Vol. 63, No. 18 (2014)
2014-09-20
GENERAL
2014, 63 (18): 180505.
doi: 10.7498/aps.63.180505
Abstract +
The line spectrum characteristics of the radiated waterborne noises of an underwater vehicle can be reconstructed using the technique of chaotification, which can improve the acoustic stealth of the underwater vehicle. According to the particular application background, in this paper we study the chaotification issue with nonlinear time-delay feedback control for a double-layer vibration isolation floating raft system under multi-source excitation. From a simplified two-dimensional floating raft system model, a chaotification method with nonlinear time-delay feedback control is presented completely. It provides a standard procedure for line spectrum chaotification design. Numerical simulation results show the feasibility of this method. Under multi-source excitation, the effects of the control gain, time-delay and feedback frequency parameters on chaotification are investigated, and discussion is also extended to the case of the single-source excitation.
2014, 63 (18): 180203.
doi: 10.7498/aps.63.180203
Abstract +
In this paper, based on the improved complex variable least-square (ICVMLS) approximation, the improved complex variable element-free Galerkin (ICVEFG) method for two-dimensional viscoelasticity problems is proposed. The ICVMLS approximation is used to form the shape function, the Galerkin weak form is used to obtain the system equations, and the penalty method is used to impose the essential boundary conditions, then the corresponding formulae of the ICVEFG method for two-dimensional viscoelasticity problems are obtained. Finally, some numerical examples are given, and the numerical results from the ICVEFG method are compared with those from the CVEFG method and finite element method, and the results show that the ICVEFG method in this paper has the high computational precision and efficiency.
2014, 63 (18): 180401.
doi: 10.7498/aps.63.180401
Abstract +
In the paper [Wu D et al. Sci. sin. G: Phys. Mech. Astron. 43 115], starting from the action of a massive particle's Lagrangian, we have made a new, unified derivation of the timelike and null geodesics of a rotating Kerr black hole. Our results demonstrate that one need not constrain himself to adopt the dragging coordinate system to investigate the tunneling radiation of rotating black holes. That work completely overcomes all shortcomings existing in the previous related researches, thus making Parikh-Wilczek's semi-classical approach more perfect and consistent. In this paper, we extend that work to the case of a rotating charged black hole to present a new derivation of the geodesic equation of a massive charged particle in the Kerr-Newman black hole and to reinvestigate its tunneling radiation.
2014, 63 (18): 180501.
doi: 10.7498/aps.63.180501
Abstract +
Social networks have been developed into one of the most important media for information propagation, and it is necessary to disclose how the information disseminates over social networks. In this paper, we explore the spreading mechanism including information stifling and forgetting, establish a spreading model, and elaborate the spreading rules. According to the spreading model, we build the mean field equation, calculate the two equilibriums and the basic reproduction number R0, and prove theoretically the asymptotical stability of the equilibriums. We analyze the effects of stifling mechanism and forgetting mechanism on the information spreading process, and validate the results of theoretical analysis by numerical simulations.
2014, 63 (18): 180503.
doi: 10.7498/aps.63.180503
Abstract +
Since most of the work relevant to the control of Chen system is based on the same time scale, and the results associated with the coupled systems with two time scales are mainly for the cases with only one slow variable, in this paper we investigate the dynamical evolution of the Chen system with the controller described by Duffing oscillator on a slow time scale, which implies two slow variables may be involved in the coupled vector field. Different types of bursting oscillations such as the symmetric fold/fold bursting, symmetric fold/Hopf bursting, symmetric homoclinic/homoclinic bursting, and mechanism are presented, revealing that the mutual influence between the two slow variables may cause the bursting behaviors similar to those in the periodic excited systems.
2014, 63 (18): 180504.
doi: 10.7498/aps.63.180504
Abstract +
Aiming at the shortcomings of current method of calculating finite-time Lyapunov exponent (FTLE), such as low accuracy, inability to obtain boundary values, etc., a method of highly accurately computing FTLE is proposed based on dual number theory. Firstly, the weakness and disadvantages of the finite difference method used widely for computing FTLE are described. Secondly, the dual number theory is introduced to evaluate the derivatives accurately and efficiently, and its distinct virtues are also presented. The computation of Cauchy-Green deformation tensors for a dynamical system is transformed into a numerical integration problem of solving the nonlinear ordinary differential equation in dual number space by the new method. Finally, the proposed method is applied to typical pendulum system and nonlinear Duffing oscillator separately. The results of simulation experiments indicate that the new method is effective, convenient and accurate for computing the field of FTLE, from which Lagrangian coherent structures can be identified successfully.
2014, 63 (18): 180201.
doi: 10.7498/aps.63.180201
Abstract +
In this paper, we study the influence of the bifocal lens on the focusing properties of Bessel beam. Based on the generalized Huygens-Fresnel diffraction integral, a more general expression of the light intensity distribution of nonsymmetrical optical system which is described by 4×4 matrix is deduced. The optical field distribution of Bessel beam passing through bifocal lens is given and simulated numerically. The influence of the focal length of the bifocal lens on Bessel beam is analyzed in detail. The generalized expression of the light intensity distribution can involve three cases, i.e., ordinary lens, bifocal lens and cylindrical lens. The greater the astigmation, the poorer the bottle beam quality will be. The ability to imprison microscopic particles decreases.
2014, 63 (18): 180202.
doi: 10.7498/aps.63.180202
Abstract +
Aiming at the problem of fault estimation in a class of time-varying discrete switched system with arbitrary sequence, in this paper we propose a novel fault estimation algorithm. The algorithm uses the introduced virtual fault signal to construct fault estimator, and uses the residual signal to modify the introduced virtual fault step by step through using the iterative learning method and making the virtual fault gradually approach to the actual fault by increasing the iterative number. The convergence of the algorithm in each subinterval is strictly proven by the use of contraction mapping method, and the convergent condition of the algorithm is provided. Theoretical analyses indicate that the proposed algorithm can estimate different types of faults occurring in a switched system accurately in a finite interval. Finally, the validity of the algorithm is verified by simulations.
2014, 63 (18): 180508.
doi: 10.7498/aps.63.180508
Abstract +
With the phase field crystal approach, the structure of asymmetrical tilt subgrain boundaries and their motion micmechanism under stress are studied. The effects of temperature, inclination angle and stress direction on structure and migration process are also analyzed and discussed. Simulated results show that the subgrain boundary is composed of a row of edge dislcations with the same bugers vectors and the double-array dislocations with a vertical distribution. The motion process of asymmetrical tilt subgrain boundaries contains dislocation glide and climb, dislocation separation, dislocation reaction, individual dislocation decomposition and dislocation annihilation. The decrease of temperature and the increase of inclination angle hinder the subgrain boundary migration process. The change of stress direction causes the variation of dislocation motion and thus lead to the change in migration manner of subgrain boundary.
2014, 63 (18): 180702.
doi: 10.7498/aps.63.180702
Abstract +
In order to better apply the NaI scintillation spectrometer to bremsstrahlung measurements, the energy response function of a NaI detector spectrometer system is studied by using 137Cs and 60Co sources based on Monte Carlo N particle transport code (MCNP) process. Simulated and measured almighty peak efficiency are in good agreement. An energy response matrix (ERM) is obtained by simulating photons with a certain energy incident on the NaI crystal in MCNP process, through deconvoluting the detected spectrum of NaI using the ERM, and the results of the deconvolution accord well with those from the original spectrum. Furthermore, the NaI detector is used to preliminarily detect its response to bremsstrahlung generated by high intensity electrons bombarding a target of 1.5 mm thickness.
Accurate measurement of templates and imprinted grating structures using Mueller matrix ellipsometry
2014, 63 (18): 180701.
doi: 10.7498/aps.63.180701
Abstract +
In order to control nanoimprint lithography (NIL) processes for achieving good fidelity, the fast, low-cost, non-destructive and accurate measurement of geometric parameters of templates and imprinted grating structures is of great importance. Compared with conventional ellipsometric scatterometry, which only obtains two ellipsometric angles and has 2 changeable measurement conditions, i.e., the wavelength and the incidence angle, Mueller matrix ellipsometry (MME) can provide up to 16 quantities of a 4×4 Mueller matrix in each measurement with 3 changeable measurement conditions, i.e., the wavelength, the incidence angle and the azimuthal angle. Therefore, MME can acquire much more useful information about the sample. It is expected that much more accurate measurements of nanostructures can be achieved by choosing proper measurement configurations and completely using the rich information hidden in the measured Mueller matrices. Accordingly, the templates and imprinted grating structures in NIL processes are measured using an in-house developed Mueller matrix ellipsometer. We experimentally demonstrate that more accurate quantification of geometric parameters, such as line width, line height, sidewall angle and residual layer thickness, can be achieved by performing MME measurements in the optimal configuration and meanwhile by incorporating depolarization effects into the optical model. Moreover, as for the imprinted grating structures, the residual layer thickness variation over the illumination spot can also be directly determined by MME. The comparison between MME-extracted template and imprinted resist profiles also indicates an excellent fidelity of the nanoimprint pattern transfer process.
2014, 63 (18): 180502.
doi: 10.7498/aps.63.180502
Abstract +
In this work, we propose a novel memristor chaotic circuit, which combines current feedback op amp with four basic electronic components, such as capacitance, inductance, resistance and memristor. The dynamic properties of the new circuit are demonstrated, such as system dissipation, equilibrium stability, phase portrait, Lyapunov exponent spectrum, and parameter influence. Numerical simulation results show that the circuit produces a kind of special chaotic attractor and exhibits complicated chaotic behaviour with the evolution of the system parameters. In order to confirm the correctness of the system, a realizing circuit is designed, Pspice simulation results verify the correctness of theoretical analysis.
2014, 63 (18): 180506.
doi: 10.7498/aps.63.180506
Abstract +
In this paper, a method is proposed to realize the grid multi-scroll chaotic system with the current feedback operational amplifier (CFOA). Firstly, nonlinear circuit is designed based on the CFOA. Then the grid multi-scroll chaotic circuit is designed and relevant circuit parameters are calculated. Finally circuit simulation is conducted, and the results show that the circuit has a higher central frequency, needs less components, and possesses simpler circuit structure, good frequency characteristic and port characteristic of the CFOA.
2014, 63 (18): 180507.
doi: 10.7498/aps.63.180507
Abstract +
In this paper, we discuss the effects of heterogeneous neuron arrangement on the frequency synchronization of a ring-coupled FitzHugh-Nagumo neuronal network. The obtained numerical results reveal that the threshold of coupling strength for frequency synchronization may be different for different arrangements of the heterogeneous neurons on a ring. On average, the closer to each other the neurons which are less heterogeneous on a ring, the larger the critical coupling strength needed for neuronal network to achieve frequency synchronization is; the closer to each other the neurons which are more heterogeneous, the smaller the critical coupling strength needed for neuronal network to achieve frequency synchronization is. Furthermore, we give the underlined mechanism for this phenomenon by analyzing the process of frequency synchronization.
2014, 63 (18): 180205.
doi: 10.7498/aps.63.180205
Abstract +
In this paper, using the mechanization-method obtained nonlocal symmetry and reduction of the Kaup-Kupershmidt equation and solving the reduction equation, new solutions to the equation are obtained.
2014, 63 (18): 180204.
doi: 10.7498/aps.63.180204
Abstract +
The wave motion characteristic of large-scale barotropic atmospheric circulation, which can be described by the original nonlinear shallow water equations, is important for comprehending the climatic change. Employing the complex solution of linear equation, and transplanting it twice, the new analytic solution of disturbed height field of the nonlinear evolution equation is obtained which is constructed by the basic flow term and fluctuation term. The basic flow is codetermined by the wave number, wave velocity, β effect, radius of deformation and arbitrary function of time. The fluctuation term is related to β effect, and displays that in the disturbed height field there exist the periodic wave and solitary wave of curved face, which modulate each other and present instability; several periodic-solitary waves can propagate independently when they appear simultaneously; the arbitrary function of time in the fluctuation term has a modulation effect on the amplitude of periodic-solitary wave, and can control the occurrence, development and vanishing of wave. The results have a certain theoretical reference value for studying the atmospheric fluctuation phenomena and climatic change.
2014, 63 (18): 180301.
doi: 10.7498/aps.63.180301
Abstract +
The wavelength dependence of the electron localization in dissociating molecular ion D2+ is investigated via solving the time-dependent Schrödinger equation of the two-state model of the molecular ion. Our results reveal an anomalous dependence of the electron localization on the laser wavelength. Overall, the degree of the electron localization shows a growing trend with the increase of wavelength, but it drops off obviously at some wavelengths. It is found that the localization asymmetries for some vibrational states become opposite in phase when the wavelength is changed, leading to the decline of the electron localization. Further analysis shows that the nuclear and electronic motions that determine the electron localization respond inconsistently to the variation of the wavelength, ultimately resulting in the non-linear dependence of the electron localization on the laser wavelength.
2014, 63 (18): 180206.
doi: 10.7498/aps.63.180206
Abstract +
We numerically investigate the interaction between multi-compactons of the K(m,n,p) equation by a finite difference scheme that is of the second-order accuracy and absolutely stable in linearization sense. By adding an artificial dissipation term, it works well for preventing the break-up phenomena of the numerical solutions. Firstly, we simulate the long-time evolution behaviors of the single-compacton to verify the validity of the numerical method. It is shown that the numerical method is effective for solving this problem. Secondly, we study the nonlinear interaction between two-compacton and three-compacton by this numerical method. The numerical results indicate that the wave-frame and wave-velocity after collision are nearly the same as before collision. However, compacton-anticompacton pair induced behind the wave arises with small amplitudes.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (18): 184301.
doi: 10.7498/aps.63.184301
Abstract +
To suppress the noise and increase the accuracy of feature extraction for ultrasonic Lamb wave signals, we present a new method based on the Tsallis mode and the fractional-order differential in this paper. Firstly, the fractional-order differentials of the amplitude spectrum of the noisy Lamb signal at different orders are obtained by using the fractional differential theory. Then, the cubic polynomial between the peak amplitude and the derivative order, and that between the peak frequency and the derivative order are proposed based on the Tsallis mode. The characteristic parameters of the amplitude spectrum are extracted with the developed equations. Finally, the Lamb signal without the noise is restored by combining the amplitude spectrum with the phase spectrum. Simulated and experimental results show that the proposed method can improve the performance parameters such as mean square error, r, and signal-to-noise ratio. Consequently, the new method based on the Tsallis mode and the fractional-order differential has the effective noise suppression performance for Lamb wave signals.
2014, 63 (18): 184205.
doi: 10.7498/aps.63.184205
Abstract +
Aming at the coherent superposition of laser pulse reflected from the cavity mirror in multi-pass amplification process, a physical model for describing the amplification of coherent superstition of the rising part and the falling part of the pulse in a gain medium is established. According to theoretical analysis, standing wave is formed by the coherent superposition of the rising part and falling part of the pulse. The inversion population density shows up the effect of hole-burning by the standing wave, and the gain and pulse shape are affected. Based on this physical model, three conditions, i.e., no superposition, coherent superposition, and incoherent superposition are compared. This study will provide the instructions for high power solid laser design.
2014, 63 (18): 184101.
doi: 10.7498/aps.63.184101
Abstract +
A hollowed-out cross-shaped meta-material structure is designed and fabricated in this work. A kind of conventional magnetic material which works at low frequency is used as the absorber substrate. The simulation results demonstrate that an absorber can reach an absorption of less than -10 dB in a range between 2 GHz and 4 GHz, and the absorption band is expanded by a 0.5 GHz when the meta-material structure is unloaded. The experimental results indicate that a similar absorption band appears between 2.5 GHz and 5.1 GHz, which is 0.48 GHz wider than meta-material structure and the absorption band is expanded by 23% when the depth of absorption band below -9 dB. Compared with the cross meta-material, the hollowed-out structure has ability to increase the magnetic energy loss and strengthen the coupling between the units. The influence of magnetic layer thickness on absorption capability of wave absorber is analyzed. The result indicates that the position of addition absorption band does not apparently move with variation in thickness of the magnetic material layer. Based on these results, two different meta-material structures are combined to obtain a wider absorber. The simulation result and the experimental result both show another 0.9 GHz expansion of the absorption band and it can also reduce the thickness of the magnetic layer.
2014, 63 (18): 184203.
doi: 10.7498/aps.63.184203
Abstract +
The time evolution properties of the quantum fidelity in a system of multi-mode coherent light field resonantly interacting with a two-level atom via any Nj-degenerate N∑-photon transition process are studied by the fully quantum theory and numerical calculations. The analytical expressions of the quantum fidelity of field and atom, and the numerical calculation results for three-mode field interacting with the atom are obtained. Our attention focuses on the discussion of the influences of the initial average photon number, the atomic distribution angle, the phase angle of the atom dipole, the field excitation angle, and the atomic degeneracy on the evolution of the quantum fidelity. The results obtained from the numerical calculation indicate that the above factors lead to the quantum fidelity changing with oscillation behavior. The quantum fidelity of field and atom will drastically decrease as the initial light increases, which is correlated sensitively with the fidelity. The speed change of quantum fidelity is strongly dependent on the atomic degeneracy and the intensity coupling between atoms and fields. The value and frequency of the quantum fidelity change lightly with the atomic distribution angle and the angle of light field excitation as well. The phase angles of the atom dipole almost have no influences on the quantum fidelity of field and atom. According to these properties of the quantum fidelity, we can control the speed and value of quantum fidelity in the system by these constraint conditions.
2014, 63 (18): 184207.
doi: 10.7498/aps.63.184207
Abstract +
In this paper, the nonlocal nonlinear medium, nematic liquid crystals (NLCs) with negative dielectric anisotropy, are studied. Theoretical research shows that NLCs with negative dielectric anisotropic have a negative nonlinear coefficient. The analytical expressions for characteristic length of the nonlocal response function and for nonlinear coefficient are given. Secondly, the solutions for spatial optical solitons in NLCs with negative dielectric anisotropic are obtained by numerical computation. Finally, the influences of beam power and bias voltage on the propagation of the beam in NLCs with negative dielectric anisotropic are investigated. The result shows that the critical power of the nonlocal spatial solitons in NLCs with negative dielectric anisotropic varies with bias voltage.
2014, 63 (18): 184208.
doi: 10.7498/aps.63.184208
Abstract +
The optimized crystal structure, electronic structure and optical properties of Na2Ge2Se5, an excellent nonlinear crystal, are investigated by using pseudo-potential plane-wave method based on the first principles. The band structure, density of states, bond population, dielectric function, reflection spectrum, absorption spectrum, and codex refractive index of optimized structure of Na2Ge2Se5 are calculated. The results indicate that Na2Ge2Se5 is indirect wide-band semiconductor. The electronic transitions are mainly composed of Ge-4s, Ge-4p, Se-4s and Se-4p. The optical properties are determined by the interaction between Ge and Se, while Na contributes little. The reflectance spectrum and absorption spectrum indicate that there is strong absorption to ultraviolet radiation and static refractive index is 2.133. Na2Ge2Se5 possesses moderate birefringence. The results indicate that Na2Ge2Se5 is a good candidate for the optical crystals in the infrared region.
2014, 63 (18): 184209.
doi: 10.7498/aps.63.184209
Abstract +
Large-scale high-accuracy measurement plays an important role in many applications, such as large-scale equipment manufacturing, space technology and national defense industry. High-accuracy absolute distance measurement by laser is an important research topic in the field of large-scale high-accuracy measurement. And frequency modulated continuous wave (FMCW) laser ranging is a hot point of research nowadays. Because this method is better than pulsed time-of-flight method in measurement resolution, and the problem of ambiguity in measurement, which is the main disadvantage of phase-related method, does not exist. In this paper, the principle of FMCW laser ranging and the main factors reducing the measurement resolution are analyzed. In order to improve the ranging resolution, the method using an auxiliary interferometer to sample the signal in equal intervals of optical frequency is employed. A dual interferometer FMCW laser ranging system is designed and the experiments are carried out. The experimental results show that the measurement resolution is 50 μm at a distance of 10 m.
2014, 63 (18): 184206.
doi: 10.7498/aps.63.184206
Abstract +
In this paper, the dependences of the third harmonic generation (THG) of a probe filament on the relative position of the probe filament interacting with the plasma grating and the position of the plasma grating interacting with the probe filament are investigated. The phase matching between the third harmonic of the probe filament and the fundamental wave of the plasma grating is earlier to achieve when the head of the probe filament interacts with the plasma grating, inducing the enhancement of the third harmonic generation, while the phase mismatching happens when the trail of the probe filament interacts with the plasma grating. The distribution of the clamping laser intensity inside the plasma grating results in the dependence of the THG on the positions of the plasma grating interacting with the probe filaments. It is an effective method of promoting the THG by setting the crossing angle between the probe filament and the plasma grating to be very small.
2014, 63 (18): 184102.
doi: 10.7498/aps.63.184102
Abstract +
An optimal layered inhomogeneous background which can be used in an embedded microwave tomography system is proposed. The method is based on a new evaluation method of integral radiation operator with respect to an configuration and optimal methods such as simulated annealing method. First, the integral radiation operator is calculated using the finite element method. Then, a kind of metric which can be used to evaluate the operator is proposed. The metric contains information about the whole singular value spectrum of a integral radiation operator. A set of synthetic researches is performed to show the correlation between the metric and inversion error. The method can evaluate an integral radiation operator using a number, and it can be used in optimal process easily as the cost function. Simulated annealing method is employed to obtain the permittivity of each layer in the optimal layered inhomogeneous background. Finally, synthetic researches are employed both on simple target and complex target to test the optimal layered inhomogeneous background. The results show that the optimal layered inhomogeneous background can expedite the convergence process and more accurate inversion results can be obtained.
2014, 63 (18): 184701.
doi: 10.7498/aps.63.184701
Abstract +
This study focuses on the dynamic behavior of rising bubble in water with taking surface tension and viscous effect into consideration. The Young-Laplace equation is adopted to obtain the viscous component of the normal stress, and the tangential component is evaluated by viscous correction pressure, which is based on viscous dissipation energy equivalence principle. Firstly, both axi-symmetric and three-dimensional model is established by employing boundary integral method. The validation of our model is confirmed by comparing the analytical results with the experimental results, and they are in good agreement with each other. Secondly, the shape and balanced velocity of millimetre-sized bubble are studied, and the influences of initial condition, surface tension and viscosity on the dynamic behaviour of the bubble are also discussed. Finally a numerical technic is put forward to handle the coalescence of two rising bubbles, which can show some detailed information about the coalescence process.
2014, 63 (18): 184210.
doi: 10.7498/aps.63.184210
Abstract +
A novel eigenvalue method is proposed to calculate the band structure of lossy and dispersive photonic crystal (PC). Using an idea from quantum transport problem, a standard linear eigenvalue equation rather than a nonlinear eigenvalue equation is obtained by a rigorous and artful transformation. And the physical parameters of lossy and dispersive PC are obtained by solving the linear eigenvalue equation using finite-difference frequency-domain (FDFD) method. Compared with other methods, the proposed method has great features, such as clear concept, simple calculation, less computing time and storage. A dielectric PC is simulated by the proposed method, and the results accord well with those from the traditional FDFD method, which verifies the validity of the proposed method. Moreover, the dispersion relation of the lossy and dispersive PC is calculated by the proposed method, and the surface plasmon frequency is obtained. Furthermore, the influence of loss on the dispersion relation and eigenmode field distribution is studied. The results provide some theoretical guidance for studying the lossy and dispersive PC.
2014, 63 (18): 184202.
doi: 10.7498/aps.63.184202
Abstract +
In the infrared and visible light image fusion, the noise interference always exists. There is also the disadvantage that image fusion is easy to produce artifacts which cause blurred edge and low contrast. In order to solve these problems, in this study we propose an image fusion method based on deep model segmentation. First of all, deep Bolzmann machine is adopted to learn prior target and background contour and construct a contour deep segmentation model. After the optimal energy segmentation, Split Bregman iteration is used to obtain the infrared and visible image contour. Then non-subsampled contourlet transform is adopted to decompose the source images. The segmented background contour coefficients are fused by the structure similarity rule. Finally, the fused image is reconstructed by the non-subsampled contourlet inverse transform. The experimental results show that this algorithm can effectively obtain fused images with clear target contour and background contour. The fused images also have high contrast and low noise. The results show that it is an effective method of achieving the infrared and visible image fusion.
2014, 63 (18): 184204.
doi: 10.7498/aps.63.184204
Abstract +
Pixelated polarizer array can be used in the real-time measurement of Stokes parameters. In this paper, pixelated polarizer array based on the aluminum nano-grating is designed and fabricated, and the fabrication technology is electron beam exposure technology. The size of each unit is 7.4 μm, and the polarization directions of each adjacent 2×2 units in the polarizer array are 0, π/4, π/2, and 3π/4. The period, duty cycle, depth and surface type of the grating are 140 nm, 0.5, 100 nm and rectangle type, respectively. The scanning electron micrographs of the pixelated polarizer array show that there is no disconnection, cross and pollution on the fabricated metal nano-grating lines. The nano-grating lines are straight and uniform in thickness, and the surface type of the grating is ideal rectangular type. The polarization optical micrographs show that the pixelated polarizer array has good polarization characteristics. The maximum polarization transmissivity can reach 79.3%, and the extinction ratio can arrive at 454. Furthermore, the pixelated polarizer array is integrated with the charge coupled devise chip, and the Stokes parameters can be calculated from one frame, then the degree of linear polarization and angle of linear polarization can be obtained. Thus, the polarization enhancement of image is achieved, which can be used in the anti-stealth and recognition.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (18): 186801.
doi: 10.7498/aps.63.186801
Abstract +
ZnO:Tb nanofibers are fabricated by electrospinning method. X-ray diffraction and Raman results show that the sample is of hexagonal phase. The positions of doped diffraction peaks shift toward the small angle and the shift does not change with Tb content. Photoluminescence (PL) spectra of Tb-doped ZnO nanofibers show a strong defect-related emission and indicate that the doping affects the crystallinity of ZnO. It is found that Ti-capped can enhance the ultraviolet emission of ZnO nanofiber, while the defect-related emission is depressed. The enhancement in ultraviolet emission is mostly attributed to the surface plasmon coupling effect at the interface. The PL results indicate that the ZnO is not a proper matrix for Tb3+ ion.
2014, 63 (18): 186101.
doi: 10.7498/aps.63.186101
Abstract +
According to the first principles, we investigate the structure, electronic, and magnetic properties of fluorinated graphene doped with external X (Al, P, Ga, As, Si) atoms at double vacancies, and find that like double vacancy doping of graphene, this kind of the fluorinated graphene divacancy substitution is also an ideal choice for substitutional doping. The results show that the electronic property and magnetic property of the fluorinated graphene both have large changes: the fluorinated graphene doped with Al (Ga) atoms can cause the semiconductor-to-metal transitions and induce magnetic moments. The fluorinated graphene doped with P (As) atoms becomes spin-polarized semiconductor. The Si doped fluorinated graphene keeps the semiconductor properties unchanged and has no magnetic moments. Through the further discussion about the mechanism of magnetism the relation between the doping concentration and magnetic property is obtained, and the magnetic properties in different doping situations are found to be caused by the different orbital electrons of different atoms. The divacancy substitutional doping behaviors enrich not only the doping ways of fluorinated graphene materials, but also its distinctive electronic and magnetic characteristics, which make this doping structure have potential applications in future electronic devices.
2014, 63 (18): 186401.
doi: 10.7498/aps.63.186401
Abstract +
The structural phase transition, elastic, electronic properties and hardness for boride rhodium (RhB) under high pressure are systematically investigated by using the pseudopotential plane-wave density functional. The obtained lattice parameters, bulk modulus and elasitc constants are in good agreement with the available experimental and previous theoretical results at zero pressure. Furthermore, the mechanism of the high pressure structural phase transition is studied in detail. Our results show that RhB undergoes a structural phase transition from anti-NiAs-type to FeB-type at 25.3 GPa, which is in good agreement with other reported theoretical result. We also predict the pressure induced elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's coefficients, and elastic anisotropy factors, and find that the pressure has an important influence on the elastic properties. The calculated electronic density of states reveals that the pressure will strengthen the orbital hybridization between the Rh states and B states, the nonlocal effect and the strength of the covalent bond. Finally, on the basis of the Mulliken overlap populationanalysis, we obtain that the hardness of anti-NiAs-RhB is 18.1 GPa, which is compatible to the experimental value.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (18): 188401.
doi: 10.7498/aps.63.188401
Abstract +
Two-dimensional estimation for direction of arrival and direction of departure is required in the target location of bistatic multiple-input multiple-output (MIMO) system. In view of the huge calculation of array covariance matrix processing and the sensitivity to the array manifold mismatch, a beam optimization algorithm which can resist array manifold mismatch is proposed based on the virtual array of bistatic MIMO. Optimization for beam pattern through the second-order cone programming is used in the algorithm. The waveform diversity technology and location of bistatic system are combined. The relationship between direction of arrival at and direction of departure from the ellipse locating line is used to convert the two-dimensional synthesis direction vector into one-dimensional virtual array manifold. It is proved that the beam pattern of virtual array manifold transformed in bistatic MIMO can be equivalent to the combination of the beam pattern of transmitting array mapping on the receiving array angle domain and the beam pattern of receiving array. The algorithm can not only control the side lobe and null the beam pattern but also improve the ability to resist array manifold mismatch. The validity of the method is verified by the computer simulation of the optimized beam pattern and spectrum.
2014, 63 (18): 188102.
doi: 10.7498/aps.63.188102
Abstract +
Investigating the dendritic competitive growth mechanism is of great importance for directional solidification, and the numerical simulation technique is regarded as an effective approach to a description of microstructural evolution. Therefore, a modified cellular automaton model with decentered square algorithm is developed for quantitatively simulating the dendritic competitive growth process. The model takes into account the simplified thermal field, solute diffusion, growth kinetics, etc., and the solid fraction increment calculation is achieved through local level rule method. The model is successfully used to describe the dendrites with various growth orientations and its availability in simulating dendritic competitive growth is verified by comparing with the experimental results of transparent alloy. For the nickel-based superalloy, the simulated results reveal that in the case of converging dendrites, the unfavorably oriented dendrite is able to overgrow the favorably oriented dendrite, which is dependent on the preferential growth angle. For the divergence case, the favorably oriented dendrite can overgrow the unfavorably oriented dendrite through side branching at the grain boundary. The competitive growth process is mainly controlled by the pulling rate and the preferential growth angle. Furthermore, the model is successfully extended to the simulation of three-dimensional dendritic competitive growth.
2014, 63 (18): 188402.
doi: 10.7498/aps.63.188402
Abstract +
This paper presents a low-cost low-power humidity sensor for applications of ultra-high frequency radio frequency identification sensing tag. The humidity sensor element, based on standard SMIC 0.35 μm complementary metal-oxide-semiconductor technology, utilizes polyimide as sensing material and fabricates the interdigitated electrodes in top metal layer without any further post-processing. The humidity sensor interface, based on phase-locked loop theory, employs fully-digital architecture and achieves direct capacitance-to-digital conversion, which allows the supply voltage to be close to threshold voltage. The measurements at 25 ℃ show that the proposed humidity sensor achieves a sensitivity of 36.5 fF%RH, maximum hysteresis error of 7%, response time of 20 ms, and 2.1 μW power dissipation at 0.6 V supply voltage.
2014, 63 (18): 188101.
doi: 10.7498/aps.63.188101
Abstract +
In this paper, the dark electrical properties are studied by measuring the dark current-voltage characteristics of a type of domestic single-junction (SJ) GaAs/Ge solar cell after proton irradiation. Using a double exponential mode for the dark electrical properties of p-n junction, the dark I-V curves of the proton-irradiated SJ cells are mathematically fitted, and there are four kinds of typical parameters, namely serious resistance (Rs), parallel resistance (Rsh), diffusion current (Is1), and recombination current (Is2), which are determined to characterize the irradiation effects. Hence, four parameters such as Rs, Rsh, Is1 and Is2 are significantly changed after proton irradiation, where Rs, Rsh, Is1 increase while Rsh decreases with increasing the displacement damage dose. In addition, R_{s } increases with displacement damage dose, which is unrelated to proton energies. Theoretical analysis indicates that the above-mentioned changes of the parameters result from the damage distributions in different regions of the solar cells. Irradiation-induced damage in the base and emitter regions of the cells could induce Rs and Is1 to augment, while junction-region damage causes the Rsh to decrease but the Is2 to increase.
2014, 63 (18): 188301.
doi: 10.7498/aps.63.188301
Abstract +
The dynamic response of particles in hyper/supersonic flow is one of the key points of techniques using tracer particles, such as particle image velocimetry (PIV). In the literature, it is validated by the single oblique shock response testing. However, particles suffer intensive variation of velocity, density and viscosity, when used to trace and measure the complex flow field in the high speed vehicle engine. To test and validate the dynamics of particles in such a flow field with intensive gradient, in this paper we conduct a series experiments dealing with this issue. The study includes the measurements on the velocity field at the exit of the wind tunnel nozzle to testify the performance of PIV system, the measurements on the oblique shock response of particles in Mach 4.2 and Mach 3.0 supersonic flows over a 10° wedge and a 15° wedge respectively, and measurements on the double oblique shock response of particles in the flow field which is designed to simulate the flow field inside the vehicle engine with gradients and without the influence of expansion wave. Based on the particle dynamic models, the relaxation time, relaxation distance, Stokes numbers of different cases can be gained. And the influence of unstable shock oscillation is analyzed and revised based on image method and statistic analysis. It can be found that the relaxation time and distance increase with the Mach number, given the same wedge degree. However, with the same incoming Mach number, the relaxation time and distance drop when the wedge degree increases. Due to the intensive variation of Reynolds number and viscosity, the results show that in a certain extent particles lose their following ability by 5.7%, while its Stokes number increases by 1%. In the flow condition herein, the Stokes number still meets the requirement of supersonic flow. However the decrease of particle following ability is worth being concerned, especially when using particles in the complex flow field with more intensive gradients.
REVIEW
EDITOR'S SUGGESTION
2014, 63 (18): 184201.
doi: 10.7498/aps.63.184201
Abstract +
By controlling the spectral amplitude, phase and polarization of the femtosecond laser pulse in the frequency domain, a shaped femtosecond laser pulse with almost arbitrary pulse shape in time domain can be obtained, and this femtosecond laser pulse shaping technique provides a new experimental tool to study the nonlinear interaction between light and atoms or molecules. In this paper, we introduce the development history, technical method, control technique and relevant applications of the femtosecond laser pulse shaping technique, and also carry out a prospect on the research trends of this technique.
2014, 63 (18): 187301.
doi: 10.7498/aps.63.187301
Abstract +
Memristors are the fourth basic circuit element in addition to the three classical elements: resistor, capacitor, and inductor, which have great application prospects in the fields of information storage, logic operations and neuromorphic networks. The recent development of memristors and memristive mechanism is reviewed, including connotations and characteristics of memristors, memristive mechanism, types of memristive mateirals, and application prospects of memristors. Finally, the key problems and development proposals are presented and a prospect on the development trend is also given.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
EDITOR'S SUGGESTION
2014, 63 (18): 187304.
doi: 10.7498/aps.63.187304
Abstract +
Silicene is a two-dimensional honeycomb lattice formed by a monolayer of silicon atoms, which has similar electrical properties to those of graphene. Silicene attracts much attention due to its relatively large spin-orbit coupling. The transport properties through a silicene quantum wire controlled by a gate are studied by using the non-equilibrium Green function formalism. A pair of gapless and spin-polarized edge states appears only when the gate voltage is strong and the silicene quantum wire has perfect zigzag or armchair boundaries in which additional silicon atoms are absent. Moreover, the edge states controlled by gate are spin valley-polarized, that is, the directions of spins are opposite in different valleys, which is different from that of the edge state at the interface between the silicene and vacuum. These results can be helpful to design and fabricate the practical silicene nanostructure.
2014, 63 (18): 187302.
doi: 10.7498/aps.63.187302
Abstract +
Transport properties of Cd0.96Zn0.04S/Cd0.97Mn0.03S/Cd0.96Zn0.04S multilayer nanowires, deposited in porous anodic aluminum oxide templates by DC electrochemical method, are studied. It is found that the transmission current oscillates against the applied magnetic field, even the thickness of the spin doping barrier is about 96 nm. s-d exchange constant N0 is obtained from the resonant transmission measurement. A e-(1/T) temperature dependence of N0α ndicates the electrostatic interaction nature of the s-d exchange interaction.
2014, 63 (18): 187101.
doi: 10.7498/aps.63.187101
Abstract +
The effect of S impurity on adhesion of Fe(110)/Al2O3(0001) interface is studied by the first-principles plane wave pseudopotential method within the density functional theory. It is shown that S impurity prefers to occupy the site of Fe3 at Fe(110)/Al2O3(0001) interface substitutionally due to the smallest interface segregation energy. The adhesion of Fe(110)/Al2O3(0001) interface is mainly governed by the interaction between Fe and O atoms on both sides of interface. The calculation results of the partial density of states, Mulliken overlap population and the electron density all suggest that Fe-O interaction is weakened by the segregated S impurity at Fe/Al2O3 interface, and the presence of S impurity gives rise to stronger electrostatic repulsion between Fe and O atoms across Fe/Al2O3 interface, which all leads to a reduced adhesion for Fe/Al2O3 interface. As a result, the results obtained by the first principles can give us a deeper understanding of the mechanism of a reduced interface adhesion and the oxidation film spallation by the segregation of S impurity at FeCrAl alloy interface.
2014, 63 (18): 187701.
doi: 10.7498/aps.63.187701
Abstract +
Hexagonal YMnO3 is a special kind of multiferroics which shows unique advantages in magneto-electric field due to its low permittivity and only c-axis polarization. However, its ferroelectric properties, especially domain structures, have not been intensively investigated. In this study, YMnO3 film about 270 nm in thickness is prepared on Si(100) substrate by sol-gel spin coating. Structure and morphology of the film are characterized by grazing incidence X-ray diffraction and atomic force microscopy. Domain structure and its reversal behavior on a nanoscale are examined by piezoresponse force microscopy (PFM). The leakage current and ferroelectric property are also investigated. The results show that the film displays a hexagonal perovskite structure with good crystallinity and has smooth surface with a root-mean-square roughness of 7.209 nm. PFM images and typical local piezoresponse loops reveal the good piezoelectric and ferroelectric properties of the YMnO3 film at room temperature. Meanwhile, the offsets of amplitude loop and phase loop are observed due to the internal electric field. Leakage current density of YMnO3 film is lower than 10-6 A·cm-2, so saturated hysteresis loop can be obtained.
2014, 63 (18): 187801.
doi: 10.7498/aps.63.187801
Abstract +
The area of sandy land is extending in China because the natural environment suffers the destruction by the human activity. The estimation of the properties and area of sandy land is an important indicative information for improving the environment. Remote sensing technique can provide scientific and effective data sources using its unique advantage. In this study, we measure the bidirectional reflectance information from sandy land surfaces with different particle sizes and analyze the effect of particle size on the reflection characteristics. Then, a comparison is performed between the measured reflectance and the reflectance of sandy land surface with different particle sizes which is computed based on existing model. The results show that the effect of particle size on the bidirectional reflectance distribution is apparent We also find that the bidirectional reflectance of sandy land surface with different particle sizes can be computed using the bidirectional reflectance model when the difference between measured reflection information and modeled reflection information is small. This study not only defines the effect of particle size on the reflectance from sandy land surface, but also provides valuable reference for estimating the particle size from sandy land surface using remote sensing technique and studying the intrinsic optical property of land surface.
2014, 63 (18): 187303.
doi: 10.7498/aps.63.187303
Abstract +
By using first-principles method, we study the stacking effects on the electronic structure, topological phase and spin splitting in the bulk and film of topological insulator Bi2Se3. It is found that the different stackings can lead to different interlayer interactions and change the centrosymmetry of Bi2Se3. The centrosymmetric ABC and AAA stackings in bulk Bi2Se3 have similar band structures. ABA stacking breaks the centrosymmetry, giving rise to considerable changes of the band structure and large spin splitting. We further study the stacking effects in the film of Bi2Se3 and find that the non-centrosymmetric ABA stacking can induce large spin splitting in Bi2Se3 film. It is proposed and illustrated that the strain can tune the spin splitting effectively.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2014, 63 (18): 185201.
doi: 10.7498/aps.63.185201
Abstract +
The effective measurement of plasma turbulence flow field is of great help for better understanding the turbulence in magnetically confined plasmas, and experimentally verifying the theoretically predicted phenomenon such as zonal flows. In this article, the dynamic programming based time-delay estimation technique is employed for the first time to estimate azimuthal velocity fluctuation of drift-wave turbulence in a linear magnetized plasma generated via a hot cathode plasma source. Analysis results clearly reproduce the zonal flow structure which is spontaneously generated by nonlinear energy transfer from the drift-wave turbulence. Moreover, via the comparison among the zonal flow (ZF) characteristics estimated respectively by the turbulent fluctuations of plasma located in different frequency regions, we further evaluate the dependences of accuracy and response for estimating ZF property using this newly developed time-delay estimation algorithm on the level of relative incoherent noise in the carrier waves. This work provides an example and reference value for deeper exploration on plasma turbulence and in particular the relevant flow field with the help of the dynamic programming based time-delay estimation technique.
2014, 63 (18): 185203.
doi: 10.7498/aps.63.185203
Abstract +
In this paper the physical model and numerical algorithm of particle-in-cell (PIC) simulation for gas-puff Z-pinch in two-dimensional cylindrical coordinates are briefly introduced. The code is also developed according to the model and algorithm. The rarefied gas-puff Z-pinch driven by a low current is simulated through the code, and some reasonable results are obtained. The results include the spatiotemporal distributions of current, electromagnetic field, particle positions and density, as well as the trailing mass and current. It is found that the simulated current reflects the plasma Z-pinch characteristics, i.e., the plasma current arrives at a minimum when the plasma enters into stagnation, and it begins to increase after the plasma has moved outwards. The simulated magnetic field agrees well with the theoretic value. The electric field force and magnetic field force experienced by electron are almost the same in magnitude, while the force acting on ion is mainly the electric field force. Firstly the electron is accelerated in the z direction and reaches a velocity, then it moves inward the axis in the same time by the Lorentz force. That causes the separation between electron and ion, and a strong electric field is produced. The produced electric field attracts the ion inward the electron. When the electrons arrive at the axis, they move inversely due to the static repellency among them, while the ions continue to move initially inwards, and later enter into stagnation, and finally collapse. The trailing mass is about 20% of the total Z-pinch plasma, and the maximum trailing current is about 7% of the driven current. In the future the code needs to develop further and realize parallel computation in order to simulate the practical Z-pinch processes by PIC simulation.
2014, 63 (18): 185205.
doi: 10.7498/aps.63.185205
Abstract +
A N2-H2 capacitively coupled rf discharge has potential applications in etching of organic low dielectric constant (low-k) material for microelectronics technology. In this paper, we investigate the characteristic and electrical asymmetry effect (EAE) on the N2-H2 capacitively coupled plasma used for low-k material etching by particle-in-cell/Monte Carlo (PIC/MC) model, in which the two frequency sources of 13.56 MHz and 27.12 MHz are applied separately to the two electrodes in geometrically in symmetry. It is found that the plasma density profiles, the ion flux density profiles and the energy distribution of ion bombarding electrodes can be changed by adjusting the phase angle θ between the two harmonics. When the phase angle θ is 0°, the density of primary ion (H3+) near low frequencie electrode (LFE) (wafer) is smallest, whereas flux and average energy of ion (H+, H3+, H2+) bombarding LFE are biggest; if the phase angle θ is tuned from 0° to 90°, the dc self-bias increases almost linearly from -103 V to 106 V, ion flux bombarding the LFE decreases by ±18%, the maximum of the ion bombarding energy at the LFE decreases by a factor of 2.5. For the N2-H2 capacitively coupled rf discharge, for the case of two frequencies (13.56 MHz/27.12 MHz) applied separately to the two electrodes, can realize separate control of ion energy and flux via the EAE, and is generally in qualitative agreement with experimental and modeling investigation on the Ar and O2 plasma for a dual-frequency voltage source of 13.56 MHz and 27.12 MHz is applied to the powered electrode. This work supplies a references basis for experimental research and technology that the EAE on the H2-N2 plasmas is used for organic low-k material etching process.
2014, 63 (18): 185208.
doi: 10.7498/aps.63.185208
Abstract +
Dielectric barrier discharge (DBD) can produce non-equilibrium plasma at atmospheric pressure, and it has become a hot point in recent years. For the DBD excited by pulsed or alternated currents, the effects of the loading performance of power supply, the matching between supply and discharge reactor and the discharge phenomena on its discharge are interesting issues. The studies of these issues are of great importance for understanding the DBD processes and improving the power supply efficiency. In this paper, the Lissajous figures of a DBD reactor with coaxial electrode configuration are measured. The loading performance of the DBD reactor and the dependences of excitation voltage and air flow rate on the dielectric layer equivalent capacitance are studied in atmospheric air. According to the experimental data and circuit modeling analysis, it is proved that the dielectric layer capacitance decreases with the increase of air flow rate, but increases with the increase of excitation voltage. The amplitude-frequency performance of the reactor reveals significant RLC circuit resonance. The resonance frequency of the reactor has the same behavior as its dielectric layer capacitance. Therefore it shows that the dielectric layer capacitance is the main factor for the resonance frequency evolution. A possible mechanism responsible for the dielectric layer capacitance is also presented.
2014, 63 (18): 185202.
doi: 10.7498/aps.63.185202
Abstract +
Laser indirect-drive has the potential to obtain ultra-high pressure which is very useful for shock physics. The isentropic compression can be obtained with reservoir target in laser indirect-drive experiment. The free surface velocity and interface velocity are the two important parameters in isentropic compression experiment. The efficiency with reservoir target is lower than that in the isentropic compression experiment with long pulse laser direct-drive. However, the isentropic compression experiment with long pulse in laser direct-drive is very sensitive to the laser intensity variation. In this paper, the isentropic compressions with reservoir target with indirect-drive and direct-drive on Shen Guang-Ⅲ prototype laser facility are investigated separately. And the important technique is introduced to provide the reference data in this field. And the isentropic compression with long pulse laser direct-drive is analyzed on Shen Guang-Ⅲ prototype laser facility. The interface velocity on Al/LiF is achieved with three steps. The blank effect is provided and analyzed. These data show that with long pulse in laser direct-drive, a pressure, which has been highest in China up to now, can be obtained. With these experiment data, the feasibility to do the isentropic compression experiment on Shen Guang-Ⅲ prototype laser facility has been approved.
EDITOR'S SUGGESTION
2014, 63 (18): 185207.
doi: 10.7498/aps.63.185207
Abstract +
Plasma source ion implantation and deposition, as an effective technology to produce functional coatings with high adhesion and density, possesses the wide application prospect, especially in the deposition of coatings that work in high loading service conditions. The key component of this technology is the metal plasma source, which is now based on pulsed cathodic arc with complex source structure and magnetic filtration because of the macro-droplets in the ion flux. In this paper, we present another metal plasma source, high power pulsed magnetron sputtering (HPPMS), and investigate the discharge characteristics at different coupling high-voltages by optical emission spectroscopy. The results show that significant improvements are found in the discharge target current and main particles in the plasma. The improvement in gas discharge by the coupling high-voltage is greater than in metal discharge which could increase obviously in the self-sputtering stage with higher target voltage discharge. Last but not least, in this paper we discuss the discharge enhancing mechanism of coupling high-voltage. It is found that the self-excited glow discharge of coupling high-voltage, the hollow-cathodic effect induced by face-to-face negative voltages of HPPMS and coupling high-voltage, and the enhanced ambipolar diffusion of the coupling high-voltage can all play a considerable role in HPPMS discharge.
2014, 63 (18): 185206.
doi: 10.7498/aps.63.185206
Abstract +
In this paper, an electromagnetic-field FDTD method coupled with plasma fluid model is put forward to investigate the different physical phenomena of high power microwave (HPM) flashover and breakdown on inner and outer surface of output-window. Based on the above theoretical models, a one-dimensional (1D) electromagnetic field and plasma interaction code is programmed by authors. By using the code, the HPM flashover and breakdown on inner and outer surface of output-window are simulated. The numerical results could be concluded as follows. For flashover and breakdown on outer surface, output microwave pulse is shortened without cut-off; there is a standing-wave distribution of electric field RMS (Root-Mean-Square) value before the window with fixed-positions of wave nodes and antinodes; there is a ultra-high-density (～1021 m-3) and ultra-thin (～mm) plasma shell with slow diffusion, microwave could penetrate the plasma-shell partly; the shortening of output microwave is caused by plasma absorption mostly. The output pulse of microwave could be lengthened by reducing the initial density or depth of plasmas; the other way is to shorten incident microwave pulse or reduce the value of incident microwave power. For flashover and breakdown on inner surface, there is also a standing-wave distribution of electric field RMS value before the window but the positions of wave nodes and antinodes vary with time; the plasma region moves toward the microwave source; with strong-outgassing, output microwave pulse is shortened without cut-off, there are “thread-like” ultra-high-density (～ 1021 m-3) and ultra-thin (～mm) plasma regions with slow diffusion, the distance between two “thread-like” regions is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and low electric field value, the output pulse of microwave is lengthened but cut-off finally, there are “belt-like” high-density (～ 1018 m-3) and thin (mm-cm) plasma regions with fast diffusion, the distance between two “belt-like” region is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and high electric field value, output pulse of microwave is cut-off quickly, “block-like” diffuse ultra-high-density (～1021 m-3) and deep (～ cm) plasma regions are formed with very fast diffusion, and the shortening of output microwave is caused by plasma reflection mostly.
2014, 63 (18): 185204.
doi: 10.7498/aps.63.185204
Abstract +
A series of SiC intermediate layers with different preparation temperatures is prepared by radio frequency magnetron sputtering on 316L stainless steel substrates by use of SiC crystal target and Argon as source gases. And then depositing fluorinated diamond-like carbon films (F-DLC) on a series of SiC intermediate layers under the same deposition condition with trifluromethane (CHF3) and Argon as source gases, and pure graphite as a target, a series of SiC/F-DLC composite films are obtained. The results show that the composite films have stronger adhesion and better hemocompatibility than that of the F-DLC films. The structure evolves with preparation temperatures of SiC intermediate layers and SiC/F-DLC composite films are studied by their Raman and Infrared transmission spectra. The results show that the proportion of C=C bonds and density of C-C unsaturated bonds in the SiC intermediate layers can be modulated by controlling the preparation temperature of SiC intermediate layers. The composite films have better hemocompatibility, especially with about 500 ℃ preparation temperature, may be attributed to holding higher proportion of aromatic ring structure and higher ratio of F/C in the composite films than the others. Formation of a considerable number of Si-C bonds and C=C bonds between SiC and F-DLC films may be the direct cause of strong adhesion. The addition of modest SiC intermediate layers between 316L stainless steel substrates and F-DLC films is feasible and effective to enhance films adhesion and improve film hemocompatibility.
NUCLEAR PHYSICS
2014, 63 (18): 182801.
doi: 10.7498/aps.63.182801
Abstract +
Polarized neutron radiography allows the direct and real-space visualization of magnetic field distribution by detecting the polarization change in the transmitted beam. Two approaches to magnetic field quantification by means of polarized neutron images are studied. They are energy-selective method and spin-echo method. Both approaches need no corrections of parameters, such as polarization efficiency, and can quantify magnetic field integral without periodic uncertainty. The quantification ability, applicability and feasibility of two approaches at research reactor neutron source are verified by numerical simulation with key parameters such as monochromator resolution and polarization efficiency. The results will be helpful to process image data and designing instruments.
2014, 63 (18): 182901.
doi: 10.7498/aps.63.182901
Abstract +
The optics is one of the main components of an ion thrust, which influences the performance and thruster lifetime. The operation of ion thruster can be evaluated by numerical simulation based on the current-voltage entrance condition, especially for thruster with a variety of operating modes. The plasma transport process is simulated with 3D-PIC (particle in cell) method for a two-grids optic. The performances of the NSTAR thruster under different operating modes are calculated and compared with the results of in-orbit test, verifying the correctness of the simulation mode. The influences of operation modes on the electric field distribution and the beam state are analyzed, and the requirements of multi-mode design for ion thruster are discussed. The results show that a convex sheath and concave zero equipotential surface away from the optic, low value of “saddle point”, and gentle downstream potential distribution, which help to improve ion pass rate, suppress electronic reflux and reduce Pits-and-Grooves corrosion, are the target of ion thruster mode design. Increasing beam voltage will result in a high loss caused by the divergence angle, and extend the beam current range for a good operation condition. For a large beam current mode, high beam voltage will make the beam have a better “focus” state, and reduce the Barrel corrosion. The results will provide a reference for the operation mode design for the multi-mode ion thruster.
2014, 63 (18): 182802.
doi: 10.7498/aps.63.182802
Abstract +
In order to study the stability of perovskite-type SrTiO3 used for immobilizing Y3+, Sr (NO3)2, TiO2 and Y2O3 are used as starting materials. The synthesized Y2O3-doped SrTiO3 can be generally represented as Sr1-1.5xYxTiO3 (0≤ x≤0.12) with the high temperature solid reaction. The phases, structures and microcosmic shapes of synthetic condensates are characterized by the X-ray diffraction, Raman and scanning electron microscopy, and long-term chemical stability is studied at 90 ℃. The results indicate that the phases of compounds change from perovskite to pyrocholre phase when the value of x is more than 0.08. The leaching rates of Sr2+ and Y3+ in waste form increase with the increase of immersion time. The highest leaching concentrations of Sr2+ and Y3+ for 42-day immersion are no more than 0.004 and 0.02 μg·mL-1, respectively.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (18): 189201.
doi: 10.7498/aps.63.189201
Abstract +
Based on radar reflectivity image features, an automatic recognition method is proposed to identify the hail and rainstorm. We extract the image features of hail echo areas and rainstorm echo areas from radar reflectivity images. By analyzing both the differences in single feature between hail and rainstorm and the classified complementarity among different features, we determine the effective image features, including the intensity and texture features, to identify the hail and rainstorm. The hail and rainstorm objective recognition model can be established through the data mining of the extracted sample features and sounding data by using the Rough Set Theory. Through the test and identification of the 362 test samples, the hit ratio of hail reaches 93.29% and the hit ratio of rainstorm reaches 89.07%. The false alarm ratios of hail and rainstorms can be also at a low level. Compared with those from the PUP system, the experimental results from the present system show that it has a good effect to identify and classify hail and rainstorm by using the radar reflectivity image features.
2014, 63 (18): 189501.
doi: 10.7498/aps.63.189501
Abstract +
Total variation is a hot point of research on speckle reduction. The nonconvex regularizer can better preserve or even enhance the information about the edges of an image. Spatially adaptive regularization parameters can reasonably control the level of speckle reduction according to the region in which the pixels are, and improve the speckle reduction effect. In this paper, we present a new total variation model for speckle reduction by integrating nonconvex regularizer and spatially adaptive regularization parameters. In order to solve the model, a new algorithm is designed based on Newton's method, augmented Lagrange multiplier, alternating direction method of multipliers, and iteratively reweighted method. The numerical examples demonstrate that the proposed model can obtain the better speckle reduction effect.
