Vol. 63, No. 2 (2014)
2014, 63 (2): 020201. doi: 10.7498/aps.63.020201
Aiming at the problem of trajectory tracking in a class of discrete time-varying switched system with arbitrary sequence, in this paper we propose a discrete iterative learning control algorithm. Under the precondition that the switched sequence does not change along the iterative axis but it does along the time axis, this algorithm divides the whole finite time region into several finite subintervals, and uses -norm to prove the convergence strictly, and provides the sufficient convergent condition of the algorithm in the norm form. This method not only realizes the complete tracking for a discrete time-varying switched system within a limited time, but also has a simple structure easy to be realized in engineering. Simulation results verify the validity of the method.
2014, 63 (2): 020301. doi: 10.7498/aps.63.020301
We investigate the entanglement dynamics of two cavities interacting respectively with reservoir in non-inertial frames. We consider not only the influence of acceleration, but also the influence of different rates between right and left components of the Unruh single-particle state on entanglement. The result shows that the reservoir-entanglement will increase with the decrease of the cavity-entanglement when the acceleration parameter is fixed. In addition, there appears the redistribution of entanglement between particle mode and antiparticle mode, when the initial state is in a maximal by entangled state with |qR|=1. We also find that the sudden death of entanglement happens in infinite acceleration limit when |qR|=|qL|=1/√2, whereas the death of entanglement happens at finite acceleration when qR2.
2014, 63 (2): 020302. doi: 10.7498/aps.63.020302
Combining quantum mechanics and the normal distribution in statistics we study the coherent state from the point of view of statistics and by using the integration method within ordered product of operators. We find that the pure coherent state |z >z| exhibits a bivariate normal distribution of randon variables in (q,p) phase space, z=(q+ip)/√2, with a real k-parameter which is related to the quantization scheme, and the correlation coefficient is ik. For k=±1, |z >z| respectively is arranged as P-ordering (all P stand on the left of all Q) and Q-ordering (all Q stand on the left of all P), while in the case of k=0, |z >z| is arranged as the Weyl-ordering. In the cases of P-ordering and Q-ordering, in the classical correspondence function of |z >z||z=(q+ip)/√2 the bivariates (q,p) are correlated, only in the case of Weyl correspondece, (q,p) are independent. In other words, the Weyl ordering of operators is liable to decouple the correlation in bivariates.
Asymptotic stability for non-cooperative program game model of the capacity analysis for mobile ad-hoc networks with variable time delay
2014, 63 (2): 020501. doi: 10.7498/aps.63.020501
Stability of capacity is one of the key properties for quality of service (QoS) support in mobile ad hoc networks (MANETs). In this paper, a novel technique is proposed for controlling the stability of capacity analysis model for non-cooperative program game MANETs, with the time-varying propagation delay taken into consideration. First, based on the obtained source node flow transmitting rate evolution aligns of capacity analysis model for non-cooperative program game mobile ad-hoc network, when adding the time-varying propagation delay term, which is a class of nonlinear time-varying delay differential aligns, the asymptotic stability criteria of the model are presented in the form of descriptor and linear matrix inequalities. Then, an iterative algorithm is also provided for controlling the stability of the model. The proposed criteria are less conservative since they are based on an equivalent model transformation. Simulation experiments verify the effectiveness of this algorithm. Although the model used in this paper focuses on a specific algorithm, we believe that this method has a great potential in analyzing and understanding the general capacity of MANETs stability control issues.
2014, 63 (2): 020502. doi: 10.7498/aps.63.020502
The stochastic resonance (SR) of two-dimensional Duffing oscillator is studied in this paper. We propose the generalized parameter-adjustment SR of Duffing oscillator. On the basis of Kramers rate, we build a discrimination function of the SR of Duffing oscillator, and we expound the generalized parameter-adjustment SR laws of Duffing oscillator under different noise intensity and signal frequency conditions. The general method of generating the generalized parameter-adjustment SR of Duffing oscillator is also given in this paper.
2014, 63 (2): 020503. doi: 10.7498/aps.63.020503
The study of a novel amplitude spiral wave in complex Ginzburg-Landau equation system is performed. The competition results between amplitude spiral waves and phase spiral waves and spatiotemporal chaos can be divided into four kind of regimes: regimes I and Ⅲ, in which the space of amplitude spiral waves is invaded by phase spiral waves, regime Ⅱ, in which the amplitude spiral waves are stronger than phase spiral waves, and regime IV, in which we have various results due to the existence of spatiotemporal chaos. Analysing the frequencies of amplitude spirals, phase spirals and spatiotemporal chaos, we find that when the parameters of spiral wave system α1=-1.34 and β1=0.35, the spiral wave with higher frequency will have better stability and can invade into low-frequency pattern space. The competition results are influenced by frequency of real part of the system variable. Our frequency analyses accord well with the numerical observations.
2014, 63 (2): 020504. doi: 10.7498/aps.63.020504
Through mathematical modeling analysis of Chua’s memristive circuit, the problem of dimensionality reduction for dynamical modeling of memristive circuit is proposed. Taking memristive circuit with two memristors for example, dimensionality reduction modeling of the memristive circuit is performed, on which a three-dimensional system model is established. Based on this model, the equilibrium points and stabilities are analyzed, and the dynamical characteristics, when the parameters are varied, are investigated. Furthermore, the analysis results from the conventional model are compared with the results from the dimensionality reduction model of memristive cicuit with two memristors. The results indicate that the dimensionality of the dimensionality reduction model of memristive circuit is related to the number of capacitors and inductors only, but unrelated to the number of memristors; there exist nonlinear phenomena about the coexistence of bifurcation modes in the memristive circuit when circuit parameters are varied; the dimensionality reduction modeling reduces the complexity of system modeling, which is conducive to dynamical charateristic analysis of the system but eliminates the effect of the initial conditions of the memristors internal state variables on dynamical charateristics of memristive circuit.
2014, 63 (2): 020505. doi: 10.7498/aps.63.020505
Model of a heat transfer process in heat exchanger with heat leakage is established in this paper. Both the heat flux between the hot and cold fluids and the heat leakage between the cold fluid and outside environment are assumed to obey Newtonian heat transfer law. On condition that the net amount of heat transferred by the cold fluid is given, the optimal temperature configurations of the hot and cold fluids for the minimum entransy dissipation of the heat transfer process are derived by using the optimal control theory. Optimal paths are also compared with the conventional strategies of heat transfer under constant hot fluid temperature and constant heat flux rate operation. The results obtained in this paper could provide some theoretical guidelines for the optimal design and operation of real heat exchangers.
2014, 63 (2): 020701. doi: 10.7498/aps.63.020701
In this article, we propose an image authentication and a recovery algorithm based on chaos and Hamming code. In this algorithm, the Hamming code that is widely used in the channel coding is used, the error control is applied to the image authentication and recovery, and the validity and security of the algorithm are ensured by chaotic mapping. Analytical and experimental results show that the algorithm has a good visual effect and an effectively tampering detection ability with less embedding authentication information, at the same time the algorithm can recover a tampered image to some extent.
2014, 63 (2): 020702. doi: 10.7498/aps.63.020702
This paper, based on the rate equation theory, astablishes a model for optical pump waveguides to generate terahertz laser. By analyzing and solving the rate equation, the expressions of pump absorption coefficient, terahertz small-signal gain coefficient and terahertz output power are obtained. The calculation shows that the THz power increases first and reduces gradually with the increase of pressure of the working material, and it will increase with the increase of pumping power and the decrease of the output mirror reflectivity. The best working pressure increases with the rise of the pumping power. The number of particles in the excited state and the THz flux increase in the waveguide radial direction from the center, while the small-signal gain coefficient shows the opposite trend. Pump saturation, weak pump absorption and excited state terahertz absorption are the primary cause limiting the increase of the laser conversion efficiency. Results based on this model are in good agreement with the data from the relevant literature.
ATOMIC AND MOLECULAR PHYSICS
2014, 63 (2): 023101. doi: 10.7498/aps.63.023101
The electronic structures of Heusler alloys X2RuPb (X=Lu, Y) under different conditions are investigated using the first-principles calculations. It is found that the alloys become the real topological insulators under a proper lattice deformation or doping. The spin-orbital coupling and the interatomic hybridization effect reinforce each other to perform the band inversion in X2RuPb (X=Lu, Y) compounds and they play roles to different degrees for the materials with different compositions. The ideal topological insulators are easier to obtain using simultaneously lattice deformation and doping artifices, which is available in practical material preparation.
2014, 63 (2): 023102. doi: 10.7498/aps.63.023102
In order to study the influence of external electric field on ZrO2, molecular structure of ZrO2 ground state is optimized by density functional theory (B3P86) method with 6-311++G* basis sets for O atom and aug-cc-pVTZ-PP for Zr atom. The effects of electric field ranging from 0 to 0.025 a.u. are investigated on bond length, total energy, charge distribution, dipole moment, HOMO (the highest occupied molecular orbital) energy level, LUMO (the lowest unoccupied molecular orbital) energy level and energy gap. The excitation energies, transition wavelengths and oscillator strengths under the same intense external electric fields are calculated by the time dependent density functional theory (TD-B3P86) method. The result shows that the bond length of Zr-2O and total energy increase with external field increasing, but the bond lengths of Zr-3O, LUMOs and energy gaps decrease, and HOMOs almost keep the same. The excitation energies decrease and the transition wavelengths of the six excited states are red shifted toward longer wavelength as the applied electric field increases. Therefore the spectral region of zirconiumdioxide molecule can be expanded in visible-infrared region by the use of external electric fields.
2014, 63 (2): 023103. doi: 10.7498/aps.63.023103
The geometries, stabilities and electronic properties of PtnAl (n=18) clusters are calculated using density functional theory at BPW91/LANL2DZ level. The stabilities of the ground states of PtnAl (n=18) clusters are discussed by means of the binding energy, the second difference in energy and energy gaps, and the magnetic properties. Mulliken charges are studied. The growth patterns for different sized PtnAl (n=18) clusters are of Al-substituted Ptn+1 clusters and they keep a similar framework of the most stable Ptn+1 clusters except Pt2Al. Al atoms in the ground state PtnAl isomer tend to occupy the most highly coordinated positions. The analyses of stabilities show that PtAl and Pt4Al are more stable than other clusters. Mulliken population analysis shows that charges are transferred from Al atoms to Pt atoms, which indicates that Al atom acts as electron donor in all PtnAl clusters. The analysis of magnetic property shows that doping an Al atom reduces the average atomic magnetic moment of the host Pd cluster. Pt-rich clusters which have a strong nonlinear optical effect and are easy to polarize by external electromagnetic field.
2014, 63 (2): 023301. doi: 10.7498/aps.63.023301
The vibration/rotation modes and the corresponding infrared spectra of deuterium molecules with the D2d/D2h structures are calculated using the coupled cluster singles and doubles method with the cc-PVTZ basis sets within the framework of the density function theory. The infrared (IR) absorption spectrum of liquid deuterium is experimentally measured in a home-made cryogenic target system by a home-made low-temperature infrared spectroscope. The experimental results show that the strongest IR absorption peak of liquid deuterium is related to the Q1(0)+S0(0) mode, which is in good agreement with the theoretical calculation.
Theoretical study of the influence of femtosecond pump-probe pluse on the photoionization of NaLi molecule
2014, 63 (2): 023302. doi: 10.7498/aps.63.023302
In this work, using three-state model and time-dependent wave packet method, the wave packet dynamic process and time-resolved photoelectron spectrum of NaLi molecule in femtosecond pump-probe intense laser field are investigated and the relation between the parameter of the femtosecond laser and time-resolved photoelectron spectrum is obtained. It is found that the vibrational periods of wave packet are different for different laser wavelengths and the photoelectron spectra are different for different pump-probe delay times. The height and position of the peak of the photoelectron spectrum change with pump-probe delay time. When 1=352 nm and t=400 fs, the corresponding signal in the outer well (0.5 eV) is obviously smaller than that in the inner well (1.35 eV). The result reveals that the time-resolved photoelectron spectrum reflects the information about the wave packet dynamic of the excited state 41+ The results may be useful for realizing the optical control of molecule and the process of quantum manipulation of molecule experimentally, and provide some important basis for further theoretical research in this respect.
2014, 63 (2): 023303. doi: 10.7498/aps.63.023303
Using classical ensemble method, we investigate the laser ellipticity dependence of double ionization (DI) of H2 molecules. The results show that DI mechanism of H2 molecules depends strongly on laser polarization. As the ellipticity increases, the DI mechanism changes from nonsequential DI to sequential DI. For sequential DI in the case of large ellipticity, the momentum distribution of the two electrons depends sensitively on ellipticity, which indicates the sensitive dependence of the release time of two electrons on ellipticity.
2014, 63 (2): 023401. doi: 10.7498/aps.63.023401
Using the time-dependent density functional theory and non-adiabatic coupling in molecular dynamics, the reaction dynamics of collisions between energetic proton and hydroxy is studied. The variations in kinetic energy of proton and hydroxy and the motions of electron of hydroxyl and ion before and after collisions are investigated. It is found that when a proton is incident in the direction perpendicular to the molecular axis, it that has lose kinetic energy rebounds, and captures electrons from hydroxy, while the hydroxy that has lost part of electrons gains kinetic energy, and thus translates toward the calculating boundary in the manner of contracting vibration. The larger the kinetic energy of incident proton, the more the number of electrons captured from hydroxy is. Therefore the bond length of hydroxy lengthens, oscillation strengthens, and vibrational frequency decreases. In addition, it is found that the incident direction of proton has a great influence on the dynamic behavior of excitation in a collision process. Considering the case where the proton is incident from different directions, the results show that the larger the kinetic energy of incident proton, the more the lost energy is, and the lost energy is linearly related to the initial kinetic energy of incident proton. For hydroxy, when the incident kinetic energy of proton is less than 25 eV, the kinetic energy gained by the proton is linearly related to the initial kinetic energy, but unrelated to incident direction, while when the initial kinetic energy of incident proton is larger than 25 eV, the increment in kinetic energy of hydroxyl is much larger in the case where the proton is incident along the axis of hydroxyl molecule than in the case where the proton is incident in the direction perpendicular to the axis of the hydroxyl molecule.
Influence of collision energy and reagent vibrational excitation on the stereodynamics of reaction Ar+H2+→ArH++H
2014, 63 (2): 023402. doi: 10.7498/aps.63.023402
The quasi-classical trajectory is calculated for the reaction Ar+H2+→ArH++H (12A’) on the latest potential surface. The correlated integral reaction cross section, P(θr), P(φr) distribution and the polarization dependent differential cross sections polariztion dependent differential cross sections (PDDCSs) are discussed in detail. The results show that the integral reaction cross sections are well consistent with the experimental values at different collision energies and reagent vibrational excitations which indicates that our potential energy surface is accurate. The results indicate that the vibration excitation has less influence on the P(θr) distribution than the collision energy. The P(φr) distribution, and PDDCS are quite sensitive to collision energy and reagent vibrational excitation.
Improving the single atom probability by using the blue-detuned laser-assisted-collisions between the cold atoms trapped in the for-off-resonance trap
2014, 63 (2): 023701. doi: 10.7498/aps.63.023701
Using the light-assisted-collisions (LAC) and the feedback controlling loop on a quadrupole magnetic field, we have realized high probability of single atoms in the far-off-resonance trap (FORT). We analyzed the principle of LAC irradiated by a red-detuning laser or by a blue-detuning laser. And we also experimentally proved that using the red-detuned laser (the blue-detuned laser) we can realize 50% (80%) of single atom probability in the FORT. Using the feedback controlling loop, we realized 95% of single atom probability in the FORT, which opens a way for a two-dimensional FORT array. When the number of atom was zero, we decreased the gradient of the quadrupole magnetic field to quickly load atoms, and when we had more than one atom in the FORT, we switched on the blue-detuned laser to irradiate the atoms to play LAC. We measured the second-order coherence degree of the fluorescence photons emitted by the atom trapped in the FORT by using HBT scheme and found it was g(2)(τ=0)=0.08.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (2): 024101. doi: 10.7498/aps.63.024101
A novel type of slow-wave structure for Smith-Purcell device called dielectric loaded metal grating, is proposed in this article. The “hot” dispersion align of the structure is obtained by using the eigen-function method and single-mode approximation. The first-and second-order growth rate of beam-wave interaction are obtained at the synchronization point. The effects of grating groove width and depth on dispersion characteristic are analyzed, and the influences of electron beam parameters and distance between electron beam and grating surface on growth rate characteristic are also studied. The results show that dielectric-loaded metal grating can effectively weaken the structure dispersion, and that with the increases of relative dielectric permittivity, groove width and depth, the dispersion curve becomes flatter and moves toward low frequency. When the electron beam voltage or current changes, the first-order growth rate curve can only roughly describe the change trend, while the second-order growth rate can accurately show the change values. The simulation of the structure is performed by using two-dimensional particle-in-cell code MAGIC, and the simulation results accord well with the theoretical results.
Simultaneous demultiplexing into two 10 Gbit/s using a bidirectionally operated highly nonlinear fiber
2014, 63 (2): 024201. doi: 10.7498/aps.63.024201
A simultaneous two-channel optical time division multiplexing (OTDM) demultiplexing is proposed and experimentally demonstrated by using a bidirectionally operated highly nonlinear fiber followed by a narrow-band offset filter. The performance of the proposed demultiplexer is evaluated in an 80 Gbit/s OTDM transmission system. A maximum power penalty of 2.6 dB is obtained for the worst demultiplexed channel. The proposal might be interesting since it offers a powerful tool for developing ultrafast photonic networks.
2014, 63 (2): 024202. doi: 10.7498/aps.63.024202
The Yb3+ doped double clad polarization-maintaining photonic crystal fiber is prepared from SiO2-Al2O3-P2O5 core glass of an optical fiber perform through a conventional modified chemical-vapor deposition technique and solution doping method, which contains a large core of around 30 m in diameter. Through simulated calculation, the mode area of the double clad polarization maintaining photonic crystal fiber reaches about 232 m2 and the double refraction coefficient B can be 510-5. In experiment, amplification tests of both pulse laser and continuous laser are conducted. The first domestic high efficient femtosecond laser amplification is achieved by using the photonic crystal fiber. A 2 m long photonic crystal fiber laser generates up to 1.64 W output power with a slope efficiency of 49.8%. And 5 m long fiber can reach 8.12 W continuous laser output, in which the slope efficiency is 55.9% and performs good amplification effect. Besides, the extinction ratio is about 10 dB, which indicates good polarization performance of the fiber.
2014, 63 (2): 024203. doi: 10.7498/aps.63.024203
By adding periodic signal into two-mode laser, we take the first-order approximation to the multiplication noise of the laser intensity equation, and use a linear approximation to calculate the correlated function and power spectrum. We find that the signal-to-noise ratio presents stochastic resonance as the intensities of pump noise and quantum noise and the frequency of signal vary.
2014, 63 (2): 024204. doi: 10.7498/aps.63.024204
Due to their future applications in optical communication, nonlocal dark solitons in bulk medium and surface bright solitons have received much attention recently. However, nonlocal surface dark solitons have not been investigated till now. In this paper, 1+1 dimensional nonlocal fundamental and second-order surface dark solitons have been found numerically at the interface between thermal nonlinear medium and linear medium. The relation between the wave shape of nonlocal surface dark soliton and propagation constant and nonlocality degree is investigated. Moreover, the stability of them is analyzed theoretically. The numerical simulation results show that 1+1 dimensional nonlocal fundamental surface dark Solitons are always stable in the domain of their existence, while second-order surface dark solitons are oscillatorily unstable and the width of unstable domain depends more greatly on propagation constant than nonlocality degree of nonlocal nonlinear medium. The figure showing the propagation, with the initial input of noise added, confirms the correctness of stability analysis results.
2014, 63 (2): 024205. doi: 10.7498/aps.63.024205
Cylindrical macroporous silica structures are fabricated on the surfaces of glass capillary with different diameters by a sol-gel cooperative assembly method. The cylindrical inverse opals are characterized by scanning electron microscope, showing that the (111)-like plane of face-centered-cubic (fcc) structure is parallel to the surface of the cylindrical capillary. Transmission spectra demonstrate typical photonic band gaps (PBGs) of about 40% in the direction of  lattice orientation, which accords well with the result from the Bragg formula. The excellent optical properties not only affirm the success of sol-gel coassembled macroporous silica inverse opals on cylindrical substrates, but also introduce PBG materials to meet the requirements of the practical applications of optical communication, optical switching and sensors.
Simultaneous measurement of temperature and bending-curvature using a single local micro-structured longperiod fiber grating
2014, 63 (2): 024206. doi: 10.7498/aps.63.024206
A local micro-structured long-period fiber grating (LMSLPFG) is proposed and investigated experimentally. The LMSLPFG is fabricated by using hydrofluoric acid (HF) to partially etch a standard long-period fiber grating (LPFG), thereby forming a local defect in the cladding. The theoretical analysis and experimental results show that partially etching will change the effective refractive index modulation in the cladding mode, which equivalently introduces a phase shift into the part of defect and manifests, in the spectrogram, as openning a transmission window between the stopbands, forming two transmission stopbands and one transmission passband. On this basis we study the temperatures and bending characteristics of the two stopbands and one passband. The results show that the temperature sensitivities of the two stopbands and one passband are all approximately 0.05 nm/℃; the bending sensitivity of the passband (2.61 nm/m-1) is less than those of two stopbands (4.71 nm/m-1). Thus by using the sensitive matrix, we can simultaneously measure the curvature and temperature, with only one grating used.
2014, 63 (2): 024301. doi: 10.7498/aps.63.024301
In this pager, we theoretically propose a model for low-frequency multi-channel filtering of phononic crystal composed of locally resonant units By introducing the resonance units with different filling rates into two-dimensional three-component locally resonant phononic crystal, a waveguide is built Its band structure transmission curve and transmitted sound pressure field map are calculated by the finite element method This design results in a low frequency range of the band gap emergence of new discrete mode around the different resonant frequencies of the scatterer These discrete modes enable the corresponding sound wave to propagate along the waveguide direction in phononic crystal waveguide The discrete model is only associated with the respective resonant unit, so it has a strong anti-jamming capability It provides a new theoretical basis for the multi-channel low-frequency filter.
2014, 63 (2): 024701. doi: 10.7498/aps.63.024701
Hypervelocity impact (HVI) characteristics of Ti6Al4V/Ly12 Al/polyamide fibre density-grade thin-plate are investigated experimentally in a velocity range of 4.0–6.5 km/s by using two-stage light gas gun. The perforation in target, damage to witness wall, and ballistic limit curve are obtained and compared with those in the case of aluminum thin-plate. The results show that the diameter of the perforation hole is larger than that of aluminum thin-plate, the crater size in witness plate is smaller, and the ballistic limit curve is 50% larger than the latter. The analysis of shock wave propagation and the calculation of energy dissipation property in the density-grade thin-plate show that higher peak shock pressure is produced in it, and it has longer pressure duration time. Thus, more dissipation energy is consumed than in the case of aluminum thin-plate. So the density-grade thin-plate has a very good performance in withstanding HVI, and is promising in engineering application, e.g. protecting spacecraft from HVI of micro-meteoroid and orbital debris.
Phase transition in liquid due to zero-net-mass-flux jet and its numerical simulation using lattice Boltzmann method
2014, 63 (2): 024702. doi: 10.7498/aps.63.024702
The phase transition in liquid due to the excitation of zero-net-mass-flux jet is simulated using the lattice Boltzmann method. First, the scheme for inlet/outlet boundary of the specific zero-net-mass-flux jet is derived. Then, with the model proposed by Shan and Doolen for single component and multiphase flow, the process of a single bubble formation in a liquid-filled square cavity is simulated, with the excitation of zero-net-mass-flux jet taken into consideration. Further, the investigation of the effects of three significant parameters, ε/T, T and vout/vin, on phase transition in the square cavity is carried out. The results show that the number of vapor nodes increases rapidly in the early stage of phase transition, and then achieves a constant after a long term fluctuation. In some sense, the previously mentioned parameters except T reflect the rapid change of jet velocity when the stages of inflow and outflow are transformed into each other. Thus the evolution of phase transition in liquid can be affected by the parameters ε/T and vout/vin mainly, but by parameter T negligibly. When ε/T is small, the single bubble resulting from phase transition is separated from the boundary. On the contrary, when ε/T is large, the corresponding single bubble attaches to the bottom boundary, and the process of phase transition is accelerated. Moreover, with vout/vin increases, the domain filled by vapor phase in the square cavity, decreases slightly. In summary, this study reveals the details of phase transition process in liquid subjected to the zero-net-mass-flux jet.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (2): 026101. doi: 10.7498/aps.63.026101
In order to investigate the dose rate effect and the radiation response of the voltage comparator, a group of bipolar voltage comparators are irradiated by 60Co at high-and low-dose rates under different bias conditions. The results show that many of the parameters for the voltage comparator subjected to ionization radiation, such as power current, input bias current, input offset voltage, and output voltage, are degraded to a certain extent; the irradiation response of the voltage comparator is severely affected by bias condition. What is more, the same type of circuits manufactured from different companies exhibit different dose rate effects; the reasons for the degradation are discussed by analyzing the experiment results. The mechanism for the formation of dose rate effect is also analyzed from the annealing characteristics. The results obtained in this paper are not only useful for the applications of the radiation hardness device, but also helpful for its design.
2014, 63 (2): 026201. doi: 10.7498/aps.63.026201
Optical gradient force, as a novel type of actuation force for nano-resonators, has recently attracted a lot of attention. In this paper, the inherent nonlinear characteristics of the optical gradient force are analyzed. A nonlinear dynamic model of the ring and spoke resonant system driven by optical gradient force is proposed. The influences of optical input power and geometric parameters on the nonlinear dynamic responses of the system are investigated. The results show that the optical gradient force can cause stiffness to soften. The amplitude increases and the resonance frequency shifts as the input optical power increases. Moreover, the amplitude and resonance frequency of the nano-resonator decrease as the initial gap of the rings increases. Therefore, the resonance frequency can be adjusted by changing the optical input power. This work can be useful for the further design and performance prediction of nano-resonators driven by the optical gradient force.
2014, 63 (2): 026202. doi: 10.7498/aps.63.026202
A series of reverse-impact experiments is performed on vanadium at peak shock pressures from 32 GPa to 88 GPa. A displacement interferometer is used to measure the particle velocity profile at the vanadium/LiF window interface. Analysis of these profile provides a measure of sound velocity of vanadium in the Hugoniot state. The transition from body-centered cubic structure to rhombohedral structure phase at ～ 60 GPa is identified by the discontinuity of the sound velocity against shock pressure. This transition pressure is consistent with the data from high pressure diamond anvil cell experiments and first-principle calculations.
2014, 63 (2): 026401. doi: 10.7498/aps.63.026401
Three-dimensional simulations of particles coarsening in a solid-liquid two-phase system are investigated using the multiphase-field model. The evolution of the interface shape distribution during coarsening is analyzed. And the influences of the volume fraction on the interface shape distribution and coarsening rate are studied under different coalescence conditions. The simulation results show that the influence of volume fraction on the change of coarsening rate is delayed when there exists coalescence between solid particles under high volume fraction. Moreover, with the evolution of coarsening, proportion of the hyperboloid with high curvature decreases and the proportion of ellipsoid with low curvature increases. No matter whether the coalescence between particles occurs, the interface shape distribution has self-similarity after a period of time of evolution. But it will take a longer time for the system to reach the steady state with the increasing of volume fraction.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (2): 027301. doi: 10.7498/aps.63.027301
Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3, 4-b]thiophenediyl]] (PTB7) is used as an anode modification layer to fabricate organic light-emitting diode (OLED) with the configuration of ITO/PTB7 (with different concentrations)/NPB(40 nm)/Alq3(60 nm)/LiF(1 nm)/Al, and the effect of PTB7 concentration on the performance of device is investigated. The best concentration of PTB7 is 0.25 mg/mL, while the best device turn-on voltage is 4.3 V. For the best device, its maximum luminance is 45800 cd/m2 at a driving voltage of 14.6 V, its maximum current efficiency is 9.1 cd/A, its turn-on voltage is reduced by 1.9 V and the maximum luminance is increased by 78.5% compared with that of the device without PTB7. The improvement of its performance is ascribed to the fact that the hole injection and transport ability are improved by the layer of PTB7.
2014, 63 (2): 027302. doi: 10.7498/aps.63.027302
Flexible organic non-volatile memory field-effect transistors (ONVMFETs) are promising candidates in the field of flexible organic electronic devices, which can be used in flexible radio frequency tags, memories, integrated circuits and large-area displays, because of their remarkable advantages such as flexibility, lightweight, low cost and large-area organic electronics. On the basis of the introduction of the development of flexible ONVMFETs in terms of substrates, structures and characteristics, the classification of flexible ONVMFETs is summarized. Meanwhile, we discuss the effects of mechanical stress and temperature on the performance of flexible ONVMFET. Finally, some prospects as well as the challenges are pointed out.
Growth of micro-devices of topological insulator thin films by molecular beam epitaxy on substrates pre-patterned with photolithography
2014, 63 (2): 027303. doi: 10.7498/aps.63.027303
In the fabrication of micrometer-sized structures from an epitaxial topological insulator thin film with photolithography, the film is usually deteriorated by the chemicals used in the process. By molecular beam epitaxy of (BixSb1-x)2Te3 topological insulator onto Hall bar-shaped plateaus pre-lithographed on SrTiO3 substrate, we have directly prepared Hall bar devices of epitaxial topological insulator thin film, avoiding the degradation of film quality in photolithography. Atomic force microscope and transport measurements have demonstrated that the Hall bar devices have the similar properties as that of (BixSb1-x)2Te3 films epitaxied on ordinary SrTiO3 substrates. The new microfabrication method can not only help to realize various novel quantum phenomena predicted in topological insulators but be applied to other epitaxial low-dimensional systems as well.
2014, 63 (2): 027401. doi: 10.7498/aps.63.027401
Based on our previous work, we have systematically investigated the molecular beam epitaxy growth of single unit-cell FeSe films on SrTiO3(001) substrates and studied the surface morphology by scanning tunneling microscopy. We found that there are three key steps to obtain large-scale uniform one unit-cell superconducting FeSe films. First, the STO(001) substrates should be treated by HCl etching and thermal annealing under oxygen flux so that a specific TiO2-terminated STO(001) surface with well-defined step-terrace structure could be obtained. Second, the Fe and Se fluxes and substrate temperature have to be controlled delicately. At last, post-growth annealing is also critical, which can remove extra Se adatoms, and more importantly facilitate the necessary electron transfer for superconductivity transition.
Properties of the internal excited state of the strong-coupling magneto-bipolaron in a parabolic quantum dot
2014, 63 (2): 027501. doi: 10.7498/aps.63.027501
The properties of the internal excited state of the strong coupling magneto-bipolarons in a parabolic quantum dot are studied by using the variational method of Pekar type based on the Lee-Low-Pines’ unitary transformation. With the influences of the electronic spin and the external magnetic field taken into consideration, the change law of ground state energy E0, the average number of phonon N0, the first excited state energy E1 and the average number of phonon N1 of the magneto-bipolarons with the confinement strength ω0, the dielectric constant ratio η, the electron-phonon coupling α, and the cyclotron frequency ωc are derived in two-dimensional quantum dot. Numerical results indicate that the ground state energy E0 and the first excited state energy E1 consist of four parts: the single-article energy Ee of two electrons, the Coulomb interaction energy EC between two electrons, the interaction energy Es between the electronic spin and the external magnetic field, and the interaction energy Ee-ph of the electron with the longitudinalo optical phonons. The energy E1 of the first excited state splits into two lines, i.e., E1(1+1) and E1(1-1) due to the interaction between the “orbital” motion of the single-particle and the magnetic field, and each level of the ground-state energy and the first excited state energies set produces three “fine structures” due to the interaction between the electronic spin and the magnetic field. N0 and N1 increase with ω0, α and ωc increasing; Ee-ph is always less than zero, and absolute value |Ee-ph| increases with ω0, α and ωc increasing. The electron-phonon interaction has an important influence on the formation of bound state of the magneto-bipolaron; but the confinement potential and coulomb repulsive energy between electrons are unfavorable for the formation of magneto-bipolaron in the bound state.
2014, 63 (2): 027701. doi: 10.7498/aps.63.027701
The 1-3 ceramic/polymer piezoelectric composites have greater dielectric, piezoelectric and ferroelectric properties than 0-3 composites. In this paper, electrophoresis is introduced into the fabrication procedure of traditional 0-3 ceramic/polymer piezoelectric composite to move and pearl-serially align the piezoelectric particles in the polymer matrix, which is called pseudo 1-3 composite. In this work, the PZT/epoxy pseudo 1-3 piezoelectric is fabricated via using a 500 V/mm, 4 kHz AC electric field to form the electrophoresis phenomenon during the curing procedure. Compared with the traditional 0-3 piezoelectric composites, the pseudo 1-3 piezoelectric composites behave as the significantly-enhanced dielectric, piezoelectric and ferroelectric performances on basis of our theoretical analysis and experimental measurement result. Electrophoresis–assisted fabricating pseudo 1-3 piezoelectric composite possesses the advantages of simple operation, low cost and significant performance improvement, which make it hopeful to be used to prepare high-performance ceramic/polymer piezoelectric composites for practical application.
2014, 63 (2): 027801. doi: 10.7498/aps.63.027801
Photoluminescences (PLs), time-resolved PL spectra, and PL intensities each as a function of excitation power from plasmon-enhanced single InAs quantum dots (QDs) are measured for studying the effect of photoluminescence enhancement at a low temperature of 5 K. The 5 nm gold films are deposited on the surface of InAs QD sample by using electron beam evaporation technique, which form nano-gold island membrane structures. It is found that the gold island film is conducive to the enhancement of QD PL intensity and the maximal PL intensity increases up to about 5 times the PL intensity without gold island film. The physical mechanism of the PL increase is that the gold island film nanostructure can improve the QD PL collection efficiency which is very important for realizing the bright single photon sources.
Active tunable metamaterial transmission line based on lumped elements and negative differencial devices
2014, 63 (2): 027802. doi: 10.7498/aps.63.027802
To overcome the defects of metamaterials, such as high dispersion, the high loss, and the problem of homogenization, we design and implement an active tunable metamaterial transmission line, and measure the characteristics of active tunable metamaterial transmission line that is based on lumped elements and negative differential devices. From the measured results, it exhibits not only electronically tunable scattering parameters (electro-control tunable characteristic) but also the negative attenuation constant (the propagation amplification) in the left-handed frequency band (active characteristic).
Particle-in-cell simulation on effect of outgassing on flashover and breakdown on dielectric surface in high-power microwave environment
2014, 63 (2): 027901. doi: 10.7498/aps.63.027901
For investigating the mechanism of high power microwave flashover and breakdown on dielectric surface with outgassing, firstly, the theoretical modeling is put forward, including dynamic equations, particle-in-cell (PIC) method, secondary emission, Monte-Carlo collision (MCC) method and outgassing model. Secondly, based on the theoretical modeling, the 1D3V PIC-MCC code is programmed by authors. By using this code, the flashover and breakdown on dielectric surface with weak and strong outgassing course under different gas moving velocities are studied numerically. The numerical results are concluded in the following. The flashover and breakdown on dielectric surface are caused by continuous increase of deposited power. For weak outgassing, multipacting is dominant. As outgassing coefficient increases, multipacting is promoted by ionization collision. The typical phenomena are the increases of space-charge field, average energy of surface-collision electrons and the number of surface-collision electrons. Here, the surface-collision electrons are caused by multipacting mostly. With the increase of gas molecule velocity, ionization course is suppressed by gas pressure decreasing near to the dielectric surface. For strong outgassing, ionization collision is dominant. As outgassing coefficient increases, the number of ions increases exponentially with ionization frequency increasing, multipacting is suppressed by ionization collision. The typical phenomena are the negative value of space-charge field on dielectric surface, the decrease of average energy of surface-collision electrons, and the exponential increase of surface-collision electrons caused by ionization collision near to dielectric surface. Here, the surface-collision electrons are caused by ionization mostly. With the increase of gas molecule velocity, the depth of gas is enlarged, thereby promoting the ionization collision.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (2): 028101. doi: 10.7498/aps.63.028101
For a long time, empirical formulars have been used to predict the steady-state creep rate due to lack of clear microscopic description of the mechanism, which frequently leads to unreliable predictions. In this work, a statistical model of single atom developed recently is used to predict the steady-state creep rate at an atomic diffusion level. To test the model, we measure the creep rates of three kinds of materials, i.e., 42CrMoA, 2Cr12Ni, and 1Cr12Mo, and collect the experimental data of other materials, such as IN738LC and K435. The results show that our theoretical predicts are in good agreement with the experimental results.
High temperature oxidation resistance of cluster model designed alloys Cu-Cu12-[Mx/(12+x)Ni12/(12+x)]5 (M=Si, Cr, Cr+Fe)
2014, 63 (2): 028102. doi: 10.7498/aps.63.028102
Based on the stable solid solution cluster model, cupronickel is microalloylized in this paper. Alloys with different Ni-M (M=Si, Cr, Cr+Fe) ratios are designed at constant atomic ration of Cu (72.22 at.%). The high temperature oxidation resistance and mechanism of alloy are also investigated. In the Cu-Ni-Si system, the addition of Ni-Si can enhance the oxidation resistance of the alloy from two aspects: firstly, the Ni-Si is in solid solution state when being added as a cluster, it can inhibit the chemical reactivity of Cu-Ni-Si alloy; secondly, anti-oxidation precipitation can be obtained with the increase of Si/Ni ratio. Therefore, the oxidation resistance of the alloy is not because of the formation of the compact silicon oxide film. In the Cu-Ni-Cr system, the oxidation is obviously inhibited at medium temperatures (lower than 800 ℃). But at higher temperatures, the oxidation resistance is relevant to the integrality of chrome oxide layer. The high temperature oxidation resistance is closely related to Cr/Ni ratio, hence an appropriate Cr/Ni ratio is necessary for the good high temperature oxidation resistance. Compared with the third element Cr, the forth element Fe cannot be oxidized first. Therefore, combined addition of Cr and Fe can only inhibit the medium temperature oxidation, but not high temperature oxidation.
2014, 63 (2): 028103. doi: 10.7498/aps.63.028103
In this paper, we propose a new metamaterial absorber based on magnetic absorbing material. This absorber has the characteristics of low-frequency transmission and high-frequency broadband absorption. The transmission coefficient of the metamaterial absorber is-0.5 dB at 1 GHz: the good low-frequency transmission property can realize intercommunication between the low-frequency signals. The absorptivity is greater than 80% in the frequency range above 8.4 GHz, which almost covers all the X-band and Ku-band frequencies. In addition, the metamaterial absorber is polarization-independent due to the fourfold rotational symmetry of the unit cell metallic periodic structure. The metamateiral absorber has the advantages of simple design, strong practicability, and high potential application value.
Effect of deposition temperature on growth, structure and mechanical properties of diamond-like carbon films co-doped by titanium and silicon
2014, 63 (2): 028104. doi: 10.7498/aps.63.028104
Titanium and silicon co-doped diamond-like carbon films are deposited on Si substrates by middle-frequency magnetron sputtering Ti80Si20 composite target. The influences of deposition temperature on the growth rate, chemical composition, structure, surface and mechanical properties of the film are investigated. The results show that the growth rate of the film decreases as substrate temperature increases. With the increasing of substrate temperature, Ti and Si atom content values in the film increase, while C atom content value decreases. At high temperatures, the film has low sp3C fraction, surface contact angle, compressive stress, and high hardness, and elastic modulus. The influences of deposition temperature on the growth and bonding structure of the film are analyzed in view of the subplantation growth model. The changes in surface and mechanical properties are correlated with the growth mechanism and microstructures of the film.
Identification for hole transporting properties of NPB based on particle swarm optimization algorithm
2014, 63 (2): 028105. doi: 10.7498/aps.63.028105
In order to study the carrier transporting properties in organic semiconductors (OSCs), the samples of single layer structure ITO/NPB/Ag are prepared, and the corresponding admittance model in theory is built. Impedance samples of the structure under different DC bias voltages are obtained by small sinusoidal signal frequency test method. The particle swarm optimization (PSO) algorithm, in which fitness function includes both the real part and the imaginary part of OSC impedance, is used to identify the model parameter including dispersion coefficient M, α and charge-carrier transit time τdc. To validate the proposed method, an equivalent circuit model of the structure, whose time constant τc is identified by least squares method, is built. Two single-layer structures, whose NPB thickness values are respectively 1000 nm and 1200 nm, are tested. Test results show that the charge-carrier transit time τdc is proportional to the time constant τc and the two hole mobility μdc values both satisfy the famous Poole-Frenkel formula.
Self-similarity and frequency-mixing phenomena analysis of multi-frequency controlled switching converter
2014, 63 (2): 028401. doi: 10.7498/aps.63.028401
Based on the operation principle and state equations of multi-frequency (MF) controlled switching converter, the discrete iterative map model is established, the corresponding characteristics equation and Lyapunov exponent of MF controlled switching converter operating in discontinuous conduction mode are derived. According to the discrete iterative map model, its bifurcation behaviors are investigated. It is found that the border-collision bifurcation and the multi-period behaviors occur in converter, when the circuit parameters are varied. When the voltage error boundary is too large, the converter behaves as self-similarity phenomenon, and when the voltage error boundary is too small, the converter behaves as frequency-mixing phenomenon. The converter stability is investigated by Lyapunov exponent, which validates the correctness of bifurcation analysis. Time-domain waveforms and phase portraits of converter with the load varied, are analyzed by circuit simulation, which validates the validity of discrete iterative map model and the correctness of theoretical analysis. Finally, simulation results in this paper are verified by experimental results.
Research on equivalent circuit of multi-gap output cavity for sheet beam extended-interaction klystron
2014, 63 (2): 028402. doi: 10.7498/aps.63.028402
Sheet beam extended interaction klystron, which has both the advantages of sheet beam klystron and extended-interaction klystron (EIK), has become a key technique for developing high power microwave and millimeter-wave vacuum electron devices. An equivalent circuit of the five-gap output cavity for sheet beam EIK is proposed in this paper. The mode, resonant frequency, and the cavity impedance can be calculated by using the method of equivalent circuit efficiently. The bandwidth could be estimated by the curve of cavity impedance versus frequency. The influences of coupling coefficient (k) and external Q (Qe) on mode frequency interval and bandwidth are discussed. In order to test and verify the method of equivalent circuit, the 3D-PIC simulation of output cavity is conducted. The bandwidths under different values of external Q are calculated in two ways. The results accord well with each other. It is confirmed that the method of equivalent circuit for sheet beam EIK is accurate and credible. This is useful for the design of the whole tube.
Focusing bistatic forward-looking synthetic aperture radar based on modified hyperbolic approximating
2014, 63 (2): 028403. doi: 10.7498/aps.63.028403
The conventional monostatic synthetic aperture radar (SAR) shows a limitation if a forward-looking geometry is used. However, bistatic forward-looking SAR gives a good solution, providing a high resolution image in the flight path direction. Due to the fact that the range history of bistatic SAR is a double square root, classical imaging algorithm cannot be applied to the bistatic SAR directly. Also it is difficult to deduce imaging algorithm from double square root directly. The hyperbolic approximating method can transform double square root into single one, when being used in forward-looking geometry, and the high order term error is obvious and cannot be ignored. In this paper, we propose a modified hyperbolic approximating method, which makes a cubic term approximation and improves the precision, then we apply the new method to bistatic forward-looking SAR and deduce the bistatic point spectrum. Based on the spectrum, a modified range Doppler algorithm is proposed for focusing bistatic forward-looking SAR. Finally, numerical simulation is used to compare the original hyperbolic approximating method with the modified one for veridating the proposed algorithm and processing approach.
2014, 63 (2): 028501. doi: 10.7498/aps.63.028501
Wireless sensor nodes deployed at remote and inaccessible locations need long lifetime power sources to prevent cost prohibitive periodic replacement. In this work, we present a radioisotope 63Ni energy converter using radioisotope-powered electrostatic vibration-to-electricity conversion. Free damped vibration happening in a suspended parallel plate structure with a mass enables a variable capacitance, which can be used to realize the generation of electricity energy by an external circuit. The MATLAB/Simulink is used to simulate the vibration and output power, and the Ansys is used to optimize the structure design. The results show that the optimized design structure with a first-order natural frequency of 500 Hz, a plate gap of 75 μm, and an external resistance of 90 kΩ can generate an average output power of 0.416 μW and conversion efficiency of 8.25%.
2014, 63 (2): 028701. doi: 10.7498/aps.63.028701
Optical tweezer technology is widely used in trapping and manipulating micro-and nano-sized particles, mainly including the trapping of transparent particles in water and the trapping of absorbing particles in air. In this paper, a frosted glass diffuser is irradiated by laser beam, and a subjective speckle field is generated in the image plane of a lens after the laser has transmitted the lens. The speckle field is spatially distributed, and contains multiple bright spots and dark spots. A large number of dark spots surrounded by bright spots are spatial energy traps, and can be used to trap a large number of absorbing particles. The sizes and densities of trapped particles are about 2–8 μm and 1–2 g/cm3. In addition, an infrared microscope is used to record the infrared images of the particles trapped by the speckle field, and the infrared images show that the temperature of trapped particles rises by absorbing the light energy, which verifies that the mechanism of trapping absorbing particles by speckle field is photophoretic force.
Study of boron-doped zinc oxide film serving as front contact with high haze used in amorphous silicon thin film solar cells
2014, 63 (2): 028801. doi: 10.7498/aps.63.028801
Boron-doped zinc oxide (BZO) deposited by metal organic chemical vapor deposition (MOCVD) method is used as front contact in amorphous silicon thin film solar cells. Asahi-U type SnO2:F is used as the reference front contact for comparison. When the a-Si:H intrinsic layer thickness is changing changed, the performance of a-Si:H solar cells shows different evolution trends. These different results can be understood from the shadowing effect during the growth of intrinsic silicon material, which is caused by the as-grown pyramid texture in the surface of BZO substrate. In order to reduce this negative effect on the performance of solar cells, the deposition temperature of the a-Si:H intrinsic layer is optimized, to thereby improving improve the open circuit voltage and fill factor. The conversion efficiency of a-Si:H solar cells can reach up to 7.34%, with the thickness of absorber layer being only around 200 nm. and only Al back reflector is being used.
Optimization design of hydrogenated amorphous silicon germanium thin film solar cell with graded band gap profile
2014, 63 (2): 028802. doi: 10.7498/aps.63.028802
The simulation program AMPS-1D (analysis of microelectronic and photonic structures) employed to simulate and compare the performances of hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cell with and without band gap grading at a radiation of AM1.5G (100 mW/cm2) and room temperature by introducing energy band engineering. The simulation results show that the efficiency of the solar cell with band gap grading is 0.477% higher than that without band gap grading due to the higher open circuit voltage (Voc) and better fill factor (FF). Subsequently, a-SiGe:H thin film solar cells with three different window layers such as hydrogenated amorphous silicon (a-Si:H), hydrogenated amorphous silicon carbide (a-SiC:H) and hydrogenated nanocrystalline silicon (nc-Si:H) are simulated, respectively. The numeric calculation results indicate that the fermi level EF of the a-SiGe:H thin film solar cell crosses the valence band when nc-Si:H window layer is employed in the simulation. This will improve the conductivity and the open circuit voltage of the solar cell. In addition, the electric field at front contact interface is reduced due to the lower contact barrier height. This may be more beneficial to the carrier collection by front contact. On the other hand, thanks to the wider band-gap difference between the window layer and the intrinsic layer, a potential barrier is built at the valence-band p/i interface due to the band offset. This will hinder the hole migration and collection. Thus, an nc-Si:H buffer layer, which can relax the valence-band offset and be more beneficial to the carrier migration and collection, is introduced at p/i interface. Finally, the optimum conversion efficiency of the a-SiGe:H thin film solar cell with graded band gap is achieved to be 9.104%.
2014, 63 (2): 028803. doi: 10.7498/aps.63.028803
In this paper, the laws of light-induced degradation (LID) in silicon wafers and solar cells are investigated by using xenon lamp as light source. There are tested 15 types of the silicon wafers contain the including primary wafer, chemical thinned wafer, thermal oxidation passivation wafer, passivation SiNx:H wafer deposited by plasma enhanced chemical vapor deposition, iodine passivation wafers of three different types of silicons: B-doped CZ-Silicon, B-doped Multicrystalline (MC) silicon, and B-doped Upgraded-Metallurgical-grade (UMG) silicon. There are tested 3 types of silicon solar cells: CZ solar cell, MC solar cell, and UMG solar cell. The light intensity is 1000 W/m2 in test. By using WT-2000 tester and solar cells I-V tester, the variations of minority carrier lifetimes of silicon wafers and the I-V characteristic parameters of solar cells with time of light exposure are tested and recorded. Finally the law of LID is found. Under our light condition (light source is a xenon lamp with a light intensity of 1000 W/m2), all kinds of silicon wafers and solar cells are degraded rapidly within the first 60 min, then slowly until the 180 min, finally the rate tends to 0. The LID becomes very slight after 180 min lighting.
2014, 63 (2): 028901. doi: 10.7498/aps.63.028901
There are many existing routing strategies in complex networks, but there is no uniform standard to measure whether the strategies achieve optimal transmission effect. A pervasive optimized algorithm is proposed. The key factor restricting transmission capacity is maximum betweenness centrality and minimizing it becomes the uniform standard. In order to make betweenness centrality more evenly distributed and balance the traffic load of each node, we use punishment selection method to avoid the nodes with larger betweenness centrality. The simulation results show that the new algorithm could reduce maximum betweenness centrality of existing strategies and improve the network transmittability greatly.
2014, 63 (2): 028902. doi: 10.7498/aps.63.028902
In order to study the influences of network coupling strength, subnetwork edge, and coupling edge of interdependent networks on the network robustness, symmetrically and asymmetrically coupled interdependent network models are constructed based on three typical network models. Firstly, we calculate the cost thresholds of six different interdependent networks, and find that the coupling edges have a greater influence on the cost of interdependent network than the edges of sub-networks. Furthermore, the relationship of the two parameters (α, β) with the cost of network is obtained by simulation and theoretical analysis, and the cost of network correlated with the two parameters is proved. Finally, by setting the cost of network as a variable measuring the robustness, the simulations on interdependent networks for suppressing cascading failure provide the values of the parameters corresponding to the strongest robustness and the relationship between the robustness and the coupling strength, and it is found that the robustness of network neither increases nor decreases monotonically with the increase coupling strength.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The theoretical study of the turning period in numerical weather prediction models based on the Lorenz equations
2014, 63 (2): 029201. doi: 10.7498/aps.63.029201
Based on the Lorenz equations, the dynamics of the weather turning period is studied about numerical weather prediction. Through the analysis of the stability of equilibrium points of the Lorenz equations, we get the surfaces which separate the quasi-stable region and quasi-unstable region. In the quasi-stable region, the path curve of the Lorenz equations can remain relatively stable around the equilibrium points, however in the quasi-unstable region, the path curve of the Lorenz equations can spring from this equilibrium point to another one. This is one of the important dynamic characteristics of the Lorenz system, and the paper give new method and theory for the detection of the abrupt change of climate.
2014, 63 (2): 029202. doi: 10.7498/aps.63.029202
In this article, information source characteristic degree, information sink characteristic degree and transfer equilibrium characteristic degree are defined based on transfer entropy. According to the definition, the information transfer in air-sea interaction is examined with sea surface temperature (SST) and geopotential height (GH). And the information transfer between central and eastern equatorial Pacific (20°S–20°N, 170°E–100°W) and tropics (20°S–20°N), and that between atmospheres in high latitude regions of northern hemisphere (north of 20°N) and southern hemisphere (south of 20°S) are analyzed too. In addition, decadal changes and seasonal differences in information transfer between central and eastern equatorial Pacific ocean and atmosphere are discussed by the defined indices of SST and HG. In a word, the information source distribution of ocean is mainly in tropics and the information sink distribution of atmosphere is mainly in mid-latitude. From the low-latitude to the mid-latitude, the ocean forcing the atmosphere is weakened while the atmosphere forcing the ocean is strengthened. Significant regional difference, decadal change and seasonal difference exist in information transfer from the tropical ocean to the atmosphere.
2014, 63 (2): 029203. doi: 10.7498/aps.63.029203
In order to obtain the shapes, sizes, fall velocities, orientations of raindrops in the natural condition, starting from the particle imaging velocimetry transient visual measurement technology, an image restoration algorithm based on point spread function and a velocity calculation algorithm based on auto-correlation image are investigated, and a natural precipitation imaging velocimetry system based on a CCD sensor is designed and developed in this paper. The diameters, terminal velocities, axis ratios, orientations and their distributions of raindrops are investigated by the field experiment. The velocities of raindrops increase exponentially with the diameter, and axis ratios of raindrops decrease linearly with the diameter, the orientations of raindrops are easily affected by the wind, the average canting angle for all drops tends to be nearly symmetric 2.1° with a standard deviation of 11.5°. The empirical relations between velocity and diameter, between axis ratio and diameter are fitted by nonlinear fitting and linear fitting of observed data. In this paper we further provide microphysical characteristics of raindrops with local features. compared with those from the existing model. These conclusions are of important significance for the research on cloud precipitation physics, ground calibration of weather radar, assessment of rain induced microwave attenuation, etc.
2014, 63 (2): 029204. doi: 10.7498/aps.63.029204
Determination of the aircraft lightning attachment points which can provide the basis for the design of aircraft lightning protection, is a prerequisite for the division of lightning strike zones and the lightning test of aircraft components. In this paper, a novel numerical simulation method based on fractal theory is presented to simulate lightning attachment points on airplane. Firstly, the discharge gap distance, lightning starting coordinates, aircraft attitudes, discharge times and other parameters are determined according to the relevant provisions about aircraft lightning attachment point test in standard SAE-ARP5416. Then, according to the fractal theory, the dielectric breakdown model is used to simulate the fractal growth of the lightning leaders, which accords with physical mechanisms and geometric characteristics of nature lightning. Finally, considering the case where the aircraft itself triggers the bi-directional leader, we obtain the distribution of aircraft lightning attachment points. Because the probability distribution of lightning attachment points on aircraft F-4 obtained through the simulating is almost in line with those obtained through actual aircraft flight test and laboratory test, the proposed method is verified. The proposed method provides a potential way of simulating the lightning attachment points on aircraft. And this method can be used as the foundation of the aircraft lightning protection design and future related research work.
2014, 63 (2): 029501. doi: 10.7498/aps.63.029501
Ultraviolet surface plasmon polariton propagation for ZnO semiconductor-insulator-metal waveguide is investigated by means of the finite-element method. The field distribution, effective refractivity, propagation distance, and mode area of the hybrid mode supported by the waveguides were detailed analyzed, which are dependent on the dielectric constant and geometrical parameters. In order to achieve low propagation loss and subwavelength field confinement, several materials are calculated. Our investigation indicated that air and aluminum are better, which act as the insulator and metal respectively, and the effective mode area of such a waveguide can be as small as λ2/100. The results can help the development of nano-sized light sources which can enhance the sensitivity for bio-detection devices and diagnostic equipments.