Vol. 60, No. 9 (2011)
2011-05-05
GENERAL
2011, 60 (9): 090201.
doi: 10.7498/aps.60.090201
Abstract +
In the paper, to construct new infinite sequence exact solutions of nonlinear evolution equations, several kinds of new solutions of the second kind of elliptic equation Bäcklund transformation are proposed. The KdV equation containing variable coefficients and forcible term, combined with (2+1)-dimensional and (3+1)-dimensional Zakharov-Kuznetsov equation with variable coefficients is taken as example to construct new infinite sequence exact solutions of these equations with the help of symbolic computation system Mathematica, which include infinite sequence compact soliton solutions of Jacobi elliptic function and triangular function, and infinite sequence peak soliton solutions.
2011, 60 (9): 090202.
doi: 10.7498/aps.60.090202
Abstract +
For elliptic nonlinear partial differential equations with boundary value problem, based on difference method and dynamic design variable optimization method, by taking unknown function value on discrete net point as design variables, difference equation of all the discrete net points is constructed as an objective function. A kind of optimization algorithm about solving unknown function value on discrete net point is proposed. Universal computing program is designed. Practical example is analyzed. By comparing the computing result with the analytical solution, effectiveness and feasibility are verified. Thus complicated nonlinear mathematical physics equations can be solved by the numerical calculation method.
2011, 60 (9): 090203.
doi: 10.7498/aps.60.090203
Abstract +
A kind of disturbed Vakhnemko equation is considered. The modified asymptotic method is given. Firstly, we obtain corresponding traveling wave solution of the typical Vakhnemko equation. Secondly, introducing a functional, constructing the iteration expansion of solution, the nonlinear equation is converted into a set of iteration sequence. And then, the corresponding approximations of solution are solved successively. Finally, the approximate expansion for arbitrary order accuracy of the travelling wave solution for the original disturbed Vakhnemko model is obtained and its accuracy is discussed.
2011, 60 (9): 090204.
doi: 10.7498/aps.60.090204
Abstract +
In the present study we analyze the biomechanical properties of life-form parenchyma, derive the relationship between MR displacement-phase image and the elasticity of life-form parenchyma, thereby study the local frequency estimation(LFE) algorithm. Finally the algorithm is relized by Matlab, and the inversion results of phantom MRE image demonstrate the effectiveness of the LFE algorithm, which would form a basis for subsequent research on liver fibrosis classification .
2011, 60 (9): 090205.
doi: 10.7498/aps.60.090205
Abstract +
According to Runge-Kutta theory, in this paper we present a new algorithm of calculating the eigenmodes of gyrotron resonators. Different from in the traditional algorithm, all properties of the eigenmodes can be determined by solving the minimum of a function with two variables, namely the resonant frequency and Q factor, in the new algorithm. Through examples of numerical calculation, it is verified that the calculation efficiency of the new algorithm is much higher than the traditional algorithm.
2011, 60 (9): 090206.
doi: 10.7498/aps.60.090206
Abstract +
In order to improve the accuracy and the stability of the conventional smoothed particle hydrodynamics (SPH) method for simulating the transient heat conduction problems, a first order symmetric smoothed particle hydrodynamics (FO-SPH) method is proposed.In order to solve the heat conduction problem with second derivative, the proposed FO-SSPH method is first to decompose the problem into two first order partial differential equations (PDEs), and then the first order kernel gradient is corrected based on the discretization of gradient and the concept of Taylor series. Finally, the obtained local matrix is locally symmetrized. All the numerical results demonstrate that the FO-SSPH possesses a higher accuracy and better stability than the SPH method, that the mixed boundary conditions can be well imposed using FO-SSPH method, and that the reliability and the flexibility of the FO-SSPH method can also be observed for PDEs with multi-boundary conditions. Finally, the one-dimensional nonlinear heat conduction problem is investigated by the FO-SSPH method, and the phenomena of concave and bulge are observed when the temperature achieves the stable state, in which the influence of the coefficients for heat flux is discussed.
2011, 60 (9): 090301.
doi: 10.7498/aps.60.090301
Abstract +
A transient analysis in time domain of beam-wave interaction for gyroklystron is made with self-consistent field theory in this paper. A nonlinear theory for gyroklystron with multiple cavities is established, but also electron motion equations and transient electromagnetic field equations in the complex form are given. Research methods of beam-wave interaction in input cavity, idler cavity and output cavity are investigated. The infuence of speedspread is taken into account. For a Kα-band gyroklystron with four cavities, some numerical results of beam-wave interaction are given, and analyzed in Fortran Language finally. The numerical results are compared with the experimental data and the PIC results, showing that they are in good agreement.
2011, 60 (9): 090302.
doi: 10.7498/aps.60.090302
Abstract +
We study the entanglement dynamics of the system composed of two two-level atoms resonantly interacting with two coupled cavities. The evolutions of atom-atom entanglement, cavity-cavity entanglement and atom-cavity entanglement are investigated. The influence of coupling constant between cavities on entanglement property is discussed. The numerical results show that atom-atom entanglement property is strengthened while atom-cavity entanglement property and cavity-cavity entanglement property are weakened with the increasing of the coupling constant between cavities.
2011, 60 (9): 090303.
doi: 10.7498/aps.60.090303
Abstract +
The atomic-state quantum teleportation in a dissipative environment is investigated by the quantum theory of damping - density operator approach and the numerical calculations. The effects of fidelity for different initial atomic-states are discussed. The results show that, when only the input atomic-state is exposed to the squeezed vacuum reservoirs, the fidelity of atomic-state with larger probability in the ground state is larger than that of other state; on the other hand, when the quantum channel is exposed to the reservoirs, the input state with equal probability in the ground state and the excited state has the largest fidelity in all the teleported states.
2011, 60 (9): 090304.
doi: 10.7498/aps.60.090304
Abstract +
We discuss the entangled coherent states in symmetry phase space by introducing orthogonal basis, calculate their entanglement by means of concurrence, and investigate their squeezing effects of single-mode and two-mode and antibunching effects. The calculations indicate that the entangled coherent state in symmetry phase space is closely related to nonclassical effect.
2011, 60 (9): 090305.
doi: 10.7498/aps.60.090305
Abstract +
In this paper, the expression of Wigner operator in the coherent state is derived using the IWOP technology. The Wigner function of a kind of special single-mode squeezed state is calculated. When the rotation parameter value changes, the numerical calculations show that the Wigner function in the phase space possesses a rotation displacement feature.
2011, 60 (9): 090306.
doi: 10.7498/aps.60.090306
Abstract +
Kinetics of solidification of liquid benzene under high pressure has attracted much attention of scientists, and it is also one of long-standing disputes. In the present work, the gas-gun technique is combined with a recently developed measurement method of light transmittance, and the time dependence of light transmittance of liquid benzene is directly observed during successive multiply shock-compressions. The analysis shows that the transmittance decrease is caused by light scattering effects in a non-uniform optical medium, which is formed by local phase transformation of liquid-solid, and that the scattering feature reflects both the time relaxation and the spacial accumulation of transition process. The argument whether the liquid-solid phase transformation happens under multi-shock compression is clarified, and important experimental evidence is provided for the study of phase transformation Kinetics.
2011, 60 (9): 090307.
doi: 10.7498/aps.60.090307
Abstract +
Quantum state in the channel is affected by several factors, which will bring detection error and make secure threshold of quantum distribution protocol unable to judge whether eavesdropping exists. We analyze the factors in real quantum channel, which affects the quantum state, develop a channel model, and derive a judging eavesdrop secure threshold formula of BB84 protocol based on an imperfect channel. Through calculating and simulating, the formula is proved to be more accurate to estimate the secure threshold of the BB84 protocol and more effective to judge eavesdropping. Meanwhile, this method can improve the security and the efficiency of key distribution.
2011, 60 (9): 090401.
doi: 10.7498/aps.60.090401
Abstract +
In this paper, we study on mass-defect effect in the black hole with a global monopole, calculate the mass defect of the neutral particle adsorbed by the central mass(or falling down to the central mass), and then compute the mass defect of the adsorbing homogeneous spherical shell and the solid sphere in the limit case.Finially, the mass defects of these substances are converted into the energy radiations.
2011, 60 (9): 090402.
doi: 10.7498/aps.60.090402
Abstract +
When a Hamiltonian can be split into integrable and nonintegrable parts, the former part is solved analytically, and the latter one is integrated numerically by means of implicit symplectic integrators such as the first-order semi-implicit Euler method or the second-order implicit midpoint rule. These analytical and numerical solutions are used to construct a second-order mixed symplectic integrator with the semi-implicit Euler method and one with the implicit midpoint rule. A theoretical analysis shows that the Euler mixed integrator is inferior to the midpoint one in the sense of numerical stability. Numerical simulations of the circularly-restricted three-body problem also support this fact. It is further shown through numerical integrations of the post-Newtonian Hamiltonian of spinning compact binaries that the qualities of the Euler mixed integrator and the midpoint mixed method do depend on the type of orbits. Especially for chaotic orbits, the Euler mixed integrator often becomes unstable. In addition, the Euler mixed integrator has an advantage over the midpoint mixed method in computational efficiency, and is almost equivalent to the latter in the numerical accuracy if the two mixed integrators are stable. In spite of this, the midpoint mixed integrator is worth recommending for the study of the dynamics of post-Newtonian Hamiltonians of spinning compact binaries.
2011, 60 (9): 090403.
doi: 10.7498/aps.60.090403
Abstract +
Hawking radiation from a dynamical Kerr black hole is investigated using a new tortoise coordinate and the improved Damour-Ruffini method. The local temperature changing with time and latitude angle and the Hawking radiation with quasi-blackbody spectrum are obtained. The present results are different from the existing results obtained by using usual tortoise coordinate. There exists a certain problem in dimension for the usual tortoise coordinate and the present results may be more reasonable.
2011, 60 (9): 090501.
doi: 10.7498/aps.60.090501
Abstract +
The discrete-time iterative map of digitally controlled DC-AC H-bridge inverter with outer load-voltage loop and inter inductance-current loop plus voltage-reference feedforward loop is derived by considering the effect of the time delay problems inherent in digital control system. The type of the bifurcation point when the system loses stability is predicted in terms of the eigenvalues of the Jacobian matrix,and it is found that the type is of the Hopf bifurcation. The analytic expressions of the stability boundaries and the oscillation frequency are deduced, and the underlying mechanism of this nonlinear phenomenon is analyzed. Finally, the theoretical results are verified by simulations and circuit experiments.
2011, 60 (9): 090502.
doi: 10.7498/aps.60.090502
Abstract +
Through introducing two piecewise-linear functions into a three-dimensional linear system, a grid-scroll chaotic system with relatively simple algebraic of system structure is constructed. By deploying the zero points of the introduced saw-tooth function and modified saw-tooth function, the designs of the number and the distribution of the index-2 equilibrium points of the system are performed, and the controls of the scroll number and the scroll distribution of the chaotic attractor generated from the system are achieved. By using analog components such as operational amplifier, multiplier, etc., the saw-tooth function circuit, the modified saw-tooth function circuit and the three-dimensional linear system circuit are designed and the proposed grid-scroll chaotic system is implemented. The experimental results are in agreement with both theoretical analyses and numerical simulations, which verify the feasibility of the designs of the scroll number and scroll distribution of chaotic attractors.
2011, 60 (9): 090503.
doi: 10.7498/aps.60.090503
Abstract +
We demonstrate experimentally a method to measure breakpoints and impedance mismatch for dielectric transmission lines by using broadband chaotic signals. Chaotic signal serving as a probe signal is obtained from the chaotic laser diode with optical feedback. Correlation method can realize breakpoint location, impedance estimation, and live test. Experimental results show that the location deviation is less than 1%, the impedance error is within the nominal rating, and interference margin is about 48 dB for 2 MHz square pulse signal on wire.
2011, 60 (9): 090504.
doi: 10.7498/aps.60.090504
Abstract +
A chaotic parallel genetic algorithm for the allocation of a multi-objective cross-layer wireless sensor network resource is provided, in which chaotic sequence and parallel genetic algorithm are used to dynamically adjust target selection, communication time slots and other parameters for optimizing the global cross-layer resource allocation. Simulations are conducted to compare the chaotic parallel genetic algorithm method with random allocation algorithm, dynamic programming algorithm, T-MAC protocol and the S-MAC protocol separalely. The simulation results show that the chaotic parallel genetic algorithm has a small communication delay and high success rate of target detection, which reduces the power consumption and improves the real-time characteristic of wireless sensor network.
2011, 60 (9): 090505.
doi: 10.7498/aps.60.090505
Abstract +
Synchronization and parameter identification of globally coupled network constructed by discrete spatiotemporal chaos systems with unknown parameters are studied. The control law designed by Milosavljevic is extended, and applied to the identification of unknown parameters in spatiotemporal chaos systems at the nodes of the network and the study of global synchronization of the network. The one-dimensional convective equation with spatiotemporal chaos behaviour in physics is further taken for example to imitate analysis.
2011, 60 (9): 090506.
doi: 10.7498/aps.60.090506
Abstract +
In this paper, the transport characteristics of the electrons in the double-barrier heterostructure under adding periodic positive and negative bias ("rocked" ratchet) are numerically simulated by the transfer matrix method. The expressions of net current and net heat flow between the two electronic reservoirs are obtained. Further, the performance characteristics of net current, net heat flow and coefficient of performance are analyzed. The results obtained here may provide some significant guidance for the design and manufacture of mecro-thermoelectric devices.
2011, 60 (9): 090507.
doi: 10.7498/aps.60.090507
Abstract +
In this paper,the dynamic behavior of Duffing-Rayleigh oscillator subjected to combined bounded noise and harmonic excitations is investigated. Theoretically, the random Melnikov's method is used to establish the conditions of existence of chaotic motion. The result implies that the chaotic motion of the system turns into the periodic motion with the increase of nonlinear damping parameter, and the threshold of random excitation amplitude for the system to change from chaotic to periodic motion in the oscillator turns from increasing to constant as the intensity of the noise increases. Numerically,the largest Lyapunov exponents and the Poincare maps are also used for verifying the conclusion.
2011, 60 (9): 090508.
doi: 10.7498/aps.60.090508
Abstract +
Chaotic oscillator can be produced by a single piecewise-linear element connected to a linear circuit. In this paper, the process of synthesizing the piecewise-linear chaotic circuit is discussed. Firstly, The parameters of the nonlinear element and the admittance function of the one-port circuit are determined by the eigenvalues of the system. Secondly, the one-port circuit is designed according to the admittance function. The one-port circuit can be realized with two kinds of basic admittance functions in parallel. The inductance and the capacitance of the circuit are always positive, and the negative resistances are always commonly grounded. Finally, the example of synthesizing chaotic circuit with the proposed method in presented.
2011, 60 (9): 090701.
doi: 10.7498/aps.60.090701
Abstract +
In Shack-Hartmann wavefront sensor(SH-WFS) based adaptive optics system, the centroiding algorithm is usually used to estimate the centroid of a point source spot. But the detecting accuracy of the centroiding algorithm is affected by many factors such as threshold selection, so that the centroid position of the spot cannot be evaluated accurataly under the condition of low signal-to-noise ratio(SNR) . Comparatively the correlating algorithm for Shack-Hartmann wave front-sensing is more robust because it need not reduce the thresholding. In this paper, based on the the principle of the correlating SH-WFS, the measurement error of the correlating SH-WFS is derived by building up the noise model of the correlating SH-WFS. The influences of spot size, photon noise, read out noise and background light noise on the measurement of the correlating SH-WFS are analyzed systematically. The numerically simulation results and the experimental results are consistent well with the theoretical analyses.
2011, 60 (9): 090702.
doi: 10.7498/aps.60.090702
Abstract +
A method of fast scanning X-ray microprobe fluorescence imaging, on-the-fly scan, has been recently accomplished in BL15U1 hard X-ray micro-focus beamline of Shanghai Synchrotron Radiation Facility, based on the software platform of EPICS; the high technology of precise motion control, the X-ray flux detection and the X-ray fluorescence spectrum detection are integrated into this system. By the method of X-ray microprobe fluorescence imaging, the images of standard nickel mask and the elemental distribution of copper, zinc, kalium and iron in specimen of mouse spleen are obtained. The results demonstrate that this method not only enhances the efficiency on a large scale, but also achieves high quality fluorescence mapping.
2011, 60 (9): 090703.
doi: 10.7498/aps.60.090703
Abstract +
A novel complex multi-valued discrete Hopfield neural network (CMDHNN) is proposed in this paper. A multi-valued discrete activation function and a new energy function for CMDHNN are constructed. The stabilities for multi-valued CMDHNN with asynchronous and synchronous operating modes are also analyzed seperately. The special energy functions own the ability to describe the dynamic characteristics of CMDHNN which the energy functions of existing references cannot explain. Meantime, these energy functions can make the true source signal vector correspond to the minimum point of the energy function of CMDHNN. Furthermore, to verify effectiveness of CMDHNN, the weighted matrix of CMDHNN is constructed by the specific cost function for the blind detection of signals. Simulation results show that the proposed CMDHNN can be used to blindly detect the dense MQAM constellation signals with shorter received signals and the global minimal value of the CMDHNN energy function is verified.
REVIEW OF FRONTIER AREA
2011, 60 (9): 090704.
doi: 10.7498/aps.60.090704
Abstract +
Recently, due to the potential applications, the developing of compact, portable, low cost, and tunable THz wave became a research focus of THz technology. The light source with a wavelength range from 600—2000 nm frequently serves as a pumped source of THz wave due to its property of compact size, low cost, tunable frequency and stable operation. In this paper, tunable dual-wavelength continuous-wave pumping source and THz generator with an internal-cavity optical parameter oscillator are overviewed and analyzed in detail. It is shown that pumping source in the near-infrared wave band is more advantageous than those in the mid-infrared wave band for compactness in size. It is also shown that the difference frequency and nonlinear cascade processes have become an important way to generate THz radiation for wide tuning merit in such a system.
2011, 60 (9): 097507.
doi: 10.7498/aps.60.097507
Abstract +
In recent years, it was found that antiperovskite compounds Mn3AX(A=Cu, Zn, Sn, Ni, Al, Ga etc.;X=N/C) exhibit abundant physical properties. Their useful functionalities arising from the interplay between crystal lattice and magnetism, such as superconductivity, giant magnetoresistance, near-zero temperature coefficient of resistance, negative thermal expansion, magnetostriction, piezomagnetic effect, the magnetocaloric effect, etc, have aroused the great interest. The thorough study of the crystal structure and physical properties of Mn3AX is important for understanding the relationship of "nature-structure". In this article, we review the progress in the peculiar physical properties of Mn3AX, especially the progress of strong correlations among lattice, electronic transport and magnetic ordering. Meanwhile, the control over the lattice,magnetoresistance and magnetic transition is also reviewed. Finally, some perspectives are proposed.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2011, 60 (9): 091101.
doi: 10.7498/aps.60.091101
Abstract +
A coaxial Bragg reflector with tapered inner rode corrugated ripples and phase matching section used in relativistic diffraction generator (RDG) with overmode cylindrical structure in Ka-band is presented and analyzed in this paper. The conservation of complex power technique(CCPT) is introduced to analyze the frequency response of the Bragg reflector. The influences of the phase matching section length, the corrugated sinusoidal slots depth and the tapered angle of the reflector on frequency response are studied. It is found by analyzing the influence of the initial ripple phase that the reflector has a favourable characteristic for mode selection. The research results provide important theoretical analysis and data reference for designing coaxial Bragg reflector structure.
2011, 60 (9): 091201.
doi: 10.7498/aps.60.091201
Abstract +
A novel scheme of all-optical 3R regeneration has been proposed in this paper. Using degraded data signal rather than clock as a pump, all-optical 40Gbps 3R regeneration based on a fiber optical parametric amplification effect (FOPA) is realized with improved performance compared with previous regeneration schemes. Theoretical analysis of the noise suppression mechanism under different pump power (corresponding to "0" code or "1" code) is provided. By properly adjusting the parameters of FOPA, amplitude noise on both "0" code and "1" code can be suppressed simultaneously. The clock extraction is based on wavelenth conversion and a Fabry-Pérot (F-P) filter with a high Q value of 1000. The theoretical analysis conclusions are verified through experiments, and the imbalance of the 3R regeneration using fiber optical parametric amplication is eliminated. The root mean square (RMS) jitter of the clock extracted is only 180fs. The signal-to-noise ratio of the regenerated signal is improved from 4.52 to 11.43.
2011, 60 (9): 091301.
doi: 10.7498/aps.60.091301
Abstract +
In this paper,we develop a numerical model of electron cyclotron emission in three-dimensional Yee grid model, combine the FDTD algorithm to simulate electron cyclotron maser, and use the MPI parallel lgorithms to drastically reduce cmputation time. Finally, we simulate a 94GHZ Gyrotron oscillator, and verify its correctness through spectrum, power, operating mode.
ATOMIC AND MOLECULAR PHYSICS
2011, 60 (9): 093101.
doi: 10.7498/aps.60.093101
Abstract +
By the full-potential linearized augmented plane-wave method (FP-LAPW), we investigate the electronic structure, the band structure, the dielectric function, the absorption spectrum, the reflectivity and the refraction of Cr doped SnO2 superlattice. The generalized gradient approximation (GGA) is used for handling correlation energy. Calculation results show that due to the Cr doping, SnO2 superlattice forms new electron occupied state near Fermi energy level and uncentinuous impurity band comes into being, which is contributed by Cr-3d and O-2p, Sn-5s. In dielectric spectrum appear three new dielectric peaks between 0 eV to 5.5 eV. In high-energy area, the position of main peak has a blue-shift and the peak intensity reduces. Absorption spectrum, reflectivity spectrum and refraction spectrum also have peaks corresponding to the dielectric peaks, which are caused by d—d transition of Cr atom.
2011, 60 (9): 093102.
doi: 10.7498/aps.60.093102
Abstract +
The ground state parameters, the dipole moment, the charge distribution and the energies of MOs of methyl acrylate under different intense electric fields are optimized using the density functional theory (DFT)B3LYP based on the 6-311+ +G* * basis set level. The excitation energies, the wavelengths, the oscillator strengths from ground state to the first nine different excited states are calculated employing the revised hybrid CIS-DFT method (CIS-B3LYP) without external electric field, and the excited states under different electric fields are also investigated. The results show that the molecular geometry is strongly dependent on electric field strength, and the energy proves to increase before decreasing but the dipole moment behaves in a contrary manner. The excitation energies of the first nine excited states of methyl acrylate decrease with the increase of the applied electric field, indicating that the molecule is easy to excite and dissociate in the electric field .The wavelength is also increase with the increase of electric field, and its electronic transition spectrum covers from the ultraviolet to infrared.
2011, 60 (9): 093103.
doi: 10.7498/aps.60.093103
Abstract +
Based on the improved atomic model with considering temperature and density, the density distribution of the free electrons is dealt with by partial wave method based on the central field approximation. By an average of approximate treatment, the energy band split is given. In the atomic structure of the self-consistent calculation the band overlap is used as the free electron dynamic criterion. Electronic pressure, energy, heat capacity and other thermodynamic factors of gold are calculated
2011, 60 (9): 093201.
doi: 10.7498/aps.60.093201
Abstract +
Absolute photoabsorption spectrum of CO molecule in the region 14—20 eV(620—890 Å) is measured using synchrotron radiation and multi-stage photoionization chamber, and its ionization energy is obtained. According to the absorption spectrum of CO and theoretical calculation, the Rydberg series converging to the Χ2Σ+, Α2Π, and B2Σ+ states of CO+ are assigned separately. Rydberg series assigned before are extended, Rydberg series converging to the Χ2Σ+ (ν+=2 and 3) of CO+, and n=2 (the real value of n is 3) progressions of the series converging to the Α2Π state of CO+ are identified. At the same time, the absorption spectrum of CO in the region 17.0—17.5 eV (710—730 Å) is also discussed deeply.
2011, 60 (9): 093202.
doi: 10.7498/aps.60.093202
Abstract +
With 20—45 MeV O5+ ion bombardment we investigate L-shell X-ray emission processes on Ta film at HI-13 tandem accelerator in the Chinese Institute of Atomic Energy (CIAE). The ratios of X-ray emission cross section: σ(Lβ)/σ(Lα),σ(Lγ)/σ(Lα), and σ(Ll)/σ(Lα) are obtained. The results are compared with the predictions by the ECPSSR theory. Reasonable agreement between the ECPSSR theory and the experiment is obtained.
EDITOR'S SUGGESTION
2011, 60 (9): 093203.
doi: 10.7498/aps.60.093203
Abstract +
The ionization process of the interaction of nonmonochromatic laser with isotope atom system is studied. The multimode laser field is described by a stochastic model of chaotic field. By using the Fokker-Planck equation, the excited dynamic equation ofinteraction of the finite-bandwidth chaotic fields with K-level atom is derived. The influences of laser bandwidth and intensity on ionization efficiency and selectivity of three-level isotope atoms are also discussed.
EDITOR'S SUGGESTION
2011, 60 (9): 093204.
doi: 10.7498/aps.60.093204
Abstract +
The nonsequential double ionization of helium by high-intensity (1.5×1015 W/cm2) few-cycle laser pulses is investigated using a three-dimensional semi-classical rescattering model, with emphasis on the longitudinal correlated momentum spectra. We find that the percentage of opposite-hemisphere emission in this case is remarkably higher than those produced by laser pulses with medium-intensity (e.g., 7×1014 W/cm2) and low-intensity (e.g., 2.5×1014 W/cm2) those procuced by the laser pulses pulses with, and also the same intensies but longer laser pulses. Meanwhile, the V-shape structure is more pronounced. We identify the underlying mechanisms with tracing back the individual trajectories, and find that the single-and the multi-return induced collision-ionization are mainly responsible for the opposite- and the same-hemisphere emission, respectively. The dependences of these two different mechanisms on peak intensity and pulse length are predicted.
2011, 60 (9): 093301.
doi: 10.7498/aps.60.093301
Abstract +
This paper deals with the dual- band response of double ring metal array structure and anti-double ring structure in a terahertz wave range. The two samples are complementary in structure and their responses in the terahertz band are also complementary. The double ring structure shows two absorption crests and the anti-double ring structure shows two corresponding peaks at the same frequencies. The inner ring of the double ring structure is a source of high-frequency response, while the outer ring leads to the low-frequency vibration. Therefore, we can change the inner and the outer ring size respectively to control the terahertz response. And this response is unaffected by the period of the structure. The double ring structures provide a new method to produce multi-frequency terahertz resonator.
2011, 60 (9): 093401.
doi: 10.7498/aps.60.093401
Abstract +
The dissociative ionization process of methane induced by 54eV electron impact is investigated using an advanced reaction microscope. In the present paper, our attention is specially paid to the kinetic energy distributions of the CH+2,CH+ and C+ fragments. Energy deposition spectra are presented for these fragments of different kinetic energies. It is shown that the dissociations from the (2a1) -1 and (1t2) -2(3a1) states of CH+4 are the dominant contributions of the CH+2, CH+ and C+ fragments. The kinetic energy of fragment is sensitive to the electronic state of its parent ion. Fragment ions with kinetic energies lower than 0.1 eV are mainly from the dissociation of (2a1) -1 state, and partly from the dissociation of (1t2) -2(3a1) state; the ions with energies between 0.1 eV and 0.3 eV are contrituted equally by the two states; the ions with energies higher than 0.4 eV are formed dominantly from the dissociation of (1t2) -2(3a1) state.
2011, 60 (9): 093601.
doi: 10.7498/aps.60.093601
Abstract +
The effects of initial temperature and cooling rate on the freezing behaviors of clusters Co531, Cu531, and Ni531 are studied by the molecular dynamics with a general embedded atom method. The results show that their freezing points are obviously influenced by initial temperature and cooling rate. Higher initial temperature or smaller cooling rate results in a higher freezing point. The variations of freezing structures for all clusters with the change of freezing condition are different. The icosahedron is formed for Cu531 and Ni531 in spite of their different freezing points. The HCP structure similar to the Co bulk is formed for Co531 under higher initial temperature and smaller cooling rate, the icosahedron is formed for other conditions.
2011, 60 (9): 093602.
doi: 10.7498/aps.60.093602
Abstract +
Molecular dynamics simulations is performed to study the diffusion of several short alkanes in a flexible and rigid metal-organic framework, IRMOF-1. The results show that the self-diffusivities of alkanes in the flexible framework are larger than in a rigid framework and the activation energies in the flexible framework are less than in the rigid framework. The effect of framework flexibility on the self-diffusiviy increases with temperature inereasing and loading or chain length decreasing. Therefore, in the study of the diffusion behavior of alkanes in the metal-organic framework materials using molecular simulation method, especially for the case of the high temperature and shorter alkane molecules, flexible force field may give more reasonable results.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2011, 60 (9): 094101.
doi: 10.7498/aps.60.094101
Abstract +
The transport properties of one-dimensional photonic crystal consisting of single-negative materials, with an impurity layer, are studied by using the transfer matrix method. The results show that the defect mode appears in the forbidden band of the photonic crystal when there is a defect layer. The position of defect mode moves from the high frequency of the forbidden band to the low frequency with permeability μ increasing. And the position of defect mode moves from the low frequency of the forbidden band to the high frequency with permittivity ε increasing. These characteristics can be used to dynamically control the optical transmission.
2011, 60 (9): 094102.
doi: 10.7498/aps.60.094102
Abstract +
In this paper, a novel fast algorithm is presented for electromagnetic (EM) dyadic Green’s functions in horizontal layered medium using direct-waves’ extraction combining with self-adaptive digital filter method. First of all, the direct-waves which characterize effects of homogeneous medium in spectral domain Green’s functions(SDGF) are extracted, and their integrals are obtained by analytical calculations. In this method, the singularity of SDGF is reduced and the integral convergence range is shortened remarkably. Then, we transform the remnant integrals of SDGF into three rapid declining integrals, and self-adaptive digital filter method is introduced to obtain solution quickly. Finally, our numerical results validate the efficiency of the algorithm.
2011, 60 (9): 094103.
doi: 10.7498/aps.60.094103
Abstract +
Reduced permittivity and permeability profiles are proposed based on the electromagnetic transformation theory to achieve spherical reshapers with a split-ring-resonator(SRRs) microstructure. The effective radial permittivity distribution depending on the structure parameters, is obtained to implement a reshaper impinged by a TE incident wave. Finite-element simualtions are carried out and the results show that a good reshaping effect can be achieved at a working frequency despite the reduced and the discreted material parameters as well as unneglectable dipersion and loss effects. And the frequency band can be broadened by choosing proper microstructures such that the resonance point is far from the distribution range of the structural factors.
2011, 60 (9): 094201.
doi: 10.7498/aps.60.094201
Abstract +
Novel axicon for generating bottle beam is proposed for the first time. We discuss concave and convex types, which are formed by grinding and scuffing a frustum of a cone on the bottom of a traditional axicon. The results show that when a plane wave illuminates on the concave axicon, a single bottle beam is formed. If the light illuminates on the convex axicon, periodic bottle beam is formed. The formation mechanism of the bottle beam is analyzed by geometrical optics, and the relevant parameters are also calculated. The transverse and the longitudinal intensity distribution are simulated by diffraction and interference theory. The results are basically consistent with the geometrical optics.
2011, 60 (9): 094202.
doi: 10.7498/aps.60.094202
Abstract +
Based on the rigorous definition of light intensity of nonparaxial vectorial beams in the transverse plane, beam width, far-field divergence angles and M2 factors are defined by the power in the bucket. Taking nonparaxial vectorial Gaussian beam as an example, the detailed theoretical analyses and numerical calculations about the propagation characteristics are performed, and the results are compared with those from the nonparaxial scalar theory. Showing that when the half width of light source ω0 is less than Λ, there are obvious differences between the propagation characteristics described by the nonparaxial scalar and the vectorial theory, and their propagation characteristics tend to be consistent with ω0 increasing, change to that obtained in the paraxial scalar approximation gradually.
2011, 60 (9): 094203.
doi: 10.7498/aps.60.094203
Abstract +
Transformation of edge-dislocations to screw-dislocations in the optical field is experimentally and numerically demonstrated. A special multi-edge-dislocation structure is designed by arranging multiple edge-dislocations, which have the same phase-step value, periodically along the azimuthal orientation. Experimentally, in virtue of the computer-generated holography, a Gaussian beam is modulated by the multi-edge-dislocation, whose propagation dynamics is investigated as well. The results reveal that the multi-edge-dislocation can be converted into a screw-dislocation with the evolution of the Gaussian beam into a vortex-like beam. What is more, the sum phase change of the dislocations is conserved in this process. Then, the experimental results are verified by numerical simulations, and discussed in detail by analyzing the evolutions of the linear momentum density. Furthermore, the influence of the phase-step value of the edge-dislocation on the transformation is discussed, which illustrates the quantitative relation between the phase-step value and the topological charge of crew-dislocation.
2011, 60 (9): 094204.
doi: 10.7498/aps.60.094204
Abstract +
For Laguerre Gaussian vortex beam, the analytical expression of the electric field is derived in the observation plane after propagation. Theoretical analysis shows that the definition of Gaussian beam is unsuitable to describing the size of the laguerre Gaussian vortex beam while propagation. It is more convenient that the radius of the point where intensity is maximum is used to define the vortex beam after propagation. Besides the beam broadening effect induced by diffraction, phase distribution exhibits special change in the observation plane. Isophase line changes from radial to arc. If the topological charge of the vortex beam is positive, the isophase line will bend clockwise after propagation; if the topological charge of the vortex beam is negative, the isophase line will bend anticlockwise.
2011, 60 (9): 094205.
doi: 10.7498/aps.60.094205
Abstract +
In this paper, we study the spin Hall effect (SHE) of light in a multilayer-medium. By taking three-layer medium for example, the three-dimensional transmission model of beams passing through a prim-air-prim barrier is build. The various factors in SHE of light, such as thickness of the air gap, refractive index gradient, and incidence angle are investigated. For a certain circularly polarized component, the transverse shift can be modulated by Changing the refractive index gradient associated with the two prisms: whether the transverse shift of reflection and transmission fields is positive or negative depends on the refractive index gradient. Compared with the SHE in the two-layer medium, the SHE in the Gaussian beam refraction can be evidently enhanced via three-layer medium. Based on the theory of SHE of light,the theoretical basis for regulating and enhancing optical spin Hall effect is obtained.
2011, 60 (9): 094206.
doi: 10.7498/aps.60.094206
Abstract +
Based on the method of generalized truncated second-order moment, the analytical formula of the generalized beam propagation factor (M2G factor) of truncated partially coherent Hermite-Gaussian(H-G) beams is derived. The analytical results obtained from truncated fully coherent H-G beam, truncated Gaussian Shell Model (GSM) beam and truncated Gaussian beam are given as particular examples in this paper. It is shown that the M2G factor of truncated partially coherent H-G beam depends on truncated parameter δ, beam order m, and beam coherence parameter α. When the value of δ is very small, the odd-even groups happen to the M2G factor, i.e., the values of M2G factor with different values of the odd m are nearly the same, and so are they for the even m case. However, this phenomenon disappears as δ increases. For the truncated GSM beams with different values of δ, there exist the cross points between the curves of the M2G factor versus α. However, this phenomenon may disappear for truncated partially coherent H-G beams. In addition, the larger the m is, the more the M2G factor is affected by the δ, and the effect of aperture on M2G factor may be neglected when the δ is larger.
2011, 60 (9): 094207.
doi: 10.7498/aps.60.094207
Abstract +
We propose and numerically demonstrate that the feedback induced time-delay signature in an external cavity semiconductor laser can be eliminated by randomly modulating feedback phase. We find that when the rate of the random modulation signal is within the range of 0.1—1 Gb/s, and the number of the random variation amplitudes reaches 5, the time-delay signature corresponding to the external cavity can be effectively suppressed in the parameter space of injection current (1.2—2.8Ith) and feedback rate (8—26 GHz).
2011, 60 (9): 094208.
doi: 10.7498/aps.60.094208
Abstract +
It is the inevitable trend of the development for the optical frequency comb based on the Ti: sapphire femtosecond laser to be replaced by that based on the Er: fiber femtosecond laser. The detection of the carrier-envelope offset f0 in the femtosecond laser is a key to the realization of an optical frequency comb. In this paper, the structure of the optical part of an Er: fiber optical frequency comb is introduced. The optical pulses from an Er: fiber femtosecond laser with a repetition of 230 MHz are first amplified with a two stage amplifiers, spectrally broadened in a highly nonlinear fiber, and then pass through a single-beam f—2f self-referencing interferometer. By optimizing the optical parameters, the f0 with a signal-to-noise ratio of 30 dB is obtained in the Er: fiber femtosecond laser, which is favorable for the realization of an Er: fiber frequency comb.
LD end-pumped c-cut Nd:YVO4 laser at 589 nm generated by sef-Raman conversion and frequency doubling
2011, 60 (9): 094209.
doi: 10.7498/aps.60.094209
Abstract +
In this paper we report a LD end-pumped c-cut Nd:YVO4 yellow laser generated by sef-Raman conversion and frequency doubling. A 10-mm-length KTP with critical phase matching (θ=69°, ø=0°) cut is adopted as a second-harmonic generation. For the lower stimulated-emission cross section of c-cut Nd:YVO4 crystal, the resonator cavity and the coating of crystals are carefully designed to reduce the insert loss and diffraction loss. Finally, at a repetition rate of 10 kHz and an incident pump power of 11.2 W, the average power of yellow light up to 570 mW is achieved, corresponding to an overall diode-yellow conversion efficiency of 5.1% and a slope efficiency of 6.6%. The central wavelength is at 589.17 nm with a width of 0.2 nm, which is well fitted to the sodium D2 resonance radiation.
EDITOR'S SUGGESTION
2011, 60 (9): 094210.
doi: 10.7498/aps.60.094210
Abstract +
To investigate the output of ultraviolet of ShenguangII upgrade project, and study the relevant problem in the harmonics generation in high power laser driver, an experiment with 'Ⅰ+Ⅱ" phase match is conducted in the Shenguang-Ⅱ NO.9 device.The maximal output energy of ultraviolet reaches 2740 J, the maximal fluency exceeds 3.6 J/cm2, and the maximal conversion efficiency is ~63%. The parameters that affect the conversion efficiency are preliminary discussed with experimenal results; the amplitude modulation caused by phase modulation and traverse stimulation Raman scattering is observed in experiment. The design program and parameters for Shenguang-Ⅱ upgrade device are testified by the experimental results.
2011, 60 (9): 094211.
doi: 10.7498/aps.60.094211
Abstract +
The effect of atmosphere turbulence on phase modulation signal in coherent beam combination with multi-dithering technique is studied. Analytical formulas for the phase modulation signal of beam array propagating in a turbulent atmosphere are derived based on extended Huygens-Fresnel integral. Then the effects of propagation distance, turbulence intensity, filling factor and size of beam array on phase modulation signal are numerically calculated. The results show that with transmission distance increasing, there occurs a maximum of the amplitude of phase modulation signals. With the intensity of atmosphere turbulence increasing, the maximum of amplitude of phase modulation signals will appear in a shorter distance. When fill factor does not change, the distance between the laser source and the maximum of amplitude of phase modulation signals will be increased with of the dimension of laser beam increasing. When the dimension of laser beam does not change, the distance between the laser source and the maximum of amplitude of phase modulation signals will be increased with fill factor decreasing. Finally, the effects of parallel beam array and conformal focused beam array on phase modulation signal are compared, finding that the distance between the laser source and the maximum of amplitude of phase modulation signals can be changed by changing the focusing distance of conformal focused beam array.
2011, 60 (9): 094212.
doi: 10.7498/aps.60.094212
Abstract +
In the Fraunhofer diffraction approximation, a general model for calculating the transmission grating diffraction efficiency is deduced from wave optics under the condition of far field. Diffraction efficiency of transmission grating with any cross section can be obtained from such a general model. Rectangular, trapezoidal, 5-side quasi-trapezoidal and 7-side quasi-trapezoidal cross section calculation method are established with this model. And two examples are given to demonstrate the correctness of this general model.
2011, 60 (9): 094213.
doi: 10.7498/aps.60.094213
Abstract +
According to the full-vector finite element method, a new kind of V-shape photonic crystal fiber with high birefringence is proposed. Simulation results show that the V-shape photonic crystal fiber has a birefringence of 1.239×10-2 at a wavelength of 1.55 μm, when its cladding air hole pitch, large air hole diameter, small air hole diameter are 1.0 μm, 0.95 μm and 0.6 μm, respectively. There are two zero dispersion wavelengths in the visible and the near-infrared region respectively, and the abnormal dispersion zone includes the operation wavelength of Ti:sapphire laser, which is advantageous for nonlinear generation of photonic crystal fibers. The difference in air filling fraction between fast and slow axis can be used as a sensor for the weak strain.
2011, 60 (9): 094214.
doi: 10.7498/aps.60.094214
Abstract +
Dielectric waveguide with deep subwavelength mode confinement based on coupled semiconductor nanowires is proposed.Through the coupling between two adjacent nanowires with high refractive indexes, light can be efficiently confined in the nano-gap between the nanowires with a low refractive index. Numerical simulations indicate that the effective mode area of such a waveguide can be as small as Λ20/200, which is one order of magnitude smaller than that of a single nanowire, and such a mode confinement is comparable to that of hybrid plasmonic waveguide. It is also shown that from the view of real applications, possible existing low refractive index oxidization layers of nanowires, low refractive index substrate and small deviation of nanowire dimensions do not have significant influence on the property of the waveguide. As the propagation length is theoretically infinite for dielectric waveguides, such a coupled nanowire waveguide with deep subwavelength mode confinement may have important applications in future integrated photonic circuits.
A new differential phase shift quantum key distribution system with Faraday-Michelson interferometer
2011, 60 (9): 094216.
doi: 10.7498/aps.60.094216.2
Abstract +
A new differential phase shift quantum key distribution system based on the intensity modulator with Faraday-Michelson interferometer is demonstrated experimentally. Some technologies are employed to improve the performance of the quantum key distribution system. These technologies include the clock generation technology of arbitrary frequency by a small scale frequency-split and phase locked loop scheme, the new method to acquire the half-wave voltage of the phase modulator with a high accuracy in the condition of the single photon count, and the auto-compensated polarization technology by the Faraday-Michelson interferometer. Finally, the quantum key distribution is achieved with a quantum bit error rate of 3.9% when the transmission distance reaches 50 km.
2011, 60 (9): 094216.
doi: 10.7498/aps.60.094216.1
Abstract +
The value of the half-wave voltage of the phase modulator must be measured with high accuracy to reduce the quantum bit error rate (QBER) in a quantum key distribution system based the phase-coding scheme. A new method to measure the half-wave voltage of the phase modulator in an accuracy of 2 mV by adjusting the quantum bit error rate (QBER) of the deterministic quantum key distribution is proposed experimentally to increase the accuracy of the half-wave voltage and reduce the error rate of the quantum key distribution system. The experimental results show that this method can be used to acquire efficiently the half-wave voltage of the phase modulator in a high accuracy which can make the error rate from adding the inaccurate voltage to the phase modulator decrease to the greatest extent.
2011, 60 (9): 094217.
doi: 10.7498/aps.60.094217
Abstract +
Stimulated Raman scattering(SRS) of binary solution of toluene and m-xylene are studied at different volume concentrations in liquid-core optical fiber. The experimental results show that the vibration modes of 1002 cm-1, 2920 cm-1 and 3058 cm-1 bands are simultaneously stimulated to generate the SRS, and the SRS thresholds of the 1st-order Stokes of 2920 cm-1 and 3058 cm-1 bands are lowered compared with the 2nd-order Stokes of 1002 cm-1 band, and the main peaks of 2920 cm-1 and 3058 cm-1 bands are different as volume concentration changes. We assume that the intermolecular Fermi resonance is the main mechanism for these phenomena, which is explained by the Raman scattering cross section theory.
2011, 60 (9): 094218.
doi: 10.7498/aps.60.094218
Abstract +
The soliton propagations in lead glass separately with circle and rectangle boundaries are theoretically and experimentally investigated. Based on the image beam method the soliton propagation in lead glass is comprised of two independent processes: the soliton forming and the soliton steering as a whole. The soliton-forming process is boundary independent, which is caused by the source beam itself induced refractive index distribution. The force which leads to the soliton steering essentially comes from the boundary effect and is equal to the force between the soliton beam and all of the image beams. The numbers of the images are one and infinite respectively for the boundaries of circle and rectangle. This results in a different steering force with a different boundary. The closed-form solutions of the soliton critical power and the steering trajectories are in good agreement with the experimental results.
2011, 60 (9): 094301.
doi: 10.7498/aps.60.094301
Abstract +
Acoustic field characteristics of an ultrasonic linear phased array are studied under the condition of an interface. The issue about a phased array transducer with a wedge is reasonably simplified into a liquid-solid interface problem. According to ray acoustics theory, the acoustic field produced by a single element on the liquid-solid interface is computed. Then focus laws are derived and the expressions of the sound field and the displacement of the ultrasonic linear array with a liquid-solid interface are obtained. Simulations are carried out for a phased array transducer mounted on a wedge. The focusing-generated effects on axial and horizontal acoustic field of transducer are discussed. It is shown that the focusing can enhance sensitivity and resolution, but degrades the performance of beams beyond the focal region. So focusing should be reasonably used in actual testing.
2011, 60 (9): 094501.
doi: 10.7498/aps.60.094501
Abstract +
The dynamical equation of a relative-rotation nonlinear dynamic system, which contains quasi-periodic parametric excitation and time delays, is established. Bifurcation response equation of 1/2 subharmonic primary parametric resonance is obtained by the method of multiple scales, and the stability of the system is analyzed. By solving the steady state solutions of the uncontrolled system, the effect of quasi-periodic parametric excitation on system response is studied through discussing the dynamics of the system. Time-delay feedback control method is used to control the bifurcation and limit cycle(region). Numerical results show that the bifurcation and the stability of the limit cycle(region) are controlled effectively by changing the time-delay parameters.
2011, 60 (9): 094701.
doi: 10.7498/aps.60.094701
Abstract +
Digital objects, such as images, videos, digital warehouse are diverse in the sense of dimension and representation-precision. Conventional encryption algorithms treat all digital objects as one-dimensional data, thus they cannot make it effective to take advantage of their spatial characteristics. A cryptosystem is constructed by combining RE arrays with extended HPP model we proposed. The cryptosystem is applicable to digital object of arbitrary dimension and representation-precision. Moreover, it has the merits of spatiality, parallelism, and high efficiency. Experimental results demonstrate that the cryptosystem has satisfactory randomness and sensitivity.
2011, 60 (9): 094702.
doi: 10.7498/aps.60.094702
Abstract +
Based on detailed results of direct numerical simulation with high order accuracy and resolution at the late-stages of the transitional boundary layer, new properties are found, such as discontinuous event in the evolution of low-speed streamwise streaks and the appearance called high speed spots in the development of high-speed streamwise streaks. In the present paper, the complex vortex structures and the ejection-sweep phenomenon in the transition process of boundary layers are analyzed thoroughly, and the new properties of high-speed /low-speed streamwise streaks are confirmed to be closely relatcd to the evolution process of vortex structures in the flow-field.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2011, 60 (9): 095201.
doi: 10.7498/aps.60.095201
Abstract +
A proposal is presented to enhance the saturation output power of a small-orbit coaxial gyro-amplifier by employing an external electrostatic voltage. Nonlinear simulations show that improved saturation output power increases 19 % for a transverse electric mode at a frequency of 0.14 THz. Both the ratio of the electron-beam transverse velocity to the axial velocity and the spread of transverse velocity do not cause obvious influence on the saturation power. Therefore the performance of gyro-amplifier is effectively improved.
2011, 60 (9): 095202.
doi: 10.7498/aps.60.095202
Abstract +
To accelerate the electrons efficiently in the laser wake-field accelerator, it is necessary to suppress the instability induced by the diffraction and the defocusing of the laser pulse. The gas-filled capillary discharge waveguide can generate an approximately parabolic density distribution, which can guide the laser pulse efficiently and suppress the instability. Using the Stark effect, this plasma density distribution is measured in this paper, and the relationship between plasma density and filled pressure is presented. By using the MHD code CRMHA, the formation of the capillary waveguide is simulated and researched in detail.
2011, 60 (9): 095203.
doi: 10.7498/aps.60.095203
Abstract +
In this study, molecular dynamics simulations are used to investigate atom F interacting with SiC at 300 K. Simulation results show that with the saturation of the deposition of F atoms on the surface, the compositions (SiFx and CFx groups (x4 is dominant. And the main etching mechanism of Si atoms is chemical etching.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2011, 60 (9): 096101.
doi: 10.7498/aps.60.096101
Abstract +
A series of Ge quantum dot samples with different Ge thickness is grown on n-Si(100) substrates by ion beam sputtering. Their morphology and structure are characterizated using AFM and Raman spectra, in which the evolution of the morphology, density, dimension, crystalline, and composition of the Ge quantum dots are discussed in detail. The results show that after the growth mode transiting from 2-D to 3-D, the shape of the Ge quantum dot changes directly into a dome shape and no pyramid dots are observed. Besides, with the increase of the Ge deposition, the density of the quantum dots increases to a maximum and then decreases, the crystalline becomes better, but the Ge/Si alloying processing is enhanced and the Ge composition decreases in quantum dots at the same time.
2011, 60 (9): 096102.
doi: 10.7498/aps.60.096102
Abstract +
ZnO nanoparticles and Zn/ZnO core/shell structured nanoparticles are synthesized by ablating zinc target in deionized water and sodium dodecyl sulfate (SDS) solutions, respectively, using pulsed laser ablation with 532 nm pulsed infrared laser. The microstructures and photoluminescence properties of the products are characterized by X-ray diffraction, transmission electron microscopy, ultraviolet-visible and PL spectrophotometer. The formation mechanism of ZnO and Zn/ZnO nanoparticles is discussed. The results show that the mean diameters of ZnO nanoparticles are 43 nm and 19 nm, respectively, after ablating the zinc target for 2 and 4 hours in deionized water. The longer-time ablation may lead to the interaction of the ablating laser beam with the ZnO nanoparticles, resulting in the decrease of the mean diameter of ZnO. Zn/ZnO core/shell structured nanoparticles can be obtained in 0.005 mol/L SDS solution due to the enwrapping of SDS to the Zn nanoparticles. A blue photoluminescence at about 450 nm (2.76 eV) and a green one at about 558 nm (2.22 eV) are observed for the colloidal solutions of ZnO and Zn/ZnO nanoparticles.
2011, 60 (9): 096103.
doi: 10.7498/aps.60.096103
Abstract +
Dislocation climb plays a vital role in the plastic behavior of crystals at high temperatures. In order to reveal the intrinsic mechanism of climb and its effect on plasticity, a new dislocation climb model is first developed based on the combination of the diffusion theory with both bulk diffusion and pipe diffusion in a three-dimensional discrete dislocation dynamics (DDD) simulation, which is considered to be more physical and widely applicable. Using our model the shrinkage processes of a single prismatic loop group and prismatic loop group are simulated. It is concluded that the climb rate is not directly determined by mechanical climb force as believed in classical theories, but by the gradient of the vacancy concentration around (bulk diffusion) and along (pipe diffusion) the dislocation line. Loop coarsening process is also simulated, and the three pronounced evolving stages of the loop radii and the average vacancy concentrations in crystal are reproduced.
2011, 60 (9): 096104.
doi: 10.7498/aps.60.096104
Abstract +
In order to investigate the dose rate effects and the radiation response of the voltage regulator, a group of bipolar linear regulators are irradiated by60Co γ at high and low dose rate. The results show that many of the parameters of the regulator, such as the max drive current, the output voltage, the line regulation and the dropout voltage, are sensitive to ionizing irradiation. Compared the radiation responses of the devices between high and low dose rate, the dose-rate effect is found to be dependent on device. The reasons for the degradation are discussed by combining the radiation response of the transistor and the amplifier with the circuit characteristic of the linear regulator. The dose rate effects are also analyzed from the annealing characteristics. So this is not only useful for their applicalion in space, but also helpful for the design of radiation hardness device.
2011, 60 (9): 096105.
doi: 10.7498/aps.60.096105
Abstract +
In this paper, we present a systematic investigation on phase transition and coalescence behavior of fcc Fe nanoparticles under heating by molecular dynamics approach with Finnis-Sinclair many-body potential. The simulation results show that for fcc Fe nanoparticles, the martensitic transformation from fcc to bcc phase occurs prior to the melting. Relative rotation occurs between two like nanoparticles, but it does not happen in two nanoparticles with different sizes. A small nanoparticle prfers to adhere to a large one and is melted with temperature increasing, resulting in the final formation of a larger particle.
2011, 60 (9): 096201.
doi: 10.7498/aps.60.096201
Abstract +
In the alloy with solute content higher than the limiting solubility, the solute atoms failing to dissolve will precipitate from the solid solution and form precipitations. In this study, the Portevin-Le Chatelier (P-LC) effects in annealed 5456 and 5052 aluminum alloys with different precipitation content are investigated under different applied strain rates respectively. The findings suggest that precipitations have a significant effect on the P-LC effect and different precipitation content has different effects. Furthermore, the solute diffusion is pipe diffusion in 5052 alloy with lower precipitation content. However, for 5456 alloy with higher precipitation content, the diffusion is no longer the case but more complex.
2011, 60 (9): 096202.
doi: 10.7498/aps.60.096202
Abstract +
Using the modified finite element method, the nonlinear shell-spring finite element model is established with taking the van der waals force into account. Based on the B-R motion criterion, the dynamic bucking behaviors of multi-walled carbon nanotubes are examined systemically. The dynamic critical loads for buckling and failure of double-walled carbon nanotubes under axial impact load are obtained. It is shown that in the dynamic buckling process of multi-walled carbon nanotubes, the deformation of each wall is harmonious to each other and the change of interlayer spacing is very small. The magnitude and the duration of impact load as well as the length of carbon nanotube have greater effects on the dynamic buckling of carbon nanotubes. For the shorter carbon nanotubes, asymmetrical buckling mode appears earlier. The simulations further show that the stress wave propagation in carbon nanotubes induces the asymmetrical buckling mode. In the dynamic buckling process of carbon nanotubes, there are four circumferential lobes that can be observed obviously, and their wave crest and trough of the lobes change alternately.
2011, 60 (9): 096301.
doi: 10.7498/aps.60.096301
Abstract +
The model of the ternary compound ZnCrS2 is constructed by replacing the Zn atoms in the zinc-blend phase ZnS with Cr at two different positions a and b in a ratio of 1∶1. Then the electronic and the magnetic properties of ZnCrS2 are invescigated by using the plane wave pseudopotential (PWPP) method with the density functional theory (DFT). The results show that both kinds of ZnCrS2 are more stable in the ferromagnetic state than in the anti-ferromagnetic state, and are half-metallic ferromagnets with half-metallic band gaps of 0.964eV and 0.755 eV, respectively. The comparison of two different models reveals that ZnCrS2 in a-position replacement is more sable and also has a larger half-metallic band gap. Furthermore, the spin-polarized electronic density of states, the band structure and the magnetic moment of ZnCrS2 are analyzed in detail. The present results should be useful for the future experimental study.
2011, 60 (9): 096801.
doi: 10.7498/aps.60.096801
Abstract +
The ZnO/Zn0.85Mg0.15O multiple quantum wells(MQWs)are fabricated on m-Al2O3 substrates by plasma-assisted molecular beam epitaxy (P-MBE) using a ZnMgO buffer layers. The reflection high-energy electron diffraction (RHEED) images indicate that the MQWs are of two-dimensional growth .The temperature dependent photoluminescence (PL) of the MQW also shows the quantum confine effect even at room temperature. The PL peak of 3nm MQW is 3.405 eV at 290 K.The PL spectrum in ZnO/Zn0.85Mg0.15O MQW is dominated by localized exciton emission at low temperatures, while the free exciton transition gradually dominates the spectrum at higher temperatures up to room temperature. The exciton binding energy in the 3 nm ZnO/Zn0.85Mg0.15O MQW is about 73 meV.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2011, 60 (9): 097101.
doi: 10.7498/aps.60.097101
Abstract +
The analysis of the frequency dispersion characteristics of the gate-drain capacitance of GaN HEMT indicates that the gate fringe capacitance is responsible for the dispersion difference between the gate-drain capacitance and circle Schottky diode. By fitting the relationship between the additional capacitance of trap and frequency, we discover that the additional capacitance of trap can meet single energy level model only under small gate bias, and meet both single and consecutive energy level model under strong reverse gate bias. The gate fringe capacitance dispersion appears after SiN passivation. It suggests that the trap observed by fringe capacitance is introduced by passivation, which lies in the surface of the ungated region between source and drain. Finally, the low frequency noise technology is used to validate the feasibility of abstracting trap parameter by the gate fringe capacitance. The time constant of single energy level trap obtained by low frequency noise technology is consistent with the result obtained by the gate fringe capacitance under strong reverse gate bias.
2011, 60 (9): 097102.
doi: 10.7498/aps.60.097102
Abstract +
The lattice structures and the electronic structures of different ordered structures in Ba0.5Sr0.5TiO3 are calculated by the first-principles method. The results of geometry structures and overlap populations reveal that the BST{100} ordered structure is tetragonal. The O atoms in Ti-O octahedron parallel to Ba plane and Sr plane are shifted ward Sr plane by 0.065 Å. And the Ti atom in Ti-O octahedron has a off-center displacement of 0.040 Å. The off-center displacements of O atoms and Ti atoms result in the distortion of Ti-O octahedron, and the occurrence of antiparallel spontaneous polarization. Therefore the BST{100} ordered structure is in antiferroelectric phase. The O atoms in BST{110} ordered structure also have a off-center displacement of 0.029 Å, while the Ti atom in Ti-O octahedron is still in-center. This tetragonal structure is in paraelectric phase. The BST{111} ordered structure is in cubic paraelectric phase. The calculated density of states shows that the hybridization between Ti 3d and O 2p plays a primary role in the generation of ferroelectricity. The results of the present work imply that the local order of A site can significantly influences the structural phase transition of disordered BST solid solution.
2011, 60 (9): 097103.
doi: 10.7498/aps.60.097103
Abstract +
The energy band structure, the transmission spectrum and the current-voltage characteristics of the N-doped zigzag graphene nanoribbons (z-GNRs) have been investigated by performing first-principles calculations. The results show the appearance of energy gap and a metal-semiconductor transition induced by N-doping of z-GNRs. With impurity concentration increasing, the current under the same bias decreases significantly, while the transmission coefficient near the Fermi surface decreases gradually. In addition, the length, the width and the N-doping position of z-GNR affect the transport property. Especially, the impurity concentration competes with the N-doping position in the influence on the transport property for narrow z-GNRs.
2011, 60 (9): 097104.
doi: 10.7498/aps.60.097104
Abstract +
We study the wave packet dynamics of two extended Harper models by using the second moment M2(t) and probability distribution Wn(t) numerically. The dynamical behaviors of two extended Harper models in all phases, on all phase boundary lines, and at the bicritical points are studied. For the first extended Harper model, we find that the wave packet is of ballistic diffusion in two metal phases, localized in the insulator phase, and of anomalous diffusion on the phase boundary lines and at the bicritical point. We also find the dynamical behavior on the boundary line of the metal-metal phase transition is the same as that on the metal-insulator phase transition. The spreading at the bicritical point is different from that on the phase boundary lines. For the second extended Harper model, we find that the wave packet is of ballistic diffusion in the metal phase, localized in the insulator phase, and of anomalous diffusion in the critical phase, on the phase boundary lines, and at the bicritical point. We also find the dynamical behavior on the boundary line of the critical-metal phase transition is similar to that at the bicritical point and the critical-insulator phase transition, but different from that of the metal-insulator phase transition.
2011, 60 (9): 097201.
doi: 10.7498/aps.60.097201
Abstract +
Within the tightly-binding Su-Schrieffer-Heeger (SSH) model and a nonadiabatic dynamic evolution method, we study the influence of the choice of zero electric potential energy on the charge injection in a metal/polymer structure. Through the theoretical calculation, we find that the influence of the choice of zero electric potential energy increases with the electric field strength increasing.
2011, 60 (9): 097202.
doi: 10.7498/aps.60.097202
Abstract +
In the study of the noise characteristics of devices by traditional scattering theory,the incoherent transport and the effect of Coulomb interaction on shot noise are not taken into account, which may not be ignored in real nanoscale devices. Based on the equivalent contact model of the scattering region, we derive a unified scattering theory model for current noise, including the effects mentioned above. Our model covers the whole range of transport regime from coherent transport to incoherent transport. Our model also includes the effects of Pauli exclusion and Coulomb interaction on shot noise. Then, a numerical simulation approach is presented for our model. The approach coincides with the equivalent contact model in the property of the scattering region.
2011, 60 (9): 097203.
doi: 10.7498/aps.60.097203
Abstract +
We report on a novel charge generation layer(CGL) of LiF/Al/V2O5 for a stacked organic light-emitting device(SOLED). The two emitting units of SOLED based on the CGL are independent as if they are individual devices. The CGL has an ability to inject electrons and holes into two adjacent emitting units. The luminance efficiency of the SOLED based the CGL is 1.7 times of the control device at the same current density. Moreover, the novel CGL can be prepared only with thermal evaporation without sputtering TIO or co-evaporation of metal and organic material during device fabrication, thus making the device processing.
2011, 60 (9): 097301.
doi: 10.7498/aps.60.097301
Abstract +
Using the density-functional theory, the structural stability and the effect of in-plane electric field on the electronic structure of zigzag graphene nanoribbin (OH-ZGNR), which is terminated by hydroxyl, are explored. It is found that hydroxyl bonding on the ZGNR edge is much more stable than H-terminated ZGNR(H-ZGNRs). The ground state of the ZGNR is spin-polarized with a narrow energy gap. Furthermore, transition from semiconducting to metallic phase in ZGNR can be achieved if a proper in-plane electric field is applied across the edges OH-ZGNR.
2011, 60 (9): 097302.
doi: 10.7498/aps.60.097302
Abstract +
Based on quantum mechanics, a tunneling current of uniaxially strained Si nMOSFET is bulit. The relationships between the tunneling current and device structure parameter, biased voltage and stress are analyzed. The simulation result is shown to accord well with the reported experimentalal result, implying that our model is correct. Our result is also compared with the result of biaxially stressed silicon nMOSFET, which shows that the current of uniaxially straining Si nMOSFET is lower than that of biaxially stressed silicon nMOSFET, and so uniaxial devices have advantages over biaxial devices. The model has a definite physical mechanism and it is suitable not only for uniaxially strained Si nMOSFET, but also for uniaxially strained Si pMOSFET,as long as changing the relevant parameters.
2011, 60 (9): 097401.
doi: 10.7498/aps.60.097401
Abstract +
In this paper, we present the ab initio calculations of S substituting for P point defects (Sp) in KDP crystal. The electronic structure and the relaxing configuration of Sp are studied. The properties of density of states and band structure of KDP with Sp are discussed. The Sp’s in neutral, ±1, and +2 charge states lead to the formation of an isolated SO4 in KDP and no defect state appearing in the energy gap. However, Sp in the -2 charge states induces defect states in the energy gap and therefore laser-induced damage threshold will be reduced.
2011, 60 (9): 097405.
doi: 10.7498/aps.60.097405
Abstract +
Pure ZnO films and In/ZnO films are prepared by sol-gel process on Si substrates.The ratio of In/(Zn+In) are 5%, 8% and 10% separately. Crystal phase structures and photoelectric properties of these films are characterized and these chromaticity coordinates of different samples are also calculated in a CIE-XYZ color system. The results show that preferred growth direction of ZnO film changes from (002) plane to (001) plane and interplanar distance becomes shorter. When doping amount of In is 5%, Zn atoms are replaced by In atoms. Resistivity of the film first decreases and the increases with the increase of the amount of In. Ultraviolet emission peak of spectrum has a redshift; a new peak emerges at 670nm with the increase of In. The sample of 5% emits white-light.The band structures of pure and 5% doping content of film are calculated based on first principles.The mechanism of emitting white-light is discussed from the view point of additional energy level.
2011, 60 (9): 097501.
doi: 10.7498/aps.60.097501
Abstract +
In this paper, band structures of two-dimensional magnonic crystals with square arrangement, triangle arrangement and honeycomb arrangement of Fe cylinders in matrix of EuO are calculated by the plane-wave expansion method. And the effects of arrangements of scatterers on the band gaps of two-dimensional magnonic crystals are discussed. The numerical results show that the gap of the triangle arrangement is the largest in the above three lattices.
2011, 60 (9): 097502.
doi: 10.7498/aps.60.097502
Abstract +
In this paper, the influence of annealing temperature on AC magnetic property of Fe15.38Co61.52Cu0.6Nb2.5Si11B9 nanocrystalline alloy is investigated, and the possible reasons for better high-frequency soft magnetic properties are analyzed. The resistivity decreases as annealing temperature increases. The value of μ'f0 is not in direct proportion to saturation magnetization Ms because of irregular variation of the gyromagnetic ratio with annealing temperature. At annealing temperature Ta=873 K, the alloy has the largest quality factor and relaxation frequency, i.e., Q(1 MHz)=23.1 and f0=25.02 MHz.
2011, 60 (9): 097503.
doi: 10.7498/aps.60.097503
Abstract +
The geometry optimization, the electronic and magnetic properties of the compound Ni4NdB are studied by using first-principles within the local spin-density approximation (LSDA) and the LSDA+U approximation. The results indicate that the system is a metallic conductor with very small band gap, and that the total magnetic moment is provided by the local Nd magnetic moment. The system has very complex bonding, where Nd atoms and the neighboring Ni atoms form metal bonding, also Nd atoms and the neighboring B atoms form the strong ionic banding, besides Ni atoms and the neighboring Ni atoms forming an indirect exchange interaction. Under coulomb interaction, the system magnetic moment is consistent with that of the local Nd atom, and the collapse of magnetic ordering in 2.75 eV happens to the local Ni magnetic moment.
2011, 60 (9): 097504.
doi: 10.7498/aps.60.097504
Abstract +
By using the first principles method based on the density function theory (DFT) and the local density approximation (LDA), we study the ferromagnetic properties in N-doped(1120) ZnO thin films. Magnetic properties in one-N-doped ZnO are investigated. The spontaneous spin polarization comes from N 2p, O 2p and Zn 3d. Magnetic properties in two-N-doped ZnO are also investigated. The calculated results show that ferromagnetism (FM) coupling between N atoms is more energetically favorable for nine geometrically distinct configurations. The origin of the FM state in N-doped ZnO is also discussed by analyzing the coupling of N levels. Finally, the magnetic exchange coefficient and the Curie temperature are discussed. The result indicates that N-doped ZnO thin films show weak FM properties.
2011, 60 (9): 097505.
doi: 10.7498/aps.60.097505
Abstract +
Fe81Ga19 single crystals and polycrystals with different orientations are prepared by zone melting directional solidification. Pole figures show that the deviation degrees between [001] orientation and axis are 12°, 5° and 3°, and the in corresponding axial magnetostrictions parallel to external magnetic field are 254×10-6, 271×10-6 and 291×10-6. The[001]orientation single crystal is determined by back-reflection Laue, and the magnetostriction is 312×10-6. The results reveal the relationship between crystallographic orientation and magnetostriction, and the increase of magnetostrictions with deviation degree decreasing. The deviation degrees between [001]orientation and axis of polycrystals are determined by Electron Backscattered Diffraction to be 18.4°, 15.2° and 14.8°, and thir corresponding magnetostrictions are 180×10-6m, 230×10-6 and 235×10-6.
2011, 60 (9): 097506.
doi: 10.7498/aps.60.097506
Abstract +
A FeCuNbSiB/FeNi/PZT laminated composite is developed and comparatively studied with a FeNi/PZT laminated composite. The influence of high-permeability FeCuNbSiB alloy on applied DC magnetic field, piezomagnetic coefficient and optimal bias magnetic field of FeNi is investigated. The experimental results show that compared with in the two-phase FeNi/PZT, in the three-phase FeCuNbSiB/FeNi/PZT laminated composite, (i) the optimal bias magnetic field decreases from 200Oe to 55Oe, and the maximum magnetoelectric(ME) voltage coefficient increases from 1.59V/Oe to 2.77V/Oe; (ii) under small bias magnetic field, the ME voltage coefficient increases by a factor of 1.7—7.8; (iii) the sensitivity of the ME voltage coefficient for the laminated composite to a DC magnetic field increases from 19.1mV/Oe to 158.6mV/Oe. The variations in ME effect of three-phase composie result from the enhancement of magnetizetion at end faces, which is generated by introducing the high permeability material phase.
2011, 60 (9): 097701.
doi: 10.7498/aps.60.097701
Abstract +
Pb(Zr0.52,Ti0.48)Nb0.04O3 (Nb-doped PZT, PZTN) films are deposited on Pt/TiOx/SiO2/Si substrates with BaPbO3(BPO) buffer layers by RF-magnetron sputtering method. The magnitudes of tensile stress in PZTN films can be changed by adjusting the thickness of BPO layer. For PZTN films with 68 nm and 135 nm-BPOs, the tensile stresses measured by 2θ-sin2ψ method are 0.786 and 0.92 GPa respectively. Enhanced ferroelectric is observed in PZTN film with raised tensile stress. The remanent polarization and the coercive field for PZTN films with tensile stresses of 0.786 GPa and 0.92 GPa are 41.2μC/cm2(70.7 kV/cm) and 44.1μC/cm2(58.1 kV/cm) respectively. The leakage current decreases from 6.57×10-7A/cm-2 to 5.54×10-8A/cm-2 while tensile stress of PZTN film is raised from 0.786 to 0.92GPa. Fine XRD scan is performed with grazing incidence geometry to investigate the phase composition of PZTN films. Rietveld analysis shows that an increased tensile stress in PZTN film can promote the amount of monoclinic phase,which may be the reason for the ferroelectric property improvement.
2011, 60 (9): 097801.
doi: 10.7498/aps.60.097801
Abstract +
The electronic structures and the optical properties of pyrite containing twenty natural impurities, Co, Ni, As, Se, Te, Cu, Au, Ag, Mo, Zn, Tl, Sn, Ru, Pd, Pt, Hg, Cd, Bi, Pb and Sb, are investigated using the density functional theory and the plane wave pseudopotential method, and the catalytic activity of pyrite is discussed. For the transition metal-bearing pyrite, there are introduced impurity energy levels in the band contributing from impurity d orbital, while for the other metal and non-metal-bearing pyrite, the impurity energy levels are contributed from impurities s or p orbital. The presences of Cu, Mo, As, Au, Ag or Ni can enhance the electrocatalytic ability of pyrite to the oxygen reduction. All the impurities, except Zn, Mo, Ru, As, Sb, Se and Te, can enhance the ability of pyrite surface to capture electrons and hence the recombination rate of photoinduced electrons and holes wile be reduced. Calculations of optical properties indicate that Cd, Hg, Ru, Se, Te and Zn impurities each have small influence on the absorption band edge, while the presence of other impurity makes a red shift of absorption band edge of pyrite. Especially, the presences of Au and Ag impuritie increase the adsorption coefficient of pyrite by two orders of magnitude.
2011, 60 (9): 097802.
doi: 10.7498/aps.60.097802
Abstract +
Bi:α-BaB2O4 crystal samples are grown by the traditional Czochralski method and the obtained samples are irradiated by electron beam. Absorption and emission spectra of the samples are measured at room temperature before and after their electron irradiation. Under 808 nm LD excitation, broadband (FWHM at 52 nm) near-infrared emissions centered at about 1135 nm are observed in electron-irradiated Bi:α-BaB2O4 samples. Both the emissions are believed to be due to Bi+ ions. Electron beam helps to reduce Bi3+ and Bi2+ into univalence. The formation processes in the samples with different radiation doses are not the same, which is primarily discussed in this work.
2011, 60 (9): 097901.
doi: 10.7498/aps.60.097901
Abstract +
In high-power microwave diode design, the space-charge-limited current is important because of its relation to the diode property and the formation of the virtual cathode. Although the Langmuir–Blodgett law, as a numerical solution, is helpful, a simple functional expression is more convenient for practical research and can avoide the divergence of the series for large R\-c/R\-a. First principle is used to generalize two-dimensional space-charge-limited current for planar plane capacitor and coaxial cylinders, and its reliability has been examined adequately. In this paper we obtain the functional expression of space-charge-limited current for concentric sphere, and the space-charge field factor in this expression by comparing the classical Langmuir current with the current from concentric sphere.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2011, 60 (9): 098101.
doi: 10.7498/aps.60.098101
Abstract +
AlN nanowire macro-arrays are successfully synthesized and characterized by the second template method. In the article we mainly research the process of preparing the AlN nanowire macro-arrays each with a certain orientation and uniform diameter by the chemical vapor deposition (CVD) method. Metal nanoparticles are prepared by CVD and self-assembled PS sphere templates, and then AlN nanowires macro arrays are compounded by the CVD on template and the metal nanoparticles on the template as a catalyst. The samples are observed by SEM and TEM, AlN nanowire macro-arrays have an area of about 0.3 mm×0.2 mm, they are well distributed, and have an average diameter of about 41 nm, an average length of about 1.8μm, distributed density and coverage of large macro-hexagonal AlN nanowire arrays. So a method to controllably prepare AIN macroscopic nanowire arrays is obtained.
2011, 60 (9): 098102.
doi: 10.7498/aps.60.098102
Abstract +
A series of white organic electroluminescent devices with a quantum well structure were fabricated based on a new type of organic metal complex bis(2-(4-trifluoromethyl-2-hydroxyphenyl) benzothiazolate) zinc (Zn(4-TfmBTZ)2) by electroplex at NPB/Zn(4-TfmBTZ)2 interface. The results show that the introduction of the hetero-junction quantum well structure can increase effectively the efficiency of electroplex emission, color rendering index(CRI),and the color coordination stability. The optimized device ITO/NPB (60 nm)/Zn(4-TfmBTZ)2(3.0 nm)/NPB (4.0 nm)i> /Zn(4-TfmBTZ)2(30 nm) /Alq3 (30 nm)/LiF(1.5 nm)/Al(150 nm) is obtained with color coordinates of (0.324, 0.337), the highest CRI of 92.5, a maximal brightness of 2013 cd/m2, and a maximal efficiency of 1.03 cd/A,. This device shows very high color stability when the driving voltage is varied from 10 V to 14 V.
2011, 60 (9): 098103.
doi: 10.7498/aps.60.098103
Abstract +
In order to describe the pore scale fractal distribution, we present a 3D network model for fractal porous medium in this paper. According to the proposed model we simulate the immiscible two-phase flow displacement in a medium and study the viscous fingering pattern of displacement front influenced by the fractal dimension Df for pore size distribution and viscosity ratio M. The simulation results show that the capacity dimension Dh of the viscous fingering pattern decreases with Df and M increasing, and their quantitative relationship is derived by fitting the obtained data.
2011, 60 (9): 098104.
doi: 10.7498/aps.60.098104
Abstract +
Based on thermo-optical phase transition effect, VO2/ZnO nanostructure composite films are designed and successfully prepared by depositing ZnO films with high (002) orientation on soda-lime glass substrates first, and then the vanadium dioxide films are fabricated by depositing vanadium metal films on ZnO films at room temperature and thermal oxidation treatment. The thermochromic properties of VO2/ZnO nanocomposite films are measured and compared with the single-layer VO2 films on SiO2 glass substrates with the same thickness. The lattice distortion and bonding state of the VO2/ZnO nanocomposite films before and after phase transition are observed and analyzed by Raman spectroscopy at the different temperatures. The relations of infrared switching properties and phase transition temperature to nanostructure and film thickness are discussed. The results show that the thermochromic optical properties are improved significantly. VO2/ZnO nano-composite films have high (002) orientation so that the infrared transmittance before phase transition is more than twice as large as that after phase transition, and the width of thermal hysteresis is narrowed by about 5℃ and phase transition temperature is decreased about 8℃. It suggestes that the nano-composite films can significantly reduce the phase transition temperature and enhance the infrared light switch modulation capabilities of VO2 thin films.
2011, 60 (9): 098105.
doi: 10.7498/aps.60.098105
Abstract +
TiO2 particle single layer and SiO2-TiO2 particle double layers on glass substrate are obtained by self-assembly technique. For SiO2-TiO2 particle double layers, SiO2 Particle layer is made by spin-coating with SiO2 particles closely packed,while TiO2 Particle layer is obtained through layer-by-layer method in both cases of TiO2 particle single layer and SiO2-TiO2 particle double layers, with TiO2 particles non- closely packed. The theoretical roughness of TiO2 particle single layer and SiO2-TiO2 particle double layers are analyzed. Microstructures of these two coatings are studied with scanning electron microscope. Water contact angles before and after exposure to UV light are measured by drop meter separately. Light catalytic ability of organics degradation is determined by spectrophotometer. The experimental results show that the water contact angles of the as-prepared particle films increase if these coatings are stored in dark for days till the contacts become stable, while if exposed to UV light, they become super-hydrophilic with contact angles approaching 0°,that the roughness greatly affects water contact angle, and that the catalytic ability of SiO2-TiO2 particle double layers is superior to TiO2 particle single layer.
2011, 60 (9): 098106.
doi: 10.7498/aps.60.098106
Abstract +
The directional cellular growth of SCN-0.2%Salol transparent alloy in the presence of shear flow at the liquid-solid interface is in-situ observed, and the cellular spacing adjusting mechanism is carefully investigated. It is found that the cellular array deflects forward the incoming flow direction, and the stable cellular spacing decreases with the increase of the flow rate. This is due mainly to the reducing destabilization wavelength caused by shear flow. Instead of the double symmetric splitting mode under static condition, the splitting mechanism of cellular growth exhibits multiplicity, which is characterized mainly by (i) multi-splitting and asymmetric splitting, and (ii) secondary branches appearing on the upstream side whose growth direction subsequently shifts to ward the direction paralleled to the trunk to form new cells. Meanwhile, the selected mechanism transits from the weak cells eliminated by the relatively strong ones on both sides during static solidification to the growth of weak cells on the downstream side suppressed by the stronger cells at the upstream side when shear flow is applied.
2011, 60 (9): 098107.
doi: 10.7498/aps.60.098107
Abstract +
A new growth method of roughed p-GaN has been demonstrated in this paper. First, some crystal seeds of p-GaN are obtained by utilizing low-temperature growth. Then, a p-GaN high-temperature expitaxy layer is grown on it subsequently with a fast growth rate, which will enlarge the roughness degree. Compared with the luminous flux of the conventional light emitting diode with flat p-GaN, the luminous flux is improved by 45%. Meanwhile, it is found that the problems of large reverse current and high forward bias aroused by the low-temperature epitaxy are also solved.
2011, 60 (9): 098108.
doi: 10.7498/aps.60.098108
Abstract +
We have investigated the growth of thin selenium layer on Si (100) substrate by molecular beam epitaxy (MBE). By controlling the temperatures of the silicon substrate and the selenium source during growth, an ultrathin film of Se is successfully grown on the Si (100) substrate. As the Si (100) surface is passivated by the ultrathin film of Se, the electrical property of the Ti/n-Si (100) contact is shown to be ideally ohmic, with low resistance and relatively high thermal stability.
2011, 60 (9): 098109.
doi: 10.7498/aps.60.098109
Abstract +
Molecular alignment of nano-thin liquid crystal 5CB film confined between highly polished steel ball and quartz disk under shear is studied using Raman spectroscopy. The results show that an acceptable signal-to-noise ratio as high as 20:1 can be obtained under certain experimental conditions. In addition, the intensity of the Raman spectrum reaches its peak (minimum) value when polarization of the laser is parallel (perpendicular) to the direction of shear motion. This indicates that the molecules of liquid crystal 5CB film are oriented along the direction of shear motion. Furthermore, the influence of shear speed on the intensity of Raman spectroscopy of nano-thin liquid crystal 5CB film was investigated, and its film thickness was analyzed based on a relative optical interference intensity technique.
2011, 60 (9): 098110.
doi: 10.7498/aps.60.098110
Abstract +
In this paper,the degradation of irradiated GaAs/Ge single junction (SJ) solar cells is evaluated under the orbital environments using the displacement damage dose method. Firstly the electric-property changes of the SJ solar cells are experimentally obtained with the fluencies of electrons and protons of various energies under ground-based irradiation simulators. Based on the experimenal results and the calculated non-ionization energy losses (NIELs) of the electrons and protons in GaAs, the equivalent exponent n is obtained to be 1.7 for various electron energies,while the equivalent coefficient Rep for electron displacement damage converted into that of protons is 5.2. Furthermore, a degradation formula of the electrical property of the domestic SJ solar cell is established as a function of displacement damage dose during the particle irradiation. Using the displacement damage technique, the orbital evolution of the electric property degradation of the domestic SJ cell is predicted in this paper. In the meantime, the shielding effects of the cover glass with different thicknesses are also evaluated.
2011, 60 (9): 098111.
doi: 10.7498/aps.60.098111
Abstract +
The armchair (n,n) single walled carbon nanotubes with n=2—20 are studied by using the first principle density functional theory at the B3LYP/3-21G(d) level of theory combined with the periodic boundary conditions in simulating the ultra long tube model. The structure parameter, the energy, the band structure, and the energy gaps are obtained. The results show that the tube diameter and the energy of formation are closely related to n. The fitted analytical equations are developed with a correlation coefficient larger than 0.999. The energy gaps of (2,2) and (3,3) carbon nanotubes are 1.836 eV and 0.228 eV and the tubes have indirect energy gaps. For n=4 to 20, the energy gaps are quite small (between 0.027 eV and 0.079 eV), showing metal conductivity as well as direct energy gaps.
2011, 60 (9): 098401.
doi: 10.7498/aps.60.098401
Abstract +
Two-color quantum well infrared photodetectors (QWIPs) with two stacks of QW series have been grown by molecular beam epitaxy and processed into mesa structure devices with only two ohmic contacts by photolithography and wet chemical etching. By changing QWIP parameters, including barrier height, well width, doping level and period number, the total bias voltage can be distributed to the two stacks in such a way that the stacked structure will show different photoresponse characteristics. The photocurrent spectrum measurements demonstrate that sample 1 can work alternately between the two atmospheric windows of 3—5 μm and 8—12 μm by tuning the voltage, while sample 2 can photorespond simultaneously to the irradiation of the two atmospheric windows. In this paper, the physics behind the two-contact type of QWIP is discussed. The voltage tunability and the simultaneous photoresponse are attributed to the change of photoconductive gain with the bias voltage and the distribution of the total bias between the two series. We here focus the discussion on the voltage tunability of sample 1. Compared with the three-contact-per-pixel structure, two-contact-per-pixel structure can greatly facilitate the dual-band focal plane array (FPA) device fabrication and increase the FPA fill factor.
2011, 60 (9): 098402.
doi: 10.7498/aps.60.098402
Abstract +
In this paper, N-type Bi2Te3 and p-type Sb2Te3 thermoelectric thin films are deposited by ion beam sputtering with Bi/Te and Sb/Te binary compound target. Sb2Te3 thin films and Bi2Te3 thin films are annealed at different annealing temperatures for 1 h and their thermoelectric properties are characterized. When the annealing temperature is 150 ℃, both the Seebeck coefficient and power factor of the Bi2Te3 thin films have maximal values of -148 μVK-1 and 0.893×10-3 Wm-1K-2 respectively. Sb2Te3 thermoelectric thin film has a seebeck coefficient of 117 μVK-1 and a maximal power factor of 0.797×10-3 Wm-1K-2 when the annealing temperature is 200 ℃. Therefore, Sb2Te3 thin films at the annealing temperature of 200 oC and Bi2Te3 thin films at the annealing temperature of 150 ℃ are selected to fabricate the single thin film thermoelectric generation. When the temperature difference between the cold side and the heat side is 50K, the output voltage of the single thin film thermoelectric generation is 15.26 mV and the maximal output power is 0.129 μW.
2011, 60 (9): 098501.
doi: 10.7498/aps.60.098501
Abstract +
In this paper, quasi-2D threshold voltage model of strained Si nMOS with polycrystalline SiGe gate is established based on the Guass Law and its I-V character model is also built based on the current density equation. The influence of relevant parameter on threshold voltage is analyzed by numerical analysis, and the validity of the model is verified by device simulator.
2011, 60 (9): 098502.
doi: 10.7498/aps.60.098502
Abstract +
Threshold voltage drift is one of the most important characteristics of device degradation. Based on the research of threshold drifts of the front and the back gate of SOI SONOS EEPROM, device degradation is studied in irradiation environment. Physical mechanism of threshold drifts is analyzed through physical band and mobile carrier analysis. And measures to improve device performance are proposed.
2011, 60 (9): 098503.
doi: 10.7498/aps.60.098503
Abstract +
In this paper, switching behaviors of MQCA inverter and majority logic gate with various nanomagnet thicknesses and spacings are studied. Single domain approximation Landau-Lifshitz-Gilbert equation is employed to model and simulate the circuits. It is shown that thicker nanomagnet needs larger switching magnetic pulse and logic circuits comprised of thicker nanomagnet demonstrate slower switching; majority logic gate needs more time to switch than inverter when they have the same nanomagnet thicknesses and spacings. Moreover, it is also shown that nanomagnet spacing has a larger effect on switching behavior of inverter than on majority logic gate.
2011, 60 (9): 098701.
doi: 10.7498/aps.60.098701
Abstract +
Neuron is a basic unit of information transmission in the nervous system . Neuron encodes the information input from the dendrites by generating action potential sequences of different firing patterns. The different firing patterns result from different action potential initial dynamic mechanisms for neurons to generate spikes. The result of competition between neuron ion currents with different dynamic features in the sub threshold potential determines the action potential initial dynamic mechanism. In this paper, we adopt a minimum neuron model to design the wash-out filter from a physiological view for achieving the transition between different action potential initial dynamic mechanisms and for verifying that the wash-out filter control changes the action potential initial dynamic mechanism of neuron by affecting the result of competition between currents with different dynamic features in the sub-threshold potential.
2011, 60 (9): 098702.
doi: 10.7498/aps.60.098702
Abstract +
A low loss and broadband photonic bandgap (PBG) terahertz photonic crystal fiber (PCF) with high birefingence is proposed. Terahertz wave is confined within the core surrounded by the cladding with triangular lattice arrangement of subwavelength air holes. The birefringence and the loss of the fiber are investigated by using a full-vectorial finite element method. The numercal simulation shows that within a broadband area of about 0.3THz, the loss of the near-rectangle core THz PBG photonic crystal fiber is less than 0.009cm-1, the phase birefringence is on the order of 10-3, and the group birefringence even can reach 10-2.
2011, 60 (9): 098703.
doi: 10.7498/aps.60.098703
Abstract +
In this paper, we develop a new method to eliminate the background noise in the image of biomacromolecule with complex conformation in order to obtain highly effective and accurately quantitative information. By using this algorithm, we are able to deal with the atomic force microscopic imags of both linear DNA and branch DNA. Furthermore, our method can be extended to the study of the images in the other field.
2011, 60 (9): 098801.
doi: 10.7498/aps.60.098801
Abstract +
One main factor of restricting industrial crystalline solar cell efficiency is the optical losses caused by the metal front side contacts, including the absorption loss and reflection loss. Based on screen-printed and screen-printed seed layers thickened by light-induced electroplating solar cells, in this paper various cases of optical losses due to the metal contacts are analyzed. Taking into account the reflections in the air-glass interface and the edge regions of metal contacts, the optical losses are simulated by assuming approximately half-oval cross-section of metal contacts. The results show that the effective width ratio is about 40% of the metal contact geometry width. By measuring and calculating the reflection spectra of different types of samples, the optical losses of the metal front side contacts of solar cells are obtained in theoretical simulation and experimental measurement. The corresponding theory and the experimental results are in good agreement with each other.
2011, 60 (9): 098901.
doi: 10.7498/aps.60.098901
Abstract +
As a typical open complex system, airline network usually interplays with the economic environment during its self-organized evolution. In this paper, we investigate empirically the correlation between gross domestic product (GDP) and the Chinese airline network (CAN). It is found that the degree of the node has formed a linear correlation with its corresponding GDP since 1998 while a year later the CAN began to exhibit double-power-law degree distribution. Based on the observation, the dynamical equation of CAN is derived. A multiplicative process-like evolution pattern, which strongly depends on the GDP growth rate, is obtained. We demonstrate that such a process coupled with the exponential increase of nodes can yield a double-power-law distribution. The simulation is applied to CAN and we find that the simulation result is in agreement with real CAN.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2011, 60 (9): 099201.
doi: 10.7498/aps.60.099201
Abstract +
For the case of severe convection occurring in the southern region of North China on July 8, 2009, the three dynamical factors, namely, vertical component of convective vorticity vector, moist thermodynamic advection parameter and wave-activity density are diagnosed. The result shows that the anomalous-value regions of dynamical factors are located mainly in middle and lower troposphere over the strong precipitation area. Since the dynamical factors can effectively describe the synthetical characteristics of strong convective system, such as vertical shear of horizontal wind, advection of potential temperature, vorticity perturbation and baroclinicity of moist atmosphere, they correspond to the observation of 6-h accumulative rainfall in horizontal distribution patterns. Using the 6-h, 12-h, 18-h and 24-h forecasting dataset of U.S. NCEP/NCAR 0.5-Degree GFS, the dynamical factors are calculated to analyze their indications of precipitation forecasting during a longer period. The results show that during June 2 – Oct 1, 2009, the 6-h, 12-h, 18-h and 24-h forecasted dynamical factors each have an indication of strong precipitation. The moist thermodynamic advection parameter suggests that the precipitation is best among the three dynamical factors.
2011, 60 (9): 099202.
doi: 10.7498/aps.60.099202
Abstract +
The sliding spectral (SS) method of processing radio occultation data in multipath zone is introduced in detail and compared with back propagation (BP) method through processing simulated data and COSMIC soundings. The modeled signals are inverted with the use of two methods: BP method and SS method. Both methods can solve the problem of calculating bending angle profiles in multipath regions. Better agreement with Abel integral is indicated by the BP method. The BP method is almost free from noise, while the SS method will be affected severely by noise. About 4500 COSMIC radio occultation soundings are retrieved by the BP method and the SS method, and the statistical comparison of retrieved refractivity with that from ECMWF analyses shows that the SS method has better penetration ability than the BP method in the lower moist troposphere. The mean of fractional difference in refractivity retrieved by the BP method is generally smaller than that by the SS method.
2011, 60 (9): 099203.
doi: 10.7498/aps.60.099203
Abstract +
Variational data assimilation is an advanced technique to provide correct and high quality initial fields for the numerical model. Digital filter is not restricted to initialization; it may also be implemented as a weak constraint penalizing the analysis towards a balanced state in a preoperational 4D-Var system. The constraint is imposed only on the analysis increments to damp spurious fast oscillations associated with gravity–inertia waves. The influence of DFI as a weak constraint on 4D-Var forecast is assessed by assimilation experiments with the recently occurring severe snow weather. It is shown that the weak constraint imposed only on the increments manages to control efficiently the emergence of fast oscillations in the resulting forecast while maintaining a closer fitting to the observations.
2011, 60 (9): 099204.
doi: 10.7498/aps.60.099204
Abstract +
Based on the concept of entropy in information theory, the entropy of meteorological elements is determined and used to analyze the uncertainty of the global temperature field anomaly from the climate state (1971—2000) on different time and spatial scales. It is found that the temperature climate entropy (CE) possesses a zonal distribution, increases from tropics to mid-high latitudes and has an obvious difference between the ocean region and the continent, thereby being able to distinguish the climatic zones properly. The temperature CE in low-mid troposphere increases with altitude increasing, while in extratropical the situation retains above 300 hPa but below 300 hPa the situation is reversed, and this feature is more obvious in high latituderegions. On the whole, the temperature monthly entropy (ME) is obviously dependent on season change: it is smallest in summer and largest in winter. Besides, there exists a distinguishable interdecadal period. Different monthly ME values from low atmosphere to high atmosphere each have an obvious five -to-ten year quasi-period oscillation. All the spatiotemporal characteristics and their relationships with annual temperature range verify the usefulness of the entropy in meteorology, and it is an effective method to measure the uncertainty of the meteorological elements.
2011, 60 (9): 099205.
doi: 10.7498/aps.60.099205
Abstract +
With nonlinear similarity method, we divised the seasons for whole China on the basis of daily mean temperature, pressure, relative humidity and precipitation at 752 stations for the period 1961—2008, and analyze the seasonal division for eight regions of China and seasonal times. In addition, the relevant statistic data are established which contain the annual variation in frequency of extreme temperature in China. By combining these two research findings, their relationship over the past 48 years is found through correlation analysis and sensitivity test. The results show that: (1) in most areas of China, the spring and summer starting time move up, their durations are extended, autumn starting time changes a litter, and its duration is extended, while winter is pushed back the starting time, and its duration is shortened. (2) With the summer extending, the frequency of extreme high temperature is increased in most areas of China except East China, while the shortening of winter results in the frequency of extreme low temperature declining markedly. (3) The existence and the annual change of extreme high and low temperature are the reason why the lengths of summer and winter change, and they are also the main reason why the substantial fluctuations of the lengths of summer and winter take place.
2011, 60 (9): 099401.
doi: 10.7498/aps.60.099401
Abstract +
Faraday rotation (FR) is one of the important error sources for passive microwave remote sensing from space. In this paper, the principle of FR variation is studied. The influence of FR on accuracy for microwave radiometer measurement is analyzed. We concentrate on FR correction both at 1.4 GHz for the orthogonal channel brightness temperature Tv and at 10.7 GHz for the correlative channel brightness temperature U. By using the simulated observational data of spaceborne microwave radiometry at one point in Hainan province in 2006, we compare the effects of two approaches: correction by auxiliary data (IRI model correction) and correction by polarimetric mode (Yueh and Ribó methods). Noise generated by the Monte Carlo mode is included in the simulation. Then a new method of using TEC data released by international GNSS service (IGS) is proposed. For correction of Tv at 1.4 GHz, correction made by polarimetric mode is better than that by auxiliary data. Yueh method is best in effectiveness while IRI model method is worst. For the correction of U at 10.7 GHz, the correction by polarimetric mode is invalid, only correction by auxiliary data is valid. IGS data method greatly improves the correction accuracy and can replace the method of IRI model for nearly real time correction or final data correction.
2011, 60 (9): 099402.
doi: 10.7498/aps.60.099402
Abstract +
As one of important and effective means for modifying the ionosphere, chemical release can produce artificial ionospheric holes attributed to ionization depletion, which also greatly affect the short-wave propagation. In this paper, a neural gas multi-point release dynamics model is proposed baseed on mono-point one, and then the morphological control effects of chemical substances, releasing altitude, releasing mode and mass on artificial ionospheric hole are discussed. Furthermore, the short-wave propagation effect of artificial ionospheric hole is simulated and investigated by the 3-D numerical ray tracing.
