Vol. 60, No. 1 (2011)
2011, 60 (1): 010201. doi: 10.7498/aps.60.010201
The EI Ni o/La Ni a and the Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific Ocean-atmosphere interactions. This paper, aims at creating an approximate solving method of nonlinear equation for the ENSO models. And based on a class of oscillator of ENSO models, employing the method of homotopic mapping, the approximate and exact solutions of the corresponding problem is studied. The accuracy of approximate solution is discussed. It is proved from the results that homotopic method can be used for analyzing the SST anomaly in the equatorial eastern Pacific and the thermocline depth anomaly of the atmosphere-ocean oscillation for ENSO model.
2011, 60 (1): 010202. doi: 10.7498/aps.60.010202
To seek new infinite sequence complexiton solutions to nonlinear evolution equations(NEE(s)), the formula of nonlinear superposition of the solutions and Bcklund transformation of Riccati equation are presented, and as an illusrative exapmle, the generalized Boussinesq equation is chosen to obtain new infinite sequence complexiton solutions with the aid of symbolic computation system Mathematica, which includes complexiton solutions of hyperbolic function, triangular function type with rational function and hyperbolic function with triangular function. The method is of significance to construct infinite sequence complexiton solutions to other NEEs.
2011, 60 (1): 010203. doi: 10.7498/aps.60.010203
Based on topological horseshoe map theory, the paper analyses the existence of topological horseshoe in a 3-D four-wing chaotic system. As the chaotic system is continuous, the paper first choses a Poincaré section, then under which defines a first return Poincaré map. A conclusion that the Poincaré map is semi-conjugate to 2-shift map can be obtained by utilizing computer-assisted verification, showing that the topological entropy of the 3-D four-wing system is larger than or equal to ln2, which further verifies the chaotic characteristic of the system.
Bistatic scattering from three-dimensional target on perfectly conducting rough surface by using G-SMFSIA/CAG
2011, 60 (1): 010301. doi: 10.7498/aps.60.010301
This paper presents a novel and powerful numerical technique called general sparse-matrix flat-surface iterative approach-canonical grid (G-SMFSIA/CAG), which combines the sparse-matrix flat-surface iterative approach-canonical grid (SMFSIA/CAG) for 2D conducting rough surface and the method of moment (MoM) based on Rao-Wilton-Glisson (RWG) function for PEC target, to compute the electromagnetic scattering from a three-dimensional PEC target on conducting rough surface. The coupling surface integral equations (SIEs) for the composite model are derived based on Huygens surface equivalence principle. The SMFSIA/CAG is applied to solve the SIE of rough surface, and the targets’ SIE is solved using MoM. The iteration of SMFSIA/CAG and MoM takes account the interactions between target and the rough surface. Combining the PM(Pierson-Moskowitz)sea surface generated using Monte-Carlo method, the bistatic scattering coefficient for different targets on sea surface are computed. Convergence and effectivity of the G-SMFSIA/CAG is numerically validated. The bistatic scattering coefficient from ship on sea surface is calculated finally,and the dependence of bistatic scattering pattern upon the wind speed is discussed.
2011, 60 (1): 010302. doi: 10.7498/aps.60.010302
A type of Josephson charge qubit circuit is constructed in this paper, and properties of four-qubit quantum state transfer through this system is also investigated. By modulating the external magnetic flux, we show that ideal transfer of an excited state 1〉 from the first qubit to the fourth qubit can be realized for both homogeneous and inhomogeneous transmission channels. Moreover, the average fidelity of state transfer across this system is also analyzed, the result revealed that it cannot be used to transfer an arbitrary quantum state.
2011, 60 (1): 010501. doi: 10.7498/aps.60.010501
In this paper, chaotic light generated by optical feedback semiconductor laser is employed as entropy source. The output waveform of chaotic laser is converted into a binary bit stream by an 8-bit ADC. The generated binary sequences are optimized to equalize the ratio of 1 and 0 by the difference between consecutive sampled 8-bit values. Finally a random bit sequence at rates of up to 1 Gbit/s is realized, and the randomness of long bit strings is verified by the NIST Special Publication 800-22 tests.
2011, 60 (1): 010502. doi: 10.7498/aps.60.010502
The Hopf bifurcation of van der Pol system with random parameter is studied. Firstly according to the orthogonal polynomial approximation in Hilbert space, the van der Pol system with random parameter can be reduced into the equivalent deterministic system. Then the Hopf bifurcation can be explored by the traditional methods in deterministic bifurcation theory. After the critical point of Hopf bifurcation in stochastic van der Pol system is obtained, the influence of the random parameter on Hopf bifurcation in stochastic van der Pol system is analyzed. At last we verified these results by numerical simulations.
Complex subharmonic oscillation phenomenon of peak current controlled buck converter with current source load
2011, 60 (1): 010503. doi: 10.7498/aps.60.010503
Peak current controlled buck converter with current source load shows the complex phenomenon of fast-scale and slow-scale subharmonic oscillations. Its piecewise smooth switching model and discrete iterative map model are established in this paper. According to its discrete iterative map model, the effects of circuit parameters on the nonlinear dynamic behaviors of buck converter are analyzed by numerical simulation. It is found that attractive regions of fast-scale and slow-scale subharmonic oscillations and dual tori phenomena exist in the bifurcation diagram and Poincaré mapping, respectively. Time-domain simulation waveforms and phase portraits of buck converter are obtained by Runge-Kutta algorithm using the piecewise smooth switching model. The research results indicate that n-type subharmonic oscillation constituted by subharmonic oscillation and frequency-reduced subharmonic oscillation exists in the inductor current, and sine-type subharmonic oscillation constituted by fast scale and low scale exists in the output voltage, respectively. Analysis and simulation results are verified by experimental results.
2011, 60 (1): 010504. doi: 10.7498/aps.60.010504
By extending and nonlinearly coupling two one-dimensional parabolic discrete maps, a new two-dimensional parabolic discrete map is achieved. By using stability analysis of fixed points and bifurcation analysis of map, the complex dynamical behavior and attractor evolution of the proposed two-dimensional discrete map are investigated, and its peculiar dynamical characteristics, such as the coexisting bifurcation modes and fast-slow periodic oscillation effects, etc., are illustrated. The research results indicate that two-dimensional parabola discrete map has two control parameters with different functions of adjustable dynamical behaviors and adjustable dynamic amplitudes, and there emerge nonlinear physical phenomena of Hopf bifurcation, bifurcation mode coexisting, locked-frequency and periodic oscillation fast-slow effect. Furthermore, the corresponding theoretical analysis and numerical simulation results are verified based on a digital circuit realized by microcontroller.
2011, 60 (1): 010505. doi: 10.7498/aps.60.010505
In order to improve the complexity of chaotic signals, a new fractional-order four-dimensional hyperchaotic system is presented. Some dynamical properties of the system are investigated. The circuit implementation of this new system is simulated using Multisim. The results prove that chaos actually exists in the system with order as low as 3.2. A simple linear feedback controller is designed, and the simulation results are presented to demonstrate the effectiveness of the method.
2011, 60 (1): 010506. doi: 10.7498/aps.60.010506
The problem of Hopf bifurcation control for a predator-prey system with three delays is considered. A new hybrid strategy is proposed to control the Hopf bifurcation, in which the state feedback and parameter perturbation are used to delay the onset of an inherent bifurcation or make the bifurcation disappear. The stability and the existence of bifurcation are researched. In particular, the formulae determining the direction of the bifurcations and the stability of the bifurcating periodic solutions are derived by using the normal form theory and center manifold theorem. Finally, numerical simulation results confirm that the new hybrid controller is efficient in controlling Hopf bifurcation.
2011, 60 (1): 010507. doi: 10.7498/aps.60.010507
Based on the comprehensive analysis of the basic dynamic characters of the coupled dynamos system, we have calculated the Lyapunov exponent spectra, bifurcation diagrams and so on, and discussed the chaotic bifurcation and mutative characteristic thoroughly in the periodic windows of the system, and the dual-parameter characteristic is also analyzed. It is found that a boundary line is absent in period-doubling bifurcations and a complicated bifurcation structure appears in 2D parameter space, the influences of two control parameters to the dynamic behavior are different.
2011, 60 (1): 010508. doi: 10.7498/aps.60.010508
For studying the statistical character of the random signal, the width and amplitude of two relatively independent characteristic parameters are used to establish the two-parameter pulse model of the random signal. On the basis of this, the counting distributions of random signal for aerosol’s scattering pulse and background noise of photoelectric sensor are statistically analyzed by using the high-speed data acquisition card PCI-9812. The experimental results show that the counting distributions of amplitude and width subsets for the random pulse signals match well with the form of the lognormal distribution while using the natural number as the independent variable. Further more, the calculating results indicate that the amplitude and width of the distribution have nonlinear transform relation in the field of definition of them for pulsed signal. Namely, the two parameters' statistical distributions have the fractal character with non-integral dimension.
In this paper, nonfeedback chaos control of Chens system is realized with nonresonant parametric drive. A periodic signal whose frequency is far higher than the systems mean frequency is used as the input. And the system variables of the controlled system are decomposed into slowly varying variables which change according to the systems mean frequency and fast varying variables which change according to the frequency of periodic signal. Then, by averaging method, a slowly varying dynamics is obtained. According to the dynamical characteristics of the slowly varying dynamics, the available control parameter range is obtained. Numerical simulation results show that this method can lead the controlled system to the target state rapidly, even when the control signal is disturbed by noise in certain SNR ranges, so the proposed method is feasible.
Active radial basis function sliding mode controller for unified chaotic system with disturbance and uncertainties
2011, 60 (1): 010510. doi: 10.7498/aps.60.010510
An adaptive active radial basis function (RBF) sliding mode controller is designed to control a unified chaotic system with parametric uncertainties under external disturbance. The controlled system is divided into a controllable subsystem and a free subsystem. Based on the controllable canonical form of controllable sub-systems state errors at the target points, a sliding surface is defined as the only input to the RBF controller. The weight of the controller is tuned on-line based on the sliding mode reaching law. The simulation results show that this method is applicable and effective, and the robustness to parametric uncertainties and external disturbance is provided. And the chattering of conventional sliding controls doesn’t occur.
2011, 60 (1): 010511. doi: 10.7498/aps.60.010511
Chaos and chaos control received extensive attention. The fuzzy controller is used to control chaotic systems in this paper. The accuracy of fuzzy controller is not high and there is contradiction between the number of control rules and accuracy. Accordingly a variable universe fuzzy controller based on ant colony optimization algorithm is proposed. By analyzing the two kinds of contraction-expansion factors, one of them was found unable to satisfy the general contraction-expansion factor condition. A method for optimizing the contraction-expansion factors intelligently via ant colony optimization algorithm is proposed. A variable universe fuzzy controller based on ant colony optimization algorithm is constituted and used to control the Duffing chaotic system. Simulation results show that the control method is superior to the others both in convergence speed and steady-state performance.
2011, 60 (1): 010512. doi: 10.7498/aps.60.010512
A kind of fast generalized predictive control algorithm without static error for Hénon chaotic system is proposed. Firstly, the chaotic system is identified by improved recursive least squares parameter of time-varying forget factor. Then the softness factor is adjusted on line through combining MP neural network with BP algorithm, thus the fast tracking without static error of reference signa1 is realized by introducing the feedforward gain matrix and softening coefficient matrix into regular performance index function of generalized predictive control. The algorithm avoids the matrix inversion computation and has strong ability of tracking the reference signal. The simulated results show the effectiveness of this algorithm.
2011, 60 (1): 010513. doi: 10.7498/aps.60.010513
The existence of heteoclinic loop which connects the saddle focus equilibrium points is analyzed for a three-dimensional differential system based on heteoclinic orbit Shilnikov method, which proves the system possesses "horseshoe" chaos. Then the system bifurcation, Lyapunov exponent, Poincare mapping are studied by numerical analysis. In addition, adaptive backstepping design is used to control this system with three unknown key parameters, and an algorithm of this controller is presented. Finally, we make some numerical simulations of the system in order to verify the analytic results.
Time-delayed generalized projective synchronization of piecewise chaotic system with unknown parameters
2011, 60 (1): 010514. doi: 10.7498/aps.60.010514
The time-delayed generalized projective synchronization problem for a class of piecewise modified Lorenz-Stenflo chaotic system with unknown parameters is discussed. The adaptive nonlinear feedback controller and the parameter update rules are designed based on the Lyapunov stability theory, and the feedback gain can be adjusted adaptively according to the error values and the states. The method can make all full states asymptotically generalized projected synchronization and identify the real-time drive system and the time-delayed response system’s unknown parameters. Results of simulation verified the realistic feasibility and effectiveness of the proposed method to the time-delayed generalized projective synchronization of the piecewise chaotic system.
2011, 60 (1): 010515. doi: 10.7498/aps.60.010515
It was investigated whether the phenomenon of "order+order=chaos" exists for chaotic continuous systems. It was shown that the bidirectional coupling of two ordered continuous dynamics can originate a chaotic dynamics via synchronization. We provide an explicit example of "order+order=chaos" by taking the Lorenz and Rssler systems in their periodic dynamics.
Electrorotation manipulation of microparticles induced by torque and electroosmotic slip in microsystem
2011, 60 (1): 010701. doi: 10.7498/aps.60.010701
Electrorotation is an effective technique to characterize the electrical properties of dispersed particles. For the low Reynolds number microsystem, the mechanism of the electrorotation of microparticles induced by torque was analyzed based on the Maxwell-Wagner polarization. Characteristic frequency corresponding to the peak value of the electrorotation speed was deduced and the effect of the relaxation time on the particles' electrorotation direction was analyzed by the simulation of the electrorotation speed induced by the torque. The mechanism of the electrorotation of the microparticles induced by electroosmotic slip was qualitative analyzed based on the double layer and the idea about the gold surface being favorable to the electrorotation was proposed. Experiments on the electrorotation of the polystyrene with the carboxy surface and gold modified surface were performed, respectively. The results show that, the direction of the electrorotation of polystyrene spheres with carboxy surface is opposite to the electric field and, the corresponding frequency is higher with the torque playing the leading role. On the other hand, direction of the rotation of polystyrene spheres with the gold surface is homodromous with the electric field and the corresponding frequency is lower with the electroosmotic slip playing the leading rose.
In this paper, a new scheme, which is more precise in comparison with the previous ones in dealing with diffusivity factor is presented. The new scheme and the previous ones are applied to a radiative transfer model to calculate the atmospheric heating rate. The results show that the new scheme is generally better than previous ones, especially in the upper atmosphere al a height of more than 45 km.
2011, 60 (1): 012101. doi: 10.7498/aps.60.012101
The structure of water molecules encapsulated in single-walled carbon nanotubes (SWCNTs) was studied using a self-consistent charge density functional tight binding method with dispersion correction. The most interesting and important feature observed is the diameter shrinkage of SWCNTs when water chains are confined inside them. The diameter shrinking of SWCNTs may be due to the van der Waals and H-π interaction between water chains and SWCNTs. The binding energy decreases with the increase of the nanotube radius. But when the radius is increased to 6.78 ?, the binding energy is a little increased, and the water chain has changed as a "book-like" structure, which suggests that the weak hydrogen bonding in the isolated water chains is larger than the interaction between water chains and the SWCNTs.
2011, 60 (1): 012501. doi: 10.7498/aps.60.012501
In the present paper, the effective mass and energy of kaon in dense and hot nuclear matter is studied. Our special attention is paid to the comparison of various definitions of quasi-particle model of kaons used in transport theories. The effective mass of kaon defined in popular mean field theory increases with increasing of the density of nuclear matter, while the quantity used in covariant kaon dynamics decreases with the density increasing. The properties of mean field acting on kaon by hot and dense nuclear matter depends not only on the form of quasiparticle model of kaons, but on the motion of nucleons around it.
2011, 60 (1): 012901. doi: 10.7498/aps.60.012901
Neutron radiation was specially correlated with the type and the power of the radio frequency (RF) heating for deuterium plasma on HT-7 tokamak. We hare researched the production mechanism of the fast neutron under different RF heating conditions by the fast time-resolved neutron flux measurement system make up of BF3 and 3He proportional counters. Lower power of LHW heating was apt to bring abont runaway discharge and produce a mass of photoneutrons. The rate of fusion neutron and the total neutron yield will rapidly increase with the ion cyclotron resonance heating at the special frequencies of (27 MHz and 24 MHz).
ATOMIC AND MOLECULAR PHYSICS
Theoretical calculation of the vib-rotational interaction potential and the partial wave cross sections for He-H2(D2, T2) system
2011, 60 (1): 013101. doi: 10.7498/aps.60.013101
The interaction potential surfaces of He-H2(D2, T2)have been calculated by employing supermolecule method and the single and double excitation coupled-cluster with a noniterative perturbation treatment of triple excitation CCSD(T) approach using a large basis set containing the atomic centre Gaussian function and the 3s3p2d1f key function when the key-lengths of H2 was different. The vib-rotational interaction potentials of He-H2(D2, T2)system were fitted using the Tang-Toennies potential function and nonlinear least square method in a center of mass coordinate system. The partial wave cross sections at the energies of 60,90 and 120 meV have been calculated by using the quantum close-coupling method. On the basis of the above results, the change rules of the partial wave cross sections with change of quantum number have been obtained. Furthermore, corresponding connection and scattering characteristics of partial wave cross sections and scattering parameter were discussed in combination with classical collision theory.
2011, 60 (1): 013201. doi: 10.7498/aps.60.013201
Cerium-doped yttrium aluminium garnet (Y3Al5O12, YAG) samples were synthesized by the conventional solid state reaction method. The structure, photoluminescence and thermoluminescence properties were studied. The prepared samples are identified as pure garnet structure by the XRD results. The doping of a small amount of cerium ions has no influence on the structure of the host. Fluorescence spectra show that in the process of the preparation of Y2.95Al5O12 ∶Ce4+0.05 there is self reduction of Ce4+ when calcined in air, Which makes Y2.95Al5O12 ∶Ce4+0.05 emit yellow light peaking at 531 nm when excited by blue light, because a part of Ce4+ have been reduced into Ce3+. Y2.95Al5O12 ∶Ce3+0.05 prepared in weak reducing atmosphere has long yellow afterglow lasting for 35 minutes after it is excited by ultraviolet light. Thermoluminescence measurements show that YAG samples doped with Ce3+ can emit light at higher temperature. There are two obvious thermoluminescence peaks located at 112 ℃ and 256 ℃ in the thermoluminescence curve of Y2.95Al5O12 ∶Ce3+0.05 prepared in weak reducing atmosphore while there is only one located at 128 ℃ in the thermoluminescence curve of Y2.95Al5O12 ∶Ce4+0.05 prepared in air. A conclusion that the thermoluminescence of YAG ∶Ce3+ originates mainly from the Ce3+ trapped by defect energy level can be made out by comparing the cases of doped samples and the un-doped ones.
2011, 60 (1): 013401. doi: 10.7498/aps.60.013401
Shell model potential is widely applied to molecular dynamics simulations of ionic crystal, and the parameters of shell model potential function are crucial to the simulation veracity. The parameters of shell model of multi-oxide are numerous, and the optimization is a challenging task. In this paper, the sensitivity analysis is applied to find the key parameters which affect structure and properties mostly in all the shell model potential parameters of BaTiO3. Whereafter, the genetic algorithm is applied to optimize the key parameters, and the insignificant parameters are kept constant in optimization. The results show that the structures, physical properties and phase transition of BaTiO3 simulated by the optimized potential agree well with the experimental data.
Structural, electronic, and optical properties of Li-n-1, Lin and Li+ n+1(n=20, 40) clusters by first-principles calculations
2011, 60 (1): 013601. doi: 10.7498/aps.60.013601
The lowest-energy structures of Li-n-1, Lin and Li+n+1 clusters (n=20, 40) were determined from first-principles simulated annealing followed by geometry optimization within the density functional theory. The growth mechanism of Lin clusters is based on nested multiple polyhedron. Other atoms form pentagonal pyramid centered on the core polyhedron. From our first-principles calculations, the molecular orbital levels can be divided into several groups, which are in good agreement with the electron shells described by structureless jellium model. With the same amount of valence electrons, the number of ions and charge states in the Li clusters have only little effect on the electronic structures. Li-19, Li20, Li+21 and Li-39, Li40, Li+41 exhibit similar energy level distributions, respectively, indicating that the momentum order is the dominating factor for these clusters. The optical absorption spectra of Li-n-1, Lin and Li+n+1 (n=20, 40) clusters from time-dependent density functional theory calculations show giant resonance phenomenon and the simulated resonance peaks agree with experimental values. With same amount of valence electrons, the polarizability decreases with the number of ions and the optical resonance peaks blueshift as the ionic number increases.
2011, 60 (1): 013602. doi: 10.7498/aps.60.013602
In this paper, Path-integral Monte Carlo calculations have been performed to study structure and superfluid behavior of para-H2 clusters(number of molecules N≤40).Energy difference and superfluid fractions at T=0.4 K and 1.6 K were compared to explore quantum melting of para-H2 clusters. We discussed the interplay between quantum localization and quantum melting of para-H2 clusters, and the differences between quantum localization and superfluidity of para-H2 and ortho-D2 clusters at T = 0.4 K.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2011, 60 (1): 014101. doi: 10.7498/aps.60.014101
Perfect absorbing metamaterial based on model of metallic dendritic cell is fabricated. A S-wave band microstrip antenna with perfect absorbing metamaterial substrate is proposed. The results show that compared to the conventional microstrip antenna, the performance of the novel microstrip antenna with perfect absorbing metamaterial substrate has improved remarkably. The direction of the antenna is enhanced, the gain is improved by 1.8dB and its efficiency is increased by 51%. It is proved that the performance of the microstrip antenna is improved by using perfect absorbing metamaterial as its substrate.
Study on the dispersion relations of a relativistic annular electron beam guided by a finite axial magnetic field
2011, 60 (1): 014102. doi: 10.7498/aps.60.014102
The relativistic annular electron beam guided by a finite axial magnetic field is studied in this paper, in which the electron beam is considered as a special media. Making use of the constitutive transformation and the Lorentz transformation in the four-dimensional space, the permittivity tensor of the stationary magnetized plasma, the permittivity tensor, the permeability tensor and the chiral tensor of the electron beam in the rest (laboratory) frame are acquired. And the boundary conditions, including the surface current density due to the ripple of the beam, have been obtained. As an example of the applications of this approach, the dispersion relations of a relativistic annular electron beam guided by a finite axial magnetic field in a waveguide has been studied. The results of numerical calculation show that the present approach is more accurate and can provide clearer mode information for the electron beam. In addition, the results also show the axial magnetic field can affect the dispersion curves of space charge wave via the surface current density of an electron beam. Thus this approach can be exploited in a number of electron beam-wave interaction systems, including some kinds of free electron devices, plasma filled Cherenkov radiated free electron lasers and masers.
2011, 60 (1): 014103. doi: 10.7498/aps.60.014103
ZnS is one of the excellent materials that are used as long wave window in infrared, but the reflection of the surface is high. In order to reduce the reflection of the ZnS surface, we designed the sub-wavelength antireflective structure on ZnS by coupled-wave theory. The parameters of the sub-wavelength antireflective structure were optimiged and the two-dimensional sub-wavelength antireflective structure on ZnS was fabricated by reactive ion etching technique. The results show that the transmittance of etched ZnS is significantly better than that of bare ZnS at wavelengths of 8—12 μm. This is a new antireflection method using ZnS.
2011, 60 (1): 014104. doi: 10.7498/aps.60.014104
The effective radius of photonic-band-gap cavity (PBGC) is defined, the validity of using it to treat PBGC as a mode selective cylindrical metal cavity is demonstrated, the guiding role of it in the design of PBGC is revealed, and a self-consistent nonlinear theory is established for gyrotron oscillator with PBGC (PBG gyrotron) based on it. The results of theoretical analysis and numerical calculation show that the azimuthal polarized form (traveling wave or standing wave) of RF field has an obvious effect on the beam-wave interacting process and the device operating at second harmonic can achieve higher electron efficiency than that working at fundamental wave under TE-32 mode, which means PBG gyrotron is capable of operating at both high order electromagnetic mode and high order electronic cyclotron harmonic effectively owing to the excellent mode selective ability of PBGC. This gives a new clue to the research of gyrotron oscillator.
2011, 60 (1): 014201. doi: 10.7498/aps.60.014201
We numerically investigated four-wave mixing (FWM) and supercontinuum generation in photonic crystal fibers (PCFs) in the long pump pulse scheme for the first time. We showed that simply based on phase-matching condition and energy conservation with quasi-continuous-wave approximation, one can theoretically determine the FWM signal and idler wavelengths with pump in the normal-dispersion regime, and the two symmetrical modulation instability sidebands with pump in the anomalous-dispersion regime. Using adaptive split-step Fourier method, we quantitatively simulated FWM and supercontinuum generation in PCFs with different dispersion profiles when pumping with a 1064 nm sub-nanosecond laser. Our simulation results agree with the experimental results very well.
2011, 60 (1): 014202. doi: 10.7498/aps.60.014202
A new type of terahertz photonic crystal filter is presented, which includes the waveguide parts realized by line defects, and the frequency selection parts realized by micro cavities. The band gap property was investigated by using plane wave method (PWM), and then the transmission characteristic of terahertz in this kind of filter was studied by means of the finite difference time domain method (FDTD) simulation. The results show that, the filter can achieve high coupling efficiency filtering of single-channel and single-frequency, by changing the point defects structure and increasing the radius of certain dielectric cylinder. High efficiency THz-band photonic crystal filter was designed in this thesis.
The dependence of radiation characteristics of random laser on the size and arrangement of crystal grains in PCs
2011, 60 (1): 014203. doi: 10.7498/aps.60.014203
The modulation on radiation characteristics of random laser caused by photonic crystals(PCs) was studied, and its dependence on the size and arrangement of the crystal grains was analyzed. For a random medium, if it is covered by different photonic crystals on its upper and lower surfaces respectively, its output characteristics should be different. The results showed that the grain size of the PCs has a great effect on the radiation characteristics of the system. The PC with a suitable grain size plays a better role in trapping the energy in the system and it can modulate the laser modes effectively. It leads the light to oscillate back and forth, enhancing the interaction between the random gain medium and the light to achieve a greater amplification, and conseguently reducins the lasing threshold. It also controls the spontaneous emission and leads it to the target frequency in the emission spectra. However, if crystal grain size daeznot match the structure of random gain medium, the laser modes could not be modulated as we wish and the energy of the light field could not be localized effectively in the system, thus the laser system has a higher lasing threshold. The arrangement of crystal grains should affect the output characteristics also. In short, there exists an optimum PC/ random medium combination for lasing, for which the lasing threshold reaches a minimum.
2011, 60 (1): 014204. doi: 10.7498/aps.60.014204
An analysis of the propagation of Laguerre-Gaussian beam in fluctuation turbulent atmosphere is performed. Under the Rytov approximation, the integral expression of the spiral spectrum of the beam at the receiver aperture is obtained. It is found that the atmospheric turbulence will induce the spread of the spiral spectrum. With increasing topological charge, propagation distance, refractive index structure constant and radius of receiver aperture, the spectrum spread becomes more serious. It is also shown that the dimensionless variance describing the degree of the spread is a quadratic function of the refractive index structure constant and the radius of receiver aperture respectively, while it is an 11th order function of the topological charge and a 6th order function of the propagation distance. The analytical expression of the spiral spectrum is derived by taking account of the simulation results that both radial index and waist radius have little effect on the spiral spectrum.
Study on intensity distribution inside the frequency conversion crystals for continuous phase plate front-located in inertialconfinement fusion driver
2011, 60 (1): 014205. doi: 10.7498/aps.60.014205
This paper studies the intensity distribution inside the frequency conversion crystals when the continuous phase plate (CPP) is placed in 1ω light of final optics assembly for inertial confinement fusion (ICF) driver. Our study shows that the modulation of 1ω light caused by CPP makes the frequency conversion efficiency and the uniformity of intensity field inside the frequency conversion crystals decrease. It leads to the possibility of laser induced damage for frequency conversion crystals to increase. What worth paying special attention to is: the modulation and maximum intensity in the vicinity of entrance and exit surface of frequency conversion crystal is much higher than in other areas, so the possibility of laser induced damage is also relatively greater there. However, if the intensity of 1ω light before the frequency conversion system becomes even greater, for the normal running of final optics assembly the modulation and maximum intensity inside the frequency conversion crystals should be confined within the permitted range.
Polarization characteristics of the wave reflection at the interface of vacuum and Faraday chiral medium
2011, 60 (1): 014206. doi: 10.7498/aps.60.014206
This paper rigorously derives the formulas of reflection coefficients originating from Maxwell’s equations. The relationship between the polarization characteristics of the reflected wave and the constitutive parameters of the Faraday chiral medium is analyzed for all polarization states. Special polarization cases in the research are calculated, and the results are in good agreement with theoretical expectations.
First-principles calculations of electronic structure, optical and elastic properties of LiGaX2(X=S, Se, Te)
2011, 60 (1): 014207. doi: 10.7498/aps.60.014207
The density of states, electronic structure, optical and elastic properties of LiGaX2 (X=S, Se, Te) are investigated by the first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The results show that the band gaps of LiGaX2 (X=S, Se, Te) are 4.146 eV, 3.301 eV and 2.306 eV, respectively. It can be confirmed that the valence bands are mainly composed of X-np or Ga-4p states. The complex dielectric functions, reflectivity, index of refraction and elastic property are precisely calculated by band structure and density of states. The obtained results are in agreement with the available experimental data.
2011, 60 (1): 014208. doi: 10.7498/aps.60.014208
An experimental setup was built to detect orbital angular momentum (OAM) states of light beams. The helical beams with different OAM states were generated by using a spatial light modulator. A Mach-Zehnder (M-Z) interferometer was used to detect helical beams with odd or even OAM number. Sorting of coaxial helical beams was also experimentally realized.
2011, 60 (1): 014209. doi: 10.7498/aps.60.014209
Based on asymmetric one-dimensional photonic crystal structure,a dual-wavelength vertical-cavity surface-emitting laser (VCSEL) with modified standing wave field distribution has been constructed. The defect layer is Al0.8Ga0.2As with 5λ/4 thickness. Specifically, the dual-wavelength output spectrum of the VCSEL has low absorption loss, easy wavelength adjustment and same output direction. In addition, the two wavelengths and their spacing could be tuned by changing the refractive index contrast of the asymmetric PC structure and the thickness of defect layer. Such dual-VCSEL structure can be applied in optical bistable switches, amplifiers, modulators and detectors, etc..
2011, 60 (1): 014210. doi: 10.7498/aps.60.014210
In a double optical feedback semiconductor laser chaotic system, by fixing the feedback time and feedback strength of the one mirror (named as fixed cavity M1), the influences of the feedback time and feedback strength of the other mirror (named as tunable cavity M2) on the time delay feedback signatures of the chaotic system have been investigated experimentally. The results show that, for the case of the two cavities with identical feedback strengths, time delay feedback signatures of chaotic output can be suppressed efficiently when the cavity length of M2 is approximately equal (but can not exactly equal) to the cavity length of M1 (or half of the cavity length of M1). Fixing the length of M2 to approximately equal to the cavity length of M1 (or half of the cavity length of M1), the time delay feedback signature suppression can be further improved through adjusting the feedback strength of M2 carefully. Therefore, adopting a double optical feedback semiconductor laser chaotic system can make the system behave with higher security due to the efficient hiding of delay feedback parameter of the system.
Comparative study on the spectroscopic and laser propertiesof mixed vanadates Ybt:Y x Gd1-t-x VO4with different compositions
2011, 60 (1): 014211. doi: 10.7498/aps.60.014211
The room-temperature polarized absorption and emission spectra of Yb doped mixed vanadates Yb0.005:Y0.298Gd0.697VO4, Yb0.007:Y0.407Gd0.586VO4, and Yb0.009:Y0.575Gd0.416VO4 have been studied. The results show that the strongest absorption and emission, occurring at wavelength of 985 nm, correspond to the π polarization, depending on the composition the maximum absorption cross section ranges from 4.8 to 8.5×10-20 cm2, with bandwidths of 9.5—9.9 nm, whereas the maximum stimulated emission cross section varies in the range of 5.8—10.3×10-20 cm2. Continuous-wave laser operation has been realized at room temperature with the mixed crystals through longitudinal pumping with a diode laser. It was found that the laser oscillation behavior differs significantly from one mixed crystal to another:in the case of T=2% (T is the output coupling of the resonator), the coexistence and switching of σ, π polarization states occur on reducing the pump power in the laser oscillation of Yb0.005:Y0.298Gd0.697VO4 and Yb0.009:Y0.575Gd0.416VO4, while the laser oscillation of Yb0.007:Y0.407Gd0.586VO4 is capable of maintaining its π polarization state. In the case of T=5%, however, the laser oscillation generated with Yb0.009:Y0.575Gd0.416VO4 is purely σ-polarized, whereas the laser behavior of Yb0.005:Y0.298Gd0.697VO4 is similar to that exhibited in the case of T=2%.
Research on thermal contact conductance between crystal rod and heat sink in LD end-pumped solid-state laser
2011, 60 (1): 014212. doi: 10.7498/aps.60.014212
In LD end-pumped solid-state laser, the crystal rod is held and cooled by the metal heat sink. The force applied to the side surface of the crystal is non-axisymmetric. Under such circumstances, three kinds of thermal contact conductance (TCC) models are established, including not using thermal interface material, using thermal interface material with its thickness equal to the average thickness of the gaps and using thermal interface material with its thickness much greater than the thickness of the gaps. Regarding to the first two models, the influences of the assembly force and the equivalent root-mean-square (RMS) roughness on thermal contact conductance are discussed based on the Truncated-Gaussian model and the plastic-deformation model. The contact heat dissipation model of the crystal rod and the heat sink is established. For the Gaussian heat consumption, the spatial distributions of temperature inside the crystal with and without thermal interface material are obtained by the finite element method. The results show that without thermal interface material, the thermal contact conductance between the crystal rod and the heat sink changes significantly in the circumferential direction, which reaches a maximum on the bottom of the heat sink groove and a minimum on the contact area of the heat sink couple. With the assembly force increasing and the equivalent root-mean-square roughness decreasing, the thermal contact conductance gets larger and more nonuniform, and the temperature of the whole crystal rod reduces. When the indium foil is used as thermal interface material, the thermal contact conductance gets larger and more uniform, the temperature of the whole crystal rod reduces as well and its distribution is axisymmetric.
2011, 60 (1): 014213. doi: 10.7498/aps.60.014213
A kind of narrow-linewidth fiber laser was developed. A segment of Er-doped fiber is connected after the active phase-shifted fiber grating. A distributed feedback (DFB) fiber laser is realized using a 980 nm laser for pump. The erbium ions in the Er-doped fiber are pumped from ground-state to excited state by the residual pump power, so the output power of the DFB fiber laser is amplified effectively, and the pump power is fully used. In this way, the power consumption and the cost are reduced greatly. Temperature-control techniquc is used to deal with the temperature-sensitivity of the DFB fiber laser. The high-frequency modulation is realized by using a piezo-electric actuator when the phase-shifted fiber grating is mounted on its surface. In our experiment, the highest modulation frequency, the output power and the linewidth of the fiber laser are 2 kHz, 15.6 dBm and 300 kHz, respectively.
2011, 60 (1): 014214. doi: 10.7498/aps.60.014214
We report the new theoretical analysis method to obtain net gain in silicon waveguide by stimulated Raman scattering, and the key parameters of the free carrier lifetime and the pump light intensity are analyzed. The free carrier lifetime threshold and pump light intensity threshold are deduced. The gain characteristics of silicon Raman amplifiers with different pumping schemes are investigated, and the results show that the gain can be significantly enhanced in the bidirectional pump scheme.
Method for determining the characteristic parameters of the turbulence based on the measurement of M2-factor
2011, 60 (1): 014215. doi: 10.7498/aps.60.014215
Based on the extended Huygens-Fresnel principle and theory for the turbulence, the analytical expression for the beam propagation factor (M2-factor) of partially coherent beams propagating in a turbulent atmosphere has been derived. The effects of the structure constant of the refractive index fluctuations C2n and the inner scale of the turbulence l0on the M 2 factor have been analyzed quantitatively. Consequently, a new method for determining the characteristic parameters of the turbulence based on the measurement of the M 2 factor by experiments has been proposed. The results show that the laser beams with better spatial coherence property are more sensitive to the effects of turbulence, so the fundamental Gaussian beams with fully coherence can be used as the source in the measurement, and the usual instruments for measuring the M 2-factor can be adopted as the experiment equipments. It is very simple and convenient to determine the characteristic parameters of the turbulence by applying the method proposed in this paper.
2011, 60 (1): 014216. doi: 10.7498/aps.60.014216
The analytical formula for the beam propagation factor ( M 2-factor) of cosh-Gaussian (ChG) array beams propagating through atmospheric turbulence is derived, and the influence of turbulence on the M 2-factor is studied by using the relative M 2-factor. It is shown that the M 2-factor is not a propagation invariant in turbulence, and the turbulence results in an increase of the M 2-factor. For the incoherent combination, the M 2-factor of ChG array beams increases with increasing propagation distance, beam parameter, relative beam separation distance and beam number. For the coherent combination, the M 2-factor of ChG array beams increases with oscillatory behavior as the beam parameter or the relative beam separation distance increases. For the coherent combination the M 2-factor is always smaller than that for the incoherent combination. However, for the incoherent combination the M 2-factor is always less sensitive to turbulence than that for the coherent combination. In particular, the influence of turbulence on the M 2-factor can be reduced by a suitable choice of the relative beam separation distance. With increasing beam number, the M 2-factor becomes more sensitive to turbulence for the coherent combination, while for the incoherent combination the M 2-factor becomes less sensitive to turbulence.
2011, 60 (1): 014217. doi: 10.7498/aps.60.014217
The quantum effect of light wave mode is studied under restriction condition of light wave in 1-D cylindrical anisotropic doped photonic crystal. The defect mode character of TE wave and TM wave are calculated by characteristic matrix method . New defect mode structure of 1-D cylindrical anisotropic doping photonic crystal was obtained. The defect mode frequency and transmission angle increases with increasing quantum number. The defect mode frequency of the same pattern decreases with increasing cylinder radius.
Design and fabrication of sub-wavelength metal wire-grid and its application to experimental study of polarimetric imaging
2011, 60 (1): 014218. doi: 10.7498/aps.60.014218
Metal wire-grid whose period is far less than the illuminating wavelength exhibits strong polarization selectivity within a large field of view over a wide wave length range. Thus it could be used as the polarization-controller in the polarimetric imaging system. For infrared polarimetric imaging system, an aluminum wire-grid on the CaF substrate with period of 200nm and depth of 100nm was designed based on effective medium theory. The calculation results demonstrate that the designed wire-grid has the extinction ratio larger than 35 dB within a field of view ±20° over both middle wave infrared (MWIR) (3—5 μm) and long wave infrared (LWIR) (8—12 μm). The aluminum wire-grid was fabricated by electron beam lithography, reactive ion etching and plasma stripping. A clear-cut polarimetric image was obtained when wire-grid was placed in front of a MWIR thermal infrared imager.
The new insight into the optical pulse propagation theory and minimum-distortion propagation based on thefractional Fourier transformation
2011, 60 (1): 014219. doi: 10.7498/aps.60.014219
The theoretical derivation of optical time-domain fractional Fourier transformation is achieved and implemented. Based on the understanding of fractional Fourier transformation, we propose a new method for analyzing the influence of combined effects of dispersion and self-phase modulation on the propagation of optical pulses. And the simulation results show that when the dispersion is dominant in the transmission, a fractional Fourier transformation with a negative order number will help reduce the broadening of optical pulses induced by the dispersion. On the other hand, when the self-phase modulation is dominant, a positive order fractional Fourier transmission can help eliminate the pulse splitting effect.
2011, 60 (1): 014220. doi: 10.7498/aps.60.014220
Based on the temperature-dependent complex dielectric constant of indium antimonide, an InSb-dielectric-InSb plasmonic waveguide structure with the grating was realized. At the frequency of 1 THz, a directional beam was obtained, and its radiation direction can be controlled by changing the temperature difference between the grating structures on each side. Finite difference time domain (FDTD) method was adopted to evaluate the relationship between the off-axis angle of the beam and the temperature difference. The tunable directional beaming can be attributed to the grating coupling of the TM surface modes in plasmonic waveguides.
Measurement of the group refractive index of bulk material using white-light spectral interferometry
2011, 60 (1): 014221. doi: 10.7498/aps.60.014221
It is a radical but pressing problem to measure the group refractive index of dispersive material both accurately and rapidly in optical engineering field. In this paper, a white-light spectral interferometric system employing a fiber-optic spectrometer is developed for solving this problem. The system takes advantage of the characteristic of fiber-optic spectrometer which can get all the interferometric information by a single shot image without any mechanical scanning. Compared with the traditional windowed Fourier transform, a wavelet transform algorithm is used to directly extract the group delay rather than the phase from the interferogram. Therefore, the new method can provide a simple and fast solution, while still maintaining high accuracy. Based on this white-light Michelson interferometric system, fused silica and BK7 glass samples are measured respectively and the results agree well with the theoretical values over a broad spectral range. At the end of this paper, different mirror positions are used to verify the repeatability of our method.
2011, 60 (1): 014401. doi: 10.7498/aps.60.014401
This paper reports the temperature relaxation process at melting iron/sapphire interface under shock compression, and interpretes the phenomenon basing on transformation kinetics and heat conduction equation. Analysis shows that if iron keeps melting, the history of interface temperature is affected by the melting speed. The interface temperature undergoes a slow cooling process when the melting speed of iron is finite, which is different from the result of previous researches. Simulation signal can be made accord ant with the experimental signal by adjusting some parameters. It was found that the melting temperature and melting speed of iron at high pressure can be dctermined by researching the relaxation process. So, this paper shows a new theoretical method and its experimental verification.
2011, 60 (1): 014501. doi: 10.7498/aps.60.014501
The structure transition from compression state to dilation state in both heavy-particle sections gives rise to the crossover of the energy decay in one-dimensional composite granular chain. And the structure transition closely relates to the change in state of motion of heavy grain at both interfaces. The analysis demonstrates that the change in state of motion gives rise to the great difference of reflectivity in both branches, which induces different rates of energy decay of light-particle section in both branches.
2011, 60 (1): 014502. doi: 10.7498/aps.60.014502
The congestion of pedestrian traffic occurs easily at the bottleneck. Barriers could impede pedestrian channel, but it can ensure the smooth flow of pedestrians. Quasi-sliding mode control will be introduced in LWR model.The control variable can be derived for simulation at the impact of barriers. Based on the three-lane macroscopic traffic flow model, we carry out simulation to verify our control methods.The results indicate that the maximum pedestrian flow can be maintained due to the threshold value of the quasi-sliding mode control variables as the threshold value corresponds to one of the maximum flows in the fundamental diagram. Optimization of control variables can improve efficiency of one-way pedestrian at bottleneck.
2011, 60 (1): 014701. doi: 10.7498/aps.60.014701
In order to study different flow patterns’ dynamic characteristics of gas-liquid two-phase flow, three time-frequency analysis methods are introduced to process the dynamic differential pressure signal of gas-liquid two-phase flow, such as the wavelet transform, Hilbert-Huang transform and adaptive optimal-kernel method. The results show that the main part of energy is transferred from frequency band 15—35 Hz to 0—8 Hz when the flow pattern changes from bubbly flow to slug flow and plug flow, and two spectrum peaks are observed at slug flow. The experimental results show that the time-frequency resolution of Hilbert-Huang transform and adaptive optimal-kernel is higher than that of wavelet transform. The extractions of ridge information based on adaptive optimal-kernel overcome the influence of fuzzy plane windowing effect, and enhance the readability of time-frequency plane information. The time-frequency analysis clearly shows the dynamic characteristics of different flow patterns, and describes the variation rules with time. It is helpful to further study the mechanism of gas-liquid two-phase flow.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2011, 60 (1): 015101. doi: 10.7498/aps.60.015101
The atmospheric pressure dc gliding arc plasma was investigated through its electrical and optical signals. The arc voltages of various gas discharges were compared. The arc voltage, current, power and resistance of a nitrogen gliding arc in one period were studied. Influences of gas type, gas flow rate and external resistor on the gliding arc fluctuation behaviour were studied using FFT spectrum analysis. Increased main oscillation frequency was observed as gas flow rate or external resistance value increased. Furthermore, major radical species in nitrogen, oxygen and air discharges were determined by means of optical emission spectroscopy. Additionally, the effect of external resistor on the relative intensity of radical emission and axial distribution of relative intensity at 337.1 nm (N2(C3Πu→B3Πg), Δv=0) were studied. Experimental results showed that radical emission relative intensity decreases with the increasing of external resistance value. The axial distribution of relative intensity exhibits the tendencies of increasing first and then decreasing. The radical emission relative intensity decreases dramatically out of the plasma area.
2011, 60 (1): 015201. doi: 10.7498/aps.60.015201
The two-dimensional numerical model used is based on solutions of fluid equations in the drift-diffusion approximation for the electron and ion transport coupled with Poisson’s equation for electric field to simulate microcavity discharge qualities. The computation results show the potential profile, electron density distribution, ion density distribution, and electron temperature spatial distribution at the argon pressure of 100 Torr. The potential contour shows that the radial component of the electric field becomes very important as the forming of the cathode sheath. The results indicate the peak electron density is 1020 m-3, and the electron temperature is on the order of several to tens of eV.
2011, 60 (1): 015202. doi: 10.7498/aps.60.015202
As a novel method to assemble and ignite thermonuclear fuel, shock ignition offers several significant advantages, including low ignition threshold, high gain, and good hydrodynamic stability. In this paper, the mechanism of shock ignition is analyzed theoretically and simulated numerically. First, using one-dimensional planer model, the principles of shock collision in shock ignition are analyzed. Then simulations are performed to study the mechanism of the shock ignition scheme. The simulation results are compared with the theoretically analysis, and the robustness of the ignition scheme in terms of shock launching time is studied.
2011, 60 (1): 015203. doi: 10.7498/aps.60.015203
The main results of investigation on K-shell X-ray production of double-shell neon gas puff Z-pinch, driven by Qiangguang-I facility (1.6 MA, 70 ns), are reported. The exit radii of the outer and inner shells are 1.5—1.4 cm and 0.75—0.6 cm, respectively. Both shells have a throat width of 0.32 mm, while the ratio of the throat radii is 2.8 ∶1, to which the mass ratio would be approximately equal for identical plenum pressures. K-shell yield and peak power up to 7 kJ and 0.28 TW, respectively, for a 20 ns full width at half maximum pulse have been obtained with about 120 ns implosions, the load mass per unit length of which are estimated to be 60—70 μg/cm. Time-resolved X-ray images show that RT instability during the implosion stage has been well suppressed, resulting in a final pinch diameter compressed to less than 2.5 mm. The final implosion velocity exceeds 25 cm/μs. K-shell yields and peak powers are largely reduced with longer implosion time. For shots with lower mass, i.e. 28—63 μg/cm, the electron temperature inferred from time-gated K-shell spectra should be greater than 500 eV, implying an overheated plasma column being formed in the stagnation stage. While for shots with load mass of 72—80 μg/cm, time resolved electron temperatures are in the range of 300—400 eV. The inferred ion densities of the K-shell emitting region are in the range of (3—9)×1019 cm-3, which have been used to calculate the mass fractions that contribute to K-shell radiation. Those shots with near 7 kJ yields also have maximum K-shell emitting load mass (about 46 μg/cm).
Analysis on the ionization of high power pulsed unbalanced magnetron sputtering powered by direct current
2011, 60 (1): 015204. doi: 10.7498/aps.60.015204
High Power impulse Unbalanced Magnetron Sputtering has been coupled to a direct current source (dc-HPPUMS or dc-HiPUMS). A coaxial coil and an attached hollow cathode were applied to control discharge properties and improve pulsed power density. A large extent breakdown was induced for avalanche discharge mechanism. The magnetic trap on sputtering target traps the secondary electrons excited by the avalanche and forms a drift current in magnetic trap. The peak pulse current density is higher than 100 A/cm2 with a pulse frequency less than 40 Hz. The space charge limited condition controls the discharge for plasma far away from equilibrium. The discharge theory was taken to describe the high ionization mechanism in dc-HPPUMS discharge. The parameters deduced from Child law agree with the experimental results.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2011, 60 (1): 016101. doi: 10.7498/aps.60.016101
The influence of the major compensating defects As antisites (AsGa) and Mn interstitials (MnI) in the Ga0.946Mn0.054As diluted magnetic semiconductor (DMS) were studied by X-ray absorption spectra (XAS). The experimental results show that the defects in Ga0.946Mn0.054As grown at lower temperature (TS=200℃) is mainly AsGa, but at TS>230℃ MnI is the major defects. On the other hand, a higher LT-annealing temperature (250℃) can remove MnI out of the Ga0.946Mn0.054As lattice, and the highest Curie temperature (TC=130 K) is reached. Moreover, it is indicated that the LT-annealing process can increase the number of MnGa atoms by reducing the concentration of AsGa defects and driving MnI defects to fill up the holes left by AsGa.
Small angle X-ray scattering study of the microstructure and interface characteristics of single crystal superalloys during creep process
2011, 60 (1): 016102. doi: 10.7498/aps.60.016102
The two-dimensional scattering patterns for micro-structural changes during creep observed by SAXS are different from that obtained by SANS technique. The changes in morphology and size characteristics of different regions of the secondary γ' precipitates have been demonstrated by the variation of SAXS scattering intensity. The results show that the secondary γ' precipitates have two types of feature sizes, which have similar trends of change during the creep process characterized by decreasing in the first and second stage and increasing in the final stage. As comparison shows, the larger γ' precipitates have more noticeable changes. The elements of the secondary γ' precipitates diffuse seriously in the second stage with the character of creep 15 h, the surfaces of γ' phase are blurred, and interfaces of two-phase become clear again in the final stage. Due to the increasing size or the reducing number of the secondary γ' phase, the total ares of interfaces between the secondary γ' precipitates and matrix phase then decreases.
2011, 60 (1): 016103. doi: 10.7498/aps.60.016103
Atomic structures of Zr48Cu45Al7 ternary and Zr50Cu50 binary metallic glasses were investigated by performing reverse Monte Carlo (RMC) simulation upon synchrotron radiation based X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) data. Bond shortening in Zr-Al and Cu-Al atomic pairs was detected in Zr48Cu45Al7, which is attributed to strong interactions between Al atoms and its neighbors. Subsequently, their atomic structure was further analyzed by Voronoi tessellation method, it was found that all kinds of Voronoi clusters have smaller volume in Zr48Cu45Al7 than their counterparts in Zr50Cu50. Accordingly it is suggested that atoms may be more densely packed in atomic structure of Zr48Cu45Al7 ternary than in corresponding Zr50Cu50 binary MG at cluster scale, which may be the structural origin of high glass-forming ability of CuZr-based bulk metallic glass prepared by Al addition.
Influence of grain size on the magnetic orientation growth of films prepared by vapor deposition in high magnetic field
2011, 60 (1): 016104. doi: 10.7498/aps.60.016104
The vacuum evaporation has been applied to prepare Zn and Bi films with different growth directions in order to investigate the orientation of films in magnetic fields. XRD results showed that magnetic orientation occurred in the Zn films with a smaller difference between magnetic susceptibilities of a-axis and c-axis compared with those of Bi in the magnetic field of 4T but the orientation did not take place in the Bi films prepared in a 5T magnetic field despite of a larger difference in magnetic susceptibilities. It was observed by SEM that the grain sizes in Zn and Bi films were markedly different. The relation between the grain size and the magnetic orientation was established in a magnetic field of 4T. The condition of orientation in films is that the magnetic energy should be 420 times larger than the thermal energy kT. The occurences of magnetic orientation growth in the films depends on the grain size of the film, the difference in magnetic susceptibility of the material and the intensity of the applied magnetic field, respectively.
The bistable state of a nematic liquid crystal cell with surface order-electricity polarization and flexoelectric polarization at saturation point
2011, 60 (1): 016105. doi: 10.7498/aps.60.016105
Using both numerical simulations and an analytical theory we study the influence of the surface order-electricity polarization and flexoelectric polarization on the bistable state of a non-xymmetric weak anchoring nematic liquid crystal cell at saturation point.The equilibrium equation and boundary condition of the director have been obtained when surface order-electricity polarization and flexoelectric polarization coexistence. By adopting a new state parameter, the physical effects caused by the two polarizations have been discussed from the energy point of view. The results show that the bistable state can be induced under certain condition and by changing the anchoring energy at saturation point. The condition for the bistable state existence is deduced and it accord well with the numerical results.
2011, 60 (1): 016106. doi: 10.7498/aps.60.016106
Distortion and friction of bundle of SWCNT(10,10) sandwiched between two hydrogen-terminated Si(1,1,0) surfaces are investigated by molecular dynamics simulation. After reaching the equilibrium state, a compressive force is applied to the carbon nanotubes until structural destruction appears on carbon nanotubes or substrates. Friction of the system is then investigated when the upper substrate slides along X direction under no load and high load conditions. Distortion of carbon nanotubes can be observed during loading process and no structural destruction occurs even under the pressure as high as 3.8GPa because of their flexibility. Bundles of SWCNT (10,10) roll randomly and slightly under no pressure condition, but exhibit slide-and-roll combined motion under 3.8GPa pressure. The results also show relatively low lateral forces in both cases. The low friction is attributed to the relatively weak Lennard-Jones interaction between substrate and carbon nanotubes with no hanging bond. Excellent performance is therefore expected when carbon nanotubes without defects are used as lubricant or addictives.
2011, 60 (1): 016107. doi: 10.7498/aps.60.016107
The shock front structure and the plastic deformation of nanocrystalline aluminum under shock loading are investigated by using molecular dynamics simulations. The simulation results show that: after the elastic wave was generated, the grain boundary sliding and deformation dominated the early plastic deformation mechanisms, then the partial dislocations were nucleated at the deformed grain boundaries and spread within the grains, finally the process of stacking faults, deformation twins and full dislocation formation in the grain dominated the latter stage of the plastic deformation. The structural characteristics after the shock front swept over is that the stacking faults and the deformation twins are left in grains, and the majority of the full dislocations are annihilated at the opposite grain boundaries. It is reported for the first time that the shock front structure reflects the time sequence of two different plastic deformation mechanisms in nanocrystalline aluminum.
2011, 60 (1): 016108. doi: 10.7498/aps.60.016108
In the High-power InGaN/GaN-based LED structures, p-AlGaN layer plays a role as electron blocking layer. In this paper, GaN/InGaN-based LED have been grown on sapphire by metal organic chemical vapor deposition (MOCVD), and the p-type doping mechanism and structural optimization of AlGaN layer were studied. The ways to change AlGaN components have been discussed. We found that the growth temperature, growth pressure and flow TMAl (mole ratio) have strong effect on the Al components through different mechanisms. In the AlGaN electron blocking layer, the Al composition is between 10%—30% and the electron could be well limited to the quantum well region, maintaining a high quality crystal material. The p-type doping efficiency of AlGaN layer is low, and there is a magnesium droop problem due to lack of hole injection. A new growth method is suggestece to solve the problem. Grown under optimal conditions, the p-type AlGaN inserted in a LED structure greatly improves the output optical power of LED device.
Study on temperature calibration and surface phase transition of GaAs crystal substrate in MBE growth by RHEED real-time monitoring
2011, 60 (1): 016109. doi: 10.7498/aps.60.016109
Using RHEED as a real-time monitoring tool, the MBE temperature measurement system was calibrated according to the relationship between GaAs (100) surface reconstruction phase and the substrate temperature, As4 beam equivalent pressure of the substrate. This approach can also be applied to other MBE systems. It provides an experimental basis of the growth of high-quality epitaxial thin films for studying of the surface roughness of InGaAs, the phase transformation process and the surface morphology.
Effect of the reactive pressure on the structure and optical properties of silver oxide films deposited by direct-current reactive magnetron sputtering
2011, 60 (1): 016110. doi: 10.7498/aps.60.016110
Using direct-current reactive magnetron sputtering technique, a series of silver oxide (AgxO) films were deposited at a substrate temperature of 250 ℃ by modifying the reactive pressure (RP). Effect of the RP on the film structure and optical properties was investigated by X-ray diffractometry, energy dispersive spectroscopy and spectrophotometry. An evolution of the phase structure from biphased (AgO+Ag2O) to single-phased (Ag2O), and then to biphased (Ag2O+AgO) occurred with the RP increasing from 0.5 to 3.5 Pa for the AgxO films. Single-phase Ag2O film, specially, was deposited at RP=2.5 Pa, which was capable of lowering the threshold of thermal decomposition temperature of the AgxO film. The film transmissivity in transparent region increased with the RP increasing, while the film reflectivity and absorptivity decreased with the RP increasing. This result is attributed to the evolution of the phase structure and the decrease of the film thickness. The absorption edge of the biphased (AgO+Ag2O) AgxO film was located near 2.75 eV, whereas the absorption edge of the single-phase (Ag2O) and Ag2O-dominated biphased (Ag2O+AgO) AgxO film was located near 2.5 eV.
Scalar phonon transport in helix nanobelts is studied by employing differential geometry method and formal scattering theory. Phonon transmission coefficients and thermal conductance are calculated. The numerical results reveal that curvature and torsion induce quantum interference between phonon modes, which makes the quantized stairs of the total transmission coefficient exhibit oscillation behavior which in turn suppresses the thermal conductance considerably.
2011, 60 (1): 016401. doi: 10.7498/aps.60.016401
A thorough analysis of the mechanism of vibrational force field on polymer processing was carried out to investigate the effect of vibration parameters on polymer viscoelasticity and plastic forming processing. The relationship between phase angle and lagging heat generation rate as well as the expression of polymer plasticizing rate under vibrational force field was obtained. To verify the theory, PET was adopted for example calculation and in expriments with dynamic capillary rheometer and mlti-dimentional vibration induced plastic forming equimpment. The result from calculation agrees well with that from experiment. Besides, it can be concluded that the plasticizing rate of PET increases at first and decreases afterwards with increasing vibration frequency. It reaches the peak at vibration frequency equivalent to the natural frequency of PET of about 15 Hz. The value remains at 22 g/min with the natural vibration frequency when the vibration amplitude is 6 MPa, being 1.75 fold that with vibration frequency of 10 Hz. Therefore, the plasticizing rate of polymer can be significantly improved by increasing the vibration amplitude. The exploration in this paper supplies reliable thoeretical reference for novel polymer low temperature moulding technique and equipments.
2011, 60 (1): 016601. doi: 10.7498/aps.60.016601
In the atomic scale, the surface energy anisotropy analysis of 38 surface planes of 10 fcc metals Cu, Ag, Au, Ni, Pd, Pt, Rh, Al, Ir and Pb have been simulated by using the elemental variables φ* and nWS and modified analytical embedded-atom method (MAEAM). The results show that the close-packed surface (111) of fcc metals which have the lowest surface energies will grow preferentially, the surface energies for all the other surface planes increase linearly with cosθ(hkl), where cosθ(hkl) are the angles between the surface planes (hkl) and (111), which is consistent with the experimental and the linear-muffin-tin-orbital atomic-sphere approximation (LMTO－ASA) results. A graphical approach which correctly explains the relation of the surface segregation energy and surface energy is employed. We conclude that the surface segregation takes place or not is mainly determined by the rule that an impurity (solute) with lower surface energy will segregate to the surface of the host (solution) with higher surface energy.
Influence of sputtering pressure on microstructure and mechanical properties of TiN/SiNx multilayer coatings
2011, 60 (1): 016801. doi: 10.7498/aps.60.016801
TiN/SiNx multilayer coatings were deposited at different deposition pressure by reactive magnetron sputtering. The microstructure and mechanical properties of the coatings were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation. The results showed that the layer structure became rough and the preferred orientation of TiN transferred from (200) to (111) plane with the increase of deposition pressure. Surface roughness of the coatings increased but the hardness and elastic modulus decreased with increasing deposition pressure. The variation of mechanical properties are attributed to the changes in layer structures and the densities of the coatings.
Influence of oxygen pressure on the lattice constants of Ba0.6Sr0.4TiO3 thin films and preparation of BaTiO3/Ba0.6Sr0.4TiO3 superlattices
2011, 60 (1): 016802. doi: 10.7498/aps.60.016802
Using pulsed laser deposition (PLD) technology, BaTiO3 (BT) and Ba0.6Sr0.4TiO3 (BST) single-layer films were successfully prepared through a series of optimization experiments. X-ray diffraction investigations indicated that BT and BST thin films were nearly (001)-epitaxially grown on LaAlO3 (001) substrates. And functional relation between the lattice constants of BST thin films and the oxygen pressure was close to Boltzmann function from 10-3 to 25 Pa. Then the high-quality BT/BST superlattices were also prepared under these optimal conditions. The surface topography measurement by atomic force microscopy (AFM) demonstrated that the root-mean-square (RMS) roughness of BT/BST superlattice was only 0.3048 nm. The surface smoothness has achieved the atomic scale. In addition, satellite peaks were clearly observed in the XRD spectrum. According to the position of satellite peaks that belong to (002) diffraction peak, the superperiod of superlattices was calculated and the deposition rates of BT and BST thin films were deduced. Finally, laser induced thermoelectric voltage (LITV) effect was measured for the first time in BT/BST superlattices grown on vicinal-cut single crystal substrates, which was not found in BT and BST single-layer films.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2011, 60 (1): 017101. doi: 10.7498/aps.60.017101
The geometrical structures,band structures,density of states(DOS) and optical properties of undoped and doped rare earth elements(Y,La) in ZnO have been calculated from the first principles of plane wave ultra-soft pseudo-potential method based on density functional theory. After doping,the stability of structures are enhanced and the band gap becomes wider. When doped with Y(La), the Fermi energy of the system goes into the conduction band,the system shows metallicity and transforms into degenerate semiconductor. Furthermore, the change of optical properties after doping have been analyzed.
2011, 60 (1): 017102. doi: 10.7498/aps.60.017102
Using the first principle based on the density-functional theory, we have studied the electronic structures and optical properties of zigzag graphene nanoribbon with different Stone-Wales defects. We take two kinds of models, namely that with and without spin polarization, into consideration. The results suggest that graphene nanoribbon with symmetrical Stone-Wales defect has the concavo-convex geometry structure in the defective region without considering spin polarization, both kinds of Stone-Wales defects give rise to the charge redistribution. The spin density of graphene nanoribbon with Stone-Wales defects is obviously affected by considering spin polarization, which leads to the changes of density of states for different kinds of spin. We have further investigated the optical properties of the graphenen nanoribbons; it was found that the peaks of absorption and reflectance have significent changes in the graphene nanoribbon with the presence of Stone-Wales defects, and red shift is observed when compared with the perfect graphene nanoribbon.
Effect of annealing treatment on the 386 nm and 388 nm emission peaks in unintentionally doped 4H-SiC epilayer
2011, 60 (1): 017103. doi: 10.7498/aps.60.017103
Under different annealing treatment conditions, the low temperature PL properties of unintentionally doped 4H-SiC epilayer have been studied by photoluminescence (PL) technique at 10 K. The results show that there are three emission peaks in the range from 370 nm to 400 nm and the maximum energy is about 3.26 eV, which is in accordance with the energy gaps (Eg) of 4H-SiC at room temperature. The 386 nm and 388 nm peaks (corresponding to ~3.21 eV and ~3.19 eV, respectively) are related with N impurity. When keeping annealing time at 30 min, the PL intensity of 386 nm and 388 nm peaks increases and then decreases with the annealing temperature increasing and reaches a maximum at 1573 K. The PL at 386 nm and 388nm change in quite the same manner with annealing time during isothermal annealing at temperature of 1573 K, whereas the difference is small. With the same annealing treatment, the low temperature PL results of 386 nm and 388 nm coincide with that of intrinsic defects in unintentionally doped 4H-SiC, which results from the interaction of infinitesimal disturbance potential energy between N impurity and native defects.
Thickness dependence of the interfacial interaction for the Fe/ZnO (0001) system studied by photoemission
2011, 60 (1): 017104. doi: 10.7498/aps.60.017104
Synchrotron radiation photoemission spectroscopy (SRPES) and conventional X-ray photoelectron spectroscopy (XPS) were used to study the Fe/ZnO(0001 ) interface formation at room temperature. The interaction extent of Fe overlayer during the ZnO substrate was carefully monitored during the increase of Fe coverage, the results showed obvious Fe2+ formation at the initial stage of Fe deposition. Based on the photoemission spectra (PES) changes observed during the deposition of Fe on ZnO up to 3 nm, three meaningful and critical thicknesses have been observed which may be related to the surface charge transport, chemical reaction, and magnetic property, respectively. The new finding may be helpful to the design of related devices based on Fe/ZnO interface.
2011, 60 (1): 017105. doi: 10.7498/aps.60.017105
A general form of Hamiltonian for vibronic Jahn-Teller systems is derived on the basis of adiabatic approximation and group theory. The electronic operators and active Jahn-Teller modes appearing in a vibronic system are also discussed. Further calculations of excited states in minima are carried out using unitary transformation method and energy minimization procedure. The results of energy splitting for an electronic triplet Jahn-Teller system are analyzed and compared with particular reference to tetrahedral and its related crystal systems. It is shown that the lift of electronic degeneracy can be quantitatively described by the decomposition of irreducible representations of related group and subgroups.
2011, 60 (1): 017201. doi: 10.7498/aps.60.017201
The Changes of resistivity with temperature of bulk nanocrystalline metal dysprosium samples with different grain sizes were studied in this paper. The value of the resistivity is a sum of the residual rsistivity ρres=ρ (0), magnetic scatter resistivity ρmag(T) and phonon scatter resistivity ρpho(T). The mean grain sizes are 10 nm, 30 nm, 100 nm and 1000 nm. It was experimentally found that the magnetic scatter resistivity ρmag(T) and phonon scatter resistivity ρpho(T) increase as temperature increases. The measured values of the resistivities of the four samples are in the range of (0.8—252)×10-8Ω ·m, representing metalloid features. Experiments also showed that the residual rsistivity ρ (0) of the sample with 10nm mean grain size is about 98.6×10-8Ω ·m, which is about one order of magnitude greater than those of the other three samples. This is an experimental example of the energy band narrowing and the appearance of electron localization with the increase of disorder degree.
Model of electron mobility in inversion layer of strained Si/Si1-xGex n type metal-oxide-semiconductor field-effect transistors
2011, 60 (1): 017202. doi: 10.7498/aps.60.017202
In order to describe the electron mobility enhancement in inversion layer in strained-Si on Si1-xGex n type metal-oxide-semiconductor field-effect transistors (nMOSFETs), a new physically-based electron mobility model is presented in the paper. This model can not only show the dependence of acoustic phonon-limited mobility and surface roughness-limited mobility on transverse electrical field normal to the semiconductor-insulator interface, but also explains the electron mobility enhancement mechanism due to scattering suppression caused by germanium (Ge) content. The expression of the new model is simple and can simulate the mobility for any Ge content. Numerical analysis results show that this model fits the reported experimental data very well. In addition, this model can be easily included in the device simulator ISE and gives good agreement with simulated results of device simulator with built-in model.
A supercontinuum in the plateau generated by asymmetric molecular gases exposed to a two-color field
2011, 60 (1): 017203. doi: 10.7498/aps.60.017203
The high order harmonic generation (HHG) from asymmetric molecular gas in two-color field has been investigated and a method for broadband supercontinuum generation in the plateau by asymmetric molecular gas exposed to multicycle laser pulse is proposed. The numerical simulation shows that the harmonics at the end of the plateau become continuous and form a supercontinuum with a bandwidth of about 80 eV, from which a 50 as pulse in the transform limited case can be generated, when asymmetric molecules are exposed to a multicycle two-color field, which is synthesized by a 10 fs/800 nm fundamental pulse and a 15 fs/1200 nm control pulse. After propagation through the molecular gas, most of the modulations in the supercontinuum are eliminated, and the supercontinuum becomes smoother, from which a 90 as isolated pulse can be produced.
Parametric properties of the electron spin relaxation due to spin-orbit interaction in InAs quantum dots
2011, 60 (1): 017204. doi: 10.7498/aps.60.017204
To deal with the Hamiltonian model in InAs QDs with a single electron, we’ve taken the SO interaction as a perturbation term, calculated the SO matrix elements under Fock-Darwin eigenfunction which are used for second order corrections on the energies and wave functions, and considered the influence of new energy levels on g factor and effective mass m*. The expression of phonon-assisted electron spin relaxation rate Γ in InAs QDs is deduced, which shows different dependences on confined potential frequency ω0, temperature T, vertical height z0 and magnetic field B. Among them, temperature for the electron spin relaxation plays a dominant role, followed by lateral confinement potential frequency, magnetic field and the vertical height, in order of importance. (1) Growth of ω0, which corresponds to the decrease of the effective transverse size d in InAs QDs, suppresses the increase of the rate Γ. (2) The temperature T affects the rate Γ evidently, which will reduce the inhibition of ω0 on Γ. With increase of the temperature from 1 K to 7 K, the spin inversion relaxation rate grows explosively from 103 s－1 to 108 s－1. (3) The rate Γ decreases with the growth of the vertical height z0 and have the order of magnitude 100－103 s-1 at T=1 K, whereas the influence of the temperature increase (at T=6 K) on the rate will gradually exceed that of the height growth. (4) At different frequencies ω0 all curves of the rate Γ versus magnetic field B have a peak that almost appears at the same field, which is attributed to the contribution of the Zeeman term H ^ Z exceeding that of H ^ SO since there is a considerable g factor in InAs material.
Study on the suppression mechanism of current collapse with field-plates in GaN high-electron mobility transistors
2011, 60 (1): 017205. doi: 10.7498/aps.60.017205
The physical mechanisms underlying current collapse effects in the passivated GaN high-electron mobility transistors(HEMTs), the gate field-plated GaN HEMTs and the gate-source field-plated GaN HEMTs are investigated in experiments and numerical device simulations. And the intrinsic relationships of the current collapse with the carrier concentration, the probability of traps ionization, and the electric field within the cap layer are established. Results show that the direction of the longitudinal electric field, as well as the intensity distribution of both the transverse and longitudinal electric fields within the cap layer, can be modulated effectively by the field-plates. The electric field intensity near the gate is reduced and that beneath the field-plates increased. Due to the effects of the field-plates on electric field, the transverse movement of electrons near the gate is reduced, and the longitudinal electron movement beneath the field-plates is increased. These affects the electron concentration distribution and the ionization probability of the traps in the cap layer, which makes field-plates effective for the reduction in the current collapse.
2011, 60 (1): 017301. doi: 10.7498/aps.60.017301
Transmission properties of finite curved slot arrays were investigated based on an extension of mutual admittance approach. One-dimensional curvature effects were analyzed, with the influence of column number and flare angle on magnetic current distribution, scattering patterns and frequency response curves. Results show that the curvature effect depends on the flare angle. When the flare angle is large (above 120°), strong curvature effect leads to violent fluctuation of magnetic current distribution, wide beamwidth and high side lobes, and considerable changes also occur in frequency-response characteristics, including resonant frequency, transmission bandwidth and transmission coefficient. When the flare angle is small enough, generally below 60°, only the magnetic current distributions of marginal elements would get influenced, consequently the scattering patterns and transmission characteristics are similar to those of finite planar arrays. The curvature effect may became very weak and be ignored on this condition.
2011, 60 (1): 017302. doi: 10.7498/aps.60.017302
Using first-principles density functional theory and non-equilibrium Green’s function method, we investigate the electronic transport properties of Na@C20H20 molecule. The calculational results show that the I-V curve exhibits good linear characteristic in the range of bias V, and shows obvious negative differential resistance (NDR) characteristics. The equilibrium conductance of Na@C20H20 molecule is 0.0101 G0. Comparing the results with those of Li@C20H20 molecule, we find that doping Na can improve both the electronic transport capacity and the chemistry stability of C20H20 molecule, which makes it more suitable as candidate of molecular device.
Collector junction depletion-layer width model of SiGeheterojunction bipolar transistor with intrinsic SiGe layer
2011, 60 (1): 017303. doi: 10.7498/aps.60.017303
By solving Poisson equation, models of voltage and electric field distribution are build respectively in collector junction depletion layer of SiGe HBT (heterojunction bipolar transistor) with intrinsic SiGe layer. On this basis, models of the collector junction depletion layer width and delay time are obtained. Applying MATLAB, the impact of physical and electrical parameters on SiGe HBT collector junction depletion layer width and depletion delay time are quantitatively analyzed. When base doping concentration and collector junction reverse bias are large, the depletion delay time is quite long. But, when base doping external diffusion depth and collector region doping are large, the depletion delay time is quite short.
Geometric structure and electronic transport property of single alkanemonothiol molecule junction: external force effect and terminal group effect
2011, 60 (1): 017304. doi: 10.7498/aps.60.017304
The hybrid density functional theory is used to study formation of the junction of alkanemonothiol molecules with different terminal groups. The relationship between geometric structures of the molecular junction and the external force is obtained. On the basis of the relationship, the electronic transport properties of the molecular junctions under different external forces are investigated using the elastic-scattering Green’s function method. The results show that the C11S molecular junction is broken when the distance of the two electrodes is larger than 2.1 nm. While for C11SOH and C10SCOOH molecular junctions, their critical distances are similarly 2.15 nm. Taking the same external force, we find that the C11S molecule has the largest conducting ability, and the C10SCOOH molecule has the smallest conducting ability. Furthermore, the conductance of the three molecular junctions is monotonically enhanced with the increase of the external force. The numerical results are consistent with the experimental findings qualitatively.
The two-band Ginzburg-Landau theory analysis of the surface critical field of the two-band superconductor Lu2Fe3Si5
2011, 60 (1): 017401. doi: 10.7498/aps.60.017401
Two-band Ginzburg-Landau (GL) theory is adopted to analyze the surface critical field Hc3 of Lu2Fe3Si5 . When the surface of a superconductor coincides with any of crystallographic planes and is parallel to the external magnetic field H, the ratio Hc3/Hc2 (where Hc2 is the upper critical field of Lu2Fe3Si5) is strongly dependent on temperature. When the surface of a superconductor coincides with the bc plane and is parallel to H, the ratio depends not only on temperature, but also on the angle between the c axis and H. However, the ratio is constant for single-band superconductors.
2011, 60 (1): 017501. doi: 10.7498/aps.60.017501
We prepared the magnetic nanoparticles of Fe3O4from thermal decomposition of the Fe oleates precursors synthesized by iron chlorides and sodium oleate,and the SiO2-coated Fe3O4nanoparticles by combining the reverse microemulsion and organic template methods. FTIR was adopted to investigate the surface of Fe oleate under different treatments,and the growth of Fe3O4 nanoparticles with different reactant concentrations of oleic acid and heating rates. The results indicated that the superficial oleic acid of the waxy solid Fe oleates after extraction from ethanol and acetone was partially removed,which impairs the formation of monodispersion Fe3O4 naoparticles. The effect of heating rate on the growth of nanoparticles was weak compared with that of the concentration of Fe oleates. When the concentration of oleic acid is 0.09 mol/L, a characteristic peak of Fe3O4 at 576 cm-1(assignable to the bending vibrations of Fe-O) is enhanced significantly. The XRD (X-ray diffraction) spectra,TEM (transmission electron microscopy) images and SQUID (superconducting quantum interference device) confirmed that the Fe3O4 nanoparticles are spinel cubic crystal and have a good monodispersity and super-paramagnetism. Whats more,the TEM of SiO2-coated Fe3O4 nanoparticles also confirmed that the Fe3O4 nanoparticles were well coated by mesoporous SiO2.
2011, 60 (1): 017502. doi: 10.7498/aps.60.017502
The macrospin model based on Landau-Lifshitz-Gilbert equation is used to study the current-induced magnetization dynamics in magnetic spin valves. We find that the DC spin-polarized current could either switch the magnetization of free layer or excite the steady-state precessional motion via the so-called spin-transfer torque effect. The AC current could drive the chaotic oscillations. The route to chaotic oscillation depending on the strength of current is demonstrated through a series of period doubling bifurcations.
2011, 60 (1): 017503. doi: 10.7498/aps.60.017503
Impurity effects on the stability of a charge-ordered antiferromagnetic state in La0.4Ca0.6MnO3 are investigated by Fe3+/Cr3+ doping on Mn-site. All the samples with different doping concentrations possess the same orthorhombic crystalline structure,and no evident variation in the structure can be seen. Our results reveal that the Fe3+/Cr3+ doping effects on the transport behavior are rather different, although both impurities have the same valance and are commonly antiferromagnetically coupled with other transition metal ions. We assign this remarkable different doping effects to the different electronic structure of the doping cations.
2011, 60 (1): 017504. doi: 10.7498/aps.60.017504
Amorphous Fe43Co43Hf7B6Cu1 alloy prepared by melt-spun technique were annealed at temperature 200 ℃, 300 ℃, 400 ℃ and 500 ℃ for 30 min. The structure and structural defects in annealed specimens were investigated by positron annihilation lifetime spectra, X-ray diffraction (XRD) and Mssbauer spectroscopy (MS), etc. . The results show that in the as-quenched amorphous alloy, more than 85% of the positrons are localized at vacancy-sized free volumes in the amorphous based phase, annihilation lifetime τ1=158.4 ps, and the other 11.9% of positrons are trapped by microvoids, with lifetime τ2=397 ps. After annealing at temperature 200 ℃, 300 ℃ and 400 ℃ for 30 min, the atomic short range diffusion will give rise to the migration and annihilation of vacancy-like defects. The major component τ1 will be reduced continuously. The value of τ1 will decrease to 149 ps at 400 ℃, their relative intensities I1 decreases and reaches 80.8%. Meanwhile the annihilation lifetime of positrons in the microvoids τ2 will change from 353 ps to 364 ps, their relative intensities I2 are increased to 18.0%. When annealed at temperature 500 ℃ for 30 min, new trapping centers of positrons are produced owing to the crystallization of amorphous phase, I2 increases drastically to 26.7%.
The effect of AlO and C elements addition on magnetic properties and frequency response of FeCo alloy film
2011, 60 (1): 017505. doi: 10.7498/aps.60.017505
FeCoAlOC thin films with various C contents were fabricated by magnetron sputtering. The effect of C and Al2O3 addition on magnetic properties and frequency response of FeCo alloy films was studied. The microstructure of FeCo alloy films changed from polycrystalline to nano-crystalline, and became amorphous eventually with the increasing of content of AlO and C. It was found that the soft magnetic properties of FeCo alloy film was improved and resistivity increased from 87 μΩ·cm to 900 μΩ·cm because of C, Al-O addition. Frequency characteristics were improved: the cut-off frequency increased up to 2. 9 GHz, the permeability at low-frequency reached 400.
Spin-polarized electron transport and magnetoresistance effect in symmetric parabolic-well magnetic tunneling junction
2011, 60 (1): 017506. doi: 10.7498/aps.60.017506
We investigated the spin-dependent transmission coefficient and tunneling magnetoresistance in symmetric parabolic-well with two ferromagnetic contacts (F/SPW/F). The quantum size effect and Rashba spin-orbit interaction are discussed simultaneously. The results indicate that the transmission coefficient and tunneling magnetoresistance are periodic function of the parabolic-well width. The oscillation frequencies of the transmission coefficient and tunneling magnetoresistance decrease with the increasing of the parabolic-well depth. The oscillation frequencies of the transmission coefficient and tunneling magnetoresistance increase with the increasing of the Rashba spin-orbit coupling strength. The amplitude and peak-to-valley ratio of the transmission coefficient and tunneling magnetoresistance are strongly dependent on the difference in orientations of the two magnetizations in the left and right ferromagnets.
2011, 60 (1): 017507. doi: 10.7498/aps.60.017507
Cobalt nanowires with c-axis perpendicular to the axial direction have been fabricated by the pulsed electrodeposition method. The hysterisis loops of the cobalt nanowire array show little anisotropy due to the competition between shape anisotropy and factors such as magnetocrystalline anisotropy and magnetostatic interaction. The permittivity and permeability dispersion spectra of the nanowire/paraffin composite were measured in the frequency range of 2—18 GHz. It was found that the imaginary part of the permittivity spectra shows a strong peak around 5 GHz and a weak peak around 10 GHz, which are contributed by the Debye relaxation and the conductivity of the nanowires. In the meantime, the imaginary part of the permeability spectra for the nanowire/paraffin composite samples exhibits a strong absorption peak at 6.1 GHz and two minor peaks above 10 GHz. The peak at 6.1 GHz is attributed to the natural resonance mechanism and the other two peaks are duc to eddy current effect. The permeability spectra attributed to natural resonance are fitted using the Landau–Lifshitz–Gilbert equation. Calculation based on the Kittel equation substantiates our fitting results. The electromagnetic wave reflection loss of the nanowire/paraffin composite sample is lower than -20 dB when the thickness of the nanowire/paraffin composite has been adjusted, suggesting that the cobalt nanowire composites can find application as a novel type of microwave absorbers.
Theoretical and experimental study on magnetoelectric effect in laminated composites of magnetostrictive and piezoelectric materials with finite input impedance
2011, 60 (1): 017508. doi: 10.7498/aps.60.017508
Combining the motion equation with the constitutive equations of the magnetostrictive and piezoelectric materials and considering the influence of the finite input impedance of the capacitance of coaxial cable and the measuring instrument on output voltage produced by magnetoelectric element, the theoretical formula of magnetoelectric voltage sensitivity was derived. A sandwich structureed magnetoelectric element consisting of one-dimensional terfenol-D thin bars and transversely polarized Pb(Zr1-xTix)O3 piezoelectric materials was developed. The property of the element was tested also. The theoretical results are in better agreement with the experimental after taking account of the finite input impedance. The theoretical results show that the magnetic sensitivity of the magnetoelectric element at lower excitation frequency and with finite input impedance is about 150 mV/Oe, while the magnetic sensitivity in open circuit situation is about 290 mV/Oe.
Dielectric relaxation of (Pb(1-3x/2)Lax)(Zr0.5Sn0.3Ti0.2)O3 antiferroelectric ceramics induced by lanthanum doping
2011, 60 (1): 017701. doi: 10.7498/aps.60.017701
The (Pb(1-3x/2)Lax)(Zr0.5Sn0.3Ti0.2)O3(PLZST, 0.00≤x≤0.18)antiferroelectric ceramics were prepared by traditional ceramic process. The effect of La modification on phase structures, phase transition, and electrical properties of PLZST ceramics were investigated by X-ray diffraction, P-E hysteresis loop and dielectric spectroscopy. With the increase of La content x,the samples at room temperature are rhombohedral ferroelectric phase (x≤0.0.04),tetragonal antiferroelectric phase(AFEt, 0.06x≤0.0.08, and cubic phase (PE' cx≥0.1), respectively. The dielectric spectroscopy shows that with the increase of La content x, AFE-PE phase transformation temperature decreases, and for samples with La content x exceeding 0.12, strong dielectric frequency dispersion is observed around dielectric ε' and tanδ peaks. The peak temperatures Tm corresponding to the maxim dielectric constant shifts to higher temperatures with the increase of frequency, indicating that PLZST antiferroelectric transform to typical relaxors. The curves of dielectrics as functions of temperatures in the PLZST systems are fitted by a modified Curie–Weiss law proposed by Santos.
2011, 60 (1): 017801. doi: 10.7498/aps.60.017801
The transmission characteristics of a 2D photonic crystal waveguide with point defects were investigated by the plane wave expansion method (PWM) and finite difference time domain (FDTD) method. It was found that by introducing two resonant cavities (point defects) in the photonic crystal waveguide, light waves near the resonance frequencies can be totally reflected back to the waveguide. Since the resonance frequencies change with the variation of the refractive index of point defects, this phenomenon may be used to design a tunable optical switch.
2011, 60 (1): 017802. doi: 10.7498/aps.60.017802
In this paper,taking one-magnetic-center NiO and two-magnetic-center nanostructures composed of Co and Ni as examples,we review our recent works in this field.To theoretically achieve ultrafast spin flip and transfer in magnetic nanostructures,an ultrafast spin dynamics mechanism,namely Λ process,was proposed.To properly simulate the laser-matter interaction,the accurate intragap d-states were predicted firstly through quantum chemistry calculations; then the spin localizations on magnetic atoms were analyzed considering external magnetic field and spin-orbit coupling; at last,laser pulse term was turned on to study the time history of the spin switching scenario via the Λ process.It was shown that spin flip and transfer can be achieved in a subpicosecond regime with linearly polarized light.In order to further realize checking and monitoring of the spin manipulations in magnetic molecules,a CO molecule was attached to one magnetic center to serve as an infrared marker.The calculated spin-state-dependent C-O stretching frequencies indicate that spin manipulations can be indirectly monitored through infrared spectrum experiments.
2011, 60 (1): 017803. doi: 10.7498/aps.60.017803
The ambipolar diffusion coefficient of (110) GaAs/AlGaAs multiple quantum wells was measured by the transient spin grating technique.The ambipolar diffusion coefficient and carrier life time,which are Da=13.0 cm2/s and τR=1.9 ns,were obtained directly by this technique under carrier concentration nex=3.4×1010/cm2 at room temperature.The measured Da keeps almost a constant value when the photoexcited carrier concentration is increased up to 1.2×1011/cm2.
2011, 60 (1): 017804. doi: 10.7498/aps.60.017804
Single InAs quantum dot (QD) sample was grown by molecular-beam epitaxy (MBE). The Photoluminescences (PL) of the exciton and biexciton in a single QD were measured at 5 K. The PL intensity as a function of the laser excitation power, the fine structure splittings of the exciton and biexciton, and the corresponding linearly polarized emissions were analyzed. By means of Hanbury-Brown and Twiss (HBT) setup, the photon correlation between the PL of exciton and biexciton were measured, which is gave an evidence of the quantum cascade emissions between biexciton and exciton PL.
2011, 60 (1): 017805. doi: 10.7498/aps.60.017805
Silicon quantum dots fabricated by nanosecond pulse laser in nitrogen, oxygen or air environment have enhancement in photoluminescence emission. The stimulated emission was observed at about 700 nm. It is difficult to recognize the difference between the photoluminescence peaks from samples in different environments, which is because of the same structure of the electron states in the band gap for different samples. The calculation results show that the same structure of the localized states forms in the band gap when silicon dangling bonds on surface of quantum dots are passivated by nitrogen or oxygen. It is the localized states that could catch the electrons from the conduction band to form metastable states, which is the key factor to enhance photoluminescence emission.
Experimental study on nonlinear absorption and Kerr effect in undoped GaP induced by femtosecond laser
2011, 60 (1): 017806. doi: 10.7498/aps.60.017806
A modified Z-scan experimental setup based on a Yb-doped photonic crystal fiber amplifier was used to achieve polarization-resolved measurement of the nonlinear properties of bulk intrinsic GaP. The experiment results reveal that three-photon absorption dominated the nonlinear absorption processe at room temperature. The anisotropy and crystal orientation dependence of the nonlinear absorption and nonlinear refractive index was experimentally studied and the nonlinearities showed saturation at high pump intensities.
2011, 60 (1): 017807. doi: 10.7498/aps.60.017807
Adding two scattering dielectric cylinders in a photonic crystal ring resonator, a new type of ring resonator filter is achieved, the transmission of which attains 90% and the bandwidth are relatively small. By taking two different measures, the filter wavelength and bandwidth are modulated arbitrarily: (1) With the scattering dielectric cylinder radius decreasing, the bandwidth of output wavelength from the load waveguide gets larger, while the wavelength bandwidth of the bus waveguide decreases; and when the radius increases, they change adversely. (2) Changing the radius of dielectric cylinder in the coupling region, the wavelength in the filter will change accordingly, and the amount of change was proportional to the radius of dielectric cylinder, and the transmission changes significantly. This may serve as the foundation for applications in the preparation of integrated photonic device.
2011, 60 (1): 017901. doi: 10.7498/aps.60.017901
The dynamic process of femtosecond laser pulse ablation of silica glass has been experimentally investigated by ultrafast time-resolved optical diagnosis. The digital holograms of material ejections outside the silica glass are recorded, and two-dimensional phase difference maps at different delay times are obtained, from which the composition and the structure of the ejected materials are deduced. Besides, the time-resolved shadowgraphs of the phenomena inside the silica glass are also recorded, and the evolution process of two stress waves inside the silica glass is observed in the shadowgraphs, which are believed to be related to two material ejections outside the target.
The degradation of activated GaAs vacuum electron source as a function of time has been investigated by using X-ray photoelectron spectroscopy (XPS).We found that the cathode surface element content changes with time and the significant decrease in sensitivity of electron source is mainly due to the change of dipole direction caused by the adsorption of harmful gases on the cathode surface.Based on the above results,we deduced the degradation model of GaAs electron source through analyzing the adsorption process of harmful gases on the surface in vacuum system.The model reveals the exponential degradation rule of GaAs electron sources and the inverse relationship between lifetime and pressure.The theoretical results are in full agreement with the experimental fact.
2011, 60 (1): 017903. doi: 10.7498/aps.60.017903
In order to investigate the decay tendency and the recovery status of the quantum efficiency of reflection-mode NEA GaN photocathode, the quantum efficiency curves have been studied after the photocathode was fully activated, stored in system and supplemented with Cs. The quantum efficiency decay and recovery processes of reflection-mode NEA GaN photocathode were observed and the mechanism was discussed. The quantum efficiency value of reflection-mode NEA GaN photocathode can be recovered up to more than 94% of the best value in the shortwave region between 240nm and 300nm, and more than 88% in the long wave region between 300nm and 375nm after Cs supplement. Based on the changes of surface potential barrier profiles of the reflection-mode NEA GaN photocathode before and after the quantum efficiency degradation and the quantum yield formula, the decay characteristic and the recovery status of quantum efficiency curve after supplement with Cs have been related to the changes of surface barrier shapes.
REVIEW OF FRONTIER AREA
As the scaling of MOSFETs continues towards 45 nm technology node, it is inevitable that Hf-based high-k materials replace the traditional SiO2 as the gate dielectrics of MOSFETs. But there are still many issues to be settled. Rare earth doping can increase the k value of dielectrics, decrease the defect densities of dielectrics and modulate the threshold voltage shift of MOSFETs. This paper reviews recent progress, the challenge of Hf-based high-k materials, the influence of rare earth doping on Hf-based high-k materials and its future trend.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2011, 60 (1): 018101. doi: 10.7498/aps.60.018101
According to the requirement of Ti: sapphire laser, the optimized chirped mirrors(CM) are designed to provide group delay dispersion (GDD) of around -60 fs2 with bandwidth 200 nm at a center wavelength of 800 nm. The CMs are manufactured by time controlled ion beam sputtering.The GDD is determined by using a home-built white light interferometer. The measurement results show that the manufactured CM can meat our requirement. By balancing the intra-cavity dispersion with our manufactured chirped mirrors, 12 fs and 9.5 fs pulses have been obtained respecitively.
The extended inertia fluid model to interpret the size distribution of Si nanoparticles prepared by pulsed laser ablation
2011, 60 (1): 018102. doi: 10.7498/aps.60.018102
The inertia fluid model proposed by Yoshida et al. can only interpret the influence of ambient pressure on the average size of nanoparticles prepared by pulsed laser ablation. Basing on the model, the Maxwell velocity distribution of the initial ablated particles is considered, a new analytic expression of the size-distribution of nanoparticles is obtained. The simulation results are consistent with the statistic data from Yoshidas experiments under different He pressures. Additionally, the size-distribution of nanoparticles is simulated using the modified model under different ambient gases (He, Ne and Ar),the simulation results coincide with experimental data. The conclusions may serve as the basis for realizing the uniformity and controllability of Si nanoparticles.
rf excited optical emission spectrum of radicals generated during hot wire chemical vapour deposition for the preparation of microcrystalline silicon thin film
2011, 60 (1): 018103. doi: 10.7498/aps.60.018103
To study the radicals behavior in the hot wire chemical vapour deposition (HWCVD) process for the preparation of microcrystalline Si (μc-Si: H) thin film, a weak radio frequency (rf) power was introduced to excite the radicals generated in HWCVD chamber. The spectrum of rf-excited HWCVD (rf-HWCVD) was obtained by subtracting the emission of hot wires from the spectrum measured by OES. The influence of the rf power on the rf-HWCVD spectrum can be neglected as the rf power density was less than 0.1 W/cm2. Under the same deposition parameters,the emission spectra for rf-HWCVD and plasma enhanced CVD (PECVD) processes are different. Under the low deposition pressure (7.5 Pa), the intensities of SiH* and Hα vary with the hot wire temperature reversely, which is characteristic of HWCVD with high gas dissociation rate and high concentration of atomic H. The ratio of intensity of Hα to SiH* in the emission spectrum of rf-HWCVD varying with deposition pressure is consistent with the crystalline fraction of μc-Si: H film. The results indicate that the optical emission spectroscopy measurement is a suitable method for the investigation of the HWCVD process excited by a weak rf-power.
We demonstrate an approach to create a high Q factor two-dimensional (2D) electromagnetic band gap (EBG) structure with composite defects in the center of the structures. By theoretical calculation, we show that a single-mode 2D EBG structure can be created with different ratios of diameter, d, to the lattice period, Λ, in this structure. This structure can achieve high Q factor and single mode operation with large d/Λ of the defect at the first circle around the removed rod in the center. With our structure, the single mode operation can be achieved within d/Λat the defect rods and d/Λat the others. In comparison, the condition of d/Λ should be strictly satisfied for the traditional design. These results provide very important guidelines for designing of the 2D EBG structure which can be used in traveling-wave tube device.
Study on photonic crystal grating slow-wave circuits for millimeter-wave ribbon-beam traveling wave tubes
2011, 60 (1): 018402. doi: 10.7498/aps.60.018402
A kind of photonic crystal grating slow-wave circuit, namely the cross-section distributing two-dimensional photonic crystal slow-wave circuit (CD2DPhSWC), was proposed. And the way of designing CD2DPhSWC was put forward. To simply the design, the process was realized in two steps, firstly the calculation of the photonic band gap (PBG) for the TE polarization, and then the dispersion of the equivalent rectangular waveguide grating. The numerical results show that the bandwidth of the traveling wave tubes (TWTs) based on CS2DPhSWC is wider, and the operating voltage is lower, than that of the rectangular waveguide grating. Correspondingly, the cost of the TWTs is reduced.
2011, 60 (1): 018403. doi: 10.7498/aps.60.018403
Nonstoichiometric AgSbTe2+x (x=0—0.05) compounds have been prepared by combining melting-quench and spark plasma sintering. The effects of excessive Te on thermoelectric properties were investigated at 300 K to 600 K. Results indicated that the concentration of Ag+ ion vacancy, hole concentration and electrical conductivity increase remarkably with the increasing amount of Te, while the Seebeck coefficient decreases. In addition, the total thermal conductivity of the samples increases slightly as Te content increases. The lattice thermal conductivities of nonstoichiometric samples range from 0.32 to 0.49 W/mK, which are less than the value of the stoichiometric sample, and close to the theoretical minimum thermal conductivity. For AgSbTe2.01 (x=0.01), a maximum figure of merit ZT=1.41 was obtained at 562K. This value is 15% higher than that of the stoichiometric sample.
2011, 60 (1): 018501. doi: 10.7498/aps.60.018501
A large signal equivalent circuit model of SOI LDMOS is proposed. Power gain and power-added efficiency of n-type LDMOS are modeled. Deep sub-micron SOI LDMOS was fabricated and measured. We investigated the dependence of SOI LDMOS power characteristics on channel length, single gate finger width, supply voltage and working frequency. Power gain and power-added efficiency are increased by 44％ and 9％, respectively, with channel length reduction from 0.5 μm to 0.35 μm. When single gate finger width is increased from 20 μm to 40 μm, power gain and power-added efficiency of 600 μm /0.5 μm device are decreased by 23％ and 9.3％, respectively. Power-gain and power-added efficiency are increased by 13％ and 5.5％, respectively, with supply voltage increased from 3 V to 5 V. When the working frequency is increased from 2.5 GHz to 3.0 GHz, power gain and power added efficiency of LDMOS are decreased by 15％ and 4.5％, respectively.
Theoretical study of GaN interval layers and quantum well barrier layers of different doping types in dual-wavelength LED
2011, 60 (1): 018502. doi: 10.7498/aps.60.018502
A 2D simulation of electrical and optical characteristics of dual-wavelength LED with GaN interval layers and quantum well barrier layers of different doping types was conducted with APSYS software. It showed that with the use of p-type doped GaN interval layer and quantum well barrier layers, we can greatly improve the hole concentration in QWs and reduce the electron overflow of the chip. We can also increase the luminous intensity and dramatically improve the dropping of internal quantum efficiency of the LED when the current increases.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Using conditional nonlinear optimal perturbation method in parameter optimization of land surface processes model
2011, 60 (1): 019201. doi: 10.7498/aps.60.019201
In this paper, we attempted to entend the application of conditional nonlinear optimal perturbation(CNOP) to the optimization of parameters in land surface model. We used the common land model and data of Tongyu station,which is a reference site of the CEOP in the semi-arid regions, and used three key parameters (soil color, soil sand/lay proportion and leaf area index) as parameters to be optimized. Two experiments are designed in our work, namely the single-parameter optimization and the triple-parameter optimization. Notable improvements in simulating sensible heat flux (SH), latent heat flux (LH), soil temperature (TS) and moisture (MS) at shallow layers were achieved by using the optimized parameters. In addition, the latter experiment shows a better performance than the former. All results above illustrate that the application of CNOP method can be extended to parameters optimization of land surface model. And what is more, due to its other advantages, such as the clear mathematical meaning, the simple design structure, and the fast computing speed, it shows a great potential for further applications in parameters optimization of related problems.
Active disturbance rejection control of a chaotic system based on immune binary-state particle swarm optimization algorithm
2011, 60 (1): 019501. doi: 10.7498/aps.60.019501
The active disturbance rejection control (ADRC) has the property of requiring no knowledge about the precise mathematical model, but the parameters of controller is difficult to be tuned. An active disturbance rejection control based on immune binary-state particle swarm optimization algorithm (IBPSO-ADRC) is proposed, which takes advantage of the combination of the artificial immune systems (AIS) and particle swarm optimization (PSO). The proposed algorithm is applied to optimize the parameters of ADRC and then to control chaotic system. Furthermore, a new ADRC for the chaotic system is constructed. The simulation experiments indicate that the scheme requires no knowledge about the mathematical model with fast response speed, while restraining the parameter perturbation of chaotic system effectively and is robust to noise.
2011, 60 (1): 019502. doi: 10.7498/aps.60.019502
The detrended fluctuation analysis method is applied to analyse the complexity of traffic flow time series and the scale index is obtained, which is a parameter to depict the long term evolutionary behaviour of the mixed traffic flow time series. According to the changes of the scale index, it is shown that the traffic flow time series has long-range correlation characteristics or short-range correlation characteristics. It is found that the traffic flow series shows long-range correlation when the density ρ12; and when ρ1 or ρ>ρ2, the time series displays short-range correlation. That is to say, the vehicle density plays an important role in the changes of the scale index. Additionally, we also found that the ratio of slow vehicles have influence on the changes of the scale index.
The influence of different opening shapes of split-ring resonator on its transmittance in terahertz band
2011, 60 (1): 019503. doi: 10.7498/aps.60.019503
Through the FDTD simulation of the transmittance in terahertz band of the split-ring resonator (SRR) with different opening shapes, we found a mean gap effect of SRR during the resonance and a particular conduction phenomenon in case of very sharp edge of the split.