Vol. 60, No. 4 (2011)
2011-02-20
GENERAL
2011, 60 (4): 040201.
doi: 10.7498/aps.60.040201
Abstract +
Mei symmetry and Mei conserved quantity deduced directly from Mei symmetry for Appell equations in a dynamical system of the relative motion are investigated. The definition and the criterion of Mei symmetry of Appell equations in a dynamical system of the relative motion under the infinitesimal transformations of groups are given. The expressions of the determining equation of Mei symmetry of Appell equations and Mei conserved quantity deduced directly from Mei symmetry in a dynamical system of the relative motion are gained. An example is given to illustrate the application of the results.
2011, 60 (4): 040202.
doi: 10.7498/aps.60.040202
Abstract +
In this paper, we study the vibrational populations of diatomic molecules in infrared fields using algebraic approach, and obtain the explicit analytical expression of the transition probability. The influences of frequency, intensity and pulse duration on the vibrational populations, which belong to, respectively, the ground state and the first excited state of vibration in NaCl and LiH molecular systems, are discussed.
2011, 60 (4): 040203.
doi: 10.7498/aps.60.040203
Abstract +
A class of relative rotation nonlinear dynamical model with nonlinear damping force and forcing periodic force is investigated. First, a homotopic mapping is constructed, and then the initial approximate solution is determined. Finally, using the homotopic mapping method, the arbitrarily degree approximation for corresponding model is found.
EDITOR'S SUGGESTION
2011, 60 (4): 040301.
doi: 10.7498/aps.60.040301
Abstract +
The present work devotes to study the delocalization effect of 5f electrons for the actinide elements Th to Es using the quantum mechanical calculation based on the full symmetry group. Follow the definition of quantum mechanics for delocalization effect, it is founded that the variation of the delocalization energy and atomic volume for elements Th to Es is in the opposite tendency each other. The energy gap of HOMO- LUMO and atomic volume for elements Th to Es is nearly the 1 to 1 mapping, and they are the source and image one another.
2011, 60 (4): 040302.
doi: 10.7498/aps.60.040302
Abstract +
The present work devotes to the energy levels of positron under molecules XH(X=O, S, Se and Te)and the relations with nuclear field using Dirac equation based on the full symmetry group. Under these nuclear fields, the energy of positron is about e+=-1.022 MeV. For the lower energy level, the energy of positron is increased with nuclear field; for the higher energy level, the energy of positron is nearly invariant with nuclear field. In this case, it is the three-photon annihilation. The formation of the positronium is in orthopositronium 3S, excited state, followed the conservation of charge parity.
2011, 60 (4): 040303.
doi: 10.7498/aps.60.040303
Abstract +
In non-commutative spaces the invariant eigen-operator method is used to derive and calculate Hamiltonian spectra for three kinds of three coupled harmonic oscillators: no coupling, coordinate coupling and momentum coupling. According to the comparison with the results in commutative space, it is shown that when the non-commutative parameter is zero the obtained energy levels are equal to the energy levels in commutative space. Finally the effect of the coupling coefficient on Hamiltonian spectrum in non-commutative space is discussed.
2011, 60 (4): 040304.
doi: 10.7498/aps.60.040304.2
Abstract +
The principle of the quantum switch is introduced by means of entanglement swapping. With the help of quantum switch operating entanglement swapping one by one, quantum correlations between Alice and Bob can be established. Adding entangled particle generator into conventional interconnection equipments, such as switch, and keeping quantum correlations between adjacent devices in the network leisure time, one can upgrade the classic internet to quantum teleportation internet. In quantum teleportation internet, the routing is selected also by utilizing the routing algorithm of classical internet. The routing selection can be synchronized with the establishment of quantum channel in static routing strategy. When the dynamic routing strategy is selected, quantum switch first selects a route to generate a router sequence table and then operates entanglement swapping one by one according to the table to establish the quantum correlations between Alice and Bob.
2011, 60 (4): 040304.
doi: 10.7498/aps.60.040304.1
Abstract +
In one-dimensional trapped Bose-Fermi mixture, described by time-dependent one-dimensional nonlinear equations that are derived from a three-dimensional Bose-Fermi system, we study the effect of atom-interactions on stability using a Gaussian Variational approach. We investigate the stable and the unstable conditions as functions of the atoms number and s-wave scattering length. We find that the interaction between the different species of atoms has significant effect on the stability of Bose-Fermi mixture. We also give critical conditions of the atoms number and s-wave scattering length for both special and general cases.
2011, 60 (4): 040501.
doi: 10.7498/aps.60.040501
Abstract +
Mobile communication applications provide a unique data source for the research of human mobility pattern. Based on the distribution data of urban mobile phone users, in this paper is explored the macroscopic dynamical behavior of urban mobility human by using the method of random matrix theory. The largest eigenvalue and the corresponding eigenvector of mobile phone user data deviate far from the distribution of random matrix. The deviations from random matrix vary with time. We find that the largest eigenvalue corresponds to a whole behavior common to all urban human mobility. The results indicate the temporal trends of the mean of correlation coefficient and the largest eigenvalue. We also find that the spatio temporal evolution of the weight of eigenvector components for the eigenvector corresponding to the largest eigenvalue is very consistent with the fluctuation pattern of the macroscopic behavior of urban human mobility.
2011, 60 (4): 040502.
doi: 10.7498/aps.60.040502
Abstract +
We report a stochastic resonance with the signal-to-noise ratio gain in a monostable system, by the fourth-order Runge-Kutta method, and on some occasions the signal-to-noise ratio gain exceeds 1. Tuning the parameters in the monostable stochastic resonance system can change the signal-to-noise ratio gain. This research result is the latest development of the monostable stochastic resonance, and has potential applications in the signal detection, processing and communications.
2011, 60 (4): 040503.
doi: 10.7498/aps.60.040503
Abstract +
In this paper, a novel pseudo-random sequence generator (PRSG) based on spatial chaos system is proposed. The statistical tests and correlation analysis on the proposed PRSG are performed by the well-known Federal Information Processing Standards FIPS140-1, and the experimental results show that the image encryption based on spatial chaos ergodic matrix has good random statistical characteristics, large key space and great sensitivity of the sequence.
2011, 60 (4): 040504.
doi: 10.7498/aps.60.040504
Abstract +
The alternans behavior is considered in the Greenberg-Hasting model of discrete excitable medium. The effect of the alternans behavior on spiral wave is investigated. The numerical results show that when the relevant parameters are appropriately chosen the alternans behavior has a significant influence on spiral waves. For example, the alternans behavior leads to the oscillation of the shape of the spiral wave and to the generation of the breathing spiral wave. The alternans behavior induces the meandering and the drifting of spiral waves, even causes spiral wave to move out of the system. Spiral wave can break up into multiple spiral waves, anti-target wave and spatiotemporal chaos due to the alternans behavior. The phenomena that the alternans behavior leads to the conduction barrier in homogeneous medium and causes spiral wave to break up or vanish, are observed for the first time. The physical mechanisms about these phenomena are briefly analyzed.
2011, 60 (4): 040505.
doi: 10.7498/aps.60.040505
Abstract +
A nonlinear function of unified chaotic system, the family of switched unified chaotic system is generated which contains six kinds of subsystems. Each subsystem can be switched by changing systematic parameter values in parameter space, and these subsystems can be switched continuously from one to another via changing nonlinear function in state space. The features of these subsystems are analyzed in detail using Lyapunov exponent and bifurcation diagram. The division-time switching of unified chaotic system is realized based on digital signal processing (DSP).
2011, 60 (4): 040506.
doi: 10.7498/aps.60.040506
Abstract +
The projective synchronization in the unified hyperchaotic system using two control method is studied in this paper. Based on the Lyapunov stability theory, the full state hybrid projective synchronization is achieved via an adaptive controller. It is proved theoretically that the controller can make the states of the dynamical system and the response system with known parameters achieve the asymptotically full state hybrid projective synchronization. An active controller is designed to achieve the projective synchronization. Finally, Numerical simulations show the effectiveness of the two schemes.
2011, 60 (4): 040507.
doi: 10.7498/aps.60.040507
Abstract +
Phase-field model is used and The dendrite growth of a Ni-40.83%Cu binaryalloy under were simulated by the model coupled with solute field and temperature field.The effects of solidification latent heat on the growth of equiaxed dendrite, distribution of solute field and temperature field in undercooled liquid alloy were analyzed.The results indicate that the dendritic has well-developed secondary arms as undercooling degree increases.Correspondently, the solute Peclet number and the tip speed increases, the tip radius decreases, and the solute segregation in solid-liquid interface increases. The results agree well with Ivantsov theory.
2011, 60 (4): 040508.
doi: 10.7498/aps.60.040508
Abstract +
With the help of the symbolic computation system Maple and an improved Riccati equation mapping approach, a series of exact solutions of the (2+1)-dimensional Zakharov-Kuznetsov equation (ZK) is derived. Based on the derived solution, we obtain some special soliton structures.
2011, 60 (4): 040509.
doi: 10.7498/aps.60.040509
Abstract +
In this paper, the electron transports through a three-barrier nanowire heterostructure between two reservoirs with different temperatures and chemical potentials are studied. The transport probability of electron is obtained by using the transfer matrix method,and the heat flow carried by the electrons transfer is calculated out. The performance characteristic curves of the refrigerator are plotted by numerical calculations. The influence of bias voltage and heterostructure on the performance of the refrigerator is analyzed. Especially, the effects of the height and the width of the middle barrier on transport probability, cooling rate, and colling coefficient are emphasized.
2011, 60 (4): 040701.
doi: 10.7498/aps.60.040701
Abstract +
We investigate the optical properties of Ⅲ-Ⅴ and Ⅱ-Ⅵ semiconductors. The results show that the sensitivity of the interferometer can be greatly enhanced by the dispersive property of semiconductor. Furthermore, the analyses show that the semiconductor slow light medium has a more wider working spectral range than gas slow light medium. Moreover, we experimentally demonstrate that the sensitivity of the interferometer based on the semiconductor GaAs is 3.2 times higher than those of traditional interferometers.
2011, 60 (4): 040702.
doi: 10.7498/aps.60.040702
Abstract +
Quartz tuning forks have been widely used as force sensors in scanning probe microscopes. The anti-phase and in-phase eigenmodes of a tuning fork are involved during microscope operations. Dynamic characteristics of both eigenmodes are studied by experiments and finite element analysis simulations. It is demonstrated that elastic couplings exist between not only both the prongs but also two prongs and the base of the tuning fork. Experimental results show that the coupling between both the prongs increases the anti-phase mode eigenfrequency while the coupling between two prongs and the base of the tuning fork decreases the in-phase mode eigenfrequency. A mechanical model of the tuning fork is introduced and simplified. Parameters of the simplified model are calculated, which is described as a four-springs-three-point-masses system. The quantitative relation between the effective mass of one prong and the eigenfrequency of the anti-phase mode of the mechanical model is in good agreement with that of finite element simulations.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2011, 60 (4): 041301.
doi: 10.7498/aps.60.041301
Abstract +
We choose a correlation function of chiral current to calculate the form factors f+Bπ(q2), f Bπ(q2) and the scalar form factor of f0(q2), thereby we can study the effect of leptonic mass on B0→π－l+ν l (l=e, μ, τ) decay. In this paper, we calculate the branching ratio of B0→π－l+ν l(l=e, μ, τ) decay for the first time, and find the leptonic mssses me and mμ may be ignored, but the heavy leptonic mass mτ may not be ignored and it can affect the branching ratio. The calculation results are consistent with the experimental data.
NUCLEAR PHYSICS
2011, 60 (4): 042901.
doi: 10.7498/aps.60.042901
Abstract +
Tb-doped oxyfluoride tellurite glasses are synthesized by high-temperature melting method. Densities, transmission and luminescence properties at different concentrations of Tb3+ and Gd3+ ions are investigated. The results indicate that all the samples have good physical properties, especially those with high density. Increasing the concentration of Tb3+ ions has a positive effect on luminescence property. Gd3+ ions could sensitize the luminescence of Tb3+, and the best concentration of Gd3+ is 4mol%.
2011, 60 (4): 042902.
doi: 10.7498/aps.60.042902
Abstract +
Effect of the deuterium ion beam bombarding time on characteristic of the deuteride titanium target is studied by measuring the neutron yield as a function of bombarding time with the associated-particles method in ZF-300 neutron generation. Slow positron annihilation spectroscopy for defect structure analysis and scanning electron microscopy for the surface morphology analysis are used to characterize the targets. The results show that the beam bombardment cause the changes of the defect structure and the surface morpholoy of the deuteride titanium target, but the different bombarding times do not lead to the changes of the neutron yield, the defect structure, and the surface morphology of the deuteride titanium target under the work condition. The prominent physical mechanism of the interaction between deuterium ion beam and deuteride titanium target is discussed in detail based on the numerical study of the interaction between beam and solid.
ATOMIC AND MOLECULAR PHYSICS
2011, 60 (4): 043101.
doi: 10.7498/aps.60.043101
Abstract +
The theoretical investigation of the chiral optics is induive to the elucidation of the optically rotational mechanism and the design of the novel chiral drugs. The optical rotation (OR), the vibrational circular dichroism (VCD),and the electronic circular dichroism (ECD) spectra of a series of newly-found bio-active molecules, bruguierols A—C, are calculated with the gradient-corrected density functional theory method. On the basis of molecular structure, normally vibrational modes and electronic structure, we explore the microscopic origin of molecular chirality and discuss the solvent effects of OR and ECD spectra. The results show that the introduction of OH modulates the molecular chirality. The methyl group and the phenyl group enhance the molecular chirality. The normal vibrations and the electronic transitions on the chiral skeleton play critical roles in producing the chiral spectra. The solvent effect decreases OR and weakens the ECD spectra.
2011, 60 (4): 043102.
doi: 10.7498/aps.60.043102
Abstract +
The potential energy curves (PECs) of CS+(X2Σ+) and CS+(A2Π) have been investigated using the full valence complete active space self-consistent field (CASSCF) method through the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach over the internuclear separation range from 0.05 to 0.60 nm. In the present calculations, the basis sets for S and C are both aug-cc-pV6Z. The spectroscopic parameters of three main isotopes (12C32S+, 12C33S+, 12C34S+) have been determined. The present D0, De, Re, ωe, ωeχe, αe and Be for 12C32S+(X2Σ+) are 6.4694 eV, 6.5542 eV, 0.14975 nm, 1371.89 cm-1, 7.5746 cm-1, 0.006481 cm-1 and 0.8616 cm-1, respectively; and those for CS+(A2Π) are 4.8460 eV, 4.9084 eV, 0.16449 nm, 1009.31 cm-1, 6.4970 cm-1, 0.006110 cm-1 and 0.7134 cm-1, respectively, which have been compared with those of previous results reported in the literature. And the comparison shows that the present results and the experimental results are in excellent agreement with each other. With the PECs of CS+(X2Σ+) and CS+(A2Π) determined here, the vibrational states for each electronic state are determined when the rotational quantum number J equals zero (J = 0). For the first 30 vibrational states, the vibrational level G(υ), inertial rotation constant Bυ and centrifugal distortion constant Dυ for 12C32S+(X2Σ+) and 12C32S+(A2Π) are evaluated when J = 0, which are in good accordance with the available RKR data.
2011, 60 (4): 043201.
doi: 10.7498/aps.60.043201
Abstract +
A very simple and highly accurate method of investigating the behavior of atomic system in a strong magnetic field has been developed based on the generalized pseudospectral discretization. As examples, we present the calculations of the binding energies and quadruple moments for the ground and low-lying excited states of the hydrogen atom in a magnetic field ranging from zero up to 1000 a.u.. The obtained results are found to be in excellent agreement with other high-accuracy theoretical calculations. The present method may be straightforwardly applied to cross electric-magnetic field in an arbitrary orientation.
2011, 60 (4): 043202.
doi: 10.7498/aps.60.043202
Abstract +
The characteristics of terahertz (THz) radiations from the surfaces of two kinds of narrow-band semiconductors InN and InAs excited by femtosecond laser pulses with different pump powers (from 10 to 320mW) are investigated experimentally. The results show that InAs can irradiate a stronger THz signal than that of InN under the same pump power so its radiation efficiency is higher. However, the spectral widths of THz radiations from these semiconductor surfaces increase with the increase of pump power. When the intensity of pump laser is high enough, the spectral Half-Maximum-Full-Width (HMFW) of THz radiation tends to be a constant. Compared with InAs, InN can reach this constant HMFW THz spectrum at a lower pump power. This research is significant for investigating the THz radiation mechanism from semiconductor surfaces, and it is also a good reference for exploring a THz radiation source with low cost and high efficiency.
2011, 60 (4): 043203.
doi: 10.7498/aps.60.043203
Abstract +
By solving numerically the time-dependent Schrödinger equation with the split-operator method, we investigate the characteristic of the high-order harmonic of one-dimensional helium atom exposed to two laser pulses with the same color and half cycle pulses. It is shown that the harmonic spectrum is extended to Ip+9.6Up in the case of the combined fields, and an isolated 63 as pulse can be obtained by superposing the high-order harmonic spectra generated around the cut-off position. An analysis shows that the plateau of the high-order harmonic spectrum is extended greatly and the contribution of the long electron trajectory is suppressed by adding the half cycle pulses.
2011, 60 (4): 043301.
doi: 10.7498/aps.60.043301
Abstract +
Using a three-dimensional classical ensemble, we have investigated the internuclear distance (R) dependence of nonsequential double ionization (NSDI) of H2 molecules. In all alignments, as R increases, the double ionization (DI) rate first increases and then decreases, and it reaches its maxima when R is 4a.u.. The dependence of NSDI of H2 on R weakens as the angle between molecular axis and laser polarization(φ) increases. When φ is zero, the NSDI of H2 provides rich correlation patterns, which is strongly dependent on R. When φ is π/2, the correlation patterns are similar for different values of R and recollisions play a more important role in DI process. These results indicate that molecular structure has an important influence on NSDI of diatomic molecules.
2011, 60 (4): 043401.
doi: 10.7498/aps.60.043401
Abstract +
Elastic and inelastic differential and integral cross sections for low-energy vibrational excitation of H2 by electron impact are studied with exact exchange. The resulting coupled integrodifferential equations are solved using a combination of linear-algebraic and R-matrix-propagator techniques. The converged (0→0,0→1,0→2) differential and integral cross sections are obtained. The calculated results are in good agreement with experimental resalts and other calculations, showing that the exact exchange based on equations of vibrational close coupling plays an important role in low-energy electron scattering from H2 molecule.
2011, 60 (4): 043601.
doi: 10.7498/aps.60.043601
Abstract +
(H2O)6 is the smallest water cluster to form three-dimensional(3-D) structure, and there exist a few low-energy isomers. The stability of the isomers and the isomerization process are studied by ab initio calculations. The difference in energy between the ring structure and the most stable prism is 0.31 eV, which is the energy of one hydrogen bond. The isomerization process of water clusters corresponds to the breaking and/or the reforming of hydrogen bonds. For (H2O)6, the isomerization among the low-energy structures involves the breaking or the reforming of only one hydrogen bond, and the energy barriers separating the isomers range from 0.07—0.21 eV.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2011, 60 (4): 044101.
doi: 10.7498/aps.60.044101
Abstract +
In this paper, we design a three-dimensional isotropic left-handed metamaterial (LHM) composed of sphere-thorn shaped cells at visible frequencies. Adopting the metallic Drude's principle, we simulate and study its transmission properties for the incident plane electromagnetic wave. The dimension of unit cell here is far below the resonant wavelength, and thus the effective medium theory is well satisfied. With appropriate geometric parameters, this structure can realize negative refractive index with simultaneous negative permittivity and permeability at visible frequencies. The LHM proposed in this paper has advantages of simplicity and isotropy, moreover, our numerical model provides a new method for 'top-to-bottom’approach to preparing visible three-dimensional metamaterials.
2011, 60 (4): 044102.
doi: 10.7498/aps.60.044102
Abstract +
In order to suppress high order mode self-oscillation in a high gain amplifier, some special procedures, such as decreasing the coupling between beam and rf field in the forepart of the amplifier, are taken such that the tube works in a fully amplified state in an operation range. In simulation, the rf output power is 1.7 GW with a beam of 7.5 kA at 750 kV when input power is 6.8 kW and the corresponding gain is 53.9dB. Based on the results from 2D PIC simulation, the experiment is performed on the Sinus accelerator. In experiment, the amplifier is driven by a beam of 8 kA at 800 kV, and the maximum output power is 2.04 GW when input power is 62 kW; the maximum gain reaches 46.7dB when the input reduces to 39 kW, the corresponding output power is about 1.84 GW. Both the simulation and the experiment prove that a kW-level rf power can drive the tube to generate a GW-level output power.
2011, 60 (4): 044201.
doi: 10.7498/aps.60.044201
Abstract +
When the lensless Fourier transform digital holography is applied to the microscopic phase-contrast imaging on live cells, the motion of cells will lead to a non-coplanary phenomenon between the object recorded and the reference source. This could result in the imaging aberration. An effective and robust autofocus procedure based on the phase distribution is presented in the paper. With the initial measurement of the distance between the reference source and the hologram, the optimal parameters corresponding to the phase-contrast image can be achieved by a single hologram combined with the linearity fitting. Lensless Fourier transform digital holographic system is built and the experiments on the phase-contrast imaging of the live cervical carcinoma cells are performed. Finally, the good experimental results are obtained. Both the theoretical analysis and the experimental investigation verify the feasibility and the validity of the automatic procedure for non-coplanar aberration compensation.
2011, 60 (4): 044202.
doi: 10.7498/aps.60.044202
Abstract +
Theoretical derivation and numerical calculation achieve the quantum dot numerically exact multi-photon emission spectra starting from the interaction of quantum dot and cavity,using the master equation that includes incoherent pumping and pure dephasing and combines with the quantum regression theorem, and considering the relevant initial conditions.Then comparing the multi-photon(fermion statistics) spectra with the one-thoton(boson system) correlation level, our analysis shows that according to the fermion statistics the pure dephasing, and the thermal bath model, an excellent fitting to the data is obtained with the recent experimental of Ref[22] results in a quantum dot-micropiller cavity system. The theory and the recent experiments both show pump-induced stimulated emission and anharmonic cavity-QED in quantum dot-cavity systems.
2011, 60 (4): 044203.
doi: 10.7498/aps.60.044203
Abstract +
In the n-type four-level atomic system, we have studied the nonlinear theory of electromagnetically induced absorption. The results show that the probe light Rabi frequency and the attenuation distribution coefficient A affect the nonlinear absorption and then the absorption of a medium. When the probe light intensity is weak, the absorption of the medium and the linear absorption are the same, showing the characteristics of electromagnetic induction absorption. When the probe light intensity is increased, the absorption of the medium and the linear absorption are no longer the same, and now the medium absorption curve will show hole burning phenomenon, and then it will show the gain phenomenon. At the same time, the nonlinear absorption is affected by the value of A. Even if the probe light is weak, the medium absorption will change the electromagnetic induction absorption into the gain phenomenon with the A value decreasing.
2011, 60 (4): 044204.
doi: 10.7498/aps.60.044204
Abstract +
Based on a delayed mutually coupled system consisting of two semiconductor lasers (SL) with different injection currents, the influences of the asymmetric bias currents of two SLs and the frequency detuning Δf (Δf=f1-f2, where f1 and f2 are the free frequencies of SL1 and SL2 respectively) on synchronization performance have been investigated experimentally. The results show that for the case of the two SLs with identical free oscillation frequencies, the mutually coupled system can achieve excellent chaos synchronization under relatively large asymmetrical injection currents. Furthermore, the frequency detuning, controlled by adjusting the temperature of one of the two SLs, has an obvious influence on synchronization performance. For the case of the SL1 biased at a relatively much larger current than that of SL2, the synchronization performance will degrade with the increase of the positive frequency detuning (f1>f2), while the synchronization performance can be further improved with suitable negative frequency detuning. The simulated results are basically consistent with experimental results.
2011, 60 (4): 044205.
doi: 10.7498/aps.60.044205
Abstract +
Longitudinally polarized subwavelength beams have found many applications such as particle acceleration, single molecule dipole detection, second harmonic generation imaging, longitudinally polarization confocal microscopy. We present a radially modulated Bessel-Gaussian beam model which produces longitudinally polarized beams with high purity after being focused by high numerical aperture objective. Based on the vector diffraction theory, the electric field intensity distribution, magnetic field intensity distribution and energy flux density near the focal plane are numerically simulated. The result shows that the full-width at half-maximum is as small as 0.4λ. The method does not require a physical annulus or annular phase filter and it features high energy efficiency, high resolution, thus improving application performances.
2011, 60 (4): 044206.
doi: 10.7498/aps.60.044206
Abstract +
One of the important factors of the low laser induced damage threshold is the defects in the subsurface of fused silica. The three-dimensional model of a spherical inclusion in the subsurface is established in this study. Three-dimensional finite-difference time-domain method is used to calculate and simulate the light field distribution in the vicinity of inclusions. The effects of dielectric constant and inclusion size are analyzed, separately. The results show that the light intensity enhancement factor (LIEF) does not change with the size and the dielectric constant of the inclusions when the dielectric constant is smaller than that of fused silica, where the LIEF is kept at about 4. When the dielectric constant is 6.0, the LIEFs are 50.1588, 73.3904 and 102.9953 for the inclusions with sizes of 1.5λ, 2λ and 2.5λ respectively. When the inclusion size is constant, the LIEF will increase with the increase of dielectric constant. The light enhancement for the round inclusions is much higher than that for the ellipsoidal inclusions. Therefore, the round inclusions with large size and dielectric constant significantly enhance the electric field.
2011, 60 (4): 044207.
doi: 10.7498/aps.60.044207
Abstract +
By adding a periodic signal of the fluctuating frequency to the gain-noise model of the single-mode lasers, we calculate the correlated function and power spectrum of the output laser intensity and discuss the variation of signal-to-noise ratio(SNR) with the intensity of the noise and system parameter. The result indicates that the SNR shows stochastic resonances with the variations of intensities of the frequency noise, pump noise and quantum noise, also with the variations of gain coefficient and loss coefficient.
2011, 60 (4): 044208.
doi: 10.7498/aps.60.044208
Abstract +
In this paper, we investigate spatial dark solitons in nonlocal nonlinear media. Based on the nonlocal nonlinear Schrödinger equation and the diffusion equation, the numerical solutions with different propagation constants are obtained by using the Newton iterative method. And it is found that there exist dark soliton solutions .and the relation between the width of dark soliton and the degree of nonlocality for any propagation constant under arbitrary nonlocal degrees different propagation constants. In experiments, we observe the formation of the spatial dark solitons in the solution of dye. The influence of Gaussian background on dark solitons is also discussed, and the numerical results are in agreement with the experimental results.
2011, 60 (4): 044209.
doi: 10.7498/aps.60.044209
Abstract +
Photocathode materials with the lower surface doping density need a longer time to raise photocurrent in the first Cesium activation process when the system vacuum level is not high enough, which can be found from the photocurrent curves during the activation of negative-electron-affinity (NEA) GaAs photocathodes. At the same time, with the enhancement of system vacuum level, these differences in time will become unobvious. It is indicated that the adsorption efficiency of Cesium on cathode surface has the direct relationships with the surface doping density and system vacuum level. In order to analyze these relationships quantitively, in this paper, a mathematical model of the adsorption efficiency of Cesium on cathode surface is established according to the experimental data. The simulation results by the model are in good accordance with the experimental phenomenon. This study is of very important value and significance for the further investigation of structure design and preparation techniques for varying doping GaAs photocathode materials.
2011, 60 (4): 044210.
doi: 10.7498/aps.60.044210
Abstract +
According to the ratios of the peak-values of photocurrents arising separately during the single Cs activation and during the Cs-O activation for negative electron affinity(NEA) GaAs photocathode, and the theoretical energy distributions of the photoelectrons passing separately through the single and the double potential barriers, a new method of evaluating the surface potential barrier parameters of NEA GaAs photocathode is presented. The results obtained by this method accord well with the double-dipole model theory and are in agreement with the results by fitting the experimental electrons energy distribution curve. The method is simple and efficave, which enriches the approaches to the evaluation of activation effect and surface characteristic of NEA GaAs photocathodes without increasing other test means.
2011, 60 (4): 044211.
doi: 10.7498/aps.60.044211
Abstract +
A novel side-chain conjugated polythiophene copolymer with a narrow band gap of 1.72eV, poly -thiophene (POTVTh-Th), is synthesized by the Stille coupling reaction. The third order nonlinear optical properties of the copolymer are measured by femtosecond Z-scan technique at 800nm. The results indicate that the third order nonlinear susceptibilities of the polymer solution and the film are 8.84×10-10esu and 7.25×10-9esu, respectively, which are 2.17 and 1.68 times bigger than those of its homopolymer, showing enhanced third order nonlinear optical properties and the good nonlinear optical properties of this side-chain conjugated copolymers.
2011, 60 (4): 044212.
doi: 10.7498/aps.60.044212
Abstract +
We propose a compact, high efficient full photonic crystal Mach-Zehnder (MZ) interferometer based on the self-collimation and photonic band gap in two-dimensional photonic crystals. Line defected photonic crystals are used as the beam splitter and the mirror. The interference theory is used to discuss the interferometer output mechanism, and compared with the finite-difference time-domain (FDTD) simulation results. The designed MZ interferometer can surve as micro-detectors of gas and liquid, which may play an important role in integrated optics.
2011, 60 (4): 044213.
doi: 10.7498/aps.60.044213
Abstract +
Holographic recording characteristics of the hydrophilic TiO2-nanoparticle-dispersed polyvinyl alcohol/acrylamide-based thick photopolymer are studied. The experimental results show that not only the volume shrinkage during the holographic exposure can be suppressed by the inclusion of the nanoparticles, but also the diffraction efficiency and other performance parameters can be improved in the hydrophilic TiO2-nanoparticles dispersed photopolymer compared with those traditional samples. There exists an optimum concentration of TiO2-nanoperticals, in which the maximum diffraction efficiency can reach 92.3%, the maximum refractive index modulation arrives at 2.09×10-3, and the volume shrinkage reduces to 0.80%.
2011, 60 (4): 044214.
doi: 10.7498/aps.60.044214
Abstract +
According to the wavelength characteristic of fiber coupler,its spectrum characteristics was analysed as a comb filter, and all-fiber comb-filter based on fiber couplers with different wavelength intervals were experimentally fabricated by splicing a section of single mode twin-core fiber (TCF) of different lengths between two single mode fibers (SMFs),and the extinction ratio is 25 dB. CO2 laser was used to trim the wavelength firstly,which results in the spectrum shifting to long wavelength and the change of extinction ratio.The trimming is based on the mechanism of residual stress and melting deformation between fiber and CO2 laser,and hydrogen-loaded TCF was used to improve the trimming efficiency.
2011, 60 (4): 044301.
doi: 10.7498/aps.60.044301
Abstract +
We propose an acoustic metamaterial (AM) composed of local resonant split hollow sphere (SHS). The results of numerical simulation and acoustic experiment show that the effective modulus of the AM with SHS is negative. To further investigate the intrinsic resonant mechanism of the SHS, we study the transmission of the AM by adjusting the geometry sizes of the SHS, such as the diameter of split hole and the diameter of hollow sphere. It is found that the geometry sizes of SHS will greatly affect the frequency of transmission dip, say, the resonant frequency. Moreover, we investigate the effects of the arrangement in AM on transmission feature. When the lattice constant and the number of SHSs change, the frequency range of resonance in the single-layer AM keeps unchanged. However, the resonant intensity of AM becomes stronger with the increase of the number of SHSs in single layer and the number of SHS layers.
2011, 60 (4): 044302.
doi: 10.7498/aps.60.044302
Abstract +
For the analytic study of the defect mode of 1D doped phononic crystal, the multiple-beam interference method and Bloh theorem are adopted, the analytical formula of defect mode is derived and the defect mode of 1D doped phononic crystal is studied. The varition law of defect mode is obtained. The method in freed from the weaknewes of other methods that cannot carry on the analysis of defect mode. The method is valid and accurate method of studying the defect mode of 1D doped phononic crystal.
2011, 60 (4): 044401.
doi: 10.7498/aps.60.044401
Abstract +
The ratchet effect in heat conductions of one-dimensional Morse lattices is studied when the system is located between two averagely isothermal reserviors, of which one keeps the temperature constant and the other is periodically modulated in temperature,and their temperatures averaged over a long time are equal to each other. Unidirectional heat current can be observed when one of the heat baths is periodically modulated in temperature. The efficiency and the direction of heat conduction can be rectified and controlled by adjusting the frequency and the amplitude of the modulation. An interesting non-stationary negative thermal conductivity, i.e., a reversed heat flow against the temperature gradient, is found in an appropriate region of frequency of the modulation. A heat wave scheme in revealing the spatiotemporal behavior of the heat conduction is proposed to study the this phenomenon. The influence of the parameters of the Morse lattice on the directional heat current is investigated, and so this provides theoretical support for practical applications.
2011, 60 (4): 044402.
doi: 10.7498/aps.60.044402
Abstract +
As is well known, direct-current (DC) characteristic, frequency characteristic and noise characteristic of SiGe heterojunction bipolar transistor(HBT) can be improved by "bandgap engineering"(by Ge composition). However, the effect of "bandgap engineering" on the thermal characteristic of HBT has not been reported. In this paper, the effect of "bandgap engineering" is analyzed by the use of 3D thermal-electric feedback model. Considering the temperature dependence of emitter junction voltage and current gain, the expression of the minimum emitter ballasting resistance (REmin), which is necessary for SiGe HBT thermal stability, is presented. Furthermore, non-uniform ballasting resistance design is given so as to further enhance the thermal stability of device. It is found that the surface temperature of the device decreases with the increase of Ge composition in SiGe base. This is because SiGe HBT internally possesses the thermal-electrical negative feedback. For the same dissipated power, the REmin decreases as Ge composition increases, which is beneficial to the improvment of the performance of radio frequancy(RF) power SiGe HBT. These results provide a good guide to further optimization of RF power SiGe HBT performance, especially thermal design.
Dynamic modeling of flexible beam with considering shear deformation in non-inertial reference frame
2011, 60 (4): 044501.
doi: 10.7498/aps.60.044501
Abstract +
In this paper, the effect of shear deformation is considered into flexural deflection of the geometrically nonlinear deformation of a flexible beam. Then, considering the coupling effect of deformation in to the extensional and flexural deflection, the second-order coupling terms of deformation in two displacement fields are developed and the axial inertial force and transverse distributed force are considered. The finite element method is used for the system discretization and the coupling dynamic equations of flexible beam are obtained by Lagrange’s equations. In this way, the new governing differential equations of the beam in the geometrically non-linear kinematics of deformation are derived. Numerical examples of a flexible beam are studied to analyze the effect of shear deformation on the dynamic character and to investigate the coupling effect. Furthermore, from this present method, a moving Timoshenko beam can also produce the dynamic stiffening phenomenon and some new properties can be shown.
2011, 60 (4): 044502.
doi: 10.7498/aps.60.044502
Abstract +
A method of constructing canonoid transformations with respect to a Hamiltonian is presented. First, the Hamiltonian system is transformed into a Birkhoffian system. Second, the Birkhoffian system is transformed into a new one under gauge transformation. Finally, the Hamiltonization of new Birkhoffian system is realized. It is pointed out that there exist many different canonoid transformations for one Hamiltonian system. Two examples are given to illustrate the application of the results.
2011, 60 (4): 044503.
doi: 10.7498/aps.60.044503
Abstract +
A new approach to the construction of Lagrangian and Hamiltonian for a second-order differential equation is presented. By writing the second-order equation in the first-order form and constructing first-order Lagranian corresponding to the set of the first-order equations, the second-order Lagrangian and Hamiltionian are deduced from the first-order Lagrangian directly. By using the above method the first-order ane the second-order Lagrangians and the Hamiltonians for some of dissipative and dissipative-like systems are obtained. The advantage of the approach is discussed. Four examples are given to illustrate the applications of the results.
2011, 60 (4): 044701.
doi: 10.7498/aps.60.044701
Abstract +
It is well known that some simple physical models can lead to complex behaviors. Moreover, some simple models possess a strongly logical expression ability. A cryptosystem is proposed based on two simple physical modes, which has the performances of its reversibility, parallelism, simplicity and efficiency. The simulation results show that the system presents satisfactory randomness and sensitivity. It is a promising method to use simple physical models for constructing a good cryptosystem.
2011, 60 (4): 044702.
doi: 10.7498/aps.60.044702
Abstract +
Making a basic description of a typical characteristic of multichromatic multidirectional ocean surface waves and taking into account widespread wave-current interactions and the rich effects of capillary waves, a complete symmetric solution of trichromatic tri-directional waves in water of finite depth is presented, leading to a sufficient inclusion of and a centralized reflection of the existing monochromatic and multichromatic multidirectional wave theories.
2011, 60 (4): 044703.
doi: 10.7498/aps.60.044703
Abstract +
In this paper, an stability theorem is proposed for a fractional state space system based on Lyapunov stability theory. Controller can be achieved easily by this theory without calculating any equilibrium point. The fractional unified chaotic system is used to improve the stability theorem. The effectiveness of the theory is verified by the simulation results.
2011, 60 (4): 044704.
doi: 10.7498/aps.60.044704
Abstract +
Experiments are conducted to examine the characteristics of internal waves generated by a towing hemispheroid model alongside the side wall of stratified fluid flume with a linear density distribution. By the measured results with multi-channel conductivity arrays, the wave patterns, the vertical displacement and the correlation velocity for such internal waves are analyzed. Two distinct types of internal waves are obtained in experiments. One is the body-generated internal wave by the steady source with respect to the hemispheroid model, and the other is the wake-generated internal wave by the unsteady source. The transition between these two types of internal waves occurs at a critical Froude number of FrS=1.6. The corresponding comparison with towing spheroid model experiments is carried out. It follows that the number FrS is about 2/3 that of the spheroid and that the transition is more rapid and its borderline is more clear-cut than those of the spheroid modes. The body-generated internal waves of both experimental models have identical characteristics, but the draining-water volume is about 2/3 that of the spheroid model. Their wake-generated internal waves possess similar variation tendencyies, but their wave speed is about 2/3 that of the spheroid model . It also proves that this mirror-image experimental method in the flume can increase the effective range of spatio-temporal evolvement of body-generated internal waves.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2011, 60 (4): 045201.
doi: 10.7498/aps.60.045201
Abstract +
Based on drift-diffusion approximation and under axis-symmetric assumption, a two-dimensional(2D) fluid model is established for the plasma in the chamber of electron cyclotron resonance plasma source. A finite difference method is used for self-consistent numerically simulating the model. Numerical results of uniformity evolution of plasma density are obtained. From the analysis of the numerical results, the effects of background gas pressure, microwave power and current in magnetic field coil on uniformity of the plasma density are studied. The results shows that during the initial ionization, the uniformity of electron density is better than that of ion density. During the later ionization, the uniformity of ion density is better than that of electron density. As background gas pressure increases, the uniformities of both electron and ion densities increase, and the uniformity of ion density increases faster. As microwave power increases, the uniformities of both electron and ion densities increase with almost the same rates. As current in magnetic field coil increases, the uniformities of both electron and ion densities increase at almost the same rates. However, when the current in magnetic field coil becomes big enough, the uniformities of both electron and ion densities decrease at almost of same rates.
2011, 60 (4): 045202.
doi: 10.7498/aps.60.045202
Abstract +
An atmospheric pressure plasma torch is generated with a hollowneedle-to-plate dielectric barrier discharge and the electron densities in the inside and at the surface of the plasma torch are measured by optical emission spectroscopy (OES). A plasma torch with 1cm long is generated in atmospheric ambient when argon gas is introduced through the hollwneedle. The Stark broadenings of Hα and ArⅠ(696.54 nm) lines, which are decomposed from the experimental profiles by using deconvolution method, are used to estimate the corresponding electron densities. The electron densities are 1.0×1015 cm－3 and 3.78×1015 cm－3 corresponding to the Stark broadening of Hα and ArⅠ(696.54 nm) lines, respectively. The electron density calculated from the Stark broadening of Hα is the same as that at the surface of the plasma because Hα line originates from the dissociation and the excitation of H\-2O at the plasma torch surface where argon can meet with atmosphere. While the electron density calculated from the Stark broadening of ArⅠ(696.54 nm)line is the same as that in the insid of plasma.
2011, 60 (4): 045203.
doi: 10.7498/aps.60.045203
Abstract +
By simulating the field distributions of two optical dipole antenna models with the finite-difference time-domain (FDTD) method, the variation regularity of their far-field radiation with their length increasing and the factors which can influence their far-field directivity are studied. The results show that the variation regularity of optical dipole antenna is analogous to that of classic symmetrical dipole antenna. But in the far-field directivity plot of optical dipole antenna, side-lobes occur much more quickly, owing to the existence of high-order localized surface plasmon modes. These results hold a significant promise of improving the performance of optical antennas.
2011, 60 (4): 045204.
doi: 10.7498/aps.60.045204
Abstract +
The characteristics of proton beams generated from ultra-intense laser-foil interactions under varied focal offsets are experimentally studied on XL-Ⅱ laser facility.The experimental results show that when strong femtosecond prepulses are presented before the main pulse, the conversion efficiency from the laser energy to the protons is enhanced by 3 orders of magnitude with effective improvement of the beam collimation by properly defocusing the laser pulses. The depression of the prepulse effect on the proton acceleration is believed to be one of the main reasons for the significant optimization. Besides, the particle-in-cell (PIC) simulation results indicate that the population of moderate energy electrons increases under large focal offsets, which in turn effectively improves the acceleration electric field and the beam quality.
2011, 60 (4): 045205.
doi: 10.7498/aps.60.045205
Abstract +
A fluid model has been used to study the Bohm criterion of the plasma sheath with different species. The charge particle includes electrons, ions, negative ions and secondary electrons from the wall striked by the electrons. Numerical calculation results are obtained through quasi-Newton method. It is found that secondary electron emission(SEE) can increase the critical ion Mach number of the plasma sheath. The critical ion Mach number decreases with the increase of the temperature of the electrons emitted. Negative ions reduce this critical number. In addition, it is obvious that the SEE affects the ion Mach number when the density of negative ions is small, but the ion Mach number is mainly affected by negative ions when the density of negative ions is high in the presence of secondary electron emission and negative ions.
2011, 60 (4): 045206.
doi: 10.7498/aps.60.045206
Abstract +
We quantitatively analyze the content of element Cr in the national standard soil samples by the method of plasma atomic emission spectroscopy, through using Nd:YAG (Wavelength:1064 nm) laser as an excitation source to induce soil plasma in ambient environment of the laboratory. The calibration curve of element Cr is measured by studying the characteristics of laser-induced breakdown spectroscopy of element Cr in soil under optimal conditions. The experimental results demonstrate that the element content (60—400)×10-6 and the spectral line intensity are in good linear relation, and the relative standard deviation of element analysis of concentration measurement from the standard value is 7.89%. The relative deviation of the quantitative analytic result from the standard value is 5.3%, and the detection limit of Cr in soil is 16.3×10-6. The relative deviation by the internal standard method is 2.7%, which indicates that the internal standard method can improve the accuracy of the measurement. Using the same type of soil to achieve the calibration curves, the relative deviation by the quantitative analysis is 8%.
2011, 60 (4): 045207.
doi: 10.7498/aps.60.045207
Abstract +
In this paper, the performance of shock ignition with varying ignitor is analyzed theoretically and simulated numerically. First, based on the formation and the collision of shock waves, effects of ignitor pulse on shock ignition are investigated theoretically. Then simulations are performed using a variety of ignitor pulses, determined by their peak powers, pulse widths and rise times, and the ignition window is employed as an evaluation criterion of the shock ignition performance. The obtained results show that the peak power of ignitor pulse is one of the key factors to successfully ignite the core, and the ignitor pulse must be wide enough to provide sufficient ignition energy, however, as the rise time of ignitor is not so long(~ns), it will not degrade the performance of shock ignition significantly.
2011, 60 (4): 045208.
doi: 10.7498/aps.60.045208
Abstract +
Dynamics of double tungsten-wire array and dynamic hohlraum are investigated on the Angara-5 facility. X-ray power and hohlraum temperature are obtained to be as high as 5.6 TW and 63 eV respectively. Main experimental results together with the design idea are also given in this paper.
2011, 60 (4): 045209.
doi: 10.7498/aps.60.045209
Abstract +
In this study, molecular dynamics simulation method is used to investigate the interactions of Cl continuously bombarding a crystalline Si (100) surface in an incident energy range of 0.3—10 eV.The surface temperature is set to be 300 K for all the incident energies. The improved Tersoff-Brenner type potential is employed.The simulation results show that a Cl-rich reaction layer is formed on the surface due to Cl continuously bombarding. The SiCl group is the predominant species in the reaction layer.The thickness of the reaction layer increases with incident energy. The etching ratio increases with incident energy increasing. The main etching product is SiCl4 when the incident energies are 0.3, 1 and 5 eV, but it is SiClx(x<4) when the incident enery is 10 eV.With the incident energy increasing, the main etching mechanism changes from chemical etching to physical etching.
2011, 60 (4): 045210.
doi: 10.7498/aps.60.045210
Abstract +
The X-ray spectrum of radiatively heated tracer Al in the doped foam was recorded by using a flat crystal spectrometer. The radiation thermal bath with a peak temperature of 150 eV is created inside the hohlraum irradiated by 8 laser beams, each delivering 250J. From the measured spectrum, we have observed that the intensities of jkl Li-like satellite were smaller than those of qr Li-like satellites, which is not a case usually encountered in electron collision dominated low density plasmas. The analyses of various generation and loss channels of doubly excited states indicate that in the radiatively heated plasma considered in the present work, the photo excitation and the photo ionization processes are fully responsible for the generation of doubly excited states instead of dielectronic recombination. Besides the satellite features, intercombination lines are also observed which imply the existence of a low density plasma region. Finally, we compare the calculated spectrum with the measured spectrum, and find that they are in fairly good agreement was achiered.
2011, 60 (4): 045211.
doi: 10.7498/aps.60.045211
Abstract +
Time-integrated X-ray continuum spectra measured with spherical bent quartz crystal and CCD in aluminum wire array Z-pinches, provide electron temperature by fitting the continuum slope. More data obtained for fitting and markedly reduced influence of line radiation by removing the data superimposed with line spectra, make the temperature in hot core region of plasma more reliable. In experiment of shot No. 09076, the core temperature is around 250 eV, ranging from 241 eV to 258 eV at a 95% confidence level.
2011, 60 (4): 045212.
doi: 10.7498/aps.60.045212
Abstract +
High dynamic range and large format technique of micro-chanunel plate (MCP), gated framing camera is developed to diagnose high-power laser-plasma X-ray emission spectra. The single frame format is 13 mm×36 mm, and exposure time is adjustable from 0.5 ns to 5 ns. Its spectral response in 1.0—10 keV is more flat than that of X-ray charge-coupled device (CCD), and there exists no energetic enhancement effect. Performance evaluation has been conducted on high power laser devices, and the results show that the system has a high signal-to-noise ratio and the dynamic range is greater than 3 × 103. The system has been applied successfully to inertial confinement fusion (ICF) physics experiment.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2011, 60 (4): 046101.
doi: 10.7498/aps.60.046101
Abstract +
In order to obtain holographic polymer dispersed liquid crystal( HPDLC) grating with high diffraction efficiency and low threshold, the effect of parallel rubbing alignment on electro-optical properties of HPDLC grating is investigated. According to the theoretical analysis, the improvement of phase separation structure and the lower order difference of the liquid crystal droplets are essential for perfect electro-optical properties of the grating. The phase separation is significantly improved due to the diffusion match between monomers and liquid crystals in the case of parallel alignment treatment. So the diffraction capability is enhanced while the driven voltage is reduced obviously. Moreover, the order difference of liquid crystal droplets is reduced because of the uniform liquid crystal alignments and consequently the scattering loss is reduced greatly. Experimental results indicate that the diffraction efficiency of grating with rubbing alignment increases from 75.6% (traditional HPDLC grating) to 98.1% and the driving voltage is lowered from 9.2 V/μm to 4.8 V/μm. And also, only in the case of certain surface rubbing strength, the HPDLC with high diffraction efficiency and low threshold will be realized.
2011, 60 (4): 046102.
doi: 10.7498/aps.60.046102
Abstract +
The effects of ellipse shape, polarization direction of incident light, shell thickness, and dielectric constants of core and embedding medium on the localized surface plasmon resonance (LSPR) of elliptical gold nanotube have been investigated by the Finite Difference Time Domain (FDTD) method. When the semimajor axis is fixed, it is found that with the increase of the semiminor axis of the ellipse the extinction peak of the gold nanotube has a red-shift. With the increase of the angle between the incident polarization and the semimajor axis, the extinction peak has a red-shift. With the shell thickness decreasing, the extinction peak of gold nanotube also has a red-shift. Furthermore, we also find that the increase of the dielectric constant for core or embedding medium will induce a red-shift of LSPR in gold nanotube. The change of the extinction peak is ascribed to the plasmon hybridization and the competition between the variations of conduction and oscillation electrons.
2011, 60 (4): 046103.
doi: 10.7498/aps.60.046103
Abstract +
A new rigid-body refinement method for protein crystal structures is described. It is based on "Variable Metric Methods in Multidimensions" and "the Electron Density Map Correlation Coefficient". Test shows that the orientation and translation of the initial models can be improved effectively by this new method. And it can escape from the local extremum and reach the global optimum more easily than the maximum likelihood method when the search space has a large number of local extremum points.
2011, 60 (4): 046104.
doi: 10.7498/aps.60.046104
Abstract +
The effect of temperature on motion of misfit dislocation in the γ/γ' interface of a Ni-based superalloy is studied in periodic simulation cells subjected to an applied shear stress. The simulation results show that no matter what temperature is, the motion of misfit dislocation occurs through the nucleation and the propagation of the double kink; at low temperature, the interaction of the misfit dislocation facilitates the motion of the misfit dislocation; on the contrary, at higher temperature, it can obstruct the motion of the misfit dislocation, and improves the mechanical properties of nickel-base superalloys.
2011, 60 (4): 046105.
doi: 10.7498/aps.60.046105
Abstract +
Radiation displacement effect is studied using shell model molecular dynamics simulations. Using oxygen atom as a primary knock-on atom, the creation and the evolution of various defects in the system corresponding to the primary knock-on atom(PKA) energy of 1 keV are studied. The results show that a largest number of defects are created when the incidence is along the [001]direction. Among all the defect species, oxygen atom defects are dominant, and its concentration reaches 80%. The creation of defects does not change the spontaneous polarization of the system significantly, and the polarization reversal also changes little. Defect migration is observed under an applied electric field.
2011, 60 (4): 046106.
doi: 10.7498/aps.60.046106
Abstract +
This paper deals with the effect of doping concentration in p+ deep well on charge sharing in 90nm dual well CMOS technology. TCAD simulation results show doping concentration in p+ deep well has a more significant effect on charge sharing in PMOS tube than in NMOS tube. By increasing doping concentration of p+ deep well appropriately, the charge sharing in PMOS can be restrained effectively, which is useful for reinforcing the charge sharing.
2011, 60 (4): 046201.
doi: 10.7498/aps.60.046201
Abstract +
Shock loading-release is performed on the porous aluminum with micropore and porosity m=1.04. Time-resolved interfacial velocity between the porous aluminum and LiF window is measured with diatance interferometer system for any reflector (DISAR) under five pressures ranging from 53 GPa to 99 GPa . From the interfacial velocity, the Euler longitudinal sound velocities under five pressures and the bulk sound velocities under 53 GPa, 72 GPa and 91 GPa are obtained. The melting pressure of the material is about 81 GPa. The poisson ratio before shock melting is about 0.37. From the analysis, the existence of the micropore in the material reduces the the shock melting obviously. So, its induced anharmonic effect cannot be neglected. Considering anharmonic effect into the equation of state, the anharmonic parameter is calculated to be about 30.
2011, 60 (4): 046202.
doi: 10.7498/aps.60.046202
Abstract +
Double-bubble ultrasonic cavitation dynamic differential equation obtained from superposition principle is normalized. MATLAB is used to analyse the effects of bubble linearity, double-bubble distance, sound frequency, sound pressure amplitude on cavitation process. Bifrequency ultrasound is introduced into the equation under discussion in this article. The calculation results show that bubble linearity is a main factor, which determines cavitation characteristics. The effect of sound pressure is strongest, and the frequency effect is the next strongest. Double bubble interactions affect cavitation characteristics to a certain extent, which reduces with distance increasing. Bifrequency ultrasound has a limited effect on cavitation characteristics, and it turns biggest when two component pressure amplitudes are equal.
2011, 60 (4): 046301.
doi: 10.7498/aps.60.046301
Abstract +
We have calculated the electronic structure of ZnVSe2 by the method of first-principles plane wave pseudopotential (PWP) with density functional theory (DFT) combined with generalized gradient approximation (GGA), such as spin polarized energy band structure, density of states, Mulliken population, magnetic moments and so on. The calculation results show that ternary compound ZnVSe2 is a half-metallic ferromagnet that shows significant ferromagnetism, its half-metallic energy band gap reaches 0.443 eV. The electron spin polarization is as high as almost 100%, and therefore, ZnVSe2 may be a useful material for spintronics.
2011, 60 (4): 046401.
doi: 10.7498/aps.60.046401
Abstract +
This paper provides an investigation of the phase transition and the spalling characteristics induced during shock loading and unloading in an α phase Fe-based alloy. Two kinds of impact set-ups are used. One is referred to as the direct impact, and the other is the reverse impact. The shock Hugoniot and the release stress-volume adiabat of the α phase Fe-based alloy are obtained. And the results show that the history of loading and unloading is determined by the relationship among the phase transition threshold and the reverse transition threshold and the shock pressure. It is found that abnormal spallations happen in the α phase Fe-based alloy sample as the pressure exceeds the phase transition threshold. Such abnormal spalling phenomena are believed to be related to the shocked α→ε phase transition, and a possible reason for the abnormal spalling is discussed also from the interaction process of stress wave.
2011, 60 (4): 046601.
doi: 10.7498/aps.60.046601
Abstract +
The method of crucible rotating oscillation damping was employed to measure the kinematic viscosity of magnesium melt and the curve of viscosity v versus temperature T from 935 K to 1190 K was obtained. It is exponential increase (decrease) law of viscosity with the temperature during heating and cooling process; Besides, based on the physical model for evolution behavior of atomic cluster in liquid structure, the main structural information of magnesium melt in this temperature interval — the curve of size d of atomic cluster versus temperature T was obtained; By analyzing the experimental and calculated data, it is found that both kinematic viscosity and size of atomic cluster of magnesium melt are monodrome function of the temperature and the relation between them is linear function, i.e., v=v0 + K·d(T). This relation reveals the change characteristic of viscosity for magnesium melt microstructure, which presents a new way for calculating kinematic viscosity of metal melt and understanding the micro-nature deeply.
2011, 60 (4): 046602.
doi: 10.7498/aps.60.046602
Abstract +
Based on dual supply and dual threshold voltages technique, a novel methodology optimizing global interconnect performance in presented in this paper. The new figure of merit (FOM) is first defined as a function of bandwidth, delay and power consumption of global interconnect. Then, the optimal dual voltages can be obtained to save interconnect power by maximizing FOM function within a given delay penalty. Simulations show that in 65 nm technology, for the allowed delay penalties of 5%, 10% and 20%, the proposed methodology saves 27.8%, 40.3% and 56.9% power compared with the case with single supply and single threshold voltages, respectively. It can also be found that more power savings are achieved with the technology improving. The proposed methodology can be used to design and optimize global interconnects.
2011, 60 (4): 046603.
doi: 10.7498/aps.60.046603
Abstract +
We perform the first-principles study of the structural properties and the high temperature phase stabilization of Cr, W-doped β-La2Mo2O9. We find that Cr prefers the site with four coordination numbers and W atom preferentially occupies the site with five coordination numbers. The nonlinear dependence of cell parameter on W content in W-doped systems results from the nonlinear change in Mo(W)-O and La-O bond lengths with W content and the decrease of coordination number around W occupied site. The decrease of cohesive energy with the W-doped concentration is conducive to the understanding of the stabilization of the β-La2Mo2-xWxO9 at lower temperature. The appearance of stronger W-O bond leads to the increase of the energy barrier of oxygen-ion concerted motion in W-dopedβ-La2Mo2O9.
2011, 60 (4): 046604.
doi: 10.7498/aps.60.046604
Abstract +
Based on the theory for random-walk with an absorption wall, the characteristics of thermal release of helium in materials are studied. The influences of the initial depth distribution and the diffusion coefficient of helium in materials on the thermal release are investigated. A comparison is made between the thermal releases induced by the random-walk mechanisms and the thermal desorption mechanisms. It is pointed out that the initial depth distribution and the states that Helium atoms stay in are required for the correct understanding of experimental observations of thermal releases of helium in materials.
2011, 60 (4): 046801.
doi: 10.7498/aps.60.046801
Abstract +
La0.67Ca0.33MnO3(001) thin films have been grown with pulsed laser deposition method, and the surface structures and electronic states have been characterized using scanning tunneling microscopy/spectroscopy (STM/STS). In the Mn-O terminated surface, insulating ( 2 × 2 )R45° reconstruction surface and metallic (1×1) reconstruction surface are observed. In the (La,Ca)-O terminated surface, the surface presents the stripe structure. The results obtained from the variable temperature STM/STS show that the ( 2 × 2 )R45° reconstructed surface persists in insulating phase in a temperature range of 144—300 K, which may shield the signal of possible insulator-metal transition occurred in bulk in STS measurements.
2011, 60 (4): 046802.
doi: 10.7498/aps.60.046802
Abstract +
Tetrahedral amorphous carbon (ta-C) films are deposited on single crystalline silicon with filtered cathodic vacuum arc by changing the magnetic filtering coil current from 5 A to 13 A. Visible Raman measurements show that the content of the sp3 hybridization decreases with magnetic filtering coil current increasing, and it deereased down to a minimum value as the coil currew increases up to 13 A. The surface morphology is investigated by atomic force microscope (AFM), and the surface roughness (RMS) of the film increases with the current of magnetic filtering coil increasing from 0.13 to 0.38, The friction test indicates that the minimum of friction coefficient is about 0.08 when the magnetic filtering coil current is 5 A. The friction coefficient increases when the magnetic filtering coil current is 7A. But the friction coefficient decreases again down to 0.1 with magnetic filtering coil current inereasing from 7 A to 13 A.
2011, 60 (4): 046803.
doi: 10.7498/aps.60.046803
Abstract +
The discrete metallic-pole-planar slow wave structure (SWS) is introduced in this paper, and the high frequency characteristics are studied. And procedures based on three-dimensional finite-difference time-domain (3-D FDTD) arithmetic are used to calculate the dispersive characteristics of the new SWS, and HFSS simulation software is used to analyze the coupling impedance. Results show the high frequency characteristics of the pole structure not only have a general similarity in comparison with these of the grating, but also have itself advantages. For the electrons moving between multiple poles of the structure, the interaction impedances are symmetry; relatively thick electron beams can efficiently interact with the high-frequency field while it used as the high frequency system of vacuum electronic devices. This kind of SWS is promising to lower the starting current density and have better efficiency than the traditional grating SWS. According to the results, a sub-millimeter radiation source driven by the multiple beams can be designed at a low operating current density.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2011, 60 (4): 047101.
doi: 10.7498/aps.60.047101
Abstract +
This paper expresses the experiential relationship between Fermi level and the density of two-dimensional electron gas, based on the capacitance voltage (C-V) characteristics of the AlGaN/AlN/GaN high electron mobility transistor (HEMT) on sapphire substrate. The expression provides important references for establishing the device charge control model and simpliying the transconductance and capacitance. Parameter α is introduced for describing the ability for the two-dimensional potential well to restrict electrons, and we believe that the smaller the value of α, the stronger the restricting ability is. A coherent fitting effect, compared with the measurement, is obtained by making use of the experiential relationship said above.
2011, 60 (4): 047102.
doi: 10.7498/aps.60.047102
Abstract +
Based on the π-electron tight-binding model, for zigzag graphene nanoribbons(ZGNRs) the influence of boundary structure on band structure, specially the electrons of the valence band and the conductor band near the Fermi level, are studied in detail. We investigate the band structures and the distributions of electrons of different atoms in a unit cell of the valence band near the Fermi level of ZGNRs with seven reasonable boundary structures. We find NN-ZGNRs with no dangling atoms on both edges, DN-ZGNRs with dangling atoms only on one edge, SPP-ZGNRs and ASPP-ZGNRs each with pentagons on both two edges and being metallic, DD-ZGNRs with dangling atoms on both two edges, PN-ZGNRs each with a defective structure of pentagons on one edge and no dangling atoms on the other edge, PD-ZGNRs with a pentagon on one edge and dangling atoms on the other edge being semiconducting, and the energy gap being inversely proportional to the width of nanoribbons. But for DD-ZGNRs and PD-ZGNRs, the energy gaps quickly reduce to zero with the increase of width; for PN-ZGNRs, the energy gaps decrease exponentially to a limited value of 0.154 eV. It is found that different boundary structures have different effects on the distribution of electrons in the valence band near the Fermi level. And the probability for electrons staying in the atoms on two edges of nanoribbons is relatively large.
2011, 60 (4): 047103.
doi: 10.7498/aps.60.047103
Abstract +
By using the first-principles plane-wave pseudopotential method based on the density functional theory, substitution behavior and alloying effect of Nb in Ni3Al are studied. The analyses of the formation enthalpies,the cohesive energies and the densities of states of systems with different substitution behaviors show that Nb prefers to occupy the Al site. The site preference is determined primarily by the electronic structure, and the calculated result is in good agreement with the experimental result. In order to further study the site preference, the occupied sites are divided into being of relaxed distribution and unrelaxed distribution, which are two different distributions. The calculations of total energy, the formation enthalpy, the cohesive energy and the density of states of system indicate that Nb has a preference for unrelaxed distribution. In order to study the alloying effect of Nb in Ni3Al, the calculations of cohesive energy, density of states of system and electronic charge density indicate that Nb in Ni3Al could increase the stability of the alloy. The study also indicates that the limited solubility of Nb in Ni3Al lie between6.25at % and 12.5at %.
2011, 60 (4): 047104.
doi: 10.7498/aps.60.047104
Abstract +
We optimize the geometric structure and calculate total densities of states, band structures, the relative number of electrons and mobility ratios of electrons of ZnO mode established at different concentrations of Al, in the condition of high concentration of Al heavily doped ZnO semiconductor at low temperature, by adopting the ab-initio study of plane wave ultra-soft pseudo potential technique based on the density function theory (DFT). It is found that the relative number of electrons increases, but the mobility ratio of electrons of ZnO decreases, with the concentration of Al increasing. On the contrary, the lower the Al doping concentration, the stronger the conductivity of ZnOis. The conductivity is compared. We can draw a conclusion that the conductivity of ZnO semiconductor decreases with Al doping concentration increasing. The calculation results are consistent with the change trend of experiments with Al concentrations exceeding o.z, i.e., x≥0.02.
2011, 60 (4): 047105.
doi: 10.7498/aps.60.047105
Abstract +
We use the density functional theory B3LYP/6-31G(d) to study the graphene quantum dots with zigzag edges. The result shows that the ground states of different size graphene quantum dots are all ferromagnetic spin-triplet states. The magnetic properties orignate both from the boundary carbon atom occuping protruding position, and from the carbon atom with unpaired electron. On the whole, the energy gap of other structures decreases with the increase of the number of benzene rings as excepted for the structure of 6b, and the system energy gap decreases significantly by the added charges. In addition, using time-dependent density functional theory (TD-DFT), the excited states of the triangular structure composed of six carbon rings which have an energy gap is 3.83 eV are calculated, and the results show that the 17th excited state has the greatest excitation strength, the excitation energy is 3.93 eV, corresponding to a wavelength of 315.8 nm, close to experimental result.
2011, 60 (4): 047106.
doi: 10.7498/aps.60.047106
Abstract +
There has been aroused a lot of interest in the strained Si technology in the microelectronic field. Density of states (DOS) is an important physical parameter in strained Si materials. Based on the Kleinerts Variational perturbation (KP) theory related to stress, DOSs of electrons and holes near the bottom of conduction band and the top of valence band are obtained in tetragonal, rhombohedral and monoclinic strained Si grown from (001), (101) and (111) substrates respectively. It is found that their DOSs are obviously different from the ones of cubic unstrained Si, except DOSs of electrons near the bottom of conduction band in rhombohedral and monoclinic strained Si. The quantized model obtained can provide valuable references for understanding the strained Si material physics and developing the theoretical model of the other important physical parameters.
2011, 60 (4): 047107.
doi: 10.7498/aps.60.047107
Abstract +
Electronic structure and magnetic properties of Post-perovskite CaRhO3 have been studied by density functional theory calculations through using the projected augmented wave method. The Generalized-gradient approximation (GGA) calculations indicate a half-metallic ferromagnetic ground state and a low-spin configuration of Rh4+ ion with a magnetic moment of 0.57μB. While the experimental insulating antiferromagnetic ground state can be obtained only by GGA plus on-site Coulomb interaction U(GGA+U) calculations, which indicates the crucial role of corelation effect of 4d electron for the Post-perovskite CaRhO3.
2011, 60 (4): 047108.
doi: 10.7498/aps.60.047108
Abstract +
Compared with the experiment results,the atomic moment of Co50Fe25-xMnxSi25 dependending on composition and half-metalic of these alloys have been investigated by GGA + U method. It has been found that with the increase of Mn content, Co50Fe25-xMnxSi25 alloys always maintain a high ordered L21 structure and the total moment of these alloys decrease linearly which is mainly attribute to the reduction of Co atomic moment. It has also been found that with the increase of Mn content,Co50Fe25-xMnxSi25 alloys maintain 100% spin polarization and Fermi level move from the edge of the energy gap to the middle of the energy gap while the gap-width has changed.
2011, 60 (4): 047109.
doi: 10.7498/aps.60.047109
Abstract +
A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the dehydrogenation properties and the influence mechanism of Li4BN3H10 hydrogen storage materials. The binding energy, the density of states and the Mulliken overlap population are calculated. The results show that the binding energy of crystal has no direct correlation with the dehydrogenation ability of (LiM)4BN3H10(M=Ni,Ti,Al,Mg). The width of band gap and the energy level of impurity are key factors to affect the dehydrogenation properties of (LiM)4BN3H10 hydrogen storage materials: the wider the energy gap is, the more strongly the electron is bound to the bond, the more difficultly the bond breaks, and the higher wile the dehydrogenation temperature be. Alloying introduces the impurity energy level in band gap, which leads the Fermi level to enter into the conduction band and the bond to be weakened, thereby resulting in the improvement of the dehydrogenation properties of Li4BN3H10. It is found from the charge population analysis that the bond strengths of N—H and B—H are weakened by alloying, which improves the dehydrogenation properties of Li4BN3H10.
2011, 60 (4): 047110.
doi: 10.7498/aps.60.047110
Abstract +
Using the first-principles density functional theory, we calculate the crystal structures, magnetisms and electronic structures of Sb-containing half-Heusler alloys XYSb(X=Ni, Pd, Pt; Y=Mn, Cr). The calculation results show that alloy NiMnSb is half-metal and the others are metals at equilibrium lattice constant. The contribution of the spin magnetic moment of Y element to the total moment is largest for all alloys. It is found that the Fermi level of the minority spin band shifts closer to the bottom of spin-down conduction band with atomic number of X element reducing. The Fermi level moves up due to the compressive strain, away from p bands of Sb atom. Under the compresive stress, PtMnSb, PdMnSb and NiCrSb can induce metal half-metal transitions.
2011, 60 (4): 047201.
doi: 10.7498/aps.60.047201
Abstract +
Time-resolved linearly polarized pump-probe spectroscopy is used to investigate carrier relaxation dynamics in instrinsic GaAs. Absorption saturation and absorption enhancement are observed. It is found that the absorption saturation can be observed obviously when the photon energy is smaller than 1.549eV, otherwise, the absorption enhancement can be observed at a carrier density of 2×1017 cm-3. When the carrier density is above 7×1016 cm-3, the absorption enhancement increases rather than decreases with delay time. The simulation results with consideration of the competition between band filling effect and band-gap renormalization effect are in good agreement with our experimental results. With the band filling effect and band-gap renormalization effect considered, we develop a new analytical model to retrieve the carrier lifetime.
2011, 60 (4): 047202.
doi: 10.7498/aps.60.047202
Abstract +
Based on the mechanism of ionization radiation damage in optoelectronic coupled devices (OCDs), the characteristic models of current transmitting rate (CTR) and 1/f noise are established. The results show that CTR degradation and noise increase are due to the increase of SiO2/Si interface defects at the collector junction and emit junction in phototransistor. The relationship between CTR degradation and noise change is established by the radiation dose. The correctnesses of characteristic models are validated in experiment. By the relationship between noise change and radiation dose, the high-dose radiation degradation can be predicted through the low-dose irradiation experiment. So noise can be used to evaluate the radiation tolerance of OCDs.
2011, 60 (4): 047301.
doi: 10.7498/aps.60.047301
Abstract +
We have performed density-functional theory calculations of the atomic structure and the oxygen adsorption properties of Au(110) surfaces. The relaxations of missing-row reconstructed Au(110)-(1×2) surface are calculated to be -15.0%(Δd12/d0) and -1.1%(Δd23/d0). The relevant surface energy and workfunction are calculated to be 52.7 meV/2 and 5.00 eV, respectively. In the case of missing-row reconstructed Au(110)-(1×3) surface the surface atomic relaxations are calculated to be -20.5 %(Δd12/d0) and +2.7 %(Δd23/d0) which are quite differente from those of Au(110)-(1×2). However, in the later case, the surface energy and workfunction are found to be very close to those of missing-row reconstructed Au(110)-(1×2) surface, i.e., 53.4 meV/2 and 4.98 eV. We have simulated the scanning tunneling microscope (STM) images of both reconstructed surfaces and found that the missing row exhibits a remarkable hollow in the STM morphology. The further calculation of oxygen adsorption on both surfaces reveals that the adsorption energies in these cases are negative. These results indicate that the Au(110) surface is free from oxygen adsorption and reaction, showing highly chemical inertia.
EDITOR'S SUGGESTION
2011, 60 (4): 047302.
doi: 10.7498/aps.60.047302
Abstract +
The epitaxial graphene (EG) layers are grown on Si-terminated 6H-SiC (0001) substrates and C-terminated 6H-SiC (000 1 - ) substrates separately by thermal annealing in an ultrahigh vacuum chamber. Low energy electron diffraction(LEED) and synchrotron radiation photoelectron spectroscopy(SRPES) are used to in-situ study the synthesis process, and the prepared samples are characterized by Raman spectrum, and near edge X-ray absorption fine structure(XANEX). The results show that we have successfully prepared high-quality EG layers on the two polar surfaces of 6H-SiC. The comparisons studies indicate that Si terminated EG is highly oriented while C terminated EG is anisotropic, and that the interface interaction similar to that of C-sp3 bond of diamond exists on the Si terminated EG, the interaction between the epitaxial film and substrate is stronger, while on the C terminated EG there is no such interaction, and the interaction between the epitaxial film and substrate is weaker.
2011, 60 (4): 047303.
doi: 10.7498/aps.60.047303
Abstract +
By combining merits of both SJ structure and SiGe material, a novel super junction (SJ) SiGe power diode is presented. The two important characteristics of SJ SiGe diode are its columnar structure of alternating p/n pillars substituting n- base region of conventional Si p+n-n+ diode and its far thinner strained SiGe p+ layer, which can overcome the drawbacks of conventional Si power switching diodes, such as when the reverse blocking voltage is higher, the forward voltage drop is larger and the reverse recovery time becomes longer. For the SJ SiGe diode with 20% Ge content, the following conclusions can be obtained compared with comparable conventional Si power diodes: the breakdown voltages increase by 1.6 times, the forward voltage drop is reduced by 60 mV (at a current density of 10 A/cm2) and the softness factor S increases by 2 times. Though the reverse recovery time is shortened slightly, the peak reverse current density decreases by 17% and the soft recovery characteristics is improved notedly. The key parameters of the p and n pillar widths have imporant effects on the forward conduction characteristic, reverse blocking characteristic and reverse recovery characteristic of SJ SiGe power diode. The smaller the pillar width becomes, the higher the breakdown voltage is and the lower the reverse leakage current is, whereas the forward voltage drop increases slightly. The pillar width has no obviously monotonic effect on the reverse recovery characteristic. If the width is too small, the soft reverse recovery characteristic is degenerated. To optimize the parameter of pillar width, we can obtain excellent SJ SiGe diode with fast recovery speed, high breakdown voltage and low forward drop at the same time.
2011, 60 (4): 047304.
doi: 10.7498/aps.60.047304
Abstract +
Molecular nano-junction is modeled by 'metal/single molecule/metal’ structure. With the generalized master equation method, the inelastic current induced by the sequential charge transmission through the junction is studied under the excitation of infrared fields in the case of weak lead-molecule coupling.The interaction between infrared field and molecule is described with the models of exponential coupling, square coupling, and linear coupling respectively. In the excitation of varieties of infrared fields, the inelastic current-voltage characteristics and the effects of intramolecular vibrational energy redistribution are discussed.
2011, 60 (4): 047401.
doi: 10.7498/aps.60.047401
Abstract +
Top seeded infiltration and growth method (TSIG) is improved by adopting a new liquid source and novel configuration. And single-domain Gd-Ba-Cu-O (GdBCO) bulk superconductors are successfully prepared using the improved method. Experimental observations on the morphology and the microstructure show that the samples exhibit good texture and homogeneous distribution of fine Gd2BaCuO5 (Gd-211) inclusions. Superconductive measurements reveal that the sample exhibits high superconducting transition temperature, self-field critical current density, and strong levitation force. In addition, the improved method can be used to simplify the process flow, shorten the experimental cycle, and hance the stability of the process, thus reducing the experimental difficulties. The results lay a good foundation for the batch production of large single domain bulks.
2011, 60 (4): 047501.
doi: 10.7498/aps.60.047501
Abstract +
Nano-structure CoxFe3-xO4 porous microspheres are synthesized in ethylene glycol (EG) solution, using FeCl3·6H2O, CoCl2·6H2O and NH4Ac as the starting materials through solvothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to characterize the structures of synthesized products. The results show that monodisperse CoxFe3-xO4porous microspheres with polycrystal structures are assembled by nanoparticles, and the average diameters is about 300 nm. The magnetic properties are evaluated with a vibrating sample magnetometer (VSM). The results indicate that the saturation magnetization ( Ms) and the Curie temperature (Tc) first increase and then decrease, and the coercivity (Hc) increase with the increase of Co2+ content. According to the hysteresis loops at different temperatures, CoxFe3-xO4 porous microspheres possess remarkable exchange bias effects at low temperatures.
2011, 60 (4): 047502.
doi: 10.7498/aps.60.047502
Abstract +
The electronic and the magnetic properties of Fe single-layered atomic shees separately with two-dimensional square and hexagonal structures are calculated by the first-principles method based on the spin-polarized density functional theory. The calculations show that planar square and hexagonal as well as the bcc structures manifest their magnetisms at their equilibrium lattice constants. The magnetic moments for these structures are 2.65, 2.54 and 2.20μВ, respectively. The calculated magnetic properties for the elongated and the compressed bond lengths suggest that when the bond is stretched to a length larger than 4.40, the bond should be broken and the magnetic moments of the systems reach the magnetic moment of an independent Fe atom, 4μВ. When the bond lengths are reduced, the magnetic moments of all the systems studied decrease correspondingly. At the critical bond lengths (1.80 for planar square lattice, and 1.75 for hexagonal lattice), the magnetisms of the two planar lattices disappear. Using the Stoner theory, the change from magnetism to non-magnetism for the lattice compression is elucidated.
2011, 60 (4): 047801.
doi: 10.7498/aps.60.047801
Abstract +
To improve thermal capability of repetitive-rate laser,in this paper bonded Yb ∶YAG slices are chosen as gain medium, the doping-concentration in gain medium in chosen to be distributed in gradient manner. The distributions of stored energy, temperature and stress are obtained by calculating pumping process inside gain medium. From among the obtained results optimal parameters are chosen for an optimized design. The calculation indicate that using grad-doping medium can reduce temperature, deform, stress and wave aberration. In this paper, the feasibility of improving thermal-management by using grad-doping medium is demonstrated theoretically.
2011, 60 (4): 047802.
doi: 10.7498/aps.60.047802
Abstract +
The volume absorptions and the interface absorptions of SiO2 and HfO2 single layers are studied using the thermal lens method. Based on the fact that electric field distributions in single layers are different when the films are illuminated from the coating side and substrate side, an equation is given to calculate volume and interface absorptions of single layers. Half wave HfO2 and SiO2 single layers are prepared by electron beam evaporation method. With the absorption data measured by thermal lens technique, we separate the volume absoption from the interface absorption for these two single layers. The results show that interface absorption is non negligible when the absorption of film approaches to a ppm level. Additionally, the HfO2 single layer shows bigger volume and interface absorptions than SiO2 single layer.
2011, 60 (4): 047803.
doi: 10.7498/aps.60.047803
Abstract +
Optical properties, stress and microstructure of Nb2O5 thin films prepared by ion beam sputtering (IBS) are investigated, and the effects of assist ion beam energy and ion current on characteristics of Nb2O5 thin films are systematically discussed. The results show that with different parameters of assisted ion source, the refractive index changes from 2.310 to 2.276 and residual stress varies from -281MPa to -152 MPa. The extinction coefficient of Nb2O5 can be under 10-4, and the surface is very smooth in an optimum deposition condition. Thin films deposited by IBS exhibit better optical properties and microstructures than those deposited by ion assisted deposition (IAD).
2011, 60 (4): 047804.
doi: 10.7498/aps.60.047804
Abstract +
Two green emitting phosphors, Ba3Tb(BO3)3 and Ba3Tb(BO3)3 ∶Ce3+, are synthesized by the high temperature solid-state method, and their luminescent characteristics are investigated. Ba3Tb(BO3)3 phosphor shows several emission peaks located at 439, 493, 547, 589 and 629 nm separately. The emission peaks correspond to the 5D3→7F4 and 5D4→7FJ=6. 5, 4, 3 transitions of Tb3+, respectively, and the maximal peak is 547 nm. For the 547 nm emission, the excitation spectrum consists of several bands, and the maximal peak is located at 380 nm. The Ce3+-activated Ba3Tb(BO3)3 phosphor is studied, and the result shows that the emission spectrum distribution of Ba3Tb(BO3)3 ∶Ce3+ is the same as that of Ba3Tb(BO3)3 phosphor, however, its emission intensity is higher than that of Ba3Tb(BO3)3,which is attributed to the sensitizing action of Ce3+ on Tb3+ in Ba3Tb(BO3)3. For the 547 nm emission, the excitation spectrum of Ba3Tb(BO3)3 ∶Ce3+presents a broad band, differing from that of Ba3Tb(BO3)3 phosphor. The effect of H3BO3 on the emission intensity of Ba3Tb(BO3)3 ∶Ce3+ phosphor is investigated, and the results show that the emission intensity can reach a maximum for 15 wt% excessive H3BO3. All the results show that Ba3Tb(BO3)3 ∶Ce3+ is a green emitting phosphor for white LED.
2011, 60 (4): 047805.
doi: 10.7498/aps.60.047805
Abstract +
We report on the magnetic field (up to 53 T) dependence of photoluminescence (PL) spectra occurring as a spacially direct optical transition of the ZnSe layer in undoped ZnSe/BeTe/ZnSe type-II quantum structures at a low temperature (4.2 K). With magnetic field increasing, the PL intensity (IX) of exciton (X) shows an oscillation feature opposite to the PL intensity (IX－) of charged exciton (X－). As IX- increases, IX decreases, but as IX－ decreases, IX increases. In all fields, the oscillation behaviour shows a periodic change approximately with magnetic field interval. The results are attributed to the periodic resonance of the Fermi level with the Landau level, which results in the modulation of the density of states of the 2DEG system at the Fermi energy.
EDITOR'S SUGGESTION
2011, 60 (4): 047806.
doi: 10.7498/aps.60.047806
Abstract +
In this paper we report on a new kind of tri-color luminescence glass which can be excited efficiently by long-wavelength ultraviolet. These samples are prepared by melting silicon-borate raw material co-doped with Ce3+/Mn2+, Ce3+/Tb3+ and Eu2+, respectively. Among these doped ions, Mn2+, Tb3+ and Eu2+ are activators and Ce3+ is sensibilizer. Because the sencibilzer can provide energy for activator so the intense tri-color luminescence can be obtained by long-wavelength ultraviolet excitation. At the same time, the role of Al in the fluorescence enhancement, the energy transfer process, and the control of the ions valence are discussed.
2011, 60 (4): 047807.
doi: 10.7498/aps.60.047807
Abstract +
Nanospheres are widely used as the substrates for surface enhanced Raman scattering (SERS). In order to further enhance the electric fields around nanospheres and improve the SERS intensity, in this paper, we introduce a novel nanostructure which is composed of a couple of parallel clapboards and a clamped nanosphere. The discrete dipole approximation calculation results indicate that when the parallel clapboards are used, the electric fields around the nanosphere are much enhanced. Therefore, the nanospheres clamped by parallel clapboards may work well as the SERS substrates. In addition, the effects of the structural parameters of parallel clapboards are also investigated.
2011, 60 (4): 047808.
doi: 10.7498/aps.60.047808
Abstract +
The extinction spectrum and the electric field distribution of gold nanoring structure have been calculated and compared with those of gold nanoplate structure by using the discrete dipole approximation method. It is found that the plasmon resonance peaks can have a red-shift or blue-shift when the radius size and the shape of the nanoring change. The gold nanoring with square cross section has a largest extinction coefficient.At the main plasmon peak,the nanoring with circlar cross section has much stronger electric field and larger electric field distribution,which can serves as the surface enhanced Raman scattering substrate for biological and chemical detections.
2011, 60 (4): 047901.
doi: 10.7498/aps.60.047901
Abstract +
In order to enhance the quantum efficiencies of negative electron affinity (NEA) GaN photocathodes, gradient-doping reflection-mode GaN photocathodes are grown by metal organic chemical vapor deposition (MOCVD)at doping concentrations of 1×1018cm-3, 4×1017cm-3, 2×1017cm-3 and 6×1016cm-3 from the body to the surface, with the thickness of each doping region being about 45nm and the total thickness of GaN 180 nm. The gradient-doping GaN photocathodes are activated in an ultra-high vacuum system and are compared with two kinds of uniform-doping GaN photocathodes whose thicknesses are both 150 nm and doping concentrations are 1.6×1017cm-3 and 3×1018cm-3 separately. The results show that both the photocurrent growth rate and the maximum photocurrent of the gradient-doping GaN photocathodes are greater than those of the uniform-doping GaN in the Cs/O activation process, and the multi-test system measured maximum quantum efficiency of the gradient-doping NEA GaN photocathode is about 56% which is as high as the double of the uniform-doping. Calculations show that the energy band bendings of the gradient-doping GaN photocathodes are 0.024eV, 0.018eV and 0.031eV from the body to the surface, a larger electron drift and diffusion length are gained due to the built-in electric field formed by the energy band bending, because of the 0.073eV total energy band bending the photoelectrons reaching the surface have higher energies and pass through the surface barrier more easily. Therefore the gradient-doping NEA GaN photocathodes have greater quantum efficiencies.
Original Articles
2011, 60 (4): 047809.
doi: 10.7498/aps.60.047809
Abstract +
Organic light-emitting device (OLED) technology shows tremendous commercial applications in communication, information, display, and lighting. It has been one of the most attractive projects in optoelectronic information field over the last decade. However, the internal efficiency is quite different from the external efficiency, and to some extent, a low external efficiency restrictes the development and application of OLEDs. The light out-coupling has been improved by a number of different techniques through the modification of device architecture. In this paper we present various light out-coupling techniques that have been implemented to enhance the external efficiency of OLEDs. Various OLED device modification techniques, e.g., micro-lens array, photonic crystal structure, nano-patterned and nanoporous films, and microcavity technique, have been reviewed and discussed. Finally, some perspectives on light out-coupling techniques are proposed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2011, 60 (4): 048101.
doi: 10.7498/aps.60.048101
Abstract +
A novel molten salt synthsis technology is developed to prepare single phase and V-doped MnNb2O6powder. The prepared samples are characterized by XRD, SEM, EDS, TEM, HRTEM and SAED. The results show that the MnNb2O6 powder has an orthorhombic structure.and the samples prepared in different molten salts exhibit different shapes:flake shape, rod shape, and rectangular shape. The effects of temperature and doped on structure and morphology are discussed. HRTEM and SAED indicate the rod-shape MnNb2O6 has the properties of anisotropic growth and crystalline integrality. Magnetic properties are measured by superconducting quantum interference device (SQUID) in a temperature range of 2—30 K under a magnetic field of 2T. The magnetic measurement results indicate that MnNb1.8V0.2O6 undergoes an antiferromagnetic transition with a Néel temperature of 5.4 K. Above 20 K, the inverse susceptibility is fitted well to the Curie-Weiss law θ=-33.9 K,C=10.52 K emu mol ·f.u.-1 and effective moment 5.82 μ B can be obtained. With V-doped amount increases, antiferromagnetic interaction increases. According to the Anderson model, the MnNb2-xVxO6 is antiferromagnet in a low temperature range, which is induced by the superexchange interaction of Mn2+-O2--Mn2+.
2011, 60 (4): 048102.
doi: 10.7498/aps.60.048102
Abstract +
A two-dimensional axisymmetric model of free burning tangsten inert gas (TIG) arc under the action of pulsed current is developed. Using the FLUENT software and choosing appropriate boundary conditions and strongly coupling control equations, a pulsed TIG arc is simulated. The variations of arc form, temperature field, temperature and velocity on the arc axis and surface pressure distribution of the workpiece are obtained and analyzed in the periodic current process; under the action of different values of peak current, duty ratio and pulse frequency, the arc pressure distributions are obtained and analyzed. The results show that they lag behind the variation of pulse current, the variation from base current to peak current is faster, then eventually reaches a relativly stable state; with the increase of peak current, the arc pressure increase greatly; with the increase of duty ratio, the arc pressure increases slowly; with the increase of pulse frequency, the arc pressure cannot reach a stable state gradually, and the max arc pressure tends to decrease.
2011, 60 (4): 048401.
doi: 10.7498/aps.60.048401
Abstract +
In this paper we determine multiple resonant operating points (ROPs) of inductive power transfer (IPT) systems and perform the corresponding stability analysis of a series-tuned IPT system, which is taken for example, through using nonlinear dynamics theories. The stroboscopic mapping model of the system is built and a piecewise analytical function of the steady-state response is derived with the fixed-point theory. Then a criterion for assessing the system ROPs is given mathematically. The stability analysis of ROPs is achieved according to the locations of the eigenvalues of the Jacobi matrix of the Poincare mapping model of the system. A case study of the phenomenon of multiple ROPs is conducted, and both simulation and experimental results verify the theoretical results of the proposed method. Furthermore, the proposed method can provide useful theoretical reference for modeling and steady-state analysing other similar resonant converters.
2011, 60 (4): 048402.
doi: 10.7498/aps.60.048402
Abstract +
In this paper, the low-frequency oscillation phenomenon in a pulse train (PT) controlled buck converter operating in continuous conduction mode (CCM) is found and studied. The mechanism of this low-frequency oscillation phenomenon and the way to suppress it are studied. The time-domain simulation results and their corresponding phase portraits indicate that the equivalent series resistance (ESR) of the output filter capacitor has a critical effect on this low-frequency oscillation phenomenon. When the ESR is zero or small enough, such a low-frequency oscillation phenomenon appears in the PT controlled CCM buck converter because the output voltage can not be regulated timely. With the increase of ESR, the PT controlled CCM buck converter operates chaotically. The output voltage can be regulated timely and such a low-frequency oscillation phenomenon can be suppressed effectively. Experimental results are provided to verify the theoretical analyses and the simulations.
2011, 60 (4): 048403.
doi: 10.7498/aps.60.048403
Abstract +
Based on the analyses and the calculations of the gyroklystron amplifiers self-consistent nonlinear theory, a scheme of Kα-band, TE01 mode, four-cavity fundmetal wave gyroklystron is designed.At the same time, a gyroklystron amplifier is made and tested. The hot test experiment shows that the gyroklystron amplifier can produce 245 kW peak output power, and 3 kW average power at a 35% efficiency and saturated gain of 36.1 dB at central frequency 34 GHz, when using 60 W driving power, and a 70 kV, 10 A annular electron beam in a magnetic field of 1.31 T. The full width half maximum (FWHM) bandwidth is higher than 280 MHz. The amplifier is zero-drive stable. Experimental results are found to be in excellent agreement with theoretical predictions.
2011, 60 (4): 048404.
doi: 10.7498/aps.60.048404
Abstract +
High power microwave (HPM) pulse compression is a main method to obtain high power microwave with non-relativistic devices. The mature HPM pulse compression systems are nearly all based on rectangular resonant cavity, and the pulse compression systems based on cylindrical resonant cavity are in progress. A new type pulse compression system based on cylindrical resonant cavity is proposed in this paper, and the structure of the system is different from those of all other HPM pulse compression systems ever reported. The structure and the numerical simulation results of the key parts are presented, and a preliminary analysis of the power capability of the system and the quality factor of the resonant cavity is also given. For a pulse compression system, the power capacity is a key factor for the output microwave pulse power, and the quality factor of the resonant cavity has a close relationship with the system energy efficiency. According to the experimental results, the pulse capacity of the pulse compression system based on cylindrical resonant cavity can be 10 times higher than that of the systems based on the rectangular resonant cavity, and the quality factor of the resonant cavity can be improved by a factor of 5.
2011, 60 (4): 048501.
doi: 10.7498/aps.60.048501
Abstract +
The size of charge cloud is examined as a function of acceleration voltage, distance between MCP and anode, and MCP gain. The performance of photon counting imaging detector is significantly affected by charge cloud size. In this paper, the influence of charge cloud size on the performance of UV photon-counting imaging systems is investigated. Modulation distortion, "S" distortion and their cause are discussed. Then, Monte Carlo simulations for anode decode with different charge cloud sizes are carried out. And finally, the effects of acceleration voltage, distance between MCP and WSA, and MCP gain on the system performance are tested and some practical solutions of modulation and "S" distortion are suggested.
2011, 60 (4): 048701.
doi: 10.7498/aps.60.048701
Abstract +
Based on the three-dimensional structure of NaK channel, the permeabilities of the NaK channel for Na+, K+, Rb+, Ca2+ ions and the Ba2+ ion blockage mechanisms are investigated. The results show that the interaction is fundamental for determining the selectivities of the channels and the potential curve reflects the external behaviors for the permeabilities of different ions.
2011, 60 (4): 048702.
doi: 10.7498/aps.60.048702
Abstract +
Influenza viruses are divided into three types: A, B and C. Among them, type A virus is the most virulent human pathogen and causes the most severe disease. In this paper, we propose a new time series model for influenza A virus DNA sequence, i.e.chaos game representation (CGR) radians series. The CGR coordinates are converted into a time series model, and a long-memory ARFIMA(p,d,q) model is introduced to simulate the time series model. We select randomly 10 H1N1 sequences and 10 H3N2 sequences in analysis. we find in these data a remarkably long-range correlation and fit the model reasonably by ARFIMA(p,d,q) model, and also find that we can use different ARFIMA models to identify the two kinds of sequences, i.e. ARFIMA(0,d,5) model and ARFIMA(1,d,1) model that can identify H1N1 and H3N2 respectively.
2011, 60 (4): 048703.
doi: 10.7498/aps.60.048703
Abstract +
Correlations in time courses of scalp electroencephalogram(EEG) may be represented by the phase synchronization in cerebral cortex sources to a certain some degree. Therefore, it is very important to localize the sources of phase synchronization and find corresponding time courses in the brain imaging study. Based on coupled Rössler oscillators with different coupling strengths, we propose a new method of simulating phase synchronized dipole sources and use a concentric 4-sphere head model to obtain simulation forward scalp EEG data. In addition, we propose the spatiotemporal dynamic analysis of phase synchronized sources based on the maximum likelihood factor analysis, verify the simulated and real scalp EEG data, and further compare the results with those of principal component analysis. Simulation results demonstrate that time courses estimated by maximum likelihood factor analysis have higher correlation with simulated sources, and less locational error between estimated sources and simulated sources. Factor analysis shows a better robust to the spatial resolution and the noise than principal component analysis. Furthermore, real data from spatial attention experiments show that factor analysis is capable of obtaining time courses and spatial distribution under the physiological base.
2011, 60 (4): 048901.
doi: 10.7498/aps.60.048901
Abstract +
A novel science branch, econophysics, is set up because various physical theories and methods are applied to economic and financial fields. More and more researchers are fascinated by the complex dynamical behavior of the fractional-order dynamical system. The paper analyzes the stability of the fractional-order financial system, and then simulates the generalized model complexity with Adams-Bashforth-Moulton predictor-corrector scheme by using bifurcation diagram, phase portrait and history time-series.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2011, 60 (4): 049201.
doi: 10.7498/aps.60.049201
Abstract +
Estimation models of economic losses due to flood are established by combining drainage times of urban road waterlogging-theoretical models and economic loss assessment models, etc. And then the "loss" curves are determined by discussing the relationships between daily mean precipitation and economic losses of urban transportation departments. Some socioeconomic variables, which are closely related to the anti-flood capability of urban transportation departments, are adopted in the models in this paper. By model testing, the economic loss assessment model established in this paper shows good simulation performance and applicability. And it has simple computation, needs few input variables, and is suited for the rapid assessment of the economic loss of some region. Based on the models established in this paper, the thresholds of the precipitation intensity and the total storm precipitation of each year in Shanghai are calculated. And a new definition of extreme precipitation, called "fixed thresholds varying with the influence factors", is given. This definition underlines the socioeconomic character of extreme precipitation which would cause economic loss and possesses high social practical values compared with other definitions of extreme precipitation.
2011, 60 (4): 049202.
doi: 10.7498/aps.60.049202
Abstract +
Approximate entropy (ApEn) is valid index which can be used to quantitatively reflect dynamic characteristics and complexity of a time series. The ApEn has been developed to detect an abrupt change in one-dimension time series by sliding a fixed widow, which can be identified with an abrupt dynamic change to some extent, but the sliding ApEn results depend on the window scale, and cannot accurately position the time-instant of an abrupt change. Based on this, a new method is proposed in the present paper, i.e., moving cut data-approximate entropy (MC-ApEn), which can be used to detect an abrupt dynamic change in time series. Tests on model time series indicate that the detection results from the present method show relatively good stability and high accuracy, obviously better than those from the sliding ApEn method and the Mann-Kendall method. The applications in daily precipitation records further verify the validity of the present method.
2011, 60 (4): 049701.
doi: 10.7498/aps.60.049701
Abstract +
Integrated profile, flux and period are three major characteristics of pulsar. Taking advantage of these characteristics, a time domain detecting method is presented based on Bayesian estimation to detect pulsar periodic radiation signals. The signal probability distribution is deduced based on the Poisson distribution model of X-ray pulsar, with noise observation of non-pulse region used as the priori knowledge. The cumulative distribution function of the signal probability is used as a criterion to detect weak signals of X-ray pulsars and extract the phase offset. The RXTE data and the simulation data are used for experimental verification, and the results show that the method outperforms a similar method which is based on the Gauss distribution model, in addition, it can give the phase offset in a certain accuracy.
2011, 60 (4): 049702.
doi: 10.7498/aps.60.049702
Abstract +
Degenerate electronic Fermi system with intrinsic (spin) magnetic moment and Landau diamagnetic moment of the electrons in a neutron star interior is magnetized. Taking the magnetizing effect into consideration, the magnetic induced equation must be changed: the resulting equation has an additional magnetic induction term and a magnetic diffusion coefficient that is different from the original one for plasma. When effective magnetic diffusion coefficient equals critical value ( zero) the fully degenerate electronic system approaches a new phase. In this phase, the magnetic field of neutron star will become very large until other mechanisms suppress the increasing of the field in the neutron star lowered crust. For a stable or de Hass-Van Alphen oscillatory state, it is possible for the neutron star to become a magnetar .
