Vol. 64, No. 6 (2015)
2015, 64 (6): 060201. doi: 10.7498/aps.64.060201
In this paper, the process of the free dendritic growth of Mg-0.5 wt.%Al alloy in the basal plane (0001) is simulated in two-dimensional system by using a quantitative phase-field model. A convergence study is carried out to choose the optimal coupling parameter λ and grid width Δx/W0 in simulation. Then we systematically discuss the effects of the anisotropic strength ε and the supersaturation Ω on dendritical tip growth velocity, radius, Péclet number, and stability parameter σ *. Results show that the stability parameter σ * defined by the theory of microscopic solvability is a function of the anisotropy strength ε, i.e., σ* ≅ ε1.81905, which is obviously closest to σ * (ε) ≅ ε 1.75 obtained from the analytical solution. Moreover, for Ω σ * is approximately a constant while it sharply and monotonically decreases with the augment of the value of ε for Ω > 0.6. This indicates that there is a transition from solute-controlled dendrite to kinetic dendrite as Ω increases. Furthermore, the transition of the growth pattern from the snow-like to the circle-like patterns occurs as Ω increases.
A new fast algorithm based on compressive sensing for composite electromagnetic back scattering from a 2D ship located on a 1D rough sea surface
2015, 64 (6): 060301. doi: 10.7498/aps.64.060301
As one of the most popular numerical methods, the method of moments (MoM) is known for its high accuracy. Besides, MoM has other advantages. For example, the integral equations satisfy the Sommerfeld radiation condition automatically, the additional boundary conditions are not needed., etc. But if the wide angle problem, especially the composite electromagnetic back scattering from a ship place on sea surface, is considered, the MoM needs to solve the integral equation at every incident angle, which needs a large calculating quantity, and is time consuming. To solve this problem, a new efficient method based on the compressive sensing and the MoM is proposed and validated in this paper. A new incident source derived through multiplying the transform matrix by the voltage matrix is first introduced. And then the measurements of the induced currents can be obtained by solving the integral equation under the new incident source. Finally the original electromagnetic currents can be recovered by using the recovery algorithms (the orthogonal matching pursuit is used in this paper). The validity and the efficiency of the new method are demonstrated by comparing with the traditional MoM.
Ground state of a two-component dipolar Bose-Einstein condensate confined in a coupled annular potential
2015, 64 (6): 060302. doi: 10.7498/aps.64.060302
By using the imaginary-time propagation method, we study the ground state structure of a two-component dipolar Bose-Einstein condensate confined in a coupled annular potential. The effects of contact and dipole-dipole interaction on the ground state density distribution of such a system are investigated in detail. The results show that the dipole-dipole interaction, acting as a new degree of freedom, can be used to obtain the desired ground state phases, and to control the phase transition between different ground states.
Stochastic P-bifurcations in tri-stable van der Pol-Duffing oscillator with multiplicative colored noise
2015, 64 (6): 060501. doi: 10.7498/aps.64.060501
This article aims at studying the stochastic P-bifurcation of tri-stable van der Pol-Duffing oscillator subjected to multiplicative colored noise. First, the stationary probability density of amplitude is derived by using the stochastic averaging method. Then the critical parameter conditions of stochastic P-bifurcation are obtained based on the singularity theory. And the different types of stationary probability densities of amplitude are also obtained, which are in good agreement with the results from Monte-Carlo numerical simulation. Based on these results, the effects of the noise correlation time, noise intensity and linear damping coefficient on the P-bifurcation and the stable response behavior of the system are studied.
Magnetic force of piezoelectric cantilever energy harvesting system with an externally applied magnetic field based on magnetizing current method
2015, 64 (6): 060502. doi: 10.7498/aps.64.060502
This paper focuses on the piezoelectric cantilever energy harvesting system with an externally applied magnetic field. The calculation method and model for the magnetic force are proposed from the magnetizing current method, and the calculation results are compared with a set of experimental data. The study shows that there is a deviation in the calculation model derived by the magnetizing current method, which increases as the distance between two magnets decreases. The calculation model is improved by introducing the deflection angle of the magnet at the end of the cantilever beam, and is reliable to calculate the magnetic force of piezoelectric cantilever energy harvesting system with an externally applied magnetic field for further studying this energy harvesting system.
Blind angle elimination method in weak signal detection with Duffing oscillator and construction of detection statistics
2015, 64 (6): 060503. doi: 10.7498/aps.64.060503
Aiming at the blind angle in detecting weak signals of the same frequency by Duffing oscillator, a novel method of dephasing for the driving signals is proposed to eliminate the blind angle. According to the characteristic of weak signals, expression of blind angle is analyzed, and then the range of blind angle is found out, which corresponds to the amplitude of a new driven signal synthesized from the original driven signals and the unknown one. By making the original driven signal phase shift a degree of π, detection for the same frequency signal can be realized when the synthesized signal is located in the blind angle region, whose feasibility is proven by an experiment that it remains in chaotic status in the case of blind angle but becomes a great period status after the original driven signal's phase is dephased by π. To overcome the drawbacks of qualitative analysis and distinguish effectively different status in signal detection course, a detection statistics based on likelihood-Halmiton system is constructed. On the basis of it, a diagram of detection for any frequency signal is drawn. The key point is to make it as an unknown signal's frequency range where there are two adjacent frequency values whose corresponding detection statistics both located in the range of intermittent chaotic status, while one of them is just corresponding to the maximum value of the detection statistics. By simulations of different circumstances, detection statistics for numerical ranges of chaos, intermittent chaos, and great period is summarized. Furthermore, detection for any frequency signal may be realized by use of the numerical range. It is shown that the proposed method could not only provide quantitative judgment for the system status, but improve the signal detection performance. Also, it could be combined well with the traditional oscillator array method or adaptive step intermittent chaotic oscillator method, which further can improve some existing signal detection methods with Duffing oscillator.
2015, 64 (6): 060504. doi: 10.7498/aps.64.060504
In order to remain the structure of the neural network in the process of the optimization unchanged, taking the hysteretic chaotic neuron and the hysteretic chaotic neural network as controlled plants, a novel control strategy based on the filtered tracking error is proposed to perform the stability control for the single hysteretic chaotic neuron or the hysteretic chaotic neural network. Especially, the hysteretic chaotic neuron and the hysteretic chaotic neural network can be used to solve the optimization problem through using the control strategy on condition that the generation mechanisms of the nonlinear characteristics, hysteresis and chaos, are unchanged. The control law is composed of two terms: one is the equivalent control term in the ideal filtered tracking error surface, and the other is the control term which can make the system reach the filtered tracking error surface quickly. Lyapunov stability method is used to prove the stability of the control strategy for the single hysteretic chaotic neuron and hysteretic chaotic neural network. The control laws of hysteretic chaotic neurons can be obtained according to the optimization function. The state of the single hysteretic chaotic neuron or the hysteretic chaotic neural network can converge to an extreme point of the optimization function gradually by the control law. In this way, the optimization problem can be solved effectively. Simulation results prove the feasibility and validity of the control strategy for optimization problem.
2015, 64 (6): 060505. doi: 10.7498/aps.64.060505
The simulation of pedestrian push-force in evacuation with arched congestion before exit is presented based on cell automata. The generation, absorption, transfer and gather of pedestrian push-force are analyzed. Initial push-force facing to exit is generated based on the distance between pedestrian and exit. The scalar and vector sum of push-force are introduced to respectively describe the push effect and resultant force of outside jam push-force in crowded evacuation. Absorption coefficient and anti-crush coefficient are introduced to respectively describe the ability for pedestrian to absorb and resist the outside jam push-force. Simulation results show that the increase of absorption coefficient or anti-crush coefficient can effectively prevent pedestrian from being injured. It is found that three phases: weak protection, strong protection and complete protection are distinguished based on two critical absorption coefficients and an anti-crush coefficient. Pedestrian casualties will increase with the number of evacuation pedestrian rising. It is also shown that pedestrian casualties in jam occur in a reverse bell-shape symmetry zone before exit.
Analytical model of electrostatic force generated by edge effect of a Kelvin capacitor based on conformal transformation
2015, 64 (6): 060601. doi: 10.7498/aps.64.060601
We present a new realization of weak electrostatic force based on Kelvin capacitor, which, compared with the conventional realization, simplifies the mechanical design without synchronously moving the central and guard-ring electrodes. However, a residual force due to the edge effect of the capacitor should be accurately known. In this paper, an analytic model of the electrostatic force generated from the edge effect is presented based on conformal transformations. The accuracy of the model is verified by the finite element calculation based on a micro-Newton weak force generation.
2015, 64 (6): 060701. doi: 10.7498/aps.64.060701
In the division of time imaging polarimetry, polarization information of field under measurement (I, Q, U), is obtained by rotating the analyzer. In the process of measurement, the beam deviation caused by the wedge of the analyzer reduces the spatial resolution and polarization accuracy of imaging polarimetry. In this paper we present that the beam deviation above can be reduced or even compensated for by adjusting the tilt angle of analyzer with respect to the incident optical axis. Taking Glan prism as the analyzer, we establish the first-order approximate compensation model of beam deviation based on the theory of geometric optics, acquiring the function relation between the tilt angle and wedge of Glan prism, and verify the feasibility and effectiveness of the compensation method by simulation. The study shows that the first-order approximation error of beam deviation can be compensated for by adjusting the tilt angle of Glan prism if only Glan prism is placed in a convergent beam; the tilt angle is proportional to Glan prism wedge angle, refractive index, and distance to CCD, but inversely proportional to Glan prism thickness. The results provide a theoretical basis for developing the time division imaging polarimetry with high spatial resolution and polarization accuracy.
ATOMIC AND MOLECULAR PHYSICS
2015, 64 (6): 063101. doi: 10.7498/aps.64.063101
In this paper, the time-dependent wave-packet method is used to study the three-dimensional dynamical properties of the H+Li2 reactive system on its ground state potential energy surface. The reaction probabilities for J=0 with different vibrational quantum numbers v=0, 1, 2, 3 and for v=0 with different total rotational quantum numbers, integral cross sections and rate constants are calculated for collision energies in a range between 0 and 0.4 eV. The features of the reaction probabilities and reaction threshold energy are analyzed. The results show that the vibrational excitation has a certain inhibitory effect on the reaction process and the reaction threshold energy increases with the increase of J. These phenomena are associated with the type of the exothermic reaction of the reactive system. The influence of the collision energy on the integral cross sections and the effect of the temperature on reaction rate constants are also investigated.
A density functional method DFT/B3P86 with relativistic effective core potential basis for U and 6-311+G(d) basis for N is used to study the energy gap and harmonic frequency of UN2 ground state molecule under the action of the uranium-produced spontaneous radiation fields ranging from -0.005 to 0.005 a.u.. The results show that UN2 has an anti-symmetry expansion vibrational frequency ν3 (σg) that is close to experimental value 1051.1 cm-1 under the action of different spontaneous radiation fields, and a symmetrical expansion vibrational frequency ν1(σg) that is close experimental value 1008.3 cm-1. The energy gap is found to decrease with increasing the spontaneous radiation field. The electron which occupies an orbital is easy to excite to empty orbital and transform into an excited state. The UN2 molecule turns unstable in the spontaneous radiation field; N2, O2 and others more easily diffuse into the surface interior, thus corroding the uranium surface and aggravating the corrosion of uranium in the spontaneous radiation field.
2015, 64 (6): 063401. doi: 10.7498/aps.64.063401
The geometric parameters are optimized at the B3LYP and CI levels under the constraints of the C2v, C2v and C2h symmetry point groups for the three isomers of dichloroethylene. The theoretical two-dimensional electron momentum distributions and momentum profiles of four core orbitals for iso-dichloroethylene, cis-dichloroethylene and trans-dichloroethylene are calculated by non-relativistic density functional method. Comparing the electron distributions in position and momentum space of these orbitals, it is found that the interference effects, which do not exit in position space, appear and produce the evident periodical multipeaked momentum distributions in momentum space. The distances between atoms and the alignments of molecular axes for these three isomers can be obtained by computing their values of period and the axis directions of period, respectively.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2015, 64 (6): 064201. doi: 10.7498/aps.64.064201
In this paper, the characteristics of the azimuthally polarized non-diffracting beam (APB) propagating in the free space and obstruction space are investigated theoretically and experimentally. The variations in intensity distribution and polarization characteristics of the APB in propagation process are simulated. In the experiment, the APB is generated by using the polarization converter and axicon. And then, we investigate its transmission and analyze the intensity distribution of APB which is behind a sector-shaped opaque obstacle. We also discuss the influences of obstacles on the polarization and self-healing features of the APB. The results show that the light intensity in obstacle block area gradually restores along the z axis and the shadow area moves toward the direction opposite to the location of obstacle. The polarization of the light beam changes partly and the change relates to the obstacle location. Theoretical simulations accord well with experimental results.
2015, 64 (6): 064202. doi: 10.7498/aps.64.064202
The formation environment and the evolution of dark soliton with environment parameters are investigated by using the electromagnetically induced transparency effect produced high dispersion and nonlinearity. To improve the stability and operability, a dual-well semiconductor is used. Combining the quantum theory and the classical field theory, we derive the nonlinear Schrodinger equation to describe the formations and evolutions of wave and soliton. It is demonstrated that the dark soliton can form and propagate in the medium when the medium is anomalously dispersive and cross phase modulation is negative simultaneously, and that in the evolution of the soliton, the width, gray scale and phase are related to each other, the smaller the pulse duration, the bigger the gray scale is and the faster the growth is. In addition, the modulation instability of the nonlinear system is analyzed, and the gain spectrum of the nonlinear system is also discussed.
2015, 64 (6): 064203. doi: 10.7498/aps.64.064203
In image processing, in order to well preserve corners, peaks, and thin edges of the image, a new biharmonic diffusion model is established, which takes into account the stress balance of the biharmonic equation and local maximum values of higher-order partial derivatives. If the noise is very strong in the image, some isolated spots will leave on the processed image, and texture of the image has statistical properties in a large range, and the new model retains only local details, the information of image in a wide range is not kept well. Further improvement on the above model is made by using the wavelet transform to extract the high frequency part of the image, and by processing this part with stress balance to establish wave field biharmonic diffusion model, which stably controls the image details locally. Analysis and simulation results show that this model retains more image information than the Perona-Mailik model, effectively well preserves the edges, corners, peaks of the image, and also maintains thin edges of the image. So it is an ideal model.
2015, 64 (6): 064204. doi: 10.7498/aps.64.064204
A test system including light path system and software system is built for measuring the refractive index of fiber by using the digital holographic tomography technology. Based on the phase distribution curve of object wave the optimal hologram is recorded. The spectral range corresponding to the object wave is selected accurately based on the optimization of the spectrum. The phase distribution information of object wave is extracted with the angular spectrum reconstraction. The accuracy of extracted phase information has been verified through the simulation holograms of optical fiber. Combined with the multilayers model of fiber, the refractive index distribution along the diameter direction of fiber tomogram is recovered from a single hologram. Single-mode and multi-mode optical fiber are tested as samples. The experiment results are consistent with the results of S14 refractive index profiler, the precision is 10-4. The compare result shows that our method is simple, fast and accurate for the measurement of the refractive index of fibers. We have also studied the measurement of the refractive index distribution of the special optical fiber.
Amplification without population inversion in tree-level system driven by an additional microwave field
2015, 64 (6): 064205. doi: 10.7498/aps.64.064205
In this paper, we investigate the spectrum properties of the lasing without population inversion in a three-level atomic system under an action of an externally applied microwave field. The probed absorption spectrum is obtained by solving the density matrix equation of this system. The results show that the absorption profile has a multi-peak structure, and exhibits obviously negative absorption (light amplification) in a specific range under the action of strong microwave field. The characteristic of the light amplification without population inversion according to the three level atomic system is demonstrated by the quantitative analysis of populations related to the probe levels.
2015, 64 (6): 064206. doi: 10.7498/aps.64.064206
We demonstrate a high-repetition-rate Er-doped all fiber laser with nonlinear-polarization-rotation mode-locking. The highest repetition rate of the laser is 217 MHz. The fiber laser has a very simple and compact structure and can output a stable mode-locking pulse only by using one polarization-dependent isolator and a polarization controller. The pulse width, spectral width and signal-to-noise ratio are measured to be 69 fs, 56 nm and 76 dB respectively.
2015, 64 (6): 064207. doi: 10.7498/aps.64.064207
The transmission spectra of the model of photonic double quantum well consisting of two photonic crystals with two different single-negative materials are calculated by the transfer matrix method. It is found that these resonance modes split into pairs, owing to a coupling between two photonic wells. The distance of resonant modes can be controlled by the coupling strength between the two wells. It is observed that when two photonic quantum wells are far from each other, resonance modes appear as single peak. And the quality factors of the transmittance resonance peaks can be greatly improved by increasing the period number of outer barriers. The resonance modes are affected weakly by the incident angle and polarization. The effects of the losses coming from epsilon-negative and mu-negative materials on the resonance modes are also specifically explored, respectively.
2015, 64 (6): 064208. doi: 10.7498/aps.64.064208
Photonic crystal not only can be used to inhibit the spontaneous emission and redistribute the energy into useful forms, but also can be designed to control and confine photons. Since the concept was introduced by John and Yablonovitch in 1987, there have been discussed the machinery of broadening the band bap and a quest for the optimal structure. Band structures of two-dimensional photonic crystals with different lattices and scatters of air hole of various shapes, orientations and sizes are investigated by the plane wave expansion method. The calculation results suggest that the variation of the photonic crystal band bap is attributed to the competition between symmetry and quantum confinement effects.
Physical mechanism of super-broadband and all-angle self-collimation transmission in photonic crystal with low rotational symmetry
2015, 64 (6): 064209. doi: 10.7498/aps.64.064209
We propose a two-dimensional photonic crystal structure with low rotational symmetry and investigate its band structure characteristics over the whole first Brillouin zone by the plane wave expand method. The physical mechanism of broadband all-angle self-collimation effect and the influence of aspect ratio on the bandwidth are clarified. Furthermore, we obtain the existence criterion for self-collimation modes covering almost the whole fourth band for TE polarization. Especially, there exist two wide flat regions spanning over the first Brillouin zone which exhibit unique properties: one dimension corresponds to broad band from 0.47 to 0.53 (2πc/a), while the other corresponds to all incident angles of 0°–90°. Based on the above unique properties, the broadband all-angle self-collimation propagation with a bandwidth of 187 nm around 1550 nm is demonstrated by the finite-difference time-domain method.
Mode division multiplexing of two-dimensional triangular lattice photonic crystal based on magneto-optical effect
2015, 64 (6): 064210. doi: 10.7498/aps.64.064210
With the rapid development of all-optical communication, the wavelength division multiplexing transmission system cannot meet the requirements of high capacity in optical networks, while mode division multiplexing uses the limited stability modes as independent channels to transmit information, improving the system capacity and spectrum efficiency, which is one of the key technologies in the construction of future optical network. In this paper, a mode division multiplexer of two-dimensional triangular lattice photonic crystal in 1.55 μm band based on the magneto-optic effect of Bi-doped compound rare earth iron garnet bulk single crystal is proposed. The defects of TbYbBiIG medium are introduced as mode splitting waveguides in photonic crystal, of which the permeability changes with the applied magnetic field in different polarization modes. Therefore, mode division multiplexing in 1.55 μm band can be achieved by controlling the propagations of TE and TM mode. The band and transmission characteristics of this device can be analyzed by using the plane wave expansion and finite difference time domain method. The results show that the transmission rates of TE and TM modes both exceed 92% and channel segregation degrees reach 19.7 dB and 42.1 dB respectively. These features indicate the important application prospect in the future high-capacity optical transmission system.
2015, 64 (6): 064211. doi: 10.7498/aps.64.064211
Based on the theoretical model of optical wave propagation in parity-time (PT) symmetric waveguide, the transmission and control of bright solitons in PT symmetric Kerr nonlinear planar waveguide with Gaussian distribution are studied numerically. The PT symmetric waveguide requires that the refractive index distribution of waveguide should have to be an even symmetry, whereas the gain/loss distribution should be odd. The results show that when the strength of refractive index distribution of waveguide is positive, the refractive index has a maximum value in the center of the PT symmetric waveguide. Without the self-focusing Kerr nonlinear effect, the waveguide can also restrict optical wave to form the wavy light beam and transmit with long distance. When the strength of refractive index distribution is negative, the refractive index has a minimum value in the center of the PT symmetric waveguide. The transmission direction of optical wave is shifted. The gain/loss distribution can control the transmission direction of optical wave: if the strength of gain/loss distribution is positive, the optical wave is shifted toward the left; if the strength is negative, the optical wave is shifted toward the right; if the strength equals zero, the optical wave is divided into two beams. And when the refractive index distribution is negative, the interaction between adjacent bright solitons can be suppressed very well. The results of this research can provide a theoretical basis for the application of PT symmetric waveguide in all-optical control in the future.
2015, 64 (6): 064212. doi: 10.7498/aps.64.064212
Two different types of few mode fibers (FMFs) are considered: a graded-core with a cladding FMF and a multi-step-index FMF. The characteristics of mode field distribution and the effective index are analyzed based on Comsol software. Then differential mode delay is analyzed. The structure and profile parameters are optimized in order to achieve the lowest possible differential mode delay (DMD). Under the condition of supporting four modes, a graded-core with a cladding FMF is designed. The DMD absolute values of LP11, LP21, LP02 are all below 0.015 ps·m-1. Under the condition of supporting two modes, a multi-step-index FMF is designed. The DMD of LP11 is 0.185 ps·m-1. The designed fibers have low DMD, which is suitable for mode division multiplexing.
2015, 64 (6): 064213. doi: 10.7498/aps.64.064213
Fiber-optic surface plasmon resonance sensor (SPR) plays an important role in the fields of high sensitivity sensor and online real time monitor. We propose a novel six-fold symmetric photonic quasi-crystal fiber SPR sensor with two large semi circular channels. Its sensing properties and influence of fiber structure are simulated numerically by the finite element method. Numerical results demonstrate that its highest sensitivity can reach up to 26400 nmRIU-1, and the measuring range is 1.25-1.331. The novel quasi-crystal fiber SPR sensor, which has characteristics of large measuring range, high sensitivity, mode loss spectrum with less interference peak, design and optical path flexibility, are used widely for biochemical detection, public safety, environmental pollution monitoring and high sensitivity sensor.
Sparse channel estimation of underwater acoustic orthogonal frequency division multiplexing based on basis pursuit denoising
2015, 64 (6): 064301. doi: 10.7498/aps.64.064301
To solve the problem of poor performance of the traditional l2-norm channel estimation, a sparse channel estimation approach based on basis pursuit denoising (BPDN) is proposed in orthogonal frequency division multiplex underwater acoustic communication. Owing to the sparsity of the underwater acoustic channel, only a few observations are needed to recover the channel impulse response with a high accuracy. Compared with greedy pursuit algorithm, BPDN algorithm has the globally excellentest solution. The signal is estimated based on the l2-l1 norm rule and the observations containing the noise are considered. The regularization parameter can be changed to balance the signal's sparsity against the residual error. The influences of the pilot distribution and the regularization parameter on the BPDN algorithm are discussed in the simulation. The BPDN channel estimator is compared with the least square (LS) and also with orthogonal matching pursuit (OMP). The data collected from lake experiment show that the BPDN channel estimator outperforms the LS and OMP channel estimator over spare underwater acoustic channel.
Characteristics of the geometrical scattering waves from underwater target in fractional Fourier transform domain
2015, 64 (6): 064302. doi: 10.7498/aps.64.064302
The components of the underwater target scattering waves alias together in time domain and frequency domain realistically. They are affected by the incident angle, and show great differences under different angles. It is necessary to build an analytical model of scattering waves under all-direction incident angles theoretically. The analytical expressions of geometrical scattering components changing with the incident angle in fractional Fourier transform domain are deduced in this paper. The all-direction model in optimal fractional Fourier transform domain of the scattering waves is built. Based on this, the geometrical feature of underwater target echo is provided. In addition, the relationships between the resolution and the bandwidth of transmitted signal, and between the calculation accuracy and the length of observational signal are given. By processing experimental data, it is indicated that the model in fractional Fourier transform domain is in accordance with the characteristics of underwater target. It can provide a theoretical basis for target recognition under unknown incident angle.
2015, 64 (6): 064501. doi: 10.7498/aps.64.064501
Chaotic motion of a kind of nonlinear relative rotation system with load Coulomb frictional damping is investigated. Based on the Lagrange equation of a dissipative system, the dynamic equation of a kind of nonlinear relative rotation system with two pieces of mass is established, which contains a kind of nonlinear load Coulomb frictional damping. The eigenvalue of the autonomous system is discussed using Cardano formula. On this basis, the existence of homoclinic orbits is given by the undetermined coefficient method, and the chaotic motion of the system is investigated by means of Silnikov theorem. Finally the chaotic motion of the system with the known parameters is studied numerically. With the variation of Coulomb frictional damping, a route to chaos through period-doubling bifurcations is exhibited. Numerical calculation can confirm the validity of the analytical results.
Form invariance and Mei conserved quantity for generalized Hamilton systems after adding additional terms
2015, 64 (6): 064502. doi: 10.7498/aps.64.064502
Form invariance and Mei conserved quantity for generalized Hamilton systems after adding additional terms are studied. By introducing infinitesimal transformation group and its infinitesimal transformation vector of generators, the definition and determining equations of the Mei symmetry for generalized Hamilton systems after adding additional terms are provided. By means of the structure equation satisfied by the gauge function, the Mei conserved quantity corresponding to the form invariance for the system is derived. Finally an illustrative example is given to verify the results.
Fine structures and characteristics on supersonic flow over backward facing step with tangential injection
2015, 64 (6): 064701. doi: 10.7498/aps.64.064701
The fine flow structure over backward facing step with supersonic injection at the free-stream Mach number of 3.4 is investigated via nano-tracer planar laser scattering (NPLS). The Mach number of injection is measured to be 2.45 actually, even though designed to be 2.5 nominally. The shock wave, shear layer, mixing layer, Kelvin-Helmholtz vortex, horn-like vortex, coherent structures, etc, are clearly revealed. Flow images with the high spatiotemporal resolution are captured involving the streamwise and spanwise flow field in planes at different heights. Based on a large number of fine images, the spatial correlation analysis is conducted to reveal the structure scale and incline angle. The results indicate that with the flow developing, the structure angle tends to be larger and the structure scale becomes smaller. While the injection is working, the downstream surface of step will be covered by a thin film layer. In addition, the schlieren technique is used to compare with NPLS results, and the surface pressure coefficients are measured. In the downstream of injection, the coefficient is 0.0146. The fractal dimensions of different zones in NPLS image are calculated, showing that in the initial stage of flow the fractional dimension is approximate to 1 and the closer to downstream, the higher the dimension is.
2015, 64 (6): 064702. doi: 10.7498/aps.64.064702
The problem of calculating the equation of state (EOS) of a material mixture often comes from fluid-dynamical system containing multiple materials. Generally, the EOS of a material mixture is a system of nonlinear equations which are usually solved by the tabular method and the Newton iterative method. However, the former has poor accuracy, and the later has a finite radius of convergence and hence will converge only if the initial guess is sufficiently close to the final solution. So, a procedure different from the above two method is presented for calculating the EOS of a material mixture whose constituents are in pressure equilibrium and temperature equilibrium. An imbedding method is used to determine the constituent partial thermodynamic variables subjected to the constraints that the total volume and energy of mixture and the constituent mass fractions are specified. The imbedding method has a large radius of convergence, introducing a parameter defined in the interval [0, 1] and a system of imbedding equations which is linearly composed of the to-be-solved EOS of a material mixture and the easy-to-solve EOS of a material mixture. While the parameter changes continuously from 0 to 1, the imbedding method continuously changes the solution of the to-be-solved EOS which the easy-to-solve EOS of a material mixture is continuously converted into. The system of imbedding equations can be changed into a system of ordinary differential form by taking the parameter as independent variable, easily solved by a matured computational method such as trapezoidal rule. By using thermodynamic formulae, two equations in the generalized Maxwellian form are obtained, relating respectively the pressure rate and temperature rate to the strain rate and the constituent mass fraction rate. Finally, the computational method is verified by calculating the EOS of various mass fractions of lead and tin mixture.
2015, 64 (6): 064703. doi: 10.7498/aps.64.064703
In recent years, the motion of nanodroplets on energy gradient surface on a microscale has attracted widespread attention, however, experimental studies are still irrealizable. In this work, the motions of nanodroplets driven by the energy gradient on surfaces with different microstructures are studied by molecular dynamics method. The results show that: the groove-shaped and post-shaped microstructures can remarkably enhance the motion efficiency of the nanodroplets, while the nail-shaped microstructures decrease the motion efficiency, despite they can achieve a stable hydrophobicity. The hybrid microstructures composed of groove-shaped and nail-shaped textures inherit both the advantages of the two microstructure, which not only enhances the motion efficiency of nanodroplets, but also increases the hydrophobic stability. Furthermore, small change in surface energy can significantly affect the velocity of nanodroplet.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2015, 64 (6): 066401. doi: 10.7498/aps.64.066401
Thermodynamics basic and alloy phase evolution of Mg-Sn-Si alloy are studied. The results indicate that for Mg-Sn-Si alloy, the specific heat of alloy phase increases with temperature, and it changes quickly at low temperature while gently at high temperature. In the range of low temperature, its thermal expansion increases exponentially with the increase of temperature, and in the range of high temperature the thermal expansion increases linearly. In the two structures of Mg2 (Six, Sn1-x) and Mg2 (Snx,Si1-x) phases, the replacement position of Si or Sn is indefinite, they could be face-center location or vertex location. Under the conditions of conventional solidification, the range of values for x is fluctuant, for it is in nonequilibrium state: x values are around 0.25 and 0.75 for Mg2(Six, Sn1-x) and Mg2(Snx, Si1-x) structure, respectively. The generation temperature of Mg2 (Si, Sn) phase is quite high, it can be precipitated directly from liquid phase, or be transformed from Mg2Si. The generation temperature of Mg2(Sn, Si) phase is lower than that of Mg2(Si, Sn), and it can be precipitated only from the matrix, the initial precipitation temperature of Mg2(Sn, Si) tends to rise with Sn content increasing.
2015, 64 (6): 066402. doi: 10.7498/aps.64.066402
The Ni50-xFexMn37In13(x=1, 3, 5) polycrystalline samples are prepared by arc melting method. The martensitic transformations and crystal structures for Ni50-xFexMn37In13(x=1, 3, 5) samples are systematically analyzed by measuring the structure and magnetism. The results show that the three samples present different structures at room temperature. In the mean time, with the increase of the content of Fe, the martensitic transformation temperature rapidly decreases, while the ferromagnetism is gradually enhanced for these alloys. Furthermore, both the magnetoresistance and the magnetocaloric effect are also investigated in Fe3 and Fe5 alloys. For an applied magnetic field of 3 T, it is found that the magnetoresistance effects of two samples are about -46% and -15%, while their isothermal entropy changes are about 6 J·kg-1 and 9.5 J·kg-1·K-1 during reverse martensitic transformation, respectively. Accompanied with the disappearing of a very wide transforming range and a slight magnetic hysteresis loss, the net refrigerating capacity of Fe3 sample reaches 96 J·kg-1 in the process of reverse martensitic transformation.
2015, 64 (6): 066801. doi: 10.7498/aps.64.066801
The sliding friction between a rigid tip and an amorphous polymer film is studied using large scale molecular dynamics simulation. We focus on the changes of surface microstructure on the polymer film caused by friction, and study the effects of the interaction between tip and substrate, the sliding speed and the molecular chain length on the change of surface microstructure. When there is an adhesive force between tip and substrate, the bond reorientation caused by friction occurs in the sliding region of polymer substrate, and radius of gyration of the molecular chains on the surface layer of polymer substrate elongates along the sliding direction. Moreover, the extent of surface microstructure changes increases with the decrease of sliding speed. During the process of microstructure changes caused by friction, the chain loops and chain ends make different contributions, leading to different deformation mechanisms of molecular chain. The drag action between the tip and chain end monomers plays a more important role in making molecular chains deformation, when the degree of entanglement of polymer substrate becomes greater or when the sliding speed of tip becomes lower. Our results also show that change of surface microstructure is a key mode of friction energy dissipation in this tip and polymer film tribology system.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effect of In–2N heavy co-doping and preferred orientation on the optical band gap and absorption spectrum of ZnO
2015, 64 (6): 067101. doi: 10.7498/aps.64.067101
Nowadays although the In–N co-doping effects on the optical band gap and absorption spectrum of ZnO are studied extensively, all of the In–N co-doped ZnO materials are of random doping, and the preferred orientation doping using the unpolarized structure of ZnO has not been considered so far. Therefore, in this paper, based on the density functional theory using first principles plane-wave ultrasoft pseudopotential (GGA+U) method, the densities of states and absorption spectra of un-doped and the In–N heavily co-doped Zn1-xInxO1-yNy (x= 0.0625-0.03125, y=0.0625-0.125) in different orientations are calculated. The results show that in the same doping mode, the larger the volume of doping system, the higher the total energy and the formation energy are and the narrower the optical band gap is; the red shifting of absorption spectrum becomes more significant with the increase of In–2N co-doping amount. Those are in good agreement with the experimental results. Under the condition of different doping manners and the same In–2N co-doped concentration, the co-coped In–N atoms along the c-axis orientation, have the narrower optical band gap and more significant red shifting of absorption spectrum than the In–N atoms with the orientation perpendicular to the c-axis. We believe that these results may be helpful for designing and preparing the new photocatalyst materials of In–N heavily co-doped ZnO.
2015, 64 (6): 067102. doi: 10.7498/aps.64.067102
The electronic structures and optical properties of boron/phosphorus mono- and co-doped β silicon nitride are studied by the first-principles plane-wave ultrasoft pseudopotential method with the generalized gradient approximation. The results are obtained as follows. The B-doped system has a better stability than the P-doped system, while the P-doped structure has a stronger ionicity. The mono-doping and co-doping can narrow the band gap of β silicon nitride while the co-doping introduces the deep impurity levels and strengthens the localized states. The mono-doping causes the imaginary part of dielectric function, the peaks of absorption spectra and energy loss spectra to red-shift, and their amplitudes to decrease, resulting in a significant difference from the intrinsic state. The co-doping induces the peak of imaginary part of the dielectric function to blue-shift, broadens the energy loss peak, greatly enhances the electronic transition in the high energy region, and controlling the ratio of the numbers of atoms (B and P) in co-doping can achieve a low charged defect concentration, implying its potential application in the field of microelectronics.
2015, 64 (6): 067201. doi: 10.7498/aps.64.067201
Within the framework of the Su-Schrieffer-Heeger model modified to include uniform disorder and an external electric field, the polaron transport process in conjugated polymer material is simulated using a nonadiabatic evolution method. It is found that the polaron dynamic mechanism is determined by both the electric field and the uniform disorder. The effect of uniform disorder is not obvious and almost negligible in most cases, except for the case of very weak electric field. Compared with the effects of Gaussian disorder, the film morphology with uniform disorder is conductible to the polaron transport.
2015, 64 (6): 067301. doi: 10.7498/aps.64.067301
We theoretically investigate the electromagnetic properties of the multilayer graphene-dielectric composite materials based on the effective medium theory. It is found that the structure exhibits hyperbolic isofrequency wavevector dispersions at THz and far-infrared frequencies, hence thereby realizing the effective graphene-based hyperbolic metamaterials (HMM). The frequncy band of the hyperbolic dispersion can be tuned by changing the Fermi energy of graphene sheet, the thickness of the dielectric layer and the layer number of graphene sheets. Because of the hyperbolic dispersion, graphene-based HMM possesses a negative energy refraction and positive phase refraction for oblique incidence at far below the critical frequency. The highly confined bulk polariton modes are also supported. Based on the attenuated total reflection configuration, the excitation of the bulk polariton mode is studied, in addition, such properties used in the tunable optical reflection modulation are also explored.
2015, 64 (6): 067302. doi: 10.7498/aps.64.067302
Frequency selective surface based on metallic mesh can realize the physical properties of both high infrared transmittance and millimeter-wave band-pass filter. In order to improve the optical transmittance, reduce surface resistance and suppress the effect of high order diffraction energy on the imaging quality of the optical system, a new design of frequency selective surface based on hybrid period metallic mesh is obtained. In this paper, the diffraction intensity distribution and surface current of frequency selective surface are analyzed based on metallic mesh. Simulation and experimental results show that frequency selective surface based on hybrid period metallic mesh realizes a stable millimeter-wave band-pass filter property, at the same time, it obtains 5% increase of infrared transmittance and 4 Ω reduce of surface resistance. New design of frequency selective surface based on hybrid period metallic mesh effectively suppresses the effect of high order diffraction energy on the imaging quality of the optical system.
2015, 64 (6): 067303. doi: 10.7498/aps.64.067303
Nickle ohmic contacts on the Si-face of n-type 4H-SiC are prepared by both rapid thermal annealing (RTA) and laser spark annealing (LSA). The effects of the different annealing procedures on the cathode surface morphology, cathode/substrate cross sectional morphology, element composition, microscopic structure of carbon clusters in the SiC substrate near surface, are characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), transmission electron microscopy (TEM), and Raman spectra, respectively. The tests and analyses show that both thermal treatments can help to form ohmic contacts. The specific contact resistances of RTA sample and LSA sample are measured to be 5.2× 10-4 Ω ·cm2 and 1.8× 10-4Ω·cm2 by transmission line model, respectively. The Ni film of RTA sample shrinks badly thus forms tiny islands on the surface, while the surface of LSA sample remains relatively smooth. The root-mean-square (RMS) values of surface roughness of the Ni films of as-deposited, RTA and LSA samples are 8.65 nm, 91.3 nm and 17.5 nm, respectively. The Ni/SiC interface of RTA sample corrodes badly, and Si can be found in the whole Ni film, indicating an overall consumption of Ni to react with Si forming NiSi compounds; C atoms, which do not react with Ni atoms，cluster to the average size of about 40 Å, and gather approximately as a layer located about 20-30 nm off the Ni/SiC interface. The Ni/SiC interface of LSA sample is relatively smooth, and a small quantity of Ni atoms diffuse into the SiC wafer, forming lots of ternary phase diffusion zones of about tens of nanometers deep into the SiC wafer, in which C, Si, Ni atoms are distributed uniformly; the average size of C clusters is smaller than that in RTA sample and no obvious C enriched zone was found, while neither Si atom nor C atom is found to diffuse into the Ni film.#br#The ohmic contacts prepared by LSA have obvious advantages compared with those by RTA in many aspects such as cathode surface morphology, interface morphology, uniformity of components in cathode films, etc. All the results mentioned above make LSA a promising method of thermal treatment in preparation of ohmic contacts.
New folding lateral double-diffused metal-oxide-semiconductor field effect transistor with the step oxide layer
2015, 64 (6): 067304. doi: 10.7498/aps.64.067304
In order to design the power devices with the low loss required for the power integrated circuits (PIC), a new folded silicon LDMOS with the folding step oxide layer (SOFLDMOS) is proposed in this paper for the first time. In this structure, the step oxide layer is covered on the folded silicon surface with a periodic distribution. The surface electric field is optimized to be uniform by introducing a new electric field peak due to the electric field modulation effect by the step oxide layer. The breakdown voltage is improved to solve the breakdown voltage limitation problem in FALDMOS. Obtained in virtue of the ISE simulation are the results that the silicon limit is broken by applying the effects of the electric field modulation, accumulation of majority carriers, and conductive silicon region multiplier in the proposed SOFLDMOS. The saturation current of the drain electron is increased by about 3.4 times compared with that of the conventional LDMOS. When the breakdown voltage is 62 V, an ultra-low specific on-resistance of 0.74 mΩ·cm2 is obtained, which is far less than 2.0 mΩ·cm2 in the conventional LDMOS with the same breakdown voltage. The low loss requirements is achieved for the PIC with the low voltage region by the proposed SOFLDMOS.
A model of capacitance characteristic for uniaxially strained Si N-metal-oxide-semiconductor field-effect transistor
2015, 64 (6): 067305. doi: 10.7498/aps.64.067305
The capacitance model is fundamental for the transient analysis, AC analysis and noise analysis of uniaxially strained Si MOSFET device and circuit. Firstly, the 16-differential capacitance model for uniaxially strained Si NMOSFET is developed. Secondly, the simulation results from that model match the experimental results well, which validates the accuracy of the model. Meanwhile the simulated relations of key gate capacitance Cgg to stress intensity, bias voltage，channel length and concentration of poly gate are obtained and analyzed, showing that the value of Cgg is a little larger than that of strainless bulk device while the changing tendency keeps the same.
Magnetic and transport properties of perovskite manganites (La1-xGdx)4/3Sr5/3Mn2O7 (x=0, 0.025) polycrystalline samples
2015, 64 (6): 067501. doi: 10.7498/aps.64.067501
The polycrystalline samples of two-layered perovskite manganites (La1-xGdx)4/3Sr5/3Mn2O7 (x=0, 0.025) are prepared by traditional solid state reaction method. X-ray diffraction measurements show that both samples are of the Sr3Ti2O7 -type tetragonal phase (space groups I4/mmm). Magnetic measurements show that Gd3+ doping reduces the magnetic transition temperature (TC3D) and magnetization (M) of the doped sample (La0.975Gd0.025)4/3Sr5/3Mn2O7, which is because Gd3+ doping induces lattice distortion and change the lattice constant, and subsequently weakens the double exchange interactions. It is found from electron spin resonance measurements that short-range ferromagnetic clusters appear in the paramagnetic background of both samples at temperatures TC3DTTC3DT0.975Gd0.025)4/3Sr5/3Mn2O7 has a higher resistance. This is because Gd3+ doping reduces the localization length of carriers, and makes conducting carriers absorb more energy to overcome the bound potentials in the lattice.
Effects of high magnetic field on the growth and magnetic properties of Fe-Ni nano-polycrystalline thin films with different thickness values
2015, 64 (6): 067502. doi: 10.7498/aps.64.067502
The Fe-Ni nano-polycrystalline thin films of 21 nm and 235 nm in thickness are prepared by molecular beam vapor deposition in the absence and the presence of a magnetic field as high as 6 T. The results show that in the absence of the magnetic field, the 21-nm-thick thin films are formed by the grain stacks, and the sizes of grains are about 6-7 nm. In the presence of 6 T, the 5-nm-thick flat layers of interconnected grains of 21-nm-thick thin films are first formed on the surfaces of the substrates, and the grains are then elongated along the surfaces of substrates. Later on, the 21-nm-thick thin films are formed by 6-7 nm-size-grain stacks. In the absence of the magnetic field, the average grain size of the 235-nm-thick thin film is 3.6 nm in the early growth stage, and it is 5.6 nm in the middle growth stage. The growth way of thin film is akin to columnar growth in the final growth stage, and the grains are elongated along the growth direction. In the presence of 6 T, the 5-nm-thick flat layers of interconnected grains of 235-nm-thick thin films are also formed on the surfaces of the substrates, and the grains are elongated along the surfaces of substrates. Later on, the 235-nm-thick thin films are formed by about 6.1-nm-size-grain stacks. Accordingly, the coercive forces in the out-of-plane and in the in-plane of thin films of different thickness values decrease by the 6 T magnetic field.
The microstructure and optical properties of SiNx deposited by linear microwave chemical vapor deposition
2015, 64 (6): 067801. doi: 10.7498/aps.64.067801
SiNx films are synthesized on Si substrates in a home-made linear microwave plasma enhanced chemical vapor deposition system at different microwave powers, duty cycles, substrate temperatures, and ratios of silane (SiH4) flow to ammonia (NH3) gas flow. The effects of technological parameters on morphology of film surface, stoichiometric proportion, refractive index and deposition rate of SiNx film are characterized by scanning electron microscopy (SEM) and elliptical polarization instrument, and the relationships among stoichiometric proportion, refractive index and deposition rate are investigated. The results from SEM analysis indicate that the surfaces are smooth and the elements are homogeneously distributed in the films obtained under different deposition parameters. The ratio of SiH4 flow to NH3 gas flow and the duty cycle are the most critical factors determining the refractive index which can be changed from 1.92 to 2.33. The thickness measurements show that the deposition rate of SiNx film is affected by microwave power, duty cycle, substrate temperature and flow ratio. The maximum deposition rate achieved in the paper is 135 nm·min-1.
Effect of Pt NPs in the film on the performances of ZnO-based metal-semiconductor-metal structured ultraviolet photodetector
2015, 64 (6): 067802. doi: 10.7498/aps.64.067802
In this paper, by a radio frequency magnetron sputtering equipment, the ZnO/Pt nanoparticles/ZnO thin film structure is fabricated on a SiO2 substrate via three-step. And the metal-semiconductor-metal (MSM) structured ultraviolet (UV) photodetectors are built up. It is studied that the Pt nanoparticles in different depths of the layer of ZnO thin film affect the photoresponse performances of the MSM ultraviolet photodetector. The results show that the responsivity of the detector increases as Pt nanoparticles in ZnO thin film layers augment with the depth increasing. The responsivity of device is measured under 60 V bias, its photoresponse peak is at 365 nm, and the peak photoresponse is 1.4 A·W-1, which is enhanced by 7 times that of the photodetector without Pt NPs. Considering the performance analyses of ZnO films and the photodetectors, it is clear that the excellent performances of the detector with Pt NPs in the film can result from the scattering of Pt NPs.
2015, 64 (6): 067503. doi: 10.7498/aps.64.067503
This article first gives a brief review of magnetic structures, magnetic domains and topological magnetic textures and their relations. On the one hand, the magnetic domains are determined by the magnetic structures, the intrinsic magnetic properties and the micro-structural factors of a material. On the other hand, the magnetic domains could control the magnetization and demagnetization processes and also the technical magnetic properties of a material. Topology is found to have a close relation with physical properties of material. Recent interest has focused on topological magnetic textures, such as vortex, bubble, meron, skyrmion, and it has been found that the topological behaviors of these topological textures are closely related with magnetic properties of a material. Then this article introduces recent advances in magnetic structures, magnetic domains and topological magnetic textures, from views of the size effect, defects and interfaces. Finally, this article reviews briefly some results of investigation on the relations between microstructures, magnetic domains and magnetic properties of rare-earth permanent magnetic thin films, the topological magnetic textures and their dynamic behaviors of exchange coupled nanodisks. It has been concluded from the reviews on the literature that the investigation on anisotropic exchange-coupled rare-earth permanent magnets with high performance benefits the high efficient utilization of rare-earth resources. One could achieve optimal magnetic properties through magnetic domain engineering by adjusting the microstructures of magnetic materials. The concepts of topology is applied to various research fields, while the contributions from topological behaviors to physical properties are discovered in different materials. The researches on magnetic domains, topological magnetic ground state and excitation states and their dynamic behaviors are very important for a better understanding of quantum topological phase transitions and other topological relevant phenomena. It can be quite helpful for understanding the correlation between different topological states and their relationship with magnetic properties of a material, and also it will definitely contribute to the applications in various fields of magnetic materials.
2015, 64 (6): 068801. doi: 10.7498/aps.64.068801
Recently, Cu2ZnSnS4 (CZTS) has emerged as one of the most promising thin film materials due to its being environment friendly, abundant in storage and low cost. To date, solar cell with up to 12.6% efficiency have been reached with using Cu2ZnSn(S, Se)4 (CZTSSe) absorber by hydrazine solution method. In this paper, the structural, optical, electrical, interface layer properties of CZTS thin films are introduced and the effect of sodium diffusion on the CZTS thin film is also discussed. Furthermore, different methods to fabricate CZTS thin films and the corresponding device performances are discussed. Finally, the existing problems and future researches are summarized.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Effect of As pressure-modulated InAlAs superlattice on the morphology of InAs nanostructures grown on InAs/InAlAs/InP
2015, 64 (6): 068101. doi: 10.7498/aps.64.068101
InAs/InAlAs/InP(001) nanostructure materials are grown using solid-source molecular beam epitaxy equipment. Effect of As pressure-modulated InAlAs superlattice on the morphology of InAs nanostructure is investigated. The results show that As pressure-modulated InAlAs superlattice can suppress the quantum wires formation and results in quantum dot growth with a uniform size distribution. The analysis indicates that the morphology of InAs nanostructure is caused mainly by the anisotropic strain relaxation of InAlAs layers and the anisotropic surface migration of In adatoms.
2015, 64 (6): 068301. doi: 10.7498/aps.64.068301
The influences of medium and temperature on the shear thickening behavior of silica colloids are investigated. The nano fumed silica colloids in four media (ethylene glycol, polyethylene glycol 400, propylene glycol, and polypropylene glycol 400) exhibit continuous or discontinuous shear thickening behaviors. With the increase of temperature, the medium viscosity decreases, thus the apparent viscosity of colloids decreases. The relationship between the critical viscosity of shear thickening and temperature is well described by the Arrhenius equation. The ratio of viscosity of colloids to medium visocosity is used to scale the steady-shear rheological curves of the colloids under various temperatures. In the shear thinning regime at low shear rate, the form of rheological curve is independent of medium viscosity but correlates with the chemical properties of dispersing medium. In the shear thickening regime at high shear rate, a higher medium viscosity results in stronger shear thickening behavior.
2015, 64 (6): 068701. doi: 10.7498/aps.64.068701
Terahertz (THz) spectra for different palm leaves are measured by Fourier transformed infrared spectroscopy-attenuated total reflection, and the physical morphologies and chemical compositions of the leaves are characterized by scanning electron microscopy and infrared spectroscopy, respectively. Accordingly, the THz fingerprint peaks of chlorophyll and carotenoid are experimentally identified. In addition, the results indicate that the influence of the chemical composition in plant leave on optical response is significantly stronger than that of the physical morphology. Moreover, among the main chemical components of palm leave, the THz response of chlorophyll is stronger than that of carotenoid. In this work, new methods of investigating the optical properties of the planes and of developing novel THz sensitive organic materials are also proposed. Particularly, some important results are reported for the first time in this article. These valuable results will be helpful not only for an in-depth understanding of the physiological behavior of the plants, but also for the obtaining of inspiration for designing functional materials of device with higher performance, higher pertinency and wider applications, and thus promoting the development of related theories and applications.
2015, 64 (6): 068702. doi: 10.7498/aps.64.068702
Biological memory is a ubiquitous phenomenon, which could be found in a variety of biological subsystems. Based on a model of dual feedback gene regulatory circuit, in this paper we investigate the influence of time delay on memory time. The results show that the memory time is enhanced dramatically due to the existence of time delay, and the memory time increases linearly with increase of time delay. This enhancement pattern is completely different from that induced by noise. The raising of biological memory by time delay and noise can be controlled and reinforced mutually without affecting the reinforcement mode of opposite side.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Applications of random balance design Fourier amplitude sensitivity test and extended Fourier amplitude sensitivity test in the parameter sensitivity analysis of land surface process model
2015, 64 (6): 069201. doi: 10.7498/aps.64.069201
In this paper, we discuss the applications of random balance design Fourier amplitude sensitivity test (RBD-FAST) and extended Fourier amplitude sensitivity test (EFAST) in the parameter sensitivity analysis of land surface process model. We use the common land model and data of Tongyu station, which is a reference site of CEOP in the semi-arid regions, use five model outputs (sensible heat flux, latent heat flux, surface temperature, temperature of air at 2 m over surface, moisture of air at 2 m over surface) as focus output, and use 11 model parameter (soil depth, the soil proportion of 1-5 layers of soil, the porosity of soil, the max dew depth, the roughness of the air between surface and the canopy, and the drag coefficient under the canopy) as the parameters to be analyzed. After the 10 RBD-FAST experiments, we obtain the first-order sensitivity results, and we gain not only first-order sensitivity but also the total sensitivity after the EFAST experiment. The first-order results of two methods show their consistency. The RBD-FAST takes less computing time and is easy to implemente, while the EFAST also has a more comprehensive and reasonable total sensitivity result. All results above illustrate the applications of both RBD-FAST and EFAST in the parameter sensitivity analysis of land surface model. Researchers can choose the suitable one to solve the different problems.
Diffusing loss effects of radiation belt energetic electrons caused by typical very low frequency electromagnetic wave
2015, 64 (6): 069401. doi: 10.7498/aps.64.069401
Radiation belt energetic electrons can interact with very low frequency (VLF) electromagnetic wave due to wave-particle resonance; then the particles are imposed to enter into the loss cone and sink to dense atmosphere resulting from changing of its pitch angle. To investigate the diffusion mechanism of interaction of VLF electromagnetic wave with radiation belt energetic electrons, according to quasi-linear diffusion theory, in this paper we use a physical model to calculate diffusion coefficients of Coulomb scatting and wave-particle resonance interaction. Bounce-averaged pitch angle diffusion coefficients of energetic electrons due to the interaction of wave-particle resonance with two groups of VLF electromagnetic waves are obtained. The influence of interaction caused by VLF electromagnetic wave and Coulomb scatting on diffusion of radiation belt energetic electrons for different L shells and various energies are analyzed. Take the case for example, where L equals 2.2 and electron energy E equals 0.5 MeV, the diffusion equation of energetic electrons are solved by using the finite difference method. The time evolutions of precipitation of directional particle flux and omnidirectional particle flux are analyzed. The results show that the resonance interaction caused by VLF electromagnetic wave plays a dominant role when E>0.5 MeV and L>1.6; the higher the L shell or electron energy value, the more significant the high order resonance interaction caused by the oblique propagation VLF electromagnetic wave will be; approximately, the omnidirectional particle flux of radiation belt energetic electrons decreases exponentially with time.