Vol. 62, No. 19 (2013)
2013, 62 (19): 190201. doi: 10.7498/aps.62.190201
This paper presents a gradient-based response surface (GBRS) model and its applications to the aerodynamic design optimization. Since the widely used polynomial response surface model is continuous and differentiable, the gradients of the original response can be involved in constructing the quadratic polynomial response surface model. For the quadratic GBRS model, the number of the required samples depends linearly, instead of quadratically on the number of design parameters. Firstly, the samples are determined through the modified design of experiment with shortened sampling time to construct the GBRS model. Then function experiments are performed to evaluate the accuracy of GBRS model and its effectiveness in searching for the global minimum. Finally the gradients for constructing the GBRS model are calculated by the adjoint method and then an inverse design and an optimization design for improving the efficiency of a cascade are performed based on the GBRS model and the complex method. Results demonstrate that the optimization method based on the GBRS model is feasible and effective for obtaining the global optimum with high optimization efficiency; and the aerodynamic performance of the cascade can be significantly improved.
2013, 62 (19): 190202. doi: 10.7498/aps.62.190202
Pseudo-collision (Pc) as a common but neglected phenomenon in swarm optimization algorithm is revealed in this paper. Mechanism analysis on the inevitability of Pc indicates that both the lack of relation among samples and the unconstrained behavior of sampling are the inherent character of agent operation causing Pc in state-of-the-art swarm algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO). Based on the result of mechanism analysis, a novel partition management and classification sampling strategy is proposed to reduce Pc. In addition, both uniform and non-uniform principles are designed to facilitate the trade-off between exploration and exploitation during optimization. Rain forest algorithm (RFA), of which the evolution mechanism is identical with the above strategy and the principles, is proposed in this paper. By examining the rapidity, accuraty, and generalization capability across six benchmark nonconvex functions, RFA is found to be competitive with or even superior to GA and PSO in dealing with complex multi-peak optimization.
Sudden birth versus sudden death of entanglement during the interaction of macroscopic fields with environments
2013, 62 (19): 190301. doi: 10.7498/aps.62.190301
Decoherence of two initially entangled macroscopic fields each interacting with a loss environment is investigated; environment only have an effect on the leakage of field’s photons. The cavity-cavity entanglement is characterized by concurrence. The results obtained by resolvable values show a surprising result: the two entangled macroscopic fields become completely disentangled even though the leakage rate of the cavities fields is very tiny. Then we find that when the cavity entanglement disappears, the environment entanglement appears. Finally, we present an explanatory study of other entanglement partitions.
2013, 62 (19): 190302. doi: 10.7498/aps.62.190302
We have investigated the properties of thermal entanglement in a triangular spin ring of the single molecular magnet (SMM) Na9[Cu3Na3(H2O)9 (α-AsW9O33)2]·26H2O in a magnetic field, and the pairwise concurrences of arbitrary two Cu2+ ion qubits are calculated numerically, hereafter abbreviated as C12, C23 and C13, respectively. Results show that the magnitude and direction of magnetic field as well as temperature have important effects on the pairwise thermal entanglement. Moreover, C12, C23 and C13 have difference variations with the change of the parameters. We also plot the changes of the critical temperatures Tc of C12, C23 and C13 with the magnetic fields along three different directions, and from the critical temperature-magnetic field phase diagrams one can obtain the ranges of parameters in which the pairwise thermal entanglement in a triangular spin ring of the SMM exists. Therefore, the pairwise entanglement can be controlled and enhanced in the SMM by choosing appropriate magnitude and direction of magnetic field and temperature.
The single-direction energy transition model of molecular motor based on the control of adenosine triphosphate
2013, 62 (19): 190501. doi: 10.7498/aps.62.190501
The dynamic principle of molecular motor transport in overdamped solution remains unclear. Starting from the transport characteristics and phenomenon of the molecular motor system, the single-direction energy transition model is established, which conforms to the Langevin equation, and the stochastic dynamics of molecular motors is analyzed by Monte Carlo simulations. Results show that with the right transition energy, molecular motors could take a stable stepping motion and effective transport by means of the environment noise, and the load force can weaken material transportation of the molecular motor system. The potential field between a molecular motor and its orbit can affect the magnitude of the velocity of motor, but cannot change the direction of the velocity, the direction of motion of the molecular motor therefore is adjusted by the transition energy of the motor. In addition, although the average velocity is not zero for different noise intensities, the efficient transport of a molecular motor system indicates that the system is selective for the noise intensity.
Work done by a periodical external force on an overdamped harmonic oscillator with frequency fluctuation and energetic stochastic resonance
2013, 62 (19): 190502. doi: 10.7498/aps.62.190502
Characterization of the work done by a periodic external force on an overdamped harmonic oscillator with frequency fluctuation is studied. Results indicate that the instantaneous power with periodic variations of time shows asymmetry. It is also revealed that the work done by a periodic external force on the system in one period with the variation of multiplicative noise intensity exhibits non-monotonic behavior. Whether the system shows the coexistence of energetic stochastic resonance and suppression or not is determined by the sign of the correlation coefficient between the multiplicative noise and the additive noise.
2013, 62 (19): 190503. doi: 10.7498/aps.62.190503
The cardiac muscle, which is composed of many discrete cells, is a typical excitable medium. In this paper, we study the effect of refractory period with stochastic perturbations on dynamical behaviors of spiral wave using the model of discrete excitable medium. When the perturbations are random in space, the stability of spiral wave is related to the amplitude of the perturbations and the number of perturbation cells. Computer simulation results show that refractory period perturbations can result in meandering, breakup and disappearance of the spiral waves under suitable conditions, and then their mechanisms are analyzed.
2013, 62 (19): 190504. doi: 10.7498/aps.62.190504
A novel class of the associated chaotic systems with switching and synchronization features is proposed in this paper. The system can be switched between the same-dimensional systems, can also be switched between different-dimensional systems, when the system is switched to a four-dimensional system, the synchronization between the system variables can be realized. Basic dynamic properties and the internal synchronization mechanism of the new system are investigated via theoretical analysis, numerical simulation, Lyapunov dimension and Lyapunov exponent spectrum. Finally, the hardware for circuit of the switching chaotic system is designed and realized by using Multisim software; the chaotic system and its synchronization characteristics are simulated and achieved at the same time. The numerical simulation and circuit simulation confirm that the switching chaotic system can be realized physically, and the system has shown rich dynamic properties.
Analysis of transfer orbit deviation propagation mechanism and robust design for manned lunar landing
2013, 62 (19): 190505. doi: 10.7498/aps.62.190505
Earth-moon transfer orbit for manned lunar landing needs a long flight time, complex, nonlinear and variable coefficient dynamics model, and asks for a high reliability. Analysis of deviation propagation mechanism and robust design of transfer orbit are investigated in this paper. It is not only practical for projecting, but also significant for exploring the role of earth-moon space gravitational field upon transfer orbit deviation. This paper analyses firstly the boundary and the amplitude of the sun, earth, and moon central gravitation, the earth J2 perturbation that affect the transfer orbit deviation transmission. And then a method to analyse the deviation propagation mechanism based on nominal orbital data is obtained analytically. A robust indicator of transfer orbit based on deviation transition matrix is proposed,and a robust optimization design method that employs NSGA-II(nondominated sorting genetic algorithms) for earth-moon transfer orbit with robust indicator is proposed.Simulation shows that the analysis of transfer orbit deviation propagation mechanism can obtain earth-moon transfer orbit deviation propagation matrix quickly and precisely, and the deviation propagation matrix can be used to obtain the covariance matrix and mid-course correction delta V analytically and exactly. The quality of nominal transfer orbit is improved by optimizing with robust indicator.
Based on a proposed voltage-controlled memristor, a simplest parallel memristor chaotic system is constructed. The dynamical characteristics of the new chaotic system are analyzed, including Lyapunov exponent, Lyapunov dimension, time domain waveforms, portrait diagrams, Lyapunov exponent spectrum, bifurcation diagrams and Poincar mapping. An electronic circuit of the new system is designed and verified by simulations using the EWB software. Research results show that with the parameter change, the i-v characteristic of the memristor, instead of keeping inclined 8-shaped, becomes a fan-shape with a tail. The differences between the chaotic system and the magnetic-controlled memristor chaotic system are in two aspects: only one equilibrium point in the chaotic system, and the initial conditions do not affect the state of the system when the system can oscillate. Good matching between numerical simulation and circuit experimental simulation proves the existence and physical realizability of the new chaotic system.
Fuzzy fast terminal sliding mode controller using an equivalent control for chaotic oscillation in power system
2013, 62 (19): 190507. doi: 10.7498/aps.62.190507
Chaotic oscillation in a power system is taken to be the main cause for power blackouts in large-scale interconnected power grid. This paper studies a 2-D power system with chaotic oscillation dynamic behaviors through parameter phase portraits, Lyapunov exponents, time-domain waveform graph and proposes fuzzy fast terminal sliding mode controller based on equivalent control to stabilize the power system to synchronization status. Simulation results show that our control scheme can not only speed up convergence rate, but also have smooth control action, reduce control energy and suppress chattering phenomenon effectively.
2013, 62 (19): 190508. doi: 10.7498/aps.62.190508
Aiming at the parameter identification problem in chaotic systems, we propose the quantum particle swarm optimization algorithm based on the swarm intelligence particle swarm optimization. The test functions show that the method has good global optimization. Then the method is applied to the parameter identification problem of the chaotic system. We transform the parameter identification problem into the optimization in the multi-dimensional function space. Through research on the balance board thermal convection in a typical chaotic Lorenz system, the proposed method has been compared with the basic algorithm and the genetic algorithm. Simulation results show that the proposed algorithm is effective, and is very important to the development of chaos theory.
2013, 62 (19): 190509. doi: 10.7498/aps.62.190509
Time delay and optimal embedding dimension for the real measurement traffic flow series, which are used by mutual information method and false nearest-neighbor method, respectively, are determined for phase space reconstruction of the traffic flow series. The saturation correlation dimension and the largest Lyapunov exponent for traffic flow series are calculated to estimate its chaotic characteristics. Based on the least mean square (LMS) algorithm, a novel second-order Volterra model using Davidon-Fletcher-Powell method (DFPSOVF) is constructed, in which a variable convergence factor based on a posteriori error assumption, characteristic of real-time change with the input signal, is applied. DFPSOVF model can avoid some problems caused by improper selection of parameters when using LMS adaptive algorithm for coefficient adjustment in Volterra model. DFPSOVF model can also be applied to short-term traffic flow prediction with chaotic characteristics. Results show that when model memory length is consistent with embedding dimension of traffic flow series, it obtains higher prediction accuracy, which can meet the needs for traffic guidance and traffic control, and can also provide a new method, a new idea and engineering application reference for intelligent traffic control.
The reliability of logical operation in a one-dimensional bistable system induced by non-Gaussian noise
2013, 62 (19): 190510. doi: 10.7498/aps.62.190510
Using success probability as a measure of logical stochastic resonance, we mainly studied the phenomenon of logical stochastic resonance (LSR) in a one-dimensional bistable system induced by non-Gaussian noise in this paper. And we explained the cause of this phenomenon via the method of the mean first-passage time. Results show that the resonance peak of the success probability can be achieved only when in an appropriate range of noise intensity or correlation time. Through an optimization of system parameters, we have improved the reliability of realizing logic operation in the system.
2013, 62 (19): 190511. doi: 10.7498/aps.62.190511
A transport model of elastically coupled particles in a two-dimensional potential is investigated. Here, we propose that one dimension of the model is exerted by an AC drive and an external noise, and the other dimension by neither AC drive nor external noise. The effects of system and external parameters on the directed current under an overdamped case are discussed. The studies show that particles can transfer energy from one direction to its perpendicular direction through coupling, thereby producing a directed current. There is an optimal value of the spring free length or the coupling intensity at which the directed current can reach a maximum. For a fixed coupling intensity or noise intensity, the directed current will oscillate as the free length of spring varies, that is, multiple peaks appear. Moreover, a stochastic resonance appears in the directed current as noise intensity varies. Finally, when the degree of asymmetry of the ratchet potential achieves a maximum value, the current reversion takes place.
2013, 62 (19): 190601. doi: 10.7498/aps.62.190601
A laser-induced fluorescence lifetime measurement method is presented to evaluate living status for plant growth and the environmental monitoring. A 355 nm laser is used as excitation source for exciting chlorophyll fluorescence, and the fluorescence signals are received by a photomultiplier. Because the measured signal is the convolution of the reliable fluorescence decay signals, laser pulse and instrument response function, according to their characteristics, the time-resolved measurement method is used to estimate the chlorophyll fluorescence and background signals separately; the real fluorescence decay signals are separated by combining a novel deconvolution method, and the chlorophyll fluorescence lifetime can be retrieved. Experiment shows that the method proves to be a high accuracy and real-time monitoring chlorophyll fluorescence lifetime technique; and the chlorophyll solution fluorescence lifetime is measured for different concentrations. The result can prove that the chlorophyll concentration is related to its fluorescence lifetime, and the calibration curves of chlorophyll concentration and fluorescence lifetime is fitted.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2013, 62 (19): 191301. doi: 10.7498/aps.62.191301
Since to break the limitation of traditional single anode magnetron injection electron gun can only produce a lower power, this paper, based on an independent research and development of particle simulation software CHIPIC, will take the 110 GHz, 220 GHz coaxial cavity double-beam gyrotron for full three-dimensional numerical simulation study. By theoretical analysis for the initial parameters of the coaxial double-beam electron gun and to optimize the design by CHIPIC, we obtain the high-performance electron beam with the horizontal and vertical velocity ratio of 1.0 and the maximum velocity spread of 5.4%, and use the optimized electron gun to replace the traditional gyrotron emission for numerical simulation of the 110 GHz, 220 GHz gyrotron system, as well as the four-process parallel MPI in computing. Finally we obtain that the double bands are 110 and 220 GHz respectively, a TE02 mode, and the average output power about 70 kW. The efficiency can reach 8.75% for the high performance double-beam gyrotron oscillating tube.
2013, 62 (19): 192901. doi: 10.7498/aps.62.192901
A single-channel pulsed-power vacuum device is studied. Based on the platform of CHIPIC, the limitation of memory and computation speeds of a single computer is broken through by the method of parallel computation of multi-computers. For the model of the whole device, the models of the parts of feed-in, convergence and transmission in the single-channel pulsed-power device are built, and the parameters are set up. The obtained voltages between the cathode and anode, as well as the currents of the cathode and the anode using the proposed models are in accordance with the theoretical ones. The single-channel pulsed-power vacuum device also can retain magnetically insulated and achieve the function of convergence of power. This shows the feasibility of the single-channel pulsed-power vacuum device.
ATOMIC AND MOLECULAR PHYSICS
The ab initio coupled-cluster theory and the configuration interaction method have been used to optimize the possible ground state structures of NH, NO and HNO. The potential energy functions of HNO have been derived from the many-body expansion theory. In the symmetric stretching vibration and rotation potential energy diagram of HNO, there are saddle points in reaction kinetics O+NH→HNO, H+NO→HNO, N+HO→HNO, when O, H, N atoms with the energies surpassing 1.153 eV, 1.683 eV, 2.216 eV respectively, a stable HNO molecule could be formed. These are reported for the first time so for as we know. In addition, It is reported that the position of HNO’s isomer in the curve and the energy of transition from HNO to HON are also determined.
The present work is mainly to study two-photon process in H2X (X=O, S, Se, Te) by using the full relativistic theory. For comparison, we also study the single-photon process by SAC-CI method. The transition probability of two-photon excitation is 10-2–10-5 times of the single-photon process; the relativistic effects become more and more obvious with the increase of atomic number. In addition, every molecule observes the selection principles; dipole transition component and oscillator strength of individual symmetrical states are greater than those of other individual states. This is due to the symmetry of molecule and it should be an important basis for selecting transition energy.
First-principles study on the electronic and optical properties of the (Eu,N)-codoped anatase TiO2 photocatalyst
2013, 62 (19): 193103. doi: 10.7498/aps.62.193103
We have calculated the electronic and optical properties of Eu-doped, N-doped, and (Eu,N)-codoped TiO2 using plane-wave pseudopotential method based on the density functional theory. The calculated results show that there are impurity levels of Eu 4f appearing in the band gap of Eu-doped system, and N-doped system can lead to narrowing of the band gap. Moreover, the synergistic effect of the Eu and N codoped TiO2 leads to the lattice distortion and band gap narrowing. Optical absorption curves indicate that the (Eu,N)-codoped system exhibits a significant red-shift of absorption edge, which enhances the visible-light photocatalytic activity.
2013, 62 (19): 193104. doi: 10.7498/aps.62.193104
Based on the Gupta-type semi-empirical inter-atomic many body potential, the melting properties of Aln(n=13–32) clusters are systematically investigated by using the molecular dynamics method combined with the simulated annealing and quenching techniques. Our results show that, except for several sizes (Al13 and Al19), in general the heat capacity curves all are in disorder (no obvious single-peak), which are consistent with the experimental observations that small aluminum clusters have messy heat capacity curves in the melting process. Reasons for the different melting behaviors (whether they exhibit regular or irregular heat capacity curves) of these small Al clusters can be explored by analyzing the energy distributions of the simulated quenching structures of these clusters at different temperatures. For the clusters with disordered heat capacity curves one can obtain the melting points from analyzing the atomic equivalence indexes of those clusters, and the variations of the calculated melting points of the aluminum clusters with increasing cluster size are in agreement with the experimental observations.
Investigation on the potential energy curves and spectroscopic properties of the low-lying excited states of BP
2013, 62 (19): 193301. doi: 10.7498/aps.62.193301
The multi-reference configuration interaction (MRCI) method in quantum chemistry is used to investigate the BP+ at the level of aug-cc-pVQZ basis set. The potential energy curves of 6 Λ-S states of BP+ radical are obtained, which can be correlated to the dissociation limit B+(1Sg)+P(4Su), B+(1Sg)+P(2Du) and B+(1Sg)+P(2Pu). In order to get the accurate potential energy curves, the Davidson correction (+Q) and scalar relativistic effect are taken into consideration. Analyses of the electronic structures of Λ-S states demonstrate that the Λ-S electronic states are multi-configurational in nature. The spin-orbit interaction is considered for the first time sofar as we have, which makes 6 Λ-S states split to 10 Ω states. The calculation results show that the crossing between the Ω states of the same symmetry can be aveided. Then the spectroscopic constants of the bound Λ-S and Ω states are obtained by solving the radial Schrödinger equation with the program LEVEL8.0 according to the MRCI wave functions. By comparing with available experimental results, the spectroscopic constants of ground states are in good agreement with the available theoretical values. The remaining computational results in this paper are reported also for the first time.
2013, 62 (19): 193601. doi: 10.7498/aps.62.193601
Pt-Pd alloy nanoparticles exhibit better catalytic activity and selectivity than pure Pt and Pd ones, and thus to explore their stable structures is crucial for understanding the catalytic performance of nanoparticles. In this paper, the particle swarm optimization algorithm and the quantum Sutton-Chen potentials are employed to investigate the stable structures of tetrahexahedral Pt-Pd alloy nanoparticles with different sizes and different composition. Results show that in Pt-Pd alloy nanoparticles, Pt atoms are preferential to locate of the core and Pd atoms to occupy the surface. Furthermore, the more symmetrical and ordered the structure, the lower the energy of the structure. The Warren-Cowley chemical short-range order parameters of three different sizes of nanoparticles increase accordingly with rising fraction Pt. The segregation degree of small sized nanoparticle is more remarkable than large sized one for the same content of Pt.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (19): 194101. doi: 10.7498/aps.62.194101
We propose a method of designing ultrathin broadband perfect metamaterial absorber (PMA) which is based on the parameters of the cell. The bandwidth is enhanced via the method which combines the multilayer and multi-resonance in a layer. And it is not complex due to having no lumped elements in it, so it is easy to fabricate and apply. In order to illustrate the method, a double-layer perfect metamaterial absorber with three resonance peaks is designed using the above method. The equivalent circuit of the proposed absorber is analyzed so as to better understand the mechanism of the high absorption. By adjusting geometric parameters of the structure, we can obtain a polarization-insensitive and wide-incident-angle ultra-thin absorber. Simulated and experimental results show that the full-width at half-maximum is 14.1% when the thickness of the filer is only 0.01λ, and the bandwidth of-3 dBsm radar cross section reduction is 18.9%. At resonance, the reduction value may exceed 23 dBsm while the absorber has a good characteristic of RCS reduction at the boresight direction from-40° to +40°.
2013, 62 (19): 194201. doi: 10.7498/aps.62.194201
Based on the linear property of silicon microring resonators, we experimentally observed that such resonator can transform square-wave signal into pulse-wave signal, and the output waveform is strongly dependent on the input wavelength. We then proposed a mathematical model, which utilized linear coupling mode theory, Fourier transform and electro-optical Mach-Zehnder (MZ) intensity modulation functions. The numerical simulation results fit well with the experimental results. Besides, we gave a detailed explanation based on the transfer function of microrings. Furthermore, we have studied the case when the ring resonator is deviated from the critical coupling condition, and found that the coupling state, over coupling or under coupling, can be easily judged through the output waveform.
2013, 62 (19): 194202. doi: 10.7498/aps.62.194202
Mx2 and My2 are provided for characterizing and measuring the beam quality of an astigmatic elliptical Gaussian beam. The value undergoes certain changes when the beam is not at an arbitrary azimuth angle . Accordingly, problem arises: merely using Mx2 and My2 cannot characterize beam quality effectively. So in this paper M2 factor matrix is introduced. The M2 factor matrix for the beam at an azimuth angle is theoretically derived. It is found that elements of the matrix for the original field are related to that beam at azimuth angle . The matrix elements, including diagonal and off-diagonal elements, versus azimuth angle have been presented on the basis of calculation results. Theoretical results are in agreement with experimental ones. Results imply that the sum of Mx2 and My2 for an astigmatic elliptical Gaussian beam is to be minimum as the principal axes correspond to the laboratory coordinate axes; off-diagonal elements, however, vary periodically with the variation in , and are to be zero as the principal axes correspond to the laboratory coordinate axes.
Precision measurement of resonate frequency and the effective cavity length of the high finesse optical micro-cavity
2013, 62 (19): 194203. doi: 10.7498/aps.62.194203
Ultra-high finesse micro-resonator plays an important role in realizing the interaction between atoms and cavity field in the study of cavity quantum electrodynamics (QED) system, weak optical nonlinear effects and micro-optic devices. By measuring basic parameters of the microcavity, the atom-cavity coupling coefficient and the cavity decay rate can be determined precisely. It is also useful for exploring the dynamic characteristics of the system. However, it has difficulty in determining resonate frequency and effective cavity length due to the structure of the ultra-high finesse optical microcavity itself and the characteristics of multilayer coating. In this paper, we demonstrate the precision measurement of effective cavity length under different resonant frequencies which our cavity mirror is coated with 37 layers of dielectric film. The theoretical expectation when using the revised model of the multilayer coating agrees well with that of the experiment; and the measurement error for longitudinal mode interval is below 0.004 nm which is two orders of magnitude better than that obtained in previous unrevised model. The tiny depths into mirror coatings that the standing-wave light field inside the cavity penetrates are given for different mode numbers. This method may be applied to other micro resonator in the precision measurement.
2013, 62 (19): 194204. doi: 10.7498/aps.62.194204
The dispersion of optical resonator structures can be used to increase the sensitivity of rotation sensing. Using coupled resonator waveguides can realize strong dispersion. In this paper, the transfer matrix method is used to analyze the phase sensitivity of rotation sensing in coupled resonator waveguides, and investigate the influences of resonator arrangement and waveguide parameters on the phase sensitivity. Results show that phase curves and phase sensitivity are dependent on resonator arrangement. The number of resonator and coupling coefficients can influence not only the number and bandwidths of peaks for phase sensitivity of rotation sensing but also the variation of phase sensitivity. However, loss can reduce the phase sensitivity. The results can be used to design the phase sensitivity of coupled resonator waveguides using the resonator arrangement and waveguide parameters, and are beneficial for applications of coupled resonator waveguides in rotation sensing.
2013, 62 (19): 194205. doi: 10.7498/aps.62.194205
In order to solve the problem of low light absorption efficiency of single photon detectors based on quantum-dot gated field effect transistor (QDFET), a new type of quantum-dot gated field effect enhanced single-photon detectors (QDFEE-SPD) was proposed. QDFEE-SPD was designed with a resonant cavity, and the GaAs/AlAs multilayer was used as the basic mirror. The light absorption efficiency and responsivity of QDFEE-SPD were analyzed and simulated. Results show that, compared with that without cavity, the absorption efficiency and responsivity of the QDFEE-SPD is greatly improved. Also for the optimization of light absorption efficiency, the thickness of the absorption layer should normally be 0.10.5 m. Then the material samples of QDFEE-SPD were grown and tested. Reflection spectroscopy and PL spectroscopy testing results show that the light absorption efficiency has been significantly enhanced. The achievements in this article provide a new way for researching high-efficiency single-photon detection technology based on QDFET.
Flat-top Brillouin gain spectrum with a controllable bandwidth produceal from multiple-lines pump modulation in liquid-core optical fibers
2013, 62 (19): 194206. doi: 10.7498/aps.62.194206
We present a method of achieving a flat-top Brillouin gain spectrum (BGS) with a controllable bandwidth based on multiple-lines pump modulation in a CS2/CCl4 mixture liquid-core optical fiber. The influences of the pump spectrum separation, the intensity of each spectrum line, and the mixing ratio of core liquid media on the BGS are theoretically investigated, and the conditions of producing the flat-top BGS with an adjustable bandwidth are obtained. Results show that 2–9 spectral lines are generated based on single-frequency and multifrequency modulation using an intensity or phase modulator. The flat-top BGS with bandwidths of 50 MHz–2 GHz are obtained by controlling spectrum separation, the intensity ratio of each spectral line and CS2 volume fraction. This method has advantages of convenient operation and wide bandwidth range. It can be applied in Brillouin amplification with high gain and low distortion, and hence satisfies the requirements of weak signal detection and slow light systems.
Study on scattering properties of the metal wire gating in a THz band based on Green function method
2013, 62 (19): 194207. doi: 10.7498/aps.62.194207
The present paper utilizes the Green function method to analyze the scattering properties of the metal wire grating in the THz band, and further to study the influence of the diffraction on the transfer characteristic of the metal wire grating. Results prove that the transmission amplitude of the incident electromagnetic wave is increasing monotonously with the enlargement of the value of a/, and it arrives at the maximum in the zero-order diffraction limit. Due to the strengthened effect of diffraction, transmission curves of the incident electromagnetic wave show oscillation in the critical frequency transition region. Due to the diffraction effect, the transmission amplitude of the incident electromagnetic wave demonstrates an overall decline in the diffraction zone, and it is decreasing monotonously with the enlargement in the value of a/. Compared with microwave transmission line method, this method can aliminate the restriction that the wavelength of the incident electromagnetic wave must be greater than the wire grating constant, and the thickness of wire grating must be far less than the metal line width. This method could be used to analyze the distribution of the electromagnetic properties of the system accurately; and it will be a generally suitable one.
2013, 62 (19): 194208. doi: 10.7498/aps.62.194208
Plane wave expansion method was employed to study the complete photonic band gap (PBG) of two-dimensional air annular photonic crystals (PCs). Comparison of the complete PBG of the air annular photonic crystal and the commonly used PCs (square-and triangular-lattice dielectric rods in air and square-and triangular-lattice air holes in dielectric background) reveals that a larger complete PBG can be obtained for the air annular PCs. Furthermore, the complete PBG is observed for the air annular PCs even if the dielectric contrast is low, while it is difficult to achieve a complete PBG for the commonly used PCs. For example, for the square and triangular lattice air-hole PCs, the complete PBG is observed when the refractive index of the dielectric materials is arger than 2.8 and 3.2, respectively. But the complete PBG can be observed when the refractive index is arger than 2 for the air annular PCs.
Curvature sensor based on side-leakage photonic crystal fiber with high sensitivity and broad linear measurement range
2013, 62 (19): 194209. doi: 10.7498/aps.62.194209
Based on Sagnac interferometer by incorporating a segment of side-leakage photonic crystal fiber (SLPCF), a curvature sensor with high sensitivity and broad linear measurement range was proposed and demonstrated experimentally. Experimental results show that high sensitivity to curvature can be achieved by measuring group modal birefringence and wavelength shift of transmission dip when the linear side-leakage defect is in the same direction as the bending, but the linear measuring range is not large enough to cover the small curvature. When the linear side-leakage defect is in the vertical direction to the bending, the sensitivity can be as high as 10.798 nm·m-1 and the linear measurement range as wide as 0–5.03 m-1 by measuring wavelength shift of transmission. Combined with the introduction of the measurement matrix, the measurement of temperature and curvature can be realized simultaneously, which would offer a way to eliminate the perturbation of the environment temperature to the measurement values of the curvature. Under the same conditions, though the sensitivity obtained by measuring group modal birefringence is low, it can be regarded as a curvature sensor which is insensitive to temperature.
2013, 62 (19): 194210. doi: 10.7498/aps.62.194210
Silicon electro-optical modulators based on add-drop micro-ring resonators have the advantage of more freedom in designing high-extinction-ratio and large-bandwidth modulators without changing the ion doping processes of the chip. Here we design a high-speed silicon modulator based on an add-drop micro-ring resonator with a radius of 20 m; it demonstrates high extinction ratio with low reverse bias. How the coupling between the straight waveguide and the ring resonator affects the performances is studied theoretically and it is found that a lower coupling coefficient at drop port leads to a higher extinction ratio but not the best bandwidth. Therefore, a balance should be considered between extinction ratio and bandwidth. According to the optimized result of the parameters the device is fabricated and tested. The spectrum testing indicates that the device can have 12 dB extinction ratio when it is operated at 3 V reverse bias. Furthermore, we have observed 8 Gbps open-eye diagram with only 1.2 V peak-to-peak signal voltage.
Analysis and experimental verification of the relation between Scholte wave velocity and sediment containing two-phase fluid properties
2013, 62 (19): 194301. doi: 10.7498/aps.62.194301
Based on several ultrasonic suspension models, i.e. Urick, Urick-Ament, HT and Mcclements, the Scholte wave propagation characteristics are analyzed at the interface between sediment concentration two-phase fluid and porous medium solid. The interface wave propagation characteristic equation are found using the complex wave number equation given by the aforementioned four models. Relationships between Scholte velocity and the two-phase fluid properties, (e.g., dispersion, volume content, particle size) are discussed. Scholte wave propagation and signal are obtained by Comsol simulation. By using the time delay estimation method, it is found that the obtained Scholte wave velocity are in accord with that given in Urick-Ament and HT models.
2013, 62 (19): 194302. doi: 10.7498/aps.62.194302
In order to establish quantitative timbre representation of underwater noise, this paper tries to build a relationship between essential timbre scores and central auditory responses to stimulus based on partial least squares regression, and use regression coefficients to interpret the physical meaning of each dimension. In order to verify the utility of this method, this paper extracts a large amount of timbre descriptors as independent variables for comparisons, and it is shown that the predictive ability of the central auditory model is better. Finally it is found from two types of timbre representations that the first three dimensions in the timbre space can be respectively interpreted as high-frequency energy ratio, spectral flatness and temporal continuity; however, dimension 4 cannot be related to any acoustical features.
2013, 62 (19): 194701. doi: 10.7498/aps.62.194701
For a class of two-dimensional nonlinear partial differential equation with the source term,a simple lattice Boltzmann model with amending function is proposed and studied using the Chapman-Enskog expansion technique and multiple-scale analysis. In this paper, some partial differential equation are simulated, the numerical results and exact solutions are shown to be almost completely fitting with each other. The lattice Boltzmann method is further extended to two-dimensional partial differential equation.
2013, 62 (19): 194702. doi: 10.7498/aps.62.194702
The formation mechanism and evolution characteristics of a submerged round jet in a uniform fluid of finite depth are investigated experimentally. A spillover system is designed to produce a continuous horizontal jet in the background fluid with a constant velocity, and the flow is visualized by the dyed liquid. Experiments are conducted under different combinations of Reynolds number Re, confinement number C and nondimensional draft d/H, where d is the vertical distance from the jet to the free surface, and H is the depth of the ambient fluid. Four flow patterns are identified for various C. When C1, the jet shows a deep-water pattern, while for 1 C2, it shows the transitional pattern, the jets do not develop a structured flow for the two jet patterns. When 2 C10, the jet shows the shallow-water pattern, while if C10, the jet shows the extreme-shallow-water pattern. In both these two patterns, the jets generate vortex dipole structures. In the extreme-shallow water pattern, the nondimensional vortex formation time tf* for the vortex dipole structure is proportional to the nondimensional injection time Tinj* for various draft d/H. In the shallow-water pattern, tf* depends linearly on Tinj*Re1/2 when the draft d/H=0.5; however, there is no observable relationships between tf* and Tinj* for other draft d/H.
2013, 62 (19): 194703. doi: 10.7498/aps.62.194703
Strong interaction between bubble and free-surface will cause complex phenomena, producing many different types of spike. Based on potential flow theory, a numerical model was established to simulate the crown spike. A downward jet was formed during the bubble’s collapsing, and simulation of the free-surface was continued regard less of the ring bubble’s effect on it. Simulation results show good agreement with the experiment conducted with a high speed camera and a spark-generated device, and the relative error was less than 10%. Some special phenomena were found through numerical calculation, such as apron-shrink and peak-dropped. Finally, the effects of initial condition and Weber number on crown-type water column were studied.
2013, 62 (19): 194704. doi: 10.7498/aps.62.194704
To investigate the process of droplet impact on an orifice plate, a two-dimensional SPH model is established. An improved linked-list search algorithm with improvement of computational domain changing with fluid is described. By analyzing the numerical results with the experimental data, influences of viscosity, gravity, and internal pressure on the spreading of droplet over the orifice are studied. It is demonstrated that spreading will change to jet flow after the droplet reaches the orifice, and then the jet will pass it rapidly and in this rather short time the effect of gravity contributes very litte to the motion. However, viscosity can induce the jet to move in a curve into the orifice. Besides, with the internal pressure and inertial effect, the lower part of the jet will fluctuate regularly. The fluctuations make the jet repeat inflation and absorption to absorb the fluid from higher pressure area, resulting in Hole Suction phenomenon. Through analyzing the pressure of the vertical section of orifice edge, we find that internal pressure plays a significant role to the droplet which is absorbed into the orifice and finally leads to splashing. Numerical results are in good agreement with the experimental data.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Investigations on radiative opacity measurement by the method of direct laser-heating and self-backlighting
2013, 62 (19): 195201. doi: 10.7498/aps.62.195201
A target designed for opacity studies of dense plasmas by laser direct heating and self-backlighting technique was presented and tested. The backlight source and sample plasma were generated by directing a frequency-tripled Nb-glass laser onto an Au/CH/Al/CH multilayer target on the XG-II laser facility, and the absorption of the sample plasma was obtained by measuring the attenuated backlight spectrum of the sample plasma. One-dimensional radiative hydrodynamic code Multi-1D was used to simulate the laser heating of the multilayer target, and the temperature and density profiles in the target were given. Experimental data were compared with the theoretically calculated spectra using the detailed-term-accounting model, which showed a temperature range from 20 eV to 70 eV in the sample plasma, a result in quite good agreement with the Multi-1D simulations.
2013, 62 (19): 195202. doi: 10.7498/aps.62.195202
The C-W co-deposition layer prepared by radio frequency magnetron sputtering was investigated to identify the characteristic of the C-W mixed layers in fusion experimental reactors. Layers were characterized by ion beam analysis (IBA), Raman spectra (RS) and scanning electron microscopy (SEM). It was found that D atoms in C-W layers are mainly trapped by the trapping site of C atoms, only a few of them are arrested by W atoms or defects. D concentration in the C-W layers deposited at 5.0Pa with a fixed flow rate ratio QD2/QAr=2.5 was lower than 10% and decreased slightly with increasing temperature. D concentration increased with the gas pressure from zero to 5 Pa and then decreased from 5 Pa to 10 Pa. RS revealed that the crystal structure of the C-W layers became graphite-like with increasing temperature. SEM images showed that the caves disappeared and convex bodies were dotted on the surfaces as the temperature increased.
2013, 62 (19): 195203. doi: 10.7498/aps.62.195203
To investigate the process and mechanism of the impulse generation of laser ablation target, a comprehensive model including one-dimensional heat conduction and fluid dynamics is developed. The target Al, the most common space debris material, is used based on the proposed numerical model in the calculation of ns laser pulse ablation impulse and impulse coupling coefficient as a function of time. Numerical results agree well with experimental data available. Numerical simulations show that, during the laser pulse the impulse the target gained increases greatly with time; after the laser pulse terminates, the impulse tends to be stable with time. In the process of laser impulse coupling, the laser ablation plasma expands into vacuum and its size also gradually increases; meanwhile the plasma plume absorbs the incident laser energy and leads to the reduction in the laser energy deposited onto the target.
2013, 62 (19): 195204. doi: 10.7498/aps.62.195204
A surface-wave plasma (SWP) source based on surface plasmon polariton (SPP) has fine performances such as high density, low temperature, high production, and so on. It is applied in electronic device micro or nano processing, material modification, etc. Because the ionization of SWP heated by SPP is difficult to describe by theoretical analysis and experimental measurement, the ionization process of producing uniform stable SWP source is not yet well understood. The method in this paper is a numerical simulation of SWP discharges. The electromagnetic energy coupling mechanism of ionization process, influenced by gas pressure, which is studied by combining particle-in-cell (PIC) simulation of reciprocity between plasma and electromagnetic wave with Monte Carlo Collide (MCC) method in merit of dealing with particle collision. Simulated results suggest that the efficient production of SWP is induced by locally enhanced electric field of SPP, and the gas pressure influences the ionization process of SWP by altering the appearance time of wave-mode resonant conversion. Results of this paper show the ionization process of SWP discharge maintained by SPP, and further provide some advices for designing the parameter optimization of next generation meter-scale SWP source.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
A track study on icosahedral clusters inherited from liquid in the process of rapid solidification of Cu64Zr36 alloy
2013, 62 (19): 196101. doi: 10.7498/aps.62.196101
The rapid solidification process of liquid Cu64Zr36 alloy is simulated using a molecular dynamics method. The evolution in micro-structures are analyzed by means of pair distribution functions (PDF), Honeycutt-Andersen (H-A) bond-type index method and cluster-type index method (CTIM). It is found that both of liquid and rapidly solidified solid mostly consist of (12 0 12 0) icosahedra and their distorted (12 8/1551 2/1541 2/1431) configurations at a cooling rate of 50 K/ns, most of which are Cu-centered Cu8Zr5 clusters, followed by Cu7Zr6 and then Cu9Zr4 clusters. Size distribution of icosahedral medium-range order (IMRO) clusters linked by intercross-sharing (IS) atoms in the liquid and the glassy solid presents the magic number sequences of 13, 19, 25,···and 13, 19, 23, 25, 29, 37···, respectively. The track of atoms reveals no icosahedral clusters in rapidly solidified solid that can be detected in the liquid alloy. Onset temperature of configuration heredity emerges in the supercooled liquid region of Tm–Tg. A direct and perfect heredity of icosahedra is found to be dominant and a distinct ascent in heredity fraction takes place at Tg. Compared with (12 8/1551 2/1541 2/1431) distorted icosahedra, (12 0 12 0) standard icosahedra are of high structural stability and configurational genetic ability below Tg, whereas only a few can keep their chemical composition unchanged. By partial heredity, even some IMRO clusters in super-cooled liquid can be transmitted to glassy alloy.
Deposition of colloidal particles in a drying droplet is important in many scientific researches and technological applications. In this work, the ring deposition of drying droplets on a solid substrate is investigated experimentally at a microscopic level. A ring deposition is formed at the contact line as the water solution droplet containing SiO2 particles is drying, just like the formation of coffee ring. Contact line pinning is crucial to the ring deposition formation. There will be a replenish flow in the droplet towards the edge, and the particles are driven to the contact line, deposited on the substrate. As the particle mass fraction is large, the particles which are left inside the spot, when the droplet dries out, may form a single particle layer, packing in order. The contact angle of the droplet on glass substrate is very small, the SiO2 particles will gather at the rim of the droplet, which initially form a chain along the contact line. As more particles come to the rim, they are deposited in a line by line way to form a 2D close packing. Since the contact angle decreases with evaporation when the contact line is pinned, a capillary force between liquid surface and particles arises once the height of droplet surface near the contact line is lower than that of the particle, pushing the particles to move inward. The effect on the larger particles is more pronounced-it even leads to a separation of the particles, with the smaller ones at the outer side.
2013, 62 (19): 196103. doi: 10.7498/aps.62.196103
In this paper, the ZnO nanorod arrays (NRAs) with a diameter of 50nm and a length of 250 nm were synthesized by chemical bath deposition method. Two devices with structures of ITO (indium tin oxides)/ZnO/poly-(3-hexylthiophene) (P3HT)/Au and ITO/ZnO@ZnS/P3HT/Au were fabricated and their performances were tested and evaluated separately. The I-V curves were measured for discussion of the threshold voltage, series resistance, reverse leakage current, and rectification ratio. Results show that the device with modified ZnO shows a decline in the threshold voltage, series resistance and reverse leakage current, but has an enhanced rectification ratio. The effect of ZnS coating on the improvement of conductive properties of the device could be attributed to the suppression of the non-radiative recombination of surface defects as shown by means of photoluminescence spectrum.
Study on ionization damage of silicon-germanium heterojunction bipolar transistors at various dose rates
2013, 62 (19): 196104. doi: 10.7498/aps.62.196104
Ionizing radiation effects in silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) at different dose rates were investigated. Experimental results show that the base current increases with increasing accumulated dose for the high and low dose rates of irradiation, causing a significant drop in current gain. Besides, the lower the dose rate, the higher the radiation damage, which demonstrates a significantly enhanced low-date-rate sensitivity (ELDRS) effect in the SiGe HBTs. The different degradation behaviors for high and low dose rates of irradiation are compared with each other and discussed; furthermore, the underlying physical mechanisms are analyzed and investigated in detail.
2013, 62 (19): 196105. doi: 10.7498/aps.62.196105
Polycrystalline rare-earth hexaboride (LaxCe1-x)B6 were prepared by means of the reactive spark plasma sintering (SPS), using mixed powders of GdH2, NdH2 and B. The crystal structure, surface texture, mechanical property, electrical resistivity, and thermionic emission properties of the sintered samples were investigated. It is found that all the samples sintered by SPS exhibit high densily (>96%) and high value of Vickers hardness (2310 kg/mm2), which are much higher than those made by traditional method. Thermionic emission results indicate that the maximum emission current density of La0.6Ce0.4B6 is 40.7 A/cm2 under the applied voltage of 1 kV at 1873 K, which is larger than that of LaB6 and CeB6. Thus, the mixed cystal of borides (LaxCe1-x)B6, as a cathode, promises good prospects in application.
Generation and evolution of vacancy-type defects in nano-Cu films during plastic deformation by means molecular dynamics
2013, 62 (19): 196201. doi: 10.7498/aps.62.196201
Molecular dynamics simulations were performed to study the plastic deformation of Cu films under uniaxial tension. The generation and evolution mechanisms of vacancy-type defects were carefully studied. In the simulations, embedded atom method (EAM) was selected as the interatomic potential function. Simulation results indicate that the plastic deformation is due to the dislocation nucleation near free surfaces. Both the generation and evolution of vacancy-type defects are related to dislocation activities. Vacancy-type defects prefer to nucleate at the position of dislocation jogs and the intersection of stacking faults initially, and finally exist in the form of single vacancy, vacancy clusters and stacking-fault tetrahedrons.
2013, 62 (19): 196801. doi: 10.7498/aps.62.196801
As one of the most important ignition capsules, the polyimide capsule was prepared by depolymerizable mandrels technique combined with vapor deposition polymerization method. Instead of the plane pan and piezoelectric vibration model, the mesh pan and pulse tapping was selected to reduce microsphere collision so that surface quality was improved in polyimide fabrication. Experimentsal and theoretical results show that the capsule surface becomes more rough because of collisions between microspheres and the pan. The mesh pan could reduce microsphere collisions, which was also reduced by changing piezoelectric vibration into pulse tapping. As a result, root-mean-square value ranges from 5293 nm to 2844 nm. There are many advantages with pulse tapping model, such as better controllability,lower bounce rate and less static; however piezoelectric vibration model is slightly better than the pulse taping in wall thickness uniformity. Measurements of single microsphere show that the deviation of the former is 0.68 which is better than that of the latter (0.73 m). For the average value of microspheres in the same batch, the former has a value 0.26 which also is better than the latter (0.57 m).
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Low frequency noise analysis and resistance relaxation in Au/SrTiO3/Au for bipolar resistive switching
2013, 62 (19): 197201. doi: 10.7498/aps.62.197201
The resistance relaxation in Au/SrTiO3/Au sandwiches with bipolar resistance switching has been investigated by the low frequency analysis. The power spectral density of the conducting current fluctuation in the high resistance state and the low resistance state shows 1/f behaviors. By contrast experiment, the low frequency noise for the high resistance state is ascribed to the Schottky barrier under reverse bias and the oxygen vacancy diffusion, while the noise in the low resistance state is due to the carriers fluctuation arising from the oxygen vacancy migration. The resistance relaxation can be further understood as the diffusion of oxygen vacancies under an electric field.
2013, 62 (19): 197202. doi: 10.7498/aps.62.197202
The thickness of an active layer is limited by its low mobility of carriers in a polymer solar cell composed of the blend bulk-heterojunction formed by P3HT as donor material and PCBM as acceptor material, which can affect the light absorption of the polymer solar cell. Metal nanocrystals-doped polymer active layer can enhance its inner electrical field and absorb light due to the surface plasmon resonance (SPR) effect of the nanocrystals. Two-dimensional electrical field distributions in the polymer solar cells are simulated based on finite difference time domain (FDTD) approach, under the assumption that the diameter of doping nano-Ag is 50 nm, the distance between two nanocrystals is 50nm and the incident light wavelength is 400 nm or 500 nm. The electrical field distributions over the cross-section of nano-Ag are also simulated at the incident light angle of 15°, 45°, 60°, respectively. The light absorption of different devices are calculated, in which the sizes of nano-Ag take 10 nm, 20 nm and 50 nm, respectively, Particles of nano-Ag are dispersed in PEDOT:PSS layer. Moreover, the light absorption is calculated at the incident light angles of 15°, 45°, 60°, respectively. Results show that the electrical field is redistributed due to the SPR effect caused by nano-Ag in the polymer active layer. A larger size of nano-Ag leads to light scattering in a wider angle, thus results in more light absorption by the device. Here, the colloid of nano-Ag is prepared from an organic salt of Ag, and the polymer solar cell with nano-Ag is fabricated in the structure of glass /ITO (～100 nm) /PEDOT:PSS (40 nm) /P3HT:PCBM (～100 nm)/(nano-Ag) /LiF (1 nm) /Al (120 nm). Furthermore, experimental results show that the nano-Ag doped in P3HT:PCBM layer increases light absorption and improves the electrical performance of the device, which enhances the incident photon conversion efficiency (IPCE) in spectrum at 520nm by 17.9%.
2013, 62 (19): 197203. doi: 10.7498/aps.62.197203
The Ni/Au/Al2O3/n-GaN metal-oxide-semiconductor structure with circular transparent electrode has been fabricated by using atomic layer deposition technique. Effects of ultra-violet (UV) light illumination on the capacitance characteristics and deep interface states are analyzed. Physical origin of bias-induced capacitance drop in the accumulation region of some non-ideal devices is explored. Due to the extremely long electron emission time and the extremely slow minority carrier generation rate, a typical deep depletion behavior can be observed in the dark room-temperature capacitance-voltage sweep curve, and the deep-level interface state occupancy above the electron quasi-Fermi level remains unchanged. Under the UV illumination, photo-induced holes will empty the deep interface traps above the electron quasi-Fermi level, and also de-charge the deep donor-like traps in the oxide layer. The anomalous capacitance drop in the accumulation region is attributed to the bias-dependent excessive leakage conductance across the dielectric layer, which might be induced by a charge-to-breakdown process related to electrical traps in the oxide and the inferior interface quality.
2013, 62 (19): 197204. doi: 10.7498/aps.62.197204
Highly efficient all fluorescent white organic light-emitting devices (WOLED) have been fabricated by means of sequential doping. Fluorescent materials PT-01, PT-86 and PT-05 serve as the yellow guest, blue guest and fluorescent host, respectively. The emission layer consists of a few repeating cells, which are made of sequentially evaporated host and guest layers. From the analyses of the singlet exciton distribution and the influences of the thickness of the host layer, PT-86 and PT-01 are evaporated at the proper locations in the emission layer (EML), yielding a high efficiency and stable all fluorescent WOLEDs. The maximum current efficiency of the WOLED is 11.2 cd/A. In addition, the emission color of this WOLED is fairly stable, consistent with the Commission International de L’Eclairage coordinates, only showing changes (±0.004,±0.005) when luminance increasing from 159 cd/m2 to 20590 cd/m2. The devices based on the method of sequential doping not only have the similar performance compared with that fabricated by co-evaporation doping, but also have higher repeatability, which makes them appropriate for mass-production.
Study on the properties and optical emission spectroscopy of the intrinsic silicon thin film in silicon heterojunction solar cells
2013, 62 (19): 197301. doi: 10.7498/aps.62.197301
The intrinsic silicon thin film for passivation of the crystalline silicon wafer surfaces in silicon heterojunction cells was prepared by very high fregucency plasma enhanced CVD (VHF-PECVD). Plasma emission versus time was recorded by optical emission spectroscopy (OES) during the silicon thin film deposition. Results show that the Hα* and SiH* signals stabilize soon (about 25 s after deposition) under the optimized deposition conditions, and the variation of SiH*/Hα* ratio is little, thus avoiding the structure non-uniformity of silicon film during the growth. The reason is that the SiH4 back diffusion is avoided owing to SiH4 being not fully depleted. The study of the influence of the deposition parameters on steady-state plasma emission spectra and properties of silicon films shows that as the SiH4 concentration increases, the Hα* decreases and the SiH* increases, the silicon film will transit from microcrystalline to amorphous, and the good passivation effect can be achieved in the amorphous silicon film. Hα* and SiH* increase firstly and then decrease with the deposition pressure, the decrease of Hα* and SiH* under high pressure can be attributed to a high polymer formation which is not beneficial to the formation of high quality silicon film, and therefore the passivation effect of silicon films decreases under high pressures. Hα* and SiH* increase with power density, and are saturated when the power density is 150 mW/cm2; for this the quality and passivation effect of the silicon film begin to decrease, the passivation effect of the silicon film at a power density of 50 mW/cm2 is poor, which may be due to the low concentration of atomic H being unable to fully passivate the dangling bonds at the silicon surface.
2013, 62 (19): 197302. doi: 10.7498/aps.62.197302
The polaron confined in a GaAs film deposited on AlxGa1-xAs substrate are investigated in the framework of the fractional-dimensional space approach. We propose a new approach to define the effective length of quantum confinement. Limitations of the definition of original effective well width are discussed. The dimension and the binding energy of a polaron confined in a GaAs film deposited on Al0.3Ga0.7As substrate are obtained and investigated.
2013, 62 (19): 197303. doi: 10.7498/aps.62.197303
Based on the strong coupling of the complementary frequency selective surface (CFSS), a frequency selective surface with polarization selective performance is presented. When there is lateral displacement along the periodic arrangement direction between the capacitive surface and the inductive surface, the CFSS becomes the polarization selective surface (PSS) with TM pass-band and TE stop-band filtering characteristics. The equivalent circuit model of the PSS is used to analyze its polarization selective mechanism. Its frequency responses and the electric field distribution on the capacitive and inductive surfaces have been simulated by the coupled integral equation method. The simulated and experimental results show that the PSS has good polarization selectivity, and it provides reference for the design of polarization wave generator and polarization filter.
Thickness dependence of critical current density in MgB2 films fabricated by hybrid physical-chemical vapor deposition
2013, 62 (19): 197401. doi: 10.7498/aps.62.197401
MgB2 superconducting films with a thickness of 10 nm to 8 μ have been prepared on SiC substrates by hybrid physical-chemical vapor deposition (HPCVD). The study on Tc and Jc shows that as the film grows thicker, Tc increases and then keeps stable, which Jc increases at first, and then drops dramatically. We get the maximum Tc at 41.4 K and Jc at 2.3× 108 A·cm-2. This also shows that we can use the method of HPCVD to prepare high-quality of clean MgB2 film. And its thickness can be from 10nm ultrathin films and 100 nm thin films up to 8 μm thick film. It is the first time so far as we know that Tc and Jc are studied in this range of thickness. This will lead to a complete and systematical understanding of the superconducting MgB2 films. And it is also important and practical to choose the thickness when preparing MgB2 films.
2013, 62 (19): 197501. doi: 10.7498/aps.62.197501
The characteristics of martensitic transformation and magnetostructural coupling have been investigated for MnNiGe1-xGax (x=00.30) alloys. It has been found that the martensitic transformation temperature of the system can be deceased about 400 K by doping a low content of Ga to substitute for Ge. Adding Ga may weaken the hybridization and at the same time enhance the magnetic exchange interaction, which are responsible for the increase of the atomic moment and the Curie temperature in the austenitic phase. The structural and magnetic phase diagram was obtained to show some important points: 1) the decreased transition temperature successively pass through the Neel temperature and the Curie temperature; 2) the Curie temperature window still opens during the doping; 3) the magnetism can effectively affect the transformation behavior. The metamagnetization and the preparation influence on the transformation are also observed. These properties are significantly beneficial to the development of new magnetostructural materials.
2013, 62 (19): 197801. doi: 10.7498/aps.62.197801
A novel Ca3Si3O9:Dy3+ phosphor for white LED was prepared by sol-gel method. The structure and luminescent properties of Ca3Si3O9:Dy3+ phosphors with different concentration of Dy3+ and charge compensator Li+ were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. Results show that the emission spectrum consists of two main band peaks locatied at 483 nm and 577 nm, while the peaks of excitation spectrum are located in the rang of 290–480 nm. Both of luminescent intensity and the ratio of yellow to blue emission (Y/B) increase first and then decrease with increasing Dy3+ concentration; and the luminescent intensity reaches a maximum when Dy3+ concentration is of 1 mol%. The luminescent intensity of Ca3Si3O9:Dy3+can be enhanced by Li+, and the blue emission increases greatly when Li+ concentration is within the range of 2 to 4 mol%.
Low-temperature combustion synthesis and luminescent properties of SrMgAl10O17：Eu2+, Er3+ high brightness blue phosphors
2013, 62 (19): 197802. doi: 10.7498/aps.62.197802
The SrMgAl10O17:Eu2+ and SrMgAl10O17:Eu2+, Er3+ blue phosphors were synthesized by the combustion synthesis method. Their crystal structures and luminescent properties were analyzed by X-ray diffraction (XRD)、scanning electron microscope (SEM) and photoluminescence spectra, respectively. The XRD and SEM results indicate that the sample is well-crystallized in the combustion procedure, and its crystal structure has not changed when doped with low concentrations of rare-earth ions. PL results show that the phosphor of SrMgAl10O17:Eu2+ can be effectively excited by near UV LED chip with a broad emission spectrum extending from 430 nm to 520 nm, and has main peaks located at 460nm. Furthermore, the sample of the luminous intensity is the largest when the Er2+, Er3+ co-doped concentration is 4%, and the emission intensity of Sr0.95MgAl10O17:0.05Eu2+, Er3+ phosphor is significantly enhanced 54.9% higher than that of SrMgAl10O17:Eu2+ phosphor. It is indicated that Er3+has good sensitization effect for Eu2+ in luminescence, and this can be explained by the theory of energy transfer.
Simulation study based on the COMSOL Mutiphysics to the surface plasmon resonance of Cu2S quantum dots
2013, 62 (19): 197803. doi: 10.7498/aps.62.197803
As a new type of nano-semiconductor material, Cu2S quantum dot (QD) has received much attention due to its particular chemical and optical properties. In this paper we use COMSOL Multiphysics 4.2a software, select Radio Frequency model and combine the Maxwell theory to simulate and analyze the factors influencing Cu2S with its SPR. By using the Kretschmann prism coupling model, changing the QD size, the refractive index of QD solvent, the wavelength of incident light and coated substance of the QD, the data about how the SPR appears and the effectsof those factors are obtained. So the simulation results will be a theoretical foundation and reference to the further study.
2013, 62 (19): 197804. doi: 10.7498/aps.62.197804
The scheelite-structured CaWO4 phosphors doped with different concentrations of Sm3+ were prepared by precipitation method. Photoluminescence properties of Sm3+-doped CaWO4 samples were studied. Results indicate that red light emission of Sm3+ with higher color purity in the samples can be excited by 404 nm blue light. There are 4f-4f intrinsic emission of Sm3+ and a strong self-excitation emission of CaWO4 when excited by 240 nm short-wave ultraviolet, and the white light emission can be obtained. Experiments show that the best Sm3+ doping concentration is 2%. The energy transfer type between Sm3+ ions was determined to be the electric dipole-electric dipole interaction and the critical energy transfer distance (Dc) was calculated to be 2.0 nm.
Effects of transverse electromagnetic field distribution in the multipactor discharge on dielectric window surface
2013, 62 (19): 197901. doi: 10.7498/aps.62.197901
By using a P3D3V PIC code programmed by the authors, the multipactor discharge effects on dielectric inner and outer surface under high-power microwave with TE10 mode in the BJ32 rectangular waveguide are numerically studied. The electron spatial distribution, distribution of electric field in the normal direction of the dielectric surface, and electron density spatial distribution are presented. Numerical results could be concluded as follows. For inner surface, the multipacting first occurs in the area with large electric-field of microwave; for the outer surface, multipacting first occurs in the area with small electric-field of microwave. The above phenomena could be explained as follows. Poynting direction of microwave is the same as the outer surface normal direction and opposite to the inner surface normal direction. So the drift in the area with large electric-field of microwave causes electrons easy to move back to inner surface, and so electrons are easy to leave from outer surface. Compared with 1D3V model, in P3D3V model, we have for inner surface multipactor discharge with long oscillator forming time, small secondary electron number, high average electron energy, low incident power of microwave, and low level deposited power; for outer surface, we have multipactor discharge with short oscillator forming time, small secondary electron number, low average electron energy, low incident power of microwave, and low level deposited power. The deposited power is about 1%–2% of incident microwave power both in 1D3V and P3D3V models; while the ratio between deposited power and incident power of microwave has nothing to do with microwave parameters and inner or outer surface.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (19): 198101. doi: 10.7498/aps.62.198101
Three kinds of polystyrene spheres with different sizes were fabricated on glasses by drifting method of nanosphere lithography. Au thin films with various thicknesses were prepared by magnetron sputtering under controlled deposition time. Triangle-shaped Au nanoparticles array in three different heights after removing the PS template were observed using scanning electron microscopy. The absorption characteristics of all samples were measured by ultraviolet-visible spectrophotometer. Surface plasmon resonance peak was seen to shift to the longer wavelength with increasing diameter of Au nanoparticles. And the surface plasmon resonance peak was shifted to the shorter wavelength with increasing height of Au nanoparticles. Based on Mie theory, we simulated the extinction properties, which vary with the diameter of Au nanoparticles, using Matlab software. The conclusion is in accordance with our experimental results.
2013, 62 (19): 198102. doi: 10.7498/aps.62.198102
Monocrystal Pt nanoparticles, amorphous Al2O3 thin film, polycrystalline ZnO and TiO2 thin films were fabricated on black carbon nanoparticles by means of atomic layer deposition (ALD). Using high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometer (XPS), energy dispersive spectroscopy (EDS), We have characterized and analyzed the surface morphology, crystal structure and composition of the ranopasticles and thin filins. Results indicate that the ALD method is an ideal method to prepare core-shell stuctured nanometer materials. In addition, the reasons why the formation of ALD films with different crystal morphologies, such as monocrystal, amorphous, polycrystalline, were discussed.
2013, 62 (19): 198103. doi: 10.7498/aps.62.198103
Carbon-doped titanium monoxide films were successfully fabricated using CO2 as reactive gas by means of DC reactive magnetron sputtering. Phase tructure, composition and resistivity of the fabricated films were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and four point probe method. Results show that the fabricated film has a cubic phase structure, and the carbon element exists mainly as anion in the lattice of C-TiO. The resistivity of C-TiO is 52.2 μΩ·cm which is lower than that of pure TiO. Results of first principles calculation show that the Fermi levels of both TiO and C-TiO lie in their conduction bands, thus TiO and C-TiO have characteristics of metal conduction. Also the results of first principles calculation show that impurity levels of C 2p lie near the conduction band of C-TiO, which extend the width of conduction band and increase the density of states near the Fermi level of C-TiO, so the conductivity of C-TiO is larger than that of undoped TiO. The theoretical calculations are in agreement with experiment results.
2013, 62 (19): 198104. doi: 10.7498/aps.62.198104
Manganese cobalt nickel complex oxide is a thermal-sensitive material with the property of semiconductor. In this paper, Mn1.74Co0.72Ni0.54O4 (MCN) thin film was prepared in air using metal-organic-deposition method at room temperature on Si substrate, and the crystallization synthesis of the MCN thin film was prepared using alcohol-thermal reaction. According to X-ray diffraction, field emission scanning electron microscope (FESEM) and the relationship between resistivity and temperature, effects of MCN thin film made by alcohol-thermal reaction on crystalline microstructure, surface morphology and electrical properties were investigated. X-ray diffraction pattern showed that the MCN thin film appears to be spinel structure with predominant spinel peaks. Field emission scanning electron microscope showed that the surface morphology of MCN thin film is crack-free and compact surface. The relationship between resistivity and temperature of the thin film Mn1.74Co0.72Ni0.54O4 was that the resistivity decreases with the increase in temperature. The room temperature(≈ 27℃) resistivity of the MCN thin film was 303.13 Ω·cm.
2013, 62 (19): 198201. doi: 10.7498/aps.62.198201
In some cases, the extracellular concentration of potassium ions cannot be regarded as being constant. The potassium lateral diffusion leads to extracellular accumulation of potassium ions and the generation of potassium diffusive coupling. The effect of potassium diffusive coupling on spiral wave is investigated by using the Luo-Rudy phase I cardiac model with potassium diffusive coupling. The numerical results show that when the strength of potassium diffusive coupling is relatively strong, the potassium diffusive coupling makes extracellular potassium ion concentration rise first and then regularly oscillate, leading to the irregular meandering of spiral wave. It is observed that the width of spiral arm and the frequency of spiral wave decrease as the strength of potassium diffusive coupling increases. Thus, when the strength of the potassium diffusive coupling is strong enough, the potassium diffusive coupling can eliminate spiral wave and spatiotemporal chaos.
Direction of arrival of EMW and polarization parameter estimation using tripole near the earth surface
2013, 62 (19): 198402. doi: 10.7498/aps.62.198402
Based on the principal theory of tripole antenna in free space to compute the polar angle and azimuth angle of the incident electromagnetic wave (EMW), and the relations between each component of electric field and polarization, the formula for computing direction of arrival (DOA) of left-hand polarization electromagnetic wave and the method of determining the sense of the incident wave are presented. A novel method to filter out the reflected wave from the earth surface is put forward, which ensures the accuracy of the DOA, various polarization parameters are gained from DOA computed and electric field intensity, these polarization parameters serve as reference data for research of ionosphere and electromagnetic wave propagation in the ionosphere.
2013, 62 (19): 198701. doi: 10.7498/aps.62.198701
Image reconstruction algorithms implemented in existing computed tomography (CT) scanners require that the projection data should be available in proportional-space. The image reconstruction from the projections viewed from few angles has already been one of the hot problems in the research of iterative reconstruction algorithms. Total variation (TV)-based CT image reconstruction has shown to be experimentally capable of producing accurate reconstructions from sparse-view data. Reconstruction algorithms based on alternating direction method (ADM) show higher performance among these TV-based algorithms. However, computing the pseudoinverse at each iteration is too costly to implement numerically in the exact ADM algorithm. For this problem, then inexact ADM is adopted, which uses linearization and proximal points techniques such that computing the pseudoinverse can be accomplished by fast Fourier transforms. Experimental results demonstrate that the proposed method can accelerate the exact ADM algorithm, with little accuracy loss, and the computing time is approximatively reduced by 30%.
2013, 62 (19): 198801. doi: 10.7498/aps.62.198801
The -Si:H/SiNx stack-layer films are piepared by plasm-enhanced chemical vapor deposition to passivate crystalline silicon solar cells. Effective lifetime of minority carrier is used to characterize their passivation property and the passivation mechanism is analyzed by simulating the high-frequency capacitance-voltage curves. It is found that compared to -Si:H films prepared by the same method, -Si:H/SiNx films show better passivation property. Through thermal treatment at different temperatures, the passivation property of -Si:H/SiNx films is improved to the best at 300 ℃ first, and then degraded with rising temperature. Annealing at 300 ℃ can make -Si:H/SiNx films show a better passivation property than -Si:H films in 90 min. Simulation results indicate that the passivation property of -Si:H/SiNx films is mainly determined by the state density at the -Si:H/Si interface.
2013, 62 (19): 198901. doi: 10.7498/aps.62.198901
In this paper, by considering the collaborative scientific behaviors, a model for evolving hyper-network is proposed based on the hypergraph theory. We study analytically the dynamics of authors’ hyper-degree using mean-field approach. Results of both theoretical and numerical studies indicate that such a hyper-degree distribution follows a power-law decay, with the exponent γ=1+L/M, where L/M suggests the author growth rate of an evolving scientific network. In addition, empirical studies on ten-year journal data of Science China and Acta Physica Sinica from 2003 to 2012, shows that the present model can find good agreement with the empirical data. The proposed model may shed some light on the in-depth understanding of the structure and scientific collaboration networks.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2013, 62 (19): 198401. doi: 10.7498/aps.62.198401
Due to the working characteristics of radar system, i.e. it has to ensure the emission and acceptance of its own radar wave, frequency selective surface (FSS) radome is the most effective stealthy way to give radome the function of frequency-selective. Combining the FSS technique and the radome together, FSS radome provides bandpass transmission properties in the operating frequency of radar, and changes the RCS characteristics of the antenna compartment when it is beyond the antennas operating frequency range, thus it is a realization of out-of-band stealth. This paper introduces the basic design of FSS radome technology and summarizes the research status of FSS radome in the structure design and the technology. The muti-band FSS radome, intelligent FSS radome, thick-screen FSS radome, miniaturized element FSS radome and the technologies to construct radome are predicted to be the perspective of FSS radome.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Feasibility research on the method of rain rate detection based on space-earth link signals at 1–10 GHz
2013, 62 (19): 199201. doi: 10.7498/aps.62.199201
Satellite signals across the space-earth link are always seriously affected by rain, inducing attenuation and depolarization. In this paper, two methods of estimating the rain rate are investigated based on the space-earth link signals in a frequency range of 1–10 GHz. Firstly, the effects of rain rate (R) on attenuation (A) and cross-polarization discrimination (XPD) are studied, according to the complex interaction between signals and raindrops. Then, two relevant models A-R and XPD-R are established, which are the key techniques to estimate the rain rate. The feasibilities of the above models are analyzed. In addition, their applicabilities at various frequencies, polarization and satellite elevations are also investigated systematically. The results show that for the space-earth link signal with horizontal or circular polarization and higher frequency, the A-R relation can be used to estimate the heavy rain; for signals with different frequencies and polarizations, XPD-R is suited to estimate various rain rates, especially in a frequency range of 1–50 mm·h-1; A-R and XPD-R are both applicable at different elevations. Moreover, the XPD-R relation is consistent with the prediction model of XPD proposed by ITU at 4–10 GHz. The results obtained in this work will play an important role in the future verification experiment, the nowcasting automatic detection of rain rate and global rain observations.
Spatial and temporal characteristics of moisture cycle factors over China analyzed with ERA-Interim reanalysis data
2013, 62 (19): 199202. doi: 10.7498/aps.62.199202
In this paper, we analyze the spatial and temporal characteristics of different moisture cycle factors over China by using the ERA-Interim data supplied by the European Centre for medium-range weather forecasts (ECMWF). The methods used in this paper include mainly the empirical orthogonal function (EOF), similarity coefficients, one-dimensional linear regression and so on. Results show that the spatial distribution of evaporation, zonal and meridional moisture flux are all extremely similar to that of precipitable water. While the spatial distribution of precipitable water and precipitation are both very similar to that of evaporation. The similarity coefficient between precipitation and zonal moisture flux is a little larger than that between precipitation and meridional moisture flux. In terms of temporal characteristics, it is shown that precipitation has an obvious upward trend during 1979–2002 and an obvious downward trend during 2002–2011. The trend of evaporation is the same as that of precipitation during the same period, but the former is more obvious than the latter. Besides, evaporation also shows an obvious upward trend during 1979–2011. Both of precipitable water and moisture flux divergence show a slightly downword trend. Zonal and meridional moisture flux change in a period of 2–3 years. Further, zonal moisture flux has an obvious downward trend during 1979–2011. The vapor flux has an obvious downward trend both in spring and autumn, and changes in a period of 2–3 years for all four seasons. Besides, the vapor flux in summer presents a decadal transition.
An accurate macro-cell-method for extracting dispersion characteristics of 1D reciprocal microwave structures with finite periodicity
2013, 62 (19): 199203. doi: 10.7498/aps.62.199203
A novel macro-cell-method (MCM) has been proposed, which is capable of accurately extracting the dispersion characteristics of 1D reciprocal microwave structures with finite periodicity. In practice a single macro-cell consists of multiple periodic unit cells, therefore the electromagnetic coupling effects among unit cells can be rigorously considered. The eigen transfer factors ξN and 1/ξN corresponding to the forward and backward Bloch waves can be calculated in terms of the Bloch theory. Imposing complex logarithmic operation to ξN, the attenuation constant α can be univocally determined, while multiple integer branches exist in the solution of the phase shift constant β due to the multiroots property of the complex logarithm function. The rational integer branch is uniquely selected by comparing β from the MCM with that extracted from the unwrapping-method (UPM), regarding β from the UPM as the approximate value. Compared to the conventional eigenmode-method, UPM and single-cell-method, the MCM has no requirements to the coupling intensity among unit cells comprising finitely periodic structures, and with such good generality and accuracy, the MCM can be an effective tool for characterizing 1D reciprocal finitely periodic structures, facilitating their wide applications in microwave engineering.
2013, 62 (19): 199601. doi: 10.7498/aps.62.199601
We use the data obtained from empirical forecast model and satellite remote sensing to analyze and assess the accuracy of the data obtained from first near space meteorological rocket sounding in Jiuquan Satellite Launch Center (JSLC) in November 2004. Analysis shows that the data of empirical forecast model has great difference from meteorological rocket sounding data for the middle-upper stratosphere. Because the empirical forecast model has low spatial and temporal resolution, especially it lacks of the sounding data for the middle-upper stratosphere in China, the deviation between the data of meteorological rocket and the satellite data is obviouslly lower than the empirical forecast model gave. The deviation is caused by the systematic error between the two and the difference of time, latitude and longitude. Comprehensive comparison results show that the data of meteorological rocket is of high accuracy and credibility compared to the data of the empirical forecast model and satellite remote sensing. These data can be used to specify the probe’s results from other ways.