Vol. 63, No. 11 (2014)
2014, 63 (11): 110201. doi: 10.7498/aps.63.110201
The ensemble empirical mode decomposition has been proposed in order to alleviate mode mixing in empirical mode decomposition, but the ensemble average in it can always result in new mode mixing, spectrum losing, and computational cost increasing, which can affect the analysis and extraction of signal physical characteristics. To tackle these problems, a noise-assisted signal decomposition method based on complex empirical mode decomposition is proposed, in which the mode mixing is reduced by taking the projection of intrinsic mode functions decomposed from white noise as basis functions for signal extrema extraction. While the problems result from ensemble average are reduced because the effects of noise projection are eliminated in the process of calculating the envelope barycenter. Simulation results show that our method has further reduced mode mixing, and speeded up the operation rate visibly and alleviated spectrum losing to a certain degree.
2014, 63 (11): 110202. doi: 10.7498/aps.63.110202
A gradient system is generalized to a system in which the time appears in the potential function, and the system is called generalized gradient system. The condition under which a holonomic mechanical system can be considered as a generalized gradient system is given. If the potential function of the system can be considered as a Lyapunov function, then the Lyapunov theorems can be used to study the stability of the system.
2014, 63 (11): 110203. doi: 10.7498/aps.63.110203
A class of nonlinear solitary waves in dusty plasma is considered. Firstly, a non-disturbed solitary wave solution is stated. Then the iteration is constructed by using the homotopic mapping, and the traveling wave solution of the nonlinear single-disturbed solitary waves in dusty plasma is obtained. Finally, every degree of approximate solutions for corresponding single solitary wave model can be found.
2014, 63 (11): 110204. doi: 10.7498/aps.63.110204
The solitary wave approximate solutions for a class of nonlinear-disturbed time delay long-wave system are considered. First, we introduce into exact solution of a non-disturbed typical long-wave system. Then, by using the homotopic mapping and an improved technique, the approximate expansions of the traveling wave solutions for the nonlinear-disturbed time delay long-wave systems are constructed.
2014, 63 (11): 110205. doi: 10.7498/aps.63.110205
It is very important in practice to avoid cascading failures by increasing the dynamic fault-tolerance of the network. Firstly, a cascading failure model is proposed in this paper, based on the characteristics of the variable load and the fixed capacity of the nodes in wireless sensor network scale-free topology. Then the influences of the load parameter and topology parameters on the fault tolerance are investigated in the case of cascading failure caused by random failure nodes. Finally the critical value of load for the large-scale cascading failure of network is deduced. Simulation result shows that the network's cascading failure fault-tolerance is positively related with the degree parameters, coefficient and power-law exponent. Researches provide regulation to avoid the cascading failure caused by the random failure nodes effectively from optimizing the parameters viewpoint.
2014, 63 (11): 110301. doi: 10.7498/aps.63.110301
For the first time, as far as we know, we use the approach of solving the amplitude-decaying master equation of density matrix to study the quantum dissipation of a mesoscopic RLC circuit, and thus find out the attenuation law of circuit energy. We then use the entangled state representation and the technique of integration within an ordered product of operators to explore this problem.
Effects of different Dzyaloshinskii-Moriya interaction and magnetic field on entanglement and fidelity intrinsic decoherence in a spin system
2014, 63 (11): 110302. doi: 10.7498/aps.63.110302
Using the Milburn equation, we have studied the properties of the entanglement and fidelity dynamics in a spin system with different Dzyaloshinskii-Moriya interaction and magnetic field in detail. Effects of different Dzyaloshinskii-Moriya interaction, different magnetic fields, and the initial states on the entanglement and fidelity are discussed. Results show that entanglement decoherence can be suppressed by inhomogeneous magnetic fields. Initial state affects greatly the entanglement, and a proper entanglement can be obtained by adjusting the directions of Dzyaloshinskii-Moriya interaction. For a particular initial state, an optimal fidelity is obtained by changing the direction of the Dzyaloshinskii-Moriya interaction. Moreover, no matter how homogeneous or inhomogeneous the magnetic fields are, they cannot enhance the fidelity. The dependence of entanglement and fidelity on the angle of initial state shows periodicity. Hence we can select an optimal initial state for a specific condition according to requirement.
Quantum discord in the system of two atoms trapped in weak coherent state cavities connected by an optical fiber
2014, 63 (11): 110303. doi: 10.7498/aps.63.110303
Geometrical quantum discord (GQD) is an effective measure of quantum correlation in quantum systems. We study GQD dynamics in an atom-cavity-fiber system. GQD between atoms and that between cavities are investigated. The influences of coupling constant between cavity and fiber and the intensity of the cavity field on GQD are discussed. Results show that GQD between atoms and that between cavities all display periodical evolutions, and their evolution frequencies increase with increasing coupling constant between cavity and fiber. On the other hand, the GQD between atoms and that between cavities are all strengthened with increasing intensity of the cavity field.
2014, 63 (11): 110304. doi: 10.7498/aps.63.110304
We propose an operator Hermite polynomial method, namely, to replace the special functions' argument by quantum mechanical operator, and in this way we have derived two binomial theorems related to two-variable Hermite polynomials. This method is concise and may be of help in deducing many operator identities, which may become a new branch in mathematical physics theory.
2014, 63 (11): 110305. doi: 10.7498/aps.63.110305
In this paper, we study carefully the quantum teleportation by means of a channel of a three-qubit Heisenberg XXZ ring, and calculate the fidelity of quantum teleportation. Comparing the four XXZ models: one without three-site interaction, one with XZX +YZY type three-site interaction, one with XZY-YZX type three-site interaction, one with both the two kinds of the three-site interaction, we find some ideal models by which the teleportation only needs a weakest magnetic field and a highest temperature to work successfully. The result could provide a theoretical basis for later experiments.
2014, 63 (11): 110306. doi: 10.7498/aps.63.110306
The scattering process when spin-orbit coupled Bose-Einstein condensate gets through cusp barrier is numerically simulated by adopting time-split spectrum method; the Klein tunneling phenomena exist in the scattering process. The regions of Klein block and Klein tunneling will appear at higher barrier height as compared to the scattering process on getting through Gaussian barrier. In the Klein tunneling region, the transmission coefficient oscillates with the barrier height, and the oscillation amplitude decreases with increasing barrier height. Besides, the effect of non-linear atomic interaction has been discussed for different barrier heights as well.
2014, 63 (11): 110501. doi: 10.7498/aps.63.110501
In this paper, a temporal-asymmetric fractional Langevin-like ratchet is constructed for the operation of a 1D linear molecular motor subjected to both spatial-symmetric periodic potential and temporal-asymmetric unbiased Langevin-like noise. In this ratchet, the Langevin-like noise is used to simulate the intracellular fluctuation induced by ATP hydrolysis. Then, for numerical study of this ratchet, the corresponding discrete mapping is derivated. Finally, as an example, the unidirectional transport of the ratchet driven by unbiased Langevin-like noise, generated by the Logistic mapping, is numerically studied. Negative transport of the ratchet indicates that without the spatial asymmetry of potential, the temporal asymmetry is enough for the presence of unidirectional transport. Since temporal asymmetry has to be regarded as a generic property of nonequilibrium system, this ratchet is expected to be resonably used for the operation of molecular motor.
Suppression of chaos and basin erosion in a nonlinear relative rotation system by delayed position feedback
2014, 63 (11): 110502. doi: 10.7498/aps.63.110502
A typical relative rotation system is considered whose chaotic motion and basin erosion caused by external excitation is investigated in this paper. And a delayed position feedback control is applied in the system for suppressing the two types of complex dynamical behaviors. Firstly, the excitation amplitude threshold of chaotic motion and the basin erosion of an uncontrolled relative rotation system is obtained by the Melnikov method. Secondly, the condition of Hopf bifurcation of a delay controlled system is discussed so as to obtain the available ranges of control parameters in the Melnikov method. Then the necessary condition for the global bifurcation of a delay controlled system is obtained. Finally, the evolutions of the dynamical behavior of the delay controlled system together with its control parameters are presented numerically using the 4th Runge-Kutta method and the point-to-point mapping method, which confirm the validity of the theoretical prediction. It is found that the chaotic motion and basin erosion can be suppressed effectively by delayed position feedback control when the gain is positive and the time delay is short.
2014, 63 (11): 110503. doi: 10.7498/aps.63.110503
In this paper, the differential invariants of Lie symmetry groups of the CDG equation and the coupled KdV-MKdV equations are obtained. Their syzygies and recurrence relations are classified, which are based on the algorithms of equivariant moving frames.
2014, 63 (11): 110504. doi: 10.7498/aps.63.110504
A new control method to suppress traffic jams is proposed by considering headway of the front and rear. With the control signals or not the stability conditions are derived. It is shown that the vehicle speed fluctuation by the simulations disappears when the feedback control signals are introduced. Therefore, serious congestion will not occur in the system. Illustration shows that the feedback control signal can effectively suppress and alleviate the traffic congestion.
2014, 63 (11): 110505. doi: 10.7498/aps.63.110505
To solve the degeneracy phenomenon and to improve the ability for tracking the breaking states are two difficult problems in the application of particle filter. Sequential important re-sampling can reduce orilliminate degeneracy, but the sample impoverishment is a secondary result. Extended particle filter can also reduce the degeneracy, but it cannot track the breaking states. The ability to track the breaking states can be improved by a strong tracking particle filter, but the degeneracy phenomenon will not be well solved still. A stochastic perturbation strong tracking particle filter is proposed for solving the above problems, in which a stochastically perturbative re-sampling is introduced into a strong tracking particle filter. Thus a stochastic perturbation is added to the particle with maximal weight to form some new particles, and the degenerative particles are displaced by the new particles to solve the degeneracy phenomenon and so the sample impoverishment improves the diversity of the samples. The ability of the proposed algorithm to track breaking states is also improved, and the feasibility and validity of the proposed algorithm are demonstrated by the simulation results of the standard validation model and the system with constants in different periods of time.
Nonlinear dynamics of stochastic resonance and its application in the method of weak signal detection
2014, 63 (11): 110506. doi: 10.7498/aps.63.110506
According to the exited stochastic resonance theory, we cannot obtain the dynamic behavior of a stochastic resonance (SR) system intuitively. In order to reveal the dynamic mechanism of SR, a kind of first-order Duffing equation attractor is analyzed at first, and then the property of nonlinear Duffing equation is studied, based on which the nonautonomous Duffing equation attractor curve is deduced. The output of SR system can be obtained by mapping the input signal on the attractor curve, and the dynamic mechanism of SR is explained by using the mapping method. Analysis of the result indicates that the intrinsic signal can push the system to move along the attractor curve, and the noise can evoke a transition response of the system under the given conditions. Some exited SR weak signal detection methods, such as the parameter-adjustment and damping-adjustment are extended by the proposed dynamic mechanism.
study on sensitivity-related parameters of distributed feedback laser-pumped cesium atomic magnetometer
2014, 63 (11): 110701. doi: 10.7498/aps.63.110701
This article reports a distributed feedback (DFB) laser-pumped cesium atomic experimental magnetometer, showing how the sensitivity is influenced by the following 5 kinds of parameters: laser light intensity, laser frequency, radiofrequency intensity, temperature of cesium absorption cell, and the pressure of the buffer gas in the cell. Results of the experiments show that each of the five parameters has some influence on the sensitivity of the magnetometer, especially the laser frequency, radiofrequency intensity, and temperature of cesium absorption cell, which can even improve the sensitivity by 10 times. Recently we have obtained a sensitivity of 2.5 pT/Hz1/2.
2014, 63 (11): 110702. doi: 10.7498/aps.63.110702
The magnetic noise of a vehicle has a strong impact on the magnetic gradiometer, so a vehicle magnetic noise compensation method is proposed. Based on the production mechanism of the vehicle magnetic noise, a mathematic model for vehicle magnetic noise on the tetrahedron magnetic gradiometer is proposed, in which the difference algorithm of the magnetic gradiometer is used to fuse the magnetic noise of each vector magnetometer. In terms of this mathematic model, we propose the noise compensation algorithm and the compensation coefficients recognition method by using the mathematic relations of the 9 components of the magnetic gradient tensor. Simulation results show that the proposed method can efficiently compensate 95.9% vehicle magnetic noise on the magnetic gradiometer. This method can compensate vehicle magnetic noise on the magnetic gradiometer output directly by the compensation coefficients, and realize the holistic noise compensation of the magnetic gradiometer theoretically.
To increase the output power of the surface wave oscillator (SWO) at the terahertz band, this paper presents a new type of coaxial-structured SWO, and its dispersive curve of TM01 mode is calculated numerically. The working properties of this new device are numerically simulated by using the self-developed fully electromagnetic particle code UNIPIC. Numerical results show that the working frequency of the coaxial-structured SWO is identical to that of the cylindrical-structured SWO, and the output power from this new coaxial-structured SWO is 67.8% more than that from the cylindrical-structured SWO, and the output mode of the terahertz wave is the transverse electromagnetic mode.
2014, 63 (11): 110704. doi: 10.7498/aps.63.110704
A static, compact, high optical throughput polarization-difference interference imaging spectrometer is presented. It is based on the combination of the angular shear of Wollaston prism and the lateral shear of Savart polariscope. Its remarkable characteristic is the simultaneous acquisition of the interferograms and two-dimensional images for the orthogonal polarization components of targets. Polarization spectral images of the components can be reconstructed using the algorithms of Fourier transformation and image fusion. A summation of the orthogonal polarization spectral images is equivalent to that of the conventional intensity spectral image. The difference is that the orthogonal polarization spectral images is named as polarization-difference spectral image. A higher contrast of the polarization-difference spectral image can not only provide more detailed texture information for the targets, but also can derive the size, concentration, and refractive index of elastic-scattered particles. The principle of polarization-difference interference imaging spectrometer is demonstrated in this paper. Expressions for interference intensities and theoretical simulation are presented. The mode for acquiring data is described. Approximate paraxial conditions of Fourier imaging lens for the formation of straight fringes are analyzed by using the Young's interference mode; and the influence factors for the visibility of fringes are analyzed. For the realization of a more compact system, the relationship between the collimating lens and imaging lens is analyzed in terms of optical field diffraction theory. The feasibility of the system is demonstrated by numerical simulation. This research can provide a novel development strategy for imaging spectropolarimeter.
2014, 63 (11): 110705. doi: 10.7498/aps.63.110705
The static polarization-difference interference imaging spectrometer, based on the combination of Wollaston prism and Savart polariscope, can simultaneously acquire hyperspectral images for orthogonal polarization components. Optical specifications are determined according to the principle of interference spectroscopy and the technical parameters of an actual detector. A design scheme is demonstrated. The Savart polariscope, Wollaston prism and Glan-Taylor prism are designed according to the birefringent features of uniaxial crystal and the wave normal tracing. More emphasis is put on the influences of the dispersion of uniaxial crystal on the incident angle, thickness, and apex angle. This research can provide a theoretical guide in the engineering of the polarization-difference interference imaging spectrometer.
2014, 63 (11): 110706. doi: 10.7498/aps.63.110706
A low loss broadband THz polarization splitter made from suspended dual-core porous fiber is proposed. The property of low loss is due to the porous structure of the fiber, and the match of single polarization mode is achieved by the orthogonal relationship of the microstructure in the two fiber cores. Structure of the fiber is designed by using index converse matching coupling method. Numerical simulation is carried out by employing full vector finite element method. The background material is cyclo olefin polymer COC with low loss property in THz region. Firstly, the properties of a suspended porous fiber with a single core has been analyzed in detail, including the effective refractive index, birefringence, fraction of modal power in air, and material absorption loss in the fundamental mode. Moreover, the properties of THz polarization splitter made from suspended dual-core porous fibers have been investigated theoretically. Numerical simulation results show that the operation bandwidth is 1.5 THz (from 0.8 THz to 2.3 THz). At 1 THz, the splitting length is only 0.66 cm. The extinction ratios for x and y polarization modes can reach -14.64 dB and -14.84 dB, respectively. The practical material absorption loss is less than 0.12 dB for both x and y polarization modes. Compared with other dual-core-PCF-based polarization splitters, the dual-core porous fiber has several advantages such as simplicity for structure designing, ease of fabrication, better feasibility in practical applications, low transmission loss, and wide operation frequency bandwidth.
2014, 63 (11): 110707. doi: 10.7498/aps.63.110707
This article presents an external modulation diode laser (with wavelength 661.85 nm and line width 0.3 nm) cavity ring-down spectrometer for measurement of NO3 radical in the atmosphere. The output spectrum of the diode laser is optimized by changing the external modulation signal; the effective cross-section of the instrument is a convolution of the measured cross-section and the laser spectrum. Interference of other gases (O3, NO2, and water vapor)in NO3 radical detection has also been investigated. Considering the loss from the PFA tube wall collision and the membrane filtration, NO3 radical inlet transmission efficiencies of the system is about 70% through the preliminary quantitative analysis. When the time resolution is 7 s, the laboratory detection limit of the system is 2.0 pptv. This instrument was deployed in the night atmosphere to measure the NO3 radical. NO3 concentration varied from 17.9 to 51.7 pptv with an average level of 36.3 pptv. A typical detection sensitivity in the night atmosphere is 3.5 pptv. Because of the uncertainty in the inlet transmission efficiencies and other factors, the total uncertainty of the measured NO3 radicals is about 8%(1 ). Experimental results show that the diode laser cavity ring-down spectroscopy can achieve high sensitivity in insitu detection of NO3 radicals in the atmosphere.
Research of classification of cloud and aerosol using multi-axis differential optical absorption spectroscopy
2014, 63 (11): 110708. doi: 10.7498/aps.63.110708
The classification of cloud and aerosol by means of multi-axis differential optical absorption spectroscopy (MAX-DOAS) is studied in this paper. Firstly, the characters of variation of color index (CI), radiance, and O4 air mass factor (AMF) are analyzed in the following kinds of weather cases, i.e. clear and low aerosol load, clear and high aerosol load, broken cloud, continuous and thin cloud as well as continuous and thick clouds. We found that the CI consecutively decreases with the growing up of optical depth of cloud and aerosol. And the speedy temporal variation of CI is always going along with the occurrence of broken cloud. For the case of continuous cloud, the CIs of observations for all the elevation angles are similar to each other. At the same time, the thick cloud case normally causes radiance dropping and O4 AMF growing up strongly. Based on these characters, the scheme of cloud classification for MAX-DOAS is built. Using this scheme, the classification results for the MAX-DOAS observations in the period from 1 June 2012 to 30 October 2012 are analyzed statistically. The occurrence probabilities of the broken cloud and thin continuous cloud are the two largest weather kinds. The percentage of the broken cloud in all the observations is 66%, and that of the thin continuous cloud case is 14.3%. For these two kinds of weathers, the mean NO2 tropospheric vertical column densities (VCD) are respectively 35% and 66% larger than the value for the clear and low aerosol. Meanwhile, the standard deviation, which represents the stability of the measured NO2 VCD is two times larger than that of the clear and low aerosol cases. In the weather of thick continuous cloud, suddenly appearing of peak and valley are often observed. In conclusion, the real time classification of cloud and aerosol is very important and valuable in analyzing of MAX-DOAS data and the guarantee of data quality.
ATOMIC AND MOLECULAR PHYSICS
2014, 63 (11): 113101. doi: 10.7498/aps.63.113101
Geometries, stabilities, and polarizations of PdnAl(n=18) have been calculated using the density functional theory at BPW91/LANL2DZ level. The growth pattern for different sized PdnAl(n=18)clusters is of Al-substituted Pdn+1 clusters, which shows the similar configuration of most stable Pdn+1 clusters except that of Pd6Al and Pd8Al. Geometries of ground state PdnAl(n=18) clusters keep the same structures of PdnAl clusters except that of Pd2Aland Pd6Al+. Al atoms in the ground state PdnAl and PdnAl isomers tend to occupy the most highly coordinated position. Analysis of stabilities shows that Pd4, Pd3Al and Pd3Al are more stable than other clusters. Study of polarizations shows that Pd-rich clusters have a strong nonlinear optical effect and are easy to be polarized by external electromagnetic field.
All-electron configuration interaction study on potential energy curves of low-lying excited states and spectroscopic properties of SiS
2014, 63 (11): 113102. doi: 10.7498/aps.63.113102
The 18 -S states correlated to the lowest dissociation (Si(3Pg)+S(3Pg)) limit are computed with high-level multireference configuration interaction (MRCI(SD)) approach through utilizing all-electron aug-cc-pwCVQZ-DK basis set. The scalar relativistic effect and the core-valence correlation effect of Si (2s22p6) and S (2s22p6) are taken into account. On the basis of calculated potential energy curves, the spectroscopic constants of the bound states are fitted, including equilibrium distance Re, adiabatic transition energies Te, harmonic vibrational frequencies e, anharmonic terms exe, and rotational constant Be. The electronic configurations at different bond lengths are given. The electronic dipole moments of 18 -S states are calculated, illuminating the influence of electronic configuration variation on electronic dipole moment. With the help of nonvanishing spin-orbit matrix elements including b3 and A1 as a function of the internuclear distance, the nearby state perturbations to b3 and A1 are discussed in detail. Finally, the transition dipole moments and Franck-Condon factors of A1X1+ and E1+X1+ transitions are obtained, and radiative lifetimes of five lowest vibrational levels of the two singlet excited states are evaluated.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (11): 114201. doi: 10.7498/aps.63.114201
To solve the issues in the modeling of skylight polarization, we build a new analytical model of skylight polarization patterns, which is based on the classic Rayleigh scattering and takes into consideration the multiple scattering properties of atmospheric particles, especially the aerosol. In this paper, we first build the model by the combination of single Rayleigh scattering and classic Perez sky models. Then we analyze the influence of secondary scattering by solving scattering phase function of different particle sizes and components of aerosol in OPAC data. Finally, the integral function for secondary scattering is simplified with the preferences of scattering phase function in forward direction. Compared with the Rayleigh model, our model can depict the existence of neutral points in the sky. The comparisons between our model and the measured results of clear sky further validate that the model not only exhibits characters of measured skylight polarization, such as the variation tendency, neutral points and the pattern symmetry, but also consists with the acquired values than the single scattering model; for example, the degree of similarity of polarization can be up to 75%.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
The base current broadening effect and charge separation method of gate-controlled lateral PNP bipolar transistors
2014, 63 (11): 116101. doi: 10.7498/aps.63.116101
In order to study the total dose effect and hardness assurance technology for the bipolar devices, we have designed and fabricated different gate-controlled lateral PNP bipolar transistors by various technologies, and preformed 60Co-γ low-dose rate irradiation. The test results show that: 1) Irradiation characteristics of the gate-controlled bipolar transistor are strongly dependent on the fabrication technology, and the passivation layer has a great influence on the irradiation response of the device. The device with a passivation layer will have more interface traps in ionizing radiation environments, and its resistance to ionizing irradiation is greatly weakened. 2) A domestic gated-controlled lateral PNP transistor exhibited a peak current broadening effect at low-dose rate irradiation. In this paper, we analyze the mechanism of the broadening effect, and put forward a new separation method for reducing the base current broadening effect, which not only provides the basis for the design of hardened devices, but also a powerful tool for the study of the enhanced low-dose rate sensitivity of the bipolar device.
2014, 63 (11): 116401. doi: 10.7498/aps.63.116401
Based on the GRAY equation of state (EOS), we establish a solid-liquid-gas three-phase complete EOS, and compare it with the experimental isothermal compression data, Hugoniot data, melting data and thermodynamic functions under ambient pressure. It is indicated that the EOS in this paper can describe reasonably the thermodynamic state of aluminum in a wide region.
Effect of oxygen pressure on structure and optical band gap of gallium oxide thin films prepared by sputtering
2014, 63 (11): 116701. doi: 10.7498/aps.63.116701
Gallium oxide (Ga2O3) thin films are deposited on silicon and quartz glass substrates by reactive DC magnetron sputtering under different oxygen pressure η (η =O2/[Ar+O2]), and the effect of oxygen pressure on the structure and optical band gap (Eg) is investigated. X-ray diffraction (XRD) and Raman scattering reveal that the products are beta-gallium oxide after heat treatment at 900 ℃, and that the grain size and optical band gap of gallium oxide are increased, the band gap Eg varies from 4.68 to 4.85 eV when tested by a room-temperature ultraviolet-visible (UV-VIS) spectrophotometer, and the (Eg) has also been calculated by using Tauc formula while the oxygen pressure η gradually increases.
Atomic force microscopy studies on self-organized wrinkles in constrained metallic films deposited on silicone oil substrates
2014, 63 (11): 116801. doi: 10.7498/aps.63.116801
Silicone oil droplets with varied sizes (micrometer to millimeter) were sprayed onto a clean glass slide and then Cr films were deposited on the droplets by DC-magnetron sputtering. Self-organized wrinkles induced by thermal stress have been investigated using atomic force microscope. It is found that the Cr films are limited by the droplet edges and thus possess constrained edges, which can well control the wrinkle morphologies: the wrinkles may exhibit radiated strips perpendicular to the edge. The wavelength and amplitude will decrease when approaching to the constrained edge. Morphologies of the wrinkles are closely related to the film thickness and oil drop size. As the film thickness increases, the wrinkles first form near the edge, and then propagate to the central region. The wavelength at the droplet center is almost unchanged for different oil sizes, but the amplitude first increases and then decreases with increasing film thickness. When the film thickness is fixed, the wavelength and amplitude may increase accordingly with increasing droplet size. Further studies show that the top surface of the silicone oil is modified to form a polymer layer during the deposition due to the bombardment from high-energy particles and heat radiation from the sputtering source. Morphologies of the wrinkles and amplitude evolutions are then explained in detail.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (11): 117101. doi: 10.7498/aps.63.117101
The chemical doping of organic molecules adsorbed on MoS2 monolayers are systematically studied by using plane-wave pseudo-potential method based on the density functional theory. Our results indicate that the interaction between organic molecules and the MoS2 monolayer substrate is of van der Waals' type of force. Structure of monolayer MoS2 which adsorbs different organic molecules, exhibits indirect bandgap characteristics, and the energy band structure of monolayer MoS2 which adsorbs TTF molecules exhibits n-type conducting characteristics. However, the structures of monolayer MoS2 which adsorbs TCNQ or TCNE molecules would exhibit p-type conductivity characteristics. Thus, the results indicate that the doping type of molecules in monolayer MoS2 can be regulated by adsorbing different molecules. Results of this study may provide a theoretical basis for single-layer MoS2 transistor and guidance for it in the application.
2014, 63 (11): 117102. doi: 10.7498/aps.63.117102
Edge reconstructions of graphene nanoribbons and their stable defective configurations were identified by experimental characterization. First principles calculations are performed to evaluate the effects of atomic edge arrangement on the electronic transport properties of zigzag graphene nanoribbons. It is found that these two defective edge structures affect effectively the high stable nanostructure configuration and give rise to pronounced modifications on electronic bands, leading to the shift of Fermi level as well as the occurrence of resonant energies. Both of these two atomic reconstructions would limit the electron transport around the Fermi level, and result in the complete resonant backscattering taking place at different locations. The suppression of conductance is not only related with increasing defect size, but more sensitive to the distribution of defect state, and the modifications on the electronic bands that are influenced by the edge reconstructions.
2014, 63 (11): 117301. doi: 10.7498/aps.63.117301
Topological insulator Bi2Te3 crystals were grown and their thermal expansion was studied with X-ray diffraction at various temperatures. It was shown that the linear thermal expansion coefficients, || and , which reflect, respectively, the thermal expansion within and out-off a-a plane of the Bi2Te3 crystal, exhibit quite different temperature dependent features. The obeys the Debye law in a relatively wide temperature range, while || deviates qualitatively from the Debye law at 100 K. Possible mechanisms behind the observed phenomena were explained using the crystal structure and the bonding features between the atoms in Bi2Te3 crystal.
2014, 63 (11): 117302. doi: 10.7498/aps.63.117302
In this paper, the AlGaN/GaN HEMT (high electron mobility transistors) with different ohmic contact structures are fabricated, and the effect of different ohmic contact pattern on GaN HEMT electrical properties is studied. A conventional ohmic contact electrode structure and a new ohmic contact structure with a contact hole are fabricated and subjected to rapid thermal annealing (RTA) in flowing N2. After different structured AlGaN/GaN HEMTs are annealed at 750 ℃ for 30 seconds, in HEMTs with a conventional structure ohmic contact still does not form while in the device with ohmic contact holes a good ohmic contact is already formed. Then the surface morphology of different multilayer electrode structures is measured. Comparing Ti/Al/Ti/Au with Ti/Al/Ni/Au, we can conclude that the structure Ti/Al/Ni/Au has a more smooth surface after annealing. After testing the HEMT devices with different structures, higher transconductance and saturation current are found for the devices with ohmic contact holes. But a serious current collapse phenomenon has been observed when the gate voltage is set between 0.5 V and 2 V.
Study on electrical transport properties of strained Si nanowires by in situ transmission electron microscope
2014, 63 (11): 117303. doi: 10.7498/aps.63.117303
Strain engineering in semiconductor nanostructure has been received great attention because their ultra-large elastic limit can induce a broad tuning range of the physical properties. Here, we report how the electrical transport properties of the p-type -oriented Si nanowires may be tuned by bending strain and affected by the plastic deformation in a transmission electron microscope. These freestanding nanowires were prepared from commercial silicon-on-insulator materials using the focusing ion beam technique. Results show that the conductivity of these Si nanowires is improved remarkably by bending strain when the strain is lower than 2%, while the improvement is nearly saturated when the strain approaches to 2%. The electric current will reduce a little sometimes when strain exceeds 3%, which may result from plastic events. Our experimental results may be helpful to Si strain engineering.
2014, 63 (11): 117701. doi: 10.7498/aps.63.117701
With the improvement of voltage level of electrical equipment, the requirement for the reliability of polymer dielectric materials in electrical equipment is much more strict. However, there are inevitably some defects in the manufacturing process of polymer dielectric materials, such as bubbles, inclusions, and so on. Therefore the life of electrical equipment will be greatly decreased when partial discharge occurs in a high electric field. In order to prevent and reduce the accident caused by the aging of polymer dielectric material in the electrical equipment, electrical aging life needs to be reasonably estimated. Based on the microscopic mechanism of partial discharge aging model, this paper suggests a stochastic differential equation for the electrical crack growth by using a non-equilibrium statistical physics theory, and then functions of breakdown probability, reliability, and electrical aging life due to the application of electric field are derived. Finally, a detailed analysis for the polyetllyleneterephthalate (PET) film is carried out, and the theoretical life of electrical aging is compared with experimental data. Results show that the theoretical values are consistent with the experimental data. So the aging life equations of polymer dielectrics derived in this paper can be used effectively in the quantitative analysis and may be helpful for the estimation of electrical life.
2014, 63 (11): 117702. doi: 10.7498/aps.63.117702
Single-crystal hexagonal wurtzite GaN nanowires were successfully synthesized by using plasma-enhanced chemical vapor deposition (PECVD) via vapor-liquid-solid (V-L-S) mechanism, under the condition of non-ammonia at 1050 ℃. Raman spectra show that the as-synthesized nanowires have large disorder surface, in which there is a significantly small size effect. Furthermore, it is also observed that the prepared nanowires have typical photoluminescence characteristics and good field emission properties.
2014, 63 (11): 117703. doi: 10.7498/aps.63.117703
Ferroelectric and antiferroelectric HfO2 nano-films were prepared by changing silicon doping concentration, and their basic properties conpared in terms of polarization hysteresis, capacitance-voltage and leakage-voltage behavior, as well as the effect of temperature on phase stability. Antiferroelectric thin film exhibits a higher dielectric constant than the ferroelectric film, and is characterized by the double polarization hysteresis loops due to reversible antiferroelectric-ferroelectric phase transition induced during loading and unloading processes of electric field. No antiferroelectric-paraelectric phase transition is observed at measuring temperatures up to 185 ℃. The negative differential resistivity effect observed in leakage measurements is attributed to the contributions from slow response mechanisms like polarization relaxation.
2014, 63 (11): 117801. doi: 10.7498/aps.63.117801
Coherent longitudinal acoustic phonons in Bi0.8La0.2Fe0.99Nb0.01O3 (BLFNO) films are photo-induced and detected by the femtosecond time-resolved reflectance spectroscopy. The generation mechanism of coherent longitudinal acoustic phonons is attributed to the transient photostriction effect. The strain modulation of the out-of-plane elastic properties C is realized in BLFNO films deposited on different substrates (ZrO2 and PbMg1/3Nb2/3-PbTiO3). Strain modulation of the thin film is demonstrated by applying an electromotive force on the piezoelectric substrate PbMg1/3Nb2/3-PbTiO3.
2014, 63 (11): 117802. doi: 10.7498/aps.63.117802
Optical properties of nanoparticles are related to their surface plasmon resonance. In this work, we use Mie theory to compute the extinction, absorption, and scattering properties of noble metal nanoparticles. The calculated results agree well with the experimental values. With increasing particle size, particle dipole absorption peak will be red-shifted; and the peak position and the size of the nanoparticles have a linear relationship. It is found that the ratio of core to shell size determines the absorption properties of spherical Au/Ag core/shell nanoparticles. When the Au shell is thin, the optical properties vary with the adjustable shell. When the Au shell is thick, its optical properties are similar to the pure Au nanoparticle. Through the calculation and analysis we made, the Mie theory can be generalized to nanocavity structures when the shell thickness reaches a certain value. Furthermore, it is found that the absorption peaks of alloy nanoparticles have a linear relationship with the alloy composition.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Study of Cu45Zr55-xAlx (x=3, 7, 12) bulk metallic glasses by ab-initio molecular dynamics simulation
2014, 63 (11): 118101. doi: 10.7498/aps.63.118101
Local structural changes from liquid to amorphous state in three Cu45Zr55-xAlx (x=3, 7, 12) ternary metallic glasses have been investigated by the ab initio molecular dynamics simulation. The atomic structure of the glasses has been analyzed by means of bond-type index method in Honeycutt-Andersen and Voronoi tessellation method. Al-centered icosahedral clusters are identified as the basic local structural units and these Al-centered stable clusters play a key role in the structural heterogeneity and glass-forming ability of the Cu-Zr-Al bulk metallic glasses.
2014, 63 (11): 118102. doi: 10.7498/aps.63.118102
In this paper we present a novel dual-band metamaterial absorber (MA), which is composed of a periodically arranged 2nd order Koch curve array and a metal ground separated by a dielectric spacer. By employing the fractal characteristic of space-filling, more compact unit cell with a size reduction of 17.5% has been achieved as compared with the conventional square-shaped MA. The dual-band operation is not originated from the hybrid or stacked methods as reported before, but from the two distinct resonance modes of the 2nd order Koch curves induced by the incident electromagnetic wave, and can be realized within a single unit cell. Due to its rotationally symmetric pattern, the absorptivity of the above presented MA is insensitive to the polarization of the incident waves and can perform well in a wide range of incident angles. The effective medium theory has been employed to investigate the underlying physical mechanism of the fractal MA, and good agreements between simulation and experimental results have been achieved.
Influence and mechanism of H2 in the epitaxial growth of ZnO using metal-organic chemical vapor deposition method
2014, 63 (11): 118103. doi: 10.7498/aps.63.118103
This paper focuses on the influence and mechanism of H2 in the eptaxial growth of ZnO using metal-organic chemical vapor deposition method. Studies show that hydrogen has a significant influence on the structure and properties of ZnO films. Hydrogen produces a mainly negative impact on crystal quality, surface structure, and optical properties of ZnO films when tert-butanol (t-BuOH) is used as the O sources. Raman scattering shows that hydrogen has a very good effect on the suppression of carbon contamination. When nitrous oxide is used as the O sources, the surface of ZnO films becomes smooth, and the crystal quality and optical property are improved. It is shown that hydrogen can play a positive role when N2O is used as O source. In this paper we highly estimate hydrogen's ability of reducing the surface growth energy, improving the migration of the surface atoms and the corrosion effect on the surface. Studies show that the optimization of hydrogen has a significant effect during the epitaxial growth of ZnO using the MOCVD method.
Scaling behaviours in the competing processes between aggregation and complete annihilation of two species of particles
2014, 63 (11): 118201. doi: 10.7498/aps.63.118201
A two-species system is considered, in which irreversible aggregations occur between particles of the same species while irreversible complete annihilations occur between particles of different species. Such competing processes between aggregation and annihilation reactions are performed by Monte Carlo simulations under various parameter conditions, and the influences of aggregation rate, annihilation rate, and initial particle distribution on the dynamics of the system are analyzed in detail. Simulation results indicate that the particle size distributions always obey a certain scaling law. When the aggregation rates of the two kinds of particles are both twice as fast as the annihilation rate, the scaling exponents of the particle size distributions have relation with the initial particle distribution; while in the remaining cases, the scaling exponents depend crucially on the reaction rates. Moreover, when both aggregation rates are larger than or equal to the double of the annihilation rate, all particles will annihilate each other completely; while at least one of the aggregation rates is slower than the double of the annihilation rate, the species with slower aggregation rate could survive finally. Simulation results are in good agreement with the reported theoretical solutions.
2014, 63 (11): 118401. doi: 10.7498/aps.63.118401
A design of 220 GHz third harmonic photonic band gap cavity gyrotron oscillator is proposed. Higher photonic crystal band gap is used to ensure the interaction between the high order electromagnetic mode (TE63-like) and the third harmonic electron cyclotron mode in gyrotron. The weak mode competition between TE63-like and TE92-like mode is studied by using a nonlinear theory, and the working conditions that ensure the start-up of the gyrotron to work in the third harmonic mode, as well as the nonlinear characteristics during the start-up process, are achieved. These results are in good agreement with the PIC (particle-in-cell) simulation. Our study shows that by using the photonic crystal as the high-frequency structure of gyrotron, high-order electromagnetic modes can interact with harmonic electron cyclotron modes efficiently.
2014, 63 (11): 118402. doi: 10.7498/aps.63.118402
In a cognitive radio system, it is still a problem that resource scheduling among secondary users (SUs) is distributed unfairly when spectrum aggregation technology is involved to support high-speed data transmission. A global proportional fair scheduling algorithm is proposed based on spectrum aggregation to solve the problem. This paper focuses on the relation between the fairness for SUs and spectrum aggregation. Throughput fairness can be guaranteed as much as possible after considering two parameters, the span of spectrum aggregation and the remaining data queue length of SUs. Simulation results show that the proposed scheduling algorithm takes advantage of fairness and the delay of system service as compared with the other two scheduling algorithms, max C/I and partial proportional fairness. Meanwhile, it is shown that the proposed scheduling algorithm has lower throughput shake to make sure of fairness among SUs and high efficiency of system.
2014, 63 (11): 118403. doi: 10.7498/aps.63.118403
Since the Doppler parameters vary according to the slant distance, the resolution is lower when using an imaging algorithm of traditional pulse compression in processing raw echo data of the missile-borne synthetic aperture radar (SAR). Moreover, an algorithm is proposed to solve these problems, which is based on the fractional Fourier transform (FrFT) for missile-borne SAR imaging. Firstly, an echo signal model is built for the terminal guidance stage of the missile-borne SAR. Secondly, the chirp rate of the echo signal is measured through the local optimum processing and obtains the optimum angles for the FrFT, and then the entire SAR image can be obtained by using FrFT with the optimum azimuth angles and operating range. Finally, the performances of the algorithms are assessed using simulated and real Radarsat-1 data sets. Results confirm that the FrFT-based missile-borne SAR processing methods can provide enhanced resolution that yields both lower-side lobes effects and improved target detection. The method introduced in this paper has important theoretical significance in detection and recognition of military targets and for precision guidance.
2014, 63 (11): 118404. doi: 10.7498/aps.63.118404
In order to extract the ocean dynamic parameters from shallow water, water depth, and current inversion at multiple (three or more) sites, HFSWR (high frequency surface wave radar) sea echo is developed. In this paper the inversion principle and theoretical model are presented in detail, and the proposed idea is verified for three or more than three sites, which shows prospects in practice. By analyzing the data collected from three HFSWR detection experiments in northern Jiangsu province, the inversion results show good performance, which is promising for extracting ocean water depth in inner zone and shallow water by HFSWR in engineering application.
2014, 63 (11): 118501. doi: 10.7498/aps.63.118501
Lately much interest is focused on SOI SiGe HBT in high-speed low-power BiCMOS applications. The frequency characteristics of the core device, SOI SiGe HBT in BiCMOS, determine its operating speed. So, this paper studies the frequency characteristics of SOI SiGe HBT on the basis of our proposed device structure, and analyzes the frequency characteristics in terms of the collector capacitance model we established. It is found that: 1) The characteristic frequency of SOI SiGe HBT increases with increasing doping concentration in the collector; 2) variations between the characteristic frequency and collector current of SOI SiGe HBT are consistent with those of the traditional SiGe HBT; 3) under the normal operating conditions, the maximum oscillation frequency of SOI SiGe HBT (a collector region with 3×1017 cm-3 dopant) is greater than 140 GHz, and the characteristic frequency is greater than 60 GHz. Compared with the traditional SiGe HBT, the maximum value of the characteristic frequency is increased by 18.84%. The conclusions above can provide important references to the design and research of SOI SiGe HBT and BiCMOS.
2014, 63 (11): 118502. doi: 10.7498/aps.63.118502
Hafnium indium zinc oxide (HIZO) thin film transistors with zirconium aluminum oxide (AZO) gate dielectric were fabricated by solution-process. The HIZO and AZO oxide thin films have smooth surfaces with root-mean-square roughness of 0.62 nm and 0.35 nm respectively. The thin film transistor with channel length = 6 μm and the ratio of width/length =5 exhibits a high saturation field-effect mobility of 21.3 cm2/V·s, a low threshold voltage of 0.3 V, a high on-off ratio of 4.3×107 and a small subthreshold swing of 0.32 V/dec. And these properties of TFT may be impacted by highly-coherent and low trapping states interface between the AZO dielectric and HIZO semiconductors.
2014, 63 (11): 118503. doi: 10.7498/aps.63.118503
Local interfacial delamination and cracking, appearing in the top surface of InSb infrared focal plane arrays (IRFPAs), are typical failure patterns observed in liquid nitrogen shock tests. In order to explore the delamination mechanism and cracking process, based on the thought of three-dimensional equivalent modeling, we employ the cohesive zone model (CZM) for the interface where delamination appears most easily, and create the structural model of 128×128 InSb IRFPAs. Simulation results contain all the deformation characteristics appearing in the typical optical fracture photographs. That is, firstly, in the photosensitive element array, the global square checkerboard buckling pattern reappears; secondly, in the negative electrode material, the InSb chip is gradually separated from the negative electrode, and the width of delamination is widened gradually; thirdly, on the periphery of InSb IRFPAs, the surface is flat. All these findings suggest that the model created in this paper is correct, and the parameters selected are suitable. Based on the delamination model, it is possible to find the initiation and propagation rule of cracks in the research that follows.
2014, 63 (11): 118701. doi: 10.7498/aps.63.118701
This paper proposes a novel multiresolution level set algorithm to segment breast MR images, which have a large amount of information, intensity inhomogeneities, and weak boundary. The core of the algorithm is to get the coarse scale image by analyzing the image in multi-scale space with wavelet multiscale decomposition. Then, to segment the analysed results in terms of improved CV model. In order to deal with the effect of bias field on the global images, the algorithm introduces a local fitting term into the improved CV model and optimizes the coarse-scale segmentation result by using the Kernel function to further improve the CV model. Experimental results on both synthetic and real breast MR images demonstrate that the proposed algorithm can segment the images with intensity inhomogeneity effectively and efficiently, also it can segment the images far more accurately, computationally efficiently, and much less sensitively to the initial contour.
Photo-generated current is important in solar cell current equation. The value of photo-generated current cannot be labeled in the conventional single origin coordinate system, and a novel dual-origin coordinate system is designed. This article provides a process in how to mark the Kirchhoff's law in a dual-origin coordinate system; besides, the current items (photo-generated current, diode current, shunt resistance current) and the voltage items (diode voltage, series resistance voltage) are also shown. A dual-origin coordinate system clearly points out that the difference between photo-generated current and short-circuit current will increase with increasing short-circuit current. This difference can be ignored only in low light, but it must be considered in high light. The proportions of output power and internal friction power may change with photo-generated current. Assuming that the output power is greater than the internal friction power, the solar cell should not be used to work under high light. A dual-origin coordinate system can provide an adaptation for solar cell study.
2014, 63 (11): 118802. doi: 10.7498/aps.63.118802
In the sequential sputtering/selenization process, Ga segregation at the back of Cu(In, Ga)Se2 (CIGS) absorber is frequently observed. In this paper, Ga diffusion in CIGS absorber is investigated during the sputtering and selenization process. Results show that Ga diffusion is closely related to Cu/(In+Ga) ratio in the metallic precursors and the selenization temperature, but barely influenced by Ga/(In+Ga) ratio in the metallic precursors. Based on Fick's second law, a simplified model is established to describe Ga diffusion from the back to the surface of CIGS absorber, which suggests that Ga diffusion coefficient is the dominant factor to constrain Ga content near the absorber surface. By process optimization, Ga/(In+Ga) ratio near the absorber surface is successfully increased. Accordingly, a CIGS solar cell device with efficiency of 12.42% has been obtained.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
A new algorithm for P-wave reverse time migration (RTM) in a fracture-induced TTI double-porosity medium is proposed in this paper, by combining RTM with the method of P-and S-wave field separation in high-order staggered grid finitedifference scheme. Simulation results show that for the fracture-induced TTI double-porosity medium the conventional migration with a background velocity without fractures would cause the imaging position to be under the true interface. To study the influence of fracture parameters, the phase velocity formulae are derived from Christoffel equations, and the effects of fracture angles and density are analyzed. In the 2D case, the imaging position gets closer to the real interface along with increasing fracture dip angles, while a bigger fracture density can cause much more deviation.
Plateau surface energy balance components and interannual variability in response to climate fluctuations
2014, 63 (11): 119201. doi: 10.7498/aps.63.119201
In this paper land surface observations and meteorological data are received from Semiarid Climate and Environment Observatory of Lanzhou University (SACOL) and Yuzhong Station from 2006 to 2012. The climate changes of temperature and precipitation in the seven years are analyzed in Yuzhong, and the inter-annual variation of the components of surface energy balance in land surface is discussed. The Bowen ratio and the energy inter-annual fluctuation imbalance are also studied. Explorations of surface energy balance components as well as the land surface process parameters feedback on the temperature, precipitation interannual fluctuations on the Loess Plateau are carried out. Results show that the surface energy components are responsible to the fluctuations of the climate background. But the sensitivity varies; the net radiation and air temperature are more relevant to each other, and the sensible heat and latent heat have a better correlation with precipitation. Discussions are divided into summer and winter half year results, in which the winter half year balance component surface has a better correlation with climatic fluctuations. In the winter half year, each component has a high degree of correlation with temperature, showing that in this area each component of the land surface energy balance component corresponding to the change of temperature is more remarkable The rising trend of Bowen ratio is corresponding to the reduction of precipitation, indicating that the drought is deepened The change of the energy closure shows that the deepening of energy balance unclosure is due to the change of the climate background.
The analogy and predictability of the forecasting model error for the precipitation over the mid-lower reaches of the Yangtze River in summer
2014, 63 (11): 119202. doi: 10.7498/aps.63.119202
This paper reports an effective method to improve the forecasting level of the numerical model through analogue prediction of errors and correction of the results. The analogy of the precipitation model errors and its predictability are studied for the mid-lower reaches of the Yangtze River in summer time in the perspective of analogy, which exists in the error field in the forecasting numerical model. The content of the analogy is also investigated according to the historical data. It is found that the forecasting errors could be improved remarkably by analogue error prediction over the regions researched in summer time. The forecasting error field is decomposed by EOF, and then the geographic distribution and time coefficient evolution of the first three principal components are analyzed. The prediction of the precipitation could be simplified by analogue forecasting of the principal components separately, and it is more targeted to improve the potential forecasting level. On the basis of the analogy of the forecasting error field, its analogue predictability is defined to measure the predictability of the errors. The analogue predictability of the first three principal components is significantly higher than that of the original field. It has potential applications to precipitation predication by forecasting the error field principal components.
Application of digital filter weak constraint four dimensional variational data assimilation on typhoon initialization I. Numerical experiments
2014, 63 (11): 119203. doi: 10.7498/aps.63.119203
Traditional four-dimensional variational (4D-Var) bogus data assimilation (BDA) will upset the internal dynamical balance of wind and mass fields, which will generate spurious fast oscillations in the prediction and cause the numerical simulation failure. How to effectively suppress the spurious fast oscillations is very important. In this paper (part I), the digital filter weak constraint 4D-Var is tested in BDA experiments. Initialization and simulation experiments are conducted for typhoon Chaba (2010) using this approach. Results show that the initial noise property is different for typhoon case and rainfall case, and the difference in surface pressure tendency is small in assimilation time and large at the initial stage in different digital filter weight setting BDA experiments. The vertical velocity field of 700 hPa and divergence field of 850 hPa in typhoon areas are both weakened in digital filter weak constraint 4D-Var experiments. Compared with the traditional 4D-Var experiment, the track and intensity predictions are improved obviously in digital filter weak constraint 4D-Var experiment with a proper digital filter weight setting, and the track prediction is apparently improved. Meanwhile, the optimal digital filter weight for different typhoon cases is different, and how to optimally select the digital filter weight is very important. In Part Ⅱ, a digital filter weight selection method will be proposed for BDA experiment.
Effect of rocket flame on high-frequency echo and its frequency energy agglomerated detection method
2014, 63 (11): 119401. doi: 10.7498/aps.63.119401
According to the problem that the mass matter from rocket flame consumes the electron density in atmosphere and disturbs high-frequency electromagnetic wave propagation, based on the characteristic of high-frequency radar echo from rocket flame, this paper reports the physical mechanism of high-frequency electromagnetic wave attenuation and flame electromagnetic characteristics, and analyses the radar cross section characteristic of the flame and the procreant time of flame's high-frequency echo. Then the detection method of frequency energy agglomerated for flame is put forward. By simulation analysis and experimental observation, the relations among flame high-frequency echo, altitude, flame electromagnetic characteristic, electric wave frequency, angle of incidence are obtained. The detection method is reliable and can decrease false-alarm and missing-alarm.
2014, 63 (11): 119601. doi: 10.7498/aps.63.119601
Small space debris impact that induces discharge can trigger disturbance of a spacecraft, which is a big threat to the safety of it. Research on this effect has already been carried out, but due to the limit of the facilities the research is also restricted. Since the primary cause of small space debris impact that induces discharge is to induce the plasma, similar to the laser inducing the plasma, this paper tries to simulate the space debris impact inducing discharge using a laser-induced discharge method. The analysis and experimental results are given, and they prove that this method is reliable.