original image. Second, a double layer overall shape model is proposed to enhance the adaptability of ASM. Third, strong constraints are achieved by an on-line learning of the distribution characteristics of the model parameters. The results show that the proposed algorithm is robust to the variation of illumination and driver's pose.
Incoherent broadband cavity enhanced absorption spectroscopy for trace gases detection and aerosol extinction measurement
2012, 61 (6): 060702. doi: 10.7498/aps.61.060702
We report on the development of incoherent broadband cavity enhanced absorption spectroscopy system based on a short arc Xenon lamp for trace gas detection and aerosol optical properties measurements. A minimum detection sensitivity of 1.8 10-7cm-1 (1, 0.12 s integrating time, and 50 times average) is obtained on the basis of absorption spectroscopy of NO2 in a spectral range of 520560 nm, which corresponds to a minimum detection concentration of ～33 nmol/mol for NO2. Combining a laboratory aerosol generation system, the extinction coefficients of 600 nm diameter monodispersed ammonium sulfate aerosol are measured under different particle concentrations. A cross-section of 1.12 10-8cm2 for ammonium sulfate at 532 nm wavelength is obtained, which agree well with the literature result of 1.167 10-8cm2. The results demonstrate the ability of our system to quantitativly measure aerosol optical properties.
Label-free and real-time detection of interactional dynamic processes of rabbit IgG with different concentrations and goat anti-rabbit IgG by oblique-incidence reflectivity difference method
2012, 61 (6): 060703. doi: 10.7498/aps.61.060703
We successfully label-free and real-time detecte the interactional dynamic processes of rabbit IgG with different concentrations (1.25 mg/mL, 2.50 mg/mL and 5.00 mg/mL), and goat anti-rabbit IgG with a concentration of 0.02 mg/mL by the oblique-incidence reflectivity difference method (OIRD). The dynamic curves and times of interaction, response to concentration of rabbit IgG, are obtained. The experimental results demonstrate that the OIRD method can not only can distinguish the biomolecular interactions, but also real-time detect the interactional dynamic processes of biomolecules, indicating that the OIRD method has promising and extensive applications for the investigating of biomolecular interactions.
2012, 61 (6): 062801. doi: 10.7498/aps.61.062801
In this paper, molecular dynamics is used to simulate dynamic properties and micro-structure of the water-hydrogen particle system under various conditions: 1 atm, 293 K; pressurized water reactor (PWR) environment of 155 atm, 626 K; the number of water molecules of 256, numbers of hydrogen (H2) molecules of 0, 25, 50, 75 and 100, and the mean square displacement (MSD) in the particle system increases with the number of particles of the hydrogen increasing. Under the PWR environment, with hydrogen molecule number being 75, the MSD is about 6 times higher than that in chamber ambient. At the same time, under such a condition, the MSD of particle system increases 131.8829% higher than that in the case of the number being 0. In addition, the micro-structure of particle systems, from the view of the radial distribution functions (RDF), increase with the increase of concentration of hydrogen in chamber ambient, which coincides with the fact that the hydrogen dissolution in water increases the particle density around oxygen ions at nomal temperature and normal pressure. While in the PWR environment, the radial distributions of the water with the numbers of hydrogen molecules of 75, 50, 25 and 0 have no big change, but the radial distribution with the number of hydrogen molecules of 100 increases significantly and it is 22.0048% higher than that in the case of the number being 0. It can be seen from simulation data that hydrogen added to PWR significantly inhibits the oxygen dissolution in water. This phenomenon and its cause are revealed comprehensively in this paper.
2012, 61 (6): 062802. doi: 10.7498/aps.61.062802
In this paper, the internal mechanism of solid deuterium spatial distribution induced by infrared radiation is studied. The changes in spatial distribution and micro-structure of solid deuterium are also discussed as the results of wavelength and heating time of IR light. It is found that the micro-structure of solid deuterium which is irradiated by a special IR light is changed from polycrystal to monocrystal, the solid deuterium is redistributed and becomes more uniform and transparent. The best wavelength of IR light for heating solid deuterium is 3140 nm. When the output power of 3140 nm IR light is 100 upW, the redistribution time of solid deuterium is about 18 min.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (6): 063101. doi: 10.7498/aps.61.063101
The first-principls theory is used to study the interaction between the Ge atom and the vacancies in Ge-doped czochralski silicon. The CASTEP calculation shows the stable structural model of Ge atom and one vacancy, two vacancies and three vacancies through the distance between the Ge atom and vacancy (or the vacancy centers) and the size of the area (or volume). The calculation shows that the Ge atom introduced into the GCZ Si crystal tends to accumulate with the vacancy and then seeds for the Ge-vacancy complexes.
2012, 61 (6): 063102. doi: 10.7498/aps.61.063102
Charge transport is one of the most important properties in organic electronic materials. On the basis of Marcus theory, the charge-transfer is the course of electron-electron interaction and electron-phonon interaction, and the greater the electron-phonon interaction coupling strength, the greater the reorganization energy is, which is not conducive to the charge transport. The greater the electron-electron interaction coupling strength, the greater the charge transfer matrix element is, which is beneficial to the charge transport. Charge transport properties of triphenylene derivative discogens molecules with a 1, 2, 3-triazole, 1, 2, 4-triazole or 1, 2, 3-trinitrogen-2, 3- cyclopenten side chain are investigated computationally. The results show that the electronic mobility and the hole mobility of 1, 2, 3-triazole triphenylene derivative are nearly equal, and the rate constant is 21012s-1. The hole transfer rate constant of the 1, 2, 4-triazole triphenylene derivative molecules is 51012s-1, which is ten times higer than the electronic transfer rate constant. Triphenylene containing 4, 5-dihydro-1, 2, 3-triazole has better electronic mobility but smaller hole mobility than triphenylene discogens containing 1, 2, 3-triazole or 1, 2, 4-triazole, and the electronic mobility is 31012s-1, which is equal to ten times of the hole mobility. The hole transfer or electron transfer rate of the target molecules is affected mainly by the transfer matrix element, in other words, electron-electron interaction coupling strength determines the magnitude of mobility rate variation.
2012, 61 (6): 063103. doi: 10.7498/aps.61.063103
The electronic properties of the ZNWs (ZnO nanowire) as one of important part of novel SC (solar cells) are very important, which can greatly affect the performance of the SC. Based on the density function theory combined with the plane-wave ultra soft pseudo-potential method, the structures, the adsorption energies and the electronic structures of the C2H6O (ethanol), C6H5FS (4-fluoro-benzenethiol), C7HF7FS (2, 3, 5, 6- tetrafluoro-4-(trifluoromethyl) benzenethiol) clusters adsorbed (0001) hexangular ZNWs are calculated. Firstly, the most stable configuration is found out from different adsorbed ones based on the principle of lowest energy by calculating their total energy. The results also indicate that C7HF7FS adsorption is energetically favorable. Then, the densities of state and the electronic structures of different adsorbed systems are calculated. Furthermore, the mechanism for adjusting the band-gap of the absorbed system is investigated and the results indicate that the chemical modification of ZNWs with the small molecule groups results in little change in the electronic property of the system. Meanwhile, charge transfer takes place to a certain extent between the C7H7FS and C6H5FS.
2012, 61 (6): 063104. doi: 10.7498/aps.61.063104
The potential energy curves (PECs) of the PH (X3-, a1 and A3) are investigated by the highly accurate valence internally contracted multireference configuration interaction (MRCI) method and the MRCI method including the Davidson modification (+Q) in combination with the correlation-consistent basis sets, aug-cc-pV5Z. With these PECs obtained here, the spectroscopic parameters of three isotopologues, PH (X3-, a1 and A3), PD (X3-, a1 and A3) and PT (X3-, a1 and A3), are determined. These parameters are compared in detail with those previously reported in the literature, and agreement is found between the present results and the experimental data. The values of vibrational level G(), inertial rotation constant B and centrifugal distortion constant B for the first 12 vibrational levels of PH (X3 -), PD (X3 -) and PT (X3 -), are calculated when the rotational quantum number J equals zero, which are in agreement with the available measurements. Comparison with the available experimental data shows that the present molecular constants are accurate.
2012, 61 (6): 063201. doi: 10.7498/aps.61.063201
The X-ray emission due to the impact of 129Xe30+ ions of 1.07.0 MeV kinetic energies on Au surface is detected. The experimental result shows that when ion kinetic energy is larger the incident ion excits not only Au M X-ray but also Xe L X-ray. The X-ray yield and the ion kinetic energy have a strong correlation with each other. The relationship between the X-ray yield with ion kinetic energy is analyzed.
2012, 61 (6): 063202. doi: 10.7498/aps.61.063202
Using the closed orbit theory, we study the photo-detachment of H- in a magnetic field near a dielectric surface. The photo-detachment cross section of this system is also derived and calculated. It is found that the photo-detachment cross section is not only related to the magnetic field strength, but also depends on the dielectric constant. For a given ion-surface distance and dielectric constant, with the increase of the magnetic field strength, the number of the closed orbits increases greatly and the oscillatory structure in the photo-detachment cross section becomes much more complicated. On the other hand, for a given magnetic field strength, the dielectric constant also has a great influence on the photo-detachment process of negative ion. Above the ionization threshold, the photo-detachment cross section becomes oscillatory. With the increase of the dielectric constant, the oscillatory structure in the cross-section becomes much more complicated. Therefore we can control the photo-detachment of negative ion by changing the magnetic field strength and the dielectric constant. This study provides a new understanding of the photo-detachment process of negative ion in the presence of external fields and surfaces.
2012, 61 (6): 063203. doi: 10.7498/aps.61.063203
In the present paper, by analyzing the microscopic mechanism of forced vibration of interfacial atoms, it is shown that the atomic vibration is actually the superposition of the self-excited vibration and the forced vibration. The phonon excitation and annihilation due to the thermal vibration of the interfacial atoms in a non-equilibrium state are studied based on solid state physics and quantum mechanics. Then, the temperature effect on vibration energy levels of interfacial atoms are investigated, which shows that when the temperature is low, the probability for a quantum harmonic oscillator being in an excited state rises with temperature, causing the friction coefficient to rise with temperature. When the temperature is around 100 K, the probability for a harmonic oscillator being in the excited state reaches the peak, causing a peak friction coefficient at this point. When the temperature is above 100 K, the friction coefficient decreases with temperature. The trends of our analytical results and the experimental results of others are the same, indicating that the proposed theory and method are feasible.
2012, 61 (6): 063301. doi: 10.7498/aps.61.063301
In this paper, we present a new method to determine the first ionization limit of europium atom. Firstly, time delayed field ionization is used to detect highly excited Rydberg states of europium atom. Secondly, reversed static electric field is used to exclude ion signal from photoionization, autoionization and other path. The law of first ionization limit shift of europium atom in electric field is studied. First ionization limit in zero electric field is deduced from data of first ionization limit shift in electric field. This value is well coincident with the reported values deduced by other methods.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (6): 064101. doi: 10.7498/aps.61.064101
Time reversal electromagnetics is a new branch of science. The critical factor for the practical implementation of time reversal technique is to obtain time reversed signal efficiently. In this paper, based on the principle of time lens, a method of obtaining time-reversed microwave signal is studied. First, according to the principle of time lens, conditions for realizing time-reversed waveform are derived. The process for obtaining time reversed signals is simulated numerically. Then two chirp electromagnetic bang gap (CEBG) structures are fabricated to construct dispersion channels. And a time reversed signal on a 1.5 ns time scale is obtained in experiment. Due to the difference between CEBG and ideal dispersion channel, there exists a distortion in the experiment results, for whitch the reasons are analyzed.
2012, 61 (6): 064102. doi: 10.7498/aps.61.064102
Based on the nonlinear self-consistent theory and the three-dimensional electromagnetic simulation software CST, the beam-wave interaction of gyrotron with irregular cross section is studied. Through importing high frequency fields which are the results of CST, the beam-wave interaction efficiency, coupling coefficient and starting current can be obtained. In addition, a 0.4 THz third harmonic TE33 mode gyrotron with a corrugated interaction cavity is presented according to this approach. The gyrotron with a 40.5 kV/1 A electron beam, magnetic field of 5.09 T, and pitch factor of 1.5 can produce radiation with an output power of 3.3 kW.
2012, 61 (6): 064103. doi: 10.7498/aps.61.064103
The center of the Gaussian beam from solid laser cannot be completely aligned with the center of the spiral phase panel (SPP) while vortex beam is produced by SPP. The projecting beam from the SPP is actually an off-center vortex beam. Based on the diffraction theory, the propagation of off-center vortex beam is investigated. The analytic expressions of the electric field and the intensity are derived in the observation plane while the beam propagates a certain distance. It is shown that the intensity distribution of the beam changes asymmetricly. Besides the spreading, the core of the vortex beam moves while propagating, which is quite different from that of the ideal vortex beam. The magnitude of topological charge determines the spreading of the beam and has no influence on the motion of the vortex core. Furthermore, the sign of the topological charge determines the direction along which the core moves. If the topological charge is positive, the core will move in the tangential direction anticlockwise; if it is negative, the core will move in the tangential direction clockwise, from which the conclusion can provide a guidance for the beam aligning while the vortex beam is detected under the condition of long distance propagation.
2012, 61 (6): 064201. doi: 10.7498/aps.61.064201
The ionizing radiation effects on fiber Bragg grating are theoretically analyzed based on the color center model. And the relationship between the radiation induced refractive index change and dose is deduced. Fiber Bragg grating sample are irradiated by ray with a total dose of 1 106 rad. Under radiation the reflected spectrum peak wavelength of FBG sample is red shifted, but the full width at half maximent and the reflectivity are not changed obviously. The experiment results accord well with our function. With the low level radiation experiment, this expression can screen the FBG samples and predict their performances under high level radiation.
2012, 61 (6): 064202. doi: 10.7498/aps.61.064202
Scattering of the focused Laguerre-Gaussian beams by a spherical particle is performed. According to the generalized Mie theory, the scattering coefficient expressions are gained. From the numerical simulations of the electric field distribution and scattering intensity of the focused Laguerre-Gaussian beams, the scattering intensities are discussed for different scattering angles, radii of spherical particles and topology changes, and the oscillatory behavior of the scattered intensity distribution is explained by the scattering coefficients. The results show that in the focused Laguerre-Gaussian beams, the backscattering intensity increases with the particle radius; and the particle radius when the scattering intensity begins to increase is related to the topological charge. Comparing with the Gaussian beams, we can see that the focuced Laguerre-Gaussian beams have different the scattering characteristics, so they have potential value for particle size measurement, optical communication, atmospheric backscattering detection, etc.
A technique for tunable microwave/millimeter-wave generation based on a polarization-stable dual-wavelength polarization maintaining fiber Bragg grating laser
2012, 61 (6): 064203. doi: 10.7498/aps.61.064203
A technique for tunable microwave/millimeter-wave generation based on a polarization-stable dual-wavelength polarization maintaining fiber Bragg grating (PMFBG) laser is proposed in which the frequency selecting of PMFBG is used to produce two polarization-stable lasing signals, the polarization scrambler is adopted to ensure the consistency of the orthogonal polarization's power, and then the beating frequency in high-speed photodetector is used to generate the microwave/millimeter-wave. Lateral strain loading on the PMFBG allows the frequency of the microwave/millimeter to be controlled. In the experiment, a scheme for tunable microwave/millimeter-wave generation based on a polarization-stable dual-wavelength PMFBG laser is produced, and the microwave signals of 20.407 GHz and 22.050 GHz are generated by different axial pulls loading on PMFBG. In the simulation, the millimeter-wave of 60 GHz is generated and transmission performance of the millimeter-wave in radio-over-fiber downlink is analyzed. The results show that the eye diagrams demodulated in the mobile station are excellent when the optical carrier which is modulated as the millimeter-wave sub-carrier transmits over 80 kilometers from center station to base station. The excellent performance of the system is verified.
2012, 61 (6): 064204. doi: 10.7498/aps.61.064204
Using the numerical result, the influence of the Doppler broadening on the two-photon absorption related to vacuum induced coherence is discussed. In the absence of Doppler broadening, when VIC is absent, the absorption curve has a double-peak structure and the electromagnetically induced transparency phenomenon can occur; when VIC is present, the absorption curve has a single-peak structure and EIT phenomenon does not appear. In the presence of Doppler broadening, regardless of VIC being present or not, EIT phenomenon always can occur; when VIC is absent, no matter whether the propagation directions of the probe and driving fields are the same or opposite, with the Doppler broadening width (D) increasing, the absorption first increases and then decreases and the absorption curve changes gradually from a double-peak structure to a single-peak structure; when VIC is present, if propagation directions of the probe and driving fields are the same, with the value of D increasing, the absorption first increases and then decreases and the absorption curve changes gradually from a single-peak structure to a double-peak structure; if propagation directions of the probe and driving fields are opposite, with the value of D increasing, the absorption decreases monotonieally and the absorption curve remains a single-peak structure.
2012, 61 (6): 064205. doi: 10.7498/aps.61.064205
One- and two-mode successively squeezed state, obtained through re-squeezing two single mode squeezed states by the two-mode squeezing operator, is studied in terms of the technique of integration within an ordered product (IWOP) of operators. We first derive the normally ordered form of this one- and two-mode successively squeezing operator, and then investigate the quantum statistical properties of the corresponding squeezed state. Particularly, we use the Weyl ordering invariance under a similar transformation to derive the analytical expression of its Wigner function, which seems very easy and concise. Finally, the experimental generation of one- and two-mode successively squeezed state is also proposed simply.
2012, 61 (6): 064206. doi: 10.7498/aps.61.064206
The chemical reactions in combustor are described by integrating Eddy-Dissipation Model with Arrhenius rate coefficients. The cold and react flow fields of triplet impingement injector and combustor are simulated using the three-dimensional computational fluid dynamics method. Both helicity and mixing length are introduced to study the mixing mechanism and the effect of triplet impingement injector. The key characteristic parameters of combustor, e.g., spatial distributions of total temperature and pressure, residence time of gas flow in combustor, are obtained. The flow field characteristics of triplet impingement injector and combustor for Fuel-Oxidizer-Fuel (F-O-F) and Oxidizer-Fuel-Oxidizer (O-F-O) triplet arrangements are analyzed. The degree of F2 dissociation in combustor exit plane for O-F-O triplet arrangement is 13.5% higher than that for the F-O-F triplet arrangement under conditions of specified composition proportioning and combustor characteristic length. Experimental result demonstrates that the output power of laser is increased by 17%.
High power polarization-maintaining master oscillator power amplifier fiber laser in all-fiber format
2012, 61 (6): 064207. doi: 10.7498/aps.61.064207
Experimental study on all-fiber polarization maintaining master oscillator power amplifier fiber laser is performed. A 5 m small core diameter double clad polarization-maintaining Yb-doped fiber is employed in the experiment by means of two-level cascade amplification. A more than 67 W polarization maintaining laser is obtained under a maximal 88 W pump power. In this case, the laser density in the fiber core is about 3.4 W/m2, and the optical-to-optical efficiency is 76%. A higher power laser output can be realized as the pump power is further enhanced.
Experimental study on detection of the high signal-to-noise ratio of the carrier-envelope offset frequency in an Er-doped fiber femtosecond laser
2012, 61 (6): 064208. doi: 10.7498/aps.61.064208
The key techniques for the realization of the femtosecond optical frequency comb are the detection of the carrier-envelop-offset frequency (f0) and the improvement of the signal to noise ratio (S/N) of f0. The influence of the length and the vibration of the fiber between the oscillator and the amplifier, and the pump power of the amplifier on the S/N of the f0 is experimentally studied. With optimized parameters, a f0 with 40 dB S/N is obtained in the Er-doped fiber femtosecond laser.
2012, 61 (6): 064209. doi: 10.7498/aps.61.064209
Study on power limit of fiber lasers and analysis of their physical limits are helpful to develop high power fiber lasers both in theory and in experiment. In this paper, power limits and physical limits of ytterbium-doped and thulium-doped fiber lasers are analyzed by considering several limits to the power scalability of fiber laser, including thermal effect, optical effect, nonlinear effect and the brightness of pump source. Then combining these considerations with the basic requirement for single-mode fiber, the power limits of single-mode ytterbium-doped and thulium-doped fiber lasers are calculated. It is found that using traditional 976 nm and 793 nm laser diodes, separately, as a pump source, based on current technical conditions, power limits of single-mode ytterbium-doped and thulium-doped fiber lasers are 4.2 kW and 7.8 kW, respectively. It is concluded that the fact that the actual power presented by the single-mode thulium-doped fiber laser is much lower than its limit power is due to the pump brightness limitation. Finally the principal approaches to enhancing power limits of single-mode fiber lasers are summarized, including reducing numerical aperture of fiber core and improving beam quality of few-mode fiber lasers.
2012, 61 (6): 064210. doi: 10.7498/aps.61.064210
The generation of fractional vortex beams and their propagation have been interesting research topics in recent years. In this paper we introduce a new type of fractional double-vortex beam, which is generated by the coaxial superposition of the vortex beams with two different fractional topological charges, and its total intensity distribution is of double-ring. We study the generation of this kind of beam theoretically and experimentally. It is shown that the rings of the fractional double-vortex beams carry different orbital angular momenta, from each other and propagate independently. The fractional double-vortex beams possess diverse manipulations as compared with the vortex beams with integer or single fractional charges. Therefore, the fractional double-vortex beam will be of great significance in optical rotation and manipulation of microscopic particles.
Temperature dependence of elastic modulus of single crystal sapphire investigated by laser ultrasonic
2012, 61 (6): 064211. doi: 10.7498/aps.61.064211
The longitudinal ultrasonic wave launched by ns-laser pulse is used to measure the temperature dependence of the elastic modulus C33 of single crystal sapphire. The result shows that in a temperature from room temperature to 1000 ℃ the elastic modulus of sapphire C33 reduces as the temperature increases, following the relationship C33 = - 1.541 10-5T2 - 0.021T + 498.3. In this method, the ablation mechanism is adopted to launch strong longitudinal waves, therefore, the result is accurate that the error of the measurement is estimated to be no more than 0.1%.
2012, 61 (6): 064212. doi: 10.7498/aps.61.064212
The effect of line width compression of stimulated Brillouin scattering (SBS) is investigated experimentally. It is found that the line width compression is directly related to the compression of pulse duration. A new method of measuring the line width of SBS through measuring the pulse duration is proposed. The temporal coherence of SBS is also investigated. It is revealed that the temporal coherence of SBS varies with the compression ratio of pulse duration. High pulse duration compression and good temporal coherence cannot be obtained simultaneously.
Separate holographic-Hamiltonian screening soliton pairs in a biased series photorefractive crystal circuit
2012, 61 (6): 064213. doi: 10.7498/aps.61.064213
Separate holographic-Hamiltonian screening soliton pairs are predicted in a biased series photorefractive crystal circuit consisting of two photorefractive crystals connected electronically by electrode leads in a chain with a voltage source. The existence of four types of the separate soliton pairs:dark-dark, bright-dark, dark-bright and bright-bright, in such a circuit is proved. Under the limit that the spatial extent of the optical wave is much less than the width of the crystal, the Hamiltonian dark soliton can affect the other soliton by the light-induced current whereas the Hamiltonian bright soliton and holographic soliton cannot affect the other soliton in the soliton pair.
Linear electro-optic effect of ultrashort laser pulses in LiNbO3 crystal and its dispersion compensation
2012, 61 (6): 064214. doi: 10.7498/aps.61.064214
For the linear electro-optic (EO) effect of ultrashort laser pulses in LiNbO3crystal, we investigate in this paper the compensation of the group-velocity dispersion, as well as the first- and second-order refractive dispersion by means of optical phase conjugation (OPC). It is found that for arbitrary input pulse durations, these dispersions can be compensated. And the waveforms of output pulses are almost the same as those of input ones. Also, the durations of output pulses can be compressed further when the phases of output pulses of OPC are modulated by EO effect in another LiNbO3for dispersion compensation. And the narrower the input duration, the more evident the compression of output duration becomes.
2012, 61 (6): 064215. doi: 10.7498/aps.61.064215
In the paper, we describe the structure of colloidal photonic crystal microstructure fiber and investigate the propagation characteristics using the finite-difference time-domain method. A structure model is eastablished to simulate the transmission spectra and propagation field distributions under different wavelengths. Experimental system is built to measure the transmission spectrum of fabricated colloidal photonic crystal microstructure fiber. Experimental result is in good agreement with numerical result. The propagation field distribution result shows that the colloidal crystal changes the propagation mode of optical fiber under different wavelengths.
2012, 61 (6): 064216. doi: 10.7498/aps.61.064216
In order to design an angular magnifier based on multiplexed volume holographic grating, the physical model of multiplexed angular magnifier (MAM) is established. The design principle is summarized from two aspects, namely, uniform angular distribution and optimum diffraction efficiency. The effect of production error on MAM is studied. The effect of beam divergence on the performance of MAM is investigated. The results show that the desired angular distribution of MAM is achieved by controlling the spatial frequency and the tilted angle of the grating while the optimum diffraction efficiency is achieved by controlling the thickness and the amplitude of refractive index modulation of the gratings. The 10 VHGs can be multiplexed in the MAM at most. The raising of the grating tilted angle or the ratio between the wavelength of recording beam and working beam can weaken the effect of angular error of reference beam on the output angle distribution of MAM, and the reducing of the thickness is beneficial for reducing the effect of error of thickness and refractive index modulation on diffraction efficiency. When the beam divergence is greater than the angular half width, the optimum diffraction efficiency falls down to 50% or lower and the local minimum values disappear. The raising of the spatial frequency or thickness of the gratings can reduce the desired amplitude of refractive index modulation and multiplex more VHGs, but is not beneficial for achieving uniform diffraction efficiency distribution and weakening the effect of divergent beam.
2012, 61 (6): 064217. doi: 10.7498/aps.61.064217
Stimulated Raman scattering is studied in liquid water using pulse laser at a wavelength of 532 nm. At a lower excitation energy, Stokes line and anti-Stokes line 3426 cm-1 can be observed in the forward Raman scattering. When excitation intensity is increased to 140 mJ, the low frequency 313 cm-1 line in the forward Raman scattering can be observed, and the 3389 cm-1 Stokes line and 3268 cm-1 Stokes line in the backward Raman scattering can also be observed. The experimental results demonstrate that the structure of water under the action of the intense excitation energy is similar to that of ice Ⅷ.
2012, 61 (6): 064301. doi: 10.7498/aps.61.064301
The conventional exterior acoustic Helmholtz boundary integral equation is prohibitively expensive for solving large-scale engineering problems. In order to effectively overcome this problem, the fast multipole method is introduced to the BIE, and accelerates the iterative solution for the system matrix equation. Due to using the diagonal form multipole expansions of the fundamental solution in the BIE, the computational efficiency of the new fast multipole boundary element method (FMBEM) is improved significantly compared to the conventional BEM. Both the computational complexity and memory requirement of the FMBEM are drastically reduced to O(N), where N is the number of degrees of freedom (DOFs). Numerical examples including a large submarine model with more than 420000 DOFs demonstrate the accuracy and efficiency of the FMBEM, and clearly show the advantage of the new algorithm for solving the large-scale acoustic problems. The developed FMBEM would be potential for engineering applications.
Code divided multiple access underwater acoustic communication based on active acoustic intensity average
2012, 61 (6): 064302. doi: 10.7498/aps.61.064302
Code divided multiple access (CDMA) underwater communication based on single vector sensor is studied in this paper. The most common methods to estimate azimuth with self-directivity of single vector sensor are average sound intensity method and complex sound intensity method, however, for the same frequency band multi-users, these methods are limited to the measurement of azimuths only for two users at the same time theoretically. An active average intensity method, which measures the azimuths of multi-users simultaneously with the excellent correlative characteristics of pseudo-random code in spread spectrum communication, is proposed in this paper. With the estimated azimuth, vector combination can be generated to adjust the directivity of vector sensor, achieve multi-user beam communication, inhibit multi-path interference, and enhance processing gain and lower error rate. Simulation and experiment for same frequency band spread spectrum multi-user communication testify the feasibility and utility of active average sound intensity method.
2012, 61 (6): 064401. doi: 10.7498/aps.61.064401
A 10.6 m CO2 big size laser beam is used to passivate the ablation deposit on surface of damage site which is repaired with single laser pulse. When the irradiated region is placed on front surface, modulation by 355 nm UV ns laser pulse is inhibited effectively; when the irradiated region is situated on rear surface, the initial damage threshold exceeds the substrate initial damage threshold. Second repair makes the thermal stress distribution enlarged obviously and the thermal stress magnitude weakened. The damage growth examination shows that once thermal stress is released, the initial phase damage growth exhibits an exponential tendency and as shoot number increases the damage size approaches to a constant value.
Noether symmetry and Noether conserved quantity of Nielsen equation in a dynamical system of the relative motion with nonholonomic constraint of Chetaev's type
2012, 61 (6): 064501. doi: 10.7498/aps.61.064501
Noether symmetry and Noether conserved quantity of Nielsen equation in a dynamical system of the relative motion with nonholonomic constraint of Chetaev's type are studied. The differential equation of motion of Nielsen equation for the system, the definition and the criterion of Noether symmetry, and the expression of Noether conserved quantity deduced directly from Noether symmetry for the system are obtained. An example is given to illustrate the application of the results.
2012, 61 (6): 064601. doi: 10.7498/aps.61.064601
Aiming at the requirements for multi-zero dispersion points and high birefringence of photonic crystal fibers, a new kind of photonic crystal fiber with rhombus air-core structure is composed of four air holes locate at four points of rhombus is proposed. By using the numerical analysis method based on the finite element, we simulate the dispersion and the birefringence characteristics of photonic crystal fiber, and obtain the relationships between dispersion and wavelength, dispersion and size of structure, birefringence and wavelength, birefringence and size of structure. Simulation results show that better birefringence can be obtained when the requirement of power is met. In addition, two zero dispersion points can be obtained when diameter d1 is 0.4 m or 0.6 m. The results are of significance for the further development of photonic crystal fiber with multi-zero dispersion points.
2012, 61 (6): 064602. doi: 10.7498/aps.61.064602
The Kirchhoff thin elastic rod models and related systems are always the important basis to research the topology and stability of the flexible structures in not only the macroscopic but also microscopic scale. Firstly the initial Kirchhoff equations are rebuilt in a complex style to suit the character of obvious asymmetry embodied on the cross section by considering the mathematical background of DNA double helix. Then we introduce a complex form variable solution of the torque, and extend the knowledge of effective bending coefficients as well as its facility in the high dimensional system by using the complicated system. As the result, a simplified second order ordinary differential equation with single variable is obtained. Furthermore the periodically varying bending coefficients of the DNA molecular are considered as the appended components to the effective bending coefficients. The whole reduction process makes the numerical simulation become not solely the exclusively eligible approach, and produces adaptable channel to quantitative analysis.
Numerical simulation of the spread of internal waves see from deep sea to shallow sea from the mixed model
2012, 61 (6): 064701. doi: 10.7498/aps.61.064701
From remote sensing images, it is found that the internal wave spreads from deep sea, by shelf slope, to shallow sea in the South Chinese sea. Because of the different environmental conditions and model applicabilities, it is the best to use two models to simulate the spread of ocean internal waves in deep or shallow sea. The spread of waves in deep sea is simulated with the nonlinear Schrdinger (NLS) equation first and then the spread of wave in shallow sea is simulated with the extended Korteweg de Vries (EKdV) equation by differential mathod. It can be found that the results are in good agreement with the actual remote sensing images, compared with those obtained by single model which consists of the NLS equation or the EKdV equation.
2012, 61 (6): 064702. doi: 10.7498/aps.61.064702
When shock waves passes through a triangle wedge (Schardin's problem), some complicated physical phenomena, including shock wave Mach refection and diffraction, wedge wake, vortexlet, etc. may occur. In this paper, the Schardin's problem is investigated numerically with the combination of the third-order WENO scheme, structured adaptive mesh refinement (AMR) method and immersed boundary method. Our numerical results show clearly the interaction between the incident shock wave and the triangle wedge, the Mach reflection on the wedge surface, its diffraction at the wedge tips, and the induction of the main vortex, which accord excellently with Schardin's experimental and previous numerical results. In addition, our numerical results display in detail the induction process of the vortexlet along the slip layer of the main vortex and the interaction of the shock wave with the vortexlet, and the generation of the serial acoustic waves, which have not been reported in the literature.
Cooling efficiency investigation of forward-facing cavity and opposing jet combinatorial thermal protection system
2012, 61 (6): 064703. doi: 10.7498/aps.61.064703
The cooling efficiency of a forward-facing cavity and opposing jet combinatorial thermal protection system is investigated, by which the flow field parameters, the aerodynamic force, and the surface heat flux distribution are obtained. The numerical simulation method is validated by experiment with no opposing jet model. The analysis of the numerical simulation results shows that this kind of combinatorial thermal protection system has an excellent effect on cooling the outer body surface of the nose-tip. By introducing an opposing jet with a small total pressure (total pressure ratio PR is 0.1), the cooling effect of combinatorial configuration can be much better than that of a single cavity. With the opposing jet speed increasing, the cooling efficiency is improved and the aerodynamic resistance is reduced. The combinatorial system is suited for the thermal protection of hypersonic aircraft that needs a long-distance and long-time flight.
Dissipative particle dynamics simulation of flow around a mesoscopic sphere with different Reynolds numbers
2012, 61 (6): 064704. doi: 10.7498/aps.61.064704
Dissipative particle dynamics (DPD) is used to investigate the flow passing through a three-dimensional sphere within two parallel plates. The sphere and the plates are composed of frozen DPD particles which are in an equilibrium state. The fluid is driven by a dimensionless external force exerting on each fluid particle. The force on the sphere is computed from the total particles consistituting the sphere. After the flow is fully developed, the obtained results, including the force exerted on the sphere is computed, and then we can calculate the drag coefficient. The accuracy and the reliability are compared with classical results. The results show that the DPD method can predict drag coefficient accurately when Re is less than 100. However, when Re is bigger than 100, the results deviate from analytical values, which is due mainly to the fluid compressibility.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (6): 066101. doi: 10.7498/aps.61.066101
The freezing behaviors of Al nanowires with different section sizes and cooling rates are studied by using the classic molecular dynamics simulation via embedded atom potentials. In order to invesligate the evolution of the local clusters in the transformation of Al nanowires, the pair analysis technique is employed. The simulation results indicate that the final structure of Al nanowires is strongly affected not only by cooling rate, but also by the size effect during solidification from liquid. At a rapid cooling rate, the final structures are all helical multi-shelled structures. However, at a slower cooling rate, the structure changes from helical multi-shelled to crystalline via near-hexagonal shell structure with the increase of section size except that the thinnest Al nanowires break down.
2012, 61 (6): 066801. doi: 10.7498/aps.61.066801
Manganese silicides are promising candidates for microelectronics and spintronics materials. A good understanding of their growth mechanisms is a crucial step toward their practical applications. In this paper, a Mn film of ～4 monolayer is deposited on a Si(100)-21 surface by molecular beam epitaxy. The solid reaction between the Mn film and the silicon substrate in a temperature range of 250750℃ is studied using scanning tunneling microscopy. At room temperature, the as-deposited Mn atoms do not react with the silicon atoms and the film consists of disordered Mn clusters. When the sample is annealed at a higher temperature than 290℃, the Mn begins to react with the Si and forms small three-dimensional (3D) islands of Mn-rich silicides and silicide islands of dendritic shapes. When the annealing temperature reaches 325℃, small tabular islands, which correspond to MnSi, start to grow on the Si substrate. At an annealing temperature of 525℃, silicide islands with dendritic shapes all disappear; meantime several large tabular islands, which correspond to MnSi1.7, are formed. When the annealing temperature is higher than 600℃, 3D islands and small tabular islands all disappear while large tabular islands remain there. These results demonstrate that the morphology and the structure of the film strongly depend on annealing temperature. The average size (area) of the remaining islands increases with the increase of annealing time. Time dependence of the averaged island area indicates that the growth of the islands follows the diffusion limited Ostwald ripening mechanism.
2012, 61 (6): 066802. doi: 10.7498/aps.61.066802
Kinetics of diffusion-limited aggregation-annihilation process on globally coupled networks is investigated by the Monte Carlo simulation. In the system, when two clusters of the same species meet at the same node, they will aggregate and form a larger one; while if two clusters of different species meet at the same node, they will annihilate each other. The simulation results show that, (i) if the two species have equal initial concentrations, the concentration of clusters c(t) and the concentration of particles g(t) follow power laws at large time, c(t)～t- and g(t)～t-, with the exponents and satisfying =2 and =2/(2 + q); meanwhile, the cluster size distribution can take the scaling form ak(t)=k-t-(k/tz), where -1.27q, (3 + 1.27q)/(2 + q) and z=/2=1/(2 + q); (ii) if the two species have different initial concentrations, the cluster concentration of the heavy species cA(t) follows the power law at large time, cA (t)～t-, where =1/(1 + q), and the cluster size distribution of the heavy species can obey the scaling law at large time, ak(t)=k-t-\varPhi (k/tz), with the scaling exponents -1.27q, (2 + 1.27q)/(1 + q) and z==1/(1 + q). The simulation results accord well with the reported theoretic analyses.
The influence of new additive in alkaline solution on the shape of pyramid on the monocrystal Si surface
2012, 61 (6): 066803. doi: 10.7498/aps.61.066803
The controlling technology of micro-structure on the surface of monocrystal silicon is a hot spot issue in semiconductor and solar cell fields because the conversion efficiency of monocrystal solar cell is affected by the structure of pyramid. With the traditional alkaline solution, monocrystal Si surface is easily textured, and becomes the surface full of the pyramid. However, it is difficult to control the sizes, the shapes and the distribution of pyramids in the process. In this paper, we discuss how a new additive influences the sizes, and the shapes of pyramids during the etching process. In experiment, silicon is etched in traditional alkaline solution with addition of the new additive at a fixed temperature and time. Samples are scanned by SEM. The SEM result shows that the samples are uniformly-densely filled with pyramids with smooth edges. The size of pyramid is smaller than that etched in the traditional alkaline solution. The etched surface is covered by pyramids with 24m in size. The reflectance spectrum of the textured surface is measured. The measured reflectance decreases to 12.51%. These experimental results show that the new additive can effectively cantrol the sizes and the distribution of pyramids on the silicon surface during the texturing process, which is very meaningful to control the textured structures of single crystal silicon surface.
The effects of substrate temperature and oxygen pressure on the crystal strcture and transport properties of Bi2Sr2Co2Oy thermoelectric films deposited by pulsed laser deposition
2012, 61 (6): 066804. doi: 10.7498/aps.61.066804
We fabricate Bi2Sr2Co2Oy films on c-Al2O3 by pulsed laser deposition and investigate the effects of substrate temperature and oxygen pressure on the crystal stucture and the transport properties of the films. The resulting single phase c-axis Bi2Sr2Co2Oy films obtained under the optimal condition have a room temperature resistivity of about 2.9 m/cm and a seebeck coefficient of 110 V/K, leading to a larger power factor than that of the single crystal. In addition, a negative magnetroresistance of 40% at 2K and 9T is observed in the films.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (6): 067101. doi: 10.7498/aps.61.067101
The band structure, the density of states, the surface energy, the work function, and the optical properties of GaN(0001)(22) clean surface are calculated systematically by the first-principles plane-wave ultro-soft pseudopotential method based on the density function theory. It is found that the band structure of GaN(0001) surface changes greatly after relaxation, the surface has metallic conductive properties, and there is obvious surface state near the bottom of conduction band. In the effect of dipole moment, the surface charges shift and Ga-terminated surface is positive polar surface. the surface energy and the work function of GaN (0001) surface are obtained to be 2.1 J.m-2 and 4.2 eV, respectively. The optical properties of GaN (0001) surface and bulk phase GaN are analyzed and compared. It is found that there is big difference between them.
Effects of heterogeneous interfaces on microstructure and dielectric properties of Ca(Mg1/3Nb2/3)O3/CaTiO3 multilayered thin films
2012, 61 (6): 067401. doi: 10.7498/aps.61.067401
The effects of heterogeneous interfaces on the microstructure, the morphology and the dielectric properties of Ca(Mg1/3Nb2/3)O3/CaTiO3(CMN/CT) multilayered(ML) thin film prepared in the layer-by-layer mode with a certain thickness are investigated. According to the experimental results, an equivalent circuit of CMN/CT ML thin film is simulated, and the theoretical formulae of the dielectric constant and loss of thin film are established. The results indicate that CMN/CT ML thin film, in which CT and CMN phases can exist independently, possesses a pure orthorhombic perovskite structure, dense smooth surfaces and intermediate layers at the heterogeneous interfaces, and that the dielectric constant increases and the dielectric loss decreases with the increase in the number of heterogeneous interfaces, and reducing the thickness of the interfacial transition layer is useful to improve the dielectric properties of CMN/CT multilayered thin film.
The rare earth-transition (R-T) intermetallics has excellent physical and chemical properties. The electronic structure, the band structure and the magnetic properties of the compound Ni13Nd3B2 are studied by using the first-principles plane wave pseudopotential method and the local spin-density approximation (LSDA). The calculation results indicate that this system is a metallic conductor with a very small band gap. The system has very complex bonding, where Nd atoms and the neighboring Ni and B atoms form ionic banding, whereas Ni atoms and the neighboring Ni atoms form covalent bonding. Under LSDA approximation, the system has Nd-Ni ferromagnetic coupling, and the total magnetic moment ( 8.4329B) is provided by the local Nd magnetic moment. The Nd-4f, Ni-3p, Nd-5p electron spin splittings due to spin polarization result in the magnetic system.
A kind of ferromagnetic-antiferromagnetic alternating spin chain equivalent to the mixed spin Heisenberg chain
2012, 61 (6): 067502. doi: 10.7498/aps.61.067502
By using the method of exact diagonalization, the properties of the spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain are investigated. The spin-spin correlation, the sublattice magnetizations, the spin excitation spectrum and the magnetization curve of the model are calculated and compared with the corresponding properties of the mixed spin chain. The results show that the behaviors of the alternating Heisenberg chain are equivalent to those of the mixed spin chain when the ratio of antiferromagnetic to ferromagnetic coupling strength is very small. So, the properties of the mixed spin chain can be analyzed by using the spin-1/2 ferromagnetic-antiferromagnetic-antiferromagnetic alternating Heisenberg chain.
2012, 61 (6): 067701. doi: 10.7498/aps.61.067701
Trap levels in nanoparticle doped low density polyethylene (LDPE) are investigated by photo-stimulated discharge (PSD). The PSD spectra in MgO/LDPE and Al2O3/LDPE nanocomposites with the different mass percentages and different nanocomposites with the same mass percentage are obtained by continuous scanning mode, which can be qualitatively estimate the trap energy distribution. The trap levels in Al2O3/LDPE nanocomposite are quantitatively described by step scanning mode. The experimental results indicate that the trap levels in Al2O3/LDPE nanocomposites with the Al2O3 content of more than 0.2% and MgO/LDPE nanocomposites with the MgO content of more than 0.5% are deeper than those of the virgin LDPE. According to the relevant reports on the effect of nanoparticle doping on space charge injection, it is considered that the suppression of space charge is probably correlated with the deeper trap levels in nanocomposites.
A latent defect degradation model of metal-oxide-semiconductor field effect transistor based on pre-irradiation1/f noise
2012, 61 (6): 067801. doi: 10.7498/aps.61.067801
Based on metal-oxide-semiconductor field effect transistor (MOSFET) microscopic mechanism of radiation damage, a relation between radiation induced increase in number of oxide hole-traps and post-irradiation threshold voltage drift is proposed. Then, Based on MOSFET microscopic mechanism of1/f noise generation, a quantitative relationship between pre-irradiation1/f noise power spectral amplitude and post-irradiation threshold voltage drift is founded, which accords well with the experimental results. This relationship shows that pre-irradiation1/f noise power spectral amplitude is proportional to post-irradiation threshold voltage drift, which can reflect the degradation of latent defect in MOSFET. So, this modal is helpful to characterize the quantity and severity of latent defect in MOSFET by using1/f noise parameters.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (6): 068001. doi: 10.7498/aps.61.068001
Through-silicon-via (TSV) is one of the major design techniques in three- dimensional integrated circuit (3D IC). Based on the parasitic parameter extraction model, the parasitic resistance-capacitance (RC) parameters for different size TSVs are acquired and validated with Q3D simulation data. Using the results of this model, closed-form delay and power consumption expressions for buffered interconnect used in 3D IC are presented. Comparative results with 3D net without TSV in various cases show that TSV RC effect has a huge influence on delay and power of 3D IC, which leads maximum delay and power comsumption to extra increase 10% and 21\% on average, respectively. It is crucial to correctly establish a TSV-aware 3D interconnect model in 3D IC front-end design.
2012, 61 (6): 068401. doi: 10.7498/aps.61.068401
The resonance properties of surface plasmon in the AMM/dielectric/AMM waveguide are theoretically studied by using the finite-difference time-domain technique, where the claddings are anisotropic metamaterial (AMM) . From the dispersion relation, it is found that the AMM/dielectric/AMM waveguide supports TE polarized surface plasmon if AMM is always-cutoff with negative permeability. The wavelength of the surface plasmon becomes shorter when both the thickness of the dielectric core and the magnetic plasma frequency of AMM decrease. For an AMM/dielectric/AMM waveguide with a finite length, a subwavelength plasmon microcavity can be formed by Fabry-Perot resonance caused by the reflection of the guided mode at the entrance and the exit surfaces. At the resonant frequency, the electric field is maximized in the center, the magnetic field is maximized at the dielectric core entrance and exit, and the electromagnetic energy is strongly concentrated around the dielectric core. Such electromagnetic properties will have potential applications in the tunable subwavelength microcavity with strongly localized field and in the cavity quantum electrodynamics.
2012, 61 (6): 068402. doi: 10.7498/aps.61.068402
Thick screen frequency selective surface (FSS) is a very effective means of realizing the stealth radome, since it can better improve the bandwidth performance of FSS. In order to fully grasp the transmission characteristics of thick screen FSS and to provide a sound foundation of realizing their applications for bandpass radomes, a dielectric-metal-loaded thick-screen FSS is designed in this paper. The transmission properties of this structure are analyzed by using the moment method. The transmission characteristics of this structure are investigated when some parameters including the diameter of filling dielectric, the diameter of filling metal, the thickness of filling dielectric, incidence angle of electromagnetic wave, and unit spacing are changed. Simulation results show that the diameter of filling dielectric, the diameter of filling metal, the thickness of loading dielectric, thickness of filling metal, incidence angle of electromagnetic wave, and unit spacing can influence the transmission properties of the dielectric-metal-loaded thick-screen FSS. The diameter of filling metal and the thickness of loading dielectric can be adjusted appropriately in order to obtain a wide passband width and a better penetrating percentage of the central frequency. The novel structure provides a valuable reference for the application in stealth curved streamlined radomes.
2012, 61 (6): 068501. doi: 10.7498/aps.61.068501
Aiming to inverstigate the effect of surface potential barrier on electron escape probability of negative electron affinity GaN photocathode, the electron escape probability is calculated by using the Boltzmann distribution and the method of transfer matrix based on Airy function. It is found that barrier I is a key influencing factor of electron escape probability, while barrier II has a limited influence. The activation photocurrent curve of the transmission-mode GaN photocathode is measured by using our built activation and evaluation experimental system of NEA GaN photocathode. The obvious increase of electron escape probability can be achieved mainly by activating Cs only. The increase of electron escape probability is not large in Cs/O activation process with only Cs activated sufficiently. The theoretical calculations are in good agreement with the photocurrent curves from experimental test. The reason is that the contribution of activating only Cs to the reducing of vacuum level for obtaining NEA state is much larger than that of activating Cs/O.
2012, 61 (6): 068701. doi: 10.7498/aps.61.068701
We study the characteristics of motion modes of epidermal growth factor receptor (EGFR) trafficking in single cell, by using the automatic method of trajectory identification which is based on the directional persistence and mean square displacement analysis. Each trajectory of EGFRs is divided into four modes of motion: directional motion, super-diffusion, Brownian motion and sub-diffusion. The corresponding dynamic parameters of different modes of motion are calculated and discussed, providing an insight into intracellular trafficking of receptors.
2012, 61 (6): 068702. doi: 10.7498/aps.61.068702
Noise exists widely in biological neural systems, and plays an important role in system functions. A complex neural network, which contains several small-world subnetworks, is constructed based on a two-dimensional neural map. The phenomenon of stochastic resonance induced by Gaussian white noise is studied. It is found that only with an appropriate noise, can the frequency response of the network to input signal reach a peak value. Moreover, network structure has an important influence on the stochastic resonance of the neural system. With a fixed coupling strength, there exists an optimal local small-world topology, which can offer the best frequency response of the network.
2012, 61 (6): 068703. doi: 10.7498/aps.61.068703
With the development of the research on inertial confinement fusion (ICF), there is needed a diagnostic technique for low Z materials.The phase contrast imaging, which relies on gradients in the refractive index and wave interference, is proposed to characterize the typical ICF (inertial confinement fusion) capsule shell. In our work it is indicated that the phase contrast imaging obtained with a micro-focus X-ray source provides complementary information about the capsule shell with high resolution 2 upm, and has advantages of absorb imaging. Such a capsule shell diagnostic technique is very useful for ICF diagnoses. Besides, we propose an approach to obtaining of the optimum contrast and spatial resolution in phase contrast imaging. It is a guidance in obtaining an excellent result in phase contrast imaging experiment, and can be widely used in biomedicine, materials science.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (6): 069201. doi: 10.7498/aps.61.069201
Various trends exist in many observation data, such as periodical trend caused by seasonal variation, linear trend and polynomial trend brought about by global warming. In the present paper, the effects of different trends on moving cut data-approximate entropy are investigated. The numerical tests on model time series indicate that the detection results of moving cut data-approximate entropy are little affected by periodical trend, linear trend and nonlinear trend. The reliability of abrupt change detection of moving cut data-approximate entropy is demonstrated, which provides an experimental basis for the wide applications of the present method in real observation data.
2012, 61 (6): 069202. doi: 10.7498/aps.61.069202
A lightning VHF radiation source location system based on short-baseline technology is used to study the location of VHF radiation source in the lightning discharge process. The observation was conducted in Daxing'anling during summer of 2009. Positive cloud-to-ground (CG) lightning, negative CG lightning, and intra-cloud (IC) lightning are analyzed based on the locating results and simultaneous electric field changes. The long lasting preliminary breakdown process of CG flash appears as two-level structure of discharge channel in cloud. There are obvious recoil streamers during the final stage of preliminary breakdown process. The preliminary breakdown process propagates at a speed of about 104 m/s. The preliminary breakdown seems to be necessary for the initiation of stepped leader. The stepped leader starts from the source region of preliminary breakdown and propagates downwards. The stepped leader produces intensive VHF radiation. The propagation speed of stepped leader is about 105 m/s. The K process is caused by the streamers propagating backwards and forwards along the electrified channel. Characteristics of discharge processes before and after the return stroke of positive CG flash are different from those of negative CG flash obviously. During long continuing current after the return stroke of positive CG flash, discharges in cloud produce intensive VHF radiation. The energy spectrum of the VHF radiation produced by lightning is studied statistically. It is found that the energy spectrum of VHF radiation decreases quickly with the frequency at a rate of about f-2.9 between 125 and 200 MHz.
2012, 61 (6): 069301. doi: 10.7498/aps.61.069301
Particle filter(PF) is an effective algorithm for the state recursive estimation in nonlinear and non-Gaussian dynamic systems by utilizing the Monte Carlo simulation, and it is applicable for solving the nonlinear and non-Gaussian RFC(refractivity from radar clutter) problems. The basic idea and the specific algorithm of PF are introduced; the implementation of the iterative inversion algorithm is derived finally. The experimental result indicates that the particle filter is suited to solve the nonlinear inversion problem and can effectively increase the stability and the accuracy of inversion results compared with the extended Kalman filter (EKF) and the unscented kalman filter (UKF).
2012, 61 (6): 069501. doi: 10.7498/aps.61.069501
Phase diversity wavefront sensing technology has been implemented successfully in many domains because of its simple and compact optical configuration, lower environment requirement, better measurement accuracy, and so on. In this paper, the co-phasing technique for segment primary mirrors is studied by using the phase diversity wavefront sensing technology, and the corresponding experimental optical system is also set up. The experimental results show that the measurement accuracy of phase diversity wavefront sensing technology for piston error is better than /20 and that it can be used to detect the piston errors of segment mirrors.
2012, 61 (6): 069701. doi: 10.7498/aps.61.069701
The estimation of pulsar period is important for pulsar searching, observation and timing. In this paper, the frequency-domain method which is popular in periodicity searches is analyzed, and further more, a novel method in time-domain is proposed to estimate the cyclo-period of pulsars based on the second-order cyclo-stationary model of the radiation signal. Firstly, the discrete-time observing signal is blocked by assumed period which is alterable. Then, the correlation estimations and their sample variances are computed each as a function of blocking operator index, where the largest peaks display a periodic pattern, from which the cyclo-period can be obtained. Using this method, the period of PSR J0437-4715 with single pulse is estimated well based on original signal, and the period of PSR B1821-24 with double pulses is also estimated based on the simulated signal. The same work is done for the observed data from ATNF EPN pulsar database. The simulation results and the experimental results for many pulsars show that compared with the classical Fourier-transform method, this algorithm is non-sensitive to the noise, and it is effective even though in the case of low signal-to-noise ratio. And it is of low computation complexity compared with the bispectrum coherence method. This method possesses higher popularization value in real-time observation and processing for weak pulsar signal, though it does not work well in dealing with noncontinuous observing data.