Vol. 62, No. 10 (2013)
Polarization switching dynamics of vertical-cavity surface-emitting laser subject to negative optoelectronic feedback
2013, 62 (10): 104208. doi: 10.7498/aps.62.104208
Using the extended spin-flip model, we theoretically investigate the polarization switching dynamics of a vertical-cavity surface-emitting laser subject to negative optoelectronic feedback. The results show that when the laser operates at two different the spin-flip rates, the feedback intensity and delay time have great influence on polarization switching dynamics. At a slow spin-flip rate, with the increase of feedback intensity, switching current increases linearly, that the X polarization mode is compressed is contrary to the reported results based on isotropic optical feedback. The reason may be due to the fact that the negative optoelectronic feedback improves the X polarization mode threshold; the effect of delay time will vary with feedback intensity. At a fast spin-flip rate, the effect of feedback strength is different from at a slow spin-flip rate, the switching point current undergoes a process in which the current increases first and then decreases gradually, the switching point current is more sensitively dependent on the feedback strength; while effect of the delay time is similar to that at a slow spin-flip rate. In addition, we find that the spontaneous emission noise has a great influence on polarization switching dynamics.
Temperature-dependent relation between junction temperature and 1/f noise in high power semiconductor laser
2013, 62 (10): 104209. doi: 10.7498/aps.62.104209
The junction temperature rise may not only affect its output power, slope efficiency, threshold current and lifetime, but also will cause the spectral broadening and wavelength shift in a high power semiconductor laser. Therefore, thermal management becomes one of the main problems in research and development of pump laser. In this paper the physical model of the noise power spectrum and junction temperature variation is first established; according to the compression sensing theory, and after sparsing the measured aliasing composite noise signal containing Gaussian white noise and 1/f noise, the basic pursuit denoising algorithm is used to do denoising; through changing the iterations times of the used algorithm and the size of measurement matrix, the curves of the ration between noise voltage power spectrum and junction temperature variation are obtained, thereby avoiding the complexity of direct measurement of the junction temperature. The numerical estimation results can better guid us in doing the thermal management work in high power semiconductor lasers.
2013, 62 (10): 107301. doi: 10.7498/aps.62.107301
Within the framework of the single-band effective mass approximation method, the Floquet theorem, and the transfer-matrix technique, we investigate single-electron photon-assisted tunnelling in a double-well potential with the time-periodic field and Rashba and Dresselhaus spin-orbit coupling. The transmission probability displays statellite peaks on both sides of the field-free resonant peaks. The results show that the single-electron spin tunnelling can be controlled through changing the structure of the double-quantum-well and the intensity of the applied electric field. These advantages are useful for optimizing the semiconductor spintronic devices.
2013, 62 (10): 100201. doi: 10.7498/aps.62.100201
Riemann theta function and other several kinds of new solutions to the second kind of elliptic equation are obtained to construct the infinite sequence complexiton solutions of nonlinear evolution equations. Based on this, applying Bcklund transformation and nonlinear superposition formula of the solutions to the second kind of elliptic equation and Riccati equation, mKdV equation is chosen as an example to seek infinite sequence new complexiton solutions with the help of symbolic computation system Mathematica, which are composed of Riemann theta function, Jacobi elliptic function, hyperbolic function, triangular function and rational function in several forms.
Exact traveling wave solutions for simplified model of Gross-Pitaevskii equation in the 1D-Tonks-Girardeau gas
2013, 62 (10): 100202. doi: 10.7498/aps.62.100202
By using a dynamical system method, in this paper studied are some exact traveling wave solutions and dynamic behaviors of these traveling wave solutions for simplified model of Gross-Pitaevskii (GP) equation in the 1D-Tonks-Girardeau gas. The effects of the behaviors on the parameters of the systems are also studied. Under different parametric conditions, six exact explicit parametric representations of the traveling wave solutions for simplified model of GP equation in the 1D-Tonks-Girardeau gas are given.
2013, 62 (10): 100301. doi: 10.7498/aps.62.100301
Phonon scattering has a non-negligible influence on the characteristics of carbon nanotube field effect transistor (CNTFET). Using the ballistic transport model, the device parameters under phonon scattering are analyzed, and then the CNTFET phonon scattering model is established. To reduce the complexity of this model so that simulation speed can be improved, the effects of phonon scattering is studied through analyzing chirality, temperature and energy, and therefore a new CNTFET phonon scattering model is established with linear approximation. By analyzing the scattering current changes, correctness and validity of the model are demonstrated. The proposed model is easier for calculation and has less computational complexity compared with semi-classical scattering model.
Berry phase and Hannay's angle of an electromagnetic mode system driven by harmonic field with Born-Oppenheimer approximation
2013, 62 (10): 100302. doi: 10.7498/aps.62.100302
In this paper, we investigate the Berry phase and Hannay's angle of an electromagnetic mode system driven by harmonic field with Born-Oppenheimer approximation and obtain their algebraic expressions by theoretical calculation. The semiclassical relation between Berry phase and Hannay's angle is discussed. We find that besides the usual connection term, the Berry phase of BO hybrid system contains a novel term brought forth by the coupling induced effective gauge potential. This quantum modification can be viewed as an effective Aharonov-Bohm effect. Moreover, a similar phenomenon is founded in the Hannay's angle of classical BO hybrid system, which indicates that the Berry phase and Hannay's angle possess the same relation as the usual one. Besides, our theory can also be used to generate Artificial gauge potentials for neutral atoms.
2013, 62 (10): 100303. doi: 10.7498/aps.62.100303
In this paper, we present a high-speed physical quantum random number generator using analog/digital converter (ADC), which is based on the random time distribution of single photons emitted by the stongly attenuated pulsed laser diode. With this scheme, the generation rate of random numbers can increase more than tenfold. A preliminary experiment consists of the time amplitude converter and 16 bit ADC, and the data generated by the system pass the pseudo-random number test program test standards. The experimental setup is efficient and robust against mechanical and temperature disturbances.
Quantum nondemolition measurement of two-photon Bell-state and three-photon Greenberger-Horne-Zeilinger-state based on weak nonlinearities
2013, 62 (10): 100304. doi: 10.7498/aps.62.100304
The scheme for quantum nondemolition measurement of two-photon Bell-state and three-photon Greenberger-Horne-Zeilinger (GHZ)-state is proposed based on weak nonlinearities and linear-optics elements. We first describe a scheme of the symmetry analyzer for two-photon Bell-state by using beam splitters and cross-Kerr nonlinear medium. According to this symmetry analyzer for two-photon Bell-state and the controlled-NOT gates we construct a three-photon state analyzer which can completely and nondestructively discriminate eight three-photon GHZ states.
2013, 62 (10): 100305. doi: 10.7498/aps.62.100305
The canonical quantization of Dirac field in a finite volume is studied. Following the idea of taking the boundary conditions as primary Dirac constraints, we propose a method to treat both the intrinsic constraints and boundary conditions equally. We shall work in the discrete version and quantize the model canonically. In order to verify our method to treat the intrinsic constraints and boundary conditions on the same footing, we obtain the same results by choosing two different subsets of constraints to construct the intermediate Dirac brackets.
2013, 62 (10): 100306. doi: 10.7498/aps.62.100306
In this paper, the phenomenon of double barrier scattering in spin-orbit coupling Bose-Einstein condensate is studied and the analytical expression of transmission coefficient of the system is therefore obtained. On the basis of the above study, how to deal with Klein tunneling and bound Dirac particles is also discussed to devise an experimental scheme of trapping Dirac particles in captivity. Besides, numerical simulation of the barrier scattering pattern of Dirac particles is performed in this paper by the time splitting spectral method. Through the analysis of transmission situation of Dirac particles directing at the Klein barrier in both the center and margin part of blocked area and the study of the influence of non-linear interaction on the evolution of Dirac particles from both repelling and attracting effect, the conclusion can be drawn that although the influence of non-linear interaction on scattering property of particles is negligible to some extent, the strong non-linear interaction will completely destroy the momentum distribution of wave packets so that the result of barrier scattering of Dirac particles can be dramatically changed.
2013, 62 (10): 100501. doi: 10.7498/aps.62.100501
Detecting homoclinic orbits is a key problem in nonlinear dynamical systems, especially in the study of bifurcation and chaos. In this paper, we propose a new method to solve the problem with trajectory optimization. By defining a distance between a saddle point and its near trajectories, the problem becomes a common problem in unconstrained nonlinear optimization to minimize the distance. A subdivision algorithm is also proposed in this paper to improve the integrity of results. By applying the algorithm to the Lorenz system, the Shimizu-Morioka system and the hyperchaotic Lorenz system, we successfully find many homoclinic orbits with the corresponding parameters, which suggests that the method is effective.
The mean extinction time and stability for a metapopulation system driven by colored cross-correlated noises
2013, 62 (10): 100502. doi: 10.7498/aps.62.100502
In this paper, the stability for a metapopulation system driven by colored cross-correlated noises is investigated based on the Levins model. The stationary probability distribution and the explicit expression of the mean extinction time are derived according to the Fokker-Planck equation. Numerical results show that in the case of colored correlation between two noises, the addictive noise and the multiplicative noise intensity weaken the stability of metapopulation, and the correlation strength enhances the stability of metapopulation. If the correlation strength between the two noises is negative, the mean extinction time is a decreasing function of intensities of the two noises, but a increasing function of correlation time; if the correlation strength between the two noises is positive, then the mean extinction time is a decreasing function of addictive noise intensity and correlation time, but a non-monotonic function of multiplicative noise intensity.
2013, 62 (10): 100503. doi: 10.7498/aps.62.100503
The Euler's dynamical equation which describes the attitude motion of a perturbed rigid spacecraft is studied. A series of chaos systems is found from Euler's dynamical equation by selecting different parameter matrixes of perturbed torque. Based on the Lyapunov function, adaptive controller is designed such that the chaos control of unknown parameters of this system is accomplished, the state variables go to any appointed equilibrium points, and the unknown parameters are estimated simultaneously. Finally, the Newton-Leipnik system as an example is considered here to demonstrate the proposing technique. Simulation results show the feasibility and efficiency of this method.
2013, 62 (10): 100504. doi: 10.7498/aps.62.100504
Conventional chaos control methods need model information of the chaos system, but model parameter is always unknown in engineering practice and the dynamic uncertainty of model-building often appears inevitably. In this case it is impossible to acquire best control performance index of optimization. To resolve this problem an adaptive control algorithm of chaotic systems based on model free method is proposed. It is a low cost controller. With this method, we can easily know a priori knowledge of chaos system only be adjusting a few parameters online without training before hand. We prove that this algorithm has a good stability mathematically. Simulation results show the effectiveness of this theory.
2013, 62 (10): 100701. doi: 10.7498/aps.62.100701
Optical tweezers are unique tools for studying biophysical properties of single molecules. Design and construction of optical tweezers are very important. The optical path, the radial manipulation equation and axial manipulation equation of optical tweezers based on a finite conjugate microscope system are calculated using matrix optics. The influences of axial position adjustment of the objective, the installation location error of the coupling lens, the installation location error of the laser beam control system, and the installation location error of the confocal system lens' on radial trap position manipulation accuracy and axial trap position manipulation accuracy are analyzed. The results show that axial position adjustment of objective introduces no error in radial and axial trap position manipulation. The misalignment of laser beam control system has no effect on the radial manipulation, nor on axial manipulation when the coupling lens maintains alignment. It is concluded that misalignment of components of optical tweezers based on a finite conjugate microscope system has a greater effect on trap position manipulation error than misalignment of components of optical tweezers based on a infinite conjugate microscope system. The radial trap position manipulation error is less than 5.9% and the axial trap position manipulation error is less than 11.4% when the coupling lens installation location error is less than 10 mm. It is shown that optical tweezers can be modified from a finite conjugate microscope system. The formulations provide the basis for theoretical analysis of experimental alignment and adjustment.
ATOMIC AND MOLECULAR PHYSICS
Theoretical study of level structure and transitions of configurations 3d94s2 3d94s4p, 3d94p2 for Nb XIII
2013, 62 (10): 103101. doi: 10.7498/aps.62.103101
Fine-structure energy levels of two-electron excitation configurations 3d94s2, 3d94s4p, 3d94p2 are calculated by Hartree-Fock method, which includes the configuration interaction, relativistic correction and approximate Breit correction, for copper-like Nb XIII. More accurate levels are obtained by the least-square-fit technique. The wavelengths and transition probabilities of 3d94s4p-3d104s, 3d94s2-3d104p, 3d94p2-3d104p, 3d94s4p-3d94s2 transition array are obtained, and some unknown results are predicted. Computing research shows that the 40.92 nm line should belong to 3d94s(1D)4p2F7/2-3d9(2D)4s2 2D5/2 transition, but not to the 3d94s(1D)4p4D7/2-3d9(2D)4s2 2D5/2 transition, and the upper term level should be 2F7/2, but not 4D7/2.
2013, 62 (10): 103102. doi: 10.7498/aps.62.103102
First-principles theory is adopted to analyze the characteristics of defects in ZnTe induced by In doping. The geometry structures, formation energies, band structures, densities of states and transition levels of the defects are calculated. The results show that there are two kinds of major defects in In-doped ZnTe. One is the atomic substitution defect of Zn replaced by In, which gives rise to a transition level located at 2.6 eV beneath the conduction band. The other is a complex defect, consisting of one In substituting Zn and one nearby Zn vacancy, which results in a transition level 0.33 eV higher than the top level of valance band. Electron transition between these two transition levels can be regards as the origin of the near-infrared light observed experimentally in In-doped ZnTe.
Influence of external electric field on the molecular structure and electronic spectrum of paranitrochlorobenzene
2013, 62 (10): 103103. doi: 10.7498/aps.62.103103
In order to achieve the goal of degenerating organic pollutant nitrochlorobenzene, the influence of electric field on molecular structure and electronic spectrum and so on is studied by applying an external parallel electric field. Take paranitrochlorobenzene as a study object, the method B3LYP of the density functional theory at 6-311+g(d, p) level is used to calculate its molecucar structure, dipole moments and total energies of the ground state under different external electric fields (from 0 to 0.025 a.u.) in this paper. On this basis, the time-dependent density functional theory is used to study the influences of external electric field on excited wavelength and oscillator strength of the first six excited states. The results show that bond lengths (C–Cl, C–N) increase rapidly and bond energy decrease rapidly with the increase of field intensity. At the same time, bond length (C–C, C–H) changes of benzene ring are very small, and the increases or decreases are not uniform. This illustrates that molecular degradation may lead to the fractures of bonds (C–Cl, C–N), and the benzene ring is relatively stable. what is more, the molecular total energy first increases then decreases, and the dipole moment first decreases then increases with the increase of the field intensity. In addition , the maximum absorption wavelength first slowly decreases, and then increases rapidly with the increase of the field intensity, which causes the electron transition to be relatively easy, while oscillator strength changes relatively complex in anner.
2013, 62 (10): 103104. doi: 10.7498/aps.62.103104
Molecular dynamics simulation based on the rigid-ion potential is carried out to investigate the surface energies of low miller index crystallographic faces such as (100), (110) and (111) in UO2 in a temperature range of 300 K-1500 K. The results indicate that the surface energies of the three low miller index crystallographic faces decline gradually with temperature rising, and the variation of the surface energy with temperature is confirmed to be consistent with the experimental data. The (111) crystallographic face which is the closest surface has the lowest surface energy; the (100) crystallographic face has the biggest surface energy; the (100) crystallographic face has a surface energy in between them. The surface atoms have compressed towards the vertical line of surface with respect to the inside atoms layer obviously. The symmetry of surface atoms declines. Surface phenomena such as relaxation and reconstruction occur on the surface atoms and the relaxation effect extends to the five layers. The results presented in the study are useful for understanding the behaviors of fission gas bubbles growing up and cracking up due to the swelling in fuels under the irradiation.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (10): 104101. doi: 10.7498/aps.62.104101
To analyze the time-varying plasma, a modified finite-difference time-domain (LTJEC-FDTD) algorithm is derived. By using Laplace transform and inverse Laplace transform, we can deduce the FDTD iteration expression for calculating 3D time-varying problem from Maxwell equation and plasma constitutive equation. The iteration expression is proven to be correct by mode-coupling theory, while the correctness of the relevant boundary is tested by calculating the radar cross-section (RCS) of plasma sphere. So, the method is suitable to the calculation of time-varying plasma. Then, the RCS of complex time-varying plasma object is also analyzed.
A polarization-independent transmission absorption metamaterial absorber based on electromagnetic resonance
2013, 62 (10): 104102. doi: 10.7498/aps.62.104102
In this paper, we simulate and experimentally validate a polarization-independent transmission absorption metamaterial absorber based on electromagnetic resonance. The metamaterial absorber can absorb the high-frequency electromagnetic wave, and the low-frequency wave can transmit through the absorber. The tested results indicate that the metamaterial absorber can achieve a narrow bandwidth high absorption with a peak absorption of 83.6% at 6.77 GHz, and a full width at half maximum (FWHM) of 4.3%. To further broaden the absorption bandwidth of the resonant metamaterial absorber, we place two absorbers with different working frequencies together for its low-frequency transmitted characteristic. The measured data show that the composite metamaterial absorber can increase the FWHM to 10.9%, and can enhance the absorption slightly. The metamaterial absorber has some advantages, such as simple design, strong practicability, and important application foreground.
Stationary phase method of calculating Čerenkov radiation spectrum of a charged particle moving in curved path
2013, 62 (10): 104103. doi: 10.7498/aps.62.104103
Based on the general expression for spectral-angular distribution of the radiation emitted by a charged particle moving in exterior medium, the essential role of stationary phase points in Čerenkov effect is investigated. And the stationary phase method of calculating spectral-angular distribution of Čerenkov radiation from a charged particle moving in curved path is proposed. By the stationary phase method, the asymptotic form of spectral-angular distribution of synchrotron-Čerenkov radiation is calculated, and the result indicates that the spectrum of synchrotron-Čerenkov radiation near critical angle c is quite different from that near the plane of particle's orbit.
2013, 62 (10): 104104. doi: 10.7498/aps.62.104104
In the relativistic klystron driven by intense relativistic electron beam, due to the influences of intense current and high electric field, especially the high Q value for the intermediate cavity, the nonlinear interaction between the intermediate cavity and the electron beam is very strong. It will significantly affect the performance of the device. According to the Maxwell equations and one-dimensional motion equation of electron, the self-consistent equation of the beam-wave interaction is obtained in the intermediate cavity. Based on these equations, the influences of the modulation depth and the modulation frequency on the amplitude and phase of gap voltage are studied respectively. The voltage amplitude obtained by the self-consistent equation is close to the voltage amplitude of particle in cell simulation, especially under the higher modulation depth compared with that obtained from the equivalent circuit model of conventional klystron. Meanwhile, the bandwidth of device becomes wide with the increase of the modulation depth. Finally, an S-band high-gain RKA is designed, and the corresponding experiments are done on the LTD accelerator. The output power with 1.1 GW is obtained, the gain is 49 dB.
2013, 62 (10): 104105. doi: 10.7498/aps.62.104105
The thin magnetic resonance dielectric plate is equivalent to a surface magnetic current. Using periodic boundary conditions, the exponential form of the surface magnetic current density is given. The dispersion relation and Bloch impedance of a periodic magnetic resonator metamaterial are derived by calculating the total electric and magnetic fields at the different positions excited by the infinite number of surface magnetic currents, and thus the theoretical formulas for Bloch constitutive parameters are obtained. Since the electric anti-resonance influence on the Bloch permittivity and permeability of magnetic resonator metamaterial is considered, thus the Bloch constitutive parameter difference between theoretical values and retrieval results based on simulations is very small, which shows that the Bloch constitutive parameter formula derived in the paper is very effective to describe the electromagnetic properties of the periodic magnetic resonant material. These theoretical formulas will provide important theoretical basis for the interpretation of the magnetic resonance phenomenon, the design and optimization of the periodic magnetic resonant material.
2013, 62 (10): 104201. doi: 10.7498/aps.62.104201
The general reflection and refraction laws at the metasurface with an abrupt phase shift are derived by two methods based on Fermat's principle and the boundary conditions of continuity, it is found that one or two critical angles for total internal reflection exist not only when a light beam impinges on the optical sparse material from the optical denser material, but also when a light beam spreads from the optical sparse material to the optical denser material. Anomalous reflection and refraction, such as, negative reflection and negative refraction may occur when a light beam passes through the metasurface, and the conditions of their occurrence are given. Finally, a kind of metasurface based on one-dimensional phase mask is designed to control the light propagation.
Study of the focusing features of spatial amplitude and phase modulated radially polarized vortex beams in a 4pi focusing system
2013, 62 (10): 104202. doi: 10.7498/aps.62.104202
The focusing properties of phase and amplitude modulated radially polarized vortex beams in a 4pi focusing system are theoretically investigated near the focal plane by using Richards-Wolf vectorial diffraction method. The amplitude modulation of vortex beams can be adjusted by changing the start integration value. The phase modulation of vortex beams can be realized by adding liquid crystal variable retarder with the phase delay angle δ. The simulated results show that multiple spherical spots can be obtained near the focus of the 4pi focusing system with the decrease of amplitude. The phase delay angle δ of the input beams can generate extruding effect for the electrical field distribution near the focus of the 4pi focusing system. Some special intensity distributions can be obtained by changing topological charge m and phase delay angle δ. Optical chain can be generated in the case of m=1. Dark channel can be obtained in the case of m=2. These special focusing beams can also transform with phase modulation. With the increase of phase δ, the multiple spherical spots at m=0 change slowly into an optical chain, and finally become a dark channel. In contrast, the optical chain at m=1 changes slowly into multiple spherical spots; and the dark channel at m=2 changes into the superposition of optical spherical spots and the optical chain. These special focusing beams have potential applications in optical trapping and micro-manipulation.
2013, 62 (10): 104203. doi: 10.7498/aps.62.104203
Traditional phase retrieval algorithm, which iteratively reconstructs the phase from 2-intensity measurement or 1-intensity measurement, requires Shannon sampling theorem to be satisfied. This could lead to more requirements for data storage when high resolution imaging is concerned. In order to lower the sampling budget, in this paper we purpose a compressed sensing based phase retrieval algorithm. Through 1-intensity measurement in Fourier plane, our improved Hybrid I/O algorithm is used to reconstruct the exact phase retribution of pure phase object. The algorighm proposed in this paper can reconstruct piecewise regular phase distributed pure phase object from far less amplitude measurements than ones for which the sampling theorem requires to be satisfied. The simulated data indicate that the algorithm has a good converge performance.
2013, 62 (10): 104204. doi: 10.7498/aps.62.104204
The forward problem of diffuse optical tomography (DOT) is commonly solved by the finite element method (FEM) currently. However, with the increase of the model scale, the computational complexity of FEM increases significantly; while the boundary element method (BEM) attracts much attention because of its reduction in calculated dimensions. In this paper, the fast multipole boundary element method (FMBEM) for DOT is studied using a model of highly scattering homogenous medium. In FMBEM, by the multipole expansions of kernel functions, the product of matrix coefficient and iterative vector can be equivalent to the recursion of a quadtree; and then a generalized minimal residual method is used to solve the BEM equation iteratively. The calculations of the FMBEM are compared with Monte Carlo simulations. The results show that the calculations of the FMBEM are in good agreement with Monte Carlo simulations. This demonstrates the feasibility of FMBEM in DOT and indicates that the FMBEM has a bright future for large-scale and real-time imaging.
2013, 62 (10): 104205. doi: 10.7498/aps.62.104205
In this paper we present a quantum secret sharing scheme based on a single qubit protocol using two polarization beam splitters. This scheme guarantees an auto compensation of birefringence and phase jitter in single mode fiber and optical device. The visibility is higher than 99.3% over 5 km communication distance with an excellent stability.
2013, 62 (10): 104206. doi: 10.7498/aps.62.104206
We study a four-level atomic system controlled by a three-level closed loop subsystem in order to obtain the phase-sensitive probe gain without population inversion. In the case of three-photon resonance, a large steady-state inversionless probe gain can be obtained. Due to the quantum interference effect, the inversionless gain is sensitive to the relative phase of the three-level closed loop subsystem. Further, the field intensity of the three-level closed loop subsystem is also an important parameter that can affect gain characteristic of the probe field.
Optical generation of tunable millimeter-wave based on dual-beam optical injection Locked 1550 nm vertical-cavity surface-emitting laser
2013, 62 (10): 104207. doi: 10.7498/aps.62.104207
Based on the spin-flip model, the nonlinear dynamics of a 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) subject to dual-beam optically injection is investigated theoretically. The results show that a slave 1550 nm-VCSEL (S-VCSEL) under the injection of dual-beam output from two master VCSELs (M-VCSELs) can be driven to enter into an injection locking state under suitable injection parameters. In this case, the outputs of both X and Y polarization modes of the S-VCSEL exhibit periodic oscillation whose frequency is equal to the frequency detuning between the two M-VCSELs, and its optical spectrum contains only two main frequency components and possesses a single sideband spectrum structure. As a result, two mutually orthogonal optical millimeter-waves can be obtained based on the periodic oscillation in a VCSEL subject to dual-beam optically injected locking. Through adjusting the frequency detuning between the two M-VCSELs, the frequency of the millimeter-wave can be tuned continuously in a large range, while the power and modulation depth can also be controlled by adjusting the system parameters.
2013, 62 (10): 104210. doi: 10.7498/aps.62.104210
An all-normal-dispersion multi-wavelength mode-locked dissipative soliton Yb-doped fiber laser with a periodic birefringence fiber filter is investigated in this paper. Numerical simulations show that multi-wavelength dissipative solitons can be generated by adding a filter into the fiber laser, and adjusting the bandwidth of filter can generate multi-wavelength dissipative solitons with different wavelength numbers and separations. Dissipative soliton molecules (DSM) can be observed in four- and five-wavelength dissipative solitons. Adjusting the parameters of the filter and saturation power can change the number and wavelength of DSM in the multi-wavelength pulses. This is the first time that multi-wavelength mode-locked dissipative solitons with DSM generated from mode-locked fiber laser have been observed, and that the dual-wavelength mode-locked disspative solitons have been obtained from an all-normal-dispersion Yb-doped fiber laser in experiment.
2013, 62 (10): 104211. doi: 10.7498/aps.62.104211
Based on chirped-pulse amplification technology, a ring cavity Ti:sapphire regenerative amplifier with high output energy is demonstrated. Under the 532 nm pump energy of 33.1 mJ at a repetition rate of 100 Hz, the chirped laser pulse with energy of 9.84 mJ is obtained, corresponding to a slope efficiency of 33.1%. Instead, using the pump laser with energy of 32.0 mJ at a repetition rate of 10 Hz, we also obtain 9.64 mJ pulse energy with a corresponding slope efficiency of 36.8%. By optimizing the dispersion among all optical materials, stretcher and compressor, the shortest pulse has an energy of 6.36 mJ and a pulse width of 59.7 fs, and the energy fluctuation is 1.85 % (RMS) over 4000 shots after the compressor. The performances show that it may pave the way for ultrafast applications and serves as a front stage toward TW even PW laser system with high contrast ratio.
2013, 62 (10): 104212. doi: 10.7498/aps.62.104212
Using the nonlinear Schrödinger equation (NLSE) including Raman gain effect but ignoring fiber loss situation, the linear operator and nonlinear operator specific expression are obtained based on MATLAB fractional Fourier numerical algorithm. They are applied to the NLSE including Raman gain, and the evolutions of soliton pulse are simulated in optical fiber through changing parameters. The result shows that soliton propagation stability is destroyed compared with the case considering no Raman gain, leading to the rapid attenuation of optical soliton. The influence degree depends on input soliton pulse peak power. The effects of Raman gain on ground state soliton and high order soliton are not the same.
Measurement of gain coefficients of stimulated Brillouin scattering in water at different temperatures
2013, 62 (10): 104213. doi: 10.7498/aps.62.104213
In this paper, the influences of medium temperature on threshold and gain coefficient of stimulated Brillouin scattering (SBS) in water are investigated theoretically and experimentally. Based on the theoretical analysis, a new method is proposed to determine the gain coefficient of SBS of the material by measuring the threshold. The experimental results indicate that the gain coefficient of SBS increases exponentially with the increase of medium temperature.
2013, 62 (10): 104214. doi: 10.7498/aps.62.104214
The retrieval sensitivity of NO2 profile based on airborne muti-axis observation is studied, and the influences of different wavelengths, different view angles, different surface albedos, different aerosol modes, and different altitude are evaluated by calculating the weighting function and average kernels. The results show that higher vertical resolution is obtained at 370 nm than at 500 nm for averaging kernels, more conducive to profile retrieval; not too much profile information is found in upper view angles, while more profile information is achieved in downward looking angles; surface albedos have no obvious influence on profile retrieval; high aerosol mode increases the sensitivity of profile retrieval; the averaging kernels at low flight attitude have no obvious differences in different altitudes, nor are they conducive to the profile retrieval.
2013, 62 (10): 104215. doi: 10.7498/aps.62.104215
In this paper, we present a new and highly efficient solar concentrating mirror. It is composed of partial high-order cylinder inner wall which is determined by two sets of specific coefficients a2, a4, a6, a8, a10, a12, a14, a16 and C. According to the higher-order cylindrical equation and the optical law of reflection, the relationship between the direction vectors of sunbeams reflected from the cylindrical inner wall and the coefficients of a higher order polynomial equation, a2,a4, a6, a8, a10, a12, a14, a16 and C is derived. By optimizing these coefficients, all sunbeams incident on the inner wall of higher-order cylinder can be reflected and focused into a very thin line segment parallel to the cylindrical busbar, which means line focus. Two sets of particular coefficients associated with the high- order cylindrical surface are obtained by using particle swarm optimization algorithm. The focusing effect of the solar concentrating mirror, defined by the particular set of coefficients, is demonstrated by using computer simulations. The concentrator mirror has a light compression ratio of about 148 : 1 and its linear spot can be used as a strong light source or a high temperature heat source. The higher-order cylindrical mirror can be made of metal or glass in three steps: cutting, grinding, and polishing, and may also be formed by a higher order cylindrical framework and an aluminized polyester film laid on the framework.
2013, 62 (10): 104216. doi: 10.7498/aps.62.104216
A new method of generating periodic linear chirped pulse is proposed, and a 0.52 nm bandwidth periodic chirped pulse is generated. Numerical simulation shows that the gain saturation, group velocity dispersion and synchronization jitter have great influences on chirped pulse; and self-phase modulation has little influence since the peak power stays at a low level. The experimental results indicate that the polarization mode dispersion will lead to a great intensity modulation, and the amplified spontaneous emission will break the light stability, which leads to the fewer round-trips of light. Research shows that the direct phase modulation is a novel method of generating periodic linear chirped pulse, which could be used for smoothing the spectral dispersion.
2013, 62 (10): 104217. doi: 10.7498/aps.62.104217
A high-compatibility low-bending-loss photonic crystal fiber (PCF) with standard single mode fiber (SMF) is designed and manufactured successfully. From the point of the view of fiber fabrication and application, a feasible structure with a germanium-doped core surrounded by one layer of six air holes running along fiber axis is adopted in fiber design. The properties of the fabricated PCF such as modal property, bending characteristic and dispersion are systemically evaluated with indirect measurement method. Analysis results demonstrate that this fiber has a mode field area of 79.26 μm2 and dispersion of 21.7 ps·km-1·nm-1, which exhibits high compatibility with SMF. The bending loss is 0.0365 dB/turn at a wavelength of 1550 nm for a bending radius of 5 mm, which is less than the bending loss of 0.5 dB/turn of G.657B. This fiber offers an efficient way to develop the low-bending-loss fibers for the application of fiber-to-the-home.
2013, 62 (10): 104218. doi: 10.7498/aps.62.104218
Using the fiber Bragg grating equation and the functional relation of the fundamental effective mode refractive index (RI), the mathematical model of the wavelength shift and the relational function of wavelength sensitivity are established, when the reflected wavelength of the micro/nanofiber Bragg grating (MNFBG) changes with ambient RI and the fiber radius. The theoretical relationship demonstrates that the variation of MNFBG reflected wavelengths is dependent on the change of effective RI with fiber radius and ambient RI. Meanwhile, we also study the variation of effective RI and its sensitivity in detail. The results show that the effective RI nonlinearly decreases with fiber-core radius and ambient refractive index decreasing, and its sensitivity increases as the ambient refractive index increases, and the sensitivity, linearity and the linear response range increase with the decrease of the fiber radius. For a fiber radius of 0.5 μm, by simulating the curves of the effective index versus ambient RI in the index ranges of 1.20-1.30 and 1.33-1.43 respectively, the values of wavelength sensitivity of 477.33 nm/RIU and 856.30 nm/RIU and the values of high linearity of 99.2% and 99.7% are obtained, which not only verifies the analysis conclusions and the measurement program for RI sensing with MNFBG, but also supplies references for the RI sensor design, optimization and the application.
Based on the Hankel wave theory, reconstruction property of Bessel beam generated by incoherent source is analyzed. The section light intensity distribution of Bessel beam after on-axis circular obstacle is simulated by optical design software ZEMAX. Light emitting diode (LED) has a certain spectrum width, therefore we describe it by using a continuous spectrum with a certain range of spectral width. From the simulation results we can see visually that Bessel beam gradually realizes the reconstruction after circular obstacles on-axial shelter. It is proved that LED has the reconstruction property. We use LED and axcion element to generate Bessel beam. This Bessel beam passes though an on-axis circular obstacle and an on-axis square obstacle. We take the pictures of the section light intensity distribution at different positions. The reconstruction properties of the LED incoherent source are verified. Experimental results accord well with the simulation results.
A novel approach to research on feature extraction of seismic wave signal based on wireless sensor networks
2013, 62 (10): 104301. doi: 10.7498/aps.62.104301
In order to solve the problems of high sampling rate which could shorten the lifetime of wireless sensor networks in wild relics security system, the power spectrum reprocessing is applied to the feature extraction of seismic wave signal. This method is used to solve the target recognition problem, and three data sets are used to verify its effectiveness. The result shows that the power spectrum reprocessing can reduce the communication consumption and prolong the lifetime of networks. This method can also increase the accuracy of target classification. This method, indicating its good performance, had been applied to wild relics security system of Museum of the Terra-cotta Warriors and Horses of Qin Shihuang.
Novel microwave power sige heterojunction bipolar transistor with high thermal stability over a wide temperature range
2013, 62 (10): 104401. doi: 10.7498/aps.62.104401
Thermal instability of power SiGe heterojunction bipolar transistor (HBT) at high current over a wide temperature range restricts the applications of the device in RF and microwave circuits. In order to improve the thermal instability, the influences of Ge profile in a base region on the electrical and thermal characteristics of microwave power SiGe HBT are studied with the aid of the model of multi-finger power SiGe HBT established by SILVACO TCAD. It is shown that for the HBT with graded step Ge profile, a higher cut-off frequency fT can be achieved due to the accelerating electric field caused by the graded step Ge concentration in the base region when compared with the device with uniform Ge profile. The influences of temperature on current gain β and fT are weakened, which avoids the drift of electrical characteristics over a wide temperature range. Although the temperature of device is lowered, the temperature of each emitter finger is still non-uniform. Considering the difference in heat dissipation among emitter fingers, a new device with non-uniform emitter finger spacing in layout and a graded step Ge profile in base region is designed. For the new device, the uniformity of temperature among emitter fingers is achieved, higher fT is kept, β and fT are less sensitive to temperature variation. Hence the thermal instability is obviously improved compared with the device with uniform emitter finger spacing and uniform Ge profile in base region, indicating the superiority of the new device at high current over a wide temperature range.
2013, 62 (10): 104601. doi: 10.7498/aps.62.104601
Based on the recursive stiffness matrix method, the effective surface permittitivity model of multilayered surface acoustic wave structure is established. By this model, the frequency dispersive characteristic of phase velocity for the ZnO/Si layered structure is calculated. The calculation results are in agreement with the experimental results, which verifies the effectiveness and accuracy of the model. Furthermore, the model is also established for the determination of the phase velocity and electromechanical coupling coefficients of ZnO/Diamond/Si structure. The best combination of high velocity and high coupling coefficient of the structure is obtained, which provides a good reference for the design of a high-performance and high-capability surface acoustic wave device.
2013, 62 (10): 104701. doi: 10.7498/aps.62.104701
A wavelet multi-resolution technique is applied to analysing the temperature field simultaneously obtained by a rake of 16 cold-wires in the turbulent near-wake of a slightly heated circular cylinder with a diameter of d = 12.7 mm in a range of x/d from 3 to 20, where x is the downstream distance from the cylinder axis. This technique enables us to decompose the fluctuating temperature field into a number of wavelet components based on different characteristic frequency bandwidths or scales, which are representative of the temperature fields of different scales. The turbulent mixing characteristics of various fluctuating scales are examined in terms of instantaneous temperature contours of each wavelet component. The flow structures and intermittent processing of various scales are visualized. The streamwise evolutions of temperature variance of various scales suggest that the intermediate-scale structures make larger contribution to the total temperature than the large- and small-scale structures. The wavelet auto-correlation function indicates that the large- and intermediate-scale structures display larger correlation and the wavelet component of higher frequency loses coherence quickly.
Experimental investigation on the evolution of dielectric barrier discharge plasma induced flow at different operating pressures
2013, 62 (10): 104702. doi: 10.7498/aps.62.104702
The evolutions of dielectric barrier discharge (DBD) plasma induced starting vortex and the transformation of the DBD plasma induced flow field at different operating pressures are obtained by particle image velocimetry. The results show that the starting vortex will diffuse to the embedded electrode side and then disappear, and the diffusivity will decrease as the time goes on at high operating pressure. But the starting vortex will not change in location, and it will not disappear at low operating pressure. As the operating pressure decreases, the starting time of plasma induced flow field decreases, the ordinate orientation of the induced flowfield increases, and the landscape orientation of the induced flowfield decreases. The form of the induced streamline will come through L→U→V as the pressure decreases. There is no induced vortex in the form of L. There are two induced vortexes in the form of U which lay in the middle and on the right hand of the form U respectively, and there is one induced vortex in the form of V which lays in the middle of form V.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (10): 106101. doi: 10.7498/aps.62.106101
Based on Stone-Wales (SW) defect evolution theory and molecular dynamics, we simulate the docking process of two caped carbon nanotubes (CNTs) of different types to form a heterojunction using Monte Carlo methods. First, an algorithm for a fast simulation of the cap change in CNTs is put forward and the cap formation of single CNTs with open ends is simulated, by applying this method. SW defect evolution is designed as a leap change simulation of these caps, represents C-C bond formation and breakage, while molecular dynamics is used to simulate the gradient change of the relative bond distance between the C atoms. The coalescence process of forming heterojunction is also studied here. These simulations show that the process of docking is first to generate a large number of defects, which will precipitate the coalescence, then many defects disappear through the compound, finally the remaining defects transfer to the ends of this heterojunction in the form of pentagon/heptagon rings, thus leading to the reduced overall energy.
2013, 62 (10): 106201. doi: 10.7498/aps.62.106201
Molecular dynamics simulations of polyethylene/silver-nanoparticle composites are implemented to calculate the structures, electrical, thermal and mechanical properties, thereby investigating their relationships with the nanoparticle dimension and simulation temperature. The results show that polyethylene/silver-nanoparticle composites are of isotropic amorphous structure, and the dispersion of nanoparticles in composite can be enhanced at a relatively higher temperature. Multi-layers of atoms on nanoparticle surface change into amorphous configurations, and electrical polarization interface layers are formed between silver nanoparticles and polyethylene matrix. The interface region shrinks and expends respectively with nanoparticle dimension and temperature increasing. Compared with polyethylene system, the polyethylene/silver-nanoparticle composite presents explicitly high polarizability which increases with temperature and nanoparticle size rising simultaneously. The silver nanopaticle dimension directly influences the intensity and frequency of interfacial dipole moment, resulting in corresponding variations of peak position and intensity in infrared spectrum. The polyethylene/silver-nanoparticle composite also shows higher isometric heat capacity and negative thermal pressure coefficient with better temperature stability, which decreases explicitly with temperature and nanoparticle size increasing respectively, than polyethylene system. The mechanical property of polyethylene/silver-nanoparticle composite shows isotropic elastic constant tensor with considerably higher Young modulus and Poisson ratio than the polyethylene system, both of which decrease with temperature and nanoparticle dimension increasing, which indicates the improvement on mechanical property with Ag nanoparticle filler.
2013, 62 (10): 106401. doi: 10.7498/aps.62.106401
Lateral constrain in the presence of melting has a significant effect on microstructure evolution of crystal growth, and this effect is related to the size and property of lateral constrain, thus determining microstructure formation during solidification. In the paper, microstructure evolution in the presence of lateral constrain during the solidification of pure Ni metal is simulated using a non-isothermal phase-field model. Effects of size and properties of lateral constrain are simulated and studied, also microstructures formed at different initial dendritic arm distances are discussed. Results indicate that the presence of lateral constrain has a direct influence on pattern evolution which determines the microstructure formation. Microstructure changes significantly with lateral constrain distance turning small, initial constrain temperature low becoming low and initial dendrite arm distance growing. Different heights of lateral constrains have almost the same effects on microstructure change during solidification.
Phase field modeling of the influence of interfacial wettability and solid volume fraction on the kinetics of coarsening
2013, 62 (10): 106402. doi: 10.7498/aps.62.106402
Coarsening of solid particles in a solid-liquid two-phase system with high solid volume fraction is studied using the multiphase-field model. The influences of interfacial wettability and solid volume fraction on growth exponent, coarsening rate, and particle size distribution (PSD) are analyzed. It is found that the growth exponent is independent of the volume fraction, while the coarsening rate constant and the PSD are closely related to the interfacial wettability and the solid volume fraction. Under the completely wetting condition the coarsening rate constant increases with volume fraction increasing, but this variation is insignificant under the incompletely wetting condition. Moreover, when the wettability is low and volume fraction is high, the coarsening rate may also decrease with volume fraction increasing. The simulation results also show that with the increase of volume fraction, the peak frequency decreases and the PSD becomes broader, but the fall of the peak frequency under the incompletely wetting condition is slower than under the completely wetting condition. The simulation results provide an insight into the discrepancy between different experimental observations.
2013, 62 (10): 106801. doi: 10.7498/aps.62.106801
As is well known, the surface topography strongly determines the tribological performance and all practical surfaces are rough. Since the actual friction process has apparently random characteristics, in order to obtain the friction suitable to the rough surface, it is necessary to set up a random friction model. In the present paper, the friction between a randomly roughness surface and an atomic-level smooth rigid plane is studied based on the Lennard-Jones potential model. A micro friction model is proposed. In the model, the potential energy between interfaces is determined by the normal load and the balanced spacing. With the numerical technique, the frictional force is calculated and the relationship between the frictional force and the normal load is analyzed as well. The results show that the friction force increases with the normal load increasing, but it increases nonlinearly. The results also show that the interfacial potential may be an essential origin of micro friction.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (10): 107101. doi: 10.7498/aps.62.107101
The structural and electronic properties of β-SiC/(15, 0) carbon nanotube (CNT) and β-SiC/(16, 0)CNT core-shell structure are studied by using first-principles method based on the density functional theory. The results show that the two heterostructures are metallic. Their metallic properties are contributed by the atoms from the CNTs and the surface of SiC nanowires. The metallic property of the SiC nanowire is determined by its structure. However, the fact that the metallic (15, 0) and semiconducting (16, 0) CNTs both show the metallic properties after filling the SiC nanowires, is due to not the deformation of CNTs, but the charge transfer between CNTs and SiC nanowires.
Theoretical study of the ground and excited state properties of newly designed size-expanded adenine analogue x-adenine
2013, 62 (10): 107102. doi: 10.7498/aps.62.107102
Recently, creating unnatural fluorescent nucleobase analogues has gained increasing attention. In this work, a detailed computational investigation on the photophysical properties of the fluorescent adenine analogue x-adenine (xA) is carried out. The ten lowest low-lying exited states are analyzed and assigned. The effects of methanol solution, linking to deoxyribose, and base pairing on its absorption and emission processes are considered. The calculated excitation and emission energies are in good agreement with the measured data available. It is found that linking to deoxyribose and methanol solution have a hyperchromic effect on xA. Also it is found that methanol solution and linking to deoxyribose will lead to the red shift of fluorescence, while base pairing does not have obvious effects on the lowest ππ* state and fluorescence emission but produces the blue shift of lowest nπ* to some extent.
Temperature dependence of fatigue properties of ultrathin copper films: molecular dynamics simulations
2013, 62 (10): 107103. doi: 10.7498/aps.62.107103
The molecular dynamics simulations are performed with single-crystal copper thin films under cyclic loading to investigate temperature effects on the mechanical responses. First, the method to determine the number of cycles to failure is reported: the total energy-the number of cycles curve and the stress-the number of cycles curve for nanoscale copper film are obtained; using the two curves and an additional quantitative expression, we obtain the additional quantity-the number of cycles curve, from which fatigue life of copper film is obtained. Next, under cyclic loading, with temperature rising, the number of cycles to failure of copper films increases in different manners at different temperatures: when the temperature is above about 370 K, the number of cycles to failure goes up quickly with temperature; when below about 370 K, the number of cycles rises slowly. Finally, the mechanisms of the strange temperature dependence of cyclic deformation can be explained by our developed model based on the evolutionary features of dislocation.
Electrostatic potential distribution of high-order weakly nonlinear composites under external direct current electric field
2013, 62 (10): 107201. doi: 10.7498/aps.62.107201
By using the homotopy analysis method (HAM), the electrostatic potential distribution problems of a type of high-order weakly nonlinear composite with a cylindrical inclusion randomly embedded in a host medium, which obeyes a current-field constitutive relation of J = σ E + χ |E|2E + η|E|4E, are investigated under the action of an external direct current electric field. With the mode expansion method, the current-field constitutive relation and their boundary conditions are transformed into a series of boundary value problems of nonlinear ordinary differential equations. Then the HAM is used to solve the boundary value problems of nonlinear ordinary differential equations and the asymptotic analytical solutions of electrostatic potential distribution in the inclusion and the host regions are given.
2013, 62 (10): 107202. doi: 10.7498/aps.62.107202
Within an one-dimensional tight-binding Su-Schreiffer-Heeger model, we investigate the effect of interchain coupling on inelastic scattering of oppositely charged polarons in conjugated polymer by using a nonadiabatic evolution method. It is found that the yield of the neutral exciton depends sensitively on the interchain coupling. The yield of the neutral exciton increases with the enhancement of overlapping which can make the wave functions of oppositely charged polarons more largely overlapped. The formation yield of excitons also increases with the number of overlapping sites increasing to its maximum value, where the length of overlapping sites is almost of the same order of magnitude as the width of the polaron, the reason is that the number of overlapping sites can affect the overlap of oppositely charged polaron wave functions. In turn, the charge transfer between them depends on the overlap of their wave functions. Therefore, when the size of overlapping sites is almost of the same order of magnitude as the width of the polaron, their wave functions have a largest overlap, thereby making charge transfer more easily. So the yield of excitons has the largest value.
2013, 62 (10): 107401. doi: 10.7498/aps.62.107401
The transport property of silicon sandwiched between Au (100) and Au (100) is investigated with a combination of density functional theory and non-equilibrium Green's function method. It is found that the conductance decreases with distance increasing. When dz =9.72 Å, the structure of junctions is the most stable and the conductance is 1.227G0 (G0=2e2/h) , which is contributed by the px, py and pz electron orbits of silicon atom. The I-V curve of junctions in stable station show linear characteristics under external bias vottage. With the increase of an external positive and negative voltage, the conductance decreases slightly, and the asymmetry change appears.
First-principles study on the elastic, electronic and thermodynamic properties of ErNi2B2C under high pressure
2013, 62 (10): 107402. doi: 10.7498/aps.62.107402
The elastic, electronic and thermodynamic properties of the superconducting ErNi2B2C material at high pressure are investigated using the plane-wave pseudopotential density functional theory. The analysis shows the dependences of the elastic constants, bulk modulus, shear modulus, Young's modulus and elastic anisotropy factors on the applied pressure. The calculated electronic density of states (DOS) reveals that the DOS peak at the Fermi level (EF) will decrease noticeably with pressure. It can be concluded that the pressure may reduce the superconducting temperature (Tc) of ErNi2B2C since the relatively high Tc originates from the peak in the DOS. This phenomenon is also found in some other superconductors such as MgB2 and SrAlSi. Moreover, based on the quasi-harmonic Debye model, the results of the thermodynamic properties indicate that the pressure and temperature have significant influences on the thermal expansion coefficient and heat capacity.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Study on interface of Al/depleted uranium and Au/depleted uranium layers deposited by magnetron sputtering
2013, 62 (10): 108101. doi: 10.7498/aps.62.108101
Aluminum/depleted uranium/aluminum (Al/DU/Al) and gold/depleted uranium/gold (Au/DU/Au) "sandwich structure" films are deposited by magnetron sputtering. Diffusions of Al/DU and Au/DU interface of these samples are investigated by high resolution scanning electronic microscope, X-ray diffraction, X-ray photoelectron spectrometer and scanning auger microprobe. The results show that deposited DU layer is of columnar grain. Significant diffusion takes place at Al/DU interface. Intermetallic compounds of Al2U and Al3U are formed at Al/DU interface by chemical reaction between Al and DU which induces chemical shift toward high binding energy of Al 2p and toward low binding energy of U 4f. Microdosages of O exist in Al over-layers as Al2O3, in Al/DU interface as Al2O3 and oxidation of uranium, and in DU layers as oxidation of uranium respectively. Just simple physical diffusion takes place at Au/DU interface. Binding energies of Au 4f and U 4f shift toward high-energy tail induced by cluster effect at the Au/DU interface. Microdosages of O exist at Au/DU interface and in DU layers as oxidation of uranium. Diffusion at the Al/DU interface is more obvious than at Au/DU surface. Under the condition of the same thickness valuses Al over-layer is more effective than Au over layer to protect uranium layer from oxidging.
2013, 62 (10): 108102. doi: 10.7498/aps.62.108102
Copper/carbon core/shell structure nanoparticles and nanowires are successfully synthesized by using a one-step low-temperature metal-organic chemical vapor with copper (II) acetylacetonate powders as precursor. Morphology and structure of copper/carbon core/shell nanomaterial can be well controlled by deposition temperature For instance, copper/carbon core/shell nanowires about 200 nm in diameter can be produced at 400 ℃. The mixture of nanowires and nanoparticles can be produced at 450 ℃. At 600 ℃ the production is the copper/carbon core/shell nanoparticles about 22 nm in diameter. The obtained copper/carbon core/shell nanostucture is found to be formed by a novel coalescence mechanism that is quite different from the well-known dissolution-precipitation mechanism The optical property of copper/carbon core/shell nanostructure is investigated Uv-vis spectrometer and the fluorescence spectrometer (PL). The results show that the surface plasma resonance peaks of copper/carbon core/shell nanowire and nanoparticle are located at 620 nm and 616 nm respectively. At 225 nm, copper absorbing peak can be found. The PL peaks of copper/carbon core/shell nanowires are located at 312 nm and 348 nm, and the PL peaks of copper/carbon core/shell nanoparticles are observed at 304 nm and 345 nm.
2013, 62 (10): 108103. doi: 10.7498/aps.62.108103
Dendrite is a typical pattern in directional solidification, attracting many theoretical and experimental researches. However, the effect of crystallographic orientation on dendrite growth is less considered in these researches. In this paper, using a transparent model alloy SCN-1.0 wt% Eth, the effects of crystallographic orientation on the incubation time of planar interface instability, the dendritical morphological feature, and the primary dendrite spacing in directional solidification are investigated. Three crystal grains with different angles between the dendrite axis direction and thermal gradient direction are chosen in our experimental. The experimental results show that the incubation time of planar interface instability increases with the deviation of dendrite axis from thermal gradient direction, which suggests that the deviation of dendrite axis favors the planar interface stability. And with the increase of deviation angle of dendrite axis, the side branches of dendrite become more asymmetric and the preferred side-branches suppress neighboring dendrite growth. Also it is found that the primary dendrite spacing becomes larger as the angle between the dendrite axis direction and thermal gradient direction increases.
Effect of the direct correlation function on phase diagram of the two-mode phase field crystal model
2013, 62 (10): 108104. doi: 10.7498/aps.62.108104
Effects of the width of direct correlation function peak and the peak at k=0 on the phase diagram for the two-mode phase field crystal model are examined carefully. The results indicate that increasing the width of direct correlation function peak will expand the stability region of the ordered phases; however, increasing the ratio of peak width will significantly increase the fcc phase region but reduce the bcc phase region. Adding a negative Gaussian peak at k=0 to the two-mode approximate direct correlation function will compress the phase diagram and make the two-phase coexisting region narrow.
2013, 62 (10): 108201. doi: 10.7498/aps.62.108201
In order to get a better understanding of etching mechanism and provide optimization guidance for manufacturing process, a three-dimensional (3D) profile evolution simulator based on cellular model is developed to investigate the surface evolution of etching process, and discuss emphatically the effect of ions on the surface evolution. According to the solving problem for angle of ion incidence, a component fitting-based dimension reduction method is presented to convert a 3D surface fitting problem into a two-dimensional (2D) curve fitting problem, and achieve fast solution for the surface normal vector of the incident point. Compared with least squares polynomial fitting method, this method improves computational accuracy and efficiency of the ion incidence angle. The improvement on the accuracy of fitting is achieved by improving the selection method of surface cellular for fitting. The fitting method is applied to 3D simulation of silicon etching process, and the simulation results verify the simulated surface by comparing with relevant experimental results.
Threshold voltage analytical model of fully depleted strained Si single Halo silicon-on-insulator metal-oxide semiconductor field effect transistor
2013, 62 (10): 108501. doi: 10.7498/aps.62.108501
A single Halo fully depleted strain Si Silicon-On-insulator (SOI) structure, which has the advantages of strained Si, Halo doping, and SOI structure, is proposed to improve driving current, suppress the short channel effect (SCE) and drain induced barrier lowering (DIBL) effect. A two-dimensional analytical model for the surface potential, the surface electric field and the threshold voltage is proposed by solving Poisson's equation. The effects of Ge fraction in the relaxed layer on surface potential and threshold voltage are investigated. In the paper we analyze the influence of drain voltage on surface potential. Finally the effects of Halo doping on threshold voltage and DIBL are investigated. The results show that the novel device can suppress the short channel effect and DIBL effect, and increase carrier transport speed.
Drain-induced barrier-lowering effect in surrounding-gate schottky barrier metal-oxide semiconductor field transistor
2013, 62 (10): 108502. doi: 10.7498/aps.62.108502
Based on surrounding-gate schottky barrier metal-oxide semiconductor field transistor (MOSFET) structure, the distribution of surface potential is obtained by solving two-dimensional Poisson equation in cylindrical coordinates, and the threshold voltage model of surrounding-gate schottky barrier NMOSFET which is applicable to the low voltage of drain is built. According to the calculation results, the dependences of threshold voltage and drain-induced barrier-lowering on voltage of drain, channel radius and channel length are studied in detail, which can provide some reference for the design of surrounding-gate schottky barrier MOSFET device and circuit.
Stability of low temperature and transparent amorphous InGaZnO thin film transistor under illumination
2013, 62 (10): 108503. doi: 10.7498/aps.62.108503
The amorphous indium-gallium-zinc-oxide (a-IGZO) thin films are prepared by radio frequency magnetron sputtering at ambient temperature. The transparent thin film transistors (TFT) fabricated at low temperature (a-IGZO active channel exhibits good electrical properties with a field effect mobility of around 10 cm2·V-1·s-1, subthreshold swing of 0.4 V/decade, and high Ionoff current ratio of over 107. Hysteresis is not observed when gate voltage sweeps forward and reverses. And the dependence of white LED illumination on characteristic of a-IGZO TFT is investigated. The results show that output characteristic is hardly affected, indicating the potential of the devices for transparent electronics In particular, illumination stability is investigated under white LED illumination stress test, and the a-IGZO TFT shows only 04 V shift in threshold voltage. The negative shift can be explained on the basis of trap of interface state.
2013, 62 (10): 108504. doi: 10.7498/aps.62.108504
LiSrBO3:xEu3+ phosphors were synthesized by conventional solid-state reaction and were systematically characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. The excitation and emission spectra reveal that the LiSrBO3:Eu3+ phosphor can be effectively excited by ultraviolet (395 nm) and blue (466 nm) light and exhibits a satisfactory red performance which peaked at around 612 nm corresponding to the 5D0 → 7F2 transitions of Eu3+. The concentration quenching mechanism was verified to be a dipole–dipole interaction. The dopant R+ (R+ = Li+, Na+ and K+) as charge compensator can further enhance luminescence intensity, and the emission intensity of the phosphor doped Li+ is higher than that doped with Na+ or K+. Introduction of Al3+ reduced the symmetry of the crystal field and increased the emission of 612 nm (5D0 → 7F2), which improved the chromaticity coordinates of LiSrBO3: Eu3+ phosphor.
A new approach to fabricating silicon nanowire/poly(3, 4-ethylenedioxythiophene) hybrid heterojunction solar cells
2013, 62 (10): 108801. doi: 10.7498/aps.62.108801
The silicon/poly(3, 4-ethylenedioxythiophene) core/shell organic/inorganic nanowire array (SiNWs/PEDOT) hybrid heterojunction solar cells are successfully fabricated by silver-assisted chemical etching method and vapor phase polymerization processes. The SiNWs/PEDOT hybrid solar cell shows that the performance is improved greatly and an excellent power conversion efficiency of 3.23% is achieved, which is as seven times as large as that of the planar cell without the nanowire structure. In addition, the studies of the reflectance, the I-V curve and the external quantum efficiency show that the great enhancement of performance for the SiNWs/PEDOT cell is due to the fact that the Si/PEDOT core/shell nanowire structure is successfully fabricated by vapor phase polymerization method, resulting in a high light trapping effect, a large junction area and an enhancement of the carrier collection efficiency.
2013, 62 (10): 108901. doi: 10.7498/aps.62.108901
In order to depict the real car-following behaviors better, in this paper we present a new car-following model by introducing the effect parameter of lateral separation distance and proposing the concepts of overtaking expectation and virtual front car based on OV model. The stability condition of the model is obtained by using the linear stability theory. It is found that with the increase of lateral separation and overtaking expectation, the stability region of traffic flow increases at a low density while it decreases at a high density. The results of numerical simulation verify the analytic results. Thus, in some places like traffic bottlenecks, which usually have a high traffic density, it is necessary to restrict the lateral movement and overtaking behavior of vehicles for suppressing the traffic jam.
2013, 62 (10): 108902. doi: 10.7498/aps.62.108902
The K-shell decomposition for identifying influential nodes plays an important role in analyzing the spreading performance in complex networks, which generates lots of nodes with the smallest K-shell value. The spreading influences of these nodes cannot be distinguished by the K-shell decomposition method, as well as the degree and betweeness indices. In this paper, by taking into account the K-shell information of the target node, we develop a new method to identify the node spreading ability with the minimum K-shell value. The experimental results for pretty good privacy and autonomous system networks show that the presented method could generate more accurate spreading list than the degree and betweeness indices.
2013, 62 (10): 108903. doi: 10.7498/aps.62.108903
Weighted networks can give the detailed description of interaction between the agents of complex systems, so weighted networks is more resemble real-networks than unweighted networks. It is a new way to improve the properties of complex networks by adjusting the weight distribution. Based on the synchronization of unweighted complex networks, the synchronizability of weighted generalized local-world networks can be measured by eigenratio R. We find that weight distribution has an important effect on the synchronization of weighted generalized local-world networks. The uniform weight distribution will lead to better synchronizability.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Study on the radius and energy transmission properties of lightning discharge channel by the spectra
2013, 62 (10): 109201. doi: 10.7498/aps.62.109201
Combining the spectra of could-to-ground lightning discharge processes obtained by a slit-less spectrograph with the synchronous electrical information, the temperature, the linear charge density, the channels initial radius, the final radius and the energy per unit length are calculated. The results of these parameters are in agreement with the values reported in other work. The correlative analysis indicates that the arc initial radius mainly depends on the duration of the discharge current, the radius increases with temperature rising, and the total intensity of spectra is correlated positively with initial radius and energy per unit length. The energy per unit length is directly proportional to the square of initial radius.
2013, 62 (10): 109202. doi: 10.7498/aps.62.109202
In this paper, singular value decomposition (SVD) is used to correct the National Climate Center business model CGCM, thus improving the forecast results. By performing the SVD decomposition using field coupling between the summer rainfall patterns forecasted in 1983-2011 and actual rainfall values, by selecting the mode forecast and 3-7 modals that are best correlated with the live precipitation, and comparing these revised results of the different numbers of modal number, and by selecting the number of modals with the best correction effect in the China region, the revised results are obtained from the model predictions. The 2004-2009 cross hindcast experiments and the return results tested by using the anomaly correlation coefficient and the root mean square error as evaluation criterion show that the best corrections are obtained by taking the first five modals in 2004-2009 as the number of modal revised in the year. The examinations of 2004-2009 mode and actual precipitation data demonstrate the correction effect obtained by the five modals is indeed best. A comparison between the result and the systematic errors shows that the Dhamma revised results are better than the systematic errors. Taking the year of 2010 as the forecast year, using the results of the cross-examination of 27 years 1983-2009 to determine the number of modals, and analyzing the forecast results by the determined number of modals constitute a method that has a potential business value.
The application of ensemble empirical mode decomposition method in multiscale analysis of region precipitation and its response to the climate change
2013, 62 (10): 109203. doi: 10.7498/aps.62.109203
Recently, ensemble empirical mode decomposition (EEMD) method has been developed for non-linear and non-stationary signal analysis. The method can work on nature signals (non-linear and nonstationary signals) and reduce the speckle noise. With the EEMD method, the signal is decomposed into several intrinsic mode functions (IMFs) and the frequencies of IMFs are arranged in decrease order (high to low) after the EEMD processing. The scaling mode of the EEMD method is similar to wavelet transform, but the signal resolutions in different frequency domains do not decrease by down-sampling. There are a large population and a developed economy in Weihe watershed, the disasters of droughts and floods caused by the autumn precipitation (here is precipitation in September and October) less or more than normal cause great loss and serious influence. In this paper, we propose the EEMD method to decompose the autumn precipitation series in the Weihe river basin during last 50 years into several IMFs, then extract the information including in the precipitation series and get the characteristics of multi-scales. The result shows that it is well response to the autumn precipitation series in the Weihe river basin and to the abrupt climate change in late 1970s and early 1980s of last century. The response appears earlier for high time scales than for low time scales In addition, the expression of the response for high time scales is the form of variability, but it is the amplitude of variability for low time scales.
A convolution algorithm of differential coefficients of liquid water based on vibrational Raman scattering
2013, 62 (10): 109301. doi: 10.7498/aps.62.109301
Inelastic vibrational Raman scattering by liquid water is one significant limitation to the accuracy of the retrieval of trace gas constituents in atmosphere over waters, particularly over clear ocean waters, while using satellite data with differential optical absorption spectroscopy technique (DOAS). The effect which is similar to the Ring effect in atmosphere results in the filling-in of Fraunhofer lines, which is known as solar absorption lines. The inelastic component of the liquid water scattering causes a net increase of radiance in the line because more radiations shift to the wavelength of an absorption line than from this wavelength to other wavelengths. The solar spectrum transmitting atmosphere is convolved with vibrational Raman scattering coefficient of liquid water, divided by the original computed spectrum, with a cubic polynomial subtracted off, to create differential water Ring spectrum. This method is suggested in order to obtain an effective differential water Ring coeffient for the DOAS fitting process, which could be used to improve the accuracy of the retrieval of the trace gases concentration. The method does not rely on radiative transfer model of water, which would be time-consuming and depending on lot of parameters. Therefore, it is very fast and convenient.
2013, 62 (10): 109701. doi: 10.7498/aps.62.109701
A simulation experiment system is required presently, for the space flight experiment of X-ray pulsar based navigation is very costly. To solve the crucial issues of the timing stability and the profile precision in existing simulation techniques of pulsar signal, a new simulation technique which utilizes visible light is proposed. The simulation experiment system is set up based on the proposed technique. And some experiments are carried out to test the proposed technique. The results demonstrate that the proposed technique can be used to simulate any of known pulsars. The timing stability of simulated X-ray pulsars is raised from 10-4 to 10-9. And the accuracy of pulsar profile simulation is noticeably improved. Within the X-ray band 1-10 keV, when the observation time reaches 1200 s, and the area of the X-ray detector is 1 m2, the Pearson correlation coefficient of pulsar's observation profile with the standard template profile arrives at 0.993. And the simulation experiment system can be realized with high flexibility and low cost. On the basis of the simulation experiment system, the signal characteristic of X-ray pulsar can be investigated. On the other hand, the performances of X-ray pulsar signal processing algorithms and navigation algorithms can be surveyed in detail.