Vol. 63, No. 14 (2014)
2014, 63 (14): 140502. doi: 10.7498/aps.63.140502
A chaotic signal in an observation area of network nodes is sent to a fusion center for reconstruction. As the communication bandwidth is limited, the signal must be quantified before sending to the fusion center, which will add quantization noise to the observed signal, which makes the signal reconstruction more difficult. A chaotic signal reconstruction algorithm is proposed in this paper based on square-root cubature Kalman filter. Firstly the probability density function of the observed signal is estimated, and then the optimal quantizer is used to quantify the observed signal. Under the limited budget of quantization bits, the best performance can be achieved. Compared with the unscented Kalman filter counterpart, our algorithm has fewer cubature points and has the merit of small computation load; meanwhile, it uses the square root of error variance for iteration, this will be more stable and accurate when iterating for parameter estimation. Simulation results show that the algorithm can reconstruct the observed signal quickly and effectively, with consuming less computation time and being more accurate than the one based on unscented Kalman filter.
Second-order Stokes wave solutions for gravity capillary water waves in three-layer dendity-stratified fluid
2014, 63 (14): 140301. doi: 10.7498/aps.63.140301
In this paper, gravity-capillary water waves in a three-layer stratified fluid are investigated by using a perturbation method, and the second-order asymptotic solutions of the velocity potentials and the second-order Stokes solutions of the associated elevations of the gravity-capillary water waves are presented based on the small amplitude wave theory. As expected, both the first-order and second-order solutions derived depend on not only the depth and density of the three-layer fluid but also the surface tension.
2014, 63 (14): 140503. doi: 10.7498/aps.63.140503
Neural mass model is a typical nonlinear system with rich and complex dynamics. Up to now, most bifurcation researches of neural mass model (NMM) have focused on the influence of input or connection parameters between subpopulations on the dynamics of NMM. Actually, the synaptic strength is varied temporally, owing to synaptic plasticity, and plays a crucial role in regulating the dynamics of NMM. However, there are no researches on synaptic strength bifurcation analysis of NMM, and how excitatory and inhibitory synaptic plasticity exerts an influence on the dynamics of NMM is still little known. Motivated by this idea, the bifurcation analysis of excitatory and inhibitory synaptic strength of NMM is conducted in this study. Firstly, codimension-one bifurcation analyses of excitatory and inhibitory synaptic strengths are performed, respectively, through which the parameters regions of stability, bistablility, normal and abnormal oscillation are determined. Secondly, codimension-two bifurcation analysis is conducted, through which we can further gain an insight into the influence of the interaction between excitatory and inhibitory synaptic strengths on the dynamics of NMM. Finally, the bifurcation analysis results is verified by the simulation results. This study of bifurcation reveals two kinds of oscillation mechanisms: limit cycle oscillation mechanism and input-induced transition between two states of the bistability.
Geometrical statistical channel model and performance investigation for multi-antenna systems in wireless communications
2014, 63 (14): 140506. doi: 10.7498/aps.63.140506
For testing an adaptive array algorithm in cellular communications, we develop a geometry based statistical channel model that provides the statistics of angle-of-arrival and doppler spectra of the multi-path components, into which introduced are the new concepts of effective scatterers and reflection probability. This channel model is suitable for describing the outdoor and indoor propagation environments, which is applied to the performance of multiple input multiple output (MIMO) system. A comparison between our theoretical calculations and customary results shows that the analysis is correct and applicable to microcell environments, which can promote the research of the statistical channel models and provide accurate and flexible channel models for the MIMO multi-antenna systems.
2014, 63 (14): 140203. doi: 10.7498/aps.63.140203
Communication delay and packet loss highly degrade the control performances of networked multi-agent systems (NMAS). This paper addresses the problem by presenting a novel predictive control technique using a time-delay and packet-loss compensation scheme. The principle of the time-delay and packet-loss compensation scheme is employed to remove the effects of network delay and packet loss. Furthermore, another key part of this paper is to analyse the stability and consensusability of close-loop NMAS on the basis of the designed predictive controller. Finally, simulation results illustrate the efficacy of the proposed method.
2014, 63 (14): 140505. doi: 10.7498/aps.63.140505
The chimera states and cluster chimera states in a globally coupled both discontinuous-and-non-invertible-map lattices are studied using the order parameters and spatial-time-amplitude patterns. The result show that chimera states and cluster chimera states are sensitive depends on the choice of the coupling strength, and they are induced by the interaction between the discontinuity and the non-invertibility in coupled system. We also discuss the conditions for the chimera states existing in this system.
2014, 63 (14): 140701. doi: 10.7498/aps.63.140701
In this paper, we study the effects of laser scanning step length and width characteristic on tunable diode laser absorption spectrum detection system, theoretically derive the principle of interaction between laser and gas absorption line, and analyse the principle of effects of step duration and height about scanning signal (ramp) on the laser central wavelength. After setting the simulation parameters, the curve between the number of ramp steps and the maximum scanning error is obtained. If the scanning signal has 4000 steps in one cycle, the error is less than 1‰ with full width at half maximum (FWHM) value being greater than 0.01 cm-1. The curves between laser linewidth and maximum amplitude or linewidth error are simulated, and also the relationship between laser linewidth and minimum FWHM is given with linewidth error maximum values being 1% and 0.5%. On condition that temperature coefficient n is 0.9 and air-broadened coefficient is 0.005, this paper gives the relationship among pressure, temperature and FWHM, from which the suitable pressure P and temperature T range are deduced. It can provide the relevant theoretical basis for selecting the laser and gas absorption lines and also for improving the system detection limit.
Simulation of frequency discrimination for spaceborne Doppler wind lidar (Ⅱ)：Study on the retrieval of atmospheric wind speed for Rayleigh channel based on Fabry-Perot interferometer
2014, 63 (14): 140703. doi: 10.7498/aps.63.140703
Based on the principle of spaceborne Doppler wind lidar, a simulation system of frequency discrimination is built based on the double sequential Fabry-Perot (F-P) interferometer. The wind retrieval algorithm of Rayleigh channel is simulated and studied. The influence on the retrieved atmospheric line-of-sight (LOS) wind speed in Rayleigh channel by the Rayleigh-Brillouin effect and Mie contamination is systematically analyzed. The horizontal line-of-sight (HLOS) wind error is analysed using the simulated result of the radiosonde dataset. The results show that the wind speeds of the middle and upper atmosphere can be retrieved in Rayleigh channel based on the double sequential F-P interferometer; the Rayleigh-Brillouin effect and Mie contamination influence the accuracy of LOS wind speed retrieval in Rayleigh channel; the Rayleigh channel requires more accurate temperature; Mie contamination can be ignored in clear atmosphere; when Brillouin effect is not considered, below 2 km, the HLOS wind speed cannot be retrieved in Rayleigh channel, and above 2 km, the HLOS wind speed error in Rayleigh channel is less than 0.4 m/s and its standard deviation is 1-4 m/s. Just as the Mie channel, distributions of aerosol and cloud have an influence on wind error for spaceborne Doppler wind lidar in Rayleigh channel. The research results have an important reference value for the development of spaceborne lidar wind technology.
2014, 63 (14): 140704. doi: 10.7498/aps.63.140704
We observe the intercombination transition spectrum of alkaline-earth strontium, using a stable narrow 689 nm laser which is locked to a high fineness ultralow expansion reference cavity. The finesse is measured using cavity ring down techniques in different transverse modes of the cavity. Additionally, the response time of optical switch and PD monitor are taken into consideration in the measurement. Using a fiber-based optical frequency comb, the Allan deviation calculated from the counter value of the beat frequency shows a stability of 2.8× 10-13 in a 1 s averaging time. The saturation spectrum is measured with a minimum sub-Doppler width of 55 kHz. The high resolution intercombination transition spectrum can be used for absolute frequency stabilization.
Conformal invariance and Hojman conserved quantity of Lie symmetry for Appell equations in a holonomic system
2014, 63 (14): 140201. doi: 10.7498/aps.63.140201
The conformal invariance and Hojman conserved quantity of Lie symmetry for Appell equations in a holonomic system are studied. Under the special infinitesimal transformations in which the time is not variable, the Lie symmetry and conformal invariance of differential equations of motion for a holonomic system are defined, and the determining equations of the conformal invariance of Lie symmetry and the Hojman conserved quantity for the system are given. Finally, an example is presented to illustrate the application of the results.
Entanglement of one- and two-mode combination squeezed thermal states and its application in quantum teleportation
2014, 63 (14): 140302. doi: 10.7498/aps.63.140302
In view of the fact that one- and two-mode combination squeezed vacuum states may exhibit stronger squeezing in a certain range, we introduce one- and two-mode combination squeezed thermal states (OTCSTS) and investigate the property of entanglement in detail. Using the remarkable property of Weyl ordering, i.e., the order-invariance of Weyl ordered operator under similar transformations, we conveniently derive the analytical expression of entanglement degree-logarithmic negativity, and then present the condition of keeping entanglement for these squeezed thermal states. It is found that the OTCSTS possesses higher entanglement than the usual two-mode squeezed thermal states for any non-zero squeezing parameter. As an application, the quantum teleportation for coherent state is considered by using the OTCSTS as an entangled channel. It is shown that the teleportation fidelity can only be enhanced within a certain range of parameters, which is just the same as the condition of exhibiting stronger squeezing in one quadrature. In addition, the condition of realizing effective quantum teleportation (>1/2) is obtained analytically.
Simulation of frequency discrimination for spaceborne Doppler wind lidar (I)：Study on the retrieval of atmospheric wind speed for Mie channel based on Fizeau interferometer
2014, 63 (14): 140702. doi: 10.7498/aps.63.140702
System structure of spaceborne Doppler wind lidar is investigated. Simulation system of frequency discrimination is built based on Fizeau interferometer. The wind retrieval algorithm of Mie channel is simulated and studied. The horizontal line-of-sight (HLOS) wind error is analysed using the simulated result of the radiosonde dataset. The result shows that the wind speed of lower troposphere can be retrieved in Mie channel based on Fizeau interferometer. The average values of HLOS wind error deviation and standard deviation in lower troposphere are less than 1 m·s-1 and 2 m·s-1, respectively. Distributions of aerosol and cloud have an influence on wind error for spaceborne Doppler wind lidar, and the maximum wind deviation will increase twice.
2014, 63 (14): 140204. doi: 10.7498/aps.63.140204
In nature, the motion of swarm intelligence has a regularity such as the line motion based bird migration, the circle motion based fish swarming, etc., which has important theoretical significance and vast application prospect in engineering practice. In this paper, we investigate the distributed encirclement control problem of a group of multi-agent systems. With considering the feature that each agent can achieve local target information, we design an averaging estimator to achieve the target information, and propose a distributed control scheme to achieve the encirclement and keep the formation changing with the target states. By Lyapunov theory analysis, it is proved that each individual agent can achieve the information about the marked arerage position in a finite time, encircle and pursue the targets based on the encirclement formation. Finally, a numerical example is presented to illustrate the obtained theoretical results.
2014, 63 (14): 140303. doi: 10.7498/aps.63.140303
This paper mainly solves the photon polarization encoding problem of quantum key distribution (QKD) between different media. The influence of the transmission rate of different photon component on quantum bit error rate (QBER) has been quantitatively analyzed, with a practical analysis of QBER of QKD between air and water. Furthermore, we have put forward a single-photon compensation scheme for eliminating such non-ideal BB84 protocol, as well as a more robust and practical dual-photon encoding scheme to offset such interfacial non-unitary noise. This takes an important step towards the air-sea-ground wide area quantum communication in the future.
2014, 63 (14): 140504. doi: 10.7498/aps.63.140504
Traffic state prediction is a key basis of traffic flow guidance system and traffic information publishing system. This paper presents a new method of forecasting the traffic state of unban expressway based on competence region. This method can predict the traffic state grade of road based on the distance between the sample data and the traffic state cluster center by creating a competence region of neural network classifier. And this method can effectively integrate the temporal and spatial features together without considering the correlation between the different features, and thus it has a strong adaptability. The experimental results show that this traffic state prediction method can reduce the prediction error and improve the equality coefficients compared with the classical algorithms. The prediction method used in this paper is effective and accurate for forecasting traffic state based on the competence region.
We study the classical and quantum correspondence for a two-dimensional Sinai billiard system. By using the Stationary state expansion method and Gutzwiller's periodic orbit theory, we analyze the quantum length spectrum obtained through the Fourier transformation of the quantum density of state for the Sinai billiard system, and by comparing the peak position with the length of the classical periodic orbit we find their excellent correspondence. We observe that some quantum states are localized near some short period orbits, forming the quantum scarred states or superscarred states. In this paper we also investigate the nearest-neighbor spacing distribution of levels for both concentric and nonconcentric Sinai billiard systems, and find that the concentric Sinai billiard system is nearintegrable, and for the nonconcentric Sinai billiard system with =3/8 its nearest-neighbor spacing distribution of levels transits from nearintegrable to the Wigner distribution as the distance between the two centers increases.
Parameters estimation for a one-dimensional time fractional thermal wave equation with fractional heat flux conditions
2014, 63 (14): 140202. doi: 10.7498/aps.63.140202
An inversion problem of estimating parameters for a one-dimensional time fractional thermal wave equation with fractional heat flux conditions and Caputo fractional derivatives is investigated. To begin with, the analytical solution of the direct problem is obtained. Then, based on the parameter sensitivity analysis, the least-squares method is used to estimate both the fractional order α and the relaxation time τ simultaneously. Finally, two different heat flux distributions are given as different boundary conditions to perform the simulation experiments, respectively. By analyzing the degree of fitting curves, results show that the least-squares method performs well in parameter estimation for this fractional thermal wave equation. This study provides an effective method of estimating the parameters of fractional thermal wave equations.
2014, 63 (14): 140501. doi: 10.7498/aps.63.140501
In the numerical calculation, the projected entangled pair state (PEPS) algorithm is the most important tensor network algorithm for two-dimensional strongly correlated electron quantum lattice system. In this paper, the optimization of PEPS for two-dimensional quantum system is discussed. An optimization connection between how to update the PEPS tensor and how to calculate the physical observable is investigated, for the tensor network algorithm based on the PEPS representation, which can greatly improve the utilization of computing resources. In this case, optimized PEPS algorithm, as a powerful tool, can be used to study quantum phase transitions and quantum critical phenomena in the thermodynamic limit of the two-dimensional strongly correlated electron quantum lattice system. Of course, optimization of PEPS algorithm program has many other applications, such as adding U(1) and SO(2) symmetry in PEPS algorithm, etc.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2014, 63 (14): 145203. doi: 10.7498/aps.63.145203
In this paper, the evolution of laser-induced copper plasma spectrum intensity under magnetic field confinement is studied. The evolution process of plasma spectrum intensity and laser energy effect on spectral enhancement are analyzed. Experimental results show that the atomic spectrum and ion spectrum of copper plasma are enhanced as magnetic field increases. In the spectral intensity evolution plot of Cu I 510.55 nm there appears double peak structure in a time range from 1.2 μs to 5.7 μs. The spectral intensity of Cu I 510.55 nm is significantly enhanced in a space range from 0 mm to 1.4 mm away from the target surface. The spectral enhancement factors of Cu I 510.55 nm and Cu I 515.32 nm monotonically decrease with the laser pulse energy increasing, and the maximum enhancement factors for Cu I 510.55 nm and Cu I 515.32 nm are 11 and 8 respectively at the laser energy 20 mJ. The enhancement mechanism of magnetic confinement plasma spectrum is also discussed.
Numerical simulation of energy deposition improvment in electrical wire explosion using a parallel wire
2014, 63 (14): 145206. doi: 10.7498/aps.63.145206
The energy deposition process of electrical wire explosion under vacuum or low gas pressure circumstances is usually terminated prematurely, owing to the flashover along the surfaces of wires. Therefore energy deposited into wires can be far less than the amount needed to fully vaporize them. In this paper, a parallel connection method of wire is introduced in order to improve the energy deposition of the concerned wire before flashover takes place. Wire explosion driven by a current with a rise time of tens of ns and an amplitude of about 1 kA is studied numerically, and the simulation results show that by connecting a wire of a certain size in parallel with both ends of the exploding wire, the voltage rising rate is suppressed and the flashover is delayed; therefore the energy deposited into the concerned wire is increased effectively.
2014, 63 (14): 145204. doi: 10.7498/aps.63.145204
Divertor is a component that directly contacts the plasma in tokamak. To ensure the lifetime of the device, it is necessary to reduce the erosion of the divertor wall by plasma. In this work, a particle-in-cell model is used to study the influences of plasma temperature and impurity concentration on the erosion of tungsten divertor wall by carbon and beryllium ions. The steady-state sheath, particle and energy fluxes to the wall, and the energies and angle of the incident ions can be obtained. Then, these data can be used as the input parameters for the plasma-surface interaction model, to evaluate the erosion rate of the plate based on the empirical formulas for physical sputtering. It is found that the erosion by heating plays a negligible role under the plasma condition of this work. Due to the low physical sputtering threshold energy of tungsten by impurities and the impurity ions accelerated by sheath, the physical sputtering of the tungsten by the impurities plays an dominant role in the total erosion. In addition, the erosion rate increases with the increase of plasma temperature and impurity concentration.
2014, 63 (14): 145205. doi: 10.7498/aps.63.145205
Vacuum arc ion sources have been used in a wide range including vacuum coating, materials surface modification, switching devices and other fields. At present, researches on the vacuum arc ion source are mainly targeting the pure metal or alloy electrodes, but the researches on the hydrogenous electrode are rarely reported. The axial and radial distributions of the hydrogenous electrode vacuum arc discharge plasma are studied by using high speed four-frame camera equipped with the narrow-band filters of strong lines of H I and Ti I. It is found that the anode is intensively luminous in the vacuum breakdown. The observation from the camera with the filter reveals that the vacuum breakdown is ignited mainly by the anode hydrogen desorption. The vacuum arc is sustained by plasmas emitted from either the cathode spots or the electrode inner wall. The cone-shaped cathode spot located at the cathode-insulator-vacuum junction is the main plasma source. It is found that the distribution of hydrogen atoms is much more homogeneous than that of titanium atoms, which may be due to the earlier beginning of hydrogen desorption, the bigger emitting area and faster diffusion speed of hydrogen atom.
2014, 63 (14): 145201. doi: 10.7498/aps.63.145201
Dual Al plasma jets are generated with eight Shenguang Ⅱ lasers. With Euler MHD scale law we find that the jet produced in the laboratory is highly similar to astronomical observations after transformation. We propose that the reconnection electric filed should have a possible direct influence on the formation and collimation of the plasma jet.
2014, 63 (14): 145202. doi: 10.7498/aps.63.145202
We quantitatively analyze the concentration of element chromium in edible gelatin sample by the laser-induced breakdown spectroscopy. As the excitation source, Nd:YAG pulsed laser (wavelength 355 nm) is used to generate a laser plasma in edible gelatin. We study the relationship between spectral intensity and delay time, and find that the optimal condition is 1.7 μs. The experimental data show that the relation between the spectral line intensity (CrI: 425.43 nm) and the concentration of chromium is linear when we use the internal standard method to quantitatively analyze the concentration of chromium in a range from 10 ppm to 200 ppm. This study shows that internal standard method of quantitative analysis works well on measuring the chromium concentration in edible gelatin.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Two-dimensional analytical models for the symmetrical triple-material double-gate strained Si MOSFETs
2014, 63 (14): 148502. doi: 10.7498/aps.63.148502
A novel double-gate strained Si metal-oxide-semiconductor field-effect transistor (MOSFET), in which the top and bottom gates consist of three laterally contacting materials with different work functions, is proposed in this paper. The two-dimensional (2D) analytical models for the surface potential, surface electric field and threshold voltage are presented. The effects of Ge fraction on surface potential, surface electric field and threshold voltage are investigated. The effects of the triple-material length ratio on threshold voltage and drain induced barrier lowering are discussed. The characteristics of the device are studied by comparing with those of the single-material double-gate MOSFETs. The results show that the structure can increase the carrier transport speed and suppress the drain induced barrier lowering effect. The three-material gate length ratio is optimized to minimize short-channel effect and drain induced barrier lowering effect.
The microstructural and electrochemical properties of oxygen ion implanted nanocrystalline diamond films
2014, 63 (14): 148102. doi: 10.7498/aps.63.148102
The nanocrystalline diamond (NCD) films are implanted by oxygen ions with a dose of 1×1012 cm-2 and subsequently annealed at 700, 800, 900 and 1000 ℃, respectively. The microstructure and electrochemical properties of these NCD films are investigated systematically and the results show that the potential windows of the unannealed sample (O120) and 1000 ℃ annealed sample (O121000) increase up to 4.6 V and 3.61 V, respectively. The mass transfer efficiencies of the two samples are also better, indicating that the oxygen ion implantation and 1000 ℃ annealing can improve the mass transfer efficiency of NCD film. The results of infrared spectrum measurements show that there are no hydrogen atoms that are terminated to the surfaces of samples O120 and O121000, while hydrogen atoms terminate to the surfaces of the other samples. It is indicated that oxygen ion implantation and 1000 ℃ annealing can damage hydrogen terminations in the surface, which improves the electrochemical performances of NCD films. Raman spectrum measurements suggest that high content of diamond phase, small internal stress and more disordered amorphous carbon can improve the electrochemical properties of NCD films. When the number or size of sp2 carbon clusters in amorphous carbon grain boundaries decreases, the electrochemical properties of NCD films become better.
2014, 63 (14): 148702. doi: 10.7498/aps.63.148702
According to the cross-correlation between the ultrasonic echo signals of ultrasonic imaging system, ultrasonic imaging algorithm based on cross-correlation adaptive weighting is introduced. This method determines the weight on the correlation between the echo signals of scatters at different positions, and then the adaptive weighted imaging is performed. The sidelobe and the noise which has the low correlation are suppressed. Simulations to points object and speckle object pattern using Field Ⅱ show that the method of imaging fast, and it can give a high horizontal and longitudinal resolution. Compared with delay and sum (DAS) algorithm, the contrast of the image to point object is increased by 16 dB. The contrast of the image to sound-absorbing speckle is increased by 0.85 dB. The results of experiments in which the complete data sets are used, show that the resolution is better than that of DAS algorithm and the contrast is increased by 17 dB.
First-principles characterization of lanthanum occupying tendency in -Fe and effect on grain boundaries
2014, 63 (14): 148101. doi: 10.7498/aps.63.148101
The -Fe 3 (112) symmetrical tilt grain boundary model is established by the coincidence site lattice theory. First-principles plane wave ultrasoft pseudopotential method based on the density functional theory is used to calculate the La occupying tendency in -Fe. The results show that La elements tend to be located at grain boundary in the -Fe since the impurity formation energy keeps lowest. On this basis, the electronic structure of La doped in -Fe grain boundary is also calculated. The results indicate that the charges in the system are redistributed to provide more electrons for the grain boundary bonding when the La occupies -Fe grain boundary. Meanwhile, Fe atoms obtain more electrons, and the La doped region combination has the ion-tendency toward strengthening the interaction between La atom and Fe atoms in the adjacent boundary region, and the Fe atom bonds in the grain boundaries and on both sides of the grain boundary also strengthen, which is the reason why the mechanical properties change from the energy point of view. Moreover, La addition also makes the atomic density of states on the grain boundary move to the left, reduce the total energy of the system, and make the grain boundary more stable.
2014, 63 (14): 148401. doi: 10.7498/aps.63.148401
Error analysis is carried out to test the variational model of synthetic aperture radar sea surface wind retrieval. On condition that the background error is maximum, the analysis error is lower than the background error, and with the increase of the background wind direction, the analysis error changes periodically; on condition that the background error gradually increase, the analysis error increases gradually and its deviation direction coincides with the background error deviation direction; under the condition of specific background field, the variational model is compared with the direct inversion model: when the background wind speed is low, the variational model error is slightly high, when the background wind speed is high, the variational model error is significantly low. Generally, the variational model wind speed error is less than 1.60 m/s, and the wind direction error is less than 17.15°, which are better than those of the direct inversion model.
2014, 63 (14): 148503. doi: 10.7498/aps.63.148503
A novel SiGe heterojunction bipolar transistor (HBT) with a trench-type emitter is presented. Effects of the trench-type emitter on device performance are analyzed in detail, and current transport mechanism of the novel device is studied. The emitter resistances are parallel partitions by changing current path. Under the precondition without increasing the junction capacitance, the resistances of the new emitter are reduced effectively, and the frequency characteristics of the device are improved. Results show that the cutoff frequency and the maximum oscillation frequency of the new device are increased to 100.2 GHz and 134.4 GHz, respectively. More important is that the frequency characteristics are improved by the introduction of the trench-type emitter, while the current gain is not reduced and the junction capacitance is also not increased. A good trade-off is achieved among frequency, current gain, and junction capacitance. The trench-type emitter is designed to be optimal. With the change in sidewall height, no effects are found on the emitter resistances, and the frequency characteristics do not change, while the frequency characteristics are reduced when the sidewall width is increased.
2014, 63 (14): 148701. doi: 10.7498/aps.63.148701
The paper describes the principle of 0.2 THz stepped-frequency radar system which is utilized to achieve a one-dimensional range profile and range resolution. Terahertz (THz) stepped frequency radar is more susceptible to the phase error which will cause the spread and shift of range profile, thus affecting the quality of the high resolution range profile and signal-to-noise ratio. Therefore, a method of phase compensation is proposed to improve the range resolution. After phase compensation, the resolution and signal-to-noise ratio are improved remarkably. The range resolution can reach centimeter scale. Experimental and simulation results indicate that THz stepped frequency radar can reach high resolution range profile with the phase compensation method, which provides a foundation for further research on two-dimensional and three-dimensional image in the THz band.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (14): 144203. doi: 10.7498/aps.63.144203
We propose a scheme for the generation of narrowband triphoton frequency-entangled states. This scheme uses the four-wave mixing and the electromagnetically induced transparency in two cold-atom ensembles. By using the second-order perturbation theory, some relevant calculations are performed. By analyzing the coincidence-counting rate, we study the correlation and nonclassical properties of these states, and find that they have a similar feature to that of the discrete-variable W state, and can show the antibunching effect.
2014, 63 (14): 144501. doi: 10.7498/aps.63.144501
The method of constructing Birkhoffian funcations of mechanical systems is investigated. The redundant term is discovered in Santilli's second method. As a result, a simpler construction formula for self-adjoint systems is obtained by cancelling the redundant term. An example is given to illustrate the application of the results.
2014, 63 (14): 144204. doi: 10.7498/aps.63.144204
Using discrete method, N,N-Dimethylformamide (DMF) and tetrahydrofuran(THF) are adopted as solvent to fabricate MoS2 suspension solution, and its nonlinear optical properties in the visible and near infrared region are studied by open aperture Z-scan method. The results show that under the intense laser, in MoS2 (in DMF) suspension solution, saturable absorption property can be detected in the visible waveband (530 nm), showing that its transmittance is 1.54 times of ordinary, and reverse saturable absorption can be observed in the near infrared region (790 nm), indicating that its transmittance is 0.6 time of ordinary one and very good wavelength selection optical limiting effect. As a comparison, in the MoS2 (in DMF) suspension solution there does not appear the wavelength selection feature, but the reverse saturable absorption is present in all band. This phenomena may be produced through the two mechanisms: saturableabsorption and thermally-induced self-diffraction.
2014, 63 (14): 144205. doi: 10.7498/aps.63.144205
Er3+-doped Y3Sc2Ga3O12 (Er:YSGG) single crystal is grown by Czochralski method successfully, and the absorption spectra are measured in a wider spectral wavelength range (340-1700 nm). The experimental energy levels are analyzed and identified. The free-ion and crystal-field parameters are fitted by the experimental energy levels with a root mean square deviation of 10.34 cm-1, and 102 Stark energy levels of Er3+ in YSGG host crystals are assigned. It indicates that the fitting results of Stark energy levels are more satisfactory with the experimental spectra. Finally, the fitting results of free-ion and crystal-field parameters are compared with those already reported of Er:YAG crystal. A conclusion is drawn that the Er:YSGG has higher laser efficiency than Er:YAG, which may result from Er:YSGG that has a strong crystal field interaction.
2014, 63 (14): 144701. doi: 10.7498/aps.63.144701
The error of humidity sensor induced by solar radiation seriously affects the accuracy of the relative humidity measurement. To solve this problem, this paper presents a novel numerical analysis method of correcting the error of relative humidity based on computational fluid dynamics. In view of the external thermal environmental conditions of radiosonde humidity sensors, the convection-solar radiation coupled thermal boundary conditions are adopted in the numerical simulation with analysis method of fluid-solid coupled heat transfer. The temperature error analysis model is first established from the ground to 32 km altitude with different pressures and temperatures. Combined with Goff-Gratch approximation formulas of saturation vapor pressure, the corresponding fluid dynamic numerical analysis model of relative humidity is put forward for error correction. Moreover, the relative humidity errors are reported in the different physical parameters such as the direction of the solar radiation, the reflectivity of sensor, thermal conductivity of the substrate material, the size of sensor, etc. The data analysis shows that the error of relative humidity, caused by solar radiation nonlinearly increases with altitude. The humidity measurement accuracy is affected notably by the direction of solar radiation. Among the errors caused by solar radiation, the error in the direction perpendicular to the front of the sensor is biggest, the error in the direction of the top of the sensor is the next, and the error in the direction of the side of the sensor is smallest. The data analysis also indicates that the solar heating error of the relative humidity can be reduced by reducing the size of the sensor, reducing the thermal conductivity of the substrate material, or improving the reflectivity of sensor. However, the solar heating error can not be neglected under low air pressure at high altitude. A comparison with experimental results shows that the numerical analysis method of the relative humidity error based on fluid dynamics simulation provides a new way to enhance the radiation error correction.
2014, 63 (14): 144702. doi: 10.7498/aps.63.144702
An improved pre-processing method for smooth particle hydrodynamics is proposed, which can rapidly distribute the uniform particles for the fluid field with an arbitrary boundary. The improved pre-processing method is obtained by improving the algorithm proposed by Colagrossi et al., whose method can distribute the uniform particles in a simple shape. However, when the ratio of the smoothing length to the initial particle space is bigger than unity, the algorithm proposed by Colagrossi et al. has a numerical oscillation and a slow convergence rate; and the fluid particles may penetrate the solid boundary. For solving the problems, the XSPH model is added to improve the algorithm stability, and the boundary force is exerted on the fluid particles near the solid boundary to prevent fluid particles from penetrating wall surface. Verified by showing some exmples, the improved pre-processing method can rapidly distribute the more uniform particles for the fluid field with an arbitrary boundary and prevent fluid particles from penetrating wall surface.
2014, 63 (14): 144201. doi: 10.7498/aps.63.144201
In the applications of deep-space exploration, surveillance, threat detection and high resolution investigation on the ground, space optical systems need not only both the high resolution and width of view zoom system, but also the small size, light weight, low power and fast focusing system. As the traditional mechanical zoom system requires complex and precision mechanical motion, many problems are usually caused. Thus, based on active optics, the active optical elements are applied to the imaging system, and it is proposed that the optical element curvature radius should be variable to realize the transition among the different focal lengths. According to third-order aberration theory and dimension calculation of optical system requirement, the active zoom theory is studied, and the third-order aberration equation constraints are confirmed. Then the initial construction parameters of coaxial active zoom system are achieved by solving the equations. The system is optimized with using the optical design software ZEMAX. The system consists of the static primary mirror, the secondary and third mirror with the variable curvature radius, and the plane mirror with zero-power. As two times the light is obscured by the elements in the coaxial active zoom system, the amount of the energy on the image plane will be affected. For this reason, it is proposed that the unobstructed off-axis optimization should be necessary to the coaxial system. The off-axis system design theory is studied and the off-axis active zoom system is designed.
Highly birefringent ZrF4-BaF2-LaF3-AlF3-NaF photonic quasi-crystal fiber with twin grapefruits holes
2014, 63 (14): 144202. doi: 10.7498/aps.63.144202
A novel design of highly birefringent photonic quasi-crystal fiber based on ZrF4-BaF2-LaF3-AlF3-NaF glass with twin grapefruit air holes near the core and twofold symmetry is proposed. The basic unit is composed of one square and its neighboring regular triangle. Using the finite element method, the birefringence and confinement loss are investigated simultaneously by changing the pitch of air holes and sizes of air holes. Numerical results show that the fiber maintains single mode operation in a wide wavelength range from 1.8 μm to 2.2 μm, and the birefringence is on the order of 10-2, two orders of magnitude larger than that of the conventional polarization-maintaining fibers, which is largest (around 2 μm) ever reported to our knowledge and the same order of magnitude as that obtained by fiber using elliptic air holes But this designed fiber is easy to fabricate compared with the fibers using elliptic air holes.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (14): 146102. doi: 10.7498/aps.63.146102
The two-, three- and four-body interaction energies in face-centered cubic (fcc) krypton are evaluated using the many-body expansion method and the coupled cluster theory with full single and double excitations plus perturbative treatment of triples, and both self-consistent-field (SCF) Hartree-Fock energy and correlation one are accurately determined in a wide volume range (from 27 to 4 cm3/mol). All different three- and four-atom clusters existing in the first three and two nearest and two neighbor shells of fcc lattice are considered. It is found that the three-body interaction energy is positive at low compression, where the dispersive forces play a dominant role, with increasing the compression the three-body contribution becomes attractive, and the SCF energy overwhelms the dispersive one. At pressures higher than 30 GPa, the four-body contribution becomes important and significantly cancels the over-softening effects of the three-body potential. It shows that the combination of the four-body effects with two- and three-body interactions leads to an excellent agreement with the measurements from the equation of state in the whole experimental range of 0-130 GPa.
2014, 63 (14): 146801. doi: 10.7498/aps.63.146801
Polycrystalline cesium iodide (CsI) thin films were prepared on glass substrates by thermal evaporation. The Influences of air exposure on the structure, resistivity and infrared transmittance of CsI film were investigated by scanning electron microscopy, X-ray diffraction (XRD), high resistance meter and infrared spectrophotometer (IR). It is found that the coalescence of grains occurs and the average grain size increases from 0.36 μm to 1.25 μm. The mechanism of grain growth is attributed to the diffusion of water molecules along grain boundaries and the migration of grain boundaries driven by minimization of total free energy. XRD results indicate the formation of (110/220) texture when exposed to ambient air and the relaxation of tensile stress during recrystallization. The average crystallite sizes obtained from Debye-Scherrer's formula are 25.6 nm, 28.4 nm and 45.1 nm respectively. The resistivity of the film decreases from the order of 1010 Ω·cm to 108 Ω· cm. The IR absorption bands in the ranges of 3675-3750 cm-1 and 3560-3640 cm-1 closely resemble that of free water rather than liquid water. The observed split bands are assigned to the non-hydrogen-bonded OH associated with ion-dipole bonds and dangling OH at air-water interface respectively.
Negative piezo-optical effect and the inverse mode piezo-o ptical effect of stressed liquid crystals
2014, 63 (14): 146101. doi: 10.7498/aps.63.146101
The concepts of polymer dispersed liquid crystal (PDLC) and stressed liquid crystal (SLC) are introduced; the three kinds of definitions, i.e., “positive piezo-optical effect”, “negative piezo-optical effect” and “inverse mode piezo-optical effect” of PDLC switchable glass are given. The new types of stressed switchable glass samples of negative piezo-optical effect and inverse mode piezo-optical effect are prepared. The experimental results show that the haze is above 90% in a scattering state and the transmittance is nearly 30% in a translucent state. The principle of piezo-optical effect is analyzed with polarization microscopy. The results show that the vertical surface pressure or stretching stress applied to the sample will result in the special reorientation of LC molecules in LC droplets, which causes the optical characteristics of the sample to change significantly. The mode of vertical stretched liquid crystal droplet is proposed, the computation results and graph plotting conform with the results from the micrographs of polarizing microscope very well, so that the experimental phenomena are reasonably explained. The research on SLC piezo-optical effect has the fundamental significance for studying the PDLC and the application value for developing non-electro-optic switchable glass.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First-principle study of the effects of oxygen vacancy on the electronic structure and the absorption spectrum of ZnO
2014, 63 (14): 147101. doi: 10.7498/aps.63.147101
Nowadays, the studies of the influence of oxygen vacancy on forming impurity level of ZnO have obtained contrary conclusions. The experimental results about both the deep impurity level and the shallow impurity level are reported. However, under the high temperature heating condition, the origin of free electron increasing in conduction band of ZnO with oxygen vacancy is not sufficiently understood. To slove this problem, according to the first-principles plane-wave ultrasoft pseudopotential of the density functional theory, we set up the models for a pure ZnO cell and two different oxygen vacancy concentration supercells of ZnO, and perform the geometrical optimization for three models. The density of state, band structure, population and differential electron density are also calculated. Calculation results indicate that with the increase of oxygen vacancy concentration, the total energy increases and the formation energy will be greater. It makes the stability decline and the oxygen vacancy harder. Meanwhile, its conduction band minimum shifts toward low energy, the electron transition width decreases, and the absorption spectrum is red-shifted. It shows that these results may be helpful for the future experimental design and also for the preparation of optical device with oxygen vacancy of ZnO.
2014, 63 (14): 147701. doi: 10.7498/aps.63.147701
The polycrystalline Bi5-xPrxFe0.5Co0.5Ti3O15 (BPFCT-x: x=0.25, 0.50, 075, 0.80) ceramics are prepared by an improved solid state reaction method. X-ray diffraction structure analysis shows that the content of Pr has an influence on the microstructure of sample, but all the samples are layered perovskite structure. The remanent polarization (2Pr) first increases and then decreases with the increase of Pr content (x), so do the magnetic and ferroelectric properties. The remanent polarization reaches a maximum vaule of 6.43 μC/cm2, when x = 0.75. The remanent magnetization (2Mr) increases to a maximum value of 0.097 emu/g when x=0.75, and then decreases with the increase of Pr content (x). with the increase of Pr doping the ferroelectric and ferromagnetic properties of sample at room temperature can be obviously improved, and when x=0.75, multiferroic properties of the sample at room temperature is the best. The improvement in ferroelectric properties of sample is related to Pr doping. With the increase of Pr content (x), the defect concentration of the sample can be reduced, ferroelectric domain of movement can be improved, and the improvement in ferromagnetic property is possibly related to the lattice deformation which is affected by Pr.
2014, 63 (14): 147902. doi: 10.7498/aps.63.147902
In order to find a rapid and accurate numerical method to compute the multipactor threshold in microwave device, three enhanced Monte-Carlo (MC) methods are proposed which are single particle-multiple collision MC, multiple particle-single collision MC and multiple particle-multiple collision MC method. The three MC methods all give the random nature of the secondary electrons, including their initial energies, phases and angles. And in all of the methods, the electron trajectory is computed with Runge-Kutta method and the secondary electron yield (SEY) per collision is computed with Furman model. The effective SEY is taken as the criterion to judge whether multipactor occurs, the definition of which is a little different from those of the three MC methods. As a verification, the multipactor in a parallel plate transmission line is investigated with the presented MC methods and the traditional MC method. The numerical results of the four MC methods are compared with the results of the statistical theory. It is demonstrated that the single particle-multiple collision MC method has the smallest error and the best stability.
Electric characteristics and resistive switching mechanism of Ni/HfO2/Pt resistive random access memory cell
2014, 63 (14): 147301. doi: 10.7498/aps.63.147301
Electric characteristics and resistive switching mechanism of Ni/HfO2/Pt cell are investigated. The cell has a forming-free property and shows an abnormal non-polar switching behavior. A high ON/OFF resistance ratio (>105) is obtained. The resistance of the on-state is independent of cell size, which implies that a conductive filament is formed in HfO2 film. X-ray photoelectron spectroscopy is used to investigate the compositions and valences of Ni and Hf in HfO2 film for the on-state cell. The results show that there is a hybrid filament comprised of a Ni filament and an oxygen vacancy filament in the HfO2 film for the on-state.
First-principle study on the effects of Tl doping on the band gap and the band-edge of optical absorption of InI
2014, 63 (14): 147102. doi: 10.7498/aps.63.147102
According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, models for a pure InI and different concentrations of Tl-doped InI are set up, and the geomertry optimizations for the modes are carried out. The total density of states, the band structures and the optical absorption are also calculated. The results show that the smaller the doping concentration of Tl, the smaller the formation energy of InI is, thus the more stable the crystal structure is. The Tl doping causes the bottom of conduction band shift to a higher energy, while the location of the top of valence band has no change. This makes the band gap of InI broadened, and the absorption spectrum obviously blue-shifted.
2014, 63 (14): 147401. doi: 10.7498/aps.63.147401
The generalized gradient approximation based on the density functional theory is used to study the adsorption process of H2O molecules by the Li decorated C6Li and the catalytic process of decomposition of H2O molecules. The geometry optimization shows that the most stable adsorption position of the Li is above the C atom of C6. Research shows that the adsorption of the first H2O molecule on C6Li needs to overcome an energy barrier of 1.77 eV, then H2O is decomposed into H and OH and bonding with Li atoms. Furthermore, the adsorption of the second H2O molecule needs to overcome an energy barrier of 1.2 eV and then the H2O molecule is decomposed into H and OH, the H atom in which and the H atom on the Li atom combine into an H2 molecule. OH replacing H atoms on Li atoms combines with the Li atom. Therefore, C6Li can be used as a catalyst for H2O molecules, and thus provide a new train of thought for the preparation of hydrogen storage material. The analysis shows that C6Li mainly adsorbs the H2O molecules through the dipole moment formed by the positive charge of Li and negative charge of H2O.
2014, 63 (14): 147502. doi: 10.7498/aps.63.147502
Due to the cell volume mutations and the phase transition latent heat existing during phase transition of the first-order phase transition magnetic refrigeration material, many basic problems need to further explore in the magnetization process. In this paper, taking LaFe13-xSixalloys as the research object, we discuss in detail some problems, such as a phase-change, entropy change, isothermal entropy change, adiabatic temperature change, thermal and magnetic hysteresis, the temperature range and magnetic field range in which the ferromagnetic and paramagnetic state coexist, and magnetic refrigeration capacity calculation, The analysis shows that the magnetic entropies calculated by Maxwell equation and Clausius-Clapeyron equation are equivalent when neglecting the contributions of ferromagnetic and paramagnetic state to magnetocaloric effect. The area surrounded by the curve in heating of isothermal magnetization process and curve in cooling of isothermal magnetization process (hysteresis size) is actually the net work done by magnetic field during the heating process and cooling process. The values of magnetic and thermal hysteresis are related to the measurement time: the longer the measurement time, the smaller the hysteresis is. When the transformation is of the equilibrium phase, the hysteresis should be equal to zero. In addition, the temperature and magnetic field induced magnetic transition processes are discussed, and different calculation models of the first-order phase transition material for magnetic refrigeration refrigeration capacity are proposed.
Magnetic and transport properties of layered perovskite manganites (La1-xEu x)4/3Sr5/3Mn2O7(x=0, 0.15)
2014, 63 (14): 147503. doi: 10.7498/aps.63.147503
The samples (La1-xEux)4/3Sr5/3Mn2O7 (x=0, 0.15) were prepared by the traditional solid-state reaction, and their magnetic and electrical properties were investigated. The magnetzation measurement reveals that as temperature lowers, all the samples undergo a complex magnetic transition process: they transform from the two-dimensional short-range ferromagnetic order at T* into the three-dimensional long-range ferromagnetic state at TC. With the increase of Eu doping, T* and TC are both reduced, and the sample (La0.85Eu0.15)4/3Sr5/3Mn2O7 exhibits spin-glass-like behaviour in a low temperature region. Electrical property measurements show that with the increase of Eu concentration, resistivity sharply increases, the metal-insulator transition temperature decreases and the magnetoresistance peak increases. These effects are attributed to the decrease of the average ionic radius diminution and the lattice distortion due to the substitution of the smaller Eu3+ ions for La3+ ions. In addition, the small-sized Eu3+ ion preferentially occupies the R site in the rock-salt layer, then the distributions of La3+, Sr3+, Eu3+ ions in the sample (La0.85Eu0.15)4/3Sr5/3Mn2O7 should be more orderly, so there is only one peak in the ρ-T curve of the sample with x=0.15.
Hydrothermal diffusion of Eu3+ in EuVO4@YVO4 core-shell nanoparticles and its influence on luminescent properties
2014, 63 (14): 147801. doi: 10.7498/aps.63.147801
EuVO4@YVO4 core-shell nanoparticles (NPs) are synthesized, coated by poly(sodium 4-styrenesulfonate) and hydrothermally treated at 200 ℃ for 0-48 h. The photoluminescence (PL) intensity of as-prepared sample is enhanced by about 5 times after 48-hour hydrothermal treatment, and the average lifetime is raised up from 0.410 ms to 0.579 ms. Further studies of hydrothermal time-dependent PL decay curves provide evidence for the diffusion of Eu3+ in core-shell NPs, which could reduce the concentration quenching in particle core and hence enhance the PL efficiency. This thermal diffusion strategy based on ion-doped core-shell NPs could be used to prepare luminescent NPs with high efficiency if designed elaborately.
2014, 63 (14): 147802. doi: 10.7498/aps.63.147802
In this paper, Raman modes of bi-layer graphene are investigated in detail in the frequency region between 1800 and 2150 cm-1. There are four dominant Raman modes in this frequency region. The frequencies of these modes dependent on excitation energy are revealed from the measurement with multi-wavelength lasers, which can be fully understood based on double resonance Raman scattering and the phonon dispersion relation of monolayer graphene. The results show that these Raman modes can be assigned to the combinational modes from the fundamental modes of iTA, LA and LO phonons, but not from iTO and oTO phonons as reported in the previous works. This study benefits us toward the full understanding of lattice dynamics of monolayer and multilayer graphenes.
2014, 63 (14): 147901. doi: 10.7498/aps.63.147901
Suppression of secondary electron yield attracted much attention in areas such as accelerator and high power microwave components in recent years. To evaluate the suppression efficiencies of different surface topographies, the secondary electron yields (SEYs) of four kinds of micro-structured surfaces for trapping secondary electrons, i.e., triangular groove, rectangular groove, cuboid, cylindrical, are obtained by the phenomenological probabilistic model of secondary electron emission. The simulation results show that the SEYs of these structures are much dependent on the shape parameters such as aspect ratio or porosity. There are mainly three findings: 1) the SEY decreases with increasing aspect ratio and porosity; 2) the traps with cuboid or cylindrical shape are more efficient than triangular or rectangular traps for the SEY suppression; 3) the SEY dependence of micro-structured surface on incident angle is not as obvious as that of flat surface. Micro-trapping structure surfaces are fabricated by mechanical method, photolithography process and chemical etching respectively. The measured SEYs of these samples validate the theoretical results. All these results show that the proposed micro-structures as secondary electron traps have potential applications in SEY suppression in fields such as multipactor and electron-cloud effects.
2014, 63 (14): 147501. doi: 10.7498/aps.63.147501
In this paper, band structure of two-dimensional magnotic crystal composed of elliptic rods triangularly arranged is calculated by using the plane-wave expansion method. The results show that under the condition of the same filling ratio, the width and central frequency of band gap obviously change with the ratio between two radii of ellipse, and that elliptic cylinder scattering body can open the lower frequency band gap or widen the low frequency band gap.
2014, 63 (14): 148501. doi: 10.7498/aps.63.148501
Space environment and space resources have become a new field of competition among countries, and this field is to be developed. To achieve these purposes, some countries have established the detection sites and communication network by launching satellites, space stations, space shuttles and other spacecrafts into the space. Photoelectric systems in space play a crucial role in developing new fields and exploring new resources. Presently, the space environment factors including point-to-point long distance, intense space radiation, large temperature difference challenge the high requirements of the stability and reliability for the optoelectronic system. A new type of technology with quantum dot infrared photodetector, which may be used in the space, is proposed, which potentially provides higher detectivity, operation temperature, radiation tolerance, responsive bandwidth, etc. The basic working principle and the advantages of the quantum dot infrared photodetectorare discussed. And the basic technical requirements for the quantum dot infrared photodetector in space application are pointed out. Finally, feasible applications of the quantum dot infrared photodetector in the field of space laser radar, satellite optical communications and imaging system are analyzed.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Application of digital filter weak constraint four-dimensional variational data assimilation on typhoon initialization Ⅱ. Digital filter weight chosen
2014, 63 (14): 149201. doi: 10.7498/aps.63.149201
In Part I, the digital filter weak constraint four-dimensional variational (4D-Var) data assimilation is implemented with different digital filter weight settings through two typhoon cases. The results show that the influence of the digital filter weight on typhoon track and intensity prediction is large, and how to choose an appropriate digital filter weight is important. In this paper, seven different initial time typhoon cases in 2010 are selected to analyze the effects of different digital filter weight settings on typhoon track and intensity prediction. Based on the track and intensity prediction information of the seven cases, and the three-hour pressure tendency information for the whole domain and the area with 800 km radius from the typhoon center, a method of choosing digital filter weight is proposed for typhoon initialization with bogus data assimilation. Also, the ordinary digital filter weight setting is proposed, which is 1000 and obviously different from the operational and storm cases weight setting.
Predictive reliability of summer precipitation in China based on error distribution of numerical model
2014, 63 (14): 149202. doi: 10.7498/aps.63.149202
In this paper, we made some statistical analyses on precipitation prediction errors of coupled global climate model of National Climate Center based on CPC merged analysis of precipitation. Through the statistics of the forecast results of summer precipitation in many years and the errors, we find that the distribution of the model prediction errors satisfies the Gaussian distribution. Based on the Gaussian distribution characteristics, the ability to predict the mode for summer precipitation in China can be analyzed and compared. The forecast performance of the dynamic-statistics scheme is significantly better than that of system error correction scheme of the model. The dynamic-statistics optimal combination of factor revise is corrected, relative to error distribution pattern of the system revised forecast, and there are obtained two kinds of error distribution characteristics: 1) improvement of the amplitude; 2) improvement of the displacement. Based on the statistical characteristics of the prediction error, measure of the credibility of model forecast results is proposed to quantitatively assess the credibility of the numerical model forecast results in different regions. Taking the summer precipitations in 2012 and 2013 for example, we analyze the credibility of actual observations, prediction and drought or flood level. Comparing actual observations and prediction, we find that there is a good consistency where the credibility of them is larger, while there are many bad predictions in the region where the credibility of them is smaller. What is more, compared with other reliability test method, the credibility of the abnormal precipitation forecast by this method is more accurate, showing the effectiveness of the method.
2014, 63 (14): 149203. doi: 10.7498/aps.63.149203
Initial error and model error are key factors restricting the accuracy of numerical weather prediction (NWP). The purpose of the present study is to estimate the errors of spatiotemporal evolution model by using recent observations. By considering the continuous evolution of atmosphere, the observed data (ignoring the measurement error) can be viewed as a series of solutions of accurate model governing the actual atmosphere, and the model errors can be objectively assumed to be an unknown functional term (a missing forcing term) of the numerical model, thus the NWP can be considered as an inverse problem to uncover the unknown model error term by using the long periods of observed data. In this study, we first construct an inverse problem model with its optimization problem, which is constrained by the numerical model, to estimate the errors of spatiotemporal evolution model, then we present a derivative-free optimization (DFO) method to find the minimum solution of the optimization problem by running the numerical model with an external forcing term. The DFO method does not need to compute the gradient of the objective functional and the tangent linear model or adjoint model of the original numerical model. The numerical study of Burgers equation indicates that the presented methods can effectively uncover the model errors from the past data and evidently improve the numerical prediction. The precedures described in this paper open up possibilities for utilizing the past observation data to extract useful information about model errors and enhance the prediction efficiency in the operational models.
2014, 63 (14): 149501. doi: 10.7498/aps.63.149501
The interaction matrix of an adaptive optical system is directly computed. In this method, based on the correlation between the measured and theoretical slope influence vectors of the selected actuators, the misalignment between the wavefront sensor and wavefront corrector is first estimated, and then an interaction matrix more close to the real one is obtained. Experimental results show that with considering the misalignment, the interaction matrix acquired by direct computation becomes more effective in closed-loop correction, and the slope residual error is reduced.
2014, 63 (14): 149401. doi: 10.7498/aps.63.149401
Charging characteristics of polymer irradiated by multi-energetic electrons is a basis to study and prevent electrostatic discharge in space radiation environment. The polymer irradiated by multi-energetic electrons is modeled and simulated. The space charge distribution, surface potential, space potential, surface potential and maximum field strength under the condition of sample parameters are obtained. The results show that because of electron drift and diffusion, electrons can transit through the electron scattering region, forming negative space charges. Some electrons can flow to the substrate of polymer. In the equilibrium state, the surface potential of the film negatively charged decreases with film thickness and trap density increasing, and it increases with electron mobility and relative permittivity increasing. The maximum field strength increases with film thickness and trap density increasing, and it decreases with electron mobility and relative permittivity increasing. The high-energy electrons section of multi-energetic electrons will shorten the equilibrium of charging process.