Vol. 63, No. 17 (2014)
2014-09-05
GENERAL
2014, 63 (17): 170202.
doi: 10.7498/aps.63.170202
Abstract +
This paper studies the Noether symmetry and Mei symmetry of a discrete holonomic mechanical system with variable mass. Firstly, by the difference discrete variation approach, the discrete equations of motion of the system are established. Secondly, the definitions of Noether symmetry and Mei symmetry are given, and the conditions under which the Noether conserved quantity can be induced by Noether symmetry and Mei symmetry are obtained. Finally, an example is discussed to illustrate these results.
2014, 63 (17): 170201.
doi: 10.7498/aps.63.170201
Abstract +
For an existing network and in limited link addition resources, it is a valuable task to determine optimally the new link resources such that the resulting network is the most robust and efficient. In this paper, we investigate the modeling and analysing of network topological reconfiguration optimization with limited link addition (NTRLA). The network survivability metric is proposed to quantitatively characterize the robustness and efficiency of a network. To approximately solve the NTRLA problem, a heuristic algorithm based on the preferential configuration of enhanced node-protecting cycles (PCNC) is proposed. Simulation results show that the PCNC method can effectively improve the network robustness and communication efficiency at the cost of the least added link resources under either random or targeted attack.
2014, 63 (17): 170301.
doi: 10.7498/aps.63.170301
Abstract +
Method of moments (MOM) is a common numerical method for solving electromagnetics, which is used widely owing to its high accuracy. As the traditional MOM is applied to solving electromagnetic problem in both spatial and frequency domains, the matrix equation generated from the integral equation must be solved repeatedly since small spatial increments and frequency increments are both required. To resolve problems of this kind, the compressive sensing (CS) theory combined with the asymptotic waveform evaluation (AWE) is introduced to form a new efficient computational method. Firstly, a new incident source is constructed based on CS theory, in which much spatial information is included. Secondly, illuminated by the new incident source, the new equation is solved by AWE technique, and finally a fast implement is formed for solving electromagnetic scattering characteristics in both spatial and frequency domains.
2014, 63 (17): 170302.
doi: 10.7498/aps.63.170302
Abstract +
Fisher information is an important concept in estimation theory, which has recently been found closely related with the criteria of the entanglement in quantum information. Under the condition of non-rotating wave approximation, the classical phase space of the Dicke model displays chaotic dynamic properties. This paper studies the quantum Fisher information and the dynamic properties of spin squeezing in the interaction system of light and matter described in the Dicke model. Results reveal that, in the short-time instant state, wherever the initial state is, in a regular region or a chaotic region, the system displays entanglement; but in the long-time stable state, when the initial state is in the regular region, the system entanglement disappears, however, when the initial state is in the chaotic region, the system is always entangled. Compared with the spin-squeezing dynamic properties of the system, Fisher information is found to be able to effectively characterize quantum chaos. On further examination on the dynamic evolvement properties of the density matrix and purity of the system when in the regular and chaotic regions, we find that chaos gives rise to decoherence of the system, showing that quantum information become more sensitive to chaos.
2014, 63 (17): 170701.
doi: 10.7498/aps.63.170701
Abstract +
A novel design of X-ray spectrometer is implemented, using a high efficiency HOPG (highly oriented pyrolitic graphite) Bragg crystal. The spectral resolution of it can reach above 350 with energy ranging from 6.891 to 9.193 keV, theoretically. And the efficiency are 3 order of magnitude higher than the ordinary X-ray crystal spectrometer. Application of this instrument is demonstrated in high intensity laser-foil interaction experiments. It is shown that HOPG spectrometer has much lower threshold of X-ray intensity than ordinary one. The spectral resolution for 8.048 keV (Cu Kup -line) can reach 40 eV, which gives the spectral resolution 200.
2014, 63 (17): 170204.
doi: 10.7498/aps.63.170204
Abstract +
A class of nonlinear generalized Duffing equation for disturbed oscillator is considered. Firstly, the typical Duffing equation is solved. Then approximate solutions to the nonlinear Duffing equation for disturbed oscillators in stochastic resonance is obtained using the generalized functional variation principle, and the uniform validity is proved.
2014, 63 (17): 170203.
doi: 10.7498/aps.63.170203
Abstract +
According to the advantages of nonuniformly sampled bivariate empirical mode decomposition and the characteristics of noise after it, an adaptive chaotic signal denoising method is proposed based on the noise-assisted nonuniformly sampled bivariate empirical mode decomposition. Firstly, a complex signal is constructed for the noise-assisted nonuniformly sampled bivariate empirical mode decomposition, by using noisy chaotic signal and gaussian white noise as the real part and imaginary part respectively; secondly, the noise energy of each intrinsic mode function in the real part is estimated according to the energy of each intrinsic mode function in the imaginary part; and finally, from the above results, each intrinsic mode function in the real part is denoised by using the singular value decomposition. Noise energy estimate numerical experiment validates the feasibility of this method, and the denoising tests for Lorenz signal and monthly sunspot data indicate that our method shows advantages in both noise reduction and chaotic attractor topological configuration reversion.
2014, 63 (17): 170205.
doi: 10.7498/aps.63.170205
Abstract +
In this paper, finite-time stability and stabilization of switched singular systems are studied. Firstly, we discuss the solvability condition of the switched singular system and introduce the concepts of finite-time stability and finite-time boundness. Secondly, using the mode-dependent average dwell time method and the Lyapunov function method, we provide sufficient conditions to guarantee that the switched singular system is regular, impulse free, and finite-time stable or finite-time bounded. Then, we design the state feedback controllers to ensure that a closed-loop system is finite-time stable and finite-time bounded with a present H disturbance attenuation level . Finally, numerical examples are given to verify the efficiency of the proposed theory.
2014, 63 (17): 170501.
doi: 10.7498/aps.63.170501
Abstract +
By defining the characteristic length, the boundary effects of Bose-Einstein condensation in a three-dimensional harmonic trap are investigated using the Euler-MacLaurin formula. Results show that the condensed fraction of particles reduces due to the finite-size effects and the effects of finite particle number; the corrections of the condensation fraction and the condensation temperature have, respectively, a maximum value due to the boundary effect, hence it is very effective to optimize the parameters of the harmonic traps for improving the condensation fraction and the condensation temperature. In the jump of heat capacity exist the boundary effects and the effects of finite particle number, and the jump of heat capacity has a minimum because the parameters of harmonic traps are selected to be reasonable. The equation of state is derived for a finite ideal Bose gas system in a three-dimensional harmonic trap; the anisotropy (or isotropy) of the pressure is determined by the anisotropy (or isotropy) of the frequency of the harmonic potential.
2014, 63 (17): 170502.
doi: 10.7498/aps.63.170502
Abstract +
We have studied two probability potentials of a collinear oscillator atom chain and developed a Langevin dynamics approach for calculation. In the case of the harmonic chains, results of the Monte Carlo simulations are compared with the analytical solutions to verify the validity of this approach. In the case of 4-times coupled oscillator chains, the results of numerical simulations are used to the calculation of Hamiltonian. Then the system's energy distribution and the Maxwell-Boltzmann distribution are compared, and found to be in agreement with each other.
2014, 63 (17): 170508.
doi: 10.7498/aps.63.170508
Abstract +
Performance of a generalized Redlich-Kwong gas Stirling heat engine is investigated, in which the multi-irreversibilities including thermal resistance, regenerative and heat leak losses are taken into account. General expressions for power output and efficiency of the Stirling heat engine are derived, and effects of the nonperfect regeneration and some important performance parameters such as the volume ratio and the temperature ratio are analyzed and discussed. Moreover, it is shown that the efficiency of the gas Stirling heat engine with perfect regeneration and no heat leak can reach that of the Carnot heat engine.
2014, 63 (17): 170503.
doi: 10.7498/aps.63.170503
Abstract +
A discrete iterative map model of valley V2 controlled Boost converter is established, based on which the bifurcation diagrams are obtained with the variation of input voltage, output capacitance and its equivalent series resistance (ESR). Jacobi matrix at a fixed point is also derived, and according to it, the converter stability is analyzed using characteristic values and maximum Lyapunov exponent, thus the correctness of bifurcation analysis is validated. The effect of input voltage, output capacitance and its ESR on the dynamic characteristics of valley V2 controlled Boost converter is mainly investigated. It is found that as the input voltage increases continuously, the valley V2 controlled Boost converter changes from continuous conduction mode (CCM) period-1 to CCM period-2 due to period-doubling bifurcation, and comes into CCM chaos due to border collision bifurcation. The converter has the same bifurcation routes at output capacitance and its ESR: with gradual reduction of output capacitance or its ESR, the valley V2 controlled Boost converter behaves the evolutive dynamic behavior from CCM period-1 to CCM period-2, CCM period-4, CCM period-8, and CCM chaos. Finally, the simulation and experimental circuits are set up, and the correctness of theoretical analysis is verified by simulation and experimental results.
2014, 63 (17): 170509.
doi: 10.7498/aps.63.170509
Abstract +
We have studied the chaotic escape of particles in a two-dimensional weakly opened mesoscopic components of the Bunimovich Stadium devices. Within the framework of classical statistics, we get the change of the fractal dimensions and the escape rates in several parameters of the device, such as the opening width, the arc radius and the cavity length. We first find the good agreement between the fractal dimensions and the escape rates, and reveal that the exponential law of escape is affected by the shape of device. We count and fit the relationship between the escape rates and the wave numbers of the particles. As is shown in the numerical results, the relation between the escape rates and the wave numbers is a quadratic function, but the escape rates are not strictly linearly varied with the change of the energy. Furthermore, we analyze the influence of diffraction at the lead opening on the escape of the particles. Numerical results show that the diffraction effect makes the escape rates increase, and the evolution of the number of particles no longer obeys the law of exponential decay in a short time, but observes it again in a long time.
2014, 63 (17): 170504.
doi: 10.7498/aps.63.170504
Abstract +
The steady-state problems of a tristable system are studied under the action of color correlated multiplicative and additive colored noise. Firstly, the expression of the steady-state probability density function is derived based on the uniform colored noise approximation, and then the change regulation of the steady-state probability density function is analyzed with the change of the strength and relevance of multiplicative noise and additive noise. Results show that the non-equilibrium phase transition of the system can be induced by the correlation strength and time of additive noise and multiplicative noise as well as the additive noise strength.
2014, 63 (17): 170505.
doi: 10.7498/aps.63.170505
Abstract +
Variations of the geomagnetic field drive geomagnetically induced currents (GIC) in the buried steel pipelines, which may contribute to the pipeline corrosion and the pipeline network interfered by the solar wind and magnetic storm, are actually a complex nonlinear dynamical system. This paper shows that the induced current in the buried steel pipeline system has chaotic characteristics. To prove this, we first establish the lump-constant geomagnetic interference model based on the distributed source transmission line theory. Then we analyze this model by using Melnikov method and find out the condition under which the chaotic phenomenon will occur. In order to get a sufficient proof to validate the existence of chaos in pipelines, we also obtain the actual GIC time series by utilizing the measured data provided by national geomagnetic observatory and analyze its chaotic characteristics using multiple chaotic criteria. Analysis results of both the model and the measured data indicate that the pipeline's GICs have chaotic characteristics. This provides a theoretical basis for protecting pipeline from the effects of space weather.
2014, 63 (17): 170506.
doi: 10.7498/aps.63.170506
Abstract +
A wireless sensor network in practice often suffers from environment damage and energy depletion. In order to solve the problem, this paper establishes a comprehensive fault model first. Then according to the demand for comprehensive fault tolerance ability and network lifetime, a relationship between the network node degree and the maximum node degree is obtained. And the relational expression between the two kinds of node degrees derived from the scale-free characteristics is acquired. Thus the optimal maximum node degree can be solved. Finally, based on the fitness function for the maximum node degree introduced, a scale-free fault tolerant topology evolution model is put forwarded which can effectively tolerate comprehensive fault. Simulation results show that the scale-free topology obtained has strong fault tolerance for environment damage and energy depletion. And it also can effectively prolong the network lifetime.
2014, 63 (17): 170507.
doi: 10.7498/aps.63.170507
Abstract +
As a kind of ultra-efficient thermal energy harvesting cell, thermal concentrator has recently attracted great attention from researchers. An analytical expression which describes the temperature distribution in the concentrator is deduced from the heat conduction equation and coordinate transformation relations. The expression is validated by numerical experiments based on COMSOL. Influence of the anisotropy due to cladding and device geometry on the performance of the thermal concentrator is analyzed. It is demonstrated that the greater the anisotropy, the better the thermal concentration effect. Besides, increasing the aspect ratio between the cladding and the core radius also gives rise to a better performance. Based on the temperature distribution relations between the core and the background region, we further explore a method to practically realize such a thermal concentrator by using naturally available materials. It is suggested that different levels of thermal concentration can be achieved by arranging alternately two isotropic conductivities along the azimuth direction and tuning their thermal localizations respectively.
Measurement of device-independent quantum key distribution for the rotation invariant photonic state
2014, 63 (17): 170303.
doi: 10.7498/aps.63.170303
Abstract +
The original measurement of device-independent(MDI)quantum key distribution(QKD) is reviewed, and a modified protocol using rotation-invariant photonic state is proposed. Initial encoding and final decoding of information in our MDI-QKD implementation protocol can be conveniently performed in the polarization space, while the transmission is done in the rotation-invariant hybrid space. Our analysis indicates that both the secure key rate and transmission distance can be improved by our modified protocol owing to its lower error rate. Furthermore, our hybrid polarization-OAM qubits approach only needs to insert four q-plates in a practical experiment, and our simulation results show that the modified protocol is practical.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (17): 177301.
doi: 10.7498/aps.63.177301
Abstract +
The hybrid quantum dot (QD) electroluminescent devices are fabricated by mixing every two kinds of QDs in the red, green, blue three types of QDs in a ratio 1:1, which are based on the structure of ITO/PEDOT:PSS/QDs/Al. In the systematical investigation of the electroluminescent spectrum, when the voltage increases, we find that the luminance intensity of the controlling devices continues to grow, while the hybrid QD devices first increase then decrease, showing that there is an energy transfer in the hybrid QD devices. And we also obtain the relationships among the energy transfer efficiency, the critical energy transfer distance, the donor-acceptor distance, and the electric field.
2014, 63 (17): 177101.
doi: 10.7498/aps.63.177101
Abstract +
The energies and binding energies of the bound polarons in a wurtzite In0.19Ga0.81N/GaN quantum well are investigated by means of a modified Lee-Low-Pines variational method. Contributions of ground state binding energies and different branches of a longwave optical phonon mode to the energies and binding energies of the bound polarons as a function of the well width and impurity center position are given. Effects of the anisotropy of phonon frequency and built-in electric field in the system on the energies and binding energies, and the electron and impurity center-optical phonon interaction, are included in the calculations. Results show that the contributions of optical phonons and built-in electric field to the ground state energy and binding energy of the bound polarons in a wurtzite In0.19Ga0.81N/GaN quantum well are very large, and result in the reduction of energy and binding energy. The binding energy decreases monotonically with increasing well width, and the speed of decrease is fast in the narrower well while the speed of decrease is slow in the wider well. Contributions of different branches of phonons to the energies and binding energies as a function of well width are different. In the narrower well, contributions of the confined phonon (withoud built-in electric field) are smaller than those of the interface and half-space phonons, while in the wider well, contributions of the confined phonons are larger than those of the interface and half-space phonons. Contributions of the confined phonon (with built-in electric field) become larger, whereas those of the interface and half-space phonons become smaller, and the total contribution of phonons also have obvious change. Contributions of these optical phonons to the ground state energies and binding energies of the bound polarons in In0.19Ga0.81N/GaN quantum wells are larger than the corresponding values (about 3.11.6 meV and 1.50.3 meV) of those in GaAs/Al0.19Ga0.81As quantum wells. The binding energies in In0.19Ga0.81N/GaN quantum wells decrease monotonically with increasing location Z0 of the impurity center for a constant well width d =8 nm, and the decrease of speed becomes faster. As the position of the impurity center is increasing, the contributions of the the interface and half-space phonons decrease slowly, and those of the confined phonons increase slowly as well.
2014, 63 (17): 177201.
doi: 10.7498/aps.63.177201
Abstract +
Based on semiconductor physics and the essential structure of insulated gate bipolar transistor (IGBT), the model of dV_{CE}/\d t is established through reasonable simplification and theoretical derivation. The influencing factors and temperature characteristics of dV_{CE}/\d t are studied in depth. It is concluded that dV_{CE}/\d t increases linearity with the increase of voltage or current, and decreases with the increase of junction temperature also linearly. On the basis of the model for dV_{CE}/\d t, the prediction model of junction temperature is established. Results of simulations and experiments verify the correctness and accuracy of the models. It is significant in theory and practical application for realizing IGBT junction temperature monitoring on-line and improving the reliability of IGBT module and power electronic equipment.
2014, 63 (17): 177401.
doi: 10.7498/aps.63.177401
Abstract +
Mg-doped Sn-based single crystalline samples Ba8Ga16-XMgXSn30(0 X 1.5) were grown from Sn flux to characterize their structural and electrical transport properties. Research results show that the prepared compounds are well indexed by the type-Ⅷ clathrate structure with a space group I43 m. With the increase in Mg content, the melting point of the corresponding compounds increases. On the contrary, the lattice constant decreases. The actual content of filling atomic Ba in doped samples is below the ideal value of 8.0, the occupancy of Ba in the dodecahedron is about 0.93 for the sample with X=1.5. All the samples show n-type conduction. The Mg atoms have an effect on the band structure of the materials, and the carrier concentrations in the doped samples are reduced. However, the absolute values of Seebeck coefficient and the resistivity of doped compounds increase, respectively. By calculation, the sample of X=1.5 obtains the maximum value of power factor 1.2610-3 Wm-1K-2 near 430 K.
EDITOR'S SUGGESTION
2014, 63 (17): 177402.
doi: 10.7498/aps.63.177402
Abstract +
Starting with the mean field Dirac-Bogoliubov-de-Gennes model and the Bolonder-Tinkham-Klapwijk formalism, we study the transport properties of a graphene ferromagnet-insulator-superconductor junction by taking into account the effect of the finite width of the insulating region. The tunneling conductance oscillations as a function of the bias energy are revealed together with a non-monotonic behavior for the exchange field in the ferromagnet layer. These phenomena, which are quite different from those in the conventional counterparts, are understood by examining the electron scattering processes associated with the unique dispersion-relation of the graphene junctions.
2014, 63 (17): 177501.
doi: 10.7498/aps.63.177501
Abstract +
Relations between the spin-Hamiltonian (SH) parameters including the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), the Zeeman g-factors: g//, g, g(=g//-g) and the structural parameters of ZnGa2O4:Fe3+ crystals have been established by means of the microscopic spin Hamiltonian theory and Newman's crystal field (CF) superposition model. On the basis of this, the SH parameters for Fe3+ magnetic ions in ZnGa2O4:Fe3+ crystals are investigated theoretically using the CFA/MSH (crystal field analysis/microscopic spin-Hamiltonian) software based on the full configuration complete diagonalization method. It is found that the theoretically calculated parameters including the ZFS parameters D, (a-F), and the Zeeman g-factors: g//, g, g(=g//-g) for ZnGa2O4:Fe3 + crystals are in good agreement with experimental data when taking into account the lattice distortions: R=0.0487 nm and =0.192. This investigation reveals that there is a slight local structure distortion due to Fe3 + ions in ZnGa2O4:Fe3+ crystals, but the site of Fe3+ still retains D3d symmetry. On the other hand, it is found for Fe3+ ions in ZnGa2O4:Fe3+ crystals that the contribution to the SH parameters from the spin-orbit (SO) mechanism is the most important one, whereas the contributions to the SH parameters from other four mechanisms, including the spin-spin (SS), spin-other-orbit (SOO), orbit-orbit (OO), and SO-SS-SOO-OO mechanisms, are small.
2014, 63 (17): 177701.
doi: 10.7498/aps.63.177701
Abstract +
Growth property of electrical treeing is an important parameter to evaluate the insulation performance of a polymer. The complex non-uniform state of aggregation structure determines the electrical treeing growth in polypropylene (PP), a typical semi-crystalline polymer. In this paper, the electric treeing resistance property experiments for PP as well as the PP sample with nucleating agents are carried out. Effects of crystal shape, crystallinity, and crystalline structure on the electrical treeing growth characteristics in PP and PP with nucleating agents have been analyzed using polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Thermodynamic and dynamic mechanisms of electrical treeing propagation are represented respectively by the thermodynamically driven action of phase interfacial free energy and the discharge-avalanche theory, demonstrating the essential role of electric field distribution in electrical treeing growth. According to physical properties of crystalline phase and amorphous phase in semi-crystalline materials, a computational model of interior electric field distribution has been established to simulate local electric field distribution in the polymer material under needle-plate electrode configuration, and used to analyze the characteristics of electrical treeing channel growing along the grain boundary in semi-crystalline materials. Inhibition effects of crystalline structure changed due to the nucleating agents on electrical treeing growth along the electric field direction are investigated.
2014, 63 (17): 177801.
doi: 10.7498/aps.63.177801
Abstract +
Diffraction imaging spectrometer cannot acquire imaging spectral data without calculation and inversion. In this paper, the imaging process of the diffraction imaging spectrometer and the principle of the data error from both space and spectra are analyzed. To solve the problems of low definition of the reconstruction and the ringing in it occurring under the condition that the point spread function (PSF) is larger, a new algorithm is proposed based on improved inverse Wiener filtering. The improved method regards the reconstruction result of Wiener filtering as a new fuzzy image, and recalculates the PSF of the new fuzzy image based on the analysis of the diffraction characteristics and error. Inverse iterative Wiener filtering is used to improve the definition of the reconstruction, and then the noise needs to be removed according to the distribution of the spatial and spectral features. Simulated diffraction imaging spectral data are used to verify the correctness of the algorithm proposed in this paper. A reconstruction without ringing can be obtained when the standard deviation of PSF is 2.5, and both of the definition and detail ability are higher than those of the traditional reconstruction. The reconstruction using the improved algorithm proposed in this paper can satisfy the applications of the diffraction imaging spectral data.
2014, 63 (17): 177802.
doi: 10.7498/aps.63.177802
Abstract +
Micro-cavities play an important role in the light-matter interaction. The cross section of wurtzite-structured ZnO microwire is a hexagon, which gives a high quality factor. Exciton-polariton, micro-and nanowire lasers and polariton condensation have been investigated using the micro-cavities of ZnO microwires at room temperature. Strain, which changes the dielectric index of a material, is one of the methods to tune the interaction between the light and the matter. In this work, the photoluminescence spectra of strain free and bent ZnO microwires are measured across the wires, and the modes shifts are observed only in the bent one near the band edge. Shifting of the cavity modes across the wire can be observed in both TE and TM polarized spectra. For a bent ZnO microwire, the microcavity can be modified by the strain from bending, and the exciton energies may shift due to the strain. The shifted exciton energy induces a change of dielectric constant, resulting in the shifting of the cavity modes across the microwire.
2014, 63 (17): 177803.
doi: 10.7498/aps.63.177803
Abstract +
On the basis of Lee-Low-Pines unitary transformation, the properties of strong-coupling magnetopolarons in quantum disks (QDs) induced by the Rashba spin-orbit interaction are studied using the Tokuda improved linearly combined operator method. Results show that the state properties of magnetopolarons are closely linked with the sign of the interaction energy Eint, and the Eint of magnetopolarons changes with the transverse confinement strength 0, the cyclotron frequency of the external magnetic field c, the electron-LO phonon coupling strength , and the thickness L of QDs. The average number N of phonons increases with increasing c, 0 and , but the oscillation decreases with increasing thickness L of QDs. The effective mass m0* of magnetopolarons splits into two (m+*, m-*), induced by the Rashba spin-orbit interaction, and the values of them increase with increasing c, 0 and , but the oscillation decreases with increasing thickness L of QDs. For the ground state of magnetopolarons in QDs, the electron-LO phonon interaction plays a significant role, meanwhile, the Rashba spin-orbit coupling effect cannot be ignored. Only for the lower volocity of the electrons, can the polaron effect and the Rashba spin-orbit interaction effect on the magnetopolaron be obvious.
2014, 63 (17): 177302.
doi: 10.7498/aps.63.177302
Abstract +
Low-voltage (current) driven electroluminescence (EL) has been achieved in the light-emitting device (LED) with a SnO2/p+-Si heterostructure, which is formed by sputtering SnO2 film on a p+-Si substrate, followed by annealing at 800 ℃ in O2 ambient. Furthermore, by means of capping a TiO2 film onto the SnO2 film, the modified LED exhibits significantly enhanced EL. The densification of SnO2 film as a result of the TiO2-capping is responsible for reducing the non-radiative centers. Moreover, the large refractive index and appropriate thickness of TiO2-capped layer are favorable for the extraction of emitted light from SnO2 film. Such two effects of TiO2-capping contribute to the aforementioned enhanced EL.
2014, 63 (17): 177303.
doi: 10.7498/aps.63.177303
Abstract +
Influences of gas incident angle () on surface morphology and microstructure of hydrogenated amorphous silicon (a-Si:H) thin films are investigated, which were grown using an oblique angle hot wire chemical vapor deposition (OAD-HWCVD) technique. An exponential relationship between the tan and RMS roughness is observed. The film surface morphology transforms from a self-affine surface into a mounded surface when the incident angle is larger than a critical angle c(60 c 75). Influences of on the microstructural properties of silicon thin films are characterized using Raman scattering and FT-IR measurements. As c, owing to the qusai-local shadowing effect, increasing increases the quantity and size of micro-voids, leading to the decrease of film density and quality. For c, the nonlocal shadowing effect causes the formation of large voids or cracks and the proportion of multi-hydride (SiHn, n 2) increases. Combined with the scaling theory, the relationship between the shadowing effect and the surface morphologies and microstructures of amorphous silicon thin films is discussed.
2014, 63 (17): 177304.
doi: 10.7498/aps.63.177304
Abstract +
The ground structure of Si60 clusters, which was obtained by optimization when using the density functional theory method, is a fullerene structure with C1 point group, a diameter 1.131 nm, the average bond length 0.239 nm, and the difference between the energies of the lowest unoccupied molecular orbital and the highest occupied molecular orbital is 0.72 eV. A Si60 cluster with optimized structure is sandwiched between two semi-infinite Au(100)-44 electrodes, and the Au-Si60-Au molecular junctions is constructed, whose electron transport properties is investigated with a combination of density functional theory and non-equilibrium Green's function method. When the distance between the two electrodes is 1.74 nm, the equilibrium conductance of the junctions is 1.93 G0 (G0=2e2/h). In the range of voltage from -2.02.0 V, we have calculated the current and conductance under different voltages, and find that the Ⅰ-Ⅴ curve of the junctions show linear characteristics. We also analyze the properties of transport from transmission and frontier molecular orbitals, and discuss the relationship of transfer charge with conductance.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (17): 174201.
doi: 10.7498/aps.63.174201
Abstract +
A rate equation model is established to describe the threshold characteristics of a diode-pumped Cs vapor laser in this paper. With the help of the numerical solution for the model, the influences of several parameters (waist position and waist radius of pump laser, length of vapor cell, and operating temperature) on the threshold pump power are analyzed. Results show that there are optimal values of the pump waist position and radius, vapor cell length and operating temperature to ensure a lowest threshold pump power. Besides, the decrease of divergence angle can reduce threshold pump power effectively. Simulation results are in good agreement with the experimental data. It is shown that the model can be used to reveal the threshold characteristics of diode-pumped alkali vapor laser and may serve as a theoretical guidance for the optimization design of this laser.
2014, 63 (17): 174101.
doi: 10.7498/aps.63.174101
Abstract +
In this paper, an ultra-thinspiral-structured metamaterial absorber is demonstrated both numerically and experimentally, whose thickness (1.034 mm) is about (1/60th, 1/44th, 1/32th, 1/23th, 1/21th) of the respective working wavelengths (4.81, 6.59, 9.16, 12.69 and 13.71 GHz). Simulation results show that the absorber can achieve absorption up to 94.41%, 99.89%, 99.73%, 99.26% and 99.41% at 4.81, 6.59, 9.16, 12.69 and 13.71 GHz respectively. Thus multi-band absorptions are realized. From the two aspects of surface current and power loss density, the mechanism of strong absorption is analyzed. Theoretical analysis shows that the multi-band absorption arises from multi-order plasmon resonances at five neighboring frequencies. Strong absorptions are induced due to strong electric resonances within/between the spiral structures. Design of the metamaterial absorber is simple and is easy to be implemented, so such absorbers may have application values in designing novel electromagnetic absorbers.
2014, 63 (17): 174202.
doi: 10.7498/aps.63.174202
Abstract +
Recently, studies by Jure Grgic et al. (Phys. Rev. Lett. 108 183903, 2012) show that in a periodic structure, the large gain can be eventually turned to decreasing the effect of slow light on the structure. In this paper, one-dimensional periodic structures are taken as an instance, and the influences of gain on slow light are further investigated. It is shown that different influences can exhibit in the finite-length and infinite-length one-dimensional periodic structures. For the infinite-length structures, the addition of gain can decrease the slow light effect, whereas for finite-lengh structures, the compensation of gain can, to a certain degree, increase the slow light effect. Our results verify a feasible way in the application of such a periodic structure, as a slow-light device, and especially as the tunable slow-light devices, in the high-density integration of optical circuits.
2014, 63 (17): 174701.
doi: 10.7498/aps.63.174701
Abstract +
A gas-liquid-solid three-phase coupling dynamic model is established using lattice Boltzmann method (LBM). Interaction between rising bubble and complex solid walls at the same scale is studied. Firstly, based on the viscous fluid theory, a group of lattice Boltzmann equations are developed to describe the gas-liquid two-phase campaign by considering the viscosity, surface tension, and gravity in the form of a LB discrete body force. At the same time, combined with the finite difference scheme, the half-way bounce back model in LBM is adopted to deal with the solid boundary condition. Then, under the conditions of different feature size ratios, the coupling characteristics between bubbles and plane wall, taking into consideration the effect of boundaries and curved wall, are studied using the newly built model. Results show that both the solid wall condition and the feature size ratio have significant nonlinear effects on bubble movement and topology changes. Finally, the effect of fluid properties on the coupling regularity of bubbles and complex walls is researched.
2014, 63 (17): 174502.
doi: 10.7498/aps.63.174502
Abstract +
The dynamic equation of a nonlinear relative rotation system with a triple-well Mathieu-Duffing oscillator is investigated. Firstly, a codimension three-bifurcation characteristic is deduced by combining with the multi-scale method and singularity theory under the condition of nonautonomy. Secondly, the threshold value of chaos about Smale horseshoe commutation is given from Melnikov method. Finally, the numerical simulation exhibits safe basins and chaos, and the erosion process of safe basins, which is closely related to the process, leading to chaos.
EDITOR'S SUGGESTION
2014, 63 (17): 174203.
doi: 10.7498/aps.63.174203
Abstract +
In order to improve the inversion precision of CO2 lidar, the fine structure in CO2 absorption spectrum (at around 1.572 m) has been detected accurately, with tunable diode laser absorption spectroscopy (TDLAS) technique in a double beam differential system. Differences between absorption spectra were analyzed. The five kinds of pressure-broadened coefficients and absorption cross sections are obtained respectively at 287, 297, 311, 315 and 324 K. The temperature-dependent exponents of CO2 are also calculated, these parameters would be a series of corrections and supplements for the existing database. These results may help improve the detection capability of CO2 lidar.
2014, 63 (17): 174501.
doi: 10.7498/aps.63.174501
Abstract +
The influence of friction coefficient, in terms of fixed static friction coefficient (sfc) and different rolling friction coefficients (rfc), on the accumulation characteristics of particle, including the angle of repose and accumulation body, is simulated using the discrete element method. The sfc of a particle is measured with a home-made cant instrument, and a linear equation is developed to describe the relationship between the rfc and the angle of repose. Results show that rfc has obviously an influence on the accumulation characteristics of particles: the angle of repose of particles increases as rfc increases, the gap between the boundary circle and the continuous circle decreases with increasing rfc. Based on the change of rotational kinetic energy in the process of accumulation of particles, the above results can be explained. And the linear equation can provide ideas for numerical measure of granular rfc. For some difficultly measured parameters of bulk materials, the simulation of accumulation process is a valid virtual calibration test.
2014, 63 (17): 174204.
doi: 10.7498/aps.63.174204
Abstract +
Transmission of light waves at the frequency near the edge of the band gap in two-dimensional square lattice photonic crystals is studied by using the plane wave expansion method (PWM) and finite difference in time domain (FDTD) method. It is found that, directional emission from two-dimensional photonic crystals can be realized if the effective refractive index is nearly zero. Moreover, the direction of the emitting beam is independent of the orientation of the crystal lattice, but dependent on the direction of the crystal surface. This is quite different from the self-collimation phenomenon in photonic crystals.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (17): 176101.
doi: 10.7498/aps.63.176101
Abstract +
It is very important to take into consideration the distribution of range, range straggling, and lateral spread of ions implanted into semiconductor materials during designing and fabrication of semiconductor integration devices by means of ion implantation. Er ions with energies between 200 and 500 keV are implanted in SOI (silicon-on-insulator) samples. The mean projection range Rp and the range stragglings Rp of Er ions with a dose of 21015 cm-2 implanted in SOI samples are measured by Rutherford backscattering (RBS) technique. The obtained data are then compared with those predicted by TRIM codes. It is seen that the experimental data of Rp agree well with the theoretical values. However, there are great differences between the experimental data and the theoretical values of Rp.
2014, 63 (17): 176201.
doi: 10.7498/aps.63.176201
Abstract +
Nanoindentation made by diamond indenter on pure Ni and the /'-phase in a Ni-base single-crystal superalloy is simulated respectively with molecular dynamics method. Elasticity modulus and hardness of the two models are calculated. Initiation and growth of dislocations and the influence of misfit dislocations of /'-phase in Ni-base single-crystal superalloy at different indentation depths are analyzed with center symmetry parameter. Results show that the relationship between indentation load and depth for the two models is similar when the indentation depth below 0.641 nm, indicating that the misfit dislocation on interface little affects the indentation. When the indentation depth reaches 0.995 nm, the dislocation nucleation can be found in misfit dislocations and the crystals that have slipped along {111}-oriented crystal surface in -phase. As a result, the indentation load of the latter model decreases and is smaller than that in pure Ni model before the indentation depth reaches 1.487 nm. When the indentation depth reaches 1.307 nm, owing to the inhibition caused by misfit dislocations at the interface, the indentation load for the /'-phase model in Ni-base single-crystal superalloy increases rapidly.
2014, 63 (17): 176802.
doi: 10.7498/aps.63.176802
Abstract +
Density functional calculations are used to investigate the mechanism of the distinctly different behaviors of Pd and Pt coating on graphene. Geometric and electronic structural analysis indicates that the electrons on the dz2 orbital of Pd may transfer to the dxz+dyz orbital of Pd by the aid of the up electrons of the graphene. This charge-transfer mechanism enhances the interactions between the Pd coating and the graphene substrate, driving the Pd coating to grow on the graphene, while Pt does not have this behavior. Metal self-assembly hinders Pt atoms to cover the graphene.
2014, 63 (17): 176801.
doi: 10.7498/aps.63.176801
Abstract +
Graphene synthesis by chemical-vapor-deposition (CVD) has attracted great interest. As the substrates for graphene growth, copper has become a common choice because its capacity could produce high-quality and uniform monolayer graphene. Morphology and surface conditions of the copper foil have great influence on the quality of the graphene grown on it. Here we report a rapid and effective copper pre-treatment method to improve the quality of graphene. After a pre-etching in 1 mol/L Fe(NO3)3 aqueous solutions for 90 s, the quality of the copper foil surface has been improved. Compared with the HCl treatment and electro-chemical polishing, Fe(NO3)3 pre-etching can generate a better result and has been verified to have general applicability for different types of copper foils.
2014, 63 (17): 176803.
doi: 10.7498/aps.63.176803
Abstract +
Porous micro-spheres of ZnO have been synthesized with Zn(NO3)26H2 O and urea as the raw materials and hexamine as a surfactant via a hydrothermal method. Structure, morphology, specific surface area, and pore size distribution of ZnO porous micro-sphere are characterized by X-ray diffraction, scanning electron microscopy, and micromeritics ASAP 2420 apparatus, respectively. Gas sensors are fabricated from the ZnO porous micro-spheres and their gas-sensing properties are measured. The gas sensitivity of sensor samples at different temperatures to acetone gas is examined. Results show that the sensitivity of ZnO porous micro-spheres sensors to 50 ppm acetone gas is 26.8 at 280 ℃, and the response and recovery durations are 4-10 seconds, respectively. Also, the sensor possesses an excelent selectivity for acetone.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2014, 63 (17): 175201.
doi: 10.7498/aps.63.175201
Abstract +
As one of the burgeoning physical vapor deposition (PVD) techniques, high power pulsed magnetron sputtering (HPPMS), which boasts high ionization rates of sputtered materials and does not suffer from macro-particles, has been investigated extensively recently. Herein, a new method to break down the discharge current into different characteristic components is employed to study the changes of the various parameters as the target voltage is increased at different pressure. Results show a phasic HPPMS discharge when the target voltage is increased, exhibiting an alternate rise of the peak and the platform of the target current. A small change at the discharge stage is observed with increasing pressure, and some stages are missing in some instances. Five discharge stages are found to correspond to the discharge of Ar atoms, Cr atoms, Ar ions, Cr ions, as well as multiply-charged Ar and Cr ions, respectively, according to the optical emission spectra obtained from the HPPMS discharge plasma. Adjacent discharge stages are also found to overlap under certain discharge conditions.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (17): 178401.
doi: 10.7498/aps.63.178401
Abstract +
Accurate physical modeling and parameter extraction for the nonlinear current-voltage (Ⅰ-Ⅴ) characteristics of photovoltaic (PV) cells and modules are essential prerequisites for the design calculation, performance analysis, and optimal control of PV generation systems. In contrast to the traditional implicit single-diode models, this paper first derives the explicit single-diode models of PV cells and modules using the Lambert Wfunction, and then proposes a simple and efficient parameter extraction method on the basis of restarting the bound constrained Nelder-Mead simplex method (rbcNM). For comparing and analyzing the accuracy of implicit and explicit single-diode models, experimental data of the two typical PV cells and modules are tested and verified. Simulation results indicate that the proposed rbcNM method can rapidly and accurately extract the optimal parameters of implicit and explicit single-diode models, the simulation data produced by the extracted parameters of rbcNM method are in very good agreement with the experimental data in all cases. Comparison results show that the accuracy of rbcNM method is quite promising and outperforms the existing methods reported in the literature. Furthermore, the accuracy of explicit single-diode models is significantly higher than that of implicit single-diode models, and thus fit the Ⅰ-Ⅴ characteristic curves better.
2014, 63 (17): 178101.
doi: 10.7498/aps.63.178101
Abstract +
The study focuses on studying the basic properties of memristors in RLC circuit and diode circuit. Mathematical models are built up separately for memristors in the two types of circuits. In order to understand the influence of the model's parameters on the circuits' properties, simulations are made for the two mathematical models. The model's parameters include properties such as the capacitance, resistance and inductance. In the final part of the paper, we give and make conclusions based on the simulation results.
2014, 63 (17): 178901.
doi: 10.7498/aps.63.178901
Abstract +
In this paper, we present a new approach to partitioning communities in a complex network via degree of dependence of nodes. We define the dependence degree of a node on its neighbors, the dependencetce degree and the conditional dependence degree of a node on a cluster. The main point of the approach is to partition the nodes, which have the biggest dependence degree and are only dependent on nodes, firstly to clusters, then to absorb nodes whose dependence degree or conditional dependence degree on cluster gets the right value, until all the nodes are partitioned to the right communities. The partition of our approach in some real-world network satisfies the definition of communities, and in the network whose communities are already known, our partition method fits the physical truth.
2014, 63 (17): 178102.
doi: 10.7498/aps.63.178102
Abstract +
Cd1-xLuxO(x=0%, 0.1%, 0.5%, 0.75%, 1.0%, 1.25%, 1.5%, 2%) ceramics have been synthesized by the traditional solid phase sintering method; and the effects of Lu3+-doping on the electric and thermal transport properties of these samples are investigated. With the increase of Lu3+-doping concentration, the room temperature carrier concentration in Cd1-xLuxO increases while the mobility first increases and then decreases. In the measuring temperature range of 300 to 1000 K, the electric conductivity of Cd1-xLuxO exhibites a metallic conducting behavior, and both their electric conductivity and thermal conductivity increase with the Lu3+-doping concentration. The Seebeck coefficient S of Cd1-xLuxO is negative in the whole measuring temperature range, and the dependence of S on the carrier concentration can be describedby a free electron model.
2014, 63 (17): 178103.
doi: 10.7498/aps.63.178103
Abstract +
A polarization-insensitive and broadband terahertz (THz) absorber based on metamaterial (MM) is presented. The absorber consists of two layers of metal and a single layer of medium. Each periodic cell of the upper metallic layer consists of five different sizes of metal patches which form a square array of 55. In the array, the size of each metal patch is different from that of its adjacent one, and each size of the metal patch generates a single resonance absorption peak. The broadband absorption is actually produced by the overlapping of five adjacent resonance absorption peaks. By studying the distribution of the surface current and the z-component of electric field, it is easy to know that the energy of the incident THz wave is absorbed by two factors: one is the electric dipole oscillation caused by the electric field in the y direction, and the other is the magnetic polariton caused by the magnetic field in the z direction. And the ohmic loss of metal layers plays a major role on the absorption of the absorber. Simulation results show that the bandwidth achieves 1.2 THz for the absorption beyond 80%, and the maximum absorption is up to 98.7%. It's full width at half maximum (FWHM) is 1.6 THz, and the thickness of the broadband absorber is only about one twentieth of the center wavelength. In addition, the absorber is insensitive to the polarization and has a wide-angle feature, and the potential applications of the absorber are electromagnetic stealth, THz thermal radiation detectors, and THz communication.
2014, 63 (17): 178201.
doi: 10.7498/aps.63.178201
Abstract +
Control of molecular dynamics in an intense laser field has been studied by employing the time-dependent wave packet approach. A system of K2 molecule in three states (ground state|X, excited state |B and ionized state|X+) serves as a prototype which interacts with pump-probe laser fields. Interacting with an intense pump field, the excited state |B splits into two substates: | and |. Information of the energies and probability distributions of dresses states | and | can be obtained by analysing the photoelectron spectra (PES) of K2 molecule. Meanwhile, the scheme of selective population of dressed states (SPODS) has been put forward according to the dressed states theory of K2 molecule. It is found that regulating the laser intensity can control the dressed state energies, and altering the laser wavelength can make the high selectivity of the dressed state population readied.
2014, 63 (17): 178501.
doi: 10.7498/aps.63.178501
Abstract +
Power consumption has been the major bottleneck in the development of integrated circuits with reduced critical dimensions and improved integrated level. Tunnel field effect transistor (TFET) has been investigated as one of the promising replacements for traditional metal oxide semiconductor field effect transistor (MOSFET), owing to the introduction of band to band tunneling (BTBT) mechanism based on which a smaller subthreshold slope is achieved. However, a thinner oxide layer and a shorter channel length in TFET may induce localization of high current density, high electrical field distribution, and generation of heat, which abate the probability to survive electrostatic discharge (ESD). Besides, the novel BTBT operating principles also present a challenge to TFET ESD protection design. In this paper transmission line pulse test method is adopted to analyze the working principle of conventional TFET at onset, holding, discharge, and second breakdown during an ESD event. Based on these a new TFET ESD device protection design is proposed and characterized with a deeply doped n+ pocket near the source region beneath the gate, which can make effective adjustments of contact potential barrier, reduce tunneling junction width, thus better ESD design windows are obtained.
2014, 63 (17): 178502.
doi: 10.7498/aps.63.178502
Abstract +
To seek a photocathode with good stability and repeatability in an ultrahigh vacuum system, activation and recesiation experiments are carried out on reflection-mode GaAlAs and GaAs photocathodes grown by metalorganic chemical vapor deposition, and the spectral response curves and photocurrent decay curves are measured after Cs/O activation and recesiation. Experimental results show that the photocurrent decay lifetime for GaAlAs photocathode illuminated by white light with an intensity of 100 lx is longer than that for GaAs photocathode after Cs/O activation and recesiation under ultrahigh vacuum condition. Moreover, GaAlAs photocathode exhibits a coincident blue-green response capability and a photocurrent decay lifetime after multiple recesiations, reflecting the superiority in stability and repeatability for GaAlAs photocathode operating in the vacuum system, and may provide an experimental guidance for exploring marine vacuum detectors and vacuum electron sources.
2014, 63 (17): 178503.
doi: 10.7498/aps.63.178503
Abstract +
Recently, magnetic force microscope (MFM) for dynamic imaging of AC magnetic field has attracted considerable attention due to its potential applications and special requirements in industry. In this paper, we develop an alternating force MFM technique based on the frequency modulation of MFM tip oscillation, which provides a powerful tool for the development of key technologies in magnetic information storage industry. Different from conventional MFM, the main points of the present work are: 1) the investigation of the frequency-modulation phenomenon; 2) optimization of the MFM tip parameter, and introduction of the MFM signal processing apparatus; 3) observation of the AC magnetic field. For dynamic evaluation of AC magnetic field, we need to theoretically analyze the mechanical and magnetic properties of MFM tips, to technically develop the MFM signal processing apparatus, and to experimentally image the dynamic magnetic signals. Finally, we demonstrate the alternating force MFM technique, which can measure and analyze the nano-scale magnetic domain structures in advanced magnetic materials.
2014, 63 (17): 178701.
doi: 10.7498/aps.63.178701
Abstract +
A method is proposed to calculate and analyze electro-encephalogram signal to improve the situation that there is an urgent need for an effective quantitative indicator to describe brain mental disorders. The method defines a spectral entropy in terms of the power spectrum division of time series. Then, the entropy is applied to numerical calculation of electroencephalogram signals of depression patients and normal control group. Meanwhile, the differences are compared between them. Experimental results show that the power spectral entropy in depression patients is significantly weaker than the normal healthy people's in some brain regions. Further analysis proves two facts. One is that the entropy is positively correlated to brain electrical physiological activity, and the other tells that the entropy can be used as a parameter to measure brain electrical activity, to characterize brain electrical physiological activities, and to provide the activity intensity information. This paper determines that the power spectral entropy for electroencephalogram plays an important role in diagnosis of brain mental disorder.
2014, 63 (17): 178801.
doi: 10.7498/aps.63.178801
Abstract +
The multi-junction bonding GaInP/GaAs/InGaAsP solar cell was developed. Bonding technology can reduce dislocations and defects produced in the epitaxial growth process of the lattice mismatch materials, and the defects are restricted within dozens of nanometer layers at the interface without spreading into the inner layers. Bonding solar cell is one of the efficient developing trends in the future. The solar cell interface uses p+ GaAs/n+ InP tunneling junction, and the open circuit voltage is greater than 3.0V. The efficiency is 24% when the structural parameter is not optimized and the anti-reflective film is not prepared. Open circuit voltage shows that the two solar sub cells are connected in series. Results are analyzed and the improvement measures are given. This bonding technology provides a new way for monolithic integration high efficient multi-junction cells.
EDITOR'S SUGGESTION
2014, 63 (17): 178802.
doi: 10.7498/aps.63.178802
Abstract +
To study combustion characteristics of solid fuels at the meso-scale, this paper presents a study on trap, ignition, and diffusion combustion characteristics of active carbon micro-particles at a meso-scale by optical tweezers. In the meso-scale combustor, minimum trap power for active carbon micro-particles with a diameter of 7.0 m is 3.2 mW, and the trap velocity is in the range of 103.770.0 m/s. The active carbon micro-particles in static air flow can be ignited when the laser power is 3.2 mW. The effective diameter, perimeter, area and roundness of the particles have little effect on the minimum power for ignition. The ignition delay time is ～ 48 ms for active carbon micro-particles with a diameter of 3.0 m, and it will decrease till below 6 ms with increasing laser power. After ignited, the active carbon micro-particle shows flameless combustion first. The diffusion combustion velocity agrees with the diameter square linear-relationship, and the velocity is of 15.08.0 m/s. Then the active carbon micro-particle continues to carry out combustion reactions with bright flames repetitiously, and the flash frequency is 29.1 Hz. For the active carbon micro-particle with a diameter of 3.0 m, it can burn out thoroughly in an overall time ～ 0.648 s (including the heating and combustion processes). Results demonstrate that ignition of the active carbon micro-particle heated by high power density laser belongs to the combined ignition mode. Before volatile matter precipitates, the active carbon micro-particle is ignited heterogeneously and carries out a flameless combustion. However, after the volatile components are precipitated, it is ignited homogeneously, and the ombustion flame always shows a spheried shape.
2014, 63 (17): 178902.
doi: 10.7498/aps.63.178902
Abstract +
In the fire of the factory of Jilin poultry company occurred on 3 June, 2013, which was the biggest fire disaster in the recent 13 years, 120 people were burned. One of the most important reasons lies in the shut off of 3 out of 6 exits, and further, the staff did not know which exit can be used to evacuate. In this paper, we simulate the evacuation process of the fire of Jilin using the foor field model, and show the importance of each exit and the influence of the shut off of exits. Results show that, if only there had been one more exit opened when the fire occurred, about 54.3% of the burned pedestrians could survive, and if all the exits ware opened, 76.6% of the burned pedestrians would survive. In addition, if the pedestrians had got the information of the availability of each exit, the number of burned pedestrians would reduce 21.6%. Hence, it is crucial to maintain the availability of the exits and spread the availability information for preventing loss of life and property.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (17): 179501.
doi: 10.7498/aps.63.179501
Abstract +
The tracking errors of large-caliber optical telescope in the process of observing astral target consists of telescope tracking jitter error which is mainly caused by wind-load, and wave-front tilt error caused by atmospheric turbulence. A simplified model concerning telescope tracking error is established, and a new kind of algorithm based on AR model to separate the telescope tracking jitter error from the tracking error caused by atmospheric turbulence is proposed. Finally, an experiment is conducted on the platform of the 1.8 M telescope in Gaomeigu Observing Station to test this algorithm. Experimental results show that the telescope tracking jitter error caused by wind-load is directly related to the direction and speed of the wind, which conforms to the theoretical analysis.
2014, 63 (17): 179502.
doi: 10.7498/aps.63.179502
Abstract +
An anisotropic diffusion filtering method is proposed to reduce multiplicative speckle noise in synthetic aperture radar images. A new anisotropic diffusion equation, which can effectively smooth speckles near the edges and reduce blocking artifacts in homogeneous regions, is established by embedding the mean curvature motion controlled by an adaptive coupling function into a traditional speckle reducing anisotropic diffusion equation. Moreover, a new direction-constrained diffusion function formed by combining the local directional ratios with the improved Frost filtering is introduced into the new anisotropic diffusion equation, so that it can further reduce blocking artifacts and obviously improve the edge distortion problem in the despeckled synthetic aperture radar images. Experimental results show that the proposed method can obviously reduce blocking artifacts, sufficiently smooth speckle noise in homogeneous regions and near the edges while preserving edges, and effectively improve the edge distortion problem. Visual quality and performance indexes of the despeckled images show that the proposed method outperforms several despeckling methods.
2014, 63 (17): 179503.
doi: 10.7498/aps.63.179503
Abstract +
A unified regression method to calculate fast transmittance coefficients is used in fast radiative transfer calculation of satellite infrared channel by a convoluted transmittances database from LBL (Line_By_Line) model. Comparison is performed between the fast calculated brightness temperature and LBL calculations for VISSR/FY-2F and IRAS/FY-3B. The examination indicates that STD (Standard Deviation) of fast calculated brightness temperature in window channels are much larger than the values in sounding channels. The lower atmosphere the channel detects, the larger the STD is available. And the largest the STD is less than 0.4 K. In this paper, a discussion is given to the improvement of fast radiative transfer calculation brought about by Planck weighted correction for convoluted channels' transmittances. Analysis shows that overlap between 2350 cm-1 and spectral response filter of the channel is a requirement to the Planck weighted correction. It is shown that STDs of brightness temperature between LBL calculation and fast computation are decreased by 25% after Planck weighted correction. And the improvement is available only for such channels with an overlap between their filter function and 2350 cm-1. Also it is indicated that the improvement from Planck weighted correction could be used not only to the imaging channels that have wide spectral coverage, but also to the sounding channels with very narrow spectral fields.
2014, 63 (17): 179201.
doi: 10.7498/aps.63.179201
Abstract +
Vorticity and divergence can be calculated using wind field in numerical forecast. The issue involves the problem of calculating differentiation using observation data, and it is ill-posed in mathematics. In a limited domain, the one-dimensional numerical differentiation can be used to calculate vorticity and divergence, but the method requires that the data along the boundary be accurate. This paper suggests a new method of calculating vorticity and divergence using the periodical function's one-dimensional numerical differentiation algorithm, and comparison is made with usually used difference method. The stream function and velocity potential are calculated using vorticity and divergence, and the initial wind field is reconstructed using the stream function and velocity potential. Results show that the algorithm proposed in this paper is stable, feasible, and its accuracy is superior to the difference method. It provides a new idea that the method mag be used in global meteorology data diagnosis analysis and forecast.
