Vol. 62, No. 20 (2013)
2013, 62 (20): 200201. doi: 10.7498/aps.62.200201
Using Mawhin’s continuation theorem, the existence of periodic solution for a class of nonlinear problem is discussed, and then by using it, the problem of periodic solution of nonlinear model in zero-dimensional climate system is investigated. A result about the existence of periodic solution to the model is obtained.
2013, 62 (20): 200202. doi: 10.7498/aps.62.200202
We generalize the (G/G)-expansion method, introduce new auxiliary equation and add negative power exponent. We obtain some new exact solutions of Zakharov equations using the extended (G/G)-expansion method. This method can also be applied to other nonlinear evolution equations.
2013, 62 (20): 200203. doi: 10.7498/aps.62.200203
There models of complex information system security risk propagation are proposed in this paper based on cellular automata, and the probabilistic behaviors of security risk propagation in complex information systems are investigated by running the proposed models on nearest-neighbor coupled network, Erdos-Renyi random graph network, Watts-Strogatz small world network and Barabasi-Albert power law network respectively. Analysis and simulations show that the proposed models describe the behaviors of security risk propagation in the above four kinds of networks perfectly. By researching on the propagation threshold of security risks in four kinds of network topology and comparing with the existing research result, the correctness of the models is verified. The relationship between the heterogeneity of degree distribution and the value of the propagation threshold is analyzed and verified in this paper. Through the research on the evolutionary trends of security risk propagation, the relationship between the heterogeneity of degree distribution and the influence sphere and speed of security risk propagation is analyzed and verified as well. Meanwhile, the relationship between the heterogeneity of degree distribution and the effect of the immune mechanism on controlling security risk propagation is pointed out. Furthermore, the result of simulations describes the negative exponent relationship between security risk extinction rate and the propagation rate. The key factors affecting the security risk propagation are analyzed in this paper, providing the guidance for the control of security risk propagation in complex information systems.
2013, 62 (20): 200301. doi: 10.7498/aps.62.200301
The double ring-shaped Hulthn potential is proposed in this paper. By using the analytical method of function, the approximate analytical solutions of bound state solutions of Schrdinger equation for the double ring-shaped Hulthn potential are presented within the framework of an exponential approximation of the centrifugal potential for arbitrary l-states. The normalized angular and radial wave function expressed in terms of hypergeometric polynomials are presented. The energy spectrum equations are obtained. The wave function and the energy spectrum equations of the system are related to three quantum numbers and parameters of double ring-shaped Hulthn potential. The polar angular wave functions of the central potential and ring-shaped potential and the energy spectrum equations of Hulthn potential turn out to be the special cases of the double ring-shaped Hulthn potential.
Performance analysis of decoy-state quantum key distribution with a heralded pair coherent state photon source
2013, 62 (20): 200302. doi: 10.7498/aps.62.200302
A comprehensive analysis is made on the performance of decoy-state quantum key distribution with a heralded pair coherent state photon source from the effectiveness, stability and feasibility. The key generation rate, quantum bit error rate, and optimal signal intensity each as a function of secure transmission distance are simulated and analyzed by the three-intensity decoy-state method based on a heralded pair coherent state photon source with four groups of experimental data. Considering the intensity fluctuation, the stability of this method is simulated and discussed. Furthermore, the feasibility of the simple and easy method that is proposed with a heralded pair coherent state photon source is analyzed. The simulation results show that the key generation rate and secure transmission distance obtained from the decoy-state method with a heralded pair coherent state photon source are better than those obtained from the methods with a weak coherent state source and heralded single photon source. With the same intensity fluctuation, the heralded pair coherent state photon source is less stable than the heralded single photon source, but more robust than the weak coherent state source. However, the advantage in the effectiveness of the heralded single photon source can give rise to the shortage of the stability. Moreover, the two same modes of the heralded single photon source provide the feasibility to design a simple and easy passive decoy-state method.
2013, 62 (20): 200303. doi: 10.7498/aps.62.200303
Higher efficiency of error reconciliation technique is for data post-processing for quantum key distribution. Based on the one way error reconciliation scheme of Hamming syndrome concatenation, the error correction performances of there kinds of Hamming codes are demonstrated by data simulation analysis. The simulation results indicate that when the initial error rates are (-∞, 1.5%], (1.5%, 3%], and (3%, 11%], if using Hamming (31, 26), (15, 11), and (7, 4) codes to correct the errors, respectively, the key generation rate is maximized. Base on these outcomes, we propose a kind of modified error reconciliation scheme which is based on the mixed pattern of Hamming syndrome concatenation. The ability to correct the errors and the key generation rate are verified through data simulation. Meanwhile, using the parameters of the posterior distribution based on the tested data, a simple method of estimating bit error rates (BER) with a confidence interval is estimated. The simulation results show that when the initial bit error rate is 9.50%, after correcting error 8 times error, the error bits are eliminated completely and the key generation rate is 9.94%. The BER expectation is 5.21×10-12, when the confidence is 90% the corresponding upper limit of BER is 2.85×10-11. The key generation rate increased by about 3-fold compared with that of original error reconciliation scheme.
2013, 62 (20): 200304. doi: 10.7498/aps.62.200304
According to multistage quantum teleportation, we here propose a quantum routing scheme which teleports a quantum state from one quantum device to another wirelessly even though the two devices which do not share entangled photon pairs mutually. By the quantum routing scheme, the model of quantum wireless wide-area networks is presented. In terms of time complexity, the proposed scheme transports a quantum bit in the time almost the same as the quantum teleportation regardless of the number of hops between the source and destination node. From this point of view, the quantum routing scheme is close to optimal scheme in data transmission time. The correlative routing process is proposed under different conditions. The quantum state is transferred by multistage quantum teleportation, therefore, the information transfer between any two nodes in quantum wireless wide-area networks is realized.
2013, 62 (20): 200305. doi: 10.7498/aps.62.200305
An algorithm to generate unitary transformation (UT) of two orthogonal base kets is proposed in this paper. Certain requirements that UT must meet are as follows: four typical base kets in the first category can be transformed into states with the last qubit |0>, and the other four atypical base kets can be transformed into states with the last qubit |1>. This UT is applied to quantum data compression, with a result that the fidelity of the compression is 0.942. This method provides an important basis for realizing quantum compression and decompression. And it can be an important reference of other UT generation method which must fulfill some requirements.
2013, 62 (20): 200306. doi: 10.7498/aps.62.200306
Using the damped projecting Gross-Pitaevkii align, we study the vortex pattern in the two-dimensional spin-orbit coupled spin-1 Bose-Einstein condensate of 23Na. We concentrate on the influence of spin-orbit coupling on the vortex pattern and find that the periodic vortex lattice which would occur without any spin-orbit coupling, can be completely destroyed although the strength of spin-orbit coupling is not very strong. With a strong spin-orbit coupling, vortexes in the condensate of each spin state tend to form some vortex groups and then they create a flower-like lattice around the center.
2013, 62 (20): 200501. doi: 10.7498/aps.62.200501
In this paper studied is the crises in the Duffing vibro-impact oscillator with non-viscously damping by the composite cell coordinate system method. It is assumed that the non-viscously damping depends on the past history of the velocities other than the instantaneous generalized velocities. The energy dissipation behaviors of real structural materials can be preferably represented in the non-viscously damping models. Numerical simulations show that as the damping coefficient or the relaxation parameter or the recovery coefficient is varied, there appear two kinds of crises: one is the interior crisis, which results from the collision between a chaotic attractor and a chaotic saddle on the basin boundary, and the other is the regular/chaotic boundary crisis, which is due to the collision of a chaotic attractor with a periodic/chaotic saddle on its basin boundary. All the crises result in a sudden change in size and shape of the attractor.
2013, 62 (20): 200502. doi: 10.7498/aps.62.200502
In this paper, the chaotic behaviour in the transverse vibration of an axially moving viscoelastic tensioned beam under the external harmonic excitation is studied. The parametric excitation comes from harmonic fluctuations of the moving speed. A nonlinear integro-partial-differential governing equation is established to include the material derivative in the viscoelastic constitution relation and the finite axial support rigidity. Moreover, the longitudinally varying tension due to the axial acceleration is also considered. The nonlinear dynamics of axially moving beam is investigated under incommensurable relationships between the forcing frequency and the parametric frequency. Based on the Galerkin truncation and the Runge-Kutta time discretization, the numerical solutions of the nonlinear governing equation are obtained. The time history of the center of the axially moving viscoelastic beam is chosen to represent the motion of the beam. Based on the time history of the axially moving beam, the Poincaré map is constructed by sampling the displacement and the velocity of the center. The bifurcation diagram of the axially moving beam is used to show the influence of the external excitation. Furthermore, quasi-periodic motions are identified using different methods including the Poincaré map, the phase-plane portrait, and the fast Fourier transforms.
Bifurcation and chaos in sliding mode controlled first-order h-bridge inverter based on pulse width modulation
2013, 62 (20): 200503. doi: 10.7498/aps.62.200503
Sliding mode control (SMC) is recognized as a robust controller with fast dynamic response and high stability in a wide range of operating conditions, and therefore it is widely used in the control of inverter. The sliding mode controlled inverter is in nature a nonlinear controlled time-varying nonlinear system, and it has complicated nonlinear behaviors in practice. In this paper the sliding mode controlled first-order H-bridge inverter based on pulse width modulation is taken for example. First, through observation of the waveforms under different SMC parameters, a new type of bifurcation is discovered for the first time, in which diverse multi-period bifurcations exist at the same time. Second, the discrete time iterative model is established for the system and the folded diagram is employed to observe the waveforms. These analyses of current waveforms prove that the new type of bifurcation proposed in this paper is not a route to chaos. Moreover, the stability of the system is much concerned in engineering applications. However, because of the nonlinear characteristics of sliding mode controller, the method using eigenvalues of Jacobian matrix and other analytical methods are unsuitable for the system, and the graphic methods are not accurate enough. Finally, a criterion of fast-scale stability which can accurately distinguish the stability of the system is proposed, and it can be used to provide reliable reference for the parameter design of sliding mode controller.
2013, 62 (20): 200504. doi: 10.7498/aps.62.200504
In this paper, we give indirect methods constructed Wronskian solution of a general nonlinear evolution equations. Under the properties of the computing of Young diagram we have proved the proposition of this paper and discuss the relationship between the permutation group character and Young diagram expressions coefficient.
2013, 62 (20): 200701. doi: 10.7498/aps.62.200701
Multi-frame super-resolution reconstruction is a technology which obtains a high-resolution image from several low-resolution images of the same scene. Among various super resolution methods, the regularized method is widely used since it has advantages for solving the ill-posed problems. However, the super-resolution reconstruction results based on this method strongly depend on the estimation accuracy of the optimum estimator. In this paper, a double-threshold Huber norm based maximum likehood estimator is proposed, which improves the threshold tolerance of the estimator and increases the estimation accuracy. Then a regularized algorithm based on this estimator is presented. The super-resolution reconstruction results of synthetic low resolution images confirm that the proposed algorithm has better performance over the existing algorithms. The proposed algorithm is also used to deal with the low-resolution images obtained from a plenoptic camera. The results confirm the effectiveness of the proposed algorithm.
2013, 62 (20): 200702. doi: 10.7498/aps.62.200702
According to the theory of traditional Maxwell-Wagner interface polarization, the metal micro/nano particles have no obvious electrorotation behavior under the alternating current electric field. However, we find the opposite experimental results. In this paper, electrorotation experiments are carried out, and the basic mechanism of gold-coated SU-8 microrods is presented. Therefore the electrorotation characteristics of gold-coated microrod at low frequency are analysed by considering the surface electric double layer at the microrod-electrolyte interface. Specifically, first we establish an approximate ellipsoid model in the electric field, analyze the polarization mechanism of metal particles under the action of solid-liquid interface electric double layer, and then calculate the electrorotation torque and present an electrorotation angular speed formula of the gold-coated microrod. Secondly, electrorotation experiments of gold-coated SU-8 microrods suspended in electrolytes with different conductivities are presented in a frequency range of 100 Hz to 30 MHz. Finally, the experimental results are discussed, and compared with the theoretical analysis, showing the experimental results are in good agreement with theoretical analyses by considering the friction between the microrods and substrate.
Investigation of enhancing higher harmonics by changing the shape of atomic force microscope cantilever
2013, 62 (20): 200703. doi: 10.7498/aps.62.200703
Higher harmonics of tapping-mode atomic force microscope carries information about the mechanical properties of the sample on a nanometer scale. Unfortunately, the vibration amplitudes of traditional atomic force microscope (AFM) cantilever at higher harmonics are too small for practical AFM imaging. Ritz method demonstrates that specific cutout on the cantilever can realize internal resonance to enhance higher harmonics. In this paper, by COMSOL finite element simulation, the laws for fundamental frequency, second resonance frequency and their ratio each as a function of the size of the cutout and the position of the cutout on the cantilever are achieved. Using focused ion beam to hole the cantilever makes the second resonance frequency close to 6 times that of the fundamental frequency and also the 6th harmonic enhanced. Moreover, we obtain the image of the 6th harmonic on our home-made higher harmonic system.
2013, 62 (20): 200704. doi: 10.7498/aps.62.200704
NO and NO2 are the common gases and have serious harmfulness to the atmosphere pollution of environment. To detect the concentration of the two gases in pollution, we construct a low cost photoacoustic spectrum gas measurement system based on the thermal radiation light source. Absorption lines of the NO and NO2 between 2500 and 6667 nm are calculated. By modeling the photoacoustic transmission line the relations between quality factor, acoustic pressure and cavity length, cavity radius, modulation frequency are obtained, and the design of geometric construction of photoacoustic cell is also guided. The experiment show that there exists a good linearity between photoacoutic signal detected in the system and gas concentration, and the system ultimate detection sensitivities to the NO and NO2 are 4.01 and 1.07 μL/L respectively. When the emission wavelength of laser is regulated suitably and the edmund optics is chosen reasonably, this system is also suitable for the concentration-detection of other trace gas.
Measuring tropospheric vertical distribution and vertical column density of NO2 by multi-axis differential optical absorption spectroscopy
2013, 62 (20): 200705. doi: 10.7498/aps.62.200705
The inversion method of the vertical profile and vertical column density (VCD) of tropospheric NO2 using multi-axis differential optical absorption spectroscopy (MAX-DOAS) is investigated in this paper. An inversion method of two-step procedure is operated. In this method firstly the aerosol vertical profile is retrieved. Then the vertical distribution of trace gases is retrieved based on the corresponding aerosol status. Nonlinear optimal estimation algorithm is extended to acquire NO2 profile to reduce the dependence of the inversion on priori information. It is more advantageous to automatically obtain trace gases profile. At first we investigate how to calculate some parameters (weighting function, the covariance matrices of measurement, and a priori information) of the algorithm and design nonlinear iteration strategy suited to the region where NO2 vertical distribution usually shows rapid variation. Then this inversion algorithm is verified by computer simulation in the cases of box profile and elevated profile of NO2. It is indicated that the distribution of NO2 below 2 km could be well rebuilt and the retrieval accuracy of surface-near NO2 volume mixing ratio is 0.6%. The study of how accurately this algorithm can rebuild the same true profile in three aerosol status of low aerosol, high aerosol and elevated aerosol indicates that similar retrieval results could be acquired. In addition, the effect of wrong aerosol status on the retrieving of NO2 profile and the error sources of this algorithm are analyzed. After that a continuous observation is reported in the city of Hefei. NO2 VCDs derived from MAX-DOAS are compared with those from satellite observations, and the correlation coefficient is 0.85. The surface-near NO2 concentrations measured by MAX-DOAS are compared with those from LP-DOAS, and the correlation coefficient is 0.76. In addition, the simplified MAX-DOAS inversion method of obtaining the trace gas profile usually uses invariable typical aerosol status as input. The comparison with the tropospheric NO2 VCD from simplified method indicates that the using of invariable typical aerosol status would cause large deviation of NO2 VCD, and its maximum relative deviation is about 112%. So exactly acquiring aerosol status, aerosol optical density especially, is necessary to exactly retrieve tropospheric NO2 vertical column density.
ATOMIC AND MOLECULAR PHYSICS
Density functional study on the electronic and magnetic properties of two-dimensional hexagonal boron nitride containing vacancy
2013, 62 (20): 203101. doi: 10.7498/aps.62.203101
According to density functional first-principles calculations, we study the electronic and magnetic properties of two-dimensional h-BN containing lattice vacancies: B atom vacancy (VB), N atom vacancy (VN) and BN pair vacancies (VBN). In microstructures, the neighbored N atoms around vacancy in VB system are constructed into an isosceles triangle; the neighbored B atoms around vacancy in VN system are constructed into an equilateral triangle; and the neighbored atoms around BN pair vacancies are constructed into a keystone. The calculations on band structures and density of states show that the significant spin polarization exists in two-dimensional h-BN containing single vacancy defects, while the BN pair vacancy system exhibits non-spin polarization. Three kinds of vacancy defects make the band gap change from direct band gap to indirect band gap. For the VB system, the total magnetic moment is 1.00 μB, due to the contribution from the neighbored N atoms around vacancy. The directions of magnetic moment in three neighbored N atoms around vacancy are different. Among them, ferromagnetic and anti-ferromagnetic coupling are coexisting. For the VN system, the total magnetic moment in the entire calculated supercell is also 1.00 μB and presents a certain distribution in the area around the vacancy.
2013, 62 (20): 203102. doi: 10.7498/aps.62.203102
The global and local activity of benzotrialole (BTA) and 2,5-Dimercapto-1,3,4-thiadiazole (DMTD) are calculated by density function theory. Thermodynamic properties of BTA and DMTD are simulated by molecular dynamics. The corrosion inhibition effect of mixed system inhibitor is studied through corrosion test. The results show that the inhibition efficiency of DMTD is larger than that of BTA. There are several active sites which focus on N and S atoms. So the inhibitors are absorbed on the surface of Cu in the parallel direction. The specific heat capacities of Cu absorbing inhibitor are the same as those without Cu adsorbing inhibitor at room temperature. The specific heat capacities increase with inhibitor increasing. They provide the reference for the selection of the inhibitor. The effect of mixed system inhibitor is better and the best mixed ratio is BTA: DMTD=1:1.
Synergistic effects in Fe/N codoped anatase TiO2 (101) surface：a theoretical study based on density functional theory calculation
2013, 62 (20): 203103. doi: 10.7498/aps.62.203103
The interaction between implanted nitrogen atom and transition metal iron at the anatase TiO2(101) surface is investigated by the periodic density functional theory calculations. Substitutional and interstitial configurations and formation energies for Fe-doping, and several N and Fe atom codopings at different sites of the (101) surface are considered. Our formation energy calculations suggest that when Fe atom transfers from surface to body, it is subjected to a larger energy barrier while asynergetic effect takes place between the nitrogen and the codoped Fe in the surface. The analyses of the electronic structure and densities of states show that the property of half-metallic appears, with N and Fe codoped.
2013, 62 (20): 203104. doi: 10.7498/aps.62.203104
The potential energy curve (PEC) of ground X2Π state of PS radical is studied using highly accurate internally contracted multireference configuration interaction approach with the Davidson modification. The Dunning’s correlation-consistent basis sets are used for the present study.To improve the quality of PECs, scalar relativistic and core-valence correlation corrections are considered. Scalar relativistic correction calculations are performed using the third-order Douglas-Kroll Hamiltonian approximation at the level of a cc-pV5Z basis set. Core-valence correlation corrections are calculated with an aug-cc-pCV5Z basis set. All the PECs are extrapolated to the complete basis set limit. Using the PEC, the spectroscopic parameters (Re, ωe, ωexe, ωeye, Be, αe and De) of the X2Π state of PS are determined and compared with those reported in the literature. With the Breit-Pauli operator, the PECs of two Ω states of the ground Λ-S state are calculated. Based on these PECs, the spectroscopic parameters (Te, Re, ωe, ωexe, ωeye, Be and αe) of two Ω states of PS are obtained. Compared with those reported in the literature, the present results are accurate. The vibration manifolds are evaluated for each Ω and Λ-S state of non-rotation PS radical by numerically solving the radical Schrödinger equation of nuclear motion. For each vibrational state, the vibrational level and inertial rotation constants are obtained, which are in excellent accordance with the experimental findings.
Up-conversion luminescence in Tm3+/Yb3+ Co-doped NaY(MoO4)2 phosphors by optimal design of experiments
2013, 62 (20): 203301. doi: 10.7498/aps.62.203301
The method of optimally designing experiments is introduced to study the properties of up-conversion luminescence in Tm3+/Yb3+ co-doped NaY(MoO4)2 phosphors. The design of experiment, data analysis and objective are all optimized. Uniform design is used to seek for the doping concentration range, and quadratic general rotary unitized design is included to build the equation between the luminescent intensity and the Tm3+/Yb3+doping concentration. In order to obtain the best luminescent intensity, genetic algorithm is introduced into our calculation. The optimal Tm3+/Yb3+ co-doped NaY(MoO4)2 phosphor is synthesized by high temperature solid state method. The up-conversion emission spectrum under the 980 nm laser excitation is detected and the luminescence mechanism is proposed. We observe intense blue light (476 nm) and week red light (649 nm) at room temperature, which are emitted from the Tm3+ transition of 1G4→3H6 and 1G4→3F4, respectively. In this up-conversion uminescence system, the up-conversion emission of 1G4 is due to the cooperation energy transfer of two photons. We also discuss the temperature effect of the sample, and as the temperature increases its luminescent intensity decreases.
Dynamical properties of Rydberg hydrogen atom interacting with a metal surface and an electric field
2013, 62 (20): 203401. doi: 10.7498/aps.62.203401
The dynamical properties of Rydberg hydrogen atom in an electric field near a metal surface are presented by analyzing the phase space. The dynamical behavior of the excited hydrogen atom depends sensitively on the atom-surface distance and the electric field strength. The evolutions of the Poincar surface of section and the electric orbit are analyzed for a certain atom-surface distance and different electric field strengths. The results indicate that the electric field accelerates the adsorption of electron. With the increase of the electric field strength, the controlling factor of dynamical behavior changes from the atom-surface distance to the electric field strength. As the electric field strength becomes very large, the system is integrable and all the electric orbits become vibrational type of orbits.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (20): 204101. doi: 10.7498/aps.62.204101
Regarding the forest as a mixture of air and plants, the refractive model is used to obtain the effective dielectric constant of forest, and the correctness is verified by comparing with the experimental result. The parabolic equation model of forest can be improved by introducing the method of effective dielectric constant for forest. Compared with the traditional model, the improved model takes into account the effect of various elements of forest on radio wave propagation and is more suitable for the radio propagation problems with different plant species in different regions. Otherwise the non-uniform mesh technique is introduced and improves the computational efficiency effectively. Finally, in this paper we analyze the effects of various elements of forest, such as the volume content of plant, the gravimetric moisture content, etc. on the radio propagation.
Fast analyses of electromagnetic scattering characteristics from conducting targets using improved and the adaptive cross approximation algorithm
2013, 62 (20): 204102. doi: 10.7498/aps.62.204102
Constructing characteristic basis functions (CBFs) is a key step of characteristic basis function method (CBFM). But it is required to set adequate plane wave excitations in each sub-block, which leads to the increased number of characteristic basis functions and the longer time consumed in singular value decomposition of traditional method. In order to accelerate the construction of CBFs, an improved CBFM is presented, which fully considers the mutual coupling effects among sub-blocks and then the secondary level characteristic basis function (SCBF) is obtained, therefore the number of plane wave excitations is reduced greatly, and so is the number of characteristic basis functions. The adaptive cross approximation algorithm is also used to accelerate the matrix-vector multiplication procedure of generating SCBF and constructing the reduced matrix. Numerical results demonstrate that the proposed method is accurate and efficient.
Design and implementation of sub-reflector for Ka band antenna based on quartz wafer coating technology
2013, 62 (20): 204103. doi: 10.7498/aps.62.204103
The design, fabrication and performance of a frequency selective surface (FSS) which is required to operate as broadband sub-reflector of Ka band antenna for satellite communication application is proposed and validated experimentally. In order to obtain this spatial filter which exhibits low insertion losses and insensitivities to the variation of oblique incident angle for TE and TM polarized wave, the mode-matching method is applied to the analysis of the geometrical structure and electrical parameters of FSS unit cell, and the fabrication process of this Ka FSS sub-reflector utilizing sophisticated quartz wafer coating technology is described. Electromagnetic field simulations and measurements results demonstrate that this FSS filter has virtually identical spectral responses in the two polarization planes.
2013, 62 (20): 204201. doi: 10.7498/aps.62.204201
A simulation method by air and space integrated fusion based on hyper-/multispectral imagery is proposed. The transformations of spectra, scale-space, radiative intensity, mixed pixel, noise are adopted in the simulation method on the basis of aviatic multispectral imagery according to parameters of space multispectral imagery, and certain ground objects in the aviatic hyperspectral imagery are mapped into the space multispectral imagery to obtain simulative space multispectral imagery for these ground objects through the simulation method. Experimental results demonstrate that the simulation method is effective and easy to implement; the heavy workload on model establishment of three-dimensional scene and sensor response is reduced in this simulation method; it is successful for the method to simulate space multispectral imagery of certain ground objects. A new domain on simulation method of remote sensing imagery is developed. This simulation method is valuable in research and application.
2013, 62 (20): 204202. doi: 10.7498/aps.62.204202
In compressive sensing, signal sparsity is an important parameter which influences the number of data sampling in reconstruction process and the quantity of the reconstructed result. But in practice, undersampled and oversampled phenomenon will occur because of the unknown sparsity, which may lose the advantages of compressive sensing. So how to determine the image sparsity quickly and accuratly is significant in the compressive sensing process. In this paper, we calculate the image sparsity based on the data acquired during compressive sensing recontruction projection which sparses the origin image in wavelets domain, but we find that its procession is complex, and the final results are seriously influenced by wavelet basis function and the transform scales. We then introduce the principle component analysis (PCA) theory combined with compressive sensing, and establish a linear relationship between image sparsity and coefficient founction variance based on the assumption that PCA is of approximately normal distribution. Multiple sets of experiment data verify the correctness of the linear relationship mentioned above. Through previous analysis and simulation, the sparsity estimation based on PCA has an important practical value for compressive sensing study.
Influence of recording parameters on particle field measurement by digital holographic microscopy：a numerical investigation
2013, 62 (20): 204203. doi: 10.7498/aps.62.204203
Digital holographic microscopy plays a key role in micro-fluid measurement,and appears to be a strong contender as the next-generation technology for diagnostics of three-dimensional (3D) particle field. However, various recording parameters, such as the recording distance, the particle size, the wavelength, the size of the CCD chip, the pixel size and the particle concentration, will affect the results of the reconstruction, and may even determine the success or failure of a measurement. In this paper, we numerically investigate the effects of particle concentration and the volume depth on reconstruction efficiency, to evaluate the capability of digital holographic microscopy. Standard particle holograms with all known recording parameters are numerically generated by using a common procedure based on Lorenz-Mie scattering theory. Reconstruction of those holograms are then performed by a wavelet-transform based method. Results show that on the premise that the value of volume depth is 24 μm, the reconstruction efficiency Ep decreases quickly until particle concentration reaches 6.89×105 mm-3, and decreases slowly with the increase of particle concentration from 6.89×105 mm-3 to 55.08×105 mm-3. And on the premise that the value of particle concentration is 13.77×105 mm-3, the reconstruction efficiency Ep decreases linearly with the increase of the volume depth. When shadow density is constant, the variance of the construction efficiency presents a certain regularity. When the volume depth is small, the effect of particle concentration on the reconstruction efficiency becomes larger than one of volume depth, while it comes to a completely opposite result with a larger volume depth.
2013, 62 (20): 204204. doi: 10.7498/aps.62.204204
The traditional opto-mechanical coupling in an opto-mechanical system is a linear coupling which is proportional to the field intensity I and oscillator displacement x. The nonlinear spatial coupling effect becomes obvious and important in a strong cavity field with large oscillating amplitude, and then the nonlinear effect with quadratic coupling in opt-mechanical device is also significant. In this article, we find that a general opto-mechanical system with quadratic coupling will produce a stable self-sustained oscillation when the energy injected by external driving equals that of dissipations in certain parametric regions. We numerically solve the semi-classical equation of motion of the system and find high-dimensional limit circles in its phase space under the control of driving and damping. We verify the high-dimensional limit circles by the closed orbits in all the projective three-dimensional phase space and show a highly controllable topological structure of the phase orbit which is very similar to Lissajous figures formed in a two-dimensional case. The self-sustained oscillations of the driving resonator with controllable amplitudes and frequencies demonstrate a reliable physical application of opto-mechanical system under quadratic coupling.
Thermally induced frequency difference characteristics of dual-frequency microchip laser used optical generation millimeter-wave
2013, 62 (20): 204205. doi: 10.7498/aps.62.204205
The thermal effect of laser diode end-pumped double longitudinal mode dual-frequency microchip laser on dual-frequency laser spectrum is investigated in detail. Through solving the heat conduction equation of isotropic material, a general expression of temperature field within Nd:YVO4 microchip crystal is obtained, then the thermally induced refractive index change of microchip laser is analyzed, and thus the thermally induced frequency difference change of dual-frequency microchip laser is calculated. According to the theoretical results, an experiment is designed. The experimental results show that with a small pumping power, astable doublelongitudinal mode dual-frequency is obtained; increasing the pumping power, the thermal effect of crystal makes the frequencydifference decrease gradually, and the width of each mode spectrum broaden. The experimental results are in good agreement with the theoretical analyses.
2013, 62 (20): 204206. doi: 10.7498/aps.62.204206
A kind of lead silicate photonic crystal fiber (PCF) is proposed in this paper. The dispersion characteristics of this SF57 PCF are studied by the finite element method. The reasults demonstrate that the PCF presents all-normal dispersion profiles in the visible and infrared spectral regions. We use an adaptive split-step Fourier method to study the propagations of the 1550 nm and 150 fs laser pulse in the PCF. The resulting spectral profiles are extremely flat from 1300 nm to 1900 nm and have excellent stabibities and coherence properties.
2013, 62 (20): 204207. doi: 10.7498/aps.62.204207
The chirped mirror (CM) pair is designed to provide group delay dispersion (GDD) of around-60 fs2 with bandwidth 500 nm at a central wavelength of 800 nm. The GDD oscillation decreases from 100 fs2 to 20 fs2. CM pair is fabricated using ion beam sputtering. The GDD is determined by using a white light interferometer. The measurement results show that the manufactured CM can meet our requirements. By balancing the extra-cavity dispersion with the fabricated chirped mirrors, the pulse 24-27 fs is compressed to 12 fs.
2013, 62 (20): 204208. doi: 10.7498/aps.62.204208
An array of periodic slits, combined with classic grid two-dimensional gratings, can acquire a dual band-pass characteristic in radar and optical wave band. The concentrated distribution of stray light energy will severely restrict the applications of classic composite film structure in high precision detection and imaging. To solve this problem, a novel composite film structure is developed in this paper, which is composed of slit elements and annular gratings. A scalar diffractive model is built based on Fraunhofer diffractive theory through contrasting the diffractive properties of two kinds of composite film structures. The theoretical simulations and experimental results both prove that the annular composite film structure can suppress the stray light effectively, for its higher transmittance, lower ratio and more uniform distribution of stray light, and enhance the reliability of composite film structure in the practical optical applications.
2013, 62 (20): 204301. doi: 10.7498/aps.62.204301
The propagation process of intense acoustic shock wave, generated by the discharge of underwater plasma sound source, is analyzed based on a modified Rayleigh model. The bunching sound field model of underwater plasma sound source is established by using the Euler equation as the control equations. The formation mechanism of the shock wave negative pressure is analyzed theoretically and intuitively through the sound field charts obtained by simulation. The results demonstrate that the water around the bunching wave will be stretched and form a zone of negative pressure with the combination of the rarefaction wave and the inertia of water. It will make the water form a discontinuous phenomenon if the stretching force is greater than the ultimate tensile strength of the water, the phenomenon of cavitation bubble will appear at this time. Besides that, negative pressure will be aggravated by the diffracted wave generated at the edge of the energy-gathered reflector, and the shock wave negative pressure will reach a maximum value by the superimposition of the edge diffraction wave and the stretch wave. The reasons for the formation of the shock wave negative pressure is testified and revealed further by comparing the waveforms of simulation and experiment. The study results provide a theoretical guide for understanding the propagation law of underwater shock wave and further improving the design of the underwater plasma sound source.
Acoustic band fracture variation of low frequency transmission zone in one-dimensional solid-fluid periodic structures under omnidirectional incidence
2013, 62 (20): 204302. doi: 10.7498/aps.62.204302
In order to study the characteristics of acoustic/elastic wave propagation in one-dimensional (1D) solid-fluid periodic structure incited by omnidirectional incidence, a theoretical model of wave propagation in 1D solid-fluid periodic structure is established using a transfer matrix method. Based on this model, the band structures of the infinite case and the transmission properties of the finite one are further calculated and analyzed. The results show that an acoustic band fracture appears in the low frequency transmission zone for a certain incident angle. The corresponding incident angle of the fracture is non-relevant to the mass densities or the thicknesses of the solid and fluid layers constituting the periodic structure, and determined only by the wave velocity of the constituent material.
2013, 62 (20): 204303. doi: 10.7498/aps.62.204303
The content of pollution gas in atmosphere is generally small, so the photoacoustic signal detected by photoacoustic spectroscopy to monitor is very weak. In this paper, on the basis of Holmes Duffing equation, we propose a new method i.e. variable scale difference method which is quite suitable for photoacoustic signal detection. This method can be used to detect weak signal by transforming the size of signal and then substracting the resulting signal. Theoretical analysis and experimental measurements show that it can well restrain the common-mode noise of system phase space, and it can also highlight the chaos state of critical value. This method has a relative error less than 5%, indicating that it can be effectively used to detect the amplitude of weak photoacoustic signal that has a higher frequency and unknown phase and frequency.
Starting from the thermodynamic framework of a mixture, granular solid hydrodynamics (GSH), which has been developed in recent years, is generalized to the cases in which water and/or gas are present in the interstitials of a granular solid. A preliminary model for the free energy of the mixture is proposed. The three-phase system of grains, water and air is a material relevant to soil mechanics and rock engineering, especially geological catastrophies, for which the macroscopic physics has not been clarified as yet. The engineering theory used currently for analyzing this mixture contains the Darcys law of intersticial flow, the effective stress by Terzaghi, including its equation of motion (i.e., the constitutive relation). Comparing it with the theory of GSH, we clarify that Darcys equation represents mass diffusion, and the effective stress can be explained by the specific model of free energy that is volumetric filling.The usual engineering approach and GSH, a theory based on physics, are consistent, but we do find some discrepancies, especially on how to parameterize the model: the engineering appraoch employs varying constitutive relation, but the physical approach considers the free energy and the transport coefficients. Clarifying this, we believe, is important for eventually obtaining a unified continuous mechanical theory of soils,especially nonsaturated ones, which is complete and satisfying from physicss point of view.
2013, 62 (20): 204701. doi: 10.7498/aps.62.204701
In this paper, based on the boundary element method, the cavitation shape of the three-dimensional slender at a small attack angle in a steady flow is simulated through the iterative method, while Dirichlet boundary conditions and Neumann boundary conditions are satisfied in cavitation and slender respectively. The linear triangular elements are adopted and the control points are arranged in grid nodes. The velocity potential for cavity surface is determined through an iterative method in a local orthogonal coordinate system, and then the distribution of cavitation thickness can be determined by the boundary integral equation. To prevent the remeshing operation in the iterative process, the Lagrange interpolation method is used to determine the thickness at the end of cavity. The numerical results are in good agreement with the experimental data. The influence of those on cavitation shape of the three-dimensional slender are investigated, such as cavitation number, attack angle and cone angle. Numerical results show that the cavitation shape of the three-dimensional slender is asymmetric at an attack angle and is analogous to the cavitation stacking in the lee side. While with the decrease in the cavity number or the increase in cone angle, the asymmetry for the cavity shape will be more serious.
2013, 62 (20): 204702. doi: 10.7498/aps.62.204702
Due to the complexity inside the drop after impact on solid surfaces and the interaction among gas, liquid and solid phases, it is difficult to investigate the shape variation of the drop through the theoretical analysis, and most studies have focused on experiments and numerical simulations. In this paper, expressions for empirical coefficients of inertia, viscosity and surface tension are acquired by analyzing the force state. The drop oscillation model after impact is built further. The expression of the drop spreading radius, and the effects of surface tension and viscosity on the spreading process are obtained. Finally, the correction factor in the drop oscillation model is determined and the feasibility of the model is verified by comparing the computational results with the numerical results.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (20): 205201. doi: 10.7498/aps.62.205201
The energy loss induced by electron collisions in weakly ionized air plasma is calculated based on the electron energy distribution function that we obtained. Since there are a lot of low-energy-threshold molecular rotation and vibration excitations and the electron-molecule energy transfer is inefficient in elastic collision, the fraction of energy loss for electron elastic collision (less than 6%) is negligible. Among different collision processes the electron energy loss is dominant in different energy regions. As the effective electron temperature (or the reduced electric field) increases, the dominant energy loss process becomes sequentially rotational excitation, vibrational excitation, electronic excitation, collisional ionization, and accelerating ionized electrons. When E/N=1350 Td (or Te=14 eV), the average energy loss per ion-electron pair reaches a minimum value of 57 eV. By controlling the electric field according to the requirement in applications, we can control the electric field to achieve a higher energy efficiency.
2013, 62 (20): 205202. doi: 10.7498/aps.62.205202
Air breakdown by perpendicularly intersecting high-power microwave (HPM) is investigated by numerical solution of fluid-based plasma equations coupled with the Maxwell equations. For two coherently intersecting HPM beams, collisional cascade breakdown takes place only when the initial free electrons appear in or arrive at a region of strong electric field, where the electron can be accelerated. At the initial stage of discharge, the filamentary plasma moves along the strong field and forms plasma-filament band. When the plasma-filament band grows long enough, in the vicinity of which the two HPM beams are separated due to its scattering and absorption by plasma. The new plasma-filament bands continue to appear as time increases. It is also found that under the same condition, the plasma region produced by incoherent beams is smaller than by coherent beams.
Effects of pulse temporal profile on electron bow-wave injection of electrons in laser-driven bubble acceleration
2013, 62 (20): 205203. doi: 10.7498/aps.62.205203
Effects of pulse temporal profile on electron injection and trapping in the electron bow-wave injection regime are investigated by two-dimensional particle-in-cell simulations. It is found that a positive skew pulse can enhance the wake-field amplitude, extends the accelerating aera, and improves the initial velocity of electrons injected into the bubble. Thus more energetic electrons are driven into the bubble accelerating phase. The total injection number for a positive skew pulse is higher than those of negative skew and usual Gaussian pulses in the same conditions, and the quality of electron beam is also improved. The obtained result is very important and beneficial for the future experimental investigation of the laser wake-field acceleration to obtain an energetic electron beam with a large charge quantity.
2013, 62 (20): 205204. doi: 10.7498/aps.62.205204
X-ray radiation with an average flux of 1.3×107 photons·sr-1·s-1 is generated by the interaction between ultra-short laser and solid target working at 1 kHz repetition rate. A knife edge is introduced to measure the source size. The X-ray emission shows obvious dependences on the laser contrast and intensity. It is discovered that at lower intensity the Kα yield increases with lower laser contrast. However, by using high contrast and high intensity laser pulses, high flux and high signal-to-noise ratio Kα X-ray can be generated. The generated source is used in proof-of-principle radiograghic imaging of simple specimens.
2013, 62 (20): 205205. doi: 10.7498/aps.62.205205
In this paper, the effect of electron temperature on the characteristics of plasma sheath in the channel of Hall thruster is studied by using two-dimensional (2D) particle-in-cell simulation method. The change laws of electron number density, sheath potential, electric field and secondary electron emission coefficient at different electron temperatures are discussed. The results show that when the electron temperature is low, electron number density decreases exponentially in the radial direction and reaches a minimum at the wall, the sheath potential drops and variation of electric field in the radial direction is larger, and the wall potential stays at a stable value, the stability of sheath is better. However, when the electron temperature is high, the electron number density inside the sheath region approximates to that at the sheath boundary, but in a narrow area near the wall it increases rapidly and reaches a maximum at the wall, sheath potential changes slowly, the sheath potential drops and variation of electric field in the radial direction is smaller, and the wall potential tends to maintain a persistent oscillation and the stability of sheath is reduced. The influence of electron temperature on electric field in the axial direction is small. With the increase of the electron temperature, wall secondary electron emission coefficient increases in the early stage, and reduces later.
2013, 62 (20): 205206. doi: 10.7498/aps.62.205206
In the direct drive, since the target is becoming smaller in compression process, the initial focal spot will no longer match the compressed target, leading to large losses of energy from target edge. Optical zooming means making the focal spot smaller when the target compresses. In this way, the coupling efficiency between the beam and target can be improved. It has great significance. The primary problem of solving the optical zooming is the qualification of small focal spot. According to the full-band optical transmission rules, in this paper constructed are low and medium-high frequency wavefront distortion sources under different smoothing conditions, and then given is a scaling relation between wavefront and focal spot size. The scaling relation can be regarded as a wavefront criterion of small focal spot. Using this wavefront criterion, the correction range of low and medium-high frequency wavefront distortion can be known to achieve a small focal spot.
The full three-dimensional electromagnetic PIC/MCC numerical algorithm research of Penning ion source discharge
2013, 62 (20): 205207. doi: 10.7498/aps.62.205207
In this article, we study the physical mechanism of the Penning discharge, develop a full three-dimensional particle simulation software of high-quality algorithm (PIC), design and add the corresponding physical scenario of Monte Carlo collisions (MCC) module, and track electron, hydrogen molecular ion (H2+), hydrogen positive ion (H+), and tri-n-hydrogen ion (H3+) at the same time, and successfully develop a full three-dimensional electromagnetic PIC/MCC numerical algorithm. Combined with the Penning discharge model extensively studied in china, the algorithm is verified through simulation. The simulation results show that the use of effective filtering algorithm can suppress the electromagnetic numerical noise. Electron energy is of Maxwell distribution. Due to the radial drift and accelerate of electrons, the H2+ yield is larger at the top of the ion source.
2013, 62 (20): 205208. doi: 10.7498/aps.62.205208
In this article we use phase resolved optical emission spectroscopy to study emission pattern in plasma sheath of dual frequency capacitively coupled plasma in Ar and Ar-O2 discharge. Two emission patterns are found in sheath region of radio frequency coupled powered electrode. The first pattern is related to electron impact excitation because of the sheath expansion. The second pattern is caused by electron impact excitation of secondary electrons. Two emission patterns are also highly modulated with the low frequency cycle. Under the condition of argon discharge, the emission intensities of the two excitation processes are very similar. The emission structure by secondary electrons becomes weak with the increase of O2 content in the gas mixture. In addition, we also use phase resolved optical emission spectroscopy to study low frequency cycle averaged axial emission profile of excited atomic argon at 751 nm in Ar-O2 mixture gas. Distance from the powered electrode (about 3.8 mm) is defined as the boundary sheath of dual frequency capacitively coupled plasma.
2013, 62 (20): 205209. doi: 10.7498/aps.62.205209
In order to investigate the validity of the scale-down experiment on gas discharge, the discharge in argon at low pressure is numerically simulated with scale-down discharge gap based on the conjecture of discharge similarity that if the product of gas pressure p and gap length d is kept constant, p1d1=p2d2, and the spatial distributions of the reduced field E/p along these two gaps are the same, the gas discharges in these two discharge gaps would be similar. In the simulation, three scale-down discharge gaps are used. Gap A is 30 mm long and works at a pressure of 1 Torr (1 Torr=133.322 Pa). Gap B is 15 mm long at 2 Torr and gap C 10 mm long at 3 Torr. The results show that the discharges in these three gaps are glow discharges with a cathode fall layer. The values of thickness of the cathode fall layer, dC, for gaps A, B and C are 2.71 mm, 1.35 mm and 0.87 mm, respectively, which corresponds to more or less the same value of pdC≈2.70 Torr·mm that is close to the lowest point of Paschen curve of argon where pd≈2.86 Torr·mm. The proportionalities of the parameters (working voltage, electric field, current density, electron density and ion density) between the discharges in the scale-down gaps are found to be in good agreement with those determined by the discharge similarity. It is concluded that the conjecture of discharge similarity is correct for the glow discharge in argon in the scale-down gap.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (20): 206101. doi: 10.7498/aps.62.206101
The two-dimensional, single-layer MoS2 with a direct band-gap of 1.8 eV, which makes it very suitable for nanoelectronic applications, such as field-effect transistors, has aroused great interest because of its distinctive electronic, optical, and catalytic properties. In this paper, we present a detailed theoretical study of the electronic transport property of single-layer MoS2 on the basis of the usual momentum-balance equation. We obtain the analytical electric mobility at low temperature. It shows that the electric mobility of MoS2 is linear with respect to substrate dielectric constant squared and the rate between the electron density and charged impurity density at low temperature. It is found that by using relatively high dielectric constant materials as substrates, reducing impurity densities and increasing carrier densities high mobilities in MoS2-substrate wafer systems can be achieved.
The study of oxygen and sulfur adsorption on the InSb (110) surface, using first-principle energy calculations
2013, 62 (20): 206102. doi: 10.7498/aps.62.206102
In this paper, we analyze the difference between oxygen and sulfur adsorption on the InSb (110) surface by using the first-principles energy calculations. The merits of sulfur adsorption are demonstrated theoretically. Thus the reason why the sulfur passivation that is necessary in technology can be well explained.
2013, 62 (20): 206201. doi: 10.7498/aps.62.206201
The wetting process and the wetting state transition stages are studied on hydrophilic rough surfaces covered with microscale pillar arrays of different geometrical morphologies and distributions. The effects of geometrical morphology, distribution, parameters, hydrophilicity, and contact angle hysteresis of pillar arrays on wetting state transition are analyzed by an energy method. The results indicate that on the hydrophilic rough surface covered with hexagonal arrays of square pillars, the water droplet tends to stay in a stable Cassie state, or the wetting state transits only from a Cassie state to an intermediate state. Moreover, smaller pillar interval, larger square pillar width or diameter of cylinder, higher pillar height, strong hydrophilicity are beneficial to the stability of Cassie state, therefore, the wetting state could be prevented from transforming to pseudo-Wenzel state or Wenzel state. However, smaller area fraction of solid-liquid interface under the water drop and weaker hydrophilicity is beneficial to increasing the apparent contact angle. Therefore, the stability of wetting state and the large apparent contact angle should be considered in hydrophilic surface design. The contact angle hysteresis gives rise to an opposite effect on wetting state stability and the hydrophobicity or superhydrophobicity of rough solid surface. The results provide a theoretical foundation for designing the substrates covered with hydrophilic rough structures, on which the water droplet will obtain a stable Cassie state.
2013, 62 (20): 206801. doi: 10.7498/aps.62.206801
In this paper, we investigate the effect of annealing conditions on the characteristic of Ni/Au Ohmic contact to p-GaN. The specific contact resistivities under different annealing temperature and different annealing atmosphere are tested using the circular transmission line model. It is found that the best annealing temperature is about 500 ℃. The annealing atmosphere of nitrogen-oxygen gas mixture can lead to lower specific contact resistivity than that of pure nitrogen, and the specific contact resistivity has no relationship with the content of oxygen. Finally, we obtain the lowest specific contact resistivity to be 7.65×10-4 Ω·cm2 at the best annealing temperature and atmosphere.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (20): 207101. doi: 10.7498/aps.62.207101
By using the first-principles method based on the density-functional theory, electrical and magnetic properties of graphene nanoribbons (GNRs) with the BN-chain doping are systematically studied. For the zigzag-edge graphene nanoribbon (ZGNR), its multispin-state properties: spin-unpolarized non-magnetism (NM) state, spin-polarized ferromagnetic (FM), and anti-ferromagnetic (AFM) states, are considered. The emphasis on our investigations is the effect of doping position for a single BN-chain. It is found that the BN-chain doping armchair-edge graphene nanoribbon (AGNR) has an increase in bandgap and becomes semiconductors with various different bandgaps upon the doping positions. When the ZGNR at the NM state is doped by the BN-chain, its metallic property is weakened, and the quasi-metallic property can also occur. The BN-chain doping ZGNR at the AFM state makes it change from a semiconductor to a metal or half-metal, depending on doping positions. And the BN-chain doping ZGNR at the FM state always keeps its metallic property unchanged regardless of the doping positions. These results indicate that the BN-chain doping can effectively modulate the electronic structure to form abundant electrical and magnetic properties for GNRs. It is of important significance for developing various kinds of nanodevices based on GNRs.
Non-classical energy state and quantum tunnling coherence dissipation for the two-state system with the spin coupled to the lattice phonon
2013, 62 (20): 207201. doi: 10.7498/aps.62.207201
Including the spin-two-phonon interaction, for the two-state tunneling system with the spin coupled to the lattice phonon (i.e., spin-lattice phonon coupling model) at a finite temperature, the non-classical energy state and the quantum coherence dissipation are studied by the expansion approach of the correlated squeezed-coherent state of phonon. To restrain the quantum coherence loss caused by the Debye-Waller’s coherent scattering of the particle spin by the coherent phonons, the non-classical correlation effects are used in our research with the special consideration of the spin-two-phonon interaction, i.e., 1) the particle spin-displaced phonon state correlation; 2) the process coherence between the one-phonon coherent state and the phonon squeezed state which originates from the squeezed-coherent state of phonon; 3) the renormalization of the phonon displacement. We find the new phenomena that the phonon squeezed state is enhanced significantly due to the particle spin-two phonon interaction, in particular, at the same time the effects of the squeezed coherent state and the representation correlation will be essentially increased. Therefore, the striking decline in the quantum tunneling (Δ0σx) and the serious quantum coherence loss by the Debye-Waller coherent scattering are restricted more noticeably, as a result, the energy of the non-classical state for the two-level system with spin coupled to the lattice phonon is much lower.
Quick analysis of miniaturized-element frequency selective surface that loaded with lumped elements by using an equivalent circuit model
2013, 62 (20): 207301. doi: 10.7498/aps.62.207301
In order to quicken the pace of the frequency selective surface (FSS) design and optimization, an equivalent circuit method is used to analyze the miniaturized-element FSS structure loaded with lumped elements. According to the physical structure of the FSS, an equivalent circuit model is established. These parameters values of the equivalent circuit model are obtained by a curve-fitting process using ADS to obtain the best fitting between the circuit response and the full-wave analysis response. The fitting accuracy is improved by increasing the curve frequency and the extrema. By using the circuit model, the frequency responses of the FSS at different LC values of lumped components are obtained. The transmissions at center frequencies calculated by the circuit model are slight higher than the exact results from the full-wave analysis, and the relative errors between the center frequencies and the –3 dB bandwidths are smaller than 10%. This paper proves that it is feasible to analyze the complex FSS structure by the equivalent circuit model based on curve-fitting process. It will give some references to the quick design and optimization of the FSS.
Comparison bwtween intrinsic and interfacial electrical pulse induced resistance effects in La0.5Ca0.5MnO3 ceramics
2013, 62 (20): 207302. doi: 10.7498/aps.62.207302
In general, the electrical pulse induced resistance (EPIR) effect of perovskite manganite originates from the interfacial Schottky barrier between the metal electrode and the surface of sample. In this work, La0.5Ca0.5MnO3 (LCMO) ceramic samples are synthesized by solid state reaction and the transport properties, especially the EPIR effect are investigated using 4-wire measurement mode. Although the I-V curve of LCMO shows ohmic linearity under the 4-wire measurement mode at room temperature, a stable and remarkable EPIR effect can still be observed when the pulse voltage is more than the critical value. Through the comparison between the intrinsic EPIR under 4-wire mode and the interface one under 2-wire mode, we find that the intrinsic EPIR of LCMO has a smaller critical pulse voltage to induce the effect, but it has a better anti-fatigue property. The intrinsic EPIR effect is a novel one which is observed in rare earth doped manganites.
2013, 62 (20): 207303. doi: 10.7498/aps.62.207303
The δ-doped GaAs/AlxGa1-xAs 2DEG samples are grown with molecular beam epitaxy. In this process, the doping concentration (Nd), spatial isolation layer thickness (Wd) and Al component of AlxGa1-xAs (xAl) are changed separately. Then Hall measurements on the samples are made in the two temperature conditions (300 and 78 K). According to the test results, the relationships of Nd, Wd and xAl to the carrier density and mobility of GaAs/AlxGa1-xAs 2DEG are discussed respectively. The δ-doped GaAs/AlxGa1-xAs 2DEG with embedded InAs quantum dot samples are grown, and InAs quantum dots with different densities are grown with gradient growth method. The Hall measurement results show that the mobility of GaAs/AlxGa1-xAs 2DEG greatly decreases with density of InAs quantum dots steadily increasing. In experiments, the lowest density of 16×108/cm2 InAs quantum dot sample is obtained. The experimental results can provide a reference for the study and application of δ-doped GaAs/AlxGa1-xAs 2DEG with embedded InAs quantum dots.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (20): 208101. doi: 10.7498/aps.62.208101
In this paper, the processing parameters of growing GaN epilayer by hydride vapor phase epitaxy are optimized. The influences of the low-temperature (LT) nucleation layer growth time, V/Ⅲ precursor ratio and the growth temperature on GaN layer are investigated by the high-resolution X-ray diffraction (HRXRD) signature for the asymmetric and symmetric reflections. The investigation finds that the LT-nucleation layer not only supplies the nucleation centers having good crystal quality, but also promotes the lateral growth of the sequent high temperature (HT) growth. The optimal LT nucleation layer growth time, V/Ⅲ precursor ratio and the growth temperature can effectively enhance lateral growth to reduce the crystal defects and are favorable to converting the growth mechanism from three-dimension to two-dimension in HT growth. The structural and optoelectronic properties of the as-grown GaN layer with a thickness of 15 μat the optimal parameters are studied by scanning electron microcopy, atomic force microscopy (AFM), HRXRD, Raman spectra, and photoluminescence (PL) measurements. X-ray rocking curves show that the full widths at half maximum of (002) and (102) are 317 and 343 arcsec, respectively. The surface roughness (rms: root mean square) is 0.334 nm detected using AFM. These characteristics show that the sample has good lattice quality and smooth surface morphology. In PL spectrum, the near band edge emission is dominated by emission from excitons bound to neutral donors (D0X) near 3.478 eV with 11 meV blue-shift and the yellow band emission is very weak. The results indicate that the GaN layer has good crystal quality and excellent optoelectronic properties, but a little biaxial in-plane compressive strain also exists in it due to the lattice and thermal mismatch.
Preparation of W-doped VO2/FTO composite thin films by DC magnetron sputtering and characterization analyses of the films
2013, 62 (20): 208102. doi: 10.7498/aps.62.208102
In order to obtain low phase transition temperature and superior thermochromic optical material, W-doped VO2/FTO composite thin films are prepared by depositing metallic vanadium on FTO (F:SnO2) conductive glass substrate in argon atmosphere at room temperature and then annealed in air ambient. XPS, XRD and SEM are used for analyzing the structures and surface morphologies of the films. The results indicate that no mixed oxides of V, W and F are produced during high-temperature thermal oxidation. W is doped by replacing V atoms. Compared with the pure VO2/FTO composite thin film prepared using the same process, the crystal orientation of W-doped VO2 thin film is not changed and still retains preferred crystal orientation in the (110) direction. The phase transition temperature drops down to about 35 ℃, and the thermal hysteresis loop narrows to 4 ℃. The variation of IR transmittance between the high temperature and the low temperature reaches 28%. SEM results show that the crystallinity of the thin film is improved significantly, showing smooth, compact and uniform surface morphology. This brings about many new opportunities for optoelectronic devices and industrial production.
2013, 62 (20): 208103. doi: 10.7498/aps.62.208103
In this paper, we present the simulation and experimental validation of an ultra-thin planar metamaterial absorber, which is composed of Jerusalem crosses loaded by interdigital capacitors. By increasing the coupling capacitance between adjacent unit cells, we are able to significantly lower the operating frequency of the absorber. The measured results indicate that the metamaterial absorber achieves a peak absorption of 88.48% at 1.58 GHz. The total thickness and the unit cell size of the absorber are 2 mm and 11 mm, which are approximately 1/95 and 1/17 of the working wavelength, respectively. Additionally, the Jerusalem crosses and the metallic ground plane are connected by vias, which makes the metamaterial absorber achieve wide-angle absorption for both transverse electric and transverse magnetic polarizations electromagnetic wave. The absorptivity is still large even at the incident angle of 60°, and the frequency of the absorption peak almost has no deviation, which makes the absorber more practical.
2013, 62 (20): 208104. doi: 10.7498/aps.62.208104
Tungsten oxide nanowire has a great potential application to gas sensor with high sensitivity and low power consumption. Its gas-sensing properties can be greatly improved after doping the nanowires. In this paper, vanadium (V)-doped W18O49 nanowires are synthesized by solvothermal method, with WCl6 serving as precursor and NH4VO3 as dopant. The microstructures of the pure and the doped nanowires are characterized by using SEM, TEM, XRD, and XPS techniques, and the NO2-sensing properties are evaluated in a static gas-sensing measurement system. The obtained results indicate that the introduction of V dopant suppresses the growth of one-dimensional nanowires along their axis direction and causes the secondary assembly of nanowires bundles. At room temperature, the V-doped W18O49 nanowires show an abnormal p-type response characteristic upon being exposed to NO2 gas, and a conductivity transition from p-to n-type occurs when operating temperature is raised to about 110 ℃. The doped nanowires-based sensor exhibits obvious sensitivity and good response stability to dilute NO2 gas of 80 ppb at room temperature. The origin for the p-n conductivity transition and the high sensitivity at room temperature for the V-doped W18O49 nanowires are analyzed, and they can be attributed to the strong surface adsorption of oxygen and NO2 molecules due to the large density of unstable surface states.
2013, 62 (20): 208105. doi: 10.7498/aps.62.208105
Sulfur metal-organic complex Pb(S2CNEt2)2 is synthesized with Pb(NO3)2 and Na(S2CNEt2)·3H2O as reactants in deionized water. Under the protection of argon, PbS quantum dots are synthesized by pyrolysis of the precursor Pb(S2CNEt2)2 in oleic and octadecene mixed solution. Four samples a, b, c, and d of PbS quantum dots are synthesized on the condition that the reaction times are 30, 60, 90, and120 min, respectively. Infrared spectrum of the precursor Pb(S2CNEt2)2 shows that two sulfur atoms of the ligand Na(S2CNEt2)·3H2O have successfully coordinated with Pb2+. X-ray powder diffraction and transmission electron microscopy results show that the PbS nano crystals are of pure cubic phase structure, and are well-dispersed spherical particles. UV-visible absorption spectrum and photoluminescence spectra of PbS quantum dots show that absorption spectrum and photoluminescence spectra both have red-shift along with reaction time extending. This indicates that absorption spectrum and photoluminescence spectra can be modulated by optimizing the thermal decomposition reaction time. The emission peak of sample is located at 1080 nm, which is matched to the silicon solar cell. It can be used as the fluorescent material of silicon luminescent solar concentrator.
Influence of high magnetic fields on phase transition and solidification microstructure in Mn-Sb peritectic alloy
2013, 62 (20): 208106. doi: 10.7498/aps.62.208106
In recent years, the application of high magnetic field in material processing has received much attention from many researchers. However, most studies focus on single-phase solidification or eutectic solidification. The effect of high magnetic field on peritectic alloy is rarely reported. In this study, the solidification experiments on a Mn-56.5 wt%Sb peritectic alloy are carried out under high magnetic fields up to 11.5 T. According to the temperature curve recorded during solidification, it is revealed that high magnetic field increases the liquidus temperature and this rise increases with magnetic flux density increasing. The liquidus temperature rises by about 3 ℃ when the magnetic flux density is 11.5 T. On the contrary, no obvious change in peritectic temperature is found. In addition, the solidified microstructure is analyzed by quantitative metallographic analysis and the result shows that the amount of MnSb phase decreases markedly by the application of high magnetic field. This result consists with the change of phase transition temperature. By the X-ray diffraction, it is found that the c axis of MnSb crystal and (311) plane of Mn2Sb are perpendicular and parallel to the direction of high magnetic field,respectively. Furthermore, the solidification experiments with different cooling rates are also carried out. The quantitative metallographic analysis reveals that the effect of high magnetic field on solidified microstructure is affected by cooling rate. With the increase in cooling rate, the effect of high magnetic field on the fraction of MnSb phase fraction is weakened.
2013, 62 (20): 208201. doi: 10.7498/aps.62.208201
In order to study the mechanism of the profile evolution process, a three-dimensional (3D) profile evolution method based on compression representation is proposed to simulate the plasma etching process and consider emphatically ion etching. To solve the problem of large memory requirements of 3D cellular model, the presented method adopts a new data structure, which combines two-dimensional array with dynamic storage, to represent cellular information. The structure realizes the lossless compression of cellular information and keeps the spatial correlation between 3D cells. The experimental results show that the method not only significantly reduces the memory, but also has a higher searching efficiency of surface cell which ion first passes through in high-resolution simulation. The method is applied to 3D profile evolution simulation of silicon etching process. A comparison between the simulation results and the experimental results also verifies the effectiveness of the proposed method.
2013, 62 (20): 208202. doi: 10.7498/aps.62.208202
ReaxFF/lg reactive force field is the extention of ReaxFF by adding a van der Waals attraction term. It can be used to well describe density and structure of crystal, moreover, the macroscopic property of detonation is significantly influenced by the density of energetic material. We report on the initial thermal decomposition of condensed phase CL20-TNT cocrystal under high temperature here. The time evolution curve of the potential energy can be described reasonably well by a single exponential function from which we obtain the initial equilibration and induction time, overall characteristic time of pyrolysis. Afterward, we also obtain the activation energy Ea (185.052 kJ/mol) from these simulations. All the CL20 molecules are completed before TNT decomposition in our simulations. And as the temperature rises, the TNT decomposition rate is significantly accelerated. The higher the temperature at which complete decomposition occurs, the closer to each other the times needed for CL20 and TNT to be completely decomposed will be. Product identification analysis with the limited time steps shows that the main products are NO2, NO, CO2, N2, H2O, HON, HNO3. C–NO2 and N–NO2 bond homolysis jointly contribute to the results of the NO2. The NO2 yield rapid increases to the peak and then decreases subsequently. This process is accompanied with NO2 participating in other reactions so that the N atom of NO2 enters into the other N-containing molecule. Secondary products are mainly CO, N2O, N2O5, CHO. N2O has a strong oxidation ability, so that the distribution has a dramatic fluctuation characteristics.
A Colpitts chaotic oscillator based on metal oxide semiconductor transistors and its synchronizaiton research
2013, 62 (20): 208401. doi: 10.7498/aps.62.208401
A Colpitts chaotic oscillator is proposed by replacing the bipolar transistor with metal oxide semiconductor (MOS) transistor. Through a series of variable transformations, a state model of proposed circuit similar to one of traditional Colpitts oscillators with bipolar transistors is established. The system parameters are easily obtained by matching the two similar models. Indexes of the balance point show that chaos mechanisms of the two structures are not the same. After the process of parameter inversion and scaling transformation, the detailed circuit parameters are determined. Chaotic attractor and chaotic signal frequency diagrams are generated on PSpice platform. The simulations show that the proposed structure can work under low voltage and can generate chaotic signal with high frequency. Finally, using the linear error feedback method, a synchronization of two identical chaotic circuits is achieved.
Mode-matching analytic method of a coaxial Bragg structure corrugated with rectangular ripples and its experimental verification
2013, 62 (20): 208402. doi: 10.7498/aps.62.208402
Based on the mode-matching method, an analytical model with full-wave coupling is presented for the coaxial Bragg structures corrugated with rectangular ripples, where the expressions of the reflectivity and transmission rate for each involved mode are derived. The validity of the analytical model is examined in terms of a reported experiment, and good agreement between the theoretical results and the experimental measurements is demonstrated. Comparative study is carried out between the present model and the published theoretical results. It is found that the approximate treatment adopted by the previous model leads to notable deviation of the transmission response curve due to the neglect of the evanescent modes excited by rectangular ripples. The analytical method presented in this paper can be expected to provide a useful approach to the characteristic investigation and engineering practice of the coaxial Bragg structures with rectangular ripples.
Numerical simulation of single-event-transient effects on ultra-thin-body fully-depleted silicon-on-insulator transistor based on 22 nm process node
2013, 62 (20): 208501. doi: 10.7498/aps.62.208501
Single-event-transient response of 22-nm technology ultra-thin-body fully-depleted silicon-on-insulator transistor is examined by technology computer-aided design numerical simulation. The influences of ground plane doping, heavy ion injection location, gate work function and substrate bias on single-event-transient characteristic are systematically studied and analyzed. Simulation results show that the influences of ground plane doping and quantum effects on single-event-transient (SET) are relatively small. The SET characteristics and collected charge are strike-location sensitive. The most SET-sensitive region in ultra-thin-body fully-depleted silicon-on-insulator transistor is located near the drain region. When gate work function varies from 4.3 eV to 4.65 eV, the transient current peak is reduced from 564 μA to 509 μA and the collected charge decreases from 4.57 fC to 3.97 fC. The transient current peak is strongly affected by substrate bias. In contrast, the total collected charge depends only weakly on substrate bias.
Relations between traversal time in ferromagnetic/semiconductor(insulator)/ferromagnetic heterojunction and the relative magnetic moment angle in two ferromagnetic layers
2013, 62 (20): 208502. doi: 10.7498/aps.62.208502
Based on the concept of group velocity, the relations between traversal time of spin-polarized electrons in ferromagnetic/semiconductor(insulator)/ferromagnetic heterojunction and relative magnetic moment angle in two ferromagnetic layers are studied. The results show that when the middle layer is semiconductor layer, influenced by the Rashba spin-orbit coupling, the minimum transverse times difference between the spin-up and down electrons can appear if the relative angle values in two ferromagnetic layers are nearly the π/2 and 3π/2, respectively. When the middle layer is insulator, the transverse time difference between the different spin orientations can be varied with the potential barrier heights and flip if the height exceeds a critical value.
2013, 62 (20): 208701. doi: 10.7498/aps.62.208701
With the continuous development of medical imaging technology, medical image processing has played an increasingly prominent role in computer-aided diagnosis and disease management. Kidney segmentation in abdominal computed tomography (CT) sequences is a key step. In this paper, combining with the contextual property of renal tissues, a new energy minimization model based on active contour and graph cuts is proposed for kidney extraction in CT sequence. According to the relationship between the shape difference in adjacent slices and corresponding layer thickness, the optimal search range of the contour evolution is calculated for graph cut optimization. The energy function, combining the geodesic active contour with Chan-Vese model, takes into account the boundary and regional information. Then, graph cut methods are used to optimize the discrete energy function and drive the active contour towards object boundaries. Thirty abdominal CT sequences are used to evaluate the accuracy and effectiveness of the proposed algorithm. The experimental results reveal that this approach can extract renal tissues in CT sequences effectively and the average Dice coefficient reaches about 93.7%.
2013, 62 (20): 208702. doi: 10.7498/aps.62.208702
Optical tweezers technology is widely used to trap and manipulate particles, and the trapping mechanism generally accepted by researchers is due to the action of photophoretic force. In this paper, infrared microscopic observation of absorbing particles trapped in gaseous medium is first achieved. When the laser power is about 1.0 W, the temperature of trapped toner particles (diameter is about 7 μm) and toluidine blue particles (diameter is from 1 μm to 20 μm) rises by about 14 K, which provides strong evidence for the photophoretic force mechanism. In addition, the periodic oscillation of trapped particles is first observed by both optical microscope and infrared microscope, and the oscillation principle is analyzed.
2013, 62 (20): 208703. doi: 10.7498/aps.62.208703
Diffusion anisotropy indices (DAIs) are parameters derived from diffusion tensor imaging (DTI) data which describe the morphological characteristics of diffusion tensor within a specific range. DAIs are the measurements used to quantitatively describe the diffusion direction and strength of the hydrone in vivo, so that DAIs enable one to indirectly probe the internal structure of an imaging subject. The reliability of DAIs is of great importance for the analysis and interpretation of DTI data. Based on the geometric characteristic of the diffusion tensor ellipsoid, we propose a new DAI, the ellipsoidal geometric ratio (EGR), to describe the hydrone diffusion anisotropy property. The analysis results of Monte Carlo simulation and human brain DTI data show that the EGR has better contrast and robustness than fractional anisotropy, the most commonly used DAI, and ellipsoidal area ratio at different noise levels. Furthermore, since EGR makes full use of the ellipsoidal volume information, it is more robust than any other DAIs in the fiber crossing case. EGR may be a superior measure of diffusion anisotropy both in quantifying deep white matter with relatively high anisotropy and pericortical white matter with relatively low anisotropy.
2013, 62 (20): 208801. doi: 10.7498/aps.62.208801
In this paper, we study hydrogenated amorphous silicon germanium thin film solar cells prepared by the radio frequency plasma-enhanced chemical vapor deposition. In the light of the inherent characteristics of hydrogenated amorphous silicon germanium material, the modulation of the germanium/silicon ratio in silicon germanium alloys can separately control open circuit voltage (Voc) and short circuit current density (Jsc) of a-SiGe:H thin film solar cells. By the structural design of band gap profiling in the amorphous silicon germanium intrinsic layer, hydrogenated amorphous silicon germanium thin film solar cells, which can be used efficiently as the component cell of multi-junction solar cells, are obtained.
2013, 62 (20): 208901. doi: 10.7498/aps.62.208901
Mobile phone data record the people’s communication behaviors in detail, and become an important resource for studying people’s social relationships and behavior patterns. The call numbers, call volumes and call durations are the basic properties of the mobile phone data network. Based on the theory of complex networks and the statistic method, studied in this paper are the degree distribution and average values of the call numbers, call volumes, call durations, by using the mobile phone call data of different holidays and workdays and different scales of day and period, which are produced by the 3.3 million subscribers registered in a western city in China. Research shows that at all scales the number degrees, volume degrees and duration degrees are all of power-law distribution, and the power exponents are different depending on the scale, date and index, and fluctuate from 1.3 to 4. In general, the number degree exponent is greater than that of the volume degree and duration degree, and the exponents of three indexes of in-degree are greater than those exponents of out-degree; the exponents in holidays are greater than those of the workdays, and the exponents in working periods are greater than those of non-working periods. Compared with in workdays, in holidays the average number degree and volume degree are small, and the average duration degree is large. It reveals that most of the subscribers call only one number in a day or a period, and the call numbers, call volumes and call durations all decrease on holidays or working periods, however the average call duration increases meanwhile.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Effects of clouds and precipitation disturbance on the surface radiation budget and energy balance over loess plateau semi-arid grassland in China
2013, 62 (20): 209201. doi: 10.7498/aps.62.209201
The feedback effect of land surface radiation budget and energy distribution on land-atmosphere system is one of the most important physical processes in climate models. Studying the effects of disturbance of cloud and precipitation on radiation budget and energy distribution is a crucial link to increase the parameterization effect of evaluating land surface radiation budget and energy balance in numerical models. Based on the data observed at the Semi-Arid Climate and Environment Observatory of Lanzhou University in 2008, the weakening influences of disturbance of cloud and precipitation on components in radiation budget and on land surface energy balance are studied. The annual average results showed that cloudy situation could be thought of as climatic background of annual average; weakening influences of cloud and precipitation on short-wave radiation are the strongest, and atmospheric long-wave radiation increases while surface long-wave radiation decreases with cloud amount increasing; the influences of cloud and precipitation on the ratio of net radiation to global radiation is small. The seasonal average results show that daily integral value of short-wave radiation decreases with cloud amount increasing both in growing season and in non-growing season, and weakening influences of cloud and precipitation on short-wave radiation in growing season are obviously stronger than in non-growing season. In growing season, there is no substantial difference among surface long-wave radiations on clear days, partly cloudy days and cloudy days, and atmospheric and surface long-wave radiation decrease apparently on overcast days. In non-growing season, the influences of cloud and precipitation on surface long-wave radiation are smaller, and its daily integral value changes a little, and atmospheric long-wave radiation increases with cloud amount increasing. The surface albedo has obvious diurnal and seasonal variation characteristics and it is higher in winter than in autumn; the diurnal variation curves of albedo present unsymmetrical “V” shapes. In growing season, sensible heat flux and soil heat flux decreased along with cloud amount increasing; latent heat flux increases with cloud amount increasing on clear, partly cloudy and cloudy days; due to the precipitation on obscure days, latent heat flux decreases greatly because net radiation is seriously weakened. In non-growing season, daily integral value of net radiation is greatest on partly cloudy days, and net radiation on clear days is very close to it on cloudy and overcast days; sensible and latent heat flux decreases with cloud amount increasing, average daily integral value of soil heat flux is negative in non-growing season. In growing season, energy closure degree on cloudy days is best, and imbalance energy accounts for 3.9% of net energy; energy closure degree on overcast days is worst, and imbalance energy accounts for 16.8% of net energy; imbalance energy accounts for 7% of net energy under both clear and partly cloud situations. Due to snow effect in non-growing season, energy closure degree in non-growing season is greater obviously than it in growing season.
2013, 62 (20): 209401. doi: 10.7498/aps.62.209401
As one of important and effective means for modifying the ionosphere, releases of neutral gases including H2O, CO2, H2, SF6, etc. can produce artificial ionospheric holes. In this paper, the ionospheric disturbances produced under various release conditions, including use of different release species (H2O and SF6), different release altitudes, and different amounts of released substance, are investigated based on an improved three-dimensional chemical release dynamics model which includes neutral gas diffusion, chemical reaction and the ambipolar diffusion of the plasma. The effects of release altitudes and release amount on ionospheric disturbances, morphology and the dynamics of ionospheric hole are studied. Furthermore, the results are also briefly discussed.
2013, 62 (20): 209701. doi: 10.7498/aps.62.209701
In order to improve the de-noising effect of the pulsar signal, an empirical mode decomposition (EMD) denoising algorithm based on the prediction of noise mode cell is put forward. The core steps of the proposed method is as follows: firstly, the noisy pulsar signal is decomposed into a group intrinsic mode function (IMF) by EMD, and the noise mode cell is predicted according to the IMF coefficients statistics and local minimum mean square error criteria. The selected noise mode cells are set to be zero. Then the IMF which has been processed according to noise mode cell prediction is denoised by optimal mode cell proportion shrinking, for removing the noise and retaining the signal details. The experimental results show that compared with the Sure Shrink wavelet threshold algorithm, Bayes Shrink wavelet threshold algorithm and the EMD mode cell proportion shrinking algorithm, the proposed method performs well in removing the pulsar signal noise and retaining the signal details information. The proposed method can achieve a higher signal-to-noise, the lower root mean square error, error of the peak position, relative error of the peak value and phase error.