Vol. 63, No. 3 (2014)
2014, 63 (3): 034305. doi: 10.7498/aps.63.034305
By taking a two-dimensional solid local resonant phononic crystal as an example, we investigated the mechanism of the defect state on a subwavelength scale. It is well known that, when the working wavelength is much greater than the distance between resonators, the dispersion of the phononic crystal is insensitive to the lattice structure, and the whole structure can be described in terms of the effective medium theory. As a result, it is hard to introduce a defect state in the system by a local real-space disorder. It is shown in this paper that the dispersion of the local resonant phononic crystal can be understood from the long-range feature of the interaction between resonators, so the creation of a defect state in the system is in fact to break such a long-range interaction. Based on this understanding, the mechanisms of the recently reported methods, that are used to create defect states, are discussed. In addition, a waveguide structure that can guide the longitude or transverse waves separately is realized by introducing an anisotropic defect resonator.
2014, 63 (3): 034702. doi: 10.7498/aps.63.034702
Granular flow is usually divided into three kinds of flow pattern, namely quasi static flow, slow flow, and rapid flow. The core issue of the research is the constitutive relation. A series of constitutive relations of application value have been received up to now, however, the study on principal theory is insufficient. Granular flow has an emergent mesoscopic structure, such as force chain network and vortex, involving complex irreversible processes. This paper studies its mesoscopic structure and principal characters, introduces the concept of two granular temperatures Tconf and Tkin of the granular flow to characterize the degree of chaotic motion and disordered configuration evolution, sets them as the non-equilibrium variables to constitute the thermodynamic state variables set for granular flow with the classical irreversible thermodynamic (CIT) variables, also determines the granular flow law of energy conversion and the entropy production rate, etc., and develops the two granular temperatures (TGT) model. Taking the simple shear quasi-static granular flow in a constant volume as example, and combining it with the discrete element method (DEM), this work confirms the material parameters needed for the TGT model, and analyzes the law of developing period and the effective coefficient of friction of steady period of granular flow.
2014, 63 (3): 038102. doi: 10.7498/aps.63.038102
Sublimation of SiC substrates is a promising way to prepare high-quality graphene on large scale. Nowadays, growth of high-quality epitaxial graphene is still a crucial issue. In this work, monolayer epitaxial graphene is grown on Si-terminated 4H-SiC (0001) substrate. By introducing argon inert gas and silicon vapor as background atmosphere, the Si evaporation rate and condensation rate on the SiC surface is close to equilibrium and the growth of monolayer epitaxial graphene with very low speed is realized. The growth duration of monolayer epitaxial graphene is prolonged to 75 minutes from 15 minutes. It is found that the disorder-induced Raman D peak shows an obvious decrease as the growth speed decreases, indicating the improvement of crystal quality, which makes the electrical properties of the monolayer epitaxial graphene is improved. The maximum carrier mobility and sheet resistance have reached 1200 cm2/Vs and 604 /, respectively. The above results indicate that slowing down of growth speed by controlling of growth atmosphere is an efficient way to prepare high-quality epitaxial graphene.
New complex soliton-like solutions of combined KdV equation with variable coefficients and forced term
2014, 63 (3): 030201. doi: 10.7498/aps.63.030201
The [G()]/[G()] expansion method is extensively studied to search for new infinite sequence of complex solutions to nonlinear evolution equations with variable coefficients. According to a function transformation, the solving of homogeneous linear ordinary differential equation with constant coefficients of second order can be changed into the solving of a one-unknown quadratic equation and the Riccati equation. Based on this, new infinite sequence complex solutions of homogeneous linear ordinary differential equation with constant coefficients of second order are obtained by the nonlinear superposition formula of the solutions to Riccati equation. By means of the new complex solutions, new infinite sequence complex soliton-like exact solutions to the combined KdV equation with variable coefficients and forced term are constructed with the help of symbolic computation system Mathematica.
2014, 63 (3): 030202. doi: 10.7498/aps.63.030202
The quantum plasma system in a class of environment is discussed. A nonlinear dynamic disturbed equation is studied. Using the revised generalized functional variational iteration method, the solitary-like wave approximate analytic solution of corresponding system is obtained.
2014, 63 (3): 030203. doi: 10.7498/aps.63.030203
Band structures of silicon photonic crystal (PC) with different lattices and shapes of air holes at telecom wavelengths were investigated by plane-wave expansion method, and the related physical models were proposed. Calculated results demonstrate that photonic band gap (PBG) can be effectively manipulated by photon confinement effect and lattice symmetry effect. With the increase of filling fraction, the ability with which photons are confined by PC is enhanced, PBG is opened and the central frequency undergoes a blue-shift. PBG is enlarged as the lattice symmetry increases. Shape and rotation of lattice element are also studied. Band gap with the rotation angle which follows periodicity and symmetry indicates its anisotropy. The optimal cavity structures for different lattices are also found.
2014, 63 (3): 030301. doi: 10.7498/aps.63.030301
The geometrical quantum discord (GQD) is an effective measure of quantum correlation in quantum systems. We have studied GQD dynamics of the system comprising two two-level atoms resonantly interacting with two coupled cavities. GQD between atoms and that between cavities are investigated. The influences of coupling constant between cavities and initial entanglement between atoms on GQD are discussed. Results obtained using a numerical method show that GQD between atoms is strengthened, and GQD between cavities is weakened with increasing initial entanglement between atoms. On the other hand, the evolution regularity of GQD between atoms and that between cavities are all strengthened with increasing coupling constant between cavities.
Analysis of measurement device independent quantum key distribution with an asymmetric channel transmittance efficiency
2014, 63 (3): 030302. doi: 10.7498/aps.63.030302
Measurement-device-independent quantum key distribution is immune from all the detection attacks, thus when it is combined with the decoy state method, the final key is unconditional secure. In this paper, the performance of three-intensity decoy state measurement-device-independent quantum key distribution at an asymmetric channel transmittance efficiency is considered and compared with each other at the symmetric choice scenario. Simulation result shows that the key rate at the symmetric scenario can tolerate 62 dB channel loss, otherwise when the distance ratio changes, the tolerated channel loss will decrease to 37 dB and 19 dB. A method to choose the optimal intensity is proposed for asymmetric channel transmittance regardless of distance ratio, which can be easily adapted to practical experimental settings.
2014, 63 (3): 030401. doi: 10.7498/aps.63.030401
Dynamically accessible perturbation is a type of Lie perturbation for noncanonical Hamiltonian systems. Firstly, a set of first-order constraint variations that preserve all the Casimir functions is presented based on the two-fluid Poisson bracket. Then the equilibrium equations are given by minimizing the two-fluid Hamiltonian with these variations.
2014, 63 (3): 030501. doi: 10.7498/aps.63.030501
To better explore the robustness against cascading failures on complex networks, according to the redistribution rule of the real networks always lie between global preferential rule and local preferential rule or between even shared rule and extremely heterogeneous rule. A new cascading model is proposed based on a tunable load redistribution model. It can tune the load redistribution range and the redistribution heterogeneity of extra load respectively by a redistribution range coefficient and a redistribution heterogeneity coefficient. With this model, we further investigate cascading failures on scale-free networks in terms of numerical simulation and theoretical analysis respectively. Numerical simulation and analytic results show that the model can achieve better robustness against cascading failure than the previous model by adjusting the redistribution range and heterogeneity.
Solution of the fractional-order chaotic system based on Adomian decomposition algorithm and its complexity analysis
2014, 63 (3): 030502. doi: 10.7498/aps.63.030502
Based on the definitions of fractional-order differential and Adomian decomposition algorithm, the numerical solution of the fractional-order simplified Lorenz system is investigated. Results show that compared with the Adams-Bashforth-Moulton algorithm, Adomian decomposition algorithm yields more accurate results and needs less computing as well as memory resources. It is even more accurate than Runge-Kutta algorithm when solving the integer order system. The minimum order of the simplified Lorenz system solved by using Adomian decomposition algorithm is 1.35, which is much smaller than 2.79 achieved by the Adams-Bashforth-Moulton algorithm. Dynamical characteristics of the system are studied by the phase diagram, bifurcation analysis, and complexities are calculated by employing the spectral entropy (SE) algorithm and C0 algorithm. Complexity results are consistent with the bifurcation diagrams, for which mean complexity can also reflect the dynamic characteristics of a chaotic system. Complexity decreases with increasing order q, and there are little influences on complexity versus changes of parameter c when the system is chaotic. It provides a theoretical and experimental basis for the application of fractional-order chaotic system in the field of encryption and secure communication.
2014, 63 (3): 030503. doi: 10.7498/aps.63.030503
According to the characteristics of railway line and NaSch model a cellular automata model for simulating multi-train tracking of railway curve is proposed. The computer numerical simulation is carried out and the influence of different curve radius, outer rail superelevation curve and curve length on railway traffic flow are studied using the propose model. Simulation results show that the model can reflect accurately traffic flow situation of the special line; and the train line curve has a great influence on the running safety and reveals the traffic wave phenomena in running and stopping. With increasing curve radius, train delay time decreases gradually according to the simulation results. Reasonable selection of curve radius, the outer rail superelevation and curve length can significantly improve the line capacity and reduce the wheel rail wear, so that these can guarantee the safety and comfort of the train running. The results have certain guiding significance for the railway line design and operational management.
2014, 63 (3): 030701. doi: 10.7498/aps.63.030701
Existing spectrum sensing systems are commonly designed based on the famous Nyquist theorem. With the rapid development of radio frequency technology, the corresponding sampling frequency is so high that many problems may be brought about, such as the increasing hardware complexity, large volume of measurements and difficulties to meet the real time requirement etc. To tackle these problems caused by high sampling frequency, a novel scheme, adaptive modulated wideband converter, is proposed. By exploiting the band width of the narrow bands, the total sampling frequency is proved to be as low as four times of the sum of the narrow bands. There is a trade-off between the sampling complexity and the total sampling frequency for different choices of the repeating frequency of the random function. Sufficient conditions are derived to guarantee exact signal recovery from sub-Nyquist measurements. Conditions of full row rank of the equivalent unknown matrix are also explored to guarantee that the multiple signal classification can be adopted to implement the signal reconstruction. The simulations verify the analysis. This novel scheme can be used to implement front-end spectrum analysis for absorbing materials and detect the active channels in cognitive radio.
2014, 63 (3): 030702. doi: 10.7498/aps.63.030702
Aiming at the peaks overlapping in the field of X-ray diffraction, a new method for peaks separation was developed, and the parameters and recovery behaviors of crystal lattice of 30CrMnSiNi2A were investigated using RU-200V X-ray powder diffractmeter, by which the relationship between lattice parameters and carbon content at different tempering temperatures was obtained. Results show that the variation of lattice parameters of 30CrMnSiNi2A is consistent with high-carbon martensite on the whole, however there are some differences in the rate of change. The lattice parameter a is independent of carbon content, and slightly decreases with the rise of tempering temperature, while the amplitude of change for the lattice parameter c and carbon content is large, and a steep drop is observed in the process of quenching to the tempering temperature at 180 ℃, while the amplitude becomes flat aferwards for a higher tempering temperature.
2014, 63 (3): 032801. doi: 10.7498/aps.63.032801
In this paper, collisional quenching rate for Li(2P) atoms with argon molecules is studied in photochemical isotope separations. In the weak laser irradiation, the absorption spectra and fluorescence emission spectra of lithium atom vapor is measured by changing the argon pressure. The quenching rate constant of (12.29±0.92)×10-18 m3·s-1 for Li(2P) atoms quenched with argon molecules have been determined. This value is much smaller than the spontaneous emission rate of Li(2P) atoms. The experimental result shows that in photochemical lithium isotope separation collisional quenching effect on the separation selectivity is very small and can be neglected.
2014, 63 (3): 032802. doi: 10.7498/aps.63.032802
During high-temperature gas refrigeration reactor (HTGR) operation, SiC in the fuel particles is the key structure for stopping radionuclides diffusing from the particles. Researchers put forward the concept of breakthrough time, which is the time of a large amount of radionuclides released through SiC from the particles, for the consideration of HTGR safety. However, this concept is not so accurate. This paper gives a strict expression of cumulative fractional release interims of classic and improved methods, and also analyses the relevant physical content of breakthrough time in the use of Fick’s law of diffusion. By computing the cumulative fractional release of three kinds of important radionuclides 137Cs, 90Sr and 110mAg, and using the above two methods, we find that the traditional meaning of the physical quantity is not the time of radionuclides released from SiC. The improved method is more accurate for describing the release and transport condition of radionuclides in nuclear fuel particles.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2014, 63 (3): 034101. doi: 10.7498/aps.63.034101
A novel design for high gain and low radar cross section (RCS) waveguide slot antenna is proposed. Low RCS screen composed of orthogonal array of complementary split ring resonator etched square patch artificial magnetic conductor (CSRR-AMC) is exploited on the antenna for radiation improvement and broadband RCS reduction. Measured results demonstrate that the operating bandwidth is increased by 100 MHz and the gain is enhanced by 3.2 dB with the proposed structure. Meanwhile, 10 dB RCS reduction is achieved over the range of 5.52–6.63 GHz, implying 20% relative bandwidth.
A time-domain Gauss-Newton inversion algorithm for solving two-dimensional electromagnetic inverse scattering problems
2014, 63 (3): 034102. doi: 10.7498/aps.63.034102
The Gauss-Newton inversion (GNI), an iterative algorithm, is developed from the frequency domain to the time domain in order to simultaneously reconstruct the electrical permittivity and electric conductivity of a two-dimensional object of interest by directly using the ultra-wideband time-domain measurement data. The resulting forward problem is solved by the finite difference time domain method, while the ill-posedness of the corresponding inverse problem is restrained by an adaptive regularization technique at each iteration. Furthermore, the modified GNI algorithm is applied to four types of numerical examples where a noise model is considered, and the simulated results preliminarily demonstrate its feasibility and robustness. The reconstructed images present super resolution, thus it is expected to be used in the engineering practice such as the detection of the early-stage breast cancer.
2014, 63 (3): 034201. doi: 10.7498/aps.63.034201
Some bonds on the curved surface (CS) of silicon nanostructures can produce localized electron states in the band gap. Calculated results show that different curvature can form the characteristic electron states for some special bonding on nanosilicon surface, which are related to a series peaks in photoluminescience (PL), such as LN, LO1 and LO2 lines in PL spectra due to SiN, Si=O and SiOSi bonds on the curved surface, respectively. In the same way, SiYb bond on the curved surface of Si nanostructures can manipulate the emission wavelength into the window of optical communication by the CS effect, which is marked as LYb line near 1550 nm in the electroluminescience (EL).
A 147 fs mode-locked erbium-doped fiber laser with a carbon nanotubes saturable absorber in evanescent field
2014, 63 (3): 034202. doi: 10.7498/aps.63.034202
A saturable absorber of 3.9% modulation depth was prepared on the surface of a fiber clad with single-walled carbon nanotubes (SWCNT) using chemical corrosion method. An all-fiber Er-doped fiber laser was setup with a ring cavity, and was mode-locked successfully by evanescent field mode-locking using prepared saturable absorber of single-walled carbon nanotubes. A 147 fs mode-locking pulse is obtained near 1556 nm with a 3 dB bandwidth of 24 nm. The output power is 21 mW at a pump power of 520 mW, corresponding to a pulse energy of 0.14 nJ with a repetition rate of 150 MHz.
2014, 63 (3): 034203. doi: 10.7498/aps.63.034203
A method for multiple sub-beams coherently emitting is put forward to improve the ability of laser to detect small targets in a long distance. The laser beam is split into many sub-beams with equal power parallelly emitted to the target in a certain arrangement. The sub-beams produce interference pattern on the target plane due to the fact that they are from the same laser source and have good coherence. Calculated results show that an interference peak is produced. Ideally, the maximum intensity would be N times as large as the intensity of the single beam emitted directly, where N is the number of the sub-beams. The detection is realized by using the interference peaks, and it will benefit especially to the detection of small targets. Beams divergence should be reduced to let a greater power to the target. In order to control the light intensity instability and the spot distortion, the jitters of the emitting mirrors must be controlled as well. Results show that a position accuracy of 0.1λ and an angle accuracy of 0.2θ are needed to have a stable and ideal interference peak, where λ is the wavelength and θ is the divergence angle of the beam.
2014, 63 (3): 034204. doi: 10.7498/aps.63.034204
We report the visible supercontinuum (SC) generation in the double zero dispersion multi-core photonic crystal fiber (PCF), pumped by picosecond pulses from Yb-doped fiber laser. Such a dual-concentric-core-like PCF provides two closely spaced zero-dispersion wavelengths (ZDW). The redshift solitons will be canceled out at the vicinity of the second ZDW, and the steady solitons will cause considerable dispersive waves at the edges of the output SC which spans from 550 to 1700 nm at an average pump power 1 W. Moreover, the optical field is transferred from the inner core to the outer core. Experimental results agree well with the theoretical calculations.
Improvement of the filtering performance of a heterostructure photonic crystal ring resonator using PSO algorithm
2014, 63 (3): 034205. doi: 10.7498/aps.63.034205
To improve the filtering performance of a heterostructure photonic crystal ring resonator filter, the filtering structural parameters were optimized globally by using particle swarm optimization (PSO) algorithm. By taking the square lattice photonic crystal ring resonator filter structure as the optimized object, according to the position-velocity updating formula of the PSO method, the radius of scattering rods, coupling rods, and internal rods at the photonic crystal defect were optimized globally. From the theoretical analysis and numerical simulation results, it can be seen that after the filter structural parameters were optimized, single narrowband filtering can be achieved. At the same time, its normalized transmission rate is increased from 53% to 97%, indicating the effectiveness of the optimization algorithm, which provides a basis for the application in photoelectric device.
2014, 63 (3): 034206. doi: 10.7498/aps.63.034206
Large-mode-area single-mode fibers play an important role in the field of high power lasers, high power delivery, and high sensitivity sensor. A novel all-solid large-mode-area single-mode photonic quasi-crystal fiber with extremely low loss is proposed. This kind of fiber contains a hexagonal quasi-crystal array of slightly fluorine-doped silica rods in a silica background. Its structure and properties are simulated numerically in virtue of finite element method. Effects of variation of d/Λ, or Λ on fiber loss and effective mode-area properties are investigated. Numerical results demonstrate that an effective mode-area of 5197 μm2, low confinement loss of 10-5 dB/km for fundamental mode and high confinement loss of 100 dB/km of second-order mode at a wavelength of 1064 nm. Numerical simulations show that this fiber can operate effectively in single-mode and remove the conflict between large-mode-area and low loss. Moreover, the bending loss for a bending radius of 10 cm is as low as 0.01 dB/m. This fiber can increase the thermal damage threshold of the PQF, decrease the coupling loss and simplify the fabrication process. The design of new fibers is highly meaningful for the development of high power delivery, fiber lasers, and fiber amplifiers.
2014, 63 (3): 034207. doi: 10.7498/aps.63.034207
A prism surface plasmon resonance (SPR) incentive model based on the dielectric-aided layer structure is studied. The model consists of four structure layers: prism-dielectric-aided layer-gold-environmental media. According to the thin film optics and waveguide theory, the excited mechanism and modulation characteristic of SPR effect are explored based on resonance composite film composed of dielectric-aided layer and gold film. Numerical simulation is conducted on the relation of layer thickness, film dispersion characteristics and resonance energy transfer by the finite difference time domain method. Thereby, the wavelength modulation prism dielectric-aided layer SPR excitation system is also developed. Results show that with the same refractive index of liquid, the SPR resonance spectrum of dielectric-aided layer incentive model shifts to the longer wavelength region and the resonant halfwave width is wider than the spectrum of common Kretschmann incentive model based on prism-gold-environmental media. With increasing refractive index, the SPR resonance spectrum redshifts, and its sensitity is 75% higher than the common incentive model. The designed model can effectively improve the sensitivity of the prism surface plasmon resonance effect, and in the areas such as high sensitivity detection, new types of optical filter, the modulator and other fields the SPR technology may provide a theoretical and practical basis.
2014, 63 (3): 034208. doi: 10.7498/aps.63.034208
Based on the analysis of the periodic error in the reconstructed image of the ptychographic iterative engine (PIE), the cause in mathematics for this kind of error is found out, and then a method is proposed to eliminate it. By replacing the 2D periodic scanning of fixed step interval in common PIE imaging with the 2D raster scanning of changing step interval, the periodical error in the reconstructed images can be dramatically reduced, and then the accuracy of the PIE imaging is remarkably improved. Both the theoretical investigation and numerical simulations are presented.
2014, 63 (3): 034209. doi: 10.7498/aps.63.034209
Using the technique of electromagnetically induced transparency, three photonic bandgaps can be established and manipulated at any time due to the refraction modulated periodically by the one-dimensional optical lattice in a tripod atomic system which is trapped in a one-dimensional optical lattice with a Gaussian density distribution. Using the density-matrix equations to describe the interaction between laser and atoms and the transfer-matrix equation to describe the scattering of light waves in periodic media, we can obtain the steady reflection and transmission spectra. It can be found that the position and width as well as the reflectivity of the photonic band-gap could be tuned by changing the detunings and intensities of the coupling fields and the geometric Bragg detuning.
2014, 63 (3): 034301. doi: 10.7498/aps.63.034301
An important factor that causes the nonlinearity in the bubbly liquids when the acoustic wave is propagating is the bubbles. So we study the nonlinear propagation of acoustic waves in the bubbly liquids. The influence of the gas content is introduced into the equation of the wave propagation in the liquid, so one can get the model of wave propagation in the bubbly liquids. Through numerical simulation of the model one can get the gas content, the pressure amplitude of driving sound and the acting time of the driving sound can all affect the distribution of the sound field and the pressure amplitude of the wave in the bubbly liquids. The bubbles in the liquid will “block” the acoustic wave to propagate and “gather” the energy near the sound source field. For continuous and high power driving sound, the bubbles in the liquid will “block” the wave propagation and the transmission of energy.
2014, 63 (3): 034302. doi: 10.7498/aps.63.034302
Based on the multipath structure of shallow water ray acoustics, a new robust high-precision motion parameter estimation method using single hydrophone was proposed. Aiming at uniform linear motion target, colligating multipath delay difference and kinematic geometric relation, we have constructed a tridimensional multipath delay model. Then nonlinear time map can be obtained from motion parameters to delay difference, and the cepstrum expression of typical underwater acoustic channel can be studied. The delay difference is extracted from it, and the extraction strategy is put forward. Differential evolution algorithm is used to estimate motion parameters, and the robustness can be improved. Theoretical and simulation results show that the time resolution of cepstrum is not restricted by the bandwidth of signals, which depends mainly on the type of signals and the signal to noise ratio. The cepstrum of CW is not sensitive to Doppler effect. The precision of parameter estimation depends mainly on the accuracy of time delay estimation and the amount of information attached to the differential evolution algorithm. When the information includes recent data points, parameter estimation can be better. Pool test results further verify the correctness and validity of this method.
Influences of sound absorption material on acoustic characteristics of acoustic vector sensor installed on a small underwater carrier
2014, 63 (3): 034303. doi: 10.7498/aps.63.034303
In this paper the influences of viscoelastic absorption of materials on the directivity and DOA estimation of acoustic vector sensor installed on the carrier are investigated by virtue of theoretical analysis and experimental results. First, the mathematical model, consisting of absorption material and carrier structure, is established, and the acoustic characteristics of the composite materials in the case of sound propagation are analyzed. On that basis, the acoustic characteristics picked up by the vector sensor are studied by finite element method (FEM) coupling boundary element method (BEM) before and after the covering of absorption material. The influences of absorption material on the directivity of vector sensor are studied by theoretical calculation and numerical analysis, and the DOA estimation accuracy of the vector sensor before and after covering by sound absorption material is calculated. Results are proved to be valid by the experiment in the anechoic tank.
Robust source localization based on mode subspace reconstruction in uncertain shallow ocean environment
2014, 63 (3): 034304. doi: 10.7498/aps.63.034304
Existing localization methods have mismatch problem when applied to the real uncertain ocean, and this will lead to performance degradation. In normal mode models, some modal eigenfunctions remain to be more correlated than others in the presence of environmental uncertainties. Based on this, we have proposed a mode subspace reconstruction robust localization method, which uses stable modes to reconstruct the replica vector to grantee the localization performance. The data from simulation and experiment are used to verify the effectiveness of the proposed method. Performances of the matched field processor (MFP) and the robust ML (maximum localization) estimator are also given here for comparison. Results show that: (1) the generally used MFP method has a low localization performance even at high SNR values; (2) the proposed method outperforms the robust ML estimator and the generally used MFP.
Characteristics of mapping domain of the acoustic field interference structures radiated by a moving target
2014, 63 (3): 034306. doi: 10.7498/aps.63.034306
In shallow water exist the stable and significant interference characteristics of low frequency sound propagation, which contain the information of the sound source state and waveguide peculiarity. A simplified mapping method for describing the scalar and vector sound field interference structure radiated by a moving target, and an indicatory mechanism of the target state implicated in the energy distribution of the mapping domain are investigated in this paper. The mapping characteristics of two-dimensional Fourier transform of the vector sound field time (space) frequency interference spectrum are analyzed theoretically. Relations among waveguide invariant, range-rate, heading angle, and energy ridge slope of the mapping domain for time-frequency interference spectrum produced by a uniformly moving target are derived. Indication of target attacking or moving away, and the degree of threatening through symbols or the absolute value change of mapping domain’s ridge slope are demonstrated. Then numerical simulation and sea trial research are carried out. Experimental results with theoretical analysis and simulation results are in good agreement with each other. Research results show that the scalar and vector field time (space) frequency interference structure can be simplified by the two-dimensional Fourier transform. The mapping domain ridges, range-rate, heading angle and waveguide invariant show an analytic relationship among them. Variation embodied in the form of scalar and vector field interference structure obtained after mapping are more consistent with each other. The ridge of mapping domain can indicate the moving state of target concisely.
2014, 63 (3): 034401. doi: 10.7498/aps.63.034401
In order to precisely control the flying height of TFC head with consideration of microscale thermal effect, the thermal conducting characteristics and the influencing factors on TFC slider which is in an operation and multi-physics field condition were analyzed. In consideration of rarefaction effect of ultra-thin film at the head/disk interface, the models of slider heat conduction, air bearing surface heat transfer, and gas flow were established; the thermal deformation mechanism and the effect of thermal conduction on dynamic characteristics of slider were analyzed by using finite element method. Results show that the thermal conducting model and the proposed modification of Reynolds equation in this study are suitable for solving the problems of thermal deformation and dynamic characteristics of head slider. The main parameters that influence the thermal property of slider can be considered to be the heater height, heat generation rate, and the heat conductivity coefficient of the material. The change of the slider flying height is determined by the air bearing force and the air bearing surface thermal extrusion at the head/disk interface. Simulation results provide a basis for the design of heater in head slider and analysis of dynamic characteristics of air bearing.
2014, 63 (3): 034501. doi: 10.7498/aps.63.034501
Discrete element method (DEM) simulations for pile-up processes of different particle systems were performed based on linear cohesion contact model. Effects of particle shape and liquid bridge force between wet particles on the piling form were analyzed. The significant central dip profiles of normal force acting on the base surface, normal force and tangential force between particles were predicted. Effects of particle shape and cohesion energy density on the forces on the base surface and inter-particles were described. The results show that particle shape and the liquid bridge force have significant impacts on the piling form. With the increase of the cohesion energy density the angle of repose for each granular pile increases. But the angle of repose of cubical particles is bigger than that of spherical particles under the same condition. Particle shape and the liquid bridge force also significantly affect the change and the maximum amplitude of the forces acting on the base surface and the forces between the particles. The maximum amplitude of the forces increases with the increase of the cohesion energy density, and the value of the maximum force on cubical particles is bigger than that on spherical particles. When the value of cohesion energy density is very large, the mechanical properties of granular piles become more complicated, so that the liquid bridge force has a larger impact on the packing characteristic of particles than the impact on particle shape.
2014, 63 (3): 034502. doi: 10.7498/aps.63.034502
Shear test samples of different grain sizes are prepared by using mineral particles of soil, and a series of tests of quick direct shear and tri-axial shear are performed to study the size effect of granular media. Deformation curves and shear stress strength are given of test samples with particles of different size and volume fraction. On the basis of the ratio of micro-acting forces between particles to gravity and the cell element model, physical mechanism of grain size effect is, for the first time as far as we know, explained on the micro-level and mecro-level respectively. Test results show that the deformation characteristic of granular media is enhanced and its shear stress strength increases with increasing volume fraction and decreasing of particle size, and the effect of volume fraction on the deformation characteristics and strength is more notable than that of grain size. According to mechanism analysis on size effect, parameter ratio of micro-acting forces to gravity is suggested to assess aggregation and friction effects of particles in the media, and mecro-mechanism is interpreted as strain gradient and micro-cracks of deformation coordination leading to grain size effect. The cell element model presented in this paper can greatly reduce the degrees of freedom of granular media and provides an available way for calculation modeling in industry and engineering design.
2014, 63 (3): 034701. doi: 10.7498/aps.63.034701
The Lorentz force can be used to control the boundary layer flow of low-conduction fluids; however, its lowest control efficiency has become the main bottleneck in its engineering application. In order to enhance the control efficiency of Lorentz force, we need to study its potential control mechanism. In the present paper, the flow around hydrofoil when using Lorentz force has been simulated numerically by use of dual-time-step Roe method as well as studied experimentally in a water tank. Results show that the hydrofoil drag decreases sharply first and reincreases later, showing that the control effect of the Lorentz force is reduced with the increase of stream velocity, as well as the amplitude-change of the lift and drag; however, the lift increases continuously. The basic mechanism of this phenomenon is that the Lorentz force can form Lorentz force thrust, which increases the wall friction and decreases the pressure on the hydrofoil surface; at the incipient stage of control, the Lorentz force thrust decreases the drag and increases the lift immensely, soon afterwards, due to the action of Lorentz force, the drag increases with the increase of wall shear force and the lift increases with the decrease of upper surface pressure, so that the thrust can increase both the drag and lift.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
A novel scheme of beam smoothing using multi-central frequency and multi-color smoothing by spectral dispersion
2014, 63 (3): 035201. doi: 10.7498/aps.63.035201
In typical techniques of smoothing by spectral dispersion (SSD), illumination uniformity cannot be further improved by increasing the pulse bandwidth due to the limitation of high-efficiency frequency tripling. Combined with the analysis of the schemes of four-color beam smoothing and multi-frequency modulator SSD, a novel scheme of beam smoothing using multi-central frequency and multi-color smoothing by spectral dispersion has been proposed, which not only can achieve high-efficiency frequency tripling, but also can obtain laser beams with nearly continuous spectrum and exhibit some specific advantages in far-field smoothing. Results show that the focal spot will be enlarged slightly but obviously further smoothed by the use of the new scheme. Compared to the typical SSD technique, the new scheme can decrease hot spots effectively and achieve the best irradiation in less time. Moreover, with independent combination of dispersion directions in each quadrant of grating array, a multi-dimensional smoothing on focal spot can be realized.
2014, 63 (3): 035202. doi: 10.7498/aps.63.035202
The axisymmetric toroidal electrostatic mode discussed in this paper refers collectively to the nearly ideal electrostatic fluid mode with zero toroidal mode number in magnetically confined toroidal plasmas like tokamak, including geodesic acoustic mode, sound waves and the so-called nearly zero-frequency zonal flow. Use is made of cold ion fluid model in the toroidal coordinate system with a circular cross section to develop the theory of parametric excitation for the three above mentioned modes systematically to the first order of inverse large aspect ratio, which ends up with the four following observations: (1) The density zonal flow is only associated with the excitation of the first harmonic cosine sound wave and is independent of the potential zonal flow. (2) The geodesic acoustic mode is the high frequency branch of the dispersion in the form of coupling between the first harmonic sine sound wave and the nearly zero-frequency zonal flow due to geodesic curvature, while the low frequency branch of the same dispersion is identified to be the ‘toroidally modified nearly zero-frequency zonal flow’. (3) Only a weak coupling exists between the second harmonic sine sound wave and the nearly zero-frequency zonal flow. (4) All cosine sound waves and sine sound waves beyond the second harmonic are decoupled to the nearly zero-frequency zonal flow. A Gaussian type of drift wave energy spectrum with only a few parameters is introduced for calculation. Emphasis is laid on the effects resulting from the finite radial spectrum width such as double Landau-singularity, which reveal a significant modification to the δ -spectrum, thus resulting in serious restriction to the parametric excitation of geodesic acoustic mode and nearly zero-frequency zonal flow. Also discussed is the possibility of excitation of density zonal flow in the high q region. Numerical results are presented graphically and discussed in the reasonable physical regime. It is indicated that the geodesic acoustic mode and the nearly zero-frequency zonal flow cannot be parametrically excited at the same radii, and that if the geodesic acoustic mode is parametrically excited, the density zonal flow is expectedly to be observed.
2014, 63 (3): 035203. doi: 10.7498/aps.63.035203
The propagation properties of electromagnetic waves excited by helicon antenna with a parabolic radial electron density distribution in an external magnetic field were studied. Maxwell equations are numerically solved using the linear disturbance wave assumption to obtain energy distribution, when the magnetic intensity changes from 80 to 800 G. The radial electromagnetic wave and energy deposition intensity distributions were obtained. Results show that when magnetic intensity grows, the helicon wave is little damped and it can propagate into the bulk plasma; Trivelpiece-Gould (TG) wave is heavily damped at plasma-vacuum interface; the main energy absorption region moves towards the boundary gradually. When the magnetic intensity is lower than 100 G, the TG wave can propagate into the bulk plasma, and the plasma radial energy distribution is relatively uniform.
2014, 63 (3): 035204. doi: 10.7498/aps.63.035204
Edge localized modes (ELMs) in company with high-confinement mode (H-mode) will release high energy plasma fluxes to the scrape of layer (SOL). Large portions of these high heat fluxes will eventually irradiate the divertor target plates, and may erode, even melt them. In this paper, we develope a one-dimensional heat conductivity model including evaporation, radiation, melting processes of tungsten to study the erosion of the divertor tungsten targets caused by ELMs in EAST at the current and possible future operation parameters. Based on both experimental data of heat fluxes on the carbon-fibre composites divertor in EAST and possible future data of high heat fluxes, the surface temperature of slab-shaped tungsten is evaluated numerically by solving the one-dimensional model. It is found that the current Type I ELMs do not cause any noticeable changes of the tungsten target, the surface temperature being raised only several tens of degrees. Simulation results show that ELMs will not become a problem for EAST tungsten wall for the time being and the near future as long as much more severe transient events, e.g., disruption, can be avoided. When deposition energy is increased to 1 MJ/m2 with a duration of 600 μs, the tungsten plate will melt for a layer as thick as 6.8 μm.
2014, 63 (3): 035205. doi: 10.7498/aps.63.035205
In order to obtain a single brighter point X-ray source, tungsten X-pinch experiments were carried out on the QiangGuang-1 facility. The equilibrium radius of the bright spots was estimated based on the energy balance equation. X-pinch load test covered wire diameters from 25 to 100 μm, wire number from 2 to 48, and the load linear mass from 0.18 to 6.9 mg/cm. The load peak current was 1.0–1.4 MA and the rise time for 10%–90% was 60–70 ns. From the experiments, the matched load for “QiangGuang-1” facility was the 30 or 32 wire-25 μm X pinch with the load linear mass of 2.8–3.0 mg/cm, which can produce a single nanosecond X-ray pulse around current peak with a certain probability. A typical keV X-ray radiation had a pulse width of 1 ns, the radiation power from the bright spot being 35 GW, the radiation yield being 40 J, and the spot size being about 30 μm. Multiple bright spots and multiple X-ray bursts at the crossing were usually observed in the experiments. Multiple X-ray bursts were probably caused by secondary pinches or partial pinches, and multiple bright spots were caused by long wavelength perturbations or localized short wavelength perturbations along the “min Z-pinch” axis. Compared with hundreds of kilo-ampere devices, mega-ampere facilities produced greater X-ray radiation, but further improvements are needed to produce a single X-ray burst steadily.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2014, 63 (3): 036101. doi: 10.7498/aps.63.036101
For the two-dimensional (2D) 8-fold solid-fluid quasi-periodic photonic nanocrystal (QPNC) (steel-water system), the transmission spectra of the systems with different sizes are obtained by experimentation. At the same time, combined with the supercell method, the finite element method (FEM) is used to calculate the dispersion curves and transmission spectrum of the system. The transmission spectra obtained by means of these two methods are in good agreement with each other, but the band gaps appearing in the transmission spectrum calculated using the FEM are clearer than those obtained via experimentation. The dispersion curves of the 2D 8-fold solid-fluid QPNC can be well studied by using the supercell which only contains its center puzzle.
Influence of H2 introduction on wide-spectrum Mg and Ga co-doped ZnO transparent conductive thin films
2014, 63 (3): 036801. doi: 10.7498/aps.63.036801
To meet the demands of high efficient silicon thin film solar cells, transparent conductive hydrogenated Mg and Ga co-doped ZnO (HMGZO) thin films were deposited via pulsed direct current (DC) magnetron sputtering on glass substrates at a substrate temperature of 553 K. The micro-structural, morphological, electrical, and optical properties of HMGZO thin films were investigated at various H2 flow rates. Experimental results show that all the HMGZO thin films are polycrystalline with a hexagonal wurtzite structure exhibiting a preferred (002) crystal plane orientation. Appropriate H2 flow rate increases grain size and also enhances the RMS roughness. The deposition rate of HMGZO films decreases with the increase of H2 flow rate due to the decrease of sputtering yield. Resistivity of HMGZO thin films decreases rapidly from 117 to 7.2×10-3 Ω·cm with increasing H2 flow rate from 0 to 4.0 sccm. With further increasing H2 flow rate (4.0–16.0 sccm), the resistivity increases slightly due to the reduced carrier concentration and excessive H atoms as impurity. Optical transmittance of all the HMGZO thin films is higher than 87.7% in the wavelength range from 320 to 1100 nm. Burstein-Moss band-filling determined by carrier concentrations and the incorporation of Mg atoms together contribute to the band-gap (Eg) widening phenomenon. The band gap Eg varies from ～ 3.49–3.70 eV and the maximum Eg of 3.70 eV is obtained at a H2 flow rate of 16.0 sccm.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2014, 63 (3): 037101. doi: 10.7498/aps.63.037101
Boron nitride nanoribbon (BNNR) is a one-dimensional single layer nano-material with finite width and infinite length. Bent BNNR will show some unique electronic properties because of the rotation of Pz orbit. The software DMOL3 of Material Studio, based on the first principles, can be used to calculate the energy band, and the band gap will change with the bending angle; in the armchair BN nanoribbons the change is more obvious. Band gaps of zigzag BN nanoribbons may change more than those in armchair BN nanoribbons do if the external electric field is also added on the bent BN nanoribbons. When the electric field is increased to a certain value, nanoribbons will transit from semiconductor to metal, and it is important that the corresponding critical electric field value depends on the bending angle. The modulation of electric field on the band gap is also related with the size of nanoribbons; the wider the nanoribbon, the easier the modulation, and the smaller the critical electric field.
2014, 63 (3): 037102. doi: 10.7498/aps.63.037102
In this paper, A Grove model on the homoepitaxial growth of 4H-SiC is presented, based on the structure and growth conditions of CVD system. According to the model analysis, the growth rate of 4H-SiC is quiet influenced by carrier gas flow rate and temperature, which is verified by experiments. Growth rate along the substrate has a bowl-shaped distribution, and the growth rate on the center is slightly lower than on the edge. As the carrier gas flow rate increases, the growth rate controlled by the transport changes into the reaction rate control, the growth rate first increases and then decreases. The position of highest temperature in the actor will be drifted with the carrier gas flow increasing. The reaction rate and the mass transport coefficient increase with the rise of growth temperature, which can cause the increase of growth rate. But the effect of temperature on reaction rate is much greater than on the mass transport. When the temperature rises excessively, the epitaxial growth will be determined by the mass transport. But the high reaction temperature results in forming some particles at the edge of reactor, which can reduce the growth rate, and the particles will have a chance to fall on the epitaxial layer, thus seriously affecting the quality of the epitaxial layer. All the above shows that the growth rate and thickness uniformity can effectively controlled by adjusting the flow rate of hydrogen, the rotational speed of the substrate and the growth temperature.
Investigation of the saturation characteristic and lifetime of the novel AlGaInP lightemitting diodes
2014, 63 (3): 037201. doi: 10.7498/aps.63.037201
Absorption of substrates, small angle for total reflection, and heat generated by photon blocking of electrode, all can lead to saturation and performance degradation of AlGaInP light emitting diodes(LEDs). In this paper, a novel LED composed of compound current spreading layer, compound DBR reflectors, and current blocking layer, is proposed, the saturation characteristic and lifetime are also tested. Simulation results show that there is only tiny invalid photocurrent through the electrode in the novel LEDs. Experimental results indicate that the novel LEDs have higher extraction efficiency and better saturation characteristics. Saturation current of the novel LEDs is as high as 110 mA, and the light intensity is enhanced by treble at saturation current as compared to the conventional LEDs. The accelerated aging test shows that the lifetime of the novel LEDs is as long as 17.8×104 hours, which means the novel LEDs have high reliability and can be used with high current.
Effect of thermal treatment on the structural phase transformation of the detonation-prepared TiO2 mixed crystal nanoparticles
2014, 63 (3): 037301. doi: 10.7498/aps.63.037301
Nanopaticles of TiO2 mixed crystals (anatase phase and rutile phase) are prepared by detonation method. Morphologies and structural phase transformation behaviors of the as-prepared TiO2 nanopaticles are investigated for different annealing temperatures (600 ℃ and 720 ℃) and durations of annealing time (1, 2, 3.5, and 5 h). The structural phase transformation process and transformation mechanism are also discussed within the framework of the thermodynamic theory. Results show that with the increase of the annealing temperature and annealing time, the particle size of the detonation-prepared TiO2 nanoparticles increases gradually and the relative content of rutile phase in the TiO2 mixed crystal nanopaticles is improved. Compared with the TiO2 nanoparticles prepared by the conventional methods, the mean growth rate of rutile phase is obviously slower than that of anatase phase at the same annealing temperature and annealing time. It is obvious that the temperature at which the anatase phase completely changes into the rutile phase is lower than that of the TiO2 nanoparticles prepared by using other methods. These results are helpful for realizing the control of particle size and phase transformation of TiO2 nanoparticles. Meanwhile, the results can also provide us the theoretical and experimental bases for mass production of TiO2 nanoparticles in the future.
Investigation of carrier transport properties along the c-axis in K0.8Fe2Se2 superconducting crystals
2014, 63 (3): 037401. doi: 10.7498/aps.63.037401
We have successfully prepared the iron-based superconductor K0.8Fe2Se2 crystals (Tc=27 K) and studied the carrier transport properties along the c-axis in detail. Samples are characterized by XRD, SEM and temperature-dependent resistivity. The result shows that there is “phase separation” in the samples. Based on the experimental results, the iron-based superconductor is not a simple two phases alternating along the c-axis, but the metal phases should have weak-link channels along the c-axis, forming a nearly 3D special net mode. Studies of the thermal conductivity and the complex impedance spectrum z(omega, T0) suggest that the superconducting crystals have a lot of grain boundaries along the c-axis direction, the bound polarization charges result in relative dielectric constant of about 106 in magnitude and negative phase characteristics in the vicinity of 10 MHz.
2014, 63 (3): 037801. doi: 10.7498/aps.63.037801
Dense Si nanostructures embedded in silicon nitride prepared by plasma-enhanced chemical vapor deposition (PECVD) was used as luminescence active layer to fabricate light-emitting diodes based on p-Si/SiN-based emitter/AZO structure. Visible electroluminescence from the device was observed at room temperature. It is found that the electroluminescence intensity of the device can be further enhanced significantly by inserting an ultrathin nanocrystalline Si layer between the p-Si substrate and SiN-based emitter as a hole barrier layer. Moreover, the electroluminescence efficiency is increased by more than 80% as compared to the decice without the nc-Si barrier layer.
Influence of Ce doping concentration on the luminescence properties of LaCl3：Ce scintillation crystals
2014, 63 (3): 037802. doi: 10.7498/aps.63.037802
LaCl3:Ce is an excellent rare earth halide scintillation crystal discovered in the beginning of this century. Pure LaCl3 crystal and LaCl3 crystal doped with several different Ce concentrations were grown by vertical Bridgman method. Their transmission and luminescence as well as decay time were measured and compared with each other. It was found that the cut-off edge, emission wavelength as well as decay time for pure LaCl3 crystals are respectively 215 nm, 405 nm and 1 s. This emission is explained by the self trapped exciton (STE) of LaCl3. However, with the increase of Ce concentration in the crystal, the cut-off edge of LaCl3:Ce crystal shifts to about 300 nm, and the luminescence is dominated by the emission originating from 5d-4f transition of Ce ions. Meanwhile, the increase of the luminescence intensity of Ce3+ ion emission is accompanied with the expense of STE emission, this anti-correlation between the Ce3+ and STE luminescence intensity is interpreted by the energy transfer from STE to Ce ions in LaCl3:Ce scintillation crystals.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2014, 63 (3): 038101. doi: 10.7498/aps.63.038101
An asymptotic solution of the concentration and interface morphology for a deep cellular crystal in directional solidification is obtained by using the matched asymptotic expansion method and multiple variable expansion method, and the effect of anisotropic surface tension on deep cellular crystal growth is studied. Results show that the anisotropic surface tension has a significant effect on the concentration and interface shape of deep cellular crystal growth in directional solidification. As the anisotropic surface tension parameter increases, the concentration near the front part of deep cellular crystal decays and the interface shrinks; when as the concentration near the root increases and the curvature of the interface near the root increases or the curvature radius decreases; and the amplitude of the deep cellular crystal increases. The concentration and interface shape of the deep cellular crystal in directional solidification can be calculated with the results obtained in this paper.
Since the RLC circuit is a basic circuit, attention is directed to the generalization of the fundamentals of fractional multiple RLαCβ circuit. Compared with the conventional multiple RLC circuit, the effects of fractional orders, α and β, is the key factor for extra freedom, more flexibility and novelty. First, we study the basic features including the admittance and phase. Then, the conditions for fractional-order multiple RLαCβ circuit to act as pure imaginary impedances are derived, which are unrealizable in the conventional case. As a peculiar phenomenon–resonance, the relationships among resonance frequency, fractional order and LC are studied in detail. In addition, sensitivity analysis including some interesting rules is illustrated. Finally, numerical simulations are carried out to validate the above studies.
Numerical simulation of generation and radiation of super-radiation from relativistic backward wave oscillators
2014, 63 (3): 038402. doi: 10.7498/aps.63.038402
This paper studies the issues about the X-band super-radiance from a relativistic backward wave oscillator (RBWO) with the central frequency of 9.25 GHz, and the output port of the RBWO is directly connected to a vlasov antenna. The particle simulation code UNIPIC and the self-developed antenna simulation code are combined to simulate the full process of the generation and the radiation of the microwave pulse. Effects of natural gas at difference pressures and injected voltage pulse on the working characteristics of RBWO are simulated and discussed. Simulated results indicate that the peak value of the output power can achieve 3.68 GW, and the instantaneous efficiency can exceed 100%. When the tilted angle of vlasov antenna is 20 degrees, the gain of the antenna is 15.5 dB. The power density can reach 0.728 W/cm2 at the far distance of 1 km.
2014, 63 (3): 038403. doi: 10.7498/aps.63.038403
The principle of Doppler spectra detected by HFSWR (high-frequency-surface-wave radar) is given by a nonlinear integral equation from which can be extracted ocean wave parameters. By linearization, the equation can be transferred into a first kind of Fredholm integral equation approximately and can be displayed in a quadratic form. Conjunction gradient (CG) method is proposed to solve the optimization problem. Non-negative restriction is introduced to improve the involved CG algorithm and fit to the priori knowledge so that the ocean wave parameter is non-negative. Validity and accuracy of the proposed method are demonstrated by numerical simulation with different noise levels at one site and two sites.
2014, 63 (3): 038501. doi: 10.7498/aps.63.038501
Indium-zinc-oxide thin-film transistors (IZO-TFTs) are prepared with the multilayer structure of molybdenum-aluminum-molybdenum (Mo/Al/Mo) as the source/drain (S/D) electrode. Experiment demonstrates that the sputtering power of Mo (bottom layer of Mo/Al/Mo S/D) influences the performance of TFTs significantly. As the sputtering power increases, the Von runs negative shift, and the device uniformity degrades. XPS depth profile shows that the diffusion at the interface (IZO/Mo) occurs seriously. By decreasing the sputtering power, the diffusion can be suppressed and the devices are shown in normal off state (Von ～ 0.5 V, enhanced mode), with higher mobility (～ 13 cm2·V-1·s-1) and improved uniformity.
2014, 63 (3): 038701. doi: 10.7498/aps.63.038701
The adhesion of two cylindrical colloids to a tubular membrane is investigated theoretically in terms of the full treatment of Helfrich model. By analyzing the free energy of the system, it is found that this adhesion can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. A second-order adhesion transition from the desorbed to weakly adhered state is found, and a first-order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered state can be obtained as well. Different relative positions between rigid cylinders and membrane tube will affect the phase transition and structure of the system.
2014, 63 (3): 038901. doi: 10.7498/aps.63.038901
A cellular automaton model is proposed to study the traffic at signalized intersection. The driving behaviors induced by drivers attribution (gender, driving experience, character, etc.) are numerically analyzed. Simulation results show that the rusty driving skills or tension driving, impatient driving and so on can lead to the transition from free flow to congestion more easily, and these behaviors are the important cause for low travel efficiency at the intersection; the signal cycle is the main factor influencing traffic flux and travel time fairness.
2014, 63 (3): 038902. doi: 10.7498/aps.63.038902
There have been many researches and rich results on the system risk in bank network systems that use complex network theory. Researches to date focus on the relationship between the contagion of the risk and the structure of the network after risk bursting, based on the assumptions that the accumulation of the system risk in network systems has approached the critical point of bursting and that the network is static (both the node and connection of the bank network are static).However, the problem why the system risk accumulates gradually and finally bursts in the network has not been addressed yet. The study on the system risk accumulation can only be conducted in dynamically evolving bank network systems; and the risk can be observed clearly only if the system risk is evaluated quantitatively. Therefore, a dynamically evolving complex bank network system, which has nodes of dynamic behavior and exhibits macroeconomic trends, is modelled first in the present paper. A lending-borrowing algorithm and a multi-term clearing algorithm for the dynamic bank network system are designed, and the method for calculating the system risk is proposed also. Finally, the system risk is calculated and analyzed by simulation. The curve of the system risk evolving with time is shown and the process of the accumulation of the system risk can be observed clearly. Researches in the present paper are to lay a foundation for the quantitative study of the system risk accumulation in dynamically evolving bank network systems.
2014, 63 (3): 038903. doi: 10.7498/aps.63.038903
Research on the complexity of traffic flow evolution is helpful to deeply understand the evolution rule of traffic flow system, which can provide the theoretical foundation for forecasting and controlling traffic flow. Multi-scale entropy (MSE) method is widely used in the analyses of time series of physiology and traffic of computer networks. Considering the similarity between the vehicle arrival in traffic flow system and the packet arrival in computer network, the complexity of the time headway in braking light model is analyzed to show the complexity of traffic flow evolution by using the MSE method. The analysis results show that the complexity of the time headway decreases with the increase of the time scale, which reflects that it is difficulty to predict the traffic flow in a shorttime. In addition, the difference in the complexity of the time headway between the phases of the free flow and synchronized flow is small when the time scale is small. However, with the increase of the time scale, the MSE of the time headway decreases rapidly for free flow, but rather slowly for synchronized flow. Such a difference can be used as a very important reference to distinguish the synchronized flow and the free flow. Research results in this paper can provide new ideas and methods for investigating the complexity of traffic flow evolution.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2014, 63 (3): 039101. doi: 10.7498/aps.63.039101
The silicon nanometer structure grating and the photoresist nanometer structure grating were prepared. A fitting model was built on the new self-developed generalized ellipsometer. Then, the gratings was tested and fitted. Results proved that the machine could work well in nondestructive test of nano grating. Under the condition of the incident angle of 60 and the azimuth angle of 75, the measurement accuracy can be up to 99.97% for the three-dimensional morphology parameters such as key dimension and sidewall angle and so on, and the maximum error is less than 1%. This method is significant for the nondestructive test.